JP2014198316A - Honeycomb structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a honeycomb structure capable of achieving both functions as a particulate collection filter and a carrier for an SCR (Selective Catalytic Reduction) catalyst.SOLUTION: The honeycomb structure includes: a honeycomb structure portion having porous partitioning walls 5 partitioning and forming a plurality of cells extending from inlet end surface to outlet end surface; and a plugged portion plugging open end parts on the outlet end surface side of predetermined cells and open end parts on the inlet end surface side of remaining cells of the honeycomb structure portion. The honeycomb structure is configured in such a way that: an exhaust gas flowed in from the inlet end surface into the cells permeates through partitioning walls 5 and then outflows from the outlet end surface to outside of the cells; and when p denotes a porosity of a region 5a defined from a surface 8a of, of the total partitioning walls 5, a partitioning wall 5 that functions as an inlet side of exhaust gas permeating through partitioning wall 5, to depth t, and P denotes a porosity of a remaining region 5b of partitioning wall 5, t is 50 to 100 μm, p is smaller than P and is 25 to 45%.

Description

  The present invention is used as a particulate collection filter for collecting particulate matter contained in an exhaust gas discharged from an internal combustion engine such as a diesel engine or various combustion apparatuses, and at the same time, supports an SCR catalyst. The present invention also relates to a honeycomb structure that is also used as a carrier.

  An exhaust gas discharged from an internal combustion engine such as a diesel engine or various combustion apparatuses contains a large amount of particulate matter (particulate matter (PM)) mainly composed of carbon fine particles such as soot (soot). When this PM is released into the atmosphere as it is, environmental pollution is caused. Therefore, an exhaust gas flow path from an internal combustion engine or the like is generally equipped with a particulate collection filter for collecting PM. .

  As a particulate collection filter for collecting PM, a wall flow type filter using a honeycomb structure is widely used. The honeycomb structure includes a porous partition wall that defines a plurality of cells extending from an inlet end surface serving as an exhaust gas inlet side to an outlet end surface serving as an exhaust gas outlet side, an opening end portion on an outlet end surface side of a predetermined cell, and A plugging portion for plugging the opening end portion on the inlet end face side of the remaining cell.

  The particulate collection filter using such a honeycomb structure has a structure in which exhaust gas flowing into the cell from the inlet end face passes through the partition wall and then flows out of the cell from the outlet end face. And when exhaust gas permeate | transmits a partition, a partition functions as a filtration layer and PM contained in exhaust gas is collected.

  In recent years, regulations on harmful substances in automobile exhaust gas tend to be tightened worldwide. Under such a background, as an exhaust gas treatment technique, a diesel oxidation catalyst (DOC catalyst), a selective reduction catalyst (SCR catalyst), in addition to the particulate collection filter (for example, diesel particulate filter (DPF)) as described above. Etc. are also being developed. For example, a recent diesel engine automobile exhaust gas purification device includes a device provided with a DPF and an SCR catalyst (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2007-21422

  However, in the exhaust gas purification device described in Patent Document 1, it is necessary to provide a carrier supporting the SCR catalyst and a carrier constituting the DPF (that is, a honeycomb structure for DPF) in one exhaust gas purification device. There is a large exhaust gas purification device. For this reason, there has been a problem that vehicle types that can be equipped with such an exhaust gas purification device are limited. For example, it is extremely difficult for the exhaust gas purification apparatus described in Patent Document 1 to secure a mounting space for a passenger car of a general size. Further, if the number of carriers increases, the exhaust resistance (pressure loss) increases accordingly, which causes a problem of deterioration of fuel consumption.

  Therefore, in order to solve such a problem, it has been studied that one honeycomb structure can be used as a carrier for supporting an SCR catalyst at the same time as being used as a particulate collection filter. However, it has been practically difficult to achieve both the function as the particulate collection filter and the function as the carrier of the SCR catalyst with one honeycomb structure for the following reasons.

  In order to continuously use a particulate collection filter such as DPF for a long period of time, it is necessary to periodically regenerate the filter. That is, in order to reduce the pressure loss increased by the PM accumulated with time in the filter and return the filter performance to the initial state, it is necessary to burn and remove the PM accumulated in the filter with a high-temperature gas. During this regeneration process, the honeycomb structure used for the particulate collection filter becomes high temperature due to combustion of the deposited PM, but the SCR catalyst has low heat durability, so it is supported on such a high temperature honeycomb structure. As a result, thermal deterioration occurs and sufficient catalytic performance cannot be exhibited.

  The present invention has been made in view of such circumstances, and the object of the present invention is to effectively suppress thermal degradation of the SCR catalyst, function as a particulate collection filter, and as a carrier for the SCR catalyst. An object of the present invention is to provide a honeycomb structure capable of achieving both functions.

  In order to achieve the above object, according to the present invention, the following honeycomb structure is provided.

[1] A honeycomb structure part having a porous partition wall that defines a plurality of cells extending from an inlet end face that is an exhaust gas inlet side to an outlet end face that is an exhaust gas outlet side, and the predetermined cells of the honeycomb structure part An opening end on the outlet end surface side and a plugging portion for plugging the opening end on the inlet end surface side of the remaining cells, and the exhaust gas flowing into the cell from the inlet end surface permeates the partition wall. After that, a honeycomb structure that flows out of the cell from the outlet end face, and in the entire partition wall, pores in a portion from the surface of the partition wall to the thickness t which becomes the inlet side of the exhaust gas that permeates the partition wall A honeycomb structure in which t is 50 to 100 μm, p is smaller than P, and p is 25 to 45%, where p is the rate and P is the porosity of the remaining part of the partition wall.

