JP6981397B2 - Honeycomb structure and exhaust gas purification filter - Google Patents

Description

The present invention relates to a honeycomb structure and an exhaust gas purification filter.

Particulate matter called particulate matter is contained in the exhaust gas emitted from internal combustion engines such as diesel engines and gasoline engines, and heat engines such as boilers. Particulate is hereinafter referred to as "PM" as appropriate. An exhaust gas purification filter is used to collect PM in the exhaust gas.

The exhaust gas purification filter generally has a honeycomb structure having a plurality of cells formed by being partitioned by a porous partition wall, and a catalyst supported on the pores of the partition wall in the honeycomb structure. The exhaust gas purification filter is required to reduce the pressure loss while increasing the PM collection rate. The collection rate of PM is hereinafter appropriately referred to as “collection rate”, and the pressure loss is hereinafter appropriately referred to as “pressure loss”. Conventionally, in order to suppress deterioration of collection rate and pressure loss due to catalyst support, it has been mainly practiced to define the pore diameter, porosity, and pore distribution of the partition wall before catalyst support.

In recent years, attempts have been made to improve the PM collection rate by defining the internal structure of the porous partition wall. For example, Patent Document 1 discloses a technique in which the total network length of a network obtained by thinning a 3D model of a ceramic portion of a honeycomb wall is 2200 mm / m ^{3 or more.} According to the same document, PM can be collected with high efficiency by adopting the above configuration.

Japanese Unexamined Patent Publication No. 2017-163691

However, as has been generally done in the past, simply defining the pore diameter, porosity, and pore distribution of the partition wall before supporting the catalyst, or defining the total network length formed by the ceramic portion is sufficient for the catalyst. It cannot always be said that deterioration of the collection rate and pressure loss after loading can be suppressed. This is due to the following reasons. Even if the pore diameter, porosity, and pore distribution in the partition wall are the same, if there are non-continuous vents formed from pores that do not communicate between adjacent cells, the catalyst-containing slurry is contained in the non-continuous vents when the catalyst is supported. Not flowing. Therefore, it is difficult to support the catalyst on the pore wall of the non-communicating vent. Further, the catalyst-containing slurry that did not enter the non-communicating vents when the catalyst was supported flows into the continuous vents formed from the pores communicating between the adjacent cells more than necessary. Therefore, the continuous ventilation holes are often blocked by the catalyst. As a result, it becomes difficult to suppress deterioration of collection rate and pressure loss due to catalyst support.

The technique of Patent Document 1 is intended to improve the collection rate by defining the internal structure of the partition wall as described above. That is, the technique of Patent Document 1 is a technique of simply improving the collection efficiency of PM by increasing the total length of the network formed by the ceramic portion, and the collection rate due to the reduction of pores by supporting the catalyst. In consideration of the deterioration of pressure loss, it is not intended to secure effective pores for supporting the catalyst before supporting the catalyst.

The present invention has been made in view of the above problems, and is a honeycomb structure before the catalyst is supported, which can suppress deterioration of the collection rate and pressure loss due to the catalyst support, and trapping by the catalyst support. It is an object of the present invention to provide an exhaust gas purification filter capable of suppressing deterioration of collection rate and pressure loss.

One aspect of the present invention is the honeycomb structure (1) before the catalyst is supported, which is used for the exhaust gas purification filter.
The outer skin (11) and
A partition wall (12) that partitions the inside of the exodermis and has a large number of pores (121) formed therein.
It has a cell (13) surrounded by the partition wall and
The above partition wall
It has a communication ventilation hole (122) that communicates between the adjacent cells.
The honeycomb structure (1) has a number of continuous ventilation holes of 18,000 [lines / 0.25 mm ^{2] or more.}

Another aspect of the present invention is an exhaust gas purification filter (3) having the honeycomb structure and the catalyst (2) supported on the pore wall (122a) of the communication ventilation holes.

Yet another aspect of the present invention is an exhaust gas purification filter (3) having a honeycomb structure (1) and a catalyst (2).
The honeycomb structure is
The outer skin (11) and
A partition wall (12) that partitions the inside of the exodermis and has a large number of pores (121) formed therein.
It has a cell (13) surrounded by the partition wall and
The partition wall has a communication ventilation hole (122) for communicating between adjacent cells.
The catalyst is supported on the hole wall (122a) of the communication holes.
The amount of the catalyst supported is 30 g / L or more, and the amount is 30 g / L or more.
It is in the exhaust gas purification filter (3) in which the number of the communication holes communicating between the adjacent cells in the state where the catalyst is supported is 4500 [lines / 0.25 mm ^{2] or more.}

The honeycomb structure has the above configuration, and in particular, the number of communication holes for communicating between adjacent cells (hereinafter, appropriately referred to as the number of communication holes) is 18,000 [lines / 0.25 mm ² ] or more. It is said that. Therefore, in the honeycomb structure, the number of continuous ventilation holes contributing to the catalyst support increases to the above-mentioned specific value or more, so that even when the catalyst is supported for use in the exhaust gas purification filter, the collection rate by the catalyst support is increased. And the deterioration of pressure loss can be suppressed.

The reason why such an effect is obtained is considered to be as follows. As described above, the reason why the collection rate and pressure loss are deteriorated by supporting the catalyst is that an extra catalyst is supported in the communication holes that contribute to the performance development, and the communication holes are often blocked by the catalyst. Reducing the amount of the closed continuous ventilation holes is the key to suppressing the deterioration of the collection rate and pressure loss due to the catalyst loading. In the exhaust gas purification filter, the catalyst is mainly carried in the communication holes of the partition wall. On the other hand, since the catalyst-containing slurry does not flow into the non-communicating vents when the catalyst is supported, the non-communicated vents do not contribute to the catalyst support. By increasing the number of continuous vents that contribute to supporting the catalyst, when the same amount of catalyst is supported, the larger the number of continuous vents that can support the catalyst, the smaller the amount of catalyst per continuous vent. As a result, the number of continuous ventilation holes that are filled by the catalyst when the catalyst is supported is reduced, and deterioration of the collection rate and pressure loss due to the catalyst support can be suppressed.

The exhaust gas purification filter has the above configuration. Therefore, according to the exhaust gas purification filter, it is possible to suppress deterioration of the collection rate and pressure loss due to the catalyst loading.

The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

It is a perspective view of the honeycomb structure in Embodiment 1. FIG. FIG. 5 is an enlarged partial cross-sectional view of the honeycomb structure in the axial direction in the first embodiment. (A) is an example of an enlarged sectional view of a partition wall of a honeycomb structure in the first embodiment, and (b) is another example of an enlarged sectional sectional view of a partition wall of a honeycomb structure in the first embodiment. (A) is a schematic cross-sectional view of a partition wall showing the pores of FIG. 3 (a) more simply, and (b) is a schematic cross-sectional view of a partition wall showing the pores of FIG. 3 (b) more simply. It is explanatory drawing about the CT scan of the partition wall in Embodiment 1. FIG. It is a figure which showed an example of the scan image by the CT scan of the partition wall in Embodiment 1. FIG. It is an enlarged view of the scanned image shown in FIG. It is a figure which showed an example of the binarization processing image of (a) the CT scan image of a partition wall and (b) the CT scan image of a partition wall in Embodiment 1. FIG. It is a figure which showed schematically the thinning process image of the pore path of a partition wall in Embodiment 1. FIG. It is a figure which showed the other example of the thinning process image of the pore path of a partition wall schematically in Embodiment 1. FIG. FIG. 5 is a diagram schematically showing still another example of the thinning-processed image of the pore path of the partition wall in the first embodiment. It is a figure which showed an example of the frequency histogram of the pore path length distribution in Embodiment 1. FIG. It is a figure which showed the collecting position of the measurement sample for measuring the number of continuous ventilation holes in Embodiment 1. FIG. It is an example of the enlarged cross-sectional schematic diagram of the partition wall portion of the honeycomb structure provided with the exhaust gas purification filter in Embodiment 1. It is a figure which showed the pore path length distribution of the test piece H2 in Experimental Example 2. It is a figure which showed the pore path length distribution of the test piece H3 in Experimental Example 2. It is a figure which showed the pore path length distribution of the test piece H4 in Experimental Example 2. It is a figure which showed the pore path length distribution of the test piece H5 in Experimental Example 2. It is a figure which showed the pore path length distribution of the test piece H6 in Experimental Example 2. It is a figure which showed the pore path length distribution of the test piece H7 in Experimental Example 2. It is a figure which showed the relationship between the number of continuous ventilation holes and the deterioration rate of the collection rate in the honeycomb structure before carrying a catalyst in Experimental Example 2. FIG. It is a figure which showed the relationship between the number of continuous ventilation holes and the deterioration rate of pressure loss in the honeycomb structure before carrying a catalyst in Experimental Example 2. FIG. It is a figure which showed the relationship between the number of continuous ventilation holes in a honeycomb structure before a catalyst support, and the number of continuous ventilation holes in a honeycomb structure after a catalyst support in Experimental Example 3. FIG. It is explanatory drawing for demonstrating the method of measuring a NOx purification rate in Experimental Example 4. FIG. It is a figure which showed the relationship between the bending degree before carrying a catalyst, and NOx purification rate in Experimental Example 4. It is a figure which showed the relationship between the catalyst layer thickness and NOx purification rate in Experimental Example 4. It is a figure which showed the relationship between the bending degree before carrying a catalyst, and the thickness of a catalyst layer in Experimental Example 4. FIG.

