Exhaust gas purification catalyst

Abstract

The present invention addresses the problem of providing an exhaust gas purification catalyst capable of suppressing a decrease in PM collection performance caused by exposure to a high-temperature environment. In order to solve this problem, provided is an exhaust gas purification catalyst (1) comprising a wall flow-type substrate (10) and at least one among a first catalyst layer (20) and a second catalyst layer (30), the exhaust gas purification catalyst (1) satisfying at least one among 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

Exhaust gas purification catalyst

[0001] The present invention relates to a catalyst for purifying exhaust gases.

[0002] Exhaust gases emitted from internal combustion engines of automobiles, motorcycles, etc. 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. Three-way catalysts contain precious metal elements such as Pt, Pd, and Rh.

[0003] Exhaust gas contains particulate matter (PM) in addition to harmful components such as HC, CO, and NOx, and is known to cause air pollution.

[0004] In order to comply with environmental regulations regarding PM, vehicles equipped with gasoline engines such as direct injection engines (GDI) are also required to install a filter (GPF: Gasoline Particulate Filter) having a PM trapping function, similar to vehicles equipped with diesel engines.

[0005] As a GPF, for example, a substrate having a structure called a wall-flow type is used. The wall-flow type substrate includes inlet cells that are open at the end on the exhaust gas inlet side and closed at the end on the exhaust gas outlet side, outlet cells that are closed at the end on the exhaust gas inlet side and open at the end on the exhaust gas outlet side, and a porous partition wall that separates the inlet cells from the outlet cells.

[0006] Since the space available for installing a catalyst for purifying exhaust gas is generally limited, studies have been conducted to provide a catalyst layer containing a precious metal element such as Pt, Pd, or Rh on a wall-flow substrate to capture PM and purify harmful components such as HC, CO, and NOx. In a catalyst comprising a wall-flow substrate and a catalyst layer, exhaust gas flows in from the exhaust gas inlet end (opening) of the inlet cell, passes through the catalyst layer and partition walls, and flows out from the exhaust gas outlet end (opening) of the outlet cell, whereupon PM in the exhaust gas is captured in the pores of the catalyst layer and partition walls.

[0007] It is desirable to control the air / fuel ratio (air-fuel ratio A / F) supplied to an internal combustion engine to be close to the theoretical air-fuel ratio (stoichiometry). However, the actual air-fuel ratio fluctuates from stoichiometry to the rich (excess fuel atmosphere) or lean (lean fuel atmosphere) side, and the exhaust gas also fluctuates to the rich or lean side. Therefore, in order to mitigate fluctuations in the oxygen concentration in the exhaust gas and improve the exhaust gas purification ability of the catalyst, materials having the ability to store oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low, i.e., oxygen storage capacity (OSC), such as Zr-based oxides such as Ce-Zr-based composite oxides, have been used as materials for the catalyst layer (see, for example, Patent Documents 1 and 2).

[0008] Zr-based oxides, such as Ce—Zr-based composite oxides, which have conventionally been used as materials for catalyst layers, undergo thermal shrinkage when exposed to a high-temperature environment. In this specification, "high temperature" refers to temperatures of 800°C or higher, particularly 900°C or higher.

[0009] JP 2018-187595 A JP 2023-513989 A

[0010] The present inventors have found that in an exhaust gas purification catalyst comprising a wall-flow type substrate and a catalytic layer containing a Zr-based oxide, exposure to a high-temperature environment is likely to result in a decrease in PM trapping performance. Specifically, the present inventors have found that when an exhaust gas purification catalyst comprising a wall-flow type substrate and a catalytic layer containing a Zr-based oxide is exposed to a high-temperature environment, cracks are formed in the catalytic layer due to thermal contraction of the Zr-based oxide, which tends to decrease the PM trapping performance of the catalytic layer, and that a decrease in the PM trapping performance of the catalytic layer due to thermal contraction of the Zr-based oxide is unlikely to occur in parts of the catalytic layer formed inside the partition walls but is likely to occur in parts formed on the outer surfaces of the partition walls (i.e., parts that protrude from the outer surfaces of the partition walls toward the inlet cell side or the outlet cell side).

[0011] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst that includes a wall-flow type substrate and a catalytic layer containing a Zr-based oxide, and that can suppress the deterioration of PM collection performance that occurs due to exposure to a high-temperature environment.

[0012] In order to solve the above problems, the present invention provides the following exhaust gas purification catalyst. [1] A catalyst for purifying exhaust gas, comprising a substrate extending in an exhaust gas flow direction and at least one of a first catalytic layer and a second catalytic layer, wherein the substrate comprises: inlet-side cells extending in the exhaust gas flow direction, the inlet-side cells having open ends on the exhaust gas inlet side and closed ends on the exhaust gas outlet side; outlet-side cells extending in the exhaust gas flow direction, the outlet-side cells having closed ends on the exhaust gas inlet side and open ends on the exhaust gas outlet side; and a porous partition wall portion separating the inlet-side cells and the outlet-side cells, wherein the first catalytic layer has a portion formed on an outer surface of the partition wall portion on the inlet-side cell side from the exhaust gas inlet-side end of the partition wall portion along the exhaust gas flow direction, and the second catalytic layer has a portion formed on an outer surface of the partition wall portion on the outlet-side cell side from the exhaust gas outlet-side end of the partition wall portion along a direction opposite to the exhaust gas flow direction, and the exhaust gas purifying catalyst satisfies 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 (μm) of the first catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer after the exhaust gas purifying catalyst is subjected to a heat treatment at 950° C. for 35 hours in an air atmosphere, and Ya represents the 10% flow diameter (μm) of the first catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment. [Condition 1b] Xb / Yb≦1.40 and Yb≦5.00 [In the formula, Xb represents the 10% flow diameter (μm) of the second catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer after the exhaust gas purifying catalyst is subjected to the heat treatment, and Yb represents the 10% flow diameter (μm) of the second catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment.[2] The exhaust gas purifying catalyst according to [1], wherein when the exhaust gas purifying catalyst includes the first catalyst layer but not the second catalyst layer, the percentage of the length of the first catalyst layer with respect to the length of the inlet-side cell is 100%, when the exhaust gas purifying catalyst includes the second catalyst layer but not the first catalyst layer, the percentage of the length of the second catalyst layer with respect to the length of the outlet-side cell is 100%, and when the exhaust gas purifying catalyst includes the first catalyst layer and the second catalyst layer, the percentage of the sum of the length of the first catalyst layer and the length of the second catalyst layer with respect to the length of the substrate is 100% or more. [3] The exhaust gas purifying catalyst according to [1] or [2], wherein, when the exhaust gas purifying catalyst satisfies the condition 1a but does not satisfy the condition 1b, the percentage of the length of the first catalyst layer relative to the length of the inlet-side cell is 100%; when the exhaust gas purifying catalyst satisfies the condition 1b but does not satisfy the condition 1a, the percentage of the length of the second catalyst layer relative to the length of the outlet-side cell is 100%; and when the exhaust gas purifying catalyst satisfies the conditions 1a and 1b, the percentage of the sum of the length of the first catalyst layer and the length of the second catalyst layer relative to the length of the substrate is 100% or more. [4] The exhaust gas purifying catalyst according to any one of [1] to [3], wherein, when the exhaust gas purifying catalyst satisfies the condition 1a, the mass of the first catalytic layer per unit volume of a portion of the substrate where the first catalytic layer is formed is 20 g / L or more and 150 g / L or less, and when the exhaust gas purifying catalyst satisfies the condition 1b, the mass of the second catalytic layer per unit volume of a portion of the substrate where the second catalytic layer is formed is 20 g / L or more and 150 g / L or less. [5] The exhaust gas purifying catalyst according to any one of [1] to [4], wherein, when the exhaust gas purifying catalyst satisfies the condition 1a, the first catalytic layer contains a Ce—Zr-based composite oxide as the Zr-based oxide, and when the exhaust gas purifying catalyst satisfies the condition 1b, the second catalytic layer contains a Ce—Zr-based composite oxide as the Zr-based oxide.[6] The exhaust gas purifying catalyst according to [5], wherein when the exhaust gas purifying catalyst satisfies the condition 1a, the content of the Ce—Zr-based composite oxide in the first catalytic layer is 50 mass % or more based on the mass of the first catalytic layer, and when the exhaust gas purifying catalyst satisfies the condition 1b, the content of the Ce—Zr-based composite oxide in the second catalytic layer is 50 mass % or more based on the mass of the second catalytic layer. [7] When the exhaust gas purifying catalyst satisfies the condition 1a, the Ce—Zr-based composite oxide in the first catalytic layer is represented by the following formula: R. １２ / R １１ >0.8 [wherein, R １１ represents the CeO of Ce in the Ce-Zr based composite oxide. ２ represents the content (mass%) of the converted １２ represents ZrO of Zr in the Ce-Zr based composite oxide. ２ When the exhaust gas purifying catalyst satisfies the condition 1b, the Ce—Zr-based composite oxide in the second catalyst layer is represented by the following formula: ２２ / R ２１ >0.8 [wherein, R ２１ represents the CeO of Ce in the Ce-Zr based composite oxide. ２ represents the content (mass%) of the converted ２２ represents ZrO of Zr in the Ce-Zr based composite oxide. ２ [8] When the catalyst for purifying exhaust gas satisfies the condition 1a, the catalyst for purifying exhaust gas satisfies the following condition 2a: [Condition 2a] 1.30×10 －３ ≦Ra [wherein Ra is the gas permeability (cm ) of the first catalyst layer and the partition wall portion measured using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment. ３ / (cm ２ s·Pa)) and when the exhaust gas purifying catalyst satisfies the condition 1b, the exhaust gas purifying catalyst further satisfies the following condition 2b: [Condition 2b] 1.30×10 －３≦Rb [wherein Rb is the gas permeability (cm ) of the second catalyst layer and the partition wall portion measured using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment. ３ / (cm ２ 8. The exhaust gas purifying catalyst according to any one of [1] to [7], further satisfying the following condition:

[0013] According to the present invention, there is provided an exhaust gas purification catalyst that includes a wall-flow type substrate and a catalyst layer containing a Zr-based oxide, and that can suppress a decrease in PM collection performance that occurs due to exposure to a high-temperature environment.

[0014] FIG. 1 is a partial cross-sectional view showing a state in which an exhaust gas purification catalyst according to one embodiment of the present invention is disposed in an exhaust path of an internal combustion engine. FIG. 2 is an end view taken along line A-A in FIG. 1. FIG. 3 is an end view taken along line B-B in FIG. 1. FIG. 4 is an enlarged view of the area indicated by reference symbol R1 in FIG. 2. FIG. 5 is an enlarged view of the area indicated by reference symbol R2 in FIG. 3. FIG. 6 is an end view taken along line C-C in FIG. 1. FIG. 7A is a plan view of a cut piece cut out from the exhaust gas purification catalyst (a plan view when viewed from the exhaust gas inlet side (upper side in FIG. 7B)). FIG. 7B is a cross-sectional view taken along line D1-D1 in FIG. 7A. FIG. 8A is a plan view of a cut piece used for measuring the gas permeabilities of the first catalyst layer and the partition wall portions (a plan view when viewed from the exhaust gas inlet side (upper side in FIG. 8C), i.e., a plan view corresponding to FIG. 7A). 8B is a plan view of a cut piece used to measure the gas permeability of the first catalyst layer and the partition wall portions (plan view when viewed from the exhaust gas outflow side (lower side of FIG. 8C )). FIG. 8C is a cross-sectional view along line D2-D2 of FIG. 8A (cross-sectional view corresponding to FIG. 7B ). FIG. 9A is a plan view of a cut piece cut out from the exhaust gas purification catalyst (plan view when viewed from the exhaust gas inlet side (upper side of FIG. 9B )). FIG. 9B is a cross-sectional view along line D3-D3 of FIG. 9A . FIG. 10A is a plan view of a cut piece used to measure the gas permeability of the second catalyst layer and the partition wall portions (plan view when viewed from the exhaust gas inlet side (upper side of FIG. 10C ), i.e., a plan view corresponding to FIG. 9A ). FIG. 10B is a plan view of a cut piece used to measure the gas permeability of the second catalyst layer and the partition wall portions (plan view when viewed from the exhaust gas outflow side (lower side of FIG. 10C )). FIG. 10C is a cross-sectional view taken along line D4-D4 in FIG. 10A (a cross-sectional view corresponding to FIG. 9B ). FIG. 11 is a plan view of a cut piece used to measure the gas permeability of the first catalyst layer and the partition wall sections (a plan view when viewed from the exhaust gas inlet side (the upper side of FIG. 8C ), i.e., the same plan view as FIG. 8A ). Reference numerals are omitted for some elements (members, parts, etc.) in FIG. 11 . The meanings of the elements (members, parts, etc.) in FIG. 11 can be understood by referring to FIGS. 8A to 8C . FIG. 12 is a plan view of a cut piece used to measure the gas permeability of the second catalyst layer and the partition wall sections (a plan view when viewed from the exhaust gas outlet side (the lower side of FIG. 10C ), i.e., the same plan view as FIG. 10B ).Reference numerals are omitted for some elements (members, parts, etc.) in Fig. 12. The meanings of the elements (members, parts, etc.) in Fig. 12 can be understood by referring to Figs. 10A to 10C.

[0015] <Explanation of Terms> The terms used in this specification will be explained below. The following explanations apply to the entire specification unless otherwise specified.

[0016] <Abbreviations> "SEM" means scanning electron microscope, "EDX" means energy dispersive X-ray spectroscopy, "SEM-EDX" means scanning electron microscope-energy dispersive X-ray analysis, "EPMA" means electron probe microanalyzer, "XRF" means X-ray fluorescence analysis, and "ICP-OES" means inductively coupled plasma optical emission spectroscopy.

[0017] <Metallic Elements> The term "metallic elements" also includes metalloid elements such as Si and B.

[0018] <Rare Earth Elements> "Rare earth elements" include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0019] <Noble Metal Elements> "Noble metal elements" include Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.

[0020] <Oxide> The meaning of "oxide" of a metal element is as follows: Oxides of rare earth elements other than Ce, Pr, and Tb are called sesquioxides (M ２ O ３ , M represents a rare earth element other than Ce, Pr, and Tb), and the oxide of Ce is CeO ２ Pr oxide is Pr ６ O １１ The oxide of Tb is Tb ４ O ７ The oxide of Al is Al ２ O ３ Zr oxide is ZrO ２ The oxide of Si is SiO ２ The oxide of B is B ２ O ３ Cr oxide is Cr ２ O ３, Mg oxide is MgO, Ca oxide is CaO, Sr oxide is SrO, Ba oxide is BaO, Fe oxide is Fe ３ O ４ Mn oxide is Mn ３ O ４ Ni oxide is NiO, Ti oxide is TiO ２ Zn oxide is ZnO, Sn oxide is SnO ２ means.

[0021] <Mass of Metal Element in Metal Equivalent> The "mass of a metal element in metal equivalent" refers to the mass of a metal that is determined on the assumption that the metal element exists as a metal composed of the metal element.

[0022] <Mass of Metal Element in Equivalent to Oxide> The "mass of metal element in equivalent to oxide" refers to the mass of the oxide of a metal element that is determined on the assumption that the metal element exists as an oxide of the metal element.

[0023] <Mass of catalytic layer> The "mass of catalytic layer" refers to the sum of the mass of the precious metal elements contained in the catalytic layer, calculated by classifying all the metal elements contained in the catalytic layer into precious metal elements and metal elements other than precious metal elements, and the mass of the precious metal elements calculated in terms of metal and the mass of the metal elements other than precious metal elements calculated in terms of oxide. In other words, the "mass of catalytic layer" refers to the calculated mass calculated by summing the mass of the precious metal elements contained in the catalytic layer, calculated in terms of metal, and the mass of the metal elements other than precious metal elements contained in the catalytic layer, calculated in terms of oxide.

[0024] When information (for example, composition, amount, etc.) of the raw materials used in the production of the catalyst layer is known, the mass of the catalyst layer can be determined from the information of the raw materials.

[0025] <Content of Metal Element in Catalyst Layer in Metal Equivalent or Oxide Equivalent> The "content of metal element in catalyst layer in metal equivalent" is defined by the formula: content of metal element in catalyst layer in metal equivalent (mass %)=(mass of metal element in catalyst layer in metal equivalent) / (mass of catalyst layer)×100.

[0026] The "content of the metal element in the catalytic layer in terms of oxide" is defined by the formula: content of the metal element in the catalytic layer in terms of oxide (mass %)=(mass of the metal element in the catalytic layer in terms of oxide) / (mass of the catalytic layer)×100.

[0027] When information (e.g., composition, amount, etc.) of the raw materials used to form the catalyst layer is known, the content (mass %) of the metal element in the catalyst layer in terms of metal or oxide can be determined from the information on the raw materials.

[0028] When information about the raw materials used to form the catalyst layer is unknown, the content (mass %) of the metal element in the catalyst layer in terms of metal or oxide can be determined by a conventional method such as SEM-EDX. Specifically, this is as follows.

[0029] The catalyst layer is subjected to elemental analysis using a conventional method such as SEM-EDX to identify the types of constituent elements of the catalyst layer and determine the mole percentage of each identified metal element. The mole percentage of each metal element is determined for each of 10 SEM fields, and the average mole percentage of each metal element in the 10 fields is taken as the mole percentage of each metal element in the catalyst layer.

[0030] The V value of each precious metal element in the catalyst layer is calculated using the following formula: V value of each precious metal element = (mol % of each precious metal element in the catalyst layer) x (molar mass of each precious metal element)

[0031] The W value of each metal element other than the noble metal element in the catalyst layer is calculated using the following formula: W value of each metal element = (mol % of each metal element in the catalyst layer) x (molar mass of the oxide of each metal element)

[0032] The metal-equivalent content (mass%) of each precious metal element in the catalyst layer is calculated using the following formula: Metal-equivalent content (mass%) of each precious metal element in the catalyst layer = (V value of each precious metal element) / {(total V values ​​of all precious metal elements) + (total W values ​​of all metal elements other than precious metal elements)} × 100

[0033] The content (mass %) of each metal element other than precious metal elements in the catalyst layer in terms of oxide is calculated using the following formula: Content (mass %) of each metal element other than precious metal elements in the catalyst layer in terms of oxide = (W value of each metal element other than precious metal elements) / {(total V values ​​of all precious metal elements) + (total W values ​​of all metal elements other than precious metal elements)} × 100

[0034] <Metal Oxide> The term "metal oxide" refers to an oxide containing one or more metal elements. Examples of metal oxides include Al-based oxides, Ce-based oxides, Zr-based oxides, and Ce-Zr-based composite oxides.

[0035] <Mass of Metal Oxide> The "mass of metal oxide" refers to the total mass of oxides of metal elements that can be determined on the assumption that each metal element in the metal oxide exists as an oxide.

[0036] <Content of Metal Element in Metal Oxide in Terms of Oxide> The "content of metal element in metal oxide in terms of oxide" is defined by the formula: content of metal element in metal oxide in terms of oxide (mass %) = (mass of metal element in metal oxide in terms of oxide) / (mass of metal oxide) × 100.

[0037] When the composition of the metal oxide is known, the content (mass %) of the metal element in the metal oxide calculated as oxide can be determined from the composition of the metal oxide.

[0038] When the composition of the metal oxide is unknown, the content (mass %) of the metal element in the metal oxide calculated as the oxide can be determined by a conventional method such as SEM-EDX. Specifically, this is as follows.

[0039] The metal oxide is subjected to elemental analysis using a conventional method such as SEM-EDX to identify the types of constituent elements of the metal oxide, and to determine the content (mass %) of each identified metal element in terms of oxide.

[0040] <Al-based oxide> The Al-based oxide refers to an oxide containing Al, in which Al is the element with the highest content by mass among the metal elements constituting the oxide. However, Zr-based oxides are not considered to be Al-based oxides.

[0041] The Al-based oxide is used as a support for catalytically active components and is distinguished from alumina (alumina binder) which is used as a binder. The Al-based oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytically active components, the Al-based oxide is preferably porous.

