WO2020031794A1

WO2020031794A1 - Exhaust gas purification catalyst

Info

Publication number: WO2020031794A1
Application number: PCT/JP2019/029874
Authority: WO
Inventors: 万陽城取; 大司望月; 豪人高山; 禎憲高橋
Original assignee: エヌ・イーケムキャット株式会社
Priority date: 2018-08-09
Filing date: 2019-07-30
Publication date: 2020-02-13
Also published as: CN112218719A; JP6608090B1; CN112218719B; JP2020025954A

Abstract

An exhaust gas purification catalyst that purifies exhaust gas discharged from an internal combustion engine, wherein the exhaust gas purification catalyst has: a wall-flow-type base material, in which an introduction-side cell having an end opened on the exhaust-gas-introduction side and a discharge-side cell adjacent to the introduction-side cell and having an end opened on the exhaust-gas-discharge side are divided by a porous partition wall; and a catalyst layer formed in the pores of the partition wall. In the pore diameter distribution, the mode pore diameter of the partition wall where the catalyst layer is formed is 0.9X or less, where X is the mode pore diameter of the partition wall of the wall-flow-type base material.

Description

Exhaust gas purification catalyst

The present invention relates to an exhaust gas purifying catalyst.

排ガス The exhaust gas discharged from the internal combustion engine contains particulate matter (PM) mainly composed of carbon, ash composed of non-combustible components, etc., and is known to cause air pollution. Conventionally, the emission of particulate matter was strictly regulated in diesel engines, which emit relatively more particulate matter than gasoline engines, but in recent years, regulations on emission of particulate matter have also been tightened in gasoline engines. Is being done.

As a means for reducing the emission of particulate matter, there is known a method of providing a particulate filter for depositing and collecting particulate matter in an exhaust gas passage of an internal combustion engine. In particular, in recent years, from the viewpoint of space saving of mounting space, etc., emission control of particulate matter and removal of harmful components such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) have been carried out. In order to perform the treatment at the same time, it has been studied to apply a catalyst slurry to a particulate filter and to provide a catalyst layer by firing the catalyst slurry.

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

WO2016 / 060048

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

従来 Also, particulate matter emitted from automobile diesel engines has been regulated by emission mass. However, the ultra-fine particles, which easily enter the human body and are likely to have an effect on health, are hardly reflected in the numerical value. Therefore, in recent years, a PN (Particle Rate Number) regulation that regulates particles by the number of discharged particles has been introduced.

ガソリン In the past, gasoline engines emitted much less particulate matter than diesel engines. Therefore, emission control of particulate matter for gasoline engines has not been actively carried out compared to diesel engines. In recent years, however, PN regulations have been introduced for gasoline engines.

The amount of particulate matter emitted from a gasoline engine is different from the amount of particulate matter emitted from a diesel engine. For example, the PM particle number regulation (6 × 10 ¹¹ / km) in the case of a gasoline engine is said to correspond to 0.4 to 0.5 mg / km in terms of PM mass. On the other hand, the regulation value of particulate matter in diesel engines is 5 mg / km (0.005 g / km). As described above, even with regard to the regulation of particulate matter, there is a difference in required collecting performance between a gasoline engine and a diesel engine.

Generally, in order to improve the trapping performance, a fine filter is used, which causes an increase in pressure loss. Therefore, technology that can reduce the number of soot emissions from gasoline engines without increasing pressure loss while complying with PN regulations for gasoline engines whose combustion method and exhaust temperature are completely different from diesel engines Is desired.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust gas purifying catalyst in which soot collection performance is increased without increasing pressure loss in order to comply with PN regulations. is there. In addition, the present invention is not limited to the object described above, and is an operation and effect derived from each configuration shown in the embodiment for carrying out the invention described later, and also has an operation and effect that cannot be obtained by the conventional technology. It can be positioned for other purposes.

The present inventors have conducted intensive studies on a method for improving soot collecting performance. As a result, it has been found that the soot collection performance is improved by forming a catalyst layer that does not reduce the small-diameter pores suitable for soot collection, while reducing the large-diameter pores through which soot can easily pass, The present invention has been completed. That is, the present invention provides various specific embodiments described below.

[1]
An exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,
The introduction-side cell whose end on the exhaust gas introduction side is open, and the discharge-side cell whose end on the exhaust gas discharge side is open adjacent to the introduction-side cell, a wall flow type substrate defined by a porous partition wall, ,
And a catalyst layer formed in the pores of the partition wall,
In the pore diameter distribution, when the mode pore diameter of the partition wall of the wall flow type substrate is X, the mode pore diameter of the partition wall on which the catalyst layer is formed is 0.9X or less,
Exhaust gas purification catalyst.
[2]
The mode pore diameter X of the partition wall of the wall flow type substrate is 10 to 30 μm;
The exhaust gas purifying catalyst according to [1].
[3]
The mode pore diameter of the partition wall on which the catalyst layer is formed is 0.6X or more,
The exhaust gas purifying catalyst according to [1] or [2].
[4]
In the pore size distribution where the minimum pore size is 1 μm,
When the D30 pore diameter of the partition wall of the wall flow type substrate is Y, the D30 pore diameter of the partition wall on which the catalyst layer is formed is 0.6 to 0.9Y,
When the D70 pore diameter of the partition wall of the wall flow type substrate is Z, the D70 pore diameter of the partition wall on which the catalyst layer is formed is 0.5 to 0.8Z.
The exhaust gas purifying catalyst according to any one of [1] to [3].
[5]
The internal combustion engine is a gasoline engine,
The exhaust gas purifying catalyst according to any one of [1] to [4].
[6]
A method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,
An introduction-side cell in which the end on the exhaust gas introduction side is open, and a discharge-side cell in which the end on the exhaust gas discharge side is open adjacent to the introduction-side cell, a wall flow type substrate defined by a porous partition wall. The step of preparing,
A catalyst layer forming step of applying a catalyst slurry to at least a part of the pore surface in the partition wall of the wall flow type substrate to form a catalyst layer,
In the catalyst layer forming step, in the pore diameter distribution, when the mode pore diameter of the partition of the wall flow type substrate is X, the mode pore diameter of the partition on which the catalyst layer is formed is 0.9X or less. Obtaining the exhaust gas purifying catalyst,
A method for producing an exhaust gas purifying catalyst.
[7]
The internal combustion engine is a gasoline engine,
The method for producing an exhaust gas purifying catalyst according to [6].

