JP2021137766A - Exhaust emission control device - Google Patents

Abstract

To provide an exhaust emission control device enabling improvement of clarification performance thereof and enabling suppression of pressure loss thereof.SOLUTION: The exhaust emission control device of the present invention is an exhaust emission control device comprising a honeycomb substrate and an outflow cell side catalyst layer, the honeycomb substrate has a porous partition wall that defines a plurality of cells extending from the inflow side end surface to the outflow side end surface, the plurality of cells includes inflow cell and outflow cell which are adjacent to each other with the partition wall sandwiched therebetween, the inflow cell is opened at an inflow side end, and is sealed at an outlet side end, the outlet cell is sealed at an inflow side end, is opened at an outflow side end, and the outflow cell side catalyst layer is provided in an internal region on the outflow cell side in the outflow cell side catalyst region extending from the outflow side end of the partition wall to a predetermined position on the inflow side, a gas transmission coefficient of the outflow side partition wall portion including the outflow cell side catalyst region of the partition wall and the outflow cell side catalyst layer decreases from the predetermined position of the partition wall towards the outflow side end.SELECTED DRAWING: Figure 2

Description

The present invention relates to an exhaust gas purification device in which a catalyst is provided in a filter having a wall flow structure.

Exhaust gas emitted from internal combustion engines in automobiles is composed of carbon-based particulate matter (PM: Particulate Matter, hereinafter sometimes abbreviated as "PM") and non-combustible components that cause air pollution. Some ash etc. are included. A wall flow structure filter is widely used as a filter for collecting and removing PM from exhaust gas.

A filter having a wall flow structure usually includes a honeycomb base material, and the honeycomb base material has a porous partition wall that defines a plurality of cells extending from the inflow side end face to the outflow side end face, and the plurality of cells sandwich the partition wall. Includes adjacent inflow and outflow cells. Then, the inflow side end of the inflow cell is open and the outflow side end is sealed, and the outflow cell is sealed at the inflow side end and the outflow side end is open. Therefore, the exhaust gas that has flowed into the inflow cell from the inflow side end flows into the outflow cell by passing through the partition wall, and is discharged from the outflow side end of the outflow cell. Then, when the exhaust gas permeates the partition wall, PM is collected in the pores of the partition wall. As a filter having a wall flow structure, for example, a diesel particulate filter (DPF) for a diesel engine, a gasoline particulate filter (GPF) for a gasoline engine, and the like are known.

On the other hand, the exhaust gas contains harmful components such as CO (carbon monoxide), HC (hydrocarbon), and NOx (nitrogen oxide) in addition to PM. Hazardous components can be removed from the exhaust gas by a filter coated with a catalyst such as a precious metal catalyst. Therefore, in recent years, an exhaust gas purification device in which a catalyst is provided in a filter having a wall flow structure has been used in order to remove both PM and harmful components from the exhaust gas.

As an exhaust gas purification device in which a catalyst is provided in a filter having a wall flow structure, for example, as described in Patent Document 1, at least a part of a partition wall inside a partition wall and facing an outflow cell is provided with a partition wall. An exhaust gas purification device including a catalyst layer provided from an outflow side end to a predetermined position on the inflow side is known.

International Publication No. 2018/173557

In an exhaust gas purification device in which a catalyst is provided in a filter having such a wall flow structure, when the exhaust gas that has flowed into the inflow cell from the inflow side end permeates the partition wall and flows into the outflow cell, the exhaust gas flows into the outflow side of the partition wall. The flow rate distribution of the exhaust gas that permeates the partition wall biased to the region near the end and permeates the partition wall in the extending direction of the partition wall is generated. In particular, since the GPF has a higher transmittance of the partition wall than the DPF, the flow rate distribution of the exhaust gas that permeates the partition wall in the extending direction of the partition wall is likely to occur remarkably.

When the exhaust gas permeates the partition wall in a region close to the outflow side end of the partition wall and the flow rate distribution of the exhaust gas permeates the partition wall in the extending direction of the partition wall occurs, the catalyst layer near the outflow side end of the partition wall contains the exhaust gas. Exhaust gas cannot be sufficiently purified because the permeation flow rate is too large, and the catalyst layer away from the outflow side end of the partition wall can permeate the exhaust gas at a flow rate much smaller than the maximum permeation flow rate that can be purified. As a result of the inability, the purification performance may be insufficient.

On the other hand, in order to make up for the lack of purification performance of the exhaust gas, when the contact property of the exhaust gas and the catalyst layer is to be improved in the region near the outflow side end of the partition wall by simply increasing the density of the catalyst layer. Even if the purification performance can be improved, the transmittance of the exhaust gas from the partition wall may decrease and the pressure loss may increase.

The present invention has been made in view of these points, and an object of the present invention is to provide an exhaust gas purification device capable of improving purification performance and suppressing pressure loss. be.

In order to solve the above problems, the exhaust gas purification device of the present invention is an exhaust gas purification device including a honeycomb base material and an outflow cell side catalyst layer, and the honeycomb base material extends from the inflow side end face to the outflow side end face. The plurality of cells include an inflow cell and an outflow cell adjacent to each other with the partition wall in between, and the inflow cell has an inflow side end open and an outflow side end. Is sealed, the inflow side end of the outflow cell is sealed, the outflow side end is opened, and the outflow cell side catalyst layer extends from the outflow side end of the partition wall to a predetermined position on the inflow side. The gas permeation coefficient of the outflow side catalyst region including the outflow cell side catalyst region and the outflow cell side catalyst layer of the partition wall provided in the inner region of the outflow cell side in the cell side catalyst region is the predetermined position of the partition wall. It is characterized in that it decreases from the to the outflow side end.

According to the present invention, the purification performance can be improved and the pressure loss can be suppressed.

