Oxidation catalyst compositions include a catalytic material containing ceria and alumina each having a surface area of at least about 10 m.sup.2 /g, for example, ceria and activated alumina in a weight ratio of from about 1.5:1 to 1:1.5. Optionally, platinum may be included in the catalytic material in amounts which are sufficient to promote gas phase oxidation of CO and HC but which are limited to preclude excessive oxidation of SO.sub.2 to SO.sub.3. Alternatively, palladium in any desired amount may be included in the catalytic material. The catalyst compositions have utility as oxidation catalysts for pollution abatement of exhausts contianing unburned fuel or oil. For example, the catalyst compositions may be used in a method to treat diesel engine exhaust by contacting the hot exhaust with the catalyst composition to promote the oxidation of the volatile organic fraction component of particulates in the exhaust.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a catalyst composition and method for the 
oxidation of oxidizeable components of a gas-borne stream, e.g., for the 
treatment of diesel engine exhaust, and more specifically to the treatment 
of such diesel exhaust to reduce the particulates content thereof. 
2. Background and Related Art 
As is well-known, gas-borne streams or engine exhausts often contain 
oxidizeable pollutants such as unburned fuel and vaporized or condensed 
oils. For example, diesel engine exhaust contains not only gaseous 
pollutants such as carbon monoxide ("CO") and unburned hydrocarbons 
("HC"), but also soot particles which, as described in more detail below, 
comprise both a dry carbonaceous fraction and a hydrocarbon liquid which 
is sometimes referred to as a volatile organic fraction ("VOF"), which 
terminology will be used herein, or a soluble organic fraction. 
Accordingly, although sometimes loosely referred to as an "exhaust gas", 
the exhaust of a diesel engine is actually a heterogeneous material, 
comprising gaseous, liquid and solid components. The VOF may exist in 
diesel exhaust either as a vapor or as an aerosol (fine droplets of liquid 
condensate) depending on the temperature of the diesel exhaust. 
Oxidation catalysts comprising a platinum group metal dispersed on a 
refractory metal oxide support are known for use in treating the exhaust 
of diesel engines in order to convert both HC and CO gaseous pollutants 
and particulates, i.e., soot particles, by catalyzing the oxidation of 
these pollutants to carbon dioxide and water. One problem faced in the 
treatment of diesel engine exhaust is presented by the presence of sulfur 
in diesel fuel. Upon combustion, sulfur forms sulfur dioxide and the 
oxidation catalyst catalyzes the SO.sub.2 to SO.sub.3 ("sulfates") with 
subsequent formation of sulfuric acid. The sulfates also react with 
activated alumina supports to form aluminum sulfates, which render 
activated alumina-containing catalysts inactive. In this regard, see U.S. 
Pat. No. 4,171,289 at column 1, line 39 et seq. Previous attempts to deal 
with the sulfation problem include the incorporation of large amounts of 
sulfate-resistant materials such as vanadium oxide into the support 
coating, or the use of alternative support materials such as 
.alpha.-alumina, silica and titania, which are sulfation-resistant 
materials. Further, as is known, the oxidation of SO.sub.2 to SO.sub.3 
also adds to the particulates in the exhaust by forming condensible sulfur 
compounds, such as sulfuric acid, which condense upon, and thereby add to, 
the mass of particulates. 
Generally, the prior art has attempted to deal with these problems by 
dispersing a suitable oxidation catalyst metal, such as one or more 
platinum group metals, upon a refractory metal oxide support which is 
resistant to sulfation. 
Examples of catalysts designed for the treatment of diesel exhaust fumes 
and soot include U.S. Pat. No. 4,849,399 to Joy et al dated Jul. 18, 1989. 
This Patent discloses catalytic composites which incorporate 
sulfur-resistant refractory inorganic oxides selected from the group 
consisting of titania, zirconia, and alumina treated with titania and/or 
zirconia (see column 6, lines 62-68). 
U.S. Pat. No. 4,759,918 to Homeier et al dated Jul. 26, 1988 discloses 
catalysts for the treatment of diesel exhaust fumes and soot which 
incorporate sulfur-resistant refractory inorganic oxides selected from a 
group which includes silica, alumina, and silica-alumina (see column 3, 
lines 16-27). 
SUMMARY OF THE INVENTION 
Generally, in accordance with the present invention, there is provided an 
oxidation catalyst composition and a method for oxidizing oxidizeable 
components of a gas-borne stream, e.g., for treating diesel engine exhaust 
in which at least a volatile organic fraction component (described below) 
of the diesel exhaust particulates is converted to innocuous materials, 
and in which gaseous HC and CO pollutants may also be similarly converted. 
The objectives of the invention are attained by an oxidation catalyst 
comprising a base metal oxide catalytic material consisting essentially of 
a mixture of high surface area ceria and high surface area alumina, which 
optionally may have dispersed thereon a low loading of platinum catalytic 
metal. The method of the invention is attained by flowing a gas-borne 
stream, e.g., a diesel engine exhaust, into contact under reaction 
conditions with a catalyst composition as described above. In the case of 
treating diesel exhaust, the exhaust may be contacted under reaction 
conditions with a catalyst composition which contains palladium instead of 
a low loading of platinum but is otherwise as described above. 
Specifically, in accordance with the present invention there is provided an 
oxidation catalyst composition which comprises a refractory carrier on 
which is disposed a coating of a ceria-alumina catalytic material 
consisting essentially of a combination of ceria and alumina each having a 
BET surface area of at least about 10 m.sup.2 /g, preferably the alumina 
having a surface area of from about 25 m.sup.2 /g to 200 m.sup.2 /g and 
the ceria having a surface area of from about 25 m.sup.2 /g to 200 m.sup.2 
/g. 
In one embodiment of the invention, the ceria and alumina each comprises 
from about 5 to 95 percent, preferably from about 10 to 90 percent, more 
preferably from about 40 to 60 percent, by weight of the combination. 
One aspect of the invention provides that the catalyst composition 
optionally further comprises a catalytically effective amount of platinum 
dispersed on the catalytic material in an amount not to exceed about 15 
g/ft.sup.3 of the catalyst composition. For example, the platinum may be 
present in the amount of from about 0.1 to 15 g/ft.sup.3 of the 
composition, preferably from about 0.1 to 5 g/ft.sup.3 of the composition. 
When the catalyst composition includes platinum, another aspect of the 
invention provides that at least a catalytically-effective amount of the 
platinum is dispersed on the ceria. At least a catalytically effective 
amount of the platinum may also be dispersed on the alumina. Such 
dispersal of the platinum may be utilized whether the alumina and ceria 
are mixed in a single layer or are present in discrete layers of, 
respectively, ceria and alumina and, in the latter case, irrespective of 
which of the two layers is the top layer. 
Still another aspect of the invention provides that the ceria comprises an 
aluminum-stabilized ceria. The alumina may also be stabilized against 
thermal degradation. 
The ceria and alumina may be combined as a mixture and the mixture 
deposited as a single layer coating on the refractory carrier, or the 
ceria and alumina may be present in respective discrete superimposed 
layers of ceria and alumina. The ceria layer may be above or below the 
alumina layer. 
In accordance with the method of the present invention, there is provided a 
method of treating diesel engine exhaust containing a volatile organic 
fraction. The method includes contacting the exhaust with a catalyst 
composition comprised of components as described above or with a catalyst 
composition comprised of components as described above but which 
optionally includes palladium instead of the optional platinum. Thus, the 
method includes contacting the gas-borne stream to be treated with a 
catalyst composition comprising ceria and alumina as described above, and 
optionally including platinum or palladium. When the optional palladium is 
employed in the composition, it may be present in the amount from about 
0.1 to 200 g/ft.sup.3, preferably in the amount of from about 20 to 120 
g/ft.sup.3, of the catalyst composition. In accordance with the method of 
the present invention, contacting of the diesel exhaust with the catalyst 
composition is carried out at a temperature high enough to catalyze 
oxidation of at least some of the volatile organic fraction of the 
exhaust, for example, an inlet temperature of from about 100.degree. C. to 
800.degree. C. 
DEFINITIONS 
As used herein and in the claims, the following terms shall have the 
indicated meanings. 
The term "gas-borne stream" means a gaseous stream which may contain 
non-gaseous components such as solid particulates and/or vapors, liquid 
mist or droplets, and/or solid particulates wetted by a liquid. 
The term "BET surface area" has its usual meaning of referring to the 
Brunauer, Emmett, Teller method for determining surface area by N.sub.2 
adsorption. Unless otherwise specifically stated, all references herein to 
the surface area of a ceria, alumina or other component refer to the BET 
surface area. 
The term "activated alumina" has its usual meaning of a high BET surface 
area alumina, comprising primarily one or more of .gamma.-, .THETA.- and 
.delta.-aluminas (gamma, theta and delta). 
The term "catalytically effective amount" means that the amount of material 
present is sufficient to affect the rate of reaction of the oxidation of 
pollutants in the exhaust being treated. 
The term "inlet temperature" shall mean the temperature of the exhaust, 
test gas or other stream being treated immediately prior to initial 
contact of the exhaust, test gas or other stream with the catalyst 
composition. 
The term "ceria-alumina catalytic material" means a combination of ceria 
particles and alumina particles each having a BET surface area of at least 
about 10 m.sup.2 /g, i.e., a combination of high surface area bulk ceria 
and high surface area bulk alumina, sometimes referred to as "activated 
alumina". 
The term "combination" when used with reference to a combination of ceria 
and alumina includes combinations attained by mixtures or blends of ceria 
and alumina as well as superimposed discrete layers of ceria and alumina. 
The term "aluminum-stabilized ceria" means ceria which has been stabilized 
against thermal degradation by incorporation therein of an aluminum 
compound. A suitable technique is shown in U.S. Pat. No. 4,714,694 of C. 
Z. Wan et al (the disclosure of which is incorporated by reference 
herein), in which ceria particles are impregnated with a liquid dispersion 
of an aluminum compound, e.g., an aqueous solution of a soluble aluminum 
compound such as aluminum nitrate, aluminum chloride, aluminum 
oxychloride, aluminum acetate, etc. After drying and calcining the 
impregnated ceria in air at a temperature of, e.g., from about 300.degree. 
C. to 600.degree. C. for a period of 1/2 to 2 hours, the aluminum compound 
impregnated into the ceria particles is converted into an effective 
thermal stabilizer for the ceria. The term "aluminum-stabilized" is used 
for economy of expression although the aluminum is probably present in the 
ceria as a compound, presumably alumina, and not as elemental aluminum. 
Reference herein or in the claims to ceria or alumina being in "bulk" form 
means that the ceria or alumina is present as discrete particles (which 
may be, and usually are, of very small size, e.g., 10 to 20 microns in 
diameter or even smaller) as opposed to having been dispersed in solution 
form into another component. For example, the thermal stabilization of 
ceria particles (bulk ceria) with alumina as described above with respect 
to U.S. Pat. No. 4,714,694 results in the alumina being dispersed into the 
ceria particles and does not provide the dispersed alumina in "bulk" form, 
i.e., as discrete particles of alumina. 
