Exhaust gas purification device

Abstract

To provide an exhaust gas purification device reduced in pressure loss and improved in exhaust gas purification performance.SOLUTION: An exhaust gas purification device is provided with a honeycomb substrate and an outflow cell-side catalyst. The honeycomb substrate has a porous partition wall defining a plurality of cells extending to an outflow-side end face from an inflow-side end face. The plurality of cells include an inflow cell and an outflow cell adjacent to each other while sandwiching the partition wall.The inflow cell is opened at the inflow-side end and blocked at the outflow-side end. The outflow cell is blocked at the inflow-side end and opened at the outflow-side end. The outflow cell-side catalyst is provided in a partition wall inside area on the outflow cell side in the outflow cell-side catalyst disposition range extending to a position separated by a prescribed distance from the outflow-side end of the partition wall along an extending direction. A minimum value of a void ratio in the outflow cell-side catalyst disposition range of the partition wall and in a width direction of the outflow cell-side catalyst disposition wall including the outflow cell-side catalyst is set within a range of 20-30%.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an exhaust gas purification device in which a catalyst is provided in a filter having a wall-flow structure. [Background technology]

[0002] Exhaust gas emitted from internal combustion engines of automobiles and other vehicles contains particulate matter (PM, hereafter sometimes abbreviated as "PM"), whose main component is carbon and which causes air pollution, as well as ash, which is a non-combustible component. Filters with a wall-flow structure are widely used as filters to capture and remove PM from exhaust gas.

[0003] A filter with a wall-flow structure usually includes a honeycomb substrate, and the honeycomb substrate has porous partition walls that define a plurality of cells extending from an inlet end face to an outlet end face, and the plurality of cells include inlet cells and outlet cells that are adjacent to each other with the partition walls in between. The inlet cells have an open inlet end and a sealed outlet end, and the outlet cells have a sealed inlet end and an open outlet end. Therefore, exhaust gas that flows into the inlet cells from the inlet end passes through the partition walls and flows into the outlet cells, and is discharged from the outlet ends of the outlet cells. When the exhaust gas passes through the partition walls, PM is deposited in the gaps present in the partition walls. As a filter with a wall-flow structure, for example, a diesel particulate filter (DPF) for diesel engines and a gasoline particulate filter (GPF, hereinafter sometimes abbreviated as "GPF") for gasoline engines are known.

[0004] On the other hand, in addition to PM, exhaust gas contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). The harmful components can be removed from exhaust gas by a catalyst containing a catalytic metal that is provided on the partition wall of the filter. In recent years, exhaust gas purification devices in which a catalyst is provided on the filter have been used to remove both PM and harmful components from exhaust gas.

[0005] As such an exhaust gas purification device, a device is known in which a catalyst is appropriately arranged on the inner region or surface of the cell side of the partition wall in the inlet side portion or outlet side portion of the partition wall in order to ensure the purification performance of the exhaust gas, suppress the decrease in the PM capture rate, and suppress the pressure loss at the same time. For example, Patent Document 1 describes an exhaust gas purification device including an upstream catalyst layer arranged in the upstream portion (inlet side portion) including the end of the exhaust gas inlet side of the substrate and a downstream catalyst layer arranged in the downstream portion (outlet side portion) including the end of the exhaust gas outlet side of the substrate, in which the upstream catalyst layer and the downstream catalyst layer contain at least one precious metal (catalytic metal) of Pt, Pd, and Rh, and the precious metal species contained in the upstream catalyst layer and the precious metal species contained in the downstream catalyst layer are different. According to this device, the exhaust gas purification performance can be significantly improved while reducing the pressure loss by arranging the catalyst in the inner region on the cell side of the partition wall. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-78016 A Summary of the Invention [Problem to be solved by the invention]

[0007] Conventionally, in exhaust gas purification devices in which a catalyst is provided in a filter, attempts have been made to improve the characteristics of pressure loss and purification performance by providing a suitable structure in which the catalyst is disposed in the inner region of the cell side of the partition wall, as in the exhaust gas purification device described in Patent Document 1, for example. Meanwhile, in recent years, various efforts have been made in internal combustion engines, apart from electrification, in response to fuel consumption regulations that are becoming stricter than before in various regions around the world. One of these efforts is the reduction in displacement, and there is an increasing demand for reducing the back pressure of the exhaust system due to the need to improve the output per displacement. Under these circumstances, there is a demand to further reduce pressure loss while maintaining exhaust gas purification performance and PM collection performance. However, the conventional structure in which the catalyst is disposed in the inner region of the cell side of the partition wall does not sufficiently reduce pressure loss.

[0008] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide an exhaust gas purification device capable of reducing pressure loss and improving exhaust gas purification performance. [Means for solving the problem]

[0009] In order to solve the above problems, the exhaust gas purification device of the present invention is an exhaust gas purification device comprising a honeycomb substrate and an outflow cell side catalyst, wherein the honeycomb substrate has porous partition walls defining a plurality of cells extending from an inflow side end face to an outflow side end face, the plurality of cells including an inflow cell and an outflow cell adjacent to each other across the partition wall, the inflow cell has an open inflow side end and a sealed outflow side end, the outflow cell has a sealed inflow side end and an open outflow side end, the outflow cell side catalyst is provided in an internal region of the partition wall on the outflow cell side in an outflow cell side catalyst installation range extending to a position a predetermined distance away from the outflow side end of the partition wall along an extension direction, and the minimum value of the porosity in the thickness direction of the outflow cell side catalyst installation range of the partition wall and the outflow cell side catalyst arrangement wall including the outflow cell side catalyst is within a range of 20% or more and 30% or less. Effect of the Invention

[0010] According to the exhaust gas purification device of the present invention, the pressure loss can be reduced and the exhaust gas purification performance can be improved. [Brief description of the drawings]

[0011] [Figure 1] 1 is a perspective view that shows a schematic diagram of an exhaust gas purification device according to a first embodiment. [Diagram 2] 1 is a cross-sectional view that illustrates a schematic view of a main part of a cross section parallel to the extending direction of a cell in an exhaust gas purification device according to a first embodiment. [Diagram 3] 5 is a cross-sectional view that illustrates a schematic view of a main part of a cross section parallel to the extending direction of a cell in an exhaust gas purification apparatus according to a second embodiment. FIG. [Figure 4] FIG. 11 is a cross-sectional view that illustrates a schematic view of a main part of a cross section parallel to the extending direction of a cell in an exhaust gas purification apparatus according to a third embodiment. [Diagram 5] 1 is a cross-sectional image by X-ray CT of a region between adjacent corners of an inlet cell in a cross section perpendicular to the extension direction of a reference position of an outflow cell side catalyst arrangement wall in the exhaust gas purification apparatus of Example 1. [Figure 6] 13 is a flowchart showing a procedure for obtaining a minimum value of void ratio in the thickness direction at a reference position in the extension direction of the outflow cell side catalyst placement wall. [Figure 7] 1 is a cross-sectional image showing a cross section perpendicular to the extension direction at one photographing position (reference position) in a reference region of an outflow cell side catalyst placement wall in the exhaust gas purification apparatus of Example 1. [Figure 8] 1 is a graph showing the relationship between the initial pressure loss and the maximum NOx purification rate and the minimum value of the porosity in the thickness direction at a reference position in the extension direction of the outflow cell side catalyst placement wall obtained in the exhaust gas purification apparatuses of Examples 1 and 2 and Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of an exhaust gas purification apparatus according to the present invention will be described. An exhaust gas purification device according to an embodiment is an exhaust gas purification device comprising a honeycomb substrate and an outflow cell side catalyst, wherein the honeycomb substrate has porous partition walls defining a plurality of cells extending from an inflow side end face to an outflow side end face, the plurality of cells including an inflow cell and an outflow cell adjacent to each other on either side of the partition wall, the inflow cell has an open inflow side end and a sealed outflow side end, the outflow cell has a sealed inflow side end and an open outflow side end, the outflow cell side catalyst is provided in an internal region of the partition wall on the outflow cell side in an outflow cell side catalyst installation range extending to a position a predetermined distance away from the outflow side end of the partition wall along an extension direction, and the minimum value of the porosity in the thickness direction of the outflow cell side catalyst installation range of the partition wall and the outflow cell side catalyst arrangement wall including the outflow cell side catalyst is within a range of 20% or more and 30% or less.

