Structural Effects on the High Temperature Adsorption of CO₂ on a Synthetic Hydrotalcite

Hydrotalcite-like compounds (HTlcs) are solid sorbents that may potentially be used for high-temperature separation and capture of CO 2 . The high-temperature adsorption of CO 2 on Mg−Al−CO 3 HTlc is affected by structural changes that take place upon heating of the material. The structural changes of a synthetic HTlc upon heating to 200 and 400 °C in a vacuum were characterized using various analytical techniques. These structural changes were then related to observed behavior with respect to the physisorption and chemisorption of CO 2 at 200 °C. Upon heating to 200 °C, the material retains its layered structure, though the interlayer spacing is decreased by ∼0.6 Å due to loss of interlayer water. Chemisorption of CO 2 at 200 °C represents more than half of the total adsorption capacity (at 107 kPa) due to increased availability of the framework Mg 2+ cation and the subsequent formation of MgCO 3 . There is no significant increase of surface area or pore volume after heating to 200 °C. Upon heating to 400 °C the CO 3 2 - in the interlayer is decomposed and the material is completely dehydrated and partially dehydroxylated. The resulting amorphous 3-D structure with increased surface area and pore volume and decreased availability of the Mg 2+ cation favors physisorption over chemisorption for these samples. An increased understanding of structure−property relationships will help in the further development of HTlcs as viable CO 2 solid sorbents.