[Alumina-supported catalysts for the catalytic purification of lean-burn automobile exhaust].

Catalytic properties of Ag/Al2O3, In/Al2O3, Sn/Al2O3, Co/Al2O3, Pt/Al2O3 and a two-stage catalyst composed of Ag/Al2O3 and Pt/Al2O3 were investigated for the selective reduction of NO by C3H6 or C2H5OH in excess oxygen. The Ag/Al2O3 showed the highest NO reduction activity among the catalysts studied. A substantial amount of CO was formed over alumina-based transient metal oxides. HC and CO oxidations over Pt/Al2O3 occurred in relatively low temperatures, compared with the other catalysts. The sequential use of Ag/Al2O3 and Pt/Al2O3 was effective to broaden the temperature window for the reduction of NO, to improve oxidation of HC and CO and to inhibit the formation of N2O and CH3CHO.