Catalysts for exhaust gas purification

Abstract

An object of the present invention is to provide a catalyst for exhaust gas purification, which comprises a wall flow type substrate and a catalyst layer, and the exhaust gas purification catalyst has improved exhaust gas purification performance. In order to achieve the purpose, an exhaust gas purification catalyst is provided, which comprises a wall flow type substrate, a first catalyst layer and a second catalyst layer, wherein the first catalyst layer and the second catalyst layer satisfy the following formulas (1) to (3): L1<L2...(1), T1<T2...(2), WC1>WC2...(3) In the formulas, L1 represents the length of the first catalyst layer, L2 represents the length of the second catalyst layer, T1 represents the thickness of the raised portion of the first catalyst layer, T2 represents the thickness of the raised portion of the second catalyst layer, WC1 represents the mass of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer is provided, and WC2 represents the mass of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer is provided.

Description

Technical Field

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

[0002] The exhaust gas discharged from the 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 these harmful components and render them harmless, a three-way catalyst is used. As a three-way catalyst, precious metal catalysts such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used. Pt and Pd are mainly involved in the oxidation purification of HC and CO, and Rh is mainly involved in the reduction purification of NOx.

[0003] It is known that exhaust gas contains harmful components such as HC, CO, and NOx, and also contains particulate matter (PM), which causes air pollution.

[0004] On the other hand, in vehicles equipped with gasoline engines, direct injection engines (GDI: Gasoline Direct Injection engine) are used. GDI is known to have low fuel consumption and high output, but the amount of PM discharged in the exhaust gas is larger than that of conventional intake port injection engines. In order to cope with environmental regulations related to PM, it is expected that in vehicles equipped with gasoline engines such as GDI, a filter (GPF: Gasoline Particulate Filter) with a PM trapping function is provided, similar to vehicles equipped with diesel engines.

[0005] As the GPF, for example, a substrate having a so-called wall-flow type structure is used. In the wall-flow type substrate, when the exhaust gas flowing in from the cell inlet passes through the porous partition wall portion that separates the cells and flows out from the cell outlet, PM in the exhaust gas is captured in the pores inside the partition wall portion.

[0006] Since the space for mounting exhaust gas purification catalysts is generally limited, studies are underway to load precious metal catalysts such as Pt, Pd, and Rh on the GPF to simultaneously capture PM and purify harmful components such as HC, CO, and NOx.

[0007] For example, Patent Document 1 describes an exhaust gas purifying catalyst in which a palladium-containing layer and a rhodium-containing layer are stacked such that one of the palladium-containing layer and the rhodium-containing layer is located inside a partition wall and the other of the palladium-containing layer and the rhodium-containing layer is located on a surface of the partition wall.

[0008] In addition, Patent Document 2 describes a catalyst for exhaust gas purification, which comprises: a substrate of a wall flow structure, which has an inlet side chamber whose end is open only on the exhaust gas inlet side, an outlet side chamber adjacent to the inlet side chamber and whose end is open only on the exhaust gas outflow side, and a porous partition wall portion that separates the inlet side chamber and the outlet side chamber; an upstream side catalyst layer, which is arranged inside the partition wall portion; and a downstream side catalyst layer, which is arranged inside the partition wall portion, wherein the upstream side catalyst layer and the downstream side catalyst layer respectively contain a carrier and at least one precious metal selected from platinum (Pt), palladium (Pd) and rhodium (Rh) loaded on the carrier, and the precious metal contained in the upstream side catalyst layer is different from the precious metal contained in the downstream side catalyst layer.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2009-82915

[0012] Patent Document 2: Japanese Patent Application Publication No. 2016-78016 Summary of the invention

[0013] Problem that the invention aims to solve

[0014] However, when a catalyst layer is formed on a wall-flow type substrate and harmful components such as HC, CO, and NOx are purified while PM is captured, the exhaust gas purification performance may not be fully exerted. In particular, during high-speed operation, the temperature rise in the combustion chamber leads to significant generation of NOx, so improving the NOx purification performance during high-speed operation has become a major issue.

[0015] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst including a wall flow type substrate and a catalyst layer and having improved exhaust gas purification performance.

[0016] Solutions for solving problems

[0017] In order to solve the above-mentioned problems, the present invention provides a catalyst for exhaust gas purification, which extends along the exhaust gas flow direction, wherein the exhaust gas purification catalyst comprises a substrate, a first catalyst layer arranged on the substrate and a second catalyst layer arranged on the substrate, and the substrate comprises: an inlet side chamber, which extends along the exhaust gas flow direction, the end of the exhaust gas inlet side of the inlet side chamber is open, and the end of the exhaust gas outflow side of the inlet side chamber is closed; an outlet side chamber, which extends along the exhaust gas flow direction, the end of the exhaust gas inlet side of the outflow side chamber is closed, and the end of the exhaust gas outflow side of the outflow side chamber is closed. The first catalyst layer comprises a first catalyst layer and a second catalyst layer, wherein the first catalyst layer comprises a first catalyst layer and a second catalyst layer. The first catalyst layer comprises a first catalyst layer and a second catalyst layer. The first catalyst layer comprises a first catalyst layer and a second catalyst layer. The first catalyst layer comprises a first catalyst layer and a second catalyst layer. The first catalyst layer comprises a first catalyst layer and a second catalyst layer.

[0018] L1<L2...(1)

[0019] T1<T2...(2)

[0020] WC1>WC2...(3)

[0021] In the formula, L1 represents the length of the first catalyst layer, L2 represents the length of the second catalyst layer, T1 represents the thickness of the portion of the first catalyst layer, T2 represents the thickness of the portion of the second catalyst layer, WC1 represents the mass of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer is provided, and WC2 represents the mass of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer is provided.

[0022] Effects of the Invention

[0023] According to the present invention, it is possible to provide an exhaust gas purification catalyst having PM trapping performance and improved exhaust gas purification performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a cross-sectional perspective view of an exhaust gas-purifying catalyst according to an embodiment of the present invention.

[0025] Figure 2 yes Figure 1 Magnified view of region R1 in FIG.

[0026] Figure 3 yes Figure 2 Magnified view of region R2 in FIG.

[0027] Figure 4 yes Figure 3 An enlarged view of region R3 in FIG.

[0028] Figure 5 yes Figure 3 An enlarged view of region R4 in FIG.

[0029] Figure 6 It is used to illustrate Figure 1 A cross-sectional view showing the flow of exhaust gas in an exhaust gas purifying catalyst shown.

[0030] Figure 7 This is a SEM observation image obtained by cutting the exhaust gas-purifying catalyst produced in Example 1 on a plane perpendicular to the axial direction of the substrate and observing the first catalyst layer present on the cut surface using a scanning electron microscope (SEM).

[0031] Figure 8 This is a SEM observation image obtained by cutting the exhaust gas-purifying catalyst prepared in Example 1 on a plane perpendicular to the axial direction of the substrate and observing the second catalyst layer present on the cut surface using a scanning electron microscope (SEM). DETAILED DESCRIPTION

[0032] Hereinafter, embodiments of the exhaust gas purifying catalyst of the present invention will be described with reference to the drawings.

[0033] like Figure 1 to Figure 6 As shown, an exhaust gas-purifying catalyst 10 according to an embodiment of the present invention includes a substrate 20 , a first catalyst layer 30 provided on the substrate 20 , and a second catalyst layer 40 provided on the substrate 20 .

[0034] The exhaust gas purification catalyst 10 is arranged in the exhaust path of the internal combustion engine. The exhaust gas purification catalyst 10 is arranged in the exhaust path of a gasoline engine (such as a GDI engine) and is used as a gasoline particulate filter (GPF). In each of the drawings, the exhaust gas flow direction in the exhaust path of the internal combustion engine is indicated by the reference symbol X. In this specification, the upstream side (such as the upstream side) of the exhaust gas flow direction X is sometimes referred to as Figure 2 The left side of the exhaust gas flow direction X is called the "exhaust gas inflow side", and the downstream side of the exhaust gas flow direction X (for example Figure 2 The right side of the exhaust gas outlet is called the "exhaust gas outlet side".

[0035] The exhaust gas purifying catalyst 10 is arranged in the exhaust path of the internal combustion engine in such a manner that the axial direction of the substrate 20 is substantially consistent with the exhaust gas flow direction X, and the exhaust gas purifying catalyst 10 extends along the exhaust gas flow direction X. In this specification, "length" refers to the dimension in the axial direction of the substrate 20 unless otherwise specified, and "thickness" refers to the dimension in the direction perpendicular to the axial direction of the substrate 20 unless otherwise specified.

[0036] Substrate

[0037] Next, the substrate 20 will be described.

[0038] The material constituting the substrate 20 can be appropriately selected from materials commonly used as the material of the substrate of the exhaust gas purification catalyst. The material constituting the substrate 20 is preferably a material that can give the substrate 20 a stable shape even when the substrate 20 is exposed to high temperature (e.g., 400° C. or higher) exhaust gas. Examples of such materials include ceramics such as cordierite, silicon carbide (SiC), and aluminum titanate, and alloys such as stainless steel.

[0039] like Figure 1 and Figure 2 As shown, the substrate 20 includes a cylindrical portion 21 and a porous partition wall portion 22 formed in the cylindrical portion 21 .

[0040] The axial direction of the substrate 20 coincides with the axial direction of the cylindrical portion 21. In the present embodiment, the cylindrical portion 21 is cylindrical, but may be other cylindrical shapes. Examples of other cylindrical shapes include an elliptical cylindrical shape and a polygonal cylindrical shape.

[0041] like Figure 1 and Figure 2 As shown, the substrate 20 has a wall flow structure. Specifically, the substrate 20 has an inflow-side cell C1 and an outflow-side cell C2, and the inflow-side cell C1 and the outflow-side cell C2 are partitioned by a porous partition wall portion 22.

[0042] like Figure 1 and Figure 2 As shown, a recess (hole portion) opening on the exhaust gas inlet side and a recess (hole portion) opening on the exhaust gas outlet side are formed on the substrate 20. The space inside the recess opening on the exhaust gas inlet side is the inlet side chamber C1, and the space inside the recess opening on the exhaust gas outlet side is the outlet side chamber C2.

[0043] like Figure 1 and Figure 2 As shown, the inlet side chamber C1 extends along the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side. Figure 1 and Figure 2As shown, the end of the inlet side chamber C1 on the exhaust gas inlet side is open, and the end of the inlet side chamber C1 on the exhaust gas outlet side is closed. In addition, hereinafter, the end of the inlet side chamber C1 on the exhaust gas inlet side is sometimes referred to as the "opening of the inlet side chamber C1".

[0044] like Figure 1 and Figure 2 As shown, the base 20 is provided with a first sealing portion 24 that seals the end portion of the inlet-side cell C1 on the exhaust gas outflow side. The end portion of the inlet-side cell C1 on the exhaust gas outflow side is closed by the first sealing portion 24 .

[0045] like Figure 1 As shown in the figure, the top view shape of the opening of the inlet side chamber C1 (the shape when the substrate 20 is viewed from the exhaust gas flow direction X) is a square, but the top view shape of the opening of the inlet side chamber C1 may be other shapes. As other shapes, for example, various geometric shapes such as parallelograms, rectangles, trapezoids, polygons such as triangles, hexagons, and octagons, circles, and ellipses can be cited.

[0046] like Figure 1 and Figure 2 As shown, the outflow side chamber C2 extends along the exhaust gas flow direction X and has an end on the exhaust gas inflow side and an end on the exhaust gas outflow side. Figure 1 and Figure 2 As shown, the end of the exhaust gas inlet side of the outlet side chamber C2 is closed, and the end of the exhaust gas outlet side of the outlet side chamber C2 is open. In addition, hereinafter, the end of the exhaust gas outlet side of the outlet side chamber C2 is sometimes referred to as the "opening of the outlet side chamber C2".

[0047] like Figure 1 and Figure 2 As shown, the substrate 20 is provided with a second sealing portion 25 that seals the end of the outflow-side cell C2 on the exhaust gas inflow side. The end of the outflow-side cell C2 on the exhaust gas inflow side is closed by the second sealing portion 25 .

