| Coal is the main source of energy in China,while coal-fired power plants are considered to be the main anthropogenic source of air pollutants.The emissions of nitrogen oxide(NO)and elemental mercury(Hg0)have adverse impact on the environment and human health.Therefore,how to effectively control the emissions of NO and Hg0 of coal-fired flue gas has become a hot issue in current research.At present,selective catalytic reduction(SCR)technology has been extensively applied to reduce NO emission from coal-fired power plants.Meanwhile,it has the co-benefit of promoting Hg0 oxidation during NO reduction process.Nevertheless,the Hg0 oxidation capacity of SCR catalysts vastly depends on the chlorine content in coal.In addition,the existing control units for NO and Hg0 removal are run on independent equipments,which not only leads to cumbersome process,large footprint,but also makes high investment and operation costs.Therefore,it is of great practical significance to realize the simultaneous removal of multiple pollutants from coal-fired flue gas.In view of this,this paper proposes to adopt selective catalytic oxidation technology(SCO)for the simultaneous removal of NO and Hg0.Cu-Fe binary oxides(CFs)are synthesized using sol-gel method,and then modified by non-thermal plasma treatment(NTP)to improve its catalytic oxidation activity.The physicochemical properties of CF samples before and after NTP modification are analyzed by many characterization methods,mainly including specific surface area(BET),scanning electron microscopy(SEM),X-ray diffraction(XRD),H2-programmed temperature reduction(H2-TPR),and X-ray photoelectron spectroscopy(XPS).The results exhibit that the BET surface area,pore volume,average pore diameter,and surface morphology of CF samples are not obviously changed after non-thermal plasma treatment.XPS results indicate that the contents of Fe3+,Cu2+,and lattice oxygen(O1)on the surface of CF samples are largely increased after NTP treatment.The experiments of NO removal over raw and modified CF samples are carried out in a fixed-bed system.The results indicate that NTP treatment can markedly enhance the NO removal performance of CF samples.And longer discharge time(0-30 min)and higher oxygen content(N2、50%N2+50%O2、O2)is beneficial for NO removal.The NO removal efficiency is decreased with the enhancement of discharge power(32-96 VA).The optimal reaction temperature of CF samples for NO removal is 300℃,which is extremely closed to the active temperature window of commercial SCR catalysts.To interpret the mechanism of NO removal over CF samples,XPS analysis is conducted to identify the valence state changes of O,Fe,and Cu for the fresh and spent samples(after NO removal).It is concluded that O2 is of great significance during NO removal process,which can further oxidize Fe2+and Cu+into Fe3+and Cu2+,respectively.Finally,the Hg0 removal performance of CF samples are explored.The results show that the Hg0 removal efficiency of the modified CF samples is obviously improved.The behavior of Hg0 adsorption/oxidation,mercury temperature programmed desorption(Hg-TPD)and XPS method are applied to analyze the mechanism of Hg0 removal.The results manifest that the contents of Fe3+,Cu2+,and lattice oxygen in all modified CF samples are largely improved,which can serve as active sites for Hg0 removal.The Hg0 catalytic oxidation dominated the Hg0 removal process because Hg0 adsorption equilibrium is achieved in a short time.The simultaneous removal performance of NO and Hg0 over CF samples is further investigated.The results indicate that the optimal reaction temperature of CF samples for the simultaneous removal of NO and Hg0 is 300℃.NO facilitates Hg0 removal,but Hg0 has a slight inhibitory influence on NO removal.O2 facilitates Hg0 and NO removal.H2O has adverse effect on Hg0 and NO removal.To some extent,the CF samples show better resistant to sulfur poisoning because of the presence of Fe species. |
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