Porous composite

Abstract

A porous composite has a base material that is porous, and a trapping layer (3) that is porous and is provided on a trapping surface of the base material. The trapping layer (3) contains particles that are packed in pores on the trapping surface. In a plan view of the trapping surface, the proportion of the area of a coated region in the trapping surface that is coated with the trapping layer (3) is 70% or less, and the proportion of the area of a pore region (26) in a non-coated region that is not coated with the trapping layer (3) is 15% or less. Accordingly, low pressure loss and high trapping efficiency can be achieved.

Description

Technical Field

[0001] This invention relates to porous composites.

[0002] [Reference for related applications]

[0003] This application claims priority to Japanese Patent Application JP2021-127462, filed on August 3, 2021, the entire disclosure of which is incorporated herein by reference. Background Technology

[0004] Vehicles equipped with diesel engines, gasoline engines, and the like are equipped with filters that capture particulate matter in exhaust gases. One type of such filter is a honeycomb filter in which a portion of the openings on the outflow side of a portion of the multiple compartments of a porous honeycomb substrate and the openings on the inflow side of the remaining compartments are sealed.

[0005] For example, in the honeycomb filter of Japanese Patent No. 5597153 (Document 1), a porous trapping layer is provided on the surface of the compartment with a sealing portion at the opening on the outflow side. The trapping layer is composed of multiple particles that are bonded or entangled with each other, including plate-shaped particles. Furthermore, the opening ratio of the trapping layer surface is 10% or more. The honeycomb filter of Document 1 can suppress the increase in initial pressure loss and the rise in pressure loss due to the accumulation of particulate matter.

[0006] Furthermore, in the cellular filter described in International Publication No. 2020 / 194681 (Document 2), the arithmetic mean height of the surface roughness of the trapping layer installed in a specified compartment is 0.1 μm or more and 12 μm or less, and the average film thickness of the trapping layer is 10 μm or more and 40 μm or less. Based on this, it is possible to reduce pressure loss and improve the trapping efficiency of particulate matter.

[0007] It should be noted that in the honeycomb filter of Japanese Patent Application Publication No. 2020-1032 (Document 3), the trapping layer includes a portion on the surface composed of a sintered body of CeO2 particles with an average particle size of 1.1 μm or less. Accordingly, the trapped particulate matter can be oxidized and burned at a lower temperature. Furthermore, Japanese Patent Application Publication No. 2021-53537 (Document 4) discloses a composite oxide catalyst capable of lowering the oxidation start temperature of particulate matter. This composite oxide catalyst contains the following metals: cerium as the first metal, lanthanum as the second metal, and a third metal. The third metal is a transition metal or a rare earth metal other than cerium and lanthanum. The content of cerium in the metal is 5 mol% or more and 95 mol% or less, the content of lanthanum is 2 mol% or more and 93 mol% or less, and the content of the third metal is 2 mol% or more and 93 mol% or less.

[0008] In the porous composite material constituting the cellular filter in Reference 1, as mentioned above, a reduction in pressure loss is achieved. However, in recent years, there has been a demand not only for a reduction in pressure loss but also for an increase in the capture efficiency of particulate matter. Usually, there is a trade-off between the two, therefore, achieving both low pressure loss and high capture efficiency is not easy. In the porous composite material in Reference 2, while both a reduction in pressure loss and an increase in capture efficiency are achieved, the increase in capture efficiency is sometimes insufficient. Summary of the Invention

[0009] This invention relates to porous composites, with the aim of achieving low pressure loss and high capture efficiency.

[0010] A preferred embodiment of the present invention relates to a porous composite comprising: a porous substrate; and a porous trapping layer disposed on a trapping surface of the substrate. The trapping layer contains particles deposited within the pores of the trapping surface. Viewed from above, the area of ​​the trapped surface covered by the trapping layer constitutes 70% or less of the area of ​​the covered region and the area of ​​the pore region in the uncovered region not covered by the trapping layer constitutes 15% or less of the area of ​​the porous region.

[0011] According to the present invention, low pressure loss and high capture efficiency can be achieved.

[0012] Preferably, when viewed from above, the area of ​​the covered region in the trapping surface is 25% or more.

[0013] Preferably, the particle has cavities inside.

[0014] Preferably, the volume density of the particles is less than 0.50 g / ml.

[0015] Preferably, the cumulative particle size distribution of the particles has a d10 of 0.3 μm or more and a d90 of 20 μm or less.

[0016] Preferably, the porosity of the trapping layer is 70% or more and 90% or less.

[0017] Preferably, the particles comprise catalyst particles that promote the oxidation of the trap.

[0018] 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.

[0019] Preferably, the substrate has a honeycomb structure with internal partitions dividing it into multiple compartments, and the inner surface of at least a portion of the multiple compartments is the trapping surface.

[0020] Preferably, the porous composite is a gasoline particulate filter that captures particulate matter in the exhaust gas from a gasoline engine.

[0021] The above-described objectives, as well as other objectives, features, solutions, and advantages, will become clear from the following detailed description of the invention with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a plan view of a porous complex.

[0023] Figure 2 This is a cross-sectional view of a porous composite.

[0024] Figure 3 This is a diagram representing the capture surface.

[0025] Figure 4 It is a SEM image representing the capture surface.

[0026] Figure 5 This is a diagram showing the configuration of a dry film-forming device.

[0027] Figure 6 This is a diagram used to illustrate the formation of the trapping layer. Detailed Implementation

[0028] Figure 1 This is a simplified plan view illustrating a porous composite 1 according to one embodiment of the present invention. The porous composite 1 is a cylindrical component that is longer in one direction. Figure 1 The image shows one end face of the porous composite 1 along its length. Figure 2 This is a cross-sectional view of porous composite 1. Figure 2The image shows a portion of a cross-section along this length direction. The porous composite 1 is used, for example, as a gasoline particulate filter (GPF) to capture particulate matter such as soot from exhaust gases emitted from gasoline engines such as automobiles.

