| abstract |
An SOx trap catalyst (11) able to trap SOx contained in exhaust gas is arranged in an engine exhaust passage upstream of an NOx storing catalyst (12). When the SOx trap rate by the SOx trap catalyst (11) falls, the air-fuel ratio of the exhaust gas flowing into the SOx trap catalyst (11) is maintained lean and in that state the SOx trap catalyst (11) is raised in temperature. The SOx trapped at that time diffuses inside the SOx trap catalyst (11), whereby the SOx trap rate is restored. |