Catalytic article for treating engine exhaust gas

Abstract

A catalytic article for treating an exhaust stream, particularly a TWC catalytic article, includes a substrate including a plurality of longitudinally extending walls and a plurality of channels defined by the walls for the passage of the exhaust stream, the channels having corners at the junctions of the walls, a catalytic coating including a platinum group metal component in supported form on the surfaces of the walls, the catalytic coating consisting of portions of the coating located at the corners and portions of the coating located on the remaining areas of the walls, the corner portions including cavities extending longitudinally along the channels. Also disclosed are processes for preparing the catalytic article, exhaust treatment systems including the catalytic article, and methods for treating an exhaust stream.

Description

[Technical Field]

[0001] The present invention relates to catalytic articles useful for treating engine exhaust gases, particularly TWC catalytic articles for saddle-ride vehicle engines, processes for preparing the catalytic articles, and exhaust treatment systems including the catalytic articles. [Background technology]

[0002] Engine exhaust essentially consists of particulate matter, unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO x In the case of stoichiometric engines operating near the optimum air-fuel ratio, such as gasoline engines, a three-way catalyst (hereinafter interchangeably referred to as TWC catalyst or TWC) is 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 one or more platinum group metals (PGMs), such as rhodium (Rh), platinum (Pt), palladium (Pd), ruthenium (Ru), osmium (Os), and iridium (Ir), as the catalytically active species, which are typically supported on support particles of refractory metal oxides and / or oxygen storage capacity materials. Support particles carrying the PGMs are typically coated onto a ceramic or metal honeycomb substrate to provide a TWC catalyst article. A TWC catalyst article can have a single coating layer or multiple different coating layers of TWC catalyst.

[0004] As one type of TWC catalyst for various vehicles, TWC catalyst articles for saddle-type vehicles must exhibit high purification capacity, particularly because the installation space for the catalyst article is limited, resulting in a small volume capacity, and they are subject to rapid atmospheric fluctuations and high temperatures. When a TWC catalyst article has a single thick coating layer or multiple coating layers, it is difficult for exhaust gas to diffuse into the catalytic coating near the substrate. Furthermore, when the TWC catalyst article is used under high space velocity, it is difficult for exhaust gas to diffuse deep into the catalytic coating, especially to the thick catalytic coating at the corners of the exhaust channel of the substrate, preventing the catalyst performance from being fully utilized.

[0005] To solve this problem of insufficient exhaust gas diffusion in the catalyst coating, several special catalyst compositions, configurations, or structures have been proposed for TWC catalyst articles.

[0006] For example, International Publication No. 2015 / 037613(A) discloses an exhaust gas purification catalyst having a catalyst layer including two or more types of inorganic porous particles having different particle sizes, a catalytically active component, and voids, and as a first feature, L / 2 / (πS) 1 / 2 The document discloses an exhaust gas purification catalyst in which pores satisfying the condition of ≧2 account for 50% or more by number of all pores in the catalyst layer (where S represents the pore cross-sectional area and L represents the pore cross-sectional perimeter), and as a second feature, the average pore diameter in the pore cross-sectional area in the catalyst layer is 10 μm to 20 μm, assuming that the pore shape is a perfect circle.The document also discloses that the miscibility and diffusibility of gases in the catalyst layer are improved, thereby enabling excellent purification performance to be exhibited.

[0007] US Patent Application Publication No. 2017 / 0232425(A1) describes an exhaust gas purification catalyst having a first catalyst layer formed on the surface of a substrate and a second catalyst layer formed on the upper side of the first catalyst layer, wherein the first catalyst layer contains a noble metal, an OSC material, and alumina, and the mass ratio of the OSC material to the alumina is in the range of 1:7 to 1:3, and the second catalyst layer contains a noble metal, an OSC material, and alumina, and the mass ratio of the OSC material to the alumina is in the range of 1:1 to 10:0, and the average particle size (D 50 ) is 10 to 16 μm, and the average particle size (D 50 The document discloses an exhaust gas purification catalyst in which the particle size is 3 to 12 μm. It states that even in an internal combustion engine exposed to high-temperature exhaust gas and used in an exhaust gas atmosphere where the space velocity of the passing exhaust gas is very high, the gas diffusion in the catalyst layer can be improved, there is almost no decrease in catalytic activity, and the entire catalyst layer can be effectively utilized.

[0008] WO 2013118425(A1) discloses a porous apatite catalyst layer containing apatite, in which a logarithmic differential pore volume distribution measured by mercury intrusion porosimetry has a peak top within a pore volume diameter range of 100 nm to 1000 nm. It also describes that a novel catalyst structure is provided that can maintain gas diffusion deep into the catalyst layer even under conditions of high gas flow velocity.

[0009] WO 2014156676(A1) discloses a catalyst structure including a substrate, an upper catalyst layer, and a lower catalyst layer, which has a first peak at a pore volume diameter of 10 nm to 50 nm and a second peak at a pore volume diameter of 50 nm to 100 nm, respectively, in a logarithmic differential pore volume distribution analyzed by mercury intrusion porosimetry. It is stated that this catalyst structure can enhance gas diffusion deep into the catalyst layer and can fully function as a three-way catalyst.

[0010] There remains a need to provide a catalyst article that exhibits improved interaction between the feed gas and the catalytic active surfaces, particularly the active surfaces at the corners of the channels of the substrate, and that can improve the performance of exhaust gas purification. Summary of the Invention

[0011] The object of the present invention is to provide a catalyst for reducing HC, CO, and NO compared to conventional TWC catalysts for saddle-ride vehicles. x Reduction of NO x The present invention provides a catalyst article, particularly a catalyst article for a saddle-type vehicle, which has improved overall catalytic performance in terms of improved reduction of CO₂.

[0012] Surprisingly, it has been found that the objects of the present invention are achieved by a catalytic article comprising a substrate including channels and a coating including cavities extending longitudinally along the walls of the substrate at the corners of the channels.

