Catalyst composition for exhaust gas purification, catalyst for exhaust gas purification, and exhaust gas purification system

Abstract

The purpose of the present invention is to provide a novel technique capable of achieving exhaust gas purification performance in a low-temperature environment and maintaining NOx adsorbed at a low temperature to a high temperature while using Pt, and to provide a catalyst composition for exhaust gas purification, which contains Pt and Sr, and in which the content of Sr in the catalyst composition for exhaust gas purification is less than 1% by mass based on the mass of the catalyst composition for exhaust gas purification. The amount of Sr in terms of metal is from 0.1% by mass to 9.0% by mass (inclusive).

Description

Technical Field

[0001] The present invention relates to a catalyst composition for purifying exhaust gas, a catalyst for purifying exhaust gas, and an exhaust gas purifying system. Background Art

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

[0003] In order to improve the exhaust gas purification performance of the catalyst, various technologies have been developed. For example, Patent Document 1 describes a technology in which a catalyst layer having a lower layer containing Pd and alkaline earth metal elements and an upper layer containing Rh is provided on the upstream side of the substrate, and a catalyst layer having a lower layer containing Pt and alkaline earth metal elements and an upper layer containing Rh is provided on the downstream side of the substrate. In addition, Patent Document 2 describes a technology in which a catalyst layer having a lower layer containing Pd and Ba and an upper layer containing Rh is provided on the upstream side of the substrate, and a catalyst layer having a lower layer containing Pt and Ba and an upper layer containing Rh is provided on the downstream side of the substrate.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-157263

[0007] Patent Document 2: Japanese Patent Application Publication No. 2016-185495 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] From the viewpoint of cost reduction, it is necessary to utilize Pt rather than Rh and Pd in ​​the catalyst.

[0010] When the catalyst is in a low temperature environment just after the internal combustion engine is started, the catalytically active components in the catalyst are not sufficiently activated, so the exhaust gas purification performance of the catalyst is insufficient. Therefore, the catalyst needs to have exhaust gas purification performance in a low temperature environment.

[0011] If the catalyst is endowed with NOx adsorption performance, the exhaust gas purification performance of the catalyst in a low temperature environment can be compensated. Specifically, if the NOx that the catalyst cannot purify in a low temperature environment is adsorbed by the catalyst and retained in the catalyst until the environment in which the catalyst is located becomes a high temperature environment, and is released after the environment in which the catalyst is located becomes a high temperature environment (that is, after the catalytic active components in the catalyst are activated), the released NOx is effectively purified by the activated catalytic active components, thereby compensating for the exhaust gas purification performance of the catalyst in a low temperature environment. Therefore, the catalyst is required to have the ability to retain the NOx adsorbed at low temperatures until high temperatures.

[0012] As described above, the catalyst is required to achieve exhaust gas purification performance in a low-temperature environment and performance of retaining NOx adsorbed at a low temperature until a high temperature while utilizing Pt.

[0013] Therefore, an object of the present invention is to provide a new technology capable of achieving exhaust gas purification performance in a low-temperature environment and performance of maintaining NOx adsorbed at a low temperature until a high temperature while utilizing Pt.

[0014] In the present specification, the term "low temperature" means a temperature of preferably 370°C or lower, more preferably 350°C or lower, and further preferably 330°C or lower.

[0015] In the present specification, "high temperature" means a temperature preferably higher than 500°C, more preferably 520°C or higher, and further preferably 540°C or higher.

[0016] Solutions for solving problems

[0017] The present inventors discovered that when Ba or Mg is added to a catalyst layer containing Pt, exhaust gas purification performance in a low-temperature environment and the performance of maintaining NOx adsorbed at low temperatures until high temperatures cannot be achieved, and that when Sr is added to a catalyst layer containing Pt, exhaust gas purification performance in a low-temperature environment and the performance of maintaining NOx adsorbed at low temperatures until high temperatures can be achieved, but when an excessive amount of Sr is added to the catalyst layer containing Pt, the exhaust gas purification performance in a low-temperature environment instead decreases, thereby completing the present invention.

[0018] The present invention includes the following technical solutions.

[0019] [1] An exhaust gas-purifying catalyst composition comprising Pt and Sr, wherein the metal-converted amount of Sr is 0.1 mass % or more and 9.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

[0020] [2] The exhaust gas-purifying catalyst composition according to [1], wherein the metal conversion amount of the alkaline earth metal element other than Sr is 4.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

[0021] [3] The exhaust gas purification catalyst composition according to [1] or [2], wherein Sr is present in the form of one or both selected from SrO and SrCO 3 .

[0022] [4] The exhaust gas purification catalyst composition according to any one of [1] to [3], wherein the exhaust gas purification catalyst composition comprises modified alumina containing La, and the La2O3 conversion amount of La from the modified alumina is 0.20 mass% or more and 5.0 mass% or less, based on the mass of the exhaust gas purification catalyst composition.

[0023] [5] An exhaust gas-purifying catalyst comprising a substrate and a first catalyst layer provided on the substrate, wherein the first catalyst layer is composed of the exhaust gas-purifying catalyst composition according to any one of [1] to [4].

[0024] [6] The exhaust gas purification catalyst according to [5], wherein the exhaust gas purification catalyst further comprises a second catalyst layer and / or a third catalyst layer arranged on the substrate, the second catalyst layer is arranged on the upper side of the first catalyst layer, and the third catalyst layer is arranged on the upstream side of the first catalyst layer.

[0025] [7] The exhaust gas purification catalyst according to [6], wherein the second catalyst layer and / or the third catalyst layer contains Rh.

[0026] [8] The exhaust gas purification catalyst according to [6] or [7], wherein the metal conversion amount of the alkaline earth metal element in the second catalyst layer is 5.0 mass% or less based on the mass of the second catalyst layer, and the metal conversion amount of the alkaline earth metal element in the third catalyst layer is 5.0 mass% or less based on the mass of the third catalyst layer.

[0027] [9] An exhaust gas purification system comprising: an exhaust passage through which exhaust gas flows, a first exhaust gas purification catalyst disposed on a downstream side in the exhaust passage, and a second exhaust gas purification catalyst disposed on an upstream side in the exhaust passage.

[0028] The first exhaust gas-purifying catalyst comprises a first substrate and a catalyst layer provided on the first substrate.

[0029] The catalyst layer provided on the first substrate is composed of the exhaust gas-purifying catalyst composition described in any one of [1] to [4].

[0030]

[10] The exhaust gas purification system according to [9], wherein the second exhaust gas purification catalyst includes a second substrate and a catalyst layer provided on the second substrate.

[0031]

[11] The exhaust gas purification system according to

[10] , wherein the catalyst layer provided on the second substrate contains Rh.

[0032]

[12] The exhaust gas purification system according to

[10] or

[11] , wherein the metal conversion amount of the alkaline earth metal element in the catalyst layer provided on the second substrate is 5.0 mass % or less, based on the mass of the catalyst layer provided on the second substrate.

[0033] Effects of the Invention

[0034] According to the present invention, a new technology can be provided which can achieve both exhaust gas purification performance in a low-temperature environment and performance of retaining NOx adsorbed at a low temperature until a high temperature while utilizing Pt. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a partial cross-sectional view showing a state in which the exhaust gas purifying catalyst according to the first embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine.

[0036] Figure 2 for Figure 1 AA line cross-section diagram.

[0037] Figure 3 for Figure 2 An enlarged view of the area indicated by the mark R in FIG.

[0038] Figure 4 for Figure 1 BB line cross-section diagram.

[0039] Figure 5 2 is a cross-sectional view of an exhaust gas purification catalyst according to a second embodiment of the present invention (with Figure 4 corresponding cross-section).

[0040] Figure 6 2 is a cross-sectional view of an exhaust gas purification catalyst according to a third embodiment of the present invention (with Figure 4 corresponding cross-section).

[0041] Figure 7 It is a plan view of an exhaust gas purification system according to one embodiment of the present invention.

[0042] Figure 8 for Figure 7 DD line profile. DETAILED DESCRIPTION

[0043] 《Explanation of Terminology》

[0044] In the present specification, the "alkaline earth metal element" refers to an element selected from the group consisting of Be, Mg, Ca, Sr, Ba and Ra.

[0045] 《Catalyst composition for exhaust gas purification》

[0046] The exhaust gas-purifying catalyst composition of the present invention is described below. In addition, in this specification, the "exhaust gas-purifying catalyst composition" may be referred to as a "catalyst composition".

[0047] The catalyst composition of the present invention may be in the form of, for example, a powder, a molded body, or a layer.

[0048] The catalyst composition of the present invention comprises Pt.

[0049] Pt is contained in the catalyst composition of the present invention in a form that can function as a catalytically active component, such as a catalytically active component containing Pt, such as metallic Pt, an alloy containing Pt, a compound containing Pt (such as an oxide of Pt), etc. From the viewpoint of improving exhaust gas purification performance, the catalytically active component containing Pt is preferably in a granular form.

[0050] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, based on the mass of the catalyst composition of the present invention, the metal conversion amount of Pt in the catalyst composition of the present invention is preferably 0.050 mass % or more and 5.0 mass % or less, more preferably 0.10 mass % or more and 3.0 mass % or less, and further preferably 0.30 mass % or more and 1.0 mass % or less.

[0051] In this specification, the "mass of the catalyst composition" refers to the value obtained by adding the metal-converted mass of the precious metal element and the oxide-converted mass of the metal elements other than the precious metal element, among all the metal elements contained in the catalyst composition. That is, the "mass of the catalyst composition" refers to the calculated mass obtained by adding the metal-converted mass of the precious metal element contained in the catalyst composition and the oxide-converted mass of the metal elements other than the precious metal element contained in the catalyst composition. It should be noted that "metal elements" also include semi-metal elements such as Si and B.

[0052] In this specification, the “precious metal element” includes Pt, Pd, Rh, Au, Ag, Ru, Ir, and Os.

[0053] In this specification, the oxide of Al refers to Al2O3, the oxide of Si refers to SiO2, the oxide of B refers to B2O3, the oxide of Zr refers to ZrO2, the oxide of Be refers to BeO, the oxide of Mg refers to MgO, the oxide of Ca refers to CaO, the oxide of Sr refers to SrO, the oxide of Ba refers to BaO, the oxide of Ra refers to RaO, the oxide of Ti refers to TiO2, the oxide of Ni refers to NiO, and the oxide of P refers to P2O5. The oxide of rare earth elements refers to sesquioxides (Ln2O3) other than the oxides of Ce, Pr and Tb, the oxide of Ce refers to CeO2, and the oxide of Pr refers to Pr6O 11 , the oxide of Tb refers to Tb4O7.

[0054] When the composition of the raw material used to produce the catalyst composition of the present invention is known, the metal equivalent amount of Pt in the catalyst composition of the present invention can be determined from the composition of the raw material used to produce the catalyst composition of the present invention.

[0055] When the composition of the raw material used to produce the catalyst composition of the present invention is unknown, the metal equivalent amount of Pt in the catalyst composition of the present invention can be measured by conventional methods such as scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX).

[0056] The sample obtained from the catalyst composition of the present invention is subjected to elemental analysis using conventional methods such as SEM-EDX to determine the types of constituent elements of the entire sample and to determine the metal conversion amount (mass %) of the specified element. The metal conversion amount (mass %) of the specified element is determined for each of the 10 fields of view of the SEM, and the average value of the metal conversion amount (mass %) of the specified element in the 10 fields of view is taken as the metal conversion amount (mass %) of the specified element in the catalyst composition of the present invention.

[0057] The catalyst composition of the present invention may contain precious metal elements other than Pt. As precious metal elements other than Pt, for example, Au, Ag, Pd, Rh, Ir, Ru, Os, etc. can be listed. Precious metal elements other than Pt are contained in the catalyst composition of the present invention in a form that can function as a catalytically active component, such as a metal, an alloy containing precious metal elements, a compound containing precious metal elements (such as an oxide of precious metal elements), etc., which contain catalytically active components of precious metal elements other than Pt. From the viewpoint of improving exhaust gas purification performance, the catalytically active component containing precious metal elements other than Pt is preferably in a granular form.

[0058] In the case where the catalyst composition of the present invention contains Pt and precious metal elements other than Pt, Pt may form an alloy with precious metal elements other than Pt, and the active sites of Pt participating in the exhaust gas purification performance are reduced. Therefore, the catalyst composition of the present invention preferably does not substantially contain precious metal elements other than Pt. "Substantially free of precious metal elements other than Pt" means that the metal conversion amount of precious metal elements other than Pt in the catalyst composition of the present invention is preferably 0.050% by mass or less, and more preferably 0.010% by mass or less, based on the mass of the catalyst composition of the present invention. The lower limit is zero. "The metal conversion amount of precious metal elements other than Pt in the catalyst composition of the present invention" refers to the metal conversion amount of this precious metal element when the catalyst composition of the present invention contains a precious metal element other than Pt, and refers to the sum of the metal conversion amounts of the two or more precious metal elements when the catalyst composition of the present invention contains two or more precious metal elements other than Pt. The metal conversion amount of precious metal elements other than Pt in the catalyst composition of the present invention can be measured in the same way as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0059] The catalyst composition of the present invention contains Sr.

[0060] The catalyst composition of the present invention contains Sr in addition to Pt, and can achieve exhaust gas purification performance in a low-temperature environment and performance of retaining NOx adsorbed at a low temperature until a high temperature while utilizing Pt.

[0061] These effects are related to the amount of basic sites per unit mass of Sr and the strength of the basic sites of Sr. The amount of basic sites per unit mass is related to the amount of NOx adsorbed, and the strength of the basic sites is related to the NOx adsorption power (that is, for a certain element, the greater the amount of basic sites per unit mass of the element, the greater the NOx adsorption amount of the element, the greater the strength of the basic sites of the element, and the greater the NOx adsorption power of the element). Ba and Mg are unable to maintain the NOx adsorbed at low temperatures until high temperatures due to insufficient amount of basic sites per unit mass and / or insufficient strength of basic sites (insufficient NOx adsorption amount and / or NOx adsorption power). On the other hand, since the amount of basic sites per unit mass of Sr and the strength of the basic sites of Sr are sufficient, the NOx adsorbed at low temperatures can be maintained until high temperatures. Thus, the NOx that is not purified in a low temperature environment is adsorbed on Sr and held on Sr until the environment where the catalytic active component (for example, Pt in the catalyst composition of the present invention can be cited, but not limited to) becomes a high temperature environment, and is released after the environment where the catalytic active component becomes a high temperature environment (that is, after the catalytic active component is activated). The released NOx is effectively purified by the activated catalytic active component. In this way, Sr can make up for the exhaust gas purification performance of the catalytic active component in a low temperature environment.

