Exhaust gas purification catalyst

Abstract

The purpose of the present invention is to provide an exhaust gas purification catalyst having excellent exhaust gas purification performance, and to provide an exhaust gas purification catalyst (1) provided with a substrate (10), a first catalyst layer (20) provided on the upstream side of the substrate (10), and a second catalyst layer (30) provided on the downstream side of the substrate (10), the first catalyst layer (20) containing a noble metal element and a Ce-Zr-based composite oxide, and the second catalyst layer (30) containing a noble metal element and a Ce-Zr-based composite oxide. The second catalyst layer (30) contains a noble metal element and Al2O3, the mass content of Al in the first catalyst layer (20) in terms of Al2O3 is 12 mass% or less, and the ratio of the mass content of Al in the first catalyst layer (20) in terms of Al2O3 to the mass content of Al in the second catalyst layer (30) in terms of Al2O3 is 0-0.65.

Description

TECHNICAL FIELD

[0001] The present application relates to a catalyst for exhaust gas purification. BACKGROUND

[0002] Exhaust gas emitted from internal combustion engines of automobiles, motorcycles, and the like contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). In order to purify these harmful components to make them harmless, a catalyst for exhaust gas purification containing a noble metal element such as Pt, Pd, and Rh is used. Pt and Pd mainly participate in the oxidation purification of HC and CO, and Rh mainly participates in the reduction purification of NOx.

[0003] In an exhaust gas purification catalyst, in order to maximize the performance of a noble metal element, a catalyst has been proposed in which a catalyst layer is composed of an upstream side portion and a downstream side portion different from the upstream side portion (for example, Patent Document 1).

[0004] Due to the recent increase in the demand for exhaust gas purification performance, an exhaust gas purification catalyst having excellent exhaust gas purification performance is required.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-136695 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] The present application aims to provide a catalyst for exhaust gas purification having excellent exhaust gas purification performance.

[0010] SOLUTION TO PROBLEM

[0011] The present application provides the following invention.

[0012] [1] A catalyst for exhaust gas purification comprising a substrate, a first catalyst layer provided on an upstream side of the substrate, and a second catalyst layer provided on a downstream side of the substrate, wherein

[0013] The first catalyst layer contains a noble metal element and a Ce-Zr-based composite oxide,

[0014] The second catalyst layer contains a noble metal element and Al2O3,

[0015] The mass content of Al in the first catalyst layer in terms of Al2O3 is 12 mass% or less,

[0016] The ratio of the mass content of Al in the first catalyst layer to the mass content of Al in the second catalyst layer, calculated as Al₂O₃, is greater than 0 and less than 0.65.

[0017] [2] According to the catalyst for purifying exhaust gas as described in [1], the ratio of the mass of the first catalyst layer per unit volume of the portion in which the first catalyst layer is formed in the substrate to the mass of the second catalyst layer per unit volume of the portion in which the second catalyst layer is formed in the substrate is 0.95 or less.

[0018] [3] The catalyst for purifying exhaust gas according to [1] or [2], wherein the first catalyst layer and the second catalyst layer respectively contain Pd and / or Pt.

[0019] [4] According to the catalyst for purifying exhaust gas described in [3], the catalyst for purifying exhaust gas further comprises a third catalyst layer disposed on the upper side of the first catalyst layer and / or a fourth catalyst layer disposed on the upper side of the second catalyst layer, wherein the third catalyst layer and the fourth catalyst layer respectively contain Rh.

[0020] [5] The catalyst for purifying exhaust gas according to any one of [1] to [4], wherein the first catalyst layer comprises Pd.

[0021] [6] The catalyst for purifying exhaust gas according to any one of [1] to [5], wherein the mass content of Al in the second catalyst layer, converted to Al2O3, is 50 or more and 600 or less relative to the mass content of the noble metal element in the second catalyst layer, converted to metal.

[0022] [7] The catalyst for purifying exhaust gas according to any one of [1] to [6], wherein the mass content of Ce in the first catalyst layer, calculated as CeO2, is 32% by mass or more.

[0023] The effects of the invention

[0024] According to the present invention, a catalyst for purifying waste gas with excellent purification performance is provided. Attached Figure Description

[0025] Figure 1 A partial cross-sectional view showing the state of the exhaust gas purification catalyst according to the first embodiment of the present invention disposed in the exhaust path of an internal combustion engine.

[0026] Figure 2 for Figure 1 AA-line cross-section view.

[0027] Figure 3 for Figure 1 BB line cross-section.

[0028] Figure 4 is an enlarged view of the area indicated by symbol R1 in Figure 2

[0029] Figure 5 is an enlarged view of the area indicated by symbol R2 in Figure 3

[0030] Figure 6 is a C-C line profile of Figure 1

[0031] Figure 7 is a profile of the exhaust gas purification catalyst according to the second embodiment of the present invention (corresponding to Figure 6 DETAILED DESCRIPTION

[0032] <Explanation of Terms>

[0033] Hereinafter, the terms used in the present specification are explained. The following explanation applies throughout the present specification, unless otherwise specified.

[0034] <Rare Earth Element>

[0035] As the rare earth element, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, for example, can be cited.

[0036] <Oxide>

[0037] The oxide of the rare earth element other than Ce, Pr and Tb means sesquioxide (M2O3, M represents the rare earth element other than Ce, Pr and Tb), the oxide of Ce means CeO2, the oxide of Pr means Pr6O 11 , the oxide of Tb means Tb4O7, the oxide of Al means Al2O3, the oxide of Zr means ZrO2, the oxide of Si means SiO2, the oxide of B means B2O3, the oxide of Cr means Cr2O3, the oxide of Mg means MgO, the oxide of Ca means CaO, the oxide of Sr means SrO, the oxide of Ba means BaO, the oxide of Fe means Fe3O4, the oxide of Mn means Mn3O4, the oxide of Ni means NiO, the oxide of Ti means TiO2, the oxide of Zn means ZnO, and the oxide of Sn means SnO2.

[0038] <Al-based Oxide>

[0039] ​​​​The Al-based oxide refers to an oxide containing Al, in which, among the elements other than oxygen that constitute the oxide, the element having the largest content ratio in terms of mass is Al. Among them, a substance belonging to the Ce-Zr-based composite oxide is not included in the Al-based oxide. The Ce-Zr-based composite oxide will be described later. The Al-based oxide is distinguished from alumina used as a binder. In this specification, alumina used as a binder is sometimes referred to as "alumina binder".

[0040] The Al-based oxide is, for example, in the form of particles. The Al-based oxide is used as a carrier of a catalytically active component. From the viewpoint of improving the loadability of the catalytically active component, the Al-based oxide is preferably porous.

[0041] The Al-based oxide can contain one or two or more elements other than Al and O. The element other than Al and O can be selected from, for example, rare earth elements (for example, Ce, Y, Pr, La, Nd, Sm, Eu, Gd, and the like), alkaline earth metal elements (for example, Mg, Ca, Sr, Ba, and the like), B, Si, Zr, Cr, and the like.

[0042] As the Al-based oxide, for example, alumina (an oxide composed of Al and O), an oxide obtained by modifying the surface of alumina with other elements, an oxide obtained by solid-solution of other elements in alumina, and the like can be listed. As the Al-based oxide containing an element other than Al and O, for example, alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, and the like can be listed.

[0043] In one embodiment, the Al-based oxide contains one or two or more rare earth elements. From the viewpoint of improving the heat resistance of the Al-based oxide, the rare earth element is preferably selected from La, Y, Ce, Nd, Pr, and the like. From the viewpoint of improving the heat resistance of the Al-based oxide, the content ratio of the rare earth element in the Al-based oxide in terms of oxide is preferably 0.1% by mass or more and 50% by mass or less, more preferably 0.1% by mass or more and 30% by mass or less, further preferably 0.2% by mass or more and 20% by mass or less, further preferably 0.3% by mass or more and 10% by mass or less, based on the mass of the Al-based oxide. With respect to the "content ratio of the rare earth element in the Al-based oxide in terms of oxide", when the Al-based oxide contains one rare earth element, it refers to the content ratio of the one rare earth element in terms of oxide, and when the Al-based oxide contains two or more rare earth elements, it refers to the total content ratio of the two or more rare earth elements in terms of oxide.

[0044] When the composition of the Al-based oxide is known, the content ratio of each element in the Al-based oxide in terms of oxide can be calculated from the composition of the Al-based oxide.

[0045] In the case where the composition of the Al-based oxide is unknown, the content of each element in the Al-based oxide in terms of an oxide can be calculated from an elemental map and EDX elemental analysis of a specified particle obtained by analyzing a sample containing the Al-based oxide using energy dispersive X-ray spectroscopy (EDX). Specifically, the Al-based oxide particles and other particles can be qualitatively identified (color-coded) from the elemental map, and the composition of a specified particle can be analyzed (elemental analysis) to calculate the content of each element in the specified particle in terms of an oxide.

[0046] < Ce-based oxide >

[0047] The Ce-based oxide refers to an oxide containing Ce, in which the element having the largest content by mass among the elements other than oxygen that constitute the oxide is Ce. Among them, a substance belonging to a Ce-Zr-based composite oxide is not included in the Ce-based oxide. The Ce-Zr-based composite oxide will be described later. The Ce-based oxide is distinguished from ceria used as a binder. In the present specification, ceria used as a binder is sometimes referred to as "ceria binder".

[0048] The Ce-based oxide is, for example, in the form of particles. The Ce-based oxide is used as a carrier of a catalytically active component. From the viewpoint of improving the loading of the catalytically active component, the Ce-based oxide is preferably porous.

[0049] The Ce-based oxide can contain one or two or more elements other than Ce and O. The elements other than Ce and O can be selected from, for example, rare earth elements other than Ce, alkaline earth metal elements (for example, Mg, Ca, Sr, Ba, and the like), Fe, Mn, Ni, Zr, Al, and the like.

[0050] As the Ce-based oxide, for example, ceria (an oxide composed of Ce and O), an oxide obtained by modifying the surface of ceria with other elements, an oxide obtained by solid-solutionizing other elements in ceria, and the like can be listed.

[0051] The content of each element in the Ce-based oxide in terms of an oxide can be calculated in the same manner as the content of each element in the Al-based oxide in terms of an oxide.

[0052] < Ce-Zr-based composite oxide >

[0053] The Ce-Zr-based composite oxide refers to a composite oxide containing Ce and Zr, in which the content of Ce in terms of CeO2 in the composite oxide is 5 mass% or more and 95 mass% or less based on the mass of the composite oxide, and the content of Zr in terms of ZrO2 in the composite oxide is 5 mass% or more and 95 mass% or less based on the mass of the composite oxide.

[0054] The Ce-Zr-based composite oxide is, for example, particulate. The Ce-Zr-based composite oxide is used as a support of the catalytically active component. From the viewpoint of improving the loading of the catalytically active component, the Ce-Zr-based composite oxide is preferably porous.

[0055] The Ce-Zr-based composite oxide can contain one or two or more elements other than Ce, Zr and O. The element other than Ce, Zr and O can be selected from, for example, a rare earth element other than Ce, an alkaline earth metal element (for example, Mg, Ca, Sr, Ba and the like), Fe, Mn, Ni, Al and the like.

[0056] In the Ce-Zr-based composite oxide, Ce can form a solid solution phase (for example, a solid solution phase of CeO2and ZrO2, and the like), can form a single phase of a crystalline phase or an amorphous phase (for example, a CeO2single phase), can form both a solid solution phase and a single phase, and preferably at least a part of Ce forms a solid solution phase.

[0057] In the Ce-Zr-based composite oxide, Zr can form a solid solution phase (for example, a solid solution phase of CeO2and ZrO2, and the like), can form a single phase of a crystalline phase or an amorphous phase (for example, a ZrO2single phase), can form both a solid solution phase and a single phase, and preferably at least a part of Zr forms a solid solution phase.

[0058] When the Ce-Zr-based composite oxide contains an element other than Ce, Zr and O (hereinafter referred to as "other element"), the other element can form a solid solution phase (for example, a solid solution phase of CeO2and an oxide of the other element, a solid solution phase of ZrO2and an oxide of the other element, a solid solution phase of CeO2and ZrO2and an oxide of the other element, and the like), can form a single phase of a crystalline phase or an amorphous phase (for example, a single phase of an oxide of the other element), can form both a solid solution phase and a single phase, and preferably at least a part of the other element forms a solid solution phase.

[0059] The content of each element in the Ce-Zr-based composite oxide can be calculated in the same manner as the content of each element in the Al-based oxide.

[0060]

[0061] Hereinafter, based on the above-described background art, a description will be given of the first embodiment. Figures 1 to 6 A description will be given of an exhaust gas purification catalyst 1A (hereinafter referred to as "catalyst 1A") according to the first embodiment.

[0062] As described above, the catalyst 1A according to the first embodiment is a catalyst for purifying exhaust gas, and includes a substrate 1, a first layer 2, a second layer 3 and a third layer 4. Figure 1 ​As shown, catalyst 1A is disposed in the exhaust passage within the exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine. Exhaust gas emitted from the internal combustion engine flows from one end of the exhaust pipe P to the other through the exhaust passage within the exhaust pipe P, and is purified by catalyst 1A disposed within the exhaust pipe P. In the attached figure, the direction of exhaust gas flow is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side" or "upstream side," and the downstream side of the exhaust gas flow direction X is referred to as the "exhaust gas outflow side" or "downstream side."

[0063] Other exhaust gas purification catalysts can be configured in the exhaust passage within the exhaust pipe P on the upstream and / or downstream side of the catalyst 1A.

[0064] like Figures 2 to 6 As shown, catalyst 1A includes a substrate 10, a first catalyst layer 20 disposed on the upstream side of the substrate 10, a second catalyst layer 30 disposed on the downstream side of the substrate 10, a third catalyst layer 40 disposed on the upper side of the first catalyst layer 20, and a fourth catalyst layer 50 disposed on the upper side of the second catalyst layer 30.

[0065] In this specification, the content of Ce in the first catalyst layer 20, calculated as CeO2 based on the mass of the first catalyst layer 20, is sometimes referred to as "the mass content of Ce in the first catalyst layer 20 calculated as CeO2," the content of Al in the first catalyst layer 20, calculated as Al2O3 based on the mass of the first catalyst layer 20, is sometimes referred to as "the mass content of Al in the first catalyst layer 20 calculated as Al2O3," the content of noble metal elements in the second catalyst layer 30, calculated as metal content based on the mass of the second catalyst layer 30, is sometimes referred to as "the mass content of noble metal elements in the second catalyst layer 30 calculated as metal content," and the content of Al in the second catalyst layer 30, calculated as Al2O3 based on the mass of the second catalyst layer 30, is sometimes referred to as "the mass content of Al in the second catalyst layer 30 calculated as Al2O3."

[0066] Catalyst 1A is characterized in that the first catalyst layer 20 contains a noble metal element and a Ce-Zr composite oxide, the second catalyst layer 30 contains a noble metal element and Al2O3, the mass content of Al in the first catalyst layer converted to Al2O3 is less than 12% by mass, and the ratio of the mass content of Al in the first catalyst layer 20 converted to Al2O3 to the mass content of Al in the second catalyst layer 30 converted to Al2O3 is more than 0 and less than 0.65.

[0067] In the catalyst 1A, the first catalyst layer 20 is provided on the upstream side of the substrate 10, and the second catalyst layer 30 is provided on the downstream side of the substrate 10. Therefore, exhaust gas flowing into the substrate 10 comes into contact with the first catalyst layer 20 earlier than the second catalyst layer 30.

