JP2014050808A - Exhaust gas cleaning filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning filter including an Ag-based catalyst, the exhaust gas cleaning filter enabling contact property of a catalyst and PM to be improved, and thereby capable of effectively cleaning PM by a small catalyst supporting amount.SOLUTION: The exhaust gas cleaning filter includes: a filter body which has pores having an average pore diameter of 20-35 μm, thereby having a rugged surface; and a catalyst coating film that is supported on a surface of the filter body and comprises an Ag-based catalyst cleaning a captured particulate substance, where a supported amount of the Ag-based catalyst is 10-45 g/L per a unit volume of the filter body, thereby the catalyst coating film is supported in a rugged state along the ruggedness of a surface of the filter body. A surface of the catalyst coating film is observed by enlarging the same by 3,000 times, and a surface observation image including the pores of the average pore diameter is obtained. The obtained surface observation image is three dimensionally processed to obtain dimensional image information. A surface area of a surface of the catalyst coating film calculated based on the three dimensional image information is 2,300-2,950 μm.

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. This Ag-based catalyst contains Ag that burns PM by releasing active oxygen, and has a characteristic that the contact property with PM greatly affects the PM purification rate. For this reason, various techniques for improving the contact between the Ag-based catalyst and PM have been proposed.

For example, a technique has been proposed in which a needle-shaped substance such as TiO ₂ is contained in an Ag-based catalyst to form a void having a predetermined size in the catalyst layer (see Patent Document 1). According to this technique, since PM can be penetrated into the voids in the catalyst layer, PM can be prevented from being deposited in a layered manner on the surface of the filter. As a result, it is said that a good contact state between the Ag-based catalyst and PM can be ensured (that is, a large contact area can be ensured), and PM can be purified more efficiently than in the past.

  In addition, for example, a technique for improving the coverage of an Ag-based catalyst by supporting an Ag-based catalyst on a DPF by a fine foaming method using citric acid or the like has been proposed (see Patent Document 2). According to this technique, since the surface of the DPF can be sufficiently covered with the Ag-based catalyst, a good contact state between the Ag-based catalyst and the PM can be secured, and the PM can be purified more efficiently than in the past.

  Further, for example, a technique has been proposed in which the surface of each ceramic particle constituting the cell wall of the DPF is individually covered with a catalyst layer (see Patent Document 3). Although this technique is not a technique aimed at improving the contact between the catalyst and PM, as a result, the contact between the catalyst and PM is improved.

JP 2011-36742 A JP 2010-264359 A Japanese Patent No. 4275406

  However, in the technique of Patent Document 1, although it is ideal to form a needle-like structure in an Ag-based catalyst in which good contact with PM is important, in reality, it is formed by containing a needle-like substance. It was not easy to infiltrate PM into the voids in the catalyst layer and burn it. Specifically, a so-called cake layer of PM is formed on the catalyst layer, and as a result, the amount of PM that can enter into the voids in the catalyst layer becomes small, so that good contact between the catalyst and PM may not be ensured. there were.

  In the technique of Patent Document 2, it is important to improve the coverage of the DPF surface with a catalyst. However, in order to improve the coverage, it is necessary to increase the amount of catalyst supported (the amount of washcoat WC). It was. Therefore, as a result of the DPF pores being buried in the catalyst layer by a large amount of catalyst, there is a possibility that good contact between the catalyst and PM cannot be ensured.

  In the technique of Patent Document 3, since the surface of each ceramic particle itself constituting the cell wall of the DPF is individually covered with a catalyst layer, the amount of catalyst supported (wash coat amount) becomes excessive. On the other hand, since it has been found by the applicant's investigation that PM can only enter the surface on the exhaust inflow side of the DPF and the pores in the vicinity of the surface, the catalyst inside the cell wall is PM. It could not contribute to combustion, and was not preferable from the viewpoint of effective utilization of the catalyst. In addition, this technique has a problem that the manufacturing process becomes complicated.

  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 with a small amount of catalyst supported, and can effectively purify PM. To provide a filter.

In order to achieve the above object, an exhaust purification filter (for example, exhaust purification filters 1 and 2 described later) according to the present invention is provided in an exhaust passage of the internal combustion engine, and particulate matter (for example, described later) in the exhaust of the internal combustion engine. PM5) is an exhaust purification filter that captures and purifies the filter body, and has an average pore diameter of 20 to 35 μm (for example, pores 13 and 23 to be described later) so that the surface of the filter body is uneven (for example, DPF 11 and 21), which will be described later, and a catalyst film (for example, catalyst films 12 and 22 which will be described later) made of an Ag-based catalyst that purifies the particulate matter supported and trapped on the surface of the filter body. When the loading amount of the system catalyst is 10 to 45 g / L per unit volume of the filter main body, the catalyst coating is supported unevenly along the unevenness of the surface of the filter main body. The surface of the catalyst coating was magnified 3000 times to obtain a surface observation image including pores having the average pore diameter (for example, FIG. 11 described later), and obtained by three-dimensionally processing this image 3 The surface area of the surface of the catalyst coating calculated based on the dimensional image information is 2300-2950 μm ² .

