Preparation of nano-structured cryptomelane materials for catalytic oxidation reactions

S Said,M Riad,M Helmy,L Khalil,S Mikhail

doi:10.1007/s40097-016-0192-3

Abstract

Manganese-based octahedral molecular sieves of the type K-OMS-2 (cryptomelane structure) were prepared via reflux method by synproportionation of KMnO4 and Mn2+ in acidic aqueous suspension. For this method, different manganese anions (sulphate, chloride and acetate) were used, which exert a strong influence on the prepared materials. Several techniques such as X-ray diffraction, Fourier transformer infrared, Raman spectroscopy, transmission electron microscopy, differential and gravimetric thermal analysis and H2-temperature programmed reduction were used to characterize the prepared samples. The results revealed that the prepared samples were mainly pure mono-phase cryptomelane materials. The obtained K-OMS-2 material on using the sulphate anion has more available lattice oxygen as compared to that prepared by the other anions. The catalytic activity of the prepared samples was tested towards the oxidative dehydrogenation of cyclohexane. Over the K-OMS-2RS sample, cyclohexane conversion was significantly higher than the other prepared samples.

Highlights

Catalytic partial oxidation of hydrocarbons ‘‘ alkanes’’, using oxygen or air as oxidant, is significant and economical for the chemical industry
Cyclohexene is a precursor to adipic acid, maleic acid, dicyclohexyl adipate, and cyclohexene oxide and can be used as a specific solvent. This reaction is operated in liquid phase using heterogeneous catalysts, but required high temperature (*150 °C), besides high selectivity ([80 %) to the sum of cyclohexanol and cyclohexanone only could be observed at low cyclohexane conversion [1]
The catalytic activity of the K-OMS-2 is higher than Ba-OMS-2 materials, which directly correlated to their higher surface area

Summary

Introduction

Catalytic partial oxidation of hydrocarbons ‘‘ alkanes’’, using oxygen or air as oxidant, is significant and economical for the chemical industry. The selective oxidation of cyclohexane is much attractive because of its formed product, cyclohexene. Cyclohexene is a precursor to adipic acid, maleic acid, dicyclohexyl adipate, and cyclohexene oxide and can be used as a specific solvent. This reaction is operated in liquid phase using heterogeneous catalysts, but required high temperature (*150 °C), besides high selectivity ([80 %) to the sum of cyclohexanol and cyclohexanone only could be observed at low cyclohexane conversion [1]. Modi and Trivedi, [2] studied the catalytic behaviour of zeolite-Y-entrapped Ru(III) and Fe(III) complexes over the oxidation of cyclohexane forming cyclohexanone and cyclohexanol. The development of effective homogeneous catalysts could offer advantages

Methods

Results

Conclusion