Exhaust gas purification catalyst

Abstract

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

Description

[Technical field]

[0001] The present invention relates to a catalyst for purifying exhaust gas. [Background technology]

[0002] Exhaust gas emitted from internal combustion engines of automobiles, motorcycles, etc. contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). In order to purify and detoxify these harmful components, exhaust gas purification catalysts containing precious metal elements such as Pt, Pd, and Rh are used. Pt and Pd are mainly involved in the oxidation purification of HC and CO, while Rh is mainly involved in the reduction purification of NOx.

[0003] In order to maximize the performance of precious metal elements in exhaust gas purification catalysts, catalysts have been proposed in which the catalyst layer is composed of an upstream portion and a downstream portion having a composition different from that of the upstream portion (for example, Patent Document 1).

[0004] Due to the increasing demand for exhaust gas purification performance in recent years, there is a demand for exhaust gas purification catalysts with excellent exhaust gas purification performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-136695 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an exhaust gas purifying catalyst having excellent exhaust gas purifying performance. [Means for solving the problem]

[0007] The present invention provides the following inventions. [1] A catalyst for purifying exhaust gas comprising a substrate, a first catalyst layer provided on the upstream side of the substrate, and a second catalyst layer provided on the downstream side of the substrate, the first catalytic layer contains a precious metal element and a Ce-Zr based composite oxide, The second catalyst layer is composed of a precious metal element and Al 2 O 3 and Al in the first catalyst layer 2 O 3 The mass content in terms of the converted amount is 12% by mass or less, Al in the second catalyst layer 2 O 3 The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer 2 O 3 A catalyst for exhaust gas purification, in which the ratio of the converted mass content is 0 or more and 0.65 or less. [2] The exhaust gas purifying catalyst according to [1], wherein a ratio of a mass of the second catalyst layer per unit volume of a portion of the substrate on which the second catalyst layer is formed to a mass of the first catalyst layer per unit volume of a portion of the substrate on which the first catalyst layer is formed is 0.95 or less. [3] The exhaust gas purifying catalyst according to [1] or [2], wherein the first catalyst layer and the second catalyst layer each contain Pd and / or Pt. [4] The exhaust gas purification catalyst according to [3], further comprising a third catalyst layer provided on the upper side of the first catalyst layer and / or a fourth catalyst layer provided on the upper side of the second catalyst layer, wherein the third catalyst layer and the fourth catalyst layer each contain Rh. [5] The exhaust gas purifying catalyst according to any one of [1] to [4], wherein the first catalyst layer contains Pd. [6] The ratio of Al in the second catalyst layer to the mass content of precious metal elements in the second catalyst layer in terms of metal. 2 O 3 The catalyst for purifying exhaust gas according to any one of [1] to [5], wherein a ratio of the converted mass content is 50 or more and 600 or less. [7] CeO in the first catalyst layer 2 The catalyst for purifying exhaust gas according to any one of [1] to [6], having a mass content calculated as a carbon content of 32 mass % or more. Effect of the Invention

[0008] According to the present invention, there is provided an exhaust gas purifying catalyst having excellent exhaust gas purifying performance. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a partial end view showing a state in which an exhaust gas purifying catalyst according to a first embodiment of the present invention is disposed in an exhaust path of an internal combustion engine. [Diagram 2] FIG. 2 is an end view taken along line AA in FIG. [Diagram 3] FIG. 3 is an end view taken along line BB in FIG. [Figure 4] FIG. 4 is an enlarged view of the area indicated by the reference character R1 in FIG. [Diagram 5] FIG. 5 is an enlarged view of the area indicated by the symbol R2 in FIG. [Figure 6] FIG. 6 is an end view taken along line CC in FIG. [Figure 7] FIG. 7 is an end view of an exhaust gas purifying catalyst according to a second embodiment of the present invention (an end view corresponding to FIG. 6). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Terminology explanation> The following describes terms used in this specification. The following descriptions apply to the entire specification unless otherwise specified.

[0011] <Rare earth elements> Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0012] <Oxide> The oxides of rare earth elements except Ce, Pr and Tb are sesquioxides (M 2 O 3 , M represents a rare earth element other than Ce, Pr, and Tb), and the oxide of Ce is CeO 2 The oxide of Pr is Pr6 O 11 Regarding the oxide of Tb, it is Tb 4 O 7 Regarding the oxide of Al, it is Al 2 O 3 Regarding the oxide of Zr, it is ZrO 2 Regarding the oxide of Si, it is SiO 2 Regarding the oxide of B, it is B 2 O 3 Regarding the oxide of Cr, it is Cr 2 O 3 Regarding the oxide of Mg, it is MgO; regarding the oxide of Ca, it is CaO; regarding the oxide of Sr, it is SrO; regarding the oxide of Ba, it is BaO; regarding the oxide of Fe, it is Fe 3 O 4 Regarding the oxide of Mn, it is Mn 3 O 4 Regarding the oxide of Ni, it is NiO; regarding the oxide of Ti, it is TiO 2 Regarding the oxide of Zn, it is ZnO; regarding the oxide of Sn, it is SnO 2 It means.

[0013] <Al-based oxide> The Al-based oxide is an oxide containing Al, and among the elements other than oxygen that constitute the oxide, the element with the highest content rate by mass is Al. However, those corresponding to the Ce-Zr composite oxide shall not be regarded as corresponding to the Al-based oxide. The Ce-Zr composite oxide will be described later. The Al-based oxide is distinguished from the alumina used as a binder. In this specification, the alumina used as a binder may be referred to as "alumina binder" in some cases.

[0014] The Al-based oxide is, for example, in particulate form. The Al-based oxide is used as a carrier for the catalytic active component. From the viewpoint of improving the loading property of the catalytic active component, the Al-based oxide is preferably porous.

[0015] The Al-based oxide may contain one or more elements other than Al and O. The elements other than Al and O can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0016] Examples of Al-based oxides include alumina (oxides composed of Al and O), oxides obtained by modifying the surface of alumina with other elements, oxides obtained by dissolving other elements in alumina, etc. Examples of Al-based oxides containing elements other than Al and O include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, etc.

[0017] In one embodiment, the Al-based oxide contains one or more rare earth elements. From the viewpoint of improving the heat resistance of the Al-based oxide, the rare earth elements are preferably selected from La, Y, Ce, Nd, Pr, etc. From the viewpoint of improving the heat resistance of the Al-based oxide, the content of the rare earth elements in the Al-based oxide in terms of oxide is preferably 0.1 mass% or more and 50 mass% or less, more preferably 0.1 mass% or more and 30 mass% or less, still more preferably 0.2 mass% or more and 20 mass% or less, and still more preferably 0.3 mass% or more and 10 mass% or less, based on the mass of the Al-based oxide. The "content of the rare earth elements in the Al-based oxide in terms of oxide" means the content of the rare earth element in terms of oxide when the Al-based oxide contains one rare earth element, and means the total content of the two or more rare earth elements in terms of oxide when the Al-based oxide contains two or more rare earth elements.

[0018] When the composition of the Al-based oxide is known, the content of each element in the Al-based oxide calculated as an oxide can be determined from the composition of the Al-based oxide.

[0019] When the composition of the Al-based oxide is unknown, the content rate in terms of oxide of each element in the Al-based oxide can be determined from the elemental mapping obtained by analyzing a sample containing the Al-based oxide by energy dispersive X-ray spectroscopy (EDX) and the EDX elemental analysis of the specified particles. Specifically, the Al-based oxide particles and other particles are qualitatively identified (color-coded) by elemental mapping, and the content rate in terms of oxide of each element in the specified particles can be determined by performing a composition analysis (elemental analysis) on the specified particles.

[0020] <Ce-based oxide> A Ce-based oxide is an oxide containing Ce, and means an oxide in which, among the elements other than oxygen constituting the oxide, the element with the largest content rate on a mass basis is Ce. However, those corresponding to Ce-Zr composite oxides shall not be regarded as Ce-based oxides. Ce-Zr composite oxides will be described later. Ce-based oxides are distinguished from ceria used as a binder. In this specification, ceria used as a binder may be referred to as "ceria binder".

[0021] The Ce-based oxide is, for example, particulate. The Ce-based oxide is used as a carrier for a catalytically active component. From the viewpoint of improving the supportability of the catalytically active component, the Ce-based oxide is preferably porous.

[0022] The Ce-based oxide may contain one or more elements other than Ce and O. The elements other than Ce and O can be selected, for example, from rare earth elements other than Ce, alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0023] Examples of the Ce-based oxide include ceria (an oxide composed of Ce and O), an oxide obtained by modifying the surface of ceria with other elements, an oxide obtained by dissolving other elements in ceria, and the like.

[0024] The content rate in terms of oxide of each element in the Ce-based oxide can be determined in the same manner as the content rate in terms of oxide of each element in the Al-based oxide.

[0025] <Ce-Zr composite oxide> The Ce-Zr composite oxide is a composite oxide containing Ce and Zr, and the content rate of Ce in terms of CeO 2 in the composite oxide is 5% by mass or more and 95% by mass or less based on the mass of the composite oxide, and the content rate of Zr in terms of ZrO 2 in the composite oxide is 5% by mass or more and 95% by mass or less based on the mass of the composite oxide.

[0026] The Ce-Zr composite oxide is, for example, particulate. The Ce-Zr composite oxide is used as a carrier for a catalytic active component. From the viewpoint of improving the supportability of the catalytic active component, the Ce-Zr composite oxide is preferably porous.

[0027] The Ce-Zr composite oxide may contain one or more elements other than Ce, Zr, and O. The elements other than Ce, Zr, and O can be selected, for example, from rare earth elements other than Ce, alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.

[0028] In the Ce-Zr composite oxide, Ce may form a solid solution phase (e.g., a solid solution phase of CeO 2 and ZrO 2 etc.), a single phase that is a crystalline phase or an amorphous phase (e.g., a single phase of CeO 2 single phase), or both a solid solution phase and a single phase, but at least a part of Ce preferably forms a solid solution phase.

[0029] In the Ce-Zr composite oxide, Zr may form a solid solution phase (e.g., a solid solution phase of CeO 2 and ZrO 2 etc.), a single phase that is a crystalline phase or an amorphous phase (e.g., a single phase of ZrO 2Although Zr may form a solid solution phase or both a solid solution phase and a single phase, it is preferable that at least a part of Zr forms a solid solution phase.

[0030] When the Ce-Zr-based composite oxide contains elements other than Ce, Zr, and O (hereinafter referred to as "other elements"), the other elements are in the form of a solid solution phase (e.g., CeO 2 and oxides of other elements, ZrO 2 and oxides of other elements, CeO 2 and ZrO 2 The other element may form a solid solution phase or a single phase which is a crystalline phase or an amorphous phase (e.g., a single phase of an oxide of the other element), or may form both a solid solution phase and a single phase, but it is preferable that at least a portion of the other element forms a solid solution phase.

[0031] The content of each element in the Ce-Zr based composite oxide calculated as its oxide can be determined in the same manner as the content of each element in the Al based oxide calculated as its oxide.

[0032] First Embodiment Hereinafter, an exhaust gas purifying catalyst 1A (hereinafter referred to as "catalyst 1A") according to a first embodiment will be described with reference to Figs.

[0033] As shown in Fig. 1, a catalyst 1A is disposed in an exhaust passage in an exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine. Exhaust gas discharged from the internal combustion engine flows through an exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P, and is purified by the catalyst 1A provided in the exhaust pipe P. In the drawings, the exhaust gas flow direction is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas inflow side" or "upstream side", and the downstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas outflow side" or "downstream side".

[0034] In the exhaust passage in the exhaust pipe P, other exhaust gas purifying catalysts may be arranged on the upstream side and / or downstream side of the catalyst 1A.

[0035] As shown in Figures 2 to 6, catalyst 1A includes a substrate 10, a first catalyst layer 20 provided on the upstream side of the substrate 10, a second catalyst layer 30 provided on the downstream side of the substrate 10, a third catalyst layer 40 provided on the upper side of the first catalyst layer 20, and a fourth catalyst layer 50 provided on the upper side of the second catalyst layer 30.

[0036] In this specification, the CeO of Ce in the first catalyst layer 20 based on the mass of the first catalyst layer 20 is 2 The content of Ce in the first catalyst layer 20 is expressed as "CeO 2 "Al converted mass content" refers to the Al content of the first catalyst layer 20 based on the mass of the first catalyst layer 20. 2 O 3 The converted content of Al in the first catalyst layer 20 is 2 O 3 "mass content in metal conversion of precious metal elements in the second catalytic layer 30" based on the mass of the second catalytic layer 30; "mass content in metal conversion of precious metal elements in the second catalytic layer 30" based on the mass of the second catalytic layer 30; 2 O 3 The content of Al in the second catalyst layer 30 is expressed as "Al 2 O 3 This is sometimes called the "converted mass content."

[0037] In the catalyst 1A, the first catalyst layer 20 contains a precious metal element and a Ce-Zr based composite oxide, and the second catalyst layer 30 contains a precious metal element and Al. 2 O 3 and the Al in the first catalyst layer is 2 O 3 The mass content of Al in the second catalyst layer 30 is 12 mass % or less in terms of Al. 2 O 3 The ratio of Al in the first catalyst layer 20 to the mass content of Al converted 2 O 3 The ratio of the converted mass content is 0 or more and 0.65 or less.

[0038] In the catalyst 1A, a first catalyst layer 20 is provided on the upstream side of the substrate 10, and a second catalyst layer 30 is provided on the downstream side of the substrate 10. Therefore, the exhaust gas that has flowed into the substrate 10 comes into contact with the first catalyst layer 20 earlier than with the second catalyst layer 30.

[0039] When the catalyst 1A is placed in a low-temperature environment immediately after the start of an internal combustion engine, the activity of catalytically active components (e.g., precious metal elements such as Pd and Pt) in the first catalyst layer 20 and the second catalyst layer 30 is low, and therefore the exhaust gas purification performance of the catalyst 1A is low. Therefore, from the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, it is necessary to improve the temperature rise characteristics of the first catalyst layer 20 and the second catalyst layer 30. In particular, improving the temperature rise characteristics of the first catalyst layer 20, which comes into contact with exhaust gas earlier than the second catalyst layer 30, is effective in improving the exhaust gas purification performance of the catalyst 1A.

