WO2020110379A1

WO2020110379A1 - Exhaust gas cleaning catalyst and production method therefor

Info

Publication number: WO2020110379A1
Application number: PCT/JP2019/032177
Authority: WO
Inventors: 万陽城取; 禎憲高橋
Original assignee: エヌ・イーケムキャット株式会社
Priority date: 2018-11-28
Filing date: 2019-08-16
Publication date: 2020-06-04
Also published as: CN112512687B; JPWO2020110379A1; JP7319293B2; CN112512687A

Abstract

The invention is an exhaust gas cleaning catalyst for cleaning exhaust gas discharged from an internal combustion engine, comprising: a wall-flow type substrate having, delineated by a porous partition wall, an introduction side cell, the end portion on the exhaust gas introduction side of which is open, and adjacent to the introduction side cell, a discharge side cell, the end portion on the exhaust gas discharge side of which is open; and a catalyst layer formed within the partition wall. The catalyst layer comprises a first region formed so as to follow the direction in which the partition wall extends from the end portion of the exhaust gas introduction side, a second region formed so as to follow the direction in which the partition wall extends from the end portion of the exhaust gas discharge side, and a third region wherein the first region and the second region overlap with one another. The ratio (D_in/D_mid), of the pore diameter D_in calculated from the pore distribution in the first region, over the pore diameter D_mid calculated from the pore distribution in the third region, is 1.2 or higher. The ratio (D_out/D_mid), of the pore diameter D_out calculated from the pore distribution in the second region, over the pore diameter D_mid, is 1.2 or higher.

Description

Exhaust gas purifying catalyst and manufacturing method thereof

The present invention relates to an exhaust gas purifying catalyst and a method for manufacturing the same.

Exhaust gas emitted from an internal combustion engine contains particulate matter (PM) containing carbon as the main component, ash containing non-combustible components, etc., and is known to cause air pollution. Conventionally, the emission of particulate matter has been strictly regulated in diesel engines, which are relatively easier to emit particulate matter than in gasoline engines, but in recent years, emission regulations of particulate matter have also been regulated in gasoline engines. It is being strengthened.

As a means to reduce the emission of particulate matter, a method of providing a particulate filter for depositing and collecting particulate matter in the exhaust gas passage of an internal combustion engine is known. Particularly in recent years, from the viewpoint of space saving of mounting space, etc., it is necessary to suppress emission of particulate matter and remove harmful components such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). In order to carry out at the same time, it has been considered to apply a catalyst slurry to a particulate filter and fire this to provide a catalyst layer.

An introduction-side cell whose end on the exhaust-gas introduction side is open, and a discharge-side cell which is adjacent to the introduction-side cell and whose end on the exhaust-gas discharge side is open are wall-flow-type substrates defined by porous partition walls. As for the method of forming such a catalyst layer with respect to the particulate filter provided, the properties such as the viscosity and the solid content of the slurry are adjusted, and one of the introduction side cell or the discharge side cell is pressurized to introduce the introduction side cell. There is known a method of adjusting the permeation of the catalyst slurry into the partition wall by creating a pressure difference between the cell and the discharge side cell (see, for example, Patent Document 1).

WO2016/060048

The particulate filter as described in Patent Document 1 has a wall flow type structure from the viewpoint of removing particulate matter, and exhaust gas is configured to pass through the pores of the partition wall. However, there is still room for improvement in soot collection performance, pressure loss, and exhaust gas purification performance.

The present invention has been made in view of the above problems, and an object thereof is to provide an exhaust gas purifying catalyst having improved NOx purification performance and a method for producing the same. It should be noted that the present invention is not limited to the purpose described here, and it is also possible to achieve the operational effects that are obtained by the respective configurations shown in the modes for carrying out the invention to be described later and are not obtained by the conventional technology. It can be positioned as another purpose.

The inventors of the present invention have earnestly studied how to improve the purification performance. As a result, they have found that the above problems can be solved by adjusting the pore size in the stretching direction of the partition walls on which the catalyst layer is formed, and have completed the present invention. That is, the present invention provides various specific embodiments shown below.

[1]
An exhaust gas purification catalyst for purifying exhaust gas emitted from an internal combustion engine,
An introduction-side cell having an open end on the exhaust-gas introduction side, and a discharge-side cell adjacent to the introduction-side cell and having an end on the exhaust-gas discharge side opened, and a wall-flow type substrate defined by a porous partition wall. ,
A catalyst layer formed in the partition wall,
A first region in which the catalyst layer is formed from an end portion on the exhaust gas introduction side along the extending direction of the partition wall, and a second region formed from an end portion on the exhaust gas discharge side along the extending direction of the partition wall. An area and a third area in which the first area and the second area overlap,
The ratio (D _in /D _mid ) of the pore diameter D _in calculated from the pore distribution of the first area to the pore diameter D _mid calculated from the pore distribution of the third area is 1.2 or more. ,
Wherein the ratio of the pore diameter _{D out} which is calculated from the pore distribution of the second region with respect to the pore diameter _{_{_{D mid (D out / D mid}}} ) it is 1.2 or more,
Exhaust gas purification catalyst.
[2]
Ratio (V _in) of pore volume V _in having a pore diameter of 1 μm or more calculated from the pore distribution of the first area to pore volume V _{mid having} a pore diameter of 1 μm or more calculated from the pore distribution of the third area /V _mid ) is 1.3 or more,
The ratio (V _out /V _mid ) of the pore volume V _out having a pore diameter of 1 μm or more calculated from the pore distribution of the second region with respect to the pore volume V _mid is 1.3 or more.
The exhaust gas purifying catalyst according to [1].
[3]
The difference between the pore diameter D _in or the pore diameter D _out and the pore diameter D _mid is 2.5 to 10 μm, respectively.
The exhaust gas purification catalyst according to [1] or [2].
[4]
The first region contains Pd,
The exhaust gas purifying catalyst according to any one of [1] to [3].
[5]
The second region includes Rh,
The exhaust gas purifying catalyst according to [4].
[6]
The first region includes Rh,
The exhaust gas purifying catalyst according to any one of [1] to [3].
[7]
The second region contains Pd,
The exhaust gas purifying catalyst according to [6].
[8]
The catalyst layer is formed in the thickness direction of the partition wall from the cell wall surface on the introduction side cell side to the cell wall surface on the discharge side cell side,
The exhaust gas purifying catalyst according to any one of [1] to [7].
[9]
The formation range of the third region is 2 to 20% with respect to 100% of the total length of the partition wall in the stretching direction.
The exhaust gas purifying catalyst according to any one of [1] to [8].
[10]
The internal combustion engine is a gasoline engine,
The exhaust gas purifying catalyst according to any one of [1] to [9].
[11]
A method for producing an exhaust gas purifying catalyst for purifying exhaust gas emitted from an internal combustion engine,
An introduction-side cell whose end on the exhaust-gas introduction side is open, and a discharge-side cell which is adjacent to the introduction-side cell and whose end on the exhaust-gas discharge side is open are wall-flow-type base materials defined by porous partition walls. The process of preparing,
At least a part of the pore surface in the partition wall of the wall flow type substrate, a catalyst layer is applied by applying a catalyst slurry, and a catalyst layer forming step,
In the catalyst layer forming step,
A first region formed along the extending direction of the partition wall from the exhaust gas introduction side end, a second region formed along the extending direction of the partition wall from the exhaust gas discharge side end, A pore size calculated from the pore distribution of the first region with respect to a pore size D _mid calculated from the pore distribution of the third region, having a third region in which one region and the second region overlap. D _in the ratio of _{_(D} in _/ D _mid) is, is 1.2 or more, the ratio of the pore diameter _{D out} which is calculated from the pore distribution of the second region with respect to the pore diameter _{_{D mid} _(D} out _/ _{D mid} ) Is for producing the exhaust gas purifying catalyst having the catalyst layer of 1.2 or more,
Method for manufacturing exhaust gas purifying catalyst.

