Exhaust gas purification catalyst

Abstract

An exhaust gas purification catalyst provided with 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, the upstream catalyst having a substrate A and a layer a1 provided on the substrate A, and the downstream catalyst having 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-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 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% by mass or more with respect to the mass of the layer a1, and the layer b1 does not contain Al, or the layer b1 contains Rh and a Ce-Zr-Al-based composite oxide in terms of Al2O3. When Al is contained, the content of Al contained in the layer b1 in terms of Al2O3 is 30% by mass or less with respect to the mass of the layer b1.

Description

Technical Field

[0001] This invention relates to catalysts for purifying waste gas. Background Technology

[0002] The exhaust gases (also known as waste gases) from internal combustion engines in automobiles, motorcycles, and other vehicles contain harmful components such as HC (hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides). Traditionally, three-way catalysts have been used to purify and neutralize these harmful components. Three-way catalysts using precious metals such as Pt (platinum), Pd (palladium), and Rh (rhodium) are known. Pt and Pd primarily function to oxidize and purify HC and CO, while Rh primarily functions to reduce and purify NOx. In recent years, due to stricter emissions regulations and increased environmental awareness, attempts have been made to improve the waste gas purification performance of the aforementioned precious metal catalysts.

[0003] Patent Document 1 describes a catalyst for waste gas purification, which consists of a starting catalyst and a substrate catalyst positioned further back than the starting catalyst relative to the flow direction of the waste gas, forming a dual catalyst. The average thickness and porosity of the catalyst coating layer on the substrate catalyst are within a specific range. Furthermore, Patent Document 1 describes a waste gas purification catalyst in which the catalyst coating layers of both the starting catalyst and the substrate catalyst comprise Rh, a cerium dioxide-zirconia composite oxide material, and Al2O3.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-185495 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] However, in recent years, there has been a growing demand for catalysts with superior exhaust gas purification performance. In particular, due to the high temperature of the exhaust gas upstream in the flow direction, catalysts with even better durability are required.

[0009] Therefore, the purpose of this invention is to provide a waste gas purification catalyst with excellent durability.

[0010] Solution for solving the problem

[0011] That is, the main idea of ​​this invention is as follows. [1]

[0013] An exhaust gas purification catalyst comprises an upstream catalyst disposed on the upstream side of the exhaust gas flow direction and a downstream catalyst disposed on the downstream side of the exhaust gas flow direction.

[0014] The upstream catalyst has a substrate A and a layer a1 disposed on the substrate A.

[0015] The downstream catalyst has a substrate B and a layer b1 disposed on the substrate B.

[0016] The layer a1 contains Rh and Ce-Zr-Al composite oxides.

[0017] The layer b1 comprises Rh and Ce-Zr composite oxides.

[0018] The content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is more than 30% by mass relative to the mass of the Ce-Zr-Al composite oxide.

[0019] The content of the Ce-Zr-Al composite oxide in layer a1 is 50% by mass or more relative to the mass of layer a1.

[0020] The layer b1 does not contain Al, or, if it does contain Al, the Al2O3 content of the Al contained in the layer b1 is less than 30% by mass relative to the mass of the layer b1. [2]

[0022] According to the waste gas purification catalyst described in [1], the Ce content of Ce in the Ce-Zr composite oxide contained in layer b1, calculated as CeO2, is less than 25% by mass relative to the mass of the Ce-Zr composite oxide. [3]

[0024] According to the waste gas purification catalyst described in [1] or [2], wherein layer b1 comprises Al-based oxides,

[0025] The Al-based oxide does not contain La, or, if it does contain La, the La content in the Al-based oxide, calculated as La2O3, is less than 7% by mass relative to the mass of the Al-based oxide. [4]

[0027] According to any one of [1] to [3], the content of Ce in the Ce-Zr-Al composite oxide contained in layer a1, calculated as CeO2, is more than 2% by mass and less than 40% by mass relative to the mass of the Ce-Zr-Al composite oxide. [5]

[0029] According to any one of [1] to [4], the content of Zr in the Ce-Zr-Al composite oxide contained in layer a1, calculated as ZrO2, is 10% by mass or more and 70% by mass or less relative to the mass of the Ce-Zr-Al composite oxide. [6]

[0031] According to any one of [1] to [5], the content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is less than 60% by mass relative to the mass of the Ce-Zr-Al composite oxide. [7]

[0033] According to any one of [1] to [6], the waste gas purification catalyst wherein more than 60% by mass of Rh contained in layer b1 is loaded in the Ce-Zr composite oxide. [8]

[0035] According to any one of [1] to [7], the waste gas purification catalyst is provided with layer a2 between the substrate A and layer a1.

[0036] The layer a2 contains Pd and Ce-Zr composite oxides.

[0037] The layer a2 does not contain Ce-Zr-Al composite oxides, or, if it does contain Ce-Zr-Al composite oxides, the content of the Ce-Zr composite oxides in the layer a2 is 50% by mass or more relative to the total mass of the Ce-Zr composite oxides and the Ce-Zr-Al composite oxides in the layer a2.

[0038] The effects of the invention

[0039] According to the present invention, a waste gas purification catalyst with excellent durability can be provided. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0041] Figure 2 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention. Detailed Implementation

[0042] The following is a detailed description of the methods for carrying out the present invention.

[0043] The exhaust gas purification catalyst of the present invention comprises an upstream catalyst disposed on the upstream side of the exhaust gas flow direction and a downstream catalyst disposed on the downstream side of the exhaust gas flow direction.

[0044] The aforementioned upstream catalyst has a substrate A and a layer a1 disposed on the aforementioned substrate A.

[0045] The aforementioned downstream catalyst has a substrate B and a layer b1 disposed on the aforementioned substrate B.

[0046] The aforementioned layer a1 contains Rh and Ce-Zr-Al composite oxides.

[0047] The aforementioned layer b1 comprises a Rh and Ce-Zr composite oxide.

[0048] The content of Al in the aforementioned Ce-Zr-Al composite oxide contained in the aforementioned layer a1, calculated as Al2O3, is more than 30% by mass relative to the mass of the aforementioned Ce-Zr-Al composite oxide.

[0049] The content of the aforementioned Ce-Zr-Al composite oxide in the aforementioned layer a1 is 50% by mass or more relative to the mass of the aforementioned layer a1.

[0050] The aforementioned layer b1 does not contain Al, or, if it does contain Al, the Al2O3 content of the Al contained in the aforementioned layer b1 is less than 30% by mass relative to the mass of the aforementioned layer b1.

[0051] A schematic diagram of one embodiment of the waste gas purification catalyst of the present invention is shown in the figure. Figure 1 .

