Photocatalytic Dissociation of Ethanol on TiO2(110) by Near-Band-Gap Excitation

Ethanol on TiO2(110) has been studied using the temperature-programmed desorption (TPD), femtosecond two-photon photoemission spectroscopy (2PPE), and density functional theory (DFT) calculations. The first layer of ethanol (binds to Ti-5c) whose molecular state has been predicted to be more stable by DFT desorbs at 295 K. A photoinduced excited state that is associated with bridging hydroxyls has been detected at similar to 2.4 eV above the Fermi level on ethanol/TiO2(110) interface using 2PPE. Detailed TPD studies show that ethanol on Ti-5c can be photocatalytically converted to acetaldehyde by near-band-gap excitation with the hydrogen atoms transfer to bridging-bonded oxygen sites, which is consistent with the 2PPE results. TPD results also show a low-temperature water TPD peak that seems to bind to the Ti-5c sites in addition to the ethylene TPD product. These results suggest that the Ti-5c sites on TiO2(110) are the primary active sites for photocatalysis of ethanol on TiO2(110), while bridging-bonded oxygen sites also play an important role, as in the case of methanol. The kinetics of photocatalyzed ethanol dissociation on TiO2(110) has also been measured using the 2PPE technique, which is of heterogeneous nature.