Investigation of the solid state reaction of LaMnO3 with Fe and its effect on the catalytic reactions with H2O2

Abstract

In this work, the reaction of the perovskite LaMnO3.15 with Fe has been promoted by thermal treatment of the mixture Fe/LaMnO3.15 at 200, 400 and 600 §C. Mössbauer spectroscopy, X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed desorption (O2-TPD) analyses suggested that at 400 and 600 §C oxygen from perovskite is transferred to Fe§ to produce an oxygen deficient perovskite, LaMnO3-d, and highly dispersed iron oxides, mainly Fe3O4 and FeO. XRD lattice parameters and crystallite size showed that LaMnO3 suffers a strong lattice distortion after reaction but no collapse of the perovskite structure. Reactivity studies pointed to a special interface effect of Fe/LaMO3 towards two reactions with H2O2, the decomposition to O2 and the oxidation of the model molecule, the methylene blue dye. As the treatment temperature of the Fe/LaMnO3.15 increased, the activity for H2O2 decomposition decreased, whereas the activity for the dye oxidation increased. These results are discussed in terms of a decrease in the concentration of Mn4+surf and Mn3+surf species, active for the H2O2 decomposition, with the formation of Mn2+surf and Fe2+surf species, active for the Fenton reaction.