Rhodium-free TWC catalyst articles

Abstract

The present invention relates to a rhodium-free TWC catalyst article comprising a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region comprising: i) a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii) a bottom layer comprising a second platinum composition in supported form; and optionally a second region downstream of the first region comprising: iii) a top layer comprising a third platinum composition in supported form; and iv) a bottom layer comprising a fourth platinum composition in supported form. The present invention relates to an exhaust treatment system comprising the rhodium-free TWC catalyst article.

Description

[Technical field]

[0001] The present invention relates to a non-rhodium-containing TWC catalyst article useful for treating engine exhaust gases, and to an exhaust treatment system including the non-rhodium-containing TWC catalyst article. In particular, the present invention relates to a non-rhodium-containing catalyst article useful for treating exhaust gases from stoichiometric engines, particularly motorcycle engines. [Background technology]

[0002] Engine exhaust consists essentially of particulate matter and gaseous pollutants such as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). For stoichiometric engines operating near the optimum air-fuel ratio, such as gasoline engines, three-way conversion catalysts (hereinafter referred to interchangeably as TWC catalysts or TWC) are typically used to simultaneously oxidize unburned hydrocarbons and carbon monoxide and reduce nitrogen oxides. TWC catalysts are known to be effective near stoichiometric conditions, under which the basic reactions involving reduction and oxidation can be illustrated as follows: 2NO+2CO→N2+2CO2 2CO+O2→2CO2 2C2H6+7O2→4CO2+6H2O.

[0003] TWC catalysts generally utilize platinum group metals (PGMs), such as rhodium (Rh), platinum (Pt) and palladium (Pd), as catalytically active species. It is known that Pt and Pd are primarily responsible for catalysis of HC and CO oxidation, while Rh is primarily responsible for catalysis of NOx reduction. For that reason, the three PGMs, namely Pt, Pd and Rh, were used in combination in most TWC catalysts, but some TWC catalysts may contain only rhodium and one of platinum and palladium as catalytically active species. Rhodium plays an important role in TWC catalysts due to its NOx reduction ability. However, the price of rhodium has increased significantly, currently about 15 times that of Pt and about 7 times that of Pd, and is expected to remain high in price compared to Pt and Pd. It would be beneficial to investigate the effectiveness of Pt and Pd and eliminate Rh in TWC catalysts for exhaust treatment.

[0004] Some rhodium-free catalysts for exhaust gas treatment have been reported. For example, a Pt / Pd diesel oxidation catalyst (DOC) with CO / HC light-off and HC storage functions is described in US7576031B2, which includes two separate washcoat layers containing two distinctly different ratios of Pt:Pd. It was not described that a Pt / Pd diesel oxidation catalyst could be useful as a TWC catalyst. In fact, it can be reasonably expected that a Pt / Pd diesel oxidation catalyst would not be effective for TWC applications, since different catalytic performances, and therefore catalytic compositions, are required for DOC and TWC applications. For example, the Pt / Pd diesel oxidation catalyst in this patent application must contain a HC storage composition to treat oxidizing exhaust gas from a diesel engine, whereas a TWC catalyst does not require such a HC storage function, since the exhaust gas to be treated is non-oxidizing.

[0005] Therefore, there is a need to provide a TWC catalyst that eliminates the use of expensive rhodium and remains effective in removing HC, CO and NOx from stoichiometric engine exhaust gases without undesirable degradation of catalyst performance. Summary of the Invention

[0006] It is an object of the present invention to provide a non-rhodium containing TWC catalyst article that has at least equivalent catalytic performance for the reduction of HC, CO and NOx as compared to its rhodium containing counterpart.

[0007] It has surprisingly been found that the objects of the present invention are achieved by a layered catalyst article which includes a Pt / Pd-containing top layer and a Pt-containing bottom layer at least in the inlet region of the catalyst article.

[0008] Thus, in one aspect, the present invention is a rhodium-free TWC catalyst article comprising a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii. a bottom layer comprising a second platinum composition in supported form; and - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; and iv. a bottom layer comprising a fourth platinum composition in supported form.

[0009] In another aspect, the present invention provides an emission treatment system comprising a non-rhodium containing TWC catalyst article as described herein disposed downstream of a stoichiometric engine, particularly a gasoline engine.

[0010] In a further aspect, the present invention provides a method for treating an exhaust stream from a stoichiometric engine comprising contacting the exhaust stream with a non-rhodium containing TWC catalyst article or an exhaust treatment system described herein. [Brief description of the drawings]

[0011] [Figure 1A] FIG. 1 is a schematic diagram of the layer configuration of a catalyst module according to Example 1.1. [Figure 1B] FIG. 1 is a schematic diagram of the layer configuration of a catalyst module according to Example 1.2. [Figure 1C] FIG. 1 is a schematic diagram of the layer configuration of a catalyst module according to Example 1.3. [Diagram 2] FIG. 2 is a schematic diagram of the catalyst article configuration of comparative sample R1 shown in Example 2. [Diagram 3] FIG. 2 is a schematic diagram of the catalyst article configuration of comparative sample R2 shown in Example 2. [Figure 4] FIG. 2 is a schematic diagram of the catalyst article configuration of comparative sample R3 shown in Example 2. [Diagram 5] FIG. 2 is a schematic diagram of the catalyst article configuration of comparative sample R4 shown in Example 2. [Figure 6] FIG. 2 is a schematic diagram of the catalyst article configuration of comparative sample R5 shown in Example 2. [Figure 7] FIG. 1 is a schematic diagram of the catalyst article configuration of sample S1 of the present invention shown in Example 2. [Figure 8] FIG. 1 is a schematic diagram of the catalyst article configuration of sample S2 of the present invention shown in Example 2. [Figure 9] FIG. 1 is a graph showing tailpipe emissions for NMHC, THC, CO, and NOx after treating engine exhaust with samples as shown in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail herein below. It should be understood that the present invention can be embodied in many different ways and should not be construed as being limited to the embodiments set forth herein.

