Tuning electronic structure and chemical reactivity via oxidation state in molybdenum oxide

Abstract

Molybdenum oxide has a broad range of applications in areas such as catalysis, antimicrobial coatings, medicine, and sensors. In this study, we have investigated the geometric and electronic structure, thermal stability, and chemical reactivity of molybdenum oxide at different oxidation and electronic charge states using cluster models of Mo7On with density functional theory calculations. A decrease in the energy of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) has been identified as n increases from 0 to 21. Ionization potential and electron affinity of Mo7On correlate strongly with the energies of HOMO and LUMO, and both increase with increasing n. We have identified the most stable CO binding sites on Mo7On, calculated CO binding energy and simulated IR absorption spectrum of COMo7On. An n-dependent increase in CO stretching frequencies and decrease in CO binding energies indicate that electron backdonation from Mo7On to CO governs the changes in CO binding energy as a function of oxide composition. CO stretching frequency in COMo7O21 is 2197 cm−1, which is 55 cm−1 higher than in the gas phase CO molecule, indicating that CO is an electron density donor and the oxide acts as an electron acceptor at this stoichiometric composition. Comparing CO binding energies in neutral and ionic (q=+/-1) COMo7On, there is, in average, a stabilizing effect of excess (missing) charge on CO binding energy at low (high) n.