According to the present invention, it is possible to provide an exhaust gas purifying catalyst and the like having improved soot trapping performance. The exhaust gas purifying catalyst can be effectively used as a gasoline particulate filter (GPF) supporting the catalyst, and the performance of an exhaust gas treatment system equipped with such a particulate filter can be further enhanced.

It is a sectional view showing typically one mode of an exhaust gas purification catalyst of this embodiment. FIG. 3 is a view showing a pore size distribution of Example 1, Comparative Example 1, and a substrate. FIG. 9 is a graph showing a relationship between a soot collection rate and a pore narrowing ratio (a ratio of a mode pore diameter of a partition wall on which a catalyst layer is formed to a mode pore diameter of a partition wall of a wall flow type substrate) in Examples and Comparative Examples. is there.

Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these. In addition, the present invention can be arbitrarily modified and implemented without departing from the gist thereof. In this specification, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. The dimensional ratios in the drawings are not limited to the illustrated ratios. In this specification, the “mode pore diameter” refers to the pore diameter (maximum value of the distribution) having the largest appearance ratio in the frequency distribution of the pore diameter, and the “D30 pore diameter” refers to the minimum pore diameter of 1 μm. In the cumulative distribution of volume-based pore diameters, the pore diameter when the integrated value from the small pore diameter reaches 30% of the whole is referred to. "D70 pore diameter" is the volume-based pore diameter with the minimum pore diameter being 1 µm. Means the pore size when the integrated value from the small pore size reaches 70% of the total in the cumulative distribution of. The “D90 particle size” refers to the particle size when the integrated value from the small particle size reaches 90% of the whole in the cumulative distribution of the volume-based particle size. Further, in the present specification, when a numerical value or a property value is sandwiched before and after using “to”, it is used as including the values before and after. For example, the notation of the numerical range of “1 to 100” includes both the lower limit “1” and the upper limit “100”. The same applies to the notation of other numerical ranges.

[Exhaust gas purification catalyst]
The exhaust gas purifying catalyst of the present embodiment is an exhaust gas purifying catalyst 100 for purifying exhaust gas discharged from a gasoline engine which is an internal combustion engine, and includes an inlet cell 11 having an open end 11a on the exhaust gas inlet side, A discharge-side cell 12 adjacent to the cell 11 and having an open end 12 a on the exhaust gas discharge side has a wall-flow-type substrate 10 defined by a porous partition wall 13, and a catalyst layer formed in pores of the partition wall 13. In the pore diameter distribution, when the mode pore diameter of the partition 13 of the wall flow type substrate 10 is X, the mode pore diameter of the partition 13 on which the catalyst layer 21 is formed is 0.6X or more. In a pore size distribution of 0.9X or less and a minimum pore size of 1 μm, when the pore size D30 of the partition wall of the wall flow type substrate is Y, the D3 of the partition wall on which the catalyst layer is formed is D3. When the pore diameter is 0.55 to 0.80Y and the D70 pore diameter of the partition wall of the wall flow type substrate is Z, the D70 pore diameter of the partition wall on which the catalyst layer is formed is 0.70 to 0.80Y. 0.90Z.

Hereinafter, each configuration will be described with reference to a cross-sectional view schematically illustrating the exhaust gas purification catalyst of the present embodiment illustrated 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, the exhaust gas discharged from the internal combustion engine flows into the introduction-side cell 11 from the end portion 11a (opening) on the exhaust gas introduction side, passes through the pores of the partition wall 13, and passes through. Flows into the adjacent discharge-side cell 12 and flows out from the end portion 12a (opening) on the exhaust gas discharge side. In this process, the particulate matter (PM) that hardly passes through the pores of the partition 13 is generally deposited on the partition 13 in the introduction-side cell 11 and / or in the pores of the partition 13, and the deposited particulate matter is: The fuel is removed by burning due to the catalytic function of the catalyst layer 21 or at a predetermined temperature (for example, about 500 to 700 ° C.). Further, the exhaust gas comes into contact with the catalyst layer 21 formed in the pores of the partition 13, whereby carbon monoxide (CO) and hydrocarbon (HC) contained in the exhaust gas are converted into water (H ₂ O) and carbon dioxide ( CO ₂ ) and the like, nitrogen oxides (NOx) are reduced to nitrogen (N ₂ ), and harmful components are purified (made harmless). In this 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”. Hereinafter, each configuration will be described in more detail.

(Pore diameter)
Since gasoline engines operate at higher temperatures than diesel engines, the size of particulate matter in exhaust gas tends to be smaller than diesel engines. The collection mode of the particulate matter differs depending on the diameter. The particle size of particulate matter discharged from a gasoline engine is generally about 100 nm. As a mode for trapping such small-diameter particulate matter, the diffusion contribution of the particles is large. That is, it is considered that the filter is designed so as to reduce the diameter of the pores through which the particulate matter passes and to increase the frequency of contact with the particle, thereby leading to an improvement in the trapping performance of the particulate matter.