In the present invention, an Ag-based catalyst having a pore having an average pore diameter of 20 to 35 μm and having a surface with an uneven surface and having a smaller supported amount (wash coat WC amount) of 10 to 45 g / L than before. Is supported. Thus, in the exhaust purification filter according to the present invention, the catalyst coating made of an Ag-based catalyst is supported in an uneven shape along the unevenness of the surface of the filter body, and the unevenness due to the pores of the filter body is maintained. In addition, the surface of the catalyst coating was magnified 3000 times to obtain a surface observation image including pores having an average pore diameter, and this was calculated based on the three-dimensional image information obtained by three-dimensional processing. The surface area (hereinafter referred to as “morphological index”) of the surface of the catalyst coating is 2300-2950 μm ² which is larger than the conventional one.
According to the present invention, in an exhaust purification filter including an Ag-based catalyst having a characteristic that the contact property with PM greatly affects the PM purification rate, a larger morphological index than the conventional one can be obtained with a smaller amount of supported catalyst. It is done. Therefore, the contact property between the catalyst and PM can be improved (the contact area can be increased), and PM can be efficiently burned and purified. As a result, since the regeneration speed of the exhaust purification filter can be improved and the regeneration time can be shortened, deterioration of fuel consumption and EM due to regeneration and thermal deterioration of the catalyst can be suppressed.

  In this case, it is preferable that the Ag-based catalyst contains a convex material having a convex shape, and the amount of the convex material supported is 5 to 45 g / L per unit capacity of the filter body.

  In this invention, a convex material is contained in the Ag-based catalyst, and the amount of the convex material supported is 5 to 45 g / L. Thereby, a finer uneven shape can be formed on the surface of the catalyst coating formed in an uneven shape along the unevenness of the filter body surface. Therefore, a larger morphological index can be obtained, the contact property between the catalyst and PM can be further improved, and the effect of the invention can be enhanced.

  In this case, it is preferable that the convex material has a needle-like structure, a flower-like structure, a plate-like structure, or a dish-like structure.

  In the present invention, a convex material having a needle-like structure, a flower-like structure, a plate-like structure or a dish-like structure is contained in the Ag-based catalyst. Thereby, the effect of the said invention is exhibited reliably.

  In this case, it is preferable that the convex material includes an oxygen releasing material having an oxygen releasing ability.

  In this invention, the oxygen releasing material provided with oxygen releasing ability shall be included as a convex material contained in Ag type catalyst. Thereby, PM combustion by discharge | release of active oxygen can be accelerated | stimulated and PM can be purified more efficiently.

  In this case, it is preferable that the cell shape of the filter main body is any one of 4-8 octagons, and the number of cells of the filter main body is 200-400 cells per square inch.

  In the present invention, the cell shape of the filter body is any one of 4 to 8 squares, and the number of cells of the filter body is 200 to 400 cells per square inch. That is, the cell shape is a polygonal shape and the number of cells is increased. Thereby, a larger morphological index can be obtained, and the contact area between the catalyst and PM can be increased, so that the effects of the above-described inventions can be enhanced.

  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 with a small catalyst carrying amount, and the exhaust gas purification filter which can purify PM efficiently can be provided.

It is a cross-sectional observation image of the DPF surface where PM deposited. It is a figure for demonstrating the PM combustion mechanism of Ag type catalyst. It is sectional drawing which shows the catalyst film of this embodiment formed in uneven | corrugated shape along the unevenness | corrugation by the pore of the DPF surface. It is sectional drawing which shows the catalyst film of this embodiment formed in uneven | corrugated shape along the unevenness | corrugation by the pore of a DPF surface, and the fine unevenness | corrugation was formed in the surface. It is an enlarged observation image of a convex material having a flower-like structure It is an enlarged observation image of a convex material having a plate-like structure and a dish-like structure. It is a figure which shows the relationship between a morphology index and a 2-minute reproduction | regeneration speed. 4 is a surface observation image (250 times image) of a catalyst surface in an exhaust purification filter of Comparative Example 1; 10 is a surface observation image (200-fold image) of a catalyst surface in an exhaust purification filter of Comparative Example 2. 2 is a surface observation image (200-fold image) of a catalyst surface in the exhaust gas purification filter of Example 1. FIG. 2 is a surface observation image (3000 times image) of a catalyst surface in the exhaust gas purification filter of Example 1. FIG. It is a figure which shows the relationship between the average pore diameter of DPF, and a 2 minute regeneration speed. It is a figure which shows the relationship between the load of a catalyst, and a 2 minute regeneration speed. For needle-shaped exhaust gas purifying filter that the amount of supported catalyst film made of Ag-based catalyst was 100 g / L containing CeO _2, a cross-sectional observation image obtained with near-surface and cross-sectional observation. For needle-shaped exhaust gas purifying filter that the amount of supported catalyst film made of Ag-containing catalyst containing CeO ₂ was 30 g / L, a cross-sectional observation image obtained with near-surface and cross-sectional observation.

