Oxidation of cyclohexene with molecular oxygen catalyzed by cobalt porphyrin complexes immobilized on montmorillonite

Abstract

Composite materials were prepared by intercalating cationic porphyrinato cobalt complexes with the substituents of the quaternary ammonium salt of heterocyclic amine into a montmorillonite interlayer. Using these clay interlayer-fixed porphyrinato cobalt complexes as catalyst, the epoxidation of cyclohexene by oxygen molecules was examined. The prepared intercalation compounds have mesopores with an average diameter of about 12 nm, and their specific surface area increased in proportion to the amount of the intercalated porphyrinato cobalt complexes. It was proven that the porphyrinato cobalt complex was intercalated between montmorillonite layers functioned as a pillaring agent. A pillared clay catalyst, which was prepared by intercalating a [meso-tetrakis(1-ethyl-3-pyridinio)porphyrinato] cobalt complex into the montmorillonite interlayer, showed the highest catalytic activity forming 1,2-epoxycyclohexane preferentially in the presence of isobutyraldehyde. It is suggested that montmorillonite contributes to the stabilization of the porphyrinato cobalt complex, and also plays a role in accelerating oxidation by activating oxygen molecules by way of constructing a reaction field that is regulated three-dimensionally through electrostatic interaction with guest molecules.