[0013] In the exhaust gas purification device according to the embodiment, the "inlet side" refers to the side into which the exhaust gas flows in the exhaust gas purification device, and the "outlet side" refers to the side into which the exhaust gas flows out of the exhaust gas purification device. The "extension direction of the partition wall" refers to the direction in which the partition wall extends. The axial direction of the honeycomb substrate is usually substantially the same as the extension direction of the partition wall, and the extension direction of the cell (the direction in which the cell extends) is usually substantially the same as the extension direction of the partition wall. The "thickness direction of the partition wall" refers to the direction perpendicular to the partition wall surface on the cell (inlet cell and outlet cell) side of the partition wall. The "width direction of the partition wall" refers to the direction perpendicular to both the extension direction and the thickness direction of the partition wall. In the following description, the "extension direction" refers to the extension direction of the partition wall, which is substantially the same as the axial direction of the honeycomb substrate and the extension direction of the cell. The "thickness direction" refers to the thickness direction of the partition wall. The "width direction" refers to the width direction of the partition wall.

[0014] First, an outline of the exhaust gas purification apparatus according to the embodiment will be described by taking the exhaust gas purification apparatus according to the first to third embodiments as examples.

[0015] [First embodiment] Fig. 1 is a perspective view that shows a schematic diagram of an exhaust gas purification apparatus according to the first embodiment. Fig. 2 is a cross-sectional view that shows a schematic diagram of a main part of a cross section parallel to the extension direction of a cell in the exhaust gas purification apparatus according to the first embodiment.

[0016] As shown in FIG. 1 and FIG. 2, the exhaust gas purifying device 1 according to the first embodiment includes a honeycomb substrate 10, plugs 16, an inlet cell side catalyst 20, and an outlet cell side catalyst 30. The honeycomb substrate 10 is a substrate in which a cylindrical frame 11 and partition walls 14 that divide the space inside the frame 11 into a honeycomb shape are integrally formed. The partition walls 14 are porous bodies that define a plurality of cells 12 extending from the inlet side end face 10Sa to the outlet side end face 10Sb of the honeycomb substrate 10. The partition walls 14 are shaped such that the cross-sectional shape perpendicular to the extension direction of the plurality of cells 12 is rectangular, and include a plurality of wall parts 14A that are arranged parallel to each other and spaced apart from each other, and a plurality of wall parts 14B that are perpendicular to the plurality of wall parts 14A and arranged parallel to each other and spaced apart from each other, and have a lattice-like cross section perpendicular to the extension direction.

[0017] The multiple cells 12 include an inflow cell 12A and an outflow cell 12B adjacent to each other with a partition wall 14 in between. The inflow cell 12A has an open inflow end 12Aa and an outflow end 12Ab sealed with a sealing portion 16, and the outflow cell 12B has an open inflow end 12Ba and an open outflow end 12Bb. The cross-sectional shape perpendicular to the extension direction of the inflow cell 12A and the outflow cell 12B is rectangular and has four corners.

[0018] The inflow cell side catalyst 20 is provided on a partition wall surface 14SA on the inflow cell 12A side in an inflow cell side catalyst installation range 14X that extends from an inflow side end 14a of the partition wall 14 along the extension direction to a position 14b on the outflow side at a distance of 50% of the extension direction length of the partition wall 14. The inflow cell side catalyst 20 includes a powdered carrier, catalytic metal particles containing platinum (Pt) or palladium (Pd) supported on the carrier, and an OSC material.

[0019] The outflow cell side catalyst 30 is provided in a gap present in a partition wall inner region 14NB on the outflow cell 12B side in an outflow cell side catalyst installation range 14Y extending from an outflow side end 14d of the partition wall 14 along the extension direction to a position 14e on the inflow side at a distance of 70% of the extension direction length of the partition wall 14. The outflow cell side catalyst 30 includes a powdered carrier, catalytic metal particles containing rhodium (Rh) supported on the carrier, and an OSC material.

[0020] The outflow cell side catalyst arrangement wall is a wall including the outflow cell side catalyst installation range 14Y of the partition wall 14 and the outflow cell side catalyst 30. The reference position 14c in the extension direction of the outflow cell side catalyst arrangement wall is a position on the outflow side in a range that does not overlap with the arrangement area of ​​the plugging portion 16 in the extension direction. The balloon in FIG. 2 shows a part of a cross-sectional image taken by X-ray CT of a region between adjacent corners of the inflow cell 12A (outflow cell 12B) in a cross section perpendicular to the extension direction of the reference position 14c of the outflow cell side catalyst arrangement wall. A graph explaining the change in porosity in the thickness direction (Z direction) of the outflow cell side catalyst arrangement wall at the reference position 14c in the extension direction is also shown together with the part of the cross-sectional image.

[0021] As shown in the balloon in FIG. 2, the minimum value of the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst-arranged wall (the minimum value of the porosity in the thickness direction of the outflow cell side catalyst-arranged wall) is in the range of 20% to 30%. Specifically, the minimum value of the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst-arranged wall is the minimum value of the porosity (the proportion of voids) at each position in the thickness direction in the reference region of the outflow cell side catalyst-arranged wall, with the reference region being the region between adjacent corners of the inflow cell 12A (outflow cell 12B) in the range of ±1 mm in the extension direction from the reference position 14c of the outflow cell side catalyst-arranged wall. Note that the portion where the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst-arranged wall is the minimum value (the portion where the porosity in the thickness direction of the outflow cell side catalyst-arranged wall is the minimum value) is sometimes called the "neck portion".

[0022] In the exhaust gas purification device, which is different from the exhaust gas purification device 1 according to the first embodiment in that the minimum value of the porosity in the thickness direction at the reference position 14c of the outflow cell side catalyst arrangement wall is less than 20%, when the exhaust gas tries to pass through the outflow cell side catalyst arrangement wall in the thickness direction from the inlet cell 12A side to the outflow cell 12B side, the passage of the exhaust gas may be hindered at the neck part where the porosity in the thickness direction at the reference position 14c of the outflow cell side catalyst arrangement wall is the minimum value (less than 20%). This may cause a significant increase in pressure loss. In addition, the porosity of the outflow cell side catalyst arrangement wall is too small, so that the frequency of the exhaust gas contacting the outflow cell side catalyst 30 is insufficient, and the exhaust gas purification performance in the gas diffusion rate-limiting region may be reduced.

[0023] On the other hand, in an exhaust gas purification device which differs from the exhaust gas purification device 1 of the first embodiment in that the minimum porosity in the thickness direction at the reference position 14c of the outflow cell side catalyst mounting wall exceeds 30%, the amount of outflow cell side catalyst 30 arranged in the outflow cell side catalyst mounting wall is insufficient, and as the exhaust gas attempts to pass through the outflow cell side catalyst mounting wall, the frequency with which the exhaust gas comes into contact with the outflow cell side catalyst 30 is insufficient, which may result in a significant decrease in exhaust gas purification performance in the gas diffusion rate-limiting region.

[0024] In contrast, in the exhaust gas purification device 1 according to the first embodiment, the minimum value of the porosity in the thickness direction at the reference position 14c of the outflow cell side catalyst arrangement wall is 20% or more. As a result, when the exhaust gas passes through the outflow cell side catalyst arrangement wall in the thickness direction from the inlet cell 12A side to the outflow cell 12B side, the passage of the exhaust gas is not hindered in the entire area including the neck part in the thickness direction of the outflow cell side catalyst arrangement wall. Therefore, a significant increase in pressure loss can be avoided. In addition, since the porosity of the outflow cell side catalyst arrangement wall is not too small, the frequency with which the exhaust gas contacts the outflow cell side catalyst 30 is sufficient, and a decrease in the exhaust gas purification performance in the gas diffusion rate-limiting region can be avoided. Furthermore, the minimum value of the porosity in the thickness direction at the reference position 14c on the outflow cell side is 30% or less. As a result, the amount of the outflow cell side catalyst 30 arranged in the outflow cell side catalyst arrangement wall is sufficient, so that the exhaust gas contacts the outflow cell side catalyst 30 with sufficient frequency when the exhaust gas passes through the outflow cell side catalyst arrangement wall. Therefore, it is possible to avoid a significant decrease in exhaust gas purification performance in the gas diffusion rate-limiting region.

