EXHAUST GAS PURIFICATION APPARATUS FOR AN INTERNAL COMBUSTION ENGINE

摘要

An exhaust purification apparatus for an internal combustion engine is provided which allows an NOx purification rate to be improved by restraining NOx from slipping through a selective reduction catalyst without being purified regardless of whether the selective reduction catalyst is active or inactive. The exhaust purification apparatus includes an NOx adsorbent (25) temporarily adsorbing NOx, a selective reduction catalyst (40) provided downstream of the NOx adsorbent in the exhaust passage (15) to selectively reduce the NOx contained in the exhaust gas, an aqueous-solution-of-urea addition valve (70) supplying ammonia as a reducing agent to the selective reduction catalyst, and a burner (20) desorbing the NOx adsorbed to the NOx adsorbent. When NOx is desorbed from the NOx adsorbent, at least one of purification rate of the selective reduction catalyst and the amount of NOx desorbed by the burner (20) is adjusted to restrain NOx from being emitted to the exterior.