PREPARATION AND CHARACTERIZATION OF THE SILICOALUMINOPHOSPHATE SAPO-39

SAPO-39, a silicon-containing aluminophosphate molecular sieve analogo us to AlPO4-39 and MAPO-39 (ATN topology, 4.0-Angstrom wide pore openi ng and tetragonal symmetry), was synthesized as a pure phase by hydrot hermal crystallization from a gel with molar composition: 1.3 di-n-pro pylamine: 0.3 SiO2: 1.0 AI(2)O(3): 1.0 P2O5: 50 H2O at 200 degrees C i n 48 h. Investigations on the crystal structure, morphology, thermal c onversion, adsorption, acidity, and catalytic properties were carried out using XRD, SEM, t.g., TT i.r. methods and methanol-to-olefins conv ersion (MTO) reaction. The product of maximum crystallinity was obtain ed in 48 h, beyond which a new phase started forming and after around 56 h a mixture of SAPO-31 and SAPO-41 was produced. The crystals of SA PO-39 were found to be irregular aggregates of thin and elongated stic k-like particles. The nature of the surface hydroxyl groups in SAPO-39 was studied by FT i.r. spectroscopy of adsorbed NH3. The studies reve al the presence of silicon in the framework. Further, the conversion o f methanol to hydrocarbons gives a selectivity for C-2 and C-3 hydroca rbons of about 43%, which corroborates the presence of considerable Br onsted acidity in the synthesized SAPO-39. The morphology, thermal dec omposition, sorption properties, acidity, and catalytic properties hav e been compared with those of MAPO-39 and AlPO4-39. (C) Elsevier Scien ce Inc. 1997.