Zone-type ternary conversion catalyst containing platinum, palladium, and rhodium

Abstract

The present invention provides a catalytic article comprising a) a substrate, b) a first zone coated with a first catalyst layer, and c) a second zone coated with a second catalyst layer, wherein the first catalyst layer comprises platinum supported on ceria-zirconia mixed oxide or ceria-alumina composite or both, and rhodium supported on ceria-zirconia mixed oxide or ceria-alumina composite or both, the second catalyst layer comprises palladium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof, and rhodium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof, the first zone occupies the inlet end portion of the substrate, and the second zone occupies the outlet end portion of the substrate. The present invention also provides a process for the preparation of the catalytic article. The present invention further provides an exhaust gas treatment system for an internal combustion engine comprising the catalytic article according to the present invention. The present invention further provides a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides.

Description

Technical Field

[0001] The invention claimed in the present application relates to a catalyst useful for the treatment of exhaust gas to reduce contaminants contained in the exhaust gas. Specifically, the invention claimed in the present application relates to a catalyst article comprising a zone-type three-way conversion (TWC) catalyst containing platinum, palladium, and rhodium.

Background Art

[0002] Three-way conversion (TWC) catalysts are well known for their catalytic activity in reducing pollutants such as NO, CO, and HC using platinum group metals (PGMs). Conventional TWC catalysts use Pd and Rh as active catalyst components. Considering the current PGM market prices, replacing a portion of the more expensive palladium (Pd) with the less expensive platinum (Pt) in TWC catalysts would help catalyst converter manufacturers and automotive manufacturers significantly reduce costs. Therefore, the present invention focuses on developing a highly active zone-type TWC catalyst containing platinum, palladium, and rhodium as PGM components. Substitution of a substantial amount of Pd with Pt in TWC catalysts (e.g., 50%) is known to usually result in lower catalytic activity, especially under particularly severe TWC operating conditions, probably due to the relatively low thermal stability of Pt towards high-temperature aging.

[0003] Therefore, in order to improve the emission control efficiency, it is desirable to design a Pt / Pd / Rh-based TWC catalyst with an appropriate structure.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The object of the present invention is to improve the accumulated non-methane hydrocarbon (NMHC) and NOx performance of a three-way conversion (TWC) catalyst containing Pt, Pd, and Rh as active platinum group metal (PGM) components.

Means for Solving the Problems

[0005] The present invention provides a catalyst article comprising a) a substrate, b) a first zone coated with a first catalyst layer, and c) a second zone coated with a second catalyst layer, wherein the first catalyst layer comprises platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof, and the second catalyst layer comprises palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, the first zone occupies the inlet end portion of the substrate, and the second zone occupies the outlet end portion of the substrate.

[0006] The present invention also provides a process for the preparation of a catalytic article, the process comprising preparing a first catalytic layer slurry comprising platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof; preparing a second catalytic layer slurry comprising palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof; coating the first catalytic layer slurry on the inlet end portion of the substrate to obtain a first zone; coating the second catalytic layer slurry on the outlet end portion of the substrate to obtain a second zone; and subjecting the substrate to 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.

[0007] The present invention further provides an exhaust gas treatment system for an internal combustion engine comprising a catalytic article according to the invention claimed herein. The present invention still further provides a method of treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides, the method comprising contacting the exhaust stream with a catalytic article or an exhaust stream treatment system according to the invention claimed herein.

Brief Description of the Drawings

[0008] 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 wherein reference numerals refer to components of exemplary embodiments of the present invention. The drawings are merely exemplary and are not to be construed as limiting the present invention. The above and other features, their nature, and various advantages of the invention claimed herein will become more apparent when considered in conjunction with the following detailed description and the accompanying drawings.

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Mode for Carrying Out the Invention

[0009] The invention claimed in the present application will be more fully described below. The invention claimed in the present application can be embodied in many different forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided so that the invention claimed in the present application will be detailed and complete and will fully convey the scope of the present invention to those skilled in the art. No term in this specification should be construed as indicating any non-claimed element essential to the practice of the disclosed materials and methods.

[0010] All of the methods described in this specification can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by the context. The use of any and all examples or exemplary terms (e.g., "such as") provided herein is merely intended to better illustrate the materials and methods and is not intended to impose a limitation on the scope unless otherwise claimed.

[0011] Definition: The use of the terms "a", "an", "the", and similar referents in the context of describing the materials and methods considered in this specification (in particular, in the context of the following claims) shall be construed to include both the singular and the plural unless otherwise indicated herein or otherwise clearly contradicted by the context.

[0012] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range unless otherwise indicated herein, and each separate value is incorporated herein as if it were individually recited herein.

[0013] In the context of the present invention, the term "washcoat" is used interchangeably with "first catalyst layer and / or second catalyst layer" which respectively form a first zone and a second zone on a part of a substrate. As used herein, the term "washcoat" has its ordinary meaning in the art, which is a thin adhesive coating of a catalyst material or other material applied to the material of the substrate. Generally, a washcoat is formed by preparing a slurry containing particles with a specific solids content (e.g., 15 - 60 wt%) in a liquid vehicle, which is then coated onto the substrate and dried to provide a washcoat layer.

[0014] The term "overcoat" is used interchangeably with "topcoat", or "top washcoat", or "second layer", and the overcoat is deposited on at least a part of the first zone.

[0015] 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 catalyst article in the flow direction, the relative position of the catalyst article when disposed within the exhaust gas treatment system. The first zone is disposed upstream, while the second zone is disposed 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 a first end (inflow end portion) capable of receiving the flow of engine exhaust gas from the engine, while the outlet of the substrate is a second end (outflow end portion) from which the treated exhaust gas flow exits.

[0016] The term "three-way conversion catalyst" or TWC 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.

[0017] The term "NOx" refers to nitrogen oxide compounds such as NO and / or NO2.

[0018] As used herein, the term "flow" broadly refers to any combination of flowing gases that may contain particulate matter of solids or liquids.

[0019] As used herein, the terms "upstream" and "downstream" refer to the relative direction due to the flow of engine exhaust gas from the engine towards the exhaust pipe, with the engine in an upstream position and any pollution control articles such as the exhaust pipe and filters and catalysts downstream of the engine.

[0020] In the context of the present invention, the amount of platinum group metals such as platinum / palladium / rhodium, and / or support materials such as ceria-zirconia mixed oxides, ceria-alumina composites, alumina, etc. is calculated as a weight percentage based on the total weight of the washcoat including any optional top washcoat present on the substrate. That is, although the substrate is also part of the catalyst article, the amount is calculated without considering the amount of the substrate.

[0021] The present invention focuses on addressing the low HC activity associated with conventional Pt / Pd / Rh trimetal TWC technology. Accordingly, a Pt / Pd / Rh-based TWC catalyst article having a zone-type structure is designed. The design of the present invention features a Pt / Rh synergy in the front zone for improving HC performance, a low washcoat loading for promoting warm-up during cold start, and a PGM-free overcoat for improving resistance to phosphorus poisoning.

[0022] Catalyst article: In a first aspect, the present invention provides an article comprising: a) a substrate, b) a first zone coated with a first catalyst layer, and c) a second zone coated with a second catalyst layer, The first catalyst layer comprises platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof. The second catalyst layer comprises palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof. The first zone occupies the inlet end portion of the substrate, and the second zone occupies the outlet end portion of the substrate.

[0023] The total loading of the first catalyst layer and the second catalyst layer divided by the substrate volume is less than 3.2 grams per cubic inch.

[0024] Amount of platinum group metals: The amount of platinum in the first catalyst layer and the second catalyst layer is preferably in the range of 0.02 to 3.0% by weight based on the total weight of the first catalyst layer and the second catalyst layer. More preferably, the amount of platinum in the first catalyst layer and the second catalyst layer is in the range of 0.05 to 2.0% by weight based on the total weight of the first catalyst layer and the second catalyst layer.

[0025] The amount of palladium in the first catalyst layer and the second catalyst layer is preferably in the range of 0.02 to 5.0% by weight based on the total weight of the first catalyst layer and the second catalyst layer. More preferably, the amount of palladium in the first catalyst layer and the second catalyst layer is in the range of 0.05 to 3.0% by weight based on the total weight of the first catalyst layer and the second catalyst layer.

[0026] The amount of rhodium in the first catalyst layer and the second catalyst layer is preferably in the range of 0.01 to 1.0% by weight based on the total weight of the first catalyst layer and the second catalyst layer. More preferably, the amount of rhodium in the first catalyst layer and the second catalyst layer is in the range of 0.05 to 0.5% by weight based on the total weight of the first catalyst layer and the second catalyst layer.

[0027] The weight ratio of palladium to platinum in the first catalyst layer and the second catalyst layer is preferably 4:1 to 1:4. More preferably, the weight ratio of palladium to platinum in the first catalyst layer and the second catalyst layer is 3:1 to 1:3.

[0028] Preferably, the weight ratio of rhodium supported on ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer to rhodium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is in the range of 1.5:1 to 4:1.

[0029] Preferably, the amount of platinum in the first catalyst layer is 0.02 to 3.0% by weight based on the total weight of the first catalyst layer. More preferably, the amount of platinum in the first catalyst layer is 0.02 to 2.5% by weight based on the total weight of the first catalyst layer. Even more preferably, the amount of platinum in the first catalyst layer is 0.05 to 2.0% by weight based on the total weight of the first catalyst layer.

