JP6824770B2 - Honeycomb structure - Google Patents

Description

The present invention relates to a honeycomb structure. More specifically, the present invention relates to a honeycomb structure capable of activating the catalyst at an early stage due to a low pressure loss when used as a catalyst carrier for supporting a catalyst for purifying exhaust gas.

Conventionally, a honeycomb structure in which a catalyst is supported has been used for purification treatment of harmful substances such as HC, CO, and NOx contained in exhaust gas discharged from an engine of an automobile or the like. In this way, when treating exhaust gas with a catalyst supported on a honeycomb structure, it is necessary to raise the temperature of the catalyst to its active temperature, but when the engine is started, the catalyst has not reached the active temperature, so the exhaust gas is sufficient. There was a problem that it was not purified.

Further, in order to purify the exhaust gas immediately after starting an internal combustion engine such as an engine, it is necessary to activate the catalyst supported on the honeycomb structure at an early stage. Further, as other means, for example, a means for increasing the amount of the catalyst supported on the honeycomb structure (hereinafter, also referred to as “supported amount”) to enhance the catalytic effect can be considered. However, when the amount of the catalyst supported is increased, the size of the opening of the cell formed in the honeycomb structure is narrowed, which causes a problem that the pressure loss is increased. Hereinafter, the pressure loss may be referred to as "pressure loss".

Currently, as a honeycomb structure as a catalyst carrier for supporting a catalyst for gas purification, for example, the following honeycomb structures have been proposed (see, for example, Patent Documents 1 to 3).

Patent Document 1 discloses a catalytic converter (Catalytic converter) composed of a cell-structured base material through which exhaust gas flows and a catalyst layer formed on the cell wall surface of the base material. This base material is composed of a central region and a peripheral region. The central region is in the range of 50-90% of the diameter of the substrate. A solid solution of ceria-zirconia (seria-zirconia solid solution) is applied to the carrier that forms the catalyst layer in the central region. Further, an alumina-ceria-zirconia solid solution (Alumina-ceria-zirconia solid solution) is applied to the carrier forming the catalyst layer in the peripheral region. The catalytic converter described in Patent Document 1 is said to have excellent oxygen absorption / release ability while effectively utilizing the entire catalyst.

Patent Document 2 discloses a honeycomb structure used as a carrier of a catalyst for purifying exhaust gas. This honeycomb structure has a plurality of cell density regions in which the cell densities are constant, and in a cross section orthogonal to the axial direction, the plurality of cell densities having different cell densities in the radial direction from the central portion to the outer peripheral portion. It has a region. In addition, a boundary region is provided between adjacent cell density regions having different cell densities. The honeycomb structure described in Patent Document 2 has a diameter of Φ1 / Φ2 when the average hydraulic diameter of the boundary cell in the boundary region is Φ1 and the average hydraulic diameter of the cell in the cell density region immediately inside the boundary region is Φ2. It is characterized in that ≧ 1.25. The honeycomb structure described in Patent Document 2 is said to be able to reduce pressure loss and improve exhaust gas purification performance by the above configuration.

In Patent Document 3, a carrier base material having a plurality of through holes in the flow direction of exhaust gas, one or more catalyst-supporting layers formed on the inner wall surface of the through-holes, and the catalyst-supporting layer are supported. Exhaust gas purification catalysts containing noble metals are disclosed. In the exhaust gas purification catalyst described in Patent Document 3, the thickness of the catalyst-supporting layer is adjusted so that the flow pressure of the passing exhaust gas becomes uniform among all the through holes, and the flow pressure of the passing exhaust gas is generally adjusted. It is said to be uniform.

JP 2015-71140 Japanese Unexamined Patent Publication No. 2013-173133 JP-A-2010-131526

The catalyst converter described in Patent Document 1 makes effective use of the entire catalyst by changing the type of catalyst carried in the central portion and the outer peripheral portion. However, simply changing the catalyst type does not necessarily improve the catalytic activity in the low temperature state immediately after the engine is started, and there is a problem that the exhaust gas purification performance at the low temperature is not yet sufficient.

The honeycomb structure described in Patent Document 2 aims to improve the exhaust gas purification performance by increasing the cell density in the central portion of the honeycomb structure as compared with the outer peripheral portion. However, simply increasing the cell density in the central part to increase the contact area between the catalyst and the exhaust gas does not mean that the catalytic activity at low temperature is sufficient, and the exhaust gas purification performance at low temperature is still sufficient. There was a problem that it was not.

Regarding the exhaust gas purification catalyst described in Patent Document 3, although the thickness of the catalyst supporting layer is changed according to the height of the exhaust gas flow pressure, the catalytic activity in a low temperature state is not necessarily improved, and the low temperature is not necessarily improved. There was a problem that the exhaust gas purification performance at that time was not yet sufficient.

The present invention has been made in view of the problems of the prior art. The present invention provides a honeycomb structure capable of activating the catalyst at an early stage due to a low pressure loss when used as a catalyst carrier for supporting a catalyst for purifying exhaust gas.

According to the present invention, the honeycomb structure shown below is provided.

[1] A columnar honeycomb structure having a porous partition wall arranged so as to surround a plurality of cells serving as a flow path for a fluid extending from an inflow end face to an outflow end face is provided.
The honeycomb structure portion has a porous boundary wall at a boundary between a central portion and an outer peripheral portion in a cross section orthogonal to the extending direction of the cell, and the shape of the boundary wall in the cross section is circular or elliptical. Yes,
In the honeycomb structure portion, the thickness and cell pitch of the partition wall in the central portion and the thickness and cell pitch of the partition wall in the outer peripheral portion are the same, and the porosity of the partition wall in the central portion is the outer circumference. A honeycomb structure configured to be larger than the porosity of the partition wall in the portion.

[2] The honeycomb structure according to the above [1], wherein the porosity of the central portion of the honeycomb structure portion is 50% or more and 70% or less.

[3] The honeycomb structure according to the above [1] or [2], wherein the porosity of the outer peripheral portion of the honeycomb structure portion is 25% or more and 50% or less.

[4] The honeycomb according to any one of [1] to [3], wherein the thickness of the partition wall of the central portion and the outer peripheral portion of the honeycomb structure portion is 0.038 mm or more and 0.500 mm or less. Structure.

[5] The honeycomb structure according to any one of [1] to [4], wherein the average pore diameter of the porous material constituting the partition wall is 2 μm or more and 200 μm or less.

[6] The honeycomb structure according to any one of [1] to [5], wherein the cell pitch of the central portion and the outer peripheral portion of the honeycomb structure portion is 0.70 mm or more and 2.60 mm or less.

