Exhaust gas purification catalyst

Abstract

An exhaust gas purification catalyst comprising: an upstream catalyst provided on the upstream side in the flow direction of exhaust gas; and a downstream catalyst provided on the downstream side in the flow direction of exhaust gas, wherein the upstream catalyst has a base A and a layer a1 provided on the base A, the downstream catalyst has a base B and a layer b1 provided on the base B, the layer a1 contains Rh and a Ce-Zr-Al complex oxide, the layer b1 contains Rh and a Ce-Zr complex oxide, the contained amount of Al calculated as Al2O3 in the Ce-Zr-Al complex oxide contained in the layer a1 is at least 30 mass% with respect to the mass of the Ce-Zr-Al complex oxide, the contained amount of the Ce-Zr-Al complex oxide contained in the layer a1 is at least 50 mass% with respect to the mass of the layer a1, and the layer b1 does not contain Al or, if the layer b1 contains Al, the contained amount of Al calculated as Al2O3 in the layer b1 is at most 30 mass% with respect to the mass of the layer b1.

Description

exhaust gas purification catalyst

[0001] The present invention relates to an exhaust gas purification catalyst.

[0002] Exhaust gas (also referred to as exhaust gas) emitted from internal combustion engines of automobiles, motorcycles, and the like contains harmful components such as HC (hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides). Conventionally, three-way catalysts have been used to purify and neutralize these harmful components. Known three-way catalysts use precious metals such as Pt (platinum), Pd (palladium), and Rh (rhodium), with Pt and Pd primarily acting to oxidize and purify HC and CO, and Rh primarily acting to reduce and purify NOx. In recent years, due to stricter exhaust gas regulations and growing environmental awareness, attempts have been made to improve the exhaust gas purification performance of such precious metal catalysts.

[0003] Patent Document 1 describes an exhaust gas purification catalyst that is composed of two catalysts: a start-up catalyst and an underfloor catalyst that is installed behind the start-up catalyst in the direction of exhaust gas flow, and the average thickness and porosity of the catalyst coating layer of the underfloor catalyst are set within specific ranges. Patent Document 1 also describes that the catalyst coating layers of the start-up catalyst and the underfloor catalyst contain Rh, a ceria-zirconia composite oxide material, and Al. ２ O ３ The present invention describes an exhaust gas purification catalyst comprising:

[0004] Japanese Patent Application Publication No. 2016-185495

[0005] However, in recent years, there has been a demand for even better exhaust gas purification performance from exhaust gas purification catalysts. In particular, because the temperature of exhaust gas is high on the upstream side of the flow direction, there is a demand for exhaust gas purification catalysts with even better durability.

[0006] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst having excellent durability.

[0007] The gist of the present invention is as follows.

[0008] [1] An exhaust gas purification catalyst comprising an upstream catalyst provided upstream in the flow direction of exhaust gas and a downstream catalyst provided downstream in the flow direction of exhaust gas, wherein the upstream catalyst has a substrate A and a layer a1 provided on the substrate A, the downstream catalyst has a substrate B and a layer b1 provided on the substrate B, the layer a1 contains Rh and a Ce—Zr—Al-based composite oxide, the layer b1 contains Rh and a Ce—Zr-based composite oxide, and Al in the Ce—Zr—Al-based composite oxide contained in the layer a1 is ２ O ３ the content of the Ce-Zr-Al-based composite oxide contained in the layer a1 is 30 mass % or more with respect to the mass of the Ce-Zr-Al-based composite oxide, the content of the Ce-Zr-Al-based composite oxide contained in the layer a1 is 50 mass % or more with respect to the mass of the layer a1, and the layer b1 does not contain Al, or if it contains Al, the Al content of the Al contained in the layer b1 is ２ O ３ [2] The CeO content of the Ce in the Ce-Zr-based composite oxide contained in the layer b1 is 30 mass % or less based on the mass of the layer b1. ２ [3] The layer b1 contains an Al-based oxide, and the Al-based oxide does not contain La, or when it contains La, the La content in the Al-based oxide is La. ２ O ３ [4] The exhaust gas purifying catalyst according to [1] or [2], wherein the content of Ce in the Ce—Zr—Al-based composite oxide contained in the layer a1 is 7 mass % or less based on the mass of the Al-based oxide. ２ [5] The exhaust gas purifying catalyst according to any one of [1] to [3], wherein the content of Zr in the Ce-Zr-Al based composite oxide contained in the layer a1 is 2 mass % or more and 40 mass % or less based on the mass of the Ce-Zr-Al based composite oxide. ２[6] The exhaust gas purifying catalyst according to any one of [1] to [4], wherein the Al content in the Ce-Zr-Al based composite oxide contained in the layer a1 is 10 mass % or more and 70 mass % or less based on the mass of the Ce-Zr-Al based composite oxide. ２ O ３ [7] The exhaust gas purifying catalyst according to any one of [1] to [5], wherein the content of Rh in layer b1, calculated as Pd, is 60 mass % or less relative to the mass of the Ce—Zr—Al-based composite oxide. [7] The exhaust gas purifying catalyst according to any one of [1] to [6], wherein 60 mass % or more of the Rh contained in layer b1 is supported on the Ce—Zr-based composite oxide. [8] The exhaust gas purifying catalyst according to any one of [1] to [7], further comprising a layer a2 between the substrate A and the layer a1, the layer a2 containing Pd and a Ce—Zr-based composite oxide, and the layer a2 does not contain a Ce—Zr—Al-based composite oxide, or, if the layer a2 contains a Ce—Zr—Al-based composite oxide, the content of the Ce—Zr-based composite oxide contained in layer a2 is 50 mass % or more relative to the total mass of the Ce—Zr-based composite oxide and the Ce—Zr—Al-based composite oxide contained in layer a2.

[0009] According to the present invention, it is possible to provide an exhaust gas purification catalyst having excellent durability.

[0010] 1 is a schematic diagram of an embodiment of an exhaust gas purification catalyst according to the present invention; 2 is a schematic diagram of an embodiment of an exhaust gas purification catalyst according to the present invention;

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst comprising an upstream catalyst provided upstream in the flow direction of exhaust gas, and a downstream catalyst provided downstream in the flow direction of exhaust gas, wherein the upstream catalyst has a substrate A and a layer a1 provided on the substrate A, the downstream catalyst has a substrate B and a layer b1 provided on the substrate B, the layer a1 contains Rh and a Ce-Zr-Al based composite oxide, the layer b1 contains Rh and a Ce-Zr based composite oxide, and the Al in the Ce-Zr-Al based composite oxide contained in the layer a1 is Al. ２ O ３the content of the Ce-Zr-Al-based composite oxide contained in the layer a1 is 30 mass % or more with respect to the mass of the Ce-Zr-Al-based composite oxide, the content of the Ce-Zr-Al-based composite oxide contained in the layer a1 is 50 mass % or more with respect to the mass of the layer a1, and the layer b1 does not contain Al, or if it contains Al, the Al content of the Al contained in the layer b1 is ２ O ３ The content of the catalyst in terms of carbon black is 30 mass % or less relative to the mass of the layer b1.

