The conversion of CO2 and CO2/H2O mixtures on a TiO2 supported NiO catalyst in a pulsed surface-wave sustained microwave discharge has been investigated. The influence of the catalyst preparation method (conventional calcination (in air or Ar) vs. Ar plasma-assisted decomposition) on the CO2 conversion and its energy efficiency has been studied. The results demonstrate that the Ar plasma-treated catalyst is more active compared to the conventional calcined one. The plasma-treated catalyst increases the CO2 conversion and its energy efficiency almost by a factor of two, compared to the plasma only assisted CO2 dissociation, while the conventional calcined catalysts affect the CO2 conversion rather insignificantly. The conversion of CO2 is found to be about 45% at 70 Ton in pure CO2 with Ar plasma-treated catalyst, having an energy efficiency of 56%. In the case of CO2/H2O mixture, the CO2 conversion efficiency reaches 42% (energy efficiency is 52%) at 60 Torr. The catalyst characterization shows that Ar plasma treatment may result in a higher density of oxygen vacancies and a comparatively uniform distribution of NiO on the TiO2 surface. The dissociative electron attachment of CO2 at the catalyst surface enhanced by the oxygen vacancies and plasma electrons may explain the increase of conversion and energy efficiencies in this case. A mechanism of plasma-catalytic conversion of CO2 at the catalyst surface in CO2/H2O mixture is proposed. (C) 2017 Elsevier B.V. All rights reserved.