天然丰度下多相催化反应的顺磁弛豫增强固体NMR研究

Solid-state NMR(ssNMR)can provide unique insights into the analysis of the structures of heterogeneous catalysts and give a brief description of surface chemical processes. The introduce of paramagnetic metal ions into heterogeneous solid catalysts not only can act as active reaction center, but also serve as a probe to explore the structure-property relationship in heterogeneously catalyzed reaction from a new sight. However, solid-state NMR studies of paramagnetic systems have been hindered by the existence of paramagnetic shifts as well as paramagnetically enhanced relaxation, both of which hamper NMR data acquisition and spectral assignments. In this project, versatile solid state NMR techniques are developed to facilitate the investigation of the detailed structure and dynamic behavior from paramagnetic relaxation enhancement (PRE) in heterogeneously catalyzed systems having paramagnetic centers. By utilizing PRE solid-state NMR techniques, it is comprehensively studied for exploration of the location of the paramagnetic metal ions and host-guest interactions and characterization of the acid property through distance constraints in heterogeneous solid catalysts. Meanwhile, the combination of in-situ ssNMR and PRE potentially enables the elucidation of the catalysis reaction mechanism and detection of active centers by using nature abundance instead of 13C-isotope enriched reactants. The project might provide basis and new insights into the application of PRE ssNMR techniques to heterogeneous catalysis.

固体核磁共振是表征多相催化剂微观结构和催化反应机理的有力工具。顺磁金属离子引入到多相催化剂既可扮演催化反应的活性中心，亦可作为探针从一个全新的视角来探测多相催化体系的内在构效关系。尽管如此, 固体核磁共振研究顺磁体系通常受到顺磁位移及弛豫速率增强的干扰, 进而影响了核磁信号采集以及谱峰信号归属。本项目拟通过应用和发展固体核磁共振方法来研究顺磁多相催化体系结构和动力学性质。通过固体核磁共振测得顺磁弛豫速率增强, 从获取的距离参数来得到顺磁离子在催化体系中的位置、主客体相互作用以及进行多相催化剂的酸性表征。本项目致力于推进天然丰度下的原位固体核磁共振技术及其在阐述顺磁体系反应机理历程和反应活性中心等方面的应用。本项目的实施开展将为顺磁弛豫增强固体核磁共振技术研究多相催化提供一些基础和参考性依据。

本项目通过发展和应用顺磁弛豫增强固体核磁共振方法来研究多相催化剂活性中心的结构性质以及观测多相催化反应机理。本项目发展了在天然丰度下探测多相催化体系催化反应机理的顺磁弛豫增强固体NMR技术，不仅可以节约13C同位素富集的成本，而且还大大缩短固体NMR 的采样时间。并且建立了超高场超快魔角旋转下强顺磁体系1H-13C及1H-1H二维相关谱技术, 明确了强顺磁体系1H, 13C NMR信号的全归属，节省了谱仪采集时间。另外, 利用顺磁弛豫增强固体NMR 技术，不仅可以表征金属离子活性中心的价态变化，而且能实时监测催化反应过程，推测催化反应机理。此外,利用固体NMR 技术研究了含顺磁离子的Cu-H-MOR 分子筛上甲醇羰基化反应的过程，探讨了铜物种对羰基化反应的影响。提出的13C-27Al NMR新方法可以用来研究沸石分子筛催化体系活性中心与吸附分子主客体相互作用模式。借助固体核磁共振实验技术研究了几种功能材料分子动力学性质以及主客体相互作用模式, 揭示了内在的构效关系。另外, 我们为物理化学学报以及催化学报撰写综述来说明固体核磁共振在固体酸催化剂上活性中心表征以及阐述多相催化反应机理上的应用发展趋势以及前景展望。在基金委的资助下,本项目代表性的研究成果包括以下: 1) Solid State Nucl. Magn. Reson. 2015, 66:29 2) J. Magn. Reson. 2015, 251:36-42 3) Solid State Nucl. Magn. Reson. 2016, 74-75: 10 4) Solid State Nucl. Magn. Reson. 2016, 80: 1-6 5) J. Phys. Chem. Lett. 2014, 5, 3068 6. ) Molecules 2014, 19:1353 7) Acta Phys. -Chim. Sin., 2017, 33 : 270 8)Chin. J. Catal.2015, 36 : 789 9) J. Phys. Chem. C 2017， 121， 14261 10) Solid State Nucl. Magn. Reson. 2018, 90:1 11) Zeolites in Sustainable Chemistry 20