The abbreviation "TGA" stands for thermogravimetric analysis which is 
measure of the weight change (e.g., loss) of a sample as a function of 
temperature and/or time. The abbreviation "DTA" stands for differential 
thermal analysis which is measure of the amount of heat emitted (exotherm) 
or absorbed (endotherm) by a sample as a function of temperature and/or 
time.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF 
The present invention provides an oxidation catalyst composition which is 
effective for oxidizing oxidizeable components of a gas-borne stream, for 
example, for treating diesel engine exhaust. In the latter case, the 
composition is particularly effective with regard to reducing the total 
particulates in the exhaust. The carbonaceous particulates ("soot") 
component of diesel engine exhaust is, as is well-known, comprised of two 
major components. One component is relatively dry carbonaceous particles 
and the other, usually referred to as a volatile organic fraction ("VOF"), 
is a mixture of high molecular weight hydrocarbons comprised of unburned 
and partially burned diesel fuel and lubricating oil. The volatile organic 
fraction is present in the diesel exhaust as either a vapor phase or a 
liquid phase, or both, depending on the temperature of the exhaust. 
Generally, it is not feasible to attempt to remove or treat the dry, solid 
carbonaceous particulates component of the total particulates by catalytic 
treatment, and it is the VOF component which can be most effectively 
removed by conversion via utilization of an oxidation catalyst. Therefore, 
in order to reduce the total particulates discharged so as to meet present 
and impending Government regulations concerning maximum allowable total 
particulates, the volatile organic fraction, or at least a portion 
thereof, is oxidized to innocuous CO.sub.2 and H.sub.2 O by being 
contacted with an oxidation catalyst under suitable reaction conditions. 
The required U.S. Government limits for 1991 l on HC, CO, nitrogen oxides 
("NO.sub.x ") and total particulate emissions ("TPM") in diesel engine 
exhaust have been largely met by suitable engine design modifications. For 
1994 the HC, CO and NO.sub.x limits remain unchanged from 1991 standards 
but the upper limit on TPM will be reduced from the 1991 level of 0.25 
grams per horsepower-hour ("g/HP-hr") to 0.10 g/HP-hr. Although the 
oxidation catalysts of the present invention, when employed as a diesel 
exhaust treatment catalyst, are primarily concerned with effectuating a 
reduction in total particulates, they are also capable, with the optional 
addition of platinum in limited amounts of providing the added advantage 
of also oxidizing a portion of the HC and CO contained in the gaseous 
component of the diesel engine exhaust without promoting excessive 
oxidation of SO.sub.2 to SO.sub.3. The oxidation catalysts of the present 
invention avoid or reduce the unwanted side effect of promoting the 
oxidation of SO.sub.2 to SO.sub.3 which, as noted above, contributes to 
the particulates problem because the condensation of sulfuric acid and 
other sulfate condensibles which accumulate on, and add to, the mass of 
the particulates in the exhaust. 
However, the oxidation catalysts of the present invention have utility for 
uses other than the treatment of diesel engine exhaust. Generally, the 
catalysts of the present invention are useful for oxidation of gas-borne 
oxidizeable components in engine exhausts generally, such as any 
application in which lubricating oils are discharged, e.g., the exhaust of 
compressed natural gas engines, ethanol-fueled engines, compressors, gas 
turbines, etc. Many alternate-fueled engines such as compressed natural 
gas engines are built on diesel engine carcasses and therefore inherently 
discharge significant quantities of lubricating oil. 
In accordance with the teachings of the present invention it has been 
found, surprisingly, that the beneficial effect of oxidizing pollutants 
generally, and in particular of reducing diesel exhaust particulates 
emissions by oxidation of the volatile organic fraction thereof, can be 
attained by a mixture of high surface area, i.e., activated, alumina and a 
high surface area ceria, each having a BET surface area of 10 m.sup.2 /g 
or higher. For purposes of illustration, the benefits of the present 
invention will be described in detail below with respect to the treatment 
of diesel engine exhaust. The basic and novel characteristics of the 
present invention are believed to reside in the use of the defined 
combination of ceria and alumina as an oxidation catalyst without the 
addition of metal catalytic components thereto, except as specifically 
otherwise defined in certain dependent claims. Preferably, the bulk ceria 
and the bulk alumina will each have a surface area of at least about 10 
m.sup.2 /g, preferably at least about 20 m.sup.2 /g. For example, the bulk 
alumina may have a surface area of from about 120 to 180 m.sup.2 /g and 
the bulk ceria may have a surface area of from about 70 to 150 m.sup.2 /g. 
The fact that a catalyst composition which can serve as a diesel oxidation 
catalyst and which contains activated alumina as a major component thereof 
has proven to be successful is in itself surprising, in view of the 
consensus of the prior art that alumina, if used at all in diesel 
oxidation catalysts, must be a low surface area alumina (.alpha.-alumina) 
and/or be used in conjunction with sulfate-resistant refractory metal 
oxides such as zirconia, titania or silica. It has nonetheless been found 
that, in accordance with the present invention, surprisingly, a 
combination of high surface area alumina and a high surface area ceria 
provides a catalytic material which effectively catalyzes the oxidation of 
the volatile organic fraction so as to provide a significant reduction in 
total particulates in diesel engine exhaust and exhibits good durability, 
that is, long life, both in laboratory and diesel engine tests. It should 
be noted that the prior art generally considers refractory base metal 
oxides used in diesel oxidation catalysts to be merely supports for the 
dispersal thereon of catalytically active metals such as platinum group 
metals. In contrast, the present invention teaches that a ceria-alumina 
catalytic material comprising essentially only ceria and alumina of 
sufficiently high surface area (10 m.sup.2 /g or higher), dispersed on a 
suitable carrier, provides a durable and effective diesel oxidation 
catalyst. 
It has further been found that beneficial effects are attained by the 
optional incorporation of platinum in the catalyst composition, provided 
that the platinum is present at loadings much lower than those 
conventionally used in oxidation catalysts. It has been discovered that, 
most surprisingly, a limited quantity of platinum in the catalyst 
composition actually reduces the undesirable oxidation of SO.sub.2 to 
SO.sub.3 relative to that encountered by using the ceria-alumina catalytic 
material alone, while nonetheless promoting some oxidation of CO and HC 
gaseous components of the diesel exhaust. The suppression of the oxidation 
of SO.sub.2 to SO.sub.3 by the addition of low loadings of platinum is a 
very surprising finding, given the powerful catalytic activity of platinum 
in promoting oxidation reactions generally. Without wishing to be bound by 
any particular theory, it may be that the presence of a low loading of 
platinum on the ceria occupies some catalytic sites on the ceria, thereby 
moderating the tendency of ceria to promote the oxidation of SO.sub.2 to 
SO.sub.3. If the catalytic metal platinum is added to the catalytic 
composition, it serves to catalyze the oxidation of gas phase HC and CO 
pollutants as an added benefit. However, such catalytic metal is not 
needed to supplement the action of the ceria-alumina catalytic material in 
reducing total particulate emissions. The platinum catalytic metal does 
not appear to play a role in controlling particulates, as indicated by 
data discussed elsewhere herein, which show that the quantity of platinum 
utilized does not significantly affect the rate of particulates 
conversion. 
The catalysts of the present invention may take the form of a carrier or 
substrate, such as a monolithic "honeycomb" structure (a body having a 
plurality of gas flow passages extending therethrough), on which is 
applied a coating of the catalytic material comprising a mixture of high 
surface area ceria and alumina and, optionally, a low loading platinum. As 
discussed below, discrete coatings of the ceria and alumina may be 
employed. 
The Carrier (Substrate) 
The carrier used in this invention should be relatively inert with respect 
to the catalytic composition dispersed thereon. The preferred carriers are 
comprised of ceramic-like materials such as cordierite, .alpha.-alumina, 
silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia or 
zirconium silicate, or of refractory metals such as stainless steel. The 
carriers are preferably of the type sometimes referred to as honeycomb or 
monolithic carriers, comprising a unitary cylindrical body having a 
plurality of fine, substantially parallel gas flow passages extending 
therethrough and connecting both end-faces of the carrier to provide a 
"flow-through" type of carrier. Such monolithic carriers may contain up to 
about 700 or more flow channels ("cells") per square inch of cross 
section, although far fewer may be used. For example, the carrier may have 
from about 7 to 600, more usually from about 200 to 400, cells per square 
inch ("cpsi"). 
While this discussion and the following examples relate to flow-through 
type carrier substrates, wall-flow carriers (filters) may also be used. 
Wall-flow carriers are generally similar in structure to flow-through 
carriers, with the distinction that each channel is blocked at one end of 
the carrier body, with alternate channels blocked at opposite end-faces. 
Wall-flow carrier substrates and the support coatings deposited thereon 
are necessarily porous, as the exhaust must pass through the walls of the 
carrier in order to exit the carrier structure. 
The Catalytic Material 
The ceria-alumina catalytic material may be prepared in the form of an 
aqueous slurry of ceria and alumina particles, the particles optionally 
being impregnated with the platinum catalytic metal component if one is to 
be utilized. The slurry is then applied to the carrier, dried and calcined 
to form a catalytic material coating ("washcoat") thereon. Typically, the 
ceria and alumina particles are mixed with water and an acidifier such as 
acetic acid, nitric acid or sulfuric acid, and ball milled to a desired 
particle size. 
The optional platinum catalytic metal component is, when used, preferably 
incorporated into the ceria particles or into the ceria and alumina 
particles. In such case, the ceria-alumina acts not only as a catalyst but 
also as a support for the optional platinum catalytic metal component. 
Such incorporation may be carried out after the ceria-alumina catalytic 
material is coated as a washcoat onto a suitable carrier, by impregnating 
the coated carrier with a solution of a suitable platinum compound, 
followed by drying and calcination. However, preferably, the ceria 
particles or both the ceria and alumina particles are impregnated with a 
suitable platinum compound before a coating of the ceria-alumina catalytic 
material is applied to the carrier. In either case, the optional platinum 
metal may be added to the ceria-alumina catalytic material as, e.g., a 
solution of a soluble platinum compound, the solution serving to 
impregnate the ceria and alumina particles (or the ceria-alumina coating 
on the carrier), which may then be dried and the platinum fixed thereon. 
Fixing may be carried out by calcination or by treatment with hydrogen 
sulfide or by other known means, to render the metal in water-insoluble 
form. 
