Research On Preparation And Properties Of Modified Dolomite-palygorskite Clay Supported Catalysts For Low Temperature NH₃-SCR

Selective catalytic reduction?SCR?technique is currently the most widely used technology for flue gas denitration in coal-fired power plants.The key is catalyst.Development of low-temperature SCR catalyst,associated with low cost,high efficiency,environmental-friendliness and good prospects in industrial application,has become a hot topic in this field.In this paper,Mn-based catalysts loaded on modified Dolomite-palygorskite clay?DPC?were successfully prepared and their catalytic performances for selective catalytic reduction of NO_x by NH₃?NH₃-SCR?at low temperature were investigated.In this paper,DPC was firstly modified by using different approaches such as acid treatment and thermal treatment,then utilized as support to prepare Mn-based catalysts.Their catalytic performances were studied and compared with that of catalyst supported on raw DPC.The results showed that catalyst supported on thermally modified DPC?MnO_x/M-DPC?demonstrated better activity than those supported on acid modified DPC and raw DPC,which yielded about less than 40%and 20%NO conversion at 120?,respectively,while the NO conversion of the former increased to 55%at this temperature.Obviously,thermally modified DPC was more suitable to be employed as catalyst carrier in the SCR process at low temperature,especially the DPC heat-treated at 300?for 1h.Based on the previous study,MnO_x/M-DPC catalyst was further investigated from the aspects of preparation method,loading,calcination temperature etc.It was found that its activity was affected by the above preparation parameters.Among them,the precipitated sample,loaded with 10%manganese oxide and calcinated at 400??MnO_x/M-DPC-PM?,showed the highest NO conversion,and yielded about 83%NO conversion at 120?,and nearly 100%NO conversion in the temperature range of180?-300?.Combined with the results of surface area,pore size distribution,XRD,SEM-EDS as well as XPS,it was found that MnO_x/M-DPC-PM catalyst had larger surface area?52.90m²/g?and pore volume?0.170cm³/g?.Irregular multi-modal mesoporous structure would provide more acitive sites.What's more,good dispersion of manganese oxide,higher concentration of Mn as well as higher surface Mn⁴⁺species,high lattice oxygen content on the surface were beneficial to its superior catalytic efficiency.In addition,effect of metals addition?Zr,Fe,Ce and Cu?on the MnO_x/M-DPC-PM catalyst for low-temperature SCR of NO_x with NH₃ was also investigated.The results revealed that the effect of metals addition on catalyst's activity was related both to manganese loading and doping amount.After Fe addition,the activity of MnO_x/M-DPC-PM catalyst with 8%manganese decreased greatly,while the activity of that with 10%manganese increased.And the addition of Cu was just the opposite,only addition of Zr and Ce could improve the activity of MnO_x/M-DPC-PM catalyst.Furthermore,when the manganese loading was the same?8%?,the ratio of doping element to Mn had effects on the catalytic performance of catalyst.Fe,Ce,Zr doping?molar ratio of Fe,Ce,Zr to manganese was 0.1-0.3?was effective to improve the catalytic activity of MnO_x/M-DPC-PM catalyst,by using which 95%NO_x could be converted at 120?,while overdoping?molar ratio of Fe,Ce,Zr to manganese was 0.4?had adverse effects.As for Cu addition,Cu doping in small quantity?molar ratio of Cu to Mn was 0.1?could promote the activity of MnO_x/M-DPC-PM catalyst,otherwise it would have a negative impact on the catalytic performance of MnO_x/M-DPC-PM catalyst.Obviously,proper amount of metal doping could contribute to the improved activity of MnO_x/M-DPC-PM catalyst.The characterization results revealed that catalyst with metal doping had different physical and chemical properties;manganese oxide would be better dispersed in the catalyst,the interaction between active components and the carrier increased.Even Fe₂O₃ or CuMn₂O₄ was formed.What'more,metal addition had impacts on the morphology of the catalyst.Particles were more uniform and well dispersed on the catalyst surface.Thereby,the catalytic performance of MnO_x/M-DPC-PM was improved by metal doping.In the end,water-resistance and sulfur-resistance performances of the MnO_x/M-DPC-PMcatalystwasstudied.Besides,the influences of reaction temperature,space velocity,ammonia-nitrogen ratio and O₂ concentration were also researched.Based on the steady-state kinetic studies and corresponding experiment data,the reaction activation energy over MnO_x/M-DPC-PM was determined.