[0030] Preferably, the amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 60 to 100% by weight based on the total weight of platinum in the first and second catalyst layers. More preferably, the amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 70 to 100% by weight based on the total weight of platinum in the first and second catalyst layers. Most preferably, the amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 80 to 100% by weight based on the total weight of platinum in the first and second catalyst layers.

[0031] Preferably, the total amount of rhodium in the first catalyst layer is 0.01 to 1.0% by weight based on the total weight of the first catalyst layer. More preferably, the total amount of rhodium in the first catalyst layer is 0.01 to 0.5% by weight based on the total weight of the first catalyst layer.

[0032] Preferably, the amount of palladium is in the range of 0.02 to 5.0% by weight based on the total weight of the second catalyst layer. More preferably, the amount of palladium is in the range of 0.02 to 4.0% by weight based on the total weight of the second catalyst layer.

[0033] Preferably, the amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite, or any combination thereof in the second catalyst layer is preferably 50 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer. More preferably, the amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite, or any combination thereof in the second catalyst layer is 60 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer. Most preferably, the amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite, or any combination thereof in the second catalyst layer is 75 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer.

[0034] Preferably, the amount of rhodium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite, or any combination thereof in the second catalyst layer is 0 to 50% by weight based on the total weight of rhodium in the first catalyst layer and the second catalyst layer. More preferably, the amount of rhodium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite, or any combination thereof in the second catalyst layer is 0 to 25% by weight based on the total weight of rhodium in the first catalyst layer and the second catalyst layer.

[0035] Support material: In a catalyst material, catalyst composition, or catalyst washcoat, "support" refers to a material that receives a metal (e.g., PGM), stabilizer, promoter, binder, etc. by precipitation, association, dispersion, impregnation, or other suitable methods.

[0036] Throughout this application, the term "supported" has its general meaning in the field of heterogeneous catalysis. Generally, the term "supported" refers to a catalytically active species or its respective precursor attached to a support material. The support material may be inert or may participate in the catalytic reaction. General supported catalysts are prepared by an impregnation method or a coprecipitation method and optionally subsequent calcination.

[0037] Ceria-alumina composite: The ceria-alumina composite is a composite in which CeO2 is distributed on the surface and / or in the bulk of alumina as particles and / or nanoclusters. Each oxide may have its separate chemical and solid physical states. The surface CeO2 modification of alumina can be in the form of separated portions (particles or clusters) or in the form of a layer of ceria that partially or completely covers the surface of alumina.

[0038] Preferably, the amount of the ceria-alumina composite present in the first catalyst layer and the second catalyst layer is in the range of 5.0 to 80% by weight based on the total weight of the first catalyst layer and the second catalyst layer. More preferably, the amount of the ceria-alumina composite present in the first catalyst layer and the second catalyst layer is in the range of 10 to 60% by weight based on the total weight of the first catalyst layer and the second catalyst layer. Even more preferably, the amount of the ceria-alumina composite present in the first catalyst layer and the second catalyst layer is in the range of 15 to 40% by weight based on the total weight of the first catalyst layer and the second catalyst layer.

[0039] The amount of CeO2 (cerium oxide) in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is preferably 1.0 to 60% by weight based on the total weight of the ceria-alumina composite in each catalyst layer. More preferably, CeO2 in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is 5.0 to 50% by weight based on the total weight of the ceria-alumina composite in each catalyst layer. Even more preferably, CeO2 in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is 5.0 to 30% by weight based on the total weight of the ceria-alumina composite in each catalyst layer. And even more preferably, CeO2 in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is 8.0 to 20% by weight based on the total weight of the ceria-alumina composite in each catalyst layer.

[0040] The amount of Al2O3 (aluminum oxide) in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is preferably 40 to 99% by weight based on the total weight of the ceria-alumina composite in each catalyst layer. More preferably, the Al2O3 in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is 50 to 95% by weight based on the total weight of the ceria-alumina composite in each catalyst layer. Even more preferably, the Al2O3 in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is 70 to 95% by weight based on the total weight of the ceria-alumina composite in each catalyst layer. Most preferably, the Al2O3 in the ceria-alumina composite present in the first catalyst layer or the second catalyst layer is 80 to 92% by weight based on the total weight of the ceria-alumina composite in the first catalyst layer.

[0041] Preferably, the average particle size of ceria in the ceria-alumina composite is less than 200 nm. More preferably, the particle size is in the range of 5.0 nm to 50 nm. The particle size is determined by a transmission electron microscope.

[0042] The ceria-alumina composite present in the first catalyst layer or the second catalyst layer may contain a dopant selected from zirconia, lanthana, titania, hafnia, magnesia, calcia, strontian, barium or any combination thereof. The total amount of the dopant in the ceria-alumina composite is preferably in the range of 0.001 to 15% by weight based on the total weight of the ceria-alumina composite in each catalyst layer.

[0043] The ceria-alumina composite can be prepared by methods known to those skilled in the art, such as coprecipitation or surface modification. In these methods, a suitable cerium-containing precursor is contacted with a suitable aluminum-containing precursor, and then the mixture thus obtained is converted into a ceria-alumina composite. Suitable cerium-containing precursors are, for example, water-soluble cerium salts and colloidal ceria suspensions. Ceria-alumina can also be prepared by atomic layer deposition, in which a ceria compound is selectively reacted with the alumina surface to form ceria on the alumina surface after calcination. This deposition / calcination step may be repeated until a layer of the desired thickness is reached. Suitable aluminum-containing precursors are, for example, aluminum oxides such as gibbsite, boehmite, gamma-alumina, delta-alumina, or theta-alumina, or combinations thereof. Then, the conversion of the mixture thus obtained into a ceria-alumina composite can be achieved by a calcination step of the mixture.

[0044] Ceria-zirconia mixed oxide (CZO): The term "mixed metal oxide" refers to a mixed metal oxide containing oxygen anions and at least two different metal cations. In the ceria-zirconia mixed oxide, cerium cations and zirconium cations are distributed within the oxide lattice structure. The terms "composite oxide" and "mixed oxide" can be used interchangeably. Since the metal cations are distributed within the oxide lattice structure, these structures are generally also referred to as solid solutions.

[0045] Preferably, the amount of the ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer is 20 to 80% by weight based on the total weight of the first catalyst layer and the second catalyst layer. More preferably, the amount of the ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer is in the range of 30 to 70% by weight based on the total weight of the first catalyst layer and the second catalyst layer. Most preferably, the amount of the ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer is in the range of 40 to 60% by weight based on the total weight of the first catalyst layer and the second catalyst layer.

[0046] Preferably, the ceria (calculated as CeO2) of the ceria-zirconia mixed oxide present in the first layer or the second layer is present in an amount of 10 to 60% by weight based on the total weight of the ceria-zirconia mixed oxide present in each layer, and the zirconia (calculated as ZrO2) of the ceria-zirconia mixed oxide present in the first layer or the second layer is present in an amount of 40 to 90% by weight based on the total weight of the ceria-zirconia mixed oxide present in each layer.

[0047] More preferably, the ceria (calculated as CeO2) of the ceria-zirconia mixed oxide present in the first layer or the second layer is present in an amount of 20 to 50% by weight based on the total weight of the ceria-zirconia mixed oxide in each layer, and the zirconia (calculated as ZrO2) of the ceria-zirconia mixed oxide present in the first layer or the second layer is present in an amount of 50 to 80% by weight based on the total weight of the ceria-zirconia mixed oxide in each layer.

[0048] Even more preferably, the ceria (calculated as CeO2) of the ceria-zirconia mixed oxide present in the first layer or the second layer is present in an amount of 30 to 50% by weight based on the total weight of the ceria-zirconia mixed oxide in each layer, and the zirconia (calculated as ZrO2) of the ceria-zirconia mixed oxide present in the first layer or the second layer is present in an amount of 50 to 70% by weight based on the total weight of the ceria-zirconia mixed oxide in each layer.

[0049] The ceria-zirconia mixed oxide functions as an oxygen storage component. The term "oxygen storage component" (OSC) refers to an entity that has multiple valence states and can react actively with reductants such as carbon monoxide (CO) and / or hydrogen under reducing conditions and then react with oxidants such as oxygen or nitrogen oxides under oxidizing conditions.

[0050] In a preferred embodiment, the ceria-zirconia mixed oxide present in the first layer or the second layer contains a dopant selected from lanthanum, titania, hafnia, magnesia, calcia, strontia, barium, yttrium, hafnium, praseodymium, neodymium, or any combination thereof. The dopant metal may be incorporated into the crystal structure of the composite metal oxide in cationic form, deposited on the surface of the composite metal oxide in oxide form, or present in the form of a blend of a mixture of microscale dopants and the composite metal oxide in oxide form, i.e., in a composite form having the composite metal oxide. Preferably, the dopant is included in an amount of 1.0 to 20 wt%, or more preferably 5.0 to 15 wt%, based on the total weight of the ceria-zirconia mixed oxide present in each layer.

[0051] Alumina: The alumina present in the first catalyst layer and the second catalyst layer is preferably gamma alumina or activated alumina. It typically exhibits a BET surface area of more than 60 square meters / gram ("m2 / g"), often up to about 200 m 2 / g or more for fresh materials. Activated alumina is usually a mixture of the gamma and delta phases of alumina, but may also contain significant amounts of the eta, kappa, and theta alumina phases. Preferably, the activated alumina is high bulk density gamma-alumina, low or medium bulk density macroporous gamma-alumina, low bulk density macroporous boehmite, or gamma-alumina.

