Hydrogen-atom abstraction from methane by stoichiometric vanadium-silicon heteronuclear oxide cluster cations.
Vanadium-silicon heteronuclear oxide cluster cations were prepared by laser ablation of a V/Si mixed sample in an O(2) background. Reactions of the heteronuclear oxide cations with methane in a fast-flow reactor were studied with a time-of-flight (TOF) mass spectrometer to detect the cluster distribution before and after the reactions. Hydrogen abstraction reactions were identified over stoichiometric cluster cations [(V(2)O(5))(n)(SiO(2))(m)](+) (n=1, m=1-4; n=2, m=1), and the estimated first-order rate constants for the reactions were close to that of the homonuclear oxide cluster V(4)O(10) (+) with methane. Density functional calculations were performed to study the structural, bonding, electronic, and reactivity properties of these stoichiometric oxide clusters. Terminal-oxygen-centered radicals (O(t)*) were found in all of the stable isomers. These O(t)* radicals are active sites of the clusters in reaction with CH(4). The O(t)* radicals in [V(2)O(5)(SiO(2))(1-4)](+) clusters are bonded with Si rather than V atoms. All the hydrogen abstraction reactions are favorable both thermodynamically and kinetically. This work reveals the unique properties of metal/nonmetal heteronuclear oxide clusters, and may provide new insights into CH(4) activation on silica-supported vanadium oxide catalysts.
Ding
Xun-Lei
XL
Beijing National Laboratory for Molecular Science, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun North First Street 2, Beijing, 100190 P. R. China.
Zhao
Yan-Xia
YX
Wu
Xiao-Nan
XN
Wang
Zhe-Chen
ZC
Ma
Jia-Bi
JB
He
Sheng-Gui
SG