Platinum group metal catalyst composition

Abstract

The present invention provides a catalyst composition comprising: a) platinum; and b) at least one composite, the platinum being supported on the composite, the composite comprising ceria (calculated as CeO2) in an amount of 5.0-50 wt. %, based on the total weight of the composite; alumina (calculated as Al2O3) in an amount of 10-80 wt. %, based on the total weight of the composite; and magnesia (calculated as MgO) in an amount of 80 wt. %, based on the total weight of the composite. The present invention also provides a process for the preparation of the catalyst composition. The present invention further provides a catalyst article and the preparation thereof.

Description

[Technical field]

[0001] The presently claimed invention relates to catalyst compositions useful in the treatment of exhaust gases to reduce contaminants contained therein. In particular, the presently claimed invention relates to platinum group metal based catalyst compositions. [Background technology]

[0002] Platinum (Pt) has a tendency to sinter under high-temperature hydrothermal aging conditions, and therefore it is difficult to use Pt in conventional ternary conversion (TWC) formulations that require aging at 900-1050 °C. Platinum deposited on conventional refractory alumina can grow to submicron size via the well-established Oswald ripening mechanism. Therefore, further research on stabilizing platinum using appropriate support materials is needed. The problem of platinum sintering when loaded on alumina can be solved by using ceria as the support. It has been found that platinum can often form a partially or fully oxidized monolayer on the ceria surface due to the strong Pt-CeO2 interaction. However, bulk ceria itself can undergo sintering upon high-temperature aging. Therefore, recently, ceria-alumina composites have been proposed as platinum supports for TWC catalysts, where platinum is selectively deposited on the ceria-alumina composite. However, there remains a need for improved support materials that can provide the catalyst with high temperature hydrothermal stability at aging temperatures above 950° C., thereby improving the catalyst performance. Summary of the Invention

[0003] The present invention provides a catalyst composition comprising platinum and at least one composite, the platinum being supported on the composite, the composite comprising ceria (calculated as CeO2) in an amount of 5.0 to 50 wt. %, based on the total weight of the composite, alumina (calculated as Al2O3) in an amount of 10 to 80 wt. %, based on the total weight of the composite, and magnesia (calculated as MgO) in an amount of 10 to 80 wt. %, based on the total weight of the composite.

[0004] The present invention also provides a process for the preparation of the catalyst composition.The present invention further provides a catalyst article and the preparation thereof. [Brief description of the drawings]

[0005] To provide an understanding of embodiments of the present invention, reference is made to the accompanying drawings, which are not necessarily drawn to scale, and in which reference numerals refer to components of exemplary embodiments of the present invention. The drawings are merely illustrative and should not be construed as limiting the present invention. The above and other features of the present invention, its nature and various advantages will become more apparent from the consideration of the following detailed description in conjunction with the accompanying drawings. [Figure 1A] 1 shows the CO, NO and HC conversions for aged samples 1-6. [Figure 1B] 1 shows the CO, NO and HC conversions for aged samples 1-6. [Figure 1C] 1 shows the CO, NO and HC conversions for aged samples 1-6. [Figure 2A] CO, NO and HC conversion for aged samples 5, 8 and 9 are shown. [Figure 2B] CO, NO and HC conversion for aged samples 5, 8 and 9 are shown. [Figure 2C] CO, NO and HC conversion for aged samples 5, 8 and 9 are shown. [Figure 3A] CO, NO and HC conversions for aged samples 1, 2, 5, 7 and 10 are shown. [Figure 3B] CO, NO and HC conversions for aged samples 1, 2, 5, 7 and 10 are shown. [Figure 3C] CO, NO and HC conversions for aged samples 1, 2, 5, 7 and 10 are shown. [Figure 4A] CO, NO and HC conversions for aged samples 5, 7 and 10 before and after activation are shown. [Figure 4B] The CO, NO and HC conversions for aged samples 5, 7 and 10 before and after activation are shown. [Figure 4C] The CO, NO and HC conversions for aged samples 5, 7 and 10 before and after activation are shown. [Figure 5A] CO, NO and HC conversions for aged samples 11, 13, 14, 16, 17 and 18 are shown. [Figure 5B] CO, NO and HC conversions for aged samples 11, 13, 14, 16, 17 and 18 are shown. [Figure 5C] CO, NO and HC conversions for aged samples 11, 13, 14, 16, 17 and 18 are shown. [Figure 6A] 1 shows the CO, NO and HC conversions for aged samples 12, 15, 17 and 19. [Figure 6B] 1 shows the CO, NO and HC conversions for aged samples 12, 15, 17 and 19. [Figure 6C] 1 shows the CO, NO and HC conversions for aged samples 12, 15, 17 and 19. [Figure 7A] 1 is a perspective view of a honeycomb-type substrate support that may include a catalyst composition according to one embodiment of the presently claimed invention. [Figure 7B] 7B is an enlarged partial cross-sectional view of FIG. 7A taken along a plane parallel to an edge surface of the substrate support of FIG. 7A, showing an expanded view of a number of gas flow passages shown in FIG. 7A. [Figure 8]FIG. 7B is an enlarged cross-sectional cutaway view of FIG. 7A, in which the honeycomb-shaped substrate of FIG. 7A represents a wall-flow filter substrate monolith. [Figure 9] 4 shows the X-ray diffraction patterns of fresh and aged Mg30 and Mg70 supports. [Figure 10] 4 shows the X-ray diffraction patterns of Mg30-550 and Mg70-550, as well as Mg30-550-aged and Mg70-550-aged samples. [Figure 11A] 1 shows the X-ray diffraction patterns of fresh (A) and aged (B) Pt catalysts. [Figure 11B] 1 shows the X-ray diffraction patterns of fresh (A) and aged (B) Pt catalysts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] The invention claimed herein will now be described more fully below. The invention claimed herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; these embodiments are provided so that the invention claimed herein will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the disclosed materials and methods.

[0007] All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended merely to further describe the materials and methods and does not impose limitations on scope unless otherwise stated.

[0008] Definition: The use of the terms "a," "an," "the," and similar referents in the context of describing the materials and methods discussed herein (particularly in the context of the claims which follow) should be construed to encompass both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0009] The recitation of ranges of values ​​herein, unless otherwise stated herein, is merely intended to serve as a shorthand method of referring individually to each separate value within the range, and each separate value is incorporated herein as if it were individually recited herein.

[0010] In the context of the present invention, the term "first layer" is used interchangeably with "bottom layer" or "bottom coat", while the term "second layer" is used interchangeably with "top layer" or "top coat". The first layer is deposited on at least a portion of a substrate, and the second layer is deposited on at least a portion of the first layer.

[0011] The term "three-way conversion catalyst" refers to a catalyst that simultaneously promotes a) the reduction of nitrogen oxides to nitrogen and oxygen, b) the oxidation of carbon monoxide to carbon dioxide, and c) the oxidation of unburned hydrocarbons to carbon dioxide and water.

[0012] The term "NOx" refers to nitrogen oxide compounds such as NO and / or NO2.

[0013] As used herein, the term "washcoat" has its ordinary meaning in the art of a thin, adherent coating of catalytic or other material applied to a substrate material. Generally, washcoats are formed by preparing a slurry containing particles of a particular solids content (e.g., 15-60% by weight) in a liquid vehicle, which is then coated onto the substrate and dried to provide the washcoat layer.

