Catalyst for exhaust gas purification

Abstract

To provide a wall-flow-type exhaust gas purification catalyst which has excellent PM collection performance and a small initial pressure drop.SOLUTION: There is provided an exhaust gas purification catalyst 1 comprising a catalyst coated filter 2 and powdery inorganic particles 3. The catalyst coated filter 2 comprises a filter base material 21 and a catalyst layer 22 provided on a pore wall of the filter base material 21. The catalyst coated filter 2 has a first end part, a second end part, a filter partition wall 21W, an inlet side cell and an outlet side cell. The filter partition wall 21W is porous. The inlet side cell is opened by the first end part and closed by the second end part. The outlet side cell is opened by the second end part and closed by the first end part. The outlet side cell and the outlet side cell are adjacent through the filter partition wall 21W. The powdery inorganic particles 3 are unevenly distributed on the surface adjacent to the inlet side cell of the filter partition wall 21W in a cross-section parallel to the thickness direction of the filter partition wall.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a catalyst for purifying exhaust gas.

Background Art

[0002] Exhaust gas discharged from an internal combustion engine contains harmful substances such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO x x). For purifying such exhaust gas, for example, a straight flow type exhaust gas purification catalyst containing a platinum group metal as a catalyst metal is used.

[0003] In addition, exhaust gas discharged from a diesel engine contains particulate matter (PM) at a relatively high concentration in addition to the above harmful substances. Therefore, a diesel particulate filter (DPF) is further used to remove PM from the exhaust gas for purifying the exhaust gas discharged from a diesel engine.

[0004] In recent years, regulations on PM emissions have been strengthened, and there has been a need to remove PM not only from exhaust gas discharged from diesel engines but also from exhaust gas discharged from gasoline engines. Therefore, a gasoline particulate filter (GPF) is being used for purifying exhaust gas discharged from gasoline engines.

[0005] Examples of these particulate filters include a wall flow type exhaust gas purification catalyst in which a supported catalyst is supported on the partition walls of the filter. When such an exhaust gas purification catalyst is used, it is possible to reduce the installation space of the exhaust gas purification system and to reduce the cost of the exhaust gas purification system.

[0006] The wall flow type exhaust gas purification catalyst is described in, for example, Patent Document 1. Patent Document 1 describes that, for example, a powder made of a metal oxide is deposited only in the pores of a porous partition wall that is the filter wall of the wall flow type exhaust gas purification catalyst, and the powder fills up to 50% of the total pore volume at maximum.

Prior Art Documents

Patent Document

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a wall flow type exhaust gas purification catalyst having excellent PM collection performance and a small initial pressure loss.

Means for Solving the Problems

[0009] According to one aspect of the present invention, there is provided a catalyst-coated filter including a filter substrate and a catalyst layer provided on the pore walls of the filter substrate, the catalyst-coated filter having a first end portion, a second end portion, a filter partition wall, an inlet side cell, and an outlet side cell, the filter partition wall being porous, the inlet side cell extending from the first end portion toward the second end portion, opening at the first end portion, and being closed at the second end portion, the outlet side cell extending from the second end portion toward the first end portion, opening at the second end portion, and being closed at the first end portion, the inlet side cell and the outlet side cell being adjacent to each other with the filter partition wall interposed therebetween, and a powdery inorganic particle unevenly distributed on the surface of the filter partition wall adjacent to the inlet side cell in a cross section parallel to the thickness direction of the filter partition wall. Hereinafter, the above exhaust gas purification catalyst is also referred to as a "powder-added catalyst-coated filter".

[0010] Here, the term "powdery inorganic particle" may be in a state where the particles are not fixed to each other or to other articles, or may be in a state where such particles are immobilized on other articles by heat treatment or chemical solution treatment. The inorganic particles may be primary particles or secondary particles.

[0011] Here, the uneven distribution of the inorganic particles as described above can be confirmed by the following method. First, an image of the cross-section of the porous partition wall of the exhaust gas purification catalyst, that is, the cross-section of the portion corresponding to the filter partition wall in the exhaust gas purification catalyst, is taken with a scanning electron microscope to obtain a grayscale image. This imaging is performed on the cross-section of the portion of the porous partition wall where the distance from the first end and the distance from the second end are equal. Next, the analysis position by the energy dispersive X-ray analyzer is specified in the previous grayscale image, and the intensity of the characteristic X-ray derived from the element contained only in the inorganic particles is measured. Here, line analysis along the thickness direction of the porous partition wall is performed. From this analysis result, it can be confirmed that the inorganic particles are unevenly distributed as described above. In addition, the uneven distribution of the inorganic particles as described above can also be confirmed from a composite image obtained by superimposing dots having brightness corresponding to the intensity of the characteristic X-ray and colored on the previous grayscale image. Note that the first end and the second end are portions corresponding to the first end portion and the second end portion, respectively, in the exhaust gas purification catalyst.

[0012] The configuration in which the inorganic particles are unevenly distributed as described above can be used to reduce the number of pores with a large opening diameter.

[0013] This exhaust gas purification catalyst is a particulate filter including a catalyst layer. More specifically, in this exhaust gas purification catalyst, the exhaust gas sequentially passes through a first cell which is a space corresponding to the inlet side cell in the exhaust gas purification catalyst, the pores of the porous partition wall, and a second cell which is a space corresponding to the outlet side cell in the exhaust gas purification catalyst, and in this process, the PM in the exhaust gas is collected by the porous partition wall, and it is a wall flow type exhaust gas purification catalyst.

[0014] Generally, the wall flow type exhaust gas purification catalyst is used to remove PM from the exhaust gas discharged from internal combustion engines such as gasoline engines and diesel engines. For example, the wall flow type exhaust gas purification catalyst is used in a self-propelled vehicle including a gasoline engine or a diesel engine as at least a part of the power source.

[0015] In a wall-flow type exhaust gas purification catalyst, the catalyst layer is provided to promote the combustion of PM collected by the filter partition walls.

[0016] For example, in a gasoline vehicle that uses the power generated in a gasoline engine as driving force and is equipped with a wall-flow type exhaust gas purification catalyst, the catalyst layer promotes the combustion of the collected PM particularly during high-load operation periods when the gasoline engine discharges high-temperature exhaust gas, such as when driving in the suburbs or on highways.

[0017] In addition, the exhaust gas discharged from a diesel engine has a lower temperature compared to the exhaust gas discharged from a gasoline engine. Therefore, in a diesel vehicle that uses the power generated in a diesel engine as driving force and is equipped with a wall-flow type exhaust gas purification catalyst, the temperature of the exhaust gas is raised by injecting fuel into the exhaust gas to burn the collected PM. The catalyst layer promotes this combustion and thus contributes to a reduction in the fuel injected into the exhaust gas.

[0018] Among the above-described wall-flow type exhaust gas purification catalysts, there are those in which powdery inorganic particles are arranged in the pores throughout the thickness of the filter partition walls. Since the inorganic particles reduce the effective pore diameter of the pores of the filter partition walls, such exhaust gas purification catalysts have excellent PM collection performance. However, since such exhaust gas purification catalysts have inorganic particles present in the pores throughout the thickness of the filter partition walls, the initial pressure loss is large.

[0019] When powdery inorganic particles are unevenly distributed on the surface adjacent to the inlet-side cells of the filter partition wall in a cross-section parallel to the thickness direction of the filter partition wall, the effective diameter of the pores on the said surface becomes smaller. Therefore, the PM collection performance can be improved. Also, when inorganic particles are unevenly distributed on the surface adjacent to the inlet-side cells of the filter partition wall in a cross-section parallel to the thickness direction of the filter partition wall, almost no inorganic particles exist in parts of the filter partition wall other than the vicinity of the said surface. For this reason, the exhaust gas purification catalyst adopting this configuration has a small initial pressure loss.

[0020] In addition, in a cross-section parallel to the thickness direction of the filter partition wall, the exhaust gas purification catalyst with powdery inorganic particles unevenly distributed on the surface of the filter partition wall can exhibit the effects described below.

[0021] As described above, the catalyst layer can promote the combustion of PM, but the PM combustion by the catalyst layer is not always sufficiently promoted. For example, in a gasoline vehicle equipped with a wall flow type exhaust gas purification catalyst, when repeatedly stopping and going and traveling a short distance, the amount of PM collected exceeds the amount of PM that burns, and as a result, PM accumulates in the wall flow type exhaust gas purification catalyst. Also, in a diesel vehicle equipped with a wall flow type exhaust gas purification catalyst, PM accumulates in the wall flow type exhaust gas purification catalyst during the period before fuel injection into the exhaust gas.

[0022] When PM accumulates, the pressure loss that occurs in the wall flow type exhaust gas purification catalyst increases. When the pressure loss increases, the fuel consumption performance deteriorates. Therefore, it is desirable that the increase in pressure loss associated with the accumulation of PM is small.

[0023] In a general wall flow type exhaust gas purification catalyst, for example, a wall flow type exhaust gas purification catalyst not provided with the above-described powdery inorganic particles, at the initial stage of PM deposition, the PM accumulates in pores located in the surface region adjacent to the inlet cells of the filter partition wall, that is, pores where the distance from the surface adjacent to the inlet cells of the filter partition wall is, for example, 30% or less of the thickness of the filter partition wall, and the amount of PM deposited in these pores increases. When the amount of PM deposited in these pores increases, the gas flow path in the filter partition wall narrows or is blocked, and as a result, the pressure loss increases significantly. For this reason, at the initial stage of PM deposition, as the PM collection amount increases, the pressure loss increases rapidly.

[0024] When the deposition of PM into the pores located within the above-described surface area progresses to a certain extent, the PM starts to deposit on the surface adjacent to the inlet cell of the filter partition wall. The deposited layer composed of PM on this surface is a granular layer with a low apparent density. In this granular layer, it is difficult for the gas flow path to become narrow or blocked as the amount of PM deposition increases. Therefore, during this period, the increase in pressure loss accompanying the increase in PM collection amount is gentle.

