New synthesis route of hydrocalumite-type materials and their application as basic catalysts for aldol condensation

An attempt was made to directly synthesize a Brønsted-type catalyst based on the hydrocalumite-like structure by controlled hydrolysis of calcium and aluminium alkoxides. Solids belonging to the AFm and hydrogrossular families were obtained by dissolution of calcium methoxide and aluminium triethoxide precursors in water at a molar ratio [Ca2+]/[Al3+] = 2.0, followed by an aging of the precipitate at different temperatures. At 273 K, a mixture of gibbsite, layered hydrocalumite-like phase, and 3 dimensional cubic Si-free katoite compounds was obtained. At 298 K, the XRD pattern reveals the presence of hydrocalumite-like phases intercalated by OH− and CO32− species, respectively, as confirmed by IR spectroscopy. This as-prepared sample behaved as an efficient Brønsted-type catalyst able to perform the condensation reaction of benzaldehyde and acetone into benzylideneacetone. At 333 K, the catalytically inactive katoite phase alone was formed.