JP2020001032A - Honeycomb filter - Google Patents

Abstract

To provide a honeycomb filter capable of collecting a particulate material in exhaust gas by a collection layer, and oxidizing and burning the collected particulate material at a lower temperature.SOLUTION: A honeycomb filter includes a honeycomb structure 4 having a porous partition wall 1, and a plugging part 5. The honeycomb structure 4 further has a collection layer 14 on the inner surface side of the partition wall 1 enclosing an inflow cell 2a, and the collection layer 14 includes a part constituted of a sintered body of CeOparticles at least on a surface layer of the collection layer 14, and an average particle diameter of the CeOparticles constituting the collection layer 14 is 1.1 μm or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a honeycomb filter. More specifically, the present invention relates to a honeycomb filter capable of collecting particulate matter in exhaust gas by a collection layer and oxidizing and burning the collected particulate matter at a lower temperature.

  In recent years, regulations on the removal of particulate matter contained in exhaust gas discharged from gasoline engines have become stricter worldwide, and honeycomb filters having a honeycomb structure have been used as filters for removing particulate matter. I have. Hereinafter, the particulate matter may be referred to as “PM”. PM is an abbreviation of “Particulate Matter”.

  For example, as a honeycomb filter, a filter including a honeycomb structure having a porous partition wall for forming a plurality of cells and a plugging portion for plugging any one end of the cell is exemplified. be able to. Such a honeycomb filter has a structure in which a porous partition wall serves as a filter for removing PM. Specifically, after exhaust gas containing PM flows in from the inflow end face of the honeycomb filter and is filtered by collecting PM with a porous partition wall, the purified exhaust gas is discharged from the outflow end face of the honeycomb filter. I do. Thus, PM in exhaust gas can be removed.

  Conventionally, as a technique for improving the trapping performance of a honeycomb filter, a technique of increasing the thickness of a partition wall of a honeycomb structure or reducing the size of pores formed in the partition wall has been proposed. However, when the trapping performance is improved by the above-described technique, PM (for example, soot) is easily clogged in the pores formed in the partition walls, and the pressure loss of the honeycomb filter increases. There was a problem that it would. That is, the above-described technique is not an effective solution because the effect of improving the trapping performance and the effect of suppressing the increase in pressure loss are in a trade-off relationship.

  For this reason, a honeycomb filter in which a trapping layer for trapping PM is disposed on the surface of the partition wall of the honeycomb structure has been proposed (for example, see Patent Documents 1 to 4). For example, the trapping layer is formed of a porous membrane having an average pore diameter smaller than the average pore diameter of the partition walls. According to such a honeycomb filter, PM can be deposited on the surface of the trapping layer. Therefore, when trapping PM while suppressing a sudden rise in pressure loss due to clogging of PM in pores of partition walls, Can improve collection efficiency.

Patent No. 4426381 Patent No. 5524178 Patent No. 5524179 Patent No. 5726414

  As described above, the honeycomb filter in which the trapping layer is provided on the surface of the partition wall is less likely to be clogged with the PM in the pores of the partition wall, and can suppress a rapid increase in pressure loss. There is a problem that a countermeasure is required because a problem occurs. That is, in the honeycomb filter provided with the trapping layer, a large amount of soot as PM is deposited on the trapping layer. Therefore, it is necessary to suppress an increase in pressure loss caused by such a soot deposition layer. In particular, in a use environment where soot is difficult to burn, such as in a cold region, it is necessary to frequently perform a filter regeneration operation by backwashing, forced heating of soot, or the like. In addition, instead of frequently performing the regeneration operation, a technique of carrying an oxidation catalyst on the trapping layer and combusting and removing a deposited layer of soot deposited on the trapping layer by a catalytic reaction has been studied. Regarding the technology that burns and removes the deposited layer of soot deposited on the trapping layer by catalytic reaction, reducing the oxidation start temperature of soot greatly contributes to the effect of suppressing the rise in pressure loss. There is a strong demand for the development of technologies that can be burned.

  The present invention has been made in view of such problems of the related art. According to the present invention, there is provided a honeycomb filter capable of collecting particulate matter in exhaust gas by a collection layer and oxidizing and burning the collected particulate matter at a lower temperature.

  According to the present invention, the following honeycomb filter is provided.

