Exhaust gas purification catalyst

Abstract

The purpose of the present invention is to provide an exhaust gas purification catalyst having improved exhaust gas purification performance, and provides an exhaust gas purification catalyst (1) provided with a base material (10) and a first catalyst layer (20) provided on the base material (10), the first catalyst layer (20) containing Rh, Ce, and Y, the value of a / b is 0.010-0.400 (inclusive), where a is the molar percentage of the molar amount of Ce in the first catalyst layer (20) based on the total molar amount of all metal elements in the first catalyst layer (20), and b is the molar percentage of the molar amount of Y in the first catalyst layer (20) based on the total molar amount of all metal elements in the first catalyst layer (20).

Description

Technical Field

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

[0002] The exhaust gas emitted from the internal combustion engines of cars, motorcycles, etc. contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). In order to purify these harmful components and render them harmless, a three-way catalyst is used. As a three-way catalyst, a catalyst containing precious metal elements such as Pt, Pd, and Rh is used. Pt and Pd are mainly involved in the oxidation purification of HC and CO, and Rh is mainly involved in the reduction purification of NOx.

[0003] Patent document 1 describes a catalyst for exhaust gas purification, which includes a substrate and a catalyst layer formed on the substrate, the catalyst layer comprising Rh-loaded ZrLaY composite oxide, Rh-loaded ZrLa-activated alumina, and Rh-loaded ZrCe-based composite oxide, the Rh loading amount in the Rh-loaded ZrLa-activated alumina is greater than the Rh loading amount in the Rh-loaded ZrLaY composite oxide, and the Rh loading amount in the Rh-loaded ZrCe-based composite oxide is greater than the Rh loading amount in the Rh-loaded ZrLa-activated alumina. The Rh-loaded ZrLaY composite oxide is formed by loading Rh in a ZrLaY composite oxide containing ZrO2 as a main component, 2% by mass or more and 10% by mass or less La2O3, and 2% by mass or more and 20% by mass or less Y2O3. The Rh-loaded ZrLa-activated alumina is formed by loading Rh in an activated alumina loaded with a ZrLa composite oxide containing Zr and La. The Rh-loaded ZrCe-based composite oxide is a ZrCe-based composite oxide containing Zr and Ce in which Rh is loaded. It should be noted that the ZrLa composite oxide does not contain Y and is different from the ZrLaY composite oxide.

[0004] According to the exhaust gas purification catalyst described in Patent Document 1, deactivation of Rh caused by a part of Rh being dissolved in alumina due to exposure to high-temperature exhaust gas can be suppressed, thereby improving exhaust gas purification performance.

[0005] In the example of patent document 1, an upper catalyst layer including Rh-loaded ZrCeNd composite oxide, Rh-loaded ZrLaY composite oxide, La alumina, and Rh-loaded ZrLa alumina included as the case may be, is formed on the lower catalyst layer. In the example of patent document 1, when the molar percentage of the molar amount of Ce in the upper catalyst layer based on the total molar amount of all metal elements in the upper catalyst layer is set to a, and the molar percentage of the molar amount of Y in the upper catalyst layer based on the total molar amount of all metal elements in the upper catalyst layer is set to b, the value of a / b is calculated to be about 1.6 (Example 5A), about 3.3 (Example 5B), about 3.9 (Examples 4A and 4B), about 19.7 (Examples 11A, 11B, 12A and 12B), and about 2.0 (Examples 13A, 13B, 14A and 14B).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2015-073961 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] There is a demand for improvement in exhaust gas purification performance.

[0011] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst having improved exhaust gas purification performance.

[0012] Solutions for solving problems

[0013] The present invention provides the following exhaust gas purification catalyst.

[0014] [1] An exhaust gas purification catalyst comprising a substrate and a first catalyst layer provided on the substrate,

[0015] The first catalyst layer comprises Rh, Ce and Y,

[0016] When the molar percentage of the molar amount of Ce in the first catalyst layer based on the total molar amount of all metal elements in the first catalyst layer is set to a, and the molar percentage of the molar amount of Y in the first catalyst layer based on the total molar amount of all metal elements in the first catalyst layer is set to b, the value of a / b is greater than 0.010 and less than 0.400.

[0017] [2] The exhaust gas purification catalyst according to [1], wherein the first catalyst layer further contains Zr.

[0018] [3] The exhaust gas purification catalyst according to [1] or [2], wherein b is 11 mol % or more.

[0019] [4] The exhaust gas purification catalyst according to [1] or [2], wherein b is 15 mol % or more.

[0020] [5] The exhaust gas purification catalyst according to [1] or [2], wherein b is 19 mol % or more.

[0021] [6] The exhaust gas purification catalyst according to any one of [1] to [5], wherein, when the molar percentage of the molar amount of Rh in the first catalyst layer based on the total molar amount of all metal elements in the first catalyst layer is set to c, the value of c / b is greater than or equal to 0.0010 and less than or equal to 0.0270.

[0022] [7] The exhaust gas purification catalyst according to any one of [1] to [6], further comprising a second catalyst layer provided on the substrate.

[0023] [8] The exhaust gas purification catalyst according to [7], wherein the first catalyst layer is provided on an upper side of the second catalyst layer.

[0024] [9] The exhaust gas purification catalyst according to [7] or [8], wherein the second catalyst layer contains Pd.

[0025] Effects of the Invention

[0026] According to the present invention, there is provided an exhaust gas purification catalyst having improved exhaust gas purification performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a partial cross-sectional view showing a state in which an exhaust gas purifying catalyst according to an embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine.

[0028] Figure 2 for Figure 1 AA line cross-section diagram.

[0029] Figure 3 for Figure 2 An enlarged view of the area indicated by symbol R in FIG.

[0030] Figure 4 for Figure 1 BB line cross-section diagram. DETAILED DESCRIPTION

[0031] 《Explanation of Terminology》

[0032] The following is an explanation of the terms used in this specification.

[0033] <Rare earth elements>

[0034] Examples of the rare earth element include Ce, Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In addition, in this specification, the rare earth element may be referred to as "Ln".

[0035] <Oxide>

[0036] The oxide of Al refers to Al2O3, the oxide of Si refers to SiO2, the oxide of B refers to B2O3, the oxide of Zr refers to ZrO2, the oxide of Cr refers to Cr2O3, the oxide of Mg refers to MgO, the oxide of Ca refers to CaO, the oxide of Sr refers to SrO, the oxide of Ba refers to BaO, the oxide of Fe refers to Fe3O4, the oxide of Mn refers to Mn3O4, and the oxide of Ni refers to NiO. The oxide of rare earth elements refers to sesquioxide (Ln2O3), excluding the oxides of Ce, Pr and Tb; the oxide of Ce refers to CeO2, and the oxide of Pr refers to Pr6O 11 , Tb oxide refers to Tb4O7.

[0037] <Ce-based oxides>

[0038] Ce-based oxides refer to oxides containing Ce. It should be noted that, for oxides containing Ce and Y, when the content of Ce oxide is the same as or greater than the content of Y oxide, it belongs to Ce-based oxides, and when the content of Ce oxide is less than the content of Y oxide, it belongs to Y-based oxides. In addition, for oxides containing Ce and Al, when the content of Ce oxide is the same as or greater than the content of Al oxide, it belongs to Ce-based oxides, and when the content of Ce oxide is less than the content of Al oxide, it belongs to Al-based oxides.

[0039] The Ce-based oxide is in, for example, a granular form.

[0040] Ce-based oxides are used as carriers of catalytically active components. In order to improve the supportability of the catalytically active components, Ce-based oxides are preferably porous.

[0041] Ce-based oxides have the ability to absorb and store oxygen when the oxygen concentration in the exhaust gas is high, and release oxygen when the oxygen concentration in the exhaust gas is low (sometimes referred to as "oxygen storage capacity" in this specification), which can reduce the fluctuation of the oxygen concentration in the exhaust gas and expand the working window of the catalytic active component. Therefore, when Ce-based oxides are used, the exhaust gas purification ability of the exhaust gas purification catalyst is improved.

[0042] The Ce-based oxide may or may not contain one or more elements other than Ce and O.

[0043] One or more elements other than Ce and O can be selected from, for example, rare earth elements (Ln) other than Ce, alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0044] The Ce-based oxide may contain at least one selected from, for example, La, Nd, Y, Gd, and Sm as Ln other than Ce. Thus, the heat resistance of the Ce-based oxide can be improved. In order to improve the heat resistance of the Ce-based oxide, Ln other than Ce is preferably selected from La, Nd, and Y.

[0045] The Ce-based oxide may contain, for example, Pr as Ln other than Ce. This can improve the oxygen storage capacity of the Ce-based oxide.

[0046] Examples of the Ce-based oxide include cerium oxide (oxide composed of Ce and O), oxides obtained by modifying the surface of cerium oxide with an element other than Ce and O, and oxides obtained by dissolving an element other than Ce and O in cerium oxide.

[0047] In Ce-based oxides, elements other than Ce and O may form a solid solution phase together with Ce and O, or may form a single crystalline or amorphous phase (e.g., an oxide phase of elements other than Ce and O), or may form both a solid solution phase and a single phase.