[0013] Accordingly, in a first aspect, the present invention provides a catalytic article, in particular a TWC catalytic article, for treating an exhaust stream, comprising: a substrate comprising a plurality of longitudinally extending walls and a plurality of channels defined by the walls for the passage of an exhaust flow, the channels having corners at junctions of the walls; a catalytic coating comprising a platinum group metal component in supported form on the surface of the wall, the catalytic coating consisting of coating portions located at the corners and coating portions located on the remaining area of ​​the wall, The corner-located coating portions provide a catalytic article that includes cavities extending longitudinally along the channels.

[0014] In a second aspect, the present invention provides a process for preparing a catalyst article according to the first aspect, comprising: - applying a solution or suspension of a cavity former to the surface of the wall of the substrate and drying to provide a dry layer of the cavity former; - providing a catalytic coating on the dried layer of cavity former by applying, optionally drying and calcining, a slurry comprising a platinum group metal component in supported form; The cavity former is used in an amount of 0.05 wt % to 9.0 wt % based on the loading of the catalyst coating, the process provides.

[0015] In a third aspect, the present invention provides an exhaust treatment system including a catalytic article as described herein positioned downstream of a stoichiometric engine, particularly a gasoline engine such as a saddle-ride vehicle engine.

[0016] In a fourth aspect, the present invention provides a method of treating an exhaust stream from a stoichiometric engine, the method comprising contacting the exhaust stream with a catalytic article or an exhaust treatment system described herein. [Brief explanation of the drawings]

[0017] [Figure 1A] 1 shows a microscopic image of a cross section of a catalyst article according to Example 1. [Figure 1B] 1 shows an SEM image of a cross section of a catalyst article according to Example 1. [Figure 1C] 1 shows an SEM image of a cross section of a catalyst article according to Example 1. [Figure 2A] 1 shows a microscopic image of a cross section of a catalyst article according to Example 2. [Figure 2B] 1 shows an SEM image of a cross section of a catalyst article according to Example 2. [Figure 2C] 1 shows an SEM image of a cross section of a catalyst article according to Example 2. [Figure 3A] 1 shows a microscopic image of a cross section of a catalyst article according to Example 3. [Figure 3B] 1 shows an SEM image of a cross section of a catalyst article according to Example 3. [Figure 3C] 1 shows an SEM image of a cross section of a catalyst article according to Example 3. [Figure 4A] 1 shows a microscopic image of a cross section of a catalyst article according to Example 4. [Figure 4B]1 shows an SEM image of a cross section of a catalyst article according to Example 4. [Figure 4C] 1 shows an SEM image of a cross section of a catalyst article according to Example 4. [Figure 5A] 1 shows a microscopic image of a cross section of a catalyst article according to Example 5. [Figure 5B] 1 shows an SEM image of a cross section of a catalyst article according to Example 5. [Figure 5C] 1 shows an SEM image of a cross section of a catalyst article according to Example 5. [Figure 6A] Shown are equivalent triangles that approximately represent the cross section of the cavity and the cross section of the catalytic coating, respectively. [Figure 6B] Shown are equivalent triangles that approximately represent the cross section of the cavity and the cross section of the catalytic coating, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0018] 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 limited to the embodiments set forth herein.

[0019] As used herein, 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 encompassed by "comprises" or cognates.

[0020] As used herein, the terms "platinum group metal component," "palladium component," "platinum component," and "rhodium component" are intended to describe the presence of the respective platinum group metal in any possible valence state, which may be, for example, the metal or metal oxide in its catalytically active form, or may be a metal compound, complex, etc. that decomposes or is otherwise converted to its catalytically active form upon, for example, calcination or use of the catalyst.

[0021] As used herein, the term "support" refers to a material in particulate form for receiving and supporting one or more platinum group metal (PGM) compositions, and optionally one or more other components, such as stabilizers, promoters, and binders.

[0022] Any reference herein to a platinum-group metal composition in "supported form" is intended to mean that the platinum-group metal component is supported on and / or in the support particles.

[0023] In this specification, "g / ft 3 " or "g / in 3 Any reference to amount of loading in units of " is intended to mean the weight of the particular component or coating layer per unit volume of the substrate or substrate portion on which the particular component or coating layer is carried.

[0024] As used herein, the term "catalytic coating" refers to a catalyst-containing coating deposited on the surface of a substrate wall defining a channel for the exhaust stream to pass through. The catalytic coating may have a non-laminar or laminar configuration. In a non-laminar configuration, the catalytic coating consists of a single coating layer. In a laminar configuration, the catalytic coating consists of two or more coating layers, at least one of which is a catalyst-containing coating layer. It should be understood that a coating layer may be prepared by only one coating operation, or by repeating the coating operation two or more times to achieve a target loading. In the latter case, the coating layer will include two or more sublayers with the same chemical composition and catalytic activity, which may be distinguishable only by SEM analysis. Such a coating layer including two or more sublayers with the same chemical composition and catalytic activity is referred to as a single or one coating layer. Thus, when referring to two or more coating layers herein, the coating layers have different chemical compositions or catalytic activities from each other.

[0025] As used herein, the term "catalytic coating layer" refers specifically to a coating layer that includes a platinum group metal component in supported form.

[0026] Any reference herein to a coating "on a wall surface" is intended to mean that a layer or coating is deposited on a wall, and the wall may be blank or may already bear one or more coating layers. Any reference herein to "applying to a wall surface" is intended to mean that the applying is directed to the wall, and the wall may be blank or may already bear one or more coating layers.

[0027] As used herein, the term "solids content" is intended to refer to the content of materials that are non-volatile under calcination conditions, expressed as a ratio of weights measured before and after a calcination process, e.g., at 500°C for 1 hour.

[0028] As used herein, the terms "exhaust," "exhaust gas," "exhaust stream," and the like are used interchangeably and refer to any engine emissions that may also contain particulate matter.

