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 for improving exhaust gas purification performance by imparting NOx adsorption performance to a Pt-containing catalyst layer while suppressing a decrease in Pt dispersibility, and to provide an exhaust gas purification catalyst composition containing Pt and Mg, the mass of the exhaust gas purification catalyst composition being less than or equal to the mass of the catalyst composition, the mass of the Mg being less than or equal to the mass of the catalyst composition, and the mass of the Mg being less than or equal to the mass of the catalyst composition. And the amount of Mg in terms of metal is from 2.0% 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 exhaust gas purification catalysts, 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 a 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 a 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] It is believed that if the catalyst layer is given NOx adsorption performance, the exhaust gas purification performance can be compensated and improved. In the past, Ba was generally considered as a NOx adsorbent. On the other hand, from the perspective of cost reduction, Pt is more necessary than Rh and Pd. However, the inventors found that when Ba is added to the catalyst layer containing Pt, the dispersibility of Pt is reduced due to the added Ba, which in turn reduces the exhaust gas purification performance.

[0010] Therefore, an object of the present invention is to provide a new technology for improving the exhaust gas purification performance by imparting NOx adsorption performance to a catalyst layer containing Pt while suppressing a decrease in Pt dispersibility.

[0011] Solutions for solving problems

[0012] In order to solve the above technical problems, the present invention provides the following technical solutions.

[0013] [1] An exhaust gas-purifying catalyst composition comprising Pt and Mg, wherein the metal-converted amount of Mg is 2.0 mass % or more and 9.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

[0014] [2] The exhaust gas-purifying catalyst composition according to [1], wherein the metal conversion amount of the alkaline earth metal element other than Mg is 4.0 mass % or less based on the mass of the exhaust gas-purifying catalyst composition.

[0015] [3] The exhaust gas purification catalyst composition according to [1] or [2], wherein Mg is selected from MgO and MgCO 3 One or both forms exist.

[0016] [4] The exhaust gas-purifying catalyst composition according to any one of [1] to [3], wherein Mg is present in a form other than a composite oxide containing Mg and Al.

[0017] [5] The exhaust gas purification catalyst composition according to any one of [1] to [4], wherein in the X-ray diffraction pattern of the exhaust gas purification catalyst composition, 2 O 4 The diffraction intensity of the peak at 2θ = 64-67° is set as A, and the standard material 674a issued by the National Institute of Standards and Technology of the United States, namely α-Al 2 O 3 In the X-ray diffraction pattern, the 2 O 3 When the diffraction intensity of the peak existing at 2θ=55 to 58° among the peaks is defined as B, the ratio of A to B is less than 0.060.

[0018] [6] The exhaust gas purification catalyst composition according to any one of [1] to [5], wherein the exhaust gas purification catalyst composition comprises La-containing modified alumina, and the La derived from the La in the modified alumina is 0.1% based on the mass of the exhaust gas purification catalyst composition. 2 O 3 The converted amount is 0.20 mass % or more and 5.0 mass % or less.

[0019] [7] 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 [6].

[0020] [8] The exhaust gas purification catalyst according to [7], 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.

[0021] [9] The exhaust gas purification catalyst according to [8], wherein the second catalyst layer and / or the third catalyst layer contains Rh.

[0022]

[10] The exhaust gas purification catalyst according to [8] or [9], 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.

[0023]

[11] An exhaust gas purification system comprising: an exhaust passage through which exhaust gas flows, a first exhaust gas purification catalyst arranged on a downstream side in the exhaust passage, and a second exhaust gas purification catalyst arranged on an upstream side in the exhaust passage, wherein the first exhaust gas purification catalyst comprises a first substrate and a catalyst layer arranged on the first substrate, and the catalyst layer arranged on the first substrate is composed of the exhaust gas purification catalyst composition described in any one of [1] to [6].

[0024]

[12] The exhaust gas purification system according to

[11] , wherein the second exhaust gas purification catalyst includes a second substrate and a catalyst layer provided on the second substrate.

[0025]

[13] The exhaust gas purification system according to

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

[0026]

[14] The exhaust gas purification system according to

[12] or

[13] , 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.

[0027] Effects of the Invention

[0028] According to the present invention, it is possible to provide a new technology for improving the exhaust gas purification performance by imparting NOx adsorption performance to a catalyst layer containing Pt while suppressing a decrease in Pt dispersibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] Figure 2 for Figure 1 AA line cross-section diagram.

[0031] Figure 3 for Figure 2 An enlarged view of the area indicated by the mark R in FIG.

[0032] Figure 4 for Figure 1 BB line cross-section diagram.

[0033] 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).

[0034] 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).

[0035] Figure 7 It is a plan view of an exhaust gas purification system according to one embodiment of the present invention.

[0036] Figure 8 for Figure 7 DD line profile. DETAILED DESCRIPTION

[0037] 《Explanation of Terminology》

[0038] In this specification, "alkaline earth metal element" refers to an element selected from the group consisting of Be, Mg, Ca, Sr, Ba and Ra.

[0039] 《Catalyst composition for exhaust gas purification》

[0040] 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".

[0041] The catalyst composition of the present invention may be in the form of, for example, a powder, a molded body, or a layer.

[0042] The catalyst composition of the present invention comprises Pt.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] In this specification, the “precious metal element” includes Pt, Pd, Rh, Au, Ag, Ru, Ir, and Os.

