honeycomb filter

Abstract

Honeycomb filter (100, 200, 300), which includes: a honeycomb structure (5, 25, 45) having porous partitions (1, 21, 41) arranged such that they surround several cells (2, 22, 42) as fluid channels running from an inflow end surface (11, 31, 51) to an outflow end surface (12, 32, 52); and Sealing sections (5, 25, 45) arranged in such a way as to seal one of the end sections of each of the cells (2, 22, 42) on the side of the inflow end surface (11, 31, 51) or on the side of the outflow end surface (12, 32, 52), wherein the cells (2, 22, 42) in which the sealing sections (5, 25, 45) are arranged in an end section on the side of the outflow end surface (12, 32, 52) and which are open on the side of the inflow end surface (11, 31, 51) are defined as inflow cells (2a, 22a, 42a), and the cells (2, 22, 42) in which the sealing sections (5, 25, 45) are arranged in the end section on the side of the inflow end surface (11, 31, 51) and which are open on the side of the outflow end surface (12, 32, 52) are defined as outflow cells (2b, 22b, 42b), the honeycomb structure (5, 25, 45) further includes a catalyst layer (14, 34, 54) containing a platinum group element, formed by an exhaust gas purification catalyst containing a platinum group element, the catalyst layer (14, 34, 54), which contains an element of the platinum group, is arranged only on one side of an inner surface of the partitions (1, 21, 41) surrounding the inflow cells (2a, 22a, 42a), and the catalyst layer (14, 34, 54), which contains an element of the platinum group, is arranged in a direction of the cells (2, 22, 42) of the honeycomb structure (5, 25, 45) in a region of at least up to 40% with respect to a total length of the cells (2, 22, 42), starting from the outflow end surface (12, 32, 52), and is not arranged in a region of at least up to 30% with respect to a total length of the cells (2, 22, 42), starting from the inflow end surface (11, 31, 51), wherein in a cross-section orthogonal to the direction of the cells (2, 22, 42) of the honeycomb structure (5, 25, 45) an area within 60% of a length from a centroid of the cross-section to a circumferential edge of the cross-section is defined as a central section (38) of the cross-section, and the catalyst layer (14, 34, 54) which contains an element of the platinum group is arranged only on the partitions (1, 21, 41) which is present in the central section (38) of the cross-section.

Description

[0001] The present application is based on JP-2018-066811, filed with the Japanese Patent Office on 30 March 2018, the contents of which are incorporated herein in full by reference. BACKGROUND OF THE INVENTION Area of ​​the invention

[0002] The present invention relates to a honeycomb filter. In particular, the present invention relates to a honeycomb filter that has excellent capture performance for capturing suspended solids contained in exhaust gas and excellent cleaning performance for removing harmful substances contained in the exhaust gas. Description of the related area

[0003] In recent years, regulations concerning the removal of particulate matter from exhaust gases emitted by gasoline engines have become stricter worldwide, with honeycomb filters being used as a particulate filter. Hereinafter, particulate matter may be referred to as "PM." PM is an abbreviation for "particulate matter."

[0004] Examples of honeycomb filters include a honeycomb structure with porous partitions defining multiple cells and sealing sections that seal the end of any one of the cells. In such a honeycomb filter, each of the porous partitions is structured to act as a filter for PM removal. More precisely, PM-containing exhaust gas is introduced through an inlet end of the honeycomb filter, the PM particles are trapped by the porous partitions for filtration, and the cleaned exhaust gas is then emitted through an outlet end of the honeycomb filter. This process removes the PM particles from the exhaust gas.

[0005] To improve the cleaning performance of such a honeycomb filter, a catalyst for exhaust gas purification is loaded onto the porous partition (see, for example, patent document 1). Examples of the exhaust gas purification catalyst include a catalyst containing a platinum group element. Hereinafter, the catalyst containing a platinum group element may be referred to as a "PGM catalyst." "PGM" is an abbreviation for "platinum group metal." The PGM contains ruthenium, rhodium, palladium, osmium, iridium, and platinum.

[0006] Patent document 2 further discloses a honeycomb filter comprising porous partitions whose pores are of a size that allows the passage of ash and ash aggregates in order to suppress deposits of ash and ash aggregates. The honeycomb filter also includes a cover layer with pores that are smaller than the pores of the partitions.

[0007] Furthermore, patent document 3 discloses a honeycomb filter in whose inlet cells a collection layer is provided, such that between 5 and 30% of the length of an inlet cell is formed without said collection layer.

[0008] Furthermore, patent document 4 discloses a filter in which the filter walls are at least partially provided with a catalytically active coating. It is provided that the radially outer areas exhibit increased catalytic activity compared to the inner area. [Patent Document 1] JP 2015- 066 536 A [Patent document 2] US 2015 / 0 059 321 A1 [Patent document 3] WO 2011 / 125 768 A1 [Patent document 4] DE 10 2006 061 685 A1 SUMMARY OF THE INVENTION

[0009] In the honeycomb filter for the gasoline engine, it was investigated whether to use a honeycomb structure with high porosity of the partition walls to suppress an increase in pressure drop. When the PGM catalyst is loaded onto the partition walls of such a honeycomb structure, it is filled into the pores of the porous partition walls.

[0010] Conventional honeycomb filters, which utilize a honeycomb structure with high porosity, exhibit a problem: their PM capture efficiency deteriorates when loaded with PGM catalyst. The following reasons are conceivable for this deterioration: When the PGM catalyst is loaded onto the highly porous partitions, it fills the pores of the partitions in order of increasing porosity, starting with those of relatively small diameter. Therefore, in partitions where a given amount of PGM catalyst is loaded, the pores with relatively small diameters are closed by the catalyst, leaving only the pores with relatively larger diameters open.In the following, pores with a relatively smaller diameter are referred to as "small pores," and pores with a relatively larger diameter are referred to as "large pores." In a honeycomb structure with high porosity, if the small pores of the partitions are preferentially closed by the PGM catalyst, the ratio of large pores in the partitions increases, and the flow of exhaust gas passing through the partitions concentrates at the large pores. This means that exhaust gas becomes less able to flow through the small pores, which contribute to improved capture efficiency, and consequently, the capture efficiency of the honeycomb filter deteriorates.

[0011] The present invention was made in light of such problems of the prior art. According to the present invention, a honeycomb filter is created which has excellent capture performance for capturing PM contained in exhaust gas and excellent cleaning performance for removing harmful components contained in the exhaust gas.

