JP2003053117A - Filter for collecting particulate in exhaust gas and method for coating catalyst of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filter for collecting particulates in exhaust gas in which a plurality of cell spaces are formed by partitioning the filter with porous lattice type cell walls of a honeycomb structure and the cell spaces are alternately sealed in such a manner that one cell space between adjacent cell spaces is sealed in the exit side while the other cell space is sealed in the entrance side, the a catalyst is effectively used without loss when the inner face of the cell space 12A where exhaust gas enters is to be coated with the catalyst. SOLUTION: After the corners in the cross section of the cell space 12A where the exhaust gas enters are filled with a porous filler 16 such as alumina, the inner face of the cell space 12A is coated with a catalyst to form a catalyst layer 15. When the catalyst is coated, a slurry prepared by mixing the catalyst component in a fluid medium is passed through the cell walls 11 to deposit the catalyst component on the cell walls 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for collecting exhaust particulates having a catalytic function, which is used as an exhaust purification device for an internal combustion engine, and a method for coating the catalyst on the filter.

[0002]

2. Description of the Related Art In order to prevent air pollution, it is necessary to suppress the release of fine particles (particulate matter; PM) contained in the exhaust gas of internal combustion engines, especially diesel engines, into the atmosphere.
Therefore, an exhaust particulate collection filter (DPF) called an exhaust particulate collection filter has been attached to the exhaust system.

A filter for collecting exhaust particulates is disclosed in Japanese Unexamined Patent Publication No. Sho 56-56.
As described in Japanese Patent Publication No. 148607, a honeycomb structure is formed, and a plurality of cell spaces are provided by being partitioned by the porous lattice-shaped cell walls, and adjacent cell spaces are adjacent to each other. The outlet side and the other cell space are alternately sealed (filled) at the inlet side, and exhaust gas from the internal combustion engine flows into the cell space where the inlet side is open and the outlet side is sealed, and the porous Through the cell wall (its pores),
When flowing out into a cell space where the inlet side is sealed and the outlet side is open, the fine particles in the exhaust gas are collected by the cell wall.

Further, by coating the catalyst on the inner surface of at least one of the cell spaces on the exhaust inflow side or the exhaust outflow side (the surface of the cell wall facing the cell space), the effect of this catalyst is achieved. , HC in the exhaust,
We are trying to purify NO etc. at the same time. by the way,
As a method of coating the catalyst on the carrier, conventionally, a method of immersing the carrier in a slurry in which a catalyst component is mixed in a liquid medium, pulling it up, and then carrying out a drying and firing step to catalyze is generally adopted. It has been.

[0005]

However, the above-mentioned conventional catalyst coating method has the following problems when the catalyst layer is formed on a carrier having a special structure such as DPF. That is, in a DPF or the like, the cell space inside the carrier has a structure in which the outlet side or the inlet side is alternately sealed, so that the catalyst layer attached as a result of immersing the whole carrier in the slurry and then raising it Non-uniformity tends to occur, and as a result, a large amount of catalyst adheres to the corners of the rectangular cross section of the cell space due to surface tension.

On the other hand, in the DPF or the like, the exhaust gas passes through the cell wall, but at that time, it is difficult for the exhaust gas to pass through the cell wall in the vicinity of the corner of the rectangular cross section of the cell space. That is, in a conventional DPF or the like, the central portion of each side of the rectangular cross section of the cell space through which exhaust gas passes intensively has a small amount of catalyst or is non-uniform, but the exhaust gas is wasted in the corners that are difficult to pass through. There is a problem that a large amount of catalyst is attached, an expensive catalyst is unnecessarily coated, and the catalyst cannot be effectively used.

In view of such circumstances, it is an object of the present invention to provide a catalyst-carrying exhaust particulate collection filter which can effectively use the catalyst without waste and a method of coating the catalyst on the filter.

[0008]

Therefore, the exhaust particulate collection filter according to the present invention is provided with a plurality of cell spaces which are partitioned by the porous lattice-like cell walls of the honeycomb structure, and which are adjacent to each other. In the spaces, one cell space is an outlet side, and the other cell space is an exhaust particulate trapping filter in which the inlet side is alternately sealed, and at least among the cell spaces on the exhaust inflow side or the exhaust outflow side. In one in which the inner surface of one cell space is coated with a catalyst, the corner portion in the rectangular cross section of the cell space on the side to be coated with the catalyst is filled with a porous filler, and then the catalyst is formed on the inner surface of the cell space. Is coated to form a catalyst layer (Claim 1).