[0052] Figure 1 The exhaust gas purification catalyst 10 includes an upstream catalyst 1 and a downstream catalyst 2. The upstream catalyst 1 is disposed upstream of the exhaust gas flow direction X, and the downstream catalyst 2 is disposed downstream of the exhaust gas flow direction X.

[0053] The upstream catalyst 1 has a substrate A and a layer a1 disposed on the substrate A. The layer a1 contains Rh and Ce-Zr-Al composite oxides.

[0054] The content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is more than 30% by mass relative to the mass of the Ce-Zr-Al composite oxide.

[0055] The content of Ce-Zr-Al composite oxides in layer a1 is more than 50% by mass relative to the mass of layer a1.

[0056] The downstream catalyst 2 has a substrate B and a layer b1 disposed on the substrate B. The layer b1 contains Rh and Ce-Zr composite oxides.

[0057] Layer b1 contains no Al, or, if it contains Al, the Al2O3 content of Al in layer b1 is less than 30% by mass relative to the mass of layer b1.

[0058] The exhaust gas purification catalyst of the present invention exhibits excellent durability through the above-described configuration. The mechanism by which the above-described effects are achieved is not fully understood, but the inventors presume the following. However, the present invention is not limited by the following presumed mechanism.

[0059] If the concentration of oxidizing components such as O2 and NOx in the exhaust gas reaches a certain level, Rh will become oxidized and deactivated. Deactivated Rh will be reduced and its activity restored when the concentration of reducing components such as HC and CO reaches a certain level.

[0060] Al2O3 has excellent heat resistance, which improves the heat resistance of catalysts used for waste gas purification. On the other hand, Al2O3 has the property of stabilizing the oxidation state of Rh.

[0061] The temperature of the exhaust gas on the upstream side is high, thus requiring higher heat resistance from the upstream catalyst. On the other hand, since the exhaust gas from the internal combustion engine arrives directly, the concentration of reducing components such as HC and CO varies more significantly than on the downstream side, easily reaching a high concentration sufficient to reduce Rh, which has been stabilized by Al2O3 in its oxidized state.

[0062] The temperature of the exhaust gas is lower downstream than upstream, so the heat resistance requirement for the downstream catalyst is lower than that for the upstream catalyst. On the other hand, the exhaust gas from the internal combustion engine is partially purified by the upstream catalyst before reaching the downstream side, so the concentration of reducing components such as HC and CO varies less than that upstream, making it difficult to reach a high concentration that would reduce Rh, which has been stabilized by Al2O3, to the extent that the oxidized state is reduced.

[0063] Based on the above, it is believed that on the upstream side, where the improvement of heat resistance is more important than the reduction of Rh inactivation, the content of Al2O3 should be increased, and on the downstream side, where the reduction of Rh inactivation is more important than the improvement of heat resistance, the content of Al2O3 should be decreased.

[0064] However, as described in the upstream catalyst layer in the aforementioned Patent Document 1, it is known that when the catalyst contains Ce-Zr composite oxide and Al2O3 respectively, sufficient exhaust gas purification performance cannot be obtained after the catalyst is exposed to a high-temperature environment.

[0065] In contrast, in this invention, instead of adding Ce-Zr composite oxides and Al2O3 separately to the catalyst layer of the upstream catalyst, a Ce-Zr-Al composite oxide is prepared. This ensures sufficient exhaust gas purification performance even after exposure to high-temperature environments. This is because, when adding the same amounts of Ce, Zr, and Al to the catalyst layer, adding the Ce-Zr-Al composite oxide results in higher heat resistance compared to adding Ce-Zr composite oxides and Al2O3 separately. However, to achieve such high heat resistance, the Al2O3 content of Al relative to the mass of the Ce-Zr-Al composite oxide needs to be at least 30% by mass to form a good composite oxide. If the Al2O3 content of Al relative to the mass of the Ce-Zr-Al composite oxide is less than 30% by mass, a good composite oxide cannot be formed. Therefore, adding Ce-Zr composite oxides and Al2O3 separately yields good performance.

[0066] The substrate A of the upstream catalyst 1 and the substrate B of the downstream catalyst 2 can be different substrates or the same substrate (i.e., they can have layers a1 and b1 on one substrate).

[0067] exist Figure 1 In the diagram, upstream catalyst 1 and downstream catalyst 2 are depicted separately, but upstream catalyst 1 and downstream catalyst 2 can also be in contact.

[0068] Upstream catalyst 1 and downstream catalyst 2 can be housed in the same housing or in different housings.

[0069] Layer a1 and layer b1 are catalyst layers containing Rh, but the exhaust gas purification catalyst of the present invention may further have other catalyst layers. Figure 2 A schematic diagram showing one embodiment of the exhaust gas purification catalyst of the present invention having another catalyst layer is shown. Figure 2 The exhaust gas purification catalyst 20 includes an upstream catalyst 11 and a downstream catalyst 12. The upstream catalyst 11 is disposed upstream of the exhaust gas flow direction X, and the downstream catalyst 12 is disposed downstream of the exhaust gas flow direction X. The upstream catalyst 11 has a layer a2 between the substrate A and layer a1, except that it has a layer a2 between the substrate A and layer a1. Figure 1 The upstream catalyst 1 is the same. The downstream catalyst 12 is the same as the upstream catalyst 1 except that it has a layer b2 between the substrate B and layer b1. Figure 1 The upstream catalyst 2 is the same.

[0070] Upstream catalysts

[0071] The upstream catalyst has a substrate A and a layer a1 disposed on the substrate A.

[0072] <Substrate A>

[0073] Substrate A can be any substrate conventionally used in catalysts for exhaust gas purification. For example, a substrate having a partition wall made of porous material and exhaust gas flow paths (spaces between the partition walls) divided by the partition wall is preferred. As for the shape of substrate A, known substrates such as honeycomb, DPF, or GPF are preferred. Furthermore, the materials used for the partition walls of substrate A include, for example, ceramics such as alumina (Al2O3), mullite (3Al2O3-2SiO2), cordierite (2MgO-2Al2O3-5SiO2), aluminum titanate (Al2TiO5), silicon carbide (SiC), and stainless steel.

[0074] <Layer a1>

[0075] Layer a1 contains Rh and Ce-Zr-Al composite oxides.

[0076] Rh is the catalytically active component.

[0077] The Rh content in layer a1 is preferably 0.010% by mass or more, more preferably 0.050% by mass or more, and even more preferably 0.10% by mass or more, relative to the mass of layer a1. Furthermore, the Rh content in layer a1 is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, relative to the mass of layer a1.

