Honeycomb filter

Abstract

The present invention provides a honeycomb filter that offers sufficient HC and CO purification efficiency even when an oxidation catalyst support (DOC) is not installed in the preceding stage. [Solution] A honeycomb filter comprising porous cell partitions that divide and form a plurality of cells that serve as exhaust gas flow paths, an exhaust gas introduction cell with an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side, and an exhaust gas discharge cell with an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, wherein the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas introduction cell and the exhaust gas discharge cell is the same at all locations in each cell from the exhaust gas inlet side end to the exhaust gas outlet side end, except for the sealed portion, and the total volume of the exhaust gas introduction cell is greater than the total volume of the exhaust gas discharge cell. The honeycomb filter is supported with an oxidation catalyst consisting of a catalytic metal and an oxide support that supports the catalytic metal, and has a first region A1 and a second region A2 with different concentrations of oxidation catalyst.

Description

Technical Field

[0001] The present invention relates to a honeycomb filter.

Background Art

[0002] Exhaust gas discharged from internal combustion engines such as diesel engines contains particulate matter such as soot (hereinafter also referred to as PM). In recent years, there has been a problem that this PM harms the environment or the human body. Further, since the exhaust gas also contains harmful gas components such as CO, HC, or NOx, there are concerns about the effects of these harmful gas components on the environment or the human body.

[0003] Therefore, as an exhaust gas purification device that collects PM in exhaust gas or purifies harmful gas components in exhaust gas such as CO, HC, or NOx contained in exhaust gas by being connected to an internal combustion engine, filters having a honeycomb structure (honeycomb filters) made of porous ceramics such as cordierite and silicon carbide have been variously proposed.

[0004] In addition, in order to meet the increasingly strict exhaust gas regulations year by year, efforts have been made to improve the utilization efficiency of the catalyst supported on the honeycomb filter.

[0005] For example, Patent Document 1 describes that a honeycomb filter is divided into three regions: a first zone, a second zone, and a third zone from the exhaust gas inlet side, and by changing the amount of catalyst supported and the type of catalyst supported in each zone, the catalyst is efficiently used to improve the exhaust gas purification efficiency.

[0006] Further, Patent Document 2 discloses that an oxidation catalyst of 5 to 60 g / L is supported on the cell partition wall of a honeycomb filter to purify CO generated by PM combustion and HC and CO that have leaked out without being completely purified by the oxidation catalyst installed in front of the honeycomb filter.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Special Publication No. 2023-542164 [Patent Document 2] Japanese Patent Publication No. 2015-29939 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In recent years, in order to comply with strict NOx emission regulations, there has been a need to increase the volume of NOx purification catalyst carriers. However, since it is difficult to enlarge the entire exhaust gas purification system, it is necessary to secure the increased volume of the NOx purification catalyst carrier by reducing the volume of other parts. Therefore, methods are being considered in which, for example, the role of an oxidation catalyst support (DOC) that oxidizes HC and CO is assigned to the honeycomb filter, and the volume increase for the NOx purification catalyst support is secured by not installing the DOC.

[0009] The honeycomb filter described in Patent Document 1 has good catalyst utilization efficiency because the amount of catalyst supported varies in each region, but further improvement in purification performance is required.

[0010] Furthermore, the honeycomb filter described in Patent Document 2 is based on the premise that a DOC is installed in the preceding stage. Therefore, if the preceding DOC is removed, there is a problem in that sufficient purification of HC and CO cannot be performed.

[0011] This invention was made to solve the above problems, and aims to provide a honeycomb filter that has sufficient HC and CO purification efficiency even when an oxidation catalyst support (DOC) is not installed in the preceding stage. [Means for solving the problem]

[0012] The honeycomb filter of the present invention comprises porous cell partitions that divide a plurality of cells that form a flow path for exhaust gas, an exhaust gas introduction cell having an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side, and an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, wherein the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas introduction cell and the exhaust gas discharge cell is the same at all locations in each cell from the exhaust gas inlet side end to the exhaust gas outlet side end, except for the sealed portion, and the total volume of the exhaust gas introduction cell is larger than the total volume of the exhaust gas discharge cell. The honeycomb filter has an oxidation catalyst supported on it, comprising a catalytic metal and an oxide support that supports the catalytic metal. The honeycomb filter has a first region extending from the exhaust gas inlet end toward the exhaust gas outlet end, on which the oxidation catalyst is supported at a concentration of 30 g / L or more, and a second region extending from the exhaust gas outlet end of the first region toward the exhaust gas outlet end of the honeycomb filter, on which the oxidation catalyst is supported at a concentration of less than 30 g / L, or on which no oxidation catalyst is supported. The length of the first region in the longitudinal direction is 20-60% of the length of the honeycomb filter.

[0013] In the honeycomb filter of the present invention, a first region is arranged in a region extending 20-60% of the length of the honeycomb filter from the exhaust gas inlet end, on which an oxidation catalyst is supported at a concentration of 30 g / L or more. Furthermore, the total volume of the exhaust gas introduction cells is larger than the total volume of the exhaust gas discharge cells. Therefore, compared to the case where the total volume of the exhaust gas introduction cells is less than or equal to the total volume of the exhaust gas discharge cells, the velocity of the exhaust gas flowing into the honeycomb filter is slower, improving the contact between the oxidation catalyst supported in the first region on the exhaust gas inlet side and the exhaust gas, thereby improving the exhaust gas purification performance.

[0014] If the length of the first region is less than 20% of the length of the honeycomb filter, the contact time between the exhaust gas flowing into the exhaust gas introduction cell and the oxidation catalyst becomes too short, resulting in reduced purification performance.

[0015] If the length of the first region exceeds 60% of the length of the honeycomb filter, the first region on which the oxidation catalyst is supported becomes too long, resulting in a large pressure drop. Additionally, the amount of catalyst supported increases.

[0016] If the total volume of the exhaust gas introduction cells is less than or equal to the total volume of the exhaust gas discharge cells, the velocity of the exhaust gas flowing into the honeycomb filter will not decrease, and therefore the contact between the oxidation catalyst supported in the first region and the exhaust gas cannot be improved.

[0017] In the honeycomb filter of the present invention, it is preferable that the average cross-sectional area of ​​the section perpendicular to the longitudinal direction of each exhaust gas discharge cell is greater than the average cross-sectional area of ​​the section perpendicular to the longitudinal direction of each exhaust gas introduction cell.

[0018] In the honeycomb filter of the present invention, the concentration of the oxidation catalyst in the first region is preferably 40 to 120 g / L. When the concentration of the oxidation catalyst in the first region is within the above range, the exhaust gas purification performance is particularly good.

