Synthesis of Porous Fe₃ C-Based Composite Beads as Heterogeneous Oxidation Catalysts

A series of multiscale cementite/iron/porous carbon (CIPC-T) composites with extremely low nitrogen content and millimeter-size spherical morphology were prepared by simple carbothermal pyrolysis of resin spheres exchanged with ferric oxalate anions. CIPC-T materials are composed of highly disperse core-shell-structured Fe₃ C/Fe@graphitic carbon (CI@GC) nanoparticles embedded in a porous amorphous carbon framework. A mechanism for the formation of the composites is proposed on the basis of the results of XRD, SEM, TEM, and thermogravimetric analysis. The Fe₃ C content can be easily controlled just by using different carbothermal temperatures. The CIPC-T materials proved to be active as heterogeneous catalysts for oxidation of ethylbenzene to acetophenone and Fenton-like oxidation of methylene blue. For the first time, the role of Fe₃ C in catalytic oxidation was confirmed. The spherical morphology of the composites and magnetic property facilitate separation of the catalyst from the reaction solution. More importantly, no leaching of iron active sites occurs during the reactions and the catalyst can be reused in continuous runs without obvious loss of activity. Such high stability of iron sites in the composites is ascribed to the protecting outer graphitic carbon shell of CI@GC.