Low temperature oxidation of VOCs in air by catalytic ozonation

Alumina supported manganese oxides were used in the gas phase oxidation of toluene by ozone. Catalyst activity and characterization, the promotional effect of noble metals (Pt and Pd) on the activity of manganese oxides, and the kinetics and mechanism of the reaction were investigated in this PhD thesis. It was shown that MnO2 and Mn2O3 were the active sites of the catalyst capable of oxidizing toluene to CO and CO2 below 100 oC. Catalysts were deactivated at room temperature due to the accumulation of carbonaceous species on their surface. At least 65 oC was required for the stable operation of the catalysts. X-ray absorption spectroscopy was used to study the structure and electronic properties of the mono metallic and bimetallic catalysts. It was found that the catalysts with higher Mn loading resulted in higher oxidation states of Mn which were less favorable for the oxidation of toluene. The addition of Pt to the Mn containing catalyst increased the reaction rate by transferring electrons from Pt to Mn. On the other hand, no promotional effect was observed by the addition of Pd to Mn. The Oxidation state of Mn atoms was one of the most important parameters, controlling the rate of toluene oxidation. Lower oxidation states of Mn were able to easily transfer electrons to ozone, accelerating the rate of toluene oxidation. A reaction mechanism was proposed for the catalytic oxidation of toluene over manganese oxides. In this mechanism, the oxidation of toluene was carried out by the abstraction of hydrogen atoms followed by the oxidation of toluene carbon skeleton. A rate equation was derived based on this mechanism, determining the reaction orders of -1 and 2 for toluene and ozone, respectively. It was concluded that catalytic ozonation is an effective method for the low temperature oxidation of volatile organic compounds (VOCs) in air. The significance of this method is related to energy saving in air purifying systems by reducing the required temperature to oxidize VOCs. Catalytic ozonation can be used in indoor and outdoor applications for removal of VOCs from enclosed environments or polluted industrial streams