Exhaust gas purification catalyst and production method therefor

Abstract

The present invention addresses the problem of providing an exhaust gas purification catalyst capable of improving exhaust gas purification performance. In order to solve said problem, the present invention provides an exhaust gas purification catalyst (1) comprising a substrate (10) and catalyst layers (20) provided in the substrate (10), wherein: the catalyst layers (20) contain Rh, Ce, and first particles; the mass of Ce in the catalyst layers (20) per unit volume of the portions of the substrate (10) at which the catalyst layers (20) are provided are 0.5-13 g / L in terms of CeO2; the ratio of the mass of Y derived from the first particles in the catalyst layers (20) in terms of Y2O3 to the mass of Ce in the catalyst layers (20) in terms of CeO2 is 0.05-1.5; and the average particle diameter of the first particles in the catalyst layers (20) is 0.05-1.5 μm.

Description

Catalyst for exhaust gas purification and method for manufacturing the same

[0001] The present invention relates to an exhaust gas purification catalyst and a method for producing the same.

[0002] Exhaust gases emitted from internal combustion engines of vehicles such as automobiles and motorcycles contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). To purify and neutralize these harmful components, exhaust gas purification catalysts containing precious metal elements such as Pt, Pd, and Rh are used. Pt and Pd are mainly involved in the oxidation purification of HC and CO, while Rh is mainly involved in the reduction purification of NOx.

[0003] The air-fuel ratio supplied to an internal combustion engine should ideally be controlled to be close to the stoichiometric air-fuel ratio. However, the actual air-fuel ratio can become rich (excess fuel atmosphere) or lean (lean fuel atmosphere) depending on the vehicle's driving conditions. Consequently, the exhaust gas can also become rich or lean. Furthermore, in recent vehicles, CO2 emissions from the internal combustion engine are a significant concern. ２ To reduce emissions, a control system called "fuel cut (F / C)" is implemented that switches the fuel supply from continuous to intermittent during deceleration, etc. When the fuel supply is temporarily stopped, the exhaust gas becomes lean, and when the fuel supply is resumed, the exhaust gas becomes rich.

[0004] When the exhaust gas becomes lean, the Rh in the Rh layer is oxidized, and the exhaust gas purification performance of the Rh layer decreases. When the exhaust gas becomes rich, the oxidized Rh is reduced, and the exhaust gas purification performance of the Rh layer is restored.

[0005] To mitigate fluctuations in oxygen concentration in exhaust gases, materials with oxygen storage capacity (OSC) (hereinafter sometimes referred to as "OSC materials") are used. Typical OSC materials are oxides containing Ce. In response to recent stricter exhaust gas regulations, the use of OSC materials has been increasing.

[0006] When the amount of Ce in the Rh layer increases, the oxygen storage capacity of the Rh layer improves, but the exhaust gas purification performance of the Rh layer decreases. This is because the oxygen supplied by Ce promotes the oxidation of Rh, making it more difficult to reduce the oxidized Rh when the exhaust gas becomes rich. On the other hand, Y has the effect of promoting the reduction of Rh. Therefore, when the amount of Y in the Rh layer increases, the oxidized Rh is reduced more quickly when the exhaust gas becomes rich, and the exhaust gas purification performance of the Rh layer improves. However, when the amount of Y in the Rh layer increases, the heat resistance of the Rh layer decreases, and the exhaust gas purification performance of the Rh layer decreases.

[0007] In Patent Document 1, the molar ratio of Ce to Y in the Rh layer is adjusted to 0.010 or more and 0.400 or less, from the viewpoint of balancing the effects of Ce (improvement of oxygen storage capacity and promotion of Rh oxidation) and Y (early reduction of oxidized Rh and decrease in heat resistance).

[0008] International Publication No. 2023 / 234147 brochure

[0009] The technology described in Patent Document 1 had room for improvement in terms of the exhaust gas purification performance of the Rh layer (particularly the exhaust gas purification performance of the Rh layer when the amount of Ce in the Rh layer increases).

[0010] Therefore, the object of the present invention is to provide an exhaust gas purification catalyst in which the exhaust gas purification performance of the Rh layer is improved (particularly the exhaust gas purification performance of the Rh layer when the amount of Ce in the Rh layer is increased).

[0011] To solve the above problems, the present invention provides the following exhaust gas purification catalyst and method for manufacturing the same. [1] An exhaust gas purification catalyst comprising a substrate and a catalyst layer provided on the substrate, wherein the catalyst layer comprises Rh, Ce, and metal oxide particles, and Y in the metal oxide particles ２ O ３ The converted content is 50% by mass or more, and the CeO of Ce in the metal oxide particles ２ The material comprises metal oxide particles (hereinafter referred to as "first particles") whose converted content is less than 3% by mass, and the amount of Ce in the catalyst layer per unit volume of the portion of the substrate on which the catalyst layer is provided is CeO ２The converted mass is 0.5 g / L or more and 13 g / L or less, and Y of Y derived from the first particles in the catalyst layer ２ O ３ The ratio of the converted mass of Ce in the catalyst layer to the converted mass of CeO ２ is 0.05 or more and 1.5 or less, and the average particle diameter of the first particles in the catalyst layer is 0.05 μm or more and 1.5 μm or less. The exhaust gas purification catalyst according to [1]. [2] The catalyst layer is metal oxide particles, and the content rate of Ce in the metal oxide particles in terms of CeO ２ is 3% by mass or more, and the content rate of Y in the metal oxide particles in terms of Y ２ O ３ is less than 50% by mass. The exhaust gas purification catalyst according to [1], further comprising the metal oxide particles (hereinafter referred to as "second particles"). [3] The exhaust gas purification catalyst according to [2], wherein the content rate of Ce in the second particles in terms of CeO ２ is 25% by mass or less. [4] The exhaust gas purification catalyst according to [3], wherein the content rate of Ce in the second particles in terms of CeO ２ is 15% by mass or less. [5] The exhaust gas purification catalyst according to any one of [1] to [4], wherein the converted mass of Ce in the catalyst layer per unit volume of the portion of the substrate where the catalyst layer is provided is 8 g / L or less. [6] Y of Y derived from the first particles in the catalyst layer ２ O ３ The ratio of the converted mass to the converted mass of Ce in the catalyst layer ２ ​​[1] to [5] A catalyst for purifying exhaust gas according to any one of the following items, wherein the ratio of the converted mass to the total mass is 0.1 or more and 0.5 or less. [7] A catalyst for purifying exhaust gas according to any one of the following items, wherein the average particle diameter of the first particles in the catalyst layer is 0.5 μm or less. [8] A method for producing the catalyst for purifying exhaust gas according to [1], wherein the method comprises the following steps: (a) preparing a slurry containing a Rh-containing compound and the first particles; (b) coating the slurry onto a substrate to form a precursor layer; and (c) firing the precursor layer to form a catalyst layer, wherein the D95 of the first particles used as raw materials for the slurry is 0.1 μm or more and 10 μm or less, which is the particle size at which the cumulative volume accounts for 95% of the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement. [9] The method according to [8], wherein the slurry prepared in step (a) further comprises the second particles.

[10] CeO ２ The method according to [9], wherein the converted content is 25% by mass or less.

[11] CeO ２ The method according to

[10] , wherein the converted content is 15% by mass or less.

[12] CeO of Ce in the catalyst layer per unit volume of the portion of the substrate in which the catalyst layer is provided ２ The method according to any one of [8] to

[11] , wherein the converted mass is 8 g / L or less.

[13] Y of the first particles in the catalyst layer ２ O ３ The converted mass of CeO in the catalyst layer ２ The method according to any one of [8] to

[12] , wherein the ratio of the converted mass to the mass is 0.1 or more and 0.5 or less.

[14] The method according to any one of [8] to

[13] , wherein the average particle diameter of the first particles in the catalyst layer is 0.5 μm or less.

[0012] According to the present invention, an exhaust gas purification catalyst is provided in which the exhaust gas purification performance of the Rh layer (particularly the exhaust gas purification performance of the Rh layer when the amount of Ce in the Rh layer is increased) is improved.

[0013] Figure 1 is a partial end view showing an exhaust gas purification catalyst according to one embodiment of the present invention arranged in the exhaust path of an internal combustion engine. Figure 2 is an end view of the line A-A in Figure 1. Figure 3 is an enlarged view of the region indicated by the symbol R in Figure 2. Figure 4 is an end view of the line B-B in Figure 1.

[0014] <<Explanation of Terms>> The following terms used in this specification are explained below. Unless otherwise specified, the following explanations apply to the entirety of this specification.

[0015] <Abbreviations> "SEM" stands for scanning electron microscope, "EDX" for energy-dispersive X-ray spectroscopy, "SEM-EDX" for scanning electron microscope-energy-dispersive X-ray analysis, "EPMA" for electron beam microanalyzer, "XRF" for X-ray fluorescence analysis, "WDX" for wavelength-dispersive X-ray analysis, and "ICP-AES" for inductively coupled plasma emission spectroscopy.

[0016] <Metallic Elements> The term "metallic elements" also includes metalloid elements such as Si and B.

[0017] <Rare Earth Elements> The "rare earth elements" include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0018] <Precious Metal Elements> "Precious metal elements" include Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.

[0019] <Oxides> The meaning of "oxides" for metallic elements is as follows: Oxides of rare earth elements other than Ce, Pr, and Tb are sesquioxides (M ２ O ３ (M represents rare earth elements other than Ce, Pr, and Tb), and the oxide of Ce is CeO ２ The oxide of Pr is Pr ６ O １１ The oxide of Tb is Tb ４ O ７ Al oxides are Al ２ O ３ The oxide of Zr is ZrO ２ The oxide of Si is SiO ２ The oxide of B is B ２ O３ Cr oxides are Cr ２ O ３ Mg oxide produces MgO, Ca oxide produces CaO, Sr oxide produces SrO, Ba oxide produces BaO, and Fe oxide produces Fe ３ O ４ Mn oxides are Mn ３ O ４ Ni oxide is NiO, and Ti oxide is TiO ２ The oxide of Zn is ZnO, and the oxide of Sn is SnO ２ It means...

[0020] <Mass of metallic elements in metallic equivalent> "Mass of metallic elements in metallic equivalent" refers to the mass of a metallic element calculated by assuming that the metallic element exists as a metal composed of metallic elements.

[0021] <Mass of metallic elements in terms of oxides> "Mass of metallic elements in terms of oxides" refers to the mass of a metallic element's oxide, calculated by assuming that the metallic element exists as an oxide.

[0022] <Mass of the Catalyst Layer> The "mass of the catalyst layer" refers to the total mass obtained by classifying all metal elements contained in the catalyst layer into noble metal elements and non-noble metal elements, calculating the mass of the noble metal elements in terms of metal equivalent, and then calculating the mass of the non-noble metal elements in terms of oxide equivalent. In other words, the "mass of the catalyst layer" refers to the calculated mass obtained by adding the mass of the noble metal elements contained in the catalyst layer in terms of metal equivalent and the mass of the non-noble metal elements contained in the catalyst layer in terms of oxide equivalent.

[0023] <Content of metal elements in the catalyst layer in terms of metal or oxide> The "content of metal elements in the catalyst layer in terms of metal" is defined by the formula: Content of metal elements in the catalyst layer in terms of metal (mass%) = (mass of metal elements in the catalyst layer in terms of metal) / (mass of the catalyst layer) × 100.

