C=c Bond Cleavage On Neutral Vo_3(v_2o_5)_n Clusters

摘要

The reactions of neutral vanadium oxide clusters with alkenes (ethylene, propylene, 1-butene, and 1,3-butadiene) are investigated by experiments and density function theory (DFT) calculations. Single photon ionization through extreme ultraviolet radiation (EUV, 46.9 nm, 26.5 eV) is used to detect neutral cluster distributions and reaction products. In the experiments, we observe products (V_2O_5)_nVO_2CH_2, (V_2O_5)_nVO_2C_2H_4, (V_2O_5)_nVO_2C_3H_4, and (V_2O_5)_nVO_2C_3H_6, for neural V_mO_n clusters in reactions with C_2H_4, C_3H_6, C_4H_6, and C_4H_8, respectively. The observation of these products indicates that the C=C bonds of alkenes can be broken on neutral oxygen rich vanadium oxide clusters with the general structure VO_3(V_2O_5)_(n=0,1,2...). DFT calculations demonstrate that the reaction VO_3 + C_3H_6 → VO_2C_2H_4 + H_2CO is thermodynamically favorable and overall barrierless at room temperature. They also provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes is broken on VO_3(V_2O_5)_(n=0,1,2...) clusters. A catalytic cycle for alkene oxidation on vanadium oxide is suggested based on our experimental and theoretical investigations. The reactions of V_mO_n with C_6H_6 and C_2F_4 are also investigated by experiments. The products VO_2(V_2O_5)_nC_6H_4 are observed for dehydration reactions between V_mO_n clusters and C_6H_6. No product is detected for V_mO_n clusters reacting with C_2F_4. The mechanisms of the reactions between VO_3 and C_2F_4/C_6H_6 are also investigated by calculations at the B3LYP/TZVP level.