Exhaust gas purification catalyst

Abstract

The present invention addresses the problem of providing an exhaust gas purification catalyst that exhibits an improved methane purification performance during the high-speed operation of an internal combustion engine. In order to solve this problem, the present invention provides an exhaust gas purification catalyst (1A) comprising: a first catalyst layer (20) containing Pd; a second catalyst layer (30) containing Pt, Ce, and an alkaline earth metal element; and an Rh-containing third catalyst layer (40) and / or an Rh-containing fourth catalyst layer (50). The mass as metal of Pt in the second catalyst layer (30) is at least 1.0 g / L. In the second catalyst layer (30), the ratio of the mass as CeO2 of Ce to the mass as metal of Pt is 6.0-20.0. Also in the second catalyst layer (30), the ratio of the mass as CeO2 of Ce to the mass as the oxide of the alkaline earth metal element is 2.0-18.0.

Description

TECHNICAL FIELD

[0001] The present invention relates to an exhaust gas purifying catalyst.

BACKGROUND ART

[0002] Exhaust gas discharged from internal combustion engines of automobiles, motorcycles and the like contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). For the purpose of purifying these harmful components to render them harmless, noble metal elements such as Pt, Pd, and Rh are used as catalytic active components of exhaust gas purifying catalysts.

[0003] HC discharged from internal combustion engines includes methane (CH4). As an exhaust gas purifying catalyst suitable for methane purification, Patent Document 1 describes an exhaust gas purifying catalyst that includes a substrate and a catalyst layer provided on the substrate, where the catalyst layer includes a Pd layer provided on the upstream side, a Pt layer provided on the downstream side, and a Rh layer laminated on both the Pd layer and the Pt layer, and the Pt layer does not substantially contain alkaline earth metal elements.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0004]

PATENT DOCUMENT 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] The air-fuel ratio (air-fuel ratio) supplied to an internal combustion engine should ideally be controlled near the stoichiometric air-fuel ratio. However, the actual air-fuel ratio fluctuates around the stoichiometric ratio, either rich (excess fuel atmosphere) or lean (lean fuel atmosphere), depending on the operating conditions of the internal combustion engine. Consequently, the exhaust gas atmosphere also fluctuates between rich and lean states. When the exhaust gas is lean, Pt is oxidized, and its methane purification performance decreases. When the exhaust gas switches from a lean to a rich state, the oxidized Pt is reduced, and its methane purification performance recovers. Alkaline earth metal elements are electron-donating; therefore, when alkaline earth metal elements are present near Pt, electrons are donated from the alkaline earth metal elements to the Pt. Consequently, when a Pt layer contains alkaline earth metal elements, Pt becomes more adsorbent of oxygen and more stable as an oxide. In other words, if the Pt layer contains alkaline earth metal elements, the methane purification performance of Pt will not recover easily even if the exhaust gas switches from a lean state to a rich state. For this reason, Patent Document 1 states that the Pt layer is substantially free of alkaline earth metal elements.

[0006] Patent Document 1 does not include any studies on methane purification performance during high-speed operation of internal combustion engines. When the present inventors conducted a study on methane purification performance during high-speed operation of internal combustion engines, it was found that the exhaust gas purification catalyst described in Patent Document 1 does not have sufficient methane purification performance during high-speed operation of internal combustion engines.

[0007] Therefore, the object of the present invention is to provide an exhaust gas purification catalyst that has improved methane purification performance during high-speed operation of an internal combustion engine. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides the following exhaust gas purification catalyst. [1] A substrate extending in the exhaust gas flow direction, the substrate having a first substrate portion located upstream in the exhaust gas flow direction and a second substrate portion located downstream in the exhaust gas flow direction, The first catalyst layer provided on the first substrate portion, The second catalyst layer provided on the second substrate portion, A third catalyst layer provided above the first catalyst layer and / or a fourth catalyst layer provided above the second catalyst layer, An exhaust gas purification catalyst comprising, The first catalyst layer contains Pd, The second catalyst layer contains Pt, Ce, and alkaline earth metal elements. The third catalyst layer and the fourth catalyst layer each contain Rh, The metallic mass of Pt in the second catalyst layer is 1.0 g / L or more, based on the volume of the portion of the second substrate in which the second catalyst layer is provided. In the second catalyst layer, the ratio of the mass of Ce (in terms of CeO2) to the mass of Pt (in terms of metal) is 6.0 or more and 20.0 or less. The exhaust gas purification catalyst, wherein in the second catalyst layer, the ratio of the mass of Ce (in CeO2 equivalent) to the mass of alkaline earth metal elements (in oxide equivalent) is 2.0 or more and 18.0 or less. [2] The exhaust gas purification catalyst according to [1], wherein the second catalyst layer contains a Ce-Zr composite oxide as a Ce source. [3] The exhaust gas purification catalyst according to [2], wherein the content of Ce in the Ce-Zr composite oxide, on an equivalent basis to CeO2, is 18% by mass or more and 70% by mass or less, based on the mass of the Ce-Zr composite oxide. [4] The exhaust gas purification catalyst according to [3], wherein the content of Ce in the Ce-Zr composite oxide, on an equivalent basis to CeO2, is 25% by mass or more and 63% by mass or less, based on the mass of the Ce-Zr composite oxide. [5] The exhaust gas purification catalyst according to any one of [2] to [4], wherein the content of the Ce-Zr composite oxide in the second catalyst layer is 20% by mass or more and 80% by mass or less, based on the mass of the second catalyst layer. [6] The exhaust gas purification catalyst according to any one of [2] to [5], wherein at least a portion of the Pt in the second catalyst layer is supported on the Ce-Zr composite oxide in the second catalyst layer. [7] The second catalyst layer contains an alkaline earth metal compound as an alkaline earth metal element source, The exhaust gas purification catalyst according to any one of [1] to [6], wherein the alkaline earth metal compound is selected from oxides, carbonates, and sulfates. [8] The exhaust gas purification catalyst according to any one of [1] to [7], wherein the second catalyst layer comprises one or more alkaline earth metal elements selected from Ca, Sr, and Ba. [9] The exhaust gas purification catalyst according to any one of [1] to [8], wherein the third catalyst layer and the fourth catalyst layer each contain Pt.

[10] The exhaust gas purification catalyst according to [9], wherein the third catalyst layer and the fourth catalyst layer each contain Ce.

[11] The exhaust gas purification catalyst according to

[10] , wherein the third catalyst layer and the fourth catalyst layer each contain a Ce-Zr composite oxide as a Ce source.

[12] The exhaust gas purification catalyst according to

[11] , wherein at least a portion of the Pt in the third catalyst layer is supported on the Ce-Zr composite oxide in the third catalyst layer, and at least a portion of the Pt in the fourth catalyst layer is supported on the Ce-Zr composite oxide in the fourth catalyst layer. [Effects of the Invention]

[0009] According to the present invention, an exhaust gas purification catalyst is provided that has improved methane purification performance during high-speed operation of an internal combustion engine. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a partial end view showing an exhaust gas purification catalyst according to the first embodiment of the present invention, arranged in the exhaust passage of an internal combustion engine. [Figure 2] Figure 2 is an end view of line AA in Figure 1. [Figure 3] Figure 3 is an end view of line BB in Figure 1. [Figure 4] Figure 4 is an enlarged view of the region indicated by the symbol R1 in Figure 2. [Figure 5]Figure 5 is an enlarged view of the region indicated by reference sign R2 in Figure 3. [Figure 6] Figure 6 is an end view taken along line C-C in Figure 1. [Figure 7] Figure 7 is an end view (end view corresponding to Figure 6) of an exhaust gas purifying catalyst according to the second embodiment of the present invention. [Modes for Carrying Out the Invention]

[0011] «Explanation of Terms» Hereinafter, terms used in the present specification will be explained. The following explanations apply to the entire present specification unless otherwise specified. The following explanations regarding catalyst layers apply to all catalyst layers (that is, the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50).

[0012] The term "metal element" also includes metalloid elements such as Si and B.

[0013] <Rare earth element> The term "rare earth element" includes Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0014] <Precious metal element> The term "precious metal element" includes Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.

[0015] <Oxide> The meaning of the term "oxide" is as follows. Oxides of rare earth elements excluding Ce, Pr, and Tb are sesquioxides (M2O3, M represents a rare earth element other than Ce, Pr, and Tb), the oxide of Ce is CeO2, and the oxide of Pr is Pr6O 11This means that Tb oxide is Tb4O7, Al oxide is Al2O3, Zr oxide is ZrO2, Si oxide is SiO2, B oxide is B2O3, Cr oxide is Cr2O3, Mg oxide is MgO, Ca oxide is CaO, Sr oxide is SrO, Ba oxide is BaO, Fe oxide is Fe3O4, Mn oxide is Mn3O4, Ni oxide is NiO, Ti oxide is TiO2, Zn oxide is ZnO, and Sn oxide is SnO2.

[0016] <Mass equivalent of metallic elements in metallic form> The term "metallic equivalent mass of a metallic element" refers to the mass of a metal calculated by assuming that the metallic element exists as a metal composed of that metallic element.

[0017] <Mass of metallic elements in terms of oxide equivalent> The term "mass of a metallic element in terms of its oxide equivalent" refers to the mass of the oxide of the metallic element, calculated by assuming that the metallic element exists as an oxide of that metallic element. The meaning of "oxide" of a metallic element is as described above.

[0018] <Mass of metallic elements in terms of carbonate equivalent> The term "mass of a metallic element in terms of carbonate" refers to the mass of a carbonate obtained by assuming that the metallic element exists as a carbonate of that metallic element.

[0019] <Mass of metallic elements in sulfate equivalent> The term "mass of a metallic element in terms of sulfate" refers to the mass of a sulfate of the metallic element, calculated by assuming that the metallic element exists as a sulfate of that metallic element.

[0020] <Mass of the catalyst layer> The term "mass of the catalyst layer" refers to the mass obtained by classifying all metal elements contained in the catalyst layer into noble metal elements, alkaline earth metal elements, and metal elements other than noble metal elements and alkaline earth metal elements. For noble metal elements, the mass is calculated in terms of metal equivalent; for alkaline earth metal elements, if hydroxides, acetates, nitrates, or carbonates of alkaline earth metal elements are used as raw materials for the catalyst layer, the mass is calculated in terms of carbonate; if sulfates of alkaline earth metal elements are used as raw materials for the catalyst layer, the mass is calculated in terms of sulfate; and for metal elements other than noble metal elements and alkaline earth metal elements, the mass is calculated in terms of oxide equivalent, and these masses are then added together. In other words, the term "mass of the catalyst layer" refers to the calculated mass obtained by adding the mass of the noble metal elements contained in the catalyst layer in terms of metal equivalent, the mass of the alkaline earth metal elements contained in the catalyst layer in terms of carbonate or sulfate, and the mass of the metal elements other than noble metal elements contained in the catalyst layer in terms of oxide equivalent.

[0021] If information about the raw materials used in the manufacture of the catalyst layer (e.g., composition, quantity, etc.) is known, the mass of the catalyst layer can be determined from the information about the raw materials used in the manufacture of the catalyst layer.

[0022] <Content of metal elements in the catalyst layer, either in terms of metal or oxide> The term "metallic content of metal elements in the catalyst layer" is defined by the formula: Metallic content of metal elements in the catalyst layer (mass%) = (metallic mass of metal elements in the catalyst layer) / (mass of the catalyst layer) × 100. The meanings of "metallic mass of metal elements" and "mass of the catalyst layer" are as described above.

[0023] The term "concentration of metal elements in the catalyst layer in terms of oxides" is defined by the formula: Concentration of metal elements in the catalyst layer in terms of oxides (mass%) = (mass of metal elements in the catalyst layer in terms of oxides) / (mass of the catalyst layer) × 100. The meanings of "mass of metal elements in terms of oxides" and "mass of the catalyst layer" are as described above.

[0024] If information on the raw materials used to form the catalyst layer (e.g., composition, quantity, etc.) is known, the content (mass %) of metal elements in the catalyst layer, either in terms of metal or oxide, can be determined from the raw material information.

[0025] If information on the raw materials used to form the catalyst layer is unknown, the content (mass%) of metal elements in the catalyst layer, either in terms of metal or oxide, can be determined by conventional methods such as scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX). Specifically, this is as follows:

[0026] Elemental analysis of the catalyst layer is performed using conventional methods such as SEM-EDX to identify the types of constituent elements in the catalyst layer and determine the molar percentage of each identified metal element. For each of the 10 fields of view of the SEM, the molar percentage of each metal element is determined, and the average value of the molar percentages of each metal element across the 10 fields of view is taken as the molar percentage of each metal element in the catalyst layer.

[0027] The U-value for each noble metal element in the catalyst layer can be determined from the following formula. U-value for each precious metal element = (molar percentage of each precious metal element in the catalyst layer) × (molar mass of each precious metal element)

[0028] The V1 value for each alkaline earth metal element in the catalyst layer can be determined from the following formula. The V1 value for each alkaline earth metal element = (molar %) of each alkaline earth metal element in the catalyst layer × (molar mass of oxides of each alkaline earth metal element)

[0029] The V2 value for each alkaline earth metal element in the catalyst layer can be determined from the following formula. V2 value for each alkaline earth metal element = (molar %) of each alkaline earth metal element in the catalyst layer × (molar mass of carbonate or sulfate of each alkaline earth metal element)

[0030] "Molar mass of carbonate or sulfate of alkaline earth metal element" means the molar mass of the carbonate of the alkaline earth metal element when the hydroxide, acetate, nitrate, or carbonate of the alkaline earth metal element is used as a raw material for the catalyst layer, and means the molar mass of the sulfate of the alkaline earth metal element when the sulfate of the alkaline earth metal element is used as a raw material for the catalyst layer.

[0031] For each metal element in the catalyst layer other than the noble metal elements and alkaline earth metal elements, the W value can be determined from the following formula. The W value for each metal element = (molar percentage of each metal element in the catalyst layer) × (molar mass of oxide of each metal element)

[0032] The content (mass %) of each noble metal element in the catalyst layer, expressed as metal, can be calculated using the following formula. The content (mass %) of each noble metal element in the catalyst layer, in terms of metal equivalent, is calculated as follows: (U value for each noble metal element) / {(sum of U values ​​for all noble metal elements) + (sum of V2 values ​​for all alkaline earth metal elements) + (sum of W values ​​for all metal elements other than noble metal elements and alkaline earth metal elements)} × 100

[0033] The oxide content (mass %) of each alkaline earth metal element in the catalyst layer can be calculated using the following formula. The content (mass %) of each alkaline earth metal element in the catalyst layer, converted to oxides, is calculated as follows: (V1 value for each alkaline earth metal element) / {(sum of U values ​​for all precious metal elements) + (sum of V2 values ​​for all alkaline earth metal elements) + (sum of W values ​​for all metal elements other than precious metal elements and alkaline earth metal elements)} × 100

[0034] The oxide content (mass%) of each metal element other than noble metal elements and alkaline earth metal elements in the catalyst layer can be calculated using the following formula. Content percentage (mass%) in terms of oxide of each metal element other than noble metal elements and alkaline earth metal elements in the catalyst layer = (W value for each metal element other than noble metal elements and alkaline earth metal elements) / {(sum of U values for all noble metal elements) + (sum of V2 values for all alkaline earth metal elements) + (sum of W values for all metal elements other than noble metal elements and alkaline earth metal elements)} × 100

[0035] <Al-based oxide> The term "Al-based oxide" means an oxide containing Al, in which Al is the metal element with the highest content percentage on a mass basis among the metal elements constituting the oxide. However, those that fall under the Ce-Zr composite oxide shall not fall under the Al-based oxide. The Ce-Zr composite oxide will be described later. The Al-based oxide is distinguished from alumina used as a binder. In the present specification, alumina used as a binder may be referred to as "alumina binder".

[0036] The Al-based oxide is, for example, in a particulate form. The Al-based oxide is used as a carrier for catalytically active components. From the viewpoint of improving the supporting property of the catalytically active components, the Al-based oxide is preferably porous.

[0037] The Al-based oxide preferably has a particle size suitable for use as a carrier for catalytically active components. The average particle size of the Al-based oxide is preferably 1 μm or more and 35 μm or less, more preferably 2 μm or more and 25 μm or less, and even more preferably 3 μm or more and 15 μm or less. Each of the above lower limits may be combined with any of the above upper limits. The method for measuring the average particle size of the Al-based oxide is as follows. A sample containing the Al-based oxide is observed using a scanning electron microscope, the unidirectional diameters (Feret diameters) of 100 arbitrarily selected Al-based oxides within the field of view are measured, and the average value is taken as the average particle size of the Al-based oxide.

[0038] The Al-based oxide generally has higher heat resistance than other inorganic oxides. Therefore, when the catalyst layer contains the Al-based oxide, the heat resistance of the catalyst layer is improved, and the exhaust gas purification performance of the catalyst layer is enhanced.

[0039] Al-based oxides may contain one or more metallic elements other than Al (hereinafter referred to as "additional element M1"). Additional element M1 can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0040] In Al-based oxides, the additional element M1 may form a solid solution phase (for example, a solid solution phase of Al2O3 and an oxide of the additional element M1), a single phase which is either a crystalline or amorphous phase (for example, an oxide phase of the additional element M1), or both a solid solution phase and a single phase. However, it is preferable that at least a portion of the additional element M1 forms a solid solution phase.

[0041] Examples of Al-based oxides include alumina (Al2O3), oxides obtained by modifying the surface of alumina with an additional element M1, and oxides obtained by solid-solving the additional element M1 in alumina. Examples of Al-based oxides containing the additional element M1 include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, and alumina-lantana.

[0042] From the viewpoint of improving the heat resistance of Al-based oxides, the Al content in Al-based oxides, calculated as Al2O3, is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, based on the mass of the Al-based oxide. The upper limit is 100% by mass.

[0043] The Al content in Al-based oxides, converted to Al2O3, is defined by the formula: (mass of Al in Al-based oxides converted to Al2O3) / (mass of Al-based oxides) × 100. "Mass of Al-based oxides" refers to the total mass of oxides of the metal elements, calculated assuming that each metal element in the Al-based oxide exists as an oxide. The meaning of "oxide" of a metal element is as described above.

[0044] From the viewpoint of improving the heat resistance of Al-based oxides, it is preferable that the Al-based oxide contains one or more rare earth elements. The rare earth elements can be selected from, for example, La, Y, Nd, Pr, Sm, Eu, Gd, etc. In one embodiment, the Al-based oxide contains La. In addition to La, the Al-based oxide may contain one or more other rare earth elements.

