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 TiO 2 was used as a photocatalyst; samples of this TiO 2 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 TiO 2 photocatalyst. Insights for the development and operation of novel high-temperature photocatalysts are also discussed.