JP2006159020A - Filter and catalyst for purification of exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the geometric surface area while controlling deterioration of the strength and maintaining the capturing rate of PM and forming the catalyst layer more while controlling increase of the pressure loss. <P>SOLUTION: An recessed part 13 extending in the axial direction is formed in at least one corner of at least one cell. Since the geometric surface area of the gas passage and the area of cell openings increase, as compared with current filters without such a recessed part, the pressure loss decreases. The amount of the catalyst layer coated also thereby increases, permitting support of more catalyst metals, which improves the purification rate. The filling of the recessed part with the catalyst layer improves the strength of the corner parts, allowing retention of strength equal to or higher than that of current filters. The thick catalyst layer formed in the recessed part permits increasing the amount of an NOx-occluding material supported. Since the corner parts contribute little to capturing of PM, the capturing rate can be maintained comparable with that of current filters. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification filter capable of purifying exhaust gas for purifying exhaust gas containing particulates such as exhaust gas from a diesel engine, and an exhaust gas purification catalyst using the exhaust gas purification filter.

  As for gasoline engines, toxic components in exhaust gas are steadily decreasing due to strict regulations on exhaust gas and technological advances that can cope with it. On the other hand, for diesel engines, harmful components are discharged as particulates (particulate matter: carbon fine particles, sulfur fine particles such as sulfate, high molecular weight hydrocarbon fine particles (SOF), etc., hereinafter referred to as PM)) The exhaust gas is more difficult to purify than gasoline engines.

  As exhaust gas purification devices for diesel engines that have been developed so far, a trap type exhaust gas purification device (wall flow) and an open type exhaust gas purification device (straight flow) are known. Among these, as a trap type exhaust gas purification device, a ceramic plug-type honeycomb body (diesel PM filter (hereinafter referred to as DPF)) is known. This DPF is formed by alternately sealing both ends of the openings of the cells of the ceramic honeycomb structure, for example, in a checkered pattern, and is adjacent to the inflow side cells and the inflow side cells clogged on the exhaust gas downstream side. It consists of an outflow side cell clogged upstream of the exhaust gas, and a filter partition that partitions the inflow side cell and the outflow side cell, and controls exhaust by filtering exhaust gas through the pores of the filter partition and collecting PM. To do.

  However, in DPF, pressure loss (hereinafter referred to as pressure loss) increases due to PM accumulation, so it is necessary to periodically remove and regenerate PM accumulated by some means. Therefore, conventionally, when pressure loss increases, DPF is regenerated by burning high-temperature exhaust gas and burning PM. However, in this case, the higher the amount of PM deposited, the higher the temperature during combustion, and the DPF may melt or be damaged by thermal stress.

  Therefore, in recent years, for example, as described in Japanese Patent Publication No. 07-106290, a coating layer is formed on the surface of the cell partition wall of DPF from alumina or the like, and a catalytic metal such as platinum (Pt) is supported on the coating layer. A continuous regeneration type DPF has been developed. According to this continuous regeneration type DPF, the collected PM is oxidized and combusted by the catalytic reaction of the catalytic metal. Therefore, the DPF can be regenerated by combusting simultaneously with the collection or continuously with the collection. The catalytic reaction takes place at a relatively low temperature and can be burned while the amount collected is small. Therefore, the thermal stress acting on the DPF is small, and there is an advantage that damage is prevented.

Japanese Patent Application Laid-Open No. 09-094434 describes a continuous regeneration type DPF in which a coating layer supporting a catalytic metal is formed not only in the cell partition walls but also in the pores of the cell partition walls. By supporting the catalyst metal in the pores, the contact probability between the PM and the catalyst metal is increased, and the PM collected in the pores can be oxidized and burned. Also in this publication it is also described further carrying _the NO _x storage material in the coating layer. Since the them if _the NO _x storage material absorbed NO _x is released as NO ₂ at high temperatures, it is possible to further facilitate the oxidation of the PM by the NO _2.

