Investigation On ZSM-5 Zeolite Loading Fe,Ce For NO Removal By CO From Flue Gas

With the rapid development of science and industrial technology,the problem of environmental pollution has been paid more and more attention.Among them,nitrogen oxide is one of the main harmful air pollutants,which can cause environmental hazards.Such as ozone decomposition,acid rain and photochemical smog.It is urgent for us to take effective measures to control them.In the NO,emission control technology,using CO as the reducing agent in the catalytic reaction to eliminate NOx is an effective method.The rare-earth-modified ZSM-5 zeolite catalyst is widely used in petrochemical industry and automobile exhaust treatment.Therefore,the research on loading rare earth zeolite catalysts in flue gas denitrification has attracted the attention of researchers.ZSM-5 zeolite was synthesized by seed crystal method in a hydrothermal system with main raw materials of silica sol and sodium aluminate.Fe-ZSM-5 and CeFe-ZSM-5 catalysts were prepared by impregnation of transition metal Fe and rare earth Ce,which was used for the NO removal by CO.The effects of reaction temperature,active ingredient content,space velocity and CO/NO concentration ratio on denitration efficiency were examined.The resistance of catalysts to O2 and SO2 was initially reseached and the feasibility of simultaneous denitrification and desulfurization were also investigated.It was found from denitrification experiments that 10%Fe-ZSM-5 catalyst had better NO conversion more than 90%at 350? with 36000h-1 space velocity,600 ppm NO and CO.But performance of resistance to O2 and SO2 was deficient.The required temperature of 90%NO conversion of modified 10%CeFe-ZSM-5 had dropped nearly 40? contrasted with 10%Fe-ZSM-5,and the range of denitration temperature was more wide.Because of the oxygen storage capacity and the inhibition of SO2 adsorption of CeO2,the performance of anti-O2 and SO2 had been significantly improved.The catalysts were characterized by XRD,SEM,BET,FT-IR,NH3-TPD,XPS and CO-TPR to analyse the structure of catalyst and mechanism of catalysis reaction.XRD,FT-IR and SEM analysis indicated that the ZSM-5 molecular sieves had the MFI structure before and after the loading,and metallic oxides were adhered to the surface of zeolites.The nitrogen adsorption-desorption isotherm showed that the ZSM-5 zeolites had mesoporous structure,and BET specific surface area was 341.491m2/g.The specific surface area and pore volume decreased as the increase of active component content.The results of NH3-TPD stated that the addition of active metal reduced the total acid amount and the weak acid distribution,but it had little effect on the activity of the catalyst indicating that the denitration reaction did not belong to the acid-base catalysis type.The analysis of XPS demonsrated that the lattice oxygen was the main active component.So it was deduced that the denitration reaction was a type of redox catalysis.Besides there was an interaction between Ce and Fe,which made the catalyst showed stronger reducing capacity in CO-TPR and enhanced the stability of catalyst.