[0029] According to a first aspect of the present invention there is provided a catalytic article for treating an exhaust stream, the catalytic article comprising: a substrate comprising a plurality of longitudinally extending walls and a plurality of channels defined by the walls for the passage of an exhaust flow, the channels having corners at junctions of the walls; a catalytic coating comprising a platinum group metal component in supported form on the surface of the wall, the catalytic coating consisting of coating portions located at the corners and coating portions located on the remaining area of ​​the wall, The corner-located coating portion includes a cavity that extends longitudinally along the channel.

[0030] <Base material> As used herein, the term "substrate" refers to a structure suitable for withstanding the conditions encountered in the exhaust stream from a combustion engine, on which a catalyst composition is supported, typically in the form of a washcoat. Substrates are generally made of refractory materials such as ceramic or metallic materials.

[0031] 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.

[0032] Metallic materials useful for constructing the substrate can include any suitable heat-resistant metal and metal alloy, such as titanium and stainless steel, as well as other alloys in which iron is a significant or major component. Such alloys may contain one or more of nickel, chromium, and / or aluminum, with the total amount of these metals advantageously comprising at least 15% by weight of the alloy, e.g., 10-25% by weight chromium, 3-8% by weight aluminum, and up to 20% by weight nickel. The alloy may also contain minor or trace amounts of one or more metals, such as manganese, copper, vanadium, or titanium. The surface of the metal substrate may be oxidized at high temperatures, e.g., 950°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.

[0033] Within the context of the present invention, flow-through substrates are preferred, having a plurality of fine, parallel gas flow channels extending from the inlet face to the outlet face of the substrate and open to fluid flow therethrough. 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 so that gas flowing through the channels contacts the catalytic material. The flow channels of monolithic substrates are thin-walled channels, which can be of any suitable size and cross-sectional shape with corners, such as trapezoidal, rectangular, square, sinusoidal (S-shaped), and hexagonal. Such structures can contain 60 to 900 or more gas inlet openings (or "cells") per square inch of cross section. For example, substrates can have 100 to 650, more commonly 150 to 400, cells per square inch (cpsi) in cross section. The wall thickness of flow-through substrates can vary, with typical ranges being 1 mil to 0.1 inches.

[0034] Each channel defined by the walls of the substrate can have two or more corners, for example, two, three, four, five, or six corners, depending on the cross-sectional shape of the channel.

[0035] In some embodiments, the substrate for the catalytic article according to the present invention is a flow-through metal substrate having channels with cross-sectional shapes having two or more corners, such as trapezoidal, rectangular, square, sinusoidal (S-shaped), and hexagonal.

[0036] <Catalyst coating> The catalytic coating of the catalytic article according to the present invention may consist of one coating layer or two or more coating layers, at least one of which comprises a platinum group metal component in supported form and is sometimes referred to as a catalytic coating layer.

[0037] In some embodiments, the catalytic coating of a catalyst article according to the present invention may comprise or consist of two catalytic coating layers, each comprising a platinum group metal component in supported form, For example, the catalytic coating of a catalyst article according to the present invention may consist of a top catalytic coating layer comprising a first platinum group metal component in supported form and a bottom catalytic coating layer comprising a second platinum group metal component in supported form.

[0038] The catalytic coating on the surface of the wall may be divided into two parts, one part located on the surface of the wall at the corner of the channel (also referred to herein as the corner-located coating part), and the other part located on the remaining surface of the wall.

[0039] The corner-located coating portion may include a cavity that extends continuously longitudinally through the entire corner-located coating portion, a cavity that extends longitudinally through a portion of the length of the coating portion, or both.

[0040] As used herein, the term "corner-located coating portion" is intended to collectively refer to coating portions at corners of channels in a substrate that extend a particular length (e.g., full length and partial length) of the substrate.

[0041] It will be understood that the coating portion within a single channel may include two or more portions located at each corner if the channel has more than one corner, for example, two, three, four, five, or six corners.

[0042] It will also be understood that where a coating portion includes a cavity that extends longitudinally along a channel in the substrate for part of the length of the coating, two or more cavities may be included consecutively at a single corner within the channel for the entire length of the coating.

[0043] The cavities may have any cross-sectional shape, such as a triangle, a sector, or a non-circular shape. The volume of the cavities may account for 0.5% to 35%, preferably 2.0% to 30%, of the volume of the coating portion located at the corner. The volume percentage of the cavities may also be referred to as the void volume fraction. The void volume fraction may be determined by calculation based on a microscopic image, as described in the Examples below.

[0044] The platinum group metal (PGM) component useful in any catalytic coating in the catalyst article is not particularly limited. Typically, the PGM component may be a rhodium (Rh) component, a platinum (Pt) component, a palladium (Pd) component, a ruthenium (Ru) component, an osmium (Os) component, an iridium (Ir) component, or any combination thereof, of which a Pt component, a Pd component, a Rh component, or any combination thereof is usually used.

[0045] In particular, the catalytic coating of the catalyst article according to the present invention comprises a PGM component selected from a Rh component in combination with either or both of a Pt component and a Pd component. These platinum group metal components may be contained in the same catalytic coating layer in the catalyst article. Alternatively, when the catalytic coating of the catalyst article comprises two or more catalytic coating layers containing the PGM components in supported form, the PGM components may be disposed in different catalytic coating layers.

[0046] For example, in some embodiments, the catalytic coating of the catalyst article includes two catalytic coating layers each comprising a PGM component in supported form, one catalytic coating layer comprising a supported Rh component and, optionally, either or both a supported Pt component and a supported Pd component as the PGM component, and the other catalytic coating layer comprising a supported Pt component and, optionally, a supported Pd component.

[0047] In some particular embodiments, the catalyst coating of the catalyst article comprises or consists of a top catalyst coating layer comprising a PGM component in supported form and a bottom catalyst coating layer comprising a PGM component in supported form, wherein the top catalyst coating layer comprises a Rh component in supported form and, optionally, either or both a Pt component in supported form and a Pd component in supported form as the PGM component, and the bottom catalyst coating layer comprises a Pt component in supported form and, optionally, a Pd component in supported form as the PGM component.