[0052] Preferably, the amount of alumina present in the first catalyst layer and the second catalyst layer is in the range of 1.0 to 40% by weight based on the total weight of the first catalyst layer and the second catalyst layer. More preferably, the amount of alumina present in the first catalyst layer and the second catalyst layer is in the range of 5.0 to 30% by weight based on the total weight of the first catalyst layer and the second catalyst layer. Most preferably, the amount of alumina present in the first catalyst layer and the second catalyst layer is in the range of 5.0 to 20% by weight based on the total weight of the first catalyst layer and the second catalyst layer.

[0053] The alumina present in the first catalyst layer and the second catalyst layer is preferably doped with a dopant selected from barium, lanthana, zirconia, neodymian, yttria, ceria or titania, and the amount of the dopant is preferably 1.0 to 30% by weight based on the total weight of the alumina and the dopant present in the first catalyst layer and the second catalyst layer. More preferably, the alumina doped with the dopant is selected from lanthana-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, lanthana-zirconia-alumina, barium-alumina, barium-lanthana-alumina, barium-lanthana-neodymia-alumina, or any combination thereof.

[0054] Substrate: The substrate of the catalyst article claimed in the present application may be composed of any material typically used for preparing automotive catalysts. In a preferred embodiment, the substrate is a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, or a woven fiber substrate. In a more preferred embodiment, the substrate is a ceramic or metal monolithic honeycomb structure.

[0055] The substrate provides a plurality of wall surfaces to which the catalyst layer or washcoat described above in this specification is applied and adhered, thereby acting as a carrier for the catalyst material.

[0056] Preferred metal substrates include heat-resistant metals and metal alloys such as titanium and stainless steel, and other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium, and / or aluminum, and the total amount of these metals may advantageously be 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, for example, at a high temperature of 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 the adhesion of the washcoat layer to the metal surface.

[0057] Preferred ceramic materials used to construct the substrate include any suitable refractory materials, such as cordierite, mullite, cordierite-alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminosilicate, etc.

[0058] Any suitable substrate such as a monolithic flow-through substrate having a plurality of fine parallel gas flow paths extending from an inlet surface to an outlet surface of the substrate so that the flow path is open to the flow of fluid may be used. The passage, which is essentially a straight path from the inlet to the outlet, is defined by walls coated with a catalyst material as a washcoat such that the gas flowing through the passage contacts the catalyst material. The flow paths of the monolithic substrate are thin-walled channels of any suitable cross-sectional shape such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. Such a structure includes gas inlet openings (i.e., "cells") of about 60 to about 1200 or more, more typically about 300 to 900 cells per square inch of cross section (cpsi). The wall thickness of the flow-through substrate can vary, but a typical range is 0.002 to 0.1 inches. A representative commercially available flow-through substrate is a cordierite substrate having 400 cpsi and a wall thickness of 6 mils, or 600 cpsi and a wall thickness of 4 mils. However, it will be understood that the present invention is not limited to a particular substrate type, material, or shape. In an alternative embodiment, the substrate may be a wall-flow substrate, each passage being blocked by a non-porous plug at one end of the substrate body and alternating passages being blocked at opposite end faces. This requires the gas to flow through the porous walls of the wall-flow substrate and reach the outlet. Such a monolithic substrate can contain up to about 700 cpsi or more, for example about 100 to 400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of the cells can be various as described above. The wall-flow substrate typically has a wall thickness of 0.002 to 0.1 inches. A representative commercially available wall-flow substrate is constructed from porous cordierite, examples of which have 200 cpsi and a wall thickness of 10 mils or 300 cpsi and a wall thickness of 8 mils, and a wall porosity of 45 - 65%. Other ceramic materials such as aluminum titanate, silicon carbide, and silicon nitride are also used as wall-flow filter substrates. However, it will be understood that the present invention is not limited to a particular substrate type, material, or shape.When the substrate is a wall-flow substrate, it should be noted that in addition to being disposed on the surface of the wall, the catalyst composition 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.

[0059] Figures 4A and 4B illustrate an exemplary substrate 2 in the form of a flow-through substrate coated with a washcoat composition / catalyst layer described herein. Referring to Figure 4A, the exemplary substrate 2 has a cylindrical shape and has a cylindrical outer surface 4, an upstream end face 6, and a corresponding downstream end face 8 that is identical to the end face 6. The substrate 2 has a plurality of fine and parallel gas flow paths 10 formed therein. As can be seen from Figure 4B, the flow paths 10 are formed by walls 12 and extend through the substrate 2 from the upstream end face 6 to the downstream end face 8, and the passages 10 are not blocked so that a fluid, such as a gas flow, can flow longitudinally through the substrate 2 via the gas flow paths 10. As can be more readily seen in Figure 4B, the walls 12 are dimensioned and configured such that the gas flow paths 10 have a substantially regular polygonal shape. As shown, the washcoat composition / catalyst layer can be applied in a plurality of separate layers, if desired. In the illustrated embodiment, the washcoat consists of a separate first washcoat layer 14 adhered to the wall 12 of the substrate member and a second separate washcoat layer 16 coated on the first washcoat layer 14. In one embodiment, the invention claimed in the present application can also be implemented with two or more (e.g., three or four) washcoat layers and is not limited to the illustrated two-layer embodiment.

[0060] Figure 5 illustrates an exemplary substrate 2 in the form of a wall flow filter substrate coated with the washcoat composition described herein. As can be seen from Figure 5, 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 by an inlet plug 58 and at the outlet end by an outlet plug 60 to form a checkerboard pattern facing each other at the inlet 54 and the outlet 56. The gas flow 62 enters through an unblocked channel inlet 64, is stopped by the outlet plug 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 plug 58. The porous wall flow filter used in the present invention is catalyzed in that the walls of the above elements have one or more catalyst materials thereon or contain one or more catalyst materials therein. The catalyst material may be present only on the inlet side of the element wall, only on the outlet side, both on the inlet side and the outlet side, or the wall itself may consist of all or part of the catalyst material. The present invention includes using one or more layers of catalyst material on the inlet wall and / or the outlet wall of the element.

[0061] Washcoat on the substrate: The substrate is coated in a zone pattern by a catalyst layer, namely a first catalyst layer and a second catalyst layer. The first zone is coated with the first catalyst layer, and the second zone is coated with the second catalyst layer. The first catalyst layer covers 60 - 100% of the area of the first zone, and the second catalyst layer covers 60 - 100% of the area of the second zone.

[0062] The first zone occupies the inflow end portion of the substrate, and the second zone occupies the outflow end portion of the substrate.

[0063] The first zone and the second zone together cover 50 - 100% of the length of the substrate. Preferably, the first zone and the second zone together cover 90 - 100% of the length of the substrate, and more preferably, the first zone and the second zone together cover the entire length of the substrate or the entire accessible surface area of the substrate.

[0064] The term "accessible surface" refers to the surface of a substrate that can be covered by conventional coating techniques used in the field of catalyst preparation, such as impregnation techniques.

[0065] Preferably, the first zone covers 10 to 90% of the total length of the substrate from the inlet, and the second zone covers 90 to 10% of the total length of the substrate from the outlet, but the first zone and the second zone together cover 20 to 100% of the length of the substrate. More preferably, the first zone covers 20 to 80% of the total length of the substrate from the inlet, and the second zone covers 80 to 20% of the total length of the substrate from the outlet, but the first zone and the second zone together cover 40 to 100% of the length of the substrate. Even more preferably, the first zone covers 30 to 70% of the total length of the substrate from the inlet, and the second zone covers 70 to 30% of the total length of the substrate from the outlet, but the first zone and the second zone together cover 60 to 100% of the length of the substrate. Even most preferably, the first zone covers 40 to 50% of the total length of the substrate from the inlet, and the second zone covers 50 to 40% of the total length of the substrate from the outlet, but the first zone and the second zone together cover 80 to 100% of the length of the substrate.

[0066] The first zone: The first zone is coated with a first catalyst layer containing platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both.

[0067] Preferably, the first catalyst layer covers 60 to 100% of the area of the first zone. More preferably, the first catalyst layer covers 70 to 100% of the area of the first zone. Most preferably, the first catalyst layer covers 80 to 100% of the area of the first zone.

[0068] Preferably, the amount of platinum in the first catalyst layer is 0.02 to 3.0% by weight based on the total weight of the first catalyst layer. More preferably, the amount of platinum in the first catalyst layer is 0.02 to 2.5% by weight based on the total weight of the first catalyst layer. Even more preferably, the amount of platinum in the first catalyst layer is 0.05 to 2.0% by weight based on the total weight of the first catalyst layer.

[0069] The amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is preferably 60 to 100% by weight based on the total weight of platinum in the first and second catalyst layers. More preferably, the amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 70 to 100% by weight based on the total weight of platinum in the first and second catalyst layers. Most preferably, the amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 80 to 100% by weight based on the total weight of platinum in the first and second catalyst layers.

[0070] The first catalyst layer also contains rhodium supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both. Preferably, the total amount of rhodium in the first catalyst layer is 0.01 to 1.0% by weight based on the total weight of the first catalyst layer. More preferably, the total amount of rhodium in the first catalyst layer is 0.01 to 0.5% by weight based on the total weight of the first catalyst layer.

[0071] Preferably, the amount of rhodium supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 50 to 100% by weight based on the total weight of rhodium in the first and second catalyst layers. More preferably, the amount of rhodium supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 75 to 100% by weight based on the total weight of rhodium in the first and second catalyst layers.