According to the present invention, it is possible to provide an exhaust gas purification catalyst with improved NOx purification performance and a method for producing the same. The exhaust gas purifying catalyst can be effectively used as a gasoline particulate filter (GPF) carrying a catalyst, and an exhaust gas treatment system equipped with such a particulate filter can be further improved in performance.

It is sectional drawing which shows typically the one aspect|mode of the exhaust gas purification catalyst of this embodiment. 5 is a graph showing NOx purification performance in Examples and Comparative Examples. It is a figure which shows the balance of NOx purification performance and a soot collection rate in an Example and a comparative example.

Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited thereto. Further, the present invention can be implemented by being arbitrarily modified within the scope of the invention. In addition, in this specification, the positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. In the present specification, the “pore diameter” refers to a diameter (mode diameter: maximum value of distribution) having the largest appearance ratio in the frequency distribution of pore diameters (hereinafter, also referred to as pore distribution). In addition, in the present specification, when a numerical value or a physical property value is sandwiched before and after by using "to", it is used as including values before and after that. For example, the notation of a numerical range of “1 to 100” includes both the lower limit value “1” and the upper limit value “100”. The same applies to other numerical ranges.

[Exhaust gas purification catalyst]
The exhaust gas purifying catalyst of the present embodiment is an exhaust gas purifying catalyst 100 that purifies exhaust gas discharged from an internal combustion engine, and is adjacent to the introduction side cell 11 in which an end portion 11a on the exhaust gas introduction side is opened and the introduction side cell. The discharge side cell 12 having an open end 12a on the exhaust gas discharge side has a wall flow type base material 10 defined by a porous partition wall 13, and a catalyst layer 21 formed in the partition wall 13. A first region in which the catalyst layer is formed along an extending direction of the partition wall from an end portion on the exhaust gas introduction side, and a second region formed along an extending direction of the partition wall from an end portion on the exhaust gas discharge side. An area and a third area where the first area and the second area overlap, and from the pore distribution of the first area with respect to the pore diameter D _mid calculated from the pore distribution of the third area, The ratio (D _in /D _mid ) of the calculated pore diameter D _in is 1.2 or more, and the ratio of the pore diameter D _out calculated from the pore distribution of the second region to the pore diameter D _mid ( D _out /D _mid ) is 1.2 or more.

Hereinafter, each configuration will be described with reference to the cross-sectional view schematically showing the exhaust gas purification catalyst of the present embodiment shown in FIG. The exhaust gas purification catalyst of this embodiment has a wall flow type structure. In the exhaust gas purifying catalyst 100 having such a structure, the exhaust gas discharged from the internal combustion engine flows into the introduction side cell 11 from the exhaust gas introduction side end 11a (opening) and passes through the pores of the partition wall 13. Flow into the adjacent discharge side cells 12, and flow out from the exhaust gas discharge side end 12a (opening). In this process, the particulate matter (PM) that is difficult to pass through the pores of the partition wall 13 is generally deposited on the partition wall 13 in the introduction side cell 11 and/or in the pores of the partition wall 13, and the deposited particulate matter is Depending on the catalytic function of the catalyst layer 21, or by burning at a predetermined temperature (for example, about 500 to 700° C.), it is removed. Further, the exhaust gas comes into contact with the catalyst layer 21 formed in the pores of the partition wall 13, whereby carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas are converted into water (H ₂ O) and carbon dioxide ( CO ₂ ), etc., nitrogen oxides (NOx) are reduced to nitrogen (N ₂ ), and harmful components are purified (detoxified). In the present specification, removal of particulate matter and purification of harmful components such as carbon monoxide (CO) are collectively referred to as “exhaust gas purification performance”. Hereinafter, each configuration will be described in more detail.

(Pore size)
By making a difference in the pore diameter in the stretching direction of the partition wall, a portion where the exhaust gas flows easily and a portion where the exhaust gas does not flow easily occur, and the flow of the exhaust gas can be controlled. As a result, the exhaust gas passing through the exhaust gas purification catalyst can be brought into contact with the catalyst more effectively, and it is expected that the exhaust gas purification performance and the soot collection performance are improved. The exhaust gas purifying catalyst of the present embodiment controls the flow of exhaust gas to improve the exhaust gas purifying performance and the soot collecting performance, and the catalyst layer 21 is arranged in the extending direction of the partition wall from the end portion on the exhaust gas introducing side. A first region 21a formed along the first region 21a, a second region 21b formed along the extending direction of the partition wall from the end portion on the exhaust gas discharge side, and a third region 21c in which the first region 21a and the second region 21b overlap each other. To be formed. Then, the pore diameter D _mid calculated from the pore distribution of the third area 21c is calculated as the fine diameter calculated from the pore diameter D _in calculated from the pore distribution of the first area 21a and the pore distribution of the second area 21b. than the diameter _{D out,} respectively, it is increased above a predetermined value. In order for the exhaust gas to escape from the end 11a (opening) to the end 12a (opening) in the shortest distance, the exhaust gas passes through the center of the partition wall. At this time, the pore diameter of the third region 21c is made smaller than the pore diameters of the first region 21a and the second region 21b to make it difficult for the exhaust gas to pass, so that the exhaust gas also reaches the first region 21a and the second region 21b. Exhaust gas purification performance and soot collection performance are improved evenly.

