Preparation And Properties Of Three-dimensional Ordered Macroporous Fe-based Spineland CeFe-based Composite Oxides

Three-dimensional ordered macroporous?3DOM?materials show excellent performance and application potential in a variety of environmental fields due to their unique uniform macroporous structure,flexible structural composition,tunable physicochemical properties,good stability,and biocompatibility.In this paper,3DOM catalysts were characterized by means of Scanning electron microscope?SEM?,High resolution transmission electron microscope?HRTEM?,X-ray powder diffraction?XRD?,N₂physical adsorption-desorption,Raman spectra,H₂-temperature programmed reduction?H₂-TPR?,X-ray photoelectron spectroscopy?XPS?,In situ diffuse reflectance infrared fourier transform spectra?In-situ DRIFTS?,CO oxidation reaction,CO-SCR reaction,etc.The relationship between the catalytic performance of the catalyst and its composition,structure,and properties was explored,and the reaction mechanism of the two model reactions on the catalyst was discussed.A series of three-dimensional ordered macroporous?3DOM?MFe₂O₄spinel catalysts were synthesized by colloidal crystal template method for CO oxidation and selective catalytic reduction of NO_xby CO.Co and Ni did not have a good synergy with Fe,respectively,and the reduction performance of the corresponding spinel oxides is also lower than that of pure Fe₂O₃.However,the introduction of Cu into Fe to form spinel catalysts not only promotes the reduction performance,but also improves the surface active oxygen species,and the optimum 3DOM Cu Fe₂O₄catalyst has the highest catalytic activity in both reactions.Moreover,the appearance of Cu⁺-CO species in the reactions is the reason why 3DOM Cu Fe₂O₄catalyst has better catalytic activity than other catalysts at lower temperature.At the same time,the existence of oxygen vacancies at higher temperatures is conducive to the activation of O₂molecule in CO oxidation and the dissociation of NO molecule in NO+CO reaction.It is worth noting that the two reactions on the 3DOM Cu Fe₂O₄catalyst follow the Langmuir-Hinshlwood?L-H?and Eley-Rideal?E-R?mechanisms at low and high temperatures,respectively.A series of 3DOM Ce_0.7Fe_0.2M_0.1O₂catalysts were also prepared by the above method.In addition,bulk Ce_0.7Fe_0.2M_0.1O₂catalyst was prepared by the citric acid sol-gel method and all were used for CO-SCR reaction.There is a better synergistic interaction between Cu and Ce-Fe composite oxides,and the formation of 3DOM structure not only improves the reduction performance and surface active sites but also promotes the generation of more surface adsorbed oxygen species.So,3DOM Ce_0.7Fe_0.2Cu_0.1O₂catalyst shows the highest catalytic activity.Moreover,the appearance of Cu⁺-CO species and the rapid conversion 3DOM Ce_0.7Fe_0.2Cu_0.1O₂catalyst has better catalytic activity than other catalysts at lower temperature.Simultaneously,the oxygen vacancies produced by the reduction of Fe³⁺?Fe²⁺and those adjacent to Ce³⁺are more important at higher temperatures,which is conducive to the dissociation of NO.And the CO-SCR reaction on 3DOM Ce_0.7Fe_0.2Cu_0.1O₂catalyst follows the mechanism of L-H and E-R at low temperature and high temperature,respectively.