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

Abstract

Neste trabalho, reações entre a perovskita LaMnO 3,15 e Fe o foram promovidas pelo tratamento térmico da mistura Fe o /LaMnO 3,15 a 200, 400 e 600 o C. Análises por espectroscopia Mössbauer, difração de raios X (DRX), redução em temperatura programada (TPR) e desorção em temperatura programada (O 2-TPD) sugerem que a 400 o C e a 600 o C a perovskita transfere oxigênios para o Fe o , produzindo uma perovskita deficiente em oxigênio, LaMnO 3-δ , e formando óxidos de ferro altamente dispersos, principalmente Fe 3 O 4 e FeO. Os parâmetros de rede e os tamanhos de cristalitos obtidos por DRX mostram que o LaMnO 3 sofre uma forte distorção da rede cristalina após a reação, mas sem o colapso da estrutura perovskita. Estudos de reatividade sugerem um efeito especial de interface na mistura Fe o /LaMnO 3 em duas reações com H 2 O 2 , i.e. a decomposição para produzir O 2 e a oxidação da molécula modelo, o corante azul de metileno. Com o tratamento da mistura Fe o /LaMnO 3,15 a temperaturas mais altas, observa-se uma diminuição da atividade de decomposição do H 2 O 2 , porém um aumento na atividade de oxidação do corante. Estes resultados são discutidos em termos de uma diminuição da concentração das espécies Mn 3+ sup e Mn 4+ sup , ativas para a decomposição do H 2 O 2 , com a formação de espécies Mn 2+ sup e Fe 2+ sup , ativas para a reação de Fenton. In this work, the reaction of the perovskite LaMnO 3.15 with Fe o has been promoted by thermal treatment of the mixture Fe o /LaMnO 3.15 at 200, 400 and 600 o C. Mössbauer spectroscopy, X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed desorption (O 2-TPD) analyses suggested that at 400 and 600 o 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 3 O 4 and FeO. XRD lattice parameters and crystallite size showed that LaMnO 3 suffers a strong lattice distortion after reaction but no collapse of the perovskite structure. Reactivity studies pointed to a special interface effect of Fe o /LaMO 3 towards two reactions with H 2 O 2 , the decomposition to O 2 and the oxidation of the model molecule, the methylene blue dye. As the treatment temperature of the Fe o /LaMnO 3.15 increased, the activity for H 2 O 2 decomposition decreased, whereas the activity for the dye oxidation increased. These results are discussed in terms of a decrease in the concentration of Mn 4+ surf and Mn 3+ surf species, active for the H 2 O 2 decomposition, with the formation of Mn 2+ surf and Fe 2+ surf species, active for the Fenton reaction.

Preparation, Structure and Catalytic Activity of Simple Spinel as Nano-Copper-Zinc Ferrites in Industry Model

“…The ferrites contain Cu, as Cu-, and (Cu Zn) ferrites show high activity with constant reaction rates of 0.48, 0.52 and 0.72 mmol min -1 and the peroxide is consumed after 3 min of reaction. It is well confirmed in the literature that Cu 2+ plays a function in the hydrogen peroxide decomposition 23 . The difference in the activity of the Cu-ferrite likens to that of (Cu Zn) and (Cu) ferrites may be the presence of a higher concentration of Cu 3+ on the Cuferrite surface.…”

Electrocatalytic Oxygen Reduction Reaction on Perovskite Oxides: Series versus Direct Pathway

“… The ORR on LaCoO 3 and La 0.8 Sr 0.2 MnO 3 perovskites and perovskite/carbon composites in alkaline NaOH electrolyte predominantly follows a series pathway with the formation of a HO 2 − intermediate, which can either be desorbed and diffuse into the electrolyte or react further to ultimately result in a 4 e − ORR to water. Despite the fact that carbon itself is inactive in the reduction and decomposition of hydrogen peroxide, mixing it with perovskite oxides leads to a strong drop in the amount of HO 2 − detected at the ring of a RRDE. This is explained by the improvement in the electrical contact between the oxide particles within a catalytic layer, which results in an increase in the number of accessible active sites on the oxide surface. Given that perovskite oxides are active in the electrocatalysis of the reduction of hydrogen peroxide10 and in the catalysis of the decomposition of hydrogen peroxide,40–42 detection of the HO 2 − intermediate on the ring of a RRDE is only possible if the number of accessible oxide active sites is low. This occurs for low oxide loadings on the disc or in the case of a poor electronic connection between the oxide particles (in this work with no carbon in the catalytic layer).…”

“…Given that perovskite oxides are active in the electrocatalysis of the reduction of hydrogen peroxide10 and in the catalysis of the decomposition of hydrogen peroxide,40–42 detection of the HO 2 − intermediate on the ring of a RRDE is only possible if the number of accessible oxide active sites is low. This occurs for low oxide loadings on the disc or in the case of a poor electronic connection between the oxide particles (in this work with no carbon in the catalytic layer).…”

Enhanced Catalytic and Photocatalytic Degradation of Organic Pollutant Rhodamine‐B by LaMnO3 Nanoparticles Synthesized by Non‐Aqueous Sol‐Gel Route

“…In the past two decades, perovskite‐structured lanthanum manganite (LaMnO 3 ) has attained intense interest due to their interesting electronic and magnetic properties for potential technological applications in batteries, pseudocapacitors, and spintronics . Additionally, LaMnO 3 displays catalytic properties and have various environmental applications such as hydrocarbons oxidation, H 2 O 2 reactions and chlorinated organic compounds . The stoichiometric LaMnO 3 has a low Neel Temperature, (T N ≈140 K ) below which it exhibits A‐type antiferromagnetic (AFM) behavior because of super‐exchange (SE) interactions between two subsequent Mn 3+ ions via oxygen.…”