Catalytic article for treating engine exhaust gas

Abstract

A catalyst article comprising a catalyst coating on a substrate, the catalyst coating comprising at least one catalyst coating layer comprising a platinum group metal component in supported form, the catalyst article having a pore volume distribution, as determined by mercury intrusion porosimetry, in which the logarithmic differential pore volume distribution has a peak top of pore volume diameter at the nano level in the range of 90.0 nm to 140.0 nm and a peak top of pore volume diameter at the micron level in the range of 5.5 μm to 10.0 μm. The present invention also relates to a process for preparing the catalyst article and to an exhaust treatment system including the catalyst article.

Description

[Technical Field]

[0001] The present invention relates to a three-way conversion catalyst article useful for treating engine exhaust gases, and to an exhaust treatment system including the catalyst article. Specifically, the present invention relates to a catalyst article useful for treating exhaust gases from stoichiometric engines, particularly saddle-ride vehicle 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, a three-way catalyst (hereinafter interchangeably referred to as TWC catalyst or TWC) is typically used to simultaneously oxidize the unburned hydrocarbons and carbon monoxide and reduce the 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 (OSC) 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 of the various TWC catalysts for 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 volumetric 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 gases to diffuse into the catalytic coating near the substrate. Furthermore, when a TWC catalyst article is used under high space velocity, exhaust gases have difficulty diffusing deep into the catalytic coating, preventing the catalyst performance from being fully utilized. To solve this problem of insufficient exhaust gas diffusion in the catalytic coating, several special compositions, configurations, or structures of catalysts for TWC catalyst articles have been proposed.

[0005] For example, International Publication No. 2015 / 037613(A) discloses an exhaust gas purification catalyst having a catalyst layer containing 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 ≧2} (where S represents the void cross-sectional area and L represents the void cross-sectional circumferential length) accounts for 50% or more by number of all voids in the catalyst layer, and as a second feature, the average void diameter in the void cross-sectional area in the catalyst layer is 10 μm to 20 μm when the void shape is assumed to be a perfect circle.It is stated that the miscibility and diffusibility of gases in the catalyst layer are improved, and as a result, excellent purification performance can be exhibited.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] There remains a need to provide a TWC catalyst article that can improve gas diffusion deep into the catalyst, promote interaction between the feed gas and the active sites, and improve exhaust gas purification performance. Summary of the Invention

[0010] 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 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 reducing the amount of carbon dioxide emitted by the catalyst.

[0011] It has surprisingly been found that the objects of the present invention are achieved by a catalyst article comprising a PGM-based catalyst coating layer having interparticle pores on the micrometer and nanometer level on a substrate.

[0012] Accordingly, in a first aspect, the present invention provides a catalyst article, particularly a TWC catalyst article, comprising a catalyst coating on a substrate, wherein the catalyst coating comprises at least one catalyst coating layer comprising a platinum group metal component in supported form, and wherein the catalyst article has a pore volume distribution, as determined by mercury intrusion porosimetry, such that the peak top of the nano-level pore volume diameter in the logarithmic differential pore volume distribution is in the range of 90.0 nm to 140.0 nm and the peak top of the micron-level pore volume diameter is in the range of 5.5 μm to 10.0 μm.

[0013] In a second aspect, the present invention provides a process for preparing a catalyst article according to the first aspect, comprising: - applying a slurry comprising a platinum group metal component in supported form and a pore former onto a substrate and optionally drying; - calcining to form a catalyst coating layer; Including, The process provides that the pore former is in particulate form and is used in an amount of at least 0.5 wt % based on the loading of the formed catalyst coating layer.

[0014] 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.

[0015] 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]

[0016] [Figure 1A] FIG. 1 shows logarithmic differential pore volume distributions of samples S1 to S4 described in the examples. [Figure 1B] FIG. 1 shows logarithmic differential pore volume distributions of samples S1 to S4 described in the examples. [Figure 2A] FIG. 1 shows the logarithmic differential pore volume distributions of samples S5 to S8 described in the examples. [Figure 2B] FIG. 1 shows the logarithmic differential pore volume distributions of samples S5 to S8 described in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail herein below. It should be understood that the present invention may be embodied in many different ways and should not be construed as limited to the embodiments set forth herein.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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 can have a non-laminar or layered configuration. In a non-laminar configuration, the catalytic coating consists of a single coating layer. In a layered configuration, the catalytic coating consists of two or more coating layers, at least one of which is a catalyst-containing coating layer. It is understood that a coating layer can be prepared by repeating the coating step two or more times to achieve a target loading, and thus includes more than one sublayer with the same chemical composition and catalytic activity, which may be distinguishable only by SEM analysis. Such a coating layer that includes more than one sublayer with the same chemical composition and catalytic activity is referred to as a single or one coating layer. Therefore, when referring to two or more coating layers herein, the coating layers have different chemical compositions or catalytic activities from each other.

