Preparation Of Fe-based Catalysts Derived From NH₂-MIL-88B?Fe? And Their Catalytic Oxidation Performances

Metal-Organic Frameworks?MOFs?,a class of new crystalline porous materials formed by self-assembly of metal ions or clusters and organic ligands,have received extensive attention due to their fascinating characteristics of large specific surface area,high porosity and easy chemical modification.Thanks to the diverse topologies and unique physicochemical properties,MOFs can be used as sacrificial templates or precursors to derive various types of porous carbon-based materials by pyrolysis.MOF-derived materials overcome the problems of poor stability and easy deactivation of pristine MOFs,while preserving the porosity of precursor.By optimizing the pyrolysis conditions,it can realize the accurate control of catalytic active center and expand the application field of the derived materials.Based on the features of composition and structure of the Fe-based MOFs materials,in this master thesis,we have derived two efficient heterogeneous catalysts from NH2-MIL-88B?Fe?under appropriate pyrolysis and acid etching conditions.Both of the Fe/Fe₃C-containing nitrogen-doped porous carbon microspindles?Fe/Fe₃C@NC?and Fe single-atom catalysts?Fe-N-C?were systematically characterized by X-ray powder diffraction,N₂ adsorption-desorption,X-ray photoelectron spectroscopy,Raman spectroscopy,scanning electron microscope,transmission electron microscope and spherical aberration-corrected transmission electron microscope.Subsequently,these catalysts were evaluated in the catalytic oxidation reaction of sulfides and aromatic hydrocarbon,respectively.The main results are summarized as follows:?1?A series of magnetically recyclable core-/shell-structured Fe/Fe3C@N-doped carbon hybrids were developed.The Fe/Fe3C@NC-x?x stands for the pyrolysis temperature?were derived from NH₂-MIL-88B?Fe?via in-situ pyrolysis under a nitrogen atmosphere,and the catalysts show excellent catalytic activity for the selective oxidation of sulfide to sulfoxide under mild reaction conditions.Among the various investigated catalysts,the Fe/Fe₃C@NC-600 microspindles exhibit the best catalytic activity,higher than those exhibited by the analogue Fe/Fe3C@C-600 without N doping and the commercial Fe2O3,Fe3O4,Fe?acca?3,and Fe3C used for the catalytic oxidation of sulfides owing to the synergistic contribution of the Fe3C sites and adequate nitrogen doping in the porous carbon support.Furthermore,the magnetically separable properties of the Fe/Fe₃C@NC-600 microspindles enable their convenient isolation from the reaction system using an external magnet,and they can be repeatedly used for six cycles without any loss in catalytic efficiency.?2?A new strategy for directly construction of single-atom Fe catalyst from MOFs was developed.Using the mono-dispersed NH2-MIL-88B?Fe?microcrystals that were well synthesized in the previous chapter as a sacrifice template,a single-atom catalyst Fe-N-C-x?x is the pyrolysis temperature?were derived by a sequential pyrolysis-acid etching strategy.The strong coordination between N and Fe in the catalyst framework can result in the atomic dispersion of active center on the carbon support.Thus,the highly uniform active site and nitrogen doping in the porous carbon structure make the prepared Fe-N-C-600 show best catalytic activity than precursors and other commercial Fe-based catalysts in the catalytic oxidation of benzene to phenol.By comparison with the analogue Fe-C-600 without N doping,the importance of the nitrogen-doping in the porous carbon support is further illustrated.Besides,the catalyst also exhibits relatively high activity and selectivity in the selective oxidation of toluene and ethylbenzene.Moreover,the prepared Fe-N-C-600 catalyst also display excellent stability,and no catalyst deactivation occurred during its repeated usage.