JP5937381B2 - Honeycomb structure - Google Patents

Description

  The present invention relates to a honeycomb structure, and more particularly to a honeycomb structure that can support a large amount of catalyst and can be used as a carrier for a honeycomb catalyst body with good purification efficiency and has sufficient strength.

Conventionally, in order to purify exhaust gas discharged from various engines and the like, a honeycomb catalyst body having a catalyst supported on a honeycomb structure is used. Such a honeycomb catalyst body allows a fluid (exhaust gas) to flow into each cell from the end face on the inflow side, and includes carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NO _X ), etc. contained in the exhaust gas. It cleans harmful substances with a catalyst.

  In order to increase the purification efficiency of exhaust gas, the honeycomb structure used for such a honeycomb catalyst body is manufactured so as to increase the geometric area on which the catalyst is supported and to increase the contact efficiency between the exhaust gas and the catalyst. (For example, see Patent Documents 1 and 2).

JP 2003-33664 A JP 2001-269585 A

  In recent years, exhaust gas regulations have become stricter. Therefore, development of a honeycomb structure capable of supporting many catalysts is eagerly desired. Further, in the honeycomb structure which is the carrier of the honeycomb catalyst body described in Patent Documents 1 and 2, the heat capacity of the intersection part is approximately the same as or larger than the heat capacity of the partition wall part. For this reason, the catalyst supported at the intersection is difficult to reach the activation temperature, and the catalyst at the intersection does not work effectively. As a result, there has been a problem that purification efficiency of exhaust gas is deteriorated.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to support a catalyst for a honeycomb catalyst body that can carry a large amount of catalyst and has good purification efficiency. A honeycomb structure that can be used and has sufficient strength is provided.

  According to the present invention, the following honeycomb structure is provided.

[1] A plurality of cells that serve as fluid flow paths are defined and a plurality of porous partition walls formed with a plurality of pores are provided, and the partition walls include an intersection portion where the partition walls intersect with each other, and the intersection portion. The porosity of the intersection part is 40 to 70%, the porosity of the partition part is 30 to 60%, and the porosity of the intersection part is the partition part. honeycomb much larger than the porosity, to the sum of the value of the porosity value and the partition wall portion of the porosity of the intersection portion, the ratio of the value of the porosity of the intersection portion is 60 to 80% of the body.

[2] The honeycomb structure according to [1], wherein the total area of the large pores, which are the pores having the largest diameter exceeding 10 μm, is 50% or more of the total area of all the pores.

[3] The honeycomb structure according to [1] or [2], wherein an outer peripheral shape of the pores in the partition wall is at least one of a circle and an ellipse in a cross section orthogonal to a cell extending direction.

  In the honeycomb structure of the present invention, the porosity of the intersection part is 40 to 70%, and the porosity of the partition wall part is 30 to 60%. Therefore, even after the catalyst is loaded, the pressure loss hardly increases and a large number of catalysts can be loaded. In the honeycomb structure of the present invention, the porosity of the intersection part is larger than the porosity of the partition wall part. Therefore, the heat capacity of the intersection is smaller than the heat capacity of the partition wall. As a result, the temperature of the intersection part is easily increased, and the catalyst at the intersection part easily reaches the activation temperature. Therefore, when a honeycomb catalyst body is produced using the honeycomb structure as a carrier, the exhaust gas purification efficiency in the honeycomb catalyst body is improved. And the honeycomb structure of this invention has sufficient intensity | strength because the porosity of an intersection part is 40 to 70%, and the porosity of a partition part is 30 to 60%.

1 is a perspective view schematically showing an embodiment of a honeycomb structure of the present invention. FIG. 2 is a cross-sectional view schematically showing a cross section orthogonal to the cell extending direction of the honeycomb structure shown in FIG. 1. FIG. 3 is a cross-sectional view schematically showing an enlarged part of the honeycomb structure shown in FIG. 2. It is a front view which shows typically a part of nozzle | cap | die which can be used at a clay preparation process.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that modifications, improvements, and the like appropriately added to the embodiments described above fall within the scope of the present invention.

