Plasma-promoted auto-thermal methanation leading autonomous operation at room temperature

• Plasma-assisted catalysis contributes to the electrification of chemical processes towards low-carbon society. • Nonthermal plasma enables auto-thermal methanation reaction at room temperature. • Reactivity of non-precious metal catalyst (Ni/Al 2 O 3 ) is enhanced by plasma-generated reactive species. • The individual contribution of plasma-generated reactive species and the heating effect was clarified. • Conditions for autonomous operation without external energy input are clarified. In this study, scaled-up CO 2 methanation at a total gas flow rate of up to 3000 mL/min (H 2 /CO 2 = 4, without dilution gas) was conducted in a packed-bed dielectric barrier discharge (PB-DBD) reactor using 6 wt%-Ni/γ-Al 2 O 3 . Both outer and inner temperatures of catalyst bed were measured and analyzed to evaluate reaction performance appropriately. The onset reaction temperature ( T ON ), defined as the temperature at which the CH 4 yield reaches 5 %, was determined at a constant heating rate of 1 °C/min and DBD at 18 W. Compared to thermal catalysis, DBD significantly reduced T ON from 244 °C to 206 °C under a much smaller specific energy input (SEI = 8.8 kJ/mol). The packed catalyst of 6 cm (20 g) achieved a CH 4 yield of 65 %, CH 4 selectivity of >98 %, as well as energy efficiency of 73 %. After turning off both heater and DBD, the methanation reaction transitioned into an autonomous operation mode with energy efficiency of 78 %, sustained solely by its own exothermic reaction heat. Notably, DBD at 30 W successfully initiated the methanation at room temperature without external heating. After DBD was turned off, methanation proceeded autonomously. Moreover, at 65 W, autonomous operation of methanation was achieved within just 10 min. A 25-hour long-term stability test demonstrated that both CH 4 yield and catalyst temperature remained stable throughout the test period, indicating the absence of catalyst deactivation due to the hot spots formation and the high stability of the autonomous operation mode. This is the first attempt to scale up the CO 2 methanation reaction using DBD catalysis and achieve autonomous operation, offering promising insights for industrial applications of this technology.