[0025] [Second embodiment] FIG. 3 is a cross-sectional view that illustrates a schematic view of a main part of a cross section parallel to the extending direction of a cell in an exhaust gas purification apparatus according to a second embodiment.

[0026] As shown in FIG. 3, the exhaust gas purification device 1 according to the second embodiment includes an inflow cell side catalyst 20 different from that of the first embodiment in addition to the honeycomb substrate 10, plugs 16, and outflow cell side catalyst 30 similar to those of the first embodiment. The inflow cell side catalyst 20 is provided in the partition wall inner region 14NA on the inflow cell 12A side in the inflow cell side catalyst installation range 14X similar to that of the first embodiment of the partition wall 14. The inflow cell side catalyst 20 includes a powdered carrier, catalytic metal particles containing platinum (Pt) or palladium (Pd) supported on the carrier, and an OSC material. Since the exhaust gas purification device 1 includes the honeycomb substrate 10 and outflow cell side catalyst 30 similar to those of the first embodiment, the minimum value of the void ratio in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst arrangement wall is within the range of 20% to 30%, similar to that of the first embodiment. As a result, similarly to the first embodiment, when exhaust gas attempts to pass through the outflow cell side catalyst arrangement wall in the thickness direction from the inflow cell 12A side to the outflow cell 12B side, the passage of the exhaust gas is not impeded over the entire area including the neck portion in the thickness direction of the outflow cell side catalyst arrangement wall, and the exhaust gas comes into contact with the outflow cell side catalyst 30 with sufficient frequency. This makes it possible to avoid a significant increase in pressure loss and a significant decrease in exhaust gas purification performance in the gas diffusion rate-controlling region.

[0027] [Third embodiment] FIG. 4 is a cross-sectional view that illustrates a schematic view of a main part of a cross section parallel to the extending direction of a cell in an exhaust gas purification apparatus according to a third embodiment.

[0028] As shown in FIG. 4, the exhaust gas purification device 1 according to the third embodiment includes the honeycomb substrate 10, plugs 16, and outflow cell side catalyst 30 similar to those in the first embodiment, but does not include the inflow cell side catalyst 20, unlike the first embodiment. Since the exhaust gas purification device 1 includes the honeycomb substrate 10 and outflow cell side catalyst 30 similar to those in the first embodiment, the minimum value of the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst arrangement wall is in the range of 20% to 30%, similar to the first embodiment. As a result, when the exhaust gas tries to pass through the outflow cell side catalyst arrangement wall in the thickness direction from the inflow cell 12A side to the outflow cell 12B side, the passage of the exhaust gas is not hindered in the entire area including the neck part in the thickness direction of the outflow cell side catalyst arrangement wall, and the exhaust gas comes into contact with the outflow cell side catalyst 30 with sufficient frequency, similar to the first embodiment. Therefore, it is possible to avoid a significant increase in pressure loss and a significant decrease in the exhaust gas purification performance in the gas diffusion rate-controlling region.

[0029] Therefore, according to the exhaust gas purification device according to the embodiment, it is possible to reduce pressure loss and improve exhaust gas purification performance, for example, as in the first to third embodiments. Next, details of each component of the exhaust gas purification device according to the embodiment will be described.

[0030] 1.Honeycomb substrate The honeycomb substrate has porous partition walls that define a plurality of cells extending from the inlet end face to the outlet end face. The plurality of cells include inlet cells and outlet cells adjacent to each other with the partition wall therebetween, and the inlet cells have an open inlet end and a sealed outlet end, while the outlet cells have a sealed inlet end and an open outlet end. The honeycomb substrate is a so-called wall-flow type honeycomb substrate, and is a substrate in which a frame and partition walls that divide the space inside the frame into a honeycomb shape are integrally formed.

[0031] The axial length of the honeycomb substrate is not particularly limited and may be any common length, but is preferably in the range of 10 mm to 500 mm, and more preferably in the range of 50 mm to 300 mm. The capacity of the honeycomb substrate, i.e., the total cell volume, is not particularly limited and may be any common length, but is preferably in the range of 0.1 L to 5 L.

[0032] The material of the honeycomb substrate is not particularly limited, and any commonly used material can be used, for example, ceramics such as cordierite, silicon carbide (SiC), and aluminum titanate, and alloys such as stainless steel.

[0033] The shape of the frame is not particularly limited and may be any common shape, such as a cylindrical shape, an elliptical cylindrical shape, a polygonal cylindrical shape, etc. Other configurations of the frame are not particularly limited and may be any common configuration.

[0034] The shape of the partition wall is not particularly limited and a general shape can be used, but usually, as in the first embodiment, a plurality of wall parts extending in the extension direction and arranged parallel to each other at a distance from each other, and a plurality of other wall parts intersecting with the plurality of wall parts and extending in the extension direction and arranged parallel to each other at a distance from each other, are included so that the cross section perpendicular to the extension direction of the plurality of cells has a desired shape. The length of the partition wall in the extension direction is not particularly limited, but is usually approximately the same as the axial length of the honeycomb substrate. 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 to 2000 μm, and more preferably in the range of 100 μm to 300 μm. By having the thickness of the partition wall within these ranges, sufficient PM collection performance can be obtained while ensuring the strength of the substrate, and pressure loss can be sufficiently suppressed.

[0035] The partition walls are porous structures including voids formed of pores through which exhaust gas can pass. The porosity of the partition walls (porosity of the partition walls alone) is not particularly limited, and a general porosity can be used, but for example, it is preferably in the range of 40% to 70%, and more preferably in the range of 50% to 70%. When the porosity is equal to or higher than the lower limit of these ranges, pressure loss can be effectively suppressed, and when the porosity is equal to or lower than the upper limit of these ranges, sufficient mechanical strength can be ensured. The average pore diameter of the voids of the partition walls (average pore diameter of the voids of the partition walls alone) is not particularly limited, and a general average pore diameter can be used, but for example, it is preferably in the range of 1 μm to 60 μm, and more preferably in the range of 5 μm to 30 μm, and particularly preferably in the range of 5 μm to 20 μm. When the average pore diameter of the voids is within these ranges, sufficient PM collection performance can be obtained, and pressure loss can be sufficiently suppressed. The "average pore size of the partition walls" refers to a value measured by, for example, mercury intrusion porosimetry.

[0036] The inflow cells and the outflow cells are formed by dividing the space inside the frame with a partition wall, and are adjacent to each other with the partition wall between them. The inflow cells and the outflow cells are usually surrounded by the partition wall in a direction perpendicular to the stretching direction.

[0037] The inlet cell is usually sealed at the outlet end by a sealing part. The outlet cell is usually sealed at the inlet end by a sealing part. The length of the sealing part in the extension direction is not particularly limited and may be a general length, but is preferably in the range of 2 mm to 20 mm, and more preferably in the range of 2 mm to 10 mm. The material of the sealing part is not particularly limited and may be a general material.

[0038] The cross-sectional shape perpendicular to the extension direction of the inflow cells and outflow cells is not particularly limited and may be any common shape, and may be appropriately set in consideration of the flow rate and components of the exhaust gas passing through the exhaust gas purification device. Examples of the cross-sectional shape include rectangles such as squares, polygons including hexagons, and circles. The cross-sectional area perpendicular to the extension direction of the inflow cells and outflow cells is not particularly limited and may be any common cross-sectional area, but may be, for example, 1 mm2 More than 7mm 2 The length of the inflow cells and outflow cells in the extension direction is not particularly limited, but is usually approximately the same as the length obtained by subtracting the length of the plugging portion in the extension direction from the axial length of the honeycomb substrate. Examples of the arrangement of the inflow cells and outflow cells include a checkerboard pattern in which the inflow cells and outflow cells are arranged alternately, as in the arrangement according to the first embodiment.

