CN112512687B

CN112512687B - Exhaust gas purifying catalyst and method for producing the same

Info

Publication number: CN112512687B
Application number: CN201980051093.1A
Authority: CN
Inventors: 城取万阳; 高桥祯宪
Original assignee: NE Chemcat Corp
Current assignee: NE Chemcat Corp
Priority date: 2018-11-28
Filing date: 2019-08-16
Publication date: 2023-09-22
Anticipated expiration: 2039-08-16
Also published as: WO2020110379A1; JPWO2020110379A1; CN112512687A; JP7319293B2

Abstract

An exhaust gas purifying catalyst that purifies exhaust gas discharged from an internal combustion engine, the exhaust gas purifying catalyst comprising: a wall-flow type substrate in which an introduction-side chamber having an end opening on the exhaust gas introduction side and a discharge-side chamber having an end opening on the exhaust gas discharge side and adjacent to the introduction-side chamber are defined by porous partition walls; and a catalyst layer formed in the partition wall, the catalyst layer including: a first region formed along the extending direction of the partition wall from the end of the exhaust gas introduction side; a second region formed along the extending direction of the partition wall from the end of the exhaust gas discharge side; and a third region overlapping the first region and the second region, wherein the pore diameter D is calculated from the pore distribution of the first region _in With respect to the pore diameter D calculated from the pore distribution in the third region _mid Ratio (D) _in /D _mid ) A pore diameter D calculated from the pore distribution in the second region of 1.2 or more _out Relative to the pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.

Description

Exhaust gas purifying catalyst and method for producing the same

Technical Field

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

Background

Exhaust gas discharged from an internal combustion engine is known to include Particulate Matter (PM) mainly composed of carbon, ash (ash) formed of non-combustible components, and the like, and to be a cause of atmospheric pollution. Conventionally, a diesel engine that is easier to discharge particulate matter than a gasoline engine has been strictly limited in the discharge amount of particulate matter, but in recent years, the limitation of the discharge amount of particulate matter has been intensified in the gasoline engine as well.

As means for reducing the amount of particulate matter discharged, a method of providing a particulate filter for the purpose of depositing and trapping particulate matter in an exhaust passage of an internal combustion engine is known. In recent years, particularly, from the viewpoint of space saving in the mounting space, the following studies have been conducted: in order to simultaneously inhibit the discharge of particulate matter and remove harmful components such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxides (NOx), a catalyst layer is provided by applying a catalyst slurry to a particulate filter and firing the catalyst slurry

As a method for forming such a catalyst layer, a particulate filter having a wall flow type substrate in which an introduction side chamber having an end opening on the exhaust gas introduction side and an exhaust side chamber adjacent to the introduction side chamber and having an end opening on the exhaust gas exhaust side are partitioned by porous partition walls, the following method is known: by adjusting properties such as viscosity and solid content of the slurry and pressurizing one of the introduction-side chamber and the discharge-side chamber, a pressure difference is generated between the introduction-side chamber and the discharge-side chamber, whereby penetration of the catalyst slurry into the partition wall is adjusted (for example, see patent literature 1).

Prior art literature

Patent literature

Patent document 1: WO2016/060048

Disclosure of Invention

Problems to be solved by the application

The particulate filter described in patent document 1 is configured to remove particulate matter: has a wall flow type structure and the exhaust gas passes through the pores of the partition wall. However, there is still room for improvement in terms of soot trapping performance, pressure loss, and exhaust gas purifying performance.

The present application has been made in view of the above problems, and an object of the present application is to provide an exhaust gas purifying catalyst capable of improving NOx purifying performance and a method for producing the same. It is to be noted that, not only the objects mentioned here, but also other objects of the present application can be achieved by the respective configurations shown in the embodiments described below, which cannot be obtained by the conventional techniques.

Means for solving the problems

The present inventors have conducted intensive studies on a method for improving purification performance. The result shows that: the present application has been accomplished by adjusting the pore diameter in the extending direction of the partition walls on which the catalyst layer is formed, thereby solving the above-described problems. That is, the present application provides various specific modes shown below.

An exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine, the exhaust gas purifying catalyst comprising:

a wall-flow base material in which an introduction-side chamber having an end opening on the exhaust gas introduction side, an exhaust-side chamber adjacent to the introduction-side chamber and having an end opening on the exhaust gas exhaust side are defined by porous partition walls, and

a catalyst layer formed in the partition wall;

the catalyst layer has: a first region formed along the extending direction of the partition wall from the end portion on the exhaust gas introduction side, a second region formed along the extending direction of the partition wall from the end portion on the exhaust gas discharge side, and a third region overlapping the first region and the second region,

and the pore diameter D calculated from the pore distribution in the first region _in With respect to the pore diameter D calculated from the pore distribution in the third region _mid Ratio (D) _in /D _mid ) A pore diameter D calculated from the pore distribution in the second region of 1.2 or more _out Relative to the pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.

The exhaust gas purifying catalyst according to [ 2 ], wherein the pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution in the first region is 1 μm or more _in A pore volume V of 1 μm or more in pore diameter calculated from the pore distribution in the third region _mid Ratio (V) _in /V _mid ) A pore volume V of 1.3 or more, and a pore diameter of 1 μm or more calculated from the pore distribution in the second region _out Relative to the pore volume V _mid Ratio (V) _out /V _mid ) Is 1.3 or more.

The exhaust gas purifying catalyst according to [ 1 ] or [ 2 ], wherein the pore diameter D _in Or the pore diameter D _out And the pore diameter D _mid The difference is 2.5-10 μm.

The exhaust gas purifying catalyst according to any one of [ 1 ] to [ 3 ], wherein the first region contains Pd.

The exhaust gas purifying catalyst according to [ 5 ], wherein the second region contains Rh.

The exhaust gas purifying catalyst according to any one of [ 1 ] to [ 3 ], wherein the first region contains Rh.

The exhaust gas purifying catalyst according to [ 7 ], wherein the second region contains Pd.

The exhaust gas purifying catalyst according to any one of [ 1 ] to [ 7 ], wherein the catalyst layer is formed from a chamber wall surface on the introduction side chamber side to a chamber wall surface on the discharge side chamber side in a thickness direction of the partition wall.

