JP6265813B2 - Exhaust purification filter - Google Patents

Description

  The present invention relates to an exhaust purification filter. Specifically, the present invention relates to an exhaust gas purification filter that captures and purifies particulate matter in exhaust gas discharged from an internal combustion engine.

  In an internal combustion engine mounted on an automobile or the like, in particular, a compression ignition type internal combustion engine, it is known that a large amount of particulate matter is contained in the exhaust gas discharged. This particulate matter (Particulate Matter, hereinafter referred to as “PM”) is harmful to the human body and is an emission-regulated substance. Therefore, a DPF (Diesel Particulate Filter) as an exhaust gas purification filter that captures PM is usually provided in the exhaust passage of the internal combustion engine.

  In the DPF, trapped PM gradually accumulates. Then, a differential pressure is generated between the upstream side and the downstream side of the DPF, leading to a decrease in output and a deterioration in fuel consumption. For this reason, the DPF generally carries a catalyst for burning and removing the deposited PM when PM is accumulated to some extent.

  As said catalyst, the Ag type catalyst which shows the especially outstanding purification | cleaning activity with respect to PM is known. For example, a technique has been proposed in which aggregates having an average particle diameter of 0.05 μm to 0.5 μm formed by covering the periphery of Ag particles with Ce fine particles are disposed in an exhaust pipe (see Patent Document 1). According to this technique, it is said that PM can be burned and removed at a relatively low temperature.

  However, in the technique of Patent Document 1, Ag, which is an active species, is covered with Ce fine particles, and the average particle diameter of the aggregate is as small as 0.05 μm to 0.5 μm. bad. Since the Ag-based catalyst burns PM by releasing active oxygen, the contact property between Ag and PM has a characteristic that greatly affects the PM purification rate. It is clear that it cannot be burned and removed efficiently.

In view of this, a technique has been proposed in which a needle-shaped substance such as TiO ₂ is contained in an Ag-based catalyst to form voids of a predetermined size in the catalyst layer (see Patent Document 2). According to this technology, since PM can be penetrated into the voids in the catalyst layer, good contact between the Ag-based catalyst and PM can be ensured (that is, a large contact area can be ensured). It is said that PM can be purified efficiently.

Japanese Patent No. 5092281 JP 2011-036742 A

  However, in the technique of Patent Document 2, the size of the void is 0.5 μm to 1.0 μm, whereas the preferred catalyst layer thickness is 25 μm to 100 μm, so that PM penetrates deep into the catalyst layer. hard. Moreover, since the catalyst of patent document 2 is a needle-shaped catalyst using a needle-shaped substance, there are many catalysts in which the needle-shaped catalyst is folded and cannot function effectively, and the PM purification function cannot be sufficiently exhibited. Currently.

  The present invention has been made in view of the above, and an object of the present invention is to provide an exhaust purification filter equipped with an Ag-based catalyst, which can improve the contact between the catalyst and PM, and can efficiently purify PM. Is to provide.

  In order to achieve the above object, the present invention provides an exhaust purification filter that is provided in an exhaust passage of an internal combustion engine and captures and purifies particulate matter in the exhaust of the internal combustion engine, comprising a filter base material and the filter base. A catalyst layer formed on the material and oxidizing and purifying the particulate matter, wherein the catalyst layer includes a Ce-containing oxide containing Ce and Ag supported on the Ce-containing oxide. And an Ce-containing oxide on which Ag is supported has an average particle size of 0.4 μm to 6.3 μm.

In the present invention, the catalyst layer for oxidizing and purifying the particulate matter is formed of an Ag-based catalyst in which Ag is supported on a Ce-containing oxide, and the average particle size of the Ce-containing oxide on which Ag is supported is 0.4 μm to 6.3 μm.
According to the present invention, unevenness is formed on the surface of the catalyst layer by setting the average particle diameter of the Ce-containing oxide (hereinafter referred to as “catalyst particles”) supporting Ag to 0.4 μm to 6.3 μm. Therefore, a sufficient contact area between the catalyst particles and PM can be ensured. At the same time, when the catalyst particles are adjacent to each other, a large number of grooves that allow PM to enter the inside can be formed between the catalyst particles. In addition, this makes it possible to efficiently ignite PM that has entered the groove and is close to Ag, and good propagation characteristics can be obtained. Therefore, according to the present invention, the contact property between the catalyst and the PM can be improved as compared with the prior art, and the PM can be purified efficiently. As a result, the DPF regeneration time can be shortened, and fuel consumption and emission can be improved.