It is a perspective view which shows typically an example of the exhaust gas purification apparatus of embodiment. It is sectional drawing which shows roughly the main part of the cross section parallel to the extending direction of a cell in the exhaust gas purification apparatus shown in FIG. (A) to (c) are cross-sectional photographs showing the arrangement region of the first catalyst layer, the arrangement region of the second catalyst layer, and the arrangement region of the third catalyst layer in the partition wall portion on the outflow side shown in FIG. (A) is a cross-sectional view schematically showing an exhaust gas purification device of an example, and (b) is a cross-sectional view schematically showing an exhaust gas purification device of a comparative example. It is a graph which shows NOx50% purification temperature of the exhaust gas purification apparatus of an Example and a comparative example. (A) is a cross-sectional view schematically showing how the exhaust gas flows inside the exhaust gas purification device of the embodiment, and (b) shows roughly how the exhaust gas flows inside the exhaust gas purification device of the comparative example. It is sectional drawing which shows.

An embodiment of the exhaust gas purification device of the present invention is an exhaust gas purification device including a honeycomb base material and an outflow cell side catalyst layer, and the honeycomb base material defines a plurality of cells extending from an inflow side end face to an outflow side end face. The plurality of cells have a porous partition wall formed therein, and the plurality of cells include an inflow cell and an outflow cell adjacent to each other across the partition wall, and the inflow side end of the inflow cell is opened and the outflow side end is sealed. In the outflow cell, the inflow side end is sealed, the outflow side end is opened, and the outflow cell side catalyst layer extends from the outflow side end of the partition wall to a predetermined position on the inflow side. The gas permeation coefficient of the outflow side partition wall including the outflow cell side catalyst region and the outflow cell side catalyst layer of the partition wall, which is provided in the inner region on the outflow cell side of the partition, is from the predetermined position of the partition wall to the outflow side end. It is characterized by a decrease toward.
Here, the "inflow side" refers to the side on which the exhaust gas flows in the exhaust gas purification device, and the "outflow side" refers to the side on which the exhaust gas flows out in the exhaust gas purification device.

In the embodiment, the stretching direction of the partition wall is not particularly limited, but is usually substantially the same as the axial direction of the honeycomb base material, and the stretching direction of the cell is not particularly limited, but is usually substantially the same as the stretching direction of the partition wall. be. In the following description, the "stretching direction" refers to the stretching direction of the partition wall and the cell, that is, the direction in which the inflow side and the outflow side face each other, which is substantially the same as the axial direction of the honeycomb base material.

First, the outline of the exhaust gas purification device of the embodiment will be described by way of example. FIG. 1 is a perspective view schematically showing an example of the exhaust gas purification device of the embodiment. FIG. 2 is a cross-sectional view schematically showing a main part of a cross section parallel to the extending direction of the cell in the exhaust gas purification device shown in FIG.

As shown in FIGS. 1 and 2, the exhaust gas purification device 1 of this example includes a honeycomb base material 10, a sealing portion 16, an outflow cell side catalyst layer 30, and an inflow cell side catalyst layer 40. The honeycomb base material 10 is a base material in which a cylindrical frame portion 11 and a partition wall 14 that partitions the space inside the frame portion 11 in a honeycomb shape are integrally formed. The partition wall 14 is a porous body that defines a plurality of cells 12 extending from the inflow side end face 10Sa of the honeycomb base material 10 to the outflow side end face 10Sb. The shape of the partition wall 14 is orthogonal to a plurality of wall portions 14L arranged in parallel with each other separated from each other so that the cross section perpendicular to the extending direction of the plurality of cells 12 becomes a square, and these plurality of wall portions 14L. Moreover, it includes a plurality of wall portions 14S arranged in parallel with each other separated from each other, and the cross section perpendicular to the stretching direction is in a grid pattern.

The plurality of cells 12 include an inflow cell 12A and an outflow cell 12B that are adjacent to each other with the partition wall 14 interposed therebetween. In the inflow cell 12A, the inflow side end 12Aa is opened and the outflow side end 12Ab is sealed by the sealing portion 16, and in the outflow cell 12B, the inflow side end 12Ba is sealed by the sealing portion 16 and the outflow side. The end 12Bb is open. The cross-sectional shape of the inflow cell 12A perpendicular to the stretching direction is constant in the stretching direction.

The outflow cell side catalyst layer 30 is provided in the outflow cell side internal region 14NB in the outflow cell side catalyst region 14Rb extending from the outflow side end 14b of the partition wall 14 to a predetermined position 14m on the inflow side. The outflow cell side catalyst layer 30 contains a first catalyst layer 30A, a second catalyst layer 30B, and a third catalyst layer 30C, which are sequentially provided from a predetermined position 14m of the partition wall 14 toward the outflow side end 14b. .. The first catalyst layer 30A, the second catalyst layer 30B, and the third catalyst layer 30C contain catalyst metal particles (not shown) and a carrier supporting them (not shown).

In the outflow cell side catalyst layer 30, the density and thickness increase in the order of the first catalyst layer 30A, the second catalyst layer 30B, and the third catalyst layer 30C. As a result, in the outflow side partition wall portion including the outflow cell side catalyst region 14Rb and the outflow cell side catalyst layer 30 of the partition wall 14, the gas permeation coefficient is the arrangement region of the first catalyst layer 30A and the arrangement region of the second catalyst layer 30B. And, it decreases in the order of the arrangement region of the third catalyst layer 30C. As a result, the gas permeability coefficient of the outflow side partition wall of the partition wall 14 decreases in order from the predetermined position 14m of the partition wall 14 toward the outflow side end 14b.
3 (a) to 3 (c) show the arrangement region of the first catalyst layer, the arrangement region of the second catalyst layer, and the arrangement region of the third catalyst layer in the discharge side partition wall shown in FIG. 2, respectively. It is a cross-sectional photograph showing.

The inflow cell side catalyst layer 40 is provided on the inflow cell side surface 14SA in the inflow cell side catalyst region 14Ra extending from the predetermined position 14 m toward the outflow side from the inflow side end 14a of the partition wall 14 to the outflow side position. There is. The inflow cell side catalyst layer 40 contains catalyst metal particles (not shown) and a carrier supporting the catalyst metal particles (not shown).

