| Abstract
| - Four alkali cations (Li+, Na+, K+, and Rb+) and ammonium (NH4+), have been successfully used as templatesfor the synthesis of cryptomelane-type manganese oxide octahedral molecular sieves (A−OMS-2, A = thetemplate cation). H−OMS-2 material has been prepared by the calcination of NH4−OMS-2. These A−OMS-2materials have been characterized by X-ray diffraction, transmission electron microscopy, high-resolutionscanning electron microscopy, thermogravimetric analysis, temperature-programmed desorption, inductivelycoupled plasma analysis, and BET surface area pore size distribution measurements. Catalytic evaluation ofthese A−OMS-2 materials has been done with the aerobic oxidation of cyclohexanol to cyclohexanone. Allof these A−OMS-2 materials have cryptomelane tunnel structures with different degrees of crystallinity andnanofibrous morphology. The nature of the cation templates affects the formation and microstructures of theA−OMS-2 materials. The physical and chemical properties, such as the thermal stability, chemical composition,and average oxidation state of manganese, greatly depend on the nature of cations and amount of tunnelwater. Catalytic activities of these A−OMS-2 materials are related to their surface areas.
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