Exhaust aftertreatment system including three-way catalyst

Abstract

The present invention provides an exhaust gas aftertreatment system comprising 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 the second substrate wherein 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, wherein the second three-way catalyst comprises platinum supported on alumina, a ceria-zirconia mixed oxide, a ceria-alumina composite, or any combination thereof.

Description

Technical Field

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

[0002] Exhaust from vehicles powered by gasoline engines is typically treated with one or more three-way conversion (TWC) automotive catalysts that effectively reduce pollutants of 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, i.e., a first / upstream TWC catalyst installed at a location close to the exhaust manifold and the engine compartment (closely coupled location, CC), and a second / downstream TWC catalyst placed at a location directly adjacent to the first TWC catalyst (a second close coupled location, CC2) or at a location below the vehicle body (an underfloor location, UF).

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

[0004] DE 10 2019 208436A1 relates to a post-treatment method for a lean-burn engine. The method is designed to control an after-treatment system that is sequentially equipped with an ammonia production catalyst module, a selective catalytic reduction catalyst, and a CO purification catalyst on an exhaust pipe through which the exhaust gas flows.

[0005] US2010 / 061903 A1 relates to a catalyst system for an automobile exhaust purification device, which includes using two or more exhaust purification catalysts, which exhaust purification catalysts include a first catalyst supported on an inorganic structure carrier and a second catalyst supported on a part of the inorganic structure carrier positioned on the downstream side.

[0006] US 2002 / 048542 A1 discloses a method for converting NO in an exhaust gas stream. x A catalytic trap comprising a catalytic trap material and a refractory carrier member on which the catalytic trap material is coated.

[0007] US 2009 / 042722 A1 discloses a method for preparing a catalyst having a base metal undercoat layer containing an oxygen storage component.

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

[0009] Purpose of the Invention

[0010] It is an object of the presently claimed invention to provide an exhaust aftertreatment system that provides comparable or improved performance when compared to conventional Pd / Rh based TWC systems.

[0011] It is another object of the presently claimed invention to provide an exhaust aftertreatment system that delivers improved NOx performance during a fuel cut event.

[0012] Still another object of the presently claimed invention is to provide an exhaust aftertreatment system which allows substantial replacement of Pd with Pt (20-80%) thereby making the system cost effective. Summary of the invention

[0013] The present invention provides an exhaust gas aftertreatment system, the exhaust gas aftertreatment system comprising a first three-way catalyst, the first three-way catalyst being deposited on at least a portion of a first substrate; a second three-way catalyst being deposited on at least a portion of a second substrate,

[0014] wherein the first three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof,

[0015] The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof.

[0016] The present invention also provides a method of reducing the emission 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 the present invention to reduce the levels of hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gas.

[0017] The invention further provides for the use of an exhaust gas aftertreatment system according to the invention for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide and nitrogen oxides. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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 accompanying drawings are exemplary only 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 when the following detailed description is considered in conjunction with the accompanying drawings:

[0019] Figure 1 The construction of the TWC catalyst system is shown.

[0020] Figure 2 FTP-75 tailpipe cumulative NOx emissions for Examples S5 and S6 collected on a SULEV30 vehicle calibrated with frequent fuel cut-off events are shown.

[0021] Figure 3A is a perspective view of a honeycomb type substrate support that may contain a catalyst composition according to one embodiment of the presently claimed invention.

[0022] Figure 3B is relative to Figure 3A Zoom in and follow the Figure 3A A partial cross-sectional view taken through a plane of the end surface of a substrate carrier, showing Figure 3A An enlarged view of the multiple gas flow channels shown in FIG.

[0023] Figure 4 is relative to Figure 3A A cross-sectional view of an enlarged section, wherein Figure 3A The honeycomb-type substrate in ref. 3 represents a wall-flow filter substrate monolith. DETAILED DESCRIPTION

[0024] The presently claimed invention will be described more fully below. The presently claimed invention can be embodied in many different forms and should not be construed as limited to the embodiments described herein; rather, these embodiments are provided to make the presently claimed invention more complete and complete, and to fully convey the scope of the invention to those skilled in the art. Language in this specification should not be construed to indicate that any non-claimed element is essential to the practice of the materials and methods of the present disclosure.

[0025] Unless otherwise specified herein or clearly contradicted by context, all methods described herein can be performed in any suitable order. Unless otherwise stated, the use of any and all examples or exemplary language (e.g., "such as") provided herein is intended only to better illustrate materials and methods and is not intended to limit the scope.

[0026] definition :

[0027] The terms "a," "an," "the," and similar referents used in the context of describing the materials and methods discussed herein (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0028] Recitation of ranges of values ​​herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.

[0029] In the context of the present invention, the term "washcoat" is used interchangeably for "first three-way catalyst" or "second three-way catalyst" which forms one or more layers on a portion of a corresponding substrate. As used herein, the term "washcoat" has its usual meaning in the art, i.e., a thin, adherent coating of a catalytic material or other material applied to a substrate material. Typically, the washcoat is formed by preparing a slurry of particles containing a certain solid content (e.g., 15 wt%-60 wt%) in a liquid vehicle, and then applying the slurry to a substrate and drying to provide a washcoat layer on the corresponding substrate.

[0030] The term "three-way conversion catalyst" or TWC catalyst refers to a catalyst that simultaneously promotes a) the reduction of nitrogen oxides to nitrogen and oxygen; b) the oxidation of carbon monoxide to carbon dioxide; and c) the oxidation of unburned hydrocarbons to carbon dioxide and water.

[0031] The term "NOx" refers to nitrogen oxide compounds, such as NO and / or NO2.

[0032] As used herein, the term "stream" refers broadly to any combination of flowing gases that may contain solid or liquid particulate matter.

[0033] As used herein, the terms "upstream" and "downstream" refer to the relative directions of flow of engine exhaust gas from the engine to the tailpipe, with the engine being in the upstream position and the tailpipe and any pollutant abatement articles such as filters and catalysts being downstream of the engine.

[0034] The term "close coupled" refers to the location of one or more catalytic converters placed close to the engine outlet manifold.

[0035] The term "underfloor" refers to a location of one or more catalytic converters that are located away from the close-coupled location. Typically, an underfloor catalytic converter is placed under the floor of the vehicle body between the close-coupled catalytic converter and the muffler.

[0036] In the context of the present invention, the amount of platinum group metals (such as platinum / palladium / rhodium) and / or support materials (such as ceria-zirconia mixed oxides, ceria-alumina composites, alumina, etc.) is calculated in wt. % based on the total weight of the washcoat present on the substrate. That is, the amount is calculated without taking into account the amount of substrate, although the substrate is part of the catalytic system.

[0037] The present invention focuses on addressing low NOx performance during fuel cut events associated with existing exhaust aftertreatment systems and improves overall performance despite the substantial replacement of Pd with Pt (20%-80%).

[0038] In a first aspect, the present invention provides an exhaust gas aftertreatment system, the exhaust gas aftertreatment system comprising:

[0039] a. a first three-way catalyst, the first three-way catalyst being deposited on at least a portion of the first substrate; and

[0040] b. a second three-way catalyst, the second three-way catalyst being deposited on at least a portion of the second substrate,

[0041] Wherein the first three-way catalyst comprises:

[0042] i. platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof,

[0043] ii. palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, and

[0044] iii. rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof,

[0045] The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof.

[0046] Amount of platinum group metals :

[0047] Based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is preferably in the range of 0.01 wt % to 5.0 wt %. More preferably, based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 wt % to 3.0 wt %. Even more preferably, based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.03 wt % to 2.5 wt %.

[0048] Based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is preferably in the range of 0.01 wt % to 4.0 wt %. More preferably, based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 wt % to 3.0 wt %. Even more preferably, based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 wt % to 2.0 wt %.

[0049] Based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is preferably in the range of 0.01 wt % to 2.0 wt %. More preferably, based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.01 wt % to 1.5 wt %. Even more preferably, based on the total weight of the first three-way catalyst and the second three-way catalyst, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.01 wt % to 1.0 wt %.

[0050] Weight Ratio :

[0051] Preferably, the weight ratio of the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is greater than 1.

[0052] More preferably, the weight ratio of the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 2:1 to 20:1.

[0053] Even more preferably, the weight ratio of the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 2.5:1 to 12:1.

[0054] Preferably, the weight ratio of the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst to the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst is in the range of 1:3 to 50:1, more preferably in the range of 1:1 to 50:1.

[0055] Even more preferably, the weight ratio of the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 1:2 to 20:1, more preferably in the range of 1:1 to 20:1. Even more preferably, the weight ratio of the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 1:1.5 to 4:1, more preferably in the range of 1:1 to 4:1.

