CN112512687A

CN112512687A - Exhaust gas purifying catalyst and method for producing same

Info

Publication number: CN112512687A
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: 2021-03-16
Anticipated expiration: 2039-08-16
Also published as: JP7319293B2; CN112512687B; WO2020110379A1; JPWO2020110379A1

Abstract

An exhaust gas purification catalyst for purifying exhaust gas discharged from an internal combustion engine, the exhaust gas purification catalystThe reagent has: a wall-flow type base material which defines, by a porous partition wall, an inlet-side chamber having an end opening on an exhaust gas inlet side and an outlet-side chamber adjacent to the inlet-side chamber and having an end opening on an exhaust gas outlet side; and a catalyst layer formed inside the partition wall, the catalyst layer including: a first region formed along an extending direction of the partition wall from an end portion on the exhaust gas introduction side; a second region formed along an extending direction of the partition wall from an end portion on 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_inRelative to pore diameter D calculated from pore distribution of the third region_midRatio of (D)_in/D_mid) A pore diameter D of 1.2 or more calculated from the pore distribution of the second region_outRelative to the diameter D of the pore_midRatio of (D)_out/D_mid) Is 1.2 or more.

Description

Exhaust gas purifying catalyst and method for producing 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) containing carbon as a main component, ash (ash) formed of incombustible components, and the like, and to cause air pollution. Although the amount of particulate matter discharged has been strictly limited in diesel engines that are more likely to discharge particulate matter than in gasoline engines, in recent years, the amount of particulate matter discharged has been increasingly limited in gasoline engines.

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

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

Documents of the prior art

Patent document

Patent document 1: WO2016/060048

Disclosure of Invention

Problems to be solved by the invention

The particulate filter as described in patent document 1 is configured to, from the viewpoint of removing particulate matter: has a wall-flow structure and exhaust gas passes through the pores of the partition walls. However, there is still room for improvement in soot trapping 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 purification catalyst capable of improving NOx purification performance, and a method for manufacturing the same. It should be noted that the present invention is not limited to the above-mentioned objects, and other objects can be achieved by the respective configurations described in the embodiments described later, which are not achieved by the conventional techniques.

Means for solving the problems

The inventors of the present application have made intensive studies on a method for improving the purification performance. As a result, they found that: the above problems can be solved by adjusting the pore diameter in the extending direction of the partition wall on which the catalyst layer is formed, and the present invention has been completed. That is, the present invention provides various specific embodiments shown below.

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

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

a catalyst layer formed in the partition wall;

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

and the pore diameter D calculated from the pore distribution of the first region_inRelative to pore diameter D calculated from pore distribution of the third region_midRatio of (D)_in/D_mid) A pore diameter D of 1.2 or more calculated from the pore distribution of the second region_outRelative to the diameter D of the pore_midRatio of (D)_out/D_mid) Is 1.2 or more.

[ 2 ] the exhaust gas purifying catalyst according to [ 1], wherein a pore volume V having a pore diameter of 1 μm or more is calculated from the pore distribution of the first region_inA pore volume V of 1 μm or more with respect to the pore diameter calculated from the pore distribution of the third region_midRatio of (V)_in/V_mid) 1.3 or more, and a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the second region_outVolume V of the pores_midRatio of (V)_out/V_mid) Is 1.3 or more.

[ 3 ] the exhaust gas purifying catalyst according to [ 1] or [ 2 ], wherein the pore diameter D is_inOr the pore diameter D_outAnd the diameter D of the pore_midThe difference is 2.5 to 10 μm each.

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

[ 5 ] the exhaust gas purifying catalyst according to [ 4 ], 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.

[ 7 ] the exhaust gas purifying catalyst according to [ 6 ], 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 the chamber wall surface on the introduction-side chamber side to the 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% with respect to 100% of the entire length of the partition walls in the extending direction.

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

A method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine, comprising:

preparing a wall-flow substrate in which an inlet-side chamber having an end opening on an exhaust gas inlet side and an outlet-side chamber having an end opening on an exhaust gas outlet side are defined by porous partition walls;

a catalyst layer forming step of applying a catalyst slurry to at least a part of the surfaces of the pores in the partition walls of the wall flow type base material to form a catalyst layer,

in the catalyst layer forming step, the exhaust gas purifying catalyst having the catalyst layer,

the catalyst layer has: a first region formed from an end portion on the exhaust gas introduction side in the extending direction of the partition wall, a second region formed from an end portion on the exhaust gas discharge side in the extending direction of the partition wall, and a third region in which the first region overlaps the second region, and the first region is made thinner than the second regionPore diameter D calculated from pore distribution_inRelative to pore diameter D calculated from pore distribution of the third region_midRatio of (D)_in/D_mid) A pore diameter D of 1.2 or more calculated from the pore distribution of the second region_outRelative to the diameter D of the pore_midRatio of (D)_out/D_mid) Is 1.2 or more.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an exhaust gas purifying catalyst with improved NOx purification performance and a method for manufacturing the same can be provided. The exhaust gas purifying catalyst can be effectively used as a catalyst-carrying Gasoline Particulate Filter (GPF), and can realize further improvement in performance of an exhaust gas treatment system equipped with such a particulate filter.

