Layered catalyst article and method for making the catalyst article

Abstract

The present invention provides a layered catalyst article and an exhaust system. The catalyst article includes: a first layer comprising platinum, a first platinum group metal component other than platinum, a ceria-alumina composite, and an oxygen storage component, where the platinum is supported on the ceria-alumina component and the platinum group metal component is selected from palladium, rhodium, or a combination thereof, and the platinum group metal component is supported on the oxygen storage component; a second layer comprising a second platinum group metal component, a refractory alumina component, the oxygen storage component, or a combination thereof, where the second platinum group component is selected from platinum, palladium, rhodium, or a combination thereof; and a substrate, where the amount of platinum is 10 to 80 wt. % based on the total weight of the platinum, palladium, and rhodium. The present invention also provides a process for preparing the layered catalyst article and the use of the catalyst article and exhaust system for purifying a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority in its entirety to U.S. Provisional Application No. 62 / 867353, filed June 27, 2019, and European Application No. 19186665.6, filed July 17, 2019.

[0002] The present invention relates to a layered catalyst article useful for treating automotive exhaust gases to reduce the pollutants contained therein. In particular, the present invention relates to a layered catalyst article, a method for preparing the catalyst article, and its use as an emission control catalyst. [Background technology]

[0003] Three-way conversion (TWC) catalysts (hereinafter referred to interchangeably as three-way catalysts, three-way catalysts, TWC catalysts, and TWCs) have been utilized for over 30 years in the treatment of exhaust gas streams from internal combustion engines. Catalytic converters containing three-way catalysts are typically used in the exhaust gas lines of internal combustion engines to treat or purify exhaust gases containing pollutants such as hydrocarbons, nitrogen oxides, and carbon monoxide. Three-way catalysts are typically known to oxidize unburned hydrocarbons and carbon monoxide and reduce nitrogen oxides.

[0004] Typically, most commercially available TWC catalysts contain palladium as the primary platinum group metal component, with smaller amounts of rhodium. Because a large amount of palladium is used in the manufacture of catalytic converters, which help reduce the amount of exhaust gas pollutants, a palladium supply shortage may occur in the market in the coming years. Currently, palladium is significantly more expensive than platinum. At the same time, platinum prices are expected to fall due to a decrease in platinum demand. One reason for this may be the decline in diesel vehicle production.

[0005] Therefore, to significantly reduce catalyst costs, it is necessary to replace a portion of the palladium in TWC catalysts with platinum. Platinum is widely used in diesel oxidation catalysts (DOCs) and lean NOx traps (LNTs) for emission control in diesel-fueled vehicles, but its use in gasoline-fueled vehicles is limited. The proposed approach of replacing a portion of the palladium with platinum is complicated by the need to maintain or improve the desired effectiveness of the catalyst, which would not be possible by simply replacing a portion of the palladium with platinum. One of the reasons for this is the tendency of platinum to sinter under prolonged, high-temperature aging conditions. It has been found that platinum particles deposited on conventional refractory alumina can grow to submicron size via the well-established Ostwald ripening mechanism.

[0006] Therefore, an object of the present invention is a stable platinum, palladium, and rhodium based TWC catalyst, utilizing about 10-80 wt. % platinum based on total PGM loading, and capable of efficiently removing the individual CO, HC, NO x The objective is to provide a stable platinum, palladium, and rhodium-based TWC catalyst that provides improved or equivalent catalytic performance compared to commercially available palladium-rhodium-based TWC catalysts, as expressed by comparing conversion levels, and corresponding cumulative tailpipe emissions required for vehicle certification by regulatory agencies in most jurisdictions. Summary of the Invention

[0007] According to the present invention, a) a first layer comprising platinum, a first platinum group metal component other than platinum, a ceria-alumina component, and an oxygen storage component, wherein the platinum is supported on the ceria-alumina component, the first platinum group metal component is selected from palladium, rhodium, or a combination thereof, and the first platinum group metal component is supported on the oxygen storage component; b) a second layer comprising a second platinum group metal component and a refractory alumina component, an oxygen storage component, or a combination thereof, wherein the second platinum group metal is selected from platinum, palladium, rhodium, and combinations thereof; c) a substrate, A layered catalyst article is provided in which the amount of platinum is 10 to 80 wt %, based on the total weight of platinum, palladium, and rhodium.

[0008] In one embodiment, the amount of platinum is 20 to 80 wt % based on the total weight of platinum, palladium, and rhodium, and the amount of palladium and rhodium is 20 to 80 wt % based on the total weight of platinum, palladium, and rhodium.

[0009] According to another aspect of the present invention, there is provided a process for preparing a layered catalyst article according to the present invention.

[0010] According to another aspect of the present invention, there is provided a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, comprising contacting the exhaust stream with a layered catalyst article or an exhaust system according to the present invention.

[0011] According to another aspect of the present invention, there is provided a method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, comprising contacting the gaseous exhaust stream with a layered catalyst article or an exhaust system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0012] According to another aspect of the present invention there is provided the use of a catalytic article or an exhaust system according to the present invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide and nitrogen oxides. [Brief explanation of the drawings]

[0013] To provide an understanding of embodiments of the present invention, reference is made to the accompanying drawings, which are not necessarily drawn to scale, and in which reference numerals refer to components of exemplary embodiments of the present invention. The drawings are merely illustrative and should not be construed as limiting the present invention. These and other features of the present invention, its nature and various advantages, as claimed herein, will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0014] [Figure 1] 1A and 1B are schematic diagrams of a reference catalyst article design, and FIGS. 1C and 1D are schematic diagrams of catalyst article designs in exemplary configurations according to some embodiments of the present invention. [Figure 2] 1 illustrates a comparison of the light-off temperatures of various powder catalysts. [Figure 3A] 1 is a perspective view of a honeycomb-shaped substrate support that may include a catalyst composition according to one embodiment of the present invention. [Figure 3B] 3B is a partial cross-sectional view, enlarged compared to FIG. 3A and taken along a plane parallel to an edge face of the substrate carrier of FIG. 3A, showing an enlarged view of a plurality of gas flow passages shown in FIG. 3A. [Figure 4] 3B is an enlarged cross-sectional cutaway view relative to FIG. 3A, in which the honeycomb-shaped substrate of FIG. 3A represents a wall-flow filter substrate monolith. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will now be described more fully hereinafter. The present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosed materials and methods.

[0016] The use of the terms "a," "an," "the," and similar directives in the context of describing the materials and methods discussed herein (particularly in the context of the claims below) should be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0017] The term "about" is used throughout this specification to describe and account for small variations. For example, the term "about" refers to ±5% or less, e.g., ±2% or less, ±1% or less, ±0.5% or less, ±0.2% or less, ±0.1% or less, or ±0.05% or less. All numerical values are modified by the term "about," whether explicitly stated or not. Of course, values modified by the term "about" include the specific value. For example, "about 5.0" must include 5.0.

[0018] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended only to better describe the materials and methods and is not intended to limit the scope unless otherwise claimed.

[0019] The present invention provides a trimetallic layered catalyst article containing three platinum group metals (PGMs) in which a large amount of platinum can be used to substantially replace palladium.

[0020] Platinum group metal (PGM) refers to any component containing a PGM (Ru, Rh, Os, Ir, Pd, Pt, and / or Au). For example, the PGM may be in a zero-valence metallic form, or the PGM may be in an oxide form. Reference to a "PGM component" takes into account the presence of the PGM in any valence state. Terms such as "platinum (Pt) component," "rhodium (Rh) component," "palladium (Pd) component," "iridium (Ir) component," and "ruthenium (Ru) component" refer to the respective platinum group metal compounds, complexes, and the like, which decompose or otherwise convert to a catalytically active form, typically a metal or metal oxide, upon calcination or use of the catalyst.

