Exhaust gas purification catalyst

Abstract

An exhaust gas purification catalyst comprising an upstream catalyst provided on the upstream side in the flow direction of the exhaust gas and a downstream catalyst provided on the downstream side in the flow direction of the 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, the content of Al in terms of Al2O3 in the Ce-Zr-Al-based composite oxide contained in the layer a1 is 30% by mass or more based on 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% by mass or more based on the mass of the layer a1, the layer b1 does not contain Al, or when Al is contained, the content of Al in terms of Al2O3 contained in the layer b1 is 30% by mass or less based on the mass of the layer b1.

Description

Technical Field

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

Background Art

[0002] Exhaust gas (also referred to as exhaust) discharged from internal combustion engines such as automobiles and motorcycles contains harmful components such as HC (hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides). Conventionally, a three-way catalyst has been used for the purpose of purifying and detoxifying these harmful components. As the three-way catalyst, those using noble metals such as Pt (platinum), Pd (palladium), and Rh (rhodium) are known. Pt and Pd mainly act on the oxidative purification of HC and CO, and Rh mainly acts on the reductive purification of NOx. In recent years, attempts have been made to improve the exhaust gas purification performance of the noble metal catalysts as described above due to the strengthening of exhaust gas regulations and the increasing environmental awareness.

[0003] Patent Document 1 describes an exhaust gas purification catalyst composed of a combination of a startup catalyst and an underfloor catalyst installed behind the startup catalyst in the exhaust gas flow direction, with the average thickness and porosity of the catalyst coat layer of the underfloor catalyst within a specific range. Patent Document 1 also describes an exhaust gas purification catalyst in which the catalyst coat layers of the startup catalyst and the underfloor catalyst contain Rh, a ceria-zirconia composite oxide material, and Al2O3.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in recent years, exhaust gas purification catalysts have been required to have even better exhaust gas purification performance. In particular, since the temperature of the exhaust gas on the upstream side in the flow direction is high, an exhaust gas purification catalyst with even better durability is required.

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

Means for Solving the Problems

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

[0008] [1] An exhaust gas purification catalyst comprising an upstream catalyst provided on the upstream side in the flow direction of the exhaust gas and a downstream catalyst provided on the downstream side in the flow direction of the 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 composite oxide, the layer b1 contains Rh and a Ce-Zr composite oxide, the content of Al in terms of Al2O3 in the Ce-Zr-Al composite oxide contained in the layer a1 is 30% by mass or more based on the mass of the Ce-Zr-Al composite oxide, the content of the Ce-Zr-Al composite oxide contained in the layer a1 is 50% by mass or more based on the mass of the layer a1, the layer b1 does not contain Al, or when it contains Al, the content of Al in terms of Al2O3 contained in the layer b1 is 30% by mass or less based on the mass of the layer b1, Exhaust gas purification catalyst. [2] The content of Ce in terms of CeO2 in the Ce-Zr composite oxide contained in the layer b1 is 25% by mass or less based on the mass of the Ce-Zr composite oxide, the exhaust gas purification catalyst according to [1]. [3] the layer b1 contains an Al-based oxide, The Al-based oxide either does not contain La, or when it contains La, the content of La in terms of La2O3 in the Al-based oxide is 7% by mass or less based on the mass of the Al-based oxide, the exhaust gas purification catalyst according to [1] or [2]. [4] The content of Ce in terms of CeO2 in the Ce-Zr-Al-based composite oxide contained in the layer a1 is 2% by mass or more and 40% by mass or less based on the mass of the Ce-Zr-Al-based composite oxide, the exhaust gas purification catalyst according to any one of [1] to [3]. [5] The content of Zr in terms of ZrO2 in the Ce-Zr-Al-based composite oxide contained in the layer a1 is 10% by mass or more and 70% by mass or less based on the mass of the Ce-Zr-Al-based composite oxide, the exhaust gas purification catalyst according to any one of [1] to [4]. [6] The content of Al in terms of Al2O3 in the Ce-Zr-Al-based composite oxide contained in the layer a1 is 60% by mass or less based on the mass of the Ce-Zr-Al-based composite oxide, the exhaust gas purification catalyst according to any one of [1] to [5]. [7] 60% by mass or more of Rh contained in the layer b1 is supported on the Ce-Zr-based composite oxide, the exhaust gas purification catalyst according to any one of [1] to [6]. [8] There is a layer a2 between the substrate A and the layer a1, The layer a2 contains Pd and a Ce-Zr-based composite oxide, The layer a2 either does not contain a Ce-Zr-Al-based composite oxide, or when it contains a Ce-Zr-Al-based composite oxide, the content of the Ce-Zr-based composite oxide contained in the layer a2 is 50% by mass or more based on the total mass of the Ce-Zr-based composite oxide and the Ce-Zr-Al-based composite oxide contained in the layer a2, the exhaust gas purification catalyst according to any one of [1] to [7].

Advantages of the Invention

[0009] According to the present invention, an exhaust gas purification catalyst excellent in durability can be provided.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments for carrying out the present invention will be described in detail.

[0012] The exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst including an upstream catalyst provided on the upstream side in the flow direction of the exhaust gas and a downstream catalyst provided on the downstream side in the flow direction of the 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 composite oxide, the layer b1 contains Rh and a Ce-Zr composite oxide, the content of Al in terms of Al2O3 in the Ce-Zr-Al composite oxide contained in the layer a1 is 30% by mass or more based on the mass of the Ce-Zr-Al composite oxide, the content of the Ce-Zr-Al composite oxide contained in the layer a1 is 50% by mass or more based on the mass of the layer a1, the layer b1 does not contain Al, or when it contains Al, the content of Al in terms of Al2O3 contained in the layer b1 is 30% by mass or less based on the mass of the layer b1, is an exhaust gas purification catalyst.

