| 摘要 |
PURPOSE:To reduce the generation of NOx in low temp. region and to prevent losing an effect even at a high temp. by allowing the subject gas to contact with an iridium containing catalyst in a 1st zone, and next, allowing to contact with a platinum containing catalyst in a 2nd zone. CONSTITUTION:An exhaust gas of internal combustion engine operated in a lean air/fuel ratio is allowed to contact with the iridium containing catalyst in the 1st zone and the platinum containing catalyst in the 2nd zone. The iridium catalyst placed in the 1st zone is not restricted particularly if it does not contain platinum. Iridium is preferably carried on a fire resistant metal oxide carrier such as alumina, silica, titania or zirconia, a fire resistant metallic carbide such as silicon carbide or a fire resistant metallic nitride such as titanium nitride. The catalyst in the 2nd zone essentially contains platinum as the catalytic component. As the platinum component, any of single form of metal, platinum oxide, alloys of platinum with the other metals or conjugated oxides therewith is used. The carrier of the platinum containing catalyst is not restricted particularly. |