[0048] like Figure 1 As shown in the figure, the top view shape of the opening of the outlet side chamber C2 (the shape when the substrate 20 is viewed from the direction opposite to the exhaust gas flow direction X) is a square, but the top view shape of the opening of the outlet side chamber C2 may be other shapes. As other shapes, for example, various geometric shapes such as parallelograms, rectangles, trapezoids, polygons such as triangles, hexagons, and octagons, circles, and ellipses can be cited.

[0049] The area of ​​the opening of the inlet-side cell C1 in a plan view and the area of ​​the opening of the outlet-side cell C2 in a plan view may be the same as or different from each other.

[0050] The inlet side chamber C1 and the outflow side chamber C2 are arranged around one inlet side chamber C1 in a manner that multiple (4 in the present embodiment) outflow side chambers C2 are adjacent to one inlet side chamber C1, and the inlet side chamber C1 and the outflow side chamber C2 adjacent to the inlet side chamber C1 are separated by a porous partition wall portion 22.

[0051] The partition wall 22 has a porous structure through which exhaust gas can pass. The thickness of the partition wall 22 is, for example, 150 μm to 400 μm. The thickness of the partition wall 22 can be calculated by the same calculation method as the calculation method of the catalyst layer thickness described later.

[0052] like Figure 2 As shown, the substrate 20 has a length L. The length L of the substrate 20 is not particularly limited and can be adjusted as appropriate.

[0053] The number of cells per square inch of the substrate 20 is not particularly limited, and is, for example, 200 cells / square inch or more and 900 cells / square inch or less. The number of cells per square inch of the substrate 20 is the total number of inflow-side cells C1 and outflow-side cells C2 per square inch in a cut surface obtained by cutting the substrate 20 on a plane perpendicular to the exhaust gas flow direction X.

[0054] Catalyst layer

[0055] Hereinafter, the first catalyst layer 30 and the second catalyst layer 40 will be described.

[0056] like Figure 3 and Figure 4 As shown, the first catalyst layer 30 is formed on the inlet-side cell C1 side of the partition wall portion 22 .

[0057] like Figure 3 and Figure 4 As shown, the first catalyst layer 30 has a portion 31 formed on the surface of the inlet-side chamber C1 side of the partition wall portion 22 from the end of the exhaust gas inlet side of the partition wall portion 22 along the exhaust gas flow direction X. The "surface of the inlet-side chamber C1 side of the partition wall portion 22" refers to the outer surface of the inlet-side chamber C1 side that defines the outer shape of the partition wall portion 22, and the "portion formed on the surface of the inlet-side chamber C1 side of the partition wall portion 22" refers to a portion protruding from the outer surface of the inlet-side chamber C1 side of the partition wall portion 22 toward the inlet-side chamber C1 side.

[0058] like Figure 3 and Figure 4As shown, the first catalyst layer 30 has a portion 31 and a portion 32 existing inside the partition wall portion 22. Since the partition wall portion 22 is porous, when the first catalyst layer 30 is formed, the portion 32 is usually formed together with the portion 31. The region where the portion 31 exists does not overlap with the region where the partition wall portion 22 exists, but the region where the portion 32 exists overlaps with the region where the partition wall portion 22 exists. Therefore, the exhaust gas purification catalyst 10 is cut on a plane perpendicular to the axial direction of the substrate 20, and the first catalyst layer 30 existing on the cut surface is observed using a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), etc., and the portion 31 and the portion 32 can be determined based on the difference in morphology between the first catalyst layer 30 and the partition wall portion 22 of the substrate 20. When observing the cut surface, element mapping of the cut surface can be performed. Element mapping can be performed, for example, by combining observation of the cut surface using SEM and composition analysis of the cut surface. Element mapping can be performed using, for example, a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX), an electron beam microanalyzer (EPMA), a transmission X-ray inspection device, etc. By element mapping of the cut surface, the portion 31 and the portion 32 can be determined based on the difference in morphology and composition between the first catalyst layer 30 and the partition wall portion 22 of the substrate 20.

[0059] like Figure 3 and Figure 5 As shown, the second catalyst layer 40 is formed on the outflow-side cell C2 side of the partition wall portion 22 .

[0060] like Figure 3 and Figure 5 As shown, the second catalyst layer 40 has a portion 41 formed on the surface of the outflow-side chamber C2 side of the partition wall portion 22 from the end of the exhaust gas outflow side of the partition wall portion 22 in the direction opposite to the exhaust gas flow direction X. The "surface of the outflow-side chamber C2 side of the partition wall portion 22" refers to the outer surface of the outflow-side chamber C2 side that defines the outer shape of the partition wall portion 22, and the "portion formed on the surface of the outflow-side chamber C2 side of the partition wall portion 22" refers to the portion that bulges from the outer surface of the outflow-side chamber C2 side of the partition wall portion 22 toward the outflow-side chamber C2 side.

[0061] like Figure 3 and Figure 5As shown, the second catalyst layer 40 has a portion 41 and a portion 42 existing inside the partition wall portion 22. Since the partition wall portion 22 is porous, when the second catalyst layer 40 is formed, the portion 42 is usually formed together with the portion 41. The region where the portion 41 exists does not overlap with the region where the partition wall portion 22 exists, but the region where the portion 42 exists overlaps with the region where the partition wall portion 22 exists. Therefore, the exhaust gas purifying catalyst 10 is cut on a plane perpendicular to the axial direction of the substrate 20, and the second catalyst layer 40 existing on the cut surface is observed using a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), etc., and the portion 41 and the portion 42 can be determined based on the difference in morphology between the second catalyst layer 40 and the partition wall portion 22 of the substrate 20. When observing the cut surface, element mapping of the cut surface can be performed. Element mapping can be performed in the same manner as described above. Through element mapping of the cut surface, the portion 41 and the portion 42 can be determined based on the difference in morphology and composition between the second catalyst layer 40 and the partition wall portion 22 of the substrate 20.

[0062] In the exhaust gas purifying catalyst 10, the first catalyst layer 30 and the second catalyst layer 40 satisfy the following formula (1):

[0063] L1<L2...(1).

[0064] In the above formula (1), L1 represents the length of the first catalyst layer 30 (see Figure 2 ), L2 represents the length of the second catalyst layer 40 (refer to Figure 2 ).

[0065] The length L1 of the first catalyst layer 30 and the length L2 of the second catalyst layer 40 are not particularly limited as long as they satisfy the above-mentioned formula (1), but from the viewpoint of more effectively achieving the desired exhaust gas flow described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, the ratio (L2 / L1) of the length L2 of the second catalyst layer 40 to the length L1 of the first catalyst layer 30 is preferably greater than 1.0 and less than 2.3, further preferably greater than 1.1 and less than 2.2, further preferably greater than 1.2 and less than 2.1, further preferably greater than 1.3 and less than 2.0, further preferably greater than 1.4 and less than 1.9, further preferably greater than 1.5 and less than 1.8.

[0066] The length L1 of the first catalyst layer 30 is not particularly limited as long as it satisfies the above formula (1), but from the viewpoint of more effectively achieving the desired exhaust gas flow described later and the desired exhaust gas purification performance described later, the percentage of the length L1 of the first catalyst layer 30 relative to the length L of the substrate 20 (L1 / L×100) is preferably greater than 10% and less than 80%, further preferably greater than 20% and less than 70%, further preferably greater than 30% and less than 60%, further preferably greater than 40% and less than 50%.

[0067] The length L2 of the second catalyst layer 40 is not particularly limited as long as it satisfies the above formula (1), but from the viewpoint of more effectively achieving the desired exhaust gas flow described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, the percentage of the length L2 of the second catalyst layer 40 relative to the length L of the substrate 20 (L2 / L×100) is preferably greater than 30% and less than 90%, further preferably greater than 40% and less than 85%, further preferably greater than 50% and less than 80%, further preferably greater than 65% and less than 75%.

[0068] The percentage of the total length L1 of the first catalyst layer 30 and the length L2 of the second catalyst layer 40 relative to the length L of the substrate 20 ((L1+L2) / L×100) is not particularly limited as long as it satisfies the above-mentioned formula (1), but is preferably 100% to 150%, more preferably 101% to 145%, further preferably 102% to 140%, further preferably 103% to 135%, further preferably 104% to 130%, from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and more effectively achieving the desired exhaust gas purification performance described later.

[0069] An example of a method for calculating the length L1 of the first catalyst layer 30 and the length L2 of the second catalyst layer 40 is as follows.

[0070] A sample extending along the axial direction of the substrate 20 and having the same length L as the length of the substrate 20 is cut from the exhaust gas purification catalyst 10. The sample is, for example, cylindrical with a diameter of 25.4 mm. In addition, the value of the diameter of the sample can be changed as needed. The sample is cut at intervals of 5 mm using a plane perpendicular to the axial direction of the substrate 20, and the first slice, the second slice, ..., the nth slice are obtained in sequence from the end side of the exhaust gas inflow side of the sample. The length of the slice is 5 mm. A fluorescent X-ray analyzer (XRF) (such as an energy dispersive X-ray analyzer (EDX), a wavelength dispersive X-ray analyzer (WDX), etc.), an inductively coupled plasma emission spectrometer (ICP-AES), etc. are used to analyze the composition of the slice, and based on the composition of the slice, it is confirmed whether the slice contains the first catalyst layer 30.

[0071] For a slice that clearly contains the first catalyst layer 30, it is not necessary to perform composition analysis. For example, a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), or the like can be used to observe the cut surface to confirm whether the slice contains the first catalyst layer 30. When observing the cut surface, element mapping of the cut surface can be performed. Element mapping can be performed in the same manner as described above.

[0072] After confirming whether the slice includes the first catalyst layer 30 , the length of the first catalyst layer 30 included in the sample is calculated based on the following formula.

[0073] Length of the first catalyst layer 30 contained in the sample = 5 mm × (number of slices containing the first catalyst layer 30)

[0074] For example, when the first to kth slices include the first catalyst layer 30 and the (k+1)th to nth slices do not include the first catalyst layer 30 , the length of the first catalyst layer 30 included in the sample is (5×k) mm.

[0075] When measuring the length of the first catalyst layer 30 in more detail, calculation is performed as follows.

[0076] The k-th slice (i.e., the slice obtained from the exhaust gas outflow side of the sample among the slices including the first catalyst layer 30) is cut in the axial direction of the substrate 20, and the first catalyst layer 30 existing on the cut surface is observed using a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), etc., thereby measuring the length of the first catalyst layer 30 in the k-th slice. Then, the length of the first catalyst layer 30 contained in the sample is calculated based on the following formula.

[0077] The length of the first catalyst layer 30 contained in the sample = (5 mm × (k-1)) + (the length of the first catalyst layer 30 in the kth slice)

[0078] The length of the first catalyst layer 30 included in each of 8 to 16 samples randomly cut out from the exhaust gas purifying catalyst 10 was calculated, and the average value thereof was taken as the length L1 of the first catalyst layer 30 .

[0079] An example of a method for calculating the length L2 of the second catalyst layer 40 is also the same as an example of a method for calculating the length L1 of the first catalyst layer 30. In addition, in an example of a method for calculating the length L2 of the second catalyst layer 40, the sample is cut at intervals of 5 mm using a plane perpendicular to the axial direction of the substrate 20, and the first slice, the second slice, ..., and the nth slice are obtained in order from the end side of the exhaust gas outflow side of the sample.

[0080] In the exhaust gas purifying catalyst 10, the first catalyst layer 30 and the second catalyst layer 40 satisfy the following formula (2):

[0081] T1<T2...(2).

[0082] In the above formula (2), T1 represents the thickness T1 of the portion 31 of the first catalyst layer 30 (see Figure 4 ), T2 represents the thickness of the portion 41 of the second catalyst layer 40 (refer to Figure 5 ).

[0083] The thickness T1 of portion 31 of the first catalyst layer 30 and the thickness T2 of portion 41 of the second catalyst layer 40 are not particularly limited as long as they satisfy the above-mentioned formula (2), but from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, the ratio (T2 / T1) of the thickness T2 of portion 41 of the second catalyst layer 40 to the thickness T1 of portion 31 of the first catalyst layer 30 is preferably greater than 1.0 and less than 3.5, further preferably greater than 1.1 and less than 3.0, further preferably greater than 1.2 and less than 2.5, and further preferably greater than 1.3 and less than 2.1.

