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WO2025183037A1 - Catalyseur de purification de gaz d'échappement - Google Patents

Catalyseur de purification de gaz d'échappement

Info

Publication number
WO2025183037A1
WO2025183037A1 PCT/JP2025/006758 JP2025006758W WO2025183037A1 WO 2025183037 A1 WO2025183037 A1 WO 2025183037A1 JP 2025006758 W JP2025006758 W JP 2025006758W WO 2025183037 A1 WO2025183037 A1 WO 2025183037A1
Authority
WO
WIPO (PCT)
Prior art keywords
exhaust gas
catalyst
layer
catalyst layer
mass
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2025/006758
Other languages
English (en)
Japanese (ja)
Inventor
力也 妙智
真吾 秋田
有希 永尾
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mitsui Kinzoku Co Ltd
Original Assignee
Mitsui Mining and Smelting Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mitsui Mining and Smelting Co Ltd filed Critical Mitsui Mining and Smelting Co Ltd
Publication of WO2025183037A1 publication Critical patent/WO2025183037A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • B01J35/57—Honeycombs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/64—Pore diameter

Definitions

  • the present invention relates to a catalyst for purifying exhaust gas.
  • Exhaust gases emitted from internal combustion engines of automobiles, motorcycles, etc. contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx).
  • harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx).
  • Three-way catalysts are used to purify and neutralize these harmful components.
  • Three-way catalysts contain precious metal elements such as Pt, Pd, and Rh.
  • Exhaust gas contains particulate matter (PM) in addition to harmful components such as HC, CO, and NOx, and is known to cause air pollution.
  • PM particulate matter
  • a substrate with a structure known as a wall-flow type is used as a GPF.
  • a wall-flow type substrate has inlet cells that are open at the end on the exhaust gas inlet side and closed at the end on the exhaust gas outlet side, outlet cells that are closed at the end on the exhaust gas inlet side and open at the end on the exhaust gas outlet side, and a porous partition wall that separates the inlet and outlet cells.
  • a catalyst layer containing precious metal elements such as Pt, Pd, and Rh on a wall-flow substrate to capture PM and purify harmful components such as HC, CO, and NOx.
  • a catalyst comprising a wall-flow substrate and a catalyst layer
  • exhaust gas flows in from the end (opening) on the exhaust gas inlet side of the inlet cell, passes through the catalyst layer and partition walls, and flows out from the end (opening) on the exhaust gas outlet side of the outlet cell, whereupon PM in the exhaust gas is captured in the pores of the catalyst layer and partition walls.
  • materials with oxygen storage capacity which store oxygen when the oxygen concentration in exhaust gas is high and release oxygen when the oxygen concentration in exhaust gas is low, such as Zr-based oxides such as Ce-Zr composite oxides, are used as materials for the catalyst layer (see, for example, Patent Documents 1 and 2).
  • Zr-based oxides such as Ce-Zr composite oxides, which are conventionally used as materials for catalyst layers, undergo thermal shrinkage when exposed to high-temperature environments.
  • high temperature refers to temperatures of 800°C or higher, particularly 900°C or higher.
  • the inventors have discovered that in an exhaust gas purification catalyst comprising a wall-flow type substrate and a catalyst layer containing a Zr-based oxide, exposure to a high-temperature environment is likely to result in a decrease in PM capture performance. Specifically, the inventors have discovered that when an exhaust gas purification catalyst comprising a wall-flow type substrate and a catalyst layer containing a Zr-based oxide is exposed to a high-temperature environment, cracks form in the catalyst layer due to thermal contraction of the Zr-based oxide, which tends to cause a decrease in the PM capture performance of the catalyst layer.
  • the present invention therefore aims to provide an exhaust gas purification catalyst that includes a wall-flow substrate and a catalytic layer containing a Zr-based oxide, and that can suppress the deterioration of PM collection performance that occurs when exposed to high-temperature environments.
  • a catalyst for purifying exhaust gases comprising a substrate extending in an exhaust gas flow direction and at least one of a first catalytic layer and a second catalytic layer,
  • the substrate is an inlet-side cell extending in the exhaust gas flow direction, the inlet-side cell having an open end on the exhaust gas inlet side and a closed end on the exhaust gas outlet side; an outlet-side cell extending in the exhaust gas flow direction, the outlet-side cell having a closed end on an exhaust gas inlet side and an open end on an exhaust gas outlet side; a porous partition wall portion separating the inlet cell and the outlet cell; Equipped with the first catalytic layer has a portion that is formed on an outer surface of the partition wall portion on the inlet-side cell side, from an end of the partition wall portion on the exhaust gas inlet side along the exhaust gas flow direction, the second catalytic layer has a portion that is formed on an outer surface of the partition wall portion on the outlet-side
  • the exhaust gas purifying catalyst includes the first catalytic layer and does not include the second catalytic layer, the percentage of the length of the first catalytic layer relative to the length of the inlet-side cell is 100%; when the exhaust gas purifying catalyst includes the second catalyst layer but does not include the first catalyst layer, the percentage of the length of the second catalyst layer with respect to the length of the outlet-side cell is 100%; [1] The exhaust gas purifying catalyst according to [1], wherein, when the exhaust gas purifying catalyst includes the first catalytic layer and the second catalytic layer, a percentage of the total length of the first catalytic layer and the second catalytic layer relative to a length of the substrate is 100% or more.
  • the first catalyst layer contains a Ce-Zr-based composite oxide as the Zr-based oxide
  • the second catalyst layer contains a Ce—Zr-based composite oxide as the Zr-based oxide
  • the Ce—Zr-based composite oxide in the first catalyst layer has a structure represented by the following formula: R 12 /R 11 >0.8 [In the formula, R11 represents the Ce content (mass%) in the Ce—Zr-based composite oxide calculated as CeO2 , and R12 represents the Zr content (mass%) in the Ce—Zr-based composite oxide calculated as ZrO2 .] Fulfilling When the exhaust gas purifying catalyst satisfies the condition 1b, the Ce—Zr-based composite oxide in the second catalyst layer has a structure represented by the following formula: R 22 /R 21 >0.8 [In the formula, R21 represents the Ce content (mass%) in the Ce—Zr-based composite oxide calculated as CeO2 , and R22 represents the Zr content (mass%) in the Ce—Zr-based composite oxide calculated as ZrO2 .] The exhaust gas purifying catalyst according to [5] or [6], which satisfies the above.
  • the exhaust gas purifying catalyst When the exhaust gas purifying catalyst satisfies the condition 1a, the exhaust gas purifying catalyst also satisfies the following condition 2a: [Condition 2a] 1.30 ⁇ 10 ⁇ 3 ⁇ Ra [In the formula, Ra represents the gas permeability (cm 3 /(cm 2 ⁇ s ⁇ Pa)) of the first catalyst layer and the partition wall portion measured using a perm porometer before the exhaust gas purification catalyst is subjected to the heat treatment.] Further fulfilling In the case where the exhaust gas purifying catalyst satisfies the condition 1b, the exhaust gas purifying catalyst also satisfies the following condition 2b: [Condition 2b] 1.30 ⁇ 10 ⁇ 3 ⁇ Rb [In the formula, Rb represents the gas permeability (cm 3 /(cm 2 ⁇ s ⁇ Pa)) of the second catalyst layer and the partition wall portion measured using a perm porometer before the exhaust gas purification catalyst is subjected to the heat treatment.] [8] The exhaust gas purifying
  • the present invention provides an exhaust gas purification catalyst that includes a wall-flow type substrate and a catalytic layer containing a Zr-based oxide, and that can suppress the deterioration of PM collection performance that occurs when exposed to high-temperature environments.
  • FIG. 1 is a partial cross-sectional view showing a state in which an exhaust gas purifying catalyst according to one embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine.
  • FIG. 2 is an end view taken along line AA of FIG.
  • FIG. 3 is an end view taken along line BB in FIG.
  • FIG. 4 is an enlarged view of the area indicated by the symbol R1 in FIG.
  • FIG. 5 is an enlarged view of the area indicated by the symbol R2 in FIG.
  • FIG. 6 is an end view taken along line CC of FIG.
  • FIG. 7A is a plan view of a cut piece cut out from the exhaust gas purifying catalyst (a plan view when viewed from the exhaust gas inflow side (upper side of FIG. 7B)).
  • FIG. 7B is a cross-sectional view taken along line D1-D1 in FIG. 7A.
  • FIG. 8A is a plan view of a cut piece used to measure the gas permeability of the first catalytic layer and the partition wall portion (a plan view when viewed from the exhaust gas inlet side (the upper side of FIG. 8C ), i.e., a plan view corresponding to FIG. 7A ).
  • FIG. 8B is a plan view (as viewed from the exhaust gas outflow side (the lower side of FIG. 8C )) of a cut piece used to measure the gas permeability of the first catalyst layer and the partition wall portion.
  • FIG. 8C is a cross-sectional view taken along line D2-D2 in FIG.
  • FIG. 9A is a plan view of a cut piece cut out from the exhaust gas purifying catalyst (a plan view when viewed from the exhaust gas inflow side (upper side of FIG. 9B)).
  • FIG. 9B is a cross-sectional view taken along line D3-D3 in FIG. 9A.
  • FIG. 10A is a plan view of a cut piece used to measure the gas permeability of the second catalyst layer and the partition wall portion (a plan view when viewed from the exhaust gas inlet side (the upper side of FIG. 10C ), i.e., a plan view corresponding to FIG. 9A ).
  • FIG. 10A is a plan view of a cut piece used to measure the gas permeability of the second catalyst layer and the partition wall portion (a plan view when viewed from the exhaust gas inlet side (the upper side of FIG. 10C ), i.e., a plan view corresponding to FIG. 9A ).
  • FIG. 10B is a plan view (as viewed from the exhaust gas outflow side (the lower side of FIG. 10C )) of the cut piece used to measure the gas permeability of the second catalyst layer and the partition wall portion.
  • FIG. 10C is a cross-sectional view taken along line D4-D4 in FIG. 10A (a cross-sectional view corresponding to FIG. 9B).
  • FIG. 11 is a plan view of a cut piece used to measure the gas permeability of the first catalyst layer and the partition wall portion (a plan view when viewed from the exhaust gas inlet side (upper side of FIG. 8C ), i.e., the same plan view as FIG. 8A ). Reference numerals are omitted for some elements (members, parts, etc.) in FIG. 11 .
  • FIG. 12 is a plan view of a cut piece used to measure the gas permeability of the second catalyst layer and the partition wall portion (a plan view when viewed from the exhaust gas outflow side (the lower side of FIG. 10C ), i.e., the same plan view as FIG. 10B ). Reference numerals are omitted for some elements (members, parts, etc.) in FIG. 12 .
  • the meanings of the elements (members, parts, etc.) in FIG. 12 can be understood by referring to FIGS. 10A to 10C .
  • SEM scanning electron microscope
  • EDX energy dispersive X-ray spectroscopy
  • SEM-EDX scanning electron microscope-energy dispersive X-ray analysis
  • EPMA electron probe microanalyzer
  • XRF X-ray fluorescence analysis
  • ICP-OES inductively coupled plasma optical emission spectroscopy
  • metal element also includes metalloid elements such as Si and B.
  • Rare earth elements includes Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
  • Precious metal elements include Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.
  • Oxides of rare earth elements other than Ce, Pr, and Tb are called sesquioxides ( M2O3 , where M represents a rare earth element other than Ce, Pr, and Tb), oxides of Ce are called CeO2 , oxides of Pr are called Pr6O11 , oxides of Tb are called Tb4O7 , oxides of Al are called Al2O3 , oxides of Zr are called ZrO2 , oxides of Si are called SiO2, oxides of B are called B2O3 , oxides of Cr are called Cr2O3 , oxides of Mg are called MgO , oxides of Ca are called CaO , oxides of Sr are called SrO, oxides of Ba are called BaO, oxides of Fe are called Fe3O4 , oxides of Mn are called Mn3O4 , oxides of Ni are called NiO , and oxides of Ti are called TiO. 2
  • the "metal-equivalent mass of a metal element” means the mass of a metal that is determined on the assumption that the metal element exists as a metal composed of the metal element.
  • the "mass of a metal element converted into an oxide” means the mass of an oxide of a metal element that is determined on the assumption that the metal element exists as an oxide of the metal element.
  • the "mass of the catalytic layer” refers to the sum of the mass of the precious metal elements contained in the catalytic layer, calculated by classifying all the metal elements contained in the catalytic layer into precious metal elements and non-precious metal elements, and the mass of the precious metal elements calculated in terms of metal and the mass of the non-precious metal elements calculated in terms of oxide.
  • the “mass of the catalytic layer” refers to the calculated mass calculated by summing the mass of the precious metal elements contained in the catalytic layer, calculated in terms of metal, and the mass of the metal elements contained in the catalytic layer, calculated in terms of oxide.
  • the mass of the catalyst layer can be determined from that information about the raw materials.
  • the metal or oxide content (mass %) of the metal elements in the catalyst layer can be determined from the raw material information.
  • the metal or oxide content (mass%) of the metal elements in the catalyst layer can be determined using standard methods such as SEM-EDX. Specifically, this is as follows:
  • Elemental analysis of the catalyst layer is performed using standard methods such as SEM-EDX to identify the types of constituent elements of the catalyst layer and determine the mole percentage of each identified metal element.
  • the mole percentage of each metal element is determined for each of 10 SEM fields of view, and the average mole percentage of each metal element in the 10 fields of view is used as the mole percentage of each metal element in the catalyst layer.
  • V value of each precious metal element in the catalyst layer is calculated from the following formula.
  • V value of each precious metal element (mol % of each precious metal element in the catalyst layer) x (molar mass of each precious metal element)
  • the metal-equivalent content (mass %) of each precious metal element in the catalyst layer is calculated using the following formula.
  • Metal-equivalent content (mass%) of each precious metal element in the catalyst layer (V value of each precious metal element)/ ⁇ (total V values of all precious metal elements)+(total W values of all metal elements other than precious metal elements) ⁇ 100
  • the oxide-equivalent content (mass %) of each metal element other than the noble metal element in the catalyst layer is calculated using the following formula.
  • Oxide-equivalent content (mass%) of each metal element other than precious metal elements in the catalyst layer (W value of each metal element other than precious metal elements)/ ⁇ (total V values of all precious metal elements)+(total W values of all metal elements other than precious metal elements) ⁇ 100
  • Metal oxide refers to an oxide containing one or more metal elements.
  • metal oxides include Al-based oxides, Ce-based oxides, Zr-based oxides, and Ce-Zr-based composite oxides.
  • Mass of metal oxide means the total mass of oxides of metal elements that can be determined by assuming that each metal element in the metal oxide exists as an oxide.
  • the oxide-equivalent content (mass %) of the metal element in the metal oxide can be calculated from the composition of the metal oxide.
  • the oxide-equivalent content (mass%) of the metal element in the metal oxide can be determined using standard methods such as SEM-EDX. Specifically, this is as follows:
  • Elemental analysis of metal oxides is performed using standard methods such as SEM-EDX to identify the types of constituent elements of the metal oxide and calculate the oxide-equivalent content (mass%) of each identified metal element.
  • Al-based oxides are used as supports for catalytically active components and are distinct from alumina (alumina binder), which is used as a binder.
  • Al-based oxides are, for example, particulate. From the perspective of improving the supportability of catalytically active components, it is preferable that the Al-based oxides be porous.
  • Al-based oxides generally have higher heat resistance than other inorganic oxides (e.g., Ce-based oxides, Zr-based oxides, etc.). Therefore, by including Al-based oxides in the catalyst layer, the heat resistance of the catalyst layer is improved, and the exhaust gas purification performance of the catalyst layer is improved.
  • other inorganic oxides e.g., Ce-based oxides, Zr-based oxides, etc.
  • the additional element M1 may form a solid solution phase (e.g., a solid solution phase of Al 2 O 3 and an oxide of the additional element M1), or may form a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M1), or may form both a solid solution phase and a single phase.