[0024] The "concentration of metal elements in the catalyst layer in terms of oxides" is defined by the following formula: Concentration of metal elements in the catalyst layer in terms of oxides (mass%) = (mass of metal elements in the catalyst layer in terms of oxides) / (mass of the catalyst layer) × 100.

[0025] If information about the raw materials used to form the catalyst layer (e.g., composition, quantity, etc.) is known, the content (mass %) of metal elements in the catalyst layer, either in terms of metal or oxide, can be determined from the raw material information.

[0026] If information on the raw materials used to form the catalyst layer is unknown, the content (mass %) of metal elements in the catalyst layer, either in terms of metal or oxide, can be determined by conventional methods such as SEM-EDX. Specifically, this is as follows:

[0027] Elemental analysis of the catalyst layer is performed using conventional methods such as SEM-EDX to identify the types of constituent elements in the catalyst layer and to determine the molar percentage of each identified metal element. For each of the 10 fields of view of the SEM, the molar percentage of each metal element is determined, and the average value of the molar percentages of each metal element across the 10 fields of view is taken as the molar percentage of each metal element in the catalyst layer.

[0028] The V value of each precious metal element in the catalyst layer can be calculated using the following formula: V value of each precious metal element = (molar percentage of each precious metal element in the catalyst layer) × (molar mass of each precious metal element)

[0029] The W value of each metal element other than the noble metal elements in the catalyst layer can be determined from the following formula: W value of each metal element = (molar percentage of each metal element in the catalyst layer) × (molar mass of the oxide of each metal element)

[0030] The percentage of each precious metal element in the catalyst layer, expressed as metal equivalent (mass%), is calculated using the following formula: Percentage of each precious metal element in the catalyst layer, expressed as metal equivalent (mass%) = (V value of each precious metal element) / {(Sum of V values ​​of all precious metal elements) + (Sum of W values ​​of all non-precious metal elements)} × 100

[0031] The content (mass %) of each metal element other than the noble metal elements in the catalyst layer, in terms of oxides, is calculated using the following formula: Content (mass %) of each metal element other than the noble metal elements in the catalyst layer, in terms of oxides = (W value of each metal element other than the noble metal elements) / {(Sum of V values ​​of all noble metal elements) + (Sum of W values ​​of all metal elements other than the noble metal elements)} × 100

[0032] <Metal Oxide Particles> "Metal oxide particles" refers to particles composed of oxides containing one or more metal elements.

[0033] Examples of particle shapes include spherical, flake-shaped, columnar, needle-shaped, polyhedral, and irregular shapes. "Spherical" includes perfectly spherical and ellipsoidal shapes. "Flake-shaped" includes flaky, thin, and flattened shapes. "Columnar" includes cylindrical, elliptical, and polygonal prism shapes, as well as shapes where parts of cylindrical, elliptical, or polygonal prism shapes are missing.

[0034] <Mass of Metal Oxide Particles> "Mass of metal oxide particles" refers to the total mass of the oxides of the metal elements, calculated by assuming that each metal element in the metal oxide particle exists as an oxide.

[0035] <Oxide-equivalent content of metal elements in metal oxide particles> The "oxide-equivalent content of metal elements in metal oxide particles" is defined by the following formula: Oxide-equivalent content of metal elements in metal oxide particles (mass%) = (mass of metal elements in metal oxide particles in oxide equivalent) / (mass of metal oxide particles) × 100.

[0036] If the composition of metal oxide particles is known, the content (mass %) of the metal element in the metal oxide particles, in terms of oxide, can be determined from the composition of the metal oxide particles.

[0037] If the composition of metal oxide particles is unknown, the content (mass %) of the metal element in the metal oxide particles, converted to oxide equivalent, can be determined by conventional methods such as SEM-EDX. Specifically, this is as follows:

[0038] Elemental analysis of metal oxide particles is performed using conventional methods such as SEM-EDX to identify the types of constituent elements of the metal oxide particles, and the content (mass%) of each identified metal element in terms of oxide is determined.

[0039] <First Particle> The "first particle" is a metal oxide particle, and the Y in the metal oxide particle is Y ２ O ３ The converted content is 50% by mass or more, and Ce in metal oxide particles is CeO ２This refers to metal oxide particles whose converted content is less than 3% by mass. In this specification, the first particle may be referred to as "Y-type oxide particle." Two or more of the characteristics of the first particle described below can be combined.

[0040] The first particle contains Y.

[0041] The first particle may contain Ce and / or an additional element M1.

[0042] The additional element M1 consists of one or more metallic elements other than Y and Ce. For example, the additional element M1 can be selected from rare earth elements other than Y and Ce (e.g., La, Nd, Pr, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0043] Examples of the first particles include yttria particles, modified yttria particles obtained by modifying the surface of yttria particles with Ce or its oxide and / or additional element M1 or its oxide, and composite yttria particles obtained by solid-solving Ce or its oxide and / or additional element M1 or its oxide in yttria particles.

[0044] In the first particle, Y is a solid solution phase (for example, Y ２ O ３ and CEO ２ The solid solution phase, Y ２ O ３ A solid solution phase with an oxide of additional element M1, Y ２ O ３ and CEO ２ It may form a solid solution phase (such as an oxide phase of the additional element M1) or a single phase (for example, Y) which is a crystalline phase or an amorphous phase. ２ O ３ It may form a single phase, or it may form both a solid solution phase and a single phase.

[0045] In the first particle, Ce is in a solid solution phase (e.g., CeO ２ and Y ２ O ３ Solid solution phase with CeO ２ A solid solution phase with an oxide of additional element M1, CeO ２and Y ２ O ３ It may form a solid solution phase with an oxide of the additional element M1, or it may form a single phase that is a crystalline or amorphous phase (for example, CeO ２ It may form a single phase, or it may form both a solid solution phase and a single phase.

[0046] In the first particle, the additional element M1 is in a solid solution phase (for example, an oxide of the additional element M1 and Y ２ O ３ The solid solution phase, oxide of additional element M1 and CeO ２ The solid solution phase, oxide of additional element M1 and Y ２ O ３ and CEO ２ It may form a solid solution phase (such as a solid solution phase), or a single phase that is a crystalline or amorphous phase (for example, a single oxide phase of the additional element M1), or it may form both a solid solution phase and a single phase.

[0047] From the perspective of improving the action of Y in the first particle (early reduction of oxidized Rh), the Y in the first particle ２ O ３ The converted content is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more. The upper limit may be 100% by mass or less. The upper limit may be, for example, 99.999% by mass or less, 99.99% by mass or less, or 99.9% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0048] From the viewpoint of suppressing the action of Ce in the first particle (promotion of Rh oxidation), CeO ２ The converted content is less than 3% by mass, preferably 2% by mass or less, and more preferably 1% by mass or less. The lower limit may be 0% by mass or greater than 0% by mass. The lower limit may be, for example, 0.001% by mass or more, 0.01% by mass or more, or 0.1% by mass or more. Each of the above lower limits may be combined with any of the above upper limits.

[0049] The oxide content of the additional element M1 in the first particle can be adjusted as appropriate, taking into consideration the content of other components, the purpose of adding the additional element M1 (for example, to improve heat resistance), etc. In one embodiment, the oxide content of the additional element M1 in the first particle is from 100% by mass to Y in the first particle. ２ O ３ Converted content and CeO of Ce in the first particle ２ This value is obtained by subtracting the converted content. "Oxide-equivalent content of additional element M1 in the first particle" means the total oxide-equivalent content of the two or more metallic elements if the additional element M1 is composed of two or more metallic elements.

[0050] <Second Particle> The "second particle" is a metal oxide particle, and the CeO of Ce in the metal oxide particle ２ The converted content is 3% by mass or more, and the Y content in the metal oxide particles is Y ２ O ３ This refers to metal oxide particles whose converted content is less than 50% by mass. Two or more of the characteristics of the second type of particle described below can be combined.

[0051] The second particle contains Ce.

[0052] The second particle may contain Y and / or additional element M2.

[0053] The additional element M2 consists of one or more metallic elements other than Ce and Y. For example, the additional element M2 can be selected from rare earth elements other than Ce and Y (e.g., La, Nd, Pr, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0054] Examples of the second particles include ceria particles, modified ceria particles obtained by modifying the surface of ceria particles with Y or its oxide and / or an additional element M2 or its oxide, and composite ceria particles obtained by solid-solving Y or its oxide and / or an additional element M2 or its oxide in ceria particles.

[0055] In the second particle, Ce may form a solid solution phase (e.g., a solid solution phase with CeO ２ and Y ２ O ３ a solid solution phase with CeO ２ a solid solution phase with an oxide of additional element M2, a solid solution phase with CeO ２ and Y ２ O ３ a solid solution phase with an oxide of additional element M2, etc.), or may form a single phase in a crystalline phase or an amorphous phase (e.g., a CeO ２ single phase), or may form both a solid solution phase and a single phase.

[0056] In the second particle, Y may form a solid solution phase (e.g., a solid solution phase with Y ２ O ３ and CeO ２ a solid solution phase with Y ２ O ３ a solid solution phase with an oxide of additional element M2, a solid solution phase with Y ２ O ３ and CeO ２ a solid solution phase with an oxide of additional element M2, etc.), or may form a single phase in a crystalline phase or an amorphous phase (e.g., a Y ２ O ３ single phase), or may form both a solid solution phase and a single phase.

[0057] In the second particle, the additional element M2 may form a solid solution phase (e.g., a solid solution phase with an oxide of additional element M2 and CeO ２ a solid solution phase with an oxide of additional element M2 and Y ２ O ３ a solid solution phase with an oxide of additional element M2 and CeO ２ and Y ２ O ３ a solid solution phase, etc.), or may form a single phase in a crystalline phase or an amorphous phase (e.g., an oxide single phase of additional element M2), or may form both a solid solution phase and a single phase.

[0058] From the viewpoint of improving the oxygen storage capacity of the second particle, CeO of Ce in the second particle ２The converted content is 3% by mass or more, preferably 4% by mass or more, and more preferably 5% by mass or more. The upper limit may be 100% by mass or less. The upper limit may be, for example, 95% by mass or less, 90% by mass or less, or 85% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0059] From the viewpoint of suppressing the effect of Y in the second particle (decrease in heat resistance), ２ O ３ The converted content is less than 50% by mass, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. The lower limit may be 0% by mass or greater than 0% by mass. The lower limit may be, for example, 0.001% by mass or more, 0.01% by mass or more, or 0.1% by mass or more. Each of the above lower limits may be combined with any of the above upper limits.

[0060] The oxide content of the additional element M2 in the second particle can be adjusted as appropriate, taking into consideration the content of other components, the purpose of adding the additional element M2 (for example, improving heat resistance), etc. In one embodiment, the oxide content of the additional element M2 in the second particle is from 100% by mass to the CeO content of Ce in the second particle. ２ The converted content and the Y content in the second particle ２ O ３ This value is obtained by subtracting the converted content. "Oxide-equivalent content of additional element M2 in the second particle" means the total oxide-equivalent content of the two or more metallic elements if the additional element M2 is composed of two or more metallic elements.

[0061] In one embodiment, the second particle contains Zr. That is, the second particle is a Ce-Zr composite oxide particle. The above description of the second particle also applies to Ce-Zr composite oxide particles unless otherwise specified. Two or more of the features of the Ce-Zr composite oxide particles described below can be combined.