[0019] In the honeycomb filter of the present invention, the oxidation catalyst is also supported in the second region, and it is preferable that in the second region, the oxidation catalyst is present only inside the cell partitions. Even if an oxidation catalyst is supported in the second region, if the oxidation catalyst is present only inside the cell partition, a coating layer made of the oxidation catalyst will not form on the surface of the cell partition in the second region. If a coating layer made of the oxidation catalyst is formed, the resistance to exhaust gas passing through the coating layer made of the oxidation catalyst formed on the cell partition will increase, but since this is not formed, the pressure loss is less likely to increase.

[0020] In the honeycomb filter of the present invention, it is preferable that the oxidation catalyst is not supported on the cell partitions in the second region. If no oxidation catalyst is supported in the second region, the exhaust gas will not pass through the coating layer made of the oxidation catalyst in the second region, thus keeping the pressure loss low.

[0021] The honeycomb filter of the present invention is such that the exhaust gas introduction cell is adjacent to the entire periphery of the exhaust gas discharge cell with the cell partition wall therebetween. The exhaust gas introduction cell consists of two types: a first exhaust gas introduction cell and a second exhaust gas introduction cell having a cross-sectional area in a cross-section perpendicular to the longitudinal direction larger than that of the first exhaust gas introduction cell. Also, the cross-sectional area of the exhaust gas discharge cell in a cross-section perpendicular to the longitudinal direction is formed to be the same as or larger than the cross-sectional area of the second exhaust gas introduction cell in a cross-section perpendicular to the longitudinal direction. Regarding the cross-section perpendicular to the longitudinal direction, the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, the second exhaust gas introduction cell is octagonal, and it is preferable that the length of the side facing the exhaust gas discharge cell among the sides constituting the cross-sectional shape of the first exhaust gas introduction cell is longer than the length of the side facing the exhaust gas discharge cell among the sides constituting the cross-sectional shape of the second exhaust gas introduction cell. With the above cell shape, many parts of the cell partition wall can be used for collecting PM, so the PM collection efficiency is enhanced. Also, since the thickness of the PM deposited on the cell partition wall can be made more uniform, the pressure loss can be reduced.

[0022] The honeycomb filter of the present invention is preferably used in an exhaust gas purification system in which an oxidation catalyst is not provided upstream of the honeycomb filter. Since the honeycomb filter of the present invention can exhibit excellent exhaust gas purification performance, even when used in an exhaust gas purification system in which an oxidation catalyst is not provided upstream, it is possible to achieve both exhaust gas purification and PM collection.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a perspective view schematically showing an example of the honeycomb filter of the present invention. [Figure 2] FIG. 2 is a view schematically showing the cell structure of the honeycomb filter shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III of the honeycomb filter shown in FIG. 1. [Figure 4] Figure 4 is a schematic perspective view showing another example of the honeycomb filter of the present invention. [Figure 5] Figure 5 is a schematic diagram showing the cell structure of the honeycomb filter shown in Figure 4. [Figure 6] Figure 6 is a schematic perspective view showing yet another example of the honeycomb filter of the present invention. [Figure 7] Figure 7 is a schematic perspective view showing an example of a honeycomb segment. [Figure 8] Figure 8 is a schematic perspective view showing another example of a honeycomb segment. [Figure 9] Figure 9 is an enlarged view of the honeycomb filter according to Comparative Example 3, seen from the exhaust gas inlet end. [Figure 10] Figure 10 is a schematic cross-sectional view illustrating the pressure loss measurement method. [Modes for carrying out the invention]

[0024] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and can be modified and applied as appropriate without altering the essence of the invention.

[0025] [Honeycomb filter] The honeycomb filter of the present invention comprises porous cell partitions that divide a plurality of cells that form a flow path for exhaust gas, an exhaust gas introduction cell having an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side, and an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, wherein the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas introduction cell and the exhaust gas discharge cell is the same at all locations in each cell from the exhaust gas inlet side end to the exhaust gas outlet side end, except for the sealed portion, and the total volume of the exhaust gas introduction cell is larger than the total volume of the exhaust gas discharge cell. The honeycomb filter has an oxidation catalyst supported on it, comprising a catalytic metal and an oxide support that supports the catalytic metal. The honeycomb filter has a first region extending from the exhaust gas inlet end toward the exhaust gas outlet end, on which the oxidation catalyst is supported at a concentration of 30 g / L or more, and a second region extending from the exhaust gas outlet end of the first region toward the exhaust gas outlet end of the honeycomb filter, on which the oxidation catalyst is supported at a concentration of less than 30 g / L, or on which no oxidation catalyst is supported. The length of the first region in the longitudinal direction is 20-60% of the length of the honeycomb filter.

[0026] Figure 1 is a schematic perspective view showing an example of the honeycomb filter of the present invention. The honeycomb filter 1 shown in Figure 1 consists of a single honeycomb fired body 11 comprising porous cell partitions 20 that divide and form multiple cells that serve as flow paths for exhaust gas, exhaust gas introduction cells 12 and 13 with an open end 11a on the exhaust gas inlet side and an open end 11b on the exhaust gas outlet side sealed with a sealing material, and an exhaust gas discharge cell 14 with an open end 11b on the exhaust gas outlet side and an open end 11a on the exhaust gas inlet side sealed with a sealing material 15.

[0027] The cross-sectional shape of the exhaust gas introduction cells 12, 13 and the exhaust gas discharge cell 14 in the direction perpendicular to the longitudinal direction is the same at all locations in each cell, from the exhaust gas inlet end 11a to the exhaust gas outlet end 11b, except for the sealing portion.

[0028] In the honeycomb filter of the present invention, it is desirable that the sealing material 15 that seals the exhaust gas introduction cells 12, 13 and the exhaust gas discharge cell 14 be made of the same material as the honeycomb fired body 11.

[0029] Figure 2 is a schematic diagram showing the cell structure of the honeycomb filter shown in Figure 1. Figure 2 is also an enlarged view of the honeycomb filter 1 shown in Figure 1, viewed from the exhaust gas inlet end 11a. As shown in Figure 2, the exhaust gas introduction cells 12 and 13 consist of two types: a first exhaust gas introduction cell 12 adjacent to the exhaust gas discharge cell 14 in a cross section perpendicular to the longitudinal direction, and a second exhaust gas introduction cell 13 not adjacent to the exhaust gas discharge cell 14.

