NaNO₃ -Promoted Mesoporous MgO for High-Capacity CO₂ Capture from Simulated Flue Gas with Isothermal Regeneration

NaNO₃ -promoted MgO composite materials have been prepared and their ability to sorb CO₂ at a concentration relevant to CO₂ capture from flue gas is explored. The uptake kinetics and capacities of sorbents of different NaNO₃ /MgO ratios are measured at intermediate temperatures of 230-300 °C. The sorbent with a NaNO₃ /MgO ratio of 0.10 has the highest 12 h sorption capacity among sorbents with different NaNO₃ loadings, and the highest sorption capacity of 11.2 mmol $$  g^-1 is observed at 260 °C. Intriguingly, an induction period is observed in the initial stage of CO₂ sorption. In situ XRD analysis, in situ FTIR spectroscopy, and a comparison of the CO₂ sorption behavior under simulated flue gas conditions in comparison to prior studies employing pure CO₂ indicated that the sorption of CO₂ occurred through nucleation of MgCO₃ crystallites in the material. The data indicate that the concentration of CO₂ within the molten medium of NaNO₃ , which is affected by both the solubility of CO₂ in molten NaNO₃ and the partial pressure of CO₂ in the surrounding atmosphere, has a critical impact on the length of the induction period. A partially desorbed sample after sorption of CO₂ displays much-improved sorption kinetics in the next cycle and was able to sorb and desorb CO₂ over multiple cycles at isothermal conditions by simply switching the feed gas from CO₂ to inert gas.