Direct Preparation of Thermally Stable Sn-Incorporated SBA-15 Mesoporous Materials in the Self-Generated Acidic Environment

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• 作者：Shih-Yuan Chen ; Huai-De Tsai ; Wei-Tsung Chuang ; Jey-Jau Lee ; Chih-Yuan Tang ; Ching-Yen Lin ; Soofin Cheng
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：August 27, 2009
• 年：2009
• 卷：113
• 期：34
• 页码：15226-15238
• 全文大小：694K
• 年卷期：v.113,no.34(August 27, 2009)
• ISSN：1932-7455

文摘

Highly ordered Sn-incorporated SBA-15 mesoporous materials with Sn loading up to 10 mol % were prepared in one pot using P123 triblock copolymer as the template in a self-generated acidic environment with the aid of NaCl. The acidity of the synthesis solution generated by hydrolysis of Sn precursor was found suitable not only for the self-assembly of P123 micelles and tetraethyl othorsilicate (TEOS) but also to incorporate the Sn ions into the SBA-15 materials. Prehydrolysis of TEOS in the synthesis solution containing P123, NaCl, and H₂O prior to adding Sn precursor was essential to reduce the strong interference from the Sn ions in the self-assembly process. A well-ordered 2D hexagonal p6mm pore arrangement was observed in the Sn-SBA-15 materials with Sn/Si ratios of 0.01−0.10, while tetragonal SnO₂ nanocrystallites were observed when the Sn/Si ratio was higher than 0.07. In situ small-angle X-ray scattering showed that a worm-like pore arrangement appeared at the beginning of the self-assembly process. As the reaction period prolonged, further condensation of silica and rearrangement of pore structure resulted in a well-ordered 2D hexagonal p6mm mesostructure. For the Sn-SBA-15 materials with Sn/Si ratios of 0.07−0.1, it was noticeable that two sets of 2D hexagonal pore arrangements with slightly different d spacings were present. One set of larger d spacing formed by incorporation of very small tin oxide species at the interface of P123 micelles and silicate appeared faster than the other of smaller d spacing. When the Sn/Si ratio was smaller than 0.05, Sn was probably incorporated in the SBA-15 framework as isolated ions. Beyond this loading, tetragonal SnO₂ nanocrystallites (4.7 nm) aggregated into rod- or tube-like morphologies of 5−10 nm in diameter and 20−50 nm in length were formed inside the mesochannels. The mesostructure of Sn-SBA-15 was thermally stable up to 1000 °C, which is superior to pure siliceous SBA-15. Moreover, the SnO₂ nanocrystallites confined inside the mesochannels did not sinter into large SnO₂ crystals even after calcination at 1000 °C.