A novel high temperature CO2 sorbent, Na-Mg double salt, was prepared by a precipitation method. Thermogravimetric analysis was used to measure the thermal stability and to investigate the CO2 sorption behavior at high temperatures. The prepared Na-Mg double salt showed unique CO2 sorption characteristics in the temperature range of 300-500 degrees C. A remarkably high CO2 sorption uptake of 3.48 mol/kg (15.3 wt%) was measured at 375 degrees C and was maintained during repeated sorption/desorption cycles. Electronic microscopy and X-ray diffraction were used to determine the Na-Mg double salt morphology and structure, respectively. The elemental composition ratio in the Na-Mg double salt was characterized by inductively coupled plasma atomic emission spectroscopy and an elemental analysis. In situ X-ray diffraction analysis revealed that the CO2 sorption mechanism was based on the reaction of CO2 with MgO and Na2CO3 in the double salt to form Na2Mg(CO3)(2). In addition to the high CO2 sorption uptake and good cyclic stability, the Na-Mg double salt showed exceptionally fast sorption and desorption. (C) 2014 Elsevier B.V. All rights reserved.