Amphiprotic properties of OH groups in synthetic NaHY zeolites

Abstract

The ir spectra of basic (pyridine) and acidic molecules (formic, acetic and benzoic acids) adsorbed on dehydrated NaHY zeolites were studied. Adsorbed pyridine molecules were transformed into pyridinium ions by reaction with the zeolitic OH groups characterized by the absorption peak at 3660 cm −1 and also to some extent with those exhibiting the absorption peak at 3565 cm −1. In the presence of acid molecules the same OH groups reacted with the formation of carboxylic anions and water molecules. The zeolitic OH groups behave therefore as Brønsted acid centers in the presence of basic molecules and as Brønsted basic centers in the presence of acid molecules. Similar amphiprotic properties were shown by OH groups in an amorphous silica-alumina cracking catalyst.