Catalytic article and method of manufacturing the catalytic article

Abstract

To provide a platinum-rhodium based catalyst which is essentially free of palladium and exhibits high temperature hydrothermal stability at an aging temperature of higher than 950°C, and which has an equal or improved efficacy in controlling automobile emissions, compared to the palladium-rhodium based catalyst.SOLUTION: A catalytic article comprises platinum supported on a first support comprising a ceria-containing metal oxide component, rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and a substrate, wherein the catalytic article is essentially free of palladium. The present invention also provides a process for preparing the catalytic article, as well as the use of the catalytic article and the exhaust gas treatment system for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxide.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority in its entirety to U.S. Provisional Application No. 62 / 867351, filed June 27, 2019, and European Application No. 19185912.3, filed July 12, 2019.

[0002] The invention claimed in this application relates to catalytic articles useful for treating exhaust gases to reduce pollutants contained therein. In particular, the invention claimed in this application relates to platinum-based catalytic articles, methods for preparing the catalytic articles, and their use as emission control catalysts. [Background technology]

[0003] Three-way conversion (TWC) catalysts (hereinafter referred to interchangeably as three-way catalysts, three-way catalysts, TWC catalysts, and TWCs) have been utilized for several years to treat exhaust gas streams from internal combustion engines. Catalytic converters containing three-way catalysts are typically used in the exhaust gas lines of internal combustion engines to treat or purify exhaust gases containing pollutants such as hydrocarbons, nitrogen oxides, and carbon monoxide. Three-way catalysts are typically known to oxidize unburned hydrocarbons and carbon monoxide and reduce nitrogen oxides.

[0004] Typically, exhaust gas treatment systems for gasoline vehicle applications use a two-catalyst monolith system. The front brick, the close-coupled catalyst (CC1), has a higher PGM loading to handle primarily cold start and highway driving emissions. The second brick, the clean-up catalyst (CC2), has a lower PGM loading to handle additional emissions caused by acceleration, hill climbing, and other driving loads. Currently, emission treatment systems use exclusively Pd / Rh technology, in which palladium is used as the primary platinum group metal component with a smaller amount of rhodium.

[0005] Due to the large amount of palladium used in the production of catalytic converters, which help reduce the amount of exhaust gas pollutants, there may be a shortage of palladium in the market in the coming years. Currently, palladium is significantly more expensive than platinum. At the same time, platinum prices are expected to fall due to a decrease in demand for platinum. One of the reasons could be the decrease in production of diesel vehicles.

[0006] Therefore, to significantly reduce catalyst costs, it is necessary to replace a portion of the palladium in TWC catalysts with platinum. Platinum is widely used in diesel oxidation catalysts (DOCs) and lean NOx traps (LNTs) for emission control in diesel-fueled vehicles, but its use in gasoline-fueled vehicles is limited. The proposed approach of replacing a portion of the palladium with platinum is complicated by the need to maintain or improve the desired effectiveness of the catalyst, which would not be possible by simply replacing a portion of the palladium with platinum. Prior art also states that palladium has been found to be superior to platinum, although this difference appears to be greater under more stressful conditions, such as high speeds or wide operating amplitudes. One of the reasons for this is that platinum is less stable than palladium, and different supports provide different binding energies for Pd or Pt. Platinum tends to sinter under prolonged, high-temperature aging conditions. Furthermore, vehicle warranties have become longer, e.g., from 100,000 miles / 10 years to 150,000 miles / 15 years. As a result, OEMs are being mandated to use more stringent aging protocols (i.e., increasing aging temperatures from peak temperatures of 850°C to 950, 1050, 1000, and 1050°C, depending on the OEM and vehicle). It is well known that platinum particles deposited on conventional refractory alumina can grow to submicron size via the well-established Ostwald ripening mechanism. Therefore, further research is needed into stabilizing platinum using appropriate support materials. It is therefore an object of the presently claimed invention to provide a platinum-rhodium based catalyst that is essentially free of palladium, exhibits high-temperature hydrothermal stability at aging temperatures above 950°C, and has comparable or improved effectiveness in controlling automotive emissions compared to palladium-rhodium based catalysts. [Brief explanation of the drawings]

[0007] 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. These and other features of the present invention, its nature, and various advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] 1 is a schematic diagram of a catalyst article design in an exemplary configuration according to one embodiment of the presently claimed invention. [Figure 2] 1 is a graph showing comparative test results of the conversion of THC, NO, and CO for a catalyst of the present invention and a reference catalyst. [Figure 3A] Illustrates a comparison of NO conversion for Pt catalysts supported on ceria-alumina and ceria-zirconia. [Figure 3B] 1 illustrates a comparison of HC light-off of Pt catalysts supported on ceria-alumina and Pt catalysts supported on ceria-zirconia. [Figure 4A] 1 illustrates a comparison of λ-sweep NO conversion of Pt catalysts supported on ceria-alumina and ceria-zirconia. [Figure 4B] 1 illustrates a comparison of λ-sweep HC conversion of Pt catalysts supported on ceria-alumina and Pt catalysts supported on ceria-zirconia. [Figure 5A, 5B, 5C] A comparative study of the stability of Pt catalysts supported on ceria-alumina and Pt catalysts supported on alumina is illustrated. [Figure 6A] 1 is a perspective view of a honeycomb-shaped substrate support that may include a catalyst composition according to one embodiment of the presently claimed invention. [Figure 6B] 6B is a partial cross-sectional view enlarged compared to FIG. 6A and taken along a plane parallel to the edge of the substrate support of FIG. 6A, showing an enlarged view of a plurality of gas flow passages shown in FIG. 6A. [Figure 7]6B is a cutaway view of an enlarged section relative to FIG. 6A, in which the honeycomb-shaped substrate in FIG. 6A represents a wall-flow filter substrate monolith. Summary of the Invention

[0008] In accordance with the invention claimed in the present application, there is provided a catalytic article comprising platinum supported on a first support comprising a ceria-containing metal oxide component, rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and a substrate, wherein the catalytic article is essentially free of palladium.

