Oxygenate Production from Plasma-Activated Reaction of CO₂ and Ethane

Converting CO₂ to value-added chemicals using surplus light alkanes such as ethane is an attractive opportunity to move toward a circular carbon economy without requiring H₂ as a feedstock. Currently, the production of valuable oxygenated hydrocarbons such as alcohols, aldehydes, and acids from ethane involves either multistep, high-pressure heterogeneous catalysis processes or homogeneous catalytic reactions that entail significant product separation challenges. One-step conversion of ethane and CO₂ to oxygenates is not thermodynamically feasible under mild conditions and has not been previously achieved as a one-step process. To circumvent thermodynamic limitations, nonequilibrium plasma may be employed to overcome the activation barriers of the reaction under room temperature conditions. Furthermore, modular plasma-activated reactions are more easily adaptable to renewable electricity and small-scale CO₂ capture than large-scale thermally activated processes. <br/><br/>Nonthermal plasma was used to demonstrate one-step production of alcohols, aldehydes, and acids as well as C1–C5+ hydrocarbons under ambient pressure, with a maximum oxygenate selectivity of 12%. The effects of plasma power, feed gas ratio, and catalysts on activity and selectivity were investigated in an atmospheric pressure flow reactor using time-on-stream results. Isotope-labeling experiments were combined with plasma chemical kinetic modeling to reveal the reaction pathways. The reaction proceeded primarily via oxidation of activated ethane derivatives by CO₂-derived oxygen-containing species, demonstrating a mechanism that is fundamentally different from thermocatalytic alcohol synthesis. Results from this study illustrate the potential to use plasma for the direct synthesis of value-added alcohols, aldehydes, and acids from the greenhouse gas CO₂ and underutilized ethane under ambient pressure.