Continuous direct air capture and methanation using combined system of membrane-based CO2 capture and Ni-Ca based dual functional materials

Direct CO2 capture from the air by membranes (membrane-based DAC, m-DAC) is a promising new technique to achieve CO2 net zero emissions. In addition, a continuous system for CO2 capture and its reduction by hydrogen using coupled reactors has scarcely been investigated. In this study, a new continuous system consisting of a m-DAC and a methanation process (m-DAC-M) was developed. For methanation, Ni nanoparticles supported on Ca-loaded Al2O3 (Ni-Ca/Al2O3; 10 wt% Ni and 6 wt% CaO) were utilized as a dual functional material (DFM). The Ni-Ca/Al2O3 exhibited high CH4 productivity and selectivity, good stability over 100 h, and high humidity resistance properties at a low reaction temperature of 350 °C. The catalytic properties of Ni-Ca/Al2O3 were elucidated using microscopic and spectroscopic techniques. The characterization results indicated that the CaO species not only served as CO2 adsorption sites to trap concentrated CO2 from the m-DAC system but also improved the reducibility of oxidized Ni species in the hydrogenation period, thereby promoting the reduction of surface carbonate species to CH4.