Catalyst for exhaust gas purification

Abstract

The purpose of the present invention is to provide an exhaust gas purification catalyst which uses a Cu-supporting zeolite and in which the exhaust gas purification performance is unlikely to deteriorate. Provided is an exhaust gas purification catalyst (1A) provided with a base material (10) and a catalyst layer (20A) provided on the base material (10). The catalyst layer (20A) is provided with a first layer (21) containing a Cu-supporting zeolite and a Zr-based oxide, and a second layer (22) containing a platinum group element. The contained amount of Zr in the first layer (21) as expressed as ZrO2 is 10 mass% or more with respect to the mass of the first layer (21). The contained amount of Ce in the first layer (21) as expressed as CeO2 is 3 mass% or less with respect to the mass of the first layer (21).

Description

Technical Field

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

Background Art

[0002] Exhaust gas discharged from internal combustion engines such as automobiles and motorcycles contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). As a catalyst for purifying exhaust gas to purify and detoxify these harmful components, a three-way catalyst having catalytic activity to oxidize HC into water and carbon dioxide, oxidize CO into carbon dioxide, and reduce NOx into nitrogen is used. As components of the three-way catalyst, platinum group elements such as Pt, Pd, and Rh are used.

[0003] The hydrocarbon purification performance of the exhaust gas purification catalyst is easily affected by the temperature of the exhaust gas. In general, a temperature of 300°C or higher is required for the hydrocarbon purification performance of the exhaust gas purification catalyst to be effectively exerted. On the other hand, the exhaust gas immediately after the start of the internal combustion engine is less than 300°C and may contain a large amount of hydrocarbons. Therefore, the exhaust gas purification catalyst may not be able to exhibit sufficient hydrocarbon purification performance for the exhaust gas immediately after the start of the internal combustion engine. Therefore, Cu-supported zeolite may be used for the purpose of adsorbing hydrocarbons contained in the exhaust gas immediately after the start of the internal combustion engine and complementing the hydrocarbon purification performance of the exhaust gas purification catalyst.

[0004] For example, Patent Document 1 describes a catalytic coating containing 50 to 60% by mass of zeolite containing copper, 25 to 30% by mass of cerium-zirconium mixed oxide and / or cerium oxide, and 8 to 10% by mass of aluminum oxide stabilized with rare earth sesquioxide in some cases, with the balance being an inorganic binder.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the conventional exhaust gas purification catalyst using Cu-supported zeolite has a problem that the hydrocarbon adsorption performance after being subjected to a heat load is not sufficient.

[0007] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst using Cu-supported zeolite, which exhibits excellent hydrocarbon adsorption performance even after being subjected to a heat load.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention provides the following exhaust gas purification catalyst. [1] An exhaust gas purification catalyst comprising a substrate and a catalyst layer provided on the substrate, wherein the catalyst layer includes a first layer containing Cu-supported zeolite and a Zr-based oxide, and a second layer containing a platinum group element, the content of Zr in terms of ZrO2 in the first layer is 10% by mass or more based on the mass of the first layer, the content of Ce in terms of CeO2 in the first layer is 3% by mass or less based on the mass of the first layer, the exhaust gas purification catalyst. [2] The exhaust gas purification catalyst according to [1], wherein the content of Zr in terms of ZrO2 in the first layer is 50% by mass or less based on the mass of the first layer. [3] The exhaust gas purification catalyst according to [1] or [2], wherein the content of Zr in terms of ZrO2 in the Zr-based oxide is 45% by mass or more based on the mass of the Zr-based oxide. [4] The exhaust gas purification catalyst according to any one of [1] to [3], wherein the content of Ce in terms of CeO2 in the Zr-based oxide is 10% by mass or less based on the mass of the Zr-based oxide. [5] The average particle diameter of the Zr-based oxide is 1 μm or more and 10 μm or less, and the exhaust gas purification catalyst according to any one of [1] to [4]. [6] The ratio of the content of Ce to the content of Cu in the first layer is 0 or more and less than 2 in atomic ratio, and the exhaust gas purification catalyst according to any one of [1] to [5]. [7] The ratio of the content of the Cu-supported zeolite to the content of the Zr-based oxide in the first layer is 1.5 or more and 3.5 or less in mass ratio, and the exhaust gas purification catalyst according to any one of [1] to [6]. [8] The content of the Cu-supported zeolite in the first layer is 50% by mass or more and 90% by mass or less based on the mass of the first layer, and the exhaust gas purification catalyst according to any one of [1] to [7].

Advantages of the Invention

[0009] According to the present invention, there is provided an exhaust gas purification catalyst using a Cu-supported zeolite, which exhibits excellent hydrocarbon adsorption performance even after being subjected to a heat load.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0011] Hereinafter, the exhaust gas purification catalyst of the present invention will be described. Two or more of the features of the exhaust gas purification catalyst described in this specification can be combined, and the combination of two or more features is also included in the present invention.

[0012] ≪First Embodiment≫ Hereinafter, based on FIGS. 1 to 4, the exhaust gas purification catalyst 1A according to the first embodiment of the present invention will be described.

[0013] As shown in FIG. 1, the exhaust gas purification catalyst 1A is disposed in the exhaust passage in the exhaust pipe P of the internal combustion engine. The internal combustion engine is, for example, a gasoline engine, a diesel engine, or the like. The exhaust gas discharged from the internal combustion engine flows through the exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P, and is purified by the exhaust gas purification catalyst 1A provided in the exhaust pipe P. In the drawing, the exhaust gas flow direction is indicated by the reference symbol X. The upstream side in the exhaust gas flow direction X may be referred to as the "exhaust gas inflow side" or the "upstream side", and the downstream side in the exhaust gas flow direction X may be referred to as the "exhaust gas outflow side" or the "downstream side".

[0014] In the exhaust passage in the exhaust pipe P, other exhaust gas purification catalysts may be disposed together with the exhaust gas purification catalyst 1A. For example, other exhaust gas purification catalysts may be disposed upstream or downstream of the exhaust gas purification catalyst 1A. As the other exhaust gas purification catalysts, known exhaust gas purification catalysts can be used.

[0015] As shown in FIGS. 2 to 4, the exhaust gas purification catalyst 1A includes a substrate 10 and a catalyst layer 20A provided on the substrate 10.

[0016] The material constituting the substrate 10 can be appropriately selected from materials generally used as materials for substrates of catalysts for exhaust gas purification. The material constituting the substrate 10 is preferably a material that allows the substrate 10 to have a stable shape even when the substrate 10 is exposed to exhaust gas at 400°C or higher. Examples of materials for the substrate 10 include ceramics such as cordierite, silicon carbide, and aluminum titanate, and alloys such as stainless steel.

[0017] The substrate 10 is, for example, a honeycomb structure.

[0018] As shown in FIGS. 2 to 4, the substrate 10 includes a cylindrical portion 11 that defines the outer shape of the substrate 10, a partition portion 12 provided within the cylindrical portion 11, and cells 13 partitioned by the partition portion 12.

[0019] As shown in FIG. 2, the shape of the cylindrical portion 11 is, for example, cylindrical, but may be other shapes such as elliptical cylindrical or polygonal cylindrical.

[0020] As shown in FIGS. 2 to 4, a partition portion 12 exists between adjacent cells 13, and the adjacent cells 13 are partitioned by the partition portion 12. The partition portion 12 is preferably porous. The thickness of the partition portion 12 is, for example, 20 μm or more and 1500 μm or less.

[0021] As shown in FIG. 4, the cells 13 extend in the exhaust gas flow direction X and have an end on the exhaust gas inflow side and an end on the exhaust gas outflow side.

[0022] As shown in FIG. 4, both the end on the exhaust gas inflow side and the end on the exhaust gas outflow side of the cell 13 are open. Therefore, the exhaust gas flowing in from the end (opening) on the exhaust gas inflow side of the cell 13 flows out from the end (opening) on the exhaust gas outflow side of the cell 13. Such a mode is called a flow-through type.

[0023] As shown in FIGS. 2 and 3, the planar shape of the end portion (opening) on the exhaust gas inflow side of the cell 13 is a quadrilateral, but it may be other shapes such as a hexagon or an octagon. The same applies to the planar shape of the end portion (opening) on the exhaust gas outflow side of the cell 13.

[0024] The cell density per square inch of the substrate 10 is, for example, 200 cells or more and 1000 cells or less. The cell density per square inch of the substrate 10 is the total number of cells 13 per square inch in the cross section obtained by cutting the substrate 10 in a plane perpendicular to the exhaust gas flow direction X.

[0025] The volume of the substrate 10 is, for example, 0.1 L or more and 20 L or less. The volume of the substrate 10 means the apparent volume of the substrate 10. When the substrate 10 is cylindrical, if the outer diameter of the substrate 10 is 2r and the length of the substrate 10 is L, the volume of the substrate 10 is expressed by the formula: volume of the substrate 10 = π × r 2 × L.