[0025] Thus, in a general wall flow type exhaust gas purification catalyst, at the initial stage of PM deposition, the pressure loss increases rapidly and significantly. Therefore, in an automobile equipped with such an exhaust gas purification catalyst, the proportion of the period with a large pressure loss in the period from when PM starts to accumulate until the PM burns and its accumulation amount becomes sufficiently small is high.

[0026] On the other hand, in an exhaust gas purification catalyst provided with powdery inorganic particles unevenly distributed on the surface adjacent to the inlet cell of the filter partition wall in a cross-section parallel to the thickness direction of the filter partition wall, it is difficult for the PM to reach the pores located far from the surface on the first cell side of the porous partition wall. Therefore, the amount of PM deposited in the pores of the porous partition wall is small, and it is difficult for the gas flow path in the porous partition wall to become narrow or blocked. Therefore, this exhaust gas purification catalyst has a small pressure loss caused by the deposition of PM.

[0027] Also, when powdery inorganic particles are unevenly distributed on the surface adjacent to the inlet cell of the filter partition wall in a cross-section parallel to the thickness direction of the filter partition wall, it is easy to collect PM on the surface of the porous partition wall. Therefore, it is difficult for the catalytic performance to deteriorate due to the deposition of PM in the pores.

[0028] According to another aspect of the present invention, there is provided an exhaust gas purification catalyst according to the above aspect, wherein most of the inorganic particles are located in the pores of the filter partition wall. When most of the inorganic particles are located in the pores of the filter partition wall, it is difficult for PM to pass through the porous partition wall of the exhaust gas purification catalyst, so it is easy to achieve high PM collection performance. That most of the inorganic particles are located in the pores of the filter partition wall preferably means that the amount of the inorganic particles located in the pores of the filter partition wall among all the inorganic particles accounts for 70% or more.

[0029] According to still another aspect of the present invention, there is provided an exhaust gas purification catalyst according to any of the above aspects, wherein the ratio D1 / D2 of the average particle diameter D1 of the inorganic particles to the average pore diameter D2 of the pores of the filter partition wall is in the range of 0.06 to 2. When the ratio D1 / D2 is small, it is difficult to achieve high PM collection performance. Also, when the ratio D1 / D2 is small, PM is likely to accumulate in the pores, so the pressure loss caused by the deposition of PM on the porous partition wall tends to be large. When the ratio D1 / D2 is large, the initial pressure loss of the exhaust gas purification catalyst tends to be large. According to one example, the ratio D1 / D2 is in the range of 0.06 to 1. According to another example, the ratio D1 / D2 is in the range of 0.15 to 2. Preferably, the ratio D1 / D2 is in the range of 0.15 to 0.7.

[0030] According to still another aspect of the present invention, there is provided an exhaust gas purification catalyst according to any of the above aspects, wherein the filter substrate includes a honeycomb structure and a plug.

[0031] The honeycomb structure is a columnar body having a pair of opposing bottom surfaces, and a plurality of through-holes extending from one bottom surface to the other bottom surface are provided. Here, one bottom surface corresponds to the first end, and the other bottom surface corresponds to the second end. The shape of the pair of opposing bottom surfaces is, for example, circular, elliptical, oblong, or polygonal.

[0032] The honeycomb structure includes partition walls that constitute the side walls of these through-holes. These partition walls are porous and partition adjacent through-holes.

[0033] As materials for the honeycomb structure, for example, ceramics such as cordierite, aluminum titanate, and silicon carbide can be used. A non-woven fabric made of metal or alloy may be incorporated in such a honeycomb structure. Alternatively, a metal or alloy such as stainless steel may be used as the material for the honeycomb structure.

[0034] Each plug closes the through-hole of the honeycomb structure at one end side. Half of the plurality of through-holes are closed at the second end side by plugs. The first cell is a space surrounded by a plug that closes the through-hole at the second end side and a partition wall that constitutes the side wall of this through-hole.

[0035] The remaining through-holes of the honeycomb structure that are not closed at the second end side are closed at the first end side by plugs. The second cell is a space surrounded by a plug that closes the through-hole at the first end side and a partition wall that constitutes the side wall of this hole.

[0036] The first cell and the second cell are adjacent to each other with the partition wall of the filter substrate and the catalyst layer formed in the pores of the partition wall interposed therebetween.

[0037] As materials for the plugs, for example, ceramics such as cordierite, aluminum titanate, and silicon carbide can be used.

[0038] According to still another aspect of the present invention, the filter substrate is provided with an exhaust gas purification catalyst according to any one of the above aspects in which the volume V is in the range of 0.1 to 5 L. Here, the "volume" of the filter substrate is the volume including the spaces corresponding to the first and second cells and the partition walls in the filter substrate, and is calculated by multiplying the area of the bottom surface of the filter substrate by the height of the filter substrate. The volume V of the filter substrate is preferably 0.5 L or more. Also, the volume V of the filter substrate is preferably 3 L or less, and more preferably 2 L or less.

[0039] According to still another aspect of the present invention, there is provided a catalyst for purifying exhaust gas according to any one of the above aspects, wherein the filter base material has dimensions in the length direction of the inlet side cell and the outlet side cell in the range of 10 to 500 mm. This dimension is preferably in the range of 50 to 300 mm.

[0040] According to still another aspect of the present invention, there is provided a catalyst for purifying exhaust gas according to any one of the above aspects, wherein the thickness of the partition wall of the filter base material corresponding to the filter partition wall, i.e., the thickness of the partition wall of the filter base material, is in the range of 0.05 to 2 mm. If this thickness is reduced, the mechanical strength of the filter base material decreases. If this thickness is increased, the porous partition wall becomes thicker, and as a result, the pressure loss (i.e., the initial pressure loss) in a state where PM is not deposited increases. This thickness is preferably in the range of 0.1 to 1 mm.

[0041] According to still another aspect of the present invention, there is provided a catalyst for purifying exhaust gas according to any one of the above aspects, wherein the porosity of the partition wall of the filter base material corresponding to the filter partition wall, i.e., the porosity of the partition wall of the filter base material, is in the range of 30 to 90%. Note that this "porosity" is a value obtained by the mercury intrusion method. If the porosity is increased, the mechanical strength of the filter base material decreases. If this porosity is reduced, the porosity of the porous partition wall also decreases, and as a result, the pressure loss in a state where PM is not deposited increases. This porosity is preferably in the range of 40 to 80%.

[0042] According to still another aspect of the present invention, there is provided a catalyst for purifying exhaust gas according to any one of the above aspects, wherein the average pore diameter of the partition wall of the filter base material corresponding to the filter partition wall, i.e., the average pore diameter of the partition wall of the filter base material, is in the range of 5 to 50 μm. Note that this "average pore diameter" is a value obtained by the mercury intrusion method. If the average pore diameter is increased, the mechanical strength of the filter base material decreases. If the average pore diameter is reduced, the pressure loss in a state where PM is not deposited increases. This average pore diameter is preferably in the range of 10 to 40 μm.

[0043] According to still another aspect of the present invention, there is provided an exhaust gas purification catalyst according to any one of the above aspects, wherein the catalyst layer contains a noble metal. The noble metal is an example of a catalytic metal. The noble metal is, for example, a platinum group element. The catalyst layer can contain, as the noble metal, for example, one or more of platinum, palladium, and rhodium. These noble metals have a high ability to promote the combustion of PM.

[0044] According to still another aspect of the present invention, the mass M of the noble metal M and the volume V of the filter base material, the ratio M M / V is provided with an exhaust gas purification catalyst according to the above aspect in the range of 0.01 to 10 g / L. When the ratio M M / V is small, the effect of the noble metal to promote the combustion of PM is small. When the ratio M M / V is increased, the cost becomes high. The ratio M M / V is preferably in the range of 0.1 to 5 g / L.

[0045] According to still another aspect of the present invention, there is provided an exhaust gas purification catalyst according to any one of the above aspects, wherein the catalyst layer further contains at least one of a porous carrier carrying the noble metal and a promoter. When a porous carrier is used, it is easy to increase the specific surface area of the noble metal. When a promoter such as an oxygen storage material is used, for example, it is possible to reduce the change in the performance of the catalyst due to the change in the composition of the exhaust gas.

[0046] The porous carrier and the promoter are, for example, alumina; a composite oxide of ceria and zirconia; a polycrystal or single crystal containing this composite oxide as a main component and further containing one or more selected from the group consisting of oxides of rare earth elements other than cerium, oxides of alkaline earth metal elements, oxides of transition metal elements other than zirconium, alumina, and silica; or a combination of two or more thereof.

[0047] The average particle diameter of each of the porous carrier and the promoter is preferably in the range of 0.05 to 5 μm, and more preferably in the range of 0.1 to 3 μm. Note that this "average particle diameter" is the median diameter obtained by the laser diffraction / scattering method.

[0048] According to still another aspect of the present invention, the mass M of the catalyst layer C and the volume V of the filter base material, the ratio M C / V of the exhaust gas purification catalyst according to the above aspect is 300 g / L or less. The ratio M C / V is preferably 250 g / L or less, more preferably 150 g / L or less, still more preferably 120 g / L or less, and still more preferably 100 g / L or less.

[0049] According to still another aspect of the present invention, the mass M of the catalyst layer C and the volume V of the filter base material, the ratio M C / V of the exhaust gas purification catalyst according to the above aspect is in the range of 10 to 300 g / L. When the ratio M C / V is small, the contribution of the catalyst layer to reducing the number of pores with a large opening diameter is small. When the ratio M C / V is increased, the pressure loss in a state where PM is not deposited increases. The ratio M C / V is preferably in the range of 20 to 250 g / L, more preferably in the range of 20 to 200 g / L, and still more preferably in the range of 30 to 100 g / L. The lower limit value of the ratio M C / V may be 25 g / L. Also, the upper limit value of the ratio M C / V may be 150 g / L.

