High temperature adsorption of CO2 on Mg–Al hydrotalcite: Effect of the charge compensating anions and the synthesis pH

This work reported a detailed investigation on how charge compensating anions and synthesis pH affect the structural properties and CO2 adsorption capacity of Mg–Al hydrotalcites (HTs). A series of Mg3Al1–A (A = CO32−, HCO3−, NO3−, SO42−, and Cl−) HTs were synthesized and tested as high temperature CO2 adsorbents. It was found that the anions have great effect on the thermal stability and morphology, as well as on the surface area of HTs, consequently influencing the CO2 adsorption capacity of HT derivatives. Among various HTs, Mg3Al1–CO3 showed the highest CO2 adsorption capacity of 0.53 mmol/g. Next, the influence of synthesis pH on the Mg/Al ratio, BET surface area, pore size, and CO2 adsorption capacity of Mg3Al1–CO3 was investigated. Mg3Al1–CO3 synthesized at pH = 10–12 showed good performance for CO2 adsorption. By doping Mg3Al1–CO3 (pH = 10) with 20 wt.% K2CO3, the CO2 adsorption capacity was increased up to 0.85 mmol/g.