Trends in C-O and N-O bond scission on rutile oxides described using oxygen vacancy formation energies

Reactivity trends on transition metals can generally be understood through the d-band model, but no analogous theory exists for transition metal oxides. This limits the generality of analyses in oxide-based catalysis and surface chemistry and has motivated the appearance of numerous descriptors. Here we show that oxygen vacancy formation energy (Delta E-Vac) is an inexpensive yet accurate and general descriptor for trends in transition-state energies, which are usually difficult to assess. For rutile-type oxides (MO2 with M = 3d metals from Ti to Ni), we show that Delta E-Vac captures the trends in C-O and N-O bond scission of CO2, CH3OH, N2O, and NH2OH at oxygen vacancies. The proportionality between Delta E-Vac and transition-state energies is rationalized by analyzing the oxygen-metal bonds, which change from ionic to covalent from TiO2 to NiO2. Delta E-Vac may be used to design oxide catalysts, in particular those where lattice oxygen and/or oxygen vacancies participate in the catalytic cycles.