[0045] From the viewpoint of improving the heat resistance of Al-based oxides, the content of rare earth elements in Al-based oxides on an oxide basis is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.3% by mass or more and 15% by mass or less, and even more preferably 0.5% by mass or more and 10% by mass or less, based on the mass of the Al-based oxide. The lower limit above may be combined with any of the upper limits above. "Content of rare earth elements in Al-based oxides on an oxide basis" means the content of one rare earth element on an oxide basis if the Al-based oxide contains one type of rare earth element, and means the total content of two or more rare earth elements on an oxide basis if the Al-based oxide contains two or more types of rare earth elements.

[0046] The oxide content of rare earth elements in Al-based oxides is defined by the formula: (mass of rare earth elements in Al-based oxides as oxides) / (mass of Al-based oxides) × 100. The meanings of "mass of Al-based oxides" and "oxides" of metallic elements are as described above.

[0047] If the composition of an Al-based oxide is known, the oxide content of each metal element in the Al-based oxide can be determined from the composition of the Al-based oxide.

[0048] When the composition of the Al-based oxide is unknown, the oxide-equivalent content of each metal element in the Al-based oxide can be determined by analyzing a sample containing the Al-based oxide using energy-dispersive X-ray spectroscopy (EDX), from the obtained elemental mapping and the EDX elemental analysis of the designated particles. Specifically, Al-based oxide particles and other particles are qualitatively identified (color-coded) by elemental mapping, and composition analysis (elemental analysis) is performed on the designated Al-based oxide particles, whereby the oxide-equivalent content of each metal element in the designated Al-based oxide particles can be determined.

[0049] <Ce-based oxide> The term "Ce-based oxide" means an oxide containing Ce, wherein Ce is the metal element with the highest content by mass among the metal elements constituting the oxide. However, those corresponding to Ce-Zr composite oxides shall not fall under the Ce-based oxide category. The Ce-Zr composite oxides 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 may be referred to as "ceria binder".

[0050] The Ce-based oxide is, for example, in the form of particles. The Ce-based oxide is used as a carrier for catalytically active components. From the viewpoint of improving the supporting property of the catalytically active components, the Ce-based oxide is preferably porous.

[0051] The Ce-based oxide preferably has a particle size suitable for use as a carrier for catalytically active components. The average particle size of the Ce-based oxide is preferably 1 μm or more and 35 μm or less, more preferably 2 μm or more and 25 μm or less, and even more preferably 3 μm or more and 15 μm or less. Each of the above lower limits may be combined with any of the above upper limits. The method for measuring the average particle size of the Ce-based oxide is the same as the method for measuring the average particle size of the Al-based oxide.

[0052] Ce oxides possess oxygen storage capacity (the ability to absorb oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low), mitigating fluctuations in the oxygen concentration in the exhaust gas and expanding the operating window of the catalytic active component. Therefore, including Ce oxides in the catalyst layer improves the exhaust gas purification performance of the catalyst layer.

[0053] Ce-based oxides may contain one or more metallic elements other than Ce (hereinafter referred to as "additional element M2"). Additional element M2 can be selected from, for example, rare earth elements other than Ce (e.g., La, Y, Nd, Pr, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0054] In Ce-based oxides, the additional element M2 may form a solid solution phase (for example, a solid solution phase of CeO2 and an oxide of the additional element M2), a single phase which is either a crystalline or amorphous phase (for example, an oxide phase of the additional element M2), or both a solid solution phase and a single phase. However, it is preferable that at least a portion of the additional element M2 forms a solid solution phase.

[0055] Examples of Ce-based oxides include ceria (CeO2), oxides obtained by modifying the surface of ceria with an additional element M2, and oxides obtained by solid-solving the additional element M2 in ceria.

[0056] From the viewpoint of improving the oxygen storage capacity of Ce-based oxides, the Ce content in Ce-based oxides, in terms of CeO2, is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, based on the mass of the Ce-based oxide. The upper limit is 100% by mass.

[0057] The content ratio of Ce in the Ce-based oxide in terms of CeO₂ is defined by the formula: (mass of Ce in the Ce-based oxide in terms of CeO₂) / (mass of the Ce-based oxide) × 100. The "mass of the Ce-based oxide" means the total mass of oxides of metallic elements determined on the assumption that each metallic element in the Ce-based oxide exists as an oxide. The meaning of the "oxide" of a metallic element is as described above.

[0058] The content ratio of each metallic element in the Ce-based oxide in terms of oxide can be determined in the same manner as the content ratio of each metallic element in the Al-based oxide in terms of oxide.

[0059] <Zr-based oxide> The term "Zr-based oxide" means an oxide containing Zr, in which Zr is the metallic element with the highest content ratio on a mass basis among the metallic elements constituting the oxide. However, those corresponding to Ce-Zr-based composite oxides shall not fall under the Zr-based oxide. The Ce-Zr-based composite oxide will be described later. The Zr-based oxide is distinguished from zirconia used as a binder. In the present specification, zirconia used as a binder may be referred to as "zirconia binder".

[0060] The Zr-based oxide is, for example, in a particulate form. The Zr-based oxide is used as a carrier for a catalytically active component. From the viewpoint of improving the supporting property of the catalytically active component, the Zr-based oxide is preferably porous.

[0061] The Zr-based oxide preferably has a particle size suitable for use as a carrier for a catalytically active component. The average particle size of the Zr-based oxide is preferably 0.1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less. Each of the above lower limits may be combined with any of the above upper limits. The method for measuring the average particle size of the Zr-based oxide is the same as the method for measuring the average particle size of the Al-based oxide.

[0062] The Zr-based oxide has high heat resistance. Therefore, when the catalyst layer contains the Zr-based oxide, the heat resistance of the catalyst layer is improved, and the exhaust gas purification performance of the catalyst layer is enhanced.

[0063] Zr-based oxides may contain one or more metallic elements other than Zr (hereinafter referred to as "additional element M3"). Additional element M3 can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Al, Cr, etc.

[0064] In Zr-based oxides, the additional element M3 may form a solid solution phase (for example, a solid solution phase of ZrO2 and an oxide of the additional element M3), a single phase which is either a crystalline or amorphous phase (for example, an oxide phase of the additional element M3), or both a solid solution phase and a single phase. However, it is preferable that at least a portion of the additional element M3 forms a solid solution phase.

[0065] Examples of Zr-based oxides include zirconia (ZrO2), oxides obtained by modifying the surface of zirconia with the additional element M3, and oxides obtained by solid-solving the additional element M3 in zirconia.

[0066] From the viewpoint of improving the heat resistance of Zr-based oxides, the Zr content in Zr-based oxides, calculated as ZrO2, is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more, based on the mass of the Zr-based oxide. The upper limit is 100% by mass.

[0067] The Zr content in Zr oxides, converted to ZrO2, is defined by the formula: (mass of Zr in Zr oxide converted to ZrO2) / (mass of Zr oxide) × 100. "Mass of Zr oxide" refers to the total mass of the oxides of the metal elements, calculated assuming that each metal element in the Zr oxide exists as an oxide. The meaning of "oxide" for metal elements is as described above.

[0068] The oxide content of each metal element in Zr-based oxides can be determined in the same way as the oxide content of each metal element in Al-based oxides.

[0069] <Ce-Zr based composite oxide> The Ce-Zr based composite oxide is a composite oxide containing Ce and Zr, and means an oxide 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.

[0070] The content of Ce in terms of CeO₂ in the Ce-Zr based composite oxide is defined by the formula: (mass of Ce in terms of CeO₂ in the Ce-Zr based composite oxide) / (mass of the Ce-Zr based composite oxide) × 100, and the content of Zr in terms of ZrO₂ in the Ce-Zr based composite oxide is defined by the formula: (mass of Zr in terms of ZrO₂ in the Ce-Zr based composite oxide) / (mass of the Ce-Zr based composite oxide) × 100. The "mass of the Ce-Zr based composite oxide" means the total mass of oxides of metal elements determined on the assumption that each metal element in the Ce-Zr based composite oxide exists as an oxide. The meaning of the "oxide" of a metal element is as described above.

[0071] The content of each metal element in terms of oxide in the Ce-Zr based composite oxide can be determined in the same manner as the content of each metal element in terms of oxide in the Al-based oxide.

[0072] The Ce-Zr based composite oxide is, for example, in the form of particles. The Ce-Zr based composite oxide is used as a carrier for catalytically active components. From the viewpoint of improving the supporting property of the catalytically active component, the Ce-Zr based composite oxide is preferably porous.

[0073] The Ce-Zr based composite oxide preferably has a particle size suitable for use as a carrier for catalytically active components. The average particle size of the Ce-Zr based composite oxide is preferably 1 μm or more and 35 μm or less, more preferably 3 μm or more and 15 μm or less. Each of the above lower limits may be combined with any of the above upper limits. The method for measuring the average particle size of the Ce-Zr based composite oxide is the same as the method for measuring the average particle size of the Al-based oxide.

[0074] Ce-Zr composite oxides possess oxygen storage capacity, mitigating fluctuations in oxygen concentration in exhaust gas and expanding the operating window of the catalytic active components. Therefore, including Ce-Zr composite oxides in the catalyst layer improves the exhaust gas purification performance of the catalyst layer.

[0075] Ce-Zr composite oxides may contain one or more metallic elements other than Ce and Zr (hereinafter referred to as "additional element M4"). Additional element M4 can be selected from, for example, rare earth elements other than Ce (e.g., La, Y, Nd, Pr, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.

[0076] In Ce-Zr composite oxides, Ce may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2), a single phase which is either a crystalline or amorphous phase (for example, a single CeO2 phase), or both a solid solution phase and a single phase. However, it is preferable that at least a portion of the Ce forms a solid solution phase.

[0077] In Ce-Zr composite oxides, Zr may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2), a single phase which is either a crystalline or amorphous phase (for example, a single ZrO2 phase), or both a solid solution phase and a single phase. However, it is preferable that at least a portion of the Zr forms a solid solution phase.

[0078] When the Ce-Zr composite oxide contains an additional element M4, the additional element M4 may form a solid solution phase (for example, a solid solution phase of CeO2 and an oxide of the additional element M4, a solid solution phase of ZrO2 and an oxide of the additional element M4, a solid solution phase of CeO2, ZrO2 and an oxide of the additional element M4, etc.), or it may form a single phase that is a crystalline or amorphous phase (for example, a single oxide phase of the additional element M4), or it may form both a solid solution phase and a single phase, but it is preferable that at least a portion of the additional element M4 forms a solid solution phase.

[0079] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, it is preferable that Ce-Zr composite oxides contain one or more rare earth elements. Rare earth elements can be selected from, for example, La, Y, Nd, Pr, Sm, Eu, Gd, etc.

[0080] ≪First Embodiment≫ The exhaust gas purification catalyst 1A (hereinafter referred to as "catalyst 1A") according to the first embodiment will be described below with reference to Figures 1 to 6.

[0081] As shown in Figure 1, catalyst 1A is located in the exhaust passage within the exhaust pipe P of the internal combustion engine. The internal combustion engine may be a gasoline-fueled engine (e.g., a gasoline engine) or a natural gas-fueled engine (e.g., a natural gas engine) (e.g., compressed natural gas (CNG)). Both the exhaust gas emitted from a gasoline-fueled internal combustion engine and the exhaust gas emitted from a natural gas-fueled internal combustion engine contain methane. The exhaust gas emitted from the internal combustion engine flows through the exhaust passage within the exhaust pipe P from one end to the other and is purified by catalyst 1A installed in the exhaust pipe P. In the drawings, the exhaust gas flow direction is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas inlet side" or "upstream side," and the downstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas outlet side" or "downstream side." In this specification, "length" means the dimension of the exhaust gas flow direction X unless otherwise specified.

[0082] In the exhaust passage within the exhaust pipe P, other exhaust gas purification catalysts may be placed upstream and / or downstream of catalyst 1A.

[0083] As shown in Figures 2-6, catalyst 1A comprises a substrate 10 having a first substrate portion 10a located upstream and a second substrate portion 10b located downstream, a first catalyst layer 20 provided on the first substrate portion 10a, a second catalyst layer 30 provided on the second substrate portion 10b, a third catalyst layer 40 provided above the first catalyst layer 20, and a fourth catalyst layer 50 provided above the second catalyst layer 30.

[0084] Either the third catalyst layer 40 or the fourth catalyst layer 50 can be omitted. Therefore, the present invention encompasses embodiments having the third catalyst layer 40 but not the fourth catalyst layer 50, as well as embodiments having the fourth catalyst layer 50 but not the third catalyst layer 40. However, from the viewpoint of further improving the methane purification performance of catalyst 1A, it is preferable that catalyst 1A has both the third catalyst layer 40 and the fourth catalyst layer 50.

[0085] Catalyst 1A is characterized in that the first catalyst layer 20 contains Pd, the second catalyst layer 30 contains Pt, Ce and alkaline earth metal elements, and the third catalyst layer 40 and the fourth catalyst layer 50 each contain Rh, the metallic mass of Pt in the second catalyst layer 30 is 1.0 g / L or more based on the volume of the portion of the second substrate part 10b in which the second catalyst layer 30 is provided, the ratio of the metallic mass of Ce to the CeO2 equivalent mass of Pt in the second catalyst layer 30 is 6.0 or more and 20.0 or less, and the ratio of the oxide equivalent mass of Ce to the oxide equivalent mass of alkaline earth metal elements in the second catalyst layer 30 is 2.0 or more and 18.0 or less.

[0086] The effects of catalyst 1A will be explained below.

[0087] The air-fuel ratio (air-fuel ratio) supplied to an internal combustion engine should ideally be controlled near the stoichiometric air-fuel ratio. However, the actual air-fuel ratio fluctuates around the stoichiometric ratio, either rich (excess fuel atmosphere) or lean (lean fuel atmosphere), depending on the operating conditions of the internal combustion engine. Consequently, the exhaust gas atmosphere also fluctuates between rich and lean states. When the exhaust gas is lean, Pt is oxidized, and its methane purification performance decreases. When the exhaust gas switches from a lean to a rich state, the oxidized Pt is reduced, and its methane purification performance recovers. Alkaline earth metal elements are electron-donating; therefore, when alkaline earth metal elements are present near Pt, electrons are donated from the alkaline earth metal elements to the Pt. Consequently, when a Pt layer contains alkaline earth metal elements, Pt becomes more adsorbent of oxygen and more stable as an oxide. In other words, if the Pt layer contains alkaline earth metal elements, the methane purification performance of Pt will not recover easily even if the exhaust gas switches from a lean state to a rich state. For this reason, Patent Document 1 states that the Pt layer is substantially free of alkaline earth metal elements.

[0088] When the catalyst is placed in an atmosphere that fluctuates drastically between a lean state and a rich state, it is preferable that the Pt layer substantially contains no alkaline earth metal elements, as described in Patent Document 1, from the viewpoint of preventing Pt from becoming stable as an oxide.

[0089] However, during high-speed operation of an internal combustion engine, the atmosphere surrounding the catalyst remains almost constant (rich or stoichiometric), so there is no need to limit the content of alkaline earth metal elements in the Pt layer from the standpoint of preventing Pt from stabilizing as an oxide.

[0090] In the rich and stoichiometric states, the methane purification reaction by Pt proceeds primarily through the steam reforming reaction shown in equations 1-3 below. Since the steam reforming reaction is an equilibrium reaction, the concentrations of reactants and products in the reaction system are important for the steam reforming reaction to proceed.

[0091] Formula 1: CH4+H2O ⇔ CO+3H2 Formula 2: CO+H2O ⇔ CO2+H2 Formula 3: CH4+2H2O ⇔ CO2+4H2

[0092] Effect of the first catalyst layer 20 When the reaction in Equation 1 proceeds to the right, CO is produced. Therefore, the CO in the exhaust gas that comes into contact with the second catalyst layer 30 inhibits the reaction in Equation 1 by Pt in the second catalyst layer 30 from proceeding to the right. Since the first catalyst layer 20 is located upstream of the second catalyst layer 30, the exhaust gas comes into contact with the first catalyst layer 20 before coming into contact with the second catalyst layer 30. When the exhaust gas comes into contact with the first catalyst layer 20, the Pd in ​​the first catalyst layer 20 purifies and removes CO from the exhaust gas, so the CO concentration in the exhaust gas after contact with the first catalyst layer 20 (i.e., the exhaust gas that comes into contact with the second catalyst layer 30) decreases. As the CO concentration in the exhaust gas that comes into contact with the second catalyst layer 30 decreases, the reaction in Equation 1 by Pt in the second catalyst layer 30 proceeds more easily to the right. Therefore, the inclusion of Pd in ​​the first catalyst layer 20 improves the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0093] Effect of the second catalyst layer 30 Pt has higher catalytic activity in steam reforming reactions than other precious metal elements. Therefore, the more Pt used, the higher the methane purification activity. Accordingly, if the second catalyst layer 30 contains Pt, and the metallic mass of Pt in the second catalyst layer 30 is 1.0 g / L or more, based on the volume of the portion of the second substrate part 10b where the second catalyst layer 30 is provided, the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine is improved.

