ISOMORPHOUS SUBSTITUTION OF SILICON IN THE ERIONITE-LIKE STRUCTURE ALPO4-17 AND ACIDITY OF SAPO-17

AlP04/SAPO-17 samples were prepared and characterized by X-ray diffraction, adsorption isotherms, light/electron microscopy, adsorption calorimetry, temperature-programmed NH3 desorption, and i.r. spectroscopy. Especially, the isomorphous substitution of silicon was studied, and the number of generated Bronsted centers was determined from the NH3 chemisorption. It was found that the number of bridging hydroxyls generated by monomeric incorporation of silicon is limited strictly to one atom per unit cell. When the SiO2/Al2O3 ratio in the reaction mixtures is higher than 0.1, the main part of silicon is incorporated in the erionite-like structure as polymeric species.