[0056] Preferably, the weight ratio of the total amount of platinum, palladium and rhodium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst to the total amount of platinum, optionally to rhodium and palladium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst is in the range of 1.1:1 to 20:1.

[0057] More preferably, the weight ratio of the total amount of platinum, palladium and rhodium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst to the total amount of platinum, optionally to rhodium and palladium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst is in the range of 4:1 to 20:1.

[0058] Even more preferably, the weight ratio of the total amount of platinum, palladium and rhodium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst to the total amount of platinum, optionally to rhodium and palladium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst is in the range of 8:1 to 12:1.

[0059] Carrier material :

[0060] "Support" in catalytic material or catalyst composition or catalyst support coating refers to a material that receives metal (e.g., PGM), stabilizer, promoter, binder, etc. by precipitation, association, dispersion, impregnation or other suitable methods, such as alumina, ceria-alumina composite material, ceria-zirconia mixed oxide.

[0061] The term "support" throughout this application has its general meaning as in the field of heterogeneous catalysis. Generally, the term "support" refers to a catalytically active substance or its corresponding precursor attached to a support material. The support material may be inert or participate in the catalytic reaction. Typically supported catalysts are prepared by impregnation or coprecipitation and optionally subsequent calcination.

[0062] Ceria-alumina composites :

[0063] Ceria-alumina composites are composites in which CeO2 is distributed on the surface of alumina and / or in the bulk in the form of particles and / or nanoclusters. Each oxide may have its own unique chemical and solid physical state. The surface CeO2 modification of alumina may be in the form of discrete parts (particles or clusters) or in the form of a ceria layer that partially or completely covers the surface of alumina.

[0064] Preferably, the amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 wt % to 80 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst. More preferably, the amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in the range of 10 wt % to 60 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst. Even more preferably, the amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in the range of 15 wt % to 60 wt %, and more preferably in the range of 15 wt % to 40 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0065] The amount of CeO2 (cerium oxide) present in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is preferably 1.0 wt% to 60 wt%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst. More preferably, the CeO2 present in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is 10 wt% to 50 wt%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst. Even more preferably, the CeO2 present in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is 15 wt% to 50 wt%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst.

[0066] The amount of Al2O3 (alumina) present in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is preferably 40 wt% to 99 wt%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst. More preferably, the Al2O3 in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is 50 wt% to 90 wt%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst. Even more preferably, the Al2O3 in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is 50 wt% to 85 wt%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst.

[0067] Preferably, the average particle size of ceria in the ceria-alumina composite is less than 200 nm. More preferably, the particle size is in the range of 5.0 nm to 50 nm. The particle size is determined by transition electron microscopy.

[0068] The ceria-alumina composite material present in the first three-way catalyst or the second three-way catalyst may contain a dopant selected from zirconium oxide, lanthanum oxide, titanium oxide, hafnium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, or any combination thereof. The total amount of the dopant in the ceria-alumina composite material is preferably in the range of 0.001 wt % to 15 wt %, based on the total weight of the ceria-alumina composite material in the corresponding catalyst.

[0069] Ceria-alumina composite material can be prepared by methods known to those skilled in the art (such as coprecipitation or surface modification). In these methods, a suitable cerium-containing precursor is contacted with a suitable aluminum-containing precursor, and then the mixture thus obtained is converted into a cerium-alumina composite material. Suitable cerium-containing precursors are, for example, water-soluble cerium salts and colloidal cerium dioxide suspensions. Ceria-alumina can also be prepared by an atomic layer deposition method, in which a cerium oxide compound selectively reacts with an aluminum oxide surface to form cerium oxide on an aluminum oxide surface after calcination. This deposition / calcination step can be repeated until a layer of desired thickness is reached. Suitable aluminum-containing precursors are, for example, aluminum oxide, such as gibbsite, boehmite γ aluminum oxide, δ aluminum oxide or θ aluminum oxide or a combination thereof. The mixture thus obtained can then be converted to a cerium-alumina composite material by the calcination step of the mixture.

[0070] Ceria-Zirconia Mixed Oxide (CZO) :

[0071] The term composite metal oxide refers to a mixed metal oxide containing oxygen anions and at least two different metal cations. In ceria-zirconia mixed oxides, cerium cations and zirconium cations are distributed within the oxide lattice structure. The terms "composite oxide" and "mixed oxide" are used interchangeably. Since the metal cations are distributed within the oxide lattice structure, these structures are also often referred to as solid solutions.

[0072] Preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is 20 wt% to 80 wt%, based on the total weight of the first three-way catalyst and the second three-way catalyst. More preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is in the range of 25 wt% to 75 wt%, based on the total weight of the first three-way catalyst and the second three-way catalyst. Even more preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is in the range of 30 wt% to 75 wt%, and more preferably in the range of 40 wt% to 60 wt%, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0073] Preferably, the ceria (calculated as CeO2) 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 wt.% to 60 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in the respective catalyst, and the zirconium oxide (calculated as ZrO2) 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 wt.% to 90 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in the respective catalyst.

[0074] More preferably, ceria (calculated as CeO2) 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 wt.% to 50 wt.%, based on the total weight of the ceria-zirconia mixed oxide in the corresponding catalyst, and zirconium oxide (calculated as ZrO2) 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 wt.% to 80 wt.%, based on the total weight of the ceria-zirconia mixed oxide in the corresponding catalyst.

[0075] Even more preferably, the ceria (calculated as CeO2) 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 wt.% to 50 wt.%, based on the total weight of the ceria-zirconia mixed oxide in the respective catalyst, and the zirconium oxide (calculated as ZrO2) 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 wt.% to 70 wt.%, based on the total weight of the ceria-zirconia mixed oxide in the respective catalyst.

[0076] The ceria-zirconia mixed oxide is used as an oxygen storage component. The term "oxygen storage component" (OSC) refers to an entity having a multivalent state and capable of actively reacting with a reducing agent such as carbon monoxide (CO) and / or hydrogen under reducing conditions, and then reacting with an oxidizing agent such as oxygen or nitrogen oxides under oxidizing conditions.

[0077] In a preferred embodiment, the ceria-zirconia mixed oxide present in the first three-way catalyst or the second three-way catalyst contains a dopant selected from lanthanum oxide, titanium oxide, hafnium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, yttrium, hafnium, praseodymium, neodymium or any combination thereof. The dopant metal may be incorporated into the crystal structure of the composite metal oxide in the form of a cation, may be deposited on the surface of the composite metal oxide in an oxidized form, or may be present in an oxidized form as a blend of a mixture of the dopant and the composite metal oxide on a microscopic scale, that is, in a composite form with the composite metal oxide. Preferably, the dopant is included in an amount of 1.0 wt%-20 wt%, or more preferably 5.0 wt%-15 wt%, based on the total weight of the ceria-zirconia mixed oxide present in the corresponding catalyst.

[0078] Alumina :

[0079] The alumina present in the first three-way catalyst or the second three-way catalyst is preferably gamma alumina or activated alumina. The BET surface area of ​​the fresh material is usually more than 60 square meters per gram ("m 2 / g”), usually up to about 200m 2 / g or more. Activated alumina is usually a mixture of γ and δ phases of alumina, but may also contain a large amount of η, κ and θ alumina phases. Preferably, the activated alumina is a high bulk density γ-alumina, a low or medium bulk density macroporous γ-alumina, a low bulk density macroporous boehmite or a γ-alumina.

[0080] Preferably, the amount of alumina present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 wt % to 70 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst. More preferably, the amount of alumina present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 wt % to 20 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst. It is also preferred that the amount of alumina present in the first three-way catalyst and the second three-way catalyst is in the range of 10 wt % to 60 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst. Most preferably, the amount of alumina present in the catalytic article is in the range of 15 wt % to 60 wt % based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0081] The alumina present in the first three-way catalyst and the second three-way catalyst is preferably doped with a dopant selected from barium, lanthanum oxide, zirconium oxide, neodymium oxide, yttrium oxide, ceria, titania, or a combination thereof, wherein the amount of the dopant is preferably 1.0 wt% to 30 wt% based on the total weight of the alumina and the dopant present in the respective catalysts. More preferably, the alumina doped with a dopant is selected from lanthanum oxide-aluminum oxide, titania-aluminum oxide, ceria-zirconia-aluminum oxide, zirconium oxide-aluminum oxide, lanthanum oxide-zirconia-aluminum oxide, barium oxide-aluminum oxide, barium oxide-lanthanum oxide-aluminum oxide, barium oxide-lanthanum oxide-neodymium oxide-aluminum oxide, yttrium oxide-aluminum oxide, or any combination thereof.

