Study On The Performance Of Carbon-supported Multi-metallic Catalysts For The Combined Removal Of Benzene Series In The Denitration Zone

Nitrogen oxides（NO_x）and volatile organic compounds（VOC_S）have become the main pollutants in the current atmospheric environment,which have a great impact on human health and ecological environment.It is urgent to develop and put into use the purification technology with high efficiency,stable operation and low cost,which is also one of the urgent problems to be solved in the thermal power plant industry.In July 2017,the Ministry of Environmental Protection reviewed and approved the"13th five-year plan"for the prevention and control of VOC pollution,put forward the overall requirements and objectives of VOC pollution prevention and control during the"13th five-year plan"-by the end of 2020,the total VOC_Semissions will be reduced by more than 10%,and pointed out the governance idea of"strengthening the collaborative emission reduction of VOC and NO_x".At present,selective catalytic reduction（SCR）denitration is one of the mainstream technologies for NO_x treatment.The core of SCR system is catalyst.It is important to prepare high-efficient low-temperature denitration catalyst with certain water and sulfur resistance,and realize the joint removal of NO_x and VOC_Son this basis.In this study,coconut shell activated carbon was used as the support,and Fe,Mn and Ce were loaded on the surface of the support by ultrasonic-assisted equal volume impregnation method,and catalysts with different metal components were prepared.In the NH₃-SCR reaction system,the denitration performance of the catalyst was evaluated in the temperature window of 60～220℃,and two kinds of catalysts with better catalytic activity,Fe Mn₂-AC and Fe_0.1Mn Ce₁-AC,were obtained.On this basis,the effects of preparation conditions and operating conditions on the activity of the catalyst were investigated.Finally,when the metal loading was determined to be 5 wt.%,the calcination temperature was 550℃,the gas space velocity was 20000 ml·g^-1·h^-1,the oxygen concentration was 6%,and the total flue gas flow rate was 500 ml/min,the above two catalysts showed excellent denitration activity.Based on the actual flue gas environment containing a certain amount of H₂O and SO₂,the water and sulfur resistance of Fe Mn₂-AC and Fe_0.1Mn Ce₁-AC catalysts were subsequently investigated.The mechanism of H₂O and SO₂poisoning was analyzed by BET,SEM,XRD,XPS,H₂-TPR,NH₃-TPD,FTIR and TGA.The results showed that when the reaction temperature was 120℃and 180℃,and 150 ppm（429 mg/Nm³）SO₂or 5%and 10%H₂O participated in the reaction,the water and sulfur resistance of Fe_0.1Mn Ce₁-AC was better than that of Fe Mn₂-AC,and the（NH₄）₂SO₄,metal sulfate and surface hydroxyl（-OH）formed on the catalyst surface were one of the important reasons for catalyst poisoning.On the basis of the above study,the combined removal effect of Fe Mn₂-AC and Fe_0.1Mn Ce₁-AC catalysts on VOC_Sin the denitration zone was tested,and the effect of VOC_Son the denitration process of NH₃-SCR was investigated.Taking 50 ppm of benzene（174mg/Nm³）,toluene（206 mg/Nm³）and chlorobenzene（251 mg/Nm³）as the target pollutants,it was found that Fe_0.1Mn Ce₁-AC was more active when it was used to catalyze the same pollutant.Moreover,toluene is more easily decomposed than benzene,and chlorobenzene has the lowest catalytic decomposition efficiency.In addition,the presence of VOC_Scould inhibit the denitration activity of NH₃-SCR,and the presence of NO_x can also inhibit the catalytic oxidation of benzene and toluene,but NO_x has a positive effect on the catalytic reaction of chlorobenzene.SEM,NH₃-TPD and H₂-TPR were used to explain the reason why VOC_Sinhibited the denitration reaction.The results showed that there was competitive adsorption between VOC_Sand NH₃,and part of acid sites were destroyed during the catalytic reaction,resulting in the decrease of catalyst activity.At last,the stability of Fe Mn₂-AC and Fe_0.1Mn Ce₁-AC catalysts was tested.There was no obvious deactivation within 600 min,showing good catalytic activity and stability.