To possibly reduce as much as possible the number of SOx poisoning reactivation control.
A first occulsion and reduction NOx catalyst 8a is arranged on an exhaust passage of an internal combustion engine, which can perform lean burning for low temperature/low load operation. A second occulsion and reduction NOx catalyst 8b is arranged on the downstream side of the first occulsion and reduction NOx catalyst, for high temperature/high load operation. In a device having such a setup, a bypass passage 6b to the second occulsion and reduction catalyst 8b is arranged, while bypassing the first occulsion and reduction NOx catalyst. A changeover valve 25 is arranged for switching exhaust passages to the bypass passage and to the first occulsion and reduction NOx catalyst. Even when the second occulsion and reduction NOx catalyst is exposed to SOx in low-load operation, therefore, SOx poisoning reactivation treatment is not performed. Only when the second occulsion and reduction NOx catalyst is exposed to SOx in high-load operation, is the SOx poisoning reactivation treatment performed. The number of reactivation control is thus reduced.
HIROTA SHINYA
ASANUMA TAKAMITSU
TANAKA TOSHIAKI
