WO2020031792A1

WO2020031792A1 - Method for producing exhaust-gas-purifying catalyst

Info

Publication number: WO2020031792A1
Application number: PCT/JP2019/029870
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: CN112203764B; JP2020025898A; CN112203764A; JP6581262B1

Abstract

A method for producing an exhaust-gas-purifying catalyst that purifies exhaust gas discharged from a gasoline engine, wherein the method has: a step for preparing a wall-flow-type base material, in which an introduction-side cell that is open on an exhaust-gas-introduction-side end and a discharge-side cell that is adjacent to the introduction-side cell and is open on an exhaust-gas-discharge side end are divided by a porous partition wall; an impregnation step for impregnating the exhaust-gas-introduction side end or exhaust-gas-discharge side end of the wall-flow-type base material with a thixotropic catalyst slurry; an application step for introducing a gas into the wall-flow-type base material from the catalyst-slurry-impregnated end, whereby the catalyst slurry with which the wall-flow-type base material is impregnated is applied to the surfaces of pores in the partition wall; a stopping step for stopping introduction of the gas; and a firing step for firing the applied catalyst slurry to obtain an exhaust-gas-purifying catalyst in which the amount of a catalyst layer applied is 20-110 g/L, the TI value of the catalyst slurry being 10-100.

Description

Method for producing exhaust gas purifying catalyst

The present invention relates to a method for producing 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 has been strictly regulated in diesel engines, which emit relatively more particulate matter than gasoline engines.In recent years, however, the regulation of particulate matter emissions has also been regulated in gasoline engines. It is being strengthened.

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 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).

Further, in a method of producing an exhaust gas purifying catalyst other than a particulate filter, for example, in a method of forming a catalyst layer on a cell surface of a base material having a flow-through type structure that does not aim at removing particulate matter, a high shear rate region By adjusting the viscosity of the low shear rate region and the viscosity, the coating time of the catalyst slurry can be shortened, and the method of suppressing blockage of the flow-through type cell (Patent Document 2), or by using a thixotropic slurry, A method for increasing a contact area between a catalyst formed on a cell surface and exhaust gas is known (Patent Document 3).

WO2016 / 060048 JP 2009-11934 A WO2009 / 028422

The particulate filter described in Patent Literature 1 has a wall flow type structure from the viewpoint of removing particulate matter, and is configured so that exhaust gas passes through pores of partition walls. However, there is still room for improvement in soot collection performance.
Patent Documents 2 and 3 relate to a technique of forming a catalyst layer on a partition wall of a flow-through type base material, and the present invention discloses a method of coating a catalyst layer on a pore surface inside a partition wall of a wall flow type base material. Has no relevance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a production method capable of stably obtaining an exhaust gas purifying catalyst having improved soot trapping performance with good reproducibility, and an object of the invention. To provide an improved exhaust gas purifying catalyst and the like. 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 to solve the above-mentioned problems. As a result, it has been found that the soot collection performance of the exhaust gas purifying catalyst is also reduced by pore segregation or uneven coating due to segregation or uneven distribution of the catalyst layer when the catalyst layer is formed. Further, through a specific manufacturing process using a thixotropic slurry, the porosity is maintained at a relatively high level and the pore diameter is compared while suppressing the occurrence of such pore clogging and coating unevenness. The present inventors have found that the soot collection performance of the obtained exhaust gas purifying catalyst can be improved, and have completed the present invention. That is, the present invention provides various specific embodiments described below.

