Plasma Chemistry of Non-Oxidative Methane Coupling: Refinement of Theoretically Consistent Reaction Rate Coefficients by DFT Calculations for Improved Kinetic Modelling

Predictive accuracy of kinetic modelling for plasma-assisted nonoxidative CH₄ coupling largely depends on the involved rate coefficient uncertainties. Here, we perform density functional theory (DFT) calculations to derive consistent rate coefficients for reactions involving CH_x and C₂H_y species. We investigate 34 reactions, including 17 newly-reported ones and 17 previously reported reactions, of which our recommended values deviate by 1–2 orders of magnitude from the literature. Incorporating these rate coefficients into a DBD plasma kinetic model yields better alignment with experimental data. Specifically, we obtain average improvements of 9%, 23%, and 13% in the model-predicted C₂H₆, C₂H₄, and C₂H₂ selectivities, respectively, compared to a previously established chemistry set. Further kinetic analysis identifies key pathways determining CH₄ conversion and C₂ selectivity.