Based on this, the exhaust gas purifying catalyst of the present embodiment reduces the large-diameter pores through which soot passes by reducing the pore diameter by forming the catalyst layer 21, and closes the pores by forming the catalyst layer 21. By maintaining the small pores suitable for soot collection by suppressing the soot collection, soot collection performance is improved. From such a viewpoint, in the present embodiment, it is specified that the pore size distribution of the partition 13 before forming the catalyst layer 21 and the pore size distribution of the partition 13 on which the catalyst layer 21 is formed have a predetermined relationship. I do. Specifically, by defining the relationship between the mode pore diameter X of the partition 13 on which the catalyst layer 21 is formed and the mode pore diameter X of the partition 13 before the catalyst layer 21 is formed, each pore diameter distribution is obtained. Define the relationship. Further, in a preferred embodiment in which the relationship between the respective pore diameter distributions is defined in more detail, the partition walls 13 before the formation of the catalyst layer 21 and the partition walls 13 on which the catalyst layer 21 is formed have a D30 pore diameter and a D70 pore diameter. The relationship is also specified.

In the pore diameter distribution, when the mode pore diameter of the partition 13 of the wall flow type substrate 10 is X, the mode pore diameter of the partition 13 on which the catalyst layer 21 is formed is 0.9X or less, and preferably 0 or less. It is 0.6X or more and 0.89X or less, more preferably 0.65X or more and 0.88X or less, and 0.65X or more and 0.85X or less. When the mode pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.9X or less, soot collecting performance is further improved. Further, when the mode pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.6X or more, an increase in pressure loss tends to be further suppressed. The multiplier of “0.9” in the notation of “0.9X” indicates a ratio of the mode pore diameter of the partition wall on which the catalyst layer is formed to the mode pore diameter of the partition wall of the wall flow type substrate. In 100% notation is also referred to as a pore narrowing ratio. Hereinafter, the pores narrowing ratio mode pore diameter called NR _M, pore narrowing ratio of D30 pore diameter, which will be described later called _{NR D30,} the pores narrowing ratio of D70 pore diameter of _{NR D70.}

Further, from the viewpoint of suppressing pore blockage due to the formation of the catalyst layer 21 and more directly defining that small pores suitable for soot collection are maintained, the pore size distribution with the minimum pore size of 1 μm is used. When the diameter of D30 pores of the partition 13 of the wall flow type substrate 10 is Y, it is preferable to define the diameter of D30 pores of the partition 13 on which the catalyst layer 21 is formed. The D30 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.55Y or more and 0.80Y or less, preferably 0.60Y or more and 0.80Y or less, and more preferably 0.65Y or more and 0.80Y or less. And more preferably 0.65Y or more and 0.75Y or less. When the D30 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.80Y or less, the soot collecting performance tends to be further improved. Further, when the D30 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.55Y or more, an increase in pressure loss tends to be further suppressed.

Further, from the viewpoint of reducing the pore diameter by the formation of the catalyst layer 21 and more directly defining the reduction of large pores through which soot passes easily, in the pore diameter distribution where the minimum pore diameter is 1 μm, When the D70 pore diameter of the partition wall of the flow-type base material is Z, it is preferable to define the D70 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed. The D70 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.70Z or more and 0.90Z or less, preferably 0.75Z or more and 0.90Z or less, more preferably 0.80Z or more and 0.90Z or less. It is. When the D70 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.90Z or less, soot collecting performance tends to be further improved. Further, when the D70 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.70Z or more, an increase in pressure loss tends to be further suppressed.

In addition, by reducing the pore diameter by forming the catalyst layer 21, it is possible to reduce large-diameter pores through which soot is likely to pass, and to suppress so-called pore blocking due to the formation of the catalyst layer 21. from the viewpoint of maintaining the small diameter pores, pore narrowing rate NR _M mode pore diameter, D30 pore narrowing ratio of pore diameter _NR D30 pore narrowing ratio _{NR D70} of D70 pore diameter preferably has the following relationship.

The ratio of the pore narrowing ratio _{NR D30} for pore narrowing rate _{_{_{NR M (NR D30 / NR M}}} ) is preferably less than 1, more preferably 0.5 to 0.95, and more preferably 0.6 to 0 .9. The ratio of the pore narrowing ratio _{NR D70} for pore narrowing rate _{_{_{NR M (NR D70 / NR M}}} ) is preferably 0.9-1.3, more preferably 1.01 to 1.2 further Preferably it is 1.02 to 1.1. Thus, by reducing the large-diameter pores through which soot is likely to pass, by maintaining small-diameter pores suitable for soot collection, the soot collection rate tends to improve while suppressing an increase in pressure loss. It is in.

The total pore volume of the exhaust gas purifying catalyst is 0.4 cc / g or more, more preferably 0.4 to 0.8 cc / g, and still more preferably 0.5 to 0.7 cc / g. When the total pore volume is 0.4 cc / g or more, improvement in pressure loss tends to be further suppressed.

In addition, each pore diameter and total pore volume mean values calculated by the mercury intrusion method under the conditions described in the following examples.

The method for adjusting the mode pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is not particularly limited. For example, while adjusting the coating amount of the catalyst layer formed in the pores of the partition wall 13, Under the conditions of the coating amount, there is a method of reducing small-diameter pores closed by the catalyst layer 21. As a method of suppressing the blockage of the small-diameter pores, there is a method of adjusting the viscosity of the catalyst slurry by adjusting the pH of the catalyst slurry to reduce the concentration of the catalyst slurry in the small-diameter pores due to the capillary phenomenon. In addition, the mode pore diameter X, the D30 pore diameter Y, and the D70 pore diameter Z of the partition wall 13 before forming the catalyst layer 21 can be adjusted by selecting a wall flow type substrate.