[0013] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Terms such as "comprise," "comprising," and the like are used interchangeably with "contain," "containing," and the like, and are to be interpreted in an open, non-restrictive manner; that is, for example, additional components or elements may be present. The expression "consists of" or cognates may be included in "comprises" or cognates.

[0014] As used herein, the terms "palladium composition" and "platinum composition" are intended to describe the presence of the respective platinum group metals in any possible valence state, which may be, for example, the metal or metal oxide as a catalytically active form, or may be a metal compound, complex, etc. that decomposes or otherwise converts to a catalytically active form, for example, upon calcination or use of the catalyst.

[0015] As used herein, the term "rhodium-free" is intended to mean that no rhodium compositions have been intentionally added or used in the TWC catalyst articles described herein. It will be understood by those skilled in the art that trace amounts of rhodium impurity from the feedstock (e.g., platinum feedstock) cannot be avoided. Generally, it is 0.3 wt.% or less, 0.1 wt.% or less, 0.05 wt.% or less, or 0.01 wt.% or less based on the total loading of any PGM.

[0016] As used herein, the term "support" refers to a material in particulate form for receiving and supporting one or more platinum group metal compositions, and optionally one or more other compositions, such as stabilizers, promoters, and binders.

[0017] Any reference herein to a platinum group metal composition in "supported form" is intended to mean that the platinum group metal is supported on and / or in the support particles.

[0018] Reference herein to a platinum composition and a palladium composition being "supported together" is intended to mean that the two platinum group metal compositions are supported on and / or in the same support particle, for example, by simultaneous or sequential impregnation of the respective precursors onto the same support particle. When platinum and palladium compositions are supported together, it will be understood that both the platinum and palladium may be found on and / or in a single support particle.

[0019] As used herein, the terms "exhaust," "exhaust gas," "exhaust stream," and the like refer to any engine emission that may also contain particulate matter.

[0020] According to a first aspect of the present invention, there is provided a rhodium-free TWC catalyst article comprising a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii. a bottom layer comprising a second platinum composition in supported form; and - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; and iv. a bottom layer comprising a fourth platinum composition in supported form.

[0021] As used herein, any reference to "first" and "second" regions within the context is intended to indicate the relative positions of the regions, with the first region referring to a particular length of the catalyst composition coat extending from the inlet end in the longitudinal direction of the substrate, and the second region referring to a particular length of the catalyst composition coat extending downstream of the first region in the longitudinal direction of the substrate.

[0022] The catalyst composition coat in a non-rhodium containing TWC catalyst article according to the invention may include only a first region, in which case the catalyst composition coat may have a uniform composition along the length of the substrate from the inlet end to the outlet end.

[0023] Thus, in some embodiments, a non-rhodium containing TWC catalyst article according to the present invention comprises a catalyst composition coat on a substrate, i. a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii. a bottom layer comprising a second platinum composition in supported form; Both layers extend from the inlet end to the outlet end of the substrate.

[0024] Alternatively, the catalyst composition coat in a non-rhodium containing TWC catalyst article according to the present invention may include a second region located downstream of the first region.

[0025] Thus, in some other embodiments, a rhodium-free TWC catalyst article according to the invention comprises a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii. a bottom layer comprising a second platinum composition in supported form; and a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; and iv. a bottom layer comprising a fourth platinum composition in supported form.

[0026] In a rhodium-free TWC catalyst article according to the invention, the top layer in the first region of the catalyst composition coat may comprise a first platinum composition and a first palladium composition in supported form, such that the first platinum composition and the first palladium composition are supported together or individually on one or more supports.

[0027] The top layer in the second region of the catalyst composition coat may or may not include a palladium composition, ie, the second palladium composition, in supported form.

[0028] Thus, in some particular embodiments, the top layer of the second region of the catalyst composition coat comprises a third platinum composition and a second palladium composition, each present in supported form, where the third platinum composition and the second palladium composition may be supported together or separately on one or more supports.

[0029] In some other particular embodiments, the top layer in the second region of the catalyst composition coat is substantially free of the palladium composition.

[0030] In a non-rhodium-containing TWC catalyst article according to the invention, the bottom layers in the first and second regions (if present) of the catalyst composition coat may have the same or different layer compositions. Preferably, the bottom layers in the first and second regions have different layer compositions.

[0031] According to the invention, the bottom layer is supported on the substrate in either the first region or the second region, and the top layer is supported on the bottom layer without an intermediate layer.

[0032] Preferably, the bottom layer in the first region and the second region (if present) of the catalyst composition coat may be substantially free of palladium compositions, and in particular may be substantially free of any platinum group metal compositions other than the platinum composition.

[0033] As used herein, reference to a region or layer being "substantially free" of a platinum group metal (PGM) composition is intended to mean that the specified PGM composition has not been intentionally added or used in the region or layer. It will be understood that trace amounts of impurity PGM(s) from the raw materials cannot be avoided. Furthermore, migration of trace amounts of PGM(s) into a region or layer may occur inadvertently during loading, coating, and / or firing, such that trace amounts of a particular PGM(s) may be present in the region or layer as an impurity. Generally, there is less than 0.5 wt.%, less than 0.25 wt.%, or less than 0.1 wt.% of a particular PGM(s) based on the total loading of any PGM in the region or layer.

[0034] When the catalyst composition coat of the non-rhodium-containing TWC catalyst article of the present invention includes a first region and a second region, the two regions may be supported on a single piece of substrate or on respective pieces of substrate. The first region and the second region are adjacent to each other and may be precisely adjacent, but may be unintentionally interrupted by a gap, for example, when the two regions are supported on two substrates, or may be unintentionally overlapping, for example, when the two regions are supported on a single substrate.

