Oxidation of cyclohexane with molecular oxygen in presence of characterized macrocyclic heteronuclear FeCu complex catalyst ionically bonded to zirconium pillared montmorillonite clay

Heteronuclear macrocyclic complex of iron and copper, FeCuL(NO3)24H2O [L = (CH3C6H2CH2O(CH2)3N)2] was synthesized and characterized using CHN and X-ray crystallography. A general scheme for bonding the complexes ionically on acidified montmorillonite clay was evolved and the thermogravimetric analysis of the final catalyst showed that it was stable up to 400 °C. The increased thermal and chemical stability of the complex bonded to the clay has been explained through enhanced interactive energy between them and its higher catalytic efficiency has been demonstrated through the following reaction. The oxidation of cyclohexane in presence of this catalyst using molecular oxygen in the absence of intiators, promoters and coreactants was studied in the temperature range of 150–210 °C. All commercial catalyst reported are known to form cyclohexanol and cyclohexanone in about equimolar ratio, but with our catalyst, cyclohexanone along with small amount of uncharacterized waste products (D) were formed and the selectivity of the former decreases (due to the formation of large amount of D) with increase in temperature. The experimental data were analyzed against different kinetic scheme available in literature and the rate constants of the best scheme were determined using Genetic Algorithm. From the experiments carried out at different temperatures and pressures, we found that for every rate constant, an Arrhenius type relation (independent of reactor pressure) could be established.

Graphical abstractHeteronuclear macrocyclic complex of iron and copper, FeCuL(NO3)24H2O [L = (CH3C6H2CH2O(CH2)3N)2] was synthesized and a general scheme for bonding the complexes ionically on acidified montmorillonite clay was evolved. The kinetic analysis by genetic algorithm shows the catalysts to be highly efficient, specific to forming cyclohexanone.Figure optionsDownload full-size imageDownload as PowerPoint slide