JPH10205325A - Nox reducing and removing honeycomb catalyst device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an NOx reducing and removing honeycomb catalyst device in which exhaust gas containing a much amount of reducing gas is equally supplied to a downstream side catalyst, the reducing action is improved by where the catalyst, and high purifying performance can be maintained for a long period. SOLUTION: A plurality of honeycomb catalysts 6, 7 in which catalyst layers are coated on the inner surface of cells of honeycomb carriers are arranged in series and side by side in the flowing direction of exhaust gas G, and the cell size of the upstream side honeycomb catalyst 6 is formed into a size larger than that of the downstream side honeycomb catalyst 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a honeycomb catalyst device for reducing and removing NOx from exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art Various studies and proposals have been made on catalysts for reducing and removing NOx from exhaust gas of internal combustion engines such as diesel engines and lean burn gasoline engines. Such a catalyst is formed, for example, by coating a catalyst layer made of alumina or the like containing an active metal species on a cell inner surface of a carrier made of cordierite or the like formed in a honeycomb shape, and forming the catalyst in an exhaust pipe or a converter of an internal combustion engine. It is arranged and used.

[0003] In order to reduce and remove NOx by the catalyst as described above, it is necessary to mix a reducing agent into the exhaust gas. As the reducing agent, unburned HC discharged from the combustion chamber or fuel (HC) injected and supplied into the exhaust pipe is used. However, depending on the catalyst component, carbon or carbon monoxide is used. There is also. When the exhaust gas containing the reducing agent passes through each cell of the honeycomb catalyst, the reduction reaction of NOx is promoted, but this honeycomb catalyst considers exhaust pressure at the time of disposing the catalyst, etc. The diameter, length and cell dimensions must be appropriately set so that the inner surface of the cell, that is, the surface area of the catalyst layer, is obtained in accordance with the exhaust gas amount of the internal combustion engine.

[0004] However, conventionally, even if the cell size is set as described above, the purification performance as expected may not be obtained, or the purification performance may be reduced or clogged relatively early. Experiments by the present inventors have revealed that this is mainly because most of the reducing agent is consumed on the upstream side near the inlet of the catalyst, and the reduction reaction hardly occurs on the downstream side. did. In particular, as shown in FIG. 6, the consumption of the reducing agent on the upstream side of the honeycomb catalyst 1 is caused not only by the NOx reduction reaction but also by the deposition of the reducing agent on the inner surface of the cell to cause carbon deposition, that is, coking 2. This prevents the passage of exhaust gas by growing and distributing as shown in FIG.
In addition to reducing the reduction reaction on the upstream side of the honeycomb catalyst, clogging occurs near the entrance and exhaust gas containing a large amount of reducing agent cannot be evenly supplied to the downstream side of the honeycomb catalyst 1, and reduction and reaction in the entire catalyst are not performed. As a result, the purification performance cannot be obtained as expected.

On the other hand, Japanese Patent Laid-Open Publication No. Sho 61-144213 discloses a technique relating to a catalytic converter in which a monolithic catalyst is divided into a plurality of layers in the direction of the flow of exhaust gas, and the steps are configured so as to be uneven so that the lattices of adjacent catalyst layers do not match. Has been proposed. However, this technique is intended to maintain the turbulence by preventing the passing exhaust gas from being laminarized in the monolith catalyst, and to uniformly discharge exhaust gas containing a large amount of reducing agent to the downstream side of the catalyst. It is not intended to supply.

In a catalytic converter in which a plurality of monolithic catalysts each having a gas passage formed by a plurality of cells are arranged in series along a flow direction of exhaust gas with a gap between axial end faces, An invention relating to a catalytic converter in which the cell size of the monolithic catalyst on the downstream side is larger than the cell size of the monolithic catalyst on the downstream side is disclosed in JP-A-63-1812.
No. 3 proposes this.

However, this invention also aims at maintaining the turbulent flow by preventing the passing exhaust gas from being laminarized in the monolithic catalyst, and does not aim at even supply of the reducing agent. Further, in this catalytic converter, a gap for generating turbulence between the upstream catalyst and the downstream catalyst is required, and it does not consider the mutual influence of a series of monolith catalysts, There is a disadvantage that the device becomes necessarily large.

[0008]

SUMMARY OF THE INVENTION According to the present invention, an exhaust gas containing a large amount of reducing gas is uniformly supplied to a downstream catalyst, a reduction reaction in the entire catalyst is promoted, and NOx capable of maintaining high purification performance for a long period of time. An object of the present invention is to provide a honeycomb catalyst device for reduction and removal.

[0009]

To achieve the above object, a honeycomb catalyst device for reducing and removing NOx according to the present invention comprises:
A plurality of honeycomb catalysts having a catalyst layer coated on the inner surface of the cells of the honeycomb carrier are arranged in series in the exhaust gas flow direction, and adjacently, and the cell size of the upstream honeycomb catalyst is adjusted to the downstream honeycomb catalyst. It is formed so as to be larger than the cell size.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a NOx reduction employed in an exhaust pipe 10 for discharging exhaust gas G of an internal combustion engine in one embodiment. A honeycomb catalyst device 3 for removal, in which a catalyst layer 5 of a metal such as alumina or Ag or Ir is coated on the inner surface of a cell of a honeycomb carrier 4 such as cordierite as shown in FIG. It is formed.