[0035] It should be further understood that when the first and second regions of the catalyst composition coating are supported on respective substrate pieces, the substrate pieces are longitudinally oriented such that the exhaust stream to be treated passes through the first piece of substrate supporting the first region of the catalyst composition coating and then passes through the second piece of substrate supporting the second region of the catalyst composition coating.

[0036] In the catalyst composition coat of the rhodium-free TWC catalyst article of the present invention, any known support useful for the platinum group metal composition in a TWC catalyst article can be used without any restriction. The supports for the platinum composition or palladium composition in different layers or different regions in the catalyst composition coat can be the same or different. Furthermore, the supports for the platinum composition and palladium composition in the same layer of a region of the catalyst composition coat can be the same or different.

[0037] Useful support materials for the platinum group metal composition in the rhodium-free TWC catalyst articles according to the present invention can include refractory metal oxides, oxygen storage compositions, and any combination thereof.

[0038] Refractory metal oxides, which are widely used support materials for platinum group metal compositions in catalytic articles for exhaust gas treatment, are generally high surface area alumina-based materials, zirconia-based materials, or combinations thereof. Within the context of the present invention, "alumina-based materials" refer to materials that include alumina as a base and, optionally, a dopant. Similarly, "zirconia-based materials" refer to materials that include zirconia as a base and, optionally, a dopant.

[0039] Suitable examples of alumina-based materials include, but are not limited to, alumina, e.g., mixtures of gamma and delta phases of alumina which may also contain significant amounts of eta, kappa and theta alumina phases, lanthana-doped alumina, baria-doped alumina, ceria-doped alumina, zirconia-doped alumina, ceria-zirconia-doped alumina, lanthana-zirconia-doped alumina, baria-lanthana-doped alumina, baria-ceria-doped alumina, baria-zirconia-doped alumina, baria-lanthana-neodymia-doped alumina, lanthana-ceria-doped alumina, and any combination thereof.

[0040] Suitable examples of zirconia-based materials include, but are not limited to, zirconia, lanthana-doped zirconia, yttria-doped zirconia, neodymia-doped zirconia, praseodymia-doped zirconia, titania-doped zirconia, titania-lanthana-doped zirconia, lanthana-yttria-doped zirconia, and any combination thereof.

[0041] In particular, the refractory metal oxides useful as supports may be selected from baria-doped alumina, lanthana-doped alumina, ceria-doped alumina, lanthana-zirconia-doped alumina, and any combination thereof.

[0042] Generally, the amount of refractory metal oxide, if used, is from 10 to 90 weight percent, based on the total weight of a single coated layer.

[0043] Oxygen storage composition (OSC) refers to an entity that has multiple valence states and can actively react with an oxidizing agent such as oxygen or nitrogen oxide under oxidizing conditions, or can react with a reducing agent such as carbon monoxide or hydrogen under reducing conditions. Typically, the oxygen storage composition includes one or more reducible rare earth metal oxides such as ceria. The oxygen storage composition may also include one or more of lanthana, praseodymia, neodymia, europia, samaria, ytterbia, yttria, zirconia, and hafnia to form a composite oxide with ceria. Preferably, the oxygen storage composition is selected from ceria-zirconia composite oxides and stabilized ceria-zirconia composite oxides. Generally, the amount of oxygen storage composition, if used, is 20-80 wt. % based on the total weight of the single coated layer.

[0044] The support material for the first, second, third and fourth platinum compositions in the catalyst composition coat is not particularly limited and may be a refractory metal oxide, an oxygen storage composition or any combination thereof.

[0045] Preferably, the first platinum composition may be supported on particles of an alumina-based material, an oxygen storage composition, or a combination thereof, more preferably, the first platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, particularly a combination of a ceria-doped alumina and a ceria-zirconia composite oxide.

[0046] Preferably, the second platinum composition may be supported on particles of an alumina-based material, an oxygen storage composition, or a combination thereof, and more preferably, the second platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, particularly a combination of a ceria-doped alumina and a ceria-zirconia composite oxide.

[0047] The third and fourth platinum compositions are further preferably supported on particles of an alumina-based material, an oxygen storage composition, or a combination thereof. More preferably, the third platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, particularly a combination of a ceria-doped alumina and a ceria-zirconia composite oxide. The fourth platinum composition is more preferably supported on particles of an alumina-based material, particularly a ceria-doped alumina.

[0048] Furthermore, there is no particular limit to the support material for the first palladium composition and the second palladium composition (if present) in the catalyst composition coat, and they may be supported on particles of a refractory metal oxide, an oxygen storage composition, or any combination thereof. Preferably, the first palladium composition is supported on particles of a refractory metal oxide, in particular an alumina-based material. More preferably, the first palladium composition is supported on particles of alumina or lanthana-doped alumina.

[0049] In some exemplary embodiments, a non-rhodium containing TWC catalyst article according to the present invention comprises a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, the first platinum composition being supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, and the first palladium composition being supported on particles of the alumina-based material; ii. a bottom layer comprising a second platinum composition supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide; - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; and iv. a bottom layer comprising a fourth platinum composition in supported form.

[0050] In a further exemplary embodiment, a rhodium-free TWC catalyst article according to the invention comprises a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, the first platinum composition being supported on particles of a combination of ceria-doped alumina and ceria-zirconia composite oxide, and the first palladium composition being supported on particles of alumina or lanthana-doped alumina; ii. a bottom layer comprising a second platinum composition supported on particles of a combination of ceria-doped alumina and ceria-zirconia composite oxide; - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; and iv. a bottom layer comprising a fourth platinum composition in supported form.

