We have investigated the propylene oxidation on Ag(1 1 1) by means of temperature-programmed reaction spectroscopy (TPRS) and reflection-absorption infrared spectroscopy (RAIRS). Existence of atomic oxygen on the surface greatly enhances the interaction of propylene with Ag(1 1 1) at 100 K. With the coverage of oxygen adatoms increasing, a gradual transition from the pi-bonded propylene to the di-sigma-bonded propylene was observed. Only a small fraction of oxygen adatoms participate the propylene oxidation reaction. Three propylene oxidation pathways were observed, leading to the formation not only of combustion products (CO2) but also of partially oxidation products (CO and acetone). RAIRS results evidence the formation of hydroxyls on the surface at elevated temperatures. Both TPRS and RAIRS results reveal that the pi-bonded and di-sigma-bonded propylene follow different combustion mechanisms. (c) 2007 Elsevier B.V. All rights reserved.