AU669679B2 - Improved ceria-alumina oxidation catalyst and method of use - Google Patents

Description

6 9079 AUSTRAL IA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): ENGELHARD CORPORATION Invention Title: IMPROVED CERIA-ALUMINA OXIDATION CATALYST AND METHOD OF USE The following statement is a full description of this invention, including the best method of performing it known to me/us:

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IMPROVED CERIA-ALUlAINA OXIDATION CATALYST AND METHOD OF USE BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a catalyst composition and method for the oxidation of oxidizeable components of a gas-borne stream, for the treatment of diesel engine exhaust, and more specifically to the treatment of such diesel exhaust to reduce the particulates content thereof.

j 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 conEains not only gaseous pollutants such as carbon monoxide ("1CO11) and unburned hydrocarbons but also soot particles which, as described in .i.A more detail below, comprise both a dry carbonaceous fraction and a hydrocarbon liquid which is sometimes referred to as a volatile organic fraction 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 nerotol (fine droplotsi of liqjuid condensate) depending on the temperature of the diesel exhaust.

Oxidation catalysts comprising a platinum group aletal dispersed on a refractory metal oxide support are known for use in treating the exhaust of diesel engines in order to convert both 11C and CO gaseous pollutants and particu- -2lates, 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 2 to SO, ("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. Patent 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 a-alumina, silica and titania, which are sulfation-resistant materials. Further, as is known, the oxidation of SO 2 to SO, also adds to the particulates in the exhaust by forming condensible sulfur compounds, such as sulfuric acid, which condense upon, and 20 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 sul- 25 fation.

Examples of catalysts designed for the treatment of diesel exhaust fumes and soot include U.S. Patent 4,849,399 to Joy et al dated July 18, 1989. This Patent discloses catalytic composites which incorporate sulfurresistant 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. Patent 4,759,918 to Homeier et al dated July 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).

02/0q5 '90 THU 17:01 FAX 01 3 92413 8333 GRIFFITH HACK CO fa007 3 SUMMARY OF TB NVENTION According to the present invention there is provided an oxidation catalst composition comprises a refractory carrier on which is disposed a coating of a ceriaalumina catalytic material comprising a combination of oeria having a BET surface area of at least 10 ti/g and alumina, excluding a-alumina, having a BET surface area of at least 10 m 2 said catalytic material not including a catalytically active precious metal.

According to the present invention there is also provided a catalyst composition for purifying diesel engine exhaust comprises a refractory carrier on which is disposed a coating of a catalytic material comprising a combination of ceria having a BET surface area of at least 10 m 2 /g and alumina having a BET surface area of at least 10 m 2 the ceria and alumina, excluding a-alumina, each comprising from S to 95 peroont by weight of the combination, said catalytic material not including a catalytically active precious metal, 20 Accordiro. to the present invention there is also provided a iethod for oxidizing oxidizeable components of a gas-borne stream comprises contacting the stream with a catalyst composition at a temperature high enough to catalyze oxidation of at least some of the oxidizeable components, the catalyst composition comprising a catalytic erial comprising a combination of ceria having a BET 4rface area of at least 10 mn/g and alumina, excluding aalunira, having a BET surface area of at least 10 m/g, a*a S.s said catalytic vaterial not including a catalytically active precious metal.

4* a According to the present invention there is aloo provided a method for treating a gas-borne stream 02,',5 '0 THU 1701 FAX OL 3 92,13 8333 GRIFFITI HACK CO 3a Comprising a diesel engine exhaust stream containing a N latile organic fraction comprises contacting the stream with a catalyst composition at a temperature high enough to catalyze oxidation of at least Oome of the volatile organic S fraction, the catalyst composition comprising a catalytic mateial comprising a combination of ceria having a BET surface area of at least 10 m2/g and alumina, excluding aalumina, having a BET surface area of at least 10 m 2 /g, said catalytic material not including a catalytically active precious metal.

According to the present invention there is also provided an oxidation catalyst composition comprises a refractory carrier on which in disposed a coating of a ceriaalumina catalytic material comprising a combination of ceria having a BET surface area of at least 10 fM 2 /g and alumina, excluding a-alumina, having a BET surface area of at least 10 and up to 0,5 g/ft 3 of platinum dispersed on the catalytic material.

According to the present invention there is also provided the catalyst composition for purifying diesel engine exhaustt comprises a refractory carrier on which is disposed a coating of a catalytic material comprising a 4 I combination of ceria having a BET surface area of at least ml/g and alumina, excluding a-alumina, having a BET 25 surface area of at least 10 m2/g, the ceria and alumina earh comprising from 5 to 95 percent by weight of the combination, and up to 0.5 g/fO of platinum dispersed on the catalytic material.

:According to the present invention there is also provided a method &or oxiditing oxidieable components of a Ce :gas-borne stream domprisea contacting the stream with a catalyst composition at a temperature high enough to catalyze oxidation of at least nome of the oxidizoabl 10008 02.05 90l THIU 17:01 FAX 01 3 02,43 8333 GRIFFITH HACK CO Fdi0oo 00 3b components, the catalyst composition comprising a catalytic material comprising a combination of ceria having a BET surface area of at least 10 ml/g and alumina, excluding aalumina, having a BET surface area of at least 10 m2/g, and up to 0.5 g/ftW of platinum dispersed on the catalytic material.

According to the present invention there is also provided a method for treating a gas-borne stream comprising a diesel engine exhaust stream containing a volatile organic fraction comprises contacting the stream with a catalyst composition at a temperature high enough to catalyze oxidation of at least some of the volatile organic fraction, the catalyst composition comprising a catalytic material comprising a combination of ceria having a BET surface area of at least 10 vn/g and alumina, excluding aalumina, having a BET surface area of at least 10 m 2 and up to 0.5 g/ft3 of platinum dispersed on the catalytic material, Generally, in accordance with the present 2. 0 invention, there is provided an oxidation catalyst 6composition and a method for oxidizing oxidizoable components of a gas-borne stream, for treating dioeel engine exhaust in which at least a volatile organic fraction component (described below) of the diesel oxhaust S 2S particulate 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 30 high surface area caria and high ourface area alumina, which optionally may have dispeaeed thereon a low loading of platinum catalytic metal. The method of the invention Sis attained by flowing a gas-borne atreamy a diesel engine exhaust, into contact under reaction conditions with 26,4 02/0.5 'O TH1U 17;02 FAX 81 3 0243 8333.

