KR100491067B1 - Exhaust Gas Catalyst Comprising Multilayered Upstream Zones - Google Patents

Abstract

The present invention relates to an exhaust gas treating catalyst product comprising an upstream catalyst zone and one or more downstream catalyst zones. The upstream catalyst zone comprises an upstream composition comprising a first upstream support and at least one ash upstream palladium component. The upstream zone may comprise one or more layers. The downstream catalyst zone comprises a first downstream support and a first downstream layer comprising a first downstream precious metal component. The second downstream layer comprises a second downstream support and a second downstream precious metal component.

Description

Exhaust Gas Catalyst Comprising Multilayered Upstream Zones

Background of the Invention

Field of invention

The present invention relates to a catalytic device useful for treating exhaust gases, including automotive engine exhaust gases, to reduce contaminants contained therein. More specifically, the present invention relates to a catalytic device comprising an upstream catalyst zone and a downstream catalyst zone with an improved catalyst, including "three-way conversion" or "TWC" catalysts. TWC catalysts are multifunctional in that they have the ability to catalyze the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides substantially simultaneously.

Background of the Invention

Catalytic apparatus comprising an upstream catalytic zone, and also a downstream catalytic stage, also referred to as zone, useful for treating exhaust gases, including automotive engine exhaust gases, to reduce contaminants contained therein; US Pat. No. 5,010,051; It is disclosed in the art as illustrated in 5,106,588 and 5,510,086.

Three-way diverting catalysts are useful in a number of applications, including treatment of emissions from internal combustion engines such as automobiles and other gasoline fuel engines. Emission standards for unburned hydrocarbon, carbon monoxide and nitrogen oxide contaminants are set by national governments and must be met by new vehicles, for example. The TWC catalyst containing catalytic converter is located in the exhaust gas line of the internal combustion engine to meet the above criteria. The catalyst promotes oxidation of oxygen in the exhaust gas of unburned hydrocarbons and carbon monoxide and reduction of nitrogen oxides to nitrogen.

TWC catalysts, known for their high activity and long life, include one or more platinum group metals (e.g. platinum or palladium, rhodium, ruthenium and iridium) located on a high surface area refractory oxide support, such as a large surface area alumina coating. do. The support is included on a suitable carrier or substrate, such as a monolithic carrier comprising refractory particles such as refractory ceramic or metal honeycomb structures or spherical or short extruded portions of suitable refractory materials.

U. S. Patent No. 3,993, 572 discloses a catalyst for promoting selective oxidation and reduction reactions. The catalyst contains platinum group metals, rare earth metals and alumina components that can be supported on relatively inert carriers such as honeycombs. Useful rare earth metals are disclosed to include ceria.

The BET surface area of large surface area alumina materials, also called “gamma alumina” or “activated alumina”, is typically greater than 60 square meters (“m 2 / g”) per gram, often at least about 200 m 2 / g. The activated alumina is generally a mixture of gamma and delta phases of alumina, but may also contain substantial amounts of eta, kappa and theta alumina phases. It is known to use refractory metal oxides in addition to activated alumina as a support for at least a portion of the catalyst component in certain catalysts. For example, bulk ceria, zirconia, alpha alumina and other materials are known for this use. Many of these materials have the disadvantage that the BET surface area is significantly smaller compared to activated alumina, but this tends to be counteracted by the good durability of the catalyst obtained.

In mobile vehicles the exhaust gas temperature can reach 1000 ° C., and such elevated temperatures cause thermal decomposition by volume shrinkage and phase transition in activated alumina or other support materials, in particular in the presence of steam the catalytic metal has an exposed catalyst surface area. Occluded in the shrinkage support medium with a loss of and a corresponding decrease in catalytic activity. Alumina for the thermal decomposition by using materials such as zirconia, titania, alkaline earth metal oxides such as baria, calcia or strontia, or rare earth metal oxides such as ceria, lantana, and mixtures of two or more rare earth metal oxides Stabilizing the support is known in the art. See, for example, US Pat. No. 4,171,288 to C. D. Keith et al.

It is known that bulk cerium oxide (ceria) provides an excellent refractory oxide support for platinum group metals other than rhodium, and it is possible to obtain microcrystals of platinum dispersed significantly on ceria particles, which bulk ceria is a solution of an aluminum compound. It can be stabilized by calcination and after immersion. U.S. Patent 4,714,694 to C. Z. Wan et al. Discloses aluminum stabilized bulk ceria, optionally combined with activated alumina, that acts as a refractory oxide support for an impregnated platinum group metal component. In addition, the use of bulk ceria as a catalyst support for platinum group metal catalysts other than rhodium is disclosed in US Pat. No. 4,727,052 to Wang et al. And US Pat. No. 4,708,946 to Ohata et al.

US Pat. No. 4,714,694 discloses alumina stabilized ceria catalyst compositions. This patent discloses a method of making a material comprising impregnating a bulk ceria or bulk ceria precursor with an aluminum compound, and calcining the impregnated ceria to provide aluminum stabilized ceria. The composition further comprises one or more dispersed platinum group catalyst components.

U. S. Patent No. 4,808, 564 discloses a catalyst for improving exhaust gas purification comprising a support substrate, a catalyst carrier layer formed on the support substrate, and a catalyst component retained on the catalyst carrier layer. The catalyst carrier layer comprises oxides of lanthanum and cerium having a mole fraction of lanthanum atoms to total rare earth atoms of 0.05 to 0.20 and a ratio of total rare earth atoms to aluminum atoms of 0.05 to 0.25.

U.S. Patent No. 4,367,162 discloses a substructure of a refractory material in the form of a honeycomb structure, and a powder of zirconium oxide, and a mixture of zirconium oxide powder and one or more powders selected from the group consisting of alumina, alumina-magnesia spinel and cerium oxide. A carrier having a porous layer of powder formed on the surface, selected from the group consisting of; And a catalyst component supported on a carrier comprising cerium oxide and a metal selected from the group consisting of platinum, palladium and mixtures thereof.

US Pat. No. 4,438,219 discloses alumina catalysts for use on substrates. The catalyst is stable at high temperatures. Stabilizing materials are disclosed to be one of several compounds, including those derived from barium, silicon, rare earth metals, alkali and alkaline earth metals, boron, thorium, hafnium and zirconium. Among the stabilizing materials, barium oxide, silicon dioxide, and rare earth oxides including lanthanum, cerium, praseodymium, neodymium and others are suggested to be preferred. It is disclosed that these are brought into contact with the calcined alumina film such that the calcined alumina film has a large surface area at high temperatures.

U.S. Patent Nos. 4,476,246, 4,591,578 and 4,591,580 disclose three-way catalyst compositions comprising alumina, ceria, alkali metal oxide promoters and precious metals. U.S. Patent Nos. 3,993,572 and 4,157,316 attempt to improve the catalytic efficacy of Pt / Rh based TWC systems by incorporating various metal oxides, such as rare earth metal oxides such as ceria and base metal oxides such as nickel oxide. Is shown. U. S. Patent No. 4,591, 518 discloses a catalyst comprising an alumina support and components comprising essentially the lantana component, ceria, alkali metal oxide and platinum group metal deposited thereon. US Pat. No. 4,591,580 discloses an alumina supported platinum group metal catalyst. The support is subsequently modified including support stabilization with lantana or lantana rich rare earth oxides, dual promotion with ceria and alkali metal oxides and optionally nickel oxide.

For example, US Pat. No. 4,624,940 discloses that palladium containing catalyst compositions are useful for high temperature applications. It has been found that the combination of lanthanum and barium makes the hydrothermal stabilization of alumina supporting the catalyst component palladium excellent. Thus, the palladium metal is not excluded from the alumina due to the vigorous phase transformation at high temperature exposure. Using particulate bulk metal oxides improves catalytic activity. Bulk metal oxides mainly comprise ceria containing and / or ceria-zirconia containing particles. Particulate bulk metal oxides do not readily react with stabilized alumina particles, thus providing a catalytic phase promoting effect.

U. S. Patent 4,780, 447 discloses a catalyst capable of controlling HC, CO and NO _x , and H ₂ S emitted from the exhaust pipe of an automobile equipped with a catalytic converter. The use of oxides of nickel and / or iron is known as H ₂ S gettering of the compounds.

Ind. Eng. Chem. Prod. Res. In a paper by Three Way Catalyst Response To Transients, Schlatter et al., In Dev., 1980, 19, 288-293, reported that the operating environment of a three-way catalyst It is reported that it is characterized by vibration. The incorporation of "oxygen storage" components into the catalyst suggests that it mitigates the effects of rapid changes between dense and minor exhaust stoichiometry. The authors also suggested that the presence of cerium on the rhodium impregnation sphere in a "freshly prepared" three-way catalyst improves the performance of the catalyst under transient or vibratory feed stream conditions by increasing the amount or stability of rhodium oxides. Kim, author of a more recent paper published in the same document: Ceria Promoted Three-Way Catalysts for Auto Emission Control (Ind. Eng. Chem. Prod. Res. Dev., 1982, 21, 274-288). Silver ceria is the highest non-noble metal oxide promoter for conventional Pt-palladium-Rh TWC supported on alumina catalysts mainly because it improves the water-gas transfer reaction (CO + H ₂ O = CO ₂ + H ₂ ) In part, it was reported that this could be due to the additional oxygen storage provided to the TWC.

U. S. Patent No. 4,539, 311 discloses a catalyst for treating automotive exhaust fumes that is said to improve resistance to lead. Alumina having a large surface area is first impregnated with a barium portion, such as an aqueous solution of barium compound, which decomposes when ignited above 400 ° C. to produce barium oxide, and then decomposes when ignited above 400 ° C. to use a platinum group metal or catalyst. If so, it is subsequently impregnated with a dispersion of the platinum group metal moiety by immersing alumina in an aqueous metal compound solution that leaves the compound converted to metal. The catalyst is prepared by coating the honeycomb support with alumina incorporating ceria. The dried and calcined alumina coating is then immersed in an aqueous solution of barium nitrate, dried and ignited, then immersed in an aqueous solution of platinum (IV) hydrochloric acid, dried and fired. The ignition step is carried out at 550 ° C.

U.S. Patent No. 4,294,726 discloses that a gamma alumina carrier material is impregnated with an aqueous solution of cerium, zirconium and iron salts, or the alumina is mixed with oxides of cerium, zirconium and iron respectively, followed by calcination of the material at 500 to 700 ° C in air. Thereafter, platinum and rhodium containing TWC catalyst compositions obtained by drying the material with an aqueous solution of platinum and rhodium salts which have been dried and subsequently treated in a hydrogen containing gas at a temperature of 250-650 ° C. are disclosed. Alumina can be thermally stabilized with calcium, strontium, magnesium or barium compounds. The ceria-zirconia-iron oxide treatment is followed by impregnation of the treated carrier material with an aqueous salt of platinum and rhodium followed by calcination of the impregnated material.

U.S. Patent 4,965,243 discloses a method for improving the thermal stability of precious metal containing TWC catalysts by incorporating barium compounds and zirconium compounds with ceria and alumina. This patent discloses that the formation of a catalytic moiety improves the stability of the alumina washcoat when exposed to high temperatures.

J01210032 and AU 615721 disclose catalyst compositions comprising palladium, rhodium, activated alumina, cerium compounds, strontium compounds and zirconium compounds. The patent discloses the use of ceria, zirconia and alkaline earth metals to form thermally stable alumina supported palladium containing washcoats.

US Pat. Nos. 4,624,940 and 5,057,483 disclose ceria-zirconia containing particles. It has been found that ceria can be uniformly dispersed throughout the zirconia matrix at up to 30% by weight of the total amount of ceria-zirconia complex to produce a solid solution. Co-formed (eg, coprecipitation) ceria oxide-zirconia particulate composites can improve ceria availability in particles containing ceria-zirconia mixtures. Ceria provides zirconia stability and also acts as an oxygen storage component. Patent '483 discloses that neodymium and / or yttrium may be added to the ceria-zirconia composite to modify the oxide properties obtained as desired.

U.S. Patent No. 4,504,598 discloses a process for preparing high temperature resistant TWC catalysts. The method comprises the steps of preparing an aqueous slurry of gamma or activated alumina particles, and the alumina comprising cerium, zirconium, one or more iron and nickel, and one or more platinum, palladium and rhodium, and optionally one or more neodymium, lanthanum and praseodymium Impregnating with a soluble salt of the selected metal. The impregnated alumina is calcined at 600 ° C. and then dispersed in water to prepare a slurry which is coated on a honeycomb carrier and dried to obtain the final catalyst.

US Pat. Nos. 3,787,560, 3,676,370, 3,552,913, 3,545,917, 3,524,721 and 3,899,444 use of neodymium oxide for reducing nitrogen oxides in exhaust gases of internal combustion engines. Is disclosed. US Pat. No. 3,899,444 discloses that lanthanide series rare earth metals are useful in conjunction with alumina to form activation stabilizing catalyst supports, particularly when calcined at elevated temperatures. The rare earth metals are disclosed to include lanthanum, ceria, cerium, praseodymium, neodymium and others.

A TWC catalyst system is disclosed that includes a carrier and two or more layers of refractory oxide.

For example, Japanese Patent Publication No. 145281/1975 discloses a catalyst support structure for exhaust gas purification comprising an adiabatic ceramic carrier and two or more layers of alumina or zirconia containing catalyst, wherein the catalyst in the alumina or zirconia layer containing catalyst is Different from each other.

Japanese Patent Publication No. 105240/1982 discloses a catalyst for purifying exhaust gases containing two or more kinds of platinum group metals. The catalyst comprises two or more carrier layers of different platinum group metal containing refractory metal oxides. There is a refractory metal oxide layer free of platinum group metal between the carrier layers and / or on the outside of the carrier layer.