[0009] According to another aspect of the presently claimed invention, there is provided a process for preparing a catalyst article according to the presently claimed invention, the process comprising preparing a slurry comprising platinum supported on a first support comprising a ceria-containing metal oxide component and rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and depositing the slurry on a substrate to obtain the catalyst article, followed by calcination at a temperature in the range of 400 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.

[0010] According to another aspect of the presently claimed invention, there is provided an exhaust gas treatment system for an internal combustion engine, the system comprising a catalytic article according to the presently claimed invention.

[0011] According to another aspect of the presently claimed invention, there is provided a method for treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides, the method comprising contacting the exhaust stream with a catalytic article according to the presently claimed invention.

[0012] According to another aspect of the presently claimed invention, there is provided 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 presently claimed invention or an exhaust gas treatment system according to the presently claimed invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0013] According to another aspect of the presently claimed invention, there is provided the use of a catalytic article according to the presently claimed invention or an exhaust gas treatment system according to the presently claimed invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides. DETAILED DESCRIPTION OF THE INVENTION

[0014] The invention claimed in this application will now be more fully described below. The invention claimed in this application may 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 the invention claimed in this application 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 as essential to the practice of the disclosed materials and methods.

[0015] The use of the terms "a," "an," "the," and similar directives in the context of describing the materials and methods discussed herein (particularly in the context of the claims below) should be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0016] The term "about" is used throughout this specification to describe and account for small variations. For example, the term "about" refers to ±5% or less, e.g., ±2% or less, ±1% or less, ±0.5% or less, ±0.2% or less, ±0.1% or less, or ±0.05% or less. All numerical values ​​are modified by the term "about," whether explicitly stated or not. Of course, values ​​modified by the term "about" include the specific value. For example, "about 5.0" must include 5.0.

[0017] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended only to better describe the materials and methods and is not intended to limit the scope unless otherwise claimed.

[0018] The present invention provides a bimetallic catalyst article containing two platinum group metals (PGMs) in which a large amount of platinum can be used to totally replace palladium.

[0019] Platinum group metal (PGM) refers to any component containing a PGM (Ru, Rh, Os, Ir, Pd, Pt, and / or Au). For example, the PGM may be in a zero-valence metallic form, or the PGM may be in an oxide form. Reference to a "PGM component" takes into account the presence of the PGM in any valence state. Terms such as "platinum (Pt) component," "rhodium (Rh) component," "palladium (Pd) component," "iridium (Ir) component," and "ruthenium (Ru) component" refer to the respective platinum group metal compounds, complexes, and the like, which decompose or otherwise convert to a catalytically active form, typically a metal or metal oxide, upon calcination or use of the catalyst.

[0020] The terms "catalyst," "catalytic article," or "catalyst article" refer to a component in which a substrate is coated with a catalytic composition used to promote a desired reaction. In one embodiment, the catalytic article is a layered catalytic article. The term layered catalytic article refers to a catalytic article in which a substrate is coated with a PGM composition in layers. These compositions may be referred to as washcoats.

[0021] "NO x " refers to nitrogen oxide compounds such as NO, N2O, and / or NO2.

[0022] The invention claimed in this application addresses the problem of replacing palladium with platinum in conventional palladium-rhodium catalysts without affecting overall catalytic performance. It provides a platinum-rhodium catalyst that is essentially free of palladium and includes an optimized support for platinum stabilization. Therefore, the catalyst has high-temperature hydrothermal stability at aging temperatures above 950°C. The problem of platinum sintering can be solved by using ceria as a support when doped on alumina. Platinum can form a monolayer and is often partially or completely oxidized on the ceria surface due to the strong PtO-CeO2 interaction. However, bulk ceria itself can sinter after high-temperature aging. Therefore, the present invention addresses the aforementioned problem and provides a ceria-alumina composite as a platinum support for TWC catalysts. Platinum is selectively deposited on the ceria-alumina composite, thereby providing optimal three-way catalytic performance and preventing platinum migration to other catalyst components. The PGM components are distributed on different supports to optimize platinum utilization for three-way conversion catalysis after high temperature aging in a gasoline engine.

[0023] Accordingly, the presently claimed invention provides a catalytic article comprising platinum supported on a first support comprising a ceria-containing metal oxide component, rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and a substrate, wherein the catalytic article is essentially free of palladium. As used herein, the term "essentially free of palladium" refers to no externally added palladium in the catalytic article, although palladium may optionally be present in fractional amounts, such as an amount of <0.1 wt.%. In one embodiment, the first support further comprises a refractory alumina component. In one embodiment, the catalytic article comprises platinum supported on a first support comprising a ceria-containing metal oxide component and a refractory alumina component, rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and a substrate, wherein the catalytic article is essentially free of palladium. In one embodiment, the presently claimed catalyst article exhibits high temperature hydrothermal stability at aging temperatures above 950° C. The results of the stability study are set forth in FIG.

[0024] In one embodiment, the amount of platinum is in the range of 0.1 to 10.0 wt. % based on the total weight of the first support, and the amount of rhodium is in the range of 0.1 to 10.0 wt. % based on the total weight of the second support. In one embodiment, the first support comprises stabilized alumina. In one embodiment, stabilizers used to fabricate the stabilized alumina include, but are not limited to, lanthana, barium, strontium, and the like. In another embodiment, the refractory metal oxide support further comprises lanthanum-zirconium, zirconium, alumina-zirconium, titanium oxide, iron oxide, yttrium oxide, and any combination thereof.

[0025] In one embodiment, a ceria-containing metal oxide component is used as a support for platinum, and includes ceria-alumina, ceria-yttrium-alumina, ceria-silica-alumina, ceria-tin-alumina, ceria-manganese-alumina, ceria-iron-alumina, ceria-nickel-alumina, ceria-iridium-alumina, ceria-ruthenium-alumina, ceria-indium-alumina, ceria-titania-alumina, or any combination thereof. In another embodiment, the ceria-containing metal oxide component includes ceria-zirconia.

