Catalyst for exhaust gas purification

Abstract

The purpose of the present invention is to provide an exhaust gas purification catalyst that comprises a catalyst layer containing Rh and a Ce-Zr-Al-based composite oxide and can improve the oxygen storage capacity of the Ce-Zr-Al-based composite oxide and prevent deterioration of the exhaust gas purification performance of the Rh. Provided is an exhaust gas purification catalyst (1) comprising a base material (10) and a first catalyst layer (20) provided on the base material (10), wherein: the first catalyst layer (20) contains Rh and a composite oxide containing Ce, Zr and Al; the amount of the composite oxide is 70 mass% or greater based on the total mass of all components of the first catalyst layer (20) other than Rh; and the ratio of the amount of Ce in the composite oxide in terms of metal to the amount of Zr in the composite oxide in terms of metal is from 0.03 to 0.50 as a mass ratio.

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). For the purpose of purifying and detoxifying these harmful components, a catalyst, for example, a catalyst containing noble metal elements such as Pt, Pd, and Rh is used. Pt and Pd are mainly involved in the oxidative purification of HC and CO, and Rh is mainly involved in the reduction purification of NOx.

[0003] In the catalyst for purifying exhaust gas, a carrier that supports a catalyst active component (for example, noble metal elements such as Pt, Pd, and Rh) is used. As the carrier, for example, a composite oxide containing Ce, Zr, and Al (hereinafter sometimes referred to as "Ce-Zr-Al composite oxide") is used (for example, Patent Documents 1 and 2).

[0004] Patent Document 1 describes that a Ce-Zr-Al composite oxide in which the ratio of the amount of Ce to the amount of Zr (Ce / Zr) is 1 / 3 to 3 / 1 in molar ratio and the ratio of the amount of Al to the total amount of Ce and Zr (Al / (Ce + Zr)) is 2 to 10 in molar ratio is used as a carrier for supporting noble metal elements.

[0005] Patent Document 2 describes that an Al2O3-CeO2-ZrO2 ternary composite oxide and an Al2O3-ZrO2 binary composite oxide in which the mass ratio of Al2O3-CeO2-ZrO2 ternary composite oxide / (Al2O3-CeO2-ZrO2 ternary composite oxide + Al2O3-ZrO2 binary composite oxide) is in the range of 0.33 or more and 0.5 or less are used as a carrier for supporting Rh.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The air / fuel ratio (A / F ratio) supplied to an internal combustion engine is desirably controlled near the stoichiometric air / fuel ratio (stoichiometry). However, since the actual A / F ratio fluctuates on the rich (fuel-rich atmosphere) side or the lean (fuel-lean atmosphere) side centered around stoichiometry depending on the driving conditions of the vehicle, etc., the A / F ratio of the exhaust gas also fluctuates on the rich side or the lean side. The Ce-Zr-Al-based composite oxide has an oxygen storage capacity (OSC: Oxygen Storage Capacity). Therefore, by using the Ce-Zr-Al-based composite oxide, it is possible to mitigate the fluctuation of the oxygen concentration in the exhaust gas and expand the operating window of the catalytic active component.

[0008] Ce contributes to the oxygen storage capacity. Therefore, in the catalyst layer containing Rh and the Ce-Zr-Al composite oxide, as the amount of Ce in the Ce-Zr-Al composite oxide increases, the oxygen storage capacity of the Ce-Zr-Al composite oxide improves, and the exhaust gas purification performance of Rh improves. However, Ce promotes the oxidation of Rh. Here, Pt and Pd have the property that their exhaust gas purification performance is easily exhibited when moderately oxidized, while Rh has the property that its exhaust gas purification performance easily decreases when oxidized. Therefore, when the amount of Ce in the Ce-Zr-Al composite oxide is excessive, the oxidation of Rh is promoted, and the exhaust gas purification performance of Rh decreases. Therefore, when using the Ce-Zr-Al composite oxide as a carrier, it is particularly difficult to balance the oxygen storage capacity and the exhaust gas purification performance when using Rh as the catalyst active component compared to the case of using Pt and / or Pd as the catalyst active component. Also, when the amount of Ce in the Ce-Zr-Al composite oxide is excessive, the heat resistance of the Ce-Zr-Al composite oxide becomes insufficient. Therefore, in a high-temperature environment, aggregation of the Ce-Zr-Al composite oxide, disappearance of pores in the Ce-Zr-Al composite oxide (i.e., decrease in specific surface area), etc. occur, and along with them, burial of Rh, sintering of Rh, etc. are caused, and the exhaust gas purification performance of Rh after being exposed to a high-temperature environment decreases. In this specification, "high temperature" preferably means a temperature of 800 °C or higher, more preferably 850 °C or higher, and even more preferably 900 °C or higher.

[0009] On the other hand, when the proportion of components other than the Ce-Zr-Al composite oxide among all components other than Rh in the catalyst layer increases, in a high-temperature environment, due to the difference in the degree of thermal expansion and thermal contraction between the Ce-Zr-Al composite oxide and the components other than the Ce-Zr-Al composite oxide, burial of Rh, sintering of Rh, etc. are caused, and the exhaust gas purification performance of Rh after being exposed to a high-temperature environment decreases.

[0010] Therefore, in an exhaust gas purification catalyst including a catalyst layer containing Rh and a Ce-Zr-Al composite oxide, it is required to improve the oxygen storage capacity of the Ce-Zr-Al composite oxide and to prevent a decrease in the exhaust gas purification performance of Rh (particularly, to prevent a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment).

[0011] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst including a catalyst layer containing Rh and a Ce-Zr-Al composite oxide, which can improve the oxygen storage capacity of the Ce-Zr-Al composite oxide and prevent a decrease in the exhaust gas purification performance of Rh (particularly, to prevent a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment).

Means for Solving the Problems

[0012] The present inventors have found that in an exhaust gas purification catalyst including a catalyst layer containing Rh and a Ce-Zr-Al composite oxide, when the amount of the Ce-Zr-Al composite oxide is 70% by mass or more based on the total mass of all components other than Rh in the catalyst layer, and the ratio of the amount of Ce in terms of metal in the Ce-Zr-Al composite oxide to the amount of Zr in terms of metal in the Ce-Zr-Al composite oxide is 0.03 or more and 0.50 or less in terms of mass ratio, it is possible to improve the oxygen storage capacity of the Ce-Zr-Al composite oxide and to prevent a decrease in the exhaust gas purification performance of Rh (particularly, to prevent a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment), and thus have completed the present invention.

[0013] The present invention includes the following inventions. [1] An exhaust gas purification catalyst including a substrate and a first catalyst layer provided on the substrate, wherein the first catalyst layer contains Rh and a composite oxide containing Ce, Zr, and Al, the amount of the composite oxide is 70% by mass or more based on the total mass of all components other than Rh in the first catalyst layer, The exhaust gas purification catalyst, wherein the ratio of the amount of Ce in terms of metal in the composite oxide to the amount of Zr in terms of metal in the composite oxide is 0.03 or more and 0.50 or less by mass ratio. [2] The exhaust gas purification catalyst according to [1], wherein the ratio of the amount of Al in terms of metal in the composite oxide to the total amount of Ce and Zr in terms of metal in the composite oxide is 0.10 or more and 10 or less by mass ratio. [3] The exhaust gas purification catalyst according to [1] or [2], wherein the total amount of the oxides of Ce, Zr and Al in the composite oxide is 75% by mass or more based on the mass of the composite oxide. [4] The exhaust gas purification catalyst according to any one of [1] to [3], wherein the amount of the oxide of rare earth elements other than Ce in the composite oxide is 25% by mass or less based on the mass of the composite oxide. [5] The exhaust gas purification catalyst according to [4], wherein the rare earth element other than Ce is selected from La, Y, Pr and Nd. [6] The exhaust gas purification catalyst according to any one of [1] to [5], wherein the first catalyst layer contains an Al-based oxide. [7] The exhaust gas purification catalyst according to any one of [1] to [6], wherein the first catalyst layer contains a binder. [8] The exhaust gas purification catalyst according to [7], wherein the binder is an inorganic oxide other than the Ce-Zr-Al-based composite oxide. [9] The exhaust gas purification catalyst includes a second catalyst layer provided on the substrate, the first catalyst layer is provided above the second catalyst layer,

[10] The exhaust gas purification catalyst according to any one of [1] to [8], wherein the second catalyst layer contains either one of Pd or Pt, or both Pd and Pt.

[11] [Advantages of the Invention]

[0014] According to the present invention, there is provided an exhaust gas purification catalyst including a catalyst layer containing Rh and a Ce-Zr-Al-based composite oxide, which can improve the oxygen storage capacity of the Ce-Zr-Al-based composite oxide and prevent a decrease in the exhaust gas purification performance of Rh (particularly, prevent a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment).

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0016] ≪Explanation of Terms≫ Hereinafter, terms used in this specification will be explained.

[0017] <Rare earth element> Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0018] <Oxide> The oxide of Al is Al2O3, the oxide of Zr is ZrO2, the oxide of Si is SiO2, 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, and the oxide of Ti is TiO2. The oxide of a rare earth element means sesquioxide (Ln2O3, where Ln represents a rare earth element other than Ce, Pr, and Tb) except for the oxides of Ce, Pr, and Tb. The oxide of Ce is CeO2, the oxide of Pr is Pr6O 11 , and the oxide of Tb means Tb4O7.

[0019] <Al-based oxide> The Al-based oxide means an oxide containing Al. Preferably, the Al-based oxide means an oxide containing Al, and among the elements other than O constituting the oxide, the element with the largest content rate on a mass basis is Al. Among the oxides containing Al, those corresponding to the Ce-Zr-Al-based composite oxide of the present invention shall not correspond to the Al-based oxide. The Ce-Zr-Al-based composite oxide of the present invention will be described later.