[0012] According to the present invention, a honeycomb filter is created as shown below. [1] Honeycomb filter comprising: a honeycomb structure having porous partitions arranged in such a way as to surround several cells as passage channels for fluid running from an inlet end face to an outlet end face; and Sealing sections arranged in such a way as to seal one of the end sections of each of the cells on the inflow end surface side or on the outflow end surface side, wherein the cells in which the sealing sections are arranged in an end section on the side of the outflow end surface and which are open on the side of the inflow end surface are defined as inflow cells, the cells in which the sealing sections are arranged in the end section on the side of the inflow end surface and which are open on the side of the outflow end surface are defined as outflow cells, the honeycomb structure further includes a catalyst layer containing a platinum group element, formed by an exhaust gas purification catalyst containing a platinum group element, the catalyst layer, which contains an element of the platinum group, is arranged only on one side of an inner surface of the partitions surrounding the inflow cells, and the catalyst layer, which contains an element of the platinum group, is arranged in a direction of the cells of the honeycomb structure in an area of ​​at least up to 40% with respect to a total length of the cells, starting from the outflow end surface, and is not arranged in an area of ​​at least up to 30% with respect to a total length of the cells, starting from the inflow end surface, wherein in a cross-section orthogonal to the direction of the cells of the honeycomb structure, an area within 60% of a length from a centroid of the cross-section to a circumferential edge of the cross-section is defined as a central section of the cross-section, and the catalyst layer, which contains an element of the platinum group, is only arranged on the partitions that are present in the central section of the cross-section. [2] Honeycomb filter according to the above [1], wherein the porosity of the catalyst layer containing an element of the platinum group is 50 to 90%. [3] Honeycomb filter according to [1] or [2] above, wherein the thickness of the catalyst layer containing a platinum group element is 10 to 40 µm. [4] Honeycomb filter according to one of the above [1] to [3], wherein the catalyst layer containing an element of the platinum group is a catalyst layer containing an oxide of at least one element selected from the group consisting of aluminium, zirconium and cerium. [5] Honeycomb filter according to one of the above [1] to [4], wherein the honeycomb structure further includes a collection layer arranged only on one side of an inner surface of the partitions surrounding one or more of the inlet cells and which collects the suspended particles in exhaust gas, the collection layer contains no platinum group element, and The collection layer is only arranged in an area of ​​up to 50% in relation to the total length of the cells, starting from the inflow end surface. [6] Honeycomb filter according to the above [5], wherein the porosity of the collection layer is 70 to 90%. [7] Honeycomb filter according to [5] or [6] above, wherein the thickness of the collection layer is 10 to 50 µm. [8] Honeycomb filter according to one of the above [5] to [7], wherein the collecting layer is a layer containing an oxide of at least one element selected from the group consisting of aluminium, magnesium, zirconium, cerium and silicon.

[0013] The honeycomb filter according to the present invention increases the capture performance for capturing PM contained in exhaust gas and the cleaning performance for cleaning the harmful components contained in the exhaust gas.

[0014] This means that the honeycomb filter according to the present invention has, on the side of the outflow surface of the honeycomb structure where a large quantity of gas flows, a "catalyst layer containing a platinum group element," so that the catalyst layer containing a platinum group element can capture the PM and improve the capture efficiency. In particular, in the conventional honeycomb filter, the small pores of the partitions on the outflow surface of the honeycomb structure are closed by the PM, which causes a deterioration in the capture efficiency, whereas in the honeycomb filter of the present invention, it is extremely difficult for such a situation to occur.Furthermore, the contact between the catalyst layer, which contains a platinum group element, and the exhaust gas is increased because the catalyst layer is located on the outflow surface of the honeycomb structure, thus potentially enhancing the cleaning efficiency. In addition, the catalyst layer captures PM (particulate matter), thereby also mitigating the pressure drop across the honeycomb filter during operation (in other words, during PM capture). BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a perspective view that schematically shows a first embodiment of a honeycomb filter of the present invention; Fig. 2 is a top view of one side of an inflow end face of the inflow into Fig. 1 honeycomb filter shown; Fig.3 is a top view of one side of an outflow surface of the in Fig. 1 honeycomb filter shown; Fig. 4 is a cross-sectional view, schematically showing a cross-section along line AA'. Fig. 2 shows; Fig. Figure 5 is a top view of one side of an inflow end surface, which schematically shows a second embodiment of a honeycomb filter of the present invention; Fig. Figure 6 is a cross-sectional view that schematically shows a cross-section along line BB'. Fig. 5 shows; Fig. Figure 7 is a perspective view schematically showing a third embodiment of a honeycomb filter of the present invention; Fig. Figure 8 is a top view of one side of an inflow end face of the inflow into Fig. 7 honeycomb filters shown; and Fig. 9 is a cross-sectional view that schematically shows a cross-section along line CC'. Fig. 8 shows. DESCRIPTION OF PREFERRED EXECUTION FORMS

[0015] The following describes embodiments of the present invention, although the present invention is not limited to these embodiments. Thus, the following embodiments, which are suitably modified, improved, and the like based on the usual knowledge of a person skilled in the art, without deviating from the object of the invention, are naturally within the scope of protection of the present invention. (1) Honeycomb filter (first embodiment)

[0016] A first embodiment of a honeycomb filter according to the present invention is as described in Fig. Honeycomb filters 1 to 4 shown 100. Fig. Figure 1 is a perspective view that schematically shows the first embodiment of the honeycomb filter of the present invention. Fig. 2 is a top view of one side of an inflow end face of the inflow into Fig.1 honeycomb filter shown. Fig. 3 is a top view of one side of an outflow surface of the in Fig. 1 honeycomb filter shown. Fig. 4 is a sectional view, schematically showing a cross-section along line AA'. Fig. 2 shows.

[0017] As in Fig. As shown in Figures 1 to 4, the honeycomb filter 100 according to the present embodiment comprises a honeycomb structure 4 and sealing sections 5. The honeycomb structure 4 has porous partitions 1 arranged such that they surround several cells 2 as fluid passage channels running from an inlet end surface 11 to an outlet end surface 12. The Fig.The honeycomb structure 4 shown in Figures 1 to 4 is formed in a round column shape with the inflow end surface 11 and the outflow end surface 12 as both end surfaces and furthermore has a circumferential wall 3 on one of its circumferential sides. That is, the circumferential wall 3 is arranged in such a way that it surrounds the partition walls 1 arranged in a grid pattern.

[0018] The sealing sections 5 are arranged such that they seal one of the end sections of each of the cells 2 on the side of the inlet end surface 11 or on the side of the outlet end surface 12. Hereinafter, among several cells 2, those cells 2 in which the sealing sections 5 are arranged in an end section on the outlet end surface 12 and which are open on the side of the inlet end surface 11 are defined as "inlet cells 2a". Furthermore, among several cells 2, those cells in which the sealing sections 5 are arranged in the end section on the side of the inlet end surface 11 and which are open on the side of the outlet end surface 12 are defined as "outlet cells 2b". In the honeycomb filter 100 according to the present embodiment, it is preferred that the inlet cell 2a and the outlet cell 2b are arranged alternately via the partitions 1.

[0019] The honeycomb structure 4 in the honeycomb filter 100 is configured as follows. That is, the honeycomb structure 4 further contains a catalyst layer 14, which includes a platinum group element formed by an exhaust gas purification catalyst containing a platinum group element. The catalyst layer 14, containing a platinum group element, is arranged only on one side of the inner surface of the partitions 1 surrounding the inlet cells 2a. Furthermore, the catalyst layer 14, containing a platinum group element, is arranged in a region of at least up to 40% of the total length of the cells 2, starting from the outlet end surface 12 in one direction along the honeycomb structure 4. In a region of at least up to 30% of the total length of the cells 2, starting from the inlet end surface 11, the catalyst layer 14, containing a platinum group element, is not arranged.The total length of the cells 2 refers to the length from the inflow end surface 11 to the outflow end surface 12 of the honeycomb structure 4 (in other words, from the outflow end surface 12 to the inflow end surface 11 of the honeycomb structure 4). The phrase "arranged only on the side of the inner surface of the partitions 1" means that the catalyst, which contains a platinum group element, is not present in a thickness direction of the partitions 1 between 0.1T and 1.0T, starting from a position of the above 0.1T (where T denotes the thickness of the partitions 1) in the thickness direction of the partitions 1 from the inner surface of the partitions 1.