[0040] Al 2 O 3 Therefore, from the viewpoint of improving the temperature rise of the first catalytic layer 20, the Al content of Al in the first catalytic layer 20 is set to be 1.0 to 1.0. 2 O 3 The converted mass content needs to be reduced.

[0041] When the catalyst 1A is placed in a high-temperature environment during high-speed operation of an internal combustion engine, the temperatures of the first catalyst layer 20 and the second catalyst layer 30 rise sufficiently, but since the amount of harmful components in the exhaust gas (e.g., hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc.) emitted per hour increases, the number of active sites of the catalytic active components is more important than the temperature rise property.

[0042] Al 2 O 3 has the effect of suppressing the decrease in the dispersion degree of the catalytic active component after exposure to a high-temperature environment (i.e., the decrease in the active sites of the catalytic active component after exposure to a high-temperature environment). Therefore, from the viewpoint of suppressing the decrease in the dispersion degree of the catalytic active component after exposure to a high-temperature environment, the Al content of Al in the first catalytic layer 20 and the second catalytic layer 30 is 2 O 3However, from the viewpoint of improving the temperature rise property of the first catalytic layer 20, it is preferable to increase the mass content of Al in the first catalytic layer 20. 2 O 3 Since the mass content of Al in the second catalyst layer 30 cannot be increased, 2 O 3 The converted mass content needs to be increased.

[0043] As described above, in order to realize the improvement of the temperature rise property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the Al content of the first catalyst layer 20 is set to 1. 2 O 3 The mass content of Al in the second catalyst layer 30 is reduced. 2 O 3 It is necessary to increase the mass content of Al in the first catalyst layer 20. 2 O 3 The mass content of Al in the second catalyst layer 30 is calculated by 2 O 3 The converted mass content of Al in the first catalyst layer 20 is 2 O 3 The mass content of Al in the second catalyst layer is 12 mass% or less in terms of mass converted from Al. 2 O 3 The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content is adjusted to be 0 or more and 0.65 or less. This makes it possible to improve the temperature rise property of the first catalyst layer 20, which is required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and to suppress the decrease in the degree of dispersion of the catalytically active components after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine. Therefore, the catalyst 1A can exhibit superior exhaust gas purification performance compared to catalysts with the ratio outside the above range.

[0044] It is desirable that the air / fuel ratio (air-fuel ratio) supplied to an internal combustion engine is controlled to be close to the theoretical air-fuel ratio (stoichiometric). However, since the actual air-fuel ratio fluctuates from the stoichiometric ratio to the rich side (excess fuel atmosphere) or lean side (lean fuel atmosphere) side, the air-fuel ratio of the exhaust gas also fluctuates to the rich side or lean side. In order for the catalyst 1A to exhibit sufficient purification performance, it is necessary to mitigate the fluctuation of the oxygen concentration in the exhaust gas. By including a Ce-Zr-based composite oxide having an oxygen storage capacity (i.e., the capacity to store oxygen when the oxygen concentration in the exhaust gas is high and to release oxygen when the oxygen concentration in the exhaust gas is low) in the first catalyst layer 20, the fluctuation of the oxygen concentration in the exhaust gas is mitigated, and the operating window of the catalytic active component is expanded. Since the Ce-Zr-based composite oxide is contained in the first catalytic layer 20 located upstream of the second catalytic layer 30, fluctuations in the oxygen concentration in the exhaust gas are mitigated not only in the first catalytic layer 20 but also in the second catalytic layer 30 located downstream of the first catalytic layer 20, thereby improving the exhaust gas purification ability of the catalyst 1A.

[0045] From the viewpoint of more effectively realizing an improvement in the temperature rise property of the first catalyst layer 20, which is required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and a suppression of a decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the content of Al in the second catalyst layer is preferably 100% or more. 2 O 3 The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content is preferably 0 or more and 0.50 or less, more preferably 0 or more and 0.30 or less, and even more preferably 0 or more and 0.10 or less.

[0046] The improvement in the temperature rise property of the first catalyst layer 20 in a low temperature environment is remarkable when the temperature of the low temperature environment is 500°C or less, is more remarkable when the temperature of the low temperature environment is 450°C or less, and is even more remarkable when the temperature of the low temperature environment is 400°C or less.

[0047] The suppression of the decrease in the dispersion degree of the catalytically active component after exposure to a high-temperature environment is remarkable when the temperature of the high-temperature environment is 550°C or higher, is more remarkable when the temperature of the high-temperature environment is 600°C or higher, and is even more remarkable when the temperature of the high-temperature environment is 650°C or higher.

[0048] <Base material> The substrate 10 will now be described.

[0049] As shown in FIGS. 1 and 6, the substrate 10 extends in the exhaust gas flow direction X.

[0050] As shown in FIGS. 1 and 6, the substrate 10 is disposed in the exhaust passage in the exhaust pipe P so that the axial direction of the substrate 10 coincides or approximately coincides with the exhaust gas flow direction X.

[0051] As shown in FIGS. 1 to 6, the substrate 10 has a first substrate portion 10a located on the upstream side of the exhaust gas flow direction X, and a second substrate portion 10b located on the downstream side of the exhaust gas flow direction X.

[0052] As shown in FIGS. 1 and 6, the first substrate portion 10a and the second substrate portion 10b each extend in the exhaust gas flow direction X, and have an end portion on the exhaust gas inlet side and an end portion on the exhaust gas outlet side.

[0053] As shown in Figures 1 and 6, the first substrate portion 10a and the second substrate portion 10b are disposed in the exhaust passage in the exhaust pipe P such that the axial directions of the first substrate portion 10a and the second substrate portion 10b coincide or approximately coincide with the exhaust gas flow direction X.

[0054] As shown in FIGS. 1 and 6, it is preferable that the axial direction of the first base material piece 10a and the axial direction of the second base material piece 10b coincide or approximately coincide.

[0055] The first substrate part 10a and the second substrate part 10b are integral, and the end part of the first substrate part 10a on the exhaust gas outflow side and the end part of the second substrate part 10b on the exhaust gas inflow side are continuous with each other. In the drawings, the boundary between the end part of the first substrate part 10a on the exhaust gas outflow side and the end part of the second substrate part 10b on the exhaust gas inflow side is indicated by the symbol S.

[0056] Hereinafter, the common points between the first substrate portion 10a and the second substrate portion 10b will be described together with the description of the first substrate portion 10a and the second substrate portion 10b. In this case, expressions such as "substrate portion 10a, 10b", "cylindrical portion 11a, 11b", "partition portion 12a, 12b", "cell 13a, 13a", and "length L10a, L10b" will be used. These expressions mean "substrate portion 10a", "cylindrical portion 11a", "partition portion 12a", "cell 13a", and "length L10a" for the first substrate portion 10a, and mean "substrate portion 10b", "cylindrical portion 11b", "partition portion 12b", "cell 13b", and "length L10b" for the second substrate portion 10b.

[0057] The material constituting the substrate parts 10a, 10b can be appropriately selected from known materials. Examples of the material constituting the substrate parts 10a, 10b include ceramic materials and metal materials, but ceramic materials are preferred. Examples of the ceramic material include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide, nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride, and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of the metal material include alloys such as stainless steel.

[0058] The material constituting the base portion 10a and the material constituting the base portion 10b are usually the same.

[0059] 2 to 6, the base members 10a and 10b each have a cylindrical portion 11a, 11b, partition walls 12a, 12b provided in the cylindrical portions 11a, 11b, and cells 13a, 13b separated by the partition walls 12a, 12b. The base members 10a, 10b are preferably honeycomb structures.

[0060] 2 and 3, the tubular portions 11a and 11b define the outer shapes of the base portions 10a and 10b, and the axial directions of the tubular portions 11a and 11b coincide with the axial directions of the base portions 10a and 10b. As shown in Figs. 2 and 3, the tubular portions 11a and 11b have a cylindrical shape, but may have other shapes such as an elliptical cylindrical shape or a polygonal cylindrical shape.

[0061] 2 to 6, partition walls 12a and 12b are present between adjacent cells 13a and 13b, and adjacent cells 13a and 13b are separated by the partition walls 12a and 12b. The partition walls 12a and 12b may have a porous structure that allows exhaust gas to pass through. The thickness of the partition walls 12a and 12b is, for example, 20 μm or more and 1500 μm or less.

[0062] As shown in FIG. 6, the cells 13a and 13b extend in the exhaust gas flow direction X, and have an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0063] As shown in FIG. 6, both the exhaust gas inflow end and the exhaust gas outflow end of the cells 13a, 13b are open.

[0064] As shown in FIG. 6, the end (opening) of cell 13a on the exhaust gas outflow side and the end (opening) of cell 13b on the exhaust gas inflow side are continuous so that one cell 13a and one cell 13b form one exhaust gas flow path extending in the exhaust gas flow direction X.

[0065] Exhaust gas flowing in from the end (opening) of the cell 13a on the exhaust gas inlet side flows out from the end (opening) of the cell 13a on the exhaust gas outlet side. Exhaust gas flowing out from the end (opening) of the cell 13a on the exhaust gas outlet side flows into cell 13b from the end (opening) of the cell 13b on the exhaust gas inlet side, and flows out from the end (opening) of the cell 13b on the exhaust gas outlet side. This type of system is called a flow-through type.

[0066] 2 to 5, the end (opening) of the cells 13a, 13b on the exhaust gas inflow side has a rectangular shape in plan view, but may have other shapes such as a hexagon, an octagon, etc. The end (opening) of the cells 13a, 13b on the exhaust gas outflow side also has a similar shape in plan view.

[0067] The cell density per square inch of the substrate parts 10a, 10b is, for example, from 100 cells to 1200 cells. The cell density per square inch of the substrate parts 10a, 10b means the total number of cells 13a, 13b per square inch in a cross section obtained by cutting the substrate parts 10a, 10b along a plane perpendicular to the exhaust gas flow direction X.

[0068] The substrate portions 10a and 10b have lengths L10a and L10b.

[0069] The volume of the substrate parts 10a, 10b is, for example, 0.1 L or more and 20 L or less. The volume of the substrate parts 10a, 10b means the apparent volume of the substrate parts 10a, 10b. For example, when the substrate parts 10a, 10b are cylindrical and the outer diameter of the substrate parts 10a, 10b is 2r, the volume of the substrate parts 10a, 10b is calculated by the formula: Volume of substrate parts 10a, 10b = π × r 2 ×(length L10a, 10b).

[0070] The percentage (L10a / (L10a+L10b)×100) of the length L10a of the first substrate portion 10a to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b is preferably 15% or more and 80% or less, more preferably 18% or more and 70% or less, and even more preferably 20% or more and 60% or less. In one example, the percentage (L10a / (L10a+L10b)×100) of the length L10a of the first substrate portion 10a to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b is 50%.

[0071] The percentage (L10b / (L10a+L10b)×100) of the length L10b of the second substrate portion 10b to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b is preferably 20% or more and 85% or less, more preferably 30% or more and 82% or less, and even more preferably 40% or more and 80% or less. In one example, the percentage (L10b / (L10a+L10b)×100) of the length L10b of the second substrate portion 10b to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b is 50%.

[0072] <First catalyst layer> The first catalyst layer 20 will be described below.

[0073] As shown in FIGS. 4 and 6, the first catalyst layer 20 is provided on the upstream side of the substrate 10 (i.e., the first substrate portion 10a). Specifically, the first catalyst layer 20 is provided on the cell 13a side surface of the partition portion 12a. "The cell 13a side surface of the partition portion 12a" means the outer surface of the partition portion 12a extending in the exhaust gas flow direction X. The first catalyst layer 20 may be provided directly on the cell 13a side surface of the partition portion 12a or may be provided via another layer, but is usually provided directly on the cell 13a side surface of the partition portion 12a.

[0074] The first catalytic layer 20 may be composed of a portion (hereinafter referred to as a "protruding portion") protruding from the cell 13a side surface of the partition section 12a toward the cell 13a side, or may be composed of a portion (hereinafter referred to as an "internal portion") present inside the partition section 12a, or may have both a protruding portion and an internal portion. The "first catalytic layer 20 provided on the upstream side of the substrate 10" includes any of an embodiment in which the first catalytic layer 20 is composed of a protruding portion, an embodiment in which the first catalytic layer 20 is composed of an internal portion, and an embodiment in which the first catalytic layer 20 has both a protruding portion and an internal portion.

[0075] 6, the first catalyst layer 20 extends from an end of the partition section 12a on the exhaust gas inlet side to an end of the partition section 12a on the exhaust gas outlet side along the exhaust gas flow direction X. The first catalyst layer 20 may extend from an end of the partition section 12a on the exhaust gas inlet side along the exhaust gas flow direction X so as not to reach an end of the partition section 12a on the exhaust gas outlet side, or may extend from an end of the partition section 12a on the exhaust gas outlet side along the direction opposite to the exhaust gas flow direction X so as not to reach an end of the partition section 12a on the exhaust gas inlet side.

[0076] From the viewpoint of more effectively achieving an improvement in the temperature rise property of the first catalyst layer 20, which is required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start-up of an internal combustion engine, the mass (mass after calcination) of the first catalyst layer 20 per unit volume of the portion of the substrate 10 on which the first catalyst layer 20 is formed, i.e., the mass (mass after calcination) of the first catalyst layer 20 per unit volume of the portion of the first substrate portion 10a on which the first catalyst layer 20 is formed, is preferably 60 g / L or more and 200 g / L or less, more preferably 70 g / L or more and 175 g / L or less, even more preferably 80 g / L or more and 150 g / L or less, and even more preferably 90 g / L or more and 125 g / L or less. The mass of the first catalyst layer 20 per unit volume of the portion of the first substrate part 10a on which the first catalyst layer 20 is formed is calculated from the formula: (mass of the first catalyst layer 20) / ((volume of the first substrate part 10a)×(average length L20 of the first catalyst layer 20 / length L10a of the first substrate part 10a). The "length" refers to the dimension in the axial direction of the first substrate part 10a.

[0077] In this specification, the "mass of the first catalytic layer 20" refers to the sum of the masses of precious metal elements in metal equivalent and the masses of metal elements other than precious metal elements in oxide equivalent of all metal elements contained in the first catalytic layer 20. In other words, the "mass of the first catalytic layer 20" refers to the calculated mass obtained by summing the masses of precious metal elements contained in the first catalytic layer 20 in metal equivalent and the masses of metal elements other than precious metal elements contained in the first catalytic layer 20 in oxide equivalent. The "metal elements" also include metalloid elements such as Si and B.