[0039] 2. Outlet cell side catalyst and outlet cell side catalyst arrangement wall The outflow cell side catalyst is provided in a partition wall internal region (a gap present in the partition wall internal region) on the outflow cell side in an outflow cell side catalyst installation range extending from the outflow side end of the partition wall to a position a predetermined distance away in the extension direction. The minimum value of the porosity in the thickness direction of the outflow cell side catalyst installation range of the partition wall and the outflow cell side catalyst arrangement wall including the outflow cell side catalyst is within a range of 20% to 30%. When the minimum value of the porosity is equal to or higher than the lower limit of this range, pressure loss can be reduced, and when the minimum value of the porosity is equal to or lower than the upper limit of this range, exhaust gas purification performance can be improved.

[0040] The outflow cell side catalyst installation range of the partition wall is not particularly limited as long as it is a region extending from the outflow side end of the partition wall to a position away from the inflow side by a predetermined distance along the extension direction, but for example, as in the first to third embodiments, a region extending from the outflow side end of the partition wall to a position away from 50% to 100% of the length of the partition wall in the extension direction along the extension direction is preferable, among which a region extending to a position away from 55% to 90% of the length of the partition wall in the extension direction, and particularly a region extending to a position away from 60% to 80% of the length of the partition wall in the extension direction is preferable. This is because the extension direction length of the outflow cell side catalyst installation range (the extension direction length of the outflow cell side catalyst) within these distances can effectively reduce pressure loss and effectively improve exhaust gas purification performance.

[0041] The outflow cell side catalyst-arranged wall is a wall including the outflow cell side catalyst installation range of the partition wall and the outflow cell side catalyst. That is, the outflow cell side catalyst-arranged wall is a catalyst-arranged wall in which the outflow cell side catalyst is provided in the outflow cell side catalyst installation range of the partition wall. The porosity of the outflow cell side catalyst-arranged wall is smaller than the porosity of the partition wall alone by the amount of the outflow cell side catalyst filled in the voids of the partition wall alone.

[0042] The "minimum value of the porosity in the thickness direction of the catalyst-arranged wall on the outflow cell side" refers to, for example, the minimum value of the porosity in the thickness direction at a reference position in the extension direction of the catalyst-arranged wall on the outflow cell side. The reference position of the catalyst-arranged wall on the outflow cell side is not particularly limited as long as it is any position in the extension direction of the catalyst-arranged wall on the outflow cell side, but it is preferable to use a position as close to the outflow side as possible within a range that does not overlap in the extension direction with the arrangement area of ​​the plugging part that seals the outflow end of the inflow cell. Since the porosity in the thickness direction at such a position has a large effect on pressure loss and exhaust gas purification performance, by setting the minimum value of the porosity to 20% or more and 30% or less, the pressure loss can be effectively reduced and the exhaust gas purification performance can be effectively improved.

[0043] An example of a method for obtaining the minimum porosity in the thickness direction at a reference position in the extension direction of the outflow cell side catalyst-arranged wall is to measure the porosity at each position in the thickness direction in the reference region of the outflow cell side catalyst-arranged wall, using the region between adjacent corners of the inflow cells (outflow cells) in a range of ±1 mm in the extension direction from the reference position of the outflow cell side catalyst-arranged wall (limited to the range included in the outflow cell side catalyst-arranged wall), and obtain the smallest value among these porosity measurements as the minimum porosity. Note that the porosity at each position in the thickness direction in the reference region of the outflow cell side catalyst-arranged wall may be, for example, the ratio of the area of ​​the voids to the total area of ​​the cross section perpendicular to the thickness direction at each position in the thickness direction in the reference region of the outflow cell side catalyst-arranged wall.

[0044] The outflow cell side catalyst-arranged wall is not particularly limited as long as the minimum value of the porosity in the thickness direction at the reference position in the extension direction of the outflow cell side catalyst-arranged wall is within the range of 20% to 30%, but it is preferable that the average value of the minimum value of the porosity in the thickness direction at multiple calculation positions different in the extension direction of the outflow cell side catalyst-arranged wall is within the range of 20% to 30%. This is because it is possible to effectively reduce the pressure loss and effectively improve the exhaust gas purification performance. The multiple different calculation positions are not particularly limited as long as they are any multiple positions in the extension direction of the outflow cell side catalyst-arranged wall, but for example, it is preferable that the multiple positions are arranged at equal intervals in the extension direction, including the outflow side position as much as possible within a range that does not overlap in the extension direction with the arrangement area of ​​the plugging part that seals the outflow side end of the inflow cell and the position of the inflow side end in the extension direction of the outflow cell side catalyst-arranged wall. In addition, as a method for obtaining the minimum value of the porosity in the thickness direction at each calculation position in the extension direction of the outflow cell side catalyst-arranged wall, for example, a method is given in which the calculation region is a region between adjacent corners of the inflow cell (outflow cell) in the range of ±1 mm in the extension direction from each calculation position of the outflow cell side catalyst-arranged wall (limited to the range included in the outflow cell side catalyst-arranged wall), the porosity is measured at each position in the thickness direction in the calculation region of the outflow cell side catalyst-arranged wall, and the smallest value among these porosity measurements is obtained as the minimum value of the porosity. In addition, the porosity at each position in the thickness direction in the calculation region of the outflow cell side catalyst-arranged wall may be, for example, the ratio of the area of ​​the voids to the total area of ​​the cross section perpendicular to the thickness direction at each position in the thickness direction in the calculation region of the outflow cell side catalyst-arranged wall. Furthermore, it is preferable that the outflow cell side catalyst-arranged wall has a minimum value of the porosity in the thickness direction in the entire extension direction of the outflow cell side catalyst-arranged wall within a range of 20% to 30%. This is because the pressure loss can be effectively reduced and the exhaust gas purification performance can be effectively improved.In addition, as a method for obtaining the minimum value of the void ratio in the thickness direction in the entire extension direction of the outflow cell side catalyst-arranged wall, there is a method in which the region between adjacent corners of the inflow cells (outflow cells) in the entire extension direction of the outflow cell side catalyst-arranged wall is taken as the calculation region in the entire extension direction of the outflow cell side catalyst-arranged wall, the void ratio is measured at each position in the thickness direction in the calculation region in the entire extension direction of the outflow cell side catalyst-arranged wall, and the smallest value among these void ratio measurements is obtained as the minimum value of the void ratio. In addition, the void ratio at each position in the thickness direction in the calculation region in the entire extension direction of the outflow cell side catalyst-arranged wall may be, for example, the ratio of the area of ​​the voids to the total area of ​​the cross section perpendicular to the thickness direction at each position in the thickness direction in the calculation region in the entire extension direction of the outflow cell side catalyst-arranged wall.

[0045] The outflow cell side catalyst usually includes catalytic metal particles and a carrier that supports the catalytic metal particles. The outflow cell side catalyst is, for example, a sintered body including a catalyst-support in which catalytic metal particles are supported on a carrier.

[0046] The material of the catalytic metal particles is not particularly limited, and a general material can be used, for example, catalytic metals such as platinum (Pt), palladium (Pd), rhodium (Rh), etc. The material of the catalytic metal particles may be one kind of metal or two or more kinds of metals, or may be an alloy containing two or more kinds of metals. Rhodium, etc. is preferable as the material of the catalytic metal particles.

[0047] The average particle size of the catalytic metal particles is not particularly limited and may be a general average particle size, but is preferably within the range of, for example, 0.1 nm to 20 nm. By having the average particle size below the upper limit of this range, the contact area with the exhaust gas can be increased. The average particle size of the catalytic metal particles refers to the average value calculated from the particle size measured by, for example, a transmission electron microscope (TEM).

[0048] The content of the catalytic metal particles is not particularly limited and a general content can be used, but it varies depending on the material of the catalytic metal particles. For example, when the material is at least one of Pt, Pd, and Rh, it is preferably within the range of 0.01 g to 2 g per 1 L of the honeycomb substrate. When the content is equal to or more than the lower limit of this range, sufficient catalytic action can be obtained, and when the content is equal to or less than the upper limit of this range, the grain growth of the catalytic metal particles can be suppressed and at the same time, it is advantageous in terms of cost. Here, the content of the catalytic metal particles per 1 L of the substrate volume refers to the value obtained by dividing the mass of the catalytic metal particles contained in the outflow cell side catalyst by the volume of a part of the axial direction of the honeycomb substrate in which the length in the extension direction of the outflow cell side catalyst is the same as the length in the axial direction.