[0050] According to still another aspect of the present invention, at least a part of the catalyst layer is located in a portion of the filter partition wall adjacent to the inlet-side cell, that is, a portion of the filter partition wall on the inlet-side cell side, and an exhaust gas purification catalyst according to any of the above aspects is provided. Here, the "portion of the filter partition wall adjacent to the inlet-side cell" is a portion of the filter partition wall where the distance from the surface of the portion adjacent to the inlet-side cell is 80% or less of the thickness of the filter partition wall. The entire catalyst layer may be located in a portion of the filter partition wall adjacent to the inlet-side cell, that is, a portion of the filter partition wall on the inlet-side cell side. Alternatively, the catalyst layer may be provided over the entire thickness of the filter partition wall. That is, it is preferable that the catalyst layer extends from the surface on the inlet-side cell side of the partition wall of the filter substrate to the vicinity of the surface on the outlet-side cell side of this partition wall, for example, extends from the surface on the inlet-side cell side of the partition wall of the filter substrate to the surface on the outlet-side cell side of this partition wall. Such a structure is particularly advantageous in reducing the pressure loss in a state where PM is not deposited. Further, such a structure is also particularly advantageous in reliably burning PM and purifying other harmful substances.

[0051] According to still another aspect of the present invention, when the portion of the filter partition wall adjacent to the inlet-side cell, that is, the portion of the filter partition wall on the inlet-side cell side, is divided into first pores having a pore diameter of 5 μm or more and less than 10 μm, second pores having a pore diameter of 10 μm or more and less than 20 μm, and third pores having a pore diameter of 20 μm or more in a cross section perpendicular to the surface, the filling rate R of the first pores by the catalyst layer F1 , the filling rate R of the second pores by the catalyst layer F2 , and the filling rate R of the third pores by the catalyst layer F3 satisfy the inequality: R F1 < R F2 < R F3 and an exhaust gas purification catalyst according to any of the above aspects is provided.

[0052] Here, the filling rate R F1 is the total area S of the first pores in the cross section F1The total area S of the portion of the catalyst layer located within the first pores with respect to C1 is the ratio. Packing ratio R F2 is the total area S of the second pores in the cross section F2 The total area S of the portion of the catalyst layer located within the second pores with respect to C2 is the ratio. Packing ratio R F3 is the total area S of the third pores in the cross section F3 The total area S of the portion of the catalyst layer located within the third pores with respect to C3 is the ratio.

[0053] Here, the boundaries between adjacent pores and the pore diameters of each pore are determined by a method to be described later with reference to the drawings.

[0054] The configuration specified by the above inequality can be used to achieve high PM collection performance while suppressing an increase in pressure loss in a state where PM is not deposited.

[0055] According to still another aspect of the present invention, the packing ratio R F1 is 40% or less, the packing ratio R F2 is 40% or less, and the packing ratio R F3 is 45% or less, an exhaust gas purification catalyst according to the above aspect is provided.

[0056] Increasing these packing ratios increases the pressure loss in a state where PM is not deposited.

[0057] According to still another aspect of the present invention, the packing ratio R F3 is 20% or more, and an exhaust gas purification catalyst according to any of the above aspects is provided. When the packing ratio R F3 is small, a sufficient amount of catalyst cannot be disposed in the exhaust gas flow path, which is disadvantageous for purifying harmful substances.

[0058] According to still another aspect of the present invention, the packing ratio R F1 is 10% or more, and the packing ratio R F2There is provided an exhaust gas purification catalyst according to any one of the above aspects, which is 15% or more.

[0059] Packing ratio R F1 and packing ratio R F2 is preferably small. Since much of the exhaust gas flows through the third pores, from the viewpoint of PM combustion and purification of other harmful substances, the packing ratio R F1 and packing ratio R F2 are made small, and it is preferable to increase the packing ratio R F3

[0060] According to still another aspect of the present invention, the total amount A of the inorganic particles, the amount A1 of the inorganic particles located on the surface adjacent to the inlet side cell of the catalyst-coated filter, that is, on the surface on the inlet side cell side of the catalyst-coated filter, and the amount A2 of the inorganic particles in the pores of the catalyst-coated filter, where the distance from the surface adjacent to the inlet side cell of the catalyst-coated filter is 20% or less of the thickness of the filter partition corresponding to the filter partition of the catalyst-coated filter, that is, there is provided an exhaust gas purification catalyst according to any one of the above aspects that satisfies the relationship represented by the inequality (A1 + A2) / A ≧ 90%.

[0061] The ratio (A1 + A2) / A representing the degree of uneven distribution of the inorganic particles on the first cell side of the porous partition is preferably 90% or more. There is no limit to the upper limit value of the ratio (A1 + A2) / A. The ratio (A1 + A2) / A may be 100%.

[0062] According to still another aspect of the present invention, there is provided an exhaust gas purification catalyst according to any one of the above aspects, wherein the inorganic particles have an average particle diameter in the range of 1 to 50 μm.

[0063] Here, the "average particle diameter" is the median diameter obtained by the laser diffraction / scattering method. Inorganic particles having an average particle diameter within the above range are, for example, likely to achieve high PM collection performance. This average particle diameter is preferably in the range of 5 to 10 μm.

[0064] ​According to still another aspect of the present invention, there is provided an exhaust gas purification catalyst according to any of the above aspects, wherein the inorganic particles contain one or more selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, clay minerals, and porous inorganic substances.

[0065] Preferably, the inorganic particles consist of one or more selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, and porous inorganic substances.

[0066] The metal element contained in the inorganic particles is, for example, one or more selected from the group consisting of an alkali metal element, an alkaline earth metal element, a rare earth element, and a transition metal element. This metal element is preferably one or more selected from the group consisting of calcium, magnesium, strontium, barium, aluminum, silicon, titanium, zirconium, and cerium.

[0067] Specific examples of the inorganic particles include, for example, for metal oxides, calcium oxide, cerium oxide, titanium dioxide, zirconium dioxide, silicon dioxide, aluminum oxide, mixtures thereof, and mixed oxides. The clay mineral may be an artificial clay mineral or a natural clay mineral. As the porous inorganic substance, for example, one or more of zeolite and sepiolite can be used. The inorganic particles preferably contain calcium oxide, and more preferably consist of calcium oxide.

[0068] According to still another aspect of the present invention, in the powder-added catalyst-coated filter, the mass M of the inorganic particles with respect to the volume V of the filter base material P of the ratio M P / V is 3 g / L or more, and there is provided an exhaust gas purification catalyst according to any of the above aspects.

[0069] When the ratio M P / V is small, it is difficult to achieve high PM collection performance. The ratio M P / V is preferably 5 g / L or more.

[0070] According to still another aspect of the present invention, the mass M of the inorganic particles with respect to the volume V of the filter substrate P of the ratio M P / V is provided with an exhaust gas purification catalyst according to any of the above aspects, which is 50 g / L or less.

[0071] Ratio M P When / V is increased, the pressure loss in a state where PM is not deposited increases. Ratio M P / V is preferably 15 g / L or less, and more preferably 10 g / L or less.

[0072] According to still another aspect of the present invention, the mass M of the inorganic particles with respect to the volume V of the filter substrate P of the ratio M P / V is provided with an exhaust gas purification catalyst according to any of the above aspects, which is in the range of 3 to 15 g / L. Ratio M P / V is preferably in the range of 5 to 10 g / L.

[0073] According to still another aspect of the present invention, in the exhaust gas purification catalyst, the portion corresponding to the filter partition, that is, the porous partition, on the surface, the total area S of all pores, the total area S of pores having an opening diameter of less than 40 μm S of the ratio S S / S is provided with an exhaust gas purification catalyst according to any of the above aspects, which is 65% or more. Ratio S S When / S is 65% or more, the pressure loss caused by the deposition of PM is small.

[0074] Here, the "opening diameter" is a value obtained by the following method. First, the surface of the first cell side of the porous partition wall of the exhaust gas purification catalyst is imaged at a magnification of 200 times to obtain a grayscale image. An optical microscope is used for this imaging. Further, this imaging is performed on a region near the center in the length direction of the catalyst-coated filter among the surfaces of the first cell side of the porous partition wall. Here, this "length direction" is equal to the length direction of the first and second cells. Next, the obtained grayscale image is binarized to obtain a binary image. Then, the area of each black portion on the surface of the first cell side in the binary image is determined, and the diameter of a circle having an area equal to this area, that is, the equivalent circle diameter, is defined as the "aperture diameter" of the pore corresponding to the black portion. Here, as long as a certain black portion is separated from other black portions, regardless of its shape, that black portion is considered to correspond to one pore. Note that image processing software "ImageJ" can be used for this image processing.

[0075] Ratio S S / S is preferably 70% or more. Ratio S S / S has no upper limit, but according to one example, ratio S S / S is 95% or less.

[0076] According to another aspect of the present invention, in the exhaust gas purification catalyst, the portion corresponding to the filter partition wall, that is, the porous partition wall, on the surface, the total area S of the total pores, the total area S of the pores having an aperture diameter of 40 μm or more and less than 60 μm M Ratio S M / S is provided with an exhaust gas purification catalyst according to the above aspect in which / S is 30% or less.

[0077] Ratio S S When ratio S M / S increases, ratio S M / S tends to decrease. Ratio S S / S is preferably 20% or less. Ratio S M / S has no lower limit, but according to one example, ratio S

[0078] According to still another aspect of the present invention, in the exhaust gas purification catalyst, the portion corresponding to the filter partition wall, that is, the porous partition wall, on the surface, the total area S of the pores having a pore diameter of 60 μm or more in the total area S of all the pores L of the ratio S L / S is 15% or less, and an exhaust gas purification catalyst according to any of the above aspects is provided.

[0079] Ratio S S As the ratio S L / S increases, the ratio S L / S tends to decrease. The ratio S L / S is preferably 10% or less. There is no lower limit for the ratio S L / S, but according to one example, the ratio S

[0080] According to still another aspect of the present invention, in the exhaust gas purification catalyst, the portion corresponding to the filter partition wall, that is, the porous partition wall, on the surface, the total area S of the pores having a pore diameter of less than 20 μm in the total area S of all the pores SS of the ratio S SS / S is 50% or less, and an exhaust gas purification catalyst according to any of the above aspects is provided.

