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

CO2 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/Al2O3 catalyst was synthesized by impregnation of the support with an aqueous solution of Ru(OH)Cl-3, followed by liquid phase reduction using NaBH4 and gas phase activation using the stoichiometric mixture of CO2 and H-2 (1:4). Kinetics of CO2 methanation reaction over the Ru/Al2O3 catalyst was studied in a perfectly mixed reactor at temperatures from 200 to 300 degrees C. The results showed that dependence of the specific activity of the catalyst on temperature followed the Arrhenius law. CO2 conversion to methane was shown to depend on temperature, water vapor pressure and CO2:H-2 ratio in the gas mixture. The Ru/Al2O3 catalyst was later tested together with the K2CO3/Al2O3 composite sorbent in the novel direct air capture/methanation process, which combined in one reactor consecutive steps of CO2 adsorption from the air at room temperature and CO2 desorption/methanation in H-2 flow at 300 or 350 degrees C. It was demonstrated that the amount of desorbed CO2 was practically the same for both temperatures used, while the total conversion of carbon dioxide to methane was 94.2-94.6% at 300 degrees C and 96.1-96.5% at 350 degrees C.