porous composites

Abstract

This porous composite comprises a porous substrate and a porous trapping layer (3) that is provided to a trapping surface of the substrate. The trapping layer (3) includes particles that accumulate within pores of the trapping surface. When the trapping surface is seen in a planar view, the proportion of the area of a covered region that is covered by the trapping layer (3) accounts for 70% or less of the trapping surface, while the proportion of the area of a pore region (26) accounts for 15% or less of a non-covered region that is not covered by the trapping layer (3). With this configuration, it is possible to realize low pressure loss and high trapping efficiency.

Description

[Technical Field]

[0001] The present invention relates to porous composites. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2021-127462, filed on August 3, 2021, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] Vehicles equipped with diesel or gasoline engines are equipped with filters to capture particulate matter in exhaust gases. One such filter is a honeycomb filter, which has a porous honeycomb substrate with multiple cells, and plugged openings on the outlet side of some of the cells and on the inlet side of the remaining cells.

[0003] For example, in the honeycomb filter of Japanese Patent No. 5597153 (Reference 1), a porous collection layer is provided on the surface inside cells that have plugged openings on the outlet side. The collection layer is composed of a plurality of particles that are bonded or entangled with each other, and the plurality of particles includes flat, plate-like particles. The surface of the collection layer also has an opening ratio of 10% or more. The honeycomb filter of Reference 1 can suppress an increase in initial pressure loss and an increase in pressure loss when particulate matter accumulates.

[0004] Furthermore, in the honeycomb filter of WO 2020 / 194681 (Reference 2), the arithmetic mean height, which indicates the surface roughness, of the collection layer provided in a predetermined cell is 0.1 μm or more and 12 μm or less, and the average film thickness of the collection layer is 10 μm or more and 40 μm or less, thereby reducing pressure loss and improving the particulate matter collection efficiency.

[0005] In addition, in the honeycomb filter of JP 2020-1032 A (Reference 3), the collection layer includes a portion composed of a sintered body of CeO2 particles in the surface layer, and the average particle diameter of the CeO2 particles is 1.1 μm or less. This enables the collected particulate matter to be oxidized and burned at a lower temperature. Furthermore, JP 2021-53537 A (Reference 4) discloses a composite oxide catalyst capable of lowering the oxidation onset temperature of particulate matter. The composite oxide catalyst contains, as contained metals, cerium as a first metal, lanthanum as a second metal, and a third metal. The third metal is a transition metal or a rare earth metal other than cerium and lanthanum. The cerium content of the contained metals is 5 mol% or more and 95 mol% or less, the lanthanum content is 2 mol% or more and 93 mol% or less, and the third metal content is 2 mol% or more and 93 mol% or less.

[0006] As described above, the porous composite of Document 1 that constitutes a honeycomb filter achieves reduced pressure loss. However, in recent years, there has been a demand for not only reduced pressure loss but also improved collection efficiency for particulate matter and the like. Since there is usually a trade-off between the two, it is not easy to achieve both low pressure loss and high collection efficiency. The porous composite of Document 2 achieves reduced pressure loss and improved collection efficiency, but the improvement in collection efficiency may not be sufficient. Summary of the Invention

[0007] The present invention is directed to a porous composite, and aims to achieve low pressure loss and high collection efficiency.

[0008] A porous composite according to a preferred embodiment of the present invention comprises a porous substrate and a porous trapping layer provided on a trapping surface of the substrate. The trapping layer contains particles that accumulate in the pores of the trapping surface. When the trapping surface is viewed from above, the area of the region of the trapping surface that is covered by the trapping layer is 1 / 2 of the area of the region of the trapping surface that is covered by the trapping layer. , relative to the area of the collection surface The percentage is 25% or more and 60% is less than the area of the pore region in the uncovered region that is not covered by the trapping layer, , relative to the area of the uncovered regionThe percentage is 9 % or less.

[0009] According to the present invention, low pressure loss and high collection efficiency can be achieved.

[0011] Preferably, the particles have an internal cavity.

[0012] Preferably, the particles have a bulk density of less than 0.50 g / ml.

[0013] Preferably, the particles have a cumulative particle size distribution in which d10 is 0.3 μm or more and d90 is 20 μm or less.

[0014] Preferably, the porosity of the trapping layer is 70% or more and 90% or less.

[0015] Preferably, the particles include catalytic particles that promote oxidation of the trap.

[0016] Preferably, the catalyst particles are CeO2, lanthanum-cerium composite oxide, lanthanum-manganese-cerium composite oxide, lanthanum-cobalt-cerium composite oxide, lanthanum-iron-cerium composite oxide, or lanthanum-praseodymium-cerium composite oxide.

[0017] Preferably, the substrate has a honeycomb structure in which the interior is divided into a plurality of cells by partition walls, and the inner surface of at least some of the plurality of cells is the collection surface.

[0018] Preferably, the porous composite is a gasoline particulate filter that collects particulate matter in exhaust gas emitted from a gasoline engine.

[0019] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a plan view of a porous composite. [Figure 2] FIG. 1 is a cross-sectional view of a porous composite. [Figure 3] FIG. [Figure 4] 1 is an SEM image showing the collection surface. [Figure 5] FIG. 1 is a diagram showing the configuration of a dry film forming apparatus. [Figure 6] FIG. 10 is a diagram illustrating the formation of a collection layer. DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 is a simplified plan view of a porous composite 1 according to one embodiment of the present invention. The porous composite 1 is a tubular member that is long in one direction, and FIG. 1 shows one end face of the porous composite 1 in the longitudinal direction. FIG. 2 is a cross-sectional view of the porous composite 1. FIG. 2 shows a portion of the cross section along the longitudinal direction. The porous composite 1 is used, for example, as a gasoline particulate filter (GPF) that captures particulate matter such as soot in exhaust gas emitted from a gasoline engine of an automobile or the like.

[0022] The porous composite 1 includes a porous substrate 2 and a porous trapping layer 3 (see FIG. 2). In the example shown in FIGS. 1 and 2, the substrate 2 is a member having a honeycomb structure. The substrate 2 includes a cylindrical outer wall 21 and partition walls 22. The cylindrical outer wall 21 is a cylindrical portion extending in the longitudinal direction (i.e., the left-right direction in FIG. 2). The cross-sectional shape of the cylindrical outer wall 21 perpendicular to the longitudinal direction is, for example, substantially circular. The cross-sectional shape may be other shapes, such as a polygon.

