Effects of oxidant and solvent on the liquid-phase cyclohexane oxidation catalyzed by Ce-exchanged zeolite Y

The effect of several solvents on the cyclohexane oxidation to cyclohexanol and cyclohexanone under mild conditions (T=343 K, 24h) using zeolite Y (Si:Al=12.5) exchanged with Ce(III) as catalyst, and tert-butyl-hydroperoxide (I-BHP) and hydrogen peroxide (H2O2) as oxygen atom donors was studied. The results show that higher cyclohexane conversions are obtained in the following order: no solvent>1,2-dichloroethane>dichloromethane>acetone>acetonitrile>pyridine. Using t-BHP as oxidant, n-hexanal formation is observed as by-product and the selectivity increases when solvents with more basic characteristics (e.g. acetonitrile and pyridine) are used. Reactions with H2O2 as oxidant are highly selective yielding cyclohexanol as the major product, however, the conversion is low. Leaching experiments show that homogeneous Ce3+ is not responsible for the catalytic activity. However, the catalyst is deactivated in recycling experiments, probably due to the formation of carboxylic acids, which block the pore entrances and/or complex to the active sites. (C) 2000 Elsevier Science B.V. All rights reserved.