[0082] Substrate :

[0083] The substrates of the first three-way catalyst and the second three-way catalyst of the presently claimed invention, i.e., the first substrate and the second substrate, can be composed of any material commonly used to prepare automotive catalysts. In a preferred embodiment, the substrate is a ceramic substrate, a metal substrate, a ceramic foam substrate, a polymer foam substrate, or a woven fiber substrate. In a more preferred embodiment, the substrate is a ceramic or metal monolithic honeycomb structure.

[0084] The substrate provides a plurality of wall surfaces on which the catalytic layer or washcoat described above is applied and adhered, thereby serving as a support for the catalytic material.

[0085] Preferred metal substrates include heat-resistant metals and metal alloys, such as titanium and stainless steel, and other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium and / or aluminum, and the total amount of these metals may advantageously account for at least 15% by weight of the alloy, such as 10% to 25% by weight of chromium, 3% to 8% of aluminum, and up to 20% by weight of nickel. The alloy may also contain small or trace amounts of one or more metals, such as manganese, copper, vanadium, titanium, etc. The surface of the metal substrate may be oxidized at high temperatures (e.g., 1000° C. and higher) to form an oxide layer on the surface of the substrate, thereby improving the corrosion resistance of the alloy and promoting adhesion of the carrier coating to the metal surface.

[0086] Preferred ceramic materials for constructing the substrate may include any suitable refractory material, for example, cordierite, mullite, cordierite-alumina, silicon nitride, zircon-mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminosilicates, and the like.

[0087] Any suitable substrate can be used, such as a monolithic flow-through substrate having a plurality of fine parallel gas flow channels extending from the inlet face of the substrate to the outlet face so that the channel is open to allow fluid to flow. The channel, which is essentially a straight path from the inlet to the outlet, is defined by a wall, and the walls are coated with a catalytic material as a carrier coating so that the gas flowing through the channel contacts the catalytic material. The flow channels of the monolithic substrate are thin-walled channels, which are in any suitable cross-sectional shape, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. Such structures contain about 60 to about 1200 or more gas inlet openings (i.e., "cells") per square inch of cross section (cpsi), more typically about 300 cpsi to 900 cpsi. The wall thickness of the flow-through substrate can vary, with a typical range of between 0.002 inches and 0.1 inches. A representative commercially available flow-through substrate is a cordierite substrate with 400 cpsi and 6 mil wall thickness or 600 cpsi and 4 mil wall thickness. However, it should be understood that the present invention is not limited to a specific substrate type, material or geometry. In an alternative embodiment, the substrate can be a wall-flow substrate, wherein each channel is blocked with a non-porous plug at one end of the substrate body, wherein the alternating channels are blocked at the opposite end faces. This requires gas flow through the porous wall of the wall-flow substrate to reach the outlet. Such a monolithic substrate can contain up to about 700 or higher cpsi, such as about 100 cpsi to 400 cpsi, and more typically about 200 cpsi to about 300 cpsi. The cross-sectional shape of the unit cell can be varied as described above. The wall thickness of the wall-flow substrate is generally between 0.002 inches and 0.1 inches. A representative commercially available wall-flow substrate is composed of porous cordierite, an example of which has 200 cpsi and a wall thickness of 10 mils, or has 300 cpsi and a wall thickness of 8 mils, and a wall porosity of 45%-65%. Other ceramic materials (such as aluminum titanate, silicon carbide and silicon nitride) are also used as wall flow filter substrates. However, it should be understood that the present invention is not limited to a specific substrate type, material or geometry. It should be noted that in the case where the substrate is a wall flow substrate, the catalyst composition can penetrate into the pore structure of the porous wall (i.e., partially or completely block the pore openings) in addition to being disposed on the surface of the wall. In one embodiment, the substrate has a flow-through ceramic honeycomb structure, a wall flow ceramic honeycomb structure or a metal honeycomb structure.

[0088] Figure 3A and Figure 3B An exemplary substrate 2 is shown in the form of a flow-through substrate coated with a washcoat composition / catalytic layer as described herein. Figure 3A, the exemplary substrate 2 has a cylindrical shape and a cylindrical outer surface 4, an upstream end face 6, and a corresponding downstream end face 8 that is identical to the end face 6. The substrate 2 has a plurality of fine parallel gas flow channels 10 formed therein. Figure 3B As shown, the flow channel 10 is formed by the wall 12 and extends through the substrate 2 from the upstream end face 6 to the downstream end face 8, and the channel 10 is unobstructed to allow a fluid (e.g., airflow) to flow longitudinally through the substrate 2 via its airflow channel 10. Figure 3B As can be more easily seen in the , the size and configuration of the wall 12 are such that the gas flow channel 10 has a substantially regular polygonal shape. As shown, the washcoat composition / catalytic layer can be applied in multiple, distinct layers, if desired. In the illustrated embodiment, the washcoat is comprised of a discrete first washcoat layer 14 adhered to the wall 12 of the substrate member and a second discrete second washcoat layer 16 coated over the first washcoat layer 14. In one embodiment, the presently claimed invention is also practiced with two or more (e.g., 3 or 4) washcoat layers and is not limited to the illustrated two-layer embodiment.

[0089] Figure 4 An exemplary substrate 2 is shown in the form of a wall flow filter substrate coated with a washcoat layer composition as described herein. Figure 4 As shown, the exemplary substrate 2 has a plurality of channels 52. These channels are tubularly surrounded by the inner wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. Alternating channels are plugged with inlet plugs 58 at the inlet end and plugged with outlet plugs 60 at the outlet end to form a relative checkerboard pattern at the inlet 54 and outlet 56. The gas flow 62 enters through the unblocked channel inlet 64, is blocked by the outlet plug 60, and diffuses to the outlet side 66 through the channel wall 53 (which is porous). The gas cannot return to the inlet side of the wall due to the inlet plug 58. The porous wall flow filter used in the present invention is catalyzed because the wall of the element has or contains one or more catalytic materials. The catalytic material may be present alone on the inlet side of the element wall, alone on the outlet side, on both the inlet side and the outlet side, or the wall itself may be composed of catalytic material in whole or in part. The present invention includes the use of one or more layers of catalytic material on the inlet and / or outlet wall of the element.

[0090] Carrier coating on substrate :

[0091] The first substrate is coated with a first three-way catalyst, and the second substrate is coated with a second three-way catalyst.

[0092] Preferably, the first three-way catalyst covers 50% to 100% of the length of the first substrate. More preferably, the first three-way catalyst covers 70% to 100% of the length of the first substrate, and even more preferably, the first three-way catalyst covers 90% to 100% of the length of the first substrate. Most preferably, the first three-way catalyst covers the entire length or the entire accessible surface area of ​​the substrate.

[0093] Preferably, the second three-way catalyst covers 50% to 100% of the length of the second substrate. More preferably, the second three-way catalyst covers 70% to 100% of the length of the second substrate, and even more preferably, the second three-way catalyst covers 90% to 100% of the length of the second substrate. Most preferably, the second three-way catalyst covers the entire length or the entire accessible surface area of ​​the substrate.

[0094] The term "accessible surface" refers to the surface of the substrate that can be coated using conventional coating techniques used in the art of catalyst preparation, such as impregnation techniques.

[0095] First three-way conversion (TWC) catalyst

[0096] The first three-way catalyst is deposited on at least a portion of the first substrate. Preferably, the first three-way catalyst covers 50% to 100% of the length of the first substrate. More preferably, the first three-way catalyst covers 70% to 100% of the length of the first substrate, and even more preferably, the first three-way catalyst covers 90% to 100% of the length of the first substrate. Most preferably, the first three-way catalyst covers the entire length or the entire accessible surface area of ​​the substrate.

[0097] The first three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0098] Preferably, the total washcoat loading of the first three-way catalyst is 1.0 g / in 3 Up to 10g / in 3 More preferably, the total carrier coating loading of the first three-way catalyst is 2.0 g / in 3 Up to 7.0g / in 3 Even more preferably, the total washcoat loading of the first three-way catalyst is 2.5 g / in 3 Up to 4.5g / in 3 .

[0099] Preferably, the total platinum group metal (PGM) loading of the first three-way catalyst is 10 g / ft 3 Up to 200g / ft 3 More preferably, the total platinum group metal (PGM) loading of the first three-way catalyst is 50 g / ft 3 Up to 175g / ft 3 Even more preferably, the total platinum group metal (PGM) loading of the first three-way catalyst is 100 g / ft 3 Up to 130g / ft 3 .

[0100] Preferably, the first three-way catalyst is a single-layer catalyst or a double-layer catalyst or a double-layer catalyst having a partitioned configuration.