[0023] The partition walls 22 are provided inside the cylindrical outer wall 21 and are lattice-shaped sections that divide the interior into multiple cells. As described below, the multiple cells include multiple first cells 231 and multiple second cells 232. In the following description, when the first cells 231 and the second cells 232 are not distinguished from each other, the first cells 231 and the second cells 232 are simply referred to as "cells 23." Each of the multiple cells 23 is a space extending in the longitudinal direction. The cross-sectional shape of each cell 23 perpendicular to the longitudinal direction is, for example, approximately square. The cross-sectional shape may be other shapes such as polygonal or circular. In principle, the multiple cells 23 have the same cross-sectional shape. The multiple cells 23 may include cells 23 with different cross-sectional shapes. The substrate 2 is a cell structure whose interior is divided into multiple cells 23 by partition walls 22.

[0024] The cylindrical outer wall 21 and the partition walls 22 are each a porous portion. The cylindrical outer wall 21 and the partition walls 22 are formed of a ceramic such as cordierite. The material of the cylindrical outer wall 21 and the partition walls 22 may be a ceramic other than cordierite, or may be a material other than ceramics.

[0025] The length of the cylindrical outer wall 21 in the longitudinal direction is, for example, 50 mm to 300 mm. The outer diameter of the cylindrical outer wall 21 is, for example, 50 mm to 300 mm. The thickness of the cylindrical outer wall 21 is, for example, 30 μm or more, and preferably 50 μm or more. The thickness of the cylindrical outer wall 21 is, for example, 1000 μm or less, preferably 500 μm or less, and more preferably 350 μm or less. The length of the partition walls 22 in the longitudinal direction is approximately the same as that of the cylindrical outer wall 21. The thickness of the partition walls 22 is, for example, 30 μm or more, and preferably 50 μm or more. The thickness of the partition walls 22 is, for example, 1000 μm or less, preferably 500 μm or less, and more preferably 350 μm or less.

[0026] The porosity of the substrate 2 including the cylindrical outer wall 21 and the partition walls 22 is, for example, 20% or more, and preferably 30% or more. The porosity of the substrate 2 is, for example, 80% or less, and preferably 70% or less. The open porosity of the substrate 2 is, for example, 40% or more, and preferably 55% or more. The open porosity of the substrate 2 is, for example, 65% or less. The porosity and open porosity of the substrate 2 can be measured by Archimedes' method.

[0027] The average pore diameter (pore diameter) of the substrate 2 is, for example, 5 μm or more, preferably 8 μm or more. The average pore diameter of the substrate 2 is, for example, 30 μm or less, preferably 25 μm or less. The average pore diameter can be measured using a mercury porosimeter. The surface opening ratio of the substrate 2 is, for example, 20% or more, preferably 25% or more. The surface opening ratio of the substrate 2 is, for example, 60% or less, preferably 50% or less. The surface opening ratio is the ratio of the area of the region where pores are open to the surface of the substrate 2, and can be determined by image analysis of an SEM (scanning electron microscope) image of the surface. The SEM image is taken at, for example, 500x magnification. The image analysis is performed using, for example, image analysis software "Image-Pro ver. 9.3.2" manufactured by Nippon Roper Co., Ltd.

[0028] The cell density of the substrate 2 (i.e., the number of cells 23 per unit area in a cross section perpendicular to the longitudinal direction) is, for example, 10 cells / cm 2 or more, preferably 20 cells / cm 2 More preferably, 30 cells / cm or more. 2 That's all. The cell density is, for example, 200 cells / cm 2 less than or equal to 150 cells / cm 2 1, the size of the cells 23 is drawn larger than in reality, and the number of the cells 23 is drawn smaller than in reality. The size and number of the cells 23 may be variously changed.

[0029] When the porous composite 1 is used as a GPF, one end side of the porous composite 1 in the longitudinal direction (i.e., the left side in FIG. 2) serves as an inlet, and the other end side serves as an outlet, and gas such as exhaust gas flows inside the porous composite 1. Furthermore, among the plurality of cells 23 of the porous composite 1, some of the plurality of cells 23 are provided with plugging portions 24 at their inlet-side ends, and the remaining plurality of cells 23 are provided with plugging portions 24 at their outlet-side ends.

[0030] Fig. 1 depicts the inlet side of the porous composite 1. To facilitate understanding of the drawing, the plugging portions 24 on the inlet side are indicated by parallel diagonal lines in Fig. 1. In the example shown in Fig. 1, cells 23 provided with plugging portions 24 on the inlet side and cells 23 not provided with plugging portions 24 on the inlet side (i.e., cells 23 provided with plugging portions 24 on the outlet side) are alternately arranged in the vertical and horizontal directions in Fig. 1.

[0031] In the following description, the cells 23 provided with plugging portions 24 on the outlet side will also be referred to as "first cells 231," and the cells 23 provided with plugging portions 24 on the inlet side will also be referred to as "second cells 232." In the porous composite 1, a plurality of first cells 231 each having one plugged end in the longitudinal direction and a plurality of second cells 232 each having the other plugged end in the longitudinal direction are arranged alternately.

[0032] The trapping layer 3 is formed on the base material 2. In the example shown in FIG. 2, the trapping layer 3 is provided in a plurality of first cells 231 that have plugging portions 24 provided on the outlet side, and covers the inner surfaces of the plurality of first cells 231 (i.e., the surfaces of the partition walls 22). The trapping layer 3 does not cover the entire inner surfaces of the first cells 231, but only partially covers the inner surfaces. In FIG. 2, the trapping layer 3 is indicated by a thick dashed line. The trapping layer 3 may also be provided on the inner surfaces of the outlet-side plugging portions 24 in the plurality of first cells 231. On the other hand, the trapping layer 3 is not present in a plurality of second cells 232 that have plugging portions 24 provided on the inlet side. In other words, the inner surfaces of the plurality of second cells 232 are not covered by the trapping layer 3 and are exposed.