[1]
A method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from a gasoline 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,
An impregnation step of impregnating the end of the wall flow type substrate on the exhaust gas introduction side or the exhaust gas discharge side with a thixotropic catalyst slurry,
By introducing a gas into the wall flow type base material from the end side impregnated with the catalyst slurry, the catalyst slurry impregnated in the wall flow type base material is applied to the pore surfaces of the partition walls. Coating process,
A stopping step of stopping the introduction of the gas,
The coated catalyst slurry is calcined, and the amount of coating of the catalyst layer (the amount of coating of the catalyst layer excluding the weight of the catalyst metal per 1 L of the wall flow type substrate) is 20 to 110 g / L. Baking step to obtain a purification catalyst,
The catalyst slurry has a TI value of 10 to 100,
A method for producing an exhaust gas purifying catalyst.
[2]
The catalyst slurry contains at least one selected from the group consisting of methylamine, dimethylamine, trimethylamine, barium hydroxide, ammonium carbonate, ammonium hydrogen carbonate, and aqueous ammonia,
The method for producing an exhaust gas purifying catalyst according to [1].
[3]
The catalyst slurry has a pH of 3 to 10,
The method for producing an exhaust gas purifying catalyst according to [1] or [2].
[4]
In the coating step, by the stress applied by the introduction of the gas, the viscosity of the thixotropic catalyst slurry decreases,
The method for producing an exhaust gas purifying catalyst according to any one of [1] to [3].
[5]
In the stopping step, the viscosity of the thixotropic catalyst slurry increases,
The method for producing an exhaust gas purifying catalyst according to any one of [1] to [4].
[6]
An exhaust gas purifying catalyst for purifying exhaust gas discharged from a gasoline 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,
An impregnation step in which the catalyst layer impregnates the end of the wall flow type substrate on the exhaust gas introduction side or the exhaust gas discharge side with a thixotropic catalyst slurry; By introducing a gas into the, the application step of applying the catalyst slurry impregnated in the wall flow type substrate to the pore surface of the partition wall, and a stop step of stopping the introduction of the gas, Formed by the catalyst layer forming step,
The coating amount of the catalyst layer of the exhaust gas purifying catalyst (the coating amount of the catalyst layer excluding the mass of the catalyst metal per 1 L of the wall flow type substrate) is 20 to 110 g / L.
Exhaust gas purification catalyst.

According to the present invention, it is possible to provide a production method capable of stably obtaining an exhaust gas purifying catalyst having enhanced soot trapping performance with good reproducibility, and an exhaust gas purifying catalyst obtained by the production method. 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.

FIG. 3 is a process chart schematically showing a method for manufacturing the exhaust gas purifying catalyst of the embodiment. It is a sectional view showing typically one mode of an exhaust gas purification catalyst of this embodiment. It is sectional drawing which shows typically one aspect of the catalyst layer in the partition of the exhaust gas purification catalyst obtained using the catalyst slurry which does not have thixotropy. It is a sectional view showing typically one mode of a catalyst layer in a partition of an exhaust gas purifying catalyst of this embodiment. FIG. 2 is a trace diagram showing a cross section of the exhaust gas purifying catalyst of the first embodiment. FIG. 4 is a trace diagram showing a cross section of the exhaust gas purifying catalyst of Comparative Example 1.

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 the present specification, the “D50 particle size” refers to the particle size when the integrated value from the small particle size reaches 50% of the whole in the cumulative distribution of the volume-based particle size, and “D90 particle size”. Refers to the particle size when the integrated value from the small particle size reaches 90% of the total in the cumulative distribution of the particle size based on volume. Further, in the present specification, when a numerical value or a property value is inserted before and after using “to”, it is used as including the values before and after. For example, a numerical range notation of “1 to 100” includes both the lower limit value “1” and the upper limit value “100”. The same applies to the notation of other numerical ranges.

[Method of manufacturing exhaust gas purifying catalyst]
The production method according to the present embodiment is a method for producing an exhaust gas purifying catalyst 100 for purifying exhaust gas discharged from a gasoline engine. The production method includes an introduction cell 11 having an open end 11 a on the exhaust gas introduction side, and an introduction cell 11. A step S0 of preparing a wall flow-type base material 10 in which an exhaust-side cell 12 having an open end 12a on the exhaust gas discharge side adjacent to the substrate is defined by a porous partition wall 13; An impregnating step S1a for impregnating the catalyst end 21a on the introduction side or the end 12a on the exhaust gas discharge side with the thixotropic catalyst slurry 21a, and into the wall flow type substrate 10 from the end side impregnated with the catalyst slurry 21a. A coating step S1b for applying the catalyst slurry 21a impregnated in the wall flow type substrate 10 to the surface of the pores of the partition 13 by introducing the gas F; The stopping step S1c for stopping the introduction, and firing the coated catalyst slurry 21a, the coating amount of the catalyst layer (the coating amount of the catalyst layer excluding the catalyst metal mass per 1 L of the wall flow type substrate) is A firing step S1d for obtaining an exhaust gas purifying catalyst of 20 to 110 g / L, wherein the TI value of the catalyst slurry is 10 to 100.