The exhaust gas purifying catalyst according to any one of [ 1 ] to [ 8 ], wherein the third region is formed in a range of 2 to 20% relative to 100% of the entire length of the partition wall in the extending direction.

The exhaust gas purifying catalyst according to any one of [ 1 ] to [ 9 ], wherein the internal combustion engine is a gasoline engine.

The method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine, the method comprising the steps of:

a step of preparing a wall-flow-type substrate that defines an introduction-side chamber having an end opening on the exhaust gas introduction side and a discharge-side chamber adjacent to the introduction-side chamber and having an end opening on the exhaust gas discharge side by a porous partition wall;

a catalyst layer forming step of forming a catalyst layer by applying a catalyst slurry to at least a part of the pore surfaces in the partition walls of the wall-flow base material,

in this catalyst layer forming step, the exhaust gas purifying catalyst having the catalyst layer described below is produced,

the catalyst layer has: a first region formed along the extending direction of the partition wall from the end portion on the exhaust gas introduction side, a second region formed along the extending direction of the partition wall from the end portion on the exhaust gas discharge side, and a third region overlapping the first region and the second region, and the pore diameter D calculated from the pore distribution of the first region _in With respect to the pore diameter D calculated from the pore distribution in the third region _mid Ratio (D) _in /D _mid ) A pore diameter D calculated from the pore distribution in the second region of 1.2 or more _out Relative to the pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an exhaust gas purifying catalyst having improved NOx purifying performance and a method for producing the same can be provided. The exhaust gas purifying catalyst can be effectively used as a catalyst-supporting Gasoline Particulate Filter (GPF), and further, the performance of an exhaust gas treatment system in which such a particulate filter is mounted can be improved.

Drawings

Fig. 1 is a sectional view schematically showing one embodiment of the exhaust gas purifying catalyst of the present embodiment.

Fig. 2 is a graph showing NOx purification performance in the examples and the comparative examples.

Fig. 3 is a graph showing the balance of NOx purification performance and soot trapping rate in the examples and comparative examples.

Detailed Description

Embodiments of the present invention are described in detail below. The following embodiments are examples (representative examples) of embodiments of the present invention, and the present invention is not limited thereto. The present invention can be implemented with any modification within a range not departing from the gist thereof. In the present specification, unless otherwise specified, the positional relationship between the upper, lower, left, right, etc. is based on the positional relationship shown in the drawings. The dimensional ratios in the drawings are not limited to the ratios shown in the drawings. In the present specification, the term "pore diameter" means a diameter (mode diameter: maximum value of distribution) having a largest ratio in a frequency distribution of pore diameters (hereinafter, also referred to as pore distribution). In the present specification, "to" is used to indicate values inserted before and after "and physical properties, and is used to include values before and after" and "to indicate physical properties. The expression of a numerical range such as "1 to 100" includes both the lower limit value "1" and the upper limit value "100" thereof. In addition, other numerical ranges are expressed in the same manner.

[ exhaust gas purifying catalyst ]

The exhaust gas purification catalyst according to the present embodiment is an exhaust gas purification catalyst 100 for purifying exhaust gas discharged from an internal combustion engine, comprising: a wall-flow type substrate 10 in which an introduction-side chamber 11 having an opening at an end 11a on the exhaust gas introduction side and a discharge-side chamber 12 adjacent to the introduction-side chamber and having an opening at an end 12a on the exhaust gas discharge side are defined by porous partition walls 13; and a catalyst layer 21 formed in the partition wall 13, the catalyst layer having a first region formed along the extending direction of the partition wall from the end on the exhaust gas introduction side, a second region formed along the extending direction of the partition wall from the end on the exhaust gas discharge side, and a third region overlapping the first region and the second region, and including pores of the first regionDistribution of calculated pore diameter D _in With respect to the pore diameter D calculated from the pore distribution in the third region _mid Ratio (D) _in /D _mid ) A pore diameter D calculated from the pore distribution in the second region of 1.2 or more _out Relative to the pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.

Each structure of the exhaust gas purifying catalyst according to the present embodiment will be described below with reference to a cross-sectional view schematically shown in fig. 1. The exhaust gas purifying catalyst of the present embodiment has a wall flow type structure. In the exhaust gas purifying catalyst 100 having such a structure, exhaust gas discharged from the internal combustion engine flows into the guide-side chamber 11 from the end 11a (opening) on the exhaust gas guide-side, passes through the air holes of the partition wall 13, flows into the adjacent discharge-side chamber 12, and flows out from the end 12a (opening) on the exhaust gas discharge-side. In this process, 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 chamber 11 and/or in the pores of the partition wall 13, and the deposited particulate matter is removed by the catalytic function of the catalyst layer 21 or by burning at a predetermined temperature (for example, about 500 to 700 ℃). In addition, the exhaust gas contacts 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 oxidized into water (H ₂ O), carbon dioxide (CO) ₂ ) Etc., nitrogen oxides (NOx) are reduced to nitrogen (N) ₂ ) Harmful components are purified (harmless). In the present specification, the removal of particulate matter and the purification of harmful components such as carbon monoxide (CO) are also collectively referred to as "exhaust gas purification performance". Each of the configurations will be described in more detail below.

(pore diameter)

By making the pore diameters different in the direction of extension of the partition walls, it is possible to control the flow of exhaust gas by producing a portion where exhaust gas easily flows and a portion where exhaust gas hardly flows. This makes it possible to bring the exhaust gas passing through the exhaust gas purifying catalyst into contact with the catalyst more effectively, and thus it is possible to expect an improvement in the exhaust gas purifying performance and an improvement in the soot trapping performance. The exhaust gas purification catalyst according to the present embodimentThe catalyst layer 21 is formed such that the catalyst layer 21 has a first region 21a formed along the extending direction of the partition wall from the end on the exhaust gas introduction side, a second region 21b formed along the extending direction of the partition wall from the end on the exhaust gas discharge side, and a third region 21c where the first region 21a and the second region 21b overlap, from the viewpoint of improving the exhaust gas purification performance and the soot trapping performance by controlling the flow of the exhaust gas. Further, the pore diameter D calculated from the pore distribution in the third region 21c is set _mid And the pore diameter D calculated from the pore distribution of the first region 21a _in And a pore diameter D calculated from the pore distribution of the second region 21b _out Is smaller than a predetermined value or more. The exhaust gas passes through the center of the partition wall so as to leak out the shortest distance from the end portion 11a (opening) to the end portion 12a (opening). At this time, by making the pore diameter of the third region 21c smaller than the pore diameters of the first region 21a and the second region 21b, the exhaust gas is made slightly less likely to pass, and thus the exhaust gas is uniformly distributed over the first region 21a and the second region 21b, and the exhaust gas purification performance and the soot trapping performance are further improved.

