Room temperature selective oxidation of cyclohexane over Cu-nanoclusters supported on nanocrystalline Cr2O3

Abstract

Cu-nanoclustures supported on nanocrystalline Cr₂O₃ were prepared by a hydrothermal synthesis method in the presence of surfactant, cetyltrimethylammonium bromide (CTAB). It was found that the catalyst is highly active for the selective oxidation of cyclohexane with H₂O₂ at room temperature. The catalyst was characterized by XRD, ICP-AES, XPS, TPR, BET-surface area, SEM, TEM and EXAFS. The effect of Cu loading and the influence of reaction parameters, such as the substrate to oxidant molar ratio and reaction time, were investigated in detail. The investigation revealed that the size of copper plays a crucial role towards the activity by favoring the oxidation of cyclohexane. The reusability of the catalyst was tested by conducting repeat experiments with the same catalyst, where it was found that the catalyst displays no changes in its activity and selectivity even after 4 reuses. The cyclohexane conversion of 86% with a cyclohexanone selectivity of 85%, and an overall C₆ selectivity (cyclohexanol and cyclohexanone) of 100% was achieved after 3 h of reaction at room temperature, over 4.3 wt% Cu loaded on nanocrystalline Cr₂O₃.