[1] Honeycomb structure:
In an embodiment of the honeycomb structure of the present invention, like the honeycomb structure 100 shown in FIG. 1 and FIG. 2, a plurality of cells 4 serving as fluid flow paths are partitioned and a plurality of pores 12 (FIG. 3). A plurality of porous partition walls 5 formed with a reference) are provided. As shown in FIG. 3, the partition wall 5 of the honeycomb structure 100 includes an intersection point 10 where the partition walls 5 intersect each other and a partition wall part 11 other than the intersection point 10. And in the honeycomb structure 100, the porosity of the intersection part 10 is 40 to 70%, and the porosity of the partition part 11 is 30 to 60%. Furthermore, the porosity of the intersection part 10 is larger than the porosity of the partition part 11.

  In such a honeycomb structure 100, the porosity of the intersection part 10 is 40 to 70%, and the porosity of the partition wall part 11 is 30 to 60%. Therefore, even after the catalyst is loaded, the pressure loss hardly increases and a large number of catalysts can be loaded. In the honeycomb structure 100, the porosity of the intersection portion 10 is larger than the porosity of the partition wall portion 11. Therefore, in the honeycomb structure 100, the heat capacity of the intersection part 10 is smaller than the heat capacity of the partition wall part 11. As a result, the temperature of the intersection portion 10 is easily increased, and the catalyst at the intersection portion 10 easily reaches the activation temperature. Therefore, when a honeycomb catalyst body is manufactured using the honeycomb structure 100 as a carrier, the exhaust gas purification efficiency in the honeycomb catalyst body is improved. And the honeycomb structure 100 has sufficient intensity | strength because the porosity of the intersection part 10 is 40 to 70%, and the porosity of the partition part 11 is 30 to 60%. FIG. 1 is a perspective view schematically showing an embodiment of a honeycomb structure of the present invention. FIG. 2 is a cross-sectional view schematically showing a cross section perpendicular to the cell extending direction of the honeycomb structure shown in FIG.

  The “intersection point” is a region where the partition walls intersect each other in a cross section perpendicular to the cell extending direction and is surrounded by a straight line parallel to the surface of the partition wall. That is, when a straight line L (see FIG. 3) that connects the surfaces of the adjacent partition walls with the intersection portion interposed therebetween is drawn, the region is surrounded by the straight line L. As shown in FIG. 3, even when the corner of the cell 4 is chamfered, a region surrounded by a straight line L parallel to the surface of the partition wall 5 is defined as an “intersection point”. FIG. 3 is a cross-sectional view schematically showing an enlarged part P of the honeycomb structure shown in FIG. 2, that is, the intersection part and the vicinity of the intersection part.

  The porosity of the intersection 10 is 40 to 70%, preferably 50 to 65%, and more preferably 55 to 60%. When the porosity of the intersection portion 10 is in the above range, the pressure loss is hardly increased even after the catalyst is supported on the honeycomb structure 100. Therefore, the honeycomb structure 100 can carry many catalysts. In addition, an increase in pressure loss can be prevented while maintaining the strength of the honeycomb structure moderately. If the porosity of the intersection 10 is less than the lower limit, the light-off property is poor and the pressure loss increases. In addition, many catalysts cannot be supported. If it exceeds the upper limit value, the strength of the partition walls decreases, so that the strength of the honeycomb structure 100 cannot be sufficiently obtained. The porosity of the intersection 10 is a value calculated by image analysis. Specifically, the intersection point is photographed by a scanning electron microscope (SEM), and the photographed image is binarized. Thereafter, the ratio of the area of the pores existing at the intersection to the area of the entire intersection is calculated. The same operation is performed at a plurality of intersections, the ratio of the pore area is calculated, and the average value is obtained. This average value is taken as the porosity of the intersection.

