Structural Investigation of Au Catalysts on TiO2-SiO2 Supports: Nature of the Local Structure of Ti and Au Atoms by EXAFS and XANES

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• 作者：Viviane Schwartz ; David R. Mullins ; Wenfu Yan ; Haoguo Zhu ; Sheng Dai ; Steven H. Overbury
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：November 22, 2007
• 年：2007
• 卷：111
• 期：46
• 页码：17322 - 17332
• 全文大小：495K
• 年卷期：v.111,no.46(November 22, 2007)
• ISSN：1932-7455

文摘

X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supportscomposed by silica and titanium oxide, and the coordination of TiO₂ in the support phase. Particularly, wewanted to utilize the technique to probe mixing in the support phase, by using different synthetic methodssuch as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories,and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesistechniques to dope bulk mesoporous SiO₂ with TiO₂ resulted in TiO₂ being dispersed in the SiO₂ matrix;however, a second phase starts forming as the TiO₂ content increases as indicated by the EXAFS Ti-O shellshift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particleswere smaller and more stable. The study using the surface sol-gel technique for deposition of single monolayersof an oxide such as TiO₂ produced Ti environments in which the Ti-O shell and the next two Ti-Ti shellslie on the same position as expected for an anatase structure. Although undercoordinated, the presence of theTi-Ti shells indicate that the titania species are not molecularly dispersed on the SiO₂ surface as hypothesized,but there is indeed a cross-linking of the titania moieties.