Binuclear Cobalt Complex Encapsulated in Zeolites H-Y(5), H-MOR(86), H-ZSM-5 and their Catalytic Oxidation of Cyclohexane

Abstract

Binuclear Cobalt complex 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [Co₂L] was encapsulated in zeolites H-Y(5), H-MOR(86) and H-ZSM-5 by ion exchange method and these catalysts, were characterized by FTIR, powder XRD, DRS – UV-Vis and XRF studies. The surface studies performed on the catalysts showed the extent of encapsulation in the cavities of the zeolites. The electrochemical studies of the catalysts showed oxidation-reduction of metal ions whose redox potentials were influenced by the geometry of the zeolite matrix. Oxidation of cyclohexane by tertiary butyl hydroperoxide in the presence of catalysts gave products cyclohexanone and cyclohexanol with almost 99% selectivity towards cyclohexanone. The heterogenized complex displayed higher conversion than the neat complex, which was dependent on the metal content of the catalyst and the acidity of zeolites. The catalysts also showed good reusability with high TON and TOF. The proposed mechanism of oxidation involved the formation of cyclohexyl peroxyl radical, mediated by electron transfer between the peroxide and the metal center. The ΔG_ET and ΔG⁰ calculations support the electron transfer process. The kinetic studies of the catalytic oxidation reactions were followed by the initial rate determination method and the results fitted well into the bimolecular second-order rate process.