[7] The above-mentioned [1] to [6], wherein the cell densities of the central portion and the outer peripheral portion of the honeycomb structure portion are 15 cells / cm ² or more and 233 cells / cm ² or less. Honeycomb structure.

[8] At least the partition wall is selected from the group of silicon carbide, silicon-silicon carbide composite material, cordierite, mullite, alumina, spinel, silicon carbide-corgerite composite material, lithium aluminum silicate, and aluminum titanate. The honeycomb structure according to any one of [1] to [7] above, which is composed of a material containing a kind of ceramics.

[9] The honeycomb structure according to any one of [1] to [8] above, which is used as a catalyst carrier for purifying exhaust gas of an internal combustion engine.

[10] The above-mentioned [1] to [9], wherein a catalyst for purifying exhaust gas is supported on at least one of the surface of the partition wall and the pores of the partition wall of the honeycomb structure portion. Honeycomb structure.

The honeycomb structure of the present invention includes a columnar honeycomb structure portion. The honeycomb structure includes a porous partition wall arranged so as to surround a plurality of cells, and a porous boundary wall for partitioning a boundary between a central portion and an outer peripheral portion in a cross section orthogonal to the extending direction of the cells. Have. In the honeycomb structure portion, the thickness and cell pitch of the partition wall in the central portion and the thickness and cell pitch of the partition wall in the outer peripheral portion are the same, and the porosity of the partition wall in the central portion is the porosity of the partition wall in the outer peripheral portion. It is configured to be larger.

In the honeycomb structure constructed as described above, since the partition wall made of a porous material having a high porosity is arranged in the central portion, the amount of catalyst supported can be increased as compared with the outer peripheral portion. it can. In addition, it has a porous boundary wall at the boundary between the central portion and the outer peripheral portion. Therefore, the effect of increasing the amount of the catalyst supported in the central portion and the heat insulating effect of the central portion by the boundary wall are combined, and the catalyst can be activated at an early stage, and the exhaust gas purification performance can be improved. .. Further, since the thickness and cell pitch of the partition wall are the same in the central portion and the outer peripheral portion, the pressure loss does not increase due to the change in the cell structure as in the conventional honeycomb structure. Therefore, the honeycomb structure of the present invention can activate the catalyst at an early stage due to the low pressure loss.

It is a perspective view which shows typically one Embodiment of the honeycomb structure of this invention. It is a top view which shows typically the inflow end face of the honeycomb structure shown in FIG. It is sectional drawing which shows typically the XX'cross section of FIG. It is a schematic diagram for demonstrating the cell pitch in the case of a cell shape of a square. It is a schematic diagram for demonstrating the cell pitch when the cell shape is a hexagon. It is a schematic diagram for demonstrating the cell pitch when the cell shape is a triangle. It is a schematic diagram which shows the state which inserted the honeycomb structure into a can body in the thermal cycle test of an Example. It is a schematic diagram which shows the apparatus used in the HC purification test of an Example.

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. Therefore, it should be understood that the following embodiments can be appropriately modified, improved, or the like based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

(1) Honeycomb structure:
As shown in FIGS. 1 to 3, one embodiment of the honeycomb structure of the present invention is a honeycomb structure 100 including a honeycomb structure portion 4 having a porous partition wall 1. The porous partition wall 1 is arranged so as to surround a plurality of cells 2 serving as a flow path for a fluid extending from the inflow end face 11 to the outflow end face 12. The honeycomb structure portion 4 has a columnar shape having the inflow end face 11 and the outflow end face 12 as both end faces.

The honeycomb structure 4 shown in FIGS. 1 to 3 has an outer peripheral wall 3 arranged so as to surround the partition wall 1 arranged so as to surround the cell 2. Here, FIG. 1 is a perspective view schematically showing an embodiment of the honeycomb structure of the present invention. FIG. 2 is a plan view schematically showing an inflow end surface of the honeycomb structure shown in FIG. FIG. 3 is a cross-sectional view schematically showing the XX'cross section of FIG.

The honeycomb structure portion 4 constituting the honeycomb structure 100 has a porous boundary wall 5 at the boundary between the central portion 16 and the outer peripheral portion 17 in the cross section orthogonal to the extending direction of the cell 2. That is, in the honeycomb structure portion 4, the inside of the boundary wall 5 is the central portion 16, and the outside of the boundary wall 5 is the outer peripheral portion 17. In FIGS. 1 to 3, reference numeral 1a indicates a partition wall 1a of the central portion 16, and reference numeral 2a indicates a cell 2a of the central portion 16. Further, reference numeral 1b indicates a partition wall 1b of the outer peripheral portion 17, and reference numeral 2b indicates a cell 2b of the outer peripheral portion 17.

In the honeycomb structure portion 4, the thickness of the partition wall 1a in the central portion 16 and the cell pitch of the cell 2a surrounded by the partition wall 1a are the same as the thickness of the partition wall 1b in the outer peripheral portion 17 and the cell pitch of the cell 2b surrounded by the partition wall 1b. is there. Further, the honeycomb structure portion 4 is configured such that the porosity of the partition wall 1a in the central portion 16 is larger than the porosity of the partition wall 1b in the outer peripheral portion 17.

In the honeycomb structure 100 configured as described above, since the partition wall 1a made of a porous material having a high porosity is arranged in the central portion 16, the amount of catalyst supported is larger than that of the outer peripheral portion 17. You can do a lot. Further, since the porous boundary wall 5 is provided at the boundary between the central portion 16 and the outer peripheral portion 17, the heat insulating effect of the central portion 16 is excellent. Therefore, the effect of increasing the amount of the catalyst supported on the central portion 16 and the heat insulating effect of the central portion 16 by the boundary wall 5 combine to enable early activation of the catalyst and improve the exhaust gas purification performance. be able to. Further, since the thickness and cell pitch of the partition wall 1 are the same in the central portion 16 and the outer peripheral portion 17, the pressure loss does not increase due to the change in the cell structure as in the conventional honeycomb structure. Therefore, the honeycomb structure 100 of the present embodiment can activate the catalyst at an early stage due to the low pressure loss.

Here, the thickness of the partition wall 1a in the central portion 16 and the thickness of the partition wall 1b in the outer peripheral portion 17 are the same as the thickness of the partition wall 1b in the outer peripheral portion 17 with respect to the thickness of the partition wall 1a in the central portion 16. , Means within ± 25%. With this configuration, it is possible to effectively suppress an increase in pressure loss due to a difference in the thickness of the partition walls 1a and 1b. Further, the same cell pitch in the central portion 16 and the cell pitch in the outer peripheral portion 17 means that the cell pitch in the outer peripheral portion 17 is within ± 10% of the cell pitch in the central portion 16. With this configuration, it is possible to effectively suppress an increase in pressure loss due to a difference in cell pitch between the central portion 16 and the outer peripheral portion 17.