Japanese Patent Publication No. 5530/1984 has an inorganic substrate and a first porous carrier layer comprising a heat-resistant noble metal catalyst deposited on the surface of the substrate, and a second heat resistant nonporous granular carrier layer on which the noble metal catalyst is deposited. A catalyst is disclosed wherein the second carrier layer is formed on the surface of the first carrier layer and has a catalyst resistance.

Japanese Patent Publication 127649/1984 discloses an inorganic carrier substrate such as cordierite, an alumina layer formed on the surface of the substrate and deposited with one or more rare earth metals such as lanthanum and cerium and one or more platinum and palladium, and A catalyst for purifying exhaust gases is disclosed that includes a second layer formed on the first alumina base layer and on which one or more rare earth metals, such as lanthanum and rhodium, are deposited.

Japanese Patent Publication No. 19036/1985 discloses a catalyst for purifying exhaust gases with improved performance of removing carbon monoxide at low temperatures, which catalyst is laminated to, for example, a substrate comprising cordierite, and a surface of the substrate. Two layers of active alumina, the lower alumina layer containing deposited platinum or vanadium and the upper alumina layer containing deposited rhodium and platinum, or rhodium and palladium.

Japanese Patent Publication No. 3228/1985 discloses a catalyst for purifying exhaust gases comprising a honeycomb carrier and a noble metal having a catalytic action for purifying exhaust gases, and a method for preparing the catalyst, wherein the carrier is an inner and outer alumina layer. The inner layer is more adsorbed by the precious metal than the outer layer.

Japanese Patent Publication No. 232253/1985 discloses a monolith catalyst for exhaust gas purification comprising a plurality of cells in the form of a column and arranged from the exhaust gas inlet side to the exhaust gas outlet side. An alumina layer is formed on the inner wall surface of each cell, and the catalyst component is deposited on the alumina layer. The alumina layer comprises a first alumina layer having palladium and neodymium deposited thereon and a second alumina layer having platinum and rhodium deposited thereon.

Japanese Patent Laid-Open No. 7138/87 discloses a catalyst layer supported on a catalyst carrier and containing one catalyst component selected from the group consisting of platinum, palladium and rhodium. An alumina coat layer is provided on the catalyst layer. The coat layer contains one oxide selected from the group consisting of cerium oxide, nickel oxide, molybdenum oxide, iron oxide, and one or more oxides (1 to 10% by weight) of lanthanum and neodymium.

U.S. Patent Nos. 3,956,188 and 4,021,185 disclose (a) catalytically active calcination complexes with metal oxides selected from the group consisting of alumina, rare earth metal oxides and oxides of chromium, tungsten, group IVB metals and mixtures thereof, and (b A catalyst composition having a catalytically effective amount of platinum group metal added after the composite is calcined is disclosed.

US Pat. No. 4,806,519 discloses a two layer catalyst structure having alumina, ceria and platinum on the inner layer and aluminum, zirconium and rhodium on the outer layer.

Japanese Patent No. 88-240947 discloses a catalyst composite comprising ceria, ceria doped alumina, and an alumina layer containing at least one component selected from the group of platinum, palladium and rhodium. There is a second layer containing lanthanum doped alumina, praseodymium stabilized zirconium, lanthanum oxide, and one or more components selected from the group of palladium and rhodium. The two layers are individually placed on the catalyst carrier to form a catalyst for exhaust gas purification.

Japanese Patent No. J-63-205141-A discloses that the bottom layer comprises platinum dispersed on a rare earth oxide containing alumina support, or platinum and rhodium, and the top coat is dispersed on a support comprising alumina, zirconia and rare earth oxides. Laminated automotive catalysts comprising palladium and rhodium are disclosed.

Japanese Patent J-63-077544-A discloses a first layer comprising palladium dispersed on a support comprising alumina, lanthana and other rare earth oxides, and a support comprising alumina, zirconia, lanthana and rare earth oxides. Laminated automotive catalysts having a second coat comprising dispersed rhodium are disclosed.

Japanese Patent J-63-007895-A discloses an exhaust gas catalyst comprising two catalyst components, one comprising platinum dispersed on a refractory inorganic oxide support, and the other on a refractory inorganic oxide support. Palladium and rhodium dispersed therein.

U.S. Patent No. 4,587,231 discloses a process for preparing a monolith three-way catalyst for exhaust gas purification. First, the mixed oxide coating is provided to the monolith carrier by treating the carrier with a coating slip in which the cerium oxide containing active alumina powder is dispersed together with the ceria powder, and then baking the treated carrier. Platinum, rhodium and / or palladium are then deposited on the oxide coating by thermal decomposition. Optionally, zirconia powder can be added to the coating slip.

US Pat. No. 4,134,860 relates to a method of making a catalyst structure. The catalyst composition may contain refractory supports such as platinum group metals, base metals, rare earth metals and alumina. The composition can be deposited on a relatively inert carrier such as a honeycomb structure.

U.S. Patent No. 4,923,842 discloses a catalyst composition for exhaust gas treatment comprising a first support and optionally a second support, wherein one or more oxygen storage components and one or more precious metal components are dispersed and the top layer comprising lanthanum oxide is immediately dispersed. It is. The catalyst layer is separated from lanthanum oxide. Precious metals may include platinum, palladium, rhodium, ruthenium and iridium. The oxygen storage component may comprise a metal oxide from the group consisting of iron, nickel, cobalt and rare earths. Examples thereof include cerium, lanthanum, neodymium, praseodymium and the like.

U. S. Patent No. 5,057, 483 discloses a catalyst composition suitable for three-way conversion of an internal combustion engine, such as an automobile gasoline engine, wherein the exhaust gas comprises a catalytic material disposed in two discontinuous coats on a carrier. The first coat comprises a stabilized alumina support on which the first platinum catalyst component is dispersed, and bulk ceria, and is also effective as a bulk iron oxide, a metal oxide (eg bulk nickel oxide) effective for suppressing hydrogen sulfide release, and as a thermal stabilizer. It may comprise either or both of the varia and zirconia dispersed throughout one coat. A second coat, which may include a top coat overlying the first coat, comprises a coform (eg, coprecipitation) rare earth oxide-zirconia support on which the first rhodium catalyst component is dispersed, and a second on which the second platinum catalyst component is dispersed. It contains an activated alumina support. The second coat may also include a second rhodium catalyst component, and optionally a third platinum catalyst component dispersed as an activated alumina support.

Developing an inexpensive and stable three-way catalyst system is an ongoing goal. In addition, the system should have the ability to oxidize hydrocarbons and carbon monoxide while reducing nitrogen oxides to nitrogen.

Summary of the Invention

The present invention relates to catalytic exhaust gas treatment products which are particularly useful for the treatment of automotive exhaust gases. The exhaust gas treatment product includes an upstream catalyst zone and one or more downstream catalyst zones. The upstream catalyst zone comprises an upstream composition and the downstream catalyst zone comprises a downstream stream composition. The two catalyst zones can be on separate monoliths, preferably on separate substrate carriers such as honeycombs. Alternatively, the two catalyst zones can be on the same substrate carrier. The object of the mechanical design of the product is to produce a product in which the upstream zone oxidizes the oxidative component of the exhaust gas, such as carbon monoxide and hydrocarbons, and / or reduces the reducing component of the exhaust gas, such as nitrogen oxides, at a lower temperature than the downstream region. And / or to provide a chemical composition.

This can be achieved by using the catalyst composition of the first zone designed according to the invention to promote the oxidation and / or reduction of the exhaust gas in the downstream zone at low temperature compared to the upstream zone composition. The downstream zone composition is designed to more effectively promote the reaction of the exhaust gas components when the gas reaches a steady state operating temperature.

Preferred upstream compositions include a first upstream support and at least one first upstream palladium component located on the support. The downstream catalyst zone comprises a first downstream support and at least one first downstream platinum group component located on the support. Preferably, there is a first downstream layer comprising a first downstream support and at least one first downstream platinum group component, and a second downstream layer comprising a second downstream support and at least one second downstream platinum component. The first and second platinum group metal components may be the same or different and may comprise a component selected from the group consisting of rhodium, platinum and palladium. More preferably, the at least one first and second downstream platinum group component comprises a palladium component.

<Upstream Catalyst>

In a preferred embodiment, the upstream zone of the present invention comprises an upstream catalyst product that is thermally stable up to 900 ° C or higher. Preferably the upstream catalyst product comprises a catalyst which may be a single layer or multilayer catalyst composite of the type generally referred to as a three-way conversion catalyst or a TWC catalyst. The upstream zone catalyst article comprises one or more layers comprising a palladium component, which may include a palladium compound, such as a palladium metal and / or palladium oxide. If a single layer is used, the upstream catalyst composition is preferably substantially free of oxygen storage components. The upstream monolayer composition may contain an oxygen storage component that is not in intimate contact with the palladium component.

Preferred upstream catalyst composites are disclosed in US patent application Ser. No. 08 / 265,076, incorporated herein by reference and commonly assigned. TWC catalysts are multifunctional in that they can promote the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides substantially simultaneously. The counter layer of the upstream catalyst composite and the specific composition of this upstream layer provide a stable and economical system. This maintains effective oxidation of hydrocarbons and carbon monoxide, and improved conversion of nitrogen oxide compounds, even though palladium is the only platinum metal group component in the complex.

Preferred upstream laminate catalyst composite structures of the present invention are designed to include a first upstream layer with a first upstream layer composition, and a second upstream layer with a second upstream layer composition. The first upstream layer is also called the bottom or inner upstream layer, and the second upstream layer is called the top or outer upstream layer. Exhaust gas emissions comprising hydrocarbons, carbon monoxide and nitrogen oxides are first contacted with a second or tower upstream layer. The platinum group metal in the tower upstream layer serves to promote the reduction of nitrogen oxides to nitrogen and the oxidation of hydrocarbons. The top layer may comprise an oxygen storage component such as ceria. However, ceria is preferably not in intimate contact with the platinum group metal in the top layer. This can be achieved by making the top layer with a ceria-zirconia complex that is not a solution of soluble ceria salt. The composite oxygen storage composition is in bulk form. By bulk form is meant that the composition has a particle size distribution in which the composition is in solid, preferably particulate form, more preferably at least about 95% by weight of the particles, typically from 0.1 to 5.0, and preferably from 0.5 to 3 micrometers. . For a discussion of bulk particles, see US Pat. No. 5,057,483, which is incorporated herein by reference.

After passing through the top or second upstream layer, the exhaust gas contacts the first or bottom upstream layer. In this layer, the platinum group metal is in intimate contact with an oxygen storage component such as ceria. This can be accomplished by introducing the cerium component into the bottom upstream layer composition in the form of a soluble cerium salt solution impregnated with the support and other particulate material. Cerium salts are converted to cerium oxide (ceria) upon calcination. Preferably ceria in intimate contact with the platinum group metal is believed to improve the oxidation and reduction reactions. Close contact means that the effective amount of the component (eg, the platinum group metal component of the bottom layer and the oxygen storage component) is on the same support and / or is in direct contact. By not in close contact (or physically separated), the components (eg, the ceria and platinum group components of the top layer) are not on the same support or are not included in the same particles.

The present invention includes a laminated upstream catalyst composite comprising a first upstream layer and a second upstream layer. The first upstream layer comprises a first upstream support. The first layer comprises a first upstream palladium component and optionally one or more first upstream platinum group metal components in addition to palladium, an upstream oxygen storage component in intimate contact with the platinum group metal component of the first upstream layer. Preferably, the first upstream layer further comprises one or more first upstream zirconium components, one or more first upstream alkaline earth metal components, and one or more first upstream rare earth metal components selected from the group consisting of lanthanum metal components and neodymium metal components. .

Preferably the second upstream layer comprises a second upstream palladium component, and optionally at least one second upstream platinum group metal component in addition to palladium. Preferably the second upstream layer further comprises at least one second upstream rare earth metal component selected from the group consisting of a second upstream zirconium component, at least one second upstream alkaline earth metal component, and a lanthanum metal component and a neodymium metal component. Preferably, each upstream layer contains a zirconium component, at least one alkaline earth metal component and a rare earth component. Most preferably, each upstream layer comprises both at least one alkaline earth metal component and at least one rare earth component. Optionally, the first upstream layer further comprises a second upstream oxygen storage composition comprising a second oxygen storage component. Preferably the second oxygen storage component and / or the second oxygen storage composition is in the form of a bulk and may be in intimate contact with the first platinum group metal component. In a particular and preferred embodiment of the present invention the first upstream platinum group metal essentially comprises a first upstream palladium component which is a substantially unique platinum group metal component in the first upstream layer. In this preferred embodiment the second upstream platinum group metal component essentially comprises a second palladium component wherein the second palladium component is a substantially unique platinum group metal component in the second upstream layer.

Optionally, the first and / or second upstream layer comprises an upstream oxygen storage composite in particulate form. Preferably the upstream oxygen storage complex comprises ceria and zirconia and optionally and more preferably comprises a rare earth component selected from the group consisting of lanthanum and neodymium components and mixtures thereof. Particularly preferred complexes include ceria, neodymia and zirconia. Preferably from 60 to 90% by weight of zirconia, 10 to 30% by weight of ceria, and up to 10% by weight of neodymia. Ceria in the complex acts as an oxygen storage component that improves the oxidation of carbon monoxide and the reduction of nitrogen oxides and helps stabilize zirconia by preventing undesirable phase conversion. As set forth above, a particular and preferred composition of the present invention is that the first and second layers require a first palladium component and a second palladium component, respectively. Optionally, the first upstream layer may further comprise one or more additional platinum group metal components, preferably selected from the group consisting of platinum, rhodium, ruthenium, and iridium components, wherein preferably the first layer platinum group metal component added Platinum and rhodium and mixtures thereof.

