Methane generated during photocatalytic redox reaction of alcohols on TiO2 suspension in aqueous solutions

Studies on the photo-catalytic redox reaction of C1-C3 alcohols such as methanol, ethanol and 2-propanol were carried out in aqueous solution containing TiO2 photocatalyst (0.1% w/v) as suspension using 350 nm light. Other hydrocarbons such as ethane and ethene in the case of ethanol, and propene in the case of 2-propanol with low yields were produced along with the major photolytic products methane and carbon dioxide. The yields of methane and CO2 were found to be dependent on the light exposure time and ambient conditions. Methane yields were higher in 2-propanol and ethanol systems than in methanol system, showing their better hole-scavenging properties. In the aerated condition, methane was produced during photolysis of all alcohols in the presence of TiO2 and the yield was comparable to those observed in the corresponding CO2-saturated systems. The overall results reveal that the surface adsorbed, as well as in-situ-generated CO2 from photo-oxidation of alcohols are equally responsible for methane formation through photoreduction in presence of TiO2- In the O-2-saturated system, the methane yield was lower as compared to that in aerated system, in contrast to the CO2 yield. In N2O- and N-2-purged systems, the yield of methane was observed to be low, inferring that the methane generation has not taken place through photodecomposition/photodissociation of alcohols. Again, photolysis of alcohols without TiO2 did not generate any methane.