Catalyst for purification of exhaust gas

Abstract

To solve the problem, a catalyst for purifying exhaust gas (1) is provided, which comprises a wall flow type substrate (10), and at least one of a first catalyst layer (20) and a second catalyst layer (30), and satisfies at least one of the following conditions 1a and 1b, condition 1a: Xa / Ya ≤ 1.40 and Ya ≤ 5.00, and condition 1b: Xb / Yb ≤ 1.40 and Yb ≤ 5.00.

Description

Technical Field

[0001] This invention relates to catalysts for waste gas purification. Background Technology

[0002] Exhaust gases from internal combustion engines in automobiles, motorcycles, and other vehicles contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Three-way catalysts are used to purify and neutralize these harmful components. These three-way catalysts utilize precious metal elements such as Pt, Pd, and Rh.

[0003] It is known that exhaust gases contain particulate matter (PM) along with harmful components such as HC, CO, and NOx, which contributes to air pollution.

[0004] In order to cope with PM-related environmental restrictions, vehicles equipped with gasoline engines such as Gasoline Direct Injection (GDI) are required to be equipped with a Gasoline Particulate Filter (GPF) with PM-capturing function, just like vehicles equipped with diesel engines.

[0005] GPF, for example, uses a substrate having a structure known as a wall-flow type. The wall-flow type substrate includes: an inflow-side chamber with an end opening on the exhaust gas inflow side and an end closing on the exhaust gas outflow side; an outflow-side chamber with an end closing on the exhaust gas inflow side and an end opening on the exhaust gas outflow side; and a porous partition wall separating the inflow-side chamber and the outflow-side chamber.

[0006] Typically, the space available for catalysts used in exhaust gas purification is limited. Therefore, research is underway to incorporate catalyst layers containing precious metals such as Pt, Pd, and Rh onto wall-flow substrates to purify harmful components such as HC, CO, and NOx while capturing PM. In catalysts equipped with wall-flow substrates and catalyst layers, when exhaust gas flows in from the exhaust gas inflow side (opening) of the inflow chamber and flows out from the exhaust gas outflow side (opening) of the outflow chamber through the catalyst layer and partition walls, PM in the exhaust gas is captured by the fine pores of the catalyst layer and partition walls.

[0007] The air / fuel ratio (A / F) supplied to the internal combustion engine is preferably controlled near the stoichiometric air-fuel ratio. However, the actual air-fuel ratio varies towards the rich (excess fuel atmosphere) or lean (lean fuel atmosphere) side around the stoichiometric ratio, depending on the vehicle's driving conditions, and thus the exhaust gas also varies towards the rich or lean side. Therefore, in order to mitigate the fluctuation of oxygen concentration in the exhaust gas and improve the exhaust gas purification capacity of the catalyst, materials with oxygen storage capacity (OSC) are used, such as Zr-based oxides like Ce-Zr composite oxides, as catalyst layer materials (e.g., Patent Document 1 and Patent Document 2).

[0008] Previously used Ce-Zr composite oxides and other Zr-based oxides as catalyst layers have undergone thermal shrinkage when exposed to high-temperature environments. Furthermore, in this specification, "high temperature" refers to temperatures above 800°C, particularly above 900°C.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2018-187595

[0012] Patent Document 2: Japanese Patent Application Publication No. 2023-513989 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] The inventors have discovered that in exhaust gas purification catalysts comprising a wall-flow substrate and a catalyst layer containing Zr-based oxides, PM capture performance is prone to decrease when exposed to high-temperature environments. Specifically, the inventors have discovered that when an exhaust gas purification catalyst comprising a wall-flow substrate and a catalyst layer containing Zr-based oxides is exposed to a high-temperature environment, cracks are generated within the catalyst layer due to the thermal shrinkage of the Zr-based oxides, thereby easily reducing the PM capture performance of the catalyst layer. Furthermore, the reduction in PM capture performance of the catalyst layer due to the thermal shrinkage of the Zr-based oxides is less likely to occur in the portion of the catalyst layer formed within the partition wall, but is more likely to occur in the portion formed on the outer surface of the partition wall (i.e., the portion that protrudes from the outer surface of the partition wall towards the inflow-side chamber or the outflow-side chamber).

[0015] Therefore, the object of the present invention is to provide a catalyst for exhaust gas purification, which has a wall-flow substrate and a catalyst layer containing Zr-based oxides, and can suppress the reduction of PM capture performance caused by exposure to high temperature environment.

[0016] Solution for solving the problem

[0017] To address the aforementioned issues, the present invention provides the following catalyst for waste gas purification.

[0018] [1] A catalyst for purifying waste gas, comprising a substrate extending along the waste gas flow direction, and at least one of a first catalyst layer and a second catalyst layer, wherein,

[0019] The substrate comprises: an inflow-side chamber extending in the exhaust gas flow direction, with an open end on the exhaust gas inflow side and a closed end on the exhaust gas outflow side; an outflow-side chamber extending in the exhaust gas flow direction, with a closed end on the exhaust gas inflow side and an open end on the exhaust gas outflow side; and a porous partition portion separating the inflow-side chamber and the outflow-side chamber.

[0020] The first catalyst layer has a portion formed on the outer surface of the inflow-side chamber side of the partition portion from the end of the partition portion on the exhaust gas inflow side along the exhaust gas flow direction.

[0021] The second catalyst layer has a portion formed on the outer surface of the outflow side chamber of the partition portion from the end of the exhaust outflow side of the partition portion in a direction opposite to the exhaust gas flow direction.

[0022] The catalyst for waste gas purification satisfies at least one of the following conditions 1a and 1b.

[0023] Condition 1a: Xa / Ya ≤ 1.40 and Ya ≤ 5.00,

[0024] In the formula, Xa represents the 10% flow diameter of the first catalyst layer and the partition wall portion, measured by the bubble point method using a permeability meter after heat treatment at 950°C for 35 hours under atmospheric conditions, in μm; Ya represents the 10% flow diameter of the first catalyst layer and the partition wall portion, measured by the bubble point method using a permeability meter before the heat treatment, in μm.

[0025] Condition 1b: Xb / Yb≤1.40 and Yb≤5.00

[0026] In the formula, Xb represents the 10% flow diameter of the second catalyst layer and the partition wall portion, measured by the bubble point method using an air permeability meter after the heat treatment of the catalyst for waste gas purification, in μm; Yb represents the 10% flow diameter of the second catalyst layer and the partition wall portion, measured by the bubble point method using an air permeability meter before the heat treatment of the catalyst for waste gas purification, in μm.

[0027] When the catalyst for exhaust gas purification meets condition 1a, the first catalyst layer contains Zr-based oxides.

[0028] When the catalyst for exhaust gas purification satisfies condition 1b, the second catalyst layer contains Zr-based oxides.

[0029] [2] According to the catalyst for waste gas purification described in [1], wherein,

[0030] When the catalyst for exhaust gas purification has the first catalyst layer but not the second catalyst layer, the length of the first catalyst layer is 100% of the length of the inflow-side chamber.

[0031] When the catalyst for exhaust gas purification includes a second catalyst layer but not a first catalyst layer, the length of the second catalyst layer is 100% of the length of the outflow side chamber.

[0032] When the catalyst for purifying exhaust gas includes the first catalyst layer and the second catalyst layer, the sum of the length of the first catalyst layer and the length of the second catalyst layer is 100% or more of the length of the substrate.

[0033] [3] The catalyst for purifying waste gas according to [1] or [2], wherein,

[0034] When the catalyst for exhaust gas purification satisfies condition 1a but not condition 1b, the length of the first catalyst layer is 100% of the length of the inflow-side chamber.

[0035] When the catalyst for exhaust gas purification satisfies condition 1b but not condition 1a, the length of the second catalyst layer is 100% of the length of the outflow side chamber.

[0036] When the catalyst for exhaust gas purification satisfies conditions 1a and 1b, the sum of the lengths of the first catalyst layer and the second catalyst layer is 100% or more of the length of the substrate.

[0037] [4] The catalyst for purifying waste gas according to any one of [1] to [3], wherein,

[0038] When the catalyst for exhaust gas purification meets condition 1a, the mass of the first catalyst layer per unit volume of the portion of the substrate in which the first catalyst layer is formed is 20 g / L or more and 150 g / L or less.

[0039] When the catalyst for exhaust gas purification satisfies condition 1b, the mass of the second catalyst layer per unit volume of the portion of the substrate in which the second catalyst layer is formed is 20 g / L or more and 150 g / L or less.

[0040] [5] The catalyst for purifying waste gas according to any one of [1] to [4], wherein,

[0041] When the catalyst for waste gas purification meets condition 1a, the first catalyst layer contains a Ce-Zr composite oxide as the Zr oxide.

[0042] When the catalyst for exhaust gas purification meets condition 1b, the second catalyst layer contains Ce-Zr composite oxide as the Zr oxide.

[0043] [6] According to the catalyst for waste gas purification described in [5], wherein,

[0044] When the catalyst for waste gas purification meets condition 1a, based on the mass of the first catalyst layer, the content of Ce-Zr composite oxides in the first catalyst layer is 50% by mass or more.

[0045] When the catalyst for exhaust gas purification meets the condition 1b, the content of Ce-Zr composite oxide in the second catalyst layer is 50% by mass or more, based on the mass of the second catalyst layer.

[0046] [7] The catalyst for purifying waste gas according to [5] or [6], wherein,

[0047] When the catalyst for exhaust gas purification satisfies condition 1a, the Ce-Zr composite oxide in the first catalyst layer satisfies the following formula: R 12 / R 11 >0.8,

[0048] In the formula, R 11 This indicates the Ce content in the Ce-Zr composite oxide, expressed as CeO2, in mass %, R. 12 This indicates the Zr content in the Ce-Zr composite oxide, converted to ZrO2, in % by mass.

[0049] When the catalyst for exhaust gas purification satisfies condition 1b, the Ce-Zr composite oxide in the second catalyst layer satisfies the following formula: R 22 / R 21 >0.8,

[0050] In the formula, R 21R represents the CeO2 content in the Ce-Zr composite oxide, converted from Ce, in mass %. 22 The expression indicates the Zr content in the Ce-Zr composite oxide, converted to ZrO2, in mass.

[0051] [8] The catalyst for exhaust gas purification according to any one of [1] to [7], wherein, in the case that the catalyst for exhaust gas purification satisfies the condition 1a, the catalyst for exhaust gas purification further satisfies the following condition 2a.

[0052] Condition 2a: 1.30 × 10 -3 ≤Ra,

[0053] In the formula, Ra represents the gas permeability of the first catalyst layer and the partition wall portion, measured using a porosimeter before the heat treatment of the catalyst for exhaust gas purification, and the unit is cm. 3 / (cm) 2 ·s·Pa),

[0054] If the catalyst for waste gas purification satisfies condition 1b, the catalyst for waste gas purification further satisfies the following condition 2b.

[0055] Condition 2b: 1.30 × 10 -3 ≤Rb,

[0056] In the formula, Rb represents the gas permeability of the second catalyst layer and the partition wall portion, measured using a porosimeter before the heat treatment of the catalyst for exhaust gas purification, and the unit is cm. 3 / (cm) 2 ·s·Pa).

[0057] Invention Effects

[0058] According to the present invention, a catalyst for purifying exhaust gas is provided, which comprises a wall-flow substrate and a catalyst layer containing Zr-based oxides, and is capable of suppressing the reduction in PM capture performance caused by exposure to a high-temperature environment. Attached Figure Description

[0059] Figure 1 This is a partial cross-sectional view showing the state in which the exhaust gas purification catalyst of one embodiment of the present invention is disposed in the exhaust path of an internal combustion engine.

[0060] Figure 2 yes Figure 1 AA-line cross-section view.

[0061] Figure 3 yes Figure 1 BB line cross-section.

[0062] Figure 4 yes Figure 2 An enlarged view of the area indicated by reference numeral R1 in the attached figure.

[0063] Figure 5 yes Figure 3 An enlarged view of the area indicated by reference numeral R2 in the attached figure.

[0064] Figure 6 yes Figure 1 CC-line sectional view.

[0065] Figure 7A This is a top view of a slice cut from the catalyst used for exhaust gas purification (from the exhaust gas inflow side). Figure 7B (Top view from above).

[0066] Figure 7B yes Figure 7A Sectional view along line D1-D1.

[0067] Figure 8A This is a top view of a slice used in the measurement of gas permeability in the first catalyst layer and partition wall (from the exhaust gas inflow side). Figure 8C The top view (from the top side), that is, the view from above. Figure 7A (Corresponding top view).

[0068] Figure 8B This is a top view of a slice used in the measurement of gas permeability in the first catalyst layer and partition wall (from the exhaust gas outflow side). Figure 8C (Top view from below)

[0069] Figure 8C yes Figure 8A Sectional view along line D2-D2 (with) Figure 7B (Corresponding sectional view).

[0070] Figure 9A This is a top view of a slice cut from the catalyst used for exhaust gas purification (from the exhaust gas inflow side). Figure 9B (Top view from above).

[0071] Figure 9B yes Figure 9A Sectional view along line D3-D3.

[0072] Figure 10A This is a top view of a slice used in the measurement of gas permeability in the second catalyst layer and partition wall (from the exhaust gas inflow side). Figure 10C The top view (from the top side), that is, the view from above. Figure 9A (Corresponding top view).

[0073] Figure 10BThis is a top view of the slice used in the measurement of gas permeability in the second catalyst layer and partition wall (from the exhaust gas outflow side). Figure 10C (Top view from below)

[0074] Figure 10C yes Figure 10A Sectional view along line D4-D4 (with) Figure 9B (Corresponding sectional view).

[0075] Figure 11 This is a top view of a slice used in the measurement of gas permeability in the first catalyst layer and partition wall (from the exhaust gas inflow side). Figure 8C The top view (from the top side), that is, the view from above. Figure 8A (Same top view). For Figure 11 Some elements (components, parts, etc.) in the drawings have omitted reference numerals. Figure 11 The meaning of the elements (components, parts, etc.) in the text can be understood through reference. Figures 8A-8C To understand.

[0076] Figure 12 This is a top view of the slice used in the measurement of gas permeability in the second catalyst layer and partition wall (from the exhaust gas outflow side). Figure 10C The top view when looking down from the bottom (i.e., the view from the bottom of the plane). Figure 10B (Same top view). For Figure 12 Some elements (components, parts, etc.) in the drawings have omitted reference numerals. Figure 12 The meaning of the elements (components, parts, etc.) in the text can be understood through reference. Figures 10A-10C To understand. Detailed Implementation

[0077] Glossary of Terms

[0078] The following describes the terminology used in this specification. Unless otherwise specified, the following description applies to the entire contents of this specification.

[0079] <abbreviation>

[0080] “SEM” stands for Scanning Electron Microscopy, “EDX” stands for Energy Dispersive X-ray Spectroscopy, “SEM-EDX” stands for Scanning Electron Microscopy-Energy Dispersive X-ray Analysis, “EPMA” stands for Electron Probe Microscopy, “XRF” stands for Fluorescence X-ray Analysis, and “ICP-OES” stands for Inductively Coupled Plasma Emission Spectroscopy.

[0081] <Metallic Elements>

[0082] "Metallic elements" also include half-metallic elements such as Si and B.

[0083] Rare Earth Elements

[0084] Rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0085] <Precious Metal Elements>

[0086] "Noble metal elements" include Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.

[0087] <Oxides>

[0088] The meaning of "oxide" for metallic elements is as follows: Oxides of rare earth elements other than Ce, Pr, and Tb refer to sesquioxides (M₂O₃, where M represents a rare earth element other than Ce, Pr, and Tb). Ce oxide is CeO₂, and Pr oxide is Pr₆O₃. 11 The oxides of Tb are Tb4O7, Al is Al2O3, Zr is ZrO2, Si is SiO2, B is B2O3, Cr is Cr2O3, Mg is MgO, Ca is CaO, Sr is SrO, Ba is BaO, Fe is Fe3O4, Mn is Mn3O4, Ni is NiO, Ti is TiO2, Zn is ZnO, and Sn is SnO2.

[0089] <Conversion of metallic elements into the mass of metallic>

[0090] "The mass of a metal element converted into a metal" refers to the mass of a metal calculated assuming that the metal element exists as a metal composed of metal elements.

[0091] <Conversion of metallic elements into the mass of oxides>

[0092] "The mass of a metal element converted into its oxide" refers to the mass of the oxide of a metal element calculated assuming that the metal element exists as an oxide of the metal element.

[0093] <Material layer quality>

[0094] The "mass of the catalyst layer" refers to the calculated mass obtained by classifying all the metal elements contained in the catalyst layer into precious metal elements and non-precious metal elements. For precious metal elements, the mass converted to metal is calculated; for non-precious metal elements, the mass converted to oxide is calculated. In other words, the "mass of the catalyst layer" is the calculated mass obtained by adding the mass converted to metal of the precious metal elements in the catalyst layer to the mass converted to oxide of the non-precious metal elements in the catalyst layer.

[0095] Once the information (such as composition and quantity) of the raw materials used in the manufacture of the catalyst layer is known, the quality of the catalyst layer can be determined based on the information of the raw materials.

[0096] <Content of metal elements in the catalyst layer converted to metal or oxide>

[0097] The "conversion of metal elements in the catalyst layer to metal content" is defined by the following formula: Conversion of metal elements in the catalyst layer to metal content (mass%) = (conversion of metal elements in the catalyst layer to metal content) / (mass of catalyst layer) × 100.

[0098] The content of metal elements in the catalyst layer as oxides is defined by the following formula: Content of metal elements in the catalyst layer as oxides (mass%) = (mass of metal elements in the catalyst layer as oxides) / (mass of catalyst layer) × 100.

[0099] Once the information (such as composition and quantity) of the raw materials used to form the catalyst layer is known, the content (mass%) of the metal elements in the catalyst layer, converted into metals or oxides, can be determined based on the information of the raw materials.

[0100] In the absence of information about the raw materials used to form the catalyst layer, the content (mass%) of metal elements in the catalyst layer, converted to metals or oxides, can be determined using conventional methods such as SEM-EDX. Specifically, as described below.

[0101] Elemental analysis of the catalyst layer was performed using conventional methods such as SEM-EDX to determine the constituent elements and calculate the molar percentage of each metal element. For each of the 10 SEM fields, the molar percentage of each metal element was calculated, and the average of the molar percentages of each metal element across the 10 fields was taken as the molar percentage of each metal element in the catalyst layer.

[0102] The V value of each noble metal element in the catalyst layer can be calculated using the following formula.

[0103] The 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)

[0104] The W value of each metal element in the catalyst layer, excluding the noble metal element, can be calculated using the following formula.

[0105] The 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)

[0106] The following formula can be used to calculate the content (mass%) of each noble metal element in the catalyst layer as a metal.

[0107] The conversion of each noble metal element in the catalyst layer into its metal content (mass%) = (V value of each noble metal element) / {(sum of V values ​​of all noble metal elements) + (sum of W values ​​of all metal elements other than noble metal elements)} × 100

[0108] The following formula can be used to calculate the content (mass %) of each metal element in the catalyst layer, excluding noble metal elements, converted into oxides.

[0109] The content (mass%) of oxides of all metal elements other than noble metal elements in the catalyst layer = (W value of all metal elements other than noble metal elements) / {(sum of V values ​​of all noble metal elements) + (sum of W values ​​of all metal elements other than noble metal elements)} × 100

[0110] <Metal Oxides>

[0111] "Metal oxides" refer to oxides containing one or more metallic elements. Examples of metal oxides include Al-based oxides, Ce-based oxides, Zr-based oxides, and Ce-Zr composite oxides.

[0112] <Mass of metal oxides>

[0113] "Mass of metal oxides" refers to the total mass of oxides of metal elements, calculated assuming that each metal element exists as an oxide.

[0114] <Conversion of metal elements in metal oxides into oxide content>

[0115] The "conversion rate of metal elements in metal oxides to oxides" is defined by the following formula: Conversion rate of metal elements in metal oxides to oxides (mass%) = (mass of metal elements in metal oxides to oxides) / (mass of metal oxides) × 100.

[0116] When the composition of the metal oxide is known, the content (mass%) of the metal element in the metal oxide, converted to the corresponding oxide, can be calculated from the composition of the metal oxide.

[0117] When the composition of the metal oxide is unknown, the content (mass%) of the metal element in the metal oxide, converted to the corresponding oxide, can be determined by conventional methods such as SEM-EDX. Specifically, it is carried out as described below.

[0118] Elemental analysis of the metal oxide is performed by conventional methods such as SEM-EDX to determine the types of constituent elements of the metal oxide, and the content (mass%) of each determined metal element converted to the corresponding oxide is obtained.

[0119] <Al-based Oxide>

[0120] Al-based oxide refers to an oxide containing Al, and is an oxide in which Al is the element with the highest content based on mass among the metal elements constituting the oxide. However, substances classified as Zr-based oxides do not belong to Al-based oxides.