  • a solid solution phase e.g., a solid solution phase of Al 2 O 3 and an oxide of the additional element M1
  • a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M1), or may form both a solid solution phase and a single phase.
  • Al-based oxides examples include alumina (Al 2 O 3 ), oxides obtained by modifying the surface of alumina with the additional element M1 or its oxide, oxides obtained by dissolving the additional element M1 in alumina, etc.
  • Al-based oxides containing the additional element M1 include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, and alumina-lanthana.
  • the content of Al in the Al-based oxide calculated as Al2O3 is preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 90 mass% or more, based on the mass of the Al-based oxide, with the upper limit being 100 mass%.
  • the Ce-based oxide refers to an oxide containing Ce, in which Ce is the element with the highest content by mass among the metal elements constituting the oxide, provided that an oxide that falls under the category of Zr-based oxide does not fall under the category of Ce-based oxide.
  • Ce-based oxides are used as supports for catalytically active components and are distinct from ceria (ceria binders), which are used as binders. Ce-based oxides are, for example, particulate. From the perspective of improving the supportability of catalytically active components, it is preferable that the Ce-based oxides be porous.
  • Cerium-based oxides have oxygen storage capacity, mitigating fluctuations in oxygen concentration in exhaust gases and expanding the operating window of catalytically active components. Therefore, by including Ce-based oxides in the catalyst layer, the exhaust gas purification performance of the catalyst layer is improved.
  • the Ce-based oxide may contain one or more metal elements other than Ce (hereinafter referred to as "additional element M2").
  • the additional element M2 can be selected from, for example, rare earth elements other than Ce (e.g., Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.
  • the additional element M2 may form a solid solution phase (e.g., a solid solution phase of CeO2 and an oxide of the additional element M2), or may form a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M2), or may form both a solid solution phase and a single phase.
  • a solid solution phase e.g., a solid solution phase of CeO2 and an oxide of the additional element M2
  • a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M2), or may form both a solid solution phase and a single phase.
  • Ce-based oxides examples include ceria (CeO 2 ), oxides obtained by modifying the surface of ceria with the additional element M2 or its oxide, and oxides obtained by dissolving the additional element M2 in ceria.
  • the Ce content in the Ce-based oxide is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 99 mass% or more, based on the mass of the Ce-based oxide, with the upper limit being 100 mass%.
  • the Zr-based oxide refers to an oxide containing Zr, in which the content of Zr in the oxide, calculated as ZrO2 , is 5 mass% or more based on the mass of the oxide.
  • the Zr-based oxide is distinguished from zirconia used as a binder. In this specification, zirconia used as a binder may be referred to as a "zirconia binder.”
  • the Zr-based oxide is, for example, in particulate form.
  • the Zr-based oxide is used as a support for catalytically active components. From the perspective of improving the supportability of catalytically active components, it is preferable that the Zr-based oxide be porous.
  • the Zr-based oxide may contain one or more metal elements other than Zr (hereinafter referred to as "additional element M3").
  • the additional element M3 can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Al, Cr, etc.
  • the additional element M3 may form a solid solution phase (e.g., a solid solution phase of ZrO2 and an oxide of the additional element M3), or may form a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of the additional element M3), or may form both a solid solution phase and a single phase, but it is preferable that at least a part of the additional element M3 forms a solid solution phase.
  • Zr-based oxides examples include zirconia (ZrO 2 ), oxides obtained by modifying the surface of zirconia with the additional element M3 or its oxide, and oxides obtained by dissolving the additional element M3 in zirconia.
  • the content of Zr in the Zr-based oxide in terms of ZrO2 is preferably 7 mass% or more, more preferably 10 mass% or more, and even more preferably 30 mass% or more, based on the mass of the Zr-based oxide, with the upper limit being 100 mass%.
  • a Ce-Zr-based composite oxide is a composite oxide containing Ce and Zr, in which the Ce content in the composite oxide, calculated as CeO2 , is 5% by mass or more and 95% by mass or less, based on the mass of the composite oxide, and the Zr content in the composite oxide, calculated as ZrO2 , is 5% by mass or more and 95% by mass or less, based on the mass of the composite oxide.
  • Ce-Zr-based composite oxides are a type of Zr-based oxide.
  • Ce-Zr composite oxides are used as carriers for catalytically active components.
  • the Ce-Zr composite oxides are, for example, particulate. From the perspective of improving the supportability of catalytically active components, it is preferable that the Ce-Zr composite oxides be porous.
  • Ce-Zr composite oxides have oxygen storage capacity, mitigating fluctuations in oxygen concentration in exhaust gases and expanding the operating window of catalytically active components. Therefore, by including Ce-Zr composite oxides in the catalyst layer, the catalyst layer's exhaust gas purification ability is improved.
  • the Ce-Zr composite oxide may contain one or more metal 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., Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.
  • Ce may form a solid solution phase (e.g., a solid solution phase of CeO2 and ZrO2 ), or may form a single phase which is a crystalline phase or an amorphous phase (e.g., a CeO2 single phase), or may form both a solid solution phase and a single phase, but it is preferable that at least a part of Ce forms a solid solution phase.
  • a solid solution phase e.g., a solid solution phase of CeO2 and ZrO2
  • a single phase which is a crystalline phase or an amorphous phase
  • CeO2 single phase e.g., CeO2 single phase
  • Zr may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2 ), or may form a single phase which is a crystalline phase or an amorphous phase (for example, a ZrO2 single phase), or may form both a solid solution phase and a single phase, but it is preferable that at least a part of Zr forms a solid solution phase.
  • the additional element M4 may form a solid solution phase (e.g., a solid solution phase of CeO 2 and an oxide of the additional element M4, a solid solution phase of ZrO 2 and an oxide of the additional element M4, a solid solution phase of CeO 2 , ZrO 2 and an oxide of the additional element M4, etc.), or may form a single phase which is a crystalline phase or an amorphous phase (e.g., a single phase of the oxide of the additional element M4), or may form both a solid solution phase and a single phase, but it is preferable that at least a part of the additional element M4 forms a solid solution phase.
  • a solid solution phase e.g., a solid solution phase of CeO 2 and an oxide of the additional element M4, a solid solution phase of ZrO 2 and an oxide of the additional element M4, etc.
  • a single phase which is a crystalline phase or an amorphous phase e.g., a single phase of the oxide of the additional element M4
  • Ce-Zr based composite oxides include CeO 2 -ZrO 2 solid solutions, oxides obtained by modifying the surface of CeO 2 -ZrO 2 solid solutions with additional element M4 or its oxide, and oxides obtained by dissolving additional element M4 in CeO 2 -ZrO 2 solid solutions.
  • the content of Ce in the Ce—Zr-based composite oxide in terms of CeO2 is preferably 5 % by mass or more and 90% by mass or less, more preferably 7% by mass or more and 90% by mass or less, and even more preferably 10% by mass or more and 85% by mass or less, based on the mass of the Ce—Zr-based composite oxide.
  • the content of Zr in the Ce—Zr-based composite oxide in terms of ZrO2 is preferably 5% by mass or more and 90% by mass or less, more preferably 7% by mass or more and 90% by mass or less, and even more preferably 10% by mass or more and 85% by mass or less, based on the mass of the Ce—Zr-based composite oxide.
  • the total content of Ce in terms of CeO2 and Zr in terms of ZrO2 in the Ce—Zr-based composite oxide is preferably 70 mass% or more, more preferably 75 mass% or more, even more preferably 80 mass% or more, and even more preferably 85 mass% or more, based on the mass of the Ce—Zr-based composite oxide, with the upper limit being 100 mass%.
  • the Ce-Zr-based composite oxide contains one or more rare earth elements other than Ce.
  • the rare earth elements other than Ce can be selected from, for example, Y, Pr, La, Nd, Sm, Eu, Gd, etc.
  • the content of the rare earth elements other than Ce in the Ce-Zr-based composite oxide, calculated as oxides, is preferably 5% by mass or more and 35% by mass or less, more preferably 7% by mass or more and 30% by mass or less, and even more preferably 9% by mass or more and 25% by mass or less, based on the mass of the Ce-Zr-based composite oxide.
  • the content of rare earth elements other than Ce in a Ce-Zr composite oxide, calculated as oxides refers to the content of one rare earth element other than Ce when the Ce-Zr composite oxide contains one rare earth element other than Ce, and refers to the total content of the two or more rare earth elements calculated as oxides when the Ce-Zr composite oxide contains two or more rare earth elements other than Ce.
  • an exhaust gas purification catalyst 1 (hereinafter referred to as "catalyst 1") according to one embodiment of the present invention is disposed in the exhaust path within the exhaust pipe P of an internal combustion engine.
  • the internal combustion engine may be, for example, a gasoline engine (e.g., a GDI engine), a diesel engine, etc.
  • the catalyst 1 is arranged in the exhaust path of the internal combustion engine so that the axial direction of the substrate 10 coincides or approximately coincides with the exhaust gas flow direction E.
  • the catalyst 1 comprises a substrate 10, a first catalyst layer 20, and a second catalyst layer 30.
  • One of the first catalytic layer 20 and the second catalytic layer 30 can be omitted. That is, the catalyst 1 only needs to include at least one of the first catalytic layer 20 and the second catalytic layer 30.
  • the present invention includes an embodiment in which the catalyst 1 includes the first catalytic layer 20 but not the second catalytic layer 30, an embodiment in which the catalyst 1 includes the second catalytic layer 30 but not the first catalytic layer 20, and an embodiment in which the catalyst 1 includes the first catalytic layer 20 and the second catalytic layer 30.
  • the catalyst 1 satisfies at least one of the following conditions 1a and 1b.
  • Xa represents the 10% flow diameter ( ⁇ m) of the first catalyst layer 20 and partition wall portion 12 measured by the bubble point method using a perm porometer after catalyst 1 is subjected to heat treatment at 950°C for 35 hours in an atmospheric environment
  • Ya represents the 10% flow diameter ( ⁇ m) of the first catalyst layer 20 and partition wall portion 12 measured by the bubble point method using a perm porometer before catalyst 1 is subjected to the above heat treatment
  • Xb represents the 10% flow diameter ( ⁇ m) of the second catalyst layer 30 and partition wall portion 12 measured by the bubble point method using a perm porometer after catalyst 1 is subjected to the above heat treatment
  • Yb represents the 10% flow diameter ( ⁇ m) of the second catalyst layer 30 and partition wall portion 12 measured by the bubble point method using a perm porometer before catalyst 1 is subjected to the above heat treatment.
  • partition wall section 12 in the “10% flow diameter of the first catalyst layer 20 and the partition wall section 12" refers to the portion of the partition wall section 12 where the first catalyst layer 20 is provided
  • partition wall section 12 in the “10% flow diameter of the second catalyst layer 30 and the partition wall section 12" refers to the portion of the partition wall section 12 where the second catalyst layer 30 is provided.
  • the present invention includes an embodiment in which catalyst 1 satisfies conditions 1a and 1b, an embodiment in which catalyst 1 satisfies condition 1a but not condition 1b, and an embodiment in which catalyst 1 satisfies condition 1b but not condition 1a.
  • the present invention includes the following embodiments.
  • catalyst 1 includes a first catalytic layer 20, does not include a second catalytic layer 30, and satisfies condition 1a (in this embodiment, catalyst 1 does not include a second catalytic layer 30, and therefore does not satisfy condition 1b).
  • catalyst 1 includes the second catalyst layer 30 but does not include the first catalyst layer 20, and condition 1b is satisfied (in this embodiment, catalyst 1 does not include the first catalyst layer 20, and therefore condition 1a is not satisfied).
  • the material constituting the substrate 10 can be appropriately selected from known materials.
  • materials constituting the substrate 10 include ceramic materials and metal materials, with ceramic materials being preferred.
  • 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.
  • metal materials include alloys such as stainless steel.
  • the substrate 10 has a length L10 .
  • the length L10 of the substrate 10 can be adjusted as appropriate taking into consideration the exhaust gas purification performance, PM trapping performance, etc. From the viewpoint of improving the exhaust gas purification performance and PM trapping ability, the length L10 of the substrate 10 is preferably 50 mm or more and 160 mm or less, more preferably 80 mm or more and 130 mm or less. In this specification, "length" means the dimension in the axial direction of the substrate 10, unless otherwise specified.
  • Substrate 10 is a wall-flow type substrate.
  • the substrate 10 has cells 13 and porous partition walls 12 that separate the cells 13.
  • the substrate 10 is preferably a honeycomb structure.
  • the substrate 10 has a tubular portion 11, and the cells 13 and partition portions 12 are formed within the tubular portion 11.
  • the tubular portion 11 defines the outer shape of the substrate 10, and the axial direction of the tubular portion 11 coincides with the axial direction of the substrate 10.
  • the shape of the tubular portion 11 is, for example, cylindrical, but it may also be other shapes such as an elliptical cylinder or a polygonal cylinder.
  • each cell 13 extends in the exhaust gas flow direction E and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.
  • the substrate 10 is provided with first sealing portions 14 that seal the exhaust gas outlet end of some of the cells 13, and second sealing portions 15 that seal the exhaust gas inlet end of the remaining cells 13.
  • some of the cells 13 have an open exhaust gas inlet end and an end on the exhaust gas outlet side that is blocked by the first sealing portion 14, forming inlet side cells 13a
  • the remaining cells 13 have an open exhaust gas inlet end and an end on the exhaust gas outlet side that is blocked by the second sealing portion 15, forming outlet side cells 13b.
  • the inlet-side cells 13a have a length L13a .
  • the "length of the first plugged portions 14" refers to the dimension of the first plugged portions 14 in the axial direction of the substrate 10.
  • the length L13a of the inlet-side cells 13a can be adjusted as appropriate, taking into account exhaust gas purification performance, PM trapping performance, and the like.
  • the percentage of the length L13a of the inlet-side cells 13a to the length L10 of the substrate 10 is preferably 80% or more, more preferably 85% or more.
  • the upper limit of this percentage can be adjusted as appropriate, taking into account the length of the first plugged portions 14.
  • the upper limit of this percentage may be, for example, 99% or less, or 98% or less. Each of these upper limits may be combined with any of the lower limits mentioned above.
  • the outlet-side cells 13b have a length L13b .
  • the "length of the second plugged portions 15" refers to the dimension of the second plugged portions 15 in the axial direction of the substrate 10.
  • the length L13b of the outlet-side cells 13b can be adjusted as appropriate, taking into account exhaust gas purification performance, PM trapping performance, and the like.
  • the percentage of the length L13b of the outlet-side cells 13b to the length L10 of the substrate 10 is preferably 80% or more, more preferably 85% or more.
  • the upper limit of this percentage can be adjusted as appropriate, taking into account the length of the second plugged portions 15.
  • the upper limit of this percentage may be, for example, 99% or less, or 98% or less. Each of these upper limits may be combined with any of the lower limits mentioned above.
  • the inlet cells 13a and outlet cells 13b are arranged alternately in the vertical direction and alternately in the horizontal direction, with adjacent inlet cells 13a and outlet cells 13b separated by partition walls 12.
  • a plurality of (four in this embodiment) outlet cells 13b are arranged around one inlet cell 13a, and the inlet cell 13a is separated from the outlet cells 13b arranged around the inlet cell 13a by a partition wall 12.
  • a plurality of (four in this embodiment) inlet cells 13a are arranged around one outlet cell 13b, and the outlet cells 13b are separated from the inlet cells 13a arranged around the outlet cell 13b by a partition wall 12.
  • planar shape of the end (opening) on the exhaust gas inlet side of each inlet cell 13a and the planar shape of the end (opening) on the exhaust gas outlet side of each outlet cell 13b are, for example, quadrilateral (preferably square or rectangular, more preferably square).
  • planar view areas of the exhaust gas inlet side end (opening) of each inlet cell 13a are the same or approximately the same. It is preferable that the planar view areas of the exhaust gas outlet side end (opening) of each outlet cell 13b are the same or approximately the same. It is preferable that the planar view areas of the exhaust gas inlet side end (opening) of each inlet cell 13a and the exhaust gas outlet side end (opening) of each outlet cell 13b are the same or approximately the same.
