| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS-WeA |
| Session: | Adsorption & Reactions on Oxide Surfaces |
| Presenter: | Zhi-Tao Wang, Pacific Northwest National Laboratory |
| Authors: | Z.T. Wang, Pacific Northwest National Laboratory Y.G. Du, Pacific Northwest National Laboratory Z. Dohnálek, Pacific Northwest National Laboratory I. Lyubinetsky, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
The chemistry of oxygen on TiO2 surfaces is an important component in many catalytic and photocatalytic processes, such as water splitting and waste remediation, and has been extensively studied. So far, the majority of fundamental research has been carried out on the model transition-metal oxide surface of the rutile TiO2(110). The investigation of molecular adsorption of O2 can be considered as a natural first step providing information about possible O2 surface chemistry on TiO2(110). Both experiment and theory have demonstrated that O2 dissociatively adsorbs at bridging oxygen vacancies (VO) sites and five-fold coordinated terminal titanium atoms (Ti5c) at elevated temperatures. At sufficiently low temperatures, the majority of the ensemble-averaging technique studies suggested that O2 molecularly chemisorbs at VO sites on reduced surfaces (at T < 150 K). However, recent STM studies reported a contradict result that the O2 dissociation at VO sites has been observed at temperatures as low as ~ 110 K.
In this work, we investigated the initial stages of oxygen adsorption on reduced TiO2(110) with high-resolution scanning tunneling microscopy (STM) at 50 K. Molecularly chemisorbed O2 species, not directly observed until now on TiO2(110), have been imaged at two distinctive adsorption sites (VO and Ti5c) using “extremely mild” tunneling conditions. While O2 species at Ti5c site appears as a single protrusion centered on the Ti5c row, the O2 at VO manifests itself by a disappearance of the VO feature. The dissociation of chemisorbed O2 can be readily induced by tunneling conditions that are normally used for TiO2(110) imaging, and the dissociation details strongly depend on the scanning parameters and the type of the O2 adsorption site. The O2 molecules chemisorbed at low temperatures at these two distinct sites are the most likely precursors for the two O2 dissociation channels, observed at temperatures above 150 and 230 K at the VO and Ti5c sites, respectively. In general, our results provide a molecular level insight into the thermal chemistry of O2 on reduced TiO2, and assist in understanding of the surface reactivity of transition-metal oxides.