[0084] The thickness T1 of portion 31 of the first catalyst layer 30 is not particularly limited as long as it satisfies the above-mentioned formula (2), but from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, it is preferably greater than 15 μm and less than 55 μm, further preferably greater than 20 μm and less than 50 μm, further preferably greater than 25 μm and less than 45 μm, further preferably greater than 30 μm and less than 40 μm.

[0085] The thickness T2 of portion 41 of the second catalyst layer 40 is not particularly limited as long as it satisfies the above formula (2), but from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, it is preferably greater than 20 μm and less than 100 μm, further preferably greater than 30 μm and less than 90 μm, further preferably greater than 40 μm and less than 80 μm, further preferably greater than 45 μm and less than 65 μm.

[0086] An example of a method for calculating the thickness T1 of the portion 31 of the first catalyst layer 30 and the thickness T2 of the portion 41 of the second catalyst layer 40 is as follows.

[0087] The exhaust gas purification catalyst 10 is cut on a plane perpendicular to the axial direction of the substrate 20 (for example, a portion separated by 10 mm from the end of the exhaust gas inlet side of the substrate 20 in the exhaust gas flow direction X), and a scanning electron microscope (SEM) is used to observe the first catalyst layer 30 present in one inlet side chamber C1 arbitrarily selected from the cut surface, and determine the area where the partition wall portion 22 of the substrate 20 and the area where the first catalyst layer 30 are present. When observing the cut surface using SEM, the field of view magnification is set to, for example, 300 times, and the field of view width (length) is set to, for example, 500μm to 600μm. The area observed by SEM is set to not include the corners of the inlet side chamber C1. The reason is that at the corners of the inlet side chamber C1, the exhaust gas permeability is low, and the contribution to the realization of the desired exhaust gas flow described later is small. The region where the partition wall portion 22 of the substrate 20 exists and the region where the first catalyst layer 30 exists can be determined based on the difference in morphology between the first catalyst layer 30 and the partition wall portion 22 of the substrate 20. At this time, element mapping of the cut surface can also be performed. Element mapping can be performed in the same manner as described above. Through element mapping of the cut surface, the region where the partition wall portion 22 of the substrate 20 exists and the region where the first catalyst layer 30 exists can be determined based on the difference in morphology and composition between the first catalyst layer 30 and the partition wall portion 22 of the substrate 20.

[0088] In the SEM observation image, the first to Nth grid lines parallel to the thickness direction of the partition wall portion 22 of the substrate 20 are drawn in sequence at intervals of 15 μm from the left end or the right end, and the contour line of the area where the partition wall portion 22 of the substrate 20 exists and the intersection points between the grid lines are connected with each other by a straight line to determine the position of the surface of the partition wall portion 22 of the substrate 20. N is, for example, an integer such as 30 to 50. Similarly, the contour line of the area where the first catalyst layer 30 exists and the intersection points between the grid lines are connected with each other by a straight line to determine the position of the surface of the first catalyst layer 30. Preferably, when the amount of change in the thickness direction from a certain intersection P1 to an intersection P2 adjacent to the intersection P1 exceeds the interval (15 μm) of the grid lines, the intersection P2 is not used to determine the position of the surface (that is, the intersection P2 is removed from the intersections connected by the straight line). The amount of change in the thickness direction from a certain intersection point P1 to an intersection point P2 adjacent to the intersection point P1 refers to the distance between a straight line passing through the intersection point P1 and perpendicular to the thickness direction of the partition wall portion 22 of the substrate 20 and a straight line passing through the intersection point P2 and perpendicular to the thickness direction of the partition wall portion 22 of the substrate 20. Preferably, when the amount of change in the thickness direction from the intersection point P1 to the intersection point P2 adjacent to the intersection point P1 exceeds the interval (15 μm) of the grid lines and the amount of change in the thickness direction from the intersection point P1 to the intersection point P3 adjacent to the intersection point P2 also exceeds the interval (15 μm) of the grid lines, not only the intersection point P2 is not used to determine the position of the surface, but also the intersection point P3 is not used to determine the position of the surface (that is, the intersection point P2 and the intersection point P3 are removed from the intersection points connected by the straight line). Preferably, when five intersection points are continuously removed from the intersection points connected by the straight line, the thickness measurement of the SEM image is not performed.

[0089] After determining the position of the surface of the partition wall portion 22 of the substrate 20 and the position of the surface of the first catalyst layer 30, the image analysis software is used to find the area of ​​the region surrounded by the second grid line, the (N-1)th grid line, the surface of the partition wall portion 22 of the substrate 20, and the surface of the first catalyst layer 30. As image analysis software, for example, AreaQ (manufactured by ESTECH), ImageJ (public domain), Photoshop (Adobe Systems), etc. can be used. In addition, since the two ends of the image tend to become unclear and it is difficult to determine the position of the surface of the partition wall portion 22 and the position of the surface of the first catalyst layer 30, the first grid line and the Nth grid line are not used.

[0090] After the area of ​​the above region is determined, the thickness of the above region is calculated based on the following formula.

[0091] The thickness of the above region = the area of ​​the above region / (grid line spacing × the number of grid line spacings)

[0092] Furthermore, the intervals between the grid lines are 15 μm, and the number of intervals between the grid lines is (N-3).

[0093] The thickness of the above region is calculated for 20 inlet-side cells C1 randomly selected from the cut surface, and the average value thereof is taken as the thickness T1 of the portion 31 of the first catalyst layer 30 .

[0094] An example of a method for calculating the thickness T2 of the portion 41 of the second catalyst layer 40 is also the same as an example of a method for calculating the thickness T1 of the portion 31 of the first catalyst layer 30. In addition, in an example of a method for calculating the thickness T2 of the portion 41 of the second catalyst layer 40, the exhaust gas purifying catalyst 10 is cut on a plane perpendicular to the axial direction of the substrate 20 (for example, a portion separated by 10 mm from the end of the exhaust gas outflow side of the substrate 20 in the direction opposite to the exhaust gas flow direction X), and the second catalyst layer existing in the outflow side cell C2 arbitrarily selected from the cut surface is observed using a scanning electron microscope (SEM).

[0095] In the exhaust gas purifying catalyst 10, the first catalyst layer 30 and the second catalyst layer 40 satisfy the following formula (3):

[0096] WC1>WC2...(3).

[0097] In the above formula (3), WC1 represents the mass of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided, and WC2 represents the mass of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided.

[0098] The mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided and the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided are not particularly limited as long as they satisfy the above-mentioned formula (3), but from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, the ratio of WC1 to WC2 (WC1 / WC2) is preferably greater than 1.0 and less than 3.5, more preferably greater than 1.05 and less than 2.5, further preferably greater than 1.10 and less than 2.0, further preferably greater than 1.11 and less than 2.0, and further preferably greater than 1.12 and less than 1.5.

[0099] The mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided is not particularly limited as long as the above-mentioned formula (3) is satisfied, but from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, it is preferably from 50 g / L to 90 g / L, more preferably from 55 g / L to 80 g / L, and even more preferably from 60 g / L to 70 g / L.

[0100] The mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided is not particularly limited as long as the above-mentioned formula (3) is satisfied, but from the viewpoint of more effectively achieving the desired flow of exhaust gas described later and the viewpoint of more effectively achieving the desired exhaust gas purification performance described later, it is preferably not less than 40 g / L and not more than 90 g / L, further preferably not less than 50 g / L and not more than 80 g / L, and further preferably not less than 55 g / L and not more than 70 g / L.

[0101] An example of a method for calculating the mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided and the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided is as follows.

[0102] Hereinafter, an example of a method for calculating the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided will be described.

[0103] A sample extending along the axial direction of the substrate 20 and having the same length as the length L of the substrate 20 is cut from the exhaust gas purifying catalyst 10, and the sample is cut on a plane perpendicular to the axial direction of the substrate 20 to prepare a slice S2 of the exhaust gas purifying catalyst 10 including the second catalyst layer 40 but not including the first catalyst layer 30. The slice S2 is, for example, a cylindrical shape having a diameter of 25.4 mm and a length of 10 mm. In addition, the values ​​of the diameter and length of the slice S2 can be changed as needed. Since the length L1 of the first catalyst layer 30 is less than the length L2 of the second catalyst layer 40, the second catalyst layer 40 exists near the end of the exhaust gas outflow side of the exhaust gas purifying catalyst 10, but the first catalyst layer 30 does not exist. Therefore, the slice S2 can be obtained from the end of the exhaust gas outflow side of the exhaust gas purifying catalyst 10. The length of the second catalyst layer 40 contained in the slice S2 is equal to the length of the slice S2.

[0104] A slice of the substrate 20 having the same size as the slice S2 is prepared. The slice of the substrate 20 does not include the first catalyst layer 30 and the second catalyst layer 40 .

[0105] The mass of the slice S2 and the mass of the slice of the substrate 20 are measured, and the mass of the second catalyst layer 40 per unit volume of the slice S2 is calculated based on the following formula.

[0106] The mass of the second catalyst layer 40 per unit volume of the slice S2 = ((mass of the slice S2) - (mass of the slice of the substrate 20)) / (volume of the slice S2)

[0107] In addition, the volume of the slice S2 is the apparent volume of the slice S2. For example, when the slice S2 is a cylindrical shape with a diameter of 25.4 mm and a length of 10 mm, the volume of the slice S2 is π×(12.7 mm) 2 The volumes of other slices (slices S1 and S3 described later) are similar.

[0108] Regarding three slices S2 made from any parts of the exhaust gas purifying catalyst 10, the mass of the second catalyst layer 40 per unit volume of the slices S2 is calculated, and their average value is taken as the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided.

[0109] In addition, when calculating WC2, the mass of the second catalyst layer 40 per unit volume of the slice S2 can also be calculated without using the slice of the substrate 20. An example of such a calculation method is described as follows. The mass and volume of the slice S2 are measured. The composition of the substrate 20 contained in the slice S2 is determined by element mapping of the cross section of the slice S2. The composition of the slice S2 is determined by analyzing using an inductively coupled plasma emission spectrometer or the like. Based on the determined composition of the substrate 20 and the slice S2, the proportion of the mass of the second catalyst layer 40 in the mass of the slice S2 is calculated. Based on the following formula, the mass of the second catalyst layer 40 per unit volume of the slice S2 is calculated.

[0110] The mass of the second catalyst layer 40 per unit volume of the slice S2 = (the mass of the slice S2) x (the ratio of the mass of the second catalyst layer 40 to the mass of the slice S2) / (the volume of the slice S2)

[0111] Hereinafter, an example of a method for calculating the mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided will be described.

[0112] In the case where the second catalyst layer 40 does not extend to the end of the exhaust gas inflow side of the partition wall portion 22, a sample extending along the axial direction of the substrate 20 and having the same length as the length L of the substrate 20 is cut from the exhaust gas purifying catalyst 10, and the sample is cut on a plane perpendicular to the axial direction of the substrate 20 to prepare a slice S1 of the exhaust gas purifying catalyst 10 that includes the first catalyst layer 30 but does not include the second catalyst layer 40. The slice S1 is, for example, a cylindrical shape with a diameter of 25.4 mm and a length of 10 mm. In addition, the values ​​of the diameter and length of the slice S1 can be changed as needed. In the case where the second catalyst layer 40 does not extend to the end of the exhaust gas inflow side of the partition wall portion 22, the first catalyst layer 30 exists near the end of the exhaust gas inflow side of the exhaust gas purifying catalyst 10, but the second catalyst layer 40 does not exist. Therefore, the slice S1 can be obtained from the end of the exhaust gas inflow side of the exhaust gas purifying catalyst 10. The length of the first catalyst layer 30 contained in the slice S1 is equal to the length of the slice S1.

[0113] A slice of the substrate 20 having the same size as the slice S1 is prepared. The slice of the substrate 20 does not include the first catalyst layer 30 and the second catalyst layer 40 .