Specifically, the ratio (D _in /D _mid ) It is 1.2 or more, preferably 1.3 or more, more preferably 1.35 or more. In addition, the ratio (D _in /D _mid ) The upper limit of (2) is not particularly limited, but is preferably 3 or less, more preferably 2.8 or less, and further preferably 2.5 or less. In addition, the ratio (D _out /D _mid ) It is 1.2 or more, preferably 1.3 or more, more preferably 1.35 or more. In addition, the ratio (D _out /D _mid ) The upper limit of (2) is not particularly limited, but is preferably 3 or less, more preferably 2.8 or less, and further preferably 2.5 or less. By making the ratio (D _in /D _mid ) Ratio (D) _out /D _mid ) Each is 1.2 or more, so that the flow of exhaust gas in the extending direction becomes uniform, and the exhaust gas purifying performance and the soot trapping performance are further improved. In addition, by making the ratio (D _in /D _mid ) Ratio (D) _out /D _mid ) Each of which is 3 or less, the inflow of exhaust gas into the third region 21c, which is the central region of the partition wall, and the vicinity thereof is excessively blocked, and therefore exhaust gas purification performance can be suppressedThe soot trapping performance is reduced.

The pore diameter of the first region 21a is preferably 12 to 16. Mu.m, more preferably 12.5 to 15. Mu.m, and still more preferably 13 to 14.5. Mu.m. The pore diameter of the third region 21c is preferably 4 to 13. Mu.m, more preferably 5 to 11.5. Mu.m, and still more preferably 7 to 10.5. Mu.m. The pore diameter of the second region 21b is preferably 12 to 16. Mu.m, more preferably 12.5 to 15. Mu.m, and still more preferably 13 to 14.5. Mu.m. By setting the pore diameters in the above-described ranges, the exhaust gas purifying performance and the soot trapping performance tend to be further improved.

From the above point of view, the pore diameter D of the first region 21a _in Or pore diameter D of the second region 21b _out Pore diameter D of the third region 21c _mid The difference is preferably 2.5 to 10. Mu.m, more preferably 3 to 8. Mu.m, still more preferably 3 to 6. Mu.m.

The pore diameter D of the first region 21a is measured _in Pore diameter D of the second region 21b _out And pore diameter D of third region 21c _mid Is collected from the respective central portions in the extending direction of the partition wall 13 in the first region 21a, the second region 21b, and the third region 21 c. For example, the entire length L of the wall-flow base material 10 in the extending direction is set _W When the total length of the partition wall 13 in the extending direction is set to 100%, the exhaust gas purifying catalyst is set such that the first region 21a and the second region 21b are formed to have a length of 40% from the exhaust gas introduction side and discharge side ends 11a, 12a, respectively, and the third region 21c is formed between the first region 21a and the second region 21b, that is, in the region of 20% of the center in the extending direction of the wall-flow type substrate 10. In the case of such an exhaust gas purifying catalyst, the pore diameter D of the first region 21a is measured _in Pore diameter D of second region 21b _out For the measurement of the pore diameter D of the third region 21c, the samples were collected from the portions 20% (=40%/2) from the end portions 11a, 12a on the exhaust gas introduction side and the exhaust side, respectively _mid Is collected from a portion of 50% (=40% +20%/2) from the end 11a located on the exhaust gas introduction side.

The formation ranges of the first region 21a, the second region 21b, and the third region 21c are not particularly limited. For example, any of the following modes may be adopted: the first region 21a and the second region 21b are formed with the same coating length from the exhaust gas introduction side and exhaust side ends 11a, 12a, respectively, and the third region 21c is centered in the extending direction of the partition wall 13; the first region 21a has a shorter coating length than the second region 21b, and the third region 21c is positioned at the end 11a on the exhaust gas introduction side than the center of the partition wall 13; the second region 21b has a shorter coating length than the first region 21a, and the third region 21c is positioned at the end 12a on the exhaust gas discharge side than the center of the partition wall 13; etc.

Specifically, the first region 21a is formed in the extension direction (longitudinal direction) of the partition wall 13 in the range L ₁ The total length Lw (length of coating) of the wall-flow base material 10 in the extending direction (total length of the partition wall 13 in the extending direction) is set to 100%, preferably 20 to 80%, more preferably 25 to 75%, and even more preferably 30 to 70%. In addition, regarding the range L in which the second region 21b is formed ₂ (coating length) the entire length L of the wall-flow base material 10 in the extending direction _W (the total length of the partition wall 13 in the extending direction) is preferably 20 to 80%, more preferably 25 to 75%, and even more preferably 30 to 70%. Further, regarding the range L in which the third region 21c is formed ₃ The total length Lw (the total length of the partition walls 13 in the extending direction) of the wall-flow base material 10 (the coating length) is set to 100%, preferably 1 to 35%, more preferably 3 to 25%, and even more preferably 5 to 15%.

The catalyst layer 21 is formed from the chamber wall surface on the introduction side chamber 11 side to the chamber wall surface on the discharge side chamber 12 side in the thickness direction of the partition wall 13, and the catalyst layer 21 is preferably not offset on the introduction side chamber 11 side or the discharge side chamber 12 side in the thickness direction of the partition wall 13. This can further improve soot trapping performance and exhaust gas purifying performance without increasing pressure loss. When the wall thickness of the partition wall 13 is Tw, 60% or more of the total mass of the catalyst layer 21 is present in the depth region T1 from the chamber wall surface on the inlet side chamber 11 side or the outlet side chamber 12 side to Tw 5/10.