[0048] In the Ce-based oxide according to one embodiment (hereinafter referred to as the "first Ce-based oxide"), the content of Ce in terms of oxide is preferably greater than 90% by mass, more preferably greater than 95% by mass, and even more preferably greater than 99% by mass, based on the mass of the first Ce-based oxide. The upper limit is 100% by mass.

[0049] When the first Ce-based oxide contains elements other than Ce and O, in order to improve the oxygen storage capacity of the first Ce-based oxide, the content of the oxides of the elements other than Ce and O in the first Ce-based oxide is preferably greater than 0 mass% and less than 10 mass%, more preferably greater than 0 mass% and less than 5 mass%, and further preferably greater than 0 mass% and less than 1 mass% based on the mass of the first Ce-based oxide. The content of the oxides of elements other than Ce and O can be, for example, greater than 0.1 mass%, greater than 0.2 mass%, greater than 0.3 mass%, etc. These lower limits can be combined with any of the above upper limits, respectively. For the "content of the oxides of elements other than Ce and O", when the first Ce-based oxide contains one element other than Ce and O, it refers to the content of the oxide of the one element, and when the first Ce-based oxide contains two or more elements other than Ce and O, it refers to the total content of the oxides of the two or more elements.

[0050] In the Ce-based oxide involved in another embodiment (hereinafter referred to as the "second Ce-based oxide"), the content of Ce oxide converted is based on the mass of the second Ce-based oxide, and is preferably greater than 1 mass % and less than 90 mass %, more preferably greater than 2 mass % and less than 50 mass %, and further preferably greater than 3 mass % and less than 45 mass %.

[0051] In order to improve the heat resistance of the second Ce-based oxide, the content of the oxides of elements other than Ce and O in the second Ce-based oxide is preferably 10% by mass or more and 99% by mass or less, more preferably 50% by mass or more and 98% by mass or less, and further preferably 55% by mass or more and 97% by mass or less, based on the mass of the second Ce-based oxide. For the "content of the oxides of elements other than Ce and O", when the second Ce-based oxide contains one element other than Ce and O, it refers to the content of the oxide of the one element, and when the second Ce-based oxide contains two or more elements other than Ce and O, it refers to the total content of the oxides of the two or more elements.

[0052] <Ce-Zr oxides>

[0053] Ce-Zr oxide is a type of Ce oxide (preferably a type of second Ce oxide), and refers to a composite oxide containing Ce and Zr. It should be noted that, for an oxide containing Ce, Y and Zr, when the content of Ce oxide is the same as or greater than the content of Y oxide, it belongs to Ce-Zr oxide, and when the content of Ce oxide is less than the content of Y oxide, it belongs to Y-Zr oxide.

[0054] The Ce—Zr-based oxide is in, for example, a granular form.

[0055] The Ce-Zr-based oxide is used as a carrier of the catalytically active component. In order to improve the supportability of the catalytically active component, the Ce-Zr-based oxide is preferably porous.

[0056] In Ce-Zr oxides, Ce can form a solid solution phase together with Zr and O, or form a single phase of a crystalline phase or an amorphous phase (for example, a CeO2 single phase), or form both a solid solution phase and a single phase, but it is preferred that at least a portion of Ce forms a solid solution phase.

[0057] In Ce-Zr oxides, Zr can form a solid solution phase together with Ce and O, or form a single phase of a crystalline phase or an amorphous phase (for example, a ZrO2 single phase), or form both a solid solution phase and a single phase, but it is preferred that at least a portion of Zr forms a solid solution phase.

[0058] Ce-Zr oxides have oxygen storage capacity, which can reduce the fluctuation of oxygen concentration in exhaust gas and expand the working window of catalytic active components. Therefore, when Ce-Zr oxides are used, the exhaust gas purification capacity of the exhaust gas purification catalyst is improved. Ce mainly contributes to the improvement of the oxygen storage capacity of Ce-Zr oxides, and Zr mainly contributes to the improvement of the heat resistance of Ce-Zr oxides.

[0059] In order to improve the heat resistance and oxygen storage capacity of the Ce-Zr oxide, the total content of Ce and Zr oxides in the Ce-Zr oxide is preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more, based on the mass of the Ce-Zr oxide. The upper limit is 100% by mass.

[0060] In order to improve the oxygen storage capacity of Ce-Zr oxides, the content of Ce oxide in Ce-Zr oxides is preferably 5 mass % or more and 90 mass % or less, more preferably 7 mass % or more and 60 mass % or less, and further preferably 10 mass % or more and 50 mass % or less, based on the mass of Ce-Zr oxides.

[0061] In order to improve the heat resistance of Ce-Zr-based oxides, the content of Zr in Ce-Zr-based oxides converted to oxide is based on the mass of Ce-Zr-based oxides, and is preferably greater than 10 mass % and less than 95 mass %, more preferably greater than 40 mass % and less than 95 mass %, and further preferably greater than 50 mass % and less than 90 mass %.

[0062] The Ce—Zr-based oxide may or may not contain one or more elements other than Ce, Zr, and O.

[0063] One or more elements other than Ce, Zr and O can be selected from, for example, rare earth elements (Ln) other than Ce, alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.

[0064] The Ce-Zr oxide may contain at least one selected from, for example, La, Nd, Y, Gd, and Sm as Ln other than Ce. Thus, the heat resistance of the Ce-Zr oxide can be improved. In order to improve the heat resistance of the Ce-Zr oxide, Ln other than Ce is preferably selected from La, Nd, and Y.

[0065] The Ce-Zr-based oxide may contain, for example, Pr as Ln other than Ce. This can improve the oxygen storage capacity of the Ce-Zr-based oxide.

[0066] When the Ce-Zr-based oxide contains Ln other than Ce, the Ln other than Ce can form a solid solution phase together with Zr and / or Ce and O, or can form a separate phase of a crystalline phase or an amorphous phase (for example, a separate oxide phase of Ln other than Ce), or can form both a solid solution phase and a separate phase, but it is preferred that at least a portion of the Ln other than Ce forms a solid solution phase.

[0067] When the Ce-Zr oxide contains Ln other than Ce, in order to improve the heat resistance of the Ce-Zr oxide, the content of Ln other than Ce in the Ce-Zr oxide in terms of oxide conversion is preferably 1% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 30% by mass or less, and further preferably 5% by mass or more and 20% by mass or less, based on the mass of the Ce-Zr oxide. The "content of Ln other than Ce in terms of oxide conversion" refers to the content of the oxide of the Ln other than Ce when the Ce-Zr oxide contains one Ln other than Ce, and refers to the total content of the oxide of the two or more Lns when the Ce-Zr oxide contains two or more Lns other than Ce.

[0068] <Y series oxide>

[0069] Y-based oxides refer to oxides containing Y. It should be noted that, for oxides containing Y and Al, when the content of Y oxide is the same as or greater than the content of Al oxide, it belongs to the Y-based oxide, and when the content of Y oxide is less than the content of Al oxide, it belongs to the Al-based oxide.

[0070] The Y-based oxide is in, for example, a granular form.

[0071] The Y-based oxide is used as a carrier of the catalytically active component. In order to improve the supporting property of the catalytically active component, the Y-based oxide is preferably porous.

[0072] The Y-based oxide may or may not contain one or more elements other than Y and O.

[0073] One or more elements other than Y and O can be selected from, for example, rare earth elements (Ln) other than Y, alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0074] The Y series oxide may contain at least one selected from, for example, La, Nd, Gd, and Sm as Ln other than Y. Thus, the heat resistance of the Y series oxide can be improved. In order to improve the heat resistance of the Y series oxide, Ln other than Y is preferably selected from La and Nd.

[0075] The Y-based oxide may contain, for example, Ce as Ln other than Y. The Y-based oxide containing Ce has oxygen storage capacity, can reduce fluctuations in oxygen concentration in exhaust gas, and expand the operating window of the catalytically active component. Therefore, when the Y-based oxide containing Ce is used, the exhaust gas purification capacity of the exhaust gas purification catalyst is improved.

[0076] The Y-based oxide containing Ce contains, for example, Pr as Ln other than Y and Ce. This can improve the oxygen storage capacity of the Y-based oxide containing Ce.

[0077] Examples of Y-based oxides include yttrium oxide (an oxide composed of Y and O), oxides obtained by modifying the surface of yttrium oxide with elements other than Y and O, and oxides obtained by dissolving elements other than Y and O in yttrium oxide.

[0078] In Y-series oxides, elements other than Y and O can form a solid solution phase together with Y and O, or form a separate phase of a crystalline phase or an amorphous phase (e.g., an oxide phase of elements other than Y and O), or form both a solid solution phase and a separate phase.

[0079] In the Y-based oxide (hereinafter referred to as the "first Y-based oxide") according to one embodiment, the content of Y in terms of oxide is preferably greater than 90% by mass, more preferably greater than 95% by mass, and even more preferably greater than 99% by mass, based on the mass of the first Y-based oxide. The upper limit is 100% by mass.