[0114] The mass of the slice S1 and the mass of the slice of the substrate 20 are measured, and the mass of the first catalyst layer 30 per unit volume of the slice S1 is calculated based on the following formula.

[0115] The mass of the first catalyst layer 30 per unit volume of the slice S1 = ((mass of the slice S1) - (mass of the slice of the substrate 20)) / (volume of the slice S1)

[0116] The mass of the first catalyst layer 30 per unit volume of the three slices S1 prepared from any portion of the exhaust gas purifying catalyst 10 is calculated, and their average value is taken as the mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided.

[0117] Furthermore, when calculating WC1, the mass of the first catalyst layer 30 per unit volume of the slice S1 can also be calculated without using the slice of the substrate 20. An example of such a calculation method is the same as an example of a method for calculating the mass of the second catalyst layer 40 per unit volume of the slice S2 without using the slice of the substrate 20.

[0118] In the case where the second catalyst layer 40 extends to the end of the exhaust gas inflow side of the partition wall portion 22, a sample extending along the axial direction of the substrate 20 and having the same length as the length L of the substrate 20 is cut from the exhaust gas purifying catalyst 10, and the sample is cut on a plane perpendicular to the axial direction of the substrate 20 to prepare a slice S3 of the exhaust gas purifying catalyst 10 containing both the first catalyst layer 30 and the second catalyst layer 40. The slice S3 is, for example, a cylindrical shape having a diameter of 25.4 mm and a length of 10 mm. In addition, the values ​​of the diameter and length of the slice S3 can be changed as needed. In the case where the second catalyst layer 40 extends to the end of the exhaust gas inflow side of the partition wall portion 22, the first catalyst layer 30 and the second catalyst layer 40 exist near the end of the exhaust gas inflow side of the exhaust gas purifying catalyst 10. Therefore, the slice S3 can be obtained from the end of the exhaust gas inflow side of the exhaust gas purifying catalyst 10. The lengths of the first catalyst layer 30 and the second catalyst layer 40 contained in the slice S3 are both equal to the length of the slice S3.

[0119] A slice of the substrate 20 having the same size as the slice S3 is prepared. The slice of the substrate 20 does not include the first catalyst layer 30 and the second catalyst layer 40 .

[0120] The mass of the slice S3 and the mass of the slice of the substrate 20 are measured, and the total mass of the first catalyst layer 30 and the second catalyst layer 40 per unit volume of the slice S3 is calculated based on the following formula.

[0121] Total mass of the first catalyst layer 30 and the second catalyst layer 40 per unit volume of the slice S3 = ((mass of the slice S3) - (mass of the slice of the substrate 20)) / (volume of the slice S3)

[0122] Regarding the three slices S3 made from any part of the exhaust gas purification catalyst 10, the total mass of the first catalyst layer 30 and the second catalyst layer 40 per unit volume of the slice S3 is calculated, and the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided is subtracted from their average value (that is, the average value of the total mass of the first catalyst layer 30 and the second catalyst layer 40 contained in the slice S3 minus the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided) to obtain the value as the mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided.

[0123] Furthermore, when calculating WC1, the total mass of the first catalyst layer 30 and the second catalyst layer 40 per unit volume of the slice S3 can also be calculated without using the slice of the substrate 20. An example of such a calculation method is the same as an example of a method for calculating the mass of the second catalyst layer 40 per unit volume of the slice S2 without using the slice of the substrate 20.

[0124] The first catalyst layer 30 and the second catalyst layer 40 each contain a catalytically active component. The first catalyst layer 30 and the second catalyst layer 40 may each contain one catalytically active component, or may contain two or more catalytically active components. From the viewpoint of improving the exhaust gas purification performance, the second catalyst layer 40 preferably contains a catalytically active component different from the catalytically active component contained in the first catalyst layer 30. As the catalytically active component, for example, precious metal elements such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) can be cited. The precious metal element is contained in the first catalyst layer 30 and the second catalyst layer 40 in a form that can function as a catalytically active component, such as a precious metal, an alloy containing a precious metal element, a compound containing a precious metal element (such as an oxide of a precious metal element), etc. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component is preferably in a granular form. From the viewpoint of improving the exhaust gas purification performance, it is preferred that the first catalyst layer 30 and the second catalyst layer 40 each independently contain at least one catalytic active component selected from platinum (Pt), palladium (Pd) and rhodium (Rh). From the viewpoint of improving the exhaust gas purification performance, especially the NOx purification performance, it is preferred that at least one of the first catalyst layer 30 and the second catalyst layer 40 contains rhodium (Rh), and it is further preferred that both the first catalyst layer 30 and the second catalyst layer 40 contain rhodium (Rh).

[0125] The first catalyst layer 30 and the second catalyst layer 40 may each have a single layer structure or a stacked structure. The stacked structure is, for example, a two-layer structure consisting of a lower layer and an upper layer. The lower layer is located closer to the partition wall 22 than the upper layer.

[0126] When the first catalyst layer 30 has a stacked structure, the portion 31 of the first catalyst layer 30 may be formed by one layer as a whole or a part of one layer, or may be formed by one or more layers as a whole and another layer as a whole or a part of one layer. For example, when the first catalyst layer 30 has a two-layer structure, the portion 31 of the first catalyst layer 30 may be formed by the upper layer as a whole or a part of the upper layer, or may be formed by the upper layer as a whole and a part of the lower layer.

[0127] When the second catalyst layer 40 has a stacked structure, the portion 41 of the second catalyst layer 40 may be formed by one layer as a whole or a part of one layer, or may be formed by one or more layers as a whole and another layer as a whole or a part of one layer. For example, when the second catalyst layer 40 has a two-layer structure, the portion 41 of the second catalyst layer 40 may be formed by the upper layer as a whole or a part of the upper layer, or may be formed by the upper layer as a whole and a part of the lower layer.

[0128] In the stacked structure, the catalytically active components contained in a certain layer may be the same as or different from the catalytically active components contained in other layers. In the stacked structure, when the catalytically active components contained in a certain layer are different from the catalytically active components contained in other layers, it is possible to prevent the reduction of the catalyst performance caused by the inclusion of multiple catalytically active components in a single layer.

[0129] In one embodiment, the first catalyst layer 30 has a single-layer structure, and the second catalyst layer 40 has a two-layer structure (lower layer and upper layer). In addition, the lower layer is a layer located closer to the partition wall portion 22 than the upper layer. In this embodiment, it is preferred that the first catalyst layer 30 contains rhodium (Rh), the lower layer of the second catalyst layer 40 contains a precious metal element (such as palladium (Pd)) other than rhodium (Rh), and the upper layer of the second catalyst layer 40 contains rhodium (Rh). As a result, the NOx purification performance, especially the NOx purification performance during high-speed operation, can be improved, and the NOx emission can be reduced.

[0130] From the viewpoint of improving the exhaust gas purification performance, the amount of the catalytic active component contained in each of the first catalyst layer 30 and the second catalyst layer 40 is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, based on the total mass of each of the first catalyst layer 30 and the second catalyst layer 40. On the other hand, considering the balance between exhaust gas purification performance and cost, the amount of the catalytic active component contained in each of the first catalyst layer 30 and the second catalyst layer 40 is preferably 25% by mass or less, more preferably 20% by mass or less, and more preferably 15% by mass or less, based on the total mass of each of the first catalyst layer 30 and the second catalyst layer 40. The amount of the catalytic active component can be measured using a common method such as inductively coupled plasma emission spectrometry (ICP-AES). In addition, the mass of the precious metal element is the mass calculated on a metal conversion basis.

[0131] From the viewpoint of improving exhaust gas purification performance, the amount of catalytic active components contained in each of the first catalyst layer 30 and the second catalyst layer 40 is preferably 0.01 g or more, and more preferably 0.05 g or more per 1 L volume of the substrate 20. On the other hand, considering the balance between exhaust gas purification performance and cost, the amount of catalytic active components contained in each of the first catalyst layer 30 and the second catalyst layer 40 is preferably 10 g or less, and can be 5 g or less or 3 g or less depending on the circumstances. The volume of the substrate 20 is the apparent volume of the substrate 20. When the outer diameter of the cylindrical portion 21 is set to 2r, the volume of the substrate 20 is given by the formula: Volume of substrate 20 = π×r 2 It is represented by ×(the length L of the substrate 20).

[0132] An example of a method for calculating the amount of the catalytically active component contained in the second catalyst layer 40 per 1 L volume of the substrate 20 is as follows.

[0133] The slice S2 is prepared in the same manner as described above, and the amount of the catalytically active component contained in the slice S2 is measured using a common method such as inductively coupled plasma emission spectrometry (ICP-AES), and the amount of the catalytically active component per unit volume of the slice S2 is calculated. For three slices S2 prepared from any part of the exhaust gas purification catalyst 10, the amount of the catalytically active component per unit volume of the slice S2 is calculated, and their average value is calculated. Based on the following formula, the amount of the catalytically active component contained in the second catalyst layer 40 per 1L volume of the substrate 20 is calculated.

[0134] The amount of the catalytically active component contained in the second catalyst layer 40 per 1 L volume of the substrate 20 = (the average amount of the catalytically active component per unit volume of the slice S2) × (the length L2 of the second catalyst layer 40 / the length L of the substrate 20)

[0135] An example of a method for calculating the amount of the catalytically active component contained in the first catalyst layer 30 per 1 L volume of the substrate 20 is as follows.

[0136] In the case where the second catalyst layer 40 does not extend to the end of the exhaust gas inflow side of the partition wall portion 22, the slice S1 is prepared in the same manner as described above, and the amount of the catalytic active component contained in the slice S1 is measured using a common method such as inductively coupled plasma emission spectrometry (ICP-AES), and the amount of the catalytic active component per unit volume of the slice S1 is calculated. For three slices S1 prepared from any part of the exhaust gas purification catalyst 10, the amount of the catalytic active component per unit volume of the slice S1 is calculated, and their average value is calculated. Based on the following formula, the amount of the catalytic active component contained in the first catalyst layer 30 per 1L volume of the substrate 20 is calculated.

[0137] The amount of the catalytically active component contained in the first catalyst layer 30 per 1 L volume of the substrate 20 = (the average amount of the catalytically active component per unit volume of the slice S1) × (the length L1 of the first catalyst layer 30 / the length L of the substrate 20)

[0138] In the case where the second catalyst layer 40 extends to the end of the exhaust gas inflow side of the partition wall portion 22, the slice S3 is prepared in the same manner as described above, and the amount of the catalytic active component contained in the slice S3 is measured using a common method such as inductively coupled plasma emission spectrometry (ICP-AES), and the amount of the catalytic active component per unit volume of the slice S3 is calculated. For three slices S3 prepared from any part of the exhaust gas purification catalyst 10, the amount of the catalytic active component per unit volume of the slice S3 is calculated, and their average value is calculated. Based on the following formula, the amount of the catalytic active component contained in the first catalyst layer 30 per 1L volume of the substrate 20 is calculated.

[0139] The amount of the catalytically active component contained in the first catalyst layer 30 per 1L volume of the substrate 20 = ((the average amount of the catalytically active component per unit volume of the slice S3) - (the average amount of the catalytically active component per unit volume of the slice S2)) × (the length L1 of the first catalyst layer 30 / the length L of the substrate 20)

[0140] From the viewpoint of efficiently exerting the exhaust gas purification performance based on the catalytic active component, it is preferred that the first catalyst layer 30 and the second catalyst layer 40 further contain a carrier component that supports the catalytic active component. As the carrier component, for example, inorganic oxide particles can be cited, and as the inorganic oxide constituting the inorganic oxide particles, for example, oxygen storage components (also referred to as OSC materials), inorganic oxides other than oxygen storage components, etc. can be cited. From the viewpoint of stably exerting a high exhaust gas purification performance relative to the change of the air-fuel ratio, the first catalyst layer 30 and the second catalyst layer 40 preferably contain an oxygen storage component as a carrier component, and more preferably contain an oxygen storage component and an inorganic oxide other than the oxygen storage component.