  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 main body and a catalyst coating made of an Ag-based catalyst supported 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 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.

  Further, the DPF of this embodiment has pores having an average pore diameter (pore diameter) of 20 to 35 μm. Moreover, the surface is formed in uneven | corrugated shape by having these pores. Thereby, a large morphological index as described later is obtained. Thereby, PN regulation can be cleared, and a DPF having sufficient mechanical strength can be obtained.

  Here, FIG. 1 is a cross-sectional observation image of the DPF surface on which PM is deposited. As shown in FIG. 1, PM can only enter the surface on the exhaust inflow side of the DPF and the extremely shallow pores in the vicinity of the surface. Specifically, as shown in FIG. 1, the average penetration depth of PM into the DPF surface is 35 μm. Therefore, in order to improve the contact property between the catalyst and the PM, it can be said that the contact property between the catalyst and the PM in the vicinity of the DPF surface is important. Therefore, in this embodiment, as will be described later, a three-dimensional image in the vicinity of the DPF surface is analyzed to calculate a morphological index as a surface area index, and this is set to a larger value than before, thereby improving PM combustion performance. It is something to be made.

  The catalyst coating of the present embodiment is composed of an Ag-based catalyst mainly containing Ag as a catalyst metal. 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 with reference to FIG.
FIG. 2 is a diagram for explaining the PM combustion mechanism of the Ag-based catalyst, and more specifically, a diagram schematically showing the surface state of Ag / CeZrO ₂ .
Here, in the Ag-based catalyst, it is known that Ag near the surface exists as Ag ₂ O in an oxidizing atmosphere and as Ag metal in a reducing atmosphere. Ag ₂ O has the lowest oxygen desorption energy and is considered to be the most effective compound for PM combustion.

As shown in FIG. 2, when oxygen is supplied from CeZrO ₂ as a catalyst carrier having oxygen releasing ability to Ag metal in the vicinity of the surface (meaning particles displayed as Ag ^{0 in} FIG. 2), Ag The metal is converted into Ag ₂ O which is an active species (meaning particles indicated as Ag ⁺ and particles indicated as O ^* in FIG. 2). Then, the Ag ₂ O, although returns to Ag metal by reacting with PM, results immediately oxygen from CeZrO ₂ is supplied to the Ag metal, always Ag near the surface is present in the form of Ag ₂ O .
Therefore, this Ag-based catalyst can efficiently burn and remove PM at a low temperature by the action of the active species Ag ₂ O present near the surface.

In the Ag-based catalyst of the present embodiment, an oxide or composite oxide having oxygen releasing ability is preferably used as a catalyst carrier that supports Ag as a catalyst metal. Specifically, CeO ₂ or CeZrO ₂ is preferably used. Thereby, the stability of Ag ₂ O is ensured by the oxygen released from the oxide or composite oxide having oxygen releasing ability.

As the complex oxide having oxygen releasing ability, at least one selected from the group consisting of perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, ilmenite type, and fluorite type should be used. Can do. 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 this embodiment, the supported amount of the Ag-based catalyst is 10 to 45 g / L per unit capacity of DPF. As a result, a catalyst film made of an Ag-based catalyst is formed so as to cover the entire surface of the DPF, and at the same time, is formed in an uneven shape along the unevenness of the DPF surface. FIG. 3 is a cross-sectional view showing the catalyst coating of the present embodiment formed in an uneven shape along the unevenness due to the pores on the DPF surface. From FIG. 3, it can be seen that in the exhaust purification filter 1 of this embodiment, the irregularities due to the pores 13 on the surface of the DPF 11 are maintained without being buried in the catalyst coating 12.

  The Ag-based catalyst of the present embodiment preferably contains a convex material having a convex shape. The convex material may be a catalyst carrier such as the above-mentioned oxide or composite oxide. By including the convex material in the Ag-based catalyst, a finer uneven shape is formed on the surface of the catalyst film formed in an uneven shape along the unevenness of the surface of the filter body. FIG. 4 is a cross-sectional view showing the catalyst coating of the present embodiment, which is formed in an uneven shape along the unevenness due to the pores on the DPF surface, and in which fine unevenness is formed on the surface. From FIG. 4, it can be seen that in the exhaust purification filter 2 of the present embodiment, fine irregularities are formed on the surface of the catalyst coating 22 that is irregularly formed along the irregularities formed by the pores 23 on the surface of the DPF 21. .

  The convex material preferably has a needle-like structure, a flower-like structure, a plate-like structure, or a dish-like structure. Here, FIG. 5 is an enlarged observation image of a convex material having a flower-like structure. FIG. 6 is an enlarged observation image of a convex material having a plate-like structure and a dish-like structure. By including the convex material having these structures in the Ag-based catalyst, the above-described fine uneven shape can be reliably formed.

Moreover, it is preferable that a convex material contains the oxygen releasing material provided with oxygen releasing ability. As the oxygen release material, a material containing Ce is preferable, and examples thereof include CeO ₂ and CeZrO ₂ . Moreover, what carried | supported the oxygen releasing material the film can also be used. By containing the convex material having the oxygen releasing ability in the Ag-based catalyst, PM combustion due to the release of active oxygen from the Ag-based catalyst is promoted.