[0013] A schematic diagram of one embodiment of the exhaust gas purification catalyst of the present invention is shown in FIG. 1. The exhaust gas purification catalyst 10 in Fig. 1 includes an upstream catalyst 1 and a downstream catalyst 2. The upstream catalyst 1 is provided on the upstream side in the exhaust gas flow direction X, and the downstream catalyst 2 is provided on the downstream side in the exhaust gas flow direction X. 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 content of Al in terms of Al2O3 in the Ce-Zr-Al-based composite oxide contained in the layer a1 is 30% by mass or more based on 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% by mass or more based on the mass of the 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 when it contains Al, the content of Al in terms of Al2O3 contained in the layer b1 is 30% by mass or less based on the mass of the layer b1.

[0014] The exhaust gas purification catalyst of the present invention has the effect of excellent durability due to the above configuration. Although the mechanism by which the above effect is obtained by the present invention has not been completely clarified, the present inventor presumes as follows. However, the present invention is not limited by the following presumed mechanism. Rh is deactivated in an oxidized state when the concentration of oxidizing components such as O2 and NOx in the exhaust gas reaches a certain level or higher. The deactivated Rh is reduced and its activity is restored when the concentration of reducing components such as HC and CO reaches a certain level or higher. Since Al2O3 has excellent heat resistance, it improves the heat resistance of the exhaust gas purification catalyst. On the other hand, Al2O3 has the property of stabilizing the oxidized state of Rh. Since the temperature of the exhaust gas is high on the upstream side, higher heat resistance is required for the upstream catalyst. On the other hand, since the exhaust gas from the internal combustion engine directly reaches it, the fluctuation range of the concentration of reducing components such as HC and CO is larger than that on the downstream side, and it is likely to reach a high concentration sufficient to reduce Rh whose oxidation state is stabilized by Al2O3. Since the temperature of the exhaust gas is lower on the downstream side than on the upstream side, the requirement for heat resistance of the downstream catalyst is lower than that of the upstream catalyst. On the other hand, since the exhaust gas from the internal combustion engine passes through the upstream catalyst and is partially purified before reaching the downstream catalyst, the fluctuation range of the concentration of reducing components such as HC and CO is smaller than that on the upstream side, and it is difficult to reach a high concentration sufficient to reduce Rh whose oxidation state is stabilized by Al2O3. From the above, it is conceivable to increase the content of Al2O3 on the upstream side where improving heat resistance is more important than reducing Rh deactivation, and to reduce the content of Al2O3 on the downstream side where reducing Rh deactivation is more important than improving heat resistance. However, as in the case of the upstream catalyst layer described in Patent Document 1 mentioned above, when the Ce-Zr composite oxide and Al2O3 are separately contained, it has been found that sufficient exhaust gas purification performance cannot be obtained after the catalyst is exposed to a high-temperature environment. In contrast, in the present invention, in the catalyst layer of the upstream catalyst, instead of adding the Ce-Zr composite oxide and Al2O3 separately, by forming them into a Ce-Zr-Al composite oxide, sufficient exhaust gas purification performance can be obtained even after being exposed to a high-temperature environment. This is because when the same amounts of Ce, Zr, and Al are added to the catalyst layer, higher heat resistance can be obtained by adding them in the form of a Ce-Zr-Al composite oxide than by adding the Ce-Zr composite oxide and Al2O3 separately. However, in order to obtain such high heat resistance, it is necessary to make the Al2O3-converted content of Al 30% by mass or more based on the mass of the Ce-Zr-Al composite oxide so that a good composite oxide is formed. If the Al2O3-converted content of Al needs to be less than 30% by mass based on the mass of the Ce-Zr-Al composite oxide, a good composite oxide cannot be formed, so better performance can be obtained by adding the Ce-Zr composite oxide and Al2O3 separately.

[0015] The base material A of the upstream catalyst 1 and the base material B of the downstream catalyst 2 may be different base materials or the same base material (that is, it may have layer a1 and layer b1 on one base material).

[0016] In FIG. 1, the upstream catalyst 1 and the downstream catalyst 2 are depicted as being separated, but the upstream catalyst 1 and the downstream catalyst 2 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. Layers a1 and b1 are each a catalyst layer containing Rh, but the exhaust gas purification catalyst of the present invention may further have another catalyst layer. FIG. 2 shows 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 in FIG. 2 includes an upstream catalyst 11 and a downstream catalyst 12. The upstream catalyst 11 is provided on the upstream side in the exhaust gas flow direction X, and the downstream catalyst 12 is provided on the downstream side in the exhaust gas flow direction X. The upstream catalyst 11 is the same as the upstream catalyst 1 in FIG. 1 except that it has a layer a2 between the substrate A and the layer a1. The downstream catalyst 12 is the same as the upstream catalyst 2 in FIG. 1 except that it has 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] As the substrate A, a substrate used in a conventionally known exhaust gas purification catalyst can be used. For example, a substrate having a partition wall made of a porous material and an exhaust gas flow passage (space between partition walls) partitioned by the partition wall can be preferably used. As the shape of the substrate A, known substrates such as honeycomb, DPF, or GPF can be preferably used. Examples of the material of the partition wall of the substrate A include ceramics such as alumina (Al2O3), mullite (3Al2O3-2SiO2), cordierite (2MgO-2Al2O3-5SiO2), aluminum titanate (Al2TiO5), silicon carbide (SiC), and metal materials such as stainless steel.