[0033] In the porous composite 1 shown in FIGS. 1 and 2, as indicated by arrow A1 in FIG. 2, gas flowing into the porous composite 1 flows into the first cells 231 through the inlets of the first cells 231, whose inlet sides are not sealed, and then passes through the first cells 231 through the porous trapping layer 3 and the partition walls 22 to move to the second cells 232, whose outlet sides are not sealed. At this time, substances to be trapped in the gas (here, particulate matter) are efficiently trapped in the trapping layer 3. Furthermore, if the trapping layer 3 contains catalyst particles, which will be described later, the combustion (i.e., oxidative removal) of the trapped particulate matter is promoted. In the following description, the inner surfaces of the multiple first cells 231 on which the trapping layer 3 is provided will also be referred to as the "trapping surface."

[0034] FIG. 3 is a diagram showing a trapping surface on which a trapping layer 3 is provided, and FIG. 4 is an SEM image showing an example of the trapping surface. FIGS. 3 and 4 show the trapping surface and trapping layer 3 as viewed from a direction substantially perpendicular to the trapping surface (i.e., as viewed from above). In FIG. 3, the area surrounded by thick solid and dashed lines is a region 26 of pores opening to the trapping surface (hereinafter referred to as "pore region 26"). The region with parallel diagonal lines is the trapping layer 3, and the remaining region is the surface of the substrate 2. As will be described later, the trapping layer 3 is formed by the deposition of particles. In the SEM image of FIG. 4, the white portions are particles in the trapping layer 3, the black portions are portions of the pore region 26 not covered by the trapping layer 3, and the gray portions are the surface of the substrate 2. The trapping layer 3 includes a plurality of isolated regions, and in FIG. 3, each region of the trapping layer 3 is labeled with the reference symbol 3.

[0035] When the trapping surface is viewed from above as in Figures 3 and 4, the region covered by the trapping layer 3 is called the "covered region." In the porous composite 1, the area of the covered region on the trapping surface accounts for 70% or less of the area of the trapping surface. In other words, the value obtained by dividing the area of the covered region included in any region of the trapping surface in a planar view by the area of that region is 70% or less. In the following explanation, the area ratio of the covered region on the trapping surface is referred to as the "coverage ratio of the trapping surface." If the coverage ratio of the trapping surface is excessively high, the pressure loss will increase. The coverage ratio of the trapping surface is preferably 65% or less, and more preferably 60% or less.

[0036] The coverage of the collection surface is, for example, 20% or more, preferably 25% or more, and more preferably 30% or more. If the coverage of the collection surface is too small, the collection efficiency of the particulate matter to be collected will be low. As will be described later, in the porous composite 1, the collection layer 3 is selectively or preferentially formed in the pore region 26 on the collection surface. Therefore, if the coverage of the collection surface is, for example, 3 / 4 times or more the surface opening ratio of the substrate 2, the collection layer 3 will be present in most of the pore region 26. Furthermore, if the coverage of the collection surface is equal to or greater than the surface opening ratio of the substrate 2, the collection layer 3 will be present in an even greater portion of the pore region 26.

[0037] Furthermore, if the region of the trapping surface that is not covered by the trapping layer 3 is referred to as the "uncovered region," the proportion of the area of the pore region 26 in the uncovered region is 15% or less. In other words, in any region of the trapping surface viewed from above, the value obtained by dividing the area of the pore region included in the uncovered region by the area of the uncovered region is 15% or less. In the following description, the proportion of the area of the pore region 26 in the uncovered region is referred to as the "pore ratio of the uncovered region." If the pore ratio of the uncovered region is excessively large, the amount of gas that does not pass through the trapping layer 3 increases, thereby reducing the particulate matter collection efficiency. The pore ratio of the uncovered region is preferably 13% or less, and more preferably 10% or less. The pore ratio of the uncovered region is 0% or more.

[0038] In a typical porous composite 1, the porosity of the uncoated region is sufficiently lower than the surface opening ratio of the substrate 2. The porosity of the uncoated region is, for example, half or less of the surface opening ratio, and preferably two-thirds or less of the surface opening ratio. In such a porous composite 1, the trapping layer 3 is present in most of the pore region 26. This increases the particulate matter trapping efficiency. Preferably, the trapping layer 3 is present in 70% or more of the pore region 26. Meanwhile, the trapping layer 3 is unlikely to be formed in regions of the trapping surface other than the pore region 26 (hereinafter also referred to as "non-pore region"). In the porous composite 1, the trapping layer 3 is present in large amounts in and around the pore region 26 where particulate matter is trapped, and the trapping layer 3 is present in small amounts in the non-pore region, making it possible to increase the trapping efficiency while suppressing an increase in pressure loss.

[0039] To measure the coverage rate of the trapping surface and the porosity rate of the uncovered region, for example, the porous composite 1 is cross-sectionally processed to obtain a longitudinal cross section (a cross section along the longitudinal direction) of the first cell 231. Next, an SEM image of the inner surface of the first cell 231 is taken at 500x magnification from a direction approximately perpendicular to the inner surface. The SEM image is then analyzed using the image analysis software ("Image-Pro ver. 9.3.2" manufactured by Nippon Roper Co., Ltd.) to determine the coverage rate of the trapping surface and the porosity rate of the uncovered region. Preferably, multiple values indicating the coverage rate of the trapping surface are obtained from the longitudinal cross sections of multiple first cells 231, and the average of these multiple values is used as the coverage rate of the trapping surface in the porous composite 1. The same applies to the porosity rate of the uncovered region and the porosity of the trapping layer 3, which will be described later.

[0040] The trapping layer 3 contains particles that are deposited within the pores of the trapping surface. Typically, the particles deposited within the pores bond (or adhere) to each other to form a porous layer. Some of the particles are also bonded to the substrate 2. The particles in the trapping layer 3 are preferably bonded directly to each other without the use of any other material (binder). In this case, the trapping layer 3 does not contain a binder and is composed essentially of the particles alone. Depending on the method for forming the trapping layer 3, the particles may be bonded to each other via a binder. When a collection of particles that are bonded to each other is referred to as a bonded particle group, the entire bonded particle group does not necessarily need to be located within the pores; some of the bonded particle group may be located outside the pores or in non-pore regions. The trapping layer 3 may also contain particles that are present in isolation on non-pore regions and bonded particle groups.

