High-Temperature Photocatalytic Ethylene Oxidation over TiO2

Photocatalytic oxidation of ethylene was conducted in a novel two-dimensional packed bed reactor at higher temperatures (60 °C < T < 520 °C) than previously reported. Degussa P25 TiO2 was used as a photocatalyst; samples of this TiO2 were heat treated to different temperatures to obtain different phase compositions, surface areas, and surface hydroxyl concentrations. Maximum photocatalytic ethylene oxidation rates were observed between 100 and 200 °C. Further, oxidation rates greater than 75% of the maximum oxidation rate were observed over a large temperature range: 60 °C < T < 300 °C. At higher temperatures (T > 300 °C), decreasing oxidation rates were attributed to the nonradiative, multiphonon recombination of photogenerated charge carriers. Regression analysis of a nonlinear, multiphonon recombination model and a simplified chemical rate law were used to determine apparent reaction rate law parameters for the photocatalytic oxidation of ethylene and recombination parameters for the TiO2 photocatalyst. Insights for the development and operation of novel high-temperature photocatalysts are also discussed.