In the exhaust gas purification device 1 of this example, in the outflow side partition wall portion including the outflow cell side catalyst region 14Rb and the outflow cell side catalyst layer 30 of the partition wall 14, the gas permeability coefficient is the arrangement region of the first catalyst layer 30A and the second catalyst. It decreases in the order of the arrangement region of the layer 30B and the arrangement region of the third catalyst layer 30C. As a result, the gas permeability coefficient of the outflow side partition wall of the partition wall 14 decreases in order from the predetermined position 14m of the partition wall 14 toward the outflow side end 14b. Therefore, as shown in FIG. 2, the exhaust gas flowing into the inflow cell 12A from the inflow side end 14a is the exhaust gas of the partition wall 14 as compared with the case where the gas permeability coefficient of the outflow side partition wall is constant in the stretching direction. It is possible to suppress the permeation of the partition wall 14 in a region close to the outflow side end 14b, and to prevent the flow rate distribution of the exhaust gas permeating the partition wall 14 in the extending direction of the partition wall 14. As a result, in the outflow cell side catalyst layer 30, it is possible to prevent the permeation flow rate of the exhaust gas in the catalyst layer near the outflow side end 14b of the partition wall 14 from becoming excessively excessive, and the catalyst away from the outflow side end 14b of the partition wall 14 can be suppressed. The permeation flow rate of the exhaust gas in the layer can be set to a flow rate at which the purification performance of the catalyst layer is sufficiently exhibited. Therefore, the purification performance can be improved without increasing the density of the outflow cell side catalyst layer 30.

Therefore, in the exhaust gas purification device of the embodiment, the purification performance can be improved without increasing the density of the catalyst layer on the outflow cell side, as in the above example. Therefore, the purification performance can be improved and the pressure loss can be suppressed.

Subsequently, each configuration of the exhaust gas purification device of the embodiment will be described in detail.

1. 1. Outflow side partition wall The outflow side partition wall includes the outflow cell side catalyst region and the outflow cell side catalyst layer of the partition wall. The outflow cell-side catalyst region of the partition wall is a region extending from the outflow side end of the partition wall to a predetermined position on the inflow side. The outflow cell-side catalyst layer is provided in the outflow cell-side internal region in the outflow cell-side catalyst region. The gas permeability coefficient of the outflow side partition wall decreases from the predetermined position of the partition wall toward the outflow side end.

Here, the "gas permeability coefficient" means the permeability coefficient of Darcy, and refers to the one calculated by the following formula.

[Number 1]
K = QVT / AM
(However, K = gas permeation coefficient (m ² ), Q = gas flow rate (unit: m ³ / sec), V = gas viscosity (unit: Pa · sec), T = bulkhead thickness (unit: unit:) m), A = cross-sectional area (unit: m ² ) perpendicular to the gas permeation direction of the gas permeating portion of the partition wall, M = gas in the partition wall when gas is passed through the partition wall at a flow rate Q Differential pressure between inflow side and outflow side (unit: Pa))

The method for measuring the gas permeability coefficient is not particularly limited, but for example, a commercially available palm porometer (for example, a palm porometer manufactured by PMI (Porous Materials Inc.)) is used to change the gas pressure at 25 ° C. When air is permeated through a 10 mm square portion (a portion of the partition wall that allows gas to permeate) at a flow rate of 1 L / min to 200 L / min, the differential pressure between the gas inflow side and the outflow side of the partition wall portion. Examples thereof include a method of measuring the flow rate of air when becomes 10 kPa and calculating from the above formula using the measured flow rate of air.

The gas permeation coefficient of the outflow side bulkhead is obtained from the flow rate of the gas when the gas is allowed to flow through the outflow side bulkhead in the thickness direction and the differential pressure between the inflow side and the outflow side of the outflow side bulkhead. Refers to what is done.

The outflow side partition wall includes the outflow cell side catalyst region and the outflow cell side catalyst layer of the partition wall, and is not particularly limited as long as the gas permeation coefficient decreases from a predetermined position of the partition wall toward the outflow side end. , The density of the catalyst layer increases from the predetermined position of the partition wall toward the outflow side end, and above all, like the outflow side partition wall portion shown in FIG. 1, from the predetermined position of the partition wall toward the outflow side end. A catalyst layer on the outflow cell side containing a plurality of catalyst layers provided in order, and the density of the plurality of catalyst layers contained in the catalyst layer on the outflow cell side increases in the order closer to the outflow side end of the partition wall, etc. Is preferable.

The length of the outflow side partition wall in the stretching direction coincides with the length of the outflow cell side catalyst region of the partition wall and the length of the outflow cell side catalyst layer in the stretching direction, and the partition wall is stretched from the outflow side end to the inflow side predetermined position. Refers to the length in the direction.

Hereinafter, the partition wall included in the outflow side partition wall portion and the outflow cell side catalyst layer will be described. Since the partition wall is possessed by the honeycomb base material, it will be described as a part of the honeycomb base material.

(1) Honeycomb base material The honeycomb base material has a porous partition wall that defines a plurality of cells extending from the inflow side end face to the outflow side end face. The plurality of cells include an inflow cell and an outflow cell adjacent to each other with the partition wall interposed therebetween, the inflow side end of the inflow cell is opened, the outflow side end is sealed, and the outflow cell is on the inflow side. The end is sealed and the outflow side end is open.

The honeycomb base material is a base material in which a frame portion and a partition wall that divides the space inside the frame portion into a honeycomb shape are integrally formed.

The axial length of the honeycomb base material is not particularly limited, and a general length can be used. For example, it is preferably in the range of 30 mm or more and 500 mm or less, and particularly preferably in the range of 50 mm or more and 300 mm or less. .. The capacity of the honeycomb base material, that is, the total volume of the cells is not particularly limited, and a general capacity can be used, but for example, it is preferably in the range of 0.1 L or more and 5 L or less.

The material of the honeycomb base material is not particularly limited, and general materials can be used. Examples thereof include ceramics such as cordierite, silicon carbide (SiC) and aluminum titanate, and alloys such as stainless steel.

The shape of the frame portion is not particularly limited, and a general shape can be used, and examples thereof include a cylindrical shape, an elliptical cylinder shape, a polygonal cylinder shape, and the like. The other configuration of the frame portion is not particularly limited, and a general configuration can be used.