Specifically, the ratio (D _in /D _mid ) is 1.2 or more, preferably 1.3 or more, and more preferably 1.35 or more. The upper limit of the ratio (D _in /D _mid ) is not particularly limited, but is preferably 3 or less, more preferably 2.8 or less, and further preferably 2.5 or less. The ratio (D _out /D _mid ) is 1.2 or more, preferably 1.3 or more, and more preferably 1.35 or more. The upper limit of the ratio (D _out /D _mid ) is not particularly limited, but is preferably 3 or less, more preferably 2.8 or less, and further preferably 2.5 or less. When the ratio (D _in /D _mid ) and the ratio (D _out /D _mid ) are respectively 1.2 or more, the exhaust gas flow becomes uniform in the stretching direction, and the exhaust gas purification performance and the soot collection performance are improved. To improve. Further, since the ratio (D _in /D _mid ) and the ratio (D _out /D _mid ) are respectively 3 or less, the inflow of exhaust gas to the third region 21c which is the central region of the partition wall and its vicinity is obstructed. If it is too much, it is possible to prevent the exhaust gas purification performance and the soot collecting performance from being deteriorated.

The pore size of the first region 21a is preferably 12 to 16 μm, more preferably 12.5 to 15 μm, and further preferably 13 to 14.5 μm. The pore size of the third region 21c is preferably 4 to 13 μm, more preferably 5 to 11.5 μm, and further preferably 7 to 10.5 μm. Further, the pore size of the second region 21b is preferably 12 to 16 μm, more preferably 12.5 to 15 μm, and further preferably 13 to 14.5 μm. When each pore size is within the above range, the exhaust gas purification performance and the soot collection performance tend to be further improved.

From the above viewpoint, the difference between the pore diameter D _in of the first region 21a or the pore diameter D _out of the second region 21b and the pore diameter D _mid of the third region 21c is preferably 2.5 to 10 μm, respectively. , More preferably 3 to 8 μm, further preferably 3 to 6 μm.

Samples for measuring the pore diameter D _in of the first region 21a, the pore diameter D _out of the second region 21b, and the pore diameter D _mid of the third region 21c are the first region 21a, the second region 21b, and the The three regions 21c are sampled from the portions located respectively in the middle in the extending direction of the partition wall 13. For example, when the total length L _{W in} the stretching direction of the wall flow type base material 10 (the total length in the stretching direction of the partition wall 13) is 100%, the first region 21a and the second region 21b are end portions on the exhaust gas introduction side and the discharge side. The third region 21c is formed with a length of 40% from each of 11a and 12a, and the third region 21c is between the first region 21a and the second region 21b, that is, a region of 20% at the center in the stretching direction of the wall flow type base material 10. Exhaust gas purification catalysts such as those formed in 1. In the case of such an exhaust gas purifying catalyst, samples for measuring the pore diameter D _in of the first region 21a and the pore diameter D _out of the second region 21b are measured from the

end portions

11a, 12a on the exhaust gas introduction side and the discharge side. Samples for measuring the pore diameter D _mid of the third region 21c are collected from the portions located at 20% (=40%/2) respectively, and 50% (=40%+20) from the end portion 11a on the exhaust gas introduction side. %/2) from the part located.

The range in which the first area 21a, the second area 21b, and the third area 21c are formed is not particularly limited. For example, the first region 21a and the second region 21b are formed with the same coating length from the

end portions

11a and 12a on the exhaust gas introduction side and the discharge side, respectively, and the third region 21c is centered in the extending direction of the partition wall 13. A mode in which the coating length of the first region 21a is shorter than the coating length of the second region 21b, and the third region 21c is located closer to the end 11a on the exhaust gas introduction side than the center of the partition wall 13. In such a mode, the coating length of the second region 21b is shorter than the coating length of the first region 21a, and the third region 21c is located closer to the end 12a on the exhaust gas discharge side than the center of the partition wall 13. Any of them may be used.

Specifically, in the stretching direction (length direction) of the partition wall 13, the range L ₁ (coating length) in which the first region 21a is formed is the total length Lw (the coating length) of the wall flow type base material 10 in the stretching direction. The total length of the partition walls 13 in the stretching direction) is 100%, preferably 20 to 80%, more preferably 25 to 75%, and further preferably 30 to 70%. Also. The range L ₂ (coating length) in which the second region 21b is formed is preferably 20 with the total length L _W (the total length of the partition walls 13 in the stretching direction) of the wall flow type substrate 10 in the stretching direction being 100%. It is -80%, more preferably 25-75%, still more preferably 30-70%. Further, the range L ₃ (coating length) in which the third region 21c is formed is preferably 100% of the total length Lw in the stretching direction of the wall flow type base material 10 (the total length in the stretching direction of the partition wall 13). It is 1 to 35%, more preferably 3 to 25%, and further preferably 5 to 15%.

The catalyst layer 21 is formed from the cell wall surface on the introduction side cell 11 side to the cell wall surface on the discharge side cell 12 side in the thickness direction of the partition wall 13, and the catalyst layer 21 is formed in the thickness direction of the partition wall 13. It is preferable that they are not unevenly distributed on the introduction side cell 11 side or the discharge side cell 12 side. As a result, the soot collection performance and the exhaust gas purification performance can be further improved without improving the pressure loss. Note that “unevenly distributed” means that when the wall thickness Tw of the partition wall 13 is taken, the catalyst layer 21 is formed in the depth region T1 from the cell wall surface on the introduction side cell 11 side or the discharge side cell 12 side to Tw*5/10. It means that 60% or more of the total mass is present.