  • each inlet cell 13a is quadrilateral (preferably square or rectangular, more preferably square)
  • the lengths of the left sides (left sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same
  • the lengths of the right sides (right sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same
  • the lengths of the top sides (upper sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same
  • the lengths of the bottom sides (lower sides in Figures 4 and 5) of each inlet cell 13a are the same or approximately the same.
  • each outlet cell 13b is quadrilateral (preferably square or rectangular, more preferably square)
  • the lengths of the left sides (left sides in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same
  • the lengths of the right sides (right sides in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same
  • the lengths of the top sides (upper sides in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same
  • the lengths of the bottom sides (lower sides in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same.
  • each outlet cell 13b is quadrilateral (preferably square or rectangular, more preferably square)
  • the length of the left side (left side in Figures 4 and 5) of each inlet cell 13a and the length of the left side (left side in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same
  • the length of the right side (right side in Figures 4 and 5) of each inlet cell 13a It is also preferable that the lengths of the right sides (right sides in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same, that the lengths of the top sides (upper sides in Figures 4 and 5) of each inlet cell 13a and the top sides (upper sides in Figures 4 and 5) of each outlet cell 13b are the same or approximately the same, and that the lengths of the bottom sides (lower sides in Figures 4 and 5) of
  • planar shape of the end (opening) on the exhaust gas inlet side of each inlet cell 13a and the planar shape of the end (opening) on the exhaust gas outlet side of each outlet cell 13b are quadrilateral (preferably square or rectangular, more preferably square), it is preferable that the left sides (left sides in Figures 4 and 5) of the vertically arranged inlet cells 13a and outlet cells 13b are aligned on the same line or approximately aligned on the same line, that the right sides (right sides in Figures 4 and 5) of the vertically arranged inlet cells 13a and outlet cells 13b are aligned on the same line or approximately aligned on the same line, that the top sides (upper sides in Figures 4 and 5) of the horizontally arranged inlet cells 13a and outlet cells 13b are aligned on the same line or approximately aligned on the same line, and that the bottom sides (lower sides in Figures 4 and 5) of the horizontally arranged inlet cells 13a and outlet cells 13b are aligned on the same line or
  • the cell density per square inch of the substrate 10 can be adjusted as appropriate, taking into consideration PM collection performance, pressure loss, etc. From the perspective of improving PM collection performance and suppressing an increase in pressure loss, the cell density per square inch of the substrate 10 is preferably 180 cells or more and 350 cells or less.
  • the cell density per square inch of the substrate 10 is the total number of inlet cells 13a and outlet cells 13b per square inch in a cross section obtained by cutting the substrate 10 along a plane perpendicular to the axial direction of the substrate 10.
  • the partition wall 12 has a porous structure that allows exhaust gas to pass through.
  • the partition wall portion 12 has an outer surface S1a on the inlet side cell 13a side and an outer surface S1b on the outlet side cell 13b side.
  • the outer surface S1a is the region of the outer surface that defines the outer shape of the partition wall portion 12 on the inlet side cell 13a side that extends in the exhaust gas flow direction E (i.e., the region that contacts the inlet side cell 13a).
  • the outer surface S1b is the region of the outer surface that defines the outer shape of the partition wall portion 12 on the outlet side cell 13b side that extends in the exhaust gas flow direction E (i.e., the region that contacts the outlet side cell 13b).
  • the thickness of the partition wall 12 can be adjusted as appropriate, taking into consideration PM collection performance, pressure loss, etc. From the perspective of improving PM collection performance and suppressing an increase in pressure loss, the thickness of the partition wall 12 is preferably 110 ⁇ m or more and 380 ⁇ m or less, more preferably 130 ⁇ m or more and 330 ⁇ m or less, and even more preferably 150 ⁇ m or more and 310 ⁇ m or less.
  • the first catalyst layer 20 is provided on the inlet cell 13 a side of the partition wall 12 .
  • the first catalyst layer 20 extends from the end of the partition section 12 on the exhaust gas inlet side along the exhaust gas flow direction E. In this embodiment, the first catalyst layer 20 does not reach the end of the partition section 12 on the exhaust gas outlet side, but it may reach the end of the partition section 12 on the exhaust gas outlet side.
  • the first catalyst layer 20 has a portion formed on the outer surface S1a of the partition section 12, extending from the end of the partition section 12 on the exhaust gas inlet side along the exhaust gas flow direction E. This portion protrudes from the outer surface S1a of the partition section 12 toward the inlet side cell 13a. Hereinafter, this portion will be referred to as the "protruding portion.”
  • the first catalyst layer 20 having the protruding portion improves contact between the first catalyst layer 20 and the exhaust gas and PM, improving exhaust gas purification performance and PM collection performance.
  • the first catalytic layer 20 may have a portion that exists inside the partition wall 12 (hereinafter referred to as the "internal portion") in addition to the raised portion. Because the partition wall 12 is porous, the internal portion may be formed along with the raised portion when the first catalytic layer 20 is formed. The raised portion and the internal portion may be continuous. "The first catalytic layer 20 is provided on the inlet cell 13a side of the partition wall 12" includes an embodiment in which the first catalytic layer 20 has a raised portion but no internal portion, as well as an embodiment in which the first catalytic layer 20 has a raised portion and an internal portion.
  • the region where the raised portion of the first catalyst layer 20 exists does not overlap with the region where the partition wall portions 12 exist, but the region where the internal portion of the first catalyst layer 20 exists overlaps with the region where the partition wall portions 12 exist. Therefore, by cutting the catalyst 1 along a plane perpendicular to the axial direction of the substrate 10 and observing the first catalyst layer 20 and partition wall portions 12 present on the cut surface, the raised portion and internal portion of the first catalyst layer 20 can be identified based on the differences in morphology between the first catalyst layer 20 and the partition wall portions 12.
  • elemental mapping of the cut surface may be performed. Elemental mapping can be performed, for example, by combining observation of the cut surface with an SEM and compositional analysis of the cut surface.
  • Elemental mapping can be performed, for example, using SEM-EDX, EPMA, or the like. Elemental mapping of the cut surface allows the raised portion and internal portion to be identified based on the differences in morphology and composition between the first catalyst layer 20 and the partition wall portions 12.
  • the second catalyst layer 30 is provided on the outlet cell 13b side of the partition wall 12.
  • the second catalyst layer 30 extends from the end of the partition section 12 on the exhaust gas outlet side in the direction opposite to the exhaust gas flow direction E.
  • the second catalyst layer 30 does not reach the end of the partition section 12 on the exhaust gas inlet side, but it may reach the end of the partition section 12 on the exhaust gas inlet side.
  • the second catalyst layer 30 has a portion formed on the outer surface S1b of the partition section 12, extending from the end of the partition section 12 on the exhaust gas outflow side in the direction opposite to the exhaust gas flow direction E. This portion protrudes from the outer surface S1b of the partition section 12 toward the outflow side cell 13b. Hereinafter, this portion will be referred to as the "protruding portion.”
  • the second catalyst layer 30 having the protruding portion improves contact between the second catalyst layer 30 and the exhaust gas and PM, improving exhaust gas purification performance and PM capture performance.
  • the second catalyst layer 30 may have a portion that exists inside the partition wall 12 (hereinafter referred to as the "internal portion") in addition to the raised portion. Because the partition wall 12 is porous, the internal portion may be formed along with the raised portion when the second catalyst layer 30 is formed. The raised portion and the internal portion may be continuous. "The second catalyst layer 30 is provided on the outlet cell 13b side of the partition wall 12" includes an embodiment in which the second catalyst layer 30 has a raised portion but no internal portion, as well as an embodiment in which the second catalyst layer 30 has a raised portion and an internal portion.
  • first catalytic layer 20 should be read as “second catalytic layer 30.”
  • Exhaust gas emitted from an internal combustion engine flows through an exhaust path in the exhaust pipe P from one end to the other end, and is purified by a catalyst 1 arranged in the exhaust pipe P. During this process, the exhaust gas flows in from the end (opening) on the exhaust gas inlet side of the inlet-side cell 13a, travels through a predetermined path, and flows out from the end (opening) on the exhaust gas outlet side of the outlet-side cell 13b.
  • This type of system is called a wall-flow type.
  • the predetermined paths include a path in which exhaust gas that has flowed in from the end (opening) on the exhaust gas inlet side of the inlet-side cell 13a passes through the first catalytic layer 20 and the partition wall 12 in this order, reaches the outlet-side cell 13b, and flows out from the end (opening) on the exhaust gas outlet side of the outlet-side cell 13b; a path in which exhaust gas that has flowed in from the end (opening) on the exhaust gas inlet side of the inlet-side cell 13a passes through the partition wall 12 and the second catalytic layer 30 in this order, reaches the outlet-side cell 13b, and flows out from the end (opening) on the exhaust gas outlet side of the outlet-side cell 13b; and a path in which exhaust gas that has flowed in from the end (opening) on the exhaust gas inlet side of the inlet-side cell 13a passes through the first catalytic layer 20, the partition wall 12, and the second catalytic layer 30 in this order, reaches the outlet-side cell 13b
  • catalyst 1 when exhaust gas flows in through the exhaust gas inlet end (opening) of inlet cell 13a, travels through a predetermined path, and flows out through the exhaust gas outlet end (opening) of outlet cell 13b, PM in the exhaust gas is trapped in the pores of partition wall 12, first catalyst layer 20, and second catalyst layer 30. Therefore, catalyst 1 is useful as a particulate filter for gasoline engines or a particulate filter for diesel engines.
  • the catalyst layer may have a single-layer structure or a laminated structure.
  • the catalyst layer When the catalyst layer has a laminated structure, it comprises two or more layers laminated in the thickness direction of the catalyst layer.
  • the two or more layers include a lower layer and an upper layer.
  • the lower layer is a layer located closer to the partition wall 12 than the upper layer.
  • a portion of the catalyst layer may be composed of either the lower layer or the upper layer. That is, in addition to the portion composed of the lower and upper layers, the portion composed of either the lower layer or the upper layer is also part of the catalyst layer.
  • An example of a laminated structure is a two-layer structure consisting of a lower layer and an upper layer disposed on top of the lower layer.
  • the raised portion of the catalyst layer may be formed from all or part of one layer, or may be formed from all of one or more layers and all or part of another layer.
  • the raised portion of the catalyst layer may be formed from all or part of the upper layer, or may be formed from the all of the upper layer and part of the lower layer.
  • the first catalyst layer 20 and the second catalyst layer 30 each have a single-layer structure.
  • the first catalyst layer 20 has a laminated structure (e.g., a two-layer structure)
  • the second catalyst layer 30 has a single-layer structure.
  • the first catalyst layer 20 has a single-layer structure
  • the second catalyst layer 30 has a laminated structure (e.g., a two-layer structure).
  • the first catalyst layer 20 and the second catalyst layer 30 each have a laminated structure (e.g., a two-layer structure).
  • composition of the catalyst layer will be described below.
  • the following description of the composition of the catalyst layer applies to both the first catalyst layer 20 and the second catalyst layer 30, unless otherwise specified.
  • the term “catalyst layer” is replaced with “first catalyst layer 20”
  • the term “catalyst layer” is replaced with “second catalyst layer 30.”
  • the following description of the composition of the catalyst layer applies to all of Embodiments A to E, unless otherwise specified.
  • the catalyst layer contains one or more precious metal elements as catalytically active components.
  • the precious metal element is preferably selected from Pt, Pd, and Rh.
  • the precious metal element is contained in the catalyst layer in a form that can function as a catalytically active component, such as a metal, an alloy containing the precious metal element, or a compound containing the precious metal element (e.g., an oxide of the precious metal element).
  • the catalytically active component containing the precious metal element is preferably in particulate form.
  • the first catalytic layer 20 may contain the same precious metal element as the precious metal element contained in the second catalytic layer 30, or it may contain a precious metal element different from the precious metal element contained in the second catalytic layer 30.
  • the second catalytic layer 30 may contain the same precious metal element as the precious metal element contained in the first catalytic layer 20, or it may contain a precious metal element different from the precious metal element contained in the first catalytic layer 20.
  • first catalytic layer 20 and the second catalytic layer 30 each contain Rh.
  • the first catalytic layer 20 and the second catalytic layer 30 may each contain, in addition to Rh, a precious metal element other than Rh.
  • the first catalytic layer 20 and the second catalytic layer 30 each contain Rh and no precious metal elements other than Rh. In another embodiment, one of the first catalytic layer 20 and the second catalytic layer 30 contains Rh and no precious metal elements other than Rh, and the other contains Rh and a precious metal element other than Rh (e.g., Pd or Pt). In yet another embodiment, the first catalytic layer 20 and the second catalytic layer 30 each contain Rh and a precious metal element other than Rh (e.g., Pd or Pt).
  • the precious metal element contained in the lower layer and the precious metal element contained in the upper layer may be the same or different.
  • the precious metal element contained in the lower layer and the precious metal element contained in the upper layer are different, it is possible to prevent a decrease in catalytic performance that occurs when these multiple precious metal elements are contained in a single layer.
  • the precious metal elements in the lower layer are less susceptible to phosphorus poisoning, while the precious metal elements in the upper layer are more susceptible to phosphorus poisoning.
  • Pd and Pt are both susceptible to performance degradation due to phosphorus poisoning, while Rh is less susceptible to performance degradation due to phosphorus poisoning. Therefore, Pd and Pt are suitable precious metal elements to be contained in the lower layer, and Rh is suitable precious metal element to be contained in the upper layer.
  • the first catalytic layer 20 and the second catalytic layer 30 each have a single-layer structure containing Rh.
  • the first catalytic layer 20 has a laminated structure (e.g., a two-layer structure) including a lower layer containing a precious metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh, and the second catalytic layer 30 has a single-layer structure containing Rh.
  • the first catalytic layer 20 has a single-layer structure containing Rh
  • the second catalytic layer 30 has a laminated structure (e.g., a two-layer structure) including a lower layer containing a precious metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh.
  • the first catalytic layer 20 and the second catalytic layer 30 each have a laminated structure (e.g., a two-layer structure) including a lower layer containing a precious metal element other than Rh (e.g., Pd or Pt) and an upper layer containing Rh.
  • the content of precious metal elements in the catalyst layer is preferably 0.01 mass% or more and 20 mass% or less, more preferably 0.05 mass% or more and 10 mass% or less, and even more preferably 0.1 mass% or more and 5 mass% or less, based on the mass of the catalyst layer.
  • the content of precious metal elements in terms of metal equivalent in the catalyst layer means the content of one precious metal element in terms of metal equivalent when the catalyst layer contains one type of precious metal element, or means the total content of two or more precious metal elements in terms of metal equivalent when the catalyst layer contains two or more types of precious metal elements.
  • the catalyst layer preferably contains 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.
  • At least a portion of the catalytically active component is supported on the support means that at least a portion of the catalytically active component is physically or chemically adsorbed and/or retained on the outer surface and/or inner pore surfaces of the support. Support of at least a portion of the catalytically active component on the support can be confirmed, for example, using SEM-EDX. Specifically, if elemental mapping obtained by analyzing a cross section of the catalyst layer with SEM-EDX shows that at least a portion of the catalytically active component and the support are present in the same region, it can be determined that at least a portion of the catalytically active component is supported on the support.
  • the carrier can be selected from, for example, inorganic oxides.
  • the inorganic oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytically active component, the inorganic oxide is preferably porous.
  • the inorganic oxide may or may not have oxygen storage capacity (OSC).
  • OSC oxygen storage capacity
  • Inorganic oxides used as carriers are distinguished from inorganic oxides used as binders.
  • inorganic oxides include Al-based oxides, Ce-based oxides, Zr-based oxides, oxides of rare earth elements other than Ce, and oxides based on zirconia (ZrO 2 ), silica (SiO 2 ), titania (TiO 2 ), zeolite (aluminosilicate), MgO, ZnO, SnO 2, etc.
  • the support is preferably selected from Al-based oxides, Ce-based oxides, and Zr-based oxides, and more preferably Al-based oxides and Zr-based oxides.
