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 CO_x-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 the Fischer–Tropsch process, thus benefiting from energy savings, but nevertheless, are 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 CO_x-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 tuning product selectivity with plasma alone warrant further research on the role of plasma-catalysis as a promising solution to tune reaction 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, an 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.