Similarly, the second upstream layer may further comprise, in addition to the second palladium component, one or more second platinum group metal components, preferably selected from the group consisting of platinum, rhodium, ruthenium and iridium components, wherein the platinum and rhodium components are desirable.

As shown, according to the present invention the first upstream layer comprises a first oxygen storage component which is preferably in intimate contact with the first platinum group metal comprising palladium and preferably substantially only palladium. There may also be a first upstream bulk oxygen storage component, such as bulk ceria, bulk praseodymia, and / or an oxygen storage complex, such as a ceria zirconia particulate composite.

The second upstream layer comprises a second platinum group metal component comprising palladium and most preferably essentially including palladium. The presence of an oxygen storage component in the second upstream layer is preferably not in intimate contact with the platinum group metal component, preferably of ceria, zirconia, and optionally and preferably of rare earth metal oxides such as neodymia or lanthana. A bulk second oxygen storage complex, which may include the complex.

In a particular and preferred embodiment the first upstream layer comprises a first upstream support; At least one first upstream platinum group metal component comprising a first upstream palladium component dispersed on the first upstream support; And an upstream oxygen storage component, preferably ceria, in intimate contact with said upstream platinum group metal component; At least one upstream alkaline earth metal component, at least one upstream zirconium component, and at least one upstream first rare earth earth component selected from the group consisting of lanthanum metal components and neodymium metal components. The second upstream layer comprises a second upstream support, which may be the same as or different from the first upstream support; At least one second upstream platinum group metal dispersed on said second support comprising a second palladium component; At least one second upstream alkaline earth metal component, which may be the same as or different from the first alkaline earth metal component; At least one second upstream zirconium component; And at least one second upstream rare earth metal component selected from the group consisting of a lanthanum metal component and a neodymium metal component, which may be different from the first rare earth metal component.

Preferred first and second upstream supports can be the same or different compounds selected from the group consisting of silica, alumina, and titania compounds. More preferably the first and second upstream supports are activating compounds selected from the group consisting of alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia, and alumina-ceria. Most preferably the first and second upstream supports are activated alumina.

The alkaline earth metal is believed to stabilize the first and second upstream layer compositions, and the rare earth metal component selected from the lanthanum and neodymium components is believed to promote the catalytic activity of the first and second upstream layer compositions. The zirconium component in both upstream layers acts as washcoat stabilizer and promoter.

The particular structure of the upstream layers with the first and second upstream compositions has been found to be an effective three-way catalyst even when used with palladium as the only platinum group metal in each layer. The composite may be in the form of a self supporting product such as a pellet having a first layer on the inside of the pellet and a second layer on the outside. Alternatively, and more preferably the first layer is supported on a carrier, also called a honeycomb substrate, and the second layer is supported on a first layer applied to the substrate.

The at least one first and at least one second upstream alkaline earth metal may be selected from the group consisting of magnesium, barium, calcium and strontium, preferably strontium and barium. Most preferably the first alkaline earth metal component comprises barium oxide and the second alkaline earth metal component comprises strontium oxide. Stabilization means that the conversion efficiency of the catalyst composition of each layer is maintained for longer time at elevated temperature. Stabilizing supports such as alumina and catalyst components such as noble metals have greater degradation resistance to high temperature exposure and thus maintain good total conversion efficacy.

In addition and individually and preferably the first upstream layer composition and the second upstream layer composition comprise first and second rare earth metal components believed to act as accelerators. The rare earth metal component is derived from a metal selected from the group consisting of lanthanum and neodymium. In certain embodiments, the first rare earth metal component is substantially lantana and the second rare earth metal component is substantially neodymia. Accelerators improve the conversion of hydrocarbons, carbon monoxide and nitrogen oxides into harmless compounds.

In certain and preferred embodiments the first and / or second layer further comprises a nickel or iron component useful for removing sulfides, such as hydrogen sulfide emissions. Most preferably the first layer comprises a nickel or iron compound.

When the composition is applied as a thin coating to a monolith carrier substrate, the proportion of components is typically expressed as grams of material per cubic inch of catalyst and substrate. This measurement controls different gas flow passage cell sizes on different monolithic carrier substrates. The platinum group metal component is based on the weight of the platinum group metal.

Useful and preferred first upstream layers are;

From about 0.003 to about 0.6 g / in ^{3 of} at least one palladium component;

From about 0 to about 0.065 g / in ^{3 of} at least one first platinum and / or first rhodium component;

From about 0.15 to about 2.0 g / in ^{3 of} the first support;

From about 0.05 to about 2.0 g / in ³ of the total first oxygen storage component in the first layer;

0.0 and preferably about 0.025 to about 0.5 g / in ^{3 of} at least one first alkaline earth metal component;

From about 0.0 and preferably from about 0.025 to about 0.5 g / in ^{3 of} the first zirconium component; And

0.0 and preferably about 0.025 to about 0.5 g / in ^{3 of} at least one first rare earth metal component selected from the group consisting of ceria metal component, lanthanum metal component and neodymium metal component.

Useful and preferred second upstream layers are;

From about 0.003 to about 0.6 g / in ^{3 of} at least one second palladium component;

0.0 to about 0.065 g / in ^{3 of} at least one first platinum and / or rhodium component;

From about 0.15 to about 2.0 g / in ^{3 of} the second support;

0.0 and preferably about 0.025 to about 0.5 g / in ^{3 of} at least one second rare earth metal component selected from the group consisting of lanthanum metal components and neodymium metal components;

0.0 and preferably about 0.25 to about 0.5 g / in ^{3 of} at least one second alkaline earth metal component; And

From 0.0 and preferably from about 0.025 to about 0.5 g / in ^{3 of} the second zirconium component. However, the first layer requires an alkaline earth metal component and / or a rare earth component, and the second layer requires an alkaline earth metal component and / or a rare earth metal component.

The first and / or second layer may have from 0.0 to about 2.0 g / in ^{3 of} an oxygen storage composite comprising a ceria-zirconia composite in particulate form.

The laminated upstream catalyst composite may be in the form of a self supporting product such as a pellet having a first layer on the inside of the pellet and a second layer on the outside. Alternatively and more preferably the first upstream layer can be supported on a substrate, preferably a honeycomb carrier, and the second upstream layer is supported on a first upstream layer applied on the substrate.

<Downstream catalyst>

In a preferred embodiment, the downstream zone of the present invention comprises a downstream catalyst that is thermally stable up to at least 900 ° C. Preferably the downstream catalyst product comprises a catalyst which may be a single layer or multilayer catalyst composite of the type generally referred to as a three-way conversion catalyst or a TWC catalyst. Preferably the downstream zone catalyst article comprises at least one layer comprising a palladium component and at least one additional precious metal component. Preferably the additional precious metal component may be one or more additional precious metal components selected from platinum group metals, gold and silver. Preferably the metal to be added is a platinum group metal, preferably selected from platinum and / or rhodium. Most preferably, the platinum group metal comprises rhodium. The component may be a compound such as a metal and / or palladium oxide.

Preferred downstream catalyst composites are described in commonly assigned US patent application Ser. No. 08 / 563,884, which is incorporated herein by reference.

There is also a downstream first layer called the bottom or inner downstream layer, and also a second downstream layer called the top or outer downstream layer. The first downstream layer comprises one or more first palladium components. The first downstream layer may optionally contain a small amount of platinum component based on the total platinum metal of the platinum component in the first and second layers. The second downstream layer comprises at least two second platinum group metal components, one of the platinum group metal components being the second platinum component and the other being the rhodium component. Preferably the second downstream layer comprises a second downstream oxygen storage composition comprising a diluted second oxygen storage component. The second downstream oxygen storage composition includes a diluent in addition to the oxygen storage component. Useful and preferred diluents include refractory oxides. Dilution is used to mean that the second downstream oxygen storage component is present in the oxygen storage composition in a relatively small amount. The composition is a mixture that can be characterized as a complex which may or may not be a solid true solution. The second downstream oxygen storage component is diluted to minimize interaction with the rhodium component. This interaction can reduce long term catalytic activity.

Exhaust gas emissions comprising hydrocarbons, carbon monoxide and nitrogen oxides are first contacted with a second downstream layer. In a preferred layer composition the second platinum component and the rhodium component in the second downstream layer are believed to promote the reduction of nitrogen oxides to nitrogen and the oxidation of hydrocarbons and carbon monoxide. The second platinum component in the top coat is believed to promote the rhodium component to increase the rhodium catalytic activity. Preferably the second downstream layer comprises a second downstream oxygen storage composition comprising a second oxygen storage component such as a rare earth oxide, preferably ceria. The second downstream oxygen storage component is diluted with a diluent such as a refractory metal oxide, preferably zirconia. Particularly preferred second downstream oxygen storage composition is a coprecipitation ceria / zirconia complex. Preferably ceria is at most 30% by weight and zirconia is at least 70% by weight. Preferably, the oxygen storage composition comprises ceria and at least one lantana, neodymia, yttria or mixtures thereof in addition to ceria. Particularly preferred particulate composites include ceria, neodymia and zirconia. Preferably from 60 to 90% by weight of zirconia, 10 to 30% by weight of ceria and up to 10% by weight of neodymia. Ceria acts as an oxygen storage component that stabilizes zirconia by preventing undesirable phase conversion and improves oxidation of carbon monoxide and reduction of nitrogen oxides.

Preferably, the second downstream oxygen storage composition is in bulk form. By bulk form is meant a composition in which the composition has a particle size distribution of solids, preferably in particulate form, more preferably in diameter of at least about 95% by weight of the particles, typically from 0.1 to 5.0, and preferably from 0.5 to 3 micrometers. do. For a discussion of bulk particles, see US Pat. Nos. 4,714,694 and 5,057,483, incorporated herein by reference.

It is also believed that the second downstream platinum component and the second downstream rhodium component interact and increase the efficacy of the second downstream oxygen storage component in the second oxygen storage composition.

After passing through the top or second layer, the exhaust gas is in contact with the first or bottom downstream layer. In a preferred bottom downstream layer, the first downstream palladium component and any first downstream platinum component are believed to primarily improve the oxidation reaction. The reaction may be in the form of a ceria compound, preferably a bulk first oxygen storage composition as used in the top layer, or an agent such as cerium oxide, which may be an oxygen storage component in intimate contact with the first platinum group metal component. 1 by the oxygen storage component. The intimate contact can be accomplished by solution impregnation of the oxygen storage component on the platinum group metal component.

Certain and preferred embodiments of the present invention provide a first downstream having at least one palladium component and having from 0 to 50% by weight of platinum metal of at least one first layer platinum component, based on the total amount of platinum metal in the first and second downstream layers. A downstream laminated catalyst composite comprising a first downstream layer comprising a support.

Preferably, the first downstream layer comprises a first support, a first palladium component, one or more first stabilizers, and one or more first rare earth metal components selected from ceria, neodymia and lanthana. The first downstream layer can also include a first oxygen storage composition comprising a first downstream oxygen storage component. Preferably the second downstream layer comprises a second downstream support, at least one second downstream platinum component, at least one rhodium component, and a second downstream oxygen storage composition. The platinum metal of the second layer platinum component may be from 50 to 100% by weight, based on the total amount of platinum metal in the first and second downstream layers.

The platinum group metal component support components in the first and second downstream layers may be the same or different and are preferably compounds selected from the group consisting of silica, alumina and titania compounds. Preferred first and second downstream supports can be activating compounds selected from the group consisting of alumina, silica, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chromia, and alumina-ceria.

Preferably the second downstream oxygen storage component and any first downstream oxygen storage component are selected from the cerium group and preferably comprise a cerium compound, praseodymium and / or neodymium compound. When using cerium group compounds, it has been found that undesirable hydrogen sulfide can form when sulfur is present in the exhaust gas stream. If it is desired to minimize hydrogen sulfide, it is preferred to further use Group IIA metal oxides, preferably strontium oxide and calcium oxide. Where it is desired to use cerium, praseodymium or neodymium compounds, the one or more first or second downstream layers may comprise a nickel or iron component to inhibit hydrogen sulfide. Preferably, the first downstream layer further comprises a nickel or iron component.

The stabilizer may be present in the first or second downstream layer, preferably in the first downstream layer. The stabilizer may be selected from one or more alkaline earth metal components derived from metals selected from the group consisting of magnesium, barium, calcium and strontium, preferably strontium and barium.

The zirconium component is preferred in the first and / or second downstream layer and acts as a stabilizer and promoter. The rare earth oxide acts to promote the catalytic activity of the first layer composition. Preferably the rare earth metal component is selected from the group consisting of lanthanum metal components and neodymium metal components.

When the composition is applied as a thin coating on a monolith carrier substrate, the proportion of components is typically expressed as grams of material per cubic inch of catalyst, and the measurement controls different gas flow passage cell sizes in different monolith carrier substrates. The platinum group metal component is based on the weight of the platinum group metal.

Useful and preferred first downstream layers are;

From about 0.0175 to about 0.3 g / in ^{3 of the} palladium component;

From about 0 to about 0.065 g / in ^{3 of} the first platinum component;

From about 0.15 to about 2.0 g / in ^{3 of} the first support;

From about 0.025 to about 0.5 g / in ^{3 of} at least one first alkaline earth metal component;

From about 0.025 to about 0.5 g / in ^{3 of} the first zirconium component; And

And from about 0.025 to about 0.5 g / in ^{3 of} at least one first rare earth metal component selected from the group consisting of ceria metal component, lanthanum metal component and neodymium metal component.