(Embodiment 1)
The honeycomb structure of the first embodiment will be described with reference to FIGS. 1 to 13. As illustrated in FIGS. 1 to 3, the honeycomb structure 1 of the present embodiment is used as the base material of the exhaust gas purification filter before the catalyst is supported.

The honeycomb structure 1 can be formed from, for example, cordierite or the like, and has an outer skin 11, a partition wall 12, and a cell 13. The outer skin 11 can be formed in a tubular shape such as a cylindrical shape. In the present embodiment, the axial direction Y of the tubular outer skin 11 will be described below as the axial direction Y of the honeycomb structure 1. Further, the arrows in FIG. 2 indicate the flow of exhaust gas when the honeycomb structure 1 is arranged in the path of exhaust gas such as an exhaust gas pipe.

As illustrated in FIGS. 1 and 2, the partition wall 12 partitions the inside of the outer skin 11. The partition wall 12 is also commonly referred to as a cell wall. The partition wall 12 can be provided, for example, in a grid pattern. The honeycomb structure 1 is a porous body, and as illustrated in FIG. 3, a large number of pores 121 are formed in the partition wall 12. Therefore, PM contained in the exhaust gas can be deposited and collected on the surface of the partition wall 12 or in the pores 121. PM is a fine particle called particulate matter, particulate matter, particulate or the like.

The average pore diameter of the partition wall 12 can be adjusted in the range of 12 μm or more and 30 μm or less, preferably 13 μm or more and 28 μm or less, and more preferably 15 μm or more and 25 μm or less. The porosity of the partition wall 12 can be adjusted in the range of 55% or more and 75% or less, preferably 58% or more and 73% or less, and more preferably 60% or more and 70% or less. When the average pore diameter of the partition wall 12 is 12 μm or more and 30 μm or less and the porosity is 55% or more and 75% or less, the catalyst can be reliably supported on the pores 121. Further, when the porosity of the partition wall 12 is 75% or less, it becomes easy to secure the structural reliability of the honeycomb structure 1. The average pore diameter and porosity of the partition wall 12 can be measured by the mercury intrusion method as described later in the experimental example.

As illustrated in FIGS. 1 and 2, the honeycomb structure 1 has a large number of cells 13. The cell 13 is surrounded by the partition wall 12 and forms a gas flow path. The extension direction of the cell 13 usually coincides with the axial direction Y.

As illustrated in FIG. 1, the cell shape in the filter cross section in the direction orthogonal to the axial direction Y is, for example, a quadrangular shape, but the cell shape is not limited to this. The cell shape may be a polygon such as a triangle, a quadrangle, a hexagon, or a circle. Further, the cell shape may be a combination of two or more different shapes.

The honeycomb structure 1 is, for example, a columnar body such as a columnar body, and its dimensions can be appropriately changed. The honeycomb structure 1 has a first end surface 14 and a second end surface 15 at both ends in the axial direction Y. When the exhaust gas purification filter having the honeycomb structure 1 is arranged in the exhaust gas path such as the exhaust gas pipe, the first end face 14 becomes the upstream end face and the second end face 15 becomes the downstream end face.

The cell 13 may have a first cell 131 and a second cell 132. As illustrated in FIG. 2, the first cell 131 opens in the first end surface 14 and is closed by the plug portion 16 in the second end surface 15. The second cell 132 is opened to the second end surface 15, and the first end surface 14 is closed by the plug portion 16. The plug portion 16 is also referred to as a sealing portion and can be formed of, for example, ceramics such as cordierite, but may be made of other materials.

The first cell 131 and the second cell 132 are arranged alternately in the horizontal direction orthogonal to the axial direction Y and in the vertical direction orthogonal to both the axial direction Y and the horizontal direction, for example, so as to be adjacent to each other. It is formed. That is, when the first end surface 14 or the second end surface 15 of the honeycomb structure 1 is viewed from the axial direction Y, the first cell 131 and the second cell 132 are arranged in a checkered pattern, for example.

As illustrated in FIG. 2, the partition wall 12 separates the first cell 131 and the second cell 132 adjacent to each other. As illustrated in FIGS. 3A and 3B, a large number of pores 121 are formed in the partition wall 12. As illustrated in FIGS. 3A and 3B, the pores 121 in the partition wall 12 are adjacent to each other in addition to the communication ventilation holes 122 communicating between the first cell 131 and the second cell 132 adjacent to each other. It may include a non-communicating vent hole 123 that does not allow communication between the 1st cell 131 and the 2nd cell 132. Note that FIG. 4 shows the pores 121 of FIG. 3 in a more simplified manner. Further, in FIGS. 3 and 4, the pores 121 are simplified and drawn in two dimensions, but it is considered that at least the communication holes 122 intersect in three dimensions in most cases.

In the partition wall 12, the number of communication holes 122, which is the number of communication holes 122 communicating between the adjacent cells 13, is 18000 [lines / 0.25 mm ² ] or more. The number of continuous ventilation holes described here is a value in a state before the catalyst is supported in the continuous ventilation holes 122. When the number of continuous ventilation holes before supporting the catalyst is ^{less than 18,000 [lines / 0.25 mm 2} ], the collection rate and the pressure loss are deteriorated by supporting the catalyst. This is because the amount of catalyst per continuous ventilation hole 122 increases when the catalyst is supported, and as a result, the number of continuous ventilation holes 122 that are filled by the catalyst increases. Further, when the number of continuous ventilation holes before supporting the catalyst is ^{less than 18,000 [lines / 0.25 mm 2} ], the deterioration rate of the collection rate and the deterioration rate of the pressure loss remain high. This is because the region where the number of pores before the catalyst is supported is ^{less than 18,000 [lines / 0.25 mm 2} ] is a region where the exhaust gas is difficult to flow because the continuous ventilation holes 122 are blocked by the catalyst when the catalyst is supported. It is considered that the deterioration rate and the deterioration rate of the pressure loss are dominated by the contribution of the structure of the honeycomb structure 1, and the contribution of the pores in the partition wall 12 after the catalyst is supported is small.

^{The number of continuous ventilation holes is preferably 19000 [pieces / 0.25 mm 2} ] or more, and more preferably 20000 [pieces /) from the viewpoint of facilitating the deterioration rate of the collection rate and the deterioration rate of pressure loss at a low value. 0.25 mm ^2] or more, more preferably, 20600 [present /0.25mm ^2] or more, even more preferably, 21000 [present /0.25mm ^2] or more, even more preferably, 21500 [present /0.25Mm ² ] or more, even more preferably 22000 [lines / 0.25 mm ² ] or more, particularly preferably 22600 [lines / 0.25 mm ² ] or more, most preferably 23000 [lines / 0.25 mm ² ] or more. Can be. From the viewpoint of the strength of the honeycomb structure 1 and the exhaust gas purification filter to which the honeycomb structure 1 is applied, the number of stations and the number of pores ^{can be 30,000 [lines / 0.25 mm 2} ] or less.

