JP2019122894A - Exhaust gas purification catalyst and production method thereof - Google Patents

Abstract

To provide a production method of an exhaust gas purification catalyst that suppresses a pressure loss rise caused by clogging pores of a partition wall of a substrate with catalyst slurry and enhances exhaust gas purification performance, and to provide an exhaust gas purification catalyst produced by the production method.SOLUTION: A production method of an exhaust gas purification catalyst for purifying an exhaust gas discharged from an internal combustion engine includes an impregnation step for impregnating an end part of an exhaust gas introduction side or an exhaust gas discharge side of a wall flow type substrate having a plurality of passages partitioned by a porous partition wall with catalyst slurry, a coating step for introducing a gas from the end part into the wall flow type substrate and thus coating the porous partition wall with the catalyst slurry impregnated in the wall flow type substrate, and a removal step for removing an excess of the catalyst slurry clogging pores in the partition wall.SELECTED DRAWING: None

Description

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

  Exhaust gas discharged from an internal combustion engine contains particulate matter (PM) mainly composed of carbon, ash composed of non-combustible components, and the like, and is known to cause air pollution. In the past, particulate matter emissions were strictly regulated in diesel engines, which are relatively easy to emit particulate matter than gasoline engines, but in recent years, regulations on particulate matter emissions have been tightened in gasoline engines as well. Is being done.

  As means for suppressing the discharge of particulate matter, there is known a method of providing a particulate filter for the purpose of 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 the mounting space, etc., emission control of particulate matter and removal of harmful components such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) In order to carry out simultaneously, applying a catalyst slurry to a particulate filter and calcining this is considered to provide a catalyst layer.

  However, if the catalyst layer is provided on the particulate filter in which the pressure loss tends to increase due to the accumulation of particulate matter originally, the flow path of the exhaust gas becomes narrower, the pressure loss tends to further increase, and the engine output decreases. There is a problem of In order to solve such a problem, for example, in Patent Documents 1 to 3, it is possible to devise the types of catalyst layers and the positions where they are provided for the purpose of suppressing an increase in pressure loss and improving exhaust gas purification performance. Proposed. Further, in Patent Document 4, for the purpose of suppressing an increase in pressure loss, adjusting the average particle diameter of the powder in the slurry for forming the catalyst coating layer and the coating amount of the catalyst on the substrate Proposed.

WO 2016/060048 WO 2016/060049 WO 2016/060050 JP, 2017-140602, A

  When a catalyst filter is impregnated and coated on a particulate filter that can have a complicated pore shape, the catalyst slurry may block the narrow portion of the pores due to surface tension, and the particulate filter is fired while maintaining this state. If a catalyst layer is formed, it causes an excessive increase in pressure loss. Such rise in pressure loss due to blockage of the narrow portion can not be completely avoided even by devising the type of catalyst layer and the position where they are provided as in Patent Documents 1 to 3, and Even if the average particle size or the like of the powder in the slurry is adjusted as in Patent Document 4, it is impossible to completely avoid the problem.

  The present invention has been made in view of the above problems, and an object thereof is a method for producing an exhaust gas purification catalyst in which an excessive increase in pressure loss due to the formation of a catalyst layer is suppressed and an improvement in exhaust gas purification performance is also achieved. And providing an exhaust gas purification catalyst produced by the production method. The present invention is not limited to the purpose mentioned here, and is an operation and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and it is also possible to exhibit the operation and effect that can not be obtained by the prior art. It can be positioned for other purposes.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have found that plugging of excess catalyst slurry during the impregnation coating of catalyst slurry contributes to an increase in pressure loss. It has been found that the above problems can be solved by identifying and removing the blockage, and the present invention has been completed. That is, the present invention provides various specific embodiments shown below.

[1]
A method of manufacturing an exhaust gas purification catalyst for purifying an exhaust gas discharged from an internal combustion engine, comprising:
An impregnation step of impregnating and holding a catalyst slurry on the end of the exhaust gas introduction side or the exhaust gas discharge side of the wall flow type substrate having a plurality of passages defined by porous partition walls;
Applying the catalyst slurry impregnated in the wall flow substrate to the porous partition walls by flowing gas into the wall flow substrate from the end side;
And removing the excess catalyst slurry that blocks the pores of the partition walls.
Method of manufacturing exhaust gas purification catalyst.
[2]
In the removal step, a gas is allowed to flow into the wall flow type substrate from the end opposite to the end.
The manufacturing method of the exhaust gas purification catalyst as described in [1].
[3]
In the impregnation step, the catalyst slurry is impregnated and held at an end of the wall flow type substrate on the exhaust gas introduction side,
The manufacturing method of the exhaust gas purification catalyst as described in [1] or [2].
[4]
In the removal step, the retained amount of the catalyst slurry in the wall flow type substrate is reduced to 90 to 98% by mass before and after treatment.
The manufacturing method of the exhaust gas purification catalyst as described in any one of [1]-[3].
[5]
After the removing step, the wall flow type substrate further has a firing process of performing a heat treatment at 400 to 650 ° C.,
The manufacturing method of the exhaust gas purification catalyst as described in any one of [1]-[4].
[6]
Obtained by the method for producing an exhaust gas purification catalyst according to any one of [1] to [5],
Exhaust gas purification catalyst.

