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 diffrac tion, adsorption isotherms, light/electron microscopy, adsorption calo rimetry, 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 c hemisorption. It was found that the number of bridging hydroxyls gener ated 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 e rionite-like structure as polymeric species.