[0042] Al-based oxides generally have higher heat resistance than other inorganic oxides (e.g., Ce-based oxides, Zr-based oxides, etc.), and therefore, when the catalyst layer contains an Al-based oxide, the heat resistance of the catalyst layer is improved, and the exhaust gas purification performance of the catalyst layer is improved.

[0043] The 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.

[0044] In the Al-based oxide, the additional element M1 is a solid solution phase (e.g., Al ２ O ３ and an oxide of the additional element M1), or may form a single phase that is a crystalline phase or an amorphous phase (for example, an oxide phase of the additional element M1), or may form both a solid solution phase and a single phase.

[0045] Examples of Al-based oxides include alumina (Al ２ O ３ Examples of the Al-based oxide containing the additional element M1 include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, and alumina-lanthana.

[0046] From the viewpoint of improving the heat resistance of the Al-based oxide, the Al content of the Al in the Al-based oxide is ２ O ３The converted content is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the mass of the Al-based oxide, with the upper limit being 100% by mass.

[0047] <Ce-based oxide> The Ce-based oxide refers to an oxide containing Ce, in which Ce is the element with the largest content by mass among the metal elements constituting the oxide. However, an oxide that corresponds to a Zr-based oxide does not correspond to a Ce-based oxide.

[0048] The Ce-based oxide is used as a support for a catalytically active component and is distinguished from ceria (ceria binder), which is used as a binder. The Ce-based oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytically active component, the Ce-based oxide is preferably porous.

[0049] Ce-based oxides have oxygen storage capacity and reduce fluctuations in oxygen concentration in exhaust gases, widening the operating window of catalytically active components. Therefore, by including Ce-based oxides in the catalyst layer, the exhaust gas purification performance of the catalyst layer is improved.

[0050] The Ce-based oxide may contain one 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, etc.

[0051] In the Ce-based oxide, the additional element M2 forms a solid solution phase (e.g., CeO ２ and an oxide of the additional element M2), or may form a single phase that is a crystalline phase or an amorphous phase (for example, an oxide phase of the additional element M2), or may form both a solid solution phase and a single phase.

[0052] Examples of Ce-based oxides include ceria (CeO ２ ), an oxide obtained by modifying the surface of ceria with the additional element M2 or its oxide, an oxide obtained by dissolving the additional element M2 in ceria, and the like.

[0053] From the viewpoint of improving the oxygen storage capacity of the Ce-based oxide, the Ce in the Ce-based oxide is ２ The content in terms of the mass of the Ce-based oxide is preferably 90 mass % or more, more preferably 95 mass % or more, and even more preferably 99 mass % or more, with the upper limit being 100 mass %.

[0054] <Zr-based oxide> A Zr-based oxide is an oxide containing Zr, and Zr in the oxide is ZrO ２ The Zr-based oxides are oxides having a converted content of 5 mass% or more based on the mass of the oxide. Zirconia-based oxides are distinguished from zirconia used as a binder. In this specification, zirconia used as a binder may be referred to as a "zirconia binder."

[0055] The Zr-based oxide is, for example, in a particulate form. The Zr-based oxide is used as a support for a catalytically active component. From the viewpoint of improving the supportability of the catalytically active component, the Zr-based oxide is preferably porous.

[0056] The Zr-based oxide may contain one 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, etc.

[0057] In the Zr-based oxide, the additional element M3 forms a solid solution phase (e.g., ZrO ２ The additional element M3 may form a solid solution phase (a solid solution phase of the additional element M3 and an oxide of the additional element M3), or may form a single phase that is 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 single phase, but it is preferable that at least a part of the additional element M3 forms a solid solution phase.

[0058] Examples of Zr-based oxides include zirconia (ZrO ２ ), an oxide obtained by modifying the surface of zirconia with the additional element M3 or its oxide, an oxide obtained by dissolving the additional element M3 in zirconia, and the like.

[0059] From the viewpoint of improving the heat resistance of the Zr-based oxide, Zr in the Zr-based oxide is ２ The converted content is preferably 7% by mass or more, more preferably 10% by mass or more, and even more preferably 30% by mass or more, based on the mass of the Zr-based oxide, with the upper limit being 100% by mass.

[0060] <Ce—Zr-based composite oxide> The Ce—Zr-based composite oxide is a composite oxide containing Ce and Zr, and the Ce in the composite oxide is represented by CeO ２ The content of Zr in the composite oxide in terms of ZrO is 5 mass % or more and 95 mass % or less based on the mass of the composite oxide. ２ The Ce—Zr-based composite oxide refers to an oxide whose content, calculated based on the mass of the composite oxide, is 5 mass % or more and 95 mass % or less. The Ce—Zr-based composite oxide is a type of Zr-based oxide.

[0061] The Ce—Zr-based composite oxide is used as a support for a catalytically active component. The Ce—Zr-based composite oxide is, for example, in the form of particles. From the viewpoint of improving the supportability of the catalytically active component, the Ce—Zr-based composite oxide is preferably porous.

[0062] The Ce—Zr-based composite oxide has oxygen storage capacity, which mitigates fluctuations in the oxygen concentration in exhaust gas and widens the operating window of the catalytically active component. Therefore, by including the Ce—Zr-based composite oxide in the catalyst layer, the exhaust gas purification ability of the catalyst layer is improved.

[0063] The Ce—Zr-based composite oxide may contain 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.

[0064] In the Ce-Zr based composite oxide, Ce exists in a solid solution phase (e.g., CeO ２ and ZrO ２ or a single phase that is a crystalline phase or an amorphous phase (e.g., a solid solution phase with CeO ２Although Ce may form a solid solution phase or both a solid solution phase and a single phase, it is preferable that at least a part of Ce forms a solid solution phase.

[0065] In the Ce-Zr composite oxide, Zr exists in a solid solution phase (e.g., CeO ２ and ZrO ２ or a single phase that is a crystalline phase or an amorphous phase (e.g., ZrO ２ Although Zr may form a solid solution phase or both a solid solution phase and a single phase, it is preferable that at least a part of Zr forms a solid solution phase.

[0066] When the Ce—Zr-based composite oxide contains the additional element M4, the additional element M4 forms a solid solution phase (for example, CeO ２ and a solid solution phase of the oxide of the additional element M4, ZrO ２ and a solid solution phase of the oxide of the additional element M4, CeO ２ and ZrO ２ The additional element M4 may form a solid solution phase (e.g., a solid solution phase of the additional element M4 and an oxide of the additional element M4), or may form a single phase that is a crystalline phase or an amorphous phase (e.g., a single phase of an oxide of the additional element M4), or may form both a solid solution phase and a single phase, but it is preferable that at least a part of the additional element M4 forms a solid solution phase.

[0067] Examples of Ce-Zr based composite oxides include CeO ２ -ZrO ２ solid solution, CeO ２ -ZrO ２ CeO, an oxide obtained by modifying the surface of the solid solution with an additional element M4 or its oxide ２ -ZrO ２ Examples of the oxide include an oxide obtained by dissolving the additional element M4 in a solid solution.

[0068] From the viewpoint of improving the oxygen storage capacity of the Ce—Zr-based composite oxide, the Ce in the Ce—Zr-based composite oxide is converted to CeO ２ The converted content is preferably 5% by mass or more and 90% by mass or less, more preferably 7% by mass or more and 90% by mass or less, and even more preferably 10% by mass or more and 85% by mass or less, based on the mass of the Ce-Zr based composite oxide.

[0069] From the viewpoint of improving the heat resistance of the Ce-Zr based composite oxide, the Zr in the Ce-Zr based composite oxide is converted to ZrO. ２ The converted content is preferably 5% by mass or more and 90% by mass or less, more preferably 7% by mass or more and 90% by mass or less, and even more preferably 10% by mass or more and 85% by mass or less, based on the mass of the Ce-Zr based composite oxide.

[0070] From the viewpoint of improving the oxygen storage capacity and heat resistance of the Ce—Zr-based composite oxide, the Ce in the Ce—Zr-based composite oxide is converted to CeO ２ Conversion rate and ZrO ２ The total content, calculated based on the mass of the Ce—Zr-based composite oxide, is preferably 70 mass % or more, more preferably 75 mass % or more, even more preferably 80 mass % or more, and even more preferably 85 mass % or more, with the upper limit being 100 mass %.

[0071] From the viewpoint of improving the heat resistance of the Ce—Zr-based composite oxide, the Ce—Zr-based composite oxide preferably contains one or more rare earth elements other than Ce. The rare earth elements other than Ce can be selected from, for example, Y, Pr, La, Nd, Sm, Eu, Gd, etc. The content of the rare earth elements other than Ce in the Ce—Zr-based composite oxide, calculated as 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, based on the mass of the Ce—Zr-based composite oxide. The "content of rare earth elements other than Ce in a Ce-Zr-based composite oxide, calculated as oxides," when the Ce-Zr-based composite oxide contains one rare earth element other than Ce, means the content of the one rare earth element, calculated as oxides; and when the Ce-Zr-based composite oxide contains two or more rare earth elements other than Ce, means the total content of the two or more rare earth elements, calculated as oxides.

[0072] <<Catalyst for purifying exhaust gas>> Hereinafter, embodiments of the catalyst for purifying exhaust gas of the present invention will be described with reference to the drawings. In addition, when two or more of the embodiments described in this specification can be combined, such combinations of two or more embodiments are also encompassed in the present invention.

[0073] As shown in Fig. 1, an exhaust gas purification catalyst 1 (hereinafter referred to as "catalyst 1") according to one embodiment of the present invention is disposed in an exhaust path in an 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, or the like.

[0074] In Fig. 1 , the direction of exhaust gas flow in the exhaust path of the internal combustion engine is indicated by the symbol E. This is the same in other figures. In this specification, the upstream side of the exhaust gas flow direction E (e.g., the left side in Fig. 1 ) may be referred to as the "exhaust gas inlet side," "inlet side," or "upstream side," and the downstream side of the exhaust gas flow direction E (e.g., the right side in Fig. 1 ) may be referred to as the "exhaust gas outlet side," "outlet side," or "downstream side."

[0075] As shown in FIG. 1, the catalyst 1 is disposed in the exhaust path of an internal combustion engine so that the axial direction of the substrate 10 coincides or substantially coincides with the exhaust gas flow direction E.

[0076] As shown in FIGS. 1 to 6, the catalyst 1 includes a substrate 10, a first catalyst layer 20, and a second catalyst layer 30.

[0077] One of the first catalytic layer 20 and the second catalytic layer 30 may be omitted. That is, the catalyst 1 may include at least one of the first catalytic layer 20 and the second catalytic layer 30. The present invention encompasses an embodiment in which the catalyst 1 includes the first catalytic layer 20 but does not include the second catalytic layer 30, an embodiment in which the catalyst 1 includes the second catalytic layer 30 but does not include the first catalytic layer 20, and an embodiment in which the catalyst 1 includes the first catalytic layer 20 and the second catalytic layer 30.

[0078] Catalyst 1 satisfies at least one of the following conditions 1a and 1b: [Condition 1a] Xa / Ya≦1.40 and Ya≦5.00 [Condition 1b] Xb / Yb≦1.40 and Yb≦5.00

[0079] Xa represents the 10% flow diameter (μm) of the first catalyst layer 20 and the partition wall portion 12 measured by the bubble point method using a perm porometer after heat treatment of catalyst 1 at 950°C for 35 hours in an atmospheric air; Ya represents the 10% flow diameter (μm) of the first catalyst layer 20 and the partition wall portion 12 measured by the bubble point method using a perm porometer before heat treatment of catalyst 1; Xb represents the 10% flow diameter (μm) of the second catalyst layer 30 and the partition wall portion 12 measured by the bubble point method using a perm porometer after heat treatment of catalyst 1; and Yb represents the 10% flow diameter (μm) of the second catalyst layer 30 and the partition wall portion 12 measured by the bubble point method using a perm porometer before heat treatment of catalyst 1.

[0080] The "partition wall section 12" in the "10% flow diameter of the first catalytic layer 20 and the partition wall section 12" refers to the portion of the partition wall section 12 where the first catalytic layer 20 is provided, and the "partition wall section 12" in the "10% flow diameter of the second catalytic layer 30 and the partition wall section 12" refers to the portion of the partition wall section 12 where the second catalytic layer 30 is provided.

[0081] The present invention includes embodiments in which catalyst 1 satisfies conditions 1a and 1b, embodiments in which catalyst 1 satisfies conditions 1a but not 1b, and embodiments in which catalyst 1 satisfies conditions 1b but not 1a.

[0082] Specifically, the present invention includes the following embodiments: [A] An embodiment in which catalyst 1 includes a first catalyst layer 20 and a second catalyst layer 30, and satisfies condition 1a and condition 1b; [B] An embodiment in which catalyst 1 includes a first catalyst layer 20 and a second catalyst layer 30, and satisfies condition 1a but not condition 1b; [C] An embodiment in which catalyst 1 includes a first catalyst layer 20 and a second catalyst layer 30, and satisfies condition 1b but not condition 1a; [D] An embodiment in which catalyst 1 includes the first catalyst layer 20 but does not include the second catalyst layer 30, and satisfies condition 1a (in this embodiment, catalyst 1 does not include the second catalyst layer 30, and therefore does not satisfy condition 1b); [E] An embodiment in which catalyst 1 includes the second catalyst layer 30 but does not include the first catalyst layer 20, and satisfies condition 1b (in this embodiment, catalyst 1 does not include the first catalyst layer 20, and therefore does not satisfy condition 1a).

[0083] In this specification, the expressions "when catalyst 1 satisfies condition 1a," "when catalyst 1 satisfies condition 1b," "when catalyst 1 satisfies condition 1a but not condition 1b," "when catalyst 1 satisfies condition 1b but not condition 1a," and "when catalyst 1 satisfies conditions 1a and 1b" are used. "When catalyst 1 satisfies condition 1a" corresponds to embodiments A, B, and D, "when catalyst 1 satisfies condition 1b" corresponds to embodiments A, C, and E, "when catalyst 1 satisfies condition 1a but not condition 1b" corresponds to embodiments B and D, "when catalyst 1 satisfies condition 1b but not condition 1a" corresponds to embodiments C and E, and "when catalyst 1 satisfies conditions 1a and 1b" corresponds to embodiment A.

[0084] <Substrate> The material constituting the substrate 10 can be appropriately selected from known materials. Examples of materials constituting the substrate 10 include ceramic materials and metal materials, with ceramic materials being preferred. Examples of ceramic materials include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of metal materials include alloys such as stainless steel.

[0085] The substrate 10 has a length L １０ The length L of the substrate 10 １０ The length L of the substrate 10 can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １０ is preferably 50 mm or more and 160 mm or less, more preferably 80 mm or more and 130 mm or less. In this specification, "length" means the dimension of the substrate 10 in the axial direction, unless otherwise specified.

[0086] The volume of the substrate 10 can be adjusted appropriately taking into consideration the exhaust gas purification performance, PM trapping performance, etc. From the viewpoint of improving the exhaust gas purification performance and PM trapping ability, the volume of the substrate 10 is preferably 0.5 L or more and 2.5 L or less, more preferably 0.5 L or more and 2.0 L or less, and even more preferably 0.7 L or more and 1.8 L or less. In this specification, the volume of the substrate 10 means the apparent volume of the substrate 10. When the substrate 10 is cylindrical, the outer diameter of the substrate 10 is defined as 2r, and the length of the substrate 10 is defined as L. １０ Then, the volume of the substrate 10 is calculated by the formula: Volume of the substrate 10 = π × r ２ ×L １０ is required from.

[0087] The substrate 10 is a wall-flow type substrate.

[0088] 2 and 3, the substrate 10 includes cells 13 and porous partition walls 12 that separate the cells 13. The substrate 10 is preferably a honeycomb structure.

[0089] 2 and 3, the substrate 10 includes a tubular portion 11, and the cells 13 and the partition wall portions 12 are formed inside the tubular portion 11. The tubular portion 11 defines the outer shape of the substrate 10, and the axial direction of the tubular portion 11 coincides with the axial direction of the substrate 10. As shown in FIGS. 2 and 3, the shape of the tubular portion 11 is, for example, a cylindrical shape, but it may also be another shape such as an elliptical cylindrical shape or a polygonal cylindrical shape.

[0090] As shown in FIGS. 2 to 6, each of the cells 13 extends in the exhaust gas flow direction E, and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0091] 6, the substrate 10 is provided with first sealing portions 14 that seal the exhaust gas outflow side ends of some of the cells 13, and second sealing portions 15 that seal the exhaust gas inflow side ends of the remaining cells 13. As a result, some of the cells 13 are inflow side cells 13a whose exhaust gas inflow side ends are open and whose exhaust gas outflow side ends are blocked by the first sealing portions 14, and the remaining cells 13 are outflow side cells 13b whose exhaust gas inflow side ends are blocked by the second sealing portions 15 and whose exhaust gas outflow side ends are open.

[0092] The inlet cell 13a has a length L１３ａ The length L of the inlet cell 13a １３ａ is the length L of the inlet side cell 13a １３ａ = (length L of substrate 10 １０ ) - (length of the first plugged portion 14). The "length of the first plugged portion 14" refers to the dimension of the first plugged portion 14 in the axial direction of the substrate 10. Length L of the inlet-side cell 13a １３ａ The length L of the substrate 10 can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １０ The length L of the inlet cell 13a １３ａ Percentage of (L １３ａ / L １０ × 100) is preferably 80% or more, more preferably 85% or more. The upper limit of this percentage can be adjusted as appropriate, taking into consideration the length of the first sealing portion 14. The upper limit of this percentage may be, for example, 99% or less, or 98% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0093] The outflow cell 13b has a length L １３ｂ The length L of the outflow side cell 13b １３ｂ is the length L of the outflow side cell 13b １３ｂ = (length L of substrate 10 １０ ) - (length of the second plugged portion 15). The "length of the second plugged portion 15" refers to the dimension of the second plugged portion 15 in the axial direction of the substrate 10. Length L of the outlet-side cell 13b １３ｂ The length L of the substrate 10 can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １０ The length L of the outflow side cell 13b １３ｂ Percentage of (L １３ｂ / L １０ × 100) is preferably 80% or more, more preferably 85% or more. The upper limit of this percentage can be adjusted as appropriate, taking into consideration the length of second sealing portion 15. The upper limit of this percentage may be, for example, 99% or less, or 98% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0094] As shown in Figures 2 to 6, the inlet side cells 13a and the outlet side cells 13b are arranged alternately in the vertical direction and alternately in the horizontal direction, and adjacent inlet side cells 13a and outlet side cells 13b are separated by partition walls 12.

[0095] 2 to 6 , a plurality of (four in this embodiment) outlet-side cells 13b are arranged around one inlet-side cell 13a, and the inlet-side cell 13a is separated from the outlet-side cells 13b arranged around the inlet-side cell 13a by a partition wall 12. Similarly, a plurality of (four in this embodiment) inlet-side cells 13a are arranged around one outlet-side cell 13b, and the outlet-side cells 13b are separated from the inlet-side cells 13a arranged around the outlet-side cell 13b by a partition wall 12.

[0096] As shown in Figures 2 to 6, the planar shape of the end (opening) on ​​the exhaust gas inlet side of each inlet-side cell 13a and the planar shape of the end (opening) on ​​the exhaust gas outlet side of each outlet-side cell 13b are, for example, quadrilateral (preferably square or rectangular, more preferably square).

[0097] The areas of the end (opening) on ​​the exhaust gas inlet side of each inlet-side cell 13a in a plan view are preferably the same or approximately the same. The areas of the end (opening) on ​​the exhaust gas outlet side of each outlet-side cell 13b in a plan view are preferably the same or approximately the same. The areas of the end (opening) on ​​the exhaust gas inlet side of each inlet-side cell 13a and the area of ​​the end (opening) on ​​the exhaust gas outlet side of each outlet-side cell 13b in a plan view are preferably the same or approximately the same.

[0098] When the planar shape of the end (opening) on ​​the exhaust gas inlet side of each inlet cell 13a is quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the lengths of the left sides (left sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same, the lengths of the right sides (right sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same, the lengths of the top sides (upper sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same, and the lengths of the bottom sides (lower sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same.

