Exhaust gas purification equipment

Abstract

To provide an exhaust gas purification device capable of suppressing the increase of pressure loss.SOLUTION: An exhaust gas purification device has a honeycomb base material and an inflow cell side catalyst layer. The honeycomb base material has a porous partition wall forming a plurality of cells extending from an inflow side end surface to an outflow side end surface. The plurality of cells include an inflow cell and an outflow cell adjacent sandwiching the partition wall. In the inflow cell, an inflow side end is opened and an outflow side end is sealed. In the outflow cell, the inflow side end is sealed and the outflow side end is opened. An inflow cell side catalyst layer is disposed on an inflow cell side surface in an inflow cell side catalyst region extending from the inflow side end of the partition wall to a position separated by 10% or more of the length of the partition wall along an extension direction. At a reference position separated by 10% from the length of the partition wall along an extension direction from the inflow side end of the partition wall, a ratio of a filling part where the inflow cell side catalyst layer is filled among spaces in an internal region to 50% depth of the thickness of the partition wall from the surface of the inflow cell side of the partition wall is 40% or less.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"), which is primarily composed of carbon and causes air pollution, as well as ash, which is a non-combustible component. Wall-flow structure filters are widely used to capture and remove PM from exhaust gas.

[0003] Wall-flow filters typically include a honeycomb substrate with porous partition walls that define a plurality of cells extending from an inlet end face to an outlet end face. The plurality of cells includes adjacent inlet and outlet cells with the partition walls interposed therebetween. 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. Thus, exhaust gas flowing into the inlet cells from their inlet ends passes through the partition walls to flow into the outlet cells and is discharged from the outlet ends of the outlet cells. As the exhaust gas passes through the partition walls, PM accumulates in the voids present in the partition walls. Known examples of wall-flow filters include diesel particulate filters (DPFs) for diesel engines and gasoline particulate filters (GPFs, hereinafter sometimes abbreviated as "GPFs") for gasoline engines.

[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). Harmful components can be removed from exhaust gas using filters coated with catalysts such as precious metal catalysts.

[0005] In recent years, exhaust gas purification devices in which a catalyst is provided in a filter with a wall-flow structure have been used to remove both PM and harmful components from exhaust gas. For example, Patent Document 1 describes an exhaust gas purification device in which a NOx reduction catalyst layer is provided on the surface of porous partition walls in a honeycomb substrate provided in the filter, and an oxidation catalyst layer is further provided on the surface of the NOx reduction catalyst layer.

[0006] Patent Document 2 also describes an exhaust gas purification device that includes a honeycomb substrate and an inlet cell side catalyst layer, in which the inlet cell side catalyst layer is provided on the surface of the inlet cell side in an inlet cell side catalyst region from the inlet side end of the partition wall to a predetermined position close to the outlet side end, and the outlet side partition wall portion including the outlet side region from the predetermined position to the outlet side end of the partition wall has higher gas permeability than a catalyst-arranged partition wall portion including the inlet cell side catalyst region of the partition wall and the inlet cell side catalyst layer.

[0007] Furthermore, Patent Document 3 describes an exhaust gas purification catalyst that includes a substrate and a catalyst portion provided on the substrate, wherein the catalyst portion has a first catalyst portion provided on at least a part of the upstream side in the flow direction of a surface of a partition wall that faces inlet-side cells, and a second catalyst portion provided on at least a part of the downstream side in the flow direction of a surface of a partition wall that faces outlet-side cells, and wherein, with regard to the volume of pores having a pore diameter of 10 μm or more and 18 μm or less, the first pore volume is a value measured for the first catalyst portion and the partition wall at a portion where the first catalyst portion is provided, and the second pore volume is a value measured for the second catalyst portion and the partition wall at a portion where the second catalyst portion is provided, and the first pore volume is larger than the second pore volume. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-282852 [Patent Document 2] Japanese Patent Application Publication No. 2020-193569 [Patent Document 3] Re-tabled publication 2019 / 188620 Summary of the Invention [Problem to be solved by the invention]

[0009] In the exhaust gas purification device described in Patent Document 1 in which a catalyst is provided in a filter with a wall-flow structure, the catalyst layer is provided on the porous partition walls of the honeycomb substrate of the filter, which reduces the gas permeability of the partition walls and may result in increased pressure loss.

[0010] In contrast to this, in the exhaust gas purification device described in Patent Document 2, the gas permeability of the outlet-side partition wall portion of the partition wall is made higher than that of the catalyst-arranged partition wall portion of the partition wall, thereby reducing the pressure loss. Also, in the exhaust gas purification catalyst described in Patent Document 3, the pressure loss is reduced by adjusting the lengths of the first catalyst portion and the second catalyst portion in the exhaust gas flow direction, etc.

[0011] On the other hand, in these conventional exhaust gas purification devices in which a catalyst is provided in a filter with a wall-flow structure, there is a risk that pressure loss will increase as PM in the exhaust gas accumulates in the voids present in the partition walls.

[0012] The present invention has been made in view of the above points, and an object of the present invention is to provide an exhaust gas purification device that can suppress an increase in pressure loss caused by accumulation of PM. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, an exhaust gas purification apparatus of the present invention is an exhaust gas purification apparatus comprising a honeycomb substrate and an inlet cell side catalyst layer, wherein the honeycomb substrate has porous partition walls that define a plurality of cells extending from an inlet-side end face to an outlet-side end face, the plurality of cells including inlet cells and outlet cells adjacent to each other with the partition wall interposed therebetween, the inlet cells have an open inlet-side end and a sealed outlet-side end, and the outflow cells have a sealed inlet-side end and an open outlet-side end, the inlet cell side catalyst layer is provided on the inlet cell side surface of an inlet cell side catalyst region that extends from the inlet-side end of the partition wall to a position away from the inlet-side end along the extension direction by a distance of 10% or more of the length of the partition wall, and at a reference position away from the inlet-side end of the partition wall by a distance of 10% of the length of the partition wall along the extension direction, a proportion of filled portions filled with the inlet cell side catalyst layer is 40% or less of voids present in an internal region from the inlet cell side surface of the partition wall to a depth of 50% of the thickness of the partition wall.

[0014] According to the exhaust gas purification device of the present invention, it is possible to suppress an increase in pressure loss due to accumulation of PM.