The shape of the partition wall is not particularly limited, and a general shape can be used. The total length of the partition wall in the stretching direction is not particularly limited, but is usually substantially the same as the axial length of the honeycomb base material. The thickness of the partition wall is not particularly limited, and a general thickness can be used, but for example, it is preferably in the range of 50 μm or more and 2000 μm or less, and particularly preferably in the range of 100 μm or more and 1000 μm or less. This is because when the thickness of the partition wall is within these ranges, it is possible to obtain sufficient PM collection performance while ensuring the strength of the base material, and it is possible to sufficiently suppress the pressure loss.

The partition wall has a porous structure through which exhaust gas can permeate. The porosity of the partition wall is not particularly limited, and a general porosity can be used. For example, the porosity is preferably in the range of 40% or more and 70% or less, and particularly preferably in the range of 50% or more and 70% or less. This is because pressure loss can be effectively suppressed when the porosity is equal to or higher than the lower limit of these ranges, and sufficient mechanical strength can be ensured when the porosity is equal to or lower than the upper limit of these ranges. be. The average pore diameter of the pores of the partition wall is not particularly limited, and a general average pore diameter can be used. For example, it is preferably in the range of 1 μm or more and 60 μm or less, and particularly preferably in the range of 5 μm or more and 30 μm or less. This is because when the average pore diameter of the pores is within these ranges, sufficient PM collection performance can be obtained and pressure loss can be sufficiently suppressed. The "average pore diameter of the pores of the partition wall" refers to, for example, the one measured by the bubble point method using a palm poromometer.

The inflow cell and the outflow cell are formed by partitioning the space inside the frame portion by a partition wall, and are adjacent to each other with the partition wall in between. The inflow cell and the outflow cell are usually surrounded by a partition wall in a direction perpendicular to the stretching direction.

The inflow cell is usually sealed at the outflow side end by a sealing portion. The outflow cell is usually sealed at the inflow side end by a sealing portion. The length of the sealing portion in the stretching direction is not particularly limited and may be a general length, but is preferably in the range of 2 mm or more and 20 mm or less, for example. The material of the sealing portion is not particularly limited and may be a general material.

The cross-sectional shape perpendicular to the stretching direction of the inflow cell and the outflow cell is not particularly limited, and a general shape can be used, and it should be appropriately set in consideration of the flow rate and components of the exhaust gas passing through the exhaust gas purification device. Can be done. Examples of the cross-sectional shape include a rectangle such as a square, a polygon including a hexagon, a circle, and the like. The cross-sectional area perpendicular to the stretching direction of the inflow cell and the outflow cell is not particularly limited, and a general cross-sectional area can be used, but is, for example, in the range of ^{1 mm 2} or more and 7 mm ^{2 or less.} The length of the inflow cell and the outflow cell in the stretching direction is not particularly limited, but is usually substantially the same as the length obtained by subtracting the length of the sealing portion in the stretching direction from the length in the axial direction of the honeycomb base material. Examples of the arrangement mode of the inflow cell and the outflow cell include a checkered pattern in which the inflow cell and the outflow cell are arranged alternately as in the arrangement mode in the first example and the second example.

(2) Outflow Cell Side Catalyst Layer The outflow cell side catalyst layer is provided in the outflow cell side internal region in the outflow cell side catalyst region extending from the outflow side end of the partition wall to a predetermined position on the inflow side.

The outflow cell side catalyst layer is not particularly limited as long as the gas permeability coefficient of the outflow side partition wall decreases from the predetermined position of the partition wall toward the outflow side end, but for example, from the predetermined position of the partition wall to the outflow side end. Examples thereof include a plurality of catalyst layers provided in order toward each other, and the densities of the plurality of catalyst layers increase in the order closer to the outflow side end of the partition wall. Specifically, for example, like the outflow cell side catalyst layer shown in FIG. 1, the first catalyst layer, the second catalyst layer, and the third catalyst layer provided in order from a predetermined position of the partition wall toward the outflow side end. It may contain a catalyst layer and its density may increase in the order of the first catalyst layer, the second catalyst layer, and the third catalyst layer, or it may be provided in order from a predetermined position of the partition wall toward the outflow side end. It may contain a first catalyst layer and a second catalyst layer, and the density may increase in the order of the first catalyst layer and the second catalyst layer.

The length of the outflow cell side catalyst layer in the stretching direction is not particularly limited as long as it is within the range of the total length in the stretching direction of the partition wall or less, but for example, the range of 20/100 or more and 100/100 or less of the total length in the stretching direction of the partition wall. Is preferable. This is because when the length is within this range, the purification performance is improved and the pressure loss is suppressed remarkably.

When the outflow cell side catalyst layer contains the first catalyst layer, the second catalyst layer, and the third catalyst layer, the direction of extension of the first catalyst layer, the second catalyst layer, and the third catalyst layer The length ratio is not particularly limited, but for example, the ratio of the length in the stretching direction of the first catalyst layer to the length in the stretching direction of the third catalyst layer is within the range of 1/5 or more and 4/5 or less. It is preferable that the ratio of the length of the second catalyst layer in the stretching direction to the length of the third catalyst layer in the stretching direction is in the range of 1/5 or more and 4/5 or less. This is because the improvement of purification performance and the suppression of pressure loss become remarkable.

The density of the outflow cell side catalyst layer is not particularly limited, and a general density can be used, but for example, it is preferably in the range of 20 g / L or more and 200 g / L or less. This is because the purification performance can be sufficiently improved when the density is equal to or higher than the lower limit of this range, and the pressure loss can be sufficiently suppressed when the density is equal to or lower than the upper limit of this range. The density of the catalyst layer is a value obtained by dividing the total mass of the catalyst layers by a part of the volume of the honeycomb base material in the axial direction in which the length in the stretching direction and the length in the axial direction of the catalyst layer are the same. Point to.