[0099] When the planar shape of the exhaust gas outflow side end (opening) of each outlet cell 13b is quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the lengths of the left sides (left sides in Figures 4 and 5) of each outlet cell 13b are identical or approximately identical to each other, the lengths of the right sides (right sides in Figures 4 and 5) of each outlet cell 13b are identical or approximately identical to each other, the lengths of the upper sides (upper sides in Figures 4 and 5) of each outlet cell 13b are identical or approximately identical to each other, and the lengths of the lower sides (lower sides in Figures 4 and 5) of each outlet cell 13b are identical or approximately identical to each other.

[0100] When the planar shape of the end (opening) on ​​the exhaust gas inlet side of each inlet-side cell 13a and the planar shape of the end (opening) on ​​the exhaust gas outlet side of each outlet-side cell 13b are quadrilateral (preferably square or rectangular, more preferably square), the length of the left side (left side in Figures 4 and 5) of each inlet-side cell 13a and the length of the left side (left side in Figures 4 and 5) of each outlet-side cell 13b are the same or approximately the same, and the length of the right side (right side in Figures 4 and 5) of each inlet-side cell 13a It is preferable that the lengths of the right side (the right side in Figures 4 and 5) of each outlet-side cell 13b are the same or approximately the same, that the lengths of the top side (the upper side in Figures 4 and 5) of each inlet-side cell 13a and the top side (the upper side in Figures 4 and 5) of each outlet-side cell 13b are the same or approximately the same, and that the lengths of the bottom side (the lower side in Figures 4 and 5) of each inlet-side cell 13a and the bottom side (the lower side in Figures 4 and 5) of each outlet-side cell 13b are the same or approximately the same.

[0101] When the planar shape of the end (opening) on ​​the exhaust gas inlet side of each inlet-side cell 13a and the planar shape of the end (opening) on ​​the exhaust gas outlet side of each outlet-side cell 13b are quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the left sides (left sides in Figures 4 and 5) of the inlet-side cells 13a and outlet-side cells 13b arranged vertically are located on the same line or approximately on the same line, that the right sides (right sides in Figures 4 and 5) of the inlet-side cells 13a and outlet-side cells 13b arranged vertically are located on the same line or approximately on the same line, that the top sides (upper sides in Figures 4 and 5) of the inlet-side cells 13a and outlet-side cells 13b arranged horizontally are located on the same line or approximately on the same line, and that the bottom sides (lower sides in Figures 4 and 5) of the inlet-side cells 13a and outlet-side cells 13b arranged horizontally are located on the same line or approximately on the same line.

[0102] The cell density per square inch of the substrate 10 can be adjusted as appropriate, taking into consideration PM capture performance, pressure loss, etc. From the viewpoint of improving PM capture performance and suppressing an increase in pressure loss, the cell density per square inch of the substrate 10 is preferably 180 cells or more and 350 cells or less. The cell density per square inch of the substrate 10 is the total number of inlet-side cells 13 a and outlet-side cells 13 b per square inch in a cross section obtained by cutting the substrate 10 along a plane perpendicular to the axial direction of the substrate 10.

[0103] The partition wall 12 has a porous structure that allows the exhaust gas to pass through.

[0104] 4 to 6 , the partition wall portion 12 has an outer surface S1a on the inlet-side cell 13a side and an outer surface S1b on the outlet-side cell 13b side. The outer surface S1a is a region of the outer surface that defines the outer shape of the partition wall portion 12 on the inlet-side cell 13a side that extends in the exhaust gas flow direction E (i.e., the region that contacts the inlet-side cell 13a). The outer surface S1b is a region of the outer surface that defines the outer shape of the partition wall portion 12 on the outlet-side cell 13b side that extends in the exhaust gas flow direction E (i.e., the region that contacts the outlet-side cell 13b).

[0105] The thickness of the partition wall portion 12 can be adjusted as appropriate in consideration of PM trapping performance, pressure loss, etc. From the viewpoint of improving PM trapping performance and suppressing an increase in pressure loss, the thickness of the partition wall portion 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.

[0106] <First catalytic layer> As shown in FIGS. 4 and 6, the first catalytic layer 20 is provided on the inlet cell 13a side of the partition wall portion 12.

[0107] 6 , the first catalytic layer 20 extends from the end of the partition wall 12 on the exhaust gas inlet side along the exhaust gas flow direction E. In this embodiment, the first catalytic layer 20 does not reach the end of the partition wall 12 on the exhaust gas outlet side, but may reach the end of the partition wall 12 on the exhaust gas outlet side.

[0108] 4 and 6 , the first catalytic layer 20 has a portion that is formed on the outer surface S1a of the partition wall portion 12 from the exhaust gas inlet-side end of the partition wall portion 12 along the exhaust gas flow direction E. This portion protrudes from the outer surface S1a of the partition wall portion 12 toward the inlet-side cell 13a. Hereinafter, this portion will be referred to as the "protruding portion." The first catalytic layer 20 having the protruding portion improves contact between the first catalytic layer 20 and the exhaust gas and PM, thereby improving the exhaust gas purification performance and PM collection performance.

[0109] The first catalytic layer 20 may have a portion that exists inside the partition wall section 12 (hereinafter referred to as an "internal portion") in addition to the raised portion. Because the partition wall section 12 is porous, the internal portion may be formed along with the raised portion when the first catalytic layer 20 is formed. The raised portion and the internal portion may be continuous. "The first catalytic layer 20 is provided on the inlet cell 13a side of the partition wall section 12" encompasses an embodiment in which the first catalytic layer 20 has a raised portion but no internal portion, as well as an embodiment in which the first catalytic layer 20 has a raised portion and an internal portion.

[0110] The region where the protruding portions of the first catalytic layer 20 exist does not overlap with the region where the partition wall portions 12 exist, but the region where the internal portions of the first catalytic layer 20 exist overlaps with the region where the partition wall portions 12 exist. Therefore, by cutting the catalyst 1 along a plane perpendicular to the axial direction of the substrate 10 and observing the first catalytic layer 20 and the partition wall portions 12 present on the cut surface, the protruding portions and internal portions of the first catalytic layer 20 can be identified based on the differences in morphology between the first catalytic layer 20 and the partition wall portions 12. When observing the cut surface, elemental mapping of the cut surface may be performed. Elemental mapping can be performed, for example, by combining observation of the cut surface with an SEM and compositional analysis of the cut surface. Elemental mapping can be performed using, for example, SEM-EDX, EPMA, or the like. Elemental mapping of the cut surface allows the protruding portions and internal portions to be identified based on the differences in morphology and composition between the first catalytic layer 20 and the partition wall portions 12.

[0111] <Second catalytic layer> As shown in Figs. 5 and 6, the second catalytic layer 30 is provided on the outlet cell 13b side of the partition wall portion 12.

[0112] 6 , the second catalytic layer 30 extends from the end of the partition wall section 12 on the exhaust gas outflow side along the direction opposite to the exhaust gas flow direction E. In this embodiment, the second catalytic layer 30 does not reach the end of the partition wall section 12 on the exhaust gas inflow side, but may reach the end of the partition wall section 12 on the exhaust gas inflow side.

[0113] 5 and 6 , the second catalytic layer 30 has a portion that is formed on the outer surface S1b of the partition wall section 12 from the exhaust gas outflow side end of the partition wall section 12 along the direction opposite to the exhaust gas flow direction E. This portion protrudes from the outer surface S1b of the partition wall section 12 toward the outlet-side cells 13b. Hereinafter, this portion will be referred to as the "protruding portion." The second catalytic layer 30 having the protruding portion improves contact between the second catalytic layer 30 and the exhaust gas and PM, thereby improving the exhaust gas purification performance and PM collection performance.

[0114] The second catalytic layer 30 may have a portion that exists inside the partition wall section 12 (hereinafter referred to as an "internal portion") in addition to the raised portion. Because the partition wall section 12 is porous, the internal portion may be formed along with the raised portion when the second catalytic layer 30 is formed. The raised portion and the internal portion may be continuous. "The second catalytic layer 30 is provided on the outlet cell 13b side of the partition wall section 12" encompasses an embodiment in which the second catalytic layer 30 has a raised portion but no internal portion, as well as an embodiment in which the second catalytic layer 30 has a raised portion and an internal portion.

[0115] The above description regarding the method for identifying the protruding portion and the underlying portion of the first catalytic layer 20 also applies to the second catalytic layer 30. When applied, the "first catalytic layer 20" is read as the "second catalytic layer 30."

[0116] <Action of the catalyst> Exhaust gas emitted from an internal combustion engine flows through an exhaust path inside the exhaust pipe P from one end to the other end, and is purified by the catalyst 1 arranged inside the exhaust pipe P. During this process, the exhaust gas flows in from the end (opening) on ​​the exhaust gas inlet side of the inlet-side cell 13a, travels through a predetermined path, and flows out from the end (opening) on ​​the exhaust gas outlet side of the outlet-side cell 13b. This type of system is called a wall-flow type. The predetermined paths include a path in which exhaust gas that has flowed in from the end (opening) on ​​the exhaust gas inlet side of the inlet-side cell 13a passes through the first catalytic layer 20 and the partition wall 12 in this order, reaches the outlet-side cell 13b, and flows out from the end (opening) on ​​the exhaust gas outlet side of the outlet-side cell 13b; a path in which exhaust gas that has flowed in from the end (opening) on ​​the exhaust gas inlet side of the inlet-side cell 13a passes through the partition wall 12 and the second catalytic layer 30 in this order, reaches the outlet-side cell 13b, and flows out from the end (opening) on ​​the exhaust gas outlet side of the outlet-side cell 13b; and a path in which exhaust gas that has flowed in from the end (opening) on ​​the exhaust gas inlet side of the inlet-side cell 13a passes through the first catalytic layer 20, the partition wall 12, and the second catalytic layer 30 in this order, reaches the outlet-side cell 13b, and flows out from the end (opening) on ​​the exhaust gas outlet side of the outlet-side cell 13b.

[0117] In the catalyst 1, when exhaust gas flows in from the exhaust gas inlet end (opening) of the inlet-side cell 13a, travels through a predetermined path, and flows out from the exhaust gas outlet end (opening) of the outlet-side cell 13b, PM in the exhaust gas is trapped in the pores of the partition wall portion 12, the first catalyst layer 20, and the second catalyst layer 30. Therefore, the catalyst 1 is useful as a particulate filter for a gasoline engine or a particulate filter for a diesel engine.

[0118] <Structure of Catalyst Layer> The structure of the catalyst layer will be described below. The following description of the structure of the catalyst layer applies to both the first catalyst layer 20 and the second catalyst layer 30, unless otherwise specified. When applied to the first catalyst layer 20, the term "catalyst layer" is replaced with "first catalyst layer 20," and when applied to the second catalyst layer 30, the term "catalyst layer" is replaced with "second catalyst layer 30." Furthermore, the following description of the structure of the catalyst layer applies to all of Embodiments A to E, unless otherwise specified.

[0119] The catalyst layer may have a single layer structure or a laminated structure.

[0120] When the catalyst layer has a laminated structure, the catalyst layer includes two or more layers laminated 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 a layer located closer to the partition wall section 12 than the upper layer. A part of the catalyst layer may be composed of either the lower layer or the upper layer. That is, in addition to the part composed of the lower layer and the upper layer, the part composed of either the lower layer or the upper layer is also part of the catalyst layer.

[0121] An example of the laminated structure is a two-layer structure consisting of a lower layer and an upper layer provided on the lower layer.

[0122] When the catalyst layer has a laminated structure, the raised portion of the catalyst layer may be formed by the whole or part of one layer, or may be formed by the whole of one or more layers and the whole or part of another layer. For example, when the catalyst layer has a two-layer structure, the raised portion of the catalyst layer may be formed by the whole or part of the upper layer, or may be formed by the whole of the upper layer and part of the lower layer.

[0123] In one embodiment, the first catalytic layer 20 and the second catalytic layer 30 each have a single-layer structure. In another embodiment, the first catalytic layer 20 has a laminated structure (e.g., a two-layer structure), and the second catalytic layer 30 has a single-layer structure. In yet another embodiment, the first catalytic layer 20 has a single-layer structure, and the second catalytic layer 30 has a laminated structure (e.g., a two-layer structure). In yet another embodiment, the first catalytic layer 20 and the second catalytic layer 30 each have a laminated structure (e.g., a two-layer structure).

[0124] <Composition of Catalyst Layer> The composition of the catalyst layer will be described below. The following description of the composition of the catalyst layer applies to both the first catalyst layer 20 and the second catalyst layer 30, unless otherwise specified. When applied to the first catalyst layer 20, the term "catalyst layer" is replaced with "first catalyst layer 20," and when applied to the second catalyst layer 30, the term "catalyst layer" is replaced with "second catalyst layer 30." Furthermore, the following description of the composition of the catalyst layer applies to all of Embodiments A to E, unless otherwise specified.

[0125] The catalyst layer contains one or more kinds of noble metal elements as catalytically active components.

[0126] From the viewpoint of enhancing the 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 in a form that can function as a catalytically active component, for example, in the form of a catalytically active component containing a precious metal element, 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 enhancing the exhaust gas purification performance, the catalytically active component containing the precious metal element is preferably in a particulate form.

[0127] The first catalytic layer 20 may contain the same precious metal element as the precious metal element contained in the second catalytic layer 30, or may contain a precious metal element different from the precious metal element contained in the second catalytic layer 30.

[0128] The second catalytic layer 30 may contain the same precious metal element as the precious metal element contained in the first catalytic layer 20, or may contain a precious metal element different from the precious metal element contained in the first catalytic layer 20.

[0129] In one embodiment, the first catalytic layer 20 and the second catalytic layer 30 each contain Rh. The first catalytic layer 20 and the second catalytic layer 30 may each contain, in addition to Rh, a precious metal element other than Rh.

[0130] In one embodiment, the first catalytic layer 20 and the second catalytic layer 30 each contain Rh and no precious metal elements other than Rh. In another embodiment, one of the first catalytic layer 20 and the second catalytic layer 30 contains Rh and no precious metal elements other than Rh, and the other contains Rh and a precious metal element other than Rh (e.g., Pd or Pt). In yet another embodiment, the first catalytic layer 20 and the second catalytic layer 30 each contain Rh and a precious metal element other than Rh (e.g., Pd or Pt).

[0131] When the catalyst layer has a laminated structure, the precious metal element contained in the lower layer and the precious metal element contained in the upper layer may be the same or different. When the precious metal element contained in the lower layer and the precious metal element contained in the upper layer are different, it is possible to prevent a decrease in catalytic performance caused by the inclusion of multiple precious metal elements in a single layer.

[0132] Since the lower layer is covered by the upper layer, the precious metal elements in the lower layer are less susceptible to phosphorus poisoning, whereas the precious metal elements in the upper layer are more susceptible to phosphorus poisoning. On the other hand, Pd and Pt are each susceptible to performance degradation due to phosphorus poisoning, whereas Rh is less susceptible to performance degradation due to phosphorus poisoning. Therefore, Pd and Pt are each suitable as the precious metal element contained in the lower layer, and Rh is suitable as the precious metal element contained in the upper layer.

[0133] Furthermore, Pd and Pt are excellent in the oxidation reaction of reducing substances (CO and HC), while Rh is excellent in the reduction reaction of NOx. By including Rh in the upper layer, where a large amount of reducing substances (CO and HC) used in the reduction reaction of NOx are present, and including Pd or Pt in the lower layer, the reduction reaction of NOx can be efficiently promoted. Therefore, Pt and Pd are suitable as the precious metal element to be included in the lower layer, and Rh is suitable as the precious metal element to be included in the upper layer.

[0134] In one embodiment, the first catalytic layer 20 and the second catalytic layer 30 each have a single-layer structure containing Rh. In another embodiment, the first catalytic layer 20 has a laminated structure (e.g., a two-layer structure) including a lower layer containing a precious metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh, and the second catalytic layer 30 has a single-layer structure containing Rh. In yet another embodiment, the first catalytic layer 20 has a single-layer structure containing Rh, and the second catalytic layer 30 has a laminated structure (e.g., a two-layer structure) including a lower layer containing a precious metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh. In yet another embodiment, the first catalytic layer 20 and the second catalytic layer 30 each have a laminated structure (e.g., a two-layer structure) including a lower layer containing a precious metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh.

[0135] From the viewpoint of the balance between exhaust gas purification performance and cost, the content of the precious metal element in the catalyst layer, in terms of metal, is preferably 0.01 mass % to 20 mass %, more preferably 0.05 mass % to 10 mass %, and even more preferably 0.1 mass % to 5 mass %, based on the mass of the catalyst layer. The "content of the precious metal element in terms of metal in the catalyst layer" means the content of one precious metal element in terms of metal when the catalyst layer contains one kind of precious metal element, or means the total content of the two or more precious metal elements in terms of metal when the catalyst layer contains two or more kinds of precious metal elements.

[0136] The catalyst layer preferably contains one or more types of carriers, and at least a portion of the catalytically active component is preferably supported on one or more types of carriers.

[0137] The phrase "at least a portion of the catalytically active component is supported on a support" means that at least a portion of the catalytically active component is physically or chemically adsorbed and / or retained on the outer surface and / or inner pore surfaces of the support. Support of at least a portion of the catalytically active component on a support can be confirmed, for example, using SEM-EDX or the like. Specifically, when elemental mapping obtained by analyzing a cross section of a catalyst layer with SEM-EDX shows that at least a portion of the catalytically active component and the support are present in the same region, it can be determined that at least a portion of the catalytically active component is supported on a support.

[0138] The support can be selected from, for example, inorganic oxides. The inorganic oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytically active component, the inorganic oxide is preferably porous. The inorganic oxide may or may not have oxygen storage capacity (OSC). The inorganic oxide used as a support is distinguished from the inorganic oxide used as a binder.

[0139] Examples of inorganic oxides include Al-based oxides, Ce-based oxides, Zr-based oxides, oxides of rare earth elements other than Ce, and zirconia (ZrO ２ ), silica (SiO ２ ), titania (TiO ２ ), zeolite (aluminosilicate), MgO, ZnO, SnO ２ and the like.

[0140] The support is preferably selected from Al-based oxides, Ce-based oxides, and Zr-based oxides, more preferably Al-based oxides and Zr-based oxides, and the Zr-based oxide is preferably a Ce—Zr-based composite oxide.

[0141] In one embodiment, the catalyst layer contains a Zr-based oxide. The Zr-based oxide is preferably a Ce—Zr-based composite oxide. The catalyst layer may further contain a support other than a Zr-based oxide (e.g., an Al-based oxide).

[0142] When the catalytic layer contains an Al-based oxide, from the viewpoint of improving the exhaust gas purification performance, the content of the Al-based oxide in the catalytic layer (= (mass of the Al-based oxide in the catalytic layer) / (mass of the catalytic layer)×100) is preferably 5 mass % or more and 95 mass % or less, more preferably 5 mass % or more and 90 mass % or less, and even more preferably 7 mass % or more and 90 mass % or less, based on the mass of the catalytic layer.

[0143] When the composition of the raw materials used to manufacture the catalyst layer is known, the content of Al-based oxide in the catalyst layer can be determined from the composition of the raw materials.

[0144] When the composition of the raw materials used in the production of the catalyst layer is unknown, the content of Al-based oxides in the catalyst layer can be determined by a conventional method such as SEM-EDX. Specifically, this is as follows.

[0145] (1) Elemental analysis is performed on a sample obtained from the catalyst layer using a standard method such as SEM-EDX to identify the types of constituent elements of the entire sample and to determine the oxide-equivalent content (mass%) of each identified metal element. (2) Elemental mapping is performed on a sample obtained from the catalyst layer using a standard method such as SEM-EDX to identify the types of particles contained in the sample (e.g., Al-based oxide particles, Zr-based oxide particles, etc.). (3) For each type of particle, elemental analysis is performed on a number of arbitrarily selected particles (e.g., 50 particles) using SEM-EDX to identify the types of constituent elements of the particles and to determine the oxide-equivalent content (mass%) of each identified metal element. For each type of particle, the average oxide-equivalent content (mass%) of each metal element is calculated, and this is defined as the oxide-equivalent content (mass%) of each metal element in each type of particle. (4) An equation is created and solved to represent the relationship between the oxide-equivalent content (mass%) of each metal element in the sample, the oxide-equivalent content (mass%) of each metal element in each type of particle, and the content (mass%) of each type of particle in the sample, thereby determining the content (mass%) of each type of particle in the sample, and this is the content (mass%) of each type of particle in the catalyst layer.

