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

We describe a series of steamed HNaY zeolites containing large amounts of u nusual (3700)OH groups. The method of steaming and the solids obtained are well described. These hydroxyl groups are thermally stable and characterize d by their weak acid strength measured by CO adsorption at low temperature: Deltav(OH) approximate to 145 cm(-1) i.e. H-0 = -5, slightly dependent on the coverage level. Their number is estimated at 11.8 per unit cell. Intere sting catalytic properties are expected for these (3700)OH groups since the unusual soft acidity would prevent cracking and coke formation in some aci d-catalyzed reactions. Moreover, the (3670)OH groups are obtained in signif icant amount after soft leaching of the steamed zeolite with NH4+ solutions . This solid is highly crystalline (approximate to 85%), therefore, after C O adsorption, the shift of the (3670)OH groups is unambiguous: Deltav(OH) = 185 cm(-1) i.e. H-0 = -6. (C) 2001 Elsevier Science B.V. All rights reserv ed.