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  • 1
    ISSN: 1572-879X
    Schlagwort(e): Methane coupling ; molybdate-sodium ; lithium chloride ; propylene ; propane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract LiCl-Na2MoO4 was found to be an active catalyst for oxidative coupling of methane at temperatures around 620 °C. In these systems, the selectivity for the formation of C3-products exceeds the selectivity for the formation of C2-products. While the homogeneous reaction of CH4 and O2 leads to C3H6 as C3-product, the 50% LiCl-50% Na2MoO4 catalyst leads to C3H8 as the predominant C3-product, indicating that in the latter case the reaction cannot be purely homogeneous. The dependency of the product distribution on temperature, gas composition, reactor dimensions, flow rate, CH4/O2 ratio and type of catalyst has been studied. The reaction was studied by co-feeding CH4, O2 and a diluent gas at atmospheric pressure continuously in a conventional flow reactor containing the catalyst. The reaction products observed were: C2H4, C2H6, C3H6, C3H8, H2O and CO + CO2. The two latter gases were the main oxidation products observed. Characterization of the catalysts used was carried out by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 19 (1980), S. 675-696 
    ISSN: 0570-0833
    Schlagwort(e): Micelles ; Photophysics ; Photochemistry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A fascinating feature inherent to aqueous surfactant solutions is the phenomenon of self-organization: above a certain critical concentration (the critical micelle concentration, CMC) detergent molecules associate spontaneously to build up structural entities of colloidal dimensions called micelles. The architecture of these agglomerates is such that the interior contains the hydrophobic alkyl chain of the amphiphile while the hydrophilic head groups are located at the surface and are in contact with bulk water. In the case of ionic micelles the interface is charged giving rise to an electrical double layer and a potential difference of up to several hundred millivolts between the micellar pseudophase and water. Thus micellar systems are microheterogeneous in character: the electrostatic potential and polarity prevailing in the interior of the aggregate differ from those of the bulk aqueous phase. A particularly attractive aspect of photochemical studies in micellar systems is the possibility of organizing the reactants at a molecular level: by comparison of the data in micelles with similar data in homogeneous solution one can learn about the molecular details of a given reaction and establish which conditions favor one pathway or another. In simple surfactant systems differences in rate and efficiency of a reaction will often be controlled by local electrostatic potentials and the compartmentalization of the reagents within the surfactant aggregates. Through the latter effect the statistics of probe distribution over the micelles becomes important in controlling fast photochemical events. Functional micelles are distinguished by the fact that the surfactant molecule contains a group which itself participates in the photoprocess. These units are unique in that self-assembly often introduces striking cooperative effects.
    Zusätzliches Material: 27 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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