Generally, the slurry of ceria and activated alumina particles, whether or 
not impregnated with the platinum compound solution, will be deposited 
upon the carrier substrate and dried and calcined to adhere the catalytic 
material to the carrier and, when the platinum compound is present, to 
revert the platinum compound to the elemental metal or its oxide. Suitable 
platinum compounds for use in the foregoing process include potassium 
platinum chloride, ammonium platinum thiocyanate, amine-solubilized 
platinum hydroxide and chloroplatinic acid, as is well-known in the art. 
During calcination, or at least during the initial phase of use of the 
catalyst, such compounds, if present, are converted into the catalytically 
active elemental platinum metal or its oxide. 
When the catalytic material is applied as a thin coating to a suitable 
carrier, such as described above, the proportions of ingredients are 
conventionally expressed as weight of material per unit volume of 
catalyst, as this measure accommodates the presence of different sizes of 
catalyst composition voids provided by different carrier wall thicknesses, 
gas flow passages, etc. Grams per cubic inch ("g/in.sup.3 ") units are 
used to express the quantity of relatively plentiful components such as 
the ceria-alumina catalytic material, and grams per cubic foot 
("g/ft.sup.3 ") units are used to express the quantity of the sparsely 
used ingredients, such as the platinum metal. For typical diesel exhaust 
applications, the ceria-alumina catalytic material of the present 
invention generally may comprise from about 0.25 to about 4.0 g/in.sup.3, 
preferably from about 0.25 to about 3.0 g/in.sup.3 of the coated carrier 
substrate, optionally including from about 0 to 25, preferably from about 
0 to 15 g/ft.sup.3 of platinum. 
Without wishing to be bound by a particular theory, applicants offer the 
following hypothesis to explain the superior performance, when used to 
treat diesel engine exhaust, of the ceria-alumina catalytic materials 
according to this invention. It is believed that diesel exhaust contains a 
significant proportion of gases or vapors which are close to their dew 
point, i.e., close to condensing to a liquid, and thereby adding to the 
VOF portion of the particulates at the conditions obtaining in the exhaust 
pipe. These "potential particulates" condense in the ceria-alumina 
catalytic materials, their condensation being enhanced by a capillary 
condensation effect, a known phenomenon in which a capillary-like action 
facilitates condensation of oil vapors to liquid phase. The small pore 
size of the high surface area ceria-alumina catalytic material is believed 
to provide such capillary condensation action for the VOF. Generally, the 
higher the surface area of the ceria and alumina, the smaller is their 
pore size. As the exhaust temperature increases during increased work 
loads imposed on the diesel engine, the condensed hydrocarbon liquids 
(condensed VOF) are desorbed from the ceria-alumina catalytic material and 
volatilize, at which time the catalytic effect of the ceria-alumina 
catalytic material, which provides numerous acidic sites, is believed to 
enhance cracking and gas phase oxidation, i.e., combustion, of the 
desorbed, re-volatilized hydrocarbon (VOF) vapors. Even if a proportion of 
the vapors re-volatilized from the condensate is not combusted, the 
cracking of heavy VOF components to lighter hydrocarbons reduces the total 
amount of condensibles, so that the total particulates output from the 
diesel engine is concomitantly further reduced. In this latter regard, the 
ceria-alumina catalytic material is believed to act as a trap and a 
storage medium for condensed or condensible VOF during relatively cool 
phases of the exhaust, and releases the cracked VOF only upon 
re-volatilization thereof during relatively hot phases. The porous nature 
of the ceria-alumina catalytic material is also believed to promote rapid 
diffusion of the VOF throughout the washcoat structure, thereby 
facilitating relatively low temperature gasification and oxidation of the 
VOF upon increases in temperature of the catalyst during higher engine 
load (and therefore increased exhaust gas temperature) cycles. Data on 
aging show that the presence of sulfates does not significantly adversely 
affect the capacity of the ceria-alumina catalytic material to reduce 
particulate emissions. 
Generally, other ingredients may be added to the catalyst composition of 
the present invention such as conventional thermal stabilizers for the 
alumina, e.g., rare earth metal oxides such as ceria. Thermal 
stabilization of high surface area ceria and alumina to militate against 
phase conversion to less catalytically effective low surface area forms is 
well-known in the art although thermal stabilization of alumina is not 
usually needed for diesel exhaust service. Such thermal stabilizers may be 
incorporated into the bulk ceria or into the bulk activated alumina, by 
impregnating the ceria (or alumina) particles with, e.g., a solution of a 
soluble compound of the stabilizer metal, for example, an aluminum nitrate 
solution in the case of stabilizing bulk ceria. Such impregnation is then 
followed by drying and calcining the impregnated ceria particles to 
convert the aluminum nitrate impregnated therein into alumina. 
In addition, the catalyst compositions of the invention may contain other 
catalytic ingredients such as other base metal promoters or the like. 
However, in one embodiment, the catalyst composition of the present 
invention consists essentially only of the high surface area ceria and 
high surface area alumina, preferably present in a weight proportion of 
1.5:1 to 1:1.5, with or without thermal stabilizers impregnated therein, 
and, optionally, limited amounts of platinum. With respect to the method 
aspect of the invention, the use of palladium in place of platinum is 
contemplated. 
Examples and Data 
A catalyst composition in accordance with one embodiment of the invention, 
in which an optional alumina undercoat is provided beneath a coating of 
the ceria-alumina catalytic material having a platinum metal dispersed 
thereon, was prepared as follows. 
Example 1 
A. An activated alumina undercoat slurry is prepared by combining 1000 
grams of activated alumina having a nominal BET surface area of 150 
m.sup.2 /g with 50 cubic centimeters ("cc") of glacial acetic acid and 1 
cc of an anti-foamant sold under the trademark NOPCO NXZ in 1000 cc of 
deionized water. The ingredients are ball milled until an average particle 
size of at least 90 percent by volume of the particles having a diameter 
of not greater than 12 microns is attained. Cylindrical carriers 
comprising cordierite cylinders 6 inches long by 6 inches in diameter and 
having 400 gas flow passages per square inch of end face area (400 cpsi) 
are dipped into the slurry, excess slurry is blown from the gas flow 
passages and the slurry-coated carriers are dried at 110.degree. C. and 
then calcined in air at 450.degree. C. for 1 hour to provide 
alumina-coated carriers. 
B. The ceria-alumina catalytic material is prepared by utilizing 1050 grams 
of the same activated alumina as used in Part A and 900 grams of 
aluminum-stabilized ceria having a BET surface area of 164 m.sup.2 /g. The 
aluminum-stabilized ceria is attained by impregnating the ceria particles 
with a solution of an aluminum compound such as aluminum nitrate followed 
by calcining, to provide an aluminum content in the ceria of 1.35 weight 
percent aluminum, based on the total weight of ceria with the weight of 
aluminum calculated as the metal. Presumably, the aluminum is present as 
alumina. One such method of preparing an aluminum-stabilized ceria is 
shown in U.S. Pat. No. 4,714,694 issued Dec. 22, 1981 to C. Z. Wan et al, 
the disclosure of which, as noted above, is incorporated by reference 
herein. As is well-known, high surface area refractory oxides such as 
ceria are subject to loss of surface area and consequent reduction in 
catalytic efficiency upon prolonged exposure to high temperatures and 
other conditions of treating diesel exhausts. 
Aluminum-stabilized ceria is more resistant to such thermal degradation 
than is unstabilized ceria. As is also well-known, alumina may also be 
thermally stabilized, usually by a similar impregnation of the alumina 
with precursors of rare earth metal oxides such as ceria. However, thermal 
stabilization of the alumina is usually not necessary for the temperatures 
encountered in treating diesel engine exhaust. The high surface area ceria 
and high surface area alumina particles are placed in separate ball mills. 
A quantity of an amine-solubilized platinum hydroxide solution containing 
0.2894 grams of platinum, a quantity of monoethanolamine ("MEA"), 97.5 cc 
of glacial acetic acid, 2.0 cc of an anti-foamant sold under the trademark 
NOPCO NXZ and about 1950 cc of deionized water are employed. About 
one-half the water and sufficient MEA to adjust the pH to at least about 7 
are placed in the ball mill containing the alumina which is milled to 
thoroughly blend the ingredients. Then, one-half of the platinum solution 
is added and ball milling is continued for about 5 minutes. Thereafter, 
about one-half the glacial acetic acid and anti-foamant are added and 
milling is continued until a particle size of at least about 90 percent by 
weight of the particles having a diameter of less than about 12 microns is 
attained. The same process is separately repeated with the 
aluminum-stabilized ceria, except that MEA is not employed, including ball 
milling for mixing and to attain the same particle size of the ceria 
particles. The alumina and ceria slurries are then blended together to 
form a slurry of alumina and ceria particles containing a platinum 
compound. The alumina-coated carrier obtained in Part A of this Example 1 
is dipped into the blended slurry, excess slurry is blown from the gas 
flow passages of the carrier, and the coated carrier is then dried and 
calcined in air at 450.degree. C. to provide a finished catalyst 
containing a coating of a ceria-alumina catalytic material having about 
0.5 g/ft.sup.3 of platinum dispersed thereon. The catalytic material 
coating, sometimes referred to as a washcoat, inclusive of the platinum 
content, comprises about 1.95 g/in.sup.3 of the catalyst composition, the 
catalytic material overlying an alumina undercoat which comprises about 
1.00 g/in.sup.3 of the catalyst composition. Unless otherwise specified, 
catalyst samples in accordance with the present invention in subsequent 
Examples have the same type and loading of alumina undercoat and 
ceria-alumina catalytic material as a topcoat overlying the undercoat. 
Reference in the following TABLES, or elsewhere in this application, to a 
percentage conversion of constituents (rendered as "%C" in the TABLES) of 
the exhaust or test gas, means the percentage of such constituent 
initially present in the exhaust or test gas being treated which is 
converted to another species, e.g., the conversion to H.sub.2 O and/or 
CO.sub.2 of HC, CO and VOF, and the oxidation to SO.sub.3 of SO.sub.2. 
Thus, if an exhaust contains 10 volume percent CO and treatment of the 
exhaust results in an outlet gas containing 6 volume percent CO, a 40 
percent conversion of the CO has been attained. Reference in the following 
Examples, or elsewhere in this application, to "space velocity" means the 
flow rate of exhaust or test gas flowed through a catalyst, expressed as 
volumes of exhaust or test gas per volume of catalyst per hour, calculated 
with the exhaust or test gas at standard conditions of temperature and 
pressure. 