[0094] Ce has oxygen storage capacity and releases O2. When H2 produced by the reactions of Pt in the second catalyst layer 30 in equations 1, 2, and 3 reacts with the O2 released by the oxygen storage capacity of Ce in the second catalyst layer 30 to produce H2O, the amount of H2O on the left side of equations 1, 2, and 3 increases, while the amount of H2 on the right side of equations 1, 2, and 3 decreases, making it easier for the reactions of Pt in the second catalyst layer 30 in equations 1, 2, and 3 to proceed to the right. This promotes methane purification by Pt in the second catalyst layer 30. Therefore, the inclusion of Ce in the second catalyst layer 30 improves the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0095] Alkaline earth metal elements have CO2 scavenging ability. When CO2 is scavenged by the alkaline earth metal elements in the second catalyst layer 30, the amount of CO2 on the right-hand side of equations 2 and 3 decreases, and the reactions in equations 2 and 3 by Pt in the second catalyst layer 30 proceed more easily to the right. This promotes methane purification by Pt in the second catalyst layer 30. Therefore, the inclusion of alkaline earth metal elements in the second catalyst layer 30 improves the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0096] As described above, the oxygen storage capacity of Ce reduces H2, and the alkaline earth metal elements reduce CO2. If the reduction of either CO2 or H2 is sufficient, but the reduction of the other is insufficient, the reactions of equations 2 and 3 by Pt in the second catalyst layer 30 will not proceed to the right. Therefore, in order to effectively promote methane purification by Pt in the second catalyst layer 30, the balance between the content of alkaline earth metal elements and the content of Ce in the second catalyst layer 30 is important. Accordingly, in the second catalyst layer 30, the ratio of the mass of Ce (in terms of CeO2) to the mass of alkaline earth metal elements (in terms of oxides) is adjusted to be between 2.0 and 18.0. This improves the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0097] As described above, Ce in the second catalyst layer 30 contributes to improving the methane purification performance during high-speed operation of the internal combustion engine. However, Ce in the second catalyst layer 30 promotes the oxidation of Pt in the second catalyst layer 30, reducing the methane purification performance of Pt in the second catalyst layer 30. Therefore, if the relative amount of Ce to Pt in the second catalyst layer 30 is excessive, the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine will decrease. Accordingly, in the second catalyst layer 30, the ratio of the mass of Ce in CeO2 equivalent to the mass of Pt in metal equivalent is adjusted to be between 6.0 and 20.0. This improves the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0098] Effects of the third catalyst layer 40 and the fourth catalyst layer 50 If the reaction in Equation 1 proceeds to the right, CO is produced. Therefore, the CO in the exhaust gas that comes into contact with the second catalyst layer 30 inhibits the reaction in Equation 1 from proceeding to the right due to the Pt in the second catalyst layer 30. In addition, the NOx in the exhaust gas that comes into contact with the second catalyst layer 30 promotes the deactivation of the alkaline earth metal elements in the second catalyst layer 30 by forming nitrates. Since the third catalyst layer 40 is located upstream of the second catalyst layer 30 and the fourth catalyst layer 50 is located above the second catalyst layer 30, the exhaust gas comes into contact with the third catalyst layer 40 and / or the fourth catalyst layer 50 before coming into contact with the second catalyst layer 30. When exhaust gas comes into contact with the third catalyst layer 40 and / or the fourth catalyst layer 50, the Rh in the third catalyst layer 40 and / or the Rh in the fourth catalyst layer 50 purify and remove CO and NOx from the exhaust gas, thus reducing the CO and NOx concentrations in the exhaust gas after contact with the third catalyst layer 40 and / or the fourth catalyst layer 50 (i.e., the exhaust gas that comes into contact with the second catalyst layer 30). The decrease in CO concentration in the exhaust gas that comes into contact with the second catalyst layer 30 makes it easier for the reaction of Equation 1 by Pt in the second catalyst layer 30 to proceed to the right. In addition, the decrease in NOx concentration in the exhaust gas that comes into contact with the second catalyst layer 30 prevents the alkaline earth metal elements in the second catalyst layer 30 from forming nitrates and becoming inactive, allowing the CO2 scavenging ability of the alkaline earth metal elements in the second catalyst layer 30 to be effectively exercised. As a result, the reactions of Equations 2 and 3 by Pt in the second catalyst layer 30 make it easier for them to proceed to the right. Therefore, by including Rh in the third catalyst layer 40 and the fourth catalyst layer 50, the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine is improved.

[0099] The combined effects of the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50 enable catalyst 1A to exhibit improved methane purification performance during high-speed operation of an internal combustion engine.

[0100] From the viewpoint of further improving the methane purification performance of catalyst 1A, it is preferable that the second catalyst layer 30 contains a Ce-Zr composite oxide as a Ce source, and that at least a portion of the Pt in the second catalyst layer 30 is supported on the Ce-Zr composite oxide in the second catalyst layer 30.

[0101] When Pt is supported on a Ce-Zr composite oxide, the H2 produced by the reactions of equations 1, 2, and 3 by Pt reacts rapidly with the O2 released by the oxygen storage capacity of the Ce-Zr composite oxide, so that the reactions of equations 1, 2, and 3 by Pt proceed more easily to the right. This promotes methane purification by Pt. Therefore, by having the second catalyst layer 30 contain a Ce-Zr composite oxide as a Ce source, and at least a portion of the Pt in the second catalyst layer 30 being supported on the Ce-Zr composite oxide in the second catalyst layer 30, the methane purification performance by Pt in the second catalyst layer 30 is improved during high-speed operation of the internal combustion engine.

[0102] From the viewpoint of further improving the methane purification performance of catalyst 1A, it is preferable that the third catalyst layer 40 and the fourth catalyst layer 50 each contain Pt in addition to Rh.

[0103] The exhaust gas that comes into contact with the third catalyst layer 40 and the exhaust gas that comes into contact with the fourth catalyst layer 50 has a higher CO concentration than the exhaust gas that comes into contact with the second catalyst layer 30. When the CO concentration in the exhaust gas is relatively high, Pt mainly catalyzes the reaction of formula 2 among the reactions of formulas 1, 2, and 3. Therefore, the Pt in the third catalyst layer 40 and the Pt in the fourth catalyst layer 50 mainly catalyze the reaction of formula 2 among the reactions of formulas 1, 2, and 3. As the Pt in the third catalyst layer 40 and the Pt in the fourth catalyst layer 50 catalyze the reaction of formula 2 and remove CO from the exhaust gas, the CO concentration in the exhaust gas after contact with the third catalyst layer 40 and / or the fourth catalyst layer 50 (i.e., the exhaust gas that comes into contact with the second catalyst layer 30) decreases. As the CO concentration in the exhaust gas that comes into contact with the second catalyst layer 30 decreases, the reaction of formula 1 by the Pt in the second catalyst layer 30 proceeds more easily to the right. Therefore, by including Pt in addition to Rh in the third catalyst layer 40 and the fourth catalyst layer 50, the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine is improved.

[0104] The H2 generated by the reaction of Pt in the third catalyst layer 40 according to Equation 2 promotes the reduction and purification of NOx by Rh in the third catalyst layer 40, and the H2 generated by the reaction of Pt in the fourth catalyst layer 50 according to Equation 2 promotes the reduction and purification of NOx by Rh in the fourth catalyst layer 50. As a result, the NOx concentration in the exhaust gas after contact with the third catalyst layer 40 and / or the fourth catalyst layer 50 (i.e., the exhaust gas that comes into contact with the second catalyst layer 30) decreases. The decrease in the NOx concentration in the exhaust gas that comes into contact with the second catalyst layer 30 prevents the alkaline earth metal elements in the second catalyst layer 30 from forming nitrates and becoming inactive, and the CO2 scavenging ability of the alkaline earth metal elements in the second catalyst layer 30 is effectively exerted. As a result, the reactions of Pt in the second catalyst layer 30 according to Equations 2 and 3 proceed more easily to the right. Therefore, by including Pt in addition to Rh in the third catalyst layer 40 and the fourth catalyst layer 50, the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine is improved.

[0105] From the viewpoint of further improving the methane purification performance of catalyst 1A, it is preferable that the third catalyst layer 40 and the fourth catalyst layer 50 each contain Ce in addition to Rh and Pt.

[0106] A portion of the H2 generated by the reaction of Pt in the third catalyst layer 40 according to Equation 2 is not consumed by the reduction and purification of NOx by Rh in the third catalyst layer 40 and remains. The remaining H2 inhibits the reaction of Pt in the third catalyst layer 40 according to Equation 2 from proceeding to the right. When the remaining H2 reacts with O2 released by the oxygen storage capacity of Ce in the third catalyst layer 40 to produce H2O, the amount of H2O on the left side of Equation 2 increases, while the amount of H2 on the right side of Equation 2 decreases, making it easier for the reaction of Pt in the third catalyst layer 40 according to Equation 2 to proceed to the right. This promotes the reaction of Pt in the third catalyst layer 40 according to Equation 2. The above explanation regarding the third catalyst layer 40 also applies to the fourth catalyst layer 50. Therefore, by including Ce in addition to Rh and Pt in the third catalyst layer 40 and the fourth catalyst layer 50, respectively, the CO concentration in the exhaust gas after contact with the third catalyst layer 40 and / or the fourth catalyst layer 50 (i.e., the exhaust gas that comes into contact with the second catalyst layer 30) decreases, and the reaction of Equation 1 by Pt in the second catalyst layer 30 proceeds more easily to the right, thereby improving the methane purification performance by Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0107] From the viewpoint of further improving the methane purification performance of catalyst 1A, it is preferable that the third catalyst layer 40 and the fourth catalyst layer 50 each contain a Ce-Zr composite oxide as a Ce source, at least a portion of the Pt in the third catalyst layer 40 is supported on the Ce-Zr composite oxide in the third catalyst layer 40, and at least a portion of the Pt in the fourth catalyst layer 50 is supported on the Ce-Zr composite oxide in the fourth catalyst layer 50.

[0108] When Pt is supported on a Ce-Zr composite oxide, the H2 produced by the reaction of Pt in Equation 2 reacts rapidly with the O2 released by the oxygen storage capacity of the Ce-Zr composite oxide, causing the reactions of Pt in Equations 1-3 to proceed more easily to the right. This promotes the reaction of Pt in Equation 2. Therefore, since the third catalyst layer 40 and the fourth catalyst layer 50 each contain a Ce-Zr composite oxide as a Ce source, and at least a portion of the Pt in the third catalyst layer 40 is supported on the Ce-Zr composite oxide in the third catalyst layer 40, and at least a portion of the Pt in the fourth catalyst layer 50 is supported on the Ce-Zr composite oxide in the fourth catalyst layer 50, the CO concentration in the exhaust gas after contact with the third catalyst layer 40 and / or the fourth catalyst layer 50 (i.e., the exhaust gas that comes into contact with the second catalyst layer 30) decreases, and the reaction of Equation 1 by the Pt in the second catalyst layer 30 proceeds more easily to the right, thereby improving the methane purification performance by the Pt in the second catalyst layer 30 during high-speed operation of the internal combustion engine.

[0109] <Base material> As shown in Figure 1, catalyst 1A comprises a substrate 10.

[0110] As shown in Figures 1 and 6, the substrate 10 extends in the exhaust gas flow direction X.

[0111] As shown in Figures 1 and 6, the base material 10 is positioned in the exhaust passage within the exhaust pipe P such that the axial direction of the base material 10 coincides with or substantially coincides with the exhaust gas flow direction X.

[0112] As shown in Figures 1 to 6, the base material 10 has a first base material portion 10a located on the upstream side of the exhaust gas flow direction X and a second base material portion 10b located on the downstream side of the exhaust gas flow direction X.

[0113] As shown in Figures 1 and 6, the first base material portion 10a and the second base material portion 10b each extend in the exhaust gas flow direction X and have an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0114] As shown in Figures 1 and 6, the first base material portion 10a and the second base material portion 10b are arranged in the exhaust passage within the exhaust pipe P such that their axial directions coincide with or substantially coincide with the exhaust gas flow direction X.

[0115] As shown in Figures 1 and 6, it is preferable that the axial direction of the first base material portion 10a and the axial direction of the second base material portion 10b coincide or substantially coincide.

[0116] The first base material portion 10a and the second base material portion 10b are integral, and the exhaust gas outlet end of the first base material portion 10a and the exhaust gas inlet end of the second base material portion 10b are continuous. In the drawing, the boundary between the exhaust gas outlet end of the first base material portion 10a and the exhaust gas inlet end of the second base material portion 10b is indicated by the symbol S.

[0117] In the following, the common features of the first base material part 10a and the second base material part 10b will be explained together with the explanations for the first base material part 10a and the second base material part 10b. In doing so, expressions such as "base material part 10a, 10b", "cylindrical part 11a, 11b", "partition part 12a, 12b", "cell 13a, 13a", and "length L10a, L10b" will be used. For the first base material part 10a, these expressions mean "base material part 10a", "cylindrical part 11a", "partition part 12a", "cell 13a", and "length L10a", and for the second base material part 10b, they mean "base material part 10b", "cylindrical part 11b", "partition part 12b", "cell 13b", and "length L10b".

[0118] The materials constituting the base materials 10a and 10b can be appropriately selected from known materials. Examples of materials constituting the base materials 10a and 10b include ceramic materials and metallic materials, but ceramic materials are preferred. Examples of ceramic materials include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of metallic materials include alloys such as stainless steel.

[0119] The materials constituting the base material 10a and the materials constituting the base material 10b are usually the same.

[0120] As shown in Figures 2-6, the base material portions 10a and 10b have cylindrical portions 11a and 11b, partition wall portions 12a and 12b provided within the cylindrical portions 11a and 11b, and cells 13a and 13b separated by the partition wall portions 12a and 12b. The base material portions 10a and 10b are preferably honeycomb structures.

[0121] As shown in Figures 2 and 3, the cylindrical portions 11a and 11b define the outer shape of the base material portions 10a and 10b, and the axial direction of the cylindrical portions 11a and 11b coincides with the axial direction of the base material portions 10a and 10b. As shown in Figures 2 and 3, the shape of the cylindrical portions 11a and 11b is cylindrical, but other shapes such as elliptical or polygonal cylindrical shapes may also be used.

[0122] As shown in Figures 2 and 3, the partition sections 12a and 12b are provided within the cylindrical sections 11a and 11b. As shown in Figures 2 to 6, partition sections 12a and 12b exist between adjacent cells 13a and 13b, and adjacent cells 13a and 13b are separated by the partition sections 12a and 12b. The partition sections 12a and 12b may have a porous structure through which exhaust gas can pass. The thickness of the partition sections 12a and 12b is, for example, 20 μm to 1500 μm.

[0123] As shown in Figure 6, cells 13a and 13b extend in the exhaust gas flow direction X and have an end on the exhaust gas inlet side and an end on the exhaust gas outlet side. As shown in Figure 6, both the exhaust gas inlet side end and the exhaust gas outlet side end of cells 13a and 13b are open.

[0124] As shown in Figure 6, the exhaust gas outlet end (opening) of cell 13a and the exhaust gas inlet end (opening) of cell 13b are continuous such that one exhaust gas flow path is formed by one cell 13a and one cell 13b, extending in the exhaust gas flow direction X.

[0125] Exhaust gas that flows into cell 13a from the exhaust gas inlet end (opening) of cell 13a flows out from the exhaust gas outlet end (opening) of cell 13a. Exhaust gas that flows out from the exhaust gas outlet end (opening) of cell 13a flows into cell 13b from the exhaust gas inlet end (opening) of cell 13b and flows out from the exhaust gas outlet end (opening) of cell 13b. This type of system is called a flow-through type.

[0126] As shown in Figures 2-5, the plan view shape of the exhaust gas inlet end (opening) of cells 13a and 13b is rectangular, but it may be a hexagon, octagon, or other shape. The same applies to the plan view shape of the exhaust gas outlet end (opening) of cells 13a and 13b.

[0127] The cell density per square inch of the base material parts 10a and 10b is, for example, between 100 and 1000 cells. The cell density per square inch of the base material parts 10a and 10b refers to the total number of cells 13a and 13b per square inch in the cross-section obtained by cutting the base material parts 10a and 10b with a plane perpendicular to the exhaust gas flow direction X.

[0128] The base material parts 10a and 10b have lengths L10a and L10b.

[0129] The volume of the base material parts 10a and 10b is, for example, between 0.1 L and 20 L. The volume of the base material parts 10a and 10b refers to the apparent volume of the base material parts 10a and 10b. For example, if the base material parts 10a and 10b are cylindrical, and the outer diameter of the base material parts 10a and 10b is 2r, then the volume of the base material parts 10a and 10b is given by the formula: Volume of base material parts 10a and 10b = π × r 2 It is expressed as × (lengths L10a, L10b).

[0130] The percentage of the length L10a of the first base material 10a to the sum of the lengths L10a of the first base material 10a and L10b of the second base material 10b (L10a / (L10a+L10b)×100) is preferably 15% to 80%, more preferably 18% to 70%, and even more preferably 20% to 60%. Each of the above lower limits may be combined with any of the above upper limits. In one example, the percentage of the length L10a of the first base material 10a to the sum of the lengths L10a of the first base material 10a and L10b of the second base material 10b (L10a / (L10a+L10b)×100) is 50%.

[0131] The percentage of the length L10b of the second base material part 10b to the sum of the lengths L10a of the first base material part 10a and L10b of the second base material part 10b (L10b / (L10a+L10b)×100) is preferably 20% to 85%, more preferably 30% to 82%, and even more preferably 40% to 80%. Each of the above lower limits may be combined with any of the above upper limits. In one example, the percentage of the length L10b of the first base material part 10b to the sum of the lengths L10a of the first base material part 10a and L10b of the second base material part 10b (L10b / (L10a+L10b)×100) is 50%.

[0132] <First catalyst layer> As shown in Figures 4 and 6, catalyst 1A includes a first catalyst layer 20 provided on the first substrate portion 10a.

[0133] As shown in Figures 4 and 6, the first catalyst layer 20 is provided on the cell 13a side surface of the partition wall 12a. The "cell 13a side surface of the partition wall 12a" refers to the outer surface of the partition wall 12a that extends in the exhaust gas flow direction X and is in contact with the cell 13a. The first catalyst layer 20 may be provided directly on the cell 13a side surface of the partition wall 12a or via another layer, but is usually provided directly on the cell 13a side surface of the partition wall 12a. The "first catalyst layer 20 provided on the first base material 10a" includes both embodiments in which the first catalyst layer 20 is provided directly on the cell 13a side surface of the partition wall 12a, and embodiments in which the first catalyst layer 20 is provided on the cell 13a side surface of the partition wall 12a via another layer.

[0134] The first catalyst layer 20 may consist of a portion that rises from the cell 13a side surface of the partition wall portion 12a toward the cell 13a side (hereinafter referred to as the "raised portion"), or it may consist of a portion that exists inside the partition wall portion 12a (hereinafter referred to as the "internal portion"), or it may have both a raised portion and an internal portion. The "first catalyst layer 20 provided on the first substrate portion 10a" includes any embodiment in which the first catalyst layer 20 is composed of a raised portion, an embodiment in which the first catalyst layer 20 is composed of an internal portion, and an embodiment in which the first catalyst layer 20 has both a raised portion and an internal portion.

[0135] As shown in Figure 6, the first catalyst layer 20 extends along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12a to the exhaust gas outlet end of the partition wall 12a. The first catalyst layer 20 may extend along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12a so as not to reach the exhaust gas outlet end of the partition wall 12a, or it may extend along the direction opposite to the exhaust gas flow direction X from the exhaust gas outlet end of the partition wall 12a so as not to reach the exhaust gas inlet end of the partition wall 12a.

[0136] From the viewpoint of achieving a good balance between improving the CO purification performance of the first catalyst layer 20 and suppressing pressure loss by the first catalyst layer 20, the mass of the first catalyst layer 20 per unit volume of the portion of the first substrate 10a where the first catalyst layer 20 is provided (mass after firing) is preferably 80 g / L or more and 250 g / L or less, more preferably 90 g / L or more and 220 g / L or less, and even more preferably 100 g / L or more and 200 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0137] The mass of the first catalyst layer 20 per unit volume of the portion of the first substrate part 10a in which the first catalyst layer 20 is provided is calculated using the formula: (mass of the first catalyst layer 20) / ((volume of the first substrate part 10a) × (average length L20 of the first catalyst layer 20 / length L10a of the first substrate part 10a)).

