Effect of alkaline nitrate addition in the CO2 chemisorption of pentalithium ferrite (Li5FeO4) at low and moderate temperatures

Li, Na and K nitrate-containing pentalithium ferrite (Li5FeO4) samples were prepared to evaluate changes of the CO2 capture process at moderate temperatures. These experiments were performed using different CO2 partial pressures and different characterization techniques, such as TG, DSC, XRD and DRIFTS. When using a CO2 saturated atmosphere, all the samples showed high CO2 capture efficiencies at lower temperatures (150–400 °C) than those observed on the pristine Li5FeO4. Specifically, lithium nitrate-containing samples presented the best CO2 capture properties. Thus, this system was further analysed through in-situ DRIFTS and DSC experiments, elucidating the Li5FeO4-CO2 reaction path. Alkali nitrate salts are melted forming eutectic phases with the carbonate produced, where the first one works as an oxygen donor/acceptor, producing reactive intermediate species improving the CO2 capture. Moreover, at the lowest temperatures, H2O presence plays an important role during the whole CO2 capture mechanism, through the lithium hydroxide formation, enabling the process of CO2 chemisorption. Finally, it was proved that Na and K nitrate-containing samples presented similar behaviours than those described for the lithium case, although CO2 capture temperature regimes were shifted depending on the alkaline nitrate.