  The porosity of the partition wall 11 is 30 to 60%, preferably 35 to 50%, and more preferably 40 to 45%. When the porosity of the partition wall 11 is in the above range, the pressure loss is hardly increased even after the catalyst is supported on the honeycomb structure 100. Therefore, the honeycomb structure 100 can carry many catalysts. In addition, an increase in pressure loss can be prevented while maintaining the strength of the honeycomb structure moderately. When the porosity of the partition wall portion 11 is less than the lower limit value, when the catalyst is supported on the honeycomb structure 100, the catalyst does not enter the pores of the partition walls and closes the pores. Therefore, the pressure loss of the honeycomb structure 100 increases. In addition, many catalysts cannot be supported. If it exceeds the upper limit value, the strength of the partition walls decreases, so that the strength of the honeycomb structure 100 cannot be sufficiently obtained. The porosity of the partition wall 11 is a value calculated by image analysis in the same manner as the porosity of the intersection 10. Specifically, the partition wall is photographed with a scanning electron microscope (SEM), and the photographed image is binarized. Thereafter, the ratio of the area of the pores existing in the partition wall to the area of the entire field of view is calculated. The same operation is performed at a plurality of locations, the ratio of the pore area is calculated, and the average value is obtained. This average value is taken as the porosity of the partition wall.

In the honeycomb structure 100, the porosity of the intersection part 10 needs to be larger than the porosity of the partition wall part 11. Specifically, the ratio of the value of the “porosity of the intersection 10” to the sum of the value of “the porosity of the intersection 10” and the “porosity of the partition wall 11” is 60 to 80%. Ah it is, further preferably 65 to 75%, particularly preferably 65 to 70%. When the ratio is in the above range, the temperature of the intersection portion 10 is further easily increased, and the catalyst at the intersection portion 10 is more likely to reach the activation temperature. Therefore, when a honeycomb catalyst body is manufactured using the honeycomb structure 100 as a carrier, the temperature rise immediately after operation becomes faster. Therefore, the exhaust gas purification efficiency in the honeycomb catalyst body is further improved.

  In the partition wall 5 of the honeycomb structure 100, as shown in FIG. 3, it is preferable that large pores 14 having “the largest pores 12 having a largest diameter exceeding 10 μm” are formed. By forming such large pores, a honeycomb structure capable of supporting a larger amount of catalyst can be produced. The “largest diameter” is the maximum diameter of each independent pore in the binarized image that has been binarized by image analysis. The “maximum diameter” is the length of the longest line segment connecting two points on the outer peripheral edge of the independent pore in the binarized image. “Independent pore” refers to a pore in which no opening is formed on the surface of the partition wall in a cross section perpendicular to the cell extending direction. In other words, it is a pore (region) that forms one closed space in the cross section of the partition perpendicular to the cell extending direction.

  In the honeycomb structure 100, the total area of the large pores is preferably 50% or more of the total area of all the pores, more preferably 60 to 80%, and more preferably 65 to 75%. It is particularly preferred. By setting the total area of the large pores within the above range, a flow path through which exhaust gas can diffuse is ensured in the honeycomb catalyst body. Therefore, the exhaust gas diffuses into the honeycomb catalyst body. As a result, the catalyst can work effectively. That is, the number of catalysts that do not come into contact with exhaust gas can be reduced. Furthermore, the honeycomb structure 100 does not have an excessively high coefficient of thermal expansion because the pores blocked by the catalyst are reduced when the honeycomb catalyst body is manufactured. Therefore, the honeycomb catalyst body using the honeycomb structure 100 as a carrier is excellent in thermal shock resistance. If the total area of the large pores is less than 50% of the total area of all the pores, the exhaust gas purification efficiency may not be sufficiently obtained. In addition, the thermal shock resistance of the honeycomb catalyst body using the honeycomb structure as a carrier may be reduced.

“Pore” refers to those having an area of 10 μm ² or more in a cross section perpendicular to the cell extending direction. The area of the pores is a value calculated by image analysis of an arbitrary plurality of fields captured by a scanning electron microscope (SEM).