[0072] In addition, the first catalyst layer preferably contains palladium. Preferably, the palladium is supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both. More preferably, the palladium is supported on a ceria-zirconia mixed oxide. Preferably, the amount of palladium in the first layer is 0 to 50 wt% based on the total weight of palladium present in the first and second layers. More preferably, the amount of palladium in the first layer is 0.1 to 30 wt% based on the total weight of palladium present in the first and second layers.

[0073] Even more preferably, the amount of palladium in the first layer is 0.1 to 25 wt% based on the total weight of palladium present in the first and second layers.

[0074] The amount of the ceria-zirconia mixed oxide in the first catalyst layer is preferably in the range of 20 to 80 wt% based on the total weight of the first catalyst layer. More preferably, the amount of the ceria-zirconia mixed oxide in the first catalyst layer is in the range of 25 to 70 wt% based on the total weight of the first catalyst layer. Even more preferably, the amount of the ceria-zirconia mixed oxide in the first catalyst layer is in the range of 30 to 60 wt% based on the total weight of the first catalyst layer.

[0075] The ceria-zirconia mixed oxide preferably contains ceria in an amount of about 10 to 60% by weight, calculated as CeO2, based on the total weight of the ceria-zirconia mixed oxide present in the first catalyst layer, and zirconia in an amount of about 40 to about 90% by weight, calculated as ZrO2, based on the total weight of the ceria-zirconia mixed oxide present in the first catalyst layer. More preferably, the ceria-zirconia mixed oxide contains ceria in an amount of about 20 to 50% by weight, calculated as CeO2, based on the total weight of the ceria-zirconia mixed oxide present in the first catalyst layer, and zirconia in an amount of about 50 to about 80% by weight, calculated as ZrO2, based on the total weight of the ceria-zirconia mixed oxide present in the first catalyst layer. Even more preferably, the ceria (calculated as CeO2) of the ceria-zirconia mixed oxide present in the first layer is present in an amount of 30 to 50% by weight based on the total weight of the ceria-zirconia mixed oxide in the first catalyst layer, and the zirconia (calculated as ZrO2) of the ceria-zirconia mixed oxide present in the first layer is present in an amount of 50 to 70% by weight based on the total weight of the ceria-zirconia mixed oxide in the first layer.

[0076] Preferably, the amount of the ceria-alumina composite in the first catalyst layer is in the range of 10 to 80% by weight based on the total weight of the first catalyst layer. More preferably, the amount of the ceria-alumina composite in the first catalyst layer is in the range of 20 to 70% by weight based on the total weight of the first catalyst layer. Even more preferably, the amount of the ceria-alumina composite in the first catalyst layer is in the range of 30 to 60% by weight based on the total weight of the first catalyst layer.

[0077] Preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the first layer is 1.0 to 60% by weight based on the total weight of the ceria-alumina composite present in the first catalyst layer. More preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the first layer is 5.0 to 50% by weight based on the total weight of the ceria-alumina composite present in the first catalyst layer. Even more preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the first layer is 5.0 to 30% by weight based on the total weight of the ceria-alumina composite present in the first catalyst layer. Even more preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the first layer is 8.0 to 20% by weight based on the total weight of the ceria-alumina composite present in the first catalyst layer.

[0078] Second zone: The second zone is coated with a second catalyst layer comprising palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof. Preferably, the second catalyst layer covers 60 to 100% of the area of the second zone. More preferably, the second catalyst layer covers 70 to 100% of the area of the second zone. Most preferably, the second catalyst layer covers 80 to 100% of the area of the second zone.

[0079] Preferably, the amount of palladium is in the range of 0.02 to 5.0% by weight based on the total weight of the second catalyst layer. More preferably, the amount of palladium is in the range of 0.02 to 4.0% by weight based on the total weight of the second catalyst layer. The amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is preferably 50 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer. More preferably, the amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is 60 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer. Most preferably, the amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is 75 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer.

[0080] The second catalyst layer preferably contains rhodium supported on a ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof.

[0081] Preferably, the amount of rhodium is in the range of 0.01 to 1.0% by weight based on the total weight of the second catalyst layer. More preferably, the amount of rhodium is in the range of 0.03 to 0.5% by weight based on the total weight of the second catalyst layer.

[0082] Preferably, the amount of rhodium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is 0 to 50% by weight based on the total weight of rhodium in the first catalyst layer and the second catalyst layer. More preferably, the amount of rhodium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is 0 to 25% by weight based on the total weight of rhodium in the first catalyst layer and the second catalyst layer.

[0083] The second catalyst layer optionally contains platinum supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof. Preferably, the amount of platinum supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof is 0 to 50 wt% based on the total weight of platinum present in the first and second layers. More preferably, the amount of platinum supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof is 0.1 to 30 wt% based on the total weight of platinum present in the first and second layers. Even more preferably, the amount of platinum supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof is 0.1 to 25 wt% based on the total weight of platinum present in the first and second layers.

[0084] The amount of the ceria-zirconia mixed oxide in the second catalyst layer is in the range of 20 to 80 wt% based on the total weight of the second catalyst layer. Preferably, the amount of the ceria-zirconia mixed oxide in the second catalyst layer is in the range of 25 to 70 wt% based on the total weight of the second catalyst layer. More preferably, the amount of the ceria-zirconia mixed oxide in the second catalyst layer is in the range of 30 to 60 wt% based on the total weight of the second catalyst layer.

[0085] The ceria-zirconia mixed oxide preferably contains ceria in an amount of about 10 to 60% by weight, calculated as CeO2, based on the total weight of the ceria-zirconia mixed oxide present in the second catalyst layer, and zirconia in an amount of about 40 to about 90% by weight, calculated as ZrO2, based on the total weight of the ceria-zirconia mixed oxide present in the second catalyst layer. More preferably, the ceria-zirconia mixed oxide contains ceria in an amount of about 20 to 50% by weight, calculated as CeO2, based on the total weight of the ceria-zirconia mixed oxide present in the second catalyst layer, and zirconia in an amount of about 50 to about 80% by weight, calculated as ZrO2, based on the total weight of the ceria-zirconia mixed oxide present in the second catalyst layer. Even more preferably, the ceria (calculated as CeO2) of the ceria-zirconia mixed oxide present in the second layer is present in an amount of 30 to 50% by weight based on the total weight of the ceria-zirconia mixed oxide in the second catalyst layer, and the zirconia (calculated as ZrO2) of the ceria-zirconia mixed oxide present in the layer is present in an amount of 50 to 70% by weight based on the total weight of the ceria-zirconia mixed oxide in the second catalyst layer.

[0086] The amount of alumina in the second catalyst layer is preferably in the range of 5.0 to 50% by weight based on the total weight of the second catalyst layer. More preferably, the amount of alumina in the second catalyst layer is in the range of 10 to 40% by weight based on the total weight of the second catalyst layer.

[0087] Preferably, the amount of the ceria-alumina composite in the second catalyst layer is in the range of 1.0 to 40% by weight based on the total weight of the second catalyst layer. More preferably, the amount of the ceria-alumina composite in the second catalyst layer is in the range of 1.0 to 30% by weight based on the total weight of the first catalyst layer. Even more preferably, the amount of the ceria-alumina composite in the second catalyst layer is in the range of 1.0 to 20% by weight based on the total weight of the second catalyst layer.

[0088] Preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the second layer is 1.0 to 60% by weight based on the total weight of the ceria-alumina composite present in the second catalyst layer. More preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the second layer is 5.0 to 50% by weight based on the total weight of the ceria-alumina composite present in the second catalyst layer. More preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the second layer is 5.0 to 30% by weight based on the total weight of the ceria-alumina composite present in the second catalyst layer. Even more preferably, the amount of ceria calculated as CeO2 in the ceria-alumina composite present in the second layer is 8.0 to 20% by weight based on the total weight of the ceria-alumina composite present in the second catalyst layer.

[0089] Preferably, the weight ratio of rhodium supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer to rhodium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is in the range of 1.5:1 to 4:1.

[0090] Overcoat: The first zone further includes an overcoat deposited on at least a portion of the first zone. The overcoat includes a porous refractory oxide and, optionally, at least one base metal oxide.

[0091] As used herein, "porous refractory oxide" refers to a porous metal-containing oxide material that exhibits chemical and physical stability at high temperatures. Exemplary refractory oxides include alumina, silica, zirconia, titania, ceria, and physical mixtures or chemical combinations thereof, including atomically doped combinations, and active compounds such as high surface area or activated alumina.

[0092] Preferably, the porous refractory oxide is stabilized or unstabilized aluminum oxide.

[0093] Preferably, the overcoat loading divided by the substrate volume coated by the overcoat is less than 1 gram per cubic inch.

[0094] Preferably, the overcoat essentially does not contain noble metals and optionally contains an oxygen storage component. The term "essentially does not contain noble metals" means that no noble metals are added to the overcoat. It may be present as an impurity in an amount less than 0.001 wt%. Preferably, the base metal oxide is an alkaline earth metal oxide or a rare earth metal oxide. The alkaline earth metal oxide is preferably selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, or combinations thereof. More preferably, the alkaline earth metal oxide is selected from barium oxide and strontium oxide. Most preferably, the alkaline earth metal oxide is barium oxide.

[0095] Preferably, the rare earth metal oxide is an oxide of at least one rare earth metal selected from Ce, Pr, Nd, Eu, Sm, Yb, and La, or a mixture thereof. More preferably, the rare earth metal oxide is an oxide of at least one rare earth metal selected from Ce, Pr, and La, or a mixture thereof.

