The Role of CH₄ in Plasma-Assisted CO₂ and CH₄ Conversion in a Rotating Gliding Arc Plasma: Insights Revealed by Experiments and Modeling

We investigated the combined conversion of CO2 and CH4, so-called dry reforming of methane (DRM), in a rotating gliding arc (RGA) reactor by experiments and modeling for different CO2/CH4 mixing ratios. We obtained the best results at the lowest flow rate (4 L/min) and the lowest amount of CH4 in the feed gas mixture (25%), reaching a conversion of 22% and 39% for CO2 and CH4, respectively, an energy efficiency of 62% and energy cost of 3.25 eV/molecule. A lower energy cost of 2.65 eV/molecule was obtained at 8 L/min. By means of a 3D computational fluid dynamics model, we show that the addition of CH4 reduces the gas temperature inside the plasma, resulting in slower chemical kinetics, explaining why the least amount of CH4 (i.e., 25/75 CH4/CO2) yields the highest CO2 and CH4 conversion. Additionally, the 25/75 CH4/CO2 mixture also displays the highest energy efficiency, due to the high conversion, as well as due the high CO concentration produced in this gas mixture, which is the most beneficial product in terms of energy efficiency. Finally, by means of a quasi-1D chemical kinetics model, we demonstrate that the addition of CH4 suppresses the CO recombination reactions back into CO2, after the plasma, as H-based radicals from CH4 quickly react with O radicals that would otherwise recombine with CO.