[0049] The material of the carrier is not particularly limited, and a general material can be used, for example, metal oxides such as alumina (Al2O3), ceria (CeO2), zirconia (ZrO2), silica (SiO2), magnesia (MgO), and titanium oxide (TiO2), and solid solutions such as alumina-zirconia (Al2O3-ZrO2) composite oxide and ceria-zirconia (CeO2-ZrO2) composite oxide. The material of the carrier may be one or more of these. At least one of alumina and ceria-zirconia composite oxide is preferable as the material of the carrier.

[0050] The shape of the carrier is not particularly limited, and a general shape can be used, but a powder shape is preferable. This is because a larger specific surface area can be secured. The average particle size D50 of the powder carrier is not particularly limited, and may be a general average particle size, but for example, it is preferably in the range of 1 μm to 15 μm, and particularly preferably in the range of 4 μm to 10 μm. This is because sufficient heat resistance characteristics can be obtained by having the average particle size D50 be equal to or greater than the lower limit of these ranges. This is because the average particle size D50 is equal to or less than the upper limit of these ranges, and the purification performance can be effectively improved by ensuring sufficient dispersibility of the catalytic metal particles. The average particle size D50 of the powder carrier can be determined, for example, by a laser diffraction / scattering method, and can be measured, for example, by using a laser diffraction / scattering type particle size distribution measuring device LA-960 (manufactured by Horiba, Ltd.).

[0051] The mass ratio of the catalytic metal particles to the total mass of the catalytic metal particles and the carrier is not particularly limited and may be a general mass ratio, but is preferably within the range of, for example, 0.01 mass% to 10 mass%. By having the mass ratio at or above the lower limit of this range, sufficient catalytic action can be obtained, and by having the mass ratio at or below the upper limit of this range, grain growth of the catalytic metal particles can be suppressed and at the same time, it is advantageous in terms of cost.

[0052] The method for supporting the catalytic metal particles on the carrier is not particularly limited, and any common method can be used. For example, the carrier may be immersed in an aqueous solution containing a catalytic metal salt (e.g., a nitrate salt) or a catalytic metal complex (e.g., a tetraammine complex), followed by drying and calcination.

[0053] The outflow cell side catalyst may contain, in addition to the catalytic metal particles and the carrier, a promoter such as an OSC (Oxygen Storage Capacity) material.

[0054] The material of the co-catalyst is not particularly limited and may be a general material, for example, a material similar to that of the carrier. Among the co-catalysts, the material of the OSC material in particular may be ceria, a composite oxide containing ceria, and the like. The composite oxide containing ceria may be, for example, a ceria-zirconia composite oxide. The shape of the co-catalyst is not particularly limited and may be a general shape, for example, a shape similar to that of the carrier. The average particle size D50 of the powdered co-catalyst is not particularly limited and may be a general average particle size, for example, an average particle size similar to that of the powdered carrier. The mass ratio of the co-catalyst to the total mass of the catalytic metal particles, the carrier, and the co-catalyst is not particularly limited and may be a general mass ratio, for example, a range of 30 mass% to 80 mass% is preferable.

[0055] The density of the outflow cell side catalyst is not particularly limited, but is preferably, for example, in the range of 5 g / L to 100 g / L, more preferably in the range of 10 g / L to 65 g / L, and particularly preferably in the range of 30 g / L to 60 g / L. When the density of the outflow cell side catalyst is equal to or higher than the lower limit of this range, the purification performance can be effectively improved. When the density of the outflow cell side catalyst is equal to or lower than the upper limit of this range, the pressure loss can be effectively suppressed. The "density of the outflow cell side catalyst" refers to the mass of the outflow cell side catalyst divided by the volume of a part of the axial direction of a honeycomb substrate in which the extension direction length and the axial direction length of the outflow cell side catalyst are the same.

[0056] The method for forming the outflow cell side catalyst is not particularly limited, and a general method can be used. For example, there can be mentioned a method in which a slurry is prepared by mixing catalytic metal particles and a carrier carrying the catalytic metal particles in a solvent, and then the slurry is supplied to an inner region of the partition wall on the outflow cell side in the outflow cell side catalyst installation range of the partition wall, and then the slurry is dried and fired.

[0057] In the method of forming an outflow cell side catalyst by supplying a slurry to a partition wall, followed by drying and firing, the slurry may appropriately contain optional components such as a co-catalyst, a binder, an additive, etc. in addition to the catalyst metal particles, the carrier, and the solvent. The average particle size of the solid contents such as the powdered carrier and the co-catalyst contained in the slurry may be appropriately adjusted so that the slurry penetrates into the inner region of the partition wall on the outflow cell side in the outflow cell side catalyst installation range of the partition wall.

[0058] The method for preparing the slurry is not particularly limited and may be a general method, for example, the following method. First, a powdered support is immersed in a solution (e.g., an aqueous solution) containing a catalyst metal salt or a catalyst metal complex, and then dried and fired to prepare a catalyst metal-supported powder carrying the catalyst metal. Next, an OSC material, a co-catalyst, a binder, and ion-exchanged water are added to the catalyst metal-supported powder, which is thoroughly stirred and wet-pulverized so that the average particle size D50 of the solid content is a desired value. In this way, a slurry is prepared.

[0059] The average particle size D50 of the solid content of the slurry is not particularly limited and may be a general average particle size. The average particle size D50 of the solid content of the slurry can be measured, for example, by using a laser diffraction / scattering type particle size distribution measuring device LA-960 (manufactured by Horiba, Ltd.).

[0060] The method of supplying the slurry to the partition wall inner region on the outflow cell side in the outflow cell side catalyst installation range of the partition wall is not particularly limited and may be a general method, for example, a method of immersing a honeycomb substrate in the slurry from the outflow side and removing it from the slurry after a predetermined time has passed, etc. can be mentioned. In this method, the properties such as the solid content concentration and viscosity of the slurry may be appropriately adjusted so that the slurry is supplied to the partition wall inner region on the outflow cell side in the outflow cell side catalyst installation range of the partition wall. As a method of supplying the slurry to the partition wall inner region on the outflow cell side in the outflow cell side catalyst installation range of the partition wall, a method of blowing off the slurry using a blower may be used so that the slurry is not supplied to unnecessary parts of the catalyst in the inner region and surface of the partition wall when the slurry is supplied.

[0061] In the method of drying and firing the slurry after supplying it to the partition walls, the drying conditions are not particularly limited and depend on the shape and dimensions of the honeycomb substrate, carrier, etc., but are preferably, for example, dried at a temperature in the range of 80° C. to 300° C. for 1 hour to 10 hours. The firing conditions are not particularly limited, but are preferably, for example, fired at a temperature in the range of 400° C. to 1000° C. for 1 hour to 4 hours.

[0062] The minimum porosity in the thickness direction of the outflow cell side catalyst arrangement wall, the thickness of the outflow cell side catalyst, the porosity of the outflow cell side catalyst, and other properties can be adjusted, for example, by adjusting the average particle size D50 of the solid content of the slurry, the solid content concentration of the slurry, the properties of the slurry, the amount of slurry supplied, the drying conditions, the firing conditions, etc.

[0063] 3. Exhaust gas purification equipment The exhaust gas purification device includes a honeycomb substrate and an outflow cell side catalyst. The exhaust gas purification device typically further includes plugs for sealing the outflow side ends of the inflow cells and plugs for sealing the inflow side ends of the outflow cells.

[0064] (1) Inlet cell side catalyst The exhaust gas purification device may further include an inflow cell side catalyst provided in an inflow cell side catalyst installation range extending from the inflow side end of the partition wall to a position away from the inflow cell side in the extension direction by a predetermined distance, as in the first and second embodiments, or may not include an inflow cell side catalyst, as in the third embodiment. In the exhaust gas purification device, whether or not the passage of exhaust gas is obstructed at the neck portion when exhaust gas tries to pass through the outflow cell side catalyst arrangement wall in the thickness direction from the inflow cell side to the outflow cell side, regardless of the presence or absence of an inflow cell side catalyst, greatly affects pressure loss. Furthermore, regardless of the presence or absence of an inflow cell side catalyst, the amount of outflow cell side catalyst arranged on the outflow cell side catalyst arrangement wall affects exhaust gas purification performance. Therefore, regardless of the presence or absence of an inflow cell side catalyst, the effect of reducing pressure loss and improving exhaust gas purification performance can be obtained.