[0068] When the catalyst 1A is placed in a low-temperature environment immediately after the start of the internal combustion engine, the activity of the catalytically active components (for example, noble metal elements such as Pd and Pt) in the first catalyst layer 20 and the second catalyst layer 30 is low, and thus the exhaust gas purification performance of the catalyst 1A is low. Therefore, from the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, it is necessary to improve the temperature rising properties of the first catalyst layer 20 and the second catalyst layer 30. In particular, improving the temperature rising properties of the first catalyst layer 20, which comes into contact with exhaust gas earlier than the second catalyst layer 30, is effective in improving the exhaust gas purification performance of the catalyst 1A.

[0069] The specific heat of Al2O3 is large, and thus the temperature rising properties are low. Therefore, from the viewpoint of improving the temperature rising properties of the first catalyst layer 20, it is necessary to reduce the mass content of Al converted to Al2O3 in the first catalyst layer 20.

[0070] When the catalyst 1A is placed in a high-temperature environment in which the internal combustion engine is operated at high speed, the temperature of the first catalyst layer 20 and the second catalyst layer 30 sufficiently rises, but the amount of harmful components (for example, hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NOx), and the like) in the exhaust gas emitted per unit time increases, and thus the number of active sites of the catalytically active components is more important than the temperature rising properties.

[0071] Al2O3 has an effect of suppressing a decrease in the dispersion of the catalytically active components after exposure to a high-temperature environment (that is, a decrease in the number of active sites of the catalytically active components after exposure to a high-temperature environment). Therefore, from the viewpoint of suppressing a decrease in the dispersion of the catalytically active components after exposure to a high-temperature environment, it is preferable to increase the mass content of Al converted to Al2O3 in the first catalyst layer 20 and the second catalyst layer 30. However, since the mass content of Al converted to Al2O3 in the first catalyst layer 20 cannot be increased from the viewpoint of improving the temperature rising properties of the first catalyst layer 20, it is necessary to increase the mass content of Al converted to Al2O3 in the second catalyst layer 30.

[0072] As described above, from the viewpoint of the improvement in the temperature raising property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, it is necessary to reduce the mass content of Al in terms of Al203of Al in the first catalyst layer 20, and to increase the mass content of Al in terms of Al203of Al in the second catalyst layer 30. Therefore, the mass content of Al in terms of Al203of Al in the first catalyst layer 20 and the mass content of Al in terms of Al203of Al in the second catalyst layer 30 are adjusted so that the mass content of Al in terms of Al203of Al in the first catalyst layer 20 is 12 mass% or less, and the ratio of the mass content of Al in terms of Al203of Al in the first catalyst layer to the mass content of Al in terms of Al203of Al in the second catalyst layer is 0 or more and 0.65 or less. Thereby, the improvement in the temperature raising property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine can be achieved. Therefore, the catalyst 1A can exert an excellent exhaust gas purification performance compared to the catalyst whose ratio falls outside the above range.

[0073] The air / fuel ratio (air-fuel ratio) of the air supplied to the internal combustion engine is desirably controlled in the vicinity of the stoichiometric ratio (stoichiometric proportion). However, the actual air-fuel ratio varies on the rich (fuel excess atmosphere) side or the lean (fuel lean atmosphere) side from the stoichiometric ratio depending on the running conditions of the vehicle and the like, and therefore, the air-fuel ratio of the exhaust gas also varies on the rich side or the lean side. In order for the catalyst 1A to exert a sufficient purification performance, it is necessary to alleviate the variation in the oxygen concentration in the exhaust gas. By causing the first catalyst layer 20 to contain a Ce-Zr-based composite oxide having an oxygen storage capacity (i.e., the ability to occlude oxygen when the oxygen concentration in the exhaust gas is high, and to release oxygen when the oxygen concentration in the exhaust gas is low), the variation in the oxygen concentration in the exhaust gas is alleviated, and the working window of the catalytically active component is expanded. By containing the Ce-Zr-based composite oxide in the first catalyst layer 20 located on the more upstream side than the second catalyst layer 30, the variation in the oxygen concentration in the exhaust gas is alleviated not only in the first catalyst layer 20, but also in the second catalyst layer 30 located on the more downstream side than the first catalyst layer 20, and the exhaust gas purification ability of the catalyst 1A can be improved.

[0074] From the perspective of more effectively improving the heating capacity of the first catalyst layer 20 when the environment of catalyst 1A is the low temperature environment after the internal combustion engine has just started, and suppressing the decrease in the dispersion of catalytic active components after exposure to the high temperature environment when the environment of catalyst 1A is the high temperature environment during the high-speed operation of the internal combustion engine, the ratio of the mass content of Al in the first catalyst layer converted to Al2O3 to the mass content of Al in the second catalyst layer is preferably 0 or more and 0.50 or less, more preferably 0 or more and 0.30 or less, and even more preferably 0 or more and 0.10 or less.

[0075] The improvement in the heating performance of the first catalyst layer 20 under low temperature conditions is significant when the temperature is below 500℃, more significant when the temperature is below 450℃, and even more significant when the temperature is below 400℃.

[0076] The inhibition of the decrease in the dispersion of catalytically active components after exposure to high-temperature environments is significant at temperatures above 550°C, more significant at temperatures above 600°C, and even more significant at temperatures above 650°C.

[0077] <Substrate>

[0078] The substrate 10 will be described below.

[0079] like Figure 1 and 6 As shown, the substrate 10 extends in the exhaust gas flow direction X.

[0080] like Figure 1 and 6 As shown, the substrate 10 is disposed in the exhaust channel of the exhaust pipe P such that the axial direction of the substrate 10 is consistent with or approximately consistent with the exhaust gas flow direction X.

[0081] like Figures 1 to 6 As shown, the substrate 10 has a first substrate portion 10a located upstream of the exhaust gas flow direction X and a second substrate portion 10b located downstream of the exhaust gas flow direction X.

[0082] like Figure 1 and 6 As shown, the first substrate portion 10a and the second substrate portion 10b extend in the exhaust gas flow direction X, and have an end on the exhaust gas inflow side and an end on the exhaust gas outflow side.

[0083] like Figure 1 and 6 As shown, the first substrate portion 10a and the second substrate portion 10b are respectively arranged in the exhaust passage of the exhaust pipe P such that the axial direction of the first substrate portion 10a and the second substrate portion 10b is consistent with or approximately consistent with the exhaust gas flow direction X.

[0084] As shown in Figure 1 and 6 The axial direction of the first substrate portion 10a preferably coincides or approximately coincides with the axial direction of the second substrate portion 10b.

[0085] The first substrate portion 10a and the second substrate portion 10b are integrated, and the end portion of the first substrate portion 10a on the exhaust gas outflow side is continuous with the end portion of the second substrate portion 10b on the exhaust gas inflow side. In the drawings, the boundary between the end portion of the first substrate portion 10a on the exhaust gas outflow side and the end portion of the second substrate portion 10b on the exhaust gas inflow side is indicated by the symbol S.

[0086] Hereinafter, commonalities of the first substrate portion 10a and the second substrate portion 10b will be explained in conjunction with the description of the first substrate portion 10a and the second substrate portion 10b. At this time, the expressions "substrate portions 10a, 10b", "cylindrical portions 11a, 11b", "partition wall portions 12a, 12b", "chambers 13a, 13a", and "lengths L10a, L10b" and the like are used. These expressions refer to "substrate portion 10a", "cylindrical portion 11a", "partition wall portion 12a", "chamber 13a", and "length L10a" for the first substrate portion 10a, and "substrate portion 10b", "cylindrical portion 11b", "partition wall portion 12b", "chamber 13b", and "length L10b" for the second substrate portion 10b.

[0087] The material constituting the substrate portions 10a, 10b can be appropriately selected from publicly known materials. As the material constituting the substrate portions 10a, 10b, for example, ceramic materials, metal materials, and the like can be listed, and ceramic materials are preferred. As the ceramic materials, for example, carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, and the like; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, titanium nitride, and the like; oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, magnesium titanate, and the like can be listed. As the metal materials, for example, alloys such as stainless steel and the like can be listed.

[0088] The material constituting the first substrate portion 10a and the material constituting the second substrate portion 10b are usually the same.

[0089] As shown in Figures 2 to 6 the substrate portions 10a, 10b have: cylindrical portions 11a, 11b; partition wall portions 12a, 12b provided inside the cylindrical portions 11a, 11b; and chambers 13a, 13b partitioned by the partition wall portions 12a, 12b. The substrate portions 10a, 10b are preferably honeycomb structures.

[0090] As shown in Figure 2 and 3As shown, the cylindrical portions 11a, 11b define the outer shape of the substrate portions 10a, 10b, and the axial direction of the cylindrical portions 11a, 11b coincides with the axial direction of the substrate portions 10a, 10b. As shown, Figure 2 and 3 As shown, the cylindrical portions 11a, 11b are in a cylindrical shape, but can be in an elliptical cylindrical shape, a polygonal cylindrical shape, or the like.

[0091] As shown, Figures 2 to 6 As shown, the adjacent chambers 13a, 13b are separated by the partition wall portions 12a, 12b. The partition wall portions 12a, 12b can have a porous structure through which exhaust gas can pass. The thickness of the partition wall portions 12a, 12b is, for example, 20 μm or more and 1500 μm or less.

[0092] As shown, Figure 6 As shown, the chambers 13a, 13b extend in the exhaust gas flow direction X, and have an end portion on the exhaust gas inflow side and an end portion on the exhaust gas outflow side.

[0093] As shown, Figure 6 As shown, the end portion on the exhaust gas inflow side and the end portion on the exhaust gas outflow side of the chambers 13a, 13b are each open.

[0094] As shown, Figure 6 As shown, the end portion on the exhaust gas outflow side (opening portion) of the chamber 13a and the end portion on the exhaust gas inflow side (opening portion) of the chamber 13b are continuous, so that one exhaust gas flow path extending in the exhaust gas flow direction X is formed by one chamber 13a and one chamber 13b.

[0095] Exhaust gas flowing in from the end portion on the exhaust gas inflow side (opening portion) of the chamber 13a flows out from the end portion on the exhaust gas outflow side (opening portion) of the chamber 13a. Exhaust gas flowing out from the end portion on the exhaust gas outflow side (opening portion) of the chamber 13a flows into the chamber 13b from the end portion on the exhaust gas inflow side (opening portion) of the chamber 13b, and flows out from the end portion on the exhaust gas outflow side (opening portion) of the chamber 13b. This pattern is called a flow-through type.

[0096] As shown, Figures 2 to 5 As shown, the end portion on the exhaust gas inflow side (opening portion) of the chambers 13a, 13b is in a quadrangular shape in plan view, and can be in a hexagonal shape, an octagonal shape, or the like. The same applies to the end portion on the exhaust gas outflow side (opening portion) of the chambers 13a, 13b.

[0097] The chamber density per 1 square inch of the substrate portions 10a, 10b is, for example, 100 chambers or more and 1200 chambers or less. The chamber density per 1 square inch of the substrate portions 10a, 10b refers to the total number of chambers 13a, 13b per 1 square inch in a cross section obtained by cutting the substrate portions 10a, 10b in a plane perpendicular to the exhaust gas flow direction X.

[0098] The substrate portions 10a, 10b have lengths L10a, 10b.

[0099] The volume of the substrate portions 10a, 10b is, for example, 0.1 L or more and 20 L or less. The volume of the substrate portions 10a, 10b refers to the apparent volume of the substrate portions 10a, 10b. For example, in the case where the substrate portions 10a, 10b are cylindrical, the volume of the substrate portions 10a, 10b is expressed by the formula: volume of the substrate portions 10a, 10b = π x r 2 x (length L10a, 10b) when the outer diameter of the substrate portions 10a, 10b is set to 2r.

[0100] The length L10a of the first substrate portion 10a is preferably 15% or more and 80% or less, more preferably 18% or more and 70% or less, and further preferably 20% or more and 60% or less, of the percentage (L10a / (L10a+L10b) x 100) of the length L10a of the first substrate portion 10a with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b. In one example, the length L10a of the first substrate portion 10a is 50% of the percentage (L10a / (L10a+L10b) x 100) of the length L10a of the first substrate portion 10a with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b.

[0101] The length L10b of the second substrate portion 10b is preferably 20% or more and 85% or less, more preferably 30% or more and 82% or less, and further preferably 40% or more and 80% or less, of the percentage (L10b / (L10a+L10b) x 100) of the length L10b of the second substrate portion 10b with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b. In one example, the length L10b of the second substrate portion 10b is 50% of the percentage (L10b / (L10a+L10b) x 100) of the length L10b of the second substrate portion 10b with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b.

[0102] <1st catalyst layer>

[0103] Hereinafter, the first catalyst layer 20 will be described.

[0104] As Figure 4 and 6As shown, the first catalyst layer 20 is disposed on the upstream side of the substrate 10 (i.e., the first substrate portion 10a). Specifically, the first catalyst layer 20 is disposed on the chamber 13a side surface of the partition wall portion 12a. "The chamber 13a side surface of the partition wall portion 12a" refers to the outer surface of the partition wall portion 12a extending in the exhaust gas flow direction X. The first catalyst layer 20 can be disposed directly on the chamber 13a side surface of the partition wall portion 12a, or it can be disposed in between other layers, but it is usually disposed directly on the chamber 13a side surface of the partition wall portion 12a.

[0105] The first catalyst layer 20 may be composed of a portion protruding from the chamber 13a side surface of the partition wall 12a toward the chamber 13a side (hereinafter referred to as "protruding portion"), or it may be composed of a portion existing inside the partition wall 12a (hereinafter referred to as "inner portion"), or it may have both a protruding portion and an inner portion. Embodiments in which the first catalyst layer 20 is composed of a protruding portion, embodiments in which the first catalyst layer 20 is composed of an inner portion, and embodiments in which the first catalyst layer 20 has both a protruding portion and an inner portion are all included in "the first catalyst layer 20 disposed on the upstream side of the substrate 10".

[0106] like Figure 6 As shown, the first catalyst layer 20 extends along the exhaust gas flow direction X from the end of the partition wall 12a on the exhaust gas inflow side to the end of the partition wall 12a on the exhaust gas outflow side. The first catalyst layer 20 may also extend along the exhaust gas flow direction X from the end of the partition wall 12a on the exhaust gas inflow side without reaching the end of the partition wall 12a on the exhaust gas outflow side, or it may extend in a direction opposite to the exhaust gas flow direction X from the end of the partition wall 12a on the exhaust gas outflow side without reaching the end of the partition wall 12a on the exhaust gas inflow side.

[0107] From the viewpoint of more effectively achieving an increase in the warm-up properties of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is formed (the mass after firing), that is, the mass of the first catalyst layer 20 per unit volume of the portion of the first substrate portion 10a in which the first catalyst layer 20 is formed (the mass after firing) is preferably 60 g / L or greater and 200 g / L or less, more preferably 70 g / L or greater and 175 g / L or less, further preferably 80 g / L or greater and 150 g / L or less, further preferably 90 g / L or greater and 125 g / L or less. The mass of the first catalyst layer 20 per unit volume of the portion of the first substrate portion 10a in which the first catalyst layer 20 is formed is calculated according to the formula: (mass of the first catalyst layer 20) / ((volume of the first substrate portion 10a) x (average length L20 of the first catalyst layer 20 / length L10a of the first substrate portion 10a)). The "length" refers to the dimension in the axial direction of the first substrate portion 10a.

[0108] In the present specification, the "mass of the first catalyst layer 20" refers to the mass obtained by adding the mass in metal equivalent of the noble metal elements and the mass in oxide equivalent of the metal elements other than the noble metal elements contained in the first catalyst layer 20. That is, the "mass of the first catalyst layer 20" refers to the calculated mass obtained by adding the mass in metal equivalent of the noble metal elements contained in the first catalyst layer 20 and the mass in oxide equivalent of the metal elements other than the noble metal elements contained in the first catalyst layer 20. Note that the "metal elements" also include semimetal elements such as Si and B.