[2] The honeycomb structure according to [1], wherein p is 30 to 45%.

[3] When the average pore diameter of the pores existing at the site from the surface of the partition wall to the thickness t on the inlet side of the exhaust gas that permeates the partition wall is r, r is 10 μm or less [1] or The honeycomb structure according to [2].

[4] The honeycomb structure according to any one of [1] to [3], wherein R is less than 30 μm, where R is an average pore diameter of pores existing in the remaining portions of the partition walls.

[5] The honeycomb structure according to any one of [1] to [4], wherein a ratio of t to T is 4 to 40%, where T is a thickness of the entire partition wall.

[6] The honeycomb structure according to any one of [1] to [5], wherein an SCR catalyst is supported on a surface of the partition wall which is an outlet side of the exhaust gas that passes through the partition wall.

  The honeycomb structure of the present invention is configured such that the porosity of a portion from the surface of the partition wall on the inlet side of the exhaust gas that permeates the partition wall to a predetermined thickness is smaller than the remaining porosity of the partition wall in the entire partition wall Has been. Thus, by making only the porosity of the specific part where PM is collected in the whole partition smaller than the porosity of the remaining part, the whole partition can have high exhaust gas permeability. it can. For this reason, it is possible to suppress an increase in pressure loss when PM is deposited on the surface of the partition wall on the inlet side of the exhaust gas that passes through the partition wall. Further, since PM deposits on the surface of the partition wall on the inlet side of the exhaust gas that permeates the partition wall, the SCR catalyst is formed on the opposite surface, that is, on the surface of the partition wall on the outlet side of the exhaust gas that permeates the partition wall. Is deposited, the deposited PM and the supported SCR catalyst are separated from each other through the partition walls. Furthermore, the portion from the surface of the partition wall to the predetermined thickness on the inlet side of the exhaust gas that permeates the partition wall has a low porosity, that is, a large heat capacity, so that the heat generated when the deposited PM is burned by the regeneration process is reduced. , It is absorbed by the part, and the temperature rise of the remaining part is suppressed. Therefore, even if the accumulated PM is combusted by the regeneration process, heat due to the combustion is not easily transmitted to the SCR catalyst, and thermal degradation of the SCR catalyst is effectively suppressed. By having these effects, the honeycomb structure of the present invention can achieve both a function as a particulate collection filter and a function as a carrier of an SCR catalyst. For this reason, it is possible to combine the particulate collection filter and the SCR catalyst into one honeycomb structure, and as a result, it is difficult to downsize the exhaust gas purification device and secure a mounting space for the device conventionally. The apparatus can be mounted on a passenger car or the like.

1 is a schematic perspective view schematically showing an example of an embodiment of a honeycomb structure according to the present invention. 1 is a schematic cross-sectional view schematically showing an example of an embodiment of a honeycomb structure according to the present invention. FIG. 3 is a schematic enlarged view showing a portion surrounded by a dotted line in FIG. 2 in an enlarged manner. It is explanatory drawing which shows an example of the manufacturing method of the honeycomb structure which concerns on this invention. It is explanatory drawing which shows an example of the manufacturing method of the honeycomb structure which concerns on this invention. It is explanatory drawing which shows an example of the manufacturing method of the honeycomb structure which concerns on this invention. It is explanatory drawing which shows an example of the manufacturing method of the honeycomb structure which concerns on this invention.

  Hereinafter, the present invention will be described based on specific embodiments, but the present invention should not be construed as being limited thereto, and based on the knowledge of those skilled in the art without departing from the scope of the present invention. Various changes, modifications, and improvements can be added.

(1) Honeycomb structure:
FIG. 1 is a schematic perspective view schematically illustrating an example of an embodiment of a honeycomb structure according to the present invention, and FIG. 2 is a schematic cross-sectional view schematically illustrating an example of an embodiment of a honeycomb structure according to the present invention. FIG. 3 is a schematic enlarged view showing an enlarged portion surrounded by a dotted line in FIG. FIG. 3 shows a state in which the SCR catalyst is supported on one surface of the partition walls of the honeycomb structure and PM is deposited on the other surface of the partition walls.

  As shown in FIGS. 1 and 2, a honeycomb structure 1 according to the present invention includes a honeycomb structure portion 2 and a plugging portion 3. The honeycomb structure part 2 has a porous partition wall 5 that partitions and forms a plurality of cells 4 extending from an inlet end face 6 on the exhaust gas inlet side to an outlet end face 7 on the exhaust gas outlet side. Further, the plugging portion 3 plugs the opening end portion on the outlet end surface 7 side of the predetermined cell 4a of the honeycomb structure portion 2 and the opening end portion on the inlet end surface 6 side of the remaining cells 4b. The plugging portion 3 is preferably arranged so that the inlet end surface 6 and the outlet end surface 7 of the honeycomb structure portion 2 have a complementary checkered pattern.

  The honeycomb structure 1 according to the present invention includes the honeycomb structure portion 2 and the plugging portion 3 as described above, so that the exhaust gas G flowing into the cell 4 from the inlet end surface 6 passes through the partition walls 5. It has a structure that flows out of the cell 4 from the outlet end face 7. That is, the exhaust gas G containing PM first flows into a predetermined cell 4a in which the opening end is not plugged on the inlet end face 6 side and the opening end is plugged on the outlet end face 7 side. To do. Next, the exhaust gas G that has flowed into the predetermined cell 4a passes through the porous partition wall 5, and the opening end is plugged on the inlet end face 6 side, and the opening end is plugged on the outlet end face 7 side. It moves into the remaining cells 4b that are not stopped. When the exhaust gas G passes through the porous partition walls 5, the partition walls 5 become filtration layers, and PM in the exhaust gas G is captured by the partition walls 5 and deposited on the partition walls 5. Thus, the exhaust gas G from which PM has been removed and moved to the remaining cell 4b flows out of the remaining cell 4b from the outlet end face 7 thereafter.

