Oxidative dehydrogenation of propane: Differences between N2O and O2 in the reoxidation of reduced vanadia sites and consequences for selectivity

The role of vanadyl and peroxovanadate oxygen species in the oxidative dehydrogenation of propane (ODP) was analyzed by density functional theory (DFT). The dehydrogenation of C3H8 to C3H6 and the oxidation of C3H6 occurred over vanadyl oxygen of VOx species, yielding reduced VOx species. The vanadyl oxygen species were restored via reoxidation of reduced VOx species with O2 and N2O. The ODP reaction with N2O occurred via a VV(d0)/VIII(d2) redox couple, whereas both VV(d0)/VIV(d1) and VV(d0)/VIII(d2) redox cycles were active with O2. O2 was a more active oxidizing agent than N2O. Peroxovanadates as precursors of vanadyl species were formed on reoxidation of reduced vanadium oxide species with O2, but not with N2O. Peroxovanadates were highly reactive for propene oxidation. The absence of peroxovanadates may explain the superior performance of N2O compared with O2 in the selective ODP reaction over highly dispersed VOx species.