[0014] The hydrothermal stability of a catalyst may be functionally defined as the retention of sufficient catalytic function after high temperature aging. Specifically, in this context, hydrothermal stability refers to the retention of sufficient catalytic function after aging at temperatures ranging from 950°C to 1050°C with 10% water vapor for about 5 hours. x and / or a hydrocarbon light-off temperature.

[0015] As used herein, the term "stream" refers broadly to any combination of flowing gases that may contain solid or liquid particulate matter.

[0016] As used herein, the terms "upstream" and "downstream" refer to the relative directions of engine exhaust gas flow from the engine toward the exhaust pipe, with the engine being at the upstream location and the exhaust pipe and any pollution control articles such as filters and catalysts being downstream from the engine.

[0017] The present invention focuses on addressing the platinum sintering problem under high temperature hydrothermal aging conditions. The solution proposed by the present invention is to stabilize the platinum dispersion, thereby efficiently using the platinum in the TWC catalyst.

[0018] Catalyst composition: In a first aspect, the present invention provides a method for producing a composition comprising the steps of: a) platinum; b) at least one complex; A catalyst composition comprising: The platinum is supported on a composite The complex is i) ceria (calculated as CeO2) in an amount of 5.0 to 50 wt. %, based on the total weight of the composite; ii) alumina (calculated as Al2O3) in an amount of 10-80% by weight, based on the total weight of the composite; iii) magnesia (calculated as MgO) in an amount of 10-80% by weight, based on the total weight of the composite; Includes.

[0019] Preferably, the total amount of ceria (calculated as CeO2); alumina (calculated as Al2O3); and magnesia (calculated as MgO) is 80-100% by weight, based on the total weight of the composite.

[0020] Preferably, the amount of the complex is 80 to 100% by weight of the total weight of the catalyst composition.

[0021] platinum: Preferably, the total amount of platinum supported on the composite is in the range of 0.1 to 10 wt % based on the total weight of the composite. More preferably, the total amount of platinum supported on the composite is in the range of 0.1 to 5.0 wt % based on the total weight of the composite. Even more preferably, the total amount of platinum supported on the composite is in the range of 0.1 to 3.0 wt % based on the total weight of the composite.

[0022] Support material: "Support" in the context of a catalyst material or catalyst composition or catalyst washcoat refers to a material that receives metals (e.g., PGMs), stabilizers, promoters, binders, etc., by precipitation, association, dispersion, impregnation, or other suitable method.

[0023] Complex The support material used to support the platinum is a composite containing ceria, alumina, and magnesia.

[0024] The term composite can refer to a mixture of oxides. Different metal oxides can be present in the mixture as separate metal oxides, each in its separate chemical and physical state while interacting through their interfaces, in the form of a solid solution (also called a composite oxide), or as a mixture containing both species, separate metal oxides and solid solutions. In one preferred embodiment, the XRD results show that the catalyst composition has mixed CeO2, MgO, Al2O3 and MgAl2O4 phases. In one preferred embodiment, the composite can be a bulk mixture or can have one or more individual oxides present on the surface. One example is the surface modification of Mg / Al oxide by depositing CeO2 on its surface.

[0025] The term solid solution (or complex metal oxide) refers to a mixed metal oxide that contains oxygen anions and at least two different metal cations in one lattice structure. One example of a solid solution is spinel, which contains Al 3+ and Mg 2+ are contained in one lattice structure.

[0026] Preferably, the composite comprises a dopant selected from lanthana, titania, hafnia, calcia, strontia, baria, zirconia, or oxides of yttrium, praseodymium, neodymium, iron, or any combination thereof.

[0027] alumina: The term "alumina" refers to stabilized or unstabilized aluminum oxide. Stabilized and unstabilized aluminum oxide can exist in different phase modifications.

[0028] Preferably, the stabilized aluminum oxide comprises Al2O3 and one or more dopants selected from rare earth metal oxides, alkali metal oxides, alkaline earth metal oxides, silicon dioxide, or any combination of the above. Preferred dopants are lanthanum oxide (La2O3), cerium oxide (CeO2), zirconium oxide (ZrO2), barium oxide (BaO), neodymium oxide (Nd2O3), strontium oxide (SrO), a combination of lanthanum oxide and zirconium oxide, a combination of barium oxide and lanthanum oxide, a combination of barium oxide, lanthanum oxide and neodymium oxide, or a combination of cerium oxide and zirconium oxide. The dopants can impart different properties to the aluminum oxide. The dopants can delay undesired phase transformations of the aluminum oxide, stabilize the surface area, introduce defect sites, and / or change the acidity of the aluminum oxide surface. The dopant metal may be incorporated in cationic form into the crystal structure of Al2O3 to form a complex oxide, may be deposited in oxide form on the surface of Al2O3, or may be present in oxide form as a blend of mixtures of both dopant and Al2O3 on the microscale.

[0029] Exemplary stabilized and unstabilized aluminas can include large pore boehmite, gamma-alumina, or delta / theta alumina. Useful commercially available aluminas include activated aluminas such as high bulk density gamma alumina, low or medium bulk density large pore gamma alumina, or low bulk density large pore boehmite and gamma alumina. The alumina material is generally believed to impart durability to the resulting catalyst. High surface area alumina supports, also called "gamma alumina" or "activated alumina", typically have a surface area of ​​60 meters squared per gram ("m 2 / g), often up to about 300m 2 The BET surface area of ​​the alumina is preferably about 100 to about 150 m / g or more. 2 / g range. Activated alumina is usually a mixture of gamma and delta phases of alumina, but may contain significant amounts of eta, kappa, and theta alumina phases. Preferably, the alumina (calculated as Al2O3) in the composite is present in an amount of 10-80 wt. %. More preferably, the alumina (calculated as Al2O3) in the composite is present in an amount of 12-32 wt. % based on the total weight of the composite.

[0030] Celia: The term "ceria" refers to cerium oxide having a fluorite structure. The cerium oxide is preferably present as nanoparticles and / or cerium oxide crystallites. Ceria can be doped onto the surface of an alumina-containing support by methods typically used for catalyst preparation. Impregnation of the support material with a cerium precursor using an incipient wetness technique is the most commonly used preparation method, in which a cerium salt solution, such as cerium nitrate, is applied to the support material. After drying and calcination, the cerium species transform into crystalline cerium oxide particles. Another cerium precursor is a colloidal ceria dispersion, typically as an aqueous suspension. Colloidal ceria can be purchased from commercial sources, and typically the average particle size of the ceria in the colloidal suspension is between 5.0 and 100 nm. The average particle size of the ceria on the final catalyst can be determined by X-ray diffraction (XRD) spectroscopy.

[0031] The colloidal suspension can be applied to the support material in a similar manner to the cerium salt solution. Because the colloidal ceria suspension results in a specific average particle size, the final ceria size on the catalyst after the calcination step is more predictable and can be better controlled. Ceria doping and platinum deposition on the support can be performed either sequentially (e.g., first ceria, then platinum) or in one step (i.e., co-impregnation). Preferably, the ceria present in the composite is present in the form of nanoparticles. More preferably, the ceria present in the composite has a particle size in the range of 5.0 nm to 100 nm. The average particle size of the ceria on the final catalyst can be determined by X-ray diffraction (XRD) spectroscopy.

[0032] In a preferred embodiment, the ceria in the composite is at least partially supported on alumina, magnesia, or both alumina and magnesia. The amount of ceria in the composite (calculated as CeO2) is 5.0-50 wt. % based on the total weight of the composite. Preferably, the amount of ceria in the composite (calculated as CeO2) is 20-40 wt. % based on the total weight of the composite.

