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.