AMERICAN INSTITUTE OF CROP ECOLOGY
A RESEARCH ORGANIZATION DEVOTED TO PROBLEMS OF
PLANT ADAPTATION AND INTRODUCTION
AICE* SURVEY OF USSR AIR POLLUTION LITERATURE
Volume XX
CATALYTIC PURIFICATION OF EXHAUST GASES
Edited By
M. Y.
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PUBLICATIONS of Mm AMERICAN INSTITUTE OF CROP ECOLOGY
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No.
UKR^INE-Ecologicol Crop Geography -f the Ukraine ond the
Ukti:-tio^ Agro-Climc!>c Anologues in North America
POLAND-Agriculture! Cli'motology of Roland and I tl Agro-
CliwJ^c Anologues In ^rtH America
CZECHOSLOVAKIA-A9. cultural Climatology of Czechoslo-
vakia and Its Agro-Oin'otiC Analogue* in North America
4 YUGOSLAVIA-Aoricul rural Climatology of Jugoslavia and Its
Agre-Climatic Analogues m North America
5 GRCECE-Ecological Crop Geography of Greece and Irs Agro-
Climatic Analogues in North America
6 AL6AK!|A-Ecologicol Plant Geography of Albania, Its Agri-
cu'turol Crops and Some Norm American Climatic Analogues
7 CHINA-Eeologir.oi Crop Geography of China and Its Agro-
Climatic Analogues in North America
8 GERMANY-Ecological Crop Geography of Germany and Its
Agro-Qimotic Analogues in North America
•9 JAPAN (I(-Agricultural Climatology of Japan and Its Agro-
Climatic Anologues in North America
10 FINLAND-Ecologicol Crop Geography of Finland and Its Agro-
Qimottc Anologues in North America
II SWEDEN-Agricultural Climatology of Sweden and Its Agro-
Oimatic Analogues in North America
12 NOR WAY-Ecological Crop Geography of Norway ond Irs Agro-
Climatic Analogues in North America
13 SIBERIA-Agricul rural Cl imalology of Siberia, Its Natural Bel Is,
and Agro-Climatic Analogues in North America
14 JAPAN 121-Ecological Crop Geography and Field Practices of
Japan, Japan's Natural Vegetation, and Agro-Climatic
Analogues in North America
15 RYUKYU ISLANOS-Ecological Crop Geography and Field
Practices of the Ryukyu blonds. Natural Vegetation of the
Ryukyus, and Agro-Qimotic Analogues in the Northern
Hemisphere
16 PHENOL OS'' AND THERMAL ENVIRONMENT AS A MEANS
OF A PHYSIOLOGICAL CLASSIFICATION OF WHEAT
VARIETIES AND FOR PREDICTING MATURITY DATES OF
WHEAT
(Based on Data of Czechoslovakia and of Some Thermally
Analogous Areas of Czechoslovakia in the United Stores
P-jnfic Northwest)
17 WHEAT-CLIMATE RELATIONSHIPS AND THE USE OF PHE-
NOLOGY IN ASCERTAINING THE THERMAL AND PHO-
TOTr ERMAL REQUIREMENTS OF WHEAT
(Based on Data of North America and Some Thermally Anal-
ogous Area: of North America in the Soviet Union ond in
Finland)
18 A COMPARATIVE STUDY OF LOWER AND UPPER LIMITS OF
TEMPERATURE IN MEASURING THE VARIABILITY OF DAY-
DEGREE SUMMATIONS OF WHEAT, BARLEY, AND RYE
19 BARLEY-CLIMATE RELATIONSHIPS AND THE USE OF PHE-
NOLOGY IN ASCERTAINING THE THERMAIMND PHO-
TOTHERMAL REQUIREMENTS OF BARLEY
20 RYE-CLIMATE RELATIONSHIPS AND THE USE OF PHENOL-
OGY IN ASCERTAINING THE THERMAL AND PHOTO-
THERMAL REQUIREMENTS OF RYE
21 AGRICULTURAL ECOLOGY IN SUBTROPICAL REGIONS
22 MOROCCO, ALGERIA, TUNISIA-Physical Environment and
Agriculture ....
23 LIBYA ond EGYPT-Phy'ical Environment and Agriculture. . .
24 UNION OF SOUTH AFRICA-fW-,i al Environment ond Agri-
culture, With Special Refer rr.:>- to '-/inter-Rainfall Regions
26
27
28
28A
286
2«A
29B
29C
30A
308
31
32
33
34
35
37
38
39
40
41
42
43
44
45
S.E. CALIFORNIA and S.W. ARIZONA-Physieol Environment
and Agriculture of the Desert Regions
THAILAND-Physical Environment and Agriculture
BURMA-Phytical Environment and Agriculture
BURMA-Diseasei and Pats of Economic Plants
BLrRMA-dimofe. Soils and Rice Culture (Supplementary In-
formation and a Bibliography to Report 28)
VIETNAM, CAMBODIA, LAOS-fnysical Environment and
Agricul ture .........
VIETNAM, CAMBODIA, LAOS-Diseases and Pestsef Economic
Plants
VIETNAM, CAMBODIA, LAOS-Climotologicol Dora (Supple-
ment to Report 29A)
CENTRAL and SOUTH CHINA, HONG KONG,
Physical Environment and Agriculture
TAIWAN-
120.00*
TAIWAN-
25
AUSTRALIA-Pnyu'eol Environment and Agriculture, With Spe-
cial Reference to Winter-Rainfall Regions .....
CENTRAL and SOUTH CHINA, HONG KONG,
Major Plant Poll and Diseases
SOUTH CHINA-lts Agro-CD imoflc Analogues in Southeast Asia
SACRAMENTO-SAN JOAQUIN DELTA OF CALIFORNIA-
Phystical Environment and Agriculture
GLOBAL AGROCLIMATIC ANALOGUES FOR THE RICE RE-
GIONS OF THE CONTINENTAL UNITED STATE
AGRO-CLIMATOLOGY AND GLOBAL AGROCLIMATIC
ANALOGUES OF THE CITRUS REGIONS OF THE CON-
TINENTAL UNITED STATES
GLOBAL AGROCLIMATIC ANALOGUES FOR THE SOUTH-
EASTERN ATLANTIC REGION OF THE CONTINENTAL
UNITED STATES
GLOBAL AGROCLIMATIC ANALOGUES FOR THE INTER-
MOUNTAIN REGION OF THE CONTINENTAL UNITED
STATES
GLOBAL AGROCLIMATIC ANALOGUES FOR THE NORTHERN
GREAT 71AINS REGION OF THE CONTINENTAL UNITED
STATES
GLOBAL AGROCLIMATIC ANALOGUES FOR THE MAYA-
GUEZ DISTRICT OF PUERTO RICO
RICE CULTURE and RICE-CLIMATE RELATIONSHIPS Wl* Spe-
cial Reference to the United Stares Rice Areas and Their
Latitudinal and Thermal Analogue! In Other Countries!
E. WASHINGTON, IDAHO, and UTAH-Pfryileol Environment
ond Agriculture
WASHINGTON, IDAHO, and UTAH-The Use of Phenology
in Ascertaining the Temperature Requirements of Wheat
Grown in Washington, Idaho, ond Utah ond in Some of
Their Agro-Climaticolly Analogous Areas in the Eastern
Hemisphere
NORTHERN GREAT PLAINS REGION-Preliminary Study af
Phenological Temperature Requirements of a Few Varieties
of Wheat Grown In the Northern Great Plain Region and In
Some Agro-Oimotlcoily Analogous Areas in the Eastern
Hemisphere
SOUTHEASTERN ATLANTIC REGION-Phenologlcol Temper-
ature Requirements of Some Winter Wheat Varieties Grown
in the Southeastern Atlantic Region of the United Stoles and
in Several of Its Lati tudi ml ry Ana logons Areas of the Eastern
and Southern Hemispheres of Seasonally Similar Thermal
Condition!
ATMOSPHERIC AND METEOROLOGICAL ASPECTS OF AW
POLLUTION-A Survey of USSR Air Pollution Literature
EFFECTS AND SYMPTOMS OF AIR POLLUTES ON VEGETA-
TION; RESISTANCE AND SUSCEPTIBILITY OF DIFFEKENT
PLANT SPECIES IN VARIOUS HABITATS, IN RJLATJON TO
PLANT UTILIZATION FOR SHELTER BELTS AND AS BIO-
LOGICAL INOICATORS-A Survey of USSR Air Pollution
Literature.
(Continued on inside of back cover)
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AICE-AJR-73-20
AICE* SURVEY OF USSR AIR POLLUTION LITERATURE
Volume XX
CATALYTIC PURIFICATION OF EXHAUST GASES
Edited By
M. Y. Nuttonson
The material presented here is part of a survey of
USSR literature on air pollution
conducted by the Air Pollution Section
AMERICAN INSTITUTE OF CROP ECOLOGY
This survey is being conducted under GRANT R 800878
(Formerly R01 AP 00786)
OFFICE OF AIR PROGRAMS
of the
US. ENVIRONMENTAL PROTECTION AGENCY
*AMERICAN INSTITUTE OF CROP ECOLOGY
809 DALE DRIVE
SILVER SPRING, MARYLAND 20910
1973
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TABLE OF CONTENTS
Page
PREFACE [[[ iv
CATALYTIC PURIFICATION OF EXHAUST GASES
D. V. Sokol'skiy. and N. M. Popova
INTRODUCTION [[[ 1
.!
Chapter 1. TOXICITY OF INTERNAL COMBUSTION ENGINE EXHAUSTS
AND WAYSJDF REDUCING THE CONCENTRATION OF TOXIC
COMPONENTS IN THE AIR ...................................... 4
Chapter 2. CATALYTIC OXIDATION OF CARBON MONOXIDE .............. 24
;-S_
Chapter 3. OXIDATION OF CARBON MONOXIDE ON LOW-PERCENTAGE
METAL CATALYSTS .................. . ......................... 39
Methods of Preparation of Catalysts . ....................... 39
Mechanical Strength of Catalyst and Depth of
Impregnation of Granules ................................... 50
Regeneration of Precious Metals ............ ...... .......... 53
Role of the Carrier ........................................ 56
Stability, Structure and Phase Composition of
Catalysts in Prolonged Use ................................. 71
Chapter 4. COMPLETE CATALYTIC OXIDATION OF HYDROCARBONS ........ 85
Chapter 5. CATALYTIC REMOVAL OF NITROGEN OXIDES FROM
EXHAUST GASES .............................................. 103
Chapter 6. BENCH AND ROAD TESTS OF EXHAUST PURIFICATION
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PREFACE
The present volume presents a translation of a Russian monograph*
intended for the technical staff of scientific research institutes and
of industrial laboratories, for members of university faculties, for
students specializing in the field of catalysts and gas purification, and
for technicians engaged in the automotive transport industry.
The monograph deals with air pollution in large cities and in closed
industrial premises, and with the toxicity of automobile exhaust gases
under various operating conditions. It also deals with methods of reducing
the atmospheric concentration of noxious substances. Emphasis is on the
catalytic oxidation of carbon monoxide, the complete oxidation of hydrocar-
bons, and the removal of nitrogen oxide from gaseous mixtures. There is
also a survey of relevant literature. The authors present some observations
on new catalysts that were the subject of experimental investigations made
at the Institute of the Academy of Sciences of Kazakh SSR. Considerable
space in the monograph is devoted to methods of obtaining active, stable,
low-percentage catalysts of carbon monoxide oxidation, to the role of the
carrier, and to the mechanism of the process.
It is hoped that the monograph selected for presentation in this volume
will be conducive to a better appreciation of some of the air pollution
investigations conducted in the USSR. As the editor of this volume I wish
to thank my co-workers in the Air Pollution Section of the Institute for
their valuable assistance.
M. Y. Nuttonson
February 1973
* "Kataliticheskaya Ochistka Vykhlopnykh GazoV". (Catalytic Purification of Exhaust Gases )
D. V. Sokol'skiy, N. M. Popova. Akadenaya Nauk Kazakhskoy SSR. Institut Khimicheskikh Nauk
Izdatel'stvo "Nauka" Kazakhskoy SSR. Alma-Ata, 190 pages, (1970).
iv
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INTRODUCTION
The removal of noxious impurities from the atmosphere of large cities,
chemical complexes, and closed industrial spaces (shafts, holds, etc.)
constitutes at the present time one of the main problems facing mankind.
Public health is threatened by discharges from industrial enterprises and
exhaust gases of motor transport containing a number of toxic components
(carbon monoxide, nitrogen oxides, carcinogenic agents, etc.), whose
concentrations in the vicinity of industrial enterprises and heavily traveled
streets are many times the sanitary permissible levels. This is particularly
harmful for cities with poor natural aeration (Los Angeles, Alma-Ata, and
others).
The elevated content of toxic components in exhaust gases seriously
complicates the use of diesel-powered equipment
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A supported palladium catalyst whose method of preparation was worked out
at the IKhN AN KazSSR, has been recommended for road tests in gas purifiers
designed by LANE (Moscow Scientific Research and Experimental Design Labora-
tory of Exhaust Neutralization and Problems of Automobile and Tractor Power
Engineering).
Results of the first stage of efficiency tests showed that palladium-
catalyst gas purifiers achieve a high degree of purification of exhaust gases.
The overall efficiency of purification of exhaust gases, involving the re-
moval of carbon monoxide, soot, and hydrocarbons, amounts to 50-100% depend-
ing on the type of engine and its operating conditions. Palladium catalysts
are equal in efficiency to platinum catalysts produced at home and abroad
(Oxy-France).
The vigorous development of industrial organic synthesis, and of other
industries in the last decade, and the growth of motor transport have added
practical interest to the problem of purification of exhaust gases, and the
material accumulated in this field needs to be correlated. A survey of
work on the catalytic oxidation of carbon monoxide covering the period 1920-
1950 is given by M. Katz [162]. Some aspects of the reaction kinetics of
extensive oxidation of hydrocarbons are discussed in the monograph of L. Ya.
Margolis [170], but this in our view is inadequate when one considers the
large number of studies and patent material in this area.
The present book consists of six chapters. The first gives a survey of
the literature on the toxicity of exhaust gases and ways of reducing the con-
tent of noxious components in the air. The particularly favorable prospects
of catalytic purification as compared with other forms of purification of ex-
haust gases is noted.
The second, third and fourth chapters present an analysis of the litera-
ture, including patent data on the catalytic oxidation of carbon monoxide,
complete oxidation of hydrocarbons, and catalytic reduction of nitrogen oxides
as the most common method of removal of nitrogen oxides from gases. The in-
fluence of the nature of the catalysts, composition of gaseous mixtures and
nature of the toxic components on the conditions of the process is discussed.
Particular emphasis is placed on a review of studies with a practical bent
(high space velocities, etc.).
The chapter "Oxidation of Carbon Monoxide over Low-Percentage Supported
Catalysts" discusses the results of experimental studies aimed at the develop-
ment of new oxidation catalysts on supports. The effect of the method of pre-
paration and of the nature of the support on the activity and stability of
low-percentage contacts and on the depth of impregnation, mechanical strength,
and regeneration is examined. The chief characteristics of low-percentage
supported palladium catalysts are listed.
The fifth chapter contains an analysis of government tests of catalysts
- 2 -
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produced by IKhN AN KazSSR, conducted at LANE (Moscow) and KazNIPIAT (Kazakh
Scientific Research and Design Institute of Motor Transport Alma-Ata) under
the direction of I. L. Varshavskiy and based on data supplied by these orga-
nizations to IKhN AN KazSSR. Data are given on the behavior of the catalysts
during the tests and on the change of activity, surface area, strength, phase
composition, and particle size composition of the catalysts.
The book utilizes literature and patent materials from 1920 through 1968,
including some information from surveys, for example, on the toxicity of ex-
haust gases (Korenev [5], Demochka [323]), oxidation of carbon monoxide (Katz
[162]), and decomposition of nitrogen oxides (Chernyshev, Zanchko [463]).
The chapter "Oxidation of Carbon Monoxide on Low-Percentage Catalysts"
describes experimental data obtained by a group at IKhN AN KazSSR: M. B.
Syzdykbayeva, G. A. Shchelkina, N. P. Belova, L. M. Novoselova, B. S. Mukanova,
L. M. Rozmanova, and I. N. Man'ko, working under our direction.
The following persons participated in the bench and road tests conducted
by several organizations [LANE (Moscow),* Institute Giprouglegormash (Karaganda),
KazNIPIAT (Alma-Ata), Volgograd Polytechnic Institute], and in the preparation
of experimental batches of catalysts: M. B. Syzdykayeva, G. K. Alekseyeva,
Ya. A. Dorfman, Yu. V. Pichugov, T. Ye. Dovlichin, B. Daurenbekov, and others.
The phase composition, structure, and surface area were determined by L. N.
Gudkova, A. Kh. Shalamov, G. Bedel'bayev, G. A. Shchelkina, and I. N. Man'ko.
*The tests were conducted by the staff of the Gasoline Engine Neutralization Section under the
direction of L. S. Zolotarevskiy.
- 3 -
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Chapter 1
TOXICITY OF INTERNAL COMBUSTION ENGINE EXHAUSTS
AND WAYS OF REDUCING THE CONCENTRATION OF TOXIC COMPONENTS IN THE AIR
Analysis of air on streets and in closed spaces where motor transport
is operating shows that in some cases the content of noxious components is
many times greater than the sanitary permissible levels. The single maximum
permissible concentration of carbon monoxide in atmospheric air is 6 mg/m-*
[48]. According to the data of [4], the average carbon monoxide concentra-
tion in the major cities of the USSR amounts to around 20 mg/m3, which is
considerably less than the value for the air of major U.S. cities (up to
90 mg/m3). The average carbon monoxide content on the main streets of Moscow
ranges from 4.3 to 12.9 mg/m3 [48]. It is determined by the traffic density
and width of the streets and may exceed the permissible levels [52].
Analysis of air in the vicinity of traffic flow (up to 2000 automobiles
per hour) on certain arterial streets of Volgograd and Chelyabinsk has shown
that the concentration of nitrogen oxides and carbon monoxide in the air over
the pavement is 2-5 times higher than the permissible value [1, 2].
V. G. Devyatka [3], who studied the pollution of air with carbon monoxide
on streets as a function of their traffic load has pointed out that the car-
bon monoxide content ranges from 0.0004 to 0.21 mg/1, and in the vicinity of
the traffic flow it may amount to 1.5-7.1 mg/1.
The chief source of carbon monoxide pollution of air in large cities is
the motor transport, foundries of metallurgical plants (up to 10% CO), waste
gases of petroleum refineries, chemical complexes such as caprolactam plants
(6% CO), coking plants (up to 7% CO), and the like.
It is well known that on heavily traveled streets (2-3 thousand automo-
biles per hour), the carbon monoxide concentration in some cases is 10 times
higher than the maximum permissible sanitary level [7]. For the same traffic
density, the carbon monoxide contamination of areas adjacent to a main artery
varies widely. In sections with a perimetric layout, angular blocking of
houses and small gaps between them, the air is more polluted with automobile
exhausts than in sections with regular layouts. According to the data of
Kh. B. Berdyyev et al. [8], the average carbon monoxide content in living
quarters is highest on the third floor and 6-8 times greater than the maximum
permissible levels.
The problem of purifying exhaust gases in closed buildings and confine/d
spaces such as shafts, holds, sea ports, and open-pit mines is most urgent.
-------
According to the data of a sanitary-epidemiological station, the air
pollution levels in Alma-Ata in 1966 substantially exceeded the sanitary
permissible values.
According to the data of the Kazakh Oncology Institute, areas with
major highways (50th October Anniversary Prospect, Abaya Prospect), consti-
tute zones of maximum pollution with 3,4-benzpyrene, a carcinogenic compounds
causing lung cancer (up to 0.227 yg/100 m-*) [9].
The accumulation in humid air of toxic components of exhaust gases
from motor transport and waste gases from chemical plants and furnace systems
has catastrophic effects on the population. Thus, in Belgium in 1930, dam-
age to the respiratory tract and mucous membranes was observed on a mass
scale; the death rate during that period was 10.5 times the expected rate
under normal conditions. A similar phenomenon was also observed in Pennsyl-
vania in the eastern part of the U.S.A. (Donora) in 1948, in London in 1952,
and in the Ruhr region in 1962. Frequent smogs have a harmful effect on the
inhabitants of Los Angeles [10]. Frequently, the emission of large quantities
of hydrocarbons causes the formation of fogs, particularly in areas with
high contents of soot and moisture in the air. For this reason, motor trans-
port is sometimes halted for 10-12 shifts in deep open-pit mines (depth of
200 m or more) [11]. When the natural air exchange is disturbed, the pollu-
tion exceeds the permissible sanitary levels, for example, the amount of
aldehydes on the bottom of the pit is 30-40 times the allowed level [12].
A high content of toxic components in exhaust gases also seriously
hampers the use of diesel-powered equipment in underground mines, although
experience with diesel engines in underground operations abroad (U.S.A.,
France, Canada, Sweden) indicates [13] considerable advantages of trackless
self-propelled equipment over electric power (increased labor productivity,
decrease of the cost of mining of the ore). It follows from these data that
as motor transport, whose use in the national economy and present-day tech-
nology is on the increase, gradually expands, the pollution of atmospheric
air with exhaust gases grows.
The process of combustion of liquid fuel in engine cylinders involves
the formation of combustion products in the form of carbon dioxide, carbon
monoxide, water, and other compounds. Tests performed during the last two
decades in the Soviet Union and abroad, involving analysis of exhaust gases
of gasoline and diesel transport engines by means of the most recent analy-
tical methods, have shown that the composition of the exhaust gases of internal
combustion engines includes several dozen components such as hydrogen, carbon
dioxide, oxygen, nitrogen, and toxic gases: carbon monoxide, nitrogen oxides,
saturated and unsaturated hydrocarbons (methane, ethane, benzene, propane,
ethylene, hexane, etc.), aldehydes (acrolein, formaldehyde, acetaldehyde) and
soot [14]. The composition of the exhaust of engines operating on sulfur-
containing fuel also includes sulfur dioxide.
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When an engine runs on ethyl gasoline, oxides and other compounds of
lead injurious to the respiratory tract appear in the exhaust. The amount
of lead in air is directly proportional to the traffic density and may
reach 4-12 mg/m3, decreasing with the height [15].
The content of toxic substances in the exhaust of diesel and gasoline
engines varies and depends on the type of engine and its operating condi-
tions (Table 1), and also on the quality of the fuel, composition of the
fuel mixture in the engine cylinders, velocity and conditions of traffic,
systems of ignition and fuel feed control, qualifications of the service
personnel, etc. As is evident from Table 1, the amount of all the toxic
components in the exhaust gases exceeds the maximum permissible levels tens
and hundreds of times. The composition of the exhaust gases of gasoline
and diesel engines varies considerably. Engines running on gasoline are
characterized by a lower oxygen content, a higher content of carbon dioxide
and a particularly high content of carbon monoxide. This is one of the
chief factors preventing the use of gasoline engines in closed spaces, since
aeration of the latter requires 50-100 times more air than in the case of
diesel engines.
The complete combustion of fuel in engine cylinders requires a sufficient
amount of oxygen. A deficiency of the latter causes a sharp increase in the
content of hydrogen and carbon monoxide.
The extreme toxicity of carbon monoxide and its lack of odor and color
make this gas particularly dangerous. Its ability to displace oxygen from
compounds with hemoglobin is due to the greater affinity of hemoglobin for
carbon monoxide (200-300 times greater than for oxygen), so that carboxy-
hemoglobin is formed [16, 18, 22]. Carbon monoxide damages the nervous and
c ardi ovas cular sys terns [16].
The maximum permissible carbon monoxide concentration in the air of
industrial enterprises is 0.0016 vol. % (0.02 mg/1). If the carbon monoxide
content of inhaled air is 0.1%, death occurs after 30-60 min, and if 1% or
higher, immediately [17]. When nitrogen oxides are present in air, the
toxicity of carbon monoxide increases and its allowed content in air should
be decreased by a factor of 1.5, since the combined presence of these gases
intensifies their effect.
Sulfur dioxide, which is formed in the combustion of sulfur-containing
fuel, even when present in low concentrations, produces an unpleasant taste
in the mouth and causes irritation of the mucous membranes of the nose,
nasopharynx, trachea and bronchi, manifested in coughing spells, hoarseness
etc. A single inhalation of very high sulfur dioxide concentrations causes'
dyspnea and a rapid impairment of consciousness. Irritation of the mucosa
of the eyes and coughing are caused by a concentration of 0.05 mg/1. Man can
withstand a sulfur dioxide concentration of 0.3 mg/1 for only 1 minute [18].
- 6 -
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The maximum permissible sulfur dioxide concentration in the air of industrial
enterprises is considered to be 0.02 mg/1 [19].
Table 1
fypieal Content of Main Components of Exhaust Gases
of Internal Combustion Engines
Component
Carbon
Monoxide
Hydrogen
Aldehydes
Nitrogen
Hydrocarbons
Nitrogen
Oxides
(in terns
of N205)
Lead Com-
pounds
H-0 Vapor
Oxygen
Carbon
Dioxide
Soot
3,4-Benz-
pyrene
Gasoline
Engine
0,5—12,0
Vol. %
0,0—6,0
0,0-0,2
ng/1
74,0—77.0
Vol. %
0,2—3,0
Vol. °f>
0.0—0.8
Vol. %
3,0—5,5
Vol. %
0,3—8,0
Vol. %
6,0—12,0
Vol. %
0,0—0,04
10— aTy/m*
Diesel
Engine
0,01—0,50
Vol. %
0,001-0,009
ng/1
76,0—78,0
Vol. %
0,009—0,6
Vol. %
0,0002-4,5
Vol. %
0.5—4.0
Vol. %
2,0—18,0
Vol. #
1,0—10,0
Vol. f>
0,01—1,1
Up to
10v/m3
Permissible Content
in Air, ng/m*
[48, 78]
Maximum
Single
6,0
0,30****
0,035
5,0***
3,0**
0,3
Mean
Daily
1,0
Dangerously
0,1*
0,0005****
*
1,6***
3,0**
0,1
Nontoxic
»
0,15
Carcinc
0,06
genie
Fatal Dose
1 06. %
explosive
0,35 mg/1 in
the course
of 10 min
6 mg/1 in
the course
of 6-8 nil)
0,0007
rag/1
Carcinogenic
* Given for acrolein, ** propylene, *** gasoline, **** formaldehyde.
Nitrogen oxides are present in the composition of exhaust gases in the
form of nitric oxide and nitrogen dioxide. They are formed by the reaction
between atmospheric nitrogen and oxygen or water vapor at high pressure
(28-35 atm) and a temperature of 540-650° [20] during each compression in
the cylinders. The fuel does not participate directly in this reaction.
The literature indicates a direct relationship between the pollution of
the atmosphere with nitrogen oxides and the proximity of nitric acid plants
[32], and also the number of passing automobiles [12]. Nitrogen oxides are
very toxic. In the most typical cases, poisoning with nitrogen oxides begins
with a light cough which passes after awhile. At relatively high concentra-
tions, the irritation of the respiratory tract increases: a heavy cough and
sometimes headache, vomiting, etc., are observed.
- 7 -
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In nitric oxide poisoning, in addition to the general symptoms, dizzi-
ness and weakness are also observed, the face is pale, and the blood pressure
decreases. A 6-8 min inhalation of air containing approximately 6 mg/1 nitric
oxide and a 12 min inhalation of 3 mg/1 cause death. Poisoning with nitrogen
dioxide is characterized by edema of the lungs followed by bronchopneumonia.
A fatal concentration is 0.1 mg/1 inhaled for 1 hour [22]. The maximum per-
missible content of nitrogen oxides in the air of industrial enterprises is
0.005 mg/1 [18]. In Los Angeles, where 3.5 million automobiles are in use,
under certain weather conditions, a photochemical reaction is possible whereby
nitrogen oxides form substances which attack the mucosa of the eyes and also
plants and even rubber [23]. According to the data of American investigators,
the maximum permissible content of nitrogen oxides in the atmosphere is con-
sidered to be 0.025% by volume (based on nitrogen dioxide).
In their effect on the human body, nitrogen oxides are the most toxic
components of exhaust gases, and their neutralization by catalytic decompo-
sition or reduction assumes a special importance.
As is evident from Table 1, exhaust gases contain a large amount of
hydrocarbons whose concentration ranges from 0.2 to 3.0% depending on the
operating conditions of the gasoline engine. On some of Moscow's main
arteries, among other hydrocarbons, large amounts of pentane (up to 4.5 mg/m^)
and hexane (up to 4.15 mg/m^) have been observed [26]. At high concentrations,
they have a strong narcotic effect. In low concentrations, methane-series
hydrocarbons lower the blood pressure. The concentrations of these hydro-
carbons in the atmosphere of Moscow were as high as 7-8 mg/m^ in the summer
of 1967 and exceeded the level of their physiological action [25].
The composition of internal combustion engine exhausts includes aldehydes,
particularly crotonaldehyde and formaldehyde, whose amounts increase with the
load on the engine during starting, acceleration and operation on mountainous
terrain. Symptoms of poisoning with formaldehyde vapors include conjunctivitis,
head cold, bronchitis, etc. A slight irritant effect on the mucosa of the eyes
and respiratory tract was observed in cases where the formaldehyde concentra-
tion ranged from 0.001 to 0.0095 mg/1. A 0.025 mg/1 concentration of aldehydes
causes an acute irritation of the mucosa of the eyes. A 10 min stay in an
atmosphere containing acrolein in 0.35 mg/1 concentration is fatal to man. The
maximum permissible concentration is 0.001 mg/1.
Carbon dioxide present in a concentration up to 0.4% in air stimulates
breathing, and above 4% causes irritation of the respiratory tract, tinnitus,
dizziness, and headache.
Soot, whose content in the exhaust of diesel engines is high, constitutes
a major peril in air pollution. It consists mainly of carbon particles. Its
elementary analysis gives the following breakdown: 90-95% carbon, and 5^10%
balance divided equally between hydrogen and oxygen [26]. Soot has a large"
- 8 -
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adsorptive capacity for highly condensed hydrocarbons including 3,4-benzpy-
rene, a carcinogenic substance causing cancerous diseases.
Motor transport exhausts and petrochemical plants [28] constitute the
two major sources of contamination of the atmosphere with 3,4-benzpyrene.
It has been established [29] that the soot on the inner walls of exhaust
pipes of carburetor engines contains a larger amount of 3,4-benzpyrene than
the soot of diesel engines (200 y per g of soot of a gasoline engine, versus
1 Y per g of soot of a diesel engine).
Contamination of the atmosphere with 3,4-benzpyrene in major cities
increases in direct proportion to the number of inhabitants. In cities of
the Soviet Union, the concentration of 3,4-benzpyrene in air is approximately
10 times less than in England and the U.S.A. [30].
The book of L. M. Shabad and P.P. Dikun [301 notes the relationship
between the pollution of the atmosphere with 3,4-benzpyrene in major cities
and the increasing incidence of lung cancer.
Of considerable interest is the effect of the operating conditions of
an engine on the composition of the exhausts. In this sense, there is a
marked difference between the combustion of fuel in a carburetor gasoline
engine and its combustion in a diesel engine. However, in both cases the
formation of incomplete combustion products is due to a deficiency of the
oxygen required for the complete combustion of the fuel, i.e., the quantity
of these products increases as the air-fuel ratio is decreased.
The operating characteristics of diesel engines are such that as the
load decreases, the composition of the fuel mixture becomes leaner, and
therefore the content of the toxic components decreases at small loads on
the engine. Whereas during idling the carbon monoxide content amounts to
hundredths of one percent (vol. %), at maximum loads it reaches its maximum,
i.e., 0.5%. This also applies to the content of aldehydes and hydrocarbons.
One American study [31] cites data on the variation in the concentra-
tion of noxious impurities in the composition of exhaust gases of diesel
engines. The content of nitrogen oxides is maximum during acceleration
(0.085%) and normal running (0.025%), and that of carbon monoxide, during
acceleration (up to 0.1%).
In diesel engines, the composition of exhaust gases depends on the
mode of injection of the fuel into the engine cylinder. Straight injection
is better than lateral, but is associated with the formation of large amounts
of nitrogen oxides. The composition of exhaust gases of diesel engines with
different degrees of wear, cited in [32], shows that the exhaust contains
from 2.1 to 3.3% of unburned fuel (this causes the formation of soot on the
surface of catalysts during catalytic purification). The amount of soot and
- 9 -
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oil increases particularly in worn diesel engines, which run on richer
mixtures (air: fuel = 27:1) than new engines (air: fuel =40:1). In the
exhaust of worn engines, the content of aldehydes and volatile fatty acids
is 3-10 times .greater. The amount of soot in the exhaust of diesel engines
decreases when barium and other fuel additives that improve the combustion
processes are used [33].
The paper of S. S. Filatov [12] com-
pares the compositions of exhaust gases
from different makes of diesel dump trucks.
It shows that the lowest concentrations of
toxic components (carbon monoxide 0.05%,
nitrogen oxides 0.0029%, aldehydes 0.002%)
are observed in the exhaust of the most
advanced four-stroke engine of the MAZ-525
truck.
The condition of the fuel system of
diesel engines is very important. Thus,
it is shown in [63] that the replacement of
injectors in the YaAZ-210 Ye diesel engine
caused a severalfold decrease in the con-
tent of aldehydes in the exhaust gas.
The composition of gasoline engine
exhausts is chiefly determined by the air-
fuel ratio in the working mixture at the
instant of ignition. In operation with an
excess air coefficient a1 (1.01-1.1) does it approach zero (Fig. 1) [323]. 0. K. Demochka notes
that under urban conditions, the engine of the GAZ-51 motor vehicle runs
mainly on a fuel mixture with a = 0.6-0.95, which decreases to 0.5-0.7 during
idling and deep throttle conditions, substantially increasing the carbon
monoxide content in the exhaust.
Data on the composition of the exhaust gas of gasoline engines as a
function of the content of fuel vapor in the air-fuel mixture are given by
M. S. Gershenovich and N. Z. Kotelkov [6]. The lowest content of toxic
components and hydrogen in the exhaust gas is observed when engines operate
on lean mixtures.
The effect of the air-fuel ratio on the hydrocarbon content is similar/
[14, 20, 35], as indicated by the data of Fig. 2.
Fig. 1. Content of carbon monox-
ide, hydrogen, and carbon dioxide
in the exhaust of a carburetor
engine vs. excess air coefficient
[225].
- 10 -
-------
a n M
Air/fuel ratio
Fig. 2. Change in the content
of hydrocarbons in the exhaust
as a function of the mixture
ratio [14],
The amount of toxic components in
the exhaust gases of gasoline engines
varies with the run of the engine, its
load, power, and operating conditions.
Figures 3 and 4 show the content of the
various components of exhaust gases as
a function of the traveling speed of the
automobile and its loads [14].
It is evident that a considerable
content of products of incomplete fuel
combustion - carbon monoxide and hydro-
carbons - is observed under conditions
close to idling and during idling, when
because of the .combustion of an enriched
fuel mixture, the amount of carbon monox-
ide amounts to 5%, and also at higher
traveling speeds of the automobile.
'max.
Fig. 5. Change in the relative amounts of
gasoline engine exhaust components as a
function of the load
- 11 -
-------
At a speed of 120 km/hr, the carbon monoxide concentration rises to 6% of
the total gas volume. At the same time, in the range up to 50% load at a
speed of 60-70 km/hr, the content of incomplete combustion products declines
sharply, and in some cases none can be detected at all. The same applies to
nitrogen oxides and hydrocarbons. At a load of up to 20-50% on the engine,
their content is very low, but increases sharply at maximum power. As the
load of the gasoline engine increases, the carbon monoxide content can, as
is evident from Fig. 3, rise from 1 to 4-5 vol. %.
O Idling JO
Fig. 4. Composition of dry exhaust gases vs.
traveling speed of automobile with "Moskvich-40ff'
engine traveling along a horizontal hard-surface
road [ft ].
- 12 -
-------
The relative duration of the running of trucks under forced idling
(braking) and independent idling (stopping of buses during discharging
in wintertime) conditions, when they operate on enriched mixtures, amounts
to 18 and 30% respectively of the total time of operation [36], It is this
mode of operation of automobiles in cities that is primarily responsible
for air pollution [323].
In engine braking, the fuel in the cylinders burns at a = 0.67-0.68;
the ignition and combustion of such a mixture are difficult. As a result,
part of the fuel does not participate in the combustion and is discharged
in the form of spray particles, and the gases contain considerable carbon
monoxide and unsaturated hydrocarbons. A large amount of the fuel burns
incompletely, up to 4-6% under forced idling conditions of the GAZ-51 motor
vehicle and up to 8-14% on mountainous terrain [37].
iO
30
Traveling speed of automo-
bile, km/hr.
Fig. 5. Emission of carbon monoxide in the exhaust
gas under different conditions of.operation of
ZIL-150 motor vehicle [5j.
In order to decrease the content of toxic components in the exhaust
gases of carburetor engines under three types of running conditions, a vacuum
regulator is recommended which permits the admission of extra air into the
combustion chambers [36]. When this regulator is used, one can achieve an
80-90% reduction in carbon monoxide concentration and a 10-fold reduction of
the content of formaldehyde and other substances (acrolein, benzene).
An interesting calculation is given in M. S. Korenev's survey [5] of
the possible emission of carbon monoxide for different operating conditions
of the ZIL-150 motor vehicle (Fig. 5). It is evident that about 30 kg of
carbon monoxide is evolved by the combustion of 1 ton of gasoline in the
- 13 -
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engine, at a traveling speed of 20-40 kra/hr. The amount of CO increases
at a higher traveling speed and during idling. These data are somewhat
relative, but they can give an idea of the amounts of emitted carbon monox-
ide when it is necessary to have a general estimate of the toxicity of the
traffic.
In our view, a more correct method of evaluating the toxicity of exhaust
gases has been proposed by I. L. Varshavskiy, L. S. Zolotarevskiy and
L. Ye. Ignatovich [38]. They refer the amount of emitted carbon monoxide in
grains to a unit of the path traveled by the automobile (Fig. 6).
160
J20
10
Fa
g CO/tan
" 0,O/0f
V. km/hr.
S3 eg
as
Fig. 6. CO toxicity characteristic of ZIL-150 motor
vehicle after bench test data [38].
Calculation of the "specific toxicity" values (determined by the volume
of air necessary for neutralizing the individual toxic components of an
exhaust gas), carried out by L. S. Zolotarevskiy, made it possible to deter-
mine the danger contributed by each of the toxic substances. When gasoline
engines operate on lean mixtures, the main toxic components are products of
incomplete fuel combustion: carbon monoxide (up to 95% of the total toxicity)
and soot in the case of a diesel engine. In operation on rich mixtures
(gasoline engine), and as the load on the diesel engine increases, the chief
danger is due to nitrogen oxides, whose toxicity contribution climbs to
55-85% [14].
According to the data of Fitten [31], the content of toxic components
under different conditions of motion may fluctuate considerably: carbon
monoxide from 1.8 to 7.0%, hydrocarbons from 0.1 to 1.0, nitrogen oxides
from 0.002 to 0.105%, aldehydes from 0.001 to 0.03%.
- 14 -
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Table 2
Carbon Monoxide Content of Exhaust Gases (ZIL-120)
in Percent by Volume [20 ].
Traveling
Speed . of
Automobile.
km/hr
0
10
15
20
30
40
60
For Normal Technical
Condition of Engine
With Properly
Adjusted
Carburetor
1,5
1.5
—
0,2
0,2
0,2
1,2
With Carburetors
Giving a 2%
Overfeed
3.5
3,0
_
1,3
1,7
«— .
For Worn
Engine
6.6
—
6,2
6,1
8.4
2,3
^~
Data obtained by the author of [31] in a study of the operation of
22 automobiles indicate an increasing amount of CO and hydrocarbons during
idling and of nitrogen oxides in normal operation and during acceleration,
and also an increase in the amount of aldehydes during deceleration.
Among the many factors affecting the composition of the exhaust gases
are the structural characteristics of the engines, the extent of their wear,
and their technical condition (carburetor adjustment, etc.)- Thus,
N. Z. Bitkolov [20] has shown that the exhaust of a four-stroke engine con-
tains a considerably smaller amount of toxic components than that of two-
stroke engines. Furthermore, the volume of exhaust gases formed by the
combustion of 1 kg of fuel in a four-stroke engine decreases markedly
because of the absence of forced air supercharging.
Obstruction and malfunctions of air filters and a prolonged operation
of the engine cause a malfunction of the fuel- and air-feed equipment and
a decrease of the adjusted air-fuel ratio. Owing to the operation on en-
riched mixtures, the composition of the exhaust gases of improperly adjusted
and worn engines contains larger amounts of carbon monoxide and hydrocarbons
than do the exhaust gases of new engines. For example, the carbon monoxide
content in the exhaust gases of a worn ZIL-120 engine is four times greater
than in the exhaust of a new engine (Table 2).
According to the data of Zh. G. Manusadzhyants and L. L. Stepanov [39],
in 70% of 368 operating GAZ-51 and ZIL-164 motor vehicles that were studied,
the idling system of the carburetor was found to be faulty, and in 50% an
improper adjustment of the proportioning system was observed. As a result,
the exhaust gases of most automobiles contained from 6 to 13% carbon monox-
ide. After the fuel feed process was adjusted, the amount of carbon monoxide
decreased sharply (to 1%). The grade of fuel has a considerable effect on
- 15 -
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the carbon monoxide content.
and 4.
Data on this effect are listed in Tables 3
Table 3
Carbon Monoxide Content
of Exhaust Gases as a
Function of Gasoline
Grade Used During
Operation of
ZIL-120 Engine.
Table 4
Content of Carbon Monoxide and Hydrocarbons in
the Exhaust of ZIL-156 Engine
During Idling [48].
