Plasma Induced Methane Conversion: A Review on COx-Free Production of Hydrogen, Valuable Chemicals, and Functional Carbon Materials

Abstract

Catalytic decomposition and non-oxidative coupling of methane (CDM and NOCM) driven by plasma, especially non-thermal plasma, have been determined as strategic means for sustainable production of COx-free hydrogen and value-added chemicals. The ‘one-step’ direct CDM and NOCM bypass the need for intermediate syngas production to hydrogen and chemicals using Fischer-Tropsch, thus benefiting from energy savings, but nevertheless, still plagued by poor yields and stability. Thermal, warm, and non-thermal plasma technologies have gained research momentum due to the efficacy for activation of strong C-H chemical bonds in methane. Herein, the current literature is firstly reviewed to elucidate the mechanistic insights and plasma synergies (with and without catalysts) for COx-free H2 production via methane conversion with a particular focus on CDM and NOCM reactions. Our review ascertains that while plasma-assisted methane activation can resolve the need for high energy activation and dissociation of C-H bonds, the governing reaction pathways and difficulties in tunning product selectivity with plasma alone warrants further research on the role of plasma-catalysis as a promising solution to tune reactions selectivity. Additionally, we explore strategies for catalyst design and the selection of plasma sources to improve synergistic interactions in plasma-catalysis. Selected examples of catalyst use and reactor design in plasma-catalytic setups are presented. Finally, drawing from recent advancements and our research perspective, advanced plasma integrated system is proposed, especially a concept for a plasma-catalytic reactor featuring a membrane separator, which may serve as an effective unit for hydrogen production and purification.