[1] A honeycomb structure having a porous partition wall arranged so as to surround a plurality of cells serving as fluid flow paths extending from an inflow end surface to an outflow end surface,
A plugging portion arranged to seal any one end of the inflow end surface side or the outflow end surface side of the cell,
The plugging portion is disposed at an end on the outflow end surface side, and the cell in which the inflow end surface side is opened is an inflow cell,
The plugging portion is disposed at an end on the inflow end surface side, and the cell in which the outflow end surface side is open is an outflow cell,
The honeycomb structure further includes, on the inner surface side of the partition wall surrounding the inflow cell, a trapping layer for trapping particulate matter in exhaust gas,
The trapping layer includes a portion composed of a sintered body of CeO ₂ particles on at least a surface layer of the trapping layer,
A honeycomb filter, wherein the CeO ₂ particles forming the trapping layer have an average particle size of 1.1 μm or less.

[2] The honeycomb filter according to [1], wherein the average pore size of the trapping layer is smaller than the average pore size of the partition walls.

[3] The honeycomb filter according to [1] or [2], wherein the partition wall is formed of cordierite.

[4] The honeycomb filter according to any one of [1] to [3], wherein the partition has an average pore diameter of 6 to 24 μm.

[5] The honeycomb filter according to any of [1] to [4], wherein the porosity of the partition wall is 45 to 66%.

[6] The honeycomb filter according to any one of [1] to [5], wherein the thickness of the partition wall is 0.10 to 0.35 mm.

[7] The honeycomb filter according to any one of [1] to [6], wherein the thickness of the trapping layer is 20 to 50 μm.

ADVANTAGE OF THE INVENTION The honeycomb filter of this invention can collect | recover particulate matter (PM) in exhaust gas by a collection layer, and can oxidize and burn the collected PM at lower temperature. That is, it at least the surface of the trapping layer includes a portion constituted by a sintered body of CeO ₂ particles, and an average particle diameter of the CeO ₂ particles constituting the collecting layer is not more than 1.1μm Thus, the CeO ₂ particles exhibit catalytic activity as an oxidation catalyst at lower temperatures. Therefore, the PM collected by the collecting layer can be oxidized and burned at a lower temperature. The honeycomb filter of the present invention does not require frequent filter regeneration work even in a use environment where PM (particularly, soot) is difficult to burn, such as in a cold region. Further, the honeycomb filter of the present invention can satisfactorily oxidize and burn PM trapped by the trapping layer without further supporting the trapping layer with an oxidation catalyst.

It is a perspective view showing typically one embodiment of a honeycomb filter of the present invention. FIG. 2 is a plan view on the inflow end face side of the honeycomb filter shown in FIG. 1. FIG. 2 is a plan view of an outflow end face side of the honeycomb filter illustrated in FIG. 1. It is sectional drawing which shows the A-A 'cross section of FIG. 2 typically. It is sectional drawing which shows the cross section of a partition typically.

  Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Therefore, it is understood that modifications and improvements made to the following embodiments as appropriate based on ordinary knowledge of those skilled in the art also fall within the scope of the present invention without departing from the spirit of the present invention. Should be.

(1) Honeycomb filter:
An embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in FIGS. Here, FIG. 1 is a perspective view schematically showing one embodiment of the honeycomb filter of the present invention. FIG. 2 is a plan view on the inflow end surface side of the honeycomb filter shown in FIG. FIG. 3 is a plan view on the outflow end face side of the honeycomb filter shown in FIG. FIG. 4 is a sectional view schematically showing an AA ′ section in FIG.

  As shown in FIGS. 1 to 4, the honeycomb filter 100 of the present embodiment includes a honeycomb structure 4 and a plugged portion 5. The honeycomb structure 4 has a porous partition wall 1 disposed so as to surround a plurality of cells 2 serving as a fluid flow path extending from the inflow end face 11 to the outflow end face 12. The honeycomb structure 4 shown in FIGS. 1 to 4 is formed in a cylindrical shape having the inflow end surface 11 and the outflow end surface 12 as both end surfaces, and further has an outer peripheral wall 3 on the outer peripheral side surface. That is, the outer peripheral wall 3 is provided so as to surround the partition walls 1 arranged in a lattice.

  The plugging portions 5 are arranged so as to seal either one of the ends of the cells 2 on the inflow end surface 11 side or the outflow end surface 12 side. Hereinafter, of the plurality of cells 2, the plugged portion 5 is disposed at the end on the outflow end surface 12 side, and the cell 2 having the inflow end surface 11 side opened is referred to as “inflow cell 2 a”. Further, among the plurality of cells 2, the plugged portion 5 is provided at the end on the inflow end face 11 side, and the cell 2 having the outflow end face 12 side opened is referred to as “outflow cell 2 b”. In the honeycomb filter 100 of the present embodiment, it is preferable that the inflow cells 2a and the outflow cells 2b are alternately arranged with the partition wall 1 interposed therebetween.

