(189j) High-Temperature CO2 Adsorbents Derived From Layered Double Hydroxides: Influences of Trivalent Cations, Inter-Layer Anions and Synthesis pH

This work reported a detailed investigation on the influences of trivalent cations, charge compensating anions, and synthesis pH on the structural properties and CO2 adsorption capacity of layered double hydroxides (LDHs). We demonstrated that the trivalent cation (M3+) determines the structure evolution of LDH derivatives under thermal treatment, and finally influences the CO2 capture capacity. With different M3+, a very different calcination temperature is required for each LDH to obtain the maximum CO2 capture capacities; and the optimal calcination temperatures showed the following order: Mg3Al1 (400 oC) > Mg3Ga1 (350 oC) > Mg3Fe1 (300 oC) > Mg3Mn1 (250 oC). The CO2 capture capacities were also evaluated under various conditions. Then the influence of anions including CO32-, HCO3-, NO3-, SO42-, and Cl- were investigated. It was found that the anions have great effect on the thermal stability, morphology, as well as on the surface area of LDHs, consequently influencing the CO2 adsorption capacity. Among various LDHs, Mg3Al1-CO3 showed the highest CO2 adsorption capacity of 0.53 mmol/g. Finally, 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.