[0033] Magnesia: The term magnesia refers to magnesium oxide. The magnesia in the composite can be a bulk mixture of magnesia and alumina made by coprecipitation of mixed salt solutions of magnesium and aluminium, or it is present on the surface of the alumina. For supports with high magnesia / alumina ratios (e.g. 50:50), bulk mixing is the only possibility. Magnesia / alumina mixture supports are conveniently available commercially. Typically, there are two distinct crystalline phases for the mixture as measured by XRD (magnesium oxide and aluminium oxide). When magnesia / alumina mixtures are exposed to high temperatures (>800°C), a third phase, magnesium aluminate (MgAl2O4), can form, which is a spinel structure and can be easily identified by XRD. The amount of magnesia in the composite (calculated as MgO) is between 10 and 80% by weight, based on the total weight of the composite. Preferably, the amount of magnesia in the composite (calculated as MgO) is between 35 and 65% by weight, based on the total weight of the composite.

[0034] Amount of oxide in the composite The amount of ceria in the composite (calculated as CeO2) is 5.0 to 50 wt% based on the total weight of the composite. Preferably, the amount of ceria in the composite (calculated as CeO2) is 20 to 40 wt% based on the total weight of the composite. More preferably, the amount of ceria (calculated as CeO2) is 25 to 35 wt% based on the total weight of the composite.

[0035] According to the invention, the amount of alumina in the composite (calculated as Al2O3) is 10-80 wt. % based on the total weight of the composite. Preferably, the amount of alumina in the composite (calculated as Al2O3) is 12-32 wt. % based on the total weight of the composite.

[0036] According to the invention, the amount of magnesia (calculated as MgO) in the composite is 10-80% by weight based on the total weight of the composite. Preferably, the amount of magnesia (calculated as MgO) in the composite is 35-65% by weight based on the total weight of the composite.

[0037] In the composite, the weight ratio of magnesia (calculated as MgO) to alumina (calculated as Al2O3) is preferably 1:4 to 4:1. More preferably, the weight ratio of magnesia (calculated as MgO) to alumina (calculated as Al2O3) is 7:3.

[0038] In the composite, the weight ratio of ceria (calculated as CeO2) to alumina (calculated as Al2O3) is preferably in the range of 0.6 to 3.3.

[0039] The amount of the complex is 80 to 100% by weight of the total weight of the catalyst composition.

[0040] Preparation of the catalyst composition: According to another aspect of the invention claimed herein, there is also provided a process for the preparation of the above catalyst composition. The process comprises mixing magnesia and alumina to obtain a first composite comprising magnesia and alumina. In a next step, ceria is impregnated onto the first composite to obtain a second composite. Finally, platinum is impregnated onto the second composite, followed by calcination to obtain the catalyst composition. The ceria utilized in the preparation of the catalyst composition is cerium oxide nanoparticles or cerium oxide crystallites having a fluorite structure. Preferably, the ceria used is colloidal ceria having an average particle size in the range of 10 nm to 80 nm. Alternatively, the process for the preparation of the catalyst composition comprises mixing magnesia and alumina to obtain a composite comprising magnesia and alumina, followed by co-impregnation of ceria and platinum onto the composite, followed by calcination to obtain the catalyst composition.

[0041] catalyst article According to yet another aspect of the presently claimed invention, there is provided a catalytic article comprising the catalytic composition described hereinabove deposited on a substrate.

[0042] The catalyst composition comprises a) platinum and b) at least one composite, the platinum being supported on the composite, the composite comprising ceria (calculated as CeO2) in an amount of 5-50 wt.% based on the total weight of the composite, alumina (calculated as Al2O3) in an amount of 10-80 wt.% based on the total weight of the composite, and magnesia (calculated as MgO) in an amount of 10-80 wt.% based on the total weight of the composite. The composite preferably comprises lanthana, titania, hafnia, calcia, strontia, baria, zirconia, or a dopant selected from oxides of yttrium, praseodymium, neodymium, iron, or any combination thereof.

[0043] The total amount of platinum supported on the composite is in the range of 0.1 to 10 wt % based on the total weight of the composite. Preferably, the amount of platinum supported on the composite is in the range of 0.1 to 5.0 wt % based on the total weight of the composite.

[0044] Preferably, the ceria in the composite is in the form of nanoparticles having an average particle size in the range of 5.0 nm to 100 nm.

[0045] Preferably, the amount of ceria in the composite (calculated as CeO2) is 20-40 wt. %, based on the total weight of the composite.

[0046] Preferably, the amount of alumina (calculated as Al2O3) in the composite is from 12 to 32 wt.%, based on the total weight of the composite. Preferably, the amount of magnesia (calculated as MgO) in the composite is from 35 to 65 wt.%, based on the total weight of the composite.

[0047] In the composite, the weight ratio of magnesia (calculated as MgO) to alumina (calculated as Al2O3) is preferably 1:4 to 4:1. More preferably, in the composite, the weight ratio of magnesia (calculated as MgO) to alumina (calculated as Al2O3) is 7:3.

[0048] The weight ratio of ceria (calculated as CeO2) to alumina (calculated as Al2O3) ranges from 0.6 to 3.3.

[0049] In a preferred embodiment, the catalyst article is a single layer catalyst article. That is, the catalyst composition described herein above is deposited on the substrate as a single layer or a single washcoat. Preferably, the washcoat covers 90-100% of the surface of the substrate. More preferably, the washcoat covers 95-100% of the surface of the substrate, and even more preferably, the washcoat covers the entire accessible surface of the substrate. The term "accessible surface" refers to the surface of the substrate that can be covered by conventional coating techniques used in the field of catalyst preparation, such as impregnation techniques.

[0050] In another preferred embodiment, the catalyst article is a bilayer article including a first layer, a second layer, and a substrate.

[0051] First layer: A first layer (first washcoat) is deposited on at least a portion of the substrate. Preferably, the first washcoat covers 90-100% of the surface of the substrate. More preferably, the first washcoat covers 95-100% of the surface of the substrate, and even more preferably, the first washcoat covers the entire accessible surface of the substrate.

[0052] The first layer comprises a catalytic composition according to the presently claimed invention and, optionally, palladium. Preferably, the platinum loading is between 5.0 and 200 gm / ft 3 Preferably, the loading of the composite is between 0.5 and 4 gm / in 3 Preferably, the palladium loading is between 5.0 and 200 gm / ft 3 It is.

[0053] Second layer: A second layer (second washcoat) is deposited over at least a portion of the first layer, over at least a portion of the substrate, or both. Preferably, the second washcoat coat covers 90-100% of the surface of the first layer. More preferably, the second washcoat covers 95-100% of the surface of the first layer, and even more preferably, the second washcoat covers the entire accessible surface of the first layer.

[0054] The second layer comprises rhodium. Preferably, the rhodium loading is between 1.0 and 40 gm / ft 3 It is.

[0055] Alternatively, the first layer may comprise rhodium and the second layer comprises a catalytic composition according to the presently claimed invention, and optionally palladium.

[0056] Further alternatively, the first layer comprises a catalyst composition according to the presently claimed invention and, optionally, palladium, and the second layer comprises rhodium and a catalyst composition according to the presently claimed invention.

[0057] Zone Structure: The catalyst article, either single layer or bilayer, preferably has a zoned structure, which includes a first zone and a second zone, wherein the first zone, the second zone, or both, include a catalyst composition according to the presently claimed invention.

[0058] Preferably, the bilayer article comprises a first layer and a second layer, the first layer, the second layer, or both having a zonal structure, the zonal structure comprising a first zone and a second zone, and the first zone, the second zone, or both comprising a catalyst composition according to the presently claimed invention.