Speed,
Icm/hr
6
10
20
30
40
CO Content,
at
7>
A.-70
Gaso-
line
1,5
2,5
1.5
1,5
1,5
A-56
Gaso-
line
3,5
3,1
3,0
3,0
1,5
Distance of
Sample Col-
lector from
End of
Exhaust
Pipe, cm
10
200
Gasoline I Compressed Gas
Content, mg/m^
Carbon
Monox-
ide
279,3
478,8
118,7
106,4
Hydro-
Carbons
1044,2
991,1
151,4
79,8
Carbon
Monox-
ide
71,5
53,0
11,0
17,0
Hydro-
Carbons
7,3
7,46
3,83
4,75
As is evident from the tables, the use of gaseous and high-octane
fuel without tetraethyllead additives substantially decreases the carbon
monoxide and hydrocarbon contents of the exhaust gases.*
The decrease of atmospheric pressure associated with the operation of
engines in mountainous areas affects the air-fuel ratio. In automobiles
with a normally adjusted carburetor (a = 1.0-1.1), when the air pressure
is reduced [40] by 10% as compared with normal pressure for which the feed
has been adjusted, the fuel consumption increases by 7%. When the pressure
drops 30%, which corresponds to the pressure at 3000 m above sea level,
the specific fuel consumption increases by 30%. The decrease of the excess
air coefficient causes a sharp increase in the carbon monoxide concentration
of the exhaust gases.
The same effect is observed when the pressure of the air entering the
engine is reduced by passing the air through the throttle valve in a worn
engine.
Tests performed by N. Z. Bitkolov [20] on two engines at pressures of
756, 660, and 610 mm Hg also showed that as the air pressure decreases
the carbon monoxide content of the exhaust gases increases markedly and
the air-fuel ratio decreases.
* Results of Tables 2, 5 and 4, based on unpublished data of a series of studies, were
under incomparable conditions and must be considered debatable. stuQies, were
- 16 -
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Interesting relationships were found by L. M. Shabad and A. Ya. Khesina
[27] in the effect of the operating conditions of the engine on the content
of carcinogenic hydrocarbons, particularly 3,4-benzpyrene, in the exhaust of
gasoline and diesel engines. In the operation of the YaAZ-204 engine, the
amount of 3,4-benzpyrene increases from 4.3 yg/min at a load of 10% of maxi-
mum power to 20.1 yg/min at maximum power. During idling, the amount of
3,4-benzpyrene increases from 1.3 yg/min when the engine operates at 500 rpm
to 8.41 yg/min at 1500 rpm. A similar pattern was observed in other brands
of diesel engines. Thus, in [53], where the content of 3,4-benzpyrene was
studied in the exhaust gas of a two-stroke three-cylinder engine, an increase
of its concentrations was shown during idling and at a traveling speed of
30 km/hr.
The largest amounts of 3,4-benzpyrene are discharged during incomplete
combustion of the fuel resulting from an increased fuel feed, especially
when the engines are started up or turned off, when the automobile starts to
move, and at intersections.
For a carburetor engine, the content 3,4-benzpyrene increases at high
loads, in idling (particularly at low rpm), and when low-octane gasoline is
used. The content of 3,4-benzpyrene in automobiles operating on overrich
mixtures increases sharply (by a factor of two) [55].
The content of carcinogens in exhaust gases can be cut in half by
decomposing them catalytically [181, 27] in gas purifiers with a Pt and
copper oxide-chromium oxide catalysts, and also by using a special anti-
smoking additives (1%) to the diesel fuel which decrease the amount of
3,4-benzpyrene by 60-80% [41].
State road tests of catalytic gas purifiers on flat terrain in Moscow
and in Alma-Ata, located at an altitude of 800-1000 m above sea level,
conducted by LANE and KazNIPIAT, yielded some interesting data on the
change of the composition of exhaust gases from various engines.
Figures 7 and 8 show data on the average oxygen content of exhaust gases
of different engines in the areas of Moscow and Alma-Ata (processed data of
LANE and KazNIPIAT, obtained by analyzing the gases of three automobiles of
each brand with gas samples taken once and twice).
It is evident from Fig. 7 that the maximum quantity of oxygen is
present in the gas when the automobiles are idling, and as the traveling
speed increases, this quantity decreases, then increases slightly at 60 km/hr.
The average oxygen content in the exhaust during idling ranges from 5 to 15%,
reaching a maximum for GAZ-51, ZIL-130 (12-15%) and a minimum for "Moskvich"
motor vehicles, 5-6%.
During the operation of different motor vehicles, in Alma-Ata, the
average oxygen content in the exhaust decreased to 5-7% during idling and
- 17 -
-------
ranged from 3 to 5% at 30 km/hr and from 3 to 6% at 60 km/hr.
1 «J
.2
«J
• 4
B JO 45 oO
Traveling speed, km/hr.
Fig. 7. Oxygen content of exhaust gases of various
engines operating in the Moscow area as a function of
the traveling speed.
1 - ZIL-585; 2 - GAZ-51; 3 - ZIL-130; 4 - "Volga";
5 - "Moskvich-4031.
The carbon monoxide content of exhaust gases of the engines operated
in Moscow ranged from 0 to 10% during idling depending on the brand of the
motor vehicle; it decreased to 2-3% for "Moskvich" and to 0-6% for "Volga",
ZIL-585, and GAZ-51 as the traveling speed increased to 60-75 km/hr. The
minimum amount of carbon monoxide during idling was observed in the exhaust
of ZIL-130 (up to 2.0-3.0%), and the maximum in the case of "Volga" and
"Moskvich" (0-4%, 3.7-10.0%). The CO* concentration in the exhaust of the
engines of GAZ-51 and "Moskvich-408" In Alma-Ata considerably exceeded that
of the other engines in the Moscow area at speeds of 30-60 km/hr. Whereas
in Moscow the carbon monoxide content in the exhaust of the "Moskvich"
motor vehicle did not exceed 3-4% in this speed range, in Alma-Ata it ranged
from 2 to 10%, and for the engine of GAZ-51 amounted to 0-8% in Alma-Ata
and 4-6% in Moscow under all operating conditions. The lowest carbon monox-
ide content was found in the case of the structurally newer engine PAZ-652
under all operating conditions.
As was shown by the analyses, in addition to carbon monoxide, the compo-
sition of the exhaust gases from the engine of GAZ-51 contains a large amount
of hydrogen. Its content in the exhaust of some automobiles amounts to as
much as 5-6 or more volume percent.
It follows from the analysis carried out by KazNIPIAT on the exhaust
gases of 50 automobiles that the carbon monoxide concentration in the exhaust
gas of the GAZ-52 engine is related to the hydrogen content.
An arbitrary classification of the motor vehicles into two groups, in
the first of which the hydrogen content of the exhaust did not exceed 2.5%
(12 automobiles) and in the second was higher than 2.5% (38 motor vehicles),
- 18 -
-------
a
Traveling speed, km/hr.
Fig. 8. Oxygen content of exhaust gases of different engines
in the Alma-Ata area vs. traveling speed.
1 - GAZ-52; 2 - "Moskvich kOff'; 3 - ZIL-585; 4 - PAZ-652.
indicates that these groups are characterized by different limits of fluctu-
ations in carbon monoxide content. In the exhaust gas of motor vehicles of
the first group (Fig. 9 a), this content ranges from 0 to 57,'under all
operating conditions, and in the second group (Fig. 9 b), from 0 to 10-11%
at 40 and 60 km/hr and from 5 to 11% during idling. Apparently, the presence
of substantial amounts of carbon monoxide and hydrogen in the exhaust gases
of most motor vehicles is due to a partial cracking of the fuel and the
incompleteness of its combustion caused by an insufficiency of air in the
composition of the combustible mixture. This is due to an insufficient
adjustment of engines which had been little worn in (most of the motor
vehicles had a low mileage), and to the lower atmospheric pressure in Alma-Ata.
Thus, analysis of the literature data indicates that the content of
toxic components, especially carbon monoxide, in the exhaust gases of gaso-
line and diesel engines depends on many factors and shows a particular increase
during idling and at high traveling speeds, when increasing the load and
braking, stopping and starting, and also in motor vehicles with a maladjusted
fuel feed in the case of a worn engine and when the latter operates on low-
octane gasoline or when the oxygen content of the air is low (mountainous areas
and high mountains).
A substantial reduction in the air pollution of large cities, shafts,
open-pit mines, and closed industrial buildings can be achieved by carrying
through extensive organizational and technical measures [154].
It is very important to establish more rigid norms for the content of
toxic components in engine exhausts and to follow them, particularly in areas
where motor transport is the chief source of atmospheric contamination.
- 19 -
-------
CO content,
I *
•••v
*:-
•••
-•X.
•
•:•••
vi. ••••
JO W 6O
CO, vol. % before neutralization
c
/
• •••
•**
-------
At present time, the legislatures of many countries (certain states
in the U.S.A., England, the German Federal Republic [42]) have imposed
restrictions mainly on smoke discharges. For example, the city of Los
Angeles prohibits the discharge of smoke with a density of 2 or more units
on the Runkelmans scale for more than 3 minutes per hour.
In some countries and states of the U.S.A., where the traffic is par-
ticularly congested, the exhaust gases comprise the bulk of the atmospheric
pollutants (for example, in Los Angeles, 80% of the total pollution of the
atmosphere with hydrocarbons and 65% of pollution with nitrogen oxides are
due to motor transport), and restrictions are placed on the concentrations
of a number of the components of the exhaust gases. Thus, the laws of the
state of California (which apply to the first 80,000 km of the motor vehicle)
set the limiting concentrations of toxic components according to the type of
engine and its power. For engines with a displacement of 0.2-1.64 1, the
carbon monoxide content of the exhaust gas must not exceed 2.3%, and the
hydrocarbon content must not be more than 410 parts per million. As the
engine displacement increases to 1.64-2.39 1 and above, the amount of car-
bon monoxide must not exceed 1.5-2.0%, and that of hydrocarbons, 275-350
parts per million [34, 143].
In the USSR, the norm recommended for the carbon monoxide content of
exhaust gases is 2% of the total volume of these gases. To reduce the pol-
lution of the atmosphere with toxic components of exhaust gases in major
cities of the USSR, motor vehicles are converted to high-octane and gas
fuel. Thus, in Moscow, 3000 motor vehicles were running on liquefied gas
in 1965 [44, 45], continuously moving traffic with a minimum number of inter-
sections is being established, and central arteries are kept free of automotive
trucks, particularly those with diesel engines. The construction of under-
passes also sharply reduces the carbon monoxide concentration of air [48].
Thus, whereas on Mayakovskiy Plaza in Moscow before the underpass was built
the maximum carbon monoxide concentration was 70 mg/m3 (10 times the permis-
sible level), and the average was 20.7 mg/m3 (3 times greater), now the
maximum value is 15.4 and the average is 8.2 mg/m3; the hydrocarbon content
of air was reduced severalfold.
Among the technical measures aimed at reducing the content of toxic
components in the exhaust gases, one must mention first and foremost those
taken toward a rigorous observance of the rules of operation and technical
servicing of engines (carburetor adjustment, prohibition of the operation of
defective engines) and the improvement of the fuel combustion process: intro-
duction of antechamber flame ignition, a special vacuum regulator, and anti-
smoking fuel additives [41, 46, 44, 7]. A radical means of decreasing the
toxicity of engine exhausts and completely eliminating this problem would be
the conversion to electric cars operating on storage and fuel batteries [7, 49].
Among the possible steps toward reducing the toxicity of the exhaust
gases of chemical plants and internal combustion engines, major importance
- 21 -
-------
is now being assumed by their purification and neutralization by different
methods: chemical binding of aldehydes and nitrogen oxides by passing
them through liquid filters in the form of scrutibers filled with a solution
of sodium sulfate and hydroquinone, sodium carbonate, and catalytic oxida-
tion of the toxic components in the gas phase.
Liquid "neutralizers" permit the binding of 60% of nitrogen oxides and
90% of aldehydes, but do not remove carbon monoxide. The latter can be
oxidized in the liquid phase at low space velocities (3 x 10^ hr~l) by using
a low temperature (20-40°C) homogeneous catalyst consisting of a mixture of
complex salts of palladium and copper [50, 51].
Because of the low efficiency of noncatalytic liquid neutralizers with
respect to carbon monoxide, they cannot be used for purifying the exhaust
gases of gasoline engines and are chiefly employed in diesel engines operating
underground. A drawback of this type of gas purifiers is also their size and
the frequent replacement of the absorbing solution (once every shift).
The most promising method of purifying exhaust gases containing products
of incomplete fuel combustion is the catalytic oxidation of toxic components.
Studies aimed at the development of exhaust-purifying catalysts were
carried out in the 1950fs in the U.S.A. (Houdry) and in the 1960fs in the
USSR chiefly by the Institutes NIOGAZ (Central Scientific Research Laboratory
for the Purification of Industrial Gases), NAMI (State All-Union "Order of
Labor Red Banner" Automobile and Automobile Engine Scientific Research Insti-
tute) , and later by the Karpov Physicochemical Institute (Moscow), the
Institute of Chemical Sciences of the Kazakh Academy of Sciences (Alma-Ata),
and by the Azizbekov Institute of Petroleum Chemistry (Baku).
The most universal exhaust-purifying catalyst was found to be platinum.
A catalytic gas purifier with platinum deposited in a special manner on
ceramic material was patented as a catalyst by Houdry in the U.S.A. This
purifier was then adopted widely, for example, introduced into mass produc-
tion by the "Oxy-France" Co. in France.
It must be noted that the idea of using platinum as a catalyst for
purifying exhaust gases was not new. Back in 1938, M. S. Gershenovich and
N. Z. Kotelkov proposed for this purpose platinized nichrome consisting of
a screen of nichrome steel (d = 0.8 mm) on which platinum was deposited by
brazing. The device for gas purification consisted of a cylinder 25.5 cm in
diameter and 60 cm long in which 20 screens of platinum nichrome were mounted
perpendicular to the cylinder axis.
In the USSR, a platinum catalyst on Y"^!-^* was developed for thesei? .'
purposes: its bench and road tests showed a high efficiency and stability
in the purification of diesel and gasoline engine exhausts. /
- 22 -
-------
Because of its scarcity and high cost, platinum catalyst can be used
only for purifying the exhaust gases of engines operating underground. This
has led in the last 20-25 years to many attempts to replace platinum by other
metals and their oxides in the USSR and other countries. The research was
aimed primarily at selecting the catalysts and studying the kinetics and
mechanism of oxidation of the chief toxic components: carbon monoxide, hydro-
carbons, and aldehydes. The difficulty of selecting catalysts for purifying
exhaust gases lies in the rigid requirements for the specific conditions of
their subsequent operation in automobiles: a high efficiency, stability and
operational durability at considerable space velocities of the gas flows (up
to 100 x 103 hr"1), an abrupt change in the catalyst temperature (200-800°),
high concentrations of toxic components, and the presence of catalytic
poisons (lead, sulfur, soot). A major importance is assumed by the method
of preparation of catalysts with a high operational impact strength and wear
resistance during the exothermic oxidation processes.
Because of the unusual conditions of operation of exhaust-purifying
catalysts, few catalysts are known at the present time (palladium, vanadium)
which do not contain platinum and have successfully passed the stage of bench
and road tests and provide a high degree of purification of exhaust gases.
In spite of intensive research, with the exception of Prance, no mass pro-
duction of catalytic gas purifiers for mass-produced automobiles has been
set up in any country thus far.
At the Institute of Chemical Sciences of the Kazakh Academy of Sciences,
studies on the selection and perfection of exhaust-purifying catalysts have
been conducted since 1%0. A large amount of experimental material has thus
accumulated which has been published in part in the form of individual papers
and author's certificates [54, 56-62, 266, 267].
After bench and experimental and road checks (at LANE) one of the pro-
posed catalysts (palladium) has been recommended for mass road tests, the
first stage of which - efficiency tests - was carried out jointly by LANE
and KazNIPIAT in 1967. The results of the efficiency tests of palladium
catalysts under road conditions are presented in Chapter 6 of this book.
In the near future, LANE will carry out the second stage of stability and
durability tests. !
- 23 -
-------
Chapter 2
CATALYTIC OXIDATION OF CARBON MONOXIDE
The catalytic oxidation of carbon monoxide has been extensively studied
for the purpose of investigating the mechanism of the process and using dif-
ferent contacts for removing carbon monoxide from air. An exhaustive survey
of studies in this area for up to 1950 was given by M. Katz [162]. A prac-
tical result of these studies was the development and improvement of "hopca-
lite," a catalyst successfully used for removing carbon monoxide from air at
low temperatures in modern gas masks [21, 165-169, 470],
In the last decade, the rapid development of industrial organic synthe-
sis and the growth of motor transport have created the problem of purifica-
tion of the exhaust gases of internal combustion engines and waste gases of
chemical plants (cracking, caprolactam, rubber, coking, paint and varnish
plants, etc.) through removal of toxic components, the bulk of which con-
sists of carbon monoxide, nitrogen oxides, and hydrocarbons. As a result,
research on complete catalytic oxidation has assumed an even greater prac-
tical importance. In the 1950's-60's, thorough investigations were under-
taken to determine the mechanism of the processes and action of catalysts,
and their results are being applied in industry.
Table 5 summarizes the literature data on the catalytic oxidation of
carbon monoxide. Included are studies where carbon monoxide was oxidized
in laboratory units at relatively high space velocities and temperatures
approximating the conditions of their subsequent practical application and
the removal of carbon monoxide from actually occurring gaseous mixtures.
It is well known that the principal catalysts for oxidation processes
(oxidation of S02 to SOo, of ammonia to nitric acid, etc.) are metals,
alloys, and oxides (on carriers or in the form of mixtures) of elements of
group 8 and other groups of the periodic system.
As is evident from Table 5, in the case of oxidation of carbon monoxide,
the researchers' attention was directed to the study of metal and mixed cat-
alysts on carriers. The platinum catalyst in the reaction of carbon monoxide
oxidation was studied by N. Z. Kotelkov [6], L. Ya. Margolis, 0. M. Todes
[97, 374], Houdry [82, 83], Kennan and welling [87], and D. V. Sokol'skiy et
al. [54]. Results of bench tests of platinum catalyst in the USSR are de-
scribed in the papers of V. V. Goncharov and R. V. Malov [70]. Platinum on
a metal carrier - nichrome - for the removal of carbon monoxide from gaso"
line engine exhausts was first proposed by N. Z. Kotelkov back in 1938 [6].
Later, this contact was used for the quantitative analysis of gas mixtures.
Judging from the patent literature and statements in the press [82, 83],
extensive research on the selection of catalysts for the complete oxidation
of toxic components of exhaust gases was carried out by the American Scientist
- 24 -
-------
Table 5.
Catalytic Oxidation of Carbon Monoxide (Laboratory Data).
Catalyst
composition
1
Pt/Al203 «n ceramic
Pt/asbesfcos 0,05— 0,1 %Pl
Pt/Al2O3
Pt/SiOa
Pt/nichrome
Pt/AJjCb .
AP-56 platinum,
freshly prepared
AP-56 platinum,
used
Pd/chamotte
Pd/AUOa
Pd/AUO3
Pt— Pd/Al20,
Pd— Ru/AlaO3
Pd— Ag/Al-A POI P
Copper-ohromium oxide
Copper-chromium CuO :
:CraO3=l:2
Copper-chromium GIPKh- •
105
PCaOa/AUOj
FejOaicommercial
AlaO3, promoted
with CuO
CuO/AlaOa (13 6—50 wt.
% CuO)
CuO/AlaOa (1:1)
CuO/FeaOa
clay
MnFea04
CuO/MnOa
chamotte
CuMn2O4
Composition
of gas mixture
2
Exhaust gas of gasoline
engine
% CO in air
Exhaust gas of gasoline
engine ,
Close to exhaust com-
position
Exhaust gas of gasoline
engine
1% CO + air
fr
»
CO:H2=1,76:1
CO+H2-6,3%
SCO+H2/O2=3
1% CO + air
»
»
»
»
2%CO+3% 02+N2
1% CO + air
»
4% CO in air
1-6% CO, 02
9-19% C02, 1-3%, 1-
3% CO (regeneration
gases)
1% CO in air
1000—100 parts.per.
million in air
Exhaust gas with L5—
7.0% CO
1% CO in air
2.0—6% CO in air
CO:H2=1,T6:1
CO+H2=6,3%
CO+H2:Oa=l:3
2—6% CO "i air
Space velocity
x 103 hr'1
3
80— 100,0
—
80—120,0
9,0
3 I/sec, surface of spiral
i.l m2
^
»
10—18
6—30
86—72
»
»
»
9,5—52
86—72
»
6—8
4—8
40
10—16
»
36—72
2,4-6,0
10-18
2—4
- 25 -
-------
Continuation of Table 5
Degree of oxidation of CO, %
150°
4
8
—
—
^
—
95
65
—
—
40
40
—
—
—
—
—
•* -
___
60
,-
—
—
__
—
200°
5
30
20
—
80—100
100
100
100
80—90
40—75
75
30
47—100
30—40
20—30
—
™
60—65
98
100
20—40
35—62
98
250°
6
—
50
—
100
100
100
100
100
100
100
92
45
65—80
—
_
—
96
100
_
40
—
_
99
300°
~
100
73
100
100
100
100
100
100
75
100
100
100
100
91
90—100
90—95
95—100
—
94
100
—
75—90
85—96
45—75
99,6
400'
8
100
82
100
100
100
100
100
100
100
100
100
100
100
100
100
100
60
96
100
—
_
95—
—100
95—99
_
99,6
500°
9
100
—
100
100
100
100
100
100
70—90
100
100
100
100
100
100
100
100
90
97
100
—
_
100
90—95
—
Characteristics
of *the process
10
—
—
—
__
—
• —
—
—
—
—
—
—
—
—
—
Catalyst is stable to
heat in a stream of air
at 900-950°
Catalyst is stable to
heat (900-950°), sur-
face remains unchanged
—
—
—
.__
—
Refer-
ence
j
11
[82,83]
[97]
[70]
[87]
[6]
[54]
—
[86]
[85]
[54]
[54]
[267]
[90]
[62,58]
[11]
[129]
[128,
130]
[62,
113]
[110]
»
[58,62]
[91]
[86]
[91]
- 26 -
-------
Continuation of Table 5
CuO-MnO2
A1203
(3:1, 3$ oxides on
support)
Manganese ore of Nikopol?
deposit
Kazakhstan copper ore,
malachite, ohrysocolla
Aktyubinsk chromium ore
Manganese ore of Nikopof
deposit, activated with
10-20* CuO
1% CO in air
Ferromanganese acti-
vated with CuO
Pyrolusite + dunite +
CuO (1:1:1)
Dunite activated with
Mn02 + CuO
Dunite + NiO
Dunite + HiO + HnO
Ferromanganese + dunite
+ GuO !,
Homogeneous catalyst:
3.0 g/1 Pd*2
Fe+3 - 1.1 g/1
Cl~/Br~ " 0.2
CHsCOO~=13,l g/i
g/1
Exhaust gas: 16-17$ 02,
\-yf> C02, 2.5-5.6$ CO,
0.008-0.013$ acrolein
Exhaust gas: CO 0.1-
2.7#. aldehyde 0.0008-
0.01$, nitrqgen oxide
0.005-O.C
0 3 — 2% carbo
in ai
monoxide-
18
18
36
Fluidized bed, thickness
of catalyst bed 25-30 cm
0,8
1,6
2,4
- 27 -
-------
Continuation of Table 5
4
35—50
—
_
—
27—39
__
,
—
—
_
—
5
8—98
0—60
0—75
20
35
3—67
1-83
~
—
—
_^
—
6
100
—
0—85
5—50
___
_
- -
—
—
—
7
100
3—87
5—90
65
79
9—99
0—96
J *
—
—
—
8
100
2—99
8-100
85
92
8—100
87—93
74—99
60—78
90—99
80—10
90—97
75
9
—
100
100
92
95
100
2—97
—
—
^
—
Complete oxidation is achieved at 20"
75 % at 20°
60 % at 20"
10
Water vapor up to %
las no deactivating ef-
'ect on catalyst
Stable in long-term
operation
Stable in operation
with % water vapor
Up to 60-7C# of ni-
trogen oxides and 70-
8C# acrolein removed
11
[113]
[114]
[58]
*
•
.[114]
on the contact at £114]
200°
Aldehydes oxidized
completely? content of
nitrogen oxides re-
mains unchanged
Aldehydes 20-6$ oxi-
dized, amount of ni-
trogen oxides in-
creases
Acrolein and formalde-
hyde oxidized complete-
ly, nitrogen oxides re-
main unchanged
New method of catalyst
regeneration with si-
multaneous oxidation of
CO has been proposed.
[115]
»
>
t
[50, 51
58, 60]
- 28 -
-------
Houdry. In 1950, he proposed a platinum catalyst, an "oxicat" consisting
of platinum specially deposited in a thin layer (0.05 mm) on a porcelain
carrier pretreated with ground colloidal aluminum oxide. The catalyst was
found to be stable when used for 1600 hr in an automobile. He also devel-
oped a catalyst for purifying the exhaust gases of automobiles operating on
ethyl gasoline. Unfortunately, the laboratory data on this work have not
been published in the literature. Soon thereafter, a platinum catalyst on
a ceramic carrier was designed for this purpose in the USSR, and later, on
an aluminum oxide carrier, mechanically strong samples of which are made in
the form of rods and beads according to a method developed by the Karpov
Physicochemical Institute [17, 20].
The removal of carbon monoxide from artificial mixtures and exhaust
gases on platinum catalysts occurs readily. At a platinum content of 0.2-
0.5 wt.%, carbon monoxide oxidizes to the extent of 20-30% at 200°C., and
at 300°C. a complete oxidation is observed over a wide range of space ve-
locities of the gas flows (up to 120,000 1/1 of catalyst per hour).
Among the plant catalysts tested, a high degree of activity in the re-
action of oxidation of carbon monoxide is displayed by the AP-56 platinum
catalyst in both the initial and used form, palladium-ruthenium [267] and
copper-chromium catalysts [62]. However, the mechanical strength of these
contacts is low. On the platinum and copper-chromium catalysts, hydrocarbons
and soot burn completely together with carbon monoxide at 500°C. and above.
The palladium-ruthenium catalyst in a reducing atmosphere is known as a
catalyst for the removal of nitrogen oxides and hydrocarbons from gases [440].
The drawbacks of platinum catalysts are their high cost and the scar-
city of Pt throughout the world, and also their inability to bring about
the reaction of complete oxidation of carbon monoxide and hydrocarbons at
temperatures below 150-200°C. This is the temperature range of the ex-
haust gases of idling engines, when the bulk of unburned components of the
fuel are discharged. Still unexplained is the role of the platinum catalyst
in the processes of decomposition of nitrogen oxides in oxygne-containing
gas mixtures.
Not as scarce and more accessible and cheaper is the palladium catalyst,
first investigated by 0. M. Todes et al. [85]. The authors of this paper and
later D. V. Sokol'skiy et al. [54] showed the great activity of the palladium
catalyst on a carrier in the oxidation of carbon monoxide in air. At space
velocities up to 30 x 10 hr'1 in a stream of air, this catalyst Achieves a
100% oxidation of carbon monoxide to carbon dioxide even at 200°C. The paper
[54] described a comprehensive study of the oxidation reaction of carbon
monoxide both in the liquid phase [50, 51, 58] in the presence of palladium
ions, and at a high temperature in the presence of palladium, .platinum and
mixed palladium-platinum and palladium-ruthenium catalysts on carriers [54,
56-61, 267]. In addition to studying the kinetics and mechanism of this re-
action, the authors were interested in the possibility of a practical
- 29 -
-------
JOO
oxidation of CO
WC., 14.4 x 105 hr
"1
400°C., 72 x 105 hr"1
300eC., 14.4 x ID? hr"1
30Q°CM 72 x 10^ hr"1-
Ce in
f.ff
Fig. _ 12. Oxidation_of 1% CO in a stream
o:' air on cerium oxide catalysts on alu-
minum oxide at a space velocity of
14.4-72.0 x 10? hr-1.
f.ot
*» Xfy-
Fjg. 13. _Promoting effect
of palladium on the oxids.-
tion process of 1% CO in a
stream of air (36 x 10* hr-1)
over a cerium oxide .'atalyst
on bead aluminum oxide
(0.5 wt. % Ce02).
It is obvious from the data shown in Figs. 12, 13, and 14 that a mutual
promoting effect is displayed in the case of mixed contacts. The observed
effects probably have a rational explanation only if one distributes the func-
tions among the various active surface centers of the mixed catalysts. The
acceleration of one process, for example, activation of carbon monoxide on
palladium atoms added to the cerium oxide catalyst on the carrier, increases
the electron concentration in the catalyst and facilitates the acceptor stage
of the process, i. e., the activation of oxygen on the metal oxides with for-
mation of oxygen ions. There is no doubt that the promoting causes a sub-
stantial change in the binding energy of the adsorbed substances, i. e., oxygen
in the reaction under consideration. It is known that the energy binding oxy-
gen to the surface of oxides, spinels and metal catalysts has a decisive in-
fluence on their activity in oxidation reactions of carbon monoxide, hydrogen,
and hydrocarbons [147, 161, 163, 164, 186].
The use of a mixed palladium-cerium oxide catalyst on aluminum oxide sub-
stantially lowers the temperature of the process: even at 200-250°C., a 60-
80% oxidation of carbon monoxide in the stream of air is observed. The high
activity of low-percentage cerium oxide catalyst on aluminum oxide in the
oxidation reaction of carbon monoxide is not unexpected. Rienacker has shown
that at a ratio of cerium dioxide: aluminum oxide = 3:4, this contact ma'ni-'
fects a catalytic activity in this reaction at 200-300°C. A 1007e oxidation /
of carbon monoxide at 270°C. is also possible on a thorium oxide - cerium •'
oxide contact [135]. The observed strong oxidizing properties of cerium oxide
catalyst are explained by the low binding energy of the adsorbed oxygen, which
- 34 -
-------
The special properties of other spinels are indicated in the paper [91],
which notes their high activity in the oxidation reaction of CO at space
velocities of 2.4-4-6 x 103 hr"1 and a CO concentration of 2-6%.
% oxidation of CO
too
eo
T.'C
Off
Off
300
ISO
Fig. 10. Oxidation of 1% CO in a stream of air at a space velocity
of 36 x 10' hr"1 on commercial catalysts.
1 - used AP-56; 2 - Fresh AP-56; 3 - copper-chroraium-barium catalyst;
4 - RPK-1; 5 - ROSh; 6 - GIPKh-105.
80
.60
10
30
son
*>o soo T;C
Fig. 11. Oxidation of 1% CO in a stream of air at
a space velocity of 36 x 10' hr-1.
1 - Pd/Al205; 2 - MRA-5! 3 - Pt-Pd/ShAS-2; *t - Pe-
Cu oxide catalyst on clay; 5 - Cu-lin oxide catalyst/
6 - Pd-Ru.
- 31 -
-------
It has been shown that at 400-500°C., the degree of oxidation of carbon
monoxide on manganese ferrite, copper manganite and chromite, and manganese
chromite is 91-100%. As the temperature is lowered to 200-300°C., spinels
form the following sequence from the standpoint of the degree of oxidation:
copper manganite (98-99%), copper chromite (77-98%), manganese ferrite (62-
96%), and magnanese chromite (11-70%).
The copper-chromium catalyst has shown a high stability in prolonged
testing in the laboratory at temperatures above 500-600°C., and served for
620 hours without any appreciable decrease in activity [131].
T. G. Alkhazov and M. S. Belen'kiy made a thorough study of the oxida-
tion of carbon monoxide on an iron oxide catalyst on aluminum oxide [158,
130, 128, 129]. The maximum activity is reached at 1-2% Fe2C>3 in the contact:
at 200°C., 51%; 250°C., 30%; 300°C., 70%; 350°C., 90-95%.
The above authors note [129] the high stability of the iron oxide-alumi-
num catalyst during heat treatment (900-950°G. for 5-25 hours). This catalyst
withstood tests during oxidation of carbon monoxide in gases from the regenera-
tion of petroleum cracking catalysts [128]. It was shown that the most suit-
able carrier is plant aluminum oxide.
Researchers have been particularly interested in the possibility of
using hopcalite for removing CO from exhaust gases, and also mixtures of
copper and manganese oxides similar in composition to hopcalite [113, 91].
The activity of copper manganite (see Table 5) was high; starting at 200°C.,
carbon monoxide was virtually completely oxidized on this catalyst. This
showed it to be similar to hopcalite, which operates at low and even sub-
zero temperatures. However, hopcalites, copper oxide-manganese oxide and
other oxide catalysts, for example copper and copper^chromium ones, are
very sensitive to the action of water vapor and quickly lose their activity
[21-162] when used to remove CO from exhaust gases and mixtures containing
substantial concentrations of water vapor.
When oxides of copper and of copper and manganese are deposited on a
carrier, they become more resistant to the action of moisture [113]. It
has been shown that a water vapor content of up to 5% in a mixture of gases
does not reduce the activity of the copper-manganese catalyst on bentonite
clay. In hopcalite deposited on bentonite clay, the mechanical strength
simultaneously increases [116], which is very important for the pratical
application of oxide catalysts of relatively low mechanical strength. In
addition to improving their stability to moisture, the use of these con-
tacts on carriers increases their resistance to sintering, to a reduction) of(
surface area at high temperatures, and to the formation of metal beads dur-
ing oxidation of large concentrations of CO and hydrocarbons.
The stability of manganese oxide and copper oxide catalysts to water
vapor can also be increased in another way, i. e., by promoting them with
- 32 -
-------
platinum, palladium, or silver oxides. Thus, a series of patents [121-124,
285, 363] indicate the promoting influence of silver, palladium and their
mixtures, and the moisture resistance of promoted oxide catalysts.
Katz and Halpern [120] have shown that when silver nitrate is added to
manganese catalyst during its preparation, a stable catalyst is obtained.
A high moisture content (up to 80%) favors the oxidation of carbon monoxide.
At the same time, it is important to deposit the mixture on a carrier (kaolin,
talc, asbestos).
In a study of the oxidation kinetics of carbon monoxide on manganese-
containing catalysts at low temperatures and pressures, it was observed [117]
that the strongest activating effect among the additives studied (Pt, Ag,
CuO, £6263, ^2^5) was displayed by platinum. An electron-microscopic study
of the catalyst established that platinum spreads, in a thin film over the
surface of manganese dioxide. The authors hold the view that Pt and Mh02
act as two independent catalysts: carbon monoxide is adsorbed on the plati-
num surface, and this in turn accelerates the process of activation of oxy-
gen on MhOn* A similar separation of the functions of the individual com-
ponents of mixed oxidation catalysts appears possible in an intimate ad-
sorptive but not chemical interaction of the components. A fact of this kind
was observed and thoroughly investigated by Royter et al. in the oxidation
reaction of hydrogen [118, 119, 160]. It was shown that platinum accelerates
the donor process (activation of HU), which is the rate-determining step in
the oxidation reaction of Ik on vanadium oxides, which proceeds in accordance
with an electron mechanism. Platinum promotes the activation of hydrogen by
dissociating the molecules into atoms and H+ ions, which because of their
high surface mobility migrate to areas of vanadium oxides adjacent to the
platinum. This facilitates the reaction of hydrogen with oxygen activated
on the vanadium oxides.
The promoting of oxide catalysts may lead to a change in the kinetics and
mechanism of the process [160]. No positive effect was observed by mixing
platinum and vanadium oxide mechanically.
Very similar results are obtained by promoting low-percentage vanadium
oxide (1.5 wt.% V205), cobalt oxide (0.5 wt.% cobaltous-cobaltic oxide) and
cerium oxide catalysts on aluminum oxide with palladium in the oxidation
reaction of carbon monoxide.
Figures 12, 13 and 14 present comparative data on the oxidation of 1%
of carbon monoxide on cerium dioxide deposited on beads of aluminum oxide,
and on catalysts with 0.5 wt.% cerium promoted with 0.05% palladium at
space velocities of 36 x 1Q3 hr'l (Fig. 13) and 72 x 10J hr'1 (Fig. 14).
The palladium was precipitated on low-percentage oxide catalysts by chem-
ical means.
- 33 -
-------
application of the catalysts to the removal of carbon monoxide from exhaust
gases.
Particular attention was focused on the methods of preparation of highly
active, stable, mechanically strong and easily regenerable palladium caatlysts.
A number of new methods for preparing contacts and carriers of different
chemical types and structures were used for this purpose. As a result, new
methods of preparation were proposed, along with new compositions of palla-
dium and mixed catalysts with a controllable depth of impregnation, for the
purpose of removing carbon monoxide from gasoline and diesel engine exhausts.
A special chapter is devoted to a discussion of these data.
In addition to metal contacts (platinum, palladium, ruthenium, silver)
on carriers for oxidizing carbon monoxide, oxides of many transition elements
mixed with one another, on carriers, or in the form of spinels, are widely
employed for the oxidation of carbon monoxide.
Among oxide catalysts, the copper and iron-copper catalysts on carriers
[62, 110, 113], copper-chromium [62, 90], manganese-copper catalysts of the
type of hopcalites [86, 113], manganese-iron [91], and copper-chromium cata-
lysts on carriers [62] have been thoroughly investigated. A detailed analysis
of the results of oxidation of CO obtained in their presence and of the mech-
anism of their action is given by D. V. Sokol'skiy and G. K. Alekseyeva [58,
62], M. S. Belen'kiy and M. Yu. Sultanov [157], and others.
The data listed in Table 5 attest to the high activity of oxide catalysts
under laboratory conditions. A particularly high activity, comparable to that
of platinum and palladium at space velocities of 36-72 x 10^ hr~^, is dis-
played by copper oxide and copper-chromium catalysts [58, 62, 90, 110, 113,
131]. In their presence, carbon monoxide is 50-100% oxidized even at 200°C.
(Fig. 10, 11).
In the case of oxidation of carbon monoxide on copper oxide without a
carrier, the method of preparation is very important. Addition of an alkali
(KOH) decreases the rates of adsorption and oxidation of carbon monoxide and
increases the adsorptive capacity of the contact for carbon dioxide - the re-
action product, thereby slowing down the process [144]. Copper oxide cata-
lysts are poisoned by water vapor. Cohen and Nobe [159], who studied the
effect of water vapor on the oxidation of carbon monoxide at space veloc-
ities of 10 x 10^ hr~l, showed that even slight concentrations of water
vapor strongly decrease the activity. Increasing the water vapor concen-
tration above 800 parts per million has practically no effect on the ac-
tivity of the contact.
The activity of copper-chromium oxide catalysts is determined by the
quantitative ratio of the oxides and their content on the carrier, and it is
maximum at a Cu:Cr203 ratio close to 1:2 [62, 58, 90], when they form a spinel.
- 30 -
-------
is comparable in mobility to oxygen adsorbed on cobaltous-cobaltic oxide [408].
As a result, during the oxidation of carbon monoxide on cerium oxide catalyst,
the process is inhibited by a slight adsorption of carbon monoxide (activation
energy, 10-12 kcal/mole). Promoting of the catalyst with palladium facilitat-
es the donor step, and the reaction proceeds at a lower activation energy
(6.5 kcal/mole). Recently, Barrett et al. [181] obtained a patent on a mixed
cobalt oxide - cerium contact (8.6% Ce02 and 8.8% Co) on aluminum oxide, re-
commended for the oxidation of carbon monoxide and hydrocarbons.
% oxidation of CO
too
200
3QQ
too
300 400 100 200
Temperature, "C.
Fig.. 14. Comparative oxidation of 1% CO on cerium oxide (o.5 wt. %,
curve 3), palladium (0.05 wt. #, curve 2), and cerium oxide-palladium
catalysts 10.05 % Pd, 0.5 wt. % Ce02i curve l) at a space velocity of
36 r. 105 lir'1 (a) and 72 x 105 hr"1 (b)
A survey of the extensive patent literature on the catalytic purifi-
cation of exhaust gases shows that in addition to platinum and oxide cata-
lysts, other catalysts have found broad applications: mixed supported
catalysts (on aluminum oxide, silica-alumina, etc.) consisting of oxides
of polyvalent metals (copper, chromium, vanadium, molybdenum, manganese,
cobalt, nickel) in the proportion of 0.5-25 wt. %, with platinum, palladium,
iridium, rhodium, and silver as promoters [123, 124, 125, 126]. The intro-
duction of salts of phosphoric acid and phosphoric acids themselves into the
composition of the catalysts [126] increases their stability to lead and
facilitates the regeneration.
In recent years, there has been a marked increase in the researchers'
interest in natural materials: refractories (dunite), copper, chromium,
- 35 -
-------
manganese and ferromanganese ores in various deposits. As is evident from
collective Table 5, "natural catalysts" possess a high activity in the' re-
action of carbon monoxide oxidation, particularly when activated with ox-
ides of copper, nickel, manganese, and silver [58, 92-94, 114, 115, 127].
Copper and chromium ores of the Kazakhstan deposits, malachite, Aktyubinsk
chromium ore and manganese ore of the Nikopol1 deposit at space velocities
of 18-36 x 103 hr"1 yield a 50-70% oxidation of carbon monoxide at 200-250°C.
(Fig. 15) in a stream of air. Despite the higher activity of pyrolusite and
malachite, Atasu and braunite ores in the oxidation reaction of carbon mon-
oxide, their value is decreased by their poor mechanical and heat-resisting
properties.
Manganese ore of the Nikopol1 deposit has a higher wear resistance.
The activity of manganese ores increases considerably when they are acti-
vated with copper oxide (3 wt. %) and silver (0.5 wt. %) and they can be
used for purifying the exhaust gases of thermal drilling rigs and in other
processes at lower temperatures (150-200°C.). The activation of manganese
ores with copper oxide increases their stability in long-term service and in
the presence of up to 5% water vapor [113]. Natural manganese ores activated
with copper oxide promote the oxidation of hydrocarbons in addition to that
of CO, the oxidation of aldehydes (up to 70-80%), and the elimination of
nitrogen oxides (up to 70%) [395] .
In selecting the ore and carrying out the activation of copper oxide
and silver salts with it, the method and conditions of thermal treatment
become significant. It is important to obtain and select an ore with the
maximum content of pyrolusite, a 8 modification of Mh02, the promoting of
which yields a greater effect than that of ct-
Decreasing the content of nitrogen oxides in mixtures after purifying
the exhaust gases in the presence of manganese ores assumes a major impor-
tance, since no other methods of removing nitrogen oxides from oxygen-con-
taining mixtures exist to date. The purification probably is also partly
due to absorption of nitrogen oxides by the ores with formation of manganese
and iron nitrates, which are capable of dissociating (decomposing) at higher
temperatures (above 300°C.). It is necessary to explore the mechanism of
the process and to determine the service life of such a catalyst.
