Abstract:

Past decades have witnessed the flourish of single atom catalysts (SACs) owing to their high atom-utilization efficiency and completely exposed active sites, which endows SACs with remarkably enhanced catalytic activities for various reactions. In the early development stage of SACs, researchers focus on the improvement of the catalytic performance of the catalysts, whereas the intrinsic catalytic reaction mechanism and the relationship between the electronic states of the metal sites and catalytic performance are usually ignored. Moreover, some sophisticated and complex structures, such as dual-atom SACs, heteroatomic doped SACs, SACs with precise second coordination shell, and other synergetic catalysts containing SACs, were fabricated recently. The insight into electronic metal-support interaction (EMSI) aids the understanding of the catalytic mechanism and thus serves as a guide for the fabrication of heterogeneous catalysts. Notably, the uniform active sites and characteristic local coordination configuration of SACs provide excellent platforms to study EMSI and bridge the gap between homogeneous and heterogeneous catalysts, which will contribute to the understanding of structure-performance relationships and enhance the development of SACs and rational design of heterogeneous catalysts. EMSI is especially important in heterogeneous catalysis. Through the rational design of the local coordination environment of SACs, the electronic structure of active sites can be accurately regulated, which will shift their d-band centers. This significantly alters the adsorption capability of intermediates and influences the final catalytic performance of the catalysts. With the development of advanced operando characterization techniques, the evolution of configuration, electronic properties, and local coordination environment could be revealed, thus providing researchers with a clear picture of the intrinsic mechanism of the catalytic system. In addition, with the aid of theoretical calculations, catalyst screening will be considerably more convenient, which will significantly reduce the number of aimless trials. After the optimal structure is determined, researchers should devise precise fabrication methods to realize the configuration. Herein, we initially introduce the basic principles and effects of EMSI. The stabilization, electronic property regulation, and electron transfer tunneling effects of EMSI are the foundation of SACs synthesis and catalytic mechanism elucidation, of which the former requires strong coordination stabilization energies while the latter focuses on the electronic state evolution of the active sites. Subsequently, EMSI applications in several important heterogeneous catalysis processes, such as selective hydrogenation, alcohol oxidation, water-gas shift reaction, and hydroformylation, are reviewed. Finally, the review discusses the challenges and future prospects for the future development of EMSI on SACs.

Key words: Single atom catalysts, Electronic metal-support interaction, Electronic structure, Heterogeneous catalysis, Structure-performance relationship