  The carrying amount of the convex material is preferably 5 to 45 g / L per unit capacity of the DPF. When the carrying amount of the convex material is within this range, the fine concave and convex shape is more reliably formed.

As described above, the catalyst coating of the present embodiment is formed so as to cover the entire surface of the DPF, and at the same time, is formed in an uneven shape along the unevenness of the DPF surface. Then, the surface of the catalyst coating was magnified 3000 times to obtain a surface observation image including pores having an average pore diameter, and calculated based on three-dimensional image information obtained by three-dimensional processing. The surface area of the surface of the catalyst coating is 2300-2950 μm ² . The surface area calculated in this way is defined as “morphological index”. This morphological index is a surface area calculated in consideration of the fine uneven structure of the catalyst shape by observing the surface of the catalyst shape at a high magnification, and is a new index for judging the contact property between the catalyst and PM.
In the present embodiment, since the catalyst is supported on the film, the contact area between the catalyst and the PM greatly depends on the surface shape of the DPF.

The details of the calculation method of the morphological index are as follows.
For example, using a scanning electron microscope apparatus “Minscope (registered trademark) TM3000” manufactured by Hitachi, Ltd., the surface of the catalyst coating of the exhaust purification filter is magnified 3000 times to perform three-dimensional observation. Specifically, a pore having an average pore diameter of DPF known in advance is searched, and a surface observation image including the pore (for example, FIG. 11 described later) is photographed, and then the 3D processing is performed to obtain the three-dimensional image. Get an image. At this time, it is preferable to extract an image that makes the observation surface as flat as possible, and at the same time, perform flat correction of the apparatus software incidental to obtain a more accurate three-dimensional image. Next, assuming that the pores are uniformly distributed throughout the DPF, the surface area of the device software incidental surface is calculated based on the acquired three-dimensional image information, and the surface area of the catalyst-shaped surface is calculated.
The apparatus includes a backscattered electron detector arranged in four parts, and performs sample tilt and visual field alignment in order to calculate the surface shape in four directions using each signal acquired by these detectors. 3D information can be acquired without any problem.

As described above, the morphological index of the catalyst coating of the present embodiment is in the range of 2300-2950 μm ² . When the morphological index is less than 2300 μm ² , pores into which PM can enter cannot be formed, and when it exceeds 2950 μm ² , the mechanical strength of the DPF is insufficient and the catalyst coating is peeled off.

The lower limit value of the morphological index is obtained from the fact that the slope of the curve changes at 2300 μm ² in FIG. 7 showing the relationship between the morphological index and the regeneration speed in Examples and Comparative Examples described later.
In addition, the upper limit of the morphological index is an aspect in which the surface area is the largest, based on the results of Examples and Comparative Examples described later, and the DPF has a maximum pore diameter of 35 μm and contains a convex material having a flower structure. It is calculated | required by calculating the surface area at the time.
Specifically, the surface area (morphological index) of the catalyst coating of Example 1 in which the pore size of DPF is 23 μm is 2534 μm ² , and Example 3 in which CeZrO ₂ is changed to needle-like CeO ₂ with respect to Example 1 Since the surface area of the catalyst film is 2582 μm ² , when the pore size of the DPF is 23 μm, the catalyst film when a convex material having a flower structure that can increase the surface area most instead of acicular CeO ₂ is contained. The surface area is estimated to be 2534+ (2582−5344) × 8 = 2922 μm ² because the contact area is estimated to be 8 times from the shape.
Next, from the linear form based on the surface area 2534 μm ² of the catalyst coating when the pore size of the DPF is 23 μm and the surface area of the catalyst coating 2552 μm ² when the pore size of the DPF is 30 μm, the maximum pore size of the DPF is 35 μm. When the surface area is calculated as 2.6826 × 35 + 2471.9 = 2565 μm ^2, and based on this calculation result and the above calculation result, the DPF has a maximum pore diameter of 35 μm and contains a convex material having a flower structure Is determined to be 2566 × 2922 / 2534≈2950 μm ² .

In the present embodiment, as a method for supporting Ag on the catalyst carrier, 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.

According to the present embodiment having the above configuration, the following effects can be obtained.
In this embodiment, an Ag-based catalyst having a pore with an average pore diameter of 20 to 35 μm and having a surface with an uneven surface and a smaller supported amount (wash coat WC amount) of 10 to 45 g / L than conventional ones. Was supported. Thereby, in the exhaust purification filter according to the present embodiment, the catalyst coating made of an Ag-based catalyst is supported in an uneven shape along the unevenness of the surface of the DPF, and the unevenness due to the pores of the DPF is maintained. Moreover, the morphology index is 2300-2950 μm ² which is larger than the conventional one.
According to the present embodiment, in an exhaust purification filter including an Ag-based catalyst having a characteristic that the contact property with PM greatly affects the PM purification rate, a larger morphological index than the conventional one is obtained with a smaller catalyst loading than the conventional one. can get. Therefore, the contact property between the catalyst and PM can be improved (the contact area can be increased), and PM can be efficiently burned and purified. As a result, since the regeneration speed of the exhaust purification filter can be improved and the regeneration time can be shortened, deterioration of fuel consumption and EM due to regeneration and thermal deterioration of the catalyst can be suppressed.

