Aerobic epoxidation of propene over silver (111) and (100) facet catalysts

Catalytic performance of single-crystal Ag(100) and Ag(111) catalysts for propene oxidation has been investigated by means of Raman spectroscopy and mass spectrometry, and the energy profile has been obtained at the DFT-D level. It has been theoretically found and confirmed by Raman spectroscopy that Ag(100) surface is more reactive toward O2 dissociation than Ag(111) and that adsorbed oxo-species are more strongly bonded to the Ag(100) facet. The higher selectivity toward propylene oxide (PO) observed for the Ag(100) catalyst can be rationalized from theoretical calculations indicating that the activation barriers for formation of the allylic intermediate – precursor of combustion products – are rather similar on both silver surfaces, whereas energy barriers on the reaction pathways for formation of PO and carbonylic products (acetone and propanal) are systematically smaller on the Ag(100) surface.