Example 2 
A series of sample catalysts was prepared generally in accordance with the 
procedures of Example 1 to provide a series of five otherwise identical 
compositions containing a ceria-alumina catalytic material in accordance 
with the teachings of the present invention, having various amounts of 
platinum dispersed thereon, including 0, 0.5, 1.0, 2.0 and 5.0 g/ft.sup.3 
of platinum. These catalyst samples comprised cores measuring 1.5 inches 
in diameter and 3.0 inches in length, cut from cordierite carriers 6 
inches long and 6 inches in diameter, used, as in Example 1, to make the 
catalysts of this Example 2. The resulting 400 cpsi cordierite sample 
cores contained a loading of 1.95 g/in.sup.3 of the ceria-alumina 
catalytic material overlying an alumina undercoat present in the amount of 
1.00 g/in.sup.3, in addition to the specified loading of platinum metal 
dispersed on the ceria-alumina catalytic material. The test catalysts were 
aged for 10 hours at 500.degree. C. by having a mixture of 10 percent 
steam in air flowed through them. A test gas was contacted with each of 
these aged catalysts in a series of tests at a space velocity of 50,000 
and inlet temperature of, respectively, 275.degree. C., 350.degree. C., 
425.degree. C. and 500.degree. C. The test gas had a composition of 10 
percent steam, 10 percent oxygen, 4.5 percent CO.sub.2, 1000 ppm NO, 28.6 
ppm heptane, 200 ppm CO, 50 ppm SO.sub.2, balance nitrogen. All percents 
are volume percent and "ppm" means parts per million by volume. 
Measurements were taken to determine the amount of oxidation of SO.sub.2 
to SO.sub.3. The results of these tests are tabulated in TABLE I below and 
plotted in FIG. 1. 
TABLE I 
______________________________________ 
Inlet Gas 
Platinum % C.sup.a % C.sup.a 
% C.sup.a 
Temp. (.degree.C.) 
Loading (g/ft.sup.3) 
SO.sub.2 HC CO 
______________________________________ 
275 0 8.0 0.0 0.0 
275 0.5 0.0 2.4 30.5 
275 1.0 6.1 0.0 74.6 
275 2.0 16.0 10.0 99.0 
275 5.0 30.6 20.2 99.5 
350 0 8.0 0.0 5.9 
350 0.5 4.0 9.8 68.3 
350 1.0 17.6 31.7 97.9 
350 2.0 21.6 87.8 100 
350 5.0 30.0 83.1 100 
425 0 12.0 2.6 10.3 
425 0.5 11.8 31.6 84.3 
425 1.0 25.5 66.6 96.4 
425 2.0 33.3 90.5 100 
425 5.0 48.0 91.9 100 
500 0 20.0 9.3 9.3 
500 0.5 12.0 47.4 84.8 
500 1.0 28.8 80.5 98.5 
500 2.0 35.3 83.1 99.5 
500 5.0 62.0 88.0 100 
______________________________________ 
.sup.a "% C" means the percentage conversion of the indicated constituent 
The data of TABLE I, and the plot thereof in FIG. 1, clearly show that the 
ceria-alumina catalytic material containing no platinum in each case 
provided, at each temperature level tested, a somewhat higher degree of 
conversion of SO.sub.2 to SO.sub.3 than did the otherwise identical 
ceria-alumina catalyst containing 0.5 g/ft.sup.3 of platinum. As the 
platinum loading was increased to 1.0 g/ft.sup.3, at each temperature 
level, the degree of undesired conversion of SO.sub.2 to SO.sub.3 
increased as compared to the versions containing no or only 0.5 
g/ft.sup.3. Further increases in platinum loading to 2 and 5 g/ft.sup.3 
further increased, as one would expect, the oxidation of SO.sub.2. What is 
very surprising is the fact, clearly shown in FIG. 1 and the data of TABLE 
I, that the ceria-alumina catalytic material containing 0.5 g/ft.sup.3 of 
platinum dispersed thereon demonstrated less conversion of SO.sub.2 to 
SO.sub.3 than did the ceria-alumina catalytic material containing no 
platinum metal thereon. As noted above, it is believed that the presence 
of a low loading of platinum on the ceria may occupy some catalytic sites 
which otherwise are highly effective in promoting the oxidation of 
SO.sub.2 to SO.sub.3. 
FIG. 2 shows the corresponding conversion of hydrocarbons in the test gas 
at the various temperature levels tested. The HC and CO conversion data of 
TABLE I, and the plot of the HC conversion data of TABLE I in FIG. 2, show 
the expected result that as the content of platinum metal increases the 
degree of conversion of HC and CO likewise increases. As discussed 
elsewhere herein, because of successful modifications in diesel engine 
design, catalytic treatment of diesel exhaust may not be necessary in 
order to attain reductions in HC and CO to meet U.S. Government standards, 
because the modified engines have reduced the output of HC and CO to below 
that of the current and impending U.S. Government standards. Nonetheless, 
the inclusion of platinum, at least at a loading of not more than about 1 
g/ft.sup.3, preferably at from about 0.1 to 0.8 g/ft.sup.3, more 
preferably at about 0.5 g/ft.sup.3 is seen to have a beneficial effect on 
reducing the amount of oxidation of SO.sub.2 to SO.sub.3. Thus limited, 
the addition of platinum is seen to reduce SO.sub.2 oxidation and thereby 
ameliorate particulates emissions. The addition of platinum also provides 
a beneficial added effect of further reducing HC and CO emissions. 
It will be appreciated that in some cases it may be desired or necessary to 
significantly reduce HC and/or CO emissions and, in order to do so, the 
addition of moderate amounts of platinum, not more than 15 g/ft.sup.3 
preferably not more than 5 g/ft.sup.3, and most preferably not more than 2 
g/ft.sup.3, may be desirable despite the concomitant increase in SO.sub.2 
oxidation at additions of significantly more than 0.5 g/ft.sup.3. 
Example 3 
A series of test catalysts was prepared generally in accordance with the 
procedure outlined in Example 1 to provide three samples, each comprising 
an alumina undercoat at a loading of 1.0 g/in.sup.3 upon which was coated 
a topcoat layer comprised of a ceria-alumina catalytic material containing 
ceria and alumina in proportions of 46.2 weight percent 
aluminum-stabilized ceria and 53.8 weight percent alumina, and having 
dispersed thereon 0.5 g/ft.sup.3 of platinum. The ceria-alumina topcoat 
layer was present in the amount of 1.95 g/in.sup.3. The ceria had a 
surface area of about 164 m.sup.2 /g and the alumina had a surface area of 
about 150 m.sup.2 /g. One sample, designated S-3Ce, has the platinum 
dispersed only on the ceria component of the catalytic material, a second 
sample designated S-3 has equal amounts of the platinum dispersed on the 
ceria and the alumina components of the ceria-alumina catalytic material, 
and the third sample, designated S-3A1, has the platinum disposed entirely 
on the alumina component of the ceria-alumina catalytic material. The 
three catalyst samples were then tested for HC, CO and SO.sub.2 conversion 
at 350.degree. C. and a space velocity of 90,000. The results are shown in 
TABLE II below. 
TABLE II 
______________________________________ 
% C.sup.a % C.sup.a 
% C.sup.a 
Sample CO HC SO.sub.2 
______________________________________ 
S-3Ce 80.2 37.5 4.1 
S-3 49.3 7.55 4.6 
S-3Al 94.9 56.5 8.0 
______________________________________ 
.sup.a "% C" means the percentage conversion of the indicated constituent 
The data of TABLE II clearly indicate that the platinum is a more effective 
oxidation catalyst for HC and CO when dispersed on the alumina (S-3A1) as 
compared to when it is dispersed on the ceria (S-3Ce) and is much more 
effective in this regard than is the S-3 sample, wherein the platinum is 
dispersed equally on each of the ceria and alumina components. Overall, 
the best results were obtained with the S-3Ce sample in which fairly high 
levels of desired conversion of CO and HC were attained and the lowest 
level (4.1%) of the undesired oxidation of SO.sub.2 to SO.sub.3 was also 
attained. S-3 catalyst provided significant, but lesser, conversions of CO 
and HC and only slightly more (4.6%) of the undesired oxidation of 
SO.sub.2 than did S-3Ce, but was much better in terms of less promotion of 
oxidation of SO.sub.2 than was the S-3A1 sample (8.0%). TABLE II thus 
demonstrates the desirability of dispersing all or at least a part of the 
platinum metal component on the ceria component of the ceria-alumina 
catalytic material. 
Example 4 
A series of catalyst samples was prepared generally according to the 
procedures of Example 1 to provide an alumina undercoat at a loading of 
1.0 g/in.sup.3 on which a metal oxide topcoat was coated. In the case of 
comparative sample Comp.1, the topcoat contained no ceria, the topcoat of 
comparative sample Comp.2 contained no alumina, and, in a third sample in 
accordance with the present invention, S-3, the topcoat comprised a 
ceria-alumina catalytic material containing 46.2 percent ceria and 53.8 
weight percent alumina. Each of the samples contained 0.5 g/ft.sup.3 of 
platinum and had a topcoat loading of about 1.95 g/in.sup.3, inclusive of 
the platinum. In all cases the ceria had a surface area of 164 m.sup.2 /g 
and the alumina had a surface area of 150 m.sup.2 /g. The samples were 
tested with the same test gas as described in Example 2 at 275.degree. C., 
350.degree. C., 425.degree. C. and 500.degree. C., and the conversion of 
HC, CO and oxidation of SO.sub.2 to SO.sub.2 at a space velocity of 50,000 
was measured. The results of these tests are summarized in TABLE III. 
TABLE III 
______________________________________ 
Inlet Gas Sample % C % C % C 
Temp. (.degree.C.) 
No. SO.sub.2 HC CO 
______________________________________ 
275 Comp. 1 16.3 10.0 96.6 
275 S-3 0.0 2.4 30.5 
275 Comp. 2 10.2 0.0 9.4 
350 Comp. 1 18.9 86.5 99.6 
350 S-3 4.0 9.8 68.3 
350 Comp. 2 12.2 6.5 63.1 
425 Comp. 1 35.5 90.5 99.9 
425 S-3 11.8 31.6 84.3 
425 Comp. 2 22.4 18.2 70.4 
500 Comp. 1 42.2 83.7 99.7 
500 S-3 12.0 47.4 84.8 
500 Comp. 2 32.0 31.6 61.0 
______________________________________ 
The data of TABLE III indicate the conversion of hydrocarbons (HC) was 
highest for sample Comp.1, containing 100 percent alumina and no ceria, 
and lowest for sample Comp.2, containing 100 percent ceria and no alumina. 
The catalyst in accordance with the present invention, S-3, provided 
intermediate levels of conversion of HC. Comparable results were obtained 
for conversion of CO at all temperature levels. The results of TABLE III 
concerning the conversion of SO.sub.2 to SO.sub.3 are shown in the 
perspective-view plot of FIG. 3 from which it is readily seen that at each 
temperature level tested a lower degree of conversion of SO.sub.2 was 
attained by the S-3 sample in accordance with an embodiment of the present 
invention, than was attained with either the 100 percent alumina (Comp.1) 
version or the 100 percent ceria (Comp.2) version. These data demonstrate 
that utilizing a ceria-alumina catalytic material in accordance with the 
present invention reduces the oxidation of SO.sub.2 as compared to either 
a 100 percent ceria or 100 percent alumina catalyst containing 0.5 
g/ft.sup.3 of platinum. 