[0062] When the metal conversion amount of Sr in the catalyst composition of the present invention is too small, the effect brought by Sr cannot be fully exerted. On the other hand, when the metal conversion amount of Sr in the catalyst composition of the present invention is too much, the exhaust gas purification performance of Pt in a low temperature environment is reduced instead. The decline in the exhaust gas purification performance of Pt is believed to be related to Sr stabilizing the oxidation state of Pt and deactivating Pt. Therefore, based on the mass of the catalyst composition of the present invention, the metal conversion amount of Sr in the catalyst composition of the present invention is preferably 0.1 mass % or more and 9.0 mass % or less, more preferably 0.5 mass % or more and 7.0 mass % or less, and further preferably 1.0 mass % or more and 5.0 mass % or less. The metal conversion amount of Sr in the catalyst composition of the present invention can be measured in the same manner as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0063] The catalyst composition of the present invention contains one or more Sr sources. The Sr source is not particularly limited as long as it is a compound containing Sr.

[0064] From the viewpoint of more effectively achieving the exhaust gas purification performance in a low temperature environment while utilizing Pt and maintaining the performance of NOx adsorbed at low temperature to high temperature, the Sr source is preferably one or more selected from SrO, SrCO3 and Sr(NO3)2, and more preferably one or two selected from SrO and SrCO3. That is, in the catalyst composition of the present invention, Sr is preferably present in the form of one or more selected from SrO, SrCO3 and Sr(NO3)2, and more preferably in the form of one or two selected from SrO and SrCO3.

[0065] When producing the catalyst composition of the present invention, Sr(NO3)2 which can be used as a raw material is converted into SrO by calcination.

[0066] The catalyst composition of the present invention may contain one or two or more alkaline earth metal elements other than Sr. The alkaline earth metal elements other than Sr are selected from Be, Mg, Ca, Ba and Ra.

[0067] From the viewpoint of more effectively achieving the exhaust gas purification performance in a low temperature environment while utilizing Pt and maintaining the performance of NOx adsorbed at low temperature to high temperature, the metal conversion amount of the alkaline earth metal element other than Sr in the catalyst composition of the present invention is preferably 4.0 mass% or less, more preferably 2.0 mass% or less, and further preferably 1.0 mass% or less, based on the mass of the catalyst composition of the present invention. The lower limit is zero. "The metal conversion amount of the alkaline earth metal element other than Sr in the catalyst composition of the present invention" refers to the metal conversion amount of this alkaline earth metal element when the catalyst composition of the present invention contains one alkaline earth metal element other than Sr, and refers to the sum of the metal conversion amounts of the two or more alkaline earth metal elements when the catalyst composition of the present invention contains two or more alkaline earth metal elements other than Sr. The metal conversion amount of the alkaline earth metal element other than Sr in the catalyst composition of the present invention can be measured in the same way as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0068] The presence form of the alkaline earth metal element other than Sr is not particularly limited. In the catalyst composition of the present invention, the alkaline earth metal element other than Sr may be present in the form of one or more selected from oxides, carbonates, nitrates and sulfates.

[0069] The catalyst composition of the present invention may include one or more carriers. In the case where the catalyst composition of the present invention includes a carrier, it is preferred that at least a portion of the catalytically active component is loaded on the carrier. "At least a portion of the catalytically active component is loaded on the carrier" means that at least a portion of the catalytically active component is physically and / or chemically adsorbed and / or maintained on the outer surface and / or pore inner surface of the carrier. The fact that at least a portion of the catalytically active component is loaded on the carrier can be confirmed using, for example, SEM-EDX. Specifically, in the element mapping obtained by analyzing the catalyst composition using SEM-EDX, when at least a portion of the catalytically active component and the carrier are present in the same region, it can be judged that at least a portion of the catalytically active component is loaded on the carrier.

[0070] Examples of the support include inorganic oxides, etc. In the present specification, unless otherwise specified, "inorganic oxide" means inorganic oxides other than oxides of alkaline earth metal elements (ie, BeO, MgO, CaO, SrO, BaO, and RaO).

[0071] The inorganic oxide is, for example, in a granular form. From the viewpoint of being easy to load the catalytically active component, the inorganic oxide is preferably porous. The inorganic oxide may or may not have oxygen storage capacity (OSC: Oxygen Storage Capacity). In the present specification, an inorganic oxide having OSC is sometimes referred to as an "OSC material". The inorganic oxide used as a carrier is distinguished from the inorganic oxide used as a binder (for example, inorganic oxide-based binders such as alumina binders, zirconia binders, titania binders, and silica binders).

[0072] Examples of the inorganic oxides include Al-based oxides, Ce-Zr-based composite oxides, oxides of rare earth elements (eg, Y2O3, CeO2, etc.), ZrO2, SiO2, TiO2, NiO, and the like.

[0073] In this specification, when the CeO2 conversion amount of Ce is the same as or greater than the Al2O3 conversion amount of Al, the oxide containing Ce, Zr and Al is equivalent to the Ce-Zr series oxide, and when the CeO2 conversion amount of Ce is less than the Al2O3 conversion amount of Al, it is equivalent to the Al series oxide.

[0074] Al-based oxides generally have higher heat resistance than other inorganic oxides (e.g., Ce-Zr-based composite oxides). Therefore, by including Al-based oxides in the catalyst composition of the present invention, the heat resistance of the catalyst composition of the present invention is improved, thereby improving the exhaust gas purification performance of the catalyst composition of the present invention.

[0075] Al-based oxides contain Al and O. Examples of Al-based oxides include aluminum oxide (Al2O3), modified aluminum oxide, and the like. Al-based oxides are distinguished from aluminum oxide used as a binder (sometimes referred to as "alumina binder" in this specification). The alumina binder is derived from an alumina sol used as a raw material for the catalyst composition. Modified aluminum oxide contains one or more elements other than Al and O. Examples of modified aluminum oxides include oxides obtained by modifying the surface of aluminum oxide with elements other than Al and O, oxides obtained by dissolving elements other than Al and O in aluminum oxide, and the like. In Al-based oxides, elements other than Al and O may form a solid solution phase together with Al and O, may form a separate phase as a crystalline phase or an amorphous phase (e.g., an oxide phase of elements other than Al and O), or may form both a solid solution phase and a separate phase.

[0076] From the viewpoint of improving heat resistance, the Al2O3 conversion amount of Al in the Al-based oxide is preferably 90% by mass or more, more preferably 95% by mass or more, and further preferably 98% by mass or more, based on the mass of the Al-based oxide. The upper limit is 100% by mass.

[0077] When the composition of the raw material used to produce the catalyst composition of the present invention is known, the Al 2 O 3 equivalent amount of Al in the Al-based oxide can be calculated from the composition of the raw material used to produce the catalyst composition of the present invention.

[0078] In the case where the composition of the raw materials used to manufacture the catalyst composition of the present invention is unknown, the Al2O3 equivalent amount of Al in the Al-based oxide can be determined by analyzing a sample obtained from the catalyst composition of the present invention using energy dispersive X-ray spectroscopy (EDX), based on the obtained elemental mapping and EDX elemental analysis of the specified particles. Specifically, by elemental mapping, Al-based oxide particles and other particles (e.g., Ce-Zr-based composite oxide particles) are qualitatively identified (color-differentiated), and the specified particles are subjected to composition analysis (elemental analysis), and the oxide equivalent amount of the specified element in the specified particles can be determined.

[0079] From the viewpoint of improving heat resistance, based on the mass of the catalyst composition of the present invention, the amount of Al-based oxides in the catalyst composition of the present invention is preferably greater than 10 mass % and less than 95 mass %, more preferably greater than 20 mass % and less than 90 mass %, and further preferably greater than 30 mass % and less than 80 mass %.

[0080] When the composition of the raw material used to produce the catalyst composition of the present invention is known, the amount of the Al-based oxide in the catalyst composition of the present invention can be determined from the composition of the raw material used to produce the catalyst composition of the present invention.

[0081] When the composition of the raw material used to produce the catalyst composition of the present invention is unknown, the amount of the Al-based oxide in the catalyst composition of the present invention can be measured by a conventional method such as SEM-EDX. Specifically, it is as follows.

[0082] (A) A sample obtained from the catalyst composition of the present invention is subjected to elemental analysis using a conventional method such as SEM-EDX to identify the types of constituent elements of the entire sample and to determine the oxide-equivalent amount (mass %) of a predetermined element.

[0083] (B) The sample obtained from the catalyst composition of the present invention is subjected to element mapping using a conventional method such as SEM-EDX to identify the types of particles contained in the sample (e.g., Al-based oxide particles, Ce-Zr-based composite oxide particles, and other particles as appropriate).

[0084] (C) For each type of particles, an elemental analysis is performed on a plurality of particles (e.g., 50 particles) selected at random using SEM-EDX to determine the types of constituent elements of the particles and to determine the oxide-converted amount (mass %) of the predetermined element. For each type of particles, the average value of the oxide-converted amount (mass %) of the predetermined element is determined and used as the oxide-converted amount (mass %) of the predetermined element in each type of particles.

[0085] (D) By constructing an equation that expresses the relationship between the oxide conversion amount (mass %) of a specified element in a sample, the oxide conversion amount (mass %) of a specified element in various types of particles, and the amount (mass %) of various types of particles in the sample, and solving the equation, the amount (mass %) of various types of particles in the sample is calculated and used as the amount (mass %) of various types of particles in the catalyst composition of the present invention.

[0086] The element other than Al and O contained in the modified alumina can be selected from, for example, La, Zr, Ce, Pr, Ba, Mg, P, Ni, etc., and La is preferred from the viewpoint of improving heat resistance.

[0087] From the viewpoint of improving heat resistance, the La2O3 conversion amount of La in the modified alumina is preferably 0.10 mass % to 20 mass %, more preferably 0.50 mass % to 15 mass %, and further preferably 1.0 mass % to 10 mass % based on the mass of the modified alumina. The La2O3 conversion amount of La in the modified alumina can be measured in the same manner as the Al2O3 conversion amount of Al in the Al-based oxide.

[0088] From the viewpoint of improving heat resistance, the catalyst composition of the present invention preferably contains modified alumina containing La. From the viewpoint of improving heat resistance, the La2O3 conversion amount of La from the modified alumina is preferably 0.20 mass% or more and 5.0 mass% or less, and more preferably 0.30 mass% or more and 3.0 mass% or less, based on the mass of the catalyst composition of the present invention. The La2O3 conversion amount of La from the modified alumina can be calculated based on the amount of modified alumina in the catalyst composition of the present invention and the La2O3 conversion amount of La in the modified alumina.

[0089] Ce-Zr composite oxides have oxygen storage capacity (i.e., the ability to absorb oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low), which can slow down the fluctuation of the oxygen concentration in the exhaust gas and expand the working window of the catalytic active component. Therefore, by including Ce-Zr composite oxides in the catalyst composition of the present invention, the exhaust gas purification capacity of the catalyst composition of the present invention is improved. In particular, when the catalyst composition of the present invention is used as a three-way catalyst for purifying gasoline engine exhaust gas, the Ce-Zr composite oxide controls the oxygen concentration, and the Sr in the catalyst composition of the present invention controls the NOx concentration. As a result, the atmosphere of the exhaust gas is preferred for the Pt in the catalyst composition of the present invention to exert catalytic activity, and the purification performance of Pt is further improved. It should be noted that the catalyst used to purify the exhaust gas of a diesel engine generally does not contain materials with oxygen storage capacity such as Ce-Zr composite oxides. This is because in a diesel engine, the oxygen concentration in the exhaust gas increases significantly due to combustion in a lean region where too much air is inhaled, and therefore the amount of oxygen in the exhaust gas greatly exceeds the amount that can be stored in the Ce-Zr based composite oxide or the like.

[0090] Ce-Zr composite oxides contain Ce, Zr and O. In Ce-Zr composite oxides, Ce, Zr and O preferably form a solid solution phase. Ce, Zr and O can form a single phase (CeO2 phase, ZrO2 phase, etc.) as a crystalline phase or an amorphous phase in addition to the solid solution phase. The fact that Ce, Zr and O form a solid solution can be confirmed using SEM-EDX or the like.

[0091] From the viewpoint of improving oxygen storage capacity, the CeO2 conversion amount of Ce in the Ce-Zr composite oxide is preferably 5.0 mass % or more and 80 mass % or less, more preferably 10 mass % or more and 60 mass % or less, and further preferably 20 mass % or more and 50 mass % or less, based on the mass of the Ce-Zr composite oxide. The CeO2 conversion amount of Ce in the Ce-Zr composite oxide can be measured in the same manner as the Al2O3 conversion amount of Al in the Al-based oxide.

[0092] From the viewpoint of improving heat resistance, based on the mass of Ce-Zr composite oxide, the ZrO2 conversion amount of Zr in Ce-Zr composite oxide is preferably 10 mass % or more and 90 mass % or less, more preferably 30 mass % or more and 80 mass % or less, and further preferably 40 mass % or more and 70 mass % or less. The ZrO2 conversion amount of Zr in Ce-Zr composite oxide can be measured in the same manner as the Al2O3 conversion amount of Al in Al-based oxide.

[0093] From the viewpoint of improving oxygen storage capacity and heat resistance, based on the mass of the Ce-Zr composite oxide, the sum of the CeO2 conversion amount of Ce and the ZrO2 conversion amount of Zr in the Ce-Zr composite oxide is preferably 70% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. The upper limit is 100% by mass.

[0094] Ce-Zr composite oxides may contain one or more metal elements other than Ce and Zr. As metal elements other than Ce and Zr, for example, rare earth elements other than Ce may be cited. As rare earth elements other than Ce, for example, Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. may be cited. Metal elements other than Ce and Zr may form a solid solution phase with Ce, Zr and O, or may form a single phase as a crystalline phase or an amorphous phase, or may form both a solid solution phase and a single phase.

[0095] From the viewpoint of improving oxygen storage capacity and heat resistance, the amount of Ce-Zr composite oxide in the catalyst composition of the present invention is preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less, based on the mass of the catalyst composition of the present invention. The amount of Ce-Zr composite oxide in the catalyst composition of the present invention can be measured in the same manner as the amount of Al-based oxide in the catalyst composition of the present invention.

[0096] From the viewpoint of improving the dispersibility of precious metals, oxygen storage capacity and heat resistance, the amount of inorganic oxides other than Al-based oxides and Ce-Zr-based composite oxides in the catalyst composition of the present invention is preferably 1.0 mass % or more and 50 mass % or less, more preferably 2.0 mass % or more and 30 mass % or less, and even more preferably 5.0 mass % or more and 20 mass % or less, based on the mass of the catalyst composition of the present invention. "The amount of inorganic oxides other than Al-based oxides and Ce-Zr-based composite oxides in the catalyst composition of the present invention" refers to the amount of one inorganic oxide when the catalyst composition of the present invention contains one inorganic oxide other than Al-based oxides and Ce-Zr-based composite oxides, and refers to the total amount of the two or more inorganic oxides when the catalyst composition of the present invention contains two or more inorganic oxides other than Al-based oxides and Ce-Zr-based composite oxides. The amount of inorganic oxides other than Al-based oxides and Ce-Zr-based composite oxides in the catalyst composition of the present invention can be measured in the same manner as the amount of Al-based oxides in the catalyst composition of the present invention.