[0026] In one embodiment, the ceria-containing metal oxide component comprises ceria-alumina or ceria-yttrium-alumina. In a preferred embodiment, the ceria-containing metal oxide component comprises ceria-alumina. In one embodiment, the ceria content of the ceria-containing metal oxide component is in the range of 1.0 to 80 wt %, based on the total weight of the ceria-containing metal oxide component. In one embodiment, the ceria content of the ceria-containing metal oxide component is in the range of 5.0 to 50 wt %, based on the total weight of the ceria-containing metal oxide component. In one embodiment, the ceria content of the ceria-containing metal oxide component is in the range of 5.0 to 30 wt %, based on the total weight of the ceria-containing metal oxide component.

[0027] In one embodiment, the oxygen storage compound is a material that changes its valence by storing and releasing oxygen depending on the partial pressure of oxygen in the operating environment. In gasoline-powered vehicles, the environment in the exhaust gas treatment system is constantly changing and fluctuates around a lambda value equal to 1. The lambda value is defined by the ratio of oxygen content to the combined CO and HC content and is measured by a lambda sensor. In modern gasoline-powered vehicle configurations, two lambda sensors are used: one located before the TWC catalyst and the other after. If the lambda value detected by the sensor before the TWC is greater than 1, this indicates that the engine is operating with more oxygen than necessary for the combustion of CO and HC in the cylinder chambers, which is good for reducing CO / HC emissions. If the lambda value detected by the sensor before the TWC is less than 1, this means that the engine is operating with insufficient oxygen than necessary for the combustion of CO and HC in the cylinder chambers, which is good for reducing NOx emissions. To balance overall CO / HC / NOx emissions, modern vehicles operate under strict lambda fluctuations of approximately 1. However, to accommodate acceleration and stop-and-go scenarios occurring in real-world driving conditions, which cause large lambda fluctuations and result in catalyst performance degradation, oxygen storage compounds are needed to minimize lambda fluctuations during such extreme driving conditions. Ceria is well known for its good oxygen storage capacity but has poor thermal stability. Modern vehicles require catalysts with good long-term durability to provide long-term warranties to customers. Therefore, OEMs require high-temperature aging durability (>950°C) for modern TWC catalysts. To this end, zirconium-stabilized ceria has been introduced as a means to meet these requirements.

[0028] "An oxygen storage component is an entity that exhibits oxygen storage capacity, often with multiple oxidation states, and that can actively release oxygen in an oxygen-depleted environment and reoxidize (regain oxygen) in an oxygen-rich environment. Examples of suitable oxygen storage components include ceria and praseodymia, and combinations thereof."

[0029] In some embodiments, the OSC is a mixed metal oxide composite containing ceria and / or praseodymia in combination with other metal oxides. Specific metal oxides that can be included in such mixed metal oxides are zirconium oxide (ZrO), titania (TiO), yttria (YO), neodymia (NdO), lanthana (LaO), or mixtures thereof. For example, a "ceria-zirconia composite" refers to a composite containing ceria and zirconia. In some embodiments, the ceria content in the mixed metal oxide composite ranges from about 25% to about 95% by weight of the total mixed metal oxide composite.

[0030] In some embodiments, the total ceria or praseodymia content in the OSC ranges from about 5% to about 99.9% by weight of the total mixed metal oxide composite, preferably from about 5% to about 70% by weight, and even more preferably from about 10% to about 50% by weight.

[0031] In one embodiment, the second support is a combination of a refractory alumina component and an oxygen storage component. In one embodiment, the refractory alumina component comprises alumina, lanthana-alumina, ceria-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, lanthana-zirconia-alumina, baria-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, or any combination thereof. In one embodiment, 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. In one embodiment, the oxygen storage component comprises ceria in an amount of 5.0 to 100 wt %, based on the total weight of the oxygen storage component. In one embodiment, the second support further comprises stabilized alumina.

[0032] In one embodiment, the catalyst article is a single-layer catalyst article. In one embodiment, the catalyst article is a two-layer article comprising a first layer, a second layer, and a substrate, wherein the first layer comprises platinum supported on a ceria-containing metal oxide component and a refractory alumina component and is disposed on the substrate, and the second layer comprises rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof and is disposed on the first layer. In one embodiment, the catalyst article is a two-layer article comprising a first layer, a second layer, and a substrate, wherein the first layer comprises rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof and is disposed on the substrate, and the second layer comprises platinum supported on a ceria-containing metal oxide component and a refractory alumina component and is disposed on the first layer. In one embodiment, the catalyst article comprises 1.0 to 300 g / ft supported on a ceria-containing metal oxide component. 3of platinum, and 1.0 to 100 g / ft supported on a support selected from a refractory alumina component, an oxygen storage component, or any combination thereof. 3 It is filled with rhodium.

[0033] In one embodiment, the platinum is thermally or chemically bound.

[0034] In one embodiment, the catalyst article is essentially free of barium oxide. As used herein, the term "essentially free of barium oxide" refers to the absence of exogenous barium oxide added, although it may optionally be present as a fraction, such as in an amount of <0.001 wt.%.

[0035] In one exemplary embodiment, a catalyst article includes platinum supported on a first support comprising a ceria-alumina and stabilized alumina component, rhodium supported on a second support comprising a stabilized alumina and ceria-zirconia-containing oxygen storage component, and a substrate; the catalytic article is essentially free of palladium; the catalyst article is a single layer; The ceria content of the ceria-alumina is in the range of 5.0 to 50 wt %, based on the total weight of the ceria-alumina; the oxygen storage component comprises ceria in an amount of 5.0 to 100 wt. %, based on the total weight of the oxygen storage component; The amount of platinum is in the range of 0.1 to 10.0 wt % based on the total weight of the first support, and the amount of rhodium is in the range of 0.1 to 10.0 wt % based on the total weight of the second support.

