An Integrated Carbon Dioxide Capture and Methanation Process

Reducing the ever-growing level of CO₂ in the atmosphere is critical for the sustainable development of human society in the context of global warming. Integration of the capture and upgrading of CO₂ is, therefore, highly desirable since each process step is costly, both energetically and economically. Here, we report a CO₂ direct air capture (DAC) and fixation process that produces methane. Low concentrations of CO₂ (∼400 ppm) in the air are captured by an aqueous solution of sodium hydroxide to form carbonate. The carbonate is subsequently hydrogenated to methane, which is easily separated from the reaction system, catalyzed by TiO₂-supported Ru in the aqueous phase with a selectivity of 99.9% among gas-phase products. The concurrent regenerated hydroxide, in turn, increases the alkalinity of the aqueous solution for further CO₂ capture, thereby enabling this one-of-its-kind continuous CO₂ capture and methanation process. Engineering simulations demonstrate the energy feasibility of this CO₂ DAC and methanation process, highlighting its promise for potential large-scale applications.