Fang Zhongpu, Wang Qi, Li Yanli, Li Yi, Huang Shuping, Lin Wei, Chen Wenkai, Zhang Yongfan
State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou, Fujian 350116, China.
J Chem Phys. 2021 Feb 7;154(5):054703. doi: 10.1063/5.0039338.
Density functional theory calculations have been performed to study the reaction mechanism of N thermal reduction (NTR) over a single metal atom incorporated nitrogen-doped graphene. Our results reveal that the type of metal atoms and their coordination environments have a significant effect on the catalytic activity of NTR. Regarding CoN- and FeN-embedded graphene sheets that the metal atom is fourfold coordinated, they are inactive for NTR owing to the poor stability of the adsorbed H and N molecules. In contrast, if the monodisperse metal atom is surrounded by three N atoms, namely, CoN/G and FeN/G show activity toward NTR, and catalytic conversion of N into ammonia is achieved through the associative mechanism rather than the dissociative mechanism. Further investigations show that the synthesis of NH over the two surfaces is mainly through the formation of an NHNH intermediate; however, the detailed reaction mechanisms are sensitive to the type of metal atom introduced into N-doped graphene. Based on the calculated kinetic barriers, FeN/G exhibits a better catalytic activity for NTR. The superior performance of FeN/G can be attributed to the fact that this surface prefers a high spin-polarized state during the whole process of NTR, while the non-spin polarized state is predicted as the ground state for most of the elementary steps of N-fixation over CoN/G. The present study provides theoretical insights into developing graphene-based single atom catalysts with a high activity toward ammonia synthesis through NTR.
已进行密度泛函理论计算，以研究单个金属原子掺杂的氮掺杂石墨烯上的氮热还原（NTR）反应机理。我们的结果表明，金属原子的类型及其配位环境对NTR的催化活性有显著影响。对于金属原子为四重配位的CoN和FeN嵌入石墨烯片，由于吸附的H和N分子稳定性差，它们对NTR无活性。相比之下，如果单分散金属原子被三个N原子包围，即CoN/G和FeN/G对NTR表现出活性，并且通过缔合机制而非解离机制实现N到氨的催化转化。进一步研究表明，在这两个表面上合成NH主要是通过形成NHNH中间体；然而，详细的反应机理对引入氮掺杂石墨烯中的金属原子类型敏感。基于计算出的动力学势垒，FeN/G对NTR表现出更好的催化活性。FeN/G的优异性能可归因于这样一个事实，即在NTR的整个过程中，该表面倾向于高自旋极化状态，而对于CoN/G上大多数固氮基本步骤，非自旋极化状态被预测为基态。本研究为通过NTR开发对氨合成具有高活性的基于石墨烯的单原子催化剂提供了理论见解。