[0141] "Inorganic oxide particles loaded with catalytically active ingredients" refers to a state in which catalytically active ingredients are physically or chemically adsorbed or retained on the outer surface or inner surface of the pores of the inorganic oxide particles. For example, in the elemental image obtained by analyzing the cross section of the exhaust gas purification catalyst 10 using EDS (energy dispersive spectrometer), when the inorganic oxide particles and the catalytically active ingredients exist in the same area, it can be judged that the inorganic oxide particles are loaded with catalytically active ingredients. In addition, by measuring the particle size using a scanning electron microscope (SEM), it can be confirmed that the inorganic oxide particles are loaded with catalytically active ingredients. The average particle size of the catalytically active ingredients present on the surface of the inorganic oxide particles is preferably less than 10% relative to the average particle size of the inorganic oxide particles, more preferably less than 3%, and more preferably less than 1%. The average particle size referred to here refers to the average value of the Feret diameters of more than 30 particles when observed using SEM.

[0142] The oxygen storage component is not particularly limited as long as it is a metal oxide whose valence of the constituent elements changes due to the operating conditions of the exhaust gas purification catalyst and has the ability to store oxygen. Examples of the oxygen storage component include metal oxides containing cerium (Ce), and examples of metal oxides containing Ce include CeO 2 、CeO 2 -ZrO 2 (For example, cerium oxide-zirconia composite oxide containing Ce and Zr, CeO 2 and ZrO 2 By using an X-ray diffraction device (XRD), it is possible to form a solid solution derived from CeO 2 -ZrO 2 The single phase of CeO 2 and ZrO 2 From the viewpoint of facilitating the support of the catalytically active component, the oxygen storage component is preferably a porous body.

[0143] The first catalyst layer 30 may contain cerium element (Ce) in the form of oxide (CeO 2 The amount of zirconium element (Zr) in the first catalyst layer 30 is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the total mass of the first catalyst layer 30. 2) is preferably 10 mass % or more and 80 mass % or less, and more preferably 25 mass % or more and 60 mass % or less, based on the total mass of the first catalyst layer 30. The content of cerium element (Ce) in the form of oxide (CeO) can be measured using a common method such as inductively coupled plasma atomic emission spectrometry (ICP-AES). 2 ) and zirconium (Zr) in the form of oxide (ZrO 2 ) is used to convert the measured quantity.

[0144] The second catalyst layer 40 may contain cerium element (Ce) in the form of oxide (CeO 2 The amount of zirconium element (Zr) in the second catalyst layer 40 is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the total mass of the second catalyst layer 40. 2 The amount of cerium (Ce) in terms of oxide (CeO) is preferably 10% by mass or more and 70% by mass or less, and more preferably 30% by mass or more and 50% by mass or less, based on the total mass of the second catalyst layer 40. The amount of cerium (Ce) in terms of oxide (CeO) can be measured using a common method such as inductively coupled plasma atomic emission spectrometry (ICP-AES). 2 ) and zirconium (Zr) in the form of oxide (ZrO 2 ) is used to convert the measured quantity.

[0145] The oxygen storage component may contain rare earth elements other than cerium (Ce). Examples of rare earth elements other than Ce include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). These rare earth elements are added to the oxygen storage component in the form of oxides, for example. Rare earth element oxides include praseodymium (Pr), terbium (Tb), Ln 2 O 3 (Ln represents a rare earth element) and the oxide of praseodymium is usually expressed as Pr 6 O 11 The oxide of terbium is usually expressed as Tb 4 O 7 The oxides of rare earth elements can be combined with CeO 2 -ZrO 2 It may or may not form a solid solution. 2 -ZrO 2The formation of a solid solution can be confirmed by an X-ray diffraction apparatus (XRD) in the same manner as described above.

[0146] Examples of other oxygen storage components include oxides of elements (such as Mn, Fe, and Cu) that are prone to undergo changes in valence state under the conditions of use of the catalyst, and composite oxides containing these elements.

[0147] As inorganic oxides other than oxygen storage components, for example, alumina, silica, silica-alumina, titania, aluminosilicates, etc. can be cited. Among them, alumina is preferred from the viewpoint of heat resistance. From the viewpoint of easy loading of catalyst active components, inorganic oxides other than oxygen storage components are preferably porous bodies.

[0148] The amount of the inorganic oxide other than the oxygen storage component that can be contained in the first catalyst layer 30 is preferably 4 mass % or more and 50 mass % or less, and more preferably 7 mass % or more and 30 mass % or less, based on the total mass of the first catalyst layer 30. The amount of the inorganic oxide other than the oxygen storage component can be measured using a common method such as inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0149] The amount of the inorganic oxide other than the oxygen storage component that can be contained in the second catalyst layer 40 is preferably 5 mass % or more and 50 mass % or less, and more preferably 10 mass % or more and 30 mass % or less, based on the total mass of the second catalyst layer 40. The amount of the inorganic oxide other than the oxygen storage component can be measured using a common method such as inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0150] Inorganic oxides other than oxygen storage components may be modified with oxygen storage components, or may be loaded with oxygen storage components. For example, the inner surface or outer surface of the pore portion of alumina or the like may be modified with oxygen storage components. In addition, the oxygen storage component may be loaded on the inner surface or outer surface of the pore portion of alumina or the like in a dispersed state.

[0151] From the viewpoint of suppressing the decrease in catalytic activity due to phosphorus poisoning and improving heat resistance, the first catalyst layer 30 and the second catalyst layer 40 may each contain an alkaline earth metal compound. Examples of the alkaline earth metal element include barium (Ba), strontium (Sr), and calcium (Ca), and examples of the alkaline earth metal compound include nitrates, carbonates, sulfates, and oxides.

[0152] The flow of exhaust gas

[0153] Since the first catalyst layer 30 and the second catalyst layer 40 satisfy the above-mentioned formulas (1) to (3), the exhaust gas purification catalyst 10 has improved exhaust gas purification performance (especially the exhaust gas purification performance during high-speed operation of the internal combustion engine). It can be considered that this effect is related to the flow of exhaust gas in the exhaust gas purification catalyst 10. Figure 6 The flow of exhaust gas in the exhaust gas purifying catalyst 10 will be described.

[0154] like Figure 6 As shown, in the flow of the exhaust gas in the exhaust gas purifying catalyst 10, there may be a path F1 and a path F2. In the path F1, the exhaust gas flowing along the exhaust gas flow direction X flows into the exhaust gas purifying catalyst 10 from the end C11 on the exhaust gas inlet side of the inlet side chamber C1, passes through the partition wall portion 22 and the second catalyst layer 40 in sequence, reaches the outflow side chamber C2, and flows out of the exhaust gas purifying catalyst 10 from the end C21 on the exhaust gas outflow side of the outflow side chamber C2. In the path F2, the exhaust gas flowing along the exhaust gas flow direction X flows into the exhaust gas purifying catalyst 10 from the end C11 on the exhaust gas inlet side of the inlet side chamber C1, passes through the first catalyst layer 30 and the partition wall portion 22 in sequence, reaches the outflow side chamber C2, and flows out of the exhaust gas purifying catalyst 10 from the end C21 on the exhaust gas outflow side of the outflow side chamber C2.

[0155] It can be considered that by making the first catalyst layer 30 and the second catalyst layer 40 satisfy the above-mentioned formulas (1) to (3), the path F1 dominates the flow of the exhaust gas in the exhaust gas purifying catalyst 10. As its mechanism, the following mechanism can be inferred. Since the thickness T1 of the portion 31 of the first catalyst layer 30 is smaller than the thickness T2 of the portion 41 of the second catalyst layer 40, on the other hand, the mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided is greater than the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided, the density of the first catalyst layer 30 is greater than the density of the second catalyst layer 40. Therefore, the exhaust gas flowing into the exhaust gas purifying catalyst 10 from the end C11 on the exhaust gas inlet side of the inlet side chamber C1 is easier to pass through the second catalyst layer 40 than the first catalyst layer 30. Furthermore, the length L2 of the second catalyst layer 40 through which the exhaust gas can pass easily is greater than the length L1 of the first catalyst layer 30 through which the exhaust gas can pass less easily. Therefore, it can be considered that the path F1 is dominant in the flow of the exhaust gas in the exhaust gas purifying catalyst 10 .

[0156] When the path F2 is dominant, the exhaust gas flowing along the exhaust gas flow direction X flows into the exhaust gas purifying catalyst 10 from the end C11 on the exhaust gas inlet side of the inlet side chamber C1, passes through the first catalyst layer 30 and the partition wall portion 22 in sequence, reaches the outlet side chamber C2, and flows out of the exhaust gas purifying catalyst 10 from the end C21 on the exhaust gas outlet side of the outlet side chamber C2. In this case, particulate matter (PM) in the exhaust gas is easily accumulated in the first catalyst layer 30. The PM accumulated in the first catalyst layer 30 hinders the contact between the catalytic active components contained in the first catalyst layer 30 and harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the exhaust gas, thereby reducing the exhaust gas purification performance of the first catalyst layer 30. In particular, when PM in the exhaust gas discharged before the internal combustion engine reaches high-speed operation accumulates in the first catalyst layer 30, the exhaust gas purification performance of the internal combustion engine at high-speed operation is significantly reduced.

[0157] On the other hand, when the path F1 is dominant, the exhaust gas flowing along the exhaust gas flow direction X flows into the exhaust gas purifying catalyst 10 from the end C11 on the exhaust gas inlet side of the inlet side chamber C1, passes through the partition wall portion 22 and the second catalyst layer 40 in sequence, reaches the outlet side chamber C2, and flows out of the exhaust gas purifying catalyst 10 from the end C21 on the exhaust gas outflow side of the outlet side chamber C2. In this case, particulate matter (PM) in the exhaust gas is easily accumulated in the partition wall portion 22, but is not easily accumulated in the first catalyst layer 30 and the second catalyst layer 40. Therefore, the contact between the catalytic active components contained in the first catalyst layer 30 and the second catalyst layer 40 and the harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the exhaust gas is not easily hindered by PM, and the exhaust gas purification performance of the first catalyst layer 30 and the second catalyst layer 40 can be fully exerted. Therefore, the exhaust gas purification performance when the path F1 is dominant is improved compared to the exhaust gas purification performance when the path F2 is dominant. In particular, the exhaust gas purification performance during high-speed operation of the internal combustion engine is significantly improved.

[0158] When the purpose is to improve the NOx purification performance among the exhaust gas purification performance (particularly, the NOx purification performance during high-speed operation of the internal combustion engine), at least one of the first catalyst layer 30 and the second catalyst layer 40 preferably contains rhodium element (Rh).

[0159] When the path F1 is dominant, particulate matter (PM) in the exhaust gas is easily accumulated in the partition wall portion 22, but is not easily accumulated in the first catalyst layer 30 and the second catalyst layer 40. Therefore, the contact between the rhodium element (Rh) contained in the first catalyst layer 30 and / or the second catalyst layer 40 and the NOx in the exhaust gas is not easily hindered by PM, and the NOx purification performance of the first catalyst layer 30 and / or the second catalyst layer 40 can be fully exerted. Therefore, compared with the NOx purification performance when the path F2 is dominant, the NOx purification performance when the path F1 is dominant is improved. In particular, the NOx purification performance during high-speed operation of the internal combustion engine is significantly improved.

[0160] When comparing the case where the path F1 is dominant and the case where the path F2 is dominant, the NOx purification performance of the rhodium element (Rh) contained in the first catalyst layer 30 is significantly different. Therefore, when at least the first catalyst layer 30 of the first catalyst layer 30 and the second catalyst layer 40 contains the rhodium element (Rh), the effect when the path F1 is dominant is very significant.

