Combined Haber-Weiss and vacancy mechanism: Ce4+ used as intelligent isomorphic ions in iron oxides

Abstract

Cerium is known for its good ability to transition between the Ce3+ and Ce4+ forms, which modulates its ability to incorporate oxygen into different material structures. Therefore to promote the slow phase characterize by oxidative processes, related to phase of regenerating the reduced metallic sites, iron oxide-based catalysts partially replaced by cerium were synthesized, and their physical, textural and morphological properties were evaluated. The catalysts were prepared by synthesizing the magnetite phase and doping with cerium (Ce4+), such that the isomorphic ion content in the FeCex formula was 0.05> x> 0.2 mol. The X-ray diffraction (XRD) results of the oxide after Ce was incorporated exhibited peaks corresponding to magnetite, which is less crystalline than bulk iron, suggesting that the isomorphic ion was incorporated into the iron oxide crystal lattice. Furthermore, incorporating the rare earth element also favored the appearance of diffraction peaks corresponding to the formation of other iron phases, such as goethite. The results suggest a strong interaction between the metals, because even after the single addition of Ce4+, X-ray photoelectron spectrometry (XPS) analysis shows the presence of the +3 and +4 oxidation states. The materials obtained after incorporating cerium had a high catalytic capacity for removing a reactive red dye. The dye removal was significant, and the materials demonstrated a remarkable chemical stability and remained active for seven consecutive reaction cycles without the need for regenerating the active centers. The dye removal essentially occurs by a heterogeneous process, in which the active phase leaching rates are not significant.