[0020] The Al-based oxide is, for example, particulate. The Al-based oxide is used as a carrier for the catalytic active component. From the viewpoint of improving the loadability of the catalytic active component, the Al-based oxide is preferably porous. The Al-based oxide is distinguished from the alumina used as a binder. In this specification, the alumina used as a binder may be referred to as "alumina binder", and the alumina used as a carrier may be referred to as "alumina material".

[0021] The Al-based oxide may contain one or more elements other than Al and O (hereinafter sometimes referred to as "other elements"). The other elements can be selected, for example, from rare earth elements (such as Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0022] Examples of the Al-based oxide include alumina (an oxide composed of Al and O), an oxide obtained by modifying the surface of alumina with other elements, an oxide obtained by solid-solubilizing other elements in alumina, and the like. Examples of the Al-based oxide containing other elements include alumina-silica, alumina-silicate, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, and the like.

[0023] In the Al-based oxide, other elements may form a solid solution phase (e.g., a solid solution phase of Al2O3 and an oxide of other elements), a single phase in a crystalline phase or an amorphous phase (e.g., an oxide phase of other elements), or both a solid solution phase and a single phase.

[0024] From the viewpoint of improving the heat resistance of the Al-based oxide, the amount of Al in terms of oxide in the Al-based oxide is preferably 20% by mass or more, more preferably 25% by mass or more, still more preferably 30% by mass or more, still more preferably 35% by mass or more, still more preferably 40% by mass or more, based on the mass of the Al-based oxide. The upper limit is 100% by mass.

[0025] In one embodiment, the Al-based oxide contains Zr. Thereby, the heat resistance of the Al-based oxide can be improved. In this specification, the Al-based oxide containing Zr may be referred to as "Al-Zr-based oxide". From the viewpoint of improving the heat resistance of the Al-based oxide, the amount of Zr in terms of oxide in the Al-based oxide is preferably 10% by mass or more and 80% by mass or less, more preferably 15% by mass or more and 70% by mass or less, still more preferably 20% by mass or more and 60% by mass or less, still more preferably 25% by mass or more and 55% by mass or less, still more preferably 30% by mass or more and 50% by mass or less, based on the mass of the Al-based oxide.

[0026] In another embodiment, the Al-based oxide contains one or more rare earth elements. Thereby, the heat resistance of the Al-based oxide can be improved. From the viewpoint of improving the heat resistance of the Al-based oxide, the one or more rare earth elements are preferably selected from Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. From the viewpoint of improving the heat resistance of the Al-based oxide, the amount of the rare earth element in terms of oxide in the Al-based oxide is preferably 1% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 10% by mass or less, still more preferably 5% by mass or more and 7% by mass or less, based on the mass of the Al-based oxide. The "amount of the rare earth element in terms of oxide in the Al-based oxide" means the amount of the one kind of rare earth element in terms of oxide when the Al-based oxide contains one kind of rare earth element, and means the total amount of the two or more kinds of rare earth elements in terms of oxide when the Al-based oxide contains two or more kinds of rare earth elements.

[0027] In yet another embodiment, the Al-based oxide contains Zr and one or more rare earth elements. Thereby, the heat resistance of the Al-based oxide can be improved. The above description regarding the embodiment in which the Al-based oxide contains Zr and the above description regarding the embodiment in which the Al-based oxide contains one or more rare earth elements are also applicable to this embodiment.

[0028] When the composition of the Al-based oxide is known, the amount of each element in the Al-based oxide in terms of oxide can be determined from the composition of the Al-based oxide.

[0029] When the composition of the Al-based oxide is unknown, the amount of each element in the Al-based oxide in terms of oxide can be measured from the obtained element mapping and the EDX elemental analysis of the specified particles by analyzing the sample by energy-dispersive X-ray analysis (EDX). Specifically, the Al-based oxide particles and other particles (for example, Ce-Zr-Al-based composite oxide particles, etc.) are identified (color-coded) qualitatively by element mapping, and the amount of each element in terms of oxide in the specified particles can be measured by performing composition analysis (elemental analysis) on the specified particles.

[0030] <Cerium-based oxide> The cerium-based oxide is an oxide containing Ce, and among the elements other than O constituting the oxide, the oxide in which the element having the largest content rate on a mass basis is Ce is meant. Among the oxides containing Ce, those corresponding to the Ce-Zr-Al composite oxide of the present invention shall not be regarded as corresponding to the cerium-based oxide. The Ce-Zr-Al composite oxide of the present invention will be described later.

[0031] The cerium-based oxide is, for example, particulate. The cerium-based oxide is used as a carrier for a catalytic active component. From the viewpoint of improving the supportability of the catalytic active component, the cerium-based oxide is preferably porous. The cerium-based oxide is distinguished from the ceria used as a binder. In this specification, the ceria used as a binder may be referred to as "ceria binder".

[0032] The cerium-based oxide may contain one or more elements other than Ce and O (hereinafter sometimes referred to as "other elements"). The other elements can be selected, for example, from rare earth elements other than Ce, alkaline earth metal elements (for example, Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0033] Examples of the cerium-based oxide include ceria (oxide composed of Ce and O), oxide obtained by modifying the surface of ceria with other elements, oxide obtained by solid-solubilizing other elements in ceria, and the like.

[0034] In the cerium-based oxide, the other elements may form a solid solution phase (for example, a solid solution phase of CeO2 and an oxide of other elements), or may form a single phase in a crystalline phase or an amorphous phase (for example, an oxide phase of other elements), or may form both a solid solution phase and a single phase.

[0035] The amount of Ce in terms of oxide in the Ce-based oxide is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, based on the mass of the Ce-based oxide. The upper limit is 100% by mass.

[0036] The amount of Zr in terms of oxide in the Ce-based oxide is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, even more preferably 1% by mass or less, based on the mass of the Ce-based oxide. The lower limit is zero. The amount of Zr in terms of oxide in the Ce-based oxide is smaller than the amount of Zr in terms of oxide in the Ce-Zr-based composite oxide, and in this regard, the Ce-based oxide is distinguished from the Ce-Zr-based composite oxide.

[0037] The amount of each element in terms of oxide in the Ce-based oxide can be measured in the same manner as the amount of each element in terms of oxide in the above-described Al-based oxide.

[0038] <Ce-Zr-based composite oxide> The Ce-Zr-based composite oxide is a composite oxide containing Ce and Zr, wherein the content of Ce 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, and the content 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, and the content of Al in terms of oxide in the composite oxide is less than 5% by mass, based on the mass of the composite oxide. Among the composite oxides containing Ce and Zr, those corresponding to the Ce-Zr-Al-based composite oxide of the present invention are not considered to correspond to the Ce-Zr-based composite oxide. The Ce-Zr-Al-based composite oxide of the present invention will be described later.

[0039] The Ce-Zr-based composite oxide is, for example, particulate. The Ce-Zr-based composite oxide is used as a carrier for a catalytic active component. From the viewpoint of improving the supportability of the catalytic active component, the Ce-Zr-based composite oxide is preferably porous.

[0040] In the Ce-Zr composite oxide, Ce may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2, etc.), or may form a single phase (for example, a CeO2 single phase) that is a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase, but it is preferable that at least a part of Ce forms a solid solution phase.

[0041] In the Ce-Zr composite oxide, Zr may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2, etc.), or may form a single phase (for example, a ZrO2 single phase) that is a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase, but it is preferable that at least a part of Zr forms a solid solution phase.

[0042] From the viewpoint of improving the heat resistance and oxygen storage capacity of the Ce-Zr composite oxide, the total amount of Ce and Zr in terms of oxides in the Ce-Zr composite oxide is preferably 70% by mass or more, more preferably 75% by mass or more, still more preferably 80% by mass or more, and still more preferably 85% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit is 100% by mass.

[0043] From the viewpoint of improving the oxygen storage capacity of the Ce-Zr composite oxide, the amount of Ce in terms of oxide in the Ce-Zr composite oxide is preferably 5% by mass or more and 95% by mass or less, more preferably 5% by mass or more and 90% by mass or less, still more preferably 7% by mass or more and 90% by mass or less, and still more preferably 10% by mass or more and 85% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0044] From the viewpoint of improving the heat resistance of the Ce-Zr composite oxide, the amount of Zr in terms of oxide in the Ce-Zr composite oxide is preferably 5% by mass or more and 95% by mass or less, more preferably 5% by mass or more and 90% by mass or less, still more preferably 7% by mass or more and 90% by mass or less, and still more preferably 10% by mass or more and 85% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0045] The Ce-Zr composite oxide may contain one or more elements other than Ce, Zr, and O (hereinafter sometimes referred to as "other elements"). The other elements can be selected from, for example, rare earth elements other than Ce, alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, and the like.

[0046] When the Ce-Zr composite oxide contains other elements, the other elements may form a solid solution phase (for example, a solid solution phase of CeO2 and an oxide of other elements, a solid solution phase of ZrO2 and an oxide of other elements, a solid solution phase of CeO2, ZrO2, and an oxide of other elements, etc.), or may form a single phase that is a crystalline phase or an amorphous phase (for example, an oxide single phase of other elements), or may form both a solid solution phase and a single phase. However, it is preferable that at least a part of the other elements forms a solid solution phase.

[0047] Examples of the Ce-Zr composite oxide include a CeO2-ZrO2 solid solution, an oxide obtained by modifying the surface of a CeO2-ZrO2 solid solution with other elements, an oxide obtained by dissolving other elements in a CeO2-ZrO2 solid solution, and the like.

