JP2015009163A - Exhaust gas purification catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification catalyst capable of suppressing deterioration of catalyst performance.SOLUTION: An exhaust gas purification catalyst includes a carrier having a through hole 3 penetrating in an axial direction of the carrier, and a catalyst layer 11 comprising a catalyst metal and a refractory inorganic oxide and formed on the inner surface of the through hole 3. The catalyst layer 11 formed on the inner surface of the through hole 3 includes a first region 11a, a second region 11b, and a third region 11c in this order from the upstream side of an exhaust gas flow direction 9. The first and second regions 11a, 11b each contain as the catalyst metal a catalyst component selected from the group consisting of palladium, platinum, and rhodium. A ratio of the density of the catalyst component in the first region 11a to the density of the catalyst component in the second region 11b is in a range from 1:2 to 1:30.

Description

  The present invention relates to an exhaust gas purifying catalyst that removes harmful components contained in exhaust gas from internal combustion engines such as automobiles and motorcycles.

  Conventionally, many catalysts for purifying exhaust gas discharged from an internal combustion engine such as an automobile have been proposed. Currently, three-way catalysts that simultaneously purify HC, CO, and NOx have become mainstream (see Patent Documents 1 to 3). ).

  As the above-mentioned three-way catalyst, catalyst components such as palladium (Pd), platinum (Pt) and rhodium (Rh) are singly or in combination and dispersed in a refractory inorganic compound powder such as alumina and ceria-zirconia. Some of these catalyst compositions were coated on a honeycomb carrier made of cordierite or metal.

  Further, as a three-way catalyst, a cordierite or metal honeycomb support is coated with a refractory inorganic oxide such as alumina or ceria-zirconia, and then the support is coated with a catalyst component such as Pt, Pd, or Rh. It is known that these catalyst components are supported by immersing them alone or in a slurry containing a combination thereof.

  In addition, in order to efficiently treat exhaust gas when the engine is cold-started, a technique of highly supporting a catalyst noble metal at the upstream end of the gas flow has been proposed (see Patent Document 4).

Japanese Patent Laid-Open No. 3-196841 Japanese Patent Laid-Open No. 5-23593 JP 2001-259424 A JP 2001-162166 A

  The exhaust gas purification catalyst gradually deteriorates due to heat and poisoning substances. As a result, for example, there is a possibility that a desired exhaust gas purification performance cannot be obtained after long-term use. It is conceivable to increase the initial function by predicting deterioration, but in that case, it is necessary to carry a large amount of expensive Pt, Pd, and Rh in advance.

  An object of the present invention is to provide an exhaust gas purifying catalyst capable of suppressing a decrease in catalyst performance.

  The invention according to claim 1, which has been made to solve the above-described problem, includes a support having a through hole penetrating in the axial direction, a catalyst metal, and a refractory inorganic oxide, and is formed on the inner surface of the through hole. And an exhaust gas purification catalyst that forms a flow path of exhaust gas by the through hole, and further has the following characteristics.

  The catalyst layer of the exhaust gas purifying catalyst has a first region, a second region, and a third region in order from the upstream side in the exhaust gas flow direction. At least the first region and the second region contain a catalyst component selected from the group consisting of palladium, platinum, and rhodium as the catalyst metal, and the density of the catalyst component in the first region and the second region The ratio of the catalyst component to the density of the catalyst is 1: 2 to 1:30. As the density, for example, an average value of each region can be used.

Further, the density of the catalyst component in the third region is configured to be smaller than the density of the catalyst component in the second region.
Normally, the exhaust gas purification catalyst is more likely to be deteriorated by heat and poisonous substances as it is closer to the upstream end of the exhaust gas flow path. In the exhaust gas purifying catalyst of the present invention described above, at least one of the catalyst components of Pt, Pd, and Rh is supported at a high density in the second region spaced from the upstream end of the exhaust gas flow path. It is possible to suppress degradation in catalyst performance due to heat of catalyst components and poisonous substances.

  In the exhaust gas purifying catalyst of the present invention, the catalyst component is also contained in the first region. It is considered that thermal stress and poisoning occur in the first region due to the occurrence of a catalytic reaction, thereby suppressing the thermal stress and poisoning in the second region and suppressing the catalyst performance degradation in the second region.