  The average particle diameter of the Ce-containing oxide on which Ag is supported is preferably 0.8 μm to 5 μm.

  In this invention, the average particle diameter of the Ce-containing oxide supporting Ag is set to 0.8 μm to 5 μm. According to the present invention, the above-described effects are more reliably exhibited.

  The number of grooves formed between the Ce-containing oxides on which Ag is supported is preferably 2.5 to 1250 per 10 μm square of the surface of the catalyst layer.

  In the present invention, the number of grooves formed between the Ce-containing oxides on which Ag is supported is 2.5 to 1250 per 10 μm square of the surface of the catalyst layer. According to the present invention, the above-described effects are more reliably exhibited.

  The shape of the Ce-containing oxide on which Ag is supported is preferably spherical.

  In the present invention, the Ce-containing oxide has a spherical shape. According to this invention, since the shape of the Ce-containing oxide supporting Ag is spherical, the PM contact area can be increased as compared with other shapes. Moreover, since the shape of the Ce-containing oxide is spherical, the Ce-containing oxide can be packed most closely in the catalyst layer. Therefore, according to the present invention, the number of grooves between the catalyst particles can be optimized, and the above-described effects are remarkably exhibited.

  ADVANTAGE OF THE INVENTION According to this invention, in the exhaust gas purification filter provided with Ag type catalyst, the contact property of a catalyst and PM can be improved conventionally, and the exhaust gas purification filter which can purify PM efficiently can be provided.

It is sectional drawing which shows the state in which PM deposited on the surface of DPF whose average particle diameter of the catalyst particle in a catalyst layer is less than 0.4 micrometer. It is an enlarged view of the A part in FIG. It is sectional drawing which shows the state which PM accumulated on the surface of DPF whose average particle diameter of the catalyst particle in a catalyst layer is 2 micrometers. FIG. 4 is an enlarged view of a portion B in FIG. 3. It is sectional drawing which shows typically the state in which PM deposited on the surface of each DPF whose average particle diameter of the catalyst particle in a catalyst layer is less than 0.4 micrometer, 2 micrometer, and more than 6.3 micrometers. It is a figure which shows the packing structure of a catalyst particle | grain, (a) is a figure which shows the closest packing structure, (b) is a figure which shows a non-close packing structure. It is a SEM image of the surface of a catalyst layer. It is a figure which shows the relationship between T90 of an Example and a comparative example, and a catalyst average particle diameter.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The exhaust purification filter according to the first embodiment of the present invention is provided in an exhaust passage of an internal combustion engine such as a diesel engine, for example, and captures and purifies PM in the exhaust of the internal combustion engine. The exhaust purification filter according to the present embodiment includes a DPF as a filter base and a catalyst layer made of an Ag-based catalyst formed on the surface of the DPF.

  The DPF of the present embodiment has a three-dimensional network structure and is formed from a porous material such as silicon carbide or cordierite. Further, any form such as foam metal or foam ceramic having PM collecting ability, a nonwoven fabric in which metals and ceramic fibers are superimposed, a wall flow type filter, or the like can be used. Among these, a wall flow type honeycomb structure filter is preferably used from the viewpoint of PM collection efficiency and contact between the catalyst and PM.

  In the DPF of this embodiment, the cell shape is preferably any one of 4 to 8 octagons from the viewpoint of increasing the contact area between the catalyst and the PM. From the same viewpoint, the number of cells is preferably 200 to 400 cells per square inch. When the number of cells is less than 200 cells, a sufficient contact area between the catalyst and PM cannot be ensured. When the number exceeds 400 cells, PM is clogged in the cells, leading to an increase in pressure loss.