[0097] From the viewpoint of effectively suppressing A / F fluctuations, based on the mass of the catalyst composition of the present invention, the CeO2 conversion amount of Ce in the catalyst composition of the present invention is preferably 1% by mass or more, more preferably 10% by mass or more, and further preferably 13% by mass or more. From the viewpoint of suppressing the oxidation of Pt, based on the mass of the catalyst composition of the present invention, the CeO2 conversion amount of Ce in the catalyst composition of the present invention is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less. These upper limits can be combined with any one of the above lower limits, respectively. "The CeO2 conversion amount of Ce in the catalyst composition of the present invention" refers to the CeO2 conversion amount of Ce from this Ce source when the catalyst composition of the present invention contains a Ce source, and refers to the sum of the CeO2 conversion amounts of Ce from these two or more Ce sources when the catalyst composition of the present invention contains two or more Ce sources. Ce sources are not particularly limited as long as they contain Ce oxides. As Ce sources, for example, Ce-Zr composite oxides, cerium oxide (CeO2), oxides containing Ce and rare earth elements other than Ce, Al-based oxides containing Ce, etc. can be listed. When the composition of the raw materials used to manufacture the catalyst composition of the present invention is known, the CeO2 conversion amount of Ce in the catalyst composition of the present invention can be calculated from the composition of the raw materials used to manufacture the catalyst composition of the present invention. When the composition of the raw materials used to manufacture the catalyst composition of the present invention is unknown, the CeO2 conversion amount of Ce in the catalyst composition of the present invention can be measured by conventional methods such as inductively coupled plasma emission spectrometry (ICP), X-ray fluorescence analysis (XRF), SEM-EDX, etc.

[0098] The catalyst composition of the present invention can be prepared by, for example, mixing a supply source of Pt, a supply source of Sr and other components (such as inorganic oxides, binders, solvents, etc.), and then drying and calcining. The calcined product can be crushed as needed. The crushing can be carried out in a dry or wet manner using, for example, a mortar, a hammer mill, a ball mill, a bead mill, a jet mill, a roller mill, etc. As a supply source of Pt, for example, Pt salts can be listed, and as Pt salts, for example, nitrates, amine complex salts, acetates, chlorides, etc. can be listed. As a supply source of Sr, for example, Sr salts can be listed, and as Sr salts, for example, nitrates, acetates, carbonates, chlorides, etc. can be listed. As a binder, for example, alumina sol, zirconia sol, titania sol, silica sol, cerium oxide sol, etc. can be listed. As a solvent, for example, water, an organic solvent, etc. can be listed. The drying temperature is, for example, 70°C or more and 150°C or less, and the drying time is, for example, 5 minutes or more and 1 hour or less. The calcination temperature is, for example, 200° C. to 700° C., and the calcination time is, for example, 0.5 hours to 5 hours. The calcination can be performed, for example, in an air atmosphere.

[0099] 《Catalysts for exhaust gas purification》

[0100] The exhaust gas-purifying catalyst of the present invention will be described below.

[0101] <First embodiment>

[0102] The following is based on Figures 1 to 4 , an exhaust gas-purifying catalyst 1A according to a first embodiment of the present invention (sometimes referred to as “catalyst 1A” in this specification) will be described.

[0103] like Figure 1 As shown, the catalyst 1A is arranged in the exhaust passage in the exhaust pipe P of the internal combustion engine. The internal combustion engine is, for example, a gasoline engine. The exhaust gas discharged from the internal combustion engine flows through the exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P, and is purified by the catalyst 1A arranged in the exhaust pipe P. In the drawings, the exhaust gas flow direction is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side" or "upstream side", and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side" or "downstream side".

[0104] Other exhaust gas purifying catalysts may be arranged upstream or downstream of the catalyst 1A in the exhaust passage in the exhaust pipe P. Examples of other exhaust gas purifying catalysts include the exhaust gas purifying catalyst 1B and the exhaust gas purifying catalyst 1C described below.

[0105] like Figures 2 to 4 As shown, the catalyst 1A includes a substrate 10 , and a first catalyst layer 20 and a second catalyst layer 30 provided on the substrate 10 .

[0106] The second catalyst layer 30 is a layer provided as necessary, and the present invention also includes an embodiment in which the second catalyst layer 30 is omitted from the catalyst 1A. However, from the viewpoint of improving the exhaust gas purification performance, it is preferable to provide the second catalyst layer 30.

[0107] The material constituting the substrate 10 can be appropriately selected from known materials. As the material constituting the substrate 10, for example, ceramic materials, metal materials, etc. can be listed, but ceramic materials are preferred. As ceramic materials, for example, carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, tungsten carbide, etc.; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, titanium nitride, etc.; oxide ceramics such as aluminum oxide, zirconium oxide, cordierite, mullite, zircon, aluminum titanate, magnesium titanate, etc. can be listed. As metal materials, for example, alloys such as stainless steel can be listed.

[0108] like Figures 2 to 4 As shown, the substrate 10 includes a cylindrical portion 11, a partition wall portion 12 provided in the cylindrical portion 11, and cells 13 partitioned by the partition wall portion 12. The substrate 10 is preferably a honeycomb structure.

[0109] like Figure 2 As shown, the cylindrical portion 11 defines the outer shape of the substrate 10, and the axial direction of the cylindrical portion 11 is consistent with the axial direction of the substrate 10. Figure 2 As shown, the shape of the cylindrical portion 11 is a cylindrical shape, but it can also be other shapes such as an elliptical cylinder or a polygonal cylinder.

[0110] like Figure 2 and 3 As shown in FIG. 1 , the partition wall portion 12 is disposed inside the cylindrical portion 11. Figures 2 to 4 As shown, there is a partition wall 12 between adjacent chambers 13, and the adjacent chambers 13 are partitioned by the partition wall 12. The partition wall 12 may have a porous structure through which exhaust gas can pass. The thickness of the partition wall 12 is, for example, 20 μm or more and 1500 μm or less.

[0111] like Figure 4 As shown, the chamber 13 extends in the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0112] like Figure 4 As shown, both the end of the exhaust gas inlet side and the end of the exhaust gas outlet side of the chamber 13 are open. Therefore, the exhaust gas flowing in from the end (opening) of the exhaust gas inlet side of the chamber 13 flows out from the end (opening) of the exhaust gas outlet side of the chamber 13. This style is called a flow-through type.

[0113] like Figure 2 and 3As shown, the end (opening) of the chamber 13 on the exhaust gas inlet side is a quadrilateral in plan view, but may be hexagonal, octagonal, or other shapes. The same applies to the end (opening) of the chamber 13 on the exhaust gas outlet side.

[0114] The cavity density per square inch of the substrate 10 is, for example, not less than 100 cavities and not more than 1200 cavities. It should be noted that the cavity density per square inch of the substrate 10 is the total number of cavities 13 per square inch on a cross section obtained by cutting the substrate 10 in a plane perpendicular to the exhaust gas flow direction X.

[0115] The volume of the substrate 10 is, for example, not less than 0.1 L and not more than 20 L. The volume of the substrate 10 refers to the apparent volume of the substrate 10. When the substrate 10 is cylindrical, the outer diameter of the substrate 10 is 2r, and the length of the substrate 10 is L. 10 , then the volume of the substrate 10 is expressed as: Volume of substrate 10 = π × r 2 ×L 10 To express.

[0116] like Figure 4 As shown, the first catalyst layer 20 is provided on the surface of the partition wall 12 of the substrate 10. It should be noted that the surface of the partition wall 12 refers to the outer surface of the partition wall 12 extending in the exhaust gas flow direction X. The first catalyst layer 20 can be directly provided on the surface of the partition wall 12, or can be provided on the surface of the partition wall 12 through other layers.

[0117] like Figure 4 As shown, the first catalyst layer 20 has a portion that protrudes from the surface of the partition wall 12 toward the chamber 13 side (hereinafter referred to as the "protruding portion"). The first catalyst layer 20 may be composed of only the protruding portion, or may have a portion that exists inside the partition wall 12 (hereinafter referred to as the "internal portion"). In addition, the first catalyst layer 20 may be composed of only the internal portion. The "first catalyst layer 20 disposed on the substrate 10" includes: an embodiment in which the first catalyst layer 20 is composed of only the protruding portion, an embodiment in which the first catalyst layer 20 is composed of only the internal portion, and an embodiment in which the first catalyst layer 20 has both the protruding portion and the internal portion.

[0118] like Figure 4As shown, the first catalyst layer 20 extends from the end of the exhaust gas inlet side of the partition 12 to the end of the exhaust gas outlet side of the partition 12 along the exhaust gas flow direction X. The first catalyst layer 20 may also extend from the end of the exhaust gas inlet side of the partition 12 along the exhaust gas flow direction X, but not reach the end of the exhaust gas outlet side of the partition 12; or may extend from the end of the exhaust gas outlet side of the partition 12 in the direction opposite to the exhaust gas flow direction X, but not reach the end of the exhaust gas inlet side of the partition 12.

[0119] The first catalyst layer 20 is composed of the catalyst composition of the present invention. Therefore, the above description about the catalyst composition of the present invention also applies to the first catalyst layer 20. When applicable, "the catalyst composition of the present invention" is replaced with "the first catalyst layer 20".

[0120] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed (mass after calcination) is preferably greater than 50 g / L and less than 230 g / L, more preferably greater than 100 g / L and less than 180 g / L, and even more preferably greater than 130 g / L and less than 160 g / L.

[0121] The mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed is given by the formula: (mass of the first catalyst layer 20) / ((volume of the substrate 10)×(average length L of the first catalyst layer 20) 20 / length L of substrate 10 10 It should be noted that, in this specification, “length” refers to the dimension of the substrate 10 in the axial direction unless otherwise specified.

[0122] The above description about the “mass of the catalyst composition” also applies to the “mass of the first catalyst layer 20”. When applicable, “catalyst composition” can be replaced with “first catalyst layer 20” for understanding. When the information (e.g., composition, amount, etc.) of the raw materials used to manufacture the first catalyst layer 20 is known, the mass of the first catalyst layer 20 can be calculated from the information of the raw materials used to manufacture the first catalyst layer 20.

[0123] The average length L of the first catalyst layer 20 20 An example of the measurement method is as follows.

[0124] A thin film extending in the axial direction of the substrate 10 and having a length L from the substrate 10 is cut out from the catalyst 1A. 10Samples of the same length. The sample is, for example, cylindrical with a diameter of 25.4 mm. It should be noted that the value of the sample diameter can be changed as needed. The sample is cut at intervals of 5 mm along a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained in sequence from the end side of the exhaust gas inflow side of the sample. The length of the slice is 5 mm. The composition of the slice is analyzed using an X-ray fluorescence analyzer (XRF) (such as an energy dispersive X-ray analyzer (EDX), a wavelength dispersive X-ray analyzer (WDX), etc.), an inductively coupled plasma emission spectrometer (ICP-AES), SEM-EDX, etc., and based on the composition of the slice, it is confirmed whether the slice contains a part of the first catalyst layer 20.

[0125] It is not necessary to perform composition analysis on a slice that clearly includes a portion of the first catalyst layer 20. For example, the cross section may be observed using a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), or the like to confirm whether the slice includes a portion of the first catalyst layer 20. When observing the cross section, elemental mapping of the cross section may be performed.

[0126] After confirming whether the slice includes a part of the first catalyst layer 20 , the length of the first catalyst layer 20 included in the sample is calculated based on the following formula.

[0127] Length of the first catalyst layer 20 included in the sample = 5 mm × (number of slices including a portion of the first catalyst layer 20)

[0128] For example, when the 1st to kth slices include a portion of the first catalyst layer 20 but the (k+1)th to nth slices do not include a portion of the first catalyst layer 20, the length of the first catalyst layer 20 included in the sample is (5×k) mm.

[0129] An example of a more detailed method of measuring the length of the first catalyst layer 20 contained in a sample is as follows.

[0130] The k-th slice (i.e., the slice obtained from the exhaust gas outflow side of the sample among the slices including a portion of the first catalyst layer 20) is cut along the axial direction of the substrate 10, and the portion of the first catalyst layer 20 present in the cross section is observed using SEM, EPMA, etc., thereby measuring the length of the portion of the first catalyst layer 20 in the k-th slice. Then, the length of the first catalyst layer 20 contained in the sample is calculated based on the following formula.

[0131] The length of the first catalyst layer 20 included in the sample = (5 mm × (k-1)) + (the length of a portion of the first catalyst layer 20 included in the kth slice)

[0132] The lengths of the first catalyst layers 20 included in the 8 to 16 samples randomly cut out from the catalyst 1A were measured, and the average value thereof was taken as the average length L of the first catalyst layer 20. 20 .

[0133] like Figure 4 As shown, the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20. The expression "the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20" means that, among the two main surfaces of the first catalyst layer 20, part or all of the second catalyst layer 30 exists on the main surface on the opposite side of the main surface on the side of the partition wall 12 of the substrate 10. "The main surface of the first catalyst layer 20" refers to the outer surface of the first catalyst layer 20 extending in the exhaust gas flow direction X. The second catalyst layer 30 can be directly arranged on the main surface of the first catalyst layer 20, or it can be arranged through other layers. The second catalyst layer 30 can be arranged in a manner covering a part of the main surface of the first catalyst layer 20, or it can be arranged in a manner covering the entire main surface of the first catalyst layer 20. "The second catalyst layer 30 arranged on the substrate 10" includes both: an embodiment in which the second catalyst layer 30 is directly arranged on the main surface of the first catalyst layer 20 and an embodiment in which the second catalyst layer 30 is arranged on the main surface of the first catalyst layer 20 through other layers.

[0134] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed (mass after calcination) is preferably greater than 20 g / L and less than 150 g / L, more preferably greater than 50 g / L and less than 120 g / L, and even more preferably greater than 70 g / L and less than 100 g / L.

[0135] The mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed is given by the formula: (mass of the second catalyst layer 30) / ((volume of the substrate 10)×(average length L of the second catalyst layer 30) 30 / length L of substrate 10 10 )) figure it out.

[0136] The above description concerning the “mass of the catalyst composition” also applies to the “mass of the second catalyst layer 30”. When applicable, “catalyst composition” can be replaced with “second catalyst layer 30” for understanding. When the information (e.g., composition, amount, etc.) of the raw materials used to manufacture the second catalyst layer 30 is known, the mass of the second catalyst layer 30 can be calculated from the information of the raw materials used to manufacture the second catalyst layer 30.