(pore volume)

From the same viewpoint as the pore diameter, the pore volume V calculated from the pore distribution in the third region 21c is 1 μm or more _mid And a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the first region 21a _in And a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the second region 21b _out The values are larger than or equal to predetermined values.

Specifically, the ratio (V _in /V _mid ) Preferably 1.3 or more, more preferably 1.35 or more, and still more preferably 1.37 or more. In addition, the ratio (V _in /V _mid ) The upper limit of (2) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and still more preferably 1.6 or less. In addition, the ratio (V _out /V _mid ) The value =preferably 1.3 or more, more preferably 1.35 or more, and still more preferably 1.37 or more. In addition, the ratio (V _out /V _mid ) The upper limit of (2) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and still more preferably 1.6 or less. By making the ratio (V _in /V _mid ) Ratio (V) _out /V _mid ) Each is 1.3 or more, whereby the flow of exhaust gas in the extending direction becomes uniform, and the exhaust gas purifying performance and the soot trapping performance are further improved. In addition, by making the ratio (V _in /V _mid ) Ratio (V) _out /V _mid ) Each of which is 2 or less, the inflow of exhaust gas into the third region 21c is excessively blocked, and deterioration of exhaust gas purification performance and soot trapping performance can be suppressed.

The pore volume of the first region 21a of 1 μm or more is preferably 0.30 to 0.60cc/g, more preferably 0.35 to 0.55cc/g, still more preferably 0.40 to 0.50cc/g. The pore diameter of the third region 21c is preferably 0.20 to 0.45cc/g, more preferably 0.25 to 0.40cc/g, and still more preferably 0.30 to 0.35cc/g. The pore diameter of the second region 21b is preferably 0.30 to 0.60cc/g, more preferably 0.35 to 0.55cc/g, and still more preferably 0.40 to 0.50cc/g. When the pore volume of each of the pores is 1 μm or more in the above range, soot trapping performance and exhaust gas purifying performance tend to be further improved.

The pore diameters and pore volumes of the first region 21a, the third region 21c, and the second region 21b are calculated by mercury porosimetry under the conditions described in the following examples.

The method of adjusting the pore diameters and pore volumes of the first region 21a, the third region 21c, and the second region 21b to the predetermined ranges is not particularly limited, and for example, a method of increasing the thickness of the catalyst layer formed in the third region 21c is considered.

(substrate)

The wall-flow type substrate 10 has a wall-flow type structure in which an introduction-side chamber 11 having an opening at an end 11a on the exhaust gas introduction side is partitioned by a porous partition wall 13, and a discharge-side chamber 12 adjacent to the introduction-side chamber 11 and having an opening at an end 12a on the exhaust gas discharge side.

As the substrate 10, a substrate of a material and a form used for such a conventional use can be used. For example, the material of the base material is preferably a base material formed of a heat-resistant material in order to be able to cope with a case where the base material is exposed to high-temperature (for example, 400 ℃ or higher) exhaust gas generated when the internal combustion engine is operated under a high-load condition, a case where particulate matter is burned and removed at a high temperature, and the like. Examples of the heat-resistant material include: ceramics such as cordierite, mullite, aluminum titanate, and silicon carbide (SiC); stainless steel, and the like. The form of the substrate may be appropriately adjusted from the viewpoints of exhaust gas purification performance, suppression of pressure loss increase, and the like. For example, the shape of the substrate may be a cylindrical shape, an elliptical cylindrical shape, a polygonal cylindrical shape, or the like. The capacity of the substrate (total volume of the chamber) is preferably 0.1 to 5L, more preferably 0.5 to 3L, depending on the space or the like at the place of loading. The total length of the base material in the extending direction (the total length of the partition walls 13 in the extending direction) is preferably 10 to 500mm, more preferably 50 to 300mm.

The introduction side chamber 11 and the discharge side chamber 12 are regularly arranged along the axial direction of the cylinder, and one open end and the other open end of the adjacent chambers in the extending direction of each other are alternately sealed. The intake side chamber 11 and the discharge side chamber 12 may be set to an appropriate shape and size in consideration of the flow rate and composition of the supplied exhaust gas. For example, the port shapes of the inlet side chamber 11 and the outlet side chamber 12 may be: triangle; square, parallelogram, rectangle, trapezoid and other rectangles; other polygons such as hexagons and octagons; circular. Further, the inlet chamber 11 may have a mouth shape having a High Ash Capacity (HAC) structure in which the cross-sectional area of the inlet chamber 11 and the cross-sectional area of the outlet chamber 12 are different.

The number of the introduction side chamber 11 and the discharge side chamber 12 is not particularly limited, and may be appropriately set so as to promote the generation of turbulent flow of the exhaust gas and to suppress clogging due to particles or the like contained in the exhaust gas, but is preferably 200cpsi to 400cpsi. The thickness (length in the thickness direction perpendicular to the extending direction) of the partition wall 13 is preferably 6 to 12mil, more preferably 6 to 10mil.

The partition walls 13 that partition adjacent chambers are not particularly limited as long as they have a porous structure through which exhaust gas can pass, and the configuration thereof can be appropriately adjusted from the viewpoints of exhaust gas purification performance, suppression of an increase in pressure loss, improvement of mechanical strength of a substrate, and the like. For example, when the catalyst slurry described later is used to form the catalyst layer 21 on the pore surfaces in the partition walls 13, if the pore diameter (for example, the mode diameter (pore diameter at which the ratio is the largest in the frequency distribution of pore diameters (the largest value of distribution))) or the pore volume is large, the pores are less likely to be clogged by the catalyst layer 21, and the pressure loss of the obtained exhaust gas purification catalyst is less likely to increase, but the trapping ability of the particulate matter is also likely to decrease, and the mechanical strength of the base material is also decreased. On the other hand, when the pore diameter and pore volume are small, the pressure loss tends to increase, but the trapping ability of the particulate matter tends to increase, and the mechanical strength of the base material also tends to increase.

