A series of Ce-Ti mixed-oxide catalysts were prepared by the sol-gel method for selective catalytic reduction (SCR) of NO with ammonia as reductant. These catalysts were characterized by XRD, BET, and XPS techniques. The experimental results show that the best Ce-Ti mixed-oxide catalyst yielded 98.6% NO conversion, and 100% N-2 selectivity at typical SCR reaction temperatures (300-400 degrees C) and the high gas hourly space velocity of 50,000 h(-1). As the Ce loading (the mass ratio of CeO2/TiO2) Was increased from 0 to 0.6, NO conversion increased markedly, but decreased at higher Ce loading. The most active catalyst was obtained with a Ce loading of 0.6. The high activity might be attributed to high Ce loading, strong interaction between Ce and Ti, high concentration of amorphous Ce on the catalyst surface, or the increase of chemisorbed oxygen or/and weakly bonded oxygen species, resulting from the presence of Ce3+ after Ce addition. The effect of the calcination temperature was also investigated, and the optimal calcination temperature was 500 degrees C. The presence of oxygen played an essential role in NO reduction, and the activity of the Ce(0.6)Ti catalyst was not depressed when oxygen concentration was higher than 1%. The effect of SO2 and H2O on the activity of the Ce(0.6)Ti catalyst was bound up with the reaction temperature. (C) 2009 Elsevier B.V. All rights reserved.