[0030] Surrounding the exhaust gas discharge cell 14 are four first exhaust gas introduction cells 12, which face the exhaust gas discharge cell 14 across a cell partition wall 20, and four second exhaust gas introduction cells 13, which do not face the exhaust gas discharge cell 14 but face the first exhaust gas introduction cells 12 across a cell partition wall 20, arranged alternately in an alternating pattern, thus enclosing the exhaust gas discharge cell 14.

[0031] The cross-sectional shapes of the first exhaust gas introduction cell 12, the second exhaust gas introduction cell 13, and the exhaust gas discharge cell 14 are all the same rectangular shape. Therefore, the average cross-sectional area of ​​the exhaust gas discharge cell 14 is equal to the average cross-sectional area of ​​the exhaust gas introduction cells 12 and 13.

[0032] The cell partition wall 20 separating the first exhaust gas introduction cell 12 and the exhaust gas discharge cell 14 is also called the first cell partition wall 21. Furthermore, the cell partition wall 20 separating the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 13 is also called the second cell partition wall 22.

[0033] The ratio of the number of first exhaust gas introduction cells 12, second exhaust gas introduction cells 13, and exhaust gas discharge cells 14 per unit area is 2:1:1, and the cross-sectional shapes of the exhaust gas introduction cells 12, 13 and exhaust gas discharge cells 14 are all the same. From this, it can be said that the total volume of exhaust gas introduction cells 12 and 13, which are the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 13 combined, is larger than the total volume of the exhaust gas discharge cell 14.

[0034] Figure 3 is a cross-sectional view of the honeycomb filter shown in Figure 1, taken along line III-III. When exhaust gas flows into the honeycomb filter 1 and PM is collected, as shown in Figure 3, the exhaust gas G (in Figure 3, exhaust gas is indicated by G and the flow of exhaust gas is indicated by arrows) that flows into the first exhaust gas introduction cell 12 passes through the first cell partition wall 21 separating the first exhaust gas introduction cell 12 and the exhaust gas discharge cell 14, and then flows out from the exhaust gas discharge cell 14.

[0035] The exhaust gas G that flows into the second exhaust gas introduction cell 13 passes through the inside of the cell partition wall 20 between the second cell partition wall 22 and the first cell partition wall 21, and flows out from the exhaust gas discharge cell 14. As the exhaust gas G passes through the cell partitions 20 (first cell partition 21 and second cell partition 22), PM and other particles in the exhaust gas are captured, so the cell partitions 20 function as filters.

[0036] The honeycomb filter 1 is supported with an oxidation catalyst consisting of a catalytic metal and an oxide support that supports the catalytic metal.

[0037] The honeycomb filter 1 has a first region (indicated by the double-headed arrow A1 in Figure 3) and a second region (indicated by the double-headed arrow A2 in Figure 3).

[0038] The first region A1 is a region extending from the exhaust gas inlet end 11a to the exhaust gas outlet end 11b, on which an oxidation catalyst is supported at a concentration of 30 g / L or more. The second region A2 is the region from the exhaust gas outlet end of the first region A1 to the exhaust gas outlet end 11b of the honeycomb filter 1, and is a region in which the oxidation catalyst is supported at a concentration of less than 30 g / L, or a region in which the oxidation catalyst is not supported. In this specification, the concentration of the oxidation catalyst is determined by dividing the total weight of the catalyst metal and oxide support by the volume of the region on which the oxidation catalyst is supported.

[0039] In other words, one end of the first region A1 is the exhaust gas inlet side end 11a, and the other end is the exhaust gas inlet side end of the second region A2. Furthermore, one end of the second region A2 is the exhaust gas outlet end 11b, and the other end is the exhaust gas outlet end of the first region A1.

[0040] The length of the first region A1 in the longitudinal direction is 20-60% of the length of the honeycomb filter 1 (indicated by the double arrow A in Figure 3).

[0041] In the honeycomb filter of the present invention, a first region A1 is arranged in a region extending 20-60% of the length of the honeycomb filter from the exhaust gas inlet end, with an oxidation catalyst supported at a concentration of 30 g / L or more. Furthermore, the total volume of the exhaust gas introduction cells is larger than the total volume of the exhaust gas discharge cells. Therefore, compared to the case where the total volume of the exhaust gas introduction cells is less than or equal to the total volume of the exhaust gas discharge cells, the velocity of the exhaust gas flowing into the honeycomb filter is slower, improving the contact between the oxidation catalyst supported in the first region on the exhaust gas inlet side and the exhaust gas, thereby improving the exhaust gas purification performance.

[0042] The concentration of the oxidation catalyst in the honeycomb filter can be determined by cutting out a portion of the honeycomb filter as a test piece and converting the amount of oxidation catalyst contained in that test piece to the amount per liter of honeycomb filter.

[0043] In the first region A1, there may be multiple regions (parts) with different concentrations of the oxidation catalyst. For example, the first region A1 may be composed of a first portion on which the oxidation catalyst is supported at a concentration of 30 g / L and a second portion on which the oxidation catalyst is supported at a concentration of 50 g / L.

[0044] The thickness of the cell partition wall 20 is preferably 0.05 to 0.46 mm, but may also be 0.05 to 0.30 mm, 0.05 to 0.25 mm, or 0.15 to 0.25 mm. Cell partitions of this thickness possess sufficient mechanical strength while effectively suppressing the increase in pressure loss. Furthermore, the thickness of the cell partition 20 may be the same for the first cell partition 21 and the second cell partition 22, or it may be different.

[0045] The porosity of the cell septum is preferably 30 to 70% by volume. By setting the porosity of the cell partitions within the above range, the cell partitions 20 can effectively capture PM in the exhaust gas, and the increase in pressure loss caused by the cell partitions 20 can be suppressed. If the porosity of the cell partition is less than 30% by volume, the proportion of pores in the cell partition is too small, making it difficult for exhaust gas to pass through the cell partition, which may result in a large pressure loss when the exhaust gas passes through the cell partition. If the porosity of the cell septum exceeds 70% by volume, the mechanical properties of the cell septum may decrease, making it more susceptible to cracking.

[0046] The average pore size of the pores contained in the cell septum is preferably 5 to 25 μm. If the average pore diameter of the pores contained in the cell partition is within the above range, PM can be collected with high collection efficiency while suppressing an increase in pressure loss. If the average pore size of the pores in the cell partition is less than 5 μm, the pores are too small, which may result in a large pressure loss when the exhaust gas passes through the cell partition. If the average pore diameter of the pores in the cell septum exceeds 25 μm, the pores may become too large, potentially reducing the PM collection efficiency.

[0047] In this specification, "average pore diameter of pores contained in the cell partition" and "porosity of the cell partition" refer to values ​​measured by the mercury intrusion method under conditions of a contact angle of 130° and a surface tension of 485 mN / m.

