PHOTOCATALYTIC OXIDATION OF ETHANOL - ISOTOPIC LABELING AND TRANSIENTREACTION

Transient reaction techniques were combined with isotope labeling to s tudy the reaction steps for the room-temperature, photocatalytic oxida tion (PCO) of ethanol on TiO2. Carbon-13 labeled ethanol ((CH3CH2OH)-C -13) was adsorbed on the catalyst and photocatalytically oxidized in t he absence of gas-phase ethanol. The amounts of species remaining on t he surface after PCO were determined by temperature-programmed oxidati on. During PCO, only CO2 and H2O formed for low coverages of ethanol, whereas acetaldehyde also desorbed for saturation coverage. Acetaldehy de forms rapidly from ethanol oxidation during PCO. At both low and hi gh ethanol coverages, the alpha-carbon is preferentially oxidized and thus (CO2)-C-13 forms faster than (CO2)-C-12 at short illumination tim es. At longer times, the rates of (CO2)-C-13 and (CO2)-C-12 formation are nearly identical. The difference in behavior between (CO2)-C-13 an d (CO2)-C-12 formation suggests two parallel reactions of ethanol, whi ch may be due to two adsorption sites on TiO2.