Pre-combustion Co2 Capture at High Temperature with Alkaline Promoted Aluminas and Hydrotalcites: the Crucial Role of Alkaline Cations in Co2 Adsorption⁄

Alkali promotion effects on CO2 sorption have been characterised by a series of complementary analytical techniques on γ-alumina, magnesia, hydrotalcites and alkaline promoted corresponding materials under conditions representative for WGS conditions. Alkaline carbonates are destabilised when interacting with solid surface as evidenced by thermogravimetric analyses and temperature programmed desorption. Structural rearrangements have been observed in alkali promoted hydrotalcite at the temperature used for capture. Moreover, in the presence of CO2, the reconstruction of hydrotalcite cooled at room temperature after the experiment could not be observed most probably due to the formation of new carbonate species at high temperature that are stable while temperature decreases and prevent the reconstruction of crystalline hydrotalcite. In addition, in situ vibrational spectroscopies (Raman and DRIFT) showed that carbonates rearrange while heating and that alkali ions strongly interact with carbonate groups coordinated to aluminium oxide centres. Indeed both techniques highlight remarkably the loss of symmetry for carbonates group and comparison between parent material’s fingerprints evidenced that basic (KAlnO2n/CO3)-like species play a key role in CO2 fixation at 400°C.