As shown in FIG. 4, when the shape of the cell 2 is square, the length indicated by the reference numeral P in FIG. 4 is the “cell pitch P”. In FIG. 4, the length indicated by the symbol t indicates the thickness of the partition wall 1 that partitions the cell 2. As shown in FIG. 4, the cell pitch P is the mutual distance between the intermediate points of the respective thicknesses of the two partition walls 1 and 1 facing each other with the cell 2 interposed therebetween. FIG. 4 is a schematic diagram for explaining the cell pitch when the cell shape is square.

Further, as shown in FIG. 5, when the shape of the cell 2 is a hexagon, the length indicated by the reference numeral P in FIG. 5 is the “cell pitch P”. In FIG. 5, the length indicated by the symbol t indicates the thickness of the partition wall 1 that partitions the cell 2. FIG. 5 is a schematic diagram for explaining the cell pitch when the cell shape is hexagonal.

Further, as shown in FIG. 6, when the shape of the cell 2 is a triangle, the length indicated by the reference numeral P in FIG. 6 is the “cell pitch P”. In FIG. 6, the length indicated by the symbol t indicates the thickness of the partition wall 1 that partitions the cell 2. FIG. 6 is a schematic diagram for explaining the cell pitch when the cell shape is a triangle.

As shown in FIGS. 4 to 6, the "cell pitch P" is the length when one cell 2 is one unit in the array of a plurality of cells 2. Therefore, for example, when the cell pitch in the central portion 16 (see FIG. 2) and the cell pitch in the outer peripheral portion 17 (see FIG. 2) are the same, the cell density in the central portion 16 (see FIG. 2) and the outer circumference The cell density in part 17 (see FIG. 2) is the same.

The thickness of the partition wall 1b in the outer peripheral portion 17 is preferably within ± 25%, more preferably within ± 15%, with respect to the thickness of the partition wall 1a in the central portion 16. Further, the cell pitch in the outer peripheral portion 17 is preferably within ± 10%, and more preferably within ± 5% with respect to the cell pitch in the central portion 16.

The porosity of the central portion 16 of the honeycomb structure portion 4 is preferably 50% or more and 70% or less, and more preferably 55% or more and 65% or less. If the porosity of the central portion 16 is less than 50%, the amount of catalyst that can be supported on the central portion 16 is small, and early activity of the catalyst may be difficult to occur. On the other hand, if the porosity of the central portion 16 exceeds 70%, the strength of the central portion 16 may become too low.

The porosity of the outer peripheral portion 17 of the honeycomb structure portion 4 is preferably 25% or more and 50% or less, more preferably 25% or more and less than 50%, and 25% or more and 40% or less. Is particularly preferable. If the porosity of the outer peripheral portion 17 is less than 25%, the partition wall 1b itself of the outer peripheral portion 17 becomes dense, and it may be difficult to support the catalyst on the surface of the partition wall 1b. Therefore, the purification performance of the outer peripheral portion 17 may deteriorate. On the other hand, if the porosity of the outer peripheral portion 17 exceeds 50%, the strength of the honeycomb structure portion 4 itself may decrease, which is not preferable.

The porosity of the partition wall 1a in the central portion 16 and the porosity of the partition wall 1b in the outer peripheral portion 17 are values measured by a mercury porosimeter. Examples of the mercury porosimeter include Autopore 9500 (trade name) manufactured by Micromeritics. The average pore diameters of the partition 1a and the partition 1b are also the values measured by the mercury porosimeter.

Regarding the value of the difference between the porosity of the central portion 16 and the porosity of the outer peripheral portion 17, it is sufficient that there is a significant difference when comparing the porosities of each. For example, when the porosity of the central portion 16 is P1% and the porosity of the outer peripheral portion 17 is P2%, it is preferable that P1 / P2 ≧ 1.02, and P1 / P2 ≧ 1.10. Is more preferable. When P1 / P2 <1.02, it becomes difficult for a difference in the characteristics of the central portion 16 and the outer peripheral portion 17 to occur, and it may be difficult for each effect described so far to be exhibited. Further, P1 / P2 ≦ 5.0 is preferable, and P1 / P2 ≦ 4.0 is more preferable. When P1 / P2> 5.0, the honeycomb structure may be easily damaged when the honeycomb structure is housed in the metal container.

The thicknesses of the partition walls 1a and 1b of the central portion 16 and the outer peripheral portion 17 of the honeycomb structure portion 4 are preferably 0.038 mm or more and 0.500 mm or less, and preferably 0.050 mm or more and 0.300 mm or less. More preferred. In the honeycomb structure 100 of the present embodiment, the thickness of the partition walls 1a and 1b as described above is preferable in terms of suppressing damage to the honeycomb structure 100 and suppressing pressure loss. For example, if the thickness of the partition walls 1a and 1b is less than 0.038 mm, the partition walls 1a and 1b may be easily damaged. If the thickness of the partition walls 1a and 1b exceeds 0.500 mm, the pressure loss of the honeycomb structure 100 may increase. The thicknesses of the partition walls 1a and 1b are values measured by observing the shape of the cross section of the honeycomb structure 100 with a scanning electron microscope (SEM). Hereinafter, "the partition walls 1a and 1b of the central portion 16 and the outer peripheral portion 17 of the honeycomb structure portion 4" may be collectively referred to as "the partition wall 1 of the honeycomb structure portion 4" or simply "the partition wall 1".

The cell pitches of the central portion 16 and the outer peripheral portion 17 of the honeycomb structure portion 4 are preferably 0.70 mm or more and 2.60 mm or less, and more preferably 0.73 mm or more and 1.80 mm or less. If the cell pitch is less than 0.70 mm, the pressure loss of the honeycomb structure 100 may increase, or when a catalyst is supported, cell clogging may occur due to the supported catalyst. If the cell pitch exceeds 2.60 mm, the strength of the honeycomb structure 100 may be insufficient. In the honeycomb structure 100, the cell pitch of the central portion 16 and the cell pitch of the outer peripheral portion 17 are the same.

The average pore diameter of the porous material constituting the partition wall 1 of the honeycomb structure portion 4 is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 200 μm or less, and 10 μm or more and 100 μm or less. Is particularly preferable. If the average pore diameter is smaller than 2 μm, the ignition performance (light-off performance) of the catalyst (in other words, the catalyst component) may deteriorate. If the average pore diameter is larger than 200 μm, the strength of the partition walls 1a and 1b may decrease. The light-off performance (light-off performance) means a temperature characteristic in which the purification performance of the catalyst supported on the honeycomb structure 100 is exhibited.

