Reversible thermal behaviour of layered double hydroxides: A thermogravimetric study

Layered double hydroxides (LDHs) of Mg with trivalent cations such as Al, Cr and Fe show two mass loss steps on heating; the low-temperature (25-250 degrees C) loss is due to dehydration and the high-temperature (250-450 degrees C) loss is due to decomposition. Both steps are reversible and the oxide residues obtained after calcination at 700 degrees C reconstruct back to the hydroxide phase. On the other hand the LDHs of Ca and Ni dehydrate reversibly but their decomposition reaction is irreversible. The LDHs of Zn and Co lose mass continuously up to 700 degrees C without any well resolved steps and the loss is irreversible. These results have implications on the synthesis of selective catalysts by calcination of LDHs.