Electron-Scavenging Chemistry of Benzoquinone on TiO2(110)
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The chemistry of benzoquinone (BQ) on TiO2(110) was examined using temperature programmed desorption (TPD), electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES). BQ adsorbs mostly molecularly on the clean surface, although EELS demonstrates that electrons from surface Ti3+ at oxygen vacancy sites (VO) are readily oxidized by the molecule. In contrast, when the surface is covered with water, subsequently adsorbed BQ molecules that scavenge surface electrons also abstract H from surface bridging OH (OHb) groups to form hydroquinone (HQ), which desorbs at ~450 K. The ability of BQ to scavenge electrons from TiO2 also accounts for the formation of coupling products that accumulate on the surface as very stable carbon deposits, likely as polymerized aromatics.
KeywordsBenzoquinone Rutile TiO2(110) Temperature programmed desorption Electron scavenging Photocatalysis
This work was supported by the US Department of Energy, Office of Science, 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. The research was performed using the Environmental Molecular Sciences Laboratory (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.