[0024] As used herein, the term "catalytic coating layer" refers specifically to a coating layer that includes a platinum group metal component in supported form.

[0025] Any reference herein to a coating layer "on a substrate" is intended to mean that the coating layer is carried by the substrate, which may be blank or may already carry one or more other coating layers. Any reference herein to applying a slurry "on a substrate" is intended to mean that the slurry is applied onto the substrate, which may be blank or may already carry one or more coating layers.

[0026] 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 the ratio of weights measured before and after a calcination process, e.g., at 500°C for 1 hour.

[0027] 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.

[0028] According to a first aspect of the present invention, there is provided a catalyst article comprising a catalyst coating on a substrate, wherein the catalyst coating comprises at least one catalyst coating layer comprising a platinum group metal component in a supported form, and the catalyst article has a pore volume distribution, as determined by mercury intrusion porosimetry, such that the peak top of the pore volume diameter at the nano level in the logarithmic differential pore volume distribution is in the range of 90.0 nm to 140.0 nm, and the peak top of the pore volume diameter at the micron level is in the range of 5.5 μm to 10.0 μm.

[0029] It will be understood that a catalytic article according to the present invention may comprise a catalytic coating consisting of two or more coating layers on a substrate, with at least one coating layer comprising a platinum group metal component in supported form, which may also be referred to as a catalytic coating layer. When the catalytic coating of a catalytic article according to the present invention comprises two or more coating layers, it is preferred that at least the outermost coating layer has a pore volume distribution as described herein on the substrate, in order to increase gas diffusivity to the inner layers.

[0030] In some embodiments, the catalytic coating of a catalytic article according to the present invention may comprise or consist of one catalytic coating layer comprising a platinum group metal component in supported form.

[0031] In some other embodiments, the catalytic coating of a catalyst article according to the present invention may comprise or consist of two catalytic coating layers comprising a platinum group metal component in supported form, for example, a 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.

[0032] In some further embodiments, the catalytic coating of the catalytic article according to the present invention may comprise three or more coating layers, with at least one, and preferably two or more, coating layers comprising a platinum group metal component in supported form.

[0033] In any of the above embodiments, the peak top of the pore volume diameter at the nano level in the pore volume distribution is preferably in the range of 100.0 nm to 130.0 nm or 110.0 nm to 120.0 nm in the logarithmic differential pore volume distribution when determined by mercury intrusion porosimetry. Additionally or alternatively, the peak top of the pore volume diameter at the micron level in the pore volume distribution is in the range of 6.0 μm to 8.0 μm or 6.0 μm to 7.5 μm in the logarithmic differential pore volume distribution when determined by mercury intrusion porosimetry.

[0034] In the catalytic coating of the catalyst article according to the present invention, when measured by mercury intrusion porosimetry, the peak pore volume diameter at the nano level in the logarithmic differential pore volume distribution ranges from 10 nm to 250 nm, and the peak pore volume diameter at the micron level ranges from 1 to 22 μm.

[0035] Furthermore, for peak pore volume diameters at the nano level described herein, the cumulative pore volume is preferably at least 0.05 mL / g, or at least 0.09 mL / g, for example, in the range of 0.05 to 0.50 mL / g, or 0.08 to 0.30 mL / g, or 0.09 to 0.18 mL / g. For peak pore volume diameters at the micron level described herein, the cumulative pore volume is preferably at least 0.01 mL / g, or at least 0.02 mL / g, in particular at least 0.03 mL / g, for example, in the range of 0.01 to 0.10 mL / g, or 0.02 to 0.06 mL / g, or 0.03 to 0.06 mL / g.

[0036] It will be understood that the peaks in pore volume diameters at the nano- and micron-level are peaks originating from the pores of the catalyst coating. Any peaks originating from the pores of the substrate do not appear in such pore volume diameter ranges and are therefore not counted when discussing pore distribution or pore volume distribution herein.

[0037] The platinum group metal (PGM) components useful in any catalytic coating layer included in the catalyst article are not particularly limited. Typically, the PGM components may be rhodium (Rh), platinum (Pt), palladium (Pd), ruthenium (Ru), osmium (Os), iridium (Ir), or any combination thereof, of which Pt, Pd, Rh, or any combination thereof is commonly used.

[0038] 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. The platinum group metal (PGM) 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.

[0039] For example, in some embodiments, the catalytic coating of the catalyst article comprises two catalytic coating layers comprising PGM components in supported form, one catalytic coating layer comprising a Rh component in supported form as a PGM component and, optionally, a Pt component in supported form, and the other catalytic coating layer comprising a Pt component in supported form as a PGM component and, optionally, a Pd component in supported form.

