Supported manganese oxide on TiO2 for total oxidation of toluene and polycyclic aromatic hydrocarbons (PAHs): Characterization and catalytic activity

Abstract

Manganese oxide catalysts supported on titania (TiO2) were prepared by incipient wetness impregnation method in order to elaborate catalysts for total oxidation of toluene and PAHs. These catalysts have been characterized by means of X-ray diffraction (XRD), electron paramagnetic resonance (EPR), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). It has been shown that for the 5%Mn/TiO2 catalyst the reducibility and the mobility of oxygen are higher compared, in one side, to other x%Mn/TiO2 samples and, in another side, to catalysts where TiO2 support was replaced by γ-Al2O3 or SiO2. It has been shown that the content of manganese loading on TiO2 has an effect on the catalytic activity in the toluene oxidation. A maximum of activity was obtained for the 5%Mn/TiO2 catalyst where the total conversion of toluene was reached at 340 °C. This activity seems to be correlated to the presence of the Mn3+/Mn4+ redox couple in the catalyst. When the Mn content increases, large particles of Mn2O3 appear leading then to the decrease in the corresponding activity. In addition, compared to both other supports, TiO2 seems to be the best to give the best catalytic activity for the oxidation of toluene when it is loaded with 5% of manganese. For this reason, the latter catalyst was tested for the abatement of some PAHs. The light off temperature of PAHs compounds increases with increasing of benzene rings number and with decreasing of H/C ratio. All of PAHs are almost completely oxidized and converted at temperatures lower than 500 °C.