Acid-base properties of silica-alumina oxides derived from NaX zeolites. II. Infrared and temperature-programmed desorption study of adsorption of pyridine

Adsorption of pyridine on a series of silica-aluminas was investigated by means of infrared and temperature-programmed desorption (TPD) spectroscopy. On zeolitic oxides Brønsted and Lewis acid sites were detected, while only Lewis acid sites were revealed with amorphous oxides. Zeolitic oxides showed three TPD peaks, amorphous oxides showed only one TPD peak. Attribution of these peaks to adsorbate structures are discussed. In order to account for the accessibility of Lewis acid sites, we introduced the terms "maximum acceptor strength" and "apparent (measurable) acceptor strength," the latter being the maximum site strength reduced by steric constraints.