[0051] In some other exemplary embodiments, a rhodium-free TWC catalyst article according to the present invention comprises a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, the first platinum composition being supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, and the first palladium composition being supported on particles of the alumina-based material; ii. a bottom layer comprising a second platinum composition supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide; - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide; iv. a bottom layer comprising a fourth platinum composition supported on particles of an alumina-based material.

[0052] In some preferred exemplary embodiments, a rhodium-free TWC catalyst article according to the present invention comprises a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, the first platinum composition being supported on particles of a combination of ceria-doped alumina and ceria-zirconia composite oxide, and the first palladium composition being supported on particles of alumina or lanthana-doped alumina; ii. a bottom layer comprising a second platinum composition supported on particles of a combination of ceria-doped alumina and ceria-zirconia composite oxide; - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition supported on particles of a combination of ceria-doped alumina and ceria-zirconia composite oxide; iv. a bottom layer comprising a fourth platinum composition supported on particles of ceria doped alumina.

[0053] In the above exemplary embodiment, the bottom layer of the first region and the second region (if present) is preferably substantially free of palladium compositions, and in particular substantially free of any platinum group metal compositions other than platinum compositions.

[0054] According to the present invention, the rhodium-free TWC catalyst article has a platinum content of 1 to 150 g / ft, calculated as elemental platinum. 3 , 5~100g / ft 3 , 10~80g / ft 3 , or 20~60g / ft 3 The first and second platinum compositions may be included in the first region of the catalyst composition coat in a total amount of from 1 to 150 g / ft, calculated as elemental palladium. 3 , 5~100g / ft 3 , 10~80g / ft 3 , or 20~60g / ft 3 The first region may include the first palladium composition in an amount of

[0055] In the catalyst composition coat of the rhodium-free TWC catalyst article, the first palladium composition and the sum of the first and second platinum compositions may be present in a weight ratio ranging from 1:10 to 10:1, 1:5 to 5:1, or 1:2 to 2:1, calculated as elemental platinum and elemental palladium, respectively.

[0056] Further, the catalyst composition coat of the rhodium-free TWC catalyst article may include a first platinum composition and a second platinum composition in a weight ratio, calculated as elemental platinum, ranging from 1:10 to 5:1, 1:5 to 2:1, or 1:2 to 1:1.

[0057] According to the present invention, the rhodium-free TWC catalyst article has a platinum content of 1 to 150 g / ft, calculated as elemental platinum. 3 , 5~100g / ft 3 , or 20~80g / ft 3The second region of the catalyst composition coat may include a third and fourth platinum composition in a total amount of from about 1:10 to about 10:1, from about 1:2 to about 5:1, or from about 1:1 to about 2:1, calculated as elemental platinum.

[0058] In the catalyst composition coat of the rhodium-free TWC catalyst article, the first region and the second region extend at a length ratio ranging from 1:10 to 10:1, 5:1 to 1:5, 4:1 to 1:4, 3:1 to 1:3, or 2:1 to 1:1, which length refers to the length of the portion of the substrate over which the regions extend if the first and second regions are supported on a single piece of substrate, or the length of each substrate if the first and second regions are supported on separate pieces of substrate.

[0059] Furthermore, when the first and second regions of the catalyst composition coat are supported on respective pieces of substrate, the volume ratio of the first region to the second region can be in the range of 1:30 to 30:1, 1:20 to 20:1, or 1:10 to 10:1. The volume of a region refers to the volume of space occupied by the region, i.e., the volume of space occupied by the substrate on which the region is supported.

[0060] Generally, the total loading of the first region of the catalyst composition coat is between 0.2 and 10.0 g / in 3 , 1.0~5.0g / in 3 , or 1.5 to 3.0 g / in 3 Alternatively or additionally, the total loading of the second region may be in the range of 0.2 to 5.0 g / in 3 , 1.0~4.0g / in 3 , or 1.5 to 3.0 g / in 3 may be in the range.

[0061] The catalyst composition coat optionally includes a stabilizer and / or promoter, if desired. Suitable stabilizers include non-reducible oxides of metals selected from the group consisting of barium, calcium, magnesium, strontium, and any combination thereof. Preferably, one or more oxides of barium and / or magnesium are used as stabilizers. Suitable promoters include non-reducible oxides of rare earth metals selected from the group consisting of lanthanum, praseodymium, yttrium, cerium, tungsten, neodymium, gadolinium, samarium, hafnium, and mixtures thereof.

[0062] The catalyst composition coat is generally carried on the substrate in the form of a "washcoat." The term "washcoat" has its ordinary meaning in the art and refers to a thin, adherent coating of catalytic or other material applied to a substrate. Generally, a washcoat is formed by preparing a slurry containing particles of a particular solids content (e.g., 15-60% by weight) in a liquid medium, which is then applied onto the substrate, dried and calcined to provide the washcoat layer.

[0063] The term "substrate" as used herein refers to a structure suitable for withstanding the conditions encountered in the exhaust stream from a combustion engine, on which the catalyst composition is supported, typically in the form of a washcoat. The substrate is generally a ceramic or metal honeycomb structure having fine parallel gas flow passages extending from one end of the structure to the other.

[0064] Metallic materials useful for constructing the substrate may include heat-resistant metals and metal alloys such as titanium and stainless steel, as well as other alloys in which iron is a substantial or major component. Such alloys may contain one or more of nickel, chromium, and / or aluminum, and the total amount of these metals may advantageously comprise at least 15% by weight of the alloy, for example, 10-25% by weight chromium, 3-8% by weight aluminum, and up to 20% by weight nickel. The alloy may contain small or trace amounts of one or more metals such as manganese, copper, vanadium, titanium, etc. The surface of the metal substrate may be oxidized at high temperatures, for example, 1000° C. or higher, to form an oxide layer on the surface of the substrate to improve the corrosion resistance of the alloy and promote adhesion of a washcoat layer to the metal surface.

