Investigation Of The Efficient Decomposition Of Ozone Catalyzed By Mn-based Catalysts

As an important gaseous pollution at the ground level,ozone can cause serious harm to human health.Catalytic decomposition method has been widely used to remove ozone.Manganese oxide is an effective catalyst for ozone decomposition.Amorphous manganese oxides have the advantages of large surface area and excellent surface adsorption properties,which provide abundant active sites for the catalytic oxidation of ozone.However,the competitive adsorption between water and ozone restricted its application in high humidity.In this paper,a redox method was used to synthesize amorphous manganese oxides with high catalytic activity for decomposition of ozone as the basic catalyst.The performance of the amorphous manganese oxides was optimized by nitric acid acidification,calcination and Ce doping,and the Mn-based catalyst with high catalytic activity and stability for the ozone decomposition in the wide range of relative humidity will be developed.Micromorphology,chemical composition and structure of the catalyst were systematically investigated by various instruments and equipment.The structure-function relationship of composition and structure with catalytic performance has been established for the modified amorphous manganese oxide catalyst.The activity of amorphous MnOx can be improved by nitric acid acidification,and the activity is related to the concentration of nitric acid.Calcination treatment can further enhance the activity of the catalyst.The MnOx-0.4M-300 catalyst,which was prepared by acidizing 0.4 M nitric acid and then calcining at 300℃,had the obvious improvement in activity.MnOx-0.4M-300 can completely remove ozone at low relative humidity,and the removal rate of ozone can reach 98%after 3 h when RH is 60%.Nitric acid acidification increased the specific surface area,the content of Mn3+and oxygen species adsorbed on the surface of the catalyst,thus increasing the number of active sites and improving the activity of the catalyst.In addition,both acidification and calcination treatment weakened the adsorption of water molecules and improved the water resistance of the catalyst.Ce doping has a significant effect on the improvement of the activity of amorphous manganese oxide.With the increase of Ce content,the catalyst activity increased firstly and then decreased.When the molar ratio of Ce to Mn was 0.05,Ce-MnOx(0.05)catalyst showed the best performance for catalytic decomposition of ozone.Ce-MnOx(0.05)can completely remove ozone in the range of 5%～60%RH,and the ozone removal rate can also reach more than 90%after 10 h when RH is 80%.The high activity of Ce-MnOx(0.05)could be attributed to its maximum specific surface area,strong reducibility and water resistance,as well as high Mn3+ and surface adsorbed oxygen content.In addition,there may be a synergistic effect between Ce and Mn,which further improves the catalytic performance of the catalyst.