[0029] The porous composite 1 comprises a porous substrate 2 and a porous trapping layer 3 (see reference). Figure 2 ).exist Figure 1 and Figure 2 In the example shown, substrate 2 is a component with a honeycomb structure. Substrate 2 has a cylindrical outer wall 21 and partitions 22. The cylindrical outer wall 21 is along the length direction (i.e., ... Figure 2 The cylindrical portion extending in the left-right direction. The cross-sectional shape of the cylindrical outer wall 21 perpendicular to the length direction is, for example, approximately circular. This cross-sectional shape can be other shapes such as polygons.

[0030] The partition wall 22 is a grid-like portion disposed inside the cylindrical outer wall 21 and dividing the interior into multiple compartments. As described below, these multiple compartments include multiple first compartments 231 and multiple second compartments 232. In the following description, without distinguishing between the first compartments 231 and the second compartments 232, the first compartments 231 and the second compartments 232 will be simply referred to as "compartments 23". The multiple compartments 23 are spaces that extend along the length direction. The cross-sectional shape of each compartment 23 perpendicular to the length direction is, for example, approximately square. This cross-sectional shape can be other shapes such as polygons or circles. The multiple compartments 23 generally have the same cross-sectional shape. The multiple compartments 23 can include compartments 23 with different cross-sectional shapes. The base material 2 is a compartmentalized structure whose interior is divided into multiple compartments 23 by the partition wall 22.

[0031] The cylindrical outer wall 21 and the partition wall 22 are both porous components. The cylindrical outer wall 21 and the partition wall 22 are formed of ceramic, such as cordierite. The material of the cylindrical outer wall 21 and the partition wall 22 can be ceramic other than cordierite, or it can be a material other than ceramic.

[0032] 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, 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, more preferably 350 μm or less. The length of the partition wall 22 in the longitudinal direction is approximately the same as that of the cylindrical outer wall 21. The thickness of the partition wall 22 is, for example, 30 μm or more, preferably 50 μm or more. The thickness of the partition wall 22 is, for example, 1000 μm or less, preferably 500 μm or less, more preferably 350 μm or less.

[0033] The porosity of the substrate 2, including the cylindrical outer wall 21 and the partition wall 22, is, for example, 20% or more, preferably 30% or more. The porosity of the substrate 2 is, for example, 80% or less, preferably 70% or less. The open porosity of the substrate 2 is, for example, 40% or more, 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 determined using the Archimedes method.

[0034] The average pore size (pore diameter) of the substrate 2 is, for example, 5 μm or more, preferably 8 μm or more. The average pore size of the substrate 2 is, for example, 30 μm or less, preferably 25 μm or less. This average pore size 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. This surface opening ratio is the proportion of the area of ​​the surface of the substrate 2 where pores are open, and can be determined by image analysis of a SEM (scanning electron microscope) image of the surface. The SEM image is taken at, for example, 500x magnification. This image analysis is performed using, for example, the image analysis software "Image-Pro ver. 9.3.2" manufactured by Roper Co., Ltd. of Japan.

[0035] The cell density of substrate 2 (i.e., the number of cells 23 per unit area in a cross-section perpendicular to the length direction) is, for example, 10 cells / cm². 2 The preferred value is 20 compartments / cm². 2 The above is more preferably 30 compartments / cm. 2 The above. The compartment density is, for example, 200 compartments / cm³. 2 The preferred value is 150 compartments / cm. 2 the following. Figure 1 In the illustration, the size of compartment 23 is depicted as larger than it actually is, and the number of compartments 23 is depicted as fewer than it actually is. The size and number of compartments 23 can be changed in various ways.

[0036] When the porous composite 1 is used as a GPF, one end of the porous composite 1 in the length direction (i.e., Figure 2 The left side of the porous composite 1 is designated as the inlet, and the other end is designated as the outlet, allowing exhaust gases and other gases to flow inside the porous composite 1. In addition, for a portion of the multiple compartments 23 of the porous composite 1, a sealing portion 24 is provided at the end of the inlet side, and for the remaining compartments 23, a sealing portion 24 is provided at the end of the outlet side.

[0037] Figure 1 The inlet side of the porous complex 1 is depicted. Additionally, Figure 1 In order to facilitate understanding of the diagram, parallel diagonal lines are marked on the sealing section 24 on the inlet side. Figure 1 In the example shown, there are two compartments: one with a sealing section 24 at the entrance and the other without a sealing section 24 at the entrance (i.e., the compartment with a sealing section 24 at the exit). Figure 1 The arrangement alternates between vertical and horizontal directions.

[0038] In the following description, the compartment 23 with a sealing portion 24 on the outlet side will also be referred to as "first compartment 231", and the compartment 23 with a sealing portion 24 on the inlet side will also be referred to as "second compartment 232". In the porous composite 1, a plurality of first compartments 231 with one end closed in the longitudinal direction and a plurality of second compartments 232 with the other end closed in the longitudinal direction are arranged alternately.

[0039] The trapping layer 3 is formed on the substrate 2. Figure 2 In the example shown, the trapping layer 3 is disposed within a plurality of first compartments 231 having sealing portions 24 on the outlet side, and covers the inner surfaces (i.e., the surfaces of the partition walls 22) of the plurality of first compartments 231. The trapping layer 3 does not cover the entire inner surface of the first compartment 231, but rather covers only a portion of it. Figure 2 In the diagram, the trapping layer 3 is indicated by a thick dashed line. The trapping layer 3 is also provided on the inner surface of the sealing portion 24 on the outlet side within the plurality of first compartments 231. On the other hand, the trapping layer 3 is not present in the plurality of second compartments 232 where the sealing portion 24 is provided on the inlet side. In other words, the inner surfaces of the plurality of second compartments 232 are not covered by the trapping layer 3, but are exposed.

[0040] Figure 1 and Figure 2 In the porous composite 1 shown, as Figure 2 As indicated by arrow A1, gas flowing into the porous composite 1 enters the first compartment 231, which is not sealed on the inlet side, and moves from the first compartment 231 through the porous trapping layer 3 and partition wall 22 to the second compartment 232, which is not sealed on the outlet side. At this time, the trapping layer 3 efficiently traps particles (particulate matter) in the gas. Furthermore, if the trapping layer 3 contains catalyst particles (described later), the combustion (i.e., oxidation removal) of the trapped particulate matter is promoted. In the following description, the inner surfaces of the plurality of first compartments 231 on which the trapping layer 3 is provided are also referred to as "trapping surfaces".

