| abstract |
Disclosed is an exhaust gas clean-up system comprising a lean-burn engine, a Pd catalyst (1) which is placed in an exhaust gas discharged from the lean-burn engine and comprises Pd supported on a porous oxide at a high concentration of 3% by weight or higher, and a enrichment means (32) for enriching the exhaust gas atmosphere temporarily at an area surrounding the Pd catalyst. It is considered that, in the exhaust gas under the lean atmosphere, NO is oxidized on the Pd catalyst (1) into NO2 and the NO2 and NO2 originally present in the exhaust gas are adsorbed onto Pd. This reaction occurs at a low temperature of about 200 to 300ºC, whereby NOx can be occluded onto the Pd catalyst (1). Thus, it becomes possible to achieve a reduction/clean-up of NOx at a low temperature ranging from 200 to 300ºC without the need of using any occluding agent comprising an alkaline component. |