[0065] Ceramic materials useful for constructing the substrate can include any suitable refractory material, such as cordierite, mullite, cordierite-alumina, silicon nitride, zircon-mullite, spodumene, alumina-silica magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, alumina, aluminosilicate, and the like.

[0066] Within the context of the present invention, flow-through substrates are preferred, having flow channels open to fluid flow through a plurality of fine parallel gas flow channels extending from the inlet face to the outlet face of the substrate. The flow channels, which are essentially straight-line paths from their fluid inlets to their fluid outlets, are defined by walls to which a catalytic material is applied as a washcoat such that gas flowing through the flow channels contacts the catalytic material. The flow channels of the monolithic substrate are thin-walled channels and can be of any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. Such structures can contain 60 to 900 or more gas inlet openings (or "cells") per square inch of cross section. For example, the substrates may have about 200 to 750, more usually about 300 to 600 cells per square inch ("cpsi"). The wall thickness of the flow-through substrate can vary, with typical ranges being 1 mil to 0.1 inches.

[0067] The substrate may further be a wall-flow substrate having a plurality of fine parallel gas flow passages extending from the inlet face along the outlet face of the substrate, with alternating passages being blocked at opposite ends. This configuration requires the gas stream to flow through the porous walls of the wall-flow substrate to reach the outlet face. Wall-flow substrates may contain up to 700 cells per square inch (cpsi), e.g., 100-400 cpsi, more typically 200-300 cpsi. The cross-sectional geometry of the passages may vary as described above for the passages of the flow-through substrate. The wall thickness of the wall-flow substrate may vary, with typical ranges being 2 mils to 0.1 inches.

[0068] As used herein, the loading of platinum group metals (PGMs), such as Pd or Pt, is expressed in g / ft 3 The loading of the coating layer is in units of g / in and is defined as the weight of PGM in the catalyst per unit volume of the substrate or substrate portion on which the PGM is supported. 3 is defined as the total weight of all compositions of a layer (i.e., PGMs, supports, binders, etc.) per unit volume of substrate.

[0069] The rhodium-free TWC catalyst article according to the present invention can be prepared by any conventional method known in the art without any limitation.Typically, a wash-coating method may be employed, in which a slurry containing supported PGM(s) catalyst particles, optionally stabilizers and / or promoters or precursors thereof, a solvent (e.g., water), optionally a binder, and optionally auxiliary agents such as surfactants, pH adjusters and thickeners is applied onto a substrate.

[0070] The supported catalyst particles of PGM(s) may be prepared by impregnating precursors of the PGM(s), such as soluble salts and / or complexes thereof, onto the respective supports by conventional techniques such as incipient wetness impregnation or capillary impregnation, optionally followed by drying and / or calcination. Suitable precursors of the PGMs may be selected from ammine complex salts, hydroxyl salts, nitrates, carboxylates, ammonium salts, and oxides. Non-limiting examples include palladium nitrate, tetraamminepalladium nitrate, tetraammineplatinum acetate, platinum nitrate, tetraammineplatinum acetate, and diethanolamine hexahydroxyplatinate ((HOCH2CH2NH3)2[Pt(OH)6]).

[0071] The binder may be provided by one or more of alumina, boehmite, silica, zirconium acetate, colloidal zirconia, and zirconium hydroxide. When present, the binder is typically used in an amount of about 0.5 to 5.0 weight percent of the total washcoat loading.

[0072] The slurry may have a solids content, for example, in the range of 20-60% by weight, more specifically 30-50% by weight. The slurry is often milled to reduce particle size. Typically, the slurry has a D of 3.0-40 microns, preferably 10-30 microns, after milling, as measured by a laser diffraction particle size distribution analyzer. 90 It may have a granularity.

[0073] The applied slurry may be dried at an elevated temperature (e.g., 100-150°C) for a period of time (e.g., 10 minutes to 3 hours) and baked at a higher temperature (e.g., 400-700°C) for typically 10 minutes to 3 hours to deposit onto a substrate. The washcoat loading after baking can be determined by calculating the weight difference between the coated and uncoated substrate. As will be apparent to one skilled in the art, the washcoat loading can be altered by varying the slurry rheology. In addition, the process including coating / drying / baking to produce a washcoat may be repeated as necessary to build up the layer to a desired loading level or thickness, meaning that more than one washcoat may be applied.

[0074] According to another aspect of the invention, there is provided an exhaust gas treatment system including a non-rhodium containing TWC catalyst article as described herein located downstream of a stoichiometric engine, particularly a gasoline engine, hi some embodiments, the exhaust gas treatment system is particularly useful for motorcycles.

[0075] According to a further aspect of the present invention, there is provided a method for treating an exhaust stream, particularly from a stoichiometric engine, comprising contacting the exhaust stream with a non-rhodium containing TWC catalyst article or exhaust treatment system as described herein. In particular, the present invention provides a method for treating an exhaust stream from a gasoline engine, preferably a motorcycle engine.

[0076] Embodiment Various embodiments are listed below. It will be understood that the embodiments listed below can be combined with all aspects and other embodiments in accordance with the scope of the present invention.

[0077] Embodiment 1. A rhodium-free TWC catalyst article comprising a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii. a bottom layer comprising a second platinum composition in supported form; and - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; and iv. a bottom layer comprising a fourth platinum composition in supported form.

[0078] Embodiment 2. A non-rhodium containing TWC catalyst article as described in embodiment 1, wherein the catalyst composition coat comprises only a first region, preferably a bottom layer in the first region that is substantially free of the palladium composition.

[0079] Embodiment 3. The rhodium-free TWC catalyst article of embodiment 1, wherein the catalyst composition coat comprises a second region.