[0041] Figure 3 This is a diagram showing the capture surface with capture layer 3. Figure 4 This is an example of an SEM image representing the capture surface. Figure 3 and Figure 4 The image shows the trapping surface and trapping layer 3 as viewed from a direction roughly perpendicular to the trapping surface (i.e., from above). Figure 3 In the diagram, the area enclosed by thick solid and dashed lines represents region 26 (hereinafter referred to as "pore region 26"), which has open pores on the trapping surface; the area marked with parallel diagonal lines represents the trapping layer 3; and the remaining area represents the surface of the substrate 2. As described later, the trapping layer 3 is formed by particle accumulation. Figure 4 In the SEM image, the white areas represent particles of the trapping layer 3, the black areas represent the portions of the pore region 26 not covered by the trapping layer 3, and the gray areas represent the surface of the substrate 2. The trapping layer 3 comprises multiple isolated portions. Figure 3 In the middle, the various parts of the trapping layer 3 are marked with symbol 3.

[0042] picture Figure 3 and Figure 4 When viewed from above, the area covered by the trapping layer 3 is referred to as the "covered area." In the porous composite 1, the area of ​​the covered area in the trapping surface is 70% or less. In other words, the area of ​​the covered area contained in any region of the trapping surface when viewed from above, divided by the area of ​​that arbitrary region, is 70% or less. In the following description, the proportion of the area of ​​the covered area in the trapping surface is referred to as the "covering ratio of the trapping surface." If the covering ratio of the trapping surface is too large, the pressure loss increases. The covering ratio of the trapping surface is preferably 65% ​​or less, more preferably 60% or less.

[0043] The coverage ratio of the trapping surface is, for example, 20% or more, preferably 25% or more, and more preferably 30% or more. If the coverage ratio of the trapping surface is too small, the trapping efficiency of the trapping material, i.e., particulate matter, decreases. As described later, in the porous composite 1, the trapping layer 3 is selectively or preferentially formed on the pore regions 26 of the trapping surface. Therefore, if the coverage ratio of the trapping surface is, for example, 3 / 4 or more times the surface opening ratio of the substrate 2, the trapping layer 3 is present in most of the pore regions 26. Furthermore, if the coverage ratio of the trapping surface is greater than or equal to the surface opening ratio of the substrate 2, the trapping layer 3 is present in an even larger portion of the pore regions 26.

[0044] Furthermore, the area in the collection surface not covered by the collection layer 3 is referred to as the "uncovered area," and the proportion of the area of ​​the pore region 26 in the uncovered area is 15% or less. In other words, the value obtained by dividing the area of ​​the pore region contained in the uncovered area in any region of the collection surface viewed from above by the area of ​​the uncovered area is 15% or less. In the following description, the proportion of the area of ​​the pore region 26 in the uncovered area is referred to as the "pore ratio of the uncovered area." If the pore ratio of the uncovered area is too large, the amount of gas that does not pass through the collection layer 3 increases, and therefore, the collection efficiency of particulate matter decreases. The pore ratio of the uncovered area is preferably 13% or less, more preferably 10% or less. The pore ratio of the uncovered area is 0% or more.

[0045] In a typical porous composite 1, the proportion of pores in the uncoated region is sufficiently low compared to the surface opening ratio of the substrate 2. The proportion of pores in the uncoated region is, for example, less than half of the surface opening ratio, preferably less than two-thirds of the surface opening ratio. In such a porous composite 1, it can be said that a trapping layer 3 exists in most of the porous region 26. Accordingly, the trapping efficiency of particulate matter is increased. Preferably, a trapping layer 3 exists in more than 70% of the porous region 26. On the other hand, trapping layers 3 are not easily formed in the regions of the trapping surface other than the porous region 26 (hereinafter also referred to as "non-porous regions"). In the porous composite 1, a large number of trapping layers 3 exist in and around the porous region 26 where particulate matter is trapped, while fewer trapping layers 3 exist in the non-porous regions. Therefore, the increase in pressure loss can be suppressed, and the trapping efficiency can be improved.

[0046] In determining the coverage ratio of the trapping surface and the porosity of the uncoated area, for example, the porous composite 1 is cross-sectionally processed to obtain a longitudinal section (a section along the length direction) of the first compartment 231. Next, an SEM image of the inner surface of the first compartment 231 is obtained by taking a picture at 500x magnification from a direction approximately perpendicular to the inner surface. Then, the SEM image is analyzed using the aforementioned image analysis software (Image-Prover. 9.3.2, manufactured by Roper Co., Ltd.), thereby determining the coverage ratio of the trapping surface and the porosity of the uncoated area. Preferably, multiple values ​​representing the coverage ratio of the trapping surface are obtained from multiple longitudinal sections of the first compartment 231, and the average of these multiple values ​​is taken as the coverage ratio of the trapping surface in the porous composite 1. The same applies to the porosity of the uncoated area and the porosity of the trapping layer 3, which will be described later.

[0047] The trapping layer 3 contains particles deposited within the pores of the trapping surface. Typically, these particles deposited within the pores are bonded (or attached) to each other, forming a porous layer. Some particles are also bonded to the substrate 2. Preferably, the particles of the trapping layer 3 are directly bonded to each other without the aid of other materials (bonding materials). In this case, the trapping layer 3 does not contain any binding material and is essentially composed only of these particles. Depending on the method of forming the trapping layer 3, the particles may also be bonded to each other with the aid of a binding material. The collection of particles that are bonded to each other is called a bonded particle group. It is not necessary for the entire bonded particle group to be located within the pores; a portion of the bonded particle group may exist outside the pores or in non-porous regions. In addition, the trapping layer 3 may contain particles and bonded particle groups that exist in isolation in non-porous regions.

[0048] The porosity (porosity of the bound particle group) of the trapping layer 3 within the pores of the trapping surface 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 too small, 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 too large, the trapping efficiency of particulate matter decreases.