[0021] The terms "catalyst," "catalytic article," or "catalyst article" refer to a component in which a substrate is coated with a catalytic composition used to promote a desired reaction. In one embodiment, the catalytic article is a layered catalytic article. The term layered catalytic article refers to a catalytic article in which a substrate is coated with a PGM composition in layers. These compositions may be referred to as washcoats.

[0022] "NO x The term "refers to nitrogen oxide compounds such as NO and / or NO2.

[0023] The present invention addresses the problem of partially replacing palladium with platinum in conventional Pd / Rh TWC catalysts by providing a catalyst containing Pt, Pd, and Rh, along with an optimized support for platinum stabilization. The problem of platinum sintering when doped on alumina can be resolved to a certain extent by using ceria as a support. Platinum can form a monolayer and is often partially or completely oxidized on the ceria surface due to the strong PtO-CeO2 interaction. However, bulk ceria itself can sinter after high-temperature aging.

[0024] Therefore, the present invention addresses the aforementioned problems and provides a ceria-alumina composite as a platinum support for TWC catalysts. Platinum is selectively deposited on the ceria-alumina composite, thereby providing optimal three-way catalytic performance and preventing platinum migration to other catalyst components. PGM components are allocated in a layered washcoat structure to optimize platinum utilization for three-way conversion catalysis after high-temperature aging in gasoline engines.

[0025] The present invention provides a layered catalyst article comprising: (a) a first layer comprising platinum, a first platinum group metal component other than platinum, a ceria-alumina composite, and an oxygen storage component, wherein the platinum is supported on the ceria-alumina component, the first platinum group metal component being selected from palladium, rhodium, or a combination thereof, and the first platinum group metal being supported on the oxygen storage component; (b) a second layer comprising a second platinum group metal component and a refractory alumina component, an oxygen storage component, or a combination thereof, wherein the second platinum group metal component is selected from platinum, palladium, rhodium, or a combination thereof, and the amount of platinum is 10 to 80 wt. % based on the total weight of the platinum, palladium, and rhodium; and (c) a substrate. In one embodiment, about 2 to 20 wt. % palladium can be optionally deposited on the ceria-alumina along with the platinum. In one embodiment, the amount of platinum in the first layer is 50 to 100 wt %, based on the total weight of platinum in the catalytic article.

[0026] In one embodiment, the layered catalyst article of the present invention is used as a close-bound or underfloor catalyst.

[0027] In one embodiment, a first layer is deposited on the substrate as a bottom coat, and the platinum group metal component comprises palladium, and a second layer is deposited on the first layer as a top coat, and the platinum group metal component comprises rhodium.

[0028] In one exemplary embodiment, the layered catalyst article includes a first layer deposited on a substrate as a bottom layer, the first layer including platinum supported on a ceria-alumina component and palladium supported on each of the ceria-alumina and oxygen storage component; and a second layer deposited on the first layer as a top layer, the second layer including rhodium supported on the oxygen storage component and, optionally, palladium supported on the oxygen storage component, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium.

[0029] In one embodiment, the palladium and platinum are supported on a single support selected from a refractory alumina component, a ceria-alumina component, and an oxygen storage component, while in another embodiment, the palladium and platinum are supported on separate supports selected from a refractory alumina component, a ceria-alumina component, and an oxygen storage component.

[0030] In one embodiment, the second layer is deposited on the substrate as a bottom coat, and the platinum group metal component comprises palladium, and the first layer is deposited on the second layer as a top coat, and the platinum group metal component comprises rhodium.

[0031] In one exemplary embodiment, the layered catalyst article includes a second layer deposited on the substrate as a bottom layer, the second layer including palladium supported on an oxygen storage component, a refractory alumina component, or a combination thereof; and a first layer deposited on the second layer as a top layer, the first layer including rhodium supported on the oxygen storage component and platinum supported on the ceria-alumina component, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium.

[0032] In one embodiment, a layered catalyst article includes: a) a first layer (bottom coat) comprising platinum supported on a ceria-alumina component and palladium supported on the oxygen storage component and the ceria-alumina component; b) a second layer (top coat) comprising rhodium supported on the oxygen storage component; and c) a substrate, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium.

[0033] In one embodiment, a layered catalyst article includes: a) a first layer (bottom coat) comprising platinum supported on a ceria-alumina component and palladium supported on the oxygen storage component and the ceria-alumina component; b) a second layer (top coat) comprising rhodium supported on the oxygen storage component and palladium supported on the oxygen storage component; and c) a substrate, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium.

[0034] In one embodiment, the layered catalyst article includes: a) a first layer (bottom coat) comprising palladium supported on a refractory alumina component, an oxygen storage component, or a combination thereof; b) a second layer (top coat) comprising platinum supported on a ceria-alumina component and rhodium supported on the oxygen storage component; and c) a substrate, wherein the amount of platinum is 10 to 80 wt. %, based on the total weight of the platinum, palladium, and rhodium.

[0035] In one embodiment, a layered catalyst article includes: a) a first layer (bottom coat) comprising platinum supported on a ceria-alumina component and palladium supported on an oxygen storage component and the ceria-alumina component; b) a second layer (top coat) comprising palladium supported on the oxygen storage component and rhodium supported on the ceria-alumina component, the refractory alumina component, the oxygen storage component, or any combination thereof; and c) a substrate, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium.

[0036] In one embodiment, the layered catalyst article includes: a) a first layer (bottom coat) comprising palladium and rhodium supported on a ceria-alumina component, a refractory alumina component, an oxygen storage component, or any combination thereof; b) a second layer (top coat) comprising platinum supported on the ceria-alumina component and rhodium supported on the oxygen storage component; and c) a substrate, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium.

[0037] In one exemplary embodiment, the bottom coat / layer comprises platinum supported on a ceria-alumina component and, optionally, palladium supported on the ceria-alumina component and / or oxygen storage component, and the top coat comprises rhodium supported on a stabilized refractory alumina and palladium supported on the oxygen storage component. In another exemplary embodiment, the bottom coat comprises palladium supported on a stabilized refractory alumina and oxygen storage component, and the top coat / layer comprises rhodium supported on the oxygen storage component and platinum supported on the ceria-alumina component.

[0038] In one embodiment, the correlation coefficient between platinum and aluminum in the first layer is greater than 70% as measured by EPMA line scan analysis.

[0039] As used herein, the term "EPMA" refers to "electron probe microanalysis" or "electron microprobe analysis." EPMA provides a line-scanning technique that analyzes the concentration of individual elements within a probed spot. The Pearson product-moment correlation coefficient, sometimes called the Pearson correlation or simply the correlation coefficient, is used to measure the linear relationship between two variables, as explained below.

number

number

[0040] In one embodiment, the ceria-alumina component comprises ceria-alumina, ceria-yttrium-alumina, ceria-silica-alumina, ceria-tin-alumina, ceria-manganese-alumina, ceria-iron-alumina, ceria-nickel-alumina, ceria-iridium-alumina, ceria-ruthenium-alumina, ceria-indium-alumina, or ceria-titania. In one embodiment, the ceria content of the ceria-alumina component is in the range of 1.0 to 75.0 wt. %, based on the total weight of the ceria-alumina component. In one embodiment, the ceria content of the ceria-alumina component is in the range of 5.0 to 50.0 wt. %, based on the total weight of the ceria-alumina component. In one embodiment, the ceria content of the ceria-alumina component is in the range of 5.0 to 30.0 wt. %, based on the total weight of the ceria-alumina component.

[0041] In one embodiment, the amount of platinum in the first layer is in the range of 0.02 to 4.0 wt %, based on the total weight of the washcoat of the catalyst article. In one embodiment, the amount of palladium in the catalyst article is in the range of 0.02 to 4.0 wt %, based on the total weight of the washcoat of the catalyst article. In one embodiment, the amount of rhodium in the catalyst article is in the range of 0.02 to 4.0 wt %, based on the total weight of the washcoat of the catalyst article.