[0078] In this specification, the term "precious metal element" includes Pt (platinum element), Pd (palladium element), Rh (rhodium element), Ru (ruthenium element), Os (osmium element), Ir (iridium element), Au (gold) and Ag (silver).

[0079] The meaning of "oxide" is as described in the "Explanation of Terms" section above.

[0080] An example of a method for measuring the average length L20 of the first catalyst layer 20 is as follows.

[0081] A sample is cut out from the catalyst 1A, which extends in the axial direction of the first substrate portion 10a and has the same length as the length L10a of the first substrate portion 10a. The sample is, for example, cylindrical with a diameter of 25.4 mm. The diameter of the sample can be changed as necessary. When the first catalyst layer 20 extends from the end of the partition portion 12a on the exhaust gas inlet side along the exhaust gas flow direction X, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the first substrate portion 10a, and the first cut piece, the second cut piece, ..., the nth cut piece are obtained in order from the end of the sample on the exhaust gas inlet side. When the first catalyst layer 20 extends from the end of the partition portion 12a on the exhaust gas outlet side along the direction opposite to the exhaust gas flow direction X, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the first substrate portion 10a, and the first cut piece, the second cut piece, ..., the nth cut piece are obtained in order from the end of the sample on the exhaust gas outlet side. In either case, the length of the cut piece is 5 mm. The composition of the cut piece is analyzed using an X-ray fluorescence analyzer (XRF) (e.g., an energy dispersive X-ray analyzer (EDX), a wavelength dispersive X-ray analyzer (WDX), etc.), an inductively coupled plasma atomic emission spectrometer (ICP-AES), a scanning electron microscope-energy dispersive X-ray analysis method (SEM-EDX), etc., and it is confirmed whether the cut piece contains a part of the first catalyst layer 20 based on the composition of the cut piece.

[0082] It is not necessary to perform a composition analysis on a cut piece that clearly contains a part of the first catalytic layer 20. For example, a scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), or the like can be used to observe the cut surface to confirm whether or not the cut piece contains a part of the first catalytic layer 20. When observing the cut surface, elemental mapping of the cut surface may be performed.

[0083] After confirming whether the cut piece contains a part of the first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is calculated based on the following formula. Length of the first catalytic layer 20 included in the sample = 5 mm x (number of cut pieces including a part of the first catalytic layer 20)

[0084] For example, if the first through kth cut pieces include a portion of the first catalytic layer 20, but the (k+1)th through nth cut pieces do not include a portion of the first catalytic layer 20, the length of the first catalytic layer 20 included in the sample is (5×k) mm.

[0085] An example of a more detailed method for measuring the length of the first catalyst layer 20 included in a sample is as follows. The k-th cut piece (a cut piece obtained from the exhaust gas outlet side of the sample among the cut pieces including a part of the first catalyst layer 20 when the first catalyst layer 20 extends from the end of the exhaust gas inlet side of the partition portion 12a along the exhaust gas flow direction X, and a cut piece obtained from the exhaust gas inlet side of the sample among the cut pieces including a part of the first catalyst layer 20 when the first catalyst layer 20 extends from the end of the exhaust gas outflow side of the partition portion 12a along the direction opposite to the exhaust gas flow direction X) is cut in the axial direction of the first substrate portion 10a, and the part of the first catalyst layer 20 present on the cut surface is observed using SEM, EPMA, or the like, to measure the length of the part of the first catalyst layer 20 in the k-th cut piece. Then, the length of the first catalyst layer 20 included in the sample is calculated based on the following formula. Length of the first catalyst layer 20 included in the sample=(5 mm×(k−1))+(length of the part of the first catalyst layer 20 included in the kth cut piece)

[0086] For 8 to 16 samples arbitrarily cut out from the catalyst 1A, the length of the first catalyst layer 20 contained in each sample is measured, and the average value thereof is taken as the average length L20 of the first catalyst layer 20.

[0087] From the viewpoint of more effectively realizing an improvement in the temperature rise property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, the percentage (L20 / L10a×100) of the average length L20 of the first catalyst layer 20 to the length L10a of the first substrate portion 10a is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100% or more. As described later, when the end of the first catalyst layer 20 on the exhaust gas outflow side has a portion overlapping the end of the second catalyst layer 30 on the exhaust gas inflow side, the percentage may exceed 100%. When the percentage exceeds 100%, the upper limit of the percentage is preferably 600% or less, more preferably 400% or less, and even more preferably 300% or less. In addition, when the first substrate portion 10a and the second substrate portion 10b are integral, and when the first substrate portion 10a and the second substrate portion 10b are separate and the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b are in contact, this percentage can exceed 100%. However, when the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b, this percentage does not exceed 100%.

[0088] From the viewpoint of more effectively achieving the improvement in the temperature rise property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start-up of the internal combustion engine, the percentage of the average length L20 of the first catalyst layer 20 to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L20 / (L10a+L10b)×100) is preferably 15% or more and 80% or less, more preferably 18% or more and 70% or less, and even more preferably 20% or more and 60% or less.

[0089] The first catalytic layer 20 contains one or more kinds of precious metal elements as catalytically active components. The precious metal elements can be selected from, for example, Pd, Pt, Rh, Au, Ag, Ir, Ru, Os, and the like. The precious metal elements are contained in the first catalytic layer 20 in a form capable of functioning as catalytically active components, for example, in the form of catalytically active components containing precious metal elements, such as metals, alloys containing precious metal elements, and compounds containing precious metal elements (for example, oxides of precious metal elements). From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements are preferably in the form of particles.

[0090] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of the precious metal element in the first catalytic layer 20 in terms of metal conversion is preferably 0.1 mass % or more and 10 mass % or less, more preferably 0.2 mass % or more and 9 mass % or less, and even more preferably 0.3 mass % or more and 8 mass % or less, based on the mass of the first catalytic layer 20. The "content of the precious metal element in terms of metal conversion" means the content of one precious metal element in terms of metal conversion when the first catalytic layer 20 contains one type of precious metal element, and means the total content of the two or more precious metal elements in terms of metal conversion when the first catalytic layer 20 contains two or more types of precious metal elements.

[0091] The first catalyst layer 20 preferably contains Pd and / or Pt.

[0092] Since the first catalytic layer 20 is provided upstream of the second catalytic layer 30, the temperature of the exhaust gas with which the first catalytic layer 20 comes into contact tends to be higher than the temperature of the exhaust gas with which the second catalytic layer 30 comes into contact. Therefore, it is preferable that the first catalytic layer 20 contains Pd. This is because Pd has excellent heat resistance. The first catalytic layer 20 may contain Pt in addition to Pd.

[0093] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pd in ​​the first catalytic layer 20 in terms of metal is preferably 0.1 mass % or more and 10 mass % or less, more preferably 0.2 mass % or more and 9 mass % or less, and even more preferably 0.3 mass % or more and 8 mass % or less, based on the mass of the first catalytic layer 20.

[0094] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pt in the first catalytic layer 20 in terms of metal is preferably 0.1 mass % or more and 10 mass % or less, more preferably 0.2 mass % or more and 9 mass % or less, and even more preferably 0.3 mass % or more and 8 mass % or less, based on the mass of the first catalytic layer 20.

[0095] The metal-equivalent content of each metal element in the first catalytic layer 20 is calculated from the formula: (metal-equivalent mass of each metal element in the first catalytic layer 20) / (mass of the first catalytic layer 20)×100. For example, the metal-equivalent content of Pd in ​​the first catalytic layer 20 is calculated from the formula: (metal-equivalent mass of Pd in ​​the first catalytic layer 20) / (mass of the first catalytic layer 20)×100.

[0096] When the composition of the raw materials used to form the first catalytic layer 20 is known, the metal-equivalent content of each metal element in the first catalytic layer 20 can be determined from the composition of the raw materials used to form the first catalytic layer 20.

[0097] When the composition of the raw material used to form the first catalytic layer 20 is unknown, the content of each metal element in the first catalytic layer 20 in terms of metal can be determined by a conventional method such as SEM-EDX. Specifically, the method is as follows.

[0098] The sample obtained from the first catalytic layer 20 is subjected to elemental analysis using a standard 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. The content (mass%) of each metal element is determined for each of 10 SEM visual fields, and the average value of the content (mass%) of each metal element in the 10 visual fields is taken as the content (mass%) of each metal element in the first catalytic layer 20.

[0099] The first catalyst layer 20 contains a Ce-Zr based composite oxide. The Ce-Zr based composite oxide has an oxygen storage capacity. Therefore, since the first catalyst layer 20 contains a Ce-Zr based composite oxide, even if the oxygen concentration in the exhaust gas fluctuates, the exhaust gas purification capacity of the catalyst 1A can be sufficiently exhibited.

[0100] In order to improve the heat resistance and oxygen storage capacity of Ce-Zr based composite oxides, the CeO 2 and ZrO 2 The total content calculated based on the mass of the Ce-Zr based composite oxide is preferably 70 mass% or more, more preferably 75 mass% or more, even more preferably 80 mass% or more, and even more preferably 85 mass% or more. The upper limit is 100 mass%.

[0101] From the viewpoint of improving the oxygen storage capacity of Ce-Zr based composite oxides, the CeO 2 The converted content is preferably 5 mass% or more and 95 mass% or less, more preferably 5 mass% or more and 90 mass% or less, even more preferably 7 mass% or more and 90 mass% or less, and even more preferably 10 mass% or more and 85 mass% or less, based on the mass of the Ce-Zr based composite oxide.

[0102] In order to improve the heat resistance of Ce-Zr based composite oxides, the Zr in the Ce-Zr based composite oxides was converted to ZrO 2 The converted content is preferably 5 mass% or more and 95 mass% or less, more preferably 5 mass% or more and 90 mass% or less, even more preferably 7 mass% or more and 90 mass% or less, and even more preferably 10 mass% or more and 85 mass% or less, based on the mass of the Ce-Zr based composite oxide.

[0103] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the content of the Ce-Zr-based composite oxide in the first catalytic layer 20 is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, and even more preferably 80 mass% or more, based on the mass of the first catalytic layer 20. The upper limit can be appropriately adjusted in consideration of the contents of other components in the first catalytic layer 20. The content of the Ce-Zr-based composite oxide in the first catalytic layer 20 can be adjusted to, for example, 99 mass% or less, 95 mass% or less, 93 mass% or less, or 90 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.

[0104] When the composition of the raw materials used to form the first catalytic layer 20 is known, the content of the Ce-Zr-based composite oxide in the first catalytic layer 20 can be determined from the composition of the raw materials used to form the first catalytic layer 20.

[0105] When the composition of the raw material used to form the first catalytic layer 20 is unknown, the content of the Ce-Zr based composite oxide in the first catalytic layer 20 can be determined by a conventional method such as SEM-EDX. Specifically, the method is as follows.

[0106] (1) For the sample obtained from the first catalyst layer 20, elemental analysis is performed using a standard 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 element. (2) For the sample obtained from the first catalytic layer 20, elemental mapping is performed using a standard method such as SEM-EDX to identify the types of particles contained in the sample (e.g., Ce-Zr based composite oxide particles and possibly other particles). (3) For each type of particle, randomly selected multiple particles (e.g., 50 particles) are subjected to elemental analysis using SEM-EDX to identify the types of constituent elements of the particles and to determine the content (mass%) of each identified element. The average content (mass%) of each element is calculated for each type of particle. (4) An equation expressing the relationship between the content (mass%) of each element in the sample, the content (mass%) of each element in each type of particle, and the content (mass%) of each type of particle in the sample is created and solved to calculate the content (mass%) of each type of particle in the sample, and this is the content (mass%) of each type of particle in the first catalyst layer 20.

[0107] The first catalyst layer 20 is Al 2 O 3 may also include

[0108] The first catalyst layer 20 is Al 2 O 3 In the case where the first catalyst layer 20 contains one or more types of Al 2 O 3 Contains sources. Al 2 O 3 The source is not particularly limited as long as it is an oxide containing Al. 2 O 3 The source can be selected from, for example, Al-based oxides, Ce-based oxides containing Al, Ce-Zr-based composite oxides containing Al, alumina binders, and the like.

[0109] In one embodiment, the first catalyst layer 20 is Al 2 O 3 The first catalyst layer 20 contains an alumina binder as a source of the Al 2 O 3 The source may contain only alumina binder or Al 2 O 3 As a source, one or more types of Al other than alumina binder 2 O 3 The device may include a source.

[0110] In order to more effectively improve the temperature rise property of the first catalyst layer 20, which is required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of an internal combustion engine, the Al content of the Al in the first catalyst layer 20 is 2 O 3The content in terms of Al is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 3 mass% or less, based on the mass of the first catalytic layer 20. The lower limit can be appropriately adjusted taking into consideration the contents of other components in the first catalytic layer 20. 2 O 3 The content of Al converted from Al may be, for example, 0 mass %, 0.1 mass % or more, 1 mass % or more, or 2 mass % or more based on the mass of the first catalytic layer 20. Each of these lower limits may be combined with any of the above-mentioned upper limits. 2 O 3 The "converted content" is calculated by dividing the first catalyst layer 20 by the amount of one type of Al. 2 O 3 If it contains an Al source, 2 O 3 Al derived from sources 2 O 3 The first catalyst layer 20 has two or more kinds of Al. 2 O 3 If the source contains more than one Al source, 2 O 3 Al derived from sources 2 O 3 This means the total content of the conversion.

[0111] When the composition of the raw material used to form the first catalytic layer 20 is known, the Al content of the first catalytic layer 20 can be calculated by the following formula: 2 O 3 The converted content can be determined from the composition of the raw materials used to form the first catalyst layer 20.

[0112] When the composition of the raw material used to form the first catalytic layer 20 is unknown, the amount of Al in the first catalytic layer 20 is not known. 2 O 3 The converted content can be determined by a conventional method such as SEM-EDX. Specifically, it is as follows.

[0113] The sample obtained from the first catalytic layer 20 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 Al content of Al. 2 O 3 The converted content (mass%) of Al is calculated for each of the 10 SEM fields of view. 2 O 3 The converted content (mass%) of Al was calculated for 10 visual fields. 2 O 3 The average content (mass%) of Al in the first catalytic layer 20 was calculated as 2 O 3 The converted content is expressed as percentage by mass.