  According to the present invention, a method for producing an exhaust gas purification catalyst in which an excessive increase in pressure loss due to the formation of a catalyst layer is suppressed and an improvement in exhaust gas purification performance is also achieved, and an exhaust gas purification catalyst produced by the production method Can be provided. And the manufacturing method of this exhaust gas purification catalyst is not only a gasoline particulate filter (GPF) but also other particulates such as a diesel particulate filter (DPF) as a means for suppressing an increase in pressure loss of the particulate filter carrying the catalyst. It can be used also in a filter, and the performance of an exhaust gas treatment system equipped with such a particulate filter can be further enhanced.

It is process drawing which shows typically the manufacturing method of the exhaust gas purification catalyst of this embodiment. A schematic view (left figure) showing a state in which excess catalyst slurry blocks the pores of the partition wall (a left figure) and a schematic view showing a state in which the excess catalyst slurry blocking the pores of the partition wall is removed by counter blow (right figure ). It is a graph which shows the exhaust gas purification catalyst produced by the Example and the comparative example, and the measurement result of the pressure loss in the base material before coating a catalyst slurry. It is a graph which shows the result of model gas evaluation in the exhaust gas purification catalyst produced by the example and the comparative example.

  Hereinafter, embodiments of the present invention will be described in detail. The following embodiments are examples (representative examples) of the embodiments of the present invention, and the present invention is not limited thereto. In addition, the present invention can be implemented with arbitrary modifications without departing from the scope of the invention. In the present specification, positional relationships such as upper, lower, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Further, the dimensional ratio in the drawings is not limited to the illustrated ratio. 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 particle size based on volume, and "D90 particle size" The 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 particle size based on volume. Moreover, in this specification, when using and expressing a numerical value or a physical-property value in front of and behind that using "-", it is used as what contains the value before and behind that. For example, the notation of the numerical range "1 to 100" includes both of the upper limit "1" and the lower limit "100". In addition, the notation of other numerical ranges is the same.

[Method of producing exhaust gas purification catalyst]
A method of manufacturing an exhaust gas purification catalyst of the present embodiment is a method of manufacturing an exhaust gas purification catalyst for purifying an exhaust gas discharged from an internal combustion engine, which is a wall flow type substrate having a plurality of passages defined by porous partition walls. In the impregnation step (S1) of impregnating and holding the catalyst slurry at the end portion on the exhaust gas introduction side or the exhaust gas discharge side, and flowing the gas into the wall flow type substrate from the end portion side, the wall flow type substrate The method further comprises at least a coating step (S4) of applying the impregnated catalyst slurry to the porous partition walls, and a removal step (S6) of removing an excess catalyst slurry that blocks the pores of the partition walls. Do. Moreover, the manufacturing method of the exhaust gas purification catalyst of this embodiment may have a baking process which heat-treats the wall flow type | mold base material with which the catalyst slurry was coated after the said removal process. Hereinafter, each process will be described with reference to a process diagram schematically showing a method of manufacturing the exhaust gas purifying catalyst of the present embodiment shown in FIG.

<Impregnation process>
In the impregnation step S1, the end of the exhaust gas introduction side 1a or the exhaust gas discharge side 1b of the wall flow type substrate 1 (hereinafter, also simply referred to as "substrate 1") in which a plurality of passages are defined by porous partition walls. The catalyst slurry 2 is impregnated and held (FIG. 1). The impregnation method is not particularly limited. For example, the end of the substrate is immersed in the catalyst slurry, and if necessary, the catalyst slurry is pulled up by letting the gas flow out (suction) from the opposite end. It is also good. At this time, it is preferable to impregnate and hold the catalyst slurry at the end of the substrate so as to be larger than the target supported amount of the catalyst so that a small coated amount or a non-coated portion of the catalyst slurry is generated. .

