Ternary reforming catalyst composition comprising platinum-rhodium bimetallic component

Abstract

The invention provides a catalyst composition comprising a) platinum; b) rhodium; and c) a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the platinum is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof, wherein the rhodium is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof, wherein the CeO2 in the ceria-alumina composite is 1.0 to 50 wt% based on the total weight of the ceria-alumina composite, wherein the amount of ZrO2 in the zirconia composite is 50 to 99 wt% based on the total weight of the zirconia composite. The invention also provides a catalytic article comprising the catalyst composition and a preparation thereof.

Description

TECHNICAL FIELD

[0001] The presently claimed invention relates to a catalyst composition for treating exhaust gas to reduce pollutants contained therein. In particular, the presently claimed invention relates to a catalyst composition suitable for a three-way conversion catalyst and a catalytic article comprising the respective catalyst composition. BACKGROUND

[0002] Three-way conversion (TWC) catalysts are known for their catalytic activity in reducing pollutants such as NO, CO and HC using platinum group metals. Conventional TWC catalysts use Pd and Rh as active catalytic components. Considering the current market price of PGMs, replacing a portion of the expensive Pd with the cheaper Pt in TWC catalysts would help catalytic article manufacturers and automobile manufacturers to significantly reduce costs. However, platinum is much less thermally stable compared to palladium, thus posing a huge challenge for TWC applications which have to withstand severe aging treatments. Therefore, it is desirable to provide a TWC catalyst which addresses both PGM stability related issues and improves cold start performance.

[0003] OBJECT OF THE INVENTION

[0004] It is an object of the present invention to provide a catalyst which is capable of providing improved cold start performance.

[0005] The present invention addresses the cold start problem by providing a TWC catalyst based on platinum-rhodium bimetallic components which show a synergistic effect between Pt and Rh due to the selection of a suitable support material. This synergistic effect results in a significant increase in the conversion of CO, NO and HC relative to their individual metals (Pt and Rh). SUMMARY

[0006] The presently claimed invention provides a catalyst composition comprising:

[0007] a) platinum;

[0008] b) rhodium; and

[0009] c) a ceria-alumina composite, a zirconia composite or a mixture thereof,

[0010] wherein platinum is supported on the ceria-alumina composite, zirconia composite or mixture thereof in an amount of 0.1 to 10.0 wt.-%, based on the total weight of the ceria-alumina composite and / or zirconia composite,

[0011] wherein rhodium is supported on the ceria-alumina composite, zirconia composite or mixture thereof in an amount of 0.1 to 10.0 wt.-%, based on the total weight of the ceria-alumina composite and / or zirconia composite,

[0012] wherein the amount of Ce02in the ceria-alumina composite is 1.0 to 50 wt.%, based on the total weight of the ceria-alumina composite,

[0013] wherein the amount of Zr02in the zirconia composite is 50 to 99 wt.%, based on the total weight of the zirconia composite.

[0014] The present application also provides a method for preparing a catalyst composition. The present application further provides a catalytic article comprising a catalyst composition according to the presently claimed application deposited on a substrate and preparation thereof. The present application still further provides an exhaust gas treatment system for an internal combustion engine comprising a catalytic article according to the presently claimed application. BRIEF DESCRIPTION OF DRAWINGS

[0015] For the purposes of promoting an understanding of the principles of the application, reference will now be made to the accompanying drawings, which are not necessarily to scale, and wherein reference numerals have been used in the components of the exemplary embodiments of the application. The drawings are merely schematic and are not intended to limit the present application. The above and other features of the presently claimed application, its nature, and various advantages will become more apparent when the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0016] Figure 1 Light-off performance of Pt-Rh catalysts supported on Ce02 / A1203for CO, NO and HC conversion is illustrated.

[0017] Figure 2 Light-off performance of Pt-Rh catalysts supported on La203 / Zr02for CO, NO and HC conversion is illustrated.

[0018] Figure 3 Light-off performance of Pt-Rh catalysts supported on Ce02 / A1203and La203 / Zr02for CO, NO and HC conversion is illustrated.

[0019] Figure 4 Light-off performance of Pt-Rh catalysts supported on A1203for CO, NO and HC conversion is illustrated.

[0020] Figure 5 Light-off performance of Pt-Rh catalysts supported on OSC1 for CO, NO and HC conversion is illustrated.

[0021] Figure 6 Light-off performance of Pt-Rh catalysts supported on OSC2 for CO, NO and HC conversion is illustrated.

[0022] Figure 7Light-off performance of Pt-Rh catalyst supported on OSC3 for CO, NO and HC conversion.

[0023] Figure 8 Light-off performance of Pt-Rh catalyst supported on a mixture of supports for CO, NO and HC conversion.

[0024] Figure 9A is a perspective view of a honeycomb substrate carrier that can include a catalyst composition according to one embodiment of the presently claimed application.

[0025] Figure 9B is a perspective view of a honeycomb substrate carrier according to one embodiment of the presently claimed application. Figure 9A is a magnified and planar cross-sectional view taken along a plane parallel to the end face of the substrate carrier shown in Figure 9A is a magnified view of the plurality of gas flow channels shown in Figure 9A is a magnified view of the plurality of gas flow channels shown in

[0026] Figure 10 is a perspective view of a honeycomb substrate carrier according to one embodiment of the presently claimed application. Figure 9A is a cross-sectional view of a portion magnified, wherein Figure 9A the honeycomb substrate in DETAILED DESCRIPTION

[0027] The presently claimed application will now be described more fully hereinafter. The presently claimed application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art. Language of the specification should not be interpreted as indicating any non-claimed element essential to the practice of the disclosed material and methods.

[0028] Unless otherwise indicated herein, or otherwise apparent from context, all methods described herein can be performed in any suitable order. Unless otherwise stated, the use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended to be non-limiting.

[0029] Definitions:

[0030] Unless otherwise indicated herein, or otherwise apparent from context, the terms "a" and "an" and "the" and similar referents used in the context of describing the materials and methods discussed herein (especially in the context of the following claims) are to be construed to cover both the singular as well as the plural, unless otherwise indicated herein or clearly contradicted by context.

[0031] The term "about" as used throughout this specification is used to describe and account for small fluctuations. For example, the term "about" means within less than or equal to 5%, such as within less than or equal to 2%, within less than or equal to 1%, within less than or equal to 0.5%, within less than or equal to 0.2%, within less than or equal to 0.1% or within less than or equal to 0.05%. Unless explicitly stated, all numbers used herein are modified by the term "about." Numerical values modified by the term "about" include the specific value. For example, "about 5.0" must include 5.0.

[0032] In the context of the present invention, the term "first layer" can be used interchangeably with "bottom layer" or "bottom washcoat layer" or "bottom substrate coating layer" and the term "second layer" can be used interchangeably with "top layer" or "top washcoat layer" or "top substrate coating layer". The first layer is deposited at least on a portion of the substrate and the second layer is deposited at least on a portion of the first layer.

[0033] The term "three-way conversion catalyst" refers to a catalyst that simultaneously promotes a) reduction of nitrogen oxides to nitrogen and oxygen; b) oxidation of carbon monoxide to carbon dioxide; and c) oxidation of unburned hydrocarbons to carbon dioxide and water.

[0034] The term "NOx" refers to nitrogen oxide compounds, such as NO and / or NO2.

[0035] The term "washcoat" as used herein has its usual meaning in the art: a thin adherent coating of catalytic or other material applied to a substrate material. Typically, a washcoat is formed by preparing a slurry containing a certain solids content (e.g., 15-60 wt.%) of particles in a liquid vehicle, then applying the slurry to a substrate and drying to provide a layer of washcoat.

[0036] The term "oxygen storage component" (OSC) refers to an entity that has multiple valence states and can react aggressively with a reducing agent such as carbon monoxide (CO) and / or hydrogen under reducing conditions and then with an oxidizing agent such as oxygen or nitrogen oxides under oxidizing conditions.

[0037] The OSC herein refers to ceria-zirconia, which can optionally be stabilized by at least one rare earth element such as lanthanum, yttrium, neodymium and praseodymium.

[0038] The hydrothermal stability of a catalyst can be defined functionally as retaining sufficient catalytic function after high temperature aging. In particular, in the present context, hydrothermal stability means that the NOx conversion of the catalyst after an aging treatment with 10% steam at a temperature range from 950 °C to 1050 °C for about 5 hours is at least 90% of the NOx conversion of the catalyst before the aging treatment. x The light-off temperature should be below 280 °C, and the hydrocarbon light-off temperature is below 290 °C.

[0039] The platinum group metals, also referred to as "PGMs", are ruthenium, rhodium, palladium, osmium, iridium and platinum. The platinum group metal is preferably selected from platinum, rhodium or mixtures thereof.

[0040] As used herein, the term "stream" broadly refers to any combination of flowing gas that can contain solid or liquid particulate matter.

[0041] As used herein, the terms "upstream" and "downstream" refer to the relative direction of flow with respect to the flow of engine exhaust gas from the engine to the tailpipe, with the engine being located at the upstream position, and the tailpipe and any pollutant abatement article such as filters and catalysts being located downstream of the engine.

[0042] As used herein, the term "washcoat" has its usual meaning in the art: a thin adherent coating of catalytic or other material applied to a substrate material. Typically, a washcoat is formed by preparing a slurry containing particulates in a liquid vehicle having a certain solids content (e.g., 15-60 wt%), then applying the slurry to a substrate and drying to provide a layer of washcoat.