[0048] In one embodiment, the Ce-Zr composite oxide contains one or more rare earth elements other than Ce. Thereby, the heat resistance of the Ce-Zr composite oxide can be improved. From the viewpoint of improving the heat resistance of the Ce-Zr composite oxide, the one or more rare earth elements are preferably selected from Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0049] The amount of each element in the Ce-Zr composite oxide in terms of oxide can be measured in the same manner as the amount of each element in the above-described Al-based oxide in terms of oxide.

[0050] <<Catalyst for Exhaust Gas Purification>> Hereinafter, based on FIGS. 1 to 4, a catalyst 1 for exhaust gas purification according to an embodiment of the present invention (hereinafter sometimes referred to as "catalyst 1") will be described.

[0051] As shown in FIG. 1, the catalyst 1 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 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 catalyst 1 provided in the exhaust pipe P. In the drawing, the exhaust gas flow direction is indicated by the symbol X. In this specification, 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".

[0052] Other exhaust gas purification catalysts may be disposed on the upstream side and / or the downstream side of the catalyst 1 in the exhaust passage in the exhaust pipe P.

[0053] As shown in FIGS. 2 to 4, the catalyst 1 includes a substrate 10 and a first catalyst layer 20 provided on the substrate 10.

[0054] The catalyst 1 may include catalyst layers other than the first catalyst layer 20 at one or more positions selected from the lower side, upper side, downstream side, and upstream side of the first catalyst layer 20. For example, as shown in FIGS. 2 to 4, the catalyst 1 may include a second catalyst layer 30 provided on the substrate 10. The second catalyst layer 30 is a layer provided as needed, and embodiments in which the second catalyst layer 30 is omitted are also included in the present invention. However, from the viewpoint of improving the exhaust gas purification performance, it is preferable that the catalyst 1 includes the second catalyst layer 30.

[0055] <Substrate> Hereinafter, the substrate 10 will be described.

[0056] The material constituting the base material 10 can be appropriately selected from known materials. Examples of the material constituting the base material 10 include ceramic materials, metal materials, etc., and ceramic materials are preferred. Examples of the ceramic materials include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, titanium nitride, and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, magnesium titanate, etc. Examples of the metal materials include alloys such as stainless steel.

[0057] As shown in FIGS. 2 to 4, the base material 10 has a cylindrical portion 11, a partition portion 12 provided inside the cylindrical portion 11, and cells 13 partitioned by the partition portion 12. The base material 10 is preferably a honeycomb structure.

[0058] As shown in FIG. 2, the cylindrical portion 11 defines the outer shape of the base material 10, and the axial direction of the cylindrical portion 11 coincides with the axial direction of the base material 10. As shown in FIG. 2, the shape of the cylindrical portion 11 is cylindrical, but it may be other shapes such as an elliptical cylinder or a polygonal cylinder.

[0059] 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 may have a porous structure through which the exhaust gas can pass. The thickness of the partition portion 12 is, for example, 20 μm or more and 1500 μm or less.

[0060] As shown in FIG. 4, the cell 13 extends in the exhaust gas flow direction X and has an end portion on the exhaust gas inflow side and an end portion on the exhaust gas outflow side.

[0061] As shown in FIG. 4, both the end portion on the exhaust gas inflow side and the end portion on the exhaust gas outflow side of the cell 13 are open. Therefore, the exhaust gas flowing in from the end portion (opening) on the exhaust gas inflow side of the cell 13 flows out from the end portion (opening) on the exhaust gas outflow side of the cell 13. Such a mode is called a flow-through type.

[0062] 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.

[0063] The cell density per square inch of the base material 10 is, for example, 100 cells or more and 1000 cells or less. The cell density per square inch of the base material 10 means the total number of cells 13 per square inch in the cross section obtained by cutting the base material 10 in a plane perpendicular to the exhaust gas flow direction X.

[0064] The volume of the base material 10 is, for example, 0.1 L or more and 20 L or less. The volume of the base material 10 means the apparent volume of the base material 10. For example, when the base material 10 is cylindrical, if the outer diameter of the base material 10 is 2r and the length of the base material 10 is L 10 then the volume of the base material 10 is given by the formula: volume of the base material 10 = π × r 2 × L 10 as represented.

[0065] The base material 10 may be provided with a first sealing portion that seals the exhaust gas outflow side ends of some of the cells 13, and a second sealing portion that seals the exhaust gas inflow side ends of the remaining cells 13. As a result, some of the cells 13 become inflow side cells with an open end on the exhaust gas inflow side and a closed end on the exhaust gas outflow side sealed by the first sealing portion, and the remaining cells 13 become outflow side cells with a closed end on the exhaust gas inflow side sealed by the second sealing portion and an open end on the exhaust gas outflow side. A plurality (for example, four) of outflow side cells are arranged around one inflow side cell, and the inflow side cell and the outflow side cells arranged around the inflow side cell are partitioned by a porous partition portion 12. The exhaust gas flowing in from the exhaust gas inflow side end (opening) of the inflow side cell flows out from the exhaust gas outflow side end (opening) of the outflow side cell through the porous partition portion 12. Such a mode is called a wall flow type. When the exhaust gas flowing in from the exhaust gas inflow side end (opening) of the inflow side cell 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, when the base material 10 is of the wall flow type, the catalyst 1 is useful as a gasoline particulate filter or a diesel particulate filter.

[0066] <First catalyst layer> Hereinafter, the first catalyst layer 20 will be described.

[0067] As shown in FIGS. 3 and 4, the first catalyst layer 20 is provided above the second catalyst layer 30.

[0068] The statement that "the first catalyst layer 20 is provided above the second catalyst layer 30" means that a part or all of the first catalyst layer 20 exists on the main surface of the second catalyst layer 30 opposite to the main surface on the side of the partition portion 12 among the two main surfaces of the second catalyst layer 30. The "main surface of the second catalyst layer 30" means the outer surface of the second catalyst layer 30 extending in the exhaust gas flow direction X. The first catalyst layer 20 may be provided directly on the main surface of the second catalyst layer 30, or may be provided via another layer, but usually it is provided directly on the main surface of the second catalyst layer 30. The first catalyst layer 20 may be provided so as to cover a part of the main surface of the second catalyst layer 30, or may be provided so as to cover the entire main surface of the second catalyst layer 30. The "first catalyst layer 20 provided on the substrate 10" includes both an embodiment in which the first catalyst layer 20 is provided directly on the main surface of the second catalyst layer 30 and an embodiment in which the first catalyst layer 20 is provided on the main surface of the second catalyst layer 30 via another layer.

[0069] When the second catalyst layer 30 is omitted, the first catalyst layer 20 is provided on the cell 13 side surface of the partition portion 12. The "cell 13 side surface of the partition portion 12" means the outer surface of the partition portion 12 extending in the exhaust gas flow direction X. The first catalyst layer 20 may be provided directly on the cell 13 side surface of the partition portion 12, or may be provided via another layer, but usually it is provided directly on the cell 13 side surface of the partition portion 12.

[0070] When the first catalyst layer 20 is provided directly on the cell 13 side surface of the partition portion 12, the first catalyst layer 20 may be composed of a portion (hereinafter referred to as "raised portion") that bulges from the cell 13 side surface of the partition portion 12 toward the cell 13 side, or may be composed of a portion existing inside the partition portion 12 (hereinafter referred to as "intrinsic portion"), or may have a raised portion and an intrinsic portion. The "first catalyst layer 20 provided on the substrate 10" includes all of an embodiment in which the first catalyst layer 20 is composed of a raised portion, an embodiment in which the first catalyst layer 20 is composed of an intrinsic portion, and an embodiment in which the first catalyst layer 20 has a raised portion and an intrinsic portion.

[0071] As shown in FIG. 4, the first catalyst layer 20 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 first catalyst layer 20 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.

[0072] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the mass (the mass after firing) of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed is preferably 20 g / L or more and 200 g / L or less, more preferably 30 g / L or more and 150 g / L or less, still more preferably 40 g / L or more and 120 g / L or less, and yet more preferably 50 g / L or more and 100 g / L or less. The mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed is calculated by the formula: (the mass of the first catalyst layer 20) / ((the volume of the substrate 10)×(the average length L 20 of the first catalyst layer 20 / L 10 of the substrate 10)). In the present specification, unless otherwise specified, "length" means the dimension in the axial direction of the substrate 10.

[0073] The "mass of the first catalyst layer 20" means the total obtained by determining the mass in terms of metal for noble metal elements and the mass in terms of oxide for metal elements other than noble metal elements among all the metal elements contained in the first catalyst layer 20. That is, the "mass of the first catalyst layer 20" means the calculated mass obtained by summing the mass in terms of metal of the noble metal elements contained in the first catalyst layer 20 and the mass in terms of oxide of the metal elements other than the noble metal elements contained in the first catalyst layer 20. The "metal elements" include semi-metal elements such as Si and B. The "noble metal elements" include Au, Ag, Pt, Pd, Rh, Ru, Ir, and Os. The meaning of "oxide" is as described in the column of the above "Explanation of Terms".

[0074] Average length L of the first catalyst layer 20 20 An example of the measuring method is as follows.

[0075] Cut out a sample that extends in the axial direction of the substrate 10 from the catalyst 1 and has the same length as the length L of the substrate 10 10 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. When the first catalyst layer 20 extends along the exhaust gas flow direction X from the end on the exhaust gas inflow side of the partition wall portion 12, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the substrate 10, and from the end side on the exhaust gas inflow side of the sample, the first cut piece, the second cut piece, ···, the nth cut piece are obtained in order. When the first catalyst layer 20 extends 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, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the substrate 10, and from the end side on the exhaust gas outflow side of the sample, the first cut piece, the second cut piece, ···, the nth cut piece are obtained in order. In either case, 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 optical emission spectrometer (ICP-AES), a scanning electron microscope - energy dispersive X-ray analysis method (SEM-EDX), etc., and based on the composition of the cut piece, confirm whether the cut piece contains a part of the first catalyst layer 20 or not.

