SMALL-PORE MOLECULAR-SIEVES SAPO-34 AND SAPO-44 WITH CHABAZITE STRUCTURE - A STUDY OF SILICON INCORPORATION

Two small-pore silicon-substituted molecular sieves SAPO-34 and SAPO-4 4 with varying amount of silicon have been synthesized and characteriz ed by XRD, SEM, FT-IR spectroscopy, and thermal analyses. Their acidit y has been measured quantitatively by temperature-programmed desorptio n of ammonia. The results of these studies along with solid-state MAS NMR results show that the major part of silicon substitutes isolated p hosphorus atoms in the structure whereas some amount of it forms small silica patches. The extent of formation of such small patches is more noticeable in SAPO-34 than in SAPO-44.