  The catalyst layer of this embodiment is composed of an Ag-based catalyst containing Ag as a catalytic metal that is an active species. An Ag-based catalyst is currently the most effective catalyst for burning PM, and can burn PM at a lower temperature than other noble metal-based catalysts such as Pt. For example, if the contact property with the PM is good, the PM can be ignited from 200 ° C. or less, and the combustion of the PM can be completed at 400 ° C.

Here, the PM combustion mechanism of the Ag-based catalyst will be described.
In the Ag-based catalyst, Ag in the vicinity of the surface exists as Ag ₂ O in an oxidizing atmosphere and as Ag metal in a reducing atmosphere. Ag ₂ O has the smallest oxygen desorption energy and is the most effective compound for PM combustion.
When oxygen is supplied to the Ag metal near the surface from a Ce-containing oxide having an oxygen releasing ability, which will be described later, the Ag metal is converted to Ag ₂ O which is an active species. And although this Ag ₂ O returns to the Ag metal by reacting with PM, as a result of immediately supplying oxygen from the Ce-containing oxide to the Ag metal, the Ag near the surface is always in the state of Ag ₂ O. Exists. In this way, the Ag-based catalyst efficiently removes PM at a low temperature by the action of the active species Ag ₂ O existing near the surface. Therefore, the Ag-based catalyst has a characteristic that the contact property between Ag and PM greatly affects the PM purification performance.

In the Ag-based catalyst of the present embodiment, a Ce-containing oxide containing Ce is used as a catalyst carrier that supports Ag. Ce-containing oxides are known to have oxygen releasing ability. As the Ce-containing oxide, CeO ₂ , CeZrO ₂ , and CePrLaSiO ₂ are preferably used. Thereby, the stability of the Ag ₂ O is ensured by oxygen released from the Ce-containing oxide having oxygen releasing ability.

As the Ce-containing oxide, at least one selected from the group consisting of perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, ilmenite type, and fluorite type can be used. Among these, a fluorite-type complex oxide is preferably used from the viewpoint of oxygen releasing ability.
In addition, the composite oxide contains at least two kinds selected from the group consisting of alkaline earth metal elements, transition metal elements, Group 12 elements, and Group 13 elements as constituent elements. What absorbs and discharge | releases oxygen by changing a number is preferable.
In addition, since the composite oxide has an oxygen releasing ability, it is preferable that at least one element having a polyvalence is included. Specifically, Zr, V, Cr, Mn, Fe, Co, Cu, Nb, Ta, Mo, W, Ce, Pr, Sm, Eu, Tb, Yb, Pt, Pd, Rh, Ir, Ru, etc. It is preferable that at least one transition metal element is contained. Oxygen release is a phenomenon in which oxygen in the lattice of the composite oxide is desorbed in order to maintain a charge balance in accordance with a change in the valence of the elements constituting the composite oxide. For this reason, Ce, Zr, Pr, La, and Y are particularly preferable among the above transition metal elements from the viewpoint of oxygen releasing ability in combination with Ag.

  Further, the Ag-based catalyst of the present embodiment may be one in which at least one noble metal selected from the group consisting of Ru, Pd, and Pt is co-supported on the catalyst carrier together with Ag.

  In the present embodiment, the content of Ag in the Ag-based catalyst is preferably 15% by mass to 50% by mass.

