Vanadia-doped silica gels were prepared via the sol-gel process by-condensation of vanadyl acetylacetonate with tetramethoxysilane in the presence of methanol as solvent. Aerogels with densities between 200 kgm~-3 and 400 kgm~-3 were obtained via supercritical drying with respect to carbon dioxide. Specific surface areas and average pore diameters as well as pore size distributions fro mnitrogen adsorption measurements at 77K were obtained by BET and BJH analysis, respectively. Microporosity was estimated via the t-plot method. The C-parameter of the BET equation was found to depend on the voluem of primary micropores. A second BET analysis was applied after subtraction of the total micropore volume. For samples with pore size distributions that are dominated by larger mesopores (average pore diameter > 13nm), the thus obtained "reduced" C-parameters center around 41. The total micropore volume of samples for which the C-parameter could not be reduced to this value is assumed to be considerably underestimated. Small angle X-ray scattering (SAXS) was used as a second method for structural characterisation. Scattering (SAXS) was used as a second method for structural characterisation. Scattering curves were evalauted with the help of the two-phase-media model. While average pore sizes fromboth characterisation methods were found to agree well, specific surface areas by SAXS are about 100 m~2g~-1 i.e. 10
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