[0013] A schematic diagram of one embodiment of the exhaust gas purification catalyst of the present invention is shown in Figure 1. The exhaust gas purification catalyst 10 in Figure 1 comprises an upstream catalyst 1 and a downstream catalyst 2. The upstream catalyst 1 is provided upstream in the flow direction X of the exhaust gas, and the downstream catalyst 2 is provided downstream in the flow direction X of the exhaust gas. The upstream catalyst 1 has a substrate A and a layer a1 provided on the substrate A. The layer a1 contains Rh and a Ce-Zr-Al-based composite oxide. The Al in the Ce-Zr-Al-based composite oxide contained in the layer a1 is ２ O ３ The content in terms of Rh converted to Ce—Zr—Al based composite oxide is 30 mass % or more relative to the mass of the Ce—Zr—Al based composite oxide. The content of the Ce—Zr—Al based composite oxide contained in layer a1 is 50 mass % or more relative to the mass of layer a1. The downstream catalyst 2 has a substrate B and a layer b1 provided on the substrate B. The layer b1 contains Rh and a Ce—Zr based composite oxide. The layer b1 does not contain Al, or if it contains Al, the Al contained in layer b1 is ２ O ３ The converted content is 30% by mass or less with respect to the mass of the layer b1.

[0014] The exhaust gas purification catalyst of the present invention has the effect of being excellent in durability due to the above-mentioned constitution. Although the mechanism by which the above-mentioned effect is obtained by the present invention is not completely clear, the present inventors have speculated as follows. However, the present invention is not limited by the speculated mechanism below. Rh acts by absorbing O in exhaust gas. ２ When the concentration of oxidizing components such as NOx exceeds a certain level, the deactivated Rh is oxidized and deactivated. When the concentration of reducing components such as HC and CO exceeds a certain level, the deactivated Rh is reduced and its activity is restored.２ O ３ has excellent heat resistance, which improves the heat resistance of exhaust gas purification catalysts. ２ O ３ Al has the property of stabilizing the oxidation state of Rh. Since the temperature of exhaust gas is high on the upstream side, the upstream catalyst is required to have higher heat resistance. On the other hand, since exhaust gas from the internal combustion engine reaches the upstream catalyst directly, the fluctuation range of the concentration of reducing components such as HC and CO is larger than that on the downstream side. ２ O ３ The downstream catalyst is likely to have a high enough concentration to reduce Rh, whose oxidation state has been stabilized by the oxidation of Al. Since the temperature of the exhaust gas is lower on the downstream side than on the upstream side, the downstream catalyst is required to have lower heat resistance than the upstream catalyst. On the other hand, the exhaust gas from the internal combustion engine reaches the upstream catalyst after passing through it and being partially purified, so the fluctuation range of the concentration of reducing components such as HC and CO is smaller than on the upstream side. ２ O ３ Therefore, in the upstream region where improvement of heat resistance is more important than reduction of deactivation of Rh, it is difficult to reduce the concentration of Al. ２ O ３ In the downstream region where the reduction of Rh deactivation is more important than the improvement of heat resistance, the content of Al is increased. ２ O ３ However, as in the upstream catalyst layer described in the above-mentioned Patent Document 1, the Ce—Zr composite oxide and Al ２ O ３ In contrast to this, in the present invention, the upstream catalyst layer contains a Ce—Zr composite oxide and an Al ２ O ３ By adding Ce-Zr-Al composite oxide instead of adding them separately, sufficient exhaust gas purification performance was obtained even after exposure to a high-temperature environment. This is because when the same amounts of Ce, Zr, and Al are added to the catalyst layer, adding them in the form of Ce-Zr-Al composite oxide is more effective than adding Ce-Zr composite oxide and Al ２ O ３However, in order to obtain such high heat resistance, the amount of Al in the Al alloy must be increased. ２ O ３ The content of Al converted to Al needs to be 30 mass % or more relative to the mass of the Ce-Zr-Al based composite oxide so that a good composite oxide can be formed. ２ O ３ If the content in terms of Al converted to Ce—Zr—Al based composite oxide needs to be less than 30 mass % based on the mass of the Ce—Zr—Al based composite oxide, a good composite oxide cannot be formed, and therefore the Ce—Zr based composite oxide and Al ２ O ３ Better performance can be obtained by adding these separately.

[0015] The substrate A of the upstream catalyst 1 and the substrate B of the downstream catalyst 2 may be separate substrates or may be the same substrate (i.e., a single substrate may have layers a1 and b1 on it).

[0016] In FIG. 1 , the upstream catalyst 1 and the downstream catalyst 2 are depicted as being separated from each other, but they may be in contact with each other. The upstream catalyst 1 and the downstream catalyst 2 may be housed in the same casing or in separate casings. The layers a1 and b1 are each a catalyst layer containing Rh, but the exhaust gas purification catalyst of the present invention may further include another catalyst layer. FIG. 2 is a schematic diagram of an embodiment of the exhaust gas purification catalyst of the present invention having another catalyst layer. The exhaust gas purification catalyst 20 of FIG. 2 includes an upstream catalyst 11 and a downstream catalyst 12. The upstream catalyst 11 is provided upstream in the exhaust gas flow direction X, and the downstream catalyst 12 is provided downstream in the exhaust gas flow direction X. The upstream catalyst 11 is the same as the upstream catalyst 1 of FIG. 1 , except that it includes a layer a2 between the substrate A and the layer a1. The downstream catalyst 12 is the same as the upstream catalyst 2 of FIG. 1 , except that it includes a layer b2 between the substrate B and the layer b1.

[0017] [Upstream Catalyst] The upstream catalyst has a substrate A and a layer a1 provided on the substrate A.

[0018] <Substrate A> The substrate A can be a substrate used in a conventionally known catalyst for purifying exhaust gas. For example, a substrate having partition walls made of a porous material and exhaust gas flow passages (spaces between the partition walls) partitioned by the partition walls can be suitably used. As the shape of the substrate A, a known substrate such as a honeycomb, DPF, or GPF can be suitably used. In addition, as the material of the partition walls of the substrate A, for example, alumina (Al ２ O ３ ), mullite (3Al ２ O ３ -2SiO ２ ), cordierite (2MgO-2Al ２ O ３ -5SiO ２ ), aluminum titanate (Al ２ TiO ５ ), ceramics such as silicon carbide (SiC), and metal materials such as stainless steel.