[0080] When the first Y series oxide contains elements other than Y and O, in order to effectively express the performance of Y described later, the content of the oxide conversion of the elements other than Y and O in the first Y series oxide is based on the mass of the first Y series oxide, preferably greater than 0 mass% and less than 10 mass%, more preferably greater than 0 mass% and less than 5 mass%, and further preferably greater than 0 mass% and less than 1 mass%. The content of the oxide conversion of elements other than Y and O can be, for example, 0.1 mass% or more, 0.2 mass% or more, 0.3 mass% or more, etc. These lower limits can be combined with any one of the above upper limits, respectively. For "the content of the oxide conversion of elements other than Y and O", when the first Y series oxide contains one element other than Y and O, it refers to the content of the oxide conversion of the one element, and when the first Y series oxide contains two or more elements other than Y and O, it refers to the total content of the oxide conversion of the two or more elements.

[0081] In the Y-series oxide involved in another embodiment (hereinafter referred to as the "second Y-series oxide"), the content of Y converted to oxide is based on the mass of the second Y-series oxide, and is preferably greater than 1 mass % and less than 90 mass %, more preferably greater than 2 mass % and less than 50 mass %, and further preferably greater than 3 mass % and less than 45 mass %.

[0082] In order to improve the heat resistance of the second Y-based oxide, the content of the oxides of elements other than Y and O in the second Y-based oxide is preferably 10% by mass or more and 99% by mass or less, more preferably 50% by mass or more and 98% by mass or less, and further preferably 55% by mass or more and 97% by mass or less, based on the mass of the second Y-based oxide. "The content of the oxides of elements other than Y and O" refers to the content of the oxide of one element when the second Y-based oxide contains one element other than Y and O, and refers to the total content of the oxides of the two or more elements when the second Y-based oxide contains two or more elements other than Y and O.

[0083] <Y-Zr series oxide>

[0084] The Y—Zr-based oxide is a type of Y-based oxide (preferably a type of the second Y-based oxide), and refers to a composite oxide containing Y and Zr.

[0085] The Y—Zr-based oxide is in, for example, a granular form.

[0086] The Y-Zr-based oxide is used as a carrier of the catalytically active component. In order to improve the supporting property of the catalytically active component, the Y-Zr-based oxide is preferably porous.

[0087] In Y-Zr-based oxides, Y can form a solid solution phase together with Zr and O, or form a single phase of a crystalline phase or an amorphous phase (for example, a Y2O3 single phase), or form both a solid solution phase and a single phase, but it is preferred that at least a portion of Y forms a solid solution phase.

[0088] In Y-Zr series oxides, Zr can form a solid solution phase together with Y and O, or form a single phase of a crystalline phase or an amorphous phase (for example, a ZrO2 single phase), or form both a solid solution phase and a single phase, but it is preferred that at least a portion of Zr forms a solid solution phase.

[0089] In order to improve the heat resistance of the Y-Zr series oxide, the total content of Y and Zr oxides in the Y-Zr series oxide is preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more, based on the mass of the Y-Zr series oxide. The upper limit is 100% by mass.

[0090] In order to effectively express the performance of Y described later, the content of Y in the Y-Zr-based oxide converted to oxide is preferably 5 mass % or more and 90 mass % or less, based on the mass of the Y-Zr-based oxide, more preferably 7 mass % or more and 80 mass % or less, further preferably 10 mass % or more and 70 mass % or less, further preferably 15 mass % or more and 60 mass % or less, and particularly preferably 20 mass % or more and 55 mass % or less.

[0091] In order to improve the heat resistance of Y-Zr-based oxides, the content of Zr in Y-Zr-based oxides converted to oxide is preferably 10 mass % or more and 95 mass % or less, more preferably 30 mass % or more and 95 mass % or less, and further preferably 40 mass % or more and 90 mass % or less, based on the mass of Y-Zr-based oxides.

[0092] The Y—Zr-based oxide may or may not contain one or more elements other than Y, Zr and O.

[0093] One or more elements other than Y, Zr and O can be selected from, for example, rare earth elements (Ln) other than Y, alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.

[0094] The Y-Zr series oxide may contain at least one selected from, for example, La, Nd, Gd, and Sm as Ln other than Y. Thus, the heat resistance of the Y-Zr series oxide can be improved. In order to improve the heat resistance of the Y-Zr series oxide, Ln other than Y is preferably selected from La and Nd.

[0095] The Y-Zr-based oxide may contain, for example, Ce as Ln other than Y. The Y-Zr-based oxide containing Ce has oxygen storage capacity, can reduce fluctuations in oxygen concentration in exhaust gas, and expand the operating window of the catalytically active component. Therefore, when the Y-Zr-based oxide containing Ce is used, the exhaust gas purification capacity of the exhaust gas purification catalyst is improved.

[0096] The Y-Zr-based oxide containing Ce contains, for example, Pr as Ln other than Y and Ce. This can improve the oxygen storage capacity of the Y-Zr-based oxide containing Ce.

[0097] When the Y-Zr series oxide contains Ln other than Y, the Ln other than Y can form a solid solution phase together with Zr and / or Y and O, or form a separate phase of a crystalline phase or an amorphous phase (for example, a separate oxide phase of Ln other than Y), or form both a solid solution phase and a separate phase, but it is preferred that at least a portion of the Ln other than Y forms a solid solution phase.

[0098] When the Y-Zr oxide contains Ln other than Y, the content of Ln other than Y in the Y-Zr oxide in terms of oxide conversion is preferably 1% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 30% by mass or less, and even more preferably 5% by mass or more and 20% by mass or less, based on the mass of the Y-Zr oxide, in order to improve the heat resistance of the Y-Zr oxide. The "content of Ln other than Y in terms of oxide conversion" refers to the content of the oxide of the Ln other than Y when the Y-Zr oxide contains one type of Ln other than Y, and refers to the total content of the oxide of the two or more types of Ln when the Y-Zr oxide contains two or more types of Ln other than Y.

[0099] <Al-based oxides>

[0100] The Al-based oxide refers to an oxide containing Al.

[0101] The Al-based oxide is in, for example, a granular form.

[0102] The Al-based oxide is used as a carrier of the catalytically active component. In order to improve the supportability of the catalytically active component, the Al-based oxide is preferably porous.

[0103] The Al-based oxide may or may not contain one or two or more elements other than Al and O.

[0104] One or more elements other than Al and O may be selected from, for example, rare earth elements (e.g., Y, Ce, La, Nd, Pr, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0105] The Al-based oxide may contain at least one selected from, for example, La, Nd, Y, Gd, and Sm as Ln. Thus, the heat resistance of the Al-based oxide can be improved. In order to improve the heat resistance of the Al-based oxide, Ln is preferably selected from La, Nd, and Y.

[0106] The Al-based oxide may contain, for example, Ce as Ln. The Al-based oxide containing Ce has oxygen storage capacity, can reduce fluctuations in oxygen concentration in exhaust gas, and expand the working window of the catalytically active component. Therefore, when the Al-based oxide containing Ce is used, the exhaust gas purification capacity of the exhaust gas purification catalyst is improved.

[0107] The Al-based oxide containing Ce may contain, for example, Pr as Ln other than Ce. This can improve the oxygen storage capacity of the Al-based oxide containing Ce.

[0108] Examples of Al-based oxides include aluminum oxide (oxide composed of Al and O), oxides obtained by modifying the surface of aluminum oxide with elements other than Al and O, and oxides obtained by solid-dissolving elements other than Al and O in aluminum oxide. Specific examples of Al-based oxides containing elements other than Al and O include aluminum oxide-silicon dioxide, aluminum oxide-silicate, aluminum oxide-zirconia, aluminum oxide-chromium oxide, aluminum oxide-cerium oxide, and aluminum oxide-lanthanum oxide.

[0109] In Al-based oxides, elements other than Al and O may form a solid solution phase together with Al and O, or may form a separate phase of a crystalline phase or an amorphous phase (e.g., an oxide phase of elements other than Al and O), or may form both a solid solution phase and a separate phase.

[0110] In order to improve the heat resistance of the Al-based oxide, the content of Al in the Al-based oxide is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, further preferably 80% by mass or more, further preferably 90% by mass or more, further preferably 95% by mass or more, based on the mass of the Al-based oxide. The upper limit is 100% by mass.

[0111] When the Al-based oxide contains elements other than Al and O, in order to improve the heat resistance of the Al-based oxide, the content of the elements other than Al and O in the Al-based oxide in terms of oxide conversion is preferably 0.1% by mass or more and 50% by mass or less, more preferably 0.1% by mass or more and 40% by mass or less, further preferably 0.1% by mass or more and 30% by mass or less, further preferably 0.2% by mass or more and 20% by mass or less, further preferably 0.3% by mass or more and 10% by mass or less, further preferably 0.5% by mass or more and 5% by mass or less. The "content of the elements other than Al and O in terms of oxide conversion" refers to the content of the oxide of one element when the Al-based oxide contains one element other than Al and O, and refers to the total content of the oxides of the two or more elements when the Al-based oxide contains two or more elements other than Al and O.

[0112] 《Catalysts for exhaust gas purification》

[0113] The following is based on Figures 1 to 4 , an exhaust gas-purifying catalyst 1 according to an embodiment of the present invention will be described.

