Investigation of the solid state reaction of LaMnO3 with Fe o and its effect on the catalytic reactions with H2O 2

Abstract

In this work, the reaction of the perovskite LaMnO3.15 with Feo has been promoted by thermal treatment of the mixture Fe o/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 o to produce an oxygen deficient perovskite, LaMnO 3-δ, and highly dispersed iron oxides, mainly Fe 3O4 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 Feo/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 Feo/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 H2O 2 decomposition, with the formation of Mn2+surf and Fe2+surf species, active for the Fenton reaction. ©2007 Sociedade Brasileira de Química.