Next, the average particle diameter of the catalyst particles of this embodiment will be described.
FIG. 1 is a cross-sectional view showing a state where PM is deposited on the surface of a DPF in which the average particle diameter of catalyst particles in the catalyst layer is less than 0.4 μm. FIG. 2 is an enlarged view of a portion A in FIG.
As shown in FIG. 1, usually, PM is deposited as a cake layer having fine pores on the surface of the DPF. As shown in FIG. 2, the PM cake layer contacts the catalyst layer at an average interval of 0.5 μm. Further, since the average particle diameter of the catalyst particles is smaller than 0.4 μm, a dense catalyst layer is formed, and the surface thereof is substantially planar. Therefore, since the surface area of the catalyst layer is small, a sufficient contact area between the catalyst particles and PM (hereinafter referred to as “PM contact area”) cannot be ensured. In particular, since the average particle diameter of the catalyst particles is less than 0.4 μm, which is smaller than the PM contact interval of 0.5 μm, there are catalyst particles that cannot come into contact with PM, and the contact probability between the catalyst particles and PM is low. Therefore, as described above, in the Ag-based catalyst, the contact property with the PM greatly affects the purification rate. Therefore, when the average particle diameter of the catalyst particles is less than 0.4 μm, the PM is efficiently purified. I can't.

In contrast, FIG. 3 is a cross-sectional view showing a state where PM is deposited on the surface of the DPF in which the average particle diameter of the catalyst particles in the catalyst layer is 2 μm. 4 is an enlarged view of a portion B in FIG.
As shown in FIG. 3, even when the average particle diameter of the catalyst particles is 2 μm, the same PM cake layer as in FIG. 1 is deposited on the surface of the DPF. In addition, since the average particle diameter of the catalyst particles is relatively large as 2 μm, a large number of grooves are formed between the catalyst particles by adjoining the large catalyst particles, and as a result, the average particle diameter of the catalyst particles is less than 0.4 μm. Compared to the case, the surface of the catalyst layer is uneven. Therefore, since the surface area of the catalyst layer is large, a sufficient PM contact area can be ensured. Further, as shown in FIG. 4, since a large amount of PM enters the grooves formed between the catalyst particles, the PM contact area can be further increased. Furthermore, as shown in FIG. 4, at the time of DPF regeneration, a large amount of PM that has entered the groove exists closer to Ag, which is the active species in the catalyst layer, and therefore compared with the PM deposited on the surface of the DPF. It is easy to ignite, has good propagation properties and burns efficiently. Therefore, when the average particle diameter of the catalyst particles is 2 μm, a sufficient PM contact area and good propagation properties can be obtained, so that PM can be efficiently purified.

  As described above, the average particle diameter of the catalyst particles greatly affects the PM contact area and the formation of grooves between the catalyst particles. Therefore, the average particle diameter of the catalyst particles will be described in more detail with reference to FIG. FIG. 5 is a cross-sectional view schematically showing a state in which PM is deposited on the surface of each DPF in which the average particle diameter of the catalyst particles in the catalyst layer is less than 0.4 μm, 2 μm and more than 6.3 μm. As described above, PM is deposited on the surface of the DPF as a cake layer having fine pores, and the interval between the PM cake layer and the catalyst layer (PM contact interval) is averaged. 0.5 μm.

First, the relationship between the average particle diameter of catalyst particles and the PM contact area will be described.
When the average particle diameter of the catalyst particles is smaller than 0.4 μm, the surface of the catalyst layer is almost as compared with the case where the average particle diameter of the catalyst particles described later is 2 μm or exceeds 6.3 μm as described above. Since it is planar and the surface area of the catalyst layer is small, a sufficient PM contact area cannot be ensured. Here, the planar shape means a surface state in which the catalyst particles cannot enter into the grooves formed between the catalyst particles as described later.
On the other hand, when the average particle diameter of the catalyst particles is 2 μm and relatively large, the surface of the catalyst layer is uneven as described above, and the surface area of the catalyst layer is large. Can be secured.
Similarly, when the average particle diameter of the catalyst particles is larger than 6.3 μm, as shown in FIG. 5, the surface of the catalyst layer has a larger uneven shape, and the surface area of the catalyst layer is sufficiently large. The PM contact area can be secured.
When the catalyst particles are assumed to be true spheres, when the surface of the catalyst layer is uneven as compared to the case where the surface of the catalyst layer is a perfect plane, the PM contact area is geometrically as described later. To increase. Therefore, it can be seen that the PM contact area can be increased and PM can be efficiently purified by increasing the average particle diameter of the catalyst particles to such an extent that irregularities are formed on the surface of the catalyst layer.