[0096] Preferably, the length of the overcoat is 50% or less of the total length of the substrate. More preferably, the length of the overcoat is 35% or less of the total length of the substrate. Most preferably, the length of the overcoat is 32% or less of the total length of the substrate.

[0097] Preparation of the Catalyst Article: In another aspect of the invention, a process for preparing the catalyst article described above herein is also provided. The process includes the following steps: Prepare a first catalyst layer slurry comprising platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof. Prepare a second catalyst layer slurry comprising palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof. Coat the first catalyst layer slurry on the inlet end portion of the substrate to obtain a first zone. Coat the second catalyst layer slurry on the outlet end portion of the substrate to obtain a second zone. Then, subject the substrate to calcination at a temperature in the range of 400 to 700 °C.

[0098] The step of preparing the slurry includes techniques selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

[0099] For the synthesis of heterogeneous materials, i.e., catalysts, an incipient wetness impregnation technique, also generally referred to as capillary impregnation or dry impregnation, is typically used. Typically, a metal precursor is dissolved in an aqueous or organic solution, and then the metal-containing solution is added to a catalyst support having a pore volume equal to the volume of the added solution. Capillary action draws the solution into the pores of the support. Solution added in excess of 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 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.

[0100] The support particles are typically dry enough to absorb substantially all of the solution to form a wet solid. When rhodium is the active metal, an aqueous solution of a water-soluble compound or complex of the active metal such as rhodium chloride, rhodium nitrate (e.g., Rh(NO)3 and its salts), rhodium acetate, or combinations thereof; when palladium is the active metal, palladium nitrate, tetraamine palladium nitrate, palladium acetate, or combinations thereof; and when platinum is the active metal, platinum nitrate, platinum acetate, or combinations thereof are typically utilized. After treating the support particles with the active metal solution, the particles are dried, for example, by heat-treating the particles at a high temperature (e.g., 100 - 150 °C) for a certain period of time (e.g., 1 - 3 hours), and then calcined to convert the active metal into a more catalytically active form. An exemplary calcination process includes heat-treating at a temperature of about 400 - 550 °C in air for 10 minutes - 3 hours. The above process may be repeated as necessary to achieve the desired level of active metal impregnation.

[0101] Substrate coating: The above 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, an associative thickener, and / or a surfactant (including anionic, cationic, nonionic, or amphoteric surfactants) in the form of alumina, silica, zirconium diacetate, colloidal zirconia, or zirconium hydroxide. 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 load. To adjust the pH accordingly, an acidic or basic species is added to the slurry. For example, in some embodiments, the pH of the slurry is adjusted by the addition of ammonium hydroxide, an aqueous nitric acid solution, or acetic acid. A typical pH range for the slurry is from about 3.0 to 12. The slurry can be milled to reduce the particle size and promote mixing of the particles. Milling is achieved with a ball mill, a continuous mill, or other similar equipment, and the solid content of the slurry may be, for example, about 20 to 60 wt%, more specifically about 20 to 40 wt%. In one embodiment, the slurry after milling has a D 90 particle size characterized by. D 90 is determined using a dedicated particle size analyzer. The equipment used in this example measures the particle size in a small volume slurry using laser diffraction. Typically, D 90 in micrometers means the diameter below which 90% of the number of particles has that value.

[0102] The slurry is coated onto the catalyst substrate using any washcoat technology known in the art. For example, the catalyst substrate is dipped one or more times into the slurry or is otherwise coated with the slurry. The coated substrate is then dried at an elevated temperature (e.g., 100 - 150 °C) for a period of time (e.g., 10 minutes - 3.0 hours) and then calcined by heating, for example, at 400 - 700 °C, typically for about 10 minutes - about 3 hours. After drying and calcining, the final washcoat coating layer is considered to be essentially solvent-free.

[0103] After calcination, the catalyst loading obtained by the washcoat technology described above can be determined by calculating the difference between the coated weight and the uncoated weight of the substrate. As will be apparent to those skilled in the art, the catalyst loading can be varied by changing the slurry rheology. In addition, the coating / drying / calcining process for producing the washcoat may be repeated as necessary to build up the coating to the desired loading level or thickness, which means that more than one washcoat may be applied.

[0104] The coated substrate may be aged by subjecting it to a heat treatment. For example, aging is carried out at a temperature of about 850 °C - about 1050 °C for 50 - 300 hours in the presence of steam under gasoline engine exhaust conditions. Thus, according to the present invention, an aged catalyst article is provided. Effective support materials such as ceria-alumina composites maintain a high percentage (e.g., about 50 - 100%) of their pore volume during aging (e.g., aging at about 850 °C - about 1050 °C for about 50 - 300 hours in the presence of steam).

[0105] Exhaust treatment system: In another aspect of the present invention, there is also provided an exhaust gas treatment system for an internal combustion engine, the system including the catalyst article described above herein. In one exemplary solution, the system includes the catalyst article according to the invention claimed in the present application and an additional platinum group metal-based three-way conversion (TWC) catalyst article. The catalyst article of the present invention may be disposed at a close-coupled position. The close-coupled catalyst is disposed near the engine so as to reach the reaction temperature as soon as possible. Generally, the close-coupled catalyst is disposed within 3 feet of the engine, more specifically within 1 foot, and even more specifically less than 6 inches from the engine. The close-coupled catalyst is often directly attached to the exhaust gas manifold. Since the close-coupled catalyst is close to the engine, it needs to be stable at high temperatures. The catalyst article of the present invention can also be used as part of an integrated exhaust system including one or more additional components for treating exhaust gas emissions. For example, an exhaust system, also known as an emissions treatment system, may further include a close-coupled TWC catalyst, an underfloor TWC catalyst, a catalysed 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.

[0106] In another aspect of the present invention, there is also provided a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, the method including contacting the exhaust stream with the catalyst article according to the present invention or the exhaust gas treatment system according to the present invention. The present invention also provides a method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, the method including contacting the gaseous exhaust stream with the catalyst article according to the present invention or the exhaust gas treatment system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0107] In another aspect of the invention, there is also provided the use of a catalytic article or an exhaust gas treatment system according to the invention claimed herein for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides.

[0108] The present invention is further illustrated by the following set of embodiments, as well as combinations of embodiments arising from the dependencies and cross-references as shown. In particular, in each case where the scope of an embodiment is referred to, for example, in the context of terms such as "a method according to any one of Embodiments 1 to 4", all embodiments within this scope are meant to be explicitly disclosed to those skilled in the art, that is, it should be noted that this expression of the term is understood by those skilled in the art to be synonymous with "a method according to any one of Embodiments 1, 2, 3, and 4". Further, it should be clearly noted that the following series of embodiments represent a preferably structured part of the specification directed to the general and preferred aspects of the present invention, rather than a series of claims defining the scope of protection.

[0109] Embodiment 1: The present invention provides a) a substrate, b) a first zone coated with a first catalyst layer, c) a second zone coated with a second catalyst layer, The first catalyst layer comprises platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof. The second catalyst layer comprises palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof. The first zone occupies the inlet end portion of the substrate, and the second zone occupies the outlet end portion of the substrate.

[0110] Embodiment 2: The catalyst article according to Embodiment 1, wherein the first catalyst layer further comprises palladium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, or both.

[0111] Embodiment 3: The catalyst article according to Embodiment 1 or 2, wherein the second catalyst layer further comprises platinum supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof.

[0112] Embodiment 4: The catalyst article according to any one of Embodiments 1 to 3, wherein the total loading of the first catalyst layer and the second catalyst layer divided by the substrate volume is less than 3.2 grams per cubic inch.

[0113] Embodiment 5: In the catalyst article according to any one of Embodiments 1 to 4, the amount of platinum in the first catalyst layer and the second catalyst layer is in the range of 0.02 to 3.0 wt% based on the total weight of the first catalyst layer and the second catalyst layer, the amount of palladium in the first catalyst layer and the second catalyst layer is in the range of 0.02 to 5.0 wt% based on the total weight of the first catalyst layer and the second catalyst layer, and the amount of rhodium in the first catalyst layer and the second catalyst layer is in the range of 0.01 to 1.0 wt% based on the total weight of the first catalyst layer and the second catalyst layer.

[0114] Embodiment 6: The total amount of platinum supported on ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 80 to 100% by weight based on the total weight of platinum in the first catalyst layer and the second catalyst layer, and the total amount of palladium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is 75 to 100% by weight based on the total weight of palladium in the first catalyst layer and the second catalyst layer, and the weight ratio of rhodium supported on ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer to rhodium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is in the range of 1.5:1 to 4:1. The catalyst article according to any one of Embodiments 1 to 5.

[0115] Embodiment 7: The first zone further includes an overcoat deposited on at least a part of the first zone, and the overcoat includes a porous refractory oxide and optionally at least one base metal oxide. The catalyst article according to any one of Embodiments 1 to 6.

[0116] Embodiment 8: The overcoat essentially does not contain a noble metal and optionally contains an oxygen storage component. The catalyst article according to Embodiment 7.

[0117] Embodiment 9: The length of the overcoat is 50% or less of the total length of the substrate. The catalyst article according to Embodiment 7 or 8.

[0118] Embodiment 10: The loading of the overcoat divided by the volume of the substrate coated with the overcoat is less than 1 gram per cubic inch. The catalyst article according to any one of Embodiments 7 to 9.

[0119] Embodiment 11: The porous refractory oxide is stabilized or unstabilized aluminum oxide. The catalyst article according to any one of Embodiments 7 to 10.