[0121] Al-based oxide is used as a support for catalytically active components, and is distinguished from alumina used as a binder (alumina binder). Al-based oxide is, for example, in particulate form. From the perspective of improving the loading performance of catalytically active components, Al-based oxide is preferably porous.

[0122] Generally, Al-based oxide has higher heat resistance than other inorganic oxides (e.g., Ce-based oxides, Zr-based oxides, etc.). Therefore, when the catalyst layer contains Al-based oxide, the heat resistance of the catalyst layer is improved, and the exhaust gas purification performance of the catalyst layer is enhanced.

[0123] Al-based oxide may contain one or more metal elements other than Al (hereinafter referred to as "additional element M1"). The additional element M1 can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0124] In the Al-based oxide, the additional element M1 may form a solid solution phase (e.g., a solid solution phase of Al₂O₃ and the oxide of the additional element M1), may form an individual phase as a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M1), or may form both a solid solution phase and an individual phase.

[0125] As Al-based oxides, examples thereof include alumina (Al₂O₃), oxides obtained by modifying the surface of alumina with an additional element M₁ or an oxide thereof, oxides obtained by solid-dissolving the additional element M₁ in alumina, and the like. Examples of Al-based oxides containing the additional element M₁ include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, and the like.

[0126] From the viewpoint of improving the heat resistance of the Al-based oxide, based on the mass of the Al-based oxide, the content of Al in the Al-based oxide converted to Al₂O₃ is preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. The upper limit is 100% by mass.

[0127] <Ce-based oxides>

[0128] A Ce-based oxide refers to an oxide containing Ce, and refers to an oxide in which Ce is the element with the highest content based on mass among the metal elements constituting the oxide. However, substances belonging to Zr-based oxides do not belong to Ce-based oxides.

[0129] Ce-based oxides are used as carriers for catalytically active components, and are distinguished from ceria used as binders (ceria binders). Ce-based oxides are, for example, in the form of particles. From the viewpoint of improving the loadability of catalytically active components, Ce-based oxides are preferably porous.

[0130] Ce-based oxides have oxygen storage capacity, which mitigates fluctuations in oxygen concentration in exhaust gas and expands the operating window of catalytically active components. Therefore, when the catalyst layer contains a Ce-based oxide, the exhaust gas purification performance of the catalyst layer is improved.

[0131] The Ce-based oxide may contain one or two or more metal elements other than Ce (hereinafter referred to as "additional element M₂"). The additional element M₂ can be selected from, for example, rare earth elements other than Ce (e.g., Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, and the like.

[0132] In the Ce-based oxide, the additional element M₂ may form a solid solution phase (e.g., a solid solution phase of CeO₂ and an oxide of the additional element M₂), may form a separate phase as a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M₂), or may form both the solid solution phase and the separate phase.

[0133] As Ce-based oxides, examples include cerium dioxide (CeO₂), oxides obtained by modifying the surface of cerium dioxide with an additional element M2 or an oxide thereof, and oxides obtained by dissolving an additional element M2 in solid solution in cerium dioxide, etc.

[0134] From the perspective of improving the oxygen storage capacity of the Ce-based oxide, based on the mass of the Ce-based oxide, the content of Ce in the Ce-based oxide calculated as CeO₂ is preferably 90% by mass or more, more preferably 95% by mass or more, and still more preferably 99% by mass or more. The upper limit is 100% by mass.

[0135] <Zr-based oxide>

[0136] A Zr-based oxide refers to an oxide containing Zr, and refers to an oxide in which the content of Zr in the oxide calculated as ZrO₂ is 5% by mass or more based on the mass of the oxide. Zr-based oxides are distinguished from zirconia used as a binder. In this specification, zirconia used as a binder is sometimes referred to as "zirconia binder".

[0137] The Zr-based oxide is, for example, in the form of particles. The Zr-based oxide is used as a support for a catalytically active component. From the perspective of improving the loadability of the catalytically active component, the Zr-based oxide is preferably porous.

[0138] The Zr-based oxide may contain one or two or more metal elements other than Zr (hereinafter referred to as "additional element M3"). The additional element M3 can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Al, Cr, and the like.

[0139] In the Zr-based oxide, the additional element M3 may form a solid solution phase (for example, a solid solution phase of ZrO₂ and an oxide of the additional element M3), may form a separate phase as a crystalline phase or an amorphous phase (for example, an oxide phase of the additional element M3), or may form both a solid solution phase and a separate phase. However, it is preferable that at least a part of the additional element M3 forms a solid solution phase.

[0140] As Zr-based oxides, examples include zirconia (ZrO₂), oxides obtained by modifying the surface of zirconia with an additional element M3 or an oxide thereof, and oxides obtained by dissolving an additional element M3 in solid solution in zirconia, etc.

[0141] From the perspective of improving the heat resistance of the Zr-based oxide, based on the mass of the Zr-based oxide, the content of Zr in the Zr-based oxide calculated as ZrO₂ is preferably 7% by mass or more, more preferably 10% by mass or more, and still more preferably 30% by mass or more. The upper limit is 100% by mass.

[0142] <Ce-Zr based composite oxide>

[0143] The Ce-Zr based composite oxide refers to a composite oxide comprising Ce and Zr, wherein based on the mass of the composite oxide, the content of Ce in the composite oxide, calculated as CeO₂, is 5 mass% or more and 95 mass% or less, and based on the mass of the composite oxide, the content of Zr in the composite oxide, calculated as ZrO₂, is 5 mass% or more and 95 mass% or less. The Ce-Zr based composite oxide is a type of Zr-based oxide.

[0144] The Ce-Zr based composite oxide is used as a carrier for catalytic active components. The Ce-Zr based composite oxide is, for example, granular. From the perspective of improving the loading performance of the catalytic active component, the Ce-Zr based composite oxide is preferably porous.

[0145] The Ce-Zr based composite oxide has oxygen storage capacity, which mitigates fluctuations in oxygen concentration in exhaust gas and expands the working window of the catalytic active component. Therefore, when the catalyst layer comprises the Ce-Zr based composite oxide, the exhaust gas purification performance of the catalyst layer is improved.

[0146] The Ce-Zr based composite oxide may comprise one or more metal elements other than Ce and Zr (hereinafter referred to as "additional element M4"). The additional element M4 can be selected from, for example, rare earth elements other than Ce (e.g., Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.

[0147] In the Ce-Zr based composite oxide, Ce may form a solid solution phase (e.g., a solid solution phase of CeO₂ and ZrO₂), may form a separate phase as a crystalline phase or an amorphous phase (e.g., a separate CeO₂ phase), or may form both a solid solution phase and a separate phase; however, it is preferable that at least a part of Ce forms a solid solution phase.

[0148] In the Ce-Zr based composite oxide, Zr may form a solid solution phase (e.g., a solid solution phase of CeO₂ and ZrO₂), may form a separate phase as a crystalline phase or an amorphous phase (e.g., a separate ZrO₂ phase), or may form both a solid solution phase and a separate phase; however, it is preferable that at least a part of Zr forms a solid solution phase.

[0149] When Ce-Zr composite oxides contain the additional element M4, the additional element M4 can form a solid solution phase (e.g., a solid solution phase of CeO2 and oxides of the additional element M4, a solid solution phase of ZrO2 and oxides of the additional element M4, a solid solution phase of CeO2 and oxides of ZrO2 and oxides of the additional element M4, etc.), or it can form a separate phase as a crystalline or amorphous phase (e.g., a separate phase of oxides of the additional element M4), or both a solid solution phase and a separate phase, but it is preferred that at least a portion of the additional element M4 forms a solid solution phase.

[0150] Examples of Ce-Zr composite oxides include CeO2-ZrO2 solid solutions, oxides obtained by modifying the surface of CeO2-ZrO2 solid solutions with additional element M4 or its oxides, and oxides obtained by dissolving additional element M4 in CeO2-ZrO2 solid solutions.

[0151] From the perspective of improving the oxygen storage capacity of Ce-Zr composite oxides, based on the mass of Ce-Zr composite oxides, the content of Ce in Ce-Zr composite oxides converted to CeO2 is preferably 5% to 90% by mass, more preferably 7% to 90% by mass, and even more preferably 10% to 85% by mass.

[0152] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, based on the mass of Ce-Zr composite oxides, the content of Zr in Ce-Zr composite oxides converted to ZrO2 is preferably 5% to 90% by mass, more preferably 7% to 90% by mass, and even more preferably 10% to 85% by mass.

[0153] From the viewpoint of improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxides, based on the mass of the Ce-Zr composite oxide, the sum of the content of Ce converted to CeO2 and the content of Zr converted to ZrO2 in the Ce-Zr composite oxide is preferably 70% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, and even more preferably 85% by mass or more. The upper limit is 100% by mass.

[0154] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, Ce-Zr composite oxides preferably contain one or more rare earth elements other than Ce. Rare earth elements other than Ce can be selected from, for example, Y, Pr, La, Nd, Sm, Eu, Gd, etc. Based on the mass of the Ce-Zr composite oxide, the content of rare earth elements other than Ce in the Ce-Zr composite oxide, converted to oxides, is preferably 5% by mass or more and 35% by mass or less, more preferably 7% by mass or more and 30% by mass or less, and even more preferably 9% by mass or more and 25% by mass or less. "Content of rare earth elements other than Ce in the Ce-Zr composite oxide," when the Ce-Zr composite oxide contains one rare earth element other than Ce, refers to the content of that one rare earth element converted to oxide; when the Ce-Zr composite oxide contains two or more rare earth elements other than Ce, it refers to the total content of those two or more rare earth elements converted to oxides.

[0155] Catalysts for Waste Gas Purification

[0156] Hereinafter, embodiments of the catalyst for exhaust gas purification according to the present invention will be described based on the accompanying drawings. Furthermore, where two or more embodiments described in this specification can be combined, such combinations of two or more embodiments are also included in the present invention.

[0157] like Figure 1 As shown, in one embodiment of the present invention, a catalyst 1 for exhaust gas purification (hereinafter referred to as "catalyst 1") is disposed in the exhaust path within the exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine (e.g., a GDI engine), a diesel engine, etc.

[0158] exist Figure 1 In the diagram, the exhaust gas flow direction of the internal combustion engine is indicated by the reference numeral E. The same applies to other diagrams. In this specification, sometimes the upstream side of the exhaust gas flow direction E (e.g., Figure 1 The left side of the exhaust gas flow direction E is referred to as the "exhaust gas inflow side", "inflow side" or "upstream side", while the downstream side of the exhaust gas flow direction E (e.g., Figure 1 The right side of the exhaust gas flow is referred to as the "exhaust gas outflow side", "outflow side", or "downstream side".

[0159] like Figure 1 As shown, the catalyst 1 is arranged in the exhaust path of the internal combustion engine such that the axial direction of the substrate 10 is consistent with or substantially consistent with the exhaust gas flow direction E.

[0160] like Figures 1-6 As shown, catalyst 1 comprises a substrate 10, a first catalyst layer 20, and a second catalyst layer 30.

[0161] One of the first catalyst layer 20 and the second catalyst layer 30 can be omitted. That is, catalyst 1 only needs to have at least one of the first catalyst layer 20 and the second catalyst layer 30. The present invention includes embodiments in which catalyst 1 has the first catalyst layer 20 but not the second catalyst layer 30, embodiments in which catalyst 1 has the second catalyst layer 30 but not the first catalyst layer 20, and embodiments in which catalyst 1 has the first catalyst layer 20 and the second catalyst layer 30.

[0162] Catalyst 1 satisfies at least one of the following conditions 1a and 1b.

[0163] [Condition 1a]

[0164] Xa / Ya ≤ 1.40 and Ya ≤ 5.00

[0165] [Condition 1b]

[0166] Xb / Yb≤1.40 and Yb≤5.00

[0167] Xa represents the 10% flow diameter (μm) of the first catalyst layer 20 and partition wall 12 measured by the bubble point method using a perm porosimeter after heat treatment of catalyst 1 at 950°C for 35 hours in atmospheric atmosphere. Ya represents the 10% flow diameter (μm) of the first catalyst layer 20 and partition wall 12 measured by the bubble point method using a perm porosimeter before the aforementioned heat treatment of catalyst 1. Xb represents the 10% flow diameter (μm) of the second catalyst layer 30 and partition wall 12 measured by the bubble point method using a perm porosimeter after the aforementioned heat treatment of catalyst 1. Yb represents the 10% flow diameter (μm) of the second catalyst layer 30 and partition wall 12 measured by the bubble point method using a perm porosimeter before the aforementioned heat treatment of catalyst 1.

[0168] In the phrase "10% flow diameter of the first catalyst layer 20 and the partition wall portion 12", "partition wall portion 12" refers to the portion of the partition wall portion 12 in which the first catalyst layer 20 is disposed. In the phrase "10% flow diameter of the second catalyst layer 30 and the partition wall portion 12", "partition wall portion 12" refers to the portion of the partition wall portion 12 in which the second catalyst layer 30 is disposed.

[0169] The present invention includes embodiments in which catalyst 1 satisfies conditions 1a and 1b, embodiments in which catalyst 1 satisfies condition 1a but not condition 1b, and embodiments in which catalyst 1 satisfies condition 1b but not condition 1a.

[0170] Specifically, the present invention includes the following embodiments.

[0171] [A] An embodiment in which catalyst 1 comprises a first catalyst layer 20 and a second catalyst layer 30, satisfying conditions 1a and 1b.

[0172] [B] An embodiment in which catalyst 1 comprises a first catalyst layer 20 and a second catalyst layer 30, satisfying condition 1a but not condition 1b.

[0173] [C] An embodiment in which catalyst 1 comprises a first catalyst layer 20 and a second catalyst layer 30, satisfying condition 1b but not condition 1a.

[0174] [D] An embodiment in which catalyst 1 has a first catalyst layer 20 but no second catalyst layer 30, satisfying condition 1a (in this embodiment, catalyst 1 does not have a second catalyst layer 30, therefore condition 1b is not satisfied).

[0175] [E] An embodiment in which catalyst 1 has a second catalyst layer 30 but no first catalyst layer 20, satisfying condition 1b (in this embodiment, catalyst 1 does not have a first catalyst layer 20, therefore condition 1a is not satisfied).

[0176] In this specification, the following expressions are used: "Catalyst 1 satisfies condition 1a", "Catalyst 1 satisfies condition 1b", "Catalyst 1 satisfies condition 1a but not condition 1b", "Catalyst 1 satisfies condition 1b but not condition 1a", and "Catalyst 1 satisfies both conditions 1a and 1b". "Catalyst 1 satisfies condition 1a" corresponds to embodiments A, B, and D; "Catalyst 1 satisfies condition 1b" corresponds to embodiments A, C, and E; "Catalyst 1 satisfies condition 1a but not condition 1b" corresponds to embodiments B and D; "Catalyst 1 satisfies condition 1b but not condition 1a" corresponds to embodiments C and E; and "Catalyst 1 satisfies both conditions 1a and 1b" corresponds to embodiment A.

[0177] <Substrate>

[0178] The material constituting the substrate 10 can be appropriately selected from known materials. Examples of materials constituting the substrate 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, zirconium oxide, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of metallic materials include alloys such as stainless steel.

[0179] Substrate 10 has a length L 10 The length L of the substrate 10 10The length L of the substrate 10 can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. From the perspective of improving exhaust gas purification performance and PM capture, the length L of the substrate 10... 10 Preferably, the length is 50 mm or more and 160 mm or less, more preferably 80 mm or more and 130 mm or less. In this specification, unless otherwise specified, "length" refers to the axial dimension of the substrate 10.

[0180] The volume of the substrate 10 can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. From the viewpoint of improving exhaust gas purification performance and PM capture performance, the volume of the substrate 10 is preferably 0.5L or more and 2.5L or less, more preferably 0.5L or more and 2.0L or less, and even more preferably 0.7L or more and 1.8L or less. In this specification, the volume of the substrate 10 refers to the apparent volume of the substrate 10. When the substrate 10 is cylindrical, if the outer diameter of the substrate 10 is set to 2r and the length of the substrate 10 is set to L... 10 The volume of substrate 10 is given by the formula: Volume of substrate 10 = π × r 2 ×L 10 Find the answer.

[0181] Substrate 10 is a wall-flow type substrate.

[0182] like Figure 2 and 3 As shown, the substrate 10 has a cavity 13 and a porous partition 12 that separates the cavity 13. The substrate 10 is preferably a honeycomb structure.

[0183] like Figure 2 and Figure 3 As shown, the substrate 10 includes a cylindrical portion 11, a chamber 13, and a partition wall portion 12 formed within the cylindrical portion 11. The cylindrical portion 11 defines the outer shape of the substrate 10, and the axial direction of the cylindrical portion 11 is aligned with the axial direction of the substrate 10. Figure 2 and Figure 3 As shown, the shape of the cylindrical part 11 is, for example, cylindrical, but it can also be other shapes such as elliptical cylindrical or polygonal cylindrical.

[0184] like Figures 2-6 As shown, chamber 13 extends along the exhaust gas flow direction E, and has an end on the exhaust gas inflow side and an end on the exhaust gas outflow side.

[0185] like Figure 6As shown, the substrate 10 is provided with a first sealing part 14 that seals the end of a portion of the chamber 13 on the exhaust gas outflow side, and a second sealing part 15 that seals the end of the remaining chamber 13 on the exhaust gas inflow side. Thus, a portion of the chamber 13 becomes an inflow-side chamber 13a with the exhaust gas inflow side open and the exhaust gas outflow side closed by the first sealing part 14, and the remaining chamber 13 becomes an outflow-side chamber 13b with the exhaust gas inflow side closed by the second sealing part 15 and the exhaust gas outflow side open.

[0186] The inflow side chamber 13a has a length L 13a The length L of the inflow into side chamber 13a 13a Formula: The length L of the inflow into side chamber 13a 13a = (Length L of substrate 10) 10 The length of the first sealing part 14 is calculated as follows: L - (length of the first sealing part 14). The length of the first sealing part 14 refers to its axial dimension on the substrate 10. 13a The length L of the inflow side chamber 13a can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. From the perspective of improving exhaust gas purification performance and PM capture, the length L of the inflow side chamber 13a... 13a Relative to the length L of the substrate 10 10 percentage (L) 13a / L 10 (×100) is preferably 80% or more, more preferably 85% or more. The upper limit of this percentage can be appropriately adjusted taking into account the length of the first sealing part 14. The upper limit of this percentage can be, for example, 99% or less, or 98% or less. These upper limits can be combined with any of the lower limits mentioned above.

[0187] The outflow side chamber 13b has a length L 13b The length L of the outflow from side chamber 13b 13b Formula: Length L of the outflow side chamber 13b 13b = (Length L of substrate 10) 10 The length of the second sealing part 15 is calculated as follows: (The length of the second sealing part 15) refers to the axial dimension of the second sealing part 15 on the substrate 10. The length L of the outflow side chamber 13b is also calculated. 13b The length L of the outflow side chamber 13b can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. From the perspective of improving exhaust gas purification performance and PM capture, the length L of the outflow side chamber 13b is... 13b Relative to the length L of the substrate 10 10 percentage (L) 13b / L 10(×100) is preferably 80% or more, more preferably 85% or more. The upper limit of this percentage can be appropriately adjusted taking into account the length of the second sealing part 15. For example, the upper limit of this percentage can be 99% or less, or 98% or less. These upper limits can be combined with any of the lower limits mentioned above.

[0188] like Figures 2-6 As shown, the inflow side chamber 13a and the outflow side chamber 13b are alternately arranged in the longitudinal direction and in the transverse direction, and adjacent inflow side chambers 13a and outflow side chambers 13b are separated by partition wall portion 12.

[0189] like Figures 2-6 As shown, a plurality of (four in this embodiment) outflow side chambers 13b are arranged around an inflow side chamber 13a, and the inflow side chamber 13a and the outflow side chambers 13b arranged around the inflow side chamber 13a are separated by a partition wall 12. Similarly, a plurality of (four in this embodiment) inflow side chambers 13a are arranged around an outflow side chamber 13b, and the outflow side chambers 13b and the inflow side chambers 13a arranged around the outflow side chamber 13b are separated by a partition wall 12.

[0190] like Figures 2-6 As shown, the top view shape of the end (opening) of the exhaust gas inflow side of each inflow side chamber 13a and the top view shape of the end (opening) of the exhaust gas outflow side of each outflow side chamber 13b are, for example, quadrilaterals (preferably squares or rectangles, more preferably squares).

[0191] The areas of the exhaust gas inflow end (opening) of each inflow-side chamber 13a in plan view are preferably the same or substantially the same. The areas of the exhaust gas outflow end (opening) of each outflow-side chamber 13b in plan view are preferably the same or substantially the same. The areas of the exhaust gas inflow end (opening) of each inflow-side chamber 13a in plan view and the areas of the exhaust gas outflow end (opening) of each outflow-side chamber 13b in plan view are preferably the same or substantially the same.