  By the way, the honeycomb structure has a large geometric surface area of the gas passage, and is therefore suitable as an exhaust gas purifying catalyst. In the case of a honeycomb substrate having a straight flow structure, the geometric surface area can be further increased by reducing the thickness of the cell partition walls or increasing the number of cells. However, in the case of DPF, since the PM is collected by the cell partition (filter partition), the cell partition is porous having a porosity of about 40% or more, compared with a honeycomb substrate having a straight flow structure. The strength is small. Therefore, if the thickness of the filter partition is reduced, the porosity must be reduced to maintain the strength, and the pressure loss increases. Furthermore, when the thickness of the filter partition is reduced, the PM collection rate decreases. Further, when the number of cells is increased, the opening area of the end face is reduced and the gas passage resistance is increased, so that the pressure loss is increased and the opening is blocked by PM.

  Therefore, in the conventional DPF and continuous regeneration type DPF, it is difficult to adopt a means of reducing the filter partition thickness or increasing the number of cells, and it is difficult to further increase the geometric surface area of the gas passage. Yes.

In addition, in a NO _x storage reduction catalyst that supports a noble metal and a NO _x storage material, in order to increase the support amount of the NO _x storage material and increase the NO _x storage amount, the area of the catalyst layer must be increased. It is effective to form a thick catalyst layer. However, when the thickness of the catalyst layer is increased in the continuous regeneration type DPF, the opening cross-sectional area of the cell passage is reduced, and the pores in the filter partition wall are blocked by the catalyst layer, resulting in a pressure loss in a quadratic curve. It will increase. Therefore, there was a limit to the increase in NO _x storage amount.
No. 07-106290 JP 09-094434

  The present invention has been made in view of the above circumstances, and increases the geometric surface area while suppressing the decrease in strength and maintaining the PM collection rate, and forms many catalyst layers while suppressing the increase in pressure loss. This is a problem to be solved.

  A feature of the exhaust gas purification filter of the present invention that solves the above problems is an exhaust gas purification filter that purifies exhaust gas containing particulates discharged from an internal combustion engine, and has a large number of cells partitioned by porous filter partition walls. It consists of a honeycomb substrate, and at least one corner portion of at least one cell has a recess extending in the axial direction.

  The cell has an inflow side cell clogged on the exhaust gas downstream side, and an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and the recess has at least one corner of the inflow side cell. It is preferable to form in the part.

  The recess is preferably provided at least in the inflow side cell in the outer peripheral portion.

  The exhaust gas purifying catalyst of the present invention is characterized by comprising the exhaust gas purifying filter of the present invention and a catalyst layer formed on a filter partition wall by supporting a catalytic metal on a porous oxide.

It is desirable that a noble metal and a NO _x storage material are supported on the catalyst layer.

  Moreover, as for a catalyst layer, it is desirable that the thickness of the part of a recessed part is larger than the thickness of parts other than a recessed part.

  According to the exhaust gas purification filter of the present invention, the recess is formed in at least one cell or at least one corner of the inflow side cell. Accordingly, the geometric surface area of the gas passage is increased and the cell opening area is increased as compared with the conventional filter having no recess, and the pressure loss is reduced. If a recess is formed in the inflow side cell in the outer peripheral portion, the cell opening area in the outer peripheral portion is increased and the heat capacity is reduced, so that the outer peripheral portion is quickly heated, and PM is deposited in the outer peripheral portion. In addition to being suppressed, damage during reproduction is prevented.

According to the exhaust gas purifying catalyst of the present invention, since the surface area of the corner portion is increased by the concave portion, the coating amount of the catalyst layer is increased by that amount, and the catalytic metal can be supported by that amount, so that the purification rate is improved. . The strength of the corner portion is improved by the catalyst layer filled with the concave portions, and the strength equal to or higher than that of the conventional one can be maintained. Furthermore a thick catalyst layer formed in the recess, NO _x it is possible to increase the loading amount of storage material, NO _x storage amount _the NO _x purification performance is improved to increase. In addition, since the corner portion hardly contributes to PM collection, the PM collection rate can be maintained at the same level as before.

  In the exhaust gas purification filter of the present invention, a recess extending in the axial direction is formed in at least one cell or at least one corner of the inflow side cell. In the cross section perpendicular to the axial direction, the diameter of the recess is preferably within 50% of the length of one side of the filter partition. When the diameter of the recess exceeds 50% of the length of one side of the filter partition wall, the area occupied by the recess in the filter partition wall increases, and as a result, the filter partition wall becomes thin and the PM collection rate decreases. The diameter of the recess is optimally about 20% of the length of one side of the filter partition wall. Due to the presence of this recess, the cell opening area increases and the pressure loss decreases.

