Anomalia na àrea superficial de géis de composição sílica/alumina

Abstract

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The behavior of the BET surface area of gels of SiO2/Al2O3 compositions is studied for different methods of sols preparation: mixture of Si and Al alkoxide with slow or rapid hydrolysis and mixture of Si alkoxide with an Al salt with a rapid hydrolysis. The last method leads to a reduction of the BET surface area for a composition having ~47 wt % Al2O3. This reduction depends on the molar ratio H2O/Si alkoxide and reaches 2 orders of magnitude for a molar ratio of 100. We show that this particular behavior depends on the nature of the precursors, the method of preparation and the H2O/Si alkoxide molar ratio. The real cause of the anomaly is, however, not known.