[0081] Ratio S SS An exhaust gas purification catalyst with a large ratio S SS / S has a tendency to have a large pressure loss in a state where PM is not deposited as compared with an exhaust gas purification catalyst with a small ratio S SS There is no lower limit for the ratio S SS / S, but according to one example, the ratio S

[0082] According to still another aspect of the present invention, on the surface of the catalyst-coated filter, the portion of the exhaust gas purification catalyst corresponding to the filter partition wall, that is, the pores of the porous partition wall are divided into first small pores with an opening diameter of less than 40 μm and first large pores with an opening diameter of 40 μm or more. When the pores of the filter partition wall, that is, on the surface of the filter partition wall on the first cell side, are divided into second small pores with an opening diameter of less than 40 μm and second large pores with an opening diameter of 40 μm or more, the total area S S2 of the second small pores with respect to the total area S S2 and the total area S S1 of the first small pores, the difference S S2 -S S1 of the ratio (S S2 -S S1 ) / S S2 is 40% or less, and the total area S L2 of the second large pores with respect to the total area S L2 and the total area S L1 of the first large pores, the difference S L2 -S L1 of the ratio (S L2 -S L1 ) / S L2 is 60% or more, and an exhaust gas purification catalyst according to any of the above aspects is provided.

[0083] When the ratios (S L2 -S L1 ) / S L2 and (S S2 -S S1 ) / S S2 satisfy the above requirements, the large pores have a greater degree of reduction in the opening diameter due to the application of inorganic particles compared to the small pores. Such a configuration is advantageous, for example, in obtaining a structure in which the ratio S S / S is large and the ratio S SS / S is small.

[0084] According to still another aspect of the present invention, there is provided a method for manufacturing an exhaust gas purification catalyst according to any of the above aspects, including forming the catalyst layer provided on the pore walls of the filter substrate and supplying the inorganic particles to the surface.

[0085] The catalyst layer can be formed, for example, by the following method.

[0086] First, prepare a slurry containing the raw material of the catalyst layer and a dispersion medium. The raw material of the catalyst layer contains a catalyst metal and, optionally, at least one of a porous support and a promoter. The catalyst metal can be contained in the slurry in the form of, for example, a metal compound soluble in the dispersion medium or in the form of a supported catalyst in which the catalyst metal is supported on a porous support. The dispersion medium is, for example, an aqueous solvent such as water.

[0087] The slurry is prepared to have an appropriate viscosity. For example, the slurry is prepared so that the viscosity at a shear rate of 400 s -1 is greater than 50 mPa·s and within the range of 150 mPa·s or less, preferably within the range of 60 to 110 mPa·s or less.

[0088] Here, the viscosity of the slurry is the viscosity that can be measured at room temperature by a commercially available shear viscometer. For example, by using a standard dynamic viscoelasticity measuring device (rheometer) in the art, the viscosity at the above shear rate can be easily measured. Here, "room temperature" refers to a temperature within the range of 15 to 35°C, typically a temperature within the range of 20 to 30°C, for example, 25°C.

[0089] The slurry can further contain a thickener. As the thickener, for example, cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), and hydroxyethyl methyl cellulose (HEMC) can be used. The ratio of the thickener in the total solids of the slurry is not particularly limited as long as the viscosity of the slurry satisfies the above range, but is preferably within the range of 0.1 to 5% by mass, more preferably within the range of 0.3 to 4% by mass, and still more preferably within the range of 0.5 to 3% by mass.

[0090] Next, the portion of the filter substrate corresponding to the first end, i.e., the slurry is supplied from the first end side of the filter substrate, and the portion of the filter substrate corresponding to the second end, i.e., the gas in the filter substrate is sucked from the second end side of the filter substrate. As a result, the slurry flows into the cells with the first end of the filter substrate open, and the slurry also flows into the pores of the partition walls from the surface of the partition walls forming these cells.

[0091] Next, the portion of the filter substrate corresponding to the second end, i.e., the slurry is supplied from the second end side of the filter substrate, and the portion of the filter substrate corresponding to the first end, i.e., the gas in the filter substrate is sucked from the first end side of the filter substrate. As a result, the slurry flows into the holes opened in the portion corresponding to the second end of the filter substrate, and the slurry also flows into the pores of the partition walls from these partition wall surfaces. Note that this step can be omitted.

[0092] The above suction conditions may vary depending on the cross-sectional diameter of the filter substrate, etc. For example, in the case of a cylindrical filter substrate having a diameter in the range of 80 to 250 mm, it is preferable to perform suction under the condition that the linear velocity (wind speed) of the gas flow in the vicinity of the end of the filter substrate when the filter substrate is installed in the apparatus and no slurry is supplied is in the range of 10 to 80 m / s. The suction time is not particularly limited, but it is preferably in the range of 0.1 to 30 seconds. Preferred combinations of the linear velocity and the suction time are 20 to 70 m / s and 0.5 to 25 seconds; and 40 to 60 m / s and 2 to 15 seconds.

[0093] Thereafter, the filter substrate supplied with the slurry is dried and subjected to firing. In this way, a catalyst-coated filter is obtained. When a high-viscosity slurry is used and suction is performed under the above conditions, the ratio R F1 , R F2 and R F3 a catalyst-coated filter that satisfies the above-described conditions can be obtained.

[0094] Next, inorganic particles are supplied to the catalyst-coated filter. Specifically, an aerosol containing the inorganic particles as aerosol particles is supplied to the first end of the catalyst-coated filter. At the same time, the gas inside the catalyst-coated filter is sucked from the second end of the catalyst-coated filter. This suction is preferably performed with the first end of the catalyst-coated filter facing downward.

[0095] By this operation, the aerosol flows into the cells opened on the first end side of the catalyst-coated filter and is separated into gas and inorganic particles by the filter partition walls of the catalyst-coated filter. The gas flow path composed of pores with a large pore diameter has a lower ventilation resistance compared to the gas flow path composed of pores with a small pore diameter. Therefore, more inorganic particles accumulate in the pores with a large pore diameter compared to the pores with a small pore diameter.

[0096] Also, in the catalyst-coated filter having the catalyst layer formed as described above, the pores opened on the surface of the filter partition wall into which the aerosol flows are not excessively large in pore diameter even if they are pores with a large pore diameter. Therefore, the inorganic particles can be localized in the vicinity of the surface of the filter partition wall into which the aerosol flows. As described above, the exhaust gas purification catalyst according to any of the above aspects, that is, the powder-added catalyst-coated filter is obtained.

Brief Description of Drawings

[0097]

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Figure 12

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Figure 15

Figure 16

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Figure 21

Mode for Carrying Out the Invention

[0098] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific forms of any of the above aspects.

[0099] Each of the features described below can be combined with each of the above aspects. Also, combinations of two or more of the features described below can be combined with each of the above aspects.

[0100] In the drawings referred to below, elements having the same or similar functions are denoted by the same reference numerals, and redundant descriptions are omitted. Also, in each figure, the dimensional ratios and shapes may be different from the actual ones.

[0101] FIG. 1 is a cross-sectional view schematically showing an exhaust gas purification catalyst according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing the porous partition wall of the exhaust gas purification catalyst shown in FIG. 1. FIG. 3 is a further enlarged cross-sectional view showing the porous partition wall of the exhaust gas purification catalyst shown in FIG. 1. In FIGS. 1 and 2, the white arrows indicate the flow direction of the exhaust gas.

[0102] The exhaust gas purification catalyst 1 shown in FIGS. 1 to 3 is a particulate filter including the catalyst layer 22 shown in FIGS. 2 and 3. This exhaust gas purification catalyst 1 has a substantially cylindrical shape. As shown in FIG. 1, the exhaust gas purification catalyst 1 has a first end E1, a second end E2, a porous partition wall W, a first cell C1, and a second cell C2. The first end E1 and the second end E2 are the bottom surfaces of the cylinder.

[0103] The first cell C1 extends from the first end E1 toward the second end E2. The first cell C1 is open at the first end E1 and closed at the second end E2.

[0104] The second cell C2 extends from the second end E2 toward the first end E1. The second cell C2 is open at the second end E2 and closed at the first end E1.

[0105] The first cell C1 and the second cell C2 are adjacent to each other with a porous partition wall W interposed therebetween. The first cell C1 and the second cell C2 are arranged so as to form a checkered pattern at the first end E1 and the second end E2.

[0106] The exhaust gas purification catalyst 1 includes a catalyst-coated filter 2 as shown in FIGS. 1 to 3. The catalyst-coated filter 2 includes a filter base material 21 and a catalyst layer 22 as shown in FIGS. 2 and 3.

[0107] The filter base material 21 includes a honeycomb structure 211 and plugs 212a and 212b as shown in FIG. 1.

[0108] The honeycomb structure 211 is a cylinder provided with a plurality of through holes each extending from one bottom surface to the other bottom surface. One of these bottom surfaces corresponds to the first end E1, and the other bottom surface corresponds to the second end E2. The honeycomb structure 211 includes partition walls 211W that constitute the side walls of these through holes. These partition walls 211W are porous and partition adjacent through holes.

[0109] The plug 212a closes a part of the holes of the honeycomb structure 211 on the second end E2 side. The first cell C1 is located in a space surrounded by the plug 212a that closes the holes on the second end E2 side and the partition wall 211W that constitutes the side wall of this hole.

[0110] The plug 212b closes the remaining holes of the honeycomb structure 211 on the first end E1 side. The second cell C2 is located in a space surrounded by the plug 212b that closes the holes on the first end E1 side and the partition wall 211W that constitutes the side wall of this hole.