[0019] [Layer a1] Layer a1 contains Rh and a Ce-Zr-Al-based composite oxide. Rh is a catalyst active component. The content of Rh in layer a1 is preferably 0.010% by mass or more, more preferably 0.050% by mass or more, and still more preferably 0.10% by mass or more with respect to the mass of layer a1. Also, the content of Rh in layer a1 is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 2% by mass or less with respect to the mass of layer a1. The content of each element including Rh in layer a1 can be determined by a conventional method such as scanning electron microscope - energy dispersive X - ray analysis method (SEM - EDX). Specifically, it is as follows. For a sample obtained from layer a1, elemental analysis is performed using a conventional method such as SEM - EDX to identify the types of constituent elements of the entire sample and determine the content ratio (mass%) of each identified metal element. For each of the 10 fields of view of the SEM, the content ratio (mass%) of each metal element is determined, and the average value of the content ratios (mass%) of each metal element in the 10 fields of view is taken as the content ratio (mass%) of each metal element in layer a1. When calculating the content ratio (mass%) by the above method, the content ratio is calculated assuming that Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au are in the metallic state and other metal elements are in the oxide state. The specific oxide forms for each element are as follows. Oxides of rare earth elements excluding Ce, Pr, and Tb are sesquioxides (M2O3, where M represents a rare earth element other than Ce, Pr, and Tb), the oxide of Ce is CeO2, the oxide of Pr is Pr6O 11 , the oxide of Tb is Tb4O7, the oxide of Al is Al2O3, the oxide of Zr is ZrO2, the oxide of Si is SiO2, the oxide of B is B2O3, the oxide of Mg is MgO, the oxide of Ca is CaO, the oxide of Sr is SrO, the oxide of Ba is BaO, the oxide of Fe is Fe3O4, the oxide of Mn is Mn3O4, the oxide of Cu is CuO, the oxide of Ti is TiO2, and the oxide of Zn is ZnO, and the oxide of Sn is SnO2.

[0020] It is preferable that 70 mass% or more of Rh contained in layer a1 is supported on a Ce-Zr-Al composite oxide. More preferably, 80 mass% or more of Rh contained in layer a1 is supported on a Ce-Zr-Al composite oxide. Even more preferably, 90 mass% or more of Rh contained in layer a1 is supported on a Ce-Zr-Al composite oxide. The proportion of Rh supported on the Ce-Zr-Al composite oxide can be adjusted, for example, by the content rate of the Ce-Zr-Al composite oxide contained in layer a1. The definition of support will be described later.

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

[0022] The "Ce-Zr-Al composite oxide" is a composite oxide containing Ce (cerium), Zr (zirconium), and Al (aluminum), wherein the content of Ce in terms of CeO2 in the composite oxide is 1 mass% or more and 94 mass% or less with respect to the mass of the composite oxide, the content of Zr in terms of ZrO2 in the composite oxide is 1 mass% or more and 94 mass% or less with respect to the mass of the composite oxide, and the content of Al in terms of Al2O3 in the composite oxide is 5 mass% or more and less than 98 mass% with respect to the mass of the composite oxide. The Ce-Zr-Al composite oxide is 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, it is as follows. First, a sample containing layer a1 is analyzed by SEM-EDX, and particles containing 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 result of the composition analysis is within the above range, it can be determined that the material is 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 "OSC material"). In addition, the Ce-Zr-Al composite oxide can function as a carrier component for supporting the above-described catalytic active components. Note that supporting the catalytic active components means a state in which they are physically or chemically adsorbed or retained on the outer surface or the inner surface of the pores. Specifically, when it is determined that the carrier component supports the catalytic active components, for example, in the elemental mapping obtained by analyzing the cross section of the exhaust gas purification catalyst with an EDS (energy dispersive spectrometer), it can be judged that the carrier component "supports" the catalytic active components by confirming that the carrier component and the catalytic active components exist in the same region.

[0024] The content of Al in terms of Al2O3 in the Ce-Zr-Al composite oxide contained in layer a1 is 30% by mass or more with respect to the mass of the Ce-Zr-Al composite oxide. By setting the content of Al in terms of Al2O3 to 30% by mass or more, a good composite oxide is formed, and higher heat resistance and higher exhaust gas purification performance can be obtained than when the Ce-Zr composite oxide and Al2O3 are added separately. The content of Al in terms of Al2O3 in the Ce-Zr-Al composite oxide contained in layer a1 is preferably 35% by mass or more, more preferably 40% by mass or more with respect to the mass of the Ce-Zr-Al composite oxide. Also, the content of Al in terms of Al2O3 in the Ce-Zr-Al composite oxide contained in layer a1 is preferably 60% by mass or less, more preferably 55% by mass or less, and still more preferably 50% by mass or less with respect to the mass of the Ce-Zr-Al composite oxide.

[0025] From the viewpoint of improving the oxygen storage capacity and heat resistance, the content of Ce in terms of CeO2 in the Ce-Zr-Al composite oxide contained in layer a1 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 still more preferably 5% by mass or more and 15% by mass or less with respect to the mass of the Ce-Zr-Al composite oxide.

[0026] From the viewpoint of improving oxygen storage capacity and heat resistance, the content of Zr in terms of ZrO2 in the Ce-Zr-Al composite oxide contained in layer a1 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 still more preferably 20% by mass or more and 50% by mass or less, based on the mass of the Ce-Zr-Al composite oxide.

[0027] The Ce-Zr-Al composite oxide contained in layer a1 may contain rare earth elements other than Ce and 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 kind or two or more kinds.

[0028] The content of the Ce-Zr-Al composite oxide contained in layer a1 is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 85% by mass or more, based on the mass of layer a1. Also, the content of the Ce-Zr-Al composite oxide contained in layer a1 is preferably 98% by mass or less, more preferably 97% by mass or less, and still more preferably 95% by mass or less, based on the mass of layer a1. The content of the Ce-Zr-Al composite oxide contained in layer a1 can be determined by a conventional method such as SEM-EDX. Specifically, it is as follows. (1) For the sample obtained from layer a1, elemental analysis is performed using a conventional method such as SEM-EDX to identify the types of constituent elements in the entire sample and to determine the content ratio (mass %) of each identified element. (2) For the sample obtained from layer a1, elemental mapping is performed using a conventional method such as SEM-EDX to identify the types of particles contained in the sample (for example, Ce-Zr-Al composite oxide particles and possibly other particles). (3) For each type of particle, a plurality of arbitrarily selected particles (for example, 50 particles) are subjected to elemental analysis by SEM-EDX to identify the types of constituent elements of the particles and to determine the content ratio (mass %) of each identified element. For each type of particle, the average value of the content ratio (mass %) of each element is determined. (4) By creating and solving an equation representing the relationship between the content ratio (mass %) of each element in the sample, the content ratio (mass %) of each element in each type of particle, and the content ratio (mass %) of each type of particle in the sample, the content ratio (mass %) of each type of particle in the sample is calculated, and this is taken as the content ratio (mass %) of each type of particle in layer a1.