[0114] The first catalytic layer 20 may contain one or more supports other than the Ce—Zr based composite oxide.

[0115] The support other than the Ce-Zr-based composite oxide can be selected from, for example, inorganic oxides other than the Ce-Zr-based composite oxide. The inorganic oxide other than the Ce-Zr-based composite oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytically active component, the inorganic oxide other than the Ce-Zr-based composite oxide is preferably porous. When the first catalytic layer 20 contains an inorganic oxide other than the Ce-Zr-based composite oxide as a support, the inorganic oxide may or may not have oxygen storage capacity. In this specification, an inorganic oxide having oxygen storage capacity (OSC) may be referred to as an "OSC material".

[0116] Inorganic oxides other than the Ce-Zr composite oxide used as a support are distinguished from inorganic oxides used as binders (for example, inorganic oxide binders such as alumina binders, zirconia binders, titania binders, and silica binders).

[0117] Examples of inorganic oxides other than Ce-Zr composite oxides that can be used as supports include Al-based oxides, Ce-based oxides, oxides of rare earth elements other than Ce, and zirconia (ZrO 2 ), silica (SiO 2), titania (TiO 2 ), zeolite (aluminosilicate), MgO, ZnO, SnO 2 and the like.

[0118] At least a part of the catalytically active component is preferably supported on a Ce-Zr based composite oxide. When the first catalytic layer 20 contains a support other than a Ce-Zr based composite oxide, at least a part of the catalytically active component may be supported on a support other than the Ce-Zr based composite oxide.

[0119] "At least a part of the catalytically active component is supported on the carrier" means that at least a part of the catalytically active component is physically and / or chemically adsorbed or held on the outer surface and / or inner pore surface of the carrier. The fact that at least a part of the catalytically active component is supported on the carrier can be confirmed, for example, by using SEM-EDX. Specifically, when at least a part of the catalytically active component and the carrier are present in the same region in element mapping obtained by analyzing the cross section of the first catalyst layer 20 with SEM-EDX, it can be determined that at least a part of the catalytically active component is supported on the carrier.

[0120] The first catalyst layer 20 may contain components such as a binder and a stabilizer. Examples of the binder include inorganic oxide binders such as alumina sol, ceria sol, zirconia sol, titania sol, and silica sol. Examples of the stabilizer include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0121] Among the components in the first catalytic layer 20, Ce is mainly involved in the oxygen storage capacity. Therefore, in order to ensure that the catalyst 1A can fully exert its exhaust gas purification performance even when the oxygen concentration in the exhaust gas fluctuates, the Ce in the first catalytic layer 20 is reduced to CeO 2The content in terms of CeO in the first catalytic layer 20 is preferably 32 mass% or more, and more preferably 35 mass% or more, based on the mass of the first catalytic layer 20. The upper limit can be appropriately adjusted taking into consideration the contents of other components in the first catalytic layer 20. 2 The content of Ce in the first catalytic layer 20 in terms of CeO can be adjusted to, for example, 90 mass % or less, 80 mass % or less, 70 mass % or less, or 60 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. 2 When the first catalyst layer 20 contains one type of Ce source, the "concentration rate converted into CeO of Ce derived from the one type of Ce source" is 2 When the first catalytic layer 20 contains two or more Ce sources, the CeO content of Ce derived from the two or more Ce sources is calculated as 2 This means the total content of the conversion.

[0122] The Ce source is not particularly limited as long as it is an oxide containing Ce. The first catalytic layer 20 contains a Ce-Zr based composite oxide as a Ce source. The first catalytic layer 20 may contain one or more Ce sources other than the Ce-Zr based composite oxide. The Ce source other than the Ce-Zr based composite oxide can be selected from, for example, an Al based oxide containing Ce, a Ce oxide, a ceria binder, and the like.

[0123] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the Ce in the first catalyst layer 20 is changed to CeO 2 Of the converted mass, CeO 2 The proportion in terms of mass is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0124] When the composition of the raw material used to form the first catalytic layer 20 is known, the CeO 2 The converted content can be determined from the composition of the raw materials used to form the first catalyst layer 20.

[0125] When the composition of the raw material used to form the first catalytic layer 20 is unknown, the CeO 2 The converted content can be determined by a conventional method such as SEM-EDX. Specifically, it is as follows.

[0126] The sample obtained from the first catalyst layer 20 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 CeO 2 The converted content (mass%) of Ce was calculated for each of the 10 fields of view of the SEM. 2 The converted content (mass%) of Ce in 10 fields of view was calculated. 2 The average content (mass%) of Ce in the first catalyst layer 20 converted into CeO 2 The content is expressed as (mass%).

[0127] <Second catalyst layer> The second catalyst layer 30 will now be described.

[0128] As shown in FIGS. 5 and 6, the second catalyst layer 30 is provided on the downstream side of the substrate 10 (i.e., the second substrate portion 10b). Specifically, the second catalyst layer 30 is provided on the cell 13b side surface of the partition portion 12b. "The cell 13b side surface of the partition portion 12b" means the outer surface of the partition portion 12b extending in the exhaust gas flow direction X. The second catalyst layer 30 may be provided directly on the cell 13b side surface of the partition portion 12b or may be provided via another layer, but is usually provided directly on the cell 13b side surface of the partition portion 12b.

[0129] The second catalytic layer 30 may be composed of a portion protruding from the cell 13b side surface of the partition section 12b toward the cell 13b side (hereinafter referred to as a "protruding portion"), or may be composed of a portion present inside the partition section 12b (hereinafter referred to as an "internal portion"), or may have both a protruding portion and an internal portion. The "second catalytic layer 30 provided on the downstream side of the substrate 10" includes any of an embodiment in which the second catalytic layer 30 is composed of a protruding portion, an embodiment in which the second catalytic layer 30 is composed of an internal portion, and an embodiment in which the second catalytic layer 30 has both a protruding portion and an internal portion.

[0130] 6, the second catalyst layer 30 extends from the end of the exhaust gas outlet side of the partition wall portion 12b to the end of the exhaust gas inlet side of the partition wall portion 12b in the direction opposite to the exhaust gas flow direction X. The second catalyst layer 30 may extend from the end of the exhaust gas outlet side of the partition wall portion 12b in the direction opposite to the exhaust gas flow direction X so as not to reach the end of the exhaust gas inlet side of the partition wall portion 12b, or may extend from the end of the exhaust gas inlet side of the partition wall portion 12b along the exhaust gas flow direction X so as not to reach the end of the exhaust gas outlet side of the partition wall portion 12b.

[0131] 6, the second catalytic layer 30 is provided downstream of the first catalytic layer 20. "The second catalytic layer 30 is provided downstream of the first catalytic layer 20" means that the second catalytic layer 30 is present in a region downstream of the region where the first catalytic layer 20 is provided in the exhaust gas flow direction X.

[0132] 6, the end of the second catalyst layer 30 on the exhaust gas inlet side is in contact with the end of the first catalyst layer 20 on the exhaust gas outlet side at a boundary S. As shown in Fig. 6, the boundary S between the end of the first catalyst layer 20 on the exhaust gas outlet side and the end of the second catalyst layer 30 on the exhaust gas inlet side coincides with the boundary S between the end of the first substrate piece 10a on the exhaust gas outlet side and the end of the second substrate piece 10b on the exhaust gas inlet side.

[0133] The end of the second catalytic layer 30 on the exhaust gas inlet side may have a portion overlapping with the end of the first catalytic layer 20 on the exhaust gas outlet side (i.e., a portion located above the end of the first catalytic layer 20 on the exhaust gas outlet side and covering the end of the first catalytic layer 20 on the exhaust gas outlet side). The end of the first catalytic layer 20 on the exhaust gas outlet side may have a portion overlapping with the end of the second catalytic layer 30 on the exhaust gas inlet side (i.e., a portion located above the end of the second catalytic layer 30 on the exhaust gas inlet side and covering the end of the second catalytic layer 30 on the exhaust gas inlet side). These cases are also included in "the second catalytic layer 30 being provided downstream of the first catalytic layer 20".

[0134] The end of the second catalytic layer 30 on the exhaust gas inlet side may not be in contact with the end of the first catalytic layer 20 on the exhaust gas outlet side. In other words, a gap may be formed between the end of the first catalytic layer 20 on the exhaust gas outlet side and the end of the second catalytic layer 30 on the exhaust gas inlet side.

[0135] From the standpoint of more effectively suppressing the decrease in the dispersion degree of the catalytically active components after exposure to a high-temperature environment, which is required when the environment in which catalyst 1A is placed is a high-temperature environment during high-speed operation of an internal combustion engine, the mass (mass after calcination) of the second catalyst layer 30 per unit volume of the portion of the substrate 10 on which the second catalyst layer 30 is formed, i.e., the mass (mass after calcination) of the second catalyst layer 30 per unit volume of the portion of the second substrate portion 10b on which the second catalyst layer 30 is formed, is preferably 60 g / L or more and 200 g / L or less, more preferably 80 g / L or more and 200 g / L or less, and even more preferably 100 g / L or more and 190 g / L or less. The mass of the second catalyst layer 30 per unit volume of the portion of the second substrate part 10b on which the second catalyst layer 30 is formed is calculated from the formula: (mass of the second catalyst layer 30) / ((volume of the second substrate part 10b)×(average length L30 of the second catalyst layer 30 / length L10b of the second substrate part 10b). The "length" refers to the dimension in the axial direction of the second substrate part 10b.

[0136] The above description regarding the mass of the first catalytic layer 20 also applies to the mass of the second catalytic layer 30. When applied, the "first catalytic layer 20" is replaced with the "second catalytic layer 30".

[0137] The above description regarding the method for measuring the average length L20 of the first catalytic layer 20 also applies to the method for measuring the average length L30 of the second catalytic layer 30. When applied, the "first catalytic layer 20" is replaced with the "second catalytic layer 30", and the "average length L20" is replaced with the "average length L30".

[0138] In order to more effectively suppress the decrease in the degree of dispersion of the catalytically active components after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of an internal combustion engine, the percentage (L30 / L10b×100) of the average length L30 of the second catalyst layer 30 to the length L10b of the second substrate portion 10b is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100% or more. As described above, when the end of the second catalyst layer 30 on the exhaust gas inlet side has a portion overlapping the end of the first catalyst layer 20 on the exhaust gas outlet side, the percentage may exceed 100%. When the percentage exceeds 100%, the upper limit of the percentage is preferably 500% or less, more preferably 350% or less, and even more preferably 200% or less. In addition, when the first substrate portion 10a and the second substrate portion 10b are integral, and when the first substrate portion 10a and the second substrate portion 10b are separate and the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b are in contact, this percentage can exceed 100%. However, when the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b, this percentage does not exceed 100%.

[0139] From the viewpoint of more effectively suppressing the decrease in the dispersion degree of the catalytically active components after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of an internal combustion engine, the percentage of the average length L30 of the second catalyst layer 30 to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L30 / (L10a+L10b)×100) is preferably 20% or more and 95% or less, more preferably 30% or more and 92% or less, and even more preferably 40% or more and 90% or less.

[0140] From the viewpoint of more effectively realizing the improvement of the temperature rise property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the degree of dispersion of the catalytically active components after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the percentage ((L20 and L30) / (L10a+L10b)×100) of the sum of the average length L20 of the first catalyst layer 20 and the average length L30 of the second catalyst layer 30 to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b is preferably 35% or more, more preferably 48% or more, and even more preferably 60% or more. The upper limit may be 100% or more. As described above, the percentage may exceed 100% when the end of the exhaust gas outlet side of the first catalytic layer 20 has a portion overlapping with the end of the exhaust gas inlet side of the second catalytic layer 30, and when the end of the exhaust gas inlet side of the second catalytic layer 30 has a portion overlapping with the end of the exhaust gas outlet side of the first catalytic layer 20. The upper limit of the percentage is preferably 175% or less, more preferably 162% or less, and even more preferably 150% or less. In addition, when the first substrate portion 10a and the second substrate portion 10b are integral, and when the first substrate portion 10a and the second substrate portion 10b are separate and the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b are in contact, this percentage can exceed 100%. However, when the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b, this percentage does not exceed 100%.

[0141] From the viewpoint of more effectively realizing the improvement of the temperature rise property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the ratio of the mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 in which the second catalyst layer 30 is formed (i.e., the mass of the second catalyst layer 30 per unit volume of the portion of the second substrate portion 10b in which the second catalyst layer 30 is formed) to the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 in which the first catalyst layer 20 is formed (i.e., the mass of the first catalyst layer 20 per unit volume of the portion of the first substrate portion 10a in which the first catalyst layer 20 is formed) is preferably 0.95 or less, more preferably 0.93 or less, and even more preferably 0.90 or less. From the viewpoint, the ratio is preferably 0.30 or more, more preferably 0.40 or more. Each of these lower limits may be combined with any of the upper limits mentioned above.

[0142] From the viewpoint of more effectively realizing the improvement of the temperature rise property of the first catalyst layer 20 required when the environment in which the catalyst 1A is placed is a low-temperature environment immediately after the start of the internal combustion engine, and the suppression of the decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of the internal combustion engine, the ratio of the average length L20 of the first catalyst layer 20 to the average length L30 of the second catalyst layer 30 is preferably 1.0 or less, more preferably 0.8 or less, and even more preferably 0.7 or less. From the viewpoint, the ratio is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. Each of these lower limits may be combined with any of the above-mentioned upper limits.

[0143] The second catalytic layer 30 contains one or more kinds of precious metal elements as catalytically active components. The precious metal elements can be selected from, for example, Pd, Pt, Rh, Au, Ag, Ir, Ru, Os, and the like. The precious metal elements are contained in the second catalytic layer 30 in a form capable of functioning as catalytically active components, for example, in the form of catalytically active components containing precious metal elements, such as metals, alloys containing precious metal elements, and compounds containing precious metal elements (for example, oxides of precious metal elements). From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements are preferably in the form of particles.

[0144] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of the precious metal element in the second catalytic layer 30, in terms of metal conversion, is preferably 0.01 mass % or more and 5 mass % or less, more preferably 0.02 mass % or more and 4 mass % or less, and even more preferably 0.03 mass % or more and 3 mass % or less, based on the mass of the second catalytic layer 30. The "content of the precious metal element in terms of metal conversion" means the content of one precious metal element in terms of metal conversion when the second catalytic layer 30 contains one type of precious metal element, and means the total content of the two or more precious metal elements in terms of metal conversion when the second catalytic layer 30 contains two or more types of precious metal elements.

