Sn/gamma-Al2O3 were effective and highly stable catalysts for NO reduction with propene under high partial pressures of oxygen and water. The activity depended on the Sn loading. For a 10 wt% Sn/Al2O3 at 475-500 degrees C, 58% conversion of 1000 ppm NO to N-2 was obtained in the presence of 10% water and 15% O-2, at a space velocity of 30,000 h(-1), and 77% conversion at 15,000 h(-1). The NO conversion increased with O-2 partial pressure but was suppressed by water below 500 degrees C. The activity was also suppressed by SO2 but could be restored slowly after the removal of SO2.