  The partition wall 5 serving as a filtration layer has two surfaces which are in a relationship of back and front. One of these two surfaces is the surface of the partition wall (hereinafter referred to as “inlet-side partition wall surface”) 8 a on the inlet side of the exhaust gas that permeates the partition wall 5, and the other is the exhaust gas that permeates the partition wall 5. 8b is a surface of the partition wall (hereinafter referred to as “exit-side partition wall surface”) 8b. As shown in FIG. 3, PM10 in the exhaust gas captured by the partition walls 5 is deposited on the inlet-side partition wall surface 8a.

  In the honeycomb structure 1 according to the present invention, the porosity of the part 5a from the inlet side partition wall surface 8a to the thickness t in the entire partition wall 5 is p, and the porosity of the remaining part 5b of the partition wall is P. When p is smaller than P. The porosity of each part of the partition wall can be obtained by taking a scanning electron microscope (SEM) photograph of the section of the partition wall and using commercially available image analysis software (“Image Pro Plus” manufactured by Media Cybernetics). it can. Specifically, the SEM photograph of the cross section of the partition wall is bipolarized with the image analysis software, and the areas of the partition wall portions (substance portions other than the pores) and the pore portions (pore portions) of each part are measured, The porosity of each part is calculated from these measured values.

  Thus, by making only the porosity of the part 5a from the inlet-side partition surface 8a where the PM 10 is collected to a predetermined thickness out of the whole partition 5 to be smaller than the porosity of the remaining part 5b, the partition 5 As a whole, high exhaust gas permeability can be provided. For this reason, it is possible to suppress an increase in pressure loss when PM10 is deposited on the inlet side partition wall surface 8a.

  Further, since PM10 is deposited on the inlet side partition wall surface 8a, if the SCR catalyst 9 is supported on the opposite surface, that is, the outlet side partition wall surface 8b, the deposited PM10 and the supported SCR catalyst are supported. 9 are separated from each other through the partition wall 5. Furthermore, since the portion 5a from the inlet-side partition wall surface 8a to the predetermined thickness has a low porosity, that is, a large heat capacity, the heat generated when the deposited PM10 is burned by the regeneration treatment is absorbed by the portion, The temperature rise of the remaining part 5b is suppressed. Therefore, even if the accumulated PM 10 is burned by the regeneration process, the heat due to the combustion is not easily transmitted to the SCR catalyst 9, and the thermal degradation of the SCR catalyst 9 is effectively suppressed.

  By having these effects, the honeycomb structure 1 according to the present invention can achieve both a function as a particulate collection filter such as PDF and a function as a carrier of an SCR catalyst. For this reason, it is possible to combine the particulate collection filter and the SCR catalyst into one honeycomb structure, and as a result, it is difficult to downsize the exhaust gas purification device and secure a mounting space for the device conventionally. The apparatus can be mounted on a passenger car or the like.

  In the honeycomb structure 1 according to the present invention, t is 50 to 100 μm, preferably 50 to 90 μm. When t is less than 50 μm, the thermal degradation of the SCR catalyst 9 supported on the outlet-side partition wall surface 8b cannot be sufficiently suppressed during the regeneration process, and the purification performance of the SCR catalyst 9 after the regeneration process is greatly reduced. On the other hand, if t exceeds 100 μm, an increase in pressure loss when PM10 is deposited on the inlet-side partition wall surface 8a cannot be sufficiently suppressed, and a necessary strength cannot be obtained.

  Further, in the honeycomb structure 1 according to the present invention, p is 25 to 45%, preferably 30 to 45%. If p is less than 25% or more than 45%, it may not be possible to sufficiently suppress an increase in pressure loss when PM10 is deposited on the inlet-side partition wall surface 8a. Furthermore, if p exceeds 45%, the thermal degradation of the SCR catalyst 9 supported on the outlet-side partition wall surface 8b cannot be sufficiently suppressed during the regeneration process, and the purification performance of the SCR catalyst 9 after the regeneration process is large. In addition to the decrease, the required strength cannot be obtained.

  In the honeycomb structure 1 according to the present invention, when the average pore diameter of the pores 11 existing in the portion 5a from the inlet side partition wall surface 8a to the thickness t is r, r may be 10 μm or less. Preferably, it is 8 μm or less. If r exceeds 10 μm, an increase in pressure loss when PM10 is deposited on the inlet-side partition wall surface 8a may not be sufficiently suppressed.

  Furthermore, in the honeycomb structure 1 according to the present invention, the average pore diameter of the pores 12 existing in the remaining part (part excluding the part 5a from the inlet side partition wall surface to the thickness t) 5b is R. , R is preferably less than 30 μm, more preferably less than 25 μm. If R is 30 μm or more, the required strength may not be obtained.

  The average pore diameter of the pores present in each part of the partition wall is obtained by taking a scanning electron microscope (SEM) photograph of the partition wall cross section and using commercially available image analysis software (“Image Pro Plus” manufactured by Media Cybernetics). It can be determined by using. Specifically, the SEM photograph of the partition wall cross section is bipolarized with the image analysis software, the diameters of the pores (pores) existing in each part are measured, and the average value is calculated.