[0042] In one embodiment, the oxygen storage compound is a material that changes its valence by storing and releasing oxygen depending on the partial pressure of oxygen in the operating environment. In gasoline-powered vehicles, the environment in the exhaust gas treatment system is constantly changing and fluctuating around a lambda value equal to 1. The lambda value is defined by the ratio of oxygen content to the combined CO and HC content and is measured by a lambda sensor. Modern gasoline-powered vehicle configurations use two lambda sensors: one located before the TWC catalyst and one after. A lambda value greater than 1 detected by the sensor before the TWC indicates that the engine is operating with more oxygen than is needed for the combustion of CO and HC in the cylinder chambers, which is good for reducing CO / HC emissions. A lambda value less than 1 detected by the sensor before the TWC indicates that the engine is operating with insufficient oxygen than is needed for the combustion of CO and HC in the cylinder chambers, which is good for reducing NOx emissions. To balance overall CO / HC / NOx emissions, modern vehicles operate under a strict lambda fluctuation of approximately 1. However, to address acceleration and stop-start scenarios encountered in real-world driving conditions, which can cause large fluctuations in lambda values and result in catalyst performance degradation, oxygen storage compounds are needed to minimize lambda fluctuations during such extreme driving conditions. Ceria is well known for its good oxygen storage capacity but has poor thermal stability. Modern vehicles require catalysts with good long-term durability to provide extended warranties to customers. Therefore, OEMs are demanding high-temperature aging durability (>950°C) for modern TWC catalysts. To this end, zirconium-stabilized ceria has been introduced as a means to meet these requirements.

[0043] "An oxygen storage component is an entity that exhibits oxygen storage capacity, often with multiple oxidation states, and that can actively release oxygen in an oxygen-depleted environment and reoxidize (regain oxygen) in an oxygen-rich environment. Examples of suitable oxygen storage components include ceria and praseodymia, and combinations thereof."

[0044] In some embodiments, the OSC is a mixed metal oxide composite containing ceria and / or praseodymia in combination with other metal oxides. Specific metal oxides that can be included in such mixed metal oxides are zirconium oxide (ZrO), titania (TiO), yttria (YO), neodymia (NdO), lanthana (LaO), or mixtures thereof. For example, a "ceria-zirconia composite" refers to a composite containing ceria and zirconia. In some embodiments, the ceria content in the mixed metal oxide composite ranges from about 25% to about 95% by weight of the total mixed metal oxide composite.

[0045] In some embodiments, the total ceria or praseodymia content in the OSC ranges from about 5% to about 99.9% by weight of the total mixed metal oxide composite, preferably from about 5% to about 70% by weight, and even more preferably from about 10% to about 50% by weight.

[0046] In one embodiment, the oxygen storage component comprises ceria, zirconia, and a rare earth metal oxide selected from lanthana, yttria, neodymia, praseodimia, gadolinia, or any combination thereof, hi one embodiment, the oxygen storage component comprises ceria in an amount of 5.0 to 50.0 wt %, based on the total weight of the oxygen storage component.

[0047] In one embodiment, the refractory alumina component comprises alumina and, optionally, a dopant selected from lanthana, ceria, titania, zirconia, hafnia, magnesia, calcia, strontia, baria, or any combination thereof.

[0048] In one embodiment, the second layer is essentially free of platinum. As used herein, the term "essentially free of platinum" refers to the absence of exogenous platinum added in the second layer, although platinum may optionally be present as a fraction of <0.001 wt.%.

[0049] In one embodiment, the first layer and / or the second layer further comprises barium oxide, strontium oxide, lanthanum oxide, or any combination thereof.

[0050] In one embodiment, the platinum is thermally or chemically bound to the ceria-alumina component.

[0051] In one embodiment, the substrate utilized to fabricate the catalyst article is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, and a woven fiber substrate. In one embodiment, the substrate is a ceramic substrate.

[0052] In one exemplary embodiment, a layered catalyst article includes: a first layer deposited on a substrate as a bottom layer, the first layer including platinum supported on a ceria-alumina component and palladium supported on each of the ceria-alumina and oxygen storage component; and a second layer deposited on the first layer as a top layer, the second layer including rhodium supported on the oxygen storage component and, optionally, palladium supported on the oxygen storage component, wherein the amount of platinum is 20 to 50 wt. %, based on the total weight of the platinum, palladium, and rhodium; the ceria content of the ceria-alumina component is in the range of 5.0 to 30.0 wt. %, based on the total weight of the ceria-alumina component; the oxygen storage component includes ceria in an amount of 5.0 to 50.0 wt. %, based on the total weight of the oxygen storage component; and the second layer is essentially free of platinum.

[0053] In one exemplary embodiment, the layered catalyst article includes: a second layer deposited on the substrate as a bottom layer, the second layer including palladium supported on an oxygen storage component, a refractory alumina component, or a combination thereof; and a first layer deposited on the second layer as a top layer, the first layer including rhodium supported on the oxygen storage component and platinum supported on a ceria-alumina component, wherein the amount of platinum is 20 to 50 wt. %, based on the total weight of the platinum, palladium, and rhodium; the ceria content of the ceria-alumina component is in the range of 5.0 to 30.0 wt. %, based on the total weight of the ceria-alumina component; the oxygen storage component includes ceria in an amount of 5.0 to 50.0 wt. %, based on the total weight of the oxygen storage component; and the second layer is essentially free of platinum.

[0054] In one exemplary embodiment, the layered catalyst article includes a first layer deposited on a substrate as a bottom layer, the first layer including platinum supported on a ceria-alumina component and palladium supported on each of the ceria-alumina and oxygen storage component; and a second layer deposited on the first layer as a top layer, the second layer including rhodium supported on the oxygen storage component and, optionally, palladium supported on the oxygen storage component, wherein the amount of platinum is 20 to 50 wt. %, based on the total weight of the platinum, palladium, and rhodium; and the ceria content of the ceria-alumina component is in the range of 5.0 to 30.0 wt. %, based on the total weight of the ceria-alumina component. the amount of platinum in the first layer is in the range of 0.02 to 4.0 wt. %, based on the total weight of the washcoat of the catalytic article; the amount of palladium in the catalytic article is in the range of 0.02 to 4.0 wt. %, based on the total weight of the washcoat of the catalytic article; the amount of rhodium in the catalytic article is in the range of 0.02 to 4.0 wt. %, based on the total weight of the washcoat of the catalytic article; The second layer is essentially free of platinum.

[0055] As used herein, the term "substrate" refers to a monolithic material, typically in the form of a washcoat containing a plurality of particles containing a catalyst composition, on which the catalyst composition is disposed.

[0056] References to a "monolith substrate" or "honeycomb substrate" mean a unitary structure that is homogeneous and continuous from inlet to outlet.

[0057] As used herein, the term "washcoat" has its ordinary meaning in the art of a thin, adherent coating of catalyst or other material applied to a substrate material, such as a honeycomb-type support member, that is sufficiently porous to permit the passage of the gas stream to be treated. The washcoat is formed by preparing a slurry containing particles of a certain solids content (e.g., 15-60% by weight) in a liquid vehicle, which is then coated onto the substrate and dried to provide a washcoat layer.

[0058] As used herein, and as described in Heck, Ronald, and Farrauto, Robert, Catalytic Air Pollution Control, New York: Wiley-Interscience, 2002, pp. 18-19, a washcoat layer comprises a compositionally distinct layer of material disposed on the surface of a monolith substrate or an underlying washcoat layer. In one embodiment, a substrate contains one or more washcoat layers, each of which may differ in some manner (e.g., in its physical properties, such as, for example, particle size or crystallite phase) and / or may differ in chemical catalytic function.