[0048] In particular, the catalyst coating of the catalyst article comprises or consists of a top catalyst coating layer comprising PGM components in supported form and a bottom catalyst coating layer comprising PGM components in supported form, the top catalyst coating layer comprising a supported Rh component, a supported Pt component, and a supported Rd component as the PGM components, and the bottom catalyst coating layer comprising a supported Pt component and a supported Pd component as the PGM components.

[0049] Useful support materials for the PGM component in a catalyst article according to the present invention can include refractory metal oxides, oxygen storage components, and any combination thereof.

[0050] Refractory metal oxides, which are widely used support materials for PGM components 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, optionally including dopants. Similarly, "zirconia-based materials" refer to materials that include zirconia as a base, optionally including dopants.

[0051] 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.

[0052] 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.

[0053] In particular, refractory metal oxides useful as supports can be selected from baria-doped alumina, lanthana-doped alumina, ceria-doped alumina, zirconia-doped alumina, lanthana-zirconia-doped alumina, lanthana-doped zirconia, and any combination thereof.

[0054] Generally, the amount of refractory metal oxide, if used, is 10 to 90% by weight based on the total weight of a single coating layer.

[0055] An oxygen storage component (OSC) refers to an entity that has multiple valence states and can actively react with an oxidizing agent, such as oxygen or nitrogen oxides, under oxidizing conditions, or 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 component 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 component is selected from ceria-zirconia composite oxides and stabilized ceria-zirconia composite oxides.

[0056] Generally, the amount of oxygen storage component, if used, is 15 to 85 weight percent based on the total weight of a single coating layer.

[0057] The support materials for different platinum group metal (PGM) components in a catalytic coating layer may be the same or different when two or more PGMs are included in the same catalytic coating layer. Also, when two or more catalytic coating layers are included in a catalyst article, the support materials for the same platinum group metal (PGM) component in different catalytic coating layers may be the same or different. Furthermore, more than one support may be used for the same platinum group metal (PGM) component in a single catalytic coating layer.

[0058] The catalyst article of the present invention has a coating density of 0.1 to 15.0 g / in 3 , or 0.5 to 10.0 g / in 3 , or 1.0 to 4.0 g / in 3 The catalyst article may include a catalytic coating layer comprising a PGM component in supported form at a loading ranging from 0.01 to 0.05. When two or more catalytic coating layers each comprising a platinum group metal component in supported form are included in the catalytic coating of the catalytic article, the loadings referred to herein refer to the sum of all such catalytic coating layers.

[0059] The catalyst coating layer containing the PGM components in supported form as described herein may have a catalyst content of 0.1 to 50.0 g / ft, calculated as the respective PGM component. 3 , or 0.25 to 40.0 g / ft 3 , or 0.5 to 20.0 g / ft 3 The composition may contain PGM components at a total loading in the range of

[0060] The catalytic coating layer may optionally contain stabilizers and / or promoters as 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 of barium oxide and magnesium oxide 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 any combination thereof.

[0061] The catalytic coating having cavities described herein may extend along the entire length of the wall of the substrate or along only a portion of the length of the porous wall of the substrate.

[0062] The catalytic coating layer may be 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 to the substrate, dried, and calcined to provide the washcoat layer.

[0063] Catalyst articles according to the present invention may be prepared by a process which involves coating a layer of a cavity former prior to applying the catalyst coating.

[0064] Thus, in a second aspect, the present invention provides a process for preparing a catalyst article according to the first aspect, comprising: - applying a solution or suspension of a cavity former to the surface of the wall of the substrate and drying to provide a dry layer of the cavity former; - providing a catalytic coating on the dried layer of cavity former by applying, optionally drying and calcining, a slurry comprising a platinum group metal component in supported form; The cavity former is used in an amount of 0.05 wt % to 9.0 wt % based on the loading of the catalyst coating, the process provides.

[0065] As mentioned herein above, the substrate to which the solution or suspension of the cavitating agent is applied may be a blank substrate or may be pre-coated with any suitable bottom coating layer, where blank substrate is intended to mean a substrate that does not carry a coating before the solution or suspension of the cavitating agent is applied thereon.

[0066] The cavity former is preferably used in an amount of 0.2 wt % to 4.0 wt %, more preferably 0.25 wt % to 2.5 wt %, based on the loading of the catalyst coating.

[0067] The cavity former may be any organic or inorganic material that can be burned off to leave voids during the firing step of applying the coating or coating layer. For example, the cavity former may be selected from organic materials such as natural and synthetic polymers, inorganic materials such as organic low molecular weight compounds, inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof.

[0068] Natural and synthetic polymers suitable as cavity formers may include, but are not limited to, polyether polyols such as polyethylene glycol and its alkyl-capped derivatives, styrene homopolymers or copolymers such as polystyrene, poly(meth)acrylic acid and its ester derivatives such as polymethyl methacrylate or crosslinked polymethyl methacrylate, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinylpyrrolidone, and any combination thereof.

[0069] Suitable organic small molecule compounds as cavity-forming agents may include, but are not limited to, benzoic acid and its derivatives, carbamide (urea), sugar crystals, and any combination thereof.

[0070] Suitable inorganic salts as cavitating agents may include, but are not limited to, ammonium bicarbonate, magnesium carbonate, and any combination thereof.

[0071] Carbon materials suitable as cavity formers may include, but are not limited to, carbon black, carbon fiber, graphite, and any combination thereof.

[0072] Suitable cellulose-containing natural materials as cavitating agents may be granulated products from dried plants, including, but not limited to, sunflower, cotton, rice, wheat, sorghum, breadfruit, sugarcane, corn, bamboo, and any combination thereof. Granulated products may be obtained from various parts of plants, such as leaves, bark, straw, roots, husks, and any combination thereof.