  The concave portion is preferably formed at least in all corner portions of the inflow side cell. Moreover, it is preferable to form in the at least 1 corner part of an outflow side cell, and you may form in all the corner parts of an outflow side cell. The cross-sectional shape of the recess is not particularly limited, but it is preferably a cross-sectional arc shape having no edge in terms of strength or damage. The recess is preferably continuous in the axial direction by the length of the filter partition wall, but may be divided or partially formed in the axial direction of the filter partition wall.

  The exhaust gas purification filter of the present invention may have a straight flow structure made of a honeycomb base material having a large number of cells partitioned by porous filter partition walls, or an inflow side cell clogged on the exhaust gas downstream side; It is also preferable to adopt a wall flow structure including an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and a filter partition wall that partitions the inflow side cell and the outflow side cell. This exhaust gas purification filter can be manufactured from heat-resistant ceramics such as cordierite and silicon carbide. For example, a clay-like slurry containing cordierite powder as a main component is prepared, and the slurry is formed by extrusion or the like and fired. The recess is preferably formed simultaneously with the extrusion molding. Instead of cordierite powder, powders of alumina, magnesia and silica can be blended so as to have a cordierite composition. In the case of a wall flow structure filter, the cell opening of one end surface is then sealed in a checkered pattern with the same clay-like slurry, and the cell of the cell adjacent to the cell sealed at the one end surface at the other end surface. Seal the opening. Thereafter, the honeycomb structure exhaust gas purification filter can be manufactured by fixing the plugging material by firing or the like.

  The cell shape or the shape of the inflow side cell and the outflow side cell is a polygonal shape such as a triangular cross-section, a square cross-section, and six cross-sections. For example, in the case of a cell shape having a quadrangular cross section or a hexagonal cross section, it is desirable to form the recesses at least in the corner portions facing each other. Thereby, the stress which acts at the time of extrusion molding or baking becomes uniform, and it can suppress that distortion remains.

  In order to form pores in the filter partition, carbon powder, wood powder, starch, resin powder, and other combustible powders are mixed in the above-mentioned slurry, and the combustible powder disappears during firing. The pores can be formed, and the particle size and porosity of the pores can be controlled by adjusting the particle size and addition amount of the combustible powder. These vacancies allow the cells to communicate with each other or the inflow side cell and the outflow side cell, and PM is trapped in the vacancies, but gas is trapped in the adjacent cell or from the inflow side cell to the outflow side cell. It can pass.

  The porosity of the filter partition wall is desirably 50 to 70%. When the porosity is in this range, an increase in pressure loss can be suppressed even when the catalyst layer is formed at 100 to 200 g / L, and a decrease in strength can be further suppressed. And PM can be collected more efficiently.

  The exhaust gas purifying catalyst of the present invention is formed by forming a catalyst layer on the filter partition wall of the exhaust gas purifying filter of the present invention. The catalyst layer may be formed only on the surface of the filter partition wall, but is preferably formed also on the surface of the pores inside the filter partition wall. By forming on the filter partition surface, a catalyst layer is also formed on the concave surface. Due to the presence of the recess, the surface area of the filter partition is increased as compared with the conventional filter having no recess, so that the surface area of the catalyst layer is also increased as compared with the conventional filter and the purification activity is improved.

This catalyst layer is formed by supporting a catalyst metal on a porous oxide. The porous oxide functions as a catalyst metal carrier, and is a composite oxide composed of at least one of oxides such as Al ₂ O ₃ , ZrO ₂ , CeO ₂ , TiO ₂ , SiO ₂ , or a plurality of these. Can be used.

  In order to form the catalyst layer, the porous oxide powder is made into a slurry together with a binder component such as alumina sol and water, and the slurry is attached to the cell partition wall and then baked to form a coat layer. May be carried. It is also possible to prepare a slurry from a catalyst powder in which a catalyst metal is previously supported on a porous oxide powder and to use it to form a coat layer. The usual dipping method can be used to adhere the slurry to the filter partition wall, but the air is forcedly filled into the pores of the filter partition wall by air blow or suction, and the excess slurry contained in the pores is filled. It is desirable to remove things.