[0059] In the context of the present invention, the term "first zone" is used interchangeably with "inlet zone" or "front zone", and the term "second zone" is used interchangeably with "outlet zone" or "rear zone". The terms "first zone" and "second zone" also describe the relative position of the catalytic article in the flow direction, respectively, when placed in an exhaust gas treatment system. The first zone is located upstream, while the second zone is located downstream. The first zone covers at least a portion of the substrate from the inlet of the substrate, while the second zone covers at least a portion of the substrate from the outlet of the substrate. The inlet of the substrate is the first end that receives the flow of the engine exhaust gas stream from the engine, while the outlet of the substrate is the second end from which the treated exhaust gas stream exits.

[0060] Preferably, the first and second zones together cover 50-100% of the length of the substrate, more preferably, the first and second zones together cover 90-100% of the length of the substrate, and even more preferably, the first and second zones together cover the entire length of the substrate.

[0061] Preferably, the first zone covers 10-90% of the total length of the substrate from the inlet, and the second zone covers 90-10% of the total length of the substrate from the outlet, but the first and second zones together cover 20-100% of the substrate length. More preferably, the first zone covers 20-80% of the total length of the substrate from the inlet, and the second zone covers 80-20% of the total length of the substrate from the outlet, but the first and second zones together cover 40-100% of the substrate length. Even more preferably, the first zone covers 30-70% of the total length of the substrate from the inlet, and the second zone covers 70-30% of the total length of the substrate from the outlet, but the first and second zones together cover 60-100% of the substrate length. Even more preferably, the first zone covers 40-50% of the total length of the substrate from the inlet and the second zone covers 50-60% of the total length of the substrate from the outlet, but the first and second zones together cover 90-100% of the substrate length.

[0062] Base material: The substrate of the catalyst article of the presently claimed invention may be composed of any material typically used to prepare automotive catalysts. In preferred embodiments, the substrate is a ceramic substrate, a metal substrate, a ceramic foam substrate, or a woven fiber substrate. Preferably, the substrate is a ceramic or metal monolith honeycomb structure.

[0063] The substrate provides a plurality of walls to which a washcoat comprising the catalyst composition described hereinabove is applied and adhered, thereby acting as a support for the catalyst composition.

[0064] Preferred metal substrates include heat-resistant metals and metal alloys such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium, and / or aluminum, the total amount of these metals advantageously comprising at least 15% by weight of the alloy. For example, 10-25% by weight of chromium, 3-8% by weight of aluminum, and up to 20% by weight of nickel. The alloy may contain small or trace amounts of one or more metals such as manganese, copper, vanadium, titanium, etc. The surface of the metal substrate may be oxidized at high temperatures, for example 1000° C. or higher, to form an oxide layer on the surface of the substrate to improve the corrosion resistance of the alloy and promote adhesion of the washcoat layer to the metal surface.

[0065] Preferred ceramic materials used to construct the substrate may include any suitable refractory material, such as cordierite, mullite, cordierite-alumina, silicon nitride, zircon-mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminosilicate, and the like.

[0066] Any suitable substrate may be used, such as a monolith flow-through substrate having a plurality of fine parallel gas flow passages extending from the inlet face to the outlet face of the substrate such that the flow passages are open to fluid flow. The flow passages, which are essentially straight passages from the inlet to the outlet, are defined by walls on which a catalytic material is coated as a washcoat such that gas flowing through the flow passages contacts the catalytic material. The flow passages of the monolith substrate are thin-walled channels of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. Such structures have from about 60 to about 1200 or more gas inlet openings (i.e., "cells") per square inch of cross section (cpsi), more commonly about 300 to 900 cpsi. The wall thickness of the flow-through substrate may vary, but a typical range is 0.002 to 0.1 inches. A representative commercially available flow-through substrate is a cordierite substrate having a wall thickness of 400 cpsi and 6 mils, or 600 cpsi and 4 mils. However, it will be understood that the invention is not limited to a particular substrate type, material, or shape. In an alternative embodiment, the substrate may be a wall-flow substrate, with each flow passage blocked with a non-porous plug at one end of the substrate body, with the flow passages being blocked at alternating opposing end faces. This requires that the gas flow through the porous walls of the wall-flow substrate to reach the outlet. Such monolith substrates can contain up to about 700 cpsi or more, for example, about 100-400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of the cells can vary as described above. Wall-flow substrates typically have wall thicknesses of 0.008 to 0.012 inches. Representative commercially available wall-flow substrates are constructed from porous cordierite, examples of which have wall thicknesses of 300 cpsi and 12 mils (1 mil = 0.001 inches), or 300 cpsi with a wall thickness of 10 mils, or 300 cpsi with a wall thickness of 8 mils, and wall porosity of 40 to 70%. Other ceramic materials such as aluminum titanate, silicon carbide, and silicon nitride have also been used as wall-flow filter substrates, however, it will be understood that the invention is not limited to any particular substrate type, material, or shape.It should be noted that if the substrate is a wall-flow substrate, the catalyst composition, in addition to being disposed on the surface of the wall, can penetrate into the pore structure of the porous wall (i.e., partially or completely block the pore openings). In one embodiment, the substrate has a flow-through ceramic honeycomb structure, a wall-flow ceramic honeycomb structure, or a metal honeycomb structure.

[0067] 7A and 7B show an exemplary substrate 2 in the form of a flow-through substrate coated with a washcoat composition described herein. Referring to FIG. 7A, the exemplary substrate 2 has a cylindrical shape, with a cylindrical outer surface 4, an upstream end surface 6, and a corresponding downstream end surface 8 that is identical to end surface 6. The substrate 2 has a plurality of fine, parallel gas flow passages 10 formed therein. As can be seen in FIG. 7B, the flow passages 10 are formed by walls 12 and extend through the substrate 2 from the upstream end surface 6 to the downstream end surface 8, and the flow passages 10 are unobstructed to allow a fluid, e.g., gas flow, to flow longitudinally through the substrate 2 via the gas flow passages 10. As can be more easily seen in FIG. 7B, the walls 12 are sized and configured such that the gas flow passages 10 have a substantially regular polygonal shape. As shown, the washcoat composition can be applied in multiple separate layers, if desired. In the illustrated embodiment, the washcoat comprises a first separate washcoat layer 14 adhered to the wall 12 of the substrate member and a second separate washcoat layer 16 coated over the first washcoat layer 14. In one embodiment, the present invention claimed may also be practiced with more than one washcoat layer (e.g., three or four) and is not limited to the two layer embodiment shown.

[0068] FIG. 8 shows an exemplary substrate 2 in the form of a wall-flow filter substrate coated with a washcoat composition described herein. As can be seen in FIG. 8, the exemplary substrate 2 has a plurality of passages 52. The passages are tubularly surrounded by the inner wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. Alternate passages are blocked 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. Gas flow 62 enters through the unblocked channel inlet 64, is stopped by the outlet plugs 60, and diffuses through the channel wall 53 (which is porous) to the outlet side 66. The gas cannot return to the inlet side of the wall due to the inlet plugs 58. The porous wall-flow filters used in the present invention are catalyzed in that the walls of the element have one or more catalytic materials thereon or contain one or more catalytic materials therein. The catalytic material may be present only on the inlet side, only on the outlet side, on both the inlet and outlet sides of the element walls, or the walls themselves may consist entirely or in part of the 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.