Drawings

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

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

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

Detailed Description

The embodiments of the present invention will be described in detail below. The following embodiments are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these. The present invention can be implemented by arbitrarily changing the configuration without departing from the scope of the present invention. In the present specification, unless otherwise specified, positional relationships such as vertical and horizontal are based on the positional relationships shown in the drawings. The dimensional ratios in the drawings are not limited to the illustrated ratios. In the present specification, the term "pore diameter" refers to a diameter (mode diameter: maximum value of distribution) having the largest appearance ratio in a frequency distribution of pore diameters (hereinafter also referred to as pore distribution). In the present specification, the numerical values and physical property values before and after the "to" are used to indicate the values, and the values before and after the "to" are used to include the values. For example, the expression 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 purifying catalyst ]

The exhaust gas purifying catalyst according to the present embodiment is an exhaust gas purifying catalyst 100 for purifying exhaust gas discharged from an internal combustion engine, and is characterized by comprising: a wall-flow substrate 10 having porous partition walls 13 defining an introduction-side cell 11 in which an end 11a on an exhaust gas introduction side is open and a discharge-side cell 12 adjacent to the introduction-side cell and in which an end 12a on an exhaust gas discharge side is open; and a catalyst layer 21 formed in the partition walls 13, the catalyst layer having a first region formed from the end portion on the exhaust gas introduction side in the extending direction of the partition walls, a second region formed from the end portion on the exhaust gas discharge side in the extending direction of the partition walls, and a third region in which the first region and the second region overlap, and having a pore diameter D calculated from the pore distribution of the first region_inRelative to pore diameter D calculated from pore distribution of the third region_midRatio of (D)_in/D_mid) A pore diameter D of 1.2 or more calculated from the pore distribution of the second region_outRelative to the diameter D of the pore_midRatio of (D)_out/D_mid) Is 1.2 or more.

Each configuration will be described below with reference to a cross-sectional view schematically showing the exhaust gas purifying catalyst of the present embodiment 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 configuration, the exhaust gas discharged from the internal combustion engine flows into the intake-side chamber 11 from the end 11a (opening) on the exhaust gas introduction side, flows into the adjacent discharge-side chamber 12 through the pores of the partition wall 13, and flows out from the end 12a (opening) on the exhaust gas discharge side. In this process, the Particulate Matter (PM) that is difficult to pass through the pores of the partition walls 13 is generally deposited on the partition walls 13 and/or in the pores of the partition walls 13 in the introduction-side chamber 11, 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 walls 13, and carbon monoxide (CO) and Hydrocarbons (HC) contained in the exhaust gas are oxidized into water (H)₂O), carbon dioxide (CO)₂) Etc. nitrogen oxides (NOx) are reduced to nitrogen (N)₂) The harmful components are purified (made 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 configuration will be described in more detail below.

(pore diameter)

By making the pore diameter different in the extending direction of the partition wall, a portion where the exhaust gas easily flows and a portion where the exhaust gas hardly flows are generated, and the flow of the exhaust gas can be controlled. This enables the exhaust gas passing through the exhaust gas purifying catalyst to more effectively contact the catalyst, and improvement in exhaust gas purifying performance and improvement in soot trapping performance can be expected. In the exhaust gas purification catalyst of the present embodiment, from the viewpoint of improving the exhaust gas purification performance and the soot trapping performance by controlling the flow of the exhaust gas, the catalyst layer 21 is formed such that the catalyst layer 21 has a first region 21a formed along the extending direction of the partition walls from the end on the exhaust gas introduction side, a second region 21b formed along the extending direction of the partition walls from the end on the exhaust gas discharge side, and a third region 21c in which the first region 21a overlaps with the second region 21 b. Further, the pore diameter D calculated from the pore distribution of the third region 21c is set to be_midAnd the pore diameter D calculated from the pore distribution of the first region 21a_inAnd a pore diameter D calculated from the pore distribution of the second region 21b_outAre larger than the respective predetermined values or more. The exhaust gas passes through the center of the partition wall so as to leak out from the end 11a (opening) to the end 12a (opening) at the shortest distance. 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, so that the exhaust gas is slightly less likely to pass through, and the exhaust gas is uniformly distributed over the first region 21a and the second region 21b, whereby the exhaust gas purification performance and the soot trapping performance are further improved.