[0137] The average length L of the first catalyst layer 20 20The above description of the determination method also applies to the second catalyst layer 30. When applicable, replace "first catalyst layer 20" with "second catalyst layer 30" and replace "average length L 20 " is replaced by "average length L 30 "To understand.

[0138] From the viewpoint of improving NOx purification performance, the second catalyst layer 30 preferably contains Rh. Rh is contained in the second catalyst layer 30 in a form that can function as a catalytically active component, such as metal Rh, an alloy containing Rh, a compound containing Rh (such as an oxide of Rh), or the like. From the viewpoint of improving exhaust gas purification performance, the catalytically active component containing Rh is preferably in a granular form.

[0139] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the metal conversion amount of Rh in the second catalyst layer 30 is preferably 0.010 mass% or more and 1.0 mass% or less, more preferably 0.050 mass% or more and 0.50 mass% or less, and further preferably 0.10 mass% or more and 0.30 mass% or less, based on the mass of the second catalyst layer 30. The metal conversion amount of Rh in the second catalyst layer 30 can be measured in the same manner as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0140] The second catalyst layer 30 may contain precious metal elements other than Rh. Examples of precious metal elements other than Rh include Au, Ag, Pt, Pd, Ir, Ru, and Os. Precious metal elements other than Rh are contained in the second catalyst layer 30 in a form that can function as catalytically active components, such as metals, alloys containing precious metal elements, compounds containing precious metal elements (such as oxides of precious metal elements), and the like, in the form of catalytically active components containing precious metal elements other than Rh. From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements other than Rh are preferably in a granular form.

[0141] When the second catalyst layer 30 contains Rh and a precious metal element other than Rh, Rh may form an alloy with the precious metal element other than Rh, and the active sites of Rh that contribute to the exhaust gas purification performance may decrease. Therefore, the second catalyst layer 30 preferably contains substantially no precious metal element other than Rh.

[0142] In this specification, "a catalyst layer does not substantially contain precious metal elements other than Rh" means that the metal conversion amount of precious metal elements other than Rh in the catalyst layer is preferably 0.050 mass% or less, and more preferably 0.010 mass% or less, based on the mass of the catalyst layer. The lower limit is zero. In addition, in this specification, "the metal conversion amount of precious metal elements other than Rh in a catalyst layer" refers to the metal conversion amount of this precious metal element when the catalyst layer contains a precious metal element other than Rh, and refers to the sum of the metal conversion amounts of the two or more precious metal elements when the catalyst layer contains two or more precious metal elements other than Rh. The metal conversion amount of precious metal elements other than Rh in a catalyst layer can be measured in the same way as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0143] The second catalyst layer 30 may contain one or more alkaline earth metal elements. The alkaline earth metal element is selected from Be, Mg, Ca, Sr, Ba and Ra.

[0144] From the viewpoint of suppressing oxidation of Rh, the metal conversion amount of the alkaline earth metal element in the second catalyst layer 30 is preferably 5.0 mass % or less, more preferably 3.0 mass % or less, and further preferably 1.0 mass % or less, based on the mass of the second catalyst layer 30. The lower limit is zero.

[0145] In this specification, "the metal equivalent amount of the alkaline earth metal element in a certain catalyst layer" refers to the metal equivalent amount of the alkaline earth metal element when the catalyst layer contains one alkaline earth metal element, and refers to the sum of the metal equivalent amounts of the two or more alkaline earth metal elements when the catalyst layer contains two or more alkaline earth metal elements. The metal equivalent amount of the alkaline earth metal element in a certain catalyst layer can be measured in the same manner as the metal equivalent amount of Pt in the catalyst composition of the present invention.

[0146] There is no particular limitation on the form in which the alkaline earth metal element exists in the second catalyst layer 30. In the second catalyst layer 30, the alkaline earth metal element may exist in the form of one or more selected from oxides, carbonates, nitrates, and sulfates.

[0147] The second catalyst layer 30 may include one or more carriers. When the second catalyst layer 30 includes a carrier, it is preferred that at least a portion of the catalytically active component is supported on the carrier. The description of the carrier (including the description of the inorganic oxide) and the meaning and confirmation method of the support are as described above.

[0148] In the catalyst 1A, the second catalyst layer 30 is provided on the upper side of the first catalyst layer 20. Therefore, the exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the chamber 13 contacts the first catalyst layer 20 after contacting the second catalyst layer 30. The exhaust gas contacting the second catalyst layer 30 is purified by the catalytically active component (e.g., Rh) in the second catalyst layer 30. In the case where the environment of the catalyst 1A is a low-temperature environment just after the internal combustion engine is started, the activation of the catalytically active component (e.g., Rh) in the second catalyst layer 30 is insufficient, and thus the exhaust gas purification performance of the second catalyst layer 30 is low. Therefore, in a low-temperature environment, the second catalyst layer 30 may not be able to sufficiently purify NOx. However, NOx that cannot be purified by the second catalyst layer 30 in a low temperature environment is adsorbed on the Sr in the first catalyst layer 20 and is retained on the Sr in the first catalyst layer 20 until the environment in which the first catalyst layer 20 is located becomes a high temperature environment, and is released after the environment in which the first catalyst layer 20 is located becomes a high temperature environment (i.e., after the catalytically active components (e.g., Pt) in the first catalyst layer 20 and / or the catalytically active components (e.g., Rh) in the second catalyst layer 30 are fully activated). The released NOx is effectively purified by the activated catalytically active components (the catalytically active components (e.g., Pt) in the first catalyst layer 20 and / or the catalytically active components (e.g., Rh) in the second catalyst layer 30). In this way, the Sr in the first catalyst layer 20 can compensate for the exhaust gas purification performance of the catalyst 1A in a low temperature environment by retaining the NOx adsorbed at a low temperature until a high temperature.

[0149] When the metal conversion amount of Sr in the first catalyst layer 20 is too small, the effect brought by Sr cannot be fully exerted. When the metal conversion amount of Sr in the first catalyst layer 20 is too much, the exhaust gas purification performance of Pt in the first catalyst layer 20 in a low temperature environment is reduced. The reduction in the exhaust gas purification performance of Pt is believed to be related to Sr stabilizing the oxidation state of Pt and deactivating Pt. Based on the mass of the first catalyst layer 20, when the metal conversion amount of Sr in the first catalyst layer 20 is greater than 0.1 mass% and less than 9.0 mass%, it is possible to more effectively achieve the exhaust gas purification performance in a low temperature environment and the performance of maintaining the NOx adsorbed at low temperature to high temperature while utilizing Pt.

[0150] The catalyst 1A can be produced by forming the first catalyst layer 20 on the substrate 10 and then forming the second catalyst layer 30 on the upper side of the first catalyst layer 20 .

[0151] The first catalyst layer 20 can be formed by mixing a Pt supply source (such as Pt salt), a Sr supply source (such as Sr salt) and other components (such as inorganic oxides, binders, solvents, etc.) to prepare a first slurry, applying the first slurry on the substrate 10, and drying and calcining.

[0152] The second catalyst layer 30 can be formed by mixing a supply source of Rh (eg, Rh salt) and other components (eg, inorganic oxides, binders, solvents, etc.) to prepare a second slurry, applying the second slurry on the first catalyst layer 20, and drying and calcining the mixture.

[0153] The description of Pt salt, Sr salt, inorganic oxide, binder and solvent is as described above. As Rh salt, for example, nitrate, amine complex salt, acetate, chloride, etc. can be listed. The drying temperature is, for example, 70°C to 150°C, and the drying time is, for example, 5 minutes to 1 hour. The calcination temperature is, for example, 200°C to 700°C, and the calcination time is, for example, 0.5 hours to 5 hours. Calcination can be performed, for example, in an air atmosphere.

[0154] <Second embodiment>

[0155] The following is based on Figure 5 , an exhaust gas purification catalyst 1B (sometimes referred to as "catalyst 1B" in this specification) according to a second embodiment of the present invention is described. In catalyst 1B, the same components as catalyst 1A are represented by the same reference numerals as catalyst 1A. Hereinafter, unless otherwise specified, the above description of catalyst 1A also applies to catalyst 1B.

[0156] like Figure 5 As shown, the catalyst 1B includes a substrate 10, and a first catalyst layer 20, a second catalyst layer 30, a third catalyst layer 40, and a fourth catalyst layer 50 provided on the substrate 10. Unless otherwise specified, the description of the substrate 10, the first catalyst layer 20, and the second catalyst layer 30 in the first embodiment also applies to the catalyst 1B.

[0157] The second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50 are layers provided as required, and the present invention also includes an embodiment in which one or more of the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50 are omitted from the catalyst 1B (for example, an embodiment in which the second catalyst layer 30 is omitted, an embodiment in which the third catalyst layer 40 is omitted, an embodiment in which the fourth catalyst layer 50 is omitted, an embodiment in which the second catalyst layer 30 and the third catalyst layer 40 are omitted, an embodiment in which the second catalyst layer 30 and the fourth catalyst layer 50 are omitted, etc.). However, from the viewpoint of improving the exhaust gas purification performance, in an embodiment in which one or more of the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50 are omitted from the catalyst 1B, it is preferred that at least one of the second catalyst layer 30 and the third catalyst layer 40 is provided, and it is preferred that both of them are provided.

[0158] like Figure 5As shown, the difference between catalyst 1B and catalyst 1A is:

[0159] The substrate 10 is provided with a first sealing portion 14 for sealing the end of the exhaust gas outflow side of a part of the chamber 13 and a second sealing portion 15 for sealing the end of the exhaust gas inflow side of the remaining chamber 13, thereby forming an inflow side chamber 13a whose end on the exhaust gas inflow side is open and whose end on the exhaust gas outflow side is blocked by the first sealing portion 14, and an outflow side chamber 13b whose end on the exhaust gas inflow side is blocked by the second sealing portion 15 and whose end on the exhaust gas outflow side is open; and,

[0160] The first catalyst layer 20 and the second catalyst layer 30 are provided on the outflow-side chamber 13 b side of the partition wall 12 of the substrate 10 , and the third catalyst layer 40 and the fourth catalyst layer 50 are provided on the inflow-side chamber 13 a side of the partition wall 12 of the substrate 10 .

[0161] like Figure 5 As shown, a plurality of (eg, four) outflow-side chambers 13 b are adjacently arranged around one inflow-side chamber 13 a , and the inflow-side chamber 13 a and the outflow-side chamber 13 b adjacent to the inflow-side chamber 13 a are partitioned by a porous partition wall 12 .

[0162] like Figure 5 As shown, the first catalyst layer 20 extends from the end of the partition wall 12 on the exhaust gas outflow side in the direction opposite to the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas inflow side. The first catalyst layer 20 may also reach the end of the partition wall 12 on the exhaust gas inflow side.

[0163] like Figure 5 As shown, the first catalyst layer 20 has a portion that protrudes from the surface of the partition wall 12 toward the outflow side chamber 13b side (hereinafter referred to as the "protruding portion"). The first catalyst layer 20 may be composed of only the protruding portion, or may have a portion that exists inside the partition wall 12 (hereinafter referred to as the "internal portion"). In addition, the first catalyst layer 20 may be composed of only the internal portion. The "first catalyst layer 20 disposed on the substrate 10" includes: an embodiment in which the first catalyst layer 20 is composed of only the protruding portion, an embodiment in which the first catalyst layer 20 is composed of only the internal portion, and an embodiment in which the first catalyst layer 20 has both the protruding portion and the internal portion.

[0164] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed (the mass after calcination) is preferably greater than 5 g / L and less than 60 g / L, more preferably greater than 10 g / L and less than 40 g / L, and even more preferably greater than 10 g / L and less than 30 g / L.

[0165] The mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed can be obtained in the same manner as in the first embodiment.

[0166] Average length L of the first catalyst layer 20 in the second embodiment 20 The method for measuring the length L of the first catalyst layer 20 is the same as that of the first embodiment, but in the second embodiment, the average length L of the first catalyst layer 20 is 20 In the measuring method, the sample is cut at intervals of 5 mm along a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained in order from the end side of the exhaust gas outflow side of the sample.

[0167] The average length L of the first catalyst layer 20 20 The average length L of the first catalyst layer 20 may be appropriately adjusted in consideration of the exhaust gas purification performance, the PM trapping performance, etc. From the viewpoint of improving the exhaust gas purification performance and the PM trapping performance, the average length L of the first catalyst layer 20 may be 20 Relative to the length L of the substrate 10 10 Percentage (L 20 / L 10 × 100) is preferably 15% to 90%, more preferably 20% to 80%, further preferably 30% to 80%.

[0168] like Figure 5 As shown, the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20, extending from the end of the exhaust gas outflow side of the partition 12 in the direction opposite to the exhaust gas flow direction X, but does not reach the end of the exhaust gas inflow side of the partition 12. The second catalyst layer 30 can also reach the end of the exhaust gas inflow side of the partition 12. The meanings of "the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20" and "the main surface of the first catalyst layer 20" are as described above. The second catalyst layer 30 can be directly arranged on the main surface of the first catalyst layer 20, or it can be arranged through other layers. The second catalyst layer 30 can be arranged in a manner covering a portion of the main surface of the first catalyst layer 20, or it can be arranged in a manner covering the entire main surface of the first catalyst layer 20. "The second catalyst layer 30 arranged on the substrate 10" includes: an embodiment in which the second catalyst layer 30 is directly arranged on the main surface of the first catalyst layer 20 and an embodiment in which the second catalyst layer 30 is arranged on the main surface of the first catalyst layer 20 through other layers.

[0169] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed (mass after calcination) is preferably greater than 5 g / L and less than 60 g / L, more preferably greater than 10 g / L and less than 40 g / L, and even more preferably greater than 10 g / L and less than 30 g / L.

[0170] The mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed can be obtained in the same manner as in the first embodiment.

[0171] Average length L of the second catalyst layer 30 in the second embodiment 30 The method for measuring the length L of the second catalyst layer 30 is the same as that of the first embodiment, but in the second embodiment, the average length L of the second catalyst layer 30 is 30 In the measuring method, the sample is cut at intervals of 5 mm along a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained in order from the end side of the exhaust gas outflow side of the sample.

[0172] The average length L of the second catalyst layer 30 30 The average length L of the second catalyst layer 30 may be appropriately adjusted in consideration of the exhaust gas purification performance, the PM trapping performance, etc. From the viewpoint of improving the exhaust gas purification performance and the PM trapping performance, the average length L of the second catalyst layer 30 may be 100 mm / s. 30 Relative to the length L of the substrate 10 10 Percentage (L 30 / L 10 × 100) is preferably 15% to 90%, more preferably 20% to 80%, further preferably 30% to 80%.

