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 CO 2 uptake of MgO for intermediate-temperature (200–400°C) CO 2 capture. However, the slow carbonation kinetics in flue gas capture, coupled with poor stability, hinder its industrial application. In this study, the addition of Na 2 CO 3 was found to significantly improve the sorption kinetics of MgO in a 15% CO 2 atmosphere, achieving a CO 2 capacity of 19.9 mmol/g at 275°C with a 15 mol% total promoter loading (Na 2 CO 3 /NaNO 3  = 1:4). Mechanistic analysis revealed that Na 2 CO 3 promotes the formation of Na 2 Mg(CO 3 ) 2 , which acts as an effective nucleation site for MgCO 3 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 CO 2 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 CO 2 capture.