The honeycomb filter 100 is characterized in that the honeycomb structure 4 is configured as follows. That is, as shown in FIG. 5, the honeycomb structure 4 captures particulate matter (hereinafter, also referred to as “PM”) in exhaust gas on the inner surface side of the partition wall 1 surrounding the inflow cell 2a. It further has a consolidation layer 14. The trapping layer 14 includes at least a surface layer of the trapping layer 14 formed of a sintered body of CeO ₂ particles. That is, the trapping layer 14 is a porous film including a portion constituted by a sintered body of CeO ₂ particles. The average particle size of the CeO ₂ particles constituting the trapping layer 14 is 1.1 μm or less. Here, FIG. 5 is a cross-sectional view schematically showing a cross section of the partition. In FIG. 5, reference numeral 7 indicates pores formed in the partition wall 1.

The surface layer of the trapping layer 14 means a part including a range of 10 μm from the surface side of the trapping layer 14 in the thickness direction. Therefore, the honeycomb filter 100 of the present embodiment includes a portion made of a sintered body of CeO ₂ particles at least in a range of 10 μm in the thickness direction from the surface side of the trapping layer 14. In addition, the honeycomb filter 100 of the present embodiment may be configured such that the entire collection layer 14 includes a sintered body of CeO ₂ particles. When the entire trapping layer 14 includes a sintered body of CeO ₂ particles, the content of CeO ₂ contained in the trapping layer 14 preferably exceeds 70% by mass. The entire trapping layer 14 contains a sintered body of CeO ₂ particles, and the trapping layer 14 in which the content of CeO ₂ contained in the trapping layer 14 is 70% by mass is hereinafter referred to as “constituted by CeO ₂ particles”. Collected layer 14 ".

When the average particle diameter of the CeO ₂ particles constituting the trapping layer 14 is 1.1 μm or less, the CeO ₂ particles exhibit catalytic activity as an oxidation catalyst at a lower temperature. Therefore, the PM collected by the collection layer 14 can be oxidized and burned at a lower temperature. The honeycomb filter 100 of the present embodiment does not need to frequently perform filter regeneration work even in a use environment where PM (particularly, soot) is difficult to burn, for example, in a cold region. In addition, the honeycomb filter of the present embodiment can satisfactorily oxidize and burn PM trapped by the trapping layer 14 without further supporting the trapping layer 14 with an oxidation catalyst. If the average particle diameter of the CeO ₂ particles constituting the trapping layer 14 exceeds 1.1 μm, the temperature at which the CeO ₂ particles exhibit catalytic activity increases, making it difficult to oxidize and burn PM at low temperatures. Become.

In the honeycomb filter 100 of the present embodiment, the average particle diameter of the CeO ₂ particles forming the trapping layer 14 can be measured as follows. First, a part of the partition wall 1 and the trapping layer 14 is cut out from the honeycomb structure 4 constituting the honeycomb filter 100 as a test piece, and the cut out test piece is embedded in a resin. Next, the test piece embedded with the resin is cut in a direction orthogonal to the direction in which the cell 2 extends, and the cut surface is polished. Next, the polished cut surface is imaged using a scanning electron microscope (hereinafter, also referred to as “SEM”), and an SEM image with a magnification of 200 times is obtained. “SEM” is an abbreviation for “Scanning Electron Microscope”. The SEM image is an image in which one pixel is 0.261 μm in height × 0.261 μm in width. As the scanning electron microscope, for example, a scanning electron microscope “model number: S3400-N” manufactured by Hitachi High-Technologies Corporation can be used. In the measurement of the average particle size of the CeO ₂ particles, a range of 20 mm × 20 mm × 20 mm including the center position in the direction in which the cells 2 of the honeycomb filter 100 extend and the center portion farthest from the outer peripheral wall 3 of the honeycomb filter 100 is used. , One test piece is prepared. The size of the test piece to be manufactured is 6 mm × 6 mm × 6 mm. An SEM image is obtained for the test piece thus manufactured.

Next, image processing is performed on the collection layer 14 in the obtained SEM image, and the particle size of CeO ₂ particles forming the collection layer 14 is measured. Specifically, first, an SEM image of the trapping layer 14 surrounds a region of 1 μm in the thickness direction × 100 μm in the horizontal direction of the trapping layer 14 at an arbitrary position where the mass ratio of CeO ₂ is 70% by mass or more. At this time, in the SEM image, the trapping layer 14 is positioned so as to be horizontal with respect to the partition wall 1, and the above-described region is specified so as to be parallel to the horizontal line. The area specified in the SEM image in this manner is hereinafter referred to as a “specified area”. The designated area in the SEM image is binarized using “Image-Pro 9.3.2 (trade name)” of Nippon Roper Co., Ltd. The binarization processing, trapping layer 14 in the specified area in the SEM image are separated and the real part of the sintered body of CeO ₂ particles in the gap between the CeO ₂ particles mutually. The binarization process is performed with one pixel as a minimum unit. Next, the particle diameter of all the CeO ₂ particles in the specified region is measured by dividing each area of the portion of the CeO ₂ particles recognized as a substantial part as a sintered body by a width of 1 μm. The average value of the measured particle diameters of the CeO ₂ particles is calculated and calculated in two regions, and the calculated average value is defined as the average particle diameter of the CeO ₂ particles constituting the trapping layer 14.