[0026] As shown in FIG. 4, the catalyst layer 20A is provided on the surface of the partition portion 12 of the substrate 10 that extends in the exhaust gas flow direction X. Note that the surface of the partition 12 means the outer surface that defines the outer shape of the partition 12. The catalyst layer 20A may be provided directly on the surface of the partition portion 12 or may be provided via another layer. In the present embodiment, the catalyst layer 20A is provided directly on the surface of the partition portion 12 of the substrate 10.

[0027] As shown in FIG. 4, the catalyst layer 20A may be composed of a portion that bulges from the surface of the partition portion 12 toward the cell 13 side (hereinafter referred to as the "bulging portion"), or may be composed of a portion existing inside the partition portion 12 (hereinafter referred to as the "intrinsic portion"), or may have a bulging portion and an intrinsic portion. The "catalyst layer 20A provided on the substrate 10" includes any of the embodiments in which the catalyst layer 20A is composed of a bulging portion, the embodiment in which the catalyst layer 20A is composed of an intrinsic portion, and the embodiment in which the catalyst layer 20A has a bulging portion and an intrinsic portion.

[0028] As shown in FIG. 4, the catalyst layer 20A extends along the exhaust gas flow direction X from the end on the exhaust gas inflow side of the partition wall portion 12 to the end on the exhaust gas outflow side of the partition wall portion 12. The catalyst layer 20A may extend along the exhaust gas flow direction X from the end on the exhaust gas inflow side of the partition wall portion 12 without reaching the end on the exhaust gas outflow side of the partition wall portion 12, or may extend along the direction opposite to the exhaust gas flow direction X from the end on the exhaust gas outflow side of the partition wall portion 12 without reaching the end on the exhaust gas inflow side of the partition wall portion 12.

[0029] From the viewpoint of achieving a balance between the heat-up property and the exhaust gas purification performance of the catalyst layer 20A, the mass of the catalyst layer 20A per unit volume of the portion of the substrate 10 where the catalyst layer 20A is formed (mass after drying and firing) is preferably 50 g / L or more and 330 g / L or less, more preferably 70 g / L or more and 310 g / L or less, and even more preferably 90 g / L or more and 290 g / L or less. The mass of the catalyst layer 20A per unit volume of the portion of the substrate 10 where the catalyst layer 20A is formed is calculated by the formula: (mass of the catalyst layer 20A) / ((volume of the substrate 10) × (average length L of the catalyst layer 20A 20A / length L of the substrate 10 10 ).

[0030] In this specification, unless otherwise specified, "length" means the axial dimension of the substrate 10.

[0031] In this specification, "mass of the catalyst layer 20A" means the total obtained by determining the mass in terms of metal for platinum group elements and the mass in terms of oxide for metal elements other than platinum group elements among all the metal elements contained in the catalyst layer 20A. That is, "mass of the catalyst layer 20A" means the calculated mass obtained by summing the mass in terms of metal of the platinum group elements contained in the catalyst layer 20A and the mass in terms of oxide of the metal elements other than platinum group elements contained in the catalyst layer 20A. Note that "metal elements" also includes semi-metal elements such as Si and B.

[0032] In this specification, the "platinum group elements" include Pt (platinum element), Pd (palladium element), Rh (rhodium element), Ru (ruthenium element), Os (osmium element), and Ir (iridium element).

[0033] In this specification, the oxides of rare earth elements excluding Ce, Pr, and Tb are sesquioxides (M2O3, where M represents a rare earth element other than Ce, Pr, and Tb), the oxide of Ce is CeO2, the oxide of Pr is Pr6O 11 and the oxide of Tb is Tb4O7, the oxide of Al is Al2O3, the oxide of Zr is ZrO2, the oxide of Hf is HfO2, the oxide of Si is SiO2, the oxide of Cu is CuO, the oxide of B is B2O3, the oxide of Cr is Cr2O3, the oxide of Mg is MgO, the oxide of Ca is CaO, the oxide of Sr is SrO, the oxide of Ba is BaO, the oxide of Fe is Fe3O4, the oxide of Mn is Mn3O4, the oxide of Ni is NiO, the oxide of Ti is TiO2, the oxide of Zn is ZnO, the oxide of Sn is SnO2, the oxide of Li is Li2O, the oxide of Na is Na2O, the oxide of K is K2O, the oxide of Rb is Rb2O, the oxide of Cs is Cs2O, the oxide of Ag is Ag2O, the oxide of V is V2O5, the oxide of Co is Co3O4, the oxide of Nb is Nb2O5, the oxide of Mo is MoO3, the oxide of Ga is Ga2O3, the oxide of Ge is GeO2, and the oxide of P is P2O5.

[0034] The average length L of the catalyst layer 20A 20A An example of the measurement method is as follows.

[0035] From the exhaust gas purification catalyst 1A, it extends in the axial direction of the substrate 10, and the length L of the substrate 10 10Cut out a sample having the same length as [the reference]. The sample is, for example, cylindrical with a diameter of 25.4 mm. Note that the value of the diameter of the sample can be changed as needed. Cut the sample at 5 mm intervals by a plane perpendicular to the axial direction of the base material 10, and obtain a first cut piece, a second cut piece, ···, an n-th cut piece in order from the end side on the exhaust gas inflow side of the sample. The length of the cut piece is 5 mm. Analyze the composition of the cut piece using a fluorescent X-ray analyzer (XRF) (for example, an energy dispersive X-ray analyzer (EDX), a wavelength dispersive X-ray analyzer (WDX), etc.), an inductively coupled plasma atomic emission spectrometer (ICP-AES), a scanning electron microscope-energy dispersive X-ray analysis method (SEM-EDX), etc., and confirm whether the cut piece contains a part of the catalyst layer 20A based on the composition of the cut piece.

[0036] For the cut pieces that are clearly found to contain a part of the catalyst layer 20A, it is not always necessary to perform a composition analysis. For example, the cut surface can be observed using a scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), etc., and it can be confirmed whether the cut piece contains a part of the catalyst layer 20A. When observing the cut surface, elemental mapping of the cut surface may be performed.

[0037] After confirming whether the cut piece contains a part of the catalyst layer 20A, calculate the length of the catalyst layer 20A contained in the sample based on the following formula. Length of the catalyst layer 20A contained in the sample = 5 mm × (number of cut pieces containing a part of the catalyst layer 20A)

[0038] For example, when the first cut piece to the k-th cut piece contain a part of the catalyst layer 20A, but the (k + 1)-th to the n-th cut pieces do not contain a part of the catalyst layer 20A, the length of the catalyst layer 20A contained in the sample is (5 × k) mm.

[0039] An example of a more detailed measurement method for the length of the catalyst layer 20A contained in the sample is as follows. Cut the k-th cut piece (i.e., among the cut pieces including a part of the catalyst layer 20A, the cut piece obtained from the most exhaust gas outflow side of the sample) in the axial direction of the substrate 10, and observe a part of the catalyst layer 20A present on the cut surface using SEM, EPMA, etc., to measure the length of a part of the catalyst layer 20A in the k-th cut piece. Then, calculate the length of the catalyst layer 20A contained in the sample based on the following formula. Length of the catalyst layer 20A contained in the sample = (5 mm × (k - 1)) + (length of a part of the catalyst layer 20A contained in the k-th cut piece)

[0040] Regarding 8 to 16 samples arbitrarily cut out from the exhaust gas purification catalyst 1A, measure the length of the catalyst layer 20A contained in each sample, and take the average value thereof as the average length L of the catalyst layer 20A 20A and.

[0041] As shown in FIG. 4, the catalyst layer 20A includes a first layer 21 and a second layer 22.

[0042] The first layer 21 includes Cu-supported zeolite as described later. Therefore, the first layer 21 functions as a hydrocarbon adsorption part.

[0043] The first layer 21 adsorbs hydrocarbons contained in the exhaust gas immediately after the start of the internal combustion engine, and complements the hydrocarbon purification performance of the exhaust gas purification catalyst. Thereafter, the hydrocarbons adsorbed on the first layer 21 are released and purified by the second layer 22 (the second layer 22 and the third layer 23 in the second and fourth embodiments).

[0044] As shown in FIG. 4, the second layer 22 is provided above the first layer 21. According to the embodiment in which the second layer 22 is provided above the first layer 21, since the hydrocarbons released from the first layer 21 easily pass through the second layer 22, the hydrocarbons released from the first layer 21 can be efficiently purified.

[0045] In this specification, with respect to the positional relationship between two layers, the expression "one layer is provided above the other layer" is used. This expression means that a part or all of one layer is present on the main surface of the other layer that is opposite to the main surface on the side of the partition portion 12 of the base material 10 among the two main surfaces of the other layer. The "main surface of the other layer" means the outer surface of the other layer extending in the exhaust gas flow direction X. One layer may be provided directly on the main surface of the other layer, or may be provided via another layer. One layer may be provided so as to cover a part of the main surface of the other layer, or may be provided so as to cover the entire main surface of the other layer.

[0046] In the present embodiment, the second layer 22 is provided directly on the main surface of the first layer 21 so as to cover the entire main surface of the first layer 21.

[0047] The second layer 22 may be provided below the first layer 21.