  The third region may contain the catalyst component, but may not contain it. Further, the first to third regions do not need to be adjacent to each other, and may have an interval. For example, a region having the catalyst component may exist between the first region and the second region at a density between the regions.

  The above-described deterioration in catalyst performance is particularly remarkable in the region from the end of the exhaust gas flow upstream side to 10 mm. Therefore, you may comprise the 2nd area | region mentioned above so that it may exist in a downstream rather than the position of 10 mm downstream from the upstream edge part of a through-hole. By comprising in this way, the fall of catalyst performance can be suppressed highly.

  Since the catalytic performance increases as the portion where the catalyst metal is highly loaded is closer to the upstream end, the second region may be located in a range from the upstream end to a position 50 mm downstream. Good. Considering these, it is conceivable that the second region is configured to exist within a range of 10 mm to 50 mm from the upstream end.

  The density ratio of at least one of the catalyst components of Pt, Pd, and Rh in the first region and the second region is desired to be in a range where both the catalyst performance and the deterioration resistance can be obtained satisfactorily. . The catalyst by which the catalyst performance of the 1st field falls by making the density of the 1st field relatively low so that the ratio of the density of the 1st field and the 2nd field mentioned above may become lower than 1: 2. A decrease in the catalyst performance as a whole can be satisfactorily suppressed.

  On the other hand, by relatively increasing the density of the first region so that the above-mentioned ratio is higher than 1:30, the catalytic reaction in the first region can be efficiently caused particularly at the time of cold start. The catalyst performance as a whole of the catalyst can be increased, and the effect of suppressing the decrease in the catalyst performance in the second region can be sufficiently exhibited. Therefore, the ratio described above is preferably 1: 2 to 1:30.

  Moreover, by making the ratio of the catalyst component in the first region lower than 1: 5, it is possible to suppress the deterioration of the catalyst performance to a higher degree, and by making the ratio higher than 1:21, the catalyst performance is improved. Can be high.

The second region may be configured to have a length of 10 mm to 30 mm in the axial direction of the support in order to sufficiently function the catalytic reaction in the region.
By the way, palladium may be selected as the catalyst component. In the exhaust gas purifying catalyst configured as described above, the exhaust gas purifying performance particularly when the engine is cold-started can be made excellent.

It is an expansion schematic diagram of the surface part of the through-hole cross section of the catalyst for exhaust gas purification. It is a graph which shows the comparison of WU-T50 before and after the durability test of Example 2 and Comparative Example 1, and the deterioration rate after durability. It is a graph which shows WU-T50 after the endurance test of Examples 1-9 and Comparative Examples 1 and 2. It is a graph which shows the emission measurement result of Example 2 and Comparative Example 1.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, this invention is not limited to the following embodiment at all, and it cannot be overemphasized that various forms may be taken as long as it belongs to the technical scope of this invention.

  An exhaust gas purifying catalyst according to an embodiment of the present invention includes a support having a through hole penetrating in the axial direction, and a catalyst layer including a catalytic metal and a refractory inorganic oxide and formed on the inner surface of the through hole. Have.

  The carrier is not particularly limited as long as it is generally used as an exhaust gas purification catalyst, and examples thereof include a honeycomb type, a corrugated type, and a monolith honeycomb type. The material of the carrier may be any material as long as it has fire resistance. For example, a monolithic structure type made of ceramics such as cordierite or a metal such as ferrite-based stainless steel can be used. .

  Examples of the refractory inorganic oxide include alumina (particularly activated alumina), Zr oxide, Ce oxide, ZrCe composite oxide, silica, titania and the like. It is conceivable that the amount of the refractory inorganic oxide is, for example, 100 to 300 g per liter of the catalyst.

  FIG. 1 is a diagram schematically showing an enlarged surface portion of a cross section of a through hole of an exhaust gas purifying catalyst. In the through hole 3 provided in the carrier 1, the left end in FIG. 1 is the upstream end 5, and the right end is the downstream end 7. The axial direction is the left-right direction in FIG. The exhaust gas enters the through hole 3 from the upstream end 5, passes through the through hole 3, and exits to the outside from the downstream end 7.