[0015] In the exhaust gas purification device, the inlet cell side catalyst region of the partition wall may be a region that extends from the inlet side end of the partition wall along the extension direction to a position away from the inlet side end of the partition wall by a distance of 10% to 60% of the length of the partition wall. [Effects of the Invention]

[0016] According to the present invention, it is possible to suppress an increase in pressure loss due to accumulation of PM. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view schematically showing an exhaust gas purification device according to a first embodiment. [Figure 2] 1 is a cross-sectional view schematically showing a main part of a cross section parallel to the extension direction of a cell in an exhaust gas purification device according to a first embodiment. [Figure 3]2 is a cross-sectional view schematically showing the main parts of the exhaust gas purifying devices produced in Comparative Examples 1 and 2 and Examples 1 to 3, the cross-sections being parallel to the stretching direction of the cells. FIG. [Figure 4A] 10(a) and 10(b) are images taken by FE-SEM of cross sections perpendicular to the stretching direction at the reference position of the partition walls in Comparative Examples 1 and 2, respectively. [Figure 4B] 10(a) to 10(c) are images taken by FE-SEM of cross sections perpendicular to the stretching direction at the reference position of the partition walls in Examples 1 to 3, respectively. [Figure 5] 10 is a graph showing pressure loss during PM accumulation relative to the proportion of filled portions in voids in the internal regions of the partition walls on the inlet cell side in Comparative Examples 1 and 2 and Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of an exhaust gas purification apparatus according to the present invention will be described. An exhaust gas purifying apparatus according to an embodiment is an exhaust gas purifying apparatus including a honeycomb substrate and an inlet cell side catalyst layer, wherein the honeycomb substrate has porous partition walls that define a plurality of cells extending from an inlet side end face to an outlet side end face, the plurality of cells including inlet cells and outlet cells adjacent to each other with the partition walls interposed therebetween, the inlet cells have an open inlet side end and a sealed outlet side end, the outlet cells have a sealed inlet side end and an open outlet side end, and the inlet cell side catalyst layer extends from the inlet side end of the partition wall along the extension direction to a position away from the inlet side end by 10% or more of the length of the partition wall, The partition wall is characterized in that, at a reference position (hereinafter sometimes abbreviated as "reference position of partition wall") that is provided on the surface of the inlet cell side in the extending inlet cell side catalyst region and that is away from the inlet side end of the partition wall along the extension direction by a distance of 10% of the length of the partition wall, the proportion of filled parts (hereinafter sometimes abbreviated as "filled part") filled with the inlet cell side catalyst layer among voids that exist in an internal region from the surface of the inlet cell side of the partition wall to a depth of 50% of the thickness of the partition wall (hereinafter sometimes abbreviated as "inlet cell side internal region of the partition wall") is 40% or less.

[0019] In the embodiments, the "inlet side" refers to the side into which exhaust gas flows in the exhaust gas purification device, and the "outlet side" refers to the side from which exhaust gas flows out of the exhaust gas purification device. Furthermore, the "length of the partition wall" refers to the length in the extension direction of the partition wall. Furthermore, the axial direction of the honeycomb substrate is usually approximately the same as the extension direction of the partition wall, and the extension direction of the cell is usually approximately the same as the extension direction of the partition wall. In the following description of the embodiments, the "extension direction" refers to the extension direction of the partition wall, which is approximately the same as the axial direction of the honeycomb substrate and the extension direction of the cell.

[0020] Here, 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 embodiment as an example. Fig. 1 is a perspective view that shows the exhaust gas purification apparatus according to the first embodiment. Fig. 2 is a cross-sectional view that shows a cross section of a main part of the exhaust gas purification apparatus according to the first embodiment, the cross section being parallel to the extension direction of the cells. Fig. 2 shows an image of an example of a cross section perpendicular to the extension direction at a reference position that is a distance 10% of the length of the partition wall along the extension direction from the inlet-side end of the partition wall at the outlet.

[0021] As shown in FIGS. 1 and 2, the exhaust gas purification device 1 according to the first embodiment includes a honeycomb substrate 10, plugs 16, an inlet cell-side catalyst layer 20, and an outlet cell-side catalyst layer 30. The honeycomb substrate 10 is a substrate having a cylindrical frame 11 and partition walls 14 integrally formed therewith, which divide the space inside the frame 11 into a honeycomb shape. The partition walls 14 are porous and define a plurality of cells 12 extending from an inlet-side end face 10Sa to an outlet-side end face 10Sb of the honeycomb substrate 10. The partition walls 14 are shaped such that a cross section perpendicular to the extension direction of the plurality of cells 12 is square. The partition walls 14 include a plurality of wall portions 14A arranged parallel to and spaced from each other, and a plurality of wall portions 14B orthogonal to the plurality of wall portions 14A and arranged parallel to and spaced from each other, and the cross section perpendicular to the extension direction has a lattice-like shape.

[0022] The multiple cells 12 include an inlet cell 12A and an outlet cell 12B adjacent to each other with a partition wall 14 sandwiched therebetween. The inlet cell 12A has an open inlet end 12Aa and an outlet end 12Ab sealed with a sealing portion 16, and the outlet cell 12B has an open inlet end 12Ba and an open outlet end 12Bb.

[0023] The inlet cell side catalyst layer 20 is provided on the inlet cell side surface 14SA of the inlet cell side catalyst region 14X, which extends from the inlet side end 14a of the partition wall 14 to a position 14b that is 10% or more of the length of the partition wall 14 along the extension direction. Furthermore, the inlet cell side catalyst layer 20 is also provided in voids that exist in an internal region 14NA from the inlet cell side surface 14SA of the inlet cell side catalyst region 14X of the partition wall 14 to a depth that is 50% of the thickness of the partition wall 14. At a reference position 14c that is 10% of the length of the partition wall 14 along the extension direction from the inlet side end 14a of the partition wall 14, the proportion of the voids that exist in the inlet cell side internal region 14NA of the partition wall 14 that are filled with the inlet cell side catalyst layer 20 is 40% or less. The inlet cell side catalyst layer 20 includes catalytic metal particles containing at least one of palladium (Pd) and platinum (Pt) (not shown) and a carrier (not shown) that supports the catalytic metal particles.

[0024] The outflow cell side catalyst layer 30 is provided in voids present in an inner region 14NB on the outflow cell side of the outflow cell side of the outflow cell side catalyst region 14Y, which extends from the outflow side end 14d of the partition wall 14 along the extension direction to a position 14e away from the inflow side. The outflow cell side catalyst layer 30 includes catalytic metal particles (not shown) containing rhodium (Rh) and a carrier (not shown) that supports the catalytic metal particles.

[0025] In a conventional exhaust gas purification device, when the inlet cell side catalyst layer is provided in the inlet cell side catalyst region of the partition wall at a density similar to that of the inlet cell side catalyst layer according to the first embodiment, the proportion of the inlet cell side catalyst layer filled with the inlet cell side catalyst layer exceeds 40% of the voids present in the inlet cell side internal region of the partition wall at the reference position of the partition wall. Therefore, the voids for PM accumulation are not sufficiently maintained in the inlet cell side internal region of the partition wall. Furthermore, the inlet cell side catalyst layer is not provided on the inlet cell side surface of the partition wall in an amount that can prevent PM from entering the inlet cell side internal region of the partition wall and allow PM to accumulate sufficiently. Therefore, when exhaust gas passes through the inlet cell side catalyst region of the partition wall, PM is not sufficiently accumulated in the inlet cell side catalyst layer on the inlet cell side surface of the partition wall. As PM accumulates in the voids present in the inlet cell side internal region of the partition wall, the voids are likely to become clogged. As a result, there is a risk of an increase in pressure loss due to the accumulation of PM in the inlet cell side catalyst region of the partition wall.