  The end on which the catalyst slurry is impregnated and held may be either the exhaust gas introduction side or the exhaust gas discharge side, but the catalyst slurry is preferably impregnated and held on the end on the exhaust gas introduction side. As a result, the gas for the coating process described later can be introduced in the same direction as the inflow direction of the exhaust gas, and the catalyst slurry can be applied to the complicated pore shape along the flow of the exhaust gas. . Therefore, the increase in pressure loss is expected to be suppressed, and the improvement of the exhaust gas purification performance can also be expected.

(Base material)
The base material of the wall flow structure which comprises the frame | skeleton of an exhaust gas purification catalyst is demonstrated. The base material is a wall in which an introduction side cell in which an end portion on the exhaust gas introduction side is opened and a discharge side cell adjacent to the introduction side cell and in which an end portion on the exhaust gas discharge side is opened It has a flow structure. In an exhaust gas purification catalyst using a base material having such a configuration, the exhaust gas discharged from the internal combustion engine flows from the end (opening) of the exhaust gas introduction side into the introduction side cell and passes through the pores of the partition wall Flows into the adjacent discharge side cell and flows out from the end (opening) of the exhaust gas discharge side. In this process, particulate matter (PM) is difficult to pass through the pores of the partition walls, and therefore, generally, PM deposited on the partition walls in the introduction side cell is deposited by the catalytic function of the catalyst layer or For example, it is burned at about 500 to 700 ° C. and decomposed. Further, the exhaust gas comes in contact with the catalyst layer provided in the partition wall, whereby carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas are oxidized to water (H ₂ O) and carbon dioxide (CO ₂ ), etc. And nitrogen oxides (NOx) are reduced to nitrogen (N ₂ ), and harmful components are decontaminated (detoxified). In the present embodiment, removal of particulate matter and purification of harmful components such as carbon monoxide (CO) are collectively referred to as “exhaust gas purification performance”.

  As the base material, various materials and shapes used in the conventional application 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 when burning and removing particulate matter at high temperature, etc. It is preferable to use a heat-resistant material so that it can be handled. Examples of the heat resistant material include ceramics such as cordierite, mullite, aluminum titanate, and silicon carbide (SiC); and alloys such as stainless steel. In addition, the form of the base material can be appropriately adjusted from the viewpoints of the trapping ability of the particulate matter and the suppression of the pressure loss increase. For example, the outer shape of the base material can be a cylindrical shape, an elliptical cylindrical shape, a polygonal cylindrical shape, or the like. Moreover, although based also on the space etc. in which it incorporates, the volume (total volume of a cell) of a base material is preferably 0.1-5 L, More preferably, it is 0.5-3 L. The total length in the stretching direction of the substrate (the total length in the stretching direction of the partition walls) is preferably 10 to 500 mm, more preferably 50 to 300 mm.

  The introduction side cells and the discharge side cells are regularly arranged along the axial direction of the cylindrical shape, and adjacent cells are alternately sealed with one open end and the other open end in the extending direction. It is done. The introduction side cell and the discharge side cell can be set to an appropriate shape and size in consideration of the flow rate and components of the supplied exhaust gas. For example, the shape of the introduction side cell and the discharge side cell may be triangular; rectangular such as square, parallelogram, rectangular and trapezoidal; and other polygonal such as hexagonal and octagonal; circular. In addition, it may have a High Ash Capacity (HAC) structure in which the cross sectional area of the introduction side cell and the cross sectional area of the discharge side cell are different. The number of introduction-side cells and discharge-side cells can be appropriately set so as to promote the generation of turbulent flow of exhaust gas and to suppress clogging due to particles and the like contained in the exhaust gas, and is not particularly limited. , 200 cpsi to 400 cpsi are preferred.

  The partition walls separating adjacent cells are not particularly limited as long as they have a porous structure through which the exhaust gas can pass, and the configuration thereof includes suppressing the increase of the trapping ability of the particulate matter and the pressure loss, It can adjust suitably from a viewpoint of improvement of mechanical strength etc. For example, when forming a catalyst layer inside the pores of the partition wall using a catalyst slurry described later, the pore diameter (for example, mode diameter (pore diameter with the largest appearance ratio in the frequency distribution of pore diameter (maximum value of distribution)) When the pore volume is large, it is difficult for the catalyst slurry to clog the pores, and the exhaust gas purification catalyst obtained tends to have a pressure loss that is hard to increase, but the ability to collect particulate matter is lowered. Also, the mechanical strength of the substrate may be reduced. On the other hand, when the pore diameter or the pore volume is small, the catalyst slurry tends to clog the pores, and the pressure loss tends to increase, but the particulate matter collection capability is improved, and the mechanical of the substrate is Also tends to improve. In this respect, in the manufacturing method of the present embodiment, since the clogging of the pores by the catalyst slurry can be removed by the removal step described later, the increase in pressure loss is suppressed while maintaining the particulate matter collection capability high. It can be done.