[0111] These plugs 212a and 212b are arranged such that the hole with the second end E2 side blocked by the plug 212a and the hole with the first end E1 side blocked by the plug 212b are adjacent to each other with the partition wall 211W in between. The first cell C1 and the second cell C2 are adjacent to each other with the partition wall 211W of the filter substrate 21 and the catalyst layer 22 provided on the pore walls thereof in between.

[0112] As shown in FIGS. 2 and 3, the catalyst layer 22 is supported by the filter substrate 21. Specifically, the catalyst layer 22 is provided on the pore walls of the filter substrate 21. That is, the catalyst layer 22 covers the inner pore walls of the partition wall 211W.

[0113] In this structure, the catalyst layer 22 is provided over the entire thickness of the porous partition wall W or the partition wall 211W. Of the catalyst layer 22, the portion that covers the inner pore walls of the partition wall 211W and is at a distance of a predetermined value or more from the surface of the partition wall 211W on the first cell C1 side can be omitted. That is, the entire catalyst layer 22 may be located in the portion of the porous partition wall W or the partition wall 211W on the first cell C1 side.

[0114] The partition wall 211W and the portion of the catalyst layer 22 supported by the partition wall 211W constitute the filter partition wall 21W. The filter partition wall 21W is porous.

[0115] As shown in FIGS. 2 and 3, the exhaust gas purification catalyst 1 further contains inorganic particles 3. The inorganic particles 3 are unevenly distributed on the surface of the porous partition wall W or the filter partition wall 21W on the first cell C1 side or in the vicinity thereof.

[0116] The inorganic particles 3 are in powder form. At least a part of the inorganic particles 3 adheres to the catalyst-coated filter 2, but does not adhere firmly to the catalyst-coated filter 2. Also, the inorganic particles 3 are not adhered to each other, but can be adhered by heat treatment or chemical treatment.

[0117] The inorganic particles 3 reduce the pore diameter of the pores located near the surface on the first cell C1 side of the porous partition wall W. Near the surface on the first cell C1 side of the porous partition wall W, according to one example, the filling rate of the pores of the filter partition wall 21W with the inorganic particles 3 is low for the pores with a small opening diameter and high for the pores with a large opening diameter. The above filling rate does not have to follow the above tendency.

[0118] In this exhaust gas purification catalyst 1, the inorganic particles 3 are unevenly distributed on the surface or in the vicinity of the surface on the first cell C1 side of the porous partition wall W or the filter partition wall 21W. Therefore, high PM collection performance can be easily achieved. Further, in this exhaust gas purification catalyst 1, the inorganic particles 3 hardly exist in the portions other than the surface or in the vicinity of the surface on the first cell C1 side of the porous partition wall W or the filter partition wall 21W. Therefore, this exhaust gas purification catalyst 1 has a small initial pressure loss.

[0119] The catalyst layer 22 is preferably configured such that the filter partition wall 21W has the structure described below.

[0120] That is, when the portion on the first cell C1 side of the filter partition wall 21W divides the pores of the filter base material 21 into first pores with a pore diameter of 5 μm or more and less than 10 μm, second pores with a pore diameter of 10 μm or more and less than 20 μm, and third pores with a pore diameter of 20 μm or more in a cross section perpendicular to the surface on the first cell C1 side of the filter partition wall 21W, the ratio R of the total area S of the portion of the catalyst layer 22 located in the first pores to the total area S of the first pores, the ratio R of the total area S of the portion of the catalyst layer 22 located in the second pores to the total area S of the second pores, and the ratio R of the total area S of the portion of the catalyst layer 22 located in the third pores to the total area S of the third pores satisfy the inequality: R < R < R < R F3 F1 of the total area S of the portion of the catalyst layer 22 located in the first pores to the total area S of the first pores C1 ratio R F1 of the total area S of the second pores F2 to the total area S of the portion of the catalyst layer 22 located in the second pores C2 ratio R F2 and the total area S of the third pores F3 to the total area S of the portion of the catalyst layer 22 located in the third pores C3 ratio R F3 is the inequality: R F1 < R F2 < R F3It is preferable to satisfy the relationship shown. Here, the boundary between adjacent pores and the pore diameter of each pore are determined by the method described later with reference to FIG. 4.

[0121] In such a configuration, for example, the portion near the surface on the first cell C1 side of the filter partition wall 21W has a narrower pore diameter distribution width and a smaller average pore diameter compared to the portion near the surface on the first cell C1 side of the partition wall 211W.

[0122] FIG. 4 is a cross-sectional view showing a method of separating connected pores in a cross-sectional image of a porous partition wall. FIG. 4 corresponds to an image of the cross-section of the porous partition wall W. Note that in FIG. 4, the catalyst layer 22 and the inorganic particles 3 described later are omitted.

[0123] (Step S1) In this method, first, a cross-section of the porous partition wall W is imaged using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). This cross-section is a cross-section perpendicular to the surface on the first cell C1 side of the porous partition wall W, that is, a cross-section parallel to the thickness direction of the porous partition wall W.

[0124] (Step S2) Next, in the image thus obtained, the partition wall 211W (hereinafter referred to as the partition portion) of the filter substrate 21 is specified. Then, in the partition portion, the space portion is specified. Here, not only the space portion CV1 that is separated from both surfaces of the partition wall 211W but also the space portion CV2 that opens at at least one surface of the partition wall 211W are specified. A part of the catalyst layer 22 or the inorganic particles 3 may be located in the space portion. Then, one of these space portions is selected.

[0125] (Step S3) Next, the area of the selected space portion is obtained, and the diameter of a circle having the same area as this area, that is, the equivalent circle diameter is calculated. Then, it is determined whether the equivalent circle diameter is 5 μm or less.

[0126] (Step S4) When the equivalent circle diameter is 5 μm or less, it is determined that the previous space portion corresponds to one pore, and this equivalent circle diameter is defined as the pore diameter of this pore. Then, if there is an unselected space portion, one of the unselected space portions is selected, and the process returns to step S3. If there is no unselected space portion, the process ends.

[0127] In the example of FIG. 4, when the space portion CV1 is selected, since the equivalent circle diameter of the space portion CV1 is 5 μm or less, it is determined that it corresponds to one pore P1. Then, this equivalent circle diameter is defined as the pore diameter of this pore P1. Then, the unselected space portion CV2 is selected, and the process returns to step S3.

[0128] (Step S5) When the equivalent circle diameter is more than 5 μm, it is determined that the above space portion corresponds to a connection of two or more pores. Then, the space portion is divided at a position where the equivalent circle diameter decreases to 50% of this equivalent circle diameter, and the boundary between the plurality of regions generated thereby is defined as the pore boundary.

[0129] In the example of FIG. 4, when the space portion CV2 is selected, since the equivalent circle diameter of the space portion CV2 is more than 5 μm, it is determined that it corresponds to a connection of two or more pores. Then, the space portion CV2 is divided at a position where the equivalent circle diameter decreases to 50% of this equivalent circle diameter, and the boundary between the plurality of regions generated thereby is defined as the pore boundary.

[0130] (Sub-step SS1) Specifically, first, a large number of circles that are inscribed in the space portion and in contact with both of a pair of wall surface portions facing each other with the space portion in between are generated. Here, the wall surface portion is a portion corresponding to the boundary between the space portion and the partition portion. Here, only circles whose centers are located between the pair of main surfaces of the partition 211W are generated. Then, a reference line is generated by connecting the centers of these circles. In the example shown in FIG. 4, the reference line obtained by connecting the centers of the circles is the broken line CL that branches.

[0131] (Sub-step SS2) Next, among the above-mentioned circles, identify the circle with the largest diameter (hereinafter referred to as the reference circle). In the example of FIG. 4, circle IC1 is identified.

[0132] (Sub-step SS3) Subsequently, for the circles whose centers are arranged in one direction (hereinafter referred to as the first direction) along the reference line from the center of the reference circle, check the diameters in order from the circle with the shortest center-to-center distance from the reference circle. This check is performed until a circle with a diameter 50% of the diameter of the reference circle is found.

[0133] When such a circle (hereinafter referred to as the first circle) is found, define the line segment connecting the two contact points between the first circle and the wall surface portion as the boundary that divides the space portion. If the first circle is not found, for the portion of the reference line on the first direction side with respect to the center of the reference circle, no boundary that divides the space portion is defined.

[0134] In the example of FIG. 4, for the circles whose centers are arranged downward along the broken line CL from the center of circle IC1, when checking the diameters in order from the circle with the shortest center-to-center distance from circle IC1, circle IC2 is found as the circle with a diameter 50% of the diameter of circle IC1. Therefore, define the line segment B1 connecting the two contact points between circle IC2 and the wall surface portion as the boundary that divides the space portion CV2.

[0135] (Sub-step SS4) Next, for the circles whose centers are arranged in the opposite direction (hereinafter referred to as the second direction) along the reference line from the center of the reference circle, check the diameters in order from the circle with the shortest center-to-center distance from the reference circle. This check is performed until a circle with a diameter 50% of the diameter of the reference circle is found.

[0136] When such a circle (hereinafter referred to as the second circle) is found, define the line segment connecting the two contact points between the second circle and the wall surface portion as the boundary that divides the space portion. If the second circle is not found, for the portion of the reference line on the second direction side with respect to the center of the reference circle, no boundary that divides the space portion is defined.

[0137] In the example of FIG. 4, for the circles whose centers are arranged upward along the broken line CL from the center of the circular IC1, even if the diameters are checked in order from the circle with the shortest center-to-center distance from the circular IC1, a circle with a diameter of 50% of the diameter of the circular IC1 is not found. Therefore, for the portion of the broken line CL on the upper side with respect to the center of the circular IC1, the boundary that divides the space CV2 is not determined.

[0138] (Sub-step SS5) Determine whether the reference line branches within the range of the portion corresponding to the line connecting the centers of the circles whose diameters were checked in sub-step SS4 or SS5.

[0139] If the reference line branches within the above range, for each branch destination, the same processing as in sub-step SS4 is performed.