  In this case, the formation amount of the coat layer or the catalyst layer is preferably 100 to 200 g per 1 L of the exhaust gas purification filter. If the coat layer or the catalyst layer is less than 100 g / L, a decrease in the durability of the catalyst metal is unavoidable, and if it exceeds 200 g / L, the pressure loss becomes too high to be practical.

  As the catalyst metal contained in the catalyst layer, for example, a metal that promotes the oxidation of PM by a catalytic reaction can be used. As such a catalyst metal, it is preferable to use at least one selected from platinum group noble metals such as Pt, Rh, and Pd. The amount of the precious metal supported is preferably in the range of 1 to 5 g per liter of the exhaust gas purification filter. If the loading amount is less than this, the activity is too low to be practical, and if the loading amount exceeds this range, the activity is saturated and the cost is increased. In order to support the noble metal, a solution in which a nitrate of noble metal is dissolved can be used and supported by an adsorption support method, an impregnation support method, or the like.

The catalyst layer preferably contains a NO _x storage material selected from alkali metals, alkaline earth metals, and rare earth elements. If including _the NO _x storage material in the catalyst layer, since the NO _x produced by the oxidation by the catalyst metal can be occluded in _the NO _x storage material, thereby improving the purification activity of NO _x. This NO _x storage material is selected from alkali metals such as K, Na, Cs and Li, alkaline earth metals such as Ba, Ca, Mg and Sr, or rare earth elements such as Sc, Y, Pr and Nd. Can be used. In particular, it is desirable to use at least one of alkali metals and alkaline earth metals that have excellent NO _x storage ability.

The amount of the NO _x storage material supported is preferably in the range of 0.15 to 0.45 mol per liter of the exhaust gas purification filter. If the loading is less than this, the activity is too low to be practical, and if the loading is more than this range, the noble metal is covered and the activity decreases. In order to support the NO _x storage material, a solution in which acetate, nitrate or the like is dissolved may be used and supported on the coat layer by an impregnation support method or the like. The advance carries advance _the NO _x storage material on the porous oxide powders, it is also possible to form the catalyst layer by using the powder.

The catalyst layer preferably also contains a NO _x adsorbent that adsorbs NO _x at a low temperature and releases NO _x at a high temperature. The NO in the exhaust gas low temperature region is adsorbed on _the NO _x adsorption material as NO _2, NO ₂ is released from _the NO _x adsorption material is in a high temperature region, oxidized and purified of PM by desorbed NO ₂ is promoted. As this NO _x adsorbent, a powder in which a noble metal is supported on zirconia or a powder in which a noble metal is supported on CeO ₂ can be used.

It is desirable to form the catalyst layer so that the thickness of the concave portion is larger than the thickness of the portion other than the concave portion. Thereby, a corner part can be reinforced with a catalyst layer and the intensity | strength equal to or more than before can be maintained. Furthermore a thick catalyst layer formed in the recess, NO _x it is possible to increase the loading amount of storage material, NO _x storage amount _the NO _x purification performance is improved to increase.

  In order to form the catalyst layer so that the thickness of the concave portion is thicker than the thickness of the portion other than the concave portion, the thickness of the corner portion tends to be increased even with a normal washcoat method, but the particle size is small. It is also preferable to use a method in which after forming the catalyst layer using the porous oxide, the catalyst layer is formed only in the corner portion using the porous oxide having a large particle size.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1
FIG. 1 shows the filter catalyst of this example. As shown in FIG. 2 (a), the filter catalyst 1 includes an inflow side cell 10 that is clogged on the exhaust gas downstream side, and an outflow side cell 11 that is adjacent to the inflow side cell 10 and clogged on the exhaust gas upstream side. A commercially available DPF comprising a filter partition wall 12 that partitions the inflow side cell 10 and the outflow side cell 11 is used. This DPF has a volume of 2 liters, a cell count of 300 cells / inch ² (46.5 cells / cm ² ), a filter partition wall thickness of 0.3 mm, and a porosity of 60%. Is a square with a side of 1.17 mm.

  The corners of the inflow side cell 10 and outflow side cell 11 of the DPF were cut to form a concave portion 13 having a circular arc shape with a width of 0.2 mm and a depth of 0.07 mm as shown in FIG. 2 (b).