[0173] like Figure 5As shown, the third catalyst layer 40 is arranged on the upper side of the fourth catalyst layer 50. The expression "the third catalyst layer 40 is arranged on the upper side of the fourth catalyst layer 50" means that, of the two main surfaces of the fourth catalyst layer 50, part or all of the third catalyst layer 40 exists on the main surface on the side opposite to the main surface on the partition wall 12 side of the substrate 10. "The main surface of the fourth catalyst layer 50" refers to the outer surface of the fourth catalyst layer 50 extending in the exhaust gas flow direction X. The third catalyst layer 40 can be directly arranged on the main surface of the fourth catalyst layer 50, or it can be arranged through other layers. The third catalyst layer 40 can be arranged in a manner covering a portion of the main surface of the fourth catalyst layer 50, or it can be arranged in a manner covering the entire main surface of the fourth catalyst layer 50. "The third catalyst layer 40 arranged on the substrate 10" includes both an embodiment in which the third catalyst layer 40 is directly arranged on the main surface of the fourth catalyst layer 50 and an embodiment in which the third catalyst layer 40 is arranged on the main surface of the fourth catalyst layer 50 through other layers.

[0174] like Figure 5 As shown, the third catalyst layer 40 extends from the end of the partition wall 12 on the exhaust gas inlet side along the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas outlet side. The third catalyst layer 40 may also reach the end of the partition wall 12 on the exhaust gas outlet side.

[0175] like Figure 5 As shown, the third catalyst layer 40 is disposed on the upstream side of the first catalyst layer 20. The expression "the third catalyst layer 40 is disposed on the upstream side of the first catalyst layer 20" means that part or all of the third catalyst layer 40 exists in an area located on the upstream side of the exhaust gas flow direction X compared to the area where the first catalyst layer 20 is disposed in the partition wall portion 12 of the substrate 10.

[0176] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the third catalyst layer 40 per unit volume of the portion of the substrate 10 where the third catalyst layer 40 is formed (the mass after calcination) is preferably greater than 5 g / L and less than 60 g / L, more preferably greater than 10 g / L and less than 40 g / L, and even more preferably greater than 10 g / L and less than 30 g / L.

[0177] The mass of the third catalyst layer 40 per unit volume of the portion of the substrate 10 where the third catalyst layer 40 is formed is given by the formula: (mass of the third catalyst layer 40) / ((volume of the substrate 10)×(average length L of the third catalyst layer 40) 40 / length L of substrate 10 10 )) figure it out.

[0178] The above description about the “mass of the catalyst composition” also applies to the “mass of the third catalyst layer 40”. When applicable, “catalyst composition” can be replaced with “third catalyst layer 40” for understanding. When the information (e.g., composition, amount, etc.) of the raw materials used to manufacture the third catalyst layer 40 is known, the mass of the third catalyst layer 40 can be calculated from the information of the raw materials used to manufacture the third catalyst layer 40.

[0179] Regarding the average length L of the first catalyst layer 20 in the first embodiment 20 The above description of the measurement method also applies to the average length L of the third catalyst layer 40. 40 When applicable, replace "first catalyst layer 20" with "third catalyst layer 40" and replace "average length L 20 " is replaced by "average length L 40 "To understand.

[0180] The average length L of the third catalyst layer 40 40 The average length L of the third catalyst layer 40 may be appropriately adjusted in consideration of the exhaust gas purification performance, the PM trapping performance, etc. From the viewpoint of improving the exhaust gas purification performance and the PM trapping performance, the average length L of the third catalyst layer 40 may be 100 mm / s. 40 Relative to the length L of the substrate 10 10 Percentage (L 40 / L 10 × 100) is preferably 15% to 90%, more preferably 20% to 80%, further preferably 30% to 80%.

[0181] From the viewpoint of improving the exhaust gas purification performance and PM capture performance, the average length L of the first catalyst layer 20 is 20 Or the average length L of the second catalyst layer 30 30 The average length L of the third catalyst layer 40 40 The sum of the length L of the substrate 10 10 The percentage of 20 or L 30 )+L 40 ) / L 10 ×100) is preferably 100% to 180%, more preferably 105% to 150%, further preferably 110% to 130%.

[0182] From the viewpoint of improving NOx purification performance, the third catalyst layer 40 preferably contains Rh. Rh is contained in the third catalyst layer 40 in a form that can function as a catalytically active component, such as metal Rh, an alloy containing Rh, a compound containing Rh (such as an oxide of Rh), or the like. From the viewpoint of improving exhaust gas purification performance, the catalytically active component containing Rh is preferably in a granular form.

[0183] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the metal conversion amount of Rh in the third catalyst layer 40 is preferably 0.050 mass% or more and 2.0 mass% or less, more preferably 0.10 mass% or more and 1.5 mass% or less, and further preferably 0.20 mass% or more and 1.0 mass% or less, based on the mass of the third catalyst layer 40. The metal conversion amount of Rh in the third catalyst layer 40 can be measured in the same manner as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0184] The third catalyst layer 40 may contain precious metal elements other than Rh. Examples of precious metal elements other than Rh include Au, Ag, Pt, Pd, Ir, Ru, and Os. Precious metal elements other than Rh are contained in the third catalyst layer 40 in a form that can function as catalytically active components, such as metals, alloys containing precious metal elements, compounds containing precious metal elements (such as oxides of precious metal elements), and the like, in the form of catalytically active components containing precious metal elements other than Rh. From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements other than Rh are preferably in a granular form.

[0185] When the third catalyst layer 40 contains Rh and a precious metal element other than Rh, Rh may form an alloy with the precious metal element other than Rh, and the active sites of Rh that participate in the exhaust gas purification performance are reduced. Therefore, the third catalyst layer 40 preferably does not substantially contain precious metal elements other than Rh. The meanings of "substantially containing no precious metal elements other than Rh" and "the metal equivalent amount of precious metal elements other than Rh" and the method for determining the metal equivalent amount of precious metal elements other than Rh are as described above.

[0186] The third catalyst layer 40 may contain one or more alkaline earth metal elements. The alkaline earth metal element is selected from Be, Mg, Ca, Sr, Ba and Ra.

[0187] From the viewpoint of suppressing the oxidation of Rh, the metal conversion amount of the alkaline earth metal element in the third catalyst layer 40 is preferably 5.0 mass % or less, more preferably 3.0 mass % or less, and further preferably 1.0 mass % or less, based on the mass of the third catalyst layer 40. The lower limit is zero. The meaning of "metal conversion amount of alkaline earth metal element" and the method for determining the metal conversion amount of alkaline earth metal element are as described above.

[0188] There is no particular limitation on the form in which the alkaline earth metal element exists in the third catalyst layer 40. In the third catalyst layer 40, the alkaline earth metal element may exist in the form of one or more selected from oxides, carbonates, nitrates, and sulfates.

[0189] The third catalyst layer 40 may include one or more carriers. When the third catalyst layer 40 includes a carrier, it is preferred that at least a portion of the catalytically active component is supported on the carrier. The description of the carrier (including the description of the inorganic oxide) and the meaning and confirmation method of the support are as described above.

[0190] like Figure 5 As shown, the fourth catalyst layer 50 is disposed on the surface of the partition wall 12 of the substrate 10. It should be noted that the surface of the partition wall 12 refers to the outer surface of the partition wall 12 extending in the exhaust gas flow direction X. The fourth catalyst layer 50 may be disposed directly on the surface of the partition wall 12 or may be disposed on the surface of the partition wall 12 via other layers.

[0191] like Figure 5 As shown, the 4th catalyst layer 50 has a portion protruding from the surface of the partition wall 12 toward the inflow side chamber 13a side (hereinafter referred to as the "protruding portion"). The 4th catalyst layer 50 may be composed only of the protruding portion, or may have a portion existing inside the partition wall 12 (hereinafter referred to as the "internal portion"). In addition, the 4th catalyst layer 50 may be composed only of the internal portion. The "4th catalyst layer 50 disposed on the substrate 10" includes: an embodiment in which the 4th catalyst layer 50 is composed only of the protruding portion, an embodiment in which the 4th catalyst layer 50 is composed only of the internal portion, and an embodiment in which the 4th catalyst layer 50 has a protruding portion and an internal portion.

[0192] like Figure 5 As shown, the fourth catalyst layer 50 extends from the end of the partition wall 12 on the exhaust gas inlet side along the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas outlet side. The fourth catalyst layer 50 may reach the end of the partition wall 12 on the exhaust gas outlet side.

[0193] like Figure 5As shown, the fourth catalyst layer 50 is disposed on the upstream side of the first catalyst layer 20. The expression "the fourth catalyst layer 50 is disposed on the upstream side of the first catalyst layer 20" means that part or all of the fourth catalyst layer 50 exists in an area located on the upstream side of the exhaust gas flow direction X compared to the area where the first catalyst layer 20 is disposed in the partition wall portion 12 of the substrate 10.

[0194] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the 4th catalyst layer 50 per unit volume of the portion of the substrate 10 where the 4th catalyst layer 50 is formed (mass after calcination) is preferably greater than 5 g / L and less than 60 g / L, more preferably greater than 10 g / L and less than 40 g / L, and even more preferably greater than 10 g / L and less than 30 g / L.

[0195] The mass of the fourth catalyst layer 50 per unit volume of the portion of the substrate 10 where the fourth catalyst layer 50 is formed is given by the formula: (mass of the fourth catalyst layer 50) / ((volume of the substrate 10)×(average length L of the fourth catalyst layer 50) 50 / length L of substrate 10 10 )) figure it out.

[0196] The above description about the “mass of the catalyst composition” also applies to the “mass of the fourth catalyst layer 50”. When applicable, “catalyst composition” can be replaced with “fourth catalyst layer 50” for understanding. When the information (e.g., composition, amount, etc.) of the raw materials used to manufacture the fourth catalyst layer 50 is known, the mass of the fourth catalyst layer 50 can be calculated from the information of the raw materials used to manufacture the fourth catalyst layer 50.

[0197] Regarding the average length L of the first catalyst layer 20 in the first embodiment 20 The above description of the measurement method also applies to the average length L of the fourth catalyst layer 50. 50 Where applicable, replace “first catalyst layer 20” with “fourth catalyst layer 50” and replace “average length L 20 " is replaced by "average length L 50 "To understand.

[0198] The average length L of the fourth catalyst layer 50 50 The average length L of the fourth catalyst layer 50 may be appropriately adjusted in consideration of the exhaust gas purification performance, the PM trapping performance, etc. From the viewpoint of improving the exhaust gas purification performance and the PM trapping performance, the average length L of the fourth catalyst layer 50 may be 100 mm / s. 50 Relative to the length L of the substrate 10 10 Percentage (L 50 / L 10× 100) is preferably 15% to 90%, more preferably 20% to 80%, further preferably 30% to 80%.

[0199] From the viewpoint of improving the exhaust gas purification performance and PM capture performance, the average length L of the first catalyst layer 20 is 20 Or the average length L of the second catalyst layer 30 30 The average length L of the fourth catalyst layer 50 50 The sum of the length L of the substrate 10 10 The percentage of 20 or L 30 )+L 50 ) / L 10 ×100) is preferably 100% to 180%, more preferably 105% to 150%, further preferably 110% to 130%.

[0200] From the viewpoint of improving the exhaust gas purification performance, the fourth catalyst layer 50 preferably contains Pd. Pd is contained in the fourth catalyst layer 50 in a form that can function as a catalytically active component, such as a form of a catalytically active component containing Pd, such as metallic Pd, an alloy containing Pd, a compound containing Pd (such as an oxide of Pd), etc. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing Pd is preferably in a granular form.

[0201] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the metal conversion amount of Pd in ​​the fourth catalyst layer 50 is preferably 0.50 mass% or more and 10 mass% or less, more preferably 1.0 mass% or more and 7.0 mass% or less, and further preferably 2.0 mass% or more and 5.0 mass% or less, based on the mass of the fourth catalyst layer 50. The metal conversion amount of Pd in ​​the fourth catalyst layer 50 can be measured in the same manner as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0202] The fourth catalyst layer 50 may contain precious metal elements other than Pd. Examples of precious metal elements other than Pd include Au, Ag, Rh, Pt, Ir, Ru, and Os. Precious metal elements other than Pd are contained in the fourth catalyst layer 50 in a form that can function as catalytically active components, such as metals, alloys containing precious metal elements, compounds containing precious metal elements (e.g., oxides of precious metal elements), and the like, in the form of catalytically active components containing precious metal elements other than Pd. From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements other than Pd are preferably in a granular form.

[0203] When the fourth catalyst layer 50 contains Pd and a noble metal element other than Pd, Pd may form an alloy with the noble metal element other than Pd, and the active sites of Pd that contribute to the exhaust gas purification performance may decrease. Therefore, the fourth catalyst layer 50 preferably contains substantially no noble metal element other than Pd.

[0204] In this specification, "a catalyst layer does not substantially contain precious metal elements other than Pd" means that the metal conversion amount of precious metal elements other than Pd in ​​the catalyst layer is preferably 0.050 mass% or less, and more preferably 0.010 mass% or less, based on the mass of the catalyst layer. The lower limit is zero. In addition, in this specification, "the metal conversion amount of precious metal elements other than Pd in ​​a catalyst layer" refers to the metal conversion amount of this precious metal element when the catalyst layer contains a precious metal element other than Pd, and refers to the sum of the metal conversion amounts of the two or more precious metal elements when the catalyst layer contains two or more precious metal elements other than Pd. The metal conversion amount of precious metal elements other than Pd in ​​a catalyst layer can be measured in the same way as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0205] The fourth catalyst layer 50 may contain one or more alkaline earth metal elements. The alkaline earth metal element is selected from Be, Mg, Ca, Sr, Ba and Ra.

[0206] From the viewpoint of maintaining the oxidation state of Pd, the metal conversion amount of the alkaline earth metal element in the fourth catalyst layer 50 is preferably 1.0 mass % or more and 10.0 mass % or less, more preferably 2.0 mass % or more and 6.0 mass % or less, and further preferably 3.0 mass % or more and 4.0 mass % or less, based on the mass of the fourth catalyst layer 50. The meaning of "metal conversion amount of alkaline earth metal element" and the method for measuring the metal conversion amount of alkaline earth metal element are as described above.

[0207] There is no particular limitation on the form in which the alkaline earth metal element exists in the fourth catalyst layer 50. In the fourth catalyst layer 50, the alkaline earth metal element may exist in the form of one or more selected from oxides, carbonates, nitrates, and sulfates.

[0208] The fourth catalyst layer 50 may include one or more carriers. When the fourth catalyst layer 50 includes a carrier, it is preferred that at least a portion of the catalytically active component is supported on the carrier. The description of the carrier (including the description of the inorganic oxide) and the meaning and confirmation method of the support are as described above.

[0209] In the catalyst 1B, the exhaust gas flowing in from the end (opening) of the inlet chamber 13a on the exhaust gas inlet side passes through the porous partition wall 12 and flows out from the end (opening) of the outlet chamber 13b on the exhaust gas outlet side. This is called a wall flow type.