[0073] The cavity former is applied to the surface of the substrate wall as a solution or suspension in a coating vehicle. The coating vehicle can be water, any suitable organic solvent, or a mixture thereof, and the cavity former can be soluble to provide a solution or insoluble to provide a suspension. In the case of a suspension, the cavity former can have a variety of shapes, including but not limited to, spheres, tablets, cylinders, or fibers, and preferably has an average particle size D in the range of 1 to 50 μm, or 10 to 30 μm, or 15 to 20 μm. 50 The particle may have the following structure:

[0074] As described herein above, the catalytic coating may consist of two or more coating layers. When the catalytic coating consists of two or more coating layers, applying the catalytic coating may be performed by applying respective slurries to successively form coating layers. It will be understood that at least one of the applied slurries contains a platinum group metal component in a supported form to provide the catalytic coating layer. Preferably, each of the applied slurries contains a platinum group metal component in a supported form to provide the catalytic coating layer.

[0075] In some embodiments, the present invention provides a process for preparing a catalyst article according to the first aspect, comprising: - applying a solution or suspension of a cavity former to the surface of the wall of the substrate and drying to provide a dry layer of the cavity former; -below i) applying a slurry comprising a first platinum group metal component in supported form to a dried layer of cavity former, drying, and optionally calcining to form a first catalytic coating layer; ii) providing a catalytic coating by applying a slurry comprising a second platinum group metal component in supported form to the first catalytic coating layer, and optionally drying and calcining to form a second catalytic coating layer; The cavity former is used in an amount of 0.05 wt % to 9.0 wt % based on the loading of the catalyst coating, the process provides.

[0076] Preferably, in the embodiment immediately above, the cavity former is used in an amount of 0.2 wt % to 4.0 wt %, more preferably 0.25 wt % to 2.5 wt %, based on the loading of the catalyst coating.

[0077] In particular, the cavity former is used in an amount of 0.2 wt % to 15.0 wt %, preferably 0.3 wt % to 10.0 wt %, more preferably 0.4 wt % to 3.5 wt %, based on the loading of the first catalyst coating layer.

[0078] Such a process can provide a catalytic coating on a substrate that includes two catalytic coating layers and has the above-identified cavities, and by applying additional slurries that include a platinum group metal component in supported form, more catalytic coating layers and catalytic coatings that include the above-identified cavities can be provided on a substrate.

[0079] The slurry can be prepared and applied by conventional methods. Generally, a slurry for a washcoat can be prepared by suspending finely divided particles of a catalyst (e.g., a PGM component in supported form) in a suitable vehicle, such as water, to which accelerators, binders, stabilizers, viscosity modifiers, and / or surfactants may be added. The slurry can be milled / milled so that substantially all of the solids have an average particle size greater than 10 microns, e.g., in the range of 15 to 50 microns. Milling / milling can be accomplished in a ball mill, a continuous Eiger mill, or any other similar equipment. The slurry generally has a pH of 2 to less than 9, which can be adjusted, if necessary, by the addition of inorganic or organic acids and / or bases. The solids content of the slurry can be, for example, 15 to 60% by weight. If used, a cavitating agent can be incorporated into the slurry at any time during the preparation of the slurry, e.g., prior to milling / milling.

[0080] The resulting slurry may be applied to a substrate by dipping the substrate into the slurry or by otherwise coating the slurry onto the substrate so that a coating layer of the desired loading is deposited on the substrate. The coated substrate may then be dried at a temperature in the range of 100-300°C and / or calcined by heating at a temperature in the range of 350-650°C for a period of time, e.g., 1-3 hours. Drying and calcination are typically carried out in air.

[0081] The process of applying, drying, and calcining may be repeated as necessary to achieve the final desired gravimetric weight of the catalyst washcoat layer on the support. The catalyst washcoat loading can be determined by calculating the difference in weight of the substrate before and after applying the washcoat.

[0082] The catalyst article according to the present invention can be used to treat exhaust streams from automotive combustion engines, particularly gasoline engines. The catalyst article according to the present invention can be particularly effective in treating exhaust streams from saddle-type vehicle engines. In particular, the catalyst article according to the present invention is a TWC catalyst article.

[0083] Thus, in a third aspect of the present invention, there is provided an emission treatment system including a catalytic article as described herein located downstream of a stoichiometric engine, particularly a gasoline engine. In some embodiments, the emission treatment system is particularly useful for saddle-ride vehicle engines.

[0084] In a fourth aspect of the present invention, there is provided a method of treating an exhaust stream, particularly from a stoichiometric engine, comprising contacting the exhaust stream with a catalytic article or an exhaust treatment system described herein. In particular, the present invention provides a method of treating an exhaust stream from a gasoline engine, preferably a saddle-type vehicle engine.

[0085] Embodiment Various embodiments are listed below, and 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.

[0086] 1. A catalytic article, particularly a TWC catalytic article, for treating an exhaust stream, comprising: a substrate comprising a plurality of longitudinally extending walls and a plurality of channels defined by the walls for the passage of an exhaust flow, the channels having corners at junctions of the walls; a catalytic coating comprising a platinum group metal component in supported form on the surface of the wall, the catalytic coating consisting of coating portions located at the corners and coating portions located on the remaining area of ​​the wall, A catalytic article wherein the corner-located coating portion includes a cavity extending longitudinally along the channel.

[0087] 2. The catalytic article of embodiment 1, wherein the cavities occupy 0.5% to 35% by volume based on the volume of the coating portion located at the corner.

[0088] 3. The catalytic article of embodiment 2, wherein the cavities occupy 2.0% to 30% by volume based on the volume of the coating portion located at the corner.

[0089] 4. The catalytic article of any one of embodiments 1 to 3, wherein the substrate is a flow-through substrate having channels with cross-sectional shapes having two or more corners, such as trapezoidal, rectangular, square, sinusoidal, and hexagonal.

[0090] 5. The catalytic article of any one of embodiments 1-4, wherein the substrate is a flow-through metal substrate.

