Structural Regulation Of Manganese-based Oxides And Their Performance In Catalytic Decomposition Of Ozone

In recent years,ozone（O₃）has become another important secondary pollutant after fine particulate matter（PM 2.5）,which can cause serious air pollution and threaten crop growth,ecosystem stability and human health.Compared with traditional ozone treatment technologies such as adsorption,absorption and thermal decomposition,catalytic decomposition has been widely concerned because of its advantages of environmental protection and high efficiency.The development of low cost,high efficiency and environmental friendly catalyst for ozone decomposition is the key to this technology.In this paper,a series of manganese oxide catalysts were synthesized by different preparation methods,and then the prepared manganese oxides were modified by doped metal and the preparation conditions were optimized,the effect of doped metal types,doping amount and calcination temperature on the catalyst’s ozone decomposition performance was investigated,and finally the excellent Cu-OMS-2 catalyst was loaded on diatomaceous earth to prepare a composite catalyst,and the effect of the load on the decomposition performance of the composite catalyst was investigated.The above catalysts were characterized by XRD,SEM,BET,ICP-OES and XPS,and the structure-activity relationship between the catalyst and the ozone decomposition activity was explored.The study found that:（1）Manganese oxide catalysts with different properties were prepared by hydrothermal method,sol-gel method and liquid-phase precipitation method,and the ozone decomposition activity of the three catalysts was tested.The results showed that H-OMS-2 synthesized by hydrothermal method had the best ozone decomposition activity of 39%,followed by G-OMS-2 synthesized by sol-gel method with 31%,and Mn Ox synthesized by liquid precipitation method with 21%.Through various characterization methods,it is found that the catalysts synthesized by hydrothermal method and sol-gel method have the same OMS-2octahedral molecular sieve structure,while the Mn Ox catalyst synthesized by liquid-phase precipitation method is a mixture of monoclinic structure and cubic structure crystal phase.Due to the advantage of octahedral molecular sieve channels,the ozonation activity of H-OMS-2 and G-OMS-2 is obviously better than that of Mn Ox.For H-OMS-2 and G-OMS-2 with the same structure,the H-OMS-2 catalyst synthesized by hydrothermal method has smaller grain size,larger specific surface area,more Mn³⁺and abundant oxygen vacancies,which are conducive to the improvement of catalytic decomposition activity of ozone.（2）H-OMS-2 catalyst was doped with different transition metals（Co,Cu,Zn,Ti,）by hydrothermal synthesis method.The material characterization results showed that compared with Co,Zn and Ti,Cu doping reduced the grain size,increased the specific surface area,and increased the content of Mn³⁺and oxygen adsorbed on the surface,which were conducive to the adsorption and decomposition of ozone.Therefore,the catalyst showed the best ozone catalytic decomposition activity.Subsequent optimization of the preparation conditions of the Cu-OMS-2 catalyst shows that the increase in Cu doping will promote the formation of the Cu_1.5Mn_1.5O₄spinel phase,which can increase the content of Mn³⁺in the catalyst,but the excess Cu_1.5Mn_1.5O₄spinel phase will lead to the destruction of the OMS-2zeolite structure,which is not conducive to ozone decomposition.In addition,high-temperature calcination led to an increase in the crystallinity of the Cu-OMS-2 catalyst and even a change in the crystal structure,which was not conducive to the improvement of the ozone decomposition activity of the Cu-OMS-2 catalyst.（3）Cu-OMS-2/diatomite composite catalyst was prepared by hydrothermal method.A series of x Cu-OMS-2/diatomite composite catalyst with different Mn/diatomite ratio was obtained by changing the addition amount of diatomite,and the ozone decomposition performance of the synthesized composite catalyst was tested.The results show that the catalytic activity of Cu-OMS-2/diatomite composite catalyst for ozone decomposition is significantly better than that of Cu-OMS-2,and when the Mn content is 20%,the best ozone decomposition activity of 0.2Cu-OMS-2/diatomite composite catalyst is 76.5%.The catalyst characterization results also showed that the addition of diatomite did not change the octahedral structure of Cu-OMS-2 catalyst,and the abundant pore structure of diatomite was conducive to the adsorption and aggregation of ozone molecules and also provided attachment points for the active center Cu-OMS-2,thus promoting the catalytic decomposition of ozone.