[0048] The honeycomb sintered body 11 constituting the honeycomb filter 1 is not particularly limited as long as it is made of a porous material, but examples include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; oxide ceramics such as alumina, zirconia, cordierite, mullite, and aluminum titanate; and silicon-containing silicon carbide. Among these, silicon carbide or silicon-containing silicon carbide is preferred. Silicon carbide and silicon-containing silicon carbide are materials with excellent heat resistance. For this reason, a honeycomb filter made of silicon carbide or silicon-containing silicon carbide has excellent heat resistance. Furthermore, silicon-containing silicon carbide is a material in which metallic silicon is blended with silicon carbide, and silicon-containing silicon carbide containing 60 wt% or more of silicon carbide is preferred.

[0049] The number of cells per unit area in the cross-section of the honeycomb calcined body 11 is 23 to 62 cells / cm². 2 (150~400 pieces / inch 2 ) is desirable. The number of cells per unit area is the total number of the first exhaust gas introduction cells 12, the second exhaust gas introduction cells 13, and the exhaust gas discharge cells 14. In each drawing, the areas of the first exhaust gas introduction cells 12, the second exhaust gas introduction cells 13, and the exhaust gas discharge cells 14 are schematically drawn larger than the area of ​​the end face of the honeycomb firing body 111 for illustrative purposes. If the number of cells per unit area in the cross-section of the honeycomb firing body 111 is within the above range, the number of cells per honeycomb firing body will be considerably larger than the number of cells shown in each drawing.

[0050] The first region A1 may contain an oxidation catalyst supported at a concentration of 40 to 120 g / L.

[0051] Examples of catalytic metals that constitute an oxidation catalyst include Pt, Pd, Rh, and Ag.

[0052] The proportion of the catalytic metal in the oxidation catalyst is preferably 0.1 to 5.0% by weight.

[0053] Examples of oxide supports that constitute the oxidation catalyst include γ-alumina, silica, ceria, and zirconia.

[0054] The second region A2 does not necessarily need to have an oxidation catalyst supported on it.

[0055] When an oxidation catalyst is supported in the second region A2, it is preferable that the oxidation catalyst is supported only inside the cell partition. When the amount of oxidation catalyst supported in the second region is 10 g / L or less, the oxidation catalyst tends to be supported only inside the cell septum.

[0056] Furthermore, whether the oxidation catalyst is supported only inside the cell septum can be determined by checking whether the oxidation catalyst is present inside (inside the surface) of the cell septum, as identified from the SEM cross-section.

[0057] Region A2 may contain multiple regions (parts) with different concentrations of the oxidation catalyst. For example, the second region A2 may be composed of a third portion on which an oxidation catalyst is supported at a concentration of 5 g / L, and a fourth portion on which no oxidation catalyst is supported.

[0058] In the honeycomb filter of the present invention, the cell structure is not limited to the structure shown in Figures 1 to 3. Examples of cell structures other than those shown in Figures 1 to 3 will be explained with reference to Figures 4 and 5.

[0059] Figure 4 is a schematic perspective view showing another example of the honeycomb filter of the present invention. Figure 5 is a schematic diagram showing the cell structure of the honeycomb filter shown in Figure 4. Figure 5 is also an enlarged view of the honeycomb filter 2 shown in Figure 4, viewed from the exhaust gas inlet end 111a.

[0060] The honeycomb filter 2 shown in Figure 4 consists of a single honeycomb fired body 111 comprising porous cell partitions 120 that divide and form multiple cells that serve as flow paths for exhaust gas, exhaust gas introduction cells 112 and 113 with an open end 111a on the exhaust gas inlet side and a sealed end 111b on the exhaust gas outlet side, and an exhaust gas discharge cell 114 with an open end 111b on the exhaust gas outlet side and a sealed end 111a on the exhaust gas inlet side, both sealed with a sealed material 115.

[0061] As shown in Figure 5, exhaust gas inlet cells 112 and 113 are adjacent to the entire perimeter of the exhaust gas discharge cell 114, which has an octagonal cross-sectional shape, separated by cell partitions 120. The exhaust gas introduction cells 112 and 113 consist of two types: a rectangular first exhaust gas introduction cell 112 facing the exhaust gas discharge cell 114 separated by a cell partition wall 120, and an octagonal second exhaust gas introduction cell 113 facing the exhaust gas discharge cell 114 separated by the cell partition wall 120.

[0062] The cross-sectional shape of the second exhaust gas introduction cell 113 and the exhaust gas discharge cell 114 is the same octagon. The cross-sectional shape of the first exhaust gas introduction cell 112 is rectangular, and its area is smaller than the area of ​​the octagonal cross-sectional shape of the second exhaust gas introduction cell 113 and the exhaust gas discharge cell 114. In other words, the cross-sectional area of ​​the exhaust gas discharge cell 114 is either the same as or larger than the cross-sectional area of ​​the exhaust gas introduction cell.

[0063] The cell partition wall 120 separating the first exhaust gas introduction cell 112 and the exhaust gas discharge cell 114 is also called the first cell partition wall 121. Furthermore, the cell partition wall 120 separating the second exhaust gas introduction cell 113 and the exhaust gas discharge cell 114 is also called the second cell partition wall 122. Furthermore, the cell partition wall 120 separating the first exhaust gas introduction cell 112 and the second exhaust gas introduction cell 113 is also called the third cell partition wall 123.

[0064] As shown in Figure 5, the length of the first cell partition wall 121 separating the first exhaust gas introduction cell 112 and the exhaust gas discharge cell 114 (indicated by the double-headed arrow L1 in Figure 5) is longer than the length of the second cell partition wall 122 separating the second exhaust gas introduction cell 113 and the exhaust gas discharge cell 114 (indicated by the double-headed arrow L2 in Figure 5). The cell structure (cell shape) described above is also called an octagonal-square cell structure.

[0065] The ratio of the number of first exhaust gas introduction cells 112, second exhaust gas introduction cells 113, and exhaust gas discharge cells 114 per unit area is 2:1:1, and the cross-sectional shapes of the second exhaust gas introduction cells 113 and exhaust gas discharge cells 114 are the same. From this, it can be said that the total volume of exhaust gas introduction cells, including the first exhaust gas introduction cell 112 and the second exhaust gas introduction cell 113, is larger than the total volume of exhaust gas discharge cell 114.

[0066] The honeycomb filter 2 has a first region A1 and a second region A2.