When measuring the number of continuous ventilation holes, the pore path lengths in each pore 121 are calculated one by one, and when the pores 121 intersect, a short path with a lower pressure loss is selected, and the frequency distribution of the pore path length is determined. It is important to ask. However, for example, in the measurement of the pore size distribution by the mercury porosimeter, it is not possible to measure the pore path length or select the path when the pores 121 intersect. As a result, it is not possible to analyze the frequency distribution of the stomatal path length with the stomatal diameter distribution by the mercury porosimeter.

Therefore, here, each pore 121 in the partition wall 12 is thinned using the image data three-dimensionally analyzed by CT scan. Then, with respect to the pores 121 intersecting in the partition wall 12 by the image analysis software, the target data can be calculated by performing the process of selecting the one having the shorter path length. Hereinafter, the method for measuring the number of continuous ventilation holes will be described in detail.

As illustrated in FIG. 5, a scanned image of the partition wall 12 is taken by CT scanning the partition wall 12 with respect to the measurement sample collected from the honeycomb structure 1. As the CT scanning apparatus, Xradia520 Versa manufactured by ZEISS is used. The measurement conditions are a tube voltage of 80 kV and a tube current of 87 mA. The resolution of the captured image is 1.6 μm / pixel. Note that FIG. 5 shows a part of the measurement sample.

The scan direction S in the CT scan is a direction along the thickness direction of the partition wall 12, and is the surface of the partition wall 12 on the first cell 131 side that opens to the first end surface 14 that is the upstream end surface (hereinafter, appropriately, the partition wall surface 12a). The direction is toward the surface of the partition wall 12 on the second cell 132 side (hereinafter, appropriately referred to as the partition wall back surface 12b) that opens to the second end surface 15 that is the downstream end surface. 6 and 7 show examples of scanned images. FIG. 7 is an enlargement of FIG. In FIGS. 6 and 7, the direction along the axial direction Y is the Y direction, perpendicular to the Y direction, and the direction along one of the four partition walls 12 surrounding the second cell 132 is the X direction. And the direction perpendicular to the Y direction is the Z direction. The symbol M means the plug portion 16 on the first end surface 14.

Therefore, the scan direction S in FIGS. 6 and 7 is the −Z direction. An example of a scanned image in this direction is the upper left image s in FIGS. 6 and 7. This scanned image in the −Z direction is along the XY plane. For reference, the scanned image in the Y direction (image along the XZ plane) is shown in the lower left of FIGS. 6 and 7, and the scanned image in the −X direction (image along the YZ plane) is shown in FIGS. 6 and 7. It is also shown in the lower right of 7.

Next, analysis is performed using a group of captured images in the scanning direction S (= the number of captured images in the scanning direction S (= thickness μm of partition wall 12 / 1.6 μm, which is the size of 1pixel)). In the following example, the analysis image size has a range of 500 μm × 500 μm in the X and Y planes, and the number of sheets having a thickness of μm / 1.6 μm of the partition wall 12 is used in the −Z direction.

Next, the captured image in the scanning direction S is binarized. Image analysis software ImageJ (manufactured by the National Institutes of Health (NIH)) is used for binarization. The binarization aims to distinguish between the pore portion and the skeletal portion in the partition wall 12. Since the brightness differs between the pore portion and the skeleton portion, in the binarization process, noise remaining in the captured image is removed, an arbitrary threshold value is set, and then the binarization process is performed. Since the threshold value differs depending on each measurement sample, a threshold value capable of separating the pore portion and the skeleton portion is set for each captured image while visually confirming the entire image captured by the CT scan. An example of the captured image before the binarization process is shown in FIG. 8 (a), and an example of the captured image after the binarization process is shown in FIG. 8 (b). In FIG. 8B, the black region is the pore portion and the gray region is the skeleton portion.

Next, the pore path length of each pore 121 is measured based on the captured image after the binarization treatment. The pore path length is measured using IGORL manufactured by Hulinks. First, the pores 121 of the captured image after the binarization process are thinned. FIG. 9 shows an example of the result of the thinning process. As illustrated in FIG. 9, connecting the center of the pixel of each pore 121 (the part where the number is written in the pixel) with a line is the thinning process, and each pore 121 obtained by the thinning process. The path connecting the centers of the pixels with a line is the thinning path 120.

Based on the thinned image illustrated in FIG. 9, the partition wall 12 that separates the first cell 131 and the second cell 132 that are adjacent to each other is opened on the partition wall surface 12a side facing one of the first cell 131. The number of pixels that have passed from the entrance of the pore 121 to the exit of the pore 121 that opens on the back surface 12b side of the partition wall facing the other second cell 132 without making a detour is calculated as the path length. When an intersection occurs in the thinning path 120 as in the region surrounded by the broken line in FIG. 9, the one having the shorter path length is selected. In the three-dimensional analysis, the path length is calculated for all the paths from the partition wall surface 12a to the partition wall back surface 12b.

In the example of FIG. 9, the number of routes for which the route length should be calculated is 3 (lines). The path lengths represented by the number of pixels are 52, 51, and 47 from the left, respectively. The actual pore path length can be calculated by multiplying the path length of the number of pixels by 1.6 based on the resolution of the captured image of 1.6 μm / pixel. Note that FIG. 9 shows an example of the thinned image, which is different from the actual thickness of the partition wall 12.

Further, FIGS. 10 and 11 show other examples of the thinned image. It should be noted that FIGS. 10 and 11 are drawn in a simplified manner as compared with FIG. 9. In the thinning-processed image illustrated in FIG. 10, the outlets corresponding to the inlet 120a of the thinning path 120 are the outlets 120f and 120g. And, on the back surface 12b side of the partition wall, there is no outlet other than the outlets 120f and 120g. Therefore, in FIG. 10, the number of routes for which the route length should be calculated is 2 (lines). The outlets corresponding to the inlet 120b of the thinning route 120 are the outlets 120f and 120g, which are the same as described above, and therefore are not counted as routes for which the route length should be calculated. The inlet 120c of the thinning path 120 does not have an exit on the back surface 12b side of the partition wall and does not communicate with the partition wall 12, so that the path length is not counted as a route to be calculated. The inlets 120d and 120e of the thinning route 120 also do not have an outlet on the back surface 12b side of the partition wall and do not communicate with the partition wall 12, so that the route length is not counted as a route to be calculated. Further, in the thinning-processed image exemplified in FIG. 11, the exits corresponding to the inlet 120h of the thinning path 120 are the exit 120j and the exit 120k. The exits corresponding to the inlet 120i of the thinning path 120 are the outlet 120m and the exit 120n. The route leading to the outlet 120l of the thinning route 120 appears from the middle of the scan and does not communicate with the partition wall 12, so that the route length is not counted as a route to be calculated. Therefore, in FIG. 11, the number of routes for which the route length should be calculated is 4 (lines).

By measuring the pore path length of the partition wall 12 as described above, a pore path length distribution, that is, a frequency histogram can be obtained. The stomatal path length distribution is obtained by calculating the frequency (book) with a histogram for all the calculated stomatal path lengths. The frequency histogram is represented as a bar graph of data in which the stomatal path length is divided into classes of 10 μm. The sum of each frequency in the pore path length distribution is the number of continuous vent holes in the measurement sample.

The reason why the pore path length of the partition wall 12 is divided into classes of 10 μm as described above is that it is preferable to divide the pore path length into the equivalent of the pore diameter which is the minimum unit of the pore path length. The partition wall 12 has pores of various sizes having a pore diameter of, for example, 1 to 100 μm, and among them, the proportion of pores having a pore diameter of 10 to 20 μm is large. It is considered that this is because the pore diameter is derived from the particle size of the raw material silica or the like which is a pore-forming material. Therefore, it is considered that the stomatal path length can be accurately separated by dividing the histogram interval by 10 μm as described above.

