Density functional theory (DFT) study of reaction between vanadium trioxide cluster cation (VO3+) and ethylene (C2H4) to yield VO2+ + CH3CHO (acetaldehyde) and VO2CH2+ + HCHO (formaldehyde) is carried out. Structures of all reactants, products, intermediates, and transition state in the reaction have been optimized and characterized. The results show unexpected barriers in the reaction due to the existence of a η2-O2 moiety in the ground state structure of VO3+. The initial reaction steps combining ethylene adsorption, C=C activation and O-O cleavage are proposed as rate limiting processes. Comparison of reactions of VO3+ + C2H4 with VO3 + C2H4 and VO2+ + C2H4 in the previous studies is made in detail. The results of this work may shed light on the understanding of C=C bond cleavage in related heterogeneous catalysis.
WANG ZheChenDING XunLeiMA YanPingCAO HaiWU XiaoNanZHAO YanXiaHE ShengGui
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(VmOn+) toward acetylene(C2H2) molecules under gas phase(P,～ 1.14 kPa),under near room temperature(T,～ 350 K) conditions.Association products,VmOnC2H2+(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 V2O6C2H+2 and non-observation of V2O7,8C2H+2 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.