[0026] In contrast, in the exhaust gas purification device 1 according to the first embodiment, the inlet cell side catalyst layer 20 is provided on the inlet cell side surface 14SA of the inlet cell side catalyst region 14X of the partition wall 14, and at the reference position 14c of the partition wall 14, the proportion of filled portions filled with the inlet cell side catalyst layer 20 among the voids present in the inlet cell side internal region 14NA of the partition wall 14 is 40% or less. Therefore, a sufficient amount of voids for PM to accumulate is maintained in the inlet cell side internal region 14NA of the partition wall 14. Furthermore, on the inlet cell side surface 14SA of the partition wall 14, the inlet cell side catalyst layer 20 is provided in an amount that can prevent PM from entering the inlet cell side internal region 14NA of the partition wall 14 and allows PM to accumulate sufficiently. Therefore, when exhaust gas passes through the inlet cell side catalyst region 14X of the partition wall 14, PM is sufficiently deposited in the inlet cell side catalyst layer 20 on the inlet cell side surface 14SA of the partition wall 14, and the clogging of the voids present in the inlet cell side internal region 14NA of the partition wall 14 is less likely to progress during the process of PM deposition in the voids. This makes it possible to suppress an increase in pressure loss due to PM deposition.

[0027] Therefore, according to the exhaust gas purification device of the embodiment, as in the exhaust gas purification device of the first embodiment, for example, the inlet cell side catalyst layer is provided on the surface of the partition wall on the inlet cell side, and at the reference position of the partition wall, the proportion of filled portions filled with the inlet cell side catalyst layer among voids present in the internal region on the inlet cell side of the partition wall is 40% or less, thereby making it possible to suppress an increase in pressure loss due to accumulation of PM.

[0028] Next, each component of the exhaust gas purification device according to the embodiment will be described in detail.

[0029] 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 includes inlet cells and outlet cells adjacent to each other with the partition wall in between. 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.

[0030] The honeycomb substrate 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 can 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 can 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 common materials can be used, including, 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 any common shape can be used, for example, a cylindrical shape, an elliptical cylindrical shape, a polygonal cylindrical shape, etc. Other configurations of the frame are not particularly limited, and any common configuration can be used.

[0034] The shape of the partition walls is not particularly limited, and a common shape can be used. The length of the partition walls 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 walls is not particularly limited, and a common thickness can be used, but is preferably, for example, in the range of 50 μm to 2000 μm, and more preferably in the range of 100 μm to 1000 μm. By keeping the thickness of the partition walls within this range, 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 containing voids formed by pores through which exhaust gas can pass. The porosity of the portions of the partition walls where the catalyst layer is not provided is not particularly limited and can be a general porosity, but is preferably, for example, in the range of 40% to 70%, and more preferably, in the range of 50% to 70%. This is because a porosity equal to or greater than the lower limit of these ranges can effectively suppress pressure loss, and a porosity equal to or less than the upper limit of these ranges can ensure sufficient mechanical strength. The average pore diameter of the pores in the partition walls is not particularly limited and can be a general pore diameter, but is preferably, for example, in the range of 1 μm to 60 μm, and more preferably, in the range of 5 μm to 30 μm. This is because a pore average diameter within these ranges can achieve sufficient PM collection performance and sufficiently suppress pressure loss. The "average pore diameter of the pores in the partition walls" refers to a value measured, for example, by mercury intrusion porosimetry.

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

[0037] The inlet cell is usually sealed at the outlet end with a sealing portion. The outlet cell is usually sealed at the inlet end with a sealing portion. The length of the sealing portion in the extension direction is not particularly limited and may be a common length, but is preferably within the range of, for example, 2 mm to 20 mm. The material of the sealing portion is not particularly limited and may be a common material.

[0038] The cross-sectional shape perpendicular to the stretching direction of the inflow cells and outflow cells is not particularly limited, and a general shape can be used, and can be appropriately set taking into consideration 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 stretching direction of the inflow cells and outflow cells is not particularly limited, and a general cross-sectional area can be used, for example, 1 mm 2 More than 7mm 2 The length of the inlet cells and outlet 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 plugs in the extension direction from the axial length of the honeycomb substrate. The arrangement of the inlet cells and outlet cells can be, for example, a checkerboard pattern in which the inlet cells and outlet cells are arranged alternately, as in the arrangement according to the first embodiment.

[0039] 2. Inlet cell side catalyst layer The inlet cell side catalyst layer is provided on the inlet cell side surface of an inlet cell side catalyst region extending from the inlet side end of the partition wall along the extension direction to a position away from the inlet side end of the partition wall by a distance of 10% or more of the length of the partition wall. At a reference position away from the inlet side end of the partition wall along the extension direction by a distance of 10% of the length of the partition wall, the proportion of filled portions filled with the inlet cell side catalyst layer among voids present in an internal region from the inlet cell side surface of the partition wall to a depth of 50% of the thickness of the partition wall is 40% or less.

[0040] Here, the ratio of the filled portion to the voids present in the internal region on the inlet cell side of the partition wall at the reference position of the partition wall refers to the ratio of the area of the filled portion to the area of the voids present in the internal region on the inlet cell side of the partition wall in a cross section perpendicular to the extension direction of the reference position of the partition wall.

[0041] The inlet cell side catalyst layer is not particularly limited as long as the proportion of filled portions in the voids present in the internal region on the inlet cell side of the partition wall at the reference position of the partition wall is 40% or less, but a smaller proportion is preferable, and it may be 0%. This is because an increase in pressure loss due to PM accumulation can be effectively suppressed. In other words, the inlet cell side catalyst layer may or may not be provided in the voids present in the internal region on the inlet cell side of the partition wall. When the inlet cell side catalyst layer is not provided in the voids present in the internal region on the inlet cell side of the partition wall, an increase in pressure loss due to PM accumulation can be particularly effectively suppressed.

[0042] The inlet cell side catalyst region of the partition wall is not particularly limited, but is preferably a region extending from the inlet side end of the partition wall along the extension direction to a position at a distance of 10% to 60% of the length of the partition wall. This is because providing the inlet cell side catalyst layer in this region can suppress pressure loss before PM accumulates on the partition wall. Note that the inlet cell side catalyst region of the partition wall may be a region extending from the inlet side end of the partition wall along the extension direction to the outlet side end, i.e., the entire region in the extension direction of the partition wall. The closer the extension direction length of the inlet cell side catalyst region of the partition wall is to 100% of the extension direction length of the partition wall, the more the PM capture amount (rate) can be improved.

