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  • 1
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Chemisorption of CO at temperatures below 100°C has been used to evaluate the dispersion of NiO in a series of NiO/γ-Al2O3 catalysts. CO adsorption measurements were supplemented by i.r. spectroscopy to establish the CO/NiO stoichiometry. From monolayer coverage data derived from Freundlich's equation, the percentage of NiO dispersion and the average NiO crystallite size were calculated. The crystallite size of supported NiO was found to be practically constant for NiO loadings from 1 to 8 wt%, experimenting an abrupt increase for higher NiO contents. These results were consistent with additional information on the surface structure of the catalysts obtained by IR spectroscopy, X-ray diffraction, magnetic susceptibility, and reduction with H2.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectroscopy has been used to characterize various MoO3/γ-Al2O3 and CoO (or NiO)-MoO3/γ-Al2O3 catalysts containing 12 wt% MoO3 and 3 wt% CoO (or NiO) prepared by different methods. No significant differences between samples prepared by the wet impregnation and the pore volume method could be observed in molybdena-supported catalysts; in these samples the majority of Mo is present as isolated distorted MoO42- tetrahedra due probably to a low coverage of the alumina surface (SBET=240 m2 g-1). Addition of NiO to the molybdena-supported catalysts seems to cause only a slight increase in the distortion and interaction between MoO42- species. In contrast, CoO addition to the molybdena-supported catalysts changes considerably the spectra features, suggesting that the Mo species are highly distorted, presumably in different surroundings on the alumina surface, due to the strong interaction of Co with Mo species. However, simultaneous impregnation of both MoO3 and CoO or NiO results in a more regular arrangement of Mo species and an increase in formation of polymeric Mo species, particularly with Co-containing catalyst, where a relative higher degree of polymeric aggregation may occur.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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