From such a viewpoint, the pore diameter (mode diameter) of the partition wall is preferably 8 to 25 μm, more preferably 10 to 22 μm, and still more preferably 13 to 20 μm. Moreover, the thickness of the partition (the length in the thickness direction orthogonal to the stretching direction) is preferably 6 to 12 mil, more preferably 6 to 10 mil. Furthermore, the pore volume of the partition wall by mercury porosimetry 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 It is 0.8 cm ³ / g. Moreover, the porosity of the partition wall by a mercury intrusion method is preferably 20 to 80%, more preferably 40 to 70%, and preferably 60 to 70%. When the pore volume or the porosity is at least the lower limit, an increase in pressure loss tends to be further suppressed. In addition, when the pore volume or the porosity is not more than the upper limit, the strength of the substrate tends to be further improved. In addition, a pore diameter (mode diameter), a pore volume, and a porosity mean the value calculated by the mercury intrusion method on the conditions as described in the following Example.

(Catalyst slurry)
Next, a catalyst slurry for forming a catalyst layer provided on the pore surface in the partition will be described. The catalyst slurry contains catalyst powder and a solvent such as water. The catalyst powder is a group of a plurality of catalyst particles (hereinafter sometimes simply referred to as "particles" and the like) including catalyst metal particles and carrier particles supporting the catalyst metal particles, which will be described later. Through the steps, a catalyst layer is formed. The catalyst particles used in this embodiment are composite particles containing catalyst metal particles and carrier particles supporting the catalyst metal particles, but the type thereof is not particularly limited, and may be appropriately selected from known catalyst particles. It can be used. The solid content of the catalyst slurry is preferably 1 to 50% by mass, more preferably 10 to 40% by mass, and still more preferably 15 to 30%, from the viewpoint of the coatability to the inside of the pores of the partition walls. It is mass%.

  The D90 particle diameter of the catalyst powder is preferably 1 to 7 μm, more preferably 1 to 6 μm, and still more preferably 1 to 5 μm. When the D90 particle diameter is 1 μm or more, the pulverizing time in the case of crushing the catalyst powder with a milling apparatus can be shortened, and the working efficiency tends to be further improved. In addition, when the D90 particle diameter is 7 μm or less, the coarse particles are prevented from blocking the pores in the partition walls, and a rise in pressure loss tends to be suppressed. In the present specification, the D90 particle diameter means a diameter measured by a laser diffraction particle diameter distribution measuring device (for example, a laser diffraction particle diameter distribution measuring device SALD-3100 manufactured by Shimadzu Corporation).

  As the catalyst metal constituting the catalyst metal particles, metal species that can function as various oxidation catalysts or reduction catalysts can be used. Examples include platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os). Among these, palladium (Pd) and platinum (Pt) are preferable from the viewpoint of oxidation activity, and rhodium (Rh) is preferable from the viewpoint of reduction activity. These metals may be used alone or in combination of two or more. From the viewpoint of increasing the contact area with the exhaust gas, it is preferable that the average particle size of the catalyst metal particles in the catalyst slurry be small. Specifically, the average particle size of the catalyst metal particles is preferably 1 to 15 nm, more preferably 1 to 10 nm, and still more preferably 1 to 7 nm. The average particle size of the catalyst metal particles can be confirmed using, for example, a scanning transmission electron microscope (STEM) such as HD-2000 manufactured by Hitachi High-Technologies Corporation, and in this specification, no The circle equivalent diameter of the ten catalyst metal particles extracted randomly is calculated, and the average value of these is used as the average particle diameter of the catalyst metal particles.

As the carrier particles supporting the catalyst metal particles, inorganic compounds conventionally used in this type of exhaust gas purification catalyst can be considered. Not particularly limited, oxygen storage materials (OSC materials) such as cerium oxide (ceria: CeO ₂ ), ceria-zirconia complex oxide (CZ complex oxide), aluminum oxide (alumina: Al ₂ O ₃ ), zirconium oxide Examples thereof include oxides such as (zirconia: ZrO ₂ ), silicon oxide (silica: SiO ₂ ), titanium oxide (titania: TiO ₂ ), and composite oxides containing these oxides as main components. Here, the oxygen storage material (OSC material) occludes oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is lean (that is, an atmosphere of excess oxygen), and when the air-fuel ratio of the exhaust gas is rich ( That is, it means that the stored oxygen is released to the atmosphere of the excess fuel side).

