CO₂ adsorption at elevated pressure and temperature on Mg-Al layered double hydroxide

CO₂ adsorption at elevated pressure was studied in a Mg-Al (Mg/Al = 3) layered double hydroxide (LDH). The double-layered structure was prepared via a coprecipitation method. The samples structure and microstructure evolutions were characterized using X-ray diffraction, scanning electron microscopy, N₂ adsorption, and thermogravimetric and calorimetric analyses. The CO₂ adsorption experiments were performed between 5 and 4350 kPa at different temperatures (30-350 °C). Elevated pressure experiments showed that this material was able to adsorb different quantities of CO₂ depending on the thermal evolution of its structure and microstructure. The highest CO₂ adsorption (5.7 mmol/g) was produced at 300 °C before the layered structure had completely collapsed. At these specific conditions the interlayer space was reduced from 7.78 to 4.39 Å. This interlayer change was attributed to the onset of LDH structural collapse. However, at this temperature the adsorption process must be favored over the adsorption-desorption equilibrium, allowing the maximum CO₂ capture.