Therefore, the through hole 3 shown in FIG. 1 forms an exhaust gas flow path, and the direction from left to right is the exhaust gas flow direction 9. A number of through holes 3 are formed in the carrier 1 in parallel with each other.
The catalyst layer 11 formed on the inner surface of the through hole 3 has a first region 11a, a second region 11b, and a third region 11c in order from the upstream side in the flow direction 9 of the exhaust gas.

  The first region 11a may be on the upstream side of the second region 11b, but may be a region including the upstream end 5 serving as an exhaust gas inlet in the through hole 3. Moreover, although the said 3rd area | region 11c should just be downstream from the 2nd area | region 11b, the area | region including the downstream edge part 7 used as the exit of waste gas in the through-hole 3 may be sufficient.

The catalyst layer 11 can adjust the kind or metal concentration of the metal supported in each of the first to third regions, and is configured to satisfy the following conditions.
At least the first region 11a and the second region 11b include a catalyst component selected from the group consisting of palladium (Pd), platinum (Pt), and rhodium (Rh) as the catalyst metal. At this time, the ratio of the density of the catalyst component in the first region 11a and the second region 11b is in the range of 1: 2 to 1:30.

  By adjusting the region where the catalyst component is supported in this way, for example, compared with the case where the catalyst component is highly supported at a position adjacent to the upstream end 5, the catalyst performance of the same amount is used. It is possible to manufacture an exhaust gas purifying catalyst with improved durability while suppressing the decrease of the above.

  Further, by reducing the density of the catalyst component to be supported in the third region as much as possible and forming the catalyst component high-loading region on the upstream side as much as possible, it is possible to improve the catalyst performance especially during cold start.

  Furthermore, by making the ratio of the catalyst components in the first region 11a lower than 1: 5, it is possible to suppress the deterioration of the catalyst performance to a higher degree, and by making the ratio higher than 1:21, the catalyst performance can be reduced. Can be high.

  The density of the catalyst component in the 3rd area | region 11c should just be smaller than the density of the catalyst component in the 2nd area | region 11b. The third region 11c may be configured not to include Pd, Pt, and Rh.

  The first to third regions may be configured to form the entire catalyst layer 11 alone, but the first region is between the regions, upstream of the first region 11a and downstream of the third region 11c. A region having a different kind of metal or metal concentration from the third region may be formed.

  In the exhaust gas purifying catalyst of FIG. 1, the configuration in which the first to third regions are formed in the through holes 3 provided in one carrier 1 is illustrated. However, the exhaust gas purifying catalyst of the present invention may be composed of two or more (or three or more) carriers, and the exhaust gas flow path may be formed by combining through holes provided in these carriers.

  In this case, the first region can be provided in the through hole of a certain carrier, the second region can be provided in the through hole of another carrier, and the third region can be provided in another carrier. And the support | carrier provided with the 1st area | region, the support | carrier provided with the 2nd area | region, and the support | carrier provided with the 3rd area | region can be arrange | positioned along the flow direction of waste gas.

The length of the carrier 1 in the axial direction is not particularly defined, and can be widely applied to exhaust gas purification catalyst carriers for general vehicles including large vehicles, small vehicles, motorcycles, and the like.
Further, the length in the axial direction of the first to third regions is not particularly specified. If the length of the carrier 1 is short, it is necessary to shorten it, but each region may have a length of at least about 5 mm in the axial direction.

  The catalyst layer 11 may be configured by stacking two or more different metal species, or may have a single layer configuration. That is, various forms can be employed as long as the second region 11b in which any of noble metals of Pd, Pt, and Rh is highly supported is provided.

  The catalyst layer 11 may contain an alkaline earth metal compound. Further, lanthanum (La), yttrium (Y), neodymium (Nd), praseodymium (Pr), or the like may be contained.

  Examples of the exhaust gas purifying catalyst will be described below. In addition, although manufacture and a test are performed for palladium in the following examples, since platinum and rhodium have similar tendency to decrease in performance due to heat and poisoning, similar results can be obtained. Of course, the present invention can also be applied when a plurality of these metals are used at the same time.

<Example>
Examples of the present invention will be described below.
[Example 1]
A slurry 1 was prepared by mixing a Pd nitrate solution (1 g in terms of Pd content), alumina 95 g, 10 wt% alumina sol 50 g, ZrCe composite oxide 50 g, barium compound 10 g, and water 100 g.