Useful and preferred second downstream layers are;

From about 0.001 to about 0.03 g / in ^{3 of a} rhodium component;

Platinum from about 0.001 to about 0.15 g / in ³ ;

From about 0.15 to about 1.5 g / in ^{3 of} the second support;

From about 0.1 to about 2.0 g / in ^{3 of} the second oxygen storage composition;

From about 0.025 to about 0.5 g / in ^{3 of} at least one second rare earth metal component selected from the group consisting of a lanthanum metal component and a neodymium metal component; And

From about 0.025 to about 0.5 g / in ^{3 of} the second zirconium component.

The composite may be in the form of a self supporting product, such as a pellet, having a first layer on the inside and a second layer on the outside. Alternatively, and more preferably the first downstream layer can be supported on a substrate, preferably a honeycomb carrier, and the second downstream layer is supported on a first layer applied on the substrate.

In a separate embodiment, the thermal mass of the downstream zone is designed to be greater than the upstream zone. For the purposes of the present invention, thermal mass is defined as the mass of an upstream or downstream zone multiplied by the heat capacity of each zone. The design is particularly preferred when combined with a catalyst composition as listed above for use in separate zones. When upstream and downstream honeycomb monoliths are made of the same or similar materials, the useful axial lengths of the upstream monoliths are 0.5 to 3.0, 0.5 to 2.5, 0.5 to 2.0, 1.0 to 2.0 and 1.0 to 3.0 inches. Preferred ceramic upstream honeycomb monoliths are 2.0 to 3.0 inches in length, with monolith lengths of 2.5 inches being commercially available. An important factor influencing the thermal mass of the upstream and downstream zones is the material from which the substrate is made. Useful embodiments include upstream honeycombs made of metal, and downstream monoliths made of ceramic. The heat capacity of the ceramic honeycomb tends to be larger. Other factors affecting thermal mass include the number of cells per square inch (cpsi), catalyst loading, and honeycomb wall thicknesses varying from 0.001 to 0.008 inches. Typically the wall thickness of ceramic monoliths is from 0.002 to 0.014 inches and typically the wall thickness of metal monoliths is from 0.0015 to 0.003 inches. Useful honeycomb flow through monoliths have a cpsi of 300 to 600. It depends on the wall thickness, etc., the larger the monolith cpsi, the larger the thermal mass. The present invention allows the use of upstream monoliths with less cpsi in monoliths compared to downstream monoliths. The smaller upstream monolith will heat up faster.

Preferably, the light-off temperature of the smaller upstream zone composition is designed to be less than the downstream zone. Thus, the upstream zone heats up and catalyzes the reactants faster. In addition, when the delay time is longer and the space velocity is smaller than during the static state, it is designed to perform during the conditions such as idle. For the purposes of the present invention "light-off" shall mean a temperature at which the catalyst is active and can initiate the reaction of the exhaust gas component. Stated another way, lag time is expressed as the inverse of space velocity. For the purposes of the present invention "space velocity" will mean the volume of gas passing through the catalyst monolith at a given time divided by the total volume of the catalyst monolith, measured in reciprocal units of time, such as the reciprocal of time. The catalyst product of the present invention can advantageously be used at a reciprocal of space velocity of 10 to 500,000 hours, more typically reciprocal of 50 to 350,000 hours.

The present invention encompasses a process comprising the step of contacting a gas comprising nitrogen oxides, carbon monoxide, and / or hydrocarbons with a stacked catalyst composite as enumerated above.

In addition, the present invention includes the catalyst product of the present invention and a process for producing a laminated catalyst composite.

<Brief Description of Drawings>

1 is a schematic diagram illustrating upstream and downstream honeycombs in a canister located in an exhaust stream.

2 shows the product of FIG. 1 lying underneath in an automobile.

3 is a schematic cross-sectional view of an upstream honeycomb and a downstream honeycomb showing upstream and downstream catalyst layers.

<Detailed Description of the Preferred Embodiments>

The invention will be understood by those skilled in the art by the present specification with reference to FIGS.

The present invention relates to an exhaust gas treating catalyst product 10. The catalyst product 10 is arranged to be connected with the exhaust gas line 12 exiting from the motor vehicle 14 engine 16. Catalyst product 10 includes an upstream catalyst zone 18 and one or more downstream catalyst zones 20. Upstream catalyst zone 18 comprises an upstream composition comprising a first upstream support and one or more first upstream palladium components. Where there is an upstream catalyst monolayer comprising palladium, the palladium containing the composition is preferably substantially free of oxygen storage components. The downstream catalyst zone 20 comprises a first downstream layer 22 comprising a first downstream support and a first downstream precious metal component. The downstream catalyst zone 20 also includes a second downstream layer 24 comprising a second downstream support and a second downstream precious metal component. At least one first and second downstream layer comprises a palladium component.

In a preferred embodiment, the upstream catalyst zone 18 comprises a first upstream layer 26 and a second upstream layer 28. The first upstream layer 26 comprises a first upstream support and one or more first upstream precious metal components. The second upstream layer 28 comprises a second upstream support and one or more second upstream precious metal components. At least one first and second upstream layer comprises a palladium component. The downstream catalyst zone 18 comprises a first downstream layer 22 comprising a first downstream support and a first downstream precious metal component. The second downstream layer 24 comprises a second downstream support and a second downstream precious metal component. Preferably, the one or more first and second downstream layers comprise a palladium component.

Catalyst product 10 may be disposed in canister 21. Preferably the catalyst product 10 is disposed upstream of the muffler 23. Accordingly, the present invention provides a method for catalyzing the downward exhaust gas during low temperature driving, such as cold start.

The most preferred composition in the monolayer containing upstream zone 18 is the composition described in Example 1 of PCT International Publication No. 96/17671, incorporated herein by reference and commonly assigned. The most preferred composition in the two layer containing upstream zone 18 is the composition described in Example 1 of US Pat. No. 5,597,771, which is incorporated herein by reference and commonly assigned. The most preferred composition in the two-layer containing downstream zone 18 is the composition described in Example 1 of PCT International Publication No. 95/35152, incorporated herein by reference and commonly assigned. The following is a detailed description of the preferred compositions used in the upstream and downstream zones.

<Single layer upstream catalyst>

Preferred upstream monolayer catalyst compositions of the present invention comprise a palladium component of the type used in the TWC catalyst composition, and is preferably substantially free of oxygen storage components. For the purposes of the upstream single layer catalyst composition, components having oxygen storage and release performance are cerium oxide and praseodymium oxide. Equal amounts of other rare earths with less important oxygen storage performance are not considered components with substantially oxygen storage and release performance. Also, platinum group metal components are not considered oxygen storage components. In particular, the catalyst composition may be a three-way catalyst composition that is substantially ceria free. Small amounts of ceria or praseodymium may be present in impurities or in trace amounts. Oxygen storage components, such as cerium oxide, store oxygen and release it during the rich performance conditions that provide additional oxygen to more efficiently oxidize hydrocarbons and carbon monoxide. The most preferred compositions in the monolayer containing upstream zone 18 are the compositions described in WO 96/17671, incorporated herein by reference and commonly assigned.

Preferably the upstream single layer catalyst composition comprises a relatively high concentration of palladium component. Thus, during cold start-up, relatively large amounts of hydrocarbons are oxidized and not all carbon monoxide, but significant amounts of carbon monoxide are oxidized. In addition, significant amounts of nitrogen oxides are reduced. In addition, the absence of oxygen storage components, especially cerium components, of the closely coupled coupled catalysts means that carbon monoxide in the closely coupled coupled catalysts even when the engine exhaust is hot and the downstream (downstream) catalyst has reached operating temperature. Limit the amount of oxidation The unreacted carbon monoxide in the tightly coupled coupled catalyst passes through the downstream catalyst zone when catalytically oxidized and the oxidation is performed more efficiently by increasing the temperature of the downstream catalyst. Thus, the upstream single layer catalyst composition of the present invention is efficient enough to remove a significant amount of contaminants at low temperatures while at the same time stable over a long period of engine operation. The downstream catalyst zone may comprise two or more layers and may be of the same type as described below.

The upstream monolayer catalyst composition of the present invention is preferably substantially free of oxygen storage components such as ceria and praseodymia. The catalyst composition preferably comprises a support comprising at least one compound selected from the group consisting of silica, alumina, titania and a first zirconia compound, hereinafter referred to as a first zirconia compound. Preferably the composition comprises a palladium component in an amount sufficient to oxidize carbon monoxide and hydrocarbons and reduce nitrogen oxides, each light-off at a 50% conversion relative to the oxidation of hydrocarbons and preferably at 200 to 350 ° C. Has a temperature. Optionally, the composition comprises at least one alkali metal oxide selected from the group consisting of strontium oxide, calcium oxide and barium oxide, with strontium oxide being most preferred. In addition, the composition may optionally comprise other precious metal or platinum group metal components, preferably one or more metals selected from the group consisting of platinum, rhodium, ruthenium and iridium components. If additional platinum group metals are included, platinum is used in an amount of less than 60 grams per cubic foot. Other platinum group metals are used in amounts of up to about 20 grams per cubic foot. In addition, the composition may optionally include a second zirconium oxide compound as a stabilizer, and optionally one or more rare earth oxides selected from the group consisting of neodymium oxide and lanthanum oxide.

Preferably the upstream monolayer catalyst composition is in the form of a carrier supported catalyst when the carrier comprises a honeycomb type carrier. Preferred honeycomb type carriers have a palladium component of at least about 50 grams per cubic foot, activated alumina from 0.5 to 3.5 g / in ³ , and at least one alkaline earth metal component, most preferably from 0.05 to 0.5 g / in ^3. Composition. For lanthanum oxide and / or neodymium oxide, it is present in an amount up to 0.6 g / in ³ .

<2-layer upstream catalyst>

The present invention includes embodiments in which the upstream catalyst zone comprises a substrate and two or more layers. The catalyst structure relates to a layered catalyst composite of the type useful as a three-way conversion catalyst or TWC. The TWC catalyst composite of the present invention simultaneously catalyzes the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides in the gas stream. The most preferred composition in the two-layer containing upstream zone 18 is the composition described in US Pat. No. 5,597,771, incorporated herein by reference and commonly assigned.

The stacked catalyst composite comprises a first upstream layer composition and the second layer comprises a second layer composition. As noted above, the gas stream is initially in contact with a second tower or outer layer composition designed to efficiently reduce nitrogen oxides to nitrogen, cause oxidation of carbon monoxide and to oxidize hydrocarbons. The gas then passes through the first layer to convert the remaining contaminants.

The particular design of the tower or second upstream layer efficiently reduces nitrogen oxides and oxidizes hydrocarbons over a wide range of temperatures. In the composite of the present invention, palladium, an economical platinum group metal, can be used more effectively for such applications. In addition, the performance of these materials is improved by the use of alkaline earth metals, which are believed to act as stabilizers, rare earth metal components selected from lanthanum and neodymium, which are believed to act as promoters, and zirconium components.

In the first or bottom upstream layer, the first oxygen storage component is preferably in intimate contact with the platinum group metal. In the first layer, the oxidation and reduction reactions are efficient at temperatures above about 500 ° C.

The first upstream layer comprises a first platinum group metal component comprising a first palladium component, which may be the same or different than the second layer. For the first layer to achieve high temperature conversion efficiencies, the oxygen storage component is used in intimate contact with the platinum group metal. It is also preferable to use rare earth metals selected from alkaline earth metals believed to act as stabilizers, lanthanum and neodymium metal components believed to act as promoters, and zirconium components.

Preferred catalysts of the present invention comprise a palladium component present in the first and second upstream layers in an amount sufficient to provide a composition for significantly improving catalytic activity due to the palladium component. In a preferred embodiment, the first palladium component is the only platinum group metal component in the first layer and the second palladium component is the only platinum group metal component in the second layer. Optionally one or both of the first and second layers are useful firsts comprising a mixture or alloy of such metals, for example platinum, ruthenium, iridium and rhodium, and for example platinum-rhodium. And a second platinum group metal, respectively.

In a preferred embodiment the first upstream layer can comprise a relatively small amount of first platinum group metal in addition to the first palladium component, and palladium, and the second layer is relatively small in addition to the second palladium component, and the palladium component. Of the second platinum group metal. Preferred first and second platinum group components are selected from platinum, rhodium and mixtures thereof. A preferred first platinum group metal component other than palladium is platinum, and the most preferred second platinum group metal component other than palladium is selected from rhodium, platinum, and mixtures thereof. Typically, the first layer will contain up to 100% by weight of palladium as the platinum group metal. When a first platinum group metal component other than palladium is used, it is usually 40% by weight or less, preferably 0.1 to 40% by weight, based on the total amount of the first palladium component and the platinum group metal component other than palladium in the first layer, More preferably in an amount of from 5 to 25% by weight. When a second platinum group metal component other than palladium is used, it is usually 40% by weight or less, preferably 0.1 to 40% by weight, based on the total amount of the second palladium component and the platinum group metal component other than palladium in the second layer, More preferably in an amount of from 5 to 25% by weight.

Thus, the present system preferably uses a palladium-catalyzed catalyst to improve the lower temperature activity (reaction) in the second (top) layer and higher temperature activity (reaction) in the first (bottom) layer compared to the top layer. And at least two upstream layers which are believed to act primarily. Thus, the top layer is preferably designed to be reactive at temperatures below about 500 ° C., and the bottom layer is designed to be more reactive at temperatures above about 500 ° C. However, it has been found that the specific temperature and conversion percentage at which the layers become reactive depend on the particular exhaust gas environment, including, for example, space velocity.