Next, the relationship between the average particle diameter of the catalyst particles and the formation of grooves between the catalyst particles will be described.
First, when the average particle diameter of the catalyst particles is smaller than 0.4 μm, the surface of the catalyst layer is substantially planar as described above, and no groove into which PM can enter is not formed.
On the other hand, when the average particle diameter of the catalyst particles is 2 μm and relatively large, as described above, a large number of grooves are formed between the catalyst particles because the large catalyst particles are adjacent to each other. A large amount of PM enters the inside. At the time of DPF regeneration, a large amount of PM that has entered the groove is easily ignited because it exists in a position closer to Ag, and has good propagation properties and burns efficiently.
On the other hand, when the average particle diameter of the catalyst particles is larger than 6.3 μm, grooves are formed between the catalyst particles as in the case where the average particle diameter of the catalyst particles is 2 μm. However, compared with the case where the average particle diameter of the catalyst particles is 2 μm, the number of grooves into which PM per unit area can enter decreases because the catalyst particles are too large.
Therefore, it can be seen that by setting the average particle diameter of the catalyst particles in an optimal range of 0.4 μm to 6.3 μm, many grooves into which PM can enter between the catalyst particles can be formed, and PM can be burned efficiently.

  From the above, in the present embodiment, the average particle diameter of the Ce-containing oxide on which Ag is supported, that is, the catalyst particles is set to 0.4 μm to 6.3 μm. Therefore, when the average particle diameter of the catalyst particles is less than 0.4 μm, a sufficient PM contact area cannot be obtained. Moreover, since the groove | channel which PM can penetrate | invade between catalyst particles cannot be formed, favorable propagation performance cannot be obtained and PM cannot be purified efficiently. On the other hand, when the average particle diameter of the catalyst particles exceeds 6.3 μm, a sufficient PM contact area can be obtained, but the number of grooves formed between the catalyst particles decreases, so that good propagation performance cannot be obtained. PM cannot be purified efficiently. In addition, the more preferable average particle diameter of the catalyst particles is 0.8 μm to 5 μm.

  In this embodiment, the average particle diameter of the catalyst particles can be set by adjusting the milling time. By setting the milling time to be long, the average particle diameter of the catalyst particles can be reduced, and the shape of the catalyst particles can be made spherical as described later.

  The average particle diameter of the catalyst particles in the present embodiment is measured by observing the surface of the formed catalyst layer with an SEM after firing an Ag-based catalyst supported on a DPF. More specifically, first, the surface of the catalyst layer is enlarged and observed at a magnification of 500 times using a commercially available SEM. Next, in the obtained observed image, the minor axis and the major axis are measured for each of 20 arbitrarily selected catalyst particles, and the average value of these measured values is taken as the average particle diameter of the catalyst particles.

Here, the contact area between the catalyst particles and PM will be described in more detail.
First, as a premise, the catalyst particle diameter is uniform, the catalyst particles are arranged side by side, the catalyst particles do not overlap, and the contact area between the catalyst particles and the PM is a hemisphere when the catalyst particles are assumed to be true spheres. The surface area of Under such a premise, for example, when the average particle diameter of the catalyst particles is the lower limit of 0.4 μm, the surface area of the hemisphere = 4 × 3.14 × (0.4 / 2) ² /2=0.25 μm ² . Further, when 10 μm × 10 μm = 100 μm ² is defined as one unit, the number of catalyst particles entering one unit is (10 / 0.4) × (10 / 0.4) = 625. Then, the contact area between the catalyst particles and PM is 0.25 × 625 = 157 μm ² . Accordingly, the area is 1.57 times the area of 100 μm ² when one unit is a flat surface, and it can be regarded as a flat surface without forming grooves into which PM can enter as described above (that is, the average particle diameter of the catalyst particles is It can be seen that when the average particle size is 0.4 μm or more, the contact area is 1.57 times or more of the plane, and the contact area increases when the average particle size is 0.4 μm or more.