[0043] The thickness of the portion of the inlet cell-side catalyst layer on the surface of the inlet cell side of the partition wall is not particularly limited, but is preferably, for example, within a range of 10% to 40% of the thickness of the partition wall. When the thickness is equal to or greater than the lower limit of this range, an increase in pressure loss due to PM accumulation can be effectively suppressed. When the thickness is equal to or less than the upper limit of this range, narrowing of the exhaust gas path in the inlet cell can be suppressed, thereby effectively suppressing pressure loss.

[0044] The inlet cell side catalyst layer typically includes catalytic metal particles and a support on which the catalytic metal particles are supported. The inlet cell side catalyst layer is, for example, a sintered body including a catalyst-supported support in which catalytic metal particles are supported on a support. The inlet cell side catalyst layer may not include a catalytic metal and a support on which the catalytic metal is supported, but may include a support (co-catalyst, described below) that does not support catalytic metal. In this case, the inlet cell side catalyst layer cannot purify harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), but it can suppress the increase in pressure loss associated with PM accumulation, thereby improving PM filtering performance.

[0045] The material of the catalytic metal particles is not particularly limited, and common materials can be used, such as precious metals such as rhodium (Rh), palladium (Pd), and platinum (Pt). The material of the catalytic metal particles may be one type of metal, two or more types of metals, or an alloy containing two or more types of metals. The material of the catalytic metal particles is preferably at least one of Pd and Pt.

[0046] The average particle size of the catalytic metal particles is not particularly limited, and a general average particle size can be used, but it is preferably in the range of 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. Note that the average particle size of the catalytic metal particles refers to the average value determined from particle sizes measured by, for example, a transmission electron microscope (TEM).

[0047] The content of catalytic metal particles is not particularly limited and can be any common content, but it varies depending on the material of the catalytic metal particles. For example, when the material is Pd, Pt, or Rh, the content is preferably in the range of 0.05 g to 5 g per 1 L of honeycomb substrate. A content above the lower limit of this range ensures sufficient catalytic activity, while a content below the upper limit of this range suppresses grain growth of the catalytic metal particles and is cost-effective. Here, the content of catalytic metal particles per 1 L of substrate volume refers to the mass of catalytic metal particles contained in the inlet cell-side catalyst layer divided by the axial volume of a portion of the honeycomb substrate whose axial length is the same as the extension length of the inlet cell-side catalyst layer.

[0048] The carrier material is not particularly limited, and common materials can be used, including metal oxides such as alumina (Al2O3), zirconia (ZrO2), ceria (CeO2), silica (SiO2), magnesia (MgO), and titanium oxide (TiO2), as well as solid solutions thereof such as alumina-zirconia (Al2O3-ZrO2) composite oxide and ceria-zirconia (CeO2-ZrO2) composite oxide. The carrier material may be one or more of these. At least one of alumina and ceria-zirconia composite oxide is preferred.

[0049] The shape of the support is not particularly limited and any common shape can be used, but a powdered form is preferred because it ensures a larger specific surface area. The average particle size D50 of the powdered support is not particularly limited, but is preferably in the range of 1 μm to 15 μm, and particularly preferably in the range of 4 μm to 10 μm. Having an average particle size D50 above the lower limit of these ranges not only ensures sufficient heat resistance, but also reduces the proportion of filled voids in the internal region of the partition wall on the inlet cell side, thereby suppressing pressure loss before PM accumulates on the partition wall and effectively suppressing the increase in pressure loss associated with PM accumulation. Having an average particle size D50 below the upper limit of these ranges ensures sufficient dispersibility of the catalytic metal particles, effectively improving purification performance. The average particle size D50 of the powdered support can be determined, for example, by laser diffraction / scattering, using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.).

[0050] 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 can be a general mass ratio, but is preferably, for example, in the range of 0.01 mass% to 10 mass%. This is because a mass ratio equal to or greater than the lower limit of this range ensures sufficient catalytic action, and a mass ratio equal to or less than the upper limit of this range can suppress particle growth of the catalytic metal particles and is advantageous in terms of cost.

[0051] The method for supporting catalytic metal particles on a carrier is not particularly limited, and a general method can be used, for example, a method in which the carrier is 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.

[0052] The inlet cell-side catalyst layer may contain, in addition to the catalytic metal particles and the carrier, a co-catalyst that does not support catalytic metal particles. The material of the co-catalyst is not particularly limited and may be a common material, for example, a material similar to the material of the carrier. The shape of the co-catalyst is not particularly limited and may be a common shape, for example, a shape similar to the shape of the carrier. The average particle size of the powdered co-catalyst is not particularly limited and may be the same as the average particle size 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 common mass ratio, for example, a range of 30% by mass to 80% by mass is preferred.

[0053] The density of the inlet cell-side catalyst layer is not particularly limited, but is preferably in the range of 5 g / L to 250 g / L, more preferably 5 g / L to 100 g / L, and particularly preferably 10 g / L to 65 g / L. Having a density at or above the lower limit of these ranges effectively improves purification performance. Furthermore, the inlet cell-side catalyst layer can prevent PM from penetrating the inner region of the inlet cell side of the partition wall, allowing sufficient PM to accumulate, effectively suppressing an increase in pressure loss associated with PM accumulation. Furthermore, having a density at or below the upper limit of these ranges effectively suppresses pressure loss. The "density of the inlet cell-side catalyst layer" refers to the mass of the inlet cell-side catalyst layer divided by the axial volume of a honeycomb substrate whose axial length is the same as the extension length of the inlet cell-side catalyst layer.

[0054] The method for forming the inlet cell side catalyst layer is not particularly limited, and a general method can be used. For example, there can be mentioned a method in which a slurry prepared by mixing catalytic metal particles and a carrier carrying the catalytic metal particles in a solvent is supplied onto the surface of the inlet cell side in the inlet cell side catalyst region of the partition wall, and then the slurry is dried and fired.

[0055] 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 as to reduce the proportion of the filled portions filled with the inlet cell-side catalyst layer among the voids present in the internal region on the inlet cell side of the partition wall by suppressing the slurry from penetrating into the voids present in the internal region on the inlet cell side of the partition wall.

[0056] The method for preparing the slurry is not particularly limited, but examples thereof include the following methods. First, a powdered support (e.g., alumina) is immersed in a solution containing a catalytic metal salt (e.g., Pt nitrate) or a catalytic metal complex (e.g., an aqueous solution containing Pt nitrate), and then the resulting solution is dried and calcined to prepare a noble metal-supported powder (e.g., Pt-supported powder) carrying a noble metal (e.g., Pt). Next, a promoter (e.g., barium sulfate and ceria-zirconia composite oxide), a binder, and ion-exchanged water are added to the noble metal-supported powder, which is thoroughly stirred and wet-pulverized to achieve a desired average particle size D50 of the solid content. This prepares a slurry.