Further, it can be confirmed by the following qualitative analysis that the particles constituting the trapping layer 14 are CeO ₂ particles. EDS measurement is also performed at the time of SEM imaging, and the total mass ratio of the Ce element and the O element is measured. If the mass ratio is 90% by mass or more, it is regarded as CeO ₂ particles. Note that EDS is an abbreviation for Energy Dispersive X-ray Spectroscopy.

  The trapping layer 14 is preferably provided only on the inner surface of the partition wall 1 surrounding the inflow cell 2a. If the trapping layer 14 is disposed on other than the inner surface of the partition wall 1 surrounding the inflow cell 2a, the pressure loss of the honeycomb filter 100 may increase.

  The average pore diameter of the trapping layer 14 is preferably smaller than the average pore diameter of the partition wall 1. With this configuration, the PM contained in the exhaust gas can be satisfactorily collected by the collection layer 14 disposed on the inner surface side of the partition wall 1 surrounding the inflow cell 2a.

  The average pore diameter of the trapping layer 14 is preferably 0.5 to 15 μm, more preferably 0.5 to 8 μm, and particularly preferably 0.5 to 1 μm.

  The porosity of the trapping layer 14 is preferably 50 to 90%, more preferably 70 to 90%, and particularly preferably 80 to 90%. If the porosity of the trapping layer 14 is less than 50%, the pressure loss may increase. On the other hand, if the porosity of the trapping layer 14 exceeds 90%, the trapping efficiency may deteriorate.

  The porosity and the average pore diameter of the trapping layer 14 can be measured by the following method. First, the cross section of the trapping layer 14 is observed with a scanning electron microscope, and an SEM image is obtained. The SEM image is observed at a magnification of 200 times. Next, by subjecting the acquired SEM image to image analysis, the substantial part of the trapping layer 14 and the voids in the trapping layer 14 are binarized. Then, the percentage of the ratio of the void portion in the trapping layer 14 to the total area of the substantial portion and the void portion of the trapping layer 14 is calculated, and the value is defined as the porosity of the trapping layer 14. Separately, the gap between each particle diameter in the SEM image is binarized, the size is directly measured on a scale, and the pore diameter in the trapping layer 14 is determined from the measured value. calculate. The average value of the calculated pore diameters is defined as the average pore diameter of the trapping layer 14.

  The thickness of the collection layer 14 is preferably 20 to 50 μm, more preferably 20 to 40 μm, and particularly preferably 20 to 30 μm. If the thickness of the trapping layer 14 is less than 20 μm, it is not preferable because the margin for improving the trapping efficiency may decrease. On the other hand, when the thickness of the trapping layer 14 exceeds 50 μm, it is not preferable in that the trapping efficiency is kept high and the pressure loss may increase.

  The thickness of the trapping layer 14 can be measured by the following method. First, the following six intersections are determined from a cross section of the honeycomb filter 100 passing through the central axis in the direction in which the cells 2 extend and parallel to the partition wall 1. The six intersections intersect with three straight lines that divide the cross section into four in the direction in which the cell 2 extends, and two straight lines that divide the cross section into three in a direction perpendicular to the direction in which the cell 2 extends. Intersection. Then, a test piece including a region of 20 mm (longitudinal) × 20 mm (horizontal) is cut out in parallel with the cross section with each intersection as a center. The thickness of the test piece (that is, the depth parallel to the cross section) can be arbitrarily determined. An arbitrary pair of the adjacent inflow cell 2a and outflow cell 2b is selected from the test piece, and the surface height of each cell 2 (specifically, within a range of about 8 mm in the extending direction of the cell 2 by a 3D shape measuring machine) Measures the average value of the surface height of each cell 2 in the direction perpendicular to the partition wall 1). Subsequently, the difference between the surface heights of the inflow cell 2a and the outflow cell 2b is calculated, and this is set as the thickness of the trapping layer 14.

Since soot contained in the exhaust gas is collected on the surface of the trapping layer 14, it is preferable that at least the outermost surface of the trapping layer 14 has an oxidation catalyst function. Note that, as described above, the trapping layer 14 may be the trapping layer 14 composed of CeO ₂ particles.