[0078] The content of each element, represented by Rh, in layer a1 can be determined using conventional methods such as scanning electron microscopy-energy dispersive X-ray diffraction (SEM-EDX). Specifically, as described below: For the sample obtained from layer a1, elemental analysis is performed using conventional methods such as SEM-EDX to determine the types of constituent elements of the sample as a whole and to calculate the content (mass %) of each metal element. The content (mass %) of each metal element is calculated for each of the 10 fields of view of the SEM, and the average content (mass %) of each metal element in the 10 fields of view is taken as the content (mass %) of each metal element in layer a1.

[0079] It should be noted that when calculating the content (mass %) using the above method, for Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au, the content is calculated in the metallic state; for other metallic elements, the content is calculated in the oxide state. The specific oxide forms of each element are as follows. The oxides of rare earth elements other than 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, and the oxide of Pr is Pr₆O. 11The oxides of Tb are Tb4O7, Al is Al2O3, Zr is ZrO2, Si is SiO2, B is B2O3, Mg is MgO, Ca is CaO, Sr is SrO, Ba is BaO, Fe is Fe3O4, Mn is Mn3O4, Cu is CuO, Ti is TiO2, Zn is ZnO, and Sn is SnO2.

[0080] Preferably, at least 70% by mass of Rh contained in layer a1 is loaded onto the Ce-Zr-Al composite oxide; more preferably, at least 80% by mass of Rh contained in layer a1 is loaded onto the Ce-Zr-Al composite oxide; and even more preferably, at least 90% by mass of Rh contained in layer a1 is loaded onto the Ce-Zr-Al composite oxide. The proportion of Rh loaded onto the Ce-Zr-Al composite oxide can be adjusted, for example, by the content of the Ce-Zr-Al composite oxide contained in layer a1. The definition of loading is described below.

[0081] In addition to Rh, layer a1 may also contain catalytically active components other than Rh. Commonly known catalytically active components other than Rh can be used, such as Pd, Pt, gold (Au), silver (Ag), iridium (Ir), ruthenium (Ru), and osmium (Os).

[0082] "Ce-Zr-Al composite oxides" refer to composite oxides containing Ce (cerium), Zr (zirconium), and Al (aluminum). The Ce content (CeO2 equivalent) relative to the mass of the composite oxide is between 1% and 94% by mass; the Zr content (ZrO2 equivalent) relative to the mass of the composite oxide is between 1% and 94% by mass; and the Al content (Al2O3 equivalent) relative to the mass of the composite oxide is between 5% and 98% by mass. Ce-Zr-Al composite oxides are typically granular. Whether layer a1 contains Ce-Zr-Al composite oxides can be determined using conventional methods such as SEM-EDX. Specifically, as follows: First, the sample containing layer a1 is analyzed using SEM-EDX. Through the obtained elemental mapping, particles containing the three elements Ce, Zr, and Al are identified. Next, the aforementioned particles are subjected to compositional analysis (elemental analysis). If the results of the compositional analysis are within the above range, the material can be determined to be a Ce-Zr-Al composite oxide.

[0083] Ce-Zr-Al composite oxides can function as oxygen storage components (hereinafter also referred to as "OSC materials").

[0084] Furthermore, Ce-Zr-Al composite oxides can function as support components for the aforementioned catalytically active ingredients. It should be noted that the term "supported catalytically active ingredient" refers to a state where it is physically or chemically adsorbed or retained on the outer surface or inner surface of pores. Specifically, regarding the support component being supported with catalytically active ingredients, for example, elemental mapping obtained by analyzing the cross-section of the catalyst used for waste gas purification using an EDS (energy dispersive spectrometer) can confirm that the support component and the catalytically active ingredient exist in the same region, thus indicating that the support component is "supported" with catalytically active ingredients.

[0085] The content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is 30% or more by mass relative to the mass of the Ce-Zr-Al composite oxide. By ensuring that the Al2O3 content is 30% or more by mass, a good composite oxide is formed, resulting in higher heat resistance and higher exhaust gas purification performance compared to adding Ce-Zr composite oxide and Al2O3 separately.

[0086] The content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is preferably 35% by mass or more, more preferably 40% by mass or more, relative to the mass of the Ce-Zr-Al composite oxide. Furthermore, the content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, relative to the mass of the Ce-Zr-Al composite oxide.

[0087] From the viewpoint of improving oxygen storage capacity and heat resistance, the Ce content of Ce in the Ce-Zr-Al composite oxide contained in layer a1, which is converted to CeO2, is preferably 2% by mass or more and 40% by mass or less relative to the mass of the Ce-Zr-Al composite oxide, 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.

[0088] From the viewpoint of improving oxygen storage capacity and heat resistance, the Zr content of Zr in the Ce-Zr-Al composite oxide contained in layer a1, relative to the mass of the Ce-Zr-Al composite oxide, 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.

[0089] The Ce-Zr-Al composite oxide contained in layer a1 may contain rare earth elements other than Ce, as well as alkaline earth metals 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 can be added as oxides to the Ce-Zr-Al composite oxide. The Ce-Zr-Al composite oxide may contain one or more rare earth elements and / or alkaline earth metals.

[0090] The content of Ce-Zr-Al composite oxide in layer a1 is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 85% by mass or more, relative to the mass of layer a1. Furthermore, the content of Ce-Zr-Al composite oxide in layer a1 is preferably 98% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less, relative to the mass of layer a1.

[0091] The content of Ce-Zr-Al composite oxides in layer a1 can be determined using conventional methods such as SEM-EDX. Specifically, as described below.

[0092] (1) For the sample obtained from layer a1, elemental analysis was performed using conventional methods such as SEM-EDX to determine the types of constituent elements of the whole sample and to calculate the content (mass%) of each element.

[0093] (2) For the sample obtained from layer a1, elemental mapping was performed using conventional methods such as SEM-EDX to determine the types of particles contained in the sample (e.g., Ce-Zr-Al composite oxide particles and other particles as appropriate).

[0094] (3) For various particles, elemental analysis was performed on any selected number (e.g., 50) particles using SEM-EDX to determine the types of constituent elements of the particles and to calculate the content (mass%) of each element. For various particles, the average content (mass%) of each element was calculated.

[0095] (4) By creating and solving equations that represent the relationship between the content of each element in the sample (mass%), the content of each element in each particle (mass%), and the content of each particle in the sample (mass%), the content of each particle in the sample (mass%) is calculated and used as the content of each particle in layer a1 (mass%).

[0096] Layer a1 may further contain components other than those mentioned above.

[0097] For example, layer a1 may contain Ce-Zr composite oxides.