[0057] The average particle size D50 of the solid content of the slurry is not particularly limited, but is preferably, for example, in the range of 1 / 10 to 2 / 3 of the mean pore size (MPS) of the voids in the partition walls of the honeycomb substrate (for example, in the range of 10 μm to 20 μm), and more preferably in the range of 1 / 4 to 2 / 3 of the mean pore size of the voids in the partition walls of the honeycomb substrate. Specifically, for example, the range of 1 μm to 15 μm is preferable, and more preferably in the range of 4 μm to 10 μm. When the average particle size D50 of the solid content of the slurry is equal to or greater than the lower limit of these ranges, sufficient heat resistance is obtained, and the solid content of the slurry is prevented from entering the voids in the partition walls, allowing the solid content of the slurry to be disposed on the surface of the partition walls on the inlet cell side. Therefore, by reducing the proportion of filled portions among the voids present in the internal region on the inlet cell side of the partition walls, pressure loss before PM accumulates on the partition walls can be suppressed, and an increase in pressure loss due to PM accumulation can be effectively suppressed. When the average particle size D50 of the solid content of the slurry is equal to or less than the upper limit of these ranges, the dispersibility of the catalytic metal particles is sufficiently ensured, thereby effectively improving the purification performance. The average particle size D50 of the solid content of the slurry can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer LA-960 (manufactured by Horiba, Ltd.).

[0058] In the method of supplying the slurry onto the surface of the inlet cell side in the inlet cell side catalyst region of the partition wall, the slurry may be supplied into voids present in the internal region from the surface of the inlet cell side in the inlet cell side catalyst region of the partition wall to a depth of 50% of the thickness of the partition wall, so long as the proportion of filled portions in the voids present in the internal region of the inlet cell side of the partition wall is 40% or less at the reference position of the partition wall.

[0059] The method for supplying the slurry onto the surface of the inlet cell side in the inlet cell side catalyst region of the partition wall is not particularly limited, and a general method can be used. For example, a method in which a honeycomb substrate is immersed in the slurry from the inlet side and removed from the slurry after a predetermined time has elapsed can be mentioned. In this method, the outflow cells may be pressurized from the outflow side to generate a pressure difference between the outflow cells and the inflow cells so as to suppress the slurry from penetrating into voids present in the internal region of the partition wall from the surface of the inflow cell side in the inflow cell side catalyst region to a depth of 50% of the partition wall thickness, thereby reducing the proportion of filled portions among voids present in the internal region of the inflow cell side of the partition wall. Furthermore, properties such as the solids concentration and viscosity of the slurry may be appropriately adjusted as necessary to achieve a similar effect. As a method for supplying the slurry onto the surface of the inlet cell side in the inflow cell side catalyst region of the partition wall, a method in which the slurry is blown away using a blower to prevent the slurry from being supplied to the internal region of the partition wall or unnecessary portions on the surface.

[0060] In a method in which the slurry is supplied onto the inlet cell side surface of the inlet cell side catalyst region of the partition wall, followed by drying and firing, the drying conditions are not particularly limited and depend on the shape and dimensions of the honeycomb substrate or carrier, but are preferably, for example, drying conditions 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 and are, for example, preferably, firing conditions at a temperature in the range of 400°C to 1000°C for 1 hour to 4 hours. Specifically, in the drying and firing method, for example, the substrate after supplying the slurry may be dried by heating it in a dryer at 120°C for 2 hours to remove moisture, and then fired in an electric furnace at 500°C for 2 hours.

[0061] The proportion of filled portions in the voids present in the internal region on the inlet cell side of the partition walls can also be adjusted by the amount of slurry supplied, drying conditions, firing conditions, etc. Furthermore, the thickness of the portion of the inlet cell side catalyst layer on the surface on the inlet cell side of the partition walls, the porosity and other properties of the inlet cell side catalyst layer can also be adjusted by the solids concentration of the slurry, the properties of the slurry, the amount of slurry supplied, drying conditions, firing conditions, etc.

[0062] 3. Exhaust gas purification equipment The exhaust gas purification device includes a honeycomb substrate and an inlet cell side catalyst layer. The exhaust gas purification device typically further includes plugs that plug the outlet ends of the inlet cells and plugs that plug the inlet side ends of the outflow cells.

[0063] (1) Outlet cell side catalyst layer The exhaust gas purification device may further include an outflow cell side catalyst layer provided in an outflow cell side catalyst region extending from the outflow side end of the partition wall along the extension direction to a position away from the inflow side, like the exhaust gas purification device according to the first embodiment.

[0064] The outflow cell side catalyst region 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 along the extension direction to a position away from the inflow side, but for example, a region extending from the outflow side end of the partition wall along the extension direction to a position overlapping with the inflow cell side catalyst region is preferred, because this can prevent exhaust gas from permeating through a region of the partition wall where no catalyst layer is provided and being discharged unpurified from the exhaust gas purification device.

[0065] The outflow cell side catalyst layer may be provided in voids present in an internal region on the outflow cell side in the outflow cell side catalyst region of the partition wall, or may be provided on a surface on the outflow cell side in the outflow cell side catalyst region of the partition wall. Moreover, the outflow cell side catalyst layer may be provided in both voids present in an internal region on the outflow cell side in the outflow cell side catalyst region of the partition wall and on a surface.

[0066] Among these outflow cell-side catalyst layers, those provided in the gaps present in the internal region on the outflow cell side of the partition wall increase the gas permeability of the partition wall portion including the outflow cell-side catalyst region of the partition wall and the outflow cell-side catalyst layer, thereby effectively suppressing pressure loss. Furthermore, those provided on the surface on the outflow cell side of the outflow cell-side catalyst region of the partition wall increase the contact area with the exhaust gas that has flowed into the outflow cells, effectively improving purification performance. Furthermore, those provided both in the gaps and on the surface present in the internal region on the outflow cell side of the partition wall can simultaneously suppress pressure loss and improve purification performance.

[0067] The outflow cell side catalyst layer usually includes catalytic metal particles and a carrier on which the catalytic metal particles are supported, and is, for example, a sintered body including a catalyzed carrier 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 inlet cell side catalyst layer, except that rhodium (Rh) is preferred, and therefore a description thereof will be omitted here. The average particle size of the catalytic metal particles is the same as that of the catalytic metal particles contained in the inlet cell side catalyst layer, and therefore a description thereof will be omitted here.

