Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (4): 793-799.doi: 10.3866/PKU.WHXB201503021

• CATALYSIS AND SURFACE SCIENCE • Previous Articles     Next Articles

TPAOH Template Removal from High-Silica ZSM-5 by Low-Temperature Hydrocracking

ZHAO Shu-Heng1,2, LANG Lin1, YIN Xiu-Li1, YANG Wen-Shen1, WU Chuang-Zhi1   

  1. 1 CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, P. R. China;
    2 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2014-10-28 Revised:2015-02-23 Published:2015-04-03
  • Contact: YIN Xiu-Li E-mail:xlyin@ms.giec.ac.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (51106165, 51202245) and Guangdong Natural Science Foundation, China (10251007006000000, S2013010014896)

Abstract:

Zeolite membranes, especially the MFI-type zeolite membranes, have attracted significant attention for decades because of their special properties. While organic templates such as tetrapropylammonium hydroxide (TPAOH) have typically been used for the synthesis of ZSM-5 zeolite and zeolite membranes, the templates remain trapped in the as-synthesized zeolite crystals. A common method for removing organic templates and generating porous frameworks is calcination; however, during this process, the channel structure may be affected. In particular, for ZSM-5 membranes, membrane defects may be produced and the separation efficiency therefore may decrease to some extent. In this study, the low-temperature hydrocracking of TPAOH in ZSM-5 zeolite crystals was studied under H2/N2, while N2 adsorption, thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectroscopy, temperature-programmed desorption of ammonia (NH3-TPD), and Raman spectroscopy were used to characterize zeolite samples. The results show that the organic template in the pores of ZSM-5 can be effectively removed below 350 ℃ by low-temperature hydrocracking. Characterization analyses by BET specific surface area, TG, FTIR, and Raman spectroscopy demonstrated that a reducing atmosphere containing H2 was more conducive to template removal at low temperature than atmospheres of air or N2. The degree of template removal increased with temperature increasing. The BET surface area of the crystal after hydrocracking at 280 ℃ reached 252 m2·g-1, although a small amount of organic residue remained. Furthermore, after hydrocracking at 350 ℃, the BET surface area reached 399m2·g-1, and only trace amount of inorganic carbon residue remained. In addition, the introduction of hydrogen at low temperatures could prevent coke deposits on acid sites and thus ZSM-5 zeolite crystals had greater numbers of acidic sites after low-temperature hydrocracking.

Key words: ZSM-5 zeolite, Template removal, Low-temperature hydrocracking, High Si/Al ratio, Tetrapropylammonium hydroxide

MSC2000: 

  • O643