[0047] In this specification, Al oxide refers to Al 2 O 3 , Si oxide refers to SiO 2 , the oxide of B refers to B 2 O 3 , Zr oxide refers to ZrO 2 , Be oxide refers to BeO, Mg oxide refers to MgO, Ca oxide refers to CaO, Sr oxide refers to SrO, Ba oxide refers to BaO, Ra oxide refers to RaO, Ti oxide refers to TiO 2 , Ni oxide refers to NiO, P oxide refers to P 2 O 5 The oxides of rare earth elements refer to the sesquioxides (Ln 2 O 3 ), Ce oxide refers to CeO 2 , Pr oxide refers to Pr 6 O 11, Tb oxide refers to Tb 4 O 7 .

[0048] 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.

[0049] 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).

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The catalyst composition of the present invention comprises Mg.

[0054] The catalyst composition of the present invention can suppress the reduction of the dispersibility of Pt by including Mg, and give the catalyst composition of the present invention NOx adsorption performance, thereby improving the exhaust gas purification performance. It is believed that this effect is related to the weak base strength and / or high electronegativity of Mg. However, when the metal conversion amount of Mg is too small, the NOx adsorption performance brought by Mg cannot be fully exerted. On the other hand, when the metal conversion amount of Mg is too much, the exhaust gas purification performance is reduced because Pt is covered by Mg. Therefore, based on the mass of the catalyst composition of the present invention, the metal conversion amount of Mg in the catalyst composition of the present invention is preferably 2.0 mass% or more and 9.0 mass% or less, more preferably 3.0 mass% or more and 8.0 mass% or less, and further preferably 4.0 mass% or more and 7.0 mass% or less. The metal conversion amount of Mg 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.

[0055] The catalyst composition of the present invention contains one or more Mg sources. The Mg source is not particularly limited as long as it is a compound containing Mg.

[0056] From the viewpoint of imparting NOx adsorption performance to the catalyst composition and further suppressing the reduction in the dispersibility of Pt, the Mg source is preferably selected from MgO, MgCO 3 and Mg(NO 3 ) 2One or more of MgO and MgCO 3 That is, in the catalyst composition of the present invention, Mg is preferably selected from MgO, MgCO 3 and Mg(NO 3 ) 2 One or more forms of MgO and MgCO 3 One or both forms exist.

[0057] In the preparation of the catalyst composition of the present invention, Mg(NO 3 ) 2 It is converted into MgO by calcination.

[0058] The Mg source may be a composite oxide containing Mg and Al (sometimes referred to as "Mg-Al composite oxide" in this specification), but from the viewpoint of further suppressing the reduction in the dispersibility of Pt, the above-mentioned MgO, MgCO, and MgO are more preferable than the Mg-Al composite oxide. 3 and Mg(NO 3 ) 2 That is, in the catalyst composition of the present invention, from the viewpoint of further improving the dispersibility of Pt, Mg is preferably present in a form other than the Mg-Al composite oxide. When Mg is present in a form other than the Mg-Al composite oxide, the ratio of A to B (A / B) described later is preferably less than 0.060, more preferably less than 0.050, and further preferably less than 0.040.

[0059] In the X-ray diffraction pattern of the catalyst composition of the present invention, the 2 O 4 The diffraction intensity of the peak at 2θ = 64-67° is set as A, and the standard material 674a issued by the National Institute of Standards and Technology of the United States, namely α-Al 2 O 3 In the X-ray diffraction pattern, the 2 O 3 When the diffraction intensity of the peak existing at 2θ=55-58° in the peak is set as B, from the viewpoint of further improving the dispersibility of Pt, the ratio of A to B (A / B) is preferably less than 0.060, more preferably less than 0.050, and further preferably less than 0.040. The lower limit is zero. The ratio of A to B is measured according to the method described in the examples.

[0060] The Mg-Al composite oxide may include a crystal phase having a spinel crystal structure (hereinafter referred to as a "spinel crystal phase"). The spinel crystal structure is a crystal structure of a cubic system belonging to the space group Fd-3m. The stoichiometric composition of the spinel crystal phase is MgAl 2 O 4 .

[0061] The Mg-Al composite oxide may be composed of a single phase of a spinel-type crystal phase, or may be composed of a mixed phase comprising a spinel-type crystal phase and one or more other phases. Other phases may be crystalline phases or amorphous phases. Other phases include, for example, alkaline earth metal oxide phases (e.g., MgO phases), α-alumina phases, alumina phases other than α-alumina phases (e.g., γ-alumina phases, θ-alumina phases, etc.), and hydrotalcite phases.

[0062] In the case where the Mg-Al composite oxide is composed of a mixed phase, the spinel-type crystal phase may be the first phase, or the α-alumina phase may be the first phase. In the case where the α-alumina phase is the first phase, the spinel-type crystal phase is, for example, the second phase. "The first phase" refers to the crystal phase from which the peak (main peak) with the maximum intensity in the diffraction pattern obtained by the powder X-ray diffraction method (XRD) using CuKα originates. "The second phase" refers to the crystal phase from which the peak with the maximum intensity originates, except for the peak originating from the first phase.

[0063] That the Mg-Al-based composite oxide includes a spinel crystal phase can be confirmed by XRD using CuKα. XRD can be performed using a commercially available X-ray diffractometer (for example, MiniFlex 600 manufactured by Rigaku Corporation).