[0069] The content of catalytic metal particles is not particularly limited and can be any commonly used content, but it varies depending on the material of the catalytic metal particles. For example, when the material is Rh, Pd, or Pt, the content is preferably in the range of 0.01 g to 2 g per 1 L of honeycomb substrate. A content above the lower limit of this range ensures sufficient catalytic activity, while a content below the upper limit of this range suppresses particle growth of the catalytic metal particles and is cost-effective. Here, the content of catalytic metal particles per 1 L of substrate volume refers to the mass of catalytic metal particles contained in the outflow cell-side catalyst layer divided by the axial volume of a portion of the honeycomb substrate whose axial length is the same as the extension length of the outflow cell-side catalyst layer.

[0070] The material and shape of the support are the same as those of the support contained in the inlet cell side catalyst layer, and therefore a description thereof will be omitted here. The average particle size D50 of the powdered support is not particularly limited, and a general average particle size can be used. The method for measuring the average particle size D50 of the support is the same as that for measuring the average particle size D50 of the support contained in the inlet cell side catalyst layer, and therefore a description thereof will be omitted here. The mass ratio of the catalytic metal particles to the total mass of the catalytic metal particles and the support is the same as that of the inlet cell side catalyst layer, and therefore a description thereof will be omitted here. The method for supporting the catalytic metal particles on the support is the same as that of the inlet cell side catalyst layer, and therefore a description thereof will be omitted here. The outlet cell side catalyst layer may contain a co-catalyst, as in the inlet cell side catalyst layer. The co-catalyst is the same as that contained in the inlet cell side catalyst layer, and therefore a description thereof will be omitted here.

[0071] The density of the outflow cell side catalyst layer is not particularly limited, but is preferably in the range of 30 g / L to 250 g / L. When the density of the outflow cell side catalyst layer is at or above the lower limit of this range, purification performance can be effectively improved. When the density of the outflow cell side catalyst layer is at or below the upper limit of this range, pressure loss can be effectively suppressed. The "density of the outflow cell side catalyst layer" refers to the value obtained by dividing the mass of the outflow cell side catalyst layer by the volume of a portion of the axial length of a honeycomb substrate having the same length in the extension direction as the outflow cell side catalyst layer.

[0072] The method for forming the outflow cell-side catalyst layer 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 the slurry is supplied to at least one of voids present in an internal region on the outflow cell side of the outflow cell-side catalyst region of the partition wall and on the surface, followed by drying and firing.

[0073] The slurry is similar to the slurry used to form the inlet cell side catalyst layer, except that it contains the catalytic metal particles and carrier contained in the outlet cell side catalyst layer instead of the catalytic metal particles and carrier contained in the inlet cell side catalyst layer, and therefore a description thereof will be omitted here. The method for preparing the slurry is similar to that for the slurry used to form the inlet cell side catalyst layer, and therefore a description thereof will be omitted here. The average particle size D50 of the solid content of the slurry is not particularly limited, and a general average particle size can be used. The method for measuring the average particle size D50 of the solid content of the slurry is similar to the method for measuring the average particle size D50 of the solid content of the slurry used to form the inlet cell side catalyst layer, and therefore a description thereof will be omitted here.

[0074] The method for supplying the slurry to at least one of the voids present in the internal region on the outflow cell side of the partition wall in the outflow cell-side catalyst region and the surface thereof is not particularly limited, and a general method can be used, for example, a method in which a honeycomb substrate is immersed in the slurry from the outflow side and then removed from the slurry after a predetermined time has elapsed. In this method, the properties of the slurry, such as the solids concentration and viscosity, may be appropriately adjusted so that the slurry is supplied to the voids present in the internal region on the outflow cell side of the partition wall, or the inflow cells may be pressurized from the inflow side to generate a pressure difference between the inflow cells and the outflow cells so that the slurry is not supplied to the voids present in the internal region on the outflow cell side of the partition wall, or the properties of the slurry, such as the solids concentration and viscosity, may be appropriately adjusted so that the slurry is not supplied to the voids present in the internal region on the outflow cell side of the partition wall. As a method for supplying the slurry to at least one of the voids present in the internal region on the outflow cell side of the outflow cell side catalyst region of the partition wall and the surface, a method may be used in which the slurry is blown away using a blower so that the slurry is not supplied to unnecessary portions of the internal region of the partition wall or on the surface.

[0075] The drying conditions and firing conditions in the method in which the slurry is supplied to at least one of the voids and the surface present in the inner region on the outflow cell side of the outflow cell side catalyst region of the partition wall, and then dried and fired are the same as the drying conditions and firing conditions used for forming the inflow cell side catalyst layer, and therefore, description thereof will be omitted here.

[0076] The thickness, porosity, and other properties of the outflow cell side catalyst layer can be adjusted by the solids concentration of the slurry, the properties of the slurry, the amount of slurry supplied, drying conditions, firing conditions, and the like.

[0077] (2) Other If the exhaust gas purification device further includes an outflow cell side catalyst layer, it is preferable that the catalytic metal particles contained in the inflow cell side catalyst layer contain at least one of palladium (Pd) and platinum (Pt), and that the catalytic metal particles contained in the outflow cell side catalyst layer contain rhodium (Rh), as in the exhaust gas purification device according to the first embodiment. This is because the hydrocarbons (HC) contained in the exhaust gas are effectively purified by the catalytic metal particles contained in the inflow cell side catalyst layer before the exhaust gas comes into contact with the outflow cell side catalyst layer, and therefore the rhodium (Rh) contained in the catalytic metal particles contained in the outflow cell side catalyst layer can be prevented from being poisoned by the hydrocarbons (HC). [Example]

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

[0079] In the following, exhaust gas purification devices were fabricated in Comparative Examples 1 and 2 and Examples 1 to 3, and the proportion of filled portions in the voids in the internal region on the inlet cell side of the partition wall at the reference position of the partition wall, and the pressure loss during PM accumulation were evaluated for these exhaust gas purification devices. Here, Fig. 3 is a cross-sectional view that schematically shows the main parts of the cross sections parallel to the extension direction of the cells in the exhaust gas purification devices fabricated in Comparative Examples 1 and 2 and Examples 1 to 3.

[0080] [Comparative Example 1] First, a GPF was prepared that included a honeycomb substrate 10 and plugs 16 and was not coated with a catalyst. The honeycomb substrate 10 is a substrate integrally formed with a cylindrical frame (not shown) and partition walls 14 that divide the space inside the frame into a honeycomb shape. The partition walls 14 are porous and define multiple cells 12 extending from the inlet-side end face 10Sa to the outlet-side end face 10Sb of the honeycomb substrate 10. The multiple cells 12 include an inlet cell 12A and an outlet cell 12B adjacent to each other across the partition wall 14. The inlet cell 12A has an open inlet end 12Aa and an outlet end 12Ab sealed with plugs 16. The outlet cell 12B has an inlet end 12Ba sealed with plugs 16 and an open outlet end 12Bb. The configurations of the honeycomb substrate 10 and plugs 16 of the GPF are detailed below.