[0041] The porosity of the trapping layer 3 within the pores of the trapping surface (the porosity of the bound particle group) is, for example, 60% or more, preferably 70% or more, and more preferably 75% or more. If the porosity of the trapping layer 3 is excessively low, the pressure loss increases. The porosity of the trapping layer 3 is preferably 90% or less, and more preferably 85% or less. If the porosity of the trapping layer 3 is excessively high, the particulate matter collection efficiency decreases.

[0042] In measuring the porosity of the trapping layer 3, for example, an SEM image of a region including the cross section of the trapping layer 3 in the porous composite 1 that has undergone the cross-section processing described above is taken at a magnification of 2000x. The SEM image is then analyzed using the image analysis software described above (Image-Pro ver. 9.3.2, image analysis software manufactured by Nippon Roper Co., Ltd.) to determine the porosity of the trapping layer 3. The image analysis is performed, for example, by a method similar to that described in International Publication No. 2020 / 194681 (reference 2 described above). Specifically, in the region of the SEM image where the trapping layer 3 is present, the area of the bright regions where the bright portions (i.e., the particles of the trapping layer 3) are connected and the area of the dark regions where the dark portions (i.e., the pores of the trapping layer 3) are connected are calculated. The porosity of the trapping layer 3 is then calculated by dividing the total area of the dark regions by the sum of the total area of the bright regions and the total area of the dark regions.

[0043] The thickness of the trapping layer 3 is, for example, greater than 2 μm, and preferably 3 μm or greater. If the thickness of the trapping layer 3 is excessively small, the particulate matter capture efficiency will be low. The thickness of the trapping layer 3 is, for example, less than 20 μm, and preferably 18 μm or less. If the thickness of the trapping layer 3 is excessively large, the pressure loss will be high. In addition, the amount of the trapping layer 3 will be large, which will increase the production cost of the porous composite 1.

[0044] The thickness of the trapping layer 3 is measured using, for example, a 3D shape measuring machine in a manner similar to that described in International Publication No. 2020 / 194681 (reference 2 above). Specifically, longitudinal cross sections of a plurality of first cells 231 and a plurality of second cells 232 are obtained by cross-sectional processing of the porous composite 1. The average position of the surface of the trapping layer 3 in the first cells 231 and the average position of the surface of the pore regions 26 (the bottom surfaces of the pores) in the second cells 232 are measured with the 3D shape measuring machine in a direction perpendicular to the longitudinal cross sections. The difference between the average position of the surface of the trapping layer 3 and the average position of the surface of the pore regions 26 is then calculated as the thickness of the trapping layer 3.

[0045] The median diameter (d50) in the cumulative particle size distribution (volume basis) of the particles in the trapping layer 3 is, for example, 7.0 μm or less, preferably 6.5 μm or less. The median diameter is, for example, 2.0 μm or more, preferably 2.5 μm or more. When the median diameter is within the above range, it is easy to adjust the porosity of the trapping layer 3 to within the desired range. The d10 in the cumulative particle size distribution is preferably 0.3 μm or more, more preferably 0.5 μm or more. The d90 in the cumulative particle size distribution is preferably 20 μm or less, more preferably 15 μm or less. When the trapping layer 3 is formed as described below, particles are transported into the pores of the trapping surface by the gas flow. When the d10 and d90 are within the above range, it is easy to transport the particles into the pores of the trapping surface. The d10 is, for example, 3.5 μm or less, preferably 3.0 μm or less. The d90 is, for example, 5.0 μm or more, and preferably 6.5 μm or more.

[0046] To measure the cumulative particle size distribution of particles, the porous composite 1 is disassembled, and only the trapping layer 3 is scraped off using a spatula or the like, so as not to include any fragments of the substrate 2, thereby extracting particles constituting the trapping layer 3 from the porous composite 1. To extract particles from the trapping layer 3, preferably, cross-section processing is performed on the porous composite 1 to obtain a longitudinal cross-section (a cross-section along the longitudinal direction) of the second cell 232. Next, the partition wall 22 (cell wall) separating the second cell 232 from the adjacent first cell 231 located further back (inside the cross-section) than the second cell 232 is peeled off using tweezers, thereby exposing the longitudinal cross-section of the first cell 231. Then, the trapping layer 3 of the first cell 231 is scraped off using a spatula. This prevents fragments of the substrate 2 generated during cross-section processing from being mixed in with the extracted particles. The cumulative particle size distribution of the particles is then measured using laser diffraction.

[0047] The particles of the trapping layer 3 preferably have internal cavities. This results in a relatively low bulk density of the particles (i.e., the particles are bulky), which makes it easy for the particles to be transported into the pores of the trapping surface by the gas flow during the formation of the trapping layer 3. The presence or absence of cavities in the particles of the trapping layer 3 can be confirmed, for example, in a 5000x SEM image. The bulk density of the particles is preferably less than 0.50 g / ml. The lower limit of the bulk density is not particularly limited, but is, for example, 0.10 g / ml or more. To measure the bulk density of the particles of the trapping layer 3, the mass of the particles of the trapping layer 3 removed from the porous composite 1 is measured. The particles are then placed in a measuring cylinder to measure the volume, and the bulk density is calculated by dividing the mass by the volume.

[0048] The specific surface area of the particles in the trapping layer 3 is, for example, 10 m 2 / g or more, preferably 15m 2 The upper limit of the specific surface area is not particularly limited, but for example, 1000 m 2 / g or less. The specific surface area of the particles of the trapping layer 3 can be measured by the BET specific surface area method using the particles of the trapping layer 3 taken out of the porous composite 1.

[0049] The particles of the trapping layer 3 preferably include catalyst particles that promote the oxidation of the particulate matter. As described above, the trapping layer 3 is selectively or preferentially formed in the pore region 26 on the trapping surface, so that the majority of the catalyst particles are disposed in the pores on the trapping surface where particulate matter is likely to accumulate. This increases the contact area between the catalyst particles and the particulate matter, enabling higher catalytic activity to be achieved. As a result, the oxidation onset temperature of the particulate matter (i.e., low-temperature combustion of the particulate matter) can be more reliably reduced.

