Electron-Scavenging Chemistry of Benzoquinone on TiO2(110)

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 (V-O) 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 similar to 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.