[0146] When the catalytic layer contains a Ce-based oxide, from the viewpoint of improving exhaust gas purification performance, the content of the Ce-based oxide in the catalytic layer (= (mass of Ce-based oxide in catalytic layer) / (mass of catalytic layer)×100) is preferably 2 mass% or more and 30 mass% or less, more preferably 3 mass% or more and 30 mass% or less, and even more preferably 3 mass% or more and 25 mass% or less, based on the mass of the catalytic layer. The content of the Ce-based oxide in the catalytic layer can be determined in the same manner as the content of the Al-based oxide in the catalytic layer.

[0147] When the catalytic layer contains a Zr-based oxide, from the viewpoint of improving exhaust gas purification performance, the content of the Zr-based oxide in the catalytic layer (= (mass of Zr-based oxide in catalytic layer) / (mass of catalytic layer)×100) is preferably 5 mass % or more and 95 mass % or less, more preferably 10 mass % or more and 90 mass % or less, and even more preferably 15 mass % or more and 85 mass % or less, based on the mass of the catalytic layer. The content of the Zr-based oxide in the catalytic layer can be determined in the same manner as the content of the Al-based oxide in the catalytic layer.

[0148] The catalyst layer may contain other components such as a binder and a stabilizer. Examples of binders include inorganic oxide binders such as alumina binder, ceria binder, zirconia binder, titania binder, and silica binder. Examples of stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0149] <Condition 1a> Condition 1a is as follows: Xa / Ya≦1.40 and Ya≦5.00

[0150] The following describes Ya≦5.00.

[0151] When the first catalytic layer 20 contains a Zr-based oxide, when the first catalytic layer 20 is exposed to a high-temperature environment, cracks are likely to occur in the first catalytic layer 20 due to thermal contraction of the Zr-based oxide, and the PM trapping performance of the first catalytic layer 20 is likely to deteriorate. The deterioration in the PM trapping performance of the first catalytic layer 20 due to thermal contraction of the Zr-based oxide is unlikely to occur in the portions of the first catalytic layer 20 formed inside the partition wall portions 12, but is likely to occur in the portions formed on the outer surfaces S1a of the partition wall portions 12 (i.e., the raised portions). On the other hand, the 10% flow diameter (μm) of the first catalytic layer 20 and the partition wall portions 12 is an index representing the larger through-pore diameter in the distribution of through-pore diameters of the first catalytic layer 20 and the partition wall portions 12. Therefore, Ya being 5.00 μm or less means that the first catalytic layer 20 before exposure to a high-temperature environment is densely formed, cracks are not generated, and the PM trapping performance is excellent. Therefore, when the first catalytic layer 20 contains a Zr-based oxide and Ya is 5.00 μm or less, there is a strong need to suppress a decrease in the PM trapping performance of the first catalytic layer 20 that is caused by thermal shrinkage of the Zr-based oxide. In particular, since Ce-Zr-based composite oxides undergo a large degree of thermal shrinkage when exposed to a high-temperature environment, there is a strong need to suppress a decrease in the PM trapping performance of the first catalytic layer 20 that is caused by thermal shrinkage of the Ce-Zr-based composite oxide when the first catalytic layer 20 contains a Ce-Zr-based composite oxide and Ya is 5.00 μm or less.

[0152] From the viewpoint of improving PM trapping 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. As Ya becomes smaller, PM trapping performance improves, but pressure loss increases. From the viewpoint of improving PM trapping performance and suppressing an increase in pressure loss, Ya is preferably 1.60 μm or more, more preferably 1.80 μm or more, and even more preferably 2.00 μm or more. Each of these lower limit values ​​may be combined with any of the above-mentioned upper limit values.

[0153] The condition Xa / Ya≦1.40 will be explained below.

[0154] The 10% flow diameters (μm) of the first catalytic layer 20 and the partition wall portions 12 are indicators representing the larger through-pore diameters in the through-pore diameter distributions of the first catalytic layer 20 and the partition wall portions 12. Therefore, an Xa / Ya ratio of 1.40 or less means that the occurrence of cracks due to thermal contraction of the Zr-based oxide is suppressed in the first catalytic layer 20 after exposure to a high-temperature environment. Therefore, an Xa / Ya ratio of 1.40 or less can suppress a decrease in the PM trapping performance of the first catalytic layer 20 due to thermal contraction of the Zr-based oxide.

[0155] From the viewpoint of more effectively suppressing the deterioration of PM trapping performance, Xa / Ya is preferably 1.37 or less, more preferably 1.34 or less, and even more preferably 1.30 or less. The lower limit of Xa / Ya is theoretically 1, but in reality it exceeds 1. Xa / Ya may be, for example, 1.03 or more, 1.07 or more, or 1.10 or more. Each of these lower limit values ​​may be combined with any of the above-mentioned upper limit values.

[0156] The method for measuring Xa will be described below.

[0157] The catalyst 1 is subjected to a heat treatment at 950° C. for 35 hours in an air atmosphere. After the heat treatment, a portion of the catalyst 1 extends in the axial direction of the substrate 10 and has a length L of the substrate 10. １０A sample having the same length as the inlet-side cells 13a and the outlet-side cells 13b is cut out. The number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample. The planar shape of the sample when viewed in a plane from the axial direction of the sample is, for example, a quadrangle (preferably a square or rectangle, more preferably a square). The size of the planar shape when viewed in a plane from the axial direction of the sample is not particularly limited as long as the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample. For example, the vertical length is 10 mm and the horizontal length is 10 mm. When the inlet-side cells 13a and the outlet-side cells 13b are arranged alternately in the vertical direction and the horizontal direction, if the total number of inlet-side cells 13a and the outlet-side cells 13b arranged in the vertical direction of the sample is an even number and the total number of inlet-side cells 13a and the outlet-side cells 13b arranged in the horizontal direction of the sample is an even number, the number of inlet-side cells 13a included in the sample will be the same as the number of outlet-side cells 13b included in the sample.

[0158] The sample is cut along a plane perpendicular to the axial direction of the sample to prepare a cut piece P1 that includes a portion of the first catalytic layer 20 but does not include a portion of the second catalytic layer 30. The cut piece P1 can be obtained from the vicinity of the end of the sample on the exhaust gas inlet side. The axial length of the cut piece P1 is not particularly limited, but is, for example, 10 mm. The length of the portion of the first catalytic layer 20 included in the cut piece P1 is equal to the axial length of the cut piece P1. The cut piece P1 does not have the first plugging portion 14 or the second plugging portion 15.

[0159] An example of the cut piece P1 is shown in Figures 7A and 7B. The cut piece P1 is, for example, a cube with a length in the vertical direction (vertical direction in Figure 7A) of 10 mm, a length in the horizontal direction (horizontal direction in Figure 7A) of 10 mm, and a length in the axial direction (vertical direction in Figure 7B) of 10 mm. The cut piece P1 shown in Figures 7A and 7B can be obtained, for example, by cutting the sample at two locations 10 mm and 20 mm away from the end of the exhaust gas inlet side in the axial direction of the sample along a plane perpendicular to the axial direction of the sample. As shown in Figure 7B, the length of a portion of the first catalyst layer 20 included in the cut piece P1 is equal to the axial length of the cut piece P1. As shown in Figures 7A and 7B, the cut piece P1 does not have the first plugging portion 14 or the second plugging portion 15.

[0160] A first sealing portion that seals the exhaust gas outlet end of the inlet cell 13a included in the cut piece P1, and a second sealing portion that seals the exhaust gas inlet end of the outlet cell 13b included in the cut piece P1 are formed on the cut piece P1, and a third sealing portion is formed on the outermost periphery of the cut piece P1 to obtain a cut piece P1'. The first sealing portion, the second sealing portion, and the third sealing portion can be formed by applying a weatherstripping material to predetermined locations on the cut piece P1. For example, an adhesive such as an epoxy resin adhesive can be used as the weatherstripping material.

[0161] When using the cut piece P1 shown in Figures 7A and 7B, as shown in Figures 8A to 8C, a first sealing portion 14 sealing the end of the inlet cell 13a included in the cut piece P1 on the exhaust gas outlet side (lower side in Figure 8C) and a second sealing portion 15 sealing the end of the outlet cell 13b included in the cut piece P1 on the exhaust gas inlet side (upper side in Figure 8C) are formed on the cut piece P1, and a third sealing portion 16 is formed around the outermost periphery of the cut piece P1 to obtain a cut piece P1'. The first sealing portion 14, the second sealing portion 15, and the third sealing portion 16 can be formed by applying a weatherstripping material to predetermined locations on the cut piece P1. An adhesive such as an epoxy resin adhesive can be used as the weatherstripping material. The thickness of the first sealing portion 14 and the second sealing portion 15 is set to be 1 / 10 or less of the axial length of the cut piece P1' (vertical direction in Figure 8C).

[0162] For the sake of simplicity, the method for measuring Xa will be described below using the cut piece P1' shown in Figures 8A to 8C as an example. The following description can also be applied to cases where other cut pieces P1' are used.

[0163] A cut piece P1' prepared from the heat-treated catalyst 1 is set in a holder of a perm porometer, and gas is passed through the cut piece P1' at 1 to 200 L / min while changing the gas pressure, and the gas flow rate under pressure is measured (hereinafter referred to as "first measurement"). The gas passed through is air. As the perm porometer, for example, a perm porometer (e.g., CFP-1100A) manufactured by Porous Materials Inc. can be used. Gas is passed through the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 8C ) of the inlet-side cell 13a included in the cut piece P1'. The gas that flows in through the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 8C ) of the inlet-side cell 13a passes through the first catalyst layer 20 and the partition wall portion 12 and flows out from the end (opening) on ​​the exhaust gas outlet side (lower side in FIG. 8C ) of the outlet-side cell 13b.

[0164] The first measurement is performed on a dry cut piece P1' (i.e., a cut piece P1' that has not been impregnated with a non-volatile reagent (Galwick reagent manufactured by Porous Materials Inc.)). The first measurement provides a pressure-flow curve for the dry cut piece P1'.

[0165] A cut piece P1' is prepared from the heat-treated catalyst 1 in the same manner as described above. The cut piece P1' is immersed in a non-volatile test solution (Galwick reagent manufactured by Porous Materials Inc.), and vacuum degassing is performed to remove air from the cut piece P1'. The test solution-impregnated cut piece P1' is then set in a perm porometer holder, and gas is passed through the cut piece P1' at 1 to 200 L / min while changing the gas pressure, and the gas flow rate under pressure is measured (hereinafter referred to as "second measurement"). The gas passed is air. The surface tension of the Galwick reagent manufactured by Porous Materials Inc. is 15.9 dyne / cm. As the perm porometer, for example, a perm porometer manufactured by Porous Materials Inc. (e.g., CFP-1100A) can be used. The gas flows through the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 8C ) of the inlet-side cell 13a included in the cut piece P1'. The gas that flows in through the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 8C ) of the inlet-side cell 13a passes through the first catalyst layer 20 and the partition wall 12, and flows out through the end (opening) on ​​the exhaust gas outlet side (lower side in FIG. 8C ) of the outlet-side cell 13b.

[0166] The second measurement is performed on the cut piece P1' wetted with the test liquid, and the second measurement provides a pressure-flow curve for the cut piece P1' wetted with the test liquid.

[0167] In the second measurement, all of the through holes in the cut piece P1' are filled with test liquid at the start of the measurement, but as the gas pressure increases, the test liquid that had filled the through holes is pushed out, allowing the gas to pass through.

[0168] In the first and second measurements, the measurement software "Capwin" (manufactured by Porous Materials Inc.) is used, and the detailed conditions for the first measurement are designated as "dry parameters" and the detailed conditions for the second measurement are designated as "wet parameters" as follows: <Dry parameters / wet parameters> <Bubble point test / integrity test> ・bubbleflow 15.00 (cc / m) ・F / PT 200 (old bobltime) <Motor valve control> ・v2incr 2 (cts*3) <Regulator control> ・preginc 0.5 (cts*50) ・pulse delay 2 (sec) <Data confirmation routine> ・mineqtime 15 (sec) ・presslew 50 (cts*3) ・flowlew 50 (cts*3) ・equiter 30 (0.1 sec) ・aveiter 20 (0.1 sec) ・maxpdif 0.10 (PSI) ・maxfdif 30.0 (cc / m)

[0169] According to the above measurement method, the diameter of the narrowest part of the through hole (hereinafter referred to as "through hole diameter") can be measured. For example, when the through hole has a shape that is constricted in the middle like the tube of an hourglass, the through hole diameter is the diameter of the constricted part of the through hole.

[0170] The relationship between gas pressure and through-pore diameter is expressed by the following formula. The constant C is 2860. D=C×γ / ΔP (where D represents the through-pore diameter (unit: μm), γ represents the surface tension of the test liquid (unit: dyne / cm), C represents a constant, and ΔP represents the pressure difference between the upstream (upper side of FIG. 8C ) and downstream (lower side of FIG. 8C ) positions in the gas flow direction relative to the cut piece P1′ during gas flow ((pressure at a position upstream in the gas flow direction relative to the cut piece P1′ during gas flow)−(pressure at a position downstream in the gas flow direction relative to the cut piece P1′ during gas flow)) (unit: Pa).)

[0171] The gas flow rate (L / min) at a certain gas pressure is determined from the pressure-flow rate curve obtained in the first measurement and is designated as the "Dry flow rate," and the gas flow rate (L / min) at the same gas pressure is determined from the pressure-flow rate curve obtained in the second measurement and is designated as the "Wet flow rate."

[0172] The diameter of the through pores at which the percentage of the wet flow rate to the dry flow rate (wet flow rate / dry flow rate × 100) is 10% is determined. Note that in the second measurement, as the gas pressure is gradually increased, the liquid film breaks in the larger pores first, and the gas flow rate increases. Therefore, the diameter of the through pores (μm) at which the percentage is 10% is larger than the diameter of the through pores (μm) at which the percentage exceeds 10%.

[0173] Using different cut pieces P1', the through pore diameter (μm) at which the percentage is 10% is measured three times in total, and the average value thereof is defined as Xa (μm).

[0174] The method for measuring Ya will be described below.

[0175] Cut pieces P1' are prepared in the same manner as above from the catalyst 1 before the heat treatment. Ya can be measured in the same manner as Xa, except that the cut pieces P1' prepared from the catalyst 1 before the heat treatment are used instead of the cut pieces P1' prepared from the catalyst 1 after the heat treatment.

[0176] <Condition 1b> Condition 1b is as follows: Xb / Yb≦1.40 and Yb≦5.00

[0177] The following describes Yb≦5.00.

[0178] When the second catalytic layer 30 contains a Zr-based oxide, when the second catalytic layer 30 is exposed to a high-temperature environment, cracks are likely to occur in the second catalytic layer 30 due to thermal contraction of the Zr-based oxide, and the PM trapping performance of the second catalytic layer 30 is likely to deteriorate. The deterioration in the PM trapping performance of the second catalytic layer 30 due to thermal contraction of the Zr-based oxide is unlikely to occur in the portions of the second catalytic layer 30 formed inside the partition wall portions 12, but is likely to occur in the portions formed on the outer surfaces S1b of the partition wall portions 12 (i.e., the raised portions). On the other hand, the 10% flow diameter (μm) of the second catalytic layer 30 and the partition wall portions 12 is an index representing the larger through-pore diameter in the distribution of through-pore diameters of the second catalytic layer 30 and the partition wall portions 12. Therefore, a Yb of 5.00 μm or less means that the second catalytic layer 30 before exposure to a high-temperature environment is densely formed, crack-free, and has excellent PM trapping performance. Therefore, when the second catalytic layer 30 contains a Zr-based oxide and Yb is 5.00 μm or less, there is a strong need to suppress a decrease in the PM trapping performance of the second catalytic layer 30 that is caused by thermal shrinkage of the Zr-based oxide. In particular, since Ce-Zr-based composite oxides undergo a large degree of thermal shrinkage when exposed to a high-temperature environment, there is a strong need to suppress a decrease in the PM trapping performance of the second catalytic layer 30 that is caused by thermal shrinkage of the Ce-Zr-based composite oxide when the second catalytic layer 30 contains a Ce-Zr-based composite oxide and Yb is 5.00 μm or less.

[0179] From the viewpoint of improving PM trapping 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. As Yb becomes smaller, PM trapping performance improves, but pressure loss increases. From the viewpoint of improving PM trapping performance and suppressing an increase in pressure loss, Yb is preferably 1.60 μm or more, more preferably 1.80 μm or more, and even more preferably 2.00 μm or more. Each of these lower limit values ​​may be combined with any of the above-mentioned upper limit values.

[0180] The following describes Xb / Yb≦1.40.

[0181] The 10% flow diameters (μm) of the second catalytic layer 30 and the partition wall sections 12 are indicators of the larger through-pore diameters in the through-pore diameter distributions of the second catalytic layer 30 and the partition wall sections 12. Therefore, an Xb / Yb ratio of 1.40 or less means that the occurrence of cracks due to thermal contraction of the Zr-based oxide is suppressed in the second catalytic layer 30 after exposure to a high-temperature environment. Therefore, an Xb / Yb ratio of 1.40 or less can suppress a decrease in the PM trapping performance of the second catalytic layer 30 due to thermal contraction of the Zr-based oxide.

[0182] From the viewpoint of more effectively suppressing the deterioration of PM trapping performance, Xb / Yb is preferably 1.37 or less, more preferably 1.34 or less, and even more preferably 1.30 or less. The lower limit of Xb / Yb is theoretically 1, but in reality it exceeds 1. Xb / Yb may be, for example, 1.03 or more, 1.07 or more, or 1.10 or more. Each of these lower limit values ​​may be combined with any of the above-mentioned upper limit values.

[0183] The method for measuring Xb will be described below.

[0184] The catalyst 1 is subjected to a heat treatment at 950° C. for 35 hours in an air atmosphere. After the heat treatment, a portion of the catalyst 1 extends in the axial direction of the substrate 10 and has a length L of the substrate 10. １０A sample having the same length as the inlet-side cells 13a and the outlet-side cells 13b is cut out. The number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample. The planar shape of the sample when viewed in a plane from the axial direction of the sample is, for example, a quadrangle (preferably a square or rectangle, more preferably a square). The size of the planar shape when viewed in a plane from the axial direction of the sample is not particularly limited as long as the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample. For example, the vertical length is 10 mm and the horizontal length is 10 mm. When the inlet-side cells 13a and the outlet-side cells 13b are arranged alternately in the vertical direction and the horizontal direction, if the total number of inlet-side cells 13a and the outlet-side cells 13b arranged in the vertical direction of the sample is an even number and the total number of inlet-side cells 13a and the outlet-side cells 13b arranged in the horizontal direction of the sample is an even number, the number of inlet-side cells 13a included in the sample will be the same as the number of outlet-side cells 13b included in the sample.

[0185] The sample is cut along a plane perpendicular to the axial direction of the sample to prepare a cut piece P2 that includes a portion of the second catalytic layer 30 but does not include a portion of the first catalytic layer 20. The cut piece P2 can be obtained from the vicinity of the end of the sample on the exhaust gas outlet side. The axial length of the cut piece P2 is not particularly limited, but is, for example, 10 mm. The length of the portion of the second catalytic layer 30 included in the cut piece P2 is equal to the axial length of the cut piece P2. The cut piece P2 does not have the first plugging portion 14 or the second plugging portion 15.