[0138] An example of a method for measuring the average length L20 of the first catalyst layer 20 is as follows:

[0139] A sample is cut from the first base material 10a, extending in the axial direction of the first base material 10a and having the same length L10a as the first base material 10a. The sample is, for example, cylindrical with a diameter of 25.4 mm. The diameter of the sample can be changed as needed. If the first catalyst layer 20 extends from the exhaust gas inlet side end of the partition wall 12a along the exhaust gas flow direction X, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the first base material 10a, and the first cut piece, second cut piece, ..., nth cut piece are obtained in order from the exhaust gas inlet side end of the sample. If the first catalyst layer 20 extends from the exhaust gas outlet side end of the partition wall 12a along the direction opposite to the exhaust gas flow direction X, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the first base material 10a, and the first cut piece, second cut piece, ..., nth cut piece are obtained in order from the exhaust gas outlet side end of the sample. In all cases, the length of the cut piece is 5 mm. The composition of the cut piece is analyzed using an X-ray fluorescence analyzer (XRF) (e.g., energy-dispersive X-ray spectrometer (EDX), wavelength-dispersive X-ray spectrometer (WDX), etc.), an inductively coupled plasma emission spectrometer (ICP-AES), a scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDX), etc., and based on the composition of the cut piece, it is confirmed whether or not the cut piece contains a portion of the first catalyst layer 20.

[0140] For sections that clearly contain a portion of the first catalyst layer 20, compositional analysis is not necessarily required. For example, the cross-section can be observed using a scanning electron microscope (SEM), electron beam microanalyzer (EPMA), etc., to confirm whether or not the section contains a portion of the first catalyst layer 20. Elemental mapping of the cross-section may also be performed when observing the cross-section.

[0141] After confirming whether the cut piece contains a portion of the first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is calculated based on the following formula. Length of the first catalyst layer 20 in the sample = 5 mm × (number of cut pieces containing a portion of the first catalyst layer 20)

[0142] For example, if the first to kth sections contain a portion of the first catalyst layer 20, but the (k+1) to nth sections do not, the total length of the first catalyst layer 20 contained in the sample is (5 × k) mm.

[0143] An example of a more detailed method for measuring the length of the first catalyst layer 20 contained in the sample is as follows:

[0144] The kth section (when the first catalyst layer 20 extends from the exhaust gas inlet end of the partition wall 12a along the exhaust gas flow direction X, this is the section containing a portion of the first catalyst layer 20 obtained from the exhaust gas outlet side of the sample; when the first catalyst layer 20 extends from the exhaust gas outlet end of the partition wall 12a along the direction opposite to the exhaust gas flow direction X, this is the section containing a portion of the first catalyst layer 20 obtained from the exhaust gas inlet side of the sample) is cut in the axial direction of the first substrate 10a, and the length of the portion of the first catalyst layer 20 present on the cut surface is measured by observing it using SEM, EPMA, etc. Then, the length of the first catalyst layer 20 contained in the sample is calculated based on the following formula. Length of the first catalyst layer 20 in the sample = (5 mm × (k-1)) + (length of a portion of the first catalyst layer 20 in the k-th section)

[0145] For 8 to 16 samples arbitrarily cut from catalyst 1A, the length of the first catalyst layer 20 contained in each sample is measured, and the average value of these measurements is defined as the average length L20 of the first catalyst layer 20.

[0146] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the percentage of the average length L20 of the first catalyst layer 20 to the length L10a of the first substrate portion 10a (L20 / L10a × 100) is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100%, or it may exceed 100%. As will be described later, if the exhaust gas outlet side portion of the first catalyst layer 20 overlaps with the exhaust gas inlet side portion of the second catalyst layer 30, the percentage will exceed 100%. If the percentage exceeds 100%, the upper limit of the percentage is preferably 600% or less, more preferably 400% or less, and even more preferably 300% or less. Each of the above lower limits may be combined with any of the above upper limits. Furthermore, if the first base material 10a and the second base material 10b are integrated, or if the first base material 10a and the second base material 10b are separate and the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b are in contact, the percentage may exceed 100%. However, if the first base material 10a and the second base material 10b are separate and a gap is formed between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b, the percentage will not exceed 100%.

[0147] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the percentage of the average length L20 of the first catalyst layer 20 to the sum of the lengths L10a of the first substrate portion 10a and L10b of the second substrate portion 10b (L20 / (L10a+L10b)×100) is preferably 15% to 80%, more preferably 18% to 70%, and even more preferably 20% to 60%. Each of the above lower limits may be combined with any of the above upper limits.

[0148] The first catalyst layer 20 contains Pd.

[0149] Pd is included in the first catalyst layer 20 in the form of a catalytically active component containing Pd, such as metallic Pd, Pd-containing alloys, or Pd-containing compounds (e.g., Pd oxides). From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the catalytically active component containing Pd is preferably in particulate form.

[0150] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the metal equivalent mass of Pd in ​​the first catalyst layer 20 is preferably 0.5 g / L or more, more preferably 0.7 g / L or more, and even more preferably 1.0 g / L or more, based on the volume of the portion of the first substrate 10a in which the first catalyst layer 20 is provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO purification performance and cost. The upper limit is preferably 7.0 g / L or less, more preferably 6.0 g / L or less, and even more preferably 5.0 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0151] The metallic mass of Pd in ​​the first catalyst layer 20, based on the volume of the portion of the first substrate 10a in which the first catalyst layer 20 is provided, is calculated using the formula: (mass of the first catalyst layer 20 per unit volume of the portion of the first substrate 10a in which the first catalyst layer 20 is provided) × (metallic content of Pd in ​​the first catalyst layer 20).

[0152] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the Pd content in the first catalyst layer 20 in terms of metal is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, based on the mass of the first catalyst layer 20. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO purification performance and cost. The upper limit is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0153] The first catalyst layer 20 may contain one or more noble metal elements other than Pd.

[0154] Other precious metal elements can be selected from, for example, Pt, Rh, Ru, Os, Ir, Au, Ag, etc. The other precious metal elements are included in the first catalyst layer 20 in the form of a catalytically active component containing the other precious metal elements, such as a metal, an alloy containing the precious metal element, or a compound containing the precious metal element (for example, an oxide of the precious metal element). From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, it is preferable that the catalytically active component containing the other precious metal element is in particulate form.

[0155] If the first catalyst layer 20 contains Pd and other precious metal elements, the Pd and other precious metal elements may form an alloy, potentially reducing the number of active sites of Pd that are involved in CO purification. Therefore, it is preferable that the content of other precious metal elements in the first catalyst layer 20, in terms of metal equivalent, be small. Specifically, the content of other precious metal elements in the first catalyst layer 20, in terms of metal equivalent, is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total mass of all precious metal elements in the first catalyst layer 20 in terms of metal equivalent. The lower limit is 0% by mass.

[0156] "The content of noble metal elements other than Pd in ​​the first catalyst layer 20, in terms of metal equivalent," means the content of one noble metal element other than Pd if the first catalyst layer 20 contains that one noble metal element, and the total content of two or more noble metal elements in terms of metal equivalent if the first catalyst layer 20 contains two or more noble metal elements other than Pd.

[0157] The first catalyst layer 20 preferably comprises one or more types of carriers, and at least a portion of the catalytically active component is supported on one or more types of carriers.

[0158] "At least a portion of the catalytically active component is supported on the carrier" means that at least a portion of the catalytically active component is physically or chemically adsorbed or retained on the outer surface and / or the inner surface of the pores of the carrier. This definition applies to all catalyst layers (i.e., the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50).

[0159] The fact that at least a portion of the catalytically active components in a given catalyst layer are supported on a support can be confirmed, for example, using SEM-EDX. Specifically, if, in the elemental mapping obtained by analyzing a cross-section of the catalyst layer with SEM-EDX, at least a portion of the catalytically active components and the support are located in the same region, it can be determined that at least a portion of the catalytically active components are supported on a support.

[0160] The support material can be selected from, for example, inorganic oxides. Inorganic oxides are, for example, particulate. From the viewpoint of improving the support capacity of catalytically active components, it is preferable that the inorganic oxide is porous. Inorganic oxides may or may not have oxygen storage capacity (OSC). Inorganic oxides used as support materials are distinguished from inorganic oxides used as binders (for example, inorganic oxide-based binders such as alumina binders, zirconia binders, titania binders, and silica binders).

[0161] Examples of inorganic oxides include Al-based oxides, Ce-based oxides, Ce-Zr composite oxides, oxides of rare earth elements other than Ce, zirconia (ZrO2), silica (SiO2), titania (TiO2), zeolites (aluminosilicates), and oxides based on MgO, ZnO, SnO2, etc.

[0162] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the first catalyst layer 20, and thereby further improving the CO purification performance of the first catalyst layer 20, the support is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr-based composite oxides, and more preferably selected from Al-based oxides and Ce-Zr-based composite oxides. In one embodiment, the first catalyst layer 20 includes Al-based oxides and Ce-Zr-based composite oxides as support.

[0163] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, it is preferable that the first catalyst layer 20 contains Ce.

[0164] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the Ce content in the first catalyst layer 20, in terms of CeO2, is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 15% by mass or more, based on the mass of the first catalyst layer 20. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO purification performance and cost. The upper limit is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0165] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, it is preferable that the first catalyst layer 20 has a large oxygen storage capacity. On the other hand, if the content of Ce in the first catalyst layer 20 in terms of CeO2 is increased in order to improve the oxygen storage capacity of the first catalyst layer 20, the noble metal elements in the first catalyst layer 20 become more susceptible to oxidation. Here, Pd has the property that, compared to other noble metal elements such as Rh and Pt, even if it is oxidized, its CO purification performance does not decrease easily. Therefore, by including Pd as a catalytically active component in the first catalyst layer 20, a large oxygen storage capacity can be effectively achieved without a decrease in CO purification performance. Furthermore, when the first catalyst layer 20 has a large oxygen storage capacity, its effect extends not only to the first catalyst layer 20 but also to the second catalyst layer 30 located downstream of the first catalyst layer 20, and the exhaust gas that comes into contact with the second catalyst layer 30 becomes suitable for methane purification by the second catalyst layer 30.

[0166] With respect to a particular catalyst layer, "the Ce content in the catalyst layer on a CeO2 basis" means the Ce content in a CeO2 basis derived from one Ce source if the catalyst layer contains one Ce source, and the total Ce content in a CeO2 basis derived from two or more Ce sources if the catalyst layer contains two or more Ce sources. This definition applies to all catalyst layers (i.e., the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50).

[0167] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the ratio of the mass of Ce (in terms of CeO2) to the mass of Pd (in terms of metal) in the first catalyst layer 20 is preferably 1 or more and 100 or less, more preferably 2 or more and 90 or less, and even more preferably 3 or more and 80 or less. Each of the above lower limits may be combined with any of the above upper limits.

[0168] If the first catalyst layer 20 contains Ce, the first catalyst layer 20 contains one or more Ce sources.

[0169] Examples of Ce sources include Ce-containing oxides. Examples of Ce-containing oxides include Ce-based oxides, Ce-Zr composite oxides, Ce-containing Al-based oxides, Ce-containing Zr-based oxides, ceria binders, and the like.

[0170] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, it is preferable that the first catalyst layer 20 contains a Ce-Zr composite oxide as a Ce source. In addition to the Ce-Zr composite oxide, the first catalyst layer 20 may also contain one or more other Ce sources.

[0171] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the content of Ce-Zr composite oxide in the first catalyst layer 20 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 60% by mass or less, based on the mass of the first catalyst layer 20. Each of the above lower limits may be combined with any of the above upper limits.

[0172] The content of Ce-Zr composite oxide in the first catalyst layer 20 is defined by the formula: (mass of Ce-Zr composite oxide in the first catalyst layer 20) / (mass of the first catalyst layer 20) × 100.

[0173] If information on the raw materials used to form the first catalyst layer 20 (e.g., composition, quantity, etc.) is known, the content of Ce-Zr composite oxide in the first catalyst layer 20 can be determined from the information on the raw materials used to form the first catalyst layer 20.

[0174] If information on the raw materials used to form the first catalyst layer 20 is unknown, the content of Ce-Zr composite oxide in the first catalyst layer 20 can be determined by conventional methods such as SEM-EDX. Specifically, it is as follows.

[0175] (1) The sample obtained from the first catalyst layer 20 is subjected to elemental analysis using conventional methods such as SEM-EDX to identify the types of constituent elements of the entire sample, and the content (mass%) of each identified metal element in terms of oxide is determined. (2) Elemental mapping is performed on the sample obtained from the first catalyst layer 20 using a conventional method such as SEM-EDX to identify the types of particles contained in the sample (e.g., Ce-Zr composite oxide, Al oxide, etc.). (3) For each type of particle, several (e.g., 50) arbitrarily selected particles are subjected to elemental analysis using SEM-EDX to identify the constituent elements of the particles and determine the content (mass%) of each identified metal element in terms of oxides. For each type of particle, the average value of the content (mass%) of each metal element in terms of oxides is calculated and this is taken as the content (mass%) of each metal element in terms of oxides for each type of particle. (4) The content of each type of particle in the sample is calculated by creating and solving an equation that expresses the relationship between the content of each metal element in the sample on an oxide basis (mass%), the content of each metal element in each type of particle on an oxide basis (mass%), and the content of each type of particle in the sample on an oxide basis (mass%), and this is taken as the content of each type of particle in the first catalyst layer 20 on an oxide basis (mass%).

[0176] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the proportion of the mass of Ce derived from Ce-Zr composite oxides in terms of CeO2, out of the total mass of Ce in the first catalyst layer 20 in terms of CeO2, is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0177] The following describes preferred embodiments of the Ce-Zr composite oxide that may be included in the first catalyst layer 20.

[0178] From the viewpoint of improving the oxygen storage capacity of Ce-Zr composite oxides, the Ce content in Ce-Zr composite oxides, in terms of CeO2, is preferably 7% by mass or more, more preferably 10% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit can be appropriately adjusted considering heat resistance, structural stability, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 85% by mass or less. The lower limits above may be combined with any of the upper limits above.

[0179] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, the content of Zr in Ce-Zr composite oxides, in terms of ZrO2, is preferably 7% by mass or more, more preferably 10% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit can be appropriately adjusted considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 85% by mass or less. The lower limits above may be combined with any of the upper limits above.

[0180] From the viewpoint of improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxides, the sum of the Ce content (calculated as CeO2) and the Zr content (calculated as ZrO2) in the Ce-Zr composite oxide is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit is 100% by mass.

[0181] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, the content of rare earth elements in the Ce-Zr composite oxide, in terms of oxides, is preferably 0.1% to 30% by mass, more preferably 0.5% to 25% by mass, and even more preferably 1% to 20% by mass, based on the mass of the Ce-Zr composite oxide. Each of the above lower limits may be combined with any of the above upper limits.

[0182] "Oxide content of rare earth elements in Ce-Zr composite oxides" means the oxide content of a single rare earth element if the Ce-Zr composite oxide contains one such rare earth element, and the total oxide content of two or more rare earth elements if the Ce-Zr composite oxide contains two or more such rare earth elements. This definition applies to all Ce-Zr composite oxides contained in all catalyst layers (i.e., the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50).

[0183] From the viewpoint of improving the catalytic activity of Pd in ​​the first catalyst layer 20, and thereby further improving the CO purification performance of the first catalyst layer 20, it is preferable that the first catalyst layer 20 contains an alkaline earth metal element. The first catalyst layer 20 may contain one alkaline earth metal element or two or more alkaline earth metal elements.

[0184] Alkaline earth metal elements can be selected from, for example, Mg, Ca, Sr, Ba, etc., but it is preferable to select from Ca, Sr, and Ba, and more preferable to select from Sr and Ba.

[0185] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20, the content of alkaline earth metal elements in the first catalyst layer 20 in terms of oxides is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on the mass of the first catalyst layer 20. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO purification performance and cost. The upper limit is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0186] With respect to a particular catalyst layer, "the content of alkaline earth metal elements in the catalyst layer on an oxide basis" means the content of one alkaline earth metal element on an oxide basis if the catalyst layer contains one alkaline earth metal element, and the total content of two or more alkaline earth metal elements on an oxide basis if the catalyst layer contains two or more alkaline earth metal elements. This definition applies to all catalyst layers (i.e., the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50).

[0187] With respect to a particular catalyst layer, "the content of alkaline earth metal elements in oxide terms in the catalyst layer" means, if the catalyst layer contains one alkaline earth metal element source, the content of alkaline earth metal elements derived from that one alkaline earth metal element source in oxide terms, and if the catalyst layer contains two or more alkaline earth metal element sources, the total content of alkaline earth metal elements derived from those two or more alkaline earth metal element sources in oxide terms. This definition applies to all catalyst layers (i.e., the first catalyst layer 20, the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50).

[0188] If the first catalyst layer 20 contains alkaline earth metal elements, the first catalyst layer 20 contains one or more alkaline earth metal element sources.

[0189] Examples of alkaline earth metal element sources include alkaline earth metal compounds. Alkaline earth metal compounds are compounds containing alkaline earth metal elements. It is preferable to select the alkaline earth metal compound from oxides, carbonates, and sulfates, and more preferably from oxides and carbonates.

[0190] In elemental mapping obtained by analyzing a cross-section of the catalyst layer with SEM-EDX, if alkaline earth metal elements and oxygen (O) are present in the same region, and alkaline earth metal elements and carbon (C) or sulfur (S) are not present in the same region, it can be determined that the alkaline earth metal elements exist in the catalyst layer in the form of oxides. If alkaline earth metal elements, oxygen (O), and carbon (C) are present in the same region, it can be determined that the alkaline earth metal elements exist in the catalyst layer in the form of carbonates. If alkaline earth metal elements, oxygen (O), and sulfur (S) are present in the same region, it can be determined that the alkaline earth metal elements exist in the catalyst layer in the form of sulfates.

[0191] When alkaline earth metal elements are used as raw materials for the catalyst layer, the acetates, nitrates, or hydroxides become oxides during the calcination process to form the catalyst layer, and these oxides react with CO2 in the air to form carbonates. When alkaline earth metal elements are used as raw materials for the catalyst layer, the carbonates and sulfates remain as carbonates and sulfates, respectively, after calcination.

[0192] The first catalyst layer 20 may contain other components such as a binder. Examples of binders include inorganic oxide binders such as alumina binder, ceria binder, zirconia binder, titania binder, and silica binder.

[0193] <Second catalyst layer> As shown in Figures 5 and 6, catalyst 1A includes a second catalyst layer 30 provided on the second substrate portion 10b.

[0194] As shown in Figures 5 and 6, the second catalyst layer 30 is provided on the cell 13b side surface of the partition wall 12b. The "cell 13b side surface of the partition wall 12b" refers to the outer surface of the partition wall 12b that extends in the exhaust gas flow direction X and is in contact with the cell 13b. The second catalyst layer 30 may be provided directly on the cell 13b side surface of the partition wall 12b or via another layer, but is usually provided directly on the cell 13b side surface of the partition wall 12b. The "second catalyst layer 30 provided on the second base material 10b" includes both embodiments in which the second catalyst layer 30 is provided directly on the cell 13b side surface of the partition wall 12b, and embodiments in which the second catalyst layer 30 is provided on the cell 13b side surface of the partition wall 12b via another layer.

