Exhaust aftertreatment system including three-way catalyst

Abstract

The present invention provides an exhaust aftertreatment system, the system including: a first three-way catalyst deposited on at least a portion of a first substrate; and a second three-way catalyst deposited on at least a portion of a second substrate, wherein the first three-way catalyst includes platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; and the second three-way catalyst includes platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

Description

[Technical Field]

[0001] The presently claimed invention relates to an exhaust aftertreatment system including at least two three-way catalysts (TWCs). In particular, the presently claimed invention relates to an exhaust aftertreatment system including at least two three-way catalysts (TWCs), one TWC located in an upstream position and another TWC located in a downstream position. [Background technology]

[0002] Exhaust gases from vehicles powered by gasoline engines are typically treated with one or more three-way conversion (TWC) automotive catalysts that are effective in reducing the pollutants nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) in the engine exhaust. For example, a typical exhaust aftertreatment system for a gasoline engine consists of two TWC catalysts: a first / upstream TWC catalyst mounted in a location near the exhaust manifold and engine compartment (close-coupled location, CC), and a second / downstream TWC catalyst located either immediately adjacent to the first TWC catalyst (second close-coupled location, CC2) or under the vehicle body (underfloor location, UF).

[0003] Conventional TWC catalysts contain two platinum group metals (PGMs), namely palladium (Pd) and rhodium (Rh), as active catalytic components, supported on an oxygen storage component (OSC) and / or a refractory metal oxide support.

[0004] DE 10 / 2019 / 208436 A1 relates to a method for aftertreatment of a lean-burn engine, which is a method for controlling an aftertreatment system that is provided in an exhaust pipe through which exhaust gases flow, in sequence with an ammonia-generating catalyst module, a selective catalytic reduction catalyst, and a CO purification catalyst.

[0005] US Patent Application Publication No. 2010 / 061903(A1) relates to a catalyst system used in an automobile exhaust gas purification device, which includes the use of two or more exhaust gas purification catalysts, including a first catalyst supported on an inorganic structural support and a second catalyst supported on a portion of the inorganic structural support and located downstream.

[0006] U.S. Patent Application Publication No. 2002 / 048542(A1) describes a method for detecting NO in an exhaust gas stream. x The present invention discloses a catalytic trap for the conversion of toluene, the catalytic trap comprising a catalytic trap material and a refractory carrier member coated with the catalytic trap material.

[0007] US Patent Application Publication No. 2009 / 042722 A1 discloses a method for making a catalyst having a base metal undercoat with an oxygen storage component.

[0008] Existing exhaust aftertreatment systems for gasoline engines utilize high loadings of palladium, which makes the exhaust systems least cost-effective. This has led to renewed interest in the automotive industry in using significant amounts of Pt for TWC applications, given the current low price of Pt in the market. Therefore, the present invention focuses on providing a high-performance, cost-effective emission control system that includes at least two three-way catalysts (TWCs) and uses significant amounts of Pt.

[0009] Object of the invention It is an object of the presently claimed invention to provide an exhaust aftertreatment system that offers comparable or improved performance when compared to conventional Pd / Rh-based TWC systems.

[0010] Another object of the presently claimed invention is to provide an exhaust aftertreatment system that provides improved NOx performance during a fuel cut event.

[0011] It is yet another object of the presently claimed invention to provide an exhaust aftertreatment system that allows for substantial replacement (20-80%) of Pd with Pt, thereby making the system cost effective. Summary of the Invention

[0012] The present invention provides an exhaust aftertreatment system including a first three-way catalyst deposited on at least a portion of a first substrate and a second three-way catalyst deposited on at least a portion of a second substrate; the first three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; The second three-way catalyst is alumina, It includes platinum supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, or any combination thereof.

[0013] The present invention also provides a method for reducing emissions of hydrocarbons, carbon monoxide, and nitrogen oxides levels in a gaseous exhaust stream, comprising contacting the gaseous exhaust stream with an exhaust aftertreatment system according to the present invention to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the gaseous exhaust.

[0014] The present invention further provides the use of an exhaust aftertreatment system according to the present invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides. [Brief explanation of the drawings]

[0015] To provide an understanding of embodiments of the present invention, reference is made to the accompanying drawings, which are not necessarily drawn to scale, and in which reference numerals refer to components of exemplary embodiments of the present invention. The drawings are merely illustrative and should not be construed as limiting the present invention. The above and other features of the presently claimed invention, their nature and various advantages will become more apparent from the following detailed description considered in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a diagram showing the configuration of a TWC catalyst system. [Figure 2] FIG. 10 shows FTP-75 tailpipe cumulative NOx emissions for Examples S5 and S6 collected on a SULEV30 vehicle calibrated with frequent fuel cut events. [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 presently claimed invention. [Figure 3B] 3B is an enlarged partial cross-sectional view of FIG. 3A taken along a plane parallel to the edge of the substrate carrier of FIG. 3A, showing an enlarged view of a plurality of gas passages shown in FIG. 3A. [Figure 4] FIG. 3B is an enlarged cross-sectional cutaway view of FIG. 3A, in which the honeycomb-shaped substrate of FIG. 3A represents a wall-flow filter substrate monolith. DETAILED DESCRIPTION OF THE INVENTION

[0016] The presently claimed invention is described more fully below. The presently claimed 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 the presently claimed 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 essential to the practice of the disclosed materials and methods.

[0017] All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "etc.") provided herein is intended merely to better illustrate the materials and methods and does not impose a limitation on scope unless otherwise asserted.

[0018] Definition: The use of the terms "a," "an," "the," and similar referents in the context of describing the materials and methods discussed herein (particularly in the context of the claims which follow) should be construed to encompass both the singular and the plural unless otherwise indicated herein or clearly contradicted by context.

[0019] The recitation of ranges of values ​​herein, unless otherwise stated herein, is merely intended to serve as a shorthand method of referring individually to each separate value within that range, and each separate value is incorporated herein as if it were individually recited herein.

[0020] In the context of the present invention, the term "washcoat" is used interchangeably with "first three-way catalyst" or "second three-way catalyst" that form one or more layers on a portion of a respective substrate. As used herein, the term "washcoat" has its ordinary meaning in the art of a thin, adherent coating of catalytic or other material applied to the substrate material. Generally, washcoats are formed by preparing a slurry containing particles of a particular solids content (e.g., 15-60% by weight) in a liquid vehicle, which is then coated onto the substrate and dried to provide a washcoat layer on the respective substrate.

[0021] The term "three-way conversion catalyst" or TWC catalyst refers to a catalyst that simultaneously a) reduces nitrogen oxides to nitrogen and oxygen, b) oxidizes carbon monoxide to carbon dioxide, and c) oxidizes unburned hydrocarbons to carbon dioxide and water.

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

[0023] As used herein, the term "stream" refers broadly to any combination of flowing gases that may contain solid or liquid particulate matter.

[0024] As used herein, the terms "upstream" and "downstream" refer to the relative directions of engine exhaust gas flow from the engine toward the exhaust pipe, with the engine being in the upstream position and the tailpipe and any pollution control articles, such as filters and catalysts, being downstream from the engine.

[0025] The term "close coupled" refers to the location of one or more catalytic converters located in close proximity to the engine out manifold.

[0026] The term "underfloor" refers to the location of one or more catalytic converters that are located away from the close-coupled location. Typically, an underfloor catalytic converter is located under the floor of the vehicle body, between the close-coupled catalytic converter and the muffler.

[0027] In the context of the present invention, the amounts of platinum group metals such as platinum / palladium / rhodium, and / or support materials such as ceria-zirconia mixed oxide, ceria-alumina composite, alumina, etc. are calculated as weight percent based on the total weight of the washcoat present on the substrate, i.e., the amounts are calculated without taking into account the amount of the substrate, although the substrate is also part of the overall catalyst system.

[0028] The present invention focuses on addressing the poor NOx performance during fuel cut events associated with existing exhaust aftertreatment systems and improving overall performance despite substantial replacement of Pd with Pt (20-80%).