FIG. 12 shows an example of a frequency histogram showing the pore path length distribution of the partition wall 12. As illustrated in FIG. 12, for example, when the thickness of the partition wall 12 is 240 μm, the pore path length starts from 240 μm. Next, the total number (s) of pore path lengths of 240 μm or more and less than 250 μm are counted. After that, the total number (lines) of the pore path lengths every 10 μm may be counted.

The number of continuous ventilation holes in the honeycomb structure 1 is the average value of the number of continuous ventilation holes obtained as described above for the six measurement samples collected from the honeycomb structure 1. Specifically, as shown in FIG. 13, the measurement sample is a portion immediately inside the central portion 1a and the plug portion 16 on the first end surface 14 side in the axial direction Y passing through the central portion of the diameter in the honeycomb structure 1. 1b, the immediately inner portion 1c of the plug portion 16 on the second end surface 15 side, the central portion 1d in the axial direction Y passing through the central portion of the radius in the honeycomb structure 1, and the immediately inner portion of the plug portion 16 on the first end surface 14 side. Collect from 6 places of 1e and the inner portion 1f of the plug portion 16 on the second end surface 15 side. The shape of the measurement sample is a cube whose dimensions in the direction orthogonal to the axial direction Y are 5 mm in length × 5 mm in width and 5 mm in length in the axial direction Y.

In the honeycomb structure 1, the thickness of the partition wall 12 can be adjusted, for example, in the range of 100 μm or more and 400 μm or less. As shown in FIG. 13, the thickness of the partition wall 12 is the central portion 1a in the axial direction Y passing through the central portion of the diameter in the honeycomb structure 1 and the immediately inner portion 1b of the plug portion 16 on the first end surface 14 side. , The average value of the thickness measurement values measured at three points of the inner portion 1c of the plug portion 16 on the second end surface 15 side.

The honeycomb structure 1 has a number of continuous ventilation holes of 18,000 [lines / 0.25 mm ² ] or more. Therefore, in the honeycomb structure 1, the number of continuous ventilation holes contributing to the catalyst support increases to the above-mentioned specific value or more, so that even when the catalyst is supported for use in the exhaust gas purification filter, the collection rate by the catalyst support is increased. And the deterioration of pressure loss can be suppressed. Since the honeycomb structure 1 can collect PM in the exhaust gas without supporting a catalyst, it can function as an exhaust gas purification filter.

Next, the exhaust gas purification filter of the first embodiment will be described with reference to FIG. As illustrated in FIG. 14, the exhaust gas purification filter 3 of the present embodiment has the honeycomb structure 1 of the first embodiment and the catalyst 2 supported on the hole wall 122a of the continuous ventilation hole 122. The catalyst 2 may be supported at least on the hole wall 122a of the continuous ventilation hole 122, and may also be supported on the surface of the partition wall 12 (the surface of the partition wall 12 facing the cell). As a method of supporting the catalyst 2 on the hole wall 122a of the continuous ventilation hole 122, for example, a known in-wall coating method in which the catalyst-containing slurry is introduced into the continuous ventilation hole 122 of the partition wall 12 by suction can be mentioned. Further, the type of the catalyst 2 can be different depending on the application, and for example, a catalyst precious metal such as Pt, Rh, Pd can be supported at the same time as the co-catalyst.

The exhaust gas purification filter 3 has a communication ventilation hole 122 that allows communication between adjacent cells 13 even when the catalyst 2 is supported. That is, the exhaust gas purification filter 3 has a continuous ventilation hole 122 that remains without being blocked by the catalyst 2 after the catalyst is supported on the honeycomb structure 1.

According to the exhaust gas purification filter 3, since the honeycomb structure 1 is used, deterioration of the collection rate and pressure loss due to the catalyst loading can be suppressed. The exhaust gas purification filter 3 can be suitably used for purifying exhaust gas emitted from a gasoline engine.

In the exhaust gas purification filter 3, the supported amount of the catalyst 2 can be 30 g / L or more. When the catalyst 2 is supported in the continuous ventilation holes 122 in the honeycomb structure 1, the shape of the pores 121 of the exhaust gas purification filter 3 changes. However, according to the above configuration, even with the amount of the catalyst 2 supported, since the honeycomb structure 1 described above is used, the exhaust gas purification filter can easily obtain the effect of suppressing the deterioration of the collection rate and the pressure loss due to the catalyst support. 3 is obtained.

The supported amount of the catalyst 2 is preferably 30 g / L or more, more preferably 50 g / L or more, still more preferably 60 g / L, from the viewpoint of ensuring the purification performance of HC, CO, NOx and the amount of stored oxygen. The above can be done. The amount of the catalyst 2 supported is preferably 200 g / g from the viewpoint of suppressing the blockage of the continuous ventilation holes 122 in the catalyst support by the in-wall coating method and suppressing the damage of the honeycomb structure 1 due to the thermal stress caused by the heat of the catalyst reaction. It can be L or less, more preferably 150 g / L or less, still more preferably 100 g / L or less.

In the exhaust gas purification filter 3, it is preferable that the number of continuous ventilation holes 122 communicating between the adjacent cells 13 in a state where the catalyst 2 is supported is 4500 [lines / 0.25 mm ² ] or more. According to this configuration, it is possible to ensure the suppression of the deterioration of the collection rate and the pressure loss due to the catalyst loading. Further, according to this configuration, there is an advantage that it becomes easy to suppress the destruction of the exhaust gas purification filter 3 at the time of assembling to the exhaust gas pipe by reducing the amount of pores that cause a decrease in strength. The number of the continuous vent holes 122 communicating between the adjacent cells 13 in the state where the catalyst 2 is supported is preferably 4800 [lines / 0.25 mm ² ] or more, more preferably 5000 [lines / 0.25 mm]. ² ] or more, more preferably 5200 [pieces / 0.25 mm ² ] or more, even more preferably 5300 [pieces / 0.25 mm ² ] or more, even more preferably 5400 [pieces / 0.25 mm ² ]. As mentioned above, the most preferable is 5800 [lines / 0.25 mm ² ] or more. From the viewpoint of ensuring the strength described above, the number of communication holes 122 communicating between the adjacent cells 13 in the state where the catalyst 2 is supported shall be 8500 [lines / 0.25 mm ² ] or less. Can be done.

The number of the continuous ventilation holes 122 communicating between the adjacent cells 13 in the state where the catalyst 2 is supported can be measured by using the honeycomb structure 1 on which the catalyst 2 is supported according to the above-mentioned measuring method. ..

The average pore diameter of the partition wall 12 in the state where the catalyst 2 is supported can be adjusted in the range of 10 μm or more and 28 μm or less, preferably 11 μm or more and 26 μm or less, and more preferably 13 μm or more and 23 μm or less. The porosity of the partition wall 12 in the state where the catalyst 2 is supported can be adjusted in the range of 46% or more and 66% or less, preferably 49% or more and 64% or less, and more preferably 51% or more and 61% or less. .. When the average pore diameter of the partition wall 12 in the state where the catalyst 2 is supported is 10 μm or more and 28 μm or less and the porosity is 46% or more and 66% or less, the catalyst 2 is surely supported on the pores 121. Become. In addition, it is possible to ensure that the collection rate and the deterioration of pressure loss due to the catalyst support are suppressed. The average pore diameter and porosity of the partition wall 12 in the state where the catalyst 2 is supported can be measured by the mercury intrusion method as described later in the experimental example.

(Embodiment 2)
The honeycomb structure and the exhaust gas purification filter of the second embodiment will be described with reference to FIGS. 1 to 14 used in the first embodiment as appropriate. In addition, among the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-mentioned embodiments represent the same components and the like as those in the above-mentioned embodiments, unless otherwise specified.