Specifically, the ratio (D)_in/D_mid) The content of the organic acid is more than 1.2,preferably 1.3 or more, more preferably 1.35 or more. In addition, the ratio (D)_in/D_mid) The upper limit of (b) 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) Is 1.2 or more, preferably 1.3 or more, and more preferably 1.35 or more. In addition, the ratio (D)_out/D_mid) The upper limit of (b) 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 a ratio (D)_in/D_mid) And ratio (D)_out/D_mid) Each of which is 1.2 or more, the flow of the exhaust gas in the extension direction becomes uniform, and the exhaust gas purification performance and the soot trapping performance are further improved. In addition, by making the ratio (D)_in/D_mid) And ratio (D)_out/D_mid) Since each is 3 or less, the inflow of the exhaust gas into the third region 21c, which is the central region of the partition wall, and the vicinity thereof is excessively inhibited, and thus, the degradation of the exhaust gas purification performance and the soot trapping performance can be suppressed.

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

From the above viewpoint, the pore diameter D of the first region 21a_inOr the pore diameter D of the second region 21b_outAnd the pore diameter D of the third region 21c_midThe difference is preferably 2.5 to 10 μm, more preferably 3 to 8 μm, and still more preferably 3 to 6 μm.

Is used to measure the pore diameter D of the first region 21a_inThe pore diameter D of the second region 21b_outAnd the pore diameter D of the third region 21c_midThe sample (2) is located in the first region 21a, the second region 21b and the third region 21c and extends from the partition wall 13 in the extending directionThe respective median portion of (a). For example, the total length L in the extending direction of the wall flow type substrate 10_WAssuming that (the total length of the partition walls 13 in the extending direction) is 100%, the exhaust gas purification catalyst is set such that the first region 21a and the second region 21b are formed to have a length of 40% from the

end portions

11a, 12a on the exhaust gas introduction side and the exhaust side, respectively, and the third region 21c is formed between the first region 21a and the second region 21b, that is, in the region 20% of the center in the extending direction of the wall flow substrate 10. In the case of such an exhaust gas purifying catalyst, the pore diameter D of the first region 21a is measured_inAnd the pore diameter D of the second region 21b_outThe sample of (2) is collected from a portion of 20% (40%/2) each from the

end portions

11a, 12a located on the exhaust gas introduction side and the exhaust side, and is used for measuring the pore diameter D of the third region 21c_midThe sample of (2) is collected from a portion of 50% (+ 40% + 20%/2) from the end portion 11a 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 used: a first region 21a and a second region 21b are formed with coating lengths of the same degree from the

end portions

11a and 12a on the exhaust gas introduction side and the exhaust side, respectively, and a third region 21c is positioned at the center in the extending direction of the partition wall 13; a mode in which the coating length of the first region 21a is shorter than that of the second region 21b, and the third region 21c is located at the end 11a closer to the exhaust gas introduction side than the center of the partition wall 13; a mode in which the coating length of the second region 21b is shorter than that of the first region 21a, and the third region 21c is located at the end 12a closer to the exhaust gas discharge side than the center of the partition wall 13; and so on.

Specifically, the first region 21a is formed in the extension direction (longitudinal direction) of the partition wall 13 in the range L₁The total length Lw (total length of the partition walls 13 in the extending direction) of the wall-flow substrate 10 is 100%, preferably 20 to 80%, more preferably 25 to 75%, and still more preferably 30 to 70% (coating length). In addition, the range L in which the second region 21b is formed₂(coating length) of the wall flow type substrate 10 in the entire extension directionLong L_WThe total length of the partition walls 13 in the extending direction is 100%, preferably 20 to 80%, more preferably 25 to 75%, and still more preferably 30 to 70%. Further, regarding the range L where the third region 21c is formed₃The total length Lw of the wall-flow substrate 10 in the extending direction (the total length of the partition walls 13 in the extending direction) is 100%, preferably 1 to 35%, more preferably 3 to 25%, and still more preferably 5 to 15% (coating length).

The catalyst layer 21 is formed on the chamber wall surface 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 it is preferable that the catalyst layer 21 is not deviated 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 the soot trapping performance and the exhaust gas purification performance without increasing the pressure loss. The phrase "deviated" means that 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 introduction-side chamber 11 side or the discharge-side chamber 12 side to Tw × 5/10 when the wall thickness of the partition wall 13 is Tw.