[0048] In this specification, with respect to the positional relationship between two layers, the expression "one layer is provided below the other layer" is used. This expression means that a part or all of the other layer is present on the main surface of one layer that is opposite to the main surface on the side of the partition portion 12 of the base material 10 among the two main surfaces of one layer. The "main surface of one layer" means the outer surface of one layer extending in the exhaust gas flow direction X. The other layer may be provided directly on the main surface of one layer, or may be provided via another layer. The other layer may be provided so as to cover a part of the main surface of one layer, or may be provided so as to cover the entire main surface of one layer.

[0049] <The first layer> Hereinafter, the first layer 21 will be described.

[0050] From the viewpoint of achieving a balance between the temperature increase property and the exhaust gas purification performance of the first layer 21, the mass of the first layer 21 per unit volume of the portion of the substrate 10 where the first layer 21 is formed (mass after drying and firing) is preferably 40 g / L or more and 200 g / L or less, more preferably 40 g / L or more and 180 g / L or less, still more preferably 40 g / L or more and 160 g / L or less. The mass of the first layer 21 per unit volume of the portion of the substrate 10 where the first layer 21 is formed is calculated by the formula: (mass of the first layer 21) / ((volume of the substrate 10) × (average length L 21 of the first layer 21 10 / length L

[0051] The above description regarding the mass of the catalyst layer 20A also applies to the mass of the first layer 21. When applying, "catalyst layer 20A" is replaced with "first layer 21".

[0052] The average length L 20A of the catalyst layer 20A 21 The above description regarding the measurement method also applies to the measurement method of the average length L 20A of the first layer 21. When applying, "catalyst layer 20A" is replaced with "first layer 21", and "average length L 21 " is replaced with "average length L

[0053] The first layer 21 contains Cu-supported zeolite.

[0054] The Cu-supported zeolite is, for example, in particulate form.

[0055] Zeolite is an aluminosilicate-based crystalline material and is characterized by having pores (e.g., micropores) in the crystal.

[0056] Narrowly defined zeolite has a three-dimensional network structure in which TO4 tetrahedra (T = Si, Al) share the O atoms at the vertices, and is defined as an aluminosilicate having the following characteristics: (1) containing water adsorbed on the zeolite that can be desorbed without breaking the structure, and (2) having exchangeable cations.

[0057] In the present invention, zeolite includes, in addition to zeolite in the narrow sense, zeolite-related compounds. Examples of zeolite-related compounds include those containing elements other than Si and Al as T atoms, such as P, B, Ga, Ge, Zr, Cu, Fe, Zn, Sn, Co, Mn, Cr, Hf, etc., and those containing no cations, such as AlPO4.

[0058] Regarding the structure, pore diameter, framework, etc. of zeolite in the narrow sense and zeolite-related compounds, reference can be made to "ATLAS OF ZEOLITE STRUCTURES TYPES" issued by the International Zeolite Association and the database publicly available from the International Zeolite Association.

[0059] The framework structure of zeolite has been made into a database by the International Zeolite Association, and a framework code consisting of three capital letters is assigned. Examples of the framework structure of zeolite include LTA type, FER type, MWW type, MFI type, MOR type, LTL type, FAU type, BEA type, CHA type, MSE type, etc. The framework structure of zeolite can be specified, for example, based on the X-ray diffraction (XRD) pattern.

[0060] From the viewpoint of improving the hydrocarbon adsorption performance and resistance to thermal load, the framework structure of zeolite is preferably selected from BEA type, MSE type, and MFI type.

[0061] From the viewpoint of improving the crystal stability and ion exchangeability under humid conditions, the SiO2 / Al2O3 molar ratio in zeolite is preferably 1 or more and 900 or less, more preferably 5 or more and 800 or less, and even more preferably 10 or more and 700 or less.

[0062] The Cu-supported zeolite contains zeolite and Cu.

[0063] In zeolites, the periphery of Al is negatively charged, and cationic substances such as alkali metal ions, alkaline earth metal ions, transition metal ions, ammonium ions, and protons (hydrogen ions) can coordinate as countercations to cancel out this charge. Zeolites with sodium ions as countercations are called sodium type, those with copper ions as countercations are called copper type, and those with iron ions as countercations may be called iron type. Copper type zeolites can be prepared, for example, by directly exchanging alkali metal ions with copper ions or iron ions after synthesizing alkali metal type zeolites, or by exchanging alkali metal ions with ammonium ions and then exchanging with copper ions or iron ions. In copper type zeolites, copper ions can exist in one or both of the interior and exterior of the pores of the zeolite.

[0064] Copper type zeolites may contain cations other than copper ions. Examples of cations other than copper ions contained in copper type zeolites include protons (hydrogen ions), alkali metal ions, alkaline earth metal ions, transition metal ions, ammonium ions, etc. Examples of alkali metals include Li, Na, K, Rb, Cs, etc., examples of alkaline earth metals include Ca, Sr, Ba, etc., and examples of transition metals include Fe, Mn, Ni, Zn, Ag, Ti, V, Cr, Co, Zr, Nb, Mo, etc.

[0065] When a heat load is applied to copper type zeolites, some or all of the copper ions may exist in a state with the zeolite in the form of CuO. The "Cu-supported zeolite" in this specification includes both the state of copper type zeolites and the above-mentioned state where "some or all of the copper ions exist with the zeolite in the form of CuO" caused by applying a heat load to copper type zeolites. Cu-supported zeolites can exist in one or both of these states.

[0066] From the viewpoint of achieving both resistance to heat load and hydrocarbon adsorption performance, the content of Cu in terms of CuO in the Cu-supported zeolite is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 8% by mass or less, and even more preferably 0.1% by mass or more and 6% by mass or less, based on the mass of the Cu-supported zeolite.

[0067] From the viewpoint of effectively exerting the performance of the Cu-supported zeolite (e.g., hydrocarbon adsorption performance, etc.), the content of the Cu-supported zeolite in the first layer 21 is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, based on the mass of the first layer 21. From the viewpoint of achieving a good balance between the performance of the Cu-supported zeolite and the action of the Zr-based oxide (described later), the content of the Cu-supported zeolite in the first layer 21 is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on the mass of the first layer 21. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0068] The content of each element in terms of oxide in the Cu-supported zeolite can be determined from the obtained elemental mapping and the EDX elemental analysis of the specified particles by analyzing the sample obtained from the first layer 21 by energy-dispersive X-ray spectroscopy (EDX). Specifically, the Cu-supported zeolite particles and other particles (e.g., Zr-based oxide particles, etc.) are qualitatively identified (color-coded) by elemental mapping, and the content of each element in terms of oxide in the specified particles can be determined by performing compositional analysis (elemental analysis) on the specified particles.

[0069] When the composition of the raw materials used for forming the first layer 21 is known, the content of the Cu-supported zeolite in the first layer 21 can be determined from the composition of the raw materials used for forming the first layer 21.

[0070] Also, the content of the Cu-supported zeolite in the first layer 21 can be determined by a conventional method such as scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX). Specifically, it is as follows.

[0071] (1) For the sample obtained from the first layer 21, elemental analysis is performed using a conventional method such as SEM-EDX to identify the types of constituent elements of the entire sample and to determine the content (mass %) of each identified element. (2) For the sample obtained from the first layer 21, elemental mapping is performed using a conventional method such as SEM-EDX to identify the types of particles contained in the sample (for example, Cu-supported zeolite particles, Zr-based oxide particles, and optionally other particles). (3) For each type of particle, a plurality of arbitrarily selected particles (for example, 50 particles) are subjected to elemental analysis by SEM-EDX to identify the types of constituent elements of the particles and to determine the content (mass %) of each identified element. For each type of particle, the average value of the content ratio (mass %) of each element is determined. (4) By creating and solving an equation representing the relationship between the content (mass %) of each element in the sample, the content (mass %) of each element in each type of particle, and the content (mass %) of each type of particle in the sample, the content (mass %) of each type of particle in the sample is calculated, and this is taken as the content (mass %) of each type of particle in the first layer 21.

[0072] The first layer 21 contains at least one Zr-based oxide as a Zr source.

[0073] The first layer 21 may contain a zirconia binder as a Zr source.

[0074] The Zr-based oxide is an oxide containing Zr.

[0075] The Zr-based oxide, together with the Cu-supported zeolite, is a component constituting the matrix of the first layer 21. The Zr-based oxide is distinguished from zirconia used as a binder (referred to as "zirconia binder" in this specification). The zirconia binder is derived from the zirconia sol used as the first layer forming material.

[0076] When a thermal load is applied to the Cu-supported zeolite (particularly when the Cu-supported zeolite is exposed to high temperatures (e.g., 850°C or higher, particularly 950°C or higher)), the Cu contained in the Cu-supported zeolite migrates, which is considered to be a factor in the deterioration of the hydrocarbon adsorption performance of the Cu-supported zeolite and, in turn, the deterioration of the exhaust gas purification performance of the exhaust gas purification catalyst. The Zr-based oxide has the effect of suppressing the migration of the Cu contained in the Cu-supported zeolite, and is considered to be able to prevent the deterioration of the hydrocarbon adsorption performance of the Cu-supported zeolite and, in turn, the deterioration of the exhaust gas purification performance of the exhaust gas purification catalyst. In other words, due to the above-mentioned action of the Zr-based oxide, the Cu-supported zeolite is considered to be able to maintain its performance (e.g., hydrocarbon adsorption performance, etc.) even after a thermal load is applied (particularly after exposure to high temperatures).

