Acta Phys. -Chim. Sin. ›› 2006, Vol. 22 ›› Issue (12): 1495-1500.doi: 10.1016/S1872-1508(06)60077-6

• ARTICLE • Previous Articles     Next Articles

Modification of the Structure and Properties of SAPO-11 Using Rare Earths

ZHANG Yue-Wei;SHEN Mei-Qing;WU Xiao-Dong;WENG Duan;ZHANG Zhi-Hua;TIAN Ran;CHI Ke-Bin   

  1. (Key Laboratory for Green Chemical Technology of the Ministry of Education of China, School of Chemical Engineering, Tianjin University, Tianjin 300072, P. R. China; Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, P. R. China; Research Institute of PetroChina Daqing Petrochemical Company, Daqing 163714, P. R. China)
  • Received:2006-06-16 Revised:2006-07-27 Published:2006-12-06
  • Contact: WENG Duan

Abstract: Silicoaluminophosphate (SAPO)-11 molecular sieve was modified by rare earth La and Ce using impregnating and ion-exchanging methods. The RE-modified SAPO-11 samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), pore-size distribution (PSD), in-situ Fourier transform infrared spectroscopy (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD), and compared with unmodified SAPO-11 sample. The XRD patterns indicated that after RE modification, especially for the La-exchanged sample, the composition of molecular sieve was changed and the crystallinity decreased. The normalized surface area (NSA) of ion-exchanged samples proved that the unsubstituted metal oxides accumulated inside the SAPO-11 pores. Because of the RE cations that were loaded onto the surface of molecular sieve, which could be regarded as the Lewis acid sites, there was an increase in the amount of Lewis acid sites and decrease in the Brønsted acid/Lewis acid (B/L) ratio. The ability of RE cations to acquire electrons was weaker than that of Al3+; therefore, the bond strength of bridged hydroxyl decreased after modification. The total acidity of SAPO-11 decreased after RE modification.

Key words: SAPO-11, La, Ce, Modification, Surfaces properties, Acidity