  • the Zr-based oxide is preferably a Ce-Zr-based composite oxide.
  • the catalyst layer contains a Zr-based oxide.
  • the Zr-based oxide is preferably a Ce-Zr-based composite oxide.
  • the catalyst layer may further contain a carrier other than a Zr-based oxide (e.g., an Al-based oxide).
  • the content of Al-based oxides in the catalyst layer can be determined from the composition of those raw materials.
  • the Al-based oxide content in the catalyst layer can be determined using standard methods such as SEM-EDX. Specifically, this is as follows:
  • the sample obtained from the catalyst layer is subjected to elemental analysis using a conventional method such as SEM-EDX to identify the types of constituent elements of the entire sample, and to determine the content (mass %) of each identified metal element in terms of its oxide.
  • the sample obtained from the catalyst layer is subjected to elemental mapping using a standard method such as SEM-EDX to identify the types of particles contained in the sample (e.g., Al-based oxide particles, Zr-based oxide particles, etc.).
  • a number of arbitrarily selected particles for example, 50 particles
  • SEM-EDX for example, 50 particles
  • the average oxide-equivalent content (mass%) of each metal element is calculated, and this is defined as the oxide-equivalent content (mass%) of each metal element in each type of particle.
  • An equation is created and solved to represent the relationship between the oxide-equivalent content (mass%) of each metal element in the sample, the oxide-equivalent content (mass%) of each metal element in each type of particle, and the content (mass%) of each type of particle in the sample, thereby determining the content (mass%) of each type of particle in the sample, and this is the content (mass%) of each type of particle in the catalyst layer.
  • the content of Ce-based oxides in the catalyst layer can be determined in the same manner as the content of Al-based oxides in the catalyst layer.
  • the content of Zr-based oxide in the catalyst layer can be determined in the same manner as the content of Al-based oxide in the catalyst layer.
  • the catalyst layer may contain other components such as binders and stabilizers.
  • binders include inorganic oxide binders such as alumina binders, ceria binders, zirconia binders, titania binders, and silica binders.
  • stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba, etc.).
  • Condition 1a is as follows: Xa/Ya ⁇ 1.40 and Ya ⁇ 5.00
  • the first catalytic layer 20 contains a Zr-based oxide
  • the first catalytic layer 20 when the first catalytic layer 20 is exposed to a high-temperature environment, cracks occur within the first catalytic layer 20 due to thermal contraction of the Zr-based oxide, and the PM capture performance of the first catalytic layer 20 is likely to deteriorate.
  • the deterioration in the PM capture performance of the first catalytic layer 20 due to thermal contraction of the Zr-based oxide is less likely to occur in the portions of the first catalytic layer 20 formed inside the partition wall portions 12, but is more likely to occur in the portions formed on the outer surface S1a of the partition wall portions 12 (i.e., the raised portions).
  • the 10% flow diameter ( ⁇ m) of the first catalytic layer 20 and the partition wall portions 12 is an index representing the larger through-pore diameter of the through-pore diameter distribution of the first catalytic layer 20 and the partition wall portions 12. Therefore, Ya being 5.00 ⁇ m or less means that the first catalytic layer 20 before exposure to a high-temperature environment is densely formed, crack-free, and has excellent PM capture performance. Therefore, when the first catalytic layer 20 contains a Zr-based oxide and Ya is 5.00 ⁇ m or less, there is a strong need to suppress a decrease in the PM trapping performance of the first catalytic layer 20 due to thermal shrinkage of the Zr-based oxide.
  • Ya is preferably 4.70 ⁇ m or less, more preferably 4.35 ⁇ m or less, and even more preferably 4.00 ⁇ m or less.
  • Ya is preferably 1.60 ⁇ m or more, more preferably 1.80 ⁇ m or more, and even more preferably 2.00 ⁇ m or more.
  • Each of these lower limit values may be combined with any of the above-mentioned upper limit values.
  • the 10% flow diameter ( ⁇ m) of the first catalytic layer 20 and the partition wall portion 12 is an index representing the larger through-pore diameter in the distribution of through-pore diameters of the first catalytic layer 20 and the partition wall portion 12. Therefore, an Xa/Ya ratio of 1.40 or less means that the occurrence of cracks due to thermal contraction of Zr-based oxides in the first catalytic layer 20 after exposure to a high-temperature environment is suppressed. Therefore, an Xa/Ya ratio of 1.40 or less can suppress a decrease in the PM capture performance of the first catalytic layer 20 due to thermal contraction of Zr-based oxides.
  • Xa/Ya is preferably 1.37 or less, more preferably 1.34 or less, and even more preferably 1.30 or less.
  • the lower limit of Xa/Ya is theoretically 1, but in reality it exceeds 1.
  • Xa/Ya may be, for example, 1.03 or more, 1.07 or more, or 1.10 or more. Each of these lower limit values may be combined with any of the upper limit values described above.
  • the catalyst 1 is subjected to a heat treatment at 950°C for 35 hours in an air atmosphere.
  • a sample extending in the axial direction of the substrate 10 and having the same length as the length L10 of the substrate 10 is cut out from the heat-treated catalyst 1.
  • the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample.
  • the planar shape of the sample when viewed from the axial direction of the sample is, for example, a quadrangle (preferably a square or rectangle, more preferably a square).
  • the size of the planar shape when viewed from the axial direction of the sample is not particularly limited as long as the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample, but for example, the vertical length is 10 mm and the horizontal length is 10 mm.
  • the inlet side cells 13a and the outlet side cells 13b are arranged alternately in the vertical direction and also alternately in the horizontal direction, if the total number of the inlet side cells 13a and the outlet side cells 13b arranged vertically in the sample is an even number, and the total number of the inlet side cells 13a and the outlet side cells 13b arranged horizontally in the sample is an even number, then the number of the inlet side cells 13a contained in the sample will be the same as the number of the outlet side cells 13b contained in the sample.
  • the sample is cut along a plane perpendicular to the axial direction of the sample to prepare a cut piece P1 that includes a portion of the first catalytic layer 20 but does not include a portion of the second catalytic layer 30.
  • the cut piece P1 can be obtained from near the end of the sample on the exhaust gas inlet side.
  • the axial length of the cut piece P1 is not particularly limited, but is, for example, 10 mm.
  • the length of the portion of the first catalytic layer 20 included in the cut piece P1 is equal to the axial length of the cut piece P1.
  • the cut piece P1 does not have the first sealing portion 14 or the second sealing portion 15.
  • FIG. 7A and 7B An example of a cut piece P1 is shown in Figures 7A and 7B.
  • the cut piece P1 is, for example, a cube with a length in the vertical direction (vertical direction in Figure 7A) of 10 mm, a length in the horizontal direction (horizontal direction in Figure 7A) of 10 mm, and a length in the axial direction (vertical direction in Figure 7B) of 10 mm.
  • the cut piece P1 shown in Figures 7A and 7B can be obtained, for example, by cutting the sample at two locations 10 mm and 20 mm away from the end of the exhaust gas inlet side in the axial direction of the sample along a plane perpendicular to the axial direction of the sample.
  • the length of the portion of the first catalyst layer 20 included in the cut piece P1 is equal to the axial length of the cut piece P1.
  • the cut piece P1 does not have a first sealing portion 14 or a second sealing portion 15.
  • a first sealing portion that seals the exhaust gas outlet end of the inlet cell 13a included in the cut piece P1, and a second sealing portion that seals the exhaust gas inlet end of the outlet cell 13b included in the cut piece P1 are formed on the cut piece P1, and a third sealing portion is formed on the outermost periphery of the cut piece P1, thereby obtaining a cut piece P1'.
  • the first sealing portion, second sealing portion, and third sealing portion can be formed by applying a weatherstripping material to predetermined locations on the cut piece P1.
  • An adhesive such as an epoxy resin adhesive can be used as the weatherstripping material.
  • a first sealing portion 14 that seals the end of the inlet cell 13a included in the cut piece P1 on the exhaust gas outlet side (lower side in Figure 8C) and a second sealing portion 15 that seals the end of the outlet cell 13b included in the cut piece P1 on the exhaust gas inlet side (upper side in Figure 8C) are formed on the cut piece P1, and a third sealing portion 16 is formed on the outermost periphery of the cut piece P1 to obtain a cut piece P1'.
  • the first sealing portion 14, second sealing portion 15, and third sealing portion 16 can be formed by applying a weatherstripping material to predetermined locations on the cut piece P1.
  • the thickness of the first sealing portion 14 and second sealing portion 15 is each set to be 1/10 or less of the length of the cut piece P1' in the axial direction (vertical direction in Figure 8C).
  • a cut piece P1' prepared from the heat-treated catalyst 1 is placed in a perm porometer holder, and gas is passed through the cut piece P1' at a rate of 1 to 200 L/min while varying the gas pressure, and the gas flow rate under pressure is measured (hereinafter referred to as "first measurement").
  • the gas passed through is air.
  • An example of a perm porometer that can be used is a perm porometer manufactured by Porous Materials Inc. (e.g., CFP-1100A). Gas is passed through the end (opening) on the exhaust gas inlet side (upper side in Figure 8C) of the inlet cell 13a included in the cut piece P1'.
  • the gas that flows in through the end (opening) on the exhaust gas inlet side (upper side in Figure 8C) of the inlet cell 13a passes through the first catalyst layer 20 and the partition wall 12 and flows out through the end (opening) on the exhaust gas outlet side (lower side in Figure 8C) of the outlet cell 13b.
  • the first measurement is performed on a dry cut piece P1' (i.e., a cut piece P1' that has not been impregnated with a non-volatile test liquid (Galwick reagent manufactured by Porous Materials Inc.)).
  • the first measurement provides a pressure-flow curve for the dry cut piece P1'.
  • Cut pieces P1' are prepared from the heat-treated catalyst 1 in the same manner as described above.
  • the cut pieces P1' are immersed in a non-volatile test solution (Galwick reagent manufactured by Porous Materials Inc.) and vacuum degassed to remove the air from the cut pieces P1'.
  • the test solution-impregnated cut pieces P1' are then placed in the holder of a perm porometer, and gas is passed through the cut pieces P1' at 1 to 200 L/min while varying the gas pressure, and the gas flow rate under pressure is measured (hereinafter referred to as "second measurement").
  • the gas passed is air.
  • the surface tension of Galwick reagent manufactured by Porous Materials Inc. is 15.9 dyne/cm.
  • a perm porometer manufactured by Porous Materials Inc. e.g., CFP-1100A
  • CFP-1100A a perm porometer manufactured by Porous Materials Inc.
  • the gas that flows in through the end (opening) on the exhaust gas inlet side (upper side in Figure 8C) of the inlet cell 13a passes through the first catalyst layer 20 and the partition wall 12, and flows out through the end (opening) on the exhaust gas outlet side (lower side in Figure 8C) of the outlet cell 13b.
  • the second measurement is performed on the cut piece P1' wetted with the test liquid.
  • the second measurement provides a pressure-flow curve for the cut piece P1' wetted with the test liquid.
  • the measurement software "Capwin” manufactured by Porous Materials Inc.
  • the detailed conditions for the first measurement are designated as “dry parameters”
  • the detailed conditions for the second measurement are designated as "wet parameters” as follows: ⁇ Dry parameters/wet parameters> ⁇ Bubble point test/integrity test> ⁇ Bublflow 15.00 (cc/m) ⁇ F/PT 200 (old bobltime) ⁇ Motor valve control> ⁇ v2incr 2 (cts*3) ⁇ Regulator control> ⁇ preginc 0.5 (cts*50) ⁇ Pulse delay 2 (sec) ⁇ Data confirmation routine> ⁇ Mineqtime 15 (sec) ⁇ presslew 50 (cts*3) ⁇ flowslew 50 (cts*3) ⁇ Equiter 30 (0.1sec) ⁇ aveiter 20 (0.1 sec) ⁇ maxpdif 0.10 (PSI) ⁇ maxfdif 30.0 (cc/m
  • the above measurement method makes it possible to measure the diameter of the narrowest part of the through hole (hereinafter referred to as the "through hole diameter").
  • the through hole diameter is the diameter of the narrowed part of the through hole.
  • the gas flow rate (L/min) at a certain gas pressure is determined from the pressure-flow rate curve obtained in the first measurement and is designated the "Dry flow rate.”
  • the gas flow rate (L/min) at the same gas pressure is determined from the pressure-flow rate curve obtained in the second measurement and is designated the "Wet flow rate.”
  • the through-hole diameter at which the percentage of the wet flow rate to the dry flow rate (wet flow rate / dry flow rate x 100) is 10% is determined. Note that in the second measurement, as the gas pressure is gradually increased, the liquid film breaks starting from the larger pores, increasing the gas flow rate. Therefore, the through-hole diameter ( ⁇ m) at which the above percentage is 10% is larger than the through-hole diameter ( ⁇ m) at which the above percentage is greater than 10%.
  • Cut pieces P1' are prepared from catalyst 1 before heat treatment in the same manner as above. Ya can be measured in the same manner as Xa, except that cut pieces P1' prepared from catalyst 1 before heat treatment are used instead of cut pieces P1' prepared from catalyst 1 after heat treatment.
  • Condition 1b is as follows: Xb/Yb ⁇ 1.40 and Yb ⁇ 5.00
  • the second catalytic layer 30 contains a Zr-based oxide
  • the second catalytic layer 30 when the second catalytic layer 30 is exposed to a high-temperature environment, cracks occur within the second catalytic layer 30 due to thermal contraction of the Zr-based oxide, and the PM capture performance of the second catalytic layer 30 is likely to deteriorate.
  • This deterioration in the PM capture performance of the second catalytic layer 30 due to thermal contraction of the Zr-based oxide is unlikely to occur in the portions of the second catalytic layer 30 formed inside the partition wall portions 12, but is likely to occur in the portions formed on the outer surfaces S1b of the partition wall portions 12 (i.e., the raised portions).
  • the 10% flow diameter ( ⁇ m) of the second catalytic layer 30 and the partition wall portions 12 is an index representing the larger through-pore diameter of the through-pore diameter distribution of the second catalytic layer 30 and the partition wall portions 12. Therefore, a Yb of 5.00 ⁇ m or less means that the second catalytic layer 30 before exposure to a high-temperature environment is densely formed, crack-free, and has excellent PM capture performance. Therefore, when the second catalytic layer 30 contains a Zr-based oxide and Yb is 5.00 ⁇ m or less, there is a strong need to suppress a decrease in the PM trapping performance of the second catalytic layer 30 due to thermal shrinkage of the Zr-based oxide.
  • Ce-Zr-based composite oxides undergo a large degree of thermal shrinkage when exposed to high-temperature environments, there is a strong need to suppress a decrease in the PM trapping performance of the second catalytic layer 30 due to thermal shrinkage of the Ce-Zr-based composite oxide when the second catalytic layer 30 contains a Ce-Zr-based composite oxide and Yb is 5.00 ⁇ m or less.
  • Yb is preferably 4.70 ⁇ m or less, more preferably 4.35 ⁇ m or less, and even more preferably 4.00 ⁇ m or less.
  • the smaller Yb the better the PM capture performance, but the higher the pressure loss.
  • Yb is preferably 1.60 ⁇ m or more, more preferably 1.80 ⁇ m or more, and even more preferably 2.00 ⁇ m or more.
  • Each of these lower limit values may be combined with any of the above-mentioned upper limit values.
  • the 10% flow diameter ( ⁇ m) of the second catalytic layer 30 and the partition wall portion 12 is an index representing the larger through-pore diameter in the distribution of through-pore diameters of the second catalytic layer 30 and the partition wall portion 12. Therefore, an Xb/Yb ratio of 1.40 or less means that the occurrence of cracks due to thermal contraction of Zr-based oxides in the second catalytic layer 30 after exposure to a high-temperature environment is suppressed. Therefore, an Xb/Yb ratio of 1.40 or less can suppress a decrease in the PM capture performance of the second catalytic layer 30 due to thermal contraction of Zr-based oxides.