[0077] The Zr-based oxide is, for example, in the form of particles.

[0078] From the viewpoint of effectively exerting the above-mentioned function of the Zr-based oxide, the average particle diameter of the Zr-based oxide is preferably 1 μm or more and 10 μm or less, more preferably 3 μm or more and 9 μm or less, and even more preferably 3 μm or more and 8 μm or less. The method for measuring the average particle diameter of the Zr-based oxide is as follows. The first layer 21 is observed using a scanning electron microscope, and the unidirectional diameter (Ferret diameter) of 100 Zr-based oxide particles arbitrarily selected from within the field of view is measured, and the average value is taken as the average particle diameter of the Zr-based oxide. The average particle diameter of the zirconia binder is usually 1 nm or more and 200 nm or less. Both the Zr-based oxide and the zirconia binder have the function of suppressing the movement of Cu contained in the Cu-supported zeolite, but the Zr-based oxide is more preferable because it has a particle diameter more suitable for suppressing the movement of Cu.

[0079] The Zr-based oxide may or may not contain elements other than Zr and O.

[0080] Examples of Zr-based oxides include zirconia, oxides obtained by modifying the surface of zirconia with elements other than Zr and O, and oxides obtained by dissolving elements other than Zr and O in zirconia.

[0081] In the Zr-based oxide, elements other than Zr and O may form a solid solution phase together with Zr and O, may form a single phase (for example, an oxide phase of an element other than Zr and O) that is a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase.

[0082] Examples of the elements other than Zr and O include rare earth elements, Hf, Cu, Fe, and the like.

[0083] Examples of the rare earth elements include Ce, Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. From the viewpoint of effectively exerting the above action of the Zr-based oxide, the rare earth element is preferably a rare earth element other than Ce. From the viewpoint of effectively exerting the above action of the Zr-based oxide, the rare earth element other than Ce is preferably selected from La, Nd, and Y.

[0084] In addition to the viewpoint of effectively exerting the above action of the Zr-based oxide, from the viewpoint of improving the exhaust gas purification performance, the content of Zr in terms of ZrO2 in the Zr-based oxide is preferably 45% by mass or more, more preferably 65% by mass or more, still more preferably 75% by mass or more, based on the mass of the Zr-based oxide. The upper limit is 100% by mass.

[0085] From the viewpoint of effectively exerting the above action of the Zr-based oxide, the content of elements other than Zr and O in the Zr-based oxide in terms of oxide is preferably 55% by mass or less, more preferably 45% by mass or less, still more preferably 35% by mass or less, and still more preferably 25% by mass or less, based on the mass of the Zr-based oxide. The lower limit is zero. The content of elements other than Zr and O in the Zr-based oxide in terms of oxide may be, for example, 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, based on the mass of the Zr-based oxide. These lower limits may be combined with any of the above upper limits. The "content of elements other than Zr and O in terms of oxide" means the content of the oxide of one kind of element other than Zr and O when the Zr-based oxide contains one kind of element other than Zr and O, and means the total content of the oxides of two or more kinds of elements other than Zr and O when the Zr-based oxide contains two or more kinds of elements other than Zr and O.

[0086] From the viewpoint of achieving both the above action of the Zr-based oxide and the resistance to thermal load, the content of rare earth elements other than Ce in the Zr-based oxide in terms of oxide is preferably 55% by mass or less, more preferably 45% by mass or less, and still more preferably 35% by mass or less, based on the mass of the Zr-based oxide. The lower limit is zero. The content of rare earth elements other than Ce in the Zr-based oxide in terms of oxide may be, for example, 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more, based on the mass of the Zr-based oxide. These lower limits may be combined with any of the above upper limits. The "content of rare earth elements other than Ce in terms of oxide" means the content of the oxide of one kind of rare earth element other than Ce when the Zr-based oxide contains one kind of rare earth element other than Ce, and means the total content of the oxides of two or more kinds of rare earth elements other than Ce when the Zr-based oxide contains two or more kinds of rare earth elements other than Ce.

[0087] From the viewpoint of effectively exerting the above action of the Zr-based oxide, the content of Ce in the Zr-based oxide in terms of CeO2 is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 1% by mass or less, based on the mass of the Zr-based oxide. The lower limit is zero.

[0088] From the viewpoint of effectively exerting the above action of the Zr-based oxide, the content of the Zr-based oxide in the first layer 21 is preferably 10% by mass or more, more preferably 12% by mass or more, still more preferably 15% by mass or more, based on the mass of the first layer 21. From the viewpoint of achieving a good balance between the performance of the Cu-supported zeolite and the above action of the Zr-based oxide, the content of the Zr-based oxide in the first layer 21 is preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, based on the mass of the first layer 21. These upper limits may be combined with any of the above lower limits respectively. The "content of the Zr-based oxide" means the content of the single Zr-based oxide when the first layer contains one kind of Zr-based oxide, and means the total content of two or more kinds of Zr-based oxides when the first layer contains two or more kinds of Zr-based oxides.

[0089] From the viewpoint of suppressing the migration of Cu contained in the Cu-supported zeolite and sufficiently ensuring the hydrocarbon adsorption performance of the Cu-supported zeolite, the content of Zr in terms of ZrO2 in the first layer 21 is preferably 10% by mass or more, preferably 12% by mass or more, preferably 15% by mass or more, based on the mass of the first layer 21. From the viewpoint of sufficiently ensuring the content of the Cu-supported zeolite, the content of Zr in terms of ZrO2 in the first layer 21 is preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, based on the mass of the first layer 21. These upper limits may be combined with any of the above lower limits respectively. The "content of Zr in terms of ZrO2" means the content of Zr in terms of ZrO2 derived from the single Zr source when the first layer 21 contains one kind of Zr source, and means the total content of Zr in terms of ZrO2 derived from two or more kinds of Zr sources when the first layer 21 contains two or more kinds of Zr sources.

[0090] The content of each element in terms of oxide in the Zr-based oxide can be determined in the same manner as the content of each element in terms of oxide in the Cu-supported zeolite.

[0091] The content of the Zr-based oxide in the first layer 21 can be determined in the same manner as the content of the Cu-supported zeolite in the first layer 21.

[0092] When the composition of the raw materials used for the formation of the first layer 21 is known, the content of Zr in terms of ZrO2 in the first layer 21 can be determined from the composition of the raw materials used for the formation of the first layer 21.

[0093] In addition, the content of Zr in terms of ZrO2 in the first layer 21 can be determined using conventional methods such as scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX), X-ray fluorescence analysis (XRF), inductively coupled plasma atomic emission spectroscopy (ICP-AES), etc. Specifically, it is as follows.

[0094] First, after pulverizing a test piece cut out from the exhaust gas purification catalyst 1A, it is analyzed by XRF or ICP-AES, and 20 metal elements with a large content are specified from the most abundant one. Among the specified 20 metal elements, Zr is included. The test piece may contain other parts (parts derived from the base material 10, parts derived from the second layer 22, etc.) as long as it contains a part derived from the first layer 21. When the test piece contains other parts, the specified 20 metal elements may include metal elements constituting the other parts.

[0095] Next, the first layer 21 is analyzed by SEM-EDX. In SEM-EDX, the above-specified 20 metal elements are the analysis targets, and for each of the 10 fields of view of the SEM, the total mol% of the 20 metal elements = 100 mol%, and the mol% of each metal element is analyzed. The content of Zr in terms of ZrO2 in the first layer 21 is determined from the average value of the mol% of Zr in the 10 fields of view. In addition, when specifying which layer among the plurality of layers included in the catalyst layer 20A is the first layer 21 in the measurement of the composition, it may be determined that the layer with the largest Si content ratio is the first layer 21.

[0096] The content of other elements in terms of oxide in the first layer 21 can also be determined in the same manner as the content of Zr in terms of ZrO2 in the first layer 21.

[0097] From the viewpoint of suppressing the migration of Cu contained in the Cu-supported zeolite and sufficiently ensuring the hydrocarbon adsorption performance of the Cu-supported zeolite, among the content of Zr in terms of ZrO2 in the first layer 21, the proportion occupied by the content of Zr in terms of ZrO2 derived from the Zr-based oxide is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. The upper limit is 100% by mass. The "content of Zr in terms of ZrO2 derived from the Zr-based oxide" means the content of Zr in terms of ZrO2 derived from the one kind of Zr-based oxide when the first layer contains one kind of Zr-based oxide, and means the total content of Zr in terms of ZrO2 derived from the two or more kinds of Zr-based oxides when the first layer contains two or more kinds of Zr-based oxides.

