Oxidation of cyclohexane over iron and copper salen complexes simultaneously encapsulated in zeolite Y

Abstract

Fe(salen) and Cu(salen) complexes simultaneously encapsulated in zeolite Y by the flexible ligand method showed much higher activity than the neat Cu(salen) and Fe(salen) or the Cu(salen)/Y and Fe(salen)/Y or their physical mixtures in the oxidation of cyclohexane with aqueous H 2 O 2 solution as a result of the existence of a synergetic effect. Iron and copper salen complexes have been simultaneously encapsulated in zeolite Y by using the flexible ligand method, as substantiated by infrared spectroscopy, diffuse reflectance UV–vis spectroscopy, thermo-gravimetric and differential-thermal analyses and N 2 adsorption/desorption experiments at −196 °C. The prepared material showed much higher activity than the neat Cu(salen) and Fe(salen) or the Cu(salen)/Y and Fe(salen)/Y or their physical mixtures in the oxidation of cyclohexane with H 2 O 2 . The existence of a synergetic effect is the cause of this high activity. This synergetic effect may originate from the formation of dinuclear salen complexes and/or the interaction of adjacent partially coordinated Cu(salen) and Fe(salen) complex molecules through the lattice oxygen of the zeolitic host. This assumption is supported by extensive investigations of the catalytic performance of different types of catalysts as well as cyclic voltammetry and diffuse reflectance UV–vis spectroscopy. The optimum molar ratio of Cu 2+ to Fe 3+ in the prepared material is 1.93:1. The reaction time and temperature strongly influenced the catalytic performance. Although this catalyst was not highly stable because of degradation of metal salen complexes in the presence of H 2 O 2 aqueous solution, this work provides a new route for designing and preparing highly active “ship-in-a-bottle” materials.