A series of catalyst compositions was prepared in order to test catalyst 
compositions in accordance with the present invention against comparative 
catalyst compositions containing various refractory metal oxides and 
catalytic metals. These catalysts were tested both on a laboratory 
diagnostic reactor and on diesel engines. The two test engines employed 
were a Cummins 6BT engine, rated at 190 horsepower and having a 5.9 liter 
displacement and a Caterpillar 3176 engine, rated at 325 horsepower and 
having a 10.3 liter displacement. The operating characteristics of these 
two engines are shown in TABLE IV based on the operating cycle used to 
test the catalyst composition samples. 
TABLE IV 
______________________________________ 
Caterpillar 3176 
Cummins 6BT 
Temperature (.degree.C.) 
Temp. Cycle.sup.a 
Temp. Cycle.sup.a 
______________________________________ 
less than 100 0 0 
100-200 0 62.6 
200-300 57.3 36.7 
300-400 30.9 0.7 
400-500 11.8 0 
Maximum 475 305 
Temperature (.degree.C.): 
______________________________________ 
g/HP-hr.sup.b 
Wt. %.sup.c 
g/HP-hr.sup.b 
Wt. %.sup.c 
______________________________________ 
Particulates: 
VOF 0.036 21.6 0.066 38.4 
Sulfate 0.005 3.1 0.003 2.0 
Carbon/Other.sup.d 
0.127 75.3 0.103 59.6 
Totals 0.168 100.0 0.172 100.0 
Gas Phase: 
HC 0.123 -- 0.300 -- 
CO 3.48 -- 1.50 -- 
NO 5.06 -- 4.34 -- 
______________________________________ 
.sup.a Percentage of cycle time at which the inlet exhaust to the catalys 
lies within the indicated temperature range 
.sup.b "g/NPhr" = grams per brake horsepowerhour of component emitted in 
exhaust 
.sup.c Weight percentage of total particulates provided by the indicated 
constituent 
.sup.d "Carbon/Other" values are calculated by difference between the 
measured VOF and sulfate components of the exhaust and the total exhaust 
particulates. Carbon/Other comprises the dry, solid carbonaceous content 
of the particulates plus any water associated with the sulfates. Any 
measurement errors will affect the "Carbon/Other" value. 
As shown in TABLE IV, the Cummins engine runs with a cooler exhaust than 
does the Caterpillar engine and the total engine emissions are roughly 
comparable although the Cummins engine runs richer in the volatile organic 
fraction (VOF) which is the component most effectively treated by the 
diesel oxidation catalyst of the present invention. 
Example 5 
A series of catalyst samples was prepared generally by the method disclosed 
in Example 1 including two catalysts, designated samples S-3 and S-3B, 
comprising embodiments of the present invention and made exactly in 
accordance with Example 1 except that for sample S-3B palladium was 
substituted for platinum by using palladium nitrate as the source of the 
catalytic metal. Samples S-3 and S-3B each had an alumina undercoat at a 
loading of 1.0 g/in.sup.3 and a topcoat of the ceria-alumina coating at a 
loading of 1.95 g/in.sup.3. A series of comparative catalysts designated 
Comp.4, Comp.4M, Comp.4B, Comp.7, Comp.2.3, Comp.6 and Comp.5 were made by 
procedures comparable to those used in Example 1, with the following 
differences. The comparative catalysts were made without an alumina 
undercoat and, of course, using different refractory metal oxides as 
indicated by their respective compositions. For the samples containing 
niobia-silica (Comp.4, 4M, 4B and 7) the niobia was provided by dissolving 
niobium oxalate in the coating slurry. Further, the foamed .alpha.-alumina 
("FAA") of Comp.2.3 and the silica of other comparative samples were not 
ball milled but were dry-jet milled and then incorporated into the coating 
step by use of a high speed intensive mixer. The vanadia-titania of sample 
Comp.6 was incorporated into a slurry containing palladium nitrate as the 
catalytic metal source. 
The silica employed in each case except Comp.2.3 was an extremely porous 
silica designated PQ-1022 by its manufacturer, PQ Corporation. The PQ-1022 
silica has a porosity of 1.26 cc/g pore volume comprised of pores having a 
radius of from about 10 to 300 Angstroms, and a surface area of 225 
m.sup.2 /g. The high porosity of the silica accounts for the relatively 
low weight loadings of the silica-containing washcoats. A silica sol was 
used for the Comp. 2.3 sample as described in footnote c of TABLE V. Each 
of these catalysts, the general composition of which is set forth in TABLE 
V, was prepared as a slurry of the refractory metal oxide or oxides 
indicated in TABLE V which had been impregnated with the specified loading 
of catalytic metal and then coated onto 400 cpsi cylindrical cordierite 
honeycomb carriers manufactured by NGK and measuring 9 inches in diameter 
by 6 inches in length, providing a catalyst volume of 6.25 liters. 
TABLE V 
______________________________________ 
Metal Hours 
Catalyst Loading Aged 
Sample Washcoat Metal g/ft.sup.3 
24 100 
______________________________________ 
S-3 Ceria--Alumina Pt 0.5 X X 
Comp. 4 Niobia--Silica.sup.a 
Pd 50.0 X X 
Comp. 4M 
Niobia--Silica.sup.a 
Pd--Pt 25-5 X X 
S-3B Ceria--Alumina Pd 50.0 X X 
Comp. 4B 
Niobia--Silica.sup.a 
Pt 0.5 X 
Comp. 7 MnO--Niobia--Silica.sup.b 
Pt 2.2 X 
Comp. 2.3.sup.c 
Silica--FAA.sup.d 
Pt 2.2 X 
Comp. 6 Vanadia--Titania.sup.e 
Pd 27 X X 
______________________________________ 
.sup.a The niobia--silica sample catalysts (Comp. 4, 4M and 4B) had 
washcoats comprised of 10 percent by weight niobia and 90 percent by 
weight silica, with a total washcoat loading of 0.8 g/in.sup.3. 
.sup.b The MnO--niobia--silica sample catalyst (Comp. 7) had a washcoat 
comprised of 90 percent by weight silica, 4 percent by weight niobia and 
percent by weight MnO, with a total washcoat loading of 0.6 g/in.sup.3. 
.sup.c The silicafoamed alumina sample catalyst (Comp. 2.3) had a washcoa 
comprised of 10 percent by weight silica sol binder and 90 percent by 
weight of foamed alumina ("FAA"), with a total washcoat loading of 0.6 
g/in.sup.3. The alumina has a porosity of 0.0439 cc/g pore volume 
comprised of poreshaving a radius of from about 10 to 300 Angstroms, and 
surface area of 20.3 m.sup.2 /g. 
.sup.d "FAA" = foamed alumina? 
.sup.e The vanadia--titania sample catalyst (Comp. 6) had a washcoat 
comprised of 4 percent by weight vanadia and 96 percent by weight titania 
with a total washcoat loading of 1.8 g/in.sup.3. 
All eight sample catalysts were evaluated on the Cummins 6BT engine 
employing the U.S. Transient Cycle (commonly, and sometimes hereinbelow, 
referred to as the "Federal Test Procedure" or "FTP"). A description of 
the U.S. Transient Cycle is set forth in the Code of Federal Regulations, 
Title 40, Chapter 1, Subpart N, Paragraphs 86:1310-88 and 86:1312-88, 
Appendix I(f)(2). The catalyst volume-to-engine displacement ratio was 
1.06. The catalysts were evaluated for fresh activity (after 24 hours 
aging) following which the five indicated samples were aged for 100 hours 
and further evaluated. All catalysts were aged on a 1986 Cummins NTC 
diesel engine rated at 400 horsepower and having a 14.0 liter 
displacement. The aging cycle employed flowed the engine exhaust through 
three catalysts of 6.25 liter volume each, simultaneously and in parallel, 
with the engine load adjusted to provide fifteen minute cycles during 
which the exhaust attained inlet temperatures as follows for the indicated 
amount of time: 330.degree.-400.degree. C. for 14% of the time, 
400.degree.-500.degree. C. for 22% of the time, 500.degree.-550.degree. C. 
for 50% of the time, and 550.degree.-565.degree. C. for 14% of the time. 
The S-3 and S-3B samples each contain 46.2 weight percent 
aluminum-stabilized ceria and 53.8 weight percent alumina. 
TABLE VI shows the results of the fresh (aged 24 hours) catalyst samples 
tested under the Federal Test Procedure on the Cummins 6BT engine with all 
recorded exhaust emissions being given in grams per brake horsepower-hour. 
All emissions are measured quantities except for "Carbon+Other" which is 
calculated by difference. The measured values are the average of four 
different runs conducted under the Federal Test Procedure which were 
carried out over the space of two days in order to account for day-to-day 
variations. TABLE VI also shows the base line values of the diesel exhaust 
operated without catalytic treatment over an average of 24 runs. The 
difference between the runs carried out without catalytic treatment and 
the runs carried out using the various catalyst samples were utilized to 
calculate the percent conversion of each of the emissions components. The 
percent conversion is the percentage of the emissions contained in the 
untreated exhaust which were converted to innocuous components by 
utilization of the catalyst samples. The abbreviation "TPM" is used for 
"total particulate matter". 
TABLE VI 
__________________________________________________________________________ 
Catalyst 
Sample 
HC CO NOx TPM VOF Sulfate 
Carbon + Other 
__________________________________________________________________________ 
None - Untreated engine exhaust 
Grams.sup.a 
0.299 
1.5 4.34 
0.172 
0.0611 
0.0034 
0.108 
S-3 
Grams.sup.a 
0.188 
1.11 
4.3 0.118 
0.0256 
0.0016 
0.0908 
% C.sup.b 
37.4 
26 0.96 
31.7 
58.1 53.1 15.9 
Comp. 4 
Grams 0.198 
1.28 
4.22 
0.123 
0.0272 
0.0022 
0.0936 
% C 34.1 
14.9 
2.7 28.8 
55.4 37 13.3 
Comp. 4M 
Grams 0.213 
1.34 
4.22 
0.123 
0.0302 
0.0025 
0.0903 
% C 29.1 
11 2.8 28.8 
50.6 28.2 16.4 
S-3B 
Grams 0.155 
1.31 
4.31 
0.118 
0.0258 
0.0025 
0.0897 
% C 48.3 
13 0.73 
31.7 
57.7 26 16.9 
Comp. 4B 
Grams 0.208 
1.17 
4.27 
0.128 
0.0359 
0.0033 
0.0888 
% C 30.7 
22.2 
1.5 25.9 
41.2 4.8 17.8 
Comp. 7 
Grams 0.198 
1.09 
4.31 
0.135 
0.0378 
0.0028 
0.0944 
% C 34.1 
27.2 
0.79 
21.5 
38.1 17.2 12.6 
Comp. 2.3 
Grams 0.185 
1.09 
4.34 
0.135 
0.0306 
0.0049 
0.0995 
% C 38.2 
27.5 
0.1 21.5 
38.1 43.6 7.9 
Comp. 6 
Grams 0.135 
1.51 
4.35 
0.118 
0.0255 
0.003 
0.0895 
% C 54.9 
-0.3 
-0.25 
31.7 
58.3 11.4 17.1 
__________________________________________________________________________ 
.sup.a Grams per brake horsepowerhour 
.sup.b "% C" means the percentage conversion of the indicated constituent 
A negative % C means the treated exhaust contained more of the constituen 
than did the untreated exhaust. 