[0098] CeO2 is considered to have the property of destroying the crystal structure of zeolite. This is considered to be one of the reasons for the decrease in the hydrocarbon adsorption performance of the Cu-supported zeolite, and thus the decrease in the exhaust gas purification performance of the exhaust gas purification catalyst. Therefore, from the viewpoint of suppressing the destruction of the crystal structure of the Cu-supported zeolite and sufficiently ensuring the hydrocarbon adsorption performance of the Cu-supported zeolite, the content of Ce in terms of CeO2 in the first layer 21 is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less based on the mass of the first layer 21. The lower limit is zero. The "content of Ce in terms of CeO2" means the content of Ce in terms of CeO2 derived from the one kind of Ce source when the first layer 21 contains one kind of Ce source, and means the total content of Ce in terms of CeO2 derived from the two or more kinds of Ce sources when the first layer 21 contains two or more kinds of Ce sources. Examples of the Ce source contained in the first layer 21 include Zr-based oxides containing Ce, ceria binders, and the like.

[0099] From the viewpoint of achieving a good balance between the performance of the Cu-supported zeolite and the above-described action of the Zr-based oxide, the ratio of the content of the Cu-supported zeolite to the content of the Zr-based oxide in the first layer 21 is preferably 1.5 or more and 3.5 or less, more preferably 1.8 or more and 3.0 or less, and even more preferably 2.0 or more and 2.8 or less, in terms of mass ratio. The meaning of the "content of the Zr-based oxide" is the same as described above.

[0100] From the viewpoint of suppressing the destruction of the crystal structure of the Cu-supported zeolite and sufficiently ensuring the hydrocarbon adsorption performance of the Cu-supported zeolite, the ratio of the content of Ce to the content of Cu in the first layer 21 is preferably 0 or more and less than 2, more preferably 0 or more and 1.7 or less, and even more preferably 0 or more and 1.4 or less, in terms of atomic ratio. The "content of Cu" means the content of Cu derived from the single type of Cu source when the first layer 21 contains one type of Cu source, and means the total content of Cu derived from the two or more types of Cu sources when the first layer 21 contains two or more types of Cu sources. Examples of the Cu source contained in the first layer 21 include Cu-supported zeolite, Zr-based oxides containing Cu, and the like. The "content of Ce" means the content of Ce derived from the single type of Ce source when the first layer 21 contains one type of Ce source, and means the total content of Ce derived from the two or more types of Ce sources when the first layer 21 contains two or more types of Ce sources. Examples of the Ce source contained in the first layer 21 include Zr-based oxides containing Ce, ceria binders, and the like.

[0101] From the viewpoint of suppressing the migration of Cu contained in the Cu-supported zeolite and sufficiently ensuring the hydrocarbon adsorption performance of the Cu-supported zeolite, the proportion of the content of Cu derived from the Cu-supported zeolite in the content of Cu in the first layer 21 is preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more. The upper limit is 100% by mass.

[0102] The contents of Cu and Ce in the first layer 21 can be determined in the same manner as the content of Zr in terms of ZrO2 in the first layer 21.

[0103] The first layer 21 may contain a binder. Examples of the binder include inorganic binders such as alumina, zirconia, titania, silica, and ceria.

[0104] The first layer 21 preferably does not substantially contain platinum group elements. Since platinum group elements are components contained in the second layer 22, there is no need to substantially contain them in the first layer 21. By not substantially containing platinum group elements, the amount of Cu-supported zeolite and / or Zr-based oxide contained in the first layer 21 can be increased. The expression "does not substantially contain platinum group elements" means that the content of platinum group elements in terms of metal in the first layer 21 is preferably 0.1% by mass or less, more preferably 0.01% by mass or less, and even more preferably 0.001% by mass or less based on the mass of the first layer 21. The lower limit is zero. Details of the platinum group elements will be described later.

[0105] The content of platinum group elements in terms of metal in the first layer 21 can be determined in the same manner as the content of Zr in terms of ZrO2 in the first layer 21.

[0106] <The second layer> Hereinafter, the second layer 22 will be described.

[0107] From the viewpoint of achieving a balance between the temperature increase property and the exhaust gas purification performance of the second layer 22, the mass of the second layer 22 per unit volume of the portion of the substrate 10 where the second layer 22 is formed (mass after drying and firing) is preferably 40 g / L or more and 300 g / L or less, more preferably 40 g / L or more and 280 g / L or less, and even more preferably 40 g / L or more and 250 g / L or less. The mass of the second layer 22 per unit volume of the portion of the substrate 10 where the second layer 22 is formed is calculated by the formula: (mass of the second layer 22) / ((volume of the substrate 10)×(average length L of the second layer 22 22 / length L of the substrate 10 10 ). "Length" means the dimension in the axial direction of the substrate 10.

[0108] The above description regarding the mass of the catalyst layer 20A is also applicable to the mass of the second layer 22. When applying, "catalyst layer 20A" is read as "second layer 22".

[0109] The average length L of the catalyst layer 20A 20A The above description regarding the measurement method of 22 is also applicable to the measurement method of the average length L of the second layer 22. When applying, "catalyst layer 20A" is read as "second layer 22", and "average length L 20A " is read as "average length L 22 ".

[0110] The second layer 22 contains at least one platinum group element.

[0111] The platinum group element can be selected from the group of platinum group elements consisting of Pt, Pd, Rh, Ru, Os, and Ir. The platinum group element is preferably selected from Pt, Pd, and Rh.

[0112] The platinum group element is contained in the second layer 22 in a form that can function as a catalyst active component, for example, in the form of a metal composed of a platinum group element, an alloy containing a platinum group element, a compound containing a platinum group element (for example, an oxide of a platinum group element), etc. The catalyst active component is, for example, particulate.

[0113] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the content of the platinum group element in the second layer 22 is, in terms of the mass of the platinum group element in terms of metal per unit volume of the substrate 10, preferably 0.1 g / L or more and 12 g / L or less, more preferably 0.1 g / L or more and 10 g / L or less, and even more preferably 0.1 g / L or more and 8 g / L or less. "The content of the platinum group element" means the content of the single platinum group element when the second layer 22 contains one platinum group element, and means the total content of the two or more platinum group elements when the second layer 22 contains two or more platinum group elements.

[0114] In one embodiment, the second layer 22 contains Rh. When the second layer 22 contains Rh, from the viewpoint of preventing inactivation of Rh by alloying with platinum group elements other than Rh, the total content of platinum group elements other than Rh in the second layer 22 in terms of molar ratio preferably does not exceed the content of Rh in terms of molar ratio.

[0115] In another embodiment, the second layer 22 contains Pd. When the second layer 22 contains Pd, from the viewpoint of preventing inactivation of Pd by alloying with platinum group elements other than Pd, the total content of platinum group elements other than Pd in the second layer 22 in terms of molar ratio is preferably less than the content of Pd in terms of molar ratio. In the second layer 22, the ratio of the total molar amount of platinum group elements other than Pd to the molar amount of Pd is preferably 0.1 or less, more preferably 0.01 or less, and even more preferably 0.001 or less.

[0116] The content of the platinum group elements in the second layer 22 in terms of metal can be determined in the same manner as the content of Zr in terms of ZrO2 in the first layer 21.

[0117] From the viewpoint of improving the exhaust gas purification performance, the second layer 22 preferably contains a carrier, and the platinum group elements are preferably supported on the carrier.

[0118] "The platinum group elements are supported on the carrier" means a state in which a catalytic active component containing the platinum group elements is physically or chemically adsorbed or retained on the outer surface or the inner surface of the pores of the carrier. Whether the catalytic active component containing the platinum group elements is supported on the carrier can be confirmed, for example, by using a scanning electron microscope - energy dispersive X-ray analyzer (SEM-EDX) or the like. For example, in the element mapping obtained by using SEM-EDX or the like, when the platinum group elements and the carrier are present in the same region, it can be determined that the catalytic active component containing the platinum group elements is supported on the carrier.

[0119] The carrier is, for example, particulate.

[0120] Examples of the carrier include inorganic oxides and the like.

[0121] From the viewpoint of achieving a good balance between the exhaust gas purification performance and cost, the content of the inorganic oxide in the second layer 22 is preferably 80% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, based on the mass of the second layer 22. The upper limit is the value obtained by subtracting the content in terms of the metal of the platinum group elements from 100% by mass. The "content of the inorganic oxide" means the content of the single inorganic oxide when the second layer 22 contains one kind of inorganic oxide, and means the total content of the two or more kinds of inorganic oxides when the second layer 22 contains two or more kinds of inorganic oxides.

[0122] The content of the inorganic oxide in the second layer 22 can be determined in the same manner as the content of the Cu-supported zeolite in the first layer 21.

[0123] The inorganic oxide may be an inorganic oxide having an oxygen storage capacity (OSC: Oxygen Storage Capacity) (hereinafter sometimes referred to as "oxygen storage component"), or may be an inorganic oxide other than the oxygen storage component.

