Photo-oxidation of short-chain hydrocarbons over titania

The UV-induced photo-oxidation of propene, propane, ethene, ethane, n-butane and n-hexane were studied over a TiO2 photo-catalyst at 150°C with hydrocarbon concentrations up to 4000ppm and O2 concentrations up to 20%. In the absence of O2, very little reaction was observed and rapid catalyst deactivation occurred. Increasing the O2 concentration led to increased hydrocarbon conversion. Under most conditions, the selectivity of hydrocarbon conversion to CO2 was at least 95% for propene, propane, ethene and ethane. The only exception was 50% selectivity observed for the highest propene concentration studied (4000ppm) in the presence of 12% O2. For propene and propane, the extent of photo-conversion depended on the gas-phase hydrocarbon concentration, and had maxima at 500 and 1000ppm, respectively. The observed decrease at higher concentrations was attributed to hydrocarbon blocking oxygen adsorption sites, and thereby inhibiting the production of the photo-generated reactive oxygen species responsible for hydrocarbon oxidation. Durability of the photo-oxidation reaction without catalyst deactivation was demonstrated for propene, propane, ethene and ethane. In contrast with n-butane and to a greater extent n-hexane, the deposition of stable carbonaceous species on the TiO2 surface led to catalyst deactivation.