[0067] The first region A1 is a region extending from the exhaust gas inlet end 111a to the exhaust gas outlet end 111b, on which an oxidation catalyst is supported at a concentration of 30 g / L or more. The second region A2 is the region from the exhaust gas outlet end of the first region A1 to the exhaust gas outlet end 111b of the honeycomb filter 2, and is a region in which the oxidation catalyst is supported at a concentration of less than 30 g / L, or a region in which the oxidation catalyst is not supported.

[0068] In the honeycomb filter 2, a first region A1 is located in a region extending from the exhaust gas inlet end 111a to 20-60% of the length of the honeycomb filter 2, with an oxidation catalyst supported at a concentration of 30 g / L or more. Furthermore, the total volume of the exhaust gas introduction cells is larger than the total volume of the exhaust gas discharge cells. As a result, compared to the case where the total volume of the exhaust gas introduction cells is less than or equal to the total volume of the exhaust gas discharge cells, the velocity of the exhaust gas flowing into the honeycomb filter is slower. This improves the contact between the oxidation catalyst supported in the first region on the exhaust gas inlet side and the exhaust gas, thereby improving the exhaust gas purification performance.

[0069] Furthermore, because the honeycomb filter has an octagonal-square cell structure, a large portion of the cell partitions can be used for PM collection, increasing the PM collection efficiency. In addition, the thickness of the PM deposited on the cell partitions can be made more uniform, which reduces pressure loss.

[0070] The honeycomb filters shown in Figures 1-3 and 4-5 are so-called integrated honeycomb filters, but the honeycomb filter of the present invention may also be a so-called aggregated honeycomb filter.

[0071] Figure 6 is a schematic perspective view showing yet another example of the honeycomb filter of the present invention. The honeycomb filter 3 shown in Figure 6 consists of a honeycomb block 60 formed by joining multiple honeycomb fired bodies 30 via an adhesive layer 50, and an outer peripheral coating layer 70 formed on the outer periphery of the honeycomb block 60.

[0072] As the honeycomb calcined body 30, a honeycomb calcined body similar to the one that constitutes the honeycomb filter shown in Figures 1-3 and 4-5 can be suitably used. The honeycomb fired bodies 30 that are joined together via the adhesive layer 50 to form the honeycomb block 60 are also called honeycomb segments.

[0073] In other words, the honeycomb filter 3 is a so-called aggregate-type honeycomb filter composed of multiple honeycomb segments 30.

[0074] As the adhesive layer 50, for example, an adhesive paste consisting of an inorganic binder, an organic binder, and inorganic particles can be used, which has been solidified by drying or firing. Furthermore, the adhesive layer 50 may also contain inorganic fibers and / or whiskers.

[0075] Examples of inorganic particles include carbide particles and nitride particles. Specifically, these include silicon carbide particles, silicon nitride particles, and boron nitride particles. These may be used individually or in combination of two or more types. Among inorganic particles, silicon carbide particles are preferable due to their excellent thermal conductivity.

[0076] Examples of inorganic fibers and / or whiskers include silica-alumina, mullite, alumina, silica, and the like. These may be used individually or in combination of two or more. Among inorganic fibers, alumina fibers are preferred. The inorganic fibers may also be biosoluble fibers.

[0077] Furthermore, the adhesive paste may contain, if necessary, balloons which are tiny hollow spheres made of oxide ceramics, spherical acrylic particles, graphite, etc. The balloons are not particularly limited and include, for example, alumina balloons, glass microballoons, shirasu balloons, fly ash balloons (FA balloons), mullite balloons, etc.

[0078] Figure 7 is a schematic perspective view showing an example of a honeycomb segment. The honeycomb segment 31 shown in Figure 7 is prismatic in shape, having an end 31a on the exhaust gas inlet side and an end 31b on the exhaust gas outlet side, and has a cell structure similar to the honeycomb calcined body 11 that constitutes the honeycomb filter 1 shown in Figures 1 to 3.

[0079] Figure 8 is a schematic perspective view showing another example of a honeycomb segment. The honeycomb segment 32 shown in Figure 8 is prismatic in shape, having an end 32a on the exhaust gas inlet side and an end 32b on the exhaust gas outlet side, and has a cell structure similar to the honeycomb calcined body 111 that constitutes the honeycomb filter 2 shown in Figures 4 and 5.

[0080] Because the honeycomb filter of the present invention can exhibit excellent exhaust gas purification performance, it can achieve both exhaust gas purification and PM collection even when used in an exhaust gas purification system that does not have an oxidation catalyst in the preceding stage. Therefore, the honeycomb filter of the present invention can be suitably used in exhaust gas purification systems in which an oxidation catalyst is not provided in the preceding stage.

[0081] Next, a method for manufacturing a honeycomb filter according to the present invention will be described. In the following section, we will explain the case where silicon carbide is used as the ceramic powder.

[0082] (1) A molding process is performed to produce a honeycomb molded body by extruding a wet mixture containing ceramic powder and a binder. Specifically, first, a wet mixture for manufacturing honeycomb molded bodies is prepared by mixing silicon carbide powder with different average particle sizes as ceramic powder, an organic binder, a liquid plasticizer, a lubricant, and water.

[0083] The above wetted mixture may optionally contain pore-forming agents such as balloons, which are tiny hollow spheres made of oxide ceramics, spherical acrylic particles, or graphite.

[0084] Next, the wet mixture is fed into an extrusion molding machine and extruded to produce a honeycomb molded body of a predetermined shape. In this process, a honeycomb molded body is produced using a mold that produces a cross-sectional shape having the cell structure (cell shape and cell arrangement) shown in Figure 2.

[0085] (2) The honeycomb molded body is cut to a predetermined length, dried using a microwave dryer, hot air dryer, dielectric dryer, vacuum dryer, freeze dryer, etc., and then a sealing step is performed in which a sealing paste that will serve as a sealing material is filled into predetermined cells to seal the cells. Here, the above-mentioned wet mixture can be used as the sealing paste.

[0086] (3) The honeycomb molded body is heated in a degreasing furnace to 300-650°C to remove organic matter from the honeycomb molded body in a degreasing process. The degreasing honeycomb molded body is then transported to a firing furnace and heated to 2000-2200°C in a firing process to produce a honeycomb fired body as shown in Figure 1. Furthermore, the sealing paste filled into the ends of the cell is fired by heating to become a sealant. Furthermore, the conditions for the cutting, drying, sealing, degreasing, and firing processes can be those that have been conventionally used when manufacturing honeycomb fired bodies.

