JP2001020720A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high NOx reduction efficiency for exhaust of a diesel engine having low ratio of highly activated hydrocarbon under excessive oxygen condition. SOLUTION: This exhaust emission control device comprises a filter 12 interposed in an exhaust passage 10 of a diesel engine, and a less oxidative catalyst 14 and a NOx reduction catalyst 16 that are supported on the filter 12. In this configuration, the less oxidative catalyst 14 is placed upstream of exhaust gas flow passing through the filter 12 with respect to the NOx reduction catalyst 16. Therefore, partial oxidation of hydrocarbon of the exhaust gas that flows through the filter 12 is facilitated by the less oxidative catalyst 14, ratio of aldehyde and carbon monoxide with high nitrogen oxide reduction activity is increased, and concentration of the oxygen that obstructs the nitrogen oxide reduction is reduced. As a consequence of exhaust gas like this passing through the NOx reduction catalyst 16, high nitrogen oxide reduction efficiency can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas of a diesel engine, and more particularly to a device for purifying nitrogen oxides (hereinafter "NO").
x ”)).

[0002]

2. Description of the Related Art For the purpose of improving the exhaust characteristics of an internal combustion engine, there is known an exhaust gas purifying apparatus in which a reduction catalyst is provided in an exhaust passage as disclosed in Japanese Patent Application Laid-Open No. Hei 6-137136. . In the case of a diesel engine, in particular, in order to reduce NOx in exhaust gas, for example,
NOx as disclosed in JP-A-9-13955
An exhaust gas purification device provided with a reduction catalyst has also been proposed.

[0003]

However, the exhaust of a diesel engine is often in an oxygen excess state and has a low ratio of highly active hydrocarbons.
With the reduction catalyst, high NOx reduction efficiency could not be obtained.
That is, as shown in FIG. 3, the conventional NOx reduction catalyst has a configuration in which the same NOx reduction catalyst is carried over the entire length of the filter 2 interposed in the exhaust passage 1 of the diesel engine. High NOx reduction efficiency could not be obtained.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and has been developed in view of the above problem.
It is an object of the present invention to provide an exhaust gas purification device capable of obtaining a reduction efficiency.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention is directed to a filter provided in an exhaust passage of a diesel engine, a weak oxidizing catalyst and a nitrogen oxide reducing catalyst carried by the filter. Wherein the weak oxidizing catalyst is supported on the upstream side of the nitrogen oxide reduction catalyst with respect to an exhaust flow passing through the filter. There is a feature.

According to this structure, the weak oxidizing catalyst is carried on the upstream side of the exhaust flow passing through the filter (ie, on the upstream side of the filter), and is provided on the downstream side of the exhaust flow (ie, on the downstream side of the filter). Supports a nitrogen oxide reduction catalyst. Therefore, when the exhaust gas passes through the filter, first, the partial oxidation of hydrocarbons (HC) in the exhaust gas is promoted by the weak oxidizing catalyst supported on the upstream side of the filter. At this time, due to a chemical change in the exhaust gas, the ratio of carbon monoxide (CO) and aldehyde having a high nitrogen oxide reduction activity becomes high, and the concentration of oxygen which hinders the nitrogen oxide reduction becomes low. Then, such an exhaust gas passes through the nitrogen oxide reduction catalyst carried on the downstream side of the filter, so that high nitrogen oxide reduction efficiency can be obtained.

According to a second aspect of the present invention, the filter includes:
It is a diesel particulate filter that collects particulate matter contained in exhaust gas from a diesel engine.

[0008] According to such a configuration, the particulate matter contained in the exhaust gas from the diesel engine is collected by the diesel particulate filter, and the weak oxidizing catalyst and the nitrogen oxide reducing catalyst carried by the filter are used.
High nitrogen oxide reduction efficiency is obtained. At this time, the weak oxidizing catalyst and the nitrogen oxide reducing catalyst are configured to be supported by the diesel particulate filter, and therefore, it is not necessary to add a new filter.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the attached drawings. FIG. 1 shows an embodiment of an exhaust gas purification device for a diesel engine (hereinafter, referred to as “exhaust gas purification device”) according to the present invention.

