Preparation And CO-SCR Properties Of Fe Based Composite Oxides With Different Structures

In this paper,the preparation,performance test,active window and morphology of Fe based composite oxide catalysts for CO selective catalytic reduction of NO were studied.Through various characterization methods,the relationship between physical and chemical properties and structure of the catalyst was discussed,and the possible factors affecting the catalyst were analyzed.Finally,the possible active sites and reaction mechanism of the catalyst reaction process were deduced.The smooth spherical FexMnyO catalyst with different Fe content was prepared by solvent thermal method of ethylene glycol,and the CO-SCR activity of the catalyst was tested to deeply explore the influence of metal Fe doping amount on the activity of manganese based catalyst.It was found that the addition of Fe species resulted in a strong synergistic symbiosis between the two-phase composite oxides.With the optimized Fe0.3Mn0.7O catalyst at 300℃,the NO conversion rate and the N2 selectivity could reach 100%and 97.5%respectively.The experimental results showed that the doping of FeOx could promote the reaction of Fe²⁺+Mn4+→Fe3++Mn3+,which was beneficial to the generation of oxygen cavitation and reactive oxygen species.Moreover,the unique smooth spherical morphology of MnOx has a large specific surface area,which fully provides the exposure opportunity for the active species FeOx and improves the catalytic activity of the catalyst.In addition,according to the results of in-situ DRIFTS experiments,we proposed a reasonable CO-SCR model reaction mechanism.A series of Co₃O₄/CuFe₂O₄ catalysts with different CO contents were prepared by solvothermal method and ultrasonic impregnation method.The selective reduction of NO（CO-SCR）by CO at low temperature was evaluated,and the structure-activity relationship was studied.The effect of cobalt oxide on the performance of CuFe2O4 catalyst was studied by N2 adsorption/desorption,SEM and in-situ DRIFTS.The results show that the appropriate amount of Co3+can enhance the interaction with copper and iron,form a high proportion of active ions(Cu²⁺and Fe3+)and rich surface oxygen defects,which is conducive to the formation of Cux+-Coy+-Fez+（x=1 or 2,y=2 or 3,z=2 or 3）species.Promoting reaction Cu²⁺+Co²⁺（?）Cu++Co3+,Fe3++Co²⁺（?）Fe²⁺+Co3+is carried out on the Cux+-□-Coy+-□-Fez+node（□ represents the surface synergistic oxygen vacancy）,which promotes the dissociation of NO and the transfer of O₂.The NO conversion rate of the catalyst reaches 100%at 250℃.This indicates that the CuFe2O4 catalyst supported with cobalt can improve the activity of CO and NO reaction.In addition,the possible active sites and catalytic mechanism of Co₃O₄/CuFe₂O₄ catalyst were discussed.The spherical LaCu_0.5Fe_0.5O₃ and La0.8Ce_0.1Cu_0.5Fe_0.5O₃ catalysts are synthesized by solvothermal method,and the Cu in the two is exsolved in situ by the H₂-temperature programmed reduction,thereby preparing two corresponding reduction catalysts(R-LaCu_0.5Fe_0.5O₃ and R-La0.8Ce_0.1Cu_0.5Fe_0.5O₃)and used for selective catalytic reduction of NO with CO（CO-SCR）.The results show that the balance of Ce3++Cu²⁺（?）Cu++Ce4+between Ce and Cu promotes the exsolution of Cu in the Ce-doped La0.8Ce_0.1Cu_0.5Fe_0.5O₃ catalyst more obviously,and the surface Cu of the reduced catalyst is not only more reactive,but also can inhibit the generation of surface carbonate,which will occupy the active sites on the catalyst surface.At the same time,compared with the unreduced catalyst,the reduced catalyst also has more surface adsorbed oxygen species,which is conducive to the production of more NOx species,and the surface Cu can promote the dissociation and desorption of NOx species,resulting in excellent low temperature catalytic performance.In order to better study the CO-SCR reaction in depth,we combine the characterizations of in-situ DRIFTS and quasi-in-situ XPS,to get a possible reaction mechanism.