[0145] The second catalyst layer 30 preferably contains Pd and / or Pt.

[0146] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pd in ​​the second catalytic layer 30 in terms of metal, based on the mass of the second catalytic layer 30, is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.02 mass% or more and 4 mass% or less, and even more preferably 0.03 mass% or more and 3 mass% or less.

[0147] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Pt in the second catalyst layer 30 in terms of metal, based on the mass of the second catalyst layer 30, is preferably 0.01 mass% or more and 5 mass% or less, more preferably 0.02 mass% or more and 4 mass% or less, and even more preferably 0.03 mass% or more and 3 mass% or less.

[0148] The metal-equivalent content of each metal element in the second catalytic layer 30 is calculated from the formula: (metal-equivalent mass of each metal element in the second catalytic layer 30) / (mass of the second catalytic layer 30)×100. For example, the metal-equivalent content of Pd in ​​the second catalytic layer 30 is calculated from the formula: (metal-equivalent mass of Pd in ​​the second catalytic layer 30) / (mass of the second catalytic layer 30)×100.

[0149] The content of each metal element in the second catalytic layer 30 in terms of metal can be determined in the same manner as the content of each metal element in the first catalytic layer 20 in terms of metal.

[0150] The second catalyst layer 30 is Al 2 O 3 Therefore, the second catalyst layer 30 contains one or more types of Al. 2 O 3 Includes source.

[0151] Al 2 O 3 The source is not particularly limited as long as it is an oxide containing Al. 2 O 3 The source can be selected from, for example, Al-based oxides, Ce-based oxides containing Al, Ce-Zr-based composite oxides containing Al, alumina binders, and the like.

[0152] The second catalyst layer 30 is Al 2 O 3 The second catalyst layer 30 preferably contains an Al-based oxide as a source of the Al-based oxide. 2 O 3 In one embodiment, the second catalyst layer 30 may include an Al source. 2 O 3 The sources include Al-based oxides and alumina binder.

[0153] In order to more effectively suppress the decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of an internal combustion engine, the amount of Al in the second catalyst layer 30 is preferably 100%. 2 O 3The content in terms of Al is preferably 1 mass% or more, more preferably 3 mass% or more, even more preferably 5 mass% or more, and even more preferably 10 mass% or more, based on the mass of the second catalytic layer 30. The upper limit can be appropriately adjusted taking into consideration the contents of other components in the second catalytic layer 30. 2 O 3 The content of Al converted from Al is, for example, 90 mass % or less, 80 mass % or less, 70 mass % or less, or 60 mass % or less, based on the mass of the second catalyst layer 30. Each of these upper limits may be combined with any of the above-mentioned lower limits. 2 O 3 The "concentration rate converted from Al" is calculated based on the amount of Al in the second catalyst layer 30. 2 O 3 If it contains an Al source, 2 O 3 Al derived from sources 2 O 3 The second catalyst layer 30 has two or more kinds of Al. 2 O 3 If the source contains more than one Al source, 2 O 3 Al derived from sources 2 O 3 This means the total content of the conversion.

[0154] In order to more effectively suppress the decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of an internal combustion engine, the amount of Al in the second catalyst layer 30 is preferably 100%. 2 O 3 Of the converted mass, Al derived from Al-based oxides 2 O 3 The proportion in terms of mass is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0155] Al in the second catalytic layer 30 2 O 3 The converted content of Al in the first catalyst layer 20 is2 O 3 It can be calculated in the same manner as the converted content.

[0156] Al in the second catalyst layer 30 2 O 3 The effect of suppressing the decrease in the degree of dispersion of the catalytically active component after exposure to a high-temperature environment is thus the mass content of the precious metal element in the second catalytic layer 30 in terms of metal. 2 O 3 That is, in order to more effectively suppress the decrease in the degree of dispersion of the catalytically active components after exposure to a high-temperature environment, which is required when the environment in which the catalyst 1A is placed is a high-temperature environment during high-speed operation of an internal combustion engine, it is preferable that the ratio of the Al content in the second catalyst layer 30 to the mass content in metal conversion of the precious metal element in the second catalyst layer 30 is in proportion to the mass content in metal conversion of the precious metal element in the second catalyst layer 30. 2 O 3 The ratio of the converted mass content is preferably 50 or more and 600 or less, more preferably 100 or more and 500 or less, even more preferably 120 or more and 400 or less, and even more preferably 150 or more and 250 or less.

[0157] The second catalytic layer 30 preferably contains one or more types of carriers. The carriers can be selected from, for example, Ce-Zr based composite oxides and inorganic oxides other than Ce-Zr based composite oxides (e.g., Al based oxides, etc.). The explanation regarding the Ce-Zr based composite oxides and inorganic oxides other than Ce-Zr based composite oxides is the same as above.

[0158] The second catalyst layer 30 preferably contains an Al-based oxide as a carrier. 2 O 3 The second catalyst layer 30 may also include one or more supports other than the Al-based oxide. In one embodiment, the second catalyst layer 30 includes an Al-based oxide and an OSC material as a support. The OSC material can be selected from, for example, a Ce-based oxide, a Ce-Zr-based composite oxide, and the like, and is preferably a Ce-Zr-based composite oxide.

[0159] At least a part of the catalytically active component is preferably supported on a carrier. When the second catalytic layer 30 contains an Al-based oxide, at least a part of the catalytically active component is preferably supported on the Al-based oxide. When the second catalytic layer 30 contains a carrier other than an Al-based oxide, at least a part of the catalytically active component is preferably supported on a carrier other than an Al-based oxide. The meaning of "at least a part of the catalytically active component is supported on a carrier" and the confirmation method are the same as above.

[0160] The second catalyst layer 30 may contain components such as a binder and a stabilizer. Examples of the binder include inorganic oxide binders such as alumina sol, ceria sol, zirconia sol, titania sol, and silica sol. Examples of the stabilizer include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0161] Among the components in the second catalytic layer 30, Ce is mainly involved in the oxygen storage capacity. Therefore, from the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the Ce in the second catalytic layer 30 is changed to CeO 2 The content in terms of CeO in the second catalytic layer 30 is preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 20 mass% or more, and even more preferably 30 mass% or more, based on the mass of the second catalytic layer 30. The upper limit can be appropriately adjusted taking into consideration the contents of other components in the second catalytic layer 30. 2 The content of Ce in the second catalytic layer 30 in terms of CeO can be adjusted to, for example, 90 mass % or less, 80 mass % or less, 70 mass % or less, or 60 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. 2 When the second catalyst layer 30 contains one type of Ce source, the "concentration rate converted into CeO of Ce derived from the one type of Ce source" is 2 When the second catalytic layer 30 contains two or more Ce sources, the CeO content of Ce derived from the two or more Ce sources is calculated as 2 This means the total content of the conversion.

[0162] The Ce source is not particularly limited as long as it is an oxide containing Ce. The Ce source can be selected from, for example, an Al-based oxide containing Ce, a Ce-based oxide, a Ce-Zr-based composite oxide, a ceria binder, etc., and is preferably a Ce-Zr-based composite oxide.

[0163] From the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the Ce in the second catalyst layer 30 is changed to CeO 2 Of the converted mass, CeO 2 The proportion in terms of mass is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0164] CeO of Ce in the second catalyst layer 30 2 The content of Ce in the first catalyst layer 20 converted to CeO 2 It can be calculated in the same manner as the converted content.

[0165] <Third and fourth catalyst layers> As shown in FIGS. 4 to 6, the third catalyst layer 40 is provided above the first catalyst layer 20, and the fourth catalyst layer 50 is provided above the second catalyst layer 30.

[0166] The third catalyst layer 40 and the fourth catalyst layer 50 are layers provided as necessary and can be omitted. The present invention also includes an embodiment in which one or both of the third catalyst layer 40 and the fourth catalyst layer 50 are omitted from the catalyst 1A. However, from the viewpoint of improving the exhaust gas purification performance, it is preferable that one or both of the third catalyst layer 40 and the fourth catalyst layer 50 are provided. Specifically, by providing the third catalyst layer 40, it is possible to prevent phosphorus poisoning of the precious metal elements in the first catalyst layer 20, and by providing the fourth catalyst layer 50, it is possible to prevent phosphorus poisoning of the precious metal elements in the second catalyst layer 30. Pd and Pt, especially Pd, are susceptible to phosphorus poisoning. Therefore, when the first catalyst layer 20 contains Pd and / or Pt, it is preferable that the third catalyst layer 40 is provided, and when the second catalyst layer 30 contains Pd and / or Pt, it is preferable that the fourth catalyst layer 50 is provided.

[0167] "The third catalytic layer 40 is provided on the upper side of the first catalytic layer 20" means that a part or the whole of the third catalytic layer 40 is present on one of the two main surfaces of the first catalytic layer 20 opposite to the main surface on the partition wall portion 12a side. "The main surface of the first catalytic layer 20" means the outer surface of the first catalytic layer 20 extending in the exhaust gas flow direction X. The third catalytic layer 40 may be provided directly on the main surface of the first catalytic layer 20 or may be provided via another layer, but is usually provided directly on the main surface of the first catalytic layer 20. The third catalytic layer 40 may be provided so as to cover a part of the main surface of the first catalytic layer 20 or may be provided so as to cover the entire main surface of the first catalytic layer 20. The "third catalytic layer 40 provided on the upper side of the first catalytic layer 20" includes both an embodiment in which the third catalytic layer 40 is provided directly on the main surface of the first catalytic layer 20, and an embodiment in which the third catalytic layer 40 is provided on the main surface of the first catalytic layer 20 via another layer.

[0168] "The fourth catalyst layer 50 is provided on the upper side of the second catalyst layer 30" means that a part or the whole of the fourth catalyst layer 50 is present on one of the two main surfaces of the second catalyst layer 30 opposite to the main surface on the partition wall portion 12b side. "The main surface of the second catalyst layer 30" means the outer surface of the second catalyst layer 30 extending in the exhaust gas flow direction X. The fourth catalyst layer 50 may be provided directly on the main surface of the second catalyst layer 30 or may be provided via another layer, but is usually provided directly on the main surface of the second catalyst layer 30. The fourth catalyst layer 50 may be provided so as to cover a part of the main surface of the second catalyst layer 30 or may be provided so as to cover the entire main surface of the second catalyst layer 30. The "fourth catalyst layer 50 provided on the upper side of the second catalyst layer 30" includes both an embodiment in which the fourth catalyst layer 50 is provided directly on the main surface of the second catalyst layer 30, and an embodiment in which the fourth catalyst layer 50 is provided on the main surface of the second catalyst layer 30 via another layer.

[0169] 6, the third catalyst layer 40 extends along the exhaust gas flow direction X from the end of the partition section 12a on the exhaust gas inlet side to the end of the partition section 12a on the exhaust gas outlet side. The third catalyst layer 40 may extend along the exhaust gas flow direction X from the end of the partition section 12a on the exhaust gas inlet side so as not to reach the end of the partition section 12a on the exhaust gas outlet side, or may extend in the direction opposite to the exhaust gas flow direction X from the end of the partition section 12a on the exhaust gas outlet side so as not to reach the end of the partition section 12a on the exhaust gas inlet side.

[0170] 6, the fourth catalyst layer 50 extends from the end of the exhaust gas outlet side of the partition wall portion 12b to the end of the exhaust gas inlet side of the partition wall portion 12b in the direction opposite to the exhaust gas flow direction X. The fourth catalyst layer 50 may extend from the end of the exhaust gas outlet side of the partition wall portion 12b in the direction opposite to the exhaust gas flow direction X so as not to reach the end of the exhaust gas inlet side of the partition wall portion 12b, or may extend from the end of the exhaust gas inlet side of the partition wall portion 12b along the exhaust gas flow direction X so as not to reach the end of the exhaust gas outlet side of the partition wall portion 12b.

[0171] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass (mass after calcination) of the third catalyst layer 40 per unit volume of the portion of the substrate 10 where the third catalyst layer 40 is formed, i.e., the mass (mass after calcination) of the third catalyst layer 40 per unit volume of the portion of the first substrate part 10a where the third catalyst layer 40 is provided, is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 140 g / L or less, and even more preferably 50 g / L or more and 130 g / L or less. The mass of the third catalyst layer 40 per unit volume of the portion of the first substrate part 10a where the third catalyst layer 40 is provided is calculated from the formula: (mass of the third catalyst layer 40) / ((volume of the first substrate part 10a)×(average length L40 of the third catalyst layer 40 / length L10a of the first substrate part 10a)).

[0172] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass (mass after calcination) of the fourth catalyst layer 50 per unit volume of the portion of the substrate 10 where the fourth catalyst layer 50 is formed, i.e., the mass (mass after calcination) of the fourth catalyst layer 50 per unit volume of the portion of the second substrate part 10b where the fourth catalyst layer 50 is provided, is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 140 g / L or less, and even more preferably 50 g / L or more and 130 g / L or less. The mass of the fourth catalyst layer 50 per unit volume of the portion of the second substrate part 10b where the fourth catalyst layer 50 is provided is calculated from the formula: (mass of the fourth catalyst layer 50) / ((volume of the second substrate part 10b)×(average length L50 of the fourth catalyst layer 50 / length L10b of the second substrate part 10b)).

[0173] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the sum of the mass of the third catalyst layer 40 and the mass of the fourth catalyst layer 50 relative to the sum of the volume of the portion of the first substrate piece 10a where the third catalyst layer 40 is provided and the volume of the portion of the second substrate piece 10b where the fourth catalyst layer 50 is provided is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 140 g / L or less, and even more preferably 50 g / L or more and 130 g / L or less.

[0174] The above description regarding the mass of the first catalytic layer 20 also applies to the mass of the third catalytic layer 40 and the mass of the fourth catalytic layer 50. When applied, the "first catalytic layer 20" is replaced with the "third catalytic layer 40" and the "fourth catalytic layer 50", respectively.

[0175] The above description regarding the method for measuring the average length L20 of the first catalytic layer 20 also applies to the method for measuring the average length L40 of the third catalytic layer 40 and the average length L50 of the fourth catalytic layer 50. When applied, the "first catalytic layer 20" is replaced with the "third catalytic layer 40" and the "fourth catalytic layer 50", respectively, and the "average length L20" is replaced with the "average length L40" and the "average length L50", respectively.

