On the stability of the thermally decomposed Co-Al hydrotalcite against retrotopotactic transformation

Retrotopotactic transformation to the original layered double structure of Co-Al hydrotalcite, after thermal treatment at temperatures as low as 473 K, did not occur after 30 days in contact with a wet gas flow (5 vol% H2O in N2) or after 12 h in an aqueous solution of 0.5 M Na2CO3, which deviates from the typical behavior observed for Mg-based hydrotalcites and other layered compounds. The presence of oxidizable Co2+ cations in the octahedral sheets of the layered material and their diffusion to the interlayer space in the dehydrated layered structure, and the stability of the homogeneous crystalline solid solution of cobalt spinels, already identified at 423 K, are responsible for this behavior.