[0064] In the Mg-Al composite oxide, Mg, Al and O can form a solid solution phase having a spinel crystal structure, or can form a single phase (e.g., MgO phase, AlO phase) as a crystalline phase or an amorphous phase. 2 O 3 The fact that Mg, Al and O form a solid solution phase can be confirmed using conventional methods such as XRD and SEM-EDX.

[0065] Mg-Al composite oxides may include one or more metal elements other than Mg and Al. As metal elements other than Mg and Al, for example, Ba, Sr, etc. may be cited. The metal elements other than Mg and Al may form a solid solution phase with a spinel crystal structure together with Mg, Al and O, or may form a single phase (such as BaO phase, SrO phase, etc.) as a crystalline phase or an amorphous phase. The fact that the metal elements other than Mg and Al form a solid solution phase together with Mg, Al and O may be confirmed using conventional methods such as XRD, SEM-EDX.

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

[0067] From the viewpoint of further suppressing the reduction in the dispersibility of Pt, the metal conversion amount of the alkaline earth metal elements other than Mg 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 elements other than Mg 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 Mg, 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 Mg. The metal conversion amount of the alkaline earth metal elements other than Mg 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 alkaline earth metal elements other than Mg is not particularly limited. In the catalyst composition of the present invention, the alkaline earth metal elements other than Mg may be present in the form of one or more selected from oxides, carbonates, nitrates and sulfates. In the case where the catalyst composition of the present invention includes a Mg-Al composite oxide, the alkaline earth metal elements other than Mg may be present as a component in the Mg-Al composite oxide.

[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, and oxides of rare earth elements (e.g., Y 2 O 3 、CeO 2 etc.), ZrO 2 、SiO 2 、TiO 2 , NiO, etc.

[0073] In this specification, CeO 2 Al conversion amount and Al 2 O 3 Al with the same or greater conversion amount as Al 2 O 3 In terms of conversion, the oxide containing Ce, Zr and Al is equivalent to Ce-Zr oxide. 2 Al with a conversion amount less than Al 2 O 3 In the case of conversion amount, it corresponds to Al-based oxides.

[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 (Al 2 O 3), modified alumina, etc. Al-based oxides are distinguished from alumina used as a binder (sometimes referred to as "alumina binder" in this specification). The alumina binder is derived from alumina sol used as a raw material for the catalyst composition. Modified alumina contains one or more elements other than Al and O. As modified alumina, for example, oxides obtained by modifying the surface of alumina with elements other than Al and O, oxides obtained by dissolving elements other than Al and O in alumina, etc. can be listed. In Al-based oxides, elements other than Al and O can form a solid solution phase together with Al and O, or form a separate phase as a crystalline phase or an amorphous phase (for example, an oxide phase of elements other than Al and O), or form both a solid solution phase and a separate phase.

[0076] From the viewpoint of improving heat resistance, the Al content of Al in Al oxides is 2 O 3 The converted amount is preferably 90% by mass or more, more preferably 95% by mass or more, and still more preferably 98% by mass or more. The upper limit is 100% by mass.

[0077] When the composition of the raw material for producing the catalyst composition of the present invention is known, the Al content of Al in the Al-based oxide is 2 O 3 The converted amount can be determined from the composition of the raw material used to produce the catalyst composition of the present invention.

[0078] When the composition of the raw material for producing the catalyst composition of the present invention is unknown, the Al content of Al in the Al-based oxide is 2 O 3 The conversion amount can be determined by analyzing a sample obtained from the catalyst composition of the present invention by energy dispersive X-ray spectroscopy (EDX), and by using 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 composition of the specified particles is analyzed (elemental analysis), and the oxide conversion 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, Sr, P, Ni, etc., and La is preferred from the viewpoint of improving heat resistance.

[0087] From the viewpoint of improving heat resistance, the La content in modified alumina is 2 O 3 The converted amount is preferably 0.10 mass % to 20 mass %, more preferably 0.50 mass % to 15 mass %, and even more preferably 1.0 mass % to 10 mass %.2 O 3 The conversion amount can be compared with the Al content of Al in Al-based oxides. 2 O 3 The converted amount was measured in the same manner.

[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 La derived from the modified alumina is 0.0447 W / m2 of La based on the mass of the catalyst composition of the present invention. 2 O 3 The converted amount 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. La derived from La modifying alumina 2 O 3 The conversion amount can be calculated based on the amount of modified alumina in the catalyst composition of the present invention and the La content in the modified alumina. 2 O 3 Calculate the conversion amount.

[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 is included in the catalyst composition of the present invention to control the oxygen concentration, and the Mg 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 may form a single phase (CeO) as a crystalline phase or an amorphous phase in addition to a solid solution phase. 2 Phase, ZrO 2 The formation of a solid solution among Ce, Zr and O can be confirmed by using SEM-EDX or the like.

[0091] From the viewpoint of improving oxygen storage capacity, based on the mass of Ce-Zr composite oxide, the CeO in Ce-Zr composite oxide is 2 The conversion amount is preferably 5.0 mass % or more and 80 mass % or less, more preferably 10 mass % or more and 60 mass % or less, and still more preferably 20 mass % or more and 50 mass % or less. 2 The conversion amount can be compared with the Al content of Al in Al-based oxides. 2 O 3 The converted amount was measured in the same manner.