[0081] (Configuration of honeycomb substrate and sealing part of GPF) Honeycomb substrate material: Cordierite Honeycomb substrate size: outer diameter x axial length = 117 mm x 122 mm Partition wall thickness: 200 μm Average pore size of partition wall voids: 15 μm Cell density: 300 cells per square inch Length of the sealing part in the extension direction: 4 mm

[0082] Next, a catalyst-loaded support (a powdered support loaded with catalytic metal particles) was mixed with a solvent to prepare a slurry for the inlet cell-side catalyst layer. Specifically, powdered alumina (type 1, bulk density: 0.35 g / mL) (support) was immersed in an aqueous solution containing Pt nitrate (catalytic metal salt), then dried and calcined to prepare a Pt-loaded powder with 2.5 parts by weight of Pt loaded on 97.5 parts by weight of powdered alumina. Next, 35 parts by weight of the Pt-loaded powder was added with 2 parts by weight of barium sulfate (promoter 1), 5 parts by weight of ceria-zirconia composite oxide (promoter 2), 2 parts by weight of binder, and ion-exchanged water. The mixture was thoroughly stirred and wet-pulverized to a solid average particle size D50 of 6 μm. This prepared a slurry for the inlet cell-side catalyst layer. The mass ratio of alumina (support) to ceria-zirconia composite oxide (promoter 2) in the solid content of the slurry for the inlet cell side catalyst layer was 7:1.

[0083] Next, the slurry for the inlet cell side catalyst layer was poured into the inlet cells 12A from the inlet side end 12Aa to be supplied onto the inlet cell side surface 14SA of the inlet cell side catalyst region 14X of the partition wall 14. The inlet cell side catalyst region 14X of the partition wall 14 is a region extending from the inlet side end 14a of the partition wall 14 to a position 14b at a distance of 50% of the length of the partition wall 14 along the extension direction. When supplying the slurry, a blower was used to blow away the slurry to prevent it from being supplied to the internal region of the partition wall or unnecessary portions on the surface. Then, the honeycomb substrate 10 to which the slurry for the inlet cell side catalyst layer had been supplied was dried by heating at 120°C for 2 hours in a dryer to remove moisture, and then fired at 500°C for 2 hours in an electric furnace. This formed the inlet cell side catalyst layer 20.

[0084] Next, a catalyst-loaded support (a powdered support loaded with catalytic metal particles) was mixed with a solvent to prepare a slurry for the outflow cell-side catalyst layer. Specifically, a powdered ceria-zirconia composite oxide (support) was immersed in an aqueous solution containing Rh nitrate (catalytic metal salt), then dried and calcined to prepare an Rh-loaded powder in which 0.5 parts by mass of Rh was loaded on 99.5 parts by mass of the powdered ceria-zirconia composite oxide. Next, 21 parts by mass of alumina (co-catalyst), 2 parts by mass of binder, and ion-exchanged water were added to 85 parts by mass of the Rh-loaded powder, thoroughly stirred, and wet-pulverized to a solid average particle size D50 of 1.5 μm. This prepared a slurry for the outflow cell-side catalyst layer.

[0085] Next, the slurry for the outflow cell side catalyst layer was poured into the outflow cell 12B from the outflow side end 12Bb to be supplied to the outflow cell side inner region 14NB of the outflow cell side catalyst region 14Y of the partition wall 14. The outflow cell side catalyst region 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 along the extension direction. When supplying the slurry, a blower was used to blow away the slurry so as not to supply it to the inner region of the partition wall or unnecessary parts on the surface. Thereafter, the honeycomb substrate 10 to which the slurry for the outflow cell side catalyst layer had been supplied was dried by heating at 120°C for 2 hours in a dryer to remove moisture, and then fired at 500°C for 2 hours in an electric furnace. This formed the outflow cell side catalyst layer 30.

[0086] As a result of the above, an exhaust gas purification device 1 was produced, which included a honeycomb substrate 10, plugs 16, an inlet cell side catalyst layer 20, and an outlet cell side catalyst layer 30, as shown in Fig. 3. The density of the inlet cell side catalyst layer 20 was 25 g / L, and the Pt content in the inlet cell side catalyst layer 20 was 0.6 g / L. The density of the outlet cell side catalyst layer 30 was 75 g / L, and the Rh content in the outflow cell side catalyst layer 30 was 0.3 g / L.

[0087] Comparative Example 2 An exhaust gas purification device 1 was produced by the same production method as in Comparative Example 1, except that when preparing the slurry for the inlet cell side catalyst layer, wet pulverization was performed so that the average particle size D50 of the solid content would be 3 μm. In Comparative Example 2, the density of the inlet cell side catalyst layer 20 was 25 g / L, and the Pt content in the inlet cell side catalyst layer 20 was 0.6 g / L. The density of the outflow cell side catalyst layer 30 was 75 g / L, and the Rh content in the outflow cell side catalyst layer 30 was 0.3 g / L.

[0088] [Example 1] The exhaust gas purification device 1 was produced by the same production method as in Comparative Example 1, except that the mass ratio of alumina (support) to ceria-zirconia composite oxide (co-catalyst 2) in the solid content of the inlet cell side catalyst layer slurry was 4:1. In Example 1, the density of the inlet cell side catalyst layer 20 was 15 g / L, and the Pt content in the inlet cell side catalyst layer 20 was 0.6 g / L. The density of the outflow cell side catalyst layer 30 was 75 g / L, and the Rh content in the outflow cell side catalyst layer 30 was 0.3 g / L.

[0089] [Example 2] An exhaust gas purification device 1 was produced using the same production method as in Comparative Example 1, except that when preparing the slurry for the inlet cell side catalyst layer, powdered alumina (type: type 2, bulk density: 0.65 g / mL) was used instead of powdered alumina (type: type 1, bulk density: 0.35 g / mL). In Example 2, the density of the inflow cell side catalyst layer 20 was 25 g / L, and the Pt content in the inflow cell side catalyst layer 20 was 0.6 g / L. The density of the outflow cell side catalyst layer 30 was 75 g / L, and the Rh content in the outflow cell side catalyst layer 30 was 0.3 g / L.

[0090] [Example 3] An exhaust gas purification device 1 was produced by the same production method as in Comparative Example 1, except that powdered alumina-zirconia composite oxide (bulk density: 1.1 g / mL) was used instead of powdered alumina (type: Type 1, bulk density: 0.35 g / mL) when preparing the slurry for the inlet cell side catalyst layer. In Example 3, the density of the inlet cell side catalyst layer 20 was 25 g / L, and the Pt content in the inlet cell side catalyst layer 20 was 0.6 g / L. The density of the outflow cell side catalyst layer 30 was 75 g / L, and the Rh content in the outflow cell side catalyst layer 30 was 0.3 g / L.