[0019] <Layer a1> Layer a1 contains Rh and a Ce—Zr—Al composite oxide. Rh is a catalytically active component. The Rh content in layer a1 is preferably 0.010 mass% or more, more preferably 0.050 mass% or more, and even more preferably 0.10 mass% or more, relative to the mass of layer a1. The Rh content in layer a1 is preferably 5 mass% or less, more preferably 3 mass% or less, and even more preferably 2 mass% or less, relative to the mass of layer a1. The contents of Rh and other elements in layer a1 can be determined by standard methods such as scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX). Specifically, the method is as follows. A sample obtained from layer a1 is subjected to elemental analysis using standard methods such as SEM-EDX to identify the types of constituent elements of the entire sample and to determine the content (mass%) of each identified metal element. The content (mass%) of each metal element is determined for each of 10 visual fields of the SEM, and the average of the content (mass%) of each metal element in the 10 visual fields is taken as the content (mass%) of each metal element in layer a1. When calculating the content (mass%) using the above method, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au are assumed to be in a metallic state, and the other metal elements are assumed to be in an oxidized state. The specific oxide forms of each element are as follows: Oxides of rare earth elements other than Ce, Pr, and Tb are sesquioxides (M ２ O ３ , M represents a rare earth element other than Ce, Pr, and Tb), and the oxide of Ce is CeO ２ , Pr oxide is Pr ６ O １１ , the oxide of Tb is Tb ４ O ７ , the oxide of Al is Al ２ O ３ , Zr oxide is ZrO ２ , and the oxide of Si is SiO ２ , the oxide of B is B ２ O ３ , Mg oxide is MgO, Ca oxide is CaO, Sr oxide is SrO, Ba oxide is BaO, Fe oxide is Fe ３ O ４ , Mn oxide is Mn３ O ４ , Cu oxide is CuO, Ti oxide is TiO ２ Zn oxide is ZnO, Sn oxide is SnO ２ is.

[0020] Preferably, 70 mass % or more of the Rh contained in layer a1 is supported on the Ce—Zr—Al-based composite oxide, more preferably 80 mass % or more of the Rh contained in layer a1 is supported on the Ce—Zr—Al-based composite oxide, and even more preferably 90 mass % or more of the Rh contained in layer a1 is supported on the Ce—Zr—Al-based composite oxide. The proportion of Rh supported on the Ce—Zr—Al-based composite oxide can be adjusted, for example, by the content of the Ce—Zr—Al-based composite oxide contained in layer a1. The definition of "supported" will be described later.

[0021] The layer a1 may contain, in addition to Rh, a catalytically active component other than Rh. As the catalytically active component other than Rh, conventionally known components can be used, such as Pd, Pt, gold (Au), silver (Ag), iridium (Ir), ruthenium (Ru), and osmium (Os).

[0022] "Ce-Zr-Al based composite oxide" is a composite oxide containing Ce (cerium), Zr (zirconium), and Al (aluminum), and the Ce in the composite oxide is CeO ２ The content of Zr in the composite oxide is 1 mass % or more and 94 mass % or less based on the mass of the composite oxide, and ZrO ２ The content of Al in the composite oxide is 1 mass % or more and 94 mass % or less based on the mass of the composite oxide, and ２ O ３The term "Ce-Zr-Al composite oxide" refers to a material in which the content, calculated as a percentage of Ce, is 5% by mass or more and less than 98% by mass relative to the mass of the composite oxide. Ce-Zr-Al composite oxides are usually in the form of particles. Whether layer a1 contains a Ce-Zr-Al composite oxide can be determined by a conventional method such as SEM-EDX. Specifically, the method is as follows. First, a sample containing layer a1 is analyzed by SEM-EDX, and particles containing the three elements Ce, Zr, and Al are identified by the obtained elemental mapping. Next, a composition analysis (elemental analysis) is performed on the identified particles, and if the results of the composition analysis are within the above range, the material can be determined to be a Ce-Zr-Al composite oxide.

[0023] The Ce—Zr—Al composite oxide can function as an oxygen storage component (hereinafter also referred to as an "OSC material"). The Ce—Zr—Al composite oxide can also function as a support component that supports the above-mentioned catalytically active component. Supporting the catalytically active component refers to a state in which the catalytically active component is physically or chemically adsorbed or held on the outer surface or the inner surface of the pores. Specifically, the support component can be determined to "support" the catalytically active component by, for example, confirming that the support component and the catalytically active component are present in the same region in elemental mapping obtained by analyzing a cross section of an exhaust gas purification catalyst with an EDS (energy dispersive spectroscopy).

[0024] The Al in the Ce-Zr-Al composite oxide contained in layer a1 ２ O ３ The content of Al in terms of Al is 30 mass % or more relative to the mass of the Ce—Zr—Al-based composite oxide. ２ O ３ By making the content in terms of Al—Zr equivalent to 30 mass % or more, a good composite oxide is formed, and the Ce—Zr composite oxide and Al ２ O ３ The Al content of the Ce—Zr—Al composite oxide contained in layer a1 is higher than that of the Al content of the Ce—Zr—Al composite oxide contained in layer a1. ２ O ３The content of Al in the Ce—Zr—Al-based composite oxide contained in layer a1 is preferably 35 mass % or more, and more preferably 40 mass % or more, based on the mass of the Ce—Zr—Al-based composite oxide. ２ O ３ The converted content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, based on the mass of the Ce-Zr-Al based composite oxide.

[0025] From the viewpoint of improving the oxygen storage capacity and heat resistance, the Ce in the Ce—Zr—Al based composite oxide contained in layer a1 is changed to CeO ２ The converted content is preferably 2% by mass or more and 40% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less, based on the mass of the Ce-Zr-Al-based composite oxide.

[0026] From the viewpoint of improving the oxygen storage capacity and heat resistance, Zr in the Ce—Zr—Al based composite oxide contained in layer a1 is converted to ZrO ２ The converted content is preferably 10% by mass or more and 70% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, based on the mass of the Ce-Zr-Al-based composite oxide.

[0027] The Ce—Zr—Al composite oxide contained in layer a1 may contain rare earth elements other than Ce or alkaline earth metal elements such as barium (Ba), strontium (Sr), and calcium (Ca). Examples of rare earth elements other than Ce include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). These rare earth elements may be added to the Ce—Zr—Al composite oxide, for example, as oxides. The rare earth elements and / or alkaline earth metal elements contained in the Ce—Zr—Al composite oxide may be one type or two or more types.

[0028] The content of the Ce—Zr—Al-based composite oxide in layer a1 is 50 mass% or more, preferably 60 mass% or more, more preferably 70 mass% or more, and even more preferably 85 mass% or more, based on the mass of layer a1. Furthermore, the content of the Ce—Zr—Al-based composite oxide in layer a1 is preferably 98 mass% or less, more preferably 97 mass% or less, and even more preferably 95 mass% or less, based on the mass of layer a1. The content of the Ce—Zr—Al-based composite oxide in layer a1 can be determined by a conventional method such as SEM-EDX. Specifically, the method is as follows: (1) A sample obtained from layer a1 is subjected to elemental analysis using a conventional method such as SEM-EDX to identify the types of constituent elements of the entire sample and to determine the content (mass%) of each identified element. (2) Elemental mapping is performed on the sample obtained from layer a1 using a conventional method such as SEM-EDX to identify the types of particles contained in the sample (e.g., Ce-Zr-Al composite oxide particles and, optionally, other particles). (3) For each type of particle, elemental analysis is performed on a number of arbitrarily selected particles (e.g., 50 particles) using SEM-EDX to identify the types of constituent elements of the particles and determine the content (mass%) of each identified element. The average content (mass%) of each element is calculated for each type of particle. (4) An equation is created and solved that represents the relationship between the content (mass%) of each element in the sample, the content (mass%) of each element in each type of particle, and the content (mass%) of each type of particle in the sample, to calculate the content (mass%) of each type of particle in the sample, and this is defined as the content (mass%) of each type of particle in layer a1.

