EXHAUST GAS CLEANING CATALYST APPARATUS WITH CONTROL UNIT, EXHAUST GAS CLEANING METHOD USING SAID APPARATUS

摘要

An exhaust gas cleaning catalyst is provided in an exhaust passage of an internal combustion engine to convert NOx in exhaust gas. The exhaust gas cleaning catalyst includes a carrier; a plurality of kinds of metal catalysts which are supported on the carrier; and an NOx absorbent which is supported on the carrier and has an NOx storage capacity. The exhaust gas cleaning catalyst includes at least platinum and rhodium as the metal catalysts. A Pt/Rh mass ratio in an upstream portion (65 a) including an exhaust gas inlet side end is different from the Pt/Rh mass ratio in a downstream portion (65 b) including an exhaust gas outlet side end, and the Pt/Rh mass ratio in the upstream portion (65a) is higher than the Pt/Rh mass ratio in the downstream portion (65b). The Pt/Rh mass ratio is a mass ratio of platinum to rhodium.