EXHAUST GAS PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE

Provided is an exhaust purification system for an internal combustion engine. The exhaust purification system comprising: a NOpurifying catalyst arranged in an exhaust passage of the internal combustion engine, wherein the NOpurifying catalyst comprises a base metal supported on a catalyst support; an oxygen sensor arranged at the downstream side of the NOpurifying catalyst in the exhaust passage; and an air-fuel ratio control means for controlling the air-fuel ratio of exhaust gas flowing into the NOpurifying catalyst; wherein when the NOpurifying catalyst suffers from predetermined oxygen poisoning, the air-fuel ratio control means controls the air-fuel ratio of the exhaust gas, which flows into the NOpurifying catalyst, to a first air-fuel ratio wherein the first air-fuel ratio is richer than a theoretical air-fuel ratio, and then the air-fuel ratio control means switches the air-fuel ratio of the exhaust gas, which flows into the NOpurifying catalyst, to a second air-fuel ratio on the basis of an output value from the oxygen sensor wherein the second air-fuel ratio is leaner than the first air-fuel ratio.