From such a viewpoint, the pore diameter (mode diameter) of the partition walls 13 of the wall-flow type substrate 10 before the formation of the catalyst layer 21 is preferably 8 to 25 μm, more preferably 10 to 22 μm, and even more preferably 13 to 20 μm. The porosity of the partition wall 13 is preferably 20 to 80%, more preferably 40 to 70%, and even more preferably 60 to 70%. By setting the porosity to the lower limit or more, the pressure loss tends to be further suppressed from rising. Further, the porosity is set to the upper limit or less, whereby the strength of the base material tends to be further improved. The pore diameter (mode diameter) and the porosity are values calculated by mercury porosimetry under the conditions described in the following examples.

(catalyst layer)

Next, the catalyst layer 21 formed in the pores of the partition wall 13 will be described. The catalyst layer 21 may be any of various types of catalyst layers conventionally used for such applications. For example, as a mode of the catalyst layer 21, a catalyst layer obtained by firing a catalyst slurry containing catalyst metal particles and carrier particles is exemplified. The catalyst layer 21 formed by firing such a catalyst slurry containing various particles has a microporous structure in which the particles are bonded to each other by firing.

The catalyst metal included in the catalyst layer 21 is not particularly limited, and a metal species that can function as various oxidation catalysts and reduction catalysts can be used. Examples thereof include platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os). Among them, 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, the catalyst layer 21 is provided in a state where one or more catalyst metals are mixed as described above. In particular, by using two or more catalyst metals in combination, a synergistic effect due to having different catalyst activities can be expected.

The mode of combining such catalyst metals is not particularly limited, and examples thereof include a combination of two or more catalyst metals having excellent oxidation activity, a combination of two or more catalyst metals having excellent reduction activity, and a combination of a catalyst metal having excellent oxidation activity and a catalyst metal having excellent reduction activity. Among these, as one embodiment of the synergistic effect, a combination of a catalyst metal excellent in oxidation activity and a catalyst metal excellent in reduction activity is preferable, and a combination containing at least Rh, pd, and Rh, or a combination containing at least Pt and Rh is more preferable. By such a combination, the exhaust gas purifying performance tends to be further improved.

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

As the carrier particles containing the catalyst layer 21 and supporting the catalyst metal, inorganic compounds used in such an exhaust gas purifying catalyst in the past can be considered. Examples include: cerium oxide (cerium oxide: ceO) ₂ ) An oxygen storage material (OSC material) such as ceria-zirconia composite oxide (CZ composite oxide), alumina (alumina: al (Al) ₂ O ₃ ) Zirconium oxide (zirconium dioxide: zrO (ZrO) ₂ ) Silicon oxide (silicon dioxide: siO (SiO) ₂ ) Titanium oxide (titanium dioxide: tiO (titanium dioxide) ₂ ) And an oxide or a composite oxide containing these oxides as a main component. These may be composite oxides or solid solutions containing rare earth elements such as lanthanum and yttrium, transition metal elements, and alkaline earth metal elements. It should be noted that one kind of these carrier particles may be used alone, or two or more kinds may be used in combination. Here, the oxygen storage material (OSC material) refers to a material that stores oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean (i.e., an atmosphere on the oxygen excess side) and releases the stored oxygen when the air-fuel ratio of the exhaust gas is rich (i.e., an atmosphere on the fuel excess side).

The formation range of the third region is preferably 2 to 20%, more preferably 3 to 15%, and even more preferably 5 to 10% relative to 100% of the total length of the partition wall in the extending direction. As a result, the exhaust gas is uniformly spread over both the first region 21a and the second region 21b, and the exhaust gas purification performance and the soot trapping performance tend to be further improved.

In addition, in the case where the catalyst layer has a plurality of regions formed with different catalyst metals along the extending direction, the first region 21a preferably contains Pd and/or Rh, more preferably Pd. On the other hand, the second region 21b preferably contains Pd and/or Rh, more preferably contains Rh. The catalyst metal is present in the first region 21a and the second region 21b, so that the exhaust gas purifying performance tends to be further improved.

In particular, from the viewpoint of being useful for the purpose of trapping particulate matter, the amount of the catalyst layer applied (the amount of the catalyst layer applied per 1 liter of the wall-flow type substrate excluding the mass of the catalyst metal) of the exhaust gas purifying catalyst 100 is preferably 20 to 110g/L, more preferably 40 to 90g/L, and even more preferably 50 to 70g/L, as an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine, particularly a gasoline engine. The porosity of the partition wall 13 measured by mercury porosimetry of the exhaust gas purification catalyst 100 in which the catalyst layer 21 is formed is preferably 20 to 80%, more preferably 30 to 70%, and even more preferably 35 to 60%.

[ method for producing exhaust gas purifying catalyst ]

The manufacturing method of the present embodiment is characterized in that it is a manufacturing method of an exhaust gas purifying catalyst 100 that purifies exhaust gas discharged from an internal combustion engine, the manufacturing method including the steps of: a step S0 of preparing a wall-flow-type substrate 10 in which an introduction-side chamber 11 having an opening at an end 11a on the exhaust gas introduction side and a discharge-side chamber 12 adjacent to the introduction-side chamber 11 and having an opening at an end 12a on the exhaust gas discharge side are defined by porous partition walls 13; and a catalyst layer forming step S1 of forming a catalyst layer 21 by applying a catalyst slurry to at least a part of the pore surfaces in the partition walls 13 of the wall-flow type substrate 10, wherein the catalyst layer forming step S1 produces an exhaust gas purifying catalyst 100 having the catalyst layer 21, the catalyst layer 21 comprising: a first region 21a formed along the extending direction of the partition wall 13 from the end 11a on the exhaust gas introduction side, a second region 21b formed along the extending direction of the partition wall 13 from the end 12a on the exhaust gas discharge side, and a third region 21c where the first region 21a and the second region 21b overlap, and the pore diameter D calculated from the pore distribution of the first region 21a _in With respect to the pores calculated from the pore distribution of the third region 21cDiameter D _mid Ratio (D) _in /D _mid ) A pore diameter D calculated from the pore distribution of the second region 21b of 1.2 or more _out Relative to pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.

