Ship-in-bottle synthesis of NaY zeolite encapsulated Cosalen complex and its catalytic performance for cyclohexane oxidation

Abstract

N, N’-bis (salicylidene) ethylenediiminocobalt (Cosalen) was encapsulated into microporous NaY zeolite via the technique of “ship-in-bottle”. The encapsulated complex (Cosalen-NaY) was characterized by Fourier-transform infrared spectrum, ultraviolet-visible spectrum, Brunauer-Emmett-Teller surface areas, X-ray diffraction, thermogravimetry-differential thermal analysis and scanning electron microscope. The reaction of cyclohexane oxidation using oxygen was chosen to investigate the catalytic performance of Cosalen-NaY, and the effects of oxygen pressure, temperature and reaction time were also studied. The results show that Cosalen complex is encapsulated into the supercage of the zeolite and the structure of NaY zeolite remains integrity and the thermal stability of Cosalen is greatly enhanced after encapsulation. Cosalen-NaY shows the better activity in the oxidation of cyclohexane without reductant and solvent. The conversion of cyclohexane is up to 13.4% at 150 °C for 3 h under oxygen pressure of 0.85 MPa, with the higher total selectivity to cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide (CHHP) and acid (79.2%) than the neat complex (55.5%). NaY zeolite carrier maybe contributes to the results. There is no obvious induction period to initiate the reaction; furthermore, the amount of CHHP among the products is small, which indicates that the Cosalen-NaY has the strong ability to accelerate the decomposition of CHHP. Recycling tests show that the hybrid material can be used repeatedly with a negligible loss of active sites.