[0192] When the top view shape of the end (opening) of the exhaust gas inflow side of each inflow-side chamber 13a is quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the left side of each inflow-side chamber 13a ( Figure 4 and Figure 5 The lengths of the left sides are the same or approximately the same, and the right sides of each inflow side chamber 13a are ( Figure 4 and Figure 5 The lengths of the right sides are the same or approximately the same, and the upper sides of each inflow side chamber 13a are ( Figure 4 and Figure 5The lengths of the upper sides of the chambers are the same or approximately the same, and the lower sides of each inflow chamber 13a are also the same. Figure 4 and Figure 5 The lengths of the lower sides are the same or approximately the same.

[0193] When the top view shape of the end (opening) of the waste gas outlet side of each outlet side chamber 13b is quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the left side of each outlet side chamber 13b ( Figure 4 and Figure 5 The lengths of the left sides of each side are the same or approximately the same, and the right sides of each outflow side chamber 13b are ( Figure 4 and Figure 5 The lengths of the right sides are the same or approximately the same, and the upper sides of each outflow side chamber 13b are ( Figure 4 and Figure 5 The lengths of the upper sides of the chambers are the same or approximately the same, and the lower sides of each outflow chamber 13b are also the same. Figure 4 and Figure 5 The lengths of the lower sides are the same or approximately the same.

[0194] When the top view shape of the end (opening) of the exhaust gas inflow side of each inflow-side chamber 13a and the top view shape of the end (opening) of the exhaust gas outflow side of each outflow-side chamber 13b are quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the left side of each inflow-side chamber 13a ( Figure 4 and Figure 5 The length of the left side of the side and the left side of each outflow side chamber 13b ( Figure 4 and Figure 5 The lengths of the left sides are the same or approximately the same, and the right sides of each inflow side chamber 13a are ( Figure 4 and Figure 5 The length of the right side of the outflow side chamber 13b is equal to the right side of the right side of the outflow side chamber 13b. Figure 4 and Figure 5 The lengths of the right sides are the same or approximately the same, and the upper sides of each inflow side chamber 13a are ( Figure 4 and Figure 5 The length of the upper side of the cavity 13b is equal to the length of the upper side of the cavity 13b. Figure 4 and Figure 5 The lengths of the upper sides of the chambers are the same or approximately the same, and the lower sides of each inflow chamber 13a are also the same. Figure 4 and Figure 5 The length of the lower side of the cavity 13b is equal to the length of the lower side of the cavity 13b. Figure 4 and Figure 5 The lengths of the lower sides are the same or approximately the same.

[0195] When the top view shape of the end (opening) of the exhaust gas inflow side of each inflow-side chamber 13a and the top view shape of the end (opening) of the exhaust gas outflow side of each outflow-side chamber 13b are quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the left side of the inflow-side chamber 13a and the outflow-side chamber 13b arranged longitudinally ( Figure 4 and Figure 5 The left side) is located on the right side of the inflow side chamber 13a and the outflow side chamber 13b, which are arranged longitudinally on the same straight line or approximately on the same straight line. Figure 4 and Figure 5 The right side) is located on the same straight line or approximately on the same straight line, above the inflow side chamber 13a and the outflow side chamber 13b, which are arranged laterally. Figure 4 and Figure 5 The upper side of the (the same as or approximately the same as the upper side of the inflow side chamber 13a and the lower side of the outflow side chamber 13b arranged laterally) is located on the same straight line or approximately on the same straight line, and on the lower side of the inflow side chamber 13a and the outflow side chamber 13b arranged laterally. Figure 4 and Figure 5 The lower edge of the (the edge of the) is on the same straight line or roughly on the same straight line.

[0196] The chamber density per square inch of substrate 10 can be appropriately adjusted taking into account PM collection performance, pressure loss, etc. From the viewpoint of improving PM collection performance and suppressing pressure loss increase, the chamber density per square inch of substrate 10 is preferably 180 or more and 350 or less. The chamber density per square inch of substrate 10 is the total number of inflow-side chambers 13a and outflow-side chambers 13b per square inch in a cross-section obtained by cutting substrate 10 with a plane perpendicular to the axis of substrate 10.

[0197] The partition 12 has a porous structure that allows exhaust gas to pass through.

[0198] like Figures 4-6 As shown, the partition wall portion 12 has an outer surface S1a on the inflow side chamber 13a side and an outer surface S1b on the outflow side chamber 13b side. The outer surface S1a is the region on the inflow side chamber 13a side (i.e., the region in contact with the inflow side chamber 13a) that extends along the exhaust gas flow direction E of the outer surface defining the shape of the partition wall portion 12. The outer surface S1b is the region on the outflow side chamber 13b side (i.e., the region in contact with the outflow side chamber 13b) that extends along the exhaust gas flow direction E of the outer surface defining the shape of the partition wall portion 12.

[0199] The thickness of the partition wall 12 can be appropriately adjusted taking into account PM collection performance, pressure loss, etc. From the viewpoint of improving PM collection performance and suppressing pressure loss increase, the thickness of the partition wall 12 is preferably 110 μm or more and 380 μm or less, more preferably 130 μm or more and 330 μm or less, and even more preferably 150 μm or more and 310 μm or less.

[0200] <First Catalyst Layer>

[0201] like Figure 4 and Figure 6 As shown, the first catalyst layer 20 is disposed on the inflow side chamber 13a side of the partition wall portion 12.

[0202] like Figure 6 As shown, the first catalyst layer 20 extends from the end of the partition wall portion 12 on the exhaust gas inflow side along the exhaust gas flow direction E. In this embodiment, the first catalyst layer 20 does not reach the end of the partition wall portion 12 on the exhaust gas outflow side, but it may reach the end of the partition wall portion 12 on the exhaust gas outflow side.

[0203] like Figure 4 and Figure 6 As shown, the first catalyst layer 20 has a portion on the outer surface S1a of the partition wall portion 12 formed along the exhaust gas flow direction E from the end of the partition wall portion 12 on the exhaust gas inflow side. This portion protrudes from the outer surface S1a of the partition wall portion 12 toward the inflow side chamber 13a. Hereinafter, this portion will be referred to as the "protruding portion". By having the protruding portion, the first catalyst layer 20 has improved contact with exhaust gas and PM, thereby improving exhaust gas purification performance and PM capture performance.

[0204] The first catalyst layer 20 may also have a raised portion and a portion existing inside the partition wall portion 12 (hereinafter referred to as the "internal portion"). The partition wall portion 12 is porous, so when forming the first catalyst layer 20, the internal portion is sometimes formed together with the raised portion. The raised portion and the internal portion may also be continuous. "The first catalyst layer 20 is disposed on the inflow side chamber 13a side of the partition wall portion 12" includes an embodiment in which the first catalyst layer 20 has a raised portion but no internal portion, and an embodiment in which the first catalyst layer 20 has both a raised portion and an internal portion.

[0205] The area containing the raised portion of the first catalyst layer 20 does not overlap with the area containing the partition wall portion 12, but the area containing the inner portion of the first catalyst layer 20 overlaps with the area containing the partition wall portion 12. Therefore, by cutting the catalyst 1 with a plane perpendicular to the axis of the substrate 10 and observing the first catalyst layer 20 and the partition wall portion 12 present on the cut surface, the raised portion and the inner portion of the first catalyst layer 20 can be determined based on the morphological differences between the first catalyst layer 20 and the partition wall portion 12. Elemental mapping of the cut surface can also be performed during the observation of the cut surface. Elemental mapping can be performed, for example, by combining SEM-based observation of the cut surface and compositional analysis of the cut surface. Elemental mapping can be performed, for example, using SEM-EDX, EPMA, etc. By elemental mapping of the cut surface, the raised portion and the inner portion can be determined based on the morphological and compositional differences between the first catalyst layer 20 and the partition wall portion 12.

[0206] <Second Catalyst Layer>

[0207] like Figure 5 and Figure 6 As shown, the second catalyst layer 30 is disposed on the outflow side chamber 13b side of the partition wall portion 12.

[0208] like Figure 6 As shown, the second catalyst layer 30 extends from the end of the partition wall portion 12 on the exhaust gas outflow side in a direction opposite to the exhaust gas flow direction E. In this embodiment, the second catalyst layer 30 does not reach the end of the partition wall portion 12 on the exhaust gas inflow side, but it may reach the end of the partition wall portion 12 on the exhaust gas inflow side.

[0209] like Figure 5 and Figure 6 As shown, the second catalyst layer 30 has a portion on the outer surface S1b of the partition wall portion 12 formed in a direction opposite to the exhaust gas flow direction E, extending from the end of the partition wall portion 12 on the exhaust gas outflow side. This portion protrudes from the outer surface S1b of the partition wall portion 12 toward the outflow side chamber 13b. Hereinafter, this portion will be referred to as the "protruding portion". Because the second catalyst layer 30 has a protruding portion, the contact between the second catalyst layer 30 and the exhaust gas and PM is improved, thereby improving the exhaust gas purification performance and PM capture performance.

[0210] The second catalyst layer 30 may also have a raised portion and a portion existing inside the partition wall portion 12 (hereinafter referred to as the "internal portion"). The partition wall portion 12 is porous, so when forming the second catalyst layer 30, the internal portion is sometimes formed together with the raised portion. The raised portion and the internal portion may also be continuous. "The second catalyst layer 30 is disposed on the outflow side chamber 13b side of the partition wall portion 12" includes an embodiment in which the second catalyst layer 30 has a raised portion but no internal portion, and an embodiment in which the second catalyst layer 30 has both a raised portion and an internal portion.

[0211] The above description of the method for determining the raised portion and the inner portion of the first catalyst layer 20 also applies to the second catalyst layer 30. In application, "first catalyst layer 20" is replaced with "second catalyst layer 30".

[0212] <The Role of Catalysts>

[0213] Exhaust gas from the internal combustion engine flows from one end of the exhaust pipe P to the other in the exhaust path within the exhaust pipe P, and is purified by the catalyst 1 disposed within the exhaust pipe P. At this time, exhaust gas flowing in from the exhaust gas inflow side end (opening) of the inflow side chamber 13a flows out from the exhaust gas outflow side end (opening) of the outflow side chamber 13b via a predetermined path. This type of flow is called wall flow. The prescribed paths include: a path where exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow side chamber 13a passes sequentially through the first catalyst layer 20 and the partition wall portion 12 to reach the outlet side chamber 13b, and flows out from the end (opening) of the exhaust gas outflow side of the outlet side chamber 13b; a path where exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow side chamber 13a passes sequentially through the partition wall portion 12 and the second catalyst layer 30 to reach the outlet side chamber 13b, and flows out from the end (opening) of the exhaust gas outflow side of the outlet side chamber 13b; and a path where exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow side chamber 13a passes sequentially through the first catalyst layer 20, the partition wall portion 12 and the second catalyst layer 30 to reach the outlet side chamber 13b, and flows out from the end (opening) of the exhaust gas outflow side of the outlet side chamber 13b.

[0214] In catalyst 1, when exhaust gas flows in from the exhaust gas inflow side end (opening) of the inflow side chamber 13a and flows out from the exhaust gas outflow side end (opening) of the outflow side chamber 13b via a predetermined path, PM in the exhaust gas is captured by the pores of the partition wall 12, the first catalyst layer 20, and the second catalyst layer 30. Therefore, catalyst 1 is useful as a gasline particulate filter for gasoline engines or a diesel particulate filter for diesel engines.

[0215] <Structure of the catalyst layer>

[0216] The structure of the catalyst layer will now be described. Unless otherwise specified, the following description of the catalyst layer structure applies to both the first catalyst layer 20 and the second catalyst layer 30. When applied to the first catalyst layer 20, "catalyst layer" is replaced by "first catalyst layer 20," and when applied to the second catalyst layer 30, "catalyst layer" is replaced by "second catalyst layer 30." Furthermore, unless otherwise specified, the following description of the catalyst layer structure applies to embodiments A through E.

[0217] The catalyst layer 20 can have a single-layer structure or a stacked structure.

[0218] When the catalyst layer has a stacked structure, the catalyst layer comprises two or more layers stacked in the thickness direction of the catalyst layer. The two or more layers include a lower layer and an upper layer. The lower layer is the layer located on the side closer to the partition wall 12 than the upper layer. A portion of the catalyst layer may be composed of either the lower layer or the upper layer. That is, in addition to the portion composed of both the lower and upper layers, the portion composed of either the lower or upper layer is also part of the catalyst layer.

[0219] As a layered structure, a double-layer structure consisting of a lower layer and an upper layer disposed on the lower layer can be cited as an example.

[0220] When the catalyst layer has a layered structure, the raised portion of the catalyst layer can be formed entirely or partially of one layer, or it can be formed entirely of one or more layers and entirely or partially of another layer. For example, when the catalyst layer has a double-layered structure, the raised portion of the catalyst layer can be formed entirely of the upper layer or partially of it, or it can be formed entirely of the upper layer and partially of the lower layer.

[0221] In one embodiment, the first catalyst layer 20 and the second catalyst layer 30 each have a monolayer structure. In another embodiment, the first catalyst layer 20 has a stacked structure (e.g., a bilayer structure), and the second catalyst layer 30 has a monolayer structure. In yet another embodiment, the first catalyst layer 20 has a monolayer structure, and the second catalyst layer 30 has a stacked structure (e.g., a bilayer structure). In still another embodiment, the first catalyst layer 20 and the second catalyst layer 30 each have a stacked structure (e.g., a bilayer structure).

[0222] <Composition of the catalyst layer>

[0223] The composition of the catalyst layer will now be described. Unless otherwise specified, the following description of the catalyst layer composition applies to both the first catalyst layer 20 and the second catalyst layer 30. When applied to the first catalyst layer 20, "catalyst layer" is replaced by "first catalyst layer 20," and when applied to the second catalyst layer 30, "catalyst layer" is replaced by "second catalyst layer 30." Furthermore, unless otherwise specified, the following description of the catalyst layer composition applies to embodiments A through E.

[0224] The catalyst layer contains one or more noble metal elements as active components of the catalyst.

[0225] From the viewpoint of improving exhaust gas purification performance, the precious metal element is preferably selected from Pt, Pd, and Rh. The precious metal element is contained in the catalyst layer 20 in a form capable of functioning as a catalyst 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). From the viewpoint of improving exhaust gas purification performance, the catalyst active component containing the precious metal element is preferably particulate.

[0226] The first catalyst layer 20 may contain the same precious metal element as the precious metal element contained in the second catalyst layer 30, or it may contain a different precious metal element than the precious metal element contained in the second catalyst layer 30.

[0227] The second catalyst layer 30 may contain the same precious metal element as the precious metal element contained in the first catalyst layer 20, or it may contain a different precious metal element than the precious metal element contained in the first catalyst layer 20.

[0228] In one embodiment, the first catalyst layer 20 and the second catalyst layer 30 each contain Rh. The first catalyst layer 20 and the second catalyst layer 30 may also each contain other precious metal elements besides Rh.

[0229] In one embodiment, the first catalyst layer 20 and the second catalyst layer 30 each contain Rh but not any other precious metal element. In another embodiment, one of the first catalyst layer 20 and the second catalyst layer 30 contains Rh but not any other precious metal element, while the other contains Rh and a precious metal element other than Rh (e.g., Pd or Pt). In yet another embodiment, the first catalyst layer 20 and the second catalyst layer 30 each contain Rh and a precious metal element other than Rh (e.g., Pd or Pt).

[0230] In the case of a catalyst layer with a stacked structure, the noble metal elements contained in the lower layer can be the same as those contained in the upper layer, or they can be different. When the noble metal elements contained in the lower layer are different from those contained in the upper layer, it is possible to prevent the reduction in catalytic performance caused by the inclusion of multiple noble metal elements in a single layer.

[0231] Because the lower layer is covered by the upper layer, the precious metal elements in the lower layer are less prone to phosphorus poisoning, while those in the upper layer are susceptible. Furthermore, Pd and Pt are easily affected by performance degradation caused by phosphorus poisoning, while Rh is less affected. Therefore, Pd and Pt are suitable as precious metal elements in the lower layer, while Rh is suitable as precious metal elements in the upper layer.

[0232] Furthermore, Pd and Pt excel in the oxidation of reducing agents (CO and HC), respectively, while Rh excels in the reduction of NOx. By including Rh in the upper layer, where the reducing agents (CO and HC) used in the NOx reduction reaction are abundant, and Pd or Pt in the lower layer, the NOx reduction reaction can be carried out efficiently. Therefore, Pt and Pd are suitable as noble metal elements in the lower layer, while Rh is suitable as noble metal elements in the upper layer.

[0233] In one embodiment, the first catalyst layer 20 and the second catalyst layer 30 each have a monolayer structure containing Rh. In another embodiment, the first catalyst layer 20 has a stacked structure (e.g., a bilayer structure) consisting of a lower layer containing a noble metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh, and the second catalyst layer 30 has a monolayer structure containing Rh. In yet another embodiment, the first catalyst layer 20 has a monolayer structure containing Rh, and the second catalyst layer 30 has a stacked structure (e.g., a bilayer structure) consisting of a lower layer containing a noble metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh. In yet another embodiment, the first catalyst layer 20 and the second catalyst layer 30 each have a stacked structure (e.g., a bilayer structure) consisting of a lower layer containing a noble metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh.

[0234] From the perspective of balancing exhaust gas purification performance and cost, based on the mass of the catalyst layer, the content of precious metal elements in the catalyst layer, converted to metal, is preferably 0.01% by mass or more and 20% by mass or less, more preferably 0.05% by mass or more and 10% by mass or less, and even more preferably 0.1% by mass or more and 5% by mass or less. "Conversion of precious metal elements in the catalyst layer" refers to the content of that single precious metal element when the catalyst layer contains only one precious metal element, and to the total content of the two or more precious metal elements when the catalyst layer contains two or more precious metal elements.

[0235] Preferably, the catalyst layer contains one or more supports, and at least a portion of the catalyst active components are loaded onto one or more supports.

[0236] "At least a portion of the catalyst active component is supported on the support" refers to a state in which at least a portion of the catalyst active component is physically or chemically adsorbed and / or retained on the outer surface and / or inner surface of the pores of the support. This can be confirmed, for example, using SEM-EDX. Specifically, in the elemental mapping obtained by analyzing the cross-section of the catalyst layer using SEM-EDX, if at least a portion of the catalyst active component and the support exist in the same region, it can be determined that at least a portion of the catalyst active component is supported on the support.

[0237] The support can be selected from, for example, inorganic oxides. Inorganic oxides are, for example, particulate. From the viewpoint of improving the loading of the active component of the catalyst, porous inorganic oxides are preferred. Inorganic oxides may or may not have oxygen storage capacity (OSC). Inorganic oxides used as supports are distinguished from inorganic oxides used as binders.

[0238] Examples of inorganic oxides include oxides based on Al-based oxides, Ce-based oxides, Zr-based oxides, oxides of rare earth elements other than Ce, zirconium oxide (ZrO2), silicon dioxide (SiO2), titanium dioxide (TiO2), zeolite (aluminosilicate), MgO, ZnO, SnO2, etc.

[0239] The support is preferably selected from Al-based oxides, Ce-based oxides, and Zr-based oxides, and more preferably from Al-based oxides and Zr-based oxides. The Zr-based oxide is preferably a Ce-Zr composite oxide.

[0240] In one embodiment, the catalyst layer comprises a Zr-based oxide. The Zr-based oxide is preferably a Ce-Zr composite oxide. The catalyst layer may further comprise a support other than a Zr-based oxide (e.g., an Al-based oxide).

[0241] When the catalyst layer contains Al-based oxides, from the viewpoint of improving exhaust gas purification performance, based on the mass of the catalyst layer, the content of Al-based oxides in the catalyst layer (= (mass of Al-based oxides in the catalyst layer) / (mass of the catalyst layer) × 100) is preferably 5% by mass or more and 95% by mass or less, more preferably 5% by mass or more and 90% by mass or less, and even more preferably 7% by mass or more and 90% by mass or less.

[0242] If the composition of the raw materials used in the manufacture of the catalyst layer is known, the content of Al-based oxides in the catalyst layer can be determined based on the composition of the raw materials.

[0243] Even when the composition of the raw materials used in the manufacture of the catalyst layer is unknown, the content of Al-based oxides in the catalyst layer can be determined using conventional methods such as SEM-EDX. Specifically, as described below.

[0244] (1) For the sample obtained from the catalyst layer, elemental analysis was performed using conventional methods such as SEM-EDX to determine the types of constituent elements of the sample as a whole, and the content (mass%) of each metal element was calculated as oxides.

[0245] (2) For the sample obtained from the catalyst layer, use conventional methods such as SEM-EDX to perform elemental mapping to determine the types of particles contained in the sample (e.g., Al-based oxide particles, Zr-based oxide particles, etc.).

[0246] (3) For various particles, elemental analysis was performed on any selected number (e.g., 50) particles using SEM-EDX to determine the types of constituent elements of the particles and to calculate the content (mass%) of each metal element converted to oxides. For various particles, the average value of the content (mass%) of each metal element converted to oxides was calculated and used as the content (mass%) of each metal element converted to oxides in each particle.

