Evaluation of Non-catalytic Reverse Water-Gas Shift Reaction Using Microwave Discharge Plasma at Atmospheric Pressure

Abstract

Amid concerns about the progress of climate change, the development of effective utilization technologies of carbon dioxide (CO₂) has gained significant attention as a means to sustainably reduce CO₂ concentration in the atmosphere. The reverse water-gas shift (RWGS) reaction (CO₂ + H₂ → CO + H₂O) using CO₂ and hydrogen (H₂) with a ratio of 1:1, which produces carbon monoxide (CO) employed as an essential feedstock in chemical industries, is a promising and practical strategy for effective utilization of CO₂. This study investigates experimentally the non-catalytic RWGS reaction using microwave discharge plasma at atmospheric pressure. The microwave discharge plasma can be generated using a rod-electrode-type microwave plasma source (MPS). The CO₂ conversion, CO selectivity, CO yield, and specific energy input (SEI) are then evaluated in terms of the average transmission power to the rod-electrode-type MPS at a constant flow rate. The highest CO₂ conversion of 55.9%, CO selectivity of 90.6%, and CO yield of 50.7% are achieved at the SEI of approximately 2.5 eV/molecule (equivalent to approximately 9.9 kJ/L). On the other hand, the highest energy efficiency for the CO yield of 10.6% was achieved at the SEI of approximately 1.6 eV/molecule (equivalent to approximately 6.5 kJ/L). The findings highlight the potential of microwave discharge plasma as a viable approach for promoting the non-catalytic RWGS reaction at atmospheric pressure, offering a novel pathway for efficient CO₂ utilization.