[0020] The platinum group element contains ruthenium, rhodium, palladium, osmium, iridium, and platinum. In the following, the platinum group element may be referred to as "PGM".

[0021] The catalyst layer 14, containing a platinum group element, is located only on the side of the inner surface of the partitions 1 surrounding the inlet cells 2a, and in a region of up to at least 40% of the total length, starting from the outlet surface 12 in the direction of the cells 2 of the honeycomb structure 4. The catalyst layer 14, containing a platinum group element, is a catalyst coating layer formed by coating the catalyst, which contains a platinum group element, onto a predetermined surface of the partitions 1.

[0022] The honeycomb filter 100 contains the honeycomb structure 4, which further contains, as described above, the catalyst layer 14, which contains an element of the platinum group, and exhibits excellent capture performance for capturing PM and excellent cleaning performance for cleaning harmful components contained in the exhaust gas.

[0023] This means that the honeycomb filter 100 has, on the side of the outflow end surface 12 of the honeycomb structure 4 into which the large quantity of gas flows, the "catalyst layer 14, which contains an element of the platinum group," so that the catalyst layer 14, which contains an element of the platinum group, can capture the PM and increase the capture efficiency. In particular, in the conventional honeycomb filter, small pores of the partitions on the side of the outflow end surface of the honeycomb structure are closed by the PM, which causes a deterioration of the capture efficiency, whereas in the honeycomb filter 100 of the present embodiment, it is extremely unlikely that such a situation will occur.Furthermore, the contact between the catalyst layer 14, which contains a platinum group element, and the exhaust gas is increased because the catalyst layer 14, which contains a platinum group element, is located on the side of the outflow end surface 12 of the honeycomb structure 4, thus increasing the cleaning efficiency. For example, the PM captured by the catalyst layer 14, which contains a platinum group element, are continuously oxidized and removed at a relatively lower temperature due to the catalytic efficiency of the catalyst layer 14, which contains a platinum group element. In addition, the catalyst layer 14, which contains a platinum group element, captures the PM, thus also making it possible to suppress the increase in the pressure drop of the honeycomb filter 100 during the use of the honeycomb filter 100 (in other words, during the time of PM capture).

[0024] If the catalyst layer 14, which contains a platinum group element, is also arranged on sections other than the inner surface of the partitions 1 surrounding the inlet cells 2a, the pressure drop of the honeycomb filter 100 may be increased. Although the catalyst containing the platinum group element exhibits excellent catalytic performance for exhaust gas purification, it is also scarce and has a high industrial value. Therefore, the catalyst layer 14, which contains a platinum group element, is arranged only on the specified surface of the partitions 1, thus reducing the manufacturing costs of the honeycomb filter 100.

[0025] Preferably, the porosity of the catalyst layer 14, which contains a platinum group element, is 50 to 90%, more preferably 60 to 80%, and particularly preferably 60 to 70%. If the porosity of the catalyst layer 14, which contains a platinum group element, is less than 50%, the pressure drop may be increased. On the other hand, the collection efficiency may deteriorate if the porosity of the catalyst layer 14, which contains a platinum group element, exceeds 90%.

[0026] Preferably, the average pore diameter of the catalyst layer 14, which contains an element of the platinum group, is from 1 to 7 µm, more preferably from 1 to 5 µm and particularly preferably from 1 to 3 µm.

[0027] The porosity and average pore diameter of catalyst layer 14, which contains a platinum group element, can be measured by the following procedure. First, a cross-sectional section of catalyst layer 14 containing a platinum group element is viewed through a scanning electron microscope (hereinafter referred to as "SEM") to acquire the SEM image. The SEM image is magnified 200-fold for observation. SEM is an abbreviation for "scanning electron microscope." For example, a scanning electron microscope manufactured by Hitachi High-Technologies Corporation, model number S3200-N, can be used. Subsequently, a material fraction of catalyst layer 14 containing a platinum group element and an empty fraction of the catalyst layer containing a platinum group element are binarized by analyzing the acquired SEM image.Subsequently, a percentage of the ratio of the empty fraction in catalyst layer 14 containing a platinum group element is calculated with respect to the total area of ​​the material fraction and the empty fraction of catalyst layer 14 containing a platinum group element. The calculated value is defined as the porosity of catalyst layer 14 containing a platinum group element. Additionally, a hollow wall between the respective particle diameters in the SEM image is binarized, and the size of the hollow wall is directly measured using a scale. The pore diameter of catalyst layer 14 containing a platinum group element is calculated from this measured value. An average value of the calculated pore diameters is defined as the average pore diameter of catalyst layer 14 containing a platinum group element.

[0028] Furthermore, the catalyst layer 14, which contains a platinum group element, is preferably a catalyst layer formed by a catalyst containing a platinum group element with a particle diameter of 1 to 10 µm. With such a configuration, the PM in the exhaust gas can be effectively captured by the catalyst layer 14, which contains a platinum group element, arranged on the surface of the partitions 1. The captured PM are continuously oxidized and removed at a relatively lower temperature by the catalytic activity of the catalyst layer 14, which contains a platinum group element.

[0029] Preferably, the thickness of the catalyst layer 14, which contains a platinum group element, is 10 to 40 µm, more preferably 20 to 35 µm, and particularly preferably 20 to 30 µm. A thickness of less than 10 µm of the catalyst layer 14 containing a platinum group element is not preferred, as the improvement in collection efficiency may be reduced. Conversely, a thickness exceeding 40 µm of the catalyst layer 14 containing a platinum group element is not preferred, as the pressure drop may be increased.

[0030] The thickness of catalyst layer 14, which contains a platinum group element, can be measured using the following procedure. First, a cross-sectional area of ​​catalyst layer 14 containing a platinum group element is observed using a scanning electron microscope (SEM) to acquire an SEM image. Subsequently, the thickness of catalyst layer 14 containing a platinum group element is measured directly from the acquired SEM image using the scale.

[0031] It is preferred that the catalyst layer 14 containing a platinum group element is a catalyst layer containing an oxide of at least one element selected from the group consisting of aluminum, zirconium, and cerium. It is preferred that the catalyst layer containing such an oxide contains 1 to 3 wt% of a platinum group element by mass of the total mass of the catalyst layer. The composition of the catalyst layer 14 containing a platinum group element can be measured, for example, by X-ray fluorescence analysis (XRF). More precisely, the composition analysis of the catalyst layer 14 containing a platinum group element can be carried out by detecting, for each element, intrinsic fluorescent X-rays generated by irradiating a sample with X-rays.

[0032] The catalyst layer 14, which contains a platinum group element, is arranged in a region of at least up to 40% of the total length of the cells 2, starting from the outlet end surface 12, and is not arranged in a region of at least up to 30% of the total length of the cells 2, starting from the inlet end surface 11. Preferably, the region in which the catalyst layer 14, which contains a platinum group element, is not arranged is 35% of the total length, starting from the inlet end surface 11, and more preferably 40%. With such a configuration, the increase in the pressure drop of the honeycomb filter 100 can be effectively suppressed.