[0101] 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 material, or any combination thereof; and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, wherein the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0102] 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 material and palladium supported on a ceria-zirconia mixed oxide, and wherein the second layer comprises rhodium supported on a ceria-alumina composite material and a ceria-zirconia mixed oxide.

[0103] Preferably, the first layer of the carrier coating has a loading of 0.5 g / in 3 Up to 7.0g / in 3 And the carrier coating loading of the second layer is 0.5g / in 3 Up to 3.0g / in 3 More preferably, the first layer of carrier coating has a loading of 1.0 g / in 3 Up to 3.0g / in 3 And the carrier coating loading of the second layer is 0.5g / in 3 Up to 2.0g / in 3Even more preferably, the washcoat loading of the first layer is 2.0 g / in 3 Up to 3.0g / in 3 And the carrier coating loading of the second layer is 0.5g / in 3 Up to 1.5g / in 3 .

[0104] In a most preferred embodiment, the first three-way catalyst is a two-layer catalyst wherein

[0105] The total washcoat loading of the first three-way catalyst was 1.0 g / in 3 Up to 10g / in 3 ,

[0106] The first layer of carrier coating has a loading of 0.5 g / in 3 -7.0g / in 3 ,

[0107] The second layer of carrier coating has a loading of 0.5 g / in 3 Up to 3.0g / in 3 .

[0108] The total PGM loading is 10g / ft 3 Up to 200g / ft 3 ,

[0109] The first layer contains 5.0g / ft 3 Up to 100g / ft 3 Pt and 5.0 g / ft deposited on ceria-alumina composites 3 Up to 100g / ft 3 Pd deposited on ceria-zirconia mixed oxide,

[0110] The second layer contains 0.5g / ft 3 Up to 5g / ft 3 Rh and ceria-zirconia mixed oxides deposited on refractory ceria-alumina composites.

[0111] In an even more preferred embodiment, the first three-way catalyst is a two-layer catalyst wherein

[0112] The total washcoat loading of the first three-way catalyst was 2.5 g / in 3 Up to 4.5g / in 3 ,

[0113] The first layer of carrier coating has a loading of 2.0 g / in 3 Up to 3.0g / in 3 ,

[0114] The second layer of carrier coating has a loading of 0.5 g / in 3 Up to 1.5g / in 3 .

[0115] Total PGM loading is 101g / ft 3 Up to 153g / ft 3 ,

[0116] The first layer contains 50g / ft 3 Up to 75g / ft 3 Pt and 5.0 g / ft deposited on ceria-alumina composites 3 Up to 75g / ft 3 Pd deposited on ceria-zirconia mixed oxide.

[0117] The second layer contains 1g / ft 3 Up to 3g / ft 3 Rh and ceria-zirconia mixed oxides deposited on refractory ceria-alumina composites.

[0118] In another preferred embodiment, the first three-way catalyst is a double-layer catalyst comprising a first layer and a second layer.

[0119] wherein the first layer comprises a first region and a second region,

[0120] wherein the first zone comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof,

[0121] wherein the second zone comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof,

[0122] The second layer is deposited on at least a portion of the first layer, wherein the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0123] In another more preferred embodiment, the first three-way catalyst is a double-layer catalyst comprising a first layer and a second layer.

[0124] wherein the first layer comprises a first region and a second region,

[0125] Where the first and second regions are 100% of the substrate length

[0126] The first zone contains 100g / ft3 Up to 200g / ft 3 Palladium supported on alumina and ceria-zirconia mixed oxide,

[0127] The second zone contains 25g / ft 3 Up to 100g / ft 3 Platinum supported on ceria-zirconia mixed oxide and ceria-alumina composites, and 5.0 g / ft 3 Up to 25g / ft 3 Palladium supported on ceria-zirconia mixed oxide and ceria-alumina composites,

[0128] wherein the second layer is deposited on at least a portion of the first layer, wherein the second layer comprises 1.0 g / ft 3 Up to 10g / ft 3 Rhodium supported on ceria-zirconia mixed oxide and ceria-alumina composites,

[0129] The total carrier coating loading of the first three-way catalyst is 1.0 g / in 3 Up to 10g / in 3 And the total PGM loading is 10g / ft 3 Up to 200g / ft 3 ,

[0130] The carrier coating loading in the first zone is 0.25 g / in 3 Up to 4.0g / in 3 .

[0131] The carrier coating loading in the second zone is 0.25 g / in 3 Up to 4.0g / in 3 .

[0132] The second layer of carrier coating loading is 0.25 g / in 3 Up to 2.0g / in 3 .

[0133] 70% of the total platinum is deposited on the refractory ceria-alumina composite material, and 30% of the total platinum is deposited on the ceria-zirconia mixed oxide.

[0134] In the context of the present invention, the term "first zone" is used interchangeably for "inlet zone" or "front zone", and the term "second zone" is used interchangeably for "outlet zone" or "rear zone". The terms "first zone" and "second zone" also describe the relative positioning of the catalytic article in the flow direction, respectively describing the relative placement of the catalytic article when placed in the exhaust gas treatment system. The first zone will be positioned upstream, while the second zone will be positioned downstream. The first zone covers at least some portion of the substrate from the inlet of the substrate, while the second zone covers at least some portion of the substrate from the outlet of the substrate. The inlet of the substrate is the first end (inflow end portion) capable of receiving the flow of the engine exhaust flow from the engine, while the outlet of the substrate is the second end (outflow end portion) from which the treated exhaust flow leaves.

[0135] Preferably, the first and second zones together cover 50% to 100% of the length of the substrate. More preferably, the first and second zones together cover 90% to 100% of the length of the substrate, and even more preferably, the first and second zones together cover the entire length or the entire accessible surface area of ​​the substrate.

[0136] The term "accessible surface" refers to the surface of the substrate that can be coated using conventional coating techniques used in the art of catalyst preparation, such as impregnation techniques.

[0137] Preferably, the first zone covers 10% to 90% of the total substrate length from the inlet and the second zone covers 90% to 10% of the total substrate length from the outlet, while the first and second zones together cover 20% to 100% of the substrate length.

[0138] More preferably, the first zone covers 20% to 80% of the entire substrate length from the inlet and the second zone covers 80% to 20% of the entire substrate length from the outlet, while the first zone and the second zone together cover 40% to 100% of the substrate length.

[0139] Even more preferably, the first zone covers 30% to 70% of the total substrate length from the inlet and the second zone covers 70% to 30% of the total substrate length from the outlet, while the first and second zones together cover 60% to 100% of the substrate length.

[0140] Even most preferably, the first zone covers 40% to 50% of the total substrate length from the inlet and the second zone covers 50% to 40% of the total substrate length from the outlet, while the first and second zones together cover 80% to 100% of the substrate length.

[0141] Preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.05 wt% to 3.0 wt% based on the total weight of the first three-way catalyst.

[0142] More preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.1 wt% to 1.0 wt% based on the total weight of the first three-way catalyst.

[0143] Preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.05 wt % to 5.0 wt % based on the total weight of the first three-way catalyst.

[0144] More preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.1 wt% to 2.0 wt% based on the total weight of the first three-way catalyst.

[0145] Preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.001 wt % to 1.0 wt % based on the total weight of the first three-way catalyst.

[0146] More preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.005 wt % to 0.5 wt % based on the total weight of the first three-way catalyst.

[0147] Ceria-alumina composites :

[0148] Preferably, the amount of the ceria-alumina composite material present in the first three-way catalyst is in the range of 5.0 wt % to 80 wt %, based on the total weight of the first three-way catalyst. More preferably, the amount of the ceria-alumina composite material present in the first three-way catalyst is in the range of 10 wt % to 60 wt %, based on the total weight of the first three-way catalyst. Most preferably, the amount of the ceria-alumina composite material present in the first three-way catalyst is in the range of 15 wt % to 60 wt %, based on the total weight of the first three-way catalyst.

[0149] Ceria-Zirconia Mixed Oxide (CZO) :

[0150] Preferably, the amount of ceria-zirconia mixed oxide present in the first three-way catalyst is 20 wt% 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 wt% 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 wt% to 75 wt%, based on the total weight of the first three-way catalyst.

[0151] Alumina :

[0152] Preferably, the amount of alumina present in the first three-way catalyst is in the range of 5.0 wt % 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 wt % 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 wt % to 60 wt %, based on the total weight of the first three-way catalyst.

[0153] Second three-way conversion (TWC) catalyst

[0154] A second three-way catalyst is deposited on at least a portion of the second substrate. The second three-way catalyst preferably covers 50% to 100% of the length of the second substrate. More preferably, the second three-way catalyst covers 70% to 100% of the length of the second substrate, and even more preferably, the second three-way catalyst covers 90% to 100% of the length of the second substrate. Most preferably, the second three-way catalyst covers the entire length or the entire accessible surface area of ​​the substrate.