[0109] In the present specification, the "noble metal elements" include Pt (platinum element), Pd (palladium element), Rh (rhodium element), Ru (ruthenium element), Os (osmium element), Ir (iridium element), Au (gold), and Ag (silver).

[0110] The meaning of "oxide" is as described in the "Explanation of Terms" column described above.

[0111] An example of a method for measuring the average length L20 of the first catalyst layer 20 is as follows.

[0112] A sample extending in the axial direction of the first substrate portion 10a and having the same length as the length L10a of the first substrate portion 10a was cut out from the catalyst 1A. The sample was, for example, a cylindrical shape having a diameter of 25.4 mm. The value of the diameter of the sample can be changed as needed. In the case where the first catalyst layer 20 extends along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side, the sample was cut at intervals of 5 mm by a plane perpendicular to the axial direction of the first substrate portion 10a, and the first slice, the second slice, ···, the nth slice were obtained in order from the end portion on the exhaust gas inflow side of the sample. In the case where the first catalyst layer 20 extends in the direction opposite to the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas outflow side, the sample was cut at intervals of 5 mm by a plane perpendicular to the axial direction of the first substrate portion 10a, and the first slice, the second slice, ···, the nth slice were obtained in order from the end portion on the exhaust gas outflow side of the sample. In either case, the length of the slice was 5 mm. The composition of the slice was analyzed using a fluorescent X-ray analysis device (XRF) (for example, an energy dispersive X-ray analysis device (EDX), a wavelength dispersive X-ray analysis device (WDX), or the like), an inductively coupled plasma emission spectrometry device (ICP-AES), a scanning electron microscope-energy dispersive X-ray analysis method (SEM-EDX), or the like, and it was confirmed from the composition of the slice whether the slice contained the partial first catalyst layer 20.

[0113] For the slice containing the partial first catalyst layer 20, it is not necessarily required to perform the composition analysis. For example, it can be confirmed from the observation of the cross section using a scanning electron microscope (SEM), an electron probe micro-analyzer (EPMA), or the like whether the slice contains the partial first catalyst layer 20. At the time of the observation of the cross section, element mapping of the cross section can be performed.

[0114] After it was confirmed whether the slice contained the partial first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample was calculated according to the following formula.

[0115] Length of the first catalyst layer 20 contained in the sample = 5 mm x (number of slices containing the partial first catalyst layer 20)

[0116] For example, in the case where the first slice to the kth slice contain the partial first catalyst layer 20 and the (k+1)th to the nth slice do not contain the partial first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is (5 x k) mm.

[0117] An example of a more detailed method for measuring the length of the first catalyst layer 20 contained in the sample is as follows.

[0118] The length of the partial 1st catalyst layer 20 in the kth slice was measured by cutting the kth slice along the axial direction of the 1st substrate portion 10a and observing the partial 1st catalyst layer 20 present in the cross section using an SEM, EPMA, or the like, and the length of the 1st catalyst layer 20 contained in the sample was calculated according to the following equation.

[0119] Length of the 1st catalyst layer 20 contained in the sample = (5 mm x (k - 1)) + (length of the partial 1st catalyst layer 20 contained in the kth slice)

[0120] The length of the 1st catalyst layer 20 contained in each of the 8 to 16 samples cut from the catalyst 1A was measured, and the average value thereof was set as the average length L20 of the 1st catalyst layer 20.

[0121] From the viewpoint of more effectively achieving the improvement in the temperature rising properties of the 1st catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of an internal combustion engine, the percentage of the average length L20 of the 1st catalyst layer 20 with respect to the length L10a of the 1st substrate portion 10a (L20 / L10a x 100) is preferably 80% or greater, more preferably 90% or greater, and further preferably 95% or greater. The upper limit can be 100% or can exceed 100%. As described later, in the case where the end portion on the exhaust gas outflow side of the 1st catalyst layer 20 has a portion overlapping with the end portion on the exhaust gas inflow side of the 2nd catalyst layer 30, the percentage can exceed 100%. In the case where the percentage exceeds 100%, the upper limit of the percentage is preferably 600% or less, more preferably 400% or less, and further preferably 300% or less. Note that in the case where the 1st substrate portion 10a and the 2nd substrate portion 10b are integrated, and in the case where the 1st substrate portion 10a and the 2nd substrate portion 10b are separate and the end portion on the exhaust gas outflow side of the 1st substrate portion 10a contacts the end portion on the exhaust gas inflow side of the 2nd substrate portion 10b, the percentage can exceed 100%, but in the case where the 1st substrate portion 10a and the 2nd substrate portion 10b are separate and a gap is formed between the end portion on the exhaust gas outflow side of the 1st substrate portion 10a and the end portion on the exhaust gas inflow side of the 2nd substrate portion 10b, the percentage does not exceed 100%.

[0122] From the viewpoint of more effectively achieving an increase in the temperature rising property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, the percentage of the average length L20 of the first catalyst layer 20 with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L20 / (L10a+L10b) x 100) is preferably 15% or greater and 80% or less, more preferably 18% or greater and 70% or less, and further preferably 20% or greater and 60% or less.

[0123] The first catalyst layer 20 contains one or two or more kinds of noble metal elements as a catalytically active component. The noble metal elements can be selected from, for example, Pd, Pt, Rh, Au, Ag, Ir, Ru, Os, and the like. The noble metal elements are contained in the first catalyst layer 20 in a form in which they can function as a catalytically active component, such as a metal, an alloy containing a noble metal element, a compound containing a noble metal element (for example, an oxide of a noble metal element), and the like. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing a noble metal element is preferably particulate.

[0124] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the content of the noble metal elements in the first catalyst layer 20, on a metal conversion basis, with respect to the mass of the first catalyst layer 20 is preferably 0.1% by mass or greater and 10% by mass or less, more preferably 0.2% by mass or greater and 9% by mass or less, and further preferably 0.3% by mass or greater and 8% by mass or less. With respect to the "content of the noble metal elements in the first catalyst layer 20, on a metal conversion basis", when the first catalyst layer 20 contains one kind of noble metal element, it refers to the content of the one kind of noble metal element, on a metal conversion basis, and when the first catalyst layer 20 contains two or more kinds of noble metal elements, it refers to the total content of the two or more kinds of noble metal elements, on a metal conversion basis.

[0125] The first catalyst layer 20 preferably contains Pd and / or Pt.

[0126] Since the first catalyst layer 20 is disposed more upstream than the second catalyst layer 30, there is a tendency that the temperature of the exhaust gas that the first catalyst layer 20 contacts is higher than the temperature of the exhaust gas that the second catalyst layer 30 contacts. Therefore, the first catalyst layer 20 preferably contains Pd. This is because Pd has excellent heat resistance. In addition to Pd, the first catalyst layer 20 can contain Pt.

[0127] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pd in the first catalyst layer 20, on a metal conversion basis, is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 9% by mass or less, and further preferably 0.3% by mass or more and 8% by mass or less, based on the mass of the first catalyst layer 20.

[0128] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pt in the first catalyst layer 20, on a metal conversion basis, is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 9% by mass or less, and further preferably 0.3% by mass or more and 8% by mass or less, based on the mass of the first catalyst layer 20.

[0129] The content of each metal element in the first catalyst layer 20, on a metal conversion basis, is calculated according to the formula: (mass of each metal element in the first catalyst layer 20 on a metal conversion basis) / (mass of the first catalyst layer 20) x 100. For example, the content of Pd in the first catalyst layer 20, on a metal conversion basis, is calculated according to the formula: (mass of Pd in the first catalyst layer 20 on a metal conversion basis) / (mass of the first catalyst layer 20) x 100.

[0130] In the case where the composition of the raw material for forming the first catalyst layer 20 is known, the content of each metal element in the first catalyst layer 20, on a metal conversion basis, can be calculated from the composition of the raw material for forming the first catalyst layer 20.

[0131] In the case where the composition of the raw material for forming the first catalyst layer 20 is unknown, the content of each metal element in the first catalyst layer 20, on a metal conversion basis, can be calculated by a conventional method such as SEM-EDX. Details are as follows.

[0132] For a sample obtained from the first catalyst layer 20, elemental analysis is performed using a conventional method such as SEM-EDX, the types of constituent elements of the entire sample are determined, and the content (mass %) of each metal element thus determined is calculated. For each of 10 fields of view of SEM, the content (mass %) of each metal element is calculated, and the average of the content (mass %) of each metal element in the 10 fields of view is taken as the content (mass %) of each metal element in the first catalyst layer 20.

[0133] The first catalyst layer 20 contains a Ce-Zr-based composite oxide. The Ce-Zr-based composite oxide has an oxygen storage capacity. Therefore, by causing the first catalyst layer 20 to contain a Ce-Zr-based composite oxide, the exhaust gas purification performance of the catalyst 1A can be sufficiently exhibited even if the oxygen concentration in the exhaust gas fluctuates.

[0134] From the viewpoint of improving the heat resistance and oxygen storage capacity of the Ce-Zr-based composite oxide, the total content of Ce and Zr in the Ce-Zr-based composite oxide, based on the mass of the Ce-Zr-based composite oxide, is preferably 70% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, and further preferably 85% by mass or more. The upper limit is 100% by mass.

[0135] From the viewpoint of improving the oxygen storage capacity of the Ce-Zr-based composite oxide, the content of Ce in the Ce-Zr-based composite oxide, based on the mass of the Ce-Zr-based composite oxide, is preferably 5% by mass or more and 95% by mass or less, more preferably 5% by mass or more and 90% by mass or less, further preferably 7% by mass or more and 90% by mass or less, and further preferably 10% by mass or more and 85% by mass or less.

[0136] From the viewpoint of improving the heat resistance of the Ce-Zr-based composite oxide, the content of Zr in the Ce-Zr-based composite oxide, based on the mass of the Ce-Zr-based composite oxide, is preferably 5% by mass or more and 95% by mass or less, more preferably 5% by mass or more and 90% by mass or less, further preferably 7% by mass or more and 90% by mass or less, and further preferably 10% by mass or more and 85% by mass or less.

[0137] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the content of the Ce-Zr-based composite oxide in the first catalyst layer 20, based on the mass of the first catalyst layer 20, is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and further preferably 80% by mass or more. The upper limit can be appropriately adjusted in consideration of the content of other components in the first catalyst layer 20, and the like. The content of the Ce-Zr-based composite oxide in the first catalyst layer 20, based on the mass of the first catalyst layer 20, can be adjusted to, for example, 99% by mass or less, 95% by mass or less, 93% by mass or less, or 90% by mass or less. These upper limits can each be combined with any of the above lower limits.

[0138] When the composition of the raw material for forming the first catalyst layer 20 is known, the content of the Ce-Zr-based composite oxide in the first catalyst layer 20 can be found from the composition of the raw material for forming the first catalyst layer 20.

[0139] When the composition of the raw material for forming the first catalyst layer 20 is unknown, the content of the Ce-Zr-based composite oxide in the first catalyst layer 20 can be found by a conventional method such as SEM-EDX. Details are as follows.

[0140] (1) For the sample obtained from the first catalyst layer 20, element analysis is performed using a conventional method such as SEM-EDX to determine the types of constituent elements of the entire sample, and the content rates (mass %) of the determined elements are calculated.

[0141] (2) For the sample obtained from the first catalyst layer 20, element mapping is performed using a conventional method such as SEM-EDX to determine the types of particles (e.g., Ce-Zr-based composite oxide particles and optional other particles) contained in the sample.

[0142] (3) For each type of particle, element analysis is performed by SEM-EDX on a plurality of (e.g., 50) arbitrarily selected particles to determine the types of constituent elements of the particles, and the content rates (mass %) of the determined elements are calculated. For each type of particle, the average value of the content rates (mass %) of the elements is calculated.

[0143] (4) By establishing and solving an equation representing the relationship between the content rates (mass %) of the elements in the sample, the content rates (mass %) of the elements in each type of particle, and the content rates (mass %) of each type of particle in the sample, the content rates (mass %) of each type of particle in the sample are calculated, and are set as the content rates (mass %) of each type of particle in the first catalyst layer 20.

[0144] The first catalyst layer 20 can contain AI2O3.

[0145] In the case where the first catalyst layer 20 contains AI2O3, the first catalyst layer 20 contains one or two or more AI2O3 sources. The AI2O3 source is not particularly limited as long as it is an Al-containing oxide. The AI2O3 source can be selected from, for example, an Al-based oxide, an Al-containing Ce-based oxide, an Al-containing Ce-Zr-based composite oxide, an alumina binder, and the like.

[0146] In one embodiment, the first catalyst layer 20 contains an alumina binder as the AI2O3 source. The first catalyst layer 20 can contain only the alumina binder as the AI2O3 source, and can also contain one or two or more AI2O3 sources other than the alumina binder as the AI2O3 source.

[0147] From the viewpoint of more effectively achieving the improvement of the warm-up property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, the Al2O3-conversion rate content of Al in the first catalyst layer 20 is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 3% by mass or less, based on the mass of the first catalyst layer 20. The lower limit can be appropriately adjusted in consideration of the content of other components in the first catalyst layer 20, and the like. The Al2O3-conversion rate content of Al in the first catalyst layer 20 can be, for example, 0% by mass, or 0.1% by mass or more, 1% by mass or more, or 2% by mass or more, based on the mass of the first catalyst layer 20. These lower limits can each be combined with any of the above upper limits. With respect to the "Al2O3-conversion rate content of Al in the first catalyst layer 20", when the first catalyst layer 20 contains one Al2O3 source, it refers to the Al2O3-conversion rate content of Al from the one Al2O3 source, and when the first catalyst layer 20 contains two or more Al2O3 sources, it refers to the total Al2O3-conversion rate content of Al from the two or more Al2O3 sources.

[0148] When the composition of the raw material for forming the first catalyst layer 20 is known, the Al2O3-conversion rate content of Al in the first catalyst layer 20 can be calculated from the composition of the raw material for forming the first catalyst layer 20.

[0149] When the composition of the raw material for forming the first catalyst layer 20 is unknown, the Al2O3-conversion rate content of Al in the first catalyst layer 20 can be calculated by a conventional method such as SEM-EDX. Details are as follows.

[0150] For a sample obtained from the first catalyst layer 20, elemental analysis is performed using a conventional method such as SEM-EDX, the types of constituent elements of the entire sample are determined, and the Al2O3-conversion rate content of Al (mass%) is calculated. For each of 10 fields of view of the SEM, the Al2O3-conversion rate content of Al (mass%) is calculated, and the average of the Al2O3-conversion rate contents of Al (mass%) in the 10 fields of view is taken as the Al2O3-conversion rate content of Al (mass%) in the first catalyst layer 20.

[0151] The first catalyst layer 20 can further contain one or two or more carriers other than the Ce-Zr-based composite oxide.

[0152] The carrier other than the Ce-Zr-based composite oxide can be selected from, for example, inorganic oxides other than the Ce-Zr-based composite oxide. The inorganic oxides other than the Ce-Zr-based composite oxide are, for example, in the form of particles. From the viewpoint of improving the loading of the catalytically active component, the inorganic oxides other than the Ce-Zr-based composite oxide are preferably porous. In the case where the first catalyst layer 20 contains an inorganic oxide other than the Ce-Zr-based composite oxide as the carrier, the inorganic oxide can or can not have oxygen storage capacity. In the present specification, the inorganic oxide having oxygen storage capacity (OSC: Oxygen Storage Capacity) is sometimes referred to as an "OSC material".

