Study On Effects Of Crystal Phases Of Manganese Dioxide On Catalytic Oxidation Of Toluene With Ozone

Volatile organic compounds(VOCs)are the major contaminants of air pollution.And they are also the key object of environmental governance since China's 13 th five-year plan.Catalytic oxidation with ozone by MnO2 is considered as a promising way to remove VOCs at low temperature.There are many kinds of MnO2 with different structures.However,the influence of MnO2 structure on the catalytic ozone oxidation is seldom reported.Therefore,six kinds of MnO2 with different crystal phases have been made and the effects on crystal phases of MnO2 on catalytic oxidation with ozone at room temperature have been studied.However,this technology can not completely oxidize VOCs to CO2 at room temperature.So the microwave heating is used to enhance the catalytic activity and the effects on crystal phases of MnO2 on catalytic oxidation with ozone under microwave heating have been also studied.The main research contents are as follows:In this paper,six kinds of MnO2 crystal phases,i.e.?-MnO2,?-MnO2,?-MnO2,?-MnO2,?-MnO2 and ?-MnO2 were prepared and characterized by XRD,SEM,BET,H2-TPR and XPS.Then the catalytic activit ies of these catalysts were evaluated at room temperature.The result shows that the catalytic activity is followed the order of ?-MnO2 > ?-MnO2 > ?-MnO2 > ?-MnO2 > ?-MnO2 > ?-MnO2.The relative contents of Mn3+ and adsorbed oxygen are the main factors for the catalytic activity.The catalytic decomposition of ozone by MnO2 is a vital step in the process.Under microwave heating,the heating characteristics and the activity of catalytic ozone oxidation toluene were evaluated.The result shows that the catalytic activity is followed the order of ?-MnO2 > ?-MnO2 > ?-MnO2 > ?-MnO2 > ?-MnO2 > ?-MnO2.Moreover,the lattice oxygen is the key matter for the oxidation toluene.The higher relative content of lattice oxygen,the better catalytic activity.At the same time,the reducibility of MnO2 also has an impact on the catalytic activity.Catalytic oxidation of organic has become the main way to remove toluene.Afterwards,four reaction conditions,such as the ratio of ozone and toluene,the relative humidity,the toluene concentration and the space velocity,were investigated with the best MnO2 under room temperature and microwave heating.The result shows that the relative humidity at room temperature can significantly reduce the catalytic activity,but it is beneficial to enhance the catalytic activity under the microwave heating.Nevertheless,the ratio of ozone and toluene concentration,the toluene concentration and the space velocity have the same effect on catalyst activity at room temperature and under microwave heating.Under the microwave power of 190 W,?-MnO2 of 0.15 g,the ratio of ozone and toluene concentration of 9:1,toluene concentration of 5 ppm,the relative humidity of 0% and the space velocity of 30000 h-1,the toluene conversion and the CO2 yield can reach 98.7% and 91.1%,respectively.