When the outflow cell side catalyst layer contains the first catalyst layer, the second catalyst layer, and the third catalyst layer, the ratio of the densities of the first catalyst layer, the second catalyst layer, and the third catalyst layer. Is not particularly limited as long as the density increases in the order of the first catalyst layer to the third catalyst layer, but for example, the ratio of the density of the first catalyst layer to the density of the third catalyst layer is 1/5 or more and 3 /. It is preferably in the range of 5 or less, and the ratio of the density of the second catalyst layer to the density of the third catalyst layer is in the range of 2/5 or more and 4/5 or less. The density of the catalyst layer near the outflow side end of the partition wall in the outflow cell side catalyst layer becomes equal to or higher than a predetermined lower limit, and the density of the catalyst layer away from the outflow side end of the partition wall becomes equal to or lower than a predetermined upper limit, so that the outflow side of the partition wall It is possible to prevent the permeation flow rate of the exhaust gas in the catalyst layer near the end from becoming excessive to the extent that it cannot be purified, and the purification performance of the catalyst layer is sufficiently exhibited by allowing the permeation flow rate of the exhaust gas in the catalyst layer away from the outflow side end of the partition wall to be sufficiently exhibited. This is because it can be a flow rate. Further, the density of the catalyst layer near the outflow side end of the partition wall in the outflow cell side catalyst layer becomes equal to or less than a predetermined upper limit, and the density of the catalyst layer away from the outflow side end of the partition wall becomes equal to or more than a predetermined lower limit. This is because it is possible to prevent the permeation flow rate of the exhaust gas in the catalyst layer near the outflow side end from being excessively suppressed, and it is possible to prevent the permeation flow rate of the exhaust gas in the catalyst layer away from the outflow side end of the partition wall from becoming excessively excessive. Is.

The thickness of the outflow cell side catalyst layer is not particularly limited, and a general thickness can be used, but for example, the thickness of the partition wall is preferably in the range of 50/100 or more and 100/100 or less. This is because when the thickness is at least the lower limit of these ranges, the contact frequency between the catalyst layer and the exhaust gas can be ensured when the exhaust gas passes through the partition wall.

When the outflow cell side catalyst layer contains the first catalyst layer, the second catalyst layer, and the third catalyst layer, the thickness of the first catalyst layer, the second catalyst layer, and the third catalyst layer The combination is not particularly limited, but for example, those in which the first catalyst layer, the second catalyst layer, and the third catalyst layer are increased in this order are preferable, and among them, the thickness of the first catalyst layer is the thickness of the partition wall. The thickness of the second catalyst layer is within the range of 10/100 or more and 60/100 or less, the thickness of the second catalyst layer is within the range of 30/100 or more and 80/100 or less of the thickness of the partition wall, and the thickness of the third catalyst layer is the partition wall. The thickness is preferably in the range of 50/100 or more and 100/100 or less. This is because when the thickness of each catalyst layer is within these ranges, it is advantageous in terms of improving purification performance and suppressing pressure loss.

The outflow cell side catalyst layer usually contains catalyst metal particles and a carrier that supports the catalyst metal particles. The outflow cell-side catalyst layer is formed by, for example, arranging a catalysted carrier carrying catalyst metal particles in pores in an internal region of a partition wall. The method for supporting the catalyst metal particles on the carrier is not particularly limited, and a general method can be used. For example, a catalyst metal particle salt (for example, nitrate) or a catalyst metal particle complex (for example, tetraammine complex) or the like can be used. ) Is impregnated with the carrier, and then dried and fired.

The material of the catalyst metal particles is not particularly limited, and general materials can be used, and examples thereof include precious metals such as Rh (rhodium), Pd (palladium), and Pt (platinum). The material of the catalyst metal particles may be one kind of metal, two or more kinds of metals, or an alloy containing two or more kinds of metals. Rh is preferable as the material of the catalyst metal particles.

The average particle size of the catalyst metal particles is not particularly limited, and a general average particle size can be used, but for example, it is preferably in the range of 0.1 nm or more and 20 nm or less. This is because the contact area with the exhaust gas can be increased when the average particle size is equal to or less than the upper limit of this range. The average particle size of the catalyst metal particles refers to, for example, an average value obtained from the particle size measured by a transmission electron microscope (TEM).

The content of the catalyst metal particles per 1 L of the volume of the base material is not particularly limited, and a general content can be used, but it depends on the material of the catalyst metal particles, for example, the material is Rh, Pd, or Pt. In the case of, it is preferably in the range of 0.01 g or more and 2 g or less. This is because a sufficient catalytic action can be obtained when the content is at least the lower limit of this range, and when the content is at least the upper limit of this range, the grain growth of the catalytic metal particles can be suppressed and at the same time, the cost aspect. This is because it becomes advantageous. Here, the "content of the catalyst metal particles per 1 L of the volume of the base material" means that the mass of the catalyst metal particles contained in the catalyst layer has the same length in the stretching direction and the length in the axial direction of the catalyst layer. It refers to a value divided by a part of the volume of the honeycomb base material in the axial direction.

The material of the carrier is not particularly limited, and general materials can be used. For example, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), ceria (CeO ₂ ), silica (SiO ₂ ), magnesia. (MgO), a metal oxide such as titanium oxide (TiO _2), or, for example, ceria - zirconia _{(CeO 2} -ZrO 2) include those solid solutions such as a composite oxide. The material of the carrier may be one of these or two or more of them. As the material of the carrier, at least one kind such as alumina and a ceria-zirconia composite oxide is preferable. The shape of the carrier is not particularly limited, and a general shape can be used, but a powdery form is preferable. This is because a larger specific surface area can be secured.

The average particle size of the powdered carrier is not particularly limited, but is preferably in the range of 0.1 μm or more and 4 μm or less, for example. This is because when the average particle size is at least the lower limit of this range, sufficient heat resistance characteristics can be obtained. When the average particle size is not more than the upper limit of this range, the slurry is allowed to permeate into the inner region of the partition wall when the slurry containing the powdery carrier is supplied to the inner region of the partition wall in order to form the catalyst layer on the outflow cell side. Because it can be done. The "average particle size of the powdered carrier" refers to, for example, the average particle size obtained by a laser diffraction / scattering method.

