Highly Selective pH-Dependent Ozonation of Cyclohexane over Mn/γ-Al2O3 Catalysts at Ambient Reaction Conditions

Siphumelele Thandokwazi Mkhondwane,Viswanadha Srirama Rajasekhar Pullabhotla

doi:10.3390/catal9110958

Siphumelele Thandokwazi Mkhondwane, Viswanadha Srirama Rajasekhar Pullabhotla

Open Access

https://doi.org/10.3390/catal9110958

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Journal: Catalysts	Publication Date: Nov 15, 2019
Citations: 5	License type: CC BY 4.0

Affiliation: University of Zululand

Abstract

The selective oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone (KA oil) is one of the imperative reactions in industrial processes. In this study, the catalytic performance of manganese-supported gamma alumina (Mn/γ-Al2O3) catalysts is investigated in the selective oxidation of cyclohexane at ambient conditions using ozone. The catalysts were prepared by the wet impregnation method, and their physio-chemical properties were studied by Fourier Transform Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma (ICP) spectroscopy, and Brunauer Emmett and Teller (BET). The reaction conditions were optimised considering various parameters such as reaction time, pH, and various percentages of the manganese supported in gamma alumina. The oxidation of cyclohexane was conducted in an impinger reactor unit at pH 3, 7, and 11 for 1 h of ozonation time. The aliquots were collected after 30 min and 1 h of ozonation time and analysed with GC-MS and FT-IR spectroscopy. The 2.5% Mn/γ-Al2O3 catalyst exhibited a significantly enhanced catalytic performance at pH 3 and 7 with a percentage conversion of 9% and 15% at pH 3 and 7, respectively, after 30 min of ozonation time. However, after 1 h of ozonation time, the percentage conversions were increased to 23% and 29% at pH 3 and 7, respectively. At pH 11, 5% Mn/γ-Al2O3 exhibit high catalytic performance with a percentage conversion of 19% and 31% after 30 minutes and 1 h of ozonation time, respectively. The percentage selectivity obtained is 100% toward KA oil and/or cyclohexanone depending on pH and reaction time.

Highlights

The functionalisation of the saturated aromatic and aliphatic hydrocarbon’s C-H bond is one of the utmost important industrial processes in the quest for economic viability and a sustainable approach for the production of oxygenates
We report the catalytic ozonation of cyclohexane over Mn/γ-Al2 O3 catalysts using ozone
The broad band is observed in the Fourier Transform Infrared (FT-IR) spectra of γ-Al2 O3 support and all the as-synthesised Mn/γ-Al2 O3 catalysts at a wavelength of cm−1, which becomes more perceptive with an increase in metal loading

Summary

Introduction

The functionalisation of the saturated aromatic and aliphatic hydrocarbon’s C-H bond is one of the utmost important industrial processes in the quest for economic viability and a sustainable approach for the production of oxygenates. The corresponding oxygenates are more reactive than their respective parent hydrocarbons, and as a result, they subsequently react to form un-wanted products [1]. One of such processes is the oxidation of cyclohexane, which has shown increasing importance for the production of cyclohexanol and cyclohexanone (a mixture called KA oil). The constituents of KA oil are prominent intermediates for the production of caprolactam and adipic acid. Caprolactam and adipic acid are important precursors for the production of nylon 6 and nylon 6,6 polymers, respectively [2,3,4]

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