In the honeycomb structure 1 of the present embodiment, the bending degree L / T defined by the ratio of the average flow path length Lμm of the continuous ventilation holes 122 to the thickness Tμm of the partition wall 12 is 1.2 or more. The average flow path length L μm of the communication holes 122 is obtained as follows. In the same manner as in the first embodiment, the captured image after the binarization process is prepared. The captured image after the binarization process is read into the analysis software GeoDoct (manufactured by SCSK Corporation), and a virtual model in which the structure of the pore portion and the skeleton portion is three-dimensionally modeled is created under the condition of 0.685 μm per Voxel. .. Then, for the obtained virtual model, the flow path lengths (μm) of all the continuous ventilation holes 122 are measured. Here, PM flows along the flow of gas. The gas, as a fluid, tries to flow through the shortest flow path in the communication hole 122. The flow path for measuring the length in the above is the shortest flow path through which the gas flows in the communication ventilation hole 122. That is, it can be said that the flow path length in the continuous ventilation hole 122 is a parameter that does not necessarily match the length of the line connecting the center of the hole diameter of the continuous ventilation hole 122. The average value of the flow path lengths of all the obtained continuous ventilation holes 122 is defined as the average flow path length Lμm of the continuous ventilation holes 122. Further, the thickness (μm) of the virtual model is defined as the thickness Tμm of the partition wall 12 when calculating the tortuosity. Then, the tortuosity of the measurement sample is calculated by dividing the average flow path length L μm of the continuous ventilation holes 122 obtained as described above by the thickness T μm of the partition wall 12. The tortuosity in the honeycomb structure 1 is calculated from the average value of the tortuosity of each measurement sample obtained as described above for the six measurement samples collected from the honeycomb structure 1. In addition, each measurement sample is collected from the same collection position as the measurement sample of the number of continuous ventilation holes described above in the first embodiment.

The honeycomb structure 1 of the present embodiment has a bending degree within the above range. When the degree of bending is within the above range, the flow path structure of the continuous ventilation hole 122 becomes complicated, and the pipeline resistance caused by the pipeline friction which is the resistance of the continuous ventilation hole 122 increases. Therefore, when the catalyst 2 is supported on the honeycomb structure 1, the fluidity of the catalyst-containing slurry containing the catalyst 2 is lowered, and it becomes easy to support the catalyst 2 on the pore wall 122a of the continuous ventilation hole 122 in a predetermined amount.

In the honeycomb structure 1, the bending degree is preferably 1.25 or more, more preferably 1.30 or more, still more preferably 1.35, from the viewpoint of improving the supportability of the catalyst 2 in the continuous ventilation holes 122. The above can be done. If the degree of bending becomes excessively high, the pipeline resistance of the catalyst-containing slurry increases in the catalyst supporting step at the time of manufacturing the exhaust gas purification filter, and the catalyst 2 tends to increase the blockage of the pores 121. Therefore, the tortuosity can be preferably 1.8 or less, more preferably 1.7 or less, and even more preferably 1.6 or less.

The exhaust gas purification filter 3 of the present embodiment is different from the exhaust gas purification filter 3 of the first embodiment in that it has the honeycomb structure 1 of the present embodiment. Since the exhaust gas purification filter 3 of the present embodiment uses the honeycomb structure 1 of the present embodiment, it is easy to ensure that a predetermined amount of the catalyst 2 is retained.

In the exhaust gas purification filter 3 of the present embodiment, the bending degree in the state where the catalyst 2 is supported on the continuous ventilation holes 122 of the honeycomb structure 1 is 1.4 or more. The tortuosity in the state where the catalyst 2 is supported in the continuous ventilation holes 122 can be determined by the above-mentioned method using the honeycomb structure 1 in which the catalyst 2 is supported in the continuous ventilation holes 122.

The exhaust gas purification filter 3 of the present embodiment has a tortuosity in the above range in a state where the catalyst 2 is supported. When the bending degree is within the above range, it is possible to ensure that a predetermined amount of the catalyst 2 is supported on the hole wall 122a of the continuous ventilation hole 122.

In the exhaust gas purification filter 3, the tortuosity in the state where the catalyst 2 is supported is preferably 1.45 or more, more preferably 1.50 or more, and further, from the viewpoint of improving the collection rate and suppressing pressure loss. It can be preferably 1.55 or more, and even more preferably 1.60 or more. If the bending degree becomes excessively high, the pressure loss tends to increase. Therefore, the tortuosity can be preferably 2.2 or less, more preferably 2.1 or less, and even more preferably 2.0 or less. Other configurations and operational effects are the same as those of the exhaust gas purification filter 3 of the first embodiment.

(Embodiment 3)
The exhaust gas purification filter of the third embodiment will be described with reference to FIGS. 1 to 14 used in the first embodiment as appropriate. The exhaust gas purification filter 3 has a honeycomb structure 1 and a catalyst 2. The honeycomb structure 1 has an exodermis 11, a partition wall 12 that partitions the inside of the exodermis 11 and has a large number of pores 121 formed therein, and a cell 3 surrounded by the partition wall 12. The partition wall 12 has a communication ventilation hole 122 that communicates between the adjacent cells 3. The catalyst 2 is supported on the hole wall 122a of the continuous ventilation hole 122. The supported amount of the catalyst 2 is 30 g / L or more. The number of communication holes 122 communicating between the adjacent cells 3 in the state where the catalyst 2 is supported is 4500 [lines / 0.25 mm ² ] or more.

The exhaust gas purification filter 3 of the present embodiment uses the honeycomb structure 1 having the number of continuous ventilation holes of 18,000 [lines / 0.25 mm ² ] or more shown in the first and second embodiments, and is a catalyst in the pores 121. It can be obtained by supporting the catalyst 2 at 30 g / L or more by the in-wall coating method in which the catalyst 2 is supported.

According to the exhaust gas purification filter 3 of the present embodiment, it is possible to suppress deterioration of the collection rate and pressure loss due to the catalyst loading. Regarding the configuration and operation / effect of the exhaust gas purification filter 3 of the present embodiment, the description of the first and second embodiments can be appropriately referred to and applied.

(Experimental Example 1)

The honeycomb structure can contain cordierite as a main component. In this case, in the production of the honeycomb structure, a cordierite forming raw material containing a Si source, an Al source, and an Mg source is used so as to generate a cordierite composition. The cordierite forming raw material is a raw material capable of producing a cordierite composition by firing. As the raw material for forming cordierite, a mixture in which silica, talc, aluminum hydroxide, alumina, kaolin and the like are appropriately mixed can be used. As the silica, it is preferable to use porous silica. Further, from the viewpoint of increasing the porosity, it is preferable to use aluminum hydroxide as the Al source. In the production of the honeycomb structure, water, a binder, a lubricating oil, a pore-forming material and the like can be appropriately mixed with the cordierite-forming raw material to prepare a clay containing the cordierite-forming raw material. The mixing conditions of the cordierite-forming raw material at the time of soil preparation will be described in detail in Experimental Example 2. Then, the prepared clay is extruded, fired, and then a stopper is formed, whereby a honeycomb structure can be obtained.

In order to increase the number of continuous ventilation holes in the partition wall of the manufactured honeycomb structure to the above-mentioned specific range, it is effective to make the pore path length distribution of the partition wall related to the number of continuous ventilation holes uniform. The raw material conditions that can make the stomatal length distribution uniform were examined as follows.

Silica and talc can be called pore-forming materials because they can be melted at a high temperature to form pores. The higher the ratio of the number of particles of the pore-forming material, the better the contact property between the particles, and the more uniform the pore path length distribution becomes possible. Therefore, when the clay containing the cordierite forming raw material is extruded, the ratio of the number of particles of silica and talc contained in the clay may be controlled.

However, it is difficult to measure the particle number ratio, and it is assumed that the measured value varies depending on the molding conditions. Therefore, an index capable of adjusting the stomatal path length distribution by controlling the conditions of raw material powders such as silica, talc, and Al source is desired. From this point of view, the following studies were conducted focusing on the pressurized bulk density of the raw material powder.

Specifically, consider the clay of the composition shown in Table 1. Here, as shown in Table 1, the raw material for forming cordierite is prepared by appropriately blending porous silica or molten silica, talc, and aluminum hydroxide. In the present specification, the "average particle size" is the particle size at a volumetric integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method. A pore-forming material made of graphite, water, a lubricating oil, and a binder made of methyl cellulose are appropriately added to the cordierite forming raw material. Consider making a clay from such a mixed raw material.