[0247] (4) By establishing and solving the equations that represent the relationship between the content of each metal element in the sample converted to oxide (mass%), the content of each metal element in various particles converted to oxide (mass%), and the content of each particle in the sample (mass%), the content of each particle in the sample (mass%) is calculated and used as the content of each particle in the catalyst layer (mass%).

[0248] When the catalyst layer contains Ce-based oxides, from the viewpoint of improving exhaust gas purification performance, based on the mass of the catalyst layer, the content of Ce-based oxides in the catalyst layer (= (mass of Ce-based oxides in the catalyst layer) / (mass of the catalyst layer) × 100) is preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 30% by mass or less, and even more preferably 3% by mass or more and 25% by mass or less. The content of Ce-based oxides in the catalyst layer can be calculated in the same way as the content of Al-based oxides in the catalyst layer.

[0249] When the catalyst layer contains Zr-based oxides, from the viewpoint of improving exhaust gas purification performance, based on the mass of the catalyst layer, the content of Zr-based oxides in the catalyst layer (= (mass of Zr-based oxides in the catalyst layer) / (mass of the catalyst layer) × 100) is preferably 5% by mass or more and 95% by mass or less, more preferably 10% by mass or more and 90% by mass or less, and even more preferably 15% by mass or more and 85% by mass or less. The content of Zr-based oxides in the catalyst layer can be calculated in the same way as the content of Al-based oxides in the catalyst layer.

[0250] The catalyst layer may contain other components such as binders and stabilizers. Examples of binders include inorganic oxide binders such as alumina binders, cerium dioxide binders, zirconium oxide binders, titanium dioxide binders, and silica binders. Examples of stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (such as Sr, Ba, etc.).

[0251] <Condition 1a>

[0252] Condition 1a is as follows:

[0253] Xa / Ya≤1.40 and Ya≤5.00.

[0254] The following explains the value of Ya≤5.00.

[0255] When the first catalyst layer 20 contains Zr-based oxides, if the first catalyst layer 20 is exposed to a high-temperature environment, cracks will form within the first catalyst layer 20 due to the thermal shrinkage of the Zr-based oxides, and the PM collection performance of the first catalyst layer 20 will easily decrease. The decrease in PM collection performance of the first catalyst layer 20 caused by the thermal shrinkage of the Zr-based oxides is unlikely to occur in the portion of the first catalyst layer 20 formed inside the partition wall portion 12, but is more likely to occur in the portion formed on the outer surface S1a of the partition wall portion 12 (i.e., the raised portion). On the other hand, the 10% flow diameter (μm) of the first catalyst layer 20 and the partition wall portion 12 is an indicator of the larger side of the through-pore diameter distribution in the first catalyst layer 20 and the partition wall portion 12. Therefore, a Ya of 5.00 μm or less means that the first catalyst layer 20 is densely formed before exposure to a high-temperature environment, without cracks, and exhibits excellent PM collection performance. Therefore, when the first catalyst layer 20 contains Zr-based oxides and Ya is 5.00 μm or less, it is highly necessary to suppress the decrease in PM collection performance of the first catalyst layer 20 caused by the thermal shrinkage of the Zr-based oxides. In particular, Ce-Zr composite oxides undergo significant thermal shrinkage due to exposure to high-temperature environments, thus, when the first catalyst layer 20 contains Ce-Zr composite oxides and Ya is 5.00 μm or less, it is highly necessary to suppress the decrease in PM collection performance of the first catalyst layer 20 caused by the thermal shrinkage of the Ce-Zr composite oxides.

[0256] From the viewpoint of improving PM capture performance, Ya is preferably 4.70 μm or less, more preferably 4.35 μm or less, and even more preferably 4.00 μm or less. The smaller Ya is, the better the PM capture performance, but the pressure drop increases. From the viewpoint of achieving both improved PM capture performance and suppression of pressure drop increase, Ya is preferably 1.60 μm or more, more preferably 1.80 μm or more, and even more preferably 2.00 μm or more. These lower limits can be combined with any of the upper limits mentioned above.

[0257] The following explains the condition Xa / Ya≤1.40.

[0258] The 10% flow diameter (μm) of the first catalyst layer 20 and the partition wall portion 12 is an indicator of the larger side of the through-pore diameter distribution in the first catalyst layer 20 and the partition wall portion 12. Therefore, a Xa / Ya ratio of 1.40 or less means that the generation of cracks caused by the thermal shrinkage of Zr-based oxides in the first catalyst layer 20 after exposure to a high-temperature environment is suppressed. Thus, by having a Xa / Ya ratio of 1.40 or less, the reduction in PM collection performance of the first catalyst layer 20 caused by the thermal shrinkage of Zr-based oxides can be suppressed.

[0259] From the viewpoint of more effectively suppressing the decline in PM capture performance, Xa / Ya is preferably 1.37 or less, more preferably 1.34 or less, and even more preferably 1.30 or less. Theoretically, the lower limit of Xa / Ya is 1, but in practice it exceeds 1. Xa / Ya can be, for example, 1.03 or more, 1.07 or more, or 1.10 or more. These lower limits can be combined with any of the upper limits mentioned above.

[0260] The method for determining Xa is described below.

[0261] Catalyst 1 was heat-treated at 950°C for 35 hours in an atmospheric atmosphere. A section extending axially along the substrate 10 and having a length L equal to that of the substrate 10 was cut from the heat-treated catalyst 1. 10 Samples of the same length. The number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample. The top view shape of the sample when viewed from the axial direction is, for example, a quadrilateral (preferably a square or rectangle, more preferably a square). There is no particular limitation on the size of the top view shape when viewed from the axial direction, as long as the number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample; for example, the longitudinal length is 10 mm and the transverse length is 10 mm. When the inflow-side chambers 13a and outflow-side chambers 13b are arranged alternately in the longitudinal direction and alternately in the transverse direction, if the total number of inflow-side chambers 13a and outflow-side chambers 13b arranged in the longitudinal direction of the sample is even, and the total number of inflow-side chambers 13a and outflow-side chambers 13b arranged in the transverse direction of the sample is even, then the number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample.

[0262] The sample is sectioned with a plane perpendicular to its axis to prepare a slice P1 containing a portion of the first catalyst layer 20 but not a portion of the second catalyst layer 30. Slice P1 can be obtained near the end of the sample on the exhaust gas inflow side. The axial length of slice P1 is not particularly limited, for example, it is 10 mm. The length of the portion of the first catalyst layer 20 contained in slice P1 is equal to the axial length of slice P1. Slice P1 does not have a first sealing portion 14 and a second sealing portion 15.

[0263] An example of slice P1 is shown below. Figure 7A and Figure 7B Slice P1 is, for example, longitudinal ( Figure 7A The longitudinal length is 10mm, and the transverse length is... Figure 7A The transverse length is 10mm, and the axial length is... Figure 7B A cube with a length of 10mm (vertical). Figure 7A and Figure 7BThe slice P1 shown can be obtained, for example, by cutting two portions 10 mm and 20 mm from the end of the sample on the exhaust gas inflow side along the sample's axial direction using a plane perpendicular to the sample's axial direction. Figure 7B As shown, a portion of the length of the first catalyst layer 20 contained in slice P1 is equal to the axial length of slice P1. Figure 7A and Figure 7B As shown, slice P1 does not have a first sealing part 14 and a second sealing part 15.

[0264] A first sealing portion is formed on slice P1 to seal the end of the waste gas outflow side of the inflow-side chamber 13a included in slice P1, and a second sealing portion is formed to seal the end of the waste gas inflow side of the outflow-side chamber 13b included in slice P1. A third sealing portion is formed on the outermost periphery of slice P1, resulting in slice P1'. The first, second, and third sealing portions can be formed by applying a filling material to predetermined locations on slice P1. As the filling material, an adhesive such as an epoxy resin-based adhesive can be used, for example.

[0265] In use Figure 7A and Figure 7B In the case of slice P1 shown, as Figures 8A-8C As shown, in slice P1, the waste gas flows out of the inflow side chamber 13a contained in slice P1. Figure 8C The first sealing part 14, which seals the end of the slice P1 (the lower side), and the exhaust gas flowing into the outflow side chamber 13b contained in the slice P1 (the lower side) Figure 8C A second sealing portion 15 is formed at the upper end of the slice P1, and a third sealing portion 16 is formed at the outermost periphery of the slice P1 to obtain slice P1'. The first sealing portion 14, the second sealing portion 15, and the third sealing portion 16 can be formed by applying a filling material to predetermined locations on the slice P1. As the filling material, an adhesive such as an epoxy resin-based adhesive can be used. The thicknesses of the first sealing portion 14 and the second sealing portion 15 are respectively set to the axial ( Figure 8C The length is less than 1 / 10 of the length of the longitudinal direction.

[0266] The following is for the purpose of simplification and will be used in the context of... Figures 8A-8C The method for determining Xa will be explained using the example of section P1' shown below. The following explanation can also be applied to cases using other sections P1'.

[0267] A cut piece P1' prepared from heat-treated catalyst 1 is placed in the holder of a permeability apparatus. While varying the gas pressure, gas flows through the cut piece P1' at a rate of 1-200 L / min, and the flow rate of the pressurized gas is measured (hereinafter referred to as "first measurement"). The flowing gas is air. For example, a permeability apparatus manufactured by PorousMaterials Inc. (e.g., CFP-1100A) can be used. The gas flows from the waste gas inflow side of the inflow-side chamber 13a contained in the cut piece P1'. Figure 8C The exhaust gas flows from the upper side (opening) of the inflow side chamber 13a. Figure 8C Gas flowing in from the end (opening) of the upper side of the chamber passes through the first catalyst layer 20 and the partition wall 12, and exits from the exhaust gas outlet side of the outlet side chamber 13b. Figure 8C It flows out from the end (opening) of the lower side.

[0268] A first determination was performed on the dried slice P1' (i.e., slice P1' without impregnation with the non-volatile reagent (Galwick reagent manufactured by Porous Materials Inc.)). The pressure-flow curves associated with the dried slice P1' were obtained from the first determination.

[0269] Slice P1' was prepared from heat-treated catalyst 1 in the same manner as described above. Slice P1' was immersed in a non-volatile test solution (Galwick reagent manufactured by Porous Materials Inc.) and vacuum degassed to remove air from slice P1'. Then, slice P1' containing the test solution was placed in the holding element of a permeability apparatus, and gas was passed through slice P1' at a rate of 1-200 L / min while the gas pressure was varied. The flow rate of the pressurized gas was measured (hereinafter referred to as "second measurement"). The gas being passed through was air. The surface tension of Galwick reagent manufactured by Porous Materials Inc. was 15.9 dyne / cm. For example, a permeability apparatus manufactured by Porous Materials Inc. (e.g., CFP-1100A) could be used as the permeability apparatus. Gas flowed from the waste gas inflow side of the inflow-side chamber 13a contained in slice P1'. Figure 8C The exhaust gas flows from the upper side (opening) of the inflow side chamber 13a. Figure 8C Gas flowing in from the end (opening) of the upper side of the chamber passes through the first catalyst layer 20 and the partition wall 12, and exits from the exhaust gas outlet side of the outlet side chamber 13b. Figure 8C It flows out from the end (opening) of the lower side.

[0270] A second measurement was performed on the slide P1' wetted with the test solution. The pressure-flow rate curves related to the wetted state of slide P1' were obtained through this second measurement.

[0271] In the second determination, all the through holes of the slice P1' were filled with the test liquid at the beginning of the determination, but as the gas pressure increased, the test liquid filling the through holes was squeezed out, and the gas was able to pass through.

[0272] In addition, in the first and second measurements, the measurement software "Capwin" (made by Porous Materials Inc.) was used. The detailed conditions for the first measurement were set to "drying parameters", and the detailed conditions for the second measurement were set to "wetting parameters", as specified below.

[0273] Drying parameters / Humidity parameters

[0274] <Bubble Point Test / Integrity Test>

[0275] • Bubble flow rate: 15.00 (cc / m³)

[0276] • F / PT 200 (Old-style bubble time)

[0277] <Motor Valve Control>

[0278] • v2incr 2 (cts*3): Valve 2 increment 2 (count × 3)

[0279] <Regulator Control>

[0280] •preginc 0.5 (cts*50): Pressure regulator increment (count × 50)

[0281] • Pulse delay 2 (sec): Pulse delay of 2 (seconds)

[0282] <Data Determination Procedure>

[0283] •mineqtime 15 (sec): Minimum balancing time of 15 seconds

[0284] •presslew 50 (cts*3): Pressure change rate 50 (counts × 3)

[0285] •flowslew 50 (cts*3): Flow rate change rate 50 (counts × 3)

[0286] • eqiter 30 (0.1 sec): 30 balancing iterations (0.1 seconds).

[0287] • aveiter 20 (0.1 seconds): Average number of iterations 20 (0.1 seconds)

[0288] • maxpdif 0.10 (PSI): Maximum pressure difference 0.10 (PSI)

[0289] • maxfdif 30.0 (cc / m): Maximum flow difference of 30.0 (cc / m)

[0290] According to the above measurement method, the diameter of the finest part of the through hole (hereinafter referred to as "through hole diameter") can be determined. For example, in the case where the through hole has a shape that is constricted in the middle like an hourglass tube, the through hole diameter is the diameter of the constricted neck of the through hole.

[0291] The relationship between gas pressure and the diameter of the through-hole is expressed by the following formula, where the constant C is 2860.

[0292] D=C×γ / ΔP

[0293] [In the formula, D represents the diameter of the through pore (unit: μm), γ represents the surface tension of the test liquid (unit: dyne / cm), C represents a constant, and ΔP represents the upstream side of the slice P1' relative to the gas flow direction during gas flow ( Figure 8C (upper side) and downstream side ( Figure 8C The pressure difference at the lower side (relative to the pressure at the upstream side of slice P1' in the gas flow direction) - (relative to the pressure at the downstream side of slice P1' in the gas flow direction) (unit: Pa).

[0294] The flow rate (L / min) of the gas at a certain gas pressure is determined based on the pressure-flow curve obtained in the first measurement, and this is set as the "drying flow rate". The flow rate (L / min) of the gas at the same gas pressure is determined based on the pressure-flow curve obtained in the second measurement, and this is set as the "wetting flow rate".

[0295] The pore size with a percentage of 10% relative to the drying flow rate (wetting flow rate / drying flow rate × 100) is determined. Furthermore, in the second measurement, if the gas pressure is gradually increased, the liquid film ruptures sequentially from the larger pores, causing the gas flow rate to increase. Therefore, the pore size with a percentage of 10% (μm) is greater than the pore size with a percentage exceeding 10% (μm).

[0296] Using different slices P1', the permeable pore diameter (μm) was measured three times in total, with each slice representing 10% of the diameter. The average value of these measurements was set as Xa (μm).

[0297] The method for determining Ya is explained below.

[0298] Slices P1' were prepared from catalyst 1 before heat treatment in the same manner as described above. Ya can be measured in the same way as Xa, except that slices P1' prepared from catalyst 1 before heat treatment are used instead of slices P1' prepared from catalyst 1 after heat treatment.

[0299] <Condition 1b>

[0300] Condition 1b is as follows:

[0301] Xb / Yb≤1.40 and Yb≤5.00.

[0302] The following explains Yb≤5.00.

[0303] When the second catalyst layer 30 contains Zr-based oxides, if the second catalyst layer 30 is exposed to a high-temperature environment, cracks will form within the second catalyst layer 30 due to the thermal shrinkage of the Zr-based oxides, and the PM collection performance of the second catalyst layer 30 will easily decrease. The decrease in PM collection performance of the second catalyst layer 30 caused by the thermal shrinkage of the Zr-based oxides is unlikely to occur in the portion of the second catalyst layer 30 formed inside the partition wall portion 12, but is more likely to occur in the portion formed on the outer surface S1b of the partition wall portion 12 (i.e., the raised portion). On the other hand, the 10% flow diameter (μm) of the second catalyst layer 30 and the partition wall portion 12 is an indicator of the larger side of the through-pore diameter distribution in the second catalyst layer 30 and the partition wall portion 12. Therefore, a Yb of 5.00 μm or less means that the second catalyst layer 30 is densely formed before exposure to a high-temperature environment, without cracks, and exhibits excellent PM collection performance. Therefore, when the second catalyst layer 30 contains Zr-based oxides and the Yb is 5.00 μm or less, it is highly necessary to suppress the decrease in PM collection performance of the second catalyst layer 30 caused by the thermal shrinkage of the Zr-based oxides. In particular, Ce-Zr composite oxides undergo significant thermal shrinkage due to exposure to high-temperature environments, thus, when the second catalyst layer 30 contains Ce-Zr composite oxides and the Yb is 5.00 μm or less, it is highly necessary to suppress the decrease in PM collection performance of the second catalyst layer 30 caused by the thermal shrinkage of the Ce-Zr composite oxides.

[0304] From the viewpoint of improving PM capture performance, Yb is preferably 4.70 μm or less, more preferably 4.35 μm or less, and even more preferably 4.00 μm or less. The smaller the Yb, the better the PM capture performance, but the pressure drop increases. From the viewpoint of achieving both improved PM capture performance and suppression of pressure drop increase, Yb is preferably 1.60 μm or more, more preferably 1.80 μm or more, and even more preferably 2.00 μm or more. These lower limits can be combined with any of the upper limits mentioned above.

[0305] The following explains the condition Xb / Yb≤1.40.

[0306] The 10% flow diameter (μm) of the second catalyst layer 30 and the partition wall portion 12 is an indicator of the larger side of the through-pore diameter distribution in the second catalyst layer 30 and the partition wall portion 12. Therefore, an Xb / Yb ratio of 1.40 or less means that the generation of cracks caused by the thermal shrinkage of Zr-based oxides in the second catalyst layer 30 after exposure to a high-temperature environment is suppressed. Thus, by having an Xb / Yb ratio of 1.40 or less, the reduction in PM collection performance of the second catalyst layer 30 caused by the thermal shrinkage of Zr-based oxides can be suppressed.

[0307] From the viewpoint of more effectively suppressing the decline in PM capture performance, Xb / Yb is preferably 1.37 or less, more preferably 1.34 or less, and even more preferably 1.30 or less. Theoretically, the lower limit of Xb / Yb is 1, but in practice it exceeds 1. Xb / Yb can be, for example, 1.03 or more, 1.07 or more, or 1.10 or more. These lower limits can be combined with any of the upper limits mentioned above.

[0308] The method for determining Xb is described below.

[0309] Catalyst 1 was heat-treated at 950°C for 35 hours in an atmospheric atmosphere. A section extending axially along the substrate 10 and having a length L equal to that of the substrate 10 was cut from the heat-treated catalyst 1. 10 Samples of the same length. The number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample. The top view shape of the sample when viewed from the axial direction is, for example, a quadrilateral (preferably a square or rectangle, more preferably a square). There is no particular limitation on the size of the top view shape when viewed from the axial direction, as long as the number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample; for example, the longitudinal length is 10 mm and the transverse length is 10 mm. When the inflow-side chambers 13a and outflow-side chambers 13b are arranged alternately in the longitudinal direction and alternately in the transverse direction, if the total number of inflow-side chambers 13a and outflow-side chambers 13b arranged in the longitudinal direction of the sample is even, and the total number of inflow-side chambers 13a and outflow-side chambers 13b arranged in the transverse direction of the sample is even, then the number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample.

[0310] The sample is sectioned with a plane perpendicular to its axis to prepare a slice P2 containing a portion of the second catalyst layer 30 but not a portion of the first catalyst layer 20. Slice P2 can be obtained near the end of the sample on the exhaust side. The axial length of slice P2 is not particularly limited, for example, it is 10 mm. The length of the portion of the second catalyst layer 30 contained in slice P2 is equal to the axial length of slice P2. Slice P2 does not have the first sealing portion 14 and the second sealing portion 15.

[0311] An example of slice P2 is shown below. Figure 9A and Figure 9B .like Figure 9A and Figure 9B As shown, slice P2 is, for example, longitudinal ( Figure 9A The longitudinal length is 10mm, and the transverse length is... Figure 9A The transverse length is 10mm, and the axial length is... Figure 9B A cube with a length of 10mm (vertical). Figure 9A and Figure 9B The slice P2 shown can be obtained, for example, by cutting two portions 10 mm and 20 mm away from the end of the sample's exhaust outlet side along the sample's axial direction using a plane perpendicular to the sample's axial direction. Figure 9B As shown, a portion of the second catalyst layer 30 contained in slice P2 has a length equal to the axial length of slice P2. Figure 9A and Figure 9B As shown, slice P2 does not have a first sealing part 14 and a second sealing part 15.

[0312] A first sealing portion is formed in slice P2 to seal the end of the waste gas outflow side of the inflow-side chamber 13a contained in slice P2, and a second sealing portion is formed to seal the end of the waste gas inflow side of the outflow-side chamber 13b contained in slice P2. A third sealing portion is formed at the outermost periphery of slice P2, resulting in slice P2'. The first, second, and third sealing portions can be formed by applying a filling material to predetermined locations on slice P2. As the filling material, an adhesive such as an epoxy resin adhesive can be used, for example.