GRIFFITH HACK CO roj o 3c a catalyst composition as described above. Xn 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 ossentially of a combination of ceria and alumina each having a BET surface area of at least about m2/g, preferably the alumina having a surface area of from about 25 n/g to 200 m 2 /g and the ceria having a surface area of from about 25 m*'g to 200 m/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 20 catalyst composition optionally further comprises a catalytically otfective amount of platinum disperaod on the Cafca- 9 4 *9* 9 9

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9 S 9 4* 9.* lytic material in an amount not to exceed about 15 g/ft 3 of the catalyst composition. For example, the platinum may be present th 1 e amount of from about 0.1 to 15 g/ft of the composition, preferably frcm about 0.1 to 5 g/ft of the composition. When the catalyst composition includes platinum, another aspect of the invention provides that at lease 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 degrada- 9 tion.

*too The ceria and alumina may be combined as a mixture 20 and the mixture deposited as a single layer coating on the o refractory carrier, or the ceria and alumina may be pres- .ent in respective discrete superimposed layers of ceria and alumina. The ceria layer may be above or below the alumina layer.

25 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 metht oo od includes contacting the exhaust with a catalyst composition comprised of components as described above or with a catalyst composition comprised of components as deto's scribed above but which optionally includes palladium instead of the optional platinum. Thuso the method includes ontacting 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/t% preferably in the amount of from about 20 to 120 g/ft3, of the catalyst composition. In accordance with the method of the present invention, contacting of the diesel exhaust with the catalyst composition is carv'ied 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 0 C to 800 0

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 de- 'sot termining surface area by N 2 adsorption. Unless otherwise 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 0- and 6-aluminas (gamma, theta and delta).

4 25 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 ex- S: haust being treated.

The term "inlet temperature" shall mean the temperature of the exhaust, test gas or other stream being treated immediA ily prior 1.o initial contact of the exhaust, teat gas or other stream with the catalyst cumposlt.1on.

The term "ceria-alumina catalytic material" means a combination of ceria particles and aluminta particles each having a BET surface area of at least about 10 mo i.e., a combination of high surface area bulk ceria and high surface area bulk alumina, sotutimen referred to as "activated alumina".

-6- 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. Patent 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, 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, from about 3004C to 600'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 20 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 25 present as discrete particles (which may be, and usually are, of very small size, 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 4 30 alumina as described above with respect to U.S. Patent 4,714,694 results in the alumina being dispersed into the ceria particles and does not provide the dispersed alumina in "bulk" form, as discrete particles of alumins.

The abbrevibtion "'TGA" stands for thermogravimetric analysis which is measure of the weight change 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.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plot of oxidation of SO, to SO in a gas stream being treated with an oxidation catalyst, the degree of oxidation being plotted on the ordinate versus the platinum loading of the catalyst on the abscissa; Figure 2 is a plot similar to that of Figure 1 but showing the degree of HC oxidation on the ordinate versus platinum loading on the atscissa; Figure 3 is a perspective plot of oxidation of SO, to SO, in a gas stream being treated with an oxidation catalyst, with the degree of oxidation indicated by the height of the vertical bars for three different samples, each containing 0.5 g/ft 3 of platinum and having different weight percentages of ceria in the ceria-alumina catalytic material; Figure 4 is a plot of a factor (DTA peak area) corre- 20 lating combustion of engine lubricating oil (simulating 9 the unburned lubricating oil in "VOF", described below) too.

plotted on the ordinate versus the platinum content of a ceria-alumina washcoat used to catalyze the combustion of the lubricating oil plotted on the abscissa; and Figures 5 through 8 are plots showing various aspects of diesel engine exhaust treatment performance of three aged catalyst samples made in accordance with certain embodiments of the present invention as a function of the operating temperature of the catalysts, as follows: Fig- 30 ure 5 shows the percentage conversion of the volatile organic fraction Figure 6 shows the percentage conversion of total particulate matter ("TM in th ex- 9 "haust; Figure 7 shows the gas phase conversion of hydrocarbons and Figure 8 shows the gas phase conversion of carbon monoxide DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMB~ODIMENTS THEREOF The present invention provides an oxidation catalyst composition which is effective for oxidizing oxidizeable components ofr a gas-borne stream, for example, for treating diesel engine exhaust. In the latter case, the composition isq particularly effective with regard to reducing the total particulates in the exhaust. The carbonaceous particulates 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 ("VOF11), 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 cotal particulates discharged so as to meet present and impending Government regul.ations concerning maximum allowtotal pafticulates, the volatile organic fraction, or at least a portion thereof, is oxidized to innocuous CO 2 ;and 1120 by being contacted with an oxidation catalyst under suitable reaction conditions. The required U.S. Goverment limits for 1991 on HC, CO, nitrogen oxides ("NOX" and total particulate emissions (IITPM11) in diesel engine exhaust haive been largely met by suitable engine design modifications. For 1994 the H1-C CO and NO, limits remain unchanged from 1991 standards but the upper limit on TPM will he reduced from the 1991 level of 0.25 grams per horsepower-hour 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 SO02 to SO,. The oxidation catalysts of the pregent invention avoid or reduce the unwanted side effect of promoting the oxidation of S2to SO 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, the exhaust of compressed natural gas engirnes, 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 25 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 par..

ticular of reducing diesel exhaust particulates emissions by oxidation of the volatile organic fraction thereof, can be attained by a mix~ture of high surface area, activatedt alumina and a high surface area ceria) each havinq a BET surface area of 10 m 2 /g or higher. For purpoies of illustration, the benefits ot the present invention will be described in detail below with rrispect 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 su.face area of at least about 10 m2/g, preferably at least about m 2 For example, the bulk alumina may have a surface area of from about 120 to 180 m 2 /g and the bulk ceria may have a surface area of from about 70 to 150 m The fact that a catalyst composition which can serve as a diesel oxidation catalyst and which contains ictivated 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 (a-alumina) and/or be used in conjunction with sulfateresistant 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 aluma.na of sufficiently high surface area (10 m 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 -11in 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, to SO, 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, to SO, 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 2 to SO. 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 O"I 30 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 -12of ceramic-like materials such as cordierite, a-alumina, silicon nitride, zirconia, mullite, spodumene, aluminasilica-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 carri- S 20 ers, with the distinction that each channel is blocked at S: one end of the carrier body, with alternate channels blocked at opposite end-faces. Wall-flow carrier sub- 0 strates 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 struc- 'ture.

