| Abstract
| - X-ray absorption fine structure combined with X-ray fluorescence spectrometry was applied to various V+TiO2hybrid samples. Emitted V Kα1 fluorescence from the sample was selectively counted by using a high-energy-resolution (0.4 eV) spectrometer equipped with a Ge(331) crystal. Two advantages of this method,extremely high signal/background ratio and the compatibility of measurements in the atmosphere of reactiongas (in situ study in relation to heterogeneous catalysis), were effective at the V K-edge. Structure transformationof the V sites was spectroscopically followed for the V/TiO2 catalyst. The monooxo tetrahedral vanadate sitewas demonstrated to exist at 473 K. It transformed into dispersed species of 5-fold coordination in ambientair and further into polymeric VOx species in 0.85 kPa of water at 290 K. In the presence of 3.2 kPa of2-propanol, dissociative adsorption of 2-propanol on the dispersed V species was strongly suggested at290−473 K. In situ structure changes of V sites on TiO2 were reported by means of XAFS for the first time.The VV sites for the V/TiO2 catalysts were essentially identical with those for V supported on mesoporous(high-surface-area) TiO2 and V−TiO2 sample prepared by the sol−gel method. However, predominant VIVsites were found for mesoporous V−TiO2. The VIV sites substituted on the Ti sites of TiO2. When the molarratio of V/Ti increased from 1/100 to 1/5.0, major octahedral V sites in the TiO2 matrix looked to transforminto tetrahedral ones.
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