[0155] The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0156] Preferably, the second three-way catalyst additionally comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0157] In a preferred embodiment, the second three-way catalyst is substantially free of palladium. The term "substantially free of palladium" means that palladium is not added to the second three-way catalyst. It may be present as an impurity in an amount less than 0.001% by weight. In another preferred embodiment, the second three-way catalyst comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0158] 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, the washcoat loading is the primary means of achieving the desired backpressure.

[0159] Preferably, the second three-way catalyst is at 1.5 g / in 3 Up to 3.2g / in 3 More preferably, the total washcoat loading in the second three-way catalyst is between 2.0 g / in 3 Up to 3.0g / in 3 Most preferably, the total carrier coating loading in the second three-way catalyst is 2.5 g / in 3 Up to 2.8g / in 3 within the range.

[0160] Preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst ranges from 0.01 wt% to 1.0 wt% based on the total weight of the second three-way catalyst.

[0161] More preferably, the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst ranges from 0.05 wt.% to 0.5 wt.% based on the total weight of the first three-way catalyst.

[0162] Preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.01 wt% to 1.0 wt% based on the total weight of the first three-way catalyst.

[0163] More preferably, the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst is in the range of 0.01 wt.% to 1.0 wt.% based on the total weight of the first three-way catalyst.

[0164] Preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.001 wt % to 0.5 wt % based on the total weight of the first three-way catalyst.

[0165] More preferably, the amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst ranges from 0.002 wt% to 0.1 wt% based on the total weight of the first three-way catalyst.

[0166] Ceria-alumina composites :

[0167] Preferably, the amount of the ceria-alumina composite material present in the second three-way catalyst is in the range of 5.0 wt % to 80 wt %, based on the total weight of the second three-way catalyst. More preferably, the amount of the ceria-alumina composite material present in the second three-way catalyst is in the range of 10 wt % to 60 wt %, based on the total weight of the second three-way catalyst. Most preferably, the amount of the ceria-alumina composite material present in the second three-way catalyst is in the range of 15 wt % to 60 wt %, based on the total weight of the second three-way catalyst.

[0168] Ceria-Zirconia Mixed Oxide (CZO) :

[0169] Preferably, the amount of ceria-zirconia mixed oxide present in the second three-way catalyst is 20 wt% 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 wt% 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 wt% to 75 wt%, based on the total weight of the second three-way catalyst.

[0170] Alumina :

[0171] Preferably, the amount of alumina present in the second three-way catalyst is in the range of 5.0 wt % 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 wt % 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 wt % to 60 wt %, based on the total weight of the second three-way catalyst.

[0172] Preparation of TWC :

[0173] The first three-way catalyst or the second three-way catalyst is prepared by depositing at least a platinum group metal on a portion of the first substrate or the second substrate.

[0174] Preferably, platinum group metal deposition involves forming a slurry of the platinum group metal and the support material, which is subsequently applied as a washcoat to the substrate.

[0175] The step of preparing the slurry comprises a technique selected from the group consisting of incipient wetness impregnation, incipient wetness co-impregnation and post addition.

[0176] The incipient wetness impregnation technique, also known as capillary impregnation or dry impregnation, is commonly used to synthesize heterogeneous materials, i.e., catalysts. Typically, a metal precursor is dissolved in an aqueous or organic solution, and the metal-containing solution is then added to a catalyst support that contains a pore volume equal to the volume of solution added. Capillary action draws the solution into the pores of the support. The volume of the added solution exceeding the pores of the support causes the transport of the solution to shift from a capillary action process to a much slower diffusion process. The catalyst is dried and calcined to remove the volatile components in the solution, depositing the metal on the surface of the catalyst support. The concentration profile of the impregnated material depends on the mass transfer conditions in the pores during impregnation and drying.

[0177] The support particles are typically dried enough to absorb substantially all of the solution to form a wet solid. An aqueous solution of a water-soluble compound or complex of an active metal is typically utilized, such as rhodium chloride, rhodium nitrate (e.g., Rh(NO)3 and its salts), rhodium acetate, or a combination thereof (where rhodium is the active metal); palladium nitrate, palladium tetraamine nitrate, palladium acetate, or a combination thereof (where palladium is the active metal); and platinum nitrate, platinum acetate, or a combination thereof, where platinum is the active metal. After the support particles are treated with the active metal solution, the particles are dried, such as by heat treating the particles at an elevated temperature (e.g., 100°C-150°C) for a period of time (e.g., 1 hour-3 hours), and then calcined to convert the active metal to a more catalytically active form. An exemplary calcination method involves heat treatment in air at a temperature of about 400°C-550°C for 10 minutes to 3 hours. The above method may be repeated as needed to achieve the desired level of active metal impregnation.

[0178] Substrate coating :

[0179] The three-way conversion catalyst as described above is usually prepared in the form of catalyst particles as described above. These catalyst particles are mixed with water to form a slurry to coat catalyst substrates such as honeycomb substrates. In addition to the catalyst particles, the slurry may optionally contain a binder, an associative thickener and / or a surfactant (including anionic, cationic, nonionic or amphoteric surfactants) in the form of aluminum oxide, silicon dioxide, zirconium acetate, colloidal zirconium oxide or zirconium hydroxide. Other exemplary binders include boehmite, γ-alumina or δ / θ alumina and silica sol. When present, the binder is usually used in an amount of about 1.0 wt %-5.0 wt % of the total carrier coating loading. Acidic or alkaline substances are added to the slurry to adjust the pH accordingly. For example, in some embodiments, the pH of the slurry is adjusted by adding ammonium hydroxide, aqueous nitric acid solution or acetic acid. The typical pH range of the slurry is about 3.0 to 12. The slurry can be ground to reduce the particle size and enhance particle mixing. Grinding is done in a ball mill, continuous mill or other similar equipment, and the solid content of the slurry can be, for example, about 20% to 60% by weight, more specifically about 20% to 40% by weight. In one embodiment, the slurry after grinding is characterized by D 90 The particle size is about 10 microns to about 40 microns, preferably 10 microns to about 30 microns, and more preferably about 10 microns to about 15 microns. Use a dedicated particle size analyzer to determine D 90 The equipment used in this example uses laser diffraction to measure particle size in small volumes of slurry. Typically, D 90 In micrometers it is meant that 90% of the particles by number have a diameter smaller than this value.

[0180] The slurry is coated on the catalyst substrate using any washcoat technique known in the art. For example, the catalyst substrate is dip-coated in the slurry one or more times or otherwise coated with the slurry. Thereafter, the coated substrate is dried at an elevated temperature (e.g., 100° C.-150° C.) for a period of time (e.g., 10 minutes-3.0 hours), and then calcined by heating, for example, at 400° C.-700° C., typically for about 10 minutes to about 3 hours. After drying and calcining, the final washcoat coating is considered to be substantially free of solvent.

[0181] After calcination, the catalyst loading obtained by the above washcoat technique can be determined by calculating the difference between the coated and uncoated weights of the substrate. As will be apparent to one skilled in the art, the catalyst loading can be modified by altering the slurry rheology. In addition, the coating / drying / calcining process to produce the washcoat can be repeated as needed to build up the coating to the desired loading level or thickness, meaning that more than one washcoat may be applied.

[0182] The coated substrate can be aged by heat treating the coated substrate. For example, aging is performed at a temperature of about 850°C to about 1050°C in the presence of steam under gasoline engine exhaust conditions for 50 hours to 300 hours. Thus, an aged catalyst article is provided according to the present invention. Effective support materials (such as ceria-alumina composites) maintain a high percentage (e.g., about 50%-100%) of their pore volume when aged (e.g., aged at about 850°C to about 1050°C in the presence of steam for about 50 hours to 300 hours).

[0183] Preferably, the first three-way catalyst is prepared by depositing a platinum group metal on at least a portion of the first substrate or the second substrate, wherein the platinum group metals comprise platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or a combination thereof, palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or a combination thereof, and rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or a combination thereof.

[0184] Preferably, the second three-way catalyst is prepared by depositing platinum and optionally rhodium on at least a portion of the second substrate, wherein the platinum is supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or a combination thereof, and wherein the rhodium is supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or a combination thereof.

[0185] The invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the indicated dependencies and back-references. In particular, it should be noted that in each case where the scope of an embodiment 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", each embodiment within this scope is meant to be explicitly disclosed to the skilled person, i.e. the wording of this term should be understood by the skilled person as synonymous with "an exhaust aftertreatment system according to any one of embodiments 1, 2, 3 and 4". In addition, it should be explicitly pointed out that the following set of embodiments represents a properly structured part of a general description of preferred aspects of the invention and therefore properly supports but does not represent the claims of the invention.