[0091] 6. The catalyst article of any one of embodiments 1-5, wherein the PGM component is a Pt component, a Pd component, a Rh component, or any combination thereof.

[0092] 7. The catalytic article of any one of embodiments 1 to 6, wherein the catalytic coating comprises or consists of two catalytic coating layers each comprising a platinum group metal component in supported form.

[0093] 8. The catalytic article of any one of embodiments 1-7, wherein the catalytic coating comprises, or consists of, a top catalytic coating layer comprising a first platinum group metal component in supported form and a bottom coating layer comprising a second platinum group metal component in supported form.

[0094] 9. The catalyst article of any one of embodiments 1-8, wherein the catalyst coating comprises or consists of two catalyst coating layers each comprising a PGM component in supported form, one catalyst coating layer comprising a Rh component in supported form and, optionally, either or both of a Pt component in supported form and a Pd component in supported form as the PGM component, and the other catalyst coating layer comprising a Pt component in supported form and, optionally, a Pd component in supported form as the PGM component.

[0095] 10. The catalyst article of any one of embodiments 1-9, wherein the catalyst coating comprises, or consists of, a top catalyst coating layer comprising a Rh component in supported form, and optionally one or both of a Pt component in supported form and a Pd component in supported form as PGM components, and a bottom catalyst coating layer comprising a Pt component in supported form, and optionally a Pd component in supported form as PGM components.

[0096] 11. The catalyst article of embodiment 10, wherein the top catalyst coating layer comprises a supported Rh component, a supported Pt component, and a supported Pd component as PGM components, and the bottom catalyst coating layer comprises a supported Pt component and a supported Pd component as PGM components.

[0097] 12. NO exhibited by a catalyst article having the same catalyst coating composition but without voids in the coating portion located at the corners, when measured on a catalyst article aged according to GB14622-2016, Type I. x 12. The catalyst article of any one of embodiments 1-11, exhibiting an improvement in NOx reduction rate that is at least 10% greater than the reduction rate.

[0098] 13. A process for preparing a catalyst article according to any one of embodiments 1 to 12, comprising: - applying a solution or suspension of a cavity former to the surface of the wall of the substrate and drying to provide a dry layer of the cavity former; - providing a catalytic coating on the dried layer of cavity former by applying, optionally drying and calcining, a slurry comprising a platinum group metal component in supported form; The cavity former is used in an amount of 0.05 wt.% to 9.0 wt.% based on the loading of the catalyst coating, the process.

[0099] 14. The process of embodiment 13, wherein the cavity former is used in an amount of 0.2 wt.% to 4.0 wt.%, based on the loading of the catalyst coating.

[0100] 15. The process of embodiment 14, wherein the cavity former is used in an amount of 0.25 wt.% to 2.5 wt.%, based on the loading of the catalyst coating.

[0101] 16. The process of any one of embodiments 13-15, wherein the cavity-forming agent is selected from organic materials such as natural and synthetic polymers, organic low-molecular-weight solid compounds, inorganic materials such as inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof.

[0102] 17. The process according to embodiment 16, wherein the cavity-forming agent is selected from polyether polyols, such as polyethylene glycol and its alkyl-capped derivatives, styrene homopolymers or copolymers, such as polystyrene, poly(meth)acrylic acid and its ester derivatives, such as polymethyl methacrylate or crosslinked polymethyl methacrylate, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinylpyrrolidone, and any combination thereof.

[0103] 18. The process of embodiment 17, wherein the cavity-forming agent is polyvinyl alcohol.

[0104] 19. The process of any one of embodiments 13 to 18, wherein providing a catalytic coating comprises: i) applying a slurry comprising a first platinum group metal component in supported form to a dried layer of cavity former, drying, and optionally calcining to form a first catalytic coating layer; ii) applying a slurry comprising the second platinum group metal component in supported form to the first catalytic coating layer, and optionally drying and calcining to form a second catalytic coating layer.

[0105] 20. The process of embodiment 19, wherein calcining is performed to form a first catalytic coating layer.

[0106] 21. The process of embodiment 19 or 20, wherein the cavity former is used in an amount of 0.2 wt.% to 15.0 wt.%, based on the loading of the first catalyst coating layer.

[0107] 22. The process of embodiment 21, wherein the cavity former is used in an amount of 0.3 wt.% to 10.0 wt.%, based on the loading of the first catalyst coating layer.

[0108] 23. The process of embodiment 22, wherein the cavity former is used in an amount of 0.4 wt.% to 3.5 wt.%, based on the loading of the first catalyst coating layer.

[0109] 24. An exhaust treatment system comprising the catalytic article of any one of embodiments 1-12 located downstream of a stoichiometric engine.

[0110] 25. The exhaust treatment system of embodiment 24, wherein the stoichiometric engine is a gasoline engine, particularly a saddle-type vehicle engine.

[0111] 26. A method for treating an exhaust stream, particularly from a stoichiometric engine, comprising contacting the exhaust stream with the catalytic article of any of embodiments 1-12 or the exhaust treatment system of embodiment 24 or 25.

[0112] 27. The method of embodiment 26, wherein the exhaust stream is from a gasoline engine, preferably a saddle-type vehicle engine. [Example]

[0113] Aspects of the present invention will be more fully described by the following examples, which are set forth to illustrate certain aspects of the invention and should not be construed as limiting thereof.