(pore volume)

From the same viewpoint as the pore diameter, the pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the third region 21c_midAnd a pore volume V of 1 μm or more in pore diameter calculated from the pore distribution of the first region 21a_inAnd a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the second region 21b_outCompared with the above, the values are respectively larger than the predetermined values.

Specifically, the ratio (V)_in/V_mid) Preferably 1.3 or more, more preferably 1.35 or more, and further preferably 1.37 or more. In addition, the ratio (V)_in/V_mid) The upper limit of (b) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and further preferably 1.6 or less. In addition, the ratio (V)_out/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)_out/V_mid) The upper limit of (b) is not particularly limited, but is preferably 2 or less, more preferably 1.8 or less, and further preferably 1.6 or less.By making a ratio (V)_in/V_mid) And ratio (V)_out/V_mid) Each of the amounts is 1.3 or more, whereby the flow of the exhaust gas in the extension direction becomes uniform, and the exhaust gas purification performance and the soot trapping performance are further improved. In addition, by making the ratio (V)_in/V_mid) And ratio (V)_out/V_mid) Since each is 2 or less, the inflow of the exhaust gas into the third region 21c is excessively inhibited, and the degradation of the exhaust gas purification performance and the 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, and still more preferably 0.40 to 0.50 cc/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 0.35 cc/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 0.50 cc/g. When the pore volume of each pore of 1 μm or more is within the above range, soot collection performance and exhaust gas purification 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 values calculated by mercury intrusion methods under the conditions described in the following examples.

The method of adjusting the pore diameter and pore volume of each of the first region 21a, the third region 21c, and the second region 21b to 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 may be considered.

(substrate)

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

As the substrate 10, a substrate of a material and a form used in the conventional application as described above can be used. For example, a substrate made of a heat-resistant material is preferable in order to be able to cope with exposure to high-temperature (for example, 400 ℃ or higher) exhaust gas generated when an internal combustion engine is operated under high load conditions, removal of particulate matter by high-temperature combustion, 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 outer shape of the substrate may be a cylindrical shape, an elliptic cylindrical shape, a polygonal cylindrical shape, or the like. In addition, also depending on the space of the loading place, the volume of the substrate (total volume of the chamber) is preferably 0.1-5L, more preferably 0.5-3L. 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, and more preferably 50 to 300 mm.

The introduction-side chambers 11 and the discharge-side chambers 12 are regularly arranged along the cylindrical axial direction, and one open end and the other open end in the extending direction of adjacent chambers are alternately sealed. The introduction-side chamber 11 and the discharge-side chamber 12 may be set to have appropriate shapes and sizes in consideration of the flow rate and composition of the exhaust gas to be supplied. For example, the shapes of the mouths of the introduction-side chamber 11 and the discharge-side chamber 12 may be: a triangle shape; rectangles such as square, parallelogram, rectangle and trapezoid; other polygons such as a hexagon and an octagon; and (4) a circular shape. Further, the port shape may have a High Ash Capacity (HAC) structure in which the cross-sectional area of the introduction-side chamber 11 and the cross-sectional area of the discharge-side 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 the turbulent flow of the exhaust gas and suppress clogging due to particles and the like contained in the exhaust gas, but is preferably 200cpsi to 400 cpsi. The thickness (length in the thickness direction orthogonal to the extending direction) of the partition wall 13 is preferably 6 to 12 mils, and more preferably 6 to 10 mils.

The partition wall 13 partitioning the adjacent chambers is not particularly limited as long as it has 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 in mechanical strength of the base material, and the like. For example, in the case where the catalyst layer 21 is formed on the pore surfaces in the partition walls 13 using a catalyst slurry described later, when the pore diameter (for example, the mode diameter (pore diameter (maximum value of distribution) at which the ratio appears in the frequency distribution of the pore diameter)) and the pore volume are 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 ability to trap particulate matter tends to decrease, and the mechanical strength of the substrate also tends to decrease. On the other hand, when the pore diameter and pore volume are small, the pressure loss tends to increase, but the ability to collect 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 substrate 10 before the catalyst layer 21 is formed is preferably 8 to 25 μm, more preferably 10 to 22 μm, and still more preferably 13 to 20 μm. The porosity of the partition wall 13 is preferably 20 to 80%, more preferably 40 to 70%, and still more preferably 60 to 70%. By setting the porosity to the lower limit or more, the increase in pressure loss tends to be further suppressed. Further, the strength of the base material tends to be further improved by setting the porosity to be not more than the upper limit. The pore diameter (mode diameter) and the porosity are values calculated by the mercury intrusion method under the conditions described in the following examples.

