Patent ID: 8813480

Claim:
An exhaust purification system of an internal combustion engine comprising: a first NO X selective reduction catalyst that is arranged inside of an engine exhaust passage and that selectively reduces NO X by feed of a reducing agent, a second NO X selective reduction catalyst that is arranged inside of the engine exhaust passage at the downstream side of the first NO X selective reduction catalyst and that selectively reduces NO X by feed of a reducing agent, a reducing agent feed device that feeds a reducing agent to the first NO X selective reduction catalyst, and an electronic control unit having control logic configured to cause the electronic control unit to control the exhaust purification system, wherein the reducing agent includes ammonia, the second NO X selective reduction catalyst has an activation temperature region that is lower than an activation temperature region of the first NO X selective reduction catalyst, the first NO X selective reduction catalyst and the second NO X selective reduction catalyst are configured so that a temperature difference between the first NO X selective reduction catalyst and the second NO X selective reduction catalyst arises that enables the ammonia that flows out from the first NO X selective reduction catalyst to be adsorbed at the second NO X selective reduction catalyst, and the electronic control unit estimates the amount of adsorption of the reducing agent that is adsorbed at the second NO X selective reduction catalyst, without estimating the amount of adsorption of the reducing agent that is adsorbed at the first NO X selective reduction catalyst, and prevents the amount of adsorption of the reducing agent of the second NO X selective reduction catalyst from exceeding the allowable value by adjusting the amount of feed of reducing agent from the reducing agent feed device.