Clean synthesis of hierarchically structured boehmite and γ-alumina with a flower-like morphology

Flower-like boehmite, composed of the nanosheets with 1-5 nm thickness, was synthesized from a bayerite precursor via phase transformation in a clean way. This template-free method is featured with the advantages that the mother solution containing ethanol, water and ammonium sulfate could be recovered and reused. The transformation procedure of bayerite to boehmite was clarified, in which bayerite gradually dehydrated and evolved to boehmite from the crystal outside to the inside, with the primary crystallite size of boehmite and the coordination state of aluminum remaining almost unchanged. The corresponding flower-like γ-Al₂O₃ derived by calcination of flower-like boehmite exhibited not only a large specific surface area (281 m² g^-1) but also bimodal porosities with the diameter distributions centered at 5.2 nm and 18.4 nm, respectively. Possessing large pore size and open pore structures, the flower-like γ-alumina showed an improved catalytic performance in the cracking of 1,3,5-triisopropylbenzene in comparison to the commercial alumina catalysts.