Paper SS2-MoM8
Oxygen Interactions with Hydroxylated TiO₂(110) Surfaces

Monday, November 9, 2009, 10:40 am, Room N

Reactions leading from O₂ to H₂O on catalytically active surfaces often involve intricate mechanisms with a number of possible surface-bond intermediates, such as OH, HO₂, or H₂O₂. Such reactions on surfaces are challenging to explore with ensemble-average techniques because of the extremely small number of participating molecules and the difficulty in resolving intermediates spectroscopically.

In this work, the reaction of O₂ with both partially and fully hydroxylated TiO₂(110) surface was directly followed by STM. The consecutive steps of both primary and secondary site-specific reactions have been tracked by comparing the atomically resolved STM images of same surface area before and after O₂ exposure. As a result, we have directly imaged two chemical intermediates, terminal OH and OOH, which have been proposed to play key roles in the interconversion of oxygen and water. By combining the site-specific STM and ensemble-averaging TPD/ESD studies, we also find that H₂O can participate in the reaction process in multiple ways – as a reactant, product, and catalyst. Specifically, water mediates the diffusion of surface species that would otherwise be stationary, and thus brings reactants together, catalyzing the reactions with O₂. As a result, most of the OH_b’s can be removed via reaction with O₂ such that a fully hydroxylated surface can be converted to a nearly stoichiometric surface.