[0120] Embodiment 12: The base metal oxide is an alkaline earth metal oxide or a rare earth metal oxide, the alkaline earth metal oxide is selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, or a combination thereof, and the rare earth metal oxide is an oxide of at least one rare earth metal selected from Ce, Pr, Nd, Eu, Sm, Yb, and La, or a mixture thereof. The catalyst article according to any one of Embodiments 7 to 11.

[0121] Embodiment 13: The first zone covers 10 to 90% of the total substrate length from the inlet end portion, the second zone covers 10 to 90% of the total substrate length from the outlet end portion, the first catalyst layer covers 60 to 100% of the area of the first zone, and the second catalyst layer covers 60 to 100% of the area of the second zone. The catalyst article according to any one of Embodiments 1 to 12.

[0122] Embodiment 14: The first zone covers 40 to 60% of the total substrate length from the inlet end portion, and the second zone covers 60 to 40% of the total substrate length from the outlet end portion. The catalyst article according to any one of Embodiments 1 to 13.

[0123] Embodiment 15: The amount of ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer is 40 to 60% by weight based on the total weight of the first catalyst layer and the second catalyst layer. The catalyst article according to any one of Embodiments 1 to 14.

[0124] Embodiment 16: The amount of alumina present in the first catalyst layer and the second catalyst layer is in the range of 5 to 20% by weight based on the total weight of the first catalyst layer and the second catalyst layer. The catalyst article according to any one of Embodiments 1 to 15.

[0125] Embodiment 17: The alumina is doped with a dopant selected from barium, lanthanum, zirconia, neodymium, yttria, ceria or titania, and the amount of the dopant is 1.0 to 30% by weight based on the total weight of the alumina and the dopant present in the first catalyst layer and the second catalyst layer, the catalyst article according to any one of Embodiments 1 to 16.

[0126] Embodiment 18: The alumina is selected from alumina, lanthanum-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, ceria-alumina, lanthanum-zirconia-alumina, barrier-alumina, barrier-lanthanum-alumina, barrier-lanthanum-neodymium-alumina, or any combination thereof, the catalyst article according to any one of Embodiments 1 to 17.

[0127] Embodiment 19: The amount of the ceria-alumina composite present in the first catalyst layer and the second catalyst layer is in the range of 15 to 40% by weight based on the total weight of the first catalyst layer and the second catalyst layer, the catalyst article according to any one of Embodiments 1 to 18.

[0128] Embodiment 20: The amount of ceria calculated as CeO2 in the ceria-alumina composite is 5.0 to 30% by weight based on the total weight of the ceria-alumina composite, the catalyst article according to any one of Embodiments 1 to 19.

[0129] Embodiment 21: The ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer contains ceria calculated as CeO2 in an amount of 15 to 50% by weight based on the total weight of the ceria-zirconia mixed oxide in each catalyst layer, and zirconia calculated as ZrO2 in an amount of 50 to about 85% by weight based on the total weight of the ceria-zirconia mixed oxide in each catalyst layer, the catalyst article according to any one of Embodiments 1 to 20.

[0130] Embodiment 22: The catalyst article according to any one of Embodiments 1 to 21, wherein the ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer contains a dopant selected from lanthanum, titania, hafnia, magnesia, calcia, strontia, barium, yttrium, hafnium, praseodymium, neodymium, or any combination thereof.

[0131] Embodiment 23: The catalyst article according to any one of Embodiments 1 to 22, wherein the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, or a woven fiber substrate.

[0132] Embodiment 24: The present invention provides a process for preparing the catalyst article according to any one of Embodiments 1 to 23, the process comprising: - preparing a first catalyst layer slurry comprising platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, alumina, or any combination thereof; - preparing a second catalyst layer slurry comprising palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite, or a combination thereof; - coating the first catalyst layer slurry on the inlet end portion of the substrate to obtain a first zone; - coating the second catalyst layer slurry on the outlet end portion of the substrate to obtain a second zone; - subjecting the substrate to calcination at a temperature in the range of 400 to 700 °C, The step of preparing the slurry includes a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

[0133] Embodiment 25: The present invention provides an exhaust gas treatment system for an internal combustion engine, the system comprising a catalytic article as described in any of Embodiments 1-23.

[0134] Embodiment 26: The present invention provides a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, the method comprising contacting the exhaust stream with a catalytic article as described in any of Embodiments 1-23 or an exhaust gas treatment system as described in Embodiment 25.

[0135] Embodiment 27: The present invention provides a method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust gas stream, the method comprising contacting the gaseous exhaust gas stream with a catalytic article as described in any of Embodiments 1-23 or an exhaust gas treatment system as described in Embodiment 25 to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0136] Embodiment 28: The present invention provides the use of a catalytic article as described in any of Embodiments 1-23 or an exhaust gas treatment system as described in Embodiment 25 for purifying a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides.

[0137] Aspects of the invention claimed in this application are more fully illustrated by the following examples, which are described to illustrate specific aspects of the invention and should not be construed as limiting them.

[0138] Example 1: Comparative Catalytic Article A Comparative Catalytic Article A is a zone-type two-layer Pt / Pd / Rh catalytic article having a PGM loading of 120 g / ft 3 coated on a cylindrical monolith cordierite substrate having a diameter of 4.66 inches and a length of 3.81 inches, a cell density of 800 cpsi, and a wall thickness of 3 mils (Pt / Pd / Rh = 58 / 58 / 4).

[0139] Bottom layer inlet zone: This zone has a PGM loading of 104.4 g / ft 3 (Pt / Pd / Rh = 0 / 104.4 / 0) and covers 50% of the substrate length from the inlet to the middle. A slurry containing approximately 25.4 wt% alumina, 62.5 wt% stabilized ceria-zirconia mixed oxide (OSC with approximately 40 wt% ceria), barium acetate that yields 7.8 wt% BaO, zirconium acetate that yields 2.0 wt% ZrO2, and palladium nitrate that yields 2.36 wt% Pd was coated onto the substrate. The washcoat loading of the bottom layer inlet zone was approximately 2.56 g / in 3 after calcination at 550 °C for 1 hour in air.

[0140] Bottom layer outlet zone: This zone has a PGM loading of 127.6 g / ft 3 (Pt / Pd / Rh = 116 / 11.6 / 0) and covers 50% of the substrate length from the outlet to the middle. A slurry containing approximately 33.0 wt% ceria-alumina composite (with approximately 8 wt% ceria), 54.4 wt% stabilized ceria-zirconia mixed oxide (OSC with approximately 40% ceria), barium acetate that yields 7.8 wt% BaO, colloidal alumina binder that yields 1.9 wt% Al2O3, platinum-amine complex that yields 2.61 wt% Pt, and palladium nitrate that yields 0.26 wt% Pd was coated onto the substrate. The washcoat loading of the bottom layer outlet zone was approximately 2.57 g / in 3 after calcination at 550 °C for 1 hour in air.

[0141] Top layer: This layer has a PGM loading of 4 g / ft 3 (Pt / Pd / Rh = 0 / 0 / 4) and covers 100% of the substrate length. A slurry mixture containing approximately 84.8 wt% ceria-alumina composite (with approximately 8 wt% ceria), 15.0 wt% ceria-zirconia composite (binder) (with approximately 50 wt% ceria), and rhodium nitrate that yields 0.23 wt% Rh was coated onto the bottom layer. The washcoat loading of the top layer was approximately 1.00 g / in3 It was.

[0142] Example 2: Comparative Catalyst Article B The comparative catalyst article B is a zone-type two-layer Pt / Pd / Rh catalyst article having a PGM loading of 120 g / ft 3 coated on a cylindrical monolith cordierite substrate having a diameter of 4.66 inches and a length of 3.81 inches, a cell density of 800 cpsi, and a wall thickness of 3 mils, with a (Pt / Pd / Rh = 29 / 87 / 4).

[0143] Bottom layer inlet zone: This zone has a PGM loading of 156.6 g / ft 3 (Pt / Pd / Rh = 0 / 156.6 / 0) and covers 50% of the substrate length from the inlet to the middle. A slurry containing about 25.1 wt% alumina, 61.8 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), barium acetate that yields 7.7 wt% BaO, zirconium acetate that yields 1.9 wt% ZrO2, and palladium nitrate that yields 3.50 wt% Pd was coated on the substrate. The washcoat loading of the bottom layer inlet zone was about 2.59 g / in 3 after calcination at 550 °C for 1 hour in air.

[0144] Bottom layer outlet zone: This zone has a PGM loading of 75.4 g / ft 3 (Pt / Pd / Rh = 58 / 17.4 / 0) and covers 50% of the substrate length from the outlet to the middle. A slurry containing about 33.4 wt% ceria-alumina composite (having about 8 wt% ceria), 55.0 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), barium acetate that yields 7.9 wt% BaO, colloidal alumina binder that yields 2.0 wt% Al2O3, platinum-amine complex that yields 1.32 wt% Pt, and palladium nitrate that yields 0.40 wt% Pd was coated on the substrate. The washcoat loading of the bottom layer outlet zone was about 2.54 g / in 3 after calcination at 550 °C for 1 hour in air.

[0145] Top layer: same as the top layer of Example 1.

[0146] Example 3: Comparative Catalyst Article C Comparative Catalyst Article C is a zone-type single-layer Pt / Pd / Rh catalyst article coated on a cylindrical monolith cordierite substrate having a diameter of 4.66 inches and a length of 3.81 inches, a cell density of 800 cpsi, and a wall thickness of 3 mils, with a PGM loading of 104 g / ft 3 (Pt / Pd / Rh = 0 / 100 / 4).

