Effects of moisture and temperature on the photooxidation of ethylene on Titania

The effect of temperature, water vapor concentration, and ethylene concentration on the photooxidation of ethylene on titania was investigated. Ultraviolet radiation from a black-light lamp together with a glass-plate reactor were used to develop intrinsic oxidation rates. Ethylene oxidation rates decreased significantly as the water vapor concentration was increased from 1000 ppmv for the three temperatures (2, 27, and 48 degrees C) investigated. The influence of water vapor on the reaction rate derived from the law adsorption of ethylene due to its low adsorption affinity relative to water. Over the range of water vapor concentration of 1000-25000 ppmv, ethylene oxidation rates increased as the temperature increased. An Arrhenius plot of the measured ethylene oxidation rates indicated an apparent activation energy of 3.4 kcal/mol. A Langmuir-Hinshelwood expression displaying an explicit temperature dependence was used to correlate the entire set of rate data. Based on this correlation, an enthalpy of adsorption for ethylene of -2.6 kcal/mol was found.