Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-III-37performed under atmospheric pressure with a quartz-made tubular reactor. The effluents fromthe reactor, containing reaction products were analyzed by gas chromatography.Results and Discussion: The X-ray diffraction peaks of Ce 1–x Pr x O 2 samples correspondto the face-centered cubic fluorite structure type CeO 2 and PrO 2 . A very homogeneousmaterials with spherical morphology and an insignificantly variation of lattice parameter wereevidenced by XRD and SEM microscopy of the WCe 1–x Pr x O 2 samples with various Prcontent. This may be due to the uniformity of Pr 4+ : Pr 3+ ratio and oxygen vacancy in thesematerials. The lattice parameter systematically increases with the Pr content for ECe 1–x Pr x O 2samples and formation of two phases was evidenced by SEM microscopy at high Pr percent.The oxidation states of cerium and praseodymium ions have been determined by XP and UV-Vis spectroscopy. While cerium is mainly in the +4 oxidation state, about one-half of thepraseodymium ions were found to be in the +3 state. The large amount of Pr 3+ cations seemsto be a particularity of the doped ceria samples.A high variation of the surface stoichiometry and Pr 4+ : Pr 3+ ratio was evidenced for the Wand E type samples. The catalytic performance of oxides depends strongly on the precipitateC CH4, %10080604020Ce0,9Pr0,1O2(W)Ce0,1Pr0,9O2(W)Ce0,5Pr0,5O2(W)Ce0,9Pr0,1O2(E)Ce0,5Pr0,5O2(E)washing. The catalytic activity is probablyattributable to the migration of Pr ions andtheir distribution at interface or into theceria network. The activity of allWCe 1–x Pr x O 2 samples in oxidation of CH 4is very high (Fig. 1). In contrast,ECe 1–x Pr x O 2 samples exhibit lower0370 420 470 520Temperature, o Cactivity. The activity of ECe 1–x Pr x O 2increases with Pr content.Fig. 1. The variation of CH 4 conversion with temperature.Acknowledgements: The financial support by the Romanian Ministry of Education andResearch -CEEX-AMCSIT 267 is highly appreciated.References1. A. Hartridge, M. Ghanashyam Krishna, A.K. Bhattacharya, Mat. Sci. Eng. B57 (1999) 173.2. L. Gerward, J. Staun Olsen, L. Petit, G. Vaitheeswaran, V. Kanchana, A. Svane, J. Alloys Compounds, 400(2005) 56.3. S. Colussi, C. de Leitenburg, G. Dolcetti, A. Trovarelli, J. Alloys Compounds, 374 (2004) 387.374