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Lamia Bourja Bahcine Bakiz Abdeljalil Benlhachemi Sylvie Villain Claude Favotto 《Journal of solid state chemistry》2011,184(3):608-614
Polycrystalline samples of (1−x) CeO2−x/2 Bi2O3 phases, where x is the atom fraction of bismuth have been synthesized by the precipitation process and after the thermal treatment at 600 °C, under air. Samples are first characterized by the X-ray diffraction and scanning electron microscopy. To determine the samples specific surface areas, Brunauer-Emmett-Teller (BET) analyses have been performed. In the composition range 0≤x≤0.20, a cubic solid solution with fluorite structure is obtained. For compositions x comprised between 0.30 and 0.90, two types of T′ (or β′) and T (or β) tetragonal phases, similar to the well-known β′ or β Bi2O3 metastable structural varieties, are observed. However, the crystal cell volumes of these β′ or β Bi2O3 phases increase with the composition x in bismuth: this might be due to the presence of defects or substitution by cerium atoms, in the tetragonal lattices. Using X-ray diffraction profile analyses, correlations between bismuth composition x and crystal sizes or lattice distortions have been established. The solid-gas interactions between these polycrystalline materials and air-CH4 and air-CO flows have been studied as a function of temperature and composition x, using Fourier transform infrared (FTIR) analyses of the conversions of CH4 and CO gases into the CO2 gas. The transformations of CH4 and CO molecules as a function of time and temperature are determined through the intensities of FTIR CO2 absorption bands. Using the specific surface areas determined from BET analyses, these FTIR intensities have been normalized and compared. For all bismuth compositions, a low catalytic reactivity is observed with air-CH4 gas flows, while, for the highest bismuth compositions, a high catalytic reactivity is observed with air-CO gas flows. 相似文献
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H. Ait Ahsaine M. Zbair M. Ezahri A. Benlhachemi B. Bakiz F. Guinneton J.-R. Gavarri 《Research on Chemical Intermediates》2017,43(2):885-899
Polycrystalline samples in the lutetium-doped zinc tungstate system Zn1?x Lu x WO4 with 0 ≤ x ≤ 0.08 were synthesized using the coprecipitation method followed by thermal treatment at 1000 °C during 4 h. The polycrystalline samples were characterized by X-ray diffraction analysis, scanning electron microscopy (SEM), infrared spectroscopy, and luminescence analysis under X-ray excitation. Rietveld analyses were performed. The variation of the wolframite structure cell parameters in the range 0 ≤ x ≤ 0.05 were congruent with substitution of Zn2+ by Lu3+. SEM micrographs of the obtained samples presented improved crystallization with morphology depending on the lutetium fraction. The luminescence spectra obtained under X-ray excitation (E < 40 keV) were in the blue–green region, and their intensity increased with x up to x = 0.05. The differences in the intensities of the X-ray luminescence spectra could be related to additional cation vacancies resulting from substitution of Zn2+ by Lu3+. 相似文献
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