In addition to the development of heterogeneous gas-phase catalysts
for oxidation of carbon monoxide, a homogeneous catalyst has been proposed
[50, 51, 58-60, 75]. The composition of the catalyst includes ions of
palladium, iron, copper, chromium, bromine, and acetic acid in certain pro-
portions. At the optimum relative amounts of the components, the catalyst;!
completely oxidizes 17. CO in a mixture at 20°C. at a space velocity of
800 1/1 of catalyst per hour (Fig. 16).
- 36 -
-------
% oxidation of CO
to
too
300
350
4tOO
via
Fig. 15. Oxidation of 1$ CO in a stream of air at a space
velocity of 36 x 103 hr-1 in the presence of manganese and
chromite ores [62, 114, 395] . 1 - Aktyubinsk chromite ore;
2 - Manganese ore of Nikopol1 deposit; 3 - same, promoted
with 3# copper oxide; 4 - same, p^moted with 0.5$ silver
oxide; 5 chrysocolla; 6 - malachite ore; 7 - pyrolusite;
8 - Atasu braunite ore.
too
to
o
o
'O
• JO
After electrochemical regeneration
if
lime, hr
to
Fig. 16. Oxidation of carbon monoxide in the presence of palla-
dium complexes in solution at 20°C. and a space velocity of 800
hr"1 with electrochemical stabilization of the catalyst [50].
A low-temperature homogeneous catalyst for oxidation of carbon monoxide
can be used successfully in plants and units where high temperatures are un-
safe (coal mines, cleaning ventilation units). An improvement of the design
of the device (the reaction occurs under foam conditions) will raise the ef-
ficiency of the catalyst and increase the space velocities of the gas flows.
- 37 -
-------
Judging from the available data, natural manganese ores activated with
copper or silver oxides appear to hold promise as inexpensive catalysts for
purifying exhaust gases containing CO, aldehydes, hydrocarbons, and nitro-
gen oxides at low temperatures. Tests of their activity and operational
stability in streams of exhaust gases should be accelerated on internal com-
bustion engine stands. Thus, in addition to platinum and mixed catalysts
of group 8 metals and also palladium and supported oxide catalysts promoted
with platinum group metals, of interest for the practical removal of car-
bon monoxide from exhaust gases may be natural ores activated with metal
oxides including oxides of precious metals.
- 38 -
-------
Chapter 3
OXIDATION OF CARBON MONOXIDE ON LOW-PERCENTAGE METAL CATALYSTS
A survey of the literature on catalytic removal of toxic components
from exhaust gases shows that the most suitable catalysts for this purpose
are low-percentage supported metal catalysts.
Because of the rigid conditions of operation of exhaust-purification
catalysts (high space velocities of up to 100 x 10^ hr~l, overheating to
800-1000°C. , stable activity for no less than 20,000 km) there follow some
special requirements with regard to the methods of their preparation. First
of all, the catalyst must be effective, stable tp thermal treatment over a
wide temperature range, and must be characterized by a strong adhesion
between the metal and the substrate and an optimum depth of impregnation of
the carrier. Of particular importance is the choice of the carrier, whose
chemical nature and structure determine the activity and operational strength
of the catalyst. There is need for simple methods of catalyst regeneration
in the course of operation and recovery of precious metals from the spent
contacts.
V
The section below discusses the development of a method of preparation
of platinum, palladium and mixed supported catalysts suitable for oxidizing
carbon monoside and other components of exhaust gases. Particular emphasis
is placed on the method of deposition of metals on the carrier, the condi-
tions of preliminary activation of the contacts, and effect of the carrier
on the activity and mechanical strength of the catalysts.
Methods of Preparation of Catalysts
There are a number of methods of preparing catalysts for oxidation-
reduction processes in the form of supported metals. They include:
1. Precipitation of metals from solutions of their salts or other
compounds, followed by roasting, and reduction.
2. Deposition of the metal layer by brazing from organic pastes.
3. Electrolytic deposition of metal on metal or on a conducting
layer previously deposited on the support.
4. Preparation of cermets by sintering.
5. Deposition of a metal layer by cathodic vaporization in a vacuum.
In practice, two variants of the first method have been most widely
adopted: adsorption by the carrier of compounds of active metals from dilute
solutions with removal of excess solution (adsorption catalysts) and impregna-
tion of the carrier with solutions of salts based on its moisture capacity.
- 39 -
-------
The second variant is simpler and more convenient, since in some cases the
steps of filtration and washing of the contacts are eliminated.
Usually, the carriers (A1203> silica gel, aluminosilicate, etc.)i from
which the moisture has been removed by drying, are impregnated with solutions
of salts of the corresponding metals, the moisture is driven off at 110-120°C.,
and reduction to metals is carried out in a stream of electrolytic hydrogen
at 200-500°C. Platinum, palladium [187-202] and palladium-ruthenium contacts
[203] are thus obtained for use in the removal of 02, NO and C2H2 from con-
verted gas.
Complex salts of platinum metals are decomposed to the metals by firing
at a high temperature. Thus, in the work of Kh. M. Minachev and N. I. Shuykin
et al., active Pt, Pd, and Re-Pd reforming catalysts were prepared by impreg-
nation of the carrier with solutions of the corresponding complex salts or
acids, followed by roasting [192, 193] or by treatment with hydrogen sulfide
at low temperature [234-238]. The activity of such contacts is positively
affected by the addition of compounds of group III metals and rare earth ele-
ments to the impregnating solution [242]. In the deposition of platinum on
nonporous carriers, the binder used by some authors is a mixture consisting of
an aqueous suspension of finely ground aluminum and beryllium oxides with an
admixture of aluminum nitrate [239-241]. Metal films strongly bound to the
base are thus formed.
The activity and stability of contacts obtained by impregnation are
greatly affected by the nature of the initial salt. Thus, a study by
M. D. Adamenkova and 0. M. Poltorak has shown (Table 6) that in the decompo-
sition of hydrogen peroxide, the greatest activity among platinum contacts
on silica gel is displayed by a catalyst prepared from a platinum ammine [227].
Table 6
Effect of the Nature of the Initial Platinum Salt on the Catalytic
Activity of Platinized Silica Gel Samples [22?].
Initial Platinum
Compounds
-------
Platinum contacts prepared from [Pt(NH3>^](OH)2 display a high sta-
bility during petroleum cracking [228] (Table 7).
Table 7
Activity and Stability of Petroleum-Cracking
Platinum Contacts
Initial Platinum
Compound
HaPtCl0
[Pt(NH3)4]Cl2
[PtOfflWiKOIO,
Platinum
Content, %
0,48
0,454
0,465
Reduction
in Octane
Number
2,5
4,0
2,0
Overall
Stability
Index
53
43
82
Other researchers [229] also indicate a high stability of platinum,
palladium, and rhodium oxidation, hydrogenation, cracking, and reforming
contacts prepared by impregnating aluminum oxide with solutions of organic
metal complexes containing no chloride ions.
In order to obtain a very uniform and strong coating of Pt, Pd, Bh, Ru,
Ag, or their mixtures (Pt-Kh, etc.) on the aluminosilicate carrier, it is
recommended that the catalyst be reduced while still moist (15-20% moisture
content) at a low temperature (up to 75°C.) with subsequent roasting in air
at 100-1000°C. [204]. The same effect is produced by the introduction of
oxidants into the impregnating solution. In US patents, it is recommended
that in the precipitation of platinum from chloroplatinic acid solution on
aluminum oxide, the oxidizing agents used be nitrates (nitric acid, 0.3-1.5
times the weight of the platinum) or hydrogen peroxide [209, 210].
In some studies, the carrier is first impregnated with solutions of
salts of metals, for example platinum and ruthenium [205], which are then
precipitated with sodium carbonate in the form of hydroxides. Lacev [206]
proposes that after the carrier has been impregnated with sodium carbonate,
the metal (Pt, Pd, Bh, Os) compound be deposited during boiling from organic
solutions (ketones). The metal' oxide, which thus deposits only on the outer
surface of the carrier, is dried after the ions of the initial salt are washed
off and is reduced in nitrogen-hydrogen mixtures at 250°C. [201, 202, 398].
A rapid reduction of the metals from the salts and formation of an active
metal layer is facilitated by a preliminary treatment of the carriers with
hydrogen or carbon monoxide [207, 208]. A positive effect on the reduction
rate is produced by the introduction of formaldehyde into the stream of hydro-
gen. Active palladium and platinum catalysts on asbestos fabric and porous
ceramic rings for industrial applications are thus obtained [77, 84, 211-213].
The method of preparation of supported metal catalysts is substantially
simplified by reducing the metals from their salts with the aid of reducing
- 41 -
-------
solutions that impregnate the carrier before or after deposition of the
salt of the initial compound. The reductants used are formaldehyde
[214-216, 219, 397], sodium formate [103, 197, 217, 218], sodium hypophos-
phite [219, 220], hydrazine [220-221], hydroxylamine [222], organic acids
in the presence of ammonia and without it [225, 226], ethylene glycol [224],
compounds of 1,4-dihydropyridine [223], or dialkyl sulfides [399]. The
temperature of preparation of the catalysts is thus substantially reduced,
thereby apparently causing the formation of metals in the form of fine crystals
with a nonequilibrium form of faceting, and a large fraction of amorphous
phase which is due to a decrease in the surface migration of the metal atoms
on the carrier.
Reduction of palladium with sodium formate [217, 218], and of platinum
and other metals of groups 8 and 1 with hydrazine and hydroxylamine [221,
222], is used to prepare active palladium, platinum and mixed catalysts for
the purification of internal combustion engine exhausts. A necessary step
in the preparation of these contacts is the washing of the catalyst to remove
extraneous ions following the interaction of the reactants on the carrier,
drying at 120-170°C., and roasting in a stream of air at 250-550°C. depending
on the type of contact.
If the composition of the complex organometallic compound includes
reducing agents such as the acetylene [230, 231], amine [233], alkyl, cyclo-
alkyl and other radicals [229, 335], the process of preparation of the
catalyst is even more simplified.
Thus, Bukhovets [230, 231] has shown that after impregnating the carriers
with complexes of palladium chloride or platinic chloride with dimethylethynyl-
carbinol, heating to 130°C. is sufficient to decompose the complexes formed
to the metals. The same method is recommended for preparing a platinum
catalyst by starting with organic complexes of platinum of the general formula
(Me, R^, Y )m, where Me is a polyvalent metal (Pt, Pd, Rh) , R is a hydrocarbon
radical of variable structure, and Y is H or OM [229].
In order to increase the stability of platinum-palladium catalysts in
the reaction of dehydrocyclization and aromatization, the carriers are impreg-
nated with solutions of complex salts of platinum and palladium with alkali
metals, for example, Na2PdCl, or K PtCl, [199, 400]. Alkali metal ions have
a stabilizing effect on platinum. The intensity of the bands of metallic
platinum in the x-ray spectra of these catalysts decreases, although the
average size of the platinum crystals remains unchanged [401].
Catalysts on metal carriers (screens, wires, sheet steel) are prepared
by electroplating, contact displacement of metals upon immersion of metal'
articles into solutions of the corresponding salts, and chemical reduction.
- 42 -
-------
The electroplating of platinum group metals has been treated in special
surveys and papers [402-407], so we shall not dwell on this method. Let us
note only that the electroplating of platinum is carried out from phosphate
electrolytes, and that of palladium, from phosphate and nitrite electrolytes
after special cleaning of the conducting surface [259-262]. A drawback of
contacts obtained by electrolytic plating of surfaces is the weak bond
between the metal layer and the support and a small surface area. Neverthe-
less, all-metal catalysts made of alloys of platinum with other metals and
deposited on special strips of alloy steels find extensive applications,
particularly abroad, in the catalytic purification of industrial waste gases
[409-411].
In applying a catalytically active layer of metal on wires, screens, and
spirals of pure metals (copper, aluminum, iron) or their alloys (nichrome,
"fekhral" [a high-resistance alloy similar to Fe'craloy] nickeline, manganin,
etc.), the method of brazing from reducing organic mixtures is frequently
employed [243-247, 254-258]. The same method is suitable for applying metal
on nonconductors: ceramics, glass, mica, etc. [248, 249, 252, 253]. It is
recommended that rosin, amyl acetate, synthetic resins such as polymethyl
methacrylate, and alcohols be included in the composition of the reducing
mixture.
N. Z. Kotelkov and M. S. Gershenovich [243-246] use this method for
applying platinum and palladium on nichrome wire for the purpose of oxidiz-
ing hydrogen, carbon monoxide, methane, and sulfur dioxide in the analysis
and purification of internal combustion engine exhausts [6].
A catalyst obtained by brazing from an organic mixture has an extended
surface coated with highly dispersed fine crystals. However, as the contact
continues to be used, sintering is observed, and the active phase is partially
carried off the surface. The authors have described the composition of
tinctures and the conditions of their brazing. Palladizing is carried out by
taking 0.05 g of palladium in the form of a saturated solution of palladium
chloride, adding 0.5 ml of pinene, 0.5 ml of alcohol, and a few drops of a
concentrated ammonia solution of salicylic acid (which produces a wetting
layer). The nichrome wire is first kept red hot for about 10 hours (to obtain
an oxide layer), then immersed in the tincture and heated for 10-15 min at a
moderate temperature to braze the mixture, and the temperature is raised to
a red heat. The brazing process is repeated two to three times, and finally
the contact is kept at a bright red heat for 30 min.
In the platinizing process, 1 g of platinum tetrachloride is dissolved
in 3 ml of alcohol, and 10 ml of a saturated solution of boric acid in alco-
hol and 20-ml of a 1:1 mixture of turpentine and lavender oil are added.
According to the authors' data, the contacts thus obtained prove to be hun-
dreds of times more active in the dehydrogenation of cyclahexane and tens of
times more active in the oxidation of hydrogen than ordinary platinum or
- 43 -
-------
palladium catalysts on asbestos (Zelinskiy's catalysts). This effect is
due to the fact that the oxide crust on the surface of nichrome protects
the thermally precipitated platinum from fusing with the metal of the base
at very high temperatures.
Brazing of metals from pastes into ceramics, glass, quartz, mica,
and plastics is used to prepare electrically conducting coatings and has
been described by B. Ya. Kaznachey [250] and F. Ya. Yevteyev [251]. The
composition of the platinizing paste includes 1 g of chloroplatinic acid,
3 g of ethyl alcohol, 10 ml of a saturated solution of boric acid in alcohol,
and 20 ml of turpentine.
The binders used are essential (lavender) and vegetable oils (linseed,
cottonseed, soy, castor) or a solution of rosin in turpentine. Prior to the
application of the paste, the ceramic is etched in hydrofluoric acid (or a
small surface is prepared mechanically), then cleaned, dried and calcined
at 550-600°C. The layer of paste applied on the surface of the carrier (by
dipping or with a brush) is dried to drive off the volatile matter, then
brazed in ovens with strong ventilation. The process of brazing of silver
to a ceramic, for example, begins at 600°C., but better results are obtained
at 800-850°C. At this temperature, the flux is more actively bound to the
ceramic, and this increases the mechanical strength of the bond. Thus,
B. Ya. Kaznachey notes that after a triple brazing of silver, an effort of
50 kg/cm2 is required to detach it from the ceramic. A layer obtained by
brazing has a porous structure and possesses no bulk conductivity.
To prepare metallized glass electrodes, M. S. Zakhar'yevskiy [252],
V. A. Rabinovich and 0. V. Kurovskaya [253] used a mixture of 1 g of chloro-
platinic acid in 10 ml of alcohol with 10 ml of a saturated solution of boric
acid in alcohol and 20 ml of a rosin solution. The rosin is first dissolved
in hot turpentine, cooled, and diluted with an equal volume of alcohol. It
is recommended that the brazing be carried out in the flame of a burner. If
metal carriers are used, the platinum or its alloy with other metals is also
brazed in the flame of a burner, but after the preliminary application of a
thin layer of A^O^, ZrO£ or any other refractory oxide [254].
The metallization of refractories is carried out in two steps [255].
First, the surface of the refractories is coated with a thin platinum film
that firmly penetrates into the fine pores, and in the second step pastes
that can contain up to 50 wt. % platinum are used. The metal content and
paste viscosity are selected according to the porosity of the refractory so
as to allow the formation of dense metal films without excess impregnation
of the interior of the refractory. The compounds of platinum and other metals
in pastes decompose to the metals in atmospheric air, the strongest borld b*eing
obtained on nonporous materials.
Heating is carried out at different temperatures depending on the base:
ordinary sodium glass 570-625°C.; Pyrex, quartz glass 650-680°C.; glazed
- 44 -
-------
ceramics 675-760°C.; unglazed ceramics 760-845°C.
Apparently, platinum was applied in a similar manner on porcelain rods
in the shape of candles by the American scientists Houdry and Hayes in the
preparation of a catalyst for removing noxious impurities from internal
combustion engine exhausts [256, 257].
When silver is used to metallize the carrier surface [258], the paste
is prepared by coprecipitation in aqueous solution of reducible silver com-
pounds with compounds of other metals (alkaline earths, etc.) that are
irreducible on heating, followed by reduction of the silver at low temper-
ature and the formation of a suspension in an organic liquid. A catalyst
with an extended surface and a high activity is prepared by applying the
paste on a support.
In the preparation of cermets, finely divided powders of metals, their
oxides and other chemical compounds are mixed in the required proportions,
then molded and subjected to sintering at a high temperature. The papers
of Ternision [263] describe the use of alloys of platinum with nickel and
metal oxides (Zr02*CaO), obtained by sintering (25% porosity), as catalysts
for the afterburning of automobile exhausts, surface combustion of rocket
fuel, synthesis of hydrocyanic acid by oxidation of an ammonia-methane
mixture with air, and other chemical transformations.
The methods of application of a metal layer by cathode sputtering and
Vacuum deposition are employed rarely and for special purposes.
It is evident from the above survey that among the methods of prepara-
tion of low-percentage platinum, palladium and mixed catalysts, those deser-
ving most attention are methods of impregnation of the carrier with solutions
of salts of the corresponding metals or their mixtures with organic reducing
agents for the purpose of excluding the stage of reduction of the oxides to
the metals in the gas phase and obtaining a strong bond between the metal
and the support. One of the variants of such procedures are the methods of
preparation of palladium and mixed catalysts containing palladium proposed
by D. V. Sokol'skiy, N. M. Popova et al. [266, 267]. A distinctive feature
of the method of preparation of a palladium contact is the small number of
steps involved, i.e., the absence of such steps as washing of the catalyst
to remove extraneous ions and reduction in hydrogen.
The effect of the conditions of preparation on the activity of contacts
in the oxidation reaction of carbon monoxide was studied in the course of
development of the method. It was shown that the degree of conversion of
carbon monoxide is affected by the duration of the impregnation and the con-
ditions of activation chiefly at temperatures of 200-250°C. (Table 8).
- 45 -
-------
Table 8
Effect of Conditions of Preparation on the Activity of Palladium Catalyst
on Synthetic Alaminosilicate (0.5 wt. % Pd) in the Reaction of Oxidation
of l°f> CO in a Stream of Air, V = 36 x 105 hr-1.
Jmpregna—
tion Tine,
Days
1
2
3
4
5
2
Treatment Following
Impregnation
Drying at 110°C., activa-
tion at 400°C. in a strean
of air for 0.5 hr
»
»
Drying at 110*0., activa-
tion, at 400°C. in a streai
of » CO and 10* Op for
0.5 hr.
Degree of Oxidation of CO, %
200°
0
35
20
15
10
17
250°
50
65
64
52
40
55
300°
84
84
84
82
83
82
400°
95
96
89
89
90
92
Figures 17 and 18 show thermograms of a palladium catalyst on synthetic
aluminosilicate and aluminum oxide, obtained during a gradual temperature
elevation (5°C./min) for undried (1) and dried (2) samples. From the Pd/A^O
thermogram it is clear that a change in the weight of the samples occurs
mainly at temperatures of 50-120°C. and 230-270°C. The granules of both
samples of catalysts blackened considerably at 50-100°C.
The activity of palladium and mixed palladium catalysts is greatly
affected by the gaseous atmosphere (Table 9) in which the process of catalyst
activation takes place. Contacts obtained by activation in hydrogen are less
active in the oxidation reaction of carbon monoxide.
Decrease in weight of
catalyst
ng
Fig. 17. Thermogram of palladium catalyst on synthetic aluminosilicate.
1 - sample before drying; 2 - sample from which moisture has been removed.
The temperature at which activation of the contacts takes place iii the
stream of air is of considerable importance. Table 10 lists data on tne '
effect of the activation temperature on the oxidation of carbon monoxide over
low-percentage platinum, palladium and platinum-palladium contacts.
- 46 -
-------
Decrease in weight of catalyst,
Pig. _ 18. Therraograms of palladium catalyst (0.5 wt. % Pd) or
aluminum oxide. 1 - sample before drying; 2 - sample from which
moisture has been removed.
Experiments have shown that palladium catalyst on many carriers dis-
plays a maximum activity after activation in a stream of air for 3 hours at
400°C., and platinum catalyst, at 500°C. In the case of mixed contacts, the
temperature of the treatment depends on the composition: for platinum-pal-
ladium and other platinum-containing contacts such as platinum-nickel and
platinum-cobalt 500°C. is required, and for palladium catalysts, 400°C. The
effect of the temperature of treatment of platinum catalysts and palladium
foil with oxygen and an explosive gas mixture on their activity in oxidation-
reduction reactions is discussed in [273-278]. In the hydrogen oxidation
reaction, the activity of platinum increases almost linearly with rising
activation temperature and rate of absorption of oxygen up to 550°C., then
falls off linearly (Fig. 19) [274].
M. I. Nikolayeva and A. I. Shlygin [295] also observed that the rate
of decomposition of hydrogen peroxide on thermally activated platinum goes
through a maximum after it is treated at 500°C. This they explain by the
formation of oxygen strongly bound to the platinum surface [295]. This was
Oxidation of 1#
Catalyst (PdsCO
Table 9
CO in a Streau of Air in th" Presence of Palladium-Cobalt
1:1) (Elte = 0.75 wt. W on Sy
at a Space Velocity of 36 x
Aluminosilicate
Activation of Catalyst
Degree of Oxidation of CO,
In a Sti
Temper-
ature,
°C
300
SCO
500
400
— ^
—
*eam of Hg
Duration,
hr.
4
2
1
1
„„,,,
—
In a Str
Temper-
ature,
°C
__
_ _
_
400
400
400
earn of Ail
Duration,
hr.
_
—
_
w^
0,5
2,0
2,5
200°
20
10—22
12
15
22
10
15
250°
42
30-45
48
31
37—54
26
47
300°
60
60-74
60
60 •
60—74
42
70
400°
77
77—88'
.77
80
76—88
64
80
- 47 -
-------
Table 10
CxUation of yf> CO in a Stream of Air at V - 36 x 105 hr"1 on Platinum,
Palladium and PlatJnam-Palladiua Catalysts on Carriers (0.5 wt. #lMe)
Percent of Carbon Monoxide Oxidation at
Different Temperatures After Activation
for 3 Hours in a Stream of Air at
Carrier
400"
200
250
300
400
500°
200
250
300
400
Platinum/carrier (obtained by brazing platinum
from an organic mixture for 2 hours in air)
Corundum
Porcelain
Aluminum oxide
Synthetic aluminosilicate
67
21
69
76
74
50
95
100
100
100
100
100
100
100
100
100
77
96
90
79
100
100
99
100
100
100
100
100
100
100
100.
100
Palladium/carrier (obtained by brazing palladium
from an organic mixture in hydrogen)
'Aluminum oxide (reduced in Hj
Synthetic aluminosilicate
(not reduced in Ho)
Synthetic aluminosilicate
(reduced in HO)
Houdry catalyst (not reduced)
Keles bentonite
clay
J45
0
36
50
95
72
35
68
75
100
100
65
100
90
100
100
95
100
99
100
40
0
28
0
80
70
18
62
42
100
100
43
100
78
100
100-
92:
100
97'
100 '
Platinum-palladium/carrier obtained by our
proposed method
Darbaza clay
Kustanay clay
Keles clay
Aluminum oxide
Ceramic
75
46
43
58
48
98
77
71
77
96
100
100
100
—
100
100
100
100
_
100
90
60
67
75
62
100
95
84
85
100
100
100
100
100
100
100
100
100
100
100
confirmed by Yu. M. Tyurin and L. G. Feoktistov [268], who noted an increase
in the strength of the bond of oxygen adsorbed on platinum after activation
of the latter at this temperature. V. P. Lebedev et al. attribute the maxi-
mum on the activity curves of platinum black and platinum on silica gel,
starting from the calcination temperature, to the supersaturation of the
surface with adsorbed oxygen [269-272]. M. Kraft and G. Spindler sueEest
that in the course of treatment of Pt/Al203 in a stream of air at 500"C
the finest particles of platinum either form a complex with oxygen, or oxveen
enters the lattice of the fine crystals [302]. The penetration of oxygen^
atoms enters the lattice of the fine crystals [302]. The penetration If I
oxygen atoms into defects of the platinum lattice was noted by S. Z. Rbeinskiv
and V. S Rozing [277]. An extensive interaction of metals (particularS on
carriers) with adsorbed oxygen causes some of the atoms tf paL to ±tite
that enables them (in contrast to massive platinum and palladium) to dissolve
- 48 -
-------
*.° K
3,0
-------
Table 12
Effect of the Method of Preparation of Palladium Catalyst on ShN-2 Bead
Aluminum Oxide (0.5 wt. % Pd) on the Activity in the Oxidation Reaction
of 1$ CO in a Stream of Air at V = 36 x 10^ hi--1
Conditions of Preparation
of Catalyst
Impregnation of aluminum oxide with
a solution of [HjjvPdCNHjJCL,,
drying, activation at 40O"C. in Ho
for 1 hr. .
Impregnation of .aluminum oxide with
a solution of PoCPdCHHjJc^, dry-
ing, activation for 2 hrs at WO°C.
in a stream of air
Impregnation of aluminum oxide with
sodium carbonate, then Ka-PdCli,
followed by washing, drying, and
activation for 2 hrs in a stream of
air at 400°C.
Impregnation of aluminum oxide with
NaoPdCli., then sodium carbonate.
followed by. washing, drying, and
activation in a stream of air at
400*C. for 2 hours
Impregnation of aluminum oxide with
sodium carbonate, then NapPdClj.,
followed by washing, drying, and
activation at 300°C. for 1 nr in H,
Impregnation of aluminum oxide with
a PdClo solution, then sodium for-
mate, followed by washing, drying,
and activation at 400°C. for 2 hrs
Impregnation of aluminum oxide
according to our proposed method
followed by drying, and activation
at 400°C. m a stream of air.
Degree of Oxidation of CO, %
150°
12
27
27
29
32
30
30-45
200°
43
67
65
60
68
60
67—80
250°
71
76
76
73
79
80
78—90
300"
91
86
91
93
94
94
94—97
400°
98
ga-
gg*
100
100
100
99—100
The activity of a palladium catalyst prepared by impregnation according
to our method was found to be higher than that of contacts obtained by the
known methods (Table 12). Palladium contacts prepared by reduction of
palladium with sodium formate or precipitation with sodium carbonate have a
similar activity, but their preparation is more complex. Activation of
palladium in hydrogen decreases the percent oxidation of carbon monoxide.
The preparation of palladium catalysts by impregnation according to our
method followed by drying and heating has a number of advantages over the
others: a single impregnation step and the elimination of the steps of
reduction of the catalyst with hydrogen and washing off of extraneous ions.
Mechanical Strength of Catalyst and Depth of Impregnation of Granules
The mechanical wear and the exothermic oxidation reactions occurring
on the surface loosen and break down the upper layers and structure of! the
catalysts, lower the content of active components, and lead to a decrease' in
the catalytic activity and service life of the contact. Exhaust purification
catalysts are subjected to particularly strict service conditions as a result
of the action of vibration during motion of the automobile and when they are
- 50 -
-------
in the form of a mobile layer after a partial breakdown and entrainment
of the catalyst. For this reason, the mechanical strength of supported
catalysts and the depth of penetration of the metal into the granules are
of great importance in the production of low-percentage catalysts.
A major influence on the mechanical strength of low-percentage catalysts
is exerted by the structure and size of the pores of the carrier. G. K. Bores-
kov, V. D. Dzis'ko, et al. have shown that in the case of aluminum oxide,
the mechanical strength is determined by the conditions of its preparation
and decreases sharply when the logarithm of the pore radius increases above
2.8 and when macropores predominate substantially over micropores [413].
The relative mechanical strength of palladium catalysts on ShN-2 alumi-
num oxide is affected by the mode of deposition of palladium on the carrier.
Table 13 presents data on the relative mechanical strength of dried palladium
catalysts (moisture content less than 0.5%) on Al^Oo as a function of the
method of their preparation.* A high mechanical strength (90-93%) was dis-
played by contacts prepared by impregnation by the method we have proposed,
especially when vacuum-dried and when the palladium was precipitated with
sodium carbonate.
The mechanical strength of palladium catalyst on synthetic bead alumino-
silicate ShAS-2 is affected by the conditions of drying and activation of the
catalyst. The drying of the supported palladium catalyst must be carried out
under equilibrium conditions at low temperatures (90-110°C.). Raising the
temperature causes a marked difference between the partial vapor pressures
of alcohol and water within the narrow pores of the bead aluminosilicate and
in the air surrounding it, and causes the formation of microcracks in the
contact pores which subsequently lead to a breakdown of the catalyst. Calcin-
ation and activation of the catalyst (after drying under equilibrium conditions)
at high temperatures in a stream of air have no adverse effect on the mechanical
properties of the catalyst.
The uniformity of distribution of the active metal on the carrier and
the depth of impregnation are determined by the conditions of preparation of
the contacts.
Usually, in catalysts obtained by impregnating a fabricated carrier, the
metal distributes itself unevenly. According to the data of Rubinshteyn
et al., this unevenness increases with the carrier grain size. The diffusion
of the impregnating solution into the pores determines the degree of distri-
bution of the metal over the carrier surface. If the diffusion rate is slow,
the metal deposits at the entrance of the pores, particularly in the presence
of reductants. A uniform distribution of the metal over the depth of the
* The relative mechanical strength of W.e samples was determined by attrition in a 2504ml bottle
2/3 Mil!» I shaker^? 6o£?00 osc/fin for 5 hours. The amount of catalyst fractions remaining on a
screen with d = 3 mm was taken as the measure of strength.
- 51 -
-------
grain takes place if the carrier is kept in the solution or in the moist
state for a long time following impregnation with solutions of the corres-
ponding metal salts. When pellets of activated charcoal are impregnated
with chloroplatinic acid then dried (120-125°C.) and reduced (330°C.), the
bulk of the metal precipitates on the surface [279].
An x-ray absorption study of the distribution of platinum with depth
in the grain has shown that as the depth of penetration into the grain
increases, the metal contact in these catalysts decreases. A similar and
Table 15
Relative Mechanical Strength of Palladium Cata-
lysts on Aluminum Oxide
Method of Preparation
Relative
Mechanical
Strength
Impregnation of carrier by our
proposed method, vacuum drying
Impregnation of carrier with sodium
carbonate followed by NaoPdClr,
washing, drying, and activation in
a stream_of air at400°C.
Impregnation of carrier by our pro-
posed method drying, and activation
in a stream of air at 400"C.
Impregnation,of carrier with Na2PdCl,
treatment with sodium carbonate,.
washing, drying, and activation in a
stream of air at 400°C.
Impregnation of carrier with
[HgQPdCNOjp^JCl^, drying, and acti-
vation at 400"C. in a stream of air.
04
93
90
79
76
still more pronounced uneven distribution of platinum and palladium within
the grains has been observed in catalysts on aluminum oxide. The authors
hold that the nonuniformity of the distribution of platinum in the carrier
grains is due to a decrease in the concentration of the initial solution
in the depth of the grain as a result of its adsorption by the surface layers
of the carrier.
Thus, in order to deposit the bulk of the metal in the surface layers
of the carrier, it is necessary to use concentrated solutions of salts of
the corresponding metals. Platinum distributes itself more evenly within
the grain when dilute solutions are employed [280].
As the pH of the impregnating solution decreases upon introduction of
organic or mineral acids (nitric, acetic) [281], the depth of penetration of
platinum into the grain increases. By occupying a part of the accessible
surface, the acids hinder the sorption of PtGlg= anions and promote their
- 52 -
-------
diffusion into the pellet. An impregnation depth of approximately 2 mm is
obtained in solutions of 2% nitric and
tion of 2 g/1 at 40-50° C. in 1-2 hours.
obtained in solutions of 2% nitric and acetic acids at an HoPtCl, concentra-
Obviously, the greater the depth of penetration of active metals into
the carrier and the stronger the adhesion, the longer the time required for
the contact to be used up, and thus its service life increases. However, a
complete impregnation of the granules is also undesirable because of a de-
crease in the metal concentration in the outer layers, and also because the
size of most stationary catalysts is limited by the size of the openings in
the catalyst shelves. Exhaust purification catalysts are placed in the form
of a thin layer between screens with a hole diameter of 2.5 mm. For an aver-
age size of carrier beads of 4-5 mm, the optimum impregnation depth is 1 mm.
The characteristics of our proposed method make it possible to control
the depth of penetration of palladium into catalyst beads (from 0.1 to 2.5-
3.0 mm) and to obtain low-percentage catalysts with a uniform distribution
of the metal over the depth of the grain.
Regeneration of Precious Metals
Of no less importance than the process of preparation of low percentage
catalysts is the regeneration of precious metals and palladium from catalysts.
The question of recovering precious metals from spent contacts arises in con-
nection with the complete deactivation of palladium and platinum reforming,
platforming, isomerization, hydrogenation5 and oxidation catalysts. The dif-
ficulty of carrying out this process sometimes lies in the fact that the
deposited metal may react chemically with the carrier.
On the other hand, the peculiar state of adsorbed atoms on carriers in
the range of high dilutions, consisting in a surface distribution that is
intermediate between a metallic and an atomic distribution, facilitates their
dissolution in acids without a simultaneous action of oxidants (HC1 + C^,
HC1 + HNOo) . Several authors have explained the ease of dissolution of plati-
num in low-percentage catalysts after treatment with air or oxygen by the
conversion of a part of the platinum to a complex with the carrier where Pt
exists in an oxidized state [302, 322].
The methods of extraction of platinum and palladium from ores, alloys
and also spent catalysts may be divided into three groups: 1) extraction of
precious metals by dry and wet chlorination; 2) dissolution of platinum and
palladium in the presence of anodic polarization current; 3) extraction by
chemical reaction with acids and alkalis with and without oxidants (chlorine ,
hydrogen peroxide, nitric acid). The extraction of precious metals by dried
chlorination followed by dissolution in mixtures of acids is used mainly to
extract platinum and palladium from ores and waste materials of low metal
- 53 -
-------
contant [283, 284]. The overall degree of extraction of platinum metals by
this method is 89%; it is as high as 92% for platinum, but only 25% of
palladium is recovered. When palladium-containing materials are treated
with 2% HC1 with an admixture of sodium chloride while a stream of dry chlor-
ine is passed, the degree of recovery of palladium increases to 30-50% [301].
This method is used to extract platinum from concentrate with a high
platinum content (25%), but dilute hydrochloric acid (1:1) is used, the
stream of chlorine is at normal pressure, and the temperature is 90-95°C.
Ore concentrates containing up to 5% of precious metal as chlorides are
subjected to the action of a mixture of hydrochloric and nitric acids
(refining), causing the formation of complex compounds of platinum and palladium.
The method of anodic dissolution of platinum, palladium and other metals
of this group, for example rhodium, is applicable in the case of massive metal
anodes or alloys [286, 287]. The anodic dissolution of palladium under the
influence of a direct current is associated with considerable polarization
and depends on the composition and pH of the solution and the temperature.
A 100% dissolution of palladium is achieved in an aqueous solution of hydro-
chloric acid (1:1, 1:3) at a current density of 10 A/dm2.
In the recovery of precious metals from catalysts, the latter are
treated with an acid or a mixture of acids. Thus, N. V. Garmonov, A. L. Kle-
banskiy, and K. K. Chevychalova [288] recommend that palladium be separated
from spent palladium catalyst on silica gel (used to hydrogenate vinylacety-
lene to divinyl) by dissolving in aqua regia then evaporating the solution,
or in hydrochloric acid in the presence of chlorine. After the palladium had
passed into the hydrochloric acid solution, the authors carried out the pre-
cipitation of palladium on silica gel by bubbling hydrogen through this solution.
There is a method of recovering platinum from a spent reforming catalyst
(0.4-1.2 wt. % Pt, after the removal of organic impurities by calcination)
involving treatment with sulfuric acid, which also dissolves aluminum oxide,
followed by precipitation with polyaerylamide [290]. Other authors [291]
recommend that the recovery of platinum from spent catalysts on aluminum oxide
be carried out by dissolution in alkali under pressure.
A simpler method has been proposed by V. A. Klevke, D. S. Kantor and
R. P. Seregina [289]. According to their data, the regeneration of palladium
from spent palladium catalyst on aluminum oxide is carried out by treatment
with dilute hydrochloric and nitric acids (10-36%) at the boiling point with-
out the addition of chlorine.
D. V. Sokol'skiy et al. recovered palladium from a catalyst on aluminum
oxide and aluminosilicate by heating in dilute nitric acid (1:1) to 40-50°C.
(Table 14).
- 54 -
-------
The regeneration of palladium from catalysts which have operated for
a long time in gas purifiers of internal combustion engines takes place
more slowly: a preliminary calcination of the contact is required in order
to drive off the soot, and in some cases a mixture of nitric and hydrochloric
acids must be used.
The precipitation of precious metals from solutions obtained in the
regeneration of the compounds is based on methods of their chemical and
electrochemical reduction, precipitation in the form of sparingly soluble
organic compounds whose decomposition forms the metal black or oxide, and
by means of selective adsorption on ion exchange resins.
Metals from solutions of salts of hydrochloric or nitric acid can be
separated by evaporating down to a small volume, then adding a small amount
of hydrochloric acid and sodium chloride in order to obtain complex sodium
salts stable to hydrolysis [292]. Metallic palladium can be readily obtained
from solutions of its compounds by reduction with formic acid, calomel, hydra-
zine, ethanol [293], and other compounds, for example, by passing reducing
gases such as ethylene, carbon monoxide, and hydrogen through the solution.
Similar methods are used for chemical separation of metallic platinum from
solutions of its complex chlorides. A greater practical importance is
assumed in this connection by a method proposed in a West German patent
[294], whereby palladium-containing acid solutions are passed from the top
downward through a column filled with packing coated with a layer of platinum
or palladium. A stream of hydrogen entering the bottom of the column is
simultaneously passed through it.
Table 14
Recovery of Palladium in Dilute Nitric Acid (isl
From 50 g of Bead Catalysts Pd/ShAS-2 (0.75 wt.
Pd3 and Pd/AljOj (0.5 wt. % PA) with Stirring.
Temper-
ature, "C.
Duration, ha Amount. of
\ Palladium
[Recovered, g
Degree of
Recovery
of Palla-
dium, 4
20
20
20
20
40—50
20
40— 50
Palladium-aluninosilicate
1
1
3
5
3
' 0,2666
0,3250
0.356
0,3598
0,3598
79,8
87,0
93,6
95,5
95,5
Palladium-aluminum oxide
3 | 0,2176
0,2466
86,9
98,6
- 55 -
-------
In the electrochemical reduction of palladium from its chloride and
nitrate solutions, the deposition rate is proportional to the total concen-
tration of the solution, is independent of the pH of the medium, but is
limited by the rate of diffusion of the ions to the electrode surface [287].
This factor determines the magnitude of the limiting current of deposition
of palladium [296]. The deposition of palladium from an alkaline solution
is associated with passivation of the palladium electrode [297].
Of interest is a study [298] of the separation of precious metals from
solutions of their salts by means of ion exchange resins. Data are available
on the quantitative absorption of platinum,.palladium, rhodium, and iridium
in the form of chloride complexes (anions). To separate the platinum group
metals (after their absorption on a cation exchange resin from a salt solution
containing no halogens), platinum should be washed with water, palladium with
0.05-5.0 M hydrochloric acid, rhodium with 2 M hydrochloric acid, and iridium
with 4 M hydrochloric acid. Studies have been made on the chromatographic
separation of platinum group metals from copper, iron, and nickel on the
KU-I cation exchange resin.
Role of the Carrier
While the method of preparation of low-percentage catalysts determines
their dispersity and amount of specific surface, the chemical nature of the
carrier and structure of its pores have a decisive influence on the effi-
ciency, stability, quantity and structure of the active centers of contacts
[303, 304, 305].
The porosity of contacts is of major importance in their practical
applications. The maximum utilization of the volume of the grain in the
case of reactions taking place at low pressures is achieved by using hetero-
geneous structures with large pores (bidisperse carriers), and at high pres-
sures, homogeneous fine-pored structures [190, 305].
For low-percentage oxidation catalysts frequently operating under dif-
fusion conditions, the best-suited may be structures with wide pores on the
surface of which the active substance deposits. With such a structure of
the carrier pores, the active phase is utilized to the maximum extent.
The study [54] compares low-percentage platinum, palladium, and platinum-
palladium catalysts on a number of carriers in the oxidation reaction of
carbon monoxide. As is evident from the results, the nature of the carrier
substantially affects the degree of oxidation of CO, particularly at low temper-
atures (200-250°C.).
The influence of the carrier is clearly manifested when one analyzes
the specific oxidation rate constants of CO, obtained by referring the rate
-56 -
-------
constant (calculated from the first-order equation K = — . — or degree
of conversion) to 1 g of metal. Tables 15 and 16 list the values of the
specific rate constants for oxidation of carbon monoxide on palladium and
platinum catalysts obtained by our proposed method. The specific activity
in the series of palladium and platinum catalysts on different carriers
decreases by one order of magnitude from aluminum oxide to ceramics and the
insulating material (Fig. 20, 21, 22). Attention is drawn to the relatively
high activity of contacts on carriers whose composition contains J-AIJ^-)
(aluminosilicate, Houdry contact, molecular sieve). A similar pattern but
not as clearly manifested is observed in the case of platinum contacts
Table 15
Specific Activity of Palladium Catalysts on Carriers (0.5 wt. %) in the
Oxidation Reaction of 1% CO in a Stream of Air at V 36 x 10* hr"
Carrier
Aluminum oxide, A-l
ShAS-2 bead
aluminosilicate
Houdry contact
Molecular sieve
ShSK silica gel
Foam glass
Keles clay
Insulating
material
Ceramic
% Conver-
sion of CO
200°
90
60
54
61
41
26
42
29
19
250°
100
100
80
100
66
60
95
93
66
Weight
of
Cata-
lyst,
6
1,18
1,32
1,07
1,68
1,02
1,03
2,14
2,30
2,30
Amount
of Pd,
fv
fc
5,90
6,60
5,35
8,4
5,1
5,15
10,7
11,5
11,5
K200°C
sec'1
37,1
14,7
11,7
15,1
8,5
4,8
8,7
5,4
3,3
Specific Activity
of 2CO°C. on 1 g
of Pd
% Conver-
sion on
Lg_of Pd
15,2
9,1
10,0
7,2
8,0
5,0
3,9
2,5
1,6
Ksp
x 10s
6,56
2,23
2,19
1,79
1,67
0,94
0,81
0,46
0,29
Table 16
Specific Activity of Platinum Catalysts, on Carriers (0.5 wt.
and Activated at 500°C. in a Stream of Air, in the Oxidation
Reaction of $ CO in a Stream of Air at V + 36 x 10? hir1
Carrier
A-l aluminum
oxide
Houdry contact
Molecular
sieve
Silica gel
Baku ShAS
Foam glass
% Conver-
sionQof
t 200°C.