The Catalytic Material The ceria-alumina catalytic material may be prepared 30 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.

-13- 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, 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, .4.

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 30 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 ics oxide.

When the catalytic material is applied as a thin coating to a suitable carrier, such as described above, -14the 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 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 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 preferably from about 0.25 to about 3.0 g/in 3 of the coated carrier substrate, optionally including from about 0 toO 5, preferably from about.\to o.sg/ft 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 ex- 20 haust, 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, 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 con- 30 densation of oil vapors to liquid phase. The small pore size of the high surface area ceria-alumina catalytic material is believed to provide cuch capillary condensation action for the VOFP 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 VOP) are desorbed from the ceria-alumina catalytic material and volatilize, 1 I ll 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, 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 ceriaalumina 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 tem- 20 perature 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, rare earth metal oxides such as ceria. Thermal stabilization of high surface area ceria and alumina to militate against 30 phase conversion to less catalytically effective low surface area forms is well-known in the art although thermal stabilization of alumina is not usually r.eeded 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, 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 -16then 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 under- S: coat 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 nom- Sinal BET surface area of 150 m 2 /g with 50 cubic centimet- Sers of glacial acetic acid and 1 cc of an antifoamant sold under the trademark NOPCO NXZ ii, 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 C and then calcined in air at 4506C for 1 hour to provide alumina-coated carri- -17ers.

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 2 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. Patent 4,714,694 issued December 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 20 other conditions of treating diesel exhausts.

Aluminum-stabilized ceria is more resistant to such 'too$* 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 30 ball mills. A quantity of an amine-solubilized platinum hydroxide solution containing 0.2894 grams of platinum, a •9 .quantity of monoethanolamine 97.5 -c 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 plat- -18inum 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 attan the same particle size of the ceria partidcles. 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 4500C to provide a finished catalyst containing a coating of a ceria-alumina catalyti material having about 0.5 g/ft 3 of platinum dispersed thereon. The catalytic material coating, sometimes re- •e 20 ferred to as a washcoat, inclusive of the platinum content, comprises about 1.95 g/in of the catalyst compositoo* eeo6 tion, the catalytic material overlying an alumina undercoat which comprises about 1.00 g/inl 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 overly.

ing the undercoat.

3 Os Reference in the following TABLES, or elsewhere in eo'e 30 this application, to a percentage conversion of constituents (rendered as in the TABLES) of the exhaust or test gas, means the percentage of such eonstituent initially present in the exhaust or test gas being treated which is converted to another species, the conversion to HO and/or CO, of IC, CO and VOF, and the oxidation to SO of SO 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, 40 percent -19conversion 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, 2.0 and 5.0 g/ft of platinum. These catalyst camples comprised cores measuring 1.5 inches in diameter and inches in length, cut from cordierite carriers 6 inches long and 6 inches in diameter, used, as in Example I, to make the catalysts of this Example 2. The resulting :400 cpsi cordierite sample cores contained a loading of 'Goo* 1.95 g/in3 of the ceria-alumina catalytic material overlying an alumina undercoat present in the amount of 1.00 g/inl, 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 0 C by haying 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 0

C,

350CC, 425 0 C and 500 0 C. The test gas had a composition of 10 percent steam, 10 percent oxygen, 4.5 percont CO, 1 ppm NO, 28.6 ppm heptane, 200 ppm CO, 5O ppm SO, 1 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. to SO. The results of these tests are tabulated in TABLE below and plotted in Figure 1.

Inlet Gas Temp. 275 275 275 275 275 350 350 350 350 350 425 425 4125 425 425 500 20 500 500 500 500 TABLE I Platinum Loading (gi/ft 0 0.5 1.0 2.0 5.0 0 0.5 1.0 2.0 5.0 0 0.5 1.0 2.0 5.0 0 0.5 1.0 2.0 5.0 %Ca so,_ 8.0 0.0 6.1 16.0 30.6 8.0 4.0 17.6 21.6 30.0 12.0 11.8 255 33.3 48.0 20.0 12.0 28.8 35.3 62.0

%C

HC

0.0 2.4 0.0 10.0 20.2 0.0 9.8 31.7 87.8 83.1 2.6 31.6 66.6 90. 5 91.9 9.3 47.4 80.5 83.1 88.0

%C

CO

0.0 30.5 74.6 99.0 99.5 5.9 68.3 97.9 100 100 10.3 84.3 96.4 100 100 9.3 84.8 98.5 99.5 100 0 *0 0* .0 0~ a 0~ 0 0 I 0 0 25 a means the percentage conversion constituent.

of the indicated The data of TABLE I, and the plot thereof in Figure 1, clearly show that the ceria-alumina catalytic material 30 containing no platinum in each case providedi at each temperature level tested, a somewhat higher degree of conversion of SO, to SO than did the otherwise identical eeriaalumina catalyst containing 0.5 g/t of platinum. As the platinum leading was increased to 1.0 q/ft at each ternperature level, the uegree of undesired conversion of SO8 to SO8 increased as compared to the versions containing no or only 0.5 g/ft Further increases in platinum loading to 2 and S g/ft- further increased, as one would expect, -21the oxidation of SO,. what is very surprising is the fact, clearly shown in Figure 1 and the data of TABLE I, that the ceria-alumina catalytic material containing g/ft3 of platinum dispersed thereon demonstrated less conversion of SO 2to SO03 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 2 to SO.

Figure 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 1, and the plot of the H-C conversion data of TABLE I in Figure 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 dosign, catalytic treatment of diesel exhaust may not be necessary in order to attain reductions in H4C and CO to meet U.S.