  In the honeycomb structure 1 according to the present invention, when the thickness of the entire partition wall 5 is T, the ratio of t to T is preferably 4 to 40%, and more preferably 15 to 35%. If the ratio of t to T is less than 4%, the thermal degradation of the SCR catalyst 9 supported on the outlet-side partition wall surface 8b cannot be sufficiently suppressed, and the purification performance by the SCR catalyst 9 after the regeneration treatment may be greatly reduced. . On the other hand, if the ratio of t to T exceeds 40%, the increase in pressure loss when PM10 is deposited on the inlet side partition wall surface 8a cannot be sufficiently suppressed, or the required strength cannot be obtained. There is a case.

  In the honeycomb structure 1 according to the present invention, T is preferably 150 to 460 μm, and more preferably 200 to 350 μm. If T is less than 150 μm, the thermal degradation of the SCR catalyst 9 carried on the outlet side partition wall surface 8b cannot be sufficiently suppressed during the regeneration process, and the purification performance by the SCR catalyst 9 after the regeneration process may be greatly reduced. is there. On the other hand, if T exceeds 460 μm, an excessive increase in pressure loss may occur.

  The honeycomb structure according to the present invention has both a function as a particulate collection filter and a function as a carrier of the SCR catalyst by supporting the SCR catalyst. In obtaining such a honeycomb structure, as shown in FIG. 3, the SCR catalyst 9 is supported on the outlet-side partition wall surface 8b. As described above, PM10 is deposited on the inlet side partition wall surface 8a. Therefore, if the SCR catalyst 9 is supported on the outlet side partition wall surface 8b opposite to the PM10, the deposited PM10 and the supported SCR catalyst are supported. 9 are separated from each other through the partition wall 5. As a result, even if the accumulated PM 10 is combusted by the regeneration process, the heat due to the combustion becomes difficult to be transmitted to the SCR catalyst 9, and thermal degradation of the SCR catalyst 9 is effectively suppressed.

Note that “SCR” is an abbreviation for “Selective Catalytic Reduction: Selective Catalyst Reduction”, and “SCR catalyst” means a catalyst (selective reduction catalyst) that selectively reduces a component to be purified by a reduction reaction. . Examples of the SCR catalyst for exhaust gas purification include a catalyst that selectively reduces nitrogen oxide (NO _x ).

  Examples of the substance that becomes the SCR catalyst include metal-substituted zeolite. Examples of the metal that replaces zeolite with metal include iron (Fe) and copper (Cu). As a zeolite, a beta zeolite can be mentioned as a suitable example.

  In addition, the SCR catalyst may be a catalyst containing at least one selected from the group consisting of vanadium and titania as a main component. The content of vanadium and titania in the SCR catalyst is preferably 60% by mass or more.

  The amount of the SCR catalyst supported is not particularly limited, but if the amount supported is too small, sufficient purification performance may not be obtained. Therefore, the amount supported per unit volume of the honeycomb structure is 200 g / liter or more. Preferably there is. However, if the loading amount is too large, the pressure loss of the honeycomb structure may increase excessively, so the upper limit of the loading amount is preferably about 400 g / liter.

  In the honeycomb structure according to the present invention, the average pore diameter of the entire partition walls 5 is preferably 10 to 25 μm, and more preferably 10 to 20 μm. If the average pore diameter of the entire partition wall 5 is less than 10 μm, the pressure loss may increase excessively. Moreover, when the average pore diameter of the partition walls 5 as a whole exceeds 25 μm, PM collection efficiency may deteriorate and it may be difficult to obtain the required strength.

  Moreover, in the honeycomb structure 1 according to the present invention, the porosity of the entire partition walls 5 is preferably 40 to 75%, and more preferably 50 to 65%. If the porosity of the entire partition wall 5 is less than 40%, an excessive increase in pressure loss may occur. Moreover, when the porosity of the whole partition 5 exceeds 75%, it may be difficult to obtain a required strength.

In the honeycomb structure 1 according to the present invention, the cell density is not particularly limited, but is preferably 15 to 80 cells / cm ² , and more preferably 30 to 65 cells / cm ² . When the cell density is less than 15 cells / cm ² , the area of the partition for collecting PM becomes small, and when the exhaust gas is circulated, the pressure loss may increase in a short time. On the other hand, when the cell density is larger than 80 cells / cm ² , the cell cross-sectional area (area of the cross section perpendicular to the cell extending direction) is decreased, and thus the pressure loss may be increased.

  The shape of the honeycomb structure 1 according to the present invention is not particularly limited. For example, the end surface is a cylindrical tube (cylindrical shape), the end surface is an oval tube, the end surface is a polygon (square, pentagon, hexagon, seven The shape may be a cylindrical shape such as a square or an octagon. The cell shape (cell shape in a cross section perpendicular to the cell extending direction) is not particularly limited, but is preferably a polygon such as a quadrangle, hexagon, or octagon.

  In the honeycomb structure 1 according to the present invention, the material for forming the honeycomb structure portion 2 is not particularly limited, but ceramic is preferable. In particular, because of its excellent strength and heat resistance, it is selected from the group consisting of cordierite, silicon carbide, silicon-silicon carbide based composite material, mullite, alumina, aluminum titanate, silicon nitride, and silicon carbide-cordierite based composite material At least one ceramic material can be suitably used.

  In the honeycomb structure 1 according to the present invention, it is preferable to use the same material as the material for forming the honeycomb structure 2 as the material for forming the plugged portions 3. By doing so, the thermal expansion difference between the partition walls 5 and the plugging portions 3 can be reduced, and the thermal stress generated between the partition walls 5 and the plugging portions 3 can be reduced.