[0092] From the viewpoint of improving heat resistance, based on the mass of Ce-Zr composite oxide, the Zr content of ZrO in Ce-Zr composite oxide is 2 The conversion amount is preferably 10 mass % or more and 90 mass % or less, more preferably 30 mass % or more and 80 mass % or less, and still more preferably 40 mass % or more and 70 mass % or less. 2 The conversion amount can be compared with the Al content of Al in Al-based oxides. 2 O 3 The converted amount was measured in the same manner.

[0093] From the viewpoint of improving oxygen storage capacity and heat resistance, based on the mass of Ce-Zr composite oxide, the CeO in Ce-Zr composite oxide is 2 Conversion amount and ZrO 2 The total amount of the converted amount is preferably 70% by mass or more, more preferably 80% by mass or more, and still more 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 fluctuation, the CeO in the catalyst composition of the present invention is based on the mass of the catalyst composition of the present invention. 2 The conversion amount is preferably 1% by mass or more, more preferably 10% by mass or more, and still more preferably 13% by mass or more. From the viewpoint of suppressing oxidation of Pt, the CeO in the catalyst composition of the present invention is preferably 1% by mass or more, more preferably 10% by mass or more, and still more preferably 13% by mass or more. 2 The conversion amount is preferably 50 mass % or less, more preferably 40 mass % or less, and further preferably 30 mass % or less. These upper limits may be combined with any one of the above lower limits. 2 When the catalyst composition of the present invention contains one Ce source, the “converted amount” refers to the CeO of Ce from the Ce source. 2 The conversion amount, when the catalyst composition of the present invention contains two or more Ce sources, refers to the CeO of Ce derived from the two or more Ce sources.2 The Ce source is not particularly limited as long as it is an oxide containing Ce. Examples of Ce sources include Ce-Zr composite oxides, cerium oxide (CeO 2 ), oxides containing Ce and rare earth elements other than Ce, Al-based oxides containing Ce, etc. When the composition of the raw material used to produce the catalyst composition of the present invention is known, Ce in the catalyst composition of the present invention is CeO 2 The conversion amount can be calculated from the composition of the raw material used to produce the catalyst composition of the present invention. When the composition of the raw material used to produce the catalyst composition of the present invention is unknown, the CeO in the catalyst composition of the present invention is 2 The converted amount can be measured by a conventional method 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 Mg 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 Mg, for example, Mg salts can be listed, and as Mg 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 1As 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 may also be other shapes such as an elliptical cylindrical shape or a polygonal cylindrical shape.

[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 4As 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 3 As shown, the end (opening) of the chamber 13 on the exhaust gas inlet side is a quadrilateral in plan view, but may be hexagonal, octagonal, 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 4As 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 4 As 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. 10 Samples 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 can 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 can 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 existing on 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 side opposite to the main surface on the partition wall 12 side 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 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.

[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 about 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 20 The above description of the measurement method also applies to the average length L of the second catalyst layer 30. 30 Where applicable, replace “first catalyst layer 20” with “second catalyst layer 30” and replace “average length L 20 " is replaced by "average length L 30 "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, since the second catalyst layer 30 is provided on the upper side of the first catalyst layer 20, the exhaust gas flowing in from the end (opening) on ​​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 is purified by the Rh in the second catalyst layer 30. NOx that passes through the second catalyst layer 30 without being purified is adsorbed on Mg in the first catalyst layer 20. In this way, the first catalyst layer 20 adsorbs NOx in the exhaust gas, compensating for the exhaust gas purification performance of the catalyst 1A. Then, the NOx adsorbed on the Mg in the first catalyst layer 20 is released and purified by, for example, the Rh in the second catalyst layer 30. As a result, the catalyst 1A can exert improved exhaust gas purification performance.

[0149] 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 .

[0150] The first catalyst layer 20 can be formed by preparing a first slurry by mixing a Pt supply source (such as Pt salt), a Mg supply source (such as Mg salt) and other components (such as inorganic oxides, binders, solvents, etc.), applying the first slurry on the substrate 10, and drying and calcining.

[0151] The second catalyst layer 30 can be formed by mixing a Rh supply source (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.

[0152] The description of Pt salt, Mg salt, inorganic oxide, binder and solvent is as described above. Examples of Rh salt include nitrate, amine complex salt, acetate, chloride and the like. 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.

[0153] <Second embodiment>

[0154] The following is based on Figure 5, an exhaust gas purification catalyst 1B according to a second embodiment of the present invention (sometimes referred to as "catalyst 1B" in this specification) 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.

[0155] 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.

[0156] 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 be provided, and it is preferred that both of them be provided.

[0157] like Figure 5 As shown, the difference between catalyst 1B and catalyst 1A is:

[0158] 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,

[0159] 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 .

[0160] like Figure 5As 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 .

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] The average length L of the first catalyst layer 20 20The 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%.

[0167] 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 may 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 may be directly arranged on the main surface of the first catalyst layer 20, or it may be arranged through other layers. The second catalyst layer 30 may be arranged in a manner covering a portion of the main surface of the first catalyst layer 20, or it may 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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%.

[0172] like Figure 5 As 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.

[0173] 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.

[0174] 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.