[0050] The catalyst particles are typically oxides, preferably CeO2 (ceria), lanthanum (La)-cerium (Ce) composite oxide, lanthanum-manganese (Mn)-cerium composite oxide, lanthanum-cobalt (Co)-cerium composite oxide, lanthanum-iron (Fe)-cerium composite oxide, or lanthanum-praseodymium (Pr)-cerium composite oxide. In other words, the particles of the trapping layer 3 preferably contain one or more of CeO2, lanthanum-cerium composite oxide, lanthanum-manganese-cerium composite oxide, lanthanum-cobalt-cerium composite oxide, lanthanum-iron-cerium composite oxide, and lanthanum-praseodymium-cerium composite oxide.

[0051] Lanthanum-cerium composite oxide is an oxide containing La and Ce, and is also expressed as "La-Ce-O." Lanthanum-manganese-cerium composite oxide is an oxide containing La, Mn, and Ce, and is also expressed as "La-Mn-Ce-O." Lanthanum-cobalt-cerium composite oxide is an oxide containing La, Co, and Ce, and is also expressed as "La-Co-Ce-O." Lanthanum-iron-cerium composite oxide is an oxide containing La, Fe, and Ce, and is also expressed as "La-Fe-Ce-O." Lanthanum-praseodymium-cerium composite oxide is an oxide containing La, Pr, and Ce, and is also expressed as "La-Pr-Ce-O."

[0052] The composite oxide particles can be produced by a method similar to that described in JP 2021-53537 A (reference 4), for example, a citric acid method. The composite oxide particles may also be produced by an impregnation method, a complex polymerization method, or the like. The trapping layer 3 containing the catalyst particles is preferably composed essentially of the catalyst particles alone, but may also contain substances other than the catalyst particles. The trapping layer 3 may be formed of catalyst particles other than the catalyst particles (e.g., Fe2O3 or MnO2), or may be formed of particles other than the catalyst particles. Examples of particles other than catalyst particles include particles of SiO2, SiC, and Al2O3. Particles of various substances, such as metal oxides, nitrides, or carbides, can be used in the trapping layer 3.

[0053] Next, an example of the production of the porous composite 1 will be described. Because the method for producing the substrate 2 is publicly known, the formation of the trapping layer 3 on the substrate 2 (substrate 2 without the trapping layer 3) will be described here. In the preferred formation of the trapping layer 3, particles are deposited on the trapping surface of the substrate 2 by a dry film-forming method. Figure 5 is a diagram showing the configuration of a dry film-forming apparatus 8. Figure 6 is a diagram for explaining the formation of the trapping layer 3, and schematically shows a portion of the cross section of the substrate 2 along the longitudinal direction.

[0054] The dry film forming apparatus 8 of FIG. 5 includes a first cylindrical portion 81, a second cylindrical portion 82, and a particle supply portion 83. The first cylindrical portion 81 and the second cylindrical portion 82 are both cylindrical members, and the cross-sectional shape perpendicular to the central axis thereof is substantially the same as the cross-sectional shape of the outer surface of the substrate 2 (the outer surface of the cylindrical outer wall 21). As described above, the substrate 2 is a member extending in the longitudinal direction, and one end of the substrate 2 in the longitudinal direction is inserted into the end of the first cylindrical portion 81, and the other end of the substrate 2 is inserted into the end of the second cylindrical portion 82. In this embodiment, the end of the substrate 2 where the first cells 231 (see FIG. 6) are open (i.e., the end where the plugging portion 24 is provided in the second cells 232) is inserted into the first cylindrical portion 81, and the end of the substrate 2 where the second cells 232 are open is inserted into the second cylindrical portion 82. The outer surface of the substrate 2 may be in contact with the first cylindrical portion 81 or the second cylindrical portion 82 via an O-ring or the like. Gas and liquid are almost unable to pass between the outer surface of the substrate 2 and the inner surface of the first cylindrical portion 81, and between the outer surface of the substrate 2 and the inner surface of the second cylindrical portion 83.

[0055] A particle supply unit 83 is connected to the end of the first cylindrical portion 81 opposite the substrate 2. The particle supply unit 83 supplies an aerosol, in which particles that will become the collection layer 3 are dispersed in a gas, into the first cylindrical portion 81. The dispersion medium of the aerosol is, for example, air. The dispersion medium of the aerosol may be a gas other than air. A pressure reduction mechanism (not shown) is connected to the end of the second cylindrical portion 82 opposite the substrate 2, and the pressure inside the second cylindrical portion 82 is reduced. As a result, the aerosol supplied into the first cylindrical portion 81 flows into the substrate 2.

[0056] As shown by arrow A2 in FIG. 6 , the aerosol flows into the first cells 231. The gas contained in the aerosol enters the partition walls 22 through pores opening on the inner surface (collection surface) of the first cells 231 and moves to the second cells 232 adjacent to the first cells 231. The gas that moves to the second cells 232 is discharged to the outside of the substrate 2 through the openings of the second cells 232. At this time, most of the particles contained in the aerosol enter the pores of the collection surface along with the gas and accumulate therein. Some particles may adhere to the non-porous region of the collection surface (the surface of the substrate 2). Preferred particles have internal cavities and / or a bulk density of less than 0.50 g / ml, which allows the particles to easily enter the pores of the collection surface along with the gas. From the viewpoint of allowing as many particles as possible to enter the pores of the collection surface, it is preferable that the d90 value in the cumulative particle size distribution of the particles be equal to or less than the average pore size of the substrate 2.

[0057] By the above process, most of the particles deposited on the substrate 2 are present in the pores of the collecting surface. That is, when the collecting surface is viewed from above, the trapping layer 3 is selectively or preferentially formed in the pore region 26 (see FIG. 3). The conditions for depositing particles on the collecting surface (including the pores) using the dry film-forming apparatus 8 may be determined appropriately depending on the coverage of the collecting surface, the pore ratio of the uncovered region, the porosity of the trapping layer 3, the thickness of the trapping layer 3, etc. In one example, the density of particles in the aerosol is 1 to 10 mg / cc, and the aerosol suction speed is 0.1 to 5 m / s.