[0029] The layer a1 may further contain components other than those described above. For example, the layer a1 may contain a Ce—Zr-based composite oxide. The term “Ce—Zr-based composite oxide” refers to a composite oxide containing Ce and Zr, and the Ce in the composite oxide is expressed as CeO ２ The content of Zr in the composite oxide in terms of ZrO is 5 mass % or more and 95 mass % or less with respect to the mass of the composite oxide. ２The content in terms of Al is 5% by mass or more and 95% by mass or less with respect to the mass of the composite oxide, and does not contain Al, or if Al is contained, the Al content of the Al in the composite oxide is ２ O ３ The content of each element in a Ce—Zr-based composite oxide in terms of oxide can be determined in the same manner as the content of each element in a Ce—Zr—Al-based composite oxide in terms of oxide.

[0030] The layer a1 may contain an inorganic oxide other than the oxygen storage component as a carrier. The inorganic oxide other than the oxygen storage component may be a metal oxide other than the oxygen storage component described above, such as Al ２ O ３ , ZrO ２ , SiO ２ , TiO ２ , La ２ O ３ Rare earth oxides such as zeolite (aluminosilicate), MgO, ZnO, SnO ２ Examples of the inorganic oxides include oxide materials based on aluminum (Al), zirconium (Zr), silicon (Si), titanium (Ti), rare earth elements, magnesium (Mg), zinc (Zn), and the like, as well as oxide materials obtained by compounding these materials together. Phosphates and borates of inorganic oxides other than the oxygen storage component are also included. Porous inorganic oxides are preferred. The porous material should have a BET specific surface area of ​​30 m or less. ２ / g or more 600m ２ / g or less.

[0031] Furthermore, the layer a1 may contain an alkaline earth metal compound from the viewpoints of suppressing a decrease in catalytic activity due to phosphorus poisoning and improving heat resistance. Preferred alkaline earth metal elements include Sr and Ba. Examples of alkaline earth metal compounds include oxides and carbonates. The layer a1 may contain a binder. The binder can be selected from, for example, alumina, zirconia, titania, silica, ceria, etc.

[0032] The mass of the layer a1 per unit volume of the substrate A is preferably 20 g / L or more and 150 g / L or less, more preferably 50 g / L or more and 120 g / L or less, and even more preferably 70 g / L or more and 100 g / L or less.

[0033] <Other Layers, Layer a2> The upstream catalyst may have other layers in addition to the substrate A and layer a1 described above. Examples of the other layers include layers containing catalytically active components other than Rh. As the catalytically active component other than Rh, conventionally known components can be used, such as Pd, Pt, Au, Ag, Ir, Ru, and Os. Among these, Pd or Pt is preferred from the viewpoint of purifying HC, CO, and NOx in exhaust gas in a balanced manner.

[0034] The other layer preferably contains, in addition to the catalytically active component, a carrier component for supporting the catalytically active component, in order to efficiently exert the exhaust gas purification performance of the catalytically active component. Examples of the carrier component include an oxygen storage component (OSC material) and an inorganic oxide other than the oxygen storage component.

[0035] The oxygen storage component can be any metal oxide capable of storing oxygen and capable of changing the valence state of its constituent elements under the operating conditions of the exhaust gas purification catalyst. Examples of preferred oxygen storage components include Ce-Zr-Al composite oxides and Ce-Zr composite oxides. The oxygen storage component may contain a rare earth element other than Ce or an alkaline earth metal element. Examples of rare earth elements other than Ce include the same rare earth elements other than Ce that may be contained in the Ce-Zr-Al composite oxide contained in layer a1. In addition to the above, other oxygen storage components include oxides of elements that are prone to change their valence state under the operating conditions of the catalyst, such as manganese (Mn), iron (Fe), and copper (Cu), as well as composite oxides containing these elements.

[0036] As the inorganic oxide other than the oxygen storage component, which is the carrier component that supports the catalytically active component, the same as that in layer a1 can be used.

[0037] Furthermore, the other layers may contain alkaline earth metal compounds from the viewpoints of suppressing a decrease in catalytic activity due to phosphorus poisoning and improving heat resistance. Preferred alkaline earth metal elements include Sr and Ba. Examples of alkaline earth metal compounds include oxides and carbonates. Layer a2 may contain a binder. The binder may be selected from, for example, alumina, zirconia, titania, silica, ceria, etc.

[0038] An example of an embodiment in which the upstream catalyst has another layer is an embodiment in which a layer a2 is provided between the substrate A and the layer a1. The layer a2 preferably contains Pd and a Ce—Zr-based composite oxide. The Pd content in the layer a2 is preferably 0.010 mass% or more, more preferably 0.050 mass% or more, and even more preferably 0.10 mass% or more, relative to the mass of the layer a2. The Pd content in the layer a2 is preferably 20 mass% or less, more preferably 15 mass% or less, and even more preferably 10 mass% or less, relative to the mass of the layer a2. The Pd content in the layer a2 can be determined in the same manner as the Rh content in the layer a1. The Ce—Zr—Al-based composite oxide is a Ce—Zr-based composite oxide containing the same amounts of Ce, Zr, and Al, and an Al-based composite oxide. ２ O ３Compared to when the oxygen storage component and the oxygen storage component are present separately, Pd has the advantage of improved heat resistance as described above, but the disadvantage of reduced OSC. Furthermore, compared to Rh, Pd has the property of being less susceptible to a decrease in catalytic activity even when the heat resistance of the oxygen storage component contained in the same layer is low. Therefore, layer a2 preferably does not contain a Ce-Zr-Al composite oxide, or, if it contains a Ce-Zr-Al composite oxide, the content of the Ce-Zr-based composite oxide contained in layer a2 is preferably 50 mass% or more relative to the total mass of the Ce-Zr-based composite oxide and the Ce-Zr-Al-based composite oxide contained in layer a2. If layer a2 contains a Ce-Zr-Al composite oxide, the content of the Ce-Zr-based composite oxide contained in layer a2 is more preferably 60 mass% or more relative to the total mass of the Ce-Zr-based composite oxide and the Ce-Zr-Al-based composite oxide contained in layer a2. The contents of the Ce--Zr-based composite oxide and the Ce--Zr--Al-based composite oxide contained in the layer a2 can be determined in the same manner as the content of the Ce--Zr--Al-based composite oxide contained in the layer a1.