[0210] In the catalyst 1B, when the exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow side chamber 13a passes through the porous partition wall 12, particulate matter (PM: Particulate Matter) in the exhaust gas is captured in the pores of the partition wall 12. Therefore, the catalyst 1B can be used as a particulate filter (Gasoline Particulate Filter) for a gasoline engine or a particulate filter (Diesel Particulate Filter) for a diesel engine.

[0211] In the catalyst 1B, the third catalyst layer 40 and the fourth catalyst layer 50 are provided on the upstream side of the first catalyst layer 20 and the second catalyst layer 30. Therefore, the exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the inflow side chamber 13a contacts the third catalyst layer 40 and the fourth catalyst layer 50, passes through the porous partition wall 12, and contacts the first catalyst layer 20 and the second catalyst layer 30. The exhaust gas contacting the third catalyst layer 40 and the fourth catalyst layer 50 is purified by the catalytically active components (e.g., Rh) in the third catalyst layer 40 and the catalytically active components (e.g., Pd) in the fourth catalyst layer 50. In the case where the environment of the catalyst 1B is a low temperature environment immediately after the internal combustion engine is started, the activation of the catalytically active components (e.g., Rh) in the third catalyst layer 40 and the catalytically active components (e.g., Pd) in the fourth catalyst layer 50 is insufficient, and thus the exhaust gas purification performance of the third catalyst layer 40 and the fourth catalyst layer 50 is low. Therefore, in a low temperature environment, the third catalyst layer 40 and the fourth catalyst layer 50 may not be able to sufficiently purify NOx. However, the NOx that the third catalyst layer 40 and the fourth catalyst layer 50 cannot purify in a low temperature environment is adsorbed on the Sr in the first catalyst layer 20 and is held on the Sr in the first catalyst layer 20 until the environment in which the first catalyst layer 20 and the second catalyst layer 30 are located becomes a high temperature environment, and is released after the environment in which the first catalyst layer 20 and the second catalyst layer 30 are located becomes a high temperature environment (that is, after the catalytically active component (e.g., Pt) in the first catalyst layer 20 and / or the catalytically active component (e.g., Rh) in the second catalyst layer 30 is activated). The released NOx is effectively purified by the activated catalytically active component (the catalytically active component (e.g., Pt) in the first catalyst layer 20 and / or the catalytically active component (e.g., Rh) in the second catalyst layer 30). In this way, the Sr in the first catalyst layer 20 can make up for the exhaust gas purification performance of the catalyst 1B in a low temperature environment by holding the NOx adsorbed at a low temperature until a high temperature.

[0212] When the metal conversion amount of Sr in the first catalyst layer 20 is too small, the effect brought by Sr cannot be fully exerted. When the metal conversion amount of Sr in the first catalyst layer 20 is too much, the exhaust gas purification performance of Pt in the first catalyst layer 20 in a low temperature environment is reduced. The reduction in the exhaust gas purification performance of Pt is believed to be related to Sr stabilizing the oxidation state of Pt and deactivating Pt. Based on the mass of the first catalyst layer 20, when the metal conversion amount of Sr in the first catalyst layer 20 is greater than 0.1 mass% and less than 9.0 mass%, it is possible to more effectively achieve exhaust gas purification performance in a low temperature environment and NOx adsorption performance in a high temperature environment while utilizing Pt.

[0213] Catalyst 1B can be produced by the following method. The production conditions and the like of catalyst 1B are the same as those of catalyst 1A.

[0214] The slurry for forming the first catalyst layer 20 may be attached to the exhaust gas outlet side of the substrate 10, and after drying the slurry, it may be baked as needed to form the first catalyst layer 20. After forming the first catalyst layer 20, the slurry for forming the second catalyst layer 30 may be attached to the exhaust gas outlet side of the substrate 10, and after drying the slurry, it may be baked as needed to form the second catalyst layer 30.

[0215] The slurry for forming the fourth catalyst layer 50 may be attached to the exhaust gas inflow side of the substrate 10, and after drying the slurry, it may be baked as needed to form the fourth catalyst layer 50. After forming the fourth catalyst layer 50, the slurry for forming the third catalyst layer 40 may be attached to the exhaust gas inflow side of the substrate 10, and after drying the slurry, it may be baked as needed to form the third catalyst layer 40.

[0216] The slurry for forming the third catalyst layer 40 can be prepared by mixing a supply source of Rh (eg, Rh salt) and other components (eg, inorganic oxide, binder, solvent, etc.) The Rh salt, inorganic oxide, binder, and solvent are as described above.

[0217] The slurry for forming the fourth catalyst layer 50 can be prepared by mixing a Pd supply source (e.g., a Pd salt) and other components (e.g., an inorganic oxide, a binder, a solvent, etc.). Examples of the Pd salt include nitrates, amine complex salts, acetates, chlorides, etc. The inorganic oxides, binders, and solvents are as described above.

[0218] <Third embodiment>

[0219] The following is based on Figure 6, an exhaust gas purification catalyst 1C (sometimes referred to as "catalyst 1C" in this specification) according to a third embodiment of the present invention is described. In catalyst 1C, components identical to those of catalyst 1A are denoted by the same reference numerals as those of catalyst 1A. Hereinafter, unless otherwise specified, the above description of catalyst 1A also applies to catalyst 1C.

[0220] like Figure 6 As shown, the catalyst 1C includes a substrate 10, and a first catalyst layer 20, a second catalyst layer 30, and a fifth catalyst layer 60 provided on the substrate 10. Unless otherwise specified, the description of the substrate 10, the first catalyst layer 20, and the second catalyst layer 30 in the first embodiment also applies to the catalyst 1C.

[0221] The second catalyst layer 30 is a layer provided as necessary, and the present invention also includes an embodiment in which the second catalyst layer 30 is omitted from the catalyst 1C. However, from the viewpoint of improving the exhaust gas purification performance, it is preferable to provide the second catalyst layer 30.

[0222] like Figure 6 As shown, the difference between catalyst 1C and catalyst 1A is:

[0223] The fifth catalyst layer 60 is disposed on the upstream side of the first catalyst layer 20; and

[0224] The second catalyst layer 30 is provided on the upper side of the first catalyst layer 20 and the fifth catalyst layer 60 .

[0225] In this embodiment, if Figure 6 As shown, a portion of the second catalyst layer 30 is disposed on the upper side of the first catalyst layer 20, and the remaining portion of the second catalyst layer 30 is disposed on the upper side of the fifth catalyst layer 60, but the entire second catalyst layer 30 may also be disposed on the upper side of one of the first catalyst layer 20 or the fifth catalyst layer 60.

[0226] like Figure 6 As shown, the first catalyst layer 20 extends from the end of the partition wall 12 on the exhaust gas outflow side in the direction opposite to the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas inflow side.

[0227] like Figure 6 As shown, the fifth catalyst layer 60 is provided on the surface of the partition wall 12 of the substrate 10. It should be noted that the surface of the partition wall 12 refers to the outer surface of the partition wall 12 extending in the exhaust gas flow direction X. The fifth catalyst layer 60 may be provided directly on the surface of the partition wall 12 or may be provided on the surface of the partition wall 12 via other layers.

[0228] like Figure 6As shown, the fifth catalyst layer 60 extends from the end of the partition wall 12 on the exhaust gas inlet side along the exhaust gas flow direction X, but does not reach the end of the partition wall 12 on the exhaust gas outlet side.

[0229] like Figure 6 As shown, the fifth catalyst layer 60 has a portion protruding from the surface of the partition wall 12 toward the chamber 13 side (hereinafter referred to as the "protruding portion"). The fifth catalyst layer 60 may consist of only the protruding portion, or may have a portion existing inside the partition wall 12 (hereinafter referred to as the "internal portion"). In addition, the fifth catalyst layer 60 may consist of only the internal portion. The "fifth catalyst layer 60 disposed on the substrate 10" includes: an embodiment in which the fifth catalyst layer 60 consists of only the protruding portion, an embodiment in which the fifth catalyst layer 60 consists of only the internal portion, and an embodiment in which the fifth catalyst layer 60 has both the protruding portion and the internal portion.

[0230] like Figure 6 As shown, the fifth catalyst layer 60 is disposed on the upstream side of the first catalyst layer 20. The expression "the fifth catalyst layer 60 is disposed on the upstream side of the first catalyst layer 20" means that part or all of the fifth catalyst layer 60 exists in an area located on the upstream side of the exhaust gas flow direction X compared to the area where the first catalyst layer 20 is disposed in the partition wall portion 12 of the substrate 10.

[0231] like Figure 6 As shown, the end of the first catalyst layer 20 on the exhaust gas inlet side and the end of the fifth catalyst layer 60 on the exhaust gas outlet side are in contact with each other at the boundary surface S.

[0232] The end of the exhaust gas inlet side of the first catalyst layer 20 may have a portion overlapping with the end of the exhaust gas outlet side of the fifth catalyst layer 60 (i.e., a portion located above the end of the exhaust gas outlet side of the fifth catalyst layer 60 and covering the end of the exhaust gas outlet side of the fifth catalyst layer 60). In addition, the end of the exhaust gas outlet side of the fifth catalyst layer 60 may have a portion overlapping with the end of the exhaust gas inlet side of the first catalyst layer 20 (i.e., a portion located above the end of the exhaust gas inlet side of the first catalyst layer 20 and covering the end of the exhaust gas inlet side of the first catalyst layer 20). These cases are also included in "the fifth catalyst layer 60 is disposed on the upstream side of the first catalyst layer 20".

[0233] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed (mass after calcination) is preferably greater than 50 g / L and less than 230 g / L, more preferably greater than 100 g / L and less than 180 g / L, and even more preferably greater than 130 g / L and less than 160 g / L.

[0234] The mass of the first catalyst layer 20 per unit volume of the portion of the substrate 10 where the first catalyst layer 20 is formed can be obtained in the same manner as in the first embodiment.

[0235] Average length L of the first catalyst layer 20 in the third embodiment 20 The method for measuring the length L of the first catalyst layer 20 is the same as that of the first embodiment, but in the third embodiment, the average length L of the first catalyst layer 20 is 20 In the measuring method, the sample is cut at intervals of 5 mm along a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained in order from the end side of the exhaust gas outflow side of the sample.

[0236] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the 5th catalyst layer 60 per unit volume of the portion of the substrate 10 where the 5th catalyst layer 60 is formed (mass after calcination) is preferably greater than 20 g / L and less than 150 g / L, more preferably greater than 50 g / L and less than 120 g / L, and even more preferably greater than 70 g / L and less than 100 g / L.

[0237] The mass of the fifth catalyst layer 60 per unit volume of the portion of the substrate 10 where the fifth catalyst layer 60 is formed is given by the formula: (mass of the fifth catalyst layer 60) / (volume of the substrate 10×(average length L of the fifth catalyst layer 60) 60 / length L of substrate 10 10 )) figure it out.

[0238] The above description about the “mass of the catalyst composition” also applies to the “mass of the fifth catalyst layer 60”. When applicable, “catalyst composition” can be replaced with “fifth catalyst layer 60” for understanding. When the information (e.g., composition, amount, etc.) of the raw materials used to manufacture the fifth catalyst layer 60 is known, the mass of the fifth catalyst layer 60 can be calculated from the information of the raw materials used to manufacture the fifth catalyst layer 60.

[0239] Regarding the average length L of the first catalyst layer 20 in the first embodiment 20 The above description of the measurement method also applies to the average length L of the fifth catalyst layer 60. 60 Where applicable, replace “first catalyst layer 20” with “fifth catalyst layer 60” and replace “average length L 20 " is replaced by "average length L 60 "To understand.

[0240] From the viewpoint of improving the exhaust gas purification performance, the fifth catalyst layer 60 preferably contains Pd. Pd is contained in the fifth catalyst layer 60 in a form that can function as a catalytically active component, such as metal Pd, an alloy containing Pd, a compound containing Pd (such as an oxide of Pd), or the like. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing Pd is preferably in a granular form.

[0241] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the metal conversion amount of Pd in ​​the fifth catalyst layer 60 is preferably 0.50 mass% or more and 10 mass% or less, more preferably 1.0 mass% or more and 7.0 mass% or less, and further preferably 2.0 mass% or more and 5.0 mass% or less, based on the mass of the fifth catalyst layer 60. The metal conversion amount of Pd in ​​the fifth catalyst layer 60 can be measured in the same manner as the metal conversion amount of Pt in the catalyst composition of the present invention.

[0242] The fifth catalyst layer 60 may contain precious metal elements other than Pd. Examples of precious metal elements other than Pd include Au, Ag, Rh, Pt, Ir, Ru, and Os. Precious metal elements other than Pd are contained in the fifth catalyst layer 60 in a form that can function as catalytically active components, such as metals, alloys containing precious metal elements, compounds containing precious metal elements (e.g., oxides of precious metal elements), and the like, in the form of catalytically active components containing precious metal elements other than Pd. From the viewpoint of improving exhaust gas purification performance, the catalytically active components containing precious metal elements other than Pd are preferably in a granular form.

[0243] When the fifth catalyst layer 60 contains Pd and a precious metal element other than Pd, Pd may form an alloy with the precious metal element other than Pd, and the active sites of Pd that participate in the exhaust gas purification performance are reduced. Therefore, the fifth catalyst layer 60 preferably does not substantially contain precious metal elements other than Pd. The meanings of "substantially containing no precious metal elements other than Pd" and "the metal equivalent amount of precious metal elements other than Pd" and the method for determining the metal equivalent amount of precious metal elements other than Pd are as described above.

[0244] The fifth catalyst layer 60 may contain one or more alkaline earth metal elements. The alkaline earth metal elements are selected from Be, Mg, Ca, Sr, Ba and Ra.

[0245] From the viewpoint of maintaining the oxidation state of Pd, the metal conversion amount of the alkaline earth metal element in the fifth catalyst layer 60 is preferably 1.0 mass % or more and 10.0 mass % or less, more preferably 2.0 mass % or more and 6.0 mass % or less, and further preferably 3.0 mass % or more and 4.0 mass % or less, based on the mass of the fifth catalyst layer 60. The meaning of "metal conversion amount of alkaline earth metal element" and the method for measuring the metal conversion amount of alkaline earth metal element are as described above.

[0246] There is no particular limitation on the form in which the alkaline earth metal element exists in the fifth catalyst layer 60. In the fifth catalyst layer 60, the alkaline earth metal element may exist in the form of one or more selected from oxides, carbonates, nitrates, and sulfates.

[0247] The fifth catalyst layer 60 may include one or more carriers. When the fifth catalyst layer 60 includes a carrier, it is preferred that at least a portion of the catalytically active component is supported on the carrier. The description of the carrier (including the description of the inorganic oxide) and the meaning and confirmation method of the support are as described above.

