In Situ Modification of CuO-Fe₂O₃ by Nonthermal Plasma: Insights into the CO₂-to-CH₃OH Hydrogenation Reaction

The hydrogenation of CO₂ to CH₃OH on the binary mixed metal oxides of CuO-Fe₂O₃ under nonthermal plasma discharge has been reported in this study. The catalysts are synthesized using the sol-gel route and characterized by XRD, FTIR, SEM, and XPS techniques. The impact of CuO mixing with Fe₂O₃ on CO₂ conversion and CH₃OH yield has been investigated. Herein, we have compared two distinct techniques, namely thermal and plasma catalytic processes. The overall outcome shows that the CO₂ conversion and CH₃OH production increase with an increase in CuO mixing with Fe₂O₃. The synthesized catalyst does not show significant CO₂ conversion and CH₃OH formation in the thermal catalytic process (100-250 °C). Interestingly, when plasma discharge is combined with thermal heating, CO₂ conversion and CH₃OH production significantly improve. The plasma discharges in the CO₂/H₂ gas stream, at low temperatures (<200 °C), reduce Cu⁺² to Cu⁺¹ and Fe⁺³ to Fe⁺², which could probably enhance the CO₂ conversion and CH₃OH production. Among the catalysts prepared, 15% CuO-Fe₂O₃ exhibited the best catalytic activity with 13.2% CO₂ conversion, 7.3% CH₃OH yield, and a space-time yield of 13 mmol_CH3OH/h g_cat, with 4.67 kJ/L of specific input energy (SIE). The CH₃OH space-time yield is 2.9-fold higher than that of the commercial catalyst Cu/ZnO/Al₂O₃, which is operated at 30 °C with 45.45 kJ/L SIE.