  The thickness of the partition wall 5 is not particularly limited, but is preferably 0.060 to 0.288 mm, more preferably 0.108 to 0.240 mm, and 0.132 to 0.192 mm. Is particularly preferred. By setting the thickness of the partition wall 5 within the above range, a honeycomb structure having high strength and reduced pressure loss can be obtained. The “thickness of the partition wall 5” means the thickness of a wall (partition wall) that partitions two adjacent cells 4 in a cross section obtained by cutting the honeycomb structure 100 perpendicularly to the cell 4 extending direction. The “thickness of the partition wall 5” can be measured by, for example, an image analysis apparatus (trade name “NEXIV, VMR-1515” manufactured by Nikon Corporation).

Cell density of the honeycomb structure 100 is not particularly limited, preferably from 15 to 140 pieces / cm ^2, further preferably from 31 to 116 pieces / cm ^2, at 46 to 93 pieces / cm ² It is particularly preferred. When the cell density of the honeycomb structure 100 is in the above range, an increase in pressure loss can be suppressed while maintaining the strength of the honeycomb structure. “Cell density” is the number of cells per unit area in a cross section perpendicular to the cell extending direction.

  The partition wall 5 is preferably made mainly of ceramic. Specifically, the partition wall 5 is made of silicon carbide, silicon-silicon carbide based composite material, cordierite, mullite, alumina, spinel, silicon carbide-cordierite based composite material, lithium aluminum silicate, and aluminum titanate. It is preferably at least one selected from the group. Among these, cordierite is preferable. When cordierite is used as the material for the partition walls 5, a honeycomb structure having a small thermal expansion coefficient and excellent thermal shock resistance can be obtained. In addition, the phrase “having ceramic as a main component” means containing 50% by mass or more of the entire ceramic.

  The outer peripheral shape of the pores formed in the partition wall is not particularly limited, but is preferably at least one of a circle and an ellipse. The outer peripheral shape of the pore is the outer peripheral shape of the pore in a cross section orthogonal to the cell extending direction. As described above, when the outer peripheral shape of the pore is at least one of a circle and an ellipse, the catalyst is uniformly supported on the surface of the pore. Therefore, the contact area between the catalyst and the exhaust gas is increased. As a result, the honeycomb catalyst body using the honeycomb structure as a carrier further improves the exhaust gas purification efficiency.

  The cell 4 serves as a fluid flow path that penetrates the honeycomb structure 100 from one end face 2 to the other end face 3 of the honeycomb structure 100. The outer peripheral shape of the cell 4 is not particularly limited, but is preferably a quadrangular shape. The outer peripheral shape of the cell 4 is the outer peripheral shape of the pore in the cross section orthogonal to the cell extending direction.

  A honeycomb structure 100 shown in FIG. 1 has an outer peripheral wall 7 disposed on the outer periphery. Although the thickness of the outer peripheral wall 7 is not specifically limited, 0.2-4.0 mm is preferable. By setting the thickness of the outer peripheral wall 7 in the above range, it is possible to prevent an increase in pressure loss while maintaining the strength of the honeycomb structure moderately. The material of the outer peripheral wall 7 is preferably the same as that of the partition wall 5, but may be different.

  The shape of the honeycomb structure 100 is not particularly limited, but a cylindrical shape, a cylindrical shape having an elliptical bottom surface, a polygonal cylindrical shape such as a quadrilateral, pentagonal, hexagonal shape, or the like is preferable, and a cylindrical shape is further preferable. preferable. Further, the size of the honeycomb structure 100 is not particularly limited, but the length in the cell extending direction is preferably 50 to 300 mm. Further, for example, when the honeycomb structure 100 has a cylindrical outer shape, the diameter of the bottom surface is preferably 110 to 350 mm.