100
97
98
CO
87
65
70
Weight
of
Catalyst,
g
1,226
1,405
1,786
1,027
1,534
0,96
2,07
imount of
'latinum,
5 x 10-s
6,1
7,0
8,9
5,1
7,69
4,8
10,35
K500°C.,
sec~^
74,2
56,48
63,03
37,1
32,9
16,8
19,38
KZOQ°C.
Ksp
xlO3
12,3
8,06
7,0
6,2
4,2
3,5
1,8
- 57 -
-------
obtained by impregnation followed bv brazing with an organic paste, when
less favorable conditions exist for the precipitation of fine platinum
crystals on the surface and for their interaction with the support (Table 17)
"sp,
*_£
!\
::>VS
'.'•y.'\
Houdry catalyst
Molecular sieve
II
Foar. glass
L
Clay
material
!vS Ceramic
Fig. 2C. Specific activity of supported palladium catalysts
in the oxidation reaction of carbon monoxide (0.5 vrt. % of metal).
The same effect of y~Al 0 as carrier was observed in the oxidation
reaction of CO on copper-chromium contacts (Table 18).
The increase in the specific activity of copper-chromium catalysts on
y-A^O., is explained in [396] by the stabilization of the copper ion in the
defect structure of aluminum oxide, as expressed in a weak EPR signal
(unsymmetric singlet, g-factor close to 2.05-2.09). The strength of the
EPR signal shows a considerable increase of the electron density in the system,
favoring a donor-acceptor mechanism of the reaction.
The high activity of copper and chromium catalysts deposited on y~Al 0
and MgO carriers in dehydrogenation reactions of cyclohexane and cyclahexanol
was reported by B. V. Yerofeyev et al. [393]. The authors attribute this to
the fact that the structure of these carriers contains octahedral cationic
sites at which the deposited metals are stabilized.
- 58 -
-------
20(>»C.
12
1.7
Houtlrv contact
Molecular sieve
f.rri si ot
Foan rl'-s
Clay
Fig. 21. specific hctivity of supported platinum catalysts in the
oxidation reaction of carbon monoxide C0.5 wt. * of metal).
Table 17
Specific ..ctivity of Supported Platinum Catalysts_(0.5 wt. % H), ire-
pared ty brazing' from ^n Organic Paste, in the Oxidation fiesction of
1% Carbon Monoxide in a Stream of Air at V = 36 x 10' hr"1 ^bd ?00°C.
Carrier
A-l aluminum oxide
Houdry contact
Porcelain
ShAS-2 bead
aluminosilicate
Keles clay
Corundum
%
lor. ver-
sion
of CO
90
81
96
79
£0
77
Weight
of
i^ata—
lyst,
g
1,3
1.-10
2,77
1,4
2,2
3,38
Amount
of
Plati-
num
e x
icr3
7,01
7.0
13,8
7,0
11,0
16,9
/2CO°C
sec'1
37.1
29,5
51,8
25.6
25,9
23,5
Specific Activity
at 200°C. on 1 g
of Pt
^Conver-
sion on
1 g of Pt
12.8
12.0
6,95
11.3
7,27
4,55
T.
K x KT
Sp
5.29
4,21
3.76
3,65
2.35
1,39
- 59 -
-------
200-C.
x 10
\-ftiO,
U
Houdry
catalyst
Porcelain
- Si
Clay
Maxted [426] pointed out that the
reaction rate for the hydrogenat ion of
cyclohoxene on platinum and palladium
depends on the nature of the carrier.
Calculation of the specific activity
(amount of hydrogen absorbed at the fourth
minute on 1 g of active metal) for 1% pal-
ladium catalyst, based on the data of the
study, indicates that this activity decreases
in the following order: Cr-O-, (25-27 x 103),
A1203 (20 x 103), Ti02 (18 x 103) , Th02
(12 x 103), MgO (9 x 103), Zr0 (4 x 103) ,
and
(3 x 103) .
Fig. 22. Specific activity of
supported platinum catalysts
(0.5 wt. Jo of metal), obtained
by brazing from an organic paste,
in the oxidation reaction of
carbon monoxide.
The special properties of "y-Al-O., as a
carrier in the oxidation reaction or carbon
monoxide become clear when one examines the
adsorptive properties and reactivity of the
deposited metals for different degrees of
surface coverage. The character of the IR
spectra of carbon monoxide adsorbed on rhodium,
ruthenium, platinum, and palladium depends not only on the nature of the metalt
but also on the carrier [421]. A study of the adsorption of carbon monoxide
Table 18
Effect of the Carrier on the Oxidation of 1% CO in a Stream of Air on
Copper-Chromium Catalysts [395].
p,
QJ
•H
h
h
a
o
Corundum
Clay
Alumino-
silicate
7-Al,03
7-AliOj
after 42
hours of
use
Cu,'vAI,03
U
rH
a
4J
CO
U
0
o
i-H
0
C_j
Black
Dark green
Black
Light
green
Light
green
Degree of
Oxidation
of CO, %
o
0
o
CM
22
12
41
42
10
o
^5
n
35
26
41
93
88
62
o
o
*
58
30
64
99
100
99
o
^5
10
80
45
80
100
100
100
7o
QJ
in
„
•
^
x
nS
**
10
6
10
52
42
23
i
a
.c
Q.
k j
V °
>M -a:
tf-t
o
to
^^
68
33
84
443
362
290
EPR Signal
Form
Narrow
signal
Broad
symmetric
singlet
Un sym-
metric
singlet
»
»
g
1,97
2.0
2,09
—
2,05
- 60 -
-------
on platinum and palladium catalysts on charcoal reveals the predominance of
the linear structure of carbon monoxide [382],
Adsorption
State
Me
Me
C-0
ml CO
Z Ft
115
57,5
ml CO
gPd
211
105,5
Whereas in the adsorption of carbon monoxide on platinum on silica gel
and on a platinum film a linear structure also predominates (there is a
strong band in the spectrum at 4.8 y) , and approximately 15% of CO is
adsorbed in the form of a bridge structure (absorption band at 5.3 y), in
the case of Pt/Al.O- as many as 50% of the CO molecules are bound to the
surface in the form of bridge structures (cf. Fig. 23) [344, 345, 383, 384]
Pt\
Pt/
C=0.
As is evident from Fig. 23, the absorption band corresponding to the
linear structure of CO shifts to 4.9 y. It is highly probable that the
bridge structure of carbon monoxide is more reactive in the reaction of its
oxidation.
Fig. 25. Spectra of carbon monoxide
chemisorbed on platinum on silica
gel and aluminum oxide [345],
Krai [382] studied the chemisorption of carbon monoxide on low-percentage
platinum and palladium catalysts on y-A^^S' T^1"66 varieties of aluminum
oxide were selected: bayerite, boehmite, and boehmite gel. It was found that
the impregnation method affects the. distribution of the metal in low-percentage
catalysts and its specific surface. Impregnation of aluminum hydroxide followed
by calcination at 500°C. and reduction in hydrogen at 200°C. allows a larger
surface and a better distribution of the precious metal than when the impregna-
tion with chloroplatinic acid solution is carried out after calcination of
aluminum oxide.
The author showed that the chemisorption of carbon monoxide increases with
decreasing amount of metal deposited on the carrier (Fig. 24). Maximum adsorp-
tion is observed when bayerite is used as the carrier. Calculation of the
ratio of the number of CO molecules to the number of metal atoms, which we
- 61 -
-------
carried out by using Krai's data, showed that this ratio increases in the
range of low degrees of coverage; for the 1% platinum catalyst it approaches
1.7, and for the 1% palladium catalyst it also exceeds unity (1.14). If
the calculation allows for the fact that part of the carbon monoxide mole-
cules are adsorbed on platinum and palladium on y-Al?0_ in the form of
bridge structures, the ratio obtained will increase even more.
100
Fig. 24. Adsorption of carbon monoxide
on platinum catalysts on varieties of
aluminum oxide as the platinum concentra-
tion changes [382], 1 - Bayerite;
2 - Boehmite gel; 3 - Boehmite.
The data obtained by Krai attest to the excess adsorption of carbon
monoxide on platinum and palladium on y-AloOo in the range of low coverages.
'} X
f> \, Fig. 25. Number of hydrogen atoms per
!• \ atom of metal as a function of the metal
1' \ ^o. content on the carrier [ 367].
«-• V. . ^M 1 - Pd/ALO,; 2 - Pt/AloO,.
; _ " '*-.-•—._«... * y y
:~ 2 ~~« s s ~u
Me (wt. % at. wt.) x IV
The high adsorptive capacity of platinum and palladium catalysts on
Y-A120_ for hydrogen was observed earlier by D. V. Sokol'skiy and Ye. I. Gil1-
deb rana [306, 307, 309]. It was shown that in the range of small coverages,
the number of hydrogen atoms per metal atom is 10 for platinum and 5 for
palladium (Fig. 25). Similar results were obtained in the 1930's by A. N.
Frumkin for platinum on charcoal [336, 419].
D. V. Sokol'skiy explains the observed effect by the peculiar state
of the carrier surface at a considerable distance from the center of atom-
ization of the hydrogen molecule, the transfer of hydrogen atoms to the
adsorption center, and diffusion of molecular hydrogen on the surface from
the adsorption centers to the centers where dissociation of the hydrogen
molecules takes place [232].
A larger-than-stoichiometric increase in the adsorptive capacity of'
platinum on A1203 for hydrogen was also observed by Adler, Spenadel and
* Editor's note: Illegible broken type.
- 62 -
-------
Boudart [352, 422]. The ratio of hydrogen atoms to platinum atoms for
0.1-0.3% platinum was 1.44, and for 0.8%, 1.65. The authors explain this
fact by an increase in the dispersity of the metal crystals on the carrier.
According to their calculations and x-ray data, the size of elementary
platinum crystals in the range of high hydrogen adsorption approaches the
size of individual atoms (10-12 A) possessing an extended surface which,
however, turned out to be greater than that which can be occupied by the
amount of platinum taken. Hence it is concluded that a certain amount of
hydrogen is adsorbed between the platinum particles. The latest studies
confirm D. K. Bond's theoretical calculation [427] of the increase in the
fraction of single surface atoms of metals (on the edges and peaks of cry-
stals) with increasing dispersity of crystals of group 8 metals, which form
a euboctahedron. Bond showed that the special catalytic and adsorptive
properties of very fine crystals are related to the properties of atoms
having low coordination numbers.
Table 19
Oxidation of 1% CO in a Stream of Air on 3.53 g of Platinum and
Palladium Catalysts on Aluminum Oxide
(ShN-2, Particle Size 0.1-0.2 mm) , ,
With Different Contents of Metals at V = 36 x 103 hr"1
• •nil
% Me
O.lPd
0,2
0.25
0,35
0,5
0,1 Pt
0.2
0,25
0,35
0,5
Pd Con-
tent,
s x*
i rn3
lw •'
3,53
7,08
9,07
12,7
17,6
3,53
7,06
9,07
12,7
17,6
% Conversion
CO
150°
12
23
25
27
30
17,5
23
24
26
26
200°
70
88
89
90
92
33
70
71
75
80
K, see'1
150°
1,85
3,77
4,16
4,55
5,15
2,77
3,77
3,95
4,34
4,34
200°
19,38
34,16
37,1
37,1
40.69
6,44
19,3
19,9
22,34
25,93
KSB> sec"1
g Pd •
•103
150°
0,525
0,533
0,458
0,358
0,292
0,786
0,533
0,436
0,342
0,247
200°
5,49
4,83
4,089
2,92
2,31
1,827
2,75
2,198
1,76
1,473
loglC^lO'
150' | 200"
2,7160
2,7267
2,6609
2,5539
2,4654
2,8954
2,7267
2,6395
2,5340
2,3927
3,7386
3,6839
3,6117
3,4654
3,3636
3,2617
3,4393
3,342
3,2452
3,1682
An increase in the adsorptive capacity of low-percentage platinum and
palladium catalysts on y-A^O-j for gases (hydrogen, carbon monoxide) whose
adsorption proceeds via an electron-donor mechanism increases the specific
catalytic activity in reactions whose rate-determining step is the activation
of hydrogen and carbon monoxide. The beneficial effect of y-Al^ as a
carrier in dilute layers was manifested in a series of reactions: exchange
of hydrogen on deuterium [414], oxidation of sulfur dioxide [338, 340] and
ammonia [418], dehydrogenation of cyclohexane [337] and hydrogenation of
ethylene and its homologs [339, 415]. Analysis of the reactivity of metal
catalysts by means of the theory of active ensembles established that the
active center in these processes, which occur on low-percentage platinum and
palladium contacts on aluminum oxide, aluminosilicate, and charcoal, is a
- 63 -
-------
sp'
*
3.0
«
monatomic ensemble which "is formed on particularly active areas of the
carrier" and forms a "mixed ensemble" from atoms of platinum and of the
active center of the carrier [339]. U-
Zh, V. Strel'nikova and V. P. Lebedev
[341, 342] proposed a mechanism for the
catalytic action of such active centers in
hydrogenation reactions, allowing for the
possibility of dissociative adsorption of
the reacting atoms and molecules on a
divalent monatomic active center followed
by diffusion to the active centers of the
carrier.
Our calculation of the specific
activity of platinum and palladium on
y-altiminum oxide in the osication reaction
of carbon monoxide, carried out (see Table
19 and Fig. 26) in the range of 0.1-0.5%
content of the metals, showed that as the
metal content on the carrier decreases,
the specific activity increases.
The rectilinear form of the dependence
of log K on the degree of coverage of the
carrier surface by platinum or palladium
(the metal content in wt. % was taken as a)
demonstrates (Fig. 27) that the oxidation
reaction of carbon monoxide proceeds at a
metal content below 0.5% on single atoms of
platinum and palladium sparsely distributed
over the carrier.
Something different is observed in the
case of palladium catalysts on synthetic
aluminosilicate with a high metal content
(ShAS-2, particle size 4 mm). As the total
activity increases with the palladium con-
tent rising from 0.1 to 1.0%, a minimum at
0.3% Pd and a maximum at 0.75% Pd appear in
the variation of the specific activity. We
were unable to calculate the number of atoms
n in the composition of the activejcenter
up to 0.3% Pd because of the limited number
of points; at a Pd content above 0.3%j this
number is equal to two, as indicated, by the
rectilinear form of the dependence of
A
2.0
1.0
0,1
0.2
0.3
O.S
He content, wt. %.
Fig. 26. Specific activity of palla-
dium (l, 2) and platinum (3, 4)
catalysts on Y-aluminum oxide in the
oxidation reaction of carbon monoxide
in a stream of air at a space velocity
of 56 x ICP hr"1 at 150*0. (solid line)
and 200°C. (dashed line).
- 64 -
-------
log K /% Pd (Fig. 28) on the palladium content of the catalysts. A similar
effeclpwas noted by N. I. Kobozev et al. [417, 339] in a study of platinum
catalysts on oxides of magnesium and chromium and on silica gel in hydrogen-
ation reactions of cyclohexene and ethylene and decomposition of hydrogen
peroxide. It was shown that at a high platinum content (second maximum), new
active centers are formed (n = 2) whose structure differs from the composition
of the structure correspodning to low coverages (n - 1).
f,t
I50»c.
J.'
Log K
0.1
0.1
Me content, wt. % Me content, wt. %
Fig. 27. Log of the specific rate constant of the oxidation reaction
of carbon monoxide vs. metal content in Pd (l) and Pt (2) catalysts
on Y -aluminum oxide: a - at 150"CM b - at 200°C.
A comparison of the adsorptive properties with respect to carbon monox-
ide [382] and catalytic properties of low percentage platinum and palladium
catalysts on Y~AloO-a in the oxidation reaction of 1% carbon monoxide in a
stream of air revealed a certain parallelism. The latter is expressed in a
substantial increase of the specific adsorption of carbon monoxide and cata-
lytic activity in the range of low content of the active metals (0.1-0.2 wt. %)
The observed relationship between the adsorptive and catalytic properties is
due to the mechanism of the oxidation reaction of carbon monoxide; when this
reaction is carried out in excess oxygen, its rate is limited by the activa-
tion of carbon monoxide. The activation of carbon monoxide improves on
metals deposited on aluminum oxide, which is capable of adsorbing carbon mon-
oxide on the surface [343] and exerting an influence on the predominant adsorp-
tion of carbon monoxide in the form of a bridge structure on low-percentage
metal catalysts.
The remarkable adsorptive properties of low-percentage platinum and
palladium catalysts on Y~A1203 and the mechanism of action of monatomic active
- 65 -
-------
Log K 200"C.
Lop
250"C.
Fig. 28. Log K l"f> Pd vs. palladium content
SP .
on aluminum oxide in the oxidation reaction
of carbon monoxide. 1 - 200°C.; 2 - 250°C.
0,3 0,6
1,0 Pd content, wt. %
centers in the oxidation reaction of CO can be explained, as in hydrogenation
processes, only by assuming the participation of the carrier in the catalytic
event.
Apparently, the adsorption and activation of carbon monoxide, as in the
case of hydrogen [341, 342], occurs in two steps. In the first step, carbon
monoxide is chemisorbed on the monatomic divalent metal centers of low^-
percentage catalysts, with the formation of a bridge structure and a linear
structure
I. Pt+CO->Pt=C=O
Ptv
2Pt+CO- N'
Pd+CO->Pd=C=0
Pd\.
This process of donor-acceptor interaction takes place at a high rate
because of the tendency of the elements with an unfilled d subshell to bring
the number of outer electrons up to 18 by acquiring two electrons of carbon
monoxide [425].
The second stage involves diffusion of carbon monoxide from the ifletafl.
centers to the active centers of the carrier, and as a result, the monatojmic
platinum and palladium centers become free and able to activate oxygeji and
fresh amounts of carbon monoxide.
- 66 -
-------
II.
IV.
III.
O 0=AK
+20=A1)c=0->C02+20=Al-+Pt.
The active centers of the carrier in the case of y-Al70^, whose face-
centered crystal lattice constitutes a defect spinel with a deficiency of
cations [325, 326] at octa- and tetrahedral interstitial sites, are aluminum
atoms (Fig. 29) [393]. The latter occupy a par^ of the octahedral inter-
stitial sites of y~Al203 an^ have a tendency to'fill the incomplete 3p sub-
shell with electron pairs [327]. The ability of the aluminum atom to enter
into a donor-acceptor interaction with adsorbed atoms and molecules in the
role of an electron acceptor is indicated by IE. spectrescopic data [327,
428, 429].
This property was confirmed by an EPR study of the adsorption of quinones
on y-Al^O., [412 ]. It was shown that when the calcination temperature is
raised from 100 to 400°C., the relative number of adsorbed radicals becomes
5 times greater as a result of an increase in the number of electron-acceptor
centers. An increase in the concentration of electron-acceptor, centers in
y-Al5Oo as the calcination temperature is raised to 900°C. is also indicated
in [£28].
Fig. 29. Octahedral and tetrahedral sites
of atoms in spinel structures. Arrows
indicate the orientation of d orbitals:
I - oxygen atom; 2 - tetrahedral sites;
3 - octahedral sites of atoms [?93l
On the surface of aluminosilicates, in addition to electron acceptor
centers, there are proton-donor centers whose proportion and number are
determined by the content of aluminum and silicon oxides and their calcina-
tion temperature [327, 428, 430].
The deficiency of electrons in the structure of y-Al203 accounts for
its slight semiconducting properties (p-type), manifested at a relatively
- 67 -
-------
low temperature and upon deposition of 1-10% platinum [324].
The imperfection of the structure of y-A^O- and the presence of
electron-acceptor centers account for its capacity to adsorb CO and hydrogen.
The amount of the latter is slight (^0.15-1 ml/m2) and increases during heat
treatment, especially above 400°C. [329-331] and in the presence of transi-
tion metal impurities [333, 387]. Metal atoms on the surface of Y~A1203
substantially accelerate the adsorption process [415].
It is possible that the adsorption of carbon monoxide takes place
directly on the surface of j-Al 0 , with migration of adsorbed molecules
to centers with a high binding energy [328]. Such centers may be electron-
acceptor areas of ^-A1^0~ and also atoms or ions of adsorbed metals Pt, Pd
[315, 317], Cr [334], or Cu [393].
Owing to the adsorption, for example of hydrogen, on Al~0o (in some
cases added to the catalyst in the form of a mechanical mixture [416, 420])
and diffusion to the platinum centers, there is an increase in the rate of
reduction of compounds whose hydrogenation has the activation of hydrogen
as its rate-limiting step.
Thus, in the case of low-percentage metal catalysts, the peculiar
structure of J-A1JO^ is conducive to involvement in the catalysis of an
extensive area of the carrier (up to 10 active centers of the carrier)
accessible to the surface diffusion of the reactants.
The ability of y-Al^Oo to form reserves of molecular and chemisorbed
forms of electron-donor molecules and atoms (carbon monoxide, hydrogen) on
their surface and also to exert a decisive influence on the form and energy
of the bonding of adsqrbed atoms (bridge and linear structures of carbon
monoxide) and on the structure of the active center causes an increase by
one order of magnitude or more in.the specific activity of platinum, palladium
and other metal catalysts on y~Al203 in oxidation, reduction, and dehydro-
genation reactions.
A necessary condition for the manifestation of the specific properties
of y-AlJd* is its extensive interaction with isolated atoms of deposited
metals. This interaction consists in the penetration of the metal atoms
into the crystal lattice of the carrier, in which there is a deficiency of
cations at octa- and tetrahedral interstial sites. Calculations of the stabil-
ization energy of atoms carried out by B. V. Yerofeyev et al., based on the
ligand field theory for chromium and molybdenum catalysts on Y~Al2°o» showed
that the principal sites of metal stabilization are octahedral vacancies'
frequently occupied by aluminum atoms. "Octahedral vacancies may comtain
atoms or ions of chromium, molybdenum, or other metals" [393]. When a tran-
sition metal ion or atom enters the carrier lattice in an octa- or tetrahedral
ligand field, the d electron orbitals are split into two groups: three t2g
orbitals and two te orbitals [392, 393].
- 68 -
-------
The electronic nature of the interaction of the deposited metals with
the carrier is indicated by experimental data obtained by studying the
deposited catalysts by methods of exoelectron emission, resonance, and
magnetic susceptibility [319, 320, 321, 334, 339]. N. I. Kobozev et al.
[320] noted that the atomization of deposited metals in the range of small
coverages causes the phenomenon of superparamagnetism. The relative magne-
tization increases with decreasing degree of coverage and is determined by
the nature of the metal and carrier (Fig. 30). An increase in magnetic
susceptibility at relatively low concentrations of oxides of nickel,
chromium, manganese, iron, and copper on the carriers was observed by
Selwood [319]. He explained this effect by a change in the valence state
of the adsorbed ions.
XadsPdx
fcv
OJOOI
',«'
aitj.
Fig. 30. Magnetic susceptibility of supported
platinum catalysts on silica gel (a) and palladium
catalysts (b) after the data of Strel'nikova,
Lebedev, Pospelova, and Tshebyatovskiy (for pal-
ladium) 320 .
1 - Palladium on charcoal; 2 - palladium on aluminum
oxide; 3 - palladium on silica gel
N. 1. Kobozev et al. also explained this phenomenon by electronic
transitions between the adsorbed metal atoms and the carrier. "This
phenomenon is due to electronic processes in the energy bands of the carrier,
since the effect of superparamagnetism is influenced not only by the degree
of dilution, but also by the nature of the substance deposited and of the
carrier. The paramagnetic susceptibility of platinum adsorbed on silica gel
varies widely with the brand of 'silica gel from 140 x 10"6 to 566 x 10~6
units" [320]. In palladium, the susceptibility is higher than in platinum
and depends on the nature of the carrier: Pd/WO - 12.5 x 10"6; Pd/Si02 -
510 x 10-6; Pd/Al203 - 580 x 10~6; Pd/charcoal - 7200 x lO'6 (Fig. 30).
Kobozev explains the high paramagnetic susceptibility of palladium by postu-
lating an easy transition of an electron from the 4d10 subshell to the 5S
subshell (0.8 eV).
The pulling off of the outer electrons of the deposited metals by the
carrier is also indicated by data obtained by Nikolau and Thorn [321]. By
studying the resonance of metallic platinum and palladium on charcoal
- 69 -
-------
(1-5 wt. %) , they showed that the metal is stabilized between the aromatic
rings of the graphite lattice with the formation of pseudo-sandwich struc-
tures in which a highly delocalized electron is supplied by the platinum.
Upon splitting of the 4 d levels of palladium and transition of an
electron to the 5S subshell, the structure of its outermost electron shell
becomes similar to that of platinum. As a result of interaction with the
carrier, the palladium atom loses many properties characteristic of the
massive metal. The "platinumlike" nature of palladium in the range of low
concentrations is manifested in its adsorptive, electrochemical and cata-
lytic properties [306-316]. These properties are expressed in a lack of
ability to dissolve hydrogen upon adsorption (the a-$ transition portion of
the charging curves disappears), and in the form of the kinetic curves of
hydrogenation of acetylenic compounds (similar to the curves for the platinum
contact).
Starting at some minimum palladium concentrations, individual atoms
may cluster during surface migration and pass to the crystalline state
[318], this being dependent on both the quantity of the metal and the nature
and structure of the carrier. The crystallization of palladium, for example,
on powdered barium and calcium sulfates takes place at 0.1-0.2%, on silica
gel at 0.4-0.5% palladium, and on charcoal, at a 0.6-0.7% metal content [315,
316]. A precise method of determining the degree of crystallization and pro-
perties of palladium on a carrier may be catalytic hydrogenation [317].
The "platinumlike" nature of the low-percentage catalyst is also dis-
played in the reaction of catalytic oxidation of carbon monoxide. It has
been noted that the activity of palladium on the y-AJ^O-j carrier in the
range of content of active components below 0.5 wt. %, when the carrier takes
an active part in the reaction, is equal to or higher than the activity of
the platinum catalyst (cf. Fig. 26). At a metal concentration of 0.5 wt. %
and above, when diatomic and more complex ensembles are responsible for the
catalysis, for a similar percent oxidation of carbon monoxide, the specific
activity of platinum on most carriers (cf. Table 15, 16) becomes higher than
that of palladium catalyst. At the same time, the influence of the chemical
nature and structure of the carrier on the specific activity of the catalysts
is manifested to a lesser degree.
The method of preparation of low-percentage catalysts has a decisive
influence on the process of formation of the active centers of metal catalysts
(cf. Tables 16 and 17). When the catalysts are prepared by our method, there
takes place a rapid reduction of palladium or platinum from the complexes at
a low temperature and the formation of fine imperfect crystals of irregular
shape with a high content of the atomic phase. Conditions are thus credted
for an atomic distribution of the metal (at a palladium concentration of less
than 0.5 wt. %) over the surface and for chemical interaction with carriers
containing active aluminum oxide.
- 70 -
-------
When catalysts are obtained by impregnation with a viscous organic
mixture followed by reduction of the metals by calcination at a high temper-
ature, coarse metal crystals are formed whose interaction with the carrier
is difficult. In this method of preparation, the influence of the nature
of the carrier is less pronounced.
The high catalytic activity of the palladium catalyst in the oxidation
reaction of carbon monoxide, comparable to that of platinum, made it possible
to recommend it for the removal of carbon monoxide and other toxic components
from motor transport exhausts and other oxygen-containing gas mixtures and
as a substitute for the more expensive and scarce platinum catalyst.
Thus, owing to its crystallographic structure, the carrier in low-per-
centage catalysts can fulfill a number of functions important in catalysis:
•' *
1. Change the nature of deposited metals by stabilizing them chemically
at the vacant sites of a defect structure, for example, in J-A1J3-.
2. Facilitate the course of the rate-determining steps by participating
in the adsorption and activation of the reacting molecules and thus accelerate
certain reactions, for example, the donor-acceptor interaction in the case of
y-Al-O-. The most active carriers for oxidation, hydrogenation and dehydro-
genation catalysts are aluminum oxide and other compounds of spinel structure
in which electronic transitions between ions in tetra- and octahedral inter-
stitial sites take place without any appreciable consumption of energy [450].
3, In the case of reactions involving the formation of intermediates,
the role of the carrier is manifested in still another way. Because of the
possibility of surface migration of the initial, final and intermediate
reaction products on the carrier, a directing function of the carrier is
observed, so that in some cases the processes occur at high rates and in a
strictly selective manner [299, 346-348, 388].
Stability, Structure and Phase Composition
of Catalysts in Prolonged Use
One of the chief requirements for catalysts to be used in the purifica-
tion of exhausts of internal combustion engines is a high chemical and thermal
stability. In bench and road tests under service conditions, the catalyst is
subjected to the action of the reaction mixture and overheatings whose char-
acter depends on the type of engine and its load, the technical condition of
the automobile, its mode of operation, and the design of the gas purifier.
The content in the exhaust gas of carbon monoxide, hydrocarbons, and aldehydes,
whose oxidation is associated with the liberation of large amounts of heat,
may vary over wide limits. At high traveling speeds of automobiles (60-100 km/
hr) with carburetor engines, during idling and braking, the carbon monoxide
- 71 -
-------
content of the exhaust gas increases sharply and may reach 10-12%. This
causes the catalyst to heat up considerably, to 800-900°C. In the course
of operation in the stream of diesel engine exhausts, the catalyst operates
in excess 02 (20-21%).
To determine their stability, low-percentage catalysts were subjected
to a prolonged heat treatment in a stream of air, were artificially over-
heated, and the possibility of increasing their activity after decreasing it
was studied [61].
Table 20
Stability of Low-Percentage (0.5 wt. % Metal) Catalysts on Keles Clay.
Catalyst
Platinum
Platinum-Palladium
Palladium
Calcination of
Catalyst
lime,
hr
2,0
26,0
2,0
26,5
2,0
27,5
Temper-
iture, "C.
500
500
4CO
400
400
400
)egree of Oxidation ofCO, %
200°
84
75
80
50
95
65
250°
1,00
100
ICO
90
100
92
300°
100
100
100
100
100
100
The heat treatment of low-percentage catalysts with air (for up to
27 hours at 400-500°C.) has little effect on their activities in the oxida-
tion reaction of CO (Table 20). At 300°C. and above, carbon monoxide is
completely oxidized. At lower temperatures, a certain decrease of the degree
of oxidation is observed which is maximum (30% at 200°C.) in the case of
palladium.
The activity of platinum catalyst (0.5 wt. % Pt) on bead alnmlnosilicate
in the course of oxidation of carbon monoxide in a mixture with air at 500°C.
also showed practically no decrease (after being tested for 32 hours). At
250-500°C., carbon monoxide was completely oxidized, and at 200°C. the degree
of oxidation ranged from 90 to 100%. Raising the service temperature of'the
catalyst to 600°C. did not decrease the degree of oxidation of carbon monoxide
either.
The platinum-palladium catalyst on bead aluminosilicate was tested
during a gradual increase of the oxidation temperature to 700°C. The results
(Fig. 31) showed that its activity (which at 200-250°C. is less than ,that of
the platinum catalyst) is preserved for a long time (170 hours) at 400-650°C.
Oxidation of 1% carbon monoxide mixed with air at 650°C. slightly raises the
degree of oxidation of carbon monoxide at 200-250°C., which again decreases
starting at 700°C.
- 72 -
-------
to
iff
oxidation of CO
, soo'c
«a
ea
co. too-
/aa /"o ieo j too lime,
\ i /\ . wc^-"'^.
\\ / \—•«••-•— \.
[fOO- 1 ffWT i*| 700'
Fig. 31. Effect of temperature and time of treatment of platinum-
palladium catalyst on aluminosilioate with a mixture of 1$ carbon
monoxide and air on the activity in the oxidation reaction of 1$
CO at lower temperatures.
~* * *
Like platinum contact, palladium catalyst on bead aluminosilicate
after a 40-hour oxidation of carbon monoxide (1%) and a gradual temperature
elevation to 6008C. oxidizes carbon monoxide completely at 250°C. and above.
At 200°C., the activity of palladium catalyst is 30% lower than that of
platinum catalyst, but does not decrease, and even increases (up to 82%)
during prolonged use, particularly for 6 hours at 600°C. Thus, the heat
treatment of low-percentage platinum, palladium and platinum-palladium
catalysts in a stream of air and during the oxidation of carbon monoxide at
temperatures up to 600-650°C. practically does not decrease their activity.
This indicates a high thermal stability of the catalyst at these temperatures.
The results obtained are a consequence of a property characteristic of
low-percentage catalysts: as the temperature is raised to 600-650°C., no
coarsening of the crystals is observed, and only their defects are eliminated.
This property has been noted by many researchers [385, 422]. Thus, in [385]
it was shown that in the course of regeneration of a platinum catalyst on
charcoal in a stream of air at temperatures up to 639°C. , the recrystalliza-
tion of platinum proceeded to a barely perceptible extent:
Time, hr ' 0 0 120 240 480 639 —
Crystal size, A 46 59 52 57 51 54,6
I
This phenomenon is attributed by the authors of the paper to a complete
insulation of the fine platinum crystals from one another by particles of the
carrier.
By hindering the process of sintering of fine metal crystals in low-per-
centage catalysts, the carrier substantially raises their recrystallization
temperature as compared with platinum metal. For platinum sponge, the mobility
of the atoms already becomes appreciable at 350°C. [356], and at 370-380°C.
an exothermic effect is observed which is explained by the re crystallization
of fine crystals [357, 358].
- 73 -
-------
It should be noted that platinum undergoes recrystallization more
readily in atmospheric air than in nitrogen [355].
If the temperature is raised above 650°C. and the training time is
extended, the platinum crystals on aluminum oxide [194, 352, 353] coarsen
appreciably as a result of an increase in surface diffusion. This process
is also considerably affected by the initial dispersity of the metal in the
fresh sample. Other things being equal, subcrystalline samples or contacts
with a low content of metals are deactivated less than obviously crystalline
ones with a high content of platinum, for example [423, 424, 425] on charcoal
or silica gel. V. P. Lebedev et al. [425] note that the most dilute plati-
num catalyst on silica gel (a = 0.001) did not change its activity at all
with time during heating. Ref. [269] also indicates that adsorption (0.0054-
0.035 wt. %) platinum catalysts did not display any tendency toward a temper-
ature-induced decline of activity; on the contrary, at 700°C., the activity
of the most dilute catalyst was three times the original value. These facts
were expounded and accounted for by G. I. Yemel'yanova and S. Khasan [386].
They noted that the sintering of adsorption catalysts (dilute metal layers)
at high temperatures (700-800°C.) may involve the dissociation of the sub-
crystalline phase formed earlier and of the coarsened ensembles as a result
of a sharp increase in the mobility of the atoms on the carrier and their
dispersal over the still-unoccupied surface. Rapid cooling of such a sintered
contact leads to freezing of the atoms or their groups on the carrier, with an
increase of the metal surface and specific activity. The authors postulate
that the discovered phenomenon is characteristic of low-percentage catalysts
used at high temperatures. A partial restoration of the initial dispersity of
the platinum catalyst on aluminum oxide after its reactivation at high temper-
ature is also reported in [422].
The results obtained are apparently related to the special properties of
finely dispersed particles in general and during their stabilization by the
carrier in particular. This is supported by the results obtained by N. I. Ko-
bozev, K. Ivanov and P. Bessalov [389, 390] in a study of the oxidation of
carbon monoxide on iron and copper aerosols. The authors showed that in con-
trast to powders, aerosol particles did not coarsen as the temperature was
raised, but became finer. Copper oxide aerosol, whose crystals were one.order
of magnitude smaller than those of copper oxide powder, had a higher activity
and adsorptive capacity for oxygen. The specific activity of copper oxide
aerosol was 1000 times greater than that of the powder. The process of oxida-
tion of carbon monoxide in the presence of aerosols began 200°C. lower than
on the oxide powders.
It is quite probable that the anomaly in the effect of sintering* on'
finely divided metal particles also exists in the case of low-percenuagef carbon
monoxide oxidation catalysts, which operate in a stream of exhaust gas, when
the temperature undergoes an abrupt change (200-800°C.) as the operating con-
ditions of the engine vary, resulting in a hardening of the samples. /
- 74 -
-------
It appeared of practical interest to elucidate the influence of pos-
sible stronger overheatings (up to 900°C.) on the activity, structure and
phase composition of a low-percentage palladium catalyst used for removing
carbon monoxide and other components from exhaust gases, and on the condi-
tions of its regeneration. A special series of experiments was set up:
after a half-hour oxidation of 1% carbon monoxide in a mixture with air at
150, 200, 300, 400, 500, 600, 700, 800 and 900°C., the activity of the
catalyst was determined in the same reaction at 200-400°C. (Fig. 32). The
experiments showed that at the oxidation temperature of carbon monoxide
(300-400°C.), overheatings of the catalyst up to 900°C. practically do not
decrease the extent of elimination of CO: the latter is 90-100% oxidized.
The activity of the catalyst at a lower temperature (200-250°C.) decreases
by 20-23% after being used at 700-900°C.
I % oxidation of CO
I .
Lil. '._Tiine,
1 ' ' ~Y hours
Fig. 32. Effect of overheatings (half-hour each) to 900°C. and of gas
treatment on the activity of palladium catalyst on aluminosilicate in
the oxidation reaction of 1% CO in air at 200-400°C. [6l1 . 1 - 150,
200, 300, 400°C. in a stream of 1% CO, 0.5 hr; 2 - 500, tOO°C. in a
stream of 1$ CO, 0.5 hr; 5 - 700°C. in a stream of 1% CO, 0.5 hr; 4 -
750°C. in a stream of 1% CO, 40 min; 5 - 800°C. in a stream of 1% CO,
0.5 hr; 6 - # CO + 1$ 02 + N~, 400°C., 1.5 hr; 7 - H2 at 250°C;
8 - air, 400°C.; 9 - 900°C., 1% CO, 20 min; 10 - 3$ CO + 10$ 0, + B2,
400°C., 1.5 hr; 11 - 3# CO + 5$ 02 + NS, 600°C., 1 hr; 12 - % C^ +
N2, 400°C.; 13 - % CO + 1$ Cg + H2, 46o°C.; 14 - 3# CO + 1C* ^ + «2,
600°C.; 15 - 8f> CO + 1<# C^ + N2, 400«C.; 16 - H2, 300°C.i 17 - H2,
350'C.; 18 - H202.
The decrease in the activity of the palladium catalyst after overheatings
in a stream of air at 700-800°C. may be explained by a number of factors, the
chief ones being a decrease in the total and specific surface of the catalyst
and the oxidation of palladium to the oxide. It is known that the temperature
of the start of an intensive migration of fine metal crystals over the surface
with formation of coarser crystals on such carriers as asbestos, zinc oxide
and others amounts to approximately 0.4-0.5 of the melting point of the metal
[354, 391]. In the case of palladium, it is close to 770°C. On the other
hand, at 800-900°C., a change is possible in the porous structure of alumino-
silicate, whose maximum calcination temperature during preparation is 800 °C.
It is known from the literature [349] that when palladium is treated
with oxygen for an extended period (20 hours), metallic films of palladium
- 75 -
-------
can be oxidized at a temperature as low as 250°C. At the same time, about
30 monolayers of oxygen are absorbed. The possibility of the appearance
of a phase oxide is also indicated by the closeness of the values of the
heats of chemisorption of oxygen on palladium black (-24.0 kcal/mole of
oxide in the 500-700°C. range for a degree of surface coverage of 1 x 10~^
to 0.7) and formation of surface (-24.6 kcal/mole of oxide) and volume
(-21 kcal/mole) palladium oxides [350]. To elucidate the causes of the
partial deactivation of palladium catalyst, its phase composition, change
of structure, and surface area were studied in the course of the above-indi-
cated treatment and regeneration of the contact.
Phase x-ray structural analysis was carried out on six samples of
palladium catalyst on aluminosilicate (0.75% Pd): 1) after use at 700°C.
in a stream of 1% CO in air; 2) after treatment at 900°C. with a mixture
of 5-6% CO + 3% 02 + N ; 3) after treatment with H202; 4) original sample
activated in a stream of air for 0.5 hr at 400°C.; 5) after testing for
stability to overheatings (600-900°C.); 6) after use for 2 hours on stand
of MZMA-407 engine.
Results of the phase x-ray structural analysis are given in Table 21.
The x-ray data showed that palladium was present in the crystalline state
in all the samples.
It is evident from the tabulated data that after their use at 700°C.
in a stream of 1% carbon monoxide, the palladium catalyst samples on bead
aluminosilicate contained chiefly palladium oxide. The results of x-ray
diffraction patterns for samples Nos. 2 and 4, not illustrated here, also
show the presence of a large amount of palladium oxide along with palladium.
Data for sample No. 5, tested for a long period of time in a laboratory
unit during oxidation of carbon monoxide in a stream of air are particularly
illustrative. In this case, no lines characteristic of palladium metal were
observed, and a new phase, palladium oxide, was formed. Similar data were
obtained by analyzing a sample of catalyst No. 6, used on the gasoline engine
stand.
Suggestions concerning the possibility of formation of platinum and
palladium oxides in oxidative catalysis (decomposition of hydrogen peroxide,
oxidation of sulfur dioxide, and other processes) can be found in the liter-
ature [359-362]. However, no concrete data are given for supported catalysts.
