Surface Acidities of Bentonite, Sepiolite, and Synthetic Silica-Aluminas

The surface acidities of Bentonite, Sepiolite, and Silica-Aluminas were determined by Hammett indicators, amine titrations, and of pyridine adsorption-IR spectroscopy. The quantitative estimation of surface acidities of silica-aluminas and their natures as Brønsted and Lewis acid sites were evaluated. Lewis and total surface acidity values of sepiolite were higher than bentonite, 0.53 and 2.22 mmole g-1, respectively. Surface acidity values of sepiolite and bentonite were much lower than Siral compounds. Among the Siral compounds, Siral 30 was found to be more effective in terms of acidity. All samples have both Lewis and Brønsted acid centers in which the Lewis sites predominated. IR spectroscopy with pyridine as a probe molecule was still very useful for the estimation of the surface acidities of the silica-alumina and also aluminosilicate structures such as clays and clay minerals.