[0153] The inorganic oxide other than the Ce-Zr-based composite oxide used as the carrier is distinguished from the inorganic oxide used as the binder (for example, an inorganic oxide-based binder such as an alumina binder, a zirconia binder, a titania binder, a silica binder, and the like).

[0154] As the inorganic oxide other than the Ce-Zr-based composite oxide used as the carrier, for example, an Al-based oxide, a Ce-based oxide, an oxide of a rare earth element other than Ce, zirconia (Zr02), silica (Si02), titania (Ti02), a zeolite (aluminosilicate), an oxide based on MgO, ZnO, Sn02, and the like can be given.

[0155] At least a part of the catalytically active component is preferably supported on the Ce-Zr-based composite oxide. In the case where the first catalyst layer 20 contains a carrier other than the Ce-Zr-based composite oxide, at least a part of the catalytically active component can also be supported on the carrier other than the Ce-Zr-based composite oxide.

[0156] The "at least a part of the catalytically active component is supported on the carrier" means that at least a part of the catalytically active component is physically and / or chemically adsorbed or held on the outer surface and / or the inner surface of the pores of the carrier. The fact that at least a part of the catalytically active component is supported on the carrier can be confirmed, for example, using SEM-EDX or the like. Specifically, when at least a part of the catalytically active component and the carrier exist in the same region in an element map obtained by analyzing the cross section of the first catalyst layer 20 using SEM-EDX, it can be determined that at least a part of the catalytically active component is supported on the carrier.

[0157] The first catalyst layer 20 can further contain a binder, a stabilizer, and the like. As the binder, for example, an inorganic oxide-based binder such as alumina sol, ceria sol, zirconia sol, titania sol, silica sol, and the like can be given. As the stabilizer, for example, a nitrate, a carbonate, an oxide, a sulfate, and the like of an alkaline earth metal element (for example, Sr, Ba, and the like) can be given.

[0158] Ce in the components in the 1st catalyst layer 20 is mainly related to the oxygen storage capacity. Therefore, from the viewpoint of sufficiently exerting the exhaust gas purification performance of the catalyst 1A even if the oxygen concentration in the exhaust gas varies, the CeO2-conversion rate content of Ce in the 1st catalyst layer 20 is preferably 32% by mass or more, more preferably 35% by mass or more, based on the mass of the 1st catalyst layer 20. The upper limit can be appropriately adjusted in consideration of the content of other components in the 1st catalyst layer 20, etc. The CeO2-conversion rate content of Ce in the 1st catalyst layer 20 can be adjusted to, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the mass of the 1st catalyst layer 20. These upper limits can each be combined with any one of the above lower limits. The "CeO2-conversion rate content of Ce in the 1st catalyst layer 20" refers to the CeO2-conversion rate content of Ce from one kind of Ce source when the 1st catalyst layer 20 contains one kind of Ce source, and refers to the total CeO2-conversion rate content of Ce from two or more kinds of Ce sources when the 1st catalyst layer 20 contains two or more kinds of Ce sources.

[0159] The Ce source is not particularly limited as long as it is a Ce-containing oxide. The 1st catalyst layer 20 contains a Ce-Zr-based composite oxide as the Ce source. The 1st catalyst layer 20 can contain one or two or more kinds of Ce sources other than the Ce-Zr-based composite oxide. The Ce source other than the Ce-Zr-based composite oxide can be selected from, for example, a Ce-containing Al-based oxide, a Ce oxide, a ceria binder, etc.

[0160] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the proportion of the CeO2-conversion rate mass of Ce from the Ce-Zr-based composite oxide in the CeO2-conversion rate mass of Ce in the 1st catalyst layer 20 is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, further preferably 90% by mass or more. The upper limit is 100% by mass.

[0161] When the composition of the raw material for forming the 1st catalyst layer 20 is known, the CeO2-conversion rate content of Ce in the 1st catalyst layer 20 can be calculated from the composition of the raw material for forming the 1st catalyst layer 20.

[0162] When the composition of the raw material for forming the 1st catalyst layer 20 is unknown, the CeO2-conversion rate content of Ce in the 1st catalyst layer 20 can be calculated by a conventional method such as SEM-EDX. Details are as follows.

[0163] For the sample obtained from the 1st catalyst layer 20, the kind of constituent elements of the sample as a whole was determined by elemental analysis using a conventional method such as SEM-EDX, and the CeO2-converted content (mass %) of Ce was calculated. For each of 10 fields of view of SEM, the CeO2-converted content (mass %) of Ce was calculated, and the average of the CeO2-converted contents (mass %) of Ce in the 10 fields of view was taken as the CeO2content (mass %) of Ce in the 1st catalyst layer 20.

[0164] <2nd catalyst layer>

[0165] Hereinafter, the 2nd catalyst layer 30 will be described.

[0166] As shown in Figure 5 and 6 , the 2nd catalyst layer 30 is provided on the downstream side of the substrate 10 (i.e., the 2nd substrate portion 10b). Specifically, the 2nd catalyst layer 30 is provided on the chamber 13b side surface of the partition wall portion 12b. The "chamber 13b side surface of the partition wall portion 12b" refers to the outer surface of the partition wall portion 12b extending in the exhaust gas flow direction X. The 2nd catalyst layer 30 can be directly provided on the chamber 13b side surface of the partition wall portion 12b, or can be provided with other layers interposed therebetween, and is typically directly provided on the chamber 13b side surface of the partition wall portion 12b.

[0167] The 2nd catalyst layer 30 can be composed of a portion (hereinafter referred to as "protruding portion") protruding from the chamber 13b side surface of the partition wall portion 12b toward the chamber 13b side, can be composed of a portion (hereinafter referred to as "intrinsic portion") present inside the partition wall portion 12b, or can have both the protruding portion and the intrinsic portion. The embodiment in which the 2nd catalyst layer 30 is composed of the protruding portion, the embodiment in which the 2nd catalyst layer 30 is composed of the intrinsic portion, and the embodiment in which the 2nd catalyst layer 30 has both the protruding portion and the intrinsic portion are all included in the "2nd catalyst layer 30 provided on the downstream side of the substrate 10".

[0168] As shown in Figure 6 , the 2nd catalyst layer 30 extends from the end portion of the partition wall portion 12b on the exhaust gas outflow side to the end portion of the partition wall portion 12b on the exhaust gas inflow side in a direction opposite to the exhaust gas flow direction X. The 2nd catalyst layer 30 can also extend from the end portion of the partition wall portion 12b on the exhaust gas outflow side to the end portion of the partition wall portion 12b on the exhaust gas inflow side in a direction opposite to the exhaust gas flow direction X without reaching the end portion of the partition wall portion 12b on the exhaust gas inflow side, or can extend from the end portion of the partition wall portion 12b on the exhaust gas inflow side to the end portion of the partition wall portion 12b on the exhaust gas outflow side in the exhaust gas flow direction X without reaching the end portion of the partition wall portion 12b on the exhaust gas outflow side.

[0169] As shown in Figure 6As shown, the second catalyst layer 30 is disposed downstream of the first catalyst layer 20. "The second catalyst layer 30 is disposed downstream of the first catalyst layer 20" means that the second catalyst layer 30 exists in a region further downstream of the exhaust gas flow direction X than the region where the first catalyst layer 20 is disposed.

[0170] like Figure 6 As shown, the end of the second catalyst layer 30 on the exhaust gas inflow side contacts the end of the first catalyst layer 20 on the exhaust gas outflow side at boundary S. Figure 6 As shown, the boundary S between the end of the first catalyst layer 20 on the exhaust gas outflow side and the end of the second catalyst layer 30 on the exhaust gas inflow side coincides with the boundary S between the end of the first substrate portion 10a on the exhaust gas outflow side and the end of the second substrate portion 10b on the exhaust gas inflow side.

[0171] The exhaust gas inflow end of the second catalyst layer 30 may also have a portion overlapping the exhaust gas outflow end of the first catalyst layer 20 (i.e., a portion located above and covering the exhaust gas outflow end of the first catalyst layer 20). Additionally, the exhaust gas outflow end of the first catalyst layer 20 may also have a portion overlapping the exhaust gas inflow end of the second catalyst layer 30 (i.e., a portion located above and covering the exhaust gas inflow end of the second catalyst layer 30). These conditions are also included in the description of "the second catalyst layer 30 being disposed downstream of the first catalyst layer 20".

[0172] The end of the second catalyst layer 30 on the exhaust gas inflow side may not be in contact with the end of the first catalyst layer 20 on the exhaust gas outflow side. That is, a gap may be formed between the end of the first catalyst layer 20 on the exhaust gas outflow side and the end of the second catalyst layer 30 on the exhaust gas inflow side.

[0173] From the viewpoint of more effectively achieving the suppression of the decrease in the dispersibility of the catalytically active component after exposure to a high-temperature environment when the environment in which the catalyst 1A is placed is a high-temperature environment at the time of high-speed operation of an internal combustion engine, the mass of the second catalyst layer 30 per unit volume of the portion of the second substrate 10 in which the second catalyst layer 30 is formed (mass after firing), that is, the mass of the second catalyst layer 30 per unit volume of the portion of the second substrate portion 10b in which the second catalyst layer 30 is formed (mass after firing) is preferably 60 g / L or greater and 200 g / L or less, more preferably 80 g / L or greater and 200 g / L or less, and further preferably 100 g / L or greater and 190 g / L or less. The mass of the second catalyst layer 30 per unit volume of the portion of the second substrate portion 10b in which the second catalyst layer 30 is formed is calculated according to the formula: (mass of the second catalyst layer 30) / ((volume of the second substrate portion 10b) x (average length L30 of the second catalyst layer 30 / length L10b of the second substrate portion 10b)). The "length" refers to the dimension in the axial direction of the second substrate portion 10b.

[0174] The above description regarding the mass of the first catalyst layer 20 also applies to the mass of the second catalyst layer 30. When applicable, replace "first catalyst layer 20" with "second catalyst layer 30".

[0175] The above description regarding the measurement method of the average length L20 of the first catalyst layer 20 also applies to the measurement method of the average length L30 of the second catalyst layer 30. When applicable, replace "first catalyst layer 20" with "second catalyst layer 30" and replace "average length L20" with "average length L30".

[0176] From the viewpoint of more effectively achieving the suppression of the decrease in the dispersibility of the catalytically active component after exposure to a high-temperature environment when the environment in which the catalyst 1A is placed is a high-temperature environment at the time of high-speed operation of the internal combustion engine, the percentage of the average length L30 of the second catalyst layer 30 with respect to the length L10b of the second substrate portion 10b (L30 / L10b x 100) is preferably 80% or greater, more preferably 90% or greater, and further preferably 95% or greater. The upper limit can be 100% or can exceed 100%. As described above, in the case where the end portion of the second catalyst layer 30 on the exhaust gas inflow side has a portion overlapping with the end portion of the first catalyst layer 20 on the exhaust gas outflow side, the percentage can exceed 100%. In the case where the percentage exceeds 100%, the upper limit of the percentage is preferably 500% or less, more preferably 350% or less, and further preferably 200% or less. Note that, in the case where the first substrate portion 10a and the second substrate portion 10b are integrated, and in the case where the first substrate portion 10a and the second substrate portion 10b are separate and the end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b are in contact with each other, the percentage can exceed 100%, but in the case where the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b, the percentage is 100% or less.

[0177] From the viewpoint of more effectively achieving the suppression of the decrease in the dispersibility of the catalytically active component after exposure to a high-temperature environment when the environment in which the catalyst 1A is placed is a high-temperature environment at the time of high-speed operation of the internal combustion engine, the percentage of the average length L30 of the second catalyst layer 30 with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L30 / (L10a+L10b) x 100) is preferably 20% or greater and 95% or less, more preferably 30% or greater and 92% or less, and further preferably 40% or greater and 90% or less.

[0178] From the viewpoint of more effectively achieving the increase in the temperature rising property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the percentage of the sum of the average length L20 of the first catalyst layer 20 and the average length L30 of the second catalyst layer 30 with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b ((L20 and L30) / (L10a + L10b) x 100) is preferably 35% or greater, more preferably 48% or greater, and further preferably 60% or greater. The upper limit can be 100% or more. As described above, in the case where the end portion on the exhaust gas outflow side of the first catalyst layer 20 has a portion overlapping with the end portion on the exhaust gas inflow side of the second catalyst layer 30, and in the case where the end portion on the exhaust gas inflow side of the second catalyst layer 30 has a portion overlapping with the end portion on the exhaust gas outflow side of the first catalyst layer 20, the percentage can exceed 100%. The upper limit of the percentage is preferably 175% or less, more preferably 162% or less, and further preferably 150% or less. Note that in the case where the first substrate portion 10a and the second substrate portion 10b are integrated, and in the case where the first substrate portion 10a and the second substrate portion 10b are separate and the end portion on the exhaust gas outflow side of the first substrate portion 10a is in contact with the end portion on the exhaust gas inflow side of the second substrate portion 10b, the percentage can exceed 100%, but in the case where the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b, the percentage is 100% or less.

[0179] From the viewpoint of more effectively achieving the increase in the temperature rising property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the ratio of the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is formed (i.e., the mass of the first catalyst layer 20 per unit volume of the portion of the first substrate portion 10a in which the first catalyst layer 20 is formed) with respect to the mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 in which the second catalyst layer 30 is formed (i.e., the mass of the second catalyst layer 30 per unit volume of the portion of the second substrate portion 10b in which the second catalyst layer 30 is formed) is preferably 0.95 or less, more preferably 0.93 or less, and further preferably 0.90 or less. From this viewpoint, the ratio is preferably 0.30 or more, and more preferably 0.40 or more. These lower limits can each be combined with any of the above upper limits.

[0180] From the viewpoint of more effectively achieving the improvement in the temperature rising property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the ratio of the average length L20 of the first catalyst layer 20 to the average length L30 of the second catalyst layer 30 is preferably 1.0 or less, more preferably 0.8 or less, and further preferably 0.7 or less. From this viewpoint, the ratio is preferably 0.3 or more, more preferably 0.4 or more, and further preferably 0.5 or more. These lower limits can each be combined with any of the above upper limits.

[0181] The second catalyst layer 30 contains one or two or more kinds of noble metal elements as catalytically active components. The noble metal elements can be selected from, for example, Pd, Pt, Rh, Au, Ag, Ir, Ru, Os, and the like. The noble metal elements are contained in the second catalyst layer 30 in a form in which they can function as catalytically active components, such as a metal, an alloy containing a noble metal element, a compound containing a noble metal element (for example, an oxide of a noble metal element), and the like. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing a noble metal element is preferably particulate.

[0182] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the content of the noble metal elements in the second catalyst layer 30, on a metal conversion basis, is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 4% by mass or less, and further preferably 0.03% by mass or more and 3% by mass or less, based on the mass of the second catalyst layer 30. With respect to the "content of the noble metal elements in the second catalyst layer 30, on a metal conversion basis", when the second catalyst layer 30 contains one kind of noble metal element, it refers to the content of the one kind of noble metal element, on a metal conversion basis, and when the second catalyst layer 30 contains two or more kinds of noble metal elements, it refers to the total content of the two or more kinds of noble metal elements, on a metal conversion basis.

[0183] The second catalyst layer 30 preferably contains Pd and / or Pt.

[0184] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the content of Pd in the second catalyst layer 30, on a metal conversion basis, is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 4% by mass or less, and further preferably 0.03% by mass or more and 3% by mass or less, based on the mass of the second catalyst layer 30.

[0185] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pt in the second catalyst layer 30, on a metal basis, is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.02 mass% or more and 4 mass% or less, and further preferably 0.03 mass% or more and 3 mass% or less, based on the mass of the second catalyst layer 30.