(Pore volume)
From the same viewpoint as the pore diameter, the pore volume V _mid having a pore diameter of 1 μm or more calculated from the pore distribution of the third area 21c is calculated as the pore volume of 1 μm or more calculated from the pore distribution of the first area 21a. The volume is set to be larger than a predetermined value by a pore volume V _in and a pore volume V _{out having} a pore diameter of 1 μm or more calculated from the pore distribution of the second region 21b.

Specifically, the ratio (V _in /V _mid ) is preferably 1.3 or more, more preferably 1.35 or more, and further preferably 1.37 or more. The upper limit of the ratio (V _in /V _mid ) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and further preferably 1.6 or less. The ratio (V _out /V _mid ) is preferably 1.3 or more, more preferably 1.35 or more, and further preferably 1.37 or more. The upper limit of the ratio (V _out /V _mid ) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and further preferably 1.6 or less. Since the ratio (V _in /V _mid ) and the ratio (V _out /V _mid ) are 1.3 or more, the exhaust gas flow becomes uniform in the stretching direction, and the exhaust gas purification performance and the soot collection performance are improved. To improve. Further, since the ratio (V _in /V _mid ) and the ratio (V _out /V _mid ) are each 2 or less, the inflow of the exhaust gas into the third region 21c is excessively obstructed, so that the exhaust gas purification performance is rather increased. Also, it is possible to suppress the deterioration of the soot collecting performance.

The pore volume of 1 μm or more in the first region 21a is preferably 0.30 to 0.60 cc/g, more preferably 0.35 to 0.55 cc/g, and further preferably 0.40 to 0. It is 0.50 cc/g. The pore size of the third region 21c is preferably 0.20 to 0.45 cc/g, more preferably 0.25 to 0.40 cc/g, and further preferably 0.30 to 0.35 cc. /G. Further, the pore size of the second region 21b is preferably 0.30 to 0.60 cc/g, more preferably 0.35 to 0.55 cc/g, and further preferably 0.40 to 0.50 cc. /G. When each pore volume of 1 μm or more is within the above range, the soot collection performance and the exhaust gas purification performance tend to be further improved.

The respective pore diameters and pore volumes of the first region 21a, the third region 21c, and the second region 21b mean the values calculated by the mercury intrusion method under the conditions described in the examples below.

The method for adjusting the pore diameter and the pore volume of the first region 21a, the third region 21c, and the second region 21b to a predetermined range is not particularly limited, but for example, a catalyst layer formed in the third region 21c It is conceivable to increase the thickness of the.

(Base material)
The wall-flow type base material 10 is composed of an introduction-side cell 11 having an open end 11a on the exhaust-gas introduction side and a discharge-side cell 12 adjacent to the introduction-side cell 11 and having an open end 12a on the exhaust-gas discharge side. It has a wall flow type structure which is partitioned by high quality partition walls 13.

The base material 10 can be made of various materials and shapes that are conventionally used for this type of application. For example, the material of the base material is such that it is exposed to exhaust gas at a high temperature (for example, 400° C. or higher) generated when the internal combustion engine is operated under a high load condition, or when the particulate matter is burned and removed at a high temperature. It is preferably made of a heat resistant material so that it can be dealt with. Examples of the heat-resistant material include cordierite, mullite, aluminum titanate, and ceramics such as silicon carbide (SiC); alloys such as stainless steel. Further, the shape of the base material can be appropriately adjusted from the viewpoints of exhaust gas purification performance and suppression of pressure loss increase. For example, the outer shape of the base material can be a cylindrical shape, an elliptic cylinder shape, a polygonal cylinder shape, or the like. The volume of the base material (total cell volume) is preferably 0.1 to 5 L, and more preferably 0.5 to 3 L, although it depends on the space into which it is incorporated. The total length of the base material in the stretching direction (total length of the partition wall 13 in the stretching direction) is preferably 10 to 500 mm, more preferably 50 to 300 mm.

The introduction-side cells 11 and the discharge-side cells 12 are regularly arranged along the axial direction of the tubular shape, and adjacent cells have alternately one open end in the extending direction and the other open end. It is sealed. The introduction-side cell 11 and the discharge-side cell 12 can be set to have appropriate shapes and sizes in consideration of the flow rate and components of the supplied exhaust gas. For example, the mouth shape of the introduction side cell 11 and the discharge side cell 12 can be a triangle; a rectangle such as a square, a parallelogram, a rectangle, and a trapezoid; another polygon such as a hexagon and an octagon; a circle. .. Further, it may have a High Ash Capacity (HAC) structure in which the cross-sectional area of the introduction side cell 11 and the cross-sectional area of the discharge side cell 12 are different.

The numbers of the introduction-side cells 11 and the discharge-side cells 12 can be appropriately set so as to promote the generation of turbulent flow of exhaust gas and suppress clogging due to fine particles contained in the exhaust gas, and are particularly limited. However, it is preferably 200 to 400 cpsi. The thickness of the partition wall 13 (the length in the thickness direction orthogonal to the stretching direction) is preferably 6 to 12 mil, and more preferably 6 to 10 mil.

The partition wall 13 for partitioning adjacent cells is not particularly limited as long as it has a porous structure through which exhaust gas can pass, and the configuration thereof is such that exhaust gas purification performance, suppression of pressure loss increase, and mechanical strength of the base material. Can be appropriately adjusted from the viewpoint of improving For example, when the catalyst layer 21 is formed on the surface of the pores in the partition wall 13 using the catalyst slurry described later, the pore diameter (for example, the mode diameter (the pore diameter having the largest appearance ratio in the frequency distribution of the pore diameter (the maximum distribution)). Value))) or a large pore volume, the pores are less likely to be blocked by the catalyst layer 21, and the resulting exhaust gas purifying catalyst tends to have less increase in pressure loss, but traps particulate matter. The collecting ability tends to decrease, and the mechanical strength of the substrate tends to decrease. On the other hand, when the pore diameter and the pore volume are small, the pressure loss tends to increase, but the ability to collect particulate matter tends to improve and the mechanical strength of the base material tends to improve.

From such a viewpoint, the pore diameter (mode diameter) of the partition wall 13 of the wall flow type base material 10 before forming the catalyst layer 21 is preferably 8 to 25 μm, more preferably 10 to 22 μm, and It is preferably 13 to 20 μm. The porosity of the partition wall 13 is preferably 20 to 80%, more preferably 40 to 70%, and further preferably 60 to 70%. When the porosity is at least the lower limit, the increase in pressure loss tends to be further suppressed. Further, when the porosity is at most the upper limit, the strength of the base material tends to be further improved. The pore diameter (mode diameter) and the porosity mean values calculated by the mercury porosimetry under the conditions described in the examples below.

