Adsorption of CO2 on Hydrotalcite-Derived Mixed Oxides: Sorption Mechanisms and Consequences for Adsorption Irreversibility

Magnesium aluminum double oxides derived from the thermal treatment of layered hydroxides (hydrotalcites) have been tested for CO2 adsorption. The effects of various preparation parameters, such as the incorporated cation (K or Na), the mode of addition of magnesium and aluminum precursors, the presence of sonication, and the calcination temperature, on the adsorption capacity under mild conditions were studied using thermogravimetry and calorimetry. Calorimetric and FTIR data were used to explain the adsorption mechanisms leading to the undesirable irreversible adsorption. This adsorption was related to the formation of unidentate CO2-adsorbent species with the strongest adsorption sites, whereas bidentate and surface bicarbonates lead to highly reversible adsorption. In conclusion, preparation procedures that lead to an increase in the strength of basic sites do not lead to significant increases in the adsorption capacity, but rather lead to more difficult regeneration of the saturated support.