The Study Of Catalytic Ozonation Of Ammonia In Water Over Magnesium-based Catalysts

Ammonia nitrogen is one of the most important pollutants discharged into natural water bodies,which is easily oxidized by microorganisms to nitrate nitrogen and nitrite nitrogen,making the surface water eutrophic,eventually leading to acute poisoning of fish and threatening human health.Therefore,the conversion of ammonia nitrogen into gaseous nitrogen to reduce total nitrogen(TN)in water has attracted widespread attention.Metal oxide catalysts show good catalytic oxidation performance for the removal of ammonia nitrogen pollutants in water,but the reaction product nitrate nitrogen remains in water and is not discharged into the atmosphere as gaseous nitrogen.Moreover,most of the catalysts require more stringent reaction conditions,such as high temperature,high pressure,and long reaction time.Therefore,it is urgent to develop some heterogeneous catalysts with mild reaction conditions to meet the requirements of low cost.As one of the advanced oxidation methods,the removal of ammonia nitrogen in water by multiphase ozonation has gradually attracted people’s attention due to its mild reaction conditions and high practicability.Mg O has been widely used in the process of ozonation of ammonia nitrogen pollutants in water due to its high activity.In this paper,a heterogeneous catalytic ozonation system was established.Starting with the preparation of catalysts,different supported catalysts were synthesized by various methods to obtain magnesium-based catalysts suitable for ozonation of ammonia nitrogen pollutants in water under mild conditions.Different carriers and active components have been used successively to improve the catalytic activity of the catalyst in the ozone catalytic oxidation of ammonia nitrogen pollutants in water and its selectivity for gaseous nitrogen.The physical and chemical properties of the catalyst,such as its structure and morphology,were studied in detail through various characterization methods,and were related to the catalytic performance.The reaction mechanism of catalytic ozonation with ammonia nitrogen pollutants in water was discussed.The main research contents and results are as follows:1.A supported iron oxide catalyst was prepared by selecting Mg O-P prepared by precipitation method as the carrier.The catalytic performance of Fe Ox/Mg O-P for catalytic ozonation of ammonia nitrogen pollutants in water was investigated by loading active species Fe on the support.When measuring the nitrate nitrogen of the reaction product,it was found that the catalyst had nitrate dissolution.Four solutions were proposed to solve the problem of nitrate dissolution of the catalyst.When the carrier was commercial magnesium oxide,the 3 wt% Fe Ox/Mg O prepared did not have nitrate nitrogen dissolution during the reaction.In the follow-up work,commercial magnesium oxide was used as the carrier to eliminate the influence of catalyst on the determination of nitrate nitrogen concentration in the process of ammonia nitrogen catalytic oxidation.2.On the basis of the above work,commercial magnesium oxide was used as the carrier,and the related oxides of transition metal oxides such as iron,cobalt,nickel,manganese and copper were used as the active components to investigate the catalytic performance of the bicomponent catalysts and the effect of the loading amount of the active components on the catalytic performance.The results showed that the catalytic performance of 3 wt% Fe Ox/Mg O was the best.When ozone was introduced for 30 min,the ammonia nitrogen removal rate exceeded 99%,and the selectivity for gaseous nitrogen reached 54%.Through XRD structure characterization and free radical quenching experiment,3 wt% Fe Ox/Mg O was selected to explore the mechanism of ozone catalytic oxidation to remove ammonia nitrogen pollutants in water.It was found that hydroxylation occurred on the surface of Mg O during the reaction process.The reaction mechanism of 3 wt% Fe Ox/Mg O used in catalytic ozonation to remove ammonia nitrogen pollutants in water was hydroxyl free radical mechanism.3.The three-component supported catalyst Mg O-Fe Ox/Si O2 was prepared by impregnation method.By changing the loading amount and impregnation order of magnesium and iron species,the catalytic performance of the catalyst on the catalytic ozonation of ammonia nitrogen pollutants in water by Mg O-Fe Ox/Si O2 was explored.The structure and morphology of Mg O-Fe Ox/Si O2 were systematically studied by a series of statistical tests,and the reaction mechanism was explored by radical scavenging experiments.Through the free radical scavenging experiment,it was found that the hydroxyl radical mechanism was dominant in the process of 10 wt%Mg O-3 wt% Fe Ox/Si O2 catalytic ozonation to remove ammonia nitrogen in water.The reaction of Mg O and H2 O generates Mg2+ and OH-,and ozone oxidizes OH-to produce ?OH,via and the reaction of ?OH,ammonia nitrogen is oxidized to NO3-,NO2-,N2 and N2 O.