[0043] The catalyst composition according to the present application:

[0044] According to the present application, there is provided a catalyst composition comprising:

[0045] a) platinum;

[0046] b) rhodium; and

[0047] c) a ceria-alumina composite, a zirconia composite, or a mixture thereof,

[0048] wherein platinum is supported on the ceria-alumina composite, zirconia composite, or mixture thereof in an amount of 0.1-10.0 wt% based on the total weight of the ceria-alumina composite and / or zirconia composite,

[0049] wherein rhodium is supported on the ceria-alumina composite, zirconia composite, or mixture thereof in an amount of 0.1-10.0 wt% based on the total weight of the ceria-alumina composite and / or zirconia composite,

[0050] wherein the amount of Ce02 in the ceria-alumina composite is 1.0-50 wt% based on the total weight of the ceria-alumina composite,

[0051] wherein the amount of Zr02 in the zirconia composite is 50-99 wt% based on the total weight of the zirconia composite.

[0052] The term "catalyst composition" refers to a composition comprising at least one catalytically active metal and at least one support. The catalytically active metal is deposited on the support. The catalyst composition can comprise further ingredients, such as stabilizers, promoters and / or binders, which are also deposited on the support. The catalytically active metal is preferably selected from PGMs, more preferably from platinum, rhodium or mixtures thereof.

[0053] The terms "deposition" and "loading" are used interchangeably. The deposition of the catalytically active metal on the support can be achieved by various methods known to the skilled person. These include coating techniques, impregnation techniques (such as incipient wetness impregnation), precipitation techniques and atomic deposition techniques (such as chemical vapor deposition). In these techniques, a suitable precursor comprising the catalytically active metal is brought into contact with the support, thereby chemically or physically bonding to the support. The precursor comprising the catalytically active metal is thus deposited on the support. Upon interaction with the support, the precursor comprising the catalytically active metal can be transformed into another species comprising the catalytically active metal. To increase the chemical or physical bonding of the deposited species to the support, different treatment steps can be carried out, such as chemical fixation and / or thermal fixation.

[0054] The term "thermal fixation" refers to the deposition of the catalytically active metal onto the respective support, e.g. via the incipient wetness impregnation method, followed by a thermal calcination of the resulting catalytically active metal / support mixture. In one embodiment, the mixture is calcined at 400-700 °C at a temperature ramping rate of 1-25 °C / min for 1.0 hour to 3.0 hours.

[0055] The term "chemical fixation" refers to the deposition of the catalytically active metal onto the respective support, followed by a fixation using additional reagents (such as barium hydroxide or acetic acid) depending on the nature of the metal precursor, to chemically link the precursor to the support material. Thus, the catalytically active metal is chemically fixed as an insoluble component in the pores and on the surface of the support.

[0056] The term "incipient wetness impregnation", also called capillary impregnation or dry impregnation, refers to the dissolution of a precursor of the catalytically active metal into an aqueous or organic solution and the addition of the resulting catalytically active metal-containing solution to the support. Capillary action draws the solution into the pores of the support. The obtained composition is dried and calcined to remove volatile components within the solution, depositing the metal on the surface of the support.

[0057] The term "support" refers to a solid material onto which the catalytically active metal(s) is deposited. The support can be inert or also participate in the catalytic reaction. Preferably, the support has a high BET surface area which is maintained under the reaction conditions and is mechanically stable. "BET surface area" has its usual meaning: refers to the Brunauer, Emmett, Teller method for determining the surface area by N2adsorption.

[0058] The support of the present application is a ceria-alumina composite, a zirconia composite, and a mixture of a ceria-alumina composite and a zirconia composite. The total amount of the ceria-alumina composite and the zirconia composite is 10 to 90 wt.%, based on the total weight of the catalyst composition.

[0059] The ceria-alumina composite:

[0060] The ceria-alumina composite, also referred to as alumina doped with ceria, is a composite in which CeO2 is distributed in the form of particles, nanoclusters, or even individual atoms on the surface or in the bulk of the alumina. In one embodiment, the composite is a mixed oxide, in which each oxide has its unique chemical and physical state, however, the oxides can interact through their interface. Any physical state or combination of states of CeO2 can be present or coexist on the surface or in the bulk of the alumina. The surface CeO2 modification of the alumina can be in the form of discrete portions (particles or clusters) or form a layer of ceria that partially or completely covers the surface of the alumina.

[0061] The amount of CeO2 (ceria) in the ceria-alumina composite is 1.0 to 50 wt.%, based on the total weight of the ceria-alumina composite. Preferably, the amount of CeO2 in the ceria-alumina composite is 5.0 to 50 wt.%, based on the total weight of the ceria-alumina composite. More preferably, the amount of CeO2 in the ceria-alumina composite is 10 to 40 wt.%, based on the total weight of the ceria-alumina composite. Even more preferably, the amount of CeO2 in the ceria-alumina composite is 10 to 30 wt.%, based on the total weight of the ceria-alumina composite. Most preferably, the amount of CeO2 in the ceria-alumina composite is 15 to 35 wt.%, based on the total weight of the ceria-alumina composite. Even most preferably, the amount of CeO2 in the ceria-alumina composite is 20 to 30 wt.%, based on the total weight of the ceria-alumina composite.

[0062] The amount of Al2O3 (alumina) in the ceria-alumina composite is 50 to 99 wt.%, based on the total weight of the ceria-alumina composite. Preferably, the amount of Al2O3 in the ceria-alumina composite is 50 to 95 wt.%, based on the total weight of the ceria-alumina composite. More preferably, the amount of Al2O3 in the ceria-alumina composite is 70 to 90 wt.%, based on the total weight of the ceria-alumina composite.

[0063] The average particle size of ceria in the ceria-alumina composite is less than 50 nm. Preferably, the average particle size of ceria in the ceria-alumina composite is less than 20 nm. More preferably, the particle size is in the range of 5 nm to 20 nm. The particle size is determined by transition electron microscopy.

[0064] The ceria-alumina composite further comprises a dopant selected from zirconium oxide, lanthanum oxide, titanium oxide, hafnium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, or any combination thereof. The dopant is incorporated into the crystal lattice structure of the ceria-alumina composite. The total amount of dopant in the ceria-alumina is preferably in the range of 0.001 - 15 wt.%, based on the total weight of the ceria-alumina composite. More preferably, the total amount of dopant in the ceria-alumina is in the range of 0.01 - 10 wt.%, based on the total weight of the ceria-alumina composite. Even more preferably, the total amount of dopant in the ceria-alumina is in the range of 0.01 - 5.0 wt.%, based on the total weight of the ceria-alumina composite.

[0065] The ceria-alumina composite can be prepared by methods known to the skilled person, such as co-precipitation or surface modification. In these methods, a suitable cerium-containing precursor is contacted with a suitable aluminium-containing precursor, and the mixture thus obtained is then converted into the ceria-alumina composite. Suitable cerium-containing precursors are, for example, water-soluble cerium salts and colloidal ceria suspensions. The ceria-alumina can also be prepared by an atomic layer deposition method, in which a ceria compound is selectively reacted with an alumina surface, forming ceria on the alumina surface upon calcination. This deposition / calcination step can be repeated until a layer of the desired thickness is achieved. Suitable aluminium-containing precursors are, for example, alumina, such as gamma alumina, delta alumina or theta alumina, or combinations thereof. The mixture thus obtained can then be converted into the ceria-alumina composite by a calcination step of the mixture.

[0066] Zirconium oxide composite:

[0067] The zirconia composite is a solid solution containing Zr02, which can form a single phase as detected by XRD. The amount of Zr02(zirconia) in the zirconia composite is 50 to 99 wt.%, based on the total weight of the zirconia composite. Preferably, the zirconia composite comprises one or more rare earth metals in oxidic form. The rare earth metals are incorporated in their oxidic form into the crystal lattice structure of the zirconia composite. The rare earth metals are preferably selected from lanthanum, praseodymium, yttrium, neodymium and mixtures thereof. Preferably, the amount of rare earth metals in oxidic form in the zirconia composite is 1.0 to 15 wt.%, based on the total weight of the zirconia composite. More preferably, the amount of rare earth metals in oxidic form in the zirconia composite is 5.0 to 15 wt.%, based on the total weight of the zirconia composite. Some rare earth metal doped Zr02composites can show a slight phase separation upon aging at high temperatures (> 1000C).

[0068] Most preferably, the zirconia composite comprises 85 to 99 wt.% Zr02and 1.0 to 15 wt.% La203, each based on the total weight of the zirconia composite. Preferably, the amount of Ce02in the zirconia composite is less than 0.001 wt.%, based on the total weight of the zirconia composite.

[0069] The zirconia composite can comprise further dopants selected from the group consisting of alumina, titania, hafnia, magnesia, calcia, strontia, baria or any combination thereof. The total amount of dopants in the zirconia is preferably in the range of 0.001 to 15 wt.%, based on the total weight of the zirconia composite.

[0070] The zirconia composite can be prepared by methods known to the person skilled in the art, such as co-precipitation or surface modification.

[0071] Mixtures of ceria-alumina composite and zirconia composite:

[0072] Mixtures of ceria-alumina composite and zirconia composite mean a physical mixture of the components. These mixtures can be prepared by methods known to the person skilled in the art. The mixture can be prepared before or after platinum and / or rhodium is deposited on the ceria-alumina composite and / or the zirconia composite.

[0073] Preferably, the weight ratio of ceria-alumina composite to zirconia composite in the mixture is in the range of 1 :4 to 4: 1. More preferably, the weight ratio of ceria-alumina to zirconia composite in the mixture is 1 : 1. For the sake of clarity, the amount of platinum and / or rhodium that can be supported on the respective composite is not taken into account for determining the weight ratio.

[0074] The total amount of ceria-alumina composite and / or zirconia composite in the catalyst composition is 10 to 90 wt.%, based on the total weight of the catalyst composition.