The following describes each step. In the present specification, the wall-flow type substrate before the formation of the catalyst layer 21 is referred to as "substrate 10", and the wall-flow type substrate after the formation of the catalyst layer 21 is referred to as "exhaust gas purifying catalyst 100".

< preparation Process >

In the preparation step S0, the wall-flow type substrate 10 described in the exhaust gas purifying catalyst 100 is prepared as a substrate.

< catalyst layer Forming Process >

In this catalyst layer forming step S1, the catalyst layer 21 is formed by applying a catalyst slurry to the pore surfaces of the partition walls 13, drying the catalyst slurry, and baking the catalyst slurry. The method of coating the catalyst slurry is not particularly limited, and examples thereof include: a method of impregnating a part of the substrate 10 with the catalyst slurry and extending the catalyst slurry over the entire partition walls 13 of the substrate 10; and a method in which the exhaust gas introduction-side end portion 11a and the exhaust gas discharge-side end portion 12a are impregnated with the catalyst slurry separately. More specifically, a method comprising a step of impregnating the catalyst slurry into the end 11a on the exhaust gas introduction side in the impregnation step S1 a; and a discharge step S1b for introducing a gas into the base material 10 from an end opposite to the end impregnated with the catalyst slurry, thereby discharging the excess catalyst slurry impregnated into the base material 10.

The impregnation method of the catalyst slurry in the impregnation step S1a is not particularly limited, and examples thereof include a method of impregnating the end portion of the substrate 10 with the catalyst slurry. In this method, the catalyst slurry may be pulled by discharging (sucking) the gas from the end portion on the opposite side, as needed. The end of the impregnated catalyst slurry may be either the exhaust gas introduction side end 11a or the exhaust gas discharge side end 12 a.

In the discharging step S1b, the catalyst slurry is sucked from the inlet side of the base material 10 to a predetermined position, and then the gas is introduced into the base material 10 from the end opposite to the end impregnated with the catalyst slurry, whereby the remaining portion is discharged from the inlet side of the base material 10. In this process, the catalyst slurry can be passed through the inside of the pores of the partition wall 13, whereby the catalyst slurry can be applied to the inside of the pores, and the catalyst slurry can be applied to the partition wall up to the position where the catalyst slurry is sucked. With such a method, for example, by repeatedly applying the catalyst slurry to the third region 21c, the pore diameter of the third region 21c can be made smaller than the pore diameters of the first region 21a and the second region 21 b.

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 is volatilized from the catalyst slurry. For example, the drying temperature is preferably 100 to 225 ℃, more preferably 100 to 200 ℃, and still more preferably 125 to 175 ℃. The drying time is preferably 0.5 to 2 hours, more 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 they are conditions that enable the catalyst layer 21 to be formed from the catalyst slurry. For example, the firing temperature is not particularly limited, but is preferably 400 to 650 ℃, more preferably 450 to 600 ℃, and even more preferably 500 to 600 ℃. The firing time is preferably 0.5 to 2 hours, more preferably 0.5 to 1.5 hours.

(catalyst slurry)

A 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 supporting the catalyst metal particles, and the catalyst layer 21 is formed through a firing step described later. The catalyst particles are not particularly limited, and may be appropriately selected from known catalyst particles. The solid content of the catalyst slurry is preferably 1 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass, from the viewpoint of the applicability to the pores of the partition wall 13. By setting such a solid content ratio, the catalyst slurry tends to be easily applied to the introduction side chamber 11 side in the partition wall 13.

The catalyst metal contained in the catalyst slurry is not particularly limited, and various metal species that can function as an oxidation catalyst and a reduction catalyst can be used. Platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) are exemplified. Among them, 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 supporting the catalyst metal particles, inorganic compounds that have been conventionally used in such exhaust gas purifying catalysts can be considered. Examples include: cerium oxide (cerium oxide: ceO) ₂ ) An oxygen storage material (OSC material) such as ceria-zirconia composite oxide (CZ composite oxide), alumina (alumina: al (Al) ₂ O ₃ ) Zirconium oxide (zirconium dioxide: zrO (ZrO) ₂ ) Silicon oxide (silicon dioxide: siO (SiO) ₂ ) Titanium oxide (titanium dioxide: tiO (titanium dioxide) ₂ ) And an oxide or a composite oxide containing these oxides as a main component. These may be composite oxides or solid solutions containing rare earth elements such as lanthanum and yttrium, transition metal elements, and alkaline earth metal elements. It should be noted that one kind of these carrier particles may be used alone, or two or more kinds may be used in combination. Here, the oxygen storage material (OSC material) refers to a material that stores oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean (i.e., an atmosphere on the oxygen excess side) and releases the stored oxygen when the air-fuel ratio of the exhaust gas is rich (i.e., an atmosphere on the fuel excess side). 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 500m ² Preferably 30 to 200m ² /g。

[ use ]

An internal combustion engine (engine) is supplied with a mixed gas containing oxygen and a fuel gas, and the mixed gas is combusted, whereby combustion energy is converted into mechanical energy. The burned mixture gas is then discharged to the exhaust system as exhaust gas. An exhaust system is provided with an exhaust gas purification device equipped with an exhaust gas purification catalyst, which purifies harmful components (e.g., carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx)) contained in exhaust gas, and traps and removes Particulate Matter (PM) contained in the exhaust gas. The exhaust gas purifying catalyst 100 of the present embodiment is particularly preferably used for a Gasoline Particulate Filter (GPF) capable of trapping and removing particulate matter contained in exhaust gas of a gasoline engine.

Examples

The features of the present invention will be described in more detail below by way of test examples, examples and comparative examples, but the present invention is not limited to these examples. That is, the materials, the amounts used, the proportions, the processing contents, the processing steps and the like shown in the following examples may be appropriately changed without departing from the gist of the present invention. The values of the various production conditions and evaluation results in the following examples have meanings as preferable upper limit values or preferable lower limit values in the embodiment of the present invention, and preferable ranges may be ranges defined by combinations of the values of the upper limit or lower limit values and the values of the following examples or values of the examples.

