Enhancement of Epoxidation Efficiencies for Ta-SBA15 Catalysts. The Influence of Modification with 鈥揈Me3 (E = Si, Ge, Sn) Groups

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• 作者：Paul J. Cordeiro ; T. Don Tilley
• 刊名：Langmuir
• 出版年：2011
• 出版时间：May 17, 2011
• 年：2011
• 卷：27
• 期：10
• 页码：6295-6304
• 全文大小：965K
• 年卷期：v.27,no.10(May 17, 2011)
• ISSN：1520-5827

文摘

Site-isolated Ta(V) centers were introduced onto the surface of a mesoporous SBA-15 support via the thermolytic molecular precursor method. After thermal treatment under oxygen, the resulting Si鈥揙H and Ta鈥揙H sites of TaSBA15-O₂were modified with a series of trimethyl group 14 species, Me₃E鈥? by treatment with Me₃E鈥揘Me₂ (E = Si, Ge, Sn) reagents. The resulting surface-modified catalysts (Me₃E)_capTaSBA15 exhibit a significantly increased rate of cyclohexene epoxidation with H₂O₂ as an oxidant, and provided a decreased amount of allylic oxidation products with respect to the unmodified material, TaSBA15-O₂. The rate of nonproductive H₂O₂ decomposition, as monitored via ¹H NMR spectroscopy, significantly decreased after the surface modification. The structure of the TaSBA15 catalysts and potential Ta(V) epoxidation intermediates (formed upon treatment of Ta(V) materials with H₂O₂) were probed using UV鈥搗isible absorbance and diffuse-reflectance UV鈥搗isible spectroscopy. A Ta(V)(畏²-O₂) intermediate species is proposed for the TaSBA15-O₂, (Me₃Si)_capTaSBA15, and (Me₃Ge)_capTaSBA15 catalysts, while intermediate species for the (Me₃Sn)_capTaSBA15 catalysts could not be characterized.