(catalyst layer)

Next, the catalyst layers 21 formed in the pores of the partition walls 13 will be described. As the catalyst layer 21, various types of catalyst layers used in the conventional application as described above can be used. For example, an embodiment of the catalyst layer 21 may be a catalyst layer obtained by firing a catalyst slurry containing catalyst metal particles and carrier particles. 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 contained in the catalyst layer 21 is not particularly limited, and various kinds of metals that can function as various oxidation catalysts and reduction catalysts can be used. Examples of the platinum group metal include 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 included in a state where one or more kinds of catalyst metals are mixed as described above. In particular, by using two or more catalyst metals in combination, a synergistic effect due to different catalytic activities can be expected.

The combination method of such a catalyst metal 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 them, as one mode 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 including at least Rh, Pd, and Rh, or a combination including at least Pt and Rh is more preferable. By combining these, exhaust gas purification performance tends to be further improved.

In addition, 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 confirmed by a scanning electron microscope or the like. Specifically, it can be confirmed by performing energy dispersive X-ray analysis in a field of a scanning electron microscope.

As the carrier particles for supporting the catalytic metal contained in the catalyst layer 21, inorganic compounds used in conventional exhaust gas purifying catalysts of this type can be considered. Examples thereof include: cerium oxide (cerium oxide: CeO)₂) Oxygen occlusion material (OSC material) such as ceria-zirconia composite oxide (CZ composite oxide), alumina (alumina: al (Al)₂O₃) Zirconium oxide (zirconium dioxide: ZrO (ZrO)₂) Silicon oxide (silicon dioxide: SiO 2₂) Titanium oxide (titanium dioxide: TiO 2₂) Etc. and complex oxygen containing these oxides as main componentsAnd (4) melting the mixture. They may be a composite oxide or a solid solution to which a rare earth element such as lanthanum or yttrium, a transition metal element, or an alkaline earth metal element is added. These carrier particles may be used alone or in combination of two or more. Here, the oxygen storage material (OSC material) is 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 third region is preferably formed in a range of 2 to 20%, more preferably 3 to 15%, and further preferably 5 to 10% with respect to 100% of the total length of the partition wall in the extending direction. This tends to spread the exhaust gas uniformly over both the first region 21a and the second region 21b, thereby further improving the exhaust gas purification performance and the soot trapping performance.

In addition, when 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, and more preferably contains Pd. On the other hand, the second region 21b preferably contains Pd and/or Rh, and more preferably contains Rh. The first region 21a and the second region 21b tend to have the catalytic metal, and the exhaust gas purification performance tends to be further improved.

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

[ method for producing exhaust gas purifying catalyst ]

The manufacturing method of the present embodiment is a manufacturing method of an exhaust gas purification catalyst 100 for purifying exhaust gas discharged from an internal combustion engine,the manufacturing method comprises the following steps: a step S0 of preparing a wall-flow-type substrate 10 in which a porous partition wall 13 defines an introduction-side cell 11 in which an end 11a on the exhaust gas introduction side is open and a discharge-side cell 12 adjacent to the introduction-side cell 11 and in which an end 12a on the exhaust gas discharge side is open; 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 surfaces of the pores in the partition walls 13 of the wall flow substrate 10, wherein in the catalyst layer forming step S1, an exhaust gas purification catalyst 100 having the following catalyst layer 21 is produced, the catalyst layer 21 having: a first region 21a formed along the extending direction of the partition walls 13 from the end 11a on the exhaust gas introduction side, a second region 21b formed along the extending direction of the partition walls 13 from the end 12a on the exhaust gas discharge side, and a third region 21c in which the first region 21a overlaps the second region 21b, and the pore diameter D calculated from the pore distribution of the first region 21a_inRelative to pore diameter D calculated from pore distribution of third region 21c_midRatio of (D)_in/D_mid) 1.2 or more, and a pore diameter D calculated from the pore distribution of the second region 21b_outRelative to pore diameter D_midRatio of (D)_out/D_mid) Is 1.2 or more.

The respective steps will be explained below. In the present specification, the wall-flow type substrate before the catalyst layer 21 is formed is referred to as "substrate 10", and the wall-flow type substrate after the catalyst layer 21 is formed is referred to as "exhaust gas purification catalyst 100".

< preparation Process >

In the preparation step S0, the wall-flow substrate 10 described above with respect to the exhaust gas purifying catalyst 100 is prepared as a substrate.

