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Title: Reaction Kinetics of Water Molecules with Oxygen Vacancies on Rutile TiO2(110)

The formation of bridging hydroxyls (OHb) via reactions of water molecules with oxygen vacancies (VO) on reduced TiO2(110) surfaces is studied using infrared reflection-absorption spectroscopy (IRAS), electron-stimulated desorption (ESD), and photon-stimulated desorption (PSD). Narrow IRAS peaks at 2737 cm-1 and 3711 cm-1 are observed for stretching vibrations of ODb and OHb on TiO2(110), respectively. IRAS measurements with s- and p-polarized light demonstrate that the bridging hydroxyls are oriented normal to the (110) surface. The IR peaks disappear after the sample is exposed to O2 or annealed in the temperature range of 400 – 600 K (correlating with the temperature at which pairs of OHb’s reform water and then desorb), which is consistent with their identification as bridging hydroxyls. We have studied the kinetics of water reacting with the vacancies by monitoring the formation of bridging hydroxyls (using IRAS) as a function of the annealing temperature for a small amount of water initially dosed on the TiO2(110) at low temperature. Separate experiments have also monitored the loss of water molecules (using water ESD) and vacancies (using the CO photooxidation reaction) due to the reactions of water molecules with the vacancies. All three techniques show that the reaction rate becomes appreciable formore » T > 150 K and that the reactions largely complete for T > 250 K. The temperature-dependent water-VO reaction kinetics are consistent with a Gaussian distribution of activation energies with Ea = 0.545 eV, ΔEa(FWHM) = 0.125 eV, and a “normal” prefactor, v = 1012 s-1. In contrast, a single activation energy with a physically reasonable prefactor does not fit the data well. Our experimental activation energy is close to theoretical estimates for the diffusion of water molecules along the Ti5c rows on the reduced TiO2(110) surface, which suggests that the diffusion of water controls the water – VO reaction rate.« less
 [1] ;  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1932-7447; KC0301050
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry. C; Journal Volume: 119; Journal Issue: 40
American Chemical Society
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
Country of Publication:
United States
74 ATOMIC AND MOLECULAR PHYSICS Rutile; titania; TiO2(110); water adsorption; bridging hydroxyl; infrared reflection-absorption spectroscopy; IRAS; electron stimulated desorption; ESD; photon stimulated desorption; PSD