Molten sodium-fluoride-promoted high-performance Li4SiO4-based CO2 sorbents at low CO2 concentrations

Highly efficient NaF-doped Li4SiO4 sorbents were synthesized by sacrifidial carbon template technology to overcome their typical kinetic limitations at low CO2 concentrations. The samples were characterized by XRD, SEM, N-2 adsorption, XPS, differential scanning calorimetry (DSC), and thermogravimetric analyses (dynamic and isothermic). The results showed that co-doped sodium and fluorine were substituted for lithium and oxygen, respectively. Such doped features induced a high concentration of Li-O sites on the molten surface when absorbing CO2 in a relatively wide temperature range (475-575 degrees C). This favorable characteristic greatly facilitated surface chemisorption processes, accelerated the transport of Li+ and O2-, and decreased the CO2 diffusion resistance. Therefore, 3 wt.% NaF doping was used to reach a maximum absorption capacity (> 33.0 wt.%) in a wide temperature range (475-575 degrees C) in 15 vol.% CO2. Moreover, the high capacity was maintained over 10 sorption/desorption cycles, suggesting that NaF-doped Li4SiO4 sorbents have high potential for CO2 capture.