The data obtained indicate that palladium oxide, like palladium, is able to
activate carbon monoxide and oxygen on its surface, i.e., function (as do
oxides of nonprecious metals) as a carbon monoxide oxidation catalys^l. {This
is confirmed in [162] by the example of activated adsorption of carbpji mjonoxide
on palladium oxide, which ends in the desorption of carbon dioxide.
- 76 -
-------
Table 21
Phase Composition of Catalysts
Intensity I
d/n — Interplanar Spacing
Found
Tabular Data
For Pd [351] | For Glass
Phase
Sample 1. Fe, Ka, 30/15, 15 hours
6
1
3
2
3
1
2,65
2,17
1,67
1,54
1,31
1,08
2,644 '10)
2,153 (2)
1,674 (3)
1,536 (2)
1,322 (2)
1,080 (1)
_
—
—
—
—
—
Palladium oxide
»
»
»
»
»
Sample 3. Cu, K« , 30/15, Ni filter, 8 hours
3
10
10
2
5—6
3-4
1—2
1—2
3—4
3—4—2
3—4
1
2,665
2,642
2,256
2,157
1,954
1,688
1,538
1,522
1,378
1,326
1,174
1,127
2,644 (10)
2,644 (10)
_
2,153 (2)
1,677(3)
1,536 (2)
1,536 (2)
—
—
—
—
— •
__
_
—
—
—
—
—
—
—
'alladium oxide
»
'alladium
'alladium oxide
'alladium
'alladium oxide
'alladium
Sample 5. Cu, K, , 30/15, Ni- filter 7,5 hoars
(recorded on glass mount)
Amorphous
halo
3
10 m
2
2
3—4
6
7—o n
7-8 m
1
1
1
1
1
3,140
2,697
2,443
2,177
1,841
1,691
1,542
1,325
1,137
1,085
1,006
0,966
0,905
—
2,644 (10)
_
2,153 (2)
—
1,674 (3)
1,536 (2)
1,322 (2)
1,135 (1)
1,0806 (1)
1,007 (2)
0,962 (1)
0,905 (1)
3,156 (3)
-i_
2,499 (2)
1,844 (3)
1,524 (4)
—
—
—
—
—
—
Glass
Palladium oxide
Glass
Palladium oxide
Glass
.Palladium oxide
Palladium oxide
Sample g. U— 35 «V, 1=20 nul. i=12
D'= 57,3 mm i=0,7 mm
10
1
4
3
3
2
2
1
1
2,673
2,157
1,683
1,538
1,322
1,080
0,998
0,905
0,834
2,667 (33)
1,153 (20)
1,674 (28)
1,536 (18)
1,322 (12)
1,081 (9)
0,998 (6)
O.S053 (6)
0,840 (6)
—
—
—
—
—
—
—
—
—
Palladium oxide
- 77 -
-------
In the case of low-percentage platinum catalysts, x-ray phase analysis
failed to detect any platinum oxide. Apparently, even if a partial oxida-
tion of platinum does occur during the action of oxygen on the supported
platinum catalyst [322], it does so without forming phase oxides. This
differentiates the low percentage catalyst from platinum black, the activa-
tion of the surface of which at 400-600°C. is attributed to the formation
of phase oxides [268]. Oxide films were formed during heating of a platinum
plate to 800°C. and above in the presence of oxygen [365] and also during the
oxidation of ammonia in the presence of water vapor at 750°C. [366] and sul-
fur dioxide [361, 367]. The appearance of Pt-jO/ as a result of treatment
with an explosive gas mixture at 600°C. did not cause any marked changes in
the catalyst's activity [365]. Under the influence of oxygen, the compact
film undergoes an exothermic phase transformation at 500-600°C. [268], These
data attest to the possibility of a phase formation of platinum oxides when
a compact metal is used.
Admixtures of platinum in supported palladium impart to the latter a
stability to oxidation. Palladium oxide was not detected in a sample of
mixed platinum-palladium catalyst (0.5% E Me) used for 4-6 hours in a stream
of exhaust gas from "Moskvich-407"-
In order to obtain a partial reduction of palladium oxide, the catalyst
was treated with a mixture of 3% carbon monoxide and 10% oxygen in nitrogen
at 400°C. for 1.5 hours. Favorable conditions were thus created for the
regeneration of palladium. As is evident from Fig. 32, it was possible to
raise the degree of oxidation of carbon monoxide at 200°C. to 30%, and at
250°C. to 85-90%.
The positive influence of the reacting mixture was observed in the
regeneration of a catalyst which was used at 900°C. (Fig. 32, see sections 10
and 18).
The x-ray pattern of a catalyst treated with hydrogen peroxide (sample 3)
also shows the reduction of a part of the palladium oxide to the metal.
Unfortunately, treatment with hydrogen of a catalyst which has partially lost
its activity failed to yield positive results (Fig. 32, see section 7, 16 and
17). This is apparently due to a strong adsorption of hydrogen on the catalyst
surface, preventing the chemisorption of carbon monoxide. A brief (25 min)
oxidation of carbon monoxide in high concentrations (5-6%) at a relatively
low oxygen content (3%) in a nitrogen mixture which approximated the composi-
tion of the exhaust gas of gasoline engines did not deactivate the catalyst
even at 900°C. (Fig. 33).
• I
X-ray patterns of a catalyst used in mixtures with a relatively
-------
oxidation of CO
Fig. 33. Influence of brief (25 min) treatment
of palladium catalyst on synthetic aluninosilicate
in a mixture of 6$ CO + Ufa 0- + nitrogen at 900°C.
on its activity at lower temperatures. Solid
line - after overheating; dashed line - before
overheating.
too
Thus, despite a partial decrease in the activity of the palladium cata-
lyst on aluminosilicate at low temperatures (200-250°C.) after the catalyst
has been used at 700-900°C., and because of its oxidation with the formation
of palladium oxide, which continues to catalyze the process, the degree of
oxidation of carbon monoxide may increase when the catalyst is treated with
hydrogen peroxide or a mixture of 3-6% carbon monoxide, 5-10% oxygen and
nitrogen, i.e., a mixture whose composition is close to that of the exhaust
gas under certain operating conditions of the engine.
The above data permit one to postulate that the state of palladium in
the catalyst and its activity under the conditions of operation prevailing
in a gas purifier in a stream of exhaust gas with a high concentration of
carbon monoxide and hydrogen will depend on the composition of the gas mix-
ture. At a relatively high oxygen concentration (up to 20%) and high temper-
atures, palladium oxide will be active, at a high content of carbon monoxide
and hydrogen and a lower oxygen concentration (5-10%), palladium metal will
be active, and thus during overheatings the contact will be sufficiently
stable, since it will be steadily regenerated. In the processes of road
testing of palladium catalysts, these assumptions were subsequently confirmed
experimentally.
In addition to studying the chemical state of palladium during prolonged
service with a steadily rising temperature, we investigated the change of the
total surface and structure of the catalyst. It is known that as the catalyst
is used, its structure undergoes changes caused by the action of high temper-
atures, water vapor, coke (cracking contacts) [369], soot (catalysts for
neutralizing exhaust gases) and other factors. Y-Aluminum oxide is character-
ized by gradual sintering of the surface as the calcination temperature is
raised, such that at 900-1000°C. there is a sharp decrease in surface and a
substantial alteration of the porous structure, which converts to corundum
[370]. The greatest structural changes occur in fine-pored samples with an
extended surface. The fine-pored structure of silica gel is also unstable
[317]. The introduction of aluminum oxide into the silica gel lattice markedly
- 79 -
-------
alters the surface properties of the alumlnosilicates formed as compared
with the original oxides [372]. Steam treatment of cracking catalysts at
750°C. decreases their total surface as a result of a reduction in the
number of pores due to the destruction of the walls by the fusion and coarsen-
ing of the pores [373]. In the absence of water vapor at high temperature,
the surface of the aluminosilicate catalyst is decreased by uniform sintering
of all the pores, and the distribution maximum of the pore volume shifts
slightly toward larger radii. Some authors have noted a rapid sintering of
the bead aluminosilicate catalyst starting at 900°C. [374, 375].
In order to elucidate the influence of heat treatment of the palladium
catalyst on aluminosilicate on the surface area and structure of its pores,
isotherms of adsorption and desorption of benzene at 20°C. were plotted by
the Rubinshteyn-Afanas'yev method [376-378]. The surface area was calculated
from the adsorption branch of the curves using the BET equation, and the
distribution of the pore volumes over the radii was calculated from the inverse
branch of the isotherm without considering the thickness of the adsorption
film of the adsorbate.
Data from the study of the porous structure of the catalysts are presented
in Figs. 34 and 35 and in Table 22.
Table 22 lists data on the surface area of the initial catalysts, deter-
mined from the BET equation with four points for low-temperature adsorption of
air [379] and with two points for low-temperature adsorption of argon, and also
by chromatography [380]. Comparison of the surface areas shows that they are
similar and agree with the reported data on the surface area of bead alumino-
silicate, 330-360 m2/g [380, 373]. Hence, the surface area of the carrier for
a small degree of coverage by the metal underwent practically no changes.
An examination of the general form of the benzene adsorption isotherms sug-
gests that both the initial palladium catalyst on bead aluminosilicate and the
initial carrier [373] have a transition-porous structure (Figs. 34, 35). The
width of the hysteresis loop for catalysts used at 700 and 900°C. is considerably
narrower than for the catalyst in the presence of which the oxidation of carbon
monoxide was carried out at 400°C. This fact attests to a certain dilation of
the catalyst pores after the reaction was carried out at 700 and 900°C.
The total volume of the pores (see Table 22) in these catalysts ranges from
0.61 to 0.52 ml of benzene/1 g of catalyst, but on the other hand there is a
sharp decrease in the volume of the finest pores (less than 201), i.e., from
0.25 to 0.09 at 700°C. and to 0.02 at 900°C.
Comparison of the curves of pore distribution over radii (Fig. 35) for
catalysts tested under different conditions shows that the structure fof (the
catalysts changes substantially at high temperatures. Whereas in the sample
after tests at 400°C. the bulk of the pore volume is accounted for by pores
with r = 20-30 1, the number of pores in the catalyst in the presence of which
- 80 -
-------
10-3 (g-
Fig. 34. Isotherms of adsorption and desorption of benzene
vapor at 20"C. for a palladium catalyst on synthetic alumin-
osilicate (0.5 wt. % Pd).
Table 22
Surface and Distribution of Pore Volumes Over Radii for Palladium
Catalyst on Synthetic Aluminosilieate
(0.75 wt. % Pd) in the Course of Use.
B
V
c
-------
the oxidation took place at 700°C. was greatly reduced (by a factor of 60).
Moreover, there appear a considerable number of pores with radii of 30-50 A
or more. After the oxidation of carbon monoxide at 900°C., the volume of
pores with radii up to 20-30 A also decreases as compared to the initial
sample, and the number of larger pores increases (Table 22).
This is also indicated by comparative data on the distribution of the
pore volumes over radii (obtained with a pore-measuring device) for the
initial palladium catalyst and a catalyst used in a stream of exhaust gas
in a gas purifier mounted on a ZIL-130 automobile which traveled about
21,000 km (Table 22 and Fig. 36).
av,
Fig. 35. Curves of Sistrib ition of pore volumes over radii for
samples of palladium catalyst on synthetic aluminosilicate after
tests at: 1 - 400°C.; 2 - 700°C.; 3 - 900"C.
- 82 -
-------
Thus, raising the oxidation temperature of carbon monoxide to 700-900°C.,
both in laboratory experiments and in' a stream of exhaust gas, causes a
rearrangement of the structure of the palladium catalyst on aluminosilicate
and a slight change of the total pore volume.
Calculation of the area of the catalyst samples studied showed that as
the oxidation temperature of carbon monoxide is raised to 700-900°C. and
in operational tests of the palladium catalyst on aluminosilicate, a decrease
in its area of approximately 30% takes place.
V, «!
B
•e-o-
'.O
2,0
Log r.
Fig. 36. Differential (l, 2) and integral (3, 4) curves
of distribution of pore volumes over equivalent radii of
palladium catalyst on synthetic aluminosilicate (0.75 wt.
% Pd), obtained by mercury porometry. 1, 3 - sample after
activation in a stream of air at 400aC.; 2. 4 - after
tests in a stream of exhaust gas of ZIL-130 engine in the
course of 21,000 km.
Summing up the results of studies of the atability, phase composition,
and structure of low-percentage platinum, palladium, and platinum-palladium
catalysts for oxidizing carbon monoxide, we can state the following. At
temperatures up to 700°C., the contacts operate stably for a long period of
time, this being due to their high stability to recrystallization. Starting
at 700-900°C., heating in air causes a reduction of the total area of the
catalyst as a result of sintering of fine pores, a partial oxidation of pal-
ladium to the oxide, and a 20-40% decrease in the degree of oxidation of
carbon monoxide at a reaction temperature of 200-250°C. The activity of the
contact at a higher temperature is close to 100%. It is possible that during
the sintering of the pores, the palladium concentration on the carrier
decreases slightly, and because of this phenomenon, the activity of the
catalyst cannot be fully restored to its original value at a low temperature.
- 83 -
-------
It is also possible, as suggested by some authors [381], that a slight
deactivation of the catalyst is caused by a coarsening of the palladium
oxide crystals which is accelerated in the presence of oxygen.
- 84 -
-------
Chapter 4
COMPLETE CATALYTIC OXIDATION OF HYDROCARBONS
The catalytic oxidation of hydrocarbons is carried out for the purpose
of obtaining intermediate organic compounds that are of considerable impor-
tance in industrial organic synthesis. The oxidation of hydrocarbons to
carbon dioxide and water is a side reaction, and had received little atten-
tion in the literature until the 1950's. Studies in the field of complete
catalytic oxidation of hydrocarbons are now being expanded in view of the
utilization of this reaction in fuel cells operating on natural gas and in
the removal of hydrocarbons from the exhaust gases of internal combustion
engines and chemical plants. The catalytic method of complete oxidation of
hydrocarbons is also used in the generation of heat used for heating cer-
tain installations and for motor transport in the Far North. The use of
catalysts for the combustion of organic discharges permits a substantial
lowering of the oxidation temperature and of the cost of building and heat-
ing the installations that burn noxious substances at various chemical
plants.
Results of known research in the field of complete catalytic oxidation
of hydrocarbons are presented in Table 23.
Analysis of the studies shows that the substances subjected to oxidation
were chiefly saturated and unsaturated open-chain hydrocarbons (acetylene,
ethylene, methane, and their derivatives), cyclic (cyclohexane) and aromatic
(benzene) compounds, and also compounds containing atoms of nitrogen, oxygen,
and halogens in their composition. The hydrocarbon concentrations were de-
termined by the specific conditions of the various processes, for example, in
the case of acetylene, up to 0.005%; hydrocarbons of cracking gases, up to
0.07-0.08%; and automobile exhaust gases, from 0.15 to 1.0%. The activity
and type of the catalysts employed depend primarily on the temperature and
nature of the organic compounds.
The problem of influence of the structure of organic compounds on the
temperature of their catalytic oxidation to C02 and H,0 has been treated in
a number of interesting studies [96, 98, 111, 112, 143]. Accomazzo and Nobe
[111] showed that the oxidation rate of hydrocarbons in a stream of air to
C02 and 1^0 over CuO/A^C^ catalyst at a space velocity of 525 1/hr slows
down with decreasing number of carbon atoms in the molecule (ethane, propane)
and accelerates with increasing degree of unsaturation of the molecule (ethane,
ethylene, propane, propylene, propadiene) and decreasing number of carbon
atoms in equally unsaturated compounds (acetylene, propyne).
The oxidation of such hydrocarbons as acetylene, propyne,.propadiene,
propylene, ethylene, propane, cyclopropane, and ethane is 80% complete at
the following temperatures: 200, 230, 240, 228, 310, 380, 400 and 420°C.
- 85 -
-------
Complete Catalytic Oxidation of Hydrocarbons.
Table 23.
I
s
Composition
of catalyst
1
Hopcalite
Composition
of gas mixture
2
20-125 ng/1
.of hydrocarbons
in air
Benzene
1, 2, 4-trim-
fithylbenze
Butylbenzene
n-Hexane
n-Decane
2,2-CHj-butan
1-Octene
Methanol
Methane
Cyclohexane
Methane
Hexane
Diootyl phthe
Iriaryl phos-
phite
Space
velocity,
hr-1
Z
—
21
»
»
»
»
»
»
»
»
»
»
»
»
^
»
% oxidation
150"
4
—
_
_
—
—
—
•- —
—
—
—
—
— -
_
—
200°
5
—
74
55
86
11
89
40
83
95
—
—
—
_
—
800°
6
—
87
98
96
97
98
84
89
98
—
.—
97
97
loo
•*uw
100
360°
7
—
92
100
96
97
96
98
94
98
91
_
__
—
400°
8
—
^^
_fff
—
—
_
—
35-40
_
—
—
30
__
•*••
500°
9
—
,^_
^_
—
—
—
—
_
—
—
—
—
—
—
550°
10
—
__
_
—
—
—
—
—
—
— •
—
—
—
—
600°
11
—
_ _
__ .
—
—
—
—
_
—
—
—
—
_
—
Characteris-
tics of cat-
alysts and
process
12
Halogen- and
nitrogen-con-
taining com-
pounds are not
oxidized com-
pletely
Refer-
ence
13
[96]
»
$
>
-------
Continuation of Table 23
Crs03/pumice
CuO.'AI,Oa(l'l)
oo
-J
Cu'Ala03 (1:1
C03
. Hydrocarbons
n air
Ethane, ethyl<
Propane, benzc
Butane, toluer
>entane, hexane,
xrtane
Methane
-0,15 % in
air
Acetylene
Propyne
PropadJene
Propylene
Ethylene
Propane
Cyclopropane
Ethane '
Methane
190-2000. parts
per million of
jcyclohexane in
air
5.7 x 10-5
mole, various
hydrocarbons
ne
ne
e,
,160-525
1/hr, 25 ml
of catalyst
31580
50 ml of
satalyst.
space veloc-
ity unknown
~
~~
'
__
—
~
—
100
=
_
—
80
80
80
—
~
—
100
_
_
^_
-
_.
80
fin
ov
—
~
20
—
^ _
__
^_
_
—
~
55—60
—
_
_
_
__
80
80
80
—
—
100
—
—
_
—
~
—
—
ICO
ICO
100
—
^—
^__
—
£0
—
*
—
__
100
__
__
__
—
_
—
—
Catalyst re-
sistant to mois
ture, used for
1000 hr
_
—
^
._„
—
^_
Rate constant
of complete ox
idation decrea
from benzene t
cyclohexane an
cyclohexene
[95]
»
^
*
•
[111]
>
»
»
»
*
*
»
^
>
ses
i
[145]
[112]
-------
Continuation of fable 2?
oo
00
1
VaOs
Co304
VnO
CraOi
FojOa
Wa03
AlaOa
ipXrt
CuO
VjOs
FeaOa— CuO
Clay
GuO— CraOa
Clay
Active
Coimnerical
MnO
'
2
2-CHj-butane
Benzene
n-Pentane
n-Hexane
1-Pentyne
2-CHj-butane
^
»
»
»
»
»
£
»
^
0.45$ of pro-
pane-butane
mixture in air
2 x 10-ty of
acetylene in
oxygen-argon
fraction of
compressed air
0.002-0.2$ of
acetylene in
oxygen
3
9
»
»
^
*
»
»
»
»
>
»
^
36000
t
60000
5000—20000
4
__
^ _
—
—
_—
—
—
— —
—
—
•~~
—
M—
100
80-96
5
_
__
—
100
.— .
~
—
—
—
"-"~
^^
—
—
_
—
97—99
6
—
__
—
100
~
—
—
—
"™~
— ~
—
"~«
12
12
100
7
—
__
—
—
100
ICO
100
—
_
"~~*
—
_ -
35
100
8
—
100
100
—
—
—
—
—
100
t A A
100
—
•»
65
52
100
9
__
.
—
—
—
—
100
100
*—
-^
100
«—
80
75
_
10
100
__
—
__
—
—
—
—
—
•—
—
_•
MM*
—
^^^
11
100
ICO
_
—
—
—
—
—
—
—
••••
—
100
""
—
_
12
. _
_
—
*.
—
_
_
—
—
—
—
.— -
-
Deactivated •
by water
vapor
_
13
^
[58]
rssi
LWJ
[92]
[99]
-------
Continuation of Table 23
oo
vo
Pyrolusite tin
ore promoted
with 1% Ag20
and AgMnO^
GoO3
Oxides of co-
balt + silver
Oxides of co-
balt + silver
Oxides of Mn
and Pe on grog
Barium ohromit
cm carriers
(Al20j, Si02)
Pd on syntheti
aluminosilicat
0,005 % in
air
Ethylene
Ethane, ethy-
lene, propane
propylene,
acetylene,
butylene in
3.1£$ methane
1.55* Hg, 16.3)
°2
Isobutane,
n-butane
0.5# of oyclo-
hexane in air
60000
Contact
ime 0.3 sec
olume of ca
lyst 0.5 ml
Space velo-
city 4-g 500
1-30 at P =
300 atin
Up to 20,OOC
at P = 50-
300 atm
450
2200—7200
6000-1200
83—
-100
—
_
100
100
__
—
—
—
__
—
10
—
—
u
^_
—
85-95
—
—
^^
_-
—
100
—
__
.
—
—
—
—
__—
60
—
—
—
—
—
.
—
—
—
~~
—
—
95
—
—
Stable to wa-
ter vapor,
carbon dioxicU
sulfur oxides.
nitrogen ox-
ides, ammonia;
poisoned with
traces of com-
pressor oils
~~~
—
—
—
1
[92—
-94]
[109]
[107]
[108]
[141]
[133]
Data of
GIAP,
IKhN AN
KAZ SSR
-------
Continuation of Table 23
vo
O
1,
»
Pt+Pd
AlaOa
2Me=l %
Pt/ alumino-
silicate
, Platinum on
AJ^Oj (AP-56)
Platinum on
refractory
alloy strip
2
0.9# cyclohex-
ane, 1# carbon
monoxide in
air
Up to ^meth-
ane in air
1% propane-bu-
tane fraction
of cooking gas
(78JJ propane,
13. 3» butane,
• 5.9# ethane,
lff> methane)
in air
Waste gas of
synthetic
acid plant
CO, H2 and or-
ganic compound
B
6000-8000
—
36000
Up to 3000
• I/kg hr
9
4
30
—
—
—
(^—
S
65
—
5
—
^~™
6
90
—
SO
At :
""'""""
7
-
—
—
8
.- -
—
80
9
__
—
96
00-350°C. odor disa
10
_ _
—
100
ppears
__
11
«_
—
<•_
12
_
Start of oxida
tion at 300"C.
used for analy
tical purposes
—
CO, Hg and or-
ganic impuri- •
. ties completel
oxidized. Cat
alyst destroy-
ed in the pre-
sence of large
amounts of in-
organic solids
in the gas
13
fl03]
[57]
[105]
[101]
-------
I
vo
Platinum on
ceramic rods
(Houdrv...
"oxicat")
Platinum on
screens,
stainless
steel per-
forated plate
or on AlgO-
Platinum,
palladium,
rhodium,
ruthenium on
carrier
Waste gases
of roasting
furnaces. _
regeneration
gases of pe-
troleum re-
fineries, etc.
-0.08 %,
Oo-19.5 %,
H20-2.5-2.7
%, CO-2.5 %
Waste gases of
chemical plants
;,
\j$h methane
y> oxygen,
. 95.9$ nitroge
—
,
100000—
—200000
—
__
—
Complete oxidation
Complete oxidation
Continuation of Table 23
Service life
of gas pvri-
fier, 2500 hr.
Units operate
for 6000 hr
using the heat
of exhaust
Complete oxidation achieved at
AOO-500eC.
gases
Jnits utiliz-
ing the heat
evolved by the
oxidation are
advantageous
[104]
[102]
[106]
-------
Continuation of Table 23
vo
N>
1
Activated
' &XinQin&
t \93Sw *J«2 3*
CuO/AIaOa
(1 ! 1)
2
0.02-0.25*
hydrocarbons
(61.7* CH4,
14.736 ethane,
23.5ft heavy
hydrocarbons
in the kryptoi
xenon fraotioi
1-Hexene
(1170 ppm
3
400
-
>
4-103
10.103
16-103
16- 103
4
^ _
—
—
—
6
_
—
—
35
6
_
—
—
_
7
8
9
10
11
60-80J» purification achieved
—
—
__
at 5
100
90
80
_
W-6000
—
—
—
^ •
—
—
_—
_
—
__
12
Catalyst serve
for several
'years under
industrial
conditions
Catalyst taste
for oxidation
of CO and hy-
drocarbons in.
exhaust gases
for 100 hrs.
13
I
[394]
1
[89]
-------
The reaction rate increases with rising temperature and concentration
of the hydrocarbons and decreasing space velocity. A similar relationship
between the structure and rate is observed in noncatalytic oxidation of hy-
drocarbons [203].
In experiments involving the complete oxidation of hydrocarbons on hop-
calite, Johnson and Christian [96] showed that a total increase of the mole-
cular weight of hydrocarbons facilitates the reaction. Methane is the most
difficult to oxidize: at 450-500°C., the oxidation is only 35-50% complete.
Bransom and Haulon [143] observed a similar relationship in a study of the
influence of the structure of paraffin hydrocarbons on the kinetics and
mechanism of their complete oxidation on copper oxide (Fig. 37). From the
results obtained by the authors it is evident that as the chain length in-
creases, the oxidation of the hydrocarbons becomes easier. Among hydrocar-
bons included in the composition of automobile exhausts, the most difficult
to oxidize are unsubstituted saturated hydrocarbons, particularly those of
isomeric structure (pentane, hexane, 2-methylbutane) and also benzene [112].
In a study of the oxidation of hydrocarbons on oxide catalysts, Stein
et alt [112] showed that the reactivity of hydrocarbons with the same number
of carbon atoms increases in the following sequence: aromatic hydrocarbons,
isoparaffins, straight-chain paraffins, olefins, and acetylenic compounds.
Similar data were obtained by V. N. Vendt and T. A. Lebedeva [95], who
used chromium oxide deposited on pumice for the analysis of a series of
organic compounds. A complete oxidation of methane on this catalyst is
achieved at 650-700°G., ethane and ethylene at 550°C., propane and benzene
at 500°C., butane and toluene at 450°C., and pentane, hexane, octane, and
amylene at 400°C.
.«•>
"N. V. %S,..\ I'". Fie. 37. Oxidation of paraffin hydrocarbons on cupric
io \T\.» C\ " oxide: 1 - methane; 2 - ethane; 3 - propane; 4 - pen-
' N* x VN\ tane; 5 - Ctj - paraffins (hexane, 2,2-dimethyl-butane,
N». heptane, 2,3-dimethylpentane)[l43i.
/.f ',• ','
Economy and Mellon [133] indicate the high activity of barium chromate
on carriers at space velocities of 2.2-7.2 x 10-* hr'1. A complete oxidation
of n-butane, isobutane and isobutene on this contact takes place at 350-450°C.
Isobutene oxidizes at the fastest rate, followed by^isobutane and n-butane.
Barium chromate is stable to overheating at 600-800 C. and operates for a
long time without a decrease in activity (600°C. - 168 hours, 700°C. - 48 hours,
800°C. - 24 hours).
- 93 -
-------
The oxidation temperatures of oxygen-containing compounds (alcohols,
ketones, aldehydes) are similar. Thus, T. G. Alanova and L. Ya. Margolis
showed [171] that for the same contact time of 0.34-0.37 sec, the oxidation
temperature of several compounds differs by 50°C.: acetone, phenol, metha-
nol (473 °C.), butyraldehyde (443°C.), diacetone alcohol (523 °C.).
In addition to their structure, the chemical composition of catalysts
has a considerable effect on the temperature of complete oxidation of hydro-
carbons. Most illustrative in this respect are the results obtained by Stein
et al. on metal oxides [112]. By oxidizing seven hydrocarbons on twelve
oxides of polyvalent metals, they obtained a general relationship whereby
the temperature of complete oxidation increased in a given sequence of oxides
for the majority of the hydrocarbons studied. Figure 38 shows data on the
temperature of complete oxidation of 2-CH3~butane and n-pentane on catalysts
consisting of oxides of different metals. In the oxidation of cyclohexane,
the reaction proceeded in the following sequence of metal oxides: vanadium
(550°C.), tungsten (540°C.), thorium (350°C.), copper (350°C.), cerium (330°C.),
aluminum (300°C.), iron (300°C.), chromium (270°C.), manganese (230°C.), cobalt
(150°C.) and in the case of 1-pentyne: vanadium (350°C.)> thorium (250°C.),
copper (270°C.), cerium (260°C.), chromium (250°C.), tungsten, aluminum (220°C.),
manganese (220°C.), cobalt (210°C.), titanium (210°C.), nickel (200°C.), iron
All the hydrocarbons display a common trend, i. e., higher oxidation
temperatures as less refractory oxides (those of manganese, iron, cobalt,
nickel) are replaced by more refractory ones (those of vanadium, thorium,
tungsten), which are characterized by a low partial pressure of oxygne above
the oxides.
too
'too
SCO
t° of decomposition
of 2-CHj-butane
Fig. 38. Oxidation of 2-methylbutane and
n-pentane on oxide catalysts [ 112].
t* of decomposition of n-pentane.
too
300
soo
- 94 -
-------
Very similar results on the influence of chemical composition of the
oxides were obtained in studies of complete oxidation of ethylene [154, 155],
Dmukhovskiy noted that the oxides €0304 and €0203 display the maximum activ-
ity, and the reaction rate at 262°C. decreases when oxides of the following
metals are used: cobalt, chromium, silver, manganese, copper, nickel, cad-
mium, iron, molybdenum, vanadium, titanium. When the oxides are deposited
on a carrier, their activity increases.
M. Ya. Rubanik et al. [155] found that the oxidation reaction of ethy-
lene in a flow-through circulating unit slows down in the following order
of metal oxides: manganese, copper, cobalt, iron, uranium, cadmium, vana-
dium, nickel, zirconium, lead, tungsten. A slight difference in the se-
quence of the oxides according to decreasing activity in the works of dif-
ferent authors is apparently due to differences in the conditions of pre-
paration of the catalysts and their use. , •
conversion to C0_.
Fig- 39. Percent conversion of propylene to C02
at 360°C. as a function of the atomic number of
the rare earth element [471].
Kh. M. Minachev et al. [471] showed that on rare earth oxides including
oxides of cerium, praseodymium, neodymium and terbium, propylene is complete-
ly oxidized. The catalytic activity of rare earth oxides in this reaction
is determined by the binding energy between oxygen and the surface of the ox-
ides acting as catalysts. Experiments show that as the atomic number of the
elements whose oxides were studied as catalysts changes, the yield of carbon
dioxide, i. e., the extent of oxidation of propylene to carbon dioxide and
water (at t = 360°C.) changes periodically, passing through two maxima (Fig.
39) characteristic of cerium and terbium oxides. The oxides of neodymium,
samarium, dysprosium, gadolinium and turbium have a stable activity in the
oxidation reaction of propylene, i. e., the carbon dioxide yield in their
presence is virtually constant. Oxides of lanthanum, cerium and praseody-
mium display a constant activity in the course of the first 30-40 min, and
then, depending on the temperature of the experiment, their activity increas-
es sharply. In all cases, a complete oxidation of propylene takes place.
- 95 -
-------
The activity of rare earth oxides is displayed in the temperature range
in which the oxygen adsorbed on the surface of these oxides is the most mobile,
Active rare earth oxides are associated with the mobility of the oxygen of
such oxides as cobaltous-cobaltic oxide, manganese oxide, and nickel oxide,
used as oxidation catalysts [408].
The combined effect of the mobility of oxygen and catalytic activity
of rare earth elements in oxidation reactions suggests that rare earth oxides
can be good oxidation catalysts for other hydrocarbons as well.
S. Z. Roginskiy, L. Ya. Margolis [97, 150, 170], and other authors have
advanced certain principles of selection of oxide catalysts for the reaction
of complete oxidation of hydrocarbons. They showed that in the oxidation of
isooctane, cyclohexane, and other compounds, the oxides of transition ele-
ments and faintly colored oxides of such transition elements as niobium, mo-
lybdenum, etc., have a weak activity. The activity of individual oxides of
transition elements decreases rapidly in the course of service, whereas bi-
nary oxides containing at least one transition element and forming colored
compounds are marked by a high activity.
The authors note further that the most active and stable systems (par-
ticularly when deposited on a carrier) are spinels, whose properties were
studied in detail. The more pronounced oxidizing properties of chromium
spinels (as compared to others) are mentioned (Table 24).
On copper chromium and magnesium-chromium catalysts, isooctane burns
up most readily, followed by cyclohexane and methylcyclohexane [146].
The high activity of copper chromite in the oxidation of cyclohexane
is indicated by Hoot and Kobe [156]. In order of rising temperature of com-
plete oxidation, the oxides which they studied are arranged as follows:
copper chromite (170°C.), cobalt oxide (207°C.), ferric oxide (288°C.), sil-
ver oxide (292°C.), uranyl vanadate (294°C.).
In the case of Co-Mn spinels, a decisive influence on the catalytic pro-
perties in the oxidation reaction of propylene [150] is their structure. The
activity of a spinel of the structure Co2+(Mi3+Mh3+)042+ is higher than that
of Co3+(Mh2"*"Co3+)042- because in the former there is an increase in the number
of Mn cations, which can act as electron donors for the chemisorption of Oo
atoms better than Co cations can.
The high activity of spinel type catalysts has stimulated the study of
their properties in the reaction of complete oxidation of hydrocarbons) [58,
171, 172, 173] and the application of, for example, copper ehromite tq priac-
tical uses.
- 96 -
-------
Table 24.
Oxidation of Isooctane (1.2-2.9#) in Air on Low-Per-
centage Catalysts on Asbestos at 7 x 10? hr-1*
Catalyst
Pt
C opper-chrpmium
Iron-chromium
Magnesium-chromium
Magnesiun^silver
Iron-aluminum
C opper-a luminum
% of cata-
lyst on
carrier
0,1
2,0
3,0
3,0
3,0
3,0
3,0
Temperature of 50-
60$ conversion of
isoootane to C02
and H^
213
300—325
300—350
350
450-500
Above 500
Above 500
*Iable compiled on the basis of data from [97].
Of major interest are studies on the "modification" of spinels by admix-
tures of acids and certain salts of alkali and alkaline earth metals. L. Ya.
Margolis et al. [138-140] showed the modifying effect of boric and hydrofluoric
acids, barium sulfate and nitrate, and sodium silicate on copper and magnesium
chromites. They noted that upon introduction of 2-5% of these compounds, the
activity of spinels in the reaction of complete oxidation of ethylene and iso-
octane increases sharply. The "modification" of contacts affects the quality
of the surface, occasionally altering the individual steps of the process.
Compounds with unsaturated (acetylenic, ethylenic) bonds oxidize readily
on spinels (cobaltides) and mixed oxides (hopcalites) at relatively high space
velocities, 21-60 x 10 hr'l [92-94, 96, 99, 111]. Promoting of manganese-
containing oxide catalysts with silver oxide and their deposition on a carrier
(manganese ore, clay [116]) increase the stability of these contacts to the
action of water vapor and to sintering, and their strength. Pyrolusite man-'
ganese ore activated with 1% silver oxide [92-94, 99] is used in the produc-
tion of inert gases for the removal of acetylene from the oxygen-argon mix-
ture.
In the preparation of manganese-containing oxide catalysts, a consider-
able importance is assumed by the method of precipitation which affects the
modification of manganese dioxide and its dispersity. Thus, in [149], a
and R-modiricationsSof manganese dioxide, prepared by different methods
differed substantially in their activities in the oxidation reaction of car-
bon monoxide, probably because of different degrees of their ^spersity. As
was noted by the authors (who studied the formation of an amalgam and the
reaction with copper oxide with the formation of an active contact), this was
manifested by a difference in their chemical properties.
In [148], the activity of the initial a- and g modifications of Mh02 was
- 97 -
-------
found to be similar. A difference in their behavior was displayed after pro-
moting Mn.02 with silver oxide. Using x-ray structural analysis, the authors
were able to establish that silver oxide was formed in large quantity on the
surface of g-Mn02, whereas on orMh02 silver is converted mainly to silver
manganite. The activity of the promoted catalyst in the latter case decreases
and approaches that of the original manganese dioxide.
Among other spinel catalysts, a complete oxidation of organic compounds
takes place at high rates in the presence of cobalt cobaltide. It is noted
that its activity is similar to that of platinum and palladium catalysts.
Andersen et al. [142], who studied the oxidation of methane (at space
velocities of 480 hr'*) in air on 26 catalysts showed that the oxidation rate
constants decrease in the following series of contacts: Pd/v-Alpps, Co3O4 -
spinel, 00304 - mullite/Y-Al203, Pt/Y-Al203, Pd/v-Al2O3, Cr2O3/Y- A12O3, Mn203/Y-Al2O3
(Fig. 40). The temperature of complete oxidation of methane on Pd/Al203 is
300°C., on Pt/Al203 400°C., and on Co203/y-Al203 500°C. Very similar re-
sults were obtained by oxidizing methane in oxygen on the same contacts
(without a carrier) in [472],
The catalysts 00304 and Pd/Al203 are more suited for hydrocarbons which
oxidize more easily: 2-pentene and benzene oxidize completely on these cat-
alysts at 200°C. On platinum catalyst on aluminum oxide, the temperature of
complete oxidation of these hydrocarbons is 50-100°C. higher.
In a study of the oxidation of methane (0.7-4%) in oxygen in a flow-
through circulating unit (circulation rate 550 1/hr) over oxides of transi-
tion metals of the fourth period, G. K. Boreskov et al. [147] showed that
cobaltous-cobaltic oxide displays the maximum activity. The reaction rate
constant for the oxidation of methane (1%) at 300°C. (for some metals the
value of K was obtained by extrapolating to 300°C. and 1% methane) decreases
in the series: 00304, NiO, MiO, CuO, 0^03, 16203, Ti02 (Fig. 41). An
analogous activity series of metal oxides was obtained by Boreskov et al.
[151] in a study of the oxidation reaction of H2 and isotopic and homomole-
cular exchange of 02.
By comparing the activity of a series of oxides in oxidation reactions
with the binding energy between oxygen and the surface of the oxides, deter-
mined by dissociating a part of the oxides, it was found that there is an
inverse proportionality between the catalytic activity and the energy binding
oxygen to the oxide surface [186]. The relationship found by Boreskov et al.
provides a rational explanation for the data reported in the literature on
the activity of transition metal oxides in oxidation reactions and offers,
new means of scientific selection of oxidation catalysts.
A relationship of this kind had been indicated earlier by Rienacker
in a study of the activity of a series of oxides in the oxidation reaction
of carbon monoxide [174]. He showed that the catalytic activity of metal
- 98 -
-------
oxides in this reaction goes through a maximum when the oxides are arranged
according to the binding energy. Oxides with a very high and very low oxygen-
oxide binding energy are not suited for this reaction. In order for the oxi-
dation reaction of carbon monoxide to proceed at the" maximum rate, a certain
optimum binding energy between oxygen and the surface of the oxides is re-
quired .
Conversion
0,93
3,0
S.O
'.0
>ot
rtji,
Pig. 41. Oxidation of 1% methane
in oxygen at 300°C. over oxides of
transition metals of period
4 [147].
0.0*6
/.ffao/r/x
Fig. 40. Catalytic oxidation of methane at a space velo-
city of 580 tar1 [142].
Data from a number of studies indicate
favorable prospects for the use of cobalt oxide
catalysts for the removal of hydrocarbons from
oxygen-containing gas mixtures. The cobalt
catalyst €0304^1203 oxidizes 93% of the hydro-
carbons in exhaust gases [152]. The authors of
the latter study noted that after 950 hours of
service, the oxidation of the hydrocarbons was
down to 87%. When cobalt catalysts are promoted
with silver, they can be used for the removal of
saturated and unsaturated C2~C^ hydrocarbons from
gas mixtures at space velocities of 20 x 10^ hr~l,
low temperatures (100°C.)> aid high pressures
(P = 50-300 atm) [107, 108].
*<9
CaO
When cobalt catalysts are tested on carriers
(silica gel, aluminum oxide, alumino-silicate)
at a high temperature, the effect of interaction of cobalt oxide with aluminum
oxide with the formation of the spinel CoAl20^ is observed; the activity of
this spinel being much less than that of cobalt cobaltide [142]. The incon-
sistency of data on the stability of the cobalt oxide catalyst on carriers
may be due to the presence of different modifications of cobalt oxides.
- 99 -
-------
The lack of reliable literature data on the stability of most oxide
catalysts hinders their practical application in reactions of complete ox-
idation of hydrocarbons. More definite data are available on the use of
Mn-pyrolusite ores promoted with oxides of silver and copper [92-94, 175]
in processes of oxidation of acetylenic compounds, and on the use of copper-
chromium catalyst for the purification of gaseous discharges of certain in-
dustrial organic processes [171, 172, 173].
Platinum and palladium catalysts, whose activity is largely determined
by the method of preparation, conditions of activation, and chemical nature
and structure of the carriers, are suitable for the complete oxidation of,
cyclic compounds, which are the most difficult to oxidize.
IfO
'SO
sto
zso
310 T.£
Fig. 42. Oxidation of 0.5$ eyclohexane.Cl) and a mixture of 0.5$ eyelo-
hexane and 1% CO (2) in air over palladium catalyst on aluminosilioate
at a space velocity of 6 x 10' hr~*.
Fig. 42* shows data on the oxidation of cyclohexane (0.5 vol. %) and its
mixture with 1% CO in air at a space velocity of 6 x 10^ hr"1. It is evident
from the figure that a 90% oxidation of cyclohexane to C0£ and B^O is achieved
at 280-300°C. both in the case of 0.57. cyclohexane and its mixture with 1% CO.
Increasing the space velocity during the oxidation of cyclohexane to 12 x 10^
hr"1 slightly decreases the activity of palladium catalyst: an 85% oxidation
of the hydrocarbon is achieved at 330°C.
The oxidation of saturated hydrocarbons (for example, 1% of a propane-
butane mixture in air) takes place at a high rate on platinum catalyst (0.5
wt. % Pt) [57]. The activity of platinum-palladium and other catalysts under
comparable conditions proved lower than on platinum, as in the case of the
oxidation of formaldehyde (Fig. 43).
