Preparation and Characterization of Tungsten Carbide Confined in the Channels of SBA-15 Mesoporous Silica

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• 作者：Linhua Hu ; Shengfu Ji ; Tiancun Xiao ; Canxiong Guo ; Pingyi Wu ; Pingying Nie
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：April 12, 2007
• 年：2007
• 卷：111
• 期：14
• 页码：3599 - 3608
• 全文大小：837K
• 年卷期：v.111,no.14(April 12, 2007)
• ISSN：1520-5207

文摘

A series of WO₃/SBA-15 materials with different Si/W ratios have been prepared by impregnating the hostmaterial SBA-15 with aqueous ammonium paratungstate solutions. After temperature-programmed carburization(TPC) in flowing CH₄/H₂ (20/80 v/v mixture), the materials are converted to the corresponding W₂C/SBA-15species. Both the oxide and carbide materials are characterized using X-ray diffraction, nitrogen adsorption-desorption, ²⁹Si NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and TEM measurements.The XRD results show that after impregnation with different amounts of tungsten and subsequent carburization,the materials retain the mesopore structure of SBA-15. The nitrogen adsorption-desorption results indicatethat a thin layer of W₂C covers the internal walls of SBA-15. Quantitative ²⁹Si single-pulse excitation MASexperiments and FTIR spectroscopy show that the incorporation of W₂C in the channels of SBA-15 is correlatedwith the formation of Si-O-W bonds. Some Si-O-W bonds are transformed into Si-O-H bonds aftercarburization. The TEM results show that the thickness of the W₂C thin layer is 1.7-1.9 nm in W₂C/SBA-15. A model involving a discrete W₂C thin layer in the channels of SBA-15 is proposed on the basis of theNMR data. The calculated thickness of the discrete W₂C thin layer is consistent with value given by HRTEM.