Catalytic Oxidation of Cyclohexane on Small Silver Clusters Supported by Graphene Oxide

Metal clusters including those supported on graphene-based materials have attracted extensive research interest in the past decade allowing dissection of the interfaces, stability, electronic properties, and catalytic activities at an atomically precise scale. Here, we have synthesized glutathione-protected Ag-6 clusters via a facile green reaction route, transferred onto graphene oxide (GO) and exploit as catalyst for cyclohexane oxidation under ambient conditions. High selectivity and high yields to produce cyclohexanone are attained with tert-butyl hydroperoxide (TBHP) as the oxidant in the oxygen-flowing atmosphere. Based on density functional theory calculations, it is demonstrated that both TBHP and oxygen interact with the GO-supported Ag-6 clusters, giving rise to the peroxide structure and hence facilitating the catalytic oxidation of cyclohexane. It is interestingly found that the hydrogen-added hydroperoxyl (-OOH) brings forth largely decreased activation barrier for the O-O bond dissociation. The O-O dissociated intermediate then reacts with cyclohexane to form cyclohexanol, followed by successive oxidative dehydrogenation to produce cyclohexanone. This finding verifies the enhanced catalysis of TBHP and O-2 for the conversion of cyclohexane to cyclohexanone and helps to develop heterogeneous catalysts of metal clusters for efficient C-H activation.