The mass ratio of the catalyst metal particles to the total mass of the catalyst metal particles and the carrier is not particularly limited, and a general mass ratio can be used. For example, it is within the range of 0.01% by mass or more and 10% by mass or less. Is preferable. This is because a sufficient catalytic action can be obtained when the mass ratio is equal to or higher than the lower limit of this range, and when the mass ratio is equal to or lower than the upper limit of this range, the grain growth of the catalytic metal particles can be suppressed and at the same time, the cost aspect. This is because it becomes advantageous.

The method for forming the outflow cell-side catalyst layer is not particularly limited, and a general method can be used. For example, after supplying the slurry to the outflow cell-side internal region in the outflow cell-side catalyst region of the partition wall, the slurry is dried. And then firing.

The slurry usually contains catalytic metal particles and a carrier in addition to the solvent. The slurry may further contain any component such as binders and additives. The solvent is not particularly limited, and a general solvent can be used, and examples thereof include water such as ion-exchanged water, a water-soluble organic solvent, or a mixture of water and a water-soluble organic solvent. The properties such as the solid content concentration and viscosity of the slurry and the shape and particle size of each component of the slurry may be appropriately adjusted so that the slurry penetrates into the partition wall.

The method for supplying the slurry to the internal region on the outflow cell side in the outflow cell side catalyst region of the partition wall is not particularly limited, and a general method can be used. Examples thereof include a method of immersing from the side and taking out from the slurry after a predetermined time has elapsed. In the method of supplying the slurry to the partition wall, drying and firing, the drying conditions and firing conditions are not particularly limited, and a general method can be used.

The properties such as the density, thickness, and porosity of the catalyst layer on the outflow cell side are the supply amount of the slurry, the properties of the slurry, the shape, particle size, and content of each component of the slurry, the drying conditions, and the firing conditions. It can be prepared by such means.

2. The inflow cell side catalyst layer The exhaust gas purification device is not particularly limited, but for example, as in the exhaust gas purification device shown in FIG. 1, the inflow in the inflow cell side catalyst region extending from the inflow side end of the partition wall toward the outflow side. An inflow cell-side catalyst layer provided on the cell-side surface may be further provided. As a result, it is possible to prevent the exhaust gas from permeating the portion of the partition wall where the catalyst layer is not formed.

The length of the inflow cell-side catalyst layer in the stretching direction is not particularly limited, but for example, the length of the partition wall is equal to or greater than the total length of the partition wall in the stretching direction minus the length of the outflow cell-side catalyst layer in the stretching direction. It is preferable that the length is equal to or less than 30/100 of the total length in the stretching direction. This is because when the length is equal to or greater than the lower limit of this range, it is possible to effectively prevent the exhaust gas from permeating the portion of the partition wall where the catalyst layer is not formed. When the length is equal to or less than the upper limit of this range, the speed at which the exhaust gas permeates the overlapping region of the inflow cell side catalyst region and the outflow cell side catalyst region in the partition wall decreases, so that the purification performance decreases and the pressure loss increases. This is because it is possible to suppress the invitation.

The density of the catalyst layer on the inflow cell side is not particularly limited, and a general density can be used, but for example, it is preferably in the range of 30 g / L or more and 350 g / L or less. This is because the purification performance can be effectively improved when the density is equal to or higher than the lower limit of this range. This is because the pressure loss can be effectively suppressed when the density is not more than the upper limit of this range.

The thickness of the catalyst layer on the inflow cell side is not particularly limited, and a general thickness can be used, but for example, the thickness of the partition wall is preferably in the range of 5/100 or more and 50/100 or less. This is because when the thickness is at least the lower limit of this range, it is possible to effectively suppress the permeation of the exhaust gas through the partition wall portion including the inflow cell side catalyst region and the inflow cell side catalyst layer of the barrier. This is because the pressure loss can be remarkably suppressed when the thickness is not more than the upper limit of this range.

The inflow cell side catalyst layer usually contains catalyst metal particles and a carrier that supports the catalyst metal particles. The inflow cell side catalyst layer is, for example, a porous sintered body of a catalysted carrier carrying catalyst metal particles. The method of supporting the catalyst metal particles on the carrier is the same as the method of supporting the catalyst metal particles on the carrier in the outflow cell side catalyst layer, and thus the description thereof is omitted here.

The material of the catalyst metal particles is not particularly limited, and general materials can be used, and examples thereof include precious metals such as Rh (rhodium), Pd (palladium), and Pt (platinum). The material of the catalyst metal particles may be one kind of metal, two or more kinds of metals, or an alloy containing two or more kinds of metals. As the material of the catalyst metal particles, at least one kind such as Pd and Pt is preferable.

The average particle size of the catalyst metal particles is not particularly limited and is the same as the average particle size of the catalyst metal particles in the catalyst layer on the outflow cell side, and thus the description thereof is omitted here.

The content of the catalyst metal particles per 1 L of the volume of the base material is not particularly limited, and a general content can be used, but it depends on the material of the catalyst metal particles, for example, the material is Pd, Pt, or Rh. In the case of, it is preferably in the range of 0.05 g or more and 5 g or less per 1 L of the honeycomb base material. This is because a sufficient catalytic action can be obtained when the content is at least the lower limit of this range, and when the content is at least the upper limit of this range, the grain growth of the catalytic metal particles can be suppressed and at the same time, the cost aspect. This is because it becomes advantageous.

The material and shape of the carrier are not particularly limited and are the same as the material and shape of the carrier in the catalyst layer on the outflow cell side, and thus the description thereof will be omitted here. The average particle size of the powdered carrier is not particularly limited, but is preferably in the range of 1 μm or more and 10 μm or less, for example. This is because sufficient heat resistance can be obtained when the average particle size is equal to or higher than the lower limit of this range, and sufficient dispersibility of the catalyst metal particles is ensured when the average particle size is equal to or lower than the upper limit of this range. This is because the purification performance can be effectively improved.

The mass ratio of the catalyst metal particles to the total mass of the catalyst metal particles and the carrier is the same as the mass ratio of the catalyst metal particles to the total mass of the catalyst metal particles and the carrier in the outflow cell side catalyst layer. Is omitted.