The cell densities of the central portion 16 and the outer peripheral portion 17 of the honeycomb structure portion 4 are preferably 15 pieces / cm ² or more and 233 pieces / cm ² or less, and 30 pieces / cm ² or more and 186 pieces / cm ² or less. It is more preferable to have. If the cell density is less than 15 cells / cm ² , the strength of the honeycomb structure 100 may be insufficient. If the cell density exceeds 233 cells / cm ² , the pressure loss of the honeycomb structure 100 may increase, or when a catalyst is supported, cell clogging may occur due to the supported catalyst.

The partition wall 1 of the honeycomb structure portion 4 is preferably made of a material containing ceramics. Further, the material constituting the partition wall 1 preferably contains at least one kind of ceramics selected from the following "material group". The "material group" is a group including silicon carbide, silicon-silicon carbide-based composite material, cordierite, mullite, alumina, spinel, silicon carbide-corgerite-based composite material, lithium aluminum silicate, and aluminum titanate.

In the honeycomb structure 100 of the present embodiment, there is no particular limitation on the shape of the cell 2 in the cross section orthogonal to the extending direction of the cell 2. Examples of the shape of the cell 2 include "polygons such as triangles, quadrangles, pentagons, hexagons, heptagons, and octagons", circles, and ellipses. Further, a mode in which a plurality of these shapes are combined is also a preferred mode. Further, among the quadrangles, a square or a rectangle is preferable. Hereinafter, the "cross section orthogonal to the extending direction of the cell 2" may be referred to as a "cross section of the honeycomb structure portion 4" or a "cross section of the honeycomb structure 100". In the present invention, the cell 2 means a space surrounded by the partition wall 1.

In the honeycomb structure 100 shown in FIGS. 1 to 3, the cells 2a formed in the central portion 16 and the cells 2b formed in the outer peripheral portion 17 are, for example, latticed in the vertical and horizontal directions of the paper surface of FIG. Although they are arranged in a shape, the arrangement of cells 2a and 2b is not limited to this. For example, in FIG. 2, the cells 2a formed in the central portion 16 may be arranged in a direction different from the arrangement of the cells 2b formed in the outer peripheral portion 17. That is, the arrangement of the cells 2a in the central portion 16 and the arrangement of the cells 2b in the outer peripheral portion 17 do not have to have a parallel positional relationship. However, as described above, even when the arrangements of the cells 2a and 2b do not have a parallel positional relationship, the thickness and cell pitch of the partition wall 1a in the central portion 16 and the partition wall in the outer peripheral portion 17 The thickness and cell pitch of 1b need to be the same.

The outer shape of the honeycomb structure 100 (in other words, the overall shape of the honeycomb structure 100) is not particularly limited. Examples of the outer shape of the honeycomb structure 100 include a columnar shape, an elliptical columnar shape, a “columnar shape having a polygonal bottom surface such as a square columnar shape”, and a “columnar shape having an irregular bottom surface”. The size of the honeycomb structure 100 is not particularly limited, but the length of the cell 2 in the extending direction is preferably 25 to 350 mm. Further, for example, when the outer shape of the honeycomb structure 100 is cylindrical, the diameter of the bottom surface thereof is preferably 30 to 500 mm.

The boundary wall 5 is arranged so as to surround the outer periphery of the central portion 16. The width of the boundary wall 5 in the cross section of the honeycomb structure 100 is preferably 0.1 to 1.0 mm, more preferably 0.3 to 0.6 mm. If the width of the boundary wall 5 is less than 0.1 mm, the heat insulating effect of the central portion may not be sufficiently exhibited. On the other hand, if the width of the boundary wall 5 exceeds 1.0 mm, the pressure loss of the honeycomb structure may increase.

The boundary wall 5 is preferably made of a material containing ceramics. The material constituting the boundary wall 5 preferably contains at least one type of ceramic selected from the "material group" exemplified as the suitable material constituting the partition wall 1 described above.

There is no particular limitation on the size of the central portion 16. Here, the size of the central portion 16 is the size of the region surrounded by the boundary wall 5, that is, the "area including the opening portion of the cell 2 formed in the region". In the cross section of the honeycomb structure 100, the percentage of the ratio of the area of the central portion 16 to the area of the cross section of the honeycomb structure 100 is preferably 10 to 80%, more preferably 25 to 75%. With such a configuration, the light-off performance in the central portion 16 of the honeycomb structure portion 4 becomes better. If the percentage of the area of the central portion 16 is less than 10%, the area of the central portion 16 may be too small and early activity of the catalyst may be difficult to occur. If the percentage of the area of the central portion 16 exceeds 80%, the strength of the honeycomb structure 100 may become too low.

The shape of the boundary wall 5 in the cross section of the honeycomb structure portion 4 is not particularly limited. In the honeycomb structure 100 shown in FIGS. 1 to 3, the shape of the boundary wall 5 is a circular ring shape similar to the outer peripheral shape of the honeycomb structure portion 4. Boundary wall 5, in the cross section, Ru Oh circular, oval.

The honeycomb structure 100 of the present embodiment can be suitably used as a catalyst carrier for purifying exhaust gas of an internal combustion engine. The catalyst carrier is a porous structure that supports fine particles of the catalyst. Therefore, in each cell 2 formed in the honeycomb structure portion 4, it is preferable that the end portions on the inflow end surface 11 side and the outflow end surface 12 side are not sealed by a mesh sealing portion or the like.

In the honeycomb structure 100 of the present embodiment, the central portion 16 and the outer peripheral portion 17 are separately formed, and the central portion 16 and the outer peripheral portion 17 are joined via a boundary wall 5. You may. For example, in the honeycomb structure 100 of the present embodiment, the boundary wall 5 is composed of a central honeycomb formed only in the central portion 16 and an outer peripheral honeycomb having a tubular shape in which the portion corresponding to the central portion 16 is hollowed out. It may be joined via a honeycomb. Examples of the material of such a boundary wall 5 include an outer peripheral coating material used for forming an outer peripheral wall in a conventionally known honeycomb structure.

Further, in the honeycomb structure 100 of the present embodiment, the central portion 16 and the outer peripheral portion 17 may be integrally formed. For example, when the honeycomb structure 100 is manufactured by extrusion molding, a molding raw material forming the outer peripheral portion 17 is arranged outside the molding raw material forming the central portion 16 to prepare a clay, and the clay is prepared. The honeycomb structure 100 may be manufactured by extrusion molding.