[0161] In the case where the second catalyst layer 40 contains rhodium (Rh), from the viewpoint of more effectively exerting the NOx purification performance of the rhodium (Rh) contained in the second catalyst layer 40, it is preferred that the second catalyst layer 40 has a two-layer structure (lower layer and upper layer), the lower layer of the second catalyst layer 40 contains a precious metal element (such as palladium (Pd)) other than rhodium (Rh), and the upper layer of the second catalyst layer 40 contains rhodium (Rh). In addition, the lower layer is a layer located closer to the partition wall portion 22 than the upper layer. When the path F1 is dominant, the exhaust gas passes through the partition wall portion 22 and the second catalyst layer 40 in sequence, but at this time, PM in the exhaust gas is easily accumulated in the lower layer of the second catalyst layer 40, and is not easily accumulated in the upper layer of the second catalyst layer 40. Therefore, the NOx purification performance of the rhodium (Rh) contained in the upper layer of the second catalyst layer 40 is not easily affected by PM. Therefore, when the second catalyst layer 40 has a two-layer structure (a lower layer and an upper layer), the lower layer of the second catalyst layer 40 contains a precious metal other than rhodium (Rh) (for example, palladium (Pd), etc.), and the upper layer of the second catalyst layer 40 contains rhodium (Rh), the NOx purification performance of the second catalyst layer 40 can be more effectively exerted.

[0162] 《Manufacturing method》

[0163] Next, a method for producing the exhaust gas-purifying catalyst 10 will be described.

[0164] Prepare a substrate 20, a slurry for forming the first catalyst layer 30, and a slurry for forming the second catalyst layer 40. When the first catalyst layer 30 has a laminated structure, two or more slurries are prepared as slurries for forming the first catalyst layer 30. When the second catalyst layer 40 has a laminated structure, two or more slurries are prepared as slurries for forming the second catalyst layer 40.

[0165] The composition of the slurry used to form the first catalyst layer 30 is adjusted according to the composition of the first catalyst layer 30. The composition of the slurry used to form the second catalyst layer 40 is adjusted according to the composition of the second catalyst layer 40. The slurry contains, for example, a supply source of a precious metal element, inorganic oxide particles, a binder, a pore former, a solvent, and the like. As a supply source of a precious metal element, for example, a salt of a precious metal element can be cited, and as a salt of a precious metal element, for example, a nitrate, an ammine complex salt, an acetate, a chloride, and the like can be cited. As inorganic oxide particles, for example, an oxygen storage component, an inorganic oxide other than an oxygen storage component, and the like can be cited. The descriptions related to the oxygen storage component and the inorganic oxide other than the oxygen storage component are the same as above. As a binder, for example, an alumina sol, a zirconia sol, a titania sol, a silica sol, and the like can be cited. As the pore-forming agent, for example, cross-linked poly(meth) methyl acrylate particles, cross-linked poly(meth) butyl acrylate particles, cross-linked polystyrene particles, cross-linked polyacrylate particles, melamine resins, etc. can be cited. As the solvent, for example, water, organic solvents, etc. can be cited. As the organic solvent, for example, alcohol, acetone, dimethyl sulfoxide, dimethylformamide, etc. can be cited. The solvent can be a single solvent or a mixture of two or more solvents. As a mixture of two or more solvents, for example, a mixture of water and one or more organic solvents, a mixture of two or more organic solvents, etc. can be cited.

[0166] The end of the exhaust gas inflow side of the substrate 20 is immersed in the slurry for forming the first catalyst layer 30, and after the slurry is sucked from the opposite side, the sucked slurry is dried. In the case where the first catalyst layer 30 has a stacked structure, this operation is repeated. Thus, the precursor layer of the first catalyst layer 30 is formed. By adjusting the solid content concentration, viscosity, etc. of the slurry, the length of the precursor layer of the first catalyst layer 30 (and thus the length L1 of the first catalyst layer 30) can be adjusted. In addition, by adjusting the coating amount of the slurry, the type of material constituting the slurry, the particle size of the pore-forming agent contained in the slurry, etc., the thickness of the precursor layer of the first catalyst layer 30 (and thus the thickness T1 of the portion 31 of the first catalyst layer 30) and the mass of the precursor layer of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the precursor layer of the first catalyst layer 30 is provided (and thus the mass WC1 of the first catalyst layer 30 per unit volume of the portion of the substrate 20 where the first catalyst layer 30 is provided) can be adjusted. The drying temperature is usually 40° C. or higher and 120° C. or lower. The drying time can be appropriately adjusted according to the drying temperature.

[0167] The end of the exhaust gas outflow side of the substrate 20 is immersed in the slurry for forming the second catalyst layer 40, and after the slurry is sucked from the opposite side, the sucked slurry is dried. In the case where the second catalyst layer 40 has a stacked structure, this operation is repeated. Thus, the precursor layer of the second catalyst layer 40 is formed. By adjusting the solid content concentration, viscosity, etc. of the slurry, the length of the precursor layer of the second catalyst layer 40 (and then the length L2 of the second catalyst layer 40) can be adjusted. In addition, by adjusting the coating amount of the slurry, the type of material constituting the slurry, the particle size of the pore-forming agent contained in the slurry, etc., the thickness of the precursor layer of the second catalyst layer 40 (and then the thickness T2 of the portion 41 of the second catalyst layer 40) and the mass of the precursor layer of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the precursor layer of the second catalyst layer 40 is provided (and then the mass WC2 of the second catalyst layer 40 per unit volume of the portion of the substrate 20 where the second catalyst layer 40 is provided) can be adjusted. The drying temperature is usually 40° C. or higher and 120° C. or lower. The drying time is appropriately adjusted depending on the drying temperature.

[0168] The particle size of the pore former can be adjusted appropriately, but from the viewpoints of suppression of peeling, suppression of pressure loss increase, PM collection performance, etc., the median particle size D of the pore former is preferably 0.1547 W / cm2. 50 The particle size of the pore-forming agent is usually 5 μm or more and 50 μm or less, preferably 5 μm or more and 40 μm or less, and more preferably 10 μm or more and 30 μm or less. The larger the particle size of the pore-forming agent, the larger the thickness of the first catalyst layer 30 (and the thickness T1 of the portion 31 of the first catalyst layer 30) and the thickness of the second catalyst layer 40 (the thickness T2 of the portion 41 of the second catalyst layer 40). 50It is the particle size at which the cumulative volume accounts for 50% in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method. 50 D is measured by using an automatic sample feeder for a laser diffraction scattering particle size distribution measuring device (Microtrac SDC manufactured by MICROTRAC-BEL), placing a pore-forming agent in an aqueous dispersion medium, irradiating 40W ultrasonic waves for 360 seconds at a flow rate of 26 mL / sec, and then using a laser diffraction scattering particle size distribution measuring device (MICROTRAC MT3300EXII manufactured by MICROTRAC-BEL). For the measurement, two measurements were performed under the conditions of setting the particle refractive index to 1.5, setting the particle shape to a true sphere, setting the solvent refractive index to 1.3, setting the zero setting to 30 seconds, and setting the measurement time to 30 seconds, and the average value of the obtained measured values ​​was taken as D 50 . Pure water was used as the aqueous dispersion medium.

[0169] The particle size of the inorganic oxide particles can be adjusted appropriately, but from the viewpoints of suppressing peeling, suppressing the increase in pressure loss, improving PM collection performance, etc., the particle size D of the inorganic oxide particles is preferably 0.1447 W / m2. 90 It is preferably 10 μm or more and 40 μm or less, more preferably 15 μm or more and 35 μm or less, and still more preferably 20 μm or more and 30 μm or less. 90 It is the particle size at which the cumulative volume accounts for 90% in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method. 90 The measurement is performed by using an automatic sample feeder for a laser diffraction scattering particle size distribution measuring device (Microtrac SDC manufactured by MICROTRAC-BEL), placing the inorganic oxide particles in an aqueous dispersion medium, irradiating 40W ultrasonic waves for 360 seconds at a flow rate of 26 mL / sec, and then using a laser diffraction scattering particle size distribution measuring device (MICROTRAC MT3300EXII manufactured by MICROTRAC-BEL). For the measurement, two measurements were performed under the conditions of setting the particle refractive index to 1.5, the particle shape to a true sphere, the solvent refractive index to 1.3, the zero setting to 30 seconds, and the measurement time to 30 seconds, and the average value of the obtained measured values ​​was taken as D 90 . Pure water was used as the aqueous dispersion medium.

[0170] After forming the precursor layer of the first catalyst layer 30 and the precursor layer of the second catalyst layer 40, calcination is performed. Thus, the first catalyst layer 30 and the second catalyst layer 40 are formed. The calcination temperature is usually 350° C. or higher and 550° C. or lower. The calcination time is usually 2 hours or higher and 5 hours or lower. The atmosphere during calcination is usually an air atmosphere.

[0171] Example

[0172] Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to the Examples.

[0173] <Example 1>

[0174] (1) Preparation of the first slurry

[0175] Prepare CeO 2 -ZrO 2 Solid solution powder and alumina powder. As CeO 2 -ZrO 2 Solid solution powder containing 15 mass% CeO 2 , 70 mass% ZrO 2 , 15 mass% of CeO oxides of rare earth elements other than Ce 2 -ZrO 2 Solid solution powder.

[0176] CeO 2 -ZrO 2 The solid solution powder and the alumina powder are mixed to prepare a mixed powder. CeO in the mixed powder 2 -ZrO 2 The mass ratio of solid solution powder to alumina powder (CeO 2 -ZrO 2 The mass of solid solution powder: mass of alumina powder) was adjusted to 84:8. D 90 is 25μm.

[0177] The mixed powder was added to an aqueous rhodium nitrate solution to obtain a mixed solution. 50 A first slurry was prepared by mixing cross-linked poly(methyl)(meth)acrylate particles having a diameter of 20 μm, alumina sol, zirconia sol, and water as a solvent.

[0178] The amount of water contained in the first slurry (water contained in the rhodium nitrate aqueous solution, water used as a solvent, water contained in the alumina sol, water contained in the zirconia sol, etc.) was adjusted to 78 mass % based on the mass of the first slurry (100 mass %).

[0179] The amounts of the pore-forming agent, alumina sol, zirconia sol and rhodium contained in the first slurry were adjusted so that, based on the mass of the catalyst layer formed by drying and calcining the first slurry (100 mass%), the pore-forming agent accounted for 10 mass%, the solid content of the alumina sol was 3 mass%, the solid content of the zirconia sol was 5 mass%, and the rhodium was 0.3 mass% in terms of metal conversion.

[0180] The mass of the catalyst layer formed by drying and calcining the first slurry is obtained by subtracting the mass of the components (such as solvent and pore former) that disappear by drying and calcining the first slurry from the mass of the first slurry.

[0181] (2) Preparation of the second slurry

[0182] Prepare CeO 2 -ZrO 2 Solid solution powder and alumina powder. As CeO 2 -ZrO 2 Solid solution powder containing 40% by mass of CeO 2 , 50 mass% ZrO 2 , 10 mass% of CeO oxides of rare earth elements other than Ce 2 -ZrO 2 Solid solution powder.

[0183] CeO 2 -ZrO 2 The solid solution powder and the alumina powder are mixed to prepare a mixed powder. CeO in the mixed powder 2 -ZrO 2 The mass ratio of solid solution powder to alumina powder (CeO 2 -ZrO 2 The mass of solid solution powder: mass of alumina powder) was adjusted to 60:22. 90 is 30μm.

[0184] The mixed powder was added to a palladium nitrate aqueous solution to obtain a mixed solution. 50 A second slurry was prepared by mixing cross-linked poly(methyl)(meth)acrylate particles having a diameter of 20 μm, barium hydroxide, alumina sol, zirconium oxide sol, and water as a solvent.

[0185] The amount of water contained in the second slurry (water contained in the palladium nitrate aqueous solution, water used as a solvent, water contained in the alumina sol, water contained in the zirconia sol, etc.) was adjusted to 85 mass % based on the mass of the second slurry (100 mass %).

[0186] The amounts of the pore-forming agent, barium hydroxide, alumina sol, zirconia sol and palladium contained in the second slurry were adjusted so that, based on the mass of the catalyst layer formed by drying and calcining the second slurry (100 mass%), the pore-forming agent was 25 mass%, the barium hydroxide was 8.6 mass% calculated as barium carbonate, the solid content of the alumina sol was 3 mass%, the solid content of the zirconia sol was 3 mass%, and the palladium was 3.8 mass% calculated as metal.