[0069] Preparation of the catalytic article: According to another aspect of the presently claimed invention, there is also provided a process for the preparation of a catalyst article according to the presently claimed invention. The process includes preparing a first slurry comprising a catalyst composition according to the presently claimed invention, depositing the first slurry on a substrate, followed by calcination at a temperature in the range of 400-700° C. The resulting catalyst article is a single layer.

[0070] Preferably, the bilayer catalyst article is prepared by a process comprising preparing a first slurry comprising the catalyst composition according to the presently claimed invention and optionally palladium, preparing a second slurry comprising rhodium, depositing the first slurry on a substrate to obtain a first layer, followed by calcination at a temperature in the range of 400-700°C, and depositing the second slurry on the first layer to obtain a second layer, followed by calcination at a temperature in the range of 400-700°C.

[0071] Preferably, the bilayer catalyst article is prepared by a process comprising preparing a first slurry comprising palladium and a catalyst composition according to the present invention; preparing a second slurry comprising rhodium and a catalyst composition according to the present invention; depositing the first slurry on a substrate to obtain a first layer, followed by calcination at a temperature in the range of 400-700°C; and depositing the second slurry on the first layer to obtain a second layer, followed by calcination at a temperature in the range of 400-700°C.

[0072] Preferably, the bilayer catalyst article is prepared by a process comprising preparing a first slurry comprising the catalyst composition according to the presently claimed invention and optionally palladium, preparing a second slurry comprising rhodium, depositing the second slurry on a substrate to obtain a first layer, followed by calcination at a temperature in the range of 400-700°C, and depositing the first slurry on the first layer to obtain a second layer, followed by calcination at a temperature in the range of 400-700°C.

[0073] The preparation of catalytic articles involves impregnating a support material in particulate form with an active metal solution, such as a palladium, platinum and / or rhodium precursor solution. As used herein, "impregnated" or "impregnation" refers to the penetration of a catalytic material into the porous structure of a support material. Techniques used to carry out the impregnation or slurry preparation include the incipient wetness technique (A), the co-precipitation technique (B), and the co-impregnation technique (C).

[0074] The synthesis of heterogeneous materials, i.e. catalysts, generally uses the incipient wetness impregnation technique, also called capillary impregnation or dry impregnation. Typically, metal precursors are dissolved in an aqueous or organic solution, and then the metal-containing solution is added to a catalyst support that contains the same pore volume as the volume of the added solution. Capillary action draws the solution into the pores of the support. The solution added beyond the support pore volume changes the solution transport from a capillary action process to a much slower diffusion process. The catalyst is dried and calcined to remove the volatile components in the solution and deposit the metal on the surface of the catalyst support. The concentration profile of the impregnated material depends on the mass transfer conditions in the pores during impregnation and drying.

[0075] The support particles are typically dry enough to absorb substantially all of the solution and form a wet solid. When rhodium is the active metal, an aqueous solution of a water-soluble compound or complex of the active metal is typically utilized, such as rhodium chloride, rhodium nitrate (e.g., Rh(NO)3 and its salts), rhodium acetate, or a combination thereof; when palladium is the active metal, palladium nitrate, palladium tetraamine, palladium acetate, or a combination thereof; and when platinum is the active metal, platinum nitrate, platinum tetraamine nitrate, platinum acetate, or a combination thereof. After treating the support particles with the active metal solution, the particles are dried, such as by heat treating the particles at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 1-3 hours), and then calcined to convert the active metal to a more catalytically active form. An exemplary calcination process includes heat treating in air at a temperature of about 400-550°C for 10 minutes to 3 hours. The above process may be repeated as necessary to achieve the desired level of active metal impregnation.

[0076] Substrate Coating: The catalyst composition is typically prepared in the form of catalyst particles as described above. To coat a catalyst substrate, such as a honeycomb-type substrate, these catalyst particles are mixed with water to form a slurry. In addition to the catalyst particles, the slurry may optionally contain a binder in the form of alumina, silica, zirconium acetate, zirconia, or zirconium hydroxide, an associative thickener, and / or a surfactant, including anionic, cationic, nonionic, or amphoteric surfactants. Other exemplary binders include boehmite, gamma-alumina, or delta / theta alumina, as well as silica sol. When present, the binder is typically used in an amount of about 1.0 to 5.0 wt.% of the total washcoat loading. Addition of acidic or basic species to the slurry is made to adjust the pH accordingly. For example, in some embodiments, the pH of the slurry is adjusted by addition of ammonium hydroxide, aqueous nitric acid, or acetic acid. A typical pH range for the slurry is about 3.0 to 12.

[0077] The slurry can be milled to reduce particle size and promote particle mixing. Milling can be accomplished in a ball mill, continuous mill, or other similar equipment, and the solids content of the slurry can be, for example, about 20-60% by weight, more specifically about 20-40% by weight. In one embodiment, the slurry after milling has a D of about 3.0 to about 40 micrometers, preferably 10 to about 30 micrometers, and more preferably about 10 to about 15 micrometers. 90 Characterized by particle size. D 90 is determined using a dedicated particle size analyzer. The instrument used in this example uses laser diffraction to measure particle size in small volumes of slurry. D is typically measured in micrometers. 90 means that 90% of the particle population have a diameter less than that value.

[0078] The slurry is coated onto the catalytic substrate using any washcoat technique known in the art. In one embodiment, the catalytic substrate is dipped into or otherwise coated with the slurry one or more times. The coated substrate is then dried at an elevated temperature (e.g., 100-150° C.) for a period of time (e.g., 10 minutes to 3.0 hours) and then calcined, for example, by heating at 400-700° C., typically for about 10 minutes to about 3 hours. After drying and calcination, the final washcoat coating layer is considered to be essentially solvent-free. After calcination, the catalyst loading obtained by the washcoat technique described above can be determined by calculating the difference between the coated and uncoated weights of the substrate. As will be apparent to one skilled in the art, the catalyst loading can be altered by varying the slurry rheology. In addition, the coating / drying / calcining process to produce the washcoat may be repeated as necessary to build up the coating to a desired loading level or thickness, meaning that more than one washcoat may be applied.

[0079] Emissions Treatment System: In another aspect of the invention, there is also provided an exhaust gas treatment system for an internal combustion engine, the system including the catalytic article described herein above. The system may include a catalytic article according to the invention claimed in this application and an additional platinum group metal-based three-way conversion (TWC) catalytic article. The catalytic article of the invention may be located in a close-coupled position. A close-coupled catalyst is located close to the engine to allow the reaction temperature to be reached as quickly as possible. Typically, a close-coupled catalyst is located within 3 feet of the engine, more specifically within 1 foot, and even more specifically less than 6 inches from the engine. A close-coupled catalyst is often mounted directly to the exhaust gas manifold. Due to its close proximity to the engine, the close-coupled catalyst needs to be stable at high temperatures.

[0080] The catalyst articles of the present invention can also be used as part of an integrated exhaust system that includes one or more additional components for treating exhaust gas emissions.

[0081] For example, the exhaust system, also known as an emissions treatment system, may further include a close-coupled TWC catalyst, an underfloor catalyst, a catalyzed soot filter (CSF) component, and / or a selective catalytic reduction (SCR) catalyst article. The foregoing list of components is merely illustrative and should not be construed as limiting the scope of the present invention.

[0082] In another aspect of the present invention, there is also provided a method of treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, comprising contacting the exhaust stream with a catalytic article according to the present invention or an exhaust gas treatment system according to the present invention.