[0087] (4) The honeycomb calcined body is immersed in a dispersion containing a catalyst metal and an oxide support. In this process, the end face of the honeycomb calcined body facing downwards is positioned downwards, and 20-60% of the length of the honeycomb calcined body from the end face is immersed in the dispersion liquid. By drying this immersion, the oxidation catalyst can be supported in the 20-60% region from the end face facing downwards. The first region can be formed by adjusting the content of the catalyst metal and oxide support in the above dispersion, or by performing the above immersion and drying process multiple times to support the oxidation catalyst at a concentration of 30 g / L or more in a region from 20 to 60% of the end on the exhaust gas inlet side.

[0088] The honeycomb filter of the present invention can be manufactured through the above process. In addition, although the above process describes a method for manufacturing a so-called integrated honeycomb filter consisting of a single honeycomb firing body, a so-called aggregated honeycomb filter may also be manufactured, which is formed by assembling multiple honeycomb firing bodies (honeycomb segments).

[0089] When manufacturing a composite honeycomb filter, for example, after preparing multiple honeycomb fired bodies (honeycomb segments) in step (3) above, a binding step is performed in which multiple honeycomb segments are sequentially stacked and bound together on a support base using adhesive paste to create a honeycomb aggregate made up of multiple stacked honeycomb segments, the adhesive paste is heated and solidified by heating the honeycomb aggregate to form an adhesive layer, a rectangular prism-shaped ceramic block is obtained, and then step (4) above is performed to support the oxidation catalyst.

[0090] A honeycomb filter of the present invention is also obtained by performing the above step (4) on a ceramic block obtained in the above step to form the first region.

[0091] Alternatively, in step (4) above, multiple honeycomb-fired bodies (honeycomb segments) on which the oxidation catalyst is supported may be prepared, and a binding process may be performed in which multiple honeycomb segments are sequentially stacked and bound together on a support base using adhesive paste to produce a honeycomb assembly, and the adhesive paste is heated and solidified by heating the honeycomb assembly to form an adhesive layer, thereby producing a ceramic block in which multiple honeycomb segments are stacked together.

[0092] The ceramic block obtained in the above process is also a honeycomb filter of the present invention.

[0093] As an adhesive paste, for example, one consisting of an inorganic binder, an organic binder, and inorganic particles may be used. The adhesive paste may also further contain inorganic fibers and / or whiskers. Furthermore, the adhesive paste may optionally contain balloons, which are minute hollow spheres made of oxide ceramics, spherical acrylic particles, graphite, etc.

[0094] The conditions for heating and solidifying the adhesive paste can be those conventionally used when manufacturing honeycomb filters.

[0095] Furthermore, the ceramic block obtained in the above process may be subjected to machining. Specifically, a ceramic block with a roughly cylindrical outer surface may be produced by cutting the outer surface of the ceramic block using a diamond cutter.

[0096] An outer coating layer formation process may be performed in which an outer coating paste is applied to the outer surface of a ceramic block that has been machined on its outer circumference, and the paste is dried and solidified to form an outer coating layer. The adhesive paste described above can be used as the outer perimeter coating paste. Alternatively, a paste with a different composition from the adhesive paste may be used as the outer perimeter coating paste. An outer coating layer is not always necessary; it can be added only if required. By applying an outer coating layer, the shape of the outer perimeter of the ceramic block can be adjusted to create a cylindrical honeycomb filter.

[0097] This specification discloses the following:

[0098] The present disclosure (1) is a honeycomb filter comprising: porous cell partitions that partition a plurality of cells that form a flow path for exhaust gas; an exhaust gas introduction cell having an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side; and an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, The cross-sectional shape of the exhaust gas introduction cell and the exhaust gas discharge cell perpendicular to the longitudinal direction is the same at all locations in each cell, from the end on the exhaust gas inlet side to the end on the exhaust gas outlet side, except for the sealing portion. The total volume of the exhaust gas introduction cells is greater than the total volume of the exhaust gas discharge cells. The honeycomb filter is supported with an oxidation catalyst comprising a catalytic metal and an oxide carrier that supports the catalytic metal. The honeycomb filter has a first region extending from the exhaust gas inlet end toward the exhaust gas outlet end on which the oxidation catalyst is supported at a concentration of 30 g / L or more, and a second region extending from the exhaust gas outlet end of the first region toward the exhaust gas outlet end of the honeycomb filter on which the oxidation catalyst is supported at a concentration of less than 30 g / L, or where the oxidation catalyst is not supported. The honeycomb filter is characterized in that the length of the first region in the longitudinal direction is 20 to 60% of the length of the honeycomb filter.

[0099] Disclosure (2) is the honeycomb filter according to Disclosure (1), wherein the average cross-sectional area of ​​each exhaust gas discharge cell perpendicular to the longitudinal direction is greater than the average cross-sectional area of ​​each exhaust gas inlet cell perpendicular to the longitudinal direction.

[0100] Disclosure (3) is the honeycomb filter according to Disclosure (1) or (2), wherein the concentration of the oxidation catalyst in the first region is 40 to 120 g / L.

[0101] This disclosure (4) also includes the oxidation catalyst supported in the second region, In the second region, the oxidation catalyst is present only inside the cell partition walls, and the honeycomb filter is any combination of any of (1) to (3) of this disclosure.

[0102] Disclosure (5) is a honeycomb filter in any combination of any of Disclosures (1) to (3), wherein the oxidation catalyst is not supported on the cell partitions of the second region.

[0103] This disclosure (6) describes an exhaust gas introduction cell adjacent to the exhaust gas discharge cell, separated by a cell partition wall, around the entire perimeter of the exhaust gas discharge cell. The exhaust gas introduction cell consists of two types: a first exhaust gas introduction cell and a second exhaust gas introduction cell having a cross-sectional area perpendicular to the longitudinal direction that is larger than that of the first exhaust gas introduction cell, and The cross-sectional area of ​​the exhaust gas discharge cell perpendicular to the longitudinal direction is the same as or larger than the cross-sectional area of ​​the second exhaust gas introduction cell perpendicular to the longitudinal direction. With respect to the cross-section perpendicular to the longitudinal direction, the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, the second exhaust gas introduction cell is octagonal, and the length of the side of the cross-sectional shape of the first exhaust gas introduction cell that faces the exhaust gas discharge cell is longer than the length of the side of the cross-sectional shape of the second exhaust gas introduction cell that faces the exhaust gas discharge cell, in any combination of any of (1) to (5) of this disclosure.

[0104] Disclosure (7) is a honeycomb filter used in an exhaust gas purification system in which an oxidation catalyst is not provided prior to the honeycomb filter, and is any combination of any of Disclosures (1) to (6).

[0105] [Examples] The following are examples that more specifically disclose the present invention. However, the present invention is not limited to these examples.