[0040] In some particular embodiments, 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 Rh component in supported form as the PGM components and, optionally, a Pt component in supported form, and the bottom catalyst coating layer comprising a Pt component in supported form as the PGM components and, optionally, a Pd component in supported form.

[0041] In particular, the catalytic coating of the catalyst article may include a top catalytic coating layer comprising the PGM components in supported form and a bottom catalytic coating layer comprising the PGM components in supported form, the top catalytic coating layer comprising the Rh component in supported form as the PGM component, and the bottom catalytic coating layer comprising the Pt component in supported form as the PGM component.

[0042] Alternatively, the catalyst coating of the catalyst article may comprise a top catalyst coating layer comprising the PGM components in supported form, and a bottom catalyst coating layer comprising the PGM components in supported form, the top catalyst coating layer comprising the PGM components in supported form of a Rh component and a Pt component, and the bottom catalyst coating layer comprising the PGM components in supported form of a Pt component and a Pd component,

[0043] Useful support materials for the platinum group metal component in a catalyst article according to the present invention can include refractory metal oxides, oxygen storage components, and any combination thereof.

[0044] 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, optionally including dopants. Similarly, "zirconia-based materials" refer to materials that include zirconia as a base, optionally including dopants.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The support materials for different platinum group metal (PGM) components in the same catalytic coating layer may be the same or different. Also, when two or more catalytic coating layers are included in a catalytic article according to the present invention, 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.

[0052] 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 catalytic article may include a catalytic coating layer comprising a platinum group metal component in supported form at a loading in the range of 0.01 to 0.01. When more than one catalytic coating layer comprising a platinum group metal component in supported form is included in the catalytic coating of the catalytic article, the loadings described herein refer to the sum of all such catalytic coating layers.

[0053] The catalytic coating layer containing the platinum group metal components in supported form described herein has a metal content of 0.5 to 100.0 g / ft, calculated as the respective PGM elements. 3 , or 1.0 to 60.0 g / ft 3 , or 5.0 to 20.0 g / ft 3 The PGM components may be present in a total loading range of 1000 ppm.

[0054] 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.

[0055] A catalytic coating having a pore volume distribution 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.

[0056] 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.

[0057] 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.

[0058] Useful metallic materials 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, 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, e.g., at high temperatures above 1000°C, 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.

[0059] 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.

[0060] Within the context of the present invention, flow-through substrates are preferred, having a plurality of fine, parallel gas flow passages extending from the inlet face to the outlet face of the substrate and open to fluid flow therethrough. The passages, which are essentially straight-line paths from their fluid inlet to their fluid outlet, are defined by walls to which a catalytic material is applied as a washcoat so that gas flowing through the passage comes into contact with the catalytic material. The flow passages of monolithic substrates are thin-walled channels, which can be of any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal (S-shaped), hexagonal, elliptical, or circular. Such structures can contain 60 to 900 or more gas inlet openings (or "cells") per square inch of cross section. For example, the substrate may have about 200 to 750, more usually about 300 to 600, cells per square inch (cpsi). The wall thickness of flow-through substrates can vary, with typical ranges being 1 mil to 0.1 inches.

[0061] The substrate may also 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 to 400 cpsi. The cross-sectional geometry of the passages may vary as described above for the passages in flow-through substrates. The wall thickness of wall-flow substrates may vary, with a typical range being 2 mils to 0.1 inches.

[0062] The catalyst article according to the present invention can be prepared by a conventional washcoating process. The washcoating process generally involves applying one or more slurries containing the respective catalysts onto a substrate. For the purposes of the present invention, a pore-forming agent is used in one or more slurries to provide interparticle pores having the pore volume distribution described in the first aspect of the present invention. The pore-forming agent is included in the slurry from which the catalyst coating layer is obtained.

[0063] Thus, in a second aspect, the present invention provides a process for preparing a catalyst article according to the first aspect, comprising: - applying a slurry comprising a platinum group metal component in supported form and a pore former onto a substrate and optionally drying; - calcining to form a catalyst coating layer; Including, The process provides that the pore former is in particulate form and is used in an amount of at least 0.5 wt % based on the loading of the formed catalyst coating layer.

[0064] As described herein above, the substrate having thereon the slurry comprising the platinum group metal component in supported form and the pore former 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 slurry comprising the platinum group metal component in supported form and the pore former is applied thereon.

[0065] The catalytic coating layer formed according to the process of the present invention may constitute the catalytic coating of a catalytic article.

[0066] Alternatively, the catalytic coating layer formed according to the process of the present invention may constitute one of the coating layers of the catalytic coating of the catalytic article, in which case the catalytic coating layer formed may be either a top coating layer or a bottom coating layer.

