Initiating CO₂ Methanation Using Nonthermal Plasma and Achieving Autonomous Operation at Room Temperature

Methanation of CO₂ using renewable H₂ offers a promising way for CO₂ valorization. Previous efforts have confirmed that nonthermal plasma enables this reaction at low temperatures by activating both CO₂ and H₂ by electron impact [1]. This study presents the first attempt to scale up nonthermal plasma-inspired CO₂ methanation, including a detailed analysis of heat generated by methanation, using a total gas flow of up to 3,000 mL/min (H₂/CO₂ =4, without dilution gas) in a packed-bed dielectric barrier discharge (PB-DBD) reactor. In this study, low-temperature promotion of plasma over a non-precious 6wt%-Ni/Al₂O₃ catalyst was confirmed, while the individual contribution of plasma-generated radicals and the heating effect was clarified. Moreover, auto-thermal initiation at room temperature was established with plasma catalysis, followed by autonomous operation without external energy input, as shown in Fig. 1 [2]. Additional experiments using non-catalytic Al₂O₃ beads as the packing material were also conducted in the identical PB-DBD reactor system. Results show limited CO₂ and H₂ conversions (both < 3%), confirming that gas-phase reactions between plasma-excited CO₂ and H₂ are negligible in the absence of a heterogeneous catalyst. This finding corrects the intuitive expectation over the past decade that plasma-activated CO₂ and H₂ can somehow promote CO₂ conversion in the gas phase without interaction with heterogeneous catalysts [3].