[0114] Preparation of the catalyst article Example 1 (Sample S1, Comparative) Bottom Coating Slurry A mixture of 89 grams of lanthana-zirconia composite oxide powder (7.5% LaO) and 83 grams of ceria-zirconia composite oxide powder (30% CeO) was impregnated with 1.1 grams of a 16% aqueous solution of hexahydroxyplatinic acid diethanolamine ((MEA)Pt(OH) by incipient wetness impregnation. 1.4 grams of a 20% Pd nitrate solution was impregnated with 89 grams of lanthana-zirconia composite oxide powder (7.5% LaO) and 83 grams of ceria-zirconia composite oxide powder (30% CeO) by incipient wetness impregnation. The resulting powder was then added with continuous stirring to a solution containing 413 grams of deionized water, 99 grams of alumina, 19 grams of barium acetate, 1.6 grams of zirconium acetate, 3 grams of lanthanum nitrate, and 21 grams of barium sulfate, and the pH was adjusted to 4.0 with nitric acid. 2.6 grams of alumina binder was then added, followed by 40 microns of D 90 was crushed into

[0115] Top Coating Slurry A mixture of 37 grams of lanthana-zirconia composite oxide powder (7.5% LaO) and 52 grams of ceria-zirconia composite oxide powder (30% CeO) was impregnated with 0.9 grams of a 16% aqueous solution of diethanolamine hexahydroxyplatinate ((MEA)Pt(OH) by incipient wetness impregnation. 0.3 grams of a 20% Pd nitrate solution was impregnated with 37 grams of lanthana-zirconia composite oxide powder (7.5% LaO) and 52 grams of ceria-zirconia composite oxide powder (30% CeO) by incipient wetness impregnation. The resulting powder was then added, with continuous stirring, to a solution containing 488 grams of deionized water, 1.2 grams of 10% Rh nitrate solution, 52 grams of lanthana-zirconia composite oxide (7.5% La2O3) powder, 6 grams of barium hydroxide, 52 grams of alumina, and 4 grams of barium sulfate, and the pH was adjusted to 4.5 with nitric acid. Then, 10 grams of alumina binder was added, followed by 30 microns of D 90 was crushed into

[0116] The bottom coating slurry was coated onto a 40 mm diameter, 90 mm long, 300 / 2 (cpsi / mil) flow-through metal substrate, with channels having a sinusoidal cross-sectional shape, by immersing the substrate in the slurry. The coated substrate was dried at 150°C for 1 hour and then calcined at 500°C for 2 hours. The bottom coating layer on each substrate was 2.07 g / in 3 and the Pt and Pd loadings in the bottom coating layer were 1.25 g / ft 3 Pt and 2.00g / 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 thickness of 1.43 g / in 3 The top coating layer had a Pt, Pd, and Rh loading of 1.25 g / ft respectively. 3 , 0.50g / ft 3 , and 1.00 g / ft 3 The morphology of the resulting catalyst coating is shown in Figures 1A, 1B and 1C.

[0117] Example 2 (Sample S2, present invention) The preparation was carried out using a 5 wt% aqueous solution of PVA, with the substrate coated at 0.01 g / in 3 PVA (Polyvinyl Alcohol, CAS No. 9002-89-5, M w =89,000~98,000, density=1.28g / cm 3 The preparation was the same as in Example 1, except that the catalyst coating was precoated with PEG-1000 (manufactured by Sinopharm Chemical Reagent Co., Ltd.) and dried at 150° C. for 30 minutes. The morphology of the resulting catalyst coating is shown in FIGS. 2A, 2B, and 2C.

[0118] Example 3 (Sample S3, present invention) The preparation was carried out with a substrate of 0.03 g / in 3 The preparation was the same as in Example 2, except that the catalyst was precoated with PVA. The morphology of the resulting catalyst coating is shown in Figures 3A, 3B, and 3C.

[0119] Example 4 (Sample S4, present invention) The preparation was carried out with a substrate of 0.05 g / in 3 The preparation was the same as in Example 2, except that the catalyst was precoated with PVA. The morphology of the resulting catalyst coating is shown in Figures 4A, 4B, and 4C.

[0120] Example 5 (Sample S5, present invention) The preparation was carried out with a substrate of 0.07 g / in 3 The preparation was the same as in Example 2, except that the catalyst was precoated with PVA. The morphology of the resulting catalyst coating is shown in Figures 5A, 5B, and 5C.

[0121] Determination of void volume ratio The void volume fraction, i.e., the percentage of void volume based on the volume of the coating portion located at the corner, is determined according to the following procedure, assuming that the cavities extend the same length as the catalytic coating at each corner. i) A microscopic image of a cross section of a catalyst article containing at least 120 corners is taken, and equivalent triangles that approximately represent the cross sections of the cavities and the catalytic coating are drawn at each of the 120 corners, for example, as shown in Figures 6A and 6B. ii) The area of ​​the equivalent triangle that approximately represents the cross section of the cavity at each corner cavity ) and the area of ​​an equivalent triangle (Aera) that approximately represents the cross section of the catalytic coating. coating )) and calculate Area cavity Area coating Divide by 1 to provide 120 corner void ratios (if there are no observable voids in a corner, the void ratio at the corner is zero (i.e., 0)). iv) The average void ratio of the 120 corners is calculated and determined as the void volume ratio of the catalyst article.

[0122] Catalyst Performance Test Test samples were prepared by placing each catalyst article prepared in the above examples, either fresh or aged for 18 hours at temperatures between 820 and 940°C and lambda values ​​between 0.9 and 1.1 according to a standard bench cycle (SBC), in a housing equipped with an inlet and an outlet for passing the gas stream to be treated.

[0123] Test samples were measured for catalytic performance on a 125cc Yamaha motorcycle (ZY125T-15). Total hydrocarbons (THC), CO, and NO were measured in the tailpipe. x The emissions were measured using the World Motorcycle Test Cycle (WMTC) in accordance with GB14622-2016, Type I. The emissions measurement includes two phases in one test cycle: P1: Cold start phase from 0 to 600 seconds. P2: high-temperature phase from 600 to 1200 seconds.

[0124] The exhaust from the two phases has the following cumulative composition under a fuel consumption of 2.17 L / 100 km: P1:1.960g / km CO, 0.447g / km THC, 0.427g / km NO x , P2:1.509g / km CO, 0.353g / km THC, 0.488g / km NO x .

[0125] Each sample was tested three times and the average was provided as the test result. The emission test results are summarized in Tables 1 and 2 below.