[0147] Inlet zone: This zone has a PGM loading of 200 g / ft 3 (Pt / Pd / Rh = 0 / 200 / 0) and covers 50% of the substrate length from the inlet to the middle. A slurry containing about 31.2 wt% refractory alumina, 54.6 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), barium acetate that yields 7.8 wt% BaO, zirconium acetate that yields 1.9 wt% ZrO2, and palladium nitrate that yields 4.51 wt% Pd was coated on the substrate. The washcoat loading of the inlet zone was about 2.57 g / in 3 after calcination at 550 °C for 1 hour in air.

[0148] Outlet zone: This zone has a PGM loading of 8 g / ft 3 (Pt / Pd / Rh = 0 / 0 / 8) and covers 50% of the substrate length from the outlet to the middle. A slurry containing about 39.0 wt% ceria-alumina composite (having about 8 wt% ceria), 54.6 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), 3.9 wt% BaSO4, colloidal alumina binder that yields 0.4 wt% Al2O3, zirconium acetate that yields 1.9 wt% ZrO2, and rhodium nitrate that yields 0.18 wt% Rh was coated on the substrate. The washcoat loading of the outlet zone was about 2.56 g / in 3 after calcination at 550 °C for 1 hour in air.

[0149] Example 4: Inventive Catalyst Article D Inventive Catalyst Article D is a zoned monolayer Pt / Pd / Rh catalyst article having a PGM loading of 120 g / ft 3 coated on a cylindrical monolith cordierite substrate having a diameter of 4.66 inches and a length of 3.81 inches, a cell density of 800 cpsi, and a wall thickness of 3 mils, with a (Pt / Pd / Rh = 29 / 87 / 4).

[0150] Inlet Zone: This zone has a PGM loading of 64 g / ft 3 covering 50% of the substrate length from the inlet to the middle, with a (Pt / Pd / Rh = 58 / 0 / 6). A slurry containing about 35.3 wt% ceria-alumina composite (having about 8 wt% ceria), 56.9 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), 3.9 wt% BaSO4, a colloidal alumina binder yielding 0.4 wt% Al2O3, zirconium acetate yielding 2.0 wt% ZrO2, rhodium nitrate yielding 0.14 wt% Rh, and a platinum-amine complex yielding 1.32 wt% Pt was coated on the substrate. The washcoat loading of the inlet zone was about 2.55 g / in 3 after calcination at 550 °C for 1 hour in air.

[0151] Outlet Zone: This zone has a PGM loading of 176 g / ft 3 covering 50% of the substrate length from the outlet to the middle, with a (Pt / Pd / Rh = 0 / 174 / 2). A slurry containing about 31.3 wt% refractory alumina, 54.9 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), barium acetate yielding 7.8 wt% BaO, zirconium acetate yielding 2.0 wt% ZrO2, rhodium nitrate yielding 0.05 wt% Rh, and palladium nitrate yielding 3.95 wt% Pd was coated on the substrate. The washcoat loading of the outlet was about 2.55 g / in 3 after calcination at 550 °C for 1 hour in air.

[0152] Example 5: Inventive Catalyst Article E The inventive catalyst article E is a zoned Pt / Pd / Rh catalyst article having a PGM loading of 120 g / ft 3 coated on a cylindrical monolith cordierite substrate having a diameter of 4.66 inches and a length of 3.81 inches, a cell density of 800 cpsi, and a wall thickness of 3 mils, with a Pt / Pd / Rh = 58 / 58 / 4.

[0153] Inlet zone: This zone has a PGM loading of 143 g / ft 3 covering 50% of the substrate length from the inlet to the middle, with a Pt / Pd / Rh = 108 / 29 / 6. A slurry containing about 42.3 wt% ceria - alumina composite (having about 8 wt% ceria), 50.2 wt% stabilized ceria - zirconia mixed oxide (OSC having about 40 wt% ceria), 3.1 wt% BaSO4, a colloidal alumina binder yielding 0.3 wt% Al2O3, zirconium acetate yielding 1.6 wt% ZrO2, rhodium nitrate yielding 0.11 wt% Rh, palladium nitrate yielding 0.53 wt% Pd, and a platinum - amine complex yielding 1.96 wt% Pt was coated on the substrate. The washcoat loading of the inlet zone was about 3.19 g / in 3 after calcination at 550 °C for 1 hour in air.

[0154] Outlet zone: This zone has a PGM loading of 97 g / ft 3The PGM loading (Pt / Pd / Rh = 8 / 87 / 2) covers 50% of the substrate length from the outlet to the middle. A slurry containing about 19.2 wt% alumina, 15.3 wt% refractory ceria - alumina composite (having about 8 wt% ceria), 53.6 wt% stabilized ceria - zirconia mixed oxide (OSC having about 40 wt% ceria), barium acetate that yields 7.7 wt% BaO, zirconium acetate that yields 1.9 wt% ZrO2, rhodium nitrate that yields 0.05 wt% Rh, a platinum - amine complex that yields 0.18 wt% Pt, and palladium nitrate that yields 1.93 wt% Pd was coated onto the substrate. The washcoat loading in the outlet zone was about 2.61 g / in 3 after calcination at 550 °C in air for 1 hour.

[0155] Example 6: Inventive Catalyst Article F Inventive Catalyst Article F is a zoned Pt / Pd / Rh catalyst article having a PGM loading of 120 g / ft 3 coated onto a cylindrical monolith cordierite substrate having a diameter of 4.66 inches and a length of 3.81 inches, a cell density of 800 cpsi, and a wall thickness of 3 mils, with a Pt / Pd / Rh ratio of 29 / 87 / 4.

[0156] Bottom layer in the inlet zone: This zone has a PGM loading of 90 g / ft 3 covering 50% of the substrate length from the inlet to the middle, with a Pt / Pd / Rh ratio of 58 / 26 / 6. A slurry containing about 35.1 wt% ceria - alumina composite (having about 8 wt% ceria), 56.6 wt% stabilized ceria - zirconia mixed oxide (OSC having about 40 wt% ceria), 3.9 wt% BaSO4, a colloidal alumina binder that yields 0.4 wt% Al2O3, zirconium acetate that yields 2.0 wt% ZrO2, rhodium nitrate that yields 0.14 wt% Rh, palladium nitrate that yields 0.59 wt% Pd, and a platinum - amine complex that yields 1.31 wt% Pt was coated onto the substrate. The washcoat loading in the inlet zone was about 2.56 g / in 3 after calcination at 550 °C in air for 1 hour.

[0157] Top layer of the inlet zone: This zone covers 31.5% of the substrate length from the inlet to the middle. A slurry containing about 95.3 wt% barium-doped alumina and 4.7 wt% Al2O3 and a colloidal alumina binder was coated onto the bottom layer. The washcoat loading of the top layer of the inlet zone divided by the substrate volume coated by the top layer of the inlet zone was about 0.75 g / in after calcination in air at 550 °C for 1 hour. 3 It was.

[0158] Outlet zone: This zone covers 50% of the substrate length from the outlet to the middle with a PGM loading of 150 g / ft 3 (Pt / Pd / Rh = 0 / 148 / 2). A slurry containing about 31.5 wt% refractory alumina, 55.2 wt% stabilized ceria-zirconia mixed oxide (OSC having about 40 wt% ceria), barium acetate that yields 7.9 wt% BaO, zirconium acetate that yields 2.0 wt% ZrO2, rhodium nitrate that yields 0.05 wt% Rh, and palladium nitrate that yields 3.37 wt% Pd was coated onto the substrate. The washcoat loading of the outlet zone was about 2.54 g / in after calcination in air at 550 °C for 1 hour. 3 It was.

[0159] Example 7: Catalyst article G Catalyst article G is a single-layer Pt / Pd / Rh catalyst article having a PGM loading of 12 g / ft 3 (Pt / Pd / Rh = 10 / 0 / 2) coated on a cylindrical monolith cordierite substrate having a diameter of 5.2 inches, a length of 3.96 inches, a cell density of 400 cpsi, and a wall thickness of 6.5 mils.

[0160] A slurry containing about 50.8 wt% of a ceria-alumina composite (having about 8 wt% ceria), 43.5 wt% of a stabilized ceria-zirconia mixed oxide (OSC having about 40 wt%), barium acetate that yields 3.6 wt% of BaO, zirconium acetate that yields 1.1 wt% of ZrO2, a colloidal alumina binder that yields 0.7 wt% of Al2O3, a platinum-amine complex that yields 0.21 wt% of Pt, and palladium nitrate that yields 0.04 wt% of Pd was coated on a substrate. The washcoat loading was about 2.76 g / in after calcination at 550 °C for 1 hour in air. 3 It was.

[0161] Example 8: Aging and Testing of Catalyst Articles The catalyst articles were aged using a 4-mode exothermic aging protocol at an effective catalyst temperature of 877 °C for 60 hours using lindoped fuel in an engine setting. Catalyst articles A - F were attached at a close-coupled front position and catalyst article G was attached at a close-coupled rear position. The engine exhaust gas feed composition alternates between rich and lean to simulate typical vehicle driving conditions.

[0162] Emission performance was tested using a 2.7L ULEV50 vehicle having a close-coupled in-line (front close-coupled catalyst (CCC1) / rear close-coupled catalyst (CCC2)) emission control system configuration operating under the FTP-75 test protocol. Catalysts A, B, C, D, E, and F were tested as CCC1 catalysts and catalyst G was used as a typical CCC2 catalyst.

