Exhaust purifying device of internal combustion engine

Abstract

An upstream catalyst and a downstream catalyst are arranged in series and are housed in a common casing disposed in an engine exhaust passage. The upstream catalyst including a NOx storage-reduction catalyst that adsorbs NOx contained in incoming exhaust gas when the air-fuel ratio of the incoming exhaust gas is lean, and releases and reduces the adsorbed NOx when the air-fuel ratio of the incoming exhaust gas becomes rich, and the downstream catalyst includes a three-way catalyst. The upstream catalyst has a higher oxidizing capability than the downstream catalyst, and the downstream catalyst has a higher reducing capability than the upstream catalyst. The upstream catalyst has a multi-layer structure including an upper layer and a lower layer, and is prepared such that the upper layer has a higher oxidizing capability than the lower layer, and the lower layer has a higher reducing capability than the upper layer.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to an exhaust purifying device of an internal combustion engine.[0003]2. Description of the Related Art[0004]In a known example of internal combustion engine (as disclosed in, for example, Japanese Patent Application Publication No. 11-44234 (JP-A-11-44234)), a NOx storage-reduction catalyst, which adsorbs NOx contained in exhaust gas flowing into the catalyst when the air-fuel ratio of the exhaust gas is lean, and releases and reduces the adsorbed NOx when the air-fuel ratio of the exhaust gas becomes rich, is disposed in an exhaust passage of the engine (i.e., lean-burn engine) in which an air-fuel mixture having a lean air-fuel ratio is normally burned. In this type of engine, the air-fuel ratio of the exhaust gas flowing into the NOx storage-reduction catalyst is temporarily switched to the rich side when the NOx stored in the NOx storage-reduction catalyst is to be released and reduced. In thi...

AI Technical Summary

Benefits of technology

[0009]The invention provides an exhaust purifying device of an internal combustion engine in which a NOx storage-reduction catalyst exhibits a high NOx adsorbing capability and a high NOx conversion efficiency.

[0019]With the above arrangements, the NOx adsorbing capability and NOx conversion efficiency of the NOx storage-reduction catalyst can be enhanced.

Problems solved by technology

However, there is a limit to the space in which the NOx storage-reduction catalyst is installed, and it is therefore necessary to increase or enhance the NOx adsorbing capability of the NOx storage-reduction catalyst while minimizing the dimensions or capacity of the NOx storage-reduction catalyst.

However, the state of the art does not provide satisfactory solutions to the above problems.

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