From the viewpoint of the exhaust gas purification performance, the specific surface area of the carrier particles is preferably 10 to 500 m ² / g, more preferably 30 to 200 m ² / g.

  Catalyst metal loading rate (amount of catalyst metal per 1 L of substrate) supported on a wall flow type substrate from the viewpoint of improvement of exhaust gas purification performance and suppression of progression of particle growth (sintering) of catalyst metal Is preferably 0.5 to 10 g / L, more preferably 1 to 8 g / L, and still more preferably 1 to 6 g / L.

<Coating process>
In the coating step S4, the gas F1 is allowed to flow into the wall flow type substrate 1 from the end side 1a impregnated with the catalyst slurry 2 (FIG. 1). As a result, the impregnated catalyst slurry moves along the gas flow from the gas introduction side to the depth of the substrate and reaches the end of the gas discharge side. In the process, the catalyst slurry can be applied to the inside of the pores by the catalyst slurry passing through the inside of the pores of the partition walls. At this time, the catalyst slurry 2 can be held so as to clog the particularly narrow portion 1c inside the pores (FIG. 2). Although the removal of the excess catalyst slurry that blocks the pores of the partition walls will be described later, if the calcination process described later is performed without removing the catalyst slurry that blocks the pores, the catalyst layer is formed so as to block the pores. Therefore, the pressure loss tends to increase. In addition, when there is a catalyst layer that blocks the pores, the exhaust gas flow path may be restricted, which may result in a decrease in the exhaust gas purification performance.

  There is no particular limitation on the direction of the base material when the gas is introduced into the base material from the end portion side impregnated with the catalyst slurry, but the stretching direction of the partition wall and the vertical direction are substantially parallel and impregnated with the catalyst slurry. Adjust the direction of the substrate so that the end is vertically upward (S2 to S3 in Fig. 1), and from the end side of the substrate impregnated with the catalyst slurry from above to below in the vertical direction Preferably, the gas is allowed to flow into the chamber (S4 in FIG. 1). As a result, the flow direction of the inflowing gas coincides with the gravity direction (vertically downward). Therefore, when the gas is allowed to flow upward from the vertically downward direction against the gravity direction, or the partition wall is stretched perpendicularly to the gravity direction The catalyst slurry can be coated uniformly by the partition walls as compared to the case where the gas is introduced with the direction being horizontal.

<Removal process>
In the removal step S6, the excess catalyst slurry 2 that blocks the pores of the partition walls is removed. The removal method is not particularly limited. For example, a method (counter blow) in which the gas F2 is flowed into the substrate from the end opposite to the end impregnated with the catalyst slurry (FIG. 1), vibration, etc. There is a method of releasing the occlusion by applying an external force such as. Thereby, the clogging of the pores by the catalyst slurry which is difficult to remove by the inflow of the gas from the end side impregnated with the catalyst slurry (for example, as shown in FIG. 2, the catalyst in the pores narrowing in the inflow direction of the gas F1 It is easy to eliminate the clogging of the slurry. Therefore, the exhaust gas purification catalyst obtained through the later-described firing step has a smaller amount of catalyst layer formed so as to block the pores, and the pressure loss is reduced and the exhaust gas purification performance is improved.

  When removing an excess catalyst slurry, it is preferable to reduce the holding amount of the catalyst slurry in a base material to 90-98 mass% before and behind processing. More specifically, the amount of the catalyst slurry supported after the removing step may be adjusted to be 90 to 98% by mass with respect to the amount of the catalyst slurry supported on the substrate after the applying step. preferable. That is, it is preferable to adjust so that 2-10 mass% of the catalyst slurry made to carry | support on the base material after a coating process may be removed by a removal process. At this time, the amount of catalyst slurry supported after the removal step is the amount of catalyst slurry supported on the substrate after the coating step so that the amount of catalyst slurry after the removal step does not decrease more than necessary. Preferably it is 90 mass% or more, More preferably, it is 95 mass% or more. In addition, from the viewpoint of sufficiently removing the excess catalyst slurry, the amount of catalyst slurry carried after the removal step is preferably 98% by mass with respect to the amount of catalyst slurry loaded on the substrate after the coating step. It is below. In particular, when the removal step is carried out by the above-mentioned counter blow method, a part of the catalyst slurry supported on the substrate after the coating step flows out from the end on the gas discharge side due to the inflow of gas in the removal step. It is preferable to adjust the inflow pressure and the inflow time of the gas so that

  When the removal step is carried out by the above-mentioned counterblow method, the direction of the base material at the time of introducing the gas into the base material is not particularly limited, but the stretching direction of the partition wall and the vertical direction are approximately parallel, and the catalyst slurry is After adjusting the direction of the base so that the impregnated end is vertically downward (S5 in FIG. 1), the inside of the base is impregnated with the catalyst slurry from the upper side of the vertical direction to the lower side. Preferably, the gas is allowed to flow into the chamber (S6 in FIG. 1). As a result, the flow direction of the inflowing gas coincides with the gravity direction (vertically downward). Therefore, when the gas is allowed to flow upward from the vertically downward direction against the gravity direction, or the partition wall is stretched perpendicularly to the gravity direction The excess catalyst slurry can be removed more effectively as compared to the case where the gas is introduced in a horizontal direction.