[0059] A catalyst article may be "virgin," meaning that the catalyst article is new and has not been exposed to any heat or thermal stress for an extended period of time. "Virgin" may also mean that the catalyst has been recently prepared and has not been exposed to any exhaust gases or high temperatures. Similarly, an "aged" catalyst article is not virgin and has been exposed to exhaust gases and high temperatures (i.e., greater than 3 hours) for an extended period of time.

[0060] According to one embodiment, the substrate of the catalyst article can be constructed from any material typically used to prepare automotive catalysts, and typically includes a ceramic or metallic monolith honeycomb structure. In one embodiment, the substrate is a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, or a woven fiber substrate.

[0061] The substrate typically provides a plurality of walls onto which a washcoat containing the catalyst composition described herein above is applied and adhered, thereby acting as a support for the catalyst composition.

[0062] Exemplary metal substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium, and / or aluminum, with the total amount of these metals advantageously comprising at least 15% by weight of the alloy, e.g., 10-25% chromium, 3-8% aluminum, and up to 20% nickel. The alloy may also contain small or trace amounts of one or more metals, such as manganese, copper, vanadium, and titanium. The surface of the metal substrate may be oxidized at high temperatures, e.g., 1000°C or higher, to form an oxide layer on the surface of the substrate, improving the corrosion resistance of the alloy and facilitating adhesion of a washcoat layer to the metal surface.

[0063] The ceramic material used in the construction of the substrate may include any suitable refractory material, such as cordierite, mullite, cordierite-alumina, silicon nitride, zircon-mullite, spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminosilicate, and the like.

[0064] Any suitable substrate can be used, such as a monolith flow-through substrate having multiple fine, parallel gas flow passages extending from the inlet to the outlet face of the substrate so that the passages are open to fluid flow. The passages, which are essentially straight-line paths from the inlet to the outlet, are defined by walls onto which a catalytic material is washcoated so that gas flowing through the passages comes into contact with the catalytic material. The flow passages in the monolith substrate are thin-walled channels that can be of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, and circular. Such structures contain from about 60 to about 1200 or more gas inlet openings (i.e., "cells") per square inch of cross section (cpsi), more commonly from about 300 to 900 cpsi. The wall thickness of the flow-through substrate can vary, with a typical range being 0.002 to 0.1 inches. A typical commercially available flow-through substrate is a cordierite substrate with a wall thickness of 6 mils at 400 cpsi or 4 mils at 600 cpsi. However, it will be understood that the present invention is not limited to a particular substrate type, material, or geometry. In an alternative embodiment, the substrate may be a wall-flow substrate, in which each passage is plugged by a non-porous plug at one end of the substrate body, with alternating passages plugged at the opposite end. This requires gas flow to pass through the porous walls of the wall-flow substrate to reach the outlet. Such monolithic substrates may contain up to about 700 or more cpsi, such as about 100 to 400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of the cells may vary, as explained above. Wall-flow substrates typically have wall thicknesses of 0.002 to 0.1 inches. Typical commercially available wall-flow substrates are constructed from porous cordierite, examples of which have 200 cpsi and a 10-mil wall thickness, or 300 cpsi with an 8-mil wall thickness, and 45 to 65% wall porosity. Other ceramic materials, such as aluminum titanate, silicon carbide, and silicon nitride, have also been used as wall-flow filter substrates, however, it will be understood that the present invention is not limited to any particular substrate type, material, or geometry.It should be noted that if the substrate is a wall-flow substrate, the catalyst composition, in addition to being disposed on the surface of the wall, may also penetrate into the pore structure of the porous wall (i.e., partially or completely block the pore openings). In one embodiment, the substrate has a flow-through ceramic honeycomb structure, a wall-flow ceramic honeycomb structure, or a metal honeycomb structure.

[0065] 3A and 3B illustrate an exemplary substrate 2 in the form of a flow-through substrate coated with a washcoat composition described herein. Referring to FIG. 3A, the exemplary substrate 2 has a cylindrical shape, including a cylindrical outer surface 4, an upstream end surface 6, and a corresponding downstream end surface 8 identical to end surface 6. The substrate 2 has a plurality of fine, parallel gas flow passages 10 formed therein. As can be seen in FIG. 3B, the passages 10 are formed by walls 12 and extend through the substrate 2 from the upstream end surface 6 to the downstream end surface 8, and the passages 10 are unobstructed, allowing a fluid, e.g., a gas stream, to flow longitudinally through the substrate 2 via the gas flow passages 10. As can be more easily seen in FIG. 3B, the walls 12 are sized and configured such that the gas flow passages 10 have a substantially regular polygonal shape. As shown, the washcoat composition can be applied in multiple distinct layers, if desired. In the illustrated embodiment, the washcoat consists of a first separate washcoat layer 14 adhered to the wall 12 of the substrate member and a second separate washcoat layer 16 coated over the first washcoat layer 14. In one embodiment, the invention is also practiced with two or more (e.g., three or four) washcoat layers and is not limited to the illustrated two-layer embodiment.

[0066] FIG. 4 illustrates an exemplary substrate 2 in the form of a wall-flow filter substrate coated with a washcoat composition described herein. As seen in FIG. 4, the exemplary substrate 2 has a plurality of passages 52. The passages are tubularly surrounded by the interior wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. Alternating passages are blocked at the inlet end by inlet plugs 58 and at the outlet end by outlet plugs 60, forming an inverted checkerboard pattern at the inlets 54 and outlets 56. Gas flow 62 enters through unblocked channel inlets 64, is stopped by outlet plugs 60, and diffuses through the (porous) channel wall 53 to the outlet side 66. Gas cannot pass back to the inlet side of the wall because of the inlet plugs 58. Porous wall filters used in the present invention have catalytic properties in the walls of the element, having or containing one or more catalytic materials thereon or therein. The catalytic material may be present only on the inlet side of the element wall, only on the outlet side, on both the inlet and outlet sides, or the wall itself may be composed entirely or partially of catalytic material. The present invention includes the use of one or more layers of catalytic material on the inlet and / or outlet walls of the element.

[0067] According to another aspect of the present invention, there is provided a process for preparing a layered catalyst article. In one embodiment, the process includes preparing a first layer (bottom coat) slurry, depositing the first bottom layer slurry on a substrate to obtain the first layer (bottom coat), preparing a second layer (top coat) slurry, and depositing the second layer (top coat) slurry on the bottom layer / coat to obtain the top layer / coat, followed by calcination at a temperature in the range of 400 to 700°C, wherein the step of preparing the bottom coat slurry or the top coat slurry includes a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition. In one embodiment, the bottom coat slurry comprises platinum, a first platinum group metal component other than platinum, a ceria-alumina composite, and an oxygen storage component, wherein platinum is supported on the ceria-alumina component, and the first platinum group metal component is selected from palladium, rhodium, or a combination thereof, and the first platinum group metal component is supported on the oxygen storage component; and the top coat slurry comprises a second platinum group metal component, and a refractory alumina component, an oxygen storage component, or a combination thereof, wherein the second platinum group metal component is selected from platinum, palladium, rhodium, or a combination thereof. In another embodiment, the bottom coat slurry comprises a second platinum group metal component selected from platinum, palladium, rhodium, and combinations thereof supported on a refractory alumina component, an oxygen storage component, or any combination thereof, and the top coat slurry comprises platinum supported on a ceria-alumina component and a first platinum group metal component selected from palladium, rhodium, or combinations thereof supported on an oxygen storage component.

[0068] In one embodiment, the process involves a preliminary step of thermally or chemically immobilizing platinum and / or palladium on the support. Thermal immobilization involves depositing platinum and / or palladium on the support, for example, via incipient wetness impregnation, followed by thermal calcination of the resulting platinum / support mixture. By way of example, the mixture is calcined at 400-700°C for 1-3 hours at a ramp rate of 1-25°C / min. Chemical immobilization involves depositing platinum and / or palladium on the support, followed by immobilization using additional reagents to chemically convert the platinum.

