Synthesis and characterization of a new type silicoaluminophosphate SAPO-53 molecular sieves

Highly crystalline SAPO-53 molecular sieves were successfully synthesized under a hydrothermal condition by using hydroxide hexane dual ammonium(R(OH)₂) as a template. The samples were characterized by a serious of techniques,including XRD,SEM-EDX,FT-IR,MAS NMR,electrophoresis apparatus,N₂ adsorption-desorption and TG-DTG. Various preparation conditions including Si/Al ratio, P/Al ratio, the amount of template and crystallization time for the synthesis of SAPO-53 molecular sieves have been systematically studied. It shows that Si has entered the AlPO₄-53 framework mainly with a form of four ligand detected by ²⁹Si MAS NMR. The results reveal that the relative crystallinity of synthesized samples increases firstly and reduces afterward with the increase of time,while the Zeta potential value increases first and then remains unchanged. Compared with the synthesis taking methylamine as a template, the template agent of hydroxide hexane dual ammonium is only half of the amount for the sample synthesis. Furthermore, this method can shorten the crystallization time and reduce the difficulty of synthesis. The apparent growth rate of SAPO-53 molecular sieve is higher than its nucleation rate through the calculation, so the nucleation process is the rate controlling step.