<Firing process>
In the firing step, the wall flow substrate is subjected to heat treatment after the removing step. The firing temperature is not particularly limited, but is preferably 400 to 650 ° C, more preferably 450 to 600 ° C, and still more preferably 500 to 600 ° C. The firing time is preferably 0.5 to 2 hours, and preferably 0.5 to 1.5 hours.

  In addition, the wall flow type substrate on which the catalyst slurry is applied may be dried prior to the heat treatment. The drying temperature is not particularly limited, but is preferably 100 to 225 ° C, more preferably 100 to 200 ° C, and still more preferably 125 to 175 ° C. The drying time is preferably 0.5 to 2 hours, preferably 0.5 to 1.5 hours.

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

The pore diameter (mode diameter) of the partition wall of the exhaust gas purification catalyst after catalyst coating obtained by the above production method according to the mercury intrusion method is preferably 10 to 23 μm, more preferably 12 to 20 μm, and still more preferably 14 to 18 μm. In addition, the pore volume of the partition wall by mercury intrusion method of the exhaust gas purification catalyst after catalyst coating is preferably 0.2 to 1.0 cm ³ / g, more preferably 0.25 to 0.9 cm ³ / g And more preferably 0.3 to 0.8 cm ³ / g. Furthermore, the porosity of the partition wall by the mercury intrusion method of the exhaust gas purification catalyst after catalyst coating is preferably 20 to 80%, more preferably 30 to 70%, and preferably 35 to 60%. In addition, a pore diameter (mode diameter), a pore volume, and a porosity mean the value calculated by the mercury intrusion method on the conditions as described in the following Example.

  EXAMPLES The features of the present invention will be more specifically described below with reference to test examples, examples and comparative examples, but the present invention is not limited thereto. That is, the materials, amounts used, proportions, treatment contents, treatment procedures and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. The values of various manufacturing conditions and evaluation results in the following examples have meanings as preferable upper limit values or preferable lower limit values in the embodiment of the present invention, and the preferable range is the value of the upper limit or the lower limit described above. And a range defined by a combination of the values of the following examples or the values of the examples.

(Example)
Alumina powder having a D50 particle diameter of 28 μm and a BET specific surface area of 141 m ² / g is impregnated with an aqueous palladium nitrate solution, and then calcined at 500 ° C. for 1 hour to obtain Pd-supporting alumina powder (Pd content: 4.3 Mass%) was obtained. Further, a zirconia-lanthanum-modified alumina powder having a D50 particle diameter of 29 μm and a BET specific surface area of 145 m ² / g is impregnated with an aqueous solution of rhodium nitrate, and then calcined for 1 hour at 500 ° C. An alumina powder (Rh content: 0.7% by mass) was obtained.

1 kg of the obtained Pd-loaded alumina powder and 1 kg of Rh-loaded zirconia-lanthanum-modified alumina powder, 1 kg of ceria-zirconia composite oxide powder having a D50 particle diameter of 10 μm and a BET specific surface area of 71 m ² / g, and 46 mass% lanthanum nitrate aqueous solution 195 g and ion exchanged water were mixed, and the obtained mixture was charged into a ball mill, and milling was performed until the catalyst powder had a predetermined particle size distribution, to obtain a catalyst slurry having a D90 particle size of 3.0 μm.

  Next, a wall flow type honeycomb substrate made of cordierite (cell number / mill thickness: 300 cpsi / 8 mil, diameter: 118.4 mm, total length: 91 mm, porosity: 65%) was prepared. The end of the substrate on the exhaust gas introduction side was immersed in the catalyst slurry, and vacuum suction was conducted from the opposite end side to impregnate and hold the catalyst slurry in the substrate. Gas is allowed to flow into the substrate from the end face side of the substrate, and the catalyst slurry is applied to the surface inside the pores of the partition walls of the substrate, and an excess of catalyst slurry is blown off from the end on the gas discharge side. (Coating process).

