Selective oxidation of benzene to phenol in the liquid phase with amorphous microporous mixed oxides Original Research Article

Amorphous microporous mixed oxides (AMM) have been investigated as catalysts for the direct oxidation of benzene to phenol with hydrogen peroxide in the liquid phase. The catalysts have been prepared by an acidic sol–gel process. The most active AMM-catalysts found have been based on Fe as active centre. The catalysts have been characterised by a variety of methods including Ar-adsorption isotherms, MAS-NMR, EXAFS, XANES and HRTEM. The most promising catalytic system was AMM-Fe3Al3Si in acetonitrile as solvent. The effect of various reaction parameters such as solvent, reaction temperature, molar ratio of benzene:hydrogen peroxide, catalyst concentration, and reaction orders have been studied. The iron containing catalysts shows substantial leaching under reaction conditions. Among several attempts to stabilise the active centres in the amorphous network doping with Al-ions was most successful. The drastic effect of Al on the nature of the active Fe in the amorphous silica framework could be documented by Moessbauer spectroscopy. Reaction calorimetry studies revealed that acetonitrile is not an inert solvent but participates directly in the reaction.