| 摘要 |
PROBLEM TO BE SOLVED: To improve the clean-up efficiency of soot included in exhaust gas without causing clogging of a catalyst. SOLUTION: Soot included in exhaust gas of an internal combustion engine is cleaned up by using a clean-up catalyst carrying an active oxygen discharge agent. An upstream clean-up catalyst and a downstream clean-up catalyst are provided on an exhaust pipe. The upstream clean-up catalyst selectively collects the soot in the exhaust gas, lets the remaining soot pass through, and cleans up only the collected soot. The downstream catalyst non-selectively collects the soot passing through the upstream clean-up catalyst, and cleans up the collected soot. Therefore, the work of cleaning up soot can be shared by the upstream clean-up catalyst and the downstream clean-up catalyst, so that the soot is efficiently cleaned up, and clogging of the catalysts is hard to occur. The upstream clean-up catalyst may collect large soot only, and positively let small soot pass through, or may let the small soot pass through by providing a bypass passage. |