[0069] Incipient wetness impregnation, also known as capillary impregnation or dry impregnation, is commonly used to synthesize heterogeneous materials, i.e., catalysts. Typically, active metal precursors are dissolved in an aqueous or organic solution, and then the metal-containing solution is added to a catalyst support, which contains a pore volume equal to the volume of the added solution. Capillary action draws the solution into the pores of the support. Adding solution beyond the pore volume of the support changes solution transport from a capillary action process to a much slower diffusion process. The catalyst is dried and calcined to remove volatile components in the solution and deposit the metal on the surface of the catalyst support. The concentration profile of the impregnated material depends on the mass transfer conditions within the pores during impregnation and drying. After appropriate dilution, multiple active metal precursors may be co-impregnated into the catalyst support. Alternatively, the active metal precursors are introduced into the slurry via post-addition under stirring during the slurry preparation process.

[0070] The support particles are typically sufficiently dry to absorb substantially all of the solution and form a wet solid. Typically, an aqueous solution of a water-soluble compound or complex of the active metal, such as rhodium chloride, rhodium nitrate, rhodium acetate, or a combination thereof (when rhodium is the active metal), and palladium nitrate, palladium tetraamine, palladium acetate, or a combination thereof (when palladium is the active metal), is utilized. After treatment of the support particles with the active metal solution, the particles are dried, such as by heat treatment, at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 1-3 hours), and then calcined to convert the active metal to a more catalytically active form. An exemplary calcination process involves heat treatment in air at a temperature of 400-550°C for 10 minutes to 3 hours. The above process can be repeated as needed by impregnation to reach the desired active metal loading level.

[0071] The catalyst composition is typically prepared in the form of catalyst particles, as described above. These catalyst particles are mixed with water to form a slurry for coating a catalyst substrate, such as a honeycomb substrate. In addition to the catalyst particles, the slurry may optionally contain a binder in the form of alumina, silica, zirconium acetate, zirconia, or zirconium hydroxide, an associative thickener, and / or a surfactant (including anionic, cationic, nonionic, or amphoteric surfactants). Other exemplary binders include boehmite, gamma-alumina, or delta / theta-alumina, as well as silica sol. When present, the binder is typically used in an amount of about 1.0 to 5.0 wt.% of the total washcoat loading. The pH is adjusted by adding acidic or basic species to the slurry. For example, in some embodiments, the pH of the slurry is adjusted by adding ammonium hydroxide, aqueous nitric acid, or acetic acid. A typical pH range for the slurry is about 3 to 12.

[0072] The slurry may be milled to reduce particle size and promote particle mixing. Milling may be accomplished in a ball mill, continuous mill, or other similar equipment, and the solids content of the slurry may be, for example, about 20 to 60% by weight, more specifically, about 20 to 40% by weight. In one embodiment, the milled slurry has a D of about 3 to about 40 micrometers, preferably 10 to about 30 micrometers, and more preferably about 10 to about 15 micrometers. 90 Characterized by particle size. D 90 is determined using a dedicated particle size analyzer. The instrument used in this example uses laser diffraction to measure particle size in small amounts of slurry. D is typically measured in microns. 90 means that 90% of the particles by number have a diameter smaller than the quoted value.

[0073] The slurry is coated onto the catalyst substrate using any washcoating technique known in the art. In one embodiment, the catalyst substrate is dipped or otherwise coated with the slurry one or more times. The coated substrate is then dried at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 10 minutes to 3 hours) and then calcined, for example, by heating at 400-700°C, typically for about 10 minutes to about 3 hours. After drying and calcination, the final washcoat coating layer is believed to be essentially solvent-free. After calcination, the catalyst loading achieved by the above washcoating technique can be determined by calculating the difference between the coated and uncoated weights of the substrate. As will be apparent to those skilled in the art, the catalyst loading can be modified by varying the rheology of the slurry. Furthermore, the coating / drying / calcining process to produce the washcoat can be repeated as necessary to build the coating to a desired loading level or thickness; i.e., two or more washcoats may be applied.

[0074] In certain embodiments, the coated substrate is aged by subjecting the coated substrate to a heat treatment. In one embodiment, aging is carried out at a temperature of about 850°C to about 1050°C in a 10% by volume moisture environment under alternating hydrocarbon / air feeds for 50 to 75 hours. Accordingly, in certain embodiments, an aged catalyst article is provided. In certain embodiments, particularly useful materials include metal oxide-based supports (including, but not limited to, substantially 100% ceria supports) that maintain a high percentage of pore volume (e.g., about 95 to 100%) upon aging (e.g., about 850°C to about 1050°C, 10% by volume moisture under alternating hydrocarbon / air feeds, aging for 50 to 75 hours).

[0075] According to another aspect of the present invention, there is provided an exhaust system (also referred to as an exhaust gas treatment system) for an internal combustion engine. The exhaust system comprises a layered catalyst article according to the present invention. In one embodiment, the exhaust system comprises a platinum group metal-based three-way (TWC) catalyst article and a layered catalyst article according to the present invention, wherein the platinum group metal-based three-way (TWC) catalyst article is located downstream of the internal combustion engine and the layered catalyst article is located downstream in fluid communication with the platinum group metal-based three-way (TWC) catalyst article. In one embodiment, the exhaust system comprises a platinum group metal-based three-way (TWC) catalyst article and a layered catalyst article according to the present invention, wherein the layered catalyst article is located downstream of the internal combustion engine and the platinum group metal-based three-way (TWC) catalyst article is located downstream in fluid communication with the platinum group metal-based three-way (TWC) catalyst article.

[0076] As used herein, the term "stream" broadly refers to any combination of flowing gases that may contain solid or liquid particulate matter.

[0077] As used herein, the terms "upstream" and "downstream" refer to relative directions relative to the flow of engine exhaust gas stream from the engine toward the tailpipe, with the engine being in the upstream position and the tailpipe and any pollution abatement items, such as filters and catalysts, being downstream from the engine.

[0078] According to yet another aspect of the present invention, there is provided a method for treating a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides, comprising contacting the exhaust stream with a layered catalyst article or exhaust system according to the present invention. Terms such as "exhaust stream," "engine exhaust stream," and "exhaust gas stream" refer to any combination of flowing engine outflow gases, which may also contain solid or liquid particulate matter. The stream is, for example, the exhaust of a lean-burn engine, which includes gaseous components and may also contain certain non-gaseous components, such as liquid droplets, solid particles, and the like. Lean-burn engine exhaust streams typically contain combustion products, incomplete combustion products, oxides of nitrogen, combustible and / or carbonaceous particulate matter (soot), and unreacted oxygen and / or nitrogen. Such terms also refer to the downstream effluent of one or more other catalyst system components as described herein.

[0079] According to yet another aspect of the present invention, there is provided a method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, comprising contacting the gaseous exhaust stream with a layered catalyst article or an exhaust system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas.

[0080] According to yet another aspect, there is provided a use of a layered catalyst article or an exhaust system according to the present invention for purifying a gaseous exhaust stream containing hydrocarbons, carbon monoxide, and nitrogen oxides. In some embodiments, the catalyst article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of carbon monoxide, hydrocarbons, and nitrogen compounds present in the exhaust gas stream prior to contact with the catalyst article. In some embodiments, the catalyst article converts hydrocarbons to carbon dioxide and water.

[0081] In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of hydrocarbons present in the exhaust gas stream prior to contact with the catalytic article. In some embodiments, the catalytic article converts carbon monoxide to carbon dioxide. In some embodiments, the catalytic article converts nitrogen oxides to nitrogen.

