Thermal ethane activation by bare [V₂O₅]⁺ and [Nb₂O₅]⁺ cluster cations: on the origin of their different reactivities.

The gas-phase reactivity of V2O5 and Nb2O5 towards ethane has been investigated by means of mass spectrometry and density functional theory (DFT) calculations. The two metal oxides give rise to the formation of quite different reaction products; for example, the direct room-temperature conversions C2H6→C2H5OH or C2H6→CH3CHO are brought about solely by V2O5. In distinct contrast, for the couple Nb2O5/C2H6, one observes only single and double hydrogen-atom abstraction from the hydrocarbon. DFT calculations reveal that different modes of attack in the initial phase of C-H bond activation together with quite different bond-dissociation energies of the M-O bonds cause the rather varying reactivities of V2O5 and Nb2O5 towards ethane. The gas-phase generation of acetaldehyde from ethane by bare V2O5 may provide mechanistic insight in the related vanadium-catalyzed large-scale process.