[0062] In another embodiment, the second particle comprises Zr and Al. That is, the second particle is a Ce-Zr-Al composite oxide particle. The above description of the second particle also applies to the Ce-Zr-Al composite oxide particle unless otherwise specified. Two or more of the features of the Ce-Zr-Al composite oxide particle described below can be combined.

[0063] From the viewpoint of improving the oxygen storage capacity of Ce-Zr composite oxide particles, CeO ２ The converted content is preferably 4% by mass or more, more preferably 5% by mass or more. The upper limit can be adjusted as appropriate considering heat resistance, structural stability, the content of other components, etc. The upper limit is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0064] From the viewpoint of improving the heat resistance of Ce-Zr composite oxide particles, Zr in Ce-Zr composite oxide particles is ZrO ２ The converted content is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more. The upper limit can be adjusted as appropriate considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0065] From the viewpoint of improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxide particles, the CeO of Ce in Ce-Zr composite oxide particles ２ Conversion of content and ZrO ２ The total converted content is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The upper limit may be 100% by mass or less. The upper limit may be, for example, 97% by mass or less, 96% by mass or less, or 95% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0066] From the viewpoint of improving the heat resistance of Ce-Zr composite oxide particles, it is preferable that the Ce-Zr composite oxide particles contain one or more rare earth elements other than Ce and Y. The rare earth elements are preferably selected from La, Nd, Pr, Sm, Eu, and Gd.

[0067] From the viewpoint of improving the heat resistance of Ce-Zr composite oxide particles, the oxide content of rare earth elements other than Ce and Y in the Ce-Zr composite oxide particles is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. The upper limit can be appropriately adjusted considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. The lower limits above may be combined with any of the upper limits above. "Oxide content of rare earth elements other than Ce and Y in the Ce-Zr composite oxide particles" means the total oxide content of the two or more rare earth elements other than Ce and Y when the Ce-Zr composite oxide particles contain two or more rare earth elements other than Ce and Y.

[0068] From the viewpoint of improving the heat resistance of Ce-Zr composite oxide particles, ２ O ３ The sum of the converted content and the oxide-converted content of rare earth elements other than Ce and Y is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. The upper limit can be adjusted as appropriate considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0069] From the viewpoint of improving the oxygen storage capacity of Ce-Zr-Al composite oxide particles, ２The converted content is preferably 4% by mass or more, more preferably 5% by mass or more. The upper limit can be adjusted as appropriate considering heat resistance, structural stability, the content of other components, etc. The upper limit is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0070] From the viewpoint of improving the heat resistance of Ce-Zr-Al composite oxide particles, Zr in Ce-Zr-Al composite oxide particles is ZrO ２ The converted content is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The upper limit can be adjusted as appropriate considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0071] From the viewpoint of improving the heat resistance of Ce-Zr-Al composite oxide particles, the Al in Ce-Zr-Al composite oxide particles ２ O ３ The converted content is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more. The upper limit can be adjusted as appropriate considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0072] From the viewpoint of improving the oxygen storage capacity and heat resistance of Ce-Zr-Al composite oxide particles, CeO in Ce-Zr-Al composite oxide particles ２ Conversion of content, Zr to ZrO ２ Conversion of content and Al ２ O ３The total converted content is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The upper limit may be 100% by mass or less. The upper limit may be, for example, 97% by mass or less, 96% by mass or less, or 95% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0073] From the viewpoint of improving the heat resistance of Ce-Zr-Al composite oxide particles, it is preferable that the Ce-Zr-Al composite oxide particles contain one or more rare earth elements other than Ce and Y. The rare earth elements are preferably selected from La, Nd, Pr, Sm, Eu, and Gd.

[0074] From the viewpoint of improving the heat resistance of Ce-Zr-Al composite oxide particles, the oxide content of rare earth elements other than Ce and Y in the Ce-Zr-Al composite oxide particles is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. The upper limit can be appropriately adjusted considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. The lower limits above may be combined with any of the upper limits above. "Oxide content of rare earth elements other than Ce and Y in the Ce-Zr-Al composite oxide particles" means the total oxide content of the two or more rare earth elements other than Ce and Y when the Ce-Zr-Al composite oxide particles contain two or more rare earth elements other than Ce and Y.

[0075] From the viewpoint of improving the heat resistance of Ce-Zr-Al composite oxide particles, Y in Ce-Zr-Al composite oxide particles ２ O ３The sum of the converted content and the oxide-converted content of rare earth elements other than Ce and Y is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. The upper limit can be adjusted as appropriate considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0076] <Third Particle> The "third particle" is a metal oxide particle, and the Al in the metal oxide particle is Al ２ O ３ The converted content is 50% by mass or more, and Ce in metal oxide particles is CeO ２ This refers to metal oxide particles whose converted content is less than 3% by mass. Two or more of the characteristics of the third type of particle described below can be combined.

[0077] The third particle contains Al.

[0078] The third particle may contain Ce and / or an additional element M3.

[0079] The additional element M3 consists of one or more metallic elements other than Al and Ce. The additional element M3 can be selected from, for example, rare earth elements other than Ce (e.g., Y, La, Nd, Pr, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0080] Examples of the third particle include alumina particles, modified alumina particles obtained by modifying the surface of alumina particles with Ce or its oxide and / or an additional element M3 or its oxide, and composite alumina particles obtained by solid-solving Ce or its oxide and / or an additional element M3 or its oxide in alumina particles.

[0081] In the third particle, Al is in a solid solution phase (for example, Al ２ O ３ and CEO ２ Solid solution phase with Al ２ O ３Al ２ O ３ and CEO ２ It may form a solid solution phase (such as an oxide phase of the additional element M3) or a single phase that is a crystalline or amorphous phase (for example, Al ２ O ３ It may form a single phase, or it may form both a solid solution phase and a single phase.

[0082] In the third particle, Ce is in a solid solution phase (e.g., CeO ２ and Al ２ O ３ Solid solution phase with CeO ２ A solid solution phase with an oxide of the additional element M3, CeO ２ and Al ２ O ３ It may form a solid solution phase with an oxide of the additional element M3, or it may form a single phase that is a crystalline or amorphous phase (for example, CeO ２ It may form a single phase, or it may form both a solid solution phase and a single phase.

[0083] In the third particle, the additional element M3 is in a solid solution phase (for example, an oxide of the additional element M3 and Al ２ O ３ The solid solution phase, oxide of additional element M3 and CeO ２ The solid solution phase, the oxide of additional element M3 and Al ２ O ３ and CEO ２ It may form a solid solution phase (such as a solid solution phase), or a single phase that is a crystalline or amorphous phase (for example, a single oxide phase of the additional element M3), or it may form both a solid solution phase and a single phase.

[0084] From the viewpoint of improving the heat resistance of the third particle, the Al in the third particle ２ O ３The converted content is 50% by mass or more, preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. The upper limit may be 100% by mass or less. The upper limit may be, for example, 99.999% by mass or less, 99.99% by mass or less, or 99.9% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0085] From the perspective of suppressing the action of Ce in the third particle (promotion of Rh oxidation), CeO ２ The converted content is less than 3% by mass, preferably 2% by mass or less, and more preferably 1% by mass or less. The lower limit may be 0% by mass or greater than 0% by mass. The lower limit may be, for example, 0.001% by mass or more, 0.01% by mass or more, or 0.1% by mass or more. Each of the above lower limits may be combined with any of the above upper limits.

[0086] The oxide content of the additional element M3 in the third particle can be adjusted as appropriate, taking into consideration the content of other components, the purpose of adding the additional element M3 (for example, to improve heat resistance), etc. In one embodiment, the oxide content of the additional element M3 in the third particle is from 100% by mass to the Al content of the third particle. ２ O ３ Converted content and CeO of Ce in the third particle ２ This value is obtained by subtracting the converted content. "Oxide-equivalent content of additional element M3 in the third particle" means the total oxide-equivalent content of the two or more metallic elements if the additional element M3 is composed of two or more metallic elements.

[0087] From the viewpoint of improving the heat resistance of the third particle, it is preferable that the third particle contains one or more rare earth elements other than Ce. The rare earth elements are preferably selected from La, Nd, Pr, Y, Sm, Eu, and Gd.

[0088] From the viewpoint of improving the heat resistance of the third particle, the content of rare earth elements other than Ce in the third particle, in terms of oxides, is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. The upper limit can be appropriately adjusted considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. The lower limits above may be combined with any of the upper limits above. "Content of rare earth elements other than Ce in the third particle, in terms of oxides" means the total content of the two or more rare earth elements other than Ce in terms of oxides when the third particle contains two or more of those rare earth elements.

[0089] <<Exhaust Gas Purification Catalyst>> Below, an exhaust gas purification catalyst 1 (hereinafter referred to as "catalyst 1") according to one embodiment of the present invention will be described based on Figures 1 to 4. Two or more of the features of catalyst 1 described below can be combined.

[0090] As shown in Figure 1, the catalyst 1 is located in the exhaust passage within the exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine. Exhaust gas discharged from the internal combustion engine flows through the exhaust passage within the exhaust pipe P from one end to the other and is purified by the catalyst 1 installed in the exhaust pipe P. In the drawings, the direction of exhaust gas flow is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas inlet side" or "upstream side," and the downstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas outlet side" or "downstream side."

[0091] Other exhaust gas purification catalysts may be placed in the exhaust passage within the exhaust pipe P, upstream and / or downstream of catalyst 1.

[0092] As shown in Figures 2 to 4, the exhaust gas purification catalyst 1 comprises a base material 10 and a first catalyst layer 20 provided on the base material 10.

[0093] Catalyst 1 may have catalyst layers other than the first catalyst layer 20 at one or more positions selected from below, above, downstream, and upstream of the first catalyst layer 20. The phrase "first catalyst layer 20 provided on the substrate 10" includes embodiments in which the first catalyst layer 20 is directly provided on the substrate 10, and embodiments in which the first catalyst layer 20 is provided on the substrate 10 via other layers.

[0094] In this embodiment, the catalyst 1 further comprises a second catalyst layer 30 provided on the substrate 10, and the first catalyst layer 20 is provided on the substrate 10 via the second catalyst layer 30. The second catalyst layer 30 is a layer provided as needed, and embodiments in which the second catalyst layer 30 is omitted are also included in the present invention. However, from the viewpoint of improving exhaust gas purification performance, it is preferable that the catalyst 1 comprises the second catalyst layer 30.

[0095] Catalyst 1 has a first catalyst layer 20 containing Rh, Ce and first particles, and the CeO content of Ce in the first catalyst layer 20 per unit volume of the portion of the substrate 10 on which the first catalyst layer 20 is provided ２ The converted mass is 0.5 g / L or more and 13 g / L or less, and Y originates from the first particle in the first catalyst layer 20. ２ O ３ The converted mass of CeO in the first catalyst layer 20 ２ The ratio of the converted mass to the total mass is 0.05 or more and 1.5 or less, and the average particle diameter of the first particles in the first catalyst layer 20 is 0.05 μm or more and 1.5 μm or less.

