| abstract |
It is an object of the present invention to realize an oxidizing catalyst having weak oxidizing capability such that NO is oxidized to NO 2 and HC is not oxidized, and high thermal durability, and to use it as a catalyst in a preceding stage for supplying NO 2 and HC stably to a catalyst in the following stage. n According to the present invention, in an exhaust gas pipe P of a vehicle engine E, a low activity NO oxidizing catalyst 1 is provided on the upstream side and a NOx selective reduction type catalyst 2 is provided on the downstream side. By introducing substituent elements into a substrate ceramic such as cordierite, the catalyst component can be chemically bonded to the substituent elements to obtain a directly supported catalyst which has excellent bonding capability, so that the catalyst component can be highly dispersed and is not easily deteriorated. Therefore, even if amount of supported catalyst is decreased to obtain a desired low activity, the oxidizing capability can be maintained, and NO 2 , and HC as a reducing agent, can be stably supplied to a NOx selective reduction type catalyst 2. |