SYNTHESIS AND CHARACTERIZATION OF CERIUM FLUORITES BASED ON Ce1-xLn xO2-δ SYSTEM (Ln: Nd3+, Sm3+, Eu3+, Gd3+, Dy3+ AND Ho3+)

Abstract

ABSTRACT This paper describes the synthesis of 18 oxides of Ce 1-x Ln x O 2 (Ln: Nd 3+ , Sm 3+ , Eu 3+ , Gd , Dy 3+ and Ho ), with x = 0.05, 0.10 and 0.15 mol% by use of a wet chemical route that involving the obtention of coordination compounds type citrate, which allow the generation of a number of chemical and surface properties with potential catalytic applications in solid oxide fuel cells technologies. The materials obtained by this route, has a high purity and homogeneity, enabling calcination temperatures and residence times considerably brief, in comparison with conventional synthetic routes. All oxides, were calcined at 300 °C under flow oxygen and were characterized by X-ray diffraction (XRD), from obtained results, we confirmed the presence of a pure fluorite structure of CeO 2 consistent with the ICSD pattern reference of 072155 with space group Fm-3m (225). Subsequent physicochemical characterization by TPR and electron microscopy (SEM-TEM), confirm that cerium oxides could be reduced in two single steps at different temperatures, kinetically detectable and clearly prolonged as well as the obtention of nanostructured solids with a crystallite size between 32-47 nm. According with obtained results, the solids show a high surface area as result of the low calcination temperature. The electrical characterization by impedance spectroscopy (IS), revealed an important concentration of charge carriers in fluorite oxides, mainly in the sample of GDC5, which is a crucial characteristic in advanced materials for SOFC applications. The catalytic studies, conducted on materials at 700 °C under stable reaction conditions, confirm that the methane conversion levels change throughout the series GDC5 → NDC5 → HDC5 → EDC5 → DDC5 → SDC5, which established that the GDC5 solid, exhibits the most promising results. Finally, a stability test was achieved with the GDC5 catalyst under the same reaction conditions established in previous form, for a period of 240 hours of continuous flux, establishing the effectiveness of the proposed method to choice the most promissory material. The results confirmed as the methane conversion vary as function of time and the obtained syngas levels change for potential technological applications.