[0096] In catalyst 1, from the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, the amount of Ce in the first catalyst layer 20 per unit volume of the portion of the substrate 10 on which the first catalyst layer 20 is provided is reduced. ２The converted mass (hereinafter sometimes referred to as "amount of Ce in the first catalyst layer 20") is adjusted to 0.5 g / L or higher. When the amount of Ce in the first catalyst layer 20 increases, the oxygen storage capacity of the first catalyst layer 20 improves, but the exhaust gas purification performance of the first catalyst layer 20 decreases. This is because the oxidation of Rh is more easily promoted by the oxygen supplied from Ce, and when the exhaust gas becomes rich, the oxidized Rh is less likely to be reduced. However, in catalyst 1, the average particle size of the first particles in the first catalyst layer 20 is between 0.05 μm and 1.5 μm, so high dispersion of the first particles in the first catalyst layer 20, that is, an increase in the proportion of first particles adjacent to Rh, is achieved. When first particles are adjacent to Rh, the action of Y in the first particles (early reduction of oxidized Rh) is more easily exerted. Therefore, in catalyst 1, the action of Y in the first particles (early reduction of oxidized Rh) improves the exhaust gas purification performance of the first catalyst layer 20 (especially the exhaust gas purification performance of the first catalyst layer 20 when the amount of Ce in the first catalyst layer 20 increases). However, if the average particle diameter of the first particles is less than 0.05 μm, the action of Y in the first particles (early reduction of oxidized Rh) is not fully exerted.

[0097] In order to improve the exhaust gas purification performance of the first catalyst layer 20 through the action of Y in the first particle (early reduction of oxidized Rh), it is necessary that the amount of Y originating from the first particle in the first catalyst layer 20 matches the amount of Ce in the first catalyst layer 20. Therefore, in catalyst 1, from the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 through the action of Y in the first particle (early reduction of oxidized Rh), the amount of Y originating from the first particle in the first catalyst layer 20 is equal to the amount of Ce in the first catalyst layer 20. ２ O ３ The converted mass of CeO in the first catalyst layer 20 ２ The ratio to the converted mass has been adjusted to 0.05 or higher.

[0098] If the amount of Ce in the first catalyst layer 20 is excessive, the exhaust gas purification performance of the first catalyst layer 20 will decrease significantly due to the promotion of Rh oxidation, making it difficult to improve the exhaust gas purification performance of the first catalyst layer 20 through the action of Y (early reduction of oxidized Rh). Furthermore, if the amount of Ce in the first catalyst layer 20 is excessive, the heat resistance of the first catalyst layer 20 will decrease, and the exhaust gas purification performance of the first catalyst layer 20 will decrease. For this reason, in catalyst 1, from the viewpoint of preventing the decrease in exhaust gas purification performance of the first catalyst layer 20 due to the promotion of Rh oxidation and the decrease in exhaust gas purification performance of the first catalyst layer 20 due to the decrease in heat resistance, the amount of Ce in the first catalyst layer 20 per unit volume of the portion of the substrate 10 on which the first catalyst layer 20 is provided is set to CeO ２ The converted mass has been adjusted to 13 g / L or less.

[0099] If the amount of Y derived from the first particles in the first catalyst layer 20 is excessive relative to the amount of Ce in the first catalyst layer 20, the heat resistance of the first catalyst layer 20 will decrease, and the exhaust gas purification performance of the first catalyst layer 20 will decrease. Therefore, in catalyst 1, from the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the amount of Y derived from the first particles in the first catalyst layer 20 is excessive. ２ O ３ The converted mass of CeO in the first catalyst layer 20 ２ The ratio of the converted mass to the mass has been adjusted to 1.5 or less.

[0100] <Base Material> The base material 10 will be described below. Two or more of the features of the base material 10 described below can be combined.

[0101] The material constituting the base material 10 can be appropriately selected from known materials. Examples of materials constituting the base material 10 include ceramic materials and metallic materials, but ceramic materials are preferred. Examples of ceramic materials include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of metallic materials include alloys such as stainless steel.

[0102] As shown in Figures 2 to 4, the base material 10 has a cylindrical portion 11, a partition wall portion 12 provided inside the cylindrical portion 11, and cells 13 separated by the partition wall portion 12. The base material 10 is preferably a honeycomb structure.

[0103] As shown in Figures 2 and 3, the cylindrical portion 11 defines the outer shape of the base material 10, and the axial direction of the cylindrical portion 11 coincides with the axial direction of the base material 10. The shape of the cylindrical portion 11 is cylindrical, but it may also be an elliptical cylinder, a polygonal cylinder, or other shapes.

[0104] As shown in Figures 2 and 3, the partition wall portion 12 is provided inside the cylindrical portion 11. As shown in Figures 2 to 4, a partition wall portion 12 exists between adjacent cells 13, and adjacent cells 13 are separated by the partition wall portion 12. The thickness of the partition wall portion 12 is, for example, 20 μm or more and 1500 μm or less. The partition wall portion 12 may have a porous structure through which exhaust gas can pass.

[0105] As shown in Figure 4, cell 13 extends in the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0106] As shown in Figure 4, both the exhaust gas inlet and exhaust gas outlet ends of cell 13 are open. Therefore, exhaust gas flowing in from the exhaust gas inlet end (opening) of cell 13 flows out from the exhaust gas outlet end (opening) of cell 13. This type of configuration is called a flow-through type.

[0107] As shown in Figures 2 and 3, the plan view shape of the exhaust gas inlet end (opening) of cell 13 is a rectangle, but it may be a hexagon, octagon, or other shape. The same applies to the plan view shape of the exhaust gas outlet end (opening) of cell 13.

[0108] The cell density per square inch of the substrate 10 is, for example, 100 cells or more and 1000 cells or less. The cell density per square inch of the substrate 10 refers to the total number of cells 13 per square inch in a cross-section obtained by cutting the substrate 10 with a plane perpendicular to the exhaust gas flow direction X.

[0109] The volume of the base material 10 is, for example, 0.1 L or more and 20 L or less. The volume of the base material 10 refers to the apparent volume of the base material 10. For example, if the base material 10 is cylindrical, the outer diameter of the base material 10 is 2r and the length of the base material 10 is L. １０ Therefore, the volume of the base material 10 is given by the formula: Volume of base material 10 = π × r ２ It is expressed as ×L. In this specification, "length" means the axial dimension of the base material 10.

[0110] The base material 10 may be provided with a first sealing portion that seals the exhaust gas outlet end of some of the cells 13, and a second sealing portion that seals the exhaust gas inlet end of the remaining cells 13. As a result, some of the cells 13 become inlet-side cells with an open end on the exhaust gas inlet side and a closed end on the exhaust gas outlet side with the first sealing portion, while the remaining cells 13 become outlet-side cells with a closed end on the exhaust gas inlet side with the second sealing portion and an open end on the exhaust gas outlet side. Multiple (for example, four) outlet-side cells are arranged around one inlet-side cell, and the inlet-side cell and the outlet-side cells arranged around it are separated by a porous partition 12. Exhaust gas flowing in from the exhaust gas inlet end (opening) of the inlet-side cell passes through the porous partition 12 and flows out from the exhaust gas outlet end (opening) of the outlet-side cell. This type of configuration is called a wall-flow type. As exhaust gas flows in from the exhaust gas inlet end (opening) of the inlet-side cell and passes through the porous partition wall 12, particulate matter (PM) in the exhaust gas is collected in the pores of the partition wall 12. Therefore, when the substrate 10 is of the wall-flow type, the catalyst 1 is useful as a particulate filter for gasoline engines or a particulate filter for diesel engines.

[0111] <First Catalyst Layer> The first catalyst layer 20 will be described below. Two or more of the features of the first catalyst layer 20 described below can be combined.

[0112] As shown in Figures 3 and 4, the first catalyst layer 20 is provided above the second catalyst layer 30.

[0113] The statement "The first catalyst layer 20 is provided on the upper side of the second catalyst layer 30" means that part or all of the first catalyst layer 20 is located on the main surface of the second catalyst layer 30 that is opposite to the main surface on the partition wall portion 12 side. "Main surface of the second catalyst layer 30" means the outer surface of the second catalyst layer 30 that extends in the exhaust gas flow direction X. The first catalyst layer 20 may be provided so as to cover a part of the main surface of the second catalyst layer 30, or it may be provided so as to cover the entire main surface of the second catalyst layer 30. The first catalyst layer 20 may be provided directly on the main surface of the second catalyst layer 30, or it may be provided via another layer, but it is usually provided directly on the main surface of the second catalyst layer 30. The "first catalyst layer 20 provided on the substrate 10" includes embodiments in which the first catalyst layer 20 is directly provided on the main surface of the second catalyst layer 30, and embodiments in which the first catalyst layer 20 is provided on the main surface of the second catalyst layer 30 via another layer.

[0114] If the second catalyst layer 30 is omitted, the first catalyst layer 20 is provided on the cell 13 side surface of the partition wall 12. The "cell 13 side surface of the partition wall 12" means the outer surface of the partition wall 12 that extends in the exhaust gas flow direction X and is in contact with the cell 13. If the second catalyst layer 30 is omitted, the first catalyst layer 20 may be provided directly on the cell 13 side surface of the partition wall 12 or via another layer, but is usually provided directly on the cell 13 side surface of the partition wall 12. The "first catalyst layer 20 provided on the base material 10" includes embodiments in which the first catalyst layer 20 is provided directly on the cell 13 side surface of the partition wall 12, and embodiments in which the first catalyst layer 20 is provided on the cell 13 side surface of the partition wall 12 via another layer.

[0115] When the first catalyst layer 20 is provided directly on the cell 13 side surface of the partition wall 12, the first catalyst layer 20 may consist of a portion that rises from the cell 13 side surface of the partition wall 12 toward the cell 13 (hereinafter referred to as the "raised portion"), or it may consist of a portion that exists inside the partition wall 12 (hereinafter referred to as the "internal portion"), or it may have both a raised portion and an internal portion. The "first catalyst layer 20 provided on the substrate 10" includes embodiments in which the first catalyst layer 20 is composed of a raised portion, embodiments in which the first catalyst layer 20 is composed of an internal portion, and embodiments in which the first catalyst layer 20 has both a raised portion and an internal portion.

[0116] As shown in Figure 4, the first catalyst layer 20 extends along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12 to the exhaust gas outlet end of the partition wall 12. The first catalyst layer 20 may extend along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12 so as not to reach the exhaust gas outlet end of the partition wall 12, or it may extend along the direction opposite to the exhaust gas flow direction X from the exhaust gas outlet end of the partition wall 12 so as not to reach the exhaust gas inlet end of the partition wall 12.

[0117] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass of the first catalyst layer 20 per unit volume of the portion of the base material 10 in which the first catalyst layer 20 is provided (hereinafter referred to as "WC amount of the first catalyst layer 20") is preferably 30 g / L or more and 120 g / L or less, more preferably 40 g / L or more and 110 g / L or less, and even more preferably 50 g / L or more and 100 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0118] The amount of WC in the first catalyst layer 20 is given by the formula: (mass of the first catalyst layer 20) / (volume of the substrate 10) × (length L of the first catalyst layer 20) ２０ / Length L of base material 10 １０ It can be obtained from ).

[0119] Length L of the first catalyst layer 20 ２０ An example of the measurement method is as follows:

[0120] The catalyst 1 extends in the axial direction of the substrate 10, and the length L of the substrate 10 is... １０A sample having the same length as the first catalyst layer 20 is cut out. The sample is, for example, cylindrical with a diameter of 25.4 mm. Note that the diameter of the sample can be changed as needed. The sample is cut at 5 mm intervals using a plane perpendicular to the axial direction of the substrate 10, and the first cut piece, second cut piece, ..., nth cut piece are obtained sequentially from the exhaust gas inlet end of the sample. The length of each cut piece is 5 mm. The composition of the cut pieces is analyzed using XRF (e.g., EDX, WDX, etc.), ICP-AES, SEM-EDX, etc., and based on the composition of the cut pieces, it is confirmed whether or not the cut pieces contain a part of the first catalyst layer 20.

