Salen-Co(II) complex incorporated into amino-functionalized MIL-101(Cr) through postsynthetic modification as a cooperative catalyst for cyclohexane selective oxidation

Abstract

A series of MOF-based catalysts, metal-salen complexes incorporated into amino-functionalized MIL-101 matrices by salicylaldehyde condensing to amino group and coordinating metal ion through one pot method, have been prepared and characterized. The successful preparation of catalysts demonstrates that postsynthetic modification (PSM) is a practical and powerful route to generate MOF-based catalyst with multiple active sites. The catalytic performances of prepared catalysts were investigated via selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA-oil) by molecular oxygen in the absence of solvent. It was found that NH2-MIL-101(Cr)-Sal-Co, as a typical case, behaves as cooperative catalyst for cyclohexane selective oxidation. That is, salen-Co(II) attached to framework of MOF is able to assist in the generation of new radicals from peroxides via a Haber–Weiss catalytic cycle to promote conversion of cyclohexane while framework Cr ion is able to catalyze the dehydration of intermediate product cyclohexyl hydroperoxide (CHHP) to improve KA-oil selectivity. Furthermore, this catalyst exhibits good recyclability and behaves as truely heterogeneous catalyst.