[0058] In the production of porous composite 1, porous composite 1 removed from dry film-forming apparatus 8 is further subjected to a baking process. The heating temperature during the baking process is, for example, 500°C or higher and 1300°C or lower. The heating time during the baking process is, for example, 0.5 hours or higher and 2 hours or lower. The heating temperature and heating time during the baking process may be determined appropriately depending on the type of particles in trapping layer 3, etc. If the adhesion strength of the particles to substrate 2 is sufficiently ensured, the baking process may be omitted.

[0059] Next, with reference to Tables 1 to 3, Examples 1 to 11 of the porous composite according to the present invention and Comparative Examples 1 to 6 for comparison with the porous composite will be described.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Table 3]

[0063] In Examples 1 to 11, a substrate made of cordierite and having the shape of a honeycomb filter (honeycomb structure) was used. The open porosity of the substrate was 55%, the surface opening ratio was 30%, and the average pore diameter was 18 μm. The open porosity was measured by Archimedes' method using pure water as a medium. The surface opening ratio was determined by image analysis of an SEM image (magnification: 500 times) of the surface of the substrate using the image analysis software described above. The average pore diameter was measured using a mercury porosimeter.

[0064] In Examples 1 to 11, a trapping layer was formed by a dry film-forming method using the dry film-forming apparatus 8 of FIG. 5. The density of particles in the aerosol was 5 mg / cc. The aerosol suction speed was 1 m / s. In Examples 1 to 7, La-Mn-Ce-O particles were used. Of Examples 1 to 7, in Examples 1, 2, 4, and 5, the film-forming weight of the trapping layer was changed by adjusting the film-forming time, etc. In Example 3, the heating temperature (baking temperature) during the baking process was lowered. In Example 6, particles with small particle diameters were used, and in Example 7, particles with large particle diameters were used. In Examples 8 and 9, CeO2 particles were used, and the film-forming weight of the trapping layer was changed. In Examples 10 and 11, SiO2 particles were used, and the film-forming weight of the trapping layer was changed. The baking temperature was also increased.

[0065] In Examples 1 to 11, the area ratio of the covered region to the collecting surface (coverage ratio of the collecting surface) was 25% to 60%, and in all cases was 70% or less. The area ratio of the pore region to the uncovered region (pore ratio of the uncovered region) was 0% to 9%, and in all cases was 15% or less. The coverage ratio of the collecting surface and the pore ratio of the uncovered region were determined by image analysis of SEM images (magnification: 500x) of the collecting surface using the image analysis software described above. The coverage ratio of the collecting surface and the pore ratio of the uncovered region in Table 2 are each the average value of values obtained from five SEM images taken of different regions of the collecting surface.

[0066] In Examples 1 to 11, the thickness (film thickness) of the trapping layer was 3 μm to 15 μm. As described above, the thickness of the trapping layer was determined as the difference between the average position of the surface of the trapping layer measured with a 3D shape measuring device and the average position of the surface of the pore region. In Examples 1 to 11, the porosity of the trapping layer within the pores on the trapping surface was 76% to 82%, and was always 70% or more and 90% or less. The porosity was determined by image analysis of an SEM image (magnification: 2000 times) of the cross section of the trapping layer 3 using the image analysis software described above.

[0067] In Examples 1 to 11, the median diameter (d50) in the cumulative particle size distribution (volume basis) of the particles was 2.8 μm to 6.3 μm. Furthermore, d10 was 0.5 to 2.8 μm, all of which were 0.3 μm or more. d90 was 7.0 to 12 μm, all of which were 20 μm or less. The cumulative particle size distribution was obtained by extracting only the particles of the trapping layer from the porous composite and measuring the particles by laser diffraction.

[0068] In Examples 1 to 9 using La-Mn-Ce-O particles or CeO2 particles, the specific surface area of the particles was 20 m 2 / g~70m 2 / g, and in Examples 10 and 11 using SiO2 particles, the specific surface area of the particles was 720 m 2 / g. The specific surface area of the particles was obtained by measuring the particles extracted from the porous composite using the BET specific surface area method. In Examples 1 to 11, the bulk density was all less than 0.50 g / ml. In Table 2, a bulk density less than 0.50 g / ml is marked as "small," and a bulk density of 0.50 g / ml or greater is marked as "large." The bulk density of the particles was obtained by measuring the mass of the particles extracted from the porous composite, then placing them in a measuring cylinder to measure the volume, and dividing the mass by the volume. Although not shown in the table, when the La-Mn-Ce-O particles were observed using a 5000x SEM image, they were found to have internal cavities. The same was true for CeO2 particles and SiO2 particles.

[0069] In Comparative Examples 1 to 6, the same substrate as in Examples 1 to 11 was used. In Comparative Examples 1 to 5, La-Mn-Ce-O particles were used, and in Comparative Example 6, SiC particles were used. In Comparative Examples 1, 2, 3, and 6, the trapping layer was formed by a dry film-forming method, as in Examples 1 to 11. In Comparative Example 1, the deposition weight of the trapping layer was made excessively small, and in Comparative Example 2, the deposition weight of the trapping layer was made excessively large. As a result, in Comparative Example 1, the coverage rate of the trapping surface was significantly small, and the porosity rate of the uncovered region was greater than 15%. In Comparative Example 2, the coverage rate of the trapping surface was significantly greater than 70%.

[0070] In Comparative Examples 3 and 6, the baking temperature was increased. As a result, in Comparative Example 3, which used La-Mn-Ce-O particles, the porosity of the uncoated region was significantly greater than 15%. In Comparative Example 6, which used SiC particles, the coverage of the collection surface was significantly greater than 70%. In both Comparative Examples 3 and 6, the bulk density of the particles was 0.50 g / ml or more.

[0071] In Comparative Examples 4 and 5, the trapping layer was formed by a wet film-forming method. Specifically, La-Mn-Ce-O particles were mixed with a liquid such as water to form a slurry, and the slurry was supplied into the first cell. The liquid such as water permeated the partition walls and flowed out of the second cell to the outside of the substrate, while the La-Mn-Ce-O particles adhered to the inner surface of the first cell without passing through the partition walls. A baking process was then performed. In Comparative Examples 4 and 5, the film weight of the trapping layer was changed. In Comparative Example 4, where the film weight was relatively small, the porosity of the uncovered region was significantly greater than 15%. In Comparative Example 5, where the film weight was relatively large, the coverage of the trapping surface was significantly greater than 70%. In both Comparative Examples 4 and 5, the porosity of the trapping layer was less than 70%.