The method for adjusting the D70 pore diameter of the partition wall on which the catalyst layer is formed and the D30 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed can be the same as described above. Further, as a method of adjusting the total pore volume to a predetermined range, a method of adjusting the coating amount of the catalyst layer can be mentioned.

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

As the base material 10, various materials and shapes used in conventional applications of this kind can be used. For example, the material of the base material may be exposed to high-temperature (for example, 400 ° C. or more) exhaust gas generated when the internal combustion engine is operated under high load conditions, or may be used to burn and remove particulate matter at a high temperature. A material made of a heat-resistant material is preferable so as to be compatible. Examples of the heat-resistant material include ceramics such as cordierite, mullite, aluminum titanate, and silicon carbide (SiC); and alloys such as stainless steel. Further, the shape of the base material can be appropriately adjusted from the viewpoint of exhaust gas purification performance, suppression of pressure loss rise, and the like. For example, the outer shape of the substrate can be a cylindrical shape, an elliptical cylindrical shape, a polygonal cylindrical shape, or the like. In addition, the capacity of the base material (total volume of the cell) is preferably 0.1 to 5 L, more preferably 0.5 to 3 L, although it depends on the space in which the substrate is incorporated. The total length of the substrate in the stretching direction (the total length of the partition 13 in the stretching direction) is preferably 10 to 500 mm, more preferably 50 to 300 mm.

The introduction-side cell 11 and the discharge-side cell 12 are regularly arranged along the axial direction of the cylindrical shape, and adjacent cells alternately have one open end and the other open end in the extending direction. It is sealed. The introduction-side cell 11 and the discharge-side cell 12 can be set to appropriate shapes and sizes in consideration of the flow rate and components of the supplied exhaust gas. For example, the opening shapes of the inlet-side cell 11 and the outlet-side cell 12 can be triangular; rectangular such as square, parallelogram, rectangular, and trapezoidal; other polygons such as hexagonal and octagonal; circular. . Further, the cross-sectional area of the introduction-side cell 11 and the cross-sectional area of the discharge-side cell 12 may have a High Ash Capacity (HAC) structure.

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

The partition wall 13 that separates adjacent cells is not particularly limited as long as it has a porous structure through which exhaust gas can pass, and the configuration thereof includes exhaust gas purification performance, suppression of increase in pressure loss, and mechanical strength of the substrate. It can be adjusted appropriately from the viewpoint of improvement of the quality. For example, when the catalyst layer 21 is formed on the surface of the pores in the partition walls 13 using a catalyst slurry described later, when the mode pore diameter X and the pore volume are large, the pores are hardly clogged by the catalyst layer 21, and the Although the exhaust gas purifying catalyst tends to have a low pressure loss, the trapping capacity of particulate matter is reduced and the mechanical strength of the base material is also reduced. On the other hand, when the pore diameter and the pore volume are small, the pressure loss tends to increase, but the trapping ability of the particulate matter is improved and the mechanical strength of the base material tends to be improved.

From such a viewpoint, the porosity of the partition wall 13 is preferably 20 to 80%, more preferably 40 to 70%, and further preferably 60 to 70%. When the porosity is equal to or more than the lower limit, an increase in pressure loss tends to be further suppressed. When the porosity is equal to or less than the upper limit, the strength of the base material tends to be further improved. The porosity means a value calculated by the mercury porosimetry under the conditions described in the following examples.

The mode pore diameter X of the partition wall of the wall flow type base material is soot when the mode pore diameter of the partition wall 13 before the catalyst layer 21 is formed and the mode pore diameter of the partition wall 13 on which the catalyst layer 21 is formed have the above relationships. From the viewpoint of exhibiting a more balanced collection performance and suppression of pressure loss increase. Specifically, in the pore diameter distribution, the mode pore diameter X of the partition wall of the wall flow type substrate is preferably 10 to 30 μm, more preferably 12 to 28 μm, and further preferably 15 to 25 μm.

(Catalyst layer)
Next, the catalyst layer 21 formed in the pores of the partition 13 will be described. As the catalyst layer 21, various modes used in conventional applications of this type can be used. For example, an embodiment of the catalyst layer 21 includes a catalyst layer obtained by firing a catalyst slurry containing catalyst metal particles and carrier particles. The catalyst layer 21 formed by firing the catalyst slurry containing various particles as described above has a microporous structure in which the particles are welded by firing.

触媒 The catalyst metal contained in the catalyst layer 21 is not particularly limited, and various metal species that can function as various oxidation catalysts and reduction catalysts can be used. For example, platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) can be used. 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 contains one or more catalyst metals in a mixed state as described above. In particular, when two or more kinds of catalyst metals are used in combination, a synergistic effect due to having different catalytic activities is expected.

The embodiment of the combination of such catalyst metals is not particularly limited, and 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 catalyst metal having excellent oxidation activity and reduction. Combinations of catalyst metals having excellent activity are mentioned. Among these, as one aspect of the synergistic effect, a combination of a catalyst metal having excellent oxidation activity and a catalyst metal having excellent reduction activity is preferable, and a combination containing at least Rh, Pd and Rh, or Pt and Rh is more preferable. With such a combination, the exhaust gas purification performance tends to be further improved.

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

As the carrier particles contained in the catalyst layer 21 and supporting the catalyst metal, inorganic compounds conventionally used in this type of exhaust gas purifying catalyst can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ) and ceria-zirconia composite oxide (CZ composite oxide), aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO ₂ ) ₂ ), oxides such as silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO ₂ ), and composite oxides containing these oxides as main components. These 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) means that when the air-fuel ratio of the exhaust gas is lean (that is, the atmosphere on the oxygen excess side), oxygen in the exhaust gas is stored and the air-fuel ratio of the exhaust gas is rich ( That is, the atmosphere that releases the occluded oxygen is referred to as the atmosphere on the side of excess fuel.