[0124] Examples of the oxygen storage component include CeO2, a composite oxide containing Ce and Zr (hereinafter sometimes referred to as "CeO2-ZrO2-based composite oxide"), and the like.

[0125] The CeO2-ZrO2-based composite oxide means an oxide in which the amount of Ce in terms of oxide in the composite oxide is 5% by mass or more and 95% by mass or less, and the amount of Zr in terms of oxide in the composite oxide is 5% by mass or more and 95% by mass or less, based on the mass of the composite oxide.

[0126] The conversion amount of the oxide of each element in the CeO2-ZrO2-based composite oxide can be determined in the same manner as the content of the oxide conversion of each element in the Cu-supported zeolite.

[0127] In the CeO2-ZrO2 based composite oxide, it is preferable that CeO2 and ZrO2 form a solid solution phase. In addition to the solid solution phase, CeO2 and ZrO2 may each form a single phase (CeO2 phase, ZrO2 phase).

[0128] The CeO2-ZrO2 based composite oxide may contain elements other than Ce and Zr. The elements other than Ce and Zr or their oxides may form a solid solution phase with CeO2 and / or ZrO2, or may form a single phase. Examples of the elements other than Ce and Zr include rare earth elements other than Ce, alkaline earth metal elements, transition metal elements, etc.

[0129] Examples of the inorganic oxides other than the oxygen storage component include alumina, silica, silica-alumina, aluminosilicate, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, titania, etc.

[0130] The second layer 22 may contain a binder. Examples of the binder include inorganic binders such as alumina, zirconia, titania, silica, and ceria.

[0131] Hereinafter, the method for forming the catalyst layer 20A will be described. Prepare a substrate 10, a slurry for forming the first layer 21, and a slurry for forming the second layer 22.

[0132] The compositions of the slurries for forming the first layer 21 and the second layer 22 are adjusted according to the compositions of the first layer 21 and the second layer 22, respectively. The slurry for forming the first layer 21 contains, for example, Cu-supported zeolite, Zr-based oxide, binder, solvent, etc. The slurry for forming the second layer 22 contains, for example, a source of platinum group elements, a carrier, a binder, a solvent, etc. Examples of the source of platinum group elements include salts of platinum group elements, and examples of the salts of platinum group elements include nitrates, ammine complex salts, acetates, chlorides, etc. Examples of the binder include alumina sol, zirconia sol, titania sol, silica sol, ceria sol, etc. Examples of the solvent include water, organic solvents, etc.

[0133] After applying the slurry for forming the first layer 21 to the substrate 10, drying it, and firing it, and then applying the slurry for forming the second layer 22 to the substrate 10, drying it, and firing it, the catalyst layer 20A can be formed. The application of the slurry can be performed, for example, by immersing the entire substrate 10 in the slurry, or by immersing the end portion of the substrate 10 on the exhaust gas inflow side or the exhaust gas outflow side in the slurry and sucking the slurry from the opposite side. The drying temperature is, for example, 60°C or higher and 120°C or lower, the drying time is, for example, 0.5 hours or longer and 120 hours or shorter, the firing temperature is, for example, 400°C or higher and 700°C or lower, and the firing time is, for example, 0.5 hours or longer and 3 hours or shorter. The firing can be performed, for example, in an air atmosphere.

[0134] ≪Second Embodiment≫ Hereinafter, based on FIG. 5, the exhaust gas purification catalyst 1B according to the second embodiment of the present invention will be described. In the exhaust gas purification catalyst 1B, the same members and parts as those in the exhaust gas purification catalyst 1A are denoted by the same reference numerals as those in the exhaust gas purification catalyst 1A. Unless otherwise specified, the above description regarding the exhaust gas purification catalyst 1A is also applicable to the exhaust gas purification catalyst 1B.

[0135] As shown in FIG. 5, the exhaust gas purification catalyst 1B is different from the exhaust gas purification catalyst 1A in that it includes a catalyst layer 20B instead of the catalyst layer 20A.

[0136] As shown in FIG. 5, the catalyst layer 20B is different from the catalyst layer 20A in that it includes the third layer 23. Unless otherwise specified, the above description regarding the catalyst layer 20A also applies to the catalyst layer 20B.

[0137] As shown in FIG. 5, the second layer 22 is provided above the first layer 21, and the third layer 23 is provided above the second layer 22. That is, the first layer 21, the second layer 22, and the third layer 23 are provided in this order from the side of the partition portion 12 of the base material 10. In the present embodiment, the second layer 22 is directly provided on the main surface of the first layer 21 so as to cover the entire main surface of the first layer 21, and the third layer 23 is directly provided on the main surface of the second layer 22 so as to cover the entire main surface of the second layer 22.

[0138] When the second layer 22 is provided above the first layer 21, the third layer 23 may be provided between the first layer 21 and the second layer 22 (that is, above the first layer 21 and below the second layer 22), or may be provided below the first layer 21 (that is, on the surface of the partition portion 12 of the base material 10). That is, the first layer 21, the third layer 23, and the second layer 22 may be provided in this order from the side of the partition portion 12 of the base material 10, or the third layer 23, the first layer 21, and the second layer 22 may be provided.

[0139] When the second layer 22 is provided below the first layer 21, the third layer 23 may be provided between the first layer 21 and the second layer 22 (that is, above the second layer 22 and below the first layer 21), or may be provided below the second layer 22 (that is, on the surface of the partition portion 12 of the base material 10), or may be provided above the first layer 21. That is, the second layer 22, the third layer 23, and the first layer 21 may be provided in this order from the side of the partition portion 12 of the base material 10, or the third layer 23, the second layer 22, and the first layer 21 may be provided, or the second layer 22, the first layer 21, and the third layer 23 may be provided.

[0140] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the third layer 23 per unit volume of the portion of the substrate 10 where the third layer 23 is formed (mass after drying and firing) is preferably 40 g / L or more and 300 g / L or less, more preferably 40 g / L or more and 280 g / L or less, and even more preferably 40 g / L or more and 250 g / L or less. The mass of the third layer 23 per unit volume of the portion of the substrate 10 where the third layer 23 is formed is calculated by the formula: (mass of the third layer 23) / ((volume of the substrate 10) × (average length L of the third layer 23 23 / length L of the substrate 10 10 ).

[0141] The above description regarding the mass of the catalyst layer 20A also applies to the mass of the third layer 23. When applying, "catalyst layer 20A" is replaced with "third layer 23".

[0142] The average length L of the catalyst layer 20A 20A The above description regarding the measurement method also applies to the average length L of the third layer 23 23 When applying, "catalyst layer 20A" is replaced with "third layer 23", and "average length L 20A " is replaced with "average length L 23 ".

[0143] The third layer 23 contains at least one platinum group element.

[0144] The platinum group element can be selected from the group of platinum group elements consisting of Pt, Pd, Rh, Ru, Os, and Ir. The platinum group element is preferably selected from Pt, Pd, and Rh.

[0145] The platinum group element is contained in the third layer 23 in a form that can function as a catalytic active component, for example, in the form of a metal composed of a platinum group element, an alloy containing a platinum group element, a compound containing a platinum group element (for example, an oxide of a platinum group element), etc. The catalytic active component is, for example, particulate.

[0146] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the content of the platinum group element in the third layer 23 is the mass in terms of the metal of the platinum group element per unit volume of the substrate 10, preferably 0.1 g / L or more and 12 g / L or less, more preferably 0.1 g / L or more and 10 g / L or less, still more preferably 0.1 g / L or more and 8 g / L or less. The "content of the platinum group element" means the content of the single platinum group element when the third layer 23 contains one kind of platinum group element, and means the total content of the two or more platinum group elements when the third layer 23 contains two or more kinds of platinum group elements.

[0147] When the second layer 22 contains Rh, from the viewpoint of improving the exhaust gas purification performance, it is preferable that the third layer 23 contains Pd. When the third layer 23 contains Pd, from the viewpoint of preventing the inactivation of Pd due to alloying of Pd and platinum group elements other than Pd, the total content of platinum group elements other than Pd in the third layer 23 in terms of molar basis is preferably not more than the content of Pd in terms of molar basis.

[0148] When the second layer 22 contains Pd, from the viewpoint of improving the exhaust gas purification performance, it is preferable that the third layer 23 contains Rh. When the third layer 23 contains Rh, from the viewpoint of preventing the inactivation of Rh due to alloying of Rh and platinum group elements other than Rh, the total content of platinum group elements other than Rh in the third layer 23 in terms of molar basis is preferably less than the content of Rh in terms of molar basis. In the third layer 23, the ratio of the total molar amount of platinum group elements other than Rh to the molar amount of Rh is preferably 0.1 or less, more preferably 0.01 or less, still more preferably 0.001 or less.

[0149] The content of the platinum group element in the third layer 23 in terms of the metal can be determined in the same manner as the content of Zr in terms of ZrO2 in the first layer 21.

[0150] From the viewpoint of improving the exhaust gas purification performance, it is preferable that the third layer 23 contains a carrier and the platinum group element is supported on the carrier.

[0151] The meaning and determination method of "the platinum group elements are supported on the carrier" are the same as above.