  The honeycomb structure according to the present invention is used as a particulate collection filter for collecting PM contained in an exhaust gas discharged from an internal combustion engine such as a diesel engine or various combustion apparatuses, and at the same time carries an SCR catalyst. It can also be used as a carrier for

(2) Manufacturing method of honeycomb structure:
Hereinafter, an example of a method for manufacturing a honeycomb structure according to the present invention will be described. First, a forming raw material containing a ceramic raw material is mixed and kneaded to obtain a clay. The ceramic raw material is selected from the group consisting of cordierite forming raw material, cordierite, silicon carbide, silicon-silicon carbide based composite material, mullite, alumina, aluminum titanate, silicon nitride, and silicon carbide-cordierite based composite material. At least one of these is preferred. The cordierite forming raw material is a raw material that becomes cordierite by being fired. Specifically, silica is 42 to 56% by mass, alumina is 30 to 45% by mass, and magnesia is 12 to 16%. It is a raw material blended to have a chemical composition that falls within the range of mass%.

  The forming raw material is preferably prepared by mixing the ceramic raw material with a dispersion medium, a sintering aid, an organic binder, a surfactant, a pore former, and the like.

  It is preferable to use water as the dispersion medium. The content of the dispersion medium is appropriately adjusted so that the clay obtained by kneading the molding raw material has a hardness that facilitates molding. The specific content of the dispersion medium is preferably 20 to 80% by mass with respect to the entire forming raw material.

  As a sintering aid, for example, yttria, magnesia, strontium oxide and the like can be used. The content of the sintering aid is preferably 0.1 to 0.3% by mass with respect to the entire forming raw material.

  Examples of the organic binder include methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The content of the binder is preferably 2 to 10% by mass with respect to the entire forming raw material.

  As the surfactant, ethylene glycol, dextrin, fatty acid soap, polyalcohol and the like can be used. These may be used individually by 1 type and may be used in combination of 2 or more type. The content of the surfactant is preferably 2% by mass or less with respect to the whole forming raw material.

  The pore former is not particularly limited as long as it becomes pores after firing, and examples thereof include graphite, starch, foamed resin, hollow resin, water absorbent resin, and silica gel. The pore former content is preferably 10% by mass or less based on the entire forming raw material. The average particle size of the pore former contained in the forming raw material is preferably less than 65 μm, and more preferably less than 30 μm. If the average particle diameter of the pore former contained in the forming raw material is less than 30 μm, R can be a preferable value of less than 30 μm. However, if the average particle diameter of the pore former contained in the forming raw material is less than 10 μm, pores may not be sufficiently formed. Therefore, the lower limit of the average particle diameter is preferably 10 μm.

  Next, the forming raw material is kneaded to form a clay. There is no restriction | limiting in particular as a method of kneading | mixing a shaping | molding raw material and forming a clay, For example, the method of using a kneader, a vacuum clay kneader, etc. can be mentioned.

  Next, the obtained kneaded material is formed to form a honeycomb formed body. The honeycomb formed body is a formed body having partition walls that partition and form a plurality of cells that serve as exhaust gas flow paths. A method for forming a kneaded clay to form a honeycomb formed body is not particularly limited, and a known forming method such as extrusion molding or injection molding can be used. For example, a preferable example includes a method of extrusion molding using a die having a desired cell shape, partition wall thickness, and cell density. As the material of the die, a cemented carbide which does not easily wear is preferable.

  The honeycomb formed body thus obtained is dried and then fired. Examples of the drying method include hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, and the like. Among them, it is preferable to perform dielectric drying, microwave drying, or hot air drying alone or in combination.

  The dried honeycomb formed body is preferably calcined before firing (main firing). Calcination is performed for degreasing. There is no restriction | limiting in particular about the method of calcination. For example, it is sufficient that at least a part of the organic matter in the honeycomb formed body can be removed. Examples of the organic material include an organic binder, a surfactant, and a pore former. The combustion temperature of the organic binder is about 100 to 300 ° C. For this reason, calcination is preferably performed at about 200 to 1000 ° C. for about 10 to 100 hours in an oxidizing atmosphere.

  The firing (main firing) of the honeycomb formed body is performed to sinter and densify the forming raw material constituting the calcined honeycomb formed body to ensure a predetermined strength. Since the firing conditions differ depending on the type of molding raw material, appropriate conditions may be selected according to the type. For example, when the cordierite forming raw material is used, the firing temperature is preferably 1350 to 1440 ° C. In addition, the firing time is preferably 3 to 10 hours as the keep time at the maximum temperature. Examples of the apparatus for performing calcination and main firing include an electric furnace and a gas furnace.

  Subsequently, plugged portions are formed in the fired honeycomb formed body (honeycomb fired body). A conventionally known method can be used to form the plugged portion. As an example of a specific method, first, a sheet is attached to the end face of the honeycomb fired body manufactured by the above method. Next, a hole is made in the sheet at a position corresponding to the cell in which the plugging portion is to be formed. Next, with the sheet attached, the end face of the honeycomb fired body is immersed in a plugging slurry in which the plugging portion forming material is slurried, and the plugs are sealed through the holes formed in the sheet. The plugging slurry is filled into the open end of the cell to be stopped. The plugging slurry thus filled is dried and then fired and cured to form a plugged portion. The plugged portions are preferably formed in such an arrangement that both end faces of the honeycomb fired body have a complementary checkerboard pattern. Moreover, it is preferable to use the same material as the forming material of the honeycomb fired body as the forming material of the plugging portion. The plugging portion may be formed at a stage after drying the honeycomb formed body and before calcination (degreasing) or before firing (main firing). FIG. 4A is a schematic cross-sectional view schematically showing a part of the honeycomb fired body 13 in which the plugging portions 3 are thus formed. At this time, the average pore diameter and porosity of the partition walls 5 are almost uniform throughout the partition walls 5.