[0195] The second catalyst layer 30 may consist of a portion that rises from the cell 13b side surface of the partition wall portion 12b toward the cell 13b side (hereinafter referred to as the "raised portion"), or it may consist of a portion that exists inside the partition wall portion 12b (hereinafter referred to as the "internal portion"), or it may have both a raised portion and an internal portion. The "second catalyst layer 30 provided on the second base material portion 10b" includes any embodiment in which the second catalyst layer 30 is composed of a raised portion, an embodiment in which the second catalyst layer 30 is composed of an internal portion, and an embodiment in which the second catalyst layer 30 has both a raised portion and an internal portion.

[0196] As shown in Figure 6, the second catalyst layer 30 extends from the exhaust gas outlet end of the partition wall 12b to the exhaust gas inlet end of the partition wall 12b in a direction opposite to the exhaust gas flow direction X. The second catalyst layer 30 may extend from the exhaust gas outlet end of the partition wall 12b in a direction opposite to the exhaust gas flow direction X, so as not to reach the exhaust gas inlet end of the partition wall 12b, or it may extend from the exhaust gas inlet end of the partition wall 12b in the exhaust gas flow direction X, so as not to reach the exhaust gas outlet end of the partition wall 12b.

[0197] As shown in Figure 6, the exhaust gas outlet end of the first catalyst layer 20 and the exhaust gas inlet end of the second catalyst layer 30 are in contact at a boundary S. As shown in Figure 6, the boundary S between the exhaust gas outlet end of the first catalyst layer 20 and the exhaust gas inlet end of the second catalyst layer 30 coincides with the boundary S between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b.

[0198] The exhaust gas outlet side portion of the first catalyst layer 20 may overlap with the exhaust gas inlet side portion of the second catalyst layer 30 (i.e., the exhaust gas outlet side portion of the first catalyst layer 20 may be located above the exhaust gas inlet side portion of the second catalyst layer 30 and cover the exhaust gas inlet side portion of the second catalyst layer 30). Alternatively, the exhaust gas inlet side portion of the second catalyst layer 30 may overlap with the exhaust gas outlet side portion of the first catalyst layer 20 (i.e., the exhaust gas inlet side portion of the second catalyst layer 30 may be located above the exhaust gas outlet side portion of the first catalyst layer 20 and cover the exhaust gas outlet side portion of the first catalyst layer 20). "Exhaust gas outlet side portion of the first catalyst layer 20" means the portion of the first catalyst layer 20 that extends from the exhaust gas outlet end in a direction opposite to the exhaust gas flow direction X. "The exhaust gas inlet side portion of the second catalyst layer 30" refers to the portion of the second catalyst layer 30 that extends from the exhaust gas inlet side end along the exhaust gas flow direction X.

[0199] The exhaust gas outlet end of the first catalyst layer 20 and the exhaust gas inlet end of the second catalyst layer 30 do not need to be in contact. In other words, a gap may be formed between the exhaust gas outlet end of the first catalyst layer 20 and the exhaust gas inlet end of the second catalyst layer 30.

[0200] From the viewpoint of achieving a good balance between improving the methane purification performance of the second catalyst layer 30 and suppressing pressure loss by the second catalyst layer 30, the mass of the second catalyst layer 30 per unit volume of the portion of the second substrate part 10b where the second catalyst layer 30 is provided (mass after firing) is preferably 80 g / L or more and 250 g / L or less, more preferably 90 g / L or more and 220 g / L or less, and even more preferably 100 g / L or more and 200 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0201] The mass of the second catalyst layer 30 per unit volume of the portion of the second base material 10b in which the second catalyst layer 30 is provided is calculated using the formula: (mass of the second catalyst layer 30) / ((volume of the second base material 10b) × (average length L30 of the second catalyst layer 30 / length L10b of the second base material 10b)).

[0202] The above explanation regarding the method for measuring the average length L20 of the first catalyst layer 20 also applies to the method for measuring the average length L30 of the second catalyst layer 30. When applying this, "first catalyst layer 20" is replaced with "second catalyst layer 30," and "average length L20" is replaced with "average length L30."

[0203] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the percentage of the average length L30 of the second catalyst layer 30 to the length L10b of the second substrate portion 10b (L30 / L10b × 100) is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100%, or it may exceed 100%. As described above, when the exhaust gas inlet side portion of the second catalyst layer 30 overlaps with the exhaust gas outlet side portion of the first catalyst layer 20, the percentage exceeds 100%. When the percentage exceeds 100%, the upper limit of the percentage is preferably 500% or less, more preferably 350% or less, and even more preferably 200% or less. Each of the above lower limits may be combined with any of the above upper limits. Furthermore, if the first base material 10a and the second base material 10b are integrated, or if the first base material 10a and the second base material 10b are separate and the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b are in contact, the percentage may exceed 100%. However, if the first base material 10a and the second base material 10b are separate and a gap is formed between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b, the percentage will not exceed 100%.

[0204] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the percentage of the average length L30 of the second catalyst layer 30 to the sum of the lengths L10a of the first substrate portion 10a and L10b of the second substrate portion 10b (L30 / (L10a+L10b)×100) is preferably 20% to 95%, more preferably 30% to 92%, and even more preferably 40% to 90%. The lower limit above may be combined with any of the upper limits above.

[0205] From the viewpoint of further improving the CO purification performance of the first catalyst layer 20 and the methane purification performance of the second catalyst layer 30, 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 relative to the sum of the length L10a of the first base material 10a and the length L10b of the second base material 10b ((L20+L30) / (L10a+L10b)×100) is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100%, or may exceed 100%. As described above, when the exhaust gas outlet side portion of the first catalyst layer 20 overlaps with the exhaust gas inlet side portion of the second catalyst layer 30, and when the exhaust gas inlet side portion of the second catalyst layer 30 overlaps with the exhaust gas outlet side portion of the first catalyst layer 20, the percentage exceeds 100%. The upper limit of the percentage is preferably 175% or less, more preferably 162% or less, and even more preferably 150% or less. The lower limit may be combined with any of the upper limits. When the first base material part 10a and the second base material part 10b are integrated, and when the first base material part 10a and the second base material part 10b are separate and the exhaust gas outlet end of the first base material part 10a and the exhaust gas inlet end of the second base material part 10b are in contact, the percentage may exceed 100%. However, when the first base material part 10a and the second base material part 10b are separate and a gap is formed between the exhaust gas outlet end of the first base material part 10a and the exhaust gas inlet end of the second base material part 10b, the percentage shall not exceed 100%.

[0206] The second catalyst layer 30 contains Pt.

[0207] Pt is included in the second catalyst layer 30 in the form of a catalytically active component containing Pt, such as metallic Pt, alloys containing Pt, or compounds containing Pt (e.g., oxides of Pt). From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, it is preferable that the catalytically active component containing Pt be in particulate form.

[0208] The metallic mass of Pt in the second catalyst layer 30 is 1.0 g / L or more, based on the volume of the portion of the second substrate 10b in which the second catalyst layer 30 is provided. From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the metallic mass of Pt in the second catalyst layer 30 is preferably 1.1 g / L or more, more preferably 1.2 g / L or more, based on the volume of the portion of the second substrate 10b in which the second catalyst layer 30 is provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 7.0 g / L or less, more preferably 6.0 g / L or less, and even more preferably 5.0 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0209] The metallic mass of Pt in the second catalyst layer 30, based on the volume of the portion of the second substrate 10b in which the second catalyst layer 30 is provided, is calculated using the formula: (mass of the second catalyst layer 30 per unit volume of the portion of the second substrate 10b in which the second catalyst layer 30 is provided) × (metallic content of Pt in the second catalyst layer 30). The oxide-converted masses of other metal elements in the second catalyst layer 30, based on the volume of the portion of the second substrate 10b in which the second catalyst layer 30 is provided, are calculated in the same manner.

[0210] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the metal equivalent content of Pt in the second catalyst layer 30 is preferably 0.40% by mass or more, more preferably 0.45% by mass or more, and even more preferably 0.50% by mass or more, based on the mass of the second catalyst layer 30. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 9% by mass or less, more preferably 8% by mass or less, and even more preferably 7% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0211] The second catalyst layer 30 may contain one or more noble metal elements other than Pt.

[0212] Other precious metal elements can be selected from, for example, Pd, Rh, Ru, Os, Ir, Au, Ag, etc. The other precious metal elements are included in the second catalyst layer 30 in the form of a catalytically active component containing the other precious metal elements, such as a metal, an alloy containing the precious metal element, or a compound containing the precious metal element (for example, an oxide of the precious metal element). From the viewpoint of further improving methane purification performance, it is preferable that the catalytically active component containing the other precious metal elements is in particulate form.

[0213] If the second catalyst layer 30 contains Pt and other precious metal elements, the Pt and other precious metal elements may form an alloy, potentially reducing the number of active sites of Pt that contribute to methane purification performance. Therefore, it is preferable that the content of other precious metal elements in the second catalyst layer 30, in terms of metal equivalent, be small. Specifically, the content of other precious metal elements in the second catalyst layer 30, in terms of metal equivalent, is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total mass of all precious metal elements in the second catalyst layer 30 in terms of metal equivalent. The lower limit is 0% by mass.

[0214] "The content of noble metal elements other than Pt in the second catalyst layer 30, in terms of metal equivalent," means the content of one noble metal element other than Pt if the second catalyst layer 30 contains that one noble metal element, and the total content of two or more noble metal elements in terms of metal equivalent if the second catalyst layer 30 contains two or more noble metal elements other than Pt.

[0215] The second catalyst layer 30 preferably comprises one or more types of carriers, and at least a portion of the catalytically active component is supported on one or more types of carriers. The carriers can be selected, for example, from inorganic oxides. The explanation regarding inorganic oxides is the same as above.

[0216] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the second catalyst layer 30, and thereby further improving the methane purification performance of the second catalyst layer 30, the support is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr-based composite oxides, and more preferably selected from Al-based oxides and Ce-Zr-based composite oxides. In one embodiment, the second catalyst layer 30 includes Al-based oxides and Ce-Zr-based composite oxides as support.

[0217] The second catalyst layer 30 contains Ce.

[0218] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the mass of Ce in the second catalyst layer 30 in terms of CeO2 is preferably 5 g / L or more, more preferably 8 g / L or more, and even more preferably 10 g / L or more, based on the volume of the portion of the second substrate part 10b in which the second catalyst layer 30 is provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 90 g / L or less, more preferably 80 g / L or less, and even more preferably 70 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0219] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the Ce content in the second catalyst layer 30, in terms of CeO2, is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, based on the mass of the second catalyst layer 30. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0220] The second catalyst layer 30 contains one or more Ce sources. The explanation regarding the Ce sources is the same as above.

[0221] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, it is preferable that the second catalyst layer 30 contains a Ce-Zr composite oxide as a Ce source. In addition to the Ce-Zr composite oxide, the second catalyst layer 30 may also contain one or more other Ce sources. In one embodiment, the second catalyst layer 30 contains a Ce-Zr composite oxide and a ceria binder as Ce sources.

[0222] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, it is preferable that the second catalyst layer 30 contains a Ce-Zr composite oxide as a Ce source, and that at least a portion of the Pt in the second catalyst layer 30 is supported on the Ce-Zr composite oxide in the second catalyst layer 30.

[0223] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the percentage of the mass of Pt supported on the Ce-Zr composite oxide in the second catalyst layer 30 (hereinafter referred to as "percentage Q1") relative to the total mass of all Pt in the second catalyst layer 30 (in terms of metal equivalent) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. The upper limit is 100% by mass.

[0224] The percentage Q1 is calculated using the formula: Q11 / Q12 × 100 [wherein Q11 represents the percentage (mass%) of the oxide-converted mass of Pt supported on the Ce-Zr composite oxide in the second catalyst layer 30 relative to the mass of the second catalyst layer 30, and Q12 represents the percentage (mass%) of the total metallic mass of all Pt in the second catalyst layer 30 relative to the mass of the second catalyst layer 30.]

[0225] The following explains how to find Q11.

[0226] Q11 can be found using the following formula. Q11 = Content (mass%) of Ce-Zr composite oxide in the second catalyst layer 30 × ratio A

[0227] The content of Ce-Zr composite oxide in the second catalyst layer 30 can be determined in the same manner as the content of Ce-Zr composite oxide in the first catalyst layer 20.

[0228] The method for finding ratio A is as follows: (1) Elemental mapping of the second catalyst layer 30 is performed using a conventional method such as SEM-EDX to identify the types of particles contained in the second catalyst layer 30 (for example, Ce-Zr composite oxide, support other than Ce-Zr composite oxide, etc.). (2) Multiple (e.g., 50) arbitrarily selected Ce-Zr composite oxides, including the metal elements supported on the Ce-Zr composite oxides (hereinafter referred to as "supported elements"), are subjected to elemental analysis by SEM-EDX to identify the constituent elements of the Ce-Zr composite oxides and the types of supported elements, and the content (mass%) of each identified metal element in terms of oxide or metal is determined. Specifically, for noble metal elements, the content (mass%) of the noble metal element in terms of metal is determined, and for metal elements other than noble metal elements, the content (mass%) of the metal element in terms of oxide is determined. From the analysis results of multiple (e.g., 50) Ce-Zr composite oxides and supported elements, the average value of the content (mass%) of each metal element in terms of oxide or metal is determined, and ratio A is calculated from the following formula. Ratio A = (Average content of Pt in metallic terms) / (Sum of average content of all constituent elements of the Ce-Zr composite oxide in oxide terms)

[0229] The following explains how to find Q12.

[0230] Q12 can be found using the following formula. Q12 = (Total mass of all Pt in metallic equivalent) / (Mass of the second catalyst layer 30) × 100

[0231] Q12 can be determined in the same way as the metal content of Pt in the second catalyst layer 30.

[0232] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the mass of the Ce-Zr composite oxide in the second catalyst layer 30 is preferably 30 g / L or more, more preferably 35 g / L or more, and even more preferably 40 g / L or more, based on the volume of the portion of the second substrate part 10b in which the second catalyst layer 30 is provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 130 g / L or less, more preferably 125 g / L or less, and even more preferably 120 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0233] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the content of Ce-Zr composite oxide in the second catalyst layer 30 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 60% by mass or less, based on the mass of the second catalyst layer 30. Each of the above lower limits may be combined with any of the above upper limits.

[0234] The content of Ce-Zr composite oxide in the second catalyst layer 30 can be determined in the same manner as the content of Ce-Zr composite oxide in the first catalyst layer 20.

[0235] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the proportion of the mass of Ce derived from Ce-Zr composite oxides in the second catalyst layer 30 in terms of CeO2 is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more. The upper limit is 100% by mass.

[0236] The following describes preferred embodiments of the Ce-Zr composite oxide that may be included in the second catalyst layer 30.

[0237] From the viewpoint of improving the oxygen storage capacity of Ce-Zr composite oxides, the Ce content in Ce-Zr composite oxides, in terms of CeO2, is preferably 18% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit can be adjusted as appropriate, taking into consideration heat resistance, structural stability, the content of other components, etc. The upper limit is preferably 70% by mass or less, more preferably 65% ​​by mass or less, even more preferably 63% by mass or less, and even more preferably 58% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0238] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, the content of Zr in Ce-Zr composite oxides, in terms of ZrO2, is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 32% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit can be appropriately adjusted considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 62% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0239] From the viewpoint of improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxides, the sum of the Ce content (calculated as CeO2) and the Zr content (calculated as ZrO2) in the Ce-Zr composite oxide is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit is 100% by mass.

[0240] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, the content of rare earth elements in the Ce-Zr composite oxide, in terms of oxides, is preferably 0.1% to 30% by mass, more preferably 0.5% to 25% by mass, and even more preferably 1% to 20% by mass, based on the mass of the Ce-Zr composite oxide. Each of the above lower limits may be combined with any of the above upper limits.

[0241] The second catalyst layer 30 contains an alkaline earth metal element. The second catalyst layer 30 may contain one alkaline earth metal element or two or more alkaline earth metal elements.

[0242] Alkaline earth metal elements can be selected from, for example, Mg, Ca, Sr, Ba, etc., but it is preferable to select from Ca, Sr, and Ba, and more preferable to select from Sr and Ba.

[0243] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the mass of alkaline earth metal elements in the second catalyst layer 30 in terms of oxides is preferably 2.5 g / L or more, more preferably 3.0 g / L or more, and even more preferably 3.5 g / L or more, based on the volume of the portion of the second substrate part 10b in which the second catalyst layer 30 is provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 30 g / L or less, more preferably 25 g / L or less, and even more preferably 20 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0244] From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, the content of alkaline earth metal elements in the second catalyst layer 30 in terms of oxides is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on the mass of the second catalyst layer 30. The upper limit can be adjusted as appropriate, taking into consideration the balance between methane purification performance and cost. The upper limit is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0245] The second catalyst layer 30 contains one or more alkaline earth metal element sources. The explanation regarding the alkaline earth metal element sources is the same as described above.

[0246] In the second catalyst layer 30, the ratio of the mass of Ce (in terms of CeO2) to the mass of Pt (in terms of metal) is 6.0 or more and 20.0 or less. From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, this ratio is preferably 7.0 or more and 19.0 or less, and more preferably 8.0 or more and 18.0 or less. Each of the above lower limits may be combined with any of the above upper limits.

[0247] In the second catalyst layer 30, the ratio of the mass of Ce (in CeO2 equivalent) to the mass of alkaline earth metal elements (in oxide equivalent) is 2.0 or more and 18.0 or less. From the viewpoint of further improving the methane purification performance of the second catalyst layer 30, this ratio is preferably 2.5 or more, more preferably 3.0 or more. From the same viewpoint, this ratio is preferably 17.0 or less, even more preferably 16.0 or less, even more preferably 15.0 or less, even more preferably 14.0 or less, even more preferably 13.0 or less, and even more preferably 12.0 or less. Each of the above lower limits may be combined with any of the above upper limits.

[0248] The second catalyst layer 30 may contain other components such as a binder. Examples of binders include inorganic oxide binders such as alumina binder, ceria binder, zirconia binder, titania binder, and silica binder.

[0249] <Third catalyst layer and fourth catalyst layer> As shown in Figures 4 and 6, catalyst 1A includes a third catalyst layer 40 provided above the first catalyst layer 20.

[0250] As shown in Figure 6, the third catalyst layer 40 extends along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12a to the exhaust gas outlet end of the partition wall 12a. The third catalyst layer 40 may extend along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12a so as not to reach the exhaust gas outlet end of the partition wall 12a, or it may extend along the direction opposite to the exhaust gas flow direction X from the exhaust gas outlet end of the partition wall 12a so as not to reach the exhaust gas inlet end of the partition wall 12a.

