Catalysts for exhaust gas purification

Abstract

The present invention provides an exhaust gas purification catalyst in which alkaline earth metals are supported on a porous carrier in a highly dispersed state. The catalyst layer of the exhaust gas purification catalyst provided by the present invention is characterized in that it has an alkaline earth metal supporting region, the region having a porous carrier, Pt and at least one alkaline earth metal sulfate supported on the porous carrier, the cross section of the region is subjected to surface analysis using FE-EPMA under the conditions of a pixel size of 0.34 μm×0.34 μm and a measurement pixel number of 256×256, the intensity of the characteristic X-ray of the alkaline earth metal element (Ae) (α: cps) and the intensity of the characteristic X-ray of Pt (β: cps) are measured for each pixel, and the Pearson correlation coefficient R is calculated using the obtained α and β of each pixel. Ae / Pt The value is 0.5 or more.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification catalyst provided in an exhaust system of an internal combustion engine. Specifically, it relates to an exhaust gas purification catalyst containing platinum (Pt) as a catalyst metal and alkaline earth metals such as barium (Ba) and strontium (Sr) as a co-catalyst component. Furthermore, this application claims priority based on Japanese Patent Application No. 2018-189365 filed on October 4, 2018, and the entire contents of the application are cited in this specification as a reference. Background Art

[0002] As a catalyst for removing hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO) from exhaust gas emitted by an internal combustion engine such as an automobile engine through oxidation or reduction reaction. x ) and other harmful components in exhaust gas, so-called three-way catalysts are used. As three-way catalysts, for example, a metal (typically a noble metal such as Pt) that functions as an oxidation catalyst and / or a reduction catalyst is supported on a porous carrier composed of an inorganic oxide such as alumina (Al2O3) or zirconium oxide (ZrO2).

[0003] In addition, in such exhaust gas purification catalysts, a promoter component that can improve the exhaust gas purification function can be used. For example, the following patent documents 1 and 2 describe existing exhaust gas purification catalysts containing Pt as a catalyst metal and alkaline earth metals such as barium (Ba) and strontium (Sr) as a promoter.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 5-237390

[0007] Patent Document 2: Japanese Patent Application Publication No. 11-285639 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] However, in order to exert the effect of the alkaline earth metal as a promoter as described above, the alkaline earth metal needs to be present near Pt in the catalyst layer of the exhaust gas purification catalyst. Moreover, in order to exert the effect of the alkaline earth metal as a promoter in the exhaust gas purification catalyst as a whole, it is important to have the alkaline earth metal and Pt exist in a highly dispersed state.

[0010] However, when using the existing catalyst layer formation technology, the alkaline earth metal is unevenly present in the catalyst layer (alkaline earth metal supporting region), and the alkaline earth metal cannot be supported in a highly dispersed state on the outer surface and pores of the porous support. In other words, in the catalyst layer (alkaline earth metal supporting region), the alkaline earth metal cannot be supported (fixed) in a highly dispersed state near the Pt supported in the outer surface and pores of the porous support in a highly dispersed state. For example, there is a problem that most of the alkaline earth metal is unevenly present on the outer surface of the porous support.

[0011] Therefore, the present invention is made to solve the above-mentioned problems of the prior art, and its purpose is to provide an exhaust gas purification catalyst in which an alkaline earth metal as a co-catalyst component is supported on a porous carrier in a highly dispersed state, and a manufacturing method that can achieve such highly dispersed support.

[0012] Technical solutions for solving technical problems

[0013] The inventors of the present invention have conducted a detailed study on the presence form of alkaline earth metals such as Ba as a co-catalyst in the catalyst layer. In addition, it has been confirmed that if alkaline earth metals such as Ba are used in the form of sulfates that are insoluble in water from the raw material stage, the alkaline earth metals are unevenly present in the catalyst layer, and a highly dispersed state cannot be achieved. In addition, when a raw material slurry containing a water-soluble compound such as a nitrate of Ba is used, and sulfuric acid or ammonium sulfate solution is provided to the slurry to generate sulfates (insolubles) of alkaline earth metals such as Ba, the pH of the raw material slurry changes in the subsequent drying and firing stages and is excessively acidic. As a result, a highly dispersed state cannot be maintained and the alkaline earth metals are unevenly present, and a highly dispersed state cannot still be achieved.

[0014] Therefore, the inventors of the present invention conducted research starting from the raw material stage of alkaline earth metals such as Ba, and found that by using a raw material in which a water-soluble compound of an alkaline earth metal coexists with a certain water-soluble organic compound containing S, alkaline earth metal sulfates such as Ba can be arranged (supported) together with Pt in a highly dispersed state on a porous carrier in the catalyst layer (alkaline earth metal supporting area), thereby completing the present invention.

[0015] According to the present invention, it is possible to provide an exhaust gas purification catalyst which is arranged in an exhaust pipe of an internal combustion engine and purifies exhaust gas exhausted from the internal combustion engine.

[0016] That is, the exhaust gas purification catalyst disclosed herein includes a substrate and a catalyst layer formed on the substrate. The catalyst layer has an alkaline earth metal supporting region, and the region has:

[0017] A porous carrier composed of an inorganic compound,

[0018] Pt supported on the porous carrier, and

[0019] At least one alkaline earth metal sulfate is supported on the porous carrier.

[0020] Furthermore, the exhaust gas purification catalyst disclosed herein is characterized in that, for a cross section of the alkaline earth metal supporting region of the above-mentioned catalyst layer, a surface analysis is performed using FE-EPMA under the conditions of a pixel (segment) size of 0.34 μm×0.34 μm and a measurement pixel (segment) number of 256×256, and the intensity of the characteristic X-ray (α: cps) of the element (Ae) of the above-mentioned alkaline earth metal and the intensity of the characteristic X-ray (β: cps) of Pt are measured for each pixel, and the Pearson correlation coefficient calculated using the obtained α and β of each pixel is set to R Ae / Pt hour,

[0021] The R Ae / Pt The value of is 0.5 or more.

[0022] The exhaust gas purification catalyst disclosed herein is a catalyst product that can be produced by the exhaust gas purification catalyst production method provided by the present invention (details of which will be described later). As described above, it is characterized in that the Pearson correlation coefficient (product-moment correlation coefficient) R calculated based on the surface analysis result using FE-EPMA is Ae / Pt It is 0.5 or more.