[0080] Embodiment 4. The rhodium-free TWC catalyst article of embodiment 3, wherein the top layer of the second region of the catalyst composition coat is substantially free of the palladium composition.

[0081] Embodiment 5. A rhodium-free TWC catalyst article as described in embodiment 3, wherein the top layer of the second region of the catalyst composition coat comprises a third platinum composition and a second palladium composition, each in supported form.

[0082] Embodiment 6. The rhodium-free TWC catalyst article of any one of embodiments 3-5, wherein the bottom layer in the first region and the second region of the catalyst composition coat is substantially free of a palladium composition.

[0083] Embodiment 7. A rhodium-free TWC catalyst article according to any one of the preceding embodiments, wherein the support for each platinum composition and each palladium composition is independently selected from a refractory metal oxide, such as an alumina-based material, an oxygen storage composition, and any combination thereof.

[0084] Embodiment 8. The rhodium-free TWC catalyst article of embodiment 7, wherein the alumina-based material is selected from baria-doped alumina, lanthana-doped alumina, ceria-doped alumina, lanthana-zirconia-doped alumina, and any combination thereof.

[0085] Embodiment 9. The rhodium-free TWC catalyst article of embodiment 7, wherein the oxygen storage composition is selected from ceria-zirconia composite oxides, stabilized ceria-zirconia composite oxides, and any combination thereof.

[0086] Embodiment 10. The rhodium-free TWC catalyst article of any one of the previous embodiments, wherein the first platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, in particular a combination of a ceria-doped alumina and a ceria-zirconia composite oxide.

[0087] Embodiment 11. The rhodium-free TWC catalyst article of any one of the previous embodiments, wherein the second platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, in particular a combination of a ceria-doped alumina and a ceria-zirconia composite oxide.

[0088] Embodiment 12. The rhodium-free TWC catalyst article of any one of the previous embodiments, wherein the third platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, in particular a combination of a ceria-doped alumina and a ceria-zirconia composite oxide.

[0089] Embodiment 13. The rhodium-free TWC catalyst article of any one of the previous embodiments, wherein the fourth platinum composition is supported on particles of an alumina-based material, particularly ceria-doped alumina.

[0090] Embodiment 14. A rhodium-free TWC catalyst article according to any one of the previous embodiments, wherein the first palladium composition is supported on particles of an alumina-based material, particularly alumina or lanthana-doped alumina.

[0091] Embodiment 15. The rhodium-free TWC catalyst article of any one of the preceding embodiments, wherein the first palladium composition and the sum of the first and second platinum compositions are included in a weight ratio ranging from 1:10 to 10:1, 1:5 to 5:1, or 1:2 to 2:1, calculated as elemental palladium and elemental palladium, respectively.

[0092] Embodiment 16. The rhodium-free TWC catalyst article of any one of the preceding embodiments, wherein the first platinum composition and the second platinum composition are included in a weight ratio, calculated as elemental platinum, in the range of 1:10 to 5:1, 1:5 to 2:1, or 1:2 to 1:1.

[0093] Embodiment 17. The rhodium-free TWC catalyst article of any one of embodiments 3 to 16, wherein the third platinum composition and the fourth platinum composition are included in a weight ratio, calculated as elemental platinum, ranging from 1:10 to 10:1, 1:2 to 5:1, or 1:1 to 2:1.

[0094] Embodiment 18. The rhodium-free TWC catalyst article of any one of the preceding embodiments, wherein the substrate is a flow-through substrate or a wall-flow substrate.

[0095] Embodiment 19. An exhaust gas treatment system comprising the non-rhodium-containing TWC catalyst article of any one of embodiments 1-18 located downstream of a stoichiometric engine.

[0096] Embodiment 20. The exhaust treatment system of embodiment 19, wherein the stoichiometric engine is a gasoline engine, in particular a motorcycle engine.

[0097] Embodiment 21. A method of treating an exhaust stream, particularly from a stoichiometric engine, comprising contacting the exhaust stream with a non-rhodium containing TWC catalyst article as described in any one of embodiments 1-18, or an exhaust treatment system as described in embodiment 19 or 20.

[0098] Embodiment 22. The method of embodiment 21, wherein the exhaust stream is from a gasoline engine, preferably a motorcycle engine. EXAMPLES

[0099] Aspects of the present invention are more fully illustrated by the following examples, which are provided to illustrate particular aspects of the invention and should not be construed as limiting thereof.

[0100] Example 1 Preparation of the catalytic module Example 1.1 Preparation of a Catalyst Module Having a Layered Catalyst Composition Coating Containing Pt as a PGM Bottom Coating Slurry: Thirty grams of a 16% aqueous solution of diethanolamine hexahydroxyplatinate ((MEA)2Pt(OH)6) was impregnated onto 360 grams of ceria-alumina (20% CeO2) powder by incipient wetness impregnation. The resulting powder was then added to a solution containing 150 grams of deionized water, 27 grams of barium nitrate powder, and 83 grams of magnesium acetate powder under continuous stirring, and the pH was adjusted to 5.0 with nitric acid. Then, 21 grams of alumina binder was added, followed by 20 microns of D 90 was crushed into

[0101] Top Coating Slurry: 57 grams of a 16% (MEA)2Pt(OH)6 aqueous solution was impregnated onto a mixture of 215 grams of ceria-alumina (20% CeO2) powder and 121 grams of ceria-zirconia (40% CeO2) powder by incipient wetness impregnation, and then the resulting powder was added to 300 grams of deionized water and then diluted with 20 microns of D 90Then, 96 grams of 28% cerium nitrate solution and 33 grams of alumina binder were added to the solution whose pH was adjusted to 5.0 with nitric acid.

