Preparation And Performance Evaluation Of Iron-Manganese Based Catalysts Modified For Catalytic Oxidation Of Toluene

Volatile organic compounds（VOCs）are not only irritating and toxic,but also easily interact with other air pollutants to form secondary aerosols and ozone,causing problems such as haze,photochemical smog,and ozone layer destruction,causing serious damage to human health and the environment.Among many VOCs treatment methods,catalytic oxidation has been widely used because of its advantages of high safety,low conversion temperature and high treatment efficiency.Among them,catalysts are the key to restrict the efficient conversion of VOCs,and Fe-Mn-based catalyst has attracted great attention because of its excellent valence change and oxidation ability.As a new technology,microwave heating has the advantages of fast startup,uniform heating,and low energy consumption,it has a broad market prospect to apply it to catalytic oxidation for performance improvement.In this paper,toluene,which is classic and difficult to degrade,was selected as the target pollutant to carry out research,and Fe-Mn-based oxides were modified and prepared by the thermal reflux-co-precipitation method and the microwave-assisted synthesis method.BET,XRD,SEM,TEM,XPS and other characterization methods were used to analyze the catalyst morphology,surface element morphology,etc.Furthermore,the study explored the influence of different process parameters such as Fe/Mn ratio,toluene concentration,space velocity ratio,and microwave conditions on the catalytic performance of toluene.In this paper,Fe_xMn_y/Al₂O₃ catalysts with different Fe/Mn ratios were modified and prepared by heat reflux-co-precipitation method.The results showed that the strong interaction between Fe and Mn metals improved the catalyst surface Fe³⁺,Mn⁴⁺,lattice oxygen content and redox performance.In the evaluation of catalytic activity,when the concentration of toluene is 500ppm and the weight hourly space velocity is 40000ml/g·h,Fe₁Mn₂/Al₂O₃ exhibits the best catalytic activity(T₉₀=260^oC),and the continuous test at280^oC in an atmosphere of alternating dry and wet gas for 60h shows the best catalytic activity,it can maintain a conversion rate of nearly 98%.The lowest apparent activation energy of Fe₁Mn₂/Al₂O₃ catalyst is 33.91k J/mol calculated by reaction kinetics.In order to further improve the low-temperature catalytic performance of Fe-Mn-based catalysts,Fe/Mn=2:1 was selected,and the Fe₂Mn₁-MW catalyst was prepared by microwave-assisted modification.At the same time,it was compared with the Fe₂Mn₁catalyst without microwave assistance.It was found that microwave-assisted synthesis can increase the oxygen vacancy concentration and surface active site of catalyst,and improve the low temperature reduction performance.At the same time,Fe₂Mn₁-MW catalyst T₉₀ decreased by 23^oC compared with Fe₂Mn₁ catalyst,and the conversion rate was nearly 95%after continuous test at 230^oC alternating dry and wet atmosphere for 60h.Finally,the influence of process parameters such as microwave temperature,power,time and molar ratio on the catalytic performance of toluene in the microwave-assisted synthesis method were explored.The study found that when the microwave parameters were 50^oC,500W and 60min,it had the best catalytic activity.When the toluene concentration was 500ppm,and the weight hourly space velocity was 40000ml/g·h,the Fe₂Mn₁-MW catalyst had the best catalytic activity(T₉₀=216^oC).The lowest apparent activation energy of Fe₂Mn₁-MW catalyst is 29.81k J/mol,which further indicates that the catalyst has the best catalytic performance and has high application value.