[0039] The mass of the layer a2 per unit volume of the substrate A is preferably 50 g / L or more and 230 g / L or less, more preferably 70 g / L or more and 180 g / L or less, and even more preferably 80 g / L or more and 150 g / L or less.

[0040] [Downstream Catalyst] The downstream catalyst has a substrate B and a layer b1 provided on the substrate B.

[0041] <Substrate B> The substrate B is the same as the substrate A described above.

[0042] <Layer b1> Layer b1 contains Rh and a Ce—Zr-based composite oxide. Rh is a catalytically active component. The Rh content in layer b1 is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.1 mass% or more, relative to the mass of layer b1. The Rh content in layer b1 is preferably 1.0 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.3 mass% or less, relative to the mass of layer b1. The Rh content in layer b1 can be determined in the same manner as the Rh content in layer a1.

[0043] Preferably, 60 mass % or more of the Rh contained in layer b1 is supported on the Ce—Zr-based composite oxide, more preferably 70 mass % or more of the Rh contained in layer b1 is supported on the Ce—Zr-based composite oxide, and even more preferably 75 mass % or more of the Rh contained in layer b1 is supported on the Ce—Zr-based composite oxide. The proportion of Rh supported on the Ce—Zr-based composite oxide can be adjusted, for example, by the content of Ce—Zr-based composite oxide in layer b1.

[0044] The layer b1 may contain, in addition to Rh, a catalytically active component other than Rh. As the catalytically active component other than Rh, conventionally known components can be used, such as Pd, Pt, Au, Ag, Ir, Ru, and Os.

[0045] The Ce—Zr-based composite oxide can function as an OSC material, and also as a support component that supports the above-mentioned catalytically active components.

[0046] Ce has the property of stabilizing the oxidation state of Rh, and therefore, the CeO ２ The converted content is preferably 35% by mass or less, and more preferably 25% by mass or less, based on the mass of the Ce—Zr-based composite oxide.

[0047] ZrO of Zr in the Ce-Zr composite oxide contained in layer b1 ２ The converted content 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-based composite oxide.

[0048] The Ce—Zr-based composite oxide contained in layer b1 may contain rare earth elements other than Ce and alkaline earth metal elements such as Ba, Sr, and Ca. Examples of rare earth elements other than Ce include those mentioned above in the description of layer a1.

[0049] The content of the Ce—Zr-based composite oxide in layer b1 is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 65 mass % or more, based on the mass of layer b1. The content of the Ce—Zr-based composite oxide in layer b1 is preferably 95 mass % or less, more preferably 90 mass % or less, and even more preferably 85 mass % or less, based on the mass of layer b1.

[0050] As mentioned above, Al ２ O ３ Since Rh has the property of stabilizing the oxidation state of Rh, from the viewpoint of enhancing the exhaust gas purification performance, the layer b1 does not contain Al, or if it contains Al, the Al contained in the layer b1 is ２ O ３ The content in terms of Al is 30 mass % or less with respect to the mass of the layer b1. When the layer b1 contains Al, the Al content of the Al contained in the layer b1 is ２ O ３ The content of Al in terms of Al content is preferably 25 mass % or less with respect to the mass of the layer b1. On the other hand, although it is lower than that of the upstream catalyst, heat resistance is also required for the downstream catalyst. ２ O ３ The content of Al in terms of Al is preferably 10% by mass or more, and more preferably 15% by mass or more, based on the mass of the layer b1. ２ O ３ The converted content can be determined in the same manner as the Rh content.

[0051] The layer b1 may further contain components other than those described above. The layer b1 may contain an Al-based oxide as a support, and the Al-based oxide may contain La. However, since La has the property of stabilizing the oxidation state of Rh, the Al-based oxide does not contain La, or if it contains La, the La content of La in the Al-based oxide may be reduced. ２ O ３ The content in terms of La is preferably 10 mass % or less with respect to the mass of the Al-based oxide. ２ O ３The content of La converted to La is more preferably 8% by mass or less, even more preferably 7% by mass or less, even more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the mass of the Al-based oxide. ２ O ３ The content in terms of oxide may be 0.5 mass % or more with respect to the mass of the Al-based oxide. The content in terms of oxide of each element in the Al-based oxide can be determined in the same manner as the content in terms of oxide of each element in the Ce-Zr-Al-based composite oxide. Layer b1 may contain an inorganic oxide other than the Al-based oxide as a support. Furthermore, layer b may contain an alkaline earth metal compound from the viewpoints of suppressing a decrease in catalytic activity due to phosphorus poisoning and of heat resistance. As the inorganic oxide other than the Al-based oxide or the alkaline earth metal compound, the same as those in layer a1 can be used. Layer b1 may contain a binder. The binder can be selected from, for example, alumina, zirconia, titania, silica, ceria, etc. Note that when the binder contained in layer b1 contains Al element, the Al content of the Al contained in layer b1 can be determined by the following formula: ２ O ３ The converted content, including Al derived from the binder, must be 30 mass % or less with respect to the mass of the layer b1.

[0052] The mass of the layer b1 per unit volume of the substrate B is preferably 20 g / L or more and 150 g / L or less, more preferably 50 g / L or more and 120 g / L or less, and even more preferably 70 g / L or more and 100 g / L or less.

[0053] <Other Layers, Layer b2> The downstream catalyst may have other layers in addition to the substrate B and layer b1 described above. Examples of the other layers include layers containing catalytically active components other than Rh. Examples of catalytically active components other than Rh include conventionally known components, such as Pd, Pt, Au, Ag, Ir, Ru, and Os, with Pd or Pt being preferred. Examples of the other layers that the downstream catalyst may have include the same as the other layers that the upstream catalyst may have.

[0054] An example of an embodiment in which the downstream catalyst has another layer is an embodiment in which a layer b2 is provided between the substrate B and the layer b1. The layer b2 may contain, for example, Pt and a Ce—Zr-based composite oxide. The layer b2 does not contain a Ce—Zr—Al-based composite oxide, or if it contains a Ce—Zr—Al-based composite oxide, the content of the Ce—Zr-based composite oxide contained in the layer b2 is preferably 50 mass% or more relative to the total mass of the Ce—Zr-based composite oxide and the Ce—Zr—Al-based composite oxide contained in the layer b2. If the layer b2 contains a Ce—Zr—Al-based composite oxide, the content of the Ce—Zr-based composite oxide contained in the layer b2 is more preferably 60 mass% or more relative to the total mass of the Ce—Zr-based composite oxide and the Ce—Zr—Al-based composite oxide contained in the layer b2. The layer b2 may contain an inorganic oxide other than the oxygen storage component as a carrier. Layer b2 may also contain an alkaline earth metal compound from the viewpoints of suppressing a decrease in catalytic activity due to phosphorus poisoning and improving heat resistance. The inorganic oxides and alkaline earth metal compounds other than the oxygen storage component may be the same as those used in layer a1. Layer b2 may also contain a binder. The binder may be selected from, for example, alumina, zirconia, titania, silica, ceria, etc.