The method for forming the inflow cell side catalyst layer is not particularly limited, and a general method can be used. For example, after supplying the slurry onto the surface of the inflow cell side catalyst region of the partition wall on the inflow cell side, drying is performed. And then firing.

The slurry usually contains catalytic metal particles and a carrier in addition to the solvent. The slurry may further contain any component such as binders and additives. The solvent is not particularly limited, and a general solvent can be used, and examples thereof include water such as ion-exchanged water, a water-soluble organic solvent, or a mixture of water and a water-soluble organic solvent. The properties such as the solid content concentration and viscosity of the slurry and the shape and particle size of each component of the slurry may be appropriately adjusted so that the slurry does not penetrate into the partition wall.

The method of supplying the slurry onto the surface of the inflow cell side in the catalyst region on the inflow cell side of the partition wall is not particularly limited, and a general method can be used. Examples thereof include a method of immersing from the side and taking out from the slurry after a predetermined time has elapsed. In this method, the outflow cell may be pressurized to create a pressure difference between the outflow cell and the inflow cell so that the slurry does not penetrate into the partition wall. In the method of supplying the slurry to the partition wall, drying and firing, the drying conditions and firing conditions are not particularly limited, and a general method can be used.

The properties such as the density, thickness, and porosity of the catalyst layer on the inflow cell side are the supply amount of the slurry, the properties of the slurry, the shape, particle size, and content of each component of the slurry, the drying conditions, and the firing conditions. It can be prepared by such means.

3. 3. Exhaust gas purification device When the exhaust gas purification device includes a honeycomb base material, an outflow cell side catalyst layer, and an inflow cell side catalyst layer, the inflow cell side catalyst layer contains at least one of Pt (platinum) and Pd (palladium). It is preferable that the catalyst layer on the outflow cell side contains catalyst metal particles containing Rh (rhodium). Since HC (hydrocarbon) of exhaust gas in a rich atmosphere can be efficiently oxidized by at least one of Pt and Pd contained in the inflow cell side catalyst layer, the outflow cell side catalyst layer is poisoned by HC starting from Ce. This is because it can be suppressed. Also, in the case of oxidation, at least one of the HC Pt and Pd, in addition to many production of heat generation is large and H _{2 O} than in the case of oxidation with Rh, steam reforming activity of Rh is Pt And because it is higher than Pd, the HC can be efficiently reformed in the outflow cell side catalyst layer. As the exhaust gas purification device, it is preferable that the catalyst layer on the inflow cell side contains a catalyst metal containing Pt. This is because the purification performance can be improved more effectively.

The exhaust gas purification device usually further includes a sealing portion for sealing the outflow end of the inflow cell and the inflow side end of the outflow cell.

Hereinafter, the exhaust gas purification device according to the present embodiment will be described in more detail with reference to Examples and Comparative Examples.

[Example]
The GPF exhaust gas purification device 1 with a catalyst shown in FIG. 4A was produced. Specifically, first, the honeycomb base material 10 and the sealing portion 16 are provided, the outflow side end 12Ab of the inflow cell 12A is sealed by the sealing portion 16, and the inflow side end 12Ba of the outflow cell 12B is the sealing portion. A catalyst-uncoated filter sealed by 16 was prepared. The materials and dimensions of the honeycomb base material 10 and the sealing portion 16 are as follows.

(Honeycomb base material and sealing part)
Honeycomb base material: Cordellite Honeycomb base shape: Cylindrical Honeycomb base size: Outer diameter x axial length = 117 mm x 122 mm
Bulkhead thickness: 10 minch
Porosity of partition wall: Approximately 63%
Cell density: 300 per square inch Length of sealing part in stretching direction: 4 mm

Next, a catalyst carrier in which catalyst metal particles composed of Rh (rhodium) are supported on a powdery carrier composed of alumina (average particle size: in the range of 0.1 μm to 1 μm) and a solvent are mixed. By doing so, a slurry for the catalyst layer on the outflow cell side was prepared.

Next, the outflow cell in the region (outflow cell side catalyst region) in which the slurry for the catalyst layer on the outflow cell side extends 80% of the length in the extending direction of the partition wall 14 from the outflow side end 14b of the partition wall 14 toward the inflow side. Amount of coating (total amount of carriers and catalyst metal particles per 1 L of volume of the axial region of the honeycomb base material having the same length in the stretching direction and the length in the axial direction of the coating region) with respect to the internal region 14NB on the 12B side. After coating so that the coating amount) was 42.5 g / L, the mixture was dried and fired. At this time, the slurry was infiltrated into the internal region 14NB of the partition wall 14 by pressurizing the outflow cell 12B from the outflow side end 12Bb. Next, the slurry for the catalyst layer on the outflow cell side is applied to the internal region 14NB on the outflow cell 12B side in the region extending 60% of the length in the extending direction of the partition wall 14 from the outflow side end 14b of the partition wall 14 toward the inflow side. On the other hand, after coating so that the coating amount was 20 g / L, it was dried and fired. At this time, by pressurizing the outflow cell 12B from the outflow side end 12Bb, the slurry was infiltrated deeper than the first application. Next, the slurry for the catalyst layer on the outflow cell side is applied to the internal region 14NB on the outflow cell 12B side in the region extending 40% of the length in the extending direction of the partition wall 14 from the outflow side end 14b of the partition wall 14 toward the inflow side. On the other hand, after coating so that the coating amount was 20 g / L, it was dried and fired. At this time, by pressurizing the outflow cell 12B from the outflow side end 12Bb, the slurry was infiltrated deeper than the second application. As a result, the outflow cell side catalyst layer 30 was formed. The total coating amount (total coating amount of carrier and catalyst metal particles per 1 L of the total volume of the honeycomb base material) is 54 g / L, and the content of the catalyst metal particles per 1 L of the total volume of the honeycomb base material is 0. It is .4 g / L.