[0036] In one exemplary embodiment, a catalytic article includes platinum supported on a first support comprising a ceria-zirconia and stabilized alumina component, rhodium supported on a second support comprising a stabilized alumina and ceria-zirconia-containing oxygen storage component, and a substrate; the catalytic article is essentially free of palladium; the catalyst article is a single layer; The ceria content of the ceria-zirconia is in the range of 5.0 to 50 wt % based on the total weight of the ceria-alumina; the oxygen storage component comprises ceria in an amount of 5.0 to 100 wt. %, based on the total weight of the oxygen storage component; The amount of platinum is in the range of 0.1 to 10.0 wt % based on the total weight of the first support, and the amount of rhodium is in the range of 0.1 to 10.0 wt % based on the total weight of the second support.

[0037] In one embodiment, the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, and a woven fiber substrate.

[0038] As used herein, the term "substrate" refers to a monolithic material, typically in the form of a washcoat containing a plurality of particles containing a catalyst composition, on which the catalyst composition is disposed.

[0039] References to a "monolith substrate" or "honeycomb substrate" mean a unitary structure that is uniform and continuous from inlet to outlet.

[0040] As used herein, the term "washcoat" has its ordinary meaning in the art of a thin, adherent coating of catalyst or other material applied to a substrate material, such as a honeycomb-type support member, that is sufficiently porous to permit the passage of the gas stream to be treated. Washcoats are formed by preparing a slurry containing particles of a certain solids content (e.g., 15-60% by weight) in a liquid vehicle, which is then coated onto the substrate and dried to provide a washcoat layer.

[0041] As used herein, and as described in Heck, Ronald, and Farrauto, Robert, Catalytic Air Pollution Control, New York: Wiley-Interscience, 2002, pp. 18-19, a washcoat layer comprises a compositionally distinct layer of material disposed on the surface of a monolith substrate or an underlying washcoat layer. In one embodiment, a substrate contains one or more washcoat layers, each of which may differ in some manner (e.g., in its physical properties, such as, for example, particle size or crystallite phase) and / or may differ in chemical catalytic function.

[0042] A catalyst article may be "virgin," meaning that the catalyst article is new and has not been exposed to any heat or thermal stress for an extended period of time. "Virgin" may also mean that the catalyst has been recently prepared and has not been exposed to any exhaust gases or high temperatures. Similarly, an "aged" catalyst article is not virgin and has been exposed to exhaust gases and high temperatures (i.e., greater than 500°C) for an extended period of time (i.e., greater than 3 hours).

[0043] In one embodiment, the substrate of the catalytic article of the presently claimed invention can be constructed from any material typically used to prepare automotive catalysts, and typically comprises a ceramic or metal monolith honeycomb structure.

[0044] The substrate typically provides a plurality of walls onto which a washcoat containing the catalyst composition described herein above is applied and adhered, thereby acting as a support for the catalyst composition.

[0045] Exemplary 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, with the total amount of these metals advantageously comprising at least 15% by weight of the alloy, e.g., 10-25% chromium, 3-8% aluminum, and up to 20% nickel. The alloy may also contain small or trace amounts of one or more metals, such as manganese, copper, vanadium, and titanium. The surface of the metal substrate may be oxidized at high temperatures, e.g., 1000°C or higher, to form an oxide layer on the surface of the substrate, improving the corrosion resistance of the alloy and facilitating adhesion of a washcoat layer to the metal surface.

[0046] The ceramic material used in the construction of 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.

[0047] Any suitable substrate can be used, such as a monolith flow-through substrate having multiple fine, parallel gas flow passages extending from the inlet to the outlet face of the substrate so that the passages are open to fluid flow. The passages, which are essentially straight-line paths from the inlet to the outlet, are defined by walls onto which a catalytic material is washcoated so that gas flowing through the passages comes into contact with the catalytic material. The flow passages in the monolith substrate are thin-walled channels that can be of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, and circular. 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 commonly from about 300 to 900 cpsi. The wall thickness of the flow-through substrate can vary, with a typical range being 0.002 to 0.1 inches. A typical commercially available flow-through substrate is a cordierite substrate with a wall thickness of 6 mils at 400 cpsi or 4 mils at 600 cpsi. However, it will be understood that the present invention is not limited to a particular substrate type, material, or geometry. In an alternative embodiment, the substrate may be a wall-flow substrate, in which each passage is plugged by a non-porous plug at one end of the substrate body, with alternating passages plugged at the opposite end. This requires gas flow to pass through the porous walls of the wall-flow substrate to reach the outlet. Such monolithic substrates may contain up to about 700 or more cpsi, such as about 100 to 400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of the cells may vary, as explained above. Wall-flow substrates typically have wall thicknesses of 0.002 to 0.1 inches. Typical commercially available wall-flow substrates are constructed from porous cordierite, examples of which have 200 cpsi and a 10-mil wall thickness, or 300 cpsi with an 8-mil wall thickness, and 45 to 65% wall porosity. 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 present 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, may also 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.

[0048] As used herein, the term "stream" broadly refers to any combination of flowing gases that may contain solid or liquid particulate matter.

[0049] As used herein, the terms "upstream" and "downstream" refer to relative directions relative to the flow of engine exhaust gas stream from the engine toward the tailpipe, with the engine being in the upstream position and the tailpipe and any pollution abatement articles, such as filters and catalysts, being downstream from the engine.

[0050] 6A and 6B illustrate an exemplary substrate 2 in the form of a flow-through substrate coated with a washcoat composition described herein. Referring to FIG. 6A, the exemplary substrate 2 has a cylindrical shape, including a cylindrical outer surface 4, an upstream end surface 6, and a corresponding downstream end surface 8 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. 6B, the 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 passages 10 are unobstructed, allowing a fluid, e.g., a gas stream, to flow longitudinally through the substrate 2 via the gas flow passages 10. As can be more easily seen in FIG. 6B, 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 distinct layers, if desired. In the illustrated embodiment, the washcoat consists of 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 invention claimed in this application may also be practiced with two or more (e.g., three or four) washcoat layers and is not limited to the illustrated two-layer embodiment.

