Solvent-free selective oxidation of cyclohexane with molecular oxygen over manganese oxides: Effect of the calcination temperature

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• 作者：Mingzhou Wu ; Wangcheng Zhan ; ^{zhanwc@ecust.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Yun Guo ; Yunsong Wang ; Yanglong Guo ; Xueqing Gong ; Li Wang ; Guanzhong Lu ; ^{gzhlu@ecust.edu.cn" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Manganese oxide catalyst ; Selective oxidation of cyclohexane ; Oxygen ; Calcination temperature ; Solvent-free reaction
• 刊名：Chinese Journal of Catalysis
• 出版年：2016
• 出版时间：January 2016
• 年：2016
• 卷：37
• 期：1
• 页码：184-192
• 全文大小：706 K

文摘

The effects of calcination temperature on the physicochemical properties of manganese oxide catalysts prepared by a precipitation method were assessed by X-ray diffraction, N₂ adsorption-desorption, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction, O₂ temperature-programmed desorption, and thermogravimetry-differential analysis. The catalytic performance of each of these materials during the selective oxidation of cyclohexane with oxygen in a solvent-free system was subsequently examined. It was found that the MnO_x-500 catalyst, calcined at 500 °C, consisted of a Mn₂O₃ phase in addition to Mn₅O₈ and Mn₃O₄ phases and possessed a low surface area. Unlike MnO_x-500, the MnO_x-400 catalyst prepared at 400 °C was composed solely of Mn₃O₄ and Mn₅O₈ and had a higher surface area. The pronounced catalytic activity of this latter material for the oxidation of cyclohexene was determined to result from numerous factors, including a higher concentration of surface adsorbed oxygen, greater quantities of the surface Mn⁴⁺ ions that promote oxygen mobility and the extent of O₂ adsorption and reducibility on the catalyst. The effects of various reaction conditions on the activity of the MnO_x-400 during the oxidation of cyclohexane were also evaluated, such as the reaction temperature, reaction time, and initial oxygen pressure. Following a 4 h reaction at an initial O₂ pressure of 0.5 MPa and 140 °C, an 8.0% cyclohexane conversion and 5.0% yield of cyclohexanol and cyclohexanone were achieved over the MnO_x-400 catalyst. In contrast, employing MnO_x-500 resulted in a 6.1% conversion of cyclohexane and 75% selectivity for cyclohexanol and cyclohexanone. After being recycled through 10 replicate uses, the catalytic activity of the MnO_x-400 catalyst was unchanged, demonstrating its good stability.