[0011] In the honeycomb catalyst device of FIG.
The exhaust gas G is contained in the casing 3a connected to the exhaust pipe 10.
Two honeycomb catalysts 6 and 7 having different cell dimensions of the honeycomb carrier 4 (FIG. 5) are arranged adjacent to each other in the flow direction of the arrow in series without leaving a space. That is, the honeycomb catalyst 6 arranged on the upstream side in the flow direction of the exhaust gas G has a cell size larger than that of the catalyst 7 of the downstream honeycomb, and the entire diameter of the honeycomb catalyst device 3 is made the same. In this case, the number of cells per unit area of the honeycomb catalyst 6 is smaller than the number of cells of the downstream honeycomb catalyst 7.

For example, the inner diameter of the casing 3a is 191 mm.
Then, the dimensions of the cells (dimensions between the inner walls of the openings) of the honeycomb catalysts 6 and 7 disposed therein are 1.2 to 2.5.
And 0.8 to 1.8 mm (catalyst 6> 7), and the length of both was 89 mm. The honeycomb carrier 4
Has a thickness of about 0.2 mm, and the entire surface of which is coated with the catalyst layer 5 has a thickness of about 0.4 mm.

FIG. 2 is a partially sectional perspective view of the honeycomb catalysts 6 and 7 shown in FIG. 1. FIG. 3 is an enlarged perspective explanatory view of the honeycomb catalyst 6 indicated by an arrow A in FIG. 2 and a honeycomb catalyst indicated by an arrow B in FIG. 7 is an enlarged perspective explanatory view of FIG. As described above, the cell size of the upstream honeycomb catalyst 6 through which the exhaust gas G containing a large amount of reducing agent passes is reduced to the downstream honeycomb catalyst 7.
, The exhaust gas G passing through the center of each cell constituting the honeycomb catalyst 6 is formed.
Will flow into the downstream honeycomb catalyst 7 without adhering to the inner surface of the cell.

Although the downstream honeycomb catalyst 7 has a large number of cells and a small area as described above, since the upstream honeycomb catalyst 6 does not consume all of the reducing agent, the downstream honeycomb catalyst 7 is not used. As a result, the reducing agent can be supplied almost uniformly from upstream to downstream of the catalyst device 3. 3 and 4 show the coking C in the honeycomb catalysts 6 and 7 of the catalyst device 3 which has processed the exhaust gas G, that is, the pattern in which the reducing component is formed on the inner surface of the cell. The caulking C is similarly formed in the cell of the honeycomb catalyst 7 on the downstream side, and it can be seen that the catalyst device 3 can be used for a long period of time.

That is, since the reducing agent is supplied together with the exhaust gas G over the entire length of the honeycomb catalysts 6 and 7, the catalyst device 3 can be operated until coking C is generated as a whole. And can be used for a long time.

[0016]

According to the honeycomb catalyst device for NOx reduction of the present invention described above, the cell size of the upstream honeycomb catalyst through which the exhaust gas containing a large amount of the reducing agent passes is formed large, The reducing agent contained in the exhaust gas passing through the inner central portion can reach the downstream honeycomb catalyst without adhering to the inside of the cell as in the conventional case, and the reducing agent is almost uniformly distributed from upstream to downstream in the entire catalytic device. Will be able to supply.

As a result, the reduction reaction is promoted in the entire catalytic device, and high purification performance is obtained. Further, since an excessive reducing agent is not supplied near the entrance of the catalyst device, carbon deposition near the entrance is also drastically reduced, and the reduction reaction of the upstream honeycomb catalyst is maintained for a long time, and clogging is less likely to occur.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a honeycomb catalyst device for NOx reduction showing one embodiment of the present invention.

FIG. 2 is a perspective view of the device shown in FIG.

FIG. 3 is an enlarged perspective explanatory view showing the state of adhesion of a reducing agent to the inner surface of the cell of the honeycomb catalyst indicated by an arrow A in FIG. 2;

FIG. 4 is an enlarged perspective explanatory view showing the state of adhesion of a reducing agent to the inner surface of the cell of the honeycomb catalyst indicated by arrow B in FIG. 2;

FIG. 5 is an enlarged front sectional view of a main part of a honeycomb catalyst used in the present invention.

FIG. 6 is an explanatory perspective view of a main part showing caulking adhering to a cell inner surface of a conventional honeycomb catalyst.

[Explanation of symbols]

3 Honeycomb catalyst device 4 Honeycomb carrier 5 Catalyst layer 6 Honeycomb catalyst 7 Honeycomb catalyst G Exhaust gas

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 35/04 301 B01J 35/04 301A 301J

Claims (2)

[Claims] 1. A plurality of honeycomb catalysts each having a catalyst layer coated on the inner surface of a cell of a honeycomb carrier are arranged in series and adjacent to each other in the flow direction of exhaust gas, and the cell size of the honeycomb catalyst on the upstream side is changed to the downstream side. A honeycomb catalyst device for reducing and removing NOx, which is formed to be larger than the cell size of the honeycomb catalyst. 2. The NOx reduction and removal according to claim 1, wherein the size of the upstream honeycomb catalyst cell is 1.2 to 2.5 mm and the size of the downstream honeycomb catalyst cell is 0.8 to 1.8 mm. For honeycomb catalyst device.