[0251] "The third catalyst layer 40 is provided on the upper side of the first catalyst layer 20" means that part or all of the third catalyst layer 40 is located on the main surface of the first catalyst layer 20 that is opposite to the main surface on the partition wall 12a side. "Main surface 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 may be provided directly on the main surface of the first catalyst layer 20 or via another layer, but is usually provided directly on the main surface of the first catalyst layer 20. The third catalyst layer 40 may be provided so as to cover a part of the main surface of the first catalyst layer 20, or so as to cover the entire main surface of the first catalyst layer 20. The phrase "third catalyst layer 40 provided above the first catalyst layer 20" includes both embodiments in which the third catalyst layer 40 is directly provided on the main surface of the first catalyst layer 20, and embodiments in which the third catalyst layer 40 is provided on the main surface of the first catalyst layer 20 via another layer.

[0252] From the viewpoint of achieving a good balance between improving the CO and NOx purification performance of the third catalyst layer 40 and suppressing pressure loss by the third catalyst layer 40, the mass of the third catalyst layer 40 per unit volume of the portion of the first substrate part 10a where the third catalyst layer 40 is provided (mass after firing) is preferably 20 g / L or more and 200 g / L or less, more preferably 30 g / L or more and 150 g / L or less, and even more preferably 40 g / L or more and 120 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0253] The mass of the third catalyst layer 40 per unit volume of the portion of the first substrate part 10a in which the third catalyst layer 40 is provided is calculated using the formula: (mass of the third catalyst layer 40) / ((volume of the first substrate part 10a) × (average length L40 of the third catalyst layer 40 / length L10a of the first substrate part 10a)).

[0254] The above explanation regarding the method for measuring the average length L20 of the first catalyst layer 20 also applies to the method for measuring the average length L40 of the third catalyst layer 40. When applying this, "first catalyst layer 20" is replaced with "third catalyst layer 40," and "average length L20" is replaced with "average length L40."

[0255] From the viewpoint of further improving the CO and NOx purification performance of the third catalyst layer 40, the percentage of the average length L40 of the third catalyst layer 40 to the length L10a of the first substrate portion 10a (L40 / L10a × 100) is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100%, or it may exceed 100%. As will be described later, if the exhaust gas outlet side portion of the third catalyst layer 40 overlaps with the exhaust gas inlet side portion of the fourth catalyst layer 50, the percentage will exceed 100%. If the percentage exceeds 100%, the upper limit of the percentage is preferably 600% or less, more preferably 400% or less, and even more preferably 300% or less. Each of the above lower limits may be combined with any of the above upper limits. Furthermore, if the first base material 10a and the second base material 10b are integrated, or if the first base material 10a and the second base material 10b are separate and the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b are in contact, the percentage may exceed 100%. However, if the first base material 10a and the second base material 10b are separate and a gap is formed between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b, the percentage will not exceed 100%.

[0256] From the viewpoint of further improving the CO and NOx purification performance of the third catalyst layer 40, the percentage of the average length L40 of the third catalyst layer 40 to the sum of the lengths L10a of the first substrate part 10a and L10b of the second substrate part 10b (L40 / (L10a+L10b)×100) is preferably 15% to 80%, more preferably 18% to 70%, and even more preferably 20% to 60%. Each of the above lower limits may be combined with any of the above upper limits.

[0257] As shown in Figures 5 and 6, catalyst 1A includes a fourth catalyst layer 50 provided above the second catalyst layer 30.

[0258] The fourth catalyst layer 50 extends from the exhaust gas outlet end of the partition wall 12b to the exhaust gas inlet end of the partition wall 12b in a direction opposite to the exhaust gas flow direction X. The fourth catalyst layer 50 may extend from the exhaust gas outlet end of the partition wall 12b in a direction opposite to the exhaust gas flow direction X, without reaching the exhaust gas inlet end of the partition wall 12b, or it may extend from the exhaust gas inlet end of the partition wall 12b in the exhaust gas flow direction X, without reaching the exhaust gas outlet end of the partition wall 12b.

[0259] "The fourth catalyst layer 50 is provided on the upper side of the second catalyst layer 30" means that part or all of the fourth catalyst layer 50 is located on the main surface of the second catalyst layer 30 that is opposite to the main surface on the partition wall portion 12b side. "Main surface of the second catalyst layer 30" means the outer surface of the second catalyst layer 30 that extends in the exhaust gas flow direction X. The fourth catalyst layer 50 may be provided directly on the main surface of the second catalyst layer 30 or via another layer, but is usually provided directly on the main surface of the second catalyst layer 30. The fourth catalyst layer 50 may be provided so as to cover a part of the main surface of the second catalyst layer 30 or so as to cover the entire main surface of the second catalyst layer 30. The phrase "fourth catalyst layer 50 provided above the second catalyst layer 30" includes both embodiments in which the fourth catalyst layer 50 is directly provided on the main surface of the second catalyst layer 30, and embodiments in which the fourth catalyst layer 50 is provided on the main surface of the second catalyst layer 30 via another layer.

[0260] From the viewpoint of achieving a good balance between improving the CO and NOx purification performance of the fourth catalyst layer 50 and suppressing pressure loss by the fourth catalyst layer 50, the mass of the fourth catalyst layer 50 per unit volume of the portion of the second substrate part 10b where the fourth catalyst layer 50 is provided (mass after firing) is preferably 20 g / L or more and 200 g / L or less, more preferably 30 g / L or more and 150 g / L or less, and even more preferably 40 g / L or more and 120 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0261] The mass of the fourth catalyst layer 50 per unit volume of the portion of the second base material 10b in which the fourth catalyst layer 50 is provided is calculated using the formula: (mass of the fourth catalyst layer 50) / ((volume of the second base material 10b) × (average length L50 of the fourth catalyst layer 50 / length L10b of the second base material 10b)).

[0262] The above explanation regarding the method for measuring the average length L20 of the first catalyst layer 20 also applies to the method for measuring the average length L50 of the fourth catalyst layer 50. When applying this, "first catalyst layer 20" is replaced with "fourth catalyst layer 50," and "average length L20" is replaced with "average length L50."

[0263] From the viewpoint of further improving the CO and NOx purification performance of the fourth catalyst layer 50, the percentage of the average length L50 of the fourth catalyst layer 50 to the length L10b of the second substrate portion 10b (L50 / L10b × 100) is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100%, or it may exceed 100%. As will be described later, if the exhaust gas inlet side portion of the fourth catalyst layer 50 overlaps with the exhaust gas outlet side portion of the third catalyst layer 40, the percentage will exceed 100%. If the percentage exceeds 100%, the upper limit of the percentage is preferably 500% or less, more preferably 350% or less, and even more preferably 200% or less. Each of the above lower limits may be combined with any of the above upper limits. Furthermore, if the first base material 10a and the second base material 10b are integrated, or if the first base material 10a and the second base material 10b are separate and the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b are in contact, the percentage may exceed 100%. However, if the first base material 10a and the second base material 10b are separate and a gap is formed between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b, the percentage will not exceed 100%.

[0264] From the viewpoint of further improving the CO and NOx purification performance of the fourth catalyst layer 50, the percentage of the average length L50 of the fourth catalyst layer 50 relative 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)×100) is preferably 20% or more and 95% or less, more preferably 30% or more and 92% or less, and even more preferably 40% or more and 90% or less. Each of the above lower limits may be combined with any of the above upper limits.

[0265] As shown in Figure 6, 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 are in contact with each other at a boundary S. As shown in Figure 6, the boundary S between 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 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.

[0266] The portion of the third catalyst layer 40 on the exhaust gas outflow side may overlap with the portion of the fourth catalyst layer 50 on the exhaust gas inflow side (that is, the portion of the third catalyst layer 40 on the exhaust gas outflow side may be located above the portion of the fourth catalyst layer 50 on the exhaust gas inflow side and cover the portion of the fourth catalyst layer 50 on the exhaust gas inflow side). Alternatively, the portion of the fourth catalyst layer 50 on the exhaust gas inflow side may overlap with the portion of the third catalyst layer 40 on the exhaust gas outflow side (that is, the portion of the fourth catalyst layer 50 on the exhaust gas inflow side may be located above the portion of the third catalyst layer 40 on the exhaust gas outflow side and cover the portion of the third catalyst layer 40 on the exhaust gas outflow side). The "portion of the third catalyst layer 40 on the exhaust gas outflow side" means a portion of the third catalyst layer 40 that extends from the end on the exhaust gas outflow side along the direction opposite to the exhaust gas flow direction X. The "portion of the fourth catalyst layer 50 on the exhaust gas inflow side" means a portion of the fourth catalyst layer 50 that extends from the end on the exhaust gas inflow side along the exhaust gas flow direction X.

[0267] When 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 are in contact at a boundary S, 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 may be continuous. That is, the third catalyst layer 40 and the fourth catalyst layer 50 may be integrated to form one single catalyst layer.

[0268] 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 do not need to be in contact with each other. That is, a gap may be formed between 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.

[0269] In one embodiment, the third catalyst layer 40 extends along the exhaust gas flow direction X from the end of the partition wall portion 12a on the exhaust gas inflow side to the end of the partition wall portion 12a on the exhaust gas outflow side, and 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 are in contact at a 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 may be continuous. In this embodiment, the fourth catalyst layer 50 may extend along the exhaust gas flow direction X from the end of the partition wall portion 12b on the exhaust gas inflow side to the end of the partition wall portion 12b on the exhaust gas outflow side, or may extend along the exhaust gas flow direction X from the end of the partition wall portion 12b on the exhaust gas inflow side so as not to reach the end of the partition wall portion 12b on the exhaust gas outflow side.

[0270] In another embodiment, the fourth catalyst layer 50 extends from the exhaust gas outlet end of the partition wall 12b to the exhaust gas inlet end of the partition wall 12b in a direction opposite to the exhaust gas flow direction X, and the exhaust gas outlet end of the third catalyst layer 40 and the exhaust gas inlet end of the fourth catalyst layer 50 are in contact at a boundary S. In this embodiment, the exhaust gas outlet end of the third catalyst layer 40 and the exhaust gas inlet end of the fourth catalyst layer 50 may be continuous. In this embodiment, the third catalyst layer 40 may extend from the exhaust gas outlet end of the partition wall 12a to the exhaust gas inlet end of the partition wall 12a in a direction opposite to the exhaust gas flow direction X, or it may extend from the exhaust gas outlet end of the partition wall 12a in a direction opposite to the exhaust gas flow direction X so as not to reach the exhaust gas inlet end of the partition wall 12a.

[0271] From the viewpoint of further improving the CO and NOx purification performance of the third catalyst layer 40 and the fourth catalyst layer 50, 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 relative to the sum of the length L10a of the first base material part 10a and the length L10b of the second base material part 10b ((L40+L50) / (L10a+L10b)×100) is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100%, or may exceed 100%. As described above, when the exhaust gas outlet side portion of the third catalyst layer 40 overlaps with the exhaust gas inlet side portion of the fourth catalyst layer 50, and when the exhaust gas inlet side portion of the fourth catalyst layer 50 overlaps with the exhaust gas outlet side portion of the third catalyst layer 40, the percentage exceeds 100%. The upper limit of the percentage is preferably 175% or less, more preferably 162% or less, and even more preferably 150% or less. The lower limit may be combined with any of the upper limits. When the first base material part 10a and the second base material part 10b are integrated, and when the first base material part 10a and the second base material part 10b are separate and the exhaust gas outlet end of the first base material part 10a and the exhaust gas inlet end of the second base material part 10b are in contact, the percentage may exceed 100%. However, when the first base material part 10a and the second base material part 10b are separate and a gap is formed between the exhaust gas outlet end of the first base material part 10a and the exhaust gas inlet end of the second base material part 10b, the percentage shall not exceed 100%.

[0272] In the following, the common features of the third catalyst layer 40 and the fourth catalyst layer 50 will be explained together with the explanations for the third catalyst layer 40 and the fourth catalyst layer 50. In doing so, expressions such as "catalyst layer 40, 50", "length L40, L50", "base material 10a, 10b", and "length L10a, L10b" will be used. For the third catalyst layer 40, these expressions mean "catalyst layer 40", "length L40", "base material 10a", and "length L10a", and for the fourth catalyst layer 50, they mean "catalyst layer 50", "length L50", "base material 10b", and "length L10b".

[0273] The catalyst layers 40 and 50 contain Rh.

[0274] Rh is included in the catalyst layers 40 and 50 in the form of a catalytically active component containing Rh, such as metallic Rh, an alloy containing Rh, or a compound containing Rh (e.g., an oxide of Rh). From the viewpoint of further improving the CO and NOx purification performance of the catalyst layers 40 and 50, the catalytically active component containing Rh is preferably in particulate form.

[0275] From the viewpoint of further improving the CO and NOx purification performance of the catalyst layers 40 and 50, the metal equivalent mass of Rh in the catalyst layers 40 and 50 is preferably 0.01 g / L or more, more preferably 0.02 g / L or more, and even more preferably 0.05 g / L or more, based on the volume of the portion of the base material 10a and 10b in which the catalyst layers 40 and 50 are provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO and NOx purification performance and cost. The upper limit is preferably 2.0 g / L or less, more preferably 1.0 g / L or less, and even more preferably 0.5 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0276] The metallic mass of Rh in the catalyst layers 40 and 50, based on the volume of the portion of the base material 10a and 10b in which the catalyst layers 40 and 50 are provided, is calculated using the formula: (mass of catalyst layers 40 and 50 per unit volume of the portion of the base material 10a and 10b in which the catalyst layers 40 and 50 are provided) × (metallic content of Rh in the catalyst layers 40 and 50).

[0277] From the viewpoint of further improving the CO and NOx purification performance of catalyst layers 40 and 50, the Rh content in metal terms in catalyst layers 40 and 50 is preferably 0.005% by mass or more, more preferably 0.010% by mass or more, and even more preferably 0.025% by mass or more, based on the mass of catalyst layers 40 and 50. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO and NOx purification performance and cost. The upper limit is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2.5% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0278] From the viewpoint of further improving the CO purification performance of the catalyst layers 40 and 50, it is preferable that the catalyst layers 40 and 50 contain Pt.

[0279] Pt is included in the catalyst layers 40 and 50 in the form of a catalytically active component containing Pt, such as metallic Pt, alloys containing Pt, or compounds containing Pt (e.g., oxides of Pt). From the viewpoint of further improving the CO purification performance of the catalyst layers 40 and 50, the catalytically active component containing Pt is preferably in particulate form.

[0280] From the viewpoint of further improving the CO purification performance of the catalyst layers 40 and 50, the metal equivalent mass of Pt in the catalyst layers 40 and 50 is preferably 0.01 g / L or more, more preferably 0.05 g / L or more, and even more preferably 0.1 g / L or more, based on the volume of the portion of the base material 10a and 10b in which the catalyst layers 40 and 50 are provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO purification performance and cost. The upper limit is preferably 1.0 g / L or less, more preferably 0.5 g / L or less, and even more preferably 0.3 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0281] The metallic mass of Pt in the catalyst layers 40 and 50, based on the volume of the portion of the base material 10a and 10b in which the catalyst layers 40 and 50 are provided, is calculated using the formula: (mass of catalyst layers 40 and 50 per unit volume of the portion of the base material 10a and 10b in which the catalyst layers 40 and 50 are provided) × (metallic content of Pt in the catalyst layers 40 and 50).

[0282] From the viewpoint of further improving the CO purification performance of catalyst layers 40 and 50, the metal equivalent content of Pt in catalyst layers 40 and 50 is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on the mass of catalyst layers 40 and 50. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO purification performance and cost. The upper limit is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0283] From the viewpoint of further improving the CO and NOx purification performance of catalyst layers 40 and 50, the ratio of the mass of Pt in metal equivalent to the mass of Rh in metal equivalent in catalyst layers 40 and 50 is preferably 0.1 or more and 5 or less, more preferably 0.3 or more and 3 or less, and even more preferably 0.5 or more and 1 or less. Each of the above lower limits may be combined with any of the above upper limits.

[0284] The catalyst layers 40 and 50 may contain one or more noble metal elements other than Rh and Pt.

[0285] Other precious metal elements besides Rh and Pt can be selected from, for example, Pd, Ru, Ir, Os, etc. The other precious metal elements are included in the catalyst layers 40 and 50 in a form that can function as a catalytically active component, such as a metal, an alloy containing the precious metal element, or a compound containing the precious metal element (for example, an oxide of the precious metal element). From the viewpoint of further improving the CO and NOx purification performance of the catalyst layers 40 and 50, the catalytically active component containing the other precious metal elements is preferably in particulate form.

[0286] The content of noble metal elements other than Rh and Pt in catalyst layers 40 and 50, in terms of metal equivalent, is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on the total mass of all noble metal elements in catalyst layers 40 and 50 in terms of metal equivalent. The lower limit is 0% by mass.

[0287] "Content rate in terms of metal of noble metal elements other than Rh and Pt in catalyst layers 40 and 50" means, when the catalyst layers 40 and 50 contain one type of noble metal element other than Rh and Pt, the content rate in terms of metal of said one type of noble metal element, and when the catalyst layers 40 and 50 contain two or more types of noble metal elements other than Rh and Pt, means the total content rate in terms of metal of said two or more types of noble metal elements.

[0288] The catalyst layers 40 and 50 preferably contain one or two or more carriers, and at least a part of the catalytically active component is supported on the one or two or more carriers.

[0289] The carrier can be selected from, for example, inorganic oxides. The description regarding the inorganic oxide is the same as that described above.

[0290] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the catalyst layers 40 and 50, and thereby further improving the CO and NOx purification performance of the catalyst layers 40 and 50, the carrier is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr-based composite oxides, and more preferably selected from Al-based oxides and Ce-Zr-based composite oxides. In one embodiment, the catalyst layers 40 and 50 contain an Al-based oxide and a Ce-Zr-based composite oxide as carriers.

[0291] From the viewpoint of improving the oxygen storage capacity of the catalyst layers 40 and 50, and thereby further improving the CO and NOx purification performance of the catalyst layers 40 and 50, the catalyst layers 40 and 50 preferably contain Ce.

[0292] From the viewpoint of further improving the CO and NOx purification performance of the catalyst layers 40 and 50, the mass of Ce in the catalyst layers 40 and 50 in terms of CeO2 is preferably 1 g / L or more, more preferably 3 g / L or more, and even more preferably 5 g / L or more, based on the volume of the portion of the substrate parts 10a and 10b in which the catalyst layers 40 and 50 are provided. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO and NOx purification performance and cost. The upper limit is preferably 50 g / L or less, more preferably 40 g / L or less, and even more preferably 30 g / L or less. Each of the above lower limits may be combined with any of the above upper limits.

[0293] From the viewpoint of further improving the CO and NOx purification performance of catalyst layers 40 and 50, the Ce content in catalyst layers 40 and 50, in terms of CeO2, is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, based on the mass of catalyst layers 40 and 50. The upper limit can be adjusted as appropriate, taking into consideration the balance between CO and NOx purification performance and cost. The upper limit is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. Each of the above lower limits may be combined with any of the above upper limits.