  Moreover, in this embodiment, the convex material was contained in the Ag-based catalyst, and the amount of the convex material supported was 5 to 45 g / L. Thereby, a finer uneven shape can be formed on the surface of the catalyst coating formed in an uneven shape along the unevenness of the DPF surface. Therefore, a larger morphological index can be obtained, the contact property between the catalyst and PM can be further improved, and the above effect can be enhanced.

  In this embodiment, the Ag-based catalyst contains a convex material having a needle-like structure, a flower-like structure, a plate-like structure, or a dish-like structure. Thereby, said effect is exhibited reliably.

  Moreover, in this embodiment, the oxygen releasing material provided with oxygen releasing ability was included as the convex material contained in Ag type catalyst. Thereby, PM combustion by discharge | release of active oxygen can be accelerated | stimulated and PM can be purified more efficiently.

  In the present embodiment, the cell shape of the DPF is any one of 4-8 octagons, and the number of DPF cells is 200-400 cells per square inch. That is, the cell shape is a polygonal shape and the number of cells is increased. Thereby, since a larger morphological index is obtained and the contact area between the catalyst and PM can be increased, each of the above effects can be enhanced.

  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.

<Example 1>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst coating load = 25 g / L, filter average pore diameter 23 μm]
Commercially available special grade silver nitrate, palladium nitrate, CeZrO ₂ (manufactured by Anan Kasei, Ce / Zr = 2/8), and water were weighed and mixed so as to have a predetermined composition. Next, this was dried under reduced pressure using an evaporator, dried at 200 ° C. for 2 hours, and then fired in the atmosphere at 700 ° C. for 2 hours to obtain catalyst powder A.

Catalyst powder A obtained as described above, commercially available SiO ₂ sol and water were weighed and mixed so as to have a predetermined composition. Thereto, a Zr ball having a diameter of 2 mm was mixed in an amount of 50% with respect to the container, and wet pulverization was performed in a ball mill for 3 days to obtain slurry A.

  To the slurry A obtained as described above, 4 times the amount of citric acid relative to the amount of catalyst was added and mixed thoroughly to dissolve the citric acid. Subsequently, this was dipped on SiC DPF (average pore diameter 23 μm, 300 cells per square inch, cell shape quadrangular), and then fired at 700 ° C. for 2 hours. Thereby, the exhaust gas purification filter of Example 1 was obtained. The catalyst loading was adjusted to be 25 g / L.

<Example 2>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst coating load = 25 g / L, filter average pore diameter 30 μm]
The same operation as in Example 1 was performed, except that a DPF made of SiC having an average pore diameter of 30 μm (the number of cells and the cell shape were the same as in Example 1) was used. As a result, an exhaust purification filter of Example 2 was obtained. The catalyst loading was adjusted to be 25 g / L.

<Example 3>
[1.7% by mass Pd 50% by mass Ag / needle-like CeO ₂ , catalyst coating load = 25 g / L, filter average pore diameter 23 μm]
First, cerium nitrate, oxalic acid and water, which are commercially available special grade reagents, were weighed and mixed so as to have a predetermined composition. Next, the mixed solution was allowed to stand at room temperature for 24 hours, and then the supernatant was removed and dried at 100 ° C. for 24 hours. The precursor obtained by drying was fired at 300 ° C. for 6 hours, then heated to 400 ° C. over 30 minutes, and then fired at 400 ° C. for 3 hours. Thereby, acicular CeO ₂ powder was obtained.

The needle-like CeO ₂ powder obtained as described above and commercially available special grade silver nitrate, palladium nitrate and water were weighed and mixed so as to have a predetermined composition. Next, this was dried under reduced pressure with an evaporator, dried at 200 ° C. for 2 hours, and then subjected to air baking at 700 ° C. for 2 hours to obtain catalyst powder B.

Catalyst powder B obtained as described above, commercially available SiO ₂ sol and water were weighed and mixed so as to have a predetermined composition. Thereto, 100 g of a φ10 mm Zr ball was mixed, and wet pulverization was performed for 1 hour in a ball mill to obtain slurry B.

  To the slurry B obtained as described above, 4 times the amount of citric acid relative to the amount of catalyst was added and mixed thoroughly to dissolve the citric acid. Next, this was dipped on the same SiC DPF as used in Example 1, and then fired at 700 ° C. for 2 hours. As a result, an exhaust purification filter of Example 3 was obtained. The catalyst loading was adjusted to be 25 g / L.

