High-Temperature Photocatalytic Ethylene Oxidation Over TiO2

Photocatalytic oxidation of ethylene was conduced at higher temperatures than previously reported (60 °C > T > 520 °C) in a novel two-dimensional packed bed reactor. Heat treated Degussa P25 TiO2 was used as a photocatalyst; each catalyst contained a different phase composition, surface area, and surface hydroxyl concentration. Maximum photocatalytic oxidation rates were observed between 100 °C to 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. Decreased oxidation rates at elevated temperatures (T > 300 °C) were attributed to the non-radiative, multi-phonon recombination of photo-generated charge carriers. Regression analysis of a nonlinear, multi-phonon recombination model and 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.