Here, alumina is desirable as the filler (claim 2). Further, the catalyst layer is formed such that the central portion of each side of the rectangular cross section of the cell space is thickest (claim 3). A method for coating a catalyst for an exhaust particulate collection filter according to the present invention comprises coating the catalyst when coating the catalyst on the inner surface of at least one of the cell spaces on the exhaust inflow side or the exhaust outflow side. It is characterized in that the corner of the rectangular cross section of the side cell space is filled with a porous filler and then the inner surface of the cell space is coated with a catalyst (claim 4).

Here, when filling with the filler, the filler may be attached to the corner by immersing the filter in a solution containing the filler and pulling it up (claim 5). Alumina is desirable as the filler (claim 6). Further, when the catalyst is coated on the inner surface of the cell space, a slurry in which a catalyst component is mixed in a fluid medium (liquid medium or gas medium) that can pass through the cell wall is used in the cell space on the side where the catalyst is coated. It is advisable that the catalyst component is further flown in and the fluid medium is allowed to pass through the cell wall and flow out from the cell space on the opposite side, while the catalyst component is deposited on the cell wall (claim 7).

[0011]

According to the inventions of claims 1 and 4, the corners of the rectangular cross section of the cell space on the side coated with the catalyst are filled with a porous filler, preferably alumina (claim 2).
By filling with 6) and then coating the inner surface of the cell space with a catalyst, it becomes possible to form a thin catalyst layer at the corner where exhaust gas does not easily pass, and the catalyst can be used effectively without waste. As a result, costs can be reduced.

According to the third aspect of the present invention, the catalyst layer is formed such that the central portion of each side of the rectangular cross section of the cell space is thickest, so that the catalyst in the portion through which exhaust gas passes intensively is increased. Thus, the catalyst can be used more effectively without waste. According to the invention of claim 5, when filling with the filler,
By immersing the filter in a solution containing the filler and pulling it up, the filler can be attached to the corners of the cell space by surface tension by a simple method.

According to the invention of claim 7, when the catalyst is coated on the inner surface of the cell space, a slurry in which a catalyst component is mixed in a fluid medium that can pass through the cell wall is used as an exhaust flow. Similarly, since the catalyst component is deposited on the cell wall by passing through the cell wall, the catalyst can be concentratedly coated on the portion passing through the exhaust gas. By this method, each side of the rectangular cross section of the cell space can be coated. The catalyst layer can be formed so that the central portion of the catalyst layer becomes thickest.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an exhaust system of an internal combustion engine showing an embodiment of the present invention. In an internal combustion engine (diesel engine) 1, air is sucked into a combustion chamber 3 of each cylinder from an intake manifold 2, while fuel is directly injected and supplied from a fuel injection nozzle 4 into the combustion chamber 3 for compression self-ignition. And the exhaust gas after combustion is discharged from the exhaust manifold 5.

An exhaust particulate collection filter (hereinafter referred to as DPF) 6 according to the present invention 6 is provided just below the exhaust manifold 5 (collecting portion thereof) in order to collect particulates (hereinafter referred to as PM) in the exhaust. Are arranged. DPF6
As shown in the perspective view of FIG. 2, is a honeycomb structure made of porous ceramic and having a cylindrical outer shape,
It is housed in a cylindrical casing 7 having an expanded diameter via a holding mat 8.

Explaining the internal structure of the DPF 6,
As shown in FIG. 3, which is an enlarged cross-sectional view of the honeycomb structure,
A plurality of parallel cell spaces 12 are provided by being partitioned by the porous lattice-shaped cell walls 11 of the honeycomb structure, and each cell space 12 extends in the exhaust flow direction. Then, in the adjoining cells of the cell space 12, one is on the outlet side and the other is on the inlet side, respectively.
Are alternately sealed.

Hereinafter, the cell space 12 whose inlet side is open and whose outlet side is sealed by the sealing material 13 is referred to as an exhaust gas inlet side cell space 12A, and the inlet side is sealed by the sealing material 14 and the outlet side is opened. The cell space 12 that operates is referred to as an exhaust gas outflow side cell space 12B. Here, the exhaust gas from the internal combustion engine 1 is
The porous cell wall 1 flows into the exhaust gas inlet side cell space 12A.
Exhaust outlet side cell space 12 only through 1 (the pores)
Since it flows out to B, the PM in the exhaust can be reliably collected by the cell wall 11.

Further, a catalyst is coated inside the cell space 12A on the exhaust inflow side (the surface of the cell wall 11 facing the cell space 12A) to form a catalyst layer 15, so that the PM in the exhaust gas is collected. At the same time, due to the action of the catalyst, H in the exhaust gas
It is possible to promote the oxidation reaction of C and CO to purify them. Further, the heat of reaction can heat the deposited PM to burn and remove it under the oxygen in the exhaust gas. In particular, when the DPF 6 is arranged immediately below the exhaust manifold 5, PM can be burned and removed to be regenerated by only the reaction heat of the catalyst under high temperature exhaust, and an electric heater or burner is used. Without being able to self-renew.

