A Novel Process for Renewable Methane Production: Combining Direct Air Capture by K2CO3/Alumina Sorbent with CO2 Methanation over Ru/Alumina Catalyst

CO 2 methanation over supported ruthenium catalysts is considered to be a promising process for carbon capture and utilization and power-to-gas technologies. In this work 4% Ru/Al 2 O 3 catalyst was synthesized by impregnation of the support with an aqueous solution of Ru(OH)Cl 3 , followed by liquid phase reduction using NaBH 4 and gas phase activation using the stoichiometric mixture of CO 2 and H 2 (1:4). Kinetics of CO 2 methanation reaction over the Ru/Al 2 O 3 catalyst was studied in a perfectly mixed reactor at temperatures from 200 to 300 °C. The results showed that dependence of the specific activity of the catalyst on temperature followed the Arrhenius law. CO 2 conversion to methane was shown to depend on temperature, water vapor pressure and CO 2 :H 2 ratio in the gas mixture. The Ru/Al 2 O 3 catalyst was later tested together with the K 2 CO 3 /Al 2 O 3 composite sorbent in the novel direct air capture/methanation process, which combined in one reactor consecutive steps of CO 2 adsorption from the air at room temperature and CO 2 desorption/methanation in H 2 flow at 300 or 350 °C. It was demonstrated that the amount of desorbed CO 2 was practically the same for both temperatures used, while the total conversion of carbon dioxide to methane was 94.2–94.6% at 300 °C and 96.1–96.5% at 350 °C.