Similarity and differences in the oxidative dehydrogenation of C2–C4 alkanes over nano-sized VOx species using N2O and O2

The effect of O2 and N2O on alkane reactivity and olefin selectivity in the oxidative dehydrogenation of ethane, propane, n-butane, and iso-butane over highly dispersed VOx species (0.79 V/nm2) supported on MCM-41 has been systematically investigated. For all the reactions studied, olefin selectivity was significantly improved upon replacing O2 with N2O. This is due to suppressing COx formation in the presence of N2O. The most significant improving effect of N2O was observed for iso-butane dehydrogenation: S(iso-butene) was ca. 67% at X(iso-butane) of 25%.Possible origins of the superior performance of N2O were derived from transient experiments using 18O2 traces. 18O16O species were detected in 18O2 and 18O2–C3H8 transient experiments indicating reversible oxygen chemisorption. In the presence of alkanes, the isotopic heteroexchange of O2 strongly increased. Based on the distribution of labeled oxygen in COx and in O2 as well as on the increased COx formation in sequential O2–C3H8 experiments, it is suggested that non-lattice oxygen species (possibly of a bi-atomic nature) originating from O2 are non-selective ones and responsible for COx formation. These species are not formed from N2O.