Patent ID: 8409536

Claim:
An exhaust gas purification apparatus of an internal combustion engine comprising: a selective reduction type NOx catalyst that is arranged in an exhaust passage of the internal combustion engine; and a reducing agent addition part that is arranged in said exhaust passage at an upstream side of said selective reduction type NOx catalyst, and adds a reducing agent for supplying NH 3 to said selective reduction type NOx catalyst; wherein said selective reduction type NOx catalyst has an active spot which purifies NOx by the use of NH 3 , and an adsorption site which adsorbs NH 3 ; a vicinity site, which is located in the vicinity of said active spot, and a distant site, which is located distant from said active spot, exist in said adsorption site; said vicinity site tends to deliver NH 3 to said active spot more easily than said distant site does, and the desorption rate of NH 3 in said vicinity site is faster than the desorption rate of NH 3 in said distant site; and a control part is provided which controls the addition of the reducing agent from said reducing agent addition part based on the desorption rate of NH 3 in said vicinity site so as to continue to cause the NH 3 adsorbed to said vicinity site to exist.