  Next, a part having a lower porosity than the remaining part of the partition is formed in a part of the partition (part from the entrance-side partition surface to a predetermined thickness). Specifically, as shown in FIG. 4B, in one end face of the honeycomb fired body 13 (the end face that finally becomes the inlet end face), the inside of a predetermined cell 4a that is open without being plugged is formed. In addition, a sol-like raw material 14 for forming a portion having a low porosity is filled. The sol-like raw material 14 is prepared by mixing a ceramic raw material with a dispersion medium, a sintering aid, an organic binder, a surfactant, a pore former, and the like, similarly to the molding raw material. However, the volume ratio of the pore former contained in the sol raw material 14 to the ceramic raw material is smaller than the volume ratio of the pore former contained in the forming raw material to the ceramic raw material. The volume ratio of the pore former contained in the sol raw material 14 to the ceramic raw material is preferably 25 to 45%, and more preferably 30 to 45%. By setting the volume ratio of the pore former contained in the sol-like raw material 14 to the ceramic raw material in such a range, p can be made 25 to 45%. Further, the average particle diameter of the pore former contained in the sol-like raw material 14 is preferably 10 μm or less, and more preferably 8 μm or less. If the average particle diameter of the pore former contained in the sol raw material 14 is 10 μm or less, r can be set to a preferable value of 10 μm or less. However, if the average particle diameter of the pore former contained in the sol-like raw material 14 is less than 4 μm, pores may not be sufficiently formed, so the lower limit of the average particle diameter is preferably 4 μm.

  Next, as shown in FIG. 4C, a rod-like instrument 15 is inserted into the predetermined cell 4a filled with the sol-like raw material 14, and the excess sol-like raw material is removed from the cell 4a and remains in the cell 4a. The sol-like raw material 14 is dried and solidified. It is preferable that the rod-shaped instrument 15 has a cross-sectional shape perpendicular to the length direction that is the same as the cell shape. Further, when the rod-shaped device 15 is inserted into the cell so that the center of the cross section coincides with the center of the cell cross section, the gap between the rod-shaped device 15 and the partition wall 5 of the honeycomb fired body 13 is 50 to 100 μm. It is preferable to have a cross-sectional dimension such that By using such a rod-shaped instrument 15, t can be set to 50 to 100 μm.

  Thus, as shown in FIG. 4D, after forming a layer made of the sol-like raw material 14 on the surface of the partition wall exposed in the predetermined cells 4a of the honeycomb fired body 13, the honeycomb fired body 13 is fired again, The layer made of the sol-like raw material 14 is integrated with the honeycomb fired body.

  By such a manufacturing method, the honeycomb structure of the present invention in which t is 50 to 100 μm, p is smaller than P, and p is 25 to 45% can be obtained.

(3) SCR catalyst loading method:
Next, an example of a method for supporting the SCR catalyst on the honeycomb structure manufactured as described above will be described. First, a catalyst slurry containing an SCR catalyst is prepared. The catalyst slurry is coated on the outlet side partition wall surface of the honeycomb structure. The coating method is not particularly limited. For example, in the cell in which the outlet side partition wall surface of the honeycomb structure is exposed (the cell in which the plugging portion is formed on the inlet end face side of the honeycomb structure), the catalyst is used. A suitable coating method is a method in which slurry is introduced and sucked from the inlet end face side of the honeycomb structure. The catalyst slurry coated on the outlet side partition wall in this way covers the outlet side partition wall surface, and a part of the catalyst slurry is filled in pores existing in the vicinity of the outlet side partition wall surface.

  The viscosity of the catalyst slurry is preferably 8 mPa · s or less, more preferably 5 to 7 mPa · s, and particularly preferably 6 to 7 mPa · s. The viscosity of the catalyst slurry can be controlled by adjusting the ratio of moisture in the catalyst slurry. The particle diameter of the SCR catalyst contained in the catalyst slurry is preferably 10 μm or less, more preferably 3 to 5 μm, and particularly preferably 4 to 5 μm. By setting the viscosity of the catalyst slurry and the particle diameter of the SCR catalyst contained in the catalyst slurry in such a range, the catalyst slurry is easily filled in the pores existing near the outlet side partition wall surface. More SCR catalyst is supported, and high catalyst purification performance can be obtained.

  After the catalyst slurry is coated on the outlet side partition wall surface of the honeycomb structure, the catalyst slurry is dried. Further, the dried catalyst slurry may be fired. In this way, a honeycomb structure carrying the SCR catalyst can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Comparative Example 1)
A forming material was prepared by adding a pore former, an organic binder, and water to a cordierite forming raw material mainly composed of talc, kaolin, and alumina. As the pore former, hollow resin particles having an average particle diameter of 20 μm were used. The average particle diameter is a value measured by a laser diffraction method. Moreover, methylcellulose and hydroxypropoxylmethylcellulose were used as the organic binder. The addition amount of each raw material was 15 parts by mass of the pore former, 4 parts by mass of the organic binder, and 27 parts by mass of water with respect to 100 parts by mass of the cordierite forming raw material.

  Next, this forming raw material was kneaded using a kneader to produce a columnar clay. Then, the obtained cylindrical clay was formed into a honeycomb shape using a vacuum extrusion molding machine to obtain a honeycomb formed body. The obtained honeycomb formed body was dried with a microwave dryer and further dried with a hot air dryer to obtain a dried honeycomb body.