[0067] In some embodiments, the present invention provides a process for preparing a catalyst article according to the first aspect, comprising: - applying a slurry comprising a first platinum group metal component in supported form and a pore former onto a substrate and drying and / or calcining to form a first catalytic coating layer; - applying a slurry comprising a second platinum group metal component in supported form and a pore former onto the first catalytic coating layer, and optionally drying and calcining to form a second catalytic coating layer; Including, The process provides that the pore former is in particulate form and is used in an amount of at least 0.5 wt % based on the loading of each formed catalyst coating layer.

[0068] Such a process can provide a catalytic coating on a substrate comprising two catalytic coating layers and having the pore volume distribution specified above, and by applying additional slurries comprising a platinum group metal component in supported form and the amount of pore former specified above, catalytic coatings can be provided on a substrate comprising more catalytic coating layers and having the pore volume distribution specified above.

[0069] The pore former is preferably used in an amount of at least 1 wt%, or at least 3 wt%, or at least 4 wt%, based on the loading of each catalyst coating layer formed from the slurry containing the pore former. More preferably, the pore former may be used in an amount of 50 wt% or less, or 30 wt% or less, based on the loading of each catalyst coating layer.

[0070] The pore former may be an organic or inorganic material that can be burned off to leave voids during the firing step to provide the coating or coating layer. For example, the pore former may be selected from organic materials such as natural and synthetic polymers, organic small molecule compounds, inorganic materials such as inorganic salts and carbon materials, cellulose-containing natural materials, and any combination thereof.

[0071] Natural and synthetic polymers suitable as pore-forming agents can 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, cellulose, ether and ester derivatives of cellulose, polyvinyl alcohol, polyvinylpyrrolidone, and any combination thereof.

[0072] Suitable organic small molecule compounds as pore-forming agents can include, but are not limited to, benzoic acid and its derivatives, carbamide (urea), sugar crystals, and any combination thereof.

[0073] Suitable inorganic salts as pore formers can include, but are not limited to, ammonium bicarbonate, magnesium carbonate, and any combination thereof.

[0074] Carbon materials suitable as pore formers can include, but are not limited to, carbon black, carbon fiber, graphite, and any combination thereof.

[0075] Suitable cellulose-containing natural materials as pore formers 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 can be obtained from various parts of plants, such as leaves, bark, straw, roots, husks, and any combination thereof.

[0076] The pore formers may be particles having a variety of shapes, including, but not limited to, spheres, tablets, cylinders, or fibers. Preferably, the pore formers have an average particle size D in the range of 1 to 50 μm, or 10 to 30 μm, or 15 to 20 μm. 50Additionally or alternatively, the pore former is in the form of particles having a maximum particle size of 60 μm, preferably 40 μm.

[0077] The steps of preparing and applying the slurry, drying the coated slurry, and calcining the coated slurry can be carried out by conventional methods without particular limitations. Generally, the slurry for the washcoat can be prepared by suspending finely divided particles of the catalyst (e.g., a PGM component in supported form) in a suitable vehicle, such as water, to which an accelerator, binder, stabilizer, viscosity modifier, and / or surfactant 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, for example, in the range of 15 to 50 microns. Milling / milling can be achieved 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 as needed by adding 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 pore-forming agent can be incorporated into the slurry at any time during the preparation of the slurry, for example, before milling / milling.

[0078] The resulting slurry may be applied to a substrate by dipping the substrate into the slurry or otherwise coating the substrate so that a desired loading of the coating layer is deposited on the substrate. The coated substrate may then be dried at a temperature ranging from 100 to 300°C and / or calcined by heating at a temperature ranging from 350 to 650°C for a period of time, e.g., 1 to 3 hours. Drying and calcination are typically performed in air. The coating, drying, and calcination process 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 the weight of the substrate before and after applying the washcoat.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 1. A catalyst article comprising a catalyst coating on a substrate, the catalyst coating comprising at least one catalyst coating layer comprising a platinum group metal component in supported form, and having a pore volume distribution, as determined by mercury intrusion porosimetry, such that the peak top of the pore volume diameter at the nano level in the logarithmic differential pore volume distribution is in the range of 90.0 nm to 140.0 nm, and the peak top of the pore volume diameter at the micron level is in the range of 5.5 μm to 10.0 μm.

[0084] 2. A catalyst article according to embodiment 1, wherein the peak top of the pore volume diameter at the nano level is in the range of 100.0 nm to 130.0 nm.

[0085] 3. A catalyst article according to embodiment 2, wherein the peak top of the pore volume diameter at the nano level is in the range of 110.0 nm to 120.0 nm.