[0098] "Ce-Zr composite oxides" refer to composite oxides containing Ce and Zr, wherein the Ce content (CeO2 equivalent) of Ce in the composite oxide is 5% to 95% by mass relative to the mass of the composite oxide, and the Zr content (ZrO2 equivalent) of Zr in the composite oxide is 5% to 95% by mass relative to the mass of the composite oxide. They contain no Al, or, if Al is included, the Al2O3 equivalent content of Al in the composite oxide is less than 5% by mass relative to the mass of the composite oxide. The oxide equivalent content of each element in Ce-Zr composite oxides can be calculated in the same way as the oxide equivalent content of each element in Ce-Zr-Al composite oxides.

[0099] Layer a1 may also contain inorganic oxides other than the oxygen storage component as a carrier. Examples of inorganic oxides other than the oxygen storage component include metal oxides other than those mentioned above, such as oxide materials based on rare earth oxides like Al2O3, ZrO2, SiO2, TiO2, and La2O3, zeolites (aluminosilicates), MgO, ZnO, and SnO2, and oxide materials formed by combining these materials. Additionally, examples include phosphates and borates of aluminum (Al), zirconium (Zr), silicon (Si), titanium (Ti), rare earth elements, magnesium (Mg), and zinc (Zn). The inorganic oxide other than the oxygen storage component is preferably a porous body. Examples of porous bodies include those with a BET specific surface area of ​​30 m². 2 / g or more and 600m 2 Porous materials with a density of less than / g.

[0100] Furthermore, from the viewpoint of suppressing the decrease in catalytic activity and heat resistance caused by phosphorus poisoning, layer a1 may contain an alkaline earth metal compound. Preferred alkaline earth metal elements include Sr and Ba. Alkaline earth metal compounds include oxides and carbonates.

[0101] Layer a1 may contain an adhesive. The adhesive may be selected from, for example, alumina, zirconium oxide, titanium dioxide, silicon dioxide, cerium dioxide, etc.

[0102] 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 even more preferably 70 g / L or more and 100 g / L or less.

[0103] <Other layers, layer a2>

[0104] In addition to the aforementioned substrate A and layer a1, the upstream catalyst may also have other layers. Examples of these other layers include layers containing catalytically active components other than Rh. Conventionally known catalytically active components other than Rh can be used, such as Pd, Pt, Au, Ag, Ir, Ru, and Os. From the viewpoint of achieving a good balance in purifying HC, CO, and NOx from the exhaust gas, Pd or Pt is preferred.

[0105] From the viewpoint of efficiently utilizing the exhaust gas purification performance brought about by the catalytically active components, the other layers preferably include a support component that supports the catalytically active components in addition to the catalytically active components. Examples of support components include oxygen storage components (OSC materials) and inorganic oxides other than oxygen storage components.

[0106] As an oxygen storage component, any metal oxide that produces a change in the valence of its constituent elements and has oxygen storage capacity under the working conditions of the waste gas purification catalyst can be used without particular restrictions. For example, Ce-Zr-Al composite oxides and Ce-Zr composite oxides are preferred.

[0107] The oxygen storage component may include rare earth elements other than Ce and alkaline earth metal elements. As rare earth elements other than Ce, the same rare earth elements other than Ce that may be included in the Ce-Zr-Al composite oxide contained in the aforementioned layer a1 can be listed.

[0108] In addition to the above, other oxygen storage components include oxides of elements such as manganese (Mn), iron (Fe), and copper (Cu) that are prone to valence state changes under the conditions of catalyst use, as well as composite oxides containing these elements.

[0109] The inorganic oxides used as the support components for the catalytically active components, excluding the oxygen storage components, can be the same substances as those used in layer a1.

[0110] Furthermore, from the viewpoint of suppressing the decrease in catalytic activity caused by phosphorus poisoning and improving heat resistance, the other layers may contain alkaline earth metal compounds. Preferred alkaline earth metal elements include Sr and Ba. Alkaline earth metal compounds include oxides and carbonates.

[0111] Layer a2 may contain an adhesive. The adhesive may be selected from, for example, alumina, zirconium oxide, titanium dioxide, silicon dioxide, cerium dioxide, etc.

[0112] As an upstream catalyst, other layers can be included, for example, by having layer a2 between substrate A and layer a1.

[0113] Layer a2 preferably contains a Pd and Ce-Zr composite oxide.

[0114] The Pd content in layer a2 is preferably 0.010% by mass or more, more preferably 0.050% by mass or more, and even more preferably 0.10% by mass or more, relative to the mass of layer a2. Furthermore, the Pd content in layer a2 is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, relative to the mass of layer a2. The Pd content in layer a2 can be calculated in the same manner as the Rh content in layer a1.

[0115] Compared to Ce-Zr-Al composite oxides containing equal amounts of Ce, Zr, and Al, and Al₂O₃, Ce-Zr-Al composite oxides offer the advantage of improved heat resistance, as described above, but suffer from reduced OSC (Optical Storage Capacity) capacity. Furthermore, compared to Rh, Pd exhibits a property where its catalytic activity is less likely to decrease even when the heat resistance of the oxygen storage components contained in the same layer is low. Therefore, layer a2 does not contain Ce-Zr-Al composite oxides, or, if it does contain Ce-Zr-Al composite oxides, the content of Ce-Zr composite oxides in layer a2 is preferably 50% by mass or more relative to the total mass of Ce-Zr and Ce-Zr-Al composite oxides contained in layer a2.

[0116] When layer a2 contains Ce-Zr-Al composite oxides, the content of Ce-Zr composite oxides in layer a2 is more preferably 60% by mass or more relative to the total mass of Ce-Zr composite oxides and Ce-Zr-Al composite oxides in layer a2. The content of Ce-Zr composite oxides and Ce-Zr-Al composite oxides in layer a2 can be calculated in the same way as the content of Ce-Zr-Al composite oxides in layer a1.

[0117] 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 even more preferably 80 g / L or more and 150 g / L or less.

[0118] Downstream catalysts

[0119] The downstream catalyst has a substrate B and a layer b1 disposed on the substrate B.

[0120] <Substrate B>

[0121] Substrate B is the same as the aforementioned substrate A.

[0122] <Layer b1>

[0123] Layer b1 contains Rh and Ce-Zr composite oxides.

[0124] Rh is the catalytically active component.

[0125] The Rh content in layer b1 is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, relative to the mass of layer b1. Furthermore, the Rh content in layer b1 is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, relative to the mass of layer b1. The Rh content in layer b1 can be calculated in the same manner as the Rh content in layer a1.