[2] Manufacturing method of honeycomb structure:
For example, the following manufacturing method can be employed for the honeycomb structure of the present invention. The method for manufacturing a honeycomb structure of the present invention includes a clay preparation step for obtaining a kneaded material for intersections and a knot for partition walls, and integrally extruding a kneaded material for intersections and a knot for partition walls. A forming step for obtaining a honeycomb formed body, and a firing step for firing the honeycomb formed body. The clay preparation step mixes and kneads the intersection portion molding raw material containing the ceramic raw material and the pore former, and mixes the intersection portion clay and the bulkhead molding raw material containing the ceramic raw material and the pore former. This is a step of kneading and obtaining a partition wall clay. In this clay preparation step, as the pore former contained in the intersection part forming raw material, an average particle diameter of 70 to 200 μm and 1 to 10% by mass of the intersection part forming raw material is used. Further, as the pore former contained in the partition wall molding raw material, an average particle diameter of 10 to 150 μm and 0.5 to 5% by mass of the partition wall molding raw material is used. However, as the pore former contained in the intersection part forming raw material, a pore former having an average particle diameter larger than the average particle diameter of the pore former contained in the partition wall forming raw material is used. The forming step is a step of obtaining the formed honeycomb body by supplying the obtained kneaded material for the intersection part and the kneaded material for the partition wall part to a mold and extruding into a honeycomb shape. The firing step is a step of firing the obtained honeycomb formed body to partition and form a plurality of cells serving as fluid flow paths, and to obtain a honeycomb structure including a porous partition wall in which a plurality of pores are formed. is there. The honeycomb structure manufacturing method as described above can satisfactorily produce the above-described honeycomb structure of the present invention.

  The method for manufacturing the honeycomb structure will be specifically described below.

[2-1] Clay preparation process:
In this step, a kneading for the intersection part and a kneading for the partition part are prepared. Thus, by preparing separately the clay for the intersection part and the clay for the partition part, the porosity of the intersection part and the partition part can be made different. That is, the porosity of the intersection can be made larger than the porosity of the partition wall.

  Examples of the pore former include starch, foamed resin, water absorbent resin, silica gel and the like. Note that the pore former contained in the intersection part forming raw material and the pore former contained in the partition wall molding raw material may be the same or different.

  As described above, the average particle diameter of the pore former contained in the intersection portion forming raw material is 70 to 200 μm, preferably 80 to 150 μm, and preferably 90 to 120 μm. When the average particle size of the pore former contained in the intersection portion forming raw material is less than the lower limit value, it becomes impossible to produce a honeycomb structure capable of supporting many catalysts. If it exceeds the upper limit, the strength of the intersection will be too low.

  The content of the pore former in the intersection part forming raw material is 1 to 10 parts by weight, preferably 2 to 8 parts by weight, based on 100 parts by weight of the ceramic raw material in the intersection part forming raw material. More preferably, it is 3-7 mass parts. When the content of the pore former contained in the intersection portion forming raw material is less than the lower limit value, it becomes impossible to produce a honeycomb structure capable of supporting many catalysts. If it exceeds the upper limit, the strength of the intersection will be too low.

  As described above, the average particle diameter of the pore former contained in the partition wall forming raw material is 10 to 150 μm, preferably 20 to 100 μm, and more preferably 30 to 80 μm. When the average particle diameter of the pore former contained in the partition wall forming raw material is less than the lower limit value, it becomes impossible to produce a honeycomb structure capable of supporting many catalysts. If it exceeds the upper limit value, the strength of the partition walls will be too low.

  The content of the pore former in the partition wall forming raw material is 0.5 to 5 parts by weight and 1 to 4 parts by weight with respect to 100 parts by weight of the ceramic raw material in the partition wall forming raw material. Preferably, it is 2 to 3 parts by mass. When the content of the pore former contained in the partition wall forming raw material is less than the lower limit value, it becomes impossible to produce a honeycomb structure capable of supporting many catalysts. If it exceeds the upper limit value, the strength of the partition walls will be too low.

  The ceramic raw material is selected from the group consisting of silicon carbide, silicon-silicon carbide based composite material, cordierite forming raw material, mullite, alumina, spinel, silicon carbide-cordierite based composite material, lithium aluminum silicate, and aluminum titanate. It is preferable that there is at least one. Among these, a cordierite forming raw material is preferable. This is because a honeycomb structure having a small thermal expansion coefficient and excellent thermal shock resistance can be obtained.

  Each forming raw material may include a dispersion medium, an additive and the like in addition to the ceramic raw material and the pore former.

  Examples of the dispersion medium include water. Examples of the additive include an organic binder and a surfactant. It is preferable that content of a dispersion medium is 30-150 mass parts with respect to 100 mass parts of ceramic raw materials.