Government standards, because the modified engines have reduced the output of HIC and CO to below that of the cur- *rent and impending U.S. Government standards. Nonetheless, the Inclusion of platinum, at least at a loading of not more than about 1 g/ft preferably at from about 0.1 to 0.8 g/ft3, more preferably at about 0.5 g/ft 3 is seen *to have a beneficial effect on reducing the amount of oxi- *dation of So 2 to SO,. Thus limited, the addition of platin: um is seen to reduce So 2 oxidation and thereby arneiiorate particulates emissions. The addition of platinum also provides a beneficial added effect of further reducing HC and C0 emissions.

will be appreciated that in some cases it may be desired or necessary to significantly reduce HIC and/or CO emissions and, in order to do so, the addition of moderate amounts of platinum, not more than 15 g/ft, preferably not more than 5 g/ftl, and mnost preferably n~ot more than 2 g/ft~, may be desirable despite the concomitant increase -22in SO 2 oxidation at additions of significantly more than g/ft 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 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 ferV'ent aluminum-stabilized ceria and 53.8 weight percenov alumina, and having dispersed thereon 0.5 g/ft 3 of platinum. The ceria-alumina topcoat layer was present in the amount of 1.95 g/in 3 The ceria had a surface area of about 164 m 2 /g and the alumina had a surface area of about 150 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 *t 20 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-alu- 09 mina catalytic material. The three catalyst samples were then tested for HC, CO and SO" conversion at 350°C and a space velocity of 90,000. The results are shown in TABLE e. II below.

*e TABLE II

%C

a %Ca 30 Sample CO IIC SO 2 S-3Ce 80.2 37.5 4,1 S-3 49.3 7.55 4.6 S-3A1 94.9 56.5 a means the percentage conversion of the indicated constituent.

The data of TABLE II clearly indicate that the platinum -23is a more effective oxidation catalyst for HC and CO when dispersed on the alumina (S-3AI) 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 ,.-3Ce sample in which fairly high levels of desired conversion of CO and HC were attained and the lowest level the undesired oxidation of SO 2 to SO 3 was also attained.

S-3 catalyst provided significant, but lesser, conversions of CO and HC and only slightly more of the undesired oxidation of So, than did S-3Ce, but was much better in terms of less promotion of oxidation of SO, than was the S-3AI sample 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 "ndercoat at a loading of 1.0 g/in on which a metal oxide topcoat was coated. In the case of comparative sample Comp.l, the topcoat contained no ceria, the topcoat of comparative sample Comp.2 contained no alumira, 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 3 of platinum and had a topcoat loading of about 1.95 g/in inclusive of the platinum. in all cases the ceria had a surface area of 164 m 2 /g and the alumina had a surface area of 150 m 2 The samples were tested with the same test gas as described in Example 2 at 2756C, 350 0 C, 425 0 C and 5000C, and the conversion of HC, CO and oxidation of SO to SO, at a space velocity of 50,000 was measured. The results of these tests are summarized in TABLE III.

-24- TABLE III Inlet Gas Sample %C %C %C Temp. (OC) No. SO 2 HC CO 275 Comp.l 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.l 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.l 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.l 42.2 83.7 99.7 500 S-3 12.0 47.4 84.8 500 Comp.2 32.0 "1.6 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, 20 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, to SO, are shown in the perspective-view plot of Figure 3 from which it is readily seen that at each temperature level tested a lower degree of conversion of SO, was attained by the S-3 sample in accordance with an embodiment of the present invention, than was attained with either the 100 30 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, as compared to either a 100 percent ceria or 100 percent alumina catalyst containing 0.5 g/ft 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.

S

0* S e *0 04 4 .4 0P Temperature less than 100 100-200 200-300 300-400 400-500 20 Maximum Temperature (OC): Particulates:

VOF

Sulfate Carbon/Otherd Totals TABLE IV Caterpillar 3176 Temp. Cycle" 0 0 57.3 30.9 11.8 475 Cummins 6BT Temp. Cyclea 0 62.6 36.7 0.7 0 305 g/HP-hrb q/lP-hrb 0.036 0.005 0.127 0.168 21.6 3.1 75.3 100.0 0.066 0.003 0.103 0.172 Wt.% 0 38.4 59.6 100.0 Gas Phase:

HC

CO

NO

X

4.

0 *r 0 0.123 3.48 5.06 0.300 1.50 4.34 a Percentage of cycle time at which the inlet exhaust to the catalyst lies within the indicated temperature range b "g/HP-hr" grams per brake horsepower-hour of compo- -26nent emitteu in exhaust Weight percentage of total particulates provided by the indicated constituent 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 20 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 25 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 3 and a topcoat of the ceria-alumina coating at a loading of 1.95 g/in 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 a-alumina of Comp.2.3 -27and 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 2 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 20 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.

25 TABLE V o Metal Catalyst Loading Hours Aged S Sample Washcoat Metal g/ft 3 24 100 S-3 Ceria-Alumina Pt 0.5 X X Comp.4 Niobia-Silica a Pd 50.0 X X Comp.4M Niobia-Silicaa Pd-Pt 25-5 X X S-3B Ceria-Alumina Pd 50.0 X X Comp.4B Niobia-Silica a Pt 0.5 X Comp.7 MnO-Niobia-Silicab Pt 2.2 X Comp.2.3 e Silica-FAAd Pt 2.2 X Comp.6 Vanadia-Titania' Pd 27 X X a The niobia-silica sample catalysts (Comp.4, 4M and -28- 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 3 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 6 percent by weight MnO, with a total washcoat loading of 0.6 g/in 3 C The silica-foamed a-alumina sample catalyst (Comp.2.3) had a washcoat comprised of 10 percent by weight silica sol binder and 90 percent by weight of foamed a-alumina with a total washcoat loading of 0.6 g/in. The a-alumina has a porosity of 0.0439 cc/g pore volume comprised of poreshaving a radius of from about 10 to 300 Angstroms, and a surface area of 20.3 m 2 /g.

d "FAA" foamed a-alumina 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 20 loading of 1.8 g/in 3 *ag* 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 "Fed- 25 eral Test Procedure" or 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 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 tem- -29peratures as follows for the indicated amount of time: 330 400 0 C for 14% of the time, 400 500 0 C for 22% of the time, 500 550 0 C for 50% of the time, and 550 565 0 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- 20 -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 util- 25 ized 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".

TAB3LE VI Catalyst Sample HC CO NOx: TPM None Untreated engine exhaust Carbon VOF Sulfate Other Gramsa 0.299 S-3 Grams 8 0.188 %Cb 37.4 1.5 4.34 0.172 0.0611 0.0034 0.108 1.11 4.3 26 0.96 comp.4 Grams

%C

Comp. 4M Grams 0.198 34. 1 0.213 29.1 1.28 14.9 1.34 11 4.22 2. 7 4.22 2.8 0.118 31.7 0.123 28.8 0.123 28.8 0.0256 58.1 0.0272 55.4 0 .0302 50.6 0. 00 16 53.1 0.0022 37 0.0025 28.2 0. 0908 i5s. 9 0. 0936 13.3 0. 0903 16. 4 .00.

