| 摘要 |
PROBLEM TO BE SOLVED: To improve the efficiency of purification of NOX as a result of a need for a secondary fuel feed device being eliminated, to effectively utilize the HC adsorption effect of a lean NOx catalyst to a maximum limit, enlarge the NOX activity temperature range of the whole of a catalyst, and to suppress an amount of discharging untreated HC through prevention of the generation of white smoke. SOLUTION: In an exhaust system for an internal combustion engine, a plurality of catalysts 3a-3c being high in HC adsorption capacity and different in an amount of coating catalyst material to effect reduction treatment of NOx in lean atmosphere are disposed in a position relation wherein an amount of coating catalyst material is increased from a spot situated upper stream of a flow of engine exhaust gas to a spot situated downstream thereof. A plurality of the catalysts 3a-3c different in an NOx activity temperature range are used and disposed in a position relation wherein an NOx activity temperature range is decreased from a spot situated upper stream of a flow of engine exhaust gas to a spot situate downstream thereof. A catalyst 3d having a lowermost amount of a coating catalyst material and being of a lowermost temperature activity type is added in a spot situated downstream therefrom to a plurality of the catalysts 3a-3c. |
