From Plasma-Generated Radicals to Value-Added Products: A Critical Review of Methane Valorisation

Methane is an abundant carbon resource with significant potential for the sustainable production of hydrogen, syngas, light hydrocarbons, oxygenates, and carbon nanomaterials. However, its efficient utilization remains challenging because of the high stability of the C–H bond, requiring energy-intensive thermocatalytic processes that often suffer from limited selectivity, carbon deposition, and high CO2 emissions. Plasma-assisted technologies have emerged as a promising alternative by activating methane through energetic electrons and reactive species under non-equilibrium conditions. Although considerable progress has been achieved, existing reviews have primarily focused on individual plasma sources, reaction pathways, or catalyst systems, with limited attention to the coupled interactions among plasma characteristics, radical chemistry, reactor engineering, and product selectivity. This review provides a comprehensive and critical analysis of plasma-assisted methane valorisation by integrating the fundamental mechanisms of electron-impact activation, radical generation, and plasma kinetics with reactor design and process performance. The major plasma reactor technologies, including dielectric barrier discharge, gliding arc, microwave, and plasma jet systems, are critically compared in terms of methane conversion pathways, energy efficiency, operating conditions, reactor configuration, and product distribution. Finally, current challenges and emerging opportunities, including plasma catalysis, advanced reactor architectures, operando diagnostics, and reactor scale-up, are discussed to provide future perspectives for the industrial implementation of plasma-assisted methane valorisation.