The first upstream layer composition and the second upstream layer composition separately comprise a first support and a second support, which may be the same or different components. The support is made of a large surface area refractory oxide support. Useful large surface area supports include one or more refractory oxides. For example, the oxides include silica, and metal oxides such as alumina including mixed oxide forms, for example silica-alumina, aluminosilicates that can be amorphous or crystalline, alumina-zirconia, alumina-chromia, Alumina-ceria and the like. Substantially the support comprises, for example, up to about 20% by weight of alumina, preferably comprising a gamma or activated alumina system such as gamma and eta alumina, and small amounts of other refractory oxides. Preferably, the specific surface area of the activated alumina is 60 to 300 m 2 / g.

The first upstream layer and the second upstream layer composition include alumina, catalyst components, stabilizers, reaction promoters, and other modifiers, if present, and exclude carriers or substrates. When the composition is applied as a thin coating on a monolith carrier substrate, the proportion of components is usually expressed as grams of material per cubic inch of catalyst, because this measurement includes different gas flow passage cell sizes in different monolith carrier substrates. Because. For conventional automotive exhaust gas catalytic converters, catalyst composites comprising a monolith substrate may generally comprise from about 0.50 to about 6.0 g / in ³ , preferably from about 1.0 to about 5.0 g / in ³ coating of the catalyst composition. .

In a preferred method of catalyst preparation, in addition to palladium, and optionally palladium such as suitable compounds and / or complexes of palladium and platinum group metals, platinum group metal components can be used to obtain dispersibility of the catalyst component on activated alumina support particles. As used herein, “palladium and any platinum group metal component” is any palladium and platinum metal compound, complex that decomposes when calcining or using a catalyst or otherwise converts to a catalytically active form, typically a metal or metal oxide. And the like. Water-soluble or water-dispersible compounds or complexes of palladium may be prepared by heating and heating the liquid used to impregnate or deposit the catalyst metal compound on the alumina support particles without adversely reacting with the catalyst metal or its complex or complex or other components of the catalyst composition. (Or) as long as it can be removed from the catalyst by volatilization or decomposition when a vacuum is applied. In some cases, the completion of liquid removal may not occur until the catalyst is used and treated at high temperatures while performing. In general, aqueous and aqueous solutions of soluble compounds or complexes of palladium and any platinum group metals are preferred from an economic and environmental standpoint. For example, suitable compounds include platinum (IV) hydrochloric acid, amine dissolved platinum hydroxide, palladium nitrate or palladium chloride, rhodium chloride, rhodium nitrate, hexaminrhodium chloride and the like. During the calcination step, or at least during the initial state of catalyst use, the compound is converted to the catalytically active form of the platinum group metal or compound thereof.

The catalyst of the present invention may contain a first upstream oxygen storage component in a first or bottom upstream layer in intimate contact with the palladium component. The oxygen storage component is any of the above known materials in the art, preferably at least one oxide of a metal selected from the group consisting of rare earth metals, more preferably cerium or praseodymium compounds, and the most preferred oxygen storage component is cerium oxide (Seria). The oxygen storage component may be present at least 5%, and preferably at least 10%, and more preferably at least 15% by weight of the first layer composition.

In the composition of the first or bottom upstream layer, the oxygen storage component can be included by dispersion methods known in the art. The method comprises impregnating an oxygen storage component on a palladium-containing support in the form of an aqueous solution and impregnating the resulting mixture on the first composition by drying and calcining in air to obtain an oxide of the oxygen storage component in intimate contact with the palladium component. The 1st layer containing these can be obtained. Typically, impregnation means that there is substantially enough liquid to fill the pores of the material to be impregnated. Examples of water soluble or water dispersible decomposed oxygen storage components that may be used include, but are not limited to, cerium acetate, praseodymium acetate, cerium nitrate, praseodymium nitrate, and the like. US Pat. No. 4,189,404 describes the impregnation of an alumina based support composition with cerium nitrate.

Optionally in the first or bottom upstream layer is a first bulk oxygen storage composition comprising an oxygen storage component, preferably in bulk form ceria and / or praseodymia. Ceria is most preferred. Bulk form means that ceria and / or praseodymia exist as discrete particles, which may be on the order of 1 to 15 microns in diameter or smaller, as opposed to dispersed in solution as in the first layer. The use and description of such bulk components is described in US Pat. No. 4,714,694, which is incorporated herein by reference. As described in US Pat. No. 4,727,052, which is also incorporated herein by reference, the bulk form of the activated alumina, as opposed to, for example, impregnating the alumina particles with a solution of a ceria compound that is converted to ceria disposed in the alumina particles when calcined. The particles and ceria particles are mixed to mean that ceria is present in solid or bulk form.

In addition to the components listed above of the first upstream layer composition and the second layer composition, each layer may contain a specific composite of zirconia and one or more ceria containing rare earth oxides. Such materials are described, for example, in US Pat. Nos. 4,624,940 and 5,057,483, which are incorporated herein by reference. Particular preference is given to particles in excess of 50% of the zirconia based compound, preferably from 60 to 90% of zirconia, from 10 to 30% by weight of ceria, and optionally up to 10% by weight, and at least 0.1% by weight of ceria rare earth oxide, if used. It is useful for stabilizing zirconia selected from the group consisting of lantana, neodymia and yttria.

The first upstream layer composition and the second upstream layer composition include a stabilization imparting component, with the first stabilizer of the first layer and the second stabilizer of the second layer being preferred. The stabilizer is selected from the group consisting of alkaline earth metal compounds. Preferred compounds include compounds derived from metals selected from the group consisting of magnesium, barium, calcium and strontium. US Pat. No. 4,727,052 discloses that support materials, such as activated alumina, can be thermally stabilized to retard alumina phase conversion from undesirable gamma to alpha at elevated temperatures by the use of stabilizers or combinations of stabilizers. Various stabilizers are disclosed and the first and second layer compositions of the present invention employ alkaline earth metal components. The alkaline earth metal component is preferably an alkaline earth metal oxide. In a particularly preferred composition, preference is given to using barium and strontium as compounds in the first and / or second layer compositions. Alkaline earth metals can be applied in soluble form, which becomes an oxide when calcined. Soluble barium is preferably provided as barium nitrate, barium acetate or barium hydroxide, and soluble strontium is preferably provided as strontium nitrate or strontium acetate, both of which become oxides when calcined.

One aspect of the present invention provides the application of one or more thermal stabilizers and / or catalyst promoters to the coating of precalcined activated alumina and catalyst components on a carrier substrate. In another aspect of the invention, one or more additives may be applied to the activated alumina before or after the alumina particles are formed in the calcined coating that is adhered to the carrier substrate. (As used herein, a “precursor” of a heat stabilizer or other modifier or other component is a compound, complex, etc., calcined or degraded when using a catalyst or converted to a heat stabilizer, other modifier or other component, respectively. Will be). The presence of one or more metal oxide thermal stabilizers tends to delay the phase conversion from large surface area aluminas such as gamma and eta alumina to alpha alumina, which is a small surface area alumina. This delay in phase conversion tends to prevent or reduce the blockage of catalytic metal components by alumina, which in turn reduces catalyst activity.

In each of the first and second upstream layer compositions, the amount of metal oxide thermal stabilizer combined with alumina is about 0.05 to 30% by weight, preferably about 0.1, based on the total amount of alumina, stabilizer and catalytic metal components combined together. To 25% by weight.

In addition, both the first upstream layer composition and the second layer composition contain a compound derived from zirconium, preferably zirconium oxide. Zirconium compounds may be provided as water-soluble compounds such as zirconium acetate or relatively insoluble compounds such as zirconium hydroxide. There should be sufficient amount to improve the stabilization and promotion of the individual compositions.

Both the first upstream layer composition and the second upstream layer composition contain at least one first promoter selected from the group consisting of lanthanum metal components and neodymium metal components, with preferred components being lanthanum oxide (lantana) and neodymium oxide (neodymia). to be. In a particularly preferred composition, lanthana and optionally a small amount of neodymia are present in the bottom layer and neodymia and optionally lanthana are present in the top coat. The compounds are known to act as stabilizers for alumina supports, but the main purpose in the compositions of the present invention is to act as reaction promoters for the first and second layer compositions, respectively. Accelerators are considered as substances that improve the conversion of the desired chemical to another. Accelerators in TWC improve the catalytic conversion of carbon monoxide and hydrocarbons to water and carbon dioxide, and the catalytic conversion of nitrogen oxides to nitrogen and oxygen.

Preferably the first and second upstream layers contain lanthanum and / or neodymium in the form of oxides. However, preferably the compound is initially provided in soluble form, such as acetates, halides, nitrates, sulfates, etc., to impregnate the solid components for conversion to oxides. It is preferred that in the top coat and the bottom coat the promoter is in intimate contact with the other components in the composition, in particular comprising the platinum group metal.

The first upstream layer composition and / or the second upstream layer composition of the present invention may contain other conventional additives such as sulfide inhibitors, for example nickel or iron components. If nickel oxide is used, about 1 to 25 weight percent of the first coat may be efficient. As described in US Pat. No. 5,057,483, which is incorporated herein by reference.

Particularly useful upstream laminate catalyst composites of the invention comprise from about 0.003 to 0.3 g / in ³ of the first palladium component in the first layer; About 0 to 0.065 g / in ³ of a first platinum group metal component other than palladium; From about 0.15 to about 2.0 g / in ^{3 of} a first support such as alumina; At least about 0.05 g / in ^{3 of} the total first oxygen storage component in intimate contact with the palladium component; From about 0.025 to about 0.5 g / in ^{3 of} at least one first alkaline earth metal component; From about 0.025 to about 0.5 g / in ^{3 of} the first zirconium component; From about 0.025 to about 0.5 g / in ^{3 of} at least one first rare earth metal component selected from the group consisting of lanthanum metal components and neodymium metal components; From about 0.003 to 0.3 g / in ³ of the second palladium component and from about 0 to 0.065 g / in ^{3 of} the second rhodium component or the second platinum component or mixture thereof in the second layer; From about 0.15 to about 2.0 g / in ^{3 of} a second support, such as alumina; And from about 0.025 to about 0.5 g / in ^{3 of} the second zirconium component. The first and / or second layer may further comprise from about 0.025 to about 0.5 g / in ³ of nickel component. The first and / or second layer may also comprise 60 to 90% by weight of zirconia, 10 to 30% by weight of ceria, and 0 to 10% by weight of rare earth oxides comprising Lantana, neodymia and mixtures thereof. The particulate composite of zirconia and ceria may be included in an amount of 0.0 to 2.0 g / in ³ . The amount of palladium component and other platinum group metal components is based on the weight of the metal.

The catalyst composite may generally be coated on a layer on a monolith substrate that may comprise from about 0.5 to about 6.0, preferably from about 1.0 to about 5.0 g / in ³ of the catalyst composition, based on grams of composition per volume of monolith.

The catalyst composite of the present invention may be prepared by any suitable method. Preferred methods include mixing a solution of at least one water soluble or water dispersible first palladium component with a first mixture of finely divided, large surface area refractory oxide sufficiently dry to absorb substantially all of the solution. The first platinum group metal component other than palladium, if used, may be supported on the same or different refractory oxide particles as the palladium component.

The supported first palladium and other components are then added to the water and preferably milled to form a first coat (layer) slurry. The supported first platinum group component other than palladium may be comminuted together or separately with the first support palladium component and combined with the other components to form a first coat slurry. Preferably, the slurry is acidic with a pH of less than 7 and preferably from 3 to 7. Preferably the pH is lowered by the addition of acid, preferably acetic acid, to the slurry. In a particularly preferred embodiment the first coat slurry is milled such that substantially all of the solids have a particle size of less than 10 micrometers in average diameter. The first coat slurry can be formed in the first layer and dried. Any platinum component other than the first palladium component and palladium component in the first mixture obtained in the first layer is converted into a water insoluble form chemically or by calcining. Preferably the first layer is calcined at 250 ° C. or higher.

A second mixture of a solution of at least one water soluble second palladium component and a finely divided large surface area refractory oxide sufficiently dry to absorb substantially all of the solution. If a second platinum group metal component is used, it can be supported on the same or different refractory oxide particles as the palladium component. Preferably, the rhodium component is supported on different refractory oxide particles other than the palladium component. The supported second palladium component and other components are added to water and preferably milled to form a second coat slurry. The supported second platinum group metal component other than palladium is ground together or separately with the palladium component and then combined together with the supported palladium component and other components to form a second coat slurry. Preferably, the second slurry is acidic with a pH of less than 7 and preferably from 3 to 7. Preferably, the pH is lowered by adding acid, preferably nitric acid, to the slurry. In a particularly preferred embodiment the second coat slurry is milled such that substantially all of the solids have a particle size of less than 10 micrometers in average diameter. The second slurry can be formed and dried in a second layer on the first layer. The second palladium group component and any second platinum group metal component other than palladium in the second coat mixture obtained can be converted to insoluble form chemically or by calcining. The second layer is then preferably calcined at 250 ° C. or higher.

Alternatively, each upstream layer of the composite may also be prepared by the method described in US Pat. No. 4,134,860 (incorporated by reference).

In order to deposit the first and second coat slurry onto the large size carrier, one or more ground slurry is applied to the carrier in any desired manner. The carrier is thus immersed one or more times in the slurry and, if necessary, intermediately dried until an appropriate amount of slurry is present on the carrier. The slurry used to deposit the catalyst promoting metal component-large area support composite onto the carrier will often contain about 20 to 60% by weight, preferably about 25 to 55% by weight, of finely divided solids.