Hereinafter, each process will be described with reference to the process diagram schematically illustrating the method for manufacturing the exhaust gas purifying catalyst of the present embodiment shown in FIG. 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, a wall flow type substrate is prepared as a substrate. 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. The capacity of the base material (total volume of the cells) is preferably 0.1 to 5 L, more preferably 0.5 to 3 L, depending on the space into which the substrate is to be 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, 200 cpsi to 400 cpsi is preferred.

The partition 13 that separates adjacent cells is not particularly limited as long as it has a porous structure through which exhaust gas can pass, and its configuration is limited to exhaust gas purification performance, suppression of increase in pressure loss, and mechanical strength of a 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 pore surface in the partition wall 13 using a catalyst slurry 21a described later, the pore diameter (for example, the mode diameter (the pore diameter having the largest appearance ratio in the pore diameter frequency distribution (the When the maximum value))) or the pore volume is large, the pores are not easily blocked by the catalyst layer 21, and the resulting exhaust gas purifying catalyst tends to have a low pressure loss. There is a tendency that the collecting ability decreases and the mechanical strength of the base material also decreases. 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 pore diameter (mode diameter) of the partition walls 13 of the wall flow type substrate 10 before the formation of the catalyst layer 21 is preferably 8 to 25 μm, more preferably 10 to 22 μm, and furthermore Preferably it is 13 to 20 μm. 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. Further, the pore volume of the partition wall 13 by the mercury intrusion method is preferably 0.2 to 1.5 cm ³ / g, more preferably 0.25 to 0.9 cm ³ / g, and still more preferably 0.3 to 0.9 cm ³ / g. ０．８0.8 cm ³ / g. The porosity of the partition walls 13 by the mercury intrusion method is preferably 20 to 80%, more preferably 40 to 70%, and further preferably 60 to 70%. When the pore volume or the porosity is equal to or more than the lower limit, an increase in pressure loss tends to be further suppressed. When the pore volume or the porosity is equal to or less than the upper limit, the strength of the base material tends to be further improved. In addition, the pore diameter (mode diameter), the pore volume, and the porosity mean values calculated by the mercury intrusion method under the conditions described in the following Examples.

<Catalyst layer forming step>
The catalyst layer forming step S1 includes an impregnating step S1a of impregnating the end portion 11a on the exhaust gas introduction side or the end portion 12a on the exhaust gas discharge side of the wall flow type substrate 10 with a thixotropic catalyst slurry 21a, and a catalyst slurry 21a. A coating step of applying the catalyst slurry 21a impregnated in the wall flow type substrate 10 to the porous partition walls 13 by introducing the gas F into the wall flow type substrate 10 from the end side impregnated with S1b, a stopping step S1c for stopping the introduction of the gas F, and a firing step S1d for firing the coated catalyst slurry 21a to obtain an exhaust gas purifying catalyst having a coating amount of the catalyst layer of 20 to 110 g / L. And

In the present embodiment, a thixotropic catalyst slurry 21a is used in which the viscosity is reduced by applying a shear stress and the viscosity is increased by standing without applying a shear stress. Thereby, in the coating step S1b, the viscosity of the catalyst slurry 21a is reduced by the stress applied by the introduction of the gas F, so that the catalyst slurry 21a is uniformly coated on the pore surfaces of the porous partition walls 13. Further, in the stopping step S1c, the viscosity of the catalyst slurry 21a is increased, so that the coated catalyst slurry 21a is prevented from moving in the pores of the partition walls, and segregation or uneven distribution of the catalyst layer is suppressed. can do. Furthermore, by suppressing the occurrence of pore blockage or coating unevenness due to segregation or uneven distribution of the catalyst layer, it is possible to maintain a relatively high porosity and relatively small pore diameter.