However, when the flow of exhaust gas passing from the exhaust gas inflow side cell space 12A to the exhaust gas outflow side cell space 12B is verified, as shown in FIG. 4, more exhaust gas is discharged in the central portion of each side of the rectangular cross section of the cell space. There is little exhaust gas that passes through and near the corners of the rectangular cross section. On the other hand, in the conventional coating method, as shown by the dotted line in FIG. 4, as a result of the large amount of catalyst adhering to the corners, the catalyst cannot be used effectively.

Therefore, in the present invention, prior to the catalyst coating, as shown in FIG. 5A, the corners (four corners) in the rectangular cross section of the exhaust gas inflow side cell space 12A are made of a porous filler such as alumina. Fill with 16. Specifically, by immersing it in a solution containing alumina and then pulling it up, the alumina is attached to the four corners by the surface tension, and then dried. In the conventional catalyst coating method, the catalyst solution accumulates in the corners of the cell space due to surface tension. Therefore, by utilizing this, the DPF is dipped in the alumina solution, and then pulled up and dried. Thus, alumina is deposited only on the four corners of the cell space.

Thereafter, as shown in FIG. 5B, a catalyst containing a noble metal such as Pt, Pd, Rh is coated thereon to form a catalyst layer 15. In particular,
For example, the catalyst coating is performed by the method shown in FIG. D
The slurry supply passage 51 is connected to the lower end surface of the DPF 6 with the opening side of the exhaust inflow side cell space 12A that is the catalyst coating side of the PF 6 facing down. An enlarged diameter portion 51a that can surround the outer periphery of the DPF 6 is provided at the connection side end of the supply passage 51, and the slurry from the supply passage 51 is stored in the enlarged diameter portion 51a and The end face can be immersed in the slurry.

A slurry suction passage 53 is connected to the upper end surface of the DPF 6. A diameter-expanded portion 53a is also provided at the connection-side end of the suction passage 53.
The reference numeral 3a is such that it is possible to seal between the DPF 6 and the expanded diameter portion 53a via an appropriate sealing means or the like. In addition to these, a slurry recovery passage 55 for recovering excess slurry is provided on the slurry supply side. An expanded diameter portion 55a that surrounds the expanded diameter portion 51a of the supply passage 51 is provided at one end of the recovery passage 55, and the excess slurry other than that sucked into the DPF 6 of all the supplied slurry is received and recovered. It is possible.

The slurry referred to here is a liquid medium in which a catalyst component is mixed, and this liquid medium can easily pass through the cell wall of the DPF 6 by the suction force from the suction passage 53. Here, the supply passage 5
When the slurry is stored in the enlarged diameter portion 51a of No. 1 and the lower end of the DPF 6 is immersed in the slurry, and the suction force is exerted through the suction passage 53, the slurry in the enlarged diameter portion 51a becomes D
Inhaled into PF6.

At this time, in the DPF 6, as can be seen by replacing the flow of the exhaust gas in FIG. 3 with the slurry, the slurry permeates the cell wall 11 from the exhaust inflow side cell space 12A as shown by the arrow in the figure, and the exhaust gas flows out. It flows out into the side cell space 12B, and thereby, escapes to the outside of the DPF 6 and is guided into the suction passage 53. At this time, although the liquid medium of the slurry itself passes through the cell wall 11, the catalyst component cannot pass through the cell wall 11 depending on its particle size, and the catalyst component is deposited on the catalyst layer 15 to form the catalyst layer 15. Form. Therefore, the catalyst layer 15 having sufficient strength can be formed by the subsequent drying and firing process.

In the above description, the slurry was introduced into the DPF 6 by suction, but the same catalyst coating can be performed by pushing the slurry into the DPF 6 by the slurry supply pressure or other compression means. . Further, it is also possible to use a gas medium instead of the liquid medium. As described above, in the present invention, the corner of the rectangular cross section of the cell space 12A on the catalyst coating side is filled with the porous filler 16 such as alumina, and then the inner surface of the cell space 12A is coated with the catalyst. However, the cell wall 1 is formed before the catalyst coating (a corner is filled with alumina) and after the catalyst coating.
When the gas flow rate distribution passing through 1 was simulated, the result was as shown in FIG.

FIG. 7A shows the flow rate distribution before the catalyst coating (the corners are filled with alumina), and FIG. 7B shows the flow rate distribution after the catalyst coating. By filling the corners with alumina, the flow rate distribution becomes more lopsided and passes through the central portion of each side of the rectangular cross section of the cell space 12A. In such a state, the slurry is passed through the cell wall 11 to coat the catalyst. By doing so, the catalyst is also deposited thickly on the central portion of each side of the rectangular cross section of the cell space 12A.