[0126] Preferably, at least 60% by mass of Rh contained in layer b1 is loaded into the Ce-Zr composite oxide; more preferably, at least 70% by mass of Rh contained in layer b1 is loaded into the Ce-Zr composite oxide; and even more preferably, at least 75% by mass of Rh contained in layer b1 is loaded into the Ce-Zr composite oxide. The proportion of Rh loaded into the Ce-Zr composite oxide can be adjusted, for example, by the content of the Ce-Zr composite oxide contained in layer b1.

[0127] In addition to Rh, layer b1 may also contain catalytically active components other than Rh. Commonly known catalytically active components other than Rh can be used, such as Pd, Pt, Au, Ag, Ir, Ru, and Os.

[0128] Ce-Zr composite oxides can function as OSC materials.

[0129] In addition, Ce-Zr composite oxides can function as carriers for the aforementioned catalytically active components.

[0130] Since Ce has the property of stabilizing the oxidation state of Rh, the Ce content of Ce in the Ce-Zr composite oxide contained in layer b1, which is converted to CeO2, is preferably 35% by mass or less, and more preferably 25% by mass or less, relative to the mass of the Ce-Zr composite oxide.

[0131] The Zr content of Zr in the Ce-Zr composite oxide contained in layer b1, calculated as ZrO2, is preferably 10% by mass or more and 90% by mass or less relative to the mass of the Ce-Zr composite oxide, 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.

[0132] The Ce-Zr composite oxide contained in layer b1 may include rare earth elements other than Ce, as well as alkaline earth metal elements such as Ba, Sr, and Ca. Elements other than Ce that are listed in the description of layer a1 can be cited as examples of rare earth elements.

[0133] The content of Ce-Zr composite oxide in layer b1 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, relative to the mass of layer b1. Furthermore, the content of Ce-Zr composite oxide in layer b1 is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, relative to the mass of layer b1.

[0134] As mentioned above, Al2O3 has the property of stabilizing the oxidation state of Rh. Therefore, from the viewpoint of improving the performance of exhaust gas purification, layer b1 does not contain Al, or, if it contains Al, the content of Al2O3 in layer b1 is less than 30% by mass relative to the mass of layer b1.

[0135] When layer b1 contains Al, the Al₂O₃ content of Al contained in layer b1, relative to the mass of layer b1, is preferably 25% by mass or less. On the other hand, although it is lower than that of the upstream catalyst, heat resistance is also required for the downstream catalyst; therefore, the Al₂O₃ content of Al contained in layer b1, relative to the mass of layer b1, is preferably 10% by mass or more, more preferably 15% by mass or more. The Al₂O₃ content of Al contained in layer b1 can be calculated in the same way as the Rh content.

[0136] Layer b1 may further contain components other than those mentioned above.

[0137] Layer b1 may contain an Al-based oxide as a support. The Al-based oxide may contain La, but La has the property of stabilizing the oxidation state of Rh. Therefore, the Al-based oxide does not contain La. Alternatively, if La is contained, the content of La in the Al-based oxide, calculated as La2O3, is preferably less than 10% by mass relative to the mass of the Al-based oxide.

[0138] When layer b1 contains Al-based oxides and the Al-based oxides contain La, the La content in the Al-based oxides, calculated as La₂O₃, is more preferably 8% by mass or less, more preferably 7% by mass or less, more preferably 5% by mass or less, and more preferably 3% by mass or less. Alternatively, the La content in the Al-based oxides, calculated as La₂O₃, can be 0.5% by mass or more. The oxide content of each element in the Al-based oxides can be calculated in the same manner as the oxide content of each element in the Ce-Zr-Al composite oxides.

[0139] Layer b1 may also contain inorganic oxides other than Al-based oxides as a support. Furthermore, from the viewpoint of suppressing the decrease in catalytic activity caused by phosphorus poisoning and improving heat resistance, layer b may contain alkaline earth metal compounds. The same materials as layer a1 can be used as inorganic oxides other than Al-based oxides or alkaline earth metal compounds.

[0140] Layer b1 may contain a binder. The binder may be selected from, for example, alumina, zirconium oxide, titanium dioxide, silicon dioxide, cerium dioxide, etc. It should be noted that if the binder in layer b1 contains Al, the Al2O3 content of Al in layer b1 also includes the Al from the binder, and should be set to less than 30% by mass relative to the mass of layer b1.

[0141] 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 even more preferably 70 g / L or more and 100 g / L or less.

[0142] <Other layers, layer b2>

[0143] In addition to the aforementioned substrate B and layer b1, the downstream catalyst may also have other layers. Examples of other layers include layers containing catalytically active components other than Rh. Conventionally known catalytically active components other than Rh can be used, such as Pd, Pt, Au, Ag, Ir, Ru, Os, etc., with Pd or Pt being preferred.

[0144] Other layers that a downstream catalyst may have include those that are the same as those that the upstream catalyst may have.

[0145] As a downstream catalyst, other layers can be included, for example, by having layer b2 between substrate B and layer b1.

[0146] Layer b2 may, for example, contain Pt and Ce-Zr composite oxides.

[0147] Layer b2 does not contain Ce-Zr-Al composite oxides, or, if it does contain Ce-Zr-Al composite oxides, the content of Ce-Zr composite oxides in layer b2 is preferably 50% by mass or more relative to the total mass of Ce-Zr composite oxides and Ce-Zr-Al composite oxides in layer b2.

[0148] When layer b2 contains Ce-Zr-Al composite oxides, the content of Ce-Zr composite oxides in layer b2 is more preferably 60% by mass or more relative to the total mass of Ce-Zr composite oxides and Ce-Zr-Al composite oxides in layer b2.

[0149] Layer b2 may also contain inorganic oxides other than oxygen storage components as a support. Furthermore, from the viewpoint of suppressing the decrease in catalytic activity caused by phosphorus poisoning and improving heat resistance, layer b2 may contain alkaline earth metal compounds. The same materials as layer a1 can be used as inorganic oxides or alkaline earth metal compounds other than oxygen storage components.

[0150] Layer b2 may contain an adhesive. The adhesive may be selected from, for example, alumina, zirconium oxide, titanium dioxide, silicon dioxide, cerium dioxide, etc.

[0151] 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 even more preferably 130 g / L or more and 160 g / L or less.

[0152] The exhaust gas purification catalyst of the present invention, as an exhaust gas purification catalyst for internal combustion engines, can efficiently purify NOx, HC, and CO. Therefore, it is possible to provide an exhaust gas purification system that introduces exhaust gas from an internal combustion engine into the exhaust gas purification catalyst in the exhaust path connected to the internal combustion engine without passing through other exhaust gas purification catalysts. It should be noted that examples of internal combustion engines include gasoline engines, engines fueled by compressed natural gas, and engines fueled by gasoline (flexible fuel) containing any amount of ethanol.

