Room Temperature Catalytic Ozonation of Toluene over MnO2/Al2O3

Five kinds of transition metal oxides supported on alumina and prepared by wetness impregnation were evaluated for the catalytic ozonation of toluene at room temperature and characterized by temperature-programmed reduction, temperature-programmed oxidation, N2 adsorption-desorption, and X-ray photoelectron spectroscopy. The catalysts with a lower reduction temperature and less H2 consumption showed a higher efficiency for ozone and toluene decomposition, such as NiO/Al2O3, CoO/Al2O3, and MnO2/Al2O3, while lower efficiency were observed on Fe2O3/Al2O3 and CuO/Al2O3. Toluene decomposition efficiency was obviously dependent on ozone. Because of the low ozone to toluene concentration ratio, a CO2 yield of less than 30% was obtained. At a toluene concentration of 666 mg/m3 and an ozone concentration between 193 and 965 mg/m3, toluene conversion was found to vary from 15.2% to 46.7%. Additionally, we observed an increase in oxidation products and lattice oxygen on the catalyst surface. A preliminary investigation into the reaction pathway was undertook by in situ diffuse reflectance Fourier transform infrared spectroscopy. With regards to the formation of COO−, C=O, and C-O groups the high ozone concentration accelerated the transformation from COO− to C=O and C–O. The substance containing COO− remained unchanged at 573 K, while the substances containing C=O and C–O underwent oxidation at higher than 373 K. A possible reaction pathway is proposed based on these findings.