Aminoiron(III)–porphyrin–alumina catalyst obtained by non-hydrolytic sol-gel process for heterogeneous oxidation of hydrocarbons

Abstract

An aminoiron(III) porphyrin immobilized on an alumina matrix was prepared and used as catalyst for the oxidation of organic substrates. Powder alumina had been prepared by a non-hydrolytic sol-gel method through condensation of aluminum chloride with anhydrous ethanol. Then, iron(III) [5,10,15,20-tetrakis(2,6-dichloro-3-aminophenyl)-porphyrin] was immobilized on the alumina powder under magnetic stirring, reflux, and inert atmosphere. Ultraviolet–visible and infrared spectroscopies, powder X-ray diffraction, scanning electron microscopy and thermal analysis were applied for characterizing the resulting material, confirming that the ironporphyrin was immobilized on the alumina support. The catalytic activity of ironporphyrin/alumina was evaluated in the oxidation of (Z)-cyclooctene and cyclohexane and in the Baeyer-Villiger oxidation of cyclohexanone using iodosylbenzene or hydrogen peroxide as oxygen donors. The novel immobilized catalyst proved to be a promising system for the efficient and selective oxidation of the organic substrates with 85–92% selectivity to the epoxide in the oxidation of alkenes and 25–41% to the ketone in the oxidation of cyclohexane. As for the Baeyer-Villiger oxidation of cyclohexanone, good conversion to ԑ-caprolactone was observed as well. The material is a reusable heterogeneous catalyst, which makes it more economically feasible than its homogeneous counterpart.