[0055] The mass of the layer b2 per unit volume of the substrate B is preferably 50 g / L or more and 230 g / L or less, more preferably 100 g / L or more and 180 g / L or less, and even more preferably 130 g / L or more and 160 g / L or less.

[0056] The exhaust gas purification catalyst of the present invention can be used as an exhaust gas purification catalyst for an internal combustion engine to efficiently purify NOx, HC, and CO. Therefore, it is possible to provide an exhaust gas purification system in which exhaust gas from an internal combustion engine is introduced into the exhaust gas purification catalyst in an exhaust path connected to the internal combustion engine without passing through another exhaust gas purification catalyst. Examples of the internal combustion engine include a gasoline engine, an engine fueled by compressed natural gas, and an engine fueled by gasoline containing any amount of ethanol (flex fuel).

[0057] <Production of catalyst> The exhaust gas catalyst of the present invention can be produced by forming layer a1 (and layer a2, if necessary) on substrate A and layer b1 (and layer b2, if necessary) on substrate B.

[0058] When forming the layer a2, a source of a catalytically active component (e.g., nitrates, ammine complex salts, acetates, chlorides, etc. of Pd, Pt, etc.), a Ce—Zr-based composite oxide, and optionally other components (e.g., Al-based oxides, binders, solvents, etc.) are mixed to prepare a slurry for forming the layer a2, which is then applied to the substrate A, dried, and fired to form the layer a2.

[0059] The layer a1 can be formed by mixing a Rh source (e.g., Rh nitrate, ammine complex salt, acetate, chloride, etc.), a Ce—Zr—Al-based composite oxide, and optionally other components (e.g., Ce—Zr-based composite oxide, binder, solvent, etc.) to prepare a layer a1-forming slurry, applying the layer a1-forming slurry onto the substrate A (or onto the layer a2, if present), drying, and firing.

[0060] When forming the layer b2, a source of a precious metal element (e.g., nitrate, ammine complex salt, acetate, chloride, etc. of Pd, Pt, etc.) and, if necessary, other components (e.g., Ce—Zr-based composite oxide, Al-based oxide, binder, solvent, etc.) are mixed to prepare a slurry for forming the layer b2, and the slurry for forming the layer b2 is applied onto the substrate B, dried, and fired to form the layer b2.

[0061] The layer b1 can be formed by mixing a Rh source (e.g., Rh nitrate, ammine complex salt, acetate, chloride, etc.), a Ce—Zr-based composite oxide, and optionally other components (e.g., Al-based oxide, binder, solvent, etc.) to prepare a layer b1-forming slurry, applying the layer b1-forming slurry onto the substrate B (or onto the layer b2, if the layer b2 is present), drying, and firing.

[0062] Next, the embodiments of the present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0063] Example 1 (1) Preparation of Slurry for Forming the Lower Layer (Layer a2) of the Upstream Catalyst An OSC material 1 (Ce—Zr-based composite oxide) having the following composition was prepared: CeO ２ Converted content: 40.0 mass% ZrO ２ Content of rare earth elements other than Ce in terms of oxides: 10.0 mass%

[0064] In a mixing vessel, a palladium nitrate aqueous solution, OSC material 1, La ２ O ３ Modified alumina (La ２ O ３ The amount of each component in the slurry for forming layer a2 was 4.0 mass% in terms of metal, Pd, 40.0 mass% in terms of OSC material 1, and La, based on the mass of the fired layer a2 (100 mass%). ２ O ３ The modified alumina was adjusted to 50.0 mass % and the binder to 6.0 mass %, with the binder not containing Al element.

[0065] (2) Formation of Lower Layer (Layer a2) of Upstream Catalyst As a flow-through type substrate, a flow-through type substrate was prepared which had cells extending in the axial direction and partitioned by partition walls with a thickness of 50 to 70 μm, at a density of 600 cells per square inch on a surface perpendicular to the axial direction, and had a volume of 1.0 L.

[0066] A flow-through substrate was immersed in the layer a2-forming slurry to obtain a flow-through substrate coated with the layer a2-forming slurry. The flow-through substrate coated with the layer a2-forming slurry was then dried at 150°C for 0.5 hours and then calcined at 500°C for 1 hour to form layer a2. The mass of layer a2 per unit volume of the portion of the flow-through substrate where layer a2 was formed was 100 g / L.

[0067] (3) Preparation of Slurry for Forming Upper Layer (Layer a1) of Upstream Catalyst OSC Material 2 (Ce—Zr—Al-based composite oxide) having the following composition was prepared: CeO ２ Converted content: 10.0 mass% ZrO ２ Conversion content: 35.0 mass% of Al２ O ３ Content of rare earth elements other than Ce in terms of oxides: 45.0 mass%

[0068] A rhodium nitrate solution, OSC material 2, binder, and water were added to a mixing vessel, and the mixture was mixed and stirred to prepare a slurry for forming layer a1. The amounts of the components in the slurry for forming layer a1 were adjusted so that, based on the mass of layer a1 after firing (100 mass%), Rh was 1.0 mass% in metal equivalent, OSC material 2 was 90.0 mass%, and the binder was 9.0 mass%. Note that the binder did not contain Al element.

[0069] (4) Formation of the upper layer (layer a1) of the upstream catalyst The flow-through substrate on which layer a2 had been formed was immersed in the layer a1 forming slurry to obtain a flow-through substrate coated with the layer a1 forming slurry. Next, the flow-through substrate coated with the layer a1 forming slurry was dried at 150°C for 0.5 hours and then calcined at 500°C for 1 hour to form layer a1 on layer a2. The mass of layer a1 per unit volume of the portion of the flow-through substrate on which layer a1 had been formed was 80 g / L.

[0070] In this manner, an upstream catalyst was produced that included the layer a2 formed on the flow-through type substrate and the layer a1 formed on the layer a2.

[0071] (5) Preparation of Slurry for Forming Lower Layer (Layer b2) of Downstream Catalyst The above-mentioned OSC material 1 was prepared.

[0072] In a mixing vessel, a platinum nitrate solution, OSC material 1, La ２ O ３ Modified alumina (La ２ O ３ The amount of each component in the slurry for forming layer b2 was 1.0 mass% in terms of metal, Pt, 60.0 mass% of OSC material 1, and La, based on the mass of the layer b2 after firing (100 mass%). ２ O ３ The modified alumina was adjusted to 30.0 mass % and the binder to 9.0 mass %, with the binder not containing Al element.

[0073] (6) Formation of Lower Layer (Layer b2) of Downstream Catalyst As a flow-through type substrate, a flow-through type substrate was prepared which had cells extending in the axial direction and partitioned by partition walls with a thickness of 50 to 70 μm, at a density of 600 cells per square inch on a surface perpendicular to the axial direction, and had a volume of 1.0 L.

[0074] A flow-through substrate was immersed in the layer b2-forming slurry to obtain a flow-through substrate coated with the layer b2-forming slurry. The flow-through substrate coated with the layer b2-forming slurry was then dried at 150°C for 0.5 hours and then calcined at 500°C for 1 hour to form layer b2. The mass of layer b2 per unit volume of the portion of the flow-through substrate on which layer b2 was formed was 140 g / L.