[0186] The content of each metal element in the second catalyst layer 30, on a metal basis, is calculated according to the formula: (mass of each metal element in the second catalyst layer 30 on a metal basis) / (mass of the second catalyst layer 30) x 100. For example, the content of Pd in the second catalyst layer 30, on a metal basis, is calculated according to the formula: (mass of Pd in the second catalyst layer 30 on a metal basis) / (mass of the second catalyst layer 30) x 100.

[0187] The content of each metal element in the second catalyst layer 30, on a metal basis, can be calculated in the same manner as the content of each metal element in the first catalyst layer 20, on a metal basis.

[0188] The second catalyst layer 30 contains Al2O3. Therefore, the second catalyst layer 30 contains one or two or more Al2O3 sources.

[0189] The Al2O3 source is not particularly limited as long as it is an Al-containing oxide. The Al2O3 source can be selected from, for example, an Al-based oxide, an Al-containing Ce-based oxide, an Al-containing Ce-Zr-based composite oxide, an alumina binder, and the like.

[0190] The second catalyst layer 30 preferably contains an Al-based oxide as the Al2O3 source. In addition to the Al-based oxide, the second catalyst layer 30 can contain one or two or more other Al2O3 sources. In one embodiment, the second catalyst layer 30 contains an Al-based oxide and an alumina binder as the Al2O3 sources.

[0191] From the viewpoint of more effectively achieving the suppression of the decrease in the dispersibility of the catalytically active component after exposure to a high-temperature environment required when the environment in which catalyst 1A is placed is a high-temperature environment at the time of high-speed operation of the internal combustion engine, the Al2O3-conversion rate content of Al in the second catalyst layer 30 is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, and further preferably 10% by mass or more, based on the mass of the second catalyst layer 30. The upper limit can be appropriately adjusted in consideration of the content of other components in the second catalyst layer 30, etc. The Al2O3-conversion rate content of Al in the second catalyst layer 30 is, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the mass of the second catalyst layer 30. These upper limits can each be combined with any of the above lower limits. With respect to the "Al2O3-conversion rate content of Al in the second catalyst layer 30", when the second catalyst layer 30 contains one Al2O3 source, it refers to the Al2O3-conversion rate content of Al from the one Al2O3 source, and when the second catalyst layer 30 contains two or more Al2O3 sources, it refers to the total Al2O3-conversion rate content of Al from the two or more Al2O3 sources.

[0192] From the viewpoint of more effectively achieving the suppression of the decrease in the dispersibility of the catalytically active component after exposure to a high-temperature environment required when the environment in which catalyst 1A is placed is a high-temperature environment at the time of high-speed operation of the internal combustion engine, the proportion of the Al2O3-conversion rate mass of Al from Al-based oxides in the Al2O3-conversion rate mass of Al in the second catalyst layer 30 is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and further preferably 90% by mass or more. The upper limit is 100% by mass.

[0193] The Al2O3-conversion rate content of Al in the second catalyst layer 30 can be calculated in the same manner as the Al2O3-conversion rate content of Al in the first catalyst layer 20.

[0194] The effect of Al2O3 in the second catalyst layer 30 is to suppress a decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment, and therefore the mass content of the noble metal element in the second catalyst layer 30 in terms of metal is preferably adapted to the mass content of Al in the second catalyst layer 30 in terms of Al2O3. That is, from the perspective of more effectively achieving the suppression of a decrease in the dispersion of the catalytically active component after exposure to a high-temperature environment when the environment in which the catalyst 1A is disposed is a high-temperature environment at the time of high-speed operation of the internal combustion engine, the ratio of the mass content of Al in the second catalyst layer 30 in terms of Al2O3 to the mass content of the noble metal element in the second catalyst layer 30 in terms of metal is preferably 50 or greater and 600 or less, more preferably 100 or greater and 500 or less, further preferably 120 or greater and 400 or less, and further preferably 150 or greater and 250 or less.

[0195] The second catalyst layer 30 preferably contains one or two or more carriers. The carrier can be selected from, for example, a Ce-Zr-based composite oxide and an inorganic oxide other than a Ce-Zr-based composite oxide (e.g., an Al-based oxide, etc.). The description of the Ce-Zr-based composite oxide and the inorganic oxide other than a Ce-Zr-based composite oxide is the same as described above.

[0196] The second catalyst layer 30 preferably contains an Al-based oxide as a carrier. Note that the Al-based oxide also belongs to the Al2O3 source. The second catalyst layer 30 can also contain one or two or more carriers other than an Al-based oxide. In one embodiment, the second catalyst layer 30 contains an Al-based oxide and an OSC material as carriers. The OSC material can be selected from, for example, a Ce-based oxide, a Ce-Zr-based composite oxide, etc., and is preferably a Ce-Zr-based composite oxide.

[0197] At least a portion of the catalytically active component is preferably supported on the carrier. In the case where the second catalyst layer 30 contains an Al-based oxide, at least a portion of the catalytically active component is preferably supported on the Al-based oxide. In the case where the second catalyst layer 30 contains a carrier other than an Al-based oxide, at least a portion of the catalytically active component is preferably supported on the carrier other than an Al-based oxide. The meaning and confirmation method of "at least a portion of the catalytically active component is supported on the carrier" are the same as described above.

[0198] The second catalyst layer 30 can also contain a binder, a stabilizer, etc. As the binder, an inorganic oxide-based binder such as alumina sol, ceria sol, zirconia sol, titania sol, silica sol, etc. can be cited. As the stabilizer, a nitrate, carbonate, oxide, sulfate, etc. of an alkaline earth metal element (e.g., Sr, Ba, etc.) can be cited.

[0199] In the second catalyst layer 30, Ce is mainly related to oxygen storage capacity. Therefore, from the perspective of improving the exhaust gas purification performance of catalyst 1A, based on the mass of the second catalyst layer 30, the Ce content of Ce converted to CeO2 in the second catalyst layer 30 is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, and even more preferably 30% by mass or more. The upper limit can be appropriately adjusted considering the content of other components in the second catalyst layer 30. Based on the mass of the second catalyst layer 30, the Ce content of Ce converted to CeO2 in the second catalyst layer 30 can be adjusted to, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less. These upper limits can be combined with any of the lower limits mentioned above. Regarding "the CeO2 content of Ce in the second catalyst layer 30", when the second catalyst layer 30 contains one Ce source, it refers to the CeO2 content of Ce from that one Ce source; when the second catalyst layer 30 contains two or more Ce sources, it refers to the total CeO2 content of Ce from those two or more Ce sources.

[0200] There are no particular limitations on the Ce source as long as it is a Ce-containing oxide. The Ce source can be selected from, for example, Ce-containing Al-based oxides, Ce-Zr-based composite oxides, cerium dioxide binders, etc., with Ce-Zr-based composite oxides being preferred.

[0201] From the perspective of improving the exhaust gas purification performance of catalyst 1A, the proportion of the mass of Ce-Zr composite oxide Ce-O2 converted from Ce in the second catalyst layer 30 is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0202] The CeO2 content of Ce in the second catalyst layer 30 can be calculated in the same way as the CeO2 content of Ce in the first catalyst layer 20.

[0203] <Third and Fourth Catalyst Layers>

[0204] like Figures 4 to 6 As shown, the third catalyst layer 40 is disposed on the upper side of the first catalyst layer 20, and the fourth catalyst layer 50 is disposed on the upper side of the second catalyst layer 30.

[0205] The third catalyst layer 40 and the fourth catalyst layer 50 are layers provided as needed, and can be omitted. Embodiments in which one or both of the third catalyst layer 40 and the fourth catalyst layer 50 are omitted from the catalyst 1A are also included in the present application. Of these, one or both of the third catalyst layer 40 and the fourth catalyst layer 50 are preferably provided from the viewpoint of improving exhaust gas purification performance. Specifically, by providing the third catalyst layer 40, phosphorus poisoning of the noble metal element in the first catalyst layer 20 can be prevented, and by providing the fourth catalyst layer 50, phosphorus poisoning of the noble metal element in the second catalyst layer 30 can be prevented. Pd and Pt, particularly Pd, are susceptible to phosphorus poisoning. Therefore, the third catalyst layer 40 is preferably provided when the first catalyst layer 20 contains Pd and / or Pt, and the fourth catalyst layer 50 is preferably provided when the second catalyst layer 30 contains Pd and / or Pt.

[0206] The "third catalyst layer 40 is provided on the upper side of the first catalyst layer 20" means that the third catalyst layer 40 is present on part or all of the side of the two main faces of the first catalyst layer 20 that is opposite the side of the partition wall portion 12a. The "main face of the first catalyst layer 20" means the outer surface of the first catalyst layer 20 that extends in the exhaust gas flow direction X. The third catalyst layer 40 can be provided directly on the main face of the first catalyst layer 20, or can be provided with another layer interposed therebetween, and is typically provided directly on the main face of the first catalyst layer 20. The third catalyst layer 40 can be provided so as to cover part of the main face of the first catalyst layer 20, or can be provided so as to cover the entire main face of the first catalyst layer 20. Embodiments in which the third catalyst layer 40 is provided directly on the main face of the first catalyst layer 20 and embodiments in which the third catalyst layer 40 is provided on the main face of the first catalyst layer 20 with another layer interposed therebetween are both included in the "third catalyst layer 40 provided on the upper side of the first catalyst layer 20".

[0207] The "4th catalyst layer 50 is provided on the upper side of the 2nd catalyst layer 30" means that the 4th catalyst layer 50 is present on part or all of the main surface on the opposite side of the main surface of the 2nd catalyst layer 30 on the side of the partition wall portion 12b. The "main surface of the 2nd catalyst layer 30" means the outer surface of the 2nd catalyst layer 30 extending in the exhaust gas flow direction X. The 4th catalyst layer 50 can be provided directly on the main surface of the 2nd catalyst layer 30 or can be provided with other layers interposed therebetween, and is usually provided directly on the main surface of the 2nd catalyst layer 30. The 4th catalyst layer 50 can be provided so as to cover part of the main surface of the 2nd catalyst layer 30 or can be provided so as to cover the entire main surface of the 2nd catalyst layer 30. The embodiment in which the 4th catalyst layer 50 is provided directly on the main surface of the 2nd catalyst layer 30 and the embodiment in which the 4th catalyst layer 50 is provided on the main surface of the 2nd catalyst layer 30 with other layers interposed therebetween are both included in the "4th catalyst layer 50 provided on the upper side of the 2nd catalyst layer 30".

[0208] As shown in FIG. 1, the 3rd catalyst layer 40 extends along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to the end portion of the partition wall portion 12a on the exhaust gas outflow side. The 3rd catalyst layer 40 can also extend along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas outflow side, or can extend in a direction opposite to the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas outflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas inflow side. Figure 6 As shown in FIG. 1, the 3rd catalyst layer 40 extends along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to the end portion of the partition wall portion 12a on the exhaust gas outflow side. The 3rd catalyst layer 40 can also extend along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas outflow side, or can extend in a direction opposite to the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas outflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas inflow side.

[0209] As shown in FIG. 1, the 3rd catalyst layer 40 extends along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to the end portion of the partition wall portion 12a on the exhaust gas outflow side. The 3rd catalyst layer 40 can also extend along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas outflow side, or can extend in a direction opposite to the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas outflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas inflow side. Figure 6 As shown in FIG. 1, the 3rd catalyst layer 40 extends along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to the end portion of the partition wall portion 12a on the exhaust gas outflow side. The 3rd catalyst layer 40 can also extend along the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas inflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas outflow side, or can extend in a direction opposite to the exhaust gas flow direction X from the end portion of the partition wall portion 12a on the exhaust gas outflow side to a position short of the end portion of the partition wall portion 12a on the exhaust gas inflow side.

[0210] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass of the third catalyst layer 40 per unit volume of the portion of the substrate 10 in which the third catalyst layer 40 is formed, that is, the mass of the third catalyst layer 40 per unit volume of the portion of the first substrate portion 10a in which the third catalyst layer 40 is provided, is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 140 g / L or less, and further preferably 50 g / L or more and 130 g / L or less. The mass of the third catalyst layer 40 per unit volume of the portion of the first substrate portion 10a in which the third catalyst layer 40 is provided is calculated according to the formula: (mass of the third catalyst layer 40) / ((volume of the first substrate portion 10a) x (average length L40 of the third catalyst layer 40 / length L10a of the first substrate portion 10a)).

[0211] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass of the fourth catalyst layer 50 per unit volume of the portion of the substrate 10 in which the fourth catalyst layer 50 is formed, that is, the mass of the fourth catalyst layer 50 per unit volume of the portion of the second substrate portion 10b in which the fourth catalyst layer 50 is provided, is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 140 g / L or less, and further preferably 50 g / L or more and 130 g / L or less. The mass of the fourth catalyst layer 50 per unit volume of the portion of the second substrate portion 10b in which the fourth catalyst layer 50 is provided is calculated according to the formula: (mass of the fourth catalyst layer 50) / ((volume of the second substrate portion 10b) x (average length L50 of the fourth catalyst layer 50 / length L10b of the second substrate portion 10b)).

[0212] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the sum of the mass of the third catalyst layer 40 and the mass of the fourth catalyst layer 50 is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 140 g / L or less, and further preferably 50 g / L or more and 130 g / L or less, with respect to the sum of the volume of the portion of the first substrate portion 10a in which the third catalyst layer 40 is provided and the volume of the portion of the second substrate portion 10b in which the fourth catalyst layer 50 is provided.

[0213] The above description regarding the mass of the first catalyst layer 20 also applies to the mass of the third catalyst layer 40 and the mass of the fourth catalyst layer 50. When applicable, "first catalyst layer 20" is replaced with "third catalyst layer 40" and "fourth catalyst layer 50", respectively.

[0214] The above description of the method of measuring the average length L20 of the first catalyst layer 20 also applies to the method of measuring the average length L40 of the third catalyst layer 40 and the average length L50 of the fourth catalyst layer 50. When applicable, "the first catalyst layer 20" is replaced by "the third catalyst layer 40" and "the fourth catalyst layer 50", respectively, and "the average length L20" is replaced by "the average length L40" and "the average length L50", respectively.

[0215] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the average length L40 of the third catalyst layer 40 relative to the length L10a of the first substrate portion 10a (L40 / L10a x 100) is preferably 80% or greater, more preferably 90% or greater, and further preferably 95% or greater. The upper limit can be 100% or can exceed 100%. As described later, in the case where the end portion of the exhaust gas outflow side of the third catalyst layer 40 has a portion overlapping with the end portion of the exhaust gas inflow side of the fourth catalyst layer 50, the percentage can exceed 100%. In the case where the percentage exceeds 100%, the upper limit of the percentage is preferably 600% or less, more preferably 400% or less, and further preferably 300% or less. Note that in the case where the first substrate portion 10a and the second substrate portion 10b are integrated, and in the case where the first substrate portion 10a and the second substrate portion 10b are separate and the end portion of the exhaust gas outflow side of the first substrate portion 10a contacts the end portion of the exhaust gas inflow side of the second substrate portion 10b, the percentage can exceed 100%, but in the case where the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the end portion of the exhaust gas outflow side of the first substrate portion 10a and the end portion of the exhaust gas inflow side of the second substrate portion 10b, the percentage does not exceed 100%.

[0216] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the average length L40 of the third catalyst layer 40 relative to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L40 / (L10a+L10b) x 100) is preferably 15% or greater and 80% or less, more preferably 18% or greater and 70% or less, and further preferably 20% or greater and 60% or less.