[0029] Layer a1 may further contain components other than those described above. For example, layer a1 may contain a Ce-Zr composite oxide. The "Ce-Zr composite oxide" is a composite oxide containing Ce and Zr, wherein the content of Ce in terms of CeO2 in the composite oxide is 5 mass % or more and 95 mass % or less with respect to the mass of the composite oxide, the content of Zr in terms of ZrO2 in the composite oxide is 5 mass % or more and 95 mass % or less with respect to the mass of the composite oxide, and it does not contain Al, or, when it contains Al, the content of Al in terms of Al2O3 in the composite oxide is less than 5 mass % with respect to the mass of the composite oxide. The content ratio in terms of oxide of each element in the Ce-Zr composite oxide can be determined in the same manner as the content ratio in terms of oxide of each element in the Ce-Zr-Al composite oxide.

[0030] Layer a1 may contain, as a carrier, an inorganic oxide other than the oxygen storage component. Examples of the inorganic oxide other than the oxygen storage component include metal oxides other than the aforementioned oxygen storage component, such as rare earth oxides such as Al2O3, ZrO2, SiO2, TiO2, and La2O3, zeolites (aluminosilicates), oxide materials based on MgO, ZnO, SnO2, etc., and oxide materials obtained by compounding these materials with each other. In addition, phosphates and borates such as aluminum (Al), zirconium (Zr), silicon (Si), titanium (Ti), rare earth elements, magnesium (Mg), and zinc (Zn) are included. The inorganic oxide other than the oxygen storage component is preferably a porous body. Examples of the porous body include those having a BET specific surface area of 30 m 2 / g or more and 600 m 2 / g or less.

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

[0032] The mass of layer a1 per unit volume of 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 still more preferably 70 g / L or more and 100 g / L or less.

[0033] <Other layers, layer a2> In addition to the aforementioned substrate A and layer a1, the upstream catalyst may have other layers. Examples of the other layers include layers containing a catalytic active component other than Rh. As the catalytic active component other than Rh, conventionally known ones can be used, such as Pd, Pt, Au, Ag, Ir, Ru, Os, etc. Among them, Pd or Pt is preferable from the viewpoint of purifying HC, CO, and NOx in exhaust gas in a well-balanced manner.

[0034] In addition to the catalytic active component, it is preferable that the other layer further contains a carrier component that supports the catalytic active component in terms of efficiently exhibiting the exhaust gas purification performance by the catalytic active component. Examples of the carrier component include an oxygen storage component (OSC material) and inorganic oxides other than the oxygen storage component.

[0035] As the oxygen storage component, any metal oxide that can store oxygen and undergoes a valence change of the constituent elements under the operating conditions of the exhaust gas purification catalyst can be used without particular limitation. For example, Ce-Zr-Al-based composite oxides and Ce-Zr-based composite oxides are preferable. The oxygen storage component may contain rare earth elements other than Ce and alkaline earth metal elements. Examples of rare earth elements other than Ce include the same ones as those contained in the Ce-Zr-Al-based composite oxide contained in layer a1 described above. In addition to those described above, examples of the oxygen storage component also include oxides of elements such as manganese (Mn), iron (Fe), and copper (Cu) that are likely to undergo valence state changes under the operating conditions of the catalyst, and composite oxides containing these elements.

[0036] As the inorganic oxide other than the oxygen storage component that is the carrier component for supporting the catalytic active component, the same ones as those of layer a1 can be used.

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

[0038] Examples of the aspect where the upstream catalyst has other layers include, for example, an aspect having layer a2 between substrate A and layer a1. Layer a2 preferably contains Pd and a Ce-Zr composite oxide. The content of Pd in layer a2 is preferably 0.010% by mass or more, more preferably 0.050% by mass or more, and still more preferably 0.10% by mass or more with respect to the mass of layer a2. Also, the content of Pd in layer a2 is preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less with respect to the mass of layer a2. The content of Pd in layer a2 can be determined in the same manner as the content of Rh in layer a1. Although the Ce-Zr-Al composite oxide has the advantage of improved heat resistance as described above compared to the case where a Ce-Zr composite oxide containing the same amounts of Ce, Zr, and Al and Al2O3 are present separately, it has the disadvantage of reduced OSC ability. Also, Pd has the property that its catalytic activity is less likely to decrease even when the heat resistance of the oxygen storage component contained in the same layer is lower compared to Rh. Therefore, layer a2 does not contain a Ce-Zr-Al composite oxide, or when it contains a Ce-Zr-Al composite oxide, the content of the Ce-Zr composite oxide contained in layer a2 is preferably 50% by mass or more with respect to the total mass of the Ce-Zr composite oxide and the Ce-Zr-Al composite oxide contained in layer a2. When layer a2 contains a Ce-Zr-Al composite oxide, the content of the Ce-Zr composite oxide contained in layer a2 is more preferably 60% by mass or more with respect to the total mass of the Ce-Zr composite oxide and the Ce-Zr-Al composite oxide contained in layer a2. The contents of the Ce-Zr composite oxide and the Ce-Zr-Al composite oxide contained in layer a2 can be determined in the same manner as the content of the Ce-Zr-Al composite oxide contained in layer a1.