[0075] (7) Preparation of Slurry for Forming Upper Layer (Layer b1) of Downstream Catalyst OSC Material 3 (Ce—Zr-based composite oxide) having the following composition was prepared: CeO ２ Converted content: 20.0 mass% ZrO ２ Content of rare earth elements other than Ce in terms of oxides: 70.0 mass%

[0076] In a mixing vessel, a rhodium nitrate solution, OSC material 3, La ２ O ３ Modified alumina (La ２ O ３ The amount of each component in the slurry for forming layer b1 was 0.2 mass% in terms of metal, Rh, 70.0 mass% of OSC material 3, and La, based on the mass of the layer b1 after firing (100 mass%). ２ O ３ The modified alumina was adjusted to 20.0 mass % and the binder to 9.8 mass %, with the binder not containing Al element.

[0077] (8) Formation of the upper layer (layer b1) of the downstream catalyst The flow-through substrate on which layer b2 had been formed was immersed in the layer b1-forming slurry to obtain a flow-through substrate coated with the layer b1-forming slurry. The flow-through substrate coated with the layer b1-forming slurry was then dried at 150°C for 0.5 hours and then calcined at 500°C for 1 hour to form layer b1 on layer b2. The mass of layer b1 per unit volume of the portion of the flow-through substrate on which layer b1 had been formed was 80 g / L.

[0078] In this manner, a downstream catalyst was produced that included the layer b2 formed on the flow-through type substrate and the layer b1 formed on the layer b2.

[0079] In this manner, an exhaust gas purifying catalyst including an upstream catalyst and a downstream catalyst was manufactured.

[0080] [Example 2] In the production of the downstream catalyst, La in the slurry for forming layer b1 ２ O ３ La modified alumina ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modification amount was 4.0 mass %.

[0081] [Example 3] In the production of the downstream catalyst, La in the slurry for forming layer b1 ２ O ３ La modified alumina ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modification amount was set to 6.0 mass %.

[0082] [Example 4] In the production of the downstream catalyst, La in the slurry for forming layer b1 ２ O ３ La modified alumina ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modification amount was set to 9.0 mass %.

[0083] Example 5 An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that in the production of the downstream catalyst, OSC material 3 used in preparing the slurry for forming layer b1 was replaced with OSC material 4 (Ce—Zr-based composite oxide) having the following composition: CeO２ Converted content: 30.0 mass% ZrO ２ Content of rare earth elements other than Ce in terms of oxides: 10.0 mass%

[0084] Example 6 An OSC material 5 (Ce—Zr—Al based composite oxide) having the following composition was prepared: CeO ２ Converted content: 20.0 mass% ZrO ２ Conversion content: 30.0 mass% of Al ２ O ３ Content of rare earth elements other than Ce in terms of oxides: 40.0 mass%

[0085] In producing the upstream catalyst, an exhaust gas purification catalyst was produced in the same manner as in Example 1, except that the amounts of each component in the layer a2-forming slurry were adjusted so that, relative to the mass of the layer a2 after firing (100 mass%), Pd was 4.0 mass%, OSC material 5 was 90.0 mass%, and the binder was 6.0 mass%, converted into metal.

[0086] Example 7 The above-mentioned OSC material 2 and the above-mentioned OSC material 3 were prepared.

[0087] In producing the upstream catalyst, an exhaust gas purification catalyst was produced in the same manner as in Example 1, except that the amounts of each component in the layer a1-forming slurry were adjusted so that, relative to the mass of the fired layer a1 (100 mass%), Rh was 1.0 mass%, OSC material 2 was 64.0 mass%, OSC material 3 was 26.0 mass%, and the binder was 9.0 mass%, converted into metal.

[0088] [Example 8] In the production of the downstream catalyst, the amounts of the components in the slurry for forming the layer b1 were set to 0.2 mass% in terms of metal for Rh, 60.0 mass% for OSC material 3, and 100 mass% for La, based on the mass of the layer b1 after calcination (100 mass%). ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modified alumina was adjusted to 30.0 mass % and the binder was adjusted to 9.8 mass %.

[0089] [Example 9] In the production of the downstream catalyst, when preparing a slurry for forming layer b1, La ２ O３ An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that no modified alumina was used, and the amounts of each component in the layer b1-forming slurry were adjusted so that, relative to the mass of the layer b1 after firing (100 mass%), Rh was 0.2 mass%, the OSC material 3 was 90.0 mass%, and the binder was 9.8 mass%, converted into metal.

[0090] Comparative Example 1 The above-mentioned OSC material 3 was prepared.

[0091] In the production of the upstream catalyst, instead of the OSC material 2 used in preparing the slurry for forming layer a1, OSC material 3 and La ２ O ３ Modified alumina (La ２ O ３ The amount of each component in the slurry for forming layer a1 was set to 1.0 mass% in terms of metal, Rh, 45.0 mass% of OSC material 3, and La, based on the mass of the layer a1 after firing (100 mass%). ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modified alumina was adjusted to 45.0 mass % and the binder was adjusted to 9.0 mass %.

[0092] Comparative Example 2 The above-mentioned OSC material 2 was prepared.

[0093] In the production of the downstream catalyst, the OSC material 3 and La used in preparing the slurry for forming layer b1 ２ O ３ Modified alumina (La ２ O ３ An exhaust gas purification catalyst was produced in the same manner as in Comparative Example 1, except that OSC material 2 was used instead of the modified amount of Rh (1.0 mass%), and the amounts of each component in the layer b1-forming slurry were adjusted so that, relative to the mass of the layer b1 after firing (100 mass%), Rh was 0.2 mass%, OSC material 2 was 90.0 mass%, and the binder was 9.8 mass%.

[0094] Comparative Example 3 An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that in the production of the upstream catalyst, OSC material 3 was further used when preparing the layer a1-forming slurry, and the amounts of the respective components in the layer a1-forming slurry were adjusted so that, relative to the mass of the layer a1 after firing (100 mass%), Rh was 1.0 mass% in metal equivalent, OSC material 2 was 46.0 mass%, OSC material 3 was 44.0 mass%, and the binder was 9.0 mass%.

[0095] Comparative Example 4 An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that in the production of the upstream catalyst, OSC material 3 was further used when preparing the layer a1-forming slurry, and the amounts of the respective components in the layer a1-forming slurry were adjusted so that, relative to the mass of layer a1 after firing (100 mass%), Rh was 1.0 mass% in metal equivalent, OSC material 2 was 27.0 mass%, OSC material 3 was 63.0 mass%, and the binder was 9.0 mass%.

[0096] Comparative Example 5 In the production of the downstream catalyst, the amounts of the components in the slurry for forming the layer b1 were set to 0.2 mass% in terms of metal for Rh, 48.0 mass% for OSC material 3, and 100 mass% for La, based on the mass of the layer b1 after calcination (100 mass%). ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modified alumina was adjusted to 42.0 mass % and the binder was adjusted to 9.8 mass %.