[0186] An example of the cut piece P2 is shown in Figures 9A and 9B. As shown in Figures 9A and 9B, the cut piece P2 is, for example, a cube with a length in the vertical direction (vertical direction in Figure 9A), a length in the horizontal direction (horizontal direction in Figure 9A), and a length in the axial direction (vertical direction in Figure 9B). The cut piece P2 shown in Figures 9A and 9B can be obtained, for example, by cutting the sample at two locations 10 mm and 20 mm away from the end of the exhaust gas outlet side in the axial direction of the sample along a plane perpendicular to the axial direction of the sample. As shown in Figure 9B, the length of a portion of the second catalyst layer 30 included in the cut piece P2 is equal to the axial length of the cut piece P2. As shown in Figures 9A and 9B, the cut piece P2 does not have the first plugging portion 14 or the second plugging portion 15.

[0187] A first sealing portion sealing the exhaust gas outlet end of the inlet cell 13a included in the cut piece P2 and a second sealing portion sealing the exhaust gas inlet end of the outlet cell 13b included in the cut piece P2 are formed on the cut piece P2, and a third sealing portion is formed on the outermost periphery of the cut piece P2 to obtain a cut piece P2'. The first sealing portion, the second sealing portion, and the third sealing portion can be formed by applying a weatherstripping material to predetermined locations on the cut piece P2. For example, an adhesive such as an epoxy resin adhesive can be used as the weatherstripping material.

[0188] When using the cut piece P2 shown in FIGS. 9A and 9B, as shown in FIGS. 10A to 10C, a first sealing portion 14 sealing the end of the inlet cell 13a included in the cut piece P2 on the exhaust gas outlet side (lower side in FIG. 10C) and a second sealing portion 15 sealing the end of the outlet cell 13b included in the cut piece P2 on the exhaust gas inlet side (upper side in FIG. 10C) are formed on the cut piece P2, and a third sealing portion 16 is formed around the outermost periphery of the cut piece P2 to obtain a cut piece P2'. The first sealing portion 14, the second sealing portion 15, and the third sealing portion 16 can be formed by applying a weatherstripping material to predetermined locations on the cut piece P2. Examples of the weatherstripping material include an epoxy resin adhesive. The thicknesses of the first sealing portion 14 and the second sealing portion 15 are each 1 / 10 or less of the axial length of the cut piece P2' (vertical direction in FIG. 10C).

[0189] For the sake of simplicity, the method for measuring Xb will be described below using the cut piece P2' shown in Figures 10A to 10C as an example. The following description can also be applied to cases where other cut pieces P2' are used.

[0190] Xb can be measured in the same manner as Xa, except that a cut piece P2' prepared from the heat-treated catalyst 1 is used instead of a cut piece P1' prepared from the heat-treated catalyst 1. In the first and second measurements, gas is passed through the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 10C ) of the inlet-side cell 13a included in the cut piece P2'. The gas that flows in from the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 10C ) of the inlet-side cell 13a passes through the partition wall 12 and the second catalyst layer 30 and flows out from the end (opening) on ​​the exhaust gas outlet side (lower side in FIG. 10C ) of the outlet-side cell 13b.

[0191] The diameter of the through pores at which the percentage of the wet flow rate to the dry flow rate (wet flow rate / dry flow rate × 100) is 10% is determined. Note that in the second measurement, as the gas pressure is gradually increased, the liquid film breaks in the larger pores first, and the gas flow rate increases. Therefore, the diameter of the through pores (μm) at which the percentage is 10% is larger than the diameter of the through pores (μm) at which the percentage exceeds 10%.

[0192] Using different cut pieces P2', the through-pore diameter (μm) at which the percentage is 10% is measured three times in total, and the average value thereof is taken as Xb (μm).

[0193] A method for measuring Yb will be described below.

[0194] Cut pieces P2' are prepared in the same manner as above from the catalyst 1 before the heat treatment. Yb can be measured in the same manner as Xb, except that the cut pieces P2' prepared from the catalyst 1 before the heat treatment are used instead of the cut pieces P2' prepared from the catalyst 1 after the heat treatment.

[0195] <Presence or Absence of Zr-Based Oxide in Catalyst Layer> When catalyst 1 satisfies condition 1a (Embodiments A, B, and D), first catalyst layer 20 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide), and when catalyst 1 satisfies condition 1b (Embodiments A, C, and E), second catalyst layer 30 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide). Specifically, this is as follows.

[0196] In embodiment A, the first catalytic layer 20 and the second catalytic layer 30 each contain a Zr-based oxide (preferably a Ce—Zr-based composite oxide). The first catalytic layer 20 and the second catalytic layer 30 may each further contain a support other than a Zr-based oxide (for example, an Al-based oxide).

[0197] In embodiment B, the first catalytic layer 20 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide). The first catalytic layer 20 may further contain a support other than a Zr-based oxide (for example, an Al-based oxide).

[0198] In embodiment B, the second catalytic layer 30 may contain a Zr-based oxide (preferably a Ce—Zr-based composite oxide), or may not contain a Zr-based oxide. When the second catalytic layer 30 contains a Zr-based oxide, the second catalytic layer 30 may further contain a support other than a Zr-based oxide (for example, an Al-based oxide). When the second catalytic layer 30 does not contain a Zr-based oxide, the second catalytic layer 30 preferably contains a support other than a Zr-based oxide (for example, an Al-based oxide).

[0199] In embodiment C, the second catalytic layer 30 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide). The second catalytic layer 30 may further contain a support other than a Zr-based oxide (for example, an Al-based oxide).

[0200] In embodiment C, the first catalytic layer 20 may contain a Zr-based oxide (preferably a Ce—Zr-based composite oxide), or may not contain a Zr-based oxide. When the first catalytic layer 20 contains a Zr-based oxide, the first catalytic layer 20 may further contain a support other than a Zr-based oxide (for example, an Al-based oxide). When the first catalytic layer 20 does not contain a Zr-based oxide, the first catalytic layer 20 preferably contains a support other than a Zr-based oxide (for example, an Al-based oxide).

[0201] In embodiment D, the first catalytic layer 20 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide). The first catalytic layer 20 may further contain a support other than a Zr-based oxide (for example, an Al-based oxide).

[0202] In embodiment E, the second catalytic layer 30 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide). The second catalytic layer 30 may further contain a support other than a Zr-based oxide (for example, an Al-based oxide).

[0203] <Content of Ce—Zr-based composite oxide in catalytic layer> When catalyst 1 satisfies condition 1a (embodiments A, B, and D), first catalytic layer 20 preferably contains a Ce—Zr-based composite oxide, and the content of Ce—Zr-based composite oxide in first catalytic layer 20 (= (mass of Ce—Zr-based composite oxide in first catalytic layer 20) / (mass of first catalytic layer 20)×100) is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more, based on the mass of first catalytic layer 20. The higher this content, the more likely it is that the PM collection performance of first catalytic layer 20 will be reduced due to thermal contraction of the Ce—Zr-based composite oxide. Therefore, when this content is within the above-mentioned range, the effect of catalyst 1 satisfying condition 1a is significant. The upper limit of this content can be adjusted as appropriate, taking into account the contents of other components in first catalytic layer 20. The content of the Ce—Zr-based composite oxide in the first catalytic layer 20 is preferably 95 mass % or less, more preferably 90 mass % or less, and even more preferably 85 mass % or less, based on the mass of the first catalytic layer 20. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0204] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), second catalytic layer 30 preferably contains a Ce—Zr-based composite oxide, and the content of the Ce—Zr-based composite oxide in second catalytic layer 30 (= (mass of Ce—Zr-based composite oxide in second catalytic layer 30) / (mass of second catalytic layer 30)×100) is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more, based on the mass of second catalytic layer 30. The higher this content, the more likely it is that the PM trapping performance of second catalytic layer 30 will be reduced due to thermal contraction of the Ce—Zr-based composite oxide. Therefore, when this content is within the above-mentioned range, the effect of catalyst 1 satisfying condition 1b is significant. The upper limit of this content can be adjusted as appropriate, taking into account the contents of other components in second catalytic layer 30. The content of the Ce—Zr-based composite oxide in the second catalytic layer 30 is preferably 95 mass % or less, more preferably 90 mass % or less, and even more preferably 85 mass % or less, based on the mass of the second catalytic layer 30. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0205] <Composition of Ce—Zr-based composite oxide in catalytic layer> When catalyst 1 satisfies condition 1a (embodiments A, B, and D), first catalytic layer 20 preferably contains a Ce—Zr-based composite oxide, and the Ce—Zr-based composite oxide in first catalytic layer 20 is represented by the following formula: １２ / R １１ >0.8 [wherein, R １１ represents the CeO of Ce in the Ce-Zr based composite oxide. ２ represents the content (mass%) of the converted １２ represents the ZrO of Zr in the Ce-Zr based composite oxide. ２ It is preferable that the above formula is satisfied.

[0206] R １２ / R １１ When the ratio exceeds 0.8, the heat resistance of the Ce—Zr-based composite oxide is improved (i.e., the degree of thermal contraction of the Ce—Zr-based composite oxide is reduced), and therefore, the first catalytic layer 20 that satisfies condition 1a (preferably conditions 1a and 2a) can be easily formed.

[0207] R １２ / R１１ is preferably 0.9 or more, more preferably 1.0 or more, and even more preferably 1.2 or more. １２ / R １１ The upper limit of R can be adjusted appropriately in consideration of the balance between the heat resistance and oxygen storage capacity of the Ce—Zr based composite oxide. １２ / R １１ is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0208] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), second catalytic layer 30 preferably contains a Ce—Zr-based composite oxide, and the Ce—Zr-based composite oxide in second catalytic layer 30 is represented by the following formula: ２２ / R ２１ >0.8 [wherein, R ２１ represents the CeO of Ce in the Ce-Zr based composite oxide. ２ represents the content (mass%) of the converted ２２ represents the ZrO of Zr in the Ce-Zr based composite oxide. ２ It is preferable that the above formula is satisfied.

[0209] R ２２ / R ２１ When the ratio exceeds 0.8, the heat resistance of the Ce—Zr-based composite oxide is improved (i.e., the degree of thermal contraction of the Ce—Zr-based composite oxide is reduced), and therefore, the second catalytic layer 30 that satisfies condition 1b (preferably conditions 1b and 2b) can be easily formed.

[0210] R ２２ / R ２１ is preferably 0.9 or more, more preferably 1.00 or more, and even more preferably 1.2 or more. ２２ / R ２１ The upper limit of R can be adjusted appropriately in consideration of the balance between the heat resistance and oxygen storage capacity of the Ce—Zr based composite oxide. ２２ / R ２１ is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0211] <Length of Catalyst Layer> If there is a portion of the exhaust gas path (hereinafter referred to as the "exhaust gas path") where neither the first catalyst layer 20 nor the second catalyst layer 30 is formed, the exhaust gas preferentially flows through that portion, which may result in a decrease in PM trapping performance. Therefore, from the viewpoint of improving the PM trapping performance of the catalyst 1, it is preferable that at least one of the first catalyst layer 20 and the second catalyst layer 30 is formed at every portion of the exhaust gas path. As a result, the exhaust gas that flows in from the exhaust gas inlet end (opening) of the inlet cell 13a passes through at least one of the first catalyst layer 20 and the second catalyst layer 30 and then flows out from the exhaust gas outlet end (opening) of the outlet cell 13b, thereby improving the PM trapping performance of the catalyst 1. Specifically, this is as follows.

[0212] In the case where the catalyst 1 includes the first catalyst layer 20 but does not include the second catalyst layer 30 (embodiment D), the length L of the inlet-side cell 13a is １３ａ The length L of the first catalyst layer 20 ２０ Percentage of (L ２０ / L １３ａ ×100) is preferably 100%.

[0213] In the case where the catalyst 1 includes the second catalyst layer 30 but does not include the first catalyst layer 20 (Embodiment E), the length L of the outlet-side cell 13b is １３ｂ The length L of the second catalyst layer 30 ３０ Percentage of (L ３０ / L １３ｂ ×100) is preferably 100%.

[0214] When the catalyst 1 includes the first catalyst layer 20 and the second catalyst layer 30 (embodiments A to C), the length L of the substrate 10 １０ The length L of the first catalyst layer 20 ２０ and the length L of the second catalyst layer 30 ３０ and the percentage of the total ((L ２０ +L ３０ ) / L １０× 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 adjusted as appropriate, taking into consideration the exhaust gas purification performance, PM collection performance, etc. The percentage is preferably 160% or less, more preferably 150% or less, and even more preferably 140% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits. As long as the percentage is within the above-mentioned range, the length L of the first catalyst layer 20 can be adjusted as needed. ２０ and the length L of the second catalyst layer 30 ３０ The length L of the substrate 10 can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １０ The length L of the first catalyst layer 20 ２０ Percentage of (L ２０ / L １０ × 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, and the length L of the substrate 10 １０ The length L of the second catalyst layer 30 ３０ Percentage of (L ３０ / L １０ × 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.

[0215] From the viewpoint of improving the PM trapping performance of the catalyst 1, it is preferable that at least one of a first catalytic layer 20 satisfying condition 1a and a second catalytic layer 30 satisfying condition 1b be formed at any location in the exhaust gas path. In this way, exhaust gas that flows in from the exhaust gas inlet end (opening) of the inlet-side cell 13a passes through at least one of the first catalytic layer 20 satisfying condition 1a and the second catalytic layer 30 satisfying condition 1b and flows out from the exhaust gas outlet end (opening) of the outlet-side cell 13b, thereby improving the PM trapping performance of the catalyst 1. Specifically, this is as follows.

[0216] When the catalyst 1 satisfies the condition 1a but does not satisfy the condition 1b (embodiments B and D), the length L of the inlet cell 13a １３ａ The length L of the first catalyst layer 20 ２０ Percentage of (L ２０ / L１３ａ × 100) is preferably 100%. When the catalyst 1 includes the second catalyst layer 30 (embodiment B), the length L of the second catalyst layer 30 ３０ The length L of the outlet cell 13b can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １３ｂ The length L of the second catalyst layer 30 ３０ Percentage of (L ３０ / L １３ｂ × 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.

[0217] When the catalyst 1 satisfies the condition 1b but does not satisfy the condition 1a (embodiments C and E), the length L of the outflow side cell 13b １３ｂ The length L of the second catalyst layer 30 ３０ Percentage of (L ３０ / L １３ｂ × 100) is preferably 100%. When the catalyst 1 includes the first catalyst layer 20 (embodiment C), the length L of the first catalyst layer 20 ２０ The length L of the inlet cell 13a can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １３ａ The length L of the first catalyst layer 20 ２０ Percentage of (L ２０ / L １３ａ × 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.

[0218] When the catalyst 1 satisfies the conditions 1a and 1b (embodiment A), the length L of the substrate 10 １０ The length L of the first catalyst layer 20 ２０ and the length L of the second catalyst layer 30 ３０ and the percentage of the total ((L ２０ +L ３０ ) / L １０× 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 adjusted as appropriate, taking into consideration the exhaust gas purification performance, PM collection performance, etc. The percentage is preferably 160% or less, more preferably 150% or less, and even more preferably 140% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits. As long as the percentage is within the above-mentioned range, the length L of the first catalyst layer 20 can be adjusted as needed. ２０ and the length L of the second catalyst layer 30 ３０ The length L of the substrate 10 can be adjusted appropriately in consideration of the exhaust gas purification performance, PM trapping performance, etc. １０ The length L of the first catalyst layer 20 ２０ Percentage of (L ２０ / L １０ × 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, and the length L of the substrate 10 １０ The length L of the second catalyst layer 30 ３０ Percentage of (L ３０ / L １０ × 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.

[0219] Length L of the first catalyst layer 20 ２０ An example of the measurement method is as follows.

[0220] Extending from the catalyst 1 in the axial direction of the substrate 10, the length L of the substrate 10 １０ A sample having the same length as the first catalyst layer 20 is cut out. The sample is, for example, cylindrical with a diameter of 25.4 mm. The diameter of the sample can be changed as needed. The sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and the first, second, ..., nth cut pieces are obtained in order from the end of the sample on the exhaust gas inlet side. The length of the cut pieces is 5 mm. The composition of the cut pieces is analyzed using ICP-OES, XRF, SEM-EDX, etc., and it is confirmed based on the composition of the cut pieces whether or not the cut pieces contain a part of the first catalyst layer 20.

[0221] It is not necessary to perform composition analysis on cut pieces that are clearly found to contain a portion of the first catalytic layer 20. For example, the cut surface can be observed using an SEM, an EPMA, or the like to confirm whether the cut piece contains a portion of the first catalytic layer 20. When observing the cut surface, elemental mapping of the cut surface may be performed. Elemental mapping can be performed in the same manner as described above.

[0222] After confirming whether the cut pieces include a part of the first catalytic layer 20, the length of the first catalytic layer 20 included in the sample is calculated based on the following formula: Length of the first catalytic layer 20 included in the sample = 5 mm × (number of cut pieces including a part of the first catalytic layer 20)

[0223] For example, if the first to kth cut pieces include a portion of the first catalytic layer 20, but the (k+1)th to nth cut pieces do not include a portion of the first catalytic layer 20, the length of the first catalytic layer 20 included in the sample is (5×k) mm.

[0224] An example of a more detailed method for measuring the length of the first catalytic layer 20 included in the sample is as follows. The kth cut piece (i.e., the cut piece obtained from the exhaust gas outflow side of the sample among the cut pieces including a portion of the first catalytic layer 20) is cut in the axial direction of the substrate 10, and the length of the portion of the first catalytic layer 20 in the kth cut piece is measured by observing the portion of the first catalytic layer 20 present on the cut surface using an SEM, an EPMA, or the like. Then, the length of the portion of the first catalytic layer 20 included in the sample is calculated based on the following formula: Length of the first catalytic layer 20 included in the sample = (5 mm × (k - 1)) + (length of the portion of the first catalytic layer 20 included in the kth cut piece)

[0225] The length of the first catalytic layer 20 included in one sample is defined as the length L of the first catalytic layer 20. ２０ Alternatively, the average value of the lengths of the first catalytic layer 20 included in a plurality of samples may be used as the length L of the first catalytic layer 20. ２０ For example, the length of the first catalytic layer 20 included in each of 8 to 16 samples arbitrarily cut out from the catalyst 1 may be measured, and the average value of the measured lengths may be used as the length L of the first catalytic layer 20. ２０ It may be adopted as.

[0226] Length L of the first catalyst layer 20 ２０ The above description of the measurement method also applies to the second catalytic layer 30. When applying, the "first catalytic layer 20" is read as the "second catalytic layer 30." However, the length L of the second catalytic layer 30 ３０ In the measurement method, the sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and the first cut piece, the second cut piece, ..., the nth cut piece are obtained in order from the end of the sample on the exhaust gas outflow side.

[0227] <Mass of catalytic layer> When catalyst 1 satisfies condition 1a (embodiments A, B, and D), the mass of first catalytic layer 20 per unit volume of the portion of substrate 10 on which first catalytic layer 20 is formed (hereinafter referred to as the "coating amount of first catalytic 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 coating amount of first catalytic layer 20 is within the above range, it is easy to form a first catalytic layer 20 that satisfies condition 1a (preferably conditions 1a and 2a).

[0228] When catalyst 1 satisfies condition 1b (embodiments A, C, and E), the mass of second catalytic layer 30 per unit volume of the portion of substrate 10 on which second catalytic layer 30 is formed (hereinafter referred to as the "coating amount of second catalytic 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 coating amount of second catalytic layer 30 is within the above range, it is easy to form a second catalytic layer 30 that satisfies condition 1b (preferably conditions 1b and 2b).

[0229] The coating amount of the first catalytic layer 20 is calculated by the formula: Coating amount of the first catalytic layer 20 = (mass of the first catalytic layer 20) / (volume of the substrate 10) × (length L of the first catalytic layer 20) ２０ / Length L of the substrate 10 １０ )) can be obtained.

[0230] The coating amount of the second catalytic layer 30 is calculated by the formula: Coating amount of the second catalytic layer 30 = (mass of the second catalytic layer 30) / (volume of the substrate 10) × (length L of the second catalytic layer 30) ３０ / Length L of the substrate 10 １０)) can be obtained.

