Characterization and catalytic properties of aerogel chromium oxide supported by alumina or silica

Alumina or silica supported chromium oxide catalysts prepared by sol-gel te chnique have been investigated by X-ray diffraction, BET analysis, combined diffuse reflectance spectroscopy, EPR and reduction-extraction by ethane 1 ,2 diol. The results reveal the presence of Cr3+, Cr5+ and Cr6+ ions. Chrom ium species Cr6+ are isolated and atomically dispersed on the alumina suppo rt as free chromate CrO42- while on silica, dichromate or polychromate spec ies like Cr2O72- or Cr3O102- predominate. Chromium oxide exhibits a better catalytic properties for paraxylene partial oxidation, when it is supported on alumina. The difference of oxidation states and degree of oligomerisati on of chromium on the two supports affects the catalytic properties.