[0294] From the viewpoint of further improving the CO purification performance of catalyst layers 40 and 50, the ratio of the mass of Ce (in terms of CeO2) to the mass of Pt (in terms of metal) in catalyst layers 40 and 50 is preferably 0.1 to 300, preferably 0.5 to 250, and more preferably 1 to 200. Each of the above lower limits may be combined with any of the above upper limits.

[0295] Ce has the effect of oxidizing Rh and reducing the CO and NOx purification performance of Rh. From the viewpoint of suppressing the reduction in CO and NOx purification performance of Rh due to Ce, it is preferable that the Ce content in catalyst layers 40 and 50, in terms of CeO2, is smaller than the Ce content in second catalyst layer 30, in terms of CeO2. The ratio of the Ce content in catalyst layers 40 and 50, in terms of CeO2, to the Ce content in second catalyst layer 30, in terms of CeO2, is preferably 0.9 or less, preferably 0.7 or less, and preferably 0.4 or less. The lower limit can be adjusted as appropriate considering the balance between CO and NOx purification performance and cost. The lower limit is preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more. Each of the above lower limits may be combined with any of the above upper limits.

[0296] If catalyst layers 40 and 50 contain Ce, then catalyst layers 40 and 50 contain one or more Ce sources. The explanation regarding the Ce sources is the same as above.

[0297] From the viewpoint of further improving the CO and NOx purification performance of the catalyst layers 40 and 50, it is preferable that the catalyst layers 40 and 50 contain a Ce-Zr composite oxide as a Ce source. In addition to the Ce-Zr composite oxide, the catalyst layers 40 and 50 may also contain one or more other Ce sources.

[0298] From the viewpoint of further improving the CO purification performance of catalyst layers 40 and 50, it is preferable that catalyst layers 40 and 50 contain a Ce-Zr composite oxide as a Ce source, and that at least a portion of the Pt in catalyst layers 40 and 50 is supported on the Ce-Zr composite oxide in catalyst layers 40 and 50.

[0299] From the viewpoint of further improving the CO purification performance of catalyst layers 40 and 50, the percentage of the mass of Pt supported on the Ce-Zr composite oxide in catalyst layers 40 and 50 (hereinafter referred to as "percentage Q2") relative to the total mass of Pt in catalyst layers 40 and 50 (in terms of metal equivalent) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. The upper limit is 100% by mass. Percentage Q2 can be determined in the same manner as percentage Q1.

[0300] From the viewpoint of further improving the CO and NOx purification performance of catalyst layers 40 and 50, the content of Ce-Zr-based composite oxide in catalyst layers 40 and 50 is preferably 5% to 80% by mass, more preferably 10% to 75% by mass, and even more preferably 15% to 70% by mass, based on the mass of catalyst layers 40 and 50. Each of the above lower limits may be combined with any of the above upper limits.

[0301] The content of Ce-Zr composite oxide in catalyst layers 40 and 50 can be determined in the same manner as the content of Ce-Zr composite oxide in the first catalyst layer 20.

[0302] From the viewpoint of further improving the CO and NOx purification performance of catalyst layers 40 and 50, the proportion of the mass of Ce derived from Ce-Zr composite oxides in terms of CeO2 among the total mass of Ce in catalyst layers 40 and 50 is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0303] The following describes preferred embodiments of Ce-Zr composite oxides that may be included in catalyst layers 40 and 50.

[0304] From the viewpoint of improving the oxygen storage capacity of Ce-Zr composite oxides, the Ce content in Ce-Zr composite oxides, in terms of CeO2, is preferably 7% by mass or more, more preferably 10% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit can be appropriately adjusted considering heat resistance, structural stability, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 85% by mass or less. The lower limits above may be combined with any of the upper limits above.

[0305] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, the content of Zr in Ce-Zr composite oxides, in terms of ZrO2, is preferably 7% by mass or more, more preferably 10% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit can be appropriately adjusted considering oxygen storage capacity, structural stability, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 85% by mass or less. The lower limits above may be combined with any of the upper limits above.

[0306] From the viewpoint of improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxides, the sum of the Ce content (calculated as CeO2) and the Zr content (calculated as ZrO2) in the Ce-Zr composite oxide is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit is 100% by mass.

[0307] From the viewpoint of improving the heat resistance of Ce-Zr composite oxides, the content of rare earth elements in the Ce-Zr composite oxide, in terms of oxides, is preferably 0.1% to 30% by mass, more preferably 0.5% to 25% by mass, and even more preferably 1% to 20% by mass, based on the mass of the Ce-Zr composite oxide. Each of the above lower limits may be combined with any of the above upper limits.

[0308] From the viewpoint of improving the catalytic activity of Rh in the catalyst layers 40 and 50, and thereby further improving the CO and NOx purification performance of the catalyst layers 40 and 50, it is preferable that the catalyst layers 40 and 50 contain alkaline earth metal elements. The catalyst layers 40 and 50 may contain one type of alkaline earth metal element, or they may contain two or more types of alkaline earth metal elements.

[0309] Alkaline earth metal elements can be selected from, for example, Mg, Ca, Sr, Ba, etc., but it is preferable to select from Ca, Sr, and Ba, and more preferable to select from Sr and Ba.

[0310] Alkaline earth metal elements have the effect of oxidizing Rh and reducing the CO and NOx purification performance of Rh. From the viewpoint of suppressing the reduction in the CO and NOx purification performance of Rh by alkaline earth metal elements, the content of alkaline earth metal elements in the catalyst layers 40 and 50 in terms of oxides is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the mass of the catalyst layers 40 and 50. The lower limit can be adjusted as appropriate considering the balance between CO and NOx purification performance and cost. The upper limit may be 0% by mass or greater than 0% by mass. The upper limit may be, for example, 0.05% by mass or more, 0.1% by mass or more, or 0.15% by mass or more. Each of the above lower limits may be combined with any of the above upper limits.

[0311] The oxide content of alkaline earth metal elements in catalyst layers 40 and 50 can be determined in the same way as the Ce content in the first catalyst layer 20, calculated as CeO2.

[0312] If catalyst layers 40 and 50 contain alkaline earth metal elements, catalyst layers 40 and 50 contain one or more alkaline earth metal element sources. The explanation regarding alkaline earth metal element sources is the same as above.

[0313] The catalyst layers 40 and 50 may contain other components such as binders. Examples of binders include inorganic oxide binders such as alumina binder, ceria binder, zirconia binder, titania binder, and silica binder.

[0314] <Catalyst Manufacturing> Catalyst 1A can be manufactured by forming a first catalyst layer 20 on a first substrate portion 10a, a second catalyst layer 30 on a second substrate portion 10b, a third catalyst layer 40 on the first catalyst layer 20, and a fourth catalyst layer 50 on the second catalyst layer 30. Alternatively, the first catalyst layer 20 and the second catalyst layer 30 may 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 may be formed on the first catalyst layer 20 and the second catalyst layer 30, respectively. Alternatively, the first catalyst layer 20 may be formed on the first substrate portion 10a, the third catalyst layer 40 on the first catalyst layer 20, the second catalyst layer 30 may be formed on the second substrate portion 10b, and then the fourth catalyst layer 50 may be formed on the second catalyst layer 30.

[0315] The first catalyst layer 20 can be formed by preparing a first slurry by mixing a source of noble metal elements (e.g., salts of noble metal elements such as Pd) and other components (e.g., inorganic oxides, binders, solvents, etc.), applying the first slurry onto the first substrate portion 10a, drying it, and firing it.

[0316] The second catalyst layer 30 can be formed by mixing a source of noble metal elements (e.g., salts of noble metal elements such as Pt), a source of Ce (e.g., Ce-based oxides, Ce-Zr-based composite oxides, ceria binders, etc.), a source of alkaline earth metal elements (e.g., acetates, nitrates, hydroxides, carbonates, sulfates, etc. of alkaline earth metal elements), and other components (e.g., inorganic oxides other than the Ce source, binders other than the Ce source, solvents, etc.) to prepare a second slurry, applying the second slurry onto the second base material 10b, drying, and firing.

[0317] The third catalyst layer 40 can be formed by preparing a third slurry by mixing a source of noble metal elements (e.g., salts of noble metal elements such as Rh) and other components (e.g., inorganic oxides, binders, solvents, etc.), applying the third slurry onto the first catalyst layer 20, drying it, and firing it.

[0318] The fourth catalyst layer 50 can be formed by preparing a fourth slurry by mixing a source of noble metal elements (e.g., salts of noble metal elements such as Rh) and other components (e.g., inorganic oxides, binders, solvents, etc.), applying the fourth slurry onto the second catalyst layer 30, drying it, and firing it.

[0319] When the exhaust gas outlet end of the third catalyst layer 40 and the exhaust gas inlet end of the fourth catalyst layer 50 are continuous (i.e., the third catalyst layer 40 and the fourth catalyst layer 50 form a single catalyst layer), the fifth slurry can be prepared by mixing a source of noble metal elements (e.g., salts of noble metal elements such as Rh) and other components (e.g., inorganic oxides, binders, solvents, etc.), applying the fifth slurry onto the first catalyst layer 20 and the second catalyst layer 30, drying, and firing.

[0320] Examples of salts of precious metal elements include nitrates, ammine complex salts, acetates, and chlorides. Examples of binders include alumina binders, zirconia binders, titania binders, silica binders, and ceria binders. Examples of solvents include water and organic solvents.

[0321] The drying temperature is, for example, between 70°C and 150°C, and the drying time is, for example, between 5 minutes and 1 hour. The firing temperature is, for example, between 200°C and 700°C, and the firing time is, for example, between 0.5 hours and 5 hours. Firing can be carried out, for example, in an air atmosphere.

[0322] ≪Second Embodiment≫ The exhaust gas purification catalyst 1B (hereinafter referred to as "catalyst 1B") according to the second embodiment will be described below with reference to Figure 7.

[0323] In catalyst 1B, components identical to those in catalyst 1A are indicated by the same reference numerals as those in catalyst 1A. Unless otherwise specified below, the above description relating to catalyst 1A also applies to catalyst 1B.

[0324] Catalyst 1B differs from catalyst 1A, in that the first substrate portion 10a and the second substrate portion 10b are separate components, while catalyst 1B is an integrated component.

[0325] The present invention includes both embodiments in which the substrate 10 is composed of one substrate, such as catalyst 1A, and embodiments in which the substrate 10 is composed of two substrates, such as catalyst 1B.

[0326] As shown in Figure 7, the first base material portion 10a and the second base material portion 10b are arranged in the exhaust passage within the exhaust pipe P such that their axial directions coincide with or substantially coincide with the exhaust gas flow direction X.

[0327] As shown in Figure 7, the axial direction of the first base material portion 10a and the axial direction of the second base material portion 10b may coincide or substantially coincide.

[0328] As shown in Figure 7, a gap is formed between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b. The distance between the exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b is, for example, 5 to 1000 mm.

[0329] The phrase "the base material 10 extends in the exhaust gas flow direction X" includes embodiments in which a gap is formed between the exhaust gas outlet end of the first base material portion 10a and the exhaust gas inlet end of the second base material portion 10b, and the axial directions of the first base material portion 10a and the second base material portion 10b coincide with or substantially coincide with the exhaust gas flow direction X.

[0330] The exhaust gas outlet end of the first base material 10a and the exhaust gas inlet end of the second base material 10b may be in contact. In this case, the arrangement of the first base material 10a and the second base material 10b may be the same as, for example, the arrangement shown in Figure 6. [Examples]

[0331] [Example 1A] (1) Preparation of slurry for forming the first catalyst layer To pure water, 0.9 parts by mass of palladium nitrate aqueous solution (calculated as Pd metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass), 44.0 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass), 4.6 parts by mass of barium hydroxide (calculated as BaO, or 5.9 parts by mass in terms of BaCO3), and 8.0 parts by mass of binder (calculated as solid content) were added, mixed, and stirred to prepare a slurry for forming the first catalyst layer.

[0332] (2) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 20% by mass, Zr content in terms of ZrO2: 70% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0333] (3) Formation of the first catalyst layer and the second catalyst layer As a substrate, a cordierite honeycomb porous substrate is used, having axially extending cells partitioned by partitions with a thickness of 95-125 μm (manufactured by NGK Insulators, Ltd., axial length: 120 mm, outer diameter: 83 mm, volume: 0.65 L, cell density: 600 cells / inch). 2 I prepared ).

[0334] The substrate was immersed in the slurry for forming the first catalyst layer, up to a position 40 mm from the upstream end in the exhaust gas flow direction X, and the slurry for forming the first catalyst layer was applied to the upstream side of the substrate. Next, the substrate was immersed in the slurry for forming the second catalyst layer, up to a position 80 mm from the downstream end in the exhaust gas flow direction X, and the slurry for forming the second catalyst layer was applied to the downstream side of the substrate. Then, the substrate coated with the slurry for forming the first and second catalyst layers was dried at 90°C and then fired at 450°C. As a result, the first and second catalyst layers were formed on the substrate without any gaps in the exhaust gas flow direction X (i.e., the exhaust gas outlet end of the first catalyst layer and the exhaust gas inlet end of the second catalyst layer were in contact). The mass of the first catalyst layer per unit volume (wash coat amount) of the portion of the substrate where the first catalyst layer was provided was 170 g / L. The mass of the second catalyst layer per unit volume (wash coat amount) in the portion of the substrate where the second catalyst layer is provided was 170 g / L. The wash coat amount refers to the mass of the catalyst layer after calcination (the same applies below). In addition, the barium hydroxide in the slurry is changed to barium oxide by calcination, and the barium oxide reacts with CO2 in the air to be converted into barium carbonate.

[0335] (4) Preparation of slurry for forming the third catalyst layer and the fourth catalyst layer To pure water, 0.2 parts by mass of rhodium nitrate aqueous solution (calculated as Rh metal), 66.7 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 15% by mass, Zr content in terms of ZrO2: 70% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 15% by mass), 22.7 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass), 0.3 parts by mass of barium hydroxide (calculated as BaO, or 0.4 parts by mass in terms of BaCO3), and 10.0 parts by mass of binder (calculated as solid matter) were added, mixed, and stirred to prepare a slurry for forming the third and fourth catalyst layers.

[0336] (5) Formation of the third and fourth catalyst layers The entire substrate on which the first and second catalyst layers were formed was immersed in a slurry for forming the third and fourth catalyst layers, thereby coating the entire substrate with the slurry for forming the third and fourth catalyst layers. Next, the substrate coated with the slurry for forming the third and fourth catalyst layers was dried at 90°C and then fired at 450°C. As a result, the third and fourth catalyst layers were formed on the first and second catalyst layers, respectively, without gaps in the exhaust gas flow direction X (i.e., the exhaust gas outlet end of the third catalyst layer and the exhaust gas inlet end of the fourth catalyst layer were continuous, and the third catalyst layer 40 and the fourth catalyst layer 50 formed a single catalyst layer). The mass of the third catalyst layer per unit volume (wash coat amount) in the portion of the substrate on which the third catalyst layer was provided was 60 g / L. The mass of the fourth catalyst layer per unit volume (wash coat amount) in the portion of the substrate on which the fourth catalyst layer was provided was 60 g / L.

[0337] In this manner, an exhaust gas purification catalyst of Example 1A was manufactured, comprising a base material, a first catalyst layer provided upstream of the base material, a second catalyst layer provided downstream of the base material, a third catalyst layer provided above the first catalyst layer, and a fourth catalyst layer provided above the second catalyst layer.

[0338] In the first catalyst layer of the exhaust gas purification catalyst of Example 1A, the mass of Pd in ​​terms of metal was 1.5 g / L, based on the volume of the portion of the substrate in which the first catalyst layer is provided.

[0339] In the second catalyst layer of the exhaust gas purification catalyst of Example 1A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 17.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 1A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 7.0, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 2.2.

[0340] In the third catalyst layer of the exhaust gas purification catalyst of Example 1A, the mass of Rh in terms of metal was 0.1 g / L, based on the volume of the portion of the substrate in which the third catalyst layer is provided.

[0341] In the fourth catalyst layer of the exhaust gas purification catalyst of Example 1A, the mass of Rh in terms of metal was 0.1 g / L, based on the volume of the portion of the substrate in which the fourth catalyst layer is provided.

[0342] [Example 2A] (A) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 30% by mass, Zr content in terms of ZrO2: 60% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO, 5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0343] The exhaust gas purification catalyst of Example 2A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (A) above was used.

[0344] In the second catalyst layer of the exhaust gas purification catalyst of Example 2A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 24.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 2A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 9.8, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 3.1.

[0345] [Example 3A] (B) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0346] The exhaust gas purification catalyst of Example 3A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (B) above was used.

[0347] In the second catalyst layer of the exhaust gas purification catalyst of Example 3A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 31.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 3A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 12.6, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 4.0.

[0348] [Example 4A] (C) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 50% by mass, Zr content in terms of ZrO2: 40% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0349] The exhaust gas purification catalyst of Example 4A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (C) above was used.

[0350] In the second catalyst layer of the exhaust gas purification catalyst of Example 4A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 38.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 4A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 15.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 4.9.

[0351] [Example 5A] (D) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 55% by mass, Zr content in terms of ZrO2: 35% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0352] The exhaust gas purification catalyst of Example 5A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (D) above was used.

[0353] In the second catalyst layer of the exhaust gas purification catalyst of Example 5A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 41.9 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 5A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 16.8, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 5.4.

[0354] [Example 6A] (E) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 60% by mass, Zr content in terms of ZrO2: 30% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0355] The exhaust gas purification catalyst of Example 6A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (E) above was used.

[0356] In the second catalyst layer of the exhaust gas purification catalyst of Example 6A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 45.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 6A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 18.2, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 5.8.

[0357] [Example 7A] (F) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 65% by mass, Zr content in terms of ZrO2: 25% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0358] The exhaust gas purification catalyst of Example 7A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (F) above was used.

[0359] In the second catalyst layer of the exhaust gas purification catalyst of Example 7A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 48.9 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 7A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 19.6, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 6.3.

[0360] [Example 8A] (G) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 30% by mass, Zr content in terms of ZrO2: 60% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 3.9 parts by mass of barium sulfate (in terms of BaO, 5.9 parts by mass in terms of BaSO4), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0361] Except for using the slurry for forming the second catalyst layer manufactured in (G) above, the exhaust gas purification catalyst of Example 8A was manufactured in the same manner as in Example 1A.

[0362] In the second catalyst layer of the exhaust gas purification catalyst of Example 8A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 24.4 g / L, and 6.6 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 8A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 9.8, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 3.7.

[0363] [Example 9A] (H) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 30.9 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 53.7 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0364] The exhaust gas purification catalyst of Example 9A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (H) above was used.

[0365] In the second catalyst layer of the exhaust gas purification catalyst of Example 9A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 24.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 9A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 9.8, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 3.1.

