title: Striking Doping Effects on Thermal Methane Activation Mediated by the Heteronuclear Metal Oxides [XAlO4].+(X=V, Nb, and Ta).
abstract: The thermal reactivity of the heteronuclear metal-oxide cluster cations [XAlO4].+(X=V, Nb, and Ta) towards methane has been studied by using mass spectrometry in conjunction with quantum mechanical calculations. Experimentally, a hydrogen-atom transfer (HAT) from methane is mediated by all the three oxide clusters at ambient conditions. However, [VAlO4].+is unique in that this cluster directly transforms methane into formaldehyde. The absence of this reaction for the Nb and Ta analogues demonstrates a striking doping effect on the chemoselectivity in the conversion of methane. Mechanistic aspects of the two reactions have been elucidated by quantum-chemical calculations. The HAT reactivity can be attributed to the significant spin density localized at the terminal oxygen atom (Ot.-) of the cluster ions, while the ionic/covalent character of the Lewis acid-base unit [X-Ob] plays a crucial role for the generation of formaldehyde. The mechanistic insight derived from this combined experimental/computational investigation may provide guidance for a more rational design of catalysts.
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.|Department of Chemistry, Fudan University, Shanghai, 200433, P. R. China.
authors.forename: Xiao-Nan
authors.initials: XN
authors.lastname: Wu
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.|Institute of Theoretical Chemistry, Jilin University, Changchun, 130023, P. R. China.
authors.forename: Jilai
authors.initials: J
authors.lastname: Li
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Schlangen
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
authors.forename: Shaodong
authors.initials: S
authors.lastname: Zhou
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
authors.forename: Patricio
authors.initials: P
authors.lastname: González-Navarrete
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Schwarz
keywords: doping; gas-phase reactions; heteronuclear metal oxide cluster; methane conversion; reaction mechanisms