On the other hand, in order to study an evaluation method simulating clay, the pressurized bulk density of the raw material powder was measured. Specifically, first, the mixed powder of the raw material powder was put into a measuring instrument having a diameter of 25 mm and a length of 20 mm in the pressure measuring machine "Autograph" manufactured by Shimadzu Corporation, and the pressurization of the mixed powder was started. The pressurizing speed is 1 mm / min. When the load corresponding to the pressure of 15 MPa reached 7 kN, the pressurization was stopped by the limit control. By this pressurization, columnar pellets made of mixed powder are obtained. The weight and height of the pellets were measured.

The height of the pellet can be measured by a caliper, a micrometer, a coordinate measuring machine or the like. Here, the measurement was performed using a micrometer. Since the diameter of the pellet is 25 mm, the volume of the pellet was calculated from the product of the diameter and the height.

In addition, the density was calculated from the volume and weight of the pellets. Density is calculated by dividing the weight by the volume. This density was defined as the pressurized bulk density. Methyl cellulose "65MP-4000" manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. is added as a binder to the mixed powder of the raw material. The binder is for facilitating the handling of the pellet-shaped mixed powder, and other binders can be used. Specifically, a total of 2 g of raw material powder (1.5 g) and binder (0.5 g) is used.

In general, there is a correlation between the particle size and the bulk density, and the smaller the particle size, the smaller the bulk density because a space is formed between the particles. As for the number of particles arranged in a certain volume, the smaller the particle diameter, the larger the number of particles. Therefore, the smaller the bulk density, the larger the number of particles. That is, the bulk density and the number of particles are inversely proportional to each other.

The particle number ratio R of the pore-forming material in the mixed powder is calculated from the following formula (x) from the _{number of particles N ST of silica and talc and the number of particles N M} of all the raw material mixed powders used in the production of the honeycomb structure. Is calculated by.
R = N _ST / N _M ... (x)

Applying the above-mentioned relationship between the bulk density and the number of particles to the formula (x), the particle number ratio R of the pore-forming material is the pressurized bulk density ρ _M of all the raw material mixed powders and the mixed powder of silica and talc. From the pressurized bulk density ρ _ST , it is expressed by the following equation (xi).
R = ρ _M / ρ _ST ... (xi)

In this experimental example, since the raw material mixed powder is silica, talc, and aluminum hydroxide, the pressurized bulk density ρ _M is the pressurized bulk density of the mixed powder of silica, talc, and aluminum hydroxide. Therefore, the particle number ratio R can be increased by increasing the pressurized bulk density of aluminum hydroxide and decreasing the pressurized bulk density of the mixed powder of silica and talc.

Therefore, the pressurized bulk density of aluminum hydroxide was set to ρ _{A, and ρ A} / ρ _ST was calculated as an index of the particle number ratio R of the pore-forming material composed of silica and talc. These pressurized bulk densities are measured by the methods described above. The results are shown in Table 2.

In addition, Table 3 shows the types of porous silica and molten silica shown in Table 1 and the bulk density by tap densers. The measurement is performed by a tap density method fluidity adhesion measuring instrument. Specifically, a tap densa manufactured by Seishin Enterprise Co., Ltd. was used. Then, the cylinder of the measuring instrument was filled with each silica which is the powder to be measured. Next, the silica was compressed by tapping, and the bulk density was calculated from the mass of the compressed silica and the volume of the cylinder. The results are shown in Table 3.

As can be seen from Tables 2 and 3, in Samples 2 to 4, porous silica B and porous silica C having a low bulk density in the tap densor are used. It can be seen that in these samples 2 to 4, the pressurized bulk density ρ _{ST of the mixed powder of porous silica and talc is low.}

Further, by using a large-diameter powder having a relatively large average particle diameter and a small-diameter powder having a relatively small average particle diameter as aluminum hydroxide in combination, the filling property is improved and the bulk density of aluminum hydroxide is increased. growing. In aluminum hydroxide composed of large-diameter powder and small-diameter powder, it is generally said that adjusting the mixing ratio of the small-diameter powder to 5 to 35% by mass is suitable for improving the filling property.

However, the optimum blending ratio of the large-diameter powder and the small-diameter powder varies depending on the combination of particle diameters, particle shape, distribution, and the like. As shown in Table 1, in Sample 1 and Sample 5, aluminum hydroxide having an average particle diameter of 5 μm is used alone. In Samples 2 and 3, a mixture of aluminum hydroxide, which is a small-diameter powder with an average particle diameter of 3 μm, and aluminum hydroxide, which is a large-diameter powder with an average particle diameter of 8 μm, mixed in a ratio of small-diameter powder: large-diameter powder = 3: 7. We are using powder. In sample 4, a mixed powder obtained by mixing aluminum hydroxide, which is a small-diameter powder having an average particle diameter of 3 μm, and aluminum hydroxide, which is a large-diameter powder having an average particle diameter of 8 μm, in a ratio of small-diameter powder: large-diameter powder = 5: 5 is used. ing.

As shown in Table 2, it can be seen that in such a combination of the particle sizes of aluminum hydroxide, the pressurized bulk density is about the same when the mixing ratio of the small diameter powder is 30 to 50% by mass. Compared with Samples 1 and 5 using a single sample without blending aluminum hydroxide having different average particle sizes, Samples 2 to 4 have a higher pressurized bulk density of aluminum hydroxide. Recognize.

As shown in Table 2, as a result of calculating the particle number ratio of porous silica and talc from the pressurized bulk density in each sample, the magnitude relationship of the particle number ratio is as follows: sample 1 and sample 5 <sample 3 and sample 4 <Represented by sample 2. According to this result, by increasing the pressurized bulk density of aluminum hydroxide and decreasing the pressurized bulk density of the mixture of porous silica and talc, the ratio of the number of particles of the pore-forming material in the raw material mixed powder is increased. It turns out that it can be done. That is, by controlling the pressurized bulk density of the Al source and the pressurized bulk density of the pore-forming material and increasing the ratio of the number of particles of the pore-forming material, the contact property between the particles is improved and the pore path length distribution is uniform. It can be said that it will be possible to do so.

In this experimental example, the pressurized bulk density ρ _{A of} aluminum hydroxide / the pressurized bulk density ρ _ST of the mixed raw material of porous silica and talc is used to determine the ratio of the number of particles of porous silica and talc as the pore-forming material. However, instead of the pressurized bulk density of aluminum hydroxide, the pressurized bulk density of the entire cordierite forming raw material can also be used. That is, the ratio of the number of particles of porous silica and talc as the pore-forming material is determined by (pressurized bulk density ρ _{M of the raw material for forming cordierite) / (pressurized bulk density ρ ST} of the mixed raw material of porous silica and talc). It may be calculated.

Specifically, when, for example, kaolin or alumina is used as the raw material for forming corgerite, the pressurized bulk density of the mixed powder containing these can be used. When a pore-forming material is used, the pressurized bulk density of the mixed powder including the pore-forming material can be used. Further, when the pore ratio of the partition wall may be reduced, alumina having an average particle size different from that of aluminum hydroxide can be added to the mixture of aluminum hydroxide. In the mixture of aluminum hydroxide and alumina, as the aluminum hydroxide, one having an average particle size of one kind may be used, or one having an average particle size of two or more kinds may be used in combination. The same applies to alumina. Further, as the Al source, alumina may be used instead of aluminum hydroxide. These combinations can be appropriately selected from the viewpoints of moldability, shrinkage rate, cost and the like.

(Experimental Example 2)
In this experimental example, 12 types of honeycomb structures having different numbers of continuous ventilation holes in the partition wall are manufactured. These honeycomb structures are referred to as test bodies H1 to H12, respectively. First, a method for manufacturing each honeycomb structure will be described.

In the production of the honeycomb structure of each test piece, as shown in Tables 4 and 5, predetermined silica, talc, and aluminum hydroxide were appropriately blended to prepare a cordierite forming raw material.