抑制 The suppression of segregation or uneven distribution of the catalyst layer is not particularly limited, but is considered as follows. The coated catalyst slurry 21a tends to move to a position where the area of the solid-liquid interface, that is, the contact area with the pore surface of the partition wall 13, increases due to the balance of the surface tension at the gas-liquid interface and the solid-liquid interface. . Therefore, in general, as the volume decreases due to the drying, the catalyst slurry 21a becomes narrower because the contact area with the pore surface of the partition wall 13 such as the small pores 13a having a relatively small pore diameter or the bag-like portion 13b having a bag-like shape is increased. And the catalyst layer tends to be segregated or unevenly distributed (see FIG. 3). On the other hand, in the present embodiment, since the catalyst slurry 21a after being applied has a high viscosity, the movement of the catalyst slurry 21a to the narrow portion is suppressed, so that the small pores 13a are closed or the catalyst is formed in the bag-like portion 13b. Concentration of the slurry 21a can be suppressed, and segregation or uneven distribution of the catalyst layer can be suppressed (see FIG. 4).

The method of applying the catalyst slurry 21a is not particularly limited, but for example, a method of impregnating a part of the base material 10 with the catalyst slurry 21a and spreading the impregnated catalyst slurry 21a over the entire partition 13 of the base material 10 can be mentioned. More specifically, the step S1a of impregnating the catalyst slurry 21a into the end 11a on the exhaust gas introduction side or the end 12a on the exhaust gas discharge side of the base material 10 and the base material from the end side impregnated with the catalyst slurry 21a A method including a coating step S1b of coating the partition walls 13 with the catalyst slurry 21a impregnated in the base material 10 by introducing a gas into the base material 10 is exemplified.

方法 The method of impregnating the catalyst slurry 21a in the impregnation step S1a is not particularly limited, and for example, a method of immersing the end of the base material 10 in the catalyst slurry 21a can be used. In this method, if necessary, the catalyst slurry 21a may be pulled up by discharging (sucking) gas from the opposite end. The end for impregnating the catalyst slurry 21a 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 21a. Thereby, the gas can be introduced in the step S1b in the same direction as the exhaust gas introduction direction, and the catalyst slurry 21a can be applied to a 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.

In the coating step S1b, the viscosity of the impregnated catalyst slurry 21a is reduced by the stress applied by the introduction of the gas F, and the reduced viscosity of the catalyst slurry 21a is reduced by the flow of the gas F from the introduction side of the base material 10 to the back. Along the air, and reaches the end on the discharge side of the gas F. In the process, the catalyst slurry 21a can be applied to the inside of the pores by passing the catalyst slurry 21a through the inside of the pores of the partition 13, and the catalyst slurry 21a is applied to the entire partition.

In the stopping step S1c, the introduction of the gas F is stopped to increase the viscosity of the catalyst slurry 21a, thereby suppressing the movement of the coated catalyst slurry 21a in the pores of the partition walls. The manufacturing method of the present embodiment may include a drying step of drying the applied catalyst slurry 21a after the stopping step S1c. The drying condition in the drying step is not particularly limited as long as the solvent evaporates from the catalyst slurry 21a. 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 21a uniformly coated as described above 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 21a. 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 firing 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 21a for forming the catalyst layer 21 will be described. The catalyst slurry 21a used in the present embodiment has thixotropic properties. In the present embodiment, “thixotropic” refers to a property in which the viscosity decreases with time when flowing at a constant shear rate, and then returns to the original viscosity again after stopping the flow and resting for a while. Further, the “viscosity” in the present embodiment refers to a value measured using a rheometer at a predetermined shear rate at 25 ° C.