[0065] The inflow cell side catalyst is provided on at least one of the partition wall surface on the inflow cell side and the partition wall inner region (gaps present in the inner region) on the inflow cell side in the inflow cell side catalyst installation range of the partition wall.

[0066] The inflow cell side catalyst installation range of the partition wall is not particularly limited as long as it is a region extending from the inflow side end of the partition wall to a position at a predetermined distance to the outflow side along the stretching direction, but for example, a region extending along the stretching direction to a position overlapping with the outflow cell side catalyst installation range, and a region extending from the inflow side end of the partition wall to a position at a distance of 80% or less of the length of the stretching direction of the partition wall, is preferable. By extending the inflow cell side catalyst installation range to a position overlapping with the outflow cell side catalyst installation range, it is possible to suppress exhaust gas from passing through the catalyst-free region of the partition wall and being discharged unpurified from the exhaust gas purification device. By making the length of the inflow cell side catalyst installation range in the stretching direction (the length of the inflow cell side catalyst in the stretching direction) 80% or less of the length of the partition wall in the stretching direction, it is possible to suppress an increase in pressure loss.

[0067] The inlet cell side catalyst usually includes catalytic metal particles and a carrier that supports the catalytic metal particles. The inlet cell side catalyst is, for example, a sintered body including a catalyst-support in which catalytic metal particles are supported on a carrier.

[0068] The material of the catalytic metal particles is the same as that of the catalytic metal particles contained in the outflow cell side catalyst, except that at least one of platinum, palladium, etc. is preferred. The average particle size of the catalytic metal particles is the same as that of the catalytic metal particles contained in the outflow cell side catalyst.

[0069] The content of the catalytic metal particles is not particularly limited and a general content can be used, but it varies depending on the material of the catalytic metal particles. For example, when the material is at least one of Pt, Pd, and Rh, it is preferably within the range of 0.05 g to 5 g per 1 L of the honeycomb substrate. When the content is equal to or more than the lower limit of this range, sufficient catalytic action can be obtained, and when the content is equal to or less than the upper limit of this range, the grain growth of the catalytic metal particles can be suppressed and at the same time, it is advantageous in terms of cost. Here, the content of the catalytic metal particles per 1 L of the substrate volume refers to the value obtained by dividing the mass of the catalytic metal particles contained in the inlet cell side catalyst by the volume of a part of the axial direction of the honeycomb substrate in which the length in the extension direction of the inlet cell side catalyst is the same as the length in the axial direction.

[0070] The material and shape of the carrier are the same as those of the carrier contained in the outflow cell side catalyst. The average particle size D50 of the powdered carrier is not particularly limited and may be a general average particle size. The mass ratio of the catalytic metal particles to the total mass of the catalytic metal particles and the carrier is the same as that of the outflow cell side catalyst. The method of supporting the catalytic metal particles on the carrier is the same as that of the outflow cell side catalyst. The inflow cell side catalyst may contain a promoter, etc., like the outflow cell side catalyst. The promoter is the same as that of the outflow cell side catalyst.

[0071] The density of the inflow cell side catalyst is not particularly limited, but is preferably, for example, in the range of 5 g / L to 100 g / L, more preferably in the range of 10 g / L to 65 g / L, and particularly preferably in the range of 10 g / L to 30 g / L. When the density of the inflow cell side catalyst is equal to or higher than the lower limit of these ranges, exhaust gas can be effectively purified by the inflow cell side catalyst. Also, when the density of the inflow cell side catalyst is equal to or lower than the upper limit of these ranges, an increase in pressure loss can be effectively suppressed. The "density of the inflow cell side catalyst" refers to the mass of the inflow cell side catalyst divided by the volume of a part of the axial direction of a honeycomb substrate having the same length in the extension direction and the axial direction of the inflow cell side catalyst.

[0072] The method for forming the inlet cell side catalyst is not particularly limited and may be a general method. For example, a method may be mentioned in which a slurry is prepared by mixing catalytic metal particles and a carrier carrying the catalytic metal particles in a solvent, and the slurry is supplied to at least one of the partition wall surface on the inlet cell side and the partition wall inner region on the inlet cell side in the inlet cell side catalyst installation range of the partition wall, and then the slurry is dried and fired.

[0073] In the method of forming an inflow cell side catalyst by supplying the slurry to the partition wall, drying and firing the slurry, the slurry may appropriately contain optional components such as a co-catalyst, a binder, and an additive in addition to the catalyst metal particles, the carrier, and the solvent. The average particle size of the solid content of the powdered carrier, the co-catalyst, and the like contained in the slurry may be appropriately adjusted so that the slurry does not penetrate into the partition wall inner region when the inflow cell side catalyst is mainly formed on the partition wall surface on the inflow cell side of the partition wall, as in the first embodiment. In addition, for example, when the inflow cell side catalyst is mainly formed in the partition wall inner region on the inflow cell side of the partition wall, as in the second embodiment, the slurry may be appropriately adjusted so that the slurry penetrates into the partition wall inner region. The method of adjusting the slurry is the same as the method of adjusting the slurry used to form the outflow cell side catalyst. The average particle size D50 of the solid content of the slurry is not particularly limited and may be a general average particle size.

[0074] The method of supplying the slurry to at least one of the partition wall surface on the inflow cell side and the partition wall inner region on the inflow cell side in the inflow cell side catalyst installation range of the partition wall is not particularly limited and may be a general method, but for example, a method of immersing a honeycomb substrate in the slurry from the inflow side and removing it from the slurry after a predetermined time has passed, etc., can be mentioned. In this method, for example, when the inflow cell side catalyst is mainly formed on the partition wall surface on the inflow cell side of the partition wall, the properties of the slurry such as the solid content concentration and viscosity may be appropriately adjusted so that the slurry is not supplied to the partition wall inner region, or the outflow cells may be pressurized from the outflow side to generate a pressure difference between the outflow cells and the inflow cells. In addition, for example, when the inflow cell side catalyst is mainly formed in the partition wall inner region on the inflow cell side of the partition wall, the properties of the slurry such as the solid content concentration and viscosity may be appropriately adjusted so that the slurry is supplied to the partition wall inner region on the inflow cell side of the partition wall. Furthermore, in the method of supplying the slurry to at least one of the partition wall surface on the inlet cell side and the partition wall internal region on the inlet cell side in the catalyst installation range on the inlet cell side of the partition wall, a method of blowing off the slurry using a blower may be used when supplying the slurry so that the slurry is not supplied to unnecessary portions of the catalyst on the partition wall surface and in the partition wall internal region.

[0075] In the method in which the slurry is supplied to the partition walls, then dried and fired, the drying and firing conditions are the same as the drying and firing conditions used in the formation of the outflow cell side catalyst.

[0076] The thickness of the inlet cell side catalyst, the properties such as porosity of the inlet cell side catalyst, the inlet cell side catalyst installation range of the partition wall, and the porosity of the inlet cell side catalyst arrangement wall including the inlet cell side catalyst can be adjusted, for example, by adjusting the average particle size D50 of the solid content of the slurry, the solid content concentration of the slurry, the properties of the slurry, the amount of the slurry supplied, the drying conditions, the firing conditions, etc.

[0077] (2)Other When the exhaust gas purification device further comprises an inlet cell side catalyst, it is preferable that the catalytic metal particles contained in the inlet cell side catalyst contain at least one of platinum (Pt) and palladium (Pd) and the catalytic metal particles contained in the outlet cell side catalyst contain rhodium (Rh) as in the first embodiment. This is because the exhaust gas comes into contact with the outlet cell side catalyst after the hydrocarbons (HC) contained in the exhaust gas have been effectively purified by the catalytic metal particles contained in the inlet cell side catalyst, and therefore the rhodium (Rh) contained in the catalytic metal particles contained in the outlet cell side catalyst can be prevented from being poisoned by the hydrocarbons (HC). EXAMPLES

[0078] The exhaust gas purification device according to the embodiment will be described in more detail below with reference to examples and comparative examples.