The amount of the catalyst layer of the exhaust gas purifying catalyst 100 is an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine, in particular, a gasoline engine, and particularly used for collecting particulate matter. (Coating amount of the catalyst layer excluding the weight of the catalyst metal per 1 L of the wall flow type substrate) is preferably 20 to 110 g / L, more preferably 40 to 90 g / L, and further preferably 50 to 70 g. / L.

[Method of manufacturing exhaust gas purifying catalyst]
The production method of the present embodiment is a method for producing an exhaust gas purifying catalyst 100 for purifying exhaust gas discharged from a gasoline engine as an internal combustion engine. The production method includes: an introduction-side cell 11 having an open end 11a on the exhaust gas introduction side; A step S0 of preparing a wall flow type base material 10 defined by a porous partition wall 13 and a discharge side cell 12 adjacent to the introduction side cell 11 and having an open end 12a on the exhaust gas discharge side; A catalyst slurry is applied to at least a part of the pore surface in the partition 13 of the material 10 to form a catalyst layer 21; and a catalyst layer forming step S1 is performed in the catalyst layer forming step S1. In the pore size distribution, when the mode pore size of the partition 13 of the wall flow type substrate 10 is X, the mode pore size of the partition 13 on which the catalyst layer 21 is formed is 0.6X or more and 0.9X or less. In the pore diameter distribution where the minimum pore diameter is 1 μm, when the D30 pore diameter of the partition 13 of the wall flow type substrate 10 is Y, the D30 pore diameter of the partition 13 on which the catalyst layer 21 is formed is 0.55 to Exhaust gas wherein the D70 pore diameter of the partition 13 on which the catalyst layer 21 is formed is 0.70 to 0.90Z, where Z is the D70 pore diameter of the partition 13 of the wall flow type substrate 10. It is characterized in that the purification catalyst 100 is obtained.

Hereinafter, each step will be described. In this specification, the wall flow type base material before forming the catalyst layer 21 is referred to as “base material 10”, and the wall flow type base material after forming the catalyst layer 21 is referred to as “exhaust gas purifying catalyst 100”. ".

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

<Catalyst layer forming step>
In the catalyst layer forming step S1, a catalyst slurry is applied to the pore surfaces of the partition walls 13, dried, and fired to form the catalyst layer 21. The method for applying the catalyst slurry is not particularly limited. For example, a method in which a part of the base material 10 is impregnated with the catalyst slurry and spread over the entire partition 13 of the base material 10 is exemplified. More specifically, the impregnating step S1a of impregnating the catalyst slurry into the end portion 11a on the exhaust gas introduction side or the end portion 12a on the exhaust gas discharge side, and gas is introduced into the base material 10 from the end portion impregnated with the catalyst slurry. A method including a coating step S1b for coating the partition walls 13 with the catalyst slurry impregnated in the base material 10 by introducing the base material 10 may be used.

(4) The method of impregnating the catalyst slurry in the impregnation step S1a is not particularly limited, and includes, for example, a method of immersing the end of the base material 10 in the catalyst slurry. In this method, if necessary, the catalyst slurry may be pulled up by discharging (sucking) gas from the opposite end. The end to be impregnated with the catalyst slurry may be either the end 11a on the exhaust gas introduction side or the end 12a on the exhaust gas discharge side, but it is preferable to impregnate the end 11a on the exhaust gas introduction side with the catalyst slurry. Thus, the gas can be introduced in the coating step S1b in the same direction as the exhaust gas introduction direction, and the catalyst slurry can be applied to the complicated pore shape along the flow of the exhaust gas. Therefore, suppression of a rise in pressure loss of the obtained exhaust gas purifying catalyst is expected, and improvement in exhaust gas purifying performance can be expected.

{Circle around (4)} In the coating step S1b, the catalyst slurry moves from the introduction side of the substrate 10 to the back along the flow of the gas F, and reaches the end on the gas F discharge side. In the process, the catalyst slurry can be applied to the inside of the pores by passing the catalyst slurry through the inside of the pores of the partition 13, and the catalyst slurry is applied to the entire partition.

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 evaporates from the catalyst slurry. For example, the drying temperature is preferably from 100 to 225 ° C, more preferably from 100 to 200 ° C, and even more preferably from 125 to 175 ° C. Further, 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 slurry is fired to form the catalyst layer 21. The firing conditions in the firing step S1d are not particularly limited as long as the catalyst layer 21 can be formed from the catalyst slurry. For example, the firing temperature is not particularly limited, but is preferably from 400 to 650 ° C, more preferably from 450 to 600 ° C, and still more preferably from 500 to 600 ° C. Further, the firing time is preferably 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

In addition, from the viewpoint of being used for exhaust gas purifying catalyst for purifying exhaust gas discharged from a gasoline engine, particularly for use in collecting particulate matter, the coating amount of the catalyst layer of the exhaust gas purifying catalyst 100 obtained through the calcination step S1d. (Coating amount of the catalyst layer excluding the weight of the catalyst metal per 1 L of the wall flow type substrate) is preferably 20 to 110 g / L, more preferably 40 to 90 g / L, and further preferably 50 to 70 g. / L.