[0023] The correlation coefficient R Ae / Pt When the first variable is set to the characteristic X-ray intensity (α) of the alkaline earth metal element (Ae) in the surface analysis by FE-EPMA, and the second variable is set to the characteristic X-ray intensity (β) of Pt in the same surface analysis,

[0024] R Ae / Pt =(covariance) / (standard deviation of α × standard deviation of β)

[0025] Calculate the correlation coefficient.

[0026] The exhaust gas purification catalyst of the present technical solution is characterized in that there is a high correlation between the location (distribution) of Pt and the alkaline earth metal element in the alkaline earth metal supporting region of the catalyst layer. In other words, the alkaline earth metal (sulfate) exists in a highly dispersed state throughout the entire porous carrier particle (i.e., both the outer surface and the interior (pores) of the carrier particle). As a result, in the alkaline earth metal supporting region of the catalyst layer, the alkaline earth metal can exist in the vicinity of the Pt particles at a high frequency, so that the alkaline earth metal can play a role as a co-catalyst component at a high level. In particular, since the alkaline earth metal is adjacent to Pt, the HC poisoning of Pt is suppressed by the electron supply of the alkaline earth metal, and the HC purification performance in a rich atmosphere can be improved.

[0027] In another preferred embodiment of the exhaust gas purification catalyst disclosed herein, the calculated Pearson correlation coefficient R Ae / Pt The value is 0.7 or more.

[0028] As R Ae / Pt As shown by the value of 0.7 or more, the exhaust gas purification catalyst of the present technical solution has high dispersibility of the alkaline earth metal component. Therefore, it is possible to exert the performance (function) as a promoter component at a high level in the catalyst layer (alkaline earth metal supporting region).

[0029] It is particularly preferred that the average particle size of the alkaline earth metal sulfate supported on the porous carrier as measured by X-ray diffraction is 30 nm or less. Alkaline earth metal components having such a fine average particle size can exhibit particularly high performance as a co-catalyst component.

[0030] In a preferred embodiment of the exhaust gas purification catalyst disclosed herein, a catalyst layer containing Rh as a catalyst metal is further provided on the downstream side of the catalyst layer in the exhaust gas flow direction.

[0031] At this time, the amount of HC flowing into the catalyst layer using Rh as the catalyst metal is reduced, so HC poisoning of Rh can be suppressed. In addition, since the alkaline earth metal is a sulfate and is fixed, Rh can be prevented from contacting with alkaline earth metals such as Ba (especially Ba), thereby preventing the metallization inhibition of Rh caused by Ba. Therefore, the coexistence of NO in the rich atmosphere of the exhaust gas purification catalyst can be improved. x The purification effect.

[0032] In a preferred embodiment of the exhaust gas purification catalyst disclosed herein, the catalyst contains at least barium sulfate (BaSO 4 ) as the alkaline earth metal sulfate.

[0033] When using the exhaust gas purification catalyst of this technical solution, the highly dispersed barium component (barium sulfate) can temporarily store NO stably. x , and Pt can be used to temporarily absorb NO in this component. x Furthermore, by making the barium component highly dispersed and supported on the carrier, NO x Therefore, the exhaust gas purification catalyst of the present technical solution can be used as a high-performance NO x A purification catalyst is suitably employed.

[0034] In addition, in order to achieve the above-mentioned object, the present invention provides a method for appropriately manufacturing the exhaust gas purification catalyst disclosed herein. That is, the manufacturing method disclosed herein is used to manufacture an exhaust gas purification catalyst that is arranged in an exhaust pipe of an internal combustion engine and purifies the exhaust gas discharged by the internal combustion engine, and the above-mentioned manufacturing method comprises:

[0035] A step of forming a catalyst layer on a substrate, wherein the catalyst layer has an alkaline earth metal supporting region in at least a portion thereof, the region having a porous support composed of an inorganic compound, Pt supported on the porous support, and at least one alkaline earth metal sulfate supported on the porous support; and

[0036] A step of firing the substrate on which the catalyst layer is formed.

[0037] In addition, in the manufacturing method disclosed herein, the step of forming the catalyst layer includes:

[0038] (1) a step of preparing a raw material suspension by mixing the following components with an aqueous solvent, wherein the above components are: inorganic compound particles constituting the above porous carrier, Pt particles or a precursor for precipitating Pt, the above water-soluble compound of the alkaline earth metal, and a water-soluble organic compound containing S as a constituent element and capable of generating a sulfate of the above alkaline earth metal;

[0039] (2) drying the raw material suspension and then firing it to prepare a powder material containing the porous support, Pt and alkaline earth metal sulfate;

[0040] (3) a step of preparing a slurry for forming an alkaline earth metal supporting region containing at least the above-mentioned powder material and an aqueous solvent; and

[0041] (4) A step of forming the alkaline earth metal supporting region on the substrate using the slurry.

[0042] In the method for producing a catalyst for exhaust purification of this technical solution, a water-soluble compound of an alkaline earth metal and a water-soluble organic compound containing S as specified above are mixed with a carrier component (inorganic compound particles) and a catalyst metal component (Pt particles or a compound serving as a precursor of Pt), and the obtained raw material (suspension) is used for the purpose of forming an alkaline earth metal supporting area.

[0043] In the prepared raw material suspension, the alkaline earth metal water-soluble compound and the S-containing water-soluble organic compound are dissolved together in the aqueous solvent. At this time, the S-containing water-soluble organic compound does not cause a sharp drop in the pH of the raw material suspension (i.e., acidification of the suspension), and the alkaline earth metal water-soluble compound and the S-containing water-soluble organic compound can diffuse into the interior (pores) of the inorganic compound particles (secondary particles) as the carrier component while maintaining their water solubility.

[0044] Next, the prepared raw material suspension is dried and fired. In this process, the water-soluble compound of the alkaline earth metal as a component reacts with the above-mentioned water-soluble organic compound containing S, and insoluble alkaline earth metal sulfate is formed inside and outside the inorganic compound particles and fixed at the existing position.

[0045] Therefore, by adopting the manufacturing method of the present technical solution, it is possible to suitably manufacture an exhaust gas purification catalyst having an alkaline earth metal supporting region in the whole or part of the catalyst layer, wherein the alkaline earth metal supporting region is characterized in that the alkaline earth metal exists in a highly dispersed state throughout the porous carrier particles (i.e., both the outer surface and the interior (pores) of the carrier particles).

