| 摘要 |
PROBLEM TO BE SOLVED: To obtain a catalyst system capable of efficiently diminishing hydrocarbons in the exhaust gas of a diesel engine without forming sulfates and to also efficiently diminish white smoke and hydrocarbons at low temperature. SOLUTION: In the catalyst system, a catalyst having a large volume (e.g. 70-97 vol.%) and low oxidizing power on the upper stream side contains at least one metal oxide selected from alumina (aluminum oxide), zirconia (zirconium oxide), titania (titanium dioxide), ceria (cerium oxide), silica (silicon dioxide), cobalt oxide and iron oxide and a catalyst having a small volume (e.g. 3-30 vol.%) and high oxidizing power on the downstream side is obtained by supporting at least one noble metal selected from platinum, palladium, rhodium, iridium and silver on a metal oxide carrier. When an absorbent type catalyst is further disposed on the upper stream side of the combined catalysts, white smoke and hydrocarbons are effectively diminished. |