(Catalyst slurry)
The catalyst slurry for forming the catalyst layer 21 will be described. The catalyst slurry contains a 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 and used. The solid content of the catalyst slurry is preferably 1 to 50% by mass, more preferably 15 to 40% by mass, and still more preferably 20 to 40% by mass, from the viewpoint of coatability into the pores of the partition wall 13. 35% by mass. With such a solid content ratio, the catalyst slurry tends to be easily applied to the introduction-side cells 11 in the partition walls 13.

触媒 The D90 particle size of the catalyst powder contained in the catalyst slurry is preferably 1 to 7 μm, more preferably 1 to 5 μm, and still more preferably 1 to 3 μm. When the D90 particle diameter is 1 μm or more, the pulverization time when the catalyst powder is crushed by a milling device can be reduced, and the working efficiency tends to be further improved. Further, when the D90 particle diameter is 7 μm or less, it is suppressed that the coarse particles block the pores in the partition wall 13 and the increase in pressure loss tends to be suppressed. In this specification, the D90 particle size can be measured with a laser diffraction particle size distribution analyzer (eg, a laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation).

触媒 The catalyst metal contained in the catalyst slurry is not particularly limited, and various metal species that can function as various oxidation catalysts and reduction catalysts can be used. For example, platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) can be used. 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 catalytic metal particles, inorganic compounds conventionally used in this type of exhaust gas purifying catalyst can be considered. For example, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ) and ceria-zirconia composite oxide (CZ composite oxide), aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide (zirconia: ZrO ₂ ) ₂ ), oxides such as silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO ₂ ), and composite oxides containing these oxides as main components. These 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) means that when the air-fuel ratio of the exhaust gas is lean (that is, the atmosphere on the oxygen excess side), oxygen in the exhaust gas is stored and the air-fuel ratio of the exhaust gas is rich ( That is, the atmosphere that releases the occluded oxygen is referred to as the atmosphere on the side of excess fuel. From the viewpoint of exhaust gas purification performance, the specific surface area of the carrier particles contained in the catalyst slurry is preferably from 10 to 500 m ² / g, and more preferably from 30 to 200 m ² / g.

In the present embodiment, in the coating step S1b to the baking step S1d, a catalyst layer is formed that reduces large-diameter pores through which soot easily passes and does not decrease small-diameter pores suitable for soot collection. Accordingly, when the mode pore diameter of the partition 13 of the wall flow type substrate 10 is X, the mode pore diameter of the partition 13 on which the catalyst layer 21 is formed is 0.6X or more and 0.9X or less, In the pore diameter distribution having a pore diameter of 1 μm, when the D30 pore diameter of the partition wall of the wall flow type substrate 10 is Y, the D30 pore diameter of the partition wall 13 on which the catalyst layer 21 is formed is 0.55 to 0.80 Y. When the D70 pore diameter of the partition 13 of the wall flow type substrate 10 is Z, the exhaust gas purification in which the D70 pore diameter of the partition 13 on which the catalyst layer 21 is formed is 0.70 to 0.90Z. Get the medium 100. Depending on its viscosity and surface tension, the catalyst slurry can have various properties, such as a property of easily drying in a state of infiltration into small-diameter pores due to a capillary phenomenon and a property of not easily penetrating into small-diameter pores. Here, by using a catalyst slurry having physical properties that are hard to penetrate into the small-diameter pores, the pore diameter can be reduced by forming the catalyst layer 21 in the large-diameter pores, soot can easily pass through. In addition to reducing the large-diameter pores, in the small-diameter pores, blockage due to the formation of the catalyst layer 21 can be suppressed, and the decrease in small-diameter pores suitable for soot collection due to pore blockage can be suppressed.

[Use]
An air-fuel mixture containing oxygen and fuel gas is supplied to an internal combustion engine, and the air-fuel mixture is burned to convert combustion energy into mechanical energy. The air-fuel mixture burned at this time is discharged as exhaust gas to an exhaust system. The exhaust system is provided with an exhaust gas purifying device provided with an exhaust gas purifying catalyst, and harmful components (for example, carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) contained in exhaust gas by the exhaust gas purifying catalyst are provided. )) Is purified, and particulate matter (PM) contained in the exhaust gas is collected and removed. In particular, the exhaust gas purifying catalyst 100 of the present embodiment is preferably used for a gasoline particulate filter (GPF) that can collect and remove particulate matter contained in exhaust gas of a gasoline engine.

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

(Example 1)
Alumina powder, zirconia powder and ceria-zirconia composite oxide powder were impregnated with an aqueous solution of palladium nitrate, and then calcined at 500 ° C. for 1 hour to obtain a Pd-supported powder. Further, an alumina powder and a zirconia powder were impregnated with an aqueous solution of rhodium nitrate, and then calcined at 500 ° C. for 1 hour to obtain a Rh-supported powder.

480 g of the obtained Pd-supported powder and 390 g of Rh-supported powder, 95 g of ceria-zirconia composite oxide powder, and ion-exchanged water are mixed, and the obtained mixture is charged into a ball mill, and the catalyst powder has a predetermined particle size distribution. To obtain a catalyst slurry having a D90 particle size of 3.0 μm. 29 g of barium hydroxide octahydrate and 60% nitric acid were mixed with the obtained catalyst slurry to obtain a catalyst slurry having a pH of 6.7.

Next, a cordierite wall flow type honeycomb substrate (cell number / mil thickness: 300 cpsi / 8.5 mil, diameter: 118.4 mm, total length: 127 mm, mode pore diameter X: 20 μm, porosity: 65%) is prepared. did. The end of the base material on the exhaust gas introduction side was immersed in the catalyst slurry, and vacuum suction was performed from the opposite end side to impregnate and hold the catalyst slurry at the end of the base material. By flowing gas into the base material from the end on the exhaust gas introduction side, coating the catalyst slurry on the pore surface in the partition wall, and blowing off excess catalyst slurry from the end on the exhaust gas discharge side of the base material The gas flow was stopped. Thereafter, the base material coated with the catalyst slurry was dried at 150 ° C., and then calcined at 550 ° C. in an air atmosphere to prepare an exhaust gas purifying catalyst. In addition, the coating amount of the catalyst layer after the firing was 59.1 g (excluding the weight of the platinum group metal) per 1 L of the base material.

