Kinetics of gas-phase photooxidation of p-xylene on nano TiO2 P25 thin film

Cam Loc Luu, Quoc Tuan Nguyen, Tri Nguyen and Si Thoang Ho

Abstract

In this investigation, the thin film of TiO₂ degussa P25 was obtained by dip coating method and calcined at 450 °C for 2 h (P25-450-2) and used as photocatalyst for gas-phase photooxidation of p-xylene. The physico-chemical properties of calcined P25-450-2 powder was studied by the methods of BET adsorption, XRD, FTIR, UV–vis, Raman spectroscopies, SEM, TEM, carbon dioxide temperature-programmed desorption (CO₂-TPD). The thickness of the film was determined on the Alpha Step IQ KLA—Ctencor equipment and the point of zero charge (PZC) of the sample was determined by salt addition method. P25-450-2, having a band gap of 3.155 eV, is advisable to use UV lamps in photocatalytic reactions. The kinetics of gas-phase photooxidation of xylene reaction on the thin films of P25-450-2 under UV illumination was studied using a gradientless flow circulating system at atmospheric pressure and 40 °C. The obtained results showed that the kinetics of the given reaction should be written by fractional equations describing the dependence of the reaction rate on the concentration of adsorbed molecules of p-xylene and oxygen, dissociative adsorbed water vapor, and also on the total intensity of light. The reaction was proposed to follow the Langmuir-Hinshelwood mechanism