[0187] The mass of the catalyst layer formed by drying and calcining the second slurry is obtained by subtracting the mass of the components (such as solvent and pore former) that disappear by drying and calcining the second slurry from the mass of the second slurry.

[0188] (3) Manufacture of catalysts for exhaust gas purification

[0189] Prepared with Figure 1 The substrate of the structure shown is a substrate having an inlet chamber extending along the axial direction of the substrate, an outlet chamber extending along the axial direction of the substrate, and a porous partition wall separating the inlet chamber and the outlet chamber. The thickness of the partition wall is 254 μm, the total number of the inlet chamber and the outlet chamber in the cross section perpendicular to the axial direction of the substrate is 300 chambers per square inch, and the volume of the substrate is 1.4 L. The area of ​​the opening of the inlet chamber in the inlet side end surface of the substrate is substantially the same as the area of ​​the opening of the outlet chamber in the outlet side end surface of the substrate.

[0190] The end of the exhaust gas inflow side of the substrate was immersed in the first slurry, and after the first slurry was sucked from the opposite side, it was dried at 70°C for 10 minutes. In this way, a precursor layer (the first catalyst layer before calcination) formed of the solid components of the first slurry was formed on the inflow side of the partition wall portion of the substrate. The formed layer extends from the end of the exhaust gas inflow side of the substrate along the exhaust gas flow direction.

[0191] After drying, the end of the exhaust gas outflow side of the substrate is immersed in the second slurry, and after the second slurry is sucked from the opposite side, it is dried at 70°C for 10 minutes. In this way, a precursor layer formed by the solid components of the second slurry is formed on the outflow side chamber side of the partition wall portion of the substrate. The formed layer extends from the end of the exhaust gas outflow side of the substrate in a direction opposite to the exhaust gas flow direction. After drying, the end of the exhaust gas outflow side of the substrate is immersed in the first slurry, and after the first slurry is sucked from the opposite side, it is dried at 70°C for 10 minutes. In this way, a layer having a lower layer formed by the solid components of the second slurry and an upper layer formed by the solid components of the first slurry is formed on the outflow side chamber side of the partition wall portion of the substrate (the second catalyst layer before calcination). The formed layer extends from the end of the exhaust gas outflow side of the substrate in a direction opposite to the exhaust gas flow direction.

[0192] Thereafter, the substrate was calcined at 450° C. for 1 hour to form the first catalyst layer and the second catalyst layer on the substrate. In this way, the exhaust gas purification catalyst of Example 1 was obtained. The first catalyst layer had a single-layer structure, and the second catalyst layer had a two-layer structure.

[0193] When the end of the exhaust gas inlet side of the substrate was immersed in the first slurry, the impregnation conditions were adjusted so that the target value of the percentage of the length L1 of the first catalyst layer relative to the length L of the substrate was 45%, and the target value of the mass WC1 of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer was provided was 55.6 g / L.

[0194] The measured value of the percentage of the length L1 of the first catalyst layer with respect to the length L of the substrate was 43.3%.

[0195] The actual measured value of WC1 calculated based on the following formula was 57.2 g / L.

[0196] Measured value of WC1 = ((mass of substrate after formation of the first catalyst layer) - (mass of substrate before formation of the first catalyst layer)) / ((volume of substrate) × (measured value of percentage of length L1 of the first catalyst layer relative to length L of the substrate))

[0197] Furthermore, the number of the first catalyst layers formed on the substrate is equal to the number of the inlet-side cells included in the substrate.

[0198] When the end of the exhaust gas outflow side of the substrate was immersed in the second slurry and the first slurry, the impregnation conditions were adjusted so that the target value of the percentage of the length L2 of the second catalyst layer relative to the length L of the substrate was 70%, and the target value of the mass WC2 of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer was provided was 50.0 g / L.

[0199] The measured value of the percentage of the length L2 of the second catalyst layer with respect to the length L of the substrate was 72.4%.

[0200] The actual measured value of WC2 calculated based on the following formula was 48.0 g / L.

[0201] Measured value of WC2 = ((mass of substrate after formation of second catalyst layer) - (mass of substrate before formation of second catalyst layer)) / ((volume of substrate) × (measured value of percentage of length L2 of second catalyst layer relative to length L of substrate))

[0202] Furthermore, the number of the second catalyst layers formed on the substrate is equal to the number of the outflow-side cells included in the substrate.

[0203] The exhaust gas purifying catalyst of Example 1 was cut on a plane perpendicular to the axial direction of the substrate, and the first catalyst layer and the second catalyst layer present on the cut surface were observed using a scanning electron microscope (SEM), and the morphologies of the first catalyst layer and the second catalyst layer were determined. When observing the first catalyst layer, the exhaust gas purifying catalyst was cut at a position separated by 10 mm from the end of the exhaust gas inflow side of the substrate in the axial direction of the substrate, and when observing the second catalyst layer, the exhaust gas purifying catalyst was cut at a position separated by 10 mm from the end of the exhaust gas outflow side of the substrate in the axial direction of the substrate.

[0204] When observing the cross section with SEM, the field magnification was 300 times, and the field width (length in the direction perpendicular to the axial direction of the substrate) was 500 to 600 μm. The area observed with SEM was set to exclude the corners of the cells.

[0205] The SEM observation images are shown in Figure 7 and Figure 8 .like Figure 7 As shown in FIG. 1 , the region where the partition wall portion of the substrate exists and the region where the first catalyst layer exists are determined based on the difference in morphology between the first catalyst layer and the partition wall portion of the substrate. Figure 8 As shown, the region where the partition wall portion of the substrate exists and the region where the second catalyst layer exists are also determined based on the difference in morphology between the second catalyst layer and the partition wall portion of the substrate.

[0206] The first catalyst layer has a portion formed on the surface of the inflow-side cell side of the partition wall portion from the end of the exhaust gas inflow side of the partition wall portion along the exhaust gas flow direction. In addition, the surface of the inflow-side cell side of the partition wall portion is the outer surface of the inflow-side cell side constituting the outer shape of the partition wall portion. The portion formed on the surface of the inflow-side cell side of the partition wall portion is a portion that bulges from the outer surface of the inflow-side cell side of the partition wall portion toward the inflow-side cell side, and is sometimes referred to as the "bulging portion of the first catalyst layer" hereinafter.

[0207] The second catalyst layer has a portion formed on the surface of the outflow-side cell side of the partition wall portion, which is formed along the direction opposite to the exhaust gas flow direction from the end of the exhaust gas outflow side of the partition wall portion. In addition, the surface of the outflow-side cell side of the partition wall portion is the outer surface of the outflow-side cell side that constitutes the outer shape of the partition wall portion. The portion formed on the surface of the outflow-side cell side of the partition wall portion is a portion that bulges from the outer surface of the outflow-side cell side of the partition wall portion toward the outflow-side cell side, and is sometimes referred to as the "bulging portion of the second catalyst layer" below.

[0208] like Figure 7 As shown, in the SEM observation image, the 1st to 38th grid lines perpendicular to the axial direction of the substrate are drawn in sequence at intervals of 15 μm from the left end side, and the contour lines of the area where the partition wall portion of the substrate exists and the intersection points between the grid lines are connected with straight lines to determine the surface position of the partition wall portion of the substrate. Similarly, the contour lines of the area where the first catalyst layer exists and the intersection points between the grid lines are connected with straight lines to determine the surface position of the first catalyst layer. When the change in the thickness direction from a certain intersection P1 to an intersection P2 adjacent to the intersection P1 exceeds the interval (15 μm) of the grid lines, the intersection P2 is not used to determine the surface position (that is, the intersection P2 is removed from the intersections connected by straight lines). In addition, when the amount of change in the thickness direction from the intersection point P1 to the intersection point P2 adjacent to the intersection point P1 exceeds the interval (15 μm) of the grid lines and the amount of change in the thickness direction from the intersection point P1 to the intersection point P3 adjacent to the intersection point P2 also exceeds the interval (15 μm) of the grid lines, not only the intersection point P2 is not used to determine the position of the surface, but also the intersection point P3 is not used to determine the position of the surface (that is, the intersection point P2 and the intersection point P3 are removed from the intersection points connected by the straight line). When five intersection points are continuously removed from the intersection points connected by the straight line in this way, the SEM image is not used for thickness measurement.

[0209] After determining the position of the surface of the partition wall portion of the substrate and the position of the surface of the first catalyst layer, the image analysis software is used to find the area of ​​the region surrounded by the second grid line, the 37th grid line, the surface of the partition wall portion of the substrate, and the surface of the first catalyst layer. As the image analysis software, AreaQ (made by ESTECH) was used. In addition, since the two ends of the image are easily unclear and it is difficult to determine the position of the surface of the partition wall portion and the position of the surface of the first catalyst layer, the first grid line and the 38th grid line are not used.

[0210] After the area of ​​the above region is determined, the thickness of the above region is calculated based on the following formula.

[0211] The thickness of the above region = the area of ​​the above region / (grid line spacing × the number of grid line spacings)

[0212] In addition, the interval between the grid lines is 15 μm, and the number of the intervals between the grid lines is 35.

[0213] The thickness of the above region was calculated for 20 first catalyst layers randomly selected from the cut surface, and the average value of the calculated values ​​was found to be 30.2 μm. The average value was taken as the thickness T1 of the raised portion of the first catalyst layer. The thickness T2 of the raised portion of the second catalyst layer was calculated in the same manner and the result was 46.6 μm.

[0214] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 1.

[0215] (4) Evaluation of exhaust gas purification performance

[0216] The exhaust gas purifying catalyst of Example 1 was subjected to the following durability conditions as a degradation treatment assuming a vehicle running for 100,000 km to 200,000 km.

[0217] <Durability conditions>

[0218] Durable engine: Passenger NA 2L gasoline engine

[0219] Gasoline used: Commercially available regular gasoline

[0220] Processing temperature: 900℃

[0221] Processing time: 100 hours

[0222] The exhaust gas purification catalyst of Example 1 was arranged in the exhaust path of the engine, and a durability test was carried out under the above conditions. The exhaust gas purification catalyst after the durability test was set in a vehicle (a passenger car equipped with a 1.5L direct injection turbo engine), and the vehicle was operated according to the operating conditions of the international harmonized exhaust gas test model (WLTC). The emission of nitrogen oxides (NOx) in the exhaust gas passing through the exhaust gas purification catalyst during low-speed operation from the start of operation to 589 seconds, medium-speed operation from the start of operation to 1022 seconds, high-speed operation from the start of operation to 1477 seconds, and ultra-high-speed operation from the start of operation to 1800 seconds was measured, and the emission per unit driving distance (mg / km) was calculated. As gasoline, a certification test fuel was used, and as an exhaust gas measuring device, an exhaust gas measuring device manufactured by Horiba, Ltd. was used. The results are shown in Table 2. Table 2 shows the WLTC discharge amount (total discharge amount) per unit running distance and the discharge amount during super high speed operation per unit running distance.

[0223] <Example 2>

[0224] In addition to changing the median particle size D of the pore former (cross-linked poly(methyl)methacrylate particles) in the first slurry and the second slurry to 50 An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the particle size was changed to 5 μm.

[0225] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 44.1%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 68.2%.

[0226] The measured value of WC1 is 56.4 g / L, and the measured value of WC2 is 50.0 g / L.

[0227] The thickness T1 of the raised portion of the first catalyst layer was 25.3 μm, and the thickness T2 of the raised portion of the second catalyst layer was 40.9 μm.

[0228] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 2, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 2 evaluated in the same manner as in Example 1.

[0229] <Example 3>

[0230] An exhaust gas purifying catalyst was produced in the same manner as in Example 1 except that the target value of the percentage of the length L1 of the first catalyst layer relative to the length L of the substrate was changed to 40%, the target value of WC1 was changed to 78.0 g / L, and the target value of WC2 was changed to 70 g / L.

[0231] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 40.9%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 71.2%.

[0232] The measured value of WC1 is 77.4 g / L, and the measured value of WC2 is 69.4 g / L.

[0233] The thickness T1 of the raised portion of the first catalyst layer was 38.2 μm, and the thickness T2 of the raised portion of the second catalyst layer was 75.6 μm.