[0114] like Figure 1 As shown, the exhaust gas purification catalyst 1 is arranged in the exhaust passage in the exhaust pipe P of the internal combustion engine. The internal combustion engine is, for example, a gasoline engine. The exhaust gas discharged from the internal combustion engine flows through the exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P, and is purified by the exhaust gas purification catalyst 1 arranged in the exhaust pipe P. In the drawings, the exhaust gas flow direction is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side" or "upstream side", and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side" or "downstream side".

[0115] The exhaust passage in the exhaust pipe P may be provided with another exhaust gas purifying catalyst on the upstream side or downstream side of the exhaust gas purifying catalyst 1. For example, the exhaust gas purifying catalyst 1 may be provided on the upstream side of the exhaust passage in the exhaust pipe P, and another exhaust gas purifying catalyst may be provided on the downstream side of the exhaust passage in the exhaust pipe P.

[0116] like Figures 2 to 4 As shown, the exhaust gas-purifying catalyst 1 includes a substrate 10 and a first catalyst layer 20 provided on the substrate 10 .

[0117] The exhaust gas purifying catalyst 1 may include a catalyst layer 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. In the present embodiment, the exhaust gas purifying catalyst 1 further includes a second catalyst layer 30 provided on the substrate 10. The second catalyst layer 30 is a layer provided as required, and the present invention also includes an embodiment in which the second catalyst layer 30 is omitted. Among them, in order to improve the exhaust gas purification performance, the exhaust gas purifying catalyst 1 preferably includes the second catalyst layer 30.

[0118] <Base material>

[0119] Next, the substrate 10 will be described.

[0120] The material constituting the substrate 10 can be appropriately selected. The material constituting the substrate 10 is preferably a material that can stably maintain the shape of the substrate even when the substrate is exposed to high-temperature exhaust gas. The material constituting the substrate 10 can be selected from, for example, ceramic materials, metal materials, and the like. The ceramic material can be selected from, for example, carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; oxide ceramics such as alumina, zirconium oxide, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. The metal material can be selected from, for example, alloys such as stainless steel.

[0121] In addition, in this specification, "high temperature" means a temperature of preferably 850°C or higher, and more preferably 900°C or higher.

[0122] like Figures 2 to 4 As shown, the substrate 10 includes a cylindrical portion 11, a partition wall portion 12 provided in the cylindrical portion 11, and cells 13 partitioned by the partition wall portion 12. The substrate 10 is preferably a honeycomb structure.

[0123] like Figure 2 and 3 As shown, the cylindrical portion 11 defines the outer shape of the substrate 10, and the axial direction of the cylindrical portion 11 is consistent with the axial direction of the substrate 10. Figure 2 As shown, the shape of the cylindrical portion 11 is cylindrical, but it can also be other shapes such as an elliptical cylinder or a polygonal cylinder.

[0124] like Figure 2 and 3 As shown in FIG. 1 , the partition wall portion 12 is disposed in the cylindrical portion 11. Figures 2 to 4 As shown, partition wall 12 exists between adjacent chambers 13, and adjacent chambers 13 are partitioned by partition wall 12. The thickness of partition wall 12 is, for example, 20 μm or more and 1500 μm or less. Partition wall 12 may have a porous structure through which exhaust gas can pass.

[0125] like Figure 4As shown, the chamber 13 extends in the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0126] like Figure 4 As shown, both the end of the exhaust gas inlet side and the end of the exhaust gas outlet side of the chamber 13 are open. Therefore, the exhaust gas flowing in from the end (opening) of the exhaust gas inlet side of the chamber 13 flows out from the end (opening) of the exhaust gas outlet side of the chamber 13. This style is called a flow-through type.

[0127] like Figure 2 and 3 As shown, the end (opening) of the chamber 13 on the exhaust gas inlet side is a quadrilateral in plan view, but may be hexagonal, octagonal, etc. The end (opening) of the chamber 13 on the exhaust gas outlet side is similar in plan view.

[0128] The cavity density per square inch of the substrate 10 is, for example, 100 cavities or more and 1000 cavities or less. It should be noted that the cavity density per square inch of the substrate 10 is the total number of cavities 13 per square inch in a cross section obtained by cutting the substrate 10 with a plane perpendicular to the exhaust gas flow direction X.

[0129] The volume of the substrate 10 is, for example, not less than 0.1 L and not more than 20 L. The volume of the substrate 10 refers to the apparent volume of the substrate 10. When the substrate 10 is cylindrical, the outer diameter of the substrate 10 is set to 2r, and the length of the substrate 10 is set to L. The volume of the substrate 10 is expressed by the formula: Volume of substrate 10 = π × r 2 ×L is used to express it.

[0130] The substrate 10 may be provided with a first sealing portion that seals the end of the exhaust gas outflow side of a part of the chambers 13 and a second sealing portion that seals the end of the exhaust gas inflow side of the remaining chambers 13. Thus, a part of the chambers 13 become inflow-side chambers with an end opening on the exhaust gas inflow side and an end on the exhaust gas outflow side blocked by the first sealing portion; the remaining chambers 13 become outflow-side chambers with an end on the exhaust gas inflow side blocked by the second sealing portion and an end on the exhaust gas outflow side open. A plurality of (for example, four) outflow-side chambers are arranged around one inflow-side chamber, and the inflow-side chamber and the outflow-side chambers arranged around the inflow-side chamber are separated by a porous partition wall 12. The exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow-side chamber passes through the porous partition wall 12 and flows out from the end (opening) of the exhaust gas outflow side of the outflow-side chamber 13b. This style is called a wall flow type. In the case of the wall flow type, the partition wall portion 12 has a porous structure that allows the exhaust gas to pass therethrough.

[0131] <First catalyst layer>

[0132] Next, the first catalyst layer 20 will be described.

[0133] like Figure 3 and 4 As shown, the first catalyst layer 20 is disposed on the upper side of the second catalyst layer 30 .

[0134] “The first catalyst layer 20 is disposed on the upper side of the second catalyst layer 30” means that, of the two main surfaces of the second catalyst layer 30, part or all of the first catalyst layer 20 exists on the main surface on the opposite side to the main surface on the partition wall portion 12 side. “The main surface of the second catalyst layer 30” refers to the outer surface of the second catalyst layer 30 extending in the exhaust gas flow direction X. The first catalyst layer 20 can be disposed in a manner covering a portion of the main surface of the second catalyst layer 30, or in a manner covering the entire main surface of the second catalyst layer 30. The first catalyst layer 20 can be directly disposed on the main surface of the second catalyst layer 30, or can be disposed thereon via other layers. Usually, it is directly disposed on the main surface of the second catalyst layer 30. An embodiment in which the first catalyst layer 20 is directly disposed on the main surface of the second catalyst layer 30 and an embodiment in which the first catalyst layer 20 is disposed on the main surface of the second catalyst layer 30 via other layers are both included in the “first catalyst layer 20 disposed on the substrate 10”.

[0135] When the second catalyst layer 30 is omitted, the first catalyst layer 20 is provided on the chamber 13 side surface of the partition wall portion 12. The "chamber 13 side surface of the partition wall portion 12" refers to the outer surface of the partition wall portion 12 extending in the exhaust gas flow direction X. The first catalyst layer 20 may be provided directly on the chamber 13 side surface of the partition wall portion 12 or may be provided thereon via another layer. Usually, it is provided directly on the chamber 13 side surface of the partition wall portion 12.

[0136] When the first catalyst layer 20 is directly disposed on the chamber 13 side surface of the partition wall portion 12, the first catalyst layer 20 may be composed of a portion that protrudes from the chamber 13 side surface of the partition wall portion 12 toward the chamber 13 side (hereinafter referred to as a "protruding portion"), or may be composed of a portion that exists inside the partition wall portion 12 (hereinafter referred to as an "internal portion"), or may have a protruding portion and an internal portion. Embodiments in which the first catalyst layer 20 is composed of a protruding portion, embodiments in which the first catalyst layer 20 is composed of an internal portion, and embodiments in which the first catalyst layer 20 has a protruding portion and an internal portion are all included in the "first catalyst layer 20 disposed on the substrate 10".

[0137] like Figure 4As shown, the first catalyst layer 20 extends from the end of the exhaust gas inlet side of the partition wall portion 12 to the end of the exhaust gas outlet side of the partition wall portion 12 along the exhaust gas flow direction X. The first catalyst layer 20 may also extend from the end of the exhaust gas inlet side of the partition wall portion 12 along the exhaust gas flow direction X, but not reach the end of the exhaust gas outlet side of the partition wall portion 12; or may extend from the end of the exhaust gas outlet side of the partition wall portion 12 in the direction opposite to the exhaust gas flow direction X, but not reach the end of the exhaust gas inlet side of the partition wall portion 12.

[0138] In order to achieve a good balance between exhaust gas purification performance and cost, 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 (the mass after drying and calcination) is preferably 30 g / L or more and 150 g / L or less, more preferably 40 g / L or more and 120 g / L or less, and further 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 according to the formula: (mass of the first catalyst layer 20) / ((volume of the substrate 10)×(average length L of the first catalyst layer 20) 20 / length L of substrate 10 10 ))Calculated.