[0153] <Catalyst Manufacturing>

[0154] The exhaust gas catalyst of the present invention can be manufactured by forming layer a1 (and layer a2 as needed) on substrate A and layer b1 (and layer b2 as needed) on substrate B.

[0155] In the case of forming layer a2, a slurry for forming layer a2 can be prepared by mixing a supply source of catalytically active components (e.g., nitrates, ammonium complex salts, acetates, chlorides, etc. of Pd, Pt, etc.), Ce-Zr composite oxides, and other components (e.g., Al oxides, binders, solvents, etc.) as appropriate. The slurry for forming layer a2 is then coated onto substrate A and dried and fired to form the layer a2.

[0156] Layer a1 can be formed by mixing a source of Rh (e.g., nitrate, ammonium complex salt, acetate, chloride, etc. of Rh), Ce-Zr-Al composite oxide, and other components as appropriate (e.g., Ce-Zr composite oxide, binder, solvent, etc.) to prepare a slurry for forming layer a1, applying the slurry for forming layer a1 onto substrate A (or layer a2 if layer a2 is present), drying, and firing to form layer a1.

[0157] In the case of forming layer b2, a slurry for forming layer b2 can be prepared by mixing a source of noble metal elements (e.g., nitrates, ammonium complex salts, acetates, chlorides, etc. of Pd, Pt, etc.) and other components (e.g., Ce-Zr composite oxides, Al oxides, binders, solvents, etc.) as appropriate, and then coating the slurry for forming layer b2 onto substrate B, followed by drying and firing to form layer b2.

[0158] Layer b1 can be formed by mixing a source of Rh (e.g., Rh nitrate, ammonium complex salt, acetate, chloride, etc.), Ce-Zr composite oxide, and other components (e.g., Al oxide, binder, solvent, etc.) as appropriate, to prepare a slurry for forming layer b1, applying the slurry for forming layer b1 onto substrate B (or layer b2 if layer b2 is present), drying, and firing, thereby forming layer b1.

[0159] Example

[0160] 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.

[0161] [Example 1]

[0162] (1) Preparation of slurry for forming the lower layer (layer a2) of the upstream catalyst

[0163] Prepare OSC material 1 (Ce-Zr composite oxide) with the following composition.

[0164] CeO2 content (calculated as Ce): 40.0% by mass; ZrO2 content (calculated as Zr): 50.0% by mass; content of oxides of rare earth elements other than Ce: 10.0% by mass.

[0165] Palladium nitrate aqueous solution, OSC material 1, La2O3-modified alumina (La2O3 modification amount: 1.0 wt%), binder, and water were added to a mixing container and 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 so that, based on the mass of the fired layer a2 (100 wt%), Pd (converted to metal) was 4.0 wt%, OSC material 1 was 40.0 wt%, La2O3-modified alumina was 50.0 wt%, and binder was 6.0 wt%. It should be noted that the binder does not contain Al.

[0166] (2) Formation of the lower layer (layer a2) of the upstream catalyst

[0167] As a flow-through substrate, a flow-through substrate is prepared having axially extending chambers divided by partition walls with a thickness of 50~70μm at a density of 600 chambers per square inch on a surface orthogonal to the axial direction, and a volume of 1.0L.

[0168] A flowable substrate is immersed in a slurry for forming layer a2 to obtain a flowable substrate coated with the slurry for forming layer a2. Next, the flowable substrate coated with the slurry for forming layer a2 is dried at 150°C for 0.5 hours and then fired at 500°C for 1 hour to form layer a2. The mass of layer a2 per unit volume in the portion of the flowable substrate where layer a2 is formed is 100 g / L.

[0169] (3) Preparation of slurry for forming the upper layer (layer a1) of the upstream catalyst

[0170] Prepare OSC material 2 (Ce-Zr-Al composite oxide) with the following composition.

[0171] Ce content (CeO2 equivalent): 10.0% by mass; Zr content (ZrO2 equivalent): 35.0% by mass; Al content (Al2O3 equivalent): 45.0% by mass; content of oxides of rare earth elements other than Ce: 10.0% by mass.

[0172] Rhodium nitrate aqueous solution, OSC material 2, binder, and water were added to a mixing container and mixed and stirred to prepare a slurry for forming layer a1. The proportions of each component in the slurry for forming layer a1 were adjusted so that, based on the mass of the fired layer a1 (100% by mass), Rh (converted to metal) was 1.0% by mass, OSC material 2 was 90.0% by mass, and binder was 9.0% by mass. It should be noted that the binder does not contain Al.

[0173] (4) Formation of the upper layer (layer a1) of the upstream catalyst

[0174] A flowable substrate having layer a2 formed is impregnated in a slurry for forming layer a1 to obtain a flowable substrate coated with the slurry for forming layer a1. Next, the flowable substrate coated with the slurry for forming layer a1 is dried at 150°C for 0.5 hours and then fired at 500°C for 1 hour to form layer a1 on layer a2. The mass of layer a1 per unit volume in the portion of the flowable substrate where layer a1 is formed is 80 g / L.

[0175] As described above, an upstream catalyst is manufactured having a layer a2 formed on a flowable substrate and a layer a1 formed on the layer a2.

[0176] (5) Preparation of slurry for forming the lower layer (layer b2) of the downstream catalyst

[0177] Prepare the aforementioned OSC materials 1.

[0178] In a mixing container, a platinum nitrate aqueous solution, OSC material 1, La2O3-modified alumina (La2O3 modification amount: 1.0 wt%), binder, and water were added, mixed, and stirred to prepare a slurry for forming layer b2. The amounts of each component in the slurry for forming layer b2 were adjusted so that, based on the mass of the fired layer b2 (100 wt%), Pt (converted to metal) was 1.0 wt%, OSC material 1 was 60.0 wt%, La2O3-modified alumina was 30.0 wt%, and binder was 9.0 wt%. It should be noted that the binder does not contain Al.

[0179] (6) Formation of the lower layer (layer b2) of the downstream catalyst

[0180] As a flow-through substrate, a flow-through substrate is prepared having axially extending chambers divided by partition walls with a thickness of 50~70μm at a density of 600 chambers per square inch on a surface orthogonal to the axial direction, and a volume of 1.0L.

[0181] A flowable substrate is immersed in a slurry for forming layer b2 to obtain a flowable substrate coated with the slurry for forming layer b2. Next, the flowable substrate coated with the slurry for forming layer b2 is dried at 150°C for 0.5 hours 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 flowable substrate in which layer b2 is formed is 140 g / L.

[0182] (7) Preparation of slurry for forming the upper layer (layer b1) of the downstream catalyst

[0183] Prepare OSC material 3 (Ce-Zr composite oxide) with the following composition.