[0075] Platinum group metal:

[0076] In the present application, the catalytically active metal supported on the ceria-alumina composite, the zirconia composite or a mixture of both is platinum and rhodium. In addition to platinum and rhodium on the respective support, other PGMs can be supported. The total amount of platinum in the catalyst composition is in the range of 0.1 to 10 wt.-%, based on the total weight of the catalyst support. Preferably, the total amount of platinum in the catalyst composition is in the range of 0.1 to 5.0 wt.-%, based on the total weight of the catalyst support. More preferably, the total amount of platinum in the catalyst composition is in the range of 0.1 to 3.0 wt.-%, based on the total weight of the catalyst support. The total amount of rhodium in the catalyst composition is in the range of 0.1 to 10 wt.-%, based on the total weight of the catalyst support. Preferably, the total amount of rhodium in the catalyst composition is in the range of 0.1 to 5.0 wt.-%, based on the total weight of the catalyst support. More preferably, the total amount of rhodium in the catalyst composition is in the range of 0.1 to 3.0 wt.-%, based on the total weight of the catalyst support.

[0077] Preferably, no additional PGM metal such as palladium is present in the catalyst composition of the present application, i.e. the catalyst composition of the present application is essentially free of palladium. The term essentially free means that palladium is present as an impurity in an amount of less than 0.01 %, preferably 0.001 %.

[0078] Alternatively, additional PGM metals such as palladium can optionally be present in the catalyst composition of the present application.

[0079] Preferably, platinum is supported on the ceria-alumina composite, the zirconia composite or a mixture of both. Preferably, the total amount of platinum supported on the ceria-alumina composite and / or the zirconia composite is in the range of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite and / or the zirconia composite. More preferably, platinum is supported on the ceria-alumina composite, the zirconia composite or a mixture of both in an amount of 0.5 to 2.0 wt.-%, based on the total weight of the zirconia composite and / or the ceria-alumina composite.

[0080] Preferably, rhodium is supported on the ceria-alumina composite, the zirconia composite or a mixture of both. Preferably, the total amount of rhodium supported on the ceria-alumina composite and / or the zirconia composite is in the range of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite and / or the zirconia composite. More preferably, rhodium is supported on the ceria-alumina composite, the zirconia composite or a mixture of both in an amount of 0.5 to 2.0 wt.-%, based on the total weight of the zirconia composite and / or the ceria-alumina composite.

[0081] More preferably, platinum is supported on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite, and rhodium is supported on the zirconia composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite; or

[0082] Platinum is supported on the zirconia composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite, and rhodium is supported on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite; or platinum is supported on the zirconia composite and on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite and the ceria-alumina composite, and rhodium is supported on the zirconia composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite; or

[0083] Platinum is supported on the zirconia composite and on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite and the ceria-alumina composite, and rhodium is supported on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite; or

[0084] Platinum is supported on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite, and rhodium is supported on the zirconia composite and on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite and the ceria-alumina composite; or platinum is supported on the zirconia composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite, and rhodium is supported on the zirconia composite and on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite and the ceria-alumina composite; or

[0085] Platinum is supported on the zirconia composite and on the ceria-alumina composite in an amount of 0.1 to 10 wt.-%, based on the total weight of the zirconia composite and the ceria-alumina composite, and rhodium is supported on the ceria-alumina composite and on the zirconia composite in a total amount of 0.1 to 10 wt.-%, based on the total weight of the ceria-alumina composite and the zirconia composite; or platinum and rhodium are supported on a mixture of the ceria-alumina composite and the zirconia composite. Preferably, the weight ratio of the ceria-alumina composite to the zirconia composite in the mixture is from 1 :4 to 4:1. More preferably, the weight ratio of the ceria-alumina composite to the zirconia composite in the mixture is 1 :1.

[0086] The present application is further described by the following embodiments. The features of each embodiment can be combined with those of any other embodiment where appropriate and practical.

[0087] Embodiment 1 :

[0088] A catalyst composition comprising:

[0089] a) platinum;

[0090] b) rhodium; and

[0091] c) a ceria-alumina composite, a zirconia composite, or a mixture thereof,

[0092] wherein platinum is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof in an amount of 0.1-10.0 wt.%, based on the total weight of the ceria-alumina composite and / or the zirconia composite,

[0093] wherein rhodium is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof in an amount of 0.1-10.0 wt.%, based on the total weight of the ceria-alumina composite and / or the zirconia composite,

[0094] wherein the amount of Ce02in the ceria-alumina composite is 5.0-50 wt.%, based on the total weight of the ceria-alumina composite,

[0095] wherein the amount of Zr02in the zirconia composite is 50-99 wt.%, based on the total weight of the zirconia composite.

[0096] Embodiment 2:

[0097] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the amount of Ce02in the zirconia composite is <0.001 wt.%, based on the total weight of the zirconia composite.

[0098] Embodiment 3:

[0099] The catalyst composition according to any of the preceding or subsequent embodiments, wherein platinum is supported on a ceria-alumina composite and rhodium is supported on a zirconia composite.

[0100] Embodiment 4:

[0101] The catalyst composition according to any of the preceding or subsequent embodiments, wherein platinum is supported on a zirconia composite and rhodium is supported on a ceria-alumina composite.

[0102] Embodiment 5:

[0103] The catalyst composition according to any of the preceding or subsequent embodiments, wherein platinum and rhodium are supported on a mixture of ceria-alumina composite and zirconia composite.

[0104] Embodiment 6:

[0105] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the catalyst composition comprises:

[0106] a) platinum;

[0107] b) rhodium; and

[0108] c) a mixture of ceria-alumina composite and zirconia composite,

[0109] wherein platinum and rhodium are supported on a mixture of ceria-alumina composite and zirconia composite,

[0110] wherein the amount of platinum is 0.1-5.0 wt.%, based on the total weight of the mixture of ceria-alumina composite and zirconia composite,

[0111] wherein the amount of rhodium is 0.1-5.0 wt.%, based on the total weight of the mixture of ceria-alumina composite and zirconia composite,

[0112] wherein the amount of CeO2 in the ceria-alumina composite is 5.0-50 wt.%, based on the total weight of the ceria-alumina composite,

[0113] wherein the amount of ZrO2 in the zirconia composite is 50-99 wt.%, based on the total weight of the zirconia composite.

[0114] Embodiment 7:

[0115] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the weight ratio of the ceria-alumina composite to the zirconia composite in the mixture of ceria-alumina composite and zirconia composite is 1:4 to 4:1.

[0116] Embodiment 8:

[0117] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the weight ratio of the ceria-alumina composite to the zirconia composite in the mixture of ceria-alumina composite and zirconia composite is 1:1.

[0118] Embodiment 9:

[0119] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the zirconia composite comprises 85 wt% or more Zr02and 15 wt% or less rare earth metal in oxide form, based on the total weight of the zirconia composite.

[0120] Embodiment 10:

[0121] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the rare earth metal in oxide form is selected from the group consisting of lanthanum, praseodymium, yttrium, neodymium oxides, and any combination thereof.

[0122] Embodiment 11:

[0123] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the zirconia composite comprises 85-95 wt% Zr02and 5.0-15 wt% lanthanum oxide, based on the total weight of the zirconia composite.

[0124] Embodiment 12:

[0125] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the ceria-alumina composite is characterized by an average ceria particle size of less than 50 nm as measured by transmission electron microscopy.

[0126] Embodiment 13:

[0127] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the ceria-alumina composite is characterized by an average ceria particle size of less than 20 nm as measured by transmission electron microscopy.

[0128] Embodiment 14:

[0129] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the ceria-alumina composite is characterized by an average ceria particle size of less than 10 nm as measured by transmission electron microscopy.

[0130] Embodiment 15:

[0131] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the ceria-alumina composite is characterized by an average ceria particle size of 1.0-10 nm as measured by transmission electron microscopy.

[0132] Embodiment 16:

[0133] The catalyst composition according to any of the preceding or subsequent embodiments, the total amount of ceria-alumina composite and / or zirconia composite is 10-90 wt.%, based on the total weight of the catalyst composition.

[0134] Embodiment 16:

[0135] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the amount of Ce02in the ceria-alumina composite is 10-40 wt.%, based on the total weight of the ceria-alumina composite.

[0136] Embodiment 17:

[0137] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the amount of Ce02in the ceria-alumina composite is 15-35 wt.%, based on the total weight of the ceria-alumina composite.

[0138] Embodiment 18:

[0139] The catalyst composition according to any of the preceding or subsequent embodiments, wherein the amount of Ce02in the ceria-alumina composite is 20-30 wt.%, based on the total weight of the ceria-alumina composite.

[0140] Preparation of the catalyst composition:

[0141] The present invention also provides a method of preparing a catalyst composition according to the present invention, wherein the method comprises:

[0142] i) impregnating platinum on the ceria-alumina composite, the zirconia composite or the mixture thereof to obtain a first mixture;

[0143] ii) impregnating rhodium on the ceria-alumina composite, the zirconia composite or the mixture thereof to obtain a second mixture; and

[0144] iii) mixing the first mixture with the second mixture to obtain the catalyst composition.

[0145] Alternatively, the method of preparing the catalyst composition comprises sequentially impregnating rhodium and platinum on a mixture of ceria-alumina composite and zirconia composite to obtain the catalyst composition.

[0146] The presently claimed invention also provides a catalytic article comprising the catalyst composition according to the presently claimed invention deposited on a substrate.

[0147] Preferably, the catalytic article is a single layer catalytic article or a double layer and has hydrothermal stability at an aging temperature of 950 °C to 1050 °C.

[0148] The double layer article comprises a) a first layer; b) a second layer and c) a substrate.