[0051] FIG. 7 illustrates an exemplary substrate 2 in the form of a wall-flow filter substrate coated with a washcoat composition described herein. As seen in FIG. 7, the exemplary substrate 2 has a plurality of passages 52. The passages are tubularly surrounded by the interior wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. Alternating passages are blocked at the inlet end by inlet plugs 58 and at the outlet end by outlet plugs 60, forming an inverted checkerboard pattern at the inlets 54 and outlets 56. Gas flow 62 enters through unblocked channel inlets 64, is stopped by outlet plugs 60, and diffuses through the (porous) channel wall 53 to the outlet side 66. Gas cannot pass back to the inlet side of the wall because of the inlet plugs 58. Porous wall-flow filters used in the present invention have catalytic properties in the walls of the element that have or contain one or more catalytic materials on or within them. The catalytic material may be present only on the inlet side of the element wall, only on the outlet side, on both the inlet and outlet sides, or the wall itself may be composed entirely or partially 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.

[0052] According to another aspect of the presently claimed invention, there is provided a process for preparing a catalyst article, which in one embodiment involves the following steps:

[0053] In a first step, a slurry is prepared comprising platinum supported on a first support comprising a ceria containing metal oxide component and optionally a refractory metal oxide, and rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof. In a next step, the slurry is deposited on a substrate to obtain a catalyst article, followed by calcination at a temperature in the range of 400-700°C. In one embodiment, preparing the slurry comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

[0054] In one embodiment, a process for preparing a catalyst article includes preparing a first layer slurry comprising platinum supported on a first support comprising a ceria-containing metal oxide component and optionally a refractory alumina component, and a second layer slurry comprising rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof; depositing the first layer slurry on a substrate to obtain a first layer, depositing the second layer slurry on the first layer to obtain a second layer, followed by calcining at a temperature in the range of 400 to 700°C, wherein the step of preparing the slurries includes a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

[0055] In one embodiment, the process involves a preliminary step of thermally or chemically fixing platinum onto the support. Thermal fixing involves depositing platinum onto the support, for example, via incipient wetness impregnation, followed by thermal calcination of the resulting platinum / support mixture. By way of example, the mixture is calcined at 400-700°C for 1-3 hours at a ramp rate of 1-25°C / min.

[0056] Chemical immobilization involves depositing platinum onto a support, followed by immobilization using additional reagents to chemically convert the platinum.

[0057] The incipient wetness impregnation technique, also called capillary impregnation or dry impregnation, is commonly used in the synthesis of heterogeneous materials, i.e., catalysts.

[0058] Typically, the active metal precursor is dissolved in an aqueous or organic solution, and then the metal-containing solution is added to the catalyst support, which contains a pore volume equal to the volume of the added solution. Capillary action draws the solution into the pores of the support. Adding a solution that exceeds the pore volume of the support changes solution transport from a capillary action process to a much slower diffusion process. The catalyst is dried and calcined to remove 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 within the pores during impregnation and drying. After appropriate dilution, multiple active metal precursors may be co-impregnated into the catalyst support. Alternatively, the active metal precursor is introduced into the slurry via post-addition under stirring during the slurry preparation process.

[0059] The support particles are typically sufficiently dry to absorb substantially all of the solution and form a wet solid. Typically, an aqueous solution of a water-soluble compound or complex of the active metal, such as rhodium chloride, rhodium nitrate, rhodium acetate, or a combination thereof (when rhodium is the active metal), and palladium nitrate, palladium tetraamine, palladium acetate, or a combination thereof (when palladium is the active metal), is utilized. After treatment of the support particles with the active metal solution, the particles are dried, such as by heat treatment, 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 involves heat treatment in air at a temperature of 400-550°C for 10 minutes to 3 hours. The above process can be repeated as needed by impregnation to reach the desired active metal loading level.

[0060] The catalyst composition is typically prepared in the form of catalyst particles, as described above. These catalyst particles are mixed with water to form a slurry for coating a catalyst substrate, such as a honeycomb substrate. 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, and 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. The pH is adjusted by adding acidic or basic species to the slurry. For example, in some embodiments, the pH of the slurry is adjusted by adding ammonium hydroxide, aqueous nitric acid, or acetic acid. The typical pH range for the slurry is about 3 to 12.

[0061] The slurry may be milled to reduce particle size and promote particle mixing. Milling may be accomplished in a ball mill, continuous mill, or other similar equipment, and the solids content of the slurry may be, for example, about 20 to 60% by weight, more specifically, about 20 to 40% by weight. In one embodiment, the milled slurry has a D of about 3 to about 40 microns, preferably 10 to about 30 microns, and more preferably about 10 to about 15 microns. 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 amounts of slurry. D is typically measured in microns. 90 means that 90% of the particles by number have a diameter smaller than the quoted value.

[0062] The slurry is coated onto the catalyst substrate using any washcoating technique known in the art. In one embodiment, the catalyst substrate is dipped 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 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 believed to be essentially solvent-free. After calcination, the catalyst loading achieved by the above washcoating technique can be determined by calculating the difference between the coated and uncoated weights of the substrate. As will be apparent to those skilled in the art, the catalyst loading can be modified by varying the rheology of the slurry. Furthermore, the coating / drying / calcining process to produce the washcoat can be repeated as necessary to build the coating to a desired loading level or thickness; i.e., two or more washcoats may be applied.

[0063] In certain embodiments, the coated substrate is aged by subjecting the coated substrate to a heat treatment. In one embodiment, aging is performed in a 10.0% by volume moisture environment at a temperature of about 850°C to about 1050°C for 20 to 100 hours with alternating hydrocarbon / air feeds. Accordingly, in certain embodiments, an aged catalyst article is provided. In certain embodiments, particularly useful materials include metal oxide-based supports (including, but not limited to, substantially 100% ceria supports) that maintain a high percentage of pore volume (e.g., about 80 to 100%) upon aging (e.g., about 850°C to about 1050°C, 10% by volume moisture with alternating hydrocarbon / air feeds, aging for 20 to 100 hours).