[0039] The mass of layer a2 per unit volume of 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 still 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> Regarding the substrate B, it is the same as the aforementioned substrate A.

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

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

[0044] In addition to Rh, the layer b1 may contain catalytic active components other than Rh. As catalytic active components other than Rh, conventionally known ones can be used, for example, Pd, Pt, Au, Ag, Ir, Ru, Os, etc.

[0045] The Ce-Zr composite oxide can function as an OSC material. Also, the Ce-Zr composite oxide can function as a carrier component for supporting the above-mentioned catalytic active components.

[0046] Since Ce has the property of stabilizing the oxidation state of Rh, the content of Ce in terms of CeO2 in the Ce-Zr composite oxide contained in layer b1 is preferably 35% by mass or less, more preferably 25% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0047] The content of Zr in terms of ZrO2 in the Ce-Zr composite oxide contained in layer b1 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, still more preferably 20% by mass or more and 80% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0048] The Ce-Zr 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 the rare earth elements other than Ce include those described above in the description of layer a1.

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

[0050] As described above, since Al2O3 has the property of stabilizing the oxidation state of Rh, from the viewpoint of improving the exhaust gas purification performance, layer b1 does not contain Al, or when it contains Al, the content of Al in terms of Al2O3 contained in layer b1 is 30% by mass or less based on the mass of layer b1. When layer b1 contains Al, the content of Al in terms of Al2O3 in layer b1 is preferably 25% by mass or less based on the mass of layer b1. On the other hand, although it is lower than the upstream catalyst, heat resistance is also required for the downstream catalyst. Therefore, the content of Al in terms of Al2O3 in layer b1 is preferably 10% by mass or more, more preferably 15% by mass or more based on the mass of layer b1. The content of Al in terms of Al2O3 in layer b1 can be determined in the same manner as the content of Rh.

[0051] Layer b1 may further contain components other than those described above. Layer b1 may contain an Al-based oxide as a carrier. The Al-based oxide may contain La. However, since La has the property of stabilizing the oxidation state of Rh, the Al-based oxide preferably does not contain La, or when it contains La, the content of La in terms of La2O3 in the Al-based oxide is preferably 10% by mass or less based on the mass of the Al-based oxide. When layer b1 contains an Al-based oxide and the Al-based oxide contains La, the content of La in terms of La2O3 in the Al-based oxide is more preferably 8% by mass or less, still more preferably 7% by mass or less, still more preferably 5% by mass or less, and still more preferably 3% by mass or less based on the mass of the Al-based oxide. Also, the content of La in terms of La2O3 may be 0.5% by mass or more based on the mass of the Al-based oxide. The content rate of each element in terms of oxide in the Al-based oxide can be determined in the same manner as the content rate of each element in terms of oxide in the Ce-Zr-Al-based composite oxide. Layer b1 may contain an inorganic oxide other than the Al-based oxide as a carrier. Also, layer b may contain an alkaline earth metal compound from the viewpoint of suppressing the decrease in catalytic activity due to phosphorus poisoning and heat resistance. As the inorganic oxide other than the Al-based oxide and the alkaline earth metal compound, the same ones as those in layer a1 can be used. Layer b1 may contain a binder. The binder can be selected, for example, from alumina, zirconia, titania, silica, ceria, etc. When the binder contained in layer b1 contains Al element, the content of Al in terms of Al2O3 in layer b1, including the Al derived from the binder, needs to be 30% by mass or less based on the mass of layer b1.

[0052] The mass of layer b1 per unit volume of 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 still more preferably 70 g / L or more and 100 g / L or less.

[0053] <Other layers, layer b2> In addition to the aforementioned substrate B and layer b1, the downstream catalyst may have other layers. Examples of other layers include layers containing catalytically active components other than Rh. As catalytically active components other than Rh, conventionally known ones can be used, such as Pd, Pt, Au, Ag, Ir, Ru, Os, etc., and Pd or Pt is preferred. Examples of other layers that the downstream catalyst may have include the same ones as those of the other layers that the aforementioned upstream catalyst may have.

[0054] An example of an embodiment where the downstream catalyst has other layers is, for example, an embodiment having layer b2 between substrate B and layer b1. Layer b2 may contain, for example, Pt and a Ce-Zr-based composite oxide. Layer b2 does not contain a Ce-Zr-Al-based composite oxide, or when it contains a Ce-Zr-Al-based composite oxide, the content of the Ce-Zr-based composite oxide in layer b2 is preferably 50% by mass or more based on the total mass of the Ce-Zr-based composite oxide and the Ce-Zr-Al-based composite oxide contained in layer b2. When layer b2 contains a Ce-Zr-Al-based composite oxide, the content of the Ce-Zr-based composite oxide in layer b2 is more preferably 60% by mass or more based on the total mass of the Ce-Zr-based composite oxide and the Ce-Zr-Al-based composite oxide contained in layer b2. Layer b2 may contain an inorganic oxide other than the oxygen storage component as a carrier. Further, layer b2 may contain an alkaline earth metal compound from the viewpoint of suppressing the decrease in catalytic activity due to phosphorus poisoning and heat resistance. As the inorganic oxide and alkaline earth metal compound other than the oxygen storage component, the same ones as those in layer a1 can be used. Layer b2 may contain a binder. The binder can be selected from, for example, alumina, zirconia, titania, silica, ceria, etc.

[0055] The mass of layer b2 per unit volume of 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 still more preferably 130 g / L or more and 160 g / L or less.

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

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

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

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

[0060] When forming the layer b2, a source of noble metal element (for example, nitrate, ammine complex salt, acetate, chloride, etc. of Pd, Pt, etc.) and optionally other components (for example, Ce-Zr 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 on the substrate B, dried, and fired to form it.