  • Xb/Yb is preferably 1.37 or less, more preferably 1.34 or less, and even more preferably 1.30 or less.
  • the lower limit of Xb/Yb is theoretically 1, but in reality it exceeds 1.
  • Xb/Yb may be, for example, 1.03 or more, 1.07 or more, or 1.10 or more. Each of these lower limit values may be combined with any of the upper limit values described above.
  • the catalyst 1 is subjected to a heat treatment at 950°C for 35 hours in an air atmosphere.
  • a sample extending in the axial direction of the substrate 10 and having the same length as the length L10 of the substrate 10 is cut out from the heat-treated catalyst 1.
  • the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample.
  • the planar shape of the sample when viewed from the axial direction of the sample is, for example, a quadrangle (preferably a square or rectangle, more preferably a square).
  • the size of the planar shape when viewed from the axial direction of the sample is not particularly limited as long as the number of inlet-side cells 13a included in the sample is the same as the number of outlet-side cells 13b included in the sample, but for example, the vertical length is 10 mm and the horizontal length is 10 mm.
  • the inlet side cells 13a and the outlet side cells 13b are arranged alternately in the vertical direction and also alternately in the horizontal direction, if the total number of the inlet side cells 13a and the outlet side cells 13b arranged vertically in the sample is an even number, and the total number of the inlet side cells 13a and the outlet side cells 13b arranged horizontally in the sample is an even number, then the number of the inlet side cells 13a contained in the sample will be the same as the number of the outlet side cells 13b contained in the sample.
  • the sample is cut along a plane perpendicular to the axial direction of the sample to prepare a cut piece P2 that includes a portion of the second catalytic layer 30 but does not include a portion of the first catalytic layer 20.
  • the cut piece P2 can be obtained from near the end of the sample on the exhaust gas outflow side.
  • the axial length of the cut piece P2 is not particularly limited, but is, for example, 10 mm.
  • the length of the portion of the second catalytic layer 30 included in the cut piece P2 is equal to the axial length of the cut piece P2.
  • the cut piece P2 does not have the first sealing portion 14 or the second sealing portion 15.
  • FIG. 9A and 9B An example of the cut piece P2 is shown in Figures 9A and 9B.
  • the cut piece P2 is, for example, a cube with a length in the vertical direction (vertical direction in Figure 9A) of 10 mm, a length in the horizontal direction (horizontal direction in Figure 9A) of 10 mm, and a length in the axial direction (vertical direction in Figure 9B) of 10 mm.
  • the cut piece P2 shown in Figures 9A and 9B can be obtained, for example, by cutting the sample at two locations 10 mm and 20 mm away from the end of the exhaust gas outlet side in the axial direction of the sample along a plane perpendicular to the axial direction of the sample.
  • the length of the portion of the second catalyst layer 30 included in the cut piece P2 is equal to the axial length of the cut piece P2.
  • the cut piece P2 does not have a first sealing portion 14 or a second sealing portion 15.
  • a first sealing portion that seals the exhaust gas outlet end of the inlet cell 13a included in the cut piece P2, and a second sealing portion that seals the exhaust gas inlet end of the outlet cell 13b included in the cut piece P2 are formed on the cut piece P2, and a third sealing portion is formed on the outermost periphery of the cut piece P2, thereby obtaining a cut piece P2'.
  • the first sealing portion, second sealing portion, and third sealing portion can be formed by applying a weatherstripping material to predetermined locations on the cut piece P2.
  • An adhesive such as an epoxy resin adhesive can be used as the weatherstripping material.
  • a first sealing portion 14 that seals the end of the inlet cell 13a included in the cut piece P2 on the exhaust gas outlet side (lower side in Figure 10C) and a second sealing portion 15 that seals the end of the outlet cell 13b included in the cut piece P2 on the exhaust gas inlet side (upper side in Figure 10C) are formed on the cut piece P2, and a third sealing portion 16 is formed on the outermost periphery of the cut piece P2, thereby obtaining a cut piece P2'.
  • the first sealing portion 14, second sealing portion 15, and third sealing portion 16 can be formed by applying a weatherstripping material to predetermined locations on the cut piece P2.
  • the thickness of the first sealing portion 14 and second sealing portion 15 is each set to be 1/10 or less of the length of the cut piece P2' in the axial direction (vertical direction in Figure 10C).
  • Xb can be measured in the same manner as Xa, except that cut piece P2' prepared from heat-treated catalyst 1 is used instead of cut piece P1' prepared from heat-treated catalyst 1.
  • gas is passed through the end (opening) on the exhaust gas inlet side (upper side in Figure 10C) of the inlet-side cell 13a included in cut piece P2'.
  • the gas that flows in from the end (opening) on the exhaust gas inlet side (upper side in Figure 10C) of the inlet-side cell 13a passes through the partition section 12 and the second catalyst layer 30, and flows out from the end (opening) on the exhaust gas outlet side (lower side in Figure 10C) of the outlet-side cell 13b.
  • the through-hole diameter at which the percentage of the wet flow rate to the dry flow rate (wet flow rate / dry flow rate x 100) is 10% is determined. Note that in the second measurement, as the gas pressure is gradually increased, the liquid film breaks starting from the larger pores, increasing the gas flow rate. Therefore, the through-hole diameter ( ⁇ m) at which the above percentage is 10% is larger than the through-hole diameter ( ⁇ m) at which the above percentage is greater than 10%.
  • first catalyst layer 20 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide)
  • second catalyst layer 30 contains a Zr-based oxide (preferably a Ce—Zr-based composite oxide).
  • the first catalytic layer 20 and the second catalytic layer 30 each contain a Zr-based oxide (preferably a Ce-Zr-based composite oxide).
  • the first catalytic layer 20 and the second catalytic layer 30 may each further contain a carrier other than a Zr-based oxide (for example, an Al-based oxide).
  • the first catalytic layer 20 contains a Zr-based oxide (preferably a Ce-Zr-based composite oxide).
  • the first catalytic layer 20 may further contain a carrier other than a Zr-based oxide (for example, an Al-based oxide).
  • the second catalytic layer 30 may or may not contain a Zr-based oxide (preferably a Ce-Zr-based composite oxide). If the second catalytic layer 30 contains a Zr-based oxide, the second catalytic layer 30 may further contain a carrier other than a Zr-based oxide (e.g., an Al-based oxide). If the second catalytic layer 30 does not contain a Zr-based oxide, it is preferable that the second catalytic layer 30 contain a carrier other than a Zr-based oxide (e.g., an Al-based oxide).
  • the second catalytic layer 30 contains a Zr-based oxide (preferably a Ce-Zr-based composite oxide).
  • the second catalytic layer 30 may further contain a carrier other than a Zr-based oxide (for example, an Al-based oxide).
  • the first catalytic layer 20 may or may not contain a Zr-based oxide (preferably a Ce-Zr-based composite oxide). If the first catalytic layer 20 contains a Zr-based oxide, the first catalytic layer 20 may further contain a carrier other than a Zr-based oxide (e.g., an Al-based oxide). If the first catalytic layer 20 does not contain a Zr-based oxide, it is preferable that the first catalytic layer 20 contain a carrier other than a Zr-based oxide (e.g., an Al-based oxide).
  • the first catalytic layer 20 contains a Zr-based oxide (preferably a Ce-Zr-based composite oxide).
  • the first catalytic layer 20 may further contain a carrier other than a Zr-based oxide (for example, an Al-based oxide).
  • the second catalytic layer 30 contains a Zr-based oxide (preferably a Ce-Zr-based composite oxide).
  • the second catalytic layer 30 may further contain a carrier other than a Zr-based oxide (for example, an Al-based oxide).
  • the upper limit of this content can be adjusted as appropriate, taking into account the contents of other components in first catalytic layer 20.
  • the content of the Ce—Zr-based composite oxide in the first catalytic layer 20 is preferably 95 mass % or less, more preferably 90 mass % or less, and even more preferably 85 mass % or less, based on the mass of the first catalytic layer 20. Each of these upper limits may be combined with any of the above-mentioned lower limits.
  • the upper limit of this content can be adjusted as appropriate, taking into account the contents of other components in the second catalyst layer 30.
  • the content of Ce-Zr composite oxide in the second catalytic layer 30 is preferably 95 mass% or less, more preferably 90 mass% or less, and even more preferably 85 mass% or less, based on the mass of the second catalytic layer 30.
  • Each of these upper limits may be combined with any of the above-mentioned lower limits.
  • first catalytic layer 20 preferably contains a Ce—Zr-based composite oxide
  • the Ce—Zr-based composite oxide in first catalytic layer 20 is represented by the following formula: R 12 /R 11 >0.8
  • R11 represents the Ce content (mass%) in the Ce—Zr-based composite oxide calculated as CeO2
  • R12 represents the Zr content (mass%) in the Ce—Zr-based composite oxide calculated as ZrO2 .
  • R 12 /R 11 is preferably 0.9 or more, more preferably 1.0 or more, and even more preferably 1.2 or more.
  • the upper limit of R 12 /R 11 can be adjusted appropriately in consideration of the balance between the heat resistance and oxygen storage capacity of the Ce—Zr-based composite oxide.
  • R 12 /R 11 is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.
  • second catalytic layer 30 preferably contains a Ce—Zr-based composite oxide
  • the Ce—Zr-based composite oxide in second catalytic layer 30 is represented by the following formula: R 22 /R 21 >0.8
  • R21 represents the Ce content (mass%) in the Ce—Zr-based composite oxide calculated as CeO2
  • R22 represents the Zr content (mass%) in the Ce—Zr-based composite oxide calculated as ZrO2 .
  • R 22 /R 21 is preferably 0.9 or more, more preferably 1.00 or more, and even more preferably 1.2 or more.
  • the upper limit of R 22 /R 21 can be adjusted appropriately in consideration of the balance between the heat resistance and oxygen storage capacity of the Ce—Zr-based composite oxide.
  • R 22 /R 21 is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.
  • exhaust gas path a portion of the exhaust gas path where neither the first catalyst layer 20 nor the second catalyst layer 30 is formed. Therefore, from the viewpoint of improving the PM trapping performance of the catalyst 1, it is preferable that at least one of the first catalyst layer 20 and the second catalyst layer 30 is formed at every portion of the exhaust gas path.
  • the percentage of the length L20 of the first catalytic layer 20 to the length L13a of the inlet-side cell 13a is preferably 100%.
  • the percentage of the length L30 of the second catalytic layer 30 to the length L13b of the outlet-side cell 13b is preferably 100%.
  • the percentage of the sum of the length L20 of the first catalytic layer 20 and the length L30 of the second catalytic layer 30 relative to the length L10 of the substrate 10 is preferably 100% or more, more preferably 105% or more, and even more preferably 115% or more.
  • the upper limit of this percentage can be adjusted as appropriate, taking into account the exhaust gas purification performance, PM trapping performance, etc.
  • the percentage is preferably 160% or less, more preferably 150% or less, and even more preferably 140% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.
  • the length L20 of the first catalytic layer 20 and the length L30 of the second catalytic layer 30 can be adjusted as appropriate, taking into account the exhaust gas purification performance, PM trapping performance, etc.
  • the percentage ( L20 / L10 x 100) of the length L20 of the first catalytic layer 20 to the length L10 of the substrate 10 is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less, and the percentage ( L30 / L10 x 100) of the length L30 of the second catalytic layer 30 to the length L10 of the substrate 10 is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less.
  • the percentage of the length L20 of the first catalytic layer 20 to the length L13a of the inlet-side cells 13a is preferably 100%.
  • the length L30 of the second catalytic layer 30 can be appropriately adjusted taking into consideration exhaust gas purification performance, PM capture performance, etc.
  • the percentage of the length L30 of the second catalytic layer 30 to the length L13b of the outlet-side cells 13b is preferably 15% or more and 100% or less, more preferably 20% or more and 90% or less, and even more preferably 30% or more and 80% or less.
  • the percentage of the length L30 of the second catalytic layer 30 to the length L13b of the outlet-side cells 13b is preferably 100%.
  • the length L20 of the first catalytic layer 20 can be appropriately adjusted taking into consideration exhaust gas purification performance, PM capture performance, etc.
  • the percentage of the length L20 of the first catalytic layer 20 to the length L13a of the inlet-side cells 13a is preferably 15% or more and 100% or less, more preferably 20% or more and 90% or less, and even more preferably 30% or more and 80% or less.
  • the percentage of the sum of the length L20 of the first catalytic layer 20 and the length L30 of the second catalytic layer 30 relative to the length L10 of the substrate 10 is preferably 100% or more, more preferably 105% or more, and even more preferably 115% or more.
  • the upper limit of this percentage can be adjusted as appropriate, taking into account exhaust gas purification performance, PM trapping performance, etc.
  • the percentage is preferably 160% or less, more preferably 150% or less, and even more preferably 140% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.
  • the length L20 of the first catalytic layer 20 and the length L30 of the second catalytic layer 30 can be adjusted as appropriate, taking into account exhaust gas purification performance, PM trapping performance, etc.
  • the percentage ( L20 / L10 x 100) of the length L20 of the first catalytic layer 20 to the length L10 of the substrate 10 is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less
  • the percentage ( L30 / L10 x 100) of the length L30 of the second catalytic layer 30 to the length L10 of the substrate 10 is preferably 15% or more and 90% or less, more preferably 20% or more and 80% or less, and even more preferably 30% or more and 80% or less.
  • An example of a method for measuring the length L20 of the first catalyst layer 20 is as follows.
  • a sample extending in the axial direction of the substrate 10 and having the same length as the length L10 of the substrate 10 is cut out from the catalyst 1.
  • the sample is, for example, cylindrical with a diameter of 25.4 mm. The diameter of the sample can be changed as needed.
  • the sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and a first cut piece, a second cut piece, ..., nth cut piece are obtained in order from the end of the sample on the exhaust gas inlet side.
  • the length of each cut piece is 5 mm.
  • the composition of the cut pieces is analyzed using ICP-OES, XRF, SEM-EDX, etc., and it is confirmed whether the cut pieces contain a portion of the first catalyst layer 20 based on the composition of the cut pieces.
  • the cut surface can be observed using an SEM, EPMA, etc. to determine whether the cut piece contains a portion of the first catalytic layer 20.
  • elemental mapping of the cut surface may also be performed. Elemental mapping can be performed in the same manner as described above.
  • the length of the first catalytic layer 20 included in the sample is (5 x k) mm.
  • a more detailed example of a method for measuring the length of the first catalyst layer 20 included in the sample is as follows.
  • the kth cut piece i.e., the cut piece obtained from the exhaust gas outflow side of the sample among the cut pieces including a portion of the first catalytic layer 20
  • the kth cut piece is cut in the axial direction of the substrate 10, and the portion of the first catalytic layer 20 present on the cut surface is observed using an SEM, an EPMA, or the like, to measure the length of the portion of the first catalytic layer 20 in the kth cut piece.
  • the length of the first catalytic layer 20 contained in one sample may be used as the length L20 of the first catalytic layer 20, or the average value of the lengths of the first catalytic layer 20 contained in multiple samples may be used as the length L20 of the first catalytic layer 20.
  • the length of the first catalytic layer 20 contained in each of 8 to 16 samples arbitrarily cut out from the catalyst 1 may be measured, and the average value may be used as the length L20 of the first catalytic layer 20.
  • the above description of the method for measuring the length L20 of the first catalytic layer 20 also applies to the second catalytic layer 30.
  • the “first catalytic layer 20" is read as the "second catalytic layer 30.”
  • the sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and a first cut piece, a second cut piece, ..., an n-th cut piece are obtained in order from the end of the sample on the exhaust gas outflow side.
  • the mass of first catalytic layer 20 per unit volume of the portion of substrate 10 on which first catalytic layer 20 is formed is preferably 20 g/L or more and 150 g/L or less, more preferably 30 g/L or more and 130 g/L or less, and even more preferably 35 g/L or more and 110 g/L or less.