[0126] [Table 1]

[0127] [Table 2]

[0128] The samples S2 to S5 of the present invention have a higher NO x In particular, the samples of the present invention show a significant improvement in the NO reduction rate exhibited by the comparative samples. x At least 10% higher NO reduction rate x This shows an improvement in the reduction rate.

[0129] Although in some cases a slight decrease in CO or THC reduction performance was observed, it is clear that all of the inventive samples exhibit improved overall catalytic performance over the comparative samples.

[0130] Although the invention 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. Therefore, 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 catalytic article, particularly a TWC catalytic article, for treating an exhaust stream, comprising: a substrate comprising a plurality of longitudinally extending walls and a plurality of channels defined by said walls for the passage of said exhaust flow, said channels having corners at the junctions of the walls; a catalytic coating comprising a platinum group metal component in supported form on the surface of said wall, said catalytic coating consisting of coating portions located at said corners and coating portions located on the remaining area of ​​said wall, The catalytic article, wherein the corner-located coating portion includes a cavity extending longitudinally along the channel.

2. 2. The catalytic article according to claim 1, wherein the cavities occupy 0.5% to 35% by volume, preferably 2.0% to 30% by volume, based on the volume of the coating portion located at the corner.

3. 3. The catalytic article of claim 1, wherein the substrate is a flow-through substrate having channels with cross-sectional shapes having two or more corners, such as trapezoidal, rectangular, square, sinusoidal, and hexagonal.

4. The catalytic article of any one of claims 1 to 3, wherein the substrate is a flow-through metal substrate.

5. The catalyst article according to any one of claims 1 to 4, wherein the PGM component is a Pt component, a Pd component, a Rh component, or any combination thereof.

6. A catalytic article according to any one of claims 1 to 5, wherein the catalytic coating comprises or consists of two catalytic coating layers each comprising a platinum group metal component in supported form.

7. 7. The catalytic article of any one of claims 1 to 6, wherein the catalytic coating comprises or consists of a top catalytic coating layer comprising a first platinum group metal component in supported form and a bottom coating layer comprising a second platinum group metal component in supported form.

8. 8. The catalyst article according to claim 1, wherein the catalyst coating comprises or consists of two catalyst coating layers each comprising a PGM component in supported form, one catalyst coating layer comprising a Rh component in supported form and, optionally, either or both of a Pt component in supported form and a Pd component in supported form as the PGM component, and the other catalyst coating layer comprising a Pt component in supported form and, optionally, a Pd component in supported form as the PGM component.

9. 9. The catalyst article of claim 1, wherein the catalyst coating comprises or consists of a top catalyst coating layer comprising a Rh component in supported form and, optionally, either or both of a Pt component in supported form and a Pd component in supported form as the PGM components, and a bottom catalyst coating layer comprising a Pt component in supported form and, optionally, a Pd component in supported form as the PGM components.

10. 10. The catalyst article of claim 9, wherein the top catalyst coating layer comprises a supported Rh component, a supported Pt component, and a supported Pd component as the PGM components, and the bottom catalyst coating layer comprises a supported Pt component and a supported Pd component as the PGM components.

11. When measured on a catalyst article aged in accordance with GB 14622-2016, Type I, the NO exhibited by a catalyst article having the same catalyst coating composition but without voids in the coating portion located at said corner. ｘ 11. The catalytic article of any one of claims 1 to 10, exhibiting an improvement in NOx reduction rate that is at least 10% greater than the reduction rate.

12. A process for preparing a catalyst article according to any one of claims 1 to 11, comprising the steps of: - applying a solution or suspension of a cavity former to the surface of said wall of the substrate and drying to provide a dry layer of said cavity former; - providing a catalytic coating on said dried layer of said cavity former by applying, optionally drying and calcining, a slurry comprising a platinum group metal component in supported form; The process wherein the cavity former is used in an amount of 0.05 wt % to 9.0 wt % based on the loading of the catalyst coating.

13. 13. The process of claim 12, wherein the cavity former is used in an amount of 0.2 wt.% to 4.0 wt.%, more preferably 0.25 wt.% to 2.5 wt.%, based on the loading of the catalyst coating.

14. 14. The process of claim 12 or 13, wherein the cavitating agent is selected from organic materials such as natural and synthetic polymers, organic low molecular weight solid compounds, inorganic materials such as inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof.

15. 15. The process of claim 14, wherein the cavitating agent is selected from polyether polyols such as polyethylene glycol and its alkyl-capped derivatives, styrene homopolymers or copolymers such as polystyrene, poly(meth)acrylic acid and its ester derivatives such as polymethyl methacrylate or crosslinked polymethyl methacrylate, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinylpyrrolidone, and any combination thereof, preferably polyvinyl alcohol.

16. providing the catalytic coating comprises: i) applying a slurry comprising a first platinum group metal component in supported form to the dried layer of the cavity former, drying, and optionally calcining to form a first catalytic coating layer; ii) applying a slurry comprising a second platinum group metal component in supported form to the first catalytic coating layer, and optionally drying and calcining to form a second catalytic coating layer.

17. 17. The process of claim 16, wherein said calcining is performed to form said first catalytic coating layer.

18. 18. The process according to claim 16 or 17, wherein the cavity former is used in an amount of 0.2 wt.% to 15.0 wt.%, preferably 0.3 wt.% to 10.0 wt.%, more preferably 0.4 wt.% to 3.5 wt.%, based on the loading of the first catalyst coating layer.

19. An exhaust treatment system comprising the catalytic article of any one of claims 1 to 11 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 straddle-type vehicle engine.

21. A method of treating an exhaust stream, particularly from a stoichiometric engine, comprising contacting the exhaust stream with a catalytic article according to any one of claims 1 to 11 or an exhaust treatment system according to claim 19 or 20.

22. 22. The method of claim 21, wherein the exhaust stream is from a gasoline engine, preferably a saddle-type vehicle engine.

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