[0082] In some embodiments, the catalytic article converts at least about 60%, or at least about 70%, or at least about 75%, or at least about 80%, or at least about 90%, or at least about 95% of the amount of nitrogen oxides present in the exhaust gas stream prior to contact with the catalytic article. In some embodiments, the catalytic article converts at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95% of the total amount of combined hydrocarbons, carbon dioxide, and nitrogen oxides present in the exhaust gas stream prior to contact with the catalytic article. [Example]

[0083] Aspects of the present invention are more fully illustrated by the following examples, which are set forth to illustrate certain aspects of the invention and should not be construed as limiting thereof.

[0084] Examples 1A-H: Preparation of various powder catalysts with 2 wt% Pt / Pd (Pt / Pd=2 / 1) on different support materials.

[0085] The composition of the support material is listed in Table 1. Using platinum-amine complex and palladium nitrate as PGM precursors, 1.33 wt. % Pt and 0.67 wt. % Pd were sequentially deposited on the support by the incipient wetness impregnation technique. The impregnated wet powder was dried at 120°C and then calcined in air at 550°C for 2 hours. [Table 1]

[0086] Example 2: Aging and testing of catalysts from Examples 1A-H

[0087] The Pt / Pd deposited powder catalysts of Examples 1A-H were individually dispersed in deionized water to approximately 30% solids. The resulting slurries were milled and then dried with stirring. The dried slurries were calcined at 550°C for 1 hour. The resulting powder catalysts were milled and sieved to collect particles of 250-500 μm size for testing in a high-throughput reactor.

[0088] Aging was carried out at 980°C for 5 hours under cyclic lean / rich conditions in the presence of 10% steam. The lean / rich aging cycle included 5 minutes of air, 5 minutes of N2, 5 minutes of 4% H2 in equilibrium with N2, and 5 minutes of N2. Such cycles were repeated until the desired aging period was reached.

[0089] The catalytic performance was evaluated in a high-throughput reactor at λ=1.000±0.025 with oscillating feeds of 1 second lean gas and 1 second rich gas. Lean gas at λ=1.025: 0.7% CO, 0.22% H, 1.8% O, 1500 ppm C1C3H6, 750 ppm C1C3H8, 750 ppm C1iso-C4H 10 , 1500 ppm NO, 14% CO2, 10% H2O, and balance N2. Rich gas at λ=0.975: 2.33% CO, 0.77% H2, 0.7% O2, 1500 ppm C1C3H6, 750 ppm C1C3H8, 750 ppm C1iso-C4H 10 , 1500 ppm NO, 14% CO2, 10% H2O, and balance N2. The sample amount was 100 mg for each liner at a flow rate of 70 L / h. The catalyst conversion was measured at constant temperatures from 250 to 550 °C at 25 °C intervals.

[0090] The light-off temperatures (T 50) are plotted in Figure 2. Figures 1A-C are 2 wt. % Pt / Pd samples deposited on conventional supports including La2O3-stabilized Al2O3, La2O3-stabilized ZrO2, and La2O3 / Y2O3-stabilized CeO2-ZrO2, respectively. 1D-H are 2 wt. % Pt / Pd samples deposited on CeO2-Al2O3 composites with varying CeO2 to Al2O3 ratios. Examples 1D-H with CeO2-Al2O3 supports were found to exhibit significantly lower HC and NOx light-off temperatures compared to Examples 1A-C with conventional supports. The better light-off activity of Examples 1D-H is likely due to the desired Pt-Ce interactions, which provide a higher degree of Pt dispersion on the surface.

[0091] Example 3: 80 g / ft 3 Preparation of a reference Pd / Rh catalyst article with a PGM loading of (Pt / Pd / Rh=0 / 76 / 4).

[0092] The two-layer washcoat structure was coated onto a cylindrical monolithic cordierite substrate with a diameter of 4.66 inches, a length of 3.58 inches, a cell density of 600 cpsi, and a wall thickness of 3.5 mils. The detailed process is described below.

[0093] Bottom coat preparation: 38 g / ft in the form of palladium nitrate 3 of Pd (50 wt. % total Pd) was impregnated onto refractory alumina, with 38 g / ft in the form of palladium nitrate. 3 of Pd (50 wt. % total Pd) was impregnated onto a stabilized ceria-zirconia composite with about 40 wt. % ceria. A slurry containing about 35.2 wt. % refractory Al2O3, 49.6 wt. % stabilized ceria-zirconia composite, barium acetate to yield 11.6 wt. % BaO, zirconium acetate to yield 1.9 wt. % ZrO2, and 1.7 wt. % Pd was coated onto the substrate. After firing at 550 °C for 1 hour in air, the washcoat loading of the bottom coat was about 2.59 g / in 3 It was.

[0094] Topcoat preparation: 4g / ft of rhodium nitrate 3 of Rh (100 wt. % total Rh) was impregnated onto refractory alumina. A slurry mixture containing about 84.8 wt. % refractory Al2O3, 15.0 wt. % ceria-zirconia composite with about 50 wt. % ceria, and 0.23 wt. % Rh was coated onto the bottom coat. After firing at 550 °C in air for 1 hour, the washcoat loading of the top coat was about 1.00 g / in 3 The reference Pd / Rh catalyst article is illustrated in Figure 1A.

[0095] Example 4: 80 g / ft 3 Preparation of a Pt / Pd / Rh catalyst article (outside the scope) with a PGM loading of (Pt / Pd / Rh=38 / 38 / 4).

[0096] Bottom coat is 38g / ft 3 of Pt and 38g / ft 3 A catalyst article was prepared by using the same washcoat material and process as in Example 3, except that it contained Pd. The detailed process is described below.

[0097] Preparation of bottom coat: 19 g / ft in the form of platinum-amine complex 3 of Pt (50 wt. % total Pt) and 19 g / ft in the form of palladium nitrate 3 of Pd (50 wt. % total Pd) was impregnated onto refractory alumina. 19 g / ft in the form of a platinum-amine complex. 3 of Pt (50 wt. % total Pt) and 19 g / ft in the form of palladium nitrate 3of Pd (50 wt. % total Pd) was impregnated onto a stabilized ceria-zirconia composite with about 40 wt. % ceria. A slurry containing about 35.2 wt. % refractory Al2O3, 49.6 wt. % stabilized ceria-zirconia composite, barium acetate to yield 11.6 wt. % BaO, zirconium acetate to yield 1.9 wt. % ZrO2, 0.85 wt. % Pt, and 0.85 wt. % Pd was coated onto the substrate. After firing at 550 °C for 1 hour in air, the washcoat loading of the bottom coat was about 2.59 g / in 3 It was.

[0098] Topcoat preparation: 4g / ft of rhodium nitrate 3 of Rh (100 wt. % total Rh) was impregnated onto refractory alumina. A slurry mixture containing about 84.8 wt. % refractory Al2O3, 15.0 wt. % ceria-zirconia composite with about 50 wt. % ceria, and 0.23 wt. % Rh was coated onto the bottom coat. After firing at 550 °C in air for 1 hour, the washcoat loading of the top coat was about 1.00 g / in 3 The reference Pt / Pd / Rh catalyst article is illustrated in FIG. 1B.

[0099] Example 5: 80 g / ft 3 Preparation of a Pt / Pd / Rh catalyst article with a PGM loading of 1000 .mu.m and Pt deposited on a ceria-alumina composite in the bottom coat (Pt / Pd / Rh=38 / 38 / 4).

[0100] The two-layer washcoat structure was coated onto a cylindrical monolithic cordierite substrate with a diameter of 4.66 inches, a length of 3.58 inches, a cell density of 600 cpsi, and a wall thickness of 3.5 mils. The detailed process is described below.