The viscosity η ₁₀ at a shear rate of 10 s ⁻¹ is preferably 50 to 1500 mPa · s, more preferably 200 to 1300 mPa · s, and still more preferably 300 to 1200 mPa · s. Viscosity eta ₁₀ is obtained by assuming the viscosity of the catalyst slurry is coated on the pores surface in the partition wall, by an in viscosity eta ₁₀ above range, movement in the pores of the catalyst slurry 21a was coated is suppressed There is a tendency. Thereby, it is possible to suppress the small pores 13a from being closed or the catalyst slurry 21a from being concentrated on the bag-like portion 13b, and to suppress segregation or uneven distribution of the catalyst layer.

Further, from the viewpoint of having a relatively low viscosity that can uniformly coat the pores in the partition wall 13, the viscosity η ₅₅₀ at a shear rate of 550 s ⁻¹ is preferably 5 to 30 mPa · s, It is more preferably 5 to 20 mPa · s, and still more preferably 5 to 15 mPa · s. The viscosity η ₅₅₀ is based on the viscosity of the catalyst slurry at the time of coating. When the viscosity η ₅₅₀ is within the above range, the uniform coating property of the catalyst slurry tends to be further improved.

Assuming that the ratio of the viscosity η _{10 to} the viscosity η ₅₅₀ (η ₁₀ / η ₅₅₀ ) is the TI value, the TI value is 10 to 100, preferably 20 to 80, and more preferably 40 to 80.

Thixotropic, that is, the viscosity η ₁₀ and the viscosity η ₅₅₀ , and the TI value, which is the ratio thereof, can be adjusted by the solid content and the pH of the catalyst slurry 21a.

(4) The catalyst slurry 21a contains a catalyst powder, a solvent such as water, and a pH adjuster. 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 S1d 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 21a is preferably 1 to 50% by mass, more preferably 10 to 50% by mass, still more preferably 15 to 40% by mass, and particularly preferably 20 to 35% by mass. is there. When the solid content is within the above range, thixotropicity, that is, viscosity η ₁₀ and viscosity η ₅₅₀ can be adjusted.

触媒 The D90 particle size of the catalyst powder contained in the catalyst slurry 21a 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 size is 7 μm or less, the coarse particles are suppressed from closing the inside of 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 21a is not particularly limited, and various metal species that can function as an oxidation catalyst or a reduction catalyst can be used. For example, platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os) can be 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.

The pH adjuster contained in the catalyst slurry is not particularly limited, and includes, for example, at least one selected from the group consisting of methylamine, dimethylamine, trimethylamine, barium hydroxide, ammonium carbonate, ammonium hydrogen carbonate, and aqueous ammonia. Can be By using such a pH adjuster, thixotropic, that is, the viscosity η ₁₀ and the viscosity η ₅₅₀ can be adjusted, and in particular, the viscosity η ₁₀ can be higher and the viscosity η ₅₅₀ can be lower. Among them, barium hydroxide is preferred from the viewpoint that the degree of ionization is large, that is, the pH can be adjusted with a small amount, and it is easily dispersed uniformly in the catalyst slurry. From the viewpoint, methylamine, dimethylamine, trimethylamine, ammonium carbonate, ammonium hydrogen carbonate, and aqueous ammonia are preferable, and ammonium carbonate is more preferable.

The pH of the catalyst slurry is preferably 3 to 10, more preferably 4 to 9, and even more preferably 5 to 8. By setting the pH of the catalyst slurry within the above range, thixotropic, that is, the viscosity η ₁₀ and the viscosity η ₅₅₀ can be adjusted, and in particular, the viscosity η ₁₀ can be higher and the viscosity η ₅₅₀ can be lower. .

