S. Ashtekar et al., SMALL-PORE MOLECULAR-SIEVES SAPO-34 AND SAPO-44 WITH CHABAZITE STRUCTURE - A STUDY OF SILICON INCORPORATION, Journal of physical chemistry, 98(18), 1994, pp. 4878-4883
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.