The reduction of nitric oxide by propene in the presence of oxygen over platinum-group metals supported on TiO2, ZnO, ZrO2, and Al2O3 has been investigated by combined diffuse reflectance FT-IR spectroscopy and catalytic activity studies under flow reaction conditions at 523-673 K and atmospheric pressure. The catalytic activity for the selective reduction of nitric oxide and the intensity of the IR bands due to reaction species depended strongly on the nature of the support, type of supported metal, reaction time and temperature. The main surface species detectable by IR were adsorbed hydrocarbons (2900-3080 cm(-1)), isocyanate (2180, and 2232-2254 cm(-1)), cyanide (2125 cm(-1)), nitrosonium (1901 cm(-1)), CO2 (2343-2357 cm(-1)), CO(2058 cm(-1)) and carbonate (1300-1650 cm(-1)) species. In the case of rhodium containing catalysts, when supported on Al2O3, they exhibited both the highest concentration of surface species and the highest activity for nitric oxide reduction and selectivity to nitrogen. The catalytic activity and the IR intensities of the nitrosonium and isocyanate bands increased with reaction temperature, reached their maximum between 570 and 620 K, and then decreased at higher temperatures. The IR band intensities due to nitrogen containing surface species were found to be strongly correlated to the activity for nitric oxide conversion and only slightly related to the selectivity to dinitrogen.