The Ce-Sm-O/Ru(Pt) structural peculiarities that provides high catalytic activity in partial methane oxidation reaction were investigated. The catalytic properties of Ce-Sm-O/Ru(Pt) samples were studied by TPR and in a solid oxide fuel cell (SOFC) type reactor. The effect of Ru(Pt) impregnation as well as reducing atmosphere (H2) treatment on the Ce-Sm-O samples surface condition were studied by the FTIR and EPR methods.
We examined powdered Ce-Sm-O (Sm 5-15 % mol) samples derived from thermally treated sol-gel products – xerogels (X) and precipitates (P) of Ce-Sm hydroxides after the ammonia-promoted hydrolysis of aqueous Ce-Sm nitrates. The crystallization of amorphous material obtained started at 600 oC resulting in highly dispersed (~10 nm) cubic Ce1–xSmxO2-ä solid solution. It was found that maximal of specific surface area (70 m2/g) posses Ce0.9Sm0.1O2-ä X-sample. The EPR measurements of P- and X-samples calcined at 600oC in air, revealed two axial paramagnetic centers signals: I – g^=1,966 and gII=1,947-1.944, assigned to the bulk and surface Ce3+-centers (2F5/2); II – gII=1,998 and g^=1,974 assigned to the Sm3+-centers (6H5/2). The treatment of Ce-Sm-O samples by Ru-containing solution leads to the drastically changes in ESR spectra of samples obtained. Namely, the concentration of Ce3+(surf.) centers (g^=1,966, gII=1,940) became 100 times higher for X-samples in contrast, for P-samples this concentration increased only 50 times. Moreover, according to XRD analysis, the sudden change of unit cell parameter for Ce0.9Sm0.1O2-ä X-samples as compared to P- one were observed. FTIR-spectra of Ce0.9Sm0.1O2-ä calcined at 600oC and treated by Ru-containing solution X-samples contains band at 1856 cm–1. This band attributed to the vibration of bonded with surface RuOx.
Methane oxidation over nanocrystalline Ce0.9Sm0.1O2-d/Pt anodes at 900oC in a SOFC type reactor shows well-developed electrocatalytic performance; CH4 conversion and CO selectivity achieve 41% and 55%, respectively. High oxygen mobility in Ce0.9Sm0.1O2-d promotes oxygen ions activation at the platinum/oxide interface and results in faster oxidation of methane and/or partial oxidation products.
The work was supported by ISTC (Project Nr.3234).
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