Preparation Of Multiphase Coexisting Copper-iron Based Composite Oxides And Study On The Propertiess Of DeNO_x

In this paper,the preparation,catalytic performance,activity window,thermal stability,physicochemical properties,structure,etc.of modified Cu,Fe-based composite oxide wide-window catalysts for catalytic reduction of NO by CO were studied.Based on the above discussion,X-ray diffraction?XRD?,N2 adsorption-desorption?N2-physisorption?,High resolution transmission Electron microscope?HR-TEM?,SEM-Mapping,Temperature-programmed reduction?H2-TPR?,In situ Infrared adsorption?In situ DRIFTS?,X-ray photoelectron spectroscopy?XPS?,In situ XRD,In situ XPS and other characterization methods were used to study the relationship between the catalytic properties of the catalyst and its structure,composition and properties.A series of Mn modified CuFeO_x catalysts were prepared by simple solid phase method,and their catalytic properties from low temperature to high temperature were studied.For a series of samples with different molar ratios?{KMn8O16}/{CuFe₂O₄}?,the results show that three phases of ?-Fe₂O₃,CuFe₂O₄ and CuO,which have strong synergistic interaction,co-exist in this catalyst system,and different phases play a leading role in different temperature ranges.Mn species are highly dispersed in the three-phase coexisting system in the form of Mn2+,Mn3+,and Mn4+.Due to the strong interaction between Mn2+and Fe species,a small amount of Cu2+ precipitates from CuFe₂O₄ and grows along CuO?110?plane which has better catalytic performance.Mn3+ can inhibit the conversion of ?-Fe₂O₃ to ?-Fe₂O₃ at high temperature and then increases the high temperature activity.The synergistic effect between Mn4+ and the surfaces of three phases generates active species Cue+-O-Mn4+ and Mn4+-O-Fe3+,which can be more easily reduced to some synergistic oxygen vacancies during the reaction.Furthermore,the formed synergistic oxygen vacancies can promote the dissociation of NO and are also propitious to the transfer of oxygen species.All of these factors make the appropriate manganese modified three-phase coexisting system have better catalytic activity than manganese-free catalyst,making NO conversion rate reach 100%at around 250 °C and maintain to 1000 ?.A modified method was used to synthesize a series of catalysts with different precursor mass ratios?{CeO2}/?CuFe₂O₄}?for selective catalytic reduction of NO by CO.The results show that:?1?The small crystal phase??-Fe₂O₃,CuFe₂O₄,CuO?species and the large CeO2 on 1.4ceFecu reach the optimal contact state among their contact faces with a large amount of highly mobile super reactive oxygen species,leading the excellent catalytic performance in low temperature.?2?The dominant Ce4+ species can inhibit the formation of Cu0 to a certain extent,resulting in the cyclic transition of Cu2+ and Cu+ during the reaction below 400 ?.?3?The copper species mainly exist in the form of Cu0 and Fe3O4 on CeO2 surface is the main active species above 400-600 ?.?4?The Ce4+ species can inhibit the formation of Fe° to a certain extent,resulting in the cyclic transition of Fe2+ and Fe3+ at high temperature.At this time,the newly generated CeFeO3 plays a leading role.For these reasons,the conversion rate of NO can reach 50%at 100 ? and reach 100%at 220 ?and maintain to 1200 ?,accompanied by an active window of 1000 ?.Here a possible NO + CO model reaction mechanism is proposed to further understand the catalytic process by combining various characterization results with in-situ infrared analysis and quasi-situ XRD and XPS results of equilibrium state.