[0234] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 3, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 3 evaluated in the same manner as in Example 1.

[0235] <Example 4>

[0236] An exhaust gas purifying catalyst was produced in the same manner as in Example 1 except that the target value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was changed to 35% and the target value of WC1 was changed to 71.4 g / L.

[0237] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 32.0%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 72.0%.

[0238] The measured value of WC1 is 78.1 g / L, and the measured value of WC2 is 48.6 g / L.

[0239] The thickness T1 of the raised portion of the first catalyst layer was 40.2 μm, and the thickness T2 of the raised portion of the second catalyst layer was 47.4 μm.

[0240] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 4, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 4 evaluated in the same manner as in Example 1.

[0241] <Example 5>

[0242] An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the target value of the percentage of the length L2 of the second catalyst layer with respect to the length L of the substrate was changed to 80%.

[0243] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 42.5%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 82.0%.

[0244] The measured value of WC1 is 59.9 g / L, and the measured value of WC2 is 44.3 g / L.

[0245] The thickness T1 of the raised portion of the first catalyst layer was 31.6 μm, and the thickness T2 of the raised portion of the second catalyst layer was 39.0 μm.

[0246] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 5, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 5 evaluated in the same manner as in Example 1.

[0247] <Example 6>

[0248] An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the target value of WC1 was reduced by 20% and the target value of WC2 was reduced by 20%.

[0249] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 44.1%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 69.3%.

[0250] The measured value of WC1 is 45.4 g / L, and the measured value of WC2 is 40.4 g / L.

[0251] The thickness T1 of the raised portion of the first catalyst layer was 24.9 μm, and the thickness T2 of the raised portion of the second catalyst layer was 37.2 μm.

[0252] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 6, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 6 evaluated in the same manner as in Example 1.

[0253] <Example 7>

[0254] In addition to mixing the mixed powder (CeO 2 -ZrO 2 D 90 An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the particle size was changed to 15 μm.

[0255] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 45.7%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 72.4%.

[0256] The measured value of WC1 is 54.5 g / L, and the measured value of WC2 is 49.7 g / L.

[0257] The thickness T1 of the raised portion of the first catalyst layer was 12.9 μm, and the thickness T2 of the raised portion of the second catalyst layer was 43.0 μm.

[0258] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 7, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 7 evaluated in the same manner as in Example 1.

[0259] <Example 8>

[0260] An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the target value of WC1 was increased by 60% and the target value of WC2 was decreased by 43%.

[0261] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 46.5%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 72.4%.

[0262] The measured value of WC1 is 86.9 g / L, and the measured value of WC2 is 28.6 g / L.

[0263] The thickness T1 of the raised portion of the first catalyst layer was 22.2 μm, and the thickness T2 of the raised portion of the second catalyst layer was 24.5 μm.

[0264] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Example 8, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Example 8 evaluated in the same manner as in Example 1.

[0265] <Comparative Example 1>

[0266] An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the first catalyst layer had a two-layer structure similar to that of the second catalyst layer and the second catalyst layer had a single-layer structure similar to that of the first catalyst layer.

[0267] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 42.5%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 69.3%.

[0268] The measured value of WC1 is 57.3 g / L, and the measured value of WC2 is 49.6 g / L.

[0269] The thickness T1 of the raised portion of the first catalyst layer was 52.8 μm, and the thickness T2 of the raised portion of the second catalyst layer was 25.7 μm.

[0270] Table 1 shows the characteristics of the exhaust gas purifying catalyst of Comparative Example 1, and Table 2 shows the exhaust gas purifying performance of the exhaust gas purifying catalyst of Comparative Example 1 evaluated in the same manner as in Example 1.

[0271] <Comparative Example 2>

[0272] An exhaust gas purification catalyst was manufactured in the same manner as in Example 1, except that no pore former was added to either the first slurry or the second slurry, the second slurry was used to form the first catalyst layer having a single-layer structure, the first slurry was used to form the second catalyst layer having a single-layer structure, the target value of the percentage of the length L1 of the first catalyst layer relative to the length L of the substrate was changed to 40%, the target value of WC1 was changed to 62.5 g / L, and the target value of WC2 was changed to 64.3 g / L.

[0273] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 42.2%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 66.0%.

[0274] The measured value of WC1 is 66.7 g / L, and the measured value of WC2 is 68.2 g / L.

[0275] The thickness T1 of the raised portion of the first catalyst layer was 55.2 μm, and the thickness T2 of the raised portion of the second catalyst layer was 30.2 μm.

[0276] Table 1 shows the characteristics of the exhaust gas purifying catalyst of Comparative Example 2, and Table 2 shows the exhaust gas purifying performance of the exhaust gas purifying catalyst of Comparative Example 2 evaluated in the same manner as in Example 1.

[0277] <Comparative Example 3>

[0278] An exhaust gas-purifying catalyst was produced in the same manner as in Example 1, except that the pore former was not added to either the first slurry or the second slurry.

[0279] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 43.3%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 71.3%.

[0280] The measured value of WC1 is 58.0 g / L, and the measured value of WC2 is 49.5 g / L.

[0281] The thickness T1 of the raised portion of the first catalyst layer was 39.8 μm, and the thickness T2 of the raised portion of the second catalyst layer was 39.8 μm.

[0282] Table 1 shows the characteristics of the exhaust gas purifying catalyst of Comparative Example 3, and Table 2 shows the exhaust gas purifying performance of the exhaust gas purifying catalyst of Comparative Example 3 evaluated in the same manner as in Example 1.

[0283] <Comparative Example 4>

[0284] An exhaust gas purification catalyst was manufactured in the same manner as in Example 1, except that the first catalyst layer had the same two-layer structure as the second catalyst layer and the second catalyst layer had the same single-layer structure as the first catalyst layer, the target value of the percentage of the length L1 of the first catalyst layer relative to the length L of the substrate was changed to 70%, the target value of WC1 was changed to 64.3 g / L, the target value of the percentage of the length L2 of the second catalyst layer relative to the length L of the substrate was changed to 40%, and the target value of WC2 was changed to 62.5 g / L.

[0285] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 71.2%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 41.1%.

[0286] The measured value of WC1 is 65.2 g / L, and the measured value of WC2 is 61.3 g / L.

[0287] The thickness T1 of the raised portion of the first catalyst layer was 48.0 μm, and the thickness T2 of the raised portion of the second catalyst layer was 35.0 μm.

[0288] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Comparative Example 4, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Comparative Example 4 evaluated in the same manner as in Example 1.

[0289] <Comparative Example 5>

[0290] In addition to making the average particle size of the first slurry smaller (D 90 ≤0.5 μm) and the first catalyst layer was formed only inside the partition wall portion of the substrate, and an exhaust gas purifying catalyst was produced in the same manner as in Example 1. 90 It is a particle diameter at which the cumulative volume accounts for 90% in a volume-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement method.

[0291] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 44.5%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 70.5%.

[0292] The measured value of WC1 is 56.2 g / L, and the measured value of WC2 is 49.6 g / L.

[0293] The first catalyst layer has no portion formed along the exhaust gas flow direction from the exhaust gas inlet side end of the partition wall on the inlet side cell side surface of the partition wall (T1=0). The thickness T2 of the raised portion of the second catalyst layer is 45.2 μm.

[0294] Table 1 shows the characteristics of the exhaust gas-purifying catalyst of Comparative Example 5, and Table 2 shows the exhaust gas purification performance of the exhaust gas-purifying catalyst of Comparative Example 5 evaluated in the same manner as in Example 1.

[0295] <Comparative Example 6>

[0296] In addition to making the average particle size of the first slurry and the second slurry smaller (D 90 An exhaust gas-purifying catalyst was produced in the same manner as in Example 1 except that the first catalyst layer and the second catalyst layer were formed only inside the partition wall portion of the substrate.

[0297] The measured value of the percentage of the length L1 of the first catalyst layer to the length L of the substrate was 46.1%, and the measured value of the percentage of the length L2 of the second catalyst layer to the length L of the substrate was 72.1%.

[0298] The measured value of WC1 is 54.2 g / L, and the measured value of WC2 is 48.5 g / L.

[0299] The first catalyst layer has no portion formed along the exhaust gas flow direction from the end of the exhaust gas inlet side of the partition wall on the surface of the inlet side of the partition wall (T1=0). The second catalyst layer has no portion formed along the direction opposite to the exhaust gas flow direction from the end of the exhaust gas outflow side of the partition wall on the surface of the outlet side of the partition wall (T2=0).

[0300] Table 1 shows the characteristics of the exhaust gas purifying catalyst of Comparative Example 6, and Table 2 shows the exhaust gas purifying performance of the exhaust gas purifying catalyst of Comparative Example 6 evaluated in the same manner as in Example 1.

[0301] [Table 1]

[0302]

[0303] [Table 2]

[0304]

[0305] As shown in Tables 1 and 2, compared with Comparative Examples 1 to Comparative Examples 6 that do not satisfy any one or more of the above equations (1) to (3), in Examples 1 to 8 that satisfy all of the above equations (1) to (3), the NOx emission (especially, the NOx emission during ultra-high speed operation) is not accidentally reduced. This confirms that by satisfying all of the above equations (1) to (3), it is possible to exert improved exhaust gas purification performance (especially, the exhaust gas purification performance during ultra-high speed operation).

[0306] Description of Reference Numerals

[0307] 10. Catalyst for exhaust gas purification; 20. Base material; 21. Cylindrical portion; 22. Partition wall portion; 24. First sealing portion; 25. Second sealing portion; C1. Inflow side chamber; C2. Outflow side chamber; 30. First catalyst layer; 40. Second catalyst layer.

Claims

1. A catalyst for exhaust gas purification, which extends along the exhaust gas flow direction, wherein: The exhaust gas purifying catalyst comprises a substrate, a first catalyst layer provided on the substrate, and a second catalyst layer provided on the substrate. The substrate has: An inlet side chamber extending along the exhaust gas flow direction, wherein an end of the inlet side chamber on the exhaust gas inlet side is open and an end of the inlet side chamber on the exhaust gas outflow side is closed; an outflow-side chamber extending along the exhaust gas flow direction, the end of the outflow-side chamber on the exhaust gas inflow side being closed, and the end of the outflow-side chamber on the exhaust gas outflow side being open; and a porous partition wall portion that separates the inflow-side chamber from the outflow-side chamber, The first catalyst layer has a portion on the surface of the inlet side chamber of the partition wall portion, which is formed along the exhaust gas flow direction from the end of the exhaust gas inlet side of the partition wall portion, and the portion is a portion that bulges from the surface of the inlet side chamber of the partition wall portion toward the inlet side chamber. The second catalyst layer has a portion on the surface of the outflow side chamber side of the partition wall portion, which is formed from the end of the exhaust gas outflow side of the partition wall portion along the direction opposite to the exhaust gas flow direction, and the portion is a portion that bulges from the surface of the outflow side chamber side of the partition wall portion toward the outflow side chamber side. The first catalyst layer contains rhodium (Rh) as a catalyst active component, The second catalyst layer contains at least one catalytically active component selected from platinum (Pt), palladium (Pd) and rhodium (Rh). The first catalyst layer and the second catalyst layer satisfy the following formulas (1) to (9): 1.1≤L2 / L1≤2.3 (1) 1.1≤T2 / T1≤3.5 (2) 1.05≤WC1 / WC2≤3.5 (3) 10%≤L1 / L0≤80% (4) 30%≤L2 / L0≤90% (5) 12.9μm≤T1≤55μm (6) 20μm≤T2≤100μm (7) 50g / L≤WC1≤90g / L (8) 40g / L≤WC2≤90g / L (9) In the formula, L0 represents the length of the substrate, L1 represents the length of the first catalyst layer, L2 represents the length of the second catalyst layer, T1 represents the thickness of the portion of the first catalyst layer, T2 represents the thickness of the portion of the second catalyst layer, WC1 represents the mass of the first catalyst layer per unit volume of the portion of the substrate where the first catalyst layer is provided, and WC2 represents the mass of the second catalyst layer per unit volume of the portion of the substrate where the second catalyst layer is provided.

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