.06.

06.

S- 3B Grams 0.155 %C 48.3 Comnp. 4B Grams 0.208 C 30.7 Comp.7 Grams 0.198 %C 34.1 Comp.2.3 Grams 0.185 %c 38.2 1.31 13 1.17 22.2 1.09 27.2 1.09 27. 5 4.31 0.73 4.27 1.5 4.31 0.79 4.34 0.1 0.118 31.7 0.128 25.9 0,135 21.5 0.135 2 1. 5 0. 0258 57.7 0. 0359 41 .2 0.0378 38.1 0. 0306 38.1 0.0025 26 0. 0033 4.8 0. 0028 17.2 0.0049 -3.6 0. 0897 16.9 0. 0888 17.8 0. 0944 12.6 0.09 0O Comp. 6 Grams 0.135 54.0 1.51 -0.3 4.35 -0.25 0.118 31.7 0.0255 50.3 0.003 11.4 0.0895 17. 1 Grams per Gras erbrake horsepower-hour -31means the percentage conversion of the indicated constituent. A negative %C means the treated exhaust contained more of the constituent 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 soxple 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 co,sistent with the relatively low temperature of the Cummins 6BT engine. With respect to gas phase emissio'ns (HC, CO and NOx) 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, emis- 20 sions as one would expect in the relatively oxygen-rich o environment of a diesel exhaust.

0 Example 6 As indicated in TABLE V, five of the catalysts tested 25 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.

*e Tn VIlr Catalyst Carbon .:Sample, ,tc CO NOx TPM VOP Sulfaite Other None Untreated engine exhaust Grams a 0.305 1.55 4.46 0.179 0.0675 0,0039 0.108 S-3 Gramsa 0.188 1.27 4.31 0.123 0.0284 0.0018 0.0928 %Cb 38.4 17.9 3,3 31.3 57.9 53.8 14.1 -32- TABLI VII Cunt'd.

Catalyst Carbon Samle HC CO NOx TPM VOF Sulfate Other 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 20 Grams per brake horsepower-hour too#b 11%C" means the percentage conversion of the indicated constituent. A negative %C means the treated exhaust contained more of the constituent than did the untreated exhaust.

Table VII shows that the best results were attained by the S-3 and S-3a 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 5-3 to 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 cempo- -33sitions of the present invention, S-3 and S-3B, yave the best overall emissions control end 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 3 of the ceria-alumina catalytic material of the invention. The ceria-alumina catalytic material contained 46.2 weight percent of aluminum-stabilized ceria ind 53.8 weight percent of activated alumina. Each catalyst had an alumina undercoat in the amount of 1.00 g/ft3 onto which the ceria-alumina catalytic material was coated. One samdesignated S-3.S5Pt had 0.5 g/ft 3 of platinum dispersed thereon, another sample, designated S-3.2OPt had 20 2.0 g/ft 3 of platinum dispersed thereon and a thi,.d samdesignated S-3Pd had 50 g/ft 3 of palladium dispersed hhereon. Each catalyst was tested under the Federal Test Procedure to treat an exhaust generated by a Cummins Cseries 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 tot- :al particulates (TPM) ind gasteus phase 1iC and CO are sot forth in TABLE

VIII,

S*

S*

-34- TABLE VIII

%C

Sample TPM 1IC CO 47 28 S-3.20Pt 48 69 74 S-3Pd 48 52 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 11C 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 :.660 substantially similar results with respect to total particulates reduction in spite of the fact that S-3 contains 20 only 0.5 g/ft 3 of platinum and S-3B contains 50 g/ft 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 in- 25 sofar as total particulate reduction is concerned, and ,too. that particulate reduction is attained by the effect of ceria-alumina catalytic material.

In order to further demonstrate the irrelevancy of too, the platinum metal loading insofar as catalytic activ.4ty "of the ceria-alumina catalytic material with reospoct to total particulate reduction is concerned, a series of samples of catalytic material powder was prepared, This was done by utilizing the coria-alumina washcoat material of Example 7 containing various quantities of platinum metal ranging from 0 to the equivalent of 5.0 g/ft' of platinum if the washcoat were to be coated upon a 400 apsi 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 20 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.

Figure 4 is a plot of the results obtained by heating the 25 mixture of catalytic material powder and lubricating oil in a temperature regime rangihq from ambient temperature to 600'C and recording the TGA/DTA data. The DTA peak area was corrected for the weight change determined by the a TGA so that the results attained are proportional to the amount of lubricating oil combusted, to the effectiveness of the tested ceria-alumina catalytic materials, :awhich are identical except for the varying platinum metal loadings. The results attained are plotted in Figure 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 -36ceria-alumina catalytic material containing no platinum as for that containing incremental amounts of platinum up to and including the equivalent of 5 g/ft 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-alumin .atalytic 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 S 20 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 25 for 50 hours on an aging cycle similar to that described in Example 5 but from a minimum of about 300 0 C to a maximum of about 530 0

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.

e -37- TABLE IX Catalyst Carbon Sample HC CO NOx TPM VOF Sulfate Other None Untreated engine exhaust Grams 8 0.123 3.48 5.06 0.168 0.0363 0.0052 0.1265 S-3 Grams 8 0.1566 2.5 4.95 0.138 0.0213 0.0039 0.1128 %Cb 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 -3171 -9.3 11 Grams per brake horsepower-hour b ICI" means the percentage conversion of the indicated constituents. A negative %C means the treated ex- :haust 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, 25 resulted in an increase of total particulate emissions, P. 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 S. contrast to the effirdency of the S-I 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 remioval levels on the Caterpillar 3176 engine than on the Cummins 6ST engine is attributalble to the smaller catalyst volume relative to engine size encountered on the Caterpillar engine test and to the fact that the concen- -38tration 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 In order to compare the effect on conversion of SO 2 to SO3 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 I 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 5000C by having a mixture of 10 percent steam in air flowed through each sample. Comparative sample Comp.1 20 comprised 50 g/ft 3 of platinum disposed on an activated J606 alumina carrier and comparative sample Comp.2 had a gift 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 3 of platinum dispersed on a ceriaalumina 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 commercia4.ly available catalyst for diesel exhaust applications was analyzed and found to comprise r catalytic material dispersed on a honeycomb-type carrier having 400 cells per square inch.