[0102] Catalyst Module: The bottom coating slurry was coated onto a 40 mm diameter, 90 mm long, 300 / 2 (cpsi / mil) flow-through metal substrate, dried at 150° C. for 1 hour, and then calcined at 500° C. for 2 hours. The bottom coating layer had a density of 1.0 g / in 3 and the Pt loading of the bottom coating layer was 20 g / ft 3 The top coating slurry was then applied, dried at 150°C for 1 hour, and then calcined at 500°C for 2 hours. The top coating layer had a density of 1.0 g / in 3 and the Pt loading of the top coating layer was 40 g / ft 3 A schematic diagram of this module is shown in Figure 1A.

[0103] Example 1.2 Preparation of a catalyst module having a layered catalyst composition coat containing Pt, Pd and Rh as PGMs Bottom Coating Slurry: 16 grams of a 16% (MEA)2Pt(OH)6 aqueous solution was impregnated onto 78 grams of ceria-alumina (20% CeO2) powder and 261 grams of ceria-zirconia (45% CeO2) powder by incipient wetness impregnation. The product was mixed with 200 grams of deionized water, then 49 grams of barium sulfate powder and 44 grams of alumina binder were added, and a 20 micron D 90 The pH was then adjusted to 5.0 by the addition of nitric acid.

[0104] Top Coating Slurry: A first composition was prepared by impregnating 25 grams of a 20% aqueous palladium nitrate solution onto 242 grams of alumina powder by incipient wetness impregnation.

[0105] A second composition was prepared by impregnating 5 grams of a 10% aqueous rhodium nitrate solution into 30 grams of lanthanum-zirconia-alumina (3% La2O3, 20% ZrO2) powder and 90 grams of ceria-zirconia (22% CeO2) powder by incipient wetness impregnation.

[0106] 13 grams of a 16% (MEA)2Pt(OH)6 aqueous solution was diluted in 200 grams of deionized water, and the first and second compositions were then added while adjusting the pH to 5.0 with nitric acid. The slurry was then filtered through a 20 micron D 90 The mixture was ground to 100 g and 7 g of barium sulfate powder was added, followed by 113 g of alumina binder.

[0107] Catalyst Module: The bottom coating slurry was coated onto a 40 mm diameter, 90 mm long, 300 cpsi / 2 (cpsi / mil) flow-through metal substrate, dried at 150° C. for 1 hour, and then calcined at 500° C. for 2 hours. The bottom coating layer had a mass of 1.5 g / in 3 The bottom coating layer had a Pt loading of 16.5 g / ft 3 The top coating slurry was then applied, dried at 150 °C for 1 h, and then calcined at 500 °C for 2 h. The top coating layer had a density of 1.3 g / in 3 The top coating layer had a PGM loading of 12.1 g / ft 3 Pt, 28.6g / ft 3 Pd and 2.9g / ft 3 A schematic diagram of this module is shown in Figure 1B.

[0108] Example 1.3 Preparation of a catalyst module having a layered catalyst composition coat containing Pt and Pd as PGMs Bottom Coating Slurry: 14 grams of a 16% (MEA)2Pt(OH)6 aqueous solution was impregnated onto 83 grams of ceria-alumina (20% CeO2) powder and 300 grams of ceria-zirconia (45% CeO2) powder by incipient wetness impregnation. The product was mixed with 300 grams of deionized water, then 14 grams of barium acetate powder and 33 grams of alumina binder were added, and the mixture was mixed to obtain a 20 micron D 90 The pH was then adjusted to 5.0 with nitric acid.

[0109] Top Coating Slurry: A first composition was prepared by impregnating 27 grams of a 20% aqueous palladium nitrate solution onto 138 grams of alumina powder by incipient wetness impregnation.

[0110] A second composition was prepared by impregnating 11 grams of a 16% (MEA)2Pt(OH)6 aqueous solution onto 184 grams of ceria-zirconia (22% CeO2) powder and 61 grams of ceria-alumina (20% CeO2) powder by incipient wetness impregnation.

[0111] The first and second compositions were added to 185 grams of deionized water while the pH was adjusted to 5.0 with nitric acid. The slurry was filtered to a 20 micron D 90 and 4 grams of barium sulfate powder and 31 grams of alumina binder were added.

[0112] Catalyst Module: The bottom coating slurry was coated onto a 40 mm diameter, 90 mm long, 300 cpsi / 2 (cpsi / mil) flow-through metal substrate, dried at 150° C. for 1 hour, and then calcined at 500° C. for 2 hours. The bottom coating layer was 2.0 g / in 3 and the Pt loading of the bottom coating layer was 20 g / ft 3 The top coating slurry was then applied, dried at 150 °C for 1 h, and then calcined at 500 °C for 2 h. The top coating layer had a density of 1.3 g / in 3and the PGM loading in the top coating layer is 10g / ft 3 Pt and 30g / ft 3 A schematic diagram of this module is shown in Figure 1C.

[0113] Example 2 Preparation of test samples Test samples having the zone arrangement as shown in Table 1 were prepared by enclosing each module in a housing having an inlet and an outlet for the gas stream to be treated. The configurations of samples R1-R5 and S1-S2 are shown diagrammatically in Figures 2-8, respectively.

[0114] [Table 1] * Comparison:Comparative composition. ** Invention: Composition of the present invention

[0115] Example 3 Catalytic performance test Testing was carried out on a 125cc motorbike using the World Autocycle Test Cycle (WMTC) according to GB14622-2016, Type I. The performance of fresh test samples was assessed by measuring tailpipe non-methane hydrocarbons (NMHC), total hydrocarbons (THC), CO and NOx emissions from two phases involved in one test cycle: P1: Cold start phase from 0 to 600 seconds. P2: high temperature phase from 600 to 1200 s.