Next, a slurry composed of Al ₂ O ₃ powder, TiO ₂ powder, ZrO ₂ powder, CeO ₂ powder, alumina sol and ion-exchanged water was prepared and milled so that the average particle size of the solid particles was 1 μm or less. Then, the DPF in which the recesses 13 are formed is immersed in this slurry, and the slurry is poured into the cell. The slurry is pulled up and sucked from the end surface opposite to the immersion side to remove excess slurry. Baked for hours. This operation was performed twice, and adjustment was performed so that the same amount of coat layer was formed in the inflow side cell 10 and the outflow side cell 11. The coating amount is 75 g per liter of the filter 1. The coat layer is formed on the surfaces and the pores of the inflow side cell 10 and the outflow side cell 11.

  Thereafter, a predetermined amount of an aqueous solution of dinitrodiammine platinum nitrate having a predetermined concentration was impregnated, dried and baked, and Pt was supported on the coating layer to form a catalyst layer 2 as shown in FIG. 2 (c). Similarly to the inflow side cell 10 and the outflow side cell 11, the catalyst layer 2 is also formed in the recess 13. The amount of Pt supported is 2 g per liter of the filter catalyst 1.

(Example 2)
A coating layer was formed in the same manner as in Example 1 except that DPF having the same recess 13 as in Example 1 was used and the coating amount was 200 g / L.

And after carrying Similarly Pt as in Example 1, Li, using nitrates of Ba and K, and further carrying _the NO _x storage material in the coating layer. Li was 0.3 mol / L, Ba was 0.05 mol / L, and K was 0.025 mol / L.

(Example 3)
The coating layer 20 was formed in the same manner using DPF in which the same recess 13 as in Example 1 was formed. Next, using a slurry made of Al ₂ O ₃ powder, TiO ₂ powder, ZrO ₂ powder, CeO ₂ powder, alumina sol and ion-exchanged water, and milled so that the average particle size of solid particles is 3 to 4 μm, The DPF on which the coat layer 20 was formed was dipped in this slurry and pulled up to remove excess slurry from the end surface on the dipping side, and then dried by ventilation and baked at 450 ° C. for 2 hours. This operation was performed twice, and adjustment was performed so that the same amount of coat layer was formed in the inflow side cell 10 and the outflow side cell 11. The coating amount for the second time is 30 g per liter of the filter catalyst 1. The second coat layer 3 was formed mainly on the surface of the recess 13 as shown in FIG.

  Next, Pt, Li, Ba and K were supported in the same manner as in Example 2.

(Comparative Example 1)
A DPF similar to that of Example 1 was used except that the concave portion 13 was not formed, no coating layer was formed, and no catalyst metal was supported.

(Comparative Example 2)
Using the same DPF as in Example 1 except that the recess 13 was not formed, a coating layer was formed and Pt was supported in the same manner as in Example 1.

(Comparative Example 3)
A DPF similar to that in Example 1 was used except that the recess 13 was not formed, and a coating layer was formed in the same manner as in Example 2 to carry Pt, Li, Ba, and K in the same manner.

<Test and evaluation>
An endurance test was conducted in which the filter catalyst of each Example and each Comparative Example was held in the atmosphere at 650 ° C. for 50 hours, and then mounted on the exhaust pipe of a diesel engine. The engine was operated at an engine speed of 2450 rpm × 35 Nm and a lean steady gas temperature of 250 ° C., and the soot collection rate and pressure loss were measured. The soot oxidation rate was calculated by setting the inlet gas temperature to 350 ° C. and measuring the residual amount of soot after 1 hour of operation.

For the filter catalysts of Examples 2 and 3 and Comparative Example 3, the input gas temperature is set to 300 ° C., light oil is injected into the exhaust gas in a spike so that 0.1 seconds every 10 seconds and A / F becomes 14.2. The NO _x purification rate under these conditions was measured.

  Further, a 10 mm × 10 mm × 100 mm prism was cut from each filter catalyst, and the bending strength was measured by a four-point bending test.

  The results are shown in Table 1.