Platinum-palladium catalyst on aluminum oxide (£Me = 1%) is used for'
analyzing mixtures containing methane [103]. At a space velocity of 36 x
103 hr'1 at 500°C., a 96-100% oxidation of the mixture to C02 and H20 is
achieved on this contact. On palladium catalyst, a complete oxidation of
.*Data of GIAP (State Institute of the Nitrogen Industry) obtained by oxidizing cyclohexane on
palladium catalyst prepared at the Institute of Chemical Sciences of the Kazakh Acadeiqy of Sciences.
- 100 -
-------
methane in a mixture with air is achieved at lower space velocities (450 hr'1)
and higher temperatures: 20% at 500°C., 80% at 750°C., and 100% at 800°C
[141].
100
10
ir
01
•a
, 60
/oo
r;c
200 300 . WO SOO
Fig. A3. Catalytic oxidation of ]# formaldehyde in a mix-
ture with air at a space velocity of 36 x HP hr"*.
Platinum catalyst of domestic manufacture [105] is successfully used at
space velocities up to 3 x 10^ hr'^ for the oxidation of waste gas from plants
producing synthetic fatty acids. At 300-350°C., the odor of toxic compounds
is completely eliminated. Platinum catalysts on ceramic rods called "oxicats"
[104], on aluminum oxide [105] and as an alloy with nickel [100] are used
abroad for these purposes (judging from reports in the literature). These
catalysts in the form of beads, screens, and metal plates purify waste gases
from petroleum-cracking plants, [104], synthetic fatty acid production [105],
coffee roasting, polymer factories [136], kitchen fumes, etc. The cost of
catalytic devices operating at 250°C. is 1.5 greater than that of installing
thermal combustion of the discharges. However, the operating cost of cata-
lytic devices is 2.5 times lower because of a sharp reduction in the amount
of fuel consumed by heating the components undergoing oxidation [102]. The
service life of such units amounts to 2.5-6 thousand hours [104],
A number of schemes for the catalytic oxidation of organic impurities
in the waste gases of chemical plants have been proposed in the literature.
The use of catalysts in the form of screens and streamlined lattices de-
creases the resistance to the gas flow and permits an increase of the space
velocities. According to the data of [137], in 1964, there were around 800
operating units for the catalytic purification of waste gases in Europe, and
around 900 units in the entire world, operating on all-metal catalysts. How-
ever, the literature does not specify the service life of all metal catalysts,
- 101 -
-------
noting only that the alloy deteriorates rapidly when large amounts of acids
and solid inorganic substances are present in the gas [101].
In recent years, a considerable amount of patent material has been pub-
lished dealing with methods of purification of exhaust gases and preparation
of catalysts for these purposes. Major attention has been given to the study
of catalysts for the oxidation of hydrocarbons and CO in the exhaust gases of
motor transport: chromites, molybdates, supported manganates [176], manganese-
chromium catalyst [177], and contacts consisting of a mixture of chromite of
nickel or cobalt deposited on A^O^ coated with manganese oxide [178], or a
mixture of oxides of cobalt and cerium [181], or oxides of cobalt, nickel
(1-75 wt. %) and thorium (5-25%) [180].
Of interest are patents [106, 182] on the complete oxidation of methane.
A series of platinum group catalysts and silver on aluminum oxide are pro-
posed for this purpose. The reaction rate decreases in the following series
of catalysts: rhodium, palladium, iridium, ruthenium, platinum, silver [182].
At 400-500°C., a complete oxidation of methane (1.5%) is observed in a mix-
ture of 3% 02 and 95.5% N£ at a space velocity of 0.1-200 hr . To purify
the exhaust gases, platinum and palladium catalysts are combined wtih oxides
of other metals [179, 183, 184], Platinum or palladium are taken in amounts
of 0.01 to 1% of the weight of the carrier; the oxide of the metal (for ex-
ample, copper or vanadium), in amounts of 0.1 to 10.0%, the carrier consti-
tuting the balance. Admixtures of phosphorus salts or acids [184] and also
compounds of sodium, lead, chromium and lanthanides in the form of salt
solutions increase the stability of the contacts to poisons and the activity
at relatively low temperatures.
An original solution to the optimum arrangement of catalysts is pro-
posed in one of the British patents [185], To lower the temperature of com-
plete oxidation of hydrocarbons and CO in the exhaust gas, the authors sepa-
rate the catalyst into two beds. At the entrance is placed a bed with the
smaller volume (2-10% of the total volume) containing 0.5% platinum or pal-
ladium on aluminum oxide. The second bed sometimes contains no platinum
(or contains 0.01% of it) and consists of the carrier and copper oxide on
y-Al203. The oxidation begins at a relatively low temperature in the first,
thin bed. The distribution of the platinum over the beds lowers the temper-
ature of the start of oxidation of the hydrocarbons and CO by 100°C.
- 102 -
-------
Chapter 5
CATALYTIC REMDVAL OF NITROGEN OXIDES FROM EXHAUST GASES
The chief source of formation of nitrogen oxides in air are plants pro-
ducing nitric acid and nitrogen fertilizers and the exhaust gases of motor
transport. The content of nitrogen oxides in nitrous gases depends on the
technological conditions and amounts to an average of 0.1-0.5 vol. "/, at most
plants after absorption purification. The content of nitrogen oxides in
"residual" gases must not exceed 0.1 vol. % if the air is to be diluted down
to the sanitary levels (in the streets down to 0.1 mg/m3, and in industrial
buildings down to 5.0 mg/m3). It is known from the literature [2] that the
concentration of nitrogen oxides in areas adjacent to chemical plants and
also on heavily traveled city streets is many time's greater than the per-
mitted level. The formation of smog, attributed by scientists to the reac-
tions of nitrogen oxides with hydrocarbons under the influence of ultra-
violet light, is a menace to the inhabitants of Los Angeles, San Francisco
and other cities with a heavy automobile traffic. Thus, the removal of
nitrogen oxides from atmospheric air and waste gases is a pressing problem
whose solution will improve the sanitary working conditions and reduce un-
productive losses of nitric acid.
Among the methods which may decrease the concentration of nitrogen
oxides in gas mixtures, two should be mentioned: absorption and catalytic
purification.
The process of absorption purification involves the absorption of ni-
trogen oxides by a volume of sorbent and in some cases a chemical reaction
with solid or liquid absorbers. Various materials [448, 449, 455, 456] have
been used as adsorbents at low temperatures, the most interesting of which
may be aluminosilicates, zeolites, silica gels [455, 265, 282], and also
iron and manganese ores [431, 432]. The use of solid absorbers may con-
siderably decrease the volume of the units as compared with the volume of
liquid purification devices, and reduce the investment in the removal of
nitrogen oxides from exhaust gases. However, absorption by liquid and
solid sorbents has many disadvantages which prevent its broad practical
application. The absorption and chemical binding of nitrogen oxides with
sorbents constitute a low-temperature process; raising the temperature sub-
stantially decreases their efficiency. The absorbing capacity of the sor-
bents is limited by the pore volume, and decreases in the presence of mois-
ture and after high-temperature regeneration in the majority of the cases
studied.
The thermal decomposition of nitrogen oxides, in particular NO to D£
and No, takes place at a high temperature (600-1900°C.) and is accelerated
in the presence of catalysts. Fraser and Daniels, who studied the decom-
position process 2NO -»• N2 + 02 in an inert atmosphere (10% NO) at
- 103 -
-------
700-1400°C. showed that the reaction rate depends on the nature of the oxide
[439]. On aluminum oxide, the decomposition rate was two orders of magnitude
higher than on other oxides, for example ZrC^. The authors account for this
fact by a variable adsorptive capacity of the oxides for NO: A1203, 1.3 x
1010*; La0, °-77 x l°8 5 Zr°> 2>5 x 1C)8; Ca°> °'96 x l°* > Zn°» lml x 10 '
23
On transition metal oxides, the catalytic decomposition of NO and N02
takes place at lower temperatures.
Sourirayan and Blumenthal [473] note that in the presence of copper oxide
on silica gel (3:7) at a space velocity of 1320 hr'l, the decomposition of NO
in nitrogen is already 69% at 510°C. The catalyst displayed on high stability
(300 hours in overheatings to 1000°C.) and was used to remove nitrogen oxides
from the exhaust gases of a two-cylinder engine operating on ethyl gasoline.
In the latter case it is pointed out that copper oxide was reduced to the
metal, and the process apparently proceeded via reduction of nitrogen oxide
by the hydrogen and carbon monoxide present in the exhaust gas. Nitrogen di-
oxide in the presence of copper oxide and cerium oxide on A1203 (1:1) is 99%
decomposed to NO, N2, and 02, and already 55% decomposed to N2 + 02 at 520°C.
[445]. The process of decomposition of NOo is affected by the nature of the
catalyst: at temperatures below 520°C., copper oxide is more active, and
above this temperature, cerium oxide contact is (cf. Fig. 44). The addition
of 02 to the reacting inert mixture slightly decreases the percent decom-
position of nitrogen oxides; for example, their decomposition in air at 520°C.
occurs to the extent of 47% as compared to nitrogen (55%). Wikstrom and
Nobe showed that the process takes place in two steps:
I"
-S"
*
•
ir
an r.-c *•
Pig. 44. Catalytic decomposition of MOg to nitrogen in an inert atmosphere
over copper oxide (a) and cerium oxide (b) on aluminum oxide [445J.
A study of the second step, the decomposition of NO to N2 in a vacuum, was
made by G. K. Boreskov et al. [457]. They showed that the catalytic decomposi-
tion of NO occurs at relatively low temperatures, 200-500°C., and the reaction
rate decreases in the following series of contacts: €0304, CuO, NiO, Fej
Cr2°3» Zn0> Tne temperature at which a similar specific activity of the
oxides at P™ = 200 mm Hg is observed increases in this series.
•Expressed in number of molecules per car.
- 104 -
-------
Oxide Wg mole NO Temperature, °C.
m^, rain
€0304 3.1 x 1CT8 275
Fe203 2.3 x 1CT8 355
Cr203 3.0 x 10-8 450
The reaction rate increases in proportion to the square of the NO concen-
tration, and as a result, the authors postulated that as the concentration of
nitrogen oxide in oxygen-containing exhaust gases decreases, the reaction rate
should be moderate.
A second-order reaction with respect to nitric oxide was also observed in
[447], where the decomposition of nitric oxide (0.40-0.43 vol. 7.) was carried
out in nitrogen in the presence of platinum-nickel' catalyst at 500-625°C. The
decomposition reaction of nitric oxide occurs at the rate ^r=_AiI£22L. , i. e.,
1 + KPo,
is inhibited by adsorbed oxygen formed in the course of the reaction.
In order to facilitate the desorption of oxygen from the surface of the
catalysts and give the reaction a different course, reducing gases are employed.
In some cases, at a high content of the reducing gas and an oxygen concentra-
tion up-to 3-4%, this makes it possible to carry out the process of reduction
of nitrogen oxides to nitrogen, water and ammonia at high space velocities.
Thus, it is noted in [459] that the rate of reduction of nitric oxide by hydro-
gen is 850 times faster than in an inert atmosphere.
The reducing agents used for the removal of nitrogen oxides from inert
and oxygen-containing gaseous media are hydrogen [443, 444, 452, 458, 459,
475], methane [443, 451], carbon monoxide [438, 441, 446, 460, 475], hydro-
carbons [436], ammonia [435, 437, 474], natural gas [433], and cyanamide
[478]. Basic data on these studies, performed for the most part during the
last decade, are listed in Table 25. It is evident that in the majority of
the studies, the concentration of nitrogen oxides was close to their content
in the effluent gases of nitric acid plants or exhaust gases of internal
combustion engines. We shall consider studies in which the reduction of ni-
trogen oxides was carried out in inert media. Schwab and Drikos [477] in-
vestigated the reduction of ^0 by carbon monoxide on a catalyst at different
concentrations of the components. They showed that the reaction rate in-
creases sharply starting at 250-300°C., is proportional to the nitric oxide
concentration in the mixture when ther is an excess of carbon monoxide, and
proportional to the carbon monoxide concentration in excess nitrous oxide.
In an excess of the reducing gas, metallic copper acts as the catalyst, and
in the presence of excess nitrogen oxides, copper oxide is formed, and the
rate of the reaction is limited by the process of its reduction (1 = 23"
kcal/mole).
- 105 -
-------
A systematic study of the reduction of nitrogen oxide by hydrogen and
carbon monoxide was made by Sourirayan and Blumenthal over a prereduced
copper catalyst on silicon oxide [475]. The authors found that the degree
of interaction is determined by the composition of the gaseous mixture and
reaches 90-100%, starting at a ratio of nitrogen oxides to hydrogen of 1:1
and to carbon monoxide of 1:3 at 250°C. (see Fig. 45, which we plotted by
using the data of [475]). An increase of the space velocity to 12 x 10-*
hr'l in the presence of a 5-10-fold excess of carbon monoxide, hydrogen or
their mixtures practically did not decrease the degree of removal of nitro-
gen oxides. The presence of hydrocarbons in the mixture had a positive
effect. The introduction of oxygen into the mixture with a large excess
of reducing agent did not affect the reaction. Analysis of the reduction
products showed that depending on the conditions, nitrogen oxides are re-
duced by hydrogen to nitrogen and ammonia.
This was also observed by Aven and Peters [444], who studied the re-
duction of nitric oxide [pressure 0.005-0.05 atm at 375-425°C. over a copper-
zinc-chromium oxide catalyst (29% Zn, 10% Cu, 31% Cr)].
The process of reduction of nitric oxide
to ammonia is limited by the step of hydrogen
activation. The rate of reduction to nitrogen
increases in proportion to the concentration
of the initial components (NO and Ho). In the
o
o
to
case of silver catalyst, the rate of reduction
of nitrogen oxides by hydrogen (taking place
at 60-180°C. with formation of water) is also
proportional to the hydrogen pressure [452].
„. „ ""tic of . „„ It is postulated that the first stage is the
CO or H2 to NO and NOg. v , . . B
decomposition of nitrogen oxides to the ele-
cabon SoS" £ef * ments > "hereupon hydrogen reacts with the
copper oxide on silica gel at 250°C. adsorbed oxygen.
Excess hydrogen in the reacting mixture (NO:H2 = 1:250) promotes the re-
duction of nitrogen oxides to ammonia. In the reduction of NO by hydrogen over
platinum and rhodium catalysts on aluminum oxide [476, 458], by using spectro-
scopic and gas chromatographic analyses of the reacting mixture at different
temperatures, Kokes observed that the reaction takes place via the formation
of N20, whose content in the mixture increases sharply at 260°C. (Fig. 46).
One of the products of the reduction of nitrogen oxides in hydrogen is
water, which does not have a negative influence in the case of platinum and
silver catalysts. Something different is observed in the reduction of ni-
trous oxide in the presence of aluminum oxide. In this case, the water i
formed in the reaction decreases both the amount and rate of adsorption of
both components on the surface [459]. The reaction rate in this case is
expressed by the equation *ipwiolp:^ where n£ = 0.33-0.66.
W= I+A/PH.O '
- 106 -
-------
Nitrous oxide is an intermediate in the reduction of nitric oxide to
nitrogen by carbon monoxide. This process was studied by Shelef and Otto
[460] over transition metal oxides and platinum on aluminosilicate in a
slight excess of carbon monoxide (1.2 moles of CO and 2 moles of NO). The
maximum of formation of nitrous oxide is observed in a certain temperature
interval characteristic of each catalyst: Fe203 (200°C.), CuCr204 (180°C.),
CuO (220°C.), Cr203 (240°C.), NiO (300°C.), Pt (300°C.), Co304 (350°C.),
and aluminosilicate (460°C.). No nitrous oxide is formed over MnO and 7205.
•8
no tooT,*c
Fig. 46. Effect of temperature on
the composition of the products in
the reduction of NO by hydrogen
[458].
From Fig. 47 (borrowed from [480]), which
shows the results for ferric oxide on alumino-
silicate (10% Fe203), it is evident that in the
case of ferric oxide catalyst, the maximum quan-
tity of nitrous oxide is formed at 200°C.5 and
at higher temperatures it is reduced by carbon
monoxide to nitrogen. The content of carbon
monoxide decreases as the reaction temperature
is raised, and that of carbon dioxide increases,
since the latter results from the reaction of
both nitrogen oxides with carbon monoxide. A
shift of the maxima of nitrous oxide formation
toward higher temperatures over a series of contacts indicates a decrease
of their activity in this reaction.
The data obtained in the present study on the mechanism of reduction of
nitric oxide by carbon monoxide were confirmed by Baker and Doer [446], who
studied this process on a copper-chromium catalyst without a carrier. The
stepwise course of the reaction and the lag at the stage of formation of ni-
trous oxide are attributed by the authors to a strong adsorption of the re-
action product, carbon dioxide, at low temperatures (below 160°C.). At
higher temperatures, the reduction of nitric oxide to nitrogen occurs smoothly
since carbon dioxide is not adsorbed on the catalyst. At 200-270°C., the de-
gree of removal of nitrogen oxides from inert gas mixtures by means of carbon
monoxide amounts to 70-90% at space velocities of the gas streams up to 36 x
hr~l (Fig. 48). These results indicate a real possibility of removing
nitrogen oxides from inert gases by means of re-
ducing agents. The rate of reduction of nitrogen
oxides under these conditions is limited by the
activation of the initial components, whose con-
centration ratio and temperature determine the
nature of the end products (^0, N2, H20, NHg,
C02) and their influence on the kinetic charac-
teristics of the process. Another important
factor is the nature of the catalyst that spe-
cifically adsorbs the starting, intermediate,
and end products, and determines the reduction
temperature.
•a*.,
£-8
Initial MO
" concentration
\Initial
Bentratioj
CO
=3F=-
•JB-V
Fig. 47. Change in the composition
of gas mixture during reaction of
MO with carbon monoxide over FegOj/
aluminosilicate (10# Fe^j) at dif-
ferent temperatures [460], 1 - C025
? - HO; 3 - IloO; 4 - Xgj 5 - CO
- 107 -
-------
A considerable excess of the reducing agent is used to reduce nitrogen
oxides in oxygen-containing gas mixtures. Thus, in the study of Roth and
Doer [441], 0.4% NO was quantitiatively reduced at a content of 6 vol. %
carbon monoxide. The introduction of oxygen into the composition of the
gas mixture changes the degree of removal of nitric oxide as well as carbon
monoxide from this mixture. If in the adsence of oxygen (cf. Fig. 49, a
and b) nitric oxide is completely reduced by carbon monoxide, and the latter
is removed to an insignificant extent, the situation changes when oxygen is
introduced. The percent oxidation of carbon monoxide is directly proportion-
al to the amount of oxygen introduced; at a close to atoichiometric oxygen
concentration, it reaches 100%. The degree of removal of nitric oxide from
the mixture remains high (100%) at a carbon monoxide content exceeding the
stoichiometric amounts relative to oxygen, then decreases as a result of
deficiency of the reducing agent. Apparently, at a carbon monoxide concen-
tration exceeding that which is necessary for com-
plete reaction with oxygen and NO, the surface is
coated with carbon monoxide. The reaction proceeds
as a result of the interaction of adsorbed carbon
monoxide with oxygen and NO molecules striking the
surface and thus becoming instantly activated.
When the oxygen concentration exceeds the stoichi-
ometric quantities, oxygen is preferentially ad-
sorbed on the surface, thus decreasing the possi-
bility of adsorption of NO. When there is an in-
sufficient quantity of carbon monoxide and acti-
vated NO molecules, the reaction of catalytic re-
duction of NO by carbon monoxide is depressed.
'•sir
a 'v *•* „•»
Space velocity, 10^ hf1.
Fig. 48. Reduction of NO by
carbon monoxide in an inert
atmosphere on copper-chro-
mium contact as the tempera-
ture and space velocity change
[446].
Op ocnasntration,
vol. %.
Op concentration)
vol. %.
Fig. 49. Effect of oxygen concentration on the percentage
of removal of nitric oxide (l) and carbon monoxide (2) from.
gas mixtures at 250°C . and a space velocity of 10 x 10' hr"1
a - over barium-promoted copper chromite; b - over copper
chromite on aluminum oxide (b.0* GuO, 6.8$ CrgOj) [441].
- 108 -
-------
On the basis of the data cited by Doer and Roth [441], one can compare
a series of tested catalysts used for the reduction of nitrogen oxides by
carbon monoxide in the presence or absence of oxygen in gas mixtures. It is
evident from Table 25 that when oxygen is absent from the mixture, the re-
duction of nitric oxide is fairly complete at low temperatures. Even at 245°C.,
in the presence of barium-promoted copper chromite and copper oxide on aluminum
oxide (3.4 wt. %), the percent age of reduction is 100. When oxygen is intro-
duced into the composition of the mixture, barium-promoted copper chromite is
the most active catalyst.
Roth and Doer [441] point out that the degree of removal of nitric oxide
from a gas mixture increases with the carbon monoxide concentration. This is
also noted by Sokol'skiy and Alekseyeva [113, 395], who studied the purifica-
tion of the exhaust gas of a two-stroke engine in the presence of 16.8-17.3%
C>2 over unactivated manganese ore (see Table 25). As the carbon monoxide
concentration in the initial mixture increases from 2.5 to 5.67e, for a simi-
lar content of nitrogen oxides, the degree of removal of the latter and car-
bon monoxide increases. The results cited in [113, 441] are of practical
interest, since the gas mixtures from which toxic components are removed are
close in composition to the actual compositions of the exhaust gases of in-
ternal combustion engines.
Additional data on the removal of nitrogen oxides from oxygen-containing
gas mixtures can be found in the patent literature. A survey of a few patents
in this area shows that the process as carried out in industry consists of
two stages [143, 451]. In the first stage, excess, higher-than-stoichiometric
amounts of hydrogen, methane or natural gas are introduced into the mixture
to be purified in order to make them react with oxygen and form carbon dioxide
and water. In the second stage, the excess reducing gas reacts with the nitro-
gen oxides. The temperature of the process is determined chiefly by the nature
of the reducing gas. When hydrogen is used, the reaction takes place at 150-
200°C., and in the case of ammonia at 150-250°C., whereas methane requires
a higher temperature (400-430°C.). Because the first stage of the reaction
is exothermic, a heating-up of the catalyst is observed which increases in
proportion to the oxygen content of the mixture. In the case of catalysts,
mainly precious metals of group 8 are used: platinum, palladium, rhodium,
ruthenium [433, 434, 436, 464], palladium-ruthenium [48, 68, 440] and their
mixtures on carriers (aluminum oxide, ceramics, etc.).
Andersen et al. [434, 435, 437, 464] showed that the process of reduction
of nitrogen oxide is considerably facilitated when the reducing agents used are
ammonia (stoiehiometric amounts relative to nitrogen oxides) or methane in
high concentrations (up to 57%). The removal of nitrogen oxides from oxygen-
containing gas mixtures can then be accomplished in a single stage at high
space velocities (60-200 x IQ hr'1) at temperatures of 125-550°C. A selective
reduction (of nitrogen oxides only) by ammonia according to the equations
2NH3+3NO—s/a N2+3H2O
4NH3+3NO2— 3»/2 N2+6H2O
- 109 -
-------
: Catalytic Removal of Nitrogen Oxides from Exhaust Gases,
Table 25.
'6
Catalyst, Composition
1
Pt, Pd, Ru, Ir, Ag, Rh
and Pd + Rh on aluminum
oxide (0.5 wt. % metal)
Pd/AljOj
Pt, Pd, Ru, Rh, Ir
&g and their mixtures
on aluminum oxide
Composition of Gases,
Concentration of ni-
trogen oxides
2
Nitrous gases: 0.1-
0.5 vol. % nitrogen ox-
ides, plus added methane
natural gas, 3-21# 02
Nitrous gases: 0.1-
0.3* nitrogen oxides,
3-4?» 02 + 1.606 methane
+ water vapor, nitrogen
Nitrous gases: tenth
of one percent of nitro
gen oxides and a few
, percent of C^ -t- NHj
Space
Velocity,
hj.il
&
_
i
20-200- 10s
5 —
"
Tempera-
ture, "C.
4
. 365-415
(not above
760)
100-600.
optimum 300-
550
—
Degree. %
of Puri-
fication
5
_
—
—
Characteristics of
Catalysts and Process
6
For mixtures with 20p r
and for those with 21%
!>2, Pd/Al203 £f450")
ire recommended
Removal of nitrogen ox-
ides is carried out after
removing Hg, Co and hydro
earbons. Reaction occurs
satisfactorily with 30-
7Cpb excess methane over
the reaction with nitro-
Sen oxides and oxygen
Nitrogen oxides reduced
in two stages:
Pt
_3H20-|-2N2
2. Hg or CHji is added to
the remaining nitrogen
oxides, and the reaction
is carried out at 150-
900* over Pt, Pd on
Alo02 or aluminosilicate
5
Ref-
erence
7
[483]
-
[434]
[436]
{436J
-------
Continuation of Table 25
Ft/carrier
Ni, Pt, Pd on aluminum
oxide
Co. Fe, Hi on aim
oxide (5-fip metals,
APC-2 + dunite
Pd-Ru on aluminum
oxide
[Inactivated manganese
ore
0.3$ nitrogen oxides,
02, H20 - 0.896, stoi-
chiometric quantity of
NH, for tha reaction wit
nitrogen oxides
Nitrogen oxides in
waste gases of chemical
plants. Natural gas or
hydrocarbons with Ho are
added, P • 0.035 kg/cm?
26—150.10*
60—90
2236 02, 2$ HO +
+ 8$ H20 + ammonia and
inert gases
Waste gases from pro-
duction of nitric acid.
Addition of carbon mon-
oxide present in gases
emitted from plants of
cuprammonium purifica-
tion, 2-5# 02, 0.2fb CO
Converted gas (nitro •
« oxides 0.2-1.0 cm'/
- 'i H2 70-71$, acetylene
02 0.1-0. 3ft
Exhaust gases of two •
stroke internal combus-
tion engine, laboratory
data
J16.8—17,8% 0», 0,0014—
20-10*
24—41.10*
(Linear 1.
2.7* 1/min
hr-1
Gas volume
77-151 m?
Catalyst
volume
10.10"
19.10*
150—250
450—1100
200—300
(Ni, CO)
160— 250 (Fe
260-470
. Over the
catalyst
705-810
(Past the .
catalyst)
160—160
,100
200
J300
(400
Isoo
90—98 %
—
92—99
50—80
86—100
95-98
0—14,6
57—70
62—62
47—62
6-89
Ammonia reacts only
with nitrogen oxides,
catalyst stable for
three months (laborato
data). Process accom-
plished in one stage.
Temperature of cherai
cal reductant controll
by introducing inert
gases into the reaction
space
[464J
[436]
[437]
[438]
Catalyst operated
stably for 6.5 months
Percent removal of
nitrogen oxides from
exhaust gas increases
with increasing CO
content of mixture
[68, 440,
264]
[118]
-------
Continuation of Table 25
to
I
1
Copper chromite
Copper ohromite
Copper chromite pro-
moted with barium
CuO— CrjOj/AljOj
(8,4% CuO, 8,4% Cr203)
CuO/AljOj (3,4% CuO)
CuO — CijOj/AljOj
(6,8% CuO, 6,8% Cr203)
20% Cr)
Pt/AljOj, ceramic
CuO— ZnO— CrjjOj
(10% Cu, 29% Zn, 31%
Cr)
2
0,0013% NO, 0,0088—
0,0032 1—
3% CO,, 2,5—5,6% CO
6% CO+0,4% NO+Nj
6% CO+0,4% NO+
302+N2
6% CO+0,4% NO+N2
6% CO+0,4% NO+N2
6% CO+0,4% NO+
+4% 02+N2
6% CO+0,4% NO+N2
6% CO+0,4% NO+
+3% 02+N2
6% CO+0,4% NO+N2
6% CO+0,4% NO+N2
6% CO+0,4% NO+N2
6% CO+0.4% NO+N2
6% CO+0,4% NO+N2
6% CO+0,4% NO+.
+N8+2,0% Os
0,3—0,5% Nitrogen
oxidesl— 4% 02, Na
0,3—0,5% Nitrogen
oxidesN2+Hj, 2—4% 02
0,3—0,5% Nitrogen ••
ojcides-)- jj2 -J-CH4+2' —
Nitrogen oxides NO>.Ag
in N2(NO:H2=1:1) P=
=0,005—0,05 atm
8
10-10'
••>
120-109
80-60.10*
»
2000
ml/inin
4
242
249,
245
215
246
246
246
242
245
200
164
105
245
400—580
150—200
400—480
876-426
6
69
26
100
77
100
83
85
100
93
91
78
32
100
Complete . •
jurifica-
tion_
—
*••
6
—
_
—
^^
—
_
__
—
_
—
—
_
_ .
Maximum allowed ovei>
heatings up to 1500°.
catalysts operate for
2-5 hours
Rate increases with
concentrations of re-
acting gases
7
[441]
•
[442]
[448]
T4U1
-------
Continuation of Table 25
Co
I
CuO/Al20, (1:1)
CeOa/AljO, (1:1)
Plant
(17%. Crs03, 82% CuO)
Ni—Pt/Al»0,
Pt, 3%Ni)
Pd on spherical
carrier (0.50» Pd)
(0,1%
NOj in nitrogen,
1260 ppm
NO, 1500 ppm. u
+1%CO+N,
0.1(0-0.43$ nitrogen
oxides, in nitrogen,-
P = 1.15.atB
0.3b nitrogen oxides
3,0-4,0%. 0,, HjO, N,+
+CH4
0,3% Nitrogen oxides
3—4% Oj+65% H2,
10% CH4, Na
0,3% Nitrogen oxides,
3-4% 0,, 40% CO,
15%. H, 6% CH«
10-7-77,8
ml/sec
»
16-10*
»
»
»
»
24.10s
86.10*
__
33.10*
66.10*
120-10*
67.10*
60.10*
350
400
520
450
460
550
200
160
138
130
122
195
195
600-626
461
486
405
649
526
26
4Q
55
20
40
60
90
80
76
65
40
78
65
—
8 ppm
(NO + NOg
in purifa
gas
14 ppm
650 ppm
128 ppm
15 ppm
—
—
—
—
•~
Jd
_
• ^^
-
—
—
[446]
[446J
[446]
*•*
[447]
[464]
[464]
[464]
-------
Continuation of Table 25
1
»
Pd on spherical i
carrier (0.59? Pd)
CuO/SlOz (3:7)
CuO/SlOa (3:7)
3% Nl+2% Cu •„,
" dtr-grog
2
0.3$ nitrogen .oxides,
J-fMfet 20-260 CH4,
and other hydrocarbons
+ NJJ are adaed
0,3% Nitrogen oxides ,
3-4% 04, Hj+N,
692 ppm NO in nitrogen
400-800 ppm NO, 550- :
1400 ppm N02 + carbon
monoxide, hydrogen
(ratio of nitrogen ox-
ides to gas reductant
was varied from 1 to 10;
NO-0,3%, Os— 2,7%,
Nj-f-Ar— 97%, Amount of
H2 is 2-3 times larger -
than the stoichiometric •
value
3
67,6.10s
66—68.10'
1820
2000—10000
•
600-800
m5/hr.
P = 3-4 atm
4
895
150—168
510
300
600—550
6
51 ppm
6-9
.ppm,
69
• M?P.
in the
presence
of excesf
gas reduc
tant
Residual
NO con-
tent i
0.000#'
,
6
_ _
— —
In the laboratory, the-
catalyst was stable for -,
300 hours, and in the
stream of exhaust gas of
a two-stroke engine, for.
5100 hours
_
The catalyst was
tested for 3 months
and was stable during
service.
7
[464]
[464]
[478]
[476]
[461, 462]
-------
can be carried out on platinum, palladium, ruthenium, cobalt, and nickel,
although the authors prefer the platinum contact. In the presence of this
catalyst, ammonia being added (1 mole of ammonia per mole of nitrogen oxides
and 10 moles of oxygen) to the gas mixture to be purified, nitrogen oxides
are almost completely removed (up to 10 ppm of nitrogen oxide by weight re-
mains) (Fig. 50). The selective reaction of ammonia with nitrogen oxides
is attributed by the authors of [464] to the low rate of reduction of oxygen
under these conditions
2NH3 + 1
N2 + 3H2O.
.9
g
r,
..'-*! A
A mo
OJ
§.
o
5
*
.-H
«
SO
£ "
-*
••••
M 220 300 T,'CJ30
Moles of NH3
per mcl* of NO.
Pig. 50. Effect of am-
monia concentration on
the content of nitrogen
oxides in the mixture
after their reduction
at 150-?00°C. (N02 + NO
0.28-0.30. Oa- 3.0-
Fig. 51. Effect of temperature
and space velocity on the per-
centage of selective reduction
of nitrogen oxides (0.36) by
ammonia over_platinum in an ox-
ygen-containing gas mixture {.'flu
02) [464]. 1 - 10 x 103 hr"1;
2 - 30 x 105 hr-1; 3 - 60 x 103
hr-1; 4 - 90 x 10* hr"1.
Of interest are data obtained by these authors on the effect of tempera-
ture and space velocity on the catalytic reduction of nitrogen oxides by am-
monia over 0.5% platinum on a carrier [464]. From Fig. 51 it is evident that
at space velocities of 60-90 x 10^ hr~l at temperatures as low as 150-250°C.
the degree of removal of nitrogen oxide from the gases amounts to 90-98%.
At lower temperatures, the process is inhibited by the adsorption of ammonium
nitrates and other salts being formed on the catalyst.
Judging from the papers [465-469] and the survey [463], the catalytic
purification of waste gases of nitric acid plants is widely employed in
foreign practice. Depending on the natural resources, the reductants used
are methane and natural gas, and in areas where these are lacking, ammonia.
Soviet researchers have used APK-2 platinum catalyst to remove nitrogen
oxides from the waste gases of nitric acid production [438]. The reducing
gas used was carbon monoxide from gases of a cuprammonium purification column.
The platinum catalyst operates with a high efficiency at space velocities of
14-27 x 10^ hr"1 and a degree of purification of 75-92% (Table 26).
- 115 -
-------
Table 26.
Decomposition of Nitrogen Oxides of Waste Gases from the Production of
Nitric Acid in an Experimental Unit [438],
Gas Composition: 2.6-5$ Og, 0.2$ CO + Nitrogen Oxides
Gas
olume,
m3
Space
Velocity.
10* hi-1
lemoerature L_*C .
Over
Catalyst
Past
• Reactor
Linear
VeSoeity.
Percent
Removal
of
Nitrogen
Oxides
Two-bed catalyst (3.15 l) APK-2 + dunite '
77
112
131
24,4
35.6
41,5
415—470
260—415
260—391
725—810
605—710
405—705
1,74-1,9
1,87—2,36
1,88—2,71
100
99
85
single-bed catalyst APK-2 (6.9 l).
298,8
123,4
155
189
14,3
17,9
22,5
27,4
160—260
165—220
170—215
185—270
590—790
580-730
615—720
640—705
1,9 —2,3
2,3 —2,7
2,98—3,31
3,5 —3,76
92,5
86,0
85,8
75,4
The use of a two-bed catalyst (the second bed being dunite) makes it
possible to increase the space velocities of the process to 41.5 x 103 hr"1
and the percentage of purification to 85-100% with a certain decrease of the
total volumes of purified gases (lower linear velocity). A two-layer con-
tact is proposed by the authors for gases with a high oxygen content.
Of major interest are data on the reduction of nitrogen oxides in oxygen-
containing mixtures in the presence of supported common metal catalysts [442,
437, 463]. Figure 52, plotted on the basis of Andersen and Keith's patent
description [437] shows the temperature dependence of the percent reduction
of nitrogen oxides by ammonia in the presence of reduced cobalt, nickel and
iron catalysts on aluminum oxide (5-6% metals) at a space velocity of 20 x
103 hr~l. It is evident that at 200-275°C., the nickel and cobalt catalysts
display the maximum activity. In their presence, nitrogen oxides are 90-
100% reduced by ammonia at a high oxygen content (22%). Iron catalyst is
active at a lower temperature: at 165°C., the percent reduction of nitrogen
oxides is close to 80%.
% reduction
of nitrogen--
oxides
SCO
its
~T.V
temperature.
Pig. 52. Reduction of nitrogen oxides (2# NO, 2jt, NOg)
by ammonia in oxygen-containing mixtures.at a space
velocity of 20 x lO5 hr** over cobalt (l), nickel. (2),
and iron (3) catalysts on aluminum oxide (5-6$ Me)
- 116 -
-------
According to the data of Fletcher [442, 443] and British patents, a
nickel-chromium alloy catalyst (80% Ni, 20% Cr) promoted with platinum is
suitable for the removal of nitrogen oxides from gases at an oxygen content
of 1-4.3%, space velocity up to 120 x 103 hr"1, and temperature of 400-580°C.
Reduced platinized and chromized nickel foil and nickel-chromium catalyst
were used to remove nitrogen oxides from gases by reduction with methane
(natural gas) in [80, 81]. The authors showed that at 500-600°C. a complete
reduction of nitrogen oxides on the nickel-chromium catalyst and chromized
nickel foil takes place at a space velocity not above 14-15 x 103 hr"1 [81].
A low stability of the nickel-chromium plant catalyst was observed (50 hours
as compared to 160-200 hours for chromized nickel foil). Platinizing of
nickel foil increases the activity (complete purification at a space velocity
of 28.6 x 10J hr"1) and stability of the contacts.
lo lower the temperature of the process, as recommended in a US patent
(2910343), 27 October 1959), the authors of [80] used a two-bed catalyst. A
bed of GIAP-3 palladium catalyst (0.16% Pd), whose volume amounted to 1/6
of the total volume of the contact, was placed above the chromized nickel foil
catalyst. Under these conditions, it was possible to reduce the nitrogen
oxides in the exhaust gas down to the sanitary permissible concentrations
(30-40 m3/hr) at 550°C. and a CH4:02 ratio below the stoichiometric value
(0.6), i. e., in an oxidizing atmosphere. A complete removal of nitrogen
oxides is achieved at CH, -.Oj = 1.1.
Over nickel catalyst with admixtures of copper on grog (37e nickel + 2%
copper), nitrogen oxides were completely reduced by hydrogen (2-3-fold excess
at 500-600°C. and a space velocity of 600 hr [461, 462].
Despite the relatively high activity, common metal catalysts are unstable,
particularly in the purification of actual exhaust gases, for example, from
nitrogen fertilizer plants [453], and can operate only in the presence of a
large excess of the reducing gas. For this reason, supported precious metal
catalysts with metal contents of 1.8-2% and space velocities of 8 x 10 hr"1
are recommended for practical adoption by plants in the USSR, [453, 454].
The purification takes place in one stage at a high temperature and pressure,
and the reducing gas is able to react with nitrogen oxides and oxygen. A
method of high temperature purification has been developed for mixtures con-
taining up to 3% oxygen. At a higher oxygen content, it is necessary to
apply the two-stage scheme described above.
A pronounced effect in the high-temperature removal of oxides from oxygen-
containing mixtures was observed by using combined [438, 80] and mixed catalysts
[454], which make it possible to reduce the consumption of the precious metal.
The method of preparation of a mixed palladium-ruthenium catalyst and the devel-
opment of a method of removal of nitrogen oxides and acetylene from converted
gas are reported by F. P. Ivanovskiy et al. [68, 440, 264]. The catalyst pro-
posed by the authors is marked by a high activity in the reduction of nitrogen
- 117 -
-------
oxides in hydrogen-containing gas mixtures (excess hydrogen). The same con-
tact may be successfully used to remove nitrogen oxides from exhaust gases
of gasoline engines containing substantial amounts of carbon monoxide and
hydrogen under most operating conditions.
- 118 -
-------
Chapter 6
BENCH AND ROAD TESTS OF EXHAUST PURIFICATION CATALYSTS
Laboratory tests of catalysts for oxidizing carbon monoxide and other
components of exhaust gases on artificial mixtures are the first and indis-
pensable steps in the selection of catalysts. A second important step
consists in testing optimum catalysts on the actual gas of internal combustion
engines mounted on benches. Bench tests proposed in the USSR for catalysts
used for purifying the exhaust gases of gasoline engines have been conducted
on a model installation at the Central Scientific Research and Experimental
Design Laboratories of Neutralizers and Automobile and Tractor Power Engineer-
ing. The design of the installation and the procedure for testing and
analyzing the mixtures, discussed in [70], made it possible to determine the
efficiency of catalysts as a function of temperature (100-500°C.), space
velocity of the gas flow (20-120 x 10^ hr~l), and carbon monoxide concentration
(up to 6% CO).
A series of catalysts supplied by various organizations were tested:
platinum (0.2%) and manganese-copper oxide catalysts on aluminum oxide (Karpov
PhysicochemLcal Institute, Moscow), copper-chromium oxide catalyst (Azizbekov
Institute of Petroleum Chemistry, Baku), copper oxide-activated iron ore
(NIOGAZ, Moscow), palladium catalyst (0.5-0.75% palladium), platinum-palladium
catalyst (0.25-0.5 wt. % total metals) on aluminum oxide, and iron-copper
oxide on clay (Institute of Chemical Sciences, Kazakh Academy of Sciences).
Bench tests were carried out on catalysts having a high activity,
stability, and thermal stability under laboratory conditions on artificial
mixtures [54, 56-62, 71]. Figure 53, based on data of LANE [70], illustrates
data comparing the efficiency of the action of these catalysts in the oxidation
of 1% carbon monoxide as the temperature of the exhaust gas of the "Moskvich-
407" engine changed (space velocity 33-38 x 103 hr"1).* The air injection
amounted to 30% of the total gas flow.
As is evident from this figure, the degree of oxidation of carbon monoxide
is substantially determined by the temperature and chemical composition of the
catalysts. At 100-200°C., the degree of oxidation is low, and at 200-220°C.
it ranges from 5 to 35%, depending on the catalyst. The maximum activity at
220°C. was displayed by platinum and palladium catalysts on carriers and acti-
vated siderite. As the temperature rises in the presence of these contacts,
the degree of oxidation increases sharply and reaches 100% for platinum and
palladium at 320-340°C. , and in the case of copper oxide-activated iron ore,
at 400°C. The platinum-palladium catalyst is also characterized by a sharp
increase in activity as the temperature changes from 240 to 270°C.; a complete
oxidation of carbon monoxide is observed at 380°C.
* A mixture of 4.5-6$ CO and 7% 02 was oxidized on the platinum catalyst.