[0091] [Proportion of the filled portion of the voids in the internal region on the inlet cell side of the partition at the reference position of the partition] For the exhaust gas purification devices 1 produced in Comparative Examples 1 and 2 and Examples 1 to 3, at a reference position 14c that was away from the inlet-side end 14a of the partition wall 14 by a distance of 10% of the length of the partition wall 14 along the extension direction, the proportion of the filled portion filled with the inlet cell-side catalyst layer 20 among the voids present in the internal region 14NA from the inlet cell-side surface 14SA of the partition wall 14 to a depth of 50% of the thickness of the partition wall 14 was determined.

[0092] Specifically, first, in the exhaust gas purification device of each example, a cross section perpendicular to the extension direction of the reference position of the partition wall was photographed using an FE-SEM. Next, by automatic determination using image analysis software ImageJ (for details, see "Rasband, WS, ImageJ, US National Institutes of Health, Bethesda, Maryland, USA, http: / / rsb.info.nih.gov / ij / , 1997-2012."), unfilled portions of voids present in the internal region on the inlet cell side of the partition wall, other than filled portions filled with the inlet cell-side catalyst layer, were identified using the brightness of each portion as a discrimination criterion in the image of the cross section perpendicular to the extension direction of the reference position of the partition wall photographed by X-ray CT of each example. Next, the area of the unfilled portion of the void (pore portion after formation of the catalyst layer) existing in the internal region of the inlet cell side of the partition wall in the cross section of the partition wall was measured, and then the ratio of the area of the filled portion of the void to the area of the void existing in the internal region of the inlet cell side of the partition wall in the cross section of the partition wall, which was determined in advance by the manufacturer of the honeycomb substrate, was calculated as the ratio of the filled portion of the void existing in the internal region of the inlet cell side of the partition wall.

[0093] 4A(a) and 4A(b) are FE-SEM images of cross sections perpendicular to the stretching direction at the reference position of the partition walls in Comparative Examples 1 and 2, respectively, and FIGS. 4B(a) to 4B(c) are FE-SEM images of cross sections perpendicular to the stretching direction at the reference position of the partition walls in Examples 1 to 3, respectively. These images show the filled and unfilled portions of the voids present in the internal region on the inlet cell side of the partition walls, as well as the locations of the substrate portions. Table 1 below shows the proportion of filled portions among the voids in the internal region on the inlet cell side of the partition walls in each example.

[0094] As shown in FIGS. 4A and 4B and Table 1 below, in Comparative Examples 1 and 2, the proportion of the filled portion of the inlet cell-side catalyst layer in the voids in the internal region on the inlet cell side of the partition wall exceeded 40%, whereas in Examples 1 to 3, the proportion of the filled portion in the voids in the internal region on the inlet cell side of the partition wall was 40% or less.

[0095] [Pressure loss during PM accumulation] For the exhaust gas purifying devices produced in Comparative Examples 1 and 2 and Examples 1 to 3, the pressure loss during PM accumulation and the NOx treatment amount at 350°C were measured.

[0096] Specifically, each example of the exhaust gas purification device was first installed in the exhaust system of a 2L diesel engine. The diesel engine was then operated at an engine speed of 1600 rpm and 30 Nm, allowing exhaust gas with a gas temperature of 200°C to flow through the exhaust gas purification device. The pressure loss [kPa] was measured when 3g of PM accumulated per 1L of honeycomb substrate, and this was calculated as the pressure loss during PM accumulation. Table 1 below shows the pressure loss during PM accumulation for each example. Furthermore, each example of the exhaust gas purification device was installed as a second catalyst below the start-up catalyst in the exhaust system of a 2.5L gasoline engine. Next, the gasoline engine was operated at an engine speed of 3000 rpm x 45 Nm with the air-fuel ratio (A / F) fluctuating between 14.1 and 15.1, and analyzers were installed before and after the exhaust gas purification device to measure the NOx concentrations in each state while exhaust gas with a gas temperature of 350°C was circulating. The difference between the NOx concentrations was calculated as the NOx treatment amount [ppm] at 350°C. Fig. 5 is a graph showing the pressure loss during PM accumulation and the NOx treatment amount relative to the proportion of the filled portion among the voids in the internal region on the inlet cell side of the partition walls in Comparative Examples 1 and 2 and Examples 1 to 3.

[0097] As shown in Figure 5 and Table 1 below, as the ratio of filled parts to the voids in the internal region on the inlet cell side of the partition wall decreases, the pressure loss during PM accumulation decreases, and when the ratio of filled parts to the voids in the internal region on the inlet cell side of the partition wall is 40% or less, the pressure loss during PM accumulation decreases significantly. In this case, the amount of NOx processed increases significantly, and it was found that the coated catalyst layer was being used effectively.

[0098] [Table 1]

[0099] 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 within the scope of the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0100] 1. Exhaust gas purification equipment 10 Honeycomb substrate 10Sa Inlet end face of honeycomb substrate Outlet end surface of 10Sb honeycomb substrate 11 Frame 12 cells 12A inflow cell 12Aa Inlet end 12Ab Outflow end 12B Effluent Cell 12Ba Inlet end 12Bb Outflow end 14 Bulkhead 14a Inlet end of bulkhead 14b At a position at least 10% of the length of the bulkhead from the inlet end of the bulkhead 14c Bulkhead reference position 14d Outlet end of bulkhead 14e A position away from the outflow end of the partition to the inflow end 14X Inlet cell side catalyst area of partition wall 14Y Outlet cell side catalyst area of partition wall 14SA On the surface of the inlet cell side of the partition 14NA Inner region of the inlet cell side of the partition 14SB On the surface of the outflow cell side of the partition 14NB Inner region of the outflow cell side of the diaphragm 16 Sealing part 20 Inlet cell side catalyst layer 30 Outlet cell side catalyst layer

Claims

[Claim 1] An exhaust gas purification device comprising a honeycomb substrate and an inlet cell side catalyst layer, the honeycomb substrate has porous partition walls that define a plurality of cells extending from an inlet end face to an outlet 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 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 inlet cell side catalyst layer is provided on the inlet cell side surface of an inlet cell side catalyst region that extends from the inlet side end of the partition wall along the extension direction to a position away from the inlet side end by 10% or more of the length of the partition wall, at a reference position away from the inlet-side end of the partition wall along the extension direction by a distance of 10% of the length of the partition wall, a proportion of filled portions filled with the inlet cell-side catalyst layer among voids present in an internal region from the inlet cell side surface of the partition wall to a depth of 50% of the thickness of the partition wall, is 40% or less, an inlet cell side catalyst region of the partition wall extending along an extension direction from the inlet side end of the partition wall to a position away from the inlet cell side catalyst region by a distance of 10% to 60% of a length of the partition wall.

Images