The Pt/Al2O3, In-Al2O3 and binary Pt-In/Al2O3 catalysts were prepared by a single sol-gel method. Their physical properties were characterized by BET, XRD, XPS and TPD, and their activities for selective catalytic reduction of NO with propene in the presence of oxygen were studied. The results showed that the inhibition by H2O and SO2 is reversible over Pt/Al2O3, whereas it is irreversible over In/Al2O3. In order to improve the activity and temperature window, various kinds of combined catalyst systems, such as physically mixed, two-stage, and intermediate addition reductants (IAR), for NO reduction by propene were investigated; the effects of H2O and SO2 on the activity and temperature window were also discussed. The results showed that the activities and temperature windows were obviously improved for both two-stage and IAR combined catalysts, but no cooperation effects were observed over binary Pt-In/Al2O3 catalyst or over physically mixed Pt/Al2O3 and In/Al2O3 combined catalysts. It was found that coexisting water vapor enhanced the catalytic activity at the medium temperature of 300-400degreesC over a two-stage catalyst of In/Al2O3 and Pt/Al2O3 in series. Intermediate addition of propene between a Pt/Al2O3 oxidation and an In/Al2O3 reduction combined catalyst system showed high NO reduction activity in a wider temperature window. The NO conversion was above 60% in the temperature range of 300-500degreesC, and the maximum NO conversion was 91% even in the presence of 2% H2O and 100 ppm SO2. (C) 2004 Elsevier B.V. All rights reserved.