| 摘要 |
<p>An NOx occluding and reducing catalyst (7) is disposed in an exhaust gas passage (2) of an internal combustion engine (1) to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas is rich. A recovery operation is executed when an estimated amount of contaminants adsorbed or absorbed by the NOx occluding and reducing catalyst (7) has reached a predetermined value. At that time, the total amount of reducing substances in the exhaust gas flowing into the NOx occluding and reducing catalyst (7) is changed depending on the degree of recovery of the capability of absorbing, releasing and reducing NOx by reduction of the NOx occluding and reducing catalyst (7) or depending on the concentration of precursors of the contaminants in the fuel. <IMAGE>An NOx occluding and reducing catalyst (7) is disposed in an exhaust gas passage (2) of an internal combustion engine (1) to absorb NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, and to release and reduce the absorbed NOx when the air-fuel ratio of the exhaust gas is rich. A recovery operation is executed when an estimated amount of contaminants adsorbed or absorbed by the NOx occluding and reducing catalyst (7) has reached a predetermined value. At that time, the total amount of reducing substances in the exhaust gas flowing into the NOx occluding and reducing catalyst (7) is changed depending on the degree of recovery of the capability of absorbing, releasing and reducing NOx by reduction of the NOx occluding and reducing catalyst (7) or depending on the concentration of precursors of the contaminants in the fuel. <IMAGE></p> |