[0248] like Figure 6 As shown, the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20 and the fifth catalyst layer 60. The meanings of "the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20" and "the main surface of the first catalyst layer 20" are as described above. The expression "the second catalyst layer 30 is arranged on the upper side of the fifth catalyst layer 60" means that, among the two main surfaces of the fifth catalyst layer 60, part or all of the second catalyst layer 30 exists on the main surface on the opposite side of the main surface on the side of the partition portion 12 of the substrate 10. "The main surface of the fifth catalyst layer 60" refers to the outer surface of the fifth catalyst layer 60 extending in the exhaust gas flow direction X. The second catalyst layer 30 can be directly arranged on the main surface of the fifth catalyst layer 60, or it can be arranged through other layers. The second catalyst layer 30 can be arranged in a manner that covers a portion of the main surface of the fifth catalyst layer 60, or it can be arranged in a manner that covers the entire main surface of the fifth catalyst layer 60.

[0249] From the perspective of achieving a good balance between exhaust gas purification performance and cost, the mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed (mass after calcination) is preferably greater than 20 g / L and less than 150 g / L, more preferably greater than 50 g / L and less than 120 g / L, and even more preferably greater than 70 g / L and less than 100 g / L.

[0250] The mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed can be obtained in the same manner as in the first embodiment.

[0251] In the catalyst 1C, the second catalyst layer 30 is arranged on the upper side of the first catalyst layer 20 and the fifth catalyst layer 60. Therefore, the exhaust gas flowing in from the end (opening) of the exhaust gas inflow side of the chamber 13 contacts the first catalyst layer 20 and the fifth catalyst layer 60 after contacting the second catalyst layer 30. The exhaust gas contacting the second catalyst layer 30 is purified by the catalytically active components (such as Rh) in the second catalyst layer 30. In the case where the environment of the catalyst 1C is a low-temperature environment just after the internal combustion engine is started, the activation of the catalytically active components (such as Rh) in the second catalyst layer 30 is insufficient, so the exhaust gas purification performance of the second catalyst layer 30 is low. Therefore, in a low-temperature environment, the second catalyst layer 30 may not be able to fully purify NOx. However, NOx that cannot be purified by the second catalyst layer 30 in a low temperature environment is adsorbed on the Sr in the first catalyst layer 20 and is retained on the Sr in the first catalyst layer 20 until the environment in which the first catalyst layer 20 and the fifth catalyst layer 60 are located becomes a high temperature environment, and is released after the environment in which the first catalyst layer 20 and the fifth catalyst layer 60 are located becomes a high temperature environment (that is, after the catalytically active components (e.g., Pt) in the first catalyst layer 20 and / or the catalytically active components (e.g., Pd) in the fifth catalyst layer 60 are fully activated). The released NOx is effectively purified by the activated catalytically active components (the catalytically active components (e.g., Pt) in the first catalyst layer 20 and / or the catalytically active components (e.g., Pd) in the fifth catalyst layer 60). In this way, the Sr in the first catalyst layer 20 can compensate for the exhaust gas purification performance of the catalyst 1C in a low temperature environment by retaining the NOx adsorbed at a low temperature until a high temperature.

[0252] When the metal conversion amount of Sr in the first catalyst layer 20 is too small, the effect brought by Sr cannot be fully exerted. When the metal conversion amount of Sr in the first catalyst layer 20 is too much, the exhaust gas purification performance of Pt in the first catalyst layer 20 in a low temperature environment is reduced. The reduction in the exhaust gas purification performance of Pt is believed to be related to Sr stabilizing the oxidation state of Pt and deactivating Pt. Based on the mass of the first catalyst layer 20, when the metal conversion amount of Sr in the first catalyst layer 20 is greater than 0.1 mass% and less than 9.0 mass%, it is possible to more effectively achieve the exhaust gas purification performance in a low temperature environment and the performance of maintaining the NOx adsorbed at low temperature to high temperature while utilizing Pt.

[0253] Catalyst 1C can be produced by the following method. The production conditions and the like of catalyst 1C are the same as those of catalyst 1A.

[0254] The slurry for forming the first catalyst layer 20 may be attached to the exhaust gas outflow side of the substrate 10, and after drying the slurry, it may be baked as needed to form the first catalyst layer 20. The slurry for forming the fifth catalyst layer 60 may be attached to the exhaust gas inflow side of the substrate 10, and after drying the slurry, it may be baked as needed to form the fifth catalyst layer 60.

[0255] The catalyst 1C can be manufactured by forming the first catalyst layer 20 and the fifth catalyst layer 60 on the substrate 10 and then forming the second catalyst layer 30 on the upper sides of the first catalyst layer 20 and the fifth catalyst layer 60 .

[0256] The slurry for forming the fifth catalyst layer 60 can be prepared by mixing a Pd supply source (eg, Pd salt) and other components (eg, inorganic oxide, binder, solvent, etc.) The Pd salt, inorganic oxide, binder, and solvent are as described above.

[0257] 《Exhaust gas purification system》

[0258] The exhaust gas purification system of the present invention is described below.

[0259] The following is based on Figure 7 and 8 , an exhaust gas purification system 100 according to an embodiment of the present invention will be described.

[0260] like Figure 7 As shown, the exhaust gas purification system 100 includes an exhaust pipe P, a first exhaust gas purification catalyst 101 (sometimes referred to as the "first catalyst 101" in this specification) arranged on the downstream side of the exhaust passage of the exhaust pipe P, and a second exhaust gas purification catalyst 102 (sometimes referred to as the "second catalyst 102" in this specification) arranged on the upstream side of the exhaust passage of the exhaust pipe P.

[0261] One end P1 of the exhaust pipe P is connected to an internal combustion engine (e.g., a gasoline engine, etc.), and the exhaust gas discharged from the internal combustion engine flows through the exhaust pipe P from the one end P1 to the other end P2 of the exhaust pipe P. That is, the exhaust pipe P forms an exhaust passage through which the exhaust gas flows. In the accompanying drawings, the exhaust gas flow direction is indicated by a mark X. The exhaust gas flowing through the exhaust pipe P is processed by the second catalyst 102 disposed on the upstream side of the exhaust passage of the exhaust pipe P, and the exhaust gas passing through the second catalyst 102 is processed by the first catalyst 101 disposed on the downstream side of the exhaust passage of the exhaust pipe P.

[0262] The first catalyst 101 includes a first substrate and a catalyst layer disposed on the first substrate. The catalyst layer disposed on the first substrate is composed of the catalyst composition of the present invention. Therefore, the above description of the catalyst composition of the present invention is also applicable to the catalyst layer disposed on the first substrate. When applicable, "the catalyst composition of the present invention" is replaced with "the catalyst layer disposed on the first substrate" for understanding.

[0263] As the first catalyst 101, for example, catalyst 1A may be used; an exhaust gas purifying catalyst in which the second catalyst layer 30 is omitted from catalyst 1A; catalyst 1B; an exhaust gas purifying catalyst in which one or more of the second catalyst layer 30, the third catalyst layer 40, and the fourth catalyst layer 50 are omitted from catalyst 1B (for example, an exhaust gas purifying catalyst in which the second catalyst layer 30 is omitted, an exhaust gas purifying catalyst in which the third catalyst layer 40 is omitted, an exhaust gas purifying catalyst in which the fourth catalyst layer 50 is omitted, an exhaust gas purifying catalyst in which the second catalyst layer 30 and the third catalyst layer 40 are omitted, an exhaust gas purifying catalyst in which the second catalyst layer 30 and the fourth catalyst layer 50 are omitted, etc.); catalyst 1C; an exhaust gas purifying catalyst in which the second catalyst layer 30 is omitted from catalyst 1C, etc. As the first catalyst 101, when these exhaust gas purifying catalysts are used, the substrate 10 corresponds to the "first substrate", and the first catalyst layer 20 corresponds to the "catalyst layer provided on the first substrate". From the viewpoint of improving exhaust gas purification performance, the exhaust gas purification catalyst in which one or more of the second catalyst layer 30, the third catalyst layer 40 and the fourth catalyst layer 50 are omitted from the catalyst 1B is preferably provided with at least one of the second catalyst layer 30 and the third catalyst layer 40, and preferably both.

[0264] The second catalyst 102 includes a second substrate and a catalyst layer provided on the second substrate.

[0265] As the second catalyst 102, for example, Figure 8 The exhaust gas purifying catalyst 1D (sometimes referred to as "catalyst 1D" in this specification) shown is an exhaust gas purifying catalyst in which the fourth catalyst layer 50 is omitted from the catalyst 1D. When the catalyst 1D is used as the second catalyst 102 or the exhaust gas purifying catalyst in which the fourth catalyst layer 50 is omitted from the catalyst 1D, the substrate 10 corresponds to the "second substrate" and the third catalyst layer 40 corresponds to the "catalyst layer provided on the second substrate".

[0266] The following is based on Figure 8 , the catalyst 1D will be described. In the catalyst 1D, the same components as those of the catalyst 1A or 1B are indicated by the same reference numerals as those of the catalyst 1A or 1B. Hereinafter, unless otherwise specified, the above description about the catalysts 1A and 1B also applies to the catalyst 1D.

[0267] like Figure 8 As shown, the catalyst 1D includes a substrate 10, and a third catalyst layer 40 and a fourth catalyst layer 50 provided on the substrate 10. Unless otherwise specified, the description of the substrate 10 in the first embodiment and the description of the third catalyst layer 40 and the fourth catalyst layer 50 in the second embodiment also apply to the catalyst 1D.

[0268] like Figure 8 As shown, the third catalyst layer 40 is disposed on the upper side of the fourth catalyst layer 50. The meanings of "the third catalyst layer 40 is disposed on the upper side of the fourth catalyst layer 50" and "the main surface of the fourth catalyst layer 50" are as described above. The third catalyst layer 40 can be directly disposed on the main surface of the fourth catalyst layer 50, or it can be disposed through other layers. The third catalyst layer 40 can be disposed in a manner covering a portion of the main surface of the fourth catalyst layer 50, or it can be disposed in a manner covering the entire main surface of the fourth catalyst layer 50.

[0269] like Figure 8 As shown, the third catalyst layer 40 extends from the end of the exhaust gas inlet side of the partition 12 to the end of the exhaust gas outlet side of the partition 12 along the exhaust gas flow direction X. The third catalyst layer 40 may also extend from the end of the exhaust gas inlet side of the partition 12 along the exhaust gas flow direction X, but not reach the end of the exhaust gas outlet side of the partition 12; or may extend from the end of the exhaust gas outlet side of the partition 12 in the direction opposite to the exhaust gas flow direction X, but not reach the end of the exhaust gas inlet side of the partition 12.

[0270] like Figure 8 As shown, the fourth catalyst layer 50 is disposed on the surface of the partition wall 12 of the substrate 10. It should be noted that the surface of the partition wall 12 refers to the outer surface of the partition wall 12 extending in the exhaust gas flow direction X. The fourth catalyst layer 50 may be disposed directly on the surface of the partition wall 12 or may be disposed on the surface of the partition wall 12 via other layers.

[0271] like Figure 8 As shown, the fourth catalyst layer 50 has a portion protruding from the surface of the partition wall 12 toward the chamber 13 side (hereinafter referred to as the "protruding portion"). The fourth catalyst layer 50 may be composed of only the protruding portion, or may have a portion existing inside the partition wall 12 (hereinafter referred to as the "internal portion") while having the protruding portion. In addition, the fourth catalyst layer 50 may be composed of only the internal portion.

[0272] like Figure 8As shown, the fourth catalyst layer 50 extends from the end of the exhaust gas inlet side of the partition 12 to the end of the exhaust gas outlet side of the partition 12 along the exhaust gas flow direction X. The fourth catalyst layer 50 may also extend from the end of the exhaust gas inlet side of the partition 12 along the exhaust gas flow direction X, but not reach the end of the exhaust gas outlet side of the partition 12; or may extend from the end of the exhaust gas outlet side of the partition 12 in the direction opposite to the exhaust gas flow direction X, but not reach the end of the exhaust gas inlet side of the partition 12.

[0273] In the exhaust gas purification system 100, the second catalyst 102 is located on the upstream side of the first catalyst 101, so the exhaust gas flowing through the exhaust pipe P passes through the first catalyst 101 after passing through the second catalyst 102. When the exhaust gas passes through the second catalyst 102, the exhaust gas is purified by the catalyst layer provided on the second substrate. In the case where the environment in which the second catalyst 102 is located is a low-temperature environment just after the internal combustion engine is started, the activation of the catalytically active components in the second catalyst 102 is insufficient, so the exhaust gas purification performance of the second catalyst 102 is low. Therefore, in a low-temperature environment, the second catalyst 102 may not be able to fully purify NOx. However, when NOx that cannot be purified by the second catalyst 102 passes through the first catalyst 101 in a low-temperature environment, it is adsorbed by the Sr in the catalyst layer provided on the first substrate and is retained on the Sr in the catalyst layer until the environment in which the first catalyst 101 is located becomes a high-temperature environment. After the environment in which the first catalyst 101 is located becomes a high-temperature environment (i.e., after the catalytically active components in the catalyst layer (e.g., the first catalyst layer 20, the second catalyst layer 30, etc.) provided on the first substrate are activated), it is released. The released NOx is effectively purified by the activated catalytically active components (the catalytically active components in the catalyst layer (e.g., the first catalyst layer 20, the second catalyst layer 30, etc.) provided on the first substrate). In this way, the Sr in the catalyst layer provided on the first substrate can compensate for the exhaust gas purification performance of the exhaust gas purification system 100 in a low-temperature environment by retaining the NOx adsorbed at a low temperature until a high temperature.

[0274] When the metal conversion amount of Sr in the catalyst layer provided on the first substrate is too small, the effect brought by Sr cannot be fully exerted. When the metal conversion amount of Sr in the catalyst layer provided on the first substrate is too much, the exhaust gas purification performance of Pt in the catalyst layer under low temperature environment is reduced instead. The reduction in the exhaust gas purification performance of Pt is believed to be related to Sr stabilizing the oxidation state of Pt and deactivating Pt. When the metal conversion amount of Sr in the catalyst layer provided on the first substrate is greater than 0.1 mass % and less than 9.0 mass % based on the mass of the catalyst layer, it is possible to more effectively achieve the exhaust gas purification performance under low temperature environment and the performance of maintaining the NOx adsorbed at low temperature to high temperature while utilizing Pt.

[0275] Example

[0276] Hereinafter, the present invention will be described in further detail based on Examples and Comparative Examples.

[0277] [Example 1]

[0278] (1) Preparation of slurry for lower layer formation

[0279] An OSC material having the following composition was prepared.