[0076] Regarding the cut piece that is clearly found to contain a part of the first catalyst layer 20, 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., to confirm whether the cut piece contains a part of the first catalyst layer 20 or not. When observing the cut surface, elemental mapping of the cut surface may be performed.

[0077] After confirming whether the cut piece contains a part of the first catalyst layer 20 or not, based on the following formula, calculate the length of the first catalyst layer 20 contained in the sample. Length of the first catalyst layer 20 included in the sample = 5 mm × (number of cut pieces including a part of the first catalyst layer 20)

[0078] For example, when the first to k-th cut pieces include a part of the first catalyst layer 20, but the (k + 1)-th to n-th cut pieces do not include a part of the first catalyst layer 20, the length of the first catalyst layer 20 included in the sample is (5 × k) mm.

[0079] An example of a more detailed measurement method for the length of the first catalyst layer 20 included in the sample is as follows. For the k-th cut piece (when the first catalyst layer 20 extends along the exhaust gas flow direction X from the end on the exhaust gas inflow side of the partition wall portion 12, it is the cut piece obtained from the most exhaust gas outflow side of the sample among the cut pieces including a part of the first catalyst layer 20; when the first catalyst layer 20 extends 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, it is the cut piece obtained from the most exhaust gas inflow side of the sample among the cut pieces including a part of the first catalyst layer 20), cut it in the axial direction of the substrate 10, and observe a part of the first catalyst layer 20 present on the cut surface using SEM, EPMA, etc., to measure the length of a part of the first catalyst layer 20 in the k-th cut piece. Then, based on the following formula, calculate the length of the first catalyst layer 20 included in the sample. Length of the first catalyst layer 20 included in the sample = (5 mm × (k - 1)) + (length of a part of the first catalyst layer 20 included in the k-th cut piece)

[0080] Regarding 8 to 16 samples arbitrarily cut out from the catalyst 1, measure the length of the first catalyst layer 20 included in each sample, and take the average value thereof as the average length L of the first catalyst layer 20 20 and.

[0081] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the total mass of all components other than Rh in the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed is preferably 20 g / L or more and 200 g / L or less, more preferably 30 g / L or more and 150 g / L or less, still more preferably 40 g / L or more and 120 g / L or less, and even more preferably 50 g / L or more and 100 g / L or less.

[0082] The "total mass of all components other than Rh in the first catalyst layer 20" means the sum of the mass in terms of metal for noble metal elements other than Rh and the mass in terms of oxide for metal elements other than noble metal elements among all metal elements other than Rh contained in the first catalyst layer 20. That is, the "total mass of all components other than Rh in the first catalyst layer 20" means the calculated mass obtained by summing the mass in terms of metal of noble metal elements other than Rh contained in the first catalyst layer 20 and the mass in terms of oxide of metal elements other than noble metal elements contained in the first catalyst layer 20. The meanings of "metal element", "noble metal element", and "oxide" are as described above.

[0083] The first catalyst layer 20 contains Rh and a composite oxide containing Ce, Zr, and Al (hereinafter sometimes referred to as "Ce-Zr-Al-based composite oxide").

[0084] Rh is contained in the first catalyst layer 20 in a form that can function as a catalytic active component, for example, in the form of catalytic active components containing Rh such as metallic Rh, alloys containing Rh, compounds containing Rh (for example, oxides of Rh), etc. From the perspective of improving exhaust gas purification performance, the catalytic active component containing Rh is preferably in particulate form.

[0085] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the amount of Rh in terms of metal in the first catalyst layer 20 is preferably 0.05 mass% or more and 5 mass% or less, more preferably 0.1 mass% or more and 3 mass% or less, and still more preferably 0.2 mass% or more and 1.5 mass% or less based on the mass of the first catalyst layer 20.

[0086] The first catalyst layer 20 may contain one or more noble metal elements other than Rh. Examples of noble metal elements other than Rh include Au, Ag, Pt, Pd, Ir, Ru, Os, etc. The noble metal elements other than Rh are contained in the first catalyst layer 20 in the form of a catalytically active component that can function as a catalytically active component, such as a metal, an alloy containing a noble metal element, a compound containing a noble metal element (e.g., an oxide of a noble metal element), etc. From the viewpoint of improving exhaust gas purification performance, the catalytically active component containing a noble metal element other than Rh is preferably in particulate form.

[0087] When the first catalyst layer 20 contains Rh and a noble metal element other than Rh, there is a possibility that Rh and the noble metal element other than Rh form an alloy, resulting in a decrease in the active sites of Rh involved in exhaust gas purification performance. Therefore, the first catalyst layer 20 preferably contains substantially no noble metal element other than Rh.

[0088] "The first catalyst layer 20 substantially contains no noble metal element other than Rh" means that the mass percentage of the noble metal element other than Rh in the first catalyst layer 20 in terms of metal, based on the mass of Rh in the first catalyst layer 20 in terms of metal, is preferably 1.0 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less. The lower limit is zero. "The mass of the noble metal element other than Rh in the first catalyst layer 20 in terms of metal" means the mass of the noble metal element in terms of metal when the first catalyst layer 20 contains one noble metal element other than Rh, and means the total mass of the two or more noble metal elements in terms of metal when the first catalyst layer 20 contains two or more noble metal elements other than Rh.

[0089] When the composition of the raw materials used for forming the first catalyst layer 20 is known, the amount of each metal element in the first catalyst layer 20 in terms of metal or oxide can be determined from the composition of the raw materials used for forming the first catalyst layer 20.

[0090] When the composition of the raw materials used for forming the first catalyst layer 20 is unknown, the amount of each metal element in the first catalyst layer 20 in terms of metal or oxide can be measured using conventional methods such as scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX), electron probe microanalyzer (EPMA), X-ray fluorescence analysis (XRF), inductively coupled plasma atomic emission spectrometry (ICP-AES), etc. Specifically, it is as follows.

[0091] First, after pulverizing a test piece cut out from the catalyst 1, it is analyzed by XRF or ICP-AES, and 20 metal elements with a large molar amount are specified in descending order. The test piece may include a portion derived from the base material 10 and / or a portion derived from the second catalyst layer 30 as long as it includes a portion derived from the first catalyst layer 20.

[0092] Next, the portion derived from the first catalyst layer 20 contained in the test piece is analyzed by SEM-EDX or EPMA. In SEM-EDX or EPMA, the 20 metal elements specified above are the analysis targets, and for each of the 10 fields of view of the SEM, the total molar% of the 20 metal elements = 100 molar%, and the molar% of each metal element is analyzed. The average value of the molar% of each metal element in the 10 fields of view is taken as the molar% of each metal element in the first catalyst layer 20. From the molar% of each metal element in the first catalyst layer 20, the mass% in terms of metal of each noble metal element in the first catalyst layer 20 and the mass% in terms of oxide of each metal element other than the noble metal element in the first catalyst layer 20 are calculated. The mass% in terms of metal of each noble metal element in the first catalyst layer 20 is calculated from the formula: (mass of each noble metal element in terms of metal calculated from molar%) / ((mass of noble metal elements in terms of metal calculated from molar%) + (mass of metal elements other than noble metal elements in terms of oxide calculated from molar%)) × 100. The mass% in terms of oxide of each metal element other than the noble metal element in the first catalyst layer 20 is calculated from the formula: (mass of each metal element other than noble metal elements in terms of oxide calculated from molar%) / ((mass of noble metal elements in terms of metal calculated from molar%) + (mass of metal elements other than noble metal elements in terms of oxide calculated from molar%)) × 100.

[0093] The air / fuel ratio (A / F ratio) supplied to an internal combustion engine is preferably controlled near the stoichiometric air / fuel ratio. However, since the actual A / F ratio fluctuates around stoichiometry to the rich (fuel-rich atmosphere) side or the lean (fuel-lean atmosphere) side depending on the driving conditions of the vehicle, etc., the A / F ratio of the exhaust gas also fluctuates to the rich side or the lean side. Since the Ce-Zr-Al composite oxide has an oxygen storage capacity, by using the Ce-Zr-Al composite oxide, fluctuations in the oxygen concentration in the exhaust gas can be mitigated and the operating window of the catalyst can be expanded.

[0094] Ce contributes to the oxygen storage capacity. Therefore, in a catalyst layer containing Rh and a Ce-Zr-Al composite oxide, as the amount of Ce in the Ce-Zr-Al composite oxide increases, the oxygen storage capacity of the Ce-Zr-Al composite oxide improves, and the exhaust gas purification performance of Rh improves. However, Ce promotes the oxidation of Rh. Here, Pt and Pd have the property that their exhaust gas purification performance is easily exhibited when appropriately oxidized, while Rh has the property that its exhaust gas purification performance easily decreases when oxidized. Therefore, if the amount of Ce in the Ce-Zr-Al composite oxide is excessive, the oxidation of Rh is promoted, and the exhaust gas purification performance of Rh decreases. Therefore, when using a Ce-Zr-Al composite oxide as a carrier, it is particularly difficult to achieve both an oxygen storage capacity and exhaust gas purification performance when using Rh as a catalyst active component compared to when using Pt and / or Pd as catalyst active components. Also, if the amount of Ce in the Ce-Zr-Al composite oxide is excessive, the heat resistance of the Ce-Zr-Al composite oxide becomes insufficient. Therefore, in a high-temperature environment, aggregation of the Ce-Zr-Al composite oxide, disappearance of the pores of the Ce-Zr-Al composite oxide (i.e., reduction in specific surface area), etc. occur, and along with these, burial of Rh, sintering of Rh, etc. are caused, and the exhaust gas purification performance of Rh after being exposed to a high-temperature environment decreases. In this specification, "high temperature" preferably means a temperature of 800 °C or higher, more preferably 850 °C or higher, and even more preferably 900 °C or higher.