  The average pore diameter of the partition walls 1 is preferably 6 to 24 μm, more preferably 9 to 24 μm, and particularly preferably 16 to 24 μm. The average pore diameter of the partition walls 1 is a value measured by a mercury intrusion method. The average pore diameter of the partition walls 1 can be measured using, for example, Autopore 9500 (trade name) manufactured by Micromeritics. When the average pore diameter of the partition walls 1 is less than 6 μm, the permeation resistance of the partition walls 1 is increased, and the pressure loss is undesirably increased. If the average pore diameter of the partition walls 1 exceeds 24 μm, it is not preferable in terms of moldability at the time of forming the trapping layer 14.

  The porosity of the partition walls 1 of the honeycomb structure 4 is preferably 45 to 66%, more preferably 52 to 66%, and particularly preferably 60 to 66%. The porosity of the partition 1 is a value measured by a mercury intrusion method. The porosity of the partition 1 can be measured using, for example, Autopore 9500 (trade name) manufactured by Micromeritics. If the porosity of the partition wall 1 is less than 45%, the permeation resistance of the partition wall 1 increases and the pressure loss increases, which is not preferable. If the porosity of the partition wall 1 exceeds 66%, the strength may be significantly reduced, which is not preferable.

  The thickness of the partition wall 1 of the honeycomb structure 4 is preferably 0.10 to 0.35 mm, more preferably 0.10 to 0.24 mm, and more preferably 0.10 to 0.18 mm. Is particularly preferred. The thickness of the partition wall 1 can be measured using, for example, a profile projector (Profile Projector). If the thickness of the partition wall 1 is less than 0.10 mm, sufficient strength may not be obtained. On the other hand, if the thickness of the partition wall 1 exceeds 0.35 mm, the pressure loss may increase when the trapping layer 14 is provided on the surface of the partition wall 1.

  There is no particular limitation on the shape of the cells 2 formed in the honeycomb structure 4. For example, as a shape of the cell 2 in a cross section orthogonal to the direction in which the cell 2 extends, a polygon, a circle, an ellipse, and the like can be given. Examples of the polygon include a triangle, a quadrangle, a pentagon, a hexagon, and an octagon. The shape of the cell 2 is preferably a triangle, a quadrangle, a pentagon, a hexagon, or an octagon. As for the shape of the cells 2, all the cells 2 may have the same shape or different shapes. For example, although illustration is omitted, a mixture of square cells and octagon cells may be used. As for the size of the cells 2, the sizes of all the cells 2 may be the same or may be different. For example, although not shown, the size of some of the plurality of cells may be increased and the size of the other cells may be relatively reduced. In the present invention, the cell 2 means a space surrounded by the partition 1.

The cell density of the cells 2 defined by the partition walls 1 is preferably 30 to 60 cells / cm ² , and more preferably 30 to 50 cells / cm ² . With this configuration, the filter can be suitably used as a filter for collecting PM in exhaust gas discharged from an engine of an automobile or the like.

  The outer peripheral wall 3 of the honeycomb structure 4 may be formed integrally with the partition 1 or may be an outer peripheral coat layer formed by applying an outer peripheral coat material so as to surround the partition 1. You may. Although not shown, the outer peripheral coat layer is formed at the time of manufacturing, after the partition and the outer peripheral wall are integrally formed, the formed outer peripheral wall is removed by a known method such as grinding, and then the outer peripheral coat of the partition is formed. Side.

  There is no particular limitation on the shape of the honeycomb structure 4. As the shape of the honeycomb structure 4, the shape of the inflow end face 11 and the outflow end face 12 may be a columnar shape such as a circle, an ellipse, and a polygon.

The size of the honeycomb structure 4, for example, the length of the honeycomb structure 4 in the direction in which the cells 2 extend (hereinafter, also referred to as “full length”), or the size of the cross section orthogonal to the direction in which the cells 2 of the honeycomb structure 4 extend. There is no particular limitation on the size (hereinafter also referred to as “cross-sectional area”). Each size may be appropriately selected so as to obtain an optimum purification performance when the honeycomb filter 100 is used. The total length of the honeycomb structure 4 is preferably 90 to 160 mm, and more preferably 120 to 140 mm. Further, the cross-sectional area of the honeycomb structure 4 is preferably 8000～16000Mm ^2, and further preferably from 10000~14000mm ^2.

  The material of the partition wall 1 is at least selected from the group consisting of cordierite, silicon carbide, a silicon-silicon carbide composite material, mullite, alumina, aluminum titanate, silicon nitride, and a silicon carbide-cordierite composite material. It is preferable to include one kind. The material constituting the partition wall 1 is preferably a material containing 30% by mass or more of the materials listed in the above group, more preferably a material containing 40% by mass or more, and a material containing 50% by mass or more. Is particularly preferred. In the honeycomb filter 100 of the present embodiment, the material forming the partition walls 1 is particularly preferably cordierite.

