Plasma Activated Co-reactants Enable Liquid Fuel Selectivity Control in CH₄–CO₂ Conversion Across Metal–Adsorbate Binding Regimes

Plasma catalytic conversion of CH₄ and CO₂ provides a low-temperature route to transform industrial tail gases into storable liquid fuels. However, rapid catalyst deactivation due to oxygen accumulation on weakly binding metals such as Cu and carbon buildup on strongly binding metals such as Ni limits both selectivity and stability. These catalysts represent distinct binding regimes where metal–adsorbate interaction energies govern surface reactions and determine the primary mechanisms of deactivation. We show that plasma-enabled active site regeneration using vibrationally activated co-reactants restores catalytic activity and tunes product selectivity by removing surface poisons under mild conditions. Plasma excitation dissociates CH₄, CO₂, and co-reactants through nonthermal processes, while subsequent surface reactions are governed by catalyst binding strength and surface temperature. This decoupling enables catalysis on materials that are otherwise inactive thermally. Vibrationally excited co-reactants then react with adsorbed oxygen or carbonaceous species, removing them without elevated temperatures and preserving access to active sites. Using hydrogen as a model co-reactant, we find that vibrationally excited H₂ reacts with surface oxygen on Cu to form H₂O, restoring access to CH₃O* intermediates and increasing methanol selectivity from approximately 8 percent to 24 percent. On Ni, accumulated CH_x* species are removed through hydrogenation, enabling C–C coupling and promoting C₂ hydrocarbon formation. In the absence of regeneration, both catalysts lose activity within minutes; with regeneration, reactivity and selectivity are sustained. We employ a combination of operando DRIFTS, XPS, GC-MS experiments, and DFT calculations to confirm that regeneration modifies surface intermediate populations and reshapes reaction pathways based on the catalyst regime. This strategy is broadly generalizable to other plasma catalytic systems where selective conversion of waste gases requires simultaneous control of activation, reaction branching, and surface regeneration.