The honeycomb structure 100 of the present embodiment has an outer peripheral wall 3 that surrounds and surrounds the outer periphery of the honeycomb structure portion 4. In the honeycomb structure 100 shown in FIGS. 1 to 3, the outer peripheral wall 3 and the partition wall 1b of the outer peripheral portion 17 of the honeycomb structure portion 4 are integrally formed. Although not shown, the honeycomb structure portion 4 may have an outer peripheral coat layer arranged so as to cover the outer periphery thereof. For example, after the outer peripheral wall 3 of the honeycomb structure portion 4 as shown in FIGS. 1 to 3 is once removed by grinding or the like, an outer peripheral coating material is applied to the outer periphery of the honeycomb structure portion 4 from which the outer peripheral wall 3 has been removed. Alternatively, an outer peripheral coat layer may be provided so as to cover the outer periphery of the honeycomb structure portion 4.

In the honeycomb structure 100 of the present embodiment, a catalyst for purifying exhaust gas (not shown) may be supported on at least one of the surface of the partition wall 1 of the honeycomb structure portion 4 and the pores of the partition wall 1. The amount of the catalyst supported is preferably 10 to 400 (g / liter), more preferably 50 to 200 (g / liter). If the amount of the catalyst supported is less than 10 (g / liter), the exhaust gas purification performance may be lowered. If the amount of the catalyst supported is more than 400 (g / liter), the pressure loss may increase. Here, the catalyst loading amount (g / liter) is a value obtained by dividing the total mass of the catalyst on the partition surface and the catalyst in the partition by the volume of the honeycomb structure (total volume of the partition and the "cell space"). When the catalyst is supported on the honeycomb structure, the catalyst-supported amount in the central portion 16 and the catalyst-supported amount in the outer peripheral portion 17 are different, and the catalyst-supported amount in the central portion 16 is larger than that in the outer peripheral portion 17.

Examples of the catalyst include conventionally known catalysts for automobile exhaust gas. For example, "three-way catalyst based on a noble metal such as Pt, Pd, Rh", an oxidation catalyst, a deodorizing catalyst, "a base metal catalyst such as Mn, Fe, Cu" and the like can be mentioned.

(2) Manufacturing method of honeycomb structure:
Next, a method for manufacturing the honeycomb structure of the present invention will be described.

When producing the honeycomb structure of the present invention, first, a molding raw material for molding the honeycomb molded body is prepared. The molding raw material preferably contains a ceramic raw material.

As the ceramic raw material contained in the molding raw material, for example, at least one kind of ceramic selected from the following "raw material group" is preferable. The "raw material group" includes silicon carbide, silicon-silicon carbide composite material, cordierite raw material, cordierite, mullite, alumina, spinel, silicon carbide-corgerite composite material, lithium aluminum silicate, and aluminum titanate. It is a group. By using these raw materials, a honeycomb structure having excellent strength and heat resistance can be obtained. The cordierite-forming raw material is a ceramic raw material having a chemical composition in which silica is in the range of 42 to 56% by mass, alumina is in the range of 30 to 45% by mass, and magnesia is in the range of 12 to 16% by mass. Then, the corderite-forming raw material is calcined to become cordierite. Examples of the raw material component that becomes the silica source include quartz and molten silica. As the raw material component to be the alumina source, it is preferable to use at least one of aluminum oxide and aluminum hydroxide because there are few impurities. Examples of the raw material component that is a source of magnesia include talc and magnesite. Talc as a magnesia source preferably has an average particle size of 10 to 30 μm. Further, the magnesia source component may contain Fe ₂ O ₃ , CaO, Na ₂ O, K ₂ O and the like as impurities.

The molding raw material is preferably prepared by mixing the ceramic raw material with a pore-forming material, a binder, a dispersant, a surfactant, a dispersion medium and the like.

Examples of the pore-forming material include graphite, wheat flour, starch, foamed resin, and water-absorbent polymer. In addition, examples of the pore-forming material include synthetic resins such as phenol resin, polymethyl methacrylate, polyethylene, and polyethylene terephthalate. These synthetic resins may be hollow particles or may be solid particles having no hollow portion. The amount of the pore-forming material added is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the ceramic raw material.

Examples of the binder include hydroxypropylmethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxylmethyl cellulose, polyvinyl alcohol and the like. The amount of the binder added is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the ceramic raw material.

Examples of the dispersant include dextrin and polyalcohol.

Examples of the surfactant include ethylene glycol and fatty acid soap. The amount of the surfactant added is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the ceramic raw material.

Water is preferable as the dispersion medium. The amount of the dispersion medium is preferably 30 to 150 parts by mass with respect to 100 parts by mass of the ceramic raw material.

When forming a honeycomb molded body using a molding raw material, it is preferable that the molding raw material is first kneaded to form a clay, and the obtained clay is molded into a honeycomb shape.

When the honeycomb structure is manufactured by one extrusion molding, a molding raw material for forming the central portion and a molding raw material for forming the outer peripheral portion are separately prepared, and each molding raw material is used. Two types of honeycombs are made using this. Then, a mass of clay is prepared by arranging the clay prepared from the molding raw material for forming the outer peripheral portion on the outside of the clay prepared from the molding raw material for forming the central portion, and this clay is prepared. Extrusion molding is performed using.

On the other hand, when the central portion and the outer peripheral portion of the honeycomb structure are separately manufactured and later joined to each other via the boundary wall, the honeycomb structure corresponding to the central portion and the honeycomb corresponding to the outer peripheral portion are formed. The structure and the structure are individually prepared. The honeycomb structure corresponding to the outer peripheral portion is a honeycomb structure having a tubular shape in which the portion corresponding to the central portion is hollowed out.

The method of kneading the molding raw materials to form the clay is not particularly limited, and examples thereof include a method using a kneader, a vacuum clay kneader, and the like.

The method for forming the honeycomb molded body by molding the clay is not particularly limited, and a molding method such as an extrusion molding method, an injection molding method, or a press molding method can be used. It is preferable to adopt an extrusion molding method because continuous molding is easy and, for example, cordierite crystals can be oriented. The extrusion molding method can be performed using an apparatus such as a vacuum clay kneader, a ram type extrusion molding machine, and a twin-screw continuous extrusion molding machine. Further, it is preferable that the apparatus used for extrusion molding is attached with a base that forms a honeycomb molded body having a desired partition wall thickness, cell pitch, cell shape, etc., and extrusion molding is performed. As the material of the base, stainless steel, cemented carbide and the like, which are hard to wear, are preferable.