[0231] <Condition 2a> When catalyst 1 satisfies condition 1a (embodiments A, B, and D), catalyst 1 satisfies the following condition 2a: 1.30 × 10 －３ ≦Ra [wherein Ra is the gas permeability (cm ) of the first catalyst layer 20 and the partition wall portion 12 measured using a perm porometer before the catalyst 1 is subjected to a heat treatment at 950°C for 35 hours in an air atmosphere. ３ / (cm ２ s Pa)).] is preferably further satisfied.

[0232] The "partition wall portion 12" in the "gas permeability of the first catalyst layer 20 and the partition wall portion 12" refers to the portion of the partition wall portion 12 where the first catalyst layer 20 is provided.

[0233] Ra is an index representing the exhaust gas permeability in the first catalyst layer 20 and the partition wall portion 12, and the larger Ra is, the higher the exhaust gas permeability in the first catalyst layer 20 and the partition wall portion 12 is. －３ (cm ３ / (cm ２ When the pressure drop is 0.1·s·Pa) or more, the permeability of exhaust gas through the first catalyst layer 20 and the partition wall portions 12 becomes sufficient, which contributes to improving the PM trapping performance and suppressing an increase in pressure drop.

[0234] From the viewpoint of more effectively realizing an improvement in PM trapping performance and suppression of an increase in pressure loss, Ra is preferably 1.50 × 10 －３ (cm ３ / (cm ２ s Pa) or more, more preferably 1.70 × 10 －３ (cm ３ / (cm ２ s Pa) or more, and more preferably 1.90 × 10 －３ (cm ３ / (cm ２ .s.Pa) or more.

[0235] If Ra is too large, the exhaust gas may pass through the first catalytic layer 20 and the partition wall portion 12 without being sufficiently diffused inside the first catalytic layer 20 and the partition wall portion 12. From the viewpoint of improving the diffusibility of the exhaust gas inside the first catalytic layer 20 and the partition wall portion 12 and improving the exhaust gas purification performance and PM trapping performance, Ra is preferably 2.00 × 10 －２ (cm ３ / (cm ２ s Pa) or less, more preferably 1.90 × 10 －２ (cm ３ / (cm ２ s Pa) or less, and even more preferably 1.80 × 10 －２ (cm ３ / (cm ２ Each of these upper limits may be combined with any of the lower limits mentioned above.

[0236] The method for measuring Ra will be described below.

[0237] A cut piece P1' (e.g., the cut piece P1' shown in Figures 8A to 8C) is prepared from the catalyst 1 before heat treatment in the same manner as described above. The cut piece P1' is set in a perm porometer holder, and gas is passed through the cut piece P1' at 1 to 200 L / min while changing the gas pressure, and the gas flow rate under pressure is measured. The gas passed is air. As the perm porometer, for example, a perm porometer (e.g., CFP-1100A) manufactured by Porous Materials Inc. can be used. The gas is passed through the end (opening) on ​​the exhaust gas inlet side (upper side in Figure 8C) of the inlet cell 13a included in the cut piece P1'. The gas that has flowed in from the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 8C ) of the inlet-side cell 13a passes through the first catalyst layer 20 and the partition wall section 12, and flows out from the end (opening) on ​​the exhaust gas outlet side (lower side in FIG. 8C ) of the outlet-side cell 13b.

[0238] The gas permeability is calculated from the following equation when the pressure difference between the upstream (upper side in FIG. 8C) and downstream (lower side in FIG. 8C) positions in the gas flow direction relative to the cut piece P1' during gas flow ((pressure at the upstream position in the gas flow direction relative to the cut piece P1' during gas flow) - (pressure at the downstream position in the gas flow direction relative to the cut piece P1' during gas flow)) is 10 kPa. The pressure at the upstream position in the gas flow direction relative to the cut piece P1' during gas flow is controlled by a perm porometer. Because the downstream side in the gas flow direction relative to the cut piece P1' during gas flow is open to the atmosphere, the pressure at the downstream position in the gas flow direction relative to the cut piece P1' during gas flow is equal to atmospheric pressure. R = Q / A １ M １ [Wherein, R is the gas permeability (unit: cm ３ / (cm ２ s Pa), and Q is the flow rate of gas under pressure (unit: cm ３ / s), A １ is the effective filtration area of ​​the cut piece P1' (unit: cm ２ ) and M １ represents the pressure difference (unit: Pa) between the upstream and downstream positions in the gas flow direction relative to the cut piece P1′ during gas flow.]

[0239] A １ can be calculated from the following formula: １ = α １ ×β １ ×γ １ [In the formula, α １ represents the average length (unit: cm) of one side of the opening of the inlet side cell 13a, and β １ represents the axial length of the cut piece P1′ (unit: cm), and γ １ represents the number of effective filtering surfaces of the cut piece P1'.]

[0240] α １ can be calculated from the following formula: α １ = Average distance D1 - Average thickness T of partition wall portion 12

[0241] The average distance D1 (unit: cm) can be determined by the following method.

[0242] In the plan view of the cut piece P1′ shown in FIG. 11, of the four sides constituting the opening of a certain inlet cell 13a, the left side in FIG. 11 is the “left side A1a”, the right side in FIG. 11 is the “right side A2a”, the upper side in FIG. 11 is the “upper side A3a”, and the lower side in FIG. 11 is the “lower side A4a”. Of the four sides constituting the opening of one outlet cell 13b adjacent to the right or left side of the inlet cell 13a, the left side in FIG. 11 is the “left side A1a”. 11 is referred to as "left side C1b", one side on the right side of FIG. 11 is referred to as "right side B2b", one side on the top side of FIG. 11 is referred to as "upper side B3b", and one side on the bottom side of FIG. 11 is referred to as "lower side B4b". Of the four sides constituting the opening of one outlet cell 13b adjacent to the bottom or top of the inlet cell 13a, one side on the left side of FIG. 11 is referred to as "left side C1b", one side on the right side of FIG. 11 is referred to as "right side C2b", one side on the top side of FIG. 11 is referred to as "upper side C3b", and one side on the bottom side of FIG. 11 is referred to as "lower side C4b". The four sides constituting the opening of the above-mentioned inlet cell 13a are sides formed by the outer surfaces S1a (see FIGS. 4 to 6) of the partition wall portions 12 of the substrate 10 in the cut piece P1', and the four sides constituting the opening of the above-mentioned outlet cell 13b are sides formed by the outer surfaces S1b (see FIGS. 4 to 6) of the partition wall portions 12 of the substrate 10 in the cut piece P1'.

[0243] In the plan view of the cut piece P1' shown in Figure 11, the distance (unit: cm) between the left side A1a of the opening of the inlet cell 13a and the left side B1b of the opening of the outlet cell 13b is measured, and the measured distance is defined as distance D11. The distance (unit: cm) between the right side A2a of the opening of the inlet cell 13a and the right side B2b of the opening of the outlet cell 13b may also be measured, and the measured distance is defined as distance D11. Distance D11 can be considered to be the sum of the length of the upper side A3a or lower side A4a of the opening of the inlet cell 13a and the thickness of the partition wall portion 12.

[0244] The distance D11 is calculated in the same manner as above for 20 inlet cells 13a and their adjacent outlet cells 13b randomly selected from the plan view of the cut piece P1' shown in Figure 11, and the average value of these is taken as the average distance D11'.

[0245] In the plan view of the cut piece P1' shown in Figure 11, the distance (unit: cm) between the bottom edge A4a of the opening of the inlet cell 13a and the bottom edge C4b of the opening of the outlet cell 13b is measured, and the measured distance is defined as distance D12. The distance (unit: cm) between the top edge A3a of the opening of the inlet cell 13a and the top edge C3b of the opening of the outlet cell 13b may also be measured, and the measured distance is defined as distance D12. Distance D12 can be considered to be the sum of the length of the left edge A1a or right edge A2a of the opening of the inlet cell 13a and the thickness of the partition wall portion 12.

[0246] The distance D12 is calculated in the same manner as above for 20 inlet cells 13a and their adjacent outlet cells 13b randomly selected from the plan view of the cut piece P1' shown in Figure 11, and the average value is taken as the average distance D12'.

[0247] The average distance D1 can be calculated as the average of the average distances D11' and D12' (i.e., D1 = (D11' + D12') / 2).

[0248] 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 (ie, D1=D11' or D1=D12').

[0249] The average thickness T (unit: cm) of the partition wall 12 can be determined by the following method.

[0250] A certain portion of the catalyst 1 (e.g., a portion 10 mm away from the end of the substrate 10 on the exhaust gas inlet side in the exhaust gas flow direction E) is cut along a plane perpendicular to the axial direction of the substrate 10, and the first catalytic layer 20 present in one inlet-side cell 13a arbitrarily selected from the cut surface is observed with an SEM to identify the region where the partition wall portion 12 of the substrate 10 and the region where the first catalytic layer 20 are present. When observing the cut surface with an SEM, the field of view magnification is, for example, 300 times, and the field of view width (length) is, for example, 500 to 600 μm. The region observed with the SEM is preferably set so as not to include the corners of the inlet-side cell 13a. The region where the partition wall portion 12 of the substrate 10 and the region where the first catalytic layer 20 are present can be identified based on the difference in shape between the first catalytic layer 20 and the partition wall portion 12 of the substrate 10. At this time, elemental mapping of the cut surface may be performed. Elemental mapping can be performed in the same manner as described above. By elemental mapping of the cut surface, it is possible to identify the region where the partition wall portion 12 of the substrate 10 exists and the region where the first catalyst layer 20 exists, based on the differences in morphology and composition between the first catalyst layer 20 and the partition wall portion 12 of the substrate 10.

[0251] In the SEM image, first to Nth grid lines parallel to the thickness direction of the partition wall portions 12 of the substrate 10 are drawn at 15 μm intervals, starting from the left end or the right end. The intersections of each grid line and the outline of the inlet-side cell side of the region where the partition wall portions 12 of the substrate 10 are present are connected by straight lines to identify the surface position of the inlet-side cell side of the partition wall portions 12 of the substrate 10. N is an integer of, for example, 30 to 50. Similarly, the intersections of each grid line and the outline of the outlet-side cell side of the region where the partition wall portions 12 of the substrate 10 are present are connected by straight lines to identify the surface position of the outlet-side cell side of the partition wall portions 12 of the substrate 10. If the amount of change in the thickness direction from a certain intersection point X1 to an intersection point X2 adjacent to the intersection point X1 exceeds the grid line spacing (15 μm), it is preferable not to use the intersection point X2 to identify the surface position (i.e., to exclude the intersection point X2 from the intersection points connected by straight lines). The change in thickness direction from a certain intersection X1 to an intersection X2 adjacent to the intersection X1 refers to the distance between a straight line passing through the intersection X1 and perpendicular to the thickness direction of the partition wall 12 of the substrate 10, and a straight line passing through the intersection X2 and perpendicular to the thickness direction of the partition wall 12 of the substrate 10. If the change in thickness direction from the intersection X1 to the intersection X2 adjacent to the intersection X1 exceeds the grid line spacing (15 μm), and the change in thickness direction from the intersection X1 to the intersection X3 adjacent to the intersection X2 also exceeds the grid line spacing (15 μm), it is preferable not to use the intersection X3 in addition to the intersection X2 to identify the surface position (i.e., it is preferable to exclude the intersections X2 and X3 from the intersections connected by straight lines). In this way, if five consecutive intersections are excluded from the intersections connected by straight lines, it is preferable not to measure the thickness of the SEM image.

[0252] After identifying the positions of the surfaces of the inlet cell side of the partition wall portion 12 of the substrate 10 and the outlet cell side of the partition wall portion 12 of the substrate 10, image analysis software is used to determine the area of ​​the region surrounded by the second grid line, the (N-1)th grid line, the surfaces of the inlet cell side of the partition wall portion 12 of the substrate 10, and the surfaces of the outlet cell side of the partition wall portion 12 of the substrate 10. Examples of image analysis software that can be used include AreaQ (manufactured by Estec Co., Ltd.), ImageJ (public domain), and Photoshop (Adobe Systems Inc.). Note that the first grid line and the Nth grid line are not used because both ends of the image tend to be unclear and it is difficult to identify the position of the surface of the partition wall portion 12.

[0253] After determining the area of ​​the region, the thickness of the region is determined based on the following formula: Thickness of the region = Area of ​​the region / (Spacing of grid lines × Number of spacings of grid lines) Note that the spacing of the grid lines is 15 μm, and the number of spacings of the grid lines is (N-3). The thickness of the region is determined for 20 inlet-side cells 13a randomly selected from the cut surface, and the average value thereof is defined as the average thickness T of the partition wall portion 12.

[0254] β １ can be obtained by measuring the length of the cut piece P1' (the length in the axial direction of the cut piece P1').

[0255] gamma １ can be determined by the following method.

[0256] 2 to 6, the shape of the end (opening) on ​​the exhaust gas inlet side of the inlet-side cell 13a and the shape of the end (opening) on ​​the exhaust gas outlet side of the outlet-side cell 13b are each quadrilateral (preferably square or rectangular, more preferably square) in plan view. Therefore, as shown in Figures 4 and 5, the outer surface S1a of the partition wall portion 12 in contact with one inlet-side cell 13a is composed of four faces, and the outer surface S1b of the partition wall portion 12 in contact with one outlet-side cell 13b is composed of four faces.

[0257] For all the inlet-side cells 13a included in the cut piece P1′, the number of the outer surfaces S1a (four faces) of the partition wall portion 12 that are in contact with each of the inlet-side cells 13a and that are not adjacent to the third plugging portion 16 was calculated, and the total number of these faces was defined as γ １ Specifically, it is as follows:

[0258] In the plan view of the cut piece P1' shown in Figure 11, three inlet-side cells 13a and three outlet-side cells 13b are arranged in a row in the horizontal direction of Figure 11. The rows are referred to as the "first row F1," "second row F2," "third row F3," "fourth row F4," "fifth row F5," and "sixth row F6" from the top of Figure 11. The three inlet-side cells 13a in the first row F1 are referred to as the "inlet-side cell F11," "inlet-side cell F12," and "inlet-side cell F13" from the left side of Figure 11. The three inlet-side cells 13a in the second row F2 are referred to as the "inlet-side cell F21," "inlet-side cell F22," and "inlet-side cell F23" from the left side of Figure 11. The three inlet-side cells 13a in the third row F3 are referred to as the "inlet-side cell F31," "inlet-side cell F32," and "inlet-side cell F33" from the left side of Figure 11. The three inlet side cells 13a in the fourth column F4 are referred to as "inlet side cell F41," "inlet side cell F42," and "inlet side cell F43," respectively, from the left side of Figure 11; the three inlet side cells 13a in the fifth column F5 are referred to as "inlet side cell F51," "inlet side cell F52," and "inlet side cell F53," respectively, from the left side of Figure 11; and the three inlet side cells 13a in the sixth column F6 are referred to as "inlet side cell F61," "inlet side cell F62," and "inlet side cell F63," respectively, from the left side of Figure 11.

[0259] Of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F11, the left surface (the surface on the left side in FIG. 11 ) and the top surface (the surface on the upper side in FIG. 11 ) are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F11, the number of surfaces that are not adjacent to the third sealing section 16 is two.

[0260] Of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F63, the right surface (the surface on the right side in FIG. 11 ) and the bottom surface (the surface on the bottom side in FIG. 11 ) are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F63, the number of surfaces that are not adjacent to the third sealing section 16 is two.

[0261] Of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F12 or F13, the upper surface (the upper surface in FIG. 11 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F12 or F13, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0262] Of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F23 or F43, the right surface (the surface on the right side in FIG. 11 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F23 or F43, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0263] Of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F31 or F51, the left surface (the surface on the left side in FIG. 11 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F31 or F51, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0264] Of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F61 or F62, the lower surface (the lower surface in FIG. 11 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F61 or F62, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0265] Of the outer surfaces S1a (four faces) of the partition section 12 that contact the inlet side cells F21, F22, F32, F33, F41, F42, F52, or F53, none of the faces are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four faces) of the partition section 12 that contact the inlet side cells F21, F22, F32, F33, F41, F42, F52, or F53, the number of faces that are not adjacent to the third sealing section 16 is four.

[0266] From the above, the number of effective filtration surfaces of cut piece P1' is 2 x 2 (inlet side cells F11 and F63) + 3 x 8 (inlet side cells F12, F13, F23, F31, F43, F51, F61 and F62) + 4 x 8 (inlet side cells F21, F22, F32, F33, F41, F42, F52 and F53) = 60.

[0267] Using different cut pieces P1', the gas permeability was measured three times in total, and the average value was calculated as Ra (cm ３ / (cm ２ .s.Pa)).

[0268] In the above measurement method, non-penetrating pores are not measured, and only the through-holes in the first catalytic layer 20 and the partition wall sections 12 are measured. Therefore, the above measurement method allows the gas permeability of the first catalytic layer 20 and the partition wall sections 12 to be measured with high accuracy.

[0269] <Condition 2b> When catalyst 1 satisfies condition 1b (embodiments A, C, and E), catalyst 1 satisfies the following condition 2b: 1.30 × 10 －３ ≦Rb [wherein Rb is the gas permeability (cm ) of the second catalyst layer 30 and the partition wall portion 12 measured using a perm porometer before the catalyst 1 was subjected to a heat treatment at 950°C for 35 hours in an air atmosphere. ３ / (cm ２ s Pa)).] is preferably further satisfied.

[0270] The "partition wall portion 12" in the "gas permeability of the second catalyst layer 30 and the partition wall portion 12" refers to the portion of the partition wall portion 12 where the second catalyst layer 30 is provided.

[0271] Rb is an index representing the exhaust gas permeability in the second catalyst layer 30 and the partition wall portion 12, and the larger Rb is, the higher the exhaust gas permeability in the second catalyst layer 30 and the partition wall portion 12 is. －３ (cm ３ / (cm ２ When the pressure drop is 0.1 s Pa or more, the permeability of the exhaust gas through the second catalyst layer 30 and the partition wall portions 12 is sufficient, which contributes to improving the PM trapping performance and suppressing an increase in pressure drop.

[0272] From the viewpoint of more effectively realizing an improvement in PM trapping performance and suppression of an increase in pressure loss, Rb is preferably 1.50 × 10 －３ (cm ３ / (cm ２ s Pa) or more, more preferably 1.70 × 10 －３ (cm ３ / (cm ２ s Pa) or more, and more preferably 1.90 × 10 －３ (cm ３ / (cm ２ .s.Pa) or more.

[0273] If Rb is too large, the exhaust gas may pass through the second catalyst layer 30 and the partition wall portion 12 without being sufficiently diffused inside the second catalyst layer 30 and the partition wall portion 12. From the viewpoint of improving the diffusibility of the exhaust gas inside the second catalyst layer 30 and the partition wall portion 12 and improving the exhaust gas purification performance and PM trapping performance, Rb is preferably 2.00 × 10 －２ (cm ３ / (cm ２ s Pa) or less, more preferably 1.90 × 10 －２ (cm ３ / (cm ２ s Pa) or less, and even more preferably 1.80 × 10 －２ (cm ３ / (cm ２ Each of these upper limits may be combined with any of the lower limits mentioned above.

[0274] The method for measuring Rb will be described below.

[0275] A cut piece P2' (e.g., cut piece P2' shown in Figures 10A to 10C) is prepared from the catalyst 1 before heat treatment in the same manner as described above. The cut piece P2' is set in a perm porometer holder, and gas is passed through the cut piece P2' at 1 to 200 L / min while changing the gas pressure, and the gas flow rate under pressure is measured. The gas passed is air. As the perm porometer, for example, a perm porometer (e.g., CFP-1100A) manufactured by Porous Materials Inc. can be used. The gas is passed through the end (opening) on ​​the exhaust gas inlet side (upper side in Figure 10C) of the inlet cell 13a included in the cut piece P2'. The gas that has flowed in from the end (opening) on ​​the exhaust gas inlet side (upper side in FIG. 10C ) of the inlet-side cell 13a passes through the partition wall 12 and the second catalyst layer 30, and flows out from the end (opening) on ​​the exhaust gas outlet side (lower side in FIG. 10C ) of the outlet-side cell 13b.