[0184] CeO2 content (calculated as Ce): 20.0% by mass; ZrO2 content (calculated as Zr): 70.0% by mass; content of oxides of rare earth elements other than Ce: 10.0% by mass.

[0185] In a mixing container, an aqueous solution of rhodium nitrate, OSC material 3, La2O3-modified alumina (La2O3 modification amount: 1.0% by mass), binder, and water were added, 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 the fired layer b1 (100% by mass), Rh (converted to metal) was 0.2% by mass, OSC material 3 was 70.0% by mass, La2O3-modified alumina was 20.0% by mass, and binder was 9.8% by mass. It should be noted that the binder does not contain Al.

[0186] (8) Formation of the upper layer (layer b1) of the downstream catalyst

[0187] A flowable substrate with layer b2 formed thereon is impregnated in a slurry for forming layer b1 to obtain a flowable substrate coated with the slurry for forming layer b1. Next, the flowable substrate coated with the slurry for forming layer b1 is dried at 150°C for 0.5 hours 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 flowable substrate in which layer b1 is formed is 80 g / L.

[0188] As described above, a downstream catalyst is manufactured having a layer b2 formed on a flowable substrate and a layer b1 formed on the layer b2.

[0189] As described above, a waste gas purification catalyst with upstream and downstream catalysts is manufactured.

[0190] [Example 2]

[0191] In the manufacturing of the downstream catalyst, the La2O3 modification amount of the alumina modified with La2O3 in the slurry to form layer b1 is 4.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0192] [Example 3]

[0193] In the manufacturing of the downstream catalyst, the La2O3 modification amount of the alumina modified with La2O3 in the slurry to form layer b1 is 6.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0194] [Example 4]

[0195] In the manufacturing of the downstream catalyst, the La2O3 modification amount of the alumina modified with La2O3 in the slurry to form layer b1 is 9.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0196] [Example 5]

[0197] In the manufacturing of the downstream catalyst, OSC material 4 (Ce-Zr composite oxide) with the following composition is used instead of OSC material 3 used in preparing the slurry for forming layer b1. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0198] CeO2 content (calculated as Ce): 30.0% by mass; ZrO2 content (calculated as Zr): 60.0% by mass; content of oxides of rare earth elements other than Ce: 10.0% by mass.

[0199] [Example 6]

[0200] Prepare OSC material 5 (Ce-Zr-Al composite oxide) with the following composition.

[0201] Ce content (CeO2 equivalent): 20.0% by mass; Zr content (ZrO2 equivalent): 30.0% by mass; Al content (Al2O3 equivalent): 40.0% by mass; content of oxides of rare earth elements other than Ce: 10.0% by mass.

[0202] In the manufacturing of the upstream catalyst, the amounts of each component in the slurry for forming layer a2 are adjusted such that, based on the mass of the fired layer a2 (100% by mass), Pd is 4.0% by mass (in metal conversion), OSC material 5 is 90.0% by mass, and binder is 6.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0203] [Example 7]

[0204] Prepare the aforementioned OSC material 2 and OSC material 3.

[0205] In the manufacturing of the upstream catalyst, the amounts of each component in the slurry for forming layer a1 are adjusted such that, based on the mass of the calcined layer a1 (100% by mass), Rh is 1.0% by mass (in metal conversion), OSC material 2 is 64.0% by mass, OSC material 3 is 26.0% by mass, and binder is 9.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0206] [Example 8]

[0207] In the manufacturing of the downstream catalyst, the amounts of each component in the slurry for forming layer b1 are adjusted so that, based on the mass of the calcined layer b1 (100% by mass), Rh is 0.2% by mass (converted to metal), OSC material 3 is 60.0% by mass, La2O3 modified alumina is 30.0% by mass, and binder is 9.8% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0208] [Example 9]

[0209] In the manufacturing of the downstream catalyst, when preparing the slurry for forming layer b1, La2O3-modified alumina is not used. The amounts of each component in the slurry for forming layer b1 are adjusted so that, based on the mass of the calcined layer b1 (100% by mass), Rh is 0.2% by mass (converted to metal), OSC material 3 is 90.0% by mass, and binder is 9.8% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0210] [Comparative Example 1]

[0211] Prepare the aforementioned OSC materials 3.

[0212] In the manufacturing of the upstream catalyst, OSC material 3 and La2O3-modified alumina (La2O3 modification amount: 1.0 wt%) were used instead of OSC material 2 used in preparing the slurry for forming layer a1. The amounts of each component in the slurry for forming layer a1 were adjusted so that, based on the mass of the calcined layer a1 (100 wt%), Rh was 1.0 wt% (in metal conversion), OSC material 3 was 45.0 wt%, La2O3-modified alumina was 45.0 wt%, and binder was 9.0 wt%. Otherwise, the exhaust gas purification catalyst was manufactured in the same manner as in Example 1.

[0213] [Comparative Example 2]

[0214] Prepare the aforementioned OSC materials 2.

[0215] In the manufacturing of the downstream catalyst, OSC material 2 was used instead of OSC material 3 and La2O3-modified alumina (La2O3 modification amount: 1.0 wt%) used in preparing the 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 the calcined layer b1 (100 wt%), Rh was 0.2 wt% (converted to metal), OSC material 2 was 90.0 wt%, and binder was 9.8 wt%. Otherwise, the exhaust gas purification catalyst was manufactured in the same manner as in Comparative Example 1.

[0216] [Comparative Example 3]

[0217] In the manufacturing of the upstream catalyst, when preparing the slurry for forming layer a1, OSC material 3 is further used to adjust the amount of each component in the slurry for forming layer a1, so that based on the mass of the calcined layer a1 (100% by mass), Rh is 1.0% by mass (converted to metal), OSC material 2 is 46.0% by mass, OSC material 3 is 44.0% by mass, and binder is 9.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0218] [Comparative Example 4]

[0219] In the manufacturing of the upstream catalyst, when preparing the slurry for forming layer a1, OSC material 3 is further used to adjust the amount of each component in the slurry for forming layer a1, so that based on the mass of the calcined layer a1 (100% by mass), Rh is 1.0% by mass (converted to metal), OSC material 2 is 27.0% by mass, OSC material 3 is 63.0% by mass, and binder is 9.0% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0220] [Comparative Example 5]

[0221] In the manufacturing of the downstream catalyst, the amounts of each component in the slurry for forming layer b1 are adjusted so that, based on the mass of the calcined layer b1 (100% by mass), Rh is 0.2% by mass (converted to metal), OSC material 3 is 48.0% by mass, La2O3 modified alumina is 42.0% by mass, and binder is 9.8% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0222] [Comparative Example 6]

[0223] In the manufacturing of the downstream catalyst, the amounts of each component in the slurry for forming layer b1 are adjusted so that, based on the mass of the calcined layer b1 (100% by mass), Rh is 0.2% by mass (converted to metal), OSC material 3 is 38.0% by mass, La2O3 modified alumina is 52.0% by mass, and binder is 9.8% by mass. Otherwise, the exhaust gas purification catalyst is manufactured in the same manner as in Example 1.