After molding the honeycomb molded product, it is preferable to dry the obtained honeycomb molded product. The drying method is not particularly limited, and examples thereof include hot air drying, microwave drying, dielectric drying, vacuum drying, vacuum drying, and freeze drying. Among these, since the entire honeycomb molded body can be dried quickly and uniformly, it is preferable to perform dielectric drying, microwave drying, or hot air drying alone or in combination. Further, the drying conditions can be appropriately determined depending on the drying method.

Next, the honeycomb molded body is main fired to produce a honeycomb structure. The "main firing" means an operation for sintering and densifying the molding raw materials constituting the honeycomb molded body to secure a predetermined strength.

Before the main firing of the honeycomb molded body, it is preferable to calcin the honeycomb molded body. The calcining is performed for degreasing, and the method is not particularly limited as long as it can remove organic substances such as binders, dispersants, and pore-forming materials in the honeycomb molded body. Generally, the combustion temperature of the organic binder is about 100 to 300 ° C. The combustion temperature of the pore-forming material varies depending on the type, but is about 200 to 1000 ° C. Therefore, as a condition for calcining, it is preferable to heat in an oxidizing atmosphere at about 200 to 1000 ° C. for about 3 to 100 hours.

Since the firing conditions in the main firing differ depending on the type of the molding raw material, appropriate conditions may be selected according to the type. Here, the firing conditions are various conditions for firing such as the firing temperature, the firing time, and the firing atmosphere. For example, when a cordierite-forming raw material is used, the maximum firing temperature is preferably 141 to 1440 ° C. The maximum temperature holding time during firing is preferably 3 to 15 hours.

As described above, the honeycomb structure of the present invention can be manufactured. A catalyst may be supported on the manufactured honeycomb structure.

There is no particular limitation on the method of supporting the catalyst. For example, a catalyst can be supported on the honeycomb structure according to a method used in a conventionally known method for producing a honeycomb structure. As an example, when a noble metal such as Pt, Pd, or Rh is supported as a catalyst for automobile exhaust gas, it can be supported as follows. First, the acid-treated and heat-treated honeycomb structure is immersed in a slurry of γ-alumina containing "a noble metal catalyst component such as an aqueous solution of chloroplatinic acid" and "a rare earth oxide such as CeO ₂ ". After a certain period of time, the honeycomb structure is taken out from the slurry. After taking out the honeycomb structure, the excess slurry adhering to the honeycomb structure may be removed by air or the like. Then, by drying the honeycomb structure taken out from the slurry, a honeycomb structure on which a catalyst is supported can be obtained. The honeycomb structure may be obtained by baking the honeycomb structure taken out from the slurry at a temperature of 500 to 600 ° C.

Examples of the catalyst supported on the honeycomb structure include "a three-way catalyst based on a noble metal such as Pt, Pd, and Rh", an oxidation catalyst, a deodorizing catalyst, and a "base metal catalyst such as Mn, Fe, and Cu". it can. Further, as another example of the method of supporting the catalyst, the catalyst is supported on the surface of the partition wall of the honeycomb structure composed of cordierite in a high specific surface area state after acid treatment, and then heat treatment is performed at 600 to 1000 ° C. Can be mentioned as a method of doing.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
Talc, kaolin, alumina, silica, and aluminum hydroxide were prepared and mixed to obtain a cordierite-forming raw material. The chemical composition of the cordierite-forming raw material is talc, kaolin, alumina, so that SiO ₂ is 42 to 56% by mass, Al ₂ O ₃ is 30 to 45% by mass, and MgO is 12 to 16% by mass. It is a mixture of silica and aluminum hydroxide in a predetermined ratio.

Next, a pore-forming material, methyl cellulose as a binder, and water as a dispersion medium were added to the obtained cordierite-forming raw material, and these were mixed to obtain a molding raw material. 10 parts by mass of the pore-forming material was added to 100 parts by mass of the cordierite-forming raw material. 3 parts by mass of the binder was added to 100 parts by mass of the cordierite-forming raw material. 50 parts by mass of the dispersion medium was added to 100 parts by mass of the cordierite-forming raw material. As the pore-forming material, a mixture of two types of graphite having different average particle diameters at a predetermined ratio was used. As the graphite, graphite having an average particle diameter of 10 μm and graphite having an average particle diameter of 50 μm were used. In Example 1, two types of molding raw materials were prepared by changing the distribution of graphite used as the pore-forming material. The two types of molding raw materials are for individually producing the central portion and the outer peripheral portion of the honeycomb structure.

Next, the obtained two types of molding raw materials were kneaded to obtain two types of clay for molding a honeycomb molded body. Since the two types of clay have different graphite distributions as described above, the respective porous materials obtained by firing have different porosity values.

Next, two types of clay were extruded using a predetermined base to obtain two types of honeycomb molded bodies having a partition wall arranged so as to surround a plurality of cells and an outer peripheral wall. .. Both of the two types of honeycomb molded bodies had a square cell shape (the shape of the cell in a cross section orthogonal to the extending direction of the cell) and a columnar shape as a whole.

Next, the obtained two types of honeycomb molded bodies were dried with hot air at 120 ° C., and then fired at 140 to 1430 ° C. for 10 hours to prepare two types of honeycomb base materials. The obtained honeycomb base material had a columnar shape having a diameter of a surface orthogonal to the cell extending direction of 100 mm and a length of the cell extending direction of 100 mm. The cell density of the honeycomb base material was 62 cells / cm ² , and the thickness of the partition wall was 0.11 mm. The partition wall thickness is a value measured by a method of cross-sectional observation using an SEM (scanning electron microscope).

Next, of the two types of honeycomb molded bodies obtained, the honeycomb base material having a low porosity after firing is designated as the "first honeycomb base material", and the honeycomb base material having a high porosity after firing is referred to as "second honeycomb". It was called "molded body". For the first honeycomb base material, a central portion having a radius of 25 mm was hollowed out from the center of the plane orthogonal to the extending direction of the cell. As a result, the central portion of the first honeycomb base material became a donut shape having a cavity having a diameter of 50 mm. On the other hand, the outer peripheral portion of the second honeycomb base material was ground to form a columnar shape having a diameter of 49.5 mm. Then, after coating the outer peripheral coating material on the outer periphery of the second honeycomb base material, the second honeycomb base material was embedded in the hollow portion of the first honeycomb base material, and the outer peripheral coating material was dried with hot air at 120 ° C. Then, the bonded body of the first honeycomb base material and the second honeycomb base material was fired at 1400 to 1430 ° C. for 10 hours to prepare the honeycomb structure of Example 1.