[0049] In determining the porosity of the trapping layer 3, for example, in the porous composite 1 that has undergone the aforementioned cross-sectional processing, a SEM image of the region including the cross-section of the trapping layer 3 is captured at 2000x magnification. Then, the SEM image is analyzed using the aforementioned image analysis software (Image-Pro ver. 9.3.2, manufactured by Roper Co., Ltd.), thereby determining the porosity of the trapping layer 3. This image analysis is performed using, for example, the same method as described in International Publication No. 2020 / 194681 (Document 2 above). Specifically, the area of ​​the bright region connected to the bright portion (i.e., particles of the trapping layer 3) and the area of ​​the dark region connected to the dark portion (i.e., pores of the trapping layer 3) in the region where the trapping layer 3 exists in the SEM image are calculated. Then, the total area of ​​the dark region is divided by the sum of the total area of ​​the bright region and the total area of ​​the dark region to calculate the porosity of the trapping layer 3.

[0050] The thickness of the trapping layer 3 is, for example, greater than 2 μm, preferably 3 μm or more. If the thickness of the trapping layer 3 is too small, the trapping efficiency of particulate matter decreases. The thickness of the trapping layer 3 is, for example, less than 20 μm, preferably 18 μm or less. If the thickness of the trapping layer 3 is too large, the pressure loss increases. In addition, since the amount of trapping layer 3 also increases, the manufacturing cost of the porous composite 1 increases.

[0051] The thickness of the trapping layer 3 is measured using, for example, a 3D shape measuring machine, in the same manner as described in International Publication No. 2020 / 194681 (Document 2 above). Specifically, longitudinal sections of multiple first compartments 231 and multiple second compartments 232 are obtained by processing the cross-section of the porous composite 1. In a direction perpendicular to these longitudinal sections, the average position of the surface of the trapping layer 3 in the first compartment 231 and the average position of the surface (bottom surface of the pores) of the pore region 26 in the second compartment 232 are measured using a 3D shape measuring machine. Then, the difference between the average position of the surface of the trapping layer 3 and the average position of the surface of the pore region 26 is calculated as the thickness of the trapping layer 3.

[0052] The median particle size (d50) in the cumulative particle size distribution (volume basis) of the trapping layer 3 is, for example, 7.0 μm or less, preferably 6.5 μm or less. This median particle size is, for example, 2.0 μm or more, preferably 2.5 μm or more. With this median particle size within the above range, the porosity of the trapping layer 3 can be easily kept within the desired range. The d10 in this cumulative particle size distribution is preferably 0.3 μm or more, more preferably 0.5 μm or more. The d90 in this cumulative particle size distribution is preferably 20 μm or less, more preferably 15 μm or less. In the formation of the trapping layer 3, as described later, particles are transported into the pores of the trapping surface using an airflow. With d10 and d90 within the above range, particles can be easily transported into the pores of the trapping surface. d10 is, for example, 3.5 μm or less, preferably 3.0 μm or less. d90 is, for example, 5.0 μm or more, preferably 6.5 μm or more.

[0053] In determining the cumulative particle size distribution, the porous composite 1 is disassembled, and the trapping layer 3 is scraped away using a scraper or similar tool, removing particles constituting the trapping layer 3 from the porous composite 1 without removing any fragments of the substrate 2. During the removal of particles from the trapping layer 3, it is preferable to process the porous composite 1 to obtain a longitudinal section (a section along the length direction) of the second compartment 232. Next, using tweezers, a portion of the partition wall 22 (compartment wall) separating the second compartment 232 from the first compartment 231, which is located further inward (inner side of the cross-section) than the second compartment 232, is peeled off, thereby exposing the longitudinal section of the first compartment 231. Then, the trapping layer 3 of the first compartment 231 is scraped away using a scraper. This prevents fragments of the substrate 2 generated during the cross-section processing from being mixed into the removed particles. Afterward, the cumulative particle size distribution is determined using laser diffraction.

[0054] The particles in the trapping layer 3 preferably have pores inside. This results in a lower particle bulk density (i.e., a larger particle volume), allowing for easy transport of particles into the pores of the trapping surface using airflow during the formation of the trapping layer 3. The presence or absence of pores in the particles of the trapping layer 3 can be confirmed, for example, in a 5000x SEM image. The particle bulk density is preferably less than 0.50 g / ml. There is no particular limitation on the lower limit of this bulk density; for example, it can be 0.10 g / ml or higher. In determining the bulk density of the particles in the trapping layer 3, the mass of the particles from the porous composite 1 is measured. Then, the particle is placed in a graduated cylinder to measure its volume; the bulk density is calculated by dividing the mass by the volume.

[0055] The specific surface area of ​​the particles in trapping layer 3 is, for example, 10 m². 2 / g or more, preferably 15m 2 / g or more. There is no specific upper limit to this specific surface area, for example, 1000 m².2 / g or less. The specific surface area of ​​the particles in the trapping layer 3 taken from the porous composite 1 can be determined using the BET specific surface area method.

[0056] The particles in the trapping layer 3 preferably include catalyst particles that promote the oxidation of the trapped material. As described above, the trapping layer 3 is selectively or preferentially formed in the porous region 26 on the trapping surface. Therefore, most of the catalyst particles are disposed in the pores on the trapping surface where particulate matter easily accumulates. Accordingly, the contact area between the catalyst particles and the particulate matter can be increased, achieving higher catalytic activity. As a result, the oxidation initiation temperature of the particulate matter can be lowered more reliably (i.e., low-temperature combustion of the particulate matter).

[0057] The catalyst particles mentioned above are typically oxides, preferably CeO2 (cerium dioxide), lanthanum (La)-cerium (Ce) composite oxides, lanthanum-manganese (Mn)-cerium composite oxides, lanthanum-cobalt (Co)-cerium composite oxides, lanthanum-iron (Fe)-cerium composite oxides, or lanthanum-praseodymium (Pr)-cerium composite oxides. In other words, the particles of the trapping layer 3 preferably contain one or more of CeO2, lanthanum-cerium composite oxides, lanthanum-manganese-cerium composite oxides, lanthanum-cobalt-cerium composite oxides, lanthanum-iron-cerium composite oxides, and lanthanum-praseodymium-cerium composite oxides.