[0140] That is, for the circles whose centers are arranged in the branch direction (hereinafter referred to as the third direction) along the reference line from the branch point, the diameters are checked in order from the circle with the shortest distance from the branch point to the center. This check is performed until a circle with a diameter of 50% of the diameter of the reference circle is found.

[0141] When such a circle (hereinafter referred to as the third circle) is found, the line segment connecting the two contact points between the third circle and the wall surface portion is defined as the boundary that divides the space. When the third circle is not found, for the portion of the reference line on the third direction side with respect to the branch point, the boundary that divides the space is not determined.

[0142] When the above processing is completed or when the reference line does not branch within the above range, proceed to the next step S6.

[0143] Note that in the example of FIG. 4, the broken line CL does not branch within the range of the portion corresponding to the line connecting the centers of the circles whose diameters were checked with the circular IC1 as the reference circle in sub-step SS4 or SS5. Therefore, in sub-step SS5, without determining an additional boundary, proceed to the next step S6.

[0144] (Step S6) In step S6, it is determined whether a boundary was defined in step S5.

[0145] (Step S7) If no boundary was defined in step S5, it is determined that the previous space part is one pore, and this equivalent circle diameter is defined as the pore diameter of this pore. Then, if there is an unselected space part, one of the unselected space parts is selected and the process returns to step S3. If there is no unselected space part, the process ends.

[0146] (Step S8) If one or more boundaries were defined in step S5, among the plurality of regions obtained by dividing the previous space part by the boundary, the one in which the center of the reference circle is located is determined to be one pore, and its equivalent circle diameter is defined as the pore diameter of this pore.

[0147] Subsequently, the part excluding the region in which the center of the reference circle is located from the above space part is defined as a new space part. Then, this space part is selected and the process returns to step S3.

[0148] In the example of FIG. 4, among the plurality of regions obtained by dividing the space part CV2 by the boundary B1, the one in which the center of the circle IC1 is located is determined to be one pore P2, and its equivalent circle diameter is defined as the pore diameter of the pore P2. Then, the part excluding the region corresponding to the pore P2 in which the center of the circle IC1 is located from the space part CV2 (hereinafter referred to as the first remainder) is defined as a new space part. Then, this space part is selected and the process returns to step S3.

[0149] Since the equivalent circle diameter of the above-mentioned first remainder is more than 5 μm, in step S5, circle IC3 is specified as the reference circle. Note that a reference line does not necessarily need to be newly generated. In step S5, circles IC4a and IC4b with a diameter of 50% of the diameter of circle IC3 and boundaries B1 and B2 are further specified. Next, through step S6, in step S8, among the plurality of regions formed by dividing the first remainder by boundaries B1 and B2, the one in which the center of circle IC2 is located is determined to be one pore P3, and its equivalent circle diameter is defined as the pore diameter of pore P3. Then, the portion excluding the region corresponding to pore P3 where the center of circle IC2 is located from the first remainder (hereinafter referred to as the second remainder) is defined as a new space portion. Then, this space portion is selected and the process returns to step S3.

[0150] Since the equivalent circle diameter of the above-mentioned second remainder is 5 μm or less, in step S4, it is determined that the second remainder corresponds to one pore P4, and this equivalent circle diameter is defined as the pore diameter of this pore P4. Then, if there is an unselected space portion, one of the unselected space portions is selected and the process returns to step S3. If there is no unselected space portion, the process ends.

[0151] The porous partition wall W preferably has a structure described below with reference to FIG. 5. FIG. 5 is a plan view schematically showing the surface on the first cell side of the porous partition wall. FIG. 5 depicts the surface on the first cell C1 side of the porous partition wall W.

[0152] On this surface, the pores P of the porous partition wall W are divided into first small pores with an opening diameter of less than 40 μm and first large pores with an opening diameter of 40 μm or more. For example, in FIG. 5, the pores P located in the lower right and upper left are first large pores, and the remaining pores P are first small pores. Note that the circle formed by the broken line LL2 has an area equal to the opening of the pore P. Therefore, the opening diameter of the pore P is the diameter of the circle formed by the broken line LL2.

[0153] Also, in the portion of the catalyst-coated filter corresponding to the porous partition wall W, that is, on the surface of the filter partition wall 21W on the first cell side, the pores of the filter partition wall 21W are classified into second small pores with an opening diameter of less than 40 μm and second large pores with an opening diameter of 40 μm or more. For example, in FIG. 5, among the pores of the filter partition wall 21W, the pores located in the lower right and upper left are second large pores, and the remaining pores are second small pores. In FIG. 5, the pores of the filter partition wall 21W are the region surrounded by the solid line LL1. Therefore, the opening diameter of the pores of the filter partition wall 21W is the diameter of a circle having the same area as the region surrounded by the solid line LL1.

[0154] The total area S of the second small pores S2 with respect to this total area S S2 and the total area S of the first small pores S1 and the difference S S2 -S S1 the ratio of (S S2 -S S1 ) / S S2 is 40% or less. Also, the total area S of the second large pores L2 with respect to this total area S L2 and the total area S of the first large pores L1 and the difference S L2 -S L1 the ratio of (S L2 -S L1 ) / S L2 is 60% or more.

[0155] In this structure, the second large pores have a greater degree of reduction in the opening diameter due to the application of the inorganic particles 3 compared to the second small pores. Such a configuration is advantageous, for example, in reducing the pores P having an excessively large or excessively small opening diameter on the surface of the first cell side of the porous partition wall.

Example

[0156] Specific examples of the present invention are described below. <1> Production of Catalyst for Exhaust Gas Purification (Example 1) The catalyst for exhaust gas purification described with reference to FIGS. 1 to 3 was produced by the following method. First, 3 parts by mass of a palladium nitrate solution, 35 parts by mass of alumina powder, 32 parts by mass of a ceria-containing oxide, and ion-exchanged water were mixed. To this mixed solution, 1 part by mass of a polycarboxylic acid was added to prepare a slurry. This slurry had a viscosity η -1 at a temperature of 25°C and a shear rate of 400 s 400 of 100 mPa·s.

[0157] Next, a filter substrate was prepared. Here, a filter substrate having a cylindrical shape with a volume of 2.1 L and a height of 127 mm was used.

[0158] Then, the above slurry was supplied to one end face (the first end face) of the filter substrate, and the gas inside the filter substrate was sucked from the other end face (the second end face) of the filter substrate. This suction was performed under the condition that the linear velocity (wind speed) of the gas flow near the end of the filter substrate when the filter substrate was installed at a temperature of 25°C and the slurry was not supplied was 50 m / s. In this way, the partition walls of the filter substrate were coated with the slurry. The supply of the slurry was carried out so that the amount of the catalyst layer with respect to the volume of the filter substrate in the catalyst-coated filter was 75 g / L.

[0159] Thereafter, the filter substrate coated with the slurry was dried and fired. In this way, a catalyst-coated filter was obtained.

[0160] Next, inorganic particles were supplied to one surface of each filter partition wall of the catalyst-coated filter. Specifically, an aerosol containing the inorganic particles as aerosol particles was supplied to the first end corresponding to the first end face of the catalyst-coated filter. At the same time, the gas inside the catalyst-coated filter was sucked from the second end corresponding to the second end face of the catalyst-coated filter. This suction was performed with the catalyst-coated filter installed so that the first end faced downward.

[0161] The amount of the inorganic particles with respect to the volume of the filter substrate was 5 g / L. As the inorganic particles, sepiolite having an average particle diameter of 6 μm was used. As described above, a catalyst for purifying exhaust gas was obtained.

[0162] <2>Measurement of Inorganic Particle Distribution Regarding the exhaust gas purification catalyst according to Example 1, the inorganic particle distribution in the thickness direction of the porous partition wall was measured. Specifically, regarding the exhaust gas purification catalyst according to Example 1, a cross-section of the porous partition wall was imaged with a scanning electron microscope to obtain a grayscale image. This imaging was performed on a cross-section of a portion of the porous partition wall where the distance from the first end and the distance from the second end were equal. Next, the analysis position by an energy dispersive X-ray analyzer was specified in the previous grayscale image, and the intensity of characteristic X-rays derived from calcium was measured. Here, line analysis along the thickness direction of the porous partition wall was performed. Then, a composite image was generated by superimposing points having brightness (shading value) corresponding to the intensity of characteristic X-rays and colored on the previous grayscale image. From this composite image, the relationship between the distance from the surface on the first cell side of the catalyst-coated filter and the shading value was obtained.

[0163] FIG. 6 is a composite image obtained by superimposing points having brightness corresponding to the intensity of characteristic X-rays derived from calcium and colored on an image showing a cross-section in the thickness direction of the porous partition wall of the exhaust gas purification catalyst according to Example 1. In FIG. 6, the first cell is located in the upper portion of the porous partition wall of the exhaust gas purification catalyst.

[0164] FIG. 7 is a composite image showing an enlarged cross-section in the thickness direction of the porous partition wall of the exhaust gas purification catalyst shown in FIG. 6. The white curve in the center in FIG. 7 indicates the boundary between the filter substrate and the first cell. In FIG. 7, the white portion indicates inorganic particles, the light gray portion indicates the catalyst layer, and the dark gray portion indicates the filter substrate. As shown in FIG. 7, many inorganic particles are present on the first cell side among the pores of the filter partition wall.

[0165] FIG. 8 is a graph showing the distribution of powdery inorganic particles in the thickness direction of the porous partition wall of the exhaust gas purification catalyst according to Example 1. In FIG. 8, the horizontal axis represents the distance from the surface on the first cell side of the catalyst-coated filter, and the vertical axis represents the above-mentioned shading value. In FIG. 8, the distances for the inorganic particles existing within the filter partition wall of the catalyst-coated filter are shown as positive values. Also, the distances for the inorganic particles existing outside the filter partition wall (i.e., within the first cell) of the catalyst-coated filter are shown as negative values.