The commercial catalyst contained about 50 g/ft3 of platinuii dispersed on a support comprised primarily of titan- -39ia, vanadia and alumina. A core 2.5 inches long and 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 2756C, 3500C, 4250° and 500 0 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,, 1000 ppm NO, 28.57 ppm heptane (equivalent to 200 ppm C I hydrocarbons), 28.6 ppm CO, ppm SO 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.

S S 99 9 II 9 99..

9 o a 9 99* 9. 9 99* 9 9l 9.oo9 99* 9.

e o ft ft ft ft f ft ft ft ft 20 Catalyst Sample/ Inlet Temp.

Comp.1 25 275°C 350 0

C

4250C 500 0

C

Comp.2 275°C 350 0

C

425 C 500°C TABLE X Percent Conversion at Indicated Space Velocity 50,000 SV 90,000 SV CO HC SO CO HC SO 2 99.5 99.5 100 100 68.6 83.0 87.4 89.0 56.9 76.9 94.3 92.2 94.9 96.5 52.4 70.5 29.4 58.5 100 52.5 99.0 77.5 99.0 84.2 98.1 90.7 11.8 31.4 47.1 98.5 96.9 96.0 95.5 47.6 61.7 74.4 73.2 9.8 23.5 37.3 TABLE X Cont'd.

Catalyst Percent Conversion at Indicated Space Velocity Sample/ 50,000 SV 90,000 SV Inlet Temp CO HC SO_ CO TC SO 2 Comp.11 275aC 97.1 16.7 0.0 84.7 4.8 350 0 C 99.0 54.5 2.0 93.0 41.0 425 0 C 99.5 75.0 23.6 97.0 63.2 15.7 500 0 C 99.5 85.9 54.9 97.4 73.2 38.0 S-3 275 0 C 30.5 2.4 0.0 10.9 0.0 0.0 350 0 C 68.3 9.8 4.0 52.4 9.5 0.0 425 0 C 84.3 31.6 11.8 59.5 24.3 3.9 500 0 C 84.4 47.4 12.0 60.0 28.6 4.1 The data of TABLE X shows that the comparative samples Comp.l and Comp.2 exhibit very high conversion of So 2 SO,, and thus high sulfate make, even at the lowest test temperature of 275 0 C and high space velocity of 90,000. Although comparative sample Comp.2 exhibits less sulfate make than Comp-l (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 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.l and Comp.2 show high HC and CO conversion. S-3, the sample in accordance with an embodiment of the present invention, ex- .hibits greatly reduced SO 2 conversion relative to both Comp.l and Comp.2 with practically no SO 2 conversion occurring in the low temperature regime and with relatively small SO, 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 -41the utilization of a low platinum loading on the ceriaalumina catalytic material of the present invention provides excellent control of SO 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.ll is seen to suppress 30, oxidation in a manner comparable to that of sample S-3, but only up to a temperature between 3500 and 425 0 C. At 425 0 C and higher temperatures the Comp.ll sample exhibits greatly increased SO, oxidation as compared to the S-3 catalyst sample. Accordingly, the catalyst sample of the present invention, even with a 0.5 g/ft 3 platinum loading, appears to be significantly better with respect to SO, oxidation in higher temperature regimes than the commercial catalyst of Comp.ll. The comparative samples Comp.1, Comp.2 and Comp.11 all contain high plat- Sinum loadings and consequently show higher HC and CO conversion than does the 0.5 g/ft 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 re- *".ducing 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.

-42- 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. The S-3P catalyst sample was 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 275OC, 350 0 C, 425 0

C

and 500 0 C. The results of this test are shown in TABLE X1.

TABLE XI Catalyst Percent Conversion at Indicated Space Velocity Sample/ 50,000 SV 90,000 SV Inlet Temp. CO tc SO2 CO HC SO_ S-3P °oee.

275 0 C 99.0 10.0 16.0 88.5 2.6 20 350 0 C 100 87.8 21.6 98.0 74.1 5.9 *see.

425 0 C 100 90.5 33.3 98.5 82.7 19.2 .:500 0 C 99.5 83.1 35.3 98.1 73.3 31.4 TABLE XI shows, as would be expected, that the S-3P 25 catalyst exhibits higher SO, oxidation at all temperature levels and space velocities as compared to the S-3 catalyst of Example 10 which contains 0.5 g/ft of platinum, one-fourth of the amount of platinum (2.0 g/ft3 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 -43in 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 3 of platinam 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 S02 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 •el• in the oxidation activity of the platinum.

0..

20 TABLE XII '.."Catalyst Percent Conversion at Indicated Space Velocity Sample/ 50,000 SV 90,000 SV Inlet Temp. CO HC S02- CO IIC SO 2 Comp.3C 25 275 0 C 96.6 10.0 16.3 85.4 4.9 4.6 350 0 C 99.6 86.5 18.9 95.0 57.4 12.6 425 0 C 99.9 90.5 35.5 98.1 74.0 33.7 500 0 C 99.7 83.7 42.2 98.3 74.0 33.7 O 8xample 13 A catalyst was prepared in accordance with the present invention generally following the teachings of Example I, except that no alumina undercoat was utilized. Thus, this sample comprised 1.95 g/ft3 of a ceria-alumina catalytic material containing 46.2 weight percent aluminumstabilized ceria (164 m 2 /g BET surface area) and 53.8 weight percent alumina (150 m 2 /g BET surface area) disposed directly upon the carrier without an alumina under- -44coat, and having 0.5 g/ft 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 ess-ntially the same as that of S-3 (Example 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 HIC SO CO iHC SO 2 S-3SC 275°C 25.4 0.0 2.0 31.0 0.0 0.0 350°C 71.9 1.1.9 5.9 62.5 15.8 4.1 425°C 85.6 28.9 9.8 78.7 29.3 5.9 *00 500°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- S 25 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 3 platinum. Each catalyst comprised a y-alumina undercoat at a loading of g/in 3 upon which was coated a top coat layer comprised of 1.05 g/inI y-alumina plus 0.90 g/in 3 alumina-stabiltzed eria (2.5 weight percent AIO 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/ftt platinum, aged 24 hours), S-5 (0.5 g/ftI platinum, aged 25 hours) and S-6 (2.0 g/ft 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 11880715, published at the International Congress and Exposition, Detroit, Michigan, February 29 through March 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 Figures 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 horlepower. 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 :spot• average (for five runs) catalyst inlet temperatures and baseline emissions (of untreated engine exhaust) are shown in TABLE XIV.