[0139] In this specification, "the mass of the first catalyst layer 20" refers to the mass obtained by adding up the mass of the precious metal element in metal conversion and the mass of the oxide conversion of the metal element other than the precious metal element among all the metal elements contained in the first catalyst layer 20. That is, "the mass of the first catalyst layer 20" refers to the calculated mass obtained by adding up the mass of the precious metal element in metal conversion and the mass of the oxide conversion of the metal element other than the precious metal element contained in the first catalyst layer 20. It should be noted that "metal elements" also include semi-metal elements such as Si and B.

[0140] In this specification, the “precious metal element” includes Pt, Pd, Rh, Au, Ag, Ru, Ir, and Os.

[0141] The meaning of "oxide" is as described in the above <oxide> column.

[0142] The average length L of the first catalyst layer 20 20 An example of a method for measuring is as follows.

[0143] A thin film extending in the axial direction of the substrate 10 and having a length L with respect to the substrate 10 is cut out from the exhaust gas purifying catalyst 1 . 10Samples of the same length. The sample is, for example, cylindrical with a diameter of 25.4 mm. It should be noted that the value of the diameter of the sample can be changed as needed. The sample is cut at intervals of 5 mm through a plane perpendicular to the axial direction of the substrate 10, and the first cut piece, the second cut piece,..., and the nth cut piece are obtained in sequence from the end side of the exhaust gas inflow side of the sample. The length of the cut piece is 5 mm. The composition of the cut piece is analyzed using an inductively coupled plasma emission spectrometer (ICP-OES), a fluorescent X-ray analyzer (XRF), a scanning electron microscope-energy dispersive X-ray analysis method (SEM-EDX), etc., and whether the cut piece contains part of the first catalyst layer 20 is confirmed based on the composition of the cut piece.

[0144] For a cut piece that clearly includes a portion of the first catalyst layer 20, it is not necessary to perform a composition analysis. For example, a scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), or the like can be used to observe the cross section to confirm whether the cut piece includes a portion of the first catalyst layer 20. When observing the cross section, element mapping of the cross section can be performed. Element mapping can be performed using, for example, a SEM-EDX, an electron probe microanalyzer (EPMA), a transmission type X-ray inspection device, or the like.

[0145] After confirming whether the cut piece includes a part of the first catalyst layer 20 , the length of the first catalyst layer 20 included in the sample is calculated according to the following formula.

[0146] The length of the first catalyst layer 20 contained in the sample = 5 mm × (the number of cut pieces containing part of the first catalyst layer 20)

[0147] For example, when the first to kth cut pieces include part of the first catalyst layer 20 and the (k+1)th to nth cut pieces do not include part of the first catalyst layer 20, the length of the first catalyst layer 20 included in the sample is (5×k) mm.

[0148] An example of a more detailed method for measuring the length of the first catalyst layer 20 contained in a sample is as follows.

[0149] The length of the partial first catalyst layer 20 in the k-th cut piece (i.e., the cut piece obtained from the exhaust gas outflow side of the sample among the cut pieces containing the partial first catalyst layer 20) is measured by cutting along the axial direction of the substrate 10 and observing the partial first catalyst layer 20 existing in the cross section using SEM, EPMA, etc. Then, the length of the partial first catalyst layer 20 contained in the sample is calculated according to the following formula.

[0150] The length of the first catalyst layer 20 contained in the sample = (5 mm × (k-1)) + (the length of the portion of the first catalyst layer 20 contained in the k-th cut piece)

[0151] The lengths of the first catalyst layer 20 included in each of 8 to 16 samples randomly cut out from the exhaust gas-purifying catalyst 1 are measured, and the average value thereof is defined as the average length L of the first catalyst layer 20. 20 .

[0152] When information (e.g., composition, quantity, etc.) about the raw materials used to manufacture the first catalyst layer 20 is known, 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 can be calculated based on the information about the raw materials used to manufacture the first catalyst layer 20.

[0153] The first catalyst layer 20 contains Rh, Ce, and Y.

[0154] The first catalyst layer 20 preferably further contains Zr. When the first catalyst layer 20 contains Zr, the heat resistance of the first catalyst layer 20 is improved.

[0155] In the present specification, the molar percentage of the molar amount of Ce in the first catalyst layer 20 based on the total molar amount of all metal elements in the first catalyst layer 20 is set to a, the molar percentage of the molar amount of Y in the first catalyst layer 20 based on the total molar amount of all metal elements in the first catalyst layer 20 is set to b, the molar percentage of the molar amount of Rh in the first catalyst layer 20 based on the total molar amount of all metal elements in the first catalyst layer 20 is set to c, and the molar percentage of the molar amount of Zr in the first catalyst layer 20 based on the total molar amount of all metal elements in the first catalyst layer 20 is set to d.

[0156] In this specification, the "molar amount of Ce in the first catalyst layer 20" refers to the molar amount of Ce from one Ce source when the first catalyst layer 20 includes one Ce source, and refers to the total molar amount of Ce from the two or more Ce sources when the first catalyst layer 20 includes two or more Ce sources. The Ce source will be described later.

[0157] In this specification, the "molar amount of Y in the first catalyst layer 20" refers to the molar amount of Y from one Y source when the first catalyst layer 20 includes one Y source, and refers to the total molar amount of Y from the two or more Y sources when the first catalyst layer 20 includes two or more Y sources. The Y source will be described later.

[0158] In this specification, the "molar amount of Zr in the first catalyst layer 20" refers to the molar amount of Zr from one Zr source when the first catalyst layer 20 includes one Zr source, and refers to the total molar amount of Zr from the two or more Zr sources when the first catalyst layer 20 includes two or more Zr sources. The Zr source will be described later.

[0159] The air / fuel ratio (air-fuel ratio) supplied to the internal combustion engine is preferably controlled near the theoretical air-fuel ratio (theoretical value, stoiki). However, the actual air-fuel ratio fluctuates toward the rich (fuel-rich atmosphere) side or the lean (fuel-lean atmosphere) side with the theoretical value as the center, depending on the vehicle driving conditions, etc. Therefore, the air-fuel ratio of the exhaust gas also fluctuates toward the rich side or the lean side. If a material with oxygen storage capacity (OSC: Oxygen Storage Capacity) such as Ce-based oxides (such as the first Ce-based oxide, the second Ce-based oxide, the Ce-Zr-based oxide, etc.), Ce-containing Y-based oxides (such as the first Y-based oxide containing Ce, the second Y-based oxide containing Ce, the Y-Zr-based oxide containing Ce, etc.), and Ce-containing Al-based oxides are used, the fluctuation of oxygen concentration in the exhaust gas can be reduced and the exhaust gas purification ability of Rh can be improved. Since Ce contributes to oxygen storage capacity, as the amount of Ce increases, the oxygen storage capacity increases, and the exhaust gas purification performance of Rh improves. However, since Ce promotes the oxidation of Rh, when the amount of Ce is too much, the oxidation of Rh is promoted, and the exhaust gas purification performance of Rh is reduced. On the other hand, since Y has the property of lowering the temperature at which oxidized Rh is redistributed, as the amount of Y increases, Rh oxidized when the exhaust gas is in a lean state is redistributed earlier when the exhaust gas is in a rich state, and the exhaust gas purification performance of Rh is improved. However, when the amount of Y is too much, the heat resistance is reduced.

[0160] In order to effectively achieve the improvement of oxygen storage capacity to improve the exhaust gas purification performance of Rh, prevent the decrease in the exhaust gas purification performance of Rh due to the promotion of Rh oxidation, early redox of oxidized Rh to improve the exhaust gas purification performance of Rh, and prevent the decrease in heat resistance, the value of a / b is preferably greater than 0.010 and less than 0.400, more preferably greater than 0.020 and less than 0.300, and further preferably greater than 0.040 and less than 0.200.

[0161] In order to more effectively achieve the improvement of oxygen storage capacity to improve the exhaust gas purification performance of Rh, prevent the decrease in the exhaust gas purification performance of Rh due to the promotion of Rh oxidation, early redox of oxidized Rh to improve the exhaust gas purification performance of Rh, and prevent the decrease in heat resistance, the value of c / b is preferably greater than 0.0010 and less than 0.0270, more preferably greater than 0.0030 and less than 0.0200, and further preferably greater than 0.0050 and less than 0.0120.

[0162] In order to more effectively improve the oxygen storage capacity and thus improve the exhaust gas purification performance of Rh, a is preferably 0.5 mol% or more, more preferably 0.7 mol% or more, and further preferably 1.0 mol% or more. In order to more effectively prevent the degradation of the exhaust gas purification performance of Rh caused by the promotion of oxidation of Rh, a is preferably 25 mol% or less, more preferably 20 mol% or less, and further preferably 15 mol% or less. These upper limits may be combined with any of the above lower limits.

[0163] In order to more effectively achieve early redox of oxidized Rh and improve the exhaust gas purification performance of Rh, b is preferably 11 mol% or more, more preferably 15 mol% or more, further preferably 19 mol% or more, and further preferably 25 mol% or more. From the perspective of effectively preventing the decrease in heat resistance, b is preferably 50 mol% or less, more preferably 45 mol% or less, and further preferably 40 mol% or less. These upper limits may be combined with any of the above lower limits.

