含掺杂原子的过渡金属氮化物团簇催化N2加氢形成NH3的反应研究

Efficient nitrogen fixation, hydrogenation and conversion to ammonia under mild conditions are one of the most challenging and important chemical processes in chemistry. By now, the corresponding reaction mechanisms, methods for manipulating reactivity, and key influencing factors are not very clear. Obtaining the information at a strictly molecular level is quite meaningful to understand these processes and to design new catalysts. As one of ideal models, atomic clusters have unique advantages, such as clear structure-property relationships and being able to investigate elementary reactions. In this project, the complex ammonia synthesis process is divided into several important reactions: efficient activation of N2, hydrogenation to form intermediates, NH3 formation, and recovery of active sites. To achieve these processes, different types of heteroatoms will be doped into transition metal nitride clusters. High-resolution reflectron time-of-flight mass spectrometer coupled with an ion trap reactor or a fast flow reactor will be used to study the reactivity. Collision-induced dissociation or photo-induced dissociation, anion photoelectron spectroscopy and infrared photodissociation spectroscopy will be performed to characterize structures of clusters. Theoretical calculations will be applied to reveal the reaction mechanisms. Through the combination of experimental and theoretical results, the key factors governing these steps and methods for manipulating reactivity will be obtained. In addition, the important roles of heteroatoms and interaction with transition metal nitride clusters can also be obtained. Then based on these information, several kinds of cluster catalysts will be synthesized to realize catalytic ammonia synthesis. Moreover, this project can provide fundamental basis in practice for designing ideal and efficient catalysts.

实现温和条件下N2高效活化加氢形成NH3是一个极具挑战的课题。目前该过程的微观反应机理、活性调控方法及核心影响因素仍不十分清楚。在分子水平获得上述信息对于理解相关反应、设计催化剂具有重要意义。本项目拟利用团簇模型构效关系清晰、可研究基元反应等优势，将合成氨这一复杂反应分解成N2高效活化、加氢形成中间产物、形成NH3及活性位复原等步骤。通过在过渡金属氮化物团簇中针对性地引入不同类型的掺杂原子以分别实现上述过程。采用离子阱或流动管反应和高分辨率反射式飞行时间质谱研究团簇反应性；碰撞和光诱导解离、光电子能谱及红外光解离光谱研究团簇或(中间)产物结构；理论计算研究反应机理。实验和理论相结合获得每个过程的核心影响因素和调控方法，获得掺杂原子的关键作用及其与氮化物团簇之间的相互作用。在此基础上，提出可能的若干类团簇催化剂，在实现气相原子团簇催化N2形成氨反应的同时，为设计理想高效催化剂提供理论指导。

N2室温活化转化是一个重要且极具挑战的课题。目前该过程的微观反应机理、活性调控方法及核心影响因素仍不十分清楚。在分子水平获得上述信息对于理解相关反应、设计催化剂具有重要意义。气相团簇可作为理想模型从分子水平研究气-固反应表面活性位的构效关系。本项目中，我们采用离子阱耦合高分辨率反射式飞行时间质谱研究团簇反应性；碰撞和光诱导解离以及光电子能谱等研究团簇或产物结构；同时结合理论计算研究反应机理。实验和理论相结合获得含掺杂原子团簇准确的构效关系。对室温下N2活化转化形成N−X键（X=C, O, H等）开展研究，取得重要进展：1）提出了单金属-配体协同活化氮气新机理(Metal-Ligand Activation, MLA)，实现了利用单金属离子体系直接偶联N2和CO2制备N−C键。2）利用团簇的芳香特性以及去芳构化过程驱动N2和O2反应制NO。3）实现了N2和H2反应制备N−H键，获得了合成氨反应中的重要中间体MNH2和MNH单元。发表第一标注SCI论文10篇，含5篇J. Phys. Chem. Lett.。上述研究结果为从电子结构水平认识室温条件下N2转化的核心影响因素提供了科学依据，也为设计新型催化剂的活性位点等提供了重要信息。