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

Example

[0062] Next, 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 composite oxide) with the following composition was prepared. Content of Ce in terms of CeO2: 40.0% by mass, content of Zr in terms of ZrO2: 50.0% by mass, content of oxides of rare earth elements other than Ce in terms of oxides: 10.0% by mass

[0064] To a blending container, an aqueous palladium nitrate solution, OSC material 1, La2O3-modified alumina (La2O3 modification amount: 1.0% by mass), a binder, and water were added, mixed, and stirred to prepare a slurry for forming layer a2. The amounts of each component in the slurry for forming layer a2 were adjusted such that, based on the mass of layer a2 after firing (100% by mass), Pd was 4.0% by mass in terms of metal, OSC material 1 was 40.0% by mass, La2O3-modified alumina was 50.0% by mass, and the binder was 6.0% by mass. Note that the binder does not contain Al element.

[0065] (2) Formation of the lower layer (layer a2) of the upstream catalyst As a flow-through type substrate, a flow-through type substrate having cells extending in the axial direction partitioned by partitions with a thickness of 50 to 70 μm and having a density of 600 cells per square inch on a plane orthogonal to the axial direction and a volume of 1.0 L was prepared.

[0066] The flow-through type substrate was immersed in the slurry for forming layer a2 to obtain a flow-through type substrate coated with the slurry for forming layer a2. Next, the flow-through type substrate coated with the slurry for forming layer a2 was dried at 150 °C for 0.5 hour and then fired 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 type substrate where layer a2 was formed was 100 g / L.

[0067] (3) Preparation of a slurry for forming the upper layer (layer a1) of the upstream catalyst OSC material 2 (Ce-Zr-Al-based composite oxide) having the following composition was prepared. Content of Ce in terms of CeO2: 10.0% by mass, content of Zr in terms of ZrO2: 35.0% by mass, content of Al in terms of Al2O3: 45.0% by mass, content of oxides of rare earth elements other than Ce in terms of oxides: 10.0% by mass

[0068] Rhodium nitrate aqueous solution, OSC material 2, a binder, and water were added to a mixing container, mixed, and stirred to prepare a slurry for forming layer a1. The amounts of the respective components in the slurry for forming layer a1 were adjusted such that, based on the mass of layer a1 after firing (100% by mass), Rh was 1.0% by mass in terms of metal, OSC material 2 was 90.0% by mass, and the binder was 9.0% by mass. Note that the binder does not contain Al element.

[0069] (4) Formation of the upper layer (layer a1) of the upstream catalyst The flow-through type substrate on which layer a2 was formed was immersed in the slurry for forming layer a1 to obtain a flow-through type substrate coated with the slurry for forming layer a1. Next, the flow-through type substrate coated with the slurry for forming layer a1 was dried at 150°C for 0.5 hour and then fired 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 type substrate where layer a1 was formed was 80 g / L.

[0070] As described above, an upstream catalyst including layer a2 formed on the flow-through type substrate and layer a1 formed on layer a2 was manufactured.

[0071] (5) Preparation of a slurry for forming the lower layer (layer b2) of the downstream catalyst The aforementioned OSC material 1 was prepared.

[0072] Platinum nitrate aqueous solution, OSC material 1, La2O3-modified alumina (La2O3 modification amount: 1.0% by mass), a binder, and water were added to a mixing container, mixed, and stirred to prepare a slurry for forming layer b2. The amounts of the respective components in the slurry for forming layer b2 were adjusted such that, based on the mass of layer b2 after firing (100% by mass), Pt was 1.0% by mass in terms of metal, OSC material 1 was 60.0% by mass, La2O3-modified alumina was 30.0% by mass, and the binder was 9.0% by mass. Note that the binder does not contain Al element.

[0073] (6) Formation of the lower layer (layer b2) of the downstream catalyst As a flow-through type substrate, a flow-through type substrate having cells extending in the axial direction partitioned by partition walls with a thickness of 50 to 70 μm and having a density of 600 cells per square inch on a plane orthogonal to the axial direction and a volume of 1.0 L was prepared.

[0074] The flow-through type substrate was immersed in the slurry for forming layer b2 to obtain a flow-through type substrate coated with the slurry for forming layer b2. Next, the flow-through type substrate coated with the slurry for forming layer b2 was dried at 150 °C for 0.5 hour and then fired 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 type substrate where layer b2 was formed was 140 g / L.

[0075] (7) Preparation of slurry for forming the upper layer (layer b1) of the downstream catalyst An OSC material 3 (Ce-Zr based composite oxide) having the following composition was prepared. Content of Ce in terms of CeO2: 20.0 mass%, content of Zr in terms of ZrO2: 70.0 mass%, content of oxides of rare earth elements other than Ce in terms of oxides: 10.0 mass%

[0076] An aqueous rhodium nitrate solution, OSC material 3, La2O3-modified alumina (La2O3 modification amount: 1.0 mass%), a binder, and water were added to a mixing container, mixed and stirred to prepare a slurry for forming layer b1. The amounts of each component in the slurry for forming layer b1 were adjusted so that, based on the mass of layer b1 after firing (100 mass%), Rh was 0.2 mass% in terms of metal, OSC material 3 was 70.0 mass%, La2O3-modified alumina was 20.0 mass%, and the binder was 9.8 mass%. Note that the binder does not contain Al element.

[0077] (8) Formation of the upper layer (layer b1) of the downstream catalyst The flow-through type substrate on which layer b2 was formed was immersed in the slurry for forming layer b1 to obtain a flow-through type substrate coated with the slurry for forming layer b1. Next, the flow-through type substrate coated with the slurry for forming layer b1 was dried at 150°C for 0.5 hour and then fired 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 type substrate where layer b1 was formed was 80 g / L.

[0078] As described above, a downstream catalyst including layer b2 formed on the flow-through type substrate and layer b1 formed on layer b2 was manufactured.

