Synthesis Of MnO_x Catalysts And Their Catalytic Performance For Toluene Oxidation

Volatile organic compounds?VOCs?are highly harmful to the environment and human health,and are also one of the main precursors for the formation of PM_2.5.5 and ozone.Compared with other emission sources,VOCs emitted from industries have relatively concentrated distribution,high intensity and complex composition.In recent years,various methods have been adopted at home and abroad to eliminate the pollution of VOCs.From the perspective of costs and industrial feasibility,catalytic combustion,as one of the VOCs removal technologies,has great development potential.Manganese oxide catalysts,due to their excellent redox properties,hydrothermal stability,higher abundance and cost advantages,have been widely studied in the research of catalytic combustion of VOCs.In this work,MnO_x catalysts were prepared via the redox mehod,the precipitation method,the solid-state reaction method,the sol-gel method and the one-step calcination method,respectively.The microstructure and surface properties of the catalysts were systematically characterized by X-ray powder diffraction?XRD?,N₂ adsorption/desorption analysis?BET?,scanning electron microscopy?SEM?,X-ray photoelectron spectroscopy?XPS?,Thermogravimetric-Differential Scanning Calorimeter?TG-DSC?and a chemisorption instrument.The catalytic performance of MnO_x catalysts was evaluated through toluene oxidation,which was chosen as the target VOC molecule.The major results are shown as follows.?1?The MnO_x catalysts prepared via the one-step calcination of manganese acetate required a relatively higher temperature?>300??to achieve the complete conversion of toluene to CO₂,while it happened at lower temperatures??260??over the other four kinds of catalysts when the GHSV=40000 mL·g^-1·h^-11 and toluene concentration=400 ppm.?2?Among the MnO_x catalysts,that synthesized by the redox mehod owned the largest specific surface area,the strongest low-temperature reducibility,and the best catalytic activity for toluene elimination.On this catalyst,90%of toluene was oxidized to CO₂ at 219?when the GHSV=40000 mL·g^-1·h^-11 and toluene concentration=400 ppm.?3?The MnO_x catalysts presented different microstructure and surface properties as the calcination temperature varied during the process of the redox method,which therefore affected the activities of the catalysts for toluene oxidation.Taking catalytic performance and energy consumption into consideration,experimental results showed that 300? was an optimized calcination temperature.