[0186] Implementation 1 :

[0187] The exhaust aftertreatment system includes:

[0188] a. a first three-way catalyst, the first three-way catalyst being deposited on at least a portion of the first substrate; and

[0189] b. a second three-way catalyst, the second three-way catalyst being deposited on at least a portion of the second substrate,

[0190] Wherein the first three-way catalyst comprises:

[0191] i) platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof,

[0192] ii) palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, and

[0193] iii) rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof,

[0194] The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof.

[0195] Implementation 2 :

[0196] The exhaust aftertreatment system according to embodiment 1, wherein the second three-way catalyst comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0197] Implementation 3 :

[0198] An exhaust aftertreatment system according to any one of embodiments 1 to 2, wherein the second three-way catalyst is substantially free of palladium.

[0199] Implementation 4 :

[0200] 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 material, or any combination thereof.

[0201] Implementation 5 :

[0202] According to the exhaust aftertreatment system of embodiment 1, a weight ratio of the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 2:1 to 20:1, preferably in the range of 2.5:1 to 12:1.

[0203] Implementation 6 :

[0204] An exhaust aftertreatment system according to Embodiment 2, wherein a weight ratio of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 1:3 to 50:1, preferably in the range of 1:1 to 50:1, more preferably in the range of 1:2 to 20:1, more preferably in the range of 1:1 to 20:1, more preferably in the range of 1:1.5 to 4:1, and more preferably in the range of 1:1 to 4:1.

[0205] Implementation Plan 7 :

[0206] An 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 each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the first three-way catalyst to the total amount of platinum, optionally to rhodium and palladium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof in the second three-way catalyst is in the range of 4:1 to 20:1.

[0207] Implementation 8 :

[0208] An exhaust aftertreatment system according to any one of embodiments 1 to 7, wherein the system is characterized in that the back pressure contribution of the second three-way catalyst is less than 38%, preferably less than 35%, and more preferably less than 32%.

[0209] Implementation Plan 9 :

[0210] An exhaust aftertreatment system according to any one of embodiments 1 to 8, wherein the second three-way catalyst is at 1.5 g / in 3 Up to 3.2g / in 3In the range of 2.0 g / in 3 Up to 3.0g / in 3 In the range of, and more preferably in the range of 2.5 g / in 3 Up to 2.8g / in 3 A monolayer catalyst is deposited on the second substrate at a total washcoat loading in the range of .

[0211] Implementation 10 :

[0212] An exhaust aftertreatment system according to any one of embodiments 1 to 9, wherein the first three-way catalyst is a two-layer catalyst comprising 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 or on a portion of the first substrate or on both,

[0213] The first layer comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof; and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, and the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof.

[0214] Implementation Plan 11 :

[0215] The exhaust aftertreatment system according to any one of claims 1 to 10, wherein the first three-way catalyst is a double-layer catalyst comprising a first layer and a second layer,

[0216] wherein the first layer comprises a first region and a second region,

[0217] wherein the first zone covers 10% to 90% of the entire substrate length from the inlet, and the second zone covers 10% to 90% of the entire substrate length from the outlet,

[0218] wherein the first zone comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof,

[0219] wherein the second zone comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof,

[0220] The second layer is deposited on at least a portion of the first layer, wherein the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

[0221] Implementation 12 :

[0222] An exhaust aftertreatment system according to any one of embodiments 1 to 11, wherein the total ceria-zirconia mixed oxide loading in the first three-way catalyst is higher than the total ceria-zirconia mixed oxide loading in the second three-way catalyst.

[0223] Implementation 13 :

[0224] An exhaust 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 material, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 wt. % to 3.0 wt. %, preferably in the range of 0.03 wt. % to 2.5 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0225] Implementation Plan 14 :

[0226] An 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 material, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.02 wt. % to 3.0 wt. %, and preferably in the range of 0.02 wt. % to 2.0 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0227] Implementation Plan 15 :

[0228] An 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 material, or any combination thereof in the first three-way catalyst and the second three-way catalyst is in the range of 0.01 wt. % to 2.0 wt. %, preferably in the range of 0.01 wt. % to 1.5 wt. %, and more preferably in the range of 0.01 wt. % to 1.0 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0229] Implementation Plan 16 :

[0230] An exhaust aftertreatment system according to any one of embodiments 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.

[0231] Implementation Plan 17 :

[0232] An exhaust aftertreatment system according to any one of embodiments 1 to 16, wherein the total amount of the ceria-zirconia mixed oxide present in the first three-way catalyst and the second three-way catalyst is in the range of 20 wt. % to 80 wt. %, preferably in the range of 25 wt. % to 75 wt. %, more preferably in the range of 30 wt. % to 75 wt. %, and more preferably in the range of 40 wt. % to 60 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0233] Implementation Plan 18 :

[0234] An exhaust aftertreatment system according to any one of embodiments 1 to 17, wherein the total amount of the aluminum oxide present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 wt % to 70 wt %, preferably in the range of 5.0 wt % to 20 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst; or wherein the amount of the aluminum oxide present in the first three-way catalyst and the second three-way catalyst is in the range of 10 wt % to 60 wt %, and more preferably in the range of 15 wt % to 60 wt %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0235] Implementation Plan 19 :

[0236] The exhaust aftertreatment system according to any one of embodiments 1 to 18, wherein the aluminum oxide present in the first three-way catalyst and the second three-way catalyst is doped with a dopant selected from barium, lanthanum oxide, zirconium oxide, neodymium oxide, yttrium oxide, ceria or titanium oxide,

[0237] Wherein the amount of the dopant is 1.0 wt % to 30 wt % based on the total weight of the alumina and the dopant present in the first three-way catalyst or the second three-way catalyst.

[0238] Implementation Plan 20 :

[0239] An exhaust aftertreatment system according to any one of embodiments 1 to 19, wherein the aluminum oxide is selected from aluminum oxide, lanthanum oxide-alumina, titanium oxide-alumina, ceria-zirconia-alumina, zirconium oxide-alumina, ceria-alumina, lanthanum oxide-zirconium oxide-alumina, barium oxide-alumina, barium oxide-lanthanum oxide-alumina, barium oxide-lanthanum oxide-neodymium oxide-alumina, yttrium-alumina or any combination thereof.

[0240] Implementation Plan 21 :

[0241] The exhaust aftertreatment system according to any one of embodiments 1 to 20, wherein the total amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in the range of 5.0 wt. % to 80 wt. %, preferably in the range of 10 wt. % to 60 wt. %, more preferably in the range of 15 wt. % to 60 wt. %, and more preferably in the range of 15 wt. % to 40 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst.

[0242] Implementation Plan 22 :

[0243] An exhaust aftertreatment system according to embodiment 1, wherein the system comprises:

[0244] i) an engine, the engine generating an exhaust gas flow;

[0245] ii) a first three-way catalyst deposited on at least a portion of the first substrate; and

[0246] iii) a second three-way catalyst, the second three-way catalyst being deposited on at least a portion of the second substrate,

[0247] Wherein the first three-way catalyst is positioned upstream of the engine and the second three-way catalyst is positioned downstream in fluid communication with the first three-way catalyst.

[0248] Implementation Plan 23 :

[0249] The system of any one of Embodiments 1 to 16 and 22, wherein the amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in a range of 5.0 wt. % 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 in a range of 20 wt. % to 80 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst, and

[0250] wherein the amount of CeO2 present in the ceria-alumina composite material in the first three-way catalyst or the second three-way catalyst is preferably 1.0 wt.% to 60 wt.%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst, wherein the CeO2 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 wt.% to 60 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in the corresponding catalyst, and the zirconium oxide (calculated as ZrO2) 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 wt.% to 90 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in the corresponding catalyst.

[0251] Implementation Plan 24 :

[0252] A method of 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 embodiments 1 to 23 to reduce the levels of hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gas.

[0253] Implementation Plan 25 :

[0254] Use of an exhaust gas aftertreatment system according to any one of embodiments 1 to 23 for purifying a gaseous exhaust stream comprising hydrocarbons, carbon monoxide and nitrogen oxides.

[0255] Various aspects of the presently claimed invention are more fully illustrated by the following examples, which are set forth for the purpose of illustrating certain aspects of the invention and are not to be construed as limiting the invention.