(Catalyst layer)
Next, the catalyst layer 21 formed in the pores of the partition wall 13 will be described. As the catalyst layer 21, various types of conventional ones used for this type of application can be used. For example, as a mode of the catalyst layer 21, there is a structure obtained by firing a catalyst slurry containing catalytic metal particles and carrier particles. The catalyst layer 21 formed by firing the catalyst slurry containing various particles in this manner has a microporous structure in which the particles are bound to each other by firing.

The catalyst metal contained in the catalyst layer 21 is not particularly limited, and various metal species capable of functioning as an oxidation catalyst or a reduction catalyst can be used. For example, platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os) can be mentioned. Among these, palladium (Pd) and platinum (Pt) are preferable from the viewpoint of oxidation activity, and rhodium (Rh) is preferable from the viewpoint of reduction activity. In the present embodiment, as described above, the catalyst layer 21 contains one or more kinds of catalyst metals in a mixed state. In particular, by using two or more kinds of catalytic metals in combination, a synergistic effect due to having different catalytic activities is expected.

The aspect of such a combination of the catalytic metals is not particularly limited, a combination of two or more types of catalytic metals having excellent oxidizing activity, a combination of two or more types of catalytic metals having excellent reducing activities, and a catalyst metal having excellent oxidizing activities and reduction. A combination of catalytic metals having excellent activity can be mentioned. Among these, as one aspect of the synergistic effect, a combination of a catalytic metal having an excellent oxidizing activity and a catalytic metal having an excellent reducing activity is preferable, and a combination containing at least Rh, Pd and Rh, or Pt and Rh is more preferable. With such a combination, the exhaust gas purification performance tends to be further improved.

The fact that the catalyst layer 21 contains the catalyst metal can be confirmed by a scanning electron microscope or the like of the cross section of the partition wall 13 of the exhaust gas purifying catalyst. Specifically, it can be confirmed by performing energy dispersive X-ray analysis in the field of view of the scanning electron microscope.

As the carrier particles contained in the catalyst layer 21 and carrying the catalyst metal, an inorganic compound conventionally used in this kind of exhaust gas purifying catalyst can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ), ceria-zirconia composite oxide (CZ composite oxide), aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO ₂ ). ₂ ), oxides of silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO ₂ ) and the like, and composite oxides containing these oxides as main components. These may be complex oxides or solid solutions to which rare earth elements such as lanthanum and yttrium, transition metal elements, and alkaline earth metal elements are added. These carrier particles may be used alone or in combination of two or more. Here, the oxygen storage material (OSC material) means that when the air-fuel ratio of the exhaust gas is lean (that is, the atmosphere on the oxygen excess side), it stores oxygen in the exhaust gas and when the air-fuel ratio of the exhaust gas is rich ( That is, the atmosphere on the excess fuel side) releases the stored oxygen.

The formation range of the third region is preferably 2 to 20%, more preferably 3 to 15%, and further preferably 5 to 10% with respect to 100% of the entire length of the partition wall in the stretching direction. As a result, the exhaust gas tends to spread evenly to the first region 21a and the second region 21b, and the exhaust gas purification performance and the soot collection performance tend to be further improved.

When the catalyst layer has a plurality of regions formed of different catalyst metals along the stretching direction, the first region 21a preferably contains Pd and/or Rh, and more preferably contains Pd. On the other hand, the second region 21b preferably contains Pd and/or Rh, and more preferably contains Rh. Since the first region 21a and the second region 21b have the catalyst metal, the exhaust gas purification performance tends to be further improved.

It should be noted that the coating amount of the catalyst layer of the exhaust gas purifying catalyst 100 is an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine, particularly a gasoline engine, and is particularly used for collecting particulate matter. (Coating amount of catalyst layer excluding catalyst metal mass per 1 L of wall-flow type substrate) is preferably 20 to 110 g/L, more preferably 40 to 90 g/L, and further preferably 50 to 70 g. /L. Further, the porosity of the partition wall 13 of the exhaust gas purifying catalyst 100 with the catalyst layer 21 formed by the mercury injection method is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to. 60%.

[Method for manufacturing exhaust gas purifying catalyst]
The manufacturing method of the present embodiment is a method for manufacturing an exhaust gas purifying catalyst 100 that purifies exhaust gas discharged from an internal combustion engine, and includes an introduction-side cell 11 having an end 11a on the exhaust-gas introduction side opened, and the introduction-side cell 11 And a discharge side cell 12 having an open end 12a on the exhaust gas discharge side, which is adjacent to, and a wall flow type base material 10 defined by a porous partition wall 13, and a partition wall of the wall flow type base material 10. 13 has a catalyst layer forming step S1 of forming a catalyst layer 21 by coating a catalyst slurry on at least a part of the surface of pores in the catalyst layer forming step S1. A first region 21a formed along the extending direction of the partition wall 13 from the portion 11a, a second region 21b formed along the extending direction of the partition wall 13 from the exhaust gas discharge side end 12a, and a first region 21a. A third region 21c overlapping the second region 21b, and a pore diameter D _in calculated from the pore distribution of the first region 21a with respect to a pore diameter D _mid calculated from the pore distribution of the third region 21c. the ratio of _{_(D} in _/ D _mid) is, is 1.2 or more, the ratio of the pore diameter _{D out} which is calculated from the pore distribution of the second area 21b against the pore diameter _{_{_{D mid (D out / D mid}}} ) is, The exhaust gas purifying catalyst 100 having the catalyst layer 21 of 1.2 or more is manufactured.

The following describes each process. In the present specification, the wall flow type base material before forming the catalyst layer 21 is referred to as "base material 10", and the wall flow type base material after forming the catalyst layer 21 is referred to as "exhaust gas purifying catalyst 100". ".

<Preparation process>
In this preparation step S0, the wall flow type base material 10 described in the above exhaust gas purifying catalyst 100 is prepared as a base material.