[0046] In a preferred embodiment of the method for producing an exhaust gas purification catalyst disclosed herein, a water-soluble organic substance having at least one functional group selected from the group consisting of a sulfonic acid group (-SO3H), a sulfonyl group (-S(=O)2-) and a sulfinyl group (-S(=O)-) is used as the S-containing water-soluble organic compound.

[0047] An organic compound having such a S-containing functional group is preferable as the S-containing water-soluble organic compound used for preparing the above-mentioned raw material suspension.

[0048] In another preferred embodiment of the exhaust gas purification catalyst production method disclosed herein, an acetate, a nitrite or an iodide of any alkaline earth metal selected from Ba, Sr and Ca is used as the water-soluble compound of the alkaline earth metal.

[0049] Such acetates, nitrites or iodides have good water solubility and are preferably used as water-soluble compounds of alkaline earth metals for preparing the above-mentioned raw material suspension. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a perspective view schematically showing an exhaust gas purification catalyst according to an embodiment.

[0051] Figure 2 It is a cross-sectional view schematically showing a catalyst layer of an exhaust gas purification catalyst according to an embodiment.

[0052] Figure 3 This is an image showing the element mapping results of Ba and Pt in the FE-EPMA surface analysis (256×256 pixels) of the Pt-containing powder material used in Example 1.

[0053] Figure 4 This is an image showing the element mapping results of Ba and Pt in the FE-EPMA surface analysis (256×256 pixels) of the Pt-containing powder material used in Comparative Example 1.

[0054] Figure 5 This is an image showing the element mapping results of Ba and Pt in the FE-EPMA surface analysis (256×256 pixels) of the Pt-containing powder material used in Comparative Example 2.

[0055] Figure 6 This is an image showing the element mapping results of Ba and Pt in the FE-EPMA surface analysis (256×256 pixels) of the Pt-containing powder material used in Comparative Example 3.

[0056] Figure 7 This is a graph comparing the HC purification performance of the Pt-containing powder material used in Example 1 and the exhaust gas purification catalyst of Comparative Example 1.

[0057] Figure 8 This is a graph comparing the HC purification performance of the exhaust gas purification catalyst of Example 1 and the exhaust gas purification catalyst of Comparative Example 1.

[0058] Fig. 9 The exhaust gas purification catalyst of Example 1 is NO x This is a graph comparing the purification performance with the exhaust gas purification catalyst of Comparative Example 1. DETAILED DESCRIPTION

[0059] Hereinafter, several preferred embodiments of the present invention will be described with appropriate reference to the accompanying drawings. In addition, matters that are necessary for implementing the present invention but are not particularly mentioned in this specification can be understood as design matters for technicians based on the prior art in the technical field. The present invention can be implemented based on the contents disclosed in this specification and the technical knowledge in the technical field. Figure 1-2 The drawings are schematically shown for understanding the contents of the present invention, and the dimensional relationships (length, width, thickness, etc.) in the drawings do not represent actual dimensional relationships.

[0060] The exhaust gas purification catalyst disclosed herein is characterized in that the alkaline earth metal sulfate with the above-mentioned properties exists in a highly dispersed state in at least a part of the catalyst layer (i.e., the pre-designed alkaline earth metal supporting region in the catalyst layer), and other components are not particularly limited. The exhaust gas purification catalyst disclosed herein can be configured in various internal combustion engines, especially the exhaust system (exhaust pipe) of automobile engines by appropriately selecting the types of carriers and substrates described later and molding them into a desired shape according to the purpose.

[0061] The following description is mainly based on the premise that the exhaust gas purification catalyst of the present invention is applied to a three-way catalyst installed in the exhaust pipe of a gasoline engine of an automobile, but the exhaust gas purification catalyst disclosed herein is not intended to be limited to this application.

[0062] <Base material>

[0063] As the substrate constituting the skeleton of the exhaust gas purification catalyst disclosed herein, a variety of raw materials and substrates currently used for such applications can be used. For example, ceramics such as cordierite and silicon carbide (SiC) with high heat resistance are suitable. Alternatively, a substrate made of alloy (stainless steel, etc.) can be used. The shape can be the same as that of the existing exhaust gas purification catalyst. As an example, the following can be listed: Figure 1 As shown in the exhaust gas purification catalyst 10, a honeycomb substrate 1 is configured to have a cylindrical outer shape, and a through hole (cell) 2 as an exhaust gas flow path is provided in the axial direction of the cylinder, and the exhaust gas can contact the partition wall (rib wall) 4 that separates each cell 2. Regarding the shape of the substrate 1, in addition to the honeycomb shape, it can also be a foam shape, a granular shape, etc. Alternatively, it can also be a so-called through-wall type (also called a wall flow type) substrate in which the exhaust gas flows from the inlet cell on one side through the cell partition wall to the outlet cell on the other side. In addition, regarding the overall shape of the substrate, an elliptical cylinder or a polygonal cylinder can be used instead of a cylindrical shape.

[0064] <Platinum (Pt)>

[0065] As the catalyst metal included in the catalyst layer of the exhaust gas purification catalyst disclosed herein, Pt is used.

[0066] From the viewpoint of increasing the contact area with the exhaust gas, Pt is preferably used in the form of fine particles with a sufficiently small particle size. Typically, the average particle size (preferably the average value of the particle size obtained by, for example, TEM observation, or the average value based on X-ray diffraction method) is 1 nm to 15 nm, preferably 10 nm to 7 nm, and particularly preferably 5 nm to 5 nm.

[0067] The support rate of the catalyst metal (the Pt content when the carrier is set to 100 mass%) is not particularly limited, and is generally suitable to be 2 mass% or less, for example, 0.05 mass% or more and 2 mass% or less, preferably 0.2 mass% or more and 1 mass% or less. When the support rate is too small compared to the above range, it is difficult to obtain the catalytic effect brought by Pt. When the support rate is too large compared to the above range, it is disadvantageous in terms of cost.

[0068] <Carrier>

[0069] As the porous carrier constituting the catalyst layer and supporting Pt and other components (for example, alkaline earth metal), the same inorganic compound as that used in the conventional exhaust gas purification catalyst can be used.