< Process for Forming catalyst layer >

In the catalyst layer forming step S1, the catalyst layer 21 is formed by applying the catalyst slurry to the pore surfaces of the partition walls 13, drying the slurry, and firing the dried slurry. The method of coating the catalyst paste 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 impregnated part over the partition walls 13 of the substrate 10; and a method of separately impregnating the end 11a on the exhaust gas introduction side and the end 12a on the exhaust gas discharge side with the catalyst slurry. More specifically, a method including an impregnation step S1a of impregnating the end portion 11a on the exhaust gas introduction side with the catalyst slurry; and a discharge step S1b of introducing a gas into the substrate 10 from the end opposite to the end impregnated with the catalyst slurry, thereby discharging the excess catalyst slurry impregnated into the substrate 10.

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

In the discharge step S1b, the catalyst slurry is sucked to a predetermined position from the introduction side of the substrate 10, and thereafter, a gas is introduced into the substrate 10 from the end opposite to the end impregnated with the catalyst slurry, thereby discharging the remainder from the introduction side of the substrate 10. In this process, the catalyst slurry can be passed through the inside of the pores of the partition walls 13, and the catalyst slurry can be applied to the inside of the pores and to the positions where the catalyst slurry is sucked up. By using 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, and preferably 0.5 to 1.5 hours.

In the firing step S1d, the catalyst layer 21 is formed by firing the catalyst slurry. 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 ℃, more preferably 450 to 600 ℃, and still more preferably 500 to 600 ℃. The firing time is preferably 0.5 to 2 hours, and preferably 0.5 to 1.5 hours.

(catalyst slurry)

A catalyst paste for forming the catalyst layer 21 will be explained. 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 forms the catalyst layer 21 through a firing step described later. The catalyst particles are not particularly limited, and can be appropriately selected from known catalyst particles. From the viewpoint of coatability to the pores of the partition walls 13, the solid content fraction of the catalyst slurry is preferably 1 to 50 mass%, more preferably 15 to 40 mass%, and still more preferably 20 to 35 mass%. By setting such a solid content fraction, 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 kinds of metals that can function as an oxidation catalyst or a reduction catalyst can be used. Examples of the platinum group metal include 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.

As the carrier particles for supporting the catalytic metal particles, inorganic compounds that have been conventionally used in such exhaust gas purifying catalysts can be considered. Examples thereof include: cerium oxide (cerium oxide: CeO)₂) Oxygen occlusion material (OSC material) such as ceria-zirconia composite oxide (CZ composite oxide), alumina (alumina: al (Al)₂O₃) Zirconium oxide (zirconium dioxide: ZrO (ZrO)₂) Silicon oxide (silicon dioxide: SiO 2₂) Titanium oxide (titanium dioxide: TiO 2₂) And composite oxides containing these oxides as a main component. They also haveCan be a composite oxide or solid solution added with rare earth elements such as lanthanum and yttrium, transition metal elements and alkaline earth metal elements. These carrier particles may be used alone or in combination of two or more. Here, the oxygen storage material (OSC material) is 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). In view of exhaust gas purification performance, the specific surface area of the carrier particles contained in the catalyst slurry is preferably 10 to 500m²A concentration of 30 to 200m²/g。

[ use ]

A mixed gas containing oxygen and fuel gas is supplied to an internal combustion engine (engine), the mixed gas is combusted, and combustion energy is converted into mechanical energy. The mixed gas burned at this time becomes an exhaust gas and is discharged to an exhaust system. An exhaust system is provided with an exhaust gas purification device provided with an exhaust gas purification catalyst, and the exhaust gas purification device purifies harmful components (for example, carbon monoxide (CO), Hydrocarbons (HC), and nitrogen oxides (NOx)) contained in exhaust gas by the exhaust gas purification catalyst and traps and removes Particulate Matter (PM) contained in the exhaust gas. The exhaust gas purification 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 with reference to test examples, examples and comparative examples, but the present invention is not limited to these. That is, the materials, the amounts used, the ratios, 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. In addition, the values of the various production conditions and evaluation results in the following examples have meanings as the preferable upper limit value or the preferable lower limit value in the embodiment of the present invention, and the preferable range may be a range defined by a combination of the above-mentioned upper limit value or lower limit value and the values of the following examples or the values of each of the examples.