[0095] Therefore, in the present invention, in order to improve the oxygen storage capacity of the Ce-Zr-Al composite oxide and prevent the deterioration of the exhaust gas purification performance of Rh (especially the deterioration of the exhaust gas purification performance of Rh after being exposed to a high-temperature environment), the ratio of the amount of Ce in terms of metal in the Ce-Zr-Al composite oxide to the amount of Zr in terms of metal in the Ce-Zr-Al composite oxide is adjusted. Specifically, the ratio of the amount of Ce in terms of metal in the Ce-Zr-Al composite oxide to the amount of Zr in terms of metal in the Ce-Zr-Al composite oxide is preferably 0.03 or more and 0.50 or less, more preferably 0.07 or more and 0.50 or less, even more preferably 0.07 or more and 0.42 or less, and even more preferably 0.10 or more and 0.42 or less, in terms of mass ratio. In the present specification, the Ce-Zr-Al composite oxide in which the above ratio is 0.03 or more and 0.50 or less in terms of mass ratio may be referred to as the "Ce-Zr-Al composite oxide of the present invention".

[0096] From the viewpoint of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the deterioration of the exhaust gas purification performance of Rh (especially the deterioration of the exhaust gas purification performance of Rh after being exposed to a high-temperature environment), the ratio of the amount of Al in terms of metal in the Ce-Zr-Al composite oxide of the present invention to the total amount of Ce and Zr in terms of metal in the Ce-Zr-Al composite oxide of the present invention is preferably 0.10 or more and 10 or less, more preferably 0.22 or more and 10 or less, even more preferably 0.26 or more and 8 or less, and even more preferably 0.41 or more and 6 or less, in terms of mass ratio.

[0097] From the viewpoint of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the deterioration of the exhaust gas purification performance of Rh (especially the deterioration of the exhaust gas purification performance of Rh after being exposed to a high-temperature environment), the total amount of the oxides of Ce, Zr, and Al in the Ce-Zr-Al composite oxide of the present invention is preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the mass of the Ce-Zr-Al composite oxide of the present invention. The upper limit is 100% by mass.

[0098] From the viewpoint of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the deterioration of the exhaust gas purification performance of Rh (particularly, preventing the deterioration of the exhaust gas purification performance of Rh after exposure to a high-temperature environment), the amount of Ce in terms of oxide in the Ce-Zr-Al composite oxide of the present invention is 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 25% by mass or less, based on the mass of the Ce-Zr-Al composite oxide of the present invention.

[0099] From the viewpoint of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the deterioration of the exhaust gas purification performance of Rh (particularly, preventing the deterioration of the exhaust gas purification performance of Rh after exposure to a high-temperature environment), the total amount of Ce and Zr in terms of oxide in the Ce-Zr-Al composite oxide of the present invention is preferably 10% by mass or more and 90% by mass or less, more preferably 15% by mass or more and 85% by mass or less, and even more preferably 20% by mass or more and 80% by mass or less, based on the mass of the Ce-Zr-Al composite oxide of the present invention.

[0100] The Ce-Zr-Al composite oxide of the present invention may contain one or more elements other than Ce, Zr, Al, and O (hereinafter sometimes referred to as "other elements"). The other elements can be selected, for example, from rare earth elements other than Ce. The rare earth elements other than Ce can be selected, for example, from Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc., but from the viewpoint of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the deterioration of the exhaust gas purification performance of Rh (particularly, preventing the deterioration of the exhaust gas purification performance of Rh after exposure to a high-temperature environment), it is preferable to select from La, Y, Pr, and Nd.

[0101] From the perspective of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the degradation of the exhaust gas purification performance of Rh (especially preventing the degradation of the exhaust gas purification performance of Rh after exposure to a high-temperature environment), the amount of rare earth elements other than Ce in the Ce-Zr-Al composite oxide of the present invention, in terms of the oxide equivalent, is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on the mass of the Ce-Zr-Al composite oxide of the present invention. The lower limit is zero. The "amount of rare earth elements other than Ce in the Ce-Zr-Al composite oxide of the present invention, in terms of the oxide equivalent" means the amount of the oxide equivalent of one kind of rare earth element other than Ce when the Ce-Zr-Al composite oxide of the present invention contains one kind of rare earth element other than Ce, and means the total amount of the oxide equivalents of two or more kinds of rare earth elements other than Ce when the Ce-Zr-Al composite oxide of the present invention contains two or more kinds of rare earth elements other than Ce.

[0102] When the Ce-Zr-Al composite oxide of the present invention contains rare earth elements other than Ce, from the perspective of more effectively improving the oxygen storage capacity of the Ce-Zr-Al composite oxide and preventing the degradation of the exhaust gas purification performance of Rh (especially preventing the degradation of the exhaust gas purification performance of Rh after exposure to a high-temperature environment), the amount of rare earth elements other than Ce in the Ce-Zr-Al composite oxide of the present invention, in terms of the oxide equivalent, is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more, based on the mass of the Ce-Zr-Al composite oxide of the present invention. These lower limits can be combined with any of the above upper limits respectively.

[0103] The amount of each element in the Ce-Zr-Al composite oxide in terms of the metal equivalent or the oxide equivalent can be measured in the same manner as the amount of each element in the Al-based oxide described above in terms of the oxide equivalent.

[0104] In the Ce-Zr-Al composite oxide of the present invention, Ce may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2, a solid solution phase of CeO2, ZrO2 and Al2O3, etc.), or may form a single phase (for example, a CeO2 single phase) that is a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase. However, it is preferable that at least a part of Ce forms a solid solution phase.

[0105] In the Ce-Zr-Al composite oxide of the present invention, Zr may form a solid solution phase (for example, a solid solution phase of CeO2 and ZrO2, a solid solution phase of CeO2, ZrO2 and Al2O3, etc.), or may form a single phase (for example, a ZrO2 single phase) that is a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase. However, it is preferable that at least a part of Zr forms a solid solution phase.

[0106] In the Ce-Zr-Al composite oxide of the present invention, Al may form a solid solution phase (for example, a solid solution phase of CeO2 and Al2O3, a solid solution phase of ZrO2 and Al2O3, a solid solution phase of CeO2, ZrO2 and Al2O3, etc.), or may form a single phase (Al2O3 single phase) that is a crystalline phase or an amorphous phase. However, it is preferable that at least a part of Al forms a solid solution phase.

[0107] In the Ce-Zr-Al composite oxide of the present invention, rare earth elements other than Ce may form a solid solution phase (for example, a solid solution phase of CeO2 and an oxide of a rare earth element other than Ce, a solid solution phase of ZrO2 and an oxide of a rare earth element other than Ce, a solid solution phase of CeO2, ZrO2 and an oxide of a rare earth element other than Ce, a solid solution phase of Al2O3 and an oxide of a rare earth element other than Ce, etc.), or may form a single phase (an oxide single phase of a rare earth element other than Ce) that is a crystalline phase or an amorphous phase. However, it is preferable that at least a part of the rare earth elements other than Ce forms a solid solution phase.

[0108] The Ce-Zr-Al composite oxide of the present invention is, for example, particulate. The Ce-Zr-Al composite oxide of the present invention is used as a carrier for a catalytic active component (for example, Rh). From the viewpoint of improving the supportability of the catalytic active component, the Ce-Zr-Al composite oxide of the present invention is preferably porous.

[0109] From the viewpoint of improving the exhaust gas purification performance of the catalytic active component (for example, Rh), at least a part of the catalytic active component (for example, Rh) is preferably supported on the Ce-Zr-Al composite oxide of the present invention. "At least a part of the catalytic active component is supported on the carrier" means a state in which at least a part of the catalytic active component is physically and / or chemically adsorbed or retained on the outer surface and / or the inner surface of the pores of the carrier. That at least a part of the catalytic active component is supported on the carrier can be confirmed, for example, by analyzing the first catalyst layer 20 by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) and finding that at least a part of the catalytic active component and the carrier are present in the same region.

[0110] The first catalyst layer 20 may contain one or more components other than Rh and the Ce-Zr-Al composite oxide of the present invention (hereinafter sometimes referred to as "other components"). However, when the proportion of components other than the Ce-Zr-Al composite oxide among all components other than Rh in the first catalyst layer 20 increases, in a high-temperature environment, due to the difference in the degree of thermal expansion and thermal contraction between the Ce-Zr-Al composite oxide and the components other than the Ce-Zr-Al composite oxide, Rh burial, Rh sintering, etc. are caused, and the exhaust gas purification performance of Rh after being exposed to a high-temperature environment deteriorates.

[0111] Therefore, in the present invention, in order to prevent the deterioration of the exhaust gas purification performance of Rh (especially to prevent the deterioration of the exhaust gas purification performance of Rh after being exposed to a high-temperature environment), the amount of the Ce-Zr-Al-based composite oxide in the first catalyst layer 20 is adjusted. Specifically, the amount of the Ce-Zr-Al-based composite oxide of the present invention in the first catalyst layer 20 is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total mass of all components other than Rh in the first catalyst layer 20. The upper limit is 100% by mass.

[0112] When the composition of the raw materials used for forming the first catalyst layer 20 is known, the amount of the Ce-Zr-Al-based composite oxide of the present invention in the first catalyst layer 20 can be determined from the composition of the raw materials used for forming the first catalyst layer 20.

