Patent ID: 8156731

Claim:
An exhaust purification device of an internal combustion engine comprising: a front end catalyst and rear end catalyst arranged sequentially in an engine exhaust passage along an exhaust gas flow path, the front end catalyst and the rear end catalyst are comprised of NO x storing catalysts storing NO x contained in the exhaust gas when an air-fuel ratio of inflowing exhaust gas is lean and releasing stored NO x when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich; and a controller, wherein when the front end catalyst should recover from SO x poisoning, the controller is configured to perform SO x poisoning recovery proceeding by raising a temperature of the front end catalyst to a SO x release temperature and making the air-fuel ratio of the exhaust gas flowing into the front end catalyst rich, when the rear end catalyst should recover from SO x poisoning, the controller is configured to perform SO x poisoning recovery proceeding by raising a temperature of the rear end catalyst to the SO x release temperature and making the air-fuel ratio of the exhaust gas flowing into the rear end catalyst rich, and a frequency of performing the SO x poisoning recovery proceeding for the rear end catalyst is made higher than a frequency of performing the SO x poisoning recovery proceeding for the front end catalyst, wherein when a NO x purification rate by both the catalysts of the front end catalyst and the rear end catalyst becomes a predetermined allowable level or less, either the SO x poisoning recovery proceeding of the front end catalyst or the SO x poisoning recovery proceeding of the rear end catalyst is performed.