(example 1)

The alumina powder was impregnated with an aqueous rhodium nitrate solution and then fired at 500 ℃ for 1 hour to obtain an Rh-supporting powder. The obtained Rh-supporting powder 0.5kg, ceria-zirconia composite oxide powder 2kg, 46% lanthanum nitrate aqueous solution 195g and ion-exchanged water were mixed, and the resulting mixture was put into a ball mill and ground until the catalyst powder reached a predetermined particle size distribution, thereby obtaining 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 aluminum oxide powder was impregnated with an aqueous palladium nitrate solution and then fired at 500 ℃ for 1 hour to obtain a Pd-supporting powder. The obtained Pd-supporting powder 0.5kg, ceria-zirconia composite oxide powder 2kg, 46% lanthanum nitrate aqueous solution 195g and ion-exchanged water were mixed, and the obtained mixture was put into a ball mill and ground until the catalyst powder reached a predetermined particle size distribution, thereby obtaining 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 cordierite wall-flow honeycomb substrate (number of cells/mil thickness: 300cpsi/10mil, diameter: 118.4mm, total length: 127mm, pore diameter (mode diameter): 16.4 μm, porosity: 65%) was prepared. The end of the substrate on the exhaust gas introduction side is immersed in a catalyst slurry containing Rh, and the catalyst slurry is sucked under reduced pressure from the end on the opposite side until the catalyst slurry is impregnated and held in the center of the substrate, and the catalyst slurry is applied to the surfaces of the pores in the partition walls. Then, gas is flowed into the substrate from the end portion on the exhaust gas discharge side, and an excessive amount of the catalyst slurry is blown off from the end portion on the exhaust gas introduction side of the substrate.

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

Thereafter, the substrate coated with the catalyst slurry was dried at 150 ℃ and then fired at 550 ℃ in an air atmosphere to produce an exhaust gas purifying catalyst. The coating amount of the catalyst layer after firing was 57.8g (excluding the weight of the 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 wall surface of the chamber on the introduction-side chamber side to the wall surface of the chamber 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 prepared in example 1 was prepared, 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% over the entire length in the extending direction.

(example 3)

A catalyst similar to the exhaust gas purifying catalyst prepared in example 1 was prepared, 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 22% of the entire length in the extending direction.

Comparative example 1

The catalyst slurry was obtained by mixing 0.5kg of the Rh-supporting powder, 0.5kg of the Pd-supporting powder, 2kg of ceria-zirconia composite oxide powder, 195g of 46% lanthanum nitrate aqueous solution, and ion-exchanged water, and then feeding the resulting mixture into a ball mill and grinding the mixture until the catalyst powder had a predetermined particle diameter distribution. 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 on the exhaust gas introduction side of the substrate is immersed in the catalyst slurry prepared as described above, and the catalyst slurry is held by being impregnated in the end portion of the substrate by suction under reduced pressure from the end portion side on the opposite side. An exhaust gas purifying catalyst was produced in the same manner as in example 6, except that gas was flowed into the substrate from the end portion on the exhaust gas introduction side, the catalyst slurry was applied to the surfaces of the pores in the partition walls, and the excessive catalyst slurry was blown off from the end portion on the exhaust gas discharge side of the substrate to stop the gas flow. The coating amount of the catalyst layer after firing was 58.8g (excluding the weight of the 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, and the catalyst slurry was coated so that the coating region of the catalyst slurry impregnated from the end on the exhaust gas introduction side and the coating region of the catalyst slurry impregnated from the end on the exhaust gas discharge side did not overlap each other. The coating amount of the catalyst layer after firing was 58.8g (excluding the weight of the platinum group metal) per 1L of the substrate.

[ calculation of pore diameter and pore volume ]

From the portions of the partition walls of the exhaust gas purification catalysts prepared in examples and comparative examples, which are located at the centers in the extending direction of the partition walls 13 of the first region 21a, the second region 21b, and the third region 21c, samples (1cm in pore volume) for measuring the pore diameter (mode diameter) and the pore volume were taken³). In the exhaust gas purifying catalysts prepared in examples and comparative examples, samples (1 cm) for measuring pore diameter (mode diameter) and pore volume were collected from the same position of the exhaust gas purifying catalyst after collection of each sample³). In this case, the total of 1cm at 10 points or more from each region³Collecting a sample for measurement. After drying the sample for measurement, pore distribution was measured by mercury intrusion method using a mercury intrusion porosimeter (product name: PASCAL140 and PASCAL440, manufactured by Thermo Fisher Scientific Co.). In this case, the low pressure region (0 to 400Kpa) was measured by PASCAL140, and the high pressure region (0.1 to 400MPa) was measured by PASCAL 440. From the resultThe pore diameter (mode diameter) was obtained from the pore distribution obtained above, 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.

The exhaust gas purifying catalyst had a porosity (%). porosity (%) of the base material x pore volume (cc/g) of the partition wall on which the catalyst layer was formed

The porosity (%) of the substrate was 65%

[ evaluation of NOx purification Performance of vehicle ]

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

Then, a commercially available flow-through type three-way catalyst after the durability treatment and the exhaust gas purification catalysts prepared in examples and comparative examples were stored in a converter, and the exhaust gas purification performance of the catalysts was examined in the WLTC mode using a gasoline car equipped with a direct injection turbine engine having an exhaust gas amount of 1.5L according to the european standard.