The first upstream layer composition of the present invention and the second layer composition of the present invention may be prepared and applied to a suitable substrate, preferably a metal or ceramic honeycomb carrier. The ground catalyst-complementary metal component-large surface area support composite can be deposited on the carrier in a desired amount, for example the composite can comprise about 2 to 40% by weight of the coated carrier, preferably a conventional ceramic honeycomb About 5 to 30% by weight relative to the phase structure. The composite deposited on the carrier is generally formed as a coating over most, if not all, of the carrier surface in contact. The combined structure is preferably at a temperature of about 250 ° C. or more, but can be dried and calcined at a temperature that does not unreasonably destroy a large area of the refractory oxide support, unless required in certain conditions.

Carriers useful in the catalysts produced by the present invention are inherently metallic and may consist of one or more metals or metal alloys. The metallic carrier can be in various shapes or monolithic form, such as corrugated sheet. Preferred metallic supports in particular comprise heat resistant base metal mixtures in which iron is a substantial or major component. The alloy may comprise one or more nickel, chromium, and aluminum, advantageously the metals comprise at least about 15% by weight of the total alloy, for example about 10-25% by weight of chromium and about 3 to about aluminum. 8 wt% and about 20 wt% or less of nickel, for example, when present in trace amounts, may comprise about 1 wt% or more of nickel. Preferred alloys may contain small or minor amounts of one or more other metals such as manganese, copper, vanadium, titanium, and the like. The surface of the metal carrier can be oxidized at significant elevated temperatures, for example at least about 1000 ° C., to improve the corrosion resistance of the alloy by forming an oxide layer on the surface of the carrier having a greater thickness and surface area than that obtained at ambient temperature oxidation. Oxidizing or stretching the surface on the alloy carrier by high temperature oxidation can improve the adhesion of the refractory oxide support and the catalyst promoting metal component to the carrier.

Any suitable carrier may be used, such as a monolithic carrier of the type having multiple fine parallel gas flow passages extending from the inlet or outlet side of the carrier, which passages open to fluid flow. The essentially straight passage from the fluid inlet to the fluid outlet is defined by the wall, on which the catalytic material is coated as a "washcoat" and the gas flowing through the passage is in contact with the catalytic material. The flow passage of the monolithic carrier is a thin wall channel that can be any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, ellipse, circle. The structure may contain about 60 to about 1200 or more gas inlet openings (“cells”) per square inch of cross section. The ceramic carrier may be any suitable refractory material, such as cordierite, cordierite-alpha alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, silimite, magnesium silicate, zircon, It can be made of petalite, alpha alumina and aluminosilicate. The metallic honeycomb can be made of stainless steel or other suitable iron based or nickel based corrosion resistant alloy.

The monolithic carrier may contain at least about 700 flow channels (“cells”) per square inch of cross section, but much less may be used. For example, the carrier may have a cell (“cpsi”) of about 60 to 600, more typically about 200 to 400 per square inch.

The discontinuous form of catalyst material, commonly referred to as "washcoat" and the second coat are coated onto a suitable carrier, preferably the first coat is adhered to the carrier and the second coat overlies and adheres to the first coat. By this arrangement, the gas, which is adhered to the catalyst and flows through, for example, a passage of the catalyst material-coated carrier, will first contact and pass through the second or top coat in order to contact the underlying bottom or first coat. will be. However, in a separate arrangement, the second coat need not be placed on the first coat, but provided on an upstream portion of the carrier (as sensed in the direction of gas flow through the catalyst composition), the first coat being downstream of the carrier. Is provided. Thus, after immersing and drying only the upstream longitudinal portion of the carrier in the slurry of the second coat catalyst material to apply the washcoat in the batch, the immersed downstream longitudinal portion of the carrier is immersed in the slurry of the first coat catalyst material and To dry. Alternatively, separate upstream carriers may be used, one carrier on which the first upstream coat is deposited and a second carrier on which the second upstream coat is deposited, the two individual carriers being placed in a canister or other holding device, and the exhaust to be treated. The gas may be arranged to flow through the first coat containing catalyst after being continuously flowed through the second coat containing catalyst. However, it is preferable to use a catalyst composition in which the second coat is placed on top of the first coat and adhered as described above, since the arrangement is believed to simplify the preparation of the catalyst composition and improve its efficacy.

<2 layers downstream catalyst>

The present invention includes embodiments in which the downstream catalyst zone comprises a substrate and two or more layers. The catalyst structure relates to a layered catalyst composite of the type useful as a three-way conversion catalyst or TWC. The TWC catalyst composite of the present invention simultaneously catalyzes the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides in the gas stream. The most preferred composition in the two-layer containing downstream zone 18 is the composition described in US patent application Ser. No. 08 / 563,884, incorporated herein by reference and commonly assigned.

The laminated catalyst composite includes a first downstream layer comprising a first downstream layer composition and a second layer comprising a second layer composition. As noted above, the gas stream is initially in contact with a second, tower, or outer downstream layer composition designed to efficiently reduce nitrogen oxides to nitrogen, cause oxidation of some carbon monoxide, and oxidize hydrocarbons. The gas then passes to the first downstream layer to divert the remainder of the contaminants.

The laminated catalyst composite includes a first downstream layer comprising a first layer composition and a second downstream layer comprising a second layer composition. The first downstream layer is also called the bottom or the inner layer and the second downstream layer is called the top or the outer layer.

As noted above, the gas stream is initially in contact with a second downstream composition designed to efficiently reduce nitrogen oxides to nitrogen, cause oxidation of some carbon monoxide and oxidize hydrocarbons. The gas then passes to a first downstream layer designed to convert contaminants, including oxidizing hydrocarbons and remaining carbon monoxide.

The specific design of the first downstream layer efficiently oxidizes the hydrocarbon over a wide range of temperatures. In a preferred composite the first downstream layer comprises a catalytically effective amount of palladium component. Optionally, based on the total platinum component used in the first and second layers, the platinum metal is present in small amounts, 0-50 wt% or less, preferably 0-20 wt% and most preferably 0-10 wt%. Can be. When platinum is used, a typical small amount is about 1% by weight, preferably 3% by weight and most preferably 5% by weight of the platinum component, based on the platinum metals in the first and second layers. The performance of the first layer platinum group noble metal component can be improved by the use of a stabilizer, an accelerator selected from alkaline earth metals, preferably lanthanum and neodymium, and a component of zirconium. Preferably an oxygen storage component is also included. The oxygen storage component may be a portion of the first oxygen storage composition impregnated in the solution or as a solution capable of intimate contact between the oxygen storage component and the first layer platinum group metal component in any form, including bulk form. The oxygen storage component improves oxidation in the bottom layer. The oxygen storage component is introduced in the form of a soluble salt solution that impregnates the support and other particulate material, and then comes in intimate contact where it can be converted to the oxide form when calcined.

The second downstream layer comprises a second platinum component and a rhodium component. The second or top downstream layer contains 50 to 100% by weight of the platinum component based on the total platinum metal in the first and second layers. In order for the second downstream layer to obtain high temperature conversion efficiencies, an oxygen storage composition is used that includes a dilute oxygen storage component. Preferred oxygen storage compositions are complexes comprising ceria and zirconia. This results in a second oxygen storage component that is in minimally intimate contact with the platinum group metal component (ie, rhodium and platinum component) even when the platinum group metal component is supported on the bulk oxygen storage composition particles. It is preferred to include a second zirconium component in the second layer.

The first downstream layer composition and the second downstream layer composition each comprise a first support and a second support, which can be the same or different support components. Preferably the support comprises a large surface area refractory oxide support. Useful large surface area supports include one or more refractory oxides. Oxides include, for example, silica and alumina, and include mixed oxide forms such as aluminosilicate, which may be amorphous or crystalline, alumina-zirconia, alumina-chromia, alumina-ceria, and the like. Preferably the support comprises substantially gamma or transitional aluminas, such as gamma and eta alumina, and, if present, alumina comprising, for example, up to about 20% by weight of other refractory oxides. Preferably, the specific surface area of activated alumina is 60 to 300 m 2 / g.

Preferred catalysts of the present invention comprise a platinum group metal component present in an amount sufficient to provide a composition with significantly improved catalytic activity against oxidation of hydrocarbons and carbon monoxide, and reduction of nitrogen oxides. It has been found that the position of the platinum group metal component, in particular the rhodium component and the palladium component, and the relative amounts of the platinum component in the first and second layers, respectively, affect the persistence of the catalytic activity. In addition, the use of a dilute second oxygen storage component that is not in intimate contact with most platinum components and rhodium components also improves long term catalytic activity.

When preparing the catalyst, platinum group metal catalyst components such as suitable compounds and / or complexes of any platinum group metal can be used to obtain dispersibility of the catalyst component on the support, preferably on activated alumina support particles. As used herein, a "platinum group metal component" includes any of the platinum, rhodium and platinum components listed and is decomposed when calcining or using a catalyst or otherwise generally converted to a catalytically active form of a metal or metal oxide. Means a platinum group metal compound, a complex, and the like. Water-soluble or water-dispersible compounds of at least one platinum group metal component, so long as the liquid used to impregnate or deposit the catalyst metal compound on the alumina support particles does not react back with the catalyst metal or its compounds or other components of the complex or slurry, or Complexes may be used, which may be removed from the catalyst by volatilization or decomposition when heating and / or vacuum is applied. In some cases, removing the liquid may not be complete until the catalyst is used during the run and treated at high temperatures. In general, from an economic and environmental standpoint, aqueous solutions of soluble compounds or complexes of platinum group metals are preferred. For example, suitable compounds include platinum (IV) hydrochloric acid, amine-soluble platinum hydroxides such as hexahydroxymonoethanolamine complexes of platinum, rhodium chloride, rhodium nitrate, hexaminlodium chloride, palladium nitrate or palladium chloride. . During the calcination step, or at least during the initial state of catalyst use, the compound is converted to the catalytically active form of the platinum group metal, or a compound thereof, typically an oxide.

The catalyst of the present invention may be in bulk form or contain a first downstream oxygen storage component in the first layer which may be in intimate contact with the platinum group metal component, ie palladium. The oxygen storage component is any of the foregoing materials known in the art, preferably at least one metal oxide selected from the group consisting of rare earth metals, more preferably cerium, praseodymium or neodymium compounds, the most preferred oxygen storage component being cerium oxide (Seria).

The oxygen storage component in the first downstream layer composition can be included by dispersion methods known in the art. The method includes impregnating onto a first support composition. The oxygen storage component may be in the form of an aqueous solution. The resulting mixture is dried in air and calcined to obtain a first layer containing an oxide of an oxygen storage component in intimate contact with the platinum group metal component. Typically, impregnation means that there is substantially enough liquid present to fill the pores of the material to be impregnated. Examples of water soluble degradable oxygen storage components that can be used include, but are not limited to, cerium acetate, praseodymium acetate, cerium nitrate, praseodymium nitrate, and the like. US Pat. No. 4,189,414 discloses impregnating an alumina based support composition with cerium nitrate.

Optionally and preferably there is a second oxygen storage composition in bulk form in the second downstream layer. The second oxygen storage composition is a second oxygen storage component, preferably ceria, praseodymia and / or neodymia, preferably ceria, most preferably comprising ceria. Bulk form means that the composition comprising ceria and / or praseodymia is present as discrete particles that can be as small as 0.1 to 15 microns or less in diameter as opposed to being dispersed in solution as in the first layer. . The description and use of such bulk components are described in US Pat. No. 4,714,694, which is incorporated herein by reference. In addition, as described in US Pat. No. 4,727,052, incorporated herein by reference, the bulk form includes particles of ceria oxygen storage composition mixed with particles of zirconia or zirconia activated alumina. Particular preference is given to diluting the oxygen storage component as part of the oxygen storage component composition.

The oxygen storage component composition used in the first downstream layer and the second downstream layer may comprise an oxygen storage component, preferably a ceria and a diluent component. The diluent component can be any suitable filler that is inert to interaction with the platinum group metal component so as not to adversely affect the catalytic activity. Useful diluent materials are refractory oxides, and preferred refractory oxides are of the same type as those listed below for use as catalyst supports. More preferred are zirconium compounds, with zirconia being most preferred. Thus, the preferred oxygen storage component is the ceria-zirconia complex. Ceria is present in the range of 1 to 99% by weight, preferably 1 to 50% by weight, more preferably 5 to 30% by weight and most preferably 10 to 25% by weight, based on ceria and zirconia. Preferred oxygen storage compositions for use in the second layer composition, and optionally in the first layer composition, may comprise a composite comprising zirconia, ceria and one or more rare earth oxides. Such materials are described, for example, in US Pat. Nos. 4,624,940 and 5,057,483, which are incorporated herein by reference. Particular preference is given to particles comprising more than 50% of a zirconia based compound, preferably from 60 to 90% of zirconia, from 10 to 30% by weight of ceria and optionally up to 10% by weight of at least 0.1% by weight of biseria Rare earth oxides are useful for stabilizing zirconia selected from the group consisting of lantana, neodymia and yttria.

Optionally and preferably the first downstream layer composition comprises a component that imparts stabilization. Stabilizers may be selected from the group consisting of alkaline earth metal compounds. Preferred compounds include compounds derived from metals selected from the group consisting of magnesium, barium, calcium and strontium. It is known from US Pat. No. 4,727,052 that support materials such as activated alumina can be thermally stabilized to delay undesirable alumina phase conversion from gamma to alpha at elevated temperatures by the use of stabilizers or combinations of stabilizers. Various stabilizers are disclosed, and the first layer composition of the present invention preferably uses an alkaline earth metal component. The alkaline earth metal component is preferably an alkaline earth metal oxide. In particularly preferred compositions it is preferred to use barium oxide and / or strontium oxide as the compound in the first layer composition. Alkaline earth metals can be applied in soluble form, which becomes an oxide when calcined. Soluble barium is provided as barium nitrate or barium hydroxide, and soluble strontium is preferably provided as strontium nitrate or strontium acetate, all of which become oxides upon calcination.

