Photo-oxidation of short-chain hydrocarbons over titania

The UV-induced photo-oxidation of propene, propane, ethene, ethane, n-butan e and n-hexane were studied over a TiO2 photo-catalyst at 150 degreesC with hydrocarbon concentrations up to 4000 ppm and O-2 concentrations up to 20% . In the absence of O-2, very little reaction was observed and rapid cataly st deactivation occurred. Increasing the O-2 concentration led to increased hydrocarbon conversion. Under most conditions, the selectivity of hydrocar bon conversion to CO2 was at least 95% for propene, propane, ethene and eth ane. The only exception was 50% selectivity observed for the highest propen e concentration studied (4000 ppm) in the presence of 12% O-2. For propene and propane, the extent of photo-conversion depended on the gas -phase hydrocarbon concentration, and had maxima at 500 and 1000 ppm, respe ctively. The observed decrease at higher concentrations was attributed to h ydrocarbon blocking oxygen adsorption sites, and thereby inhibiting the pro duction of the photo-generated reactive oxygen species responsible for hydr ocarbon oxidation. Durability of the photo-oxidation reaction without catal yst 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 deactiva tion. (C) 2001 Published by Elsevier Science B,V.