[ measurement of soot trapping Performance ]

The exhaust gas-purifying catalysts prepared in examples and comparative examples were mounted on a car equipped with a 1.5L direct injection turbine engine, and the number of soot emissions (PN) during WLTC mode operation was measured using a solid particle number measuring device (product name: MEXA-2100 SPCS, manufactured by horiba Seisakusho)_test). The soot trapping rate was determined as the amount of soot (PN) measured in the above test without the exhaust gas purifying catalyst mounted thereon_blank) The reduction rate of (d) is calculated by the following equation. The results are shown in FIG. 3.

(PN) soot trapping rate [ (% ])_blank-PN_test)/PN_blank×100(％)

[ Table 1]

As described above, in the examples, the soot collection rate was maintained at a high level and the exhaust gas purification performance was improved by adjusting the pore diameter, and in the comparative examples, the soot collection rate was low and the exhaust gas purification performance was also reduced by making the pore diameter relatively uniform in the extending direction of the partition walls.

The present application is based on the japanese patent application filed in the office on 28/11/2018 (japanese application 2018-222097), the contents of which are incorporated herein by reference.

Industrial applicability of the invention

The exhaust gas purifying catalyst of the present invention can be widely and effectively used as an exhaust gas purifying catalyst for removing particulate matter contained in exhaust gas of a gasoline engine. The exhaust gas purifying catalyst of the present invention 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 … introduction into the side chamber

11a … end part on the exhaust gas introduction side

12 … discharge side chamber

12a … end part on exhaust gas discharge side

13 … partition wall

21 … catalyst layer

21a … first region

21b … second area

21c … third region

100 … exhaust gas purifying catalyst

Claims

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

the exhaust gas purifying catalyst has:

a wall-flow type base material which defines, by a porous partition wall, an inlet-side chamber having an end opening on an exhaust gas inlet side and an outlet-side chamber adjacent to the inlet-side chamber and having an end opening on an exhaust gas outlet side; and

a catalyst layer formed inside the partition wall,

wherein the catalyst layer has:

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

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

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

pore diameter D calculated from pore distribution of the first region_inRelative to pore diameter D calculated from pore distribution of the third region_midRatio of (D)_in/D_mid) The content of the organic acid is more than 1.2,

pore diameter D calculated from pore distribution of the second region_outRelative to the diameter D of the fine hole_midRatio of (D)_out/D_mid) Is 1.2 or more.

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

a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the first region_inA pore volume V of 1 μm or more with respect to a pore diameter calculated from the pore distribution of the third region_midRatio of (V)_in/V_mid) The content of the organic acid is more than 1.3,

a pore volume V having a pore diameter of 1 μm or more calculated from the pore distribution of the second region_outRelative to the pore volume V_midRatio of (V)_out/V_mid) Is 1.3 or more.

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

diameter D of the fine hole_inOr the diameter D of the fine hole_outAnd the diameter D of the fine hole_midThe difference is 2.5 to 10 μm each.

4. The exhaust gas purifying catalyst according to any one of claims 1 to 3,

the first zone comprises Pd.

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

the second region contains Rh.

6. The exhaust gas purifying catalyst according to any one of claims 1 to 3,

the first region includes Rh.

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

the second zone comprises Pd.

8. The exhaust gas purifying catalyst according to any one of claims 1 to 5,

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 any one of claims 1 to 8,

the third region is formed in a range of 2 to 20% with respect to 100% of the total length of the partition in the extending direction.

10. The exhaust gas purifying catalyst according to any one of claims 1 to 9,

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:

preparing a wall-flow substrate in which an inlet-side chamber having an end opening on an exhaust gas inlet side and an outlet-side chamber having an end opening on an exhaust gas outlet side are defined by porous partition walls; and

a catalyst layer forming step of forming a catalyst layer by applying a catalyst slurry to at least a part of the surfaces of the pores in the partition walls of the wall flow substrate;

the catalyst layer has:

a first region formed from an end portion on the exhaust gas introduction side in the extending direction of the partition wall, a second region formed from an end portion on the exhaust gas discharge side in the extending direction of the partition wall, and a third region in which the first region and the second region overlap each other, and a pore diameter D calculated from a pore distribution of the first region_inRelative to pore diameter D calculated from pore distribution of the third region_midRatio of (D)_in/D_mid) A pore diameter D of 1.2 or more calculated from the pore distribution of the second region_outRelative to the diameter D of the fine hole_midRatio of (D)_out/D_mid) Is 1.2 or more.