  In the filter catalyst of Example 1, the recess 13 was formed, so that the end surface opening ratio increased by about 7% and the cell surface area increased by about 17% compared to the filter catalyst of Comparative Example 2. Therefore, as shown in Table 1, as compared with the filter catalyst of Comparative Example 2, the pressure loss is reduced and the soot oxidation rate is improved. Moreover, the collection rate of the soot in the filter catalyst of Examples 1-3 is equivalent to Comparative Examples 1-3, and is maintaining the high rate. That is, it can be seen that the presence of the recess 13 does not affect the collection rate of soot.

  Further, it is obvious that the bending strength is lower than that of the filter catalyst of Comparative Example 1 when the catalyst layer is not formed due to the presence of the recess 13, and the Example 1 having the catalyst layer and the Comparative Example 2 are compared. However, it can be seen that the bending strength is reduced due to the presence of the recess 13. However, since the bending strength of the filter catalyst of Example 1 is higher than that of Comparative Example 1, it is clear that the bending strength is increased by forming the catalyst layer, and there is no problem in use.

  Further, even when Example 2 and Comparative Example 2 having a thick catalyst layer are compared, the filter catalyst of Example 2 has a lower pressure loss and a higher soot oxidation rate than the filter catalyst of Comparative Example 2. This is clearly the effect of forming the recess 13.

The filter catalysts of Examples 2 to 3 show higher NO _x purification performance than the filter catalyst of Comparative Example 3, which is an effect due to the area and volume of the catalyst layer being increased by the recess 13. Further, the filter catalyst of Example 3 has a lower pressure loss than the filter catalyst of Example 2. This is because the amount of the catalyst layer of the filter partition 12 is smaller in Example 3 than in Example 2, but the soot oxidation rate is improved as compared with the filter catalyst of Example 2. It can be seen that the thick catalyst layer formed in the recess 13 compensates for the performance degradation due to the small amount of the 12 catalyst layers. It can also be seen that the bending strength is further increased by further thickening the catalyst layer of the recess 13.

  The exhaust gas purification filter and exhaust gas purification catalyst of the present invention are particularly effective when a honeycomb substrate having a wall flow structure is used. However, even if the honeycomb substrate has a streroflow structure, the present invention can be used as long as the cell wall having a high porosity is used for the reaction field.

  Furthermore, even in a normal honeycomb substrate, if the present invention is used to prevent the coating layer from becoming thick at the corners of the cell lattice, pressure loss can be reduced and purification performance can be improved while ensuring strength. .

It is a perspective view of the catalyst for exhaust gas purification (filter catalyst) of one Example of this invention. It is explanatory drawing shown in the cross section equivalent to the AA cross section of FIG. 1 which shows the method to manufacture the exhaust gas purification catalyst (filter catalyst) of one Example of this invention. It is sectional drawing which shows the catalyst for exhaust gas purification (filter catalyst) of the 3rd Example of this invention, and corresponds to the AA cross section of FIG.

Explanation of symbols

1: Filter catalyst 2: Catalyst layer 3: Second coat layer
10: Inflow side cell 11: Outflow side cell 12: Filter partition
13: Recess 20: First coat layer

Claims (6)

An exhaust gas purification filter for purifying exhaust gas containing particulates discharged from an internal combustion engine,
An exhaust gas purification filter comprising a honeycomb base material having a large number of cells partitioned by porous filter partition walls, wherein at least one corner portion of at least one of the cells has a recess extending in the axial direction.   The cell includes an inflow side cell clogged on the exhaust gas downstream side, and an outflow side cell clogged on the exhaust gas upstream side adjacent to the inflow side cell, and the recess includes at least the inflow side cell. The exhaust gas purification filter according to claim 1, wherein the exhaust gas purification filter is formed in at least one corner portion.   The exhaust gas purifying filter according to claim 2, wherein the concave portion is provided in at least the inflow side cell in the outer peripheral portion.   A catalyst for exhaust gas purification comprising the exhaust gas purification filter according to any one of claims 1 to 3, and a catalyst layer formed by supporting a catalyst metal on a porous oxide and formed on the filter partition wall. . The exhaust gas purifying catalyst according to claim 4, wherein a precious metal and a NO _x storage material are supported on the catalyst layer.   6. The exhaust gas purifying catalyst according to claim 4, wherein the catalyst layer has a thickness of a portion of the recessed portion larger than a thickness of a portion other than the recessed portion.

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