[0152] The description of the carrier (including the description of inorganic oxides) is the same as above.

[0153] From the perspective of achieving a good balance between the exhaust gas purification performance and cost, the content of the inorganic oxide in the third layer 23 is preferably 80% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, based on the mass of the third layer 23. The upper limit is the value obtained by subtracting the content in terms of the metal of the platinum group elements from 100% by mass. The "content of the inorganic oxide" means the content of the single inorganic oxide when the third layer 23 contains one kind of inorganic oxide, and means the total content of the two or more inorganic oxides when the third layer 23 contains two or more kinds of inorganic oxides.

[0154] The content of the inorganic oxide in the third layer 23 can be determined in the same manner as the content of the Cu-supported zeolite in the first layer 21.

[0155] Hereinafter, the method for forming the catalyst layer 20B will be described. Unless otherwise specified, the above description regarding the method for forming the catalyst layer 20A is also applicable to the method for forming the catalyst layer 20B.

[0156] Prepare the substrate 10, the slurry for forming the first layer 21, the slurry for forming the second layer 22, and the slurry for forming the third layer 23.

[0157] The composition of the slurries for forming the first layer 21, the second layer 22, and the third layer 23 is adjusted according to the compositions of the first layer 21, the second layer 22, and the third layer 23, respectively. The slurry for forming the third layer 23 contains, for example, a source of platinum group elements, a carrier, a binder, a solvent, and the like.

[0158] A slurry for forming the first layer 21 is applied to the substrate 10, dried, and fired. Then, a slurry for forming the second layer 22 is applied to the substrate 10, dried, and fired. Then, a slurry for forming the third layer 23 is applied to the substrate 10, dried, and fired, whereby the catalyst layer 20B can be formed.

[0159] ≪Third Embodiment≫ Hereinafter, based on FIG. 6, the exhaust gas purification catalyst 1C according to the third embodiment of the present invention will be described. In the exhaust gas purification catalyst 1C, the same members and parts as those in the exhaust gas purification catalyst 1A are denoted by the same reference numerals as those in the exhaust gas purification catalyst 1A. Unless otherwise specified, the above description regarding the exhaust gas purification catalyst 1A is also applicable to the exhaust gas purification catalyst 1C.

[0160] As shown in FIG. 6, the exhaust gas purification catalyst 1C is provided with a first sealing portion 14 that seals the end portion on the exhaust gas outflow side of a part of the cells 13 and a second sealing portion 15 that seals the end portion on the exhaust gas inflow side of the remaining cells 13 on the substrate 10. As a result, a part of the cells 13 are inflow-side cells 13a in which the end portion on the exhaust gas inflow side is open and the end portion on the exhaust gas outflow side is blocked by the first sealing portion 14, and the remaining cells 13 are outflow-side cells 13b in which the end portion on the exhaust gas inflow side is blocked by the second sealing portion 15 and the end portion on the exhaust gas outflow side is open. Also, a catalyst layer 30 is provided on the inflow-side cell 13a side of the partition portion 12 of the substrate 10, and a catalyst layer 20A is provided on the outflow-side cell 13b side of the partition portion 12 of the substrate 10. This is different from the exhaust gas purification catalyst 1A. The above description regarding the catalyst layer 20A is also applicable to the third embodiment.

[0161] As shown in FIG. 6, a plurality (for example, four) of outflow-side cells 13b are arranged adjacent to one inflow-side cell 13a, and the inflow-side cell 13a and the outflow-side cell 13b adjacent to the inflow-side cell 13a are partitioned by a porous partition portion 12.

[0162] As shown in FIG. 6, the catalyst layer 30 extends along the exhaust gas flow direction X from the end portion on the exhaust gas inflow side of the partition portion 12 so as not to reach the end portion on the exhaust gas outflow side of the partition portion 12, and the catalyst layer 20A extends along the direction opposite to the exhaust gas flow direction X from the end portion on the exhaust gas outflow side of the partition portion 12 so as not to reach the end portion on the exhaust gas inflow side of the partition portion 12. That is, the catalyst layer 30 is provided on the upstream side of the catalyst layer 20A. The expression "the catalyst layer 30 is provided on the upstream side of the catalyst layer 20A" means that a part or all of the catalyst layer 30 exists in a region on the upstream side of the exhaust gas flow direction X with respect to the region where the catalyst layer 20A is provided on the surface of the base material 10. The catalyst layer 30 may reach the end portion on the exhaust gas outflow side of the partition portion 12. The catalyst layer 20A may reach the end portion on the exhaust gas inflow side of the partition portion 12.

[0163] In the exhaust gas purification catalyst 1C, the exhaust gas flowing in from the end portion (opening) on the exhaust gas inflow side of the inflow side cell 13a passes through the porous partition portion 12 and flows out from the end portion (opening) on the exhaust gas outflow side of the outflow side cell 13b. Such a mode is called a wall flow type.

[0164] In the exhaust gas purification catalyst 1C, when the exhaust gas flowing in from the end portion (opening) on the exhaust gas inflow side of the inflow side cell 13a passes through the porous partition portion 12, particulate matter (PM) in the exhaust gas is collected in the pores of the partition portion 12. Therefore, the exhaust gas purification catalyst 1C is useful as a gasoline particulate filter or a diesel particulate filter.

[0165] As shown in FIG. 6, the catalyst layer 30 has a single-layer structure, but may have a laminated structure. The catalyst layer 30 can be configured in the same manner as a known catalyst layer.

[0166] In the exhaust gas purification catalyst 1C, a catalyst layer 20A may be provided on the inflow side cell 13a side of the partition wall portion 12 of the substrate 10, and a catalyst layer 30 may be provided on the outflow side cell 13b side of the partition wall portion 12 of the substrate 10.

[0167] In the exhaust gas purification catalyst 1C, a catalyst layer 20A may be provided on the inflow side cell 13a side of the partition wall portion 12 of the substrate 10. That is, the catalyst layer 20A may be provided on either the inflow side cell 13a side or the outflow side cell 13b side of the partition wall portion 12 of the substrate 10.

[0168] ≪Fourth Embodiment≫ Hereinafter, based on FIG. 7, the exhaust gas purification catalyst 1D according to the fourth embodiment of the present invention will be described. In the exhaust gas purification catalyst 1D, the same members and parts as those in the exhaust gas purification catalyst 1C are denoted by the same reference numerals as those in the exhaust gas purification catalyst 1C. Unless otherwise specified, the above description regarding the exhaust gas purification catalyst 1C is also applicable to the exhaust gas purification catalyst 1D.

[0169] As shown in FIG. 7, the exhaust gas purification catalyst 1D is different from the exhaust gas purification catalyst 1C in that it includes a catalyst layer 20B instead of the catalyst layer 20A. The above description regarding the catalyst layer 20B is also applicable to the fourth embodiment.

Example

[0170] 〔Example 1〕 <Formation of the First Layer> A copper-type BEA zeolite (SiO2 / Al2O3 molar ratio: 37 / 1, Cu content in terms of CuO: 1.9% by mass) was prepared according to a known method. 144 g of the copper-type BEA zeolite, 60 g of a Zr-based oxide (Zr content in terms of ZrO2: 71% by mass, oxide equivalent of rare earth elements other than Ce (La, Nd): 29% by mass), 5 g of ZrO2 sol in terms of solid content, and 21 g of SiO2 sol in terms of solid content were mixed in 320 g of pure water to obtain a slurry for forming the first layer. The slurry for forming the first layer was coated on a cordierite honeycomb-shaped porous substrate. The coated substrate was calcined at 500 °C for 1 hour in an air atmosphere (1 atm) to form a first layer on the substrate. The mass of the first layer per unit volume of the portion of the substrate where the first layer was formed was 120 g / L. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0171] <Formation of the second layer> 3.5 g of an aqueous rhodium nitrate solution in terms of the metal equivalent of the rhodium element, 207 g of a CeO2-ZrO2-based composite oxide, 65 g of alumina, 3 g of alumina sol in terms of solid content, and 7 g of zirconia sol in terms of solid content were mixed in 416 g of pure water to obtain a slurry for forming the second layer. The slurry for forming the second layer was coated on the first layer. The coated substrate was calcined at 500 °C for 1 hour in an air atmosphere (1 atm) to form a second layer on the first layer. The mass of the second layer per unit volume of the portion of the substrate where the second layer was formed was 60 g / L, and the metal equivalent amount of the rhodium element in the second layer per unit volume of the substrate was 0.7 g / L.

[0172] <Formation of the third layer> 5.9 g of an aqueous palladium nitrate solution in terms of the metal equivalent of the palladium element, 36 g of a CeO2-ZrO2-based composite oxide, 73 g of alumina, and 6.2 g of alumina sol in terms of solid content were mixed in 214 g of pure water to obtain a slurry for forming the third layer. The slurry for forming the third layer was coated on the second layer. The coated substrate was calcined at 500 °C for 1 hour in an air atmosphere (1 atm) to form a third layer on the second layer. The mass of the third layer per unit volume of the portion of the substrate where the third layer was formed was 90 g / L, and the metal equivalent amount of the palladium element in the third layer per unit volume of the substrate was 4.4 g / L.

