An improved method for the synthesis of the silicoaluminophosphate molecular sieves, SAPO-5, SAPO-11 and SAPO-31

Abstract

Medium-pore molecular sieves SAPO-11 and SAPO-31 and large-pore molecular sieve SAPO-5 were synthesized using the same template (dipropylamine) by gradual heating of the synthesis gel to obtain highly crystalline materials within 1 to 2 h. This synthesis method resulted in higher acidity and better incorporation of Si⁴⁺ at P⁵⁺ sites, resulting in a lower concentration of silica islands as evidenced from ²⁹Si magic-angle spinning nuclear magnetic resonance spectroscopy. The particles of the samples synthesized by this method were more uniform in size and morphology than conventionally synthesized samples. The rapidly crystallized samples showed a higher activity and selectivity than conventionally synthesized samples in the isomerization of m-xylene and the alkylation of toluene.