Catalytic epoxidation of propylene with CO/O2 over Au/TiO2

• Propylene undergoes gas-phase selective epoxidation with CO/O2 reactants over Au/TiO2.
• The reaction is analogous to the known epoxidation of propylene with H2/O2 mixture.
• Either CO and H2 are the necessary reducing co-reagents to perform the reaction.
• CO and H2 induce a formation of the same active oxygen species.

Gold nanoparticles supported on TiO2 are known to catalyze vapor-phase epoxidation of propylene with molecular oxygen in the presence of H2 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 O2 can be carried out in a flow reactor over Au/TiO2 at a temperature of 40–90 °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 H2/O2 mixture. Utilization efficiency of CO reaches 25%, which is comparable to that of H2 in the analogous reaction of propylene, H2 and O2. Proposed mechanism for the reaction involves the formation of specific oxygen species arising from O2 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.

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