  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. It is preferable that content of an organic binder is 1-10 mass parts with respect to 100 mass parts of ceramic raw materials.

  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. It is preferable that content of surfactant is 0.1-5.0 mass parts with respect to 100 mass parts of ceramic raw materials.

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

[2-2] Molding process:
In this step, the intersection portion kneaded material and the partition wall kneaded material obtained in the kneaded material preparing step are supplied to one mold and extruded into a honeycomb shape to obtain one honeycomb formed body. In the honeycomb formed body, a plurality of cells penetrating the honeycomb formed body from one end face to the other end face are formed. The intersecting part clay is supplied to the back hole 21 for the intersecting part in the die 20 shown in FIG. The partition wall clay is supplied to the partition wall back hole 22 in the die base 20 shown in FIG. Extrusion can be performed 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. FIG. 4 is a front view schematically showing a part of a base that can be used in the clay preparation step. The back hole for the intersection part is a back hole for injecting the raw material constituting the intersection part. The back hole for a partition part is a back hole for inject | pouring the raw material which comprises a partition part.

[2-3] Firing step:
In this step, the obtained honeycomb formed body is fired to obtain a honeycomb structure. The honeycomb structure includes a plurality of cells serving as fluid flow paths and a porous partition wall having a plurality of pores.

  The firing temperature can be appropriately determined depending on the material of the honeycomb formed body. For example, when the material of the honeycomb formed body is cordierite, the firing temperature is preferably 1380 to 1450 ° C, and more preferably 1400 to 1440 ° C. The firing time is preferably about 3 to 10 hours.

  The honeycomb formed body may be dried before firing. The drying method is not particularly limited, and examples thereof include hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze drying. Among these, it is preferable to perform dielectric drying, microwave drying, or hot air drying alone or in combination. The drying conditions are preferably a drying temperature of 30 to 150 ° C. and a drying time of 1 minute to 2 hours.

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

[Porosity (%)]:
The porosity of the intersection part and the partition part is a value calculated by image analysis. Specifically, the porosity of the intersection is calculated as follows. First, the intersection part is imaged by a scanning electron microscope (SEM), and the imaged image is binarized. Thereafter, the ratio of the area of the pores existing at the intersection to the area of the entire intersection is calculated. The above operation is performed at a total of four intersections, the proportion of the pore area is calculated, and the average value is obtained. This average value is taken as the porosity of the intersection.

  Specifically, the porosity of the partition wall is calculated as follows. First, the partition wall is photographed by a scanning electron microscope (SEM), and the photographed image is binarized. Thereafter, the ratio of the area of the pores existing in the partition wall to the area of the entire field of view is calculated. The above operation is performed in a total of four fields of view, the ratio of the pore area is calculated, and the average value is obtained. This average value is taken as the porosity of the partition wall.

( Reference Example 1)
[Preparation of honeycomb structure]
The raw material which comprises an intersection part (molding raw material for intersection parts), and the raw material which comprises a partition part (molding raw material for partition parts) were each produced. The forming material for the intersection part is added to 100 parts by mass of the cordierite forming material, 5 parts by mass of the pore former, 85 parts by mass of the dispersion medium, 8 parts by mass of the organic binder, and 3 parts by mass of the surfactant, It was prepared by mixing and kneading. As a cordierite forming raw material, alumina, aluminum hydroxide, kaolin, talc, and silica were used. Water was used as the dispersion medium, and coke having an average particle diameter of 20 to 50 μm was used as the pore former. Hydroxypropyl methylcellulose was used as the organic binder. Ethylene glycol was used as a dispersant.

  The partition wall forming raw material was added to 100 parts by mass of the cordierite forming raw material, 5 parts by mass of the pore former, 85 parts by mass of the dispersion medium, 8 parts by mass of the organic binder, and 3 parts by mass of the surfactant, It was prepared by mixing and kneading. As a cordierite forming raw material, alumina, aluminum hydroxide, kaolin, talc, and silica were used. Water was used as the dispersion medium, and methylcellulose having an average particle size of 100 μm was used as the pore former. Hydroxypropyl methylcellulose was used as the organic binder. Ethylene glycol was used as a dispersant.

