Gold nanoparticles supported on TiO2 are known to catalyze vapor-phase epoxidation of propylene with molecular oxygen in the presence of H-2 as the necessary reducing co reagent. Here, we report that carbon monoxide can be employed instead of hydrogen to accomplish similar reaction. The reaction of propylene, CO and O-2 can be carried out in a flow reactor over Au/TiO2 at a temperature of 40-90 degrees C, The propylene oxide selectivity attains 80-97% at propylene conversion of 1.7-3.7%. The propylene oxide yield goes through the maximum as a function of reaction time, the maximal value being twice higher compared to yield of propylene oxide achieved by "traditional" reaction with H-2/O-2 mixture. Utilization efficiency of CO reaches 25%, which is comparable to that of H-2 in the analogous reaction of propylene, H-2 and O-2. Proposed mechanism for the reaction involves the formation of specific oxygen species arising from O-2 on catalytic sites reduced with CO. This is in line with generation of highly reactive oxygen species (detectable by oxygen isotopic exchange) on Au/TiO2 surface treated preliminarily with CO. (C) 2014 Elsevier B.V. All rights reserved,