(2) Manufacturing method of honeycomb filter:
The method for producing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following method.

  First, a plastic clay for preparing the partition walls of the honeycomb structure is prepared. The clay for producing the partition walls of the honeycomb structure is prepared by appropriately adding an additive such as a binder, a pore former, and water to the raw material powder for producing a suitable material for the above-described partition walls. can do. As the raw material powder, for example, alumina, talc, kaolin, and silica powder can be used. Examples of the binder include methylcellulose (Hydroxypropylmethylcellulose) and the like. Further, examples of the additive include a surfactant and the like.

  Next, by extruding the kneaded clay obtained in this manner, a columnar honeycomb formed body having a partition wall for partitioning a plurality of cells, and an outer peripheral wall disposed so as to surround the partition wall. Is prepared. Next, the obtained honeycomb formed body is dried by, for example, microwaves and hot air.

  Next, plugged portions are formed on the dried honeycomb formed body. The method for forming the plugged portions can be performed according to a conventionally known method for manufacturing a honeycomb filter. For example, first, a mask is applied to the inflow end face of the honeycomb formed body so that the inflow cells are covered. Thereafter, plugging slurry is printed on the end of the honeycomb formed body provided with the mask, and the opening of the outflow cell not provided with the mask is filled with the plugging slurry. Thereafter, the plugging slurry is filled into the opening of the inflow cell in the same manner as described above for the outflow end face of the honeycomb formed body. Thereafter, the honeycomb formed body on which the plugged portions are formed is further dried by a hot air dryer.

  Next, the honeycomb formed body on which the plugged portions are formed is fired to prepare a honeycomb filter precursor before the collection layer is provided. Note that the firing temperature and the firing atmosphere when firing the honeycomb formed body differ depending on the raw material for manufacturing the honeycomb formed body, and those skilled in the art will select the optimum firing temperature and firing atmosphere for the selected material. be able to.

Next, CeO ₂ particles for preparing a trapping layer are prepared. As the CeO ₂ particles, for example, CeO ₂ particles having an average particle diameter of 0.2 to 1.1 μm can be suitably used. Then, the prepared CeO ₂ particles are made into a slurry to which water, a dispersant, a pore-forming agent, a coagulant, and a viscosity modifier are added, so that the coagulated particles containing CeO ₂ do not enter the pores of the honeycomb filter precursor. Such a slurry is supplied from below the top and bottom of the honeycomb filter precursor set in the jig of the film forming apparatus, and the permeated liquid flows from above. After the predetermined amount of slurry has been flowed, the honeycomb filter precursor is turned over together with the jig, and the jig is removed from the honeycomb filter precursor. Thereafter, the honeycomb filter precursor in a state where the aggregated particles in the slurry are arranged on the surface of the partition wall is dried and fired.

In this way, a trapping layer composed of CeO ₂ particles is formed on the inner surface side of the partition wall surrounding the inflow cell of the honeycomb filter precursor. As described above, the honeycomb filter of the present invention can be manufactured.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Example 1)
First, alumina, talc, kaolin, and silica raw materials for preparing the partition walls of the honeycomb structure were prepared. To the prepared alumina, talc, kaolin, and silica raw materials, 2 parts by mass of a dispersion medium and 7 parts by mass of an organic binder were respectively added, mixed, and kneaded to prepare a clay. Water was used as a dispersion medium. Methyl cellulose was used as the organic binder. A surfactant was used as a dispersant.

  Next, the kneaded material was extruded using a die for forming a honeycomb formed body to obtain a honeycomb formed body having a columnar overall shape. The cell shape of the honeycomb formed body was square.

  Next, the honeycomb formed body was dried with a microwave drier, and further completely dried with a hot-air drier. Then, both end surfaces of the honeycomb formed body were cut and adjusted to predetermined dimensions.

  Next, plugged portions were formed on the dried honeycomb formed body. Specifically, first, a mask was applied to the inflow end face of the honeycomb formed body so as to cover the inflow cells. Thereafter, plugging slurry was printed on the end of the honeycomb formed body provided with the mask, and the opening of the outflow cell not provided with the mask was filled with the plugging slurry. Thereafter, the plugging slurry was filled into the opening of the inflow cell in the same manner as described above for the outflow end face of the honeycomb formed body. Thereafter, the honeycomb formed body on which the plugged portions were formed was further dried with a hot air drier.

  Next, the dried honeycomb formed body was degreased and fired to manufacture a honeycomb filter precursor before the collection layer was provided.