One aspect of the present invention provides the application of one or more thermal stabilizers to a coating of precalcined activated alumina and catalyst components on a carrier substrate. In another aspect of the invention one or more modifiers may be applied to the activated alumina before or after the alumina particles are formed in the adhesive calcined coating on the carrier substrate. (As used herein, a "precursor" of a heat stabilizer, or other modifier or other component, is a compound, complex, or the like, decomposed when calcining or using a catalyst, or otherwise thermal stabilizer, other modifier or other component, respectively. Is converted to). Typically the presence of one or more metal oxide thermal stabilizers tends to delay the phase transition from large surface area aluminas such as gamma and eta alumina to alpha alumina, which is a low surface area alumina. This delay in phase conversion tends to prevent or reduce the blockage of catalytic metal components by alumina, which in turn reduces catalyst activity.

In the first downstream layer composition, the amount of heat stabilizer combined with alumina may be about 0.05-30% by weight, preferably about 0.1-25% by weight, based on the total amount of alumina, stabilizer, and catalyst metal components combined together. .

Both the first downstream layer composition and the second downstream layer composition may contain a compound derived from zirconium, preferably zirconium oxide. Zirconium compounds may be provided as water-soluble compounds such as zirconium acetate or relative insoluble compounds such as zirconium hydroxide. There should be sufficient amount to improve the stabilization and promotion of the individual compositions.

Preferably the first downstream layer composition contains at least one promoter selected from the group consisting of lanthanum metal components and neodymium metal components, with preferred components being lanthanum oxide (lantana) and neodymium oxide (neodymia). In a particularly preferred composition there is lantana and optionally a small amount of neodymia in the bottom layer and neodymia or optionally lantana in the top coat. The compounds are disclosed to act as stabilizers and may also act as reaction promoters. Accelerators are considered to be substances that improve the conversion of the desired chemical to another. Accelerators in TWC improve the catalytic conversion of carbon monoxide and hydrocarbons to water and carbon dioxide, and the catalytic conversion of nitrogen oxides to nitrogen and oxygen.

Preferably the first downstream layer contains lanthanum and neodymium in the form of neodymia and / or oxide. Preferably, the compound is initially provided in soluble form, such as acetates, halides, nitrates, sulfates, etc., to impregnate the solid components for conversion to oxides. The accelerator in the first layer is preferably in intimate contact with the other components in the composition, in particular comprising the platinum group metal.

The first downstream layer composition and / or the second downstream layer composition of the present invention may contain other conventional additives such as sulfide inhibitors, for example nickel or iron components. If nickel oxide is used, about 1 to 25% by weight of the first coat may be effective, as described in commonly-owned US patent application Ser. No. 07 / 787,192, which is incorporated herein by reference.

Particularly useful downstream layered catalyst composites of the present invention may comprise from about 0.025 to 0.10 g / in ³ of the palladium component in the first layer; From about 0 to 0.01 g / in ^{3 of} the first platinum component; From about 0.15 to about 1.5 g / in ^{3 of} a first support, ie alumina; At least about 0.05 g / in ^{3 of} the first oxygen storage component; From about 0.025 to about 0.5 g / in ^{3 of} at least one first alkaline earth metal component; From about 0.025 to about 0.5 g / in ^{3 of} the first zirconium component; From about 0.0 to about 0.5 g / in ^{3 of} at least one first rare earth metal component selected from the group consisting of a lanthanum metal component and a neodymium metal component; The second platinum component in the second layer from about 0.001 to 0.02 g / in ^3, and the rhodium component from about 0.001 to 0.01 g / in ^3, the second support, i.e., alumina about 0.15 to about 1.0 g / in ^3; From about 0.1 to about 1.5 g / in ^{3 of} a second oxygen storage composite comprising a particulate composite of zirconia and ceria; And from about 0.025 to about 0.5 g / in ^{3 of} the second zirconium component. The first and / or second layer may further comprise from about 0.025 to about 0.5 g / in ³ of a nickel component. The particulate composite of zirconia and ceria may comprise 60 to 90% by weight of zirconia, 10 to 30% by weight of ceria and 0 to 10% by weight of rare earth oxides including Lantana, neodymia and mixtures thereof.

The downstream catalyst composite is generally coated with a catalyst composition on a layer on a monolith substrate that may comprise from about 0.50 to about 6.0 g / in ³ , preferably from about 1.0 to about 5.0 g / in ³ , based on grams of composition per volume of monolith. Can be. The catalyst composite of the present invention may be prepared by any suitable method. Preferred methods include mixing a solution of at least one water soluble first palladium component and optionally a first platinum component with a first mixture of finely divided large surface area refractory oxide sufficiently dry to absorb substantially all of the solution.

The first downstream platinum and platinum components are added to water to form a first slurry and preferably milled to the first slurry. Preferably, the slurry is acidic with a pH of less than 7 and preferably from 3 to 7. Preferably the pH is lowered by the addition of acid, preferably acetic acid, to the slurry. In a particularly preferred embodiment the first slurry is comminuted so that substantially all of the solids have a particle size of less than 10 micrometers in average diameter. The first slurry can be prepared in the first layer and dried. The first palladium component and optionally the platinum component in the first mixture obtained in the first layer convert to water insoluble form. The palladium and platinum components can be converted to insoluble form chemically or by calcining. The first layer is preferably calcined at 250 ° C. or higher.

A solution of at least one water soluble second platinum component and at least one water soluble rhodium component is mixed with a second mixture of finely divided large surface area refractory oxide sufficiently dry to absorb substantially all of the solution. The second platinum component and the second rhodium component are added to water to form a second slurry, preferably milled to the second slurry. Preferably, the slurry is acidic with a pH of less than 7 and preferably from 3 to 7. Preferably the pH is lowered by the addition of acid, preferably acetic acid, to the slurry. In a particularly preferred embodiment the second slurry is comminuted so that substantially all of the solids have a particle size of less than 10 micrometers in average diameter. A second slurry can be prepared and dried in a second layer on the first layer. The second platinum group component and the second rhodium component in the second mixture obtained are converted to the water insoluble form. The platinum and rhodium components can be converted to insoluble form chemically or by calcining. The second layer is then calcined, preferably at 250 ° C. or higher.

In addition, each downstream layer of the present composites can be prepared by the methods disclosed in US Pat. No. 4,134,860, which is incorporated herein by reference in general.

The finely divided large surface area refractory oxide support is preferably in contact with a solution of a water soluble catalyst promoting metal component containing one or more platinum group metal components to provide a mixture that is essentially free of free or non-absorbing liquid. The catalytically promoted platinum group metal component of the solid, finely divided mixture can be converted to an essentially water insoluble form at this point in the step, and the mixture is essentially free of nonabsorbable liquid. The method can be achieved by using a refractory oxide support, for example alumina comprising stabilized alumina, which is sufficiently dry to absorb substantially all of the catalyst-promoting metal component containing solution, and the amount of solution and support, and the latter wetting The content is essentially free of free or nonabsorbent solutions when the addition of the catalyst promoting metal component is complete. During the latter conversion or fixation of the catalyst promoting metal component on the support, the composite is essentially dry so that there are substantially no individual or free liquid phases.

The immobilized catalyst-promoting metal component-containing mixture is preferably comminuted as an acidic slurry to advantageously provide solid particles, mainly of about 5 to 15 microns in size. The resulting slurry is preferably used to coat large size carriers with a low surface area, and the composite can be dried and calcined. The complex of the catalyst promoting metal component and the large area support in the catalyst exhibits strong adhesion to the carrier even if the latter is substantially nonporous, such as, for example, a metallic carrier, and the catalyst exhibits catalytic activity and activity when used under intense reaction conditions. The service life is quite good. Each of the first and second layers can be applied and calcined successively to form the composite of the present invention.

Since essentially all platinum group metal components added to the formulation system remain in the catalyst, the method provides a composition of uniform and specific catalyst promoting metal components, wherein the composition consists essentially of single or multiple active catalyst-promoting metal components. It contains the calculated amount. In some cases multiple catalytically active metal components may be deposited on a given refractory oxide support simultaneously or sequentially. The individually prepared catalyst-promoting metal component refractory oxide composites of the different compositions produced by the process of the invention can be tightly mixed to produce a variety of catalysts whose metal content is tightly controlled and selected for a particular catalytic effect. The mixed composite may, if desired, contain one or more catalytically promoted metal components on a portion of the refractory oxide support particles, and one or more different catalytically accelerated metal components on another portion of the refractory oxide support particles. For example, the composite may have a platinum group metal component on a portion of the refractory oxide particles, and a base metal component on a different portion of the refractory oxide particles. Alternatively, different platinum group metals or different base metals may be deposited on individual portions of the refractory oxide support particles in a given composite. Thus, it is clear that the process is quite advantageous in that it provides a catalyst that can be easily changed and tightly controlled in the composition.

The precious metal group or base metal group component may be formed on the large surface area refractory oxide alone or in a mixture in separate first and second layers, and then deposited on a large size carrier. This makes the platinum metal component present in small amounts maximally useful by depositing on the outer surface of the carrier. In order to maximize the use of expensive catalyst components, or to achieve certain catalyst benefits such as inlet portions coated with the components to provide light off or reaction starting activity at relatively low temperatures, the latter method can be applied to large surface area refractory oxides. Deposit a substantially discontinuous layer of various metal components. If the metal component is not selectively deposited on the carrier and is not fixed to the refractory oxide, it can move freely from one layer of catalyst to the next.

The mixture of the catalyst promoting metal component and the refractory oxide support in accordance with the present method can be prepared by mixing the finely divided large surface area support with an aqueous solution containing a water soluble form of the catalyst promoting metal to essentially completely absorb the solution into the support. . The solution may contain one or more water soluble compounds of precious or base metals. The water soluble platinum group metal component is preferably in the form of a basic compound such as platinum hydroxide or tetramine complex, or an acidic compound such as platinum (IV) hydrochloric acid or rhodium nitrate. Useful base metal compounds include water soluble salts such as nitrates, formate, other oxygen containing compounds and the like. Individual compounds of the catalyst promoting metal may be added to the support in one or more aqueous solutions to provide two or more metals on the desired support particles.

After the catalyst promoted metal solution and the large surface area oxide support are combined together, the catalyst promoted metal component can be immobilized on the support, essentially converted to a water insoluble form and the composite is essentially free of free or nonabsorbable media. The conversion can be effected chemically by treatment with a gas such as hydrogen sulfide or hydrogen, or other reagents which may be in acetic or liquid form, in particular an aqueous solution, for example a liquid such as hydrazine. However, the amount of liquid used is not sufficient for the composite to contain a significant or substantial amount of free or nonabsorbable liquid while fixing the catalyst promoting metal on the support. The fixation treatment can be done by reactive gas or essentially inert; For example, fixation may be accomplished by calcining the complex in air or other gas that may be reactive or essentially inert with the catalytically promoted metal component. The insoluble or fixed catalyst promoting metal component obtained can be present as sulfides, oxides, elemental metals or in other forms. If a plurality of catalyst promoting metal components are deposited on the support, the fixation can be carried out after the deposition of each metal component or after the deposition of the plurality of said metal components.

The particle size of the finely divided large surface area refractory oxide support is generally greater than about 10 or 15 micrometers. When combined with a catalyst promoting metal containing solution as described above, the large surface area support is dried to be essentially sufficient to absorb all of the solution.

In the preparation of the catalysts according to the invention the catalytically active complexes of fixed or water insoluble catalyst promoting metal components and large area supports can preferably be combined together with large size carriers with a small total surface area. This may be accomplished by first grinding a number of complexes, such as catalytically active complexes, or aqueous slurry, preferably acidic. Generally the treatment continues until the particle size of the solid particles in the slurry is predominantly less than about 10 or 15 micrometers. Grinding can take place in a ball mill or other suitable apparatus, and the solids content of the slurry can be, for example, about 20 to 50% by weight, preferably about 35 to 45% by weight. Preferably the pH of the slurry is less than about 5, and acidity can be supplied by using small amounts of water soluble organic or inorganic acids, or other water soluble acidic compounds. Thus, the acid used may be a lower fatty acid such as hydrochloric acid or nitric acid, or more preferably acetic acid, for example trichloroacetic acid may be substituted with chlorine. Fatty acids may be used to minimize any platinum group metal loss from the support.

One or more milled slurries may be combined with the carrier individually or typically in any desired manner to deposit the catalyst promoter metal support complex on the large size carrier. Thus, the carrier may be immersed one or more times in the slurry and intermediately dried if necessary until the appropriate amount of slurry is present on the carrier. The slurry used to deposit the catalyst promoting metal component-large surface area composite on the carrier will often include from about 20 to 50% by weight, preferably from about 35 to 45% by weight of finely divided solids.

The downstream laminated catalyst composites can be used in the form of self supporting structures such as pellets, or on suitable carriers or substrates such as metallic or ceramic honeycombs.