  Next, in order to remove excess catalyst slurry that blocks the pores of the partition walls, gas is allowed to flow into the substrate from the end face side opposite to the end face impregnated with the catalyst slurry (counter blow) to block the pores of the partition walls. Excess catalyst slurry was removed (removal step). At that time, the gas inflow time was adjusted so that the amount of the catalyst slurry carried after the removal step was 91% by mass with respect to the amount of the catalyst slurry carried after the coating step.

  Thereafter, the base material coated with the catalyst slurry was dried at 150 ° C., and then fired at 550 ° C. in an air atmosphere to prepare an exhaust gas purification catalyst. In addition, the coating amount of the catalyst after baking was 60.9 g (except for the weight of the platinum group metal) per 1 L of the substrate. Details are shown in Table 1.

(Comparative example)
When gas is introduced into the substrate from the end face side where the catalyst slurry is sucked, the gas inflow time is adjusted to achieve the target loading amount, and the same as the example except that the counter blow is not performed. The exhaust gas purification catalyst was prepared. Details are shown in Table 1.

Catalyst composition excludes weight of platinum group metals

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

[Calculation of porosity]
Exhaust gas purification catalysts prepared in Examples and Comparative Examples, and pore diameters (mode diameter) from the partition walls on the exhaust gas introduction side, the exhaust gas discharge side and the middle part of the substrate before coating the catalyst slurry Samples for measurement of pore volume and pore volume (1 cm ³ ) were respectively collected. After drying the measurement sample, the pore distribution was measured by mercury porosimetry using a mercury porosimeter (trade name: PASCAL140 and PASCAL440, manufactured by Thermo Fisher Scientific). At this time, the low pressure region (0 to 400 Kpa) was measured by PASCAL 140, and the high pressure region (0.1 Mpa to 400 Mpa) was measured by PASCAL 440. From the pore distribution obtained, the pore diameter (mode diameter) was determined, and the pore volume of pores having a pore diameter of 1 μm or more was calculated. In addition, as a value of a pore diameter and a pore volume, the average value of the value obtained by each of an exhaust gas introduction side part, an exhaust gas discharge side part, and an intermediate part was adopted.

Subsequently, the porosity of the exhaust gas purification catalyst produced in the example and the comparative example was calculated by the following equation. The results are shown in Table 2 below. As shown in Table 2, although the pore diameter (mode diameter) of the exhaust gas purification catalyst produced in the example and the exhaust gas purification catalyst produced in the comparative example are approximately the same, the exhaust gas purification catalyst produced in the example However, since the pore volume is high, it is inferred that in the exhaust gas purifying catalyst produced in the example, the clogging of the pores by the catalyst component is suppressed.
Post-coat catalyst porosity (%) = post-coat catalyst pore volume (cc / g) ÷ pre-coat carrier pore volume (cc / g) × porosity of the wall flow type substrate before applying the catalyst slurry (%) )
Catalyst pore volume after coating (cc / g): Pore volume of exhaust gas purification catalyst prepared in Examples and Comparative Examples Carrier pore volume before coating (cc / g): Wall flow type substrate used in Examples and Comparative Examples ( Pore volume of catalyst slurry before coating) Porosity of wall flow type substrate before coating of catalyst slurry (%) = 65%

[Measurement of pressure loss]
The exhaust gas purification catalyst prepared in the example and the comparative example and the base material before applying the catalyst slurry were respectively installed in a pressure loss measuring device (made by Tsukubarika Seiki Co., Ltd.), and the exhaust gas purification catalyst installed was at room temperature I let in the air. The pressure loss of the exhaust gas purification catalyst was determined as a value obtained by measuring the pressure difference between the air introduction side and the exhaust side when the amount of air flowing out from the exhaust gas purification catalyst was 4 m ³ / min. The results are shown in FIG. As shown in FIG. 3, it can be seen that the exhaust gas purification catalyst produced in the example has less pressure loss than the exhaust gas purification catalyst produced in the comparative example.

[Coating state observation]
Samples (1 cm ³ ) for measurement of a scanning electron microscope (SEM) were produced from the partition walls of the exhaust gas purification catalyst produced in the example and the comparative example. The sample for measurement was embedded in the resin and pretreated for carbon deposition. The measurement sample after pretreatment was observed using a scanning electron microscope (trade name: ULTRA 55, manufactured by Carl Zeiss) to confirm the support state of the catalyst on the substrate. As a result, the supported state of the catalyst on the substrate in the example is as shown in the schematic view (right figure) showing the state in which the excess catalyst slurry blocking the pores of the partition wall is removed by the counter blow, and in the comparative example The supported state of the catalyst on the substrate was as shown in the schematic view (left) showing the state in which the excess catalyst slurry blocked the pores of the partition walls.

