| 摘要 |
PROBLEM TO BE SOLVED: To provide a sulfur-resistant lean NOx catalyst for converting an exhaust gas as a useful element of an exhaust gas system for a diesel internal combustion engine by causing a combination of a precious metal and 12- phosphotungstic acid to be borne by a porous substrate containing alumina. SOLUTION: A highly sulfur-resistant lean NOx catalyst is obtained by causing 5-40wt.% of 12-phosphotungstic acid based on the weight reference of a substrate and at least, about 0.25wt.% of precious metal selected from among a group of platinum, palladium, rhodium and their mixture based on the weight reference of the substrate to be borne on a porous substrate containing alumina. This lean NOx catalyst can convert a larger quantity of NOx than the normal average at a lower temperature than a temperature at which a conventional alumina-carrying platinum lean NOx catalyst operates. That is, this lean NOx catalyst can convert efficiently NOx at a rapid rate after the start of a diesel engine ands thereby, improve the purification efficiency at the time of cold start. In this case, the platinum and rhodium of the precious metal are in the weight ratio of about 50:1. |
