Selective oxidation reactions over tri- and tetradentate oxovanadium(IV) complexes encapsulated in zeolite-Y

• New oxovanadium(IV) Schiff-base complexes were encapsulated in Y-zeolite nanopores.
• These complexes were screened for oxidation of phenol, benzene, cyclohexene and styrene using H2O2.
• These catalysts were recovered and reused without loss of its catalytic activity.

The preparation and characterization of VO(IV) complexes of 7-amino-5-aza-4-methyl-hept-3-en-2-one and 4,4′-(ethane-1,2-diyldinitrilo)dipentan-2-one inside the super cages of zeolite-Y using the flexible ligand method is described. The structures of these encapsulated complexes were established on the basis of various physico-chemical (XRD, BET and TGA) and spectroscopic studies (UV–Vis, FTIR). The results indicate that zeolite-Y can accommodate these complexes in its super cages without hindering or modifying the framework or structure of the zeolite confirming successful encapsulation of the Schiff-bases throughout the voids of zeolite-Y. These encapsulated complexes were screened as heterogeneous catalysts for various oxidation reactions, viz., phenol, benzene, styrene and cyclohexene using H2O2 as oxidant. For comparison, the corresponding neat complexes were screened as potential homogeneous catalysts for these oxidation reactions. The homogeneous complexes were found to be more active than the corresponding encapsulated VO(IV) complexes for these oxidation reactions. The results also proved that the heterogeneous systems described here represent an efficient and friendly environmental for these oxidation reactions, having advantages over homogeneous catalysts. In addition they have high turnover frequency values (TOF) and better selectivity than the corresponding homogeneous catalysts.

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