[0113] When the composition of the raw materials used for forming the first catalyst layer 20 is unknown, the amount of the Ce-Zr-Al-based composite oxide of the present invention in the first catalyst layer 20 can be measured by conventional methods such as inductively coupled plasma optical emission spectrometry (ICP), X-ray fluorescence spectrometry (XRF), and scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX). Specifically, it is as follows.

[0114] (A) For the sample obtained from the first catalyst layer 20, elemental analysis is performed using a conventional method such as ICP, XRF, or SEM-EDX to identify the types of constituent elements of the entire sample and determine the content rate (mass%) of each identified element. (B) For the sample obtained from the first catalyst layer 20, elemental mapping is performed using a conventional method such as SEM-EDX to identify the types of particles contained in the sample (for example, Ce-Zr-Al-based composite oxide particles, Al-based oxide particles, etc.). (C) 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 determine the content rate (mass%) of each identified element. For each type of particle, the average value of the content rate (mass%) of each element is determined. By creating and solving an equation representing the relationship between the content rate (mass %) of each element in the sample, the content rate (mass %) of each element in each type of particle, and the content rate (mass %) of each type of particle in the sample, the content rate (mass %) of each type of particle in the sample is calculated, and this is used as the content rate (mass %) of each type of particle in the first catalyst layer 20.

[0115] The first catalyst layer 20 may contain one or more binders. Thereby, peeling of the first catalyst layer 20 can be prevented. The binder is not particularly limited as long as it is an inorganic oxide other than the Ce-Zr-Al composite oxide. The binder can be selected, for example, from inorganic binders such as alumina, zirconia, titania, silica, ceria, and yttria. When the first catalyst layer 20 contains a binder, from the viewpoint of more effectively preventing a decrease in the exhaust gas purification performance of Rh (particularly, preventing a decrease in the exhaust gas purification performance of Rh after exposure to a high-temperature environment) and preventing peeling of the first catalyst layer 20, the amount of the binder in the first catalyst layer 20 is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less, based on the total mass of all components other than Rh in the first catalyst layer 20. The "amount of the binder in the first catalyst layer 20" means the amount of the single binder when the first catalyst layer 20 contains one type of binder, and means the total amount of the two or more binders when the first catalyst layer 20 contains two or more binders.

[0116] The first catalyst layer 20 may contain one or more carriers other than the Ce-Zr-Al composite oxide of the present invention (hereinafter sometimes referred to as "other carriers"). When the first catalyst layer 20 contains other carriers, at least a part of the catalyst active component (for example, Rh) may be supported on the other carriers.

[0117] From the viewpoint of effectively preventing the deterioration of the exhaust gas purification performance of Rh (particularly, preventing the deterioration of the exhaust gas purification performance of Rh after being exposed to a high-temperature environment), the amount of other carriers in the first catalyst layer 20 is preferably 28% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total mass of all components other than Rh in the first catalyst layer 20. The lower limit is zero. The smaller the amount of other carriers in the first catalyst layer 20, the more preferable. The "amount of other carriers in the first catalyst layer 20" means the amount of the one type of carrier when the first catalyst layer 20 contains one other type of carrier, and means the total amount of the two or more types of carriers when the first catalyst layer 20 contains two or more other types of carriers.

[0118] The amount of other carriers in the first catalyst layer 20 may be, for example, 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total mass of all components other than Rh in the first catalyst layer 20. These lower limits may be combined with any of the above upper limits respectively.

[0119] The method for measuring the amount of other carriers in the first catalyst layer 20 is the same as the method for measuring the amount of the Ce-Zr-Al composite oxide of the present invention in the first catalyst layer 20. [[ID=IO]]

[0120] The other carriers can be selected from inorganic oxides. The inorganic oxide is, for example, particulate. From the viewpoint of facilitating the loading of the catalyst active component, the inorganic oxide is preferably porous. The inorganic oxide may or may not have an oxygen storage capacity. In this specification, an inorganic oxide having an oxygen storage capacity may be referred to as an "OSC material" in some cases.

[0121] Examples of the inorganic oxide include Al-based oxides, Ce-based oxides, Ce-Zr composite oxides, Ce-Zr-Al composite oxides other than the Ce-Zr-Al composite oxide of the present invention, oxides of rare earth elements other than Ce (for example, Y2O3, etc.), oxides of alkaline earth metal elements (for example, MgO, CaO, SrO, BaO, etc.), ZrO2, SiO2, TiO2, NiO, etc.

[0122] In one embodiment, the first catalyst layer 20 contains an Al-based oxide in addition to the Ce-Zr-Al composite oxide of the present invention.

[0123] In one embodiment, the Al-based oxide contains Zr. In another embodiment, the Al-based oxide contains one or more rare earth elements. In still another embodiment, the Al-based oxide contains Zr and one or more rare earth elements. The descriptions of these embodiments are as described above.

[0124] <Second catalyst layer> Hereinafter, the second catalyst layer 30 will be described.

[0125] As shown in FIGS. 3 and 4, the second catalyst layer 30 is provided on the cell 13 side surface of the partition portion 12. The "cell 13 side surface of the partition portion 12" means the outer surface of the partition portion 12 extending in the exhaust gas flow direction X. The second catalyst layer 30 may be provided directly on the cell 13 side surface of the partition portion 12, or may be provided via another layer, but is usually provided directly on the cell 13 side surface of the partition portion 12.

[0126] The second catalyst layer 30 may be composed of a portion (hereinafter referred to as a "raised portion") that bulges from the cell 13 side surface of the partition portion 12 toward the cell 13 side, or may be composed of a portion (hereinafter referred to as an "intrinsic portion") existing inside the partition portion 12, or may have a raised portion and an intrinsic portion. The "second catalyst layer 30 provided on the substrate 10" includes any of the embodiments in which the second catalyst layer 30 is composed of a raised portion, the embodiment in which the second catalyst layer 30 is composed of an intrinsic portion, and the embodiment in which the second catalyst layer 30 has a raised portion and an intrinsic portion.

[0127] As shown in FIG. 4, the second catalyst layer 30 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 second catalyst layer 30 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.

[0128] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the mass (mass after firing) of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed is preferably 20 g / L or more and 200 g / L or less, more preferably 30 g / L or more and 150 g / L or less, still more preferably 40 g / L or more and 120 g / L or less, and even more preferably 50 g / L or more and 100 g / L or less. The mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed is calculated by the formula: (mass of the second catalyst layer 30) / ((volume of the substrate 10)×(average length L of the second catalyst layer 30 30 / length L of the substrate 10 10 ). In this specification, "length" means the dimension in the axial direction of the substrate 10 unless otherwise specified.

[0129] The above description regarding the mass of the first catalyst layer 20 is also applicable to the mass of the second catalyst layer 30. When applying, "the first catalyst layer 20" is read as "the second catalyst layer 30".

[0130] The average length L of the first catalyst layer 20 20 The above description regarding the measurement method is also applicable to the measurement method of the average length L of the second catalyst layer 30 30 When applying, "the first catalyst layer 20" is read as "the second catalyst layer 30", and "average length L 20 " is read as "average length L 30 ".

[0131] From the viewpoint of improving the exhaust gas purification performance, the second catalyst layer 30 preferably contains one of Pd and Pt, or both Pd and Pt. Since the first catalyst layer 20 is provided above the second catalyst layer 30, it is possible to prevent phosphorus poisoning of one of Pd and Pt, or both Pd and Pt, contained in the second catalyst layer 30.

[0132] Pd is contained in the second catalyst layer 30 in a form that can function as a catalytic active component, for example, in the form of catalytic active components containing Pd such as metallic Pd, alloys containing Pd, compounds containing Pd (for example, oxides of Pd), etc. Pt is contained in the second catalyst layer 30 in a form that can function as a catalytic active component, for example, in the form of catalytic active components containing Pt such as metallic Pt, alloys containing Pt, compounds containing Pt (for example, oxides of Pt), etc. The catalytic active components containing Pd and the catalytic active components containing Pt are each, for example, in particulate form.

[0133] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the amount of one of Pd and Pt, or both Pd and Pt, in terms of metal in the second catalyst layer 30 is preferably 0.07% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 6% by mass or less, and even more preferably 0.7% by mass or more and 4% by mass or less, based on the mass of the second catalyst layer 30. The "amount of one of Pd and Pt, or both Pd and Pt, in terms of metal in the second catalyst layer 30" means the amount of the one metal in terms of metal when the second catalyst layer 30 contains one of Pd and Pt, and means the total amount of the two metals in terms of metal when the second catalyst layer 30 contains both Pd and Pt.

[0134] The amounts of Pd and Pt in terms of metal in the second catalyst layer 30 can be measured in the same manner as the amounts of the respective metal elements in terms of metal in the first catalyst layer 20 described above.

[0135] From the viewpoint of improving the exhaust gas purification performance, the second catalyst layer 30 preferably contains one or more carriers, and at least a part of the catalyst active component is supported on one or more carriers. The meaning and confirmation method of "at least a part of the catalyst active component is supported on the carrier" are the same as above.

[0136] The one or more carriers can be selected from, for example, inorganic oxides and the like. The inorganic oxide is, for example, particulate. From the viewpoint of facilitating the loading of the catalyst active component, the inorganic oxide is preferably porous. The inorganic oxide may or may not have an oxygen storage capacity.

[0137] Examples of the inorganic oxide include Al-based oxides, Ce-based oxides, Ce-Zr composite oxides, Ce-Zr-Al composite oxides, oxides of rare earth elements other than Ce (for example, Y2O3, etc.), oxides of alkaline earth metal elements (for example, MgO, CaO, SrO, BaO, etc.), ZrO2, SiO2, TiO2, NiO, and the like.

