Microstructural Changes in La0.5Ca0.5Mn0.5Fe0.5O3 Solid Solutions under the Influence of Catalytic Reaction of Methane Combustion

Abstract

This article attempts to study changes in the microstructure of solid solutions with the perovskite structure La0.5Ca0.5Mn0.5Fe0.5O3 under the action of the methane oxidation reaction medium. By the methods of XRD, XPS and HRTEM the initial condition of the structure and the surface of the perovskite were both investigated. A feature of the structure of this solid solution is the presence of planar defects in the direction of the planes (101). After the methane oxidation reaction, a similar study of perovskite structure was conducted to obtain the changes. It was shown that under the action of the reaction medium, Ca1−xMnxO particles form on the surface of the perovskite phase, while planar defects in La0.5Ca0.5Mn0.5Fe0.5O3 structure remain. In situ XRD experiments on perovskite calcination in helium current up to 750 °C showed the formation of a similar Ca1−xMnxO phase on the perovskite surface.

Structural Insight into La0.5Ca0.5Mn0.5Co0.5O3 Decomposition in the Methane Combustion Process

“…The lack of oxygen in the perovskite structure leads to the appearance of extensive planar vacancies (Figure S1) and the migration of cobalt and calcium cations to the surface of the perovskite phase. Similar effects were observed in the LCMFO and LCFO systems [33,35]. According to the experimental data, it can be assumed that with further exposure to the reaction medium, the perovskite structure relaxes and a part of the solid solution returns to a state close to the initial one.…”

“…In [32], a nonlinear increase in catalytic activity was observed with the introduction of Ca into the perovskite structure. However, [33] shows that calcium cations migrate to the surface as a result of the reaction and can negatively affect catalytic properties.…”