Acta Phys. -Chim. Sin. ›› 2004, Vol. 20 ›› Issue (08): 854-859.doi: 10.3866/PKU.WHXB20040814

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Physicochemical and Catalytic Properties of ZSM-5/Y Composite Zeolites Dealuminated by the Steaming

Chen Hong-Lin;Shen Bao-Jian;Pan Hui-Fang   

  1. State Key Laboratory of Heavy Oil Processing, the Key Laboratory of Catalysis of CNPC, and Faculty of Chemical Engineering, University of Petroleum, Beijing 102249
  • Received:2004-01-19 Revised:2004-04-07 Published:2004-08-15
  • Contact: Shen Bao-Jian E-mail:baojian@bjpeu.edu.cn

Abstract: ZSM-5/Y composite zeolite, a new composite material synthesized in situ from NaY gel, was dealuminated by hydrothermal treatment to study the effect of dealumination on physicochemical properties (undertook with XRD, IR spectroscopy, N2 adsorption/desorption) and catalytic activity (in n-hexane cracking). Compared to the mechanical mixtures, Y phases of the composites had better retained crystallinity under steaming at 550 ℃ and 700 ℃.Steaming resulted in the loss of microporosity of the crystalline material but the increase of mesoporous structure (5~30 nm at 550 ℃ and 5~40 nm at 700 ℃).The size of the mesopore distribution of dealuminated composites was larger than the dealuminated mechanical mixtures, but their macro- and mesopore volume was smaller. Quantitative IR studies of pyridine sorption showed Brønsted and Lewis acid sites of the composite after dealuminated at 550 ℃ decreased (mainly the medium strength acid sites).Compared to the hydrogen type zeolite, the catalytic activity of the dealuminated zeolite for n-hexane cracking increased greatly after 550 ℃ dealumination, and then decreased by further dealumination. The analysis of the product distribution showed that the enhanced activity was related to the change of reaction mechanism.

Key words: ZSM-5/Y composite zeolite, Mechanical mixture, Hydrothermal dealumination, Mesopore, Acidity, Catalytic cracking