[0072] In the performance evaluation of the porous composites of Examples 1 to 11 and Comparative Examples 1 to 6, the initial pressure drop (i.e., the pressure drop before the capture of particulate matter, etc.), the capture efficiency, and the soot oxidation onset temperature were compared to evaluate the overall performance. In addition, a similar performance evaluation was also performed on a substrate without a capture layer as a reference example.

[0073] To evaluate the initial pressure loss of the porous composite, first, air at room temperature was blown into the porous composite at a pressure of 10 Nm 3 Air was supplied to the porous composite at a flow rate of 1 / min, and the pressure difference across the porous composite (i.e., the pressure difference between the air inlet and outlet) was measured. The pressure difference in the case of the substrate alone was defined as the reference pressure difference, and the rate of increase in the pressure difference across the porous composite relative to the reference pressure difference was defined as the rate of increase in initial pressure loss. The rate of increase in initial pressure loss (%) was calculated as (AB) / B × 100, where A is the pressure difference across the porous composite and B is the reference pressure difference across the substrate. In the evaluation of initial pressure loss, a rate of increase in initial pressure loss of 20% or less was evaluated as "◎." A rate of increase in pressure loss of more than 20% and less than or equal to 40% was evaluated as "○," and a rate of increase in pressure loss of more than 40% was evaluated as "×."

[0074] The filtering efficiency of the porous composite was determined as follows. First, the porous composite was installed as a GPF in the exhaust system of a passenger vehicle with a 2-liter direct-injection gasoline engine, and a vehicle test was conducted using a chassis dynamometer. In this vehicle test, the number of particulate matter particles emitted in the exhaust gas when driving in the European regulation driving mode (RTS95) was measured using a measurement method in accordance with PMP (European regulation particulate measurement protocol). In addition, a similar vehicle test was conducted without a GPF in the exhaust system, and the number of particulate matter particles emitted in the exhaust gas was measured using the same measurement method. The number of particulate matter particles emitted without a GPF was defined as the "reference number of particles," and the difference between the number of particulate matter particles measured with the porous composite installed and the reference number was divided by the reference number to determine the "filtering efficiency (%)." In the evaluation of filtering efficiency, a filter efficiency of 98% or higher was evaluated as "◎," and a filter efficiency of less than 98% and 95% or higher was evaluated as "○." In addition, a collection efficiency of less than 95% and 90% or more was evaluated as "△", and a collection efficiency of less than 90% was evaluated as "×".

[0075] In Examples 1 to 11, in which the coverage rate of the collecting surface was 70% or less and the porosity rate of the uncovered region was 15% or less, the initial pressure drop and the collection efficiency were both evaluated as "◎" or "◯". In contrast, in Comparative Examples 1 to 6, in which the coverage rate of the collecting surface was greater than 70% or the porosity rate of the uncovered region was greater than 15%, the initial pressure drop was evaluated as "×" or the collection efficiency was evaluated as "×" or "△". In the Reference Example, the initial pressure drop was evaluated as "◎" and the collection efficiency was evaluated as "×".

[0076] The soot oxidation onset temperature in the porous composite was determined as follows. First, a test piece measuring 118.4 mm in diameter and 127 mm in length was cut from the porous composite. A soot generator was used to deposit 0.5 g / L of soot onto the test piece to obtain a measurement sample. Next, a balance gas (mixed gas) containing 80% nitrogen (N2) and 20% oxygen (O2) was passed through the measurement sample at a flow rate of 40000 Hz (1 / hr) while the sample was heated. The CO and CO2 gases evolved from the sample upon heating were detected using ND-IR (non-dispersive infrared). The temperature at which the cumulative amount of CO2 gas produced reached 10% of the total amount of O2 gas was defined as the soot oxidation onset temperature. The lower the oxidation onset temperature, the higher the catalytic ability of the particles in the collection layer.

[0077] In the evaluation of the soot oxidation onset temperature, a temperature of 410°C or less was evaluated as "◎", a temperature of more than 410°C and less than 460°C was evaluated as "◯", and a temperature of more than 460°C was evaluated as "△".

[0078] With regard to the soot oxidation onset temperature, Examples 1 to 9, which used La-Mn-Ce-O particles or CeO2 particles, were all evaluated as "◎" or "◯". Examples 10 and 11, which used SiO2 particles, were evaluated as "△". Of Comparative Examples 1 to 5, which used La-Mn-Ce-O particles, Comparative Examples 2, 4, and 5, excluding Comparative Example 1, in which the deposition weight of the trapping layer was excessively small, and Comparative Example 3, in which the baking temperature was excessively high, were evaluated as "◎". On the other hand, Comparative Examples 1 and 3, Comparative Example 6, which used SiC particles, and the reference example in which no trapping layer was provided were evaluated as "△".

[0079] In the overall evaluation of Examples 1 to 11, Comparative Examples 1 to 6, and Reference Example, when the initial pressure loss, collection efficiency, and soot oxidation onset temperature were all evaluated as "◎", the overall evaluation was "A". When there was one or more evaluations of "◯" and no evaluations of "△" or "×", the overall evaluation was "B". When there was only one evaluation of "△" and no evaluations of "×", the overall evaluation was "C". When there was at least one evaluation of "×" or two or more evaluations of "△", the overall evaluation was "F". In the overall evaluation, "A" was the highest evaluation, and the evaluations decreased in order from "B", "C", to "F".

[0080] The overall evaluation of Examples 2, 3, and 7 was "A," the overall evaluation of Examples 1, 4 to 6, 8, and 9 was "B," and the overall evaluation of Examples 10 and 11 was "C." The overall evaluation of Comparative Examples 1 to 6 and the Reference Example was all "F."

[0081] As described above, the porous composite 1 includes a porous substrate 2 and a porous trapping layer 3 provided on the trapping surface of the substrate 2 (for example, the inner surface of the first cell 231). The trapping layer 3 contains particles that accumulate in the pores of the trapping surface. When the trapping surface is viewed from above, the proportion of the area of the covered region of the trapping surface that is covered with the trapping layer 3 (trapping surface coverage proportion) is 70% or less, and the proportion of the area of the pore region 26 of the uncovered region that is not covered with the trapping layer 3 (uncovered region pore proportion) is 15% or less. This makes it possible to achieve low pressure loss and high trapping efficiency, as in Examples 1 to 11.