[0164] In order to achieve a good balance between exhaust gas purification performance and cost, c is preferably 0.001 mol % to 10 mol %, more preferably 0.005 mol % to 5 mol %, and further preferably 0.01 mol % to 1 mol %.

[0165] In order to achieve a good balance between improvement in heat resistance and improvement in exhaust gas purification performance, d is preferably 10 mol% to 80 mol%, more preferably 13 mol% to 70 mol%, and further preferably 15 mol% to 60 mol%.

[0166] Rh is contained in the first catalyst layer 20 in the form of a catalytically active component such as metallic Rh, an alloy containing Rh, or a compound containing Rh (such as an oxide of Rh) that can function as a catalytically active component. The catalytically active component containing Rh is, for example, in the form of particles.

[0167] The first catalyst layer 20 may contain one or more noble metal elements other than Rh. The noble metal elements other than Rh may be selected from, for example, 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 catalytically active components such as metals, alloys containing noble metal elements, compounds containing noble metal elements (such as oxides of noble metal elements), etc. containing noble metal elements other than Rh. The catalytically active components containing noble metal elements other than Rh are, for example, in the form of particles.

[0168] When the first catalyst layer 20 contains Rh and a precious metal element other than Rh, Rh and the precious metal element other than Rh may form an alloy, and the active sites of Rh that contribute to the exhaust gas purification performance may decrease. Therefore, the first catalyst layer 20 preferably contains substantially no precious metal element other than Rh.

[0169] “The first catalyst layer 20 does not substantially contain any precious metal element other than Rh” means that the mass percentage of the metal-converted mass of the precious metal element other than Rh in the first catalyst layer 20 based on the metal-converted mass of Rh in the first catalyst layer 20 is preferably 1.0 mass% or less, more preferably 0.5 mass% or less, and further preferably 0.1 mass% or less. The lower limit is 0. For “the metal-converted mass of the precious metal element other than Rh in the first catalyst layer 20”, when the first catalyst layer 20 contains one precious metal element other than Rh, it refers to the metal-converted mass of the one precious metal element, and when the first catalyst layer 20 contains two or more precious metal elements other than Rh, it refers to the total metal-converted mass of the two or more precious metal elements.

[0170] The first catalyst layer 20 contains one or two or more Ce sources.

[0171] The Ce source is an oxide containing Ce. The Ce source is preferably selected from the following group:

[0172] Ce-based oxides containing Y (e.g., first Ce-based oxides containing Y, second Ce-based oxides containing Y, Ce-Zr-based oxides containing Y, etc.);

[0173] Ce-based oxides not containing Y (e.g., first Ce-based oxides not containing Y, second Ce-based oxides not containing Y, Ce-Zr-based oxides not containing Y, etc.);

[0174] Ce-containing Y-series oxides (e.g., Ce-containing first Y-series oxides, Ce-containing second Y-series oxides, Ce-containing Y-Zr-series oxides, etc.);

[0175] Al-based oxides containing Ce and Y; and

[0176] Al-based oxide containing Ce but not Y.

[0177] The Ce source does not need to be an oxide different from the Y source, and may be the same oxide as the Y source. For example, Ce-based oxides containing Y, Y-based oxides containing Ce, and Al-based oxides containing Ce and Y are both Ce and Y sources.

[0178] The first catalyst layer 20 contains one or more Y sources.

[0179] The Y source is an oxide containing Y. The Y source is preferably selected from the following group:

[0180] Ce-containing Y-series oxides (e.g., Ce-containing first Y-series oxides, Ce-containing second Y-series oxides, Ce-containing Y-Zr-series oxides, etc.);

[0181] Y-series oxides not containing Ce (e.g., first Y-series oxides not containing Ce, second Y-series oxides not containing Ce, Y-Zr-series oxides not containing Ce, etc.);

[0182] Ce-based oxides containing Y (e.g., first Ce-based oxides containing Y, second Ce-based oxides containing Y, Ce-Zr-based oxides containing Y, etc.);

[0183] Al-based oxides containing Y and Ce; and

[0184] Al-based oxide containing Y but not Ce.

[0185] The Y source does not need to be an oxide different from that of the Ce source, and may be the same oxide as that of the Ce source.

[0186] When the first catalyst layer 20 contains Zr, the first catalyst layer 20 contains one or more Zr sources.

[0187] The Zr source is an oxide containing Zr. The Zr source is preferably selected from the following group:

[0188] Ce-based oxides containing Zr (e.g., first Ce-based oxides containing Zr, second Ce-based oxides containing Zr, Ce-Zr-based oxides, etc.);

[0189] Y-series oxides containing Zr (e.g., first Y-series oxides containing Zr, second Y-series oxides containing Zr, Y—Zr-series oxides, etc.); and

[0190] The Al-based oxide containing Zr is more preferably selected from Ce-based oxides containing Zr and Y-based oxides containing Zr, and further preferably selected from Ce-Zr-based oxides and Y-Zr-based oxides.

[0191] The Zr source does not need to be an oxide different from the Ce source, and may be the same oxide as the Ce source. For example, Ce-based oxides containing Zr, Y-based oxides containing Ce and Zr, and Al-based oxides containing Ce and Zr are both Ce and Zr sources.

[0192] The Zr source does not need to be an oxide different from the Y source, and may be the same oxide as the Y source. For example, Ce-based oxides containing Y and Zr, Y-based oxides containing Zr, and Al-based oxides containing Y and Zr are both Y and Zr sources.

[0193] The Zr source may be the same oxide as the Ce source and the Y source. For example, Ce-based oxides containing Y and Zr, Y-based oxides containing Ce and Zr, and Al-based oxides containing Ce, Y, and Zr are Ce and Y sources as well as Zr sources.

[0194] The molar amount of Zr in the first catalyst layer 20 is preferably 80 mol% or more, more preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit is 100 mol%. For the "molar amount of Zr from the Ce-based oxide containing Zr and the Y-based oxide containing Zr", when the first catalyst layer 20 contains the Ce-based oxide containing Zr but does not contain the Y-based oxide containing Zr, it refers to the molar amount of Zr from the Ce-based oxide containing Zr, when the first catalyst layer 20 contains the Y-based oxide containing Zr but does not contain the Ce-based oxide containing Zr, it refers to the molar amount of Zr from the Y-based oxide containing Zr, and when the first catalyst layer 20 contains the Ce-based oxide containing Zr and the Y-based oxide containing Zr, it refers to the sum of the molar amount of Zr from the Ce-based oxide containing Zr and the molar amount of Zr from the Y-based oxide containing Zr.

[0195] When the first catalyst layer 20 contains Zr, the first catalyst layer 20 preferably contains two or more of a Ce source, a Y source, and a Zr source selected from the following group:

[0196] Ce-based oxides containing Zr (e.g., first Ce-based oxides containing Zr, second Ce-based oxides containing Zr, Ce-Zr-based oxides, etc.); and

[0197] At least one of the Y-based oxides containing Zr (e.g., the first Y-based oxide containing Zr, the second Y-based oxide containing Zr, the Y-Zr-based oxide, etc.), more preferably at least one selected from Ce-Zr-based oxides and Y-Zr-based oxides. As at least one of the Ce source, the Y source, and the Zr source, the first catalyst layer 20 may further include at least one selected from the following group:

[0198] Ce-based oxides not containing Zr (e.g., first Ce-based oxides not containing Zr, second Ce-based oxides not containing Zr, etc.);

[0199] Y-series oxides not containing Zr (e.g., first Y-series oxides not containing Zr, second Y-series oxides not containing Zr, etc.);

[0200] The Al-based oxide contains one, two or three selected from Ce, Y and Zr.

[0201] The first catalyst layer 20 may further contain Al. When the first catalyst layer 20 contains Al, the heat resistance of the first catalyst layer 20 is improved.

[0202] When the first catalyst layer 20 includes Al, the first catalyst layer 20 includes one or more Al sources.

[0203] The Al source is an oxide containing Al. The oxide containing Al can be selected from, for example, Al-based oxides, Ce-based oxides containing Al, and Y-based oxides containing Al.

[0204] The first catalyst layer 20 preferably contains an Al-based oxide as an Al source. The first catalyst layer 20 may further contain at least one selected from a Ce-based oxide containing Al and a Y-based oxide containing Al as an Al source.

[0205] When the molar percentage of the molar amount of Al in the first catalyst layer 20 based on the total molar amount of all metal elements in the first catalyst layer 20 is set to e, in order to achieve improved heat resistance and to show a good balance of the performance of the above-mentioned Ce and Y, e is preferably 5 mol% or more and 90 mol% or less, more preferably 10 mol% or more and 85 mol% or less, and further preferably 20 mol% or more and 80 mol% or less. The "molar amount of Al in the first catalyst layer 20" refers to the molar amount of Al from the one Al source when the first catalyst layer 20 contains one Al source, and refers to the total molar amount of Al from the two or more Al sources when the first catalyst layer 20 contains two or more Al sources.