[0121] For cut pieces that clearly contain a portion of the first catalyst layer 20, compositional analysis is not necessarily required. For example, the cut surface can be observed using a SEM, EPMA, etc., to confirm whether or not the cut piece contains a portion of the first catalyst layer 20. When observing the cut surface, elemental mapping of the cut surface may also be performed.

[0122] After confirming whether the cut piece contains a portion of the first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is determined based on the following formula: Length of the first catalyst layer 20 contained in the sample = 5 mm × (Number of cut pieces containing a portion of the first catalyst layer 20)

[0123] For example, if the first to kth sections contain a portion of the first catalyst layer 20, but the (k+1) to nth sections do not, the total length of the first catalyst layer 20 contained in the sample is (5 × k) mm.

[0124] An example of a more detailed method for measuring the length of the first catalyst layer 20 contained in a sample is as follows: The kth cut (i.e., the cut obtained from the exhaust gas outlet side of the sample, among the cuts containing a portion of the first catalyst layer 20) is cut in the axial direction of the substrate 10, and the length of the portion of the first catalyst layer 20 present on the cut surface is measured by observing it using an SEM, EPMA, etc. Then, the length of the first catalyst layer 20 contained in the sample is determined based on the following formula: Length of the first catalyst layer 20 contained in the sample = (5 mm × (k - 1)) + (Length of the portion of the first catalyst layer 20 contained in the kth cut)

[0125] The length of the first catalyst layer 20 contained in one sample is defined as the length L of the first catalyst layer 20. ２０ Alternatively, the length L of the first catalyst layer 20 may be adopted as the average value of the lengths of the first catalyst layer 20 contained in multiple samples. ２０ It may be adopted as such, but the latter is preferred. In one embodiment, the length of the first catalyst layer 20 contained in each of the 8 to 16 samples arbitrarily cut from the catalyst 1 is measured, and the average value of these measurements is taken as the length L of the first catalyst layer 20. ２０ Let's assume that.

[0126] The first catalyst layer 20 contains Rh as a catalytically active component.

[0127] Rh is included in the first catalyst layer 20 in the form of a catalytically active component containing Rh, such as metallic Rh, an alloy containing Rh, or a compound containing Rh (e.g., an oxide of Rh). The catalytically active component containing Rh is, for example, in particulate form.

[0128] From the viewpoint of improving the exhaust gas purification performance (especially NOx purification performance) of the first catalyst layer 20, the Rh content in the first catalyst layer 20 in terms of metal is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the first catalyst layer 20. The upper limit can be adjusted as appropriate, taking into consideration the balance between exhaust gas purification performance and cost. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0129] The first catalyst layer 20 may contain one or more noble metal elements other than Rh as catalytically active components. The noble metal elements other than Rh can be selected from, for example, Au, Ag, Pt, Pd, Ir, Ru, Os, etc. The noble metal elements other than Rh are included in the first catalyst layer 20 in a form that can function as a catalytically active component, such as a metal, an alloy containing the noble metal element, or a compound containing the noble metal element (for example, an oxide of the noble metal element). The catalytically active component containing the noble metal element other than Rh may be, for example, particulate.

[0130] If the first catalyst layer 20 contains Rh and other precious metal elements, the Rh and other precious metal elements may form an alloy, potentially reducing the number of Rh active sites involved in exhaust gas purification performance. Therefore, it is preferable that the first catalyst layer 20 substantially does not contain any precious metal elements other than Rh.

[0131] "The first catalyst layer 20 substantially does not contain noble metal elements other than Rh" means that the content of noble metal elements other than Rh in the first catalyst layer 20, in terms of metal, is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less, based on the mass of the first catalyst layer 20. The lower limit is 0% by mass. "The content of noble metal elements other than Rh in the first catalyst layer 20, in terms of metal," means the total content of those two or more noble metal elements in terms of metal, if the first catalyst layer 20 contains two or more noble metal elements other than Rh.

[0132] The first catalyst layer 20 contains the first particle.

[0133] From the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 by the action of Y in the first particles (early reduction of oxidized Rh), the average particle diameter of the first particles in the first catalyst layer 20 is 0.05 μm or more and 1.5 μm or less, preferably 0.1 μm or more and 1.0 μm or less, and more preferably 0.2 μm or more and 0.5 μm or less. The above lower limits may be combined with any of the above upper limits.

[0134] The method for measuring the average particle size of the first particles in the first catalyst layer 20 is as follows: Elemental analysis of the first catalyst layer 20 is performed using a conventional method such as SEM-EDX to identify the constituent elements of each metal oxide particle contained in the first catalyst layer 20, and the content (mass%) of each identified metal element in terms of oxide is determined to identify the first particle. The directional diameter (Ferret diameter) of 50 first particles arbitrarily selected from the SEM field of view is measured, and the average value is taken as the average particle size of the first particle.

[0135] From the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 by the action of Y in the first particles (early reduction of oxidized Rh), the amount of Y originating from the first particles in the first catalyst layer 20 per unit volume of the portion of the substrate 10 on which the first catalyst layer 20 is provided is ２ O ３ The converted mass is preferably 0.1 g / L or more, more preferably 0.3 g / L or more, and even more preferably 0.5 g / L or more. From the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the Y of Y derived from the first particles in the first catalyst layer 20 per unit volume of the portion of the base material 10 on which the first catalyst layer 20 is provided. ２ O ３ The converted mass is preferably 10 g / L or less, more preferably 4 g / L or less, even more preferably 2 g / L or less, and even more preferably 1 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0136] Y of the first particles in the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is provided. ２ O ３ The converted mass is calculated using the formula: (mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is provided) × {(content of the first particles in the first catalyst layer 20) / 100} × {(Y of Y in the first particles) ２ O ３ It can be calculated from {converted content) / 100}.

[0137] From the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 by the action of Y in the first particles (early reduction of oxidized Rh), the content of the first particles in the first catalyst layer 20 is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.3% by mass or more and 4% by mass or less, and even more preferably 0.5% by mass or more and 3% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0138] The content of the first particles in the first catalyst layer 20 is defined by the formula: Content of the first particles in the first catalyst layer 20 = (Mass of the first particles in the first catalyst layer 20) / (Mass of the first catalyst layer 20) × 100.

[0139] If information about the raw materials used to form the first catalyst layer 20 (e.g., composition, quantity, etc.) is known, the content of the first particles in the first catalyst layer 20 can be determined from the information about the raw materials used to form the first catalyst layer 20.

[0140] If information on the raw materials used to form the first catalyst layer 20 is unknown, the content of the first particles in the first catalyst layer 20 can be determined by conventional methods such as SEM-EDX. Specifically, it is as follows.

[0141] (1) Elemental analysis is performed on the sample obtained from the first catalyst layer 20 using a standard method such as SEM-EDX to identify the types of constituent elements in the entire sample and to determine the content (mass%) of each identified metal element in terms of oxides. (2) Elemental mapping is performed on the sample obtained from the first catalyst layer 20 using a standard method such as SEM-EDX to identify the types of particles contained in the sample (e.g., first particles, other metal oxide particles, etc.). (3) For each type of particle, several (e.g., 50) arbitrarily selected particles are subjected to elemental analysis using SEM-EDX to identify the types of constituent elements in the particles and to determine the content (mass%) of each identified metal element in terms of oxides. The average value of the content (mass%) of each metal element in terms of oxides for each type of particle is calculated and this is taken as the content (mass%) of each metal element in terms of oxides for each type of particle. (4) The content of each type of particle in the sample is determined by creating and solving an equation that expresses the relationship between the content of each metal element in the sample on an oxide basis (mass%), the content of each type of particle in each type of particle on an oxide basis (mass%), and the content of each type of particle in the sample (mass%), and this is taken as the content of each type of particle in the first catalyst layer 20 (mass%).

[0142] From the perspective of improving the exhaust gas purification performance of the first catalyst layer 20 by the action of Y in the first particles (early reduction of oxidized Rh), ２ O ３ Of the converted mass, Y originates from the first particle. ２ O ３The proportion of the converted mass is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 90% by mass or more. The upper limit may be 100% by mass or less than 100% by mass.

[0143] The first catalyst layer 20 contains Ce.

[0144] From the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, the amount of Ce in the first catalyst layer 20 per unit volume of the portion of the substrate 10 on which the first catalyst layer 20 is provided is reduced. ２ The converted mass is 0.5 g / L or more, preferably 1 g / L or more, more preferably 2 g / L or more, even more preferably 3 g / L or more, even more preferably 4 g / L or more, even more preferably 4.5 g / L or more, and even more preferably 5 g / L or more. From the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to the promotion of Rh oxidation and a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the CeO of Ce in the first catalyst layer 20 per unit volume of the portion of the base material 10 on which the first catalyst layer 20 is provided ２ The converted mass is 13 g / L or less, preferably 12 g / L or less, more preferably 10 g / L or less, and even more preferably 8 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0145] CeO in the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is provided ２ The converted mass is calculated using the formula: (mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is provided) × {(CeO2 in the first catalyst layer 20) ２ It can be calculated from {converted content) / 100}.

[0146] From the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, CeO ２The converted content is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the mass of the first catalyst layer 20. From the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to the promotion of Rh oxidation and a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the CeO2 in the first catalyst layer 20 ２ The converted content is preferably 15% by mass or less, more preferably 11% by mass or less, and even more preferably 8% by mass or less, based on the mass of the first catalyst layer 20. Each of the above lower limits may be combined with any of the above upper limits.

[0147] "CeO in the first catalyst layer 20" ２ The "converted mass" is the amount of CeO derived from the Ce in the first catalyst layer 20 when it contains one type of Ce source. ２ This refers to the converted mass, and if the first catalyst layer 20 contains two or more Ce sources, then CeO from the Ce derived from those two or more Ce sources. ２ This refers to the total mass after conversion.

[0148] The first catalyst layer 20 contains one or more Ce sources.

[0149] The Ce source is not particularly limited as long as it contains Ce. Examples of Ce sources include a first particle containing Ce, a second particle containing Ce, a third particle containing Ce, a ceria binder, and so on.

[0150] The first catalyst layer 20 may or may not contain the second particles, but from the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, it is preferable that the first catalyst layer 20 contains the second particles. In one embodiment, the second particles are Ce-Zr composite oxide particles. In another embodiment, the second particles are Ce-Zr-Al composite oxide particles. In addition to the second particles, the first catalyst layer 20 may contain one or more other Ce sources.

[0151] From the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, the content of the second particles in the first catalyst layer 20 is preferably 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 85% by mass or less. The lower limit above may be combined with any of the upper limits above. The content of the second particles in the first catalyst layer 20 can be determined in the same manner as the content of the first particles in the first catalyst layer 20.

[0152] From the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, CeO ２ Of the converted mass, CeO from the second particle ２ The proportion of the converted mass is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit may be 100% by mass or less than 100% by mass.

