| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS+EN-WeA |
| Session: | Metals, Alloys & Oxides: Reactivity and Catalysis |
| Presenter: | Nikolay Petrik, Pacific Northwest National Laboratory |
| Authors: | N.G. Petrik, Pacific Northwest National Laboratory G.A. Kimmel, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
TiO2 is an important photocatalyst with many practical applications. It is also a good model system for fundamental studies of thermal and non-thermal reactions, including photocatalytic water splitting. Our understanding of water’s reactions on TiO2 surface is limited. In this paper, we have investigated temperature-dependent reaction of water molecules with bridging oxygen vacancy (VO) on rutile TiO2(110) surface using three independent methods: i) infrared reflection absorption spectroscopy (IRAS) to monitor the bridging hydroxyl (OHB or ODB) formation, ii) electron-stimulated desorption (ESD) of molecular water to monitor the water coverage,1and iii) photon-stimulated desorption (PSD) of CO2 – which is a product of CO photooxidation – to monitor the unoccupied VO coverage. 2 Narrow, distinct peaks for isolated ODB and OHB at ~2736.5 cm-1 and ~3711.5 cm-1 are detected in P-polarized mode for the samples exposed to D2O and H2O, respectively. If water is dosed at low temperature and annealed, bridging hydroxyl peaks appear above 150 K, growing with temperature until ~ 250 K, then saturate. In the same temperature range, molecular water and VO coverages from the ESD and PSD data decrease in correlated fashion according to the reaction H2OTi + VO -> 2OHB. The temperature range for this conversion appears to be too broad to be fitted with a single Arrhenius term and a reasonable pre-factor. On the other hand, the data can be fitted well using a “normal” prefactor (ν = 1012 s-1 ) and a distribution of activation energy (Ea) centered at 0.545 eV with ΔEa(FWHM) = 0.125 eV. These parameters are close to those obtained from STM data3 and theory4 for the water monomer diffusivity on Ti sites, which most likely controls the water – vacancy reaction. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences.
(1) Zhang, Z.; Du, Y.; Petrik, N. G.; Kimmel, G. A.; Lyubinetsky, I.; Dohnalek, Z. Water as a Catalyst: Imaging Reactions of O2 with Partially and Fully Hydroxylated TiO2(110) Surfaces. J. Phys. Chem. C 2009,113, 1908-1916.
(2) Petrik, N. G.; Kimmel, G. A. Off-Normal CO2 Desorption from the Photooxidation of CO on Reduced TiO2(110). J. Phys. Chem. Lett. 2010,1, 2508-2513.
(3) Matthiesen, J.; Hansen, J. O.; Wendt, S.; Lira, E.; Schaub, R.; Laegsgaard, E.; Besenbacher, F.; Hammer, B. Formation and Diffusion of Water Dimers on Rutile TiO2(110). Phys. Rev. Lett. 2009, 102, 226101.
(4) Hammer, B.; Wendt, S.; Besenbacher, F. Water Adsorption on TiO2. Top. Catal. 2010, 53, 423–430.