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 (ΔE _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 ΔE _Vac captures the trends in C-O and N-O bond scission of CO₂, CH₃OH, N₂O, and NH₂OH at oxygen vacancies. The proportionality between ΔE _Vac and transition-state energies is rationalized by analyzing the oxygen-metal bonds, which change from ionic to covalent from TiO₂ to NiO₂. ΔE _Vac may be used to design oxide catalysts, in particular those where lattice oxygen and/or oxygen vacancies participate in the catalytic cycles.