[0149] The first layer (undercoat layer)

[0150] The undercoat layer is deposited on the substrate. Preferably, the undercoat layer covers 90 to 100% of the surface of the substrate. More preferably, the undercoat layer covers 95 to 100% of the surface of the substrate, and even more preferably, the undercoat layer covers the entire accessible surface of the substrate. The term "accessible surface" refers to the surface of the substrate that can be covered with conventional coating techniques used in the field of catalyst preparation, such as impregnation techniques.

[0151] Preferably, the first layer comprises platinum supported on a ceria-alumina composite, a zirconia composite or a mixture thereof. The amount of platinum in the first layer is 0.1 to 10 wt.%, based on the total weight of the first layer. Preferably, the amount of platinum in the first layer is 0.3 to 5.0 wt.%, based on the total weight of the first layer.

[0152] Alternatively, the first layer comprises rhodium supported on a ceria-alumina composite, a zirconia composite or a mixture thereof. Preferably, the amount of rhodium in the first layer is 0.1 to 10 wt.%, based on the total weight of the first layer. More preferably, the amount of rhodium in the first layer is 0.1 to 1.0 wt.%, based on the total weight of the first layer.

[0153] The amount of Ce02 in the ceria-alumina composite is 5.0 to 50 wt.%, based on the total weight of the ceria-alumina composite. The amount of Zr02 in the zirconia composite is 50 to 99 wt.%, based on the total weight of the zirconia composite.

[0154] The second layer (topcoat layer)

[0155] The topcoat layer is deposited on the undercoat layer. Preferably, the topcoat layer covers 90 to 100% of the surface of the undercoat layer. More preferably, the topcoat layer covers 95 to 100% of the surface of the substrate, and even more preferably, the topcoat layer covers the entire accessible surface of the undercoat layer.

[0156] Preferably, the second layer comprises rhodium supported on a ceria-alumina composite, a zirconia composite or a mixture thereof. The amount of rhodium in the second layer is 0.1 to 10 wt.%, based on the total weight of the second layer. More preferably, the amount of rhodium in the second layer is 0.1 to 1.0 wt.%, based on the total weight of the second layer.

[0157] Alternatively, the second layer comprises platinum supported on a ceria-alumina composite, a zirconia composite or a mixture thereof. The amount of platinum in the second layer is 0.1 to 10 wt.%, based on the total weight of the second layer. Preferably, the amount of platinum in the second layer is 0.3 to 5.0 wt.%, based on the total weight of the second layer.

[0158] The amount of Ce02in the ceria-alumina composite is 5.0 to 50 wt.%, based on the total weight of the ceria-alumina composite. The amount of Zr02in the zirconia composite is 50 to 99 wt.%, based on the total weight of the zirconia composite.

[0159] More preferably, platinum and rhodium are supported on a mixture of ceria-alumina composite and zirconia composite. Preferably, the weight ratio of ceria-alumina composite to zirconia composite in the mixture is 1 :4 to 4: 1. More preferably, the weight ratio of ceria-alumina to zirconia composite in the mixture is 1 : 1.

[0160] Preferably, platinum and / or rhodium are thermally or chemically fixed on the ceria-alumina composite, the zirconia composite, or a mixture thereof. The catalytic article further comprises an oxygen storage component in the first layer and / or the second layer. Preferably, the oxygen storage component comprises ceria-zirconia, ceria-zirconia-lanthana, ceria-zirconia-yttria, ceria-zirconia-lanthana-yttria, ceria-zirconia-neodymia, ceria-zirconia-praseodymia, ceria-zirconia-lanthana-neodymia, ceria-zirconia-lanthana-praseodymia, ceria-zirconia-lanthana-neodymia-praseodymia, or any combination thereof.

[0161] Zoned configuration:

[0162] The catalytic article, such as a single layer or a double layer, can have a zoned configuration comprising a first zone and a second zone. In a double layer catalytic article, the first layer and / or the second layer comprises the first zone and the second zone. Preferably, the first zone and the second zone together cover 50-100% of the length of the substrate. More preferably, the first zone and the second zone together cover 90-100% of the length of the substrate, even more preferably, the first zone and the second zone together cover the entire length of the substrate. Preferably, the first zone covers 10-90% of the entire length of the substrate starting from the inlet, the second zone covers 90-10% of the entire length of the substrate starting from the outlet, and the first zone and the second zone together cover 20-100% of the length of the substrate. More preferably, the first zone covers 30-70% of the entire length of the substrate starting from the inlet, the second zone covers 70-30% of the entire length of the substrate starting from the outlet, and the first zone and the second zone together cover 60-100% of the length of the substrate. Even more preferably, the first zone covers 40-60% of the entire length of the substrate starting from the inlet, the second zone covers 60-40% of the entire length of the substrate starting from the outlet, and the first zone and the second zone together cover 80-100% of the length of the substrate.

[0163] Preferably, the first and / or second zone comprises platinum supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof. The amount of platinum in the first layer is 0.1-10 wt.%, based on the total weight of the first layer. Preferably, the amount of platinum in the first layer is 0.3-5.0 wt.%, based on the total weight of the first layer. Alternatively, the first zone and / or second zone comprises rhodium supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof. The amount of rhodium in the first layer is 0.1-10 wt.%, based on the total weight of the first layer. More preferably, the amount of rhodium in the first layer is 0.1-1.0 wt.%, based on the total weight of the first layer. The amount of Ce02in the ceria-alumina composite is 5.0-50 wt.%, based on the total weight of the ceria-alumina composite. The amount of Zr02in the zirconia composite is 50-99 wt.%, based on the total weight of the zirconia composite. More preferably, platinum and rhodium are supported on a mixture of ceria-alumina composite and zirconia composite. Preferably, the weight ratio of ceria-alumina composite to zirconia composite in the mixture is 1 :4 to 4: 1. More preferably, the weight ratio of ceria-alumina to zirconia composite in the mixture is 1 : 1.

[0164] Substrate:

[0165] The substrate of the catalytic article of the presently claimed invention can be composed of any material commonly used to prepare automotive catalysts. In one embodiment, the substrate is a ceramic substrate, a metallic substrate, a ceramic foam substrate, a polymeric foam substrate, or a woven fiber substrate. In one embodiment, the substrate is a ceramic or metallic monolithic honeycomb structure.

[0166] The substrate provides a plurality of wall surfaces on which a substrate coating comprising the catalyst composition described herein above is applied and adhered, thereby serving as a carrier for the catalyst composition.

[0167] Exemplary metallic substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel and other alloys in which iron is a substantial or major component. Such alloys can contain one or more of nickel, chromium, and / or aluminum, and the total amount of these metals can advantageously comprise at least 15 wt.% of the alloy, for example, 10-25 wt.% chromium, 3-8% aluminum, and up to 20 wt.% nickel. The alloy can also contain small or trace amounts of one or more metals, such as manganese, copper, vanadium, titanium, and the like. The surface of the metallic substrate can be oxidized at high temperatures (e.g., 1000°C or higher) to form an oxide layer on the surface of the substrate, thereby increasing the corrosion resistance of the alloy and facilitating adhesion of the substrate coating to the metallic surface.

[0168] The ceramic material used to construct the substrate can include any suitable refractory material, for example, cordierite, mullite, cordierite-alumina, silicon nitride, zirconia mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminosilicate, and the like.

[0169] Any suitable substrate can be employed, such as a monolithic flow-through substrate having a plurality of fine, parallel gas flow channels extending from an inlet face of the substrate to an outlet face such that the channels are open to allow fluid flow. The channels, which are essentially straight paths from the inlet to the outlet, are defined by walls coated with a catalytic material as a substrate coating such that the gas flowing through the channels contacts the catalytic material. The flow channels of the monolithic substrate are thin-walled channels that are in any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like. Such structures contain from about 60 to about 1200 or more gas inlet openings (i.e., "cells") per square inch of cross-section (cpsi), more typically from about 300 to 900 cpsi. The wall thickness of the flow-through substrate can vary, with a typical range being between 0.002 and 0.1 inches. A representative commercially available flow-through substrate is a cordierite substrate having 400 cpsi and a 6 mil wall thickness or having 600 cpsi and a 4 mil wall thickness. However, it should be understood that the present application is not limited to a particular substrate type, material, or geometry. In alternative embodiments, the substrate can be a wall-flow substrate, in which each channel is blocked at one end of the substrate body with a non-porous plug, with alternate channels being blocked at the opposite end face. This requires the gas to flow through the porous walls of the wall-flow substrate to reach the outlet. Such monolithic substrates can contain up to about 700 or more cpsi, for example, from about 100 to 400 cpsi, and more typically from about 200 to about 300 cpsi. The cross-sectional shape of the cells can vary as described above. The wall thickness of the wall-flow substrate is typically between 0.002 and 0.1 inches. Representative commercially available wall-flow substrates are composed of porous cordierite, with examples of such substrates having 200 cpsi and a 10 mil wall thickness or 300 cpsi and an 8 mil wall thickness, and a wall porosity between 45 and 65%. Other ceramic materials such as aluminum titanate, silicon carbide, and silicon nitride are also used as wall-flow filter substrates. However, it should be understood that the present application is not limited to a particular substrate type, material, or geometry. Where the substrate is a wall-flow substrate, it is noted that the catalyst composition can penetrate into the pore structure of the porous wall (i.e., partially or completely occlude the pore openings) in addition to being deposited on the surface of the wall. In one embodiment, the substrate has a flow-through ceramic honeycomb structure, a wall-flow ceramic honeycomb structure, or a metallic honeycomb structure.

