Influence of phosphorous contents on Si incorporation mechanism and properties of SAPO-34

• SAPO-34 molecular sieves were prepared by adjusting P2O5/Al2O3 molar ratios in the initial gel.
• SP-1.5 possesses the highest crystallinity and smooth cubic crystals.
• The pore property and Si substitution mechanism can be changed with P2O5/Al2O3 molar ratio.

SAPO-34 molecular sieves with different phosphorus content were prepared by adjusting P2O5/Al2O3 molar ratios in starting gel. The crystal patterns, crystallinity, crystal morphology, element composition, functional group and thermal stability were characterized by XRD, SEM, XRF, FT-IR and TGA. It reveals that the properties and Si substitution mechanism of the framework can be changed with P2O5/Al2O3 molar ratio. Sample with P2O5/Al2O3 molar ratio of 1.5 possess the highest crystallinity and smooth cubic crystals. In addition, SP-1.5 has the lowest external surface area, the largest micropore surface area and the average pore diameter. With P2O5/Al2O3 molar ratio of 1, Si atoms directly replace P atoms during the crystallization of SAPO-34 with the formation of Si(4Al) species. When the P2O5/Al2O3 molar ratio is lower than 2, the Si substitution mechanism can be attributed to double substitution of SM2 and SM3.

SAPO-34 molecular sieves with different phosphorus content were prepared by adjusting P2O5/Al2O3 molar ratios in starting gel. The properties and Si substitution mechanism of the framework can be changed with P2O5/Al2O3 molar ratio.Figure optionsDownload as PowerPoint slide