[0029] In a first aspect, the present invention provides an exhaust aftertreatment system, the exhaust aftertreatment system comprising: a. a first three-way catalyst deposited on at least a portion of a first substrate; b. a second three-way catalyst deposited on at least a portion of the second substrate; Including, The first three-way catalyst is i. platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; ii. palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; iii. rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; Including, The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0030] Amount of platinum group metal: The amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is preferably within the range of 0.01 to 5.0 wt % based on the total weight of the first and second three-way catalysts. More preferably, the amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is within the range of 0.02 to 3.0 wt % based on the total weight of the first and second three-way catalysts. Even more preferably, the amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is within the range of 0.03 to 2.5 wt % based on the total weight of the first and second three-way catalysts.

[0031] The amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is preferably within the range of 0.01 to 4.0 wt % based on the total weight of the first and second three-way catalysts. More preferably, the amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is within the range of 0.02 to 3.0 wt % based on the total weight of the first and second three-way catalysts. Even more preferably, the amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is within the range of 0.02 to 2.0 wt % based on the total weight of the first and second three-way catalysts.

[0032] The amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is preferably within the range of 0.01 to 2.0 wt % based on the total weight of the first and second three-way catalysts. More preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is within the range of 0.01 to 1.5 wt % based on the total weight of the first and second three-way catalysts. Even more preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first and second three-way catalysts is within the range of 0.01 to 1.0 wt % based on the total weight of the first and second three-way catalysts.

[0033] Weight ratio: Preferably, the weight ratio of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is greater than 1.

[0034] More preferably, the weight ratio of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 2:1 to 20:1.

[0035] Even more preferably, the weight ratio of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 2.5:1 to 12:1.

[0036] Preferably, the weight ratio of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 1:3 to 50:1, more preferably within the range of 1:1 to 50:1.

[0037] Even more preferably, the weight ratio of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 1:2 to 20:1, more preferably 1:1 to 20:1. Even more preferably, the weight ratio of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 1:1.5 to 4:1, more preferably 1:1 to 4:1.

[0038] Preferably, the weight ratio of the total amount of platinum, palladium, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to the total amount of platinum and, optionally, rhodium and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 1.1:1 to 20:1.

[0039] More preferably, the weight ratio of the total amount of platinum, palladium, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to the total amount of platinum and, optionally, rhodium and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 4:1 to 20:1.

[0040] Even more preferably, the weight ratio of the total amount of platinum, palladium, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to the total amount of platinum and, optionally, rhodium and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 8:1 to 12:1.

[0041] Support material: "Support" in the context of a catalyst material or catalyst composition or catalyst washcoat refers to a material that receives metals (e.g., PGMs), stabilizers, promoters, binders, etc., by precipitation, association, dispersion, impregnation, or other suitable method.

[0042] Throughout this application, the term "supported" has its conventional meaning in the field of heterogeneous catalysis. In general, 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. Typical supported catalysts are prepared by impregnation or co-precipitation methods, optionally followed by calcination.

[0043] Ceria-alumina composite: Ceria-alumina composites are composites in which CeO2 is distributed on the surface and / or in the bulk of the alumina as particles and / or nanoclusters. Each oxide may have its distinct chemical and solid-state physical state. The surface CeO2 modification of the alumina may be in the form of discrete moieties (particles or clusters) or in the form of a layer of ceria that partially or completely covers the surface of the alumina.

[0044] Preferably, the amount of ceria-alumina composite present in the first and second three-way catalysts is in the range of 5.0 to 80 wt % based on the total weight of the first and second three-way catalysts. More preferably, the amount of ceria-alumina composite present in the first and second three-way catalysts is in the range of 10 to 60 wt % based on the total weight of the first and second three-way catalysts. Even more preferably, the amount of ceria-alumina composite present in the first and second three-way catalysts is in the range of 15 to 60 wt %, more preferably 15 to 40 wt %, based on the total weight of the first and second three-way catalysts.

[0045] The amount of CeO2 (cerium oxide) in the ceria-alumina composite present in the first or second three-way catalyst is preferably 1.0 to 60 wt% based on the total weight of the ceria-alumina composite in the respective three-way catalyst. More preferably, the amount of CeO2 in the ceria-alumina composite present in the first or second three-way catalyst is 10 to 50 wt% based on the total weight of the ceria-alumina composite in the respective three-way catalyst. Even more preferably, the amount of CeO2 in the ceria-alumina composite present in the first or second three-way catalyst is 15 to 50 wt% based on the total weight of the ceria-alumina composite in the respective three-way catalyst.

[0046] The amount of Al2O3 (aluminum oxide) in the ceria-alumina composite present in the first or second three-way catalyst is preferably 40 to 99 wt% based on the total weight of the ceria-alumina composite in the respective three-way catalyst. More preferably, the amount of Al2O3 in the ceria-alumina composite present in the first or second three-way catalyst is 50 to 90 wt% based on the total weight of the ceria-alumina composite in the respective three-way catalyst. Even more preferably, the amount of Al2O3 in the ceria-alumina composite present in the first or second three-way catalyst is 50 to 85 wt% based on the total weight of the ceria-alumina composite in the respective three-way catalyst.

[0047] Preferably, the average particle size of the ceria in the ceria-alumina composite is less than 200 nm, and more preferably, the particle size is in the range of 5.0 nm to 50 nm, as determined by a transmission electron microscope.

[0048] The ceria-alumina composite present in the first or second three-way catalyst may include a dopant selected from zirconia, lanthana, titania, hafnia, magnesia, calcia, strontian, baria, or any combination thereof. The total amount of dopant in the ceria-alumina composite is preferably in the range of 0.001 to 15 wt %, based on the total weight of the ceria-alumina composite in the respective catalyst.

[0049] Ceria-alumina composites 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 the resulting mixture is then converted into a ceria-alumina composite. Suitable cerium-containing precursors include, for example, aqueous cerium salts and colloidal ceria suspensions. Ceria-alumina can also be prepared by atomic layer deposition, in which a ceria compound selectively reacts with the alumina surface to form ceria on the alumina surface after calcination. This deposition / calcination process can be repeated until a layer of the desired thickness is achieved. Suitable aluminum-containing precursors include, for example, aluminum oxides such as gibbsite, boehmite, gamma alumina, delta alumina, or theta alumina, or a combination thereof. The resulting mixture can then be converted into a ceria-alumina composite by a calcination step.

[0050] Ceria-zirconia mixed oxide (CZO): The term "complex metal oxide" refers to a mixed metal oxide containing oxygen anions and at least two different metal cations. In ceria-zirconia mixed oxides, cerium and zirconium cations are distributed within the oxide lattice structure. The terms "complex oxide" and "mixed oxide" can be used interchangeably. Because the metal cations are distributed within the oxide lattice structure, these structures are also commonly referred to as solid solutions.

[0051] Preferably, the amount of ceria-zirconia mixed oxide present in the first and second three-way catalysts is 20 to 80 wt % based on the total weight of the first and second three-way catalysts. Most preferably, the amount of ceria-zirconia mixed oxide present in the first and second three-way catalysts is in the range of 25 to 75 wt % based on the total weight of the first and second three-way catalysts. Even more preferably, the amount of ceria-zirconia mixed oxide present in the first and second three-way catalysts is in the range of 30 to 75 wt %, more preferably 40 to 60 wt %, based on the total weight of the first and second three-way catalysts.

[0052] Preferably, the ceria (calculated as CeO) of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is present in an amount of 10 to 60 wt %, based on the total weight of the ceria-zirconia mixed oxide present in the respective catalyst, and the zirconia (calculated as ZrO) of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is present in an amount of 40 to 90 wt %, based on the total weight of the ceria-zirconia mixed oxide present in the respective catalyst.

[0053] More preferably, the ceria (calculated as CeO) of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is present in an amount of 20 to 50 wt %, based on the total weight of the ceria-zirconia mixed oxide in the respective catalyst, and the zirconia (calculated as ZrO) of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is present in an amount of 50 to 80 wt %, based on the total weight of the ceria-zirconia mixed oxide in the respective catalyst.

[0054] Even more preferably, the ceria (calculated as CeO) of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is present in an amount of 30 to 50 wt %, based on the total weight of the ceria-zirconia mixed oxide in the respective catalyst, and the zirconia (calculated as ZrO) of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is present in an amount of 50 to 70 wt %, based on the total weight of the ceria-zirconia mixed oxide in the respective catalyst.

[0055] 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 actively react 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.

[0056] In a preferred embodiment, the ceria-zirconia mixed oxide present in the first or second three-way catalyst contains a dopant selected from lanthana, titania, hafnia, magnesia, calcia, strontia, baria, 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 as a blend of a mixture of both the dopant and the composite metal oxide in microscale oxide form, i.e., in a composite form with the composite metal oxide. Preferably, the dopant is present 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 catalyst.