[0170] Figure 9A and 9BExemplary substrates 2 are shown in the form of flow-through substrates coated with a substrate coating composition as described herein. Referring to Figure 9A , exemplary substrate 2 has a cylindrical shape and a cylindrical outer surface 4, an upstream end face 6 and a corresponding downstream end face 8 which is identical to upstream end face 6. Substrate 2 has a plurality of parallel, fine gas flow channels 10 formed therein. As shown in Figure 9B , flow channels 10 are formed by walls 12 and extend through substrate 2 from upstream end face 6 to downstream end face 8, channels 10 being unobstructed to allow fluid (e.g., a gas stream) to flow longitudinally through substrate 2 via its gas flow channels 10. As more readily seen in Figure 9B , walls 12 are sized and configured so that gas flow channels 10 have a substantially regular polygonal shape. As shown, substrate coating compositions can be applied in multiple layers, different layers if desired. In the illustrated embodiment, the substrate coating consists of a discrete first substrate coating 14 adhered to walls 12 of the substrate member and a second discrete second substrate coating 16 coated over first substrate coating 14. In one embodiment, the presently claimed invention is also practiced with two or more (e.g., 3 or 4) substrate coatings and is not limited to the two-layer embodiment shown.

[0171] Figure 10 Exemplary substrates 2 are shown in the form of wall-flow filter substrates coated with a substrate coating composition as described herein. As shown in Figure 10 , exemplary substrate 2 has a plurality of channels 52. The channels are tubularly surrounded by inner walls 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. Alternate channels are plugged at the inlet end with inlet plugs 58 and at the outlet end with outlet plugs 60 to form an opposing checkerboard pattern at the inlet 54 and outlet 56. A gas stream 62 enters through unplugged channel inlets 64, is blocked by outlet plugs 60, and diffuses to outlet side 66 via channel walls 53, which are porous. The gas cannot return to the inlet side of the wall because of inlet plugs 58. The porous wall-flow filter used in the present invention is catalyzed in that the walls of the element contain one or more catalytic materials on or in them. The catalytic material can be present alone on the inlet side of the element walls, alone on the outlet side, on both the inlet and outlet sides, or the walls themselves can be wholly or partially composed of catalytic material. The present invention includes the use of one or more layers of catalytic material on the inlet and / or outlet walls of the element.

[0172] Preparation of catalytic articles:

[0173] In another aspect of the application, there is also provided a process for the preparation of the catalytic article described above. The process comprises the following steps. First, a slurry comprising platinum supported on ceria-alumina composite, zirconia composite or a mixture thereof and rhodium supported on ceria-doped alumina, zirconia composite or a mixture thereof is prepared. In the next step, the prepared slurry is deposited on a substrate to obtain a catalytic article, followed by calcination at a temperature in the range of 400°C to 700°C. The step of preparing the slurry comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation and post addition.

[0174] Preferably, the process for the preparation of the catalytic article comprises:

[0175] - preparing a slurry comprising platinum and rhodium supported on a mixture of ceria-alumina composite and zirconia composite;

[0176] - depositing the slurry on a substrate to obtain a catalytic article, followed by calcination at a temperature in the range of 400°C to 700°C,

[0177] wherein the step of preparing the slurry comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation and post addition.

[0178] The process can involve a pre-step of thermal or chemical fixation of platinum or rhodium or both on the support.

[0179] Substrate coating:

[0180] The catalyst composition as described above is typically prepared in the form of catalyst particles as described above. These catalyst particles are mixed with water to form a slurry to coat a catalyst substrate such as a honeycomb substrate. In addition to the catalyst particles, the slurry can optionally contain a binder in the form of alumina, silica, zirconium acetate, zirconia or zirconium hydroxide, an associative thickening agent and / or a surfactant including anionic, cationic, non-ionic or amphoteric surfactants. Other exemplary binders include boehmite, gamma-alumina or delta / theta alumina and silica sol. When present, the binder is typically used in an amount of about 1-5 wt% of the total substrate coating loading. An acidic or basic substance is added to the slurry to adjust the pH accordingly. For example, in some embodiments, the pH of the slurry is adjusted by the addition of ammonium hydroxide, aqueous nitric acid or acetic acid. The typical pH range of the slurry is about 3 to 12.

[0181] The slurry can be milled to reduce particle size and enhance particle mixing. Milling is accomplished in a ball mill, continuous mill, or other similar device, and the slurry can have a solids content of, for example, about 20 wt% to 60 wt%, more specifically about 20 wt% to 40 wt%. In one embodiment, the slurry after milling is characterized by a D90 particle size of about 3 microns to about 40 microns, preferably about 10 microns to about 30 microns, more preferably about 10 microns to about 15 microns. D 90 Determined using a specialized particle size analyzer. The equipment employed in this example uses laser diffraction to measure particle size in small volumes of slurry. Typically, D 90 In microns, means that, by number, 90% of the particles have a diameter less than the stated value.

[0182] The slurry is applied to the catalyst substrate using any substrate coating technique known in the art. In one embodiment, the catalyst substrate is dip-coated one or more times or otherwise coated with the slurry. Thereafter, the coated substrate is dried at an elevated temperature (e.g., 100-150 °C) for a period of time (e.g., 10 minutes to 3 hours), and then calcined by heating, for example, at 400-700 °C, typically for about 10 minutes to about 3 hours. After drying and calcination, the final substrate coating is considered to be substantially free of solvent. Catalyst loading obtained by the substrate coating techniques described above can be determined by calculating the difference between the coated and uncoated weight of the substrate. As will be apparent to those skilled in the art, catalyst loading can be modified by altering the slurry rheology. Additionally, the coating / drying / calcination process to produce a substrate coating can be repeated as necessary to build up the coating to the desired loading level or thickness, meaning that more than one substrate coating can be applied.

[0183] In certain embodiments, the coated substrate is aged by subjecting the coated substrate to a heat treatment. In one embodiment, the aging is conducted at a temperature of about 850 °C to about 1050 °C in an environment of 10 vol.% water-containing surrogate hydrocarbon / air feed for 50-75 hours. An aged catalyst article is thus provided in certain embodiments. In certain embodiments, particularly effective materials include metal oxide-based supports (including but not limited to substantially 100% ceria supports) that retain a high percentage (e.g., about 95-100%) of their pore volume upon aging (e.g., at about 850 °C to about 1050 °C, 10 vol.% water-containing surrogate hydrocarbon / air feed, 50-75 hours of aging).

[0184] The catalytic articles of the present invention are further described by the following embodiments. The features of each embodiment can be combined with any other embodiment, as appropriate and practical.

[0185] Embodiment 19:

[0186] The catalytic article comprises:

[0187] A. A catalyst composition comprising:

[0188] a) platinum;

[0189] b) rhodium; and

[0190] c) a ceria-alumina composite, a zirconia composite, or a mixture thereof,

[0191] wherein platinum is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof in an amount of 0.1-10.0 wt.%, based on the total weight of the ceria-alumina composite and / or the zirconia composite,

[0192] wherein rhodium is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof in an amount of 0.1-10.0 wt.%, based on the total weight of the ceria-alumina composite and / or the zirconia composite,

[0193] wherein the amount of Ce02in the ceria-alumina composite is 5.0-50 wt.%, based on the total weight of the ceria-alumina composite,

[0194] wherein the amount of Zr02in the zirconia composite is 50-99 wt.%, based on the total weight of the zirconia composite, and

[0195] B. a substrate.

[0196] Embodiment 19:

[0197] The catalytic article according to any of the preceding or subsequent embodiments, wherein the catalytic article is a single layer catalytic article and has hydrothermal stability at an aging temperature of 950 °C to 1050 °C.

[0198] Embodiment 19:

[0199] The catalytic article according to any of the preceding or subsequent embodiments, wherein the catalytic article is a double layer article comprising:

[0200] a) a first layer,

[0201] b) a second layer, and

[0202] c) a substrate,

[0203] wherein the first layer comprises platinum supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the second layer comprises rhodium supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the first layer is at least partially deposited on the substrate and the second layer is at least partially deposited on the first layer,

[0204] wherein the amount of Ce02in the ceria-alumina composite is 5.0 to 50 wt.-%, based on the total weight of the ceria-alumina composite,

[0205] wherein the amount of Zr02in the zirconia composite is 50 to 99 wt.-%, based on the total weight of the zirconia composite,

[0206] wherein the amount of platinum in the first layer is 0.3 to 5.0 wt.-%, based on the total weight of the first layer,

[0207] wherein the amount of rhodium in the second layer is 0.1 to 1.0 wt.-%, based on the total weight of the second layer.

[0208] Embodiment 22:

[0209] The catalytic article according to any of the preceding or subsequent embodiments, wherein the catalytic article is a double layer article comprising:

[0210] a) a first layer,

[0211] b) a second layer, and

[0212] c) a substrate,

[0213] wherein the first layer comprises rhodium supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the second layer comprises platinum supported on a ceria-alumina composite, a zirconia composite, or a combination thereof,

[0214] wherein the first layer is at least partially deposited on the substrate and the second layer is at least partially deposited on the first layer, wherein the amount of Ce02in the ceria-alumina composite is 5.0 to 50 wt.-%, based on the total weight of the ceria-alumina composite,

[0215] wherein the amount of Zr02in the zirconia composite is 50 to 99 wt.-%, based on the total weight of the zirconia composite,

[0216] wherein the amount of platinum in the second layer is 0.3 to 5.0 wt.-%, based on the total weight of the second layer,

[0217] wherein the amount of rhodium in the first layer is 0.1 to 1.0 wt.-%, based on the total weight of the first layer.

[0218] Embodiment 23:

[0219] The catalytic article of any of the preceding or subsequent embodiments, wherein the catalytic article has a zoned configuration comprising a first zone and a second zone.

