Chemical liquid deposition with polysiloxane of ZSM-5 and its effect on acidity and catalytic properties
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- 作者：Zhirong Zhu ; Zaiku Xie ; Qingling Chen ; Dejin Kong ; Wei Li ; Weimin Yang ; Can Li
- 关键词：ZSM-5 ; Chemical liquid deposition ; Polysiloxane ; Acidity ; Shape-selective catalysis
- 刊名：Microporous and Mesoporous Materials
- 出版年：2007
- 出版时间：19 April 2007
- 年：2007
- 卷：101
- 期：1-2
- 页码：169-175
- 全文大小：505 K
文摘
ZSM-5 acidity was modified by chemical liquid deposition of silica (SiO2-CLD), and the modification mechanism was investigated by pyrolysis gas chromatography-mass spectrometer (PGC-MS), absorbed pyridine infrared spectroscopy (Py-IR), temperature programmed desorption of ammonia (NH3-TPD), thermal gravity analysis (TGA), X-ray diffraction (XRD) and physical adsorption and probe-molecule reactions. In SiO2-CLD modification, the deposition process of polysiloxane modifier to silica over ZSM-5 is the acid-catalyzed degradation companying with the thermal pyrolysis, following oxidation at high temperature. Though the silanol hydroxyls of ZSM-5 disappear after the modification, most of the framework Al bridging hydroxyls and non-framework Al hydroxyls remain. Besides, the acidic amount of the modified ZSM-5 drops gradually with increasing extent of the modification, but the acidic strength distribution of the modified ZSM-5 is almost unchanged compared to parent ZSM-5. After the four-cycle modification, the conversion of 1,3,5-triisopropylbenzene (TIPB) in cracking over the modified ZSM-5 is reduced by 92 % , so the external surface of the modified ZSM-5 may be regarded to be almost non-acidic due to coverage of deposition silica. Moreover, the modified ZSM-5 shows the high activity for cracking of cumene. High selectivity of para-xylene up to 96.2 % is obtained in toluene disproportionation over the modified ZSM-5, compared to 24.3 % selectivity of para-xylene over parent ZSM-5. Therefore, SiO2-CLD with polysiloxane is an ideal modification for obtaining the high shape-selective ZSM-5 catalyst.