[0175] 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 100 g / L, more preferably greater than 10 g / L and less than 70 g / L, and even more preferably greater than 15 g / L and less than 50 g / L.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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%.

[0180] 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 40The 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%.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] like Figure 5 As 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.

[0193] 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 100 g / L, more preferably greater than 10 g / L and less than 70 g / L, and even more preferably greater than 15 g / L and less than 50 g / L.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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%.

[0198] 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%.

[0199] 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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] There is no particular limitation on the form in which the alkaline earth metal element exists in the fourth catalyst layer 50. 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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] In the catalyst 1B, since 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, 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. NOx in the exhaust gas is purified by Rh in the third catalyst layer 40 and Pd in ​​the fourth catalyst layer 50. NOx that passes through the third catalyst layer 40 and the fourth catalyst layer 50 without being purified is adsorbed on Mg in the first catalyst layer 20. In this way, the first catalyst layer 20 adsorbs NOx in the exhaust gas, and the exhaust gas purification performance of the catalyst 1B is supplemented. Then, the NOx adsorbed on Mg in the first catalyst layer 20 is released and purified by, for example, Rh in the second catalyst layer 30. Thus, the catalyst 1B can exert improved exhaust gas purification performance.

[0211] 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.

[0212] 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.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] <Third embodiment>

[0217] 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.

[0218] 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.

[0219] 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.

[0220] like Figure 6 As shown, the difference between catalyst 1C and catalyst 1A is:

[0221] The fifth catalyst layer 60 is disposed on the upstream side of the first catalyst layer 20; and

[0222] The second catalyst layer 30 is provided on the upper side of the first catalyst layer 20 and the fifth catalyst layer 60 .

[0223] 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 can be disposed on the upper side of one of the first catalyst layer 20 or the fifth catalyst layer 60 .

[0224] 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.

[0225] 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.

[0226] like Figure 6 As 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.

[0227] 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.

[0228] 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.

[0229] like Figure 6As 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.

[0230] 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".

[0231] 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.

[0232] 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.

[0233] 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.

[0234] 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.

[0235] 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×(length L of the fifth catalyst layer 60) 60 / length L of substrate 10 10 )) figure it out.

[0236] 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.

[0237] Regarding the average length L of the first catalyst layer 20 in the first embodiment 20 The above description of the determination 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] 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.

[0242] 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.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] like Figure 6As 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.

[0247] 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.

[0248] 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.

[0249] In the catalyst 1C, since the second catalyst layer 30 is provided on the upper side of the first catalyst layer 20 and the fifth catalyst layer 60, 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 is purified by the Rh in the second catalyst layer 30 and the Pd in ​​the fifth catalyst layer 60. NOx that passes through the second catalyst layer 30 and / or the fifth catalyst layer 60 without being purified is adsorbed on the Mg in the first catalyst layer 20. In this way, the first catalyst layer 20 adsorbs NOx in the exhaust gas and compensates for the exhaust gas purification performance of the catalyst 1C. Then, the NOx adsorbed on the Mg in the first catalyst layer 20 is released and purified by, for example, the Rh in the second catalyst layer 30 and the Pd in ​​the fifth catalyst layer 60. As a result, the catalyst 1C can exert improved exhaust gas purification performance.

[0250] 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.

[0251] 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.

[0252] 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 .

[0253] 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.

[0254] 《Exhaust gas purification system》

[0255] The exhaust gas purification system of the present invention is described below.

[0256] 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.

[0257] like Figure 7 As shown, the exhaust gas purification system 100 includes: an exhaust pipe P, a first exhaust gas purification catalyst 101 (sometimes also 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 also referred to as the "second catalyst 102" in this specification) arranged on the upstream side of the exhaust passage of the exhaust pipe P.

[0258] 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.

[0259] 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.

[0260] 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.

[0261] The second catalyst 102 includes a second substrate and a catalyst layer provided on the second substrate.

[0262] 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".

[0263] 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.

[0264] 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.

[0265] 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.

[0266] 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.

[0267] 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.

[0268] 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.

[0269] 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.

[0270] In the exhaust gas purification system 100, since the second catalyst 102 is located on the upstream side of the first catalyst 101, 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. NOx that passes through the second catalyst 102 without being purified is adsorbed on Mg in the catalyst layer provided on the first substrate when passing through the first catalyst 101. In this way, the catalyst layer provided on the first substrate adsorbs NOx in the exhaust gas, thereby compensating for the exhaust gas purification performance of the exhaust gas purification system 100. Then, the NOx adsorbed on the Mg in the catalyst layer provided on the first substrate is released and purified by, for example, Rh in the second catalyst layer 30. In this way, the exhaust gas purification system 100 can exert improved exhaust gas purification performance.

[0271] Example

[0272] Hereinafter, the present invention will be described in further detail based on Examples and Comparative Examples.

[0273] [Example 1]

[0274] (1) Preparation of slurry for lower layer formation

[0275] An OSC material having the following composition was prepared.