FIG. 1 shows an exhaust passage 10 of a diesel engine.
As shown in (A), a substantially cylindrical filter 12 made of a porous material such as ceramic is interposed. Filter 1
2, a large number of cells substantially parallel to the exhaust gas flow are formed by honeycomb-shaped partition walls 12a, and the outlet and the inlet of each cell are alternately sealed with a sealing material 12b. Then, when the exhaust gas flows into an adjacent cell through the partition wall 12a, the particulate matter contained in the exhaust gas is collected by the partition wall 12a. That is, the filter 12 having such a configuration is generally
This is called a “diesel particulate filter”. Note that the flow path cross-sectional area of each cell is formed substantially constant so that the flow resistance becomes substantially constant.

As shown in FIG. 1 (B), the filter 12 is provided on the upstream side of the exhaust gas, that is, on the partition wall surface on the side where the exhaust gas flows into an adjacent cell, such as a base metal-based material. A weak oxidation catalyst 14 is carried. On the other hand, a general NOx reduction catalyst 16 is carried on the downstream side of the exhaust gas, that is, on the partition wall surface on the side where the exhaust gas flows in via the partition wall 12a.

According to this structure, the exhaust gas is supplied to the filter 12.
First, the hydrocarbon (HC) in the exhaust gas is discharged by the weak oxidizing catalyst 14 supported on the upstream side of the filter 12.
Partial oxidation is promoted. At this time, due to a chemical change in the exhaust gas, the ratio of carbon monoxide (CO) and aldehyde having a high NOx reduction activity increases, and the concentration of oxygen that hinders NOx reduction decreases. Then, such exhaust gas passes through the NOx reduction catalyst 16 carried on the downstream side of the filter 12, so that high NOx reduction efficiency can be obtained.

Therefore, it is often in an oxygen excess state,
In addition, even with diesel engine exhaust having a low high active hydrocarbon ratio, high NOx reduction efficiency can be obtained, and N
Ox emissions can be reduced.

FIG. 2 shows another embodiment of the exhaust gas purifying apparatus according to the present invention. The feature of this embodiment is that, unlike the embodiment of FIG. 1, a filter for supporting a catalyst for reducing exhaust gas is separately provided separately from the filter 12 for collecting particulate matter contained in exhaust gas. is there. That is, in the exhaust passage 10 of the diesel engine, a filter 20 in which a number of cells substantially parallel to the exhaust flow are formed by honeycomb-shaped partitions is interposed. Then, on the upstream side of the filter 20, that is, the filter 2
On the upstream half of 0, the weak oxidizing catalyst 14 is supported, and on the downstream side of the filter 20, that is, on the downstream half of the filter 20, the NOx reduction catalyst 16 is supported.

[0015] The operation of this configuration is as follows.
Since it is the same as the previous embodiment, the description is omitted. In the above-described embodiment, two types of catalysts are supported on a single exhaust gas purification filter. However, a plurality of filters are provided, a weak oxidation catalyst is supported on an exhaust upstream filter, and a filter on the exhaust downstream side is provided. A similar effect can be obtained even if a NOx reduction catalyst is carried on the substrate.

[0016]

As described above, according to the first aspect of the present invention, the weak oxidizing catalyst supported on the upstream side of the nitrogen oxide reduction catalyst often causes an oxygen excess state.
In addition, since the exhaust of a diesel engine having a low ratio of high active hydrocarbons is improved, high nitrogen oxide reduction efficiency can be obtained, and the exhaust properties can be improved.

According to the second aspect of the present invention, since it is not necessary to add a new filter, only the cost associated with the application of the weak oxidizing catalyst and the nitrogen oxide reducing catalyst is sufficient, and the increase in cost is suppressed as much as possible. Can be. It is also advantageous in layout.

[Brief description of the drawings]

1A and 1B show an embodiment of the present invention, wherein FIG. 1A is an overall configuration diagram, and FIG. 1B is an enlarged view of a portion A in FIG.

FIG. 2 is an overall configuration diagram showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a NOx reduction catalyst according to the related art.

[Explanation of symbols]

 Reference Signs List 10 exhaust passage 12 filter 14 weak oxidizing catalyst 16 NOx reduction catalyst 20 filter

Claims (2)

[Claims] An exhaust purification device for a diesel engine comprising: a filter provided in an exhaust passage of the diesel engine; and a weak oxidizing catalyst and a nitrogen oxide reducing catalyst carried by the filter. The exhaust gas purifying apparatus for a diesel engine, wherein the weak oxidizing power catalyst is supported on an upstream side of the nitrogen oxide reduction catalyst with respect to an exhaust flow passing through the filter. 2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein said filter is a diesel particulate filter for trapping particulate matter contained in exhaust gas from a diesel engine.