Strontium and cerium tungstate materials SrWO4 and Ce2(WO4)3: Methane oxidation and mixed conduction

In this work, we report the synthesis of SrWO4 (SWO) and Ce-2(WO4)(3) (CWO) phases, based on the ethylenediaminetetraacetic- citrate complexing method. All samples were characterized by thermogravimetric analysis, X-ray diffraction and electron microscopy to identify the structure and the morphology of each compound. The catalytic reactivity of the samples was analyzed using a homemade reactor coupled to a combined system of Fourier transform infrared spectrometer (FTIR) and mass spectrometer apparatus. The measurements were performed under methane gas flows with different gas carriers (Air and Argon), in the temperature range of 500-950 degrees C. The catalytic activity was determined as a function of time and temperature. In specific circumstances, FTIR experiments show that methane is partly oxidized into CO thus giving rise to syngas production at low pressure. The reactivity could be linked to oxygen species delivered by solids. Electrical impedance spectroscopy analyses have been carried out on compacted polycrystalline samples, and Nyquist representations have been interpreted. The SWO and CWO samples presented similar semiconducting behaviors with electronic and ionic mix conductions, with higher conductivity for the CWO phase. (C) 2012 Elsevier B.V. All rights reserved.