Example 1

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

Further, the palladium oxide powder was impregnated with an aqueous palladium nitrate solution, and then calcined at 500 ℃ for 1 hour to obtain a Pd-supported powder. The obtained Pd-supported powder (0.5 kg), ceria-zirconia composite oxide powder (2 kg), a 46% lanthanum nitrate aqueous solution (195 g) and ion-exchanged water were mixed, and the obtained mixture was put into a ball mill and ground until the catalyst powder had reached a predetermined particle size distribution, to obtain a catalyst slurry. To the obtained catalyst slurry, 183g of barium hydroxide octahydrate and 60% nitric acid were mixed to obtain a catalyst slurry.

Next, a wall-flow honeycomb substrate made of cordierite (cell count/mil thickness: 300cpsi/10mil, diameter: 118.4mm, full length: 127mm, pore diameter (mode diameter): 16.4 μm, porosity: 65%) was prepared. The end of the substrate on the exhaust gas introduction side was immersed in a catalyst slurry containing Rh, and suction was performed under reduced pressure from the opposite end side, so that the catalyst slurry was held in the center of the substrate until the catalyst slurry was impregnated, and the surfaces of the pores in the partition walls were coated with the catalyst slurry. Then, the gas is flowed into the substrate from the exhaust gas outlet side end, and an excessive amount of the catalyst slurry is blown off from the exhaust gas inlet side end of the substrate.

The end of the substrate on the exhaust gas discharge side was immersed in a catalyst slurry containing Pd, and the catalyst slurry was sucked under reduced pressure from the opposite end side until the catalyst slurry was held in the center of the substrate, and the surfaces of the pores in the partition walls were coated with the catalyst slurry. Then, the gas is flowed into the substrate from the exhaust gas introduction side end, and an excessive amount of the catalyst slurry is blown off from the exhaust gas discharge side end of the substrate. The coating region of the catalyst slurry containing Pd and the coating region of the catalyst slurry containing Rh were coated so as to repeat 2% of the entire length in the extending direction.

Then, the substrate coated with the catalyst slurry was dried at 150 ℃, and then calcined at 550 ℃ in an atmosphere, to prepare an exhaust gas purifying catalyst. The amount of the catalyst layer applied after firing was 57.8g (excluding the weight of platinum group metal) per 1L of the substrate. The catalyst layer formed of the catalyst slurry containing Rh and the catalyst slurry containing Pd is formed from the chamber wall surface on the introduction side chamber side to the chamber wall surface on the discharge side chamber side in the thickness direction of the partition wall.

Example 2

A catalyst similar to the exhaust gas purifying catalyst produced in example 1 was produced except that the coated region of the catalyst slurry containing Pd and the coated region of the catalyst slurry containing Rh were coated so as to repeat 7% with respect to the entire length in the extending direction.

Example 3

A catalyst similar to the exhaust gas purifying catalyst produced in example 1 was produced except that the coated region of the catalyst slurry containing Pd and the coated region of the catalyst slurry containing Rh were coated so as to repeat 22% with respect to the entire length in the extending direction.

Comparative example 1

The Rh supporting powder 0.5kg, the Pd supporting powder 0.5kg, the ceria-zirconia composite oxide powder 2kg, a 46% lanthanum nitrate aqueous solution 195g, and ion exchange water were mixed, and the resultant mixture was put into a ball mill, and ground until the catalyst powder reached a predetermined particle diameter distribution, to obtain a catalyst slurry. To the obtained catalyst slurry, 183g of barium hydroxide octahydrate and 60% nitric acid were mixed to obtain a catalyst slurry.

In the method of applying the catalyst slurry to the substrate, the end portion of the substrate on the exhaust gas introduction side is immersed in the catalyst slurry prepared as described above, and the catalyst slurry is held by the impregnation of the end portion of the substrate by suction under reduced pressure from the opposite end portion side. An exhaust gas purifying catalyst was produced in the same manner as in example 6, except that the gas was flowed into the substrate from the end on the exhaust gas introduction side, the catalyst slurry was applied to the surfaces of the pores in the partition walls, and the excess amount of the catalyst slurry was blown off from the end on the exhaust gas discharge side of the substrate, and the gas flow was stopped. The catalyst layer after firing was applied in an amount of 58.8g (excluding the weight of platinum group metal) per 1L of the substrate.

Comparative example 2

An exhaust gas purifying catalyst was produced in the same manner as in example 1, except that the catalyst slurry prepared in comparative example 1 was used instead of the catalyst slurry containing Rh and the catalyst slurry containing Pd, respectively, so that the coating region of the catalyst slurry impregnated from the end portion on the exhaust gas introduction side and the coating region of the catalyst slurry impregnated from the end portion on the exhaust gas discharge side did not overlap. The catalyst layer after firing was applied in an amount of 58.8g (excluding the weight of platinum group metal) per 1L of the substrate.

[ calculation of pore diameter and pore volume ]

Samples for measurement of pore diameter (mode diameter) and pore volume (1 cm) were collected from the central portions of the partition walls of the exhaust gas purifying catalysts produced in examples and comparative examples in the extending direction of the partition walls 13 of the first, second and third regions 21a, 21b and 21c, respectively ³ ). In addition, regarding the substrate before the catalyst slurry was applied, samples (1 cm) for measuring pore diameter (mode diameter) and pore volume were collected from the same position after the collection of each sample in the exhaust gas purifying catalysts produced in the examples and comparative examples ³ ). In this case, the total of 10 points or more and 1cm from each region ³ The measurement sample is collected by the method of (a). After drying the measurement sample, the pore distribution was measured by mercury porosimetry using a mercury porosimeter (trade name: PASCAL140 and PASCAL440, manufactured by Thermo Fisher Scientific Co.). At this time, the low pressure region (0 to 400 Kpa) was measured by the PASCAL140, and the high pressure region (0.1 to 400 MPa) was measured by the PASCAL 440. The pore diameter (mode diameter) was obtained from the obtained pore distribution, and the pore volume in pores having a pore diameter of 1 μm or more was calculated.