[0217] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the average length L50 of the fourth catalyst layer 50 with respect to the length L10b of the second substrate portion 10b (L50 / L10b x 100) is preferably 80% or more, more preferably 90% or more, and further preferably 95% or more. The upper limit can be 100% or more. As described later, in the case where the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 has a portion overlapping with the end portion of the exhaust gas outflow side of the third catalyst layer 40, the percentage can exceed 100%. In the case where the percentage exceeds 100%, the upper limit of the percentage is preferably 500% or less, more preferably 350% or less, and further preferably 200% or less. Note that, in the case where the first substrate portion 10a and the second substrate portion 10b are integrated, and in the case where the first substrate portion 10a and the second substrate portion 10b are separate and the end portion of the exhaust gas outflow side of the first substrate portion 10a contacts the end portion of the exhaust gas inflow side of the second substrate portion 10b, the percentage can exceed 100%, but in the case where the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the end portion of the exhaust gas outflow side of the first substrate portion 10a and the end portion of the exhaust gas inflow side of the second substrate portion 10b, the percentage does not exceed 100%.

[0218] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the average length L50 of the fourth catalyst layer 50 with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L50 / (L10a+L10b) x 100) is preferably 20% or more and 95% or less, more preferably 30% or more and 92% or less, and further preferably 40% or more and 90% or less.

[0219] As shown in FIG. 1, the end portion of the exhaust gas outflow side of the third catalyst layer 40 contacts the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 at the boundary S. Figure 6 As shown in FIG. 1, the end portion of the exhaust gas outflow side of the third catalyst layer 40 contacts the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 at the boundary S. Figure 6 As shown in FIG. 1, the end portion of the exhaust gas outflow side of the third catalyst layer 40 contacts the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 at the boundary S.

[0220] The end portion of the exhaust gas outflow side of the third catalyst layer 40 can also have a portion overlapping with the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 (i.e., a portion located above the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 and covering the end portion of the exhaust gas inflow side of the fourth catalyst layer 50). In addition, the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 can also have a portion overlapping with the end portion of the exhaust gas outflow side of the third catalyst layer 40 (i.e., a portion located above the end portion of the exhaust gas outflow side of the third catalyst layer 40 and covering the end portion of the exhaust gas outflow side of the third catalyst layer 40).

[0221] In a case where the end portion of the exhaust gas outflow side of the third catalyst layer 40 contacts the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 at the boundary S, the end portion of the exhaust gas outflow side of the third catalyst layer 40 and the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 can be continuous. That is, the third catalyst layer 40 and the fourth catalyst layer 50 can be integrated to form one catalyst layer.

[0222] The end portion of the exhaust gas outflow side of the third catalyst layer 40 can also not contact the end portion of the exhaust gas inflow side of the fourth catalyst layer 50. That is, a gap can also be formed between the end portion of the exhaust gas outflow side of the third catalyst layer 40 and the end portion of the exhaust gas inflow side of the fourth catalyst layer 50.

[0223] In one embodiment, the third catalyst layer 40 extends along the exhaust gas flow direction X from the end portion of the exhaust gas inflow side of the partition wall portion 12a to the end portion of the exhaust gas outflow side of the partition wall portion 12a, and the end portion of the exhaust gas outflow side of the third catalyst layer 40 contacts the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 at the boundary S. In this embodiment, the end portion of the exhaust gas outflow side of the third catalyst layer 40 and the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 can be continuous. In this embodiment, the fourth catalyst layer 50 can extend along the exhaust gas flow direction X from the end portion of the exhaust gas inflow side of the partition wall portion 12b to the end portion of the exhaust gas outflow side of the partition wall portion 12b, and can also extend along the exhaust gas flow direction X from the end portion of the exhaust gas inflow side of the partition wall portion 12b without reaching the end portion of the exhaust gas outflow side of the partition wall portion 12b.

[0224] In another embodiment, the fourth catalyst layer 50 extends from the end of the partition wall portion 12b on the exhaust gas outflow side to the end of the partition wall portion 12b on the exhaust gas inflow side in a direction opposite to the exhaust gas flow direction X, and the end of the third catalyst layer 40 on the exhaust gas outflow side contacts the end of the fourth catalyst layer 50 on the exhaust gas inflow side at the boundary S. In this embodiment, the end of the third catalyst layer 40 on the exhaust gas outflow side and the end of the fourth catalyst layer 50 on the exhaust gas inflow side can be continuous. In this embodiment, the third catalyst layer 40 can extend from the end of the partition wall portion 12a on the exhaust gas outflow side to the end of the partition wall portion 12a on the exhaust gas inflow side in a direction opposite to the exhaust gas flow direction X, and can also extend from the end of the partition wall portion 12a on the exhaust gas outflow side to the end of the partition wall portion 12a on the exhaust gas inflow side in a direction opposite to the exhaust gas flow direction X without reaching the end of the partition wall portion 12a on the exhaust gas inflow side.

[0225] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the sum of the average length L40 of the third catalyst layer 40 and the average length L50 of the fourth catalyst layer 50 with respect to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b ((L40+L50) / (L10a+L10b)xlOO) is preferably 80% or more, more preferably 90% or more, and further preferably 95% or more. The upper limit can be 100% or more. As described above, in the case where the end of the third catalyst layer 40 on the exhaust gas outflow side has a portion overlapping with the end of the fourth catalyst layer 50 on the exhaust gas inflow side, and in the case where the end of the fourth catalyst layer 50 on the exhaust gas inflow side has a portion overlapping with the end of the third catalyst layer 40 on the exhaust gas outflow side, the percentage can exceed 100%. The upper limit of the percentage is preferably 175% or less, more preferably 162% or less, and further preferably 150% or less. Note that, in the case where the first substrate portion 10a and the second substrate portion 10b are integrated, and in the case where the first substrate portion 10a and the second substrate portion 10b are separate and the end of the first substrate portion 10a on the exhaust gas outflow side contacts the end of the second substrate portion 10b on the exhaust gas inflow side, the percentage can exceed 100%, but in the case where the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the end of the first substrate portion 10a on the exhaust gas outflow side and the end of the second substrate portion 10b on the exhaust gas inflow side, the percentage is 100% or less.

[0226] Hereinafter, commonalities of the 3rd catalyst layer 40 and the 4th catalyst layer 50 are explained in conjunction with the description about the 3rd catalyst layer 40 and the 4th catalyst layer 50. At this time, expressions such as "catalyst layer 40, 50", "length L40, L50", "substrate portion 10a, 10b", and "length L10a, L10b" are used. These expressions refer to "catalyst layer 40", "length L40", "substrate portion 10a", and "length L10a" for the 3rd catalyst layer 40, and "catalyst layer 50", "length L50", "substrate portion 10b", and "length L10b" for the 4th catalyst layer 50.

[0227] The catalyst layers 40, 50 contain one or two or more kinds of noble metal elements as catalytically active components. The noble metal elements can be selected from, for example, Pd, Pt, Rh, Au, Ag, Ir, Ru, Os, and the like. The noble metal elements are contained in the catalyst layers 40, 50 in a form in which they can function as catalytically active components, such as a metal, an alloy containing a noble metal element, a compound containing a noble metal element (such as an oxide of a noble metal element), and the like. From the viewpoint of improving exhaust gas purification performance, the catalytically active component containing a noble metal element is preferably in a particulate form.

[0228] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of the noble metal elements in the catalyst layers 40, 50, on a metal conversion basis, is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.02 mass% or more and 3 mass% or less, and further preferably 0.05 mass% or more and 2 mass% or less, based on the mass of the catalyst layers 40, 50. For the "content of the noble metal elements in the catalyst layers 40, 50, on a metal conversion basis", when the catalyst layers 40, 50 contain one kind of noble metal element, it refers to the content of the one kind of noble metal element, on a metal conversion basis, and when the catalyst layers 40, 50 contain two or more kinds of noble metal elements, it refers to the total content of the two or more kinds of noble metal elements, on a metal conversion basis.

[0229] The catalyst layers 40, 50 are provided on the upper side of the 1st catalyst layer 20 and the 2nd catalyst layer 30, respectively, and thus the noble metal elements in the catalyst layers 40, 50 are more likely to be poisoned by phosphorus than the noble metal elements in the 1st catalyst layer 20 and the 2nd catalyst layer 30. Therefore, the catalyst layers 40, 50 each preferably contain Rh. This is because Rh is a noble metal element that is difficult to be poisoned by phosphorus. In particular, when the 1st catalyst layer 20 and the 2nd catalyst layer each contain Pd and / or Pt, the catalyst layers 40, 50 each preferably contain Rh. By causing the 1st catalyst layer and the 2nd catalyst layer to each contain Pd and / or Pt, and causing the catalyst layers 40, 50 to each contain Rh, it is possible to further improve the exhaust gas purification performance of the catalyst 1A.

[0230] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the Rh metal conversion content in the catalyst layer 40, 50 is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.02% by mass or more and 3% by mass or less, and further preferably 0.05% by mass or more and 2% by mass or less, based on the mass of the catalyst layer 40, 50.

[0231] The metal conversion content of each metal element in the catalyst layer 40, 50 is calculated according to the formula: (metal conversion mass of each metal element in the catalyst layer 40, 50) / (mass of the catalyst layer 40, 50) x 100. For example, the Rh metal conversion content in the catalyst layer 40, 50 is calculated according to the formula: (metal conversion mass of Rh in the catalyst layer 40, 50) / (mass of the catalyst layer 40, 50) x 100.

[0232] The metal conversion content of each metal element in the catalyst layer 40, 50 can be calculated in the same manner as the metal conversion content of each metal element in the first catalyst layer 20.

[0233] The catalyst layer 40, 50 preferably contains one or two or more kinds of carriers. The carrier can be selected from, for example, inorganic oxides. The inorganic oxides are the same as described above.

[0234] At least a part of the catalytically active component is preferably supported on the carrier. The meaning of "at least a part of the catalytically active component is supported on the carrier" and the method for confirming the same are the same as described above.

[0235] The catalyst layer 40, 50 can contain other components such as a binder, a stabilizer, and the like. As the binder, inorganic oxide-based binders such as alumina sol, ceria sol, zirconia sol, titania sol, silica sol, and the like can be exemplified. As the stabilizer, nitrates, carbonates, oxides, sulfates, and the like of alkaline earth metal elements (for example, Sr, Ba, and the like) can be exemplified.

[0236] The catalyst layer 40, 50 can contain Al2O3. In the case where the catalyst layer 40, 50 contains Al2O3, the catalyst layer 40, 50 contains one or two or more kinds of Al2O3 sources.

[0237] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the Al2O3-converted content of Al in the catalyst layers 40, 50 is preferably 1% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more, based on the mass of the catalyst layers 40, 50. The upper limit can be appropriately adjusted in consideration of the content of other components in the catalyst layers 40, 50, and the like. The Al2O3-converted content of Al in the catalyst layers 40, 50 is, for example, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the mass of the catalyst layers 40, 50. These upper limits can each be combined with any of the above lower limits. The "Al2O3-converted content of Al in the catalyst layers 40, 50" refers to the Al2O3-converted content of Al from one Al2O3 source when the catalyst layers 40, 50 contain one Al2O3 source, and refers to the total Al2O3-converted content of Al from two or more Al2O3 sources when the catalyst layers 40, 50 contain two or more Al2O3 sources.

[0238] The Al2O3 source is not particularly limited as long as it is an Al-containing oxide. The Al2O3 source can be selected from, for example, an Al-based oxide, an Al-containing Ce-based oxide, an Al-containing Ce-Zr-based composite oxide, an alumina binder, and the like.

[0239] The catalyst layers 40, 50 preferably contain an Al-based oxide as the Al2O3 source. In addition to the Al-based oxide, the catalyst layers 40, 50 can contain other one or two or more Al2O3 sources. In one embodiment, the catalyst layers 40, 50 contain an Al-based oxide and an alumina binder as the Al2O3 source.

[0240] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the proportion of the Al2O3-converted mass of Al from the Al-based oxide in the Al2O3-converted mass of Al in the catalyst layers 40, 50 is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and further preferably 80% by mass or more. The upper limit is 100% by mass.

[0241] The Al2O3-converted content of Al in the catalyst layers 40, 50 can be calculated in the same manner as the Al2O3-converted content of Al in the first catalyst layer 20.

[0242] The Ce content in catalyst layers 40 and 50 is mainly related to oxygen storage capacity. Therefore, from the perspective of improving the exhaust gas purification performance of catalyst 1A, based on the mass of catalyst layers 40 and 50, the Ce content of Ce converted from CeO2 in catalyst layers 40 and 50 is preferably 0.1% by mass or more, more preferably 1% by mass or more, further preferably 3% by mass or more, and even more preferably 5% by mass or more. The upper limit can be appropriately adjusted considering the content of other components in catalyst layers 40 and 50. Based on the mass of catalyst layers 40 and 50, the Ce content of Ce converted from CeO2 in catalyst layers 40 and 50 can be adjusted to, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less. These upper limits can be combined with any of the lower limits mentioned above. Regarding the "CeO2 content of Ce in catalyst layers 40 and 50", when catalyst layers 40 and 50 contain one Ce source, it refers to the CeO2 content of Ce from that one Ce source. When catalyst layers 40 and 50 contain two or more Ce sources, it refers to the total CeO2 content of Ce from those two or more Ce sources.

[0243] There are no particular limitations on the Ce source as long as it is a Ce-containing oxide. The Ce source can be selected from, for example, Ce-containing Al-based oxides, Ce-Zr-based composite oxides, cerium dioxide binders, etc., with Ce-Zr-based composite oxides being preferred.

[0244] From the perspective of improving the exhaust gas purification performance of catalyst 1A, the proportion of the mass of Ce from CeO2 in the catalyst layers 40 and 50 is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0245] The CeO2 content of Ce in catalyst layers 40 and 50 can be calculated in the same way as the CeO2 content of Ce in the first catalyst layer 20.

[0246] Implementation Method 2

[0247] The following is based on Figure 7 The catalyst 1B for exhaust gas purification (hereinafter referred to as "catalyst 1B") according to the second embodiment will be described.

[0248] In catalyst 1B, components identical to those in catalyst 1A are represented by the same symbols as in catalyst 1A. Unless otherwise specified, the above description concerning catalyst 1A also applies to catalyst 1B.

[0249] The first substrate portion 10a and the second substrate portion 10b of the catalyst 1B are separate, unlike the catalyst 1A in which the first substrate portion 10a and the second substrate portion 10b are integrated.

[0250] Embodiments in which the substrate 10 is composed of one substrate, like the catalyst 1A, and embodiments in which the substrate 10 is composed of two substrates, like the catalyst 1B, are both included in the present application.

[0251] As shown in FIG. 1, the first substrate portion 10a and the second substrate portion 10b are arranged in the exhaust passage in the exhaust pipe P in such a manner that the axial directions of the first substrate portion 10a and the second substrate portion 10b coincide or approximately coincide with the exhaust gas flow direction X. Figure 7 As shown in FIG. 1, the axial direction of the first substrate portion 10a coincides or approximately coincides with the axial direction of the second substrate portion 10b.

[0252] Figure 7 As shown in FIG. 1, the axial direction of the first substrate portion 10a coincides or approximately coincides with the axial direction of the second substrate portion 10b.

[0253] As shown in FIG. 1, a gap is formed between the end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b. The distance between the end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b is, for example, 5 to 1000 mm. Figure 7 Embodiments in which a gap is formed between the end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b, and embodiments in which the axial directions of the first substrate portion 10a and the second substrate portion 10b coincide or approximately coincide with the exhaust gas flow direction X are both included in "the substrate 10 extends in the exhaust gas flow direction X".