A slurry 2 was prepared by mixing a Rh nitrate solution (0.2 g in Rh), 50 g of ZrCe composite oxide, 45 g of alumina, 50 g of 10 wt% alumina sol, and 100 g of water.
161 g of slurry 1 was coated on a monolith honeycomb carrier (volume of the whole carrier including through-holes 1 L, total length 100 mm) in terms of solid amount, dried at 250 ° C. for 1 hour, and then fired at 500 ° C. for 1 hour. Further, 100.2 g of the slurry 2 was coated in terms of solid amount, dried at 250 ° C. for 1 hour, and then fired at 500 ° C. for 1 hour. The catalyst prepared here is hereinafter referred to as a base catalyst.

  Next, a PVA (polyvinyl alcohol) resin coat is applied to the base catalyst in a range of 10 mm from the upstream end of the gas flow, and then Pd is absorbed by a water absorption method using a Pd nitrate solution in a range of 30 mm from the end. After coating and drying at 250 ° C. for 1 hour, baking was performed at 500 ° C. for 1 hour. Pd application from the end to 10 mm was suppressed by the PVA resin coat, and the PVA resin coat was removed by baking.

  Through the above steps, an exhaust gas purifying catalyst was prepared in which a Pd high support portion having a Pd density of 10 g / L (2 g in terms of Pd content) was formed between 10 mm and 30 mm from the end face. In addition, the catalyst layer of the area | region whose distance from an upstream edge part which has this Pd high carrying | support part is 10 mm-30 mm respond | corresponds to the 2nd area | region of the catalyst layer in this invention.

In this embodiment, Pd is applied by the water absorption method, but it is possible to support Pd on the carrier by various methods such as a coating method and an impregnation supporting method.
[Example 2]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in a range from the end face on the gas flow upstream side to 15 mm part, and Pd is applied to 35 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification in which a Pd high support portion having a Pd density of 10 g / L (2 g of Pd) is formed between 15 mm and 35 mm from the end face after being dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour. Was prepared.

[Example 3]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in the range from the end face on the gas flow upstream side to 20 mm part, and Pd is applied to 40 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification in which a Pd high support portion having a Pd density of 10 g / L (2 g of Pd) is formed between 20 mm and 40 mm from the end face after being dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour. Was prepared.

[Example 4]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in a range from the end face on the gas flow upstream side to 30 mm part, and Pd is applied to 50 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification, which is dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to form a Pd high support portion having a Pd density of 10 g / L (2 g of Pd) between 30 mm and 50 mm from the end face. Was prepared.

[Example 5]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in the range from the end face on the gas flow upstream side to 40 mm part, and Pd is applied to 60 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification, which is dried at 250 ° C. for 1 hour, calcined at 500 ° C. for 1 hour, and a Pd high support portion having a Pd density of 10 g / L (2 g of Pd) is formed between 40 mm and 60 mm from the end face Was prepared.

[Example 6]
In the preparation method according to Example 1, a PVA resin coat was applied to the base catalyst in the range from the end face on the upstream side of the gas flow to 15 mm part, and Pd was applied to 22.5 mm part by a water absorption method using a Pd nitrate solution. Then, after drying at 250 ° C. for 1 hour, baking is performed at 500 ° C. for 1 hour, and a Pd high support portion having a Pd density of 20 g / L (2 g of Pd) is formed between 15 mm and 22.5 mm from the end face. An exhaust gas purification catalyst was prepared.

[Example 7]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in a range from the end face on the gas flow upstream side to 15 mm part, and Pd is applied to 25 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification in which a Pd high support portion having a Pd density of 20 g / L (2 g of Pd) is formed between 15 mm and 25 mm from the end face after being dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour. Was prepared.

[Example 8]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in a range from the end face on the gas flow upstream side to 15 mm part, and Pd is applied to 45 mm part by a water absorption method using a Pd nitrate solution, Exhaust gas purification in which Pd density 6.67 g / L (2 Pd at Pd) is formed between 15 mm and 45 mm from the end face after drying at 250 ° C. for 1 hour and then firing at 500 ° C. for 1 hour A catalyst was prepared.

[Example 9]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in the range from the end face on the gas flow upstream side to 15 mm part, and Pd is applied to 55 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification, which is dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to form a Pd high support portion having a Pd density of 5 g / L (2 g of Pd) between 15 mm and 55 mm from the end face. Was prepared.