The results tabulated in TABLE VI indicate that with respect to VOF 
conversion and total particulates conversion, the best results were 
obtained by S-3, S-3B and Comp.6 catalysts, with the Comp.4 sample giving 
the next best results. As to sulfate emissions, the Comp.2.3 sample 
exhibited sulfate emissions which were greater than those of the untreated 
exhaust, all the other samples tested giving at least some reduction in 
sulfates as compared to the untreated exhaust. This finding is consistent 
with the relatively low temperature of the Cummins 6BT engine. With 
respect to gas phase emissions (HC, CO and NO.sub.x) Comp.6, S-3B and 
Comp.5 gave the best HC reduction while Comp.2.3, Comp.7 and S-3 gave the 
best CO conversion. There was little catalytic effect on NO.sub.x 
emissions as one would expect in the relatively oxygen-rich environment of 
a diesel exhaust. 
Example 6 
As indicated in TABLE V, five of the catalysts tested were then aged to a 
total of 100 hours and re-evaluated on the Cummins 6BT engine. The results 
of the evaluation of the 100-hour aged samples are summarized in TABLE 
VII. 
TABLE VII 
__________________________________________________________________________ 
Catalyst 
Sample 
HC CO NOx TPM VOF Sulfate 
Carbon + Other 
__________________________________________________________________________ 
None - Untreated engine exhaust 
Grams.sup.a 
0.305 
1.55 
4.46 
0.179 
0.0675 
0.0039 
0.108 
S-3 
Grams.sup.a 
0.188 
1.27 
4.31 
0.123 
0.0284 
0.0018 
0.0928 
% C.sup.b 
38.4 
17.9 
3.3 31.3 
57.9 53.8 14.1 
Comp. 4 
Grams 0.218 
1.47 
4.37 
0.128 
0.0327 
0.0023 
0.093 
% C 28.5 
4.9 1.9 28.5 
51.6 41 13.9 
Comp. 4M 
Grams 0.238 
1.49 
4.37 
0.13 
0.0349 
0.0031 
0.092 
% C 22 3.6 1.9 27.4 
48.3 20.5 14.8 
S-3B 
Grams 0.175 
1.27 
4.38 
0.12 
0.0282 
0.0022 
0.0896 
% C 42.6 
17.9 
1.7 33 58.2 43.6 17 
Comp. 6 
Grams 0.22 
1.69 
4.42 
0.14 
0.0308 
0.0042 
0.105 
% C 27.9 
-9.3 
0.8 21.8 
54.4 -7.7 2.8 
__________________________________________________________________________ 
.sup.a Grams per brake horsepowerhour 
.sup.b "% C" means the percentage conversion of the indicated constituent 
A negative % C means the treated exhaust contained more of the constituen 
than did the untreated exhaust. 
Table VII shows that the best results were attained by the S-3 and S-3B 
catalysts for both total particulate emissions and VOF conversion. With 
respect to HC reduction the best performance was shown by S-3B although 
the S-3 catalyst proved to be the most stable, the results attained by the 
S-3 catalyst after 100 hours aging being actually better than those 
attained by the 24-hour aged S-3 sample. The S-3B catalyst exhibited 
improved CO conversion for the 100-hour aged catalyst as compared to the 
fresh (24-hour aged) catalyst. Note that the Comp.6 sample removed 
essentially no CO at 24 hours and became a net CO producer after being 
aged for 100 hours. The results of TABLE VI and VII clearly show that the 
catalyst compositions of the present invention, S-3 and S-3B, gave the 
best overall emissions control and the best durability as evidenced by 100 
hours of aging. 
Example 7 
In order to compare the effect of different catalytic metal loadings on the 
performance of catalysts in accordance with the present invention, three 
sample catalysts in accordance with the present invention were prepared in 
accordance with the procedure of Example 1. Thus, each catalyst comprised 
a cordierite 400 cpsi substrate containing 1.95 g/in.sup.3 of the 
ceria-alumina catalytic material of the invention. The ceria-alumina 
catalytic material contained 46.2 weight percent of aluminum-stabilized 
ceria and 53.8 weight percent of activated alumina. Each catalyst had an 
alumina undercoat in the amount of 1.00 g/ft.sup.3 onto which the 
ceria-alumina catalytic material was coated. One sample, designated 
S-3.5Pt had 0.5 g/ft.sup.3 of platinum dispersed thereon, another sample, 
designated S-3.20Pt had 2.0 g/ft.sup.3 of platinum dispersed thereon and a 
third sample, designated S-3Pd had 50 g/ft.sup.3 of palladium dispersed 
thereon. Each catalyst was tested under the Federal Test Procedure to 
treat an exhaust generated by a Cummins C-series 250 HP diesel engine 
having a displacement of 8 liters, so that a catalyst volume-to-engine 
displacement ratio of 0.78 was utilized. The effectiveness of the sample 
catalyst was tested in the same manner as that of Example 6 and the 
results with respect to conversion of total particulates (TPM) and gaseous 
phase HC and CO are set forth in TABLE VIII. 
TABLE VIII 
______________________________________ 
% C.sup.a % C.sup.a 
% C.sup.a 
Sample TPM HC CO.sub.2 
______________________________________ 
S-3.5Pt 47 28 7.5 
S-3.20Pt 48 69 74 
S-3Pd 48 52 35 
______________________________________ 
.sup.a "% C" means the percentage conversion of the indicated constituent 
The data of TABLE VIII show that all three samples were nearly identical 
with respect to the percentage conversion of total particulates although 
the larger loadings of catalytic metal made a dramatic difference in the 
percentage conversions of the gaseous HC and CO. These results are 
consistent with the data of Example 6 and TABLE VII, from which it will be 
noted that S-3 and S-3B gave substantially similar results with respect to 
total particulates reduction in spite of the fact that S-3 contains only 
0.5 g/ft.sup.3 of platinum and S-3B contains 50 g/ft.sup.3 of palladium. 
The lack of pronounced effect on total particulate reduction between a 
catalyst containing 100 times more platinum group metal than another, 
strongly suggests the irrelevancy of the presence of the catalytic metal 
insofar as total particulate reduction is concerned, and that particulate 
reduction is attained by the effect of ceria-alumina catalytic material. 
Example 8 
In order to further demonstrate the irrelevancy of the platinum metal 
loading insofar as catalytic activity of the ceria-alumina catalytic 
material with respect to total particulate reduction is concerned, a 
series of samples of catalytic material powder was prepared. This was done 
by utilizing the ceria-alumina washcoat material of Example 7 containing 
various quantities of platinum metal ranging from 0 to the equivalent of 
5.0 g/ft.sup.3 of platinum if the washcoat were to be coated upon a 400 
cpsi NGK cordierite substrate. The resultant series of powders were each 
mixed with 10 weight percent of a diesel engine lubricating oil, Cummins 
SAE-15W Premium Blue Diesel Engine Lube Oil, and the sample of the mixture 
was evaluated by simultaneous thermogravimetric analysis and differential 
thermal analysis (TGA/DTA) for combustion of the lubricating oil. It 
should be noted that unburned diesel engine lubricating oil constitutes a 
significant portion of the volatile organic fraction (VOF) of diesel 
exhaust particulate emissions and the efficacy of the ceria-alumina 
catalytic material in catalyzing combustion of the lubricating oil is a 
good indication of the effectiveness of the ceria-alumina catalytic 
material in catalyzing oxidation of VOF and, thereby, reduction of 
particulate emissions. Thermogravimetric analysis measures the weight gain 
or loss of a sample (indicating a chemical reaction undergone by the 
sample) as a function of the temperature to which the sample is heated. 
Differential thermal analysis measures the amount of energy (heat) 
absorbed by the sample (indicating that the sample has undergone an 
endothermic reaction) or liberated by the sample (indicating that the 
sample has undergone an exothermic reaction) as a function of the 
temperature to which the sample is heated. FIG. 4 is a plot of the results 
obtained by heating the mixture of catalytic material powder and 
lubricating oil in a temperature regime ranging from ambient temperature 
to 600.degree. C. and recording the TGA/DTA data. The DTA peak area was 
corrected for the weight change determined by the TGA so that the results 
attained are proportional to the amount of lubricating oil combusted, 
i.e., to the effectiveness of the tested ceria-alumina catalytic 
materials, which are identical except for the varying platinum metal 
loadings. The results attained are plotted in FIG. 4 wherein, despite some 
experimental scatter in the data points, the trend line indicates 
substantially no effect of the platinum content of the catalytic material 
insofar as lubricating oil combustion is concerned. Thus, about the same 
proportion of combustion was attained for the ceria-alumina catalytic 
material containing no platinum as for that containing incremental amounts 
of platinum up to and including the equivalent of 5 g/ft.sup.3 on a 400 
cpsi carrier. 
Example 8A 
An equivalent test of silica based and silica-niobia based refractory metal 
oxide powders on which varying amounts of platinum were dispersed was 
carried out. Those test results showed that the ceria-alumina catalytic 
material of the present invention provided better performance for 
lubricating oil combustion as measured by DTA and therefore, by 
implication, for catalytic oxidation of VOF in diesel engine exhaust. 
Example 9 
S-3 and comparative Comp. 4 catalyst samples were tested on the exhaust of 
the Caterpillar 3176 engine. As previously noted, this engine runs with a 
considerably hotter exhaust than the Cummins 6BT engine and test catalysts 
of the same size (9 inches by 6 inches providing a catalyst volume of 6.25 
liters) were tested on this larger engine, providing a catalyst 
volume-to-engine displacement ratio of 0,607. S-3 and Comp.4 catalyst 
samples were aged for 50 hours on an aging cycle similar to that described 
in Example 5 but from a minimum of about 300.degree. C. to a maximum of 
about 530.degree. C. 
The results of this test are shown in TABLE IX as the average of six 
hot-start runs in accordance with the Federal Test Procedure. 