<Catalyst layer forming step>
In the catalyst layer forming step S1, the catalyst slurry is applied to the pore surface of the partition wall 13, dried and baked to form the catalyst layer 21. The method of applying the catalyst slurry is not particularly limited, but, for example, a method of impregnating a part of the base material 10 with the catalyst slurry and spreading it over the entire partition wall 13 of the base material 10, or an end portion on the exhaust gas introduction side is possible. 11a and the end part 12a on the exhaust gas discharge side are individually impregnated with the catalyst slurry. More specifically, the impregnation step S1a in which the end portion 11a on the exhaust gas introduction side is impregnated with the catalyst slurry, and the gas is introduced into the base material 10 from the end portion opposite to the end portion impregnated with the catalyst slurry. Thus, a method having a discharging step S1b for discharging the excess catalyst slurry with which the base material 10 is impregnated can be mentioned.

The method of impregnating the catalyst slurry in the impregnation step S1a is not particularly limited, and examples thereof include a method of immersing the end portion of the base material 10 in the catalyst slurry. In this method, if necessary, the catalyst slurry may be pulled up by discharging (sucking) gas from the opposite end. The end portion into which the catalyst slurry is impregnated may be either the exhaust gas introduction side end portion 11a or the exhaust gas discharge side end portion 12a.

In the discharging step S1b, the catalyst slurry is sucked up from the introduction side of the base material 10 to a predetermined position, and then gas is introduced into the base material 10 from the end opposite to the end impregnated with the catalyst slurry. By doing so, the surplus is discharged from the introduction side of the base material 10. In the process, the catalyst slurry can be applied to the inside of the pores by passing the catalyst slurry inside the pores of the partition wall 13, and the catalyst slurry is applied to the partition walls up to the position where the catalyst slurry has been sucked up. By using such a method, for example, the catalyst slurry is applied to the third region 21c in an overlapping manner so that the pore size of the third region 21c is smaller than the pore sizes of the first region 21a and the second region 21b. be able to.

In the drying step S1c, the coated catalyst slurry is dried. The drying conditions in the drying step S1c are not particularly limited as long as the solvent volatilizes from the catalyst slurry. For example, the drying temperature is preferably 100 to 225°C, more preferably 100 to 200°C, and further preferably 125 to 175°C. The drying time is preferably 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

In the firing step S1d, the catalyst slurry is fired to form the catalyst layer 21. The firing conditions in the firing step S1d are not particularly limited as long as the catalyst layer 21 can be formed from the catalyst slurry. For example, the firing temperature is not particularly limited, but is preferably 400 to 650°C, more preferably 450 to 600°C, and further preferably 500 to 600°C. The firing time is preferably 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

(Catalyst slurry)
The catalyst slurry for forming the catalyst layer 21 will be described. The catalyst slurry contains catalyst powder and a solvent such as water. The catalyst powder is a group of a plurality of catalyst particles including catalyst metal particles and carrier particles carrying the catalyst metal particles, and forms the catalyst layer 21 through a firing step described later. The catalyst particles are not particularly limited and can be appropriately selected and used from known catalyst particles. From the viewpoint of coatability of the partition walls 13 into the pores, the solid content of the catalyst slurry is preferably 1 to 50% by mass, more preferably 15 to 40% by mass, and further preferably 20 to 20% by mass. It is 35% by mass. With such a solid content, the catalyst slurry tends to be easily applied to the introduction-side cell 11 side in the partition wall 13.

The catalyst metal contained in the catalyst slurry is not particularly limited, and various metal species capable of functioning as an oxidation catalyst or a reduction catalyst can be used. For example, platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os) can be mentioned. Among these, palladium (Pd) and platinum (Pt) are preferable from the viewpoint of oxidation activity, and rhodium (Rh) is preferable from the viewpoint of reduction activity.

As the carrier particles carrying the catalytic metal particles, inorganic compounds conventionally used in this kind of exhaust gas purifying catalyst can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ), ceria-zirconia composite oxide (CZ composite oxide), aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO ₂ ). ₂ ), oxides of silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO ₂ ) and the like, and composite oxides containing these oxides as main components. These may be complex oxides or solid solutions to which rare earth elements such as lanthanum and yttrium, transition metal elements, and alkaline earth metal elements are added. These carrier particles may be used alone or in combination of two or more. Here, the oxygen storage material (OSC material) means that when the air-fuel ratio of the exhaust gas is lean (that is, the atmosphere on the oxygen excess side), it stores oxygen in the exhaust gas and when the air-fuel ratio of the exhaust gas is rich ( That is, the atmosphere on the excess fuel side) releases the stored oxygen. From the viewpoint of exhaust gas purification performance, the specific surface area of the carrier particles contained in the catalyst slurry is preferably 10 to 500 m ² /g, more preferably 30 to 200 m ² /g.

[Use]
A mixture containing oxygen and fuel gas is supplied to the internal combustion engine (engine), and the mixture is burned to convert combustion energy into mechanical energy. The air-fuel mixture burned at this time becomes exhaust gas and is discharged to the exhaust system. An exhaust gas purification apparatus including an exhaust gas purification catalyst is provided in the exhaust system, and harmful components (for example, carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) contained in the exhaust gas by the exhaust gas purification catalyst are provided. )) is purified, and particulate matter (PM) contained in the exhaust gas is collected and removed. In particular, the exhaust gas purification catalyst 100 of the present embodiment is preferably used for a gasoline particulate filter (GPF) capable of collecting and removing particulate matter contained in exhaust gas of a gasoline engine.

The features of the present invention will be described more specifically below with reference to Test Examples, Examples, and Comparative Examples, but the present invention is not limited to these. That is, the materials, usage amounts, ratios, processing contents, processing procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Further, the values of various production conditions and evaluation results in the following examples have a meaning as a preferred upper limit value or a preferred lower limit value in the embodiment of the present invention, and a preferred range is the above-mentioned upper limit value or lower limit value. And a range defined by a combination of the values of the following examples or the values of the examples.

(Example 1)
The alumina powder was impregnated with a rhodium nitrate aqueous solution and then calcined at 500° C. for 1 hour to obtain an Rh-supported powder. 0.5 kg of the obtained Rh-supported powder, 2 kg of the ceria-zirconia composite oxide powder, 195 g of a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the resulting mixture was put into a ball mill to obtain a catalyst powder. Milling was performed until a predetermined particle size distribution was obtained to obtain a catalyst slurry. 183 g of barium hydroxide octahydrate and 60% nitric acid were mixed with the obtained catalyst slurry to obtain a catalyst slurry.