[0057] alumina: The alumina present in the first or second three-way catalyst is preferably gamma alumina or activated alumina. It typically has a surface area of ​​60 square meters per gram ("m 2 / g), often up to about 200m 2 / g or greater BET surface area of ​​fresh material. Activated alumina is typically a mixture of gamma and delta phases of alumina, but may also contain significant amounts of eta, kappa, and theta alumina phases. Preferably, the activated alumina is high bulk density gamma-alumina, low or medium bulk density large pore gamma-alumina, low bulk density large pore boehmite or gamma-alumina.

[0058] Preferably, the amount of alumina present in the first and second three-way catalysts is within the range of 5.0 to 70 wt % based on the total weight of the first and second three-way catalysts. More preferably, the amount of alumina present in the first and second three-way catalysts is within the range of 5.0 to 20 wt % based on the total weight of the first and second three-way catalysts. Also preferably, the amount of alumina present in the first and second three-way catalysts is within the range of 10 to 60 wt % based on the total weight of the first and second three-way catalysts. Most preferably, the amount of alumina present in the catalyst article is within the range of 15 to 60 wt % based on the total weight of the first and second three-way catalysts.

[0059] The alumina present in the first and second three-way catalysts is preferably doped with a dopant selected from barium, lanthana, zirconia, neodymian, yttria, ceria, titania, or any combination thereof, and the amount of dopant is preferably 1.0 to 30 wt % based on the total weight of the alumina and dopant present in each catalyst. More preferably, the doped alumina is selected from lanthana-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, lanthana-zirconia-alumina, baria-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, yttrium-alumina, or any combination thereof.

[0060] Base material: The substrates of the first and second three-way catalysts of the presently claimed invention, i.e., the first and second substrates, can be composed of any material typically used to prepare automotive catalysts. In preferred embodiments, the substrate is a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, or a woven fiber substrate. In more preferred embodiments, the substrate is a ceramic or metal monolith honeycomb structure.

[0061] The substrate provides a plurality of walls to which the catalytic layers or washcoats described herein above are applied and adhered, thereby acting as supports for the catalytic material.

[0062] Preferred metal substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium, and / or aluminum, and the total amount of these metals may advantageously comprise at least 15% by weight of the alloy, e.g., 10-25% by weight chromium, 3-8% by weight aluminum, and up to 20% by weight nickel. The alloy may also contain minor or trace amounts of one or more metals, such as manganese, copper, vanadium, or 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 to improve the corrosion resistance of the alloy and promote adhesion of a washcoat layer to the metal surface.

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

[0064] Any suitable substrate may be used, such as a monolithic flow-through substrate having a plurality of fine, parallel gas flow passages extending from the inlet face to the outlet face of the substrate such that the 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 contacts the catalytic material. The flow passages in the monolithic substrate are thin-walled passages of any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, or circular. Such structures contain gas inlet openings (i.e., "cells") per square inch of cross section (cpsi), from about 60 to about 1200 or more, more commonly from about 300 to 900 cpsi. The wall thickness of the flow-through substrate can vary, but a typical range is 0.002 to 0.1 inches. Representative commercially available flow-through substrates are cordierite substrates with 400 cpsi and a 6-mil wall thickness, or 600 cpsi and a 4-mil wall thickness. 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, with each passage blocked by a non-porous plug at one end of the substrate body, and alternating passages blocked at the opposite end. This requires gas to flow through the porous walls of the wall-flow substrate to reach the outlet. Such monolithic substrates can contain pressures up to about 700 cpsi or more, e.g., about 100 to 400 cpsi, more typically about 200 to about 300 cpsi. The cross-sectional shape of the cells can vary, as described above. Wall-flow substrates typically have wall thicknesses of 0.002 to 0.1 inches. Typical commercially available wall-flow substrates are constructed from porous cordierite, examples of which have wall thicknesses of 200 cpsi and 10 mils or 300 cpsi and 8 mils, and wall porosities of 45 to 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 any particular substrate type, material, or shape.It should be noted that if the substrate is a wall-flow substrate, the catalyst composition, in addition to being disposed on the surface of the wall, can penetrate into the pore structure of the porous wall (i.e., partially or completely block the pore openings). In one embodiment, the substrate has a flow-through ceramic honeycomb structure, a wall-flow ceramic honeycomb structure, or a metal honeycomb structure.

[0065] 3A and 3B illustrate an exemplary substrate 2 in the form of a flow-through substrate coated with a washcoat composition / catalyst layer(s) 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 that is identical to end surface 6. The substrate 2 has a plurality of fine, parallel gas flow passages 10 formed therein. As can be seen in FIG. 3B, the passages 10 are defined 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 to allow a fluid, e.g., a gas stream, to flow longitudinally through the substrate 2 via the gas flow passages 10. As can be more readily 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 / catalyst layer can be applied in multiple, separate layers, if desired. In the illustrated embodiment, the washcoat comprises a first, separate washcoat layer 14 adhered to the wall 12 of the substrate member and a second, separate washcoat layer 16 coated on the first washcoat layer 14. In one embodiment, the presently claimed invention may also be practiced with more than two (e.g., three or four) washcoat layers and is not limited to the two-layer embodiment shown.

[0066] FIG. 4 shows an exemplary substrate 2 in the form of a wall-flow filter substrate coated with a washcoat composition described herein. As can be seen in FIG. 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 with inlet plugs 58 and at the outlet end with outlet plugs 60, forming an opposing 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 channel walls 53 (which are porous) to the outlet side 66. The gas cannot return to the inlet side of the wall due to the inlet plugs 58. The porous wall-flow filters used in the present invention are catalyzed in that the walls of the element have one or more catalyst materials thereon or contain one or more catalyst materials 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 consist 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] Washcoat(s) on substrate: The first substrate is coated with a first three-way catalyst and the second substrate is coated with a second three-way catalyst.

[0068] Preferably, the first three-way catalyst covers 50-100% of the length of the first substrate. More preferably, the first three-way catalyst covers 70-100% of the length of the first substrate, and even more preferably, the first three-way catalyst covers 90-100% of the length of the first substrate. Most preferably, the first three-way catalyst covers the entire length or accessible surface area of ​​the substrate.

[0069] Preferably, the second three-way catalyst covers 50-100% of the length of the second substrate. More preferably, the second three-way catalyst covers 70-100% of the length of the second substrate, and even more preferably, the second three-way catalyst covers 90-100% of the length of the second substrate. Most preferably, the second three-way catalyst covers the entire length or accessible surface area of ​​the substrate.

[0070] The term "accessible surface" refers to a surface of the substrate that can be covered by conventional coating techniques used in the field of catalyst preparation, such as impregnation techniques.

[0071] The first three-way conversion (TWC) catalyst The first three-way catalyst is deposited on at least a portion of the first substrate. Preferably, the first three-way catalyst covers 50-100% of the length of the first substrate. More preferably, the first three-way catalyst covers 70-100% of the length of the first substrate, and even more preferably, the first three-way catalyst covers 90-100% of the length of the first substrate. Most preferably, the first three-way catalyst covers the entire length or accessible surface area of ​​the substrate.

[0072] The first three-way catalyst includes platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0073] Preferably, the total washcoat loading of the first three-way catalyst is 1.0 to 10 g / in 3 More preferably, the total washcoat loading of the first three-way catalyst is 2.0 to 7.0 g / in 3 Even more preferably, the total washcoat loading of the first three-way catalyst is 2.5 to 4.5 g / in 3 is.

[0074] Preferably, the total platinum group metal (PGM) loading of the first three-way catalyst is 10 to 200 g / ft 3 More preferably, the total platinum group metal (PGM) loading of the first three-way catalyst is 50 to 175 g / ft 3 Even more preferably, the total platinum group metal (PGM) loading of the first three-way catalyst is 100 to 130 g / ft 3 is.

[0075] Preferably, the first three-way catalyst is a single layer catalyst, a two layer catalyst, or a two layer catalyst having a zone configuration.

