Effect of oxygen, moisture, and temperature on the photo oxidation of ethylene on N-doped TiO2 catalyst

• N-TiO2 catalyst enhances photocatalytic oxidation of ethylene under visible-light.
• Photocatalytic rate increased with [C2H4], [O2], temperature, and light intensity.
• Water vapor has both inhibiting and activating capabilities on PCO of ethylene.
• A Langmuir–Hinshelwood model was used to simulate the oxidation rate data.
• Reaction scheme of ethylene by PCO was proposed.

N-doped TiO2 catalyst synthesized by a sol–gel method was used for the photocatalytic oxidation of ethylene under visible-light illumination. Key parameters affecting the oxidation rate including feed composition (ethylene, oxygen, and water vapor), visible-light intensity, and reaction temperature were investigated. Results revealed that the reactivity of ethylene was greatly enhanced by increasing temperatures, light intensity, ethylene, and oxygen concentration. Feed ethylene concentrations ranging from 100 to 900 ppmv were stoichiometrically oxidized to CO2 under all experimental conditions. The positive effect of ethylene oxidation at higher temperature can be ascribed to unfavorable adsorption of water on catalysts and an increase in the heterogeneous catalytic reactions. The presence of water vapor exhibited both inhibiting and activating capabilities on the photocatalytic oxidation reactions of ethylene. A Langmuir–Hinshelwood (L–H) expression displaying an explicit temperature dependence was proposed to simulate the entire set of rate data, i.e., r=Iαk′exp-EaRTKe′exp-ΔHe/RTTCe1+Ke′exp-ΔHe/RTTCe+Kw′exp-ΔHw/RTTCwKo2′exp-ΔHo2/RTTCO21+KO2′exp-ΔHo2/RTTCO2. Based on the L–H model, the adsorption enthalpy of ethylene, water vapor, and oxygen on N-doped TiO2 catalyst were −2.61, −12.09, and −3.81 kcal mol−1, respectively.