[Comparative Example 1]
Except for applying the PVA resin coat, Pd was applied to the base catalyst in a range from the upstream end to 20 mm by a water absorption method using a Pd nitrate solution at 250 ° C. After drying for 1 hour, an exhaust gas purifying catalyst was prepared by calcining at 500 ° C. for 1 hour to form a Pd high supporting part having a Pd density of 10 g / L (2 g of Pd) between 20 mm parts from the end face.

[Comparative Example 2]
In the preparation method according to Example 1, a PVA resin coat is applied to the base catalyst in a range from the end face on the gas flow upstream side to 15 mm part, and Pd is applied to 20 mm part by a water absorption method using a Pd nitrate solution, A catalyst for exhaust gas purification, which is dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to form a Pd high support portion with a Pd density of 40 g / L (2 g of Pd) between 15 mm and 20 mm from the end face. Was prepared.

  Table 1 shows the structure of the high Pd support portion in the exhaust gas purifying catalysts of Examples 1 to 9 and Comparative Examples 1 and 2 described above.

<Evaluation>
The exhaust gas purification catalyst produced in Examples 1-9 and Comparative Example 1 was attached to a gasoline engine with a displacement of 4000 cc, and a 50 hour durability test was performed at an average engine speed of 3500 rpm and a catalyst bed peak temperature of 1000 ° C. went. Thereafter, an evaluation test was performed.

(1) Engine bench evaluation Each exhaust gas purification catalyst after an endurance test is attached to a gasoline engine with a displacement of 2400 cc, and the exhaust gas is circulated through the catalyst attached to the exhaust gas passage by operating at an average engine speed of 2400 rpm. The emission purification rates of CO and NOx were measured, and the time (WU-T50, hereinafter also referred to as WU (s)) at which the purification rate was 50% from the start of exhaust gas flow to the catalyst was obtained.

FIG. 2 is a graph showing the comparison of WU-T50 before and after the durability test between Example 2 and Comparative Example 1 and the deterioration rate after durability. The deterioration rate after durability was calculated as follows.
Deterioration rate after endurance (%) = (WU (s) after endurance test−initial WU (s)) / initial WU (s) × 100
As can be seen from FIG. 2, the result of Comparative Example 1 was better before the endurance test (the purification rate reached 50% earlier), but the result of Example 2 was better after the endurance test. It became.

  That is, as in Comparative Example 1, when the high Pd carrying portion is at the end on the upstream side of the exhaust gas flow, good results can be obtained in the initial stage (before the durability test), but the degree of reduction in catalyst performance due to use can be obtained. I understand that it is expensive. In Comparative Example 1, the deterioration rate after durability was 100%, but in Example 2, the deterioration rate decreased to about 42%. That is, by providing the high Pd support portion on the downstream side, it was possible to suppress a decrease in catalyst performance.

  Table 2 shows a list of WU-T50 comparisons before and after the durability test on the exhaust gas purifying catalysts of Examples 1 to 9 and Comparative Examples 1 and 2 and a deterioration rate after durability. The deterioration rate after durability could be suppressed to a deterioration rate of 90% or less in all of Examples 1 to 9. Therefore, it can be said that Examples 1-9 are superior to Comparative Examples 1 and 2 in which the deterioration rate exceeded 100% in that the catalyst performance can be ensured over a long period of time.

  In Examples 1 to 9, when the ratio of the density of the first region (upstream from the Pd high carrying portion) and the second region (Pd high carrying portion) is between 1: 6 and 1: 27.7. In addition, it was possible to suppress the deterioration of the catalyst performance satisfactorily. Therefore, a decrease in catalyst performance can be suppressed by adjusting the loading balance so as to increase the Pd density in the second region at such a ratio.

  In addition, if the density ratio is within a range in which the density of the first region is relatively lower than 1: 2, a decrease in the performance of the entire catalyst due to a decrease in performance after use of the first region can be suppressed. As is clear from the results of the examples, the effect is particularly remarkable in the range where the density of the first region is smaller than 1: 5.

