SPECTROSCOPIC INVESTIGATION OF THE MOLYBDENUM ACTIVE-SITES ON MO-VI HETEROGENEOUS CATALYSTS FOR ALKENE EPOXIDATION

Spectroscopic and spectromagnetic investigations on molybdenum centres in MoO3 . H2O and its polymer-supported form have been carried out. B oth were tested as catalysts for cyclohexene epoxidation in a heteroge neous phase; both needed activating pretreatment before the reaction. XPS and EPR data show that the metal is mainly present as Mo-VI. The a ctivation process increases the acidic character of Mo-VI and its effi ciency depends both on the oxidizing power of the activating reactant and on the accessibility of the metal to the reactant. The steric hind rance of Mo-VI lowers the catalytic activity owing to the replacement of H2O by carboxylic groups of the functionalized resin.