Impregnation of hydrotalcite with NaNO3 for enhanced high-temperature CO2 sorption uptake

Impregnation with alkali metals is a convenient and attractive way to enhance the CO2 sorption uptake of hydrotalcite. In this study, NaNO3 was used as a novel alkali metal precursor to increase the basicity of commercial hydrotalcite. Also, the influence of NaNO3 on the structural and textural properties and the CO2 sorption performance were investigated for hydrotalcites having different Mg:Al molar ratios. The change in the pore structure after impregnation with NaNO3 was investigated by N2 adsorption–desorption analysis, and the crystalline structures of hydrotalcites with different Mg:Al molar ratios were compared using X-ray diffraction. Because of the basicity increase caused by introducing NaNO3, enhanced CO2 sorption uptake was obtained for the hydrotalcites, and the hydrotalcite containing 30 wt% NaNO3 in a mixed MgO and Al2O3 structure showed the highest CO2 uptake of 1.15 mol·kg−1 at 200 °C and 1 atm. The degree of enhancement in the CO2 sorption uptake was dependent on the Mg:Al molar ratio in pristine hydrotalcite. Large amounts of Al2O3 appeared to highly destabilize the functional groups on the surface of the hydrotalcite, contributing to the increased basicity and CO2 sorption performance of hydrotalcite.