Experimental and Theoretical Study of the Reactions between Neutral Vanadium Oxide Clusters and Ethane, Ethylene, and Acetylene

摘要

Reactions of neutral vanadium oxide clusters with small hydrocarbons, namely C_2H_6, C_2H_4, and C_2H_2, are investigated by experiment and density functional theory (DFT) calculations. Single photon ionization through extreme ultraviolet (EUV, 46.9 nm, 26.5 eV) and vacuum ultraviolet (VUV, 118 nm, 10.5 eV) lasers is used to detect neutral cluster distributions and reaction products. The most stable vanadium oxide clusters VO_2, V_2O_5, V_3O_7, V_4O_(10), etc. tend to associate with C_2H_4 generating products V_mO_nC_2H_4. Oxygen-rich clusters VO_3(V_2O_5)_n=0,1,2..., (e.g., VO_3, V_3O_8, and V_5O_(13)) react with C_2H_4 molecules to cause a cleavage of the C=C bond of C_2H_4 to produce (V_2O_5)_nVO_2CH_2 clusters. For the reactions of vanadium oxide clusters (V_mO_n) with C_2H_2 molecules, V_mO_nC_2H_2 are assigned as the major products of the association reactions. Additionally, a dehydration reaction for VO_3 + C_2H_2 to produce VO_2C-2 is also identified. C_2H_6 molecules are quite stable toward reaction with neutral vanadium oxide clusters. Density functional theory calculations are employed to investigate association reactions for V_2O_5 + C_2H_x. The observed relative reactivity of C_2 hydrocarbons toward neutral vanadium oxide clusters is well interpreted by using the DFT calculated binding energies. DFT calculations of the pathways for VO_3+C-2H_4 and VO_3+C_2H_2 reaction systems indicate that the reactions VO_3+C_2H_4 → VO_2CH_2 + H_2CO and VO_3+C_2H_2 → VO_2C_2 + H_2O are thermodynamically favorable and overall barrierless at room temperature, in good agreement with the experimental observations.