Carbon recycling through catalysis: direct CO2-to-CH4 conversion for sustainable fuels

Abstract

Among the distinct value-added products of the catalyst-mediated CO₂ reduction reaction (CO₂RR), CH₄ stands out as a superior energy carrier on account of its high combustion heat. However, designing a highly active and selective catalytic system presents an ongoing challenge to circumvent C–C coupling that results in multi-carbon products during CO₂ methanation. Consequently, substantial strategic initiatives, including structural modulation, catalyst composition tuning, surface modification employing single-site catalysts, defect engineering, use of co-catalysts, elemental doping, and optimisation of operating conditions, have been pursued to enhance the catalytic activity for proficient CO₂ methanation. This review systematically studies the evolving ideas and strategic advances in thermocatalysis, electrocatalysis, and photocatalysis, alongside coupled catalytic systems including photothermal, electrothermal, and photo-electrocatalytic approaches for CO₂ hydrogenation to CH₄, emphasizing their evolution from foundational progresses to state-of-the-art executions driven by renewable energy inputs. Furthermore, this review highlights the catalytic mechanisms, kinetics, and roles of the active components, supports, and promoters in CO₂ methanation. In addition, the feasibility and economic potential of compressed natural gas (CNG) production through CO₂ methanation are critically examined, emphasizing its cost-effectiveness and scalability for large-scale implementation. Finally, this review provides a comprehensive roadmap for advancing catalyst design and optimizing processes to enable economically sustainable CNG production.