[0033] In the Fig.In the honeycomb filter 100 shown in Figures 1 to 4, the catalyst layer 14, containing a platinum group element, is arranged in a cross-section orthogonal to the orientation of the cells 2 of the honeycomb structure 4 on the side of the inner surface of the partitions 1, surrounding the inlet cells 2a over the entire area of ​​the cross-section. However, the catalyst layer 14, containing a platinum group element, can also be arranged on the side of the inner surface of the partitions, surrounding at least one of the inlet cells 2a in the cross-section. That is, the catalyst layer 14, containing a platinum group element, is arranged in a region extending from the outlet surface 12 of the honeycomb structure 4 to at least 40% of the total length of the cells 2 on the side of the inner surface of the partitions 1, surrounding at least one of the inlet cells 2a.

[0034] Preferably, the porosity of the partitions 1 of the honeycomb structure 4 is 50 to 70%, more preferably 55 to 65%, and particularly preferably 60 to 65%. The porosity of the partitions 1 is a value measured by mercury porosimetry. The porosity of the partitions 1 can be measured, for example, using AutoPore 9500 (product name) manufactured by Micromeritics Instrument Corp. A porosity of less than 50% is not preferred because the permeation resistance of the partitions 1 is increased, and the pressure drop is also increased. A porosity exceeding 70% is not preferred because the strength is significantly reduced.

[0035] Preferably, the average pore diameter of the partitions is 110 to 25 µm, more preferably 10 to 20 µm, and most preferably 15 to 20 µm. The average pore diameter of the partitions 1 is a value measured by mercury porosimetry. The average pore diameter of the partitions 1 can be measured, for example, using the AutoPore 9500 (product name) manufactured by Micromeritics Instrument Corp. A less than 10 µm average pore diameter of the partitions 1 is not preferred because the permeation resistance of the partitions 1 is increased, and the pressure drop is also increased. A greater than 25 µm average pore diameter of the partitions 1 is not preferred because the gas flow concentrates at the section of the large pore, thus reducing the collection efficiency.

[0036] Preferably, the thickness of the partitions 1 in the honeycomb structure 4 is 0.15 to 0.38 mm, more preferably 0.18 to 0.33 mm, and particularly preferably 0.20 to 0.31 mm. The thickness of the partitions 1 can be measured, for example, using a scanning electron microscope or a microscope. If the thickness of the partitions 1 is less than 0.15 mm, sufficient strength cannot be achieved. On the other hand, the pressure drop may be increased when the catalyst is loaded onto the partitions 1 if the thickness of the partitions exceeds 10.38 mm.

[0037] The shape of the cells 2 formed in the honeycomb structure 4 is not particularly restricted. For example, the shape of the cells 2 in cross-section orthogonal to the direction of the cells 2 can be a polygon, a circle, an ellipse, or the like. Examples of polygons include a triangle, a quadrilateral, a pentagon, a hexagon, an octagon, and the like. Preferably, the shape of the cells 2 is a triangle, a quadrilateral, a pentagon, a hexagon, or an octagon. With regard to the shape of the cells 2, all cells 2 can have the same shape, or the cells 2 can have different shapes from one another. Although not shown, for example, quadrilateral and octagonal cells can be mixed. With regard to the size of the cells 2, all cells 2 can have the same size, or the cells 2 can have different sizes from one another. Although not shown, for example,Some cells within a group of cells are larger, and other cells are smaller. In the present invention, the cells represent a space enclosed by partitions.

[0038] Preferably, the cell density of the cells 2 defined by the partitions 1 is from 31 to 54 cells / cm². 2 and preferably 39 to 47 cells / cm² 2 With such a configuration, the honeycomb filter can be used as a filter for capturing PM in exhaust gas emitted by a motor vehicle engine or the like.

[0039] The circumferential wall 3 of the honeycomb structure 4 can be formed integrally with the partitions 1 or can be formed by a circumferential coating layer created by applying a circumferential coating material in such a way that it surrounds the partitions 1. Although not shown, the circumferential coating layer can be applied to the circumferential side of the partitions during manufacturing, after the partitions have been formed integrally with the circumferential wall, and the resulting circumferential wall can then be removed by known methods such as grinding.

[0040] The shape of the honeycomb structure 4 is not particularly restricted. The shape of the honeycomb structure 4 can include a columnar shape, in which the inflow end surface 11 and the outflow end surface 12 have a circular, an elliptical, and a polygonal shape.

[0041] The size of the honeycomb structure 4, e.g., the length in the direction of the cells 2 of the honeycomb structure 4 (hereinafter also referred to as "total length") or the size of the cross-section (hereinafter also referred to as "cross-sectional area") orthogonal to the direction of the cells 2 of the honeycomb structure 4, is not particularly limited. Each size can be selected to ensure optimal cleaning performance when the honeycomb filter 100 is in use. Preferably, the total length of the honeycomb structure 4 is from 90 to 160 mm and more preferably from 120 to 140 mm. Furthermore, the cross-sectional area of ​​the honeycomb structure 4 is preferably from 8000 to 16000 mm². 2 and preferably from 10000 to 14000 mm 2 .

[0042] Preferably, the material of the partitions 1 is at least one selected from the group consisting of cordierite, silicon carbide, a silicon-silicon carbide composite material, mullite, aluminum oxide, aluminum titanate, silicon nitride, and a silicon carbide-cordierite composite material. Preferably, the material forming the partitions 1 contains 30% or more by weight, more preferably 40% or more by weight, and particularly preferably 50% or more by weight of the materials listed in the above group. In the honeycomb filter 100 of the present embodiment, the material forming the partitions 1 is particularly preferably cordierite. (2) Honeycomb filter (second embodiment)

[0043] A second embodiment of a honeycomb filter according to the present invention is described below. The second embodiment of a honeycomb filter according to the present invention is as described in Fig. 5 and Fig. 6 honeycomb filters shown 200. Fig. Figure 5 is a top view of one side of an inflow end surface, which schematically shows the second embodiment of the honeycomb filter according to the present invention. Fig. Figure 6 is a cross-sectional view that schematically shows a cross-section along line BB'. Fig. 5 shows.

[0044] As in Fig. 5 and Fig.As shown in Figure 6, the honeycomb filter 200 according to the present embodiment is a honeycomb filter 200 comprising a honeycomb structure 24 and sealing sections 25. The honeycomb structure 24 has porous partitions 21 arranged such that they surround several cells 22 as fluid passage channels extending from an inlet end surface 31 to an outlet end surface 32. Furthermore, a circumferential side surface of the honeycomb structure 24 is provided with a circumferential wall 23 to surround the partitions 21.

[0045] The sealing sections 25 are arranged such that they seal one end of the end sections of each of the cells 22 either on the side of the inflow end surface 31 or on the side of the outflow end surface 32. The cells 22 in which the sealing sections 25 are arranged at the end section on the side of the outflow end surface 32 are defined as "inflow cells 22a", and the cells 22 in which the sealing sections 25 are arranged at the end section on the side of the inflow end surface 31 are defined as "outflow cells 22b".

[0046] Furthermore, the honeycomb structure 24 in the honeycomb filter 200 also includes a catalyst layer 34 containing a platinum group element, which is formed by an exhaust gas purification catalyst containing a platinum group element. The catalyst layer 34, containing a platinum group element, is arranged only on one side of an inner surface of the partitions 21 surrounding the inlet cells 22a. Furthermore, the catalyst layer 34, containing a platinum group element, is arranged in a region of at least 40% with respect to the total length of the cells 22, starting from the outlet end surface 32, and is not arranged in a region of at least 30% with respect to the total length of the cells 22, starting from the inlet end surface 31.

