| 摘要 |
PROBLEM TO BE SOLVED: To improve NOx desorption/purification performance in an NOx trap catalyst of an engine. SOLUTION: This exhaust emission control device has an exhaust purification catalyst, that carries an NOx trap catalyst layer for low temperature as a first layer (inner layer) and an NOx trap catalyst layer for high temperature as a second layer (surface layer) on a honeycomb carrier. After starting of the engine, lean operation is performed during the low temperature period of the catalyst to trap NOx in the NOx trap catalyst layer for low temperature, the catalyst temperature rises to a high temperature to desorb the trapped NOx, the lean operation is continued, until finishing of the desorption to trap the desorbed NOx in the NOx trap catalyst layer, and rich operation for a predetermined time is conducted, after finishing the desorption to desorb the NOx from the NOx trap catalyst layer for high temperature, while reducing it with reducing materials (HC, CO, H2 ) in the exhaust.
|