(Example 2)
An alumina powder was impregnated with an aqueous solution of palladium nitrate to obtain a Pd-supported powder. Further, an alumina powder was impregnated with an aqueous rhodium nitrate solution to obtain a Rh-supported powder. Exhaust gas purification catalyst was prepared in the same manner as in Example 1 except that the obtained Pd-supported powder and Rh-supported powder were mixed with ceria-zirconia composite oxide powder, a 46% lanthanum nitrate aqueous solution, and ion-exchanged water. did. The coating amount of the catalyst layer after firing was 60.9 g per 1 L of the substrate (excluding the weight of the platinum group metal).

(Example 3)
An exhaust gas purifying catalyst was prepared in the same manner as in Example 1 except that 44.9 g of ammonium carbonate (pH adjuster) was mixed with the obtained catalyst slurry to obtain a catalyst slurry having a pH of 5.1. . The coating amount of the catalyst layer after firing was 60.0 g (excluding the weight of the platinum group metal) per 1 L of the base material.

(Example 4)
An aqueous solution of palladium nitrate was impregnated into the alumina powder and the ceria-zirconia composite oxide powder to obtain a Pd-supported powder. Further, an rhodium nitrate aqueous solution was impregnated into the alumina powder and the ceria-zirconia composite oxide powder to obtain a Rh-supporting powder. Example 2 was repeated except that 33 g of ammonium carbonate (pH adjuster) was mixed with the catalyst slurry prepared using the obtained Pd-supported powder and Rh-supported powder to obtain a catalyst slurry having a pH of 5.1. Similarly, an exhaust gas purifying catalyst was produced. The coating amount of the catalyst layer after firing was 62.0 g per 1 L of the substrate (excluding the weight of the platinum group metal).

(Example 5)
An aqueous solution of palladium nitrate was impregnated into the alumina powder and the ceria-zirconia composite oxide powder to obtain a Pd-supported powder. In addition, a rhodium nitrate aqueous solution was impregnated into the zirconia powder to obtain a Rh-supported powder. The obtained Pd-supported powder and Rh-supported powder, the ceria-zirconia composite oxide powder, a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and 96 g of barium hydroxide octahydrate was added to the obtained catalyst slurry. And 27 g of ammonium carbonate (pH adjuster) were mixed to obtain an exhaust gas purifying catalyst in the same manner as in Example 1 except that a catalyst slurry having a pH of 5.5 was obtained. The coating amount of the catalyst layer after firing was 61.8 g (excluding the weight of the platinum group metal) per 1 L of the base material.

(Comparative Example 1)
An exhaust gas purifying catalyst was prepared in the same manner as in Example 1, except that barium hydroxide octahydrate and 60% nitric acid were not mixed with the catalyst slurry in the preparation of the catalyst slurry. The coating amount of the catalyst layer after firing was 60.0 g (excluding the weight of the platinum group metal) per 1 L of the base material.

(Comparative Example 2)
An exhaust gas purifying catalyst was prepared in the same manner as in Example 1, except that barium hydroxide octahydrate and 60% nitric acid were not mixed with the catalyst slurry in the preparation of the catalyst slurry. The coating amount of the catalyst layer after firing was 60.9 g per 1 L of the substrate (excluding the weight of the platinum group metal).

(Comparative Example 3)
An aqueous solution of palladium nitrate was impregnated into the alumina powder and the ceria-zirconia composite oxide powder to obtain a Pd-supported powder. In addition, an aqueous rhodium nitrate solution was impregnated into the ceria-zirconia composite oxide powder to obtain a Rh-supported powder. An exhaust gas purifying catalyst was produced in the same manner as in Comparative Example 1, except that the obtained Pd-supported powder and Rh-supported powder, barium sulfate powder, and ion-exchanged water were mixed. The coating amount of the catalyst layer after firing was 60.0 g (excluding the weight of the platinum group metal) per 1 L of the base material.

(Comparative Example 4)
An aqueous solution of palladium nitrate was impregnated into the ceria-zirconia composite oxide powder to obtain a Pd-supported powder. Also, an aqueous rhodium nitrate solution was impregnated into the zirconia powder to obtain a Rh-supported powder. An exhaust gas purifying catalyst was produced in the same manner as in Comparative Example 1, except that a catalyst slurry was prepared using the obtained Pd-supported powder and Rh-supported powder. The coating amount of the catalyst layer after firing was 60.9 g per 1 L of the substrate (excluding the weight of the platinum group metal).

(Comparative Example 5)
An aqueous solution of palladium nitrate was impregnated into the ceria-zirconia composite oxide powder to obtain a Pd-supported powder. In addition, an rhodium nitrate aqueous solution was impregnated into alumina powder to obtain a Rh-supported powder. An exhaust gas purifying catalyst was produced in the same manner as in Comparative Example 1, except that a catalyst slurry was prepared using the obtained Pd-supported powder and Rh-supported powder. The coating amount of the catalyst layer after firing was 60.9 g per 1 L of the substrate (excluding the weight of the platinum group metal).

[Particle size distribution measurement]
The D90 particle size of the catalyst slurry was measured by a laser scattering method using a laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation.

