Plasma promotion of CO2 methanation at low temperature: Validation of nonthermal effect on large-scale biogas upgrading

Plasma catalysis enhances low-temperature reactivity of biogas methanation without precious-metal catalysts, strengthening the resilience against external disturbances, such as fluctuations in CH 4 content, and offers sustainable routes for CO 2 utilization. Methanation of CO 2 in biogas offers an efficient and sustainable pathway compared to the carbon sources from carbon capture and utilization/storage (CCU/CCS) technologies, as it avoids a separate CO 2 capture step. Moreover, CO 2 from biogas combustion does not need to be recycled, owing to the carbon-neutral nature of biogas as a renewable energy source. Herein, we report biogas methanation using plasma catalysis for the first time in a packed-bed dielectric barrier discharge (DBD) reactor over 6 wt%-Ni/γ-Al 2 O 3 . The total gas flow rate reached up to 3000 mL min −1 (CH 4 /CO 2 = 60/40, CO 2 /H 2 = 1/4), representing a large-scale study. The respective contributions of nonthermal plasma and methanation reaction heat were clarified. We observed that plasma-generated reactive species—vibrationally excited CO 2 and plasma-derived atomic hydrogen (PDAH)—play a crucial role. These species enhance CH 4 yield at low temperature and decrease reaction onset temperature ( T ON ) compared to thermal catalysis. Also, pseudo-autonomous operation was confirmed at a total gas flow of 3000 mL min −1 and DBD power of 11 W with CO 2 conversion of 77%, CH 4 selectivity >98%, and energy efficiency of 75%. Moreover, pulsed CH 4 injection experiments demonstrated that they endow the reaction system with the ability to withstand external disturbances, such as fluctuation of CH 4 content in biogas. These results demonstrate the feasibility and high efficiency of plasma-catalyzed biogas methanation. Moreover, a high flexibility of DBD makes it particularly suitable for upgrading decentralized or stranded biogas resources.