[0206] The first catalyst layer 20 may further include one or more Ln other than Ce and Y. The first catalyst layer 20 may include at least one selected from, for example, La, Nd, Gd, and Sm as Ln other than Ce and Y. Thus, the heat resistance of the first catalyst layer 20 can be improved. In order to improve the heat resistance of the first catalyst layer 20, Ln other than Ce and Y is preferably selected from La and Nd. The first catalyst layer 20 may include, for example, Pr as Ln other than Ce and Y. Thus, the oxygen storage capacity of the first catalyst layer 20 can be improved.

[0207] When the first catalyst layer 20 contains Ln other than Ce and Y, the first catalyst layer 20 contains one or more types of Ln sources.

[0208] The Ln source is an oxide containing Ln other than Ce and Y. The oxide containing Ln other than Ce and Y can be selected from, for example, Al-based oxides containing Ln other than Ce and Y, Ce-based oxides containing Ln other than Ce and Y, and Y-based oxides containing Ln other than Ce and Y.

[0209] The Ln source does not need to be an oxide different from the Ce source, and may be the same oxide as the Ce source. For example, Ce-based oxides containing Ln other than Ce and Y, Y-based oxides containing Ln and Ce other than Ce and Y, and Al-based oxides containing Ln and Ce other than Ce and Y are both Ln sources and Ce sources.

[0210] The Ln source does not need to be an oxide different from the Y source, and may be the same oxide as the Y source. For example, a Y-based oxide containing Ln other than Ce and Y, a Ce-based oxide containing Ln and Y other than Ce and Y, and an Al-based oxide containing Ln and Y other than Ce and Y are both Ln sources and Y sources.

[0211] The Ln source may be the same oxide as the Ce source and the Y source. For example, Ce-based oxides containing Ln and Y other than Ce and Y, Y-based oxides containing Ln and Ce other than Ce and Y, and Al-based oxides containing Ln, Ce, and Y other than Ce and Y are both Ln sources and Ce and Y sources.

[0212] When the molar percentage of the molar amount of Ln other than Ce and Y in the first catalyst layer 20 based on the total molar amount of all metal elements in the first catalyst layer 20 is set to f, in order to achieve a good balance between improved heat resistance and cost, f is preferably 0.5 mol% or more and 40 mol% or less, more preferably 1 mol% or more and 20 mol% or less, and further preferably 2 mol% or more and 13 mol% or less. "The molar amount of Ln other than Ce and Y in the first catalyst layer 20" refers to the molar amount of the one Ln when the first catalyst layer 20 contains one type of Ln, and refers to the total molar amount of the two or more Lns when the first catalyst layer 20 contains two or more types of Ln. In addition, for the "molar amount of Ln other than Ce and Y in the first catalyst layer 20", when the first catalyst layer 20 contains one Ln source, it refers to the molar amount of Ln other than Ce and Y from the one Ln source, and when the first catalyst layer 20 contains two or more Ln sources, it refers to the total molar amount of Ln other than Ce and Y from the two or more Ln sources.

[0213] Of the molar amount of Ln other than Ce and Y in the first catalyst layer 20, the molar amount of Ln other than Ce and Y from Al-based oxides, Ce-based oxides, and Y-based oxides is preferably 80 mol% or more, more preferably 90 mol% or more, and further preferably 95 mol% or more. The upper limit is 100 mol%. For "the molar amount of Ln other than Ce and Y from Al-based oxides, Ce-based oxides, and Y-based oxides", when the first catalyst layer 20 includes one of Al-based oxides, Ce-based oxides, and Y-based oxides, it refers to the molar amount of Ln other than Ce and Y from the one, and when the first catalyst layer 20 includes two or more of Al-based oxides, Ce-based oxides, and Y-based oxides, it refers to the total molar amount of Ln other than Ce and Y from the two or more.

[0214] In order to improve the exhaust gas purification performance, it is preferred that the first catalyst layer 20 includes one or more carriers, and at least a portion of the catalytically active components are supported on one or more carriers. One or more carriers can be selected from Ce-based oxides, Y-based oxides, and Al-based oxides.

[0215] “At least a portion of the catalytically active component is supported on the carrier” means that at least a portion of the catalytically active component is physically and / or chemically adsorbed and / or maintained on the outer surface of the carrier and / or the inner surface of the pores. The support of at least a portion of the catalytically active component on the carrier can be confirmed as follows, for example, by analyzing the first catalyst layer 20 by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), and at least a portion of the catalytically active component and the carrier are present in the same region.

[0216] The first catalyst layer 20 may include a binder. The binder may be selected from inorganic binders such as alumina, zirconia, titania, silica, cerium oxide, yttrium oxide, etc. It should be noted that when the binder includes one or more selected from the group consisting of Ce, Y and Zr, the binder is also included in one or more of the Ce source, Zr source and Y source.

[0217] When the composition of the raw material for forming the first catalyst layer 20 is known, the molar amount of each metal element in the first catalyst layer 20 can be calculated based on the composition of the raw material for forming the first catalyst layer 20 .

[0218] In addition, the molar amount of each metal element in the first catalyst layer 20 can be measured using conventional methods such as scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), electron probe microanalyzer (EPMA), fluorescent X-ray analysis (XRF), inductively coupled plasma atomic emission spectrometry (ICP-AES), etc. The details are as follows.

[0219] First, the test piece cut from the exhaust gas purification catalyst 1 is pulverized, and then analyzed by XRF or ICP-AES to determine 20 metal elements with large molar amounts in order from most to least. The 20 metal elements determined include Rh, Ce and Y. When the first catalyst layer 20 contains Zr, the 20 metal elements determined include Zr. When the first catalyst layer 20 contains Al, the 20 metal elements determined include Al. The test piece only needs to include a portion from the first catalyst layer 20, and may also include a portion from the substrate 10 and / or a portion from the second catalyst layer 30. When the test piece includes a portion from the substrate 10 and / or a portion from the second catalyst layer 30, the 20 metal elements determined may also include metal elements constituting the substrate 10 and / or metal elements constituting the second catalyst layer 30.

[0220] Next, the first catalyst layer 20 is analyzed by SEM-EDX or EPMA. In SEM-EDX or EPMA, the 20 metal elements determined above are taken as analysis objects, and for each of the 10 fields of view of the SEM, the total mole % of the 20 metal elements is set to 100 mole %, and the mole % of each metal element is analyzed. The average value of the mole % of each metal element in the 10 fields of view is taken as the molar amount of each metal element in the first catalyst layer 20.

[0221] <Second Catalyst Layer>

[0222] Next, the second catalyst layer 30 will be described.

[0223] like Figure 3 and 4 As shown, the second catalyst layer 30 is disposed on the side surface of the chamber 13 of the partition wall portion 12. The "side surface of the chamber 13 of the partition wall portion 12" refers to the outer surface of the partition wall portion 12 extending in the exhaust gas flow direction X. The second catalyst layer 30 can be directly disposed on the side surface of the chamber 13 of the partition wall portion 12, or can be disposed thereon via other layers. Usually, it is directly disposed on the side surface of the chamber 13 of the partition wall portion 12.

[0224] The second catalyst layer 30 may be composed of a portion that bulges from the side surface of the chamber 13 of the partition wall portion 12 toward the chamber 13 side (hereinafter referred to as a "bulge"), or may be composed of a portion that exists inside the partition wall portion 12 (hereinafter referred to as an "internal portion"), or may have a bulge and an internal portion. Embodiments in which the second catalyst layer 30 is composed of a bulge, embodiments in which the second catalyst layer 30 is composed of an internal portion, and embodiments in which the second catalyst layer 30 has a bulge and an internal portion are all included in the "second catalyst layer 30 disposed on the substrate 10".

[0225] like Figure 4As shown, the second catalyst layer 30 extends from the end of the exhaust gas inlet side of the partition wall portion 12 to the end of the exhaust gas outlet side of the partition wall portion 12 along the exhaust gas flow direction X. The second catalyst layer 30 may also extend from the end of the exhaust gas inlet side of the partition wall portion 12 along the exhaust gas flow direction X, but not reach the end of the exhaust gas outlet side of the partition wall portion 12; or may extend from the end of the exhaust gas outlet side of the partition wall portion 12 in the direction opposite to the exhaust gas flow direction X, but not reach the end of the exhaust gas inlet side of the partition wall portion 12.

[0226] In order to achieve a good balance between exhaust gas purification performance and cost, 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 (the mass after drying and calcination) is preferably 30 g / L or more and 250 g / L or less, more preferably 40 g / L or more and 200 g / L or less, and further preferably 50 g / L or more and 150 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 according to 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 substrate 10 10 ))Calculated.

[0227] The above description about the “mass of the first catalyst layer 20 ” also applies to the “mass of the second catalyst layer 30 .” Where applicable, “first catalyst layer 20 ” is replaced with “second catalyst layer 30 .”

[0228] Regarding the average length L of the first catalyst layer 20 20 The above description of the determination method also applies to the average length L of the second catalyst layer 30. 30 Where applicable, replace “first catalyst layer 20” with “second catalyst layer 30” and replace “average length L 20 " is replaced by "average length L 30 ”.

