A first principles analysis of the activation of propane over substituted heterpolyacids

The activation of propane over the Keggin structure of phosphomolybdic acid was studied using ab initio density functional theoretical calculations. The effects of vanadium and niobium substitution into the phosphomolybdic Keggin structure on the selective oxidation of propane were examined. Propane activation proceeded with the homolytic cleavage of the C-H bond forming radicals. The substitution of vanadium for molybdenum in the Keggin structure acted to reduce the barrier of alkane activation and thus led to a more exothermic reaction energy. Incorporating vanadium into the Keggin unit increased the oxidizing power of the HPA molecule as it stabilizes the Lowest Unoccupied Molecular Orbital (LUMO). Alkane activation resulted in a two electron reduction of the Keggin unit; therefore the stabilization of the LUMO led to more favorable reaction. This is an abstract of a paper presented at the AIChE Annual Meeting (San Francisco, CA 11/12-17/2006).