[Electric furnace durability / model gas evaluation]
A core sample (diameter 25.4 mm, overall length 91 mm) was cut out cylindrically from the central portion of the exhaust gas purification catalyst produced in the example and the comparative example, and set in an electric furnace. Then, heat treatment (electric furnace endurance) was performed by an electric furnace for 10 hours at 980 ° C., with one cycle of Rich atmosphere, N ₂ purge atmosphere, Lean atmosphere, and N ₂ purge atmosphere shown below.

Thereafter, the core sample taken out of the electric furnace was set in a model gas reactor. Then, model gas evaluation was implemented on condition shown below, and the light-off performance (temperature where purification rate reaches 80%) was measured. The results are shown in FIG. As shown in FIG. 4, the exhaust gas purification catalyst produced in the example had a lower light-off temperature than the exhaust gas purification catalyst produced in the comparative example, and it was confirmed that the light-off performance was improved. It is considered that this is because the closed pores in the partition wall decrease and the contact between the catalyst and the exhaust gas is improved.

  According to the method for producing an exhaust gas purification catalyst of the present invention, an exhaust gas purification catalyst in which an increase in pressure loss is suppressed can be obtained relatively easily. The exhaust gas purification catalyst thus produced can be widely and effectively used as an exhaust gas purification catalyst for removing particulate matter contained in the exhaust gas of a gasoline engine. In addition, the exhaust gas purification catalyst of the present invention can be effectively used as an exhaust gas purification catalyst for removing particulate matter contained in exhaust gases such as diesel engines, jet engines, boilers and gas turbines as well as gasoline engines. is there.

1 · · · Wall flow type substrate 1a · · · Exhaust gas introduction side 1b · · · Exhaust gas discharge side

[1]
A method of manufacturing an exhaust gas purification catalyst for purifying an exhaust gas discharged from an internal combustion engine, comprising:
An impregnation step of impregnating and holding a catalyst slurry on the end of the exhaust gas introduction side or the exhaust gas discharge side of the wall flow type substrate having a plurality of passages defined by porous partition walls;
Applying the catalyst slurry impregnated in the wall flow substrate to the porous partition walls by flowing gas into the wall flow substrate from the end side;
Removing the excess catalyst slurry which blocks the pores of the partition wall by flowing the gas into the wall flow type substrate from the end opposite to the end where the gas is made to flow ; , Have,
Method of manufacturing exhaust gas purification catalyst.
[2]
In the impregnation step, the catalyst slurry is impregnated and held at an end of the wall flow type substrate on the exhaust gas introduction side,
The manufacturing method of the exhaust gas purification catalyst as described in [1] .
[3]
In the removal step, the retained amount of the catalyst slurry in the wall flow type substrate is reduced to 90 to 98% by mass before and after treatment.
The manufacturing method of the exhaust gas purification catalyst as described in [1] or [2] .
[4]
After the removing step, the wall flow type substrate further has a firing process of performing a heat treatment at 400 to 650 ° C.,
The manufacturing method of the exhaust gas purification catalyst as described in any one of [1]-[3] .

Claims (6)

A method of manufacturing an exhaust gas purification catalyst for purifying an exhaust gas discharged from an internal combustion engine, comprising:
An impregnation step of impregnating and holding a catalyst slurry on the end of the exhaust gas introduction side or the exhaust gas discharge side of the wall flow type substrate having a plurality of passages defined by porous partition walls;
Applying the catalyst slurry impregnated in the wall flow substrate to the porous partition walls by flowing gas into the wall flow substrate from the end side;
And removing the excess catalyst slurry that blocks the pores of the partition walls.
Method of manufacturing exhaust gas purification catalyst. In the removal step, a gas is allowed to flow into the wall flow type substrate from the end opposite to the end.
A method of manufacturing an exhaust gas purification catalyst according to claim 1. In the impregnation step, the catalyst slurry is impregnated and held at an end of the wall flow type substrate on the exhaust gas introduction side,
The manufacturing method of the exhaust gas purification catalyst according to claim 1 or 2. In the removal step, the retained amount of the catalyst slurry in the wall flow type substrate is reduced to 90 to 98% by mass before and after treatment.
The manufacturing method of the exhaust gas purification catalyst as described in any one of Claims 1-3. After the removing step, the wall flow type substrate further has a firing process of performing a heat treatment at 400 to 650 ° C.,
The manufacturing method of the exhaust gas purification catalyst as described in any one of Claims 1-4. It is obtained by the method for producing an exhaust gas purification catalyst according to any one of claims 1 to 5.
Exhaust gas purification catalyst.