[0313] In use Figure 9A and Figure 9B In the case of slice P2 shown, as Figures 10A-10C As shown, in slice P2, the waste gas flows out of the inflow side chamber 13a contained in slice P2. Figure 10C The first sealing part 14, which seals the end of the slice P2 (the lower side), and the exhaust gas flowing into the outflow side chamber 13b contained in the slice P2 (the lower side) Figure 10CA second sealing portion 15 is formed at the upper end of the slice P2, and a third sealing portion 16 is formed at the outermost periphery of the slice P2 to obtain slice P2'. The first sealing portion 14, the second sealing portion 15, and the third sealing portion 16 can be formed by applying a filling material to predetermined locations on the slice P2. As the filling material, an adhesive such as an epoxy resin adhesive can be used. The thicknesses of the first sealing portion 14 and the second sealing portion 15 are respectively set to the axial ( Figure 10C The length is less than 1 / 10 of the length of the longitudinal direction.

[0314] The following is for the purpose of simplification and will be used in the context of... Figures 10A-10C The method for determining Xb will be explained using the example of section P2' shown below. The following explanation can also be applied to cases using other sections P2'.

[0315] Xb can be measured in the same way as Xa, except that slice P2' prepared from heat-treated catalyst 1 is used instead of slice P1' prepared from heat-treated catalyst 1. In the first and second measurements, the gas flows from the waste gas inflow side of the inflow-side chamber 13a contained in slice P2'. Figure 10C The exhaust gas flows from the upper side (opening) of the inflow side chamber 13a. Figure 10C Gas flowing in from the end (opening) of the upper side of the chamber passes through the partition wall 12 and the second catalyst layer 30, and exits from the exhaust gas outlet side of the outlet side chamber 13b. Figure 10C It flows out from the end (opening) of the lower side.

[0316] The pore size with a percentage of 10% relative to the drying flow rate (wetting flow rate / drying flow rate × 100) is determined. Furthermore, in the second measurement, if the gas pressure is gradually increased, the liquid film ruptures sequentially from the larger pores, causing the gas flow rate to increase. Therefore, the pore size with a percentage of 10% (μm) is greater than the pore size with a percentage exceeding 10% (μm).

[0317] Using different slices P2', the permeable pore diameter (μm) was measured three times in total, with a percentage of 10%. The average value of these measurements was set as Xb (μm).

[0318] The following describes the method for determining Yb.

[0319] Slices P2' were prepared from catalyst 1 before heat treatment in the same manner as described above. Yb can be measured in the same way as Xb, except that slices P2' prepared from catalyst 1 before heat treatment are used instead of slices P2' prepared from catalyst 1 after heat treatment.

[0320] <Presence or absence of Zr-based oxides in the catalyst layer>

[0321] When catalyst 1 satisfies condition 1a (embodiments A, B, and D), the first catalyst layer 20 comprises a Zr-based oxide (preferably a Ce-Zr composite oxide), and when catalyst 1 satisfies condition 1b (embodiments A, C, and E), the second catalyst layer 30 comprises a Zr-based oxide (preferably a Ce-Zr composite oxide). Specifically, as described below.

[0322] In embodiment A, the first catalyst layer 20 and the second catalyst layer 30 respectively comprise Zr-based oxides (preferably Ce-Zr composite oxides). The first catalyst layer 20 and the second catalyst layer 30 may also further comprise a support other than Zr-based oxides (e.g., Al-based oxides).

[0323] In embodiment B, the first catalyst layer 20 comprises a Zr-based oxide (preferably a Ce-Zr composite oxide). The first catalyst layer 20 may also further comprise a support other than a Zr-based oxide (e.g., an Al-based oxide).

[0324] In embodiment B, the second catalyst layer 30 may contain Zr-based oxides (preferably Ce-Zr composite oxides), or it may not contain Zr-based oxides. If the second catalyst layer 30 contains Zr-based oxides, it may also contain a support other than Zr-based oxides (e.g., Al-based oxides). If the second catalyst layer 30 does not contain Zr-based oxides, it preferably contains a support other than Zr-based oxides (e.g., Al-based oxides).

[0325] In embodiment C, the second catalyst layer 30 comprises a Zr-based oxide (preferably a Ce-Zr composite oxide). The second catalyst layer 30 may also further comprise a support other than a Zr-based oxide (e.g., an Al-based oxide).

[0326] In embodiment C, the first catalyst layer 20 may contain Zr-based oxides (preferably Ce-Zr composite oxides), or it may not contain Zr-based oxides. If the first catalyst layer 20 contains Zr-based oxides, it may also contain a support other than Zr-based oxides (e.g., Al-based oxides). If the first catalyst layer 20 does not contain Zr-based oxides, it preferably contains a support other than Zr-based oxides (e.g., Al-based oxides).

[0327] In embodiment D, the first catalyst layer 20 comprises a Zr-based oxide (preferably a Ce-Zr composite oxide). The first catalyst layer 20 may also further comprise a support other than a Zr-based oxide (e.g., an Al-based oxide).

[0328] In embodiment E, the second catalyst layer 30 comprises a Zr-based oxide (preferably a Ce-Zr composite oxide). The second catalyst layer 30 may also further comprise a support other than a Zr-based oxide (e.g., an Al-based oxide).

[0329] <Content of Ce-Zr composite oxides in the catalyst layer>

[0330] When catalyst 1 satisfies condition 1a (embodiments A, B, and D), the first catalyst layer 20 preferably contains Ce-Zr composite oxides. Based on the mass of the first catalyst layer 20, the content of Ce-Zr composite oxides in the first catalyst layer 20 (= (mass of Ce-Zr composite oxides in the first catalyst layer 20) / (mass of the first catalyst layer 20) × 100) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The higher this content, the easier it is for the PM capture performance of the first catalyst layer 20 to decrease due to the thermal shrinkage of the Ce-Zr composite oxides. Therefore, when the content is within the above range, the effect of catalyst 1 satisfying condition 1a is significant. The upper limit of this content can be appropriately adjusted taking into account the content of other components in the first catalyst layer 20. Based on the mass of the first catalyst layer 20, the content of Ce-Zr composite oxides in the first catalyst layer 20 is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. These upper limits can be combined with any of the lower limits mentioned above.

[0331] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), the second catalyst layer 30 preferably contains Ce-Zr composite oxides. Based on the mass of the second catalyst layer 30, the content of Ce-Zr composite oxides in the second catalyst layer 30 (= (mass of Ce-Zr composite oxides in the second catalyst layer 30) / (mass of the second catalyst layer 30) × 100) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The higher this content, the easier it is for the PM capture performance of the second catalyst layer 30 to decrease due to the thermal shrinkage of the Ce-Zr composite oxides. Therefore, when the content is within the above range, the effect of catalyst 1 satisfying condition 1b is significant. The upper limit of this content can be appropriately adjusted taking into account the content of other components in the second catalyst layer 30. Based on the mass of the second catalyst layer 30, the content of Ce-Zr composite oxides in the second catalyst layer 30 is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. These upper limits can be combined with any of the lower limits mentioned above.

[0332] <Composition of Ce-Zr composite oxides in the catalyst layer>

[0333] When catalyst 1 satisfies condition 1a (embodiments A, B, and D), the first catalyst layer 20 preferably contains a Ce-Zr composite oxide, and the Ce-Zr composite oxide in the first catalyst layer 20 preferably satisfies the following formula: R 12 / R 11 >0.8,

[0334] [In the formula, R] 11 R represents the Ce content (mass%) in the Ce-Zr composite oxides as converted to CeO2. 12 This indicates the Zr content (mass %) in the Ce-Zr composite oxides described above, converted to ZrO2.

[0335] R 12 / R 11 When the value exceeds 0.8, the heat resistance of Ce-Zr composite oxides improves (i.e., the degree of thermal shrinkage of Ce-Zr composite oxides decreases), thus making it easier to form the first catalyst layer 20 that satisfies condition 1a (preferably conditions 1a and 2a).

[0336] R 12 / R 11 Preferably, it is 0.9 or higher, more preferably 1.0 or higher, and even more preferably 1.2 or higher. R 12 / R 11 The upper limit can be appropriately adjusted to take into account the balance between the heat resistance and oxygen storage capacity of Ce-Zr composite oxides. 12 / R 11 Preferably, it is 20.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. These upper limits can be combined with any of the lower limits mentioned above.

[0337] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), the second catalyst layer 30 preferably contains a Ce-Zr composite oxide, and the Ce-Zr composite oxide in the second catalyst layer 30 preferably satisfies the following formula: R 22 / R 21 >0.8,

[0338] [In the formula, R] 21 R represents the Ce content (mass%) in the Ce-Zr composite oxides as converted to CeO2. 22 This indicates the Zr content (mass %) in the Ce-Zr composite oxides described above, converted to ZrO2.

[0339] R 22 / R21 When the value exceeds 0.8, the heat resistance of Ce-Zr composite oxides improves (i.e., the degree of thermal shrinkage of Ce-Zr composite oxides decreases), thus making it easier to form the second catalyst layer 30 that satisfies condition 1b (preferably conditions 1b and 2b).

[0340] R 22 / R 21 Preferably, it is 0.9 or higher, more preferably 1.00 or higher, and even more preferably 1.2 or higher. 22 / R 21 The upper limit can be appropriately adjusted to take into account the balance between the heat resistance and oxygen storage capacity of Ce-Zr composite oxides. 22 / R 21 Preferably, it is 20.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. These upper limits can be combined with any of the lower limits mentioned above.

[0341] <Length of catalyst layer>

[0342] If, in the path (hereinafter referred to as the "exhaust gas path") through which exhaust gas flows from the end (opening) of the exhaust gas inflow side of the inflow-side chamber 13a and flows out from the end (opening) of the exhaust gas outflow side of the outflow-side chamber 13b, there is a portion where neither the first catalyst layer 20 nor the second catalyst layer 30 is formed, the exhaust gas preferentially flows through that portion, and the PM capture performance may decrease. Therefore, from the viewpoint of improving the PM capture performance of the catalyst 1, it is preferable to form at least one of the first catalyst layer 20 and the second catalyst layer 30 at any point in the exhaust gas path. Thus, the exhaust gas flowing from the end (opening) of the exhaust gas inflow side of the inflow-side chamber 13a passes through at least one of the first catalyst layer 20 and the second catalyst layer 30 and flows out from the end (opening) of the exhaust gas outflow side of the outflow-side chamber 13b, thereby improving the PM capture performance of the catalyst 1. Specifically, as described below.

[0343] In the case where catalyst 1 has a first catalyst layer 20 but not a second catalyst layer 30 (Embodiment D), the length L of the first catalyst layer 20 is... 20 Relative to the length L of the inflow side chamber 13a 13a percentage (L) 20 / L 13a (×100) is preferably 100%.

[0344] In the case where catalyst 1 has a second catalyst layer 30 but not a first catalyst layer 20 (Embodiment E), the length L of the second catalyst layer 30 is... 30 Relative to the length L of the outflow side chamber 13b 13b percentage (L) 30 / L13b (×100) is preferably 100%.

[0345] When catalyst 1 has a first catalyst layer 20 and a second catalyst layer 30 (Embodiments A to C), the length L of the first catalyst layer 20 is... 20 The length L of the second catalyst layer 30 30 The sum is relative to the length L of the substrate 10 10 percentage (L) 20 +L 30 ) / L 10 The percentage (×100) is preferably 100% or more, more preferably 105% or more, and even more preferably 115% or more. The upper limit of this percentage can be appropriately adjusted taking into account exhaust gas purification performance, PM capture performance, etc. The percentage is preferably 160% or less, more preferably 150% or less, and even more preferably 140% or less. These upper limits can be combined with any of the lower limits mentioned above. As long as the percentage is within the above range, the length L of the first catalyst layer 20 is... 20 The length L of the second catalyst layer 30 30 The length L of the first catalyst layer 20 can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. 20 Relative to the length L of the substrate 10 10 percentage (L) 20 / L 10 The content of (×100) is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less. The length L of the second catalyst layer 30 is... 30 Relative to the length L of the substrate 10 10 percentage (L) 30 / L 10 The content of (×100) is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less.

[0346] From the viewpoint of improving the PM capture performance of catalyst 1, it is preferable to form at least one of a first catalyst layer 20 satisfying condition 1a and a second catalyst layer 30 satisfying condition 1b at any point in the exhaust gas path. Thus, exhaust gas flowing in from the exhaust gas inflow side end (opening) of the inflow-side chamber 13a passes through at least one of the first catalyst layer 20 satisfying condition 1a and the second catalyst layer 30 satisfying condition 1b, and exits from the exhaust gas outflow side end (opening) of the outflow-side chamber 13b, thereby improving the PM capture performance of catalyst 1. Specifically, as described below.

[0347] When catalyst 1 satisfies condition 1a but not condition 1b (implementations B and D), the length L of the first catalyst layer 20 is... 20 Relative to the length L of the inflow side chamber 13a 13a percentage (L) 20 / L 13a (×100) is preferably 100%. When catalyst 1 includes a second catalyst layer 30 (Embodiment B), the length L of the second catalyst layer 30 is... 30 The length L of the second catalyst layer 30 can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. 30 Relative to the length L of the outflow side chamber 13b 13b percentage (L) 30 / L 13b The content of (×100) is preferably 15% or more and 100% or less, more preferably 20% or more and 90% or less, and even more preferably 30% or more and 80% or less.

[0348] When catalyst 1 satisfies condition 1b but not condition 1a (implementations C and E), the length L of the second catalyst layer 30 is... 30 Relative to the length L of the outflow side chamber 13b 13b percentage (L) 30 / L 13b (×100) is preferably 100%. When the catalyst 1 has a first catalyst layer 20 (Embodiment C), the length L of the first catalyst layer 20 is... 20 The length L of the first catalyst layer 20 can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. 20 Relative to the length L of the inflow side chamber 13a 13a percentage (L) 20 / L 13a The content of (×100) is preferably 15% or more and 100% or less, more preferably 20% or more and 90% or less, and even more preferably 30% or more and 80% or less.

[0349] When catalyst 1 satisfies conditions 1a and 1b (Embodiment A), the length L of the first catalyst layer 20 is... 20 The length L of the second catalyst layer 30 30 The sum is relative to the length L of the substrate 10 10 percentage (L) 20 +L 30 ) / L 10The percentage (×100) is preferably 100% or more, more preferably 105% or more, and even more preferably 115% or more. The upper limit of this percentage can be appropriately adjusted taking into account exhaust gas purification performance, PM capture performance, etc. The percentage is preferably 160% or less, more preferably 150% or less, and even more preferably 140% or less. These upper limits can be combined with any of the lower limits mentioned above. As long as the percentage is within the above range, the length L of the first catalyst layer 20 is... 20 The length L of the second catalyst layer 30 30 The length L of the first catalyst layer 20 can be appropriately adjusted considering factors such as exhaust gas purification performance and PM capture performance. 20 Relative to the length L of the substrate 10 10 percentage (L) 20 / L 10 The content of (×100) is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less. The length L of the second catalyst layer 30 is... 30 Relative to the length L of the substrate 10 10 percentage (L) 30 / L 10 The content of (×100) is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less.

[0350] The length L of the first catalyst layer 20 20 One example of the determination method is as follows.

[0351] A section extending axially along the substrate 10 from the catalyst 1 and having a length L equal to that of the substrate 10. 10 Samples of the same length are used. For example, a cylindrical sample with a diameter of 25.4 mm is used. The diameter of the sample can be varied as needed. The sample is cut at 5 mm intervals using a plane perpendicular to the axis of the substrate 10, sequentially obtaining a first slice, a second slice, ..., an nth slice from the end side of the sample on the exhaust gas inflow side. The length of each slice is 5 mm. The composition of the slices is analyzed using ICP-OES, XRF, SEM-EDX, etc., and based on the composition of the slices, it is confirmed whether the slices contain a portion of the first catalyst layer 20.

[0352] For slices that clearly contain a portion of the first catalyst layer 20, compositional analysis may not be necessary. For example, SEM, EPMA, or other methods can be used to observe the cross-section and confirm whether the slice contains a portion of the first catalyst layer 20. Elemental mapping of the cross-section can also be performed during cross-sectional observation. Elemental mapping can be performed in the same manner as described above.

[0353] After confirming whether the slice contains a portion of the first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is calculated based on the following formula.

[0354] The length of the first catalyst layer 20 contained in the sample is 5 mm × (the number of slices containing a portion of the first catalyst layer 20).

[0355] For example, if the first to kth slices contain a portion of the first catalyst layer 20, but the (k+1) to nth slices do not contain a portion of the first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is (5×k) mm.

[0356] A more detailed method for determining the length of the first catalyst layer 20 contained in the sample is as follows.

[0357] The k-th slice (i.e., the slice obtained from the side of the sample closest to the exhaust gas outlet among the slices containing a portion of the first catalyst layer 20) is sectionalized along the axial direction of the substrate 10. The portion of the first catalyst layer 20 present on the sectional surface is observed using SEM, EPMA, etc., thereby determining the length of the portion of the first catalyst layer 20 in the k-th slice. Then, the length of the first catalyst layer 20 contained in the sample is calculated based on the following formula.

[0358] The length of the first catalyst layer 20 contained in the sample = (5mm × (k-1)) + (the length of a portion of the first catalyst layer 20 contained in the k-th slice)

[0359] The length L of the first catalyst layer 20 contained in a sample can be used as the length of the first catalyst layer 20. 20 Alternatively, the average length of the first catalyst layer 20 contained in multiple samples can be used as the length L of the first catalyst layer 20. 20 For example, for 8 to 16 samples arbitrarily cut from catalyst 1, the length of the first catalyst layer 20 contained in each sample can be measured, and their average value can be taken as the length L of the first catalyst layer 20. 20 .

[0360] Regarding the length L of the first catalyst layer 20 20 The above description of the determination method also applies to the second catalyst layer 30. In application, "first catalyst layer 20" is replaced with "second catalyst layer 30". However, the length L of the second catalyst layer 30... 30 In the measurement method, the sample is cut at 5mm intervals using a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained sequentially from the end side of the sample where the waste gas flows out.

[0361] <Material layer quality>

[0362] When catalyst 1 satisfies condition 1a (embodiments A, B, and D), the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed (hereinafter referred to as "the amount of coating of the first catalyst layer 20") is preferably 20 g / L or more and 150 g / L or less, more preferably 30 g / L or more and 130 g / L or less, and even more preferably 35 g / L or more and 110 g / L or less. When the amount of coating of the first catalyst layer 20 is within the above range, the formation of the first catalyst layer 20 that satisfies condition 1a (preferably conditions 1a and 2a) becomes easier.

[0363] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), the mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed (hereinafter referred to as "the amount of coating of the second catalyst layer 30") is preferably 20 g / L or more and 150 g / L or less, more preferably 30 g / L or more and 130 g / L or less, and even more preferably 35 g / L or more and 110 g / L or less. When the amount of coating of the second catalyst layer 30 is within the above range, the formation of the second catalyst layer 30 that satisfies condition 1b (preferably conditions 1b and 2b) becomes easier.

[0364] The coating amount of the first catalyst layer 20 is given by the formula: Coating amount of the first catalyst layer 20 = (mass of the first catalyst layer 20) / (volume of the substrate 10) × (length L of the first catalyst layer 20) 20 / Length L of substrate 10 10 Find the answer.

[0365] The coating amount of the second catalyst layer 30 is given by the formula: Coating amount of the second catalyst layer 30 = (mass of the second catalyst layer 30) / (volume of the substrate 10) × (length L of the second catalyst layer 30) 30 / Length L of substrate 10 10 Find the answer.

[0366] <Condition 2a>

[0367] When catalyst 1 satisfies condition 1a (embodiments A, B, and D), catalyst 1 preferably further satisfies the following condition 2a: 1.30 × 10 -3 ≤Ra

[0368] [In the formula, Ra represents the gas permeability (cm²) of the first catalyst layer 20 and the partition wall 12 as measured by a gas permeability meter before the catalyst 1 is heat-treated at 950°C for 35 hours in atmospheric atmosphere.] 3 / (cm) 2 ·s·Pa). ].

[0369] In the phrase “gas permeability of the first catalyst layer 20 and the partition wall 12”, “partition wall 12” refers to the portion of partition wall 12 in which the first catalyst layer 20 is disposed.

[0370] Ra is an index representing the permeability of exhaust gas in the first catalyst layer 20 and the partition wall 12. The larger the Ra value, the higher the permeability of exhaust gas in the first catalyst layer 20 and the partition wall 12. When Ra is 1.30 × 10⁻⁶... -3 (cm) 3 / (cm) 2 When the pressure drop is above 60°C (Pa), the ventilation of the exhaust gas in the first catalyst layer 20 and the partition wall 12 is sufficient, which helps to improve the PM capture performance and suppress the pressure drop increase.