[0047] In the honeycomb filter 200, the catalyst layer 34, which contains a platinum group element, is arranged on the partitions 21 that are present in a central section 38 of the honeycomb structure 24. That is, the catalyst layer 34, which contains a platinum group element, is arranged under the partitions 21 present in the central section 38 only on one side of an inner surface of the partitions 21, surrounding the inlet cells 22a. The central section 38 is referred to here in a cross-section orthogonal to the orientation of the cells 22 of the honeycomb structure 24 as a region within 60% of the length from a centroid of the cross-section to a circumferential edge of the cross-section.That is, in the honeycomb filter 200 according to the present embodiment, the catalyst layer 34, which contains an element of the platinum group, is preferably arranged only at the “central section 38” in the cross-section of the honeycomb structure 24 described above, and the catalyst layer 34, which contains an element of the platinum group, is not arranged at sections other than the central section 38.

[0048] Since the catalyst layer 34, which contains an element of the platinum group, is arranged in the honeycomb filter 200 only in the central section 38 where the flow of the exhaust gas is increased, it is possible to advantageously maintain the collection performance of the honeycomb filter 200, to suppress the increase in pressure loss and to further reduce the manufacturing costs.

[0049] In the Fig.In the honeycomb filter 100 shown in Figures 1 to 4, the catalyst layer 14, which contains a platinum group element, is arranged in a cross-section orthogonal to the orientation of the cells 2 of the honeycomb structure 4 on the side of the inner surface of the partitions 1, surrounding the inflow cells 2a of the entire cross-sectional area. It is preferred that the Fig. 5 and Fig. 6 honeycomb filters 200 shown, except that the area in which the catalyst layer 34, which contains an element of the platinum group, is arranged is limited to the central section 38 of the honeycomb structure 24, has the same structure as the one in Fig. 1 to 4 honeycomb filters shown have 100. (3) Honeycomb filter (third embodiment)

[0050] A third embodiment of a honeycomb filter according to the present invention is described below. The third embodiment of a honeycomb filter according to the present invention is as described in Fig.Honeycomb filter 300 shown in 7 to 9. Fig. Figure 7 is a perspective view that schematically shows the third embodiment of the honeycomb filter according to the present invention. Fig. Figure 8 is a top view of one side of an inflow end face of the inflow into Fig. 7 honeycomb filters shown. Fig. 9 is a cross-sectional view that schematically shows a cross-section along line CC'. Fig. 8 shows.

[0051] As in Fig. As shown in Figures 7 to 9, the honeycomb filter 300 according to the present embodiment is a honeycomb filter 300 comprising a honeycomb structure 44 and sealing sections 45. The honeycomb structure 44 has porous partitions 41 arranged such that they surround several cells 42 as passage channels for fluid, which run from an inlet end surface 51 to an outlet end surface 52. Furthermore, a circumferential side surface of the honeycomb structure 44 is provided with a circumferential wall 43 to surround the partitions 41.

[0052] The sealing sections 45 are arranged such that they seal one of the end sections of each of the cells 42 either on the side of the inflow end surface 51 or on the side of the outflow end surface 52. The cell 42 in which the sealing sections 45 are arranged at the end section on the side of the outflow end surface 52 is defined as an 'inflow cell 42a' and the cell 42 in which the sealing sections 45 are arranged at the end section on the side of the inflow end surface 51 is defined as an 'outflow cell 42b'.

[0053] Furthermore, the honeycomb structure 44 in the honeycomb filter 300 also includes a catalyst layer 54 containing a platinum group element, which is formed by an exhaust gas purification catalyst containing a platinum group element. The catalyst layer 54, containing a platinum group element, is arranged only on the side of the inner surface of the partitions 41 surrounding the inlet cells 42a. Furthermore, the catalyst layer 54, containing a platinum group element, is arranged in a region of at least up to 40% of the total length of the cells 42, starting from the outlet end surface 52, and is not arranged in a region of at least up to 30% of the total length of the cells 42, starting from the inlet end surface 51.

[0054] Furthermore, the honeycomb structure 44 in the honeycomb filter 300 includes a collection layer 55, which is provided only on the side of an inner surface of the partitions 41 surrounding one or more of the inlet cells 42a, and which is intended for collecting particulate matter (PM) in the exhaust gas. The collection layer 55 does not contain any platinum group element and is arranged only within a range of up to 50% of the total length of the cells 42, starting from the inlet end surface 51 of the honeycomb structure 44.

[0055] Furthermore, the honeycomb filter 300, configured as described above, can contain the sealing layer 55 only within the specified area on the side of the inlet end face 51 to further improve the collection performance. If the area in which the collection layer 55 is located overlaps with the area in which the catalyst layer 54, containing a platinum group element, is located, the collection layer 55 and the catalyst layer 54, containing a platinum group element, can coexist in the specified area in the direction of the cells 42. It is noted that the collection layer 55 and the catalyst layer 54, containing a platinum group element, can be arranged in such a way that they are separated from each other in the direction of the cells 42. In the Fig.In the honeycomb filter 300 shown in Figures 7 to 9, the area in which the sealing layer 55 is arranged and the area in which the catalyst layer 54, containing a platinum group element, is arranged are continuous in the direction of the cells 42, and the sealing layer 55 and the catalyst layer 54, containing a platinum group element, are arranged without any gap. The area in which the collection layer 55 is arranged is not particularly restricted, as long as it lies within a range of up to 50% with respect to the total length of the cells 42, starting from the inlet end face 51, and can, for example, be a range of up to 30% with respect to the total length, a range of up to 20% with respect to the total length, a range of up to 10% with respect to the total length, or the like.

[0056] Apart from the fact that the honeycomb structure 44 further contains the collecting layer 55, it is preferred that the in Fig.Honeycomb filters 7 to 9 shown have the same configuration as the one in Fig. 1 to 4 honeycomb filters shown have 100.

[0057] The trapping layer 55 does not contain the platinum group element and is preferably a layer containing at least one oxide selected from the group consisting, for example, of the elements aluminum, magnesium, zirconium, cerium, and silicon. In the present patent specification, "does not contain any platinum group element" means that the content of the platinum group element in the component is 0.1% by mass or less. Thus, the trapping layer 55 can contain 0.1% by mass or less of the platinum group element with respect to its total mass. Compared to the catalyst layer 54, which contains a platinum group element, such a trapping layer 55 can be prepared from a less expensive material and can further improve the trapping performance while reducing the manufacturing costs of the honeycomb filter 300.The composition of the trapping layer 55 can be measured by the same method as that of the catalyst layer 54, which contains an element of the platinum group, e.g. by X-ray fluorescence analysis (XRF).

[0058] When the composition of the trapping layer 55 is analyzed by the X-ray fluorescence analysis described above, it is preferred that the content of the platinum group element is 0.1 wt% or less and preferably equal to or less than a detection limit of an analytical device.

[0059] Preferably, the porosity of the collection layer 55 is between 70 and 90%, more preferably between 75 and 90%, and most preferably between 80 and 90%. A porosity of less than 70% is not preferred, as the pressure drop may be increased. Conversely, a porosity exceeding 90% is not preferred, as the collection efficiency may be reduced.

[0060] The average pore diameter of the trapping layer 55 is preferably 1 to 7 µm, more preferably 1 to 5 µm, and most preferably 1 to 3 µm. The porosity and average pore diameter of the trapping layer 55 can be measured by the following method. The porosity and average pore diameter of the trapping layer 55 can be measured by the same method as the method described above for measuring the porosity and average pore diameter of the catalyst layer 54, which contains a platinum group element.