Next, a trapping layer was formed on the inner surface side of the partition surrounding the inflow cell of the honeycomb filter precursor by the following method. Specifically, first, CeO ₂ particles having an average particle diameter of 1.3 μm were prepared. For CeO ₂ particles, cerium oxide powder manufactured by Tribach was used. Next, the prepared CeO ₂ particles were aggregated to prepare a slurry for forming a trapping layer. Next, the trapping layer forming slurry was supplied from below the top and bottom of the honeycomb filter precursor set in the jig of the film forming apparatus, and the permeate was flowed from above. When a predetermined amount of the slurry for forming a trapping layer was finished flowing, the honeycomb filter precursor was turned over together with the jig, and the jig was removed from the honeycomb filter precursor. Thereafter, the honeycomb filter precursor was dried at room temperature for 22 hours, dried at 80 ° C. for 24 hours, further heated to 1200 ° C. at a rate of 200 ° C./h, and fired at 1200 ° C. for 2 hours. And a collection layer.

In the honeycomb filter of Example 1, the inflow end face and the outflow end face had a circular column shape. The length of the honeycomb filter in the cell extending direction was 127.1 mm. The diameter of the end face of the honeycomb filter was 118.5 mm. The honeycomb structure constituting the honeycomb filter had a partition wall thickness of 0.158 mm and a cell density of 33.3 cells / cm ² . The partition walls of the honeycomb structure had a porosity of 48.6%.

Further, the honeycomb filter of Example 1 had a trapping layer composed of CeO ₂ particles on the inner surface side of the partition wall surrounding the inflow cell. The thickness of the trapping layer was 26 μm. The total mass of the CeO ₂ particles constituting the trapping layer was 33 g. The results are shown in the column of “mass (g) of CeO ₂ particles” in Table 1. The mass of the trapping layer per unit area was 24 g. The results are shown in Table 1 in the column of "mass of collecting layer per unit area (g / m ² )". In addition, the mass of the trapping layer per unit area means a layer composed of CeO ₂ particles and the mass per 1 m ^{2 of the} porous layer effective as the trapping layer. The CeO ₂ particles constituting the trapping layer had an average particle diameter of 1.1 μm measured by the following measurement method. Table 1 shows the results.

[Measurement method of CeO ₂ particles constituting the trapping layer]
First, a test piece for measurement was cut out from a honeycomb structure constituting a honeycomb filter and produced. In addition, the test piece was prepared in a size of 6 mm x 6 mm x 6 mm from a center position in the direction in which the cells of the honeycomb filter extend and a range of 20 mm x 20 mm x 20 mm including the center portion farthest from the outer peripheral wall of the honeycomb filter. did. Next, the cut test pieces were embedded in resin. Next, the test piece embedded with the resin was cut in a direction perpendicular to the cell extending direction, and the cut surface was polished. Next, the polished cut surface was imaged using a scanning electron microscope, and an SEM image with a magnification of 200 times was obtained. As the scanning electron microscope, a scanning electron microscope “model number: S3400-N” manufactured by Hitachi High-Technologies Corporation was used. Next, image processing was performed on the trapping layer in the obtained SEM image, and the particle diameter of CeO ₂ particles forming the trapping layer was measured. Specifically, first, an area of 1 μm in the thickness direction × 100 μm in the horizontal direction of the collection layer was surrounded at an arbitrary position from the SEM image of the collection layer. At this time, in the SEM image, the trapping layer was horizontal with respect to the partition walls of the honeycomb structure, and the above-described region was specified so as to be parallel to the horizontal line. This area was binarized using “Image-Pro 9.3.2 (trade name)” of Nippon Roper Co., Ltd. Next, the particle diameters of all the CeO ₂ particles in the designated region were measured by dividing each area of the portion of the CeO ₂ particles recognized as a substantial part as a sintered body by a width of 1 μm. The average value of the measured particle diameters of the CeO ₂ particles was calculated and calculated in two regions, and the calculated average value was defined as the average particle diameter of the CeO ₂ particles constituting the trapping layer.

  For the honeycomb filter of Example 1, the measurement of “soot oxidation start temperature (° C.)” was performed by the following method. Table 1 shows the results.