[0079] [Example 1] An example of the exhaust gas purification device according to the first embodiment was produced. Specifically, first, a GPF was prepared that had a honeycomb substrate 10 and plugging parts 16 and was not provided with a catalyst. The details of the configuration of the honeycomb substrate 10 and plugging parts 16 of the GPF are as follows.

[0080] (Configuration of honeycomb substrate and plug) Honeycomb substrate material: Cordierite Honeycomb substrate size: outer diameter x axial length = 117 mm x 122 mm Partition thickness: 240μm Porosity of partition wall (porosity of partition wall alone): 61% Average pore size of partition walls (average pore size of partition walls alone): 7 μm Cell Density: 200 cells per square inch Length of the sealing part in the extension direction: 5 mm

[0081] Next, a catalyst-loaded carrier, which is a powdered carrier carrying catalytic metal particles, was mixed with a solvent to prepare a slurry for the inflow cell side catalyst. Specifically, alumina powder (carrier) was immersed in an aqueous solution containing Pt nitrate (catalytic metal salt), and then dried and fired to prepare a Pt-loaded powder in which platinum (Pt) was loaded onto the alumina powder. Next, ceria-zirconia composite oxide (OSC material), barium sulfate (co-catalyst), binder, and ion-exchanged water (solvent) were added to the Pt-loaded powder, which was thoroughly stirred and wet-pulverized. In this way, a slurry for the inflow cell side catalyst was prepared.

[0082] Next, the inflow cell side catalyst slurry was poured into the inflow cells 12A from the inflow side end 12Aa to be supplied onto the partition wall surface 14SA on the inflow cell 12A side in the inflow cell side catalyst installation range 14X of the partition wall 14. At this time, the supply amount of the slurry was adjusted so that the density of the inflow cell side catalyst 20 became a desired value. The inflow cell side catalyst installation range 14X of the partition wall 14 is an area extending from the inflow side end 14a of the partition wall 14 along the extension direction to a position 14b away from the outflow side by a distance of 50% of the length of the extension direction of the partition wall 14. Thereafter, the honeycomb substrate 10 to which the inflow cell side catalyst slurry was supplied was dried by heating at 120°C for 2 hours using a dryer to remove moisture, and then fired at 500°C for 2 hours using an electric furnace. In this way, the inflow cell side catalyst 20 was formed.

[0083] Next, a catalyst-loaded carrier, which is a powdered carrier carrying catalytic metal particles, was mixed with a solvent to prepare a slurry for the outflow cell side catalyst. Specifically, a powdered ceria-zirconia composite oxide (carrier) was immersed in an aqueous solution containing Rh nitrate (catalytic metal salt), and then dried and fired to prepare an Rh-loaded powder in which rhodium (Rh) was loaded on the powdered ceria-zirconia composite oxide. Next, ceria-zirconia composite oxide (OSC material), alumina (co-catalyst), binder, and ion-exchanged water (solvent) were added to the Rh-loaded powder, which was thoroughly stirred and wet-pulverized. In this way, a slurry for the outflow cell side catalyst was prepared.

[0084] Next, the slurry for the outflow cell side catalyst was poured into the outflow cell 12B from the outflow side end 12Bb, and supplied to the partition wall inner region 14NB on the outflow cell 12B side in the outflow cell side catalyst installation range 14Y of the partition wall 14. The outflow cell side catalyst installation range 14Y of the partition wall 14 is a region extending from the outflow side end 14d of the partition wall 14 to a position 14e at a distance of 70% of the length of the partition wall 14 in the extension direction to the inflow side. Thereafter, the honeycomb substrate 10 to which the slurry for the outflow cell side catalyst was supplied was dried by heating at 120°C for 2 hours using a dryer to remove moisture, and then fired at 500°C for 2 hours using an electric furnace. In this way, the outflow cell side catalyst 30 was formed.

[0085] As a result of the above, an exhaust gas purification device 1 was produced, which was equipped with a honeycomb substrate 10, plugs 16, an inlet cell side catalyst 20, and an outlet cell side catalyst 30, as shown in Fig. 2. The density of the outlet cell side catalyst 30 was 49 g / L.

[0086] [Example 2] The exhaust gas purification device 1 was produced by the same production method as in Example 1, except that when the slurry for the outflow cell side catalyst was supplied to the partition inner region 14NB on the outflow cell 12B side in the outflow cell side catalyst installation range 14Y of the partition 14, the supply amount of the slurry for the outflow cell side catalyst was adjusted so that the density of the outflow cell side catalyst 30 was 39 g / L.

[0087] [Comparative Example 1] The exhaust gas purification device 1 was produced by the same production method as in Example 1, except that when the slurry for the outflow cell side catalyst was supplied to the partition inner region 14NB on the outflow cell 12B side in the outflow cell side catalyst installation range 14Y of the partition 14, the supply amount of the slurry for the outflow cell side catalyst was adjusted so that the density of the outflow cell side catalyst 30 was 109 g / L.

[0088] [Comparative Example 2] The exhaust gas purification device 1 was produced by the same production method as in Example 1, except that when the slurry for the outflow cell side catalyst was supplied to the partition inner region 14NB on the outflow cell 12B side in the outflow cell side catalyst installation range 14Y of the partition 14, the supply amount of the slurry for the outflow cell side catalyst was adjusted so that the density of the outflow cell side catalyst 30 was 94 g / L.

[0089] [Comparative Example 3] The exhaust gas purification device 1 was produced by the same production method as in Example 1, except that the density of the outflow cell side catalyst 30 was set to 79 g / L by adjusting the supply amount of the slurry for the outflow cell side catalyst when it was supplied to the partition inner region 14NB on the outflow cell 12B side in the outflow cell side catalyst installation range 14Y of the partition 14.

[0090] [Comparative Example 4] The exhaust gas purification device 1 was produced by the same production method as in Example 1, except that the outflow cell side catalyst 30 was not formed.

[0091] [evaluation] For the exhaust gas purification devices 1 produced in Examples 1 and 2 and Comparative Examples 1 to 4, a cross section perpendicular to the extension direction at the reference position 14c of the outflow cell side catalyst-arranged wall was observed, and the initial pressure loss and exhaust gas purification performance after a durability test were evaluated with respect to the minimum value of the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst-arranged wall. The outflow cell side catalyst-arranged wall is a wall including the outflow cell side catalyst installation range 14Y of the partition wall 14 and the outflow cell side catalyst 30. The reference position 14c in the extension direction of the outflow cell side catalyst-arranged wall is a position 15 mm away from the outflow side end 14d of the partition wall 14 on the inflow side along the extension direction (a position on the outflow side within a range that does not overlap with the arrangement area of ​​the plugging portion 16 in the extension direction).

[0092] (Cross-section observation) In the exhaust gas purification devices 1 of Examples 1 and 2 and Comparative Examples 1 to 4, an image of the area between adjacent corners of the inflow cells 12A (outflow cells 12B) in a cross section perpendicular to the extension direction of the reference position 14c of the outflow cell side catalyst mounting wall was taken by X-ray CT. Fig. 5 is a cross-sectional image by X-ray CT of the area between adjacent corners of the inflow cells in a cross section perpendicular to the extension direction of the reference position of the outflow cell side catalyst mounting wall in the exhaust gas purification device of Example 1. In this image, the partition wall 14 and the areas of the inflow cells 12A and outflow cells 12B are shown, as well as the gaps in the outflow cell side catalyst mounting wall (portions of the gaps in the partition wall alone that are not filled with the outflow cell side catalyst), the substrate part of the partition wall 14, and the outflow cell side catalyst 30.

[0093] (Minimum porosity in the thickness direction at the reference position of the outlet cell side catalyst placement wall) In the exhaust gas purification devices 1 of Examples 1 and 2 and Comparative Examples 1 to 4, the minimum porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst mounting wall (the minimum porosity in the thickness direction of the outflow cell side catalyst mounting wall) was obtained.

[0094] Hereinafter, a procedure for obtaining the minimum value of the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst mounting wall will be described in each example of the exhaust gas purification device 1. Fig. 6 is a flowchart showing the procedure for obtaining the minimum value of the porosity in the thickness direction at the reference position in the extension direction of the outflow cell side catalyst mounting wall.