[0070] It is suitable to use a porous carrier having a certain degree of large specific surface area (specific surface area measured by the BET method. The same applies below). As suitable porous carriers, for example, aluminum oxide (Al2O3), zirconium oxide (ZrO2), ceria (CeO2), silicon dioxide (SiO2), titanium dioxide (TiO2), solid solutions thereof (such as ceria-zirconia composite oxide (CZ composite oxide), or combinations thereof can be cited.

[0071] From the viewpoint of improving the thermal stability of exhaust purification catalysts, it is preferred that the catalyst layer contain inorganic compounds such as alumina and zirconium oxide with good heat resistance as a carrier or non-carrier (i.e., meaning a constituent component of the catalyst layer that does not carry Pt or alkaline earth metals. The same applies below).

[0072] The particles used as the carrier or non-carrier (e.g., alumina powder, CZ composite oxide powder) preferably have a specific surface area of ​​50 to 500 m2 from the viewpoint of heat resistance and structural stability. 2 / g (e.g. 200~400m 2 / g). Furthermore, the average particle size of the carrier particles determined based on TEM observation is preferably in the range of 1 nm to 500 nm (more preferably 5 nm to 300 nm).

[0073] In addition, when such an inorganic compound (ceramic) is used as a carrier, the catalyst metal content per 1L catalyst volume is appropriately 0.1 to 5 g / L, preferably 0.2 to 2 g / L. When the catalyst metal content is too much, it is not preferred from the cost point of view, and when it is too little, it is not preferred due to low exhaust purification performance. In addition, in this specification, when the catalyst volume is recorded as 1L, it means that the apparent volume including the internal void (chamber) volume (that is, including the catalyst layer formed in the void (chamber)) in addition to the pure volume of the substrate is 1L.

[0074] <Alkaline earth metal supporting region>

[0075] The catalyst layer formed on the substrate serves as a part for purifying exhaust gas and constitutes the main body of the exhaust gas purifying catalyst. In the exhaust gas purifying catalyst disclosed herein, as described above, at least a part (or the whole) of the catalyst layer constitutes an alkaline earth metal supporting region.

[0076] In this specification, "alkaline earth metal supporting region" means a part or the whole of the catalyst layer having a porous carrier, Pt and alkaline earth metal sulfate (barium sulfate, strontium sulfate, etc.). Here, "a part of the catalyst layer" refers to a section that can function as an exhaust gas purification catalyst, and does not refer to a microscopic part that cannot be functionally called a section, such as several to dozens of carrier particles.

[0077] The arrangement (distribution) of Pt supported on the catalyst layer can be appropriately set according to various purposes, similar to the determination of the alkaline earth metal supporting region. Figure 2 In the catalyst layer 6 having the stacked structure shown, the type of carrier, and the type and content ratio of the catalyst metal carried by the carrier can be made different between the upper layer 6A and the lower layer 6B, as in the conventional product.

[0078] Specifically, for example, as an example, Figure 2 When the catalyst layer 6 is a laminated structure type catalyst layer 6 having two layers with different contents formed on the substrate 1, such as the catalyst layer 6 shown in the figure, any one or both of the lower layer 6B adjacent to the substrate 1 and the upper layer 6A constituting the surface layer portion of the catalyst layer 6 can be formed as an alkaline earth metal supporting region. Alternatively, in the catalyst layer of the laminated structure or single-layer structure as shown in the figure, a part (e.g., more than 10 vol% of the whole) of the upstream side (or downstream side) along the direction of exhaust gas flow can be set as the alkaline earth metal supporting region.

[0079] Here, it is preferred to have a catalyst layer with Rh as the catalyst metal on the downstream side of the catalyst layer with the alkaline earth metal supporting region in the exhaust gas flow direction. In this case, the amount of HC flowing into the catalyst layer with Rh as the catalyst metal is reduced, thereby suppressing HC poisoning of Rh. In addition, the alkaline earth metal is a sulfate and is fixed, so it is possible to prevent Rh from contacting alkaline earth metals such as Ba (especially Ba), and to prevent the metallization inhibition of Rh caused by Ba. Therefore, it is possible to improve the coexistence of NO in the rich atmosphere of the exhaust gas purification catalyst. x The purification effect.

[0080] Examples of such a structure include: a structure in which the upper layer 6A is set as an alkaline earth metal carrying region, and Rh is contained in the lower layer 6B side which is not the alkaline earth metal carrying region; a structure in which, in a catalyst layer with a single-layer structure or a stacked structure, a part of the upstream side in the exhaust gas flow direction (for example, more than 10 vol% of the whole) is set as an alkaline earth metal carrying region, and Rh is contained in the remaining downstream side region; a structure in which the upstream side is a single-layer structure containing an alkaline earth metal carrying region, and the downstream side is a stacked structure of an upper layer containing Rh and a lower layer containing an alkaline earth metal carrying region, etc.

[0081] In addition, as alkaline earth metal elements constituting suitable sulfates contained in the alkaline earth metal supporting region, barium (Ba), strontium (Sr), and calcium (Ca) can be listed. From the viewpoint of being able to play an excellent role as a co-catalyst component, Ba and Sr are suitable, and Ba is particularly preferred. Barium sulfate (BaSO4) is suitable as an alkaline earth metal supported on a carrier because of its extremely high and stable melting point and extremely low solubility in water.

[0082] In the catalyst layer, in addition to Pt and alkaline earth metals, various auxiliary components can also be configured. As a typical example, an oxygen storage component (OSC) can be cited. As OSC materials, zirconium oxide (zirconia), cerium oxide (ceria), zeolite, etc. are suitable. In addition, from the viewpoint of high heat resistance and absorption / release rate, it is preferred to use the above-mentioned ceria-zirconia composite oxide (CZ composite oxide) as OSC material.

[0083] It is particularly preferred that the average particle size of the alkaline earth metal sulfate supported on the porous carrier as measured by X-ray diffraction is 30 nm or less. The alkaline earth metal component having such a fine average particle size can exhibit particularly high performance as a co-catalyst component.

[0084] <Pearson correlation coefficient>

[0085] Regarding the dispersibility of the alkaline earth metal in the alkaline earth metal supporting region of the exhaust gas purification catalyst disclosed herein, the cross section of the alkaline earth metal supporting region of the catalyst layer 6 was subjected to the following conditions:

[0086] Pixel size 0.34μm×0.34μm;

[0087] The number of pixels measured is 256×256;

[0088] The FE-EPMA surface analysis was performed to measure the intensity of the characteristic X-ray of the alkaline earth metal element (Ae) (α: cps) and the intensity of the characteristic X-ray of Pt (β: cps) for each pixel, and the Pearson correlation coefficient calculated using the obtained α and β of each pixel was set as RAe / Pt When R Ae / Pt The value of is 0.5 or more.