  Further, if the density ratio of the first region is higher than 1:30, the catalyst performance in the first region can be improved as a whole without reducing the catalyst performance in the first region. High performance reduction in catalyst performance. Further, as is clear from each example, the durability deterioration rate can be reduced to 73% or less in a range where the density of the first region is larger than 1:21, and the effect is particularly remarkable.

  3A and 3B show the measurement results of Examples 1 to 9 and Comparative Example 1 after the durability test. As for the exhaust gas purifying catalysts of Examples 1 to 4 and 7 to 9, as compared with Comparative Example 1, the good result that the purification rate reaches 50% at an early stage even though the supported amount of Pd is the same amount. Got. That is, in the above Examples 1 to 4 and 7 to 9, it was possible to suppress the deterioration of the catalyst performance and maintain the catalyst performance higher than the conventional after the endurance.

  In the exhaust gas purifying catalysts of Examples 1 to 5 shown in FIG. 3A, the axial length of the Pd high support portion is the same, and the positions thereof are different. Since good results were obtained in Examples 1 to 4, when the Pd high carrying portion is in the range of 10 to 50 mm from the upstream end, the Pd high carrying portion is at the upstream end ( It can be seen that good results can be obtained compared to Comparative Example 1). In particular, it can be said that good results can be obtained when it is in the range of 10 to 40 mm.

  Further, in the exhaust gas purifying catalysts of Examples 2 and 6 to 9 shown in FIG. 3B, the upstream position of the high Pd support portion is 15 mm from the upstream end portion, and the axial lengths thereof are different. It is. From this comparison, it can be seen that particularly good results can be obtained when the axial length is 10 mm or more. From the test results, it can be seen that good results can be obtained if it is 40 mm or less. However, in consideration of noble metal loading in a region other than the Pd high carrying portion, the Pd high carrying portion should be 30 mm or less, so that upstream and downstream A sufficient area can be secured.

(2) Vehicle Evaluation In both cases, the exhaust gas purifying catalyst of Example 2 and Comparative Example 1 after the durability test was attached to a vehicle equipped with a gasoline engine with a displacement of 2200 cc, and the FTP75 (Federal Test Procedure 75) test mode (http: / /www.epa.gov/nvfel/methods/ftpdds.gif) and measured emissions of HC, CO, and NOx.

  The measurement results are shown in the graph of FIG. The graph of Example 2 is a relative value when the emission of Comparative Example 1 is 100%. Emissions decreased for all of HC, CO, and NOx.

  Thus, although the exhaust gas purifying catalyst of Example 2 was inferior to the comparative example 1 in the catalyst performance before the durability test, the catalyst performance after the durability test was suppressed by suppressing the decrease in the catalyst performance due to the durability test. Was higher than that of Comparative Example 1.

DESCRIPTION OF SYMBOLS 1 ... Support | carrier, 3 ... Through-hole, 5 ... Upstream side edge part, 7 ... Downstream side edge part, 11 ... Catalyst layer, 11 ... 1st area | region, 11a ... 1st area | region, 11b ... 2nd area | region, 11c ... 3rd region.

Claims (5)

A carrier having a through-hole penetrating in the axial direction;
A catalyst layer containing a catalyst metal and a refractory inorganic oxide, and formed on the inner surface of the through hole;
An exhaust gas purifying catalyst that forms an exhaust gas flow path by the through-hole,
The catalyst layer has a first region, a second region, and a third region in order from the upstream side in the exhaust gas flow direction,
At least the first region and the second region include a catalyst component selected from the group consisting of palladium, platinum, and rhodium as the catalyst metal,
The ratio of the density of the catalyst component in the first region to the density of the catalyst component in the second region is 1: 2 to 1:30;
The exhaust gas purifying catalyst, wherein a density of the catalyst component in the third region is smaller than a density of the catalyst component in the second region. 2. The exhaust gas purifying catalyst according to claim 1, wherein the second region is present downstream of a position 10 mm downstream from the upstream end of the through hole. The exhaust gas purification catalyst according to claim 1 or 2, wherein the second region has a length of 10 mm to 30 mm in the axial direction. The ratio between the density of the catalyst component in the first region and the density of the catalyst component in the second region is 1: 5 to 1:21. The exhaust gas purifying catalyst according to claim 1. The exhaust gas purification catalyst according to any one of claims 1 to 4, wherein the catalyst component is palladium.