<Comparative Example 1>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst loading amount = 25 g / L, filter average pore diameter 23 μm]
Commercially available special grade silver nitrate, palladium nitrate, CeZrO ₂ (manufactured by Anan Kasei, Ce / Zr = 2/8), and water were weighed and mixed so as to have a predetermined composition. Next, this was dried under reduced pressure with an evaporator, dried at 200 ° C. for 2 hours, and then subjected to air baking at 700 ° C. for 2 hours to obtain catalyst powder C.

Catalyst powder C obtained as described above, commercially available SiO ₂ sol and water were weighed and mixed so as to have a predetermined composition. Thereto, 100 g of φ10 mm Zr balls were mixed, and wet pulverization was performed in a ball mill for 12 hours to obtain slurry C.

  The slurry C obtained as described above was dipped on the same SiC DPF as used in Example 1, and then fired at 700 ° C. for 2 hours. As a result, an exhaust purification filter of Comparative Example 1 was obtained. The catalyst loading was adjusted to be 25 g / L.

<Comparative example 2>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst loading = 80 g / L, filter average pore diameter 23 μm]
The same operation as in Example 1 was performed except that the amount of the catalyst supported was 80 g / L. As a result, an exhaust purification filter of Comparative Example 2 was obtained.

<Comparative Example 3>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst loading = 25 g / L, filter average pore diameter 16 μm]
The same operation as in Example 1 was performed except that a DPF made of SiC having an average pore diameter of 16 μm (the number of cells and the cell shape were the same as in Example 1) was used. As a result, an exhaust purification filter of Comparative Example 3 was obtained.

<Comparative Example 4>
[1.4% by mass Pt / Al ₂ O ₃ , catalyst coating supported, filter average pore diameter 23 μm]
A commercially available special grade reagent, dinitrodiammine platinum nitrate solution, Al ₂ O ₃ and water, were weighed and mixed so as to have a predetermined composition. Thereafter, the same operation as in Comparative Example 1 was performed. As a result, an exhaust purification filter of Comparative Example 4 was obtained.

<Comparative Example 5>
[1.4% by mass Pt / Al ₂ O ₃ , catalyst coating supported, filter average pore diameter 23 μm]
A commercially available special grade reagent, dinitrodiammine platinum nitrate solution, Al ₂ O ₃ and water, were weighed and mixed so as to have a predetermined composition. Thereafter, the same operation as in Example 1 was performed. As a result, an exhaust purification filter of Comparative Example 5 was obtained.

<Comparative Example 6>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst coating load = 25 g / L, filter average pore diameter 36 μm]
The same operation as in Example 1 was performed except that a DPF made of SiC having an average pore diameter of 36 μm (the number of cells and the cell shape were the same as in Example 1) was used. As a result, an exhaust purification filter of Comparative Example 6 was obtained. The catalyst loading was adjusted to be 25 g / L.

<Comparative Example 7>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst loading = 9 g / L, filter average pore diameter 23 μm]
The same operation as in Example 1 was performed except that the amount of the catalyst supported was 9 g / L. As a result, an exhaust purification filter of Comparative Example 7 was obtained.

<Comparative Example 8>
[1.7% by mass Pd 50% by mass Ag / CeZrO ₂ , catalyst loading = 47 g / L, filter average pore diameter 23 μm]
The same operation as in Example 1 was performed except that the amount of catalyst supported was adjusted to 47 g / L. Thereby, an exhaust purification filter of Comparative Example 8 was obtained.

<Evaluation>
For the exhaust purification filters obtained in each of the examples and comparative examples, the morphology index was calculated according to the following calculation method. In addition, the regeneration speed of each exhaust purification filter was evaluated according to the following evaluation method.

[Morphological index]
Using a scanning electron microscope apparatus “Miniscope (registered trademark) TM3000” manufactured by Hitachi, Ltd., the surface of the catalyst coating of each exhaust purification filter was magnified 3000 times to perform three-dimensional observation. Specifically, a pore having an average pore diameter of DPF known in advance was searched, a surface observation image including the pore was photographed, and then a 3D process was performed to obtain a three-dimensional image. At this time, an image in which the observation surface was as flat as possible was extracted, and at the same time, the flat correction of the apparatus software was performed to obtain a more accurate three-dimensional image. Next, assuming that the pores are uniformly distributed throughout the DPF, the surface area of the apparatus software incidental surface was calculated based on the acquired three-dimensional image information, and the surface area of the catalyst coating surface was calculated.

[Playback speed]
TP sizes (15 cc) for each exhaust purification filter were prepared, and PM collected from the actual machine was collected by suction. Then, after setting the filter inlet temperature to 500 ° C. and the filter internal temperature to 530 ° C., each model gas composed of 11% O ₂ , 150 ppm NO and N ₂ balance gas is exhausted at a space velocity SV = 100000h ^−1. It was introduced into the purification filter and regenerated. The regeneration rate mg / min, which is the amount of PM removed for 2 minutes from the start of regeneration, was measured.

FIG. 7 is a diagram showing the relationship between the morphology index and the 2-minute regeneration speed based on the evaluation results of the examples and comparative examples. In FIG. 7, the horizontal axis represents the morphology index (μm ² ), and the vertical axis represents the 2 minute regeneration rate (mg / second).
As shown in FIG. 7, the exhaust purification filters of Examples 1 to 3 were found to have a significantly higher regeneration speed than the exhaust purification filters of Comparative Examples 1 to 5. The reason will be described in detail below.