[0163] During the cold start portion of the FTP-75 test, the close-coupled catalyst is warmed up by the heat received from the engine exhaust.

[0164] Figure 2 shows that catalyst D warmed up faster than catalyst B, presumably due to a lower washcoat loading. Faster warm-up is beneficial during cold start since catalyst activity is kinetically driven.

[0165] The advantages of the inventive catalyst articles are shown in Figure 3. The inventive catalysts D and F have lower exhaust pipe emissions when tested as CCC1 than the comparative catalysts B and C. The comparative catalyst C has the same washcoat loading as the inventive catalyst D, indicating that the performance advantage of the inventive catalyst D over the comparative catalyst C is due not to a lower washcoat loading, but rather to the catalyst design (such as washcoat design and PGM loading / ratio). It is observed that the comparative catalyst C shows the highest NOx emissions, probably because the front zone does not contain Rh. This result suggests that it is necessary to distribute Rh throughout the catalyst to ensure good NOx performance. The comparative catalyst B and the inventive catalyst D have the same PGM loading / ratio, indicating that the improvement of the inventive catalyst D is due to the washcoat design. The emission performance of the inventive catalyst F is further improved by providing a PGM-free overcoat that protects the washcoat layer just below the phosphorus poisoning.

[0166] The inventive catalyst E shows lower exhaust pipe emissions than the comparative catalyst A when tested as CCC1. The catalyst E and the catalyst A have the same PGM loading / ratio, indicating that the improvement is due to the washcoat design.

[0167] Regarding the embodiments disclosed in this specification, although specific embodiments have been described with reference to them, it should be understood that these embodiments are merely illustrative of the principles and uses of the invention claimed in this application. It will be apparent to those skilled in the art that various modifications and changes can be made to the methods and apparatuses of the invention claimed in this application without departing from the spirit and scope of the invention. Therefore, the invention claimed in this application is intended to include modifications and changes within the scope of the appended claims and their equivalents, and the above-described embodiments are presented for illustrative purposes rather than for limitation.

Claims

1. A catalytic article, a) a substrate, b) a first zone coated with a first catalyst layer, c) a second zone coated with a second catalyst layer, and the first catalyst layer includes platinum supported on ceria-zirconia mixed oxide or ceria-alumina composite or both, and rhodium supported on ceria-zirconia mixed oxide, ceria-alumina composite, alumina or any combination thereof, the second catalyst layer includes palladium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof, and rhodium supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof, the first zone occupies the inlet end portion of the substrate, and the second zone occupies the outlet end portion of the substrate, a catalytic article.

2. The catalytic article according to claim 1, wherein the first catalyst layer further includes palladium supported on ceria-zirconia mixed oxide or ceria-alumina composite or both.

3. The catalytic article according to claim 1 or 2, wherein the second catalyst layer further includes platinum supported on ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof.

4. The catalytic article according to any one of claims 1 to 3, wherein the total loading of the first catalyst layer and the second catalyst layer divided by the substrate volume is less than 3.2 grams per cubic inch.

5. The amount of platinum in the first catalyst layer and the second catalyst layer is in the range of 0.02 to 3.0% by weight based on the total weight of the first catalyst layer and the second catalyst layer, The amount of palladium in the first catalyst layer and the second catalyst layer is in the range of 0.02 to 5.0 wt% based on the total weight of the first catalyst layer and the second catalyst layer. The amount of rhodium in the first catalyst layer and the second catalyst layer is in the range of 0.01 to 1.0 wt% based on the total weight of the first catalyst layer and the second catalyst layer. The catalyst article according to any one of claims 1 to 4.

6. The total amount of platinum supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer is 80 to 100 wt% based on the total weight of platinum in the first catalyst layer and the second catalyst layer. The total amount of palladium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is 75 to 100 wt% based on the total weight of palladium in the first catalyst layer and the second catalyst layer. The weight ratio of rhodium supported on the ceria-zirconia mixed oxide or ceria-alumina composite or both in the first catalyst layer to rhodium supported on the ceria-zirconia mixed oxide, alumina, ceria-alumina composite or any combination thereof in the second catalyst layer is in the range of 1.5:1 to 4:

1. The catalyst article according to any one of claims 1 to 5.

7. The first zone further includes an overcoat deposited on at least a part of the first zone, and the overcoat includes a porous refractory oxide and optionally at least one base metal oxide. The catalyst article according to any one of claims 1 to 6.

8. The overcoat essentially does not contain a noble metal and optionally contains an oxygen storage component. The catalyst article according to claim 7.

9. The length of the overcoat is 50% or less of the total length of the substrate. The catalyst article according to claim 7 or 8.

10. The catalyst article according to any one of claims 7 to 9, wherein the load of the overcoat divided by the volume of the substrate coated with the overcoat is less than 1 gram per cubic inch.

11. The catalyst article according to any one of claims 7 to 10, wherein the porous refractory oxide is stabilized or unstabilized aluminum oxide.

12. The base metal oxide is an alkaline earth metal oxide or a rare earth metal oxide, The alkaline earth metal oxide is selected from barium oxide, magnesium oxide, calcium oxide, strontium oxide, or a combination thereof, The catalyst article according to any one of claims 7 to 11, wherein the rare earth metal oxide is an oxide of at least one rare earth metal selected from Ce, Pr, Nd, Eu, Sm, Yb, and La, or a mixture thereof.

13. The first zone covers 10 to 90% of the total substrate length from the inlet end portion, The second zone covers 10 to 90% of the total substrate length from the outlet end portion, The catalyst article according to any one of claims 1 to 12, wherein the first catalyst layer covers 60 to 100% of the area of the first zone, and the second catalyst layer covers 60 to 100% of the area of the second zone.

14. The first zone covers 40 to 60% of the total substrate length from the inlet end portion, The catalyst article according to any one of claims 1 to 13, wherein the second zone covers 60 to 40% of the total substrate length from the outlet end portion.

15. The amount of the ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer is 40 to 60% by weight based on the total weight of the first catalyst layer and the second catalyst layer. The catalyst article according to any one of claims 1 to 14.

16. The amount of the alumina present in the first catalyst layer and the second catalyst layer is in the range of 5.0 to 20% by weight based on the total weight of the first catalyst layer and the second catalyst layer. The catalyst article according to any one of claims 1 to 15.

17. The alumina is doped with a dopant selected from barium, lanthana, zirconia, neodymium, yttria, ceria, or titania. The amount of the dopant is 1.0 to 30% by weight based on the total weight of the alumina and the dopant present in the first catalyst layer and the second catalyst layer. The catalyst article according to any one of claims 1 to 16.

18. The alumina is selected from alumina, lanthana-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, ceria-alumina, lanthana-zirconia-alumina, barium-alumina, barium-lanthana-alumina, barium-lanthana-neodymium-alumina, or any combination thereof. The catalyst article according to any one of claims 1 to 17.

19. The amount of the ceria-alumina composite present in the first catalyst layer and the second catalyst layer is in the range of 15 to 40% by weight based on the total weight of the first catalyst layer and the second catalyst layer. The catalyst article according to any one of claims 1 to 18.

20. The amount of ceria calculated as CeO ２ in the ceria-alumina composite is 5.0 to 30% by weight based on the total weight of the ceria-alumina composite. The catalyst article according to any one of claims 1 to 19.

21. The ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer has an amount of CeO of 15 to 50% by weight based on the total weight of the ceria-zirconia mixed oxide in each catalyst layer. ２Calculated as, ceria and, based on the total weight of the ceria-zirconia mixed oxide in each of the catalyst layers, ZrO in an amount of 50 to about 85 wt% ２ Calculated as, zirconia, and a catalyst article according to any one of claims 1 to 20. **Claim 22** The ceria-zirconia mixed oxide present in the first catalyst layer and the second catalyst layer contains a dopant selected from lanthanum oxide, titania, hafnia, magnesia, calcia, strontia, barium, yttrium, hafnium, praseodymium, neodymium, or any combination thereof, a catalyst article according to any one of claims 1 to 21. **Claim 23** The substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, or a woven fiber substrate, a catalyst article according to any one of claims 1 to 22. **Claim 24** A process for the preparation of a catalyst article according to any one of claims 1 to 23, the process comprising - preparing a first catalyst layer slurry comprising platinum supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both, and rhodium supported on a ceria-zirconia mixed oxide or a ceria-alumina composite or both; - preparing a second catalyst layer slurry comprising palladium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite or any combination thereof, and rhodium supported on a ceria-zirconia mixed oxide, alumina, a ceria-alumina composite or a combination thereof; - coating the first catalyst layer slurry on the inlet end portion of the substrate to obtain a first zone; - coating the second catalyst layer slurry on the outlet end portion of the substrate to obtain a second zone; - subjecting the substrate to calcination at a temperature in the range of 400 to 700 °C. A process in which the step of preparing the slurry includes a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

25. An exhaust gas treatment system for an internal combustion engine, wherein the system includes the catalyst article according to any one of claims 1 to 23.

26. A method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, the method including contacting the exhaust stream with the catalyst article according to any one of claims 1 to 23 or the exhaust gas treatment system according to claim 25.

27. A method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust gas stream, the method including contacting the gaseous exhaust gas stream with the catalyst article according to any one of claims 1 to 23 or the exhaust gas treatment system according to claim 25 to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

28. Use of the catalyst article according to any one of claims 1 to 23 or the exhaust gas treatment system according to claim 25 for purifying a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides.

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