[0079] As described above, an exhaust gas purification catalyst including an upstream catalyst and a downstream catalyst was manufactured.

[0080] [Example 2] In the production of the downstream catalyst, an exhaust gas purification catalyst was manufactured in the same manner as in Example 1, except that the La2O3 modification amount of La2O3-modified alumina in the slurry for forming layer b1 was 4.0% by mass.

[0081] [Example 3] In the production of the downstream catalyst, an exhaust gas purification catalyst was manufactured in the same manner as in Example 1, except that the La2O3 modification amount of La2O3-modified alumina in the slurry for forming layer b1 was 6.0% by mass.

[0082] [Example 4] In the production of the downstream catalyst, an exhaust gas purification catalyst was manufactured in the same manner as in Example 1, except that the La2O3 modification amount of La2O3-modified alumina in the slurry for forming layer b1 was 9.0% by mass.

[0083] [Example 5] In the production of the downstream catalyst, an exhaust gas purification catalyst was manufactured in the same manner as in Example 1, except that OSC material 4 (Ce-Zr composite oxide) having the following composition was used instead of OSC material 3 used when preparing the slurry for forming layer b1. Content of Ce in terms of CeO₂: 30.0 mass%, content of Zr in terms of ZrO₂: 60.0 mass%, content of oxides of rare earth elements other than Ce in terms of oxides: 10.0 mass%

[0084] [Example 6] An OSC material 5 (Ce-Zr-Al composite oxide) with the following composition was prepared. Content of Ce in terms of CeO₂: 20.0 mass%, content of Zr in terms of ZrO₂: 30.0 mass%, content of Al in terms of Al₂O₃: 40.0 mass%, content of oxides of rare earth elements other than Ce in terms of oxides: 10.0 mass%

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

[0086] [Example 7] The aforementioned OSC material 2 and the aforementioned OSC material 3 were prepared.

[0087] In the production of the upstream catalyst, except that the amounts of each component 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 terms of metal, OSC material 2 was 64.0 mass%, OSC material 3 was 26.0 mass%, and the binder was 9.0 mass%, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0088] [Example 8] In the production of the downstream catalyst, except that the amounts of each component in the slurry for forming layer b1 were adjusted so that, based on the mass of layer b1 after firing (100 mass%), Rh was 0.2 mass% in terms of metal, OSC material 3 was 60.0 mass%, La₂O₃-modified alumina was 30.0 mass%, and the binder was 9.8 mass%, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0089] [Example 9] In the production of the downstream catalyst, when preparing the slurry for forming layer b1, without using La2O3-modified alumina, and except that the amounts of each component in the slurry for forming layer b1 were adjusted so that, based on the mass of layer b1 after firing (100% by mass), Rh was 0.2% by mass in terms of metal, OSC material 3 was 90.0% by mass, and the binder was 9.8% by mass, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0090] 〔Comparative Example 1〕 The above-described OSC material 3 was prepared.

[0091] In the production of the upstream catalyst, when preparing the slurry for forming layer a1, instead of the OSC material 2 used, OSC material 3 and La2O3-modified alumina (La2O3 modification amount: 1.0% by mass) were used, and except that the amounts of each component in the slurry for forming layer a1 were adjusted so that, based on the mass of layer a1 after firing (100% by mass), Rh was 1.0% by mass in terms of metal, OSC material 3 was 45.0% by mass, La2O3-modified alumina was 45.0% by mass, and the binder was 9.0% by mass, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0092] 〔Comparative Example 2〕 The above-described OSC material 2 was prepared.

[0093] In the production of the downstream catalyst, when preparing the slurry for forming layer b1, instead of the OSC material 3 and La2O3-modified alumina (La2O3 modification amount: 1.0% by mass) used, OSC material 2 was used, and except that the amounts of each component in the slurry for forming layer b1 were adjusted so that, based on the mass of layer b1 after firing (100% by mass), Rh was 0.2% by mass in terms of metal, OSC material 2 was 90.0% by mass, and the binder was 9.8% by mass, an exhaust gas purification catalyst was produced in the same manner as in Comparative Example 1.

[0094] 〔Comparative Example 3〕 In the production of the upstream catalyst, when preparing the slurry for forming layer a1, further using OSC material 3, except that the amounts of each component in the slurry for forming layer a1 were adjusted so that, based on the mass of layer a1 after firing (100% by mass), Rh was 1.0% by mass in terms of metal, OSC material 2 was 46.0% by mass, OSC material 3 was 44.0% by mass, and the binder was 9.0% by mass, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0095] [Comparative Example 4] In the production of the upstream catalyst, when preparing the slurry for forming layer a1, further using OSC material 3, except that the amounts of each component in the slurry for forming layer a1 were adjusted so that, based on the mass of layer a1 after firing (100% by mass), Rh was 1.0% by mass in terms of metal, OSC material 2 was 27.0% by mass, OSC material 3 was 63.0% by mass, and the binder was 9.0% by mass, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0096] [Comparative Example 5] In the production of the downstream catalyst, except that the amounts of each component in the slurry for forming layer b1 were adjusted so that, based on the mass of layer b1 after firing (100% by mass), Rh was 0.2% by mass in terms of metal, OSC material 3 was 48.0% by mass, La2O3-modified alumina was 42.0% by mass, and the binder was 9.8% by mass, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0097] [Comparative Example 6] In the production of the downstream catalyst, except that the amounts of each component in the slurry for forming layer b1 were adjusted so that, based on the mass of layer b1 after firing (100% by mass), Rh was 0.2% by mass in terms of metal, OSC material 3 was 38.0% by mass, La2O3-modified alumina was 52.0% by mass, and the binder was 9.8% by mass, an exhaust gas purification catalyst was produced in the same manner as in Example 1.

[0098] [Comparative Example 7] The aforementioned OSC material 5 was prepared.