  • the coating amount of first catalytic layer 20 is within the above range, it is easy to form a first catalytic layer 20 that satisfies condition 1a (preferably conditions 1a and 2a).
  • the mass of second catalyst layer 30 per unit volume of the portion of substrate 10 on which second catalyst layer 30 is formed (hereinafter referred to as the "coating amount of second catalyst layer 30") is preferably 20 g/L or more and 150 g/L or less, more preferably 30 g/L or more and 130 g/L or less, and even more preferably 35 g/L or more and 110 g/L or less.
  • the coating amount of second catalyst layer 30 is within the above range, it becomes easy to form a second catalyst layer 30 that satisfies condition 1b (preferably conditions 1b and 2b).
  • partition wall section 12 in "gas permeability of the first catalyst layer 20 and the partition wall section 12" refers to the portion of the partition wall section 12 where the first catalyst layer 20 is provided.
  • Ra is an index representing the exhaust gas permeability in the first catalyst layer 20 and the partition wall portions 12, and a larger Ra indicates higher exhaust gas permeability in the first catalyst layer 20 and the partition wall portions 12.
  • Ra 1.30 ⁇ 10 ⁇ 3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more, the exhaust gas permeability in the first catalyst layer 20 and the partition wall portions 12 is sufficient, which contributes to improving the PM collection performance and suppressing an increase in pressure drop.
  • Ra is preferably 1.50 ⁇ 10 -3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more, more preferably 1.70 ⁇ 10 -3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more, and even more preferably 1.90 ⁇ 10 -3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more.
  • Ra is preferably 2.00 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less, more preferably 1.90 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less, and even more preferably 1.80 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less.
  • Each of these upper limit values may be combined with any of the above-mentioned lower limit values.
  • a cut piece P1' (e.g., cut piece P1' shown in Figures 8A to 8C) is prepared from catalyst 1 before heat treatment in the same manner as described above.
  • the cut piece P1' is set in a perm porometer holder, and gas is passed through the cut piece P1' at 1 to 200 L/min while changing the gas pressure, and the gas flow rate under pressure is measured.
  • the gas passed is air.
  • a perm porometer for example, a perm porometer manufactured by Porous Materials Inc. (e.g., CFP-1100A) can be used.
  • the gas is passed through the end (opening) on the exhaust gas inlet side (upper side in Figure 8C) of the inlet cell 13a included in the cut piece P1'.
  • Gas that flows in from the end (opening) on the exhaust gas inlet side (upper side in Figure 8C) of the inlet cell 13a passes through the first catalyst layer 20 and the partition wall 12, and flows out from the end (opening) on the exhaust gas outlet side (lower side in Figure 8C) of the outlet cell 13b.
  • the gas permeability is calculated from the following equation when the pressure difference between the upstream (upper side in Figure 8C) and downstream (lower side in Figure 8C) positions in the gas flow direction relative to the cut piece P1' during gas flow ((pressure at a position upstream in the gas flow direction relative to the cut piece P1' during gas flow) - (pressure at a position downstream in the gas flow direction relative to the cut piece P1' during gas flow)) is 10 kPa.
  • the pressure at the upstream position in the gas flow direction relative to the cut piece P1' during gas flow is controlled by a perm porometer.
  • R Q/A 1 M 1
  • R gas permeability (unit: cm 3 /(cm 2 ⁇ s ⁇ Pa))
  • Q represents the flow rate of the gas under pressure (unit: cm 3 /s)
  • A1 represents the effective filtration area (unit: cm2 ) of the cut piece P1'
  • M1 represents the pressure difference (unit: Pa) between the upstream and downstream positions in the gas flow direction relative to the cut piece P1' during gas flow.
  • the average distance D1 (unit: cm) can be calculated using the following method.
  • the side on the left side of Figure 11 is the "left side A1a”
  • the side on the right side of Figure 11 is the “right side A2a”
  • the side on the top side of Figure 11 is the “upper side A3a”
  • the side on the bottom side of Figure 11 is the “lower side A4a.”
  • the side on the left side of Figure 11 is the "left side A1a.”
  • 11 is referred to as "side B1b," one side on the right side in FIG.
  • FIG. 11 is referred to as "right side B2b," one side on the top side in FIG. 11 is referred to as “top side B3b,” and one side on the bottom side in FIG. 11 is referred to as “bottom side B4b.”
  • left side C1b the left side in FIG. 11
  • right side in FIG. 11 is referred to as “right side C2b”
  • top side in FIG. 11 is referred to as “top side C3b”
  • bottom side C4b The four sides that make up the opening of the above-mentioned inlet cell 13a are the sides formed by the outer surfaces S1a of the partition wall portions 12 of the substrate 10 in the cut piece P1' (see FIGS. 4 to 6), and the four sides that make up the opening of the above-mentioned outlet cell 13b are the sides formed by the outer surfaces S1b of the partition wall portions 12 of the substrate 10 in the cut piece P1' (see FIGS. 4 to 6).
  • the distance (unit: cm) between the left side A1a of the opening of the inlet cell 13a and the left side B1b of the opening of the outlet cell 13b is measured, and the measured distance is defined as distance D11.
  • the distance (unit: cm) between the right side A2a of the opening of the inlet cell 13a and the right side B2b of the opening of the outlet cell 13b may also be measured, and the measured distance is defined as distance D11.
  • Distance D11 can be considered to be the sum of the length of the upper side A3a or lower side A4a of the opening of the inlet cell 13a and the thickness of the partition wall portion 12.
  • the distance D11 is calculated in the same manner as above for 20 inlet cells 13a and their adjacent outlet cells 13b randomly selected from the plan view of the cut piece P1' shown in Figure 11, and the average value is taken as the average distance D11'.
  • the distance (unit: cm) between the bottom edge A4a of the opening of the inlet cell 13a and the bottom edge C4b of the opening of the outlet cell 13b is measured, and the measured distance is defined as distance D12.
  • the distance (unit: cm) between the top edge A3a of the opening of the inlet cell 13a and the top edge C3b of the opening of the outlet cell 13b may also be measured, and the measured distance is defined as distance D12.
  • Distance D12 can be considered to be the sum of the length of the left edge A1a or right edge A2a of the opening of the inlet cell 13a and the thickness of the partition wall portion 12.
  • the distance D12 is calculated in the same manner as above for 20 inlet cells 13a and their adjacent outlet cells 13b randomly selected from the plan view of the cut piece P1' shown in Figure 11, and the average value is taken as the average distance D12'.
  • the average thickness T (unit: cm) of the partition wall portion 12 can be determined by the following method.
  • a location of the catalyst 1 (e.g., a location 10 mm away from the end of the substrate 10 on the exhaust gas inlet side in the exhaust gas flow direction E) is cut along a plane perpendicular to the axial direction of the substrate 10, and the first catalyst layer 20 present in one inlet-side cell 13a arbitrarily selected from the cut surface is observed using an SEM to identify the region where the partition wall portion 12 of the substrate 10 is present and the region where the first catalyst layer 20 is present.
  • the field of view magnification is, for example, 300x
  • the field of view width (length) is, for example, 500 to 600 ⁇ m.
  • the region observed using the SEM be set so as not to include the corners of the inlet-side cell 13a.
  • the region where the partition wall portion 12 of the substrate 10 is present and the region where the first catalyst layer 20 is present can be identified based on the difference in shape between the first catalyst layer 20 and the partition wall portion 12 of the substrate 10.
  • elemental mapping of the cut surface may be performed. Elemental mapping can be performed in the same manner as described above. By elemental mapping of the cut surface, it is possible to identify the regions where the partition walls 12 of the substrate 10 exist and the regions where the first catalyst layer 20 exists, based on the differences in morphology and composition between the first catalyst layer 20 and the partition walls 12 of the substrate 10.
  • Nth grid lines parallel to the thickness direction of the partition wall portions 12 of the substrate 10 are drawn at 15 ⁇ m intervals, and the intersections of each grid line and the outline of the inlet cell side of the region where the partition wall portions 12 of the substrate 10 exist are connected by straight lines to identify the surface position of the inlet cell side of the partition wall portions 12 of the substrate 10.
  • N is an integer between 30 and 50, for example.
  • the intersections of each grid line and the outline of the outlet cell side of the region where the partition wall portions 12 of the substrate 10 exist are connected by straight lines to identify the surface position of the outlet cell side of the partition wall portions 12 of the substrate 10.
  • the change in thickness direction from a given intersection X1 to an adjacent intersection X2 refers to the distance between a line passing through intersection X1 and perpendicular to the thickness direction of the partition wall 12 of the substrate 10, and a line passing through intersection X2 and perpendicular to the thickness direction of the partition wall 12 of the substrate 10.
  • intersection X3 in addition to intersection X2 to identify the surface position (i.e., exclude intersections X2 and X3 from the intersections connected by straight lines). When five consecutive intersections are excluded from the intersections connected by straight lines in this way, it is preferable not to measure the thickness of the SEM image.
  • image analysis software is used to determine the area of the region surrounded by the second grid line, the (N-1)th grid line, the surfaces of the partition walls 12 of the substrate 10 on the inlet cell side, and the surfaces of the partition walls 12 of the substrate 10 on the outlet cell side.
  • image analysis software examples include AreaQ (manufactured by Estec Co., Ltd.), ImageJ (public domain), and Photoshop (Adobe Systems Inc.). Note that the first grid line and the Nth grid line are not used because the edges of the image tend to be blurred, making it difficult to identify the positions of the surfaces of the partition walls 12.
  • ⁇ 1 can be obtained by measuring the length of the cut piece P1' (the length of the cut piece P1' in the axial direction).
  • ⁇ 1 can be determined by the following method.
  • the planar shape of the end (opening) on the exhaust gas inlet side of the inlet cell 13a and the planar shape of the end (opening) on the exhaust gas outlet side of the outlet cell 13b are each quadrilateral (preferably square or rectangular, more preferably square). Therefore, as shown in Figures 4 and 5, the outer surface S1a of the partition section 12 in contact with one inlet cell 13a is composed of four faces, and the outer surface S1b of the partition section 12 in contact with one outlet cell 13b is composed of four faces.
  • the number of outer surfaces S1a (four faces) of the partition wall portion 12 that contact each inlet-side cell 13a and that are not adjacent to the third sealing portion 16 is determined, and the total number of these faces is defined as ⁇ 1 . Specifically, this is done as follows.
  • the three inlet cells 13a in the third row F3 are referred to as the "inlet cell F31,” “inlet cell F32,” and “inlet cell F33" from the left of Figure 11.
  • the three inlet side cells 13a in the fourth column F4 are referred to as "inlet side cell F41,” “inlet side cell F42,” and “inlet side cell F43” from the left side of Figure 11;
  • the three inlet side cells 13a in the fifth column F5 are referred to as "inlet side cell F51,” “inlet side cell F52,” and “inlet side cell F53” from the left side of Figure 11;
  • the three inlet side cells 13a in the sixth column F6 are referred to as "inlet side cell F61,” “inlet side cell F62,” and “inlet side cell F63” from the left side of Figure 11.
  • the left surface (the surface on the left in Figure 11) and the top surface (the surface on the top in Figure 11) are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F11, the number of surfaces that are not adjacent to the third sealing section 16 is two.
  • the right surface (the surface on the right side in Figure 11) and the bottom surface (the surface on the bottom side in Figure 11) are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four surfaces) of the partition section 12 that contact the inlet cell F63, the number of surfaces that are not adjacent to the third sealing section 16 is two.
  • the upper face (the upper face in Figure 11) is adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four faces) of the partition section 12 that contact the inlet cell F12 or F13, the number of faces that are not adjacent to the third sealing section 16 is three.
  • the right surface (the surface on the right side in Figure 11) is adjacent to the third sealing section 16. Therefore, of the four outer surfaces S1a of the partition section 12 that contact the inlet cell F23 or F43, the number of surfaces that are not adjacent to the third sealing section 16 is three.
  • the left surface (the surface on the left side in Figure 11) is adjacent to the third sealing section 16. Therefore, of the four outer surfaces S1a of the partition section 12 that contact the inlet cell F31 or F51, the number of surfaces that are not adjacent to the third sealing section 16 is three.
  • the lower face (the lower face in Figure 11) is adjacent to the third sealing section 16. Therefore, of the outer surfaces S1a (four faces) of the partition section 12 that contact the inlet cell F61 or F62, the number of faces that are not adjacent to the third sealing section 16 is three.
  • the gas permeability is measured three times in total using different cut pieces P1', and the average value thereof is taken as Ra (cm 3 /(cm 2 ⁇ s ⁇ Pa)).
  • the above measurement method allows for accurate measurement of the gas permeability of the first catalyst layer 20 and partition wall section 12.
  • condition 2b If catalyst 1 satisfies condition 1b (embodiments A, C, and E), catalyst 1 also satisfies condition 2b: 1.30 ⁇ 10 ⁇ 3 ⁇ Rb [In the formula, Rb represents the gas permeability (cm 3 /(cm 2 s Pa)) of the second catalyst layer 30 and the partition wall portion 12 measured using a perm porometer before the catalyst 1 was subjected to a heat treatment at 950°C for 35 hours in an air atmosphere.] It is preferable that the following conditions are further satisfied.
  • partition wall section 12 in "gas permeability of the second catalyst layer 30 and the partition wall section 12" refers to the portion of the partition wall section 12 where the second catalyst layer 30 is provided.
  • Rb is an index that represents the exhaust gas permeability in the second catalyst layer 30 and the partition wall portions 12, and a larger Rb indicates higher exhaust gas permeability in the second catalyst layer 30 and the partition wall portions 12.
  • Rb is 1.30 ⁇ 10 ⁇ 3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more, the exhaust gas permeability in the second catalyst layer 30 and the partition wall portions 12 is sufficient, which contributes to improving the PM trapping performance and suppressing an increase in pressure drop.
  • Rb is preferably 1.50 ⁇ 10 -3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more, more preferably 1.70 ⁇ 10 -3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more, and even more preferably 1.90 ⁇ 10 -3 (cm 3 /(cm 2 ⁇ s ⁇ Pa)) or more.
  • Rb is preferably 2.00 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less, more preferably 1.90 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less, and even more preferably 1.80 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less.
  • Rb is preferably 2.00 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less, more preferably 1.90 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less, and even more preferably 1.80 ⁇ 10 ⁇ 2 (cm 3 /(cm 2 s Pa)) or less.
  • Each of these upper limit values may be combined with any of the above-mentioned lower limit values.
  • a cut piece P2' (for example, cut piece P2' shown in Figures 10A to 10C) is prepared from catalyst 1 before heat treatment in the same manner as described above. Cut piece P2' is set in the holder of a perm porometer, and gas is passed through cut piece P2' at 1 to 200 L/min while changing the gas pressure, and the gas flow rate under pressure is measured. The gas passed is air.
  • a perm porometer for example, a perm porometer manufactured by Porous Materials Inc. (for example, CFP-1100A) can be used. Gas is passed through the end (opening) on the exhaust gas inlet side (upper side in Figure 10C) of the inlet cell 13a included in cut piece P2'.
  • Gas that flows in from the end (opening) on the exhaust gas inlet side (upper side in Figure 10C) of the inlet cell 13a passes through the partition wall 12 and the second catalyst layer 30, and flows out from the end (opening) on the exhaust gas outlet side (lower side in Figure 10C) of the outlet cell 13b.
  • the gas permeability is calculated from the following equation when the pressure difference between the upstream (upper side of Figure 10C) and downstream (lower side of Figure 10C) positions in the gas flow direction relative to cut piece P2' during gas flow ((pressure at a position upstream in the gas flow direction relative to cut piece P2' during gas flow) - (pressure at a position downstream in the gas flow direction relative to cut piece P2' during gas flow)) is 10 kPa.
  • the pressure at the upstream position in the gas flow direction relative to cut piece P2' during gas flow is controlled by a perm porometer.
  • R Q / A2M2
  • Q gas permeability (unit: cm 3 /(cm 2 ⁇ s ⁇ Pa)
  • Q represents the flow rate of the gas under pressure (unit: cm 3 /s)
  • A2 represents the effective filtration area of the cut piece P2' (unit: cm2 )
  • M2 represents the pressure difference (unit: Pa) between the upstream and downstream positions in the gas flow direction relative to the cut piece P2' during gas flow.
