Design Criteria in Plasma-Catalysis: Mapping the Multidimensional Reaction Space

Plasma-catalysis presents a unique opportunity to drive chemical conversions that transform stable molecules under mild conditions by coupling non-equilibrium plasma excitation with heterogeneous catalysis. However, achieving product selectivity and sustained catalytic activity requires rational design across a multidimensional parameter space, including gas-phase plasma states, surface properties, temperature effects, and co-reactant composition. In this work, we outline a mechanistic framework for synergistic plasma-catalyst design based on reaction classes, catalyst classes, and surface interactions. We categorize common plasma-catalyzed reactions into: (1) single-reactant systems (e.g., CH₄, NH₃, N₂O), (2) binary-reactant systems (e.g., CH₄–CO₂, CH₄–O₂, N₂–H₂), and (3) multi-component mixtures such as tail gases or syngas derivatives. For each class, we analyze how plasma parameters (electron energy distribution, vibrational excitation, radical flux), catalyst properties (binding strength, active site type, support effects), and thermal effects (surface temperature) can be tuned to control reaction branching, intermediate retention, and product selectivity. We also discuss the strategic use of plasma-activated co-reactants, such as H2, O2, or steam, as levers for active site regeneration, in situ oxidation/reduction, and competitive adsorption. Key examples include CH₄* + O* → CH₃O* (selective oxygenate formation), CH₃* + CH₃* → C₂H₆* (C–C coupling), CH₂O* → CHO* → CO* + H* (oxidative deactivation), CO₂* + H* → COOH* (activation via hydrogenation), etc. We identify optimal regimes of surface temperature, plasma electron energy distribution, and catalyst binding energy to favor desired intermediates while suppressing deactivation pathways (e.g., CH_x buildup, O* poisoning). We show that product speciation is governed by competitive kinetics of hydrogenation, oxidation, and C–C coupling, and that tuning co-reactant identity (e.g., H₂, O₂, steam) enables in-situ regeneration through reactions such as, O* + H* → OH* → H₂O, CH_x* + CH_x* → C₂H_2x, etc. This talk aims to establish foundational design criteria for controlling product speciation and sustaining catalytic performance in plasma-enabled systems.