Effects of Mn valence on catalytic oxidation of gas-phase low-concentration toluene by ozone over Mn/γ-Al₂O₃ catalyst

By coprecipitation method, using Al₂O₃ as carrier, Mn/γ-Al₂O₃ and Mn-Ce/γ-Al₂O₃ catalysts were prepared and calcined in an atmosphere of N₂ or O₂, respectively. The fixed-bed continuous flow reactor was utilized to research performances for catalytic oxidation of toluene by ozone of the above catalysts at room temperature. The structure and composition of these catalysts were characterized by means of XRD, XPS and FTIR. Results show that Mn/γ-Al₂O₃ catalysts have good performances for catalytic ozonation of toluene and catalytic ozone decomposition. And, 20% is the optimum Mn load. Calcination in an atmosphere of O₂ or addition of cocatalyst Ce can effectively improve the activity and life of the catalyst. It can be attributed that calcination in O₂ and addition of Ce can increase the oxidation state of Mn. The main reason for deactivation of the catalyst is the accumulation of organic byproducts absorbed on the catalyst surface. However, the catalytic performance of inactivated catalyst can recover after calcining under an atmosphere of air at 550°C.