Computational investigation of TiO2-supported isolated oxomolybdenum species

We present periodic density functional theory (DFT) calculations combined with thermodynamic analysis to study the structure of isolated molybdenum oxide entities supported on titania (anatase) under ambient and dehydrated conditions. The TiO2 support is represented by the perfect and hydrated (101) and (001) surfaces. The calculation of the vibrational wavenumbers of the stable structures under various conditions allows us to access to structural information by comparison with the experimental data obtained in in-situ conditions. The calculation of the most stable model on the (101) surface indicates that in dry conditions molybdenum is in a distorted tetrahedral environment with a single molybdenyl bond whereas dioxo entities are more stable on the (001) surface. Furthermore, it appears that the Mo=O stretching wavenumber is strongly influenced by the hydration state of the surface through formation of hydrogen bonds with the surface OH or H2O groups that induce a shift to lower wavenumber (more than 60 cm(-1)) in agreement with the Raman shift observed during the hydration-dehydration process.