[0371] From the perspective of more effectively improving PM collection performance and suppressing pressure loss, Ra is preferably 1.50 × 10⁻⁶. -3 (cm) 3 / (cm) 2 ·s·Pa) or more, more preferably 1.70×10 -3 (cm) 3 / (cm) 2 ·s·Pa) or higher, more preferably 1.90×10 -3 (cm) 3 / (cm) 2 ·s·Pa)) and above.

[0372] If Ra is too large, exhaust gas may sometimes pass through the first catalyst layer 20 and the partition wall 12 without sufficiently diffusing inside them. From the viewpoint of improving the diffusivity of exhaust gas inside the first catalyst layer 20 and the partition wall 12, improving exhaust gas purification performance and PM capture performance, Ra is preferably 2.00 × 10⁻⁶. -2 (cm) 3 / (cm) 2 ·s·Pa) or less, more preferably 1.90×10 -2 (cm) 3 / (cm) 2 ·s·Pa) or less, further preferably 1.80×10 -2 (cm) 3 / (cm) 2 Below ·s·Pa). These upper limits can be combined with any of the lower limits mentioned above.

[0373] The method for determining Ra is described below.

[0374] Slices P1' were prepared from catalyst 1 before heat treatment in the same manner as described above (e.g., Figures 8A-8CThe slide P1' is shown. Slide P1' is placed in the holder of the gas permeability apparatus. Gas is introduced into slide P1' at a rate of 1-200 L / min while the gas pressure is varied, and the flow rate of the pressurized gas is measured. The introduced gas is air. For example, a gas permeability apparatus manufactured by Porous Materials Inc. (e.g., CFP-1100A) can be used. Gas flows from the exhaust gas inlet side of the inlet-side chamber 13a contained in slide P1'. Figure 8C The exhaust gas flows from the upper side (opening) of the inflow side chamber 13a. Figure 8C Gas flowing in from the end (opening) of the upper side of the chamber passes through the first catalyst layer 20 and the partition wall 12, and exits from the exhaust gas outlet side of the outlet side chamber 13b. Figure 8C It flows out from the end (opening) of the lower side.

[0375] According to the following formula, the upstream side of slice P1' relative to the gas flow direction during gas flow is calculated ( Figure 8C (upper side) and downstream side ( Figure 8C The gas permeability is calculated when the pressure difference (pressure at the upstream position relative to the gas flow direction of slice P1') - (pressure at the downstream position relative to the gas flow direction of slice P1') is 10 kPa. The pressure at the upstream position relative to the gas flow direction of slice P1' is controlled by a permeability meter. The downstream position relative to the gas flow direction of slice P1' is open to the atmosphere; therefore, the pressure at the downstream position relative to the gas flow direction of slice P1' is equal to atmospheric pressure.

[0376] R=Q / A1M1,

[0377] [In the formula, R represents the gas permeability (unit: cm)] 3 / (cm) 2 Q represents the flow rate of the gas under pressure (unit: cm³ / s·Pa). 3 / s), A1 represents the effective filtration area of ​​slice P1' (unit: cm). 2 M1 represents the pressure difference (in Pa) between the upstream and downstream sides of slice P1' relative to the gas flow direction.

[0378] A1 can be calculated using the following formula.

[0379] A1=α1×β1×γ1

[0380] [In the formula, α1 represents the average length of one side of the opening of the inflow side chamber 13a (unit: cm), β1 represents the axial length of slice P1' (unit: cm), and γ1 represents the number of effective filter surfaces of slice P1'.]

[0381] α1 can be calculated using the following formula.

[0382] α1 = Average distance D1 - Average thickness T of partition 12

[0383] The average distance D1 (unit: cm) can be calculated using the following method.

[0384] exist Figure 11 In the top view of slice P1' shown, in the four sides of the opening that forms a certain inflow side chamber 13a, Figure 11 Set the left side as "Left A1a", and set the left side as "Left A1a". Figure 11 Set the right side of the symbol to "Right A2a" and set the right side of the symbol to "Right A2a". Figure 11 The top side is set to "Top A3a". Figure 11 One of the lower sides is designated as "lower side A4a". In the four sides forming the opening of an outflow side chamber 13b adjacent to the right or left side of the inflow side chamber 13a, [the following is a description of the opening]. Figure 11 Set the left side as "Left B1b" and set the left side as "Left B1b". Figure 11 Set the right side as "Right B2b" and set the right side as "Right B2b". Figure 11 Set the top side as "Top B3b" and set the top side as "Top B3b". Figure 11 One of the lower sides is designated as "lower side B4b". In the four sides forming the opening of an outflow side chamber 13b adjacent to the lower or upper side of the inflow side chamber 13a, [the following is a description of the designation]: Figure 11 Set the left side as "Left C1b" and set the left side as "Left C1b". Figure 11 Set the right side of the symbol to "Right C2b" and set it to "Right C2b". Figure 11 Set the top side as "Top C3b", and... Figure 11 The lower side is designated as "lower side C4b". The four sides of the opening of the inflow side chamber 13a are formed by the outer surface S1a of the partition wall portion 12 of the substrate 10 in the slice P1' (refer to Figures 4-6 The edges formed by the above-mentioned outflow side chamber 13b are the outer surface S1b of the partition wall portion 12 of the substrate 10 in the slice P1' (refer to...). Figures 4-6 The edges formed by ).

[0385] exist Figure 11In the top view of slice P1' shown, the distance (in cm) between the left side A1a of the opening of the inflow side chamber 13a and the left side B1b of the opening of the outflow side chamber 13b is measured, and this measured distance is designated as distance D11. Alternatively, the distance (in cm) between the right side A2a of the opening of the inflow side chamber 13a and the right side B2b of the opening of the outflow side chamber 13b can be measured, and this measured distance is designated as distance D11. Distance D11 can be considered as the sum of the length of the upper side A3a or lower side A4a of the opening of the inflow side chamber 13a and the thickness of the partition wall 12.

[0386] For from Figure 11 In the top view of slice P1' shown, arbitrarily select 20 inflow-side chambers 13a and their adjacent outflow-side chambers 13b, and calculate the distance D11 in the same way as above, and set their average value as the average distance D11'.

[0387] exist Figure 11 In the top view of slice P1' shown, the distance (in cm) between the lower edge A4a of the opening of the inflow side chamber 13a and the lower edge C4b of the opening of the outflow side chamber 13b is measured, and this measured distance is set as distance D12. Alternatively, the distance (in cm) between the upper edge A3a of the opening of the inflow side chamber 13a and the upper edge C3b of the opening of the outflow side chamber 13b can be measured, and this measured distance is also set as distance D12. Distance D12 can be considered as the sum of the length of the left side A1a or the right side A2a of the opening of the inflow side chamber 13a and the thickness of the partition wall 12.

[0388] For from Figure 11 In the top view of slice P1' shown, arbitrarily select 20 inflow-side chambers 13a and their adjacent outflow-side chambers 13b, and calculate the distance D12 in the same way as above, and set their average value as the average distance D12'.

[0389] The average distance D1 can be calculated as the average of the average distances D11' and D12' (i.e., D1 = (D11' + D12') / 2).

[0390] When the average distance D11' and the average distance D12' are equal, the average distance D11' or the average distance D12' can be regarded as the average distance D1 (i.e., D1=D11' or D1=D12').

[0391] The average thickness T (unit: cm) of the partition 12 can be determined by the following method.

[0392] A portion of the catalyst 1 (e.g., a portion 10 mm from the end of the substrate 10 on the exhaust gas inflow side along the exhaust gas flow direction E) is sectioned with a plane perpendicular to the axis of the substrate 10. The first catalyst layer 20 present in an inflow-side chamber 13a arbitrarily selected from the sectioned surface is observed using SEM to determine the areas where the partition wall portion 12 of the substrate 10 and the first catalyst layer 20 are present. When observing the sectioned surface using SEM, the field of view magnification is, for example, 300x, and the field of view width (length) is, for example, 500~600 μm. The area observed using SEM is preferably set to exclude the corners of the inflow-side chamber 13a. The areas where the partition wall portion 12 of the substrate 10 and the first catalyst layer 20 are present can be determined based on the morphological differences between the first catalyst layer 20 and the partition wall portion 12 of the substrate 10. Elemental mapping of the sectioned surface can also be performed at this time. Elemental mapping can be performed in the same manner as described above. By mapping the elements of the cross-section, based on the differences in morphology and composition between the first catalyst layer 20 and the partition wall portion 12 of the substrate 10, it is possible to determine the region where the partition wall portion 12 of the substrate 10 exists and the region where the first catalyst layer 20 exists.

[0393] In the SEM image, starting from the left or right end, first to Nth grid lines parallel to the thickness direction of the partition wall portion 12 of the substrate 10 are drawn sequentially at 15 μm intervals. The intersections of the contour lines of the region where the partition wall portion 12 of the substrate 10 exists with the grid lines are connected by straight lines to determine the position of the surface of the partition wall portion 12 of the substrate 10 on the inflow side chamber side. N is, for example, an integer from 30 to 50. Similarly, the intersections of the contour lines of the region where the partition wall portion 12 of the substrate 10 exists with the grid lines are connected by straight lines to determine the position of the surface of the partition wall portion 12 of the substrate 10 on the outflow side chamber side. If the change in thickness direction from a certain intersection point X1 to the intersection point X2 adjacent to that intersection point X1 exceeds the grid line interval (15 μm), it is preferable not to use intersection point X2 for determining the surface position (i.e., remove intersection point X2 from the intersection points connected by straight lines). The change in thickness from a certain intersection point X1 to the adjacent intersection point X2 refers to the distance between a straight line passing through intersection point X1 and perpendicular to the thickness direction of the partition wall portion 12 of the substrate 10, and a straight line passing through intersection point X2 and perpendicular to the thickness direction of the partition wall portion 12 of the substrate 10. If the change in thickness from intersection point X1 to the adjacent intersection point X2 exceeds the grid line interval (15 μm), and the change in thickness from intersection point X1 to the adjacent intersection point X3 also exceeds the grid line interval (15 μm), it is preferable that intersection point X3, except for intersection point X2, is not used for determining the surface position (i.e., intersection points X2 and X3 are removed from the intersection points connected by straight lines). If five intersection points are continuously removed from the intersection points connected by straight lines in this manner, it is preferable not to measure the thickness of the SEM image.

[0394] After determining the positions of the inflow-side chamber surface and the outflow-side chamber surface of the partition wall portion 12 of the substrate 10, image analysis software is used to calculate the area of ​​the region enclosed by the second grid line, the (N-1)th grid line, the inflow-side chamber surface of the partition wall portion 12 of the substrate 10, and the outflow-side chamber surface of the partition wall portion 12 of the substrate 10. Image analysis software such as AreaQ (manufactured by ASTECH Corporation), ImageJ (public domain software), and Photoshop (Adobe Systems Inc.) can be used. Furthermore, since the ends of the image tend to become blurry, making it difficult to determine the position of the partition wall portion 12 surface, the first grid line and the Nth grid line are not used.

[0395] After calculating the area of ​​the above region, the thickness of the above region is calculated based on the following formula.

[0396] The thickness of the aforementioned region = the area of ​​the aforementioned region / (grid line spacing × number of grid line spacings)

[0397] In addition, the grid lines are spaced 15 μm apart, and the number of grid line spacings is (N-3).

[0398] For 20 inflow-side chambers 13a arbitrarily selected from the cross-section, the thickness of the aforementioned region is calculated, and their average value is set as the average thickness T of the partition wall portion 12.

[0399] β1 can be determined by measuring the length of slice P1' (the axial length of slice P1').

[0400] γ1 can be obtained using the following method.

[0401] like Figures 2-6 As shown, the top view shape of the end (opening) of the waste gas inflow side of the inflow chamber 13a and the top view shape of the end (opening) of the waste gas outflow side of the outflow chamber 13b are both quadrilaterals (preferably squares or rectangles, more preferably squares). Therefore, as Figure 4 and Figure 5 As shown, the outer surface S1a of the partition 12 that contacts an inflow side chamber 13a is composed of four surfaces, and the outer surface S1b of the partition 12 that contacts an outflow side chamber 13b is composed of four surfaces.

[0402] Regarding all the inflow-side chambers 13a contained in slice P1', calculate the number of surfaces of the outer surface S1a (four surfaces) of the partition portion 12 that are in contact with each inflow-side chamber 13a that are not adjacent to the third sealing portion 16, and set their sum as γ1. Specifically, as described below.

[0403] exist Figure 11In the top view of slice P1' shown, three inflow side chambers 13a and three outflow side chambers 13b are... Figure 11 Arrange them horizontally in a column. Move each column from... Figure 11 From the top side, they are sequentially named "Column 1 F1", "Column 2 F2", "Column 3 F3", "Column 4 F4", "Column 5 F5", and "Column 6 F6". The three inflow side chambers 13a in Column 1 F1 are... Figure 11 From the left side, they are sequentially named "Inflow Side Chamber F11", "Inflow Side Chamber F12", and "Inflow Side Chamber F13". The three inflow side chambers 13a in the second column F2 are then... Figure 11 From the left side, they are sequentially named "Inflow Side Chamber F21", "Inflow Side Chamber F22", and "Inflow Side Chamber F23". The three inflow side chambers 13a in the third column F3 are then... Figure 11 From the left side, they are sequentially named "Inflow Side Chamber F31", "Inflow Side Chamber F32", and "Inflow Side Chamber F33". The three inflow side chambers 13a in the fourth column F4 are then... Figure 11 From the left side, they are sequentially named "Inflow Side Chamber F41", "Inflow Side Chamber F42", and "Inflow Side Chamber F43". The three inflow side chambers 13a in the fifth column F5 are then... Figure 11 From the left side, they are sequentially named "Inflow Side Chamber F51", "Inflow Side Chamber F52", and "Inflow Side Chamber F53". The three inflow side chambers 13a in the sixth column F6 are then... Figure 11 From left to right, they are called “inflow side chamber F61”, “inflow side chamber F62”, and “inflow side chamber F63” respectively.

[0404] The left surface of the outer surface S1a (four faces) of the partition 12 that contacts the inflow side chamber F11 Figure 11 The left side) and the top surface ( Figure 11 The upper side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1a of the partition wall 12 that are not adjacent to the third sealing part 16 is 2.

[0405] The right surface of the outer surface S1a (four surfaces) of the partition 12 that contacts the inflow side chamber F63 Figure 11 The right side) and the lower surface ( Figure 11 The lower side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1a of the partition wall 12 that are in contact with the inflow side chamber F63 that are not adjacent to the third sealing part 16 is 2.

[0406] The upper surface of the outer surface S1a (four faces) of the partition 12 that contacts the inflow side chamber F12 or the inflow side chamber F13. Figure 11The upper side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1a of the partition wall 12 that are not adjacent to the third sealing part 16 is 3.

[0407] The right surface of the outer surface S1a (four surfaces) of the partition 12 that contacts the inflow side chamber F23 or the inflow side chamber F43. Figure 11 The right side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1a of the partition wall 12 that are not adjacent to the third sealing part 16 is 3.

[0408] The left surface of the outer surface S1a (four faces) of the partition 12 that contacts the inflow side chamber F31 or the inflow side chamber F51 Figure 11 The left side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1a of the partition wall 12 that are not adjacent to the third sealing part 16 is 3.

[0409] The lower surface of the outer surface S1a (four sides) of the partition 12 that contacts the inflow side chamber F61 or the inflow side chamber F62 Figure 11 The lower side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1a of the partition wall 12 that are not adjacent to the third sealing part 16 is 3.

[0410] None of the four outer surfaces S1a of the partition wall portion 12 that contact the inflow-side chambers F21, F22, F32, F33, F41, F42, F52, or inflow-side chamber F53 are adjacent to the third sealing portion 16. Therefore, the number of the four outer surfaces S1a of the partition wall portion 12 that are not adjacent to the third sealing portion 16 is 4.

[0411] Based on the above, the effective number of filter surfaces of slice P1' is 2×2 (inflow side units F11, F63) + 3×8 (inflow side units F12, F13, F23, F31, F43, F51, F61, F62) + 4×8 (inflow side units F21, F22, F32, F33, F41, F42, F52, F53) = 60.

[0412] Gas permeability was measured three times using different slices P1', and the average value was set as Ra (cm). 3 / (cm)2 ·s·Pa).

[0413] In the above-described measurement method, non-through pores are not included in the measurement; only the through pores of the first catalyst layer 20 and the partition wall 12 are included. Therefore, according to the above-described measurement method, the gas permeability of the first catalyst layer 20 and the partition wall 12 can be measured with high precision.

[0414] <Condition 2b>

[0415] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), catalyst 1 preferably further satisfies the following condition 2b: 1.30 × 10 -3 ≤Rb

[0416] [In the formula, Rb represents the gas permeability (cm²) of the second catalyst layer 30 and the partition wall 12 as measured by a gas permeability meter before the catalyst 1 is heat-treated at 950°C for 35 hours in atmospheric atmosphere.] 3 / (cm) 2 ·s·Pa). ].

[0417] In the phrase “gas permeability of the second catalyst layer 30 and the partition wall 12”, “partition wall 12” refers to the portion of partition wall 12 in which the second catalyst layer 30 is disposed.

[0418] Rb is an indicator of the permeability of exhaust gas in the second catalyst layer 30 and the partition wall 12. A larger Rb indicates higher permeability of exhaust gas in the second catalyst layer 30 and the partition wall 12. When Rb is 1.30 × 10⁻⁶... -3 (cm) 3 / (cm) 2 When the pressure drop is above 60°C (Pa), the ventilation of the exhaust gas in the second catalyst layer 30 and the partition wall 12 is sufficient, which helps to improve the PM capture performance and suppress the pressure drop increase.

[0419] From the perspective of more effectively improving PM capture performance and suppressing pressure drop, Rb is preferably 1.50 × 10⁻⁶. -3 (cm) 3 / (cm) 2 ·s·Pa) or more, more preferably 1.70×10 -3 (cm) 3 / (cm) 2 ·s·Pa) or higher, more preferably 1.90×10 -3 (cm) 3 / (cm) 2 ·s·Pa)) and above.

[0420] If Rb is too large, exhaust gas may sometimes pass through the second catalyst layer 30 and the partition wall 12 without sufficiently diffusing inside them. From the viewpoint of improving the diffusivity of exhaust gas inside the second catalyst layer 30 and the partition wall 12, improving exhaust gas purification performance, and PM capture performance, Rb is preferably 2.00 × 10⁻⁶. -2 (cm) 3 / (cm) 2 ·s·Pa) or less, more preferably 1.90×10 -2 (cm) 3 / (cm) 2 ·s·Pa) or less, further preferably 1.80×10 -2 (cm) 3 / (cm) 2 Below ·s·Pa). These upper limits can be combined with any of the lower limits mentioned above.

[0421] The method for determining Rb is described below.

[0422] The catalyst 1 before heat treatment is used to prepare slices P2' in the same manner as described above (e.g., Figures 10A-10C The slide P2' is shown. Slide P2' is placed in the holder of the gas permeability apparatus. Gas is introduced into slide P2' at a rate of 1-200 L / min while the gas pressure is varied, and the flow rate of the pressurized gas is measured. The introduced gas is air. For example, a gas permeability apparatus manufactured by Porous Materials Inc. (e.g., CFP-1100A) can be used. Gas flows from the exhaust gas inlet side of the inlet-side chamber 13a contained in slide P2'. Figure 10C The exhaust gas flows from the upper side (opening) of the inflow side chamber 13a. Figure 10C Gas flowing in from the end (opening) of the upper side of the chamber passes through the partition wall 12 and the second catalyst layer 30, and exits from the exhaust gas outlet side of the outlet side chamber 13b. Figure 10C It flows out from the end (opening) of the lower side.

[0423] According to the following formula, the upstream side of slice P2' relative to the gas flow direction during gas flow is calculated ( Figure 10C (upper side) and downstream side ( Figure 10CThe gas permeability is calculated when the pressure difference (pressure at the upstream position relative to the gas flow direction of slice P2') - (pressure at the downstream position relative to the gas flow direction of slice P2') is 10 kPa. The pressure at the upstream position relative to the gas flow direction of slice P2' is controlled by a permeability meter. The downstream position relative to the gas flow direction of slice P2' is open to the atmosphere, therefore the pressure at the downstream position relative to the gas flow direction of slice P2' is equal to atmospheric pressure.

[0424] R=Q / A2M2

[0425] [In the formula, R represents the gas permeability (unit: cm)] 3 / (cm) 2 Q represents the flow rate of the gas under pressure (unit: cm³ / s·Pa). 3 / s), A2 represents the effective filtration area of ​​slice P2' (unit: cm). 2 M2 represents the pressure difference (in Pa) between the upstream and downstream sides of slice P2' in the direction of gas flow.

[0426] A2 can be calculated using the following formula.

[0427] A2 = α2 × β2 × γ2,

[0428] [In the formula, α2 represents the average length of one side of the opening of the outflow side chamber 13b (unit: cm), β2 represents the axial length of slice P2' (unit: cm), and γ2 represents the effective filtration surface number of slice P2'.]

[0429] α2 can be calculated using the following formula.

[0430] α2 = Average distance D2 - Average thickness T of partition 12

[0431] The average distance D2 (unit: cm) can be calculated using the following method.

