Red mud(RM),as an alkaline waste,was recently proved to be a promising substitute for the SCR catalyst.Dealkalization could improve the acidity and reducibility of red mud,which were critical for SCR reaction.However,the dealkalization effect depended on the reaction between acid solution and red mud.In this study,we realized the directional control of the chemical state of active sites through tuning the acid pretreatment(dealkalization)process.The pretreatment endpoint was controlled at pH values of 3-5 with diluted nitric acid.When the pH values of red mud were 3 and 5(CRM-3 and CRM-5),activated catalysts showed NOx conversion above 90％at 275℃-475℃.The high initial reaction rate,Ce3+/(Ce3++Ce4+)ratio,and surface acidity accounted for the excellent SCR performance of CRM-5 catalyst.Meanwhile,more Fe3+on the CRM-3 surface improved the NH3 adsorption.There was a strong interaction between Al and Fe in both CRM-5 and CRM-3 catalysts.DFT results showed that the adsorption capacity of the Al-O3-Fe for NH3 and NO is stronger than that of Fe-O3-Fe,which enhanced the NOx conversion of the catalyst.However,the almandine was formed in CRM-4,consumed part of Fe3+and Al3+,and the interaction between Al and Fe was weakened.Also,deposited almandine on the catalyst surface covered the active sites,thus leading to lower NH3-SCR activity.

Xiang Zhang;Yue Xuan;Bin Wang;Chuan Gao;Shengli Niu;Gaiju Zhao;Dong Wang;Junhua Li;Chunmei Lu;John C.Crittenden

National Engineering Laboratory for Coal-Burning Pollutants Emission Reduction,School of Energy and Power Engineering,Shandong University,Jinan 250061,China;Energy Institute,Qilu University of Technology(Shandong Academy of Sciences),Jinan 250013,China;School of Civil and Environmental Engineering and the Brook Byers Institute for Sustainable Systems,Georgia Institute of Technology,Atlanta,GA 30332,USA;State Key Joint Laboratory of Environment Simulation and Pollution Control,National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment,School of Environment,Tsinghua University,Beijing 100084,China

环境科学与工程前沿

[1]Xiang Zhang;Yue Xuan;Bin Wang;Chuan Gao;Shengli Niu;Gaiju Zhao;Dong Wang;Junhua Li;Chunmei Lu;John C.Crittenden-.Precise regulation of acid pretreatment for red mud SCR catalyst:Targeting on optimizing the acidity and reducibility)[J].环境科学与工程前沿,2022(07):58-68

Dealkalization,dealkalization,Ce3++Ce4+,Fe3+on

Precise,regulation,pretreatment,mud,SCR,Targeting,optimizing,acidity,reducibility,Red,alkaline,waste,recently,promising,substitute,could,which,were,critical,reaction,However,effect,depended,between,solution,In,this,study,realized,directional,chemical,state,active,sites,through,tuning,process,endpoint,controlled,values,diluted,nitric,When,CRM,activated,catalysts,showed,NOx,conversion,above,high,initial,rate,ratio,surface,accounted,excellent,performance,Meanwhile,more,improved,NH3,adsorption,There,interaction,both,DFT,results,that,capacity,O3,stronger,than,enhanced,almandine,formed,consumed,part,Fe3+and,Al3+,weakened,Also,deposited,covered,thus,leading,lower,activity

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