TA13LE XIV Cummins 6BT 190 UP Turbocharged 25 Diesel Engine, 5.9 Liter Displacement, Conditions For Steady State Catalyst Tests .Enine Conditions :Average Test Catalyst Inlet Mode No. rpm Load Temp. (OC) 8 2515 100 571±2 2515 50 338+4 6 1609 100 549+5 4 1609 50 400+4 2 1560 10 214±3 1 803 Low 128+16 -46- TABLE XIV Cont'd.

Cummins 6BT 190 [IP Turbochargcd Diesel Engine, 5.9 Liter Displacement, Conditions For Steady State Catalyst Tests Baseline Emissions Untreated Exhaust Test Average Emissions (g/bhp-hr) Mode No. TL'PM SOF 11C 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 I. 1 0.078 1.04 3.01 15 grams per brake horsepower hour .e The conditioned and aged catalyst samples S-4, and S-6 were tested for conversion of emission components in diesel exhaust generated by the test engine used to 20 generate the data of Table XXV, as a function of steady state test mode and catalyst inlet temperature, 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 ,q /f-t Mode No. m.nip. C SOP ,P c _CO S-4 2 209 72 63 31 1 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 10 343 58 28 41 63 6 549 91 -64 56 8 570 80 -201 62 -47- TABLE XV Cont'd.

Sample/ (Pt Load Test Cat. Inlet Removal q/ft 3 Mode No. Temp. "C SOF TPM IIC CO S-6 1 127 56 52 37 -1 2 215 61 61 39 8 341 53 31 74 86 4 397 61 22 82 87 6 554 89 -60 78 8 572 79 -200 71 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 15 performing as well as the catalysts containing platinum (S-5 and S-6).

With reference to TABLE XV and Figures 5-8, it is seen that the SOF removal performance as a function of inlet temperature of the three catalysts are compared in 20 Figure 5. As can be seen, all three samples are comparable across the temperature range of about 120 to 575°C with the sample containing no platinum performing as well as or better than, the platinum-containing samples S-5 and S-6.

The SOP removal performance is also reflected in the total particulate (TPM) removal levels of the three catalysts which are compared in Figure 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 2 to SO, Thus, even the platinum-froee 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 -1 8are compared in Figures 7 and 8 for, respectively, hydrocarbon and carbon monoxide gas phase conversions. Although the platinum-Cree sample S-4 exhibits some gas phase activity for HIC and CO conversion, it is clear from those 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 qas phase activity because the coria component has activity as an oxidation catalyst.

These results show quite well the surprising finding that a platinum-free catalyst in accordance with the presoent invention exhibits very good particulates removal from disel engine exhaust because of its activity for the re- 15 moval and combustion of VOP, and that the precious metal o' is not needed to accomplish this tunction. It 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.

20 While the invention has been described in detail with respect to spectfic 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.

Claims (27)

1. An oxidation catalyst composition comprises a re- fraotory carier on which in diapooed a coating of a oaria- alumina catalyic uaterial comprising a combination of caria having a BhT surface area of at least 10 m 2 /g and alumna, oxcluding' a-alumina, having a BUT ourfaco area of at 1aoat 10 m2/g, said catalytic material not including a aatalytically active precious metal.

2. The catalyse toomposition of claim 1 wherein the aeria and alumina each comprises from about 5 to 95 percent by weight of the combination. 3, The catalyat composition of claim I wlrein the oaria and alumina each comprises from 10 to 90 percunt by weight of the combination.

4. The catalyst composition of claim 1, claim 2 or claim 3 wherein the coria. and the alumina are each diaposed in respective discrete layers, ono ovorlyin the other. i' 1 The catalystt composition of claim 1, claim 2 or: I' claim 3 whereurin the cQia cona~rlacm an aluminum-stabilitod 0 46

5. T1he catalyst componition of claim I whlein the 060% cera andl alumina each comprises fLrom 40 to 60 percent by :i:weiaht ofa the combination. Who catalyst compoition of claim wherein the 2S ceri4 ah nd the alumina each haslt a SRT sP urface area~o ot fromn 2S O/V to 200 =Iria

6. A catalyst compositon fr cluaying 1dionua angin a ehaunhcomprses a refractory carr r on Whrch in o. 6 Od 11' 1: I'AN H 3 1211 11POLI WlI I VI'l 1 I lA( I N (A)i W11 1) 12 so disposed a coating of a catalytic material comprising a combination of ceria havirq a ET surface area of at least m 2 /g and alumina, excluding Cx-alumina, having a nEz surface area of at least 20 m 2 the ceria and alumina each comprising from 5 to 95 percent by weight of the combination, said catalytic material not including a catalytically active precious metal.

9. The oatalyct romponition of claim 8 wherein the ceria and alumina each comprises from 10 to 90 percent by weight of the combination The cataliyut onooition of claim 8 wherein the oeria and the alumina each comprises from 40 to 60 percent by weight of the oonib.nation.

11. The catalyot compooltion of claim 8, claim 9 or 1S claim 10 we'rein the ceeia compricao aluminumxa1-tabill zed ceria. I'd. The catalyst compofaition o claim 8, claim 9 or claim 10 wherein the coria and the alumina are each diopoeed in respective discrete layers, one overlyin tho 2 othor.