[0432] exist Figure 12 In the top view of slice P2' shown, the four sides constituting the opening of one of the outflow side chambers 13b are... Figure 12 Set the left side as "Left A1b" and set the left side as "Left A1b". Figure 12 Set the right side of the symbol to "Right A2b" and set the right side of the symbol to "Right A2b". Figure 12 Set the top side as "Top A3b", and... Figure 12 The lower side is designated as "lower side A4b", which refers to the four sides of the opening of the inflow side chamber 13a that is adjacent to the right or left side of the outflow side chamber 13b. Figure 12Set the left side as "Left B1a" and set the right side as "Left B1a". Figure 12 Set the right side of the symbol to "Right B2a" and set it to "Right B2a". Figure 12 Set the top side as "Top B3a" and set the top side as "Top B3a". Figure 12 The lower side is designated as "lower side B4a", which refers to the four sides of the opening of an inflow side chamber 13a that is adjacent to the lower or upper side of the outflow side chamber 13b. Figure 12 Set the left side as "left C1a", and set the left side as "left C1a". Figure 12 Set the right side of it as "Right C2a" and set it as "Right C2a". Figure 12 The upper side is set as "top C3a". Figure 12 The lower side is designated as "lower side C4a". The four sides of the opening of the outflow side chamber 13b are formed by the outer surface S1b of the partition wall portion 12 of the substrate 10 in the slice P2' (refer to Figures 4-6 The edges formed by the above-mentioned inflow side chamber 13a are the outer surfaces S1a of the partition wall portion 12 of the substrate 10 in the slice P2' (refer to...). Figures 4-6 The edges formed by ).

[0433] exist Figure 12 In the top view of slice P2' shown, the distance (in cm) between the left side A1b of the opening of the outflow side chamber 13b and the left side B1a of the opening of the inflow side chamber 13a is measured, and this measured distance is designated as distance D21. Alternatively, the distance (in cm) between the right side A2b of the opening of the outflow side chamber 13b and the right side B2a of the opening of the inflow side chamber 13a can be measured, and this measured distance is designated as distance D21. Distance D21 can be considered as the sum of the length of the upper side A3b or lower side A4b of the opening of the outflow side chamber 13b and the thickness of the partition wall 12.

[0434] For from Figure 12 In the top view of slice P2' shown, arbitrarily select 20 outflow side chambers 13b and their adjacent inflow side chambers 13a, and calculate the distance D21 in the same way as above, and set their average value as the average distance D21'.

[0435] exist Figure 12 In the top view of slice P2' shown, the distance (in cm) between the lower edge A4b of the opening of the outflow side chamber 13b and the lower edge C4a of the opening of the inflow side chamber 13a is measured, and this measured distance is designated as distance D22. Alternatively, the distance (in cm) between the upper edge A3b of the opening of the outflow side chamber 13b and the upper edge C3a of the opening of the inflow side chamber 13a can be measured, and this measured distance is designated as distance D22. Distance D22 can be considered as the sum of the length of the left side A1b or the right side A2b of the opening of the outflow side chamber 13b and the thickness of the partition wall 12.

[0436] For from Figure 12 In the top view of slice P2' shown, arbitrarily select 20 outflow side chambers 13b and their adjacent inflow side chambers 13a, and calculate the distance D22 in the same way as above, and set their average value as the average distance D22'.

[0437] The average distance D2 can be calculated as the average of the average distances D21' and D22' (i.e., D2 = (D21' + D22') / 2).

[0438] When the average distance D21' and the average distance D22' are equal, the average distance D21' or the average distance D22' can be regarded as the average distance D2 (that is, D2=D21' or D2=D22').

[0439] The average thickness T (unit: cm) of the partition 12 can be calculated in the same way as above.

[0440] β2 can be determined by measuring the axial length of slice P2'.

[0441] γ2 can be obtained using the following method.

[0442] like Figure 4 and Figure 5 As shown, the outer surface S1a of the partition 12 that contacts an inflow side chamber 13a is composed of four surfaces, and the outer surface S1b of the partition 12 that contacts an outflow side chamber 13b is composed of four surfaces.

[0443] Regarding all the outflow side chambers 13b contained in slice P2', calculate the number of surfaces of the outer surface S1b (four surfaces) of the partition portion 12 that do not adjoin the third sealing portion 16, and set their sum as γ2. Specifically, as described below.

[0444] exist Figure 12 In the top view of slice P2' shown, three inflow side chambers 13a and three outflow side chambers 13b are... Figure 12 Arrange them horizontally in a column. Move each column from... Figure 12 From the top side, they are sequentially named "Column 1 G1", "Column 2 G2", "Column 3 G3", "Column 4 G4", "Column 5 G5", and "Column 6 G6". The three outflow chambers 13b in Column 1 G1 are... Figure 12 From the left side, they are sequentially named "outflow side chamber G11", "outflow side chamber G12", and "outflow side chamber G13". The three outflow side chambers 13b in the second column G2 are then... Figure 12From the left side, they are sequentially named "Outflow Side Chamber G21", "Outflow Side Chamber G22", and "Outflow Side Chamber G23". The three outflow side chambers 13b in the third column G3 are then... Figure 12 From the left side, they are sequentially named "Outflow Side Chamber G31", "Outflow Side Chamber G32", and "Outflow Side Chamber G33". The three outflow side chambers 13b in the fourth column G4 are then... Figure 12 From the left side, they are sequentially named "Outflow Side Chamber G41", "Outflow Side Chamber G42", and "Outflow Side Chamber G43". The three outflow side chambers 13b in column F5 are then... Figure 12 From the left side, they are sequentially named "Outflow Side Chamber G51", "Outflow Side Chamber G52", and "Outflow Side Chamber G53". The three outflow side chambers 13b in column F6 are then... Figure 12 From left to right, they are named “outflow side chamber G61”, “outflow side chamber G62”, and “outflow side chamber G63” respectively.

[0445] The left surface of the outer surface S1b (four faces) of the partition 12 that contacts the outflow side chamber G11 Figure 12 The left side) and the top surface ( Figure 12 The upper side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1b of the partition wall 12 that are in contact with the outflow side chamber G11 that are not adjacent to the third sealing part 16 is 2.

[0446] The right surface of the outer surface S1b (four surfaces) of the partition 12 that contacts the outflow side chamber G63 Figure 12 The right side) and the lower surface ( Figure 12 The lower side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1b of the partition wall 12 that are in contact with the outflow side chamber G63 that are not adjacent to the third sealing part 16 is 2.

[0447] The upper surface of the outer surface S1b (four sides) of the partition portion 12 that contacts the outflow side chamber G12 or the outflow side chamber G13. Figure 12 The upper side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1b of the partition wall 12 that are not adjacent to the third sealing part 16 is 3.

[0448] The right surface of the outer surface S1b (four surfaces) of the partition portion 12 that contacts the outflow side chamber G23 or the outflow side chamber G43. Figure 12 The right side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1b of the partition wall 12 that are in contact with the outflow side chamber G23 or the outflow side chamber G43 that are not adjacent to the third sealing part 16 is 3.

[0449] The left surface of the outer surface S1b (four faces) of the partition portion 12 that contacts the outflow side chamber G31 or the outflow side chamber G51 Figure 12 The left side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1b of the partition wall 12 that are in contact with the outflow side chamber G31 or the outflow side chamber G51 that are not adjacent to the third sealing part 16 is 3.

[0450] The lower surface of the outer surface S1b (four sides) of the partition portion 12 that contacts the outflow side chamber G61 or the outflow side chamber G62. Figure 12 The lower side of the partition wall 12 is adjacent to the third sealing part 16. Therefore, the number of the four sides of the outer surface S1b of the partition wall 12 that do not connect with the third sealing part 16 is 3.

[0451] None of the four outer surfaces S1b of the partition wall portion 12 that contact the outflow side chambers G21, G22, G32, G33, G41, G42, G52, or outflow side chamber G53 are adjacent to the third sealing portion 16. Therefore, the number of the four outer surfaces S1b of the partition wall portion 12 that are not adjacent to the third sealing portion 16 that contact the outflow side chambers G21, G22, G32, G33, G41, G42, G52, or outflow side chamber G53 is 4.

[0452] Based on the above, the effective number of filter surfaces of slice P2' is 2×2 (outflow side chambers G11 and G63) + 3×8 (outflow side chambers G12, G13, G23, G31, G43, G51, G61, G62) + 4×8 (outflow side chambers G21, G22, G32, G33, G41, G42, G52, G53) = 60.

[0453] Gas permeability was measured three times using different slices P2', and the average value was set as Rb (cm). 3 / (cm) 2 ·s·Pa).

[0454] In the above-described measurement method, non-through pores are not included in the measurement; only the through pores of the second catalyst layer 30 and the partition wall portion 12 are included. Therefore, according to the above-described measurement method, the gas permeability of the second catalyst layer 30 and the partition wall portion 12 can be measured with high precision.

[0455] <10% flow diameter of the adjacent section>

[0456] The diameter (μm) of the partition wall portion 12 at 10% flow rate, measured by the bubble point method using an air permeability meter after heat treatment of the substrate 10 at 950°C for 35 hours in atmospheric atmosphere, is defined as Xc (μm). The diameter (μm) of the partition wall portion 12 at 10% flow rate, measured by the bubble point method using an air permeability meter before the aforementioned heat treatment of the substrate 10, is defined as Yc (μm). Typically, Xc is 5.00 μm or more and 20.00 μm or less, Yc is typically 5.00 μm or more and 20.00 μm or less, and Xc / Yc is typically 1.1 or less. Xc can be 5.50 μm or more and 18.00 μm or less, or 6.00 μm or more and 16.00 μm or less. Yc can be 5.50 μm or more and 18.00 μm or less, or 6.00 μm or more and 16.00 μm or less. Xc / Yc can be below 1.05 or below 1.03. The state of the substrate 10 remains almost unchanged before and after heat treatment, so the theoretical lower limit of Xc / Yc is 1. However, due to measurement errors or other minor variations, it is sometimes lower than 1. Xc / Yc can, for example, be above 0.98, above 0.99, or above 1.00. These lower limits can be combined with any of the upper limits mentioned above.

[0457] The method for determining Xc is described below.

[0458] The substrate 10 is heat-treated at 950°C for 35 hours in an atmospheric atmosphere. A section extending axially along the substrate 10 and having a length L equal to that of the substrate 10 is cut from the heat-treated substrate 10. 10 Samples of the same length. The number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample. The top view shape of the sample when viewed from the axial direction is, for example, a quadrilateral (preferably a square or rectangle, more preferably a square). There is no particular limitation on the size of the top view shape when viewed from the axial direction, as long as the number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample; for example, the longitudinal length is 10 mm and the transverse length is 10 mm. When the inflow-side chambers 13a and outflow-side chambers 13b are arranged alternately in the longitudinal direction and alternately in the transverse direction, if the total number of inflow-side chambers 13a and outflow-side chambers 13b arranged in the longitudinal direction of the sample is even, and the total number of inflow-side chambers 13a and outflow-side chambers 13b arranged in the transverse direction of the sample is even, then the number of inflow-side chambers 13a in the sample is the same as the number of outflow-side chambers 13b in the sample.

[0459] The sample is sectioned with a plane perpendicular to its axis to prepare a slice P3 that does not contain a portion of the first catalyst layer 20 or a portion of the second catalyst layer 30. The axial length of slice P3 is not particularly limited, for example, it is 10 mm. Slice P3 does not have the first sealing portion 14 and the second sealing portion 15.

[0460] An example of slice P3, except that it does not contain a portion of the first catalyst layer 20, is similar to... Figure 7A and Figure 7B The same applies to slice P1 shown. Slice P3 is, for example, a cube with a length of 10 mm in the longitudinal direction, a length of 10 mm in the transverse direction, and a length of 10 mm in the axial direction.

[0461] A first sealing portion is formed in slice P3 to seal the end of the waste gas outflow side of the inflow-side chamber 13a included in slice P3, and a second sealing portion is formed to seal the end of the waste gas inflow side of the outflow-side chamber 13b included in slice P3. A third sealing portion is formed at the outermost periphery of slice P3, resulting in slice P3'. The first, second, and third sealing portions can be formed by applying a filling material to predetermined locations on slice P3. As the filling material, an adhesive such as an epoxy resin-based adhesive can be used. The thicknesses of the first sealing portion 14 and the second sealing portion 15 are respectively set to be less than 1 / 10 of the axial length of slice P3.

[0462] An example of slice P3', except that it does not contain a portion of the first catalyst layer 20, is similar to... Figures 8A-8C The slice P1' shown is the same as one example.

[0463] Xc can be measured in the same way as Xa, except that slice P3' prepared from heat-treated substrate 10 is used instead of slice P1' prepared from heat-treated catalyst 1.

[0464] If there is a portion in catalyst 1 that does not contain either a portion of the first catalyst layer 20 or a portion of the second catalyst layer 30, slice P3' can be prepared from catalyst 1. If there is no portion in catalyst 1 that does not contain either a portion of the first catalyst layer 20 or a portion of the second catalyst layer 30, a substrate of the same specifications as the substrate 10 used in catalyst 1 can be prepared, and the result of measuring the prepared substrate can be presumed as the measured value of substrate 10 of catalyst 1.

[0465] The method for determining Yc is described below.

[0466] Slice P3' is prepared from substrate 10 before heat treatment in the same manner as described above. Except that slice P3' prepared from substrate 10 before heat treatment is used instead of slice P3' prepared from substrate 10 after heat treatment, Yc can be measured in the same manner as Xc.

[0467] <Gas permeability of the partition>

[0468] The gas permeability (cm²) of the partition wall 12 was measured using a gas permeability meter before the substrate 10 was heat-treated at 950°C for 35 hours in an atmospheric atmosphere. 3 / (cm) 2 ·s·Pa)) is set as Rc (cm) 3 / (cm) 2 When ·s·Pa), Rc is typically 7.00 (cm). 3 / (cm) 2 ·s·Pa)) above and 20.00 (cm) 3 / (cm) 2 Below ·s·Pa). Rc can be 9.00 (cm). 3 / (cm) 2 ·s·Pa)) above and 18.00 (cm) 3 / (cm) 2 Below ·s·Pa), it can also be 11.00 (cm). 3 / (cm) 2 ·s·Pa)) above and 16.00 (cm) 3 / (cm) 2 ·s·Pa)) and below.

[0469] The method for determining Rc is described below.

[0470] Slice P3' is prepared from substrate 10 before heat treatment in the same manner as described above. Except that slice P3' prepared from substrate 10 before heat treatment is used instead of slice P1' prepared from catalyst 1 before heat treatment, Rc can be measured in the same manner as Ra.

[0471] Methods for forming catalyst layers

[0472] The method for forming the catalyst layer will now be described. Unless otherwise specified, the following description of the method for forming the catalyst layer applies to both the first catalyst layer 20 and the second catalyst layer 30. When applied to the first catalyst layer 20, "catalyst layer" is replaced by "first catalyst layer 20," and when applied to the second catalyst layer 30, "catalyst layer" is replaced by "second catalyst layer 30." Furthermore, unless otherwise specified, the following description of the method for forming the catalyst layer applies to embodiments A through E.

[0473] When the catalyst layer has a single-layer structure, after attaching the slurry for forming the catalyst layer to a designated portion of the substrate 10, it is dried to form a precursor for the catalyst layer. After forming the precursor for the catalyst layer, it is fired. In this way, a catalyst layer with a single-layer structure can be formed.

[0474] When the catalyst layer has a double-layer structure, after attaching a slurry for forming the lower layer to a designated portion of the substrate 10, it is dried to form the lower layer precursor. Next, after attaching a slurry for forming the upper layer to the lower layer precursor, it is dried to form the upper layer precursor. After forming the lower and upper layer precursors, calcination is performed. In this way, a catalyst layer with a double-layer structure can be formed. Catalyst layers with a multilayer structure other than a double-layer structure (e.g., a triple-layer structure) can also be formed in the same way.

[0475] The drying temperature is, for example, above 40°C and below 150°C, and the drying time is, for example, above 5 minutes and below 1 hour. The firing temperature is, for example, above 350°C and below 600°C, and the firing time is, for example, above 20 minutes and below 5 hours. The firing atmosphere is usually atmospheric.

[0476] The composition of each slurry is adjusted according to the composition of the catalyst layer. Each slurry may contain, for example, a source of noble metal elements, inorganic oxide particles (e.g., Zr-based oxide particles), a binder, a pore-forming material, and a solvent. Examples of sources of noble metal elements include salts of noble metal elements, such as nitrates, ammonium complex salts, acetates, and chlorides. The inorganic oxides constituting the inorganic oxide particles are explained above. Examples of binders include alumina sol, zirconium oxide sol, titanium dioxide sol, silica sol, and cerium dioxide sol. Examples of pore-forming materials include cross-linked poly(methyl methacrylate) particles, cross-linked poly(butyl methacrylate) particles, cross-linked polystyrene particles, cross-linked polyacrylate particles, and melamine-based resins. Examples of solvents include water and organic solvents.

[0477] By adjusting the types of materials constituting each slurry, the concentration (viscosity) of the solid components of each slurry, the coating amount of each slurry, and the particle size and amount of the pore-forming material contained in each slurry, the length of the catalyst layer, the thickness of the raised portion of the catalyst layer, the coating amount of the catalyst layer, Xa, Ya, Ra, Xb, Yb, Rb, etc., can be adjusted.

[0478] Based on the mass of the catalyst layer formed by drying and firing each slurry, the amount of pore-forming material in each slurry is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less. This facilitates the formation of a catalyst layer that meets the desired conditions. Regarding "catalyst layer that meets the desired conditions," for the first catalyst layer 20, it refers to the first catalyst layer 20 that meets condition 1a (preferably conditions 1a and 2a), and for the second catalyst layer 30, it refers to the second catalyst layer 30 that meets condition 1b (preferably conditions 1b and 2b). The same applies below.

[0479] The D50 of the pore-forming material is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 9 μm or less, and even more preferably 3 μm or more and 8 μm or less. This facilitates the formation of a catalyst layer that meets the desired conditions.

[0480] D50 is the particle size at which the cumulative volume of the particle size distribution on a volume basis, as determined by laser diffraction scattering particle size distribution measurement method, is 50%.

[0481] The D50 measurement method is as follows.

[0482] Using an automatic sample feeder (Microtrac SDC, manufactured by Nikkiso Co., Ltd.) for laser diffraction particle size distribution measurement, the powder sample was placed in a water-soluble solvent and irradiated with 40W ultrasound at a flow rate of 40% for 360 seconds. The particle size distribution was then measured using a Microtrac MT3300II laser diffraction particle size distribution measurement device manufactured by Nikkiso Co., Ltd., based on a volume reference. The particle size (μm) at 50% of the cumulative volume was then determined. Two measurements were performed, and the average particle size (μm) at 50% of the cumulative volume was set as D50 (μm). The measurement conditions were set as follows: particle refractive index 1.5, particle shape spherical, solvent refractive index 1.3, zeroing time 30 seconds, and measurement time 30 seconds.

[0483] <Sintered Zr-based oxides>

[0484] When forming a catalyst layer that meets the desired conditions, pre-sintered Zr oxides are preferred as the Zr oxides contained in the slurry, and pre-sintered Ce-Zr composite oxides are more preferred. Pre-sintered Zr oxides are less prone to thermal shrinkage even when exposed to high temperatures. Therefore, by using pre-sintered Zr oxides as the Zr oxides contained in the slurry, the formation of cracks in the catalyst layer caused by the thermal shrinkage of Zr oxides after exposure to high temperatures can be suppressed. Thus, by using pre-sintered Zr oxides as the Zr oxides contained in the slurry, it is easy to form a catalyst layer that meets the desired conditions.

[0485] When the catalyst layer that meets the desired conditions has a stacked structure (e.g., a bilayer structure), sintered Zr oxides may be included in two or more slurries (e.g., a slurry for forming the lower layer and a slurry for forming the upper layer), or sintered Zr oxides may be included in any one of the slurries (e.g., a slurry for forming the lower layer or a slurry for forming the upper layer).

[0486] "Pre-calcination" refers to a calcination treatment performed before use in the preparation of the slurry. The Zr-based oxides subjected to the calcination treatment can be commercially available or manufactured using conventional methods. The conditions for calcination treatment of the Zr-based oxides are as follows: The calcination temperature is preferably 850°C or higher and 1200°C or lower, more preferably 900°C or higher and 1150°C or lower, and even more preferably 950°C or higher and 1100°C or lower. The calcination time is preferably 1 hour or higher and 10 hours or lower, more preferably 2 hours or higher and 8 hours or lower, and even more preferably 3 hours or higher and 6 hours or lower. The atmosphere during calcination is preferably an atmospheric atmosphere or an inactive atmosphere.

[0487] The specific surface area of ​​Zr oxides before calcination is preferably 85 m². 2 / g or more and 120m 2 / g or less, preferably 85m 2 / g or more and 110m 2 / g or less, more preferably 85m 2 / g or more and 100m 2 / g or less.

