过渡金属修饰ZSM-5分子筛上甲烷低温转化反应机理的固体NMR和量子化学计算研究

过渡金属（Cu，Fe，Zn）修饰的ZSM-5分子筛催化剂在甲烷的活化转化方面表现出较高的低温反应活性，这对于甲烷资源的优化转化利用具有重要的意义。但是对于过渡金属修饰分子筛活性中心的具体结构与性能、甲烷的活化机制还不清楚。本项目拟采用固体NMR技术和其他实验技术（ESR, UV-vis, FT-IR等），结合量子化学计算研究过渡金属修饰ZSM-5分子筛活性中心的结构以及分布特征，阐明催化剂活性中心具有高催化性能的微观机制。利用原位核磁共振技术跟踪13C标记的甲烷在分子筛上的反应过程，通过捕获到的反应中间体结合量子化学过渡态计算，得到反应的活化能垒，从原子分子水平揭示甲烷在金属修饰分子筛上的活化转化机理，并阐明不同金属改性催化剂性能的差异。通过系统研究活性中心结构与催化剂性能之间的关系，为新型高效催化剂的设计提供依据。

It has been found that the transition metal (Cu, Fe, Zn) modified zeolite exhibits an exceptionally high catalytic activity toward methane conversion at low temperature. However, the detailed structure of active site and the reaction mechanism of methane conversion are still poorly understood. Solid-state NMR, ESR, UV-vis, FT-IR techniques in conjunction with density functional theory (DFT) calculations will be employed to study the structures of active sites and their properties on transition metal (Cu, Fe, Zn) modified ZSM-5 zeolite. To reveal the reaction mechanism, the adsorption and conversion of 13CH4 will be studied by the 13C in-situ solid state NMR technique, which can be used to trace the pathway of the catalytic oxidation of methane. Based on the in-situ NMR experimental results, the transition states of the reaction can be studied by DFT calculation, which will reveal the reaction mechanism at atomic and molecular level. Meanwhile, the reaction energy barriers and rate constants can be determinated by theoretical calculations, which can be used to judge the catalytic activities of zeolites modified with the different metals. The systematic studies of structure-activity relationship may be helpful for rational design of new highly efficient catalysts for methane conversion.