- 119 -
-------
o
o
.•a
s
Fig. 53. Catalytic oxidation of carbon monoxide in the exhaust of
MZMA-407 engine (space velocity 33-38 x 10? nr-1) as the temperature
of the gas changes [61, 70]: I - Pt/AloO, (0.2$ Pt); 2 - CuO-MnOp/
AlgO, (CuO:Mn02 = 2:3,Eoxides 15 *t. W; 3 - CuO-Cr203 (3:2);
4 - CuO-activated siderite: 5 - Pd/aluminosilicate (o.5 wt. # Pd);
- -
- - - umnoscae . w. ;
6 - Pt-Pd alumnosilicate (0.5 wt. #ZMe); 7 - Pe00», CuO/clay,
re:Cu = 4:1 ( atomic J;i oxides : carrier = 1:2; 7 t - calcined sample;
7 b - uncalcined sample.
The activity of oxide catalysts increases slowly with rising tempera-
ture and reaches a maximum, 50-55%, for the iron-copper oxide catalyst on
clay at 350-450°C., 40% for the manganese-copper oxide catalyst on aluminum
oxide at 420°C. , and 30% for the copper-chromium catalyst at 350°C. A further
temperature elevation decreased the activity of the iron-copper oxide and
copper-chromium catalysts, apparently either because of a change in the phase
composition of the catalysts under the influence of the reacting mixture, or
as a result of poisoning by some impurities, for example, water vapor, which
may have a poisoning effect.
ta
too 10 so
Space velocity, 105 hr"1
Pig. 54. Effect_of space velocities on the catalytic oxidation of
carbon monoxide in the exhaust of MZMA-407 engine at 300eC. (a) and
400°C. (b)[ 70, 61]. Notation same as in the preceding figure.
- 150 -
-------
In view of the fact that the volume of exhaust gases changes with
different operating conditions of the engines, the effect of contact time
on the efficiency of oxidation of carbon monoxide was investigated. A space
velocity of 20-120 x 103 hr"1 was achieved by varying the volume of the
catalyst. The efficiency of the catalysts at 300 and 400°C. at various
space velocities is illustrated in Fig. 54, a and b. The experiments showed
that as the space velocity increases at 300°C., there is a sharp decrease
in the degree of oxidation of carbon monoxide to 20% at space velocities of
40-80 x 103 hr"1 in the presence of activated siderite and iron-copper oxide
catalysts. There is also observed a decrease in the activity of platinum-
palladium contact to 45% at 60-79 thousand 1/1 of catalyst per hour.
Platinum and palladium catalysts on carriers behave differently. The
degree of oxidation of carbon monoxide over platinum contact as the space
velocity is raised to 120 x 103 hr"1 varies between 90 and 100%, over pal-
ladium catalyst with 0.75% palladium it amounts to 85%, and decreases to
70% when the palladium content is lowered to 0.5 wt, %. At 400°C. , with a
wide variation of the space velocities of the gas flow, the degree of oxida-
tion of carbon monoxide over platinum, palladium and platinum-palladium
catalysts is 100% and decreases by 10-15% only at 114 x 103 hr"1 over palladium
catalyst. Raising the temperature had no positive effect on the activity of
siderite. Oxide catalysts at space velocities of 20-70 x 103 hr"1 were rela-
tively insensitive to the contact time, and their activity remained as high
as before.
In order to study the effect of carbon monoxide concentration in the
exhaust gas, a series of experiments were carried out at a space velocity of
40 x 103 hr"1 over palladium catalyst on bead aluminosilicate (0.5 wt. % Pd)
with preheating of the gas before the reactor to 286°C. Figure 55 shows the
change in percent oxidation of carbon monoxide, the temperature in the reactor
and past it, and the oxygen content in the exhaust gas before and past the
reactor as the carbon monoxide content in the exhaust gas increased from 0.2
to 6 vol. %. It is evident that as the carbon monoxide concentration increases,
the oxygen content in the exhaust gas past the catalyst decreases from 6 to 2%.
The extent of oxidation of carbon monoxide depends on its concentration: whereas
at 0.2-2.0 vol. % CO it amounts to 50%, at 2.5-3.0 vol. % it increases to 100%,
at 4% to 90%, and at 5.7% it drops to 65% because of the insufficiency of oxygen
on the surface. Because of the liberation of a large amount of heat by the
oxidation of carbon monoxide and hydrocarbons, the temperature within the cata-
lyst rises, and at a carbon monoxide concentration of about 6% reaches 795°C.
Thus, starting at 200°C. (10-20%), palladium catalyst achieves a fairly com-
plete oxidation of carbon monoxide over a wide range of space velocities and
CO concentrations in the exhaust gas, and at 340°C. all of the carbon monoxide
is eliminated.
In addition to the above-indicated contacts in the experimental gas puri-
fier, LANE (0.5 1) tested mixed palladium-copper, palladium-iron and palladium-
- 121 -
-------
'/.Off
Fig. 55. Effect of carbon monoxide concentration in the exhaust
of "Hoskvich-407" engine at 36 x 10* hr-1 on the efficiency of
palladium catalyst (the gas being preheated to 200°C.) [70, 6ll.
1 - percent oxidation of carbon monoxide; 2 - oxygen content or
exhaust gas, vol. #; 3 - temperature of catalyst; 4 - temperature
of exhaust gas past the catalyst; 5 - oxygen content past the gas
purifier, vol. #.
cobalt contacts on aluminosilicate (Table 27). During the tests, the rota-
tional speed of the crankshaft (1500-2500 rpm) and the fuel feed were varied,
the temperature was measured before and after the gas purifier, and the gases
were analyzed chromatographically for the content of carbon monoxide, carbon
dioxide, oxygen, and hydrogen before and after purification in the exhaust
gas of the "Moskvich-407" engine. (The gases were preheated to 400°C. during
the purification.) It is obvious from the data obtained that when the carbon
monoxide content of the engine exhaust was 3-5 vol. % and the hydrogen con-
tent up to 1.0-1.8 vol. % (leaned-out mixture) over mixed palladium catalysts
at 1500 rpm, the degree of removal of carbon monoxide S ranges from 0.79 to
0.97. As the speed during operation of the engine on the leaned-out mixture
is increased to 2500 over the palladium-cobalt catalyst, S decreases to 0.69,
over palladium-iron to 0.89, and over palladium-copper to 0.5. The average
degree of purification in operation on the leaned-out mixture is 0.7, and the
purification of the gas over palladium-cobalt catalyst is better. The compo-
sition of the exhaust gas past the gas purifier includes 3-7 vol. % oxygen
and 9-10% carbon dioxide. Hydrogen, which is present in the exhaust gas /in
the case of the leaned-out mixture, is completely oxidized over the catalyst
and obviously the first to undergo oxidation. From the oxygen content of the
gas past the gas purifier one can infer that the concentrations of the reacting
components on the surface of the catalyst are very similar.
- 122 -
-------
During the operation of an engine on an enriched mixture, the compo-
sition of the exhaust gas includes a large amount of carbon monoxide (7-14
vol. %) and hydrogen (2.8-4.9 vol. %), and the degree of removal of carbon
monoxide decreases sharply, apparently because of a deficiency of oxygen on
the surface of the contacts: the composition of the gas past the gas puri-
fier contains 2.6-4.0 vol. % Q^. In this case, it is evident that carbon
monoxide, hydrogen and hydrocarbons (whose analysis was not performed) are
primarily adsorbed on the surface of the catalyst, hindering the activation
of oxygen.
As is evident from an analysis of the bench tests of a series of cata-
lysts, the best catalysts from the standpoint of removal of carbon monoxide
from gasoline engine exhausts are supported platinum and palladium catalysts,
which have shown a high efficiency over a wide range of space velocities
(up to 114 x 1CH hr~l) and gas temperatures, starting at 250°C. and above.
In the case of palladium catalysts in the presence of a high carbon monoxide
and hydrogen content, the degree of oxidation varies as a result of an insuf-
ficient suction of air (1/3 of the gas flow) through the injector.
LANE conducted comparative bench and experimental road tests of platinum
and palladium catalysts in the exhaust gases of the MZMA-407 engine in KNG-150
and KNG-450A neutralizers on the ZIL-130 truck (Table 28, 29). It is apparent
that in the degree of removal of CO from the exhaust gas of the ZIL-130 engine,
palladium catalyst is identical to platinum. In the case of the MZMA-407
engine in a KNG-150 gas purifier at 1500 rpm, the degree of purification at
all loads is 10-20% lower than on platinum catalyst.
Some catalysts were tested for the purification of diesel engine exhausts:
bench tests were conducted in a gas purifier designed by GIPRouglegormash
(State Experimental Institute of Design and Construction for the Coal-Machinery
and Mining Industries) (KDM-100 four-cylinder engine), and road tests were
carried out in a thertnocatalytic gas purifier designed by S. S. Filatov [72]
in collaboration with LANE and the Mining Institute (Sverdlovsk).
Bench tests with the KDM-100 four-cylinder diesel engine were conducted
on palladium and platinum-palladium catalysts on synthetic aluminosilicate
(0.5 wt. % metals on the carrier)* and on an iron-copper oxide contact on
clay (iron-copper = 4:1, £ oxides : carrier = 1:2). The catalyst (10 1) was
placed in a shelf-type gas purifier. The exhaust gas before the catalyst
passed through a bed of aluminosilicate which partially removed water, soot and
other impurities. During the tests, the gas temperature in the catalyst bed
was measured, and the gas was analyzed before and past the gas purifier for its
content of carbon monoxide, aldehydes, nitrogen oxides, and carbon dioxide.
» The tests were conducted in the heat engineering laboratory of the GIPRouglegormash Institute.
- 123 -
-------
Table 27
Oxidation of Carbon Monoxide and Hydrogen in the Exhaust Gas of "Moskvich-407" Engine in the Presence of Mixed
Palladium Catalysts (Total Metals 0.75 wt. #, 0.5 l) in an Experimental Gas Purifier
Designed by LANE
Catalysts
Palladium
Copper
Palladium
Iron
Palladium
Cobalt
Speed,
rpm
1500
2000
2500
1600
2000
2600
1600
2000
2500
Fuel Peed
Leaned- out
mixture
Enriched
Leaned-out
Enriched
Leaned-out
Enriched
Leaned-out
Enriched
Leaned-out •
Enriched .
Leaned-out
Enriched
Leaned-out
Enriched
Leaned-out
Gas Tempeip-
ature, °C
I
660
460
610
410
576
510
490
460
520
480
650
420
500
430
650
II
620
460
460
460
610
660
520
540
520
490
610
630
600
660
610
CO
I
6,0
10,14
0,05
13,7
2,4
10,0
3,0
7,0
0,17
11
2,8
12,6
0,40
12,0
2,7
II
0,23
9—12
0,02
12,7
1.1
9,8
0,17
6,0
0.12
10,5
0,28
11,2
0,07
10,0
0,74
C0a
I
9,2
3—6
9,7
4,1
10,1
6,5
9,75
8,0
9,5
5,5
2,2
4,2
10,0
4,7
.9,6
II
11,0
3,6
9,6
4,3
10,0
5,0
10,3
7,9
10,9
4,9
9,7
4,5
8,0
4,6
9,4
o,
I
3,6
4,0
6,8
3,5
4,2
4,6
3,0
3,5
3,6
2,6
2,7
3,75
3,9
3,2
3,9
II
3,5
5,0
6,1
4,3
3,8
5,3
2,9
3,4
3,6
3,0
4,2
4,5
7,0
6,2
4,5
Ha
I
1,8
4,8
0,0
4,6
0,95
4,9
1,2
2,8
0,65
3,8
0,9
3,8
0,35
4,00
1,1
II
4,0
0,0
4,6
0,0
2,6
0,0
0,1
0,0
3.4
0,01
1,8
0,0
2,7
0,03
Injection
Coefficient
0,34
0,14
0,02
0.01
0,08
0,12
0,22
0,08
0,0
0,06
0,09
0,06
0.29
0,18
0,21
Degree of
Purifica-
tion S
0,97
0-0,07
0,49
0,02
0,5
0,0
0,93
0,1
0,3
0,05
0,89
0,046
0,79
0,056
0,69
Note. Numeral I denotes the temperature and content of the components before the gas purifier, and numeral II,
past the gas purifier.
-------
Table 28
Laboratory-Road Tests of KNG-'iSOA Neutralizer with Alumina-Platinum and
Palladium (0.75 wt. % Pd) Catalysts on ZIL-130 Truck
Conditions of
Motion
Speed,
km/hr
30
50
70
Load,
t
2,5
2,5
2.6
Alumina-Platinum Catalyst
CO Content, %
Before
Neu-
tralizer
5,0
1,0
0,40
0,76
After
NeuT
tralizer
0,10
0,10
0,07
0,15
% Purifi-
cation
i
98
90
83
£0
Palladium Catalyst
CO Content, %
Before
Neu-
tralizer
10
1,75
0,60
0,45,
After
Neu-
tralizer
0,25
0,10
0,05
0,11
% Purifi-
cation
97
94
90
. 76
Table 29
Tests of KHG-150 Neutralizer with AluminsHPlatinun and Palladium Catalysts
(0.75 wt. % Pd) in Exhaust Gases of MZMA-407 Engine
Operating
Alumina-Platinum Catalyst
Palladium Catalyst
Conditions of
Engine
rpm
1
§
t-t
Load,
*
25
50
75
100
CO Content, %
Before
Neu-
tralizer
2,3
2,5
2,0
6,9
After
Neu-
•tralizer
0
0,1
0
1,0
%
Purifica-
tion
100
96
100
83
CO Content, %
Before
Neu-
tralizer
2,7
2,4
2,0
1.0
After
Neu-
tralizer
0,6
0,6
0,4
0.3
%
Purifi-
cation
78
79
80
70
25
60
75
2,7
2,6
1,1
0.2
0,3
0.1
93
89
90
2,7
3,0
1,4
0.3
0
0.1
100
Figure 56 shows the change of the carbon monoxide content in the exhaust
gas during its oxidation over platinum-palladium catalyst as a function of the
engine load. As the latter increases, the amount of carbon monoxide in the
initial exhaust gas increases, and at a load of 70-80% amounts to 0.018 vol. %.
The oxidation causes a decrease in the carbon monoxide concentration on the
catalyst at all loads. At a load of 40-50%, the degree of oxidation reaches
90%. At the same time, the carbon monoxide concentration in the exhaust gas
is 0.0018 vol. %, which approaches the sanitary level of carbon monoxide for
the air of industrial buildings (0.0016 vol. %).
Starting with a 40% engine load and above, the temperature in the catalyst
bed rises to 220-470°C., this being apparently responsible for a 50% or higher
completion of the oxidation reaction of carbon monoxide. A 60% removal of
- 125 -
-------
2 ff.ax
i
jQ Qffrj
**.
jj
C *«/»
§ *
1
0 0MV
8 ,J
affoe
•— -
•— —
"'""'••-
-— -<
'
^
^
_x'
./.-i
^
a
•0
.**
'"" 9
~'^
\
\
'^1
H
Engine load, %
Fig. 56. Change of carbon monoxide content in the
exhaust gas of KDM-100 engine at various loads in
the presence of supported platinum-palladium cata-
lyst: 1 - CO content (°f>) before gas purifier;
2 - past gas purifier
carbon monoxide from the exhaust gas during idling was obtained after warming
up the engine under different conditions. Analysis of the gas showed that
the content of nitrogen oxides past the catalyst does not change (0.00017 vol.
%) ; no aldehydes were observed in the majority of the samples, owing to the
incompleteness of the analytical procedure.
500
Fig. 57. Oxidation of carbon monoxide in the exhaust of
KDM-100 diesel engine in the presence of platinum (Oxy-
France) platinum-palladium, palladium and iron-copper oxide
supported catalysts at different engine loads.
- 126 -
-------
Tests of palladium catalyst in the same gas purifier showed that as
the exhaust gas passes through the catalyst (initial carbon monoxide content
0*015-0.005 vol. %) , the carbon monoxide concentration starting with a load
of 40% and higher at a temperature of 250-400°C. decreases to 0.004-0.0023
vol. %. At a smaller engine load, because of a lower temperature in the
catalyst (200°C. or lower), the oxidation proceeds less intensely.
In the course of extended tests of the catalysts on diesel engines
stands, despite the use of aluminosilicate filters, the catalysts were coated
with soot. A high activity of the contacts was maintained by periodically
burning up the soot at 600°C. by passing air over them.
Figure 57 shows results of oxidation of carbon monoxide in the exhaust
gas of a KDM-100 diesel engine as a function of the load in the presence of
platinum-palladium, palladium, and iron-copper supported oxide catalysts and
also platinum in a gas purifier made by Oxy-France Co. (the platinum catalyst
was tested by R. M. Popovichenko [69]).
As is evident from the figure, the low-percentage palladium catalyst
with a small admixture of platinum (25 at. %) on synthetic aluminosilicate
is not inferior to the Oxy-France platinum catalyst in the degree of oxida-
tion of carbon monoxide in the exhaust gas, particularly at small engine loads
and during idling. However, the temperature in the platinum catalyst bed for
the same load is 100°C. or higher than that in the platinum-palladium catalyst.
Palladium catalyst operating under less favorable temperature conditions
showed poorer results because of a low carbon monoxide concentration. In
order to increase the activity of palladium catalyst (0.35 wt. % Pd) in the
shelf-type gas purifier, the exhaust gas of KDM-50 engine* was first heated
to 500°C. Results of the tests showed (Fig. 58) that even during idling,
the degree of removal of carbon monoxide from the exhaust gas amounts to 87%.
With increasing engine load (50% and higher), the degree of oxidation of
carbon monoxide reaches 90%.
Thus, platinum-palladium and also palladium (0.35-0.5 wt. %) and iron-
copper oxide catalysts can be used to remove carbon monoxide from diesel
engine exhaust gases with preheating of the latter.
The road tests for efficiency of palladium catalyst on aluminum oxide
and other catalysts were carried out in an NTK-6M thermocatalytic gas purifier
of Filatov's design at the Sokolovskiy quarry of the Sokolovskiy-Sarbay ore-
dressing complex (May 1967). The gas purifiers (two) were installed on an
MAZ-525 truck. The gas was preheated with a burner during the descent into
the quarry and during loading of the truck at the face (with the engine idling)
* Tests conducted on stand of KDM-50 engine of Volgograd Polytechnic Institute, catalyst volume 20 1.
- 127 -
-------
Fig. 58. Oxidation of CO in the exhaust gas of KDM-50 engine,
the gas being preheated to 500"C. over Pd/aluminosilieate
(20 1 of 0.35$ Pd) at different engine loads. 1 - degree of
removal of CO from exhaust gas, %\ 2, 3 - carbon monoxide
content (in vol. #) before and past gas purifier.
Table 30
Road Tests of Palladium
Catalyst on Aluminum Oxide
(0.5 wt. % Pd)** on Diesel
Engine of MAZ-525 Truck in
NTK-6M Thermocatalytic Gas
Purifier
Degree of
Purification, %
Carbcm
Monoxide
Aldev
hydes
Soot
Climb from Quarry,
Load 25 t
49
70
60
Descent into Quarry
without Load
72 I . .100 40
Idling rpm while
Standing Still
70 I- £8 I 60
Average Degree of
Purification
78
47
Table 30 lists data on the purification of the exhaust gas of the
MAZ-525 dump truck in an NTK-6M thermocatalytic gas purifier with palladium
catalyst (the figures listed are average arithmetic data of all the determin-
ations under the indicated conditions based on records of the tests).
Palladium catalysts are characterized by an average oxidation of carbon
monoxide of 66-69%, aldehydes 54-76%, and soot 36-47%. Thus, the efficiency
of operation of the NTK-6M thermocatalytic gas purifier with the catalysts
tested is above 50% for all the components. Since the catalyst operates in a
thermocatalytic gas purifier in a fluidized bed, of major practical interest
are tests of the catalysts for the duration and stability of operation under
road conditions.
** Catalyst made by the Institute of Chemical Sciences, Kazakh Academy of Sciences.
- 128 -
-------
Efficiency Road Tests of Palladium Catalysts
for Purification of Gasoline Engine Exhaust Gases
In 1967, the Scientific Research and Experimental Design Laboratory of
Neutralization and Truck and Tractor Power Engineering (KazMPIAT) in col-
laboration with the Institute of Chemical Sciences, Kazakh Academy of
Sciences, and other organizations carried out the first stage of official
efficiency road tests on palladium and a number of other catalysts.
The catalytic oxidation of the toxic components of exhaust gases was
carried out in gas purifiers whose design and theory of operation were
developed primarily for platinum and palladium catalysts prepared at the
Scientific Research and Experimental Design Laboratory of Neutralization
and Automobile and Tractor Power Engineering [14,- 73, 74]. The basic charac-
teristics of the designs of the gas purifiers employed involve the use of
bead catalysts in the form of a thin layer compressed between perforated
screens, and an additional injection of air through an injector before the
reactor to ensure an effective removal of carbon monoxide from the gas at a
space velocity of 100 x 103 hr"1. A diagram of the catalytic gas purifier
is shown in Fig. 59.
Fig. 59. Diagram of catalytic gas purifier for gasoline engine
exhaust gases.
The toxicity of exhaust gases in the tested gas purifier design decreased
as a result of two factors: dilution of the exhaust gas by the injected air
(by approximately 1/4) and as a result of catalytic oxidation. The degree of
catalytic purification S was calculated by allowing for the dilution. Results
of chromatographic analysis (the sampling was duplicated) of the exhaust gases
before and past the gas purifier (2-3 machines of each brand) were recorded.*
Tests of the catalytic gas purifiers were carried out on five types of
gas purifiers according to a specially developed procedure under the conditions
prevailing in Moscow, the Ust'-Karoa gypsum mine, and Alma-Ata in motor vehicles
of the models ZIL-585, ZIL-130, GAZ-51, GAZ-52, "Moskvich-408", M-21 and
LAZ-585, with three vehicles of each of the models. The Chemistry Institute of
• Chroraatographic analysis of exhaust gases was carried out in specialized laboratories of LANE
and KazNIPIAT.
- 129 -
-------
S.I
0)
e
ShAS-2
A
9,nZl»
t M If a i* ta f jf ff ox to- aJfff- oxtr
Traveling speed, km/hr.
Fig. 60. Degree of removal of carbon monoxide from the exhaust
gas of ZIL-130 engine in the presence of various catalysts at
various catalysts at various traveling speeds under load.
ZIL-130 Volga
too
90
w"
8 »
"8
1
3 49
o
% SO
t4
GO
o
o
.
V
ZII-585
Hoskvich
v MZ-51 i
\
V
V
OJO6O a JO O 30-6O OSOOOOJOSff
Traveling speed, km/hr
Fig. 61. Degree of removal of carbon monoxide from the
exhaust gas of various engines under different conditions
of motion in the presence of palladium catalyst on aluminum
oxide (0.5 wt. % Pd) and aluminosilicate (0.75 wt. % Pd).
- 130 -
-------
the Kazakh Academy of Sciences furnished experimental batches of palladium
catalyst on bead aluminosilicate (0.75 wt. % palladium), on bead aluminum
oxide (0.5, 0.35 wt. % palladium) and mixed catalysts on synthetic alumino-
silicate (palladium-cobalt, palladium-copper, palladium- iron, palladium-
nickel) for the tests, with a total metal content of 0.75 wt. %, which had
shown positive results in bench tests at the LANE laboratory.
Results of tests of gas purifiers with palladium catalysts in Moscow
and at the Ust'-Kama gypsum mine are considered below. Figure 60 presents
data on the degree of removal of carbon monoxide from the exhaust of the
ZIL-130 truck in the presence of various palladium catalysts under different
conditions of motion under load. The traveling speed of the truck (in kra/hr)
is plotted along the horizontal axis, and the degree of catalytic removal of
carbon monoxide from the gas (in %) , allowing for 'dilution with air, along
the vertical axis.
It is evident from Fig. 60 that the oxidation of carbon monoxide is
substantial over all the catalysts except palladium-cobalt and palladium-
copper on aluminosilicate. The carbon monoxide content of the exhaust gas
during the purification decreases to 0-0.5 vol. %.
The most efficient catalyst from the standpoint of degree of removal
of carbon monoxide from the exhaust gas is palladium on aluminum oxide
(0.35-0.5% palladium) and on aluminosilicate (0.75 wt. % palladium). In
their presence, carbon monoxide is practically completely oxidized under all
conditions, and the degree of purification ranges from 65 to 80%, whereas
over palladium-cobalt and palladium-copper catalysts on aluminosilicate, it
amounts to less than 50%, and thus the carbon monoxide content at 30-60 km/hr
remains high
According to the degree of oxidation of carbon monoxide in the exhaust
gas of ZIL-130 engine operating under load and without it, the catalysts
tested may be arranged as follows: palladium on aluminum oxide (0.5 wt. % Pd) ,
Pd/ShAS-2 (0.75 wt. % Pd) , Pd/Al203 (0.35 wt. % Pd) , Pd-Fe/ShAS-2 (0.75 wt. %
I Me), Pd-Cu/ShAS-2 (0.75 wt. % I Me), and Pd-Co/ShAS-2 (0.75 wt. % I Me) .
Figure 61 shows the results of oxidation of carbon monoxide in the
exhaust gas of various engines (with and without load) in the presence of the
best of the catalysts studied, at different traveling speeds and during idling.
Analysis of the exhaust gas before and past the gas purifiers with the
catalysts Pd/ShAS-2 (0.75 wt. % Pd) and Pd/Al203 (0.5 % Pd) , installed on
GAZ-51, ZIL-130, "Volga", and ZIL-585 motor vehicles operating with and with-
out load, showed that the degree of purification ranges from 85 to 100% during
idling and at a traveling speed of 30-60 km/hr.
- 131 -
-------
NJ
"Moskvich-408" "Volga" ZIL-130 GAZ-51 "Moskvich-'tOS" "Volga" ZIL-130 G/iZ-51 "Moskvich-408" "Volea" ZIL-130 GAZ-51
Fig. 62. Change of carbon monoxide concentration (l - beforej 2 - after purification) in the exhaust gases of various
engines during their motion under load in the course of purification over palladium catalyst on aluminum oxide (0.5 wt.
% Pd) and aluminosilicate (0.75 wt. % Pd). a - idling; b - speed 30 km/hr; c - 60 km/hr.
-------
02, vol. %
SO if .
Traveling speed, km/hr.
b
BO
-4
Traveling speed, km/hr.
Fig. 63. Average oxygen content in the exhaust gas past
the gas purifier; a - under Moscow conditions: 1 - "Mosk-
vich-taS"; 2 - ZIL-585; 3 - "Volga"; 4 - GAZ-51; 5 - ZIL-130;
b - under Alma-Ata conditions: 1 - "Moskvich-408"; 2 - GAZ-52;
3 - ZIL-585; 4 - PAZ-652.
The greatest effect of purification and maximum reduction of carbon
monoxide content under all conditions of motion is achieved (Fig. 62) in the
purification of the exhaust gas from engines of ZIL-130 and "Volga" apparently
because of the lower CO concentration in the initial exhaust gas than in the
other engines.
A different picture is observed in the testing of palladium catalysts
on "Moskvich" automobiles (city taxicabs). The carbon monoxide concentration
in the exhaust gas of the "Moskvich-408" engine at 30 km/hr and during idling
decreases insufficiently (1.5-3.5%), and the degree of purification of the
exhaust gas is 70-80% under all operating conditions.
- 133 -
-------
Thus, the reduction in the toxicity of exhaust gases depends not only
on the chemical composition of the catalysts, but also on the brand of the
engines, and is apparently caused by a different ratio of carbon monoxide
to oxygen on the surface of the catalysts depending on the type of engine
after an additional suction of air.
The relative concentrations of the reacting components on the catalyst
surface may be estimated on the basis of their gas-phase concentration from
data obtained by analyzing the exhaust gas for carbon monoxide and oxygen
past the gas purifier.
Figure 63 a shows the average oxygen content in the exhaust gases of
various engines past the gas purifier under conditions prevailing in Moscow.
It is evident that in the composition of the exhaust gas of the "Moskvich-
407" engine past the gas purifier, the amount of oxygen ranges from 4 to 8%,
which at high initial concentrations of carbon monoxide (4-8%) and hydrogen
(up to 3-4%) cannot ensure their complete oxidation, particularly at high
space velocities. In the case of other brands of trucks, ZIL-130 (8-12%),
GAZ-51 (15-18%), and ZIL-585 (7-11%), the exhaust gas contains a larger
amount of oxygen, which ensures a more complete removal of carbon monoxide
when the latter is present in the exhaust in more or less appreciable concen-
trations.
Probably the main reason for a decrease in the efficiency of a catalytic
gas purifier at high carbon monoxide concentrations for certain brands of
motor vehicles is an insufficient supply of additional air through the injector
(the air injection coefficient in all the gas purifiers was the same, about
0.25). At the same time, it is known from the literature that an injector
with an adjustable nozzle geometry constitutes the optimum design of a neu-
tralizer injector [76].
This factor had an adverse effect on the degree of removal of carbon
monoxide from gasoline engine exhaust in tests under the mountainous conditions
of Alma-Ata, where the oxygen content of air is lower. The average oxygen
content in the exhaust gas past the gas purifier for all the brands of motor
vehicles tested was lower than under Moscow conditions, i. e., did not ex-
ceed 3.6-7.0%, and for a PAZ-652 truck, 3.5-5% (Fig. 63 b). The oxidation
of higher concentrations of carbon monoxide and hydrogen (the content of hy-
drogen is as high as 2-6%) requires more substantial oxygen concentrations
on the surface of the catalysts than the analysis of the exhaust gas for
oxygen past the gas purifier. A consequence of this is a decrease in the de-
gree of removal of carbon monoxide from exhaust gases under the conditions
prevailing in Alma-Ata. It should be noted that a decrease in the activity
of platinum catalyst (at high carbon monoxide concentrations) is also attrib-
uted by a number of foreign researchers to an insufficient amount of air for
the oxidation of carbon monoxide.
- 134--
-------
Table 31.
Catalytic Removal of Carbon Monoxide from Exhaust
Gases Under Different Operating Conditions of GAZ-51
Truck in a KN-75 Gas Purifier (Alma-Ata).
0
Pig. 64. Change of the activity of palladium catalysts.after
partial service on GAZ-51 truck in the oxidation reaction of
1$ CO in air at 36 x 103 hi—1 in a laboratory unit: 1 - fresh
catalyst; 2-7 - catalysts after service on trucks.
- 135 -
-------
On palladium and palladium-cobalt catalysts, the degree of removal of
carbon monoxide from the exhaust gas of the GAZ-51 engine amounts to an aver-
age of about 50%; the maximum is 60-100% in idle operation, and drops to 30-
60% as the traveling speed increases to 60 km/hr. On palladium-copper and
platinum-palladium catalysts, the degree of purification is substantially
lower. The same pattern but with a lesser effect is observed in the purifi-
cation of the exhaust gas of the "Moskvich-408" engine in the KNT-150 gas
purifier. In idle running, the degree of oxidation of carbon monoxide is
20-40% on palladium and platinum-palladium catalysts, and during motion under
load, it decreases from palladium-cobalt (60-70%) to palladium (20-50%),
platinum-palladium (5-30%), and palladium-copper (0-20%) contacts. The aver-
ager oxygen content in the exhaust gas past the gas purifier during motion
does not exceed 4-5%, i. e., is 2-2.5 times lower than in the exhaust gas of
the GAZ-51 engine under conditions prevailing in Moscow (see Fig. 63), and
is obviously the main cause of the lessening of the purification effect.
This is confirmed by data on a slight change in the activity of palladium
catalysts after partial use, obtained by testing them in a laboratory unit in
a stream of air (Fig. 64). The activity of the contacts after one month's use
in the GAZ-52 truck decreased by 10-30% at 200-300°C., but remained unchanged
at 400°C. The phase composition of the catalysts also remained unchanged.
Table 32.
Phase Composition of Palladium Catalysts.
1
Is
Interplanar spacing
d " d/n
Found
Tabular
data for.
Pd
Phase
Pd/ShAS (0.75 wt. % Pd) after
tests on GAZ-52 (Alma-Ata)
10
8
9
10
7
2,237
1,950
1,375
1,173
1,123
2,246(100)
1,945( 2)
1,376(25)
1,173(24)
1,123(8)
Palla-
dium
»
I
Pd/AlgOj (0.5 wt, H> Pd)
after tests on GAZ-52
(Alma-Ata)
10
8
9
10
7
2,237
1,950
1,375
1,173
1,123
2,246(100)
1,946(42)
1,376(25)
1,173(24)
1,123(8)
Palla-
ditnn
»
»
Pd/ShAS (0.75 wfc. .% Pd)
after tests on ZIL-130
(Moacov, 21,000 km on
qdometer) '
6
4
4,86 — .
8,87 i —
— •
—
Intensity
6
6
6
7
4
8
2
3
4
•8
1 .
.2
1
1
2
2
1
10
1
. 1
1
2
2
Interplanar spacing
d- =.d/n
Found
3,35
3,18
2,76
2,29
2,18
21ft
,18
1,966
1,796
1,715
1,619
• 1,492
1,398
1,374
1,348
1,220
1,172
1,123
1,095
1,059
1,032
0,995
0.972
0,891
0.869
Tabular •
data for
Pd
_
—
—
2,246(100)
""™""
1,945 (42)
_
_
_
__
1,876 (25)
_
1,178 (24)
1,123 (8)
__
_
L .^
.
— .
; —
Phase
—
_
Palla-
dium
^^*
dium
««
_
_
_
Palla-
• dium '
Palla-
diuD
Palla-
• dium
•^
_
—
- 1-36 -
-------
t
t»
Q-
C
O
c
O
•r-t
•*-•
00
'C
'(. in
M>'ci
•5 °£
5 d.
in
I/I X
B "
1?
z
lA ^
1 C
•t
t* **•
O •
•e
in *
lA
co l>
a o
3
01
.c
X
u
R
/-T
a>
10
P.
c-c
a;
• H
3
0.
ti
(0
ex
g
-H
.u
V)
o
a.
B
O
o
IA
CO
O
e
8
*-. tu
0 4J
-------
catalyst loss (in wt. %) is laid off along the vertical axis,
Weight decrease
of Pd catalyst,
Distance covered, thousand km.
Fig. 65. Decrease in the weight of palladium catalyst on synthetic
aluminosilicate in the course of service in a gas purifier on a GAZ-52
truck -.aider conditions prevailing in Alma-Ata.
It is evident thst the catalyst losses are particularly significant during
the first 2000 km of run (up to 6 wt. %) and increase sharply (up to 10%) during
further run, when the catalyst begins to operate with a loose packing in the
gas purifier.
In order to evaluate the process of wear of the catalyst granules in the
course of service in trucks, the particle size distribution of the catalyst
was determined before and after the tests on different vehicles. Results of
sifting of catalyst particles from various gas purifiers into fractions are
shown in Fig. 66, where the mean diameter of the particles is plotted along
the horizontal axis and their weight fraction is plotted along the vertical
axis. For comparison, the figure shows the particle size distribution of the
initial batch of catalyst poured into the gas purifier.
It is evident from the figure that the particle size distribution of the
catalysts changes substantially during service on the trucks. The quantity
of particles measuring 4.75-6 mm and 3.75-2.5 mm decreases substantially (to
5 wt. %) in the course of the tests as a result of abrasion into dust. The
abrasion of coarse granules forms particles 4.25 mm in diameter whose number
increases. However, after the loss of more than 5-6 wt. % of the catalyst,
when the latter operates as a moving bed (catalyst from gas purifier 35, '
Fig. 66), granules larger than 3.5 mm in size break up rapidly; the quantity
of particles 4.2 mm in diameter decreases by more than 10%, and a large
quantity of fine particles is formed (3.25 mm in diameter or smaller).
-_138 -
-------
'•^Initial batch.
5 , 6-
Mean particle diameter
Fig. 66. Change in the fractional composition of palladium
catalyst on bead synthetic aluminosilicate in the course of
service on GAZ-52 truck.
Analysis of the data obtained after the use of palladium catalyst on
synthetic aluminosilicate on trucks shows that the catalyst undergoes mechan-
ical abrasion. Granules of all sizes are abraded to approximately the same
extent, but those under-going the greatest abrasion are split or fine gran-
ules up to 3 mm in size, which change into dust, the latter being then
carried off by the stream of exhaust gas through the catalyst screen. When
the weight of the catalyst is reduced by 5-6% on GAZ-52 trucks, the catalyst
begins to operate in a moving bed, and the breakdown process accelerates. As
a result of breakthrough of the gas into the unoccupied space, the degree of
carbon monoxide removal from this gas decreases sharply.
In the development of the technological process of preparation of palla-
dium catalyst on aluminosilicate, particular attention was concentrated on
its mechanical strength. The truck tests also included a catalyst whose
mechanical abrasion resistance, determined in an eccentric vibratory mill,
was 96%. However, the operational strength of the palladium catalyst on
synthetic aluminosilicate proved to be inadequate. Apparently, it is deter-
mined not so much by the abrasion of particles during jolting, as by the
nature of the chemical processes occurring on the surface and by the structure
- 139 -
-------
of the catalyst pores. The strength of the catalyst decreases because of
exothermic oxidation reactions of hydrogen, carbon monoxide, and hydrocarbons,
and the presence of substantial amounts of water vapor in the exhaust gas (up
to 5.0%), whose sorption and desorption in the presence of abrupt temperature
changes causes cracking and breakdown of a carrier with a connecting porous
structure. Slight losses of the catalyst due to cracking (up to 5-6%) create
conditions (moving bed) promoting the breakdown of the catalyst, as a result
of which channels are formed for the exhaust gas to break through to the
side of the main bulk of the catalyst. The fact that the degree of purifica-
tion is substantially decreased only by the formation of catalyst-free space
in the gas purifier is confirmed by data on an insignificant change in the
activity of the catalysts after their partial use in motor vehicles under lab-
oratory conditions (see Fig. 64).
Because of the low operational strength of palladium catalyst on synthetic
aluminosilicate, its use on trucks is possible only if it is periodically
supplemented, which causes an inconvenience in its use. Palladium catalyst
on aluminum oxide has a high operational strength and was found more suitable
for reliability and durability tests. In tests on various motor vehicles,
its efficiency does not decrease in the course of 20,000 km.
Table 34 includes the existing literature data on exhaust purification
catalysts which have passed road tests. The bulk of the data were obtained
by testing the Houdry platinum catalyst (rods, beads) manufactured by Oxy-
France and platinum catalyst on aluminum oxide made in the USSR, tested on
gasoline and diesel engines. Platinum catalyst (Oxy-France) was studied in
detail by Fitten [31], and in the USSR by NAM, LANE, and the Karpov Physico-
chemical Institute [5,44, 64, 67]. For carburetor engines, Fitten notes a
high degree of removal of carbon monoxide (50-100%), hydrogen (50-90%), and
hydrocarbons (50-90%) under various engine operating conditions (Fig. 67),
this removal being determined by the temperature in the catalyst bed: at
500°C. and above, an 80-90% purification is achieved. Fitten points out that
the catalyst did not lose its activity (degree of purification above 50%) and
did not break down in the course of 17.6 thousand km, but was poisoned by
lead compounds present in ethylized fuel.
A platinum oxicat was tested by NAKL and the Institute of Sanitation and
Hygiene on stands of "Moskvich-407" and ZIL-164 engines [5]. The degree of
removal of carbon monoxide from the exhaust gas was 99.0-99.7%. The domestic
platinum catalyst gives a high degree of removal of carbon monoxide (83-100%)
for a long period of time.
In the case of exhaust gases of diesel engines [31], the "oxicat",platinum
catalyst removes 75% carbon monoxide, 60-85% hydrocarbons, and 60% aldehydes.
Similar results were obtained by testing it on the exhaust gas of the YaMZ-236
diesel engine (188 p) at a load of over 50% (60% removal of CO, 100% aldehydes)
[64l. A lower degree of removal of CO (46-74%) is obtained over platinum
- 140 -
-------
Table 34
Road Tests of Exhaust Purification Catalysts and Characteristics of Catalytic Gas Purifiers
js
M
I
Catalyst
1
Pt/Al203 on
ceramic rod;
h a 3 mm,
1 = 6-8 mm
Pt.'Al.O,,
Oxicat
Pt/AliOs,
3X3.C8t
Type of
engine
2
Carburetor,
cylinder
volume 2.5-
2.75 1, in7
stalled on
a van with i
load-carry-
ing capacity
of 4.5 t
Diesel
Carburetor
Operating
conditions '
of engine
3
All condi-
tions durinf
motion, t 9
500-750°C.
.
above 60/6
. Power 0.5-1
1 hp, rotatioi
al speed of
crankshaft
500-2800 rpi
t° after
catalyst
350-620'
Average degree of removal, $,
8
4
40—
100
76
W—
. 100
1
ct
6
60—
90
—
—
Hydro-
carbons
6
60—
90
60—
86
—
1
1
—
—
—
AldehydeJ
8
—
60
—
of
£
ton
£.S
se'S
9
—
—
—
Duration of
service
10
17600 km,
does not
break down
—
Not tested
Stabilit;
to lead
and over-
heating
11
Stable
to heat
—
Poisoned
by lead
Country,
company,
type of
fas puri-
ier
12
France, Oxy-
France,
model V-3
—
France, Oxy
France,
V-4
Refer-
ence
18
[81]
[81]
[6]
-------
Table 54 (Continued)
Pt/AlgQ,,
2-5 mm
beads
v,o,.
VaO»/Al,0,
.Unknown :
Unknown
Al.Pt.Gr, •
C«
Pour-stroke
diesel,
YaMZ-256,
160 hp
Carburetor
Carburetor,'
diesel
Carburetor
Carburetor, .
diesel
Load over
5$
(=300—600°
Optimum tem-
perature
500°C.
Optimum tem-
perature •
1>20-650°C.,
start of
operation
120°C.,
idling
All condi-
tions
All condi-
tions
60
—
80
80-95
—
—
—
60-70
—
—
Brings the content
of CO and hydrocai
bons in the exhaus
gas down to sani-
tary norms
—
—
90-06
CO
_ ..