  Next, a honeycomb formed body was extrusion-molded using the intersection portion forming raw material and the partition wall forming raw material. In the honeycomb formed body, square cells were formed in a cross section perpendicular to the cell extending direction, and the overall shape was a columnar shape. The obtained honeycomb formed body was dried with a microwave dryer. Thereafter, it was further completely dried with a hot air dryer. Thereafter, both end faces of the dried honeycomb formed body were cut and adjusted to predetermined dimensions. As the die used for the extrusion molding, one having a back hole 21 for the intersection part and a back hole 22 for the partition part was used (see FIG. 4).

  The honeycomb formed body thus obtained was further fired at 1410 to 1440 ° C. for 5 hours to obtain a honeycomb structure.

The obtained honeycomb structure had a diameter of 266.7 mm and a length in the central axis direction (denoted as “length” in Table 1) was 152.4 mm. The partition wall thickness (referred to as “partition wall thickness” in Table 1) was 165.1 μm. The porosity of the intersection part was 40%, and the porosity of the partition wall part was 30%. The porosity of the partition walls was 50%. The cell density was 62.0 cells / cm ² . The average pore diameter of the partition walls was 23 μm. In addition, the porosity and average pore diameter of a partition are the values measured with the mercury porosimeter.

  Next, 1 kg of water was added to 200 g of β-zeolite having an average particle size of 5 μm, and wet pulverized by a ball mill. 20 g of alumina sol as a binder was added to the obtained crushed particles to obtain a catalyst slurry. The viscosity of this catalyst slurry is 5 mPa.s. s. Then, the honeycomb structure was immersed in the catalyst slurry, and the catalyst slurry layer was formed on the surfaces of the partition walls and the pores of the honeycomb structure. Thereafter, this honeycomb structure was dried at 120 ° C. for 20 minutes and then fired at 600 ° C. for 1 hour. In this way, a honeycomb catalyst body was produced.

  With respect to the manufactured honeycomb catalyst body, measurements of [purification efficiency], [pressure loss], and [isostatic strength] were performed. The measuring method is shown below.

[Purification efficiency (NO _X purification efficiency)
First, the honeycomb catalyst body of the present embodiment, flow the test gas containing NO _X. Thereafter, the NO _x amount of the exhaust gas discharged from the honeycomb catalyst body is analyzed with a gas analyzer.

Here, the temperature of the test gas flowing into the honeycomb catalyst body is set to 200 ° C. The temperature of the honeycomb catalyst body and the test gas can be adjusted by a heater. An infrared image furnace is used as the heater. As the test gas, a gas in which nitrogen is mixed with 5% by volume of carbon dioxide, 14% by volume of oxygen, 350 ppm of nitrogen monoxide (volume basis), 350 ppm of ammonia (volume basis) and 10% by volume of water is used. As the test gas, water and a mixed gas obtained by mixing other gases are prepared separately. And when performing a test, these are mixed in piping and the gas for a test is obtained. As the gas analyzer, “MEXA9100EGR manufactured by HORIBA” is used. The space velocity when the test gas flows into the honeycomb catalyst body is set to 50000 (time- ¹ ).

Table "NO _X purification rate" in 1, the amount of NO _X in the test gas, the value obtained by subtracting the amount of NO _X in the exhaust gas from the honeycomb catalyst body, divided by the amount of NO _X in the test gas, 100 It is a doubled value. Here, if NO _X purification rate is 70% or more, the evaluation of the purification efficiency is "good". When NO _X purification rate is less than 70%, the evaluation of the purification efficiency is "bad."

[Pressure loss]
Air is circulated through the honeycomb catalyst body at a flow rate of 0.5 m ³ / min at room temperature. In this state, the difference between the pressure on the air inflow side and the pressure on the air outflow side is measured. This pressure difference is calculated as a pressure loss. A pressure loss ratio is calculated based on the calculated pressure loss, and the pressure loss ratio is evaluated. The evaluation criteria for the pressure loss is “bad” when the pressure loss ratio is 1.15 or more. When the pressure loss ratio is less than 1.15, “good” is set. The “pressure loss ratio” refers to the value of the pressure loss ratio of the honeycomb catalyst body when the pressure loss of the honeycomb catalyst body of Reference Example 6 is “1.00”.