[0153] From the perspective of improving the exhaust gas purification performance of the first catalyst layer 20 through the action of Y in the first particle (early reduction of oxidized Rh), the Y originating from the first particle in the first catalyst layer 20 ２ O ３ The converted mass of CeO in the first catalyst layer 20 ２ The ratio of the converted mass is 0.05 or more, preferably 0.07 or more, more preferably 0.09 or more, and even more preferably 0.1 or more. From the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, Y derived from the first particles in the first catalyst layer 20 ２ O ３ The converted mass of CeO in the first catalyst layer 20 ２ The ratio of the converted mass is 1.5 or less, preferably 0.8 or less, more preferably 0.5 or less, and even more preferably 0.25 or less. Each of the above lower limits may be combined with any of the above upper limits.

[0154] Y originating from the first particle in the first catalyst layer 20 ２ O ３ The converted mass of CeO in the first catalyst layer 20 ２The ratio to mass for conversion is given by the formula: (Y of Y derived from the first particles in the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is provided) ２ O ３ (Converted mass) / (CeO of Ce in the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is provided) ２ It can be determined from the converted mass.

[0155] The first catalyst layer 20 may or may not contain the third particles, but from the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 by improving heat resistance, it is preferable that the first catalyst layer 20 contains the third particles.

[0156] From the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 by improving heat resistance, the content of third particles in the first catalyst layer 20 is preferably 3% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. The content of third particles in the first catalyst layer 20 can be determined in the same manner as the content of first particles in the first catalyst layer 20.

[0157] The first catalyst layer 20 preferably contains a support.

[0158] The support may consist of one type of metal oxide particle, or it may consist of two or more types of metal oxide particles. The metal oxide particles used as the support are distinguished from binders (e.g., alumina binder, zirconia binder, titania binder, silica binder, etc.) in that they have a particle size suitable for use as a support for catalytically active components.

[0159] Examples of carriers include second particles, third particles, oxide particles of rare earth elements other than Ce and Y, zirconia particles, silica particles, titania particles, zeolite particles, MgO, ZnO, and SnO. ２ Examples include oxide particles based on the above. The carrier is preferably selected from second and third particles. In one embodiment, the carrier includes second and third particles.

[0160] Preferably, at least a portion of the catalytically active components in the first catalyst layer 20 is supported on a carrier. The catalytically active components in the first catalyst layer 20 include catalytically active components containing Rh and catalytically active components containing noble metal elements other than Rh.

[0161] "At least a portion of the catalytically active component is supported on the carrier" means that at least a portion of the catalytically active component is physically or chemically adsorbed or retained on the outer surface and / or the inner surface of the pores of the carrier.

[0162] The fact that at least a portion of the catalytically active component is supported on the support can be confirmed, for example, using SEM-EDX. Specifically, if, in the elemental mapping obtained by analyzing a cross-section of the catalyst layer with SEM-EDX, at least a portion of the catalytically active component and the support are located in the same region, it can be determined that the catalytically active component is supported on the support.

[0163] Preferably, at least a portion of the first particles is supported on a carrier. The above explanation regarding "at least a portion of the catalytically active component is supported on a carrier" also applies to "at least a portion of the first particles is supported on a carrier." When applying this, "catalystically active component" is read as "first particles."

[0164] Preferably, at least a portion of the first particles are supported on a carrier on which Rh is supported. This makes it possible to more effectively increase the proportion of first particles adjacent to Rh.

[0165] The first catalyst layer 20 may contain other components such as a binder. Examples of binders include alumina binder, ceria binder, zirconia binder, titania binder, and silica binder.

[0166] The following describes preferred embodiments of the second particles in the first catalyst layer 20. Two or more of the features of the second particles described below can be combined.

[0167] From the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the CeO of the Ce in the second particles ２The converted content is preferably 35% by mass or less, more preferably 25% by mass or less, and even more preferably 15% by mass or less. The lower limits listed in the <Second Particle> column may be combined with any of the upper limits above.

[0168] From the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, Y in the second particle ２ O ３ The converted content is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 1% by mass or less. The lower limits listed in the <Second Particle> column may be combined with any of the upper limits above.

[0169] When the second particle is a Ce-Zr composite oxide particle, from the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the CeO of Ce in the Ce-Zr composite oxide particle ２ The converted content is preferably 35% by mass or less, more preferably 25% by mass or less, and even more preferably 15% by mass or less. The lower limits listed in the <Second Particle> column may be combined with any of the upper limits above.

[0170] When the second particle is a Ce-Zr composite oxide particle, from the viewpoint of preventing a decrease in the exhaust gas purification performance of the first catalyst layer 20 due to a decrease in heat resistance, the Zr in the Ce-Zr composite oxide particle is ZrO ２ The converted content is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 70% by mass or more. The upper limits listed in the <Second Particle> column may be combined with any of the lower limits above.

[0171] <Second Catalyst Layer> The second catalyst layer 30 will be described below. Two or more of the features of the second catalyst layer 30 described below can be combined. One or more of the features of the first catalyst layer 20 described above can be combined with one or more of the features of the second catalyst layer 30 described below.

[0172] As shown in Figures 3 and 4, the second catalyst layer 30 is provided on the cell 13 side surface of the partition wall 12. The "cell 13 side surface of the partition wall 12" refers to the outer surface of the partition wall 12 that extends in the exhaust gas flow direction X and is in contact with the cell 13. The second catalyst layer 30 may be provided directly on the cell 13 side surface of the partition wall 12 or via another layer, but is usually provided directly on the cell 13 side surface of the partition wall 12. The "second catalyst layer 30 provided on the base material 10" includes embodiments in which the second catalyst layer 30 is provided directly on the cell 13 side surface of the partition wall 12, and embodiments in which the second catalyst layer 30 is provided on the cell 13 side surface of the partition wall 12 via another layer.

[0173] The second catalyst layer 30 may be composed of a portion that rises from the cell 13 side surface of the partition wall portion 12 toward the cell 13 side (hereinafter referred to as the "raised portion"), or it may be composed of a portion that exists inside the partition wall portion 12 (hereinafter referred to as the "internal portion"), or it may have both a raised portion and an internal portion. The "second catalyst layer 30 provided on the substrate 10" includes embodiments in which the second catalyst layer 30 is composed of a raised portion, embodiments in which the second catalyst layer 30 is composed of an internal portion, and embodiments in which the second catalyst layer 30 has both a raised portion and an internal portion.

[0174] As shown in Figure 4, the second catalyst layer 30 extends along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12 to the exhaust gas outlet end of the partition wall 12. The second catalyst layer 30 may extend along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12 so as not to reach the exhaust gas outlet end of the partition wall 12, or it may extend along the direction opposite to the exhaust gas flow direction X from the exhaust gas outlet end of the partition wall 12 so as not to reach the exhaust gas inlet end of the partition wall 12.

[0175] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass of the second catalyst layer 30 per unit volume of the portion of the base material 10 in which the second catalyst layer 30 is provided (hereinafter referred to as "WC amount of the second catalyst layer 30") is preferably 80 g / L or more and 180 g / L or less, more preferably 90 g / L or more and 170 g / L or less, and even more preferably 100 g / L or more and 160 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0176] The amount of WC in the second catalyst layer 30 is given by the formula: (mass of the second catalyst layer 30) / (volume of the substrate 10) × (length L of the second catalyst layer 30) ３０ / Length L of base material 10 １０ It can be obtained from ).

[0177] Length L of the first catalyst layer 20 ２０ The above explanation regarding the measurement method refers to the length L of the second catalyst layer 30. ３０ This also applies to the measurement method. When applied, the "first catalyst layer 20" is "length L" of the "second catalyst layer 30". ２０ " is "Length L ３０ This can be reinterpreted as ".

[0178] The second catalyst layer 30 contains one or more noble metal elements as catalytic active components. From the viewpoint of improving the exhaust gas purification performance of catalyst 1, it is preferable to select the noble metal elements contained in the second catalyst layer 30 from Pd and Pt. Pd does not reduce exhaust gas purification performance even when oxidized. Pt reduces exhaust gas purification performance when oxidized, but the degree of reduction is less than that of Rh.

[0179] The precious metal element is included in the second catalyst layer 30 in a form that can function as a catalytic active component, such as a metal, an alloy containing the precious metal element, or a compound containing the precious metal element (e.g., an oxide of the precious metal element). The catalytic active component containing the precious metal element is, for example, in particulate form.

[0180] From the viewpoint of improving the exhaust gas purification performance of the second catalyst layer 30, the content of noble metal elements in the second catalyst layer 30 in terms of metal is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on the mass of the second catalyst layer 30. The upper limit can be adjusted as appropriate, taking into consideration the balance between exhaust gas purification performance and cost. The upper limit is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. Each of the above lower limits may be combined with any of the above upper limits. If the second catalyst layer 30 contains two or more noble metal elements, "content of noble metal elements in terms of metal" means the total content of those two or more noble metal elements in terms of metal.

[0181] The second catalyst layer 30 preferably includes a support. The description of the support is the same as above. The support is preferably selected from second particles and third particles. In one embodiment, the support includes second particles and third particles. In one embodiment, the second particles are Ce-Zr composite oxide particles. In another embodiment, the second particles are Ce-Zr-Al composite oxide particles.

[0182] Preferably, at least a portion of the catalytically active components in the second catalyst layer 30 is supported on a carrier. The meaning and method of confirming "at least a portion of the catalytically active components is supported on a carrier" are the same as described above.

[0183] The second catalyst layer 30 may contain other components such as a binder. The explanation regarding the binder is the same as described above.

[0184] <Manufacturing of Catalyst> Catalyst 1 can be manufactured by forming a second catalyst layer 30 on a substrate 10, and then forming a first catalyst layer 20 on the second catalyst layer 30. If the second catalyst layer 30 is omitted, catalyst 1 can be manufactured by forming the first catalyst layer 20 on the substrate 10.

[0185] The second catalyst layer 30 can be formed by preparing a second slurry containing a noble metal element-containing compound (e.g., a salt of a noble metal element), metal oxide particles (e.g., second particles, third particles, etc.), and other components (e.g., a binder, a solvent, etc.), coating the second slurry onto the substrate 10 to form a second precursor layer, and then firing the second precursor layer. The second precursor layer is a precursor layer of the second catalyst layer 30. The composition of the second slurry is adjusted as appropriate considering the composition of the second catalyst layer 30. The amount of second slurry applied is adjusted as appropriate considering the amount of WC in the second catalyst layer 30.

[0186] Examples of salts of precious metal elements include nitrates, ammine complex salts, acetates, and chlorides. Examples of binders include alumina sol, zirconia sol, titania sol, silica sol, and ceria sol. Examples of solvents include water and organic solvents.

[0187] The firing temperature of the second precursor layer is, for example, between 300°C and 700°C. The firing time of the second precursor layer is, for example, between 1 hour and 10 hours. The firing of the second precursor layer can be carried out, for example, in an atmospheric environment.

[0188] The second precursor layer may be dried before firing. The drying temperature of the second precursor layer is, for example, 60°C to 150°C. The drying time of the second precursor layer is, for example, 0.1 hours to 1 hour.

[0189] The first catalyst layer 20 can be formed by a method comprising the following steps: (a) preparing a first slurry containing an Rh-containing compound and first particles; (b) coating the first slurry onto the substrate 10 to form a first precursor layer; and (c) firing the first precursor layer to form the first catalyst layer 20. The first precursor layer is a precursor layer of the first catalyst layer 20. The composition of the first slurry is adjusted as appropriate considering the composition of the first catalyst layer 20. The amount of first slurry applied is adjusted as appropriate considering the amount of WC in the first catalyst layer 20.