Actually, when the catalyst deposition amount distribution was analyzed after the catalyst coating, as shown in FIG.
It was found that a large amount of catalyst was deposited in the central portion of each side of the rectangular cross section of No. 1, which was almost the same as the flow rate distribution after catalyst coating. From the above, it is considered that the exhaust gas and the catalyst are efficiently in contact with each other, and the catalyst can be effectively used.

Next, the experimental results will be described. The corner of the cell space on the exhaust gas inflow side of the DPF was filled with alumina and then coated with a catalyst. Here, the alumina species and the catalyst species were the same, and the amount of the catalyst (amount of noble metal) per DPF was also the same, and only the ratio of alumina to the catalyst was changed as follows.

Catalyst A Alumina: Catalyst = 0: 100 Catalyst B Alumina: Catalyst = 20: 80 Catalyst C Alumina: Catalyst = 40: 60 The evaluation results in this case are shown in FIG. Compared with A, B, C
In both cases, the performance was improved in all of the HC purification rate, the CO purification rate, and the PM combustion removal amount, and it became clear that the catalyst worked effectively.

In this embodiment, the catalyst is coated in the cell space 12A on the exhaust gas inflow side in order to self-regenerate the DPF by the reaction heat of the catalyst. The space 12B may be coated with the catalyst, or both may be coated with the catalyst. When the catalyst is coated in the cell space 12B on the exhaust gas outflow side, it goes without saying that the corners of the cell space 12B are filled with a filler such as alumina prior to the coating.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an exhaust system of an internal combustion engine showing an embodiment of the present invention.

FIG. 2 is a perspective view of a DPF.

FIG. 3 is an enlarged cross-sectional view showing the internal structure of the DPF.

FIG. 4 is a diagram showing a flow of exhaust gas passing through a cell wall in a DPF.

FIG. 5 is a sectional view of the cell space before and after the catalyst coating with DPF.

FIG. 6 is a diagram showing a catalyst coating method.

FIG. 7 is a diagram showing a flow rate distribution before and after catalyst coating.

FIG. 8 is a diagram showing experimental results.

[Explanation of symbols]

1 Internal combustion engine 5 exhaust manifold 6 DPF 11 cell wall 12 cell space 12A Exhaust inflow cell space 12B Exhaust outflow cell space 13 Outlet side sealing material 14 Inlet side sealing material 15 Catalyst layer 16 Filler (alumina)

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Claims (7)

[Claims] 1. A plurality of cell spaces are provided by being partitioned by a porous lattice-shaped cell wall of a honeycomb structure, and adjacent cell spaces have one cell space on the outlet side and the other cell space on the inlet side. An exhaust particulate trapping filter that is alternately sealed, wherein the catalyst is coated on the inner surface of at least one of the cell spaces on the exhaust inflow side or the exhaust outflow side, wherein the catalyst is Exhaust particulate collection characterized by forming a catalyst layer by filling the corner of the rectangular cross section of the cell space on the coating side with a porous filler and then coating the catalyst on the inner surface of the cell space. Filter. 2. The filter for collecting exhaust particulate matter according to claim 1, wherein the filler is alumina. 3. The exhaust particulate trapping device according to claim 1 or 2, wherein the catalyst layer is formed so that the central portion of each side of the rectangular cross section of the cell space has the largest thickness. filter. 4. A plurality of cell spaces are provided by being partitioned by a porous lattice-shaped cell wall of a honeycomb structure, and adjacent cell spaces have one cell space on the outlet side and the other cell space on the inlet side. When coating the catalyst on the inner surface of at least one of the cell spaces on the exhaust inflow side or the exhaust outflow side of the alternately trapped exhaust particulate collection filter, the catalyst is coated. A method for coating a catalyst for an exhaust particulate collection filter, which comprises filling a corner of a rectangular cross section of the side cell space with a porous filler and then coating the catalyst on the inner surface of the cell space. 5. The exhaust particulate matter according to claim 4, wherein, when the filter is filled with the filler, the filter is dipped in a solution containing the filler and pulled up to attach the filler to the corners. A method of coating a catalyst on a collecting filter. 6. The method of coating a catalyst for an exhaust particulate collection filter according to claim 4 or 5, wherein the filler is alumina. 7. When coating the catalyst on the inner surface of the cell space, a slurry in which a catalyst component is mixed in a fluid medium that can pass through the cell wall is introduced from the cell space on the catalyst coating side, 7. The fluid medium is allowed to pass through the cell wall and flow out from the cell space on the opposite side, while the catalyst component is deposited on the cell wall, according to any one of claims 4 to 6. A method for coating a catalyst on the exhaust particulate collection filter as described above.