Hydrogen Atom Abstraction from CH4 by Nanosized Vanadium Oxide Cluster Cations

Reactions of vanadium oxide cluster cations with methane in a fast-flow reactor were investigated with a time-of-flight mass spectrometer. Hydrogen atom abstraction (HAA) reactions were identified over stoichiometric cluster cations (V2O5)N+ for N as large as 11, and the relative reactivity decreases as the cluster size increases. Density functional calculations were performed to study the structural, bonding, and electronic properties of the stoichiometric oxide clusters with the size N = 2–6. The geometric structures were obtained by means of topological and structural unit analyses together with global optimizations. Two types of oxygen-centered radicals were found in these clusters, which are active sites of the clusters in reactions with CH4. The size-dependent reactivity is rationalized by the charge, spin, and structural effects. This work is among the first reports that HAA from CH4 can take place on nanosized oxide clusters, which makes a bridge between the small reactive species and inert condensed phase materials for CH4 activation under low temperature.