[0086] 4. A catalyst article according to any one of embodiments 1 to 3, wherein the peak top of the pore volume diameter at the micron level in the pore volume distribution is in the range of 6.0 μm to 8.0 μm.

[0087] 5. A catalyst article according to embodiment 4, wherein the peak top of the pore volume diameter at the micron level in the pore volume distribution is in the range of 6.0 μm to 7.5 μm.

[0088] 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.

[0089] 7. The catalytic article of any of embodiments 1-6, wherein the catalytic coating comprises only one catalytic coating layer comprising a platinum group metal component in supported form.

[0090] 8. The catalytic article of embodiment 7, wherein the catalytic coating consists of only one catalytic coating layer comprising the platinum group metal component in supported form.

[0091] 9. The catalytic article of any one of embodiments 1-6, wherein the catalytic coating comprises two catalytic coating layers comprising a platinum group metal component in supported form.

[0092] 10. The catalytic article of embodiment 9, wherein the catalytic coating consists of two catalytic coating layers comprising a platinum group metal component in supported form.

[0093] 11. The catalytic article of embodiment 9 or 10, wherein the catalytic coating comprises 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] 12. The catalyst article of any one of embodiments 9-11, wherein the catalyst coating comprises two catalyst coating layers comprising PGM components in supported form, one catalyst coating layer comprising a Rh component in supported form as a PGM component and, optionally, a Pt component in supported form, and the other catalyst coating layer comprising a Pt component in supported form as a PGM component and, optionally, a Pd component in supported form.

[0095] 13. The catalytic article of embodiment 12, wherein the catalytic coating comprises a top catalytic coating layer comprising a Rh component in supported form as a PGM component and, optionally, a Pt component in supported form, and a bottom catalytic coating layer comprising a Pt component in supported form as a PGM component and, optionally, a Pd component in supported form.

[0096] 14. A process for preparing a catalyst article according to any one of embodiments 1 to 8, comprising: - applying a slurry comprising a platinum group metal component in supported form and a pore former onto a substrate and optionally drying; - calcining to form a catalyst coating layer; Including, A process wherein the pore former is in particulate form and is used in an amount of at least 0.5 wt % based on the loading of the formed catalyst coating layer.

[0097] 15. A process for preparing a catalyst article according to any one of embodiments 1 to 6 and 9 to 13, comprising: - applying a slurry comprising a first platinum group metal component in supported form and a pore former onto a substrate and drying and / or calcining to form a first catalytic coating layer; - applying a slurry comprising a second platinum group metal component in supported form and a pore former onto the first catalytic coating layer, and optionally drying and calcining to form a second catalytic coating layer; Including, A process wherein the pore former is in particulate form and is used in an amount of at least 0.5 wt % based on the loading of each formed catalyst coating layer.

[0098] 16. The process of embodiment 14 or 15, wherein the pore-forming agent is used in an amount of at least 1 wt. %, based on the loading of each catalyst coating layer formed.

[0099] 17. The process of embodiment 16, wherein the pore-forming agent is used in an amount of at least 3 wt.%.

[0100] 18. The process of embodiment 17, wherein the pore-forming agent is used in an amount of at least 4% by weight.

[0101] 19. The process of any one of embodiments 14-18, wherein the pore-forming agent is used in an amount of 50 wt. % or less based on the loading of each catalyst coating layer formed.

[0102] 20. The process of embodiment 19, wherein the pore-forming agent is used in an amount of 30% by weight or less.

[0103] 21. The process of any one of embodiments 14-20, wherein the pore-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.

[0104] 22. The process of embodiment 21, wherein the pore-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.

[0105] 23. The pore former has an average particle size D in the range of 1 to 50 μm. 50 23. The process of any one of embodiments 14 to 22, wherein the compound is in the form of a powder having the formula:

[0106] 24. Average particle size D 50 24. The process of embodiment 23, wherein the thickness is in the range of 10 to 30 μm.

[0107] 25. Average particle size D 50 25. The process of embodiment 24, wherein the thickness is in the range of 15 to 20 μm.

[0108] 26. An exhaust treatment system comprising the catalytic article of any one of embodiments 1-13 located downstream of a stoichiometric engine.

[0109] 27. The exhaust treatment system of embodiment 26, wherein the stoichiometric engine is a gasoline engine, in particular a saddle-type vehicle engine.

[0110] 28. 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 1-13 or the exhaust treatment system of embodiment 26 or 27.

[0111] 29. The method of embodiment 28, wherein the exhaust stream is from a gasoline engine, preferably a saddle-type vehicle engine. [Example]

[0112] 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.