The pore diameter (mode diameter) of the partition wall 13 of the exhaust gas purifying catalyst 100 in the state where the catalyst layer 21 is formed by the mercury intrusion method is preferably 10 to 23 μm, more preferably 11 to 20 μm, and still more preferably. Is 12 to 18 μm. The pore volume of the partition wall of the exhaust gas purifying catalyst in the state where the laminated catalyst layer is formed by a mercury intrusion method is preferably 0.2 to 1.0 cm ³ / g, more preferably 0.25 to 0 cm ³ / g. 0.9 cm ³ / g, and more preferably 0.3 to 0.8 cm ³ / g. Further, the porosity of the partition wall of the exhaust gas purifying catalyst in the state where the laminated catalyst layer is formed by a mercury intrusion method is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to 70%. 60%. In addition, the pore diameter (mode diameter), the pore volume, and the porosity mean values calculated by the mercury intrusion method under the conditions described in the following Examples.

(Exhaust gas purification catalyst)
The exhaust gas purifying catalyst according to the present embodiment is an exhaust gas purifying catalyst 100 for purifying exhaust gas discharged from a gasoline engine. The exhaust gas purifying catalyst 100 includes an inlet cell 11 having an open end 11a on the exhaust gas inlet side and an inlet cell 11 adjacent to the inlet cell 11. The discharge-side cell 12 having an open end 12a on the exhaust gas discharge side comprises a wall flow-type substrate 10 defined by a porous partition wall 13 and a catalyst layer 21 formed in pores of the partition wall 13. An impregnating step S1a in which the catalyst layer 21 impregnates the end portion 11a on the exhaust gas introduction side or the end portion 12a on the exhaust gas discharge side of the wall flow type substrate 10 with a thixotropic catalyst slurry 21a; By introducing gas F into the wall flow-type base material 10 from the end side impregnated with 21a, the catalyst slurry 21a impregnated in the wall flow-type base material 10 is made porous. The catalyst layer forming step S1 includes a coating step S1b for coating the partition walls 13, a stopping step S1c for stopping the introduction of the gas F, and a firing step S1d for firing the coated catalyst slurry 21a. And the coating amount of the catalyst layer of the exhaust gas purifying catalyst 100 is 20 to 110 g / L.

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. 2. 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.

(Base material)
The same thing as the above can be used as the wall flow type substrate 10.

(Catalyst layer)
In the catalyst layer 21 formed in the catalyst layer forming step S1, segregation or uneven distribution to the small pores 13a having a relatively small pore diameter or the bag-like portion 13b having a closed shape in a bag shape is suppressed. As a result, the occurrence of pore blockage or uneven coating due to segregation or uneven distribution of the catalyst layer is suppressed, and as a result, an exhaust gas purifying catalyst capable of maintaining a relatively high porosity and having a relatively small pore diameter can be obtained. . In the exhaust gas purifying catalyst of the present embodiment, the small pores 13a that are not closed by the catalyst layer can contribute to the improvement of the soot collection rate, and can easily contact the exhaust gas other than the bag-shaped portion 13b. A catalyst layer is formed in the portion. Furthermore, the uneven distribution of the catalyst layer in the small pores 13a and the bag-like portions 13b in the partition walls is suppressed, so that a relatively large number of catalyst layers can be formed in other pores. Therefore, from the viewpoint of soot collection, a relatively large number of catalyst layers are formed on the surface of the air holes 13c that are too large, and the soot collection rate in the air holes 13c is improved by reducing the pore diameter. . That is, according to the catalyst layer 21 formed in the catalyst layer forming step S1, the blockage of the small pores 13a is suppressed, and the pore diameter of the atmospheric pores 13c is appropriately narrowed, so that the soot collection rate is reduced. Can be improved. However, the reason why the soot collection rate is improved is not limited to the above.

The catalyst layer 21 is preferably formed from the cell wall on the introduction side cell 11 side to the cell wall on the discharge side cell 12 side in the thickness direction of the partition wall 13. In the direction (length direction), it is preferable that the entirety be formed. The catalyst layer 21 can be confirmed by a scanning electron microscope on the cross section of the partition wall 13 of the exhaust gas purifying catalyst 100.

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.

In addition, from the viewpoint of being used for an 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 (wall flow type substrate 1L) The coating amount of the catalyst layer excluding the catalytic metal mass per unit) is preferably 20 to 110 g / L, more preferably 40 to 90 g / L, and further preferably 50 to 70 g / L.