[0076] In a preferred embodiment, the first three-way catalyst is a two-layer catalyst comprising a first layer deposited on at least a portion of a first substrate and a second layer deposited on at least a portion of the first layer or on a portion of the first substrate, or both, wherein the first layer comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0077] In a more preferred embodiment, the first three-way catalyst is a two-layer catalyst comprising a first layer deposited on at least a portion of a first substrate and a second layer deposited on at least a portion of the first layer or on a portion of the first substrate, or both, wherein the first layer comprises platinum supported on a ceria-alumina composite and palladium supported on a ceria-zirconia mixed oxide, and the second layer comprises rhodium supported on a ceria-alumina composite and a ceria-zirconia mixed oxide.

[0078] Preferably, the washcoat loading of the first layer is 0.5 to 7.0 g / in 3 and the washcoat loading of the second layer is 0.5-3.0 g / in 3More preferably, the washcoat loading of the first layer is 1.0 to 3.0 g / in 3 and the washcoat loading of the second layer is 0.5-2.0 g / in 3 Even more preferably, the washcoat loading of the first layer is 2.0 to 3.0 g / in 3 and the washcoat loading of the second layer is 0.5-1.5 g / in 3 is.

[0079] In a most preferred embodiment, the first three-way catalyst is a two-layer catalyst. The total washcoat loading of the first three-way catalyst is 1.0 to 10 g / in 3 and The washcoat loading of the first layer is 0.5 to 7.0 g / in 3 and The washcoat loading of the second layer is 0.5 to 3.0 g / in 3 is. Total PGM loading is 10-200g / ft 3 and The first layer was 5.0 to 100 g / ft 2 deposited on the ceria-alumina composite. 3 of Pt and 5.0-100g / ft2 deposited on ceria-zirconia mixed oxide 3 Pd and The second layer was deposited on the refractory ceria-alumina composite at 0.5-5 g / ft 3 of Rh, and ceria-zirconia mixed oxide.

[0080] In a further most preferred embodiment, the first three-way catalyst is a two-layer catalyst. The total washcoat loading of the first three-way catalyst is 2.5 to 4.5 g / in 3 and The washcoat loading of the first layer is 2.0 to 3.0 g / in 3 and The washcoat loading of the second layer is 0.5 to 1.5 g / in 3 is. Total PGM loading is 101-153g / ft3 and The first layer was 50-75 g / ft 2 deposited on the ceria-alumina composite. 3 of Pt and 50-75g / ft deposited on ceria-zirconia mixed oxide 3 Pd and The second layer was deposited on the refractory ceria-alumina composite at 1-3 g / ft 3 of Rh, and ceria-zirconia mixed oxide.

[0081] In another preferred embodiment, the first three-way catalyst is a two-layer catalyst comprising a first layer and a second layer. the first layer includes a first zone and a second zone; a first zone comprising palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; a second zone comprising platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; A second layer is deposited on at least a portion of the first layer, the second layer comprising rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof. In another more preferred embodiment, the first three-way catalyst is a two-layer catalyst comprising a first layer and a second layer.

[0082] the first layer includes a first zone and a second zone; the first zone and the second zone are 100% of the substrate length; The first zone contains 100-200 g / ft supported on alumina and ceria-zirconia mixed oxides. 3 containing palladium, The second zone consisted of 25-100 g / ft supported on ceria-zirconia mixed oxide and ceria-alumina composites. 3of platinum and 5.0 to 25 g / ft supported on ceria-zirconia mixed oxide and ceria-alumina composites 3 and palladium, A second layer is deposited on at least a portion of the first layer, the second layer being 1.0 to 10 g / ft supported on the ceria-zirconia mixed oxide and the ceria-alumina composite. 3 of rhodium, The total washcoat loading of the first three-way catalyst is 1.0 to 10 g / in 3 and the total PGM loading is 10-200g / ft 3 and The washcoat loading in the first zone is 0.25 to 4.0 g / in 3 and The washcoat loading in the second zone is 0.25 to 4.0 g / in 3 and The washcoat loading of the second layer is 0.25 to 2.0 g / in 3 and 70% of the total platinum is deposited on the refractory ceria-alumina composite and 30% of the total platinum is deposited on the ceria-zirconia mixed oxide.

[0083] In the context of the present invention, the term "first zone" is used interchangeably with "inlet zone" or "front zone," while the term "second zone" is used interchangeably with "outlet zone" or "rear zone." The terms "first zone" and "second zone" also describe the relative positioning of the catalyst article in the flow direction, respectively, when disposed in an 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 substrate inlet, while the second zone covers at least a portion of the substrate from the substrate outlet. The substrate inlet is a first end (inlet end portion) that can receive the engine exhaust gas flow from the engine, while the substrate outlet is a second end (outlet end portion) from which the treated exhaust gas flow exits.

[0084] Preferably, the first and second zones together cover 50-100% of the length of the substrate, more preferably, the first and second zones together cover 90-100% of the length of the substrate, and even more preferably, the first and second zones together cover the entire length of the substrate or the entire accessible surface area of ​​the substrate.

[0085] The term "accessible surface" refers to a surface of the substrate that can be covered by conventional coating techniques used in the field of catalyst preparation, such as impregnation techniques.

[0086] Preferably, the first zone covers 10-90% of the total length of the substrate from the inlet, and the second zone covers 90-10% of the total length of the substrate from the outlet, but the first and second zones together cover 20-100% of the length of the substrate.

[0087] More preferably, the first zone covers 20-80% of the total length of the substrate from the inlet, and the second zone covers 80-20% of the total length of the substrate from the outlet, but the first and second zones together cover 40-100% of the length of the substrate.

[0088] Even more preferably, the first zone covers 30-70% of the total length of the substrate from the inlet, and the second zone covers 70-30% of the total length of the substrate from the outlet, but the first and second zones together cover 60-100% of the length of the substrate.

[0089] Even most preferably, the first zone covers 40-50% of the total length of the substrate from the inlet, and the second zone covers 50-40% of the total length of the substrate from the outlet, but the first and second zones together cover 80-100% of the length of the substrate.

[0090] Preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.05 to 3.0 wt %, based on the total weight of the first three-way catalyst.

[0091] More preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.1 to 1.0 wt %, based on the total weight of the first three-way catalyst.

[0092] Preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.05 to 5.0 wt %, based on the total weight of the first three-way catalyst.

[0093] More preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.1 to 2.0 wt %, based on the total weight of the first three-way catalyst.

[0094] Preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.001 to 1.0 wt %, based on the total weight of the first three-way catalyst.

[0095] More preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.005 to 0.5 wt %, based on the total weight of the first three-way catalyst.

[0096] Ceria-alumina composite: Preferably, the amount of ceria-alumina composite present in the first three-way catalyst is in the range of 5.0 to 80 wt % based on the total weight of the first three-way catalyst. More preferably, the amount of ceria-alumina composite present in the first three-way catalyst is in the range of 10 to 60 wt % based on the total weight of the first three-way catalyst. Most preferably, the amount of ceria-alumina composite present in the first three-way catalyst is in the range of 15 to 60 wt % based on the total weight of the first three-way catalyst.

[0097] Ceria-zirconia mixed oxide (CZO): Preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst is 20 to 80 wt % based on the total weight of the first three-way catalyst. More preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst is 25 to 75 wt % based on the total weight of the first three-way catalyst. Most preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst is 30 to 75 wt % based on the total weight of the first three-way catalyst.

[0098] alumina: Preferably, the amount of alumina present in the first three-way catalyst is in the range of 5.0 to 70 wt % based on the total weight of the first three-way catalyst. More preferably, the amount of alumina present in the first three-way catalyst is in the range of 10 to 60 wt % based on the total weight of the first three-way catalyst. Most preferably, the amount of alumina present in the first three-way catalyst is in the range of 15 to 60 wt % based on the total weight of the first three-way catalyst.

[0099] Secondary Three-Way Conversion (TWC) Catalyst The second three-way catalyst is deposited on at least a portion of the second substrate. Preferably, the second three-way catalyst covers 50-100% of the length of the second substrate. More preferably, the second three-way catalyst covers 70-100% of the length of the second substrate, and even more preferably, the second three-way catalyst covers 90-100% of the length of the second substrate. Most preferably, the second three-way catalyst covers the entire length or accessible surface area of ​​the substrate.