—
100
—
^_
80
—
—
—
—
Not tested-
200 hr, 16-
18 thousand
km, does not
break down
132,000 km,
•abrasion re-
sistant;
after 19.COC
km no decree
in volume of
catalyst was
observed
38,bOO km
(about two
years)
1000 hr or ,
40,000 km
for gasolini
engine and
3000 hr or
120,000 km
for diesel
engine
Stable-
to Pb,
200 hr
Not poi-
soned by
Pb or S,
Overheat-
se ing to
98°C.
allowed
^^
Preheatei
to 800°C
before _
ope ratio
France, Oxy
France, DN-
200, LANE
USA, Ford
Motor Co.
USA, Tech-
nical Indus
tries, gac
purifier
designed by
Gulik-Rous
USA, Uni-
versal Oil
Products
Japan, Himo
Motors
Limited
[64]
[66]
[66]
[66]
Advertising
inf ornat" on
-------
(Continued)
1 1 •
Pd/Al.O,,
Spherical
ShPAK-0.5
Pd/AlA
Spherical
Oxide cata-
lyst A06-R-A
Pt/Al.0,
>iesel
MAZ-525
//
a
Gasoline I
M7.MA-407
3
Idle revo-
lutions,
25 t load
Ascent from
and descent
into quarry
a
n
Load on
stand from
25 to 100, '
1500-2000
rpm in raotic
no-load opei
ation, spee<
30-70 km/hr
at a load of
2.5 t
4
48—78
58—79
0-68
83—
100
n
.
6
—
—
—~
6
—
—
"™~
7
40—
60
25—
76
70—
100
^
8
60-
100
33—
01
100
*™
9
—
—
•""
10
Not tested
n
n
Laboratory-
road tests
-
11
900—
1000°
tr
—~
•
12
USSR, LANE,
UFAN, IKhH
AHKaz SSSR,
NIK-6M with
preheating,
fluidized
bed
USSR, LANE,
UFAN, Karpo
Physieocheift.
ical Insti-
tute, NTK-6B
USSR, LANE,
UFAN,
Petroleum
Jhemistry
Institute
KNG-150
13
Records
of tests
//
a
n
-------
Tsb;«
Pd ShAS-2
Pd.'AIjO,
spherical
ShPAK-0,5
pd/ShAS-2
Pd/Fe/
ShAS-2
Pd/Co
ShAS-2
it
Carburetor
engines of
ZIL-130,
"Hoskvich-
407,' "Volga*
GAZ- 51
Carburetor
GAZ-51
ZIL-130
ZIL-585
GAZ-51
ZIL-130
GAZ-51
/*
All condi-
tions of
notion
"
All condi- :
tions
No-load
operation,
30 km/hr.
50-60 km/hr
All condi-
tions
7G—
100
70—100
50 and
—
above, . —
60 and
below
Above
50
60—100
50 and
above
20—
100
70-100
46-66
60 and
below
j,m
—
—
**^
USSR, LANE,
IKhN ANKaz
SSR, KNG-15<
KN-150
KNG-150
KazNIPIAT
USSR, LANE,
IKhN ANKaz
SSR
KN-75
KN-150
KN-100
KN-75
KazNIPIAT
USSR, LANE,
IKhN ANKaz
SSR, KN-150
Moscow
USSR, IKhN
AN KazSSR,
KazNIPIAT,
KN-75,
Alma-Ata
-------
(bead) catalyst on aluminum oxide in KNG-250 and KNG-300 gas purifiers [67]
in the operation of carburetor and diesel motor vehicles at a traveling speed
of 15-20 km/hr. In the exhaust gas of carburetor engines, carbon monoxide
decreased by 46-54%, and nitrogen oxides by 50-56%, and in the case of diesel
engines, carbon monoxide by 58-74% and nitrogen oxides by 30-56%.
Contamination of catalysts with fuel residues and soot (at moderate tem-
peratures) curtail the service life of the contact: instead of 2500 hours,
it is shortened to 1200-1400 hours (diesel) and 1600 hours (carburetor engine).
For this reason, a composite gas purifier designed by LANE and a thermocatalytic
purifier designed by Filatov, which have been road-tested, are obviously more
suitable for the purification of diesel engine exhausts under all conditions.
In addition to palladium catalysts, of great interest is a catalyst con-
sisting of aluminum, platinum, chromium, and copper, proposed by the Japanese
company Himo Motors Linited for the purification of exhaust gases of gasoline
and diesel engines. According to the description, it removes 80-95% of carbon
monoxide, 60% of the hydrocarbons and 80% of the aldehydes from the exhaust,
and is stable for 40,000 km for gasoline engines and 120,000 km for Diesel
engines. A vanadium catalyst on aluminum oxide and without a carrier, proposed
by Ford Motor Co., was found to be stable to poisoning with lead compounds [65]
for 200 hours of operation. In its presence, the oxidation of hydrocarbons
(60-70%) and particularly olefins and paraffins (50-90% at 250°C.) is satis-
factory, and carbon monoxide is oxidized starting at 500°C. only at low space
velocities.
For carburetor engines, certain US firms [66] propose gas purifiers with
catalysts (whose composition is unknown to us) which provide a high degree of
removal of carbon monoxide (up to 80%) and hydrocarbons (90-95%) from the ex-
haust; they are stable in operation (up to 38,000 km) and are not poisoned by
lead. However, this information cannot be discussed without published re-
ports.
Analysis of the road tests shows that palladium catalyst on bead aluminum
oxide is the most efficient catalyst and most promising economically for the
removal of carbon monoxide from gasoline engine exhausts.
In the purification of diesel engine exhausts, in which the bulk of the
toxic components consists of aldehydes, hydrocarbons and nitrogen oxides,
the most promising is the use of platinum, palladium with preheating of the
gas (combined or thermocatalytic gas purifiers) and particularly oxide cat-
alysts and natural activated manganese, copper and iron ores, which ensure
the oxidation of the toxic components at a low temperature and are charac-
terized by a low cost.
The use of the method of catalytic purification of exhaust gases of
motor vehicles operating on ethyl gasoline will require further studies
- 145 -
-------
aimed at selecting catalysts which are not poisoned by lead compounds.
Apparently, a composite gas purifier is needed for all the gases, in the
first compartment of which nitrogen oxides will be removed from the ex-
haust gases without injection of extra air and in the second compartment
(in an oxidizing medium), carbon monoxide and other organic compounds
(aldehydes, hydrocarbons) will be removed. In each compartment of the
composite gas purifier, the optimum catalyst for the removal of the re-
spective components will probably be installed.
so
to
Efficiency of
purification
Off
SO
t.
a
o.
6 12
Fuel consumption, Ib/hr
2000 6oao toooo ' taooo
Distance traveled by vehicle, miles.
Fig. 67. Efficiency of platinum catalyst in the purification of_the exhaust gas of a_carburetor engine in
Fiti»n's experiments (cited in [5]): a - d
during changing operating conditions of engine; b - as the distance
traveled by the vehicle increases.
- 146 -
-------
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79. Fop$yHKeJib B. E. — B KH.: «Oi»CTKa u
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85. AjieKceesa F. H., P H 3 o B 3. M., T o A e c O. M. — «KKHeiu-
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91. AxyHflosaM. P., EejieHbKHiiM. c. — «HeipTB H raa», 1960,
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139. MaproJiHc JI. fl. — «Vcn. XIIM.». 1951, 20, 176.
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147. AHApyuiKCBMH T. B., IIonoBCKHH B. B., BopecKOB
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149. AJICKC eeBC KHfi E. B., PHA K. B. — «3K. 0611;. XHM.»,
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150. JI B H A e B. P., M a p r o n. H c JI. H., POTHHCKHM C. 3. —
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156. H o .o t W. F., K o b e K. A. — «Ind. Eng. Chem.» 1955, 47, 776.
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158. A a x a 3 o B T. T., B e n e H b K H fi M. C. — «H3B. ayaos, He^Tb
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161. EopecKoa r. K., IIonoBCKHff B. B., C a 3 o H o B B. A. —
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162. Kaq M.—B c6.: «KaTamiuaTopbi opraHHHecKHx peaio;HK». M.,
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163. FoJioflen F. H.— «KaTa^H3 H KaTajiH3aiopLi», 1966, T. 2.,
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164. MaproJiHc JI. H.— «VcnexH XHMHH», 1959, 28, sun. 5,
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165. Lamb A., Bray W. C., F r a z e r J. C. W. — «Ind Fng.
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170. M a pro AH c JI. H. KaxajnmmecKoe OKHCJienne
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171. AjiaHOBaT. r., MaprojiHcJI. fl.— Teancw AOKJI. KOH$epen-
HHH no MCTOABM OHHCTKH raaoBbix Bi>t6pocoB R npoii. CTOKOB or speflKbix
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172. KaaaMBTKHHE. n., CanraHOBB. C., JIo6amoBK. A. —
cij AOKJI. KOH^epeHqini no MeroAaK OTHCTKH raaoaux BuSpocos si
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173. JI o 6 a m o B K. A. H flp. — 3KBXO KM. fl. H. MeRAejieesa, 1961,
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177. E. J. Du Pont de Nemours and Co. KaiaJiHaaTOpti AO-
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187. Adams C. H., BenesiH. A., Curtis R. M., Meisennei-
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189. TpH3HOB B. M., Vcosa JI. K., 4>pocT A. B. — «BecTHHK
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190. ^[ecajiosa B. C., BopecxoB T. K. — «floiui. AH CCCP»,
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191. Ajiiy«*aH A. A., MaHTRKau M. A. — «XC. $R3. XHM.»,
1959, S3. sun. 4, 780.
192. MHHaieB X. M., XO«BKOB K). C. — «H3B. AH CCCP, OTA-
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193. MKHaies X. M., UlyftKHH H. H., 4>eo$aBOB JI. M., Ero-
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194. BopeCKOB T. K., Kapnayxos A. II.— «3K. $B3. XHM.»,
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195. MnnaieB X. M-, FapaHRH B. H. — «H3B. AH CCCP, or*.
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196. EopoHKR B. C., HRicyjiRRa B. C., HoJiTOpax O. M. —
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197. m e p 6 a e B A. H., y p M a B H. H., COTHHHBHKO B. *.,
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198. Oxy-Catalyst Inc. Cnoco6 npHroxoBJieHHH xaraJDHaTopa.
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199. B y p c H a H H. P., K o r a H C. B., flasti«OBa 3. A. Cnoco6
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204. Beck John Hubert, Stiles Alvin Barber. Ilojiy-
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207. MnnaMeB X. M., IHyHKHH H. H., Mapnos M. A. — «HaB.
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212. A^eKceescKHfi E. B., M a K a p o B H. Ill —- «3K.
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213. AjieKceescKHH £. B. Cnoco6 npHroroBneHHH
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219. Taxaxacii Xapyo, MopncHTa H c y c a « a, Cn6ara
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224. Schwarzenbeck E. T., Kellogg M. W. KaTaJiHaaiopH
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225. Edward Michalko, Holkatra J., Park E., Smith
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226. C a s c h W., S e m e n i u k K., H a r t i n g W. — «J. Org.
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227. A^aMeHKOBa M. fl., HoJiTopaK O. M. — , 1963, Mi 5, 12.
228. Connor D., Shipley K. KaTajmaaTopti, coAepxcanpce njia-
THHV, H M6TOA HX HsroTOBTOHHH. IlaT. CUIA M» 2884374, 22.10. 1954. •
229. Mignel Jeen. KarajnwaTop KOHBepcnn
4>paHu. nar. N» 1331356, kl. BOH, ClOg, 27.05.63.
230. B y x o B e n C. B. Cnoco6 no^yHeRHK nJiarHKOBoro
pa. AST. CB-BO N° 105486, kl. BOIJ, 12g, 4/01, COIg, 12n, 18.XII 65.
231. B y x o B e n C. B. CnocoS nonyieHHH najuiaAHesoro Ka
pa. AST. CB-BO M? 166307, 12g, 4/01, 18.XI 1964.
232. COKO;II>CKHH fl. B. — B c6.: 6 5, 819.
237.ro CH-CHHI., Ce AHb-xyaft H Tyo H»yH-aey. — B c6.:
«IIpo6jieMbi KHHermai H Karajniaa*. M., HBR-BO AH CCCP, 1960, X,
crp. 435.
238. PameHucBa M. A., A^aKactesa K). A., Mmia-
v e a X. M. — «He4>TexnMHfl», 1963, 3, Ms 1, 55.
239. Houdry E. H. KaTaJiHS. TpyAH IlepBoro Me«AyHapo«Horo
Konrpecca. VL, HJI., 1960, 562.
240. 3ARB., KojitaepTB. KaiajiHa. TpyAti Uepsoro MeHcnyHa-
poAKoro xoHi^ecca. M., HJI, 1960, 861.
241. 3an B^ KojiiBepT B. — «XHMHH H xHMHiecKaa TCXHOJIO-
nw», 1957, J* 11, 193.
242. Lcf ra-ncois Ph. A., Riblett E. W., Burton W. P.
tbiaTRHOBbifi MJIH naJiJiaflHeBbift KaTaARsamp c npHMeneHKeM coeAHHemia
MeraJiJiOB rpynnu III. Har. CUIA 1>& 2814599, 26.11 1957.
248. JCoTeJiKOB :H. 3. — «3K. anaa. XRM.», 1950, 5, BHH. 1, 48;
«HC. npRKn. XHK.», 1951, 24, 205.
- 155 -
-------
244. repuieHoaitiM. C., KOTCJIKOBH. 3. — «3K. npiiHJi. XHM.»,
1954, 27. 1231; «3K. npiiKJi. XHM.», 1938, 11, $& 2, 253.
245. BajiaHAHH A. A., KOTBJIKOB H. 3. — «3K. npHKJi. XHM.»,
1942, 15, J* 3, crp. 139.
246. KorejiKOB H. 3. — TpyAM CapaxoBCKoro c.-x. HH-xa, 1966,
1(12), 272; «3K. npme-i. XHM... 1957, 30, 470.
247. M a r c e 11 Sam Anthony. HeicoppoAHpyiouuiii cpjiioc H MBTOA ero
npuroTOBJieHiix. Ear. CUIA, 3003901. 10.10.61.
248. II a B ji o B a B. P., HlanoBajioB A. H., JIitSepOBa P. A.,
JKyManoBC. JI., F o p a o H O. H. CnocoS nanecewts PHCVHKOB Ha icepa-
MHiecKHe H CTCKJiHHHbie naaejiira. ABT. CB-BO CCCP, 147518 or 21.05.62.
249. Ilponecc Mexa-JumsaipiH KepaMiiKii H KepaMimecKiix HSfle.nHii, HS-
roTOBJieHHHx no 3TOMy npoueccy. paHu;. naT. CO4b, >£ 1335707, 15.07.63.
250. Ka.3Ha.ieK B. H. FajibBaHonjiacTHKa B npoMbiniJieHitocxii. M.,
Foe. USA-BO M6RT. npoM. PC4>CP, 1955, ctp. 65, 165.
251. E B T e e B 4>. E., 3K y K o B B. A. TexHo.iorHS paAHoannapaTy-
pu. JI. — M., roc3HeproH3flaT, 1952, 84.
252. SaxapbescKHfi M. C. — «3aa. jia6.», 1940, J* 5—6, 647.
253. Pa6nHOBHi B. A., KyposcKaa O. B. — «IloiBOBeAe-
HHe», 1953, >6 4, 78.
254. T 1 a g u e E. D. HPOIWBOACTBO KaTamiaaTopos 113 xeranna njia-
XHHOBofi rpynnbi. Aarn. nai. 832031, 6.04.60.
255. «Ceramics», 1960, 2, 7£ 132, 14.
256. H o u d r y E. H. and Hayes C. T. — «Platinum Metals Re-
view*, 1, 1958, 2, N« 4, 110.
257. H o u d r y E. H. KarajmsaTop oKuc^eHHa. niBeftq. naT.
J£ 322973, 31.08.57.
258. L a c r o i x Roger. HpiiroTOB^eHHe Ag-KaxaAHsaTopoB. 4>p.
naT. 1259574, 20.03.61.
259. flMno^bCKHH H. M. rajibBaHOTexHHKa AparoACHHbix H pe^-
KHX MeiaJiJioB. M. — JI., Mamma, 1958, 35.
260. K a A a H e p JI. H. SamHTHbie HJICHKH na MCTajuiax. XapbKOB,
USA. XaptK. yn-xa, 1956, 241.
261. THHfiepr A. M. rajibBaHonjiacxHiecKoe HaroTOB^eHHe TOHRBIX
nojujx Aerajieft. JI., CyAnpoiarHS, 1949, crp. 20, 23, 27.
262. MejibHiiKOBa H. B., CHS OB C. H. djiexTpoAHTHHecKne no-
KPHTHS anioMHHHH H ero cnaaBOB. M., E^BTH, 1958, 2.
263. Ternision J. A. «Metaux. Corrosion-Industries*, 1959,
Jfc 409—412, 325.
264. HsaHOBCKHH . II., CeMeHosa H AP- — B c6.: «XnMiin it
TexHOJiorHH asoiHbix yAo6peHHii. O'aicTKa rasa»". M., 1965, crp. 24.
265. T a B 3 C. H., K y a H e K o B H. E. — Teawcbi KOH$epeHnnH no
OMHCTKH raaoBbix Bbigpocos H npoM. CTOKOB OT BpeffHbix sentecrB.
1967, cxp. 171.
266. CoKo^bCKHH fl. B., n o n o B a H. M., Cbi3AtiK6ae-
B a M. B. Cnoco6 o6e3Bpe*HBaHnji raaos, coAep%am>ix OKHCB yr.iepoAa.
ABT. CB-BO CCCP, 166656, 01.12. 1964, 6wnaeTeHfc M 23, 12g, 3/01.
267. CoKOJibCKHii ft. B., IIonoBa H. M., C bis fl M K 6 a e-
B a M. B., A^eKceesa r. K. CnocoS OHHCTKH KHC^opoAcoAep»eoKTHCTOB JI. r. — «KHH6THKa w Kaxa-
JOT3», 1963, 4, swn. 2, 221. .
269. JIonaTKHH A. A., Crpe^i. HHKOsa XC. B., JI e 6 e-
A e B B. II. — «3K- 4>H3. XHM.», 1957, 31, Bbin. 8, 1820.
270. CxpeJibHHKOBa HC. B., JIonaxKHK A. A., JleSe-
A e B B. n. — «3K. $H3. XHK.t, 1956, 30, Bbin. 3, 639.
- 156 -
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271. CipejitHHKOBa 3K. B., JIonaTKHH A. A., JIe6e-
B B. H. — «3K. £ 38, 67.
278. POTHHCKII H C. 3., TpeTbHKOB H. H., UlexTep A. B. —
«3K. $R3. XKM.», 1949, 23, BUH. 1, 50.
279. Py6nHDiTeHH A. M., MnHaxeB X. M., IHy ft KHH H. H.—
ui. AH CCCP», 1950. 71. >6 6, 1073.
280. Py6HHinTeHHA. M., MHKaiesX. M., AKHMOB B. M. —
«3S. o6m. XHM.», 1959, 29, Btin. 8, 2503.
281. MacnHRCKHii r. H. K a M y m e p r. A., M y m e H K o B. M.
Cnocofi npHroroBJieHSia nJiarHHOBoro KaTajuuaTOpa. ABT. CB-BO CCCP,
J* 108258, 17.11.66, 12g, 11/16.
282. KaaaKosa E. A., X HT e p e p P. 3., JI H R A H H B. M., B o M-
m T e fi B B. E., CaBOCTbHHOsa H. C., MnpoBCKaa B. H., F y «-
36HiyK K). A., MeABeflesa B. n., KoHHKoaa C. B., BafiHm-
T e fl H P. 3., PyMHKuesaM. C. B c6.: tXmsKif H TexHOJionm
aaoTHtnc yflo6peHHft. Oie MeraflJiu. M. — JI.,
I^BeTMeTH3AaT, 1929, crp. 11—12.
284. HaameEiteB fl. H., TnMOHOBa P. H. — «3K. aeopr. H o6m.
ZKHBH», 1959, 12, 592.
285. Stover W. A., B r i g g s W. S. Mero« OHHCTKH BbixjronHbix
raaoB. HaT. CUIA 3304150, kl. 23—2, 14.3.1967.
286. Kaflanep JI., SHK T. — «3K. npHKJi. XHM.», 1962, 35, 1.
287. II H « H T e C. n., BHTOMRPCKRC P. M. H «p. — TpyAW AH
JlHTOBCKOH CCP, B., J« 1 (44), 1962. 25.
288. TapMOHOB H. B., Kjie6aHCKHii A. JI., HeBbiiaJio-
B a K. K. — «HC. o6m. XHM.», 1959, 29, 3, 836.
289. KjiesKe B. A., KaHrrop fl. C., CeperHHa P. H. CnocoS pe-
reHepaumi najuiaAHesoro KarajiHaaTopa. ABT. CB-BO CCCP, J^ 202077.
Ex>JuiereBi> H3o6pereHHH, 1967, >6 19; K JICBK e B. A., Kanxop A. C.,
CeperHHa P. n. CnocoS pereHepaipra Merajuioa nJiarHKOBoit rpynnu.
ABT. CB-BO CCCP, J* 197522, 9.6.67, 12g, 11/8.
290. Conner H. — «Chem. Ind.», 1960, 1^48, 1454.
291. Hermann B., Christa K., Werner N.— «Chem. Ind.»,
1964, 16, J* 7, 382.
292. I"HH36ypr C. H., r^aAMmeBCKaa K. A., E 3 e p-
c K a a H. A. H AP- PYKOBOACTBO no xHMHiecKOMy aHaJiHsy nnaTHHOBux
KeranJiOB R sojiora. M., «HayKa», 1965.
293. Presenins W., J a n d e r V. Handbuch der analytische
them,, 1951, 8, B4, 385, Berlin.
294. A n d o 1 f H. CnocoS BMsenemm naanaARH HS KHCJiux'pacrBOpoB.
HBT. «Pr, J« 120569, 1966; na-r. CHIA 3294483, kl. 23—87, 27.X 1966.
295. HHKOJiaesaM. H., IHJIHTHH A. H. — «W. $R3. XHM.», 1956.
30, Bun. 8, 1729.
- 157 -
-------
296. BninoMHpCKHcP. M., MoJiiaflCKHftA. M. — TpyA" AH
JlHTOBCKOH CCP B., >6 1 (44), 1968, 37.
297. BHmoMirpCKHc P. M., MopreHmrepR fl. Jl. — Tpy«H
AH JlHTOBCKofl CCP, B., J* 1 (44), 1966, 46.
298. William M., Macnevin, Warren B., — «Analyt. chem.».
1953, 25. J*ll, 1628.
299. MHHaneB X. M., IIIyfiK HH H. H. H AP- — «flojoi. AH CCCP»,
1954, 99, J*5, 1015.
300. limeHHH.HH H. K., rjiaAumeBCKas K. A., Pxzo-
B a JL M. — «3K. Heopr. XHM.», 1957, 2, sun. 5, 1057.
301. IIJiaKCHH H. H., niaSapHH C. K.— «3K. npHiui. XHM.», 19,
1949, N»7—8. cTp. 1021.
302. K p a 4> T M., IIInnHfljiep r.— B c6.: «HeTBepTtift MeJKflyna-
Konrpecc no KaTajmay*. M., 1968, ROKJI&H 69.
303. Rienacker 6. Abhandlungen der Deutschen Akad. der Wis-
senschaften zu Berlin. Beitrage zur Kenntnis der Wirkungsweise von Ka-
talysatoren und Mischkatalysatoren, 1956, 45.
304. KapHayxoB A. II.— «KnHerHKa R Karajma*, 1962, 3,
stin. 4, 583.
305. BopecROB F. K., Hecajiosa B. C.— «XnM. npOM-cn>»,
1960, te6, 38.
306. COKOA&CKK& fl. B., rHJit«e6paH« E. H. — «HOKJI. AH
CCCP», 1949, 133, J*3, 609.
307. rHJii.fle6paHfl E. H. — B c6.: «KaTajnraaTOpu na Hocme-
JIHX». Ajma-Ara, «Hayxa», 1965, 107.
308. C K o n H H IO. A. HsyqeHHe nopornxoBBiz KaTajmaaTopos ajieKTpo-
xHMHieCKHMH M6TO«aMH. AsTope$epaT flHccepra^H. AjtMa-Ara, 1963.
309. FHJibae6paHR £. H. AKTHBROCT& TOEKHX CJIOGB miaTHB&i R
nanjiaflHH na HCXTHTC^HX. KaHflKflaxcKaa flucceprauHfl. AjiKa-Ara, 1962.
310. COKOJIBCKHH fl. B., rHJiB«e6paHfl E. H.— «3K. fi8, 66.
312. CoxojibCKHfi JJ,. B.— B c6.: K Jo6n^eK» pecny6xHKK, Kas-
yxne«rH3, 1961, 215.
313. CoKOJi&cKHft ^. B., JlesqeHKO JI. B.— «Becra. AH
KaaCCP*, 1954, Nil, 92.
314. COKOJIBCKH& fl. B., IIonoBa H. M. — «BecrR. AH
KaaCCP*, 1957, ?* 1.
315. CoKOJitcKHfi fl. B. — «BecTH. AH KaaCCP», BUD. 4, 1968.
316. r o r o Ji b H. A. KaxaJiHTHiecKHe caoficrBa Pd Ha HOCHre^ax npn
rHApxpoBaHKH HenpefleflBHbix cnnproB. AsTope^epaT
AjiMa-Axa, 1967.
317. CoKOJibCKHfi ft. B. — B c6.: «HeTBepmii
KOHrpecc no Kaiamiay*. M., 1968, 45 «OKJia«.
318. KoHoaeHKO H. R. — «Vcnexn $na. HayK», 1954, 52, 7£ 4,
€61.
319. Ce JIB ay A II. V. Kaia/iHa. Bonpocti reopnH H MeroAM HCMBAO-
B8BKH, 1955, M., 391.
320. Ko6oaeB H. H., EBAOKHMOB B. B., 3y6oBHi VL. A.,
KpbiJiosa H. B., JIe6eAes B. n., Majii>n,eB A. H., HeKpacoa
JI. H., nocnejiosa T. A.— «HC. 4>H3. XHM.», 1959, 33, M 12, 2811.
321. Nikolau C., Thorn H. — «Trans. Farad. Soc.», 1959, 55,
1430.
322. BypcHaB H. P., Koran H. P., ^BBbiffOBa 3. A.— «KHHC-
THKa H icaxaJiKa*, 1967, 8, Bbin. 6, 1283.
323. fleMOHKa O. K. Hy-nt yMentiueHHa speAHOcra OTpa6oraBmHX
raaoa Kap6ropaxopHbix ABHrare^efl. HHHH ABTonpOK., cep. aBTOKoSiuie-
e. M., 1966.
- 158 -
-------
m.- ^24' ^!c«°lescu J' V" P°Pesc u A. L.—«Studii si cercctaride
Chimie», 1959, 1, p. 49.
325. E t o p o B M. M. — «floKJi. AH CCCP», 1961, 140, M° 2, cip. 401.
«„ „ njI*COBaJ*-M., KefcejiH JI. M. — «KHHerHKa H KBTajms*,
1965, 6, N»6, 1080.
327. HmaTOBa JI. A., XajiHKOua P. X. — «3K. npmui. cneKTpo-
cxonHH», 1966, 5, Ms 5, 642.
328. fl o Ji H « 3 e T. M., K o ji 6 a H o u c K H ft K>. A., n o ji a K JI. C. —
«KHH6THKa H KaTaJiHst, 1965, 6, 897.
329. BopecKOB T. K., flaucfcKO B. A.— «3K. 6 2, 87.
336. JlesHHa C., OpyMKRR A., Jlynes A. — «3K. $HS. XHM.»,
1936, 7, 664.
337. 4> p o c T A. B., JI a n n H K). n., M a n i. u e B A. II., K o 6 o-
ae B H. H. — «BecTH. Mry», 1946, Ms 1, 95.
338. IHexo6anoBaB. H., KpujioaaH. B., K o 6 o 3 e B H. H.-—
4HC. cpH3. XRM.», 1952, 26, M2 5, 703.
339. Manfcues A. H., Ko6o3es H. H. — «3K. $113. XHM.», 1955,
29, Htm. 2, 291, 142.
340. Ill e x o 6 a Ji O-B a B. H., K p u ji o B a H. B., K o 6 o 3 e B H. H. —
«3K. 6 6,
1025.
344. 3 ii m e H c P., IIJIHCKKH B. KaTaJins. HccjienosaHHe nosepx-
BOCTH KarajiHaaTopoB. M., HJI., 1960, crp. 22.
345. C e ji b B y fl II., BepHea^P., BflmeHcP. HoBMe Meioflbi
H3jrqesnfl rereporeHHoro KaTajmsa. M., HJI, 1963, crp. 80.
346. Rienficker G. — «Uber Tragerkatalyse*. Sitzungberichte
Dtsch. Acad. Wiss. Zu Berlin, Kl., Geol. Biol., 1964, M» 3.
347. BypcHan H. P., BoJifiyxHHa H. K.— «3K. HPHK«. XHM.».
1966, Ms4, 845.
348. MHHaieB X. M., JHyfiKHH H. H., EHHOTPBAOB B. A.—
4H3B. AH CCCP, OT«. XHM. HayK», 1958, M» 7, 866; MnnaieB X. M.,
HI y fi K H H H. H — «AOKJI. AH CCCP., 1954, 99, Ms 5, 1015; IUy«-
XHK H. H., MHHaies X. M., Ty jiy no BB E. fl., Eropoa K). n.—
«floiwi. AH CCCP», 1954, 99, Ms 6, 1211.
349. XaCHH A. B., BopecKOB T. K., Ciap o CT HH a T. C.—
B c6.: «MetOAH HccnefloBBHwa KaraJiHsaTopos H KaTajiiiTH^ecKnx peax-
», 1. HoBocH6npcK, H3ff. CO AH CCCP, 1965, 342.
350. BopTHep M. H., ITappaaaHO T. Karajias. Tpy»u IlepBoro-
Konrpecca. M., HJI, I960, crp. 480.
- 159 -
-------
351. M H p K ic H A. H. CnpaeoMHHK no peHTrenocTpyKTypHOMy
sy nojuiKpiicTajuioB. M., HSA. $ii3-MaT. JIHT., 1961.
352. S p e n a d e 1 B. G., B o u"~"d a r t M. — «J. Phys. Chem.», 1960,
64, J£ 2, 204.
353. KapnayxoB A. II. MeTOAbi iiccjieAOBamiH crpyKTypw BSICOKO-
AHcnepcHbix H nopiicrtix -ren. M., USA-BO AH CCCP, 1953, crp. 145.
354. Ill e x T e p A. B., EiencTona A. H., TpeTbflKOB H. H. —
4floKJi. AH CCCP», 1949, 68, J* 6, 1069.
355. C hu B. B. — «Z. Phys. Chem.», 1963, 67, J& 9, 1916.
356. I"p a 3 H o B B. M., H r o A o B c K H ii B. fl.. Ill n M y Ji n c B. H. —
«KiiHernKa n Kara^n3», 1961, 2, sun. 2, 221.
357. Hu K o n a e B A. B. — «floiwi. AH CCCP», 1938, 20, JJ° 7—8, 577.
358. BopecKOB T. K «3K. 6 2, 145.
360. K p bi Ji o B O. B., P o r H H c K H ii C. 3., T p e T b a K o B II. H. —
KJi. AH CCCP», 1953, 91, M« 6, 1353.
361. flaBTHH O. K. — «3K. $H3. XIIM.», 1964, 38, swn. 5, 1077.
362. A p H x C. M., M o p o 3 o B a M. n., P e H x a p A A. A. — «JK.
o6m. XHM.», 1953, 23. >6 9, 1455.
363. B r i g g s W. S., Stover W. A., W a r t h e n J. L. MBTOA
OMHCTKK BUXJIOHHUX FasoB. IlaT. CIIIA 3295918, kl. 23—2, 3. 1. 1967.
364. MaproJiHC JI. JI., TOABC O. M. — «floKa. AH CCCP», 1945,
N> 6, 519.
365. Kazuo Mitani, JoshioHarauo. — «Bull. Chem. Soc.
Japan*, 1960, 33, >6 2, 276.
366. AflaaypoB B. K, ^HABEKO II. fl. — «SC. npHK.i. XHM.»,
1935, J« 5, 823.
367. POTHHCKHfi C. 3. IIpo6jieMbI K1IH6THKH H KBTartHSa, 1940, 4
187.
368. K p BI JI O B 0. B., POTHHCKHH C. 3., TpCTbflKOB H. H. —
i. AH CCCP», 1953, 91, J6 6, 1353.
369. J!, o 6 w H H H fl. II., K Ji H 6 a H o B a U,. M. AjitoMocujiiiKaTHbie
KaxajiHsaTopbi. M., rocTonTexHSflar, 1952, 318.
370. BopecKOB r. K., ^ 3 H c b K o B. A., B o p c K o B a M. C.,
KpacHonojibCKan B. H. — <3K. 4>H3. XHM.», 1952, 26, van. 4.
371. Kp acH JIBHHKOB K. .r., KHcejies B. 4>., KanHraHO-
B a H. B., C u c o e B E. A. — «3K. $HS. XHM.», 1957, 31, BHH. 7, 1448.
372. KpacHAbHHKOB K. T., K H c e ^ e B B. 4>. — «IIpo6jieME>r KH-
aerHKH H KaTajiH3a>, 1960, 10, 421.
373. M a c a r y T o B P. M., r a x H M o B 3K. *., ^ y 6 n H H R a T. T.,
M o p o s o B B. . — B c6.: «MeTOflBi Hcc^eflosanHH KaTajiMsaropOB H ica-
TajiHTHiecKHx peaKUHii*, 2. HosociiGHpCK, Hsfl. CO AH CCCP, 1965, 202.
202.
374. K H c e Ji e B A. B., JleoHTbes E. A., JlyKbflHOBHi B. M.r
H H K H T H H K). C. — «3K. $H3. XHM.*, 1956, 30, Bbin. 10, 2149.
375. MoposoB B. *., MacaryTos P. M., fly6HHHHa T. T. —
B c6.: «MeTOAbi HccjieflOBanHH KaTajiiisaTOpoB H KaTajnmiHecKHx peaKiutii»,
2. HoBocH6HpCK, H3A- CO AH CCCP, 1965, 284.
376. AipaxacbeB B. A. — Asrope^epaT AHccepTai^HH. M., HH-T
opr. XHMHH AH CCCP, 1955.
377. Py6HHiiiTeftKA. M., A^aHacbesB. A. npn6op «Jia on-
peAejieHHH yAeJibHoft nosepXHOcnt KaTajinaaTopos B npoxoiHoft CHCTewe
npn BTMOCiJiepHOM flaBJienifH. nepeflOBOfr Hayino-npoiisB. OHUT. M., HH-T
RayHK. HH<{I. 1957. - 4
378. Py6HHinTefiH A. M., A$aHacbeB B. A.— «H3B. AH
CCCP, OTA. XHW. nayK», 1956, awn. 11, 1294.
- 160 -
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^cccp-
u «38°«By*HOBa H- E- ryAKoaa F. B., Kapnayxos A. II.—
B CO.: «Meroflij HC61, 159.
385. HOBHKOB C. C., Py6HHinTefiH A. M., ffiyftKHH H. H.—
iui. AH CCCP», 1948, 62, J* 3, 345.
386. EatejitHHOBa r. H., X a c a H C. — B c6.: ^erBeprwft MCJK-
apoAHtifi Konrpecc no KaTamray». M., 1968, 73 «oioiaR.
387. P. Baa XapAeaejiR, Xapxor *. —B c6.: «tIeTBeprHft
JteHCAynaposHMft Konrpecc no KarajiHsy*. M., 1968, 70 «OKJia«.
388. Sinfelt J., Hurwitz H., Rohres J.— «J. Phys. Chem.»,
1960, 64. >6 7, 892.
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Tpyflu BcecowsHoro Hayino-nccjiefl. H KOHCTpyxiopcKoro HH-Ta XIIM. Ma-
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46
THE SUSCEPTIBILITY OH RESISTANCE TO GAS
AND SMOKE OF VARIOUS ARBOREAL SPECIES
GROWN UNDER DIVERSE ENVIRONMENTAL
CONDITIONS IN A NUMBER OF INDUSTRIAL RE-
GIONS OF THE SOVIET UNtON-A Survey of USSR
Air Pollution Literature
METEOROLOGICAL AND CHEMICAL ASPECTS
OF AIR POLLUTION; PROPAGATION AND OIS
PERSAL OF AIR POLLUTANTS IN A NUMBER OF
AREAS IN THE SOVIET UNION-A Survey of USSR
Air Pollution Literature
48 THE AGRICULTURAL REGIONS OF CHINA
47
49
50.
51.
62
53
EFFECTS OF METEOROLOGICAL CONDITIONS
AND RELIEF ON AIR POLLUTION, AIR CON-
TAMINANTS - THEIR CONCENTRATION
TRANSPORT, AND DISPERSAL-A Survey of USSR
Air Pollution Literature
AIR POLLUTION IN RELATION TO CERTAIN
ATMOSPHERIC AND METO ROLOG I C A L
CONDITIONS AND SOME OF THE METHODS
EMPLOYED IN THE SURVEY AND ANALYSIS
OF AIR POLLUTANTS-A Survey of USSR Air
Pollution Literature
MEASUREMENTS OF DISPERSAL AND
CONCENTRATION, IDENTIFICATION. AND
SANITARY EVALUATION CF VARIOUS AIR
POLLUTANTS, WITH SPECIAL REFERENCE TO
THE ENVIRONS OF ELECTRIC POWER PLANTS
AND FERROUS METALLURGICAL PLANTS
-A Survey of USSR Air Pollution Literature
A COMPILATION OF TECHNICAL REPORTS ON
THE BIOLOGICAL EFFECTS AND THE PUBLIC
HEALTH ASPECTS OF ATMOSPHERIC
POLLUTANTS - A Survey of USSR Air Pollution
Litaratura
GAS RESISTANCE OF PLANTS WITH SPECIAL
REFERENCE TO PLANT BIOCHEMISTRY AND TO
THE EFFECTS OF MINERAL NUTRITION - A
Survey of USSR Air Polution Literature
THE TOXIC COMPONENTS OF AUTOMOBILE
EXHAUST GASES: THEIR COMPOSITION UNDER
DIFFERENT OPERATING CONDITIONS, AND
METHODS OF REDUCING THEIR EMISSION - A
Survey of USSR Air Pollution Literature
55 A SECOND COMPILATION OF TECHNICii-
REPORT" ON THE BIOLOGICAL EFFECTS AND
THE PUBLIC HEALTH ASPECTS OF
ATMOSPHERIC POLLUTANTS - « Survey of U33R
Air Pollution Literature
te TECHNICAL PAPERS FROM THE LENINGRAC
INTERNATIONAL SYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART I) - A Survey of USSR A.r
Pollution L,taratur»
57 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL SYMPOSIUM ON T^E
VETEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART II) - A Survey of USSR Air
Pollution Literature
58 TECHNICAL PAPERS FROM THE LENINGRAD
INTERNATIONAL AYMPOSIUM ON THE
METEOROLOGICAL ASPECTS OF ATMOSPHERIC
POLLUTION (PART III) - A Survey of USSR Air
Pollution Literature
59 A THIRD COMPILATION OF TECHNICAL
REPORTS ON THE BIOLOGICAL EFFECTS AND
THE PUBLIC HEALTH ASPECTS OF ATMOSPHER
1C .POLLUTANTS - A Survey of USSR Air Pollution
Literature
60 SOME BASIC PROPERTIES OF ASH AND INDUS-
TRIAL OUST IN RELATION TO THE PROBLEM
OF PURIFICATION OF STACK GASES - A Survey
of USSR Air Pollution Literature
(Volume XVII
61 A FOURTH COMPILATION OF TECHNICAL RE
PORTS ON THE BIOLOGICAL EFFECTS AND THE
PUBLIC HEALTH ASPECTS OF ATMOSPHERIC
POLLUTANTS A Survey of USSR Air Pollution
Literature
(Volume XVII)
62 PURIFICATION OF GASES THROUGH HIGH TEM-
PERATURE REMOVAL OF SULFUR COMPOUNDS
- A Survey of USSR Air Pollution Literature
(Volume XVIII)
63 ENVIRONMENTAL POLLUTION WITH SPECIAL
REFERENCE TO AIR POLLUTANTS AND TO
SOME OF THEIR BIOLOGICAL EFFECTS - A
Survey ol USSR Air Pollution Literature
(Volume XIX)
64 CATALYTIC PURIFICATION OF EXHAUST GASES
- A Survey of USSR Air Pollution Literature
(Volume XX)
Reprint* From various periodical!:
A INTERNATIONAL COOPERATION IN CROP IMPROVEMENT
THROUGH THE UTILIZATION OF THE CONCEPT C*
AGROCUMATIC ANALOGUES
(Tfce UK of Phenolegr, M*teorolooy and o»oropr«cal
latitude lof the rVrpoiesaf Plant Introduces* o^ fht t«-
cfxirve of l«¥»ved Ptcnr Vbri.Me, htween Vorioui
Countriet.)
I SOME WUMINARY OBSERVATIONS Of W«NOlO6ICAl
DATA AS A TOOL IN THE STUDY Of fHOTOrtRlOOIC
ANO THWMAL RCOUIRtMENTS Of VARIOUS PLANT
MATERIAL
•C AOROCtlMATOlOGY AND CHOP ECOLOGY Of THE
> UKRAINE AND CLIMATIC ANAIOGUES IN NORTH
AMttlCA
D AGRO-CHMATOIOGY ANO CROP ECOLOGY^C* •AlES-
TINE AND TRANWOROAN AND CLIMATIC ANA
lOGUIS IN TOt UNITED STATES
USSH-i>ni» "hytied on<» Agcitxlrwrcl Chamctaritilct of th*
DrojohtArea o-c in C irrct c Anologu« In 'tieUnlMdSMMi
TuE HOLE Of SIOCLIMATOLOGV IN ASRICUirWE WITH
SPECIAL RE^KENCE TO THE USE Of THE4MAI AND
PHOIO-TMERMAt ReQUIREMlNTS OF PU«E~UN£ VARI-
ETIES Of PLANTS AS A fioiociCAi. INDICATOR IN
ASCERTAINING CLIMATIC ANALOGUES (HOMO-
CLIMES)
•Oulof Pfi '
>«qu*it lot itutf 'tan Irttitve o« Cop Ecotegr, *0» Dele
Ofive, Silver Spring, Matytand 20910.
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