Conversion of CO ₂ to CO over Cu–Fe-Based Catalysts via the Reverse Water–Gas Shift (RWGS) Reaction: A Comparative Study on the Impacts of Synthesis Methods and Operating Parameters

In this work, the performance (i.e., conversion and product selectivity) of various Cu–Fe catalysts supported on samarium-doped ceria (Cu–Fe/SDC) was evaluated for the RWGS reaction under different reaction conditions. In order to determine the effect of synthesis methods, the catalysts were synthesized using several techniques, including incipient wetness impregnation (IWI), polyol reduction (PR), ultrasound-assisted polyol reduction (UPR), ultrasound-assisted impregnation (UI), and ultrasound-assisted coprecipitation (UCP). Among these, the UCP method produced catalysts with superior activity and thermal stability, achieving CO2 conversion near thermodynamic equilibrium above 550 °C (e.g., CO2 conversion of ∼35% at 600 °C, with a gas hourly space velocity (GHSV) of ∼1.2 × 105 mL·gcat–1·h–1) and nearly 100% CO selectivity. Characterization results revealed that this enhanced performance stems from improved metal dispersion, smaller active particle sizes, and synergistic interactions among Cu, Fe, and the SDC support, contributing to enhanced redox properties and resistance to sintering. Stability tests further confirmed the UCP catalyst’s suitability for sustained RWGS operation at moderate temperatures (∼600 °C), highlighting a potential trade-off between energy consumption and CO production efficiency. This opens opportunities to implement energy-efficient RWGS processes and eliminates the need for expensive superalloy materials in RWGS reactor designs.