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

Medium-pore molecular sieves SAPO-11 and SAPO-31 and large-pore molecular s ieve SAPO-5 were synthesized using the same template (dipropylamine) by gra dual heating of the synthesis gel to obtain highly crystalline materials wi thin 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 s ilica islands as evidenced from Si-29 magic-angle spinning nuclear magnetic resonance spectroscopy. The particles of the samples synthesized by this m ethod were more uniform in size and morphology than conventionally synthesi zed 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. (C) 1999 Elsevier Science B.V. All rights reserved.