Insights into the Reaction Mechanism of Cyclohexane Oxidation Catalysed by Molybdenum Blue Nanorings
Insights into the Reaction Mechanism of Cyclohexane Oxidation Catalysed by Molybdenum Blue Nanorings
复制标题
DOI：
10.1007/s10562-015-1660-y
复制
发表时间：
2016-01-01
影响因子：
2.8
通讯作者：
Hutchings, Graham J.
中科院分区：
文献类型：
--
作者：
Conte, Marco;Liu, Xi;Hutchings, Graham J.
钼蓝（MB）是具有包含Mo 5 +-O-Mo 6+桥的纳米环结构的聚氧乙烯酸盐，其对环己烷催化氧化为环己醇和环己酮具有活性。然而，很少有人知道负责这种催化活性的机械功能。在本工作中，嵌入在MB纳米环结构中的Mo 5 +-O-Mo 6+部分，其特征在于使用漫反射-紫外-可见光谱和固态EPR光谱。Mo 5+中心的量，然后通过在没有氧的情况下热处理的聚氧乙烯酸酯变化，并对催化活性的所得效果进行了研究。据观察，增加量的Mo 5+中心保持环己烷的转化率（约100%）。6%），但导致对环己醇的选择性丧失，产生主要产物环己酮，并同时形成己二酸。为了合理化这些结果的催化剂进行了研究，使用EPR自旋捕获，以调查环己基过氧化氢（CHHP），在环己烷的氧化过程中的关键中间体的分解。该分析表明，CHHP必须结合到MB表面，以解释其催化活性和产物分布。[图形]。
Molybdenum blue (MB), is a polyoxometalate with a nanoring structure comprising Mo5+-O-Mo6+ bridges, which is active for the catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone. However, little is known about the mechanistic features responsible of this catalytic activity. In the present work, the Mo5+-O-Mo6+ moieties embedded in the MB nanoring structure were characterized using diffuse reflectance-UV-Visible spectroscopy and solid state EPR spectroscopy. The amount of Mo5+ centres was then varied by thermal treatment of the polyoxometalate in the absence of oxygen, and the resultant effect on the catalytic activity was investigated. It was observed that, an increased amount of Mo5+ centres preserved the conversion of cyclohexane (ca. 6 %) but led to a loss of selectivity to cyclohexanol giving cyclohexanone as the major product, and the simultaneous formation of adipic acid. To rationalise these results the catalysts were studied using EPR spin trapping to investigate the decomposition of cyclohexyl hydroperoxide (CHHP), a key intermediate in the oxidation process of cyclohexane. This analysis showed that CHHP has to be bound to the MB surface in order to explain its catalytic activity and product distribution.[GRAPHICS].