[0100] The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0101] Preferably, the second three-way catalyst additionally comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0102] In a preferred embodiment, the second three-way catalyst is essentially free of palladium. The term "essentially free of palladium" means that no palladium is added to the second three-way catalyst. It may be present as an impurity in an amount of less than 0.001 wt. %. In another preferred embodiment, the second three-way catalyst comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0103] Preferably, the backpressure loss of the second three-way catalyst is less than 38%. More preferably, the backpressure contribution of the second three-way catalyst is less than 35%. Most preferably, the backpressure contribution of the second three-way catalyst is less than 32%. Preferably, washcoat loading is the primary means for achieving the desired backpressure.

[0104] Preferably, the second three-way catalyst has a concentration of 1.5 to 3.2 g / in 3 The second three-way catalyst is a single-coated, single-layer catalyst deposited on a second substrate with a total washcoat loading in the range of 2.0 to 3.0 g / in. More preferably, the total washcoat loading in the second three-way catalyst is 2.0 to 3.0 g / in. 3 Most preferably, the total washcoat loading in the second three-way catalyst is in the range of 2.5 to 2.8 g / in 3 is within the range.

[0105] Preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is in the range of 0.01 to 1.0 wt %, based on the total weight of the second three-way catalyst.

[0106] More preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is in the range of 0.05 to 0.5 wt %, based on the total weight of the first three-way catalyst.

[0107] Preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.01 to 1.0 wt %, based on the total weight of the first three-way catalyst.

[0108] More preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.01 to 1.0 wt %, based on the total weight of the first three-way catalyst.

[0109] Preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.001 to 0.5 wt %, based on the total weight of the first three-way catalyst.

[0110] More preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst is in the range of 0.002 to 0.1 wt %, based on the total weight of the first three-way catalyst.

[0111] Ceria-alumina composite: Preferably, the amount of the ceria-alumina composite present in the second three-way catalyst is in the range of 5.0 to 80 wt % based on the total weight of the second three-way catalyst. More preferably, the amount of the ceria-alumina composite present in the second three-way catalyst is in the range of 10 to 60 wt % based on the total weight of the second three-way catalyst. More preferably, the amount of the ceria-alumina composite present in the second three-way catalyst is in the range of 15 to 60 wt % based on the total weight of the second three-way catalyst.

[0112] Ceria-zirconia mixed oxide (CZO): Preferably, the amount of ceria-zirconia mixed oxide present in the second three-way catalyst is 20 to 80 wt % based on the total weight of the second three-way catalyst. More preferably, the amount of ceria-zirconia mixed oxide present in the second three-way catalyst is 25 to 75 wt % based on the total weight of the second three-way catalyst. Most preferably, the amount of ceria-zirconia mixed oxide present in the second three-way catalyst is 30 to 75 wt % based on the total weight of the second three-way catalyst.

[0113] alumina: Preferably, the amount of alumina present in the second three-way catalyst is in the range of 5.0 to 70 wt % based on the total weight of the second three-way catalyst. More preferably, the amount of alumina present in the second three-way catalyst is in the range of 10 to 60 wt % based on the total weight of the second three-way catalyst. Most preferably, the amount of alumina present in the second three-way catalyst is in the range of 15 to 60 wt % based on the total weight of the second three-way catalyst.

[0114] Preparation of TWC: The first or second three-way catalyst is prepared by depositing platinum group metal(s) on at least a portion of the first or second substrate.

[0115] Preferably, depositing the platinum group metal involves forming a slurry of the platinum group metal and the support material, and then coating the slurry onto the substrate as a washcoat.

[0116] The step of preparing the slurry comprises a technique selected from incipient wetness impregnation, incipient wetness co-impregnation, and post-addition.

[0117] The synthesis of heterogeneous materials, i.e., catalysts, commonly uses the incipient wetness impregnation technique, also known as capillary impregnation or dry impregnation. Typically, metal precursors are dissolved in an aqueous or organic solution, and the metal-containing solution is then added to a catalyst support containing 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 support pore volume changes solution transport from a capillary action process to a much slower diffusion process. The catalyst is then 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.

[0118] The support particles are typically sufficiently dry to absorb substantially all of the solution and form a wet solid. When rhodium is the active metal, an aqueous solution of a water-soluble compound or complex of the active metal, such as rhodium chloride, rhodium nitrate (e.g., Rh(NO)3 and its salts), rhodium acetate, or a combination thereof, is typically utilized; when palladium is the active metal, palladium nitrate, tetraamminepalladium nitrate, palladium acetate, or a combination thereof; and when platinum is the active metal, platinum nitrate, platinum acetate, or a combination thereof. After treating the support particles with the active metal solution, the particles are dried, such as by heat treating the particles at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 1-3 hours), and then calcined to convert the active metal to a more catalytically active form. An exemplary calcination process involves heat treating in air at a temperature of about 400-550°C for 10 minutes to 3 hours. The above process may be repeated as necessary to achieve the desired level of active metal impregnation.

[0119] Substrate Coating: The above-described three-way conversion catalysts are typically prepared in the form of catalyst particles, as described above. To coat a catalyst substrate, such as a honeycomb substrate, these catalyst particles are mixed with water to form a slurry. In addition to the catalyst particles, the slurry may optionally contain a binder in the form of alumina, silica, zirconium acetate, colloidal zirconia, or zirconium hydroxide, an associative thickener, and / or a surfactant (including anionic, cationic, nonionic, or amphoteric surfactants). Other exemplary binders include boehmite, gamma-alumina, or delta / theta-alumina, as well as silica sol. When present, the binder is typically used in an amount of about 1.0 to 5.0 wt.% of the total washcoat loading. Addition of acidic or basic species to the slurry is performed to adjust the pH accordingly. For example, in some embodiments, the pH of the slurry is adjusted by the addition of ammonium hydroxide, aqueous nitric acid, or acetic acid. A typical pH range for the slurry is about 3.0 to 12. The slurry can be milled to reduce particle size and promote particle mixing. Milling can be accomplished in a ball mill, continuous mill, or other similar equipment, and the solids content of the slurry can be, for example, about 20 to 60 wt. % and, more specifically, about 20 to 40 wt. %. In one embodiment, the milled slurry has a D of about 10 to about 40 micrometers, preferably 10 to about 30 micrometers, and more preferably about 10 to about 15 micrometers. 90 Characterized by particle size. D 90 is determined using a dedicated particle size analyzer. The instrument used in this example uses laser diffraction to measure particle size in small volumes of slurry. D is typically measured in micrometers. 90 means that 90% of the particle population have a diameter less than that value.

[0120] The slurry is coated onto the catalyst substrate using any washcoat technique known in the art. For example, the catalyst substrate may be dipped into or otherwise coated with the slurry one or more times. The coated substrate is then dried at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 10 minutes to 3.0 hours) and then calcined, for example, by heating at 400-700°C, typically for about 10 minutes to about 3 hours. After drying and calcination, the final washcoat coating layer is considered essentially solvent-free.

[0121] After calcination, the catalyst loading achieved by the washcoating technique described above can be determined by calculating the difference between the coated and uncoated weight of the substrate. As will be apparent to those skilled in the art, catalyst loading can be varied by changing the slurry rheology. Note that the coating / drying / calcining process to produce a washcoat may be repeated as necessary to build the coating to a desired loading level or thickness, meaning that more than one washcoat may be applied.

[0122] The coated substrate may be aged by subjecting it to a heat treatment. For example, aging may be performed at a temperature of about 850°C to about 1050°C in the presence of steam for 50 to 300 hours under gasoline engine exhaust conditions. Thus, the present invention provides an aged catalyst article. Effective support materials, such as ceria-alumina composites, retain a high percentage of their pore volume (e.g., about 50 to 100%) upon aging (e.g., aging at about 850°C to about 1050°C in the presence of steam for about 50 to 300 hours).

[0123] Preferably, the first three-way catalyst is prepared by depositing a platinum group metal on at least a portion of the first or second substrate, the platinum group metal comprising platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0124] Preferably, the second three-way catalyst is prepared by depositing platinum and optionally rhodium on at least a portion of a second substrate, wherein the platinum is supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and the rhodium is supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0125] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and reverse references as indicated. In particular, in each case where a range of embodiments is mentioned, for example, in the context of a term such as "an exhaust aftertreatment system according to any one of embodiments 1 to 4," it is to be noted that all embodiments within this range are expressly disclosed to those skilled in the art, i.e., this expression of terms is understood by those skilled in the art to be synonymous with "a system according to any one of embodiments 1, 2, 3, and 4." Furthermore, it is to be clearly noted that the following set of embodiments represents a properly structured portion of a general description directed to preferred aspects of the present invention, and therefore properly supports, but does not represent, the scope of the claims of the present invention.