[0220] Embodiment 24:

[0221] The catalytic article of any of the preceding or subsequent embodiments, wherein the catalytic article further comprises an oxygen storage component comprising ceria-zirconia, ceria-zirconia-lanthana, ceria-zirconia-yttria, ceria-zirconia-lanthana-yttria, ceria-zirconia-neodymia, ceria-zirconia-praseodymia, ceria-zirconia-lanthana-neodymia, ceria-zirconia-lanthana-praseodymia, ceria-zirconia-lanthana-neodymia-praseodymia, or any combination thereof.

[0222] Embodiment 25:

[0223] The catalytic article of any of the preceding or subsequent embodiments, wherein platinum and / or rhodium are thermally or chemically immobilized on a ceria-alumina composite, a zirconia composite, or a mixture thereof.

[0224] An exhaust treatment system:

[0225] According to another aspect of the present application, there is also provided an exhaust treatment system for an internal combustion engine, the system comprising the catalytic article described above. In one illustrative aspect, the system comprises a platinum group metal-based three-way conversion (TWC) catalytic article and a catalytic article according to the presently claimed application, wherein the platinum group metal-based three-way conversion (TWC) catalytic article is positioned downstream of the internal combustion engine in fluid communication with the engine outlet exhaust gas stream. The catalytic article of the present application can also be used as part of an integrated exhaust system comprising one or more additional components for treating exhaust emissions.

[0226] For example, an exhaust system, also referred to as an exhaust treatment system, can also include compactly coupled TWC catalysts, underfloor catalysts, catalysed soot filter (CSF) components, and / or selective catalytic reduction (SCR) catalytic articles. The foregoing list of components is merely illustrative and should not be considered limiting of the scope of the present application.

[0227] The catalytic article can be placed in a compactly coupled position. Compact coupled catalysts are placed close to the engine so that they can reach reaction temperature as quickly as possible. Typically, compactly coupled catalysts are placed within three feet of the engine, more specifically, within one foot of the engine, and even more specifically, less than six inches from the engine. Compact coupled catalysts are typically attached directly to the exhaust manifold. Because they are close to the engine, compactly coupled catalysts are required to be stable at high temperatures.

[0228] In another aspect of the application, there is also provided a method of treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, nitrogen oxides, and particulate matter, the method comprising contacting the exhaust stream with a catalytic article or exhaust treatment system according to the presently claimed application.

[0229] There is also provided a method of reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, the method comprising contacting the gaseous exhaust stream with a catalytic article or exhaust treatment system according to the presently claimed application to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0230] In another aspect of the application, there is also provided the use of a catalytic article or exhaust treatment system according to the presently claimed application for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides.

[0231] The following examples more fully demonstrate various aspects of the presently claimed application, which are set forth to illustrate certain aspects of the application and should not be construed as limiting the application.

[0232] Example 1:

[0233] Platinum supported on ceria-alumina composite (Ce02 / A1203)

[0234] A powder catalyst sample was prepared by impregnating a tetraamine platinum hydroxide solution on Ce02 / A1203 using incipient wetness technique. The Ce02 / A1203 contained 20 wt% Ce02and 80 wt% A1203. Prior to catalyst aging and testing, the catalyst powder was shaped according to the following procedure. Deionized water was added to the impregnated powder to make a slurry of about 30% solids. The pH of the slurry was adjusted to 4-4.5 using HN03. The slurry was dried under stirring and then calcined in air at 590 °C for 2 hours. The calcined catalyst was crushed and sieved to 250 to 500 microns.

[0235] Sample No. Pt (wt%) Support Sample 1 0.5 CeO2 / Al2O3 Sample 2 1 CeO2 / Al2O3 Sample 3 2 CeO2 / Al2O3

[0236] Example 2:

[0237] Rhodium supported on ceria-alumina composite

[0238] A powder catalyst sample was prepared by impregnating a rhodium nitrate solution on Ce02 / A1203 using incipient wetness technique. The Ce02in Ce02 / A1203 was 20 wt%. The A1203 in Ce02 / A1203 was 80 wt%. The sample shaping procedure was the same as in Example 1 except that Rh / Ce02 / A1203 was used.

[0239] Sample No. Rh (wt%) Support Sample 4 0.5 CeO2 / Al2O3

[0240] Example 3:

[0241] Platinum supported on lanthana-zirconia composite (La2O3 / ZrO2)

[0242] A powder catalyst sample was prepared by impregnating a tetraamine platinum hydroxide solution on La2O3 / ZrO2 using incipient wetness technique. The amount of La2O3 in La2O3 / ZrO2 was 9 wt%, and the amount of ZrO2 was 91 wt%. The sample forming procedure was the same as in Example 1 except that Pt / La2O3 / ZrO2 was used.

[0243] Sample No. Pt (wt%) Support Sample 8 0.5 La2O3 / ZrO2 Sample 9 1 La2O3 / ZrO2 Sample 10 2 La2O3 / ZrO2

[0244] Example 4:

[0245] Rhodium supported on La2O3 / ZrO2

[0246] A powder catalyst sample was prepared by impregnating a rhodium nitrate solution on La2O3 / ZrO2 using incipient wetness technique. The amount of La2O3 in La2O3 / ZrO2 was 9 wt%, and the amount of ZrO2 was 91 wt%. The sample forming procedure was the same as in Example 1 except that Rh / La2O3 / ZrO2 was used.

[0247] Sample No. Rh (wt%) Support Sample 11 0.5 La2O3 / ZrO2

[0248] Example 5:

[0249] Platinum and rhodium supported on CeO2 / Al2O3

[0250] Rh was first impregnated on CeO2 / Al2O3, followed by Pt.

[0251] Deionized water was added to the PGM impregnated powder to make a slurry with a solids content of about 30%. The pH of the slurry was adjusted to 4.0-4.5 with nitric acid. The slurry was milled for 10 minutes and then dried with agitation. The dried powder was calcined in air at 590°C for 2 hours. The powder was pulverized and sieved to 250-500 mm.

[0252] Sample No. Pt (wt%) Rh (wt%) Support Sample 5 0.5 0.5 CeO2 / Al2O3 Sample 6 1 0.5 CeO2 / Al2O3 Sample 7 2 0.5 CeO2 / Al2O3

[0253] Example 6:

[0254] Platinum and rhodium supported on La2O3 / ZrO2

[0255] The procedure of Example 5 was repeated except that La2O3 / ZrO2 was used as the support.

[0256] Sample No. Pt (wt%) Rh (wt%) Support Sample 12 0.5 0.5 La2O3 / ZrO2 Sample 13 1 0.5 La2O3 / ZrO2 Sample 14 2 0.5 La2O3 / ZrO2

[0257] Example 7:

[0258] Platinum and rhodium supported on CeO2 / Al2O3 and La2O3 / ZrO2

[0259] a. Sample 15 preparation

[0260] CeO2 / Al2O3 and La2O3 / ZrO2 were first physically mixed in a 1 : 1 weight ratio under stirring. Rh and Pt were sequentially impregnated on the mixture. The impregnated sample was shaped according to the procedure described in Example 1.

[0261] b. Sample 16 preparation

[0262] Pt was impregnated on CeO2 / Al2O3 and calcined in air at 450 °C. Separately, Rh was impregnated on La2O3 / ZrO2 and calcined in air at 450 °C. The two calcined powders were mixed in a 1 : 1 ratio. On this mixture catalyst, deionized H2O was added to make a slurry with a solid content of about 30%. The pH of the slurry was adjusted to 4.0-4.5 with nitric acid. The slurry was milled for 10 minutes and then dried under stirring. The dried powder was calcined in air at 590 °C for 2 hours. The powder was crushed and sieved to 250-500 mm.

[0263] c. Sample 17 preparation

[0264] Pt was impregnated on CeO2 / Al2O3 and calcined in air at 450 °C. Separately, Rh was impregnated on La2O3 / ZrO2 and calcined in air at 450 °C. The two calcined powders were mixed in a 1 : 1 ratio. On this mixture catalyst, deionized H2O was added to make a slurry with a solid content of about 30%. The pH of the slurry was adjusted to 4.0-4.5 with nitric acid. The slurry was milled for 10 minutes and then dried under stirring. The dried powder was calcined in air at 590 °C for 2 hours. The powder was crushed and sieved to 250-500 mm.

[0265]

[0266] Example 8:

[0267] Platinum supported on alumina (Al2O3)

[0268] A powder catalyst sample was prepared by impregnating a tetraamine platinum hydroxide solution on Al2O3 using incipient wetness technique. The sample shaping process was the same as in Example 1 except that a Pt / Al2O3 catalyst was used.

[0269] Sample No. Pt (wt%) Support Sample 18 0.5 Al2O3 Sample 19 1 Al2O3 Sample 20 2 Al2O3

[0270] Example 9:

[0271] Rhodium supported on alumina

[0272] Powder catalyst samples were prepared by impregnating rhodium nitrate solution on Al2O3 using incipient wetness technique. The sample shaping procedure was the same as in Example 1 except that Rh / Al2O3 was used.

[0273] Sample No. Rh (wt%) Support Sample 21 0.5 Al2O3

[0274] Example 10:

[0275] Platinum and rhodium supported on alumina

[0276] The procedure of Example 5 was repeated except that alumina was used as the support. The sample shaping procedure was the same as in Example 1 except that Pt_Rh / Al2O3 catalyst was used.

[0277] Sample No. Pt (wt%) Rh (wt%) Support Sample 22 0.5 0.5 Al2O3 Sample 23 1 0.5 Al2O3 Sample 24 2 0.5 Al2O3

[0278] Example 11:

[0279] Platinum and rhodium supported on oxygen storage component (OSC1)

[0280] OSC1 comprises: 11% CeO2, 74% ZrO2, 2% La2O3, 8% Y2O3, 5% Nd2O3.

[0281] The PGM deposition procedure was the same as in Example 1 (for Pt), Example 2 (for Rh) and Example 5 (for Pt and Rh) except that OSC1 was used as the support. The sample shaping procedure was the same as in Example 1 except that OSC1 supported catalyst was used.

