Liquid phase selective oxidation of cyclohexane using gamma alumina doped manganese catalysts and ozone: an insight into reaction mechanism

Abstract

Abstract In this study, we investigate the oxidation of cyclohexane using various percentages of Mn/γ-Al2O3 catalysts. The catalysts were characterized with various spectroscopic and microscopic techniques. The XRD showed the presence of γ-Al2O3 and MnO only. However, the XPS showed that AlO, AlOH, Mn2O3 and MnO2 also exist. The TEM results of pristine γ-Al2O3 showed characteristics of a spherically shaped material, whereas Mn/γ-Al2O3 catalysts displayed rod shaped particles. The EPR results showed that hydroxide radicals are the main reactive species responsible for the significant oxidation of cyclohexane and the catalysts play a profound role in the generation of hydroxide radicals. The oxidation of cyclohexane was performed for 1 h and the reaction products were analysed using GC-MS and FT-IR in 30 min intervals. The 2.5% Mn/γ-Al2O3 was the most reactive catalyst with a percentage conversion of 33% after 1 h oxidation. The cyclohexanol and the cyclohexanone were the only reaction products obtained. This study exhibited that Mn/γ-Al2O3 catalysts when used in conjunction with ozone are potential replacement for industrially used homogeneous manganese catalysts.