Optical emission spectroscopy of plasma-catalytic CO$_{\mathrm{2}}$ methanation

CO2 methanation has been proposed to generate rocket propellant fuel in Mars exploration[1]. We aim to establish CO2 methanation process using plasma and catalyst. In our previous study, we have proposed the model that CO2 is excited and decomposed in the gas phase and the methane is generated on the catalyst surface[2]. In order to clarify the reaction processes more in detail, correlation between the emission intensity of plasma and the CH4 yield was investigated. The experiments were performed under various conditions at a pressure of 3.5 to 8.0 Torr, with discharge power of 20 to 100 W,t he electrodes of SUS, Cu and Ru/TiO2 and the total flow rate of below 21 sccm. The CH4 yield increases with the highest emission intensity of CO angstrom bands during the methanation process. This result implies that the increase of high energy levels of CO promotes CH4 methanation. [1] G. Sanders, ``Current NASA Plans For Mars In Situ Resource Utilization,'' no. 281, 2018.[2] S. Toko, et al. Sci. Adv. Mater., 10 (2018) 1087.