[0126] Embodiment 1: An exhaust aftertreatment system a. a first three-way catalyst deposited on at least a portion of a first substrate; b. a second three-way catalyst deposited on at least a portion of the second substrate; Including, The first three-way catalyst is i) platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; ii) palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; iii) rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; Including, The second three-way catalyst is alumina, It includes platinum supported on a ceria-zirconia mixed oxide, a ceria-alumina composite, or any combination thereof.

[0127] Embodiment 2: 2. An exhaust aftertreatment system according to embodiment 1, wherein the second three-way catalyst further comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0128] Embodiment 3: 3. The exhaust aftertreatment system of embodiment 1 or 2, wherein the second three-way catalyst is essentially free of palladium.

[0129] Embodiment 4: 3. An exhaust aftertreatment system according to any one of embodiments 1 to 2, wherein the second three-way catalyst comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0130] Embodiment 5: 2. The exhaust aftertreatment system of embodiment 1, wherein a weight ratio of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within a range of 2:1 to 20:1, preferably within a range of 2.5:1 to 12:1.

[0131] Embodiment 6: 3. The exhaust aftertreatment system according to embodiment 2, wherein the weight ratio of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 1:3 to 50:1, preferably within the range of 1:1 to 50:1, more preferably within the range of 1:2 to 20:1, more preferably within the range of 1:1 to 20:1, more preferably within the range of 1:1.5 to 4:1, and more preferably within the range of 1:1 to 4:1.

[0132] Embodiment 7: 7. The exhaust aftertreatment system according to any one of embodiments 1 to 6, wherein the weight ratio of the total amount of platinum, palladium, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to the total amount of platinum, and optionally rhodium and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 4:1 to 20:1.

[0133] Embodiment 8: 8. The exhaust aftertreatment system according to any one of embodiments 1 to 7, wherein the back pressure contribution of the second three-way catalyst is less than 38%, preferably less than 35%, more preferably less than 32%.

[0134] Embodiment 9: The second three-way catalyst is 1.5 to 3.2 g / in 3 within the range of 2.0 to 3.0 g / in 3 in the range of 2.5 to 2.8 g / in 3 9. An exhaust gas aftertreatment system according to any one of embodiments 1 to 8, wherein the catalyst is a single layer catalyst deposited on the second substrate with a total washcoat loading in the range of

[0135] Embodiment 10: the first three-way catalyst is a two-layer catalyst including a first layer deposited on at least a portion of a first substrate and a second layer deposited on at least a portion of the first layer, a portion of the first substrate, or both; 10. An exhaust aftertreatment system according to any one of embodiments 1 to 9, wherein the first layer comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0136] Embodiment 11: the first three-way catalyst is a two-layer catalyst including a first layer and a second layer; the first layer includes a first zone and a second zone; The first zone covers 10 to 90% of the total length of the substrate from the inlet, and the second zone covers 10 to 90% of the total length of the substrate from the outlet; a first zone comprising palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; a second zone comprising platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; 11. The exhaust aftertreatment system of any one of embodiments 1 to 10, wherein a second layer is deposited on at least a portion of the first layer, and the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

[0137] Embodiment 12: 12. The exhaust aftertreatment system according to any one of embodiments 1 to 11, wherein the total amount of ceria-zirconia mixed oxide supported in the first three-way catalyst is greater than the total amount of ceria-zirconia mixed oxide supported in the second three-way catalyst.

[0138] Embodiment 13: 13. The exhaust gas aftertreatment system according to any one of embodiments 1 to 12, wherein the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 to 3.0 wt %, preferably in the range of 0.03 to 2.5 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0139] Embodiment 14: 14. The exhaust aftertreatment system according to any one of embodiments 1 to 13, wherein the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 to 3.0 wt %, preferably in the range of 0.02 to 2.0 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0140] Embodiment 15: 14. The exhaust aftertreatment system according to any one of embodiments 1 to 13, wherein the total amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.01 to 2.0 wt %, preferably in the range of 0.01 to 1.5 wt %, and more preferably in the range of 0.01 to 1.0 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0141] Embodiment 16: 16. The exhaust aftertreatment system of any one of embodiments 1-15, 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.

[0142] Embodiment 17: 17. An exhaust gas aftertreatment system according to any one of embodiments 1 to 16, wherein the total amount of ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is in the range of 20 to 80 wt %, preferably in the range of 25 to 75 wt %, more preferably in the range of 30 to 75 wt %, more preferably in the range of 40 to 60 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0143] Embodiment 18: 18. The exhaust aftertreatment system of any one of embodiments 1 to 17, wherein the total amount of alumina present in the first and second three-way catalysts is in the range of 5.0 to 70 wt %, preferably in the range of 5.0 to 20 wt %, based on the total weight of the first and second three-way catalysts; or the amount of alumina present in the first and second three-way catalysts is in the range of 10 to 60 wt %, preferably in the range of 15 to 60 wt %, based on the total weight of the first and second three-way catalysts.

[0144] Embodiment 19: the alumina present in the first three-way catalyst and the second three-way catalyst is doped with a dopant selected from barium, lanthana, zirconia, neodymian, yttria, ceria, or titania; 19. The exhaust aftertreatment system of any one of embodiments 1 to 18, wherein the amount of dopant is 1.0 to 30 wt %, based on the total weight of alumina and dopant present in the first three-way catalyst and the second three-way catalyst.

[0145] Embodiment 20: 20. The exhaust aftertreatment system of any one of embodiments 1 to 19, wherein the alumina is selected from alumina, lanthana-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, ceria-alumina, lanthana-zirconia-alumina, baria-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, yttrium-alumina, or any combination thereof.

[0146] Embodiment 21: 21. The exhaust aftertreatment system according to any one of embodiments 1 to 20, wherein the total amount of the ceria-alumina composite present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 to 80 wt %, preferably in the range of 10 to 60 wt %, more preferably in the range of 15 to 60 wt %, more preferably in the range of 15 to 40 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0147] Embodiment 22: The system is i) an engine producing an exhaust gas stream; ii) a first three-way catalyst deposited on at least a portion of the first substrate; iii) a second three-way catalyst deposited on at least a portion of the second substrate; and Including, 2. An exhaust aftertreatment system as described in embodiment 1, wherein the first three-way catalyst is disposed upstream of the engine, and the second three-way catalyst is disposed downstream in fluid communication with the first three-way catalyst.

[0148] Embodiment 23: the amount of ceria-alumina composite present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 to 80 wt %, and the amount of ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is 20 to 80 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst; 23. The system of any one of embodiments 1 to 16, and 22, wherein the amount of CeO in the ceria-alumina composite present in the first or second three-way catalyst is preferably 1.0 to 60 wt. %, based on the total weight of the ceria-alumina composite in the respective catalyst; the CeO in the ceria-zirconia mixed oxide present in the first or second three-way catalyst is present in an amount of 10 to 60 wt. %, based on the total weight of the ceria-zirconia mixed oxide present in the respective catalyst; and the zirconia (calculated as ZrO) in the ceria-zirconia mixed oxide present in the first or second three-way catalyst is present in an amount of 40 to 90 wt. %, based on the total weight of the ceria-zirconia mixed oxide present in the respective catalyst.

[0149] Embodiment 24: 24. 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 an exhaust aftertreatment system according to any one of embodiments 1-23, to reduce the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the gaseous exhaust.

[0150] Embodiment 25: 24. Use of an exhaust aftertreatment system according to any one of embodiments 1 to 23 for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide, and nitrogen oxides.

[0151] Aspects of the presently claimed invention will be more fully illustrated by the following examples, which are set forth to illustrate particular aspects of the invention and should not be construed as limiting thereof.

[0152] The washcoat component loadings and back pressure losses for upstream TWC-1 and downstream TWC-2 are shown in Table 1 below.