Next, the grooves between the catalyst particles will be described in more detail.
As described above, PM that has entered the groove contributes to the improvement of the propagating property, but the improvement of the propagating property is determined by the number of grooves and is considered not to depend on the catalyst particle size. For example, when considering the depth of the groove effective for improving the propagation property, if the groove depth is effective for improving the propagation property up to 2 μm in the depth direction, both the 2 μm catalyst particle and the 6.3 μm catalyst particle propagate. This is because the groove depth of 2 μm, which is effective for improving the property, does not change.

FIG. 6 is a view showing a packed structure of catalyst particles. Specifically, (a) shows a close-packed structure, and (b) shows a non-close-packed structure. In any of these structures, the contact area between the catalyst particles and PM is still the surface area of the hemisphere of the particles.
In the case of the close-packed structure as shown in FIG. 6A, the largest number of grooves are formed, and grooves twice as many as the number of catalyst particles are formed. On the other hand, in the non-close-packed structure as shown in FIG. 6B, the same number of grooves as the number of catalyst particles are formed. As described above, since the number of catalyst particles entering one unit when 100 μm ² squares per unit is 625, for example, when the average particle diameter of the catalyst particles is the lower limit of 0.4 μm, Since the particle diameter is small, the close-packed structure shown in FIG. 6A is formed, and 625 × 2 = 1250 grooves are formed. Further, for example, when the average particle diameter of the catalyst particles is the upper limit value of 6.3 μm, the particle diameter is relatively large, so that the non-close-packed structure shown in FIG. 6B is obtained (10 / 6.3). X (10 / 6.3) = 2.5 grooves are formed. Therefore, it can be seen that 2.5 to 1250 grooves are formed when the average particle diameter of the catalyst particles is 0.4 to 6.3 μm. That is, it can be seen that the number of grooves formed between the catalyst particles is preferably 2.5 to 1250 per 10 μm square of the catalyst surface.
Further, when calculated in the same manner, it can be seen that when the average particle diameter of the catalyst particles is 0.8 μm to 5 μm, 4 to 156 grooves are formed, and the number of grooves formed between the catalyst particles. Is more preferably 4 to 156 per 10 μm square of the catalyst surface.

Moreover, it is preferable that the shape of the catalyst particle of this embodiment is spherical. The spherical shape in the present embodiment widely includes shapes other than a rectangular parallelepiped, and includes a distorted shape having a polygonal cross section in addition to a perfect circle and an ellipse. When the shape of the catalyst particles is, for example, a needle shape, the PM contact area cannot be fully exerted by folding, but if it is spherical, the PM contact area can be reliably increased compared to other shapes. In addition, since the catalyst particles are spherical, the catalyst particles can be packed most closely in the catalyst layer. Therefore, the number of grooves between the catalyst particles can be optimized, and PM can be purified more efficiently.
More specifically, the catalyst particles of the present embodiment preferably have a particle diameter aspect ratio of 1.5 or less of 60% or more. Thereby, the shape of the catalyst particle of this embodiment becomes spherical.

In the exhaust purification filter according to the present embodiment, a fine foaming method using citric acid or the like is preferably employed in addition to the dipping method.
In the dipping method, for example, a slurry containing a predetermined amount of a constituent material of an Ag-based catalyst is prepared by wet pulverization or the like. After the DPF is immersed in the prepared slurry, the DPF is pulled up and fired at a predetermined temperature condition. Thus, an Ag-based catalyst can be supported on the DPF.
In the fine foaming method, an organic acid such as citric acid is added to the slurry produced as described above to foam and disperse the catalyst particles during firing. Thereby, the catalyst particles are dispersed and supported on the entire DPF, and the Ag-based catalyst can be uniformly supported on the surface of the DPF.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

  Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[Examples 1-8, Comparative Examples 1-3]
An Ag-based catalyst was prepared according to the following procedure at the ratio shown in Table 1.
First, a predetermined amount of CePrLaSiO ₂ , Ag nitrate Ag, and Pd nitrate calcined at 1100 ° C. × 2 hours was put in an eggplant flask and then dried under reduced pressure in an evaporator. Then, after further drying in an electric furnace, baking was performed at 700 ° C. for 2 hours.
Next, 5% by mass of an aqueous medium and Si sol was added to the catalyst, and then mixed with a ball mill to form a slurry, and citric acid was mixed as a dispersant.
Next, an Ag-based catalyst was supported on the DPF by dipping. Then, DPF with an Ag type catalyst was obtained by baking at 700 ° C. for 2 hours.
The difference in the average particle size of the catalyst in Table 1 was obtained by changing the milling time. As the DPF, an NGK honeycomb structure (inner diameter 30 mm, wall thickness 12 mil, cell number 300, material SiC) was used.

[Average catalyst particle size]
The catalyst average particle diameter of the obtained DPF with an Ag-based catalyst was measured by SEM observation. More specifically, first, the surface of the catalyst layer was enlarged and observed using a commercially available SEM. An example of the obtained SEM image is shown in FIG. Next, in the obtained SEM image, the short diameter and the long diameter were measured for each of 20 arbitrarily selected catalyst particles, and the average value of these measured values was taken as the average particle diameter of the catalyst particles. The measurement results are shown in Table 1. The catalyst particles of this example were all spherical.

[PM purification rate evaluation]
First, 6.5 g / L of PM was captured by introducing the exhaust of an actual engine into each Ag-based catalyst-provided DPF obtained in Examples and Comparative Examples. Next, each DPF with an Ag-based catalyst that captured PM was heated to 600 ° C. in a nitrogen atmosphere and stabilized. Next, exhausted model gas (O ₂ = 3%, NO = 75 ppm, N ₂ balance gas, SV = 100,000 / hour) was introduced at once to burn and remove the trapped PM. Then, using the CO and CO ₂ emission at this time as an index, a time T90 until 90% of PM was burned and removed was obtained.

  FIG. 8 is a graph showing the relationship between T90 and the average catalyst particle size in Examples 1 to 3 and Comparative Examples 1 to 3. As shown in FIG. 8, Examples 1 to 8 in which the catalyst average particle diameter is in the range of 0.4 μm to 6.3 μm are comparative examples in which the catalyst average particle diameter is outside the range of 0.4 μm to 6.3 μm. It was found that T90 time was shorter than 1 to 3. From this result, it was confirmed that the PM can be efficiently purified when the average particle diameter of the catalyst particles is 0.4 μm to 6.3 μm. Moreover, from the result of FIG. 8, it was confirmed that the more preferable range of a catalyst average particle diameter is 0.8 micrometer-5 micrometers.

Claims (3)

An exhaust purification filter that is provided in an exhaust passage of an internal combustion engine and captures and purifies particulate matter in the exhaust of the internal combustion engine,
A filter substrate;
A catalyst layer formed on the filter substrate and oxidizing and purifying the particulate matter,
The catalyst layer has a Ce-containing oxide containing Ce, and Ag supported on the Ce-containing oxide,
The content of Ag in the catalyst layer is 15% by mass to 50% by mass,
In the SEM image obtained by magnifying and observing the Ce-containing oxide supporting Ag, the average value of measured values obtained by measuring the minor axis and the major axis of each of 20 arbitrarily selected particles is the average grain size. The average particle diameter when the diameter is 0.4 μm to 6.3 μm,
The exhaust gas purification filter according to claim 1, wherein the particles having an aspect ratio of a particle diameter of 1.5 or less are 60% or more . In the SEM image obtained by magnifying and observing the Ce-containing oxide supporting Ag, the average value of measured values obtained by measuring the minor axis and the major axis of each of 20 arbitrarily selected particles is the average grain size. 2. The exhaust gas purification filter according to claim 1, wherein an average particle diameter is 0.8 μm to 5 μm.   The number of grooves formed between the Ce-containing oxides on which Ag is supported is 2.5 to 1250 per 10 μm square of the surface of the catalyst layer. Exhaust purification filter.