[0276] CeO 2 Equivalent amount: 40 mass% ZrO 2 Conversion amount: 50% by mass, excluding CeO 2 Rare earth oxide equivalent amount other than: 10 mass%

[0277] Add platinum nitrate aqueous solution, OSC material, and La into the mixing container. 2 O 3 Modified alumina (La 2 O 3Modification amount: 1 mass %), magnesium nitrate, alumina sol and water were mixed and stirred to prepare a slurry for forming the lower layer. Based on the mass of the lower layer after calcination (100 mass %), the amounts of each component in the slurry for forming the lower layer were 0.6 mass % of Pt in terms of metal conversion, 44.7 mass % of OSC material, and 1.3 mass % of La. 2 O 3 The modified alumina was adjusted to 39.8 mass %, Mg was adjusted to 3.2 mass % in terms of metal, and the solid content of the alumina sol was adjusted to 9.5 mass %. 3 ) 2 ) is converted into magnesium oxide (MgO) by calcination.

[0278] (2) Formation of the lower layer

[0279] 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.

[0280] 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 calcined 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 140.9 g / L. The amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed was 0.9 g / L in terms of metal. Based on the mass of the lower layer, the CeO in the lower layer was 0.9 g / L. 2 The converted amount was 17.9% by mass. It should be noted that the mass of the lower layer refers to the mass after calcination.

[0281] (3) Preparation of slurry for upper layer formation

[0282] An OSC material having the following composition was prepared.

[0283] CeO 2 Equivalent amount: 15.0 mass % ZrO 2 Equivalent amount: 75.0% by mass Equivalent amount of oxides of rare earth elements other than Ce: 10% by mass

[0284] Add rhodium nitrate aqueous solution, OSC material, La 2 O 3 Modified alumina (La 2 O 3Modification amount: 1 mass %), alumina sol, zirconia sol and water were mixed and stirred to prepare a slurry for forming the upper layer. Based on the mass of the upper layer after calcination (100 mass %), the amounts of each component in the slurry for forming the upper layer were adjusted to 0.2 mass % of Rh in terms of metal conversion, 69.9 mass % of OSC material, and 0.1 mass % of La. 2 O 3 The contents were adjusted so that the modified alumina content was 22.0 mass %, the solid content of the alumina sol was 3.5 mass %, and the solid content of the zirconia sol was 4.4 mass %.

[0285] (4) Formation of the upper layer

[0286] The flow-type substrate with the lower layer formed is immersed in the slurry for forming the upper layer, and the flow-type substrate coated with the slurry for forming the upper layer is dried at 150°C for 0.5 hours, and then calcined 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-type substrate where the upper layer is formed is 80.2 g / L. The amount of Rh in the upper layer per unit volume of the portion of the flow-type substrate where the upper layer is formed is 0.2 g / L in terms of metal. It should be noted that the mass of the upper layer refers to the mass after calcination.

[0287] In the above manner, an exhaust gas purifying catalyst (hereinafter simply 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.

[0288] (5) Evaluation of exhaust gas purification performance (T50)

[0289] The catalyst cored to 30 mL was heated in a quartz tube furnace at 10 vol% H 2 Heat treatment was performed at 1000° C. for 20 hours in an O atmosphere in the following FC mode.

[0290] FC mode: Alternately introduce the following composition of sample gas (model gas, 3 L / min) and air (3 L / min).

[0291] Sample gas flow: C 3 H 6 6mL / min, O 2 71mL / min, N 2 2923mL / min (3L / min in total).

[0292] 10 vol% H 2 O 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 produce the above volume % water vapor amount.

[0293] The catalyst was placed in the exhaust passage, and an exhaust gas sample (CO: 0.50%, H 2 :0.17%,O 2 :0.50%, NO:400ppm, C 3 H 6 :1180ppm, CO 2 : 14%, H 2 O: 10%, N 2 : Residue), while the temperature was raised to 500°C at a rate of 20°C / min, the purification rates of hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO) were continuously measured, and the temperature (ignition temperature T50) (°C) at which the purification rates of hydrocarbons (HC), nitrogen oxides (NOx) and carbon monoxide (CO) reached 50% was determined. The ignition temperature T50 was determined during the temperature rise. The results are shown in Table 1.

[0294] [Example 2]

[0295] In the preparation of the catalyst, based on the mass of the lower layer after calcination (100 mass%), the amounts of the components in the slurry for forming the lower layer were 0.6 mass% of Pt, 44.7 mass% of OSC material, and 10.5 mass% of La in terms of metal conversion. 2 O 3 The catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 36.8 mass %, the Mg content was 5.1 mass % in terms of metal, and the solid content of the alumina sol was 9.5 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 (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 0.9 g / L, respectively. 2 The converted amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1.

[0296] A portion of the catalyst lower layer forming slurry obtained in Example 2 was calcined at 500° C. for 1 hour to obtain a calcined powder.

[0297] The X-ray diffraction pattern of the calcined powder was compared with the standard material 674a (α-Al 2 O 3 The X-ray diffraction patterns of the calcined powders were measured under the following conditions. 2 O 4 The diffraction intensity A of the peak at 2θ=64-67° in the peaks of α-Al and the X-ray diffraction spectrum of the standard substance 674a were used to determine the diffraction intensity A of the peak at 2θ=64-67°.2 O 3 The diffraction intensity B is present at a peak at 2θ=55 to 58° among the peaks. The diffraction intensities A and B are the heights of the peaks in the X-ray diffraction pattern.