[0276] The gas permeability is calculated from the following equation when the pressure difference between the upstream (upper side in FIG. 10C) and downstream (lower side in FIG. 10C) positions in the gas flow direction relative to the cut piece P2' during gas flow ((pressure at the upstream position in the gas flow direction relative to the cut piece P2' during gas flow) - (pressure at the downstream position in the gas flow direction relative to the cut piece P2' during gas flow)) is 10 kPa. The pressure at the upstream position in the gas flow direction relative to the cut piece P2' during gas flow is controlled by a perm porometer. Because the downstream side in the gas flow direction relative to the cut piece P2' during gas flow is open to the atmosphere, the pressure at the downstream position in the gas flow direction relative to the cut piece P2' during gas flow is equal to atmospheric pressure. R = Q / A ２ M ２ [Wherein, R is the gas permeability (unit: cm ３ / (cm ２ s Pa), and Q is the flow rate of gas under pressure (unit: cm ３ / s), A ２ is the effective filtration area of ​​the cut piece P2' (unit: cm ２ ) and M ２ represents the pressure difference (unit: Pa) between the upstream and downstream positions in the gas flow direction relative to the cut piece P2′ during gas flow.]

[0277] A ２can be calculated from the following formula: ２ = α ２ ×β ２ ×γ ２ [In the formula, α ２ represents the average length (unit: cm) of one side of the opening of the outlet-side cell 13b, and β ２ represents the axial length of the cut piece P2' (unit: cm), and γ ２ represents the number of effective filtering surfaces of the cut piece P2'.]

[0278] α ２ can be calculated from the following formula: α ２ = Average distance D2 - Average thickness T of partition wall portion 12

[0279] The average distance D2 (unit: cm) can be determined by the following method.

[0280] In the plan view of the cut piece P2′ shown in FIG. 12, of the four sides constituting the opening of one particular outflow side cell 13b, the left side in FIG. 12 is referred to as the “left side A1b”, the right side in FIG. 12 is referred to as the “right side A2b”, the upper side in FIG. 12 is referred to as the “upper side A3b”, and the lower side in FIG. 12 is referred to as the “lower side A4b”. Of the four sides constituting the opening of the inflow side cell 13a adjacent to the right or left side of the outflow side cell 13b, the left side in FIG. 12 is referred to as the “left side B 12 is referred to as "left side C1a", one side on the right side of FIG. 12 is referred to as "right side B2a", one side on the top side of FIG. 12 is referred to as "upper side B3a", and one side on the bottom side of FIG. 12 is referred to as "lower side B4a". Of the four sides constituting the opening of one inlet side cell 13a adjacent to the bottom or top of the outlet side cell 13b, one side on the left side of FIG. 12 is referred to as "left side C1a", one side on the right side of FIG. 12 is referred to as "right side C2a", one side on the top side of FIG. 12 is referred to as "upper side C3a", and one side on the bottom side of FIG. 12 is referred to as "lower side C4a". The four sides constituting the opening of the above-mentioned outlet side cell 13b are sides formed by the outer surfaces S1b (see FIGS. 4 to 6) of the partition wall portions 12 of the substrate 10 in the cut piece P2', and the four sides constituting the opening of the above-mentioned inlet side cell 13a are sides formed by the outer surfaces S1a (see FIGS. 4 to 6) of the partition wall portions 12 of the substrate 10 in the cut piece P2'.

[0281] In the plan view of the cut piece P2' shown in Figure 12, the distance (unit: cm) between the left side A1b of the opening of the outlet cell 13b and the left side B1a of the opening of the inlet cell 13a is measured, and the measured distance is defined as distance D21. The distance (unit: cm) between the right side A2b of the opening of the outlet cell 13b and the right side B2a of the opening of the inlet cell 13a may also be measured, and the measured distance is defined as distance D21. Distance D21 can be considered to be the sum of the length of the upper side A3b or lower side A4b of the opening of the outlet cell 13b and the thickness of the partition wall portion 12.

[0282] The distance D21 is calculated in the same manner as above for 20 outlet cells 13b and their adjacent inlet cells 13a randomly selected from the plan view of the cut piece P2' shown in Figure 12, and the average value is taken as the average distance D21'.

[0283] In the plan view of the cut piece P2' shown in Figure 12, the distance (unit: cm) between the bottom side A4b of the opening of the outlet cell 13b and the bottom side C4a of the opening of the inlet cell 13a is measured, and the measured distance is defined as distance D22. The distance (unit: cm) between the top side A3b of the opening of the outlet cell 13b and the top side C3a of the opening of the inlet cell 13a may also be measured, and the measured distance is defined as distance D22. Distance D22 can be considered to be the sum of the length of the left side A1b or right side A2b of the opening of the outlet cell 13b and the thickness of the partition wall portion 12.

[0284] The distance D22 is calculated in the same manner as above for 20 outlet cells 13b and their adjacent inlet cells 13a randomly selected from the plan view of the cut piece P2' shown in Figure 12, and the average value is taken as the average distance D22'.

[0285] The average distance D2 can be calculated as the average of the average distances D21' and D22' (i.e., D2 = (D21' + D22') / 2).

[0286] 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 (ie, D2=D21' or D2=D22').

[0287] The average thickness T (unit: cm) of the partition wall 12 can be determined in the same manner as above.

[0288] β ２ can be obtained by measuring the axial length of the cut piece P2'.

[0289] gamma ２ can be determined by the following method.

[0290] As shown in Figures 4 and 5, the outer surface S1a of the partition wall portion 12 in contact with one inlet-side cell 13a is composed of four faces, and the outer surface S1b of the partition wall portion 12 in contact with one outlet-side cell 13b is composed of four faces.

[0291] For all the outflow-side cells 13b included in the cut piece P2′, the number of the outer surfaces S1b (four surfaces) of the partition wall portion 12 that are in contact with each outflow-side cell 13b and that are not adjacent to the third plugged portion 16 is calculated, and the total number is defined as γ ２ Specifically, it is as follows:

[0292] In the plan view of the cut piece P2' shown in Figure 12, three inlet cells 13a and three outlet cells 13b are arranged in a row in the horizontal direction of Figure 12. The rows are referred to as the "first row G1," "second row G2," "third row G3," "fourth row G4," "fifth row G5," and "sixth row G6" from the top of Figure 12. The three outlet cells 13b in the first row G1 are referred to as the "outlet cell G11," "outlet cell G12," and "outlet cell G13" from the left side of Figure 12. The three outlet cells 13b in the second row G2 are referred to as the "outlet cell G21," "outlet cell G22," and "outlet cell G23" from the left side of Figure 12. The three outlet cells 13b in the third row G3 are referred to as the "outlet cell G31," "outlet cell G32," and "outlet cell G33" from the left side of Figure 12. The three outflow side cells 13b in the fourth column G4 are referred to as "outflow side cell G41," "outflow side cell G42," and "outflow side cell G43," respectively, from the left side of Figure 12; the three outflow side cells 13b in the fifth column F5 are referred to as "outflow side cell G51," "outflow side cell G52," and "outflow side cell G53," respectively, from the left side of Figure 12; and the three outflow side cells 13b in the sixth column F6 are referred to as "outflow side cell G61," "outflow side cell G62," and "outflow side cell G63," respectively, from the left side of Figure 12.

[0293] Of the outer surfaces S1b (four surfaces) of the partition wall portion 12 that contact the outflow-side cell G11, the left surface (the surface on the left side in FIG. 12 ) and the top surface (the surface on the upper side in FIG. 12 ) are adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition wall portion 12 that contact the outflow-side cell G11, the number of surfaces that are not adjacent to the third sealing portion 16 is two.

[0294] Of the outer surfaces S1b (four surfaces) of the partition wall portion 12 that contact the outflow-side cell G63, the right surface (the surface on the right side in FIG. 12 ) and the bottom surface (the surface on the bottom side in FIG. 12 ) are adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition wall portion 12 that contact the outflow-side cell G63, the number of surfaces that are not adjacent to the third sealing portion 16 is two.

[0295] Of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G12 or G13, the upper surface (the upper surface in FIG. 12 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G12 or G13, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0296] Of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G23 or G43, the right surface (the surface on the right side in FIG. 12 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G23 or G43, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0297] Of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G31 or G51, the left surface (the surface on the left side in FIG. 12 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G31 or G51, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0298] Of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G61 or G62, the lower surface (the lower surface in FIG. 12 ) is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cell G61 or G62, the number of surfaces that are not adjacent to the third sealing portion 16 is three.

[0299] Of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cells G21, G22, G32, G33, G41, G42, G52, or G53, none of the surfaces is adjacent to the third sealing portion 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow-side cells G21, G22, G32, G33, G41, G42, G52, or G53, the number of surfaces that is not adjacent to the third sealing portion 16 is four.

[0300] From the above, the number of effective filtration surfaces of cut piece P2' is 2 x 2 (outlet cells G11 and G63) + 3 x 8 (outlet cells G12, G13, G23, G31, G43, G51, G61 and G62) + 4 x 8 (outlet cells G21, G22, G32, G33, G41, G42, G52 and G53) = 60.

[0301] Using different cut pieces P2', the gas permeability was measured three times in total, and the average value was calculated as Rb (cm ３ / (cm ２ .s.Pa)).

[0302] In the above measurement method, non-penetrating pores are not measured, and only the through-holes in the second catalytic layer 30 and the partition wall sections 12 are measured. Therefore, the above measurement method allows the gas permeability of the second catalytic layer 30 and the partition wall sections 12 to be measured with high accuracy.

[0303] <10% Flow Diameter of Partition Wall> The 10% flow diameter (μm) of the partition wall 12 measured by the bubble point method using a perm porometer after heat treatment of the substrate 10 at 950°C for 35 hours in an air atmosphere is defined as Xc (μm), and the 10% flow diameter (μm) of the partition wall 12 measured by the bubble point method using a perm porometer before the heat treatment of the substrate 10 is defined as Yc (μm). Xc is typically 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 may 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 may 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 may be 1.05 or less, or 1.03 or less. Since the state of the substrate 10 hardly changes before and after the heat treatment, the lower limit of Xc / Yc is theoretically 1, but it may be less than 1 due to measurement error or the influence of other slight changes. Xc / Yc may be, for example, 0.98 or more, 0.99 or more, or 1.00 or more. Each of these lower limit values ​​may be combined with any of the above-mentioned upper limit values.

[0304] The method for measuring Xc will be described below.

[0305] The substrate 10 is subjected to a heat treatment at 950° C. for 35 hours in an air atmosphere. After the heat treatment, a length L of the substrate 10 is formed extending in the axial direction of the substrate 10. １０ A sample having the same length as the inlet-side cells 13a and the outlet-side cells 13b is cut out. The number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample. The planar shape of the sample when viewed in a plane from the axial direction of the sample is, for example, a quadrangle (preferably a square or rectangle, more preferably a square). The size of the planar shape when viewed in a plane from the axial direction of the sample is not particularly limited as long as the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample. For example, the vertical length is 10 mm and the horizontal length is 10 mm. When the inlet-side cells 13a and the outlet-side cells 13b are arranged alternately in the vertical direction and the horizontal direction, if the total number of inlet-side cells 13a and the outlet-side cells 13b arranged in the vertical direction of the sample is an even number and the total number of inlet-side cells 13a and the outlet-side cells 13b arranged in the horizontal direction of the sample is an even number, the number of inlet-side cells 13a included in the sample will be the same as the number of outlet-side cells 13b included in the sample.

[0306] The sample is cut along a plane perpendicular to the axial direction of the sample to prepare a cut piece P3 that does not include a part of the first catalytic layer 20 or a part of the second catalytic layer 30. The axial length of the cut piece P3 is not particularly limited, but is, for example, 10 mm. The cut piece P3 does not have the first plugged portion 14 or the second plugged portion 15.

[0307] 7A and 7B , except that the cut piece P3 does not include a part of the first catalytic layer 20. The cut piece P3 has a cubic shape with a length of 10 mm in the vertical direction, a length of 10 mm in the horizontal direction, and a length of 10 mm in the axial direction, for example.

[0308] A first sealing portion sealing the exhaust gas outlet end of the inlet-side cell 13a included in the cut piece P3 and a second sealing portion sealing the exhaust gas inlet end of the outlet-side cell 13b included in the cut piece P3 are formed on the cut piece P3, and a third sealing portion is formed on the outermost periphery of the cut piece P3 to obtain a cut piece P3'. The first sealing portion, the second sealing portion, and the third sealing portion can be formed by applying a weatherstripping material to predetermined locations on the cut piece P3. For example, an adhesive such as an epoxy resin adhesive can be used as the weatherstripping material. The thicknesses of the first sealing portion 14 and the second sealing portion 15 are each 1 / 10 or less of the axial length of the cut piece P3.

[0309] An example of the cut piece P3' is similar to the example of the cut piece P1' shown in FIGS. 8A to 8C, except that it does not include a part of the first catalyst layer 20.

[0310] Xc can be measured in the same manner as Xa, except that the cut piece P3' prepared from the heat-treated substrate 10 is used instead of the cut piece P1' prepared from the heat-treated catalyst 1.

[0311] When catalyst 1 has a portion that does not include a part of either the first catalytic layer 20 or the second catalytic layer 30, cut piece P3′ may be prepared from catalyst 1. When catalyst 1 has no portion that does not include a part of either the first catalytic layer 20 or the second catalytic layer 30, a substrate having the same specifications as substrate 10 used in catalyst 1 may be prepared, and the measurement results for the prepared substrate may be estimated to be the measurement values ​​for substrate 10 of catalyst 1.

[0312] A method for measuring Yc will be described below.

[0313] A cut piece P3' is prepared in the same manner as above from the substrate 10 before the heat treatment. Yc can be measured in the same manner as Xc, except that the cut piece P3' prepared from the substrate 10 before the heat treatment is used instead of the cut piece P3' prepared from the substrate 10 after the heat treatment.

[0314] <Gas permeability of partition wall portion> Before the substrate 10 is subjected to a heat treatment at 950°C for 35 hours in an air atmosphere, the gas permeability (cm ３ / (cm２ s Pa) to Rc (cm ３ / (cm ２ s Pa), Rc is usually 7.00 (cm ３ / (cm ２ ・s・Pa)) or more 20.00(cm ３ / (cm ２ s Pa) or less. Rc is 9.00 (cm ３ / (cm ２ ・s・Pa)) or more 18.00 (cm ３ / (cm ２ s Pa) or less, or 11.00 (cm ３ / (cm ２ ・s・Pa)) or more 16.00 (cm ３ / (cm ２ .s.Pa) or less.

[0315] The method for measuring Rc will be described below.

[0316] A cut piece P3' is prepared in the same manner as above from the substrate 10 before the heat treatment. Rc can be measured in the same manner as Ra, except that the cut piece P3' prepared from the substrate 10 before the heat treatment is used instead of the cut piece P1' prepared from the catalyst 1 before the heat treatment.

[0317] <<Method of Forming Catalyst Layer>> The following describes a method of forming a catalyst layer. The following description of the method of forming a catalyst layer applies to both the first catalyst layer 20 and the second catalyst layer 30, unless otherwise specified. When applied to the first catalyst layer 20, the term "catalyst layer" is replaced with "first catalyst layer 20," and when applied to the second catalyst layer 30, the term "catalyst layer" is replaced with "second catalyst layer 30." Furthermore, the following description of the method of forming a catalyst layer applies to all of Embodiments A to E, unless otherwise specified.

[0318] When the catalyst layer has a single-layer structure, a slurry for forming the catalyst layer is applied to a predetermined portion of the substrate 10 and then dried to form a precursor of the catalyst layer. After the catalyst layer precursor is formed, it is calcined. In this way, a catalyst layer having a single-layer structure can be formed.

[0319] When the catalyst layer has a two-layer structure, a slurry for forming the lower layer is applied to a predetermined portion of the substrate 10 and then dried to form a precursor for the lower layer. Next, a slurry for forming the upper layer is applied onto the precursor for the lower layer and then dried to form a precursor for the upper layer. After the precursor for the lower layer and the precursor for the upper layer are formed, they are calcined. In this way, a catalyst layer having a two-layer structure can be formed. A catalyst layer having a stacked structure other than a two-layer structure (for example, a three-layer structure) can also be formed in the same way.

[0320] The drying temperature is, for example, 40° C. to 150° C., and the drying time is, for example, 5 minutes to 1 hour. The firing temperature is, for example, 350° C. to 600° C., and the firing time is, for example, 20 minutes to 5 hours. The firing atmosphere is usually the air atmosphere.

[0321] The composition of each slurry is adjusted depending on the composition of the catalyst layer. Each slurry contains, for example, a source of a precious metal element, inorganic oxide particles (e.g., Zr-based oxide particles), a binder, a pore-forming material, a solvent, etc. Examples of the source of a precious metal element include salts of precious metal elements, and examples of salts of precious metal elements include nitrates, ammine complex salts, acetates, and chlorides. The inorganic oxides constituting the inorganic oxide particles are as described above. Examples of binders include alumina sol, zirconia sol, titania sol, silica sol, and ceria sol. Examples of pore-forming materials include cross-linked polymethyl(meth)acrylate particles, cross-linked polybutyl(meth)acrylate particles, cross-linked polystyrene particles, cross-linked polyacrylic ester particles, and melamine-based resins. Examples of solvents include water and organic solvents.

[0322] By adjusting the type of material constituting each slurry, the solids concentration (viscosity) of each slurry, the coating amount of each slurry, the particle size and amount of the pore-forming material contained in each slurry, etc., it is possible to adjust 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.

[0323] The amount of the 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, based on the mass of the catalyst layer formed by drying and calcining each slurry. This facilitates the formation of a catalyst layer that satisfies the desired conditions. The "catalyst layer that satisfies the desired conditions" means, for the first catalyst layer 20, a first catalyst layer 20 that satisfies condition 1a (preferably conditions 1a and 2a), and for the second catalyst layer 30, a second catalyst layer 30 that satisfies condition 1b (preferably conditions 1b and 2b). The same applies hereinafter.

[0324] 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, thereby facilitating the formation of a catalyst layer that satisfies the desired conditions.

[0325] D50 is the particle size at which the cumulative volume is 50% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method.

[0326] The D50 measurement method is as follows. Using an automatic sample feeder for a laser diffraction particle size distribution analyzer ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), a powder sample is placed in an aqueous solvent and irradiated with 40W ultrasound for 360 seconds at a flow rate of 40%, and then a laser diffraction particle size distribution analyzer "Microtrac MT3300II" manufactured by Nikkiso Co., Ltd. is used to measure the volumetric particle size distribution, and the particle size (μm) at which the cumulative volume reaches 50% is measured from the volumetric particle size distribution. Measurements are performed twice, and the average value of the particle sizes (μm) at which the cumulative volume reaches 50% is taken as D50 (μm). The measurement conditions are a particle refractive index of 1.5, particle shape is spherical, solvent refractive index of 1.3, set zero for 30 seconds, and measurement time for 30 seconds.

[0327] <Bake-densified Zr-based oxide> When forming a catalyst layer that satisfies desired conditions, it is preferable to use a Zr-based oxide that has been baked in advance as the Zr-based oxide contained in the slurry, and it is more preferable to use a Ce—Zr-based composite oxide that has been baked in advance. Since a bake-densified Zr-based oxide is less likely to thermally shrink even when exposed to a high-temperature environment, using a bake-densified Zr-based oxide as the Zr-based oxide contained in the slurry can suppress the occurrence of cracks in the catalyst layer that are caused by thermal shrinkage of the Zr-based oxide after exposure to a high-temperature environment. Therefore, using a bake-densified Zr-based oxide as the Zr-based oxide contained in the slurry makes it easier to form a catalyst layer that satisfies desired conditions.

[0328] When a catalyst layer that satisfies desired conditions has a laminated structure (e.g., a two-layer structure), two or more slurries (e.g., a slurry for forming the lower layer and a slurry for forming the upper layer) may contain a sintered Zr-based oxide, or any one of the slurries (e.g., a slurry for forming the lower layer or a slurry for forming the upper layer) may contain a sintered Zr-based oxide.