[0113] Preparation of the catalyst article Example 1 (Sample S1, Comparative) 1.56 g of an aqueous solution of diethanolamine hexahydroxyplatinate ((MEA)2Pt(OH)6) (16 wt. % Pt) was diluted in water and loaded onto a support consisting of 28.83 g of ceria-doped alumina (10% CeO2) and 163.37 g of ceria-zirconia (45% CeO2) by incipient wetness. The solids content after incipient wetness was 68 wt. %. The resulting mixture was then mixed with an aqueous solution of 0.6 g of 1-octanol, 4.82 g of barium acetate, 2.1 g of zirconium acetate, 2.0 g of acetic acid, and 2.0 g of alumina to obtain a slurry with a solids content of 45%. The resulting particle size D 90 The slurry was milled until the particle size was 45 microns. The resulting slurry (hereafter referred to as Slurry A) had a final pH of 4.5 and a solids content of 41% by weight.

[0114] 6.42 g of an aqueous solution of neodymium nitrate (Nd(NO3)3) (29.8 wt% Nd) and 3.24 g of an aqueous solution of rhodium nitrate (Rh(NO3)3) (10 wt% Rh) were each diluted with water and sequentially loaded onto a support consisting of 97.64 g of lanthanum-doped zirconia (9 wt% La2O3) and 49.33 g of ceria-zirconia (10 wt% CeO2) by incipient wetness. The solids content after incipient wetness was 67 wt%. The resulting mixture was then mixed with an aqueous solution of 0.6 g of 1-octanol, 4 g of barium acetate, and 45 g of alumina to obtain a slurry with a solids content of 33 wt%. The resulting particle size D 90 The slurry was milled to a particle size of 45 microns and then adjusted to a final pH of 4.5 with nitric acid. The resulting slurry (hereafter referred to as Slurry B) had a solids content of 30% by weight.

[0115] A metallic flow-through substrate with a diameter of 40 mm and a length of 90 mm was used, which had channels with a sinusoidal cross-sectional shape, 300 cells / in², and a wall thickness of 5 mils. Slurry A and Slurry B were then sequentially deposited along the entire length of the substrate. The substrate was dried at 110°C to remove 85-95% of the moisture, and then calcined at 550°C for 2 hours after each coating. The loading of the bottom coating layer obtained from Slurry A and the top coating layer obtained from Slurry B was 2.08 g / in², respectively. 3 and 1.25 g / in 3 The bottom coating layer is 4.5g / ft 3 of Pt, and the top coating layer is 3.5 g / ft 3 Contains Rh.

[0116] Example 2 (Sample S2, present invention) 0.104g / in 3 and 0.066 g / in 3 Cross-linked polymethyl methacrylate (PMMA, SUNPMMA-S200 manufactured by SUNJIN Chemical, polydispersity, D 50 = 17 microns, D 100 = 36.24 microns) is added to Slurries A and B, respectively, before milling.

[0117] Example 3 (Sample S3, present invention) 0.208g / in 3 and 0.132 g / in 3 Prepared as in Example 2, except that 100g of PMMA is added to Slurries A and B, respectively, before milling.

[0118] Example 4 (Sample S4, Comparative) 0.416g / in 3 and 0.264 g / in 3 Prepared as in Example 2, except that PMMA was added to Slurries A and B, respectively, before milling.

[0119] Example 5 (Sample S5, Comparative) 0.119 g of an aqueous solution of diethanolamine hexahydroxyplatinate (12 wt. % Pt) was diluted in water and loaded onto a support consisting of 41.81 g of ceria-doped alumina (10% CeO) and 150.52 g of ceria-zirconia (45 wt. % CeO) by incipient wetness. The solids content after incipient wetness was 68 wt. The resulting mixture was then mixed with an aqueous solution of 0.7 g of 1-octanol, 6.99 g of barium acetate, 6.0 g of nitric acid, and 3.3 g of alumina to obtain a slurry with a solids content of 45 wt. The resulting particle size D 90 The slurry was milled until the particle size was 45 microns. The resulting slurry (hereafter referred to as Slurry C) had a final pH of 4.5 and a solids content of 41% by weight.

[0120] A 12.24 g solution of lanthanum nitrate (27 wt. % La) and a 2.335 g solution of palladium nitrate (21 wt. % Pd) were each diluted with water and sequentially loaded onto 95.48 g of lanthanum-doped alumina (1 wt. % La2O3) by incipient wetness to obtain a mixture with a solids content of 55 wt. A 0.144 g solution of neodymium nitrate (30 wt. % Nd) and a 2.465 g solution of rhodium nitrate (10 wt. % Rh) were each diluted with water and sequentially loaded onto 10.61 g of zirconia-doped alumina (20 wt. % ZrO2) and a 37.13 g solution of ceria-zirconia (22 wt. % CeO2) by incipient wetness to obtain a mixture with a solids content of 66 wt. 1.53 g of an aqueous solution of hexahydroxyplatinic acid diethanolamine (12 wt. % Pt) was diluted in water and loaded onto 42.44 g of ceria-doped alumina (10 wt. % CeO) support by incipient wetness to obtain a mixture with a solids content of 60 wt. The mixture was then mixed in an aqueous solution of 0.7 g of 1-octanol, 3.0 g of nitric acid, 2.55 g of barium sulfate, and 4.24 g of alumina to obtain a slurry with a solids content of 33 wt. The resulting particle size D 90The slurry was milled until the particle size was 20 microns. The resulting slurry (hereafter referred to as Slurry D) had a final pH of 4 and a solids content of 31% by weight.