[0058] Lanthanum-cerium composite oxides are oxides containing La and Ce, also referred to as "La-Ce-O". Lanthanum-manganese-cerium composite oxides are oxides containing La, Mn, and Ce, also referred to as "La-Mn-Ce-O". Lanthanum-cobalt-cerium composite oxides are oxides containing La, Co, and Ce, also referred to as "La-Co-Ce-O". Lanthanum-iron-cerium composite oxides are oxides containing La, Fe, and Ce, also referred to as "La-Fe-Ce-O". Lanthanum-praseodymium-cerium composite oxides are oxides containing La, Pr, and Ce, also referred to as "La-Pr-Ce-O".

[0059] The particles of the aforementioned composite oxide can be manufactured using the same method as described in Japanese Patent Application Publication No. 2021-53537 (Document 4 above), for example, using the citric acid method. The particles of the composite oxide can be manufactured using impregnation-supported methods or complexation polymerization methods. The trapping layer 3 containing the catalyst particles is preferably composed substantially only of the catalyst particles, but may also contain substances other than the catalyst particles. The trapping layer 3 can be formed from catalyst particles other than those described above (e.g., Fe2O3 or MnO2), or from particles other than catalyst particles. Examples of particles other than catalyst particles include SiO2, SiC, and Al2O3. Particles of various substances such as metal oxides, nitrides, or carbides can be used in the trapping layer 3.

[0060] Next, an example of the manufacture of the porous composite 1 will be described. The method for manufacturing the substrate 2 is well known; here, the formation of the trapping layer 3 on the substrate 2 (substrate 2 without the trapping layer 3) will be described. In the preferred formation of the trapping layer 3, particles are deposited on the trapping surface of the substrate 2 using a dry film-forming method. Figure 5 This is a diagram showing the configuration of the dry film forming apparatus 8. Figure 6 This is a diagram used to illustrate the formation of the trapping layer 3, which schematically shows a portion of the cross-section of the substrate 2 along the length direction.

[0061] Figure 5 The dry film-forming apparatus 8 includes a first cylindrical section 81, a second cylindrical section 82, and a particle supply section 83. Both the first cylindrical section 81 and the second cylindrical section 82 are cylindrical components, and their cross-sectional shape perpendicular to their central axis is approximately 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 component extending along its length direction, with one end of the substrate 2 inserted into the end of the first cylindrical section 81 and the other end inserted into the end of the second cylindrical section 82. In this embodiment, the first compartment 231 (refer to...) Figure 6 The end of the substrate 2 with an opening (i.e., the end where the sealing portion 24 is provided in the second compartment 232) is inserted into the first cylindrical portion 81, and the end of the substrate 2 with an opening in the second compartment 232 is inserted into the second cylindrical portion 82. The outer surface of the substrate 2 can contact the first cylindrical portion 81 or the second cylindrical portion 82 through an O-ring or the like. 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, almost no gas or liquid can pass through.

[0062] In the first cylindrical section 81, a particle supply section 83 is connected to the end opposite to the substrate 2. The particle supply section 83 supplies aerosol obtained by dispersing particles to be used as the trapping layer 3 in a gas into the first cylindrical section 81. The dispersion medium of the aerosol is, for example, air. The dispersion medium of the aerosol can be a gas other than air. In the second cylindrical section 82, a pressure reduction mechanism (not shown) is connected to the end opposite to the substrate 2, and the pressure in the second cylindrical section 82 is reduced. Accordingly, the aerosol supplied to the first cylindrical section 81 flows into the substrate 2.

[0063] like Figure 6As indicated by arrow A2, the aerosol flows into the first compartment 231. The gas contained in the aerosol enters the partition wall 22 through the pores that open on the inner side (collecting surface) of the first compartment 231, and moves towards the second compartment 232 adjacent to the first compartment 231. The gas that has moved to the second compartment 232 is discharged out of the substrate 2 through the opening of the second compartment 232. At this time, most of the particles contained in the aerosol enter the pores of the collecting surface along with the gas and accumulate in the pores. Some particles may adhere to the non-porous areas (surface of the substrate 2) in the collecting surface. Preferably, the particles have internal pores and / or a bulk density of less than 0.50 g / ml, so that the particles easily enter the pores of the collecting surface along with the gas. From the viewpoint of allowing more particles to enter the pores of the collecting surface, it is preferable that the d90 of the cumulative particle size distribution is less than or equal to the average pore size of the substrate 2.

[0064] Through the above treatment, most of the particles deposited on the substrate 2 are located within the pores of the trapping surface. That is, when viewed from above the trapping surface, the trapping layer 3 is selectively or preferentially formed in the pore region 26 (see reference). Figure 3 The conditions for using the dry film-forming apparatus 8 to deposit particles on the trapping surface (including within the pores) can be appropriately determined based on factors such as the coating ratio of the trapping surface, the pore ratio of the uncoated area, the porosity of the trapping layer 3, and the thickness of the trapping layer 3. In one example, the particle density in the aerosol is 1–10 mg / cc, and the aerosol attraction velocity is 0.1–5 m / s.

[0065] In the manufacture of the porous composite 1, the porous composite 1 taken from the dry film-forming apparatus 8 is further subjected to a sintering process. The heating temperature during the sintering process is, for example, 500°C or higher and 1300°C or lower. The heating time during the sintering process is, for example, 0.5 hours or higher and 2 hours or lower. The heating temperature and heating time during the sintering process can be appropriately determined according to the type of particles in the trapping layer 3. If the adhesion strength of the particles to the substrate 2 is sufficiently ensured, the sintering process can be omitted.

[0066] Next, with reference to Tables 1 to 3, Examples 1 to 11 of the porous composite of the present invention and Comparative Examples 1 to 6 for comparison with the porous composite will be described.