[0176] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage (L40 / L10a×100) of the average length L40 of the third catalyst layer 40 to the length L10a of the first substrate portion 10a is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100% or more. As described later, when the end of the third catalyst layer 40 on the exhaust gas outlet side has a portion overlapping with the end of the fourth catalyst layer 50 on the exhaust gas inlet side, the percentage may exceed 100%. When the percentage exceeds 100%, the upper limit of the percentage is preferably 600% or less, more preferably 400% or less, and even more preferably 300% or less. In addition, when the first substrate portion 10a and the second substrate portion 10b are integral, and when the first substrate portion 10a and the second substrate portion 10b are separate and the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b are in contact, this percentage can exceed 100%. However, when the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b, this percentage does not exceed 100%.

[0177] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the average length L40 of the third catalyst layer 40 to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L40 / (L10a+L10b)×100) is preferably 15% or more and 80% or less, more preferably 18% or more and 70% or less, and even more preferably 20% or more and 60% or less.

[0178] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage (L50 / L10b×100) of the average length L50 of the fourth catalyst layer 50 to the length L10b of the second substrate portion 10b is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100% or more. As described later, when the end of the fourth catalyst layer 50 on the exhaust gas inlet side has a portion overlapping the end of the third catalyst layer 40 on the exhaust gas outlet side, the percentage may exceed 100%. When the percentage exceeds 100%, the upper limit of the percentage is preferably 500% or less, more preferably 350% or less, and even more preferably 200% or less. In addition, when the first substrate portion 10a and the second substrate portion 10b are integral, and when the first substrate portion 10a and the second substrate portion 10b are separate and the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b are in contact, this percentage can exceed 100%. However, when the first substrate portion 10a and the second substrate portion 10b are separate and a gap is formed between the exhaust gas outflow side end of the first substrate portion 10a and the exhaust gas inflow side end of the second substrate portion 10b, this percentage does not exceed 100%.

[0179] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage of the average length L50 of the fourth catalyst layer 50 to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b (L50 / (L10a+L10b)×100) is preferably 20% or more and 95% or less, more preferably 30% or more and 92% or less, and even more preferably 40% or more and 90% or less.

[0180] 6, the exhaust gas outflow side end of the third catalyst layer 40 and the exhaust gas inflow side end of the fourth catalyst layer 50 are in contact with each other at a boundary S. As shown in Fig. 6, the boundary S between the exhaust gas outflow side end of the third catalyst layer 40 and the exhaust gas inflow side end of the fourth catalyst layer 50 coincides with the boundary S between the exhaust gas outflow side end of the first substrate piece 10a and the exhaust gas inflow side end of the second substrate piece 10b.

[0181] The end of the third catalytic layer 40 on the exhaust gas outlet side may have a portion overlapping with the end of the fourth catalytic layer 50 on the exhaust gas inlet side (i.e., a portion located above the end of the fourth catalytic layer 50 on the exhaust gas inlet side and covering the end of the fourth catalytic layer 50 on the exhaust gas inlet side). Furthermore, the end of the fourth catalytic layer 50 on the exhaust gas inlet side may have a portion overlapping with the end of the third catalytic layer 40 on the exhaust gas outlet side (i.e., a portion located above the end of the third catalytic layer 40 on the exhaust gas outlet side and covering the end of the third catalytic layer 40 on the exhaust gas outlet side).

[0182] When the end of the third catalytic layer 40 on the exhaust gas outlet side and the end of the fourth catalytic layer 50 on the exhaust gas inlet side are in contact with each other at the boundary S, the end of the third catalytic layer 40 on the exhaust gas outlet side and the end of the fourth catalytic layer 50 on the exhaust gas inlet side may be continuous with each other. That is, the third catalytic layer 40 and the fourth catalytic layer 50 may be integrated to form a single catalytic layer.

[0183] The end of the third catalytic layer 40 on the exhaust gas outlet side and the end of the fourth catalytic layer 50 on the exhaust gas inlet side do not have to be in contact with each other. That is, a gap may be formed between the end of the third catalytic layer 40 on the exhaust gas outlet side and the end of the fourth catalytic layer 50 on the exhaust gas inlet side.

[0184] In one embodiment, the third catalyst layer 40 extends from the end of the partition section 12a on the exhaust gas inlet side to the end of the partition section 12a on the exhaust gas outlet side along the exhaust gas flow direction X, and the end of the third catalyst layer 40 on the exhaust gas outlet side and the end of the fourth catalyst layer 50 on the exhaust gas inlet side are in contact with each other at a boundary S. In this embodiment, the end of the third catalyst layer 40 on the exhaust gas outlet side and the end of the fourth catalyst layer 50 on the exhaust gas inlet side may be continuous with each other. In this embodiment, the fourth catalyst layer 50 may extend from the end of the exhaust gas inlet side of the partition section 12b to the end of the exhaust gas outlet side of the partition section 12b along the exhaust gas flow direction X, or may extend from the end of the exhaust gas inlet side of the partition section 12b along the exhaust gas flow direction X so as not to reach the end of the partition section 12b on the exhaust gas outlet side.

[0185] In another embodiment, the fourth catalyst layer 50 extends from the end of the exhaust gas outlet side of the partition wall 12b to the end of the exhaust gas inlet side of the partition wall 12b along the direction opposite to the exhaust gas flow direction X, and the end of the exhaust gas outlet side of the third catalyst layer 40 and the end of the exhaust gas inlet side of the fourth catalyst layer 50 are in contact with each other at a boundary S. In this embodiment, the end of the exhaust gas outlet side of the third catalyst layer 40 and the end of the exhaust gas inlet side of the fourth catalyst layer 50 may be continuous. In this embodiment, the third catalyst layer 40 may extend from the end of the exhaust gas outlet side of the partition wall 12a to the end of the exhaust gas inlet side of the partition wall 12a along the direction opposite to the exhaust gas flow direction X, or may extend from the end of the exhaust gas outlet side of the partition wall 12a along the direction opposite to the exhaust gas flow direction X so as not to reach the end of the exhaust gas inlet side of the partition wall 12a.

[0186] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the percentage ((L40 and L50) / (L10a+L10b)×100) of the sum of the average length L40 of the third catalyst layer 40 and the average length L50 of the fourth catalyst layer 50 to the sum of the length L10a of the first substrate portion 10a and the length L10b of the second substrate portion 10b is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. The upper limit may be 100% or more. As described above, when the end of the third catalyst layer 40 on the exhaust gas outflow side has a portion overlapping the end of the fourth catalyst layer 50 on the exhaust gas inflow side, and when the end of the fourth catalyst layer 50 on the exhaust gas inflow side has a portion overlapping the end of the third catalyst layer 40 on the exhaust gas outflow side, the percentage may exceed 100%. The upper limit of the percentage is preferably 175% or less, more preferably 162% or less, and even more preferably 150% or less. When the first substrate part 10a and the second substrate part 10b are integral, and when the first substrate part 10a and the second substrate part 10b are separate bodies and the end part of the first substrate part 10a on the exhaust gas outflow side and the end part of the second substrate part 10b on the exhaust gas inflow side are in contact with each other, the percentage can exceed 100%, but when the first substrate part 10a and the second substrate part 10b are separate bodies and a gap is formed between the end part of the first substrate part 10a on the exhaust gas outflow side and the end part of the second substrate part 10b on the exhaust gas inflow side, the percentage does not exceed 100%.

[0187] Hereinafter, common points between the third catalyst layer 40 and the fourth catalyst layer 50 will be described together with the third catalyst layer 40 and the fourth catalyst layer 50. In this regard, expressions such as "catalyst layer 40, 50", "length L40, L50", "substrate portion 10a, 10b", and "length L10a, L10b" will be used. These expressions mean "catalyst layer 40", "length L40", "substrate portion 10a", and "length L10a" for the third catalyst layer 40, and mean "catalyst layer 50", "length L50", "substrate portion 10b", and "length L10b" for the fourth catalyst layer 50.

[0188] The catalytic layer 40, 50 contains one or more kinds of precious metal elements as catalytically active components. The precious metal elements can be selected from, for example, Pd, Pt, Rh, Au, Ag, Ir, Ru, Os, and the like. The precious metal elements are contained in the catalytic layer 40, 50 in a form capable of functioning as catalytically active components, for example, in the form of catalytically active components containing precious metal elements, such as metals, alloys containing precious metal elements, and compounds containing precious metal elements (for example, oxides of precious metal elements). From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements are preferably in the form of particles.

[0189] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of the precious metal elements in the catalyst layers 40, 50 in terms of metal conversion is preferably 0.01 mass % or more and 5 mass % or less, more preferably 0.02 mass % or more and 3 mass % or less, and even more preferably 0.05 mass % or more and 2 mass % or less, based on the mass of the catalyst layers 40, 50. The "content of the precious metal elements in terms of metal conversion in the catalyst layers 40, 50" means the content of one precious metal element in terms of metal conversion when the catalyst layers 40, 50 contain one type of precious metal element, and means the total content of the two or more precious metal elements in terms of metal conversion when the catalyst layers 40, 50 contain two or more types of precious metal elements.

[0190] Since the catalyst layers 40 and 50 are provided on the upper side of the first catalyst layer 20 and the second catalyst layer 30, respectively, the precious metal elements in the catalyst layers 40 and 50 are more susceptible to phosphorus poisoning than the precious metal elements in the first catalyst layer 20 and the second catalyst layer 30. Therefore, it is preferable that the catalyst layers 40 and 50 each contain Rh. This is because Rh is a precious metal element that is less susceptible to phosphorus poisoning. In particular, when the first catalyst layer 20 and the second catalyst layer each contain Pd and / or Pt, it is preferable that the catalyst layers 40 and 50 each contain Rh. When the first catalyst layer and the second catalyst layer each contain Pd and / or Pt and the catalyst layers 40 and 50 each contain Rh, the exhaust gas purification performance of the catalyst 1A can be further improved.

[0191] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of Rh in the catalyst layers 40, 50 in terms of metal is preferably 0.01 mass % or more and 5 mass % or less, more preferably 0.02 mass % or more and 3 mass % or less, and even more preferably 0.05 mass % or more and 2 mass % or less, based on the mass of the catalyst layers 40, 50.

[0192] The content of each metal element in the catalyst layers 40, 50 in terms of metal can be calculated from the formula: (mass of each metal element in the catalyst layers 40, 50 in terms of metal) / (mass of the catalyst layers 40, 50) x 100. For example, the content of Rh in the catalyst layers 40, 50 in terms of metal can be calculated from the formula: (mass of Rh in the catalyst layers 40, 50 in terms of metal) / (mass of the catalyst layers 40, 50) x 100.

[0193] The content of each metal element in the catalyst layers 40 and 50 in terms of metal can be determined in the same manner as the content of each metal element in the first catalyst layer 20 in terms of metal.

[0194] The catalyst layers 40 and 50 preferably contain one or more types of carriers. The carriers can be selected from inorganic oxides, for example. The description of the inorganic oxides is the same as above.

[0195] It is preferred that at least a part of the catalytically active component is supported on a carrier. The meaning of "at least a part of the catalytically active component is supported on a carrier" and the method of confirming this are the same as those described above.

[0196] The catalyst layers 40, 50 may contain other components such as a binder and a stabilizer. Examples of the binder include inorganic oxide binders such as alumina sol, ceria sol, zirconia sol, titania sol, and silica sol. Examples of the stabilizer include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0197] The catalyst layers 40 and 50 are made of Al 2 O 3 The catalyst layers 40 and 50 may contain Al. 2 O 3In the case where the catalyst layer 40, 50 contains one or more types of Al 2 O 3 Includes source.

[0198] In order to improve the exhaust gas purification performance of the catalyst 1A, the amount of Al in the catalyst layers 40 and 50 is preferably 1.0 to 1.5. 2 O 3 The content in terms of Al is preferably 1 mass % or more, more preferably 10 mass % or more, and even more preferably 15 mass % or more, based on the mass of the catalyst layer 40, 50. The upper limit can be appropriately adjusted taking into consideration the contents of other components in the catalyst layer 40, 50. 2 O 3 The content in terms of Al is, for example, 80 mass % or less, 70 mass % or less, or 60 mass % or less, based on the mass of the catalyst layer 40, 50. Each of these upper limits may be combined with any of the above-mentioned lower limits. 2 O 3 The "converted content" of catalyst layers 40 and 50 is one type of Al. 2 O 3 If it contains an Al source, 2 O 3 Al derived from sources 2 O 3 The catalyst layers 40 and 50 are made of two or more types of Al. 2 O 3 If the source contains more than one Al source, 2 O 3 Al derived from sources 2 O 3 This means the total content of the conversion.

[0199] Al 2 O 3 The source is not particularly limited as long as it is an oxide containing Al. 2 O 3 The source can be selected from, for example, Al-based oxides, Ce-based oxides containing Al, Ce-Zr-based composite oxides containing Al, alumina binders, and the like.

[0200] The catalyst layers 40 and 50 are made of Al 2 O 3The catalyst layers 40 and 50 preferably contain an Al-based oxide as a source of the Al-based oxide. 2 O 3 In one embodiment, the catalyst layers 40, 50 may include an Al source. 2 O 3 The sources include Al-based oxides and alumina binder.

[0201] In order to improve the exhaust gas purification performance of the catalyst 1A, the amount of Al in the catalyst layers 40 and 50 is preferably 1.0 to 1.5. 2 O 3 Of the converted mass, Al derived from Al-based oxides 2 O 3 The proportion in terms of mass is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. The upper limit is 100% by mass.

[0202] Al in the catalyst layers 40 and 50 2 O 3 The converted content of Al in the first catalyst layer 20 is 2 O 3 It can be calculated in the same manner as the converted content.

