Enhanced effect of plasma on catalytic reduction of CO_2 to CO with hydrogen over Au/CeO_2 at low temperature

In terms of the reaction of CO₂ reduction to CO with hydrogen, CO₂ conversion is very low at low temperature due to the limitation of thermodynamic equilibrium (TE). To overcome this limitation, plasma catalytic reduction of CO₂ to CO in a catalyst-filled dielectric barrier discharge (DBD) reactor is studied. An enhanced effect of plasma on the reaction over Au/CeO₂ catalysts is observed. For both the conventionally catalytic (CC) and plasma catalytic (PC, P_in = 15 W) reactions under conditions of 400 °C, H₂/CO₂ = 1, 200 SCCM, GHSV = 12,000 mL•g⁻¹_cat•h⁻¹, CO₂ conversions over Au/CeO₂ reach 15.4% and 25.5% due to the presence of Au, respectively, however, those over CeO₂ are extremely low and negligible. Moreover, CO₂ conversion over Au/CeO₂ in the PC reaction exceeds 22.4% of the TE conversion. Surface intermediate species formed on the catalyst samples during the reactions are determined by in-situ temperature-programmed decomposition (TPD) technique. Interestingly, it disclosed that in the PC reaction, the formation of formate intermediate is enhanced by plasma, and the acceleration by plasma in the decomposition of formate species is much greater than that in the formation of formate species on Au/CeO₂. Enhancement factor is introduced to quantify the enhanced effect of plasma. Lower reactor temperature, higher gas hourly space velocity (GHSV), and lower molar ratio of H₂/CO₂ would be associated with larger enhancement factor.