Photocatalytic Oxidation of Ethanol:  Isotopic Labeling and Transient Reaction

Transient reaction techniques were combined with isotope labeling to study the reaction steps for the room-temperature, photocatalytic oxidation (PCO) of ethanol on TiO 2 . Carbon-13 labeled ethanol (CH 3 13 CH 2 OH) was adsorbed on the catalyst and photocatalytically oxidized in the absence of gas-phase ethanol. The amounts of species remaining on the surface after PCO were determined by temperature-programmed oxidation. During PCO, only CO 2 and H 2 O formed for low coverages of ethanol, whereas acetaldehyde also desorbed for saturation coverage. Acetaldehyde forms rapidly from ethanol oxidation during PCO. At both low and high ethanol coverages, the α-carbon is preferentially oxidized and thus 13 CO 2 forms faster than 12 CO 2 at short illumination times. At longer times, the rates of 13 CO 2 and 12 CO 2 formation are nearly identical. The difference in behavior between 13 CO 2 and 12 CO 2 formation suggests two parallel reactions of ethanol, which may be due to two adsorption sites on TiO 2 .