[0254] The end portion on the exhaust gas outflow side of the first substrate portion 10a and the end portion on the exhaust gas inflow side of the second substrate portion 10b can be in contact. In this case, the arrangement of the first substrate portion 10a and the second substrate portion 10b can be the same as the arrangement shown in FIG. 1, for example.

[0255] Figure 6

[0256] <Manufacture of Catalyst>

[0257] The catalysts 1A and 1B can each be manufactured by forming the first catalyst layer 20 on the first substrate portion 10a, forming the second catalyst layer 30 on the second substrate portion 10b, forming the third catalyst layer 40 on the first catalyst layer 20, and forming the fourth catalyst layer 50 on the second catalyst layer 30.

[0258] ​​​The first catalyst layer 20 and the second catalyst layer 30 can be formed on the first substrate portion 10a and the second substrate portion 10b, respectively, and then the third catalyst layer 40 and the fourth catalyst layer 50 can be formed on the first catalyst layer 20 and the second catalyst layer 30, respectively. Alternatively, the first catalyst layer 20 can be formed on the first substrate portion 10a, and then the third catalyst layer 40 can be formed on the first catalyst layer 20, and then the second catalyst layer 30 can be formed on the second substrate portion 10b, and then the fourth catalyst layer 50 can be formed on the second catalyst layer 30.

[0259] In the case where the first substrate portion 10a and the second substrate portion 10b are integrated, or in the case where the first substrate portion 10a and the second substrate portion 10b are separate and the end portion of the first substrate portion 10a on the exhaust gas outflow side contacts the end portion of the second substrate portion 10b on the exhaust gas inflow side, the first catalyst layer 20 can be formed on the first substrate portion 10a, and then the second catalyst layer 30 can be formed on the second substrate portion 10b. Alternatively, the second catalyst layer 30 can be formed on the second substrate portion 10b, and then the first catalyst layer 20 can be formed on the first substrate portion 10a. In the former case, the end portion on the exhaust gas inflow side of the second catalyst layer 30 can have a portion overlapping with the end portion on the exhaust gas outflow side of the first catalyst layer 20 (i.e., a portion positioned on the upper side of the end portion on the exhaust gas outflow side of the first catalyst layer 20 and covering the end portion on the exhaust gas outflow side of the first catalyst layer 20). In the latter case, the end portion on the exhaust gas outflow side of the first catalyst layer 20 can have a portion overlapping with the end portion on the exhaust gas inflow side of the second catalyst layer 30 (i.e., a portion positioned on the upper side of the end portion on the exhaust gas inflow side of the second catalyst layer 30 and covering the end portion on the exhaust gas inflow side of the second catalyst layer 30).

[0260] The first catalyst layer 20 can be formed by mixing a supply source of a noble metal element (e.g., a salt of a noble metal element such as Pd, Pt, or the like), a Ce-Zr-based composite oxide, and optional other components (e.g., an inorganic oxide other than the Ce-Zr-based composite oxide, a binder other than an alumina binder, a solvent, or the like) to prepare a first catalyst layer-forming slurry, applying the first catalyst layer-forming slurry on the first substrate portion 10a, and performing drying and firing.

[0261] The second catalyst layer 30 can be formed by mixing a supply source of a noble metal element (e.g., a salt of a noble metal element such as Pd, Pt, or the like), a supply source of Al2O3 (e.g., an Al-based oxide, an Al-containing Ce-based oxide, an Al-containing Ce-Zr-based composite oxide, an alumina binder, or the like), and optional other components (e.g., an inorganic oxide other than the supply source of Al2O3, a binder other than an alumina binder, a solvent, or the like) to prepare a second catalyst layer-forming slurry, applying the second catalyst layer-forming slurry on the second substrate portion 10b, and performing drying and firing.

[0262] The third catalyst layer 40 can be formed by preparing a slurry for forming a third catalyst layer by mixing a supply source of a noble metal element (e.g., a salt of a noble metal element such as Rh) and optional other components (e.g., an inorganic oxide, a binder, a solvent, etc.), applying the slurry for forming a third catalyst layer on the first catalyst layer 20, and performing drying and firing.

[0263] The fourth catalyst layer 50 can be formed by preparing a slurry for forming a fourth catalyst layer by mixing a supply source of a noble metal element (e.g., a salt of a noble metal element such as Rh) and optional other components (e.g., an inorganic oxide, a binder, a solvent, etc.), applying the slurry for forming a fourth catalyst layer on the second catalyst layer 30, and performing drying and firing.

[0264] In the case where the end portion of the exhaust gas outflow side of the third catalyst layer 40 is continuous with the end portion of the exhaust gas inflow side of the fourth catalyst layer 50 (i.e., the case where the third catalyst layer 40 and the fourth catalyst layer 50 are integrated to form one catalyst layer), the third catalyst layer 40 and the fourth catalyst layer 50 can be formed by preparing a slurry for forming a third and fourth catalyst layer by mixing a supply source of a noble metal element (e.g., a salt of a noble metal element such as Rh) and other components (e.g., an inorganic oxide, a binder, a solvent, etc.), applying the slurry for forming a third and fourth catalyst layer on the first catalyst layer 20 and the second catalyst layer 30, and performing drying and firing.

[0265] As the salt of a noble metal element, for example, a nitrate, an ammine complex salt, an acetate, a chloride, etc. can be given. As the binder, for example, an alumina sol, a zirconia sol, a titania sol, a silica sol, a ceria sol, etc. can be given. As the solvent, for example, water, an organic solvent, etc. can be given.

[0266] The drying temperature is, for example, 60°C or higher and 150°C or lower, and the drying time is, for example, 0.1 hours or longer and 1 hour or shorter. The firing temperature is, for example, 300°C or higher and 700°C or lower, and the firing time is, for example, 1 hour or longer and 10 hours or shorter. The firing can be performed, for example, in an atmosphere of air.

[0267] Example

[0268] [Example 1]

[0269] (1) Preparation of a slurry for forming a first catalyst layer

[0270] To pure water, 1.1 parts by weight of an aqueous palladium nitrate solution calculated as Pd metal, 77.0 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 45 mass%, ZrO2conversion rate of Zr: 45 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 10 mass%), 7.7 parts by weight of La2O3modified alumina (La2O3content rate: 1 mass%), 6.1 parts by weight of barium hydroxide calculated as an oxide, and 8.1 parts by weight of a binder containing alumina sol calculated as a solid substance (Al2O3content rate in solid content: 50 mass%) were added, mixed, and stirred to prepare a slurry for forming a first catalyst layer. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming the first catalyst layer contained 1.1 mass% of Pd calculated as metal, 34.7 mass% of Ce calculated as CeO2, and 11.7 mass% of Al calculated as Al2O3.

[0271] (2) Preparation of a slurry for forming a second catalyst layer

[0272] To pure water, 0.1 parts by weight of an aqueous palladium nitrate solution calculated as Pd metal, 69.8 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 45 mass%, ZrO2conversion rate of Zr: 45 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 10 mass%), 15.3 parts by weight of La2O3modified alumina (La2O3content rate: 1 mass%), 6.1 parts by weight of barium hydroxide calculated as an oxide, and 8.7 parts by weight of a binder containing alumina sol calculated as a solid substance (Al2O3content rate in solid content: 47 mass%) were added, mixed, and stirred to prepare a slurry for forming a second catalyst layer. Note that, based on the mass of the second catalyst layer after firing (100 mass%), the slurry for forming the second catalyst layer contained 0.1 mass% of Pd calculated as metal, 31.4 mass% of Ce calculated as CeO2, and 19.2 mass% of Al calculated as Al2O3. The ratio of the mass content of Al calculated as Al2O3in the second catalyst layer to the mass content of the noble metal element calculated as metal in the second catalyst layer was 192.

[0273] (3) Formation of the first catalyst layer and the second catalyst layer

[0274] As the flow-through type base material, a cordierite honeycomb porous base material (manufactured by NGK Insulators, Ltd., axial length: 80 mm, outer diameter: 93 mm, volume: 0.54 L, cell density: 900 cells / inch 2 ) having cells extending in the axial direction divided by partition walls having a thickness of 50 to 70 μm was prepared.

[0275] The portion from the upstream end of the flow-through type base material in the exhaust gas flow direction X to a position 30 mm away was dipped in the first catalyst layer-forming slurry, and the first catalyst layer-forming slurry was applied to the upstream side of the flow-through type base material. Next, the portion from the downstream end of the flow-through type base material in the exhaust gas flow direction X to a position 50 mm away was dipped in the second catalyst layer-forming slurry, and the second catalyst layer-forming slurry was applied to the downstream side of the flow-through type base material. Next, the flow-through type base material on which the first catalyst layer-forming slurry and the second catalyst layer-forming slurry were applied was dried at 90°C, and then fired at 450°C. Thus, the first catalyst layer and the second catalyst layer were formed on the flow-through type base material without gaps in the exhaust gas flow direction X. The mass of the first catalyst layer per unit volume (coating amount) of the portion of the flow-through type base material on which the first catalyst layer was formed was 130 g / L. The mass of the second catalyst layer per unit volume (coating amount) of the portion of the flow-through type base material on which the second catalyst layer was formed was 130 g / L. Note that the coating amount refers to the mass of the catalyst layer after firing.

[0276] (4) Preparation of the third and fourth catalyst layer-forming slurries

[0277] A 0.1 parts by weight solution of platinum (II) bisnitrilo diaminate, a 0.2 parts by weight aqueous rhodium nitrate solution, 44.6 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 15 mass%), 44.6 parts by weight of La2O3modified alumina (La2O3content: 1 mass%), 0.5 parts by weight of barium hydroxide in terms of oxide, and 10 parts by weight of a binder containing alumina sol in terms of solid content (Al2O3content in the solid content: 100 mass%) were added to pure water, mixed, and stirred to prepare the third and fourth catalyst layer-forming slurries. Note that, based on the mass of the third and fourth catalyst layers after firing (100 mass%), the third and fourth catalyst layer-forming slurries respectively contained 0.1 mass% of Pt, 0.2 mass% of Rh, 6.7 mass% of Ce in terms of CeO2, and 54.2 mass% of Al in terms of Al2O3.

[0278] (5) Formation of the third and fourth catalyst layers

[0279] The entire flow-through substrate on which the first and second catalyst layers were formed was dipped in the slurry for forming the third and fourth catalyst layers, and the slurry for forming the third and fourth catalyst layers was applied to the entire flow-through substrate on which the first and second catalyst layers were formed. Subsequently, the flow-through substrate on which the slurry for forming the third and fourth catalyst layers was applied was dried at 90°C, and then fired at 450°C. Thus, the third and fourth catalyst layers were formed without a gap in the exhaust gas flow direction X over the first and second catalyst layers, respectively (i.e., the end portion of the exhaust gas outflow side of the third catalyst layer and the end portion of the exhaust gas inflow side of the fourth catalyst layer were continuous, and the third and fourth catalyst layers became integrated to form one catalyst layer). The mass of the third catalyst layer per unit volume of the portion of the substrate on which the third catalyst layer was formed (coating amount) was 100 g / L, the mass of the fourth catalyst layer per unit volume of the portion of the substrate on which the fourth catalyst layer was formed (coating amount) was 100 g / L, and the sum of the mass of the third catalyst layer and the mass of the fourth catalyst layer (coating amount) relative to the sum of the volume of the portion of the substrate on which the third catalyst layer was formed and the volume of the portion of the substrate on which the fourth catalyst layer was formed was 100 g / L. Note that the coating amount refers to the mass of the catalyst layer after firing.

[0280] The exhaust gas purification catalyst of Example 1 was produced as described above, and had a flow-through substrate, a first catalyst layer provided on the upstream side of the flow-through substrate, a second catalyst layer provided on the downstream side of the flow-through substrate, a third catalyst layer provided on the upstream side of the first catalyst layer, and a fourth catalyst layer provided on the upstream side of the second catalyst layer. In the exhaust gas purification catalyst of Example 1, the ratio of the mass content of Al in terms of Al2O3 in the first catalyst layer (11.7 mass%) relative to the mass content of Al in terms of Al2O3 in the second catalyst layer (19.2 mass%) was 0.61. The ratio of the mass of the first catalyst layer per unit volume of the portion of the substrate on which the first catalyst layer was formed (130 g / L) relative to the mass of the second catalyst layer per unit volume of the portion of the substrate on which the second catalyst layer was formed (130 g / L) was 1.00.

[0281] [Example 2]

[0282] (1) Preparation of the slurry for forming the first catalyst layer

[0283] To pure water, 1.1 parts by weight of an aqueous palladium nitrate solution calculated as Pd metal, 84.7 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 45 mass%, ZrO2conversion rate of Zr: 45 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 10 mass%), 6.1 parts by weight of barium hydroxide calculated as an oxide, and 8.1 parts by weight of a binder containing alumina sol calculated as a solid substance (Al2O3content in the solid substance: 100 mass%) were added, mixed, and stirred to prepare a slurry for forming a first catalyst layer. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming a first catalyst layer contained Pd calculated as metal: 1.1 mass%, Ce calculated as CeO2: 38.1 mass%, and Al calculated as Al2O3: 8.1 mass%.

[0284] A catalyst for exhaust gas purification of Example 2 was produced in the same manner as in Example 1, except that the slurry for forming a first catalyst layer produced in (1) above was used. In the catalyst for exhaust gas purification of Example 2, the ratio of the mass content of Al calculated as Al2O3in the first catalyst layer (8.1 mass%) to the mass content of Al calculated as Al2O3in the second catalyst layer (19.2 mass%) was 0.42. The ratio of the mass of the first catalyst layer per unit volume (130 g / L) of the portion of the substrate in which the first catalyst layer was formed to the mass of the second catalyst layer per unit volume (130 g / L) of the portion of the substrate in which the second catalyst layer was formed was 1.00.

[0285] 〔Example 3〕

[0286] (1) Preparation of a slurry for forming a first catalyst layer

[0287] To pure water, 1.1 parts by weight of an aqueous palladium nitrate solution calculated as Pd metal, 84.7 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 45 mass%, ZrO2conversion rate of Zr: 45 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 10 mass%), 6.1 parts by weight of barium hydroxide calculated as an oxide, and 8.1 parts by weight of a binder containing alumina sol calculated as a solid substance (Al2O3content in the solid substance: 50 mass%) were added, mixed, and stirred to prepare a slurry for forming a first catalyst layer. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming a first catalyst layer contained Pd calculated as metal: 1.1 mass%, Ce calculated as CeO2: 38.1 mass%, and Al calculated as Al2O3: 4.1 mass%.

[0288] Example 3 was produced in the same manner as Example 1 except that the slurry for forming the first catalyst layer produced in the above (1) was used. In the exhaust gas purification catalyst of Example 3, the ratio of the mass content of Al in terms of Al2O3 in the first catalyst layer (4.1 mass%) to the mass content of Al in terms of Al2O3 in the second catalyst layer (19.2 mass%) was 0.21. The ratio of the mass of the first catalyst layer per unit volume (130 g / L) in the portion of the substrate in which the first catalyst layer was formed to the mass of the second catalyst layer per unit volume (130 g / L) in the portion of the substrate in which the second catalyst layer was formed was 1.00.

[0289] [Example 4]

[0290] (1) Preparation of the slurry for forming the first catalyst layer

[0291] A slurry for forming the first catalyst layer was prepared by adding, to pure water, 1.1 parts by weight of an aqueous solution of palladium nitrate in terms of Pd metal, 84.7 parts by weight of a Ce-Zr-based composite oxide (mass content of Ce in terms of CeO2: 45 mass%, mass content of Zr in terms of ZrO2: 45 mass%, mass content of oxides of one or two or more rare earth elements other than Ce: 10 mass%), 6.1 parts by weight of barium hydroxide in terms of oxide, 8.1 parts by weight of a binder not containing alumina sol in terms of solid substance (mass content of Al2O3 in the solid substance: 0.0 mass%), mixing, and stirring. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming the first catalyst layer contained 1.1 mass% of Pd in terms of metal and 38.1 mass% of Ce in terms of CeO2.