[0190] Examples of Rh-containing compounds include Rh salts. Examples of Rh salts include nitrates, ammine complex salts, acetates, and chlorides.

[0191] From the viewpoint of achieving high dispersion of the first particles in the first catalyst layer 20, the D95 of the first particles used as a raw material for the first slurry is 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more and 7 μm or less, and more preferably 1 μm or more and 5 μm or less. The lower limit above may be combined with any of the upper limits above. By adjusting the D95 of the first particles used as a raw material for the first slurry to 0.1 μm or more and 10 μm or less, the average particle diameter of the first particles in the first catalyst layer 20 can be adjusted to 0.05 μm or more and 1.5 μm or less. By adjusting the D95 of the first particles used as a raw material for the first slurry to 0.5 μm or more and 7 μm or less, the average particle diameter of the first particles in the first catalyst layer 20 can be adjusted to 0.1 μm or more and 1.0 μm or less. By adjusting the D95 of the first particles used as raw material for the first slurry to 1 μm or more and 5 μm or less, the average particle size of the first particles in the first catalyst layer 20 can be adjusted to 0.2 μm or more and 0.5 μm or less.

[0192] From the viewpoint of improving the oxygen storage capacity of the first catalyst layer 20, it is preferable that the first slurry prepared in step (a) contains the second particles.

[0193] From the viewpoint of effectively enabling the second particles in the first catalyst layer 20 to function as a support, the D50 of the second particles used as a raw material for the first slurry is preferably 3 μm or more and 25 μm or less, more preferably 4 μm or more and 20 μm or less, and even more preferably 5 μm or more and 15 μm or less. Each of the above lower limits may be combined with any of the above upper limits.

[0194] From the viewpoint of improving the exhaust gas purification performance of the first catalyst layer 20 by improving heat resistance, it is preferable that the first slurry prepared in step (a) contains third particles.

[0195] From the viewpoint of effectively enabling the third particles in the first catalyst layer 20 to function as a support, the D50 of the third particles used as a raw material for the first slurry is preferably 3 μm or more and 25 μm or less, more preferably 4 μm or more and 20 μm or less, and even more preferably 5 μm or more and 15 μm or less. Each of the above lower limits may be combined with any of the above upper limits.

[0196] D95 and D50 are measured by laser diffraction scattering particle size distribution measurement. D95 and D50 represent the particle sizes at which the cumulative volume accounts for 95% and 50% of the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement, respectively. Laser diffraction scattering particle size distribution measurement can be carried out as described in the examples.

[0197] The first slurry may contain other components (e.g., binder, solvent, etc.). Specific examples of the binder and solvent are the same as described above.

[0198] The step (b) "coating the first slurry onto the substrate 10" includes embodiments in which the first slurry is coated onto a second catalyst layer 30 formed on the substrate 10 (in this embodiment, the catalyst 1 includes the second catalyst layer 30), and embodiments in which the first slurry is coated onto the substrate 10 (in this embodiment, the catalyst 1 does not include the second catalyst layer 30).

[0199] The firing temperature of the first precursor layer is, for example, 300°C to 700°C. The firing time of the first precursor layer is, for example, 1 hour to 10 hours. The firing of the first precursor layer can be carried out, for example, in an atmospheric environment.

[0200] The first precursor layer may be dried before firing. The drying temperature of the first precursor layer is, for example, 60°C to 150°C. The drying time of the first precursor layer is, for example, 0.1 hours to 1 hour.

[0201] When yttrium nitrate is used as the Y source in the first slurry, the yttrium nitrate is converted into first particles by calcination. However, the average particle size of the first particles produced from yttrium nitrate is usually less than 0.05 μm, and the action of Y in the first particles (early reduction of oxidized Rh) cannot be fully exerted.

[0202] The present invention will be described below based on examples and comparative examples.

[0203] [Example 1] (1) Preparation of slurry for lower layer formation Metal oxide particles having the following composition (hereinafter referred to as "OSC material 1") were prepared. Ce of CeO ２Conversion content: 40.0% by mass Zr of ZrO ２ Conversion content: 50.0% by mass Conversion content of rare earth elements other than Ce (in terms of oxides): 10.0% by mass

[0204] In the mixing container, combine palladium nitrate aqueous solution, OSC material 1, and La ２ O ３ Modified alumina (Al of Al ２ O ３ Conversion content: 99.0% by mass, La of La ２ O ３ A slurry for forming the lower layer was prepared by adding alumina sol and water, with a converted content of 1.0% by mass, and stirring. The amounts of each component in the slurry for forming the lower layer were as follows, based on the mass of the lower layer after firing (100% by mass): Pd was 5.0% by mass in terms of metal equivalent, OSC material 1 was 40.0% by mass, and La ２ O ３ The mixture was prepared so that it contained 50.0% by mass of modified alumina and 5.0% by mass of solids in the alumina sol.

[0205] (2) Formation of the lower layer As a flow-through type substrate, cells extending in the axial direction, partitioned by partitions with a thickness of 50 to 70 μm, are formed at a rate of 600 cells / inch in a plane perpendicular to the axial direction. ２ A flow-through type substrate with a density of 1.0 L and a volume of 1.0 L was prepared.

[0206] The entire flow-through substrate was immersed in a slurry for forming the lower layer. The flow-through substrate coated with the slurry was dried at 150°C for 0.5 hours, and then baked at 500°C for 1 hour to form the lower layer. The mass of the lower layer per unit volume in the portion of the flow-through substrate where the lower layer was formed was 100 g / L. The mass of the lower layer per unit volume in the portion of the flow-through substrate where the lower layer was formed was calculated using the following formula, where the length of the lower layer / the length of the flow-through substrate = 1. Mass of the lower layer per unit volume in the portion of the flow-through substrate where the lower layer was formed = (Mass of the lower layer) / ((Volume of the flow-through substrate) × (Length of the lower layer / Length of the flow-through substrate))

[0207] (3) Preparation of slurry for upper layer formation Metal oxide particles having the following composition (hereinafter referred to as "OSC material 2") were prepared. Ce of CeO２ Conversion content: 10.0% by mass Zr of ZrO ２ Conversion content: 80.0% by mass; Oxide content of rare earth elements other than Ce and Y: 10.0% by mass

[0208] In the mixing container, combine rhodium nitrate aqueous solution, OSC material 2, and La ２ O ３ Modified alumina (Al of Al ２ O ３ Conversion content: 99.0% by mass, La of La ２ O ３ Conversion content: 1.0% by mass), alumina sol, Y-based oxide particles (Y of Y ２ O ３ Converted content: Approximately 100% by mass (>99.5% by mass) and water were added and stirred to prepare a slurry for forming the upper layer. The amounts of each component in the slurry for forming the upper layer were, based on the mass of the upper layer after firing (100% by mass), 1.0% by mass for Rh in terms of metal equivalent, 62.5% by mass for OSC material 2, and 62.5% by mass for La ２ O ３ Modified alumina accounts for 27.5% by mass, solid content of alumina sol accounts for 8.0% by mass, and Y is derived from Y-based oxide particles. ２ O ３ The amount was adjusted to be 1.0 mass% when converted.

[0209] The D95 of the Y-type oxide particles used as raw materials for the upper layer formation slurry was measured using laser diffraction scattering particle size distribution analysis and found to be between 1 μm and 5 μm. OSC material 2 and La used as raw materials for the upper layer formation slurry ２ O ３ When the D50 of modified alumina was measured using the laser diffraction scattering particle size distribution method, the particle size was found to be between 5 μm and 15 μm.

[0210] The laser diffraction scattering particle size distribution measurement method was performed as follows: Using an automatic sample feeder for laser diffraction particle size distribution analyzers ("Microtrac SDC" manufactured by Nikkiso Co., Ltd.), the powder sample was placed in an aqueous solvent, and after irradiating with 30W ultrasound at a flow rate of 50% for 360 seconds, the volume-based particle size distribution was measured using a Nikkiso Co., Ltd. laser diffraction particle size distribution analyzer "Microtrac MT3300II". From the volume-based particle size distribution, the particle size (μm) at which the cumulative volume reached 95% and 50% was measured. The measurement was performed twice, and the average values ​​of the particle size (μm) at which the cumulative volume reached 95% and 50% were taken as D95 and D50 (μm), respectively. The measurement conditions were: particle refractive index 1.81, particle shape non-spherical, solvent refractive index 1.3, set zero 30 seconds, and measurement time 30 seconds.

[0211] (4) Formation of the upper layer The entire flow-through substrate with the lower layer formed was immersed in the upper layer forming slurry, and the flow-through substrate coated with the upper layer forming slurry was dried at 150°C for 0.5 hours, and then baked at 500°C for 1 hour to form the upper layer on the lower layer. The mass of the upper layer per unit volume of the portion of the flow-through substrate with the upper layer was 80 g / L. The mass of the upper layer per unit volume of the portion of the flow-through substrate with the upper layer was calculated using the following formula, where the length of the upper layer / the length of the flow-through substrate = 1. Mass of the upper layer per unit volume of the portion of the flow-through substrate with the upper layer = (Mass of the upper layer) / ((Volume of the flow-through substrate) × (Length of the upper layer / Length of the flow-through substrate))

[0212] The average particle size of Y-type oxide particles in the upper layer after firing was measured to be 0.3 μm. The measurement was performed as follows: Elemental analysis of the upper layer was performed using SEM-EDX to identify the constituent elements of each metal oxide particle contained in the upper layer, and the content (mass%) of each identified metal element in oxide form was determined to identify the Y-type oxide particles. The directional diameter (Ferret diameter) of 50 Y-type oxide particles arbitrarily selected from the SEM field of view was measured, and the average value was taken as the average particle size of the Y-type oxide particles.

[0213] As described above, the catalyst of Example 1 was manufactured, comprising a lower layer formed on a flow-through type substrate and an upper layer formed on the lower layer. The characteristics of Example 1 are shown in Table 1.

[0214] [Example 2] The amounts of each component in the slurry for forming the upper layer were determined based on the mass of the upper layer after firing (100% by mass), with Rh being 1.0% by mass in terms of metal equivalent, OSC material 2 being 62.5% by mass, and La ２ O ３ Modified alumina accounts for 27.5% by mass, solid content of alumina sol accounts for 7.0% by mass, and Y is derived from Y-based oxide particles. ２ O ３ The catalyst for Example 2 was prepared in the same manner as in Example 1, except that it was adjusted to be 2.0% by mass. The average particle size of the Y-based oxide particles in the upper layer after calcination was 0.3 μm. The characteristics of Example 2 are shown in Table 1.

[0215] [Example 3] The amounts of each component in the slurry for forming the upper layer were determined based on the mass of the upper layer after firing (100% by mass), with Rh being 1.0% by mass in terms of metal equivalent, OSC material 2 being 62.5% by mass, and La ２ O ３ Modified alumina accounts for 27.5% by mass, solid content of alumina sol accounts for 5.0% by mass, and Y is derived from Y-based oxide particles. ２ O ３ The catalyst of Example 3 was prepared in the same manner as in Example 1, except that it was adjusted to be 4.0% by mass. The average particle size of the Y-based oxide particles in the upper layer after calcination was 0.3 μm. The characteristics of Example 3 are shown in Table 1.