[0329] "Preliminary densification" means that the Zr-based oxide has been subjected to a calcination treatment before being used to prepare a slurry. The Zr-based oxide to be calcined may be a commercially available product or may be one produced according to a conventional method. The conditions for the calcination treatment performed on the Zr-based oxide 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 air or an inert atmosphere.

[0330] The specific surface area of ​​the Zr-based oxide before the firing treatment is preferably 85 m ２ / g or more 120m ２ / g or less, more preferably 85m ２ / g or more 110m ２ / g or less, more preferably 85m ２ / g or more 100m ２ / g or less.

[0331] The specific surface area of ​​the Zr-based oxide after the calcination treatment is preferably 30 m ２ / g or more 85m ２ / g or less, more preferably 40m ２ / g or more 80m ２ / g or less, more preferably 50m ２ / g or more 75m ２ / g or less.

[0332] The percentage of the specific surface area of ​​the Zr-based oxide after the calcination treatment to the specific surface area of ​​the Zr-based oxide before the calcination treatment (specific surface area of ​​the Zr-based oxide after the calcination treatment / specific surface area of ​​the Zr-based oxide before the calcination treatment×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.

[0333] The specific surface area was measured using powdered Zr-based oxide and QUADRASORB SI manufactured by Quantachrome. ２ It can be measured by gas adsorption method.

[0334] When forming a catalyst layer that satisfies desired conditions, the Zr-based oxide contained in the slurry preferably satisfies one or more, and more preferably two or more, of the following conditions. This makes it possible to make the Zr-based oxide less susceptible to thermal shrinkage, and effectively suppresses the occurrence of cracks in the catalyst layer due to thermal shrinkage of the Zr-based oxide after exposure to a high-temperature environment. (1) The specific surface area of ​​the Zr-based oxide is preferably 85 m ２ / g or more 120m ２ / g or less. (2) The D50 of the Zr-based oxide is 2 μm or more and 15 μm or less. (3) The D10 of the Zr-based oxide is 1 μm or more. (4) The particle size distribution of the Zr-based oxide is unimodal, not multimodal.

[0335] The meaning and measurement method of D50 are as described above. D10 is the particle size at which the cumulative volume is 10% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. The measurement method of D10 is the same as the measurement method of D50.

[0336] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0337] Example 1 (1) Preparation of Slurry Alumina powder and Ce—Zr-based composite oxide powder that had been previously subjected to a calcination treatment were added to an aqueous palladium nitrate solution, and then alumina sol, zirconia sol, a pore-forming material (crosslinked polymethyl(meth)acrylate particles having a D50 of 5 μm), and water as a solvent were added to prepare a first slurry.

[0338] The composition of the Ce—Zr-based composite oxide powder used to prepare the first slurry is as follows: Ce: CeO ２ Conversion content: 40 mass% ZrO ２ Content in terms of oxides of one or more rare earth elements other than Ce: 10% by mass

[0339] The first slurry was prepared using a Ce—Zr composite oxide powder that had been previously subjected to a firing treatment under the following conditions: N using QUADRASORB SI manufactured by Quantachrome Corporation ２ The specific surface area of ​​the Ce—Zr-based composite oxide powder before and after the calcination treatment was measured by gas adsorption. The specific surface area of ​​the Ce—Zr-based composite oxide powder before the calcination treatment was 87.1 m ２ / g, and the specific surface area of ​​the Ce-Zr composite oxide powder after the calcination treatment was 70.8 m ２ / g. [Conditions for firing treatment] Firing temperature: 950°C Firing time: 4 hours Firing atmosphere: air atmosphere

[0340] The amounts of the components in the first slurry were adjusted so that, based on the mass of the catalyst layer formed by drying and firing the first slurry, palladium was 4 mass% in metal equivalent, alumina powder was 9 mass%, Ce-Zr composite oxide powder was 78 mass%, alumina sol was 3 mass% in solid content equivalent, and zirconia sol was 6 mass% in solid content equivalent. The amount of the pore-forming material in the first slurry was adjusted so that it was 40 mass% of the mass of the catalyst layer formed by drying and firing the first slurry.

[0341] Alumina powder and Ce—Zr-based composite oxide powder that had been previously subjected to a calcination treatment were added to an aqueous rhodium nitrate solution, and then alumina sol, zirconia sol, a pore-forming material (crosslinked polymethyl(meth)acrylate particles having a D50 of 3 μm) and water as a solvent were added to prepare a second slurry and a third slurry.

[0342] The composition of the Ce—Zr-based composite oxide powder used to prepare the second and third slurries is as follows: Ce: CeO ２ Conversion content: 15 mass% ZrO ２ Content in terms of oxides of one or more rare earth elements other than Ce: 20% by mass

[0343] The second and third slurries were prepared using Ce—Zr composite oxide powder that had been previously subjected to a calcination treatment under the following conditions: N using QUADRASORB SI manufactured by Quantachrome Corporation ２ The specific surface area of ​​the Ce—Zr-based composite oxide powder before and after the calcination treatment was measured by gas adsorption. The specific surface area of ​​the Ce—Zr-based composite oxide powder before the calcination treatment was 90.1 m ２ / g, and the specific surface area of ​​the Ce-Zr composite oxide powder after the calcination treatment was 68.2 m ２ / g. [Conditions for firing treatment] Firing temperature: 950°C Firing time: 4 hours Firing atmosphere: air atmosphere

[0344] The amounts of the components in the second slurry were adjusted so that, based on the mass of the catalyst layer formed by drying and firing the second slurry, the rhodium was 0.5 mass% in metal equivalent, the alumina powder was 17.5 mass%, the Ce-Zr composite oxide powder was 74 mass%, the alumina sol was 3 mass% in solid content equivalent, and the zirconia sol was 5 mass% in solid content equivalent. The amount of the pore-forming material in the second slurry was adjusted so that it was 40 mass% of the mass of the catalyst layer formed by drying and firing the second slurry.

[0345] The amounts of the components in the third slurry were adjusted so that, based on the mass of the catalyst layer formed by drying and firing the third slurry, the rhodium was 0.5 mass% in metal equivalent, the alumina powder was 9.5 mass%, the Ce-Zr composite oxide powder was 82 mass%, the alumina sol was 3 mass% in solid content equivalent, and the zirconia sol was 5 mass% in solid content equivalent. The amount of the pore-forming material in the third slurry was adjusted so that it was 30 mass% of the mass of the catalyst layer formed by drying and firing the third slurry.

[0346] The mass of the catalyst layer formed by drying and firing each slurry is determined by subtracting the mass of components (e.g., solvent, pore-forming material, etc.) that are lost by drying and firing each slurry from the mass of each slurry.

[0347] (2) Production of exhaust gas purification catalyst A wall-flow type substrate having the structure shown in Figures 2 to 6 was prepared, i.e., a substrate including inlet cells extending in the axial direction of the substrate, outlet cells extending in the axial direction of the substrate, and porous partition walls separating the inlet and outlet cells. The thickness of the partition walls was 200 µm, the total number of inlet and outlet cells in a cross section perpendicular to the axial direction of the substrate was 300 cells per square inch, the volume of the substrate was 0.79 L, and the length of the substrate was 90 mm.

[0348] The first slurry was applied to the exhaust gas inlet side of the substrate and then dried at 90°C for 10 minutes to form a lower layer precursor. The second slurry was applied to the lower layer precursor and then dried at 90°C for 10 minutes to form an upper layer precursor. The substrate on which the lower layer precursor and upper layer precursor were formed was fired at 450°C for 1 hour to form a first catalyst layer on the substrate, comprising a lower layer and an upper layer formed on the lower layer.

[0349] Next, the third slurry was applied to the exhaust gas outflow side of the substrate and then dried at 90°C for 10 minutes to form a precursor of the second catalytic layer. The substrate on which the precursor of the second catalytic layer was formed was calcined at 450°C for 1 hour to form a second catalytic layer on the substrate. In this way, the exhaust gas purification catalyst of Example 1 was obtained.

[0350] When the slurry was applied to the exhaust gas inlet side and exhaust gas outlet side portions of the substrate, the slurry was applied so that the percentage of the length of the first catalytic layer relative to the length of the substrate was 75%, the percentage of the length of the second catalytic layer relative to the length of the substrate was 50%, the mass of the first catalytic layer per unit volume of the portion of the substrate on which the first catalytic layer was formed was 40 g / L, and the mass of the second catalytic layer per unit volume of the portion of the substrate on which the second catalytic layer was formed was 40 g / L.

[0351] The exhaust gas purification catalyst of Example 1 was heat-treated in the air at 950° C. for 35 hours.

[0352] For the exhaust gas purifying catalyst after the heat treatment, Xa and Xb were measured according to the above-mentioned method.

[0353] For the exhaust gas purifying catalyst before the heat treatment, Ya, Yb, Ra and Rb were measured according to the above-mentioned methods.

[0354] For the measurement of Xa, Ya, and Ra, a cut piece P1' shown in FIGS. 8A to 8C, which was prepared from the exhaust gas purification catalyst before or after the heat treatment, was used. For the preparation of the cut piece P1', a cut piece P1 shown in FIGS. 7A and 7B was used. The cut piece P1 used was a cube with a length in the vertical direction (vertical direction in FIG. 7A) of 10 mm, a length in the horizontal direction (horizontal direction in FIG. 7A) of 10 mm, and a length in the axial direction (vertical direction in FIG. 7B) of 10 mm. In the cut piece P1', α １(average length of one side of the opening of the inlet side cell 13a) is 0.121 cm, β １ (axial length of cut piece P1') is 1 cm, γ １ (Number of effective filtering surfaces of cut piece P1') is 60, A １ (effective filtration area of ​​cut piece P1') is 7.26 cm ２ It was.

[0355] For the measurement of Xb, Yb and Rb, a cut piece P2' shown in Figures 10A to 10C was used, which was prepared from the exhaust gas purification catalyst before or after the heat treatment. For the preparation of the cut piece P2', a cut piece P2 shown in Figures 9A and 9B was used. The cut piece P2 used was a cube with a length in the vertical direction (vertical direction in Figure 9A) of 10 mm, a length in the horizontal direction (horizontal direction in Figure 9A) of 10 mm and a length in the axial direction (vertical direction in Figure 9B) of 10 mm. In the cut piece P2', α ２ (average length of one side of the opening of the outlet side cell 13b) is 0.121 cm, β ２ (axial length of cut piece P2') is 1 cm, γ ２ (Number of effective filtering surfaces of cut piece P2') is 6, A ２ (effective filtration area of ​​cut piece P2') is 7.26 cm ２ It was.

[0356] Xc, i.e., the 10% flow diameter of the partition wall portion measured by the bubble point method using a perm porometer after the substrate was subjected to heat treatment at 950°C for 35 hours in an air atmosphere, was 14.39 µm, and Yc, i.e., the 10% flow diameter of the partition wall portion measured by the bubble point method using a perm porometer before the substrate was subjected to the heat treatment, was 14.38 µm, and Xc / Yc was 1.00.

[0357] Rc, that is, the gas permeability of the partition wall measured using a perm porometer before the substrate was subjected to heat treatment at 950°C for 35 hours in an air atmosphere, was 12.64 (cm ３ / (cm ２ ・s・Pa)).

[0358] (3) Evaluation of PM Capture Performance A gasoline engine vehicle equipped with the catalyst for purifying exhaust gas of Example 1 before or after heat treatment was driven under the driving conditions of the World Wide Harmonized Exhaust Gas Test Mode (WLTC). The number of PM particles (PN) in the exhaust gas passing through the catalyst for purifying exhaust gas was measured during low speed driving from 589 seconds after the start of driving, medium speed driving from 589 seconds to 1022 seconds after the start of driving, high speed driving from 1022 seconds to 1477 seconds after the start of driving, and ultra high speed driving from 1477 seconds to 1800 seconds after the start of driving. ｃａｔ ) was measured. In addition, the number of PM particles (PN ａｌｌ ) was measured, and the PM trapping performance of the exhaust gas purifying catalyst of Example 1 before and after the heat treatment was calculated by the following formula: PM trapping performance=1−(PN ｃａｔ / PN ａｌｌ )

[0359] The conditions for measuring PM collection performance were as follows: Evaluation vehicle: 1.5L direct injection turbo engine Gasoline used: Fuel for certification tests PM measurement device: Manufactured by Horiba Ltd.

[0360] Instead of a gasoline engine vehicle equipped with the exhaust gas purifying catalyst of Example 1 before or after the heat treatment, a gasoline engine vehicle equipped with a substrate (neither the first catalyst layer nor the second catalyst layer was formed) was used, and the PM trapping performance of the substrate was determined in the same manner as above.

[0361] The PM trapping performance ratio (%) was calculated based on the following formula: PM trapping performance ratio = (PM trapping performance of the exhaust gas purifying catalyst of Example 1 before or after heat treatment / PM trapping performance of the substrate) x 100

[0362] Example 2 The same procedure as in Example 1 was carried out to prepare the second slurry, except that a Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.

[0363] Example 3 The same procedure as in Example 1 was carried out to prepare the third slurry, except that in place of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance, a Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used.

[0364] Example 4 The same procedure as in Example 1 was carried out to prepare the first slurry, except that a Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.

[0365] Example 5 The same procedure as in Example 1 was carried out to prepare the second slurry and the third slurry, except that the Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.

[0366] Comparative Example 1 The same procedure as in Example 1 was carried out to prepare the first, second, and third slurries, except that the Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.

[0367] The results of Examples 1 to 5 and Comparative Example 1 are shown in Table 1. In Table 1, "Pre-calcined CZ" indicates whether or not a Ce-Zr based composite oxide powder that had been previously calcined was used in the preparation of the slurry ("Yes" if used, "No" if not). 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).

[0368]

[0369] From the above results, it was confirmed that the deterioration of PM trapping performance caused by exposure to a high-temperature environment can be suppressed when the exhaust gas purifying catalyst satisfies at least one of the following conditions 1a and 1b: [Condition 1a] Xa / Ya≦1.40 and Ya≦5.00 [Condition 1b] Xb / Yb≦1.40 and Yb≦5.00

[0370] DESCRIPTION OF SYMBOLS 1... Exhaust gas purification catalyst 10... Substrate 11... Cylindrical portion 12... Partition wall portion 13... Cell 13a... Inlet side cell 13b... Outlet side cell 14... First plugging portion 15... Second plugging portion 20... First catalyst layer 30... Second catalyst layer S1a... Outer surface of the partition wall portion on the inlet side cell side S1b... Outer surface of the partition wall portion on the outlet side cell side

Claims

1. A catalyst for purifying exhaust gas comprising a substrate extending in an exhaust gas flow direction and at least one of a first catalyst layer and a second catalyst layer, wherein the substrate comprises: inlet-side cells extending in the exhaust gas flow direction, the inlet-side cells having an open end on the exhaust gas inlet side and a closed end on the exhaust gas outlet side; outlet-side cells extending in the exhaust gas flow direction, the outlet-side cells having a closed end on the exhaust gas inlet side and an open end on the exhaust gas outlet side; and porous partition walls separating the inlet-side cells and the outlet-side cells, wherein the first catalyst layer has a portion formed on an outer surface of the partition walls on the inlet-side cell side from the exhaust gas inlet-side end of the partition walls along the exhaust gas flow direction, and the second catalyst layer has a portion formed on an outer surface of the partition walls on the outlet-side cell side from the exhaust gas outlet-side end of the partition walls along a direction opposite to the exhaust gas flow direction, and the exhaust gas purification catalyst satisfies 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 (μm) of the first catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer after the exhaust gas purifying catalyst is subjected to a heat treatment at 950° C. for 35 hours in an air atmosphere, and Ya represents the 10% flow diameter (μm) of the first catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment. [Condition 1b] Xb / Yb≦1.40 and Yb≦5.00 [wherein Xb represents the 10% flow diameter (μm) of the second catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer after the exhaust gas purifying catalyst has been subjected to the heat treatment, and Yb represents the 10% flow diameter (μm) of the second catalyst layer and the partition wall portion measured by the bubble point method using a perm porometer before the exhaust gas purifying catalyst has been subjected to the heat treatment.] The exhaust gas purifying catalyst satisfies at least one of the above conditions: When the exhaust gas purifying catalyst satisfies condition 1a, the first catalyst layer contains a Zr-based oxide; When the exhaust gas purifying catalyst satisfies condition 1b, the second catalyst layer contains a Zr-based oxide.

2. The exhaust gas purifying catalyst according to claim 1, wherein, when the exhaust gas purifying catalyst comprises the first catalyst layer but not the second catalyst layer, the percentage of the length of the first catalyst layer relative to the length of the inlet cell is 100%; when the exhaust gas purifying catalyst comprises the second catalyst layer but not the first catalyst layer, the percentage of the length of the second catalyst layer relative to the length of the outlet cell is 100%; and when the exhaust gas purifying catalyst comprises the first catalyst layer and the second catalyst layer, the percentage of the sum of the length of the first catalyst layer and the length of the second catalyst layer relative to the length of the substrate is 100% or more.

3. The exhaust gas purifying catalyst according to claim 1, wherein, when the exhaust gas purifying catalyst satisfies condition 1a but does not satisfy condition 1b, the percentage of the length of the first catalyst layer relative to the length of the inlet cell is 100%, when the exhaust gas purifying catalyst satisfies condition 1b but does not satisfy condition 1a, the percentage of the length of the second catalyst layer relative to the length of the outlet cell is 100%, and when the exhaust gas purifying catalyst satisfies conditions 1a and 1b, the percentage of the sum of the length of the first catalyst layer and the length of the second catalyst layer relative to the length of the substrate is 100% or more.

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

5. The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein when the exhaust gas purifying catalyst satisfies condition 1a, the first catalyst layer contains a Ce-Zr-based composite oxide as the Zr-based oxide, and when the exhaust gas purifying catalyst satisfies condition 1b, the second catalyst layer contains a Ce-Zr-based composite oxide as the Zr-based oxide.

6. The exhaust gas purifying catalyst according to claim 5, wherein, when the exhaust gas purifying catalyst satisfies condition 1a, the content of Ce-Zr based composite oxide in the first catalyst layer is 50 mass% or more, based on the mass of the first catalyst layer, and when the exhaust gas purifying catalyst satisfies condition 1b, the content of Ce-Zr based composite oxide in the second catalyst layer is 50 mass% or more, based on the mass of the second catalyst layer.

7. When the exhaust gas purifying catalyst satisfies the condition 1a, the Ce—Zr-based composite oxide in the first catalyst layer is represented by the following formula: １２ / R １１ >0.8 [wherein, R １１ represents the CeO of Ce in the Ce-Zr based composite oxide. ２ represents the content (mass%) of the converted １２ represents ZrO of Zr in the Ce-Zr based composite oxide. ２ When the exhaust gas purifying catalyst satisfies the condition 1b, the Ce—Zr-based composite oxide in the second catalyst layer is represented by the following formula: ２２ / R ２１ >0.8 [wherein, R ２１ represents the CeO of Ce in the Ce-Zr based composite oxide. ２ represents the content (mass%) of the converted ２２ represents ZrO of Zr in the Ce-Zr based composite oxide. ２ The exhaust gas purifying catalyst according to claim 5, wherein the content (mass %) of the catalyst is expressed as a converted amount (mass %).

8. When the exhaust gas purifying catalyst satisfies the condition 1a, the exhaust gas purifying catalyst also satisfies the following condition 2a: [Condition 2a] 1.30 × 10 －３ ≦Ra [wherein Ra is the gas permeability (cm ) of the first catalyst layer and the partition wall portion measured using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment. ３ / (cm ２ s·Pa)) and when the exhaust gas purifying catalyst satisfies the condition 1b, the exhaust gas purifying catalyst further satisfies the following condition 2b: [Condition 2b] 1.30×10 －３ ≦Rb [wherein Rb is the gas permeability (cm ) of the second catalyst layer and the partition wall portion measured using a perm porometer before the exhaust gas purifying catalyst is subjected to the heat treatment. ３ / (cm ２ 4. The exhaust gas purifying catalyst according to claim 1, further satisfying the following condition:

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