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 ion 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. Diverse reactivity patterns for the gas‐phase reactions of C2H6 with the structurally related cluster ions [V2O5]+ and [Nb2O5]+ have been identified by using experimental and theoretical methods. Different bond dissociation energies and the higher ability of vanadium to access multiple formal oxidation states are the main reason for the differences. The industrially relevant ethane→acetaldehyde conversion can be brought about by bare [V2O5]+ at room temperature (see figure).