On the nature and reactivity of active oxygen species formed from O 2 and N 2O on VO x/MCM-41 used for oxidative dehydrogenation of propane

Abstract

Electron paramagnetic resonance (EPR) spectroscopy under controlled atmosphere conditions has been applied to elucidate the nature and reactivity of oxygen species formed upon reoxidation of a reduced VO x (2.7 wt.%)/MCM-41 catalyst by gas-phase O 2 or N 2O. An electrophilic V n +⋯O − ( n = 4, 5) radical anion intermediate is formed from O 2 probably via dissociation of a bi-atomic adsorbed oxygen species. This radical is remarkably stable in inert atmosphere up to elevated temperatures but reacts partly with C 3H 8 and almost completely with C 3H 6 and CO already at room temperature. In contrast, no such species could be observed upon reoxidation of reduced VO x species with N 2O. This might be due to the rapid formation of nucleophilic O 2− oxide ions, which are not EPR-active. The different electronic nature of these oxygen intermediates is discussed as a reason for the higher propene selectivity obtained in propane oxidative dehydrogenation over VO x /MCM-41 with N 2O.