[0173] Through the above steps, a catalyst for purifying exhaust gas was manufactured, which includes a base material, a first layer provided on the base material, a second layer provided on the first layer, and a third layer provided on the second layer.

[0174] [Example 2] In forming the first layer, a catalyst for purifying exhaust gas was manufactured in the same manner as in Example 1, except that a Zr-based oxide (Zr conversion amount to ZrO2: 83% by mass, oxide conversion amount of rare earth elements other than Ce (La, Nd): 17% by mass) was used instead of the above Zr-based oxide. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0175] [Example 3] In forming the first layer, a catalyst for purifying exhaust gas was manufactured in the same manner as in Example 1, except that a Zr-based oxide (Zr conversion amount to ZrO2: 100% by mass) was used instead of the above Zr-based oxide. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0176] [Example 4] In forming the first layer, a catalyst for purifying exhaust gas was manufactured in the same manner as in Example 1, except that a Zr-based oxide (Zr conversion amount to ZrO2: 60% by mass, oxide conversion amount of rare earth elements other than Ce (La, Nd): 40% by mass) was used instead of the above Zr-based oxide. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0177] [Example 5] In forming the first layer, a catalyst for purifying exhaust gas was manufactured in the same manner as in Example 1, except that a Zr-based oxide (Zr conversion amount to ZrO2: 46% by mass, oxide conversion amount of rare earth elements other than Ce (La, Nd): 54% by mass) was used instead of the above Zr-based oxide. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0178] [Example 6] In the formation of the first layer, an exhaust gas purification catalyst was produced in the same manner as in Example 1, except that Cu-type MSE zeolite (SiO2 / Al2O3 molar ratio: 180 / 1, Cu content in terms of CuO: 1.5% by mass) was used instead of the above Cu-type BEA zeolite. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0179] [Comparative Example 1] In the formation of the first layer, an exhaust gas purification catalyst was produced in the same manner as in Example 1, except that a Zr-based oxide (Zr content in terms of ZrO2: 70% by mass, Ce content in terms of CeO2: 15% by mass, oxide conversion amount of rare earth elements other than Ce (La, Nd, Y): 15% by mass) was used instead of the above Zr-based oxide. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0180] [Comparative Example 2] In the formation of the first layer, an exhaust gas purification catalyst was produced in the same manner as in Example 1, except that an Al-based oxide (Al content in terms of Al2O3: 99% by mass, La content in terms of La2O3: 1% by mass) was used instead of the above Zr-based oxide. The constituent components and composition of the first layer are shown in Tables 1 and 2.

[0181] [Test Example 1] The following evaluations were performed on the exhaust gas purification catalysts obtained in the examples and comparative examples.

[0182] [Multi-humidity accelerated deterioration conditions] The exhaust gas purification catalyst cored to 30 mL was heat-treated at 980 °C for 25 hours in an atmosphere of 10% by volume H2O under the following FC mode. FC mode: A model gas (3 L / min) with the following composition and air (3 L / min) were alternately passed. Model gas flow rate: C3H6 6 mL / min, O2 71 mL / min, N2 2923 mL / min (total 3 L / min). 10% by volume H2O was vaporized from a water-filled tank and mixed into the model gas or air as water vapor. The saturated water vapor pressure was adjusted according to the temperature to obtain the above volume percentage of water vapor.

[0183] [Purification rate of adsorbed hydrocarbons] Using the exhaust gas purification catalyst after heat treatment, model gas evaluation was carried out, and the hydrocarbon relative adsorption amount and the hydrocarbon relative purification amount were evaluated as follows.

[0184] <Model gas evaluation> The exhaust gas purification catalyst cored to 30 mL after heat treatment was filled into the evaluation device, and the exhaust model gas (NO: 500 volppm, CO: 0.5 vol%, H2: 0.17 vol%, C5H 12 : 21 volppm, C3H6: 30 volppm, C7H8: 105 volppm, O2: 0.45 vol%, CO2: 14 vol%, H2O: 10 vol%) was circulated at a space velocity of 50000 / h while heating up to 500 °C at a heating rate of 20 °C / min, and the hydrocarbon emission amount was continuously measured. The hydrocarbon adsorption amount and the hydrocarbon purification amount were obtained from the following formulas.

[0185] Hydrocarbon adsorption amount (g) = [Total supply amount of hydrocarbons (g) until the hydrocarbon amount on the outlet side exceeds the model gas supply amount] - [Total emission amount of hydrocarbons (g) until the hydrocarbon amount on the outlet side exceeds the model gas supply amount]

[0186] Hydrocarbon purification amount (g) = [Total emission amount of hydrocarbons (g) from when the hydrocarbon amount on the outlet side exceeds the model gas supply amount until it falls below] - [Total supply amount of hydrocarbons (g) from when the hydrocarbon amount on the outlet side exceeds the model gas supply amount until it falls below]

[0187] Based on the hydrocarbon adsorption amount and the hydrocarbon purification amount of Comparative Example 1, the hydrocarbon relative adsorption amount of Examples 1 to 6 and the hydrocarbon relative purification amount of Examples 1 to 3 were obtained from the following formulas. The results are shown in Table 3.

[0188] Hydrocarbon relative adsorption amount = [Hydrocarbon adsorption amount (g) of each example] / [Hydrocarbon adsorption amount (g) of Comparative Example 1] × 100

[0189] Hydrocarbon relative purification amount = [Hydrocarbon purification amount (g) of each example] / [Hydrocarbon purification amount (g) of Comparative Example 1] × 100

[0190]

Table 1

[0191]

Table 2

[0192]

Table 3

[0193] As shown in Table 2, in Comparative Example 1, the content of Zr in terms of ZrO2 in the first layer was 10% by mass or more based on the mass of the first layer, and the content of Ce in terms of CeO2 in the first layer was more than 3% by mass based on the mass of the first layer. Also, in Comparative Example 2, the content of Zr in terms of ZrO2 in the first layer was less than 10% by mass based on the mass of the first layer. In contrast, in Examples 1 to 6, the content of Zr in terms of ZrO2 in the first layer was 10% by mass or more based on the mass of the first layer, and the content of Ce in terms of CeO2 in the first layer was 3% by mass or less based on the mass of the first layer. Due to such differences, as shown in Table 3, the hydrocarbon adsorption amounts of Examples 1 to 6 and the hydrocarbon purification amounts of Examples 1 to 3 were significantly higher than those of Comparative Examples 1 and 2.

Explanation of Signs

[0194] 1A, 1B, 1C, 1D ··· Catalysts for Exhaust Gas Purification 10 ··· Substrate 20A, 20B ··· Catalyst Layers 21 ··· First Layer 22 ··· Second Layer 23 ··· Third Layer

Claims

1. An exhaust gas purification catalyst comprising a substrate and a catalyst layer provided on the substrate, wherein the catalyst layer includes a first layer containing Cu-supported zeolite and a Zr-based oxide, and a second layer containing a platinum group element, The content of Zr in terms of ZrO in the first layer is 10% by mass or more based on the mass of the first layer, ２ and The content of Ce in terms of CeO in the first layer ２ is 3% by mass or less based on the mass of the first layer, and the second layer is provided above the first layer. The exhaust gas purification catalyst.

2. The content of Zr in terms of ZrO in the first layer ２ The exhaust gas purification catalyst according to claim 1, wherein the content in terms of mass is 50% by mass or less based on the mass of the first layer.

3. The content of Zr in terms of ZrO in the Zr-based oxide is 45% by mass or more based on the mass of the Zr-based oxide, the exhaust gas purification catalyst according to claim 1 or 2. ２ The exhaust gas purification catalyst according to claim 1 or 2, wherein the content of Zr in terms of ZrO in the Zr-based oxide is 45% by mass or more based on the mass of the Zr-based oxide.

4. The content of Ce in terms of CeO in the Zr-based oxide is 10% by mass or less based on the mass of the Zr-based oxide. The exhaust gas purification catalyst according to claim 1 or 2. ２ ​

5. The exhaust gas purification catalyst according to claim 1 or 2, wherein the average particle diameter of the Zr-based oxide is 1 μm or more and 10 μm or less.

6. The exhaust gas purification catalyst according to claim 1 or 2, wherein the ratio of the Ce content to the Cu content in the first layer is 0 or more and less than 2 in atomic ratio.

7. The exhaust gas purification catalyst according to claim 1 or 2, wherein the ratio of the content of the Cu-supported zeolite to the content of the Zr-based oxide in the first layer is 1.5 or more and 3.5 or less in mass ratio.

8. The exhaust gas purification catalyst according to claim 1 or 2, wherein the content of the Cu-supported zeolite in the first layer is 50% by mass or more and 90% by mass or less based on the mass of the first layer.

9. The exhaust gas purification catalyst according to claim 1 or 2, wherein the content of the platinum group element in terms of metal in the first layer is 0.01% by mass or less based on the mass of the first layer.

Images