Further, the alumina powder was impregnated with a palladium nitrate aqueous solution, and then baked at 500° C. for 1 hour to obtain a Pd-supported powder. 0.5 kg of the obtained Pd-supported powder, 2 kg of the ceria-zirconia composite oxide powder, 195 g of a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the resulting mixture was put into a ball mill to obtain a catalyst powder. Milling was performed until a predetermined particle size distribution was obtained to obtain a catalyst slurry. 183 g of barium hydroxide octahydrate and 60% nitric acid were mixed with the obtained catalyst slurry to obtain a catalyst slurry.

Next, a cordierite wall flow type honeycomb substrate (cell number/mil thickness: 300 cpsi/10 mil, diameter: 118.4 mm, total length: 127 mm, pore diameter (mode diameter): 16.4 μm, porosity: 65%) Prepared. The end of the base material on the exhaust gas introduction side is dipped in the catalyst slurry containing Rh, and vacuum suction is applied from the opposite end side to impregnate and hold the catalyst slurry to the center of the base material, and the pore surface in the partition wall. The catalyst slurry was applied to. Then, gas was caused to flow into the base material from the end portion on the exhaust gas discharge side, and excess catalyst slurry was blown off from the end portion on the exhaust gas introduction side of the base material.

Further, the end of the base material on the exhaust gas discharge side is dipped in the catalyst slurry containing Pd, vacuum suction is applied from the end side on the opposite side, and the catalyst slurry is impregnated and held to the center of the base material, and the pores in the partition wall The catalyst slurry was applied to the surface. Then, gas was caused to flow into the base material from the end portion on the exhaust gas introduction side, and the excess catalyst slurry was blown off from the end portion on the exhaust gas discharge side of the base material. The coating area of the catalyst slurry containing Pd and the coating area of the catalyst slurry containing Rh were applied so as to overlap by 2% with respect to the entire length in the stretching direction.

After that, the base material coated with the catalyst slurry was dried at 150°C and then fired at 550°C in the air atmosphere to produce an exhaust gas purification catalyst. The coating amount of the catalyst layer after firing was 57.8 g (excluding the weight of the platinum group metal) per 1 L of the substrate. Further, the catalyst layer made of the catalyst slurry containing Rh and the catalytic catalyst slurry containing Pd was formed in the thickness direction of the partition wall from the cell wall surface on the introduction side cell side to the cell wall surface on the discharge side cell side.

(Example 2)
Exhaust gas purifying catalyst produced in Example 1, except that the coating region of the catalyst slurry containing Pd and the coating region of the catalyst slurry containing Rh were coated so as to overlap by 7% with respect to the entire length in the stretching direction. A catalyst similar to the above was prepared.

(Example 3)
Exhaust gas purifying catalyst produced in Example 1, except that the coating area of the catalyst slurry containing Pd and the coating area of the catalyst slurry containing Rh overlap each other by 22% with respect to the entire length in the stretching direction. A catalyst similar to the above was prepared.

(Comparative Example 1)
0.5 kg of the Rh-supported powder, 0.5 kg of the Pd-supported powder, 2 kg of ceria-zirconia composite oxide powder, 195 g of 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the obtained mixture was placed in a ball mill. The catalyst powder was charged and milled until the catalyst powder had a predetermined particle size distribution to obtain a catalyst slurry. 183 g of barium hydroxide octahydrate and 60% nitric acid were mixed with the obtained catalyst slurry to obtain a catalyst slurry.

In the method for coating the base material with the catalyst slurry, the end portion of the base material on the exhaust gas introduction side is immersed in the catalyst slurry prepared as described above, and vacuum suction is applied from the opposite end side to the base material end. The part was kept impregnated with the catalyst slurry. Gas is allowed to flow into the base material from the end on the exhaust gas introduction side, and the catalyst slurry is applied to the pore surface in the partition walls, and excess catalyst slurry is blown off from the end on the exhaust gas discharge side of the base material. An exhaust gas purifying catalyst was produced in the same manner as in Example 6 except that the gas inflow was stopped. The coating amount of the catalyst layer after firing was 58.8 g (excluding the weight of the platinum group metal) per 1 L of the substrate.

(Comparative example 2)
The catalyst slurry prepared in Comparative Example 1 was used in place of the catalyst slurry containing Rh and the catalyst slurry containing Pd, respectively, from the coating area of the catalyst slurry immersed from the end on the exhaust gas introduction side and the end on the exhaust gas discharge side. An exhaust gas purification catalyst was produced in the same manner as in Example 1 except that the coating was performed so that it did not overlap the coating area of the immersed catalyst slurry. The coating amount of the catalyst layer after firing was 58.8 g (excluding the weight of the platinum group metal) per 1 L of the substrate.

[Calculation of pore diameter and pore volume]
From the portions of the partition walls of the exhaust gas purifying catalysts manufactured in Examples and Comparative Examples, which are located in the middle of the first region 21a, the second region 21b, and the third region 21c in the extending direction of the partition wall 13, the pore diameter (mode A sample (1 cm ³ ) for measuring the diameter) and the pore volume was collected. Further, for the base material before applying the catalyst slurry, for measuring the pore diameter (mode diameter) and the pore volume from the same position sampled in the exhaust gas purifying catalysts produced in the examples and comparative examples, respectively. Each sample (1 cm ³ ) was taken. At this time, 10 or more points were sampled from each region so that the total amount was 1 cm ³ . After drying the measurement sample, the pore distribution was measured by a mercury porosimetry method using a mercury porosimeter (trade name: PASCAL140 and PASCAL440 manufactured by Thermo Fisher Scientific). At this time, the low pressure region (0 to 400 Kpa) was measured by PASCAL140, and the high pressure region (0.1 Mpa to 400 Mpa) was measured by PASCAL440. The pore diameter (mode diameter) was determined from the obtained pore distribution, and the pore volume in pores with a pore diameter of 1 μm or more was calculated.

