Physicochemical properties of aluminas obtained from different aluminum salts

Al2O3 materials were obtained by calcination of boehmite samples of varying crystallinity at 600 °C. Boehmites were obtained from Al2(SO4)3·18H2O or AlCl3 under hydrothermal conditions and autogenous pressure at different synthesis temperatures (Ts = 40, 140 and 180 °C), and were studied by XRD, IR(Py), DTA and TGA. It was found that Ts is closely related to the physicochemical properties of boehmites, and thus of γ-Al2O3. Increased amounts of sulfur were detected in γ-Al2O3 for lower Ts using aluminum sulfate. Less-crystalline boehmites were obtained when using aluminum sulfate compared to aluminum chloride. While only Lewis acidity was found in γ-Al2O3 materials produced from aluminum chloride, aluminum sulfate produced both Lewis and Brönsted acidity, with the Brönsted/Lewis ratio depending on the crystallite size.