The second honeycomb base material, which is the central portion of the honeycomb structure, had a porosity of 35% and an average pore diameter of 5 μm. The first honeycomb base material, which is the outer peripheral portion of the honeycomb structure, had a porosity of 55% and an average pore diameter of 4 μm. Porosity and average pore size were measured by Autopore 9500 (trade name) manufactured by Micromeritics.

A honeycomb catalyst body was produced by supporting a catalyst component and a high specific surface area material on the obtained honeycomb structure of Example 1. Palladium, platinum and rhodium were used as catalyst components. As the high specific surface area material, γ-alumina was used.

Hereinafter, a method for supporting the catalyst component and the high specific surface area material will be described. First, palladium, platinum, rhodium, γ-alumina and water were mixed to obtain a catalyst slurry. The mass ratio of palladium, platinum and rhodium was 15: 1: 1 (palladium: platinum: rhodium = 15: 1: 1). The amount of γ-alumina in the catalyst slurry was set to 20 times the “total mass of palladium, platinum and rhodium”.

Next, the obtained catalyst slurry was placed in a container, and the honeycomb structure of Example 1 was immersed in the catalyst slurry. Then, the honeycomb structure was taken out from the catalyst slurry, excess catalyst slurry was removed with air, and the mixture was dried at 120 ° C. The above-mentioned immersion and drying were repeated until a predetermined amount of catalyst (catalyst components (palladium, platinum and rhodium) and γ-alumina) was supported on the honeycomb structure. Then, the honeycomb structure on which a predetermined amount of catalyst was supported was calcined at 550 ° C. in a nitrogen atmosphere to obtain a honeycomb catalyst body. The “predetermined amount of catalyst” in this embodiment is an amount in which the amount of catalyst supported is 90 g / liter at the central portion of the honeycomb structure and 60 g / liter at the outer peripheral portion of the honeycomb structure.

Table 1 shows the configurations of the central portion, the outer peripheral portion, and the boundary wall of the honeycomb structure of Example 1.

The following "thermal cycle test", "HC purification test", and "pressure drop evaluation" were performed on the obtained honeycomb catalyst body. The "HC purification test" is a hydrocarbon purification test. The results are shown in Table 2.

(Thermodynamic cycle test)
As shown in FIG. 7, the honeycomb structure 100 was mounted in a stainless steel test can body 400. Then, using a gas burner tester (not shown), combustion gas was flowed through the honeycomb structure 100 at a flow rate of 1.0 Nm ³ / min. At this time, propane was used as the fuel. Then, the honeycomb structure 100 was heated to 1100 ° C. in 240 seconds, held at 1100 ° C. for 240 seconds, and then a gas at 25 ° C. was flowed at 0.9 Nm ³ / min for 5 minutes. Then, when "from the start of flowing the combustion gas to the end of flowing the gas at 25 ° C." was set as one cycle, the cycle was repeated for 5 cycles. Then, the honeycomb structure 100 was taken out from the test can body 400, and the end face of the honeycomb structure 100 was observed using a microscope to confirm the presence or absence of cracks. If cracks are confirmed by observing the end face of the honeycomb structure 100, “cracked” is described in the “thermal cycle test” column of Table 2. On the other hand, when no crack is confirmed by observing the end face of the honeycomb structure 100, "no crack" is described in the "thermal cycle test" column of Table 2. FIG. 7 is a schematic view showing a state in which the honeycomb structure is inserted into the can body in the thermal cycle test of the example. Further, in FIG. 7, the arrow indicated by reference numeral 401 indicates the flow direction of the combustion gas and the gas at 25 ° C.

(HC purification test)
The HC purification test is a test for evaluating the purification performance of hydrocarbon (HC) in exhaust gas. Specifically, first, an exhaust system (manifold system) as shown in FIG. 8 was manufactured. The exhaust system 500 shown in FIG. 8 includes a gasoline engine 501 from the upstream and a catalytic converter 502 equipped with a honeycomb structure (not shown) as an evaluation sample. As the gasoline engine 501, a gasoline engine having a displacement of 2000 cc was used, and the power was absorbed by a dynamometer. An HC purification test was conducted using such an exhaust system 500. Here, FIG. 8 is a schematic view showing an apparatus used in the HC purification test of the example. Hereinafter, the test method of the HC purification test will be described in more detail.

In the HC purification test, the gasoline engine 501 was first started, operated for 10 minutes under the condition of 3000 rpm, and then the gasoline engine 501 was stopped. Then, the entire test apparatus of the exhaust system 500 was left at 20 ° C. for 10 hours. By this leaving, the entire test apparatus was put into a so-called cold state. The cold state means a state in which the gasoline engine body, cooling water, exhaust pipe, etc. have reached a temperature similar to 20 ° C., which is room temperature.

Next, in the HC purification test, the gasoline engine is started again from this cold state. After starting and idling for 10 seconds, the gasoline engine 501 was operated at 2000 rpm for 130 seconds or more. At this time, the amount of hydrocarbon in the gas discharged from the catalytic converter 502 is measured within 140 seconds after the start of the gasoline engine 501. The "HC ratio" is shown in the "HC purification test" column of Table 2. The "HC ratio" shown in Table 2 can be obtained by the following method. First, the HC purification test described above is performed without mounting the honeycomb structure supporting the catalyst in the catalyst converter 502 of the exhaust system 500, and the amount of hydrocarbon is measured. Next, the honeycomb structure supporting the catalyst is mounted in the catalyst converter 502 of the exhaust system 500, the same HC purification test is performed, and the amount of hydrocarbon is measured. The value of the ratio of the amount of hydrocarbon when the honeycomb structure is attached to the amount of hydrocarbon when the honeycomb structure is attached is the “HC ratio” shown in Table 2. It can be said that the smaller the "HC ratio", the more excellent the honeycomb structure is in the light-off performance, which is the ignition performance of the catalyst.

(Pressure drop evaluation)
Air was circulated through the honeycomb structure carrying the catalyst at a flow rate of 10 m ² / min under room temperature conditions, and the pressure on the inflow end face side and the pressure on the outflow end face side of the honeycomb structure were measured. The pressure difference between the pressure on the inflow end face side and the pressure on the outflow end face side was defined as a pressure loss (pressure loss). The "pressure loss ratio" shown in Table 2 indicates the pressure loss ratio before and after the honeycomb structure carrying the catalyst (that is, the upstream side and the downstream side of the flow path), and the smaller the "pressure loss ratio", the more the honeycomb structure is formed. It can be said that the low pressure loss is excellent even if the catalyst is supported.

