The selective catalytic reduction (SCR) of nitric oxide (NO) by propylene (C3H6) Over a 1 wt.% Pt/SiO2 catalyst was studied by the use of in situ Fourier transform infrared (FTIR) spectroscopy at 250 degrees C. At this temperature, introduction of NO to the catalyst did not result in the formation of any significant amounts of adsorbed NOx-type species on either the catalyst or the SiO2 support. On the contrary, introduction of C3H6 to the same catalyst resulted in the formation of surface carboxylates. Experiments conducted under reaction conditions resulted in the formation of a surface cyanide (-CN) species, and a gas phase/weakly adsorbed nitrous oxide (N2O) species. The surface cyanide is the product of the reaction between an oxygen-activated hydrocarbon derivative and NO and is reactive toward NO, NO2, and O-2, resulting in the formation of N-2 and N2O. Its behavior, as observed in this study, is consistent with a role as a potential intermediate in the selective reduction of NO by propylene over the Pt/SiO2 catalyst.