[0224] [Comparative Example 7]

[0225] Prepare the aforementioned OSC materials 5.

[0226] In the manufacturing of the upstream catalyst, OSC material 5 was used instead of OSC material 1 and La2O3-modified alumina (La2O3 modification amount: 1.0 mass%) used in the preparation of the slurry for forming layer a2. The amounts of each component in the slurry for forming layer a2 were adjusted so that, based on the mass of the calcined layer a2 (100 mass%), Pd was 4.0 mass (in metal conversion), OSC material 5 was 90.0 mass, and binder was 6.0 mass. Otherwise, the exhaust gas purification catalyst was manufactured in the same manner as in Comparative Example 1.

[0227] (Durability evaluation)

[0228] For the catalysts used for exhaust gas purification in Examples 1-9 and Comparative Examples 1-7, the following durability conditions were applied as a deterioration treatment assuming 100,000 to 200,000 kilometers of driving.

[0229] <Durability Conditions>

[0230] • Durable engine: Passenger car naturally aspirated 2L gasoline engine

[0231] • Use gasoline: Commercially available regular gasoline

[0232] Processing temperature: 900℃

[0233] Processing time: 100 hours

[0234] The exhaust gas purification catalysts (upstream and downstream catalysts) of Examples 1-9 and Comparative Examples 1-7 were placed in the exhaust path of the engine, and durability tests were conducted under the aforementioned conditions. The exhaust gas purification catalysts after the durability tests were then installed in a vehicle (a passenger car equipped with a 1.5L direct-injection turbocharged engine), and the vehicle was operated according to the international blended exhaust gas test cycle (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 at the following times: low-temperature operation from the start of operation to 589 seconds; medium-speed operation from 589 seconds to 1022 seconds; high-speed operation from 1022 seconds to 1477 seconds; and ultra-high-speed operation from 1477 seconds to 1800 seconds. The total emissions of NMHC and NOx per unit distance traveled were calculated.

[0235] As gasoline, it is used for certification testing; as an exhaust gas measuring device, it is used for exhaust gas measuring devices manufactured by Horiba, Ltd.

[0236] The results are shown in Table 1. In Table 1, the total emissions of NMHC and NOx are shown in the “Emissions (Relative Values)” column as relative values ​​when the value of Example 1 is set to 1.00.

[0237] In Table 1, “CZA” represents Ce-Zr-Al composite oxide and “CZ” represents Ce-Zr composite oxide.

[0238] [Table 1]

[0239]

[0240] As shown in Table 1, the exhaust gas purification catalyst of the embodiment can reduce the emission amount after the durability test and has excellent durability.

[0241] Industrial availability

[0242] According to the present invention, a waste gas purification catalyst with excellent durability can be provided.

[0243] The present invention has been described in detail or with reference to specific embodiments, but 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 invention.

[0244] This application is based on Japanese Patent Application No. 2023-139973, filed on August 30, 2023, the contents of which are incorporated herein by reference.

[0245] Explanation of reference numerals in the attached figures

[0246] 1.11 Upstream catalysts

[0247] 2.12 Downstream catalysts

[0248] Substrate A

[0249] a1 layer a1

[0250] a2 layer a2

[0251] B Substrate B

[0252] b1 layer b1

[0253] b2 layer b2

[0254] 10, 20 Exhaust Gas Purification Catalyst

[0255] X. Direction of exhaust gas flow

Claims

1. A waste gas purification catalyst, comprising an upstream catalyst disposed on the upstream side of the waste gas flow direction and a downstream catalyst disposed on the downstream side of the waste gas flow direction. The upstream catalyst has a substrate A and a layer a1 disposed on the substrate A. The downstream catalyst has a substrate B and a layer b1 disposed on the substrate B. The layer a1 contains Rh and Ce-Zr-Al composite oxides. The layer b1 comprises Rh and Ce-Zr composite oxides. The content of Al in the Ce-Zr-Al composite oxide contained in layer a1, calculated as Al2O3, is more than 30% by mass relative to the mass of the Ce-Zr-Al composite oxide. The content of the Ce-Zr-Al composite oxide in layer a1 is 50% by mass or more relative to the mass of layer a1. The layer b1 does not contain Al, or, if it does contain Al, the Al2O3 content of the Al contained in the layer b1 is less than 30% by mass relative to the mass of the layer b1.

2. The waste gas purification catalyst according to claim 1, wherein, The Ce content of Ce in the Ce-Zr composite oxide contained in layer b1, calculated as CeO2, is less than 25% by mass relative to the mass of the Ce-Zr composite oxide.

3. The waste gas purification catalyst according to claim 1, wherein, Layer b1 contains Al-based oxides. The Al-based oxide does not contain La, or, if it does contain La, the La content in the Al-based oxide, calculated as La2O3, is less than 7% by mass relative to the mass of the Al-based oxide.

4. The waste gas purification catalyst according to claim 1, wherein, The Ce content of Ce in the Ce-Zr-Al composite oxide contained in layer a1, calculated as CeO2, is more than 2% by mass and less than 40% by mass relative to the mass of the Ce-Zr-Al composite oxide.

5. The waste gas purification catalyst according to claim 1, wherein, The Zr content of the Ce-Zr-Al composite oxide contained in layer a1, calculated as ZrO2, is between 10% and 70% by mass relative to the mass of the Ce-Zr-Al composite oxide.

6. The waste gas purification catalyst according to claim 1, wherein, The content of Al in the Ce-Zr-Al composite oxide contained in layer a1, converted from Al2O3, is less than 60% by mass relative to the mass of the Ce-Zr-Al composite oxide.

7. The waste gas purification catalyst according to claim 1, wherein, More than 60% by mass of Rh contained in layer b1 is loaded into the Ce-Zr composite oxide.

8. The waste gas purification catalyst according to claim 1, wherein, A layer a2 is provided between the substrate A and the layer a1. The layer a2 contains Pd and Ce-Zr composite oxides. The layer a2 does not contain Ce-Zr-Al composite oxides, or, if it does contain Ce-Zr-Al composite oxides, the content of the Ce-Zr composite oxides in the layer a2 is 50% by mass or more relative to the total mass of the Ce-Zr composite oxides and the Ce-Zr-Al composite oxides in the layer a2.

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