[0292] Example 4 was produced in the same manner as Example 1 except that the slurry for forming the first catalyst layer produced in the above (1) was used. In the exhaust gas purification catalyst of Example 4, the ratio of the mass content of Al in terms of Al2O3 in the first catalyst layer (0.00 mass%) to the mass content of Al in terms of Al2O3 in the second catalyst layer (19.2 mass%) was 0.00. The ratio of the mass of the first catalyst layer per unit volume (130 g / L) in the portion of the substrate in which the first catalyst layer was formed to the mass of the second catalyst layer per unit volume (130 g / L) in the portion of the substrate in which the second catalyst layer was formed was 1.00.

[0293] [Example 5]

[0294] (1) Preparation of the slurry for forming the first catalyst layer

[0295] To pure water was added 1.2 parts by weight of an aqueous palladium nitrate solution in terms of Pd metal, 83.5 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 45 mass%, ZrO2conversion rate of Zr: 45 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 10 mass%), 6.6 parts by weight of barium hydroxide in terms of oxide, 8.7 parts by weight of a binder containing alumina sol in terms of solid substance (Al2O3content in solid component: 50 mass%), mixed and stirred to prepare a first catalyst layer forming slurry. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the first catalyst layer forming slurry contained 1.2 mass% of Pd in terms of metal, 37.6 mass% of Ce in terms of CeO2, and 4.4 mass% of Al in terms of Al2O3.

[0296] A catalyst for exhaust gas purification of Example 5 was produced in the same manner as in Example 1 except that the first catalyst layer forming slurry produced in (1) above was used and the mass of the first catalyst layer per unit volume (coating amount) of the portion of the substrate in which the first catalyst layer was formed was set to 120 g / L. In the catalyst for exhaust gas purification of Example 5, the ratio of the mass content of Al in terms of Al2O3in the first catalyst layer (4.4 mass%) to the mass content of Al in terms of Al2O3in the second catalyst layer (19.2 mass%) was 0.23. In addition, the ratio of the mass of the first catalyst layer per unit volume (120 g / L) of the portion of the substrate in which the first catalyst layer was formed to the mass of the second catalyst layer per unit volume (130 g / L) of the portion of the substrate in which the second catalyst layer was formed was 0.92.

[0297] [Comparative Example 1]

[0298] (1) Preparation of First Catalyst Layer Forming Slurry

[0299] To pure water, 1.1 parts by weight of an aqueous palladium nitrate solution calculated as Pd metal, 69.5 parts by weight of a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 45 mass%, ZrO2conversion rate of Zr: 45 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 10 mass%), 15.2 parts by weight of La2O3modified alumina (La2O3content: 1 mass%), 6.1 parts by weight of barium hydroxide calculated as an oxide, and 8.1 parts by weight of a binder containing alumina sol calculated as a solid substance (Al2O3content in the solid substance: 50 mass%) were added, mixed, and stirred to prepare a slurry for forming a first catalyst layer. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming a first catalyst layer contained 1.1 mass% of Pd calculated as metal, 31.3 mass% of Ce calculated as CeO2, and 19.1 mass% of Al calculated as Al2O3.

[0300] A catalyst for exhaust gas purification of Comparative Example 1 was produced in the same manner as in Example 1, except that the slurry for forming a first catalyst layer produced in (1) above was used. In the catalyst for exhaust gas purification of Comparative Example 1, the ratio of the mass content of Al calculated as Al2O3in the first catalyst layer (19.1 mass%) to the mass content of Al calculated as Al2O3in the second catalyst layer (19.2 mass%) was 0.99.

[0301] [Comparative Example 2]

[0302] (1) Preparation of a slurry for forming a first catalyst layer

[0303] To pure water, 1.1 parts by weight of an aqueous palladium nitrate solution calculated as Pd metal, 84.7 parts by weight of a support other than a Ce-Zr-based composite oxide (CeO2conversion rate of Ce: 0 mass%, ZrO2conversion rate of Zr: 83 mass%, oxide conversion rate of one or two or more rare earth elements other than Ce: 17 mass%), 6.1 parts by weight of barium hydroxide calculated as an oxide, and 8.2 parts by weight of a binder containing alumina sol calculated as a solid substance (Al2O3content in the solid substance: 50 mass%) were added, mixed, and stirred to prepare a slurry for forming a first catalyst layer. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming a first catalyst layer contained 1.1 mass% of Pd calculated as metal, 0.0 mass% of Ce calculated as CeO2, and 4.1 mass% of Al calculated as Al2O3.

[0304] The exhaust gas purifying catalyst of Comparative Example 2 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in the above (1) was used. In the exhaust gas purifying catalyst of Comparative Example 2, the ratio of the mass content of Al in terms of Al2O3 in the first catalyst layer (4.1 mass%) to the mass content of Al in terms of Al2O3 in the second catalyst layer (19.2 mass%) was 0.21.

[0305] [Comparative Example 3]

[0306] (1) Preparation of the slurry for forming the first catalyst layer

[0307] To pure water, 1.3 parts by weight of an aqueous palladium nitrate solution in terms of Pd metal, 67.2 parts by weight of a Ce-Zr-based composite oxide (CeO2content of Ce: 45 mass%, ZrO2content of Zr: 45 mass%, oxide content of one or two or more rare earth elements other than Ce: 10 mass%), 14.8 parts by weight of La2O3-modified alumina (La2O3content: 1 mass%), 7.2 parts by weight of barium hydroxide in terms of oxide, and 9.5 parts by weight of a binder containing alumina sol in terms of solid substance (Al2O3content in the solid substance: 50 mass%) were added, mixed, and stirred to prepare the slurry for forming the first catalyst layer. Note that, based on the mass of the first catalyst layer after firing (100 mass%), the slurry for forming the first catalyst layer contained Pd in terms of metal at 1.3 mass%, Ce in terms of CeO2at 30.2 mass%, and Al in terms of Al2O3at 19.4 mass%.

[0308] The exhaust gas purifying catalyst of Comparative Example 3 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in the above (1) was used and the mass of the first catalyst layer per unit volume (coating amount) of the portion of the substrate in which the first catalyst layer was formed was set to 110 g / L. In the exhaust gas purifying catalyst of Comparative Example 3, the ratio of the mass content of Al in terms of Al2O3 in the first catalyst layer (19.2 mass%) to the mass content of Al in terms of Al2O3 in the second catalyst layer (19.4 mass%) was 1.01. The ratio of the mass of the first catalyst layer per unit volume (110 g / L) of the portion of the substrate in which the first catalyst layer was formed to the mass of the second catalyst layer per unit volume (130 g / L) of the portion of the substrate in which the second catalyst layer was formed was 0.85.

[0309] [Experimental Example]

[0310] (1) Durability treatment

[0311] The exhaust gas purification catalysts of Examples 1 to 5 and Comparative Examples 1 to 3 were each mounted to an exhaust pipe, and the exhaust pipe was provided to a gasoline engine, and the engine speed / torque and the like were adjusted so that the catalyst temperature reached 950°C, and durability treatment was carried out for 50 hours continuously.

[0312] (2) Evaluation of exhaust gas purification performance

[0313] A vehicle provided with the exhaust gas purification catalyst after durability treatment was driven in accordance with the driving conditions of the World Harmonized Light-duty Vehicle Test Cycle (WLTC). The amounts of emission of carbon monoxide (CO), non-methane hydrocarbons (NMHC), and nitrogen oxides (NOx) in the exhaust gas that passed through the exhaust gas purification catalyst (emission values) were measured, and the amounts of emission of CO, NMHC, and NOx per unit distance traveled (g / km) were calculated. As the vehicle, a gasoline vehicle was used, as the gasoline, certified test fuel was used, and as the exhaust gas measuring device, an exhaust gas measuring device manufactured by Horiba Ltd. was used. The amounts of emission of NMHC per unit distance traveled (g / km) are shown in Table 1. In Table 1, (A) represents the mass content of Al in the first catalyst layer converted to Al2O3 (mass %), (B) represents the mass content of Al in the second catalyst layer converted to Al2O3 (mass %), (C) represents the mass of the first catalyst layer per unit volume of the portion of the substrate in which the first catalyst layer is formed (g / L), (D) represents the mass of the second catalyst layer per unit volume of the portion of the substrate in which the second catalyst layer is formed (g / L), (E) represents the ratio of the mass content of Al in the first catalyst layer converted to Al2O3 to the mass content of Al in the second catalyst layer converted to Al2O3, (F) represents the ratio of the mass of the first catalyst layer per unit volume of the portion of the substrate in which the first catalyst layer is formed to the mass of the second catalyst layer per unit volume of the portion of the substrate in which the second catalyst layer is formed, (G) represents the presence or absence of Ce-Zr-based composite oxide in the first catalyst layer, and (H) represents the amount of emission of NMHC per unit distance traveled (g / km).

[0314] [Table 1]

[0315]

[0316] The exhaust gas purification catalysts of Examples 1 to 5 each have a substrate, a first catalyst layer provided on the upstream side of the substrate, and a second catalyst layer provided on the downstream side of the substrate, the first catalyst layer contains a noble metal element and a Ce-Zr-based composite oxide, the second catalyst layer contains a noble metal element and Al2O3, the mass content of Al in the first catalyst layer, converted to Al2O3, is 12 mass% or less, and the ratio of the mass content of Al in the first catalyst layer, converted to Al2O3, to the mass content of Al in the second catalyst layer, converted to Al2O3, is 0 or more and 0.65 or less.

[0317] The exhaust gas purification catalysts of Comparative Examples 1 and 3 each have a substrate, a first catalyst layer provided on the upstream side of the substrate, and a second catalyst layer provided on the downstream side of the substrate, the first catalyst layer contains a noble metal element and a Ce-Zr-based composite oxide, and the second catalyst layer contains a noble metal element and Al2O3. However, in the exhaust gas purification catalysts of Comparative Examples 1 and 3, the mass content of Al in the first catalyst layer, converted to Al2O3, exceeds 12 mass%, and the ratio of the mass content of Al in the first catalyst layer, converted to Al2O3, to the mass content of Al in the second catalyst layer, converted to Al2O3, exceeds 0.65.

[0318] The exhaust gas purification catalyst of Comparative Example 2 has a substrate, a first catalyst layer provided on the upstream side of the substrate, and a second catalyst layer provided on the downstream side of the substrate, the first catalyst layer contains a noble metal element, and the second catalyst layer contains a noble metal element and Al2O3, the mass content of Al in the first catalyst layer, converted to Al2O3, is 12 mass% or less, and the ratio of the mass content of Al in the first catalyst layer, converted to Al2O3, to the mass content of Al in the second catalyst layer, converted to Al2O3, is 0 or more and 0.65 or less. However, in the exhaust gas purification catalyst of Comparative Example 2, the first catalyst layer does not contain a Ce-Zr-based composite oxide.

[0319] As shown in Table 1, the exhaust gas purification catalysts of Examples 1 to 5, which satisfy the conditions that the mass content of Al in the first catalyst layer, converted to Al2O3, is 12 mass% or less and the ratio of the mass content of Al2O3 in the first catalyst layer to the mass content of Al2O3 in the second catalyst layer is 0 or more and 0.65 or less, have higher exhaust gas purification performance than the exhaust gas purification catalysts of Comparative Examples 1 and 3, which do not satisfy the conditions. In addition, the exhaust gas purification catalysts of Examples 1 to 5, in which the first catalyst layer contains a Ce-Zr-based composite oxide, have higher exhaust gas purification performance than the exhaust gas purification catalyst of Comparative Example 2, in which the first catalyst layer does not contain a Ce-Zr-based composite oxide.

[0320] Explanation of Reference Signs

[0321] 1A, 1B,... catalyst for exhaust gas purification

[0322] 10... base material

[0323] 10a... first base material portion

[0324] 10b... second base material portion

[0325] 11a, 11b... cylindrical portion

[0326] 12a, 12b... partition wall portion

[0327] 13a, 13b... chamber

[0328] 20... first catalyst layer

[0329] 30... second catalyst layer

[0330] 40... third catalyst layer

[0331] 50... fourth catalyst layer

[0332] L10a... length of first base material portion

[0333] L10b... length of second base material portion

[0334] L20... average length of first catalyst layer

[0335] L30... average length of second catalyst layer

[0336] L40... average length of third catalyst layer

[0337] L50... average length of fourth catalyst layer

[0338] P... exhaust pipe of internal combustion engine

Claims

1. A catalyst for exhaust gas purification, comprising a substrate, a first catalyst layer provided on an upstream side of the substrate, and a second catalyst layer provided on a downstream side of the substrate, wherein the first catalyst layer contains a noble metal element and a Ce-Zr-based composite oxide, the second catalyst layer contains a noble metal element and AI2O3, a mass content of Al in the first catalyst layer, converted to AI2O3, is 12 mass% or less, a ratio of the mass content of Al in the first catalyst layer, converted to AI2O3, to a mass content of Al in the second catalyst layer, converted to AI2O3, is 0 or more and 0.65 or less.

2. The exhaust gas purification catalyst according to claim 1, wherein a ratio of a mass of the first catalyst layer per unit volume of a portion of the substrate in which the first catalyst layer is formed to a mass of the second catalyst layer per unit volume of a portion of the substrate in which the second catalyst layer is formed is 0.95 or less.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein the first catalyst layer and the second catalyst layer each contain Pd and / or Pt.

4. The exhaust gas purification catalyst according to claim 3, wherein the catalyst for exhaust gas purification further comprises a third catalyst layer provided on an upper side of the first catalyst layer and / or a fourth catalyst layer provided on an upper side of the second catalyst layer, and the third catalyst layer and the fourth catalyst layer each contain Rh.

5. The exhaust gas purification catalyst according to claim 1 or 2, wherein the first catalyst layer contains Pd.

6. The exhaust gas purification catalyst according to claim 1 or 2, wherein a ratio of the mass content of Al in the second catalyst layer, converted to AI2O3, to a mass content of the noble metal element in the second catalyst layer, converted to metal, is 50 or more and 600 or less.

7. The exhaust gas purification catalyst according to claim 1 or 2, wherein a mass content of Ce in the first catalyst layer, converted to CeO2, is 32 mass% or more. the second catalyst layer contains a noble metal element and AI2O3, a mass content of Al in the first catalyst layer, converted to AI2O3, is 12 mass% or less, a ratio of the mass content of Al in the first catalyst layer, converted to AI2O3, to a mass content of Al in the second catalyst layer, converted to AI2O3, is 0 or more and 0.65 or less. a ratio of a mass of the first catalyst layer per unit volume of a portion of the substrate in which the first catalyst layer is formed to a mass of the second catalyst layer per unit volume of a portion of the substrate in which the second catalyst layer is formed is 0.95 or less. the first catalyst layer and the second catalyst layer each contain Pd and / or Pt. the catalyst for exhaust gas purification further comprises a third catalyst layer provided on an upper side of the first catalyst layer and / or a fourth catalyst layer provided on an upper side of the second catalyst layer, and the third catalyst layer and the fourth catalyst layer each contain Rh. the first catalyst layer contains Pd. a ratio of the mass content of Al in the second catalyst layer, converted to AI2O3, to a mass content of the noble metal element in the second catalyst layer, converted to metal, is 50 or more and 600 or less. a mass content of Ce in the first catalyst layer, converted to CeO2, is 32 mass% or more.

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