The outflow cell side catalyst layer 30 includes a first catalyst layer 30A, a second catalyst layer 30B, and a third catalyst layer 30C, which are sequentially provided from the inflow side of the partition wall 14 toward the outflow side end 14b. The first catalyst layer 30A contains only the catalyst layer formed by the first coating and firing described above, and the second catalyst layer 30B contains the catalyst formed by the first and second coating and firing described above. The third catalyst layer 30C includes a layer, and includes a catalyst layer formed by the first, second, and third coating and firing described above.

Next, a slurry for the catalyst layer on the inflow cell side was prepared by mixing a powdery carrier composed of alumina (average particle size: within the range of 1 μm to 10 μm) and a solvent. The catalyst metal particles were not mixed in the slurry for the catalyst layer on the inflow cell side.

Next, the inflow cell in the region (inflow cell side catalyst region) in which the slurry for the catalyst layer on the inflow cell side extends 40% of the length in the extending direction of the partition wall 14 from the inflow side end 14a of the partition wall 14 toward the outflow side. The surface 14SA on the 12A side was supplied so that the coating amount was 50 g / L, and then dried and fired. As a result, the inflow cell side catalyst layer 40 was formed. From the above, the exhaust gas purification device 1 was manufactured.

[Comparison example]
The GPF exhaust gas purification device 1 with a catalyst shown in FIG. 4 (b) was produced. Specifically, when forming the outflow cell side catalyst layer 30, first, the outflow cell side catalyst layer slurry has a length in the extending direction of the partition wall 14 from the outflow side end 14b of the partition wall 14 toward the inflow side. The inner region 14NB on the outflow cell 12B side in the region extending 80% (catalyst region on the outflow cell side) was coated so that the coating amount was 67.5 g / L, and then dried and fired. As a result, the outflow cell side catalyst layer 30 (thickness: 6/10 of the thickness of the partition wall 14) was formed. Exhaust gas purification device 1 was produced by the same method as in Example 1 except for the above points.

[Comparison of purification performance of exhaust gas purification equipment]
The NOx50% purification temperature was measured for the exhaust gas purification devices of Examples and Comparative Examples.

After installing the exhaust gas purification device in the exhaust system of the gasoline engine bench, first, as a pretreatment, an exhaust gas in a stoichiometric atmosphere was flown at a catalyst floor temperature of 700 ° C. for 15 minutes.

Next, the engine conditions of the exhaust system are fixed, and the exhaust gas in a stoichiometric atmosphere is flowed to the exhaust gas purification catalyst device installed in the exhaust system at a flow rate of 35 g / sec, upstream of the exhaust gas purification device. By using the heat exchanger attached to the above, the temperature of the exhaust gas was raised from 200 ° C. to 650 ° C. at a heating rate of 20 ° C./min. The NOx concentration of the incoming gas and the outgoing gas was measured at each incoming gas temperature to calculate the NOx purification rate, and the temperature of the incoming gas at the time when NOx was 50% purified was measured as the NOx 50% purification temperature.

FIG. 5 is a graph showing the NOx50% purification temperature of the exhaust gas purification devices of Examples and Comparative Examples. FIG. 6A is a cross-sectional view schematically showing how the exhaust gas flows inside the exhaust gas purification device of the embodiment, and FIG. 6B is a state where the exhaust gas flows inside the exhaust gas purification device of the comparative example. It is sectional drawing which shows schematicly.

As shown in FIG. 5, the NOx50% purification temperature of the exhaust gas purification device of the example was lower than that of the exhaust gas purification device of the comparative example, and good results were obtained. As shown in FIGS. 4 and 6, in the exhaust gas purification device 1 of the embodiment, the gas permeation coefficient is set in the outflow cell side catalyst region of the partition wall 14 and the outflow side partition wall portion including the outflow cell side catalyst layer 30. , The arrangement region of the first catalyst layer 30A, the arrangement region of the second catalyst layer 30B, and the arrangement region of the third catalyst layer 30C decrease in this order. In the catalyst layer near the outflow side end 14b of 14, the exhaust gas can be sufficiently purified by suppressing the permeation flow rate of the exhaust gas, and in the catalyst layer away from the outflow side end 14b of the partition wall 14, the maximum permeation that can be purified. It is considered that this is because the exhaust gas having a flow rate close to the flow rate could be permeated.

Although the embodiment of the exhaust gas purification device of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment and is not deviating from the spirit of the present invention described in the claims. , Various design changes can be made.

1 Exhaust gas purification device 10 Honeycomb base material 10Sa Inflow side end face of honeycomb base material 10Sb Outflow side end face of honeycomb base material 12 Cell 12A Inflow cell 12Aa Inflow side end 12Ab Inflow cell outflow side end 12B Outflow cell 12Ba Outflow cell Inflow side end 12Bb Outflow side end 14 partition wall 14a Inflow side end 14b of partition wall Outflow side end 14m of partition wall Predetermined position in the extension direction of partition wall 14Ra Inflow cell side catalyst area 14Rb of partition wall Outflow cell side catalyst area 14SA partition wall of partition wall Inflow cell side surface 14NB Internal region of partition wall on the outflow cell side 16 Sealing part 30 Outflow cell side catalyst layer 30A First catalyst layer 30B Second catalyst layer 30C Third catalyst layer 40 Inflow cell side catalyst layer

Claims (1)

An exhaust gas purification device including a honeycomb base material and a catalyst layer on the outflow cell side.
The honeycomb substrate has a porous partition wall that defines a plurality of cells extending from the inflow side end face to the outflow side end face.
The plurality of cells include an inflow cell and an outflow cell that are adjacent to each other with the partition wall in between.
The inflow cell has an inflow side end opened and an outflow side end sealed.
The outflow cell has an inflow side end sealed and an outflow side end open.
The outflow cell side catalyst layer is provided in the inner region on the outflow cell side in the outflow cell side catalyst region extending from the outflow side end of the partition wall to a predetermined position on the inflow side.
Exhaust gas purification characterized in that the gas permeability coefficient of the outflow cell side catalyst region of the partition wall and the outflow side partition wall portion including the outflow cell side catalyst layer decreases from the predetermined position of the partition wall toward the outflow side end. Device.

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