Visualizing Elementary Reactions of Methanol by Electrons and Holes on TiO₂(110) Surface

Direct visualization and comparison of the elementary reactions induced by electrons and holes are of importance for finding a way to conduct chemical reactions and reaction sequences in a controllable manner. As a semiconductor, TiO2 provides a playground to perform the measurements, and moreover, the information can be useful for design of high-performance TiO2-based catalysts and photocatalysts. Here, we present our investigation on the elementary reactions of CH3OH on TiO2 surface through visualization of specific elementary steps by highly controllable electron and hole injection using scanning tunneling microscopy. The distinct sequential routes and their kinetics, namely, breaking C–O and O–H bonds by electrons and breaking O–H and C–H bonds by holes, respectively, have been experimentally identified and well elucidated by density functional theory calculations. Our nonlocal h-injection experimental and theoretical results suggest that the delocalized holes in the TiO2 substrate should be responsible for the temperature-dependent h-route reactions. The locally triggered e-route reaction is associated with the fact that the location of the unoccupied hybridization states is much higher than that of the conduction band onset. Our findings resolve the long-standing debate about the intermediate species and reaction mechanism in photocatalytic oxidation of CH3OH. Our proposed protocol offers a powerful means to study elementary reactions induced by electrons and holes on a semiconductor surface in general