[0083] The present invention also provides a method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream comprising contacting the gaseous exhaust stream with a catalytic article according to the present invention or an exhaust gas treatment system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0084] In another aspect of the invention, there is provided the use of a catalytic article or exhaust gas treatment system according to the presently claimed invention for purifying a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides.

[0085] The invention is further described by the following embodiments, the features of each embodiment may be combined with any of the other embodiments where appropriate and practical.

[0086] Embodiment 1: 1. A catalyst composition comprising: a) platinum; and b) at least one composite, wherein the platinum is supported on a composite, the composite comprising ceria (calculated as CeO2) in an amount of 5.0 to 50 wt. %, based on a total weight of the composite; alumina (calculated as Al2O3) in an amount of 10 to 80 wt. %, based on a total weight of the composite; and magnesia (calculated as MgO) in an amount of 10 to 80 wt. %, based on a total weight of the composite.

[0087] Embodiment 2: 2. The catalyst composition of embodiment 1, wherein the ceria is in the form of nanoparticles having an average particle size in the range of 5.0 nm to 100 nm.

[0088] Embodiment 3: 3. The catalyst composition according to any one of the preceding embodiments, wherein the weight ratio of magnesia (calculated as MgO) to alumina (calculated as Al2O3) is from 1:4 to 4:1.

[0089] Embodiment 4: 4. The catalyst composition according to any one of the preceding embodiments, wherein the weight ratio of magnesia (calculated as MgO) to alumina (calculated as Al2O3) is 7:3.

[0090] Embodiment 5: 5. The catalyst composition according to any one of the preceding embodiments, wherein the total amount of platinum supported on the composite is in the range of 0.1-10 wt. %, based on the total weight of the composite.

[0091] Embodiment 6: 6. The catalyst composition of any one of the preceding claims, wherein the composite comprises lanthana, titania, hafnia, calcia, strontia, baria, zirconia, or a dopant selected from oxides of yttrium, praseodymium, neodymium, iron, or any combination thereof.

[0092] Embodiment 7: 7. The catalyst composition of any one of the preceding embodiments, wherein the ceria (calculated as CeO2) is in an amount of 20-40 wt. %, based on the total weight of the composite.

[0093] Embodiment 8: 8. The catalyst composition of any one of the preceding embodiments, wherein the alumina (calculated as Al2O3) is in an amount of 12-32 wt.%, based on the total weight of the composite.

[0094] Embodiment 9: 9. The catalyst composition of any one of the preceding embodiments, wherein the manganese (calculated as MgO) is in an amount of 35 to 65 wt. %, based on the total weight of the composite.

[0095] Embodiment 10: 10. The catalyst composition according to any one of the preceding embodiments, wherein the weight ratio of ceria (calculated as CeO2) to alumina (calculated as Al2O3) is in the range of 0.6 to 3.3.

[0096] Embodiment 11: Catalyst composition according to any one of the preceding embodiments, wherein the amount of the complex is 80-100 wt. % of the total weight of the catalyst composition.

[0097] Embodiment 12: 12. The catalyst composition according to any one of the preceding embodiments, wherein the total amount of ceria (calculated as CeO); alumina (calculated as AlO); and magnesia (calculated as MgO) is 80-100 wt.%, based on the total weight of the composite.

[0098] Embodiment 13: A catalytic article comprising the catalytic composition of any one of embodiments 1 to 12 deposited on a substrate.

[0099] Embodiment 14: 14. The catalytic article of embodiment 13, wherein the catalytic article is a single layer catalytic article.

[0100] Embodiment 15: The catalytic article of embodiment 13, wherein the catalytic article is a two-phase article comprising a first layer, a second layer, and a substrate, the first layer being deposited on at least a portion of the substrate, the second layer being deposited on at least a portion of the first layer, at least a portion of the substrate, or both, the first layer comprising the catalytic composition of any one of embodiments 1-12 and optionally palladium, and the second layer comprising rhodium.

[0101] Embodiment 16: The catalytic article of embodiment 13, wherein the catalytic article is a bilayer article comprising a first layer, a second layer, and a substrate, the first layer being deposited on at least a portion of the substrate, and the second layer being deposited on at least a portion of the first layer, at least a portion of the substrate, or both, the first layer comprising rhodium, and the second layer comprising the catalytic composition of any one of embodiments 1-12, and optionally palladium.

[0102] Embodiment 17: 14. The catalytic article of embodiment 13, wherein the catalytic article is a bilayer article comprising a first layer, a second layer, and a substrate, the first layer being deposited on at least a portion of the substrate, the second layer being deposited on at least a portion of the first layer, at least a portion of the substrate, or both, the first layer comprising the catalytic composition of any one of claims 1 to 12 and palladium, and the second layer comprising rhodium and the catalytic composition of any one of embodiments 1 to 12.

[0103] Embodiment 18: 15. The catalytic article of any one of embodiments 13-14, wherein the catalytic article has a zoned structure, the zoned structure comprising a first zone and a second zone, and the first zone, the second zone, or both, comprise the catalytic composition of any one of embodiments 1-12.

[0104] Embodiment 19: 18. The catalyst article of any one of embodiments 15-17, wherein the catalyst article is a bilayer article comprising a first layer and a second layer, the first layer, the second layer, or both having a zonal structure, the zonal structure comprising a first zone and a second zone, and the first zone, the second zone, or both comprising the catalyst composition of any one of embodiments 1-12.

[0105] Embodiment 20: 20. The catalytic article of any one of embodiments 13-19, wherein the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymeric foam substrate, or a woven fiber substrate.

[0106] Aspects of the invention claimed herein will be more fully described by the following examples, which are provided to illustrate certain aspects of the invention and should not be construed as limiting thereof.

[0107] Example 1: Catalyst Composition Table 1 lists the catalyst samples and their compositional information.

[0108] The following five support materials were used to prepare the various catalysts: 1. Al2O3 is gamma alumina without MgO. 2. Mg20 is a support material containing about 20% MgO and about 80% Al2O3 by weight. 3. Mg30 is a support material containing about 30% MgO and about 70% Al2O3 by weight. 4. Mg70 is a support material containing about 70% MgO and about 30% Al2O3 by weight. 5. The MgO is 100% MgO and does not contain Al2O3.

[0109] [Table 1] * The amount of support is an appropriate amount to make it 100%.

[0110] Sample preparation: Samples 1, 2, 11, 13, 14, 16 and 18 were prepared by impregnating platinum nitrate solution onto the support (Al2O3, Mg20, Mg30, Mg70 or MgO) using the incipient wetness impregnation technique. The impregnated samples were calcined at 550 °C in air for 2 h.

[0111] Samples 3-6 were prepared by sequential impregnation of a Mg70 support with a (first) colloidal CeO2 suspension (having an average diameter of CeO2 particles of about 20 nm) and a (second) platinum nitrate solution. After the first impregnation, the resulting material was dried at 120 °C for 15 min. After the second impregnation, the samples were calcined in air at 550 °C for 2 h.

[0112] Sample 7 was prepared by sequentially impregnating a Mg70 support with a (first) Ce nitrate solution and a (second) platinum nitrate solution. After the first impregnation, the resulting material was dried at 120° C. for 15 min. After the second impregnation, the sample was calcined in air at 550° C. for 2 h.

[0113] Sample 8 was prepared by sequentially impregnating a Mg70 support with a (first) colloidal CeO2 suspension (having an average diameter of CeO2 particles of about 20 nm) and a (second) platinum nitrate solution. After the first impregnation, the resulting material was calcined in air at 550°C for 2 hours. After the second impregnation, the sample was again calcined in air at 550°C for 2 hours.

