Catalyst for purifying exhaust gas and exhaust gas purifying method

Abstract

A catalyst for purifying exhaust of an internal combustion engine is prepared by mixing first powders in which at least Pt is loaded on a first support and second powders in which at least Rh is loaded on a second support and loading NO occluding material, for example an alkaline-earth metal, alkali metal or rare-earth metal, at least on the first support. In such catalyst, the second support is made of a stabilized zirconia stabilized by alkaline-earth metal or rare-earth element. The second support, having been become alkaline by the alkaline-earth metal or the rare-earth element, is excellent in absorbing performance of the steam (H O), so that the steam reforming reaction by Rh advances sufficiently. Therefore, the created hydrogen greatly contributes to the reduction of NO and to the sulfur poisoning prevention of the NO occluding material. Also, the oxidizing ability of Pt is maintained high, Rh sufficiently exhibits the steam reforming reaction activity and the sulfur poisoning of NO occluding material is restrained. An exhaust gas from an internal combustion engine is combusted where mixed gas of rich atmosphere containing excessive fuel is supplied to mixed gas of lean atmosphere containing excessive oxygen like a pulse. The exhaust gas is then introduced to the catalyst wherein the exhaust gas is purified.