These Vo have been shown to act as active sites for plasma CO2 reduction and also increase the electron density of the adjacent metal cation and promote its interactions with the acidic carbon on CO2. The formation energies of Vo in Al2O3, TiO2 and ZnO have been reported to be 7.0 eV, 5.7 eV, and 4.1 eV respectively. This suggests that the formation of Vo would be suppressed on Al2O3 as compared to TiO2 or ZnO due to the higher energies required. This is supported by the observation of the formation of reduced metal centers on the TiO2 catalyst during CO2 plasma exposure. While we observed the presence of reduced Ti 3+ on the surface of the TiO2 catalyst post plasma exposure, we did not observe reduced Zn in XPS measurements.