As shown in Tables 4 and 5, a pore-forming material made of graphite, water, a lubricating oil, and a binder made of methyl cellulose were appropriately added to the cordierite-forming raw material. Soil was prepared from such a mixed raw material. For the specimens H1, H4, and H7, the kneading time of the clay is generally about 30 minutes to 2 hours, but the communication and bending degree are improved by improving the contact between the particles. The kneading time of the clay was lengthened. However, if the kneading time of the clay is too long, the water evaporates and sufficient moldability cannot be obtained. Therefore, in this experimental example, the kneading time of the clay is lengthened by about 1.3 to 1.6 times. did. The clay produced by these was extruded, fired at 1410 ° C., and then a stopper was formed to obtain each honeycomb structure. Each honeycomb structure has a cylindrical shape with a diameter of 132 mm and an axial length of 101 mm, and the thickness of the partition wall is as shown in Table 6 below. The cell shape was a quadrangular shape as illustrated in FIG.

"Porosity and average pore diameter"
The porosity and the average pore diameter in the partition wall of each honeycomb structure were measured by a mercury porosimeter using the principle of the mercury intrusion method. As the mercury porosimeter, Autopore IV9500 manufactured by Shimadzu Corporation was used. The measurement conditions are as follows.

First, a test piece was cut out from the honeycomb structure. The test piece is a rectangular parallelepiped having dimensions in the direction orthogonal to the axial direction of 15 mm in length × 15 mm in width and a length in the axial direction of 20 mm. Next, the test piece was housed in the measurement cell of the mercury porosimeter, and the pressure inside the measurement cell was reduced. Then, mercury was introduced into the measurement cell and pressurized, and the pore diameter and the pore volume were measured from the pressure at the time of pressurization and the volume of mercury introduced into the pores of the test piece.

The measurement was performed in the pressure range of 0.5 to 20000 psia. In addition, 0.5 psia ^{corresponds to 0.35 × 10 -3} kg / mm ² , and 20000 psia corresponds to 14 kg / mm ² . The range of the pore diameter corresponding to this pressure range is 0.01 to 420 μm. A contact angle of 140 ° and a surface tension of 480 dyn / cm were used as constants when calculating the pore diameter from the pressure. The average pore diameter is the pore diameter at an integrated value of 50% of the pore volume. The porosity was calculated from the following relational expression. The true relative density of cordierite is 2.52.
Porosity (%) = total pore volume / (total pore volume + 1 / true specific density of cordierite) x 100

"Number of continuous ventilation holes and bending degree L / T (before catalyst support)"
The number of continuous ventilation holes and the bending degree L / T of the partition wall in each honeycomb structure before supporting the catalyst were measured by the method described in the first embodiment. For the binarization process, image analysis software ImageJ version 1.46 manufactured by the National Institutes of Health (NIH) was used. IGORL version 6.0.3.1 manufactured by Hulinks was used to measure the pore path length. The analysis software GeoDoct version 2017 manufactured by SCSK Corporation was used for the measurement of the flow path length when calculating the bending degree. FIG. 15 shows the pore path length distribution of the test piece H2, FIG. 16 shows the pore path length distribution of the test piece H3, FIG. 17 shows the pore path length distribution of the test piece H4, and FIG. 18 shows the pore path length distribution of the test piece H5. 2 shows the pore path length distribution of the test piece H6, and FIG. 20 shows the pore path length distribution of the test piece H7.

"Deterioration rate of collection rate and deterioration rate of pressure loss"
A catalyst is supported in the pores of the partition wall in each honeycomb structure by using a known in-wall coating method in which the catalyst-containing slurry is filled into the partition wall and then the catalyst-containing slurry is sucked from one end surface or both end faces of the honeycomb structure. I let you. The amount of the catalyst supported was 60 g / L. Then, using the honeycomb structure before and after the catalyst support, the PM collection rate and the pressure loss before and after the catalyst support were measured.

Specifically, the PM collection rate and the pressure drop were measured as follows. The honeycomb structures before and after the catalyst support were attached to the exhaust pipe of the gasoline direct injection engine, and the exhaust gas containing PM was flowed through the honeycomb structure. At this time, the number of PMs in the exhaust gas before flowing into the honeycomb structure and the number of PMs in the exhaust gas flowing out from the honeycomb structure were measured, and the PM collection rate was calculated. The measurement conditions are a temperature of 450 ° C. and an exhaust gas flow rate of 2.8 m ³ / min. As for the pressure loss, the pressure before the honeycomb structure and the pressure after the honeycomb structure were measured by the pressure sensor at the same time as the collection rate was measured, and the difference was measured as the pressure loss. The measurement conditions were a temperature of 720 ° C. and an exhaust gas flow rate of 11.0 m ³ / min. All measurements were made for the initial state in which PM was not deposited in the honeycomb structure. The PM number was measured using a PM particle number counter manufactured by AVL.

Then, the absolute value calculated from 100 × (PM collection rate after catalyst support [%] − PM collection rate before catalyst support [%]) / (PM collection rate before catalyst support [%]) is absolute. The value was calculated as the deterioration rate of the collection rate. Further, the absolute value of the value calculated from 100 × (pressure loss after supporting the catalyst [kPa] − pressure loss before supporting the catalyst [kPa]) / (pressure loss before supporting the catalyst [kPa]) is obtained as the deterioration rate of the pressure loss. rice field.

Table 6 summarizes the above measurement results. Further, FIG. 21 shows the relationship between the number of continuous ventilation holes in the honeycomb structure before supporting the catalyst and the deterioration rate of the collection rate, and FIG. 22 shows the relationship between the number of continuous ventilation holes in the honeycomb structure before supporting the catalyst and the deterioration rate of pressure loss. show.

From these results, we can see the following. The test body H2 and the test body H3 have a number of continuous ventilation holes of less than ^{18,000 [lines / 0.25 mm 2] before the catalyst is supported.} Therefore, in the test body H2 and the test body H3, when the catalyst was supported, the deterioration rate of the collection rate and the deterioration rate of the pressure drop were both high values. On the other hand, in the test bodies H1 and the test bodies H4 to H12, the deterioration rate of the collection rate and the deterioration rate of the pressure drop are lower than those of the test body H2 and the test body H3 even when the catalyst is supported. , It was possible to suppress the deterioration of the collection rate and pressure loss due to the catalyst loading. This is because in the test bodies H1 and the test bodies H4 to H12, the number of continuous ventilation holes contributing to the catalyst support ^{is increased to 18,000 [lines / 0.25 mm 2} ] or more, so that when the same amount of catalyst is supported, the same amount of catalyst is supported. This is because, as a result of reducing the amount of catalyst per continuous vent, the number of continuous vents that are filled with the catalyst when the catalyst is supported is reduced, and the deterioration of the collection rate and pressure loss due to the catalyst support can be suppressed.

Further, as shown in FIGS. 21 and 22, in ^{the region where the number of continuous ventilation holes before supporting the catalyst is less than 18,000 [lines / 0.25 mm 2} ], the deterioration rate of the collection rate and the deterioration rate of the pressure loss remain high. You can see that. This is because the region where the number of pores before the catalyst is supported is ^{less than 18,000 [lines / 0.25 mm 2} ] is the region where the air vents are blocked by the catalyst when the catalyst is supported and the exhaust gas is difficult to flow. It is considered that the deterioration rate and the deterioration rate of the pressure loss are dominated by the contribution of the structure of the honeycomb structure, and the contribution of the pores in the partition wall after the catalyst is supported is small. Further, as shown in FIGS. 21 and 22, the deterioration rate of the collection rate and the deterioration rate of the pressure loss are maintained low in the region where the number of continuous ventilation holes before supporting the catalyst is 18,000 [lines / 0.25 mm ^{2] or more.} Area was seen. This is because the region where the number of continuous ventilation holes is large is the region where continuous ventilation holes where the catalyst is not supported are generated, and the collection rate and the absolute value of the pressure loss are improved, but from the viewpoint of the rate of change before and after the catalyst is supported. It is considered that this is because the contribution to the collection rate and pressure loss of the continuous ventilation holes in which the catalyst is not supported becomes large, and the deterioration rate remains small. Since the behaviors of the collection rate and the deterioration rate of the pressure drop are both caused by the gas flow, the reasons for saturating are the same.

(Experimental Example 3)
Test bodies H1 to H12, which are honeycomb structures before supporting the catalyst, shown in Experimental Example 2 on which a catalyst is supported (catalyst support amount 60 g / L) are used in the test bodies F1 to F12, respectively. Use as an exhaust gas purification filter.