[0153] [Table 1] a CeO2: Total CeO2 loading, including all CeO2 content from ceria-zirconia mixed oxide and other washcoat components b WCL: total washcoat loading c BP loss: Back pressure loss [Example]

[0154] Example 1: System 1 (S1), Comparative Example: S1 includes a conventional Pd / Rh-based upstream catalyst, S1-TWC-1, and a conventional Pd / Rh-based downstream catalyst, S1-TWC-2. S1-TWC-1 has a two-layer washcoat structure coated on a monolithic cordierite substrate with dimensions of 4.66 inches in diameter and 3.81 inches in length, a cell density of 800 cpsi (cells per square inch), and a wall thickness of 2.5 mils. The total washcoat loading was 3.61 g / in. 3 and the total PGM loading is 120 g / ft 3 (Pt / Pd / Rh=0 / 118 / 2). The catalyst was 0.59 g / in 3 The bottom layer is 118 g / ft of ceria evenly deposited on refractory alumina and ceria-zirconia mixed oxide, with a back pressure loss of about 44%. 3 of Pd and barium oxide. The washcoat loading of the bottom layer was 2.61 g / in 3 The top layer is a 2 g / ft2 refractory alumina coating. 3 of Rh and ceria-zirconia mixed oxide. The top washcoat loading was 1.00 g / in 3 S1-TWC-2 has a total PGM loading of 12 g / ft 3The downstream catalyst had the same washcoat composition as S1-TWC-1 (Pt / Pd / Rh=0 / 10 / 2), except that the downstream catalyst was coated on a monolithic cordierite substrate with dimensions of 5.20 inches in diameter and 3.96 inches in length, a cell density of 400 cpsi, and a wall thickness of 6.5 mils.

[0155] Example 2: System 2 (S2): S2 includes a Pt / Pd / Rh-based upstream catalyst, S2-TWC-1, and a Pt / Rh-based downstream catalyst, S2-TWC-2. S2-TWC-1 has a two-layer washcoat structure coated on a monolithic cordierite substrate with dimensions of 4.66 inches in diameter and 3.81 inches in length, a cell density of 800 cpsi, and a wall thickness of 2.5 mils. The total washcoat loading was 3.62 g / in. 3 and the total PGM loading is 120 g / ft 3 (Pt / Pd / Rh=59 / 59 / 2). The catalyst was 0.71 g / in 3 The bottom layer has 59 g / ft ceria deposited on a refractory ceria-alumina composite, and the back pressure loss is about 43%. 3 of Pt deposited on ceria-zirconia mixed oxide, 59 g / ft 3 of Pd and barium oxide. The washcoat loading of the bottom layer was 2.62 g / in 3 The top layer is a 2 g / ft2 refractory ceria-alumina composite. 3 of Rh and ceria-zirconia mixed oxide. The top washcoat loading was 1.00 g / in 3 S2-TWC-2 has a single-coat, single-layer washcoat structure coated on a monolithic cordierite substrate with dimensions of 5.20 inches in diameter and 3.96 inches in length, a cell density of 400 cpsi, and a wall thickness of 6.5 mils. The total washcoat loading is 2.76 g / in 3 and the total PGM loading is 12 g / ft 3 (Pt / Pd / Rh=10 / 0 / 2). The catalyst was 0.62 g / in 3The single washcoat has a 10g / ft 3 of Pt, 2g / ft 3 The Pt and 50% of the Rh were deposited on the refractory ceria-alumina composite, the ceria-zirconia mixed oxide, and barium oxide. All of the Pt and 50% of the Rh were deposited on the refractory ceria-alumina composite, and the remaining 50% of the Rh was deposited on the ceria-zirconia mixed oxide.

[0156] Example 3: System 3 (S3): S3 includes a Pt / Pd / Rh-based upstream catalyst, S3-TWC-1, and a Pt / Rh-based downstream catalyst, S3-TWC-2. S3-TWC-1 is the same as S2-TWC-1. S3-TWC-2 has a single-coat, single-layer washcoat structure coated on a monolithic cordierite substrate with dimensions of 5.20 inches in diameter and 3.96 inches in length, a cell density of 400 cpsi, and a wall thickness of 6.5 mils. The total washcoat loading was 2.82 g / in 3 and the total PGM loading is 12 g / ft 3 (Pt / Pd / Rh=10 / 0 / 2). The catalyst was 0.95 g / in 3 The single washcoat has a 10g / ft 3 of Pt, 2g / ft 3 The composite consisted of 100% of the Pt and all of the Rh on the refractory ceria-alumina composite, ceria-zirconia mixed oxide, and barium oxide. 50% of the Pt and all of the Rh were deposited on the refractory ceria-alumina composite, and the remaining 50% of the Pt was deposited on the ceria-zirconia mixed oxide.

[0157] Example 4: System 4 (S4): S4 includes a Pt / Pd / Rh-based upstream catalyst, S4-TWC-1, and a Pt / Pd / Rh-based downstream catalyst, S4-TWC-2. S4-TWC-1 is the same as S2-TWC-1. S4-TWC-2 has a single-coat, single-layer washcoat structure coated on a monolithic cordierite substrate with dimensions of 5.20 inches in diameter and 3.96 inches in length, a cell density of 400 cpsi, and a wall thickness of 6.5 mils. The total washcoat loading was 2.76 g / in3 and the total PGM loading is 12 g / ft 3 (Pt / Pd / Rh=5 / 5 / 2). The catalyst was 0.62 g / in 3 The single washcoat has 5g / ft of ceria and the back pressure loss is about 30%. 3 of Pt, 5g / ft 3 of Pd, 2g / ft 3 The samples included 100% Rh, refractory ceria-alumina composite, ceria-zirconia mixed oxide, and barium oxide. All Pt and Rh were deposited on the refractory ceria-alumina composite, and all Pd was deposited on the ceria-zirconia mixed oxide.

[0158] Example 5: System 5 (S5), Comparative Example: S5, includes a Pt / Pd / Rh-based upstream catalyst, S5-TWC-1, and a Pd / Rh-based downstream catalyst, S5-TWC-2. S5-TWC-1 has a zoned, two-layer washcoat structure with an inlet bottom zone, an outlet bottom zone (each zone covering approximately 50% of the substrate length), and a top layer covering 100% of the substrate length. The catalyst was coated onto a monolithic cordierite substrate with dimensions of 4.66 inches in diameter and 3.81 inches in length, a cell density of 800 cpsi, and a wall thickness of 2.5 mils. The total washcoat loading was 3.57 g / in 3 and the total PGM loading is 120 g / ft 3 (Pt / Pd / Rh=29 / 87 / 4). The catalyst was 0.80 g / in 3 The inlet bottom zone contains 156.6 g / ft ceria deposited equally on a refractory alumina composite and ceria-zirconia mixed oxide. 3 of Pd and barium oxide. The washcoat loading in the bottom inlet zone was 2.56 g / in 3 The bottom zone of the outlet is 58 g / ft 3 of Pt, 17.4g / ft 3The washcoat contained 100% Pt, refractory ceria-alumina composite, ceria-zirconia mixed oxide, and barium oxide. 70% of the Pt was deposited on the refractory ceria-alumina composite, 30% of the Pt, and all of the Pd was deposited on the ceria-zirconia mixed oxide. The washcoat loading in the outlet bottom zone was 2.58 g / in 3 The top layer is a 4 g / ft2 refractory ceria-alumina composite. 3 of Rh and ceria-zirconia mixed oxide. The top washcoat loading was 1.00 g / in 3 S5-TWC-2 has a single layer washcoat structure coated on a monolithic cordierite substrate with dimensions of 5.20 inches in diameter and 3.96 inches in length, a cell density of 400 cpsi, and a wall thickness of 6.5 mils. The total washcoat loading is 2.82 g / in 3 and the total PGM loading is 12 g / ft 3 (Pt / Pd / Rh=0 / 10 / 2). The catalyst was 0.32 g / in 3 The back pressure loss is about 34%. The single layer washcoat is 10 g / ft2 deposited on the ceria-zirconia mixed oxide. 3 of Pd deposited on a refractory alumina composite at 2 g / ft 3 of Rh, and barium oxide.

[0159] Example 6: System 6 (S6): S6 includes a Pt / Pd / Rh-based upstream catalyst, S6-TWC-1, and a Pd / Rh-based downstream catalyst, S6-TWC-2. S6-TWC-1 is the same as S5-TWC-1, and S6-TWC-2 is the same as S2-TWC-2.