[0166] As shown in FIG. 8, in the exhaust gas purification catalyst according to Example 1, the inorganic particles were unevenly distributed on the first cell side of the porous partition wall. And in the exhaust gas purification catalyst according to Example 1, the above-mentioned amounts A, A1, and A2 satisfied the relationship represented by the inequality (A1 + A2) / A ≧ 90%. Specifically, the ratio (A1 + A2) / A was 98.7%. Here, A1 is the sum of the respective shading values within the range where the distance from the catalyst-coated filter is -50 μm or more and less than 0 μm. A2 is the sum of the respective shading values within the range where the distance from the catalyst-coated filter is 0 μm or more and 40 μm or less. A is the sum of the respective shading values within the range where the distance from the catalyst-coated filter is -50 μm or more and 200 μm or less.

[0167] Also, in the exhaust gas purification catalyst according to Example 1, the amount of the inorganic particles located within the pores of the filter partition wall among the total amount of the inorganic particles was 70% or more. Specifically, the amount of the inorganic particles located within the pores of the filter partition wall among the total amount of the inorganic particles was 77.4%. Here, the amount of the inorganic particles located within the pores of the filter partition wall is the sum of the respective shading values within the range where the distance from the catalyst-coated filter is 0 μm or more and 200 μm or less. Also, the total amount of the inorganic particles is the sum of the respective shading values within the range where the distance from the catalyst-coated filter is -50 μm or more and 200 μm or less.

[0168] <3>Measurement of Catalyst Layer Distribution and Inorganic Particle Distribution For the exhaust gas purification catalyst according to Example 1, the catalyst layer distribution and the inorganic particle distribution were measured. Specifically, first, for the exhaust gas purification catalyst according to Example 1, the surface of the first cell side of the porous partition wall was photographed with a scanning electron microscope to obtain a micrograph. This imaging was performed on a cross-section of a portion of the porous partition wall where the distance from the first end and the distance from the second end were equal. Next, the analysis position by the energy dispersive X-ray analyzer was specified in the previous micrograph, and an image showing points having brightness corresponding to the intensity of characteristic X-rays derived from palladium and colored was obtained. Next, the analysis position by the energy dispersive X-ray analyzer was specified in the previous micrograph, and an image showing points having brightness corresponding to the intensity of characteristic X-rays derived from calcium and colored was obtained.

[0169] Figure 9 is a micrograph showing the surface of the first cell side of the porous partition wall of the exhaust gas purification catalyst according to Example 1. Figure 10 is an image showing points having brightness corresponding to the intensity of characteristic X-rays derived from palladium and colored in Figure 9. Figure 10 shows the position of the catalyst layer in Figure 9. Figure 11 is an image showing points having brightness corresponding to the intensity of characteristic X-rays derived from calcium and colored in Figure 9. Figure 11 shows the position of the inorganic particles in Figure 9.

[0170] Figure 10 shows points having brightness corresponding to the intensity of characteristic X-rays derived from palladium and colored, which are present in a portion relatively close to the surface of the porous partition wall of the exhaust gas purification catalyst. Also, Figure 11 shows points having brightness corresponding to the intensity of characteristic X-rays derived from calcium and colored, which are present in a portion relatively close to the surface of the porous partition wall of the exhaust gas purification catalyst.

[0171] Figure 12 is a composite image formed by overlapping the image shown in Figure 10 and the image shown in Figure 11.

[0172] Each of FIGS. 13 to 15 is a graph showing the result of line analysis along a certain straight line on the image shown in FIG. 12. By line analysis, the gray value of the colored points having brightness corresponding to the intensity of characteristic X-rays derived from palladium and the gray value of the colored points having brightness corresponding to the intensity of characteristic X-rays derived from calcium were analyzed on a certain straight line on the image shown in FIG. 12. FIG. 13 shows the result of line analysis along a straight line existing at the position of 60 pixels from the left end when the horizontal length of the image shown in FIG. 12 is 250 pixels and the vertical length is 200 pixels. FIG. 14 shows the result of line analysis along a straight line existing at the position of 120 pixels from the left end in the above case. FIG. 15 shows the result of line analysis along a straight line existing at the position of 180 pixels from the left end in the above case. The gray value was obtained using ImageJ. In the above line analysis, the position of the upper end of the image shown in FIG. 12 was set to 0 pixels and the position of the lower end was set to 200 pixels.

[0173] As described above, FIG. 10 shows the points having brightness corresponding to the intensity of characteristic X-rays derived from palladium and colored, which exist in a portion relatively close to the surface of the porous partition of the catalyst for exhaust gas purification. Further, FIG. 11 shows the points having brightness corresponding to the intensity of characteristic X-rays derived from calcium and colored, which exist in a portion relatively close to the surface of the porous partition of the catalyst for exhaust gas purification, that is, the inorganic particles existing in a portion relatively close to the surface of the porous partition. As shown in FIGS. 13 to 15, the gray value of palladium and the gray value of calcium are inversely correlated. Here, the portion where the gray value of palladium is small indicates the pore portion. From this, it can be seen that the inorganic particles are located in the pores of the filter partition. Further, there are pores having a relatively small pore diameter in the portion where the amount of palladium is relatively large, and there are pores having a relatively large pore diameter in the portion where the amount of palladium is relatively small or palladium is not detected. Also, in FIGS. 13 to 15, a larger amount of calcium exists in the portion where the amount of palladium is relatively small than in the portion where the amount of palladium is relatively large. From these facts, in FIGS. 13 to 15, more inorganic particles existed in the pores having a relatively large pore diameter than in the pores having a relatively small pore diameter.

[0174] (Example 2) An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that the ratio of the amount of inorganic particles to the volume of the filter substrate was changed from 5 g / L to 1 g / L.

[0175] (Example 3) An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that the ratio of the amount of inorganic particles to the volume of the filter substrate was changed from 5 g / L to 20 g / L.

[0176] (Comparative Example 1) The filter substrate used in Example 1 was prepared and used as the exhaust gas purification catalyst according to Comparative Example 1.

[0177] (Comparative Example 2) An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that the ratio of the amount of the catalyst layer to the volume of the filter substrate was changed from 75 g / L to 50 g / L and the supply of inorganic particles to the catalyst-coated filter was omitted.

[0178] (Comparative Example 3) An exhaust gas purification catalyst was produced in the same manner as in Example 1, except that the supply of inorganic particles to the catalyst-coated filter was omitted. That is, a catalyst-coated filter was produced in the same manner as in Example 1 and used as the exhaust gas purification catalyst according to Comparative Example 3.

[0179] (Comparative Example 4) An exhaust gas purification catalyst was obtained in the same manner as in Example 1, except that the ratio of the amount of the catalyst layer to the volume of the filter substrate was changed from 75 g / L to 100 g / L and the supply of inorganic particles to the catalyst-coated filter was omitted.

[0180] <4>Measurement of the ratio D1 / D2 For the exhaust gas purification catalysts according to Comparative Examples 1 to 4, the pore distribution of the filter partition was measured using the mercury intrusion method. The results are shown in Fig. 16. The vertical axis in Fig. 16 indicates the log differential pore volume (mg / L). The horizontal axis in Fig. 16 indicates the pore diameter. According to Fig. 16, the average pore diameters of the filter partitions of the exhaust gas purification catalysts according to Comparative Examples 1 to 4 were 17.0 μm, 10.5 μm, 10.0 μm, and 8.5 μm, respectively. From this, the ratio D1 / D2 of the average particle diameter D1 of the inorganic particles to the average pore diameter D2 of the pores of the filter partition in the exhaust gas purification catalysts according to Examples 1 to 3 was 0.6 in all cases.

[0181] <5>Measurement of the opening diameter For each of the exhaust gas purification catalysts according to Examples 1 to 3 and Comparative Examples 2 to 4, the opening diameter on the surface of the first cell side of the porous partition was measured by the method described above. The results are shown in Table 1.

[0182]

Table 1

[0183] Fig. 17 is an image obtained by binarizing a micrograph of the porous partition of the exhaust gas purification catalyst according to Example 1. Fig. 18 is an image obtained by binarizing a micrograph of the porous partition of the exhaust gas purification catalyst according to Comparative Example 3.

[0184] In Table 1, "S <20 / S" is the ratio of the total area S <20 of the pores with an opening diameter of less than 20 μm to the total area S of all the pores in the micrograph of the surface of the first cell side of the porous partition. "S 20-40 / S" is the ratio of the total area S 20-40 of the pores with an opening diameter in the range of 20 μm or more and less than 40 μm to the total area S of all the pores in the above micrograph. "S 40-60 / S" is the ratio of the total area S 40-60 of the pores with an opening diameter in the range of 40 μm or more and less than 60 μm to the total area S of all the pores in the above micrograph. "S 60-80"S60-80 / S" is the ratio of the total area S60-80 of pores with an aperture diameter in the range of 60 μm or more and less than 80 μm to the total area S of all pores in the above microscopic photograph. 60-80 of. "S 80-100 80-100 / S" is the ratio of the total area S80-100 of pores with an aperture diameter in the range of 80 μm or more and less than 100 μm to the total area S of all pores in the above microscopic photograph. 80-100 of. "S 100< 100+ / S" is the ratio of the total area S100+ of pores with an aperture diameter of 100 μm or more to the total area S of all pores in the above microscopic photograph. 100< of. "S S <40 / S" is the ratio of the total area S<40 of pores with an aperture diameter of less than 40 μm to the total area S of all pores in the above microscopic photograph. S of.

[0185] As shown in FIGS. 17 and 18 and Table 1, in the exhaust gas purification catalysts according to Example 1 and Example 3, the ratio of pores with a large aperture diameter on the surface of the first cell side of the porous partition wall was smaller than that of the exhaust gas purification catalysts according to Comparative Examples 2 to 4.

[0186] <6>Measurement of filling rate For the exhaust gas purification catalyst according to Example 1, the ratios (S S2 -S S1 ) / S S2 and (S L2 -S L1 ) / S L2 were calculated.

