| With the increasing emission of nitrogen oxides?NOx?,air pollution is becoming more serious,and the state has achieved stricter control over NOx emission standards.Selective catalyst reduction with NH3?NH3-SCR?is the widely used and effective technique for controlling NOx emission,and the catalyst is the key part of it.At present,V2O5-WO3?MoO3?/TiO2 is the most widely used catalyst.However,its activity temperature window is higher and narrower,which can't meet the NOx removal needs of flue gas at low temperature,and the price of is expensive.Therefore,the study of green,high efficiency and new low-temperature SCR catalysts has been a hot spot for scholars at home and abroad.In this paper,catalysts from different kinds of natural manganese ore raw materials were prepared and their low temperature denitration activity was studied.The effects of preparation and working conditions on the low temperature denitration performance of natural manganese ore catalysts were explored.Basis on this,the resistant performance to alkali metal,heavy metal,sulfur and water of superior manganese-iron ore catalyst was studied.Finally,the Mn-Fe-Al catalysts for simulating natural ore catalyst were prepared to explore the main active element and ratio of natural manganese iron ore catalyst which showed superior low temperature denitration performance.The relationship between low temperature denitrification performance of the catalyst and its physical and chemical properties was analyzed by XRF,XRD,N2-adsorption desorption,XPS,H2-TPR,NH3-TPD,SEM,TG and other characterization methods were used.The main results are as follows:?1?The calcination temperature and type of natural manganese ore have great influence on the denitrification performance.The natural manganese ore with the number of ore 2 calcinated at 450°C for 5 h can obtain the optimal low-temperature denitration performance.At 120°C,its denitration efficiency was 94%,and in the temperature range of 160-240°C,the denitration efficiency always maintained about98%.?2?Working conditions have certain influence on the low temperature denitration performance of ore 2 catalyst,such as inlet NO concentration,O2 concentration,NH3/NO ratio,airspeed ratio.The denitration efficiency decreased with the increasing of inlet NO concentration,especially that the concentration of imported NO reaches1200 ppm,the downward trend was more obviously.The increasing of O2concentration or NH3/NO ratio,the denitration efficiency increased,while the denitration efficiency decreased with the increased space velocity.?3?It can be seen from the transient and adsorption studies of ore 2 catalyst that oxygen has a great promoting on SCR,which is an important source of oxygen in the whole reaction.The ore 2 catalyst shows certain adsorption capacity for gaseous NH3and NOx as will.It is speculated that the SCR denitration process of ore 2 catalyst may follow the Langmuir-Hinshelwood?L-H?and Eley-Rideal?E-R?mechanisms simultaneously.?4?The low-temperature denitration performance of natural ferromanganese ore are affected by various physical and chemical properties.The main components of the ore2 catalyst with the highest denitrification activity are Mn,Fe,Al and Si,and the proportion of each element is Mn:Fe:Al:Si=1.51:1.26:0.34:1.The H2Si6O13compound in the ore 2 is oxidized and decomposed into SiO2 after calcination,and Al3Fe5O12 is produced at the same time,and the dispersibility is optimal.Among the ore catalysts,Mn4+/Mn3+,Fe3+/Fe2+and O?/(O??10?O??10??10??46??)have higher proportions,and have stronger reduction properties,more acid sites and more The dispersed active material has a good denitration activity.?5?The ore 2 catalyst shows superior low temperature alkali metal?K and Na?and heavy metal?Zn and Pb?properties.Adding 0.3%and 0.5%K or Na to the low temperature of the ore 2?fresh?catalyst,the denitrification performance has little effect.The denitrification efficiency of the catalyst after K poisoning is stable at about93%at 140-220°C.When 0.3%or 0.5%Na were added to the fresh catalyst,the denitration efficiencies were reduced by about 1-2%and 4-6%,respectively.The characterization of fresh,0.3K/fresh and 0.5K/fresh catalysts by means of N2-adsorption desorption,XPS,H2-TPR and NH3-TPD showed that the superior alkali metal K performance mainly derived from two aspects.The synergy which on the one hand,the content of K in the fresh catalyst is as high as 0.83%,and the catalyst after the alkali metal K poisoning contains more acid sites than the fresh catalyst;on the other hand,after alkali metal K poisoning,0.3K/fresh and 0.5K/fresh.The specific surface area of the fresh catalyst,the concentration of Mn4+,Fe3+,O?,and the reducing property are all reduced.The combined results of these promoting and inhibiting effects make the ore catalyst exhibit better alkali metal K resistance.?6?The presence of H2O and SO2 will affect the denitration performance of the ore2 catalyst.Containing 5%vol H2O,the denitration efficiency of the ore 2 catalyst at180°C will be reduced to about 89%;Containing 100 ppm SO2,the denitration efficiency of the ore 2 catalyst will be reduced to 65%.Especially for 5%vol H2O and100 ppm SO2 coexisting,the ore 2 catalyst is most poisoned,and the denitrification efficiency is only 54.6%.However,H2O is non-permanently deactivated to the ore 2catalyst,and the deactivation of the ore 2 catalyst by SO2 is permanently inactivated.The results of thermogravimetric and N2-adsorption desorption show that the main reason for the catalyst deactivation is the formation of ammonium sulfate and ammonium hydrogen sulfate on the surface,which reduces the specific surface from51.6 m2·g-1 to 33.4 m2·g-1,blocks the active site,and reduces the activation of the reaction gas.SEM-Mapping results show that the surface oxide of the ore 2 catalyst is sulfated,especially oxides such as Fe and Al,which is a permanent loss.?7?Adding additives Sn,Sm and Zr to optimize the sulfur and water resistance of ore 2 found that the sulfur resistance of ore 2 catalyst could not be improved,but the addition of additives Sm and Zr can significantly improve the water resistance of ore2.?8?The Mn-Fe-Al series catalysts were prepared by water bath magnetic stirring method.The denitration activities of the two-component catalyst?binary catalyst?and the three-way catalyst were significantly better than those of the single-component catalyst?one-way catalyst?.It is a strong synergistic effect between the active components,which can greatly improve the catalytic activity of the catalyst.The presence of the active component MnOx can greatly improve the low-temperature denitration performance of the catalyst.Especially,the low-temperature denitration performance of the catalyst is particularly improved when the two components of MnOx and FeOx coexists. |
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