[0114] Sample 9 was prepared by sequentially impregnating a Mg70 support with a (first) platinum nitrate solution and a (second) colloidal CeO2 suspension (with an average diameter of the CeO2 particles of about 20 nm). After the first impregnation, the resulting material was dried at 120°C for 15 min. After the second impregnation, the sample was calcined again in air at 550°C for 2 h.

[0115] Sample 10 was prepared by sequentially impregnating a Mg70 support with a (first) colloidal CeO2 suspension (having an average diameter of CeO2 particles of about 80 nm) and a (second) platinum nitrate solution. After the first impregnation, the resulting material was dried at 120°C for 15 minutes. After the second impregnation, the sample was calcined in air at 550°C for 2 hours.

[0116] Samples 12, 15, 17, and 19 were prepared by co-impregnation of platinum nitrate and cerium nitrate mixed solutions onto supports (Al2O3, Mg30, Mg70, or MgO). The impregnated samples were calcined in air at 550°C for 2 hours.

[0117] Catalyst aging conditions: All catalysts were aged at 950° C. for 5 h in air containing 10% H2O before activity evaluation.

[0118] Catalyst evaluation conditions: Two test runs (continuous temperature ramp and constant temperature) were performed for each sample. In the first run, the catalyst was tested by continuous temperature ramping from 100°C to 500°C at a temperature ramp rate of 10°C / min with a 30 minute hold at 500°C. In the second run, steady state testing was performed from 125°C to 500°C in temperature steps of 25°C with a 15 minute hold time at each temperature. Both tests used the same feed gas containing 1.5% CO, 0.5% H2, 667 ppm C3H6, 333 ppm C3H8, 1500 ppm NO, 14% CO2, 10% H2O, 1.4% O2, and the balance Ar. The feed gas had equal stoichiometric conditions, i.e., λ=1. The weight hourly space velocity for all tests was 400,000 mL / (g cat. The outlet gas composition was measured by infrared spectroscopy (IR) and / or mass spectroscopy (MS).

[0119] result: The data from the second run was used for activity comparison, and the results are shown in Figures 1 to 6.

[0120] As shown in Figure 1, increasing the CeO2 loading increases the TWC activity up to a point. The HC conversion is highest when the CeO2 loading is 26-34 wt%. Further increasing the CeO2 loading to 51% results in a level below the maximum activity, but still higher than the catalyst with 17% CeO2 or no Ce. x For conversion, the optimum CeO2 loading is found to be 34%.

[0121] Figure 2 compares TWC activity as a function of preparation method. x Calcination during the impregnation process has a complex effect on the CO, NO and CO conversion rates. x Without intermittent calcination, first Ce impregnation and then Pt impregnation results in the lowest conversion of HC and NO. x A higher activity is obtained for HC and CO but not for CO. On the other hand, the reverse order of impregnation has better activity for HC and CO but not for NO. x It provided a catalyst for something that was not the case.

[0122] Figure 3 shows the effect of CeO2 precursor (Ce nitrate vs. colloidal CeO2) and particle size (colloidal CeO2) on the TWC activity. Sample 5 was found to be the most active catalyst, followed by Sample 10. The catalyst prepared with Ce nitrate, Sample 7, was less active than the catalyst made with colloidal CeO2 and even less active than Sample 2.

[0123] Figure 4 shows the activation effect for samples 5, 7 and 10. The activation of the samples was carried out by reduction treatment with 10% H2 in Ar at 250 °C for 1 h. The activation treatment was carried out by reducing the samples with CO, NO x and have various promotion effects on HC conversion. The most significant activation effect was seen in aged sample 7. After activation, the most active catalyst is sample 5.

[0124] Figure 5 shows that the Pt catalyst supported on Mg70 (Sample 16) is more active for HC and NO than the Pt catalysts supported on Al2O3, Mg20, Mg30 or MgO.

[0125] Figure 6 shows that Sample 17 (1Pt-20Ce / Mg70) is more active for NO and HC conversion than Samples 12 or 15 (Al2O3 or Mg30 supported catalysts). The MgO supported catalyst (Sample 19) has activity comparable to that of Sample 17 in HC conversion, but is less active for NO conversion.

[0126] The sample catalysts were also evaluated for specific surface area and average crystallite size. The results are shown in Table 2.

[0127]

Table 2

[0128] Table 2 shows the specific surface areas of Samples 5, 7 and 10, and the average CeO2 crystallite sizes measured by XRD for both fresh and aged samples. The average CeO2 crystallite size of the fresh catalysts decreases in the order of Sample 10 > Sample 5 > Sample 7. For each catalyst, aging increases the CeO2 crystallite size by 2 - 5 times.

[0129] Table 3 shows the average CeO2 crystallite sizes of Samples 12, 15 and 17 before and after aging.

[0130]

Table 3

[0131] For the fresh samples, the CeO2 crystallite size follows the order Sample 12>Sample 15>Sample 17. That is, the CeO2 size decreases with the MgO content on the support. After aging, the CeO2 size increases significantly for all samples, and the ranking of CeO2 crystallite size is Sample 17>Sample 12>Sample 15.

[0132] The X-ray diffraction patterns of the fresh and aged Mg30 and Mg70 supports are shown in Figure 9. Aging was carried out at 950 °C for 5 hours using 10% H2O in air.

[0133] Figure 9 shows that i) the fresh Mg30 sample is a mixture of layered double hydroxide (LDH) and γ-alumina phases. Both phases are not distinct, ii) the aged Mg30 sample is a mixture of MgAl2O4 spinel and MgO phases, no alumina phase is present in aged Mg30, iii) the fresh Mg70 sample has a distinct LDH phase, and iv) the aged Mg70 sample is a mixture of MgAl2O4 and MgO phases. No alumina phase is present in aged Mg70.

[0134] The X-ray diffraction patterns of Mg30-550 and Mg70-550, as well as Mg30-550-aged and Mg70-550-aged samples are shown in Figure 10. Mg30-550 and Mg70-550 materials were calcined at 550°C for 2 hours in air. Mg30-550-aged and Mg70-550-aged were performed at 950°C for 5 hours with 10% HO in air.

[0135] FIG. 10 shows that i) the Mg30-550 sample is a mixture of MgO and g-Al2O3 phases, ii) the Mg70-550 sample has predominant MgO phase and small amount of g-Al2O3 phase, iii) the Mg30-550-aged sample consists of MgAl2O4 phase and trace amount of MgO phase, iv) the Mg70-550-aged consists of MgAl2O3 and MgO phases, and v) no alumina phase is present in any of the aged samples.

[0136] FIG. 11 shows the X-ray diffraction patterns of the fresh Pt catalyst (A) and the aged Pt catalyst (B).

[0137] The following observations were made for the fresh samples: The -1Pt-20Ce / Mg30 sample contained CeO2 and MgAl2O4 phases, and no g-Al2O3 phase was detected. The -1Pt-20Ce / Mg70 sample contained CeO2 and MgO phases, and no g-Al2O3 phase was detected. The -1Pt-20Ce / Al2O3 sample contains the CeO2 phase and the g-Al2O3 phase. - No crystalline Pt was detected in any of the fresh samples.

[0138] The following observations were made for the aged samples: The -1Pt-20Ce / Mg30-aged sample contains CeO2 and MgAl2O4 phases, but no Al2O3 phase. Pt was detected. The -1Pt-20Ce / Mg70-aged sample contains CeO2, MgO and MgAl2O4 phases, but no Al2O3 phase. Pt was detected. The -1Pt-20Ce / Al2O3-aged sample contains CeO2 and g-Al2O3 phases. Pt was detected. -Pt diffraction peak (2θ = approx. 40 ° ) intensity was found to be the highest on the 1Pt20Ce / Al2O3-aged sample, which shows the largest average Pt crystallite size among the three aged samples.