[0203] Among the components in the catalyst layers 40 and 50, Ce is mainly involved in the oxygen storage capacity. Therefore, from the viewpoint of improving the exhaust gas purification performance of the catalyst 1A, the CeO 2 The content in terms of Ce is preferably 0.1 mass% or more, more preferably 1 mass% or more, even more preferably 3 mass% or more, and even more preferably 5 mass% or more, based on the mass of the catalyst layer 40, 50. The upper limit can be appropriately adjusted taking into consideration the contents of other components in the catalyst layer 40, 50. The CeO content of Ce in the catalyst layer 40, 50 2 The content of Ce in the catalyst layers 40 and 50 in terms of CeO can be adjusted to, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, based on the mass of the catalyst layers 40 and 50. Each of these upper limits may be combined with any of the lower limits described above. 2When the catalyst layer 40, 50 contains one type of Ce source, the "converted content" is the CeO content of Ce derived from the one type of Ce source. 2 When the catalyst layer 40, 50 contains two or more Ce sources, the CeO content of Ce derived from the two or more Ce sources is calculated. 2 This means the total content of the conversion.

[0204] The Ce source is not particularly limited as long as it is an oxide containing Ce. The Ce source can be selected from, for example, an Al-based oxide containing Ce, a Ce-based oxide, a Ce-Zr-based composite oxide, a ceria binder, etc., and is preferably a Ce-Zr-based composite oxide.

[0205] In order to improve the exhaust gas purification performance of the catalyst 1A, the amount of Ce in the catalyst layers 40 and 50 is reduced by CeO. 2 Of the converted mass, CeO 2 The proportion in terms of mass is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0206] CeO of Ce in the catalyst layers 40 and 50 2 The content of Ce in the first catalyst layer 20 converted to CeO 2 It can be calculated in the same manner as the converted content.

[0207] Second Embodiment Hereinafter, an exhaust gas purifying catalyst 1B (hereinafter referred to as "catalyst 1B") according to a second embodiment will be described with reference to FIG.

[0208] In catalyst 1B, the same components as those in catalyst 1A are designated by the same reference numerals as those in catalyst 1A. Except as otherwise specified below, the above description of catalyst 1A also applies to catalyst 1B.

[0209] Catalyst 1B differs from catalyst 1A in that the first substrate portion 10a and the second substrate portion 10b are separate bodies, whereas catalyst 1A in which the first substrate portion 10a and the second substrate portion 10b are integral with each other.

[0210] The present invention encompasses both an embodiment in which substrate 10 is composed of one substrate, such as catalyst 1A, and an embodiment in which substrate 10 is composed of two substrates, such as catalyst 1B.

[0211] As shown in FIG. 7, the first substrate portion 10a and the second substrate portion 10b are disposed in the exhaust passage in the exhaust pipe P such that the axial directions of the first substrate portion 10a and the second substrate portion 10b coincide or approximately coincide with the exhaust gas flow direction X.

[0212] As shown in FIG. 7, the axial direction of the first base material piece 10a and the axial direction of the second base material piece 10b may coincide or approximately coincide.

[0213] 7, a gap is formed between the end of the first substrate part 10a on the exhaust gas outflow side and the end of the second substrate part 10b on the exhaust gas inflow side. The distance between the end of the first substrate part 10a on the exhaust gas outflow side and the end of the second substrate part 10b on the exhaust gas inflow side is, for example, 5 to 1000 mm.

[0214] "The substrate 10 extends in the exhaust gas flow direction X" also includes an embodiment in which a gap is formed between the end of the first substrate portion 10a on the exhaust gas outflow side and the end of the second substrate portion 10b on the exhaust gas inflow side, and in which the axial directions of the first substrate portion 10a and the second substrate portion 10b coincide or approximately coincide with the exhaust gas flow direction X.

[0215] The end of the first substrate part 10a on the exhaust gas outlet side and the end of the second substrate part 10b on the exhaust gas inlet side may be in contact with each other. In this case, the arrangement of the first substrate part 10a and the second substrate part 10b may be the same as that shown in FIG.

[0216] <Catalyst Production> Catalysts 1A and 1B can each be produced by forming a first catalyst layer 20 on a first substrate portion 10a, forming a second catalyst layer 30 on a second substrate portion 10b, forming a third catalyst layer 40 on the first catalyst layer 20, and forming a fourth catalyst layer 50 on the second catalyst layer 30.

[0217] The first catalyst layer 20 and the second catalyst layer 30 may be formed on the first substrate portion 10a and the second substrate portion 10b, respectively, and then the third catalyst layer 40 and the fourth catalyst layer 50 may be formed on the first catalyst layer 20 and the second catalyst layer 30, respectively. Alternatively, the first catalyst layer 20 may be formed on the first substrate portion 10a, the third catalyst layer 40 may be formed on the first catalyst layer 20, and then the second catalyst layer 30 may be formed on the second substrate portion 10b, and the fourth catalyst layer 50 may be formed on the second catalyst layer 30.

[0218] When the first substrate part 10a and the second substrate part 10b are integral, or when the first substrate part 10a and the second substrate part 10b are separate and the end of the first substrate part 10a on the exhaust gas outflow side and the end of the second substrate part 10b on the exhaust gas inflow side are in contact with each other, the first catalyst layer 20 may be formed on the first substrate part 10a, and then the second catalyst layer 30 may be formed on the second substrate part 10b, or the second catalyst layer 30 may be formed on the second substrate part 10b, and then the first catalyst layer 20 may be formed on the first substrate part 10a. In the former case, the end of the second catalyst layer 30 on the exhaust gas inflow side may have a portion overlapping the end of the first catalyst layer 20 on the exhaust gas outflow side (i.e., a portion located above the end of the first catalyst layer 20 on the exhaust gas outflow side and covering the end of the first catalyst layer 20 on the exhaust gas outflow side). In the latter case, the end of the first catalytic layer 20 on the exhaust gas outlet side may have a portion that overlaps with the end of the second catalytic layer 30 on the exhaust gas inlet side (i.e., a portion that is located above the end of the second catalytic layer 30 on the exhaust gas inlet side and covers the end of the second catalytic layer 30 on the exhaust gas inlet side).

[0219] The first catalytic layer 20 can be formed by mixing a source of a precious metal element (e.g., a salt of a precious metal element such as Pd, Pt, etc.), a Ce-Zr-based composite oxide, and optionally other components (e.g., an inorganic oxide other than the Ce-Zr-based composite oxide, a binder such as an alumina binder, a solvent, etc.) to prepare a slurry for forming the first catalytic layer, applying the slurry for forming the first catalytic layer onto the first substrate portion 10a, drying, and firing.

[0220] The second catalyst layer 30 contains a source of a precious metal element (e.g., a salt of a precious metal element such as Pd or Pt), Al 2 O 3(e.g., Al-based oxides, Ce-based oxides containing Al, Ce-Zr-based composite oxides containing Al, alumina binders, etc.) and possibly other components (e.g., Al 2 O 3 The second catalyst layer can be formed by mixing the above-mentioned components (an inorganic oxide other than the source of the alumina binder, a binder other than the alumina binder, a solvent, etc.) to prepare a slurry for forming the second catalyst layer, and then applying the slurry for forming the second catalyst layer onto the second substrate portion 10b, drying, and firing the same.

[0221] The third catalytic layer 40 can be formed by mixing a source of a precious metal element (e.g., a salt of a precious metal element such as Rh) and, if necessary, other components (e.g., an inorganic oxide, a binder, a solvent, etc.) to prepare a slurry for forming the third catalytic layer, applying the slurry for forming the third catalytic layer onto the first catalytic layer 20, drying, and firing.

[0222] The fourth catalytic layer 50 can be formed by mixing a source of a precious metal element (e.g., a salt of a precious metal element such as Rh) and, if necessary, other components (e.g., an inorganic oxide, a binder, a solvent, etc.) to prepare a slurry for forming the fourth catalytic layer, applying the slurry for forming the fourth catalytic layer onto the second catalytic layer 30, drying, and firing.

[0223] When the end of the third catalyst layer 40 on the exhaust gas outflow side and the end of the fourth catalyst layer 50 on the exhaust gas inflow side are continuous (i.e., when the third catalyst layer 40 and the fourth catalyst layer 50 are integrated to form a single catalyst layer), the third catalyst layer 40 and the fourth catalyst layer 50 can be formed by mixing a source of a precious metal element (e.g., a salt of a precious metal element such as Rh) and other components (e.g., an inorganic oxide, a binder, a solvent, etc.) to prepare a slurry for forming the third and fourth catalyst layers, and applying the slurry for forming the third and fourth catalyst layers onto the first catalyst layer 20 and the second catalyst layer 30, drying, and firing.

[0224] Examples of salts of precious metal elements include nitrates, ammine complex salts, acetates, chlorides, etc. Examples of binders include alumina sol, zirconia sol, titania sol, silica sol, ceria sol, etc. Examples of solvents include water, organic solvents, etc.

[0225] The drying temperature is, for example, 60° C. or higher and 150° C. or lower, and the drying time is, for example, 0.1 hour or higher and 1 hour or lower. The firing temperature is, for example, 300° C. or higher and 700° C. or lower, and the firing time is, for example, 1 hour or higher and 10 hours or lower. The firing can be carried out, for example, in an air atmosphere. EXAMPLES

[0226] Example 1 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.1 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.1 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 Content in terms of oxides of one or more rare earth elements other than Ce: 45% by mass%, Content in terms of oxides of one or more rare earth elements other than Ce: 10% by mass) 77.0 parts by weight, La 2 O 3 Modified alumina (La 2 O 3 Content: 7.7 parts by weight of 1% by mass, 6.1 parts by weight of barium hydroxide in terms of oxide, and 1.0 parts by weight of a binder containing alumina sol (Al in the solid content 2 O 3 The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.1 mass% Pd in ​​terms of metal and 1.2 mass% CeO 2 Converted to 34.7 mass% Al. 2 O 3 This was calculated to be 11.7% by mass.

[0227] (2) Preparation of slurry for forming second catalyst layer In pure water, 0.1 parts by weight of palladium nitrate solution (calculated as Pd metal) and 0.1 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) is 69.8 parts by weight, La 2 O 3 Modified alumina (La 2 O 3 Content: 15.3 parts by weight of 1% by mass, 6.1 parts by weight of barium hydroxide in terms of oxide, and 1.0 parts by weight of a binder containing alumina sol (Al in the solid content 2 O 3 The slurry for forming the second catalyst layer was prepared by mixing and stirring the mixture, and the mass of the second catalyst layer after firing was taken as the standard (100 mass%). In addition, the slurry for forming the second catalyst layer contained 0.1 mass% Pd in ​​terms of metal, 0.1 mass% Ce in terms of metal, and 0.1 mass% CeO 2 Converted to 31.4 mass% Al. 2 O 3 The ratio of Al in the second catalyst layer to the mass content of precious metal elements in the second catalyst layer in terms of metal was 19.2 mass%. 2 O 3 The converted mass content ratio was 192.

[0228] (3) Formation of the first and second catalyst layers As a flow-through type substrate, a honeycomb-shaped porous substrate made of cordierite (manufactured by Nippon Gaishi Co., Ltd., axial length: 80 mm, outer diameter: 93 mm, volume: 0.54 L, cell density: 900 cells / inch) was used, which has cells extending in the axial direction and divided by partitions with a thickness of 50 to 70 μm. 2 ) was prepared.

[0229] A portion of the flow-through substrate from the upstream end in the exhaust gas flow direction X to a position of 30 mm was immersed in the slurry for forming the first catalyst layer, and the slurry for forming the first catalyst layer was applied to the upstream side of the flow-through substrate. Next, a portion of the flow-through substrate from the downstream end in the exhaust gas flow direction X to a position of 50 mm was immersed in the slurry for forming the second catalyst layer, and the slurry for forming the second catalyst layer was applied to the downstream side of the flow-through substrate. Next, the flow-through substrate coated with the slurry for forming the first catalyst layer and the slurry for forming the second catalyst layer was dried at 90°C and then fired at 450°C. As a result, the first catalyst layer and the second catalyst layer were formed on the flow-through substrate without any gaps in the exhaust gas flow direction X. The mass (wash coat amount) of the first catalyst layer per unit volume of the portion of the flow-through substrate where the first catalyst layer was formed was 130g / L. The mass of the second catalyst layer per unit volume of the flow-through substrate where the second catalyst layer was formed (washcoat amount) was 130 g / L. The washcoat amount means the mass of the catalyst layer after calcination.

[0230] (4) Preparation of slurry for forming third and fourth catalyst layers In pure water, add 0.1 parts by weight of dinitrodiamine platinum (II) solution (calculated as Pt metal), 0.2 parts by weight of rhodium nitrate solution (calculated as Rh metal), and 0.5 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion rate: 44.6 parts by weight (15% by mass), La 2 O 3 Modified alumina (La 2 O 3 Content: 44.6 parts by weight of 1% by mass, 0.5 parts by weight of barium hydroxide in terms of oxide, and 1 part by weight of a binder containing alumina sol (Al in the solid content 2 O 3 The slurry for forming the third and fourth catalyst layers was prepared by adding 10 parts by weight of the sintered third and fourth catalyst layers (content: 100 mass%), mixing and stirring the mixture. The third and fourth catalyst layers were each prepared with the mass of the fired third and fourth catalyst layers as the reference (100 mass%), with Pt being 0.1 mass% in terms of metal, Rh being 0.2 mass% in terms of metal, and Ce being 0.01 mass% in terms of metal. 2 Converted to 6.7 mass% Al. 2 O3 This corresponds to a content of 54.2 mass%.

[0231] (5) Formation of the third and fourth catalyst layers The entire flow-through type substrate on which the first and second catalytic layers were formed was immersed in the slurry for forming the third and fourth catalytic layers, and the slurry for forming the third and fourth catalytic layers was applied to the entire flow-through type substrate on which the first and second catalytic layers were formed. Next, the flow-through type substrate on which the slurry for forming the third and fourth catalytic layers was applied was dried at 90°C, and then fired at 450°C. As a result, the third and fourth catalytic layers were formed on the first and second catalytic layers, respectively, without any gaps in the exhaust gas flow direction X (i.e., the end of the third catalytic layer on the exhaust gas outflow side and the end of the fourth catalytic layer on the exhaust gas inflow side were continuous, and the third and fourth catalytic layers were integrated to form one catalytic layer). The mass of the third catalyst layer per unit volume of the portion of the substrate where the third catalyst layer is formed (washcoat amount) was 100 g / L, the mass of the fourth catalyst layer per unit volume of the portion of the substrate where the fourth catalyst layer is formed (washcoat amount) was 100 g / L, and the sum of the masses of the third catalyst layer and the fourth catalyst layer relative to the sum of the volume of the portion of the substrate where the third catalyst layer is formed and the volume of the portion of the substrate where the fourth catalyst layer is formed (washcoat amount) was 100 g / L. The washcoat amount means the mass of the catalyst layer after firing.