[0121] A metallic flow-through substrate with a diameter of 40 mm and a length of 90 mm was used, which had channels with a sinusoidal cross-sectional shape, 300 cells / in², and a wall thickness of 5 mils. Slurries C and D were then sequentially deposited along the entire length of the substrate. The substrate was dried at 120°C to remove 85-95% of the moisture and then calcined at 550°C after each coating. The loading of the bottom coating layer from Slurry C and the top coating layer from Slurry D was 2.04 g / in², respectively. 3 and 0.96 g / in 3 The bottom coating layer is 2.5g / ft 3 of Pt, and the top coating layer is 1.5 g / ft 3 of Pt, 4.0g / ft 3 of Pd, and 2.0 g / ft 3 Contains Rh.

[0122] Example 6 (Sample S6, present invention) 0.102g / in 3 and 0.048 g / in 3 Cross-linked polymethyl methacrylate (PMMA, SUNPMMA-S200 manufactured by SUNJIN Chemical, polydispersity, D 50 = 17 microns, D 100 = 36.24 microns) was added to Slurries C and D, respectively, before milling.

[0123] Example 7 (Sample S7, present invention) 0.204g / in 3 and 0.096 g / in 3 Prepared as in Example 6, except that 100g of PMMA was added to Slurries C and D, respectively, before milling.

[0124] Example 8 (Sample S8, present invention) 0.408g / in3 and 0.192 g / in 3 Prepared as in Example 6, except that 100g of PMMA was added to Slurries C and D, respectively, before milling.

[0125] Characterization of logarithmic differential pore volume distribution The pore volume distribution in the catalytic coating of each catalyst article was examined using a mercury porosimeter (Poremaster 60). Measurements were performed using a standard mercury injection procedure with an automated porosimeter, Poremaster 60, manufactured by Anton Paar Quanta Tec Inc. Samples for measurement were prepared by scraping a small piece of the catalytic coating from each catalyst article.

[0126] Measurement temperature: 17.5℃; Measurement cell: Sample chamber volume 3cm 3 , penetration volume 0.39 cm 3 ; Measurement range: 0.212PSIA~59558.266PSIA; Measurement points: 1071 points (the points are spaced at equal intervals when the pore diameter is logarithmically scaled).

[0127] The pore volume distribution characterization results for each catalyst coating are summarized in Table 1 below and are also shown in Figures 1A-2B.

[0128] [Table 1]

[0129] 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 of 820-940°C and lambda values ​​of 0.9-1.1 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. The test samples were mounted on a 125cc Wuyang-Honda motorcycle (WH125T-9A) or a 125cc Dachangjiang motorcycle (DCJ-HJ125T-22A), respectively.

[0130] Measuring emissions Each pollutant (THC, CO, and NO) was measured using the World Autocycle Test Cycle (WMTC) according to GB14622-2016, Type I. x ) emissions were measured.

[0131] The performance of each test sample was evaluated by measuring tail-pipe total hydrocarbons (THC), CO, and NO from two phases included in one test cycle: x This was assessed by measuring the amount of emissions. P1: Cold start phase from 0 to 600 seconds. P2: high-temperature phase from 600 to 1200 seconds.

[0132] The exhaust from the two phases has the following cumulative composition under a fuel consumption of 2.17 L / 100 km: P1:2.200g / km CO, 0.499g / km THC, 0.440g / km NO x , P2:1.660g / km CO, 0.389g / km THC, 0.493g / km NO x .

[0133] Each sample was tested three times and the average was provided as the test result. The emission test results are summarized in Tables 2 to 5 below.

[0134] [Table 2] * Reduction rate of emissions compared to sample S1

[0135] [Table 3] * Reduction rate of emissions compared to sample S1

[0136] The test results shown in Tables 2 and 3 indicate that catalyst articles according to the present invention (S2 and S3) comprising a catalyst coating having a pore volume distribution as described herein, have significantly higher HC, CO, and NO emissions than catalyst articles (S1 and S4) comprising a catalyst coating not having a pore volume distribution as described herein. x It shows that there has been an overall improvement in emissions control.