[0067] [Table 1]

[0068]

[0069] [Table 2]

[0070]

[0071] [Table 3]

[0072]

[0073] In Examples 1-11, a substrate formed of cordierite and having a honeycomb filter shape (honeycomb structure) was used. The substrate had an open porosity of 55%, a surface opening ratio of 30%, and an average pore size of 18 μm. The open porosity was determined using Archimedes' method with pure water as the medium. The surface opening ratio was calculated by analyzing the SEM image (magnification: 500x) of the substrate surface using the aforementioned image analysis software. The average pore size was determined using a mercury porosimeter.

[0074] In Examples 1-11, the following were used Figure 5 The dry film-forming apparatus 8 forms a trapping layer using a dry film-forming method. The particle density in the aerosol is 5 mg / cc. The aerosol attraction velocity is 1 m / s. In Examples 1-7, La-Mn-Ce-O particles are used. In Examples 1, 2, 4, and 5 of Examples 1-7, the film weight of the trapping layer is varied by adjusting the film-forming time, etc. In Example 3, the heating temperature (sintering temperature) during the sintering process is lowered. In Example 6, particles with smaller particle size are used, and in Example 7, particles with larger particle size are used. In Examples 8 and 9, CeO2 particles are used, and the film weight of the trapping layer is varied. In Examples 10 and 11, SiO2 particles are used, and the film weight of the trapping layer is varied. In addition, the sintering temperature is increased.

[0075] In Examples 1-11, the proportion of the covered area in the trapping surface (coverage ratio of the trapping surface) ranged from 25% to 60%, all below 70%. The proportion of the pore area in the uncovered area (pore ratio of the uncovered area) ranged from 0% to 9%, all below 15%. The coverage ratio and pore ratio of the uncovered area of ​​the trapping surface were calculated as follows: using the image analysis software described above, the SEM image (magnification: 500x) of the trapping surface was analyzed to determine the proportions. The coverage ratio and pore ratio of the uncovered area of ​​the trapping surface in Table 2 are the average values ​​obtained from five SEM images taken from different areas of the trapping surface.

[0076] In Examples 1-11, the thickness (film thickness) of the trapping layer is 3 μm to 15 μm. The thickness of the trapping layer, as described above, is calculated as the difference between the average position of the surface of the trapping layer and the average position of the surface of the pore region, as measured using a 3D shape measuring machine. Furthermore, in Examples 1-11, the porosity of the trapping layer within the pores of the trapping surface is 76% to 82%, all exceeding 70% and falling below 90%. This porosity is calculated by performing image analysis on a SEM image (magnification: 2000x) of the cross-section of the trapping layer 3 using the aforementioned image analysis software, thereby determining the porosity.

[0077] In Examples 1-11, the median particle size (d50) in the cumulative particle size distribution (volume basis) was 2.8 μm to 6.3 μm. Additionally, d10 ranged from 0.5 to 2.8 μm, all exceeding 0.3 μm. d90 ranged from 7.0 to 12 μm, all below 20 μm. The cumulative particle size distribution was obtained by taking only the particles from the trapping layer of the porous composite and measuring these particles using laser diffraction.

[0078] In Examples 1 to 9, which used La-Mn-Ce-O particles or CeO2 particles, the specific surface area of ​​the particles was 20 m². 2 / g~70m 2 / g, in Examples 10 and 11, which used SiO2 particles, the specific surface area of ​​the particles was 720m². 2 / g. The specific surface area of ​​the particles was obtained by measuring the particles taken from the porous composite using the BET specific surface area method. In Examples 1-11, the bulk density was less than 0.50 g / ml. In Table 2, particles with a bulk density less than 0.50 g / ml are labeled "small," and particles with a bulk density of 0.50 g / ml or higher are labeled "large." The bulk density of the particles was obtained by measuring the mass of the particles taken from the porous composite, then measuring the volume in a graduated cylinder, and dividing the mass by the volume to obtain the bulk density. Although not shown in the table, the La-Mn-Ce-O particles were confirmed using 5000x SEM images, revealing internal cavities. The same method was used for CeO2 and SiO2 particles.

[0079] In Comparative Examples 1-6, the same substrate as in Examples 1-11 was used. In Comparative Examples 1-5, 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 using a dry film-forming method, similar to Examples 1-11. However, in Comparative Example 1, the film weight of the trapping layer was too small, and in Comparative Example 2, the film weight of the trapping layer was too large. As a result, in Comparative Example 1, the coverage ratio of the trapping surface was significantly reduced, and the porosity ratio in the uncoated area was greater than 15%. In Comparative Example 2, the coverage ratio of the trapping surface was significantly increased compared to 70%.

[0080] In Comparative Examples 3 and 6, the sintering temperature was increased. As a result, in Comparative Example 3, which used La-Mn-Ce-O particles, the porosity of the uncoated region increased significantly compared to 15%. In Comparative Example 6, which used SiC particles, the coverage ratio of the trapping surface increased significantly compared to 70%. In Comparative Examples 3 and 6, the particle bulk density was 0.50 g / ml or higher.

[0081] In Comparative Examples 4 and 5, a wet film-forming method was used to form the trapping layer. Specifically, La-Mn-Ce-O particles were mixed with a liquid such as water to prepare a slurry, which was then supplied to the first compartment. The liquid, such as water, permeated through the partition wall and flowed out from the second compartment to the outside of the substrate, while the La-Mn-Ce-O particles did not permeate through the partition wall and adhered to the inner surface of the first compartment. Afterwards, a sintering process was performed. In Comparative Examples 4 and 5, the film weight of the trapping layer was varied. In Comparative Example 4, with a smaller film weight, the porosity of the uncoated area increased significantly compared to 15%. In Comparative Example 5, with a larger film weight, the coating ratio of the trapping surface increased significantly compared to 70%. In Comparative Examples 4 and 5, the porosity of the trapping layer was less than 70%.

[0082] In the performance evaluation of the porous composites in Examples 1-11 and Comparative Examples 1-6, the initial pressure loss (i.e., pressure loss before the capture of particulate matter, etc.), capture efficiency, and oxidation initiation temperature of the soot were compared to evaluate the overall performance. Furthermore, a substrate without a capture layer was used as a reference example, and the same performance evaluation was performed.