  First, the exhaust gas purification filter of Comparative Example 1 is a filter in which an Ag-based catalyst is supported on a DPF by a conventionally known dipping method, and the wet pulverization time is shorter than that of Example 1 and the ball diameter by milling is also reduced. The catalyst particle size is large because it is large. Here, FIG. 8 is a surface observation image of the catalyst surface in the exhaust purification filter of Comparative Example 1. FIG. As is clear from FIG. 8, in the exhaust purification filter of Comparative Example 1, the catalyst is not uniformly supported, and the DPF coverage by the catalyst is low. Therefore, since the morphological index is small and the contact area between the catalyst and PM is small, only a low regeneration rate can be obtained.

  The exhaust purification filter of Comparative Example 2 is a filter in which an Ag-based catalyst is dispersed and supported on DPF by a citric acid foaming method (fine foaming method). Due to the small ball diameter, the catalyst particle diameter is small. However, the catalyst loading is 80 g / L, which is too much. Here, FIG. 9 is a surface observation image of the catalyst surface in the exhaust purification filter of Comparative Example 2. As is clear from FIG. 9, in the exhaust purification filter of Comparative Example 2, since the amount of catalyst supported is too large, the majority of the pores on the DPF surface are buried in the catalyst coating. Therefore, although the contact area between the catalyst and PM is larger than that of Comparative Example 1, the unevenness due to the pores on the DPF surface cannot be used effectively, so the morphological index is smaller than that of the example and the regeneration rate is lower than that of the example.

The exhaust purification filter of Comparative Example 3 has a smaller average pore diameter of DPF of 16 μm than the exhaust purification filter of Example 1. The morphological index of this exhaust purification filter was 2397 μm ^{2 when} calculated according to the above method, but taking into account that PM cannot penetrate into pores having a pore diameter of 16 μm, a surface observation image not containing pores is obtained. Then, the surface area of the catalyst coating was calculated by three-dimensionally processing this. As can be seen from the fact that the average pore diameter of DPF is as small as 16 μm and PM cannot sufficiently penetrate into the pores, the calculated morphological index is small and the contact area between the catalyst and PM is small, so only a low regeneration rate is obtained. I can't.

The exhaust purification filter of Comparative Example 4 has a Pt catalyst supported on the DPF by a conventional dipping method, and the exhaust purification filter of Comparative Example 5 has a Pt catalyst by a foaming method (fine foaming method) using citric acid. Is supported on a DPF. The average pore diameter of the DPF and the amount of the supported catalyst are the same as those in Example 1. Here, these Pt-based catalysts generate NO ₂ from NO in the exhaust, and promote combustion of PM by the generated NO ₂ . That is, the PM combustion mechanism is different from the Ag-based catalyst that burns PM by releasing active oxygen from Ag, and the contact property between the catalyst and PM is not so important in the Pt-based catalyst. Therefore, the morphological index of the exhaust purification filter of Comparative Example 5 prepared by the micro-foaming method is remarkably larger than that of Comparative Example 4, and even if it is at the same level as the Example, it is regenerated by improving the NO ₂ generation ability. The speed is only slightly increased and no significant change is seen.

  In contrast, the exhaust purification filter of Example 1 is obtained by changing the Pt-based catalyst to an Ag-based catalyst with respect to the exhaust purification filter of Comparative Example 5, and at the same time, compared with the exhaust purification filter of Comparative Example 2. The amount of catalyst supported is reduced. Here, FIGS. 10 and 11 are surface observation images of the catalyst surface in the exhaust purification filter of Example 1 (FIG. 10 is a 200 × image, FIG. 11 is a 3000 × image). As is clear from FIGS. 10 and 11, the catalyst is supported thinly and uniformly on the irregularities caused by the pores on the DPF surface. That is, the catalyst film is formed in an uneven shape along the unevenness due to the pores on the DPF surface, and the uneven shape due to the pores on the DPF surface is maintained. Therefore, the morphology index of Example 1 is larger than that of the comparative example. Thereby, in the exhaust purification filter of Example 1, PM can penetrate | invade in a pore, and since the contact area of a catalyst and PM is large, a big regeneration speed is obtained.

  In addition, the exhaust purification filter of Example 2 has a larger average pore diameter of DPF of 30 μm than the exhaust purification filter of Example 1. Therefore, the morphology index of Example 2 is larger than that of Example 1. This makes it easier for PM to penetrate into the pores of the DPF, and the contact area between the catalyst and PM becomes larger, so that a higher regeneration speed can be obtained.

Further, the exhaust purification filter of Example 3 is obtained by changing CeZrO ₂ to needle-like CeO ₂ with respect to the exhaust purification filter of Example 1. That is, in the exhaust purification filter of Example 3, since the needle-like CeO ₂ as the convex material was contained in the catalyst, the surface of the catalyst coating formed in a concavo-convex shape along the concavo-convex shape of the DPF surface was further finer. An uneven shape is formed. Therefore, the morphology index of Example 3 is larger than that of Example 2. As a result, the contact area between the catalyst and PM is further increased, and a higher regeneration speed can be obtained.