[0064] According to another aspect of the presently claimed invention, there is provided an exhaust gas treatment system for an internal combustion engine. The exhaust gas treatment system comprises a catalyst article according to the presently claimed invention. In one embodiment, the catalyst article according to the presently claimed invention is used in a first close-coupled position (CC1). In another embodiment, the catalyst article according to the presently claimed invention is used in a second close-coupled position (CC2). In one embodiment, the catalyst article according to the presently claimed invention is used as an underfloor catalyst (UF). In one embodiment, the exhaust gas treatment system comprises a platinum group metal-based three-way conversion (TWC) catalyst article and a catalyst article according to the present invention, wherein the platinum group metal-based three-way conversion (TWC) catalyst article is located downstream of the internal combustion engine, and the catalyst article is located downstream in fluid communication with the platinum group metal-based three-way conversion (TWC) catalyst article.

[0065] In another embodiment, an exhaust gas treatment system comprises a platinum group metal-based three-way (TWC) catalyst article and a catalyst article according to the present invention, wherein the layered catalyst article is located downstream of an internal combustion engine and the platinum group metal-based three-way (TWC) catalyst article is located downstream and in fluid communication with the three-way (TWC) catalyst article.

[0066] According to another aspect of the presently claimed invention, there is provided a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, comprising contacting the exhaust stream with a catalyst article according to the presently claimed invention. Terms such as "exhaust stream," "engine exhaust stream," and "exhaust gas stream" refer to any combination of flowing engine outflow gases, which may also contain solid or liquid particulate matter. The stream is, for example, the exhaust of a lean-burn engine, which includes gaseous components and may also contain certain non-gaseous components, such as liquid droplets, solid particles, and the like. Lean-burn engine exhaust streams typically include combustion products, incomplete combustion products, oxides of nitrogen, combustible and / or carbonaceous particulate matter (soot), and unreacted oxygen and / or nitrogen. Such terms also refer to the downstream effluent of one or more other catalyst system components as described herein.

[0067] According to another aspect of the presently claimed invention, there is provided 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 presently claimed invention or an exhaust gas treatment system according to the presently claimed invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0068] According to another aspect of the presently claimed invention, there is provided the use of a catalytic article according to the presently claimed invention or an exhaust gas treatment system according to the presently claimed invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides.

[0069] In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of carbon monoxide, hydrocarbons, and nitrogen compounds present in the exhaust gas stream before contacting the catalytic article. In some embodiments, the catalytic article converts hydrocarbons to carbon dioxide and water. In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of hydrocarbons present in the exhaust gas stream before contacting the catalytic article. In some embodiments, the catalytic article converts carbon monoxide to carbon dioxide. In some embodiments, the catalytic article converts nitrogen oxides to nitrogen.

[0070] In some embodiments, the catalytic article converts at least about 50%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of nitrogen oxides present in the exhaust gas stream prior to contact with the catalytic article. In some embodiments, the catalytic article converts at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95% of the total amount of combined hydrocarbons, carbon dioxide, and nitrogen oxides present in the exhaust gas stream prior to contact with the catalytic article. [Example]

[0071] Aspects of the invention claimed in this application are more fully illustrated by the following examples, which are set forth to illustrate certain aspects of the invention and should not be construed as limiting thereof.

[0072] Example 1: Preparation of a reference catalyst article (RC-1, bimetallic catalyst: Pd:Rh (20.4:13.6)) A Pd / Rh-based TWC catalyst article was prepared as a close-coupled catalyst. The total PGM loading (Pt / Pd / Rh) was 0 / 20.4 / 13.6. This resulted in a PGM loading of 2.9 g / in. 3 The Pd-containing washcoat was prepared by impregnating a Pd nitrate solution (20%, 5.7 grams) onto a mixture of stabilized alumina (138 grams) and ceria-zirconia (OSC, 40% Ce, 18 grams). The Pd-impregnated powder was slurried with 170 grams of water. The slurry was then milled to produce particles with a D of less than 10 μm. 90The washcoat was prepared by impregnating a rhodium nitrate solution (10%, 8 grams) onto a mixture of stabilized alumina (49 grams) and ceria-zirconia (40% Ce, 76 grams) with 8 grams of rhodium nitrate. The Rh-impregnated powder was added to a mixture of 50 grams of water and zirconium acetate (used as a binder) to form a slurry. The Rh-containing slurry was then milled to a D of less than 10 μm. 90 The Rh-containing washcoat was then added to the Pd-containing slurry along with strontium acetate and barium acetate (9 and 7 grams, respectively) to obtain a mixed slurry. Approximately 19 grams of NiO powder was added to the mixed slurry to obtain the final slurry. Catalyst articles were prepared by coating the combined slurry onto a 400 cpsi / 4 mil ceramic substrate. The resulting coated substrate was then dried and calcined at 500°C for 2 hours.

[0073] Example 2: Preparation of Catalyst Article (IC-A, Bimetallic, Pt and Rh in Single Layer Catalyst (Ratio: 20.4:0:13.6), No Thermal Fixation) The catalyst article was formulated with Pt and Rh to produce a 20.4 / 0 / 13.6 design. The total PGM loading was 34 g / ft 3 and the washcoat loading was 2.9 g / in. 3 The catalyst preparation procedure was the same as in Example 1 (CC2-RC-1), except that Pt was used instead of Pd. There was no thermal immobilization of the precious metal on the support. The catalyst article was prepared by coating the slurry onto a 400 / 4 ceramic substrate. The resulting coated substrate was then dried and calcined at 500°C for 2 hours.

[0074] Example 3: Preparation of Catalyst Article (IC-B, Bimetallic—Pt and Rh, No Alkaline Earth Metal Used) The catalyst article was formulated with Pt and Rh to produce a 20.4 / 0 / 13.6 design. The total PGM loading was 34 g / ft 3 The catalyst article washcoat loading was 2.84 g / in 3 The catalyst preparation procedure was the same as that of Example 2, except that no alkaline earth compound was used. The catalyst article was prepared by coating the slurry onto a 400 / 4 ceramic substrate. The resulting coated substrate was then dried and calcined at 500°C for 2 hours.

