The synthesis of SAPO-34 zeolite for an improved MTO performance: tuning the particle size and an insight into the formation mechanism

Abstract

Traditional SAPO-34 zeolites synthesized using trimethylamine (TEA) as organic templates have relatively large particle size and limited MTO performance. In this work, SAPO-34 plates have been successfully synthesized using TEA as templates with the presence of polyethylene glycol (PEG) as an assisted template. Two-step crystallization is utilized in the concentrated gel system to control the particle size in the range of 0.9–1.2 μm. The MTO catalysis shows that the as-synthesized SAPO-34 plates exhibit enhanced catalytic performance. At 99% conversion, it has a catalytic lifetime (326 min) that is eight times longer than that of the conventional sample and 80% selectivity for light olefins. Moreover, the NMR study reveals the distinct crystallization process of SAPO-34 in two gel systems. Different from silicon being the activated species and the crystal center in a normal gel system, the aluminophosphate framework is first generated and then silicon gradually enters to replace Al or P in the concentrated gel system.