[0187] Specifically, for the exhaust gas purification catalyst according to Example 1, the sum of the total areas S <20 and S 20-40 obtained when calculating the above aperture diameter was taken as the total area S S1 of the exhaust gas purification catalyst according to Example 1. Also, for the exhaust gas purification catalyst according to Example 1, the sum of the total areas S 40-60 , S 60-80 , S 80-100 and S 100< obtained when calculating the above aperture diameter was taken as the total area S L1was used. Also, for the exhaust gas purification catalyst according to Comparative Example 3, the total area S obtained when calculating the above opening diameter <20 and S 20-40 The sum of was defined as the total area S of the exhaust gas purification catalyst according to Comparative Example 3 S2 And for the exhaust gas purification catalyst according to Comparative Example 3, the total area S obtained when calculating the above opening diameter 40-60 S 60-80 S 80-100 and S 100< The sum of was defined as the total area S of the exhaust gas purification catalyst according to Comparative Example 3 L2 For the exhaust gas purification catalysts according to Examples 2 and 3 as well, by the same method as in Example 1, the above-mentioned ratios (S S2 - S S1 ) / S S2 and the ratio (S L2 - S L1 ) / S L2 were determined. The calculation results are shown in Table 2 below.

[0188]

Table 2

[0189] As shown in Table 2, for the exhaust gas purification catalyst according to Example 1, the ratio (S L2 - S L1 ) / S L2 was larger compared to the ratio (S S2 - S S1 ) / S S2 That is, in the exhaust gas purification catalyst according to Example 1, among the pores opening on the surface of the first cell side of the porous partition wall, those with a larger opening diameter had a higher filling rate with inorganic particles compared to those with a smaller opening diameter.

[0190] <7>Measurement of the capture rate with respect to the number of PM (PN) Regarding the exhaust gas purification catalyst according to Example 1, the PM collection rate was determined by the following method. Specifically, light oil was burned in a soot generator to generate PM, and the PM was accumulated in the exhaust gas purification catalyst according to Example 1. When the accumulated amount of PM reached 0.02 g / L, the number of PM discharged from the exhaust gas purification catalyst was measured. The measurement of the number of PM was carried out at a gas temperature of 240 °C and a gas flow rate of 250 kg / hour.

[0191] Next, the exhaust gas purification catalyst according to Example 1 was installed in the soot generator, and the number of PM was measured upstream of the exhaust gas purification catalyst. The measurement of the number of PM was carried out at a gas temperature of 240 °C and a gas flow rate of 250 kg / hour.

[0192] Next, the collection rate of the exhaust gas purification catalyst according to Example 1 was determined by the following formula (1).

[0193]

Equation

[0194] In the above formula (1), x1 is the number of PM discharged from the exhaust gas purification catalyst according to Example 1, and x0 is the number of PM upstream of the exhaust gas purification catalyst according to Example 1.

[0195] Next, for the exhaust gas purification catalysts according to Examples 2 and 3 and Comparative Examples 1 to 4, the collection rates were also obtained by the same method as described for Example 1. The results of the collection rates are shown in FIGS. 19 and 20.

[0196] As shown in FIGS. 19 and 20, the exhaust gas purification catalysts according to Examples 1 to 3 all had excellent PM collection performance.

[0197] <8>Evaluation of the initial pressure loss Regarding the exhaust gas purification catalyst according to Example 1, the initial pressure loss was determined. Specifically, the pressure loss at a wind speed of 10 m 3 / min was determined.

[0198] Next, for the exhaust gas purification catalysts according to Example 2, Example 3, and Comparative Example 3, the initial pressure loss was examined in the same manner as described for Example 1. The results of the initial pressure loss are shown in FIG. 21. As shown in FIG. 21, for all of the exhaust gas purification catalysts according to Examples 1 to 3, the pressure loss was small. In particular, for the exhaust gas purification catalysts according to Examples 1 and 2, the pressure loss was small.

[0199] <9>Evaluation of Pressure Loss Caused by PM Deposition For each of the exhaust gas purification catalyst bodies according to Example 1 and Comparative Examples 2 to 4, an evaluation of the pressure loss was performed. Specifically, light oil was burned in a soot generator to generate PM, and the PM was accumulated on each of these exhaust gas purification catalyst bodies. When the accumulated amount of PM reached 1 g / L, the pressure loss was measured for each of the exhaust gas purification catalysts. The pressure loss was measured with the gas temperature at 240°C and the gas flow rate at 250 kg / hour. The results are shown in Table 3.

[0200]

Table 3

[0201] As shown in Table 3, the exhaust gas purification catalyst according to Example 1 had a smaller pressure loss after PM deposition compared to the exhaust gas purification catalysts according to Comparative Examples 2 to 4.

[0202] <10>Measurement of Packing Ratio For the exhaust gas purification catalysts according to Examples 1 to 3 and Comparative Examples 2 to 4, the packing ratios R F1 , R F2 and R F3 were determined by the method described with reference to FIG. 4. As a result, for any of the exhaust gas purification catalysts according to Examples 1 to 3 and Comparative Examples 2 to 4, the packing ratios R F1 , R F2 and R F3 satisfy the relationship shown in the inequality: R F1 <R F2 <R F3 , and the packing ratio R F1 is in the range of 10 to 40%, and the packing ratio RF2 was in the range of 15 to 40%, and the filling rate R F3 was in the range of 20 to 45%. The invention originally described in the claims is appended below. [1] A catalyst-coated filter including a filter substrate and a catalyst layer provided on the pore walls of the filter substrate, having a first end, a second end, a filter partition wall, an inlet cell, and an outlet cell, wherein the filter partition wall is porous, the inlet cell extends from the first end toward the second end, is open at the first end, and is closed at the second end, the outlet cell extends from the second end toward the first end, is open at the second end, and is closed at the first end, and the inlet cell and the outlet cell are adjacent to each other with the filter partition wall therebetween, and Powdery inorganic particles unevenly distributed on the surface of the filter partition wall adjacent to the inlet cell in a cross-section parallel to the thickness direction of the filter partition wall, and An exhaust gas purification catalyst provided with the same. [2] The exhaust gas purification catalyst according to claim 1, wherein most of the inorganic particles are located in the pores of the filter partition wall. [3] The exhaust gas purification catalyst according to claim 1 or 2, wherein the inorganic particles have an average particle diameter in the range of 1 to 50 μm. [4] The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the inorganic particles contain one or more selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, and clay minerals. [5] The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the ratio D1 / D2 of the average particle diameter D1 of the inorganic particles to the average pore diameter D2 of the pores of the filter partition wall is in the range of 0.15 to 2. [6] The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the ratio of the mass of the inorganic particles to the volume of the filter substrate is in the range of 3 to 50 g / L.

Explanation of Symbols

[0203] 1... Catalyst for exhaust gas purification, 2... Catalyst-coated filter, 3... Inorganic particles, 21... Filter substrate, 21W... Filter partition wall, 22... Catalyst layer, 211... Honeycomb structure, 211W... Partition wall, 212a... Plug, 212b... Plug, B1... Boundary, B2... Boundary IC1... Circle, IC2... Circle, IC3... Circle, IC4a... Circle, IC4b... Circle, C1... First cell, C2... Second cell, CL... Dashed line, CV1... Space part, CV2... Space part, E1... First end, E2... Second end, P1... Pore, P2... Pore, P3... Pore, P4... Pore, W... Porous partition wall,

Claims

1. A catalyst-coated filter including a filter substrate and a catalyst layer provided on the pore walls of the filter substrate, having a first end, a second end, a filter partition wall, an inlet cell, and an outlet cell, wherein the filter partition wall is porous, the inlet cell extends from the first end toward the second end, is open at the first end, and is closed at the second end, the outlet cell extends from the second end toward the first end, is open at the second end, and is closed at the first end, and the inlet cell and the outlet cell are adjacent with the filter partition wall therebetween, and a catalyst-coated filter, powdery inorganic particles unevenly distributed on the surface of the filter partition wall adjacent to the inlet cell in a cross-section parallel to the thickness direction of the filter partition wall, and an exhaust gas purifying catalyst comprising: the total amount A of the inorganic particles, the amount A1 of the inorganic particles located on the surface of the catalyst-coated filter adjacent to the inlet cell, and the amount A2 of the inorganic particles within the pores of the catalyst-coated filter, where the distance from the surface of the catalyst-coated filter adjacent to the inlet cell is 20% or less of the thickness of the portion of the catalyst-coated filter corresponding to the filter partition wall, satisfy the relationship represented by the inequality (A1 + A2) / A ≥ 90%, on the surface of the porous partition wall corresponding to the filter partition wall in the exhaust gas purifying catalyst, when the pores of the porous partition wall are divided into first small pores having an aperture diameter of less than 40 μm and first large pores having an aperture diameter of 40 μm or more, and on the surface of the filter partition wall on the inlet cell side, when the pores of the filter partition wall are divided into second small pores having an aperture diameter of less than 40 μm and second large pores having an aperture diameter of 40 μm or more, the ratio (SS2 - SS1) / SS2 of the difference SS2 - SS1 between the total area SS2 and the total area SS1 of the first small pores to the total area SS2 of the second small pores is 40% or less, and the ratio (SL2 - SL1) / SL2 of the difference SL2 - SL1 between the total area SL2 and the total area SL1 of the first large pores to the total area SL2 of the second large pores is 60% or more. An exhaust gas purifying catalyst.

2. The exhaust gas purifying catalyst according to Claim 1, wherein the amount of the inorganic particles located within the pores of the filter partition wall accounts for 70% or more of the total amount of the inorganic particles.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein the inorganic particles have an average particle diameter in the range of 1 to 50 μm.

4. The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the inorganic particles contain one or more selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal phosphates, metal nitrates, metal sulfates, and clay minerals.

5. The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the ratio D1 / D2 of the average particle diameter D1 of the inorganic particles to the average pore diameter D2 of the pores of the filter partition is in the range of 0.15 to 2.

6. The exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the ratio of the mass of the inorganic particles to the volume of the filter substrate is in the range of 3 to 50 g / L.

Images