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 CO2. The high-temperature adsorption of CO2 on Mg-Al-CO3 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 CO2 at 200 C. Upon heating to 200 C, the material retains its layered structure, though the interlayer spacing is decreased by ~0.6 A due to loss of interlayer water. Chemisorption of CO2 at 200 C represents more than half of the total adsorption capacity (at 107 kPa) due to increased availability of the framework Mg2+ cation and the subsequent formation of MgCO3. There is no significant increase of surface area or pore volume after heating to 200 C. Upon heating to 400 C the CO32- 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 Mg2+ cation favors physisorption over chemisorption for these samples. An increased understanding of structureproperty relationships will help in the further development of HTlcs as viable CO2 solid sorbents