In-situ scanning tunneling microscopy is used to follow the reactions of water, alcohols, and O2 with TiO2(110) surfaces. These reactions represent important prototypes for a number of catalytic and photocatalytic reactions  on TiO2 including oxidation of hydrocarbons and water splitting. Imaging of the same area before and after the reactions is used to follow the site specific adsorption, dissociation, diffusion and rotation of surface species as well as the reactions between different surface intermediates. At elevated temperatures, isothermal STM is employed to study the diffusion dynamics of oxygen vacancies (VO's) and dissociation products such as hydroxy and alkoxy species that are formed as a result of the reactions. It is found that mobile VO's efficiently assist motion of alkoxy species by lowering their diffusion barrier. Kinetic parameters controlling the diffusion are extracted and compared to theoretical DFT calculations. Our studies also show that at room temperature the alkyl chains of the alkoxy species rotate rapidly among equivalent configurations which are dependent on the position of the OH group within the alcohol molecule. At low temperatures (~150 K), the rotation of alkyl chains is found to be hindered by a large energy barrier across the bridging oxygen rows. In the studies of O2 reactions with surface hydroxyl groups an intriguing catalytic mechanism involving water molecules is found to lead to the surface dehydroxylation and practically bare, defect-free TiO2(110).

STM studies of adsorbate dynamics on TiO<sub>2</sub>(110)

241st National Meeting (2011)

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