[0061] Furthermore, the collection layer 55 is preferably made of particles of an oxide containing at least one element selected from the group consisting of aluminum, magnesium, zirconium, cerium, and silicon, with a particle diameter of 1 to 10 µm. With such a configuration, the PM in the exhaust gas can be effectively captured by the collection layer 55 arranged on the surface of the partition walls 1.

[0062] Preferably, the thickness of the trapping layer 55 is 10 to 40 µm, more preferably 20 to 35 µm, and most preferably 20 to 30 µm. A thickness of less than 10 µm is not preferred, as the improvement in trapping efficiency may be reduced. Conversely, a thickness exceeding 40 µm is not preferred, as the pressure drop may be increased. The thickness of the trapping layer 55 can be measured using the same method as the method described above for measuring the thickness of the catalyst layer 54, which contains a platinum group element.

[0063] The collection layer 55 can be arranged on one side of an inner surface of the partitions 1, in a cross-section orthogonal to the orientation of the cells 42 of the honeycomb structure 44, surrounding at least one of the inflow cells 42a. For example, the collection layer 55 can be arranged on the side of the inner surface of the partitions 1, surrounding the inflow cells 42a over the entire area of ​​the cross-section, or it can be arranged only on the side of the inner surface of the partitions 1, surrounding the specific inflow cells 42a. If the collection layer 55 is arranged only on the side of the inner surface of the partitions 1, surrounding the specific inflow cells 42a, it is preferred that the collection layer 55 is arranged only on the side of the inner surface of the partitions 41, surrounding the inflow cells 42a in the partitions 41 present in a central section (not shown) of the honeycomb structure 44. (4) Method for manufacturing the honeycomb filter

[0064] The method for manufacturing a honeycomb filter according to the present embodiment is not particularly limited and, for example, the following method can be mentioned.

[0065] First, a plastic modeling clay is prepared for the production of honeycomb partitions. This clay can be prepared by adding suitable additives, such as a binder, a pore-forming agent, and water, to a base powder to create the partitions. Examples of the base powder include aluminum oxide, talc, kaolin, and silicon dioxide. Examples of the binder include methylcellulose, hydroxypropyl methylcellulose, or similar substances. Additionally, examples of the additives include a surfactant.

[0066] The resulting kneadable material is then extruded to form a columnar honeycomb structure with partitions to define multiple cells and a circumferential wall that surrounds the partitions. The honeycomb structure is then dried, for example, using microwaves and warm air.

[0067] The sealing sections are then formed on the dried honeycomb mold. The process for forming these sealing sections can be carried out according to the conventionally known method for manufacturing a honeycomb filter. For example, a mask is first applied to the inlet end surface of the honeycomb mold so that the inlet cell is covered. Then, the end section with the mask of the honeycomb mold is immersed in a sealing slurry, and an open end of the outlet cell without a mask is filled with the sealing slurry. Next, the open end of the inlet cell on the outlet surface of the honeycomb mold is also filled with the sealing slurry using the same method as described above. Finally, the honeycomb mold with the sealing sections formed within it is further dried using a hot air dryer.

[0068] The honeycomb body, with its formed sealing sections, is then fired to prepare a honeycomb filter precursor before the application of the catalyst layer containing a platinum group element. The firing temperature and atmosphere used to fire the honeycomb body vary depending on the starting material used to prepare the honeycomb body, and a person skilled in the art can select the most suitable firing temperature and atmosphere for the chosen material.

[0069] The catalyst containing a platinum group element is then prepared to form the catalyst layer. For example, the catalyst containing a platinum group element can be a catalyst in which a platinum group element is loaded onto an aluminum oxide with a particle diameter of 1 to 10 µm. Such aluminum oxide is applied in a zone coating over an area of ​​at least 40% of the total cell length, starting from the outflow face of the honeycomb filter precursor. Specific zone coating methods include, for example, the following: First, a catalyst layer formation slurry is prepared, containing catalyst powder such as aluminum oxide loaded with the platinum group element, a suitable solvent (e.g., ion-exchange water), and a dispersant.Subsequently, the catalyst layer formation slurry is poured from the inlet face of the honeycomb filter precursor and drawn in from the outlet face, so that the catalyst, containing a platinum group element, is deposited onto the surface of the partitions surrounding the inlet cells, in which the side of the honeycomb filter precursor's inlet face is open. The catalyst, containing the platinum group element, is then calcined at 500 °C to prepare the catalyst layer. By adjusting the viscosity of the catalyst layer formation slurry and the pressure during aspiration, the catalyst layer containing the platinum group element is deposited only on the surface of the partitions.Furthermore, as a method of zone coating, a catalyst layer containing an element of the platinum group can also be applied by immersing the catalyst layer formation slurry onto the surface of the partitions.

[0070] The honeycomb filter according to the present invention can be manufactured as described above. Furthermore, if the honeycomb structure includes the collection layer, the collection layer can be formed by the following method only in a region extending from the inflow end face of the honeycomb structure up to 50% of its total length. That is, a material for the collection layer is first prepared. For example, silicon dioxide with a particle diameter of 1 to 10 µm can be used as a starting material for the collection layer. Such silicon dioxide is applied as a zone coating in a region extending up to 50% of the total length, starting from the inflow end face of the honeycomb structure. The silicon dioxide coated in this zone is then fired at 500 °C to prepare the collection layer. (Examples)

[0071] The present invention will be described in more detail below using examples, although the present invention is not limited to these examples. (Example 1)

[0072] First, aluminum oxide, talc, kaolin, and silicon dioxide starting materials were prepared to create partitions for a honeycomb structure. To these prepared aluminum oxide, talc, kaolin, and silicon dioxide starting materials (a total of 100 parts by mass), 2 parts by mass of a dispersing medium and 7 parts by mass of an organic binder were added. These were mixed and kneaded to prepare a modeling clay. Water was used as the dispersing medium. Methylcellulose was used as the organic binder. A surfactant was used as the dispersing agent.

[0073] The modeling material was then extruded using a mold to prepare a honeycomb shape, resulting in a honeycomb shape whose overall form is a round column. The cell shape of the honeycomb shape was rectangular.

[0074] After the honeycomb mold was dried by a microwave dryer and then completely dried again by a hot air dryer, both end surfaces of the honeycomb mold were subsequently cut off and adjusted to predetermined dimensions.

[0075] Subsequently, sealing sections were formed on the dried honeycomb mold. Specifically, a mask was first applied to the inlet end surface of the honeycomb mold, covering the inlet cell. Then, the end section with the mask was dipped into a sealing slurry, and an open end of the outlet cell (without the mask) was filled with the sealing slurry. Following this, the open end of the inlet cell at the outlet surface of the honeycomb mold was also filled with the sealing slurry using the same procedure as described above. Finally, the honeycomb mold, with the sealing sections formed within it, was further dried using a hot air dryer.

[0076] Subsequently, the dried honeycomb mold was degreased and fired to prepare a honeycomb filter precursor before arranging the catalyst layer, which contains an element of the platinum group.