The pore diameter (mode diameter) of the partition wall 13 of the exhaust gas purifying catalyst 100 in the state where the catalyst layer 21 is formed by the mercury intrusion method is preferably 10 to 23 μm, more preferably 12 to 20 μm, and still more preferably. Is 14 to 18 μm. The pore volume of the partition wall 13 of the exhaust gas purifying catalyst in the state where the catalyst layer 21 is formed by the mercury intrusion method is preferably 0.2 to 1.0 cm ³ / g, more preferably 0.25 to 0. It is 9 cm ³ / g, and more preferably 0.3 to 0.8 cm ³ / g. Further, the porosity of the partition wall 13 of the exhaust gas purifying catalyst 100 in the state where the catalyst layer 21 is formed by the mercury intrusion method is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to 70%. 60%. In addition, the pore diameter (mode diameter), the pore volume, and the porosity mean values calculated by the mercury intrusion method under the conditions described in the following Examples.

[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)
The alumina powder and the 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. The zirconia powder was impregnated with an aqueous solution of rhodium nitrate, and then calcined at 500 ° C. for 1 hour to obtain a Rh-supported powder.

667 g of the obtained Pd-supported powder and 0.25 kg of Rh-supported powder, 333 g of ceria-zirconia composite oxide powder, 70 g of a 46% lanthanum nitrate aqueous solution, and ion-exchanged water were mixed, and the obtained mixture was put into a ball mill. Then, the catalyst powder was milled until a predetermined particle size distribution was obtained, thereby obtaining a catalyst slurry having a D90 particle size of 3.0 μm and a pH of 4.2. The catalyst slurry thus obtained was mixed with 32 g of barium hydroxide octahydrate (pH adjuster) and 10 g of ammonium carbonate (pH adjuster) to obtain a catalyst slurry having a pH of 6.2.

The viscosity η ₁₀ when the shear rate of the obtained catalyst slurry is 10 s ⁻¹ is 616 mPa · s, the viscosity η ₅₅₀ when the shear rate is 550 s ⁻¹ is 15 mPa · s, and the viscosity η The ratio of the viscosity η _{10 to} ₅₅₀ (η ₁₀ / η ₅₅₀ ), that is, the TI value, was 41.

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, pore diameter (mode diameter): 20 μm, porosity: 65%) Was prepared. 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. The coating amount of the catalyst layer after the firing was 58.8 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 32 g of barium hydroxide octahydrate and ammonium carbonate were not added in the preparation of the catalyst slurry. The pH of the catalyst slurry used in Comparative Example 1 was 4.2.

[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.

[Viscosity measurement]
The viscosity η ₁₀ and the viscosity η ₅₅₀ were measured at 25 ° C using a rheometer HAAKE MARS II manufactured by Thermo Fisher Scientific.

[Calculation of porosity]
The pore diameters (mode diameters) of the exhaust gas purifying catalysts prepared in Examples and Comparative Examples, and the base material before applying the catalyst slurry, from the partition walls of the exhaust gas introduction side portion, the exhaust gas discharge side portion, and the intermediate portion. And a sample (1 cm ³ ) for measuring the pore volume was 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 pore diameter (mode diameter) was obtained, 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.
Porosity of exhaust gas purifying catalyst (%) = Porous volume of exhaust gas purifying catalyst (cc / g) / Porous volume of substrate (cc / g) x Porosity of substrate (%)
Porosity (%) of base material = 65%

[Measurement of soot collection performance]
The exhaust gas purifying catalyst prepared in each of Examples and Comparative Examples was mounted on a vehicle equipped with a 1.5-liter direct injection turbo engine, and traveled in a WLTC mode using a solid particle counting device (trade name: MEXA-2100 SPCS, manufactured by Horiba, Ltd.). The soot discharge quantity at the time (PN _test ) 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.
Soot collection rate (%) = (PN _blank −PN _test ) / PN _blank × 100 (%)

As a result, the soot collection rate of the example was 73.8%, and the soot collection rate of the comparative example was 60.2%. As a reference value, the soot collection rate of the base material itself was 67.4%. From this, in the examples, the small pores are not closed and the pore diameter of the atmospheric holes is reduced, thereby improving the soot collection rate.In the comparative example, the small pores are closed, In addition, since the catalyst layer is also arranged on the bag-shaped portion, the pore diameter of the atmospheric pores is not small, which suggests that the soot collection rate is lower than that of the base material.