[0256] The washcoat component loadings and backpressure losses for upstream TWC-1 and downstream TWC-2 are provided in Table 1 below:

[0257] Table 1: Washcoat component loading and backpressure loss for upstream TWC-1 and downstream TWC-2

[0258]

[0259] a CeO2: Total CeO2 loading including all CeO2 contents from ceria-zirconia mixed oxide and other washcoat components

[0260] b WCL: Total Washcoat Loading

[0261] c BP loss: back pressure loss

[0262] Example 1: System 1 (S1), Comparative Example :

[0263] 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 dual-layer washcoat structure coated on a monolithic cordierite substrate with the following dimensions: 4.66" diameter and 3.81" length, 800 cpsi (pores per square inch) pore density and 2.5 mil wall thickness. The total washcoat loading is 3.61 g / in 3 And the total PGM loading is 120g / ft 3 (Pt / Pd / Rh=0 / 118 / 2). The catalyst has a mass fraction of 0.59 g / in 3 Ceria, and the back pressure loss is about 44%. The bottom layer comprises 118 g / ft uniformly deposited on the refractory alumina 3 Pd and ceria-zirconia mixed oxide, and barium oxide. The washcoat loading of the bottom layer was 2.61 g / in 3 The top layer consists of 2 g / ft deposited on refractory alumina. 3 Rh and ceria-zirconia mixed oxide. The top washcoat loading was 1.00 g / in 3 S1-TWC-2 has the same washcoat composition as S1-TWC-1, except that the total PGM loading is 12 g / ft 3 (Pt / Pd / Rh=0 / 10 / 2). The downstream catalyst was coated on a monolithic cordierite substrate having the following dimensions: 5.20" in diameter and 3.96" in length, 400 cpsi pore density, and 6.5 mil wall thickness.

[0264] Example 2: System 2 (S2) :

[0265] S2 includes an upstream catalyst S2-TWC-1 based on Pt / Pd / Rh and a downstream catalyst S2-TWC-2 based on Pt / Rh. S2-TWC-1 has a dual-layer washcoat structure coated on a monolithic cordierite substrate with the following dimensions: 4.66" diameter and 3.81" length, 800 cpsi pore density and 2.5 mil wall thickness. The total washcoat loading is 3.62 g / in 3 And the total PGM loading is 120g / ft 3 (Pt / Pd / Rh=59 / 59 / 2). The catalyst has a mass fraction of 0.71 g / in 3 The bottom layer comprises 59 g / ft 2 of cerium oxide deposited on a refractory ceria-alumina composite.3 Pt, 59 g / ft deposited on ceria-zirconia mixed oxide 3 Pd and barium oxide. The washcoat loading of the bottom layer is 2.62 g / in 3 The top layer comprises 2 g / ft deposited on a refractory ceria-alumina composite. 3 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 applied to a monolithic cordierite substrate having the following dimensions: 5.20" diameter and 3.96" length, 400 cpsi pore density and 6.5 mil wall thickness. The total washcoat loading was 2.76 g / in 3 And the total PGM loading is 12g / ft 3 (Pt / Pd / Rh=10 / 0 / 2). The catalyst has a mass fraction of 0.62 g / in 3 Cerium dioxide, and the back pressure loss is about 30%. A single layer of washcoat contains 10 g / ft 3 Pt, 2g / ft 3 Rh, refractory ceria-alumina composite, ceria-zirconia mixed oxide, and baria. 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.

[0266] Example 3: System 3 (S3) : S3 includes an upstream catalyst S3-TWC-1 based on Pt / Pd / Rh and a downstream catalyst S3-TWC-2 based on Pt / Rh. 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 the following dimensions: 5.20" diameter and 3.96" length, 400 cpsi pore density and 6.5 mil wall thickness. The total washcoat loading is 2.82 g / in 3 And the total PGM loading is 12g / ft 3 (Pt / Pd / Rh=10 / 0 / 2). The catalyst has a mass fraction of 0.95 g / in 3 Cerium dioxide, and the back pressure loss is about 30%. A single layer of washcoat contains 10 g / ft 3 Pt, 2g / ft 3Rh, refractory ceria-alumina composite, ceria-zirconia mixed oxide, and baria. 50% of Pt and all of the Rh were deposited on the refractory ceria-alumina composite, and the remaining 50% of Pt was deposited on the ceria-zirconia mixed oxide.

[0267] Example 4: System 4 (S4) : S4 includes an upstream catalyst S4-TWC-1 based on Pt / Pd / Rh and a downstream catalyst S4-TWC-2 based on Pt / Pd / Rh. 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 the following dimensions: 5.20" diameter and 3.96" length, 400 cpsi pore density and 6.5 mil wall thickness. The total washcoat loading is 2.76 g / in 3 And the total PGM loading is 12g / ft 3 (Pt / Pd / Rh=5 / 5 / 2). The catalyst has a mass fraction of 0.62 g / in 3 Cerium dioxide, and the back pressure loss is about 30%. A single layer of washcoat contains 5g / ft 3 Pt, 5g / ft 3 Pd, 2g / ft 3 Rh, refractory ceria-alumina composite, ceria-zirconia mixed oxide, and baria. All Pt and Rh were deposited on the refractory ceria-alumina composite, and all Pd was deposited on the ceria-zirconia mixed oxide.

[0268] Example 5: System 5 (S5) , Comparative Example: S5 comprises an upstream catalyst S5-TWC-1 based on Pt / Pd / Rh and a downstream catalyst S5-TWC-2 based on Pd / Rh. S5-TWC-1 has a partitioned two-layer carrier coating structure having an inlet bottom zone, an outlet bottom zone (each zone covers approximately 50% of the substrate length) and a top layer covering 100% of the substrate length. The catalyst was coated on a monolithic cordierite substrate having the following dimensions: 4.66" in diameter and 3.81" in length, a pore density of 800 cpsi and a wall thickness of 2.5 mils. The total carrier coating loading was 3.57 g / in 3 And the total PGM loading is 120g / ft 3 (Pt / Pd / Rh=29 / 87 / 4). The catalyst has a mass fraction of 0.80 g / in 3 Ceria, and the back pressure loss was about 45%. The inlet bottom zone contained 156.6 g / ft uniformly deposited on the refractory alumina composite. 3Pd and ceria-zirconia mixed oxides, and barium oxide. The washcoat loading in the inlet bottom zone was 2.56 g / in 3 The outlet bottom area contains 58g / ft 3 Pt, 17.4 g / ft 3 Pd, refractory ceria-alumina composite, ceria-zirconia mixed oxide, and barium oxide. 70% of Pt was deposited on the refractory ceria-alumina composite, and 30% of Pt and all of Pd were deposited on the ceria-zirconia mixed oxide. The washcoat loading in the outlet bottom zone was 2.58 g / in 3 The top layer comprises 4 g / ft2 of refractory ceria-alumina composite material deposited on 3 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 the following dimensions: 5.20" diameter and 3.96" length, 400 cpsi pore density and 6.5 mil wall thickness. The total washcoat loading is 2.82 g / in 3 And the total PGM loading is 12g / ft 3 (Pt / Pd / Rh=0 / 10 / 2). The catalyst has a mass fraction of 0.32 g / in 3 Ceria, and the back pressure loss was about 34%. The single-layer washcoat comprised 10 g / ft of ceria-zirconia mixed oxide deposited on 3 Pd, 2 g / ft deposited on refractory alumina composite 3 Rh and barium oxide.

[0269] Example 6: System 6 (S6) : S6 includes an upstream catalyst S6-TWC-1 based on Pt / Pd / Rh and a downstream catalyst S6-TWC-2 based on Pd / Rh. S6-TWC-1 is the same as S5-TWC-1, and S6-TWC-2 is the same as S2-TWC-2.

[0270] Example 7: Measurement of back pressure loss

[0271] The back pressure loss or the washcoat contribution to the back pressure loss was measured on a SuperFlow SF-1020 Flowbench at ambient temperature. The bare substrate (BP sub ) and coated monolithic catalysts (BP cat The back pressure loss of the coated monolithic catalyst is calculated as follows:

[0272] Back pressure loss = (BP cat -BP sub ) / BP cat ×100%

[0273] Example 8: Engine Aging and Vehicle Testing

[0274] Exemplary systems 1-6 were installed in steel converter cans and aged in the exhaust line of a gasoline engine operating under an exothermic 4 mode aging cycle. The duration of aging of the upstream catalyst was 100 hours with a maximum bed temperature of about 985°C. The aged catalytic converters were tested on two test vehicles that followed certified procedures and tolerances under the US FTP-75 drive cycle. The first test vehicle was certified to the US EPA ULEV70 (Ultra Low Emission Vehicle) emission standard. The second vehicle was certified to the US EPA SULEV30 (Ultra Ultra Low Emission Vehicle) emission standard and was calibrated with frequent fuel cut-off events.