[0106] (Example 1) 54.6 parts by weight of coarse silicon carbide powder having an average particle size of 24 μm and 23.4 parts by weight of fine silicon carbide powder having an average particle size of 0.5 μm were mixed. To the resulting mixture, 4.4 parts by weight of an organic binder (methylcellulose), 2.6 parts by weight of a lubricant (Unilube, manufactured by NOF Corporation), 1.2 parts by weight of glycerin, and 13.8 parts by weight of water were added and kneaded to obtain a wet mixture, after which an extrusion molding process was carried out. In this process, a raw honeycomb molded body was produced that had the same shape as the honeycomb fired body 111 shown in Figures 4 and 5, but without sealing the cell gaps.

[0107] Next, the raw honeycomb molded body was dried using a microwave dryer to produce a dried honeycomb molded body. After that, sealing paste was filled into predetermined cells of the dried honeycomb molded body to seal the cells. Specifically, the cells were sealed so that the end faces on the exhaust gas inlet side and the end faces on the exhaust gas outlet side were sealed at the positions shown in Figures 4 and 5. The above-mentioned wet mixture was used as a sealing paste. After sealing the cells, the dried honeycomb molded body filled with the sealing paste was dried again using a dryer.

[0108] Next, the dried honeycomb molded body with the cell pores sealed was degreased at 400°C, and then fired at 2150°C for 3 hours under atmospheric pressure and an argon atmosphere to obtain a fired honeycomb body.

[0109] The resulting honeycomb-type calcined body had a cell wall thickness of 0.25 mm and a cell density of 46.5 cells / cm³. 2 The pressure was 300 cpsi. The shape of the honeycomb-fired body was cylindrical, with a diameter of 5.66 inches (143.8 mm) and a length of 7 inches (177.8 mm).

[0110] A catalyst dispersion (solvent: water) containing catalyst metals (Pt and Pd) and oxide support (γ-alumina) in a weight ratio of 1:100 was prepared. The process of immersing part or all of the resulting honeycomb calcined body in the dispersion and drying was repeated multiple times, and finally calcined to obtain the honeycomb filter according to Example 1, on which an oxidation catalyst consisting of catalyst metals and oxide support was supported. Table 1 shows the concentration distribution of the oxidation catalyst in the longitudinal direction of the honeycomb filter.

[0111] (Examples 2-5, Comparative Examples 1-4) By appropriately adjusting the type of catalyst metal included in the catalyst dispersion, as well as the position, depth, and number of times the catalyst dispersion is immersed, honeycomb filters according to Examples 2-5 and Comparative Examples 1-4 were obtained, having the oxidation catalyst concentration distribution shown in Table 1. In Example 5, Ag was used as the supporting catalyst metal instead of Pt and Pd compared to Example 2. In Comparative Examples 1 and 2, the amount of oxidation catalyst shown in Table 1 was uniformly supported across the entire honeycomb filter, with a front-end filter measuring 5.66 inches (143.8 mm) in diameter, 3 inches (76.2 mm) in length, 0.1 mm in wall thickness, and a cell density of 62 cells / cm³. 2 A cylindrical oxidation catalyst support (DOC) made of cordierite with a density of (400 cpsi) was used, on which the amount of oxidation catalyst shown in Table 1 was supported. In Comparative Example 3, a honeycomb filter was used in which the position of sealing the cell by the sealing portion was changed as shown in Figure 9.

[0112] Figure 9 is an enlarged view of the honeycomb filter according to Comparative Example 3, seen from the exhaust gas inlet end. As shown in Figure 9, the honeycomb filter according to Comparative Example 3 has exhaust gas introduction cells 212 and exhaust gas discharge cells 214. The shape of the exhaust gas introduction cells 212 and exhaust gas discharge cells 214 is rectangular, and the opening area is the same. Furthermore, the exhaust gas introduction cells 212 and exhaust gas discharge cells 214 are arranged alternately (in a staggered pattern), and the number of exhaust gas introduction cells 212 and exhaust gas discharge cells 214 is equal. Therefore, the total volume of the exhaust gas introduction cell 212 and the total volume of the exhaust gas discharge cell 214 become equal.

[0113] [Confirmation of oxidation catalysts in the second region] A cell partition was cut from the second region of the honeycomb filter according to Example 1, and its cross-section was observed using a scanning electron microscope (SEM). Upon confirming the location of the oxidation catalyst on the cell partition, it was found that the oxidation catalyst was not supported on the surface of the cell partition, but was present only inside.

[0114] [Measurement of pressure loss] The pressure loss of the honeycomb filters in Examples 1-5 and Comparative Examples 1-4 was measured using the pressure loss measurement method shown in Figure 10 and evaluated according to the following criteria. The results are shown in Table 1.

[0115] Figure 10 is a schematic cross-sectional view illustrating the pressure loss measurement method. Figure 10 is also a schematic diagram illustrating a pressure loss measurement method that involves actually operating a diesel engine to measure pressure loss. In this pressure loss measuring device 310, a honeycomb filter 1 is fixed inside a metal casing 313 and placed in the exhaust gas pipe 312 of a 1.6-liter diesel engine 311, and a pressure gauge 314 is attached to enable detection of the pressure before and after the honeycomb filter 1. The end of the honeycomb filter 1 on the exhaust gas inlet side is positioned closer to the exhaust gas pipe 312 of the diesel engine 311. That is, it is positioned so that exhaust gas flows into the cell with the exhaust gas inlet end open. The distance from the diesel engine 311 to the exhaust gas inlet end of the honeycomb filter 1 in this configuration was set to 4300 mm. First, the diesel engine 311 is operated at a rotational speed of 3100 rpm and a torque of 50 Nm, and the exhaust gas from the diesel engine 311 is passed through the honeycomb filter 1, collecting 8 g of PM per liter of the honeycomb filter. Then, the diesel engine 311 was operated so that the exhaust gas temperature was 500°C and the exhaust gas flow rate was 550 kg / h, and the differential pressure before and after the honeycomb filter was measured using pressure gauge 314. For Comparative Examples 1 and 2, the DOC and honeycomb filter were placed inside the metal casing 313 with the DOC on the upstream side and the honeycomb filter on the downstream side, and the same measurements were performed. The distance from the diesel engine 311 to the exhaust gas inlet end of the DOC was set to 4300 mm, and the distance between the DOC and the honeycomb filter was set to 50 mm. ○: Pressure loss is 35kPa or less. ×: Pressure loss exceeds 35 kPa.

[0116] [Measurement of HC and CO purification performance] The HC and CO purification performance of the honeycomb filters in Examples 1-5 and Comparative Examples 1-4 was measured using the method described below. The results are shown in Table 1.