[0160] Example 7: Measurement of back pressure loss Back pressure loss, or the washcoat's contribution to back pressure loss, was measured on a SuperFlow SF-1020 Flowbench at ambient temperature. sub ) and coated monolith catalyst (BP cat) was collected at a flow rate of 294 cfm (cubic feet per minute). The backpressure loss of the coated monolith catalyst was calculated as follows: Back pressure loss = (BP cat -BP sub ) / BP cat ×100%

[0161] Example 8: Engine Aging and Vehicle Testing Example systems 1-6 were mounted in a steel converter can and aged in the exhaust pipeline of a gasoline engine operating under an exothermic four-mode aging cycle. The aging period was 100 hours with a maximum bed temperature of approximately 985°C for the upstream catalyst. The aged catalytic converters were tested in two test vehicles operated on the US FTP-75 drive cycle according to certified procedures and tolerances. The first test vehicle was certified to US EPA ULEV70 (Ultra Low Emission Vehicle) emissions standards. The second vehicle was certified to US EPA SULEV30 (Super Ultra Low Emission Vehicle) emissions standards and calibrated with frequent fuel cut-off events.

[0162] The FTP-75 tailpipe bag emissions data results for systems S1-S4 are shown in Table 2 below.

[0163] [Table 2]

[0164] Table 2 summarizes the tailpipe emissions of NMHCs, NOx, and CO obtained on a ULEV70 test vehicle. Example System 1 represents a conventional TWC system in which both the upstream and downstream catalysts are based on Pd and Rh as the active platinum group metals. Example System 2 includes a Pt / Pd / Rh-based trimetallic upstream TWC and a single-coated Pt / Rh-based single-layer downstream TWC. System 2 exhibited comparable NMHC and CO emissions and slightly better NOx emissions compared to the baseline System 1. Example System 4 is similar to System 2, except that the downstream TWC is a Pt / Pd / Rh-based trimetallic catalyst. System 4 exhibited performance comparable to System 2. Both Systems 2 and 4 utilized significant amounts of Pt to replace the more expensive Pd present in the baseline system. Additionally, a single-coated downstream catalyst with low backpressure loss was applied to these inventive systems. As a result, these inventive systems were substantially more cost-effective than the baseline system. Example System 3 used significantly more ceria in the downstream TWC, which resulted in a moderate loss in NMHC performance.

[0165] The FTP-75 tailpipe bag emissions data results for systems S5-S6 are shown in Table 3 below.

[0166] [Table 3]

[0167] Table 3 summarizes the tailpipe emissions of NMHC, NOx, and CO obtained for the SULEV30 test vehicle. The FTP-75 for this particular vehicle was calibrated with frequent fuel cut events for better fuel economy, making NOx emission control more difficult to achieve. Example System 5 utilized a Pd / Rh-based downstream TWC. In comparison, the utilization of a Pt / Rh-based single-coated downstream TWC in System 6 provided substantially improved tailpipe NOx emissions without any penalty on NMHC and CO emissions. Figure 2 shows the cumulative NOx emissions traces for System 6 versus System 5. The NOx benefit of the inventive system was primarily due to less NOx breakthrough during fuel cut events during deceleration.

[0168] References -German Patent Application Publication No. 10 / 2019 / 208436(A1) -US Patent Application Publication No. 2010 / 061903(A1) -U.S. Patent Application Publication No. 2002 / 048542(A1) -U.S. Patent Application Publication No. 2009 / 042722(A1)

Claims

1. 1. An exhaust aftertreatment system comprising: a. a first three-way catalyst deposited on at least a portion of a first substrate; b. a second three-way catalyst deposited on at least a portion of the second substrate; Including, The first three-way catalyst comprises: i. platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; ii. Palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; iii. Rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; Including, The exhaust aftertreatment system, wherein the second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

2. 10. The system of claim 1, wherein the second three-way catalyst further comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

3. 3. The system of claim 1 or 2, wherein the second three-way catalyst is essentially free of palladium.

4. 3. The system of claim 1 or 2, wherein the second three-way catalyst comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

5. 2. The system of claim 1, wherein a weight ratio of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within the range of 2:1 to 20:

1.

6. 6. The system according to claim 1, wherein a weight ratio of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within a range of 1:1 to 50:

1.

7. 7. The system according to claim 1, wherein a weight ratio of the total amount of platinum, palladium, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst to the total amount of platinum, and optionally rhodium, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the second three-way catalyst is within a range of 4:1 to 20:

1.

8. 8. The system of claim 1, wherein the backpressure contribution of the second three-way catalyst is less than 38%.

9. The second three-way catalyst is 1.5 to 3.2 g / in ３ 9. The system of claim 1, wherein the catalyst is a single layer catalyst deposited on the second substrate with a total washcoat loading in the range of 0.1 to 1.

0.

10. the first three-way catalyst is a two-layer catalyst including a first layer deposited on at least a portion of the first substrate and a second layer deposited on at least a portion of the first layer, a portion of the first substrate, or both; the first layer comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; The system of any one of claims 1 to 9, wherein the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

11. the first three-way catalyst is a two-layer catalyst including a first layer and a second layer; the first layer includes a first zone and a second zone; the first zone covers 10 to 90% of the total length of the substrate from the inlet, and the second zone covers 10 to 90% of the total length of the substrate from the outlet; the first zone comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; the second zone comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof; 11. The system of claim 1, wherein the second layer is deposited on at least a portion of the first layer, and the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof.

12. 12. The system according to claim 1, wherein a total amount of ceria-zirconia mixed oxide supported in the first three-way catalyst is greater than a total amount of ceria-zirconia mixed oxide supported in the second three-way catalyst.

13. 13. The system of claim 1, wherein a total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 to 3.0 wt %, based on a total weight of the first three-way catalyst and the second three-way catalyst.

14. 14. The system according to claim 1, wherein a total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 to 3.0 wt %, based on a total weight of the first three-way catalyst and the second three-way catalyst.

15. 14. The system according to claim 1, wherein a total amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.01 to 2.0 wt %, based on a total weight of the first three-way catalyst and the second three-way catalyst.

16. The system of any one of claims 1 to 15, 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.

17. 17. The system of claim 1, wherein the total amount of the ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is 40 to 60 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

18. 18. The system of claim 1, wherein the total amount of alumina present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 to 20 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst, or the total amount of alumina present in the first three-way catalyst and the second three-way catalyst is in the range of 15 to 60 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst.

19. the alumina present in the first three-way catalyst and the second three-way catalyst is doped with a dopant selected from barium, lanthana, zirconia, neodymium, yttria, ceria, or titania; 19. The system of claim 1, wherein the amount of the dopant is 1.0 to 30 wt. %, based on the total weight of the alumina and the dopant present in the first three-way catalyst and the second three-way catalyst.

20. 20. The system of any one of claims 1 to 19, wherein the alumina is selected from alumina, lanthana-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, ceria-alumina, lanthana-zirconia-alumina, baria-alumina, baria-lanthana-alumina, baria-lanthana-neodymia-alumina, yttrium-alumina, or any combination thereof.

21. 21. The system of claim 1, wherein a total amount of ceria-alumina composite present in the first three-way catalyst and the second three-way catalyst is in the range of 15 to 40 wt %, based on a total weight of the first three-way catalyst and the second three-way catalyst.

22. The system comprises: i) an engine producing an exhaust gas stream; ii) a first three-way catalyst deposited on at least a portion of the first substrate; iii) a second three-way catalyst deposited on at least a portion of the second substrate; and Including, The system of claim 1 , wherein the first three-way catalyst is disposed upstream of the engine and the second three-way catalyst is disposed downstream in fluid communication with the first three-way catalyst.

23. the amount of the ceria-alumina composite present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 to 80 wt %, and the amount of the ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is 20 to 80 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst; CeO in the ceria-alumina composite present in the first three-way catalyst or the second three-way catalyst ２ is preferably 1.0 to 60 wt % based on the total weight of the ceria-alumina composite in each catalyst, and the amount of CeO of the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst is ２ is present in an amount of 10 to 60 wt % based on the total weight of the ceria-zirconia mixed oxide present in each catalyst, and the zirconia (ZrO ２ 23. The system of any one of claims 1 to 16 and 22, wherein the ceria-zirconia mixed oxide (calculated as ##STR1##) is present in an amount of 40 to 90 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in each catalyst.

24. 24. A method for reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in a gaseous exhaust stream, the method comprising contacting the gaseous exhaust stream with an exhaust aftertreatment system according to any one of claims 1 to 23, thereby reducing the levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the gaseous exhaust.

25. Use of an exhaust aftertreatment system according to any one of claims 1 to 23 for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide and nitrogen oxides.

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