Chemical Journal of Chinese Universities ›› 2020, Vol. 41 ›› Issue (11): 2442-2448.doi: 10.7503/cjcu20200347

• Inorganic Chemistry • Previous Articles     Next Articles

Study on Crystallization Process of SAPO-5 Molecular Sieve

LUO Dongxia1,2, LI Bing2, WANG Quanyi2, TIAN Peng2(), LIU Zhongyi1(), LIU Zhongmin2   

  1. 1.Green Catalysis Center,College of Chemistry,Zhengzhou University,Zhengzhou 450001,China
    2.National Engineering Laboratory for Methanol to Olefins,Dalian National Laboratory for Clean Energy,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,China
  • Received:2020-06-12 Online:2020-11-10 Published:2020-11-06
  • Contact: TIAN Peng E-mail:tianpeng@dicp.ac.cn;liuzhongyi@zzu.edu.cn

Abstract:

The crystallization process of SAPO-5 molecular sieve(AFI type) was studied by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy and solid-state MAS NMR. The results show that the formation of SAPO-5 molecular sieve follows a liquid-mediated mechanism. In the early stage of crystallization, amorphous aluminophosphate particles with relatively regular morphology(named substance Am) were first formed. SAPO-5 began to appear after the crystallization temperature reached 200 ℃, and the amount of amorphous substance Am also increased significantly. Subsequently, substance Am gradually dissolved and contributed to the growth of SAPO-5. The Si atoms directly participated in the formation of SAPO-5 framework since the early stage of crystallization. As the crystallization proceeded, the Si content in the mole-cular sieve crystals gradually increases. The SAPO-5 framework can only accommodate a small amount of Si(4Al) species, and the Si islands started to appear at low Si content. XPS analysis further revealed that SAPO-5 molecular sieve has surface Si enrichment phenomenon, implying that the Si content in the crystal increases from the core to the shell. The topology of the molecular sieve and the choice of Si source affect the degree of Si enrichment on the crystal surface.

Key words: SAPO-5, Molecular sieve, Synthesis, Crystallization mechanism, Si distribution(Ed.: V, K, S)

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