[Isostatic strength]
It is measured based on an isostatic fracture strength test specified in the automobile standard (JASO standard) M505-87 issued by the Japan Society for Automotive Engineers. The isostatic strength is indicated by a pressurized pressure value (MPa) when the honeycomb structure is broken. In this specification, the isostatic strength is “good” at 1.00 MPa or more. Less than 1.00 MPa is “bad”. The isostatic fracture strength test is a test that simulates the compressive load load when the honeycomb structure is housed in a can with the outer peripheral surface being gripped when the honeycomb structure is mounted on an automobile. is there.

The honeycomb catalyst body of the present reference example, NO _X purification rate was 72%. That is, the evaluation of the purification efficiency was “good”. The pressure loss ratio was 1.13. That is, the evaluation of the pressure loss was “good”. Furthermore, the isostatic strength was 2.50 MPa. That is, the evaluation of isostatic strength was “good”. The results are shown in Table 2.

(Examples 2 to 5, Reference Example 6, Comparative Examples 1 to 5)
A honeycomb structure satisfying the diameter, the length in the central axis direction, the partition wall thickness, the cell density, the average pore diameter, the porosity at the intersection, and the porosity of the partition wall shown in Table 1 was produced. Thereafter, using the manufactured honeycomb structure, a honeycomb catalyst body satisfying the catalyst loading shown in Table 1 was manufactured in the same manner as in Reference Example 1. With respect to the manufactured honeycomb catalyst body, in the same manner as in Reference Example 1, each of [Purification Efficiency], [Pressure Loss], and [Isostatic Strength] were measured. The results are shown in Table 2.

In Comparative Example 1, since the porosity of the intersection was smaller than the porosity of the partition wall, the purification efficiency was evaluated as “bad”. In Comparative Examples 2 and 4, since the porosity of the intersection or the porosity of the partition wall is less than the lower limit, the pressure loss ratio is too high, and the evaluation of the pressure loss is “bad”. Here, in the honeycomb catalyst bodies of Comparative Examples 2 and 4, in order to reduce the pressure loss ratio, it is necessary to reduce the amount of catalyst supported. However, when reducing the amount of catalyst supported, NO _X purification rate becomes less than 70% Evaluation of the purification efficiency is "bad". In Comparative Examples 3 and 5, since the porosity of the intersection part or the porosity of the partition wall part exceeded the upper limit value, a honeycomb catalyst body having sufficient strength could not be obtained.

  The honeycomb structure of the present invention can be suitably used for purifying exhaust gas discharged from an engine.

2: one end face, 3: other end face, 4: cell, 5: partition wall, 7: outer peripheral wall, 10: intersection part, 11: partition part, 12: pore, 14: large pore, 20: base, 21: Back hole for intersection part, 22: Back hole for partition part, 100: Honeycomb structure.

Claims (3)

Comprising a plurality of cells serving as fluid flow paths, comprising a plurality of porous partition walls formed with a plurality of pores,
The partition wall has an intersection point where the partition walls intersect with each other, and a partition wall part other than the intersection point part,
The porosity of the intersection part is 40 to 70%, the porosity of the partition wall part is 30 to 60%,
Porosity of the intersection portion is much larger than the porosity of the partition wall portion,
A honeycomb structure , wherein a ratio of a porosity value of the intersection portion to a sum of a porosity value of the intersection portion and a porosity value of the partition wall portion is 60 to 80% .   The honeycomb structure according to claim 1, wherein the total area of large pores, which are the pores having the largest diameter exceeding 10 µm, is 50% or more of the total area of all the pores.   The honeycomb structure according to claim 1 or 2, wherein an outer peripheral shape of the pores in the partition walls is at least one of a circle and an ellipse in a cross section perpendicular to a cell extending direction.

Images