13. A method for oxidizing oxidiZeab1 o omponents of -i 'jae-borne stream oompriaea contacting tho Btleam with a cstaiyat compopition at a tomperature high unough to catalyze oxidation of at least some of the oxidizeable Qomponents, the catalyst composition compridng a catalytic mtral Ca1comprising a combination of uaria hiving a BET ourface area of at leact O m 2 /a and alumina, excluding a- alumina, having a BDMT surtace aroa of at least 10 2 /gq, *5 said catalytic mr ial not !Lncluding a catalytically active precious metal, rlrrrzrcllr\r~tknlyrm' S2 I-.16 0 T U ,17 03 VAX 01,, 3 92.3 80333 OR V['ll'ml HACK A(10 yd'i 1.3 51

14. A method for treating a gas-borne stream comprising a diesel engine exhaust stream containing a volatile organic fraction comprises contacting the stream with a catalyst composition at a temperature high enough to catalyze oxidation of at least some of the volatile organic fraction, the catalyst composition comprising a catalytic material comprising a combination of ceria having a BET surface area of at least 10 m 2 /g and alumina, excluding a- alumina, having a BET surface area of at least 10 m 2 /g, said catalytic material not including a catalytically active precious metal. A method of claim 13 or claim 14 wherein each of the ceria and alumina comprises from 5 to 95 percent by weight of the combination.

16. The method of claim 13 or claim 14 wherein each of the ceria and alumina comprioea from 40 to 60 percent by weight of the combination.

17. The method of claim 13 or claim 14 wherein the temperature of the exhaust initially contacted with the V 20 catalyst composition if from 100 0 C to 8000C. s 18. The method of claim 13 or claim 14 wherein the *ceria and the alumina each has a BET aurface area of from about 25 m/q to 200 m2/g. S

19. The method of claim 13 or claim 14 whorein the ceria coimprises aluminum-gtabilized ceria

20. The method of claim 313 or claim 14 wherein the coria and the alumina are each disposed in respective diacreto layera, one overlying the other.

21. An oxidation catalyst composition comprises a re- t A 025 '05 0 IJItLI 1714 0- AX 01 3 0244 4334 11!PPIT,1 IIA'K C IsJ U I4 52 fractory carrier on which is disposed a coating of a ceria- alumina catalytic material comprising a combination of ceria having a BET nurface area of at least 10 m 2 /g and alumina, excluding a-alumina, having a BET surface area of at least 10 m 2 and up to 0.5 g/ft 3 of platinum dispersed on the catalytic material.

22. The catalyst composition of claim 21 wherein the ceria and alumina each comprises from about 5 to 95 percent by weight of the combination,

23. The catalyst compomition of claim 21 wherein the ceria and alumina each comprisen from 10 to 90 percent by weight of the combination.

24. The catalyst composition of claim 21, claim 22 or claim 23 wherein the ceria and the alumina are each disposed in respective discrete layers, one overlying the other, The catalyst composition of claim 21, claim 22 or claim 23 wherein the ceria comprisea an aluminum-ctabilized c aeria.

26. The catalyst composition of claim 21 wherein the ceria and alumina each comprises from 40 to 60 percent by weight of the combination. *44

27. The catalyst composition of claim 21 wherein the coria and the alumina each has a BET 2urfaoe area of from S. 25 25 m/g to 200 m 2 /g. 0

28. The catalyst composition of claim 21 wherein the platinum in present in the aount of from 0.1 to 0,5 g/£6t of the composition. K., j l2 'O 00 ,TOil l ,17:0! I FAX 0,1. 3 02l43 83, 3I (I T 11111 IIACK CO Il 1 53

29. The catalyst composition any one of claims 21 to 28 wherein at least a catalytically effective amount of the platinum is dispersed on the ceria. The catalyst composition of claim 21 wherein at least a catalytically effective amoui. of the platinum is dispersed on the alumina.

31. The catalyst composition for purifying diesel engine exhaust comprises a refractory carrier on which is disposed a coating of a catalytic material comprising a combination of ceria having a BET surface area of at loast m/ and alumina, excluding a-alumina, having a BET surface area of at least 10 m 2 the ceria and alumina each comprising from 5 to 95 percent by weight of the combination, and up to 0.5 g/ft 3 of platinum dispersed on the catalytic material.

32. The catalyst composition of claim 31 wherein the coria and alumina each comprises from 10 to 90 percent by weight of the combination. o 4

33. The catalyst composition of claim 31 wherein the 20 coria and the alumina each comprises from 40 to 60 percent :by weight of the combination. a a

34. The catalyst composition of any one of claima 31, 32 and 33 wherein the platinum is present in the amount of from 0.1 to 0.5 /ft 3

35. The catalyst composition of claim 31 whoroin the ceria comprises aluminum-stabilized ceria.

46. Tho catalyst composition of claim 31, claim 32 or claim 33 wherein the ceria and the alumina are each disposed in respective discrote layers, one overlying the I '00 YIIU 17"O'l VA' PX kil, 3 024 3 1) 33 (w1oi IPI 'ii MICI( k VO 10, 1 1,1 -54- other 37. A method for oxidizing olcidizeable components of a gas-1borne stream comprises contacting the stream with a catalyst composition at a temperature high enough to catalyze oxidation of at least some of the oxidizeable components, the Catalyst composition comprising a catalytic material comprising a combination of oeria having a BET surface area of at least 10 m 2 /g and alumina, excluding Y- alumina, having a n3T surface area of at least 10 m 2 and up to 25 g/ft 2 of platinum and up to 200 g/ft of palladium dispersed on the Catalytic material. 38. A method for treating a gas-bornie otream comprising a diesel engine exhaust Btream containing a volatile organic fraction comprises contacting the stream with a catalyst composition at a temperaturz. high enough to catalyze oxidation of at least Dome of the volatile organic fraction, the catalyst composition comprising a catalytic material comprising a combination of coria having a BET surface area of at least 10 ml/g and alumina, excluding c- alumina, having a BBT surface area of at least 10 m2/g, and up to 25 G/ft3 of platinum and up to 200 g/ft 3 of palladium dispersed on the catalytic material. DATED THXS 2ND DAY OF MAY 1996 EN3ZL1XD COXPORATXON By its Patent Attorneyoz so.. GRZFXITH HACK CO )Fallows institute of Patent Attorneys of AUstralia a I~ S S ABSTRACT OF THE DISCLOSURE Oxidation catalyst compositions include a catalytic material containing ceria and alumina each having a sur- face area of at least about 10 m2/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 SO2 to SO). Alternatively, palladium in any desired amount may be in- cluded in the catalytic material. The catalyst composi- tions 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 15 method to treat diesel engine exhaust by contacting the hot exhaust with the catalyst composition to promote thu oxidation of the volatile organic fraction component of particulates in the exhaust. 99 9 9 9 99