High temperature conduction and methane conversion capability of BaCeO3 perovskite

The transport properties and reactivity in gases of a BaCeO3 perovskite phase have been investigated to develop new materials for methane conversion in microsystems. The polycrystalline material has been synthesized at moderate temperature using a specific modified EDTA-citrate complexing methodology. The BaCeO3 phase has been characterized by X-ray diffraction (XRD), thermogravimetry and differential thermal analyses (TG/DTA), scanning and transmission electronic microscopy techniques (SEM, TEM), energy dispersive X-ray (EDX) and surface area analyses. A Rietveld analysis of diffraction profiles has allowed determining the structural parameters of the as prepared material. Next, the catalytic efficiency of the BaCeO3 phase with air-methane gas flows has been characterized by Fourier transformed infrared (FTIR) spectroscopy: the conversion rate of CH4 into CO2 has been determined from the intensities of CO2 absorption bands, as a function of temperature (from 450 to 750 °C) and reaction time. Finally, the electrical conduction of compacted BaCeO3 pellets has been determined from electrical impedance spectroscopy analyses between 300 °C and 950 °C. A series of electrical transitions correlated with well known structural changes has been observed between 300 °C and 950 °C. The starting catalytic activity of BaCeO3 might be correlated to the enhanced ionic conduction observed above 450 °C.

In this manuscript we report a simple route to fabricate BaCeO3 perovskite composed of polycrystalline grains with small crystallite sizes. Good crystallinity of the samples allows us to evidence several electrical transitions (as shown in the figure below), in agreement to the structural changes as reported in the literatures. However, only one phase is more active under gas (methane) transformation for catalysis, which was found to be between 500 and 675 °C, corresponding to orthorhombic centred Imma phase. Figure: Logarithm of conductivity (log σ) as a function of 103/T, with T in Kelvin. Four domains can be observed. Insert figure shows to the evolution of the n exponent of CPE term.Figure optionsDownload as PowerPoint slideHighlights
► EDTA-Citrate complexing route give rise to perovskite structure with a single BaCeO3 phase at moderate temperature.
► The electrical analysis shows a semiconducting behavior as a function of temperature.
► The electrical evolution reveals for the first time various electrical transitions in good agreement to the structural transitions.
► Catalytic efficiency of BaCeO3 for steam methane reforming, show only an orthorhombic I phase as active structural phase.