[0216] [Example 4] The catalyst of Example 4 was manufactured in the same manner as in Example 1, except that the D95 of the Y-based oxide particles used as raw material for the slurry for forming the upper layer was changed to more than 5 μm and less than or equal to 10 μm. The average particle size of the Y-based oxide particles in the upper layer after calcination was 1.2 μm. The characteristics of Example 4 are shown in Table 1.

[0217] [Example 5] Metal oxide particles having the following composition (hereinafter referred to as "OSC material 3") were prepared. Ce of CeO ２ Conversion content: 20.0% by mass Zr of ZrO ２Conversion content: 70.0% by mass; Oxide content of rare earth elements other than Ce and Y: 10.0% by mass

[0218] In the mixing container, combine rhodium nitrate aqueous solution, OSC material 3, and La ２ O ３ Modified alumina (Al of Al ２ O ３ Conversion content: 99.0% by mass, La of La ２ O ３ Conversion content: 1.0% by mass), alumina sol, Y-based oxide particles (Y of Y ２ O ３ Converted content: Approximately 100% by mass (>99.5% by mass) and water were added and stirred to prepare a slurry for forming the upper layer. The amounts of each component in the slurry for forming the upper layer were, based on the mass of the upper layer after firing (100% by mass), 1.0% by mass for Rh in terms of metal equivalent, 62.5% by mass for OSC material 3, and 62.5% by mass for La ２ O ３ Modified alumina accounts for 27.5% by mass, solid content of alumina sol accounts for 8.0% by mass, and Y is derived from Y-based oxide particles. ２ O ３ The amount was adjusted to be 1.0 mass% when converted.

[0219] The D95 of the Y-type oxide particles used as raw materials for the upper layer formation slurry was measured using laser diffraction scattering particle size distribution analysis and found to be between 1 μm and 5 μm. OSC material 3 and La used as raw materials for the upper layer formation slurry ２ O ３ When the D50 of modified alumina was measured using the laser diffraction scattering particle size distribution method, the particle size was found to be between 5 μm and 15 μm.

[0220] The catalyst of Example 5 was prepared in the same manner as in Example 1, except that the upper layer forming slurry prepared above was used. The average particle size of the Y-based oxide particles in the upper layer after calcination was 0.3 μm. The characteristics of Example 5 are shown in Table 1.

[0221] [Comparative Example 1] OSC material 4 with the following composition was prepared: Ce of CeO ２ Conversion content: 30.0% by mass Zr of ZrO ２Conversion content: 60.0% by mass; Oxide content of rare earth elements other than Ce and Y: 10.0% by mass

[0222] In the mixing container, combine rhodium nitrate aqueous solution, OSC material 4, and La ２ O ３ Modified alumina (Al of Al ２ O ３ Conversion content: 99.0% by mass, La of La ２ O ３ Conversion content: 1.0% by mass), alumina sol, Y-based oxide particles (Y of Y ２ O ３ Converted content: Approximately 100% by mass (>99.5% by mass) and water were added and stirred to prepare a slurry for forming the upper layer. The amounts of each component in the slurry for forming the upper layer were, based on the mass of the upper layer after firing (100% by mass), 1.0% by mass for Rh in terms of metal equivalent, 62.5% by mass for OSC material 4, and 62.5% by mass for La ２ O ３ Modified alumina accounts for 27.5% by mass, solid content of alumina sol accounts for 8.0% by mass, and Y is derived from Y-based oxide particles. ２ O ３ The amount was adjusted to be 1.0 mass% when converted.

[0223] The D95 of the Y-type oxide particles used as raw materials for the upper layer formation slurry was measured using laser diffraction scattering particle size distribution analysis and found to be between 1 μm and 5 μm. The OSC material 4 and La used as raw materials for the upper layer formation slurry ２ O ３ When the D50 of modified alumina was measured using the laser diffraction scattering particle size distribution method, the particle size was found to be between 5 μm and 15 μm.

[0224] The catalyst for Comparative Example 1 was prepared in the same manner as in Example 1, except that the upper layer forming slurry prepared above was used. The average particle size of the Y-based oxide particles in the upper layer after calcination was 0.3 μm. The characteristics of Comparative Example 1 are shown in Table 1.

[0225] [Comparative Example 2] Y-based oxide particles were not used as raw materials for the slurry for forming the upper layer, and the amounts of each component in the slurry for forming the upper layer were as follows, based on the mass of the upper layer after firing (100% by mass): Rh was 1.0% by mass in terms of metal equivalent, OSC material 2 was 62.5% by mass, La２ O ３ The catalyst for Comparative Example 2 was prepared in the same manner as in Example 1, except that the modified alumina content was adjusted to 27.5% by mass and the solid content of the alumina sol to 9.0% by mass. The characteristics of Comparative Example 2 are shown in Table 1.

[0226] [Comparative Example 3] The catalyst of Comparative Example 3 was manufactured in the same manner as in Example 1, except that the D95 of the Y-based oxide particles used as raw material for the slurry for forming the upper layer was changed to more than 10 μm and less than or equal to 20 μm. The average particle size of the Y-based oxide particles in the upper layer after calcination was 1.8 μm. The characteristics of Comparative Example 3 are shown in Table 1.

[0227] [Comparative Example 4] The catalyst for Comparative Example 4 was manufactured in the same manner as in Example 1, except that the D95 of the Y-based oxide particles used as raw materials for the slurry for forming the upper layer was changed to more than 20 μm. The average particle size of the Y-based oxide particles in the upper layer after calcination was 6.0 μm. The characteristics of Comparative Example 4 are shown in Table 1.

[0228] [Comparative Example 5] As a raw material for the slurry for forming the upper layer, Y-based oxide particles are replaced with yttrium nitrate (Y derived from yttrium nitrate is Y ２ O ３ The catalyst of Comparative Example 5 was prepared in the same manner as in Example 1, except that 1.0 mass% was used. Yttrium nitrate was calcined to produce Y-based oxide particles (Y of Y). ２ O ３ The converted content is approximately 100% by mass (>99.5% by mass), but since no Y-type oxide particles were observed in the upper layer after firing, it was determined that the average particle size of the Y-type oxide particles in Comparative Example 5 was less than 0.05 μm. The characteristics of Comparative Example 5 are shown in Table 1.

[0229] [Test Examples] After durability treatment, each catalyst from Examples 1 to 5 and Comparative Examples 1 to 5 was subjected to the following exhaust gas purification performance test to evaluate the exhaust gas purification performance of each catalyst. Durability treatment was performed as follows: ２ Gas: 0.50%, Water vapor: 10%, and balance gas: N ２ This was carried out by heat treatment at 1000°C for 30 hours in an atmosphere through which a gas consisting of [components] was circulated.

[0230] <Exhaust Gas Purification Performance Test> The purification performance of hydrocarbons (HC) and nitrogen oxides (NOx) among the harmful components was measured. A model gas with the following composition and an A / F ratio of 14.6 was introduced into the catalyst after durability treatment (catalyst volume: 15 mL) and the CO concentration and O2 concentration were varied so that the A / F ratio fluctuated within the range of 14.4 to 14.8. ２ The gas was circulated at 32 L / min while adjusting the concentration. The gas temperature flowing into the catalyst was gradually increased from room temperature at a predetermined heating rate. The amount of HC and NOx contained in the exhaust gas that passed through the catalyst was detected using the following device, and the HC purification rate and NOx purification rate were calculated based on the following formulas. V1 represents the amount of HC detected without a catalyst, W1 represents the amount of HC detected after a catalyst is installed, V2 represents the amount of NOx detected without a catalyst, and W2 represents the amount of NOx detected after a catalyst is installed. HC purification rate (%) = (V1 - W1) / V1 × 100 NOx purification rate (%) = (V2 - W2) / V2 × 100

[0231] [Model gas (composition by volume)] CO: 0.3%, C ３ H ６ :1000ppmC,NO:500ppm,O ２ : 0.28%, CO ２ : 14%, H ２ O: 10%, N ２ Remaining portion [Heating rate] 10°C / min [Evaluation equipment] MOTOR EXHAUST GAS ANALYZER MEXA7100 manufactured by Horiba, Ltd.

[0232] The catalyst inlet gas temperature (°C) was measured when the HC purification rate and NOx purification rate reached 50%, and this was defined as the light-off temperature T50. T50 was measured during the heating process. Table 1 shows the T50 measurement results for each catalyst in Examples 1 to 5 and Comparative Examples 1 to 5.

[0233]

[0234] P... Exhaust pipe of an internal combustion engine 1... Catalyst for exhaust gas purification 10... Base material 11... Cylindrical section 12... Partition section 13... Cell 20... First catalyst layer 30... Second catalyst layer

Claims

An exhaust gas purification catalyst comprising a base material and a catalyst layer provided on the base material, The catalyst layer comprises Rh, Ce, and metal oxide particles, wherein Y in the metal oxide particles ２ O ３ The converted content is 50% by mass or more, and the CeO of Ce in the metal oxide particles ２ The material contains metal oxide particles (hereinafter referred to as "first particles") whose converted content is less than 3% by mass, CeO in the catalyst layer per unit volume of the portion of the substrate in which the catalyst layer is provided ２ The converted mass is 0.5 g / L or more and 13 g / L or less. Y originating from the first particle in the catalyst layer ２ O ３ The converted mass of CeO in the catalyst layer ２ The ratio to the converted mass is 0.05 or more and 1.5 or less. The exhaust gas purification catalyst wherein the average particle size of the first particles in the catalyst layer is 0.05 μm or more and 1.5 μm or less. 　 The catalyst layer is metal oxide particles, and the content of Ce in terms of CeO in the metal oxide particles is 3% by mass or more, and the content of Y in terms of Y in the metal oxide particles is less than 50% by mass. The metal oxide particles (hereinafter referred to as "second particles") are further included. The exhaust gas purification catalyst according to claim 1. ２ The content of Ce in terms of CeO in the metal oxide particles is 3% by mass or more, and the content of Y in terms of Y in the metal oxide particles is less than 50% by mass. ２ O ３ The exhaust gas purification catalyst according to claim 1, further comprising the metal oxide particles (hereinafter referred to as "second particles") in which the content of Ce in terms of CeO in the metal oxide particles is 3% by mass or more and the content of Y in terms of Y in the metal oxide particles is less than 50% by mass. 　 CeO in the second particle ２ The exhaust gas purification catalyst according to claim 2, wherein the converted content is 25% by mass or less. 　 CeO in the second particle ２ The exhaust gas purification catalyst according to claim 3, wherein the converted content is 15% by mass or less. 　 CeO in the catalyst layer per unit volume of the portion of the substrate in which the catalyst layer is provided ２ An exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the converted mass is 8 g / L or less. 　 Y originating from the first particle in the catalyst layer ２ O ３ The converted mass of CeO in the catalyst layer ２ An exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the ratio of the converted mass to the total mass is 0.1 or more and 0.5 or less. 　 The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the average particle diameter of the first particles in the catalyst layer is 0.5 μm or less. 　 A method for producing an exhaust gas purification catalyst as described in claim 1, The above method comprises the following steps: (a) A step of preparing a slurry containing the Rh-containing compound and the first particles; (b) A step of coating the slurry onto the substrate to form a precursor layer; and (c) A step of firing the precursor layer to form the catalyst layer. Includes, The method wherein the D95 particle size of the first particles used as a raw material for the slurry, which is the particle size at which the cumulative volume accounts for 95% of the volume-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement method, is 0.1 μm or more and 10 μm or less.

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