[0138] The second catalyst layer 30 may contain a binder. The binder can be selected from, for example, inorganic binders such as alumina, zirconia, titania, silica, ceria, yttria, and the like.

[0139] <Method for manufacturing an exhaust gas purification catalyst> The exhaust gas purification catalyst 1 can be manufactured by forming the second catalyst layer 30 on the substrate 10 and then forming the first catalyst layer 20 on the upper side of the second catalyst layer 30.

[0140] The second catalyst layer 30 can be formed by mixing a source of noble metal elements (for example, Pd salt, etc.) and other components (for example, inorganic oxide, binder, solvent, etc.) to prepare a slurry for the second catalyst layer, applying the slurry for the second catalyst layer on the partition wall portion 12 of the substrate 10, drying, and firing.

[0141] The first catalyst layer 20 can be formed by mixing a noble metal element supply source (e.g., Rh salt, etc.) and other components (e.g., Ce-Zr-Al-based composite oxide, optionally other inorganic oxides, binder, solvent, etc.) to prepare a slurry for the first catalyst layer, applying the slurry for the first catalyst layer onto the second catalyst layer 30, drying, and firing.

[0142] The binder can be selected from, for example, metal oxide sols such as alumina sol, zirconia sol, titania sol, silica sol, ceria sol, yttria sol, etc. The solvent can be selected from, for example, water, organic solvents, etc.

[0143] The drying temperature is, for example, 60°C or higher and 150°C or lower, and the drying time is, for example, 0.1 hour or longer and 1 hour or shorter. The firing temperature is, for example, 300°C or higher and 700°C or lower, and the firing time is, for example, 1 hour or longer and 10 hours or shorter. The firing can be carried out, for example, in an air atmosphere.

Examples

[0144] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

[0145] An Al-Zr-based oxide was prepared and used in Example 2 and Comparative Examples 1 to 3. The Al-Zr-based oxide may be hereinafter referred to as "AZ".

[0146] The composition of the Al-Zr-based oxide is as follows. Amount of Al in terms of Al2O3: 50 mass% Amount of Zr in terms of ZrO2: 40 mass% Amount of rare earth element oxides other than Ce in terms of oxide: 10 mass%

[0147] Ce-Zr-Al composite oxides (I) to (V) were prepared. In Example 1, Example 2, Comparative Example 1, and Comparative Example 2, Ce-Zr-Al composite oxide (II) was used. In Example 3, Ce-Zr-Al composite oxide (I) was used. In Example 4, Ce-Zr-Al composite oxide (III) was used. In Example 5, Ce-Zr-Al composite oxide (IV) was used. In Comparative Example 4, Ce-Zr-Al composite oxide (V) was used. In Comparative Example 3, none of the Ce-Zr-Al composite oxides were used. The Ce-Zr-Al composite oxide may be hereinafter referred to as "CZA".

[0148] The composition of the Ce-Zr-Al composite oxide (I) is as follows. Amount of Ce in terms of CeO2: 3 mass% Amount of Zr in terms of ZrO2: 50 mass% Amount of Al in terms of Al2O3: 42 mass% Amount of oxides of rare earth elements other than Ce in terms of oxides: 5 mass%

[0149] The composition of the Ce-Zr-Al composite oxide (II) is as follows. Amount of Ce in terms of CeO2: 10 mass% Amount of Zr in terms of ZrO2: 50 mass% Amount of Al in terms of Al2O3: 35 mass% Amount of oxides of rare earth elements other than Ce in terms of oxides: 5 mass%

[0150] The composition of the Ce-Zr-Al composite oxide (III) is as follows. Amount of Ce in terms of CeO2: 19 mass% Amount of Zr in terms of ZrO2: 50 mass% Amount of Al in terms of Al2O3: 26 mass% Amount of oxides of rare earth elements other than Ce in terms of oxides: 5 mass%

[0151] The composition of the Ce-Zr-Al composite oxide (IV) is as follows. Amount of Ce in terms of CeO2: 22.5 mass% Amount of Zr in terms of ZrO2: 50 mass% Amount of Al in terms of Al2O3: 22.5% by mass Amount of rare earth elements other than Ce in terms of oxide: 5% by mass

[0152] The composition of the Ce-Zr-Al composite oxide (V) is as follows. Amount of Ce in terms of CeO2: 38.5% by mass Amount of Zr in terms of ZrO2: 50% by mass Amount of Al in terms of Al2O3: 6.5% by mass Amount of rare earth elements other than Ce in terms of oxide: 5% by mass

[0153] The characteristics of the compositions of the Ce-Zr-Al composite oxides (I) to (V) are shown in Table 1.

[0154]

Table 1

[0155] 〔Example 1〕 (1) Formation of the lower layer An aqueous palladium nitrate solution, an OSC material, an alumina material, barium sulfate, an alumina binder, and water were added to a mixing container, mixed and stirred to prepare a slurry for forming the lower layer. A flow-through type substrate was immersed in the slurry for forming the lower layer, and the flow-through type substrate coated with the slurry for forming the lower layer was dried at 150°C for 0.5 hour using a dryer and then fired at 500°C for 1 hour using an electric furnace to form a lower layer on the flow-through type substrate.

[0156] The mass of the lower layer per unit volume of the portion of the flow-through type substrate where the lower layer was formed was 122 g / L. The mass of Pd in the lower layer per unit volume of the portion of the flow-through type substrate where the lower layer was formed was 2 g / L. The total mass of all components other than Pd in the lower layer per unit volume of the portion of the flow-through type substrate where the lower layer was formed was 120 g / L. The amounts of the respective components in the slurry for forming the lower layer were adjusted such that, based on the total mass of the components other than Pd in the lower layer (100% by mass), the OSC material was 45% by mass, the alumina material was 45% by mass, barium sulfate was 5% by mass, and the alumina binder was 5% by mass.

[0157] (2) Formation of the upper layer An aqueous rhodium nitrate solution, a Ce-Zr-Al composite oxide (II), an alumina binder, and water were added to a mixing container, mixed and stirred to prepare a slurry for upper layer formation. The flow-through type substrate with the lower layer formed thereon was immersed in the slurry for upper layer formation, and the flow-through type substrate coated with the slurry for upper layer formation was dried at 150 °C for 0.5 hour using a dryer and then calcined at 500 °C for 1 hour using an electric furnace to form an upper layer on the lower layer. Thus, the exhaust gas purification catalyst of Example 1 was obtained.

[0158] The total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was adjusted to 100 g / L. The mass of Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was adjusted to 0.5 g / L.

[0159] Based on the total mass of all components other than Rh in the upper layer (100% by mass), the amounts of each component in the slurry for upper layer formation were adjusted so that the Ce-Zr-Al composite oxide (II) in the upper layer was 95% by mass and the alumina binder in the upper layer was 5% by mass. Since the total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was 100 g / L, the mass of the Ce-Zr-Al composite oxide (II) in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was 95 g / L, and the mass of the alumina binder in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was 5 g / L.

[0160] 〔Example 2〕 (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on the flow-through type substrate.

[0161] (2) Formation of the upper layer A rhodium nitrate aqueous solution, a Ce-Zr-Al composite oxide (II), an Al-Zr oxide, an alumina binder and water were added to a mixing container, mixed and stirred to prepare a slurry for upper layer formation. A flow-through type substrate with a lower layer formed thereon was immersed in the slurry for upper layer formation, and the flow-through type substrate coated with the slurry for upper layer formation was dried at 150 °C for 0.5 hours using a dryer, and then fired at 500 °C for 1 hour using an electric furnace to form an upper layer on the lower layer. Thus, the exhaust gas purification catalyst of Example 2 was obtained.

[0162] The total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was adjusted to 100 g / L. The mass of Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was adjusted to 0.5 g / L.

[0163] Based on the total mass of all components other than Rh in the upper layer (100% by mass), the amounts of each component in the slurry for upper layer formation were adjusted so that the Ce-Zr-Al composite oxide (II) in the upper layer was 70% by mass, the Al-Zr oxide in the upper layer was 25% by mass, and the alumina binder in the upper layer was 5% by mass. Since the total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed is 100 g / L, the mass of the Ce-Zr-Al composite oxide (II) in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed is 70 g / L, the mass of the Al-Zr oxide in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed is 25 g / L, and the mass of the alumina binder in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed is 5 g / L.

[0164] [Example 3] (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on the flow-through type substrate.

[0165] (2) Formation of the upper layer Except for using Ce-Zr-Al composite oxide (I) instead of Ce-Zr-Al composite oxide (II), an upper layer was formed on the lower layer in the same manner as in Example 1 to obtain the exhaust gas purification catalyst of Example 3.

[0166] [Example 4] (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on the flow-through type substrate.

[0167] (2) Formation of the upper layer Except for using Ce-Zr-Al composite oxide (III) instead of Ce-Zr-Al composite oxide (II), an upper layer was formed on the lower layer in the same manner as in Example 1 to obtain the exhaust gas purification catalyst of Example 4.

[0168] [Example 5] (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on the flow-through type substrate.

[0169] (2) Formation of the upper layer Except for using Ce-Zr-Al composite oxide (IV) instead of Ce-Zr-Al composite oxide (II), an upper layer was formed on the lower layer in the same manner as in Example 1 to obtain the exhaust gas purification catalyst of Example 5.

[0170] [Comparative Example 1] (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on the flow-through type substrate.

[0171] (2) Formation of the upper layer Except for adjusting the amounts of each component in the upper layer forming slurry so that the total mass of all components other than Rh in the upper layer is taken as the reference (100% by mass), the Ce-Zr-Al composite oxide (II) in the upper layer is 50% by mass, the Al-Zr-based oxide in the upper layer is 45% by mass, and the alumina binder in the upper layer is 5% by mass, an upper layer was formed on the lower layer in the same manner as in Example 2 to obtain the exhaust gas purification catalyst of Comparative Example 1.