[0099] In the production of the upstream catalyst, when preparing the slurry for forming layer a2, instead of using OSC material 1 and La2O3-modified alumina (La2O3 modification amount: 1.0% by mass) used, OSC material 5 was used. Except that the amounts of each component in the slurry for forming layer a2 were adjusted so that, based on the mass of layer a2 after firing (100% by mass), Pd was 4.0% by mass in terms of metal, OSC material 5 was 90.0% by mass, and the binder was 6.0% by mass, an exhaust gas purification catalyst was produced in the same manner as in Comparative Example 1.

[0100] (Evaluation of durability) For the exhaust gas purification catalysts of Examples 1 to 9 and Comparative Examples 1 to 7, the following durability conditions were imposed as a deterioration treatment assuming a driving distance of 100,000 to 200,000 km. <Durability conditions> · Durability engine: Passenger car NA 2L 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 the engine, and a durability test was conducted under the above conditions. After the durability test, the exhaust gas purification catalyst was installed in a vehicle (a passenger car equipped with a 1.5L direct injection turbo engine), and the vehicle was driven according to the driving conditions of the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). During the low-temperature operation from the start of driving to 589 seconds, the medium-speed operation from 589 seconds to 1022 seconds after the start of driving, the high-speed operation from 1022 seconds to 1477 seconds after the start of driving, and the ultra-high-speed operation from 1477 seconds to 1800 seconds after the start of driving, the emissions of non-methane hydrocarbons (NMHC) and nitrogen oxides (NOx) in the exhaust gas passing through the exhaust gas purification catalyst were measured, and the total emissions of NMHC and NOx per unit driving distance were determined. As the gasoline, fuel for certification tests was used, and as the exhaust gas measuring device, an exhaust gas measuring device manufactured by Horiba, Ltd. was used. The results are shown in Table 1. In Table 1, the total emissions of NMHC and NOx are shown in the column of "Emissions (relative value)" as relative values when the value of Example 1 is taken as 1.00. In Table 1, "CZA" represents a Ce-Zr-Al composite oxide, and "CZ" represents a Ce-Zr composite oxide.

[0102]

Table 1

[0103] From Table 1, it can be seen that the exhaust gas purification catalyst of the example can reduce the emission amount after the durability test and has excellent durability.

Industrial Applicability

[0104] According to the present invention, an exhaust gas purification catalyst with excellent durability can be provided.

[0105] Although the present invention has been described in detail with reference to specific embodiments, it is obvious 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 (Japanese Patent Application No. 2023-139973) filed on August 30, 2023, the content of which is incorporated herein by reference.

Explanation of Reference Numerals

[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 on the upstream side in the flow direction of the exhaust gas and a downstream catalyst provided on the downstream side in the flow direction of the 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 substrate A and the substrate B are separate substrates, the layer a1 contains Rh and a Ce-Zr-Al composite oxide, the layer b1 contains Rh and a Ce-Zr composite oxide, Al in the Ce-Zr-Al composite oxide contained in the layer a1 ２ O ３ The content in terms of conversion is 30% by mass or more based on the mass of the Ce-Zr-Al composite oxide, the content of the Ce-Zr-Al composite oxide contained in the layer a1 is 50% by mass or more based on the mass of the layer a1, The layer b1 does not contain Al, or when it contains Al, the content of Al converted into Al ２ O ３ in the layer b1 is 30% by mass or less based on the mass of the layer b1. ２ O ３ ​ an exhaust gas purification catalyst.

2. An exhaust gas purification catalyst comprising an upstream catalyst provided on the upstream side in the flow direction of the exhaust gas and a downstream catalyst provided on the downstream side in the flow direction of the 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 substrate A and the substrate B are the same substrate, the layer a1 contains Rh and a Ce-Zr-Al composite oxide, the layer b1 contains Rh and a Ce-Zr composite oxide, the content of Al in terms of Al2O₃ of the Ce-Zr-Al composite oxide contained in the layer a1 is 30% by mass or more based on the mass of the Ce-Zr-Al composite oxide, the content of the Ce-Zr-Al composite oxide contained in the layer a1 is 50% by mass or more based on the mass of the layer a1, the layer b1 does not contain Al, or when it contains Al, the content of Al in terms of Al2O₃ of the Al contained in the layer b1 is 30% by mass or less based on the mass of the layer b1, an exhaust gas purification catalyst.

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

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

5. The CeO of Ce in the Ce-Zr-Al composite oxide contained in the layer a1 ２ The content in terms of conversion is 2% by mass or more and 40% by mass or less with respect to the mass of the Ce-Zr-Al composite oxide. The exhaust gas purification catalyst according to claim 1 or 2.

6. The content of Zr in terms of ZrO in the Ce-Zr-Al composite oxide contained in the layer a1 ２ is 10% by mass or more and 60% by mass or less with respect to the mass of the Ce-Zr-Al composite oxide. The exhaust gas purification catalyst according to claim 1 or 2.

7. Al in the Ce-Zr-Al composite oxide contained in the layer a1 ２ O ３ The content of Al in terms of Al is 60% by mass or less based on the mass of the Ce-Zr-Al composite oxide. The exhaust gas purification catalyst according to claim 1 or 2.

8. 60% by mass or more of the Rh contained in the layer b1 is supported on the Ce-Zr composite oxide, the exhaust gas purification catalyst according to Claim 1 or 2.

9. a layer a2 is provided between the substrate A and the layer a1, the layer a2 contains Pd and a Ce-Zr composite oxide, The exhaust gas purification catalyst according to claim 1 or 2, wherein the layer a2 does not contain a Ce-Zr-Al composite oxide, or when it contains a Ce-Zr-Al composite oxide, the content of the Ce-Zr composite oxide contained in the layer a2 is 50% by mass or more based on the total mass of the Ce-Zr composite oxide and the Ce-Zr-Al composite oxide contained in the layer a2.

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