Non-thermal plasma-enhanced reverse water-gas shift reaction over hydroxyapatite-supported Ni catalyst: Effect of severe process conditions

CO₂ hydrogenation to carbon monoxide and water (Reverse Water Gas Shift reaction) is a promising way to valorize CO_2. It is the preliminary step in the methanol and Fischer-Tropsch synthesis processes. However, the thermodynamic barrier has limited the industrial scale-up of this process, and thus, the need for a proper catalyst formulation and reactor configuration is still ongoing. In this paper, we studied the catalytic performance of a hydroxyapatite-supported nickel-zirconia catalyst in a microwave plasma reactor for the CO₂ hydrogenation to carbon monoxide. A 10 wt% Ni- ZrO₂/HAp catalyst was prepared by the wetness impregnation method, dried at 180 ^°C for 18 h and calcined at 500^°C for 3 h. The influence of the H₂/CO₂ molar ratio, power, and GHSV on CO₂ conversion and CO selectivity was studied. In the selected range of GHSV, it did not influence the output parameters. Moreover, CO selectivity remained in the range of 98–100 % in all experiments. The highest carbon yield was 83 % under H₂/CO₂ to 2:1, Power= 2.25 kW, and GHSV= 80,000 mL.gr⁻¹.hr⁻¹ while maintaining 9 % energy efficiency. The high CO₂ conversion is justified due to the interaction of a basic catalyst with the CO₂ (weak acid) which facilitated the CO₂ reduction to CO as well as the microwave discharge reactor, whose temperature characteristics meet the requirement of the RWGS reaction. In addition, an energy efficiency equal to 28 % was observed under H₂/CO₂ to 1:1, Power= 0.8 kW, and GHSV= 120,000 mL.gr⁻¹.hr⁻¹. To the best of our knowledge, these values have never been attained before. In this study, we proposed a novel catalyst formulation for the CO₂ hydrogenation reaction, tested a microwave discharge for the reaction, and operated at very high GHSV levels, which are suitable for industrial production.