Synthesis of the silicoaluminophosphate molecular sieve SAPO-31 in the presence of fluoride ions and its characterization

Abstract

Pure silicoaluminophosphate SAPO-31 was synthesized by hydrothermal crystallization at 200°C from mixtures of molar composition 1.2Al 2 O 3 :1.03P 2 O 5 : x SiO 2 :1.7( n -C 3 H 7 ) 2 NH:1HF: y H 2 O with 0.2≤ x ≥0.5 and 62≤ y ≥100. Elemental analysis and 1 H– 29 Si CP MAS NMR showed that Si is essentially substituted for P according to the mechanism Si 4+ +( n -C 2 H 7 ) 2 NH + 2 =P 5+ . By 19 F MAS NMR a chemical shift of −144.7 ppm with respect to CFCl 3 was observed. By n -hexane adsorption at 20°C ( p / p 0 =0.5) on samples calcined at 750°C, a pore volume of 0.08 cm 3 liquid n -hexane per gram was found.