[0077] Subsequently, on the inner surface of the partitions surrounding the inlet cells of the honeycomb filter precursor, a catalyst layer containing a platinum group element was prepared using the following procedure. First, a catalyst layer formation slurry containing a powder of aluminum oxide loaded with palladium (a platinum group element), ion-exchange water, and a dispersant were prepared. The catalyst layer formation slurry was then poured from the inlet surface of the honeycomb filter precursor and aspirated from the outlet surface. During aspiration, a pressure was applied such that the catalyst layer containing the platinum group element was deposited only on the inner surface of the partitions.This involved applying the catalyst, which contains a platinum group element, to the surface of the partitions surrounding the inlet cells, in which the side of the inlet end face of the honeycomb filter precursor is open. The catalyst, containing a platinum group element, applied to the surface of the partitions was then fired at 500 °C to prepare the catalyst layer.

[0078] The honeycomb filter from Example 1 had a round column shape, with both the inlet and outlet faces being circular. The cell length in one direction of the honeycomb filter was 127 mm. The diameter of the end face of the honeycomb filter was 118 mm. Within the honeycomb structure forming the filter, the partitions were 0.22 mm thick, and the cell density was 47 cells / cm². 2 The porosity of the partition walls of the honeycomb structure was 63%.

[0079] Furthermore, the catalyst layer containing a platinum group element was located only on one side of the inner surface of the partitions surrounding the inlet cells. The catalyst layer containing the platinum group element was located within a region (i.e., within 60% of the total cell length, starting from the outflow end face) of up to 60% of the total cell length, starting from the outflow end face of the honeycomb structure. The porosity of the catalyst layer containing the platinum group element was 65%. Table 1 shows the location and region of the catalyst containing the platinum group element. [Table 1] Arrangement area of ​​the catalyst containing a platinum group element Position of the catalyst containing a platinum group element Area of ​​the collection layer Comparative example 1 100 % In the pore of the partition wall absence Comparison example 2 60% of the outflow area In the pore of the partition wall absence Example 1 60% of the outflow area surface of the partition absence Example 2 50% of the outflow area surface of the partition absence Example 3 40% of the outflow area surface of the partition absence Example 4 60% of the outflow area surface of the partition 20% of the inflow end area Example 5 60% of the outflow area surface of the partition 10% of the inflow end area Example 6 50% of the outflow area surface of the partition 20% of the inflow end area Example 7 70% of the outflow area surface of the partition 30% of the inflow end area

[0080] With regard to the honeycomb filter from Example 1, the "collection efficiency performance", the "pressure drop performance", and the "exhaust gas cleaning performance" were evaluated using the following procedure. The results are shown in Table 2. (Collection efficiency performance)

[0081] First, an exhaust gas purification device using a honeycomb filter of each type was fabricated. The fabricated exhaust gas purification device was connected to one side of an exhaust manifold outlet of a 1.2-liter direct-injection gasoline engine to measure the amount of soot contained in the gas emitted from the exhaust gas purification device outlet using a particle density (PN) measurement method. The "PN measurement method" is a measurement technique proposed by a particle measurement program (PMP) at the Exhaust Gas Energy Experts Conference (GRPE) of the Automobile Standards Harmonized World Forum (WP29) within the European Economic Committee (ECE) of the United Nations (UN).More precisely, when determining the number of soot particles, the cumulative number of soot particles emitted after driving in a mode of the Worldwide Harmonized Light Duty Test Cycle (WLTC) is defined as the number of soot particles to be determined by the exhaust aftertreatment system, and the capture efficiency is measured. Capture efficiency performance was evaluated based on the following assessment criteria, which were derived from the measured capture efficiencies of each system. When the values ​​for the capture efficiency of the exhaust aftertreatment system using a honeycomb filter from Comparison Example 1 were set to 100% in a column entitled "Capture Efficiency Ratio (%)" in Table 2 below, the percentage values ​​for the exhaust aftertreatment system using a honeycomb filter from each example were shown.

[0082] Rating “excellent”: If the value of the capture efficiency of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the value of the capture efficiency of the exhaust gas cleaning device using the honeycomb filter to be evaluated was 130% or more, the rating was “excellent”.

[0083] Rating “good”: If the value of the capture efficiency of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the value of the capture efficiency of the exhaust gas cleaning device using the honeycomb filter to be evaluated exceeded 120% and was less than 130%, the rating was “good”.

[0084] Rating “Approval”: If the value of the capture efficiency of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the value of the capture efficiency of the exhaust gas cleaning device using the honeycomb filter to be evaluated was 100% and 120% or less, the rating was “Approval”. (Pressure loss performance)

[0085] The exhaust gas emitted by a 1.4-liter direct-injection gasoline engine was introduced into honeycomb filters of each sample, and soot in the exhaust gas was collected in the filter's baffles. The soot was collected until the amount of soot deposited per unit volume (1 liter) of the honeycomb filter reached 1 g / l. Subsequently, the engine exhaust gas, at 200 °C and with a soot deposit of 1 g / l, was processed at a flow rate of 1.0 Nm. 3The flow rate was set to / min, and the pressure between the inlet and outlet surfaces of the honeycomb filter was measured. The pressure drop (kPa) of the honeycomb filter was then calculated by determining the pressure difference between these surfaces. The pressure drop performance was evaluated based on the following criteria, which were derived from the measured pressure drop values ​​for each example. The column "Pressure Drop Ratio (%)" in Table 2 below shows the percentage values ​​of the pressure drop for each example honeycomb filter when the pressure drop value of the honeycomb filter in comparison example 1 was 100%.

[0086] Rating “excellent”: If the pressure loss value of the honeycomb filter in comparison example 1 was set to 100% and if the pressure loss value of the honeycomb filter being evaluated was 65% or less, the rating was “excellent”.

[0087] Rating “good”: If the pressure loss value of the honeycomb filter in comparison example 1 was set to 100% and if the pressure loss value of the honeycomb filter being evaluated exceeded 65% and was 70% or less, the rating was “good”.

[0088] Rating “Approval”: If the pressure loss value of the honeycomb filter in comparison example 1 was set to 100%, and if the pressure loss value of the honeycomb filter being evaluated exceeded 70% and was less than 100%, the rating was “Approval”. (Exhaust gas purification performance)

[0089] First, an exhaust gas purification device using a honeycomb filter of each type was manufactured. This device was connected to one side of the exhaust manifold outlet of a 1.2-liter direct-injection gasoline engine to measure the concentration of NOx in the gas emitted from the exhaust gas purification device outlet and to determine the NOx purification efficiency. The purification performance was evaluated based on the following criteria, which were derived from the measured NOx purification efficiency.If the NOx cleaning efficiency values ​​of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 were set to 100% in a column “NOx cleaning efficiency ratio (%)” in Table 2 below, the NOx cleaning efficiency values ​​(%) of the exhaust gas cleaning device using the honeycomb filters of each example are shown.

[0090] Rating “excellent”: If the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter to be evaluated was 120% or more, the rating was “excellent”.

[0091] Rating “good”: If the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter to be evaluated exceeded 110% and was less than 120%, the rating was “good”.

[0092] Rating “Approval”: If the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter to be evaluated exceeded 100% and was 110% or less, the rating was “Approval”.