[0298] [Measurement conditions of X-ray diffraction pattern]

[0299] The X-ray diffraction (XRD) of the calcined powder was performed using a commercially available powder X-ray diffractometer ("MiniFlex600" manufactured by Rigaku Co., Ltd.) under the following conditions: X-ray source: CuKα, operating axis: 2θ / θ, measurement method: continuous, counting unit: cps, start angle: 5°, end angle: 90°, sampling width: 0.02°, scanning speed: 10° / min, voltage: 40 kV, current: 150 mA. In the XRD pattern of the calcined powder, the MgAl-derived carbon was automatically calculated using analysis software ("PDXL version 2" manufactured by Rigaku Co., Ltd.). 2 O 4 The diffraction intensity A of the peak at 2θ=64-67° is present in the peak. The XRD of the standard substance 674a was performed in the same manner as the calcined powder. In the X-ray diffraction pattern of the standard substance 674a, the analysis software ("PDXL version 2" manufactured by Rigaku Co., Ltd.) was used to automatically calculate the diffraction intensity A of the peak at 2θ=64-67°. 2 O 3 Among the peaks, there is a diffraction intensity B of a peak at 2θ=55 to 58°.

[0300] As a result, A=1051, B=27892, and A / B=0.038.

[0301] Using the catalyst of Example 2, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0302] The slurry for forming the lower layer used in the preparation of the catalyst of Example 2 was dried at 150° C. for 0.5 hour and then calcined at 500° C. for 1 hour to prepare a powdery catalyst composition.

[0303] The heat-treated catalyst composition was subjected to a metal dispersion measuring device (BELMETAL3 manufactured by Microtrac BEL) and the CO adsorption amount on Pt was measured by the CO pulse method to calculate the Pt dispersion. The results are shown in Table 1. It should be noted that the Pt dispersion refers to the ratio of the number Y of Pt atoms exposed on the surface of the particles constituting the catalyst composition to the total number X of Pt atoms in the catalyst composition, and is calculated by Pt dispersion (%) = (Y / X) × 100. The number Y of Pt atoms exposed on the surface of the particles constituting the catalyst composition is calculated from the CO adsorption amount measured by the CO pulse method based on the premise that the Pt atoms exposed on the surface of the particles constituting the catalyst composition are adsorbed with CO in a 1:1 ratio.

[0304] [Example 3]

[0305] In the preparation of the catalyst, based on the mass of the lower layer after calcination (100 mass%), the amounts of the components in the slurry for forming the lower layer were 0.6 mass% of Pt, 44.7 mass% of OSC material, and 10.5 mass% of La in terms of metal conversion. 2 O 3 The catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 32.7 mass %, the Mg content was 7.5 mass % in terms of metal, and the solid content of the alumina sol was 9.5 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 (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 0.9 g / L, respectively. 2 The converted amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1.

[0306] Using the catalyst of Example 3, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0307] [Example 4]

[0308] In the manufacture of catalysts, MgAl 2 O 4 Instead of magnesium nitrate, the amount of each component in the slurry for forming the lower layer was 0.6 mass % of Pt, 44.7 mass % of OSC material, and 100 mass % of La in terms of metal conversion, based on the mass of the lower layer after calcination (100 mass %). 2 O 3The catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 15.3 mass %, the Mg content was 5.1 mass % in terms of metal, and the solid content of the alumina sol was 9.5 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 (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 140.9 g / L, 0.9 g / L, and 0.9 g / L, respectively. 2 The conversion amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1. 2 O 4 After calcination, Mg is present in the lower layer in the form of MgAl 2 O 4 exists in the form of.

[0309] The X-ray diffraction patterns of the calcined powder and the standard substance 674a were measured in the same manner as in Example 2 except that a portion of the catalyst lower layer forming slurry obtained in Example 4 was calcined at 500° C. for 1 hour to obtain a calcined powder. In the X-ray diffraction pattern of the calcined powder, the X-ray diffraction patterns of the calcined powder and the standard substance 674a were determined. 2 O 4 The diffraction intensity A of the peak at 2θ=64-67° in the peaks of α-Al and the X-ray diffraction pattern of the standard substance 674a were used to determine the diffraction intensity A of the peak at 2θ=64-67°. 2 O 3 Among the peaks, there is a diffraction intensity B of a peak at 2θ=55 to 58°.

[0310] As a result, A=1744, B=27892, and A / B=0.063.

[0311] Using the catalyst of Example 4, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0312] The slurry for forming the lower layer used in the preparation of the catalyst of Example 4 was dried at 150°C for 0.5 hours and then calcined at 500°C for 1 hour to prepare a powdered catalyst composition. Using the prepared catalyst composition, the Pt dispersion was measured in the same manner as in Example 2. The results are shown in Table 1.

[0313] [Example 5]

[0314] In the preparation of the catalyst, magnesium oxide was used instead of magnesium nitrate, and the amount of each component in the slurry for forming the lower layer was 0.6 mass % of Pt in terms of metal conversion, 44.7 mass % of OSC material, and 100 mass % of La. 2O 3 The catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 36.8 mass %, the Mg content was 5.1 mass % in terms of metal, and the solid content of the alumina sol was 9.5 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 (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 0.9 g / L, respectively. 2 The converted amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1.

