Tuning the Acid/Base and Structural Properties of Titanate-Loaded Mesoporous Silica by Grafting of Zinc Oxide

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• 作者：Bastian Mei ; Ahmet Becerikli ; Anna Pougin ; Denise Heeskens ; Ilia Sinev ; Wolfgang Gr眉nert ; Martin Muhler ; Jennifer Strunk
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：July 12, 2012
• 年：2012
• 卷：116
• 期：27
• 页码：14318-14327
• 全文大小：421K
• 年卷期：v.116,no.27(July 12, 2012)
• ISSN：1932-7455

文摘

Mesoporous silica (SBA-15) loaded with TiO_x species was synthesized by anhydrous grafting of titanium isopropoxide, and a novel procedure for the preparation of ZnO_x/SBA-15 materials by grafting of Zn(acac)₂ was explored. The TiO_x/SBA-15 and ZnO_x/SBA-15 materials as well as subsequently prepared bifunctional ZnO_x- and TiO_x-containing SBA-15 materials were characterized in depth by combining N₂ physisorption measurements, UV鈥搗is, X-ray photoelectron and X-ray absorption spectroscopy, and CO₂ and NH₃ temperature-programmed desorption experiments. The characterization results confirmed a close proximity of ZnO_x and TiO_x in the subsequently grafted materials. Because of strong interactions between the Zn precursor and the SiO₂ surface, the order of the ZnO_x and TiO_x grafting steps affected the amount of Ti鈥揙鈥揨n bonds formed in the materials. When ZnO_x is present in SBA-15, subsequently grafted TiO_x is higher coordinated and more Ti鈥揙鈥揨n bonds are formed compared to SBA-15 in which TiO_x was introduced first, indicating strong interactions between the Ti precursor and ZnO_x. While all TiO_x and ZnO_x-containing samples exhibit a large amount of acidic sites, ZnO_x present as isolated species or small clusters in SBA-15 significantly improves the CO₂ adsorption capacity by introducing basic sites. In the subsequently grafted samples the amount of acidic and basic sites is found to be unaffected by the order in which the two transition metals are introduced.