[0093] Rating “no approval”: If the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter of comparison example 1 was set to 100%, and if the NOx cleaning efficiency value of the exhaust gas cleaning device using the honeycomb filter to be assessed was 100% or less, the rating was “no approval”. [Table 2] Collection efficiency (%) Pressure loss (kPa) NOx cleaning efficiency (%) Catch-up efficiency ratio (%) Pressure loss ratio (%) NOx cleaning efficiency ratio (%) Collection efficiency performance Pressure loss performance capability Exhaust gas cleaning performance Comparison example 1 60,00 3,000 60 100 100 100 criterion criterion criterion Comparison in game 2 62,00 2,980 55 103 99 92 Permit Permit no approval Example 1 80,00 2,100 75 133 70 125 excellent good excellent Example 2 75,00 2,025 70 125 68 117 good good good Example 3 70,00 1,950 65 117 65 108 Permit excellent Permit Example 4 82,50 2,250 75 138 75 125 excellent Permit excellent Example 5 81,25 2,175 75 135 73 125 excellent Permit excellent Example 6 77,50 2,175 70 129 73 117 good Permit good Example 7 88,75 2,400 80 148 80 133 excellent Permit excellent (Examples 2 to 7)

[0094] Apart from modifying a deposition area and deposition site of a catalyst containing a platinum group element, as shown in Table 1 above, the honeycomb filters were prepared using the same procedure as in Example 1. For the honeycomb filters of Examples 2 to 7, the "collection efficiency performance," "pressure drop performance," and "exhaust gas cleaning performance" were evaluated using the same procedure as in Example 1. The results are shown in Table 2.

[0096] (Comparison examples 1 and 2)

[0095] Apart from modifying the deposition area and deposition site of a catalyst containing a platinum group element, as shown in Table 1 above, honeycomb filters were prepared using the same procedure as in Example 1. In Comparative Examples 1 and 2, the catalyst containing a platinum group element was loaded into the inner sections of the pores of partition walls in a honeycomb structure, as described in the following procedures. In Comparative Example 1, a catalyst layer-forming slurry containing a catalyst powder of aluminum oxide loaded with a platinum group element, ion-exchange water, and a dispersant was first prepared.Subsequently, the catalyst containing a platinum group element was applied to the entire surface of the partition walls of a honeycomb filter precursor by impregnating the catalyst layer-forming slurry from an inflow and an outflow surface of the precursor. The catalyst was then fired at 500°C to prepare the catalyst layer. In comparative example 2, the catalyst containing a platinum group element was loaded into the inner section of the partition wall pores by impregnating the catalyst layer-forming slurry described above in a region of 60% from the outflow surface of the precursor. (Result)

[0096] It was confirmed that the honeycomb filters of Examples 1 to 7 exceeded the respective performance levels of the honeycomb filter of Comparison Example 1, which served as a reference, in all assessments of "collection efficiency," "pressure drop performance," and "flue gas cleaning performance." Thus, it was determined that the honeycomb filters of Examples 1 to 7 also exhibited excellent collection and cleaning performance and were able to suppress the increase in pressure drop compared to the conventional honeycomb filter. On the other hand, the improvement in "collection efficiency" and "pressure drop performance" in the honeycomb filter of Comparison Example 2 compared to the honeycomb filter of Comparison Example 1 was hardly observed, while the "flue gas cleaning performance" was extremely low.

[0097] The honeycomb filter according to the present invention can be used as the filter for capturing the suspended particles in the exhaust gas. Description of reference symbols

[0098] 1, 21 and 41: partition wall, 2, 22 and 42: cell, 2a, 22a and 42a: inlet cell, 2b, 22b and 42b: outlet cell, 3, 23 and 43: circumferential wall, 4, 24 and 44: honeycomb structure, 5, 25 and 45: sealing section, 11, 31 and 51: inlet end surface, 12, 32 and 52: outlet end surface, 14, 34 and 54: catalyst layer containing a platinum group element, 38: central section, 55: collection layer and 100, 200 and 300: honeycomb filter.

Claims

[1] Honeycomb filter (100, 200, 300), which includes: a honeycomb structure (5, 25, 45) having porous partition walls (1, 21, 41) arranged to surround a plurality of cells (2, 22, 42) as fluid passages extending from an inflow end face (11, 31, 51) to an outflow end face (12, 32, 52); and Sealing sections (5, 25, 45) arranged to seal one of the end sections of each of the cells (2, 22, 42) on the inflow end face side (11, 31, 51) or on the outflow end face side (12, 32, 52), wherein the cells (2, 22, 42) in which the sealing sections (5, 25, 45) are arranged in an end section on the side of the outflow end surface (12, 32, 52) and which are open on the side of the inflow end surface (11, 31, 51) are defined as inflow cells (2a, 22a, 42a), and the cells (2, 22, 42) in which the sealing sections (5, 25, 45) are arranged in the end section on the side of the inflow end face (11, 31, 51) and which are opened on the side of the outflow end face (12, 32, 52) are defined as outflow cells (2b, 22b, 42b), the honeycomb structure (5, 25, 45) further comprises a catalyst layer (14, 34, 54) containing a platinum group element, which is formed by an exhaust gas purification catalyst containing a platinum group element, the catalyst layer (14, 34, 54) containing a platinum group element is arranged only on one side of an inner surface of the partition walls (1, 21, 41) surrounding the inflow cells (2a, 22a, 42a), and the catalyst layer (14, 34, 54) containing a platinum group element is arranged in a direction of extension of the cells (2, 22, 42) of the honeycomb structure (5, 25, 45) in a region of at least up to 40% with respect to a total length of the cells (2, 22, 42), starting from the outflow end surface (12, 32, 52), and is not arranged in a region of at least up to 30% with respect to a total length of the cells (2, 22, 42), starting from the inflow end surface (11, 31, 51), wherein, in a cross-section orthogonal to the direction of extension of the cells (2, 22, 42) of the honeycomb structure (5, 25, 45), an area within 60% of a length from a center of gravity of the cross-section to a peripheral edge of the cross-section is defined as a central portion (38) of the cross-section, and the catalyst layer (14, 34, 54) containing a platinum group element is arranged only on the partition walls (1, 21, 41) present in the central portion (38) of the cross section. [2] The honeycomb filter (100, 200, 300) according to claim 1, wherein a porosity of the catalyst layer (14, 34, 54) containing a platinum group element is from 50 to 90%. [3] The honeycomb filter (100, 200, 300) according to claim 1 or 2, wherein a thickness of the catalyst layer (14, 34, 54) containing a platinum group element is from 10 to 40 µm. [4] The honeycomb filter (100, 200, 300) according to any one of claims 1 to 3, wherein the catalyst layer (14, 34, 54) containing a platinum group element is a catalyst layer (14, 34, 54) containing an oxide of at least one element selected from the group consisting of aluminum, zirconium and cerium. [5] Honeycomb filter (100, 200, 300) according to one of claims 1 to 4, wherein the honeycomb structure (5, 25, 45) further includes a collecting layer (55) arranged only on one side of an inner surface of the partition walls (1, 21, 41) surrounding one or more of the inflow cells (2a, 22a, 42a) and collecting the suspended matter in exhaust gas, the collecting layer (55) does not contain any element of the platinum group, and the collecting layer (55) is arranged only in an area of ​​up to 50% with respect to the total length of the cells (2, 22, 42), starting from the inflow end surface (11, 31, 51). [6] Honeycomb filter (100, 200, 300) according to claim 5, wherein a porosity of the collecting layer (55) is from 70 to 90%. [7] Honeycomb filter (100, 200, 300) according to claim 5 or 6, wherein a thickness of the collecting layer (55) is from 10 to 50 µm. [8] The honeycomb filter (100, 200, 300) according to any one of claims 5 to 7, wherein the trapping layer (55) is a layer containing an oxide of at least one element selected from the group consisting of aluminum, magnesium, zirconium, cerium and silicon.

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