Fine cubic CuO nanocrystals as highly selective catalyst for propylene epoxidation with molecular oxygen.

Propylene epoxidation with O to propylene oxide is a very valuable reaction but remains as a long-standing challenge due to unavailable efficient catalysts with high selectivity. Herein, we successfully explore 27 nm-sized cubic CuO nanocrystals enclosed with {100} faces and {110} edges as a highly selective catalyst for propylene epoxidation with O, which acquires propylene oxide selectivity of more than 80% at 90-110 °C. Propylene epoxidation with weakly-adsorbed O species at the {110} edge sites exhibits a low barrier and is the dominant reaction occurring at low reaction temperatures, leading to the high propylene oxide selectivity. Such a weakly-adsorbed O species is not stable at high reaction temperatures, and the surface lattice oxygen species becomes the active oxygen species to participate in propylene epoxidation to propylene oxide and propylene partial oxidation to acrolein at the {110} edge sites and propylene combustion to CO at the {100} face sites, which all exhibit high barriers and result in decreased propylene oxide selectivity.