An overview of CO ₂ conversion in a microwave discharge: the role of plasma-catalysis

An overview of the recent progress on plasma-assisted CO 2 conversion in microwave discharges is given. Special attention is devoted to the results obtained using plasma catalysis, which are compared to the plasma-only CO 2 decomposition cases. The effects of plasma operating conditions, catalyst preparation methods, nature of plasma activation gas, gas mixture, as well as the NiO content on the TiO 2 surface on CO 2 conversion and its energy efficiency are discussed. A significant improvement in CO 2 conversion is obtained with a NiO/TiO 2 catalyst activated in Ar plasma, when the NiO content is about 10 wt.%. The catalyst characterization data show that Ar plasma treatment results in a higher density of oxygen vacancies and a comparatively more uniform distribution of NiO on the TiO 2 surface, which strongly influence CO 2 conversion and its energy efficiency. The dissociative electron attachment of CO 2 at the catalyst surface enhanced by the oxygen vacancies and by plasma electrons may also explain the increase in conversion and energy efficiencies. A mechanism for the plasma-catalytic CO 2 conversion at the surface of an Ar plasma-threated catalyst is proposed.