Importance of Diffusion in Methanol Photochemistry on TiO2(110)
The photoactivity of methanol on the rutile TiO2(110) surface is shown to depend on the ability of methanol to diffuse on the surface and find sites active for its thermal dissociation to methoxy. Temperature programmed desorption (TPD) results show that the extent of methanol photodecomposition to formaldehyde is negligible on the clean TiO2(110) surface at 100 K due to a scarcity of sites that can convert (photoinactive) methanol to (photoactive) methoxy. The extent of photoactivity at 100 K significantly increases when methanol is coadsorbed with oxygen, however only those molecules able to adsorb near (next to) a coadsorbed oxygen species are active. Preannealing coadsorbed methanol and oxygen to above 200 K prior to UV irradiation results in a significant increase in photoactivity. Scanning tunneling microscopy (STM) images clearly show that the advent of increased photoactivity in TPD correlates with the onset of methanol diffusion along the surface’s Ti4+ rows at ~200 K. These results demonstrate that optimizing thermal processes (such as diffusion or proton transfer reactions) can be critical to maximizing photocatalytic reactivity on TiO2 surfaces. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle under contract DEAC05-76RL01830. The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1060130
- Report Number(s):
- PNNL-SA-91008; 35219; KC0302010
- Journal Information:
- Journal of Physical Chemistry C, 116(48):25465-25469, Journal Name: Journal of Physical Chemistry C, 116(48):25465-25469
- Country of Publication:
- United States
- Language:
- English
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