[0089] When the alkaline earth metal is supported in a highly dispersed manner inside the carrier (particularly inside the carrier secondary particles), Pt and the alkaline earth metal are brought into proximity to such an extent that a correlation can be confirmed between the location of Pt and the location of the alkaline earth metal.

[0090] The alkaline earth metal is highly dispersed in the carrier (especially in the carrier secondary particles), and Pt is in close proximity to the alkaline earth metal. Ae / Pt The value of is 0.5 or more.

[0091] R Ae / Pt When the value is 0.5 or more, the alkaline earth metal can function as a catalyst promoter at a high level. In particular, since the alkaline earth metal is close to Pt, the electrons donated by the alkaline earth metal suppress HC poisoning of Pt, thereby improving the HC purification performance in a rich atmosphere.

[0092] R Ae / Pt The higher the value of , the higher the dispersibility of the alkaline earth metal component in the exhaust gas purification catalyst of the present technical solution. Therefore, it is possible to exert the performance (function) as a co-catalyst component at a high level in the catalyst layer (alkaline earth metal supporting region). Ae / Pt The value of is preferably 0.6 or more, more preferably 0.7 or more.

[0093] Pearson correlation coefficient R Ae / pt By performing surface analysis using FE-EPMA, the intensity of characteristic X-rays of alkaline earth metal elements (Ae) (α: cps) and the intensity of characteristic X-rays of Pt (β: cps) are measured for each pixel, and the calculated value can be obtained using the obtained α and β for each pixel.

[0094] FE (Field Emission)-EPMA (Electron Probe Micro Analysis) is an analysis method also known as field emission electron probe microanalysis, which can perform element analysis and mapping in a specified area of ​​a sample with high precision. By using this FE-EPMA, the above-mentioned α and β of the catalyst layer (alkaline earth metal supporting area) of the exhaust gas purification catalyst are measured with a specified number of pixels, and R can be calculated by using the obtained data. Ae / Pt .

[0095] That is, R, which is the Pearson correlation coefficient (product-moment correlation coefficient), Ae / Pt for

[0096] R Ae / Pt=(covariance) / (standard deviation of α×standard deviation of β), which can be specifically determined by the following formula (1).

[0097]

[0098] Based on the correlation coefficient R of formula (1) Ae / Pt The calculation can be performed using commercially available general spreadsheet software, so that it can be derived without having to perform particularly difficult calculation processing by manual calculation. For example, it can be easily derived by using the CORREL function function of EXCEL (trademark) produced by Microsoft Corporation.

[0099] In addition, regarding data collection for calculating the correlation coefficient, it is possible to perform surface analysis using FE-EPMA by following the user manual of a commercially available device.

[0100] The general description is as follows: first, the catalyst layer (alkaline earth metal supporting region) of the exhaust gas purification catalyst for surface analysis is cut out for use, or the surface of the above powder material is polished to expose the cross section, and a conductive material (typically carbon) is vapor-deposited to prepare a sample for EPMA analysis. Then, a commercially available device (e.g., an electron probe microanalyzer such as JXA-8530F manufactured by JEOL Ltd.) is used to perform surface analysis.

[0101] Here, the pixel (segment) size can be set to 0.34 μm×0.34 μm, and the number of measurement pixels (segments) can be set to 200×200 or more, for example, 256×256. The measurement conditions vary depending on the analysis device and are not particularly limited. Several typical measurement conditions can be listed as follows:

[0102] Accelerating voltage: 10kV~30kV (e.g. 20kV),

[0103] Irradiation current: 50nA~500nA (e.g. 100nA),

[0104] Minimum probe diameter: less than 500nm (e.g. 100nm),

[0105] Unit measurement time: 40ms to 100ms (e.g. 50ms).

[0106] Alternatively, the surface analysis results by FE-EPMA may be displayed as elemental mapping using application software (computer software) included with a commercially available device (see the drawings described later).

[0107] The manufacturing method of the exhaust purification catalyst of the present embodiment includes: a step of forming a catalyst layer on a substrate, the catalyst layer having an alkaline earth metal supporting region in at least a portion thereof, the region having a porous carrier composed of an inorganic compound, Pt supported on the porous carrier, and at least one alkaline earth metal sulfate supported on the porous carrier; and a step of calcining the substrate on which the catalyst layer is formed.

[0108] Among them, in the process of forming the catalyst layer, first, the inorganic compound particles constituting the porous carrier, Pt particles or a precursor material for precipitating Pt, the water-soluble compound of the alkaline earth metal, and the S-containing water-soluble organic compound which contains S as a constituent element and can generate the sulfate of the above-mentioned alkaline earth metal are mixed with an aqueous solvent to prepare a raw material suspension.

[0109] Next, the raw material suspension is dried and then fired to prepare a powder material in which the porous support, Pt, and alkaline earth metal sulfate are mixed.

[0110] Thereafter, an alkaline earth metal supporting region forming slurry containing at least the above-mentioned powder material and an aqueous solvent is prepared.

[0111] Then, the alkaline earth metal supporting region is formed on the substrate using the slurry.

[0112] The materials used are the same as those described above as examples of the inorganic compound constituting the porous support.

[0113] Examples of the precursor substance for precipitating Pt include water-soluble complexes and salts of Pt.

[0114] Examples of water-soluble compounds of alkaline earth metals include various salts, for example, hydroxides, halides, acetates, nitrates, nitrites, etc. of Ba, Sr or Ca. Particularly preferred are those having high solubility in water (for example, acetates, nitrites and iodides, particularly barium acetate, barium nitrite and barium iodide).

[0115] As the water-soluble organic compound containing S, there is no particular limitation as long as it can form an alkaline earth metal sulfate in the process of drying and firing after preparing the above-mentioned raw material suspension. As preferred examples, taurine (2-aminoethanesulfonic acid), aminobenzenesulfonic acid, aminomethanesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, cysteine, methionine, cystine, dimethyl sulfate, dimethyl sulfide, dimethyl trisulfide, 2-mercaptoethanol, diphenyl sulfide, dithiothreitol, diallyl disulfide, cyclopentane sulfone, furfuryl mercaptan, dipropyl disulfide, dimethyl sulfone, dimethyl sulfoxide, etc. can be listed.