[0101] Preparation of bottom coat (first layer): 38 g / ft in the form of platinum-amine complex 3 of Pt (100 wt. % total Pt) and 3.8 g / ft in the form of palladium nitrate 3Pd (10 wt. % total Pd) was sequentially impregnated onto a refractory ceria-alumina composite with approximately 10 wt. % ceria. The Pt / Pd-impregnated CeO2-Al2O3 composite was calcined at 550 °C for 2 hours. 22.9 g / ft2 of Pd in the form of palladium nitrate was added. 3 of Pd (60 wt. % total Pd) was impregnated onto a stabilized ceria-zirconia composite with approximately 40 wt. % ceria. A slurry containing approximately 40.2 wt. % refractory CeO2-Al2O3 composite, 50.3 wt. % stabilized ceria-zirconia composite, barium acetate to yield 4.0 wt. % BaO, zirconium acetate to yield 2.4 wt. % ZrO2, colloidal alumina dispersion to yield 1.6 wt. % Al2O3, 0.88 wt. % Pt, and 0.62 wt. % Pd was coated onto the substrate. After firing at 550 °C for 1 hour in air, the washcoat loading of the bottom coat was approximately 2.49 g / in 3 It was.

[0102] Preparation of top coat (second layer): 4 g / ft of rhodium nitrate 3 of Rh (100 wt. % total Rh) was impregnated onto refractory alumina. 11.4 g / ft in the form of palladium nitrate. 3 Pd (30 wt.% total Pd) was impregnated onto a stabilized ceria-zirconia composite with approximately 10 wt.% ceria. A slurry mixture containing approximately 38.5 wt.% refractory Al2O3, 53.9 wt.% stabilized ceria-zirconia composite, barium acetate to yield 3.8 wt.% BaO, zirconium acetate to yield 1.5 wt.% ZrO2, a colloidal alumina dispersion to yield 1.5 wt.% Al2O3, 0.51 wt.% Pd, and 0.18 wt.% Rh was coated onto the bottom coat. After firing in air at 550°C for 1 hour, the washcoat loading of the top coat was approximately 1.30 g / in 3 A Pt / Pd / Rh catalyst article of the present invention is illustrated in Figure 1C.

[0103] Example 6: 80 g / ft 3Preparation of a Pt / Pd / Rh catalyst article with a PGM loading of 1000 .mu.m and Pt deposited on a ceria-alumina composite in a topcoat (Pt / Pd / Rh=38 / 38 / 4).

[0104] The two-layer washcoat structure was coated onto a cylindrical monolithic cordierite substrate with a diameter of 4.66 inches, a length of 3.58 inches, a cell density of 600 cpsi, and a wall thickness of 3.5 mils. The detailed process is described below.

[0105] Preparation of bottom coat (second layer): 9.5 g / ft of palladium nitrate 3 of Pd (25 wt. % total Pd) was impregnated onto the refractory alumina composite, with 28.5 g / ft in the form of palladium nitrate. 3 of Pd (75 wt. % total Pd) was impregnated onto a stabilized ceria-zirconia composite with about 40 wt. % ceria. A slurry containing about 28.1 wt. % refractory Al2O3, 58.6 wt. % stabilized ceria-zirconia composite, barium acetate to yield 9.4 wt. % BaO, zirconium acetate to yield 1.9 wt. % ZrO2, a colloidal alumina dispersion to yield 1.0 wt. % Al2O3, and 1.0 wt. % Pd was coated onto a substrate. After firing at 550 °C for 1 hour in air, the washcoat loading of the bottom coat was about 2.13 g / in 3 It was.

[0106] Preparation of top coat (first layer): 4 g / ft of rhodium nitrate 3 of Rh (100 wt. % total Rh) was impregnated onto a ceria-zirconia composite with about 10 wt. % ceria. 38 g / ft in the form of a platinum-amine complex 3of Pt (100 wt. % total Pt) was impregnated onto a stabilized ceria-alumina composite with approximately 10 wt. % ceria. The Pt-impregnated CeO2-Al2O3 composite was calcined at 550 °C for 2 hours. A slurry mixture containing approximately 61.5 wt. % refractory CeO2-Al2O3 composite, 30.8 wt. % stabilized ceria-zirconia composite, barium acetate to yield 1.2 wt. % BaO, zirconium acetate to yield 2.5 wt. % ZrO2, a colloidal alumina dispersion to yield 2.5 wt. % Al2O3, 1.4 wt. % Pt, and 0.14 wt. % Rh was coated onto the bottom coat. After calcining in air at 550 °C for 1 hour, the washcoat loading of the top coat was approximately 1.62 g / in 3 A Pt / Pd / Rh catalyst article of the present invention is illustrated in Figure ID.

[0107] Example 7: 80 g / ft 3 Preparation of the presently claimed Pt / Pd / Rh catalyst article with a PGM loading of (Pt / Pd / Rh=38 / 38 / 4). The catalyst article was prepared by using the same washcoat materials and process as in Example 6, except that a refractory ceria-alumina composite with about 30% ceria was used as the support for Pt in the topcoat.

[0108] Example 8: 80 g / ft 3 Preparation of a Pt / Pd / Rh catalyst article (outside the scope) with a PGM loading of (Pt / Pd / Rh=38 / 38 / 4). Example 8 was prepared by using the same washcoat materials and process as Example 6, except that refractory ceria-free alumina was used as the support for Pt in the topcoat.

[0109] Example 9: Aging and testing of Examples 3-8

[0110] The full-size monolith catalyst articles of Examples 3-8 were mounted in a steel converter can and aged in a close-coupled position in the exhaust line of a gasoline engine operated under a fuel-cut aging cycle. The maximum bed temperature was 975°C for a duration of 50 hours. The aged catalysts were tested in a SULEV-30 gasoline test vehicle with a 1.8 L engine displacement operated under the US FTP-75 driving cycle according to certified procedures and tolerances.

[0111] The HC, NOx, and CO emissions from the FTP-75 test are summarized in Table 2. [Table 2]

[0112] The catalyst article of Example 4 was found to be less effective than the reference catalyst article of Example 3. Therefore, simply substituting Pd for Pt resulted in lower catalytic performance, i.e., higher HC, NOx, and CO emissions compared to the reference catalyst product. The catalyst article of Example 5 (which is a Pt / Pd / Rh-based bilayer TWC with a Pt / Pd bottom coat and a Pd / Rh top coat design, with Pt deposited on a ceria-alumina composite in the bottom coat) exhibited relatively higher catalytic performance in all emissions than the reference catalyst article of Example 3. The catalyst articles of Examples 6 and 7 (which are Pt / Pd / Rh-based bilayer catalyst articles with a Pd bottom coat and a Pt / Rh top coat design, with Pt deposited on a ceria-alumina composite in the top coat) exhibited lower or significantly lower NOx emissions compared to the reference catalyst articles of Examples 3 and 4, respectively. The catalyst article of Example 8 (which uses ceria-free alumina as the Pt support instead of a ceria-alumina composite) significantly worsened HC, NOx, and CO performance. This finding strongly supported Pt-ceria interaction as a key design feature for fabricating active Pt / Pd / Rh-based TWCs. The overall performance of the catalyst articles of the present invention (Examples 5-7) was found to be improved over and / or comparable to Pd / Rh-based catalyst articles for emission control applications. Furthermore, these catalyst articles of the present invention offer cost benefits over the reference Pd / Rh-based TWC due to the significant use of Pt.

[0113] References throughout this specification to “one embodiment,” “a particular embodiment,” “one or more embodiments,” or “embodiments” mean that a particular feature, structure, material, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearance of phrases such as “in one or more embodiments,” “in a particular embodiment,” “in some embodiments,” “in one embodiment,” or “in an embodiment” in various places throughout this specification do not necessarily refer to the same embodiment of the present invention. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. All of the various embodiments, aspects, and options disclosed herein can be combined in all variations, regardless of whether such features or elements are explicitly combined in the description of a specific embodiment herein. The present invention is intended to be read as a whole, and should be considered to contemplate that any separable features or elements of the disclosed invention are intended to be combinable in any of its various aspects and embodiments, unless the context clearly dictates otherwise.