[0083] In the initial pressure loss evaluation of porous composites, firstly, room temperature air is introduced at a pressure of 10 Nm. 3 A flow rate of / min is supplied to the porous composite, and the pressure difference before and after the porous composite (i.e., the pressure difference between the inflow and outflow sides of air) is measured. Then, using this pressure difference when only the substrate is present as the reference pressure difference, the increase rate of the aforementioned pressure difference of the porous composite relative to this reference pressure difference is defined as the increase rate of the initial pressure loss. With the aforementioned pressure difference of the porous composite designated as A and the reference pressure difference of the substrate designated as B, the increase rate (%) of the initial pressure loss is calculated as (A-B) / B×100. In the evaluation of the initial pressure loss, cases where the increase rate of the initial pressure loss is 20% or less are evaluated as "◎". Cases where the increase rate of the pressure loss is greater than 20% but less than 40% are evaluated as "○", and cases where the increase rate of the pressure loss is greater than 40% are evaluated as "×".

[0084] The capture efficiency of the porous composite was determined as follows. First, a vehicle test was conducted using a chassis dynamometer, with a porous composite installed as a GPF in the exhaust system of a passenger vehicle equipped with a 2-liter direct-injection gasoline engine. In this test, the number of particulate matter emitted from the exhaust gas was measured using the PMP (European Restricted Particulate Measurement Protocol) method, operating in the European Restricted Operating Mode (RTS95). The same vehicle test was then conducted without a GPF installed in the exhaust system, and the number of particulate matter emitted from the exhaust gas was measured using the same method. The number of particulate matter emitted without a GPF was defined as the "baseline emission count," and the difference (%) between the number of particulate matter emitted with the porous composite and the baseline emission count was divided by the baseline emission count. In evaluating the capture efficiency, a capture efficiency of 98% or higher was rated as "◎," and a capture efficiency of less than 98% but more than 95% was rated as "○." In addition, cases with a capture efficiency of less than 95% but more than 90% are rated as "△", and cases with a capture efficiency of less than 90% are rated as "×".

[0085] In Examples 1-11, where the coverage of the trapping surface is 70% or less and the porosity of the uncovered area is 15% or less, the evaluations of initial pressure loss and trapping efficiency are both “◎” or “○”. In contrast, in Comparative Examples 1-6, where the coverage of the trapping surface is greater than 70% or the porosity of the uncovered area is greater than 15%, the evaluation of initial pressure loss is “×”, or the evaluation of trapping efficiency is “×” or “△”. It should be noted that in the reference examples, the evaluation of initial pressure loss is “◎” and the evaluation of trapping efficiency is “×”.

[0086] The oxidation initiation temperature of soot in the porous composite was determined as follows. First, a test piece with a diameter of 118.4 mm and a length of 127 mm was cut from the porous composite. Soot was then deposited onto the test piece at a concentration of 0.5 g / L using a soot generator to obtain the test sample. Next, a balanced gas (mixed gas) containing 80% nitrogen (N2) and 20% oxygen (O2) was flowed into the test sample at an SV40000 (1 / hr) while the temperature was increased. Then, the CO and CO2 gases generated by the test sample during heating were detected using ND-IR (non-dispersive infrared spectroscopy). The temperature at which the cumulative CO2 gas generation reached 10% of the total O2 gas was defined as the oxidation initiation temperature of the soot. The lower the oxidation initiation temperature, the higher the catalytic ability of the particles in the trapping layer.

[0087] In the evaluation of the oxidation start temperature of soot, cases with an oxidation start temperature below 410°C are rated as "◎", cases with an oxidation start temperature above 410°C but below 460°C are rated as "○". Additionally, cases with an oxidation start temperature above 460°C are rated as "△".

[0088] Regarding the oxidation start temperature of the soot, in Examples 1 to 9, which used La-Mn-Ce-O particles or CeO2 particles, the evaluation was "◎" or "○". In Examples 10 and 11, which used SiO2 particles, the evaluation was "△". In Comparative Examples 1 to 5, which used La-Mn-Ce-O particles, the film weight of the trapping layer was too small in Comparative Example 1, and the sintering temperature was too high in Comparative Examples 2, 4, and 5 (excluding Comparative Example 3), the evaluation was "◎". On the other hand, in Comparative Examples 1 and 3, Comparative Example 6, which used SiC particles, and the reference example without a trapping layer, the evaluation was "△".

[0089] In the comprehensive evaluation of Examples 1-11, Comparative Examples 1-6, and Reference Examples, if the evaluations for initial pressure loss, collection efficiency, and the oxidation start temperature of the soot are all "◎", the comprehensive evaluation is set to "A". If there is one evaluation "○" and no evaluations "△" or "×", the comprehensive evaluation is set to "B". If there is only one evaluation "△" and no evaluation "×", the comprehensive evaluation is set to "C". If there is also one evaluation "×" or two or more evaluations "△", the comprehensive evaluation is set to "F". In the comprehensive evaluation, "A" has the highest evaluation, and the evaluation decreases in the order of "B", "C", and "F".

[0090] Examples 2, 3, and 7 received an overall evaluation of "A", Examples 1, 4-6, 8, and 9 received an overall evaluation of "B", and Examples 10 and 11 received an overall evaluation of "C". Furthermore, Comparative Examples 1-6 and the Reference Examples all received an overall evaluation of "F".

[0091] As described above, the porous composite 1 comprises: a porous substrate 2; and a porous trapping layer 3 disposed on the trapping surface of the substrate 2 (e.g., the inner surface of the first compartment 231). The trapping layer 3 contains particles deposited within the pores of the trapping surface. When viewed from above, the proportion of the area covered by the trapping layer 3 in the trapping surface (the coverage ratio of the trapping surface) is 70% or less, and the proportion of the area of ​​the pore regions 26 in the uncovered areas (the pore ratio of the uncovered areas) is 15% or less. Accordingly, as in Examples 1 to 11, low pressure loss and high trapping efficiency can be achieved.