The first downstream layer composition of the present invention and the second downstream layer composition of the present invention can be prepared by known methods and formed into pellets or applied to a suitable substrate, preferably a metal or ceramic honeycomb carrier. Crushed catalyst promoting metal component-large surface area support composites may be deposited on the carrier in a desired amount, for example the composite may comprise from about 2 to 30%, preferably from about 5 to 20%, by weight of the coated carrier. Can be. The composite deposited on the carrier is generally formed as a coating over most, if not all, of the carrier surface in contact. The combined structures can be dried and calcined at a temperature that does not unreasonably destroy a large area of the refractory oxide support, preferably at least about 250 ° C., unless required under certain conditions.

Carriers useful for the catalysts produced by the present invention may be metallic in nature and may consist of one or more metals or metal alloys. The metallic carrier may be in various shapes such as pellets or in monolithic form. Preferred metallic supports include heat resistant base metal alloys, especially those in which iron is a substantial or major component. The alloy may contain one or more nickel, chromium, and aluminum, advantageously the metals comprise at least about 15% by weight of the total alloy, for example about 10-25% by weight of chromium, about 3-8% by aluminum. It may comprise about 1% by weight or more of nickel by weight and up to about 20% by weight of nickel, optionally or when present in trace amounts. Preferred alloys may contain one or more small or trace amounts of other metals such as manganese, copper, vanadium, titanium, and the like. Since the metal carrier surface can be oxidized at significant elevated temperatures, it is possible to improve the corrosion resistance of the alloy by forming an oxide layer on the carrier surface having a larger thickness and surface area than that obtained by oxidizing at ambient temperature. Providing an oxidized or stretched surface on the alloy carrier by high temperature oxidation can improve the adhesion of the refractory oxide support and the catalyst promoting metal component to the carrier.

Any suitable carrier may be used, such as a monolithic carrier of the type having a plurality of fine parallel gas flow passages extending from the inlet or outlet side of the carrier, the passages opening to fluid flow. The essentially straight passage from the fluid inlet to the fluid outlet is defined by the wall, on which the catalytic material is coated as a "washcoat" and the gas flowing through the passage is in contact with the catalytic material. The flow passage of the monolithic carrier is a thin wall channel that can be any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, ellipse, circle. The structure may contain from about 60 to about 600 or more gas inlet openings (“cells”) per square inch of cross section. The ceramic carrier may be any suitable refractory material, such as cordierite, cordierite-alpha alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, silimite, magnesium silicate, zircon, It can be made of petalite, alpha alumina and aluminosilicate. The metallic honeycomb can be made of refractory metals such as stainless steel or other suitable iron based or nickel based corrosion resistant alloys.

The metal monolithic carrier may contain up to about 1200 or more flow channels (“cells”) per square inch of cross section, but much less may be used. For example, a carrier can have about 60 to 1200, more typically 200 to 800, and most typically about 400 to 600 cells per square inch.

In a separate embodiment, the downstream zone 20 is designed to have a higher thermal mass than the upstream zone 18. For the purposes of the present invention, thermal mass is expressed as the mass of an upstream or downstream zone multiplied by the heat capacity of the individual zones. This design is particularly desirable when combined with the catalyst composition as listed above for use in separate zones. When upstream and downstream honeycomb monoliths are made of the same or similar materials, the useful upstream monolith honeycomb 30 axis lengths are from 0.5 to 3.0, from 0.5 to 2.5, from 0.5 to 2.0, from 1.0 to 2.0 and from 1.0 to 3.0 inches. Preferred ceramic upstream honeycomb monoliths are from 2.0 to 3.0 inches in length and 2.5 inches of monolith are commercially available. An important factor influencing the thermal mass of the upstream and downstream zones is the material from which the substrate is made. Useful embodiments include upstream honeycombs made of metal and downstream monoliths made of ceramic. The heat capacity of the ceramic honeycomb tends to be larger. Other factors affecting thermal mass include the number of cells per square inch (cpsi), catalyst loading, and honeycomb wall thicknesses varying from 0.001 to 0.014 inches. Typically the wall thickness of ceramic monoliths is 0.002 to 0.008 inches, and typically the wall thickness of metal monoliths is 0.0015 to 0.003 inches. Useful honeycomb flow through monoliths have a cpsi of 300 to 600. The greater the monolith cpsi, the greater the thermal mass, depending on wall thickness and the like. The present invention allows the use of upstream monoliths with less cpsi in monoliths compared to downstream monoliths. Thus, the smaller the upstream monolith, the faster it will heat up. Useful and preferred honeycombs can be prepared from ceramic materials or metallic materials as listed above. Preferred upstream ceramic honeycombs are made of cordierite, have 300 to 600 cpsi and are 2.0 to 3.0 inches in the axial direction. Preferred downstream ceramic honeycombs are made of cordierite, have 300 to 600 cpsi and are greater than 3.0 to about 9.0 inches in the axial direction. The upstream and downstream honeycombs serve as substrates for supporting the catalyst compositions in the upstream and downstream zones as described above.

Preferably, the light-off temperature of the smaller upstream zone composition is designed to be lower than the downstream zone. Thus, the upstream zone heats up and catalyzes the reactants faster. In addition, when the delay time is longer and the space velocity is smaller than during the static state, it is designed to perform during the conditions such as idle. For the purposes of the present invention "light off" will mean a temperature at which the catalyst is active and can initiate the reaction of the exhaust gas component. Stated another way, lag time is expressed as the inverse of space velocity. For the purposes of the present invention, "space velocity" will mean the volume of gas passing through the catalyst monolith at a given time divided by the total volume of the catalyst monolith, expressed as the inverse of the time unit, such as the inverse of the time. Advantageously, the catalyst product of the present invention can be used at a reciprocal of space velocity of 10 to 500,000 hours and is usually an inverse of 50 to 350,000 hours.

The catalyst composition prepared by the present invention can be reduced, methanated, and in particular a product having a large percentage by weight of oxygen per molecule, such as intermediate oxidation products of carbonaceous substances such as carbon monoxide, hydrocarbons, oxygen-containing organic compounds, carbon dioxide and water. The latter two are relatively harmless from air pollution standards. Advantageously, the catalyst composition is used to remove carbon monoxide, hydrocarbons, and intermediate oxidation products comprising primarily carbon, hydrogen, and oxygen, or unburned or partially burned carbonaceous fuel components, such as nitrogen oxides, from gaseous exhaust emissions. Can be. Some oxidation or reduction reactions may occur at relatively low temperatures, but are often performed at elevated temperatures, for example at least about 150 ° C., preferably at about 200 to 900 ° C., and generally with the gaseous feedstock. Oxidized materials generally contain carbon, so that they may be designated carbonaceous, whether organic or inorganic in nature. Thus, the catalyst is useful for promoting oxidation of hydrocarbons, oxygen-containing organic components, and carbon monoxide, and reduction of nitrogen oxides. Materials of this type can be present in the exhaust gases from the combustion of carbonaceous fuels, and catalysts are useful for promoting oxidation and reduction of materials in the emissions. Exhaust gases from internal combustion engines operating on hydrocarbon fuels, and other waste gases, may be present in the gas stream as part of the emissions, or may be added as other preferred forms with higher or lower air or oxygen concentrations and It can be oxidized by contact with molecular oxygen. The product from oxidation has a higher weight ratio of oxygen to carbon than the oxidized feed material. An advantage of the present invention is that the catalyst product of the present invention can be used in the "down" position of a motor vehicle as shown in FIG. Many such reaction systems are known in the art.

The invention is further illustrated by the following examples, but is not intended to limit the scope of the invention.

<Example 1>

Cordierite monolith, approximately 2.5 inches long, having a cell density of 400 cpsi and a cross-sectional area of about 15.5 in ² , was impregnated with a large surface area alumina washcoat containing palladium at a concentration of 200 g / ft ³ . This washcoat is different from conventional washcoats in which the formulation includes stabilizers and accelerators. The upstream catalyst coating comprises the same two layer composition as listed in Example 1 of US Pat. No. 5,597,771, which is incorporated herein by reference. Since the noble metal is impregnated into the washcoat powder prior to preparing the coating slurry, the method is different from the conventional method of coating the monolith with the washcoat and then adding the noble metal. This washcoat also contains cerium stabilized zirconium and was applied on cordierite monolith as a lamination coating. For example, it was coated on a monolith as a first layer (bottom coat) at a load of 1.9 g / in ³ and coated as a second layer (top coat) at a load of 1.3 g / in ³ . The second honeycomb is about 6 inches long and has the same cross sectional area. The downstream catalyst coating comprises the same two layer composition as listed in Example 1 of US Patent Application No. 08 / 563,884, which is incorporated herein by reference. This catalyst comprises a laminated washcoat having Pd / Pt on the bottom coat and Pt / Rh on the top coat. The total precious metal loading is 105 g / ft ³ and the ratio of Pt / Pd / Rh is 1/14/1. Washcoat loading is 2 g / in ³ for the bottom coat and 1.8 g / in ³ for the top coat.

Both bricks were mounted in a single canister with a total monolith volume of about 132 in ³ . The Pd alone brick was placed upstream of the canister and the space between the two bricks was 0.5 ". The canister was engine aged for 50 hours at the inlet gas temperature of 800 ° C. After aging, the canister was evaluated for Bag2 FTP-75 The Honda Civic 2.2 L car was mounted underneath.

                    % Conversion       Catalytic system        HC        CO       NOx  Pd alone + Pt / Pd / Rh       99.50       96.90       98.50

<Example 2>

A front brick of 26.3 in ³ (diameter 3.66 "x 2.5" long) was prepared with the same washcoat as listed in Example 1 of US patent application Ser. No. 08 / 350,297, with a Pd loading of 200 g / ft ³ , and a total washcoat loading. Coated with 1.9 g / in ³ . A back brick of about 47 in ³ (diameter 3.66 "x 4.5" long) was impregnated with the same slurry as used in Example 1 for the second brick.

Two bricks were aged as in Example 1. However, instead of the temperature of 800 ° C. and 50 hours shown in Example 1, the inlet temperature was 820 ° C. and the aging time was 100 hours. The catalyst system was evaluated using the same Honda Civic 2.2 L as in Example 1. The results are shown below.

                   % Conversion      Catalytic system       HC        CO        NOx  Pd alone + Pt / Pd / Rh       98.90       95.90       98.50

Pd homocatalysts in the front batch, and bimetallic or trimetallic catalysts in the rearbatch were advantageous over systems comprising Pd monocatalysts as illustrated below.

                    % Conversion      Catalytic system        HC        CO       NOx  Pd alone + Pt / Pd / Rh       98.90       95.90       98.50  Pd alone + Pd alone       99.00       93.70       97.90

The size of the bricks for both systems is the same, but the catalyst composition is the same for the front brick only. The difference is in the rear brick. The back brick for the Pd alone catalyst system included a catalyst having the same composition as that used for the front brick of the system of Example 1 except that the Pd loading was reduced from 200 g / ft ³ to 100 g / ft ³ .

Claims (16)

An upstream palladium component comprising a first upstream support and at least one first upstream palladium component, an amount of the upstream palladium component present at an oxidation conversion rate of 50% at 200 ° C. to 350 ° C., substantially free of oxygen storage components An upstream catalyst zone comprising an upstream composition, and A first downstream layer comprising a first downstream support and a first downstream precious metal component, and a second downstream layer comprising a second downstream support and a second downstream precious metal component, wherein at least one first and second downstream At least one downstream catalyst zone wherein the layer comprises a palladium component Wherein the upstream composition has a light-off temperature lower than the downstream composition. An upstream catalyst zone comprising a first upstream layer comprising a first upstream support and at least one first upstream palladium component, and a second upstream layer comprising a second upstream support and at least one second upstream palladium component; And A first downstream layer comprising a first downstream support and a first downstream precious metal component, and a second downstream layer comprising a second downstream support and a second downstream precious metal component, wherein the first and second downstream layers One or more downstream catalytic zones, one of which comprises a palladium component and the other of which comprises a rhodium component Exhaust gas treatment catalyst product comprising a. The article of claim 1, further comprising a first upstream oxygen storage component in the first upstream layer. The method of claim 3 wherein the downstream catalyst zone is A first downstream platinum component of the first layer, A first downstream rhodium component in the first layer, A second downstream platinum component in the second layer, and Further comprising at least one precious metal selected from the group consisting of a second downstream rhodium component in the second layer. 4. The article of claim 3 further comprising at least one precious metal component selected from the group consisting of a first downstream palladium component of the first layer, a first downstream platinum component of the first layer and a first downstream rhodium component of the first layer. . The article of claim 3, wherein the second downstream layer further comprises a second oxygen storage composition comprising a dilute second oxygen storage component. The product of claim 1 or 2, wherein the first and second upstream supports are the same or different and are compounds selected from the group consisting of silica, alumina and titania compounds. The article of claim 1, further comprising an oxygen storage component selected from the group consisting of cerium and praseodymium compounds. The article of claim 1, wherein at least one of the first or second layers further comprises a nickel or iron component. The method of claim 1 or 2, further comprising at least one first alkaline earth metal component, wherein the at least one first or second upstream or downstream alkaline earth metal component is selected from the group consisting of magnesium, barium, calcium and strontium. Products derived from metals. The article of claim 1, further comprising at least one first or second upstream or downstream rare earth metal component, wherein the second rare earth metal is derived from the group selected from lanthanum and neodymium. The article of claim 1, wherein at least one of said first and second layers further comprises a particulate composite of zirconia and rare earth oxides. The product of claim 1, wherein the upstream zone is supported on an upstream substrate and the downstream zone is supported on a downstream substrate. The article of claim 13, wherein the upstream and downstream substrates comprise a honeycomb carrier. The article of claim 1, wherein said downstream zone has a greater thermal mass than said upstream zone. The article of claim 3, further comprising a second upstream oxygen storage component in the second upstream layer.