[0075] Example 4: Preparation of a catalytic article of the present invention (IC-C, bimetallic—Pt and Rh, no alkaline earth metal used, and Ce—Zr replaced with Ce—Al) The catalyst article was formulated with Pt and Rh to produce a 20.4 / 0 / 13.6 design. The total PGM loading was 34 g / ft 3 The catalyst article washcoat loading was 2.84 g / in 3 The catalyst preparation procedure was the same as that of Example 2, except that no alkaline earth compound was used. Also, one of the Pt supports, Ce-Zr, was replaced with Ce-Al (50% Ce). Catalyst articles were prepared by coating the slurry onto a 400 / 4 ceramic substrate. The resulting coated substrate was then dried and calcined at 500°C for 2 hours. Catalyst articles IC-A, IC-B, and IC-C are illustrated in Figures 1A, 1B, and 1C, and the reference catalyst article is illustrated in Figure 1D of the accompanying drawings.

[0076] Example 5: Catalyst Aging The catalyst articles according to Examples 2-4 and the reference catalyst article according to Example 1 were aged in a tubular furnace capable of generating an inlet gas flow with a gas mixture exhibiting rich and lean variations similar to the stoichiometric driving conditions observed in a gasoline-powered vehicle during an expected fuel cut cycle. The furnace temperature was generated by injecting butane fuel in front of the catalyst. The inlet aging temperature for the catalyst series was set at 875°C, and the exotherm peak temperature was 950°C. The aging period was set at 20 hours.

[0077] Example 6: Comparative Test: The catalyst articles according to Examples 2-4, along with the reference catalyst article according to Example 1, were evaluated after aging in a reactor (Gasoline Vehicle Simulator - GVS) capable of simulating vehicle driving conditions such as temperature, flow rate (velocity), and exhaust gas components (CO, HC, NO, HO, CO, etc.) under Federal Testing Procedure 1972 (FTP-72). The results of the comparative tests are listed in Table 1 and Figure 2.

[0078] [Table 1]

[0079] The results shown in Table 1 demonstrate that the Pt / Rh catalyst article according to the presently claimed invention can outperform the Pd / Rh reference catalyst article in NO conversion without compromising HC / CO performance. The overall performance of the exemplary inventive catalyst (IC-C) is found to be superior compared to the other inventive catalysts (IC-B and IC-A).

[0080] Additionally, powder catalysts containing Pt supported on different supports were prepared and tested. The first catalyst contained Pt deposited on Ce-Al, and the second catalyst contained Pt deposited on Ce-Zr with a total rare earth concentration of 45% (40% Ce and 5% La). These powders were aged in a furnace at 980 °C for 5 h with steam (10%) under rich / lean fluctuations (10 min air, 10 min 4% H2 / N2). After aging, these powders were evaluated in a reactor under a lean / rich fluctuation (λ = 1.025 & λ = 0.975) at 1 Hz and a stoichiometric (λ = 1) light-off protocol with a feed gas composition consisting of:

[0081] [Table 2]

[0082] The results shown in Figures 3A and 3B indicate that Pt on Ce-Al outperforms Pt on Ce-Zr supports in converting NO and HC during steady-state light-off tests.

[0083] These catalyst samples were also evaluated under lambda sweep testing. λ sweep testing is a test to evaluate the catalyst response to lean / rich variations observed in gasoline vehicles. This evaluation is typically performed at temperatures higher than the L / O temperature of the catalyst. A rich-to-lean λ sweep was performed at 350 °C. The results, shown in Figures 4A and 4B, clearly demonstrate that ceria-alumina (Ce-Al) is a better support for Pt than ceria-zirconium (Ce-Zr) in terms of overall performance improvement.

[0084] Example 7: Testing of Pt supports: Standard high surface area alumina support (SA:>150M 2Two supports were used to confirm the stabilization of Pt: Pt / Ce-Al (50% Ce, same as IC-C) and Ce-Al (50% Ce, same as IC-C). 1% Pt was impregnated onto both supports separately and aged. To see whether Pt / Ce-Al could withstand high-temperature aging better than Pt / Al, a standard steady-state light-off test was performed. The results, shown in Figures 5A, 5B, and 5C, indicate that the Ce-Al support helps stabilize Pt against high-temperature aging.

[0085] References throughout this specification to "one embodiment," "a particular embodiment," "one or more embodiments," or "embodiments" mean that a particular feature, structure, material, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention claimed in this application. Thus, the appearance of phrases such as "in one or more embodiments," "in a particular embodiment," "in some embodiments," "in one embodiment," or "in an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment of the invention claimed in this application. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. All of the various embodiments, aspects, and options disclosed herein can be combined in all variations, regardless of whether such features or elements are explicitly combined in the description of a specific embodiment herein. The invention claimed in this application is intended to be read as a whole, and should be considered to contemplate that any separable features or elements of the disclosed invention are intended to be combinable in any of its various aspects and embodiments, unless the context clearly dictates otherwise.

[0086] Although the embodiments disclosed herein have been described with reference to particular 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. Accordingly, the invention claimed herein is intended to include 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. All patents and publications cited herein are incorporated by reference for the specific teachings described therein, unless a statement of incorporation otherwise is specifically provided.

Claims

1. HC and NO in exhaust gas ｘ and a three-way conversion catalyst article for use in removing CO, comprising: platinum supported on a first support comprising a ceria-containing metal oxide component; rhodium supported on a second support which is a combination of a refractory alumina component and an oxygen storage component; a substrate, the catalytic article comprises palladium in an amount less than 0.1 wt. %; the first support further comprises a refractory alumina component; the ceria-containing metal oxide component comprises ceria-alumina, ceria-yttrium-alumina, ceria-silica-alumina, ceria-tin-alumina, ceria-manganese-alumina, ceria-iron-alumina, ceria-nickel-alumina, ceria-iridium-alumina, ceria-ruthenium-alumina, ceria-indium-alumina, ceria-titania-alumina ceria-titania, or any combination thereof; 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; Catalyst article.