[0366] [Example 10A] (I) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 58.8 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 25.8 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0367] Except for using the slurry for forming the second catalyst layer manufactured in (I) above, the exhaust gas purification catalyst of Example 10A was manufactured in the same manner as in Example 1A.

[0368] In the second catalyst layer of the exhaust gas purification catalyst of Example 10A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 43.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 10A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 17.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 5.6.

[0369] [Example 11A] (J) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 59.9 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 26.3 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 3.3 parts by mass of barium hydroxide (in terms of BaO, 4.2 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.1 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0370] Except for using the slurry for forming the second catalyst layer produced in (J) above, and setting the wash coat amount of the second catalyst layer to 167 g / L, the exhaust gas purification catalyst of Example 11A was produced in the same manner as in Example 1A.

[0371] In the second catalyst layer of the exhaust gas purification catalyst of Example 11A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 43.4 g / L, and 5.4 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 11A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 17.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 8.0.

[0372] [Example 12A] (K) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 60.6 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 26.6 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 2.4 parts by mass of barium hydroxide (in terms of BaO, 3.0 parts by mass in terms of BaCO3), 2.1 parts by mass of ceria binder (in terms of solid matter), and 6.2 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0373] Except for using the slurry for forming the second catalyst layer produced in (K) above, and setting the wash coat amount of the second catalyst layer to 165 g / L, the exhaust gas purification catalyst of Example 12A was produced in the same manner as in Example 1A.

[0374] In the second catalyst layer of the exhaust gas purification catalyst of Example 12A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 43.4 g / L, and 3.9 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 12A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 17.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 11.2.

[0375] [Comparative Example 1A] (L) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Zr-based oxide (Zr content in terms of ZrO2: 90% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0376] The exhaust gas purification catalyst of Comparative Example 1A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (L) above was used.

[0377] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 1A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 3.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 1A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 1.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 0.4.

[0378] [Comparative example 2A] (M) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 15% by mass, Zr content in terms of ZrO2: 75% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO, 5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0379] The exhaust gas purification catalyst of Comparative Example 2A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (M) above was used.

[0380] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 2A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 13.9 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 2A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 5.6, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 1.8.

[0381] [Comparative example 3A] (N) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 80% by mass, Zr content in terms of ZrO2: 10% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO, 5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0382] The exhaust gas purification catalyst of Comparative Example 3A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (N) above was used.

[0383] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 3A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 59.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 3A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 23.8, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 7.6.

[0384] [Comparative example 4A] (O) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-based oxide (Ce content in terms of CeO2: 95% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 5% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0385] The exhaust gas purification catalyst of Comparative Example 4A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (O) above was used.

[0386] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 4A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 69.9 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 4A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 28.0, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 9.0.

[0387] [Comparative example 5A] (P) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-based oxide (Ce content in terms of CeO2: 100% by mass) as the first support, 43.4 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO, 5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0388] The exhaust gas purification catalyst of Comparative Example 5A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (P) above was used.

[0389] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 5A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 73.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 5A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 29.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 9.4.

[0390] [Comparative Example 6A] (Q) Preparation of slurry for forming the second catalyst layer To pure water, 1.6 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 43.8 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 30% by mass, Zr content in terms of ZrO2: 60% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 46.1 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 2.1 parts by mass of ceria binder (in terms of solid matter), and 6.4 parts by mass of a Ce-free binder (in terms of solid matter) were added, and the mixture was stirred to prepare a slurry for forming the second catalyst layer.

[0391] A catalytic converter for exhaust gas purification of Comparative Example 6A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalytic layer manufactured in (Q) above was used, and the amount of wash coat in the second catalytic layer was set to 160 g / L.

[0392] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 6A, the metallic mass of Pt and the CeO2-equivalent mass of Ce were 2.5 g / L and 24.4 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 6A, the ratio of the CeO2-equivalent mass of Ce to the metallic mass of Pt was 9.8.

[0393] [Comparative Example 7A] (R) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 84.6 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as a second support, 4.6 parts by mass of barium hydroxide (in terms of BaO, 5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer. The slurry for forming the second catalyst layer does not contain any of the Ce-based oxides, Ce-Zr-based composite oxides, or Zr-based oxides that correspond to the first support.

[0394] The exhaust gas purification catalyst of Comparative Example 7A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (R) above was used.

[0395] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 7A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 3.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 7A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 1.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 0.4.

[0396] [Comparative Example 8A] (S) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 15.4 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 69.2 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0397] The exhaust gas purification catalyst of Comparative Example 8A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (S) above was used.

[0398] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 8A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 13.9 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 8A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 5.6, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 1.8.

[0399] [Comparative Example 9A] (T) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 82.4 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 2.2 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO, 5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0400] The exhaust gas purification catalyst of Comparative Example 9A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (T) above was used.

[0401] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 9A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 59.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 9A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 23.8, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 7.6.

[0402] [Comparative Example 10A] (U) Preparation of slurry for forming the second catalyst layer To pure water, 1.5 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 61.3 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 27.0 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 1.4 parts by mass of barium hydroxide (in terms of BaO) (1.8 parts by mass in terms of BaCO3), 2.1 parts by mass of ceria binder (in terms of solid matter), and 6.3 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0403] A catalytic converter for exhaust gas purification of Comparative Example 10A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalytic layer manufactured in (U) above was used, and the amount of wash coat in the second catalytic layer was set to 163 g / L.

[0404] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 10A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 43.4 g / L, and 2.3 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 10A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 17.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 18.6.

[0405] [Comparative Example 11A] (V) Preparation of slurry for forming the second catalyst layer To pure water, 1.6 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 62.1 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 27.3 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 0.5 parts by mass of barium hydroxide (in terms of BaO) (0.6 parts by mass in terms of BaCO3), 2.1 parts by mass of ceria binder (in terms of solid matter), and 6.3 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0406] The exhaust gas purification catalyst of Comparative Example 11A was manufactured in the same manner as in Example 1A, except that the slurry for forming the second catalyst layer manufactured in (V) above was used, and the amount of wash coat in the second catalyst layer was set to 161 g / L.

[0407] In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 11A, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the BaO equivalent mass of Ba were 2.5 g / L, 43.4 g / L, and 0.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Comparative Example 11A, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 17.4, and the ratio of the CeoO2 equivalent mass of Ce to the BaO equivalent mass of Ba was 55.9.

[0408] [Example 1B] The same exhaust gas purification catalyst used in Example 3A was used as the exhaust gas purification catalyst in Example 1B.

[0409] [Example 2B] (W) Preparation of slurry for forming the second catalyst layer To pure water, 1.4 parts by mass of dinitrodiamine platinum(II) solution (in terms of Pt metal), 41.2 parts by mass of Ce-Zr composite oxide (Ce content in terms of CeO2: 40% by mass, Zr content in terms of ZrO2: 50% by mass, content of one or more rare earth elements other than Ce in terms of oxides: 10% by mass) as the first support, 43.5 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass) as the second support, 4.6 parts by mass of barium hydroxide (in terms of BaO) (5.9 parts by mass in terms of BaCO3), 2.0 parts by mass of ceria binder (in terms of solid matter), and 6.0 parts by mass of a Ce-free binder (in terms of solid matter) were added, mixed, and stirred to prepare a slurry for forming the second catalyst layer.

[0410] (X) Preparation of slurry for forming the third and fourth catalyst layers To pure water, 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal), 0.2 parts by mass of dinitrodiamine platinum(II) solution (based on Pt metal), 66.7 parts by mass of Ce-Zr composite oxide (Ce content based on CeO2: 15% by mass, Zr content based on ZrO2: 70% by mass, content of one or more rare earth elements other than Ce (based on oxides): 15% by mass), 22.5 parts by mass of La2O3-modified alumina (La2O3 modification amount: 1% by mass), 0.3 parts by mass of barium hydroxide (based on BaO, or 0.4 parts by mass in BaCO3), and 10.0 parts by mass of binder (based on solid matter) were added, mixed, and stirred to prepare a slurry for forming the third and fourth catalyst layers.

[0411] Except for using the slurry for forming the second catalyst layer produced in (W) above and the slurry for forming the third and fourth catalyst layers produced in (X) above, the exhaust gas purification catalyst of Example 2B was manufactured in the same manner as in Example 1A.

[0412] In the second catalyst layer of the exhaust gas purification catalyst of Example 2B, the metallic mass of Pt, the CeoO2 equivalent mass of Ce, and the Bao equivalent mass of Ba were 2.4 g / L, 31.4 g / L, and 7.8 g / L, respectively, based on the volume of the portion of the substrate in which the second catalyst layer is provided. In the second catalyst layer of the exhaust gas purification catalyst of Example 2B, the ratio of the CeoO2 equivalent mass of Ce to the metallic mass of Pt was 13.1, and the ratio of the CeoO2 equivalent mass of Ce to the Bao equivalent mass of Ba was 4.0.

[0413] In the third catalyst layer of the exhaust gas purification catalyst of Example 2B, the metal equivalent mass of Rh and the metal equivalent mass of Pt were 0.1 g / L and 0.1 g / L, respectively, based on the volume of the portion of the substrate in which the third catalyst layer is provided. The percentage Q2 in the third catalyst layer was 67.2% by mass.

[0414] In the fourth catalyst layer of the exhaust gas purification catalyst of Example 2B, the metal equivalent mass of Rh and the metal equivalent mass of Pt were 0.1 g / L and 0.1 g / L, respectively, based on the volume of the portion of the substrate in which the fourth catalyst layer is provided. The percentage Q2 in the fourth catalyst layer was 67.2% by mass.

[0415] [Comparative example 1B] The same exhaust gas purification catalyst used in Comparative Example 6A was used as the exhaust gas purification catalyst in Comparative Example 1B.

[0416] The characteristics of the first, third, and fourth catalyst layers of each exhaust gas purification catalyst are shown in Tables 1A and 1B. In Tables 1A and 1B, "WC" represents the mass of each catalyst layer per unit volume of the portion of the substrate in which each catalyst layer is provided (wash coat amount), "Pd content" represents the metal equivalent content of Pd in ​​the first catalyst layer based on the mass of the first catalyst layer, "Rh content" represents the metal equivalent content of Rh in the third or fourth catalyst layer based on the mass of the third or fourth catalyst layer, and "Pt content" represents the metal equivalent content of Pt in the third or fourth catalyst layer based on the mass of the third or fourth catalyst layer.

[0417] The characteristics of the second catalyst layer of each exhaust gas purification catalyst are shown in Tables 2A, B, and C. In Tables 2A, B, and C, "WC" is the mass of the second catalyst layer per unit volume of the portion of the substrate in which the second catalyst layer is provided (wash coat amount), "Pt" is the mass of Pt in the second catalyst layer in terms of metal equivalent, based on the volume of the portion of the substrate in which the second catalyst layer is provided, "CeO2" is the mass of Ce in the second catalyst layer in terms of CeO2, based on the volume of the portion of the substrate in which the second catalyst layer is provided, "BaO" is the mass of Ba in the second catalyst layer in terms of BaO, based on the volume of the portion of the substrate in which the second catalyst layer is provided, and "CeO2 / Pt" is the ratio of the C in the second catalyst layer to the mass of Pt in the second catalyst layer in terms of metal equivalent. The ratio of e's mass in terms of CeO2, "CeO2 / BaO" is the ratio of the mass of Ce in the second catalyst layer in terms of CeO2 to the mass of Ba in the second catalyst layer in terms of BaO, "Type" of "First Support" is the type of oxide (Ce-Zr composite oxide, Ce-based oxide, or Zr-based oxide) used as the first support, "CeO2 Content" of "First Support" is the Ce content in the first support in terms of CeO2, based on the mass of the first support, "Quantity" of "First Support" is the amount of the first support in the second catalyst layer, based on the mass of the second catalyst layer, and "Quantity" of "Ceria Binder" is the amount of ceria binder in the second catalyst layer, based on the mass of the second catalyst layer. In the "Type" of "First Support", "CZ" represents a Ce-Zr composite oxide, "Ce" represents a Ce-based oxide, and "Zr" represents a Zr-based oxide.

[0418] [Test Example 1] (1) Durability treatment The exhaust gas purification catalysts of Examples 1A to 12A and Comparative Examples 1A to 11A were each mounted in the exhaust pipe, and this exhaust pipe was set in a gasoline engine. The engine speed / torque and other parameters were adjusted so that the catalyst temperature reached 950°C, and an endurance test was performed for 50 hours.

[0419] (2) Evaluation of model gas purification performance After durability treatment, the exhaust gas purification catalyst was cut into 12-cell x 12-cell x 120mm sections and placed in a pipe. While flowing exhaust model gas (CO 0.26 vol%, O2 0.10 vol%, NO 900 vol ppm, CH4 700 vol ppm, CO2 4.4 vol%, H2O 10 vol%, remaining N2) at a space velocity of 100,000 / h, the catalyst was heated to 600°C at a rate of 30°C / min and held for 10 minutes. The amount of methane contained in the gas flowing out of the pipe outlet was detected using a Horiba MEXA7100 engine exhaust gas measuring device, and the methane purification rate was calculated based on the following formula. In the following formula, X represents the amount of methane detected without the catalyst, and Y represents the amount of methane detected with the catalyst installed. Methane purification rate (%) = (XY) / X × 100

[0420] The measurement results for the methane purification rate are shown in Tables 2A and 2B.

[0421] [Test Example 2] (1) Durability treatment Durability treatment was performed on the exhaust gas purification catalysts of Examples 1B to 2B and Comparative Example 1B in the same manner as in Test Example 1 (1).

[0422] (2) Evaluation of actual vehicle purification performance A treated exhaust gas purification catalyst was installed in a vehicle. The vehicle was operated according to the operating conditions of the Modified Indian Driving Cycle (MIDC). The emissions of methane and nitrogen oxides (NOx) in the exhaust gas that passed through the exhaust gas purification catalyst were measured, and the methane and NOx emissions per unit distance traveled (mg / km) were determined. A compressed natural gas (CNG) vehicle was used. Table 2C shows the methane emissions (mg / km) and NOx emissions (mg / km) per unit distance traveled during the test mode.

[0423] [Table 1A]

[0424] [Table 1B]

[0425] [Table 2A]

[0426] [Table 2B]

[0427] [Table 2C] [Explanation of symbols]

[0428] 1A, 1B... Catalysts for exhaust gas purification 10...Base material 10a...First base material part 10b...Second base material part 11a, 11b... tubular section 12a,12b...Bulkhead part 13a, 13b... cells 20...1st catalyst layer 30...Second catalyst layer 40...Third catalyst layer 50...4th catalyst layer L10a...Length of the first base material L10b...Length of the second base material L20...Average length of the first catalyst layer L30...Average length of the second catalyst layer L40...Average length of the third catalyst layer L50...Average length of the fourth catalytic layer P... Exhaust pipe of an internal combustion engine

Claims

1. A substrate extending in the exhaust gas flow direction, having a first substrate portion located upstream in the exhaust gas flow direction and a second substrate portion located downstream in the exhaust gas flow direction, The first catalyst layer provided on the first substrate portion, The second catalyst layer provided on the second substrate portion, A third catalyst layer provided above the first catalyst layer and / or a fourth catalyst layer provided above the second catalyst layer, An exhaust gas purification catalyst comprising, The first catalyst layer contains Pd, The second catalyst layer contains Pt, Ce, and alkaline earth metal elements. The third catalyst layer and the fourth catalyst layer each contain Rh, The metallic mass of Pt in the second catalyst layer is 1.0 g / L or more, based on the volume of the portion of the second substrate in which the second catalyst layer is provided. In the second catalyst layer, the amount of CeO of Pt is relative to the metal equivalent mass. ２ The ratio of the converted masses is between 6.0 and 20.

0. In the second catalyst layer, the amount of Ce relative to the mass of alkaline earth metal elements in terms of oxides is CeO ２ The exhaust gas purification catalyst wherein the converted mass ratio is 2.0 or more and 18.0 or less.

2. In the second catalyst layer, the ratio of the mass of Ce on a CeO₂ basis to the mass of Pt on a metal basis is 7.0 or more and 19.0 or less, The exhaust gas purification catalyst according to claim 1, wherein in the second catalyst layer, the ratio of the mass of Ce in terms of CeO₂ to the mass of alkaline earth metal elements in terms of oxides is 3.0 or more and 16.0 or less.

3. In the second catalyst layer, the ratio of the mass of Ce on a CeO₂ basis to the mass of Pt on a metal basis is 8.0 or more and 18.0 or less, The exhaust gas purification catalyst according to claim 2, wherein in the second catalyst layer, the ratio of the mass of Ce in terms of CeO₂ to the mass of alkaline earth metal elements in terms of oxides is 5.6 or more and 12.0 or less.

4. The exhaust gas purification catalyst according to claim 1, wherein the second catalyst layer contains a Ce-Zr composite oxide as a Ce source.

5. CeO in the Ce-Zr composite oxide ２ The exhaust gas purification catalyst according to claim 4, wherein the converted content is 18% by mass or more and 70% by mass or less, based on the mass of the Ce-Zr composite oxide.

6. CeO in the Ce-Zr composite oxide ２ The exhaust gas purification catalyst according to claim 5, wherein the converted content is 25% by mass or more and 63% by mass or less, based on the mass of the Ce-Zr composite oxide.

7. The exhaust gas purification catalyst according to claim 4, wherein the content of the Ce-Zr composite oxide in the second catalyst layer is 20% by mass or more and 80% by mass or less, based on the mass of the second catalyst layer.

8. The exhaust gas purification catalyst according to claim 4, wherein at least a portion of the Pt in the second catalyst layer is supported on the Ce-Zr composite oxide in the second catalyst layer.

9. The second catalyst layer contains an alkaline earth metal compound as an alkaline earth metal element source, The exhaust gas purification catalyst according to any one of claims 1 to 8, wherein the alkaline earth metal compound is selected from oxides, carbonates, and sulfates.

10. The exhaust gas purification catalyst according to any one of claims 1 to 8, wherein the second catalyst layer contains one or more alkaline earth metal elements selected from Ca, Sr, and Ba.

11. The exhaust gas purification catalyst according to any one of claims 1 to 8, wherein the third catalyst layer and the fourth catalyst layer each contain Pt.

12. The exhaust gas purification catalyst according to claim 11, wherein the third catalyst layer and the fourth catalyst layer each contain Ce.

13. The exhaust gas purification catalyst according to claim 12, wherein the third catalyst layer and the fourth catalyst layer each contain a Ce-Zr composite oxide as a Ce source.

14. The exhaust gas purification catalyst according to claim 13, wherein at least a portion of the Pt in the third catalyst layer is supported on the Ce-Zr composite oxide in the third catalyst layer, and at least a portion of the Pt in the fourth catalyst layer is supported on the Ce-Zr composite oxide in the fourth catalyst layer.

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