[0280] CeO2 equivalent amount of Ce: 40.0 mass%, ZrO2 equivalent amount of Zr: 50.0 mass%, rare earth oxide equivalent amount other than CeO2: 10.0 mass%

[0281] Platinum nitrate aqueous solution, OSC material, La2O3 modified alumina (La2O3 modification amount: 1 mass%), strontium nitrate, alumina sol and water are added to a mixing container, mixed and stirred to prepare a slurry for forming a lower layer. Based on the mass of the lower layer after calcination (100 mass%), the amount of each component in the slurry for forming the lower layer is adjusted in such a manner that Pt is 0.5 mass% in metal conversion, OSC material is 40.0 mass%, La2O3 modified alumina is 43.6 mass%, Sr is 5.0 mass% in metal conversion, and the solid content of alumina sol is 10.0 mass%. It should be noted that strontium nitrate (Sr(NO3)2) is converted into strontium oxide (SrO) by calcination.

[0282] (2) Formation of the lower layer

[0283] As a flow-through substrate, a flow-through substrate having a volume of 1.0 L and having axially extending cavities partitioned by partition walls having a thickness of 50 to 70 μm at a density of 600 cavities / in 2 on a plane perpendicular to the axial direction was prepared.

[0284] The flow-through substrate was immersed in the slurry for forming the lower layer, and the flow-through substrate coated with the slurry for forming the lower layer was dried at 150° C. for 0.5 hours and then baked at 500° C. for 1 hour to form the lower layer. The mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 140 g / L.

[0285] (3) Preparation of slurry for upper layer formation

[0286] An OSC material having the following composition was prepared.

[0287] CeO2 equivalent amount of Ce: 15.0 mass %, ZrO2 equivalent amount of Zr: 75.0 mass %, Oxide equivalent amount of rare earth elements other than Ce: 10.0 mass %

[0288] Rhodium nitrate aqueous solution, OSC material, La2O3 modified alumina (La2O3 modification amount: 1 mass%), alumina sol and water were added to a mixing container, mixed and stirred to prepare a slurry for forming an upper layer. Based on the mass of the upper layer after calcination (100 mass%), the amount of each component in the slurry for forming the upper layer was adjusted so that Rh was 0.2 mass% in terms of metal, OSC material was 50.0 mass%, La2O3 modified alumina was 39.8 mass%, and the solid content of alumina sol was 10.0 mass%.

[0289] (4) Formation of the upper layer

[0290] The flow-through substrate on which the lower layer was formed was immersed in the slurry for forming the upper layer, and the flow-through substrate coated with the slurry for forming the upper layer was dried at 150° C. for 0.5 hours and then baked at 500° C. for 1 hour to form the upper layer on the lower layer. The mass of the upper layer per unit volume of the portion of the flow-through substrate on which the upper layer was formed was 80 g / L.

[0291] In the above manner, an exhaust gas purifying catalyst (hereinafter referred to as "catalyst") including a lower layer formed on a flow-through substrate and an upper layer formed on the lower layer was manufactured, and the manufactured catalyst was used in the test examples described below.

[0292] [Example 2]

[0293] In the manufacture of the catalyst, the catalyst was manufactured in the same manner as in Example 1 except that the amount of each component in the slurry for forming the lower layer was adjusted such that Pt was 0.5 mass% in metal conversion, OSC material was 40.0 mass%, La2O3-modified alumina was 48.3 mass%, Sr was 1.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%, based on the mass of the lower layer after calcination (100 mass%). In the catalyst of Example 2, the mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 140 g / L.

[0294] [Example 3]

[0295] In the manufacture of the catalyst, the catalyst was manufactured in the same manner as in Example 1 except that the amount of each component in the slurry for forming the lower layer was adjusted such that Pt was 0.5 mass% in metal conversion, OSC material was 40.0 mass%, La2O3-modified alumina was 47.1 mass%, Sr was 2.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%, based on the mass of the lower layer after calcination (100 mass%). In the catalyst of Example 3, the mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 140 g / L.

[0296] [Example 4]

[0297] In the manufacture of the catalyst, the catalyst was manufactured in the same manner as in Example 1 except that the amount of each component in the slurry for forming the lower layer was adjusted such that Pt was 0.5 mass% in metal conversion, OSC material was 40.0 mass%, La2O3-modified alumina was 45.4 mass%, Sr was 3.5 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%, based on the mass of the lower layer after calcination (100 mass%). In the catalyst of Example 4, the mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 140 g / L.

[0298] [Example 5]

[0299] In the manufacture of the catalyst, the catalyst was manufactured in the same manner as in Example 1 except that the amount of each component in the slurry for forming the lower layer was adjusted such that Pt was 0.5 mass% in metal conversion, OSC material was 40.0 mass%, La2O3-modified alumina was 41.2 mass%, Sr was 7.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%, based on the mass of the lower layer after calcination (100 mass%). In the catalyst of Example 5, the mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 140 g / L.

[0300] [Comparative Example 1]

[0301] In the manufacture of the catalyst, magnesium nitrate was used instead of strontium nitrate, and the amount of each component in the slurry for forming the lower layer was adjusted in the same manner as in Example 1, based on the mass of the lower layer after calcination (100 mass%), such that Pt was 0.5 mass%, OSC material was 40.0 mass%, La2O3-modified alumina was 41.2 mass%, Mg was 5.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%. In the catalyst of Comparative Example 1, the mass of the lower layer per unit volume of the portion where the lower layer was formed in the flow-through substrate was 140 g / L. It should be noted that magnesium nitrate (Mg(NO3)2) is converted into magnesium oxide (MgO) by calcination.

[0302] [Comparative Example 2]

[0303] In the manufacture of the catalyst, barium nitrate was used instead of strontium nitrate, and the amount of each component in the slurry for forming the lower layer was adjusted in the same manner as in Example 1, based on the mass of the lower layer after calcination (100 mass%), such that Pt was 0.5 mass%, OSC material was 40.0 mass%, La2O3-modified alumina was 43.9 mass%, Ba was 5.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%. In the catalyst of Comparative Example 2, the mass of the lower layer per unit volume of the portion where the lower layer was formed in the flow-through substrate was 140 g / L. It should be noted that barium nitrate (Ba(NO3)2) is converted into barium oxide (BaO) by calcination.

[0304] [Comparative Example 3]

[0305] In the manufacture of the catalyst, the catalyst was manufactured in the same manner as in Example 1 except that the amount of each component in the slurry for forming the lower layer was adjusted such that Pt was 0.5 mass% in metal conversion, OSC material was 40.0 mass%, La2O3-modified alumina was 37.7 mass%, Sr was 10.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%, based on the mass of the lower layer after calcination (100 mass%). In the catalyst of Comparative Example 3, the mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 140 g / L.

[0306] [Comparative Example 4]

[0307] In the manufacture of the catalyst, magnesium nitrate was used instead of strontium nitrate, and the amount of each component in the slurry for forming the lower layer was adjusted in such a manner that Pt was 0.5 mass% in metal conversion, OSC material was 40.0 mass%, La2O3-modified alumina was 36.2 mass%, Mg was 8.0 mass% in metal conversion, and the solid content of alumina sol was 10.0 mass%, based on the mass of the lower layer after calcination (100 mass%). The catalyst was manufactured in the same manner as in Example 1 except that. In the catalyst of Comparative Example 4, the mass of the lower layer per unit volume of the portion where the lower layer was formed in the flow-through substrate was 140 g / L. It should be noted that magnesium nitrate (Mg(NO3)2) is converted into magnesium oxide (MgO) by calcination.

[0308] [Test example]

[0309] (1) Preparation of samples for evaluation

[0310] The catalyst was cored to 30 mL and heat treated at 1000° C. for 20 hours in a 10 vol % H 2 O atmosphere using a quartz tubular furnace in the following FC mode. The heat-treated catalyst was used as an evaluation sample.

[0311] FC mode: Alternately introduce sample gas (600 mL / min) and air (600 mL / min) of the following composition.

[0312] Sample gas flow rate: C3H6 1.2mL / min, O2 14.2mL / min, N2 584.6mL / min (total 600mL / min).

[0313] 10% by volume of H2O evaporates from the water tank and mixes into the sample gas or air in the form of water vapor. The saturated water vapor pressure is adjusted by temperature to obtain the above volume % of water vapor.

[0314] (2) Evaluation of NOx Adsorption Maintenance Temperature and NOx Adsorption Amount (NOx Concentration Integrated Value) The evaluation samples of Example 1 and Comparative Examples 1 and 2 were evaluated for NOx adsorption maintenance temperature.

[0315] The evaluation samples of Examples 2 to 5 and Comparative Examples 3 and 4 were evaluated for the NOx adsorption amount (NOx concentration integrated value).

[0316] As an evaluation method, the temperature programmed desorption method (TPD) is used. The temperature programmed desorption method is a method for measuring the desorbed gas produced by continuously increasing the temperature after the probe molecule (such as NOx) is adsorbed on a solid sample. It is used as a conventional characterization for examining the amount or strength of the basic sites of the solid base catalyst. The evaluation method is as follows.

[0317] A pretreatment gas (NO: 1 volume%, O2: 20 volume%, N2: balance) was passed through the evaluation sample at 50°C for 1 hour to adsorb NO onto the evaluation sample. Then, the temperature was raised to 800°C at a rate of 10°C / min in a He atmosphere, and the NOx concentration (ppm) desorbed from the evaluation sample was detected every 0.5 seconds to obtain a NOx concentration distribution curve with temperature on the horizontal axis and NOx concentration (ppm) on the vertical axis.

[0318] For the NOx concentration distribution curve, the cumulative value of the concentration in the region above 400°C (the area under the curve in the region above 400°C) and the cumulative value of the concentration in the region above 500°C (the area under the curve in the region above 500°C) are respectively taken as the "cumulative value of NOx concentration above 400°C" and the "cumulative value of NOx concentration above 500°C". In addition, when the maximum value of the NOx concentration distribution curve above 400°C is set to X, the temperature at which the detected value in the temperature rise process after the maximum value is displayed becomes 1 / 10 of X for the first time is taken as the "NOx adsorption maintenance temperature". The results are shown in Tables 1 and 2. It should be noted that in Table 2, the "cumulative value of NOx concentration above 400°C" and the "cumulative value of NOx concentration above 500°C" are expressed as relative values ​​when the value of Comparative Example 4 is set to 1.

[0319] (3) Evaluation of exhaust gas purification performance (T50)

[0320] The evaluation samples of Examples 2 to 5 and Comparative Examples 3 and 4 were evaluated for T50.

[0321] The evaluation sample was placed in the exhaust passage, and the exhaust gas sample (CO: 0.50 volume%, H2: 0.17 volume%, O2: 0.50 volume%, NO: 400ppm, C3H6: 1180ppm, CO2: 14 volume%, H2O: 10 volume%, N2: balance) was introduced at a space velocity of 100000 / h. The temperature was raised to 500°C at a rate of 20°C / min, and the purification rate of nitrogen oxides (NOx) was continuously measured. The temperature (ignition temperature T50) (°C) when the purification rate of nitrogen oxides (NOx) reached 50% was obtained. The ignition temperature T50 was obtained during the temperature rise. The results are shown in Table 2.

[0322] [Table 1]

[0323]

[0324] [Table 2]

[0325]

[0326] As shown in Tables 1 and 2, Examples 1 to 5 that satisfy the condition that the lower layer in the catalyst contains Pt and Sr, and the metal conversion amount of Sr is 0.1 mass % or more and 9.0 mass % or less based on the mass of the lower layer, have higher exhaust gas purification performance in low temperature environments and higher performance in maintaining NOx adsorbed at low temperatures to high temperatures, compared to Comparative Examples 1 to 4 that do not satisfy this condition.

[0327] Description of Reference Numerals

[0328] P: Exhaust pipe of internal combustion engine

[0329] 1A: Exhaust gas purification catalyst according to the first embodiment

[0330] 1B: Exhaust gas purification catalyst according to the second embodiment

[0331] 1C: Exhaust gas purification catalyst according to the third embodiment

[0332] 10: Base material

[0333] 11: Cylindrical part

[0334] 12: Next door

[0335] 13: Chamber

[0336] 14: 1st closed section

[0337] 15: Second closed section

[0338] 20: First catalyst layer

[0339] 30: Second catalyst layer

[0340] 40: The third catalyst layer

[0341] 50: 4th catalyst layer

[0342] 60: 5th catalyst layer

[0343] 100: Exhaust gas purification system

[0344] 101: No. 1 exhaust gas purification catalyst

[0345] 102: Second exhaust gas purification catalyst

Claims

1. A catalyst composition for exhaust gas purification, comprising Pt and Sr, The metal-equivalent amount of Sr is 0.1 mass % or more and 9.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

2. The exhaust gas purification catalyst composition according to claim 1, wherein The metal conversion amount of the alkaline earth metal element other than Sr is 4.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

3. The exhaust gas purification catalyst composition according to claim 1, wherein Sr exists in the form of one or both selected from SrO and SrCO3.

4. The exhaust gas purification catalyst composition according to claim 1, wherein The exhaust gas-purifying catalyst composition includes La-containing modified alumina, and the La 2 O 3 conversion amount of La derived from the modified alumina is 0.20 mass % or more and 5.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

5. An exhaust gas purification catalyst comprising a substrate and a first catalyst layer provided on the substrate, The first catalyst layer is composed of the exhaust gas-purifying catalyst composition according to any one of claims 1 to 4.

6. The exhaust gas purification catalyst according to claim 5, wherein: The exhaust gas purifying catalyst further comprises a second catalyst layer and / or a third catalyst layer provided on the substrate. The second catalyst layer is disposed on the upper side of the first catalyst layer. The third catalyst layer is provided on the upstream side of the first catalyst layer.

7. The exhaust gas purification catalyst according to claim 6, wherein: The second catalyst layer and / or the third catalyst layer contains Rh.

8. The exhaust gas purification catalyst according to claim 6, wherein: The metal conversion amount of the alkaline earth metal element in the second catalyst layer is 5.0 mass % or less based on the mass of the second catalyst layer, The metal conversion amount of the alkaline earth metal element in the third catalyst layer is 5.0 mass % or less based on the mass of the third catalyst layer.

9. An exhaust gas purification system comprising: The exhaust passage through which the exhaust gas flows, a first exhaust gas purification catalyst provided on the downstream side in the exhaust passage, and a second exhaust gas purifying catalyst disposed on the upstream side of the exhaust passage; The first exhaust gas-purifying catalyst comprises a first substrate and a catalyst layer provided on the first substrate. The catalyst layer provided on the first substrate is composed of the exhaust gas-purifying catalyst composition according to any one of claims 1 to 4.

10. The exhaust gas purification system according to claim 9, wherein: The second exhaust gas-purifying catalyst includes a second substrate and a catalyst layer provided on the second substrate.

11. The exhaust gas purification system according to claim 10, wherein: The catalyst layer provided on the second substrate includes Rh.

12. The exhaust gas purification system according to claim 10, wherein: The metal conversion amount of the alkaline earth metal element in the catalyst layer provided on the second substrate is 5.0 mass % or less based on the mass of the catalyst layer provided on the second substrate.

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