Synthesis of SAPO-34 with only Si(4Al) species: Effect of Si contents on Si incorporation mechanism and Si coordination environment of SAPO-34

SAPO-34 molecular sieves with different Si coordination environment were synthesized by adjusting SiO2/Al2O3 molar ratio in starting gel. The crystal structure, element composition and Si coordination environment of the as-synthesized samples were characterized by XRD, SEM, XRF and NMR. SAPO-34 molecular sieve could be obtained when the SiO2/Al2O3 molar ratio of the starting gel was higher than 0.075. The content and modeling of Si incorporated into SAPO-34 framework varied with the SiO2/Al2O3 molar ratios in the starting gel and different Si chemical environments were formed correspondingly. SAPO-34 with only Si(4Al) coordination structure could be prepared when the SiO2/Al2O3 molar ratio of the starting gel was in range of 0.075–0.15.