[0095] In this procedure, as shown in Fig. 6, first, the region between adjacent corners of the inflow cell 12A (outflow cell 12B) in the range of ±1 mm in the extension direction from the reference position 14c of the outflow cell side catalyst arrangement wall was set as the reference region, and the cross section perpendicular to the extension direction at 1000 shooting positions set at 2 μm intervals in the extension direction in the reference region of the outflow cell side catalyst arrangement wall was photographed by X-ray CT to obtain 1000 cross-sectional images (STEP 1). Specifically, the cross section perpendicular to the extension direction at each shooting position in the reference region of the outflow cell side catalyst arrangement wall was photographed at a magnification of 150 times, and each cross-sectional image was obtained in an 8-bit format of 1280 × 960 pixels. Fig. 7 is a cross-sectional image showing a cross section perpendicular to the extension direction at one shooting position (reference position) in the reference region of the outflow cell side catalyst arrangement wall of the exhaust gas purification device of Example 1.

[0096] Next, as shown in Fig. 6, by using CAE software GEODICT (registered trademark) manufactured by Math2Market, Inc., the Import Geo module of GEODICT was used to read all 1000 cross-sectional images and integrate the 1000 cross-sectional images to construct a 3D (three-dimensional) model expressing the reference area of ​​the catalyst placement wall on the outflow cell side (STEP 2). At this time, the 1000 cross-sectional images were read and integrated according to the specifications of the Import Geo module.

[0097] Next, as shown in Figure 6, GEODICT was used to extract the central regions to be calculated in the extension and width directions from the 3D model and convert them into voxels to obtain a 3D voxel model (STEP 3). In this case, a three-dimensional space was adopted in which the width direction is the X-axis direction, the extension direction is the Y-axis direction, and the thickness direction is the Z-axis direction, and the calculation region of the 3D model was represented by voxels aligned in the X-axis direction, Y-axis direction, and Z-axis direction to obtain a 3D voxel model.

[0098] Next, as shown in Figure 6, the threshold value for binarizing each voxel of the 3D voxel model was set to a predetermined value using the mode method using the Threshold menu of the PoroDict module of GEODICT, and each voxel of the 3D voxel model was binarized to classify each voxel of the 3D voxel model into voids in the outflow cell side catalyst placement wall and other areas (the substrate portion of the partition 14 and the outflow cell side catalyst 30) (STEP 4).

[0099] Next, as shown in Figure 6, the 1D statistics menu of the PoroDict module of GEODICT was used to set the parameters (Input Map) as shown in Table 1 below to calculate the porosity at each position in the Z-axis direction (thickness direction) in the binarized 3D voxel model (STEP 5). The porosity at each position in the Z-axis direction in the binarized 3D voxel model thus calculated was then determined as the porosity at each position in the thickness direction in the reference region of the catalyst placement wall on the outflow cell side.

[0100] [Table 1]

[0101] Next, as shown in Fig. 6, the minimum value of the porosity at each position in the Z-axis direction in the binarized 3D voxel model was extracted using Excel (registered trademark) made by Microsoft Corporation (STEP 6).Then, the minimum value of the porosity thus extracted (the minimum value of the porosity at each position in the thickness direction in the reference region of the outflow cell side catalyst placement wall) was obtained as the minimum value of the porosity in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst placement wall.

[0102] The minimum void ratio in the thickness direction at the reference position 14c in the extension direction of the outflow cell side catalyst placement wall obtained by the above procedure for the exhaust gas purification devices 1 of Examples 1 and 2 and Comparative Examples 1 to 4 is shown in Table 2 below.

[0103] (Initial pressure loss) For the exhaust gas purification devices 1 of Examples 1 and 2 and Comparative Examples 1 to 4, the initial pressure loss at the reference position 14c in the extension direction of the catalyst-arranged wall on the outflow cell side was calculated. Specifically, by using the GEODICT FilterDict module, a software made by Math2Market, Inc., the pressure loss when air was caused to flow through the exhaust gas purification device 1 of each example at 0.01 m / s and 226.85°C was calculated as the initial pressure loss at the reference position 14c in the extension direction of the catalyst-arranged wall on the outflow cell side. The initial pressure loss for each example is shown in Table 2 below.

[0104] (Exhaust gas purification performance after durability testing) For the exhaust gas purification devices 1 of Examples 1 and 2 and Comparative Examples 1 to 4, the maximum NOx purification rate was measured as an index of the exhaust gas purification performance after the durability test. Specifically, first, the exhaust gas purification device of each example was installed in the exhaust system of a V-type 8-cylinder engine, and the durability test was performed by repeatedly flowing exhaust gas in each atmosphere of stoichiometric and lean for a certain period of time (ratio of 3:1) for 50 hours at a catalyst bed temperature of 900°C. Next, the exhaust gas purification device of each example after the durability test was installed in the exhaust system of an L-type 4-cylinder engine, and exhaust gas with an A / F (air-fuel ratio) of 14.4 was supplied, and the inlet gas temperature was raised from 200°C to 600°C (20°C / min) under the condition of Ga=28g / s. Then, the NOx concentration of the inlet gas and the outlet gas was measured during the temperature rise of the inlet gas, and the NOx purification rate was calculated, and the maximum NOx purification rate was obtained as the maximum NOx purification rate. Table 2 below shows the maximum NOx purification rate for each example.

[0105] [Table 2]

[0106] Fig. 8 is a graph showing the relationship between the initial pressure loss and the maximum NOx purification rate with respect to the minimum value of the porosity in the thickness direction at the reference position in the extension direction of the outflow cell side catalyst-arranged wall, obtained in the exhaust gas purification apparatus of Examples 1 and 2 and Comparative Examples 1 to 4. As shown in Table 2 and Fig. 8, when the minimum value of the porosity in the thickness direction at the reference position in the extension direction of the outflow cell side catalyst-arranged wall is less than 20%, the initial pressure loss increases sharply, whereas when the minimum value of the porosity is 20% or more, the increase in the initial pressure loss is suppressed. On the other hand, when the minimum value of the porosity exceeds 20% and becomes larger, the maximum NOx purification rate tends to decrease, whereas when the minimum value of the porosity is 20% or more and 30% or less, the maximum NOx purification rate is high.

[0107] The above describes in detail the embodiments of the exhaust gas purification device of the present invention, but the present invention is not limited to the above embodiments, and various design modifications can be made without departing from the spirit of the present invention described in the claims. [Explanation of symbols]

[0108] 1: exhaust gas purification device, 10: honeycomb substrate, 10Sa: inlet end face, 10Sb: outlet end face, 11: frame, 12: cell, 12A: inlet cell, 12Aa: inlet end, 12Ab: outlet end, 12B: outlet cell, 12Ba: inlet end, 12Bb: outlet end, 14: partition wall, 14a: inlet end, 14b: position at a predetermined distance from the inlet end along the extension direction, 14c: extension of the catalyst placement wall on the outlet cell side 14B: reference position in the extension direction, 14c: outflow side end, 14d: outflow side end, 14e: position at a predetermined distance from the outflow side end along the extension direction, 14X: inflow cell side catalyst installation range, 14Y: outflow cell side catalyst installation range, 14SA: inflow cell side partition wall surface, 14NA: inflow cell side partition wall internal region, 14SB: outflow cell side partition wall surface, 14NB: outflow cell side partition wall internal region, 16: sealing portion, 20: inflow cell side catalyst, 30: outflow cell side catalyst

Claims

[Claim 1] An exhaust gas purification device comprising a honeycomb substrate and an outflow cell side catalyst, The honeycomb substrate has porous partition walls that define a plurality of cells extending from an inlet end surface to an outlet end surface, The plurality of cells include an inflow cell and an outflow cell adjacent to each other with the partition wall therebetween, The inlet cell has an open inlet end and a sealed outlet end, The outflow cell has a sealed inflow end and an open outflow end, the outflow cell side catalyst is provided in an inner region of the partition wall on the outflow cell side in an outflow cell side catalyst installation range extending from an outflow side end of the partition wall to a position away by a predetermined distance along an extension direction, an outflow cell side catalyst installation range of the partition wall and an outflow cell side catalyst arrangement wall including the outflow cell side catalyst have a minimum porosity in a thickness direction of the partition wall, the minimum porosity being within a range of 20% or more and 30% or less.

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