[0229] When information (e.g., composition, quantity, etc.) about the raw materials used to manufacture the second catalyst layer 30 is known, 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 can be calculated based on the information about the raw materials used to manufacture the second catalyst layer 30.

[0230] In order to improve the exhaust gas purification performance, the second catalyst layer 30 preferably contains Pd. By providing the first catalyst layer 20 on the upper side of the second catalyst layer 30, phosphorus poisoning of Pd contained in the second catalyst layer 30 can be prevented.

[0231] Pd is contained in the second catalyst layer 30 in the form of a catalytically active component such as metallic Pd, a Pd-containing alloy, a Pd-containing compound (such as Pd oxide), etc. The Pd-containing catalytically active component is, for example, in a particle form.

[0232] In order to achieve a good balance between exhaust gas purification performance and cost, the content of Pd in ​​the second catalyst layer 30 is preferably 0.01 g / L or more and 10 g / L or less, more preferably 0.02 g / L or more and 7 g / L or less, and further preferably 0.05 g / L or more and 5 g / L or less, calculated as the content of Pd per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed. It should be noted that the content of Pd is the content converted to metal.

[0233] The content of Pd in ​​the second catalyst layer 30 can be measured in the same manner as the molar amount of each metal element in the first catalyst layer 20 described above.

[0234] In order to improve the exhaust gas purification performance, the second catalyst layer 30 preferably includes a carrier, and at least a portion of the catalytically active components are supported on the carrier. The meaning and confirmation method of "at least a portion of the catalytically active components are supported on the carrier" are the same as above.

[0235] The carrier can be selected from, for example, inorganic oxides, etc. The inorganic oxide is, for example, in a particle form, and can be selected from, for example, Al-based oxides, Ce-based oxides, Y-based oxides, etc.

[0236] The second catalyst layer 30 may include two or more supports. For example, the second catalyst layer 30 may include at least one Al-based oxide, at least one Ce-based oxide, and / or at least one Y-based oxide.

[0237] The second catalyst layer 30 may include a binder, which may be selected from inorganic binders such as alumina, zirconia, titania, silica, cerium oxide, and yttrium oxide.

[0238] <Method for producing exhaust gas purification catalyst>

[0239] The exhaust gas-purifying 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 .

[0240] The second catalyst layer 30 can be formed by mixing a supply source of precious metal elements (such as Pd salts, etc.) and other components (such as inorganic oxides such as Al-based oxides, Ce-based oxides, Y-based oxides, binders, solvents, etc.) to prepare a slurry for the second catalyst layer, coating the slurry for the second catalyst layer on the partition wall portion 12 of the substrate 10, and drying and calcining to form the slurry.

[0241] The first catalyst layer 20 can be formed by mixing a supply source of precious metal elements (such as Rh salts, etc.) and other components (such as inorganic oxides such as Al-based oxides, Ce-based oxides, Y-based oxides, binders, solvents, etc.) to prepare a slurry for the first catalyst layer, coating the slurry for the first catalyst layer on the second catalyst layer 30, and drying and calcining to form the slurry.

[0242] The binder may be selected from metal oxide sols such as alumina sol, zirconia sol, titania sol, silica sol, cerium oxide sol, yttrium oxide sol, etc. The solvent may be selected from water, organic solvents, etc.

[0243] The drying temperature is, for example, 60° C. to 150° C., and the drying time is, for example, 0.1 hour to 1 hour. The calcination temperature is, for example, 300° C. to 700° C., and the calcination time is, for example, 1 hour to 10 hours. Calcination can be performed, for example, in air atmosphere.

[0244] Example

[0245] Hereinafter, embodiments of the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0246] <Examples 1 to 7 and Comparative Examples 1 and 2>

[0247] (1) Formation of the lower layer

[0248] A palladium nitrate solution, a Ce-Zr-based oxide, aluminum oxide, and a binder were added in sequence to a container filled with pure water, and the mixture was stirred and mixed thoroughly to obtain a slurry for a lower layer.

[0249] A stainless steel metal honeycomb substrate (diameter: 40 mm, length: 60 mm, cavity density: 400 cavities / square inch, volume: 75 mL) was immersed in the slurry for the lower layer, excess slurry was removed, and the slurry for the lower layer was applied to the wall surface inside the substrate. After the substrate coated with the slurry for the lower layer was dried at 80°C for 1 hour, it was calcined at 500°C for 4 hours to form a lower layer on the wall surface inside the substrate. The mass of the lower layer per unit volume of the portion of the substrate where the lower layer is formed (the mass after drying and calcination) is 110 g / L. The mass of Pd in ​​the lower layer per unit volume of the portion of the substrate where the lower layer is formed is 0.8 g / L in terms of metal.

[0250] (2) Formation of the upper layer

[0251] To a container filled with pure water, add rhodium nitrate solution, one or more Ce-Zr oxides containing one or more Ln other than Ce and one or more Y-Zr oxides containing one or more Ln other than Y, aluminum oxide containing lanthanum oxide, and a binder in sequence, stir and mix thoroughly to obtain a slurry for the upper layer. Adjust the composition of the slurry for the upper layer so that the composition of the upper layer formed by the slurry for the upper layer is as shown in Table 1. In Table 1, "a" represents the molar percentage of the molar amount of Ce in the upper layer based on the total molar amount of all metal elements in the upper layer, "b" represents the molar percentage of the molar amount of Y in the upper layer based on the total molar amount of all metal elements in the upper layer, and "c" represents the molar percentage of the molar amount of Rh in the upper layer based on the total molar amount of all metal elements in the upper layer.

[0252] The substrate on which the lower layer has been formed is immersed in the slurry for the upper layer, and the excess slurry is removed, and the slurry for the upper layer is coated on the lower layer. The substrate coated with the slurry for the upper layer is dried at 80°C for 1 hour, and then calcined at 500°C for 4 hours to form an upper layer on the lower layer, thereby obtaining an exhaust gas purification catalyst. The mass of the upper layer per unit volume of the portion of the substrate on which the upper layer is formed (the mass after drying and calcination) is 60 g / L.

[0253] (3) Durability test

[0254] The exhaust gas purification catalyst obtained in (2) was mounted on an exhaust pipe, and a thermocouple was inserted into the center of the honeycomb substrate. The exhaust pipe was installed in a gasoline engine (displacement: 2300cc, fuel: gasoline with engine oil added), and the engine speed / torque were adjusted so that the temperature of the thermocouple reached a specified temperature of 850°C to 1000°C, and a durability test lasting 40 hours was carried out.

[0255] (4) Evaluation of exhaust gas purification performance

[0256] After the endurance test, the exhaust gas purification catalyst was installed in the muffler of the motorcycle, and the CO and NOx emissions (mg / km) were measured under the following conditions.

[0257] Vehicle used: Single cylinder 110cc motorcycle

[0258] Fuel: Unleaded gasoline

[0259] Driving mode: WMTC

[0260] Measurement method: Based on ISO6460

[0261] [Table 1]

[0262] surface@

[0263]

[0264] As shown in Table 1, the exhaust gas purifying catalysts of Examples 1 to 7 satisfying the condition that the a / b value is 0.010 or more and 0.400 or less have higher exhaust gas purifying performance after the endurance test than the exhaust gas purifying catalysts of Comparative Examples 1 to 2 not satisfying this condition.

[0265] Description of Reference Numerals

[0266] 1···Catalysts for exhaust gas purification

[0267] 10···Base material

[0268] 11···Tubular part

[0269] 12···Partition wall

[0270] 13···Chamber

[0271] 20···First catalyst layer

[0272] 30···Second catalyst layer

Claims

1. An exhaust gas purification catalyst comprising a substrate and a first catalyst layer provided on the substrate, The first catalyst layer comprises Rh, Ce and Y, When the molar percentage of the molar amount of Ce in the first catalyst layer based on the total molar amount of all metal elements in the first catalyst layer is set to a, and the molar percentage of the molar amount of Y in the first catalyst layer based on the total molar amount of all metal elements in the first catalyst layer is set to b, the value of a / b is greater than 0.010 and less than 0.

400.

2. The exhaust gas purification catalyst according to claim 1, wherein The first catalyst layer further includes Zr.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein: b is 11 mol% or more.

4. The exhaust gas purification catalyst according to claim 1 or 2, wherein: b is 15 mol% or more.

5. The exhaust gas purification catalyst according to claim 1 or 2, wherein: b is 19 mol% or more.

6. The exhaust gas purification catalyst according to claim 1 or 2, wherein: When the molar percentage of the molar amount of Rh in the first catalyst layer based on the total molar amount of all metal elements in the first catalyst layer is represented by c, the value of c / b is 0.0010 or more and 0.0270 or less. 7 . The exhaust gas purification catalyst according to claim 1 , further comprising a second catalyst layer provided on the substrate.

8. The exhaust gas purification catalyst according to claim 7, wherein: The first catalyst layer is disposed on an upper side of the second catalyst layer.

9. The exhaust gas purification catalyst according to claim 7 or 8, wherein: The second catalyst layer includes Pd.

Images