Preparation Of Manganese-based Catalysts And Their Application In Ozone Decomposition

In recent years,the air quality has been improved continuously,but ozone pollution is increasingly serious,especially in summer.Due to its strong oxidation,ozone could cause a huge damage to human health and ecological environment system.Therefore,it is urgent to develop an economical,high efficiency,safe and stable technology to decompose ozone.Among various ozone removal methods,catalytic decomposition is widely used due to its high efficiency,economy,and safety.Manganese oxide catalysts have been widely studied owing to their excellent performance and wide source.In this thesis,supported MnOx catalysts and OMS-2 catalysts were studied for ozone decomposition,and the effect of structure and properties of catalysts on their catalytic performance was also investigated.Firstly,manganese oxide was used as active component for ozone decomposition,and the influence of the type of support and Mn loading was investigated.Among them,20Mn/ZSM-5-27 sample exhibited the highest catalytic activity.On this basis,the ozone decomposition performance of 20Mn/ZSM-5-27 sample was further improved by optimizing Si/Al ratios of zeolite and modifying Mn active component.The results showed 20Mn/ZSM-5-81 exihibited higher catalytic activity than 20Mn/ZSM-5-27 and 20Mn/ZSM-5-200,which was mainly due to the synergistic effect of acidity and hydrophobicity.Furthermore,compared with 20Mn/ZSM-5-81,Ce doping could significantly improve the catalytic activity of yCe20Mn/ZSM-5-81 samples.The 8Ce20Mn/ZSM-5-81 exhibited the best catalytic activity under the condition of relative humidity of 50%and a space velocity of 360 L/(g×h),giving 93%conversion of 600 ppm O3 after 5 h at room temperature.XRD,H2-TPR,XPS,and oxygen isotopic exchange characterization results showed that Ce doping could enhance the amount of low valance manganese(such as Mn2+and Mn3+)and the content of adsorbed oxygen.Moreover,the reducibility of 8Ce20Mn/ZSM-5-81 was significantly increased due to the interaction between MnOx and CeO2,which was conducive to ozone decomposition.Next,the influence of Mn precusors and metal doping on the structural properties and catalytic performance of cryptomelance manganese dioxide(OMS-2)for ozone decomposition were also investigated.The results showed that OMS-2-Ac synthesized by MnAc2 exhibited the best catalytic activity under the condition of relative humidity of 50%and a space velocity of 360 L/(g×h),maintaining 80%conversion of 600 ppm ozone after 5 h at room temperatre.A series of physicochemical characterization(such as XRD,BET,H2-TPR,XPS)results showed that OMS-2-Ac possessed larger specific surface area,smaller crystal size,stronger redox ability,and increased adsorbed oxygen species.Furthermore,OMS-2 was modified by doping high valence metals(such as W,V,Nb)and the order of activity was as follows:W-OMS-2>V-OMS-2>OMS-2>Nb-OMS-2.The characterization results showed that the crystal structure of W-OMS-2 and V-OMS-2 samples were totally changed,forming new phase of orthorhombic ramsdellite MnO2.Moreover,W-OMS-2 and V-OMS-2 exhibited higher redox ability and enhanced the content of Mn3+ and surface adsorbed oxygen species,which was closely related to the enhanced catalytic activity of ozone decomposition.