[0282] Sample No. Pt (wt%) Rh (wt%) Support Sample 25 2 0 OSC 1 Sample 26 0 0.5 OSC 1 Sample 27 2 0.5 OSC 1

[0283] Example 12:

[0284] Platinum and rhodium supported on OSC2

[0285] OSC2 comprises: 20% CeO2, 70% ZrO2, 5% La2O3, 5% Y2O3.

[0286] The PGM deposition procedure was the same as in Example 1 (for Pt), Example 2 (for Rh) and Example 5 (for Pt and Rh) except that OSC2 was used as the support. The sample shaping procedure was the same as in Example 1 except that OSC2 supported catalyst was used.

[0287] Sample No. Pt (wt%) Rh (wt%) Support Sample 28 2 0 OSC 2 Sample 29 0 0.5 OSC 2 Sample 30 2 0.5 OSC 2

[0288] Example 13:

[0289] Platinum and rhodium were supported on OSC3

[0290] OSC3 comprised: 40% Ce02, 50% Zr02, 5% La203, 5% Y203.

[0291] PGM deposition procedure was identical to Example 1 (for Pt), Example 2 (for Rh) and Example 5 (for Pt and Rh) with the exception that OSC3 was used as the support. The sample forming procedure was identical to Example 1 except that an OSC3 supported catalyst was used.

[0292] Sample No. Pt (wt%) Rh (wt%) Support Sample 31 2 0 OSC 3 Sample 32 0 0.5 OSC 3 Sample 33 2 0.5 OSC 3

[0293] Example 14:

[0294] Platinum and rhodium were supported on a mixed support

[0295] Two different supports were mixed in a 1 : 1 weight ratio prior to PGM impregnation. The PGM deposition procedure was identical to that in Example 7 (Sample 15) with the exception that a mixture of La203 / Zr02and OSC3 or Ce02 / A1203and OSC2 was used instead of a mixture of Ce02 / A1203and La203 / Zr02. The sample forming procedure is described in Example 1.

[0296] Sample No. Pt (wt%) Rh (wt%) Support Sample 34 2 0.5 La2O3 / ZrO2+OSC 3 (1 :1) Sample 35 2 0.5 CeO2 / Al2O3 + OSC 2 (1 :1)

[0297] Example 15:

[0298] Platinum and rhodium were supported on a ceria-alumina composite (Ce02 / A1203) as a function of Ce02loading For samples 36, 37 and 38, the procedure of Example 5 was repeated with the exception that a Ce02 / A1203composite was used with 10% Ce02, 30% Ce02, 50% Ce02, respectively.

[0299] Sample No. Pt (wt%) Rh (wt%) Support Sample 36 2 0.5 CeO2 / Al2O3 (10% CeO2) Sample 37 2 0.5 CeO2 / Al2O3 (30% CeO2) Sample 38 2 0.5 CeO2 / Al2O3 (50% CeO2)

[0300] Example 16:

[0301] Catalytic performance measurements:

[0302] All catalysts were aged at 1050 °C and 10% H20 under dilute / rich alternating feed (10 minutes 4% air / 10 minutes 4% H2 / N2) for 5 hours. l = 1 oscillating feed (l = 0.95 / 1.05, cycled at 1 Hz) was used at 175 to 450 °C and 70,000 h -1Light-off tests at the monolithic equivalent GHSV evaluated the aged catalysts. For light-off testing, the lean feed (1 = 1.05) consisted of 0.7% CO, 0.22% H2, 3000 ppm HC(C1) (propylene:propane = 2:1), 1500 ppm NO, 14% CO2, 10% H2O, and ~1.8% O2; while the rich feed (1 = 0.95) consisted of 2.33% CO, 0.77% H2, 3000 ppm HC(C1), 1500 ppm NO, 14% CO2, 10% H2O, and ~0.7% O2. The precise lambda value was fine-tuned by adjusting the O2 level based on the upstream lambda sensor.

[0303] The degree of performance improvement of the Pt / Rh composition relative to the Rh reference was different for CO, NO, and HC for the CeO2 / Al2O3 supported catalysts. For CO conversion, the improvement was marginal. However, for NO and HC conversion, the activity increase was evident at both low and high temperature regions. For example, the HC T50 (temperature at 50% conversion) of 2% Pt / 0.5% Rh / CeO2 / Al2O3 was 55°C lower than the Rh reference. The difference in HC conversion at 325°C was 61%. At 650°C, the difference in HC conversion was 19%. The improvement in performance of the Pt / Rh composition relative to the Rh reference was more pronounced for NO and HC than for CO. Figure 1 Comparative light-off performance of CO, NO, and HC conversion for samples 1-7 (containing CeO2 / Al2O3 as the support) is provided in Table 1.

[0304] Figure 2 Comparative light-off performance of CO, NO, and HC conversion for samples 8-14 (containing La2O3 / ZrO2 as the support) is shown in Table 2. The performance improvement of the Pt / Rh catalyst relative to the Rh reference was directly proportional to the Pt loading. For 2% Pt / 0.5% Rh, the light-off T50 for CO, NO, and HC was 22, 27, and 19°C lower, respectively.

[0305] Figure 3 Comparative light-off performance of CO, NO, and HC conversion for samples 15, 16, 17 (containing two supports, CeO2 / Al2O3 and La2O3 / ZrO2) is shown in Table 3. The three samples showed similar CO conversion efficiency. Samples 15 and 17 were found to be more active for NOx conversion, while samples 15 and 16 were best for HC conversion. Overall, sample 15 was found to produce improved CO, NO, and HC conversion.

[0306] Figure 4 Light-off performance of Al2O3 supported catalysts is shown in Table 4. The Pt reference catalyst was much less active for CO, NO, and HC compared to the Rh reference. The light-off T50 for CO, NO, and HC between 2% Pt and 0.5% Rh was 22, 27, and 19°C lower, respectively. 50The differences are 58, >100 and 29°C, respectively. When Pt and Rh are combined, the activity is significantly higher than the individual sums, and the activity of the Pt / Rh combination is directly proportional to the Pt loading in the catalyst. For example, at 325°C, the HC conversion for 0.5% Pt / 0.5% Rh, 1% Pt / 0.5% Rh and 2% Pt / 0.5% Rh is 31%, 62% and 68%, respectively, while for all the individual component catalysts, the conversion is zero.

[0307] Figures 5 to 7 Performance results for 2% Pt, 0.5% Rh and 2% Pt / 0.5% Rh loaded on OSC1 (samples 25-27), OSC2 (samples 28-30) and OSC3 (samples 31-33) are shown, respectively. For CO, NO and HC conversion, the Pt / Rh combination (2% Pt and 0.5% Rh) shows significantly lower light-off temperatures relative to the Rh reference on each OSC support. The Pt / Rh combination also improves NO and HC conversion at high temperature. The degree of improvement appears to be directly proportional to the ceria content in the OSC support.

[0308] Figure 8 Performance of Pt / Rh combination (2% Pt and 0.5% Rh) loaded on support mixtures is shown. CeO2 / Al2O3 and La2O3 / ZrO2 supported Pt / Rh catalysts (samples 7 and 14) show lower light-off temperatures and lower high temperature conversions compared to OSC supported Pt / Rh catalysts (samples 30 and 33). Pt / Rh loaded on a 1:1 mixture of La2O3 / ZrO2 and OSC3 (sample 34) shows similar performance characteristics (high light-off temperature and high high temperature conversion) as Pt / Rh on OSC3. However, when the Pt / Rh combination is loaded on a 1:1 mixture of CeO2 / Al2O3 and OSC2 (sample 35), the catalyst exhibits low light-off temperature and high high temperature conversion.

[0309] The following table provides the comparative light-off temperature T50 and conversion at 400°C for Pt / Rh (2% Pt and 0.5% Rh) combination loaded on various single supports and mixed supports:

[0310]

[0311] CeO2 / Al2O3 and La2O3 / ZrO2 supported Pt / Rh catalysts show lower light-off temperature (T50) compared to Al2O3 and OSC supported Pt / Rh catalysts.

[0312] OSC-supported Pt / Rh catalysts showed higher high temperature conversion. Pt / Rh catalysts supported on Ce02 / A1203 and OSC2 mixtures had high catalytic activity at both low and high temperatures.

[0313] The following table provides the light-off temperature (T50) for Pt / Rh (2% Pt and 0.5% Rh) combinations supported on Ce02 / A1203 composites with various Ce02loadings:

[0314] Sample No. CeO2 (wt. %) CO T50 (°C) NO T50 (°C) HC T50 (°C) 24 0 292 288 308 36 10 275 280 292 7 20 260 270 271 37 30 261 268 271 38 50 281 286 299

[0315] Pt / Rh catalysts supported on Ce02 / A1203 composites with 20% and 30% Ce02showed the lowest light-off temperature (T50) for CO, NO, and HC. Increasing the Ce02loading in the composite beyond 30% or decreasing the loading below 20% tended to increase the light-off temperature. Catalyst on the undoped support (pure A1203), sample 24, resulted in the lowest activity.

[0316] Throughout this specification, reference has been made to“one embodiment,”“certain embodiments,”“one or more embodiments,” or“an embodiment.” Such references mean that a particular feature, structure, material, or characteristic being described will be included in at least one embodiment of the application claimed herein. Accordingly, appearances of the phrases such as“in one or more embodiments,”“in certain embodiments,”“in some embodiments,”“in one embodiment,” or“in an embodiment” in various places in the specification are not necessarily referring to the same embodiment of the application claimed herein. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments. All the various embodiments, aspects, and options disclosed herein can be combined in all variations, whether or not such features or elements are explicitly combined in a particular embodiment description herein. The application claimed herein is intended to be read as a whole, such that any separable features or elements of the disclosed application in any of its aspects and embodiments should be considered to be intended to be combinable, unless the context clearly indicates otherwise.

