Facet Dependence of Photochemistry of Methanol on Single Crystalline Rutile Titania

The crystal phase, morphology and facet significantly influence the catalytic and photocatalytic activity of TiO₂. In view of optimizing the performance of catalysts, extensive efforts have been devoted to designing new sophisticate TiO₂ structures with desired facet exposure, necessitating the understanding of chemical properties of individual surface. In this work, we have examined the photooxidation of methanol on TiO₂(011)-(2×1) and TiO₂(110)-(1×1) by two-photon photoemission spectroscopy (2PPE). An excited state at 2.5 eV above the Fermi level (E_F) on methanol covered (011) and (110) interface has been detected. The excited state is an indicator of reduction of TiO₂ interface. Irradiation dependence of the excited resonance signal during the photochemistry of methanol on TiO₂(011)-(2×1) and TiO₂(110)-(1×1) is ascribed to the interface reduction by producing surface hydroxyls. The reaction rate of photooxidation of methanol on TiO₂(110)-(1×1) is about 11.4 times faster than that on TiO₂(011)-(2×1), which is tentatively explained by the difference in the surface atomic configuration. This work not only provides a detailed characterization of the electronic structure of methanol/TiO₂ interface by 2PPE, but also shows the importance of the surface structure in the photoreactivity on TiO₂.