Gels of chromium and aluminium oxides have been obtained from Al(O-Bus)3 and Cr(acac)3 in sec-Butanol after acetic acid addition. The rise of chromium amount affects the dispersion and the chromium oxidation state at the support surface. The activity of the catalysts in partial oxidation of paraxylen enhances when the chromium amount increases from 5 to 10% but decreases markedly for an amount equal to 18% for which ESR study shows the presence of chromium oxid clusters Cr2O3. The amount of acetic acid added influences the solid texture. Thus, when the molar ratio K rises, the specific surface increases and the solids became more porous. The stirring time (Ta) of organic precursors governs the distribution of chromium between the surface and the support. Thus, when (Ta) increases, the chromium is more incorporated in the alumina support.
L. Barakat, A. Ghorbel
sol-gel, chromium, oxidation, paraxylen