[0275] The results of the FTP-75 tail pipe bag emissions data for systems S1-S4 are provided in Table 2 below:

[0276] Table 2: FTP-75 Tailpipe Bag Emissions Data Collected on ULEV70 Vehicles

[0277] Exemplary Systems NMHC, mg / mile <![CDATA[NO x , mg / mile]]> CO, mg / mile S1, Comparative Example 23.5 10.6 112 S2 23.9 9.5 104 S3 25.2 9.8 105 S4 23.6 9.0 91

[0278] Table 2 summarizes the tailpipe emissions of NMHC, NOx, and CO on the ULEV70 test vehicle. Exemplary system 1 represents a conventional TWC system in which both the upstream and downstream catalysts are based on Pd and Rh as active platinum group metals. Exemplary system 2 includes a tri-metal upstream TWC based on Pt / Pd / Rh and a single-layer downstream TWC based on a single-coat Pt / Rh. Compared with reference system 1, system 2 exhibits equivalent NMHC and CO emissions and slightly better NOx emissions. Exemplary system 4 is similar to system 2, except that the downstream TWC is a tri-metal catalyst based on Pt / Pd / Rh. System 4 exhibits performance comparable to system 2. Both system 2 and system 4 use a large amount of Pt to replace the more expensive Pd present in the reference system. In addition, low back pressure loss, single-coat downstream catalysts are applied in these inventive systems. Therefore, these inventive systems are substantially more cost-effective than the reference system. Exemplary system 3 uses significantly more cerium dioxide in the downstream TWC, which results in a moderate loss of NMHC performance.

[0279] The results of the FTP-75 tail pipe bag emissions data for systems S5-S6 are provided in Table 3 below:

[0280] Table 3. FTP-75 Tailpipe Bag Emissions Data Collected on a SULEV30 Vehicle Calibrated with Frequent Fuel Cut-off Events

[0281] Exemplary Systems NMHC, mg / mile <![CDATA[NO x , mg / mile]]> CO, mg / mile S5, Comparative Example 9.2 15.3 256 S6 9.5 11.7 251

[0282] Table 3 summarizes the tailpipe emissions of NMHC, NOx, and CO on the SULEV30 test vehicle. The FTP-75 on this particular vehicle was calibrated with frequent fuel cut events to achieve better fuel economy, which made NOx emission control more difficult to achieve. Exemplary System 5 used a Pd / Rh based downstream TWC. In contrast, the use of a Pt / Rh based single-coat downstream TWC in System 6 significantly improved tailpipe NOx emissions without adversely affecting NMHC and CO emissions. Figure 2 Cumulative NOx emissions traces are shown for system 6 relative to system 5. The NOx benefit of the inventive system comes primarily from less NOx breakthrough during fuel cut events during deceleration.

[0283] Citations

[0284] -DE 10 2019 208436 A1

[0285] -US 2010 / 061903 A1

[0286] -US 2002 / 048542 A1

[0287] -US 2009 / 042722 A1

Claims

1. An exhaust gas aftertreatment system, the exhaust gas aftertreatment system comprising: a. a first three-way catalyst, wherein the first three-way catalyst is deposited on at least a portion of the first substrate; as well as b. a second three-way catalyst, wherein the second three-way catalyst is deposited on at least a portion of the second substrate, Wherein the first three-way catalyst comprises: i. platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, ii. palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, and iii. rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof, The second three-way catalyst comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material or any combination thereof.

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

3. The system of any one of claims 1 to 2, wherein the second three-way catalyst is substantially free of palladium.

4. The system of any one of claims 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.

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

1.

6. The system of any one of claims 1 to 5, wherein the weight ratio of the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 1:1 to 50:

1.

7. The system of any one of claims 1 to 6, wherein the weight ratio of the total amount of platinum, palladium, and rhodium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst to the total amount of platinum, optionally to rhodium and palladium each supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the second three-way catalyst is in the range of 4:1 to 20:

1.

8. The system of any one of claims 1 to 7, wherein the system is characterized in that the back pressure contribution of the second three-way catalyst is less than 38%.

9. The system according to any one of claims 1 to 8, wherein the second three-way catalyst is present at 1.5 g / in 3 Up to 3.2g / in 3 A monolayer catalyst is deposited on the second substrate with a total washcoat loading within a range of.

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

11. The system according to any one of claims 1 to 10, wherein the first three-way catalyst is a double-layer catalyst comprising a first layer and a second layer, wherein the first layer comprises a first region and a second region, wherein the first zone covers 10% to 90% of the entire substrate length from the inlet, and the second zone covers 10% to 90% of the entire substrate length from the outlet, wherein the first zone comprises palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, wherein the second zone comprises platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, and palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof, The second layer is deposited on at least a portion of the first layer, wherein the second layer comprises rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof.

12. The system of any one of claims 1 to 11, wherein the total ceria-zirconia mixed oxide loading in the first three-way catalyst is higher than the total ceria-zirconia mixed oxide loading in the second three-way catalyst.

13. The system of any one of claims 1 to 12, wherein the total amount of platinum supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst and the second three-way catalyst ranges from 0.02 wt.% to 3.0 wt.%, based on the total weight of the first three-way catalyst and the second three-way catalyst.

14. The system of any one of claims 1 to 13, wherein the total amount of palladium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst and the second three-way catalyst ranges from 0.02 wt. % to 3.0 wt. % based on the total weight of the first three-way catalyst and the second three-way catalyst.

15. The system of any one of claims 1 to 13, wherein the total amount of rhodium supported on alumina, ceria-zirconia mixed oxide, ceria-alumina composite material, or any combination thereof in the first three-way catalyst and the second three-way catalyst ranges from 0.01 wt. % to 2.0 wt. % based on the 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. The system of any one of claims 1 to 16, wherein the total amount of the ceria-zirconia mixed oxide present in the first and second three-way catalysts is 40 wt% to 60 wt% based on the total weight of the first and second three-way catalysts.

18. The system of any one of claims 1 to 17, wherein the total amount of alumina present in the first three-way catalyst and the second three-way catalyst is in a range of 5.0 wt. % to 20 wt. % based on the total weight of the first three-way catalyst and the second three-way catalyst, or wherein the total amount of alumina present in the first three-way catalyst and the second three-way catalyst is in a range of 15 wt. % to 60 wt. % based on the total weight of the first three-way catalyst and the second three-way catalyst.

19. The system of any one of claims 1 to 18, wherein the alumina present in the first and second three-way catalysts is doped with a dopant selected from barium, lanthanum oxide, zirconium oxide, neodymium oxide, yttrium oxide, ceria, or titania, Wherein an amount of the dopant is 1.0 wt % to 30 wt % based on the total weight of the alumina and the dopant present in the first three-way catalyst or the second three-way catalyst.

20. The system of any one of claims 1 to 19, wherein the alumina is selected from alumina, lanthanum oxide-alumina, titania-alumina, ceria-zirconia-alumina, zirconia-alumina, ceria-alumina, lanthanum oxide-zirconia-alumina, barium oxide-alumina, barium oxide-lanthanum oxide-alumina, barium oxide-lanthanum oxide-neodymium oxide-alumina, yttrium oxide, or any combination thereof.

21. The system of any one of claims 1 to 20, wherein the total amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in a range from 15 wt.% to 40 wt.%, based on the total weight of the first three-way catalyst and the second three-way catalyst.

22. The system of claim 1, wherein the system comprises: i) an engine, the engine generating an exhaust gas flow; ii) a first three-way catalyst, the first three-way catalyst being deposited on at least a portion of the first substrate; as well as iii) a second three-way catalyst, the second three-way catalyst being deposited on at least a portion of the second substrate, Wherein the first three-way catalyst is positioned upstream of the engine and the second three-way catalyst is positioned downstream in fluid communication with the first three-way catalyst.

23. The system of any one of claims 1 to 16 and 22, wherein the amount of the ceria-alumina composite material present in the first three-way catalyst and the second three-way catalyst is in a range of 5.0 wt. % 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 in a range of 20 wt. % to 80 wt. %, based on the total weight of the first three-way catalyst and the second three-way catalyst, and wherein the amount of CeO2 in the ceria-alumina composite material present in the first three-way catalyst or the second three-way catalyst is preferably 1.0 wt.% to 60 wt.%, based on the total weight of the ceria-alumina composite material in the corresponding catalyst, wherein the CeO2 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 wt.% to 60 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in the corresponding catalyst, and the zirconium oxide (calculated as ZrO2) 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 wt.% to 90 wt.%, based on the total weight of the ceria-zirconia mixed oxide present in the corresponding catalyst.

24. A method of 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 to reduce the levels of hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gas.

25. Use of an exhaust gas 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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