[Mercury intrusion method]
The exhaust gas purifying catalysts prepared in Examples and Comparative Examples, and the base material before applying the catalyst slurry, from each partition of the exhaust gas introduction side portion, the exhaust gas discharge side portion, and the intermediate portion, the mode pore diameter, D30 Samples (1 cm ³ ) for measuring pore diameter, D70 pore diameter, and pore volume were collected. After drying the measurement sample, the pore distribution was measured by a mercury intrusion method using a mercury porosimeter (manufactured by Thermo Fisher Scientific, trade names: PASCAL140 and PASCAL440). At this time, the low pressure region (0 to 400 Kpa) was measured by PASCAL140, and the high pressure region (0.1 Mpa to 400 Mpa) was measured by PASCAL440. From the obtained pore distribution, the mode pore diameter, D30 pore diameter, and D70 pore diameter were determined, and the pore volume of pores having a pore diameter of 1 μm or more was calculated. In addition, as the values of the pore diameter and the pore volume, the average values of the values obtained in the exhaust gas introduction side portion, the exhaust gas discharge side portion, and the intermediate portion were used.

Next, the porosity of the exhaust gas purifying catalysts manufactured in Examples and Comparative Examples was calculated by the following equation. The results are shown in Table 1 below. FIG. 2 shows the pore volume distributions of the example and the comparative example.
Porosity of exhaust gas purifying catalyst (%) = Porous volume (cc / g) of partition wall on which catalyst layer is formed / Porous volume of substrate (cc / g) x Porosity of substrate (%)
Porosity (%) of base material = 65%

[Measurement of soot collection performance]
The soot collection performance was measured on the premise of PN regulations for gasoline engines. Specifically, the exhaust gas purifying catalysts produced in Examples and Comparative Examples were mounted on a vehicle equipped with a 1.5 L direct injection turbo engine, and a solid particle counting device (manufactured by HORIBA, Ltd., trade name: MEXA-2100 SPCS) was used. The soot emission quantity (PN _test ) during the WLTC mode running was measured. The soot collection rate was calculated by the following equation as a reduction rate from the soot amount (PN _blank ) measured when the above test was carried out without mounting the exhaust gas purifying catalyst. The results are shown in Table 1 below.
Soot collection rate (%) = (PN _blank −PN _test ) / PN _blank × 100 (%)

The results are shown as a relationship between the pore narrowing ratio (the ratio of the mode pore diameter of the partition wall on which the catalyst layer is formed to the mode pore diameter of the partition wall of the wall flow type base material) and the soot collection rate in Examples and Comparative Examples. Are collectively shown in FIG. As shown in FIG. 3, there is a correlation between the pore narrowing rate and the soot collection rate.

[Measurement of pressure loss]
The exhaust gas purifying catalysts prepared in Examples and Comparative Examples, and the base material before applying the catalyst slurry were each installed in a pressure loss measuring device (manufactured by Tsukuba Riki Seiki Co., Ltd.). Was introduced. The value obtained by measuring the differential pressure between the air introduction side and the air discharge side when the amount of air discharged from the exhaust gas purification catalyst was 4 m ³ / min was defined as the pressure loss of the exhaust gas purification catalyst. The results are shown in Table 1 below.

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

DESCRIPTION OF SYMBOLS 10 ... Wall flow type base material 11 ... Introducing cell 11a ... End part on exhaust gas introduction side 12 ... Discharge side cell 12a ... End part on exhaust gas discharge side 13 ... Partition wall 21 ..Catalyst layer 100 ... Exhaust gas purification catalyst

Claims

An exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,
The introduction-side cell whose end on the exhaust gas introduction side is open, and the discharge-side cell whose end on the exhaust gas discharge side is open adjacent to the introduction-side cell, a wall flow type substrate defined by a porous partition wall, ,
And a catalyst layer formed in the pores of the partition wall,
In the pore diameter distribution, when the mode pore diameter of the partition wall of the wall flow type substrate is X, the mode pore diameter of the partition wall on which the catalyst layer is formed is 0.9X or less,
Exhaust gas purification catalyst.
The mode pore diameter X of the partition wall of the wall flow type substrate is 10 to 30 μm;
The exhaust gas purifying catalyst according to claim 1.
The mode pore diameter of the partition wall on which the catalyst layer is formed is 0.6X or more,
The exhaust gas purifying catalyst according to claim 1.
In the pore size distribution where the minimum pore size is 1 μm,
When the D30 pore diameter of the partition wall of the wall flow type substrate is Y, the D30 pore diameter of the partition wall on which the catalyst layer is formed is 0.6 to 0.9Y,
When the D70 pore diameter of the partition wall of the wall flow type substrate is Z, the D70 pore diameter of the partition wall on which the catalyst layer is formed is 0.5 to 0.8Z.
The exhaust gas purifying catalyst according to any one of claims 1 to 3.
The internal combustion engine is a gasoline engine,
The exhaust gas purifying catalyst according to any one of claims 1 to 4.
A method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from an internal combustion engine,
An introduction-side cell in which the end on the exhaust gas introduction side is open, and a discharge-side cell in which the end on the exhaust gas discharge side is open adjacent to the introduction-side cell, a wall flow type substrate defined by a porous partition wall. The step of preparing,
A catalyst layer forming step of applying a catalyst slurry to at least a part of the pore surface in the partition wall of the wall flow type substrate to form a catalyst layer,
In the catalyst layer forming step, in the pore diameter distribution, when the mode pore diameter of the partition of the wall flow type substrate is X, the mode pore diameter of the partition on which the catalyst layer is formed is 0.9X or less. Obtaining the exhaust gas purifying catalyst,
A method for producing an exhaust gas purifying catalyst.
The internal combustion engine is a gasoline engine,
A method for producing the exhaust gas purifying catalyst according to claim 6.