[0488] The specific surface area of ​​the Zr-based oxides after sintering is preferably 30 m². 2 / g or more and 85m 2 / g or less, preferably 40m 2 / g or more and 80m 2 / g or less, more preferably 50m 2 / g or more and 75m 2 / g or less.

[0489] The percentage of the specific surface area of ​​the Zr oxide after calcination relative to the specific surface area of ​​the Zr oxide before calcination (specific surface area of ​​the Zr oxide after calcination / specific surface area of ​​the Zr oxide before calcination × 100) is preferably 25% or more and 100% or less, more preferably 40% or more and 90% or less, and even more preferably 55% or more and 85% or less.

[0490] Specific surface area can be determined using powdered Zr-based oxides and Quantachrome's QUADRASORB SI via nitrogen adsorption.

[0491] When forming a catalyst layer that meets the desired conditions, the Zr-based oxides contained in the slurry preferably meet one or more of the following conditions, more preferably two or more. This makes it difficult for the Zr-based oxides to undergo thermal shrinkage, and effectively suppresses the formation of cracks in the catalyst layer caused by the thermal shrinkage of the Zr-based oxides after exposure to high-temperature environments.

[0492] (1) The preferred specific surface area of ​​Zr-based oxides is 85 m². 2 / g or more and 120m 2 / g or less.

[0493] (2) The D50 of Zr oxides is above 2 μm and below 15 μm.

[0494] (3) The D10 of Zr oxides is above 1 μm.

[0495] (4) The particle size distribution of Zr oxides is not multimodal, but unimodal.

[0496] The meaning and measurement method of D50 are as described above. D10 is the particle size at which the cumulative volume of the particle size distribution of the volume reference, determined by laser diffraction scattering particle size distribution measurement method, reaches 10%. The measurement method of D10 is the same as that of D50.

[0497] Example

[0498] The present invention will be specifically described below based on embodiments, but the present invention is not limited to the embodiments.

[0499] <Example 1>

[0500] (1) Preparation of slurry

[0501] Alumina powder and Ce-Zr composite oxide powder that had undergone prior calcination were added to an aqueous palladium nitrate solution, followed by the addition of alumina sol, zirconium sol, pore-forming material (crosslinked poly(methyl methacrylate) particles with a D50 of 5 μm) and water as a solvent to prepare a first slurry.

[0502] The composition of the Ce-Zr composite oxide powder used in the preparation of the first slurry is as follows.

[0503] Ce content converted to CeO2: 40% by mass

[0504] Zr content converted to ZrO2: 50% by mass

[0505] The content of one or more rare earth elements other than Ce, converted to oxides: 10% by mass

[0506] In the preparation of the first slurry, Ce-Zr composite oxide powder that had undergone pre-calcination treatment under the following conditions was used. The specific surface area of ​​the Ce-Zr composite oxide powder before and after calcination treatment was determined using a nitrogen adsorption method manufactured by Quantachrome (QUADRASORB SI). The specific surface area of ​​the Ce-Zr composite oxide powder before calcination treatment was 87.1 m². 2 / g, the specific surface area of ​​the Ce-Zr composite oxide powder after calcination is 70.8m². 2 / g.

[0507] [Conditions for firing treatment]

[0508] Firing temperature: 950℃

[0509] Firing time: 4 hours

[0510] Firing atmosphere: Atmospheric atmosphere

[0511] The amounts of each component in the first slurry are adjusted so that, based on the mass of the catalyst layer formed by drying and calcining the first slurry, palladium (converted to metal) is 4% by mass, alumina powder is 9% by mass, Ce-Zr composite oxide powder is 78% by mass, alumina sol (converted to solids) is 3% by mass, and zirconium oxide sol (converted to solids) is 6% by mass. The amount of pore-forming material in the first slurry is adjusted so that the mass of the catalyst layer formed by drying and calcining the first slurry is 40% by mass.

[0512] Alumina powder and Ce-Zr composite oxide powder that has undergone pre-calcination treatment were added to an aqueous solution of rhodium nitrate. Then, alumina sol, zirconium sol, pore-forming material (crosslinked poly(methyl methacrylate) particles with a D50 of 3 μm) and water were added as solvent to prepare a second slurry and a third slurry.

[0513] The composition of the Ce-Zr composite oxide powder used in the preparation of the second and third slurries is as follows.

[0514] Ce content converted to CeO2: 15% by mass

[0515] Zr content converted to ZrO2: 65% by mass

[0516] The content of one or more rare earth elements other than Ce, converted to oxides: 20% by mass

[0517] In the preparation of the second and third slurries, Ce-Zr composite oxide powders that had undergone pre-calcination treatment under the following conditions were used. The specific surface area of ​​the Ce-Zr composite oxide powders before and after calcination treatment was determined using a nitrogen adsorption method manufactured by Quantachrome (QUADRASORB SI). The specific surface area of ​​the Ce-Zr composite oxide powder before calcination treatment was 90.1 m². 2 / g, the specific surface area of ​​the Ce-Zr composite oxide powder after calcination is 68.2m². 2 / g.

[0518] [Conditions for firing treatment]

[0519] Firing temperature: 950℃

[0520] Firing time: 4 hours

[0521] Firing atmosphere: Atmospheric atmosphere

[0522] The amounts of each component in the second slurry are adjusted so that, based on the mass of the catalyst layer formed by drying and firing the second slurry, rhodium (converted to metal) is 0.5% by mass, alumina powder is 17.5% by mass, Ce-Zr composite oxide powder is 74% by mass, alumina sol (converted to solids) is 3% by mass, and zirconium oxide sol (converted to solids) is 5% by mass. The amount of pore-forming material in the second slurry is adjusted so that it accounts for 40% by mass of the catalyst layer formed by drying and firing the second slurry.

[0523] The amounts of each component in the third slurry are adjusted so that, based on the mass of the catalyst layer formed by drying and firing the third slurry, rhodium (converted to metal) is 0.5% by mass, alumina powder is 9.5% by mass, Ce-Zr composite oxide powder is 82% by mass, alumina sol (converted to solids) is 3% by mass, and zirconium oxide sol (converted to solids) is 5% by mass. The amount of pore-forming material in the third slurry is adjusted so that it accounts for 30% by mass of the catalyst layer formed by drying and firing the third slurry.

[0524] Furthermore, the mass of the catalyst layer formed by drying and firing each slurry is determined by subtracting the mass of the components (e.g., solvents, pore-forming materials, etc.) that disappear during the drying and firing of each slurry from the mass of each slurry.

[0525] (2) Manufacturing of catalysts for waste gas purification

[0526] Prepare with Figures 2-6 The illustrated wall-flow substrate comprises an inflow-side chamber extending axially along the substrate, an outflow-side chamber extending axially along the substrate, and a porous partition separating the inflow-side and outflow-side chambers. The partition has a thickness of 200 μm, and the total number of inflow-side and outflow-side chambers in a cross-section perpendicular to the substrate axial direction is 300 chambers per square inch. The substrate has a volume of 0.79 L and a length of 90 mm.

[0527] After the first slurry is applied to the waste gas inflow side of the substrate, it is dried at 90°C for 10 minutes to form the lower precursor layer. After the second slurry is applied to the lower precursor layer, it is dried at 90°C for 10 minutes to form the upper precursor layer. The substrate with the lower and upper precursor layers formed is calcined at 450°C for 1 hour to form a first catalyst layer having the lower layer and the upper layer formed on the lower layer on the substrate.

[0528] Next, the third slurry is adhered to the waste gas outflow side of the substrate and dried at 90°C for 10 minutes to form a precursor for the second catalyst layer. The substrate with the precursor for the second catalyst layer formed is then fired at 450°C for 1 hour to form the second catalyst layer on the substrate. Thus, the catalyst for waste gas purification of Example 1 is obtained.

[0529] When the slurry is attached to the waste gas inflow side and the waste gas outflow side of the substrate, the slurry is attached in such a manner that the length of the first catalyst layer is 75% of the length of the substrate, the length of the second catalyst layer is 50% of the length of the substrate, the mass of the first catalyst layer per unit volume of the portion of the substrate in which the first catalyst layer is formed is 40 g / L, and the mass of the second catalyst layer per unit volume of the portion of the substrate in which the second catalyst layer is formed is 40 g / L.

[0530] The exhaust gas purification catalyst of Example 1 was heat-treated at 950°C for 35 hours under atmospheric conditions.

[0531] For catalysts used in the purification of waste gas after heat treatment, Xa and Xb are determined according to the above method.

[0532] For catalysts used for exhaust gas purification before heat treatment, Ya, Yb, Ra and Rb are determined according to the above method.

[0533] Xa, Ya, and Ra were determined using catalysts prepared for exhaust gas purification before or after heat treatment. Figures 8A-8C The slice P1' shown is an example. In the creation of slice P1', the following techniques were used... Figure 7A and Figure 7B The slice P1 shown is vertical ( ). Figure 7A The longitudinal length is 10mm, and the transverse length is... Figure 7A The transverse length is 10mm, and the axial length is... Figure 7B The slice P1' is a cube with a longitudinal length of 10 mm. In slice P1', α1 (the average length of one side of the opening of the inflow side chamber 13a) is 0.121 cm, β1 (the axial length of slice P1') is 1 cm, γ1 (the number of effective filtration surfaces in slice P1') is 60, and A1 (the effective filtration area of ​​slice P1') is 7.26 cm². 2 .

[0534] The determination of Xb, Yb, and Rb uses catalysts prepared for exhaust gas purification before or after heat treatment. Figures 10A-10C The slice P2' shown is an example. In the preparation of slice P2', the following techniques were used... Figure 9A and Figure 9B The slice P2 shown is vertical ( ). Figure 9A The longitudinal length is 10mm, and the transverse length is... Figure 9A The transverse length is 10mm, and the axial length is... Figure 9B The slice P2' is a cube with a longitudinal length of 10 mm. In slice P2', α2 (the average length of one side of the opening of the outflow side chamber 13b) is 0.121 cm, β2 (the axial length of slice P2') is 1 cm, γ2 (the number of effective filtration surfaces in slice P2') is 6, and A2 (the effective filtration area of ​​slice P2') is 7.26 cm². 2 .

[0535] Xc, that is, after the substrate is heat-treated at 950°C for 35 hours in an atmospheric atmosphere, the 10% flow diameter of the partition wall measured by the bubble point method using an air permeability meter is 14.39 μm; Yc, that is, before the substrate is heat-treated as described above, the 10% flow diameter of the partition wall measured by the bubble point method using an air permeability meter is 14.38 μm; Xc / Yc is 1.00.

[0536] Rc, that is, the gas permeability of the partition wall measured by a gas permeability meter before heat treatment of the substrate at 950°C for 35 hours in atmospheric atmosphere, is 12.64 (cm²). 3 / (cm) 2 ·s·Pa).

[0537] (3) Evaluation of PM capture performance

[0538] Gasoline engine vehicles equipped with the exhaust gas purification catalyst of Example 1, either before or after heat treatment, were operated under the globally harmonized light vehicle test cycle (WLTC) conditions. The PM particle number (PN) in the exhaust gas passing through the exhaust gas purification catalyst was measured at the following times: low speed operation (from 589 seconds to 1022 seconds), medium speed operation (from 1022 seconds to 1477 seconds), high speed operation (from 1477 seconds to 1800 seconds). cat Furthermore, the number of PM particles (PN) emitted directly from the engine was measured. all The PM capture performance of the catalyst for exhaust gas purification in Example 1 before or after heat treatment is determined by the following formula.

[0539] PM capture performance = 1 - (PN) cat / PN all )

[0540] The conditions for measuring PM capture performance are as follows.

[0541] Vehicle being evaluated: 1.5L direct-injection turbocharged engine

[0542] Gasoline used: fuel for certification testing

[0543] PM measuring device: manufactured by Horiba Manufacturing Co., Ltd.

[0544] Instead of a gasoline engine vehicle equipped with the exhaust gas purification catalyst of Example 1 before or after heat treatment, a gasoline engine vehicle equipped with a substrate (without either the first catalyst layer or the second catalyst layer) was used, and the PM capture performance of the substrate was determined in the same manner as above.

[0545] The PM capture performance ratio (%) is calculated based on the following formula.

[0546] PM capture performance ratio = (PM capture performance of the catalyst for exhaust gas purification in Example 1 before or after heat treatment / PM capture performance of the substrate) × 100

[0547] <Example 2>

[0548] In the preparation of the second slurry, Ce-Zr composite oxide powder that has not undergone prior calcination treatment is used instead of Ce-Zr composite oxide powder that has undergone prior calcination treatment. Otherwise, the same operation as in Example 1 is performed.

[0549] <Example 3>

[0550] In the preparation of the third slurry, Ce-Zr composite oxide powder that has not undergone prior calcination treatment is used instead of Ce-Zr composite oxide powder that has undergone prior calcination treatment. Otherwise, the same operation as in Example 1 is performed.

[0551] <Example 4>

[0552] In the preparation of the first slurry, Ce-Zr composite oxide powder that has not undergone prior calcination treatment was used instead of Ce-Zr composite oxide powder that has undergone prior calcination treatment. Otherwise, the same operation as in Example 1 was performed.

[0553] <Example 5>

[0554] In the preparation of the second and third slurries, Ce-Zr composite oxide powder that has not undergone prior calcination treatment is used instead of Ce-Zr composite oxide powder that has undergone prior calcination treatment. Otherwise, the same operation as in Example 1 is performed.

[0555] <Comparative Example 1>

[0556] In the preparation of the first slurry, the second slurry, and the third slurry, Ce-Zr composite oxide powder that has not undergone prior calcination treatment is used instead of Ce-Zr composite oxide powder that has undergone prior calcination treatment. Otherwise, the same operation as in Example 1 is performed.

[0557] The results of Examples 1-5 and Comparative Example 1 are shown in Table 1. In Table 1, "Pre-calcined CZ" indicates whether pre-calcined Ce-Zr composite oxide powder was used in the preparation of the slurry ("Yes" if used, "No" if not used). In Table 1, the units of Xa, Ya, Xb, and Yb are μm, and the units of Ra and Rb are cm. 3 / (cm) 2 ·s·Pa).

[0558] [Table 1]

[0559]

[0560] The results above confirm that by using a catalyst for exhaust gas purification that satisfies at least one of the following conditions 1a and 1b, the reduction in PM capture performance caused by exposure to high-temperature environments can be suppressed.

[0561] [Condition 1a]:

[0562] Xa / Ya≤1.40 and Ya≤5.00

[0563] [Condition 1b]:

[0564] Xb / Yb≤1.40 and Yb≤5.00.

[0565] Explanation of reference numerals in the attached figures

[0566] 1···Catalyst for exhaust gas purification; 10···Substrate; 11···Cylindrical portion; 12···Partition wall portion; 13···Cavity; 13a···Inflow side chamber; 13b···Outflow side chamber; 14···First sealing portion; 15···Second sealing portion; 20···First catalyst layer; 30···Second catalyst layer; S1a···Outer surface of the partition wall portion on the inflow side chamber side; S1b···Outer surface of the partition wall portion on the outflow side chamber side.

Claims

1. A catalyst for purifying waste gas, comprising a substrate extending along the waste gas flow direction, and at least one of a first catalyst layer and a second catalyst layer, wherein, The substrate comprises: an inflow-side chamber extending in the exhaust gas flow direction, with an open end on the exhaust gas inflow side and a closed end on the exhaust gas outflow side; an outflow-side chamber extending in the exhaust gas flow direction, with a closed end on the exhaust gas inflow side and an open end on the exhaust gas outflow side; and a porous partition portion separating the inflow-side chamber and the outflow-side chamber. The first catalyst layer has a portion formed on the outer surface of the inflow-side chamber side of the partition portion from the end of the partition portion on the exhaust gas inflow side along the exhaust gas flow direction. The second catalyst layer has a portion formed on the outer surface of the outflow side chamber of the partition portion from the end of the exhaust outflow side of the partition portion in a direction opposite to the exhaust gas flow direction. The catalyst for waste gas purification satisfies at least one of the following conditions 1a and 1b. Condition 1a: Xa / Ya ≤ 1.40 and Ya ≤ 5.00, In the formula, Xa represents the 10% flow diameter of the first catalyst layer and the partition wall portion, measured by the bubble point method using a permeability meter after heat treatment at 950°C for 35 hours under atmospheric conditions, in μm; Ya represents the 10% flow diameter of the first catalyst layer and the partition wall portion, measured by the bubble point method using a permeability meter before the heat treatment, in μm. Condition 1b: Xb / Yb≤1.40 and Yb≤5.00 In the formula, Xb represents the 10% flow diameter of the second catalyst layer and the partition wall portion, measured by the bubble point method using an air permeability meter after the heat treatment of the catalyst for waste gas purification, in μm; Yb represents the 10% flow diameter of the second catalyst layer and the partition wall portion, measured by the bubble point method using an air permeability meter before the heat treatment of the catalyst for waste gas purification, in μm. When the catalyst for exhaust gas purification meets condition 1a, the first catalyst layer contains Zr-based oxides. When the catalyst for exhaust gas purification satisfies condition 1b, the second catalyst layer contains Zr-based oxides.

2. The catalyst for purifying waste gas according to claim 1, wherein, When the catalyst for exhaust gas purification has the first catalyst layer but not the second catalyst layer, the length of the first catalyst layer is 100% of the length of the inflow-side chamber. When the catalyst for exhaust gas purification includes a second catalyst layer but not a first catalyst layer, the length of the second catalyst layer is 100% of the length of the outflow side chamber. When the catalyst for purifying exhaust gas includes the first catalyst layer and the second catalyst layer, the sum of the length of the first catalyst layer and the length of the second catalyst layer is 100% or more of the length of the substrate.

3. The catalyst for purifying waste gas according to claim 1, wherein, When the catalyst for exhaust gas purification satisfies condition 1a but not condition 1b, the length of the first catalyst layer is 100% of the length of the inflow-side chamber. When the catalyst for exhaust gas purification satisfies condition 1b but not condition 1a, the length of the second catalyst layer is 100% of the length of the outflow side chamber. When the catalyst for exhaust gas purification satisfies conditions 1a and 1b, the sum of the lengths of the first catalyst layer and the second catalyst layer is 100% or more of the length of the substrate.

4. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, When the catalyst for exhaust gas purification meets condition 1a, the mass of the first catalyst layer per unit volume of the portion of the substrate in which the first catalyst layer is formed is 20 g / L or more and 150 g / L or less. When the catalyst for exhaust gas purification satisfies condition 1b, the mass of the second catalyst layer per unit volume of the portion of the substrate in which the second catalyst layer is formed is 20 g / L or more and 150 g / L or less.

5. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, When the catalyst for waste gas purification meets condition 1a, the first catalyst layer contains a Ce-Zr composite oxide as the Zr oxide. When the catalyst for exhaust gas purification meets condition 1b, the second catalyst layer contains Ce-Zr composite oxide as the Zr oxide.

6. The catalyst for purifying waste gas according to claim 5, wherein, When the catalyst for waste gas purification meets condition 1a, based on the mass of the first catalyst layer, the content of Ce-Zr composite oxides in the first catalyst layer is 50% by mass or more. When the catalyst for exhaust gas purification meets the condition 1b, the content of Ce-Zr composite oxide in the second catalyst layer is 50% by mass or more, based on the mass of the second catalyst layer.

7. The catalyst for purifying waste gas according to claim 5, wherein, When the catalyst for exhaust gas purification satisfies condition 1a, the Ce-Zr composite oxide in the first catalyst layer satisfies the following formula: R 12 / R 11 >0.8, In the formula, R 11 This indicates the Ce content in the Ce-Zr composite oxide, expressed as CeO2, in mass %, R. 12 This indicates the Zr content in the Ce-Zr composite oxide, converted to ZrO2, in % by mass. When the catalyst for exhaust gas purification satisfies condition 1b, the Ce-Zr composite oxide in the second catalyst layer satisfies the following formula: R 22 / R 21 >0.8, In the formula, R 21 This indicates the Ce content in the Ce-Zr composite oxide, expressed as CeO2, in mass %, R. 22 The expression indicates the Zr content in the Ce-Zr composite oxide, converted to ZrO2, in mass.

8. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, If the catalyst for waste gas purification satisfies condition 1a, the catalyst for waste gas purification further satisfies the following condition 2a. Condition 2a: 1.30 × 10 -3 ≤Ra, In the formula, Ra represents the gas permeability of the first catalyst layer and the partition wall portion, measured using a porosimeter before the heat treatment of the catalyst for exhaust gas purification, and the unit is cm. 3 / (cm) 2 ·s·Pa), If the catalyst for waste gas purification satisfies condition 1b, the catalyst for waste gas purification further satisfies the following condition 2b. Condition 2b: 1.30 × 10 -3 ≤Rb, In the formula, Rb represents the gas permeability of the second catalyst layer and the partition wall portion, measured using a porosimeter before the heat treatment of the catalyst for exhaust gas purification, and the unit is cm. 3 / (cm) 2 ·s·Pa).

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