(Examples 2-28)
The configurations of the central portion, the outer peripheral portion, and the boundary wall of the honeycomb structure were changed as shown in Tables 1 and 3, and the honeycomb structures of Examples 2 to 26 were manufactured. In the honeycomb structure of Example 25, the thickness of the partition wall at the outer peripheral portion is + 18% with respect to the thickness of the partition wall at the central portion, and in the present invention, the thickness of both partition walls is the same. I reckon. Further, in the honeycomb structure of Example 26, the cell pitch in the outer peripheral portion is + 6% with respect to the cell pitch in the central portion, and in the present invention, both cell pitches are considered to be the same. Further, the thickness and cell pitch of the partition wall in the central portion and the thickness and cell pitch of the partition wall in the outer peripheral portion were changed as shown in Table 3 to prepare the honeycomb structures of Examples 27 and 28.

(Comparative Examples 1 to 3)
The configurations of the central portion, the outer peripheral portion, and the boundary wall of the honeycomb structure were changed as shown in Table 3, and the honeycomb structures of Comparative Examples 1 to 3 were manufactured. In the honeycomb structure of Comparative Example 1, the porosity of the partition wall in the central portion and the porosity of the partition wall in the outer peripheral portion are the same.

In the honeycomb structure of Comparative Example 2, the thickness of the partition wall at the central portion and the thickness of the partition wall at the outer peripheral portion are different. In particular, in the honeycomb structure of Comparative Example 2, the thickness of the partition wall at the outer peripheral portion is + 27% of the thickness of the partition wall at the central portion.

In the honeycomb structure of Comparative Example 3, the cell pitch at the central portion and the cell pitch at the outer peripheral portion are different. In particular, in the honeycomb structure of Comparative Example 2, the cell pitch in the outer peripheral portion is + 11% with respect to the cell pitch in the central portion.

The honeycomb structures of Examples 2 to 28 and Comparative Examples 1 to 3 were also subjected to "heat cycle test", "HC purification test", and "pressure drop evaluation" in the same manner as in Example 1. The results are shown in Tables 2 and 4.

(result)
As shown in Tables 2 and 4, the honeycomb structures of Examples 1 to 28 were able to obtain good results in the "heat cycle test", "HC purification test", and "pressure drop evaluation".

On the other hand, the honeycomb structures of Comparative Examples 1 and 2 had a higher pressure loss ratio than the honeycomb structures of Example 1 and the like. In the honeycomb structure of Comparative Example 1, the porosity of the partition wall in the central portion and the porosity of the partition wall in the outer peripheral portion are the same. Further, in the honeycomb structure of Comparative Example 2, the thickness of the partition wall at the central portion and the thickness of the partition wall at the outer peripheral portion are different. Further, cracks were confirmed in the honeycomb structure of Comparative Example 3 in the thermal cycle test. In the honeycomb structure of Comparative Example 3, the cell pitch at the central portion and the cell pitch at the outer peripheral portion are different.

In addition, the honeycomb structures of Examples 1 to 3 gave better results in the "HC purification test" or "pressure loss evaluation" as compared with the honeycomb structures of Examples 4 and 5. Therefore, it was found that the porosity of the central portion of the honeycomb structure portion is preferably 50% or more and 70% or less. In the honeycomb structure of the present invention, the partition wall thickness, cell pitch, and porosity parameters influence the results of the "heat cycle test", "HC purification test", and "pressure drop evaluation", respectively. Therefore, by setting the above parameters in a predetermined numerical range, it is possible to realize a honeycomb structure having a lower low voltage loss and more excellent purification performance.

The honeycomb structure of the present invention can be used as a catalyst carrier that carries a catalyst for purifying exhaust gas emitted from a gasoline engine, a diesel engine, or the like.

1: Partition, 1a: Partition (central partition), 1b: Partition (outer partition), 2: Cell, 2a: Cell (central cell), 2b: Cell (outer cell), 3: Outer wall, 4: Honeycomb structure, 5: Boundary wall, 11: Inflow end face, 12: Outflow end face, 16: Central part, 17: Outer part, 100: Honeycomb structure, 400: Test can body, 401: Gas Flow direction, 500: exhaust system, 501: gasoline engine, 502: catalytic converter.

Claims (10)

A columnar honeycomb structure having a porous partition wall arranged so as to surround a plurality of cells serving as a fluid flow path extending from an inflow end face to an outflow end face.
The honeycomb structure portion has a porous boundary wall at a boundary between a central portion and an outer peripheral portion in a cross section orthogonal to the extending direction of the cell, and the shape of the boundary wall in the cross section is circular or elliptical. Yes,
In the honeycomb structure portion, the thickness and cell pitch of the partition wall in the central portion and the thickness and cell pitch of the partition wall in the outer peripheral portion are the same, and the porosity of the partition wall in the central portion is the outer circumference. A honeycomb structure configured to be larger than the porosity of the partition wall in the portion. The honeycomb structure according to claim 1, wherein the porosity of the central portion of the honeycomb structure portion is 50% or more and 70% or less. The honeycomb structure according to claim 1 or 2, wherein the porosity of the outer peripheral portion of the honeycomb structure portion is 25% or more and 50% or less. The honeycomb structure according to any one of claims 1 to 3, wherein the thickness of the partition wall of the central portion and the outer peripheral portion of the honeycomb structure portion is 0.038 mm or more and 0.500 mm or less. The honeycomb structure according to any one of claims 1 to 4, wherein the average pore diameter of the porous material constituting the partition wall is 2 μm or more and 200 μm or less. The honeycomb structure according to any one of claims 1 to 5, wherein the cell pitch of the central portion and the outer peripheral portion of the honeycomb structure portion is 0.70 mm or more and 2.60 mm or less. The honeycomb structure according to any one of claims 1 to 6, wherein the cell densities of the central portion and the outer peripheral portion of the honeycomb structure portion are 15 pieces / cm ² or more and 233 pieces / cm ² or less. At least one ceramic in which the partition wall is selected from the group of silicon carbide, silicon-silicon carbide composite material, cordierite, mullite, alumina, spinel, silicon carbide-corgerite composite material, lithium aluminum silicate, and aluminum titanate. The honeycomb structure according to any one of claims 1 to 7, which is made of a material containing. The honeycomb structure according to any one of claims 1 to 8, which is used as a catalyst carrier for purifying exhaust gas of an internal combustion engine. The honeycomb structure according to any one of claims 1 to 9, wherein a catalyst for purifying exhaust gas is supported on at least one of the surface of the partition wall and the pores of the partition wall of the honeycomb structure portion.

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