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.