[0116] Among these, water-soluble organic substances having at least one functional group selected from sulfonic acid group (—SO 3 H), sulfonyl group (—S(═O) 2 —), and sulfinyl group (—S(═O) —) in the molecule are preferred because of their high reactivity for generating sulfates.

[0117] Furthermore, when the compound has a basic group such as an amino group (-NH2), the effect of preventing the pH of the raw material suspension from decreasing (that is, becoming strongly acidic) is high, and therefore, it is preferred.

[0118] In addition, taurine (2-aminoethanesulfonic acid), aminobenzenesulfonic acid, aminomethanesulfonic acid, 1-amino-2-naphthol-4-sulfonic acid, cysteine, methionine, and cystine are particularly preferred because they are not designated as hazardous substances (violent substances) or poisons, are easy to handle, have particularly high solubility in water, and have a sulfonic acid group and an amino group in the molecule, so that the pH change during the preparation of sulfate salts is particularly small.

[0119] As a specific operation, the various materials mentioned above (inorganic compound particles, Pt particles or precursors for precipitating Pt, water-soluble compounds of alkaline earth metals, and water-soluble organic compounds containing S) are added to an aqueous solvent (typically water, such as pure water or deionized water), and stirred evenly using a stirrer, thereby preparing a slurry-like raw material suspension. For example, initially, Pt particles or precursors for precipitating Pt are suspended in water, inorganic compound particles (powder) constituting a porous carrier are mixed in the obtained suspension and stirred, and then water-soluble compounds of alkaline earth metals are added and stirred sufficiently for a predetermined time (e.g., 10 minutes to 60 minutes), and then water-soluble organic compounds containing S are added, and the mixture is fully dried in a temperature range of 90 to 130°C (e.g., more than 6 hours, preferably more than 8 hours), and then calcined in a temperature range of 400 to 600°C for several hours (e.g., 1 to 3 hours).

[0120] By such a process, a powder material in which Pt and alkaline earth metal sulfate are supported (fixed) in a highly dispersed state on the outer surface and inside (in the pores) of porous carrier particles (secondary particles) can be prepared in the pre-stage of forming a catalyst layer (including an alkaline earth metal supporting region). The obtained powder material can be crushed as needed to adjust to a desired particle size (e.g., a particle size of 10 μm or less).

[0121] By adopting this process, the particle size of the alkaline earth metal sulfate supported on the outer surface and in the pores of the porous carrier particles can be made much smaller than that of the prior art.

[0122] Typically, using the technology disclosed here, fine alkaline earth metal sulfate (e.g., barium sulfate) particles having an average particle size of less than 30 nm (e.g., greater than 10 nm and less than 30 nm), preferably less than 20 nm, as obtained based on X-ray diffraction, can be supported in a highly dispersed state on the outer surface and pores of porous carrier particles.

[0123] Furthermore, by using the above process, the above correlation coefficient can be achieved: R Ae / Pt The dispersion state is highly dispersed, that is, 0.5 or more, further, 0.6 or more, and further, 0.7 or more.

[0124] Next, the obtained powder material (material subjected to appropriate pulverization) is used to prepare a slurry for forming a catalyst layer (alkaline earth metal supporting region). The preparation of the slurry can be similar to the case of forming a catalyst layer of a conventional exhaust gas purification catalyst, and is not particularly limited.

[0125] For example, in Figure 2 When an upper layer 6A serving as an alkaline earth metal supporting region is formed on a substrate 1 of an exhaust purification catalyst 10 having upper and lower two-layer structural types of catalyst layers 6 having different compositions, a slurry for forming a lower layer containing a desired catalyst metal component (a solution containing catalyst metal ions other than Pt (e.g., Rh)) and a desired carrier powder (an OSC material containing alumina, zirconia, or CZ composite oxide, etc.) is applied to the honeycomb substrate 1 by a wash coating method or the like.

[0126] Next, a slurry for forming an alkaline earth metal carrying area containing the powder material prepared as described above and, as required, a carrier powder that does not carry alkaline earth metal (for example, OSC materials such as alumina or zirconia, or CZ composite oxide) is layered and coated on the surface of the lower layer 6B by a known wash coating method.

[0127] Alternatively, instead of such a one-step firing process, a two-stage firing process may be adopted, that is, after applying the slurry for forming the lower layer on the honeycomb substrate 1, the lower layer is first formed by drying and firing at a specified temperature and time, and then the slurry for forming the alkaline earth metal supporting area is applied to the surface of the lower layer and dried and fired to form an upper layer of the catalyst layer.

[0128] The firing conditions of the washed slurry vary depending on the shape and size of the substrate or carrier, and are not particularly limited. Typically, the target alkaline earth metal supporting region and the catalyst layer of other regions can be formed by firing at 400 to 1000° C. for about 1 to 5 hours. In addition, the drying conditions before firing are not particularly limited, but preferably drying is performed at a temperature of 80 to 300° C. for 1 to 12 hours.

[0129] In addition, when the catalyst layer 6 is formed by the wash coating method, the slurry is appropriately and closely attached to the surface of the substrate 1, and in the case of a laminated catalyst layer, it is attached to the surface of the lower layer 6B, so it is preferred that the slurry contains a binder. As a binder for this purpose, for example, alumina sol, silica sol, etc. are preferably used. In addition, the viscosity of the slurry can be appropriately adjusted to a viscosity that allows the slurry to easily flow into the cell 2 of the substrate (e.g., honeycomb substrate) 1.

[0130] Several embodiments of the present invention will be described below, but the present invention is not intended to be limited to the scope of these specific examples.

[0131] <Test Example 1: Preparation of Catalyst for Purifying Exhaust Gas>

[0132] In this test example, the Figure 1 A cylindrical honeycomb substrate having a diameter of 103 mm and a total length of 105 mm (i.e., a cordierite honeycomb substrate having a catalyst volume of 0.875 L) was prepared as follows. Figure 2 The exhaust gas purifying catalyst shown has a two-layer catalyst layer structure.

[0133] (Example 1)

[0134] 17.5 g of dinitrosodiammine platinum in terms of Pt amount was added to 1 L of pure water and stirred to prepare a suspension. 740 g of aluminum oxide was added to the suspension, and then 72 g of barium acetate was added and stirred. Thereafter, 70 g of taurine was added and stirred to prepare a slurry-like raw material suspension.

