Abstract

Vanadium oxides are key industrial catalysts in the oxidation and functionalization of various chemical compounds, and studies of gas-phase vanadium oxide clusters provide an avenue to explore the reactive sites implicated in surface catalysis. An extensive amount of experimental data has been reported on the gas-phase fragmentation of vanadium oxide cluster ions and their reactions with environmentally-relevant halocarbons. Our computational studies aim at further understanding the structure and properties of vanadium oxide clusters, as well as their reactivity towards fluorocarbons. Accordingly, we report a systematic density-functional theory (DFT) study of the structural and electronic properties of V x O y + and V x O y clusters, and investigate their reactions with CH 2 F 2 and CH 3 CF 3 by DFT calculations. Our results suggest that both B3LYP/TZVP and PLAP4/DZVP+aux. are appropriate model chemistries to investigate vanadium oxide clusters, but the latter is less computationally intensive, and thus more suitable for large clusters. Stable ground-state and low-lying excited-state structures and their electronic properties are obtained for both V x O y + and V x O y (x = 1-4, y = 1-10) clusters with the PLAP4/DZVP+aux. model chemistry. The molecular structures and electronic properties of large polyvanadium oxide clusters are systematically investigated and reported for the first time. The reaction of V 2 O 4 + with fluorocarbons was investigated with the B3LYP/TZVP model chemistry. Oxygen transfer and stepwise HF abstraction from the fluorocarbon are observed in the reactions of V 2 O 4 + with CH 2 F 2 and CH 3 CF 3 , respectively. These reaction mechanisms help explain why larger clusters such as V 4 O 8 + were observed to be chemically inert towards CH 2 F 2 , while the reactivity of V x O y + cluster ions towards CH 3 CF 3 was not found to depend on cluster size experimentally.