Tailored mesoporous alumina prepared from different aluminum alkoxide precursors

Abstract

The importance of aluminum alkoxides precursors (ethoxide, isopropoxide and sec-butoxide) in the tailoring of the structural and textural properties of γ-alumina was reported. It has been found that the specific surface areas (336–426 m²/g), as well as the mean pore size distribution are modified in function of the length and branching of the aluminium alkoxide used in the synthesis. A narrow pore size distribution was obtained with aluminum ethoxide (14.7 nm), meanwhile a broad pore size distribution was observed in samples prepared with aluminium sec-butoxide or aluminium isopropoxide precursors (18.2 and 19.4 nm). In fresh samples, Boehmite phase and Al^VI octahedraly coordinated were identified by XRD and ²⁷Al MAS-NMR spectroscopies. After annealing at 500°C, the samples showed the γ-alumina phase formation and a mixture of aluminium in tetrahedral Al^IV and octahedral Al^VI coordination in variable proportions. The acidity of the calcined samples, determined from the pyridine-FTIR spectra, showed Lewis and Brönsted type acidity. Activity in the 2-propanol dehydration reaction showed that the highest activity corresponds to the samples showing the highest Lewis acidity.