XPD and in situ XANES on Ce-Zr-Sm nanomaterials synthesized by hydrothermal method

ROSARIO SUAREZ ANZORENA; S.A. LARRONDO.; L. M. TOSCANI; FERNANDO MUÑOZ

Campinas

Encuentro; 31st RAU Annual Users Meeting LNLS; 2021

60%NiO/Ce0.9Zr0.1O2 showed a good performance as an anode in Intermediate Temperature-Solid Oxide Fuel Cells,however, it is necessary to increase its mixed conductivity (ionic and electronic) to increase the power density of the cell[1]. The partial substitution of Zr4+ by Sm3+ is proposed to incorporate oxygen vacancies into the crystalline structurethus improving the conductivity. Ce0.9Zr0.1-xSmxO2-x/2 (x= 0.1, 0.08, 0.06, 0.04, 0.02, 0) oxides were synthesized by theurea-hydrothermal method and calcined at 550 ℃. X-ray diffraction with synchrotron radiation shows that all samples,have a single phase corresponding to a fluorite structure. Average crystallite sizes (< 11 nm) and lattice parametersincrease with Sm content. In-situ Dispersive X-ray Absorption Spectroscopy experiments were performed at the Ce LIIIabsorption edge in a 5 vol.% H2 gas-flow, from room temperature to 800 ℃. Three reduction steps are observed duringthe process, two of which can be related to the reduction of surface Ce4+ species. The incorporation of Sm3+ decreasedthe superficial reduction capacity of samples whereas it increased the reduction kinetics of bulk species. The effect ofreduction atmosphere and calcination temperature was studied for samples with x= 0.04 and 0.06. A decrease in thereduction kinetics in a diluted atmosphere of CH4 was observed. The oxidation of CH4 is activated at temperatureslower than 600 ℃. Samples calcined at 1100 ℃ showed a decrease in the reduction kinetics of superficial Ce, whilethe reduction still occurs in three steps. The composition of the exit gas was analyzed by online mass spectrometry.Since only H2 is fed, carbonaceous species detected in the exhaust can only be ascribed to adsorbed species on the highspecific surface area (83-115 m2.g-1) of samples calcined at 550 ℃. This is still observed for samples calcined at 1100 ℃.In CH4 atmosphere, at first, products related to the total oxidation are observed and then CO2, H2O, H2 and CO aredetected.