The incorporation of zirconia onto the silica supports of platinum catalysts improved the selective reduction of NO by hydrogen in comparison to platinum catalysts supported on silica and alumina. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, the temperature-programmed desorption of ammonia, X-ray photoelectron spectroscopy, and the adsorption of carbon monoxide. Their performances were examined in a flow microreactor and by in situ IR spectroscopy. The incorporation of zirconia onto silica created many strong acid sites and stabilized the dispersed platinum. It aided the adsorption of NO and enhanced the formation of ammonia on the platinum catalysts, even in the presence of excess oxygen. The formation of ammonia from NO and the subsequent removal of NO through reaction with ammonia considerably improved the conversion of NO and the yield of N-2. The presence of zirconia also improved the stability of the supported platinum against hydrothermal treatment. (C) 2012 Elsevier B.V. All rights reserved.