FTIR studies of unusual OH groups in steamed HNaY zeolites: preparation and acid properties

Abstract

We describe a series of steamed HNaY zeolites containing large amounts of unusual (3700)OH groups. The method of steaming and the solids obtained are well described. These hydroxyl groups are thermally stable and characterized by their weak acid strength measured by CO adsorption at low temperature: Δν(OH)≈145 cm −1 i.e. H 0=−5, slightly dependent on the coverage level. Their number is estimated at 11.8 per unit cell. Interesting catalytic properties are expected for these (3700)OH groups since the unusual soft acidity would prevent cracking and coke formation in some acid-catalyzed reactions. Moreover, the (3670)OH groups are obtained in significant amount after soft leaching of the steamed zeolite with NH 4 + solutions. This solid is highly crystalline (≈85%), therefore, after CO adsorption, the shift of the (3670)OH groups is unambiguous: Δν( OH)=185 cm −1 i.e. H 0=−6.