Plasma catalysis enables low-temperature CO₂ methanation and has been widely reported. However, the exothermic nature of the methanation reaction remains overlooked in these studies. For example, reaction heat generation induces hot spot formation, raising catalyst temperature to several 100 °C, yet this effect has received limited attention. We analyzed literature data on plasma-catalytic pure CO₂ and biogas methanation over a wide flow-rate range (20~3000 mL/min), corresponding to a reaction heat release rate of 0.1~44 W [1-3]. The results highlight the necessity of conducting methanation examinations at high flow rates, where both plasma nonthermal and conventional thermal effects are involved. We revealed the crucial role of reaction heat release in reducing the external energy input and enhancing the reaction-level energy efficiency of plasma-catalytic methanation. Moreover, although reaction heat release rapidly increases the hot spot temperature to above 400 °C, the temperature rise soon becomes limited by thermodynamic constraints. Additionally, the energy flows and balance analysis indicate that plasma-catalytic methanation proceeds with minimum energy input, while high-flow-rate operation reduces the heat loss and thereby potentially enhances the system-level energy efficiency [4].

This project is supported by JST CREST (JPMJCR19R3), JSPS KAKENHI 24H00199 and 22K18336.

CO2 methanation, Biogas methanation, Plasma catalysis, Dielectric barrier discharge, Hot spot.