Kinetic study of the photocatalytic oxidation of ethylene over TiO2 thin films

The photocatalytic oxidation process has been recognized as an environmental friendly, sustainable and low-cost technology for air treatment. A photocatalytic batch reactor has been employed to assess the kinetics of the oxidation of ethylene (C2H4) over immobilized titanium dioxide (TiO2) and the effect of initial pollutant concentration on the kinetics. The rate model based on the simplified mono-molecular Langmuir-Hinshelwood (LH) kinetic model was found to represent the degradation satisfactorily, however with numerical constrains. These were overcome by employing two different approaches. On one hand the Langmuir-Hinshelwood model was solved by means of the Lambert W-function and on the other hand it was reduced to a pseudo-first order rate law, both resulting in a good fit to the experimental data, thus proving that the photodegradation of C2H4 over TiO2 can be modelled by a first order rate law under low concentration conditions. Moreover, both models give a linear dependence between the reaction rate and the initial C2H4 concentration, making an estimation of reaction rate as a function of concentration possible, for a larger interval of C2H4 concentrations.