  Next, plugged portions were formed at one open end of each cell of the dried honeycomb body. The plugged portion is formed by each end surface (inlet end surface and inlet end surface) of the honeycomb dried body by a cell in which the plugged portion is formed at the opening end and a cell in which the plugged portion is not formed at the opening end. The exit end face was in a checkered pattern. As a method for forming the plugged portions, first, a sheet was attached to the end face of the dried honeycomb body, and holes were formed in the sheet at positions corresponding to the cells where the plugged portions were to be formed. Subsequently, with the sheet attached, the end face of the dried honeycomb body is immersed in a plugging slurry in which the forming material of the plugging portion is slurried, and the plugs are sealed through holes formed in the sheet. The plugging slurry was filled into the open end of the cell to be stopped. In addition, the same material as the molding raw material was used as a material for forming the plugging portion.

Thus, after the plugging slurry filled in the open end portion of the cell was dried, the dried honeycomb body was calcined (degreasing) at 550 ° C. for 3 hours in an air atmosphere. Thereafter, the honeycomb structure was fired at about 1400 ° C. to 1500 ° C. for 7 hours. This honeycomb structure has a cylindrical shape with a diameter of 144 mm and a length of 152 mm, a cell shape of square, a cell density of 47 cells / cm ² , an overall partition wall thickness (T) of 300 μm, and an overall partition wall porosity of The average pore diameter of the whole partition wall was 65 μm and 20 μm.

  Subsequently, an SCR catalyst was supported on the outlet side partition wall surface of the honeycomb structure. Cu-substituted zeolite was used as the SCR catalyst. As a specific loading method, first, a catalyst slurry containing Cu-substituted zeolite was prepared. Water was used as a dispersant for the catalyst slurry. The amount of water was adjusted so that the viscosity of the slurry was 7 mPa · s. The catalyst slurry is introduced into a cell in which the outlet side partition wall surface of the honeycomb structure is exposed (a cell in which a plugging portion is formed on the inlet end surface side of the honeycomb structure), and the inlet end surface of the honeycomb structure The outlet side partition wall surface was coated by suction from the side. Thereafter, this honeycomb structure was dried with a hot air drier to obtain a honeycomb structure of Comparative Example 1 in which the SCR catalyst was supported on the exit partition wall surface. The honeycomb structure of Comparative Example 1 serves as an evaluation standard when evaluating the honeycomb structures of Examples 1 to 22 and Comparative Examples 2 to 8 described later.

(Examples 1-22 and Comparative Examples 2-8)
Comparative Example 1 except that the step of forming a part having a smaller porosity than the remaining part was performed on a part of the partition wall (part from the inlet side partition wall surface to a predetermined thickness) before supporting the SCR catalyst. Similarly, honeycomb structures of Examples 1 to 22 and Comparative Examples 2 to 8 were obtained. In the step, first, cells in which the inlet side partition wall surface of the honeycomb structure before supporting the SCR catalyst obtained in the same manner as in Comparative Example 1 is exposed (plugging portions are formed on the outlet end face side of the honeycomb structure). The sol-like raw material for forming a portion having a low porosity was filled in the cell). The sol-like raw material is prepared by adding a pore former, an organic binder, and water to a cordierite forming raw material in the same manner as the forming raw material. However, the volume ratio of the pore former contained in the sol-like raw material to the cordierite forming raw material is made smaller than the volume ratio of the pore former contained in the molding raw material to the cordierite forming raw material.

  Next, a rod-shaped instrument was inserted into the cell filled with the sol-like raw material to remove excess sol-like raw material, and the sol-like raw material remaining in the cell was dried and solidified. Thus, after forming a layer made of the sol-like raw material on the surface of the partition wall exposed in the predetermined cell of the honeycomb structure, the honeycomb fired body is fired again, and the layer made of the sol-like raw material is formed into the honeycomb structure. And integrated.

  Thereafter, in the same manner as in Comparative Example 1, the SCR catalyst was supported on the outlet side partition wall surface of the honeycomb structure, and the honeycomb structures of Examples 1 to 22 and Comparative Examples 2 to 8 were obtained. The thickness T of the whole partition in these honeycomb structures, the porosity p of the part from the inlet side partition surface to the thickness t in the whole partition, the porosity P of the remaining part of the partition, and the ratio of t to T are: As shown in Table 1. In addition, the average pore diameter r of the pores existing in the part from the inlet side partition wall surface to the thickness t, and the average pore diameter R of the pores existing in the remaining part of the partition are also shown in the same table. Show.

  The porosity p, P of each part of the partition wall is obtained by taking a scanning electron microscope (SEM) photograph of the partition wall section and using commercially available image analysis software (“Image Pro Plus” manufactured by Media Cybernetics). Asked. Specifically, the SEM photograph of the cross section of the partition wall is bipolarized with the image analysis software, and the areas of the partition wall portions (substance portions other than the pores) and the pore portions (pore portions) of each part are measured, The porosity of each part was calculated from these measured values.

  In addition, the average pore diameters r and R of the pores present in each part of the partition wall were also obtained by taking a scanning electron microscope (SEM) photograph of the cross section of the partition wall, and commercially available image analysis software (manufactured by Media Cybernetics, “Image Pro Plus” )). Specifically, the SEM photograph of the partition wall cross section was bipolarized with the image analysis software, the diameter of the pores (pores) existing in each part was measured, and the average value was calculated.

(Evaluation)
For the honeycomb structures of Examples 1 to 22 and Comparative Examples 2 to 8, evaluation of pressure loss with scissors, purification performance, and strength is performed by the following method, and further comprehensive evaluation is performed based on those evaluations. The results are shown in Table 2.