[0092] In the preferred porous composite 1, when viewed from above, the area of ​​the covered region on the collecting surface is 25% or more. This allows for a more reliable improvement in collecting efficiency.

[0093] In the preferred porous composite 1, the particles of the trapping layer 3 have pores inside and / or have a bulk density of less than 0.50 g / ml. Accordingly, during the formation of the trapping layer 3, particles can be easily transported into the pores that are open on the trapping surface using an airflow, thereby enabling the porous composite 1 to be easily manufactured.

[0094] In the preferred porous composite 1, the cumulative particle size distribution of the particles in the trapping layer 3 has a d10 of 0.3 μm or more and a d90 of 20 μm or less. This narrow particle size distribution in the trapping layer 3 allows most particles to have a diameter less than or equal to the average pore size of the substrate 2, making it easier for particles to accumulate within the pores of the trapping surface.

[0095] In the preferred porous composite 1, the particles of the trapping layer 3 include catalyst particles that promote the oxidation of the trapped material. Accordingly, the oxidation of the trapped particulate matter can be promoted, thereby lowering the oxidation initiation temperature of the particulate matter. Furthermore, by distributing most of the catalyst particles within the pores, the contact area between the catalyst particles and the particulate matter can be increased, achieving higher catalytic activity (i.e., a lower oxidation initiation temperature).

[0096] Preferred catalyst particles are CeO2, lanthanum-cerium composite oxides, lanthanum-manganese-cerium composite oxides, lanthanum-cobalt-cerium composite oxides, lanthanum-iron-cerium composite oxides, or lanthanum-praseodymium-cerium composite oxides. This allows for a more reliable reduction in the oxidation initiation temperature of particulate materials.

[0097] In the preferred porous composite 1, the porosity of the trapping layer 3 is 70% or more and 90% or less. By making the porosity 70% or more, low pressure loss can be easily achieved in the porous composite 1. Furthermore, by making the porosity 90% or less, high trapping efficiency can be easily achieved.

[0098] In the preferred porous composite 1, the substrate 2 has a honeycomb structure internally divided into multiple compartments 23 by partitions 22, and the inner surface of at least a portion of the multiple compartments 23 (e.g., the first compartment 231) is the aforementioned trapping surface. Accordingly, a honeycomb filter achieving low pressure loss and high trapping efficiency can be provided.

[0099] As described above, the porous composite 1 achieves low pressure loss and high capture efficiency. Therefore, the porous composite 1 is particularly suitable as a GPF for capturing particulate matter in exhaust gases from gasoline engines.

[0100] Various modifications can be made to the aforementioned porous composite 1.

[0101] As long as high capture efficiency is achieved, the coverage ratio of the capture surface can be less than 25%.

[0102] The trapping layer 3 can be selectively or preferentially formed in the pore region 26 on the trapping surface, and the particle volume density of the trapping layer 3 can be 0.50 g / ml or higher. Similarly, the cumulative particle size distribution of this particle can have d10 less than 0.3 μm and d90 greater than 20 μm.

[0103] The porosity of the trapping layer 3 can be less than 70% or greater than 90%.

[0104] The porous composite 1 is not limited to the GPF described above, and can be used, for example, as a diesel particulate filter (DPF) for capturing particulate matter in exhaust gases from diesel engines. As described above, the porous composite 1 achieves low pressure loss and high capture efficiency, and therefore is particularly suitable not only for GPFs but also for DPFs. It should be noted that the porous composite 1 can be used as various filters other than GPFs and DPFs. Alternatively, the porous composite 1 can be used for applications other than filtration.

[0105] The structure of the porous composite 1 can be modified in various ways. For example, the sealing portion 24 can be omitted from the substrate 2. In addition, the inner surfaces of all compartments 23 can be used as trapping surfaces and a trapping layer 3 can be provided. Furthermore, the substrate 2 does not necessarily need to have a honeycomb structure; it can be a simple cylindrical or flat shape or other shapes without internal partitions.

[0106] The above-described embodiments and their variations can be appropriately combined as long as they do not contradict each other.

[0107] Although the invention has been described and illustrated in detail, the description is illustrative and not limiting. Therefore, it can be said that numerous modifications and solutions can be adopted without departing from the scope of the invention.

[0108] Industrial availability

[0109] This invention can be used in filters for capturing particulate matter, such as gasoline particulate filters for capturing particulate matter in exhaust gases from gasoline engines. Additionally, it can be used in other filters or for applications other than filtering.

[0110] Symbol Explanation

[0111] 1 Porous complex

[0112] 2. Substrate

[0113] 3. Capture Layer

[0114] 22 Next door

[0115] 26 Porous regions

[0116] 231 First Compartment

[0117] 232 Second compartment

Claims

1. A porous composite, wherein, have: Porous substrates; and A porous trapping layer is disposed on the trapping surface of the substrate. The trapping layer contains particles accumulated within the pores of the trapping surface. Viewed from above, the area of ​​the captured surface covered by the captured layer accounts for 20% to 70% of the total area, while the area of ​​the pore regions in the uncovered areas not covered by the captured layer accounts for 15% or less. The particle has cavities inside.

2. The porous composite according to claim 1, wherein, When viewed from above, the area of ​​the covered region in the trapping surface is 25% or more.

3. The porous composite according to claim 1 or 2, wherein, The volume density of the particles is less than 0.50 g / ml.

4. The porous composite according to claim 1 or 2, wherein, The cumulative particle size distribution of the particles has a d10 of 0.3 μm or more and a d90 of 20 μm or less.

5. The porous composite according to claim 1 or 2, wherein, The porosity of the trapping layer is above 70% and below 90%.

6. The porous composite according to claim 1 or 2, wherein, The particles contain catalyst particles that promote the oxidation of the traps.

7. The porous composite according to claim 6, wherein, 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.

8. The porous composite according to claim 1 or 2, wherein, The substrate has a honeycomb structure with internal partitions dividing it into multiple compartments. At least a portion of the compartments have their inner surfaces serving as the trapping surface.

9. The porous composite according to claim 8, wherein, The porous composite is a gasoline particulate filter that captures particulate matter in the exhaust gas from a gasoline engine.

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