[0114] Although the embodiments disclosed herein have been described with reference to particular embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Accordingly, the present invention is intended to cover modifications and variations that come within the scope of the appended claims and their equivalents, and the above-described embodiments are presented for purposes of illustration and not limitation. All patents and publications cited herein are incorporated by reference for the specific teachings described therein, unless a statement of incorporation otherwise is specifically provided.

Claims

1. a) a first layer comprising platinum, a first platinum group metal component other than platinum, a ceria-alumina composite, and an oxygen storage component, wherein platinum is supported on the ceria-alumina component, the first platinum group metal component is selected from palladium, rhodium, or a combination thereof, and the first platinum group metal component is supported on the oxygen storage component; b) a second layer comprising a second platinum group metal component and a refractory alumina component, an oxygen storage component, or a combination thereof, wherein the second platinum group metal component is selected from platinum, palladium, rhodium, or a combination thereof; c) a substrate; and a layered catalyst article for a three-way catalyst used to remove HC, NOx, and CO from an exhaust gas, comprising: the amount of platinum is 10 to 80 wt. %, based on the total weight of platinum, palladium, and rhodium; and i) the first layer is deposited on the substrate as a bottom layer, the first layer comprising platinum supported on the ceria-alumina component and palladium supported on the ceria-alumina and oxygen storage component; the second layer is deposited on the first layer as a top layer, the second layer comprising rhodium supported on the ceria-alumina component, refractory alumina component, oxygen storage component, or any combination thereof, and optionally palladium supported on the oxygen storage component, wherein the amount of platinum is 10 to 80 wt %, based on the total weight of the platinum, palladium, and rhodium; or ii) the second layer is deposited on the substrate as a bottom layer, the second layer comprising palladium supported on the oxygen storage component, a refractory alumina component, or a combination thereof, and the first layer is deposited on the second layer as a top layer, the first layer comprising rhodium supported on the oxygen storage component and platinum supported on a ceria-alumina component, the amount of platinum being 10 to 80 wt % based on the total weight of the platinum, palladium, and rhodium; and the amount of platinum in the second layer is less than 0.001 wt. %, based on the total weight of palladium and rhodium present in the second layer; and The platinum is impregnated into the ceria-alumina composite by a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and then calcined; and the oxygen storage component of the first and second layers comprises ceria, zirconia, and a rare earth metal oxide selected from lanthana, yttria, neodymia, praseodymia, gadolinia, or any combination thereof; and A layered catalyst article wherein the oxygen storage component of the first and second layers comprises ceria in an amount of 5.0 to 50.0 wt. %, based on the total weight of the oxygen storage component.

2. 10. The layered catalyst article of claim 1, wherein the amount of platinum is 20 to 50 weight percent, based on the total weight of platinum, palladium, and rhodium.

3. 10. The layered catalyst article of claim 1, wherein the amount of platinum in the first layer is from 50 to 100 weight percent, based on the total weight of platinum in the catalyst article.

4. 4. The layered catalyst article of any one of claims 1 to 3, wherein the correlation coefficient between platinum and aluminum in the first layer is greater than 70% as measured by EPMA line scan analysis.

5. 5. The layered catalyst article of any one of claims 1 to 4, wherein the ceria-alumina component comprises ceria-alumina, ceria-yttrium-alumina, ceria-silica-alumina, ceria-tin-alumina, ceria-manganese-alumina, ceria-iron-alumina, ceria-nickel-alumina, ceria-iridium-alumina, ceria-ruthenium-alumina, or ceria-indium-alumina.

6. 6. The layered catalyst article of any one of claims 1 to 5, wherein the ceria content of the ceria-alumina component is in the range of 1.0 to 75.0 wt %, based on the total weight of the ceria-alumina component.

7. 7. The layered catalyst article of any one of claims 1 to 6, wherein the ceria content of the ceria-alumina component is in the range of 5.0 to 50.0 wt %, based on the total weight of the ceria-alumina component.

8. 8. The layered catalyst article of any one of claims 1 to 7, wherein the ceria content of the ceria-alumina component is in the range of 5.0 to 30.0 wt %, based on the total weight of the ceria-alumina component.

9. 9. The layered catalyst article of any one of claims 1 to 8, wherein the amount of platinum in the first layer is in the range of 0.02 to 4.0 wt. %, based on the total weight of the washcoat of the catalyst article.

10. 9. The layered catalyst article of any one of claims 1 to 8, wherein the amount of palladium in the catalyst article is in the range of 0.02 to 4.0 wt. %, based on the total weight of the washcoat of the catalyst article.

11. 9. The layered catalyst article of any one of claims 1 to 8, wherein the amount of rhodium in the catalyst article is in the range of 0.02 to 4.0 wt %, based on the total weight of the washcoat of the catalyst article.

12. 12. The layered catalyst article of any one of claims 1 to 11, wherein the refractory alumina component comprises alumina and, optionally, a dopant selected from lanthana, ceria, titania, zirconia, hafnia, magnesia, calcia, strontia, baria, or any combination thereof.

13. The layered catalyst article of any one of claims 1 to 12, wherein no exogenous platinum is added in the second layer.

14. The layered catalyst article of any one of claims 1 to 13, wherein the first layer and / or the second layer further comprise barium oxide, strontium oxide, lanthanum oxide, or any combination thereof.

15. The layered catalyst article of any one of claims 1 to 14, wherein the substrate is selected from a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, and a woven fiber substrate.

16. The layered catalyst article of any one of claims 1 to 15, wherein the platinum is thermally or chemically fixed to the ceria-alumina component.

17. 4. A process for preparing a layered catalyst article according to any one of claims 1 to 3, comprising: preparing a first layer slurry; depositing the first layer slurry on a substrate to obtain a bottom layer; preparing a second layer slurry; depositing the second layer slurry on the bottom layer to obtain a top layer; and subsequently calcining at a temperature in the range of 400 to 700°C, wherein in the step of preparing the bottom coat slurry or the top coat slurry, platinum or platinum and palladium are deposited on the support using a technique selected from incipient wetness impregnation and incipient wetness co-impregnation.

18. 4. A process for preparing a layered catalyst article according to claim 1, comprising: preparing a first layer slurry; preparing a second layer slurry; depositing the second layer slurry on a substrate to obtain a bottom layer; depositing the first layer slurry on the bottom layer to obtain a top layer; and subsequently calcining at a temperature in the range of 400 to 700°C, wherein in the step of preparing the first layer slurry or the second layer slurry, platinum or platinum and palladium are deposited on the support using a technique selected from incipient wetness impregnation and incipient wetness co-impregnation.

19. An exhaust system for an internal combustion engine, said system comprising a layered catalyst article according to any one of claims 1 to 16.

20. 20. The exhaust system of claim 19, wherein the system comprises a platinum group metal based three-way conversion catalyst article and the layered catalyst article of any one of claims 1 to 16, wherein the platinum group metal based three-way conversion catalyst article is located downstream of an internal combustion engine, and the layered catalyst article is located downstream in fluid communication with the platinum group metal based three-way conversion catalyst article.

21. 20. The exhaust system of claim 19, wherein the system comprises a platinum group metal based three-way catalyst article and the layered catalyst article of any one of claims 1 to 16, the layered catalyst article being located downstream of an internal combustion engine, and the platinum group metal based three-way catalyst article being located downstream in fluid communication with the layered catalyst article.

22. 22. A method for treating a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides, comprising contacting the exhaust stream with the layered catalyst article of any one of claims 1-16 or the exhaust system of any one of claims 19-21.

23. 22. A method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, comprising contacting the gaseous exhaust stream with the layered catalyst article of any one of claims 1-16 or the exhaust system of any one of claims 19-21 to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the gaseous exhaust stream.

24. Use of a catalytic article according to any one of claims 1 to 16 or an exhaust system according to any one of claims 19 to 21 for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide and nitrogen oxides.

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