[Evaluation of wrinkled pressure loss]
In the honeycomb structure, 4 g / liter of soot was collected using a diesel engine having a displacement of 2.0 liter. In this state, air was flowed at a flow rate of 2.27 Nm ³ / min, and pressure was measured on the inlet side and the outlet side of the honeycomb structure. The pressure difference between the pressure on the inlet side and the pressure on the outlet side measured in this way was defined as the pressure loss with wrinkles of the honeycomb structure, and three-stage evaluation of A, B, and C was performed based on the following criteria.
A: Compared to the pressure loss of the honeycomb structure of Comparative Example 1, the pressure loss of the flange is 10% or more lower.
B: Compared with the pressure loss of the flange of the honeycomb structure of Comparative Example 1, the pressure loss of the flange is low in the range of 5% or more and less than 10%.
C: Compared with the pressure loss of the ribs of the honeycomb structure of Comparative Example 1, the pressure loss of the ribs is equal to or higher than that in the range of less than 5%.

[Evaluation of purification performance]
First, using an electric furnace, a thermal history was given by a method in which the honeycomb structure was heated in an air atmosphere at 650 ° C. for 8 hours. Thereafter, the honeycomb structure was mounted directly under the exhaust manifold of a diesel engine having a displacement of 7 liters, and exhaust gas of about 250 ° C. discharged from the diesel engine was passed through the honeycomb structure. Then, to measure the concentration of NO _x and the concentration of NO _x outlet side of the inlet side of the honeycomb structure, of the NO _x concentration / inlet side of the NO _x purification rate (1-outlet side from the measured value concentration of NO _x × 100 (%)). The _the NO _x purification rate and the purification performance of the honeycomb structure, according to the following criteria were carried out A, B, a three-step evaluation C.
A: The purification performance of the honeycomb structure is 90% or more.
B: The purification performance of the honeycomb structure is 70% or more and less than 90%.
C: The purification performance of the honeycomb structure is less than 70%.

[Evaluation of strength]
The honeycomb structure was subjected to a hydrostatic pressure test, and the pressure when the breakage was reached was measured. The pressure measured in this manner was used as the strength of the honeycomb structure, and three-stage evaluation of A, B, and C was performed according to the following criteria.
A: The honeycomb structure has a strength of 1.0 MPa or more.
B: The honeycomb structure has a strength of 0.7 MPa or more and less than 1.0 MPa.
C: The strength of the honeycomb structure is less than 0.7 MPa.

[Comprehensive evaluation]
Based on the evaluation of the three items of pressure loss with scissors, purification performance, and strength, a three-stage evaluation of A, B, and C was performed according to the following criteria.
A: The evaluation is A for all three items, or the evaluation of any two items is A, and the evaluation of the remaining one item is B.
C: The evaluation of any two or more of the three items is C.
B: Does not correspond to any of the above A and C.

(Discussion)
As shown in Table 2, the honeycomb structures of Examples 1 to 22, which are examples of the present invention, have a comprehensive evaluation of A or B, a function as a particulate collection filter, and a function as a carrier of an SCR catalyst. It is thought that it is possible to achieve both. On the other hand, the honeycomb structures of Comparative Examples 2 to 8 not included in the present invention have an overall evaluation of C, and it is difficult to achieve both the function as the particulate collection filter and the function as the carrier of the SCR catalyst. It is believed that there is.

  The present invention is used as a particulate collection filter for collecting PM contained in exhaust gas discharged from an internal combustion engine such as a diesel engine or various combustion apparatuses, and at the same time as a carrier for supporting an SCR catalyst. Can be used.

1: honeycomb structure, 2: honeycomb structure portion, 3: plugging portion, 4: cell, 5: partition wall, 6: inlet end surface, 7: outlet end surface, 8a: inlet side partition surface, 8b: outlet side partition surface 9: SCR catalyst, 10: particulate matter (PM), 11: pores, 12: pores, 13: honeycomb sintered body, 14: sol-like raw material, 15: rod-like instrument.

Claims (6)

A porous partition wall defining a plurality of cells extending from an inlet end surface serving as an exhaust gas inlet side to an outlet end surface serving as an exhaust gas outlet side; the opening end portion on the outlet end surface side of a predetermined cell; and the remaining cells A plugging portion that plugs the opening end on the inlet end face side, and the exhaust gas flowing into the cell from the inlet end face passes through the partition wall and then flows out of the cell from the outlet end face. A honeycomb structure
When the porosity of the portion from the surface of the partition wall which is the inlet side of the exhaust gas permeating the partition wall to the thickness t is p and the porosity of the remaining portion of the partition wall is P among the entire partition wall, A honeycomb structure in which t is 50 to 100 μm, p is smaller than P, and p is 25 to 45%.   The honeycomb structure according to claim 1, wherein p is 30 to 45%.   3. The r is 10 μm or less, where r is an average pore diameter of pores existing in a portion from the surface of the partition wall to the thickness t at the inlet side of the exhaust gas that permeates the partition wall. Honeycomb structure.   The honeycomb structure according to any one of 1 to 3, wherein R is less than 30 µm, where R is an average pore diameter of pores existing in the remaining portions of the partition walls.   The honeycomb structure according to any one of 1 to 4, wherein a ratio of t to T is 4 to 40%, where T is a thickness of the entire partition wall.   The honeycomb structure according to any one of claims 1 to 5, wherein an SCR catalyst is supported on a surface of the partition wall which is an outlet side of exhaust gas that permeates the partition wall.

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