Experimental and theoretical studies of the reaction between cationic vanadium oxide clusters and acetylene

The time of flight mass spectrometer coupled with a laser ablation/supersonic expansion cluster source and a fast flow reactor was adopted to study the reactivity of cationic vanadium oxide clusters (V _m O _n ⁺) toward acetylene (C₂H₂) molecules under gas phase (P, ∼ 1.14 kPa), under near room temperature (T, ∼ 350 K) conditions. Association products, V _m O _n C₂H₂⁺ (m,n = 2,4; 2,6; 3,7–8; 4,9–11; 5,12–13; 6,13–16, and 7,17), are observed. The oxidation of C₂H₂ by (V₂O₅) _n ⁺ (n = 1–3) is experimentally identified. The reactivity of (V₂O₅) _n ⁺ decreases as n increases. Density functional theory (DFT) calculations were carried out to interpret the reaction mechanisms. The DFT results indicate that a terminal oxygen atom from V₂O₅⁺ can transfer overall barrierlessly to C₂H₂ at room temperature, which is in agreement with the experimental observation. Other experimental results such as the observation of V₂O₆C₂H₂⁺ and nonobservation of V₂O_7,8C₂H₂⁺ in the experiments are also well interpreted based on the DFT calculations. The reactivity of vanadium oxide clusters toward acetylene and other hydrocarbons may be considered in identifying molecular level mechanisms for related heterogeneous catalysis. Supported by the Knowledge Innovation Program of Chinese Academy of Sciences (Grant Nos. KJCX2-YW-N24, and KZCX2-YW-205) and the Hundred Talents Funds, National Natural Science Foundation of China (Grant Nos.20577052, 20673123 and 20703048), and National Basic Research Program of China (Grant No. 2006CB403701 and 2006CB932100)