[Coat condition observation]
Samples (1 cm ³ ) for measurement by a scanning electron microscope (SEM) were produced from the partition walls of the exhaust gas purifying catalysts produced in Examples and Comparative Examples. The measurement sample was buried in a resin, and a pretreatment for carbon deposition was performed. The measurement sample after the pretreatment was observed using a scanning electron microscope (trade name: ULTRA55, manufactured by Carl Zeiss), and the state of the catalyst supported on the substrate was confirmed. The trace diagrams are shown in FIGS. As a result, it was found that, in the example, as shown in FIG. 5, an exhaust gas purifying catalyst having a catalyst layer in which segregation or uneven distribution was suppressed was easily obtained.

This application is based on a Japanese patent application filed with the JPO on August 9, 2018 (Japanese Patent Application No. 2018-149987), the contents of which are incorporated herein by reference.

The exhaust gas purifying catalyst of the present invention can be widely and effectively used as an exhaust gas purifying catalyst 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 discharging side 13 ... Partition wall 13a. ..Small pores 13b ... bag-like portion 13c ... atmospheric pores 21 ... catalyst layer 21a ... catalyst slurry 100

Claims

A method for producing an exhaust gas purifying catalyst for purifying exhaust gas discharged from a gasoline 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,
An impregnation step of impregnating the end of the wall flow type substrate on the exhaust gas introduction side or the exhaust gas discharge side with a thixotropic catalyst slurry,
By introducing a gas into the wall flow type base material from the end side impregnated with the catalyst slurry, the catalyst slurry impregnated in the wall flow type base material is applied to the pore surfaces of the partition walls. Coating process,
A stopping step of stopping the introduction of the gas,
The coated catalyst slurry is calcined, and the amount of coating of the catalyst layer (the amount of coating of the catalyst layer excluding the weight of the catalyst metal per 1 L of the wall flow type substrate) is 20 to 110 g / L. Baking step to obtain a purification catalyst,
The catalyst slurry has a TI value of 10 to 100;
A method for producing an exhaust gas purifying catalyst.
The catalyst slurry contains at least one selected from the group consisting of methylamine, dimethylamine, trimethylamine, barium hydroxide, ammonium carbonate, ammonium hydrogen carbonate, and aqueous ammonia,
A method for producing the exhaust gas purifying catalyst according to claim 1.
The catalyst slurry has a pH of 3 to 10,
A method for producing the exhaust gas purifying catalyst according to claim 1.
In the coating step, due to the stress applied by the introduction of the gas, the viscosity of the thixotropic catalyst slurry decreases,
A method for producing the exhaust gas purifying catalyst according to any one of claims 1 to 3.
In the stopping step, the viscosity of the thixotropic catalyst slurry increases,
A method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 4.
An exhaust gas purifying catalyst for purifying exhaust gas discharged from a gasoline 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,
An impregnation step in which the catalyst layer impregnates the end of the wall flow type substrate on the exhaust gas introduction side or the exhaust gas discharge side with a thixotropic catalyst slurry; By introducing a gas into the wall flow type substrate, a coating step of applying the catalyst slurry impregnated to the wall surface of the pores of the partition walls, a stop step of stopping the introduction of the gas, a coating step. Having a firing step of firing the catalyst slurry, which is formed by the catalyst layer forming step,
The coating amount of the catalyst layer of the exhaust gas purifying catalyst (the coating amount of the catalyst layer excluding the mass of the catalyst metal per 1 L of the wall flow type substrate) is 20 to 110 g / L.
Exhaust gas purification catalyst.