[0137] [Table 4] * Emission reduction rate compared to sample S5

[0138] [Table 5] * Emission reduction rate compared to sample S5

[0139] Furthermore, the test results shown in Tables 4 and 5 indicate that the catalyst articles (S6 to S8) according to the present invention, which include a catalyst coating having the pore volume distribution described herein, have significantly higher HC, CO, and NO emissions than the catalyst article (S5) which includes a catalyst coating not having the pore volume distribution described herein. x It shows that there has been an overall improvement in emissions control.

[0140] 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 comprising a catalytic coating on a substrate, wherein the catalytic coating comprises at least one catalytic coating layer comprising a platinum group metal component in a supported form, and has a pore volume distribution such that, when determined by mercury intrusion porosimetry, the peak top of the pore volume diameter at the nano level in a logarithmic differential pore volume distribution is in the range of 90.0 nm to 140.0 nm, and the peak top of the pore volume diameter at the micron level is in the range of 5.5 μm to 10.0 μm.

2. 2. The catalyst article according to claim 1, wherein the peak top of the pore volume diameter at the nano-level is in the range of 100.0 nm to 130.0 nm or 110.0 nm to 120.0 nm.

3. 3. The catalyst article according to claim 1, wherein the peak top of the pore volume diameter at the micron level in the pore volume distribution is in the range of 6.0 μm to 8.0 μm or 6.0 μm to 7.5 μm.

4. The catalyst article according to any one of claims 1 to 3, wherein the PGM component is a Pt component, a Pd component, a Rh component, or any combination thereof.

5. A catalytic article according to any one of claims 1 to 4, wherein said catalytic coating comprises or consists of only one catalytic coating layer comprising a platinum group metal component in supported form.

6. A catalytic article according to any one of claims 1 to 4, wherein said catalytic coating comprises or consists of two catalytic coating layers comprising a platinum group metal component in supported form.

7. 7. The catalytic article of claim 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 catalytic article according to claim 6 or 7, wherein the catalytic coating comprises or consists of two catalytic coating layers comprising PGM components in supported form, one catalytic coating layer comprising a Rh component in supported form as the PGM component and optionally a Pt component in supported form, and the other catalytic coating layer comprising a Pt component in supported form as the PGM component and optionally a Pd component in supported form.

9. 10. The catalytic article of claim 8, wherein the catalytic coating comprises or consists of a top catalytic coating layer comprising a Rh component in supported form as the PGM component and, optionally, a Pt component in supported form, and a bottom catalytic coating layer comprising a Pt component in supported form as the PGM component and, optionally, a Pd component in supported form.

10. A process for preparing a catalyst article according to any one of claims 1 to 5, comprising the steps of: - applying a slurry comprising a platinum group metal component in supported form and a pore former onto a substrate and optionally drying; - calcining to form a catalytic coating layer; Including, A process for preparing a catalyst article, wherein said pore former is in the form of particles and is used in an amount of at least 0.5 wt % based on the loading of the formed catalyst coating layer.

11. A process for preparing a catalyst article according to any one of claims 1 to 4 and 6 to 9, comprising the steps of: - applying a slurry comprising a first platinum group metal component in supported form and a pore former onto a substrate and drying and / or calcining to form a first catalytic coating layer; - applying a slurry comprising a second platinum group metal component in supported form and a pore former onto said first catalytic coating layer, and optionally drying and calcining to form a second catalytic coating layer; Including, A process for preparing a catalyst article, wherein said pore former is in the form of particles and is used in an amount of at least 0.5 wt % based on the loading of each formed catalyst coating layer.

12. 12. The process of claim 10 or 11, wherein the pore former is used in an amount of at least 1 wt%, at least 3 wt%, or at least 4 wt%, based on the loading of each catalyst coating layer formed.

13. A process according to any of claims 10 to 12, wherein the pore former is used in an amount of 50 wt% or less, or 30 wt% or less, based on the loading of each catalyst coating layer formed.

14. 14. The process of any of claims 10 to 13, wherein the pore-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.

15. 15. The process of claim 14, wherein the pore-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.

16. The pore former 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 16. The process according to any one of claims 10 to 15, wherein the compound is in the form of a powder having the formula:

17. An exhaust treatment system comprising the catalytic article of any of claims 1 to 9 located downstream of a stoichiometric engine.

18. 18. The exhaust treatment system of claim 17, wherein the stoichiometric engine is a gasoline engine, in particular a straddle-type vehicle engine.

19. 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 9 or an exhaust treatment system according to claim 17 or 18.

20. 20. The method of claim 19, wherein the exhaust stream is from a gasoline engine, preferably a saddle-ride vehicle engine.

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