TABLE IX 
__________________________________________________________________________ 
Catalyst 
Sample 
HC CO NOx 
TPM VOF Sulfate 
Carbon + Other 
__________________________________________________________________________ 
None - Untreated engine exhaust 
Grams.sup.a 
0.123 
3.48 
5.06 
0.168 
0.0363 
0.0052 
0.1265 
S-3 
Grams.sup.a 
0.1566 
2.5 
4.95 
0.138 
0.0213 
0.0039 
0.1128 
% C.sup.b 
54 28.2 
2.2 
17.9 
41.3 25 10.8 
Comp. 4 
Grams 0.0833 
1.76 
5.02 
0.177 
0.017 
0.0217 
0.1383 
% C 32.3 20.7 
0.8 
-5.4 
53.2 -317 -9.3 
__________________________________________________________________________ 
.sup.a Grams per brake horsepowerhour 
.sup.b "% C" means the percentage conversion of the indicated 
constituents. A negative % C means the treated exhaust contained more of 
the constituent than did the untreated exhaust. 
The results summarized in TABLE IX show that the S-3 catalyst reduced total 
particulate emissions by 17.9 percent and VOF by 41.3 percent whereas the 
Comp.4 sample, although it gave a higher VOF reduction at 53.2 percent, 
resulted in an increase of total particulate emissions, because of its 
very high sulfate make which resulted in sulfate emissions 317 percent 
higher than those emitted in the untreated exhaust. The tendency of the 
Comp.4 sample to produce large amounts of sulfate in the hot exhaust 
environment of the Caterpillar 3176 engine stands in marked contrast to 
the efficiency of the S-3 catalyst in attaining a 25 percent reduction in 
sulfate emissions and therefore an overall reduction in total 
particulates. The fact that the S-3 catalyst exhibited lower total 
particulates and VOF removal levels on the Caterpillar 3176 engine than on 
the Cummins 6BT engine is attributable to the smaller catalyst volume 
relative to engine size encountered on the Caterpillar engine test and to 
the fact that the concentration of VOF, the component most vigorously 
treated by the catalyst, is some 40 percent lower in the exhaust of the 
Caterpillar engine than in the exhaust of the Cummins engine. 
Example 10 
In order to compare the effect on conversion of SO.sub.2 to SO.sub.3, and 
thus sulfate-make of a catalyst, three comparative samples, one of which 
(designated Comp.11) is a commercially available diesel exhaust catalyst, 
and each containing high platinum group metal loadings, were compared to a 
fourth sample comprising an embodiment of the present invention. Three 
samples, Comp.1, Comp.2 and S-3, were prepared generally in accordance 
with the procedure of Example 1 to coat cylindrical carriers comprising 
400 cpsi cordierite cores measuring 1.5 inches in diameter by 3 inches in 
length. The samples were aged for 10 hours at 500.degree. C. by having a 
mixture of 10 percent steam in air flowed through each sample. Comparative 
sample Comp.1 comprised 50 g/ft.sup.3 of platinum disposed on an activated 
alumina carrier and comparative sample Comp.2 had a 50 g/ft.sup.3 platinum 
group metal loading, the platinum group metal comprising platinum and 
rhodium in a 5:1 weight ratio disposed on a ceria-alumina catalytic 
material comprising 53.8 percent by weight alumina and 46.2 percent by 
weight aluminum-stabilized ceria. The S-3 sample comprised, in accordance 
with one embodiment of the present invention, 0.5 g/ft.sup.3 of platinum 
dispersed on a ceria-alumina catalytic material comprising 46.2 percent by 
weight aluminum-stabilized ceria and 53.8 percent by weight alumina with 
one-half the platinum metal dispersed on the aluminum-stabilized ceria and 
one-half the platinum metal dispersed on the alumina. The commercially 
available catalyst for diesel exhaust applications was analyzed and found 
to comprise a catalytic material dispersed on a honeycomb-type carrier 
having 400 cells per square inch. The commercial catalyst contained about 
50 g/ft.sup.3 of platinum dispersed on a support comprised primarily of 
titania, vanadia and alumina. A core 2.5 inches long and 1.5 inches in 
diameter was cut from the commercial catalyst and this comparative 
catalyst core was designated as Comp.11. The four catalyst samples were 
tested at space velocities of 50,000 and 90,000 at temperatures of 
275.degree. C., 350.degree. C., 425.degree. C. and 500.degree. C. (In this 
Example 10 and in Example 11 below, the flow rate of the reaction gas was 
adjusted as necessary to compensate for the slight difference in catalyst 
volume so that each tested sample was evaluated at the same space 
velocity.) Each sample was held at the indicated temperature for 10 
minutes during the evaluation. The test gas used in the laboratory 
diagnostic unit comprised 10 percent steam, 10 percent oxygen, 4.5 percent 
CO.sub.2, 1000 ppm NO, 28.57 ppm heptane (equivalent to 200 ppm C.sub.1 
hydrocarbons), 28.6 ppm CO, 50 ppm SO.sub.2, balance nitrogen. (The 
percents are volume percents and "ppm" means parts per million by volume.) 
The results of these evaluations are given in TABLE X. 
TABLE X 
______________________________________ 
Catalyst Percent Conversion at Indicated Space Velocity 
Sample/ 50,000 SV 90,000 SV 
Inlet Temp. 
CO HC SO.sub.2 
CO HC SO.sub.2 
______________________________________ 
Comp. 1 
275.degree. C. 
99.5 68.6 56.9 94.9 52.4 29.4 
350.degree. C. 
99.5 83.0 76.9 96.5 70.5 58.5 
425.degree. C. 
100 87.4 94.3 -- -- -- 
500.degree. C. 
100 89.0 92.2 -- -- -- 
Comp. 2 
275.degree. C. 
100 52.5 -- 98.5 47.6 8.0 
350.degree. C. 
99.0 77.5 11.8 96.9 61.7 9.8 
425.degree. C. 
99.0 84.2 31.4 96.0 74.4 23.5 
500.degree. C. 
98.1 90.7 47.1 95.5 73.2 37.3 
Comp. 11 
275.degree. C. 
97.1 16.7 0.0 84.7 4.8 2.0 
350.degree. C. 
99.0 54.5 2.0 93.0 41.0 2.0 
425.degree. C. 
99.5 75.0 23.6 97.0 63.2 15.7 
500.degree. C. 
99.5 85.9 54.9 97.4 73.2 38.0 
S-3 
275.degree. C. 
30.5 2.4 0.0 10.9 0.0 0.0 
350.degree. C. 
68.3 9.8 4.0 52.4 9.5 0.0 
425.degree. C. 
84.3 31.6 11.8 59.5 24.3 3.9 
500.degree. C. 
84.4 47.4 12.0 60.0 28.6 4.1 
______________________________________ 
The data of TABLE X shows that the comparative samples Comp.1 and Comp.2 
exhibit very high conversion of SO.sub.2 to SO.sub.3, and thus high 
sulfate make, even at the lowest test temperature of 275.degree. C. and 
high space velocity of 90,000. Although comparative sample Comp.2 exhibits 
less sulfate make than Comp.1 (but significantly more than catalyst S-3, 
discussed below), this is believed to be due primarily to the modifying 
effect of rhodium on the SO.sub.2 oxidation activity of platinum. The 
Comp.2 catalyst has the economic disadvantage of being too costly because 
of the very high cost of rhodium even as compared to the cost of platinum. 
Both comparative samples Comp.1 and Comp.2 show high HC and CO conversion. 
S-3, the sample in accordance with an embodiment of the present invention, 
exhibits greatly reduced SO.sub.2 conversion relative to both Comp.1 and 
Comp.2 with practically no SO.sub.2 conversion occurring in the low 
temperature regime and with relatively small SO.sub.2 conversion even at 
the high temperature regime. Some activity for conversion of gaseous HC 
and CO is exhibited by catalyst S-3, especially at the high temperature 
regime where good CO and moderate HC activity is seen. The data of TABLE X 
thus clearly demonstrate that the utilization of a low platinum loading on 
the ceria-alumina catalytic material of the present invention provides 
excellent control of SO.sub.2 oxidation and consequently excellent control 
of total particulates emission in a diesel engine exhaust. It should be 
noted that the diagnostic test is a very stringent test of sulfate 
oxidation as compared to actual engine performance. Experience has shown 
that a given catalyst will perform better with respect to sulfate 
oxidation in treating an actual diesel engine exhaust than it will in the 
diagnostic engine test. 
The comparative catalyst sample Comp.11 is seen to suppress SO.sub.2 
oxidation in a manner comparable to that of sample S-3, but only up to a 
temperature between 350.degree. and 425.degree. C. At 425.degree. C. and 
higher temperatures the Comp.11 sample exhibits greatly increased SO.sub.2 
oxidation as compared to the S-3 catalyst sample. Accordingly, the 
catalyst sample of the present invention, even with a 0.5 g/ft.sup.3 
platinum loading, appears to be significantly better with respect to 
SO.sub.2 oxidation in higher temperature regimes than the commercial 
catalyst of Comp.11. The comparative samples Comp.1, Comp.2 and Comp.11 
all contain high platinum loadings and consequently show higher HC and CO 
conversion than does the 0.5 g/ft.sup.3 platinum S-3 catalyst sample. 
However, as pointed out elsewhere herein, HC and CO emissions generally 
satisfactorily controlled by engine design and the problem which the art 
is seeking to overcome is to control the total particulates emissions 
which, as noted above, is in part a function of sulfate make. The 
catalysts of the present invention, with no or a very low loading of 
platinum, show excellent activity for reducing total particulate emissions 
because of their unexpected good activity for oxidizing VOF and their low 
sulfate make. Further, it is obviously economically advantageous to 
eliminate or drastically reduce the platinum metal loading in accordance 
with the teachings of the present invention. 
Example 11 
A catalyst sample in accordance with an embodiment of the present invention 
was prepared and designated sample S-3P. Catalyst sample S-3P is identical 
to catalyst sample S-3 of Example 10 except that it contains a platinum 
loading of 2.0 g/ft.sup.3. The S-3P catalyst sample was 3.0 inches long by 
1.5 inches in diameter. Catalyst S-3P was tested by passing therethrough a 
test gas in the same manner as described in Example 10 at space velocities 
of 50,000 and 90,000 at temperatures of 275.degree. C., 350.degree. C., 
425.degree. C. and 500.degree. C. The results of this test are shown in 
TABLE XI. 
TABLE XI 
______________________________________ 
Catalyst Percent Conversion at Indicated Space Velocity 
Sample/ 50,000 SV 90,000 SV 
Inlet Temp. 
CO HC SO.sub.2 
CO HC SO.sub.2 
______________________________________ 
S-3P 
275.degree. C. 
99.0 10.0 16.0 88.5 2.6 2.0 
350.degree. C. 
100 87.8 21.6 98.0 74.1 5.9 
425.degree. C. 
100 90.5 33.3 98.5 82.7 19.2 
500.degree. C. 