[0117] Similar to the pressure loss measurement, a honeycomb filter was fixed inside a metal casing and placed in the exhaust pipe of a 1.6-liter diesel engine. The concentrations of HC and CO in the exhaust gas before and after the honeycomb filter were measured using an engine exhaust gas measuring device (Horiba MEXA-7500DEGR). The distance from the diesel engine to the exhaust gas inlet end of the honeycomb filter was set to 1300 mm. The diesel engine was operated under the following conditions: rotational speed of 2500 rpm and torque of 120 Nm. The filter was run until the temperature of the exhaust gas inlet end of the honeycomb filter reached 360°C, and the following criteria were used for evaluation. ○: The temperature at which HC purification is 60% and the temperature at which CO purification is 90% are both 260°C or lower. △: Either the temperature at which HC purification rate is 60% or the temperature at which CO purification rate is 90% is 260°C or lower, while the other is 260°C or higher. ×: The temperature at which HC purification is 60% and the temperature at which CO purification is 90% both exceed 260°C. For Comparative Examples 1 and 2, measurements were taken with the DOC placed before the honeycomb filter. The distance from the diesel engine to the exhaust gas inlet end of the DOC was set to 1300 mm, and the distance between the DOC and the honeycomb filter was set to 50 mm.

[0118] [Table 1]

[0119] The results in Table 1 show that the honeycomb filters in Examples 1 to 5 exhibit excellent HC and CO purification efficiency and low pressure loss, even when DOC is not placed in the preceding stage. The results from Comparative Examples 1 and 2 showed that while sufficient exhaust gas purification performance can be achieved when a DOC with approximately the same amount of oxidation catalyst as in Example 1 is placed in the preceding stage, the exhaust gas purification device becomes larger and pressure loss increases. The results of Comparative Example 3 showed that when the same amount of oxidation catalyst as in Example 1 was uniformly arranged in the longitudinal direction of a honeycomb filter with the same total volume for both the exhaust gas inlet cell and the exhaust gas outlet cell, the pressure loss increased and the purification efficiency of HC and CO decreased. This is presumed to be because the velocity of the exhaust gas flowing into the honeycomb filter was high, resulting in poor contact between the oxidation catalyst supported in the first region and the exhaust gas, thus reducing the exhaust gas purification performance, and also because a thick layer of PM accumulated on the cell partitions of the honeycomb filter, leading to increased pressure loss. The results from Comparative Example 4 show that when the first region of the honeycomb filter was made longer than 60%, the pressure loss increased because the first region on which the oxidation catalyst was supported was too long. [Explanation of Symbols]

[0120] 1, 2, 3 Honeycomb filters 11, 111 Honeycomb fired body 11a, 111a End of honeycomb calcined body on the exhaust gas inlet side 11b, 111b End of honeycomb calcined body on the exhaust gas discharge side 12, 112 Exhaust gas introduction cell (1st exhaust gas introduction cell) 13, 113 Exhaust gas introduction cell (2nd exhaust gas introduction cell) 212 Exhaust gas injection cells 14, 114, 214 exhaust gas emission cells 15, 115, 215 sealing material 20, 120, 220 cell partitions 21, 121 Cell 1 partition 22, 122 Second cell partition 123 Third cell partition 30, 31, 32 Honeycomb fired body (honeycomb segment) 31a, 32a End of honeycomb calcined body (honeycomb segment) on the exhaust gas inlet side 31b, 32b End of honeycomb calcined body (honeycomb segment) on the exhaust gas outlet side 50 adhesive layer 60 ceramic blocks 70 Outer coating layer 310 Pressure loss measuring device 311 Diesel engine 312 Exhaust pipe 313 Metal casing 314 Pressure Gauge A1 1st area A2 2nd area

Claims

1. A honeycomb filter comprising: porous cell partitions that divide and form multiple cells that serve as exhaust gas flow paths; an exhaust gas introduction cell having an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side; and an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, The cross-sectional shape of the exhaust gas introduction cell and the exhaust gas discharge cell perpendicular to the longitudinal direction is the same at all locations in each cell, from the end on the exhaust gas inlet side to the end on the exhaust gas outlet side, except for the sealing portion. The total volume of the exhaust gas introduction cells is greater than the total volume of the exhaust gas discharge cells. The honeycomb filter is supported with an oxidation catalyst comprising a catalytic metal and an oxide carrier that supports the catalytic metal. The honeycomb filter has a first region extending from the exhaust gas inlet end toward the exhaust gas outlet end on which the oxidation catalyst is supported at a concentration of 30 g / L or more, and a second region extending from the exhaust gas outlet end of the first region toward the exhaust gas outlet end of the honeycomb filter on which the oxidation catalyst is supported at a concentration of less than 30 g / L, or where the oxidation catalyst is not supported. A honeycomb filter characterized in that the length of the first region in the longitudinal direction is 20 to 60% of the length of the honeycomb filter.

2. The honeycomb filter according to claim 1, wherein the average cross-sectional area of ​​each exhaust gas discharge cell perpendicular to the longitudinal direction is greater than the average cross-sectional area of ​​each exhaust gas introduction cell perpendicular to the longitudinal direction.

3. The honeycomb filter according to claim 1 or 2, wherein the concentration of the oxidation catalyst in the first region is 40 to 120 g / L.

4. The oxidation catalyst is also supported in the second region, The honeycomb filter according to claim 1 or 2, wherein in the second region, the oxidation catalyst is present only inside the cell partition wall.

5. The honeycomb filter according to claim 1 or 2, wherein the oxidation catalyst is not supported on the cell partition wall of the second region.

6. The exhaust gas introduction cells are arranged adjacent to the exhaust gas discharge cell, separated by the cell partition wall, The exhaust gas introduction cell consists of two types: a first exhaust gas introduction cell and a second exhaust gas introduction cell having a cross-sectional area perpendicular to the longitudinal direction that is larger than that of the first exhaust gas introduction cell, and The cross-sectional area of ​​the exhaust gas discharge cell perpendicular to the longitudinal direction is the same as or larger than the cross-sectional area of ​​the second exhaust gas introduction cell perpendicular to the longitudinal direction. With respect to the cross-section perpendicular to the longitudinal direction, the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, the second exhaust gas introduction cell is octagonal, and the length of the side of the cross-sectional shape of the first exhaust gas introduction cell that faces the exhaust gas discharge cell is longer than the length of the side of the cross-sectional shape of the second exhaust gas introduction cell that faces the exhaust gas discharge cell.

7. A honeycomb filter according to claim 1 or 2, used in an exhaust gas purification system in which an oxidation catalyst is not provided prior to the honeycomb filter.

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