  • the average distance D2 (unit: cm) can be calculated using the following method.
  • the left side of Figure 12 is the "left side A1b”
  • the right side of Figure 12 is the “right side A2b”
  • the upper side of Figure 12 is the “upper side A3b”
  • the lower side of Figure 12 is the “lower side A4b.”
  • the left side of Figure 12 is the "left side B 1a”
  • the right side of FIG. 12 is referred to as the "right side B2a”
  • the upper side of FIG. 12 is referred to as the "upper side B3a”
  • the lower side B4a Of the four sides that make up the opening of one inlet cell 13a adjacent to the upper or lower side of the outlet cell 13b, the left side of FIG. 12 is referred to as the “left side C1a,” the right side of FIG. 12 is referred to as the “right side C2a,” the upper side of FIG. 12 is referred to as the “upper side C3a,” and the lower side of FIG. 12 is referred to as the "lower side C4a.”
  • the four sides that make up the opening of the outlet cell 13b described above are the sides formed by the outer surfaces S1b (see FIGS.
  • the distance (unit: cm) between the left side A1b of the opening of the outlet cell 13b and the left side B1a of the opening of the inlet cell 13a is measured, and the measured distance is defined as distance D21.
  • the distance (unit: cm) between the right side A2b of the opening of the outlet cell 13b and the right side B2a of the opening of the inlet cell 13a may also be measured, and the measured distance is defined as distance D21.
  • Distance D21 can be considered to be the sum of the length of the upper side A3b or lower side A4b of the opening of the outlet cell 13b and the thickness of the partition wall portion 12.
  • the distance D21 is calculated in the same manner as above for 20 outlet cells 13b and their adjacent inlet cells 13a randomly selected from the plan view of the cut piece P2' shown in Figure 12, and the average value is taken as the average distance D21'.
  • the distance (unit: cm) between the bottom edge A4b of the opening of the outlet cell 13b and the bottom edge C4a of the opening of the inlet cell 13a is measured, and the measured distance is defined as distance D22.
  • the distance (unit: cm) between the top edge A3b of the opening of the outlet cell 13b and the top edge C3a of the opening of the inlet cell 13a may also be measured, and the measured distance is defined as distance D22.
  • Distance D22 can be considered to be the sum of the length of the left edge A1b or right edge A2b of the opening of the outlet cell 13b and the thickness of the partition wall portion 12.
  • the distance D22 is calculated in the same manner as above for 20 outlet cells 13b and their adjacent inlet cells 13a randomly selected from the plan view of the cut piece P2' shown in Figure 12, and the average value is taken as the average distance D22'.
  • the average thickness T (unit: cm) of the partition wall 12 can be determined in the same manner as above.
  • ⁇ 2 can be obtained by measuring the axial length of the cut piece P2'.
  • ⁇ 2 can be determined by the following method.
  • the outer surface S1a of the partition section 12 that contacts one inlet cell 13a is composed of four faces
  • the outer surface S1b of the partition section 12 that contacts one outlet cell 13b is composed of four faces
  • the number of the outer surfaces S1b (four faces) of the partition wall portion 12 that contact each of the outflow-side cells 13b and that are not adjacent to the third sealing portions 16 is calculated, and the total number of these faces is defined as ⁇ 2 . Specifically, this is done as follows.
  • the three outlet cells 13b in the third row G3 are referred to as the "outlet cell G31,” “outlet cell G32,” and “outlet cell G33" from the left side of Figure 12.
  • the three outflow side cells 13b in the fourth column G4 are referred to as "outflow side cell G41,” “outflow side cell G42,” and “outflow side cell G43” from the left side of FIG. 12;
  • the three outflow side cells 13b in the fifth column F5 are referred to as "outflow side cell G51,” “outflow side cell G52,” and “outflow side cell G53” from the left side of FIG. 12;
  • the three outflow side cells 13b in the sixth column F6 are referred to as "outflow side cell G61,” “outflow side cell G62,” and “outflow side cell G63” from the left side of FIG. 12.
  • the left surface (the surface on the left in Figure 12) and the top surface (the surface on the top in Figure 12) are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow cell G11, the number of surfaces that are not adjacent to the third sealing section 16 is two.
  • the right surface (the surface on the right side in Figure 12) and the bottom surface (the surface on the bottom side in Figure 12) are adjacent to the third sealing section 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outflow cell G63, the number of surfaces that are not adjacent to the third sealing section 16 is two.
  • the upper surface (the upper surface in Figure 12) is adjacent to the third sealing section 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outlet cell G12 or G13, the number of surfaces that are not adjacent to the third sealing section 16 is three.
  • the right surface (the surface on the right side in Figure 12) is adjacent to the third sealing section 16. Therefore, of the four outer surfaces S1b of the partition section 12 that contact the outlet cell G23 or G43, the number of surfaces that are not adjacent to the third sealing section 16 is three.
  • the left surface (the surface on the left side in Figure 12) is adjacent to the third sealing section 16. Therefore, of the four outer surfaces S1b of the partition section 12 that contact the outlet cell G31 or G51, the number of surfaces that are not adjacent to the third sealing section 16 is three.
  • the lower surface (the lower surface in Figure 12) is adjacent to the third sealing section 16. Therefore, of the outer surfaces S1b (four surfaces) of the partition section 12 that contact the outlet cell G61 or G62, the number of surfaces that are not adjacent to the third sealing section 16 is three.
  • the gas permeability is measured three times in total using different cut pieces P2', and the average value thereof is defined as Rb (cm 3 /(cm 2 ⁇ s ⁇ Pa)).
  • the above measurement method allows for accurate measurement of the gas permeability of the second catalyst layer 30 and partition wall section 12.
  • ⁇ 10% flow rate diameter of partition wall The 10% flow diameter ( ⁇ m) of the partition wall portion 12 measured by the bubble point method using a perm porometer after heat treatment of the substrate 10 at 950°C for 35 hours in an air atmosphere is defined as Xc ( ⁇ m), and the 10% flow diameter ( ⁇ m) of the partition wall portion 12 measured by the bubble point method using a perm porometer before the heat treatment of the substrate 10 is defined as Yc ( ⁇ m).
  • Xc is typically 5.00 ⁇ m or more and 20.00 ⁇ m or less
  • Yc is typically 5.00 ⁇ m or more and 20.00 ⁇ m or less
  • Xc/Yc is typically 1.1 or less.
  • Xc may be 5.50 ⁇ m or more and 18.00 ⁇ m or less, or 6.00 ⁇ m or more and 16.00 ⁇ m or less.
  • Yc may be 5.50 ⁇ m or more and 18.00 ⁇ m or less, or 6.00 ⁇ m or more and 16.00 ⁇ m or less.
  • Xc/Yc may be 1.05 or less, or 1.03 or less. Because the state of the substrate 10 changes little before and after the heat treatment, the lower limit of Xc/Yc is theoretically 1, but it may be less than 1 due to measurement errors or the influence of other slight changes.
  • Xc/Yc may be, for example, 0.98 or more, 0.99 or more, or 1.00 or more. Each of these lower limit values may be combined with any of the above-mentioned upper limit values.
  • the substrate 10 is subjected to a heat treatment at 950°C for 35 hours in an air atmosphere.
  • a sample extending in the axial direction of the substrate 10 and having the same length as the length L10 of the substrate 10 is cut out from the heat-treated substrate 10.
  • the number of inlet cells 13a included in the sample is the same as the number of outlet cells 13b included in the sample.
  • the planar shape of the sample when viewed from the axial direction of the sample is, for example, a quadrangle (preferably a square or rectangle, more preferably a square).
  • the size of the planar shape when viewed from the axial direction of the sample is not particularly limited as long as the number of inlet cells 13a included in the sample is the same as the number of outlet cells 13b included in the sample, but for example, the vertical length is 10 mm and the horizontal length is 10 mm.
  • the inlet side cells 13a and the outlet side cells 13b are arranged alternately in the vertical direction and also alternately in the horizontal direction, if the total number of the inlet side cells 13a and the outlet side cells 13b arranged vertically in the sample is an even number, and the total number of the inlet side cells 13a and the outlet side cells 13b arranged horizontally in the sample is an even number, then the number of the inlet side cells 13a contained in the sample will be the same as the number of the outlet side cells 13b contained in the sample.
  • the sample is cut along a plane perpendicular to the axial direction of the sample to prepare a cut piece P3 that does not include a portion of either the first catalyst layer 20 or the second catalyst layer 30.
  • the axial length of the cut piece P3 is not particularly limited, but is, for example, 10 mm.
  • the cut piece P3 does not have the first sealing portion 14 or the second sealing portion 15.
  • Cut piece P3 is similar to the example of cut piece P1 shown in Figures 7A and 7B, except that it does not include a portion of the first catalyst layer 20.
  • Cut piece P3 is, for example, cubic in shape, with a vertical length of 10 mm, a horizontal length of 10 mm, and an axial length of 10 mm.
  • a first sealing portion that seals the exhaust gas outlet end of the inlet cell 13a included in the cut piece P3, and a second sealing portion that seals the exhaust gas inlet end of the outlet cell 13b included in the cut piece P3 are formed on the cut piece P3, and a third sealing portion is formed on the outermost periphery of the cut piece P3, thereby obtaining a cut piece P3'.
  • the first sealing portion, second sealing portion, and third sealing portion can be formed by applying a weatherstripping material to predetermined locations on the cut piece P3.
  • an adhesive such as an epoxy resin adhesive can be used as the weatherstripping material.
  • the thickness of the first sealing portion 14 and second sealing portion 15 is each 1/10 or less of the axial length of the cut piece P3.
  • cut piece P3' is similar to the example of cut piece P1' shown in Figures 8A to 8C, except that it does not include a portion of the first catalyst layer 20.
  • Xc can be measured in the same manner as Xa, except that cut piece P3' prepared from heat-treated substrate 10 is used instead of cut piece P1' prepared from heat-treated catalyst 1.
  • cut piece P3' may be prepared from catalyst 1. If catalyst 1 does not have a portion that does not include a part of either the first catalytic layer 20 or the second catalytic layer 30, cut piece P3' may be prepared from catalyst 1. If catalyst 1 does not have a portion that does not include a part of either the first catalytic layer 20 or the second catalytic layer 30, a substrate with the same specifications as the substrate 10 used in catalyst 1 may be prepared, and the results of measurements on the prepared substrate may be estimated to be the measured values for substrate 10 of catalyst 1.
  • Cut piece P3' is prepared from substrate 10 before heat treatment in the same manner as above.
  • Yc can be measured in the same manner as Xc, except that cut piece P3' prepared from substrate 10 before heat treatment is used instead of cut piece P3' prepared from substrate 10 after heat treatment.
  • Rc may be 9.00 (cm 3 /(cm 2 s Pa)) or more and 18.00 (cm 3 /(cm 2 s Pa)) or less, or 11.00 (cm 3 /(cm 2 s Pa)) or more and 16.00 (cm 3 /(cm 2 s Pa)) or less.
  • Cut piece P3' is prepared from substrate 10 before heat treatment in the same manner as above.
  • Rc can be measured in the same manner as Ra, except that cut piece P3' prepared from substrate 10 before heat treatment is used instead of cut piece P1' prepared from catalyst 1 before heat treatment.
  • a method for forming a catalyst layer will be described below.
  • the following description of the method for forming a catalyst layer applies to both the first catalyst layer 20 and the second catalyst layer 30, unless otherwise specified.
  • the term “catalyst layer” is replaced with "first catalyst layer 20”
  • the term “catalyst layer” is replaced with "second catalyst layer 30.”
  • the following description of the method for forming a catalyst layer applies to all of Embodiments A to E, unless otherwise specified.
  • a slurry for forming the catalyst layer is applied to a predetermined portion of the substrate 10 and then dried to form a catalyst layer precursor. After the catalyst layer precursor is formed, it is fired. In this way, a catalyst layer with a single-layer structure can be formed.
  • a slurry for forming the lower layer is applied to a predetermined portion of the substrate 10 and then dried to form a precursor for the lower layer.
  • a slurry for forming the upper layer is applied onto the precursor for the lower layer and then dried to form a precursor for the upper layer.
  • the precursor for the lower layer and the precursor for the upper layer are formed, they are fired. In this way, a catalyst layer having a two-layer structure can be formed.
  • Catalyst layers having stacked structures other than a two-layer structure (for example, a three-layer structure) can also be formed in the same way.
  • the drying temperature is, for example, 40°C or higher and 150°C or lower, and the drying time is, for example, 5 minutes or higher and 1 hour or lower.
  • the firing temperature is, for example, 350°C or higher and 600°C or lower, and the firing time is, for example, 20 minutes or higher and 5 hours or lower.
  • the firing atmosphere is usually air.
  • each slurry contains, for example, a source of precious metal elements, inorganic oxide particles (e.g., Zr-based oxide particles), a binder, a pore-forming material, a solvent, etc.
  • sources of precious metal elements include salts of precious metal elements
  • salts of precious metal elements include nitrates, ammine complex salts, acetates, and chlorides.
  • the inorganic oxides that make up the inorganic oxide particles are as described above.
  • binders include alumina sol, zirconia sol, titania sol, silica sol, and ceria sol.
  • Examples of pore-forming materials include cross-linked polymethyl(meth)acrylate particles, cross-linked polybutyl(meth)acrylate particles, cross-linked polystyrene particles, cross-linked polyacrylic ester particles, and melamine-based resins.
  • Examples of solvents include water and organic solvents.
  • the amount of pore-forming material in each slurry is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, based on the mass of the catalyst layer formed by drying and firing each slurry.
  • a catalyst layer that satisfies the desired conditions means, in the case of the first catalyst layer 20, a first catalyst layer 20 that satisfies condition 1a (preferably conditions 1a and 2a), and in the case of the second catalyst layer 30, a second catalyst layer 30 that satisfies condition 1b (preferably conditions 1b and 2b). The same applies below.
  • the D50 of the pore-forming material is preferably 1 ⁇ m or more and 10 ⁇ m or less, more preferably 2 ⁇ m or more and 9 ⁇ m or less, and even more preferably 3 ⁇ m or more and 8 ⁇ m or less. This makes it easier to form a catalyst layer that meets the desired conditions.
  • D50 is the particle size at which the cumulative volume is 50% in the volume-based particle size distribution measured using a laser diffraction/scattering particle size distribution measurement method.
  • the method for measuring D50 is as follows. Using an automatic sample feeder for laser diffraction particle size distribution measurement equipment ("Microtorac SDC” manufactured by Nikkiso Co., Ltd.), a powder sample is placed in an aqueous solvent and irradiated with 40W ultrasound for 360 seconds at a flow rate of 40%, after which a volumetric particle size distribution is measured using a laser diffraction particle size distribution measurement equipment "Microtrac MT3300II” manufactured by Nikkiso Co., Ltd., and the particle size ( ⁇ m) at which the cumulative volume reaches 50% is determined from the volumetric particle size distribution. Measurements are performed twice, and the average value of the particle size ( ⁇ m) at which the cumulative volume reaches 50% is taken as D50 ( ⁇ m). Measurement conditions are: particle refractive index 1.5, particle shape spherical, solvent refractive index 1.3, set zero 30 seconds, and measurement time 30 seconds.
  • ⁇ Burned Zr-based oxide> When forming a catalyst layer that satisfies desired conditions, it is preferable to use a Zr-based oxide that has been densified in advance as the Zr-based oxide contained in the slurry, and it is more preferable to use a Ce-Zr-based composite oxide that has been densified in advance. Since a Zr-based oxide that has been densified in advance is less likely to thermally shrink even when exposed to a high-temperature environment, using a Zr-based oxide that has been densified in advance as the Zr-based oxide contained in the slurry can suppress the occurrence of cracks in the catalyst layer that are caused by thermal shrinkage of the Zr-based oxide after exposure to a high-temperature environment. Therefore, using a Zr-based oxide that has been densified in advance as the Zr-based oxide contained in the slurry makes it easier to form a catalyst layer that satisfies desired conditions.