[0097] Comparative Example 6 In the production of the downstream catalyst, the amounts of the components in the slurry for forming the layer b1 were set to 0.2 mass% in terms of metal for Rh, 38.0 mass% for OSC material 3, and 100 mass% for La, based on the mass of the layer b1 after calcination (100 mass%). ２ O ３ An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the modified alumina was adjusted to 52.0 mass % and the binder was adjusted to 9.8 mass %.

[0098] Comparative Example 7 The above-mentioned OSC material 5 was prepared.

[0099] In the production of the upstream catalyst, the OSC material 1 and La used in preparing the slurry for forming the layer a2 ２ O ３ Modified alumina (La ２ O３ An exhaust gas purification catalyst was produced in the same manner as in Comparative Example 1, except that OSC material 5 was used instead of the modified amount of Pd (1.0 mass%), and the amounts of each component in the layer a2-forming slurry were adjusted so that, relative to the mass of the layer a2 after firing (100 mass%), Pd was 4.0 mass% in metal equivalent, OSC material 5 was 90.0 mass%, and the binder was 6.0 mass%.

[0100] (Durability Evaluation) The exhaust gas purification catalysts of Examples 1 to 9 and Comparative Examples 1 to 7 were subjected to the following durability conditions as degradation treatment assuming driving of 100,000 to 200,000 kilometers. <Durability Conditions> Durability engine: NA 2L passenger gasoline engine Gasoline used: Commercially available regular gasoline Treatment temperature: 900°C Treatment time: 100 hours

[0101] The exhaust gas purification catalysts (upstream catalyst and downstream catalyst) of Examples 1 to 9 and Comparative Examples 1 to 7 were placed in the exhaust path of an engine, and durability tests were conducted under the above conditions. The exhaust gas purification catalysts after the durability test were installed in a vehicle (a passenger car equipped with a 1.5L direct-injection turbo engine), and the vehicle was operated under the driving conditions of the World Harmonized Exhaust Gas Test Mode (WLTC). The emissions of non-methane hydrocarbons (NMHC) and nitrogen oxides (NOx) in the exhaust gas passing through the exhaust gas purification catalyst were measured during low-temperature operation from 589 seconds after the start of operation, medium-speed operation from 589 seconds to 1022 seconds after the start of operation, high-speed operation from 1022 seconds to 1477 seconds after the start of operation, and ultra-high-speed operation from 1477 seconds to 1800 seconds after the start of operation, and the total emissions of NMHC and NOx per unit driving distance were calculated. Certification test fuel was used as the gasoline, and an exhaust gas measurement device manufactured by Horiba, Ltd. was used as the exhaust gas measurement device. The results are shown in Table 1. In Table 1, the total emissions of NMHC and NOx are shown in the "Emissions (Relative Value)" column as relative values ​​when the value in Example 1 is set to 1.00. In Table 1, "CZA" represents a Ce-Zr-Al-based composite oxide, and "CZ" represents a Ce-Zr-based composite oxide.

[0102]

[0103] From Table 1, it can be seen that the exhaust gas purifying catalysts of the examples were able to reduce the amount of emissions after the durability test and were excellent in durability.

[0104] According to the present invention, it is possible to provide an exhaust gas purification catalyst having excellent durability.

[0105] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-139973) filed on August 30, 2023, the contents of which are incorporated herein by reference.

[0106] 1, 11 upstream catalyst 2, 12 downstream catalyst A substrate A a1 layer a1 a2 layer a2 B substrate B b1 layer b1 b2 layer b2 10, 20 exhaust gas purification catalyst X flow direction of exhaust gas

Claims

1. An exhaust gas purification catalyst comprising an upstream catalyst provided upstream in the flow direction of exhaust gas, and a downstream catalyst provided downstream in the flow direction of exhaust gas, wherein the upstream catalyst has a substrate A and a layer a1 provided on the substrate A, the downstream catalyst has a substrate B and a layer b1 provided on the substrate B, the layer a1 contains Rh and a Ce-Zr-Al based composite oxide, the layer b1 contains Rh and a Ce-Zr based composite oxide, and the Al in the Ce-Zr-Al based composite oxide contained in the layer a1 is 0.01 to 0.01% by weight. ２ O ３ the content of the Ce-Zr-Al-based composite oxide contained in the layer a1 is 30 mass % or more with respect to the mass of the Ce-Zr-Al-based composite oxide, the content of the Ce-Zr-Al-based composite oxide contained in the layer a1 is 50 mass % or more with respect to the mass of the layer a1, the layer b1 does not contain Al, or, if it contains Al, the Al content of the Al contained in the layer b1 is ２ O ３ The content in terms of carbon black is 30 mass % or less based on the mass of the layer b1.

2. CeO of Ce in the Ce-Zr based composite oxide contained in the layer b1 ２ 2. The exhaust gas purification catalyst according to claim 1, wherein the content in terms of the converted amount is 25 mass % or less based on the mass of the Ce-Zr based composite oxide.

3. The layer b1 contains an Al-based oxide, and the Al-based oxide does not contain La, or, if it contains La, the La content of La in the Al-based oxide is ２ O ３ 2. The exhaust gas purification catalyst according to claim 1, wherein the converted content is 7 mass % or less based on the mass of the Al-based oxide.

4. CeO of Ce in the Ce-Zr-Al based composite oxide contained in the layer a1 ２ 2. The exhaust gas purification catalyst according to claim 1, wherein the content in terms of the converted amount is 2% by mass or more and 40% by mass or less based on the mass of the Ce-Zr-Al based composite oxide.

5. ZrO of Zr in the Ce-Zr-Al based composite oxide contained in the layer a1 ２ 2. The exhaust gas purification catalyst according to claim 1, wherein the content in terms of the converted amount is 10 mass % or more and 70 mass % or less based on the mass of the Ce-Zr-Al based composite oxide.

6. The amount of Al in the Ce-Zr-Al based composite oxide contained in the layer a1 is reduced. ２ O ３ 2. The exhaust gas purification catalyst according to claim 1, wherein the converted content is 60 mass % or less based on the mass of the Ce-Zr-Al based composite oxide.

7. The exhaust gas purifying catalyst according to claim 1, wherein 60 mass % or more of the Rh contained in said layer b1 is supported on said Ce-Zr based composite oxide.

8. The exhaust gas purifying catalyst according to claim 1, further comprising a layer a2 between said substrate A and said layer a1, said layer a2 containing Pd and a Ce-Zr-based composite oxide, and said layer a2 not containing a Ce-Zr-Al-based composite oxide, or, if said layer a2 contains a Ce-Zr-Al-based composite oxide, the content of said Ce-Zr-based composite oxide contained in said layer a2 is 50 mass % or more based on the total mass of said Ce-Zr-based composite oxide and said Ce-Zr-Al-based composite oxide contained in said layer a2.

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