By the method described above in the first embodiment, the porosity, the average pore diameter, the number of continuous vent holes, and the tortuosity L / T after the catalyst was supported were measured in the same manner as in Experimental Example 2. The results are shown in Table 7. In Table 7, the deterioration rate of the collection rate and the deterioration rate of the pressure drop obtained in Experimental Example 2 are shown again. In addition, Table 7 also shows the NOx purification rate described later in Experimental Example 4 for convenience. From the results of Experimental Example 2 and the results of this Experimental Example, the relationship between the number of continuous vent holes in the honeycomb structure before the catalyst was supported and the number of continuous vent holes in the honeycomb structure after the catalyst was supported was summarized. The result is shown in FIG.

As shown in Table 7, it can be seen that at a catalyst amount of 60 g / L, the continuous ventilation holes are filled with the catalyst, and both the porosity and the pore diameter are reduced. Further, by filling the pores with the catalyst, the number of continuous ventilation holes is reduced, and as a result, the tortuosity L / T correlating with the flow path of the continuous ventilation holes communicating with the partition wall at the shortest distance is increased. As the amount of catalyst increases, this effect increases, and as the amount of catalyst decreases, this effect decreases.

Further, as shown in FIG. 23, it can be seen that there is a positive linear relationship between the number of continuous ventilation holes before the catalyst is supported and the number of continuous ventilation holes after the catalyst is supported. If the number of continuous ventilation holes before the catalyst is supported is 18,000 [lines / 0.25 mm ² ] or more, the number of continuous ventilation holes remaining after the catalyst is supported ^{can be 4500 [lines / 0.25 mm 2} ] or more.

(Experimental Example 4)
In this experimental example, the exhaust gas purification filter of the test body in Experimental Example 3 described above is used, and the bending degree L / T in the honeycomb structure before the catalyst is supported, the catalyst layer thickness after the catalyst is supported, and the NOx of the exhaust gas purification filter. The following experiments were conducted to investigate the relationship between purification performance.

As shown in FIG. 24, the evaluation converter 9 has a piping portion 91, a case portion 92 in which the exhaust gas purification filter 3 is housed, and a cone portion 93 connecting the piping portion 91 and the case portion 92. Prepared. The piping portion 91 on the upstream side of the case portion 92 is connected to the engine E that generates exhaust gas. In this experimental example, a gasoline engine having a displacement of 2.0 L, a naturally aspirated engine, and a 4-cylinder engine was used as the engine E. Further, the A / F sensor 94, the gas densitometer "ON" 95, and the gas densitometer are respectively arranged in the piping portion 91 on the upstream side and the piping portion 91 on the downstream side of the case portion 92 so as to be arranged as shown in FIG. "Exit" 96 was installed. For the gas densitometer "In" 95 and the gas densitometer "Out" 96, MEXA-7500 manufactured by HORIBA, Ltd. was used.

In the evaluation of the NOx purification rate, the A / F was controlled to 14.4, and the gas concentration was evaluated at an intake air amount of 50 g / s and 3500 rpm. The purification rate of nitrogen oxides (NOx) was calculated by the following formula.
NOx purification rate = 100 x (NOx concentration [ppm] indicated by gas densitometer "ON" -NOx concentration [ppm] indicated by gas densitometer "Out") / (NOx concentration indicated by gas densitometer "ON") [Ppm])

In addition, the thickness of the catalyst layer was determined from the following formula using the average pore diameter by the mercury intrusion method described above in Experimental Example 2.
Catalyst layer thickness = 0.5 × (average pore diameter before catalyst support-average pore diameter after catalyst support)

Increasing the number of open vents improves the area in which the catalyst can be supported. Whether or not the number of continuous ventilation holes can secure the catalyst layer thickness for developing a sufficient NOx purification rate is more preferably affected by the tortuosity L / T before the catalyst is supported. As shown in FIG. 25, when the tortuosity L / T before supporting the catalyst is low, the NOx purification performance required for the exhaust gas purification filter deteriorates. As shown in FIG. 26, regarding the NOx purification rate, when the thickness of the catalyst layer is thin, the NOx gas does not sufficiently diffuse into the catalyst layer, so that the NOx purification performance tends to decrease. As shown in FIG. 27, when the bending degree L / T before supporting the catalyst is lowered and the conduit resistance in the continuous ventilation hole is lowered, the catalyst supporting property at the time of supporting the catalyst is lowered, and the catalyst layer is easily formed thin. Therefore, in order to ensure the NOx purification performance, it is effective to set the tortuosity L / T before carrying the catalyst to 1.2 or more, as shown in the results of FIGS. 25 to 27. It can be said that. The reason why there is a clear boundary in the degree of bending L / T = 1.2 before supporting the catalyst is that the reaction time with the catalyst that purifies NOx is a constant value as a physical property value, so that a certain reaction time is guaranteed. That is, it is considered that the reaction is sufficiently completed if the catalyst layer thickness is such that the reaction distance can be guaranteed.

The present invention is not limited to each of the above embodiments and experimental examples, and various modifications can be made without departing from the gist thereof. In addition, each configuration shown in each embodiment and each experimental example can be arbitrarily combined.

1 Honeycomb structure 11 Outer skin 12 Partition wall 121 Pore 122 Communicating hole 122a Pore wall 13 Cell 2 Catalyst 3 Exhaust gas purification filter

Claims (11)

A honeycomb structure (1) used for an exhaust gas purification filter before a catalyst is supported.
The outer skin (11) and
A partition wall (12) that partitions the inside of the exodermis and has a large number of pores (121) formed therein.
It has a cell (13) surrounded by the partition wall and
The above partition wall
It has a communication ventilation hole (122) that communicates between the adjacent cells.
Honeycomb structure (1) in which the number of the communication holes is 18,000 [lines / 0.25 mm ^{2] or more.} The honeycomb structure according to claim 1, wherein the average pore diameter of the partition wall is 12 μm or more and 30 μm or less, and the porosity is 55% or more and 75% or less. The honeycomb structure according to claim 1 or 2, wherein the bending degree L / T defined by the ratio of the average flow path length Lμm of the continuous ventilation holes to the thickness Tμm of the partition wall is 1.2 or more. An exhaust gas purification filter (3) having the honeycomb structure according to any one of claims 1 to 3 and a catalyst (2) supported on the pore wall (122a) of the communication ventilation holes. The exhaust gas purification filter according to claim 4, wherein the amount of the catalyst supported is 30 g / L or more. The exhaust gas purification filter according to claim 4 or 5, wherein the number of the communication holes communicating between the adjacent cells in a state where the catalyst is supported is 4500 [lines / 0.25 mm ^{2] or more.} The exhaust gas purification filter according to any one of claims 4 to 6, wherein the average pore diameter of the partition wall in a state where the catalyst is supported is 10 μm or more and 28 μm or less, and the porosity is 46% or more and 66% or less. .. The tortuosity L / T defined by the ratio of the average flow path length Lμm of the continuous ventilation holes to the thickness Tμm of the partition wall in the state where the catalyst is supported is 1.4 or more, according to claims 4 to 7. The exhaust gas purification filter according to any one item. An exhaust gas purification filter (3) having a honeycomb structure (1) and a catalyst (2).
The honeycomb structure is
The outer skin (11) and
A partition wall (12) that partitions the inside of the exodermis and has a large number of pores (121) formed therein.
It has a cell (13) surrounded by the partition wall and
The partition wall has a communication ventilation hole (122) for communicating between adjacent cells.
The catalyst is supported on the hole wall (122a) of the communication holes.
The amount of the catalyst supported is 30 g / L or more, and the amount is 30 g / L or more.
An exhaust gas purification filter (3) in which the number of communication holes communicating between adjacent cells in a state where the catalyst is supported is 4500 [lines / 0.25 mm ^{2] or more.} The exhaust gas purification filter according to claim 9, wherein the average pore diameter of the partition wall in a state where the catalyst is supported is 10 μm or more and 28 μm or less, and the porosity is 46% or more and 66% or less. 9. Exhaust gas purification filter described.

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