[Soot oxidation start temperature (° C)]
First, exhaust gas containing soot was passed through the honeycomb filter of each example, and soot in the exhaust gas was collected by the collection layer of the honeycomb filter. Exhaust gas was ventilated until the amount of soot collected by the collecting layer became 1 g per 1 L of volume of the honeycomb filter. Next, the partition wall and the trapping layer of the honeycomb filter were cut so that each side had a length of 0.5 to 1.5 cm, to prepare a sample piece for measuring a soot oxidation start temperature. In addition, since soot adhered to the surface of the trapping layer, a sample piece was prepared so that the soot did not peel off from the surface of the trapping layer. Next, the produced sample piece was subjected to heat generated gas analysis (Temperature Programmed Desorption-Mass Spectrometry: TPD-MS). Specifically, first, the prepared sample piece was placed in a measurement cell for analyzing a gas generated by heating, and He / O ₂ (20%) gas adjusted to a flow rate of 50 mL / min was introduced into the measurement cell. Ventilated. After the temperature in the measurement cell was raised to 300 ° C., the temperature in the measurement cell was further raised to 700 ° C. at a rate of 20 ° C./min. At this time, the concentration of CO ₂ in the gas discharged from the measurement cell was measured. That is, by raising the temperature in the measurement cell, the soot collected by the collection layer burns to generate CO ₂ . Based on the measurement results of the CO ₂ concentration, and the temperature of the measuring cell transverse axis (200 to 700 ° C.), creating a graph with the vertical axis of the CO ₂ concentration (arbitrary unit (a.u.)), CO Assuming that the total area of the _two concentration peaks is A _100% , the temperature at which the area ratio of the CO ₂ concentration peak reaches A _{20% at} which the area ratio becomes _20% was determined. “The temperature at which A reached _20% ” was defined as “soot oxidation start temperature (° C.)”.

(Example 2, Comparative Examples 1 to 3)
A honeycomb filter was manufactured in the same manner as in Example 1 except that the average particle diameter of CeO ₂ particles for forming the trapping layer was changed as shown in Table 1. When the average particle diameter of the CeO ₂ particles constituting the trapping layers of the honeycomb filters of Example 2 and Comparative Examples 1 to 3 was measured, Example 2 was 0.7 μm, Comparative Example 1 was 2.1 μm, and Comparative Example 2 Was 4.5 μm and Comparative Example 3 was 5.5 μm. Table 1 shows the configurations of the partition walls and the trapping layers in the honeycomb filters of Example 2 and Comparative Examples 1 to 3.

  For the honeycomb filters of Example 2 and Comparative Examples 1 to 3, "soot oxidation start temperature (° C)" was measured in the same manner as in Example 1. Table 1 shows the results.

(result)
The soot oxidation start temperature of the honeycomb filter of Example 1 was 464 ° C., which was lower than the soot oxidation start temperature of the honeycomb filters of Comparative Examples 1 to 3. Further, the soot oxidation start temperature of the honeycomb filter of Example 2 was 455 ° C., and it was further confirmed that the soot oxidation start temperature was lowered. From the above results, by setting the average particle diameter of the CeO ₂ particles constituting the trapping layer to 1.1 μm or less, flammable PM such as soot collected by the trapping layer is oxidized and burned at a lower temperature. I knew I could do it.

  The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gas.

1: partition, 2: cell, 2a: inflow cell, 2b: outflow cell, 3: outer peripheral wall, 4: honeycomb structure, 5: plugged portion, 7: pore, 11: inflow end face, 12: outflow End face, 14: trapping layer, 100: honeycomb filter.

Claims (7)

A honeycomb structure having a porous partition wall disposed so as to surround a plurality of cells serving as a fluid flow path extending from the inflow end surface to the outflow end surface,
A plugging portion arranged to seal any one end of the inflow end surface side or the outflow end surface side of the cell,
The plugging portion is disposed at an end on the outflow end surface side, and the cell in which the inflow end surface side is opened is an inflow cell,
The plugging portion is disposed at an end on the inflow end surface side, and the cell in which the outflow end surface side is open is an outflow cell,
The honeycomb structure further includes, on the inner surface side of the partition wall surrounding the inflow cell, a trapping layer for trapping particulate matter in exhaust gas,
The trapping layer includes a portion composed of a sintered body of CeO ₂ particles on at least a surface layer of the trapping layer,
A honeycomb filter, wherein the CeO ₂ particles forming the trapping layer have an average particle size of 1.1 μm or less.   The honeycomb filter according to claim 1, wherein an average pore diameter of the trapping layer is smaller than an average pore diameter of the partition wall.   The honeycomb filter according to claim 1, wherein the partition is formed of cordierite.   The honeycomb filter according to any one of claims 1 to 3, wherein the partition walls have an average pore diameter of 6 to 24 µm.   The honeycomb filter according to any one of claims 1 to 4, wherein a porosity of the partition wall is 45 to 66%.   The honeycomb filter according to any one of claims 1 to 5, wherein the partition wall has a thickness of 0.10 to 0.35 mm.   The honeycomb filter according to any one of claims 1 to 6, wherein the thickness of the trapping layer is 20 to 50 µm.

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