Next, 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 formed with catalyst layer (cc/g)/(pore volume of substrate (cc/g) ×porosity of substrate (%)

Porosity (%) =65% of the substrate

[ evaluation of NOx purifying Performance of vehicle ]

After a commercially available flow-through three-way catalyst was housed in a converter, the exhaust gas purifying catalysts produced in examples and comparative examples were housed in the converter at the rear stage of the housed three-way catalyst, and the converter was mounted in the wake of the exhaust port of the gasoline engine. Then, the cycle of constant, deceleration, and acceleration was repeated for 10 hours. The temperature was set to 950℃at a constant temperature, and heat-durability treatment was performed.

The durability-treated commercial three-way flow-through catalyst, the exhaust gas purifying catalysts produced in examples and comparative examples were housed in a converter, and the exhaust gas purifying performance of the catalysts was studied in WLTC mode using a gasoline engine equipped with a european standard direct injection turbine engine having an exhaust gas amount of 1.5L.

[ measurement of soot trapping Performance ]

The exhaust gas purifying catalysts produced in examples and comparative examples were mounted on a vehicle having a 1.5L direct injection turbine engine mounted thereon, and the number of soot emissions (PN) during WLTC mode traveling was measured using a solid particle count measuring device (manufactured by Horikoshi corporation, trade name: MEXA-2100 SPCS) _test ). The soot collection rate was measured as the soot amount (PN) measured when the above test was performed as compared with the case where the exhaust gas purifying catalyst was not mounted _blank ) The reduction rate of (2) is calculated by the following equation. The results are shown in FIG. 3.

Soot collection rate (%) = (PN) _blank -PN _test )/PN _blank ×100(％)

TABLE 1

In summary, in the examples, by adjusting the pore diameter, the soot collection rate can be maintained at a high level, and the exhaust gas purification performance can be improved.

The present application is based on japanese patent application filed by the japanese patent office on the date of 28 of 11 in 2018 (japanese patent application publication No. 2018-222097), the contents of which are incorporated herein by reference.

Industrial applicability

The exhaust gas purifying catalyst of the present application can be widely and effectively used as an exhaust gas purifying catalyst for removing particulate matter contained in exhaust gas of a gasoline engine. In addition, the exhaust gas purifying catalyst of the present application can be effectively used not only as an exhaust gas purifying catalyst for removing particulate matter contained in exhaust gas of a gasoline engine but also as an exhaust gas purifying catalyst for removing particulate matter contained in exhaust gas of a diesel engine, a jet engine, a boiler, a gas turbine, or the like.

Description of the reference numerals

10 … wall flow substrate

11 … leading-in side chamber

11a … exhaust gas introduction side end portion

12 … discharge side chamber

12a … exhaust gas discharge side end portion

13 … partition wall

21 … catalyst layer

21a … first region

21b … second region

21c … third region

100 … exhaust gas purifying catalyst

Claims

1. An exhaust gas purifying catalyst that purifies exhaust gas discharged from an internal combustion engine,

The exhaust gas purifying catalyst has:

a wall-flow type substrate in which an introduction-side chamber having an end opening on the exhaust gas introduction side and a discharge-side chamber having an end opening on the exhaust gas discharge side and adjacent to the introduction-side chamber are defined by porous partition walls; and

a catalyst layer formed in the partition wall,

wherein the catalyst layer has:

a first region formed along an extending direction of the partition wall from an end portion of the exhaust gas introduction side;

a second region formed along an extending direction of the partition wall from an end portion of the exhaust gas discharge side; and

a third region where the first region overlaps the second region,

pore diameter D calculated from the pore distribution of the first region _in Relative to the pore diameter D calculated from the pore distribution of the third region _mid Ratio (D) _in /D _mid ) Is more than 1.2 of the total weight of the catalyst,

pore diameter D calculated from the pore distribution of the second region _out Relative to the pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.

2. The exhaust gas purifying catalyst according to claim 1, wherein,

a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution in the first region _in A pore volume V of 1 μm or more in pore diameter calculated from the pore distribution in the third region _mid Ratio (V) _in /V _mid ) Is more than 1.3 of the total weight of the catalyst,

a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution in the second region _out Relative to the pore volume V _mid Ratio (V) _out /V _mid ) Is 1.3 or more.

3. The exhaust gas purifying catalyst according to claim 1 or 2, wherein,

the pore diameter D _in Or the pore diameter D _out And the pore diameter D _mid The difference is 2.5-10 μm.

4. The exhaust gas purifying catalyst according to claim 1 or 2, wherein,

the first region comprises Pd.

5. The exhaust gas purifying catalyst according to claim 4, wherein,

the second region contains Rh.

6. The exhaust gas purifying catalyst according to claim 1 or 2, wherein,

the first region contains Rh.

7. The exhaust gas purifying catalyst according to claim 6, wherein,

the second region comprises Pd.

8. The exhaust gas purifying catalyst according to claim 1 or 2, wherein,

the catalyst layer is formed from the chamber wall surface on the introduction side chamber side to the chamber wall surface on the discharge side chamber side in the thickness direction of the partition wall.

9. The exhaust gas purifying catalyst according to claim 1 or 2, wherein,

the third region is formed in a range of 2 to 20% relative to 100% of the entire length of the partition in the extending direction.

10. The exhaust gas purifying catalyst according to claim 1 or 2, wherein,

the internal combustion engine is a gasoline engine.

11. A method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,

the manufacturing method comprises the following steps:

a step of preparing a wall-flow-type substrate that defines an introduction-side chamber having an end opening on the exhaust gas introduction side and a discharge-side chamber adjacent to the introduction-side chamber and having an end opening on the exhaust gas discharge side by a porous partition wall; and

a catalyst layer forming step of forming a catalyst layer by applying a catalyst slurry to at least a part of the pore surfaces in the partition walls of the wall-flow base material;

the catalyst layer has:

a first region formed along the extending direction of the partition wall from the end portion on the exhaust gas introduction side, a second region formed along the extending direction of the partition wall from the end portion on the exhaust gas discharge side, and a third region overlapping the first region and the second region, and a pore diameter D calculated from a pore distribution of the first region _in Relative to the pore diameter D calculated from the pore distribution of the third region _mid Ratio (D) _in /D _mid ) A pore diameter D calculated from the pore distribution in the second region of 1.2 or more _out Relative to the pore diameter D _mid Ratio (D) _out /D _mid ) Is 1.2 or more.