Then, the porosity was calculated by the following formula. Some of these results are shown in Table 3 below.
Porosity of exhaust gas purifying catalyst (%) = Pore volume of partition wall where catalyst layer is formed (cc/g) / Pore volume of base material (cc/g) x Porosity of base material (%)
Porosity of base material (%) = 65%

[Vehicle NOx purification performance evaluation]
After storing a commercially available flow-through type three-way catalyst in the converter, the exhaust gas purifying catalysts produced in Examples and Comparative Examples were stored in the converter in the latter stage of the stored three-way catalyst, and the converter was placed in the downstream of the exhaust port of the gasoline engine. I put it on. Then, the steady, decelerating and accelerating cycle was repeated for 10 hours. The temperature was set to 950° C. in the steady state, and the heat endurance treatment was performed.

After that, a commercially available flow-through type three-way catalyst after endurance treatment and the exhaust gas purifying catalyst produced in the examples and comparative examples are stored in a converter, and gasoline equipped with a direct-injection turbo engine with a displacement of 1.5 L of European specifications is installed. Exhaust gas purification performance of the catalyst was examined in a WLTC mode using a car.

[Measurement of soot collection performance]
The exhaust gas purifying catalysts produced in the examples and comparative examples were attached to a vehicle equipped with a 1.5 L direct injection turbo engine, and a WLTC mode running was performed using a solid particle number measuring device (manufactured by Horiba, Ltd., product name: MEXA-2100 SPCS). The amount of soot discharged at that time (PN _test ) was measured. The soot collection rate was calculated by the following formula as a reduction rate from the soot amount (PN _blank ) measured when the above test was carried out without mounting the exhaust gas purifying catalyst. The result is shown in FIG.
Soot collection rate (%)=(PN _blank -PN _test )/PN _blank ×100(%)

From the above, in the examples, by adjusting the pore size, while maintaining a high soot collection rate, the improvement of the exhaust gas purification performance is achieved, in the comparative example, the pore size in the stretching direction of the partition wall. As a result, the soot collection rate was low and the exhaust gas purification performance was also low.

This application is based on a Japanese patent application (Japanese Patent Application No. 2018-222097) filed with the Japan Patent Office on November 28, 2018, the content of which is incorporated herein by reference.

The exhaust gas purifying catalyst of the present invention can be widely and effectively used as an exhaust gas purifying catalyst because it removes particulate matter contained in the exhaust gas of a gasoline engine. Further, the exhaust gas purifying catalyst of the present invention can be effectively used not only as a gasoline engine, but also as an exhaust gas purifying catalyst for removing particulate matter contained in exhaust gas of jet engines, boilers, gas turbines, and the like.

10... Wall-flow type base material 11... Introduction side cell 11a... Exhaust gas introduction side end 12... Exhaust side cell 12a... Exhaust gas discharge side end 13... Partition wall 21. ..Catalyst layer 21a...first area 21b...second area 21c...third area 100...exhaust gas purifying catalyst

Claims

An exhaust gas purification catalyst for purifying exhaust gas emitted from an internal combustion engine,
An introduction-side cell whose end on the exhaust-gas introduction side is open, and a discharge-side cell which is adjacent to the introduction-side cell and whose end on the exhaust-gas discharge side is open are wall-flow type base materials defined by porous partition walls. ,
A catalyst layer formed in the partition wall,
A first region in which the catalyst layer is formed along an extending direction of the partition wall from an end portion on the exhaust gas introduction side, and a second region formed along an extending direction of the partition wall from an end portion on the exhaust gas discharge side. An area and a third area in which the first area and the second area overlap,
The ratio (D in /D mid ) of the pore diameter D in calculated from the pore distribution of the first area to the pore diameter D mid calculated from the pore distribution of the third area is 1.2 or more. ,
Wherein the ratio of the pore diameter D out which is calculated from the pore distribution of the second region with respect to the pore diameter D mid (D out / D mid ) it is 1.2 or more,
Exhaust gas purification catalyst.
Ratio (V in) of pore volume V in having a pore diameter of 1 μm or more calculated from the pore distribution of the first area to pore volume V mid having a pore diameter of 1 μm or more calculated from the pore distribution of the third area /V mid ) is 1.3 or more,
The ratio (V out /V mid ) of the pore volume V out having a pore diameter of 1 μm or more calculated from the pore distribution of the second region with respect to the pore volume V mid is 1.3 or more.
The exhaust gas purifying catalyst according to claim 1.
The difference between the pore diameter D in or the pore diameter D out and the pore diameter D mid is 2.5 to 10 μm, respectively.
The exhaust gas purifying catalyst according to claim 1 or 2.
The first region contains Pd,
The exhaust gas purifying catalyst according to any one of claims 1 to 3.
The second region includes Rh,
The exhaust gas purifying catalyst according to claim 4.
The first region includes Rh,
The exhaust gas purifying catalyst according to any one of claims 1 to 3.
The second region contains Pd,
The exhaust gas purifying catalyst according to claim 6.
The catalyst layer is formed in the thickness direction of the partition wall from the cell wall surface on the introduction side cell side to the cell wall surface on the discharge side cell side,
The exhaust gas purification catalyst according to any one of claims 1 to 5.
The formation range of the third region is 2 to 20% with respect to 100% of the total length of the partition wall in the stretching direction.
The exhaust gas purification catalyst according to any one of claims 1 to 8.
The internal combustion engine is a gasoline engine,
The exhaust gas purifying catalyst according to any one of claims 1 to 9.
A method for producing an exhaust gas purifying catalyst for purifying exhaust gas emitted from an internal combustion engine,
An introduction-side cell whose end on the exhaust-gas introduction side is open, and a discharge-side cell which is adjacent to the introduction-side cell and whose end on the exhaust-gas discharge side is open are wall-flow-type substrates defined by porous partition walls. The process of preparing,
At least a part of the pore surface in the partition wall of the wall flow type base material, a catalyst layer is formed by applying a catalyst slurry to form a catalyst layer,
In the catalyst layer forming step,
A first region formed along the extending direction of the partition wall from the exhaust gas introduction side end, a second region formed along the extending direction of the partition wall from the exhaust gas discharge side end, A pore size calculated from the pore distribution of the first region with respect to a pore size D mid calculated from the pore distribution of the third region, having a third region in which one region and the second region overlap. D in the ratio of (D in / D mid) is, is 1.2 or more, the ratio of the pore diameter D out which is calculated from the pore distribution of the second region with respect to the pore diameter D mid (D out / D mid ) Is for producing the exhaust gas purifying catalyst having the catalyst layer of 1.2 or more,
Method for manufacturing exhaust gas purifying catalyst.