[0317] While the embodiments disclosed herein have been described with reference to particular embodiments, it will be understood that these embodiments are merely illustrative of the principles and applications of the present claimed application. It will be apparent to those skilled in the art that various modifications and variations can be made to the methods and apparatuses of the present claimed application without departing from the spirit and scope of the present claimed application. Thus, it is intended that the present claimed application include modifications and variations as come within the scope of the appended claims and their equivalents, and that the embodiments described herein are presented by way of example only and not limitation. All patents and publications cited herein are incorporated by reference for the particular teachings as mentioned, unless otherwise specifically provided.

Claims

1. A three-way conversion catalyst composition comprising: a) platinum; b) rhodium; and c) a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein platinum is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof in an amount of 0.1 to 10 wt% based on the total weight of the ceria-alumina composite and / or the zirconia composite, wherein rhodium is supported on the ceria-alumina composite, the zirconia composite, or the mixture thereof in an amount of 0.1 to 10 wt% based on the total weight of the ceria-alumina composite and / or the zirconia composite, wherein the amount of Ce02 in the ceria-alumina composite is 1.0 to 50 wt% based on the total weight of the ceria-alumina composite, wherein the amount of Zr02 in the zirconia composite is 50 to 99 wt% based on the total weight of the zirconia composite, wherein the catalyst composition is substantially free of palladium, substantially free meaning that palladium is present as an impurity in an amount less than 0.01%.

2. The catalyst composition of claim 1, wherein the total amount of ceria-alumina composite and / or zirconia composite in the catalyst composition is 10 to 90 wt% based on the total weight of the catalyst composition.

3. The catalyst composition of claim 1, wherein the amount of Ce02 in the zirconia composite is <0.001 wt% based on the total weight of the zirconia composite.

4. The catalyst composition of claim 2, wherein the amount of Ce02 in the zirconia composite is <0.001 wt% based on the total weight of the zirconia composite.

5. The catalyst composition of any one of claims 1-4, wherein platinum is supported on the ceria-alumina composite and rhodium is supported on the zirconia composite.

6. The catalyst composition of any one of claims 1-4, wherein platinum is supported on the zirconia composite and rhodium is supported on the ceria-alumina composite.

7. The catalyst composition of any one of claims 1-4, wherein platinum and rhodium are supported on a mixture of the ceria-alumina composite and the zirconia composite.

8. The catalyst composition of any one of claims 1-4, wherein the weight ratio of the ceria-alumina composite to the zirconia composite is 1:4 to 4:

1.

9. The catalyst composition of any one of claims 1-4, wherein the weight ratio of the ceria-alumina composite to the zirconia composite is 1:

1.

10. The catalyst composition of any one of claims 1-4, wherein the zirconia composite comprises 85 wt% or more Zr02 and 15 wt% or less rare earth metal in oxide form based on the total weight of the zirconia composite, wherein the rare earth metal in oxide form is selected from the group consisting of lanthanum, praseodymium, yttrium, neodymium, and any combination thereof. ​ 11. The catalyst composition of any one of claims 1-4, wherein the zirconia composite comprises 85-95 wt% Zr02and 5.0-15 wt% lanthana, based on the total weight of the zirconia composite.

12. The catalyst composition of claim 8, wherein the zirconia composite comprises 85 wt% or more Zr02and 15 wt% or less rare earth metal in oxide form, based on the total weight of the zirconia composite, wherein the rare earth metal in oxide form is selected from the group consisting of lanthanum, praseodymium, yttrium, neodymium, and any combination thereof.

13. The catalyst composition of any one of claims 1-4, wherein the amount of Ce02in the ceria-alumina composite is 5.0-50 wt%, based on the total weight of the ceria-alumina composite.

14. The catalyst composition of claim 8, wherein the amount of Ce02in the ceria-alumina composite is 5.0-50 wt%, based on the total weight of the ceria-alumina composite.

15. The catalyst composition of any one of claims 1-4, wherein the average particle size of ceria in the ceria-alumina composite is less than 20 nm as measured by transmission electron microscopy.

16. The catalyst composition of claim 13, wherein the average particle size of ceria in the ceria-alumina composite is less than 20 nm as measured by transmission electron microscopy.

17. The catalyst composition of any one of claims 1-4, wherein the amount of Ce02in the ceria-alumina composite is 15-35 wt%, based on the total weight of the ceria-alumina composite.

18. The catalyst composition of claim 15, wherein the amount of Ce02in the ceria-alumina composite is 15-35 wt%, based on the total weight of the ceria-alumina composite.

19. The catalyst composition of any one of claims 1-4, wherein the amount of Ce02in the ceria-alumina composite is 20-30 wt%, based on the total weight of the ceria-alumina composite.

20. The catalyst composition of claim 15, wherein the amount of Ce02in the ceria-alumina composite is 20-30 wt%, based on the total weight of the ceria-alumina composite.

21. A method of making the catalyst composition of any one of claims 1-20, wherein the method comprises: - impregnating platinum on a ceria-alumina composite, a zirconia composite, or a mixture thereof to obtain a first mixture; - impregnating rhodium on a ceria-alumina composite, a zirconia composite, or a mixture thereof to obtain a second mixture; and - mixing the first mixture with the second mixture to obtain the catalyst composition.

22. A method of preparing the catalyst composition according to any one of claims 1-20, wherein the method comprises sequentially impregnating rhodium and platinum on a mixture of ceria-alumina composite and zirconia composite to obtain the catalyst composition.

23. A catalytic article comprising the catalyst composition according to any one of claims 1-20 deposited on a substrate.

24. The catalytic article according to claim 23, wherein the catalytic article is a single layer catalytic article and has hydrothermal stability at an aging temperature of 950 °C to 1050 °C.

25. The catalytic article according to claim 23, wherein the catalytic article is a double layer article comprising a) a first layer, b) a second layer, and c) a substrate, wherein the first layer comprises platinum supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the second layer comprises rhodium supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the first layer is at least partially deposited on the substrate and the second layer is at least partially deposited on the first layer, wherein the amount of Ce02 in the ceria-alumina composite is 5.0-50 wt.%, based on the total weight of the ceria-alumina composite, wherein the amount of Zr02 in the zirconia composite is 50-99 wt.%, based on the total weight of the zirconia composite, wherein the amount of platinum in the first layer is 0.3-5.0 wt.%, based on the total weight of the first layer, wherein the amount of rhodium in the second layer is 0.1-1.0 wt.%, based on the total weight of the second layer.

26. The catalytic article according to claim 23, wherein the catalytic article is a double layer article comprising a) a first layer, b) a second layer, and c) a substrate, wherein the first layer comprises rhodium supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the second layer comprises platinum supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, wherein the first layer is at least partially deposited on the substrate and the second layer is at least partially deposited on the first layer, wherein the amount of Ce02 in the ceria-alumina composite is 5.0-50 wt.%, based on the total weight of the ceria-alumina composite, wherein the amount of Zr02 in the zirconia composite is 50-99 wt.%, based on the total weight of the zirconia composite, wherein the amount of platinum in the second layer is 0.3-5.0 wt.%, based on the total weight of the second layer, wherein the amount of rhodium in the first layer is 0.1-1.0 wt.%, based on the total weight of the first layer.

27. The catalytic article according to any one of claims 23-26, wherein the catalytic article has a zoned configuration comprising a first zone and a second zone.

28. The catalytic article according to any one of claims 23-26, wherein the catalytic article further comprises an oxygen storage component comprising ceria-zirconia, ceria-zirconia-lanthana, ceria-zirconia-yttria, ceria-zirconia-lanthana-yttria, ceria-zirconia-neodymia, ceria-zirconia-praseodymia, ceria-zirconia-lanthana-neodymia, ceria-zirconia-lanthana-praseodymia, ceria-zirconia-lanthana-neodymia-praseodymia, or any combination thereof.

29. The catalytic article according to claim 27, wherein the catalytic article further comprises an oxygen storage component comprising ceria-zirconia, ceria-zirconia-lanthana, ceria-zirconia-yttria, ceria-zirconia-lanthana-yttria, ceria-zirconia-neodymia, ceria-zirconia-praseodymia, ceria-zirconia-lanthana-neodymia, ceria-zirconia-lanthana-praseodymia, ceria-zirconia-lanthana-neodymia-praseodymia, or any combination thereof.

30. A process for the preparation of a catalytic article according to any one of claims 23-29, wherein the process comprises: - preparing a slurry comprising platinum supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof, and rhodium supported on a ceria-alumina composite, a zirconia composite, or a mixture thereof; and - depositing the slurry on a substrate to obtain a catalytic article, followed by calcination at a temperature in the range of 400 °C to 700 °C, wherein the step of preparing the slurry comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

31. A process for the preparation of a catalytic article according to any one of claims 23-29, wherein the process comprises: - preparing a slurry comprising platinum and rhodium supported on a mixture of a ceria-alumina composite and a zirconia composite; and - depositing the slurry on a substrate to obtain a catalytic article, followed by calcination at a temperature in the range of 400 °C to 700 °C, wherein the step of preparing the slurry comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

32. An exhaust gas treatment system for an internal combustion engine, the system comprising a catalytic article according to any one of claims 23-29.

33. A method of reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous effluent stream, the method comprising contacting the gaseous effluent stream with a catalytic article according to any one of claims 23-29 or an exhaust gas treatment system according to claim 32, to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

34. Use of a catalytic article according to any one of claims 23-29 or an exhaust gas treatment system according to claim 32 for purifying a gaseous effluent stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides.

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