[0232] In the manner described above, an exhaust gas purifying catalyst of Example 1 was produced, which included a flow-through type substrate, a first catalyst layer provided on the upstream side of the flow-through type substrate, a second catalyst layer provided on the downstream side of the flow-through type substrate, a third catalyst layer provided on the upper side of the first catalyst layer, and a fourth catalyst layer provided on the upper side of the second catalyst layer. In the exhaust gas purifying catalyst of Example 1, the Al content of the Al in the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3The ratio of the converted mass content (11.7 mass%) was 0.61. The ratio of the mass (130 g / L) of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was formed to the mass (130 g / L) of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was formed was 1.00.

[0233] Example 2 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.1 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.1 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) was 84.7 parts by weight, barium hydroxide was 6.1 parts by weight in terms of oxide, and a binder containing alumina sol (Al in the solid 2 O 3 The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.1 mass% Pd in ​​terms of metal and 1.2 mass% CeO 2 Converted to 38.1 mass% Al. 2 O 3 This was calculated to be 8.1% by mass.

[0234] An exhaust gas purifying catalyst of Example 2 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in the above (1) was used. In the exhaust gas purifying catalyst of Example 2, the Al content of the Al in the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (8.1 mass%) was 0.42. The ratio of the mass (130 g / L) of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was formed to the mass (130 g / L) of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was formed was 1.00.

[0235] Example 3 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.1 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.1 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) was 84.7 parts by weight, barium hydroxide was 6.1 parts by weight in terms of oxide, and a binder containing alumina sol (Al in the solid 2 O 3 The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.1 mass% Pd in ​​terms of metal and 1.2 mass% CeO 2 Converted to 38.1 mass% Al. 2 O 3 This corresponds to a content of 4.1% by mass.

[0236] An exhaust gas purifying catalyst of Example 3 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in the above (1) was used. In the exhaust gas purifying catalyst of Example 3, the Al content of the Al in the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (4.1 mass%) was 0.21. The ratio of the mass (130 g / L) of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was formed to the mass (130 g / L) of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was formed was 1.00.

[0237] Example 4 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.1 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.1 parts by weight of Ce-Zr composite oxide (CeO 2Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) was 84.7 parts by weight, barium hydroxide was 6.1 parts by weight in terms of oxide, and a binder not containing alumina sol (Al in the solid matter 2 O 3 The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.1 mass% Pd in ​​terms of metal, and 1.2 mass% CeO 2 This was calculated to be 38.1% by mass.

[0238] An exhaust gas purifying catalyst of Example 4 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in the above (1) was used. In the exhaust gas purifying catalyst of Example 4, the Al content of the Al in the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (0.00 mass%) was 0.00. The ratio of the mass (130 g / L) of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was formed to the mass (130 g / L) of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was formed was 1.00.

[0239] Example 5 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.2 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.2 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) was 83.5 parts by weight, barium hydroxide was 6.6 parts by weight in terms of oxide, and a binder containing alumina sol (Al in the solid content 2 O 3The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.2 mass% Pd in ​​terms of metal and 1.2 mass% Ce in terms of CeO 2 Converted to 37.6 mass% Al. 2 O 3 This was calculated to be 4.4% by mass.

[0240] The catalyst for purifying exhaust gas of Example 5 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in (1) above was used, and the mass (wash coat amount) of the first catalyst layer per unit volume of the portion of the substrate on which the first catalyst layer was formed was 120 g / L. In the catalyst for purifying exhaust gas of Example 5, the Al of the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (4.4 mass%) was 0.23. The ratio of the mass (120 g / L) of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was formed to the mass (130 g / L) of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was formed was 0.92.

[0241] Comparative Example 1 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.1 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.1 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) is 69.5 parts by weight, La 2 O 3 Modified alumina (La 2 O 3 Content: 15.2 parts by weight of 1% by mass, 6.1 parts by weight of barium hydroxide in terms of oxide, and 1.0 parts by weight of a binder containing alumina sol (Al in solids) 2 O 3The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.1 mass% Pd in ​​terms of metal and 1.2 mass% CeO 2 Converted to 31.3 mass% Al. 2 O 3 This was calculated to be 19.1% by mass.

[0242] An exhaust gas purifying catalyst of Comparative Example 1 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in (1) above was used. In the exhaust gas purifying catalyst of Comparative Example 1, the Al content of the Al in the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (19.1 mass%) was 0.99.

[0243] Comparative Example 2 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.1 parts by weight of palladium nitrate solution in terms of Pd metal and 1.0 parts by weight of a support other than Ce-Zr composite oxide (CeO 2 Conversion content: 0 mass%, ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 83% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 17% by mass) is 84.7 parts by weight, barium hydroxide is 6.1 parts by weight in terms of oxide, and a binder containing alumina sol (Al in the solid 2 O 3 The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.1 mass% Pd in ​​terms of metal and 1.2 mass% CeO 2 Converted to 0.0 mass%, Al is Al 2 O 3 This corresponds to a content of 4.1% by mass.

[0244] An exhaust gas purifying catalyst of Comparative Example 2 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in (1) above was used. In the exhaust gas purifying catalyst of Comparative Example 2, the Al content of the Al in the second catalyst layer was 2 O 3 The ratio of Al in the first catalyst layer to the mass content (19.2 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (4.1 mass%) was 0.21.

[0245] Comparative Example 3 (1) Preparation of slurry for forming first catalyst layer In pure water, 1.3 parts by weight of palladium nitrate solution (calculated as Pd metal) and 1.3 parts by weight of Ce-Zr composite oxide (CeO 2 Conversion ratio: 45% by mass of ZrO 2 The content of one or more rare earth elements other than Ce in terms of oxide: 45% by mass, the content of one or more rare earth elements other than Ce in terms of oxide: 10% by mass) is 67.2 parts by weight, La 2 O 3 Modified alumina (La 2 O 3 Content: 14.8 parts by weight of 1% by mass, 7.2 parts by weight of barium hydroxide in terms of oxide, and 1.0 parts by weight of a binder containing alumina sol (Al in solids) 2 O 3 The slurry for forming the first catalyst layer was prepared by mixing and stirring the mixture, and the mass of the first catalyst layer after firing was taken as the standard (100 mass%). The slurry for forming the first catalyst layer contained 1.3 mass% Pd in ​​terms of metal and 1.2 mass% CeO 2 Converted to 30.2 mass%, Al is Al 2 O 3 This was calculated to be 19.4% by mass.

[0246] The catalyst for purifying exhaust gas of Comparative Example 3 was produced in the same manner as in Example 1, except that the slurry for forming the first catalyst layer produced in (1) above was used, and the mass (wash coat amount) of the first catalyst layer per unit volume of the portion of the substrate on which the first catalyst layer was formed was 110 g / L. In the catalyst for purifying exhaust gas of Comparative Example 3, the Al of the second catalyst layer was 110 g / L. 2 O3 The ratio of Al in the first catalyst layer to the mass content (19.4 mass%) of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content (19.2 mass%) was 1.01. The ratio of the mass of the first catalyst layer (110 g / L) per unit volume of the portion of the substrate where the first catalyst layer was formed to the mass of the second catalyst layer (130 g / L) per unit volume of the portion of the substrate where the second catalyst layer was formed was 0.85.

[0247] [Test Example] (1) Durability treatment Each of the exhaust gas purification catalysts of Examples 1 to 5 and Comparative Examples 1 to 3 was installed in an exhaust pipe, and this exhaust pipe was attached to a gasoline engine. The engine speed / torque, etc. were adjusted so that the catalyst temperature would reach 950°C, and a durability treatment was carried out for 50 hours.

[0248] (2) Evaluation of exhaust gas purification performance A vehicle equipped with the exhaust gas purification catalyst after durability treatment was driven under the driving conditions of the World Wide Harmonized Exhaust Gas Test Mode (WLTC). The emissions (emission values) of carbon monoxide (CO), non-methane hydrocarbons (NMHC) and nitrogen oxides (NOx) in the exhaust gas that passed through the exhaust gas purification catalyst were measured, and the emissions of CO, NMHC and NOx per unit driving distance (g / km) were calculated. A gasoline-powered vehicle was used, and certification test fuel was used as the gasoline, and an exhaust gas measurement device manufactured by Horiba, Ltd. was used as the exhaust gas measurement device. The emissions of NMHC per unit driving distance (g / km) are shown in Table 1. In Table 1, (A) indicates the amount of Al in the first catalyst layer. 2 O 3 (B) is the mass content (mass%) of Al in the second catalyst layer. 2 O 3 (C) is the mass (g / L) of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer is formed, (D) is the mass (g / L) of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer is formed, and (E) is the Al content (mass%) of Al in the second catalyst layer. 2 O 3The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer 2 O 3 (F) is the ratio of the mass of the first catalytic layer per unit volume of the portion of the substrate where the first catalytic layer is formed to the mass of the second catalytic layer per unit volume of the portion of the substrate where the second catalytic layer is formed, (G) is the presence or absence of Ce-Zr-based composite oxide in the first catalytic layer, and (H) is the NMHC emissions per unit driving distance (g / km).

[0249] [Table 1]

[0250] The exhaust gas purification catalysts of Examples 1 to 5 each include a substrate, a first catalytic layer provided on the upstream side of the substrate, and a second catalytic layer provided on the downstream side of the substrate. The first catalytic layer contains a precious metal element and a Ce-Zr based composite oxide, and the second catalytic layer contains a precious metal element and Al. 2 O 3 and the Al in the first catalyst layer is 2 O 3 The mass content of Al in the second catalyst layer is 12 mass% or less, 2 O 3 The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content is 0 or more and 0.65 or less.

[0251] The exhaust gas purification catalysts of Comparative Examples 1 and 3 each include a substrate, a first catalytic layer provided on the upstream side of the substrate, and a second catalytic layer provided on the downstream side of the substrate. The first catalytic layer contains a precious metal element and a Ce-Zr based composite oxide, and the second catalytic layer contains a precious metal element and Al. 2 O 3 However, in the exhaust gas purifying catalysts of Comparative Examples 1 and 3, the Al content in the first catalyst layer was 2 O 3 The mass content of Al in the second catalyst layer is more than 12 mass%, and 2 O 3 The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer2 O 3 The ratio of the converted mass contents is greater than 0.65.

[0252] The exhaust gas purifying catalyst of Comparative Example 2 includes a substrate, a first catalytic layer provided on the upstream side of the substrate, and a second catalytic layer provided on the downstream side of the substrate. The first catalytic layer contains a precious metal element, and the second catalytic layer contains a precious metal element and Al. 2 O 3 and the Al in the first catalyst layer is 2 O 3 The mass content of Al in the second catalyst layer is 12 mass% or less, 2 O 3 The ratio of Al in the first catalyst layer to the mass content of Al in the first catalyst layer 2 O 3 The ratio of the converted mass content is equal to or greater than 0 and equal to or less than 0.65. However, in the exhaust gas purifying catalyst of Comparative Example 2, the first catalyst layer does not contain a Ce—Zr based composite oxide.

[0253] As shown in Table 1, the Al content in the first catalyst layer was 2 O 3 The mass content in terms of Al in the second catalyst layer is 12 mass% or less. 2 O 3 The mass content of Al in the first catalyst layer 2 O 3 The exhaust gas purifying catalysts of Examples 1 to 5, which satisfied the condition that the ratio of the mass contents of the above is 0 or more and 0.65 or less, had higher exhaust gas purifying performance than Comparative Examples 1 and 3, which did not satisfy this condition. Moreover, the exhaust gas purifying catalysts of Examples 1 to 5, in which the first catalyst layer contained a Ce-Zr-based composite oxide, had higher exhaust gas purifying performance than Comparative Example 2, in which the first catalyst layer did not contain a Ce-Zr-based composite oxide. [Explanation of symbols]

[0254] 1A, 1B: Exhaust gas purification catalyst 10...Base material 10a...First base material part 10b...Second base material part 11a, 11b... Cylindrical portion 12a,12b...Bulkhead part 13a, 13b Cell 20...1st catalyst layer 30...Second catalyst layer 40...Third catalyst layer 50...4th catalyst layer L10a: Length of the first base material L10b: Length of second base material L20: Average length of the first catalyst layer L30: Average length of the second catalyst layer L40: Average length of the third catalyst layer L50: Average length of the fourth catalyst layer P...Exhaust pipe of internal combustion engine

Claims

1. A catalyst for purifying exhaust gas, comprising a substrate, a first catalyst layer provided on the upstream side of the substrate, and a second catalyst layer provided on the downstream side of the substrate, the first catalytic layer contains a precious metal element and a Ce—Zr based composite oxide, The second catalyst layer is composed of a precious metal element and Al ２ O ３ and Al in the first catalyst layer ２ O ３ The mass content in terms of the converted amount is 5% by mass or less, Al in the second catalyst layer ２ O ３ The mass content of Al in the first catalyst layer relative to the mass content of Al in the first catalyst layer ２ O ３ The ratio of the converted mass content is 0 or more and 0.30 or less, A catalyst for exhaust gas purification, in which a ratio of a mass of a first catalyst layer per unit volume of a portion of the substrate where the first catalyst layer is formed to a mass of a second catalyst layer per unit volume of a portion of the substrate where the second catalyst layer is formed is 0.95 or less.

2. A catalyst for exhaust gas purification as described in claim 1, wherein the mass of the first catalyst layer per unit volume of the portion of the substrate on which the first catalyst layer is formed is 80 g / L or more and 150 g / L or less.

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

4. 4. The exhaust gas purifying catalyst according to claim 3, further comprising a third catalyst layer provided on an upper side of the first catalyst layer and / or a fourth catalyst layer provided on an upper side of the second catalyst layer, each of the third catalyst layer and the fourth catalyst layer containing Rh.

5. 3. The exhaust gas purifying catalyst according to claim 1, wherein the first catalyst layer contains Pd.

6. The ratio of Al in the second catalytic layer to the mass content of the precious metal element in the second catalytic layer in terms of metal ２ O ３ 3. The exhaust gas purifying catalyst according to claim 1, wherein a ratio of the converted mass content is 50 or more and 600 or less.

7. CeO of Ce in the first catalyst layer ２ The exhaust gas purifying catalyst according to claim 1 or 2, wherein the converted mass content is 32 mass % or more.

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