[0315] Using the catalyst of Example 5, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0316] [Comparative Example 1]

[0317] In the preparation of the catalyst, based on the mass of the lower layer after calcination (100 mass%), the amounts of the components in the slurry for forming the lower layer were 0.6 mass% of Pt, 44.7 mass% of OSC material, and 10.5 mass% of La in terms of metal conversion. 2 O 3 A catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 28.6 mass %, the Mg content was 9.9 mass % in terms of metal, and the solid content of the alumina sol was 9.5 mass %. In the catalyst of Comparative Example 1, the mass of the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 0.9 g / L, respectively. 2 The converted amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1.

[0318] Using the catalyst of Comparative Example 1, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0319] [Comparative Example 2]

[0320] In the preparation of the catalyst, based on the mass of the lower layer after calcination (100 mass%), the amounts of the components in the slurry for forming the lower layer were 0.6 mass% of Pt, 44.7 mass% of OSC material, and 10.5 mass% of La in terms of metal conversion. 2 O 3The catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 42.6 mass %, the Mg content was 1.5 mass % in terms of metal, and the solid content of the alumina sol was 9.5 mass %. In the catalyst of Comparative 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 (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 1.5 g / L, ... 2 The converted amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1.

[0321] Using the catalyst of Comparative Example 2, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0322] [Comparative Example 3]

[0323] In the preparation of the catalyst, barium nitrate was used instead of magnesium nitrate, and the amount of each component in the slurry for forming the lower layer was 0.6 mass % of Pt in terms of metal conversion, 44.7 mass % of OSC material, and 100 mass % of La. 2 O 3 The catalyst was produced in the same manner as in Example 1 except that the modified alumina content was 39.5 mass %, the Ba content was 5.0 mass % in terms of metal conversion, and the solid content of the alumina sol was 9.5 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 (140.9 g / L), the amount of Pt in the lower layer per unit volume of the portion of the flow-through substrate where the lower layer was formed (0.9 g / L in terms of metal conversion), the Ce content of CeO in the lower layer, and the amount of Pt in the lower layer were 1.3 g / L and 1.2 g / L, respectively. 2 The conversion amount (17.9 mass % based on the mass of the lower layer) is the same as that of the catalyst in Example 1. It should be noted that barium nitrate (Ba(NO 3 ) 2 ) is converted into barium oxide (BaO) by calcination.

[0324] Using the catalyst of Comparative Example 3, the exhaust gas purification performance (T50) was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0325] The slurry for forming the lower layer used in the preparation of the catalyst of Comparative Example 3 was dried at 150°C for 0.5 hours and then calcined at 500°C for 1 hour to prepare a powdered catalyst composition. Using the prepared catalyst composition, the Pt dispersion was measured in the same manner as in Example 2. The results are shown in Table 1.

[0326] [Table 1]

[0327]

[0328] As shown in Table 1, Examples 1 to 5 satisfying the condition that the lower layer in the catalyst contains Pt and Mg and the metal conversion amount of Mg is 2.0 mass % or more and 9.0 mass % or less based on the mass of the lower layer have higher exhaust gas purification performance than Comparative Examples 1 to 3 not satisfying this condition.

[0329] Description of Reference Numerals

[0330] P: Exhaust pipe of internal combustion engine

[0331] 1A: Exhaust gas purification catalyst according to the first embodiment

[0332] 1B: Exhaust gas purification catalyst according to the second embodiment

[0333] 1C: Exhaust gas purification catalyst according to the third embodiment

[0334] 10: Base material

[0335] 11: Cylindrical part

[0336] 12: Next door

[0337] 13: Chamber

[0338] 14: 1st closed section

[0339] 15: Second closed section

[0340] 20: First catalyst layer

[0341] 30: Second catalyst layer

[0342] 40: The third catalyst layer

[0343] 50: 4th catalyst layer

[0344] 60: 5th catalyst layer

[0345] 100: Exhaust gas purification system

[0346] 101: No. 1 exhaust gas purification catalyst

[0347] 102: Second exhaust gas purification catalyst

Claims

1. A catalyst composition for exhaust gas purification, comprising Pt and Mg, The metal-equivalent amount of Mg is 2.0 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 Mg 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 Mg exists in the form of one or both selected from MgO and MgCO3.

4. The exhaust gas purification catalyst composition according to claim 1, wherein Mg exists in a form other than a composite oxide containing Mg and Al.

5. The exhaust gas purification catalyst composition according to claim 1, wherein In the X-ray diffraction pattern of the exhaust gas purification catalyst composition, the diffraction intensity of the peak at 2θ=64~67° in the peak from MgAl2O4 is set to A, and in the X-ray diffraction pattern of the standard substance 674a, i.e. α-Al2O3, promulgated by the National Institute of Standards and Technology of the United States, the diffraction intensity of the peak at 2θ=55~58° in the peak from α-Al2O3 is set to B, the ratio of A to B is less than 0.

060.

6. 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.

7. 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 6.

8. The exhaust gas purification catalyst according to claim 7, 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.

9. The exhaust gas purification catalyst according to claim 8, wherein The second catalyst layer and / or the third catalyst layer contains Rh.

10. The exhaust gas purification catalyst according to claim 8, 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.

11. 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 6.

12. The exhaust gas purification system according to claim 11, wherein: The second exhaust gas-purifying catalyst includes a second substrate and a catalyst layer provided on the second substrate.

13. The exhaust gas purification system according to claim 12, wherein: The catalyst layer provided on the second substrate includes Rh.

14. The exhaust gas purification system according to claim 12, 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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