[0172] The total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 100 g / L, so the mass of the Ce-Zr-Al composite oxide (II) in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 50 g / L, the mass of the Al-Zr oxide in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 45 g / L, and the mass of the alumina binder in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 5 g / L.

[0173] Comparative Example 2 (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on a flow-through type substrate.

[0174] (2) Formation of the upper layer An upper layer was formed on the lower layer in the same manner as in Example 2, except that the amounts of each component in the slurry for forming the upper layer were adjusted so that the Ce-Zr-Al composite oxide (II) in the upper layer was 25 mass%, the Al-Zr oxide in the upper layer was 70 mass%, and the alumina binder in the upper layer was 5 mass%, based on the total mass of all components other than Rh in the upper layer (100 mass%). Thus, a catalyst for purifying exhaust gases of Comparative Example 2 was obtained.

[0175] The total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 100 g / L, so the mass of the Ce-Zr-Al composite oxide (II) in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 25 g / L, the mass of the Al-Zr oxide in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 70 g / L, and the mass of the alumina binder in the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer is formed is 5 g / L.

[0176] Comparative Example 3 (1) Formation of the lower layer In the same manner as in Example 1, a lower layer was formed on a flow-through type substrate.

[0177] (2) Formation of the upper layer An upper layer was formed on the lower layer in the same manner as in Example 2, except that the amounts of the respective components in the slurry for forming the upper layer were adjusted such that the total mass of all components other than Rh in the upper layer was taken as a reference (100% by mass), the Al-Zr-based oxide in the upper layer was 95% by mass, and the alumina binder in the upper layer was 5% by mass. Note that in Comparative Example 3, no Ce-Zr-Al-based composite oxide was used.

[0178] Since the total mass of all components other than Rh in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer is formed is 100 g / L, the mass of the Al-Zr-based oxide in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer is formed is 95 g / L, and the mass of the alumina binder in the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer is formed is 5 g / L.

[0179] [Comparative Example 4] (1) Formation of the lower layer A lower layer was formed on the flow-through type substrate in the same manner as in Example 1.

[0180] (2) Formation of the upper layer An upper layer was formed on the lower layer in the same manner as in Example 1, except that Ce-Zr-Al-based composite oxide (V) was used instead of Ce-Zr-Al-based composite oxide (II), to obtain a catalyst for purifying exhaust gas of Comparative Example 4. )

[0181] [Test Example 1] (1) Deterioration treatment For each of the catalysts for purifying exhaust gas, the following durability conditions were imposed as a deterioration treatment assuming 50,000 to 100,000 km of driving. Specifically, each catalyst for purifying exhaust gas was maintained at the following temperature for the following time while being in contact with the exhaust gas discharged by operating the engine under the following conditions. (Durability conditions) · Durability engine: Passenger car NA 2L gasoline engine · Gasoline used: Commercially available regular gasoline · Temperature and time: 950 °C for 100 hours

[0182] (2) Evaluation of OSC Using a temperature-programmed reduction treatment apparatus (TPR apparatus) manufactured by Henmi Slide Rule Co., Ltd., the OSC measurement of each exhaust gas purification catalyst after the deterioration treatment was performed by the CO pulse method. In the OSC measurement, before the measurement, each exhaust gas purification catalyst after the deterioration treatment was heated to 800 °C under a He flow and maintained at that temperature for 40 minutes, and then cooled to 300 °C. Then, with the temperature maintained at 300 °C, O2 gas was injected in 4 pulses for oxidation treatment, and then the O2 gas was stopped. A test gas containing CO was injected in 10 pulses, and from the total amount of CO gas consumed, the OSC amount (μmol / g) of each exhaust gas purification catalyst at 300 °C was measured using an infrared gas concentration measuring apparatus (manufactured by Shimadzu Corporation, CGT-7000). The "OSC amount (μmol / g) of each exhaust gas purification catalyst at 300 °C" means the OSC amount per unit mass of the catalyst layer (lower layer and upper layer) of each exhaust gas purification catalyst. The test gas was prepared by diluting CO gas in He gas by 25% by volume. The percentage of the OSC amount (μmol / g) of each exhaust gas purification catalyst with respect to the OSC amount (μmol / g) of the exhaust gas purification catalyst of Example 1 was calculated and used as the relative value of the OSC amount of each exhaust gas purification catalyst. The results are shown in Table 2.

[0183] From the relative values of the OSC amounts of each exhaust gas purification catalyst, the relative value of the OSC amount of the exhaust gas purification catalyst of Comparative Example 3 (since the upper layer of Comparative Example 3 does not contain OSC such as Ce-Zr-Al composite oxide, the OSC amount of Comparative Example 3 substantially corresponds to the OSC amount due to only the lower layer.) was subtracted, and the obtained value was divided by the mass of the Ce-Zr-Al composite oxide in the upper layer per unit volume of the portion where the upper layer is formed in the flow-through type substrate. The obtained value was used as an index representing the OSC per unit mass of the Ce-Zr-Al composite oxide. The results are shown in Table 2.

[0184] (3) Evaluation of exhaust gas purification performance Each exhaust gas purification catalyst after the deterioration treatment was placed in the exhaust passage, and while flowing an exhaust model gas (CO: 0.50%, H2: 0.17%, O2: 0.50%, NO: 400 ppm, C3H6: 1180 ppm, CO2: 14%, H2O: 10%, N2: the balance) at a space velocity of 100,000 / h, the temperature of the supplied gas was raised to 500 °C at a temperature increase rate of 20 °C / min, and the purification rate of nitrogen oxides (NOx) in the discharged gas was continuously measured, and the temperature (light-off temperature T50) (°C) at which the purification rate of nitrogen oxides (NOx) reached 50% was determined. The light-off temperature T50 was determined during the temperature increase. The results are shown in Table 2.

[0185]

Table 2

[0186] As shown in Table 2, [Condition 1] The amount of the Ce-Zr-Al composite oxide is 70% by mass or more based on the total mass of all components other than Rh in the upper layer, and [Condition 2] The ratio of the amount of Ce in terms of metal in the Ce-Zr-Al composite oxide to the amount of Zr in terms of metal in the Ce-Zr-Al composite oxide is 0.03 or more and 0.50 or less in terms of mass ratio. Examples 1 to 5 that satisfy the above conditions were able to achieve an improvement in the oxygen storage capacity of the Ce-Zr-Al composite oxide and prevention of a decrease in the exhaust gas purification performance of Rh (particularly, prevention of a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment). On the other hand, Comparative Examples 1 and 2 that satisfy Condition 2 but do not satisfy Condition 1 were unable to achieve either an improvement in the oxygen storage capacity of the Ce-Zr-Al composite oxide or prevention of a decrease in the exhaust gas purification performance of Rh (particularly, prevention of a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment). Further, Comparative Example 4 that satisfies Condition 1 but does not satisfy Condition 2 was able to achieve an improvement in the oxygen storage capacity of the Ce-Zr-Al composite oxide, but was unable to prevent a decrease in the exhaust gas purification performance of Rh (particularly, prevention of a decrease in the exhaust gas purification performance of Rh after being exposed to a high-temperature environment). In addition, Comparative Example 3 that does not satisfy either Condition 1 or Condition 2 had an insufficient OSC amount.

Explanation of symbols

[0187] 1 ··· Catalyst for exhaust gas purification 10 ··· Substrate 11 ··· Cylindrical part 12 ··· Partition part 13 ··· Cell 20 ··· First catalyst layer 30 ··· Second catalyst layer

Claims

1. An exhaust gas purification catalyst comprising a substrate and a first catalyst layer provided on the substrate, wherein the first catalyst layer contains Rh and a composite oxide containing Ce, Zr, and Al, the amount of the composite oxide is 80% by mass or more and 100% by mass or less based on the total mass of all components other than Rh in the first catalyst layer, the ratio of the amount of Ce in terms of metal in the composite oxide to the amount of Zr in terms of metal in the composite oxide is 0.07 or more and 0.42 or less by mass ratio, and the exhaust gas purification catalyst is as described above.

2. The exhaust gas purification catalyst according to Claim 1, wherein the ratio of the amount of Al in terms of metal in the composite oxide to the total amount of Ce and Zr in terms of metal in the composite oxide is 0.10 or more and 10 or less by mass ratio.

3. The exhaust gas purification catalyst according to Claim 1, wherein the total amount of Ce, Zr, and Al in terms of oxide in the composite oxide is 75% by mass or more and 100% by mass or less based on the mass of the composite oxide.

4. The exhaust gas purification catalyst according to Claim 3, wherein the amount of rare earth elements other than Ce in terms of oxide in the composite oxide is 0% by mass or more and 25% by mass or less based on the mass of the composite oxide.

5. The exhaust gas purification catalyst according to Claim 4, wherein the rare earth element other than Ce is selected from La, Y, Pr, and Nd.

6. The exhaust gas purification catalyst according to Claim 1, wherein the first catalyst layer contains an Al-based oxide.

7. The exhaust gas purification catalyst according to Claim 1, wherein the first catalyst layer contains a binder.

8. The exhaust gas purification catalyst according to Claim 7, wherein the binder is an inorganic oxide other than the Ce-Zr-Al-based composite oxide.

9. The exhaust gas purification catalyst includes a second catalyst layer provided on the substrate, the first catalyst layer is provided above the second catalyst layer, and the second catalyst layer contains one of Pd or Pt, or both Pd and Pt. The exhaust gas purification catalyst is as described in Claim 1.

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