Mesoporous MgO center dot Na2CO3 center dot NaNO3 composites were prepared using supercritical drying of methanol for CO2 capture in power plants at an intermediate temperature range between 250 and 450 degrees C. The effects of the molar ratio of salt, temperature, and gas composition on the CO2 sorption were investigated under dry and wet conditions in order to clarify the sorption mechanisms and roles of NaNO3 and Na2CO3. The composites exhibited excellent sorption capacities of 56.0 wt.% at 325 degrees C in pure CO2 and 50.8 wt.% at 275 degrees C in a wet gas mixtures (10% CO2, 2.5% H2O, and balanced N-2). The CO2 sorption mechanism was dominated through the formation of MgCO3 and Na2Mg(CO3)(2) with Na2CO3 working as a CO2 carrier, while NaNO3 functioned as a reaction promoter. Under wet conditions, the formation of Mg(OH)(2) resulted in fast sorption rates and high capacities even at low CO2 concentrations in the gas feedstock. One phase (liquid) condition of NaNO3 and water vapor during a sorption and regeneration cycle resulted in a high stability of the sorbent. The working capacity in a 14 cycle test under N2 regeneration (10 min) at 450 degrees C was 31.8 wt.% at 325 degrees C in pure dry CO2 and 29.4 wt.% at 275 degrees C with a wet CO2 mixture. (C) 2016 Elsevier B.V. All rights reserved.