  • two or more slurries may contain sintered Zr-based oxide, or any one of the slurries (e.g., a slurry for forming the lower layer or a slurry for forming the upper layer) may contain sintered Zr-based oxide.
  • Pre-calcined means that the Zr-based oxide has been subjected to a calcination treatment before being used to prepare the slurry.
  • the Zr-based oxide to be calcined may be a commercially available product or may be one produced according to conventional methods.
  • the conditions for the calcination treatment of the Zr-based oxide are as follows:
  • the calcination temperature is preferably 850°C or higher and 1200°C or lower, more preferably 900°C or higher and 1150°C or lower, and even more preferably 950°C or higher and 1100°C or lower.
  • the calcination time is preferably 1 hour or higher and 10 hours or lower, more preferably 2 hours or higher and 8 hours or lower, and even more preferably 3 hours or higher and 6 hours or lower.
  • the atmosphere during calcination is preferably air or an inert atmosphere.
  • the specific surface area of the Zr-based oxide before firing is preferably 85 m 2 /g or more and 120 m 2 /g or less, more preferably 85 m 2 /g or more and 110 m 2 /g or less, and even more preferably 85 m 2 /g or more and 100 m 2 /g or less.
  • the specific surface area of the Zr-based oxide after firing is preferably 30 m 2 /g or more and 85 m 2 /g or less, more preferably 40 m 2 /g or more and 80 m 2 /g or less, and even more preferably 50 m 2 /g or more and 75 m 2 /g or less.
  • the percentage of the specific surface area of the Zr-based oxide after the calcination treatment relative to the specific surface area of the Zr-based oxide before the calcination treatment is preferably 25% or more and 100% or less, more preferably 40% or more and 90% or less, and even more preferably 55% or more and 85% or less.
  • the specific surface area can be measured by N 2 gas adsorption method using powdered Zr-based oxide and QUADRASORB SI manufactured by Quantachrome Corporation.
  • the Zr-based oxide contained in the slurry preferably satisfies one or more, and more preferably two or more, of the following conditions: This makes it possible to make the Zr-based oxide less susceptible to thermal shrinkage, and effectively suppresses the occurrence of cracks in the catalyst layer that are caused by thermal shrinkage of the Zr-based oxide after exposure to a high-temperature environment.
  • the specific surface area of the Zr-based oxide is preferably 85 m 2 /g or more and 120 m 2 /g or less.
  • the D50 of the Zr-based oxide is 2 ⁇ m or more and 15 ⁇ m or less.
  • the Zr-based oxide has a D10 of 1 ⁇ m or more.
  • the particle size distribution of the Zr-based oxide is unimodal, not multimodal.
  • D10 is the particle size at which the cumulative volume is 10% in the volume-based particle size distribution measured using a laser diffraction/scattering particle size distribution measurement method.
  • the measurement method for D10 is the same as that for D50.
  • Example 1 Preparation of Slurry Alumina powder and Ce—Zr-based composite oxide powder that had been previously subjected to a calcination treatment were added to an aqueous palladium nitrate solution, and then alumina sol, zirconia sol, a pore-forming material (crosslinked polymethyl(meth)acrylate particles having a D50 of 5 ⁇ m), and water as a solvent were added to prepare a first slurry.
  • alumina sol, zirconia sol, a pore-forming material crosslinked polymethyl(meth)acrylate particles having a D50 of 5 ⁇ m
  • the composition of the Ce—Zr-based composite oxide powder used to prepare the first slurry is as follows: 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 oxide: 10% by mass
  • the first slurry was prepared using a Ce—Zr composite oxide powder that had been calcined under the following conditions.
  • the specific surface areas of the Ce—Zr composite oxide powder before and after the calcination treatment were measured by N2 gas adsorption using a QUADRASORB SI (manufactured by Quantachrome).
  • the specific surface area of the Ce—Zr composite oxide powder before the calcination treatment was 87.1 m2 /g, and the specific surface area of the Ce—Zr composite oxide powder after the calcination treatment was 70.8 m2 /g.
  • Firing treatment conditions Firing temperature: 950°C Firing time: 4 hours
  • Firing atmosphere air atmosphere
  • the amount of each component in the first slurry was adjusted so that, based on the mass of the catalyst layer formed by drying and firing the first slurry, palladium was 4 mass% in metal equivalent, alumina powder was 9 mass%, Ce-Zr composite oxide powder was 78 mass%, alumina sol was 3 mass% in solids equivalent, and zirconia sol was 6 mass% in solids equivalent.
  • the amount of pore-forming material in the first slurry was adjusted so that it was 40 mass% of the mass of the catalyst layer formed by drying and firing the first slurry.
  • Alumina powder and pre-calcined Ce-Zr composite oxide powder were added to an aqueous rhodium nitrate solution, followed by the addition of alumina sol, zirconia sol, a pore-forming agent (crosslinked polymethyl(meth)acrylate particles with a D50 of 3 ⁇ m), and water as a solvent to prepare a second slurry and a third slurry.
  • compositions of the Ce—Zr-based composite oxide powders used to prepare the second and third slurries are as follows: Ce content in terms of CeO2 : 15% by mass Zr content in terms of ZrO2 : 65% by mass Content of one or more rare earth elements other than Ce in terms of oxide: 20% by mass
  • the second and third slurries were prepared using Ce-Zr composite oxide powders that had been calcined under the following conditions:
  • the specific surface areas of the Ce-Zr composite oxide powders before and after the calcination treatment were measured by N2 gas adsorption using a QUADRASORB SI (Quantachrome Corp.).
  • the specific surface area of the Ce-Zr composite oxide powder before the calcination treatment was 90.1 m2 /g, and the specific surface area of the Ce-Zr composite oxide powder after the calcination treatment was 68.2 m2 /g.
  • the amount of each component in the second slurry was adjusted so that, based on the mass of the catalyst layer formed by drying and firing the second slurry, rhodium was 0.5 mass% in metal equivalent, alumina powder was 17.5 mass%, Ce-Zr composite oxide powder was 74 mass%, alumina sol was 3 mass% in solids equivalent, and zirconia sol was 5 mass% in solids equivalent.
  • the amount of pore-forming material in the second slurry was adjusted so that it was 40 mass% of the mass of the catalyst layer formed by drying and firing the second slurry.
  • the amount of each component in the third slurry was adjusted so that, based on the mass of the catalyst layer formed by drying and firing the third slurry, rhodium was 0.5 mass% in metal equivalent, alumina powder was 9.5 mass%, Ce-Zr composite oxide powder was 82 mass%, alumina sol was 3 mass% in solids equivalent, and zirconia sol was 5 mass% in solids equivalent.
  • the amount of pore-forming material in the third slurry was adjusted so that it was 30 mass% of the mass of the catalyst layer formed by drying and firing the third slurry.
  • the mass of the catalyst layer formed by drying and firing each slurry can be calculated by subtracting the mass of the components (e.g., solvent, pore-forming material, etc.) that are lost during drying and firing of each slurry from the mass of each slurry.
  • the components e.g., solvent, pore-forming material, etc.
  • a wall-flow type substrate having the structure shown in Figures 2 to 6 was prepared, i.e., a substrate including inlet cells extending in the axial direction of the substrate, outlet cells extending in the axial direction of the substrate, and porous partition walls separating the inlet and outlet cells.
  • the thickness of the partition walls was 200 ⁇ m
  • the total number of inlet and outlet cells in a cross section perpendicular to the axial direction of the substrate was 300 cells per square inch
  • the volume of the substrate was 0.79 L
  • the length of the substrate was 90 mm.
  • the first slurry was applied to the exhaust gas inlet side of the substrate and then dried at 90°C for 10 minutes to form a lower layer precursor.
  • the second slurry was applied to the lower layer precursor and then dried at 90°C for 10 minutes to form an upper layer precursor.
  • the substrate with the lower layer precursor and upper layer precursor formed was fired at 450°C for 1 hour to form a first catalyst layer on the substrate, comprising a lower layer and an upper layer formed on the lower layer.
  • the third slurry was applied to the exhaust gas outlet side of the substrate and dried at 90°C for 10 minutes to form a precursor for the second catalyst layer.
  • the substrate with the precursor for the second catalyst layer formed thereon was calcined at 450°C for 1 hour to form a second catalyst layer on the substrate. In this way, the exhaust gas purification catalyst of Example 1 was obtained.
  • the slurry was applied so that the percentage of the length of the first catalyst layer relative to the length of the substrate was 75%, the percentage of the length of the second catalyst layer relative to the length of the substrate was 50%, the mass of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was formed was 40 g/L, and the mass of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was formed was 40 g/L.
  • the exhaust gas purification catalyst of Example 1 was heat-treated in an air atmosphere at 950°C for 35 hours.
  • Xa and Xb were measured for the heat-treated exhaust gas purification catalyst according to the method described above.
  • Ya, Yb, Ra, and Rb were measured for the exhaust gas purification catalyst before heat treatment using the above method.
  • a cut piece P1' shown in FIGS. 8A to 8C was used, which was prepared from the exhaust gas purification catalyst before or after the heat treatment.
  • the cut piece P1' was prepared using the cut piece P1 shown in FIGS. 7A and 7B.
  • the cut piece P1 used was a cube with a length in the vertical direction (vertical direction in FIG. 7A) of 10 mm, a length in the horizontal direction (horizontal direction in FIG. 7A) of 10 mm, and a length in the axial direction (vertical direction in FIG. 7B) of 10 mm.
  • ⁇ 1 (average length of one side of the opening of the inlet-side cell 13a) was 0.121 cm
  • ⁇ 1 axial length of the cut piece P1' was 1 cm
  • ⁇ 1 number of effective filtration surfaces of the cut piece P1' was 60
  • a 1 (effective filtration area of the cut piece P1') was 7.26 cm 2 .
  • a cut piece P2' shown in FIGS. 10A to 10C was used, which was prepared from the exhaust gas purification catalyst before or after the heat treatment.
  • the cut piece P2' was prepared using the cut piece P2 shown in FIGS. 9A and 9B.
  • the cut piece P2 used was a cube with a length in the vertical direction (vertical direction in FIG. 9A) of 10 mm, a length in the horizontal direction (horizontal direction in FIG. 9A) of 10 mm, and a length in the axial direction (vertical direction in FIG. 9B) of 10 mm.
  • ⁇ 2 (average length of one side of the opening of the outlet cell 13b) was 0.121 cm
  • ⁇ 2 axial length of the cut piece P2' was 1 cm
  • ⁇ 2 number of effective filtration surfaces of the cut piece P2' was 6
  • a 2 (effective filtration area of the cut piece P2') was 7.26 cm 2 .
  • Xc i.e., the 10% flow diameter of the partition wall portion measured by the bubble point method using a perm porometer after the substrate was heat treated in an air atmosphere at 950°C for 35 hours, was 14.39 ⁇ m
  • Yc i.e., the 10% flow diameter of the partition wall portion measured by the bubble point method using a perm porometer before the substrate was heat treated, was 14.38 ⁇ m
  • Xc/Yc was 1.00.
  • Rc that is, the gas permeability of the partition wall portion measured using a perm porometer before the substrate was subjected to heat treatment at 950°C for 35 hours in an air atmosphere, was 12.64 (cm 3 /(cm 2 ⁇ s ⁇ Pa)).
  • the conditions for measuring the PM trapping performance were as follows. Evaluation vehicle: 1.5L direct injection turbo engine Gasoline used: Fuel for certification tests PM measurement device: Manufactured by Horiba Ltd.
  • a gasoline engine vehicle equipped with the exhaust gas purification catalyst of Example 1 before or after heat treatment a gasoline engine vehicle equipped with a substrate (with neither the first catalyst layer nor the second catalyst layer formed) was used, and the PM collection performance of the substrate was determined in the same manner as above.
  • PM collection performance ratio (%) was calculated based on the following formula.
  • PM collection performance ratio (PM collection performance of the exhaust gas purifying catalyst of Example 1 before or after heat treatment/PM collection performance of the substrate) ⁇ 100
  • Example 2 The same procedure as in Example 1 was carried out to prepare the second slurry, except that a Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.
  • Example 3 The same procedure as in Example 1 was carried out to prepare the third slurry, except that a Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.
  • Example 4 The same procedure as in Example 1 was carried out to prepare the first slurry, except that a Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.
  • Example 5 The same procedure as in Example 1 was carried out to prepare the second and third slurries, except that the Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.
  • Example 1 The same operations as in Example 1 were carried out to prepare the first, second, and third slurries, except that the Ce—Zr-based composite oxide powder that had not been subjected to a calcination treatment in advance was used instead of the Ce—Zr-based composite oxide powder that had been subjected to a calcination treatment in advance.
  • Example 1 The results of Examples 1 to 5 and Comparative Example 1 are shown in Table 1.
  • "Pre-calcined CZ” indicates whether or not a Ce-Zr composite oxide powder that had been pre-calcined was used in preparing the slurry ("Yes” if used, "No” if not).
  • the units of Xa, Ya, Xb, and Yb are ⁇ m, and the units of Ra and Rb are cm 3 /(cm 2 s Pa).

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  • Chemical Kinetics & Catalysis (AREA)
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  • Organic Chemistry (AREA)
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  • Combustion & Propulsion (AREA)
  • Biomedical Technology (AREA)
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Abstract

La présente invention aborde le problème de la fourniture d'un catalyseur de purification de gaz d'échappement capable de supprimer une diminution de la performance de collecte de PM provoquée par l'exposition à un environnement à haute température. Afin de résoudre ce problème, l'invention concerne un catalyseur de purification de gaz d'échappement (1) comprenant un substrat de type écoulement sur paroi (10) et au moins l'une parmi une première couche de catalyseur (20) et une seconde couche de catalyseur (30), le catalyseur de purification de gaz d'échappement (1) satisfaisant au moins l'une parmi les conditions 1a et 1b suivantes. [Condition 1a] : Xa/Ya ≤ 1,40 et Ya ≤ 5,00, et [condition 1b] : Xb/Yb ≤ 1,40 et Yb ≤ 5,00.
PCT/JP2025/006758 2024-02-29 2025-02-27 Catalyseur de purification de gaz d'échappement Pending WO2025183037A1 (fr)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000271480A (ja) * 1999-01-18 2000-10-03 Toyota Central Res & Dev Lab Inc 排ガス浄化用触媒
JP2008178766A (ja) * 2007-01-23 2008-08-07 Mazda Motor Corp パティキュレートフィルタ
WO2018012562A1 (fr) * 2016-07-14 2018-01-18 イビデン株式会社 Structure en nid d'abeilles et procédé de production de structure en nid d'abeilles
JP2018187595A (ja) * 2017-05-11 2018-11-29 株式会社キャタラー 排ガス浄化触媒装置
WO2019188618A1 (fr) * 2018-03-30 2019-10-03 三井金属鉱業株式会社 Catalyseur de purification de gaz d'échappement
WO2021107120A1 (fr) * 2019-11-29 2021-06-03 三井金属鉱業株式会社 Catalyseur de purification de gaz d'échappement

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000271480A (ja) * 1999-01-18 2000-10-03 Toyota Central Res & Dev Lab Inc 排ガス浄化用触媒
JP2008178766A (ja) * 2007-01-23 2008-08-07 Mazda Motor Corp パティキュレートフィルタ
WO2018012562A1 (fr) * 2016-07-14 2018-01-18 イビデン株式会社 Structure en nid d'abeilles et procédé de production de structure en nid d'abeilles
JP2018187595A (ja) * 2017-05-11 2018-11-29 株式会社キャタラー 排ガス浄化触媒装置
WO2019188618A1 (fr) * 2018-03-30 2019-10-03 三井金属鉱業株式会社 Catalyseur de purification de gaz d'échappement
WO2021107120A1 (fr) * 2019-11-29 2021-06-03 三井金属鉱業株式会社 Catalyseur de purification de gaz d'échappement

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