Influence of doping nitrogen on the catalytic performance of carbon nanotubes encapsulating cobalt for selective oxidation of arylalkanes

Efficient selective oxidation of hydrocarbons to corresponding ketones has been a significant but challenging work in the past decades. Here, a nitrogen-doped bamboo-like carbon nanotubes encapsulating cobalt catalyst (NCNTs-X) using citric acid, melamine and CoCl2‧6H2O as precursors was synthesized by a simple pyrolysis method. A series of characterization techniques were employed to investigate the physicochemical properties of samples. And the results show that the as-prepared catalysts achieve a high catalytic performance for selective ethylbenzene oxidation (78.3% ethylbenzene conversion) using molecular oxygen as oxidant, especially giving a high selectivity (93.8% selectivity to acetophenone). According to the investigation of the structure-activity relationship of the catalysts, it can be deduced that the Co–Nx sites have an obvious positive effect on catalytic performance thanks to the synergistic effect between metallic cobalt and pyridinic N.

数十年来，将烃类高效选择性氧化为对应酮类始终是一项兼具重要研究价值与技术挑战的课题。本研究以柠檬酸、三聚氰胺与六水合氯化钴（CoCl₂·6H₂O）为前驱体，通过简便的热解方法合成了氮掺杂竹节状碳纳米管包覆钴催化剂（NCNTs-X）。采用一系列表征手段对样品的物理化学性质展开系统探究。实验结果表明，所制备的催化剂以分子氧为氧化剂，在乙苯选择性氧化反应中展现出优异的催化性能：乙苯转化率可达78.3%，对苯乙酮的选择性更是高达93.8%。通过对催化剂构效关系的深入分析，可推导出：金属钴与吡啶氮（pyridinic N）之间的协同效应使得Co-Nₓ位点对催化性能具有显著的正向促进作用。