  As described above, from the evaluation results of this example and the comparative example, the catalyst film is formed in an uneven shape along the unevenness due to the pores of the DPF (that is, the unevenness due to the pores is maintained), It was confirmed that PM can be efficiently purified by infiltrating PM to improve the contact property between the catalyst and PM. Moreover, it was confirmed that PM can be more efficiently purified by incorporating a convex material in the catalyst to form a finer irregular shape on the surface of the catalyst coating.

Next, FIG. 12 is a diagram showing the relationship between the average pore diameter of DPF and the regeneration rate for 2 minutes based on the evaluation results of the examples and comparative examples. In FIG. 12, the horizontal axis represents the average pore diameter (μm) of the DPF, and the vertical axis represents the regeneration rate (mg / second) for 2 minutes.
As shown in FIG. 12, it was found that the regeneration rate increases as the average pore size of the DPF increases. It was also found that when the average pore size of the DPF was 20 μm or more, the regeneration rate exceeded 20 mg / min. This is because when the average pore diameter of the DPF is 20 μm or more, PM can sufficiently enter the pores.
Further, it was found that, while the average pore diameter of the DPF is 30 μm, the regeneration speed becomes maximum, while when the average pore diameter exceeds 35 μm and becomes 36 μm, the strength of the DPF is reduced and the DPF is crushed after the evaluation. .
From the above results, it was confirmed that the preferable range of the DPF average pore diameter is 20 to 35 μm.

Next, FIG. 13 is a diagram showing the relationship between the amount of catalyst supported and the 2-minute regeneration rate based on the evaluation results of the examples and comparative examples. In FIG. 13, the horizontal axis represents the amount (g / L) of the catalyst film supported, and the vertical axis represents the regeneration rate (mg / second) for 2 minutes.
As shown in FIG. 13, it was found that the regeneration rate increased as the catalyst loading decreased, and the loading was preferably 45 g / L or less. This is because the pores on the surface of the DPF are buried in the catalyst coating when the amount of the catalyst supported is too large.
It was also found that the regeneration rate was maximum when the catalyst loading was 25 g / L, and the loading was preferably 10 g / L or more. This is because if the amount of the catalyst supported is too small, the coverage by the catalyst coating is lowered.
From the above results, it was confirmed that the preferred range of the catalyst loading was 10 to 45 g / L.

Here, FIG. 14 is a cross-sectional observation image obtained by observing a cross section of the vicinity of the surface of an exhaust purification filter in which the supported amount of a catalyst coating made of an Ag-based catalyst containing acicular CeO ₂ is 100 g / L. . FIG. 15 is a cross-sectional observation image obtained by cross-sectional observation of the vicinity of the surface of an exhaust purification filter in which the supported amount of a catalyst coating made of an Ag-containing catalyst containing acicular CeO ₂ is 30 g / L.
As shown in FIG. 14, when the amount of the catalyst coating is too large, the pores on the surface of the DPF are buried in the catalyst coating, so that PM can contact only the outermost surface portion of the catalyst coating. On the other hand, as shown in FIG. 15, when the supported amount of the catalyst film is an appropriate amount, the catalyst film is formed in an uneven shape on the surface while maintaining the uneven shape by the pores on the DPF surface. It was confirmed that the contact property between the catalyst coating and PM was improved.

1, 2 ... Exhaust gas purification filter 11, 21 ... DPF (filter body)
12, 22 ... Catalyst coating 13, 23 ... Pore 5 ... PM (particulate matter)

Claims (5)

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 body having an uneven surface with an average pore diameter of 20 to 35 μm, and a catalyst coating made of an Ag-based catalyst that purifies the particulate matter supported and captured on the surface of the filter body. Prepared,
When the amount of the Ag-based catalyst supported is 10 to 45 g / L per unit volume of the filter body, the catalyst coating is supported in an uneven shape along the surface unevenness of the filter body,
The surface of the catalyst coating was magnified 3000 times to obtain a surface observation image including pores having the average pore diameter, and was calculated based on three-dimensional image information obtained by three-dimensional processing. An exhaust purification filter, wherein the surface area of the catalyst coating is 2300-2950 μm ² . The Ag-based catalyst contains a convex material having a convex shape,
The exhaust purification filter according to claim 1, wherein the carrying amount of the convex material is 5 to 45 g / L per unit capacity of the filter body.   The exhaust purification filter according to claim 2, wherein the convex material has a needle-like structure, a flower-like structure, a plate-like structure, or a dish-like structure.   The exhaust purification filter according to claim 2 or 3, wherein the convex material includes an oxygen release material having an oxygen release capability. The cell shape of the filter body is any one of 4-8 octagons,
The exhaust purification filter according to any one of claims 1 to 4, wherein the number of cells of the filter body is 200 to 400 cells per square inch.