EPR and UV–visible spectroscopic studies of alumina-supported chromium oxide catalysts

The oxidation state, the mobility and the molecular structure of chromium species present on CrO x –Al 2O 3 catalysts have been studied by combined diffuse reflectance spectroscopy, EPR and reduction–extraction by ethane 1,2 diol. CrO 4 2− species exist on the alumina surface in the form of loosely-interacting species on hydrated surface (species A) and in the form of strongly bonded species on dehydrated Al 2O 3 surface (species B). The CrO 4 2− species show high mobility and are probably responsible for the formation of CrO x clusters.