99.5 83.1 35.3 98.1 73.3 31.4 
______________________________________ 
TABLE XI shows, as would be expected, that the S-3P catalyst exhibits 
higher SO.sub.2 oxidation at all temperature levels and space velocities 
as compared to the S-3 catalyst of Example 10 which contains 0.5 
g/ft.sup.3 of platinum, one-fourth of the amount of platinum (2.0 
g/ft.sup.3) which S-3P contains. However, the S-3P sample also exhibited 
higher HC and CO conversions, which shows that a modest increase in 
platinum loading, still keeping the total platinum loading to very low 
levels as compared to prior art catalysts, can accommodate a higher HC and 
CO conversion but at the potential cost of somewhat increased particulate 
emissions because of additional sulfate make. However, in certain 
circumstances it may be desirable to attain the higher HC and CO 
conversions attainable with the catalyst of the present invention by a 
modest increase in platinum loading. 
Example 12 
In order to evaluate the effect of ceria in the catalyst composition of the 
present invention, a comparative sample, Comp.1 of Example 4, was prepared 
generally in accordance with the procedure of Example 1 but omitting the 
ceria component of the catalytic material. Thus, the resulting catalyst 
comprised an activated alumina washcoat having 0.5 g/ft.sup.3 of platinum 
disposed thereon. This sample designated Comp.3C was subjected to the same 
test as in Examples 10 and 11 and the results thereof are summarized in 
TABLE XII and show that the SO.sub.2 conversion over this catalyst is 
significantly greater than for the S-3 catalyst, especially at low 
temperatures. Higher conversions of HC and CO were also attained. This 
data clearly indicate that the ceria plays an important modifying role in 
the oxidation activity of the platinum. 
TABLE XII 
______________________________________ 
Catalyst Percent Conversion at Indicated Space Velocity 
Sample/ 50,000 SV 90,000 SV 
Inlet Temp. 
CO HC SO.sub.2 
CO HC SO.sub.2 
______________________________________ 
Comp. 3C 
275.degree. C. 
96.6 10.0 16.3 85.4 4.9 4.6 
350.degree. C. 
99.6 86.5 18.9 95.0 57.4 12.6 
425.degree. C. 
99.9 90.5 35.5 98.1 74.0 33.7 
500.degree. C. 
99.7 83.7 42.2 98.3 74.0 33.7 
______________________________________ 
Example 13 
A catalyst was prepared in accordance with the present invention generally 
following the teachings of Example 1, except that no alumina undercoat was 
utilized. Thus, this sample comprised 1.95 g/ft.sup.3 of a ceria-alumina 
catalytic material containing 46.2 weight percent aluminum-stabilized 
ceria (164 m.sup.2 /g BET surface area) and 53.8 weight percent alumina 
(150 m.sup.2 /g BET surface area) disposed directly upon the carrier 
without an alumina undercoat, and having 0.5 g/ft.sup.3 of platinum 
dispersed thereon. This catalyst, designated S-3SC was aged and tested in 
the same manner as in Example 10 and the results thereof are shown in 
TABLE XIII. The performance of this sample is seen to be essentially the 
same as that of S-3 (Example 10, TABLE X) for the gas phase reactions, 
indicating that the presence of the alumina undercoat is not essential 
with respect to either low sulfate make or HC and CO oxidation. 
TABLE XIII 
______________________________________ 
Catalyst Percent Conversion at Indicated Space Velocity 
Sample/ 50,000 SV 90,000 SV 
Inlet Temp. 
CO HC SO.sub.2 
CO HC SO.sub.2 
______________________________________ 
S-3SC 
275.degree. C. 
25.4 0.0 2.0 31.0 0.0 0.0 
350.degree. C. 
71.9 11.9 5.9 62.5 15.8 4.1 
425.degree. C. 
85.6 28.9 9.8 78.7 29.3 5.9 
500.degree. C. 
86.3 48.7 20.4 76.1 42.5 10.7 
______________________________________ 
Example 14 
A. Catalysts were prepared generally in accordance with the procedures of 
Example 1 to provide a series of three otherwise identical compositions 
containing a ceria-alumina catalytic material in accordance with the 
teachings of the present invention having platinum dispersed thereon, 
including 0.0, 0.5 and 2.0 g/ft.sup.3 platinum. Each catalyst comprised a 
.gamma.-alumina undercoat at a loading of 1.0 g/in.sup.3 upon which was 
coated a top coat layer comprised of 1.05 g/in.sup.3 .gamma.-alumina plus 
0.90 g/in.sup.3 alumina-stabilized ceria (2.5 weight percent Al.sub.2 
O.sub.3 based on the combined weight of bulk ceria and alumina dispersed 
therein). The catalysts were coated onto a 9 inch diameter by 6 inch long, 
400 cpsi cordierite substrate. The resulting catalyst samples were 
designated as S-4 (0.0 g/ft.sup.3 platinum, aged 24 hours), S-5 (0.5 
g/ft.sup.3 platinum, aged 25 hours) and S-6 (2.0 g/ft.sup.3 platinum, aged 
24 hours). 
B. The three catalyst samples were conditioned prior to evaluation using an 
aging cycle involving 20 minutes each at Modes 2,6 and 8 of the European 
13 Mode Test Procedure (ECE R.49 Thirteen Mode Cycle). This Test Procedure 
is set forth in the Society of Automotive Engineers Publication, SAE Paper 
#880715, published at the International Congress and Exposition, Detroit, 
Mich., Feb. 29 through Mar. 4, 1988, by Georgio M. Cornetti et al. The 
disclosure of this SAE publication is incorporated by reference herein. 
Prior to testing to develop the data of TABLE XV and FIGS. 5-8, the three 
catalyst samples were aged 24 or 25 hours as indicated below on a Cummins 
6BT turbocharged diesel engine having a 5.9 liter displacement and rated 
at 190 horsepower. For both aging and test purposes, the engine was run 
with low sulfur fuel (0.05 weight percent sulfur) under steady state 
conditions using test modes selected from the aforesaid European 13 Mode 
Cycle Test Procedure. 
The engine conditions for the test modes along with average (for five runs) 
catalyst inlet temperatures and baseline emissions (of untreated engine 
exhaust) are shown in TABLE XIV. 
TABLE XIV 
______________________________________ 
Cummins 6BT 190 HP Turbocharged 
Diesel Engine, 5.9 Liter Displacement, 
Conditions For Steady State Catalyst Tests 
______________________________________ 
Engine Conditions 
Average 
Test % Catalyst Inlet 
Mode No. rpm Load Temp. (.degree.C.) 
______________________________________ 
8 2515 100 571 .+-. 2 
10 2515 50 338 .+-. 4 
6 1609 100 549 .+-. 5 
4 1609 50 400 .+-. 4 
2 1560 10 214 .+-. 3 
1 803 Low 128 .+-. 16 
______________________________________ 
Baseline Emissions - Untreated Exhaust 
Test Average Emissions (g/bhp-hr).sup.1 
Mode No. TPM SOF HC CO 
______________________________________ 
8 0.097 0.010 0.122 
0.46 
10 0.151 0.047 0.212 
0.68 
6 0.221 0.016 0.099 
2.23 
4 0.146 0.023 0.103 
0.52 
2 0.265 0.137 0.541 
2.57 
1 -- 0.078 1.04 3.01 
______________________________________ 
.sup.1 grams per brake horsepower hour 
The conditioned and aged catalyst samples S-4, S-5 and S-6 were tested for 
conversion of emission components in diesel exhaust generated by the test 
engine used to generate the data of Table XIV, as a function of steady 
state test mode and catalyst inlet temperature, i.e., the temperature of 
the diesel engine exhaust introduced to the catalyst. The results are 
summarized in TABLE XV. 
TABLE XV 
______________________________________ 
Sample/ 
(Pt Load 
Test Cat. Inlet 
% Removal 
g/ft.sup.3 
Mode No. Temp. .degree.C. 
SOF TPM HC CO 
______________________________________ 
S-4 2 209 72 63 31 1 
(0.0) 10 335 60 27 32 7 
4 399 62 18 38 18 
6 547 84 -40 44 27 
8 572 79 -181 39 -4 
S-5 2 215 60 45 27 6 
(0.5) 10 343 58 28 41 63 
6 549 91 -64 56 85 
8 570 80 -201 62 45 
S-6 1 127 56 52 37 -1 
(2.0) 2 215 61 61 39 8 
10 341 53 31 74 86 
4 397 61 22 82 87 
6 554 89 -60 78 95 
8 572 79 -200 71 70 
______________________________________ 
The data of TABLE XV show that all three catalysts are comparable in SOF 
removal performance as a function of temperature, with the catalyst 
containing no platinum (S-4) performing as well as the catalysts 
containing platinum (S-5 and S-6). 
With reference to TABLE XV and FIGS. 5-8, it is seen that the SOF removal 
performance as a function of inlet temperature of the three catalysts are 
compared in FIG. 5. As can be seen, all three samples are comparable 
across the temperature range of about 120.degree. to 575.degree. C. with 
the sample containing no platinum (S-4) performing as well as or better 
than, the platinum-containing samples S-5 and S-6. 
The SOF removal performance is also reflected in the total particulate 
(TPM) removal levels of the three catalysts which are compared in FIG. 6. 
The platinum-free catalyst sample is comparable to, or better than, the 
platinum-containing catalyst samples S-5 and S-6 at all temperatures. Note 
also, all three catalyst samples make particulates at the highest 
temperatures of the test. This is due to sulfate-make from the oxidation 
of gas phase SO.sub.2 to SO.sub.3. Thus, even the platinum-free sample 
makes sulfate at extremely high temperatures, but apparently to a slightly 
lesser extent than the platinum-containing samples, reflecting the lower 
gas phase activity of the platinum-free sample. 
The gas phase activity of the three catalyst samples are compared in FIGS. 
7 and 8 for, respectively, hydrocarbon ("HC") and carbon monoxide ("CO") 
gas phase conversions. Although the platinum-free sample S-4 exhibits some 
gas phase activity for HC and CO conversion, it is clear from these 
results that the platinum-containing samples S-5 and S-6 have 
substantially higher gas phase activity. This is especially clear in the 
case of CO conversion. The platinum-free sample S-4 has some gas phase 
activity because the ceria component has activity as an oxidation 
catalyst. 
These results show quite well the surprising finding that a platinum-free 
catalyst in accordance with the present invention exhibits very good 
particulates removal from diesel engine exhaust because of its activity 
for the removal and combustion of VOF, and that the precious metal is not 
needed to accomplish this function. If there is a need to enhance gas 
phase HC and CO activity, this can be accomplished separately by adding a 
limited amount of platinum to the catalyst. 
While the invention has been described in detail with respect to specific 
preferred embodiments thereof it will be appreciated that variations 
thereto may be made which nonetheless lie within the scope of the 
invention and the appended claims.