[0139] Although the embodiments disclosed herein have been described with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention claimed herein. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the invention claimed herein without departing from the spirit and scope of the invention. Therefore, the invention claimed herein is intended to cover modifications and variations that come within the scope of the appended claims and their equivalents, and the above-described embodiments are presented for purposes of illustration and not limitation.

Claims

1. a) platinum; b) at least one conjugate; A catalyst composition comprising: platinum is supported on the composite; The complex is i. ceria (CeO) in an amount of 20-40 wt %, based on the total weight of the composite ２ ) and ii. Alumina (Al) in an amount of 10 to 80 wt. % based on the total weight of the composite. ２ O ３ ) and iii. magnesia (calculated as MgO) in an amount of 10 to 80 wt. % based on the total weight of the composite; A catalyst composition comprising:

2. 10. The catalyst composition of claim 1, wherein the ceria is in the form of nanoparticles having an average particle size in the range of 5.0 nm to 100 nm.

3. Magnesia (calculated as MgO) and alumina (Al ２ O ３ 3. The catalyst composition according to claim 1, wherein the weight ratio of the catalyst to the hydroxy group of the hydroxy group is 1:4 to 4:

1.

4. Magnesia (calculated as MgO) and alumina (Al ２ O ３ 3. The catalyst composition according to claim 1, wherein the weight ratio of the catalyst to the amount of the hydroxyl group (calculated as hydroxyl group) is 7:

3.

5. 3. The catalyst composition of claim 1, wherein the total amount of platinum supported on the composite is in the range of 0.1 to 10 wt % based on the total weight of the composite.

6. 3. The catalyst composition of claim 1 or 2, wherein the composite comprises lanthana, titania, hafnia, calcia, strontia, baria, zirconia, or a dopant selected from oxides of yttrium, praseodymium, neodymium, iron, or any combination thereof.

7. The alumina (Al ２ O ３ 3. The catalyst composition of claim 1, wherein the cations of ...

8. 3. The catalyst composition of claim 1, wherein the manganese (calculated as MgO) in the composite is present in an amount of 35 to 65 wt. %, based on the total weight of the composite.

9. The ceria (CeO ２ ) and alumina (Al ２ O ３ 3. The catalyst composition according to claim 1, wherein the weight ratio of the catalyst to the total amount of the base is in the range of 0.6 to 3.

3.

10. 3. The catalyst composition according to claim 1, wherein the amount of the complex is 80 to 100 wt % of the total weight of the catalyst composition.

11. 3. A process for preparing the catalyst composition of claim 1 or 2, comprising: mixing magnesia and alumina to obtain a first composite comprising magnesia and alumina; impregnating ceria onto the first composite to obtain a second composite; and impregnating platinum onto the second composite, followed by calcination to obtain the catalyst composition.

12. The process of claim 11, wherein the ceria is colloidal ceria having an average particle size in the range of 10 nm to 80 nm.

13. 3. A process for the preparation of the catalyst composition according to claim 1 or 2, said process comprising: - mixing magnesia and alumina to obtain a composite comprising magnesia and alumina; - co-impregnating ceria and platinum onto said composite, followed by calcination to obtain said catalyst composition; The process includes:

14. A catalytic article comprising the catalytic composition of claim 1 deposited on a substrate.

15. 15. The catalyst article of claim 14, wherein the catalyst article is a single layer catalyst article, and the catalyst composition of claim 1 or 2 is deposited as a single layer on the substrate.

16. the catalyst article comprising: a) a first layer; b) a second layer; and c) a substrate; and A two-layer article comprising: the first layer is deposited on at least a portion of the substrate, and the second layer is deposited on at least a portion of the first layer, on at least a portion of the substrate, or both; The first layer comprises the catalyst composition of claim 1 or 2 and optionally palladium; the second layer comprises rhodium; The catalytic article of claim 14.

17. the catalyst article comprising: a) a first layer; b) a second layer; and c) a substrate; and A two-layer article comprising: the first layer is deposited on at least a portion of the substrate, and the second layer is deposited on at least a portion of the first layer, on at least a portion of the substrate, or both; the first layer comprises rhodium; The second layer comprises the catalyst composition of claim 1 or 2 and optionally palladium. The catalytic article of claim 14.

18. the catalyst article comprising: a) a first layer; b) a second layer; and c) a substrate; and A two-layer article comprising: the first layer is deposited on at least a portion of the substrate, and the second layer is deposited on at least a portion of the first layer, on at least a portion of the substrate, or both; The first layer comprises the catalyst composition of claim 1 or 2 and palladium; The second layer comprises rhodium and the catalyst composition of claim 1 or 2. The catalytic article of claim 14.

19. 15. The catalyst article of claim 14, wherein the catalyst article has a zoned structure, the zoned structure comprising a first zone and a second zone, and the first zone, the second zone, or both, comprise the catalyst composition of claim 1.

20. 17. The catalyst article of claim 16, wherein the catalyst article is a two-layer article comprising a first layer and a second layer, the first layer, the second layer, or both, having a zoned structure, the zoned structure comprising a first zone and a second zone, and the first zone, the second zone, or both, comprising the catalyst composition of claim 1.

21. 15. The catalytic article of claim 14, wherein the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, or a woven fiber substrate.

22. 15. A process for preparing a catalyst article according to claim 14, said process comprising: - preparing a first slurry comprising the catalyst composition of claim 1; - depositing said first slurry onto said substrate followed by calcination at a temperature in the range of 400-700°C; The process includes:

23. 17. A process for preparing a catalyst article according to claim 16, said process comprising: - preparing a first slurry comprising the catalytic composition of claim 1 and optionally palladium, and preparing a second slurry comprising rhodium; - depositing said first slurry onto said substrate to obtain a first layer, followed by calcination at a temperature in the range of 400-700°C; - depositing said second slurry on said first layer to obtain a second layer, followed by calcining at a temperature in the range of 400-700°C; The process includes:

24. 18. A process for preparing a catalyst article according to claim 17, said process comprising: - preparing a first slurry comprising the catalytic composition of claim 1 or 2 and optionally palladium, and preparing a second slurry comprising rhodium; - depositing said second slurry onto said substrate to obtain a first layer, followed by calcination at a temperature in the range of 400-700°C; - depositing said first slurry onto said first layer to obtain a second layer, followed by calcining at a temperature in the range of 400-700°C; The process includes:

25. 20. A process for preparing a catalyst article according to claim 18, said process comprising: - preparing a first slurry comprising the catalytic composition of claim 1 or 2 and palladium; - preparing a second slurry comprising rhodium and the catalytic composition of claim 1 or 2; depositing the first slurry onto the substrate to obtain a first layer, followed by calcining at a temperature in the range of 400 to 700°C; - depositing said second slurry on said first layer to obtain a second layer, followed by calcining at a temperature in the range of 400-700°C; The process includes:

26. 15. An exhaust gas treatment system for an internal combustion engine comprising the catalytic article of claim 14.

27. 27. A method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, nitrogen oxides and particulates, comprising contacting the exhaust stream with the catalytic article of claim 14 or the exhaust gas treatment system of claim 26.

28. 27. Use of the catalytic article of claim 14 or the exhaust gas treatment system of claim 26 to purify a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides.

Images