Warm plasma activation of CO₂ in a rotating gliding arc discharge reactor

In this study, a rotating gliding arc (RGA) warm plasma has been developed for the conversion of CO₂ into CO and O₂. The effect of feed flow rate, applied voltage, arc current, and the addition of N₂ or Ar on the reaction performance has been investigated. The results show two variation patterns of CO₂ conversion and energy efficiency, depending on the specific energy input (SEI): In Pattern A with SEI > 3.5 kJ/L, the CO₂ conversion and energy efficiency decrease simultaneously with increasing SEI, while in Pattern B with SEI ≤ 3.5 kJ/L, the energy efficiency and the CO₂ conversion show an opposite trend. The recombination of CO and O at high temperatures could be responsible for the decrease of CO₂ conversion with rising SEI due to the increased retention time or gas temperature. A CO₂ conversion of 4.0-4.4% and energy efficiency of 16-17% can be achieved. Compared to other non-thermal plasmas, the RGA plasma exhibits a lower CO₂ conversion but higher energy efficiency, whilst maintaining a flow rate (e.g, 6-7 L/min) that is significantly higher than that of typical non-thermal plasmas (e.g., 20-125 ml/min in dielectric barrier and corona discharges). Increasing the fraction of N₂ or Ar promotes the conversion of CO₂ but lowers the energy efficiency. N₂ is clearly more beneficial for enhancing the CO₂ conversion in comparison to Ar. Further enhancement of the reaction performance can be expected by cooling the plasma area to lower the gas temperature, to limit the recombination of CO and O.