[0082] In a preferred porous composite 1, when the collection surface is viewed from above, the ratio of the area of the covered region to the collection surface is 25% or more, which can more reliably increase the collection efficiency.

[0083] In a preferred porous composite 1, the particles of the trapping layer 3 have internal cavities and / or the bulk density of the particles is less than 0.50 g / ml. This makes it easy to transport the particles into the pores opening to the trapping surface by a gas flow when forming the trapping layer 3, and makes it easy to manufacture the porous composite 1.

[0084] In a preferred porous composite 1, the d10 is 0.3 μm or more and the d90 is 20 μm or less in the cumulative particle size distribution of the particles in the trapping layer 3. In this way, the particles in the trapping layer 3 have a narrow particle size distribution, which makes it possible to make the particle size of the majority of the particles equal to or less than the average pore size of the substrate 2, making it easier to deposit the particles in the pores of the trapping surface.

[0085] In a preferred porous composite 1, the particles of the trapping layer 3 contain catalyst particles that promote the oxidation of the trapped material. This promotes the oxidation of the trapped particulate matter, thereby lowering the oxidation onset temperature of the particulate matter. Furthermore, by disposing most of the catalyst particles within the pores, the contact area between the catalyst particles and the particulate matter is increased, resulting in higher catalytic activity (i.e., a lower oxidation onset temperature).

[0086] Preferred catalyst particles are CeO2, lanthanum-cerium composite oxide, lanthanum-manganese-cerium composite oxide, lanthanum-cobalt-cerium composite oxide, lanthanum-iron-cerium composite oxide, or lanthanum-praseodymium-cerium composite oxide, which can more reliably lower the oxidation onset temperature of the particulate matter.

[0087] In a preferred porous composite 1, the porosity of the trapping layer 3 is 70% or more and 90% or less. By setting the porosity to 70% or more, low pressure loss can be easily achieved in the porous composite 1. Furthermore, by setting the porosity to 90% or less, high trapping efficiency can be easily achieved.

[0088] In a preferred porous composite 1, the substrate 2 has a honeycomb structure in which the interior is divided into a plurality of cells 23 by partition walls 22, and the inner surfaces of at least some of the cells 23 (for example, first cells 231) among the plurality of cells 23 are the above-mentioned collection surfaces. This makes it possible to provide a honeycomb filter that achieves low pressure loss and high collection efficiency.

[0089] As described above, the porous composite 1 can achieve low pressure loss and high collection efficiency. Therefore, the porous composite 1 is particularly suitable for GPFs that collect particulate matter in exhaust gases emitted from gasoline engines.

[0090] The porous composite 1 described above can be modified in many ways.

[0091] The coverage of the collection surface may be less than 25% provided that high collection efficiency is achieved.

[0092] If the trapping layer 3 is formed selectively or preferentially in the pore region 26 on the trapping surface, the bulk density of the particles in the trapping layer 3 may be 0.50 g / ml or more. Similarly, the d10 in the cumulative particle size distribution of the particles may be less than 0.3 μm, and the d90 may be greater than 20 μm.

[0093] The porosity of the trapping layer 3 may be less than 70% or greater than 90%.

[0094] The porous composite 1 is not limited to the above-mentioned GPF, but may be, for example, a diesel particulate filter (DPF) that captures particulate matter in exhaust gas emitted from a diesel engine. As described above, the porous composite 1 can achieve low pressure loss and high collection efficiency, and is therefore particularly suitable for not only GPFs but also DPFs. Note that the porous composite 1 may also be used as various filters other than GPFs and DPFs. Alternatively, the porous composite 1 may be used for applications other than filters.

[0095] The structure of the porous composite 1 may be modified in various ways. For example, the plugging portions 24 may be omitted from the substrate 2. Alternatively, the inner surfaces of all the cells 23 may be used as the trapping surfaces, and the trapping layers 3 may be provided. Furthermore, the substrate 2 does not necessarily have a honeycomb structure, and may have other shapes, such as a simple cylindrical or flat shape whose interior is not divided by partition walls.

[0096] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0097] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention. [Industrial Applicability]

[0098] The present invention can be used in filters that capture particulate matter, such as gasoline particulate filters that capture particulate matter in exhaust gases emitted from gasoline engines, as well as in other filters or applications other than filters. [Explanation of symbols]

[0099] 1 Porous composite 2 Base material 3 Collection layer 22 Bulkhead 26 Stomatal Region 231 Cell 1 232 Cell 2

Claims

1. 1. A porous composite comprising: a porous substrate; a porous collection layer provided on the collection surface of the substrate; Equipped with the collection layer includes particles that deposit within pores of the collection surface; When the trapping surface is viewed from above, the ratio of the area of the covered region of the trapping surface that is covered by the trapping layer to the area of the trapping surface is 25% or more and 60% or less, and the ratio of the area of the pore region of the uncovered region that is not covered by the trapping layer to the area of the uncovered region is 9% or less.

2. 10. The porous composite of claim 1, The particles have an internal cavity.

3. 10. The porous composite of claim 1, The particles have a bulk density of less than 0.50 g / ml.

4. 10. The porous composite of claim 1, The particles have a cumulative particle size distribution in which d10 is 0.3 μm or more and d90 is 20 μm or less.

5. 10. The porous composite of claim 1, The porosity of the trapping layer is 70% or more and 90% or less.

6. 10. The porous composite of claim 1, The particles include catalytic particles that promote oxidation of the trap.

7. 7. The porous composite of claim 6, The catalyst particles are CeO ２ , lanthanum-cerium composite oxide, lanthanum-manganese-cerium composite oxide, lanthanum-cobalt-cerium composite oxide, lanthanum-iron-cerium composite oxide, or lanthanum-praseodymium-cerium composite oxide.

8. 8. The porous composite of claim 1, the substrate has a honeycomb structure in which the interior is divided into a plurality of cells by partition walls, The inner surfaces of at least some of the cells are the collection surfaces.

9. 9. The porous composite of claim 8, This is a gasoline particulate filter that captures particulate matter in the exhaust gas emitted from a gasoline engine.

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