[0135] The raw material suspension was dried at 110° C. for 8 hours or more, and then calcined at 500° C. for 2 hours. Thereafter, a pulverization treatment was appropriately performed until the particle size became 10 μm or less, thereby preparing a Pt-containing powder material.

[0136] Next, the prepared Pt-containing powder material, 1800 g of CZ composite oxide powder containing 30 wt % Ce, and 87 g of alumina binder were added to 3.6 L of pure water and wet-pulverized using a magnetic ball mill to prepare an upper layer forming slurry.

[0137] On the other hand, 5.6 g of rhodium nitrate in terms of Rh was suspended in 0.9 L of pure water. 803 g of zirconium oxide powder was added to the obtained suspension, dried, and then fired at 500° C. for 2 hours. After that, a crushing treatment was appropriately performed until the particle size reached 10 μm or less, thereby preparing a powder material containing Rh. To the powder material containing Rh, 415 g of alumina powder, 413 g of CZ composite powder with a Ce content of 20% by weight, and 61 g of alumina binder were added to 2.3 L of pure water, and wet crushed using a magnetic ball mill, thereby preparing a slurry for forming the lower layer.

[0138] First, the substrate is washed with a slurry for forming a lower layer and dried at 150°C for about 1 hour, thereby forming a lower layer (unfired coating layer) on the surface of the substrate (rib wall surface in the cell). Next, the substrate is washed with a slurry for forming an upper layer and dried at 150°C for about 1 hour, thereby forming an upper layer (unfired coating layer) on the surface of the lower layer. After that, it is fired at 500°C for 1 hour to obtain an exhaust gas purification catalyst having a catalyst layer consisting of an upper and lower layer (the coating amount of the upper and lower layers is set to 220g / L in total).

[0139] (Example 2)

[0140] When preparing the Pt-containing powder material, the exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that the raw material suspension was dried at 30° C. for 48 hours instead of drying it at 110° C. for 8 hours or more.

[0141] (Comparative Example 1)

[0142] When preparing the Pt-containing powder material, an exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that 66 g of barium sulfate was used as a Ba source instead of 72 g of barium acetate and taurine was added as a Ba-fixing material.

[0143] (Comparative Example 2)

[0144] When preparing the Pt-containing powder material, the same operation as in Example 1 was carried out except that 74 g of ammonium sulfate as an inorganic compound was used instead of 70 g of taurine as the Ba-fixing material to obtain an exhaust gas purification catalyst.

[0145] (Comparative Example 3)

[0146] An exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that taurine as a Ba-fixing material was not added when preparing the Pt-containing powder material.

[0147] <Test Example 2: Confirmation of Dispersibility of Barium Sulfate in Pt-Containing Powder Material by FE-EPMA>

[0148] Each of the Pt-containing powder materials prepared in Test Example 1 was subjected to surface analysis using a FE-EPMA apparatus (JXA-8530F) manufactured by JEOL Ltd. in accordance with the user manual.

[0149] That is, the surface of each powder material of a predetermined amount is polished to expose the cross section, and carbon as a conductive material is vapor-deposited using a commercially available carbon coating machine (Vacuum Equipment Co., Ltd.: VC-100W). Then, the area corresponding to the Pt-containing powder material on the carbon vapor-deposited surface is appropriately determined, and the area is subjected to surface analysis using FE-EPMA. The measurement conditions are set as follows.

[0150] Pixel size: 0.34μm×0.34μm,

[0151] Number of pixels: 256×256,

[0152] Accelerating voltage: 20 kV,

[0153] Irradiation current: 100nA,

[0154] Probe diameter: Set to the minimum value under the measurement conditions.

[0155] Unit measurement time: 50ms / 1 pixel,

[0156] Measurement magnification: ×1000

[0157] Then, the intensity of the characteristic X-ray of the Ba element (α: cps) and the intensity of the characteristic X-ray of Pt (β: cps) are measured for each pixel.

[0158] In this surface analysis, the threshold value of the X-ray intensity per pixel (area) was set to 15 cps for Ba and 5 cps for Pt, and pixels showing intensities below the threshold value were excluded from the data used for calculation of the correlation coefficient.

[0159] The data obtained by face analysis are then used to calculate the correlation coefficient R using the CORREL function of the spreadsheet software "EXCEL". Ba / Pt The results are shown in Table 1.

[0160] In addition, data (images) on element mapping of Ba and S for the sample of Example 1 and the samples of Comparative Examples 1 and 2 are shown in FIG. Figures 3 to 6 .

[0161] <Test Example 3: Ba dissolution test>

[0162] Each Pt-containing powder material prepared in Test Example 1 was suspended in pure water, and the amount of Ba eluted when an acid was added was measured using an ICP emission spectrometer (Agilent 5110 ICP-OES) manufactured by Agilent to determine the Ba elution rate.

[0163] [Table 1]

[0164] Table 1

[0165]

[0166] According to Table 1 and Figures 3 to 6 The results show that in Comparative Examples 1 and 2, Ba aggregates on the outside of the carrier secondary particles, whereas in Example 1, Ba is highly dispersed and supported inside the carrier secondary particles.

[0167] When the correlation coefficient value is 0.5 or more, it can be interpreted as a strong correlation, and when it is 0.7 or more, it is a particularly strong correlation. In Example 1, the correlation coefficient R Ba / Pt The value of is 0.798, confirming that the existence position of Pt and the existence position of Ba have a particularly strong correlation.

[0168] On the other hand, in Comparative Examples 1 and 2, the correlation coefficient R Ba / Pt The values ​​are -0.128 and 0.060 respectively, and no correlation was confirmed between the existence positions of Pt and Ba.

[0169] This shows that, compared with Comparative Examples 1 and 2, in Example 1, not only is Ba highly dispersed, but also Pt is adjacent to Ba.

[0170] In Comparative Example 3, the correlation coefficient R Ba / Pt The value of was 0.720, confirming that the existence positions of Pt and Ba were strongly correlated, but the Ba elution rate was 70%, and the fixation of Ba was not achieved.

[0171] <Test Example 4: Measurement of HC Purification Rate of Pt-Containing Powder Material>

[0172] Pellets of the Pt-containing powder material used in Example 1 and Comparative Example 1 were prepared and subjected to a Rich / Lean durability test using a tubular furnace. Then, the HC purification rate was measured 3 minutes after the air-fuel ratio was changed from Lean to Rich using an activity evaluation device (CATA5000) manufactured by Best Instruments Co., Ltd. The results are shown in Figure 7 .

