Optimization and deactivation mechanisms of molten salt-promoted MgO for intermediate-temperature CO2 capture

The incorporation of nitrate molten salts has been demonstrated as an effective strategy to enhance the CO₂ uptake of MgO for intermediate-temperature (200–400 °C) CO₂ capture. However, the slow carbonation kinetics in flue gas capture, coupled with poor stability, hinder its industrial application. In this study, the addition of Na₂CO₃ was found to significantly improve the sorption kinetics of MgO in a 15 % CO₂ atmosphere, achieving a CO₂ capacity of 19.9 mmol/g at 275 °C with a 15 mol% total promoter loading (Na₂CO₃/NaNO₃ = 1:4). Mechanistic analysis revealed that Na₂CO₃ promotes the formation of Na₂Mg(CO₃)₂, which acts as an effective nucleation site for MgCO₃ formation, accelerating the carbonation rate by a factor of eight. The Hard X-ray photoelectron spectroscopy (HAXPES) revealed that an increased Na/Mg ratio caused subsurface migration and aggregation of molten salts, leading to a permanent rise in local salt concentrations, which negatively affected CO₂ capture performance. These findings offer valuable insights into the structural degradation mechanisms and provide guidance for enhancing the stability of nitrate-enhanced MgO, thereby improving its potential for intermediate-temperature CO₂ capture.