A Novel Synthesis Route of Mesoporous γ-Alumina from Polyoxohydroxide Aluminum
Mesoporous gamma-aluminas (γ-Al2O3) were synthesized starting from an unusual precursor of polyoxohydroxide aluminum (POHA). This precursor was obtained from aluminum oxidation in alkaline water-ethanol solvent in the presence of d-glucose that induces the formation of a gel, which leads to the POAH powder after ethanolic treatment. Precipitated POHAs were calcined at different temperatures (300, 400, 700 and 900 °C) resulting in the metastable γ-Al2O3 phase. Whereas at 300 °C no γ-Al2O3 phase was formed, unexpectedly, mesoporous γ-Al2O3 was obtained at 400 ºC having a high specific surface area (282 m2/g) and a narrow pore size distribution. At higher temperatures, the aluminas had the expected decrease in surface area: 166 m2/g (700 °C) and 129 m2/g (900 °C), respectively. The structural change from POHA to alumina calcined at 400 ºC occurs directly without the need to isolate the hydroxide or oxyhydroxide aluminum precursors. Both POHA and transition aluminas were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 sorption and Scanning Electron Microscopy (SEM). These findings show an alternative route to produce high standard aluminas.