[0116] The exhaust from the two phases has the following cumulative composition under a fuel consumption of 2.17L / 100km: P1: 2.200g / km CO, 0.499g / km THC, 0.440g / km NOx. P2:1.660g / km CO. 0.389g / km THC. 0.493g / km NOx.

[0117] The test was carried out three times for each sample, and the average values ​​are shown as the test results in Tables 2 to 5. The emission test results are also shown in the graph in FIG.

[0118] [Table 2]

[0119] [Table 3]

[0120] [Table 4]

[0121] [Table 5]

[0122] From a comparison between the test results of Samples R1 and R3, it can be seen that removal of Rh in the catalyst composition coat of the catalyst article resulted in a significant increase in NMHC and THC emissions and a substantial increase in NOx emissions when Pd was present only in the rear region of the catalyst article.

[0123] However, it has surprisingly been found that when Pd is present in the front region or both regions of the catalyst article, removal of Rh in the catalyst composition coating of the catalyst article results in reduced NMHC, THC, CO and NOx emissions, as can be seen from a comparison of Samples R2 and S2, Samples R4 and S1, and Samples R5 and S1.

[0124] Although the invention disclosed herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.

Claims

1. 1. A rhodium-free TWC catalyst article comprising a catalyst composition coating on a substrate, the catalyst composition coating comprising: a first region, i. a top layer comprising a first platinum composition and a first palladium composition, each present in supported form; ii. a bottom layer comprising a second platinum composition in supported form; - optionally a second region located downstream of the first region, iii. a top layer comprising a third platinum composition in supported form; a second region comprising a bottom layer comprising a fourth platinum composition in supported form;

2. 2. The rhodium-free TWC catalyst article of claim 1, wherein said catalyst composition coat comprises only said first region, and preferably said bottom layer in said first region is substantially free of palladium composition.

3. The rhodium-free TWC catalyst article of claim 1 , wherein said catalyst composition coat comprises said second region.

4. 4. The rhodium-free TWC catalyst article of claim 3, wherein said top layer of said second region of said catalyst composition coat is substantially free of palladium compositions.

5. 4. The rhodium-free TWC catalyst article of claim 3, wherein the top layer of the second region of the catalyst composition coat comprises the third platinum composition and the second palladium composition, each in supported form.

6. The rhodium-free TWC catalyst article of any one of claims 3 to 5, wherein the bottom layer in the first region and the second region of the catalyst composition coat is substantially free of a palladium composition.

7. 6. The rhodium-free TWC catalyst article of any one of claims 1 to 5, wherein the support for each platinum composition and each palladium composition is independently selected from a refractory metal oxide, such as an alumina-based material, an oxygen storage composition, and any combination thereof.

8. 8. The rhodium-free TWC catalyst article of claim 7, wherein the alumina-based material is selected from baria-doped alumina, lanthana-doped alumina, ceria-doped alumina, lanthana-zirconia-doped alumina, and any combination thereof.

9. 8. The rhodium-free TWC catalyst article of claim 7, wherein the oxygen storage composition is selected from ceria-zirconia composite oxide, stabilized ceria-zirconia composite oxide, and any combination thereof.

10. The rhodium-free TWC catalyst article according to any one of claims 1 to 5, wherein the first platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, in particular a combination of ceria-doped alumina and a ceria-zirconia composite oxide.

11. The rhodium-free TWC catalyst article according to any one of claims 1 to 5, wherein the second platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, in particular a combination of ceria-doped alumina and a ceria-zirconia composite oxide.

12. The rhodium-free TWC catalyst article according to any one of claims 1 to 5, wherein the third platinum composition is supported on particles of a combination of an alumina-based material and a ceria-zirconia composite oxide, in particular a combination of ceria-doped alumina and a ceria-zirconia composite oxide.

13. A rhodium-free TWC catalyst article according to any one of claims 1 to 5, wherein the fourth platinum composition is supported on particles of an alumina-based material, in particular ceria-doped alumina.

14. A rhodium-free TWC catalyst article according to any one of claims 1 to 5, wherein the first palladium composition is supported on particles of an alumina-based material, in particular alumina or lanthana-doped alumina.

15. 6. The rhodium-free TWC catalyst article of any one of claims 1 to 5, wherein the first palladium composition and the sum of the first and second platinum compositions are included in a weight ratio, calculated as elemental palladium and elemental palladium, respectively, in the range of 1:10 to 10:1, 1:5 to 5:1, or 1:2 to 2:

1.

16. 6. The rhodium-free TWC catalyst article of any one of claims 1 to 5, wherein the first platinum composition and the second platinum composition are included in a weight ratio, calculated as elemental platinum, in a range of from 1:10 to 5:1, from 1:5 to 2:1, or from 1:2 to 1:

1.

17. 6. The rhodium-free TWC catalyst article of any one of claims 3 to 5, wherein the third platinum composition and the fourth platinum composition are included in a weight ratio, calculated as elemental platinum, in a range of from 1:10 to 10:1, from 1:2 to 5:1, or from 1:1 to 2:

1.

18. The rhodium-free TWC catalyst article of any one of claims 1 to 5, wherein the substrate is a flow-through substrate or a wall-flow substrate.

19. 10. An exhaust treatment system comprising the rhodium-free TWC catalyst article of claim 1 located downstream of a stoichiometric engine.

20. 20. The exhaust treatment system of claim 19, wherein the stoichiometric engine is a gasoline engine, in particular a motorcycle engine.

21. 20. A method of treating an exhaust stream, particularly from a stoichiometric engine, comprising contacting the exhaust stream with the rhodium-free TWC catalyst article of any one of claims 1 to 5, or an exhaust treatment system of claim 19.

22. 22. The method of claim 21, wherein the exhaust stream is from a gasoline engine, preferably a motorcycle engine.

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