2. 10. The catalyst article of claim 1, wherein the ceria-containing metal oxide component comprises ceria-alumina or ceria-yttrium-alumina.

3. The catalyst article of claim 1, wherein the ceria-containing metal oxide component comprises ceria-alumina.

4. The catalytic article of claim 1, wherein the ceria-containing metal oxide component comprises ceria-zirconia.

5. 10. The catalyst article of claim 1, wherein the catalyst article is a single layer catalyst article and exhibits hydrothermal stability at aging temperatures above 950°C.

6. 5. The catalytic article of claim 1, wherein the catalytic article is a two-layer article comprising a first layer, a second layer, and a substrate, wherein the first layer comprises platinum supported on a ceria-containing metal oxide component and a refractory alumina component and is deposited on the substrate, and the second layer comprises rhodium supported on a support selected from a refractory alumina component, an oxygen storage component, or a combination thereof and is deposited on the first layer.

7. 5. The catalytic article of claim 1, wherein the catalytic article is a two-layer article comprising a first layer, a second layer, and a substrate, wherein the first layer comprises rhodium supported on a support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and is deposited on the substrate, and the second layer comprises platinum supported on a ceria-containing metal oxide component and a refractory alumina component, and is deposited on the first layer.

8. 8. The catalytic article of claim 1, wherein the amount of platinum is in the range of 0.1 to 10.0 wt. %, based on the total weight of the first support, and the amount of rhodium is in the range of 0.1 to 10.0 wt. %, based on the total weight of the second support.

9. 9. The catalyst article of any one of claims 1 to 8, wherein the ceria content of the ceria-containing metal oxide component is in the range of 1.0 to 80 wt%, based on the total weight of the ceria-containing metal oxide component.

10. 9. The catalyst article of any one of claims 1 to 8, wherein the ceria content of the ceria-containing metal oxide component is in the range of 5.0 to 50 wt %, based on the total weight of the ceria-containing metal oxide component.

11. 9. The catalyst article of any one of claims 1 to 8, wherein the ceria content of the ceria-containing metal oxide component is in the range of 5.0 to 30 wt %, based on the total weight of the ceria-containing metal oxide component.

12. 12. The catalyst article of any one of claims 1 to 11, wherein the refractory alumina component comprises alumina, lanthana-alumina, ceria-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, lanthana-zirconia-alumina, baria-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, or any combination thereof.

13. The catalyst article of any one of claims 1 to 11, wherein the oxygen storage component comprises ceria in an amount of 5.0 to 100 wt%, based on the total weight of the oxygen storage component.

14. The catalyst article comprises 1.0 to 300 g / ft supported on the ceria-containing metal oxide component. ３ of platinum and 1.0 to 100 g / ft supported on a support selected from a refractory alumina component, an oxygen storage component, or any combination thereof. ３ 14. The catalytic article of any one of claims 1 to 13, wherein the catalytic article is loaded with rhodium.

15. Catalyst article according to any one of claims 1 to 14, wherein the platinum is thermally or chemically fixed.

16. 16. The catalytic article of any one of claims 1 to 15, wherein the amount of palladium is less than 0.001%, based on the total weight of the support in the catalytic article.

17. The catalyst article of any one of claims 1 to 16, wherein the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, and a woven fiber substrate.

18. 18. The catalyst article of any one of claims 1 to 17, wherein the catalyst article comprises barium oxide in an amount less than 0.001 wt%.

19. 19. A process for preparing the catalyst article of any one of claims 1 to 18, the process comprising preparing a slurry comprising platinum supported on a first support comprising a ceria-containing metal oxide component and optionally a refractory alumina component, and rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof, and depositing the slurry on a substrate to obtain the catalyst article, followed by calcination at a temperature in the range of 400 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.

20. 19. A process for preparing the catalyst article of any one of claims 1 to 18, the process comprising preparing a first layer slurry comprising platinum supported on a first support comprising a ceria-containing metal oxide component and optionally a refractory alumina component, and a second layer slurry comprising rhodium supported on a second support selected from a refractory alumina component, an oxygen storage component, or a combination thereof; depositing the first layer slurry on a substrate to obtain a first layer, depositing the second layer slurry on the first layer to obtain a second layer, followed by calcining at a temperature in the range of 400 to 700°C, wherein the step of preparing the slurries comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

21. An exhaust gas treatment system for an internal combustion engine, said system comprising a catalytic article according to any one of claims 1 to 18.

22. 22. The exhaust gas treatment system of claim 21, wherein the system comprises a platinum group metal-based three-way conversion (TWC) catalyst article and the catalyst article of any one of claims 1 to 18, wherein the platinum group metal-based three-way conversion (TWC) catalyst article is located downstream of an internal combustion engine, and the catalyst article is located downstream in fluid communication with the platinum group metal-based three-way conversion (TWC) catalyst article.

23. 23. The exhaust gas treatment system of claim 22, wherein the system comprises a platinum group metal-based three-way conversion (TWC) catalyst article and the catalyst article of any one of claims 1 to 18, the catalyst article being located downstream of an internal combustion engine, and the platinum group metal-based three-way conversion (TWC) catalyst article being located downstream in fluid communication with the three-way conversion (TWC) catalyst article.

24. 24. A method for treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides, the method comprising contacting the exhaust stream with the catalytic article of any one of claims 1 to 18 or the exhaust gas treatment system of any one of claims 21 to 23.

25. 24. A method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, the method comprising contacting the gaseous exhaust stream with the catalytic article of any one of claims 1 to 18 or the exhaust gas treatment system of any one of claims 21 to 23 to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

26. 24. Use of a catalytic article according to any one of claims 1 to 18 or an exhaust gas treatment system according to any one of claims 21 to 23 for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide and nitrogen oxides.

Images