[0173] like Figure 7 As shown, the Pt-containing powder material used in Example 1 exhibits a much higher HC purification rate.

[0174] It is believed that in Example 1, Ba is highly dispersed and supported on the carrier secondary particles, and Pt and Ba are close to each other and a correlation can be confirmed between the positions of Pt and Ba. Therefore, Ba supplies electrons to Pt, which inhibits HC poisoning and improves HC purification performance in a rich atmosphere.

[0175] <Test Example 5: Evaluation of Rh-containing catalyst layer by FE-EPMA>

[0176] The stacked portion of the upper catalyst layer and the lower catalyst layer of the exhaust gas purification catalyst produced in Example 1 was cut out and the cross section was polished. Carbon as a conductive material was vapor-deposited on the cross section using a commercially available carbon coating machine (Vacuum Equipment Co., Ltd.: VC-100W). The cross section was subjected to surface analysis using the above-mentioned FE-EPMA device (JXA-8530F). The measurement conditions were set as follows.

[0177] Pixel size: 0.85μm×0.85μm,

[0178] Number of pixels: 256×256,

[0179] Accelerating voltage: 20 kV,

[0180] Irradiation current: 100nA,

[0181] Probe diameter: Set to the minimum value under the measurement conditions.

[0182] Unit measurement time: 50ms / 1 pixel,

[0183] Measurement magnification: ×400

[0184] Then, the intensity of the characteristic X-ray of the Ba element (α: cps) and the intensity of the characteristic X-ray of Rh (β: cps) are measured for each pixel.

[0185] In this surface analysis, the thresholds of X-ray intensity per pixel (region) were set to 15 cps for Ba and 5 cps for Rh, and pixels showing intensities below the threshold were excluded from data used to calculate the correlation coefficient.

[0186] The obtained data was used to calculate the correlation coefficient R using the CORREL function of the spreadsheet software "EXCEL". Ba / Rh .

[0187] As a result, the correlation coefficient R Ba / RhThe value of Ba is 0.023, and no correlation is confirmed between the positions of Ba and Rh in the catalyst. It can be seen that in the exhaust gas purification catalyst of Example 1, Ba is fixed in the upper layer as the alkaline earth metal supporting region containing Pt, thereby preventing the contact between Ba in the upper layer and Rh in the lower layer.

[0188] <Test Example 6: Measurement of Purification Rate of Exhaust Gas Purification Catalyst>

[0189] The exhaust gas purification catalysts produced in Example 1 and Comparative Example 1 were installed in the exhaust system of an engine, and the engine was operated to conduct a durability test.

[0190] After the endurance test, the catalyst was used to measure the HC purification rate and NOx removal rate 3 minutes after the air-fuel ratio of the mixed gas supplied to the engine was changed from lean to rich. x The results are shown in Figure 8 and Fig. 9 .

[0191] like Figure 8 and Fig. 9 As shown in the results, the exhaust gas purification catalyst of Example 1 shows much higher HC purification rate and NO x The reason is considered to be as follows.

[0192] In Example 1, Ba is highly dispersedly carried on the secondary particles of the carrier, so Pt and Ba are adjacent to each other and the existence positions of Pt and Ba can be confirmed to be correlated. Therefore, by Ba donating electrons to Pt, HC poisoning is suppressed, and the HC purification performance in a rich atmosphere is improved. In addition, since Ba is fixed, contact between Ba and Rh is prevented, thereby preventing the metallization inhibition of Rh caused by Ba. Moreover, the HC purification effect of the upstream Pt-containing catalyst layer is improved, and the amount of HC flowing into the downstream Rh-containing catalyst layer is reduced, thereby suppressing the poisoning of Rh. Based on the above reasons, the coexistence of NO x The purification performance is also improved.

[0193] Although the specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples described above.

Claims

1. A method for producing an exhaust gas purification catalyst, wherein the exhaust gas purification catalyst is arranged in an exhaust pipe of an internal combustion engine and purifies exhaust gas discharged from the internal combustion engine, the method comprising: A step of forming a catalyst layer on a substrate, wherein the catalyst layer has an alkaline earth metal supporting region in at least a portion thereof, the region having a porous support composed of an inorganic compound, Pt supported on the porous support, and at least one alkaline earth metal sulfate supported on the porous support; and a step of firing the substrate on which the catalyst layer is formed, Wherein, the step of forming the catalyst layer comprises: A step of preparing a raw material suspension by mixing the following components with an aqueous solvent, wherein the components are: inorganic compound particles constituting the porous support, Pt particles or a precursor for precipitating Pt, a water-soluble compound of the alkaline earth metal, and a water-soluble organic compound containing S as a constituent element and capable of generating a sulfate of the alkaline earth metal; The step of drying the raw material suspension and then firing it to prepare a powder material mixed with the porous support, Pt and alkaline earth metal sulfate; a step of preparing a slurry for forming an alkaline earth metal supporting region containing at least the powder material and an aqueous solvent; and a step of forming the alkaline earth metal supporting region on the substrate using the slurry, The water-soluble organic compound containing S has a sulfonic acid group and an amino group, The cross section of the alkaline earth metal supporting region of the catalyst layer was subjected to surface analysis using FE-EPMA under the conditions of a pixel size of 0.34 μm×0.34 μm, a number of measurement pixels of 256×256, and a measurement magnification of ×1000. The intensity α of the characteristic X-ray of the element Ae of the alkaline earth metal and the intensity β of the characteristic X-ray of Pt were measured for each pixel, wherein the units of the intensity α of the characteristic X-ray of the element Ae of the alkaline earth metal and the intensity β of the characteristic X-ray of Pt were cps respectively, and the Pearson correlation coefficient calculated using the obtained α and β of each pixel was set as R Ae / Pt hour, The R Ae / Pt The value of is 0.5 or more. The porous carrier composed of inorganic compounds is a secondary particle, The alkaline earth metal sulfate is dispersed and supported on the outer surface and in the pores of the secondary particles.

2. The method for producing an exhaust gas purification catalyst according to claim 1, wherein: As the water-soluble compound of the alkaline earth metal, acetate, nitrite or iodide of any alkaline earth metal selected from Ba, Sr and Ca is used.

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