Surface and Interface Coordination Chemistry Learned from Model Heterogeneous Metal Nanocatalysts: From Atomically Dispersed Catalysts to Atomically Precise Clusters

Abstract

The surface and interface coordination structures of heterogeneous metal catalysts are crucial to their catalytic performance. However, the complicated surface and interface structures of heterogeneous catalysts make it challenging to identify the molecular-level structure of their active sites and thus precisely control their performance. To address this challenge, atomically dispersed metal catalysts (ADMCs) and ligand-protected atomically precise metal clusters (APMCs) have been emerging as two important classes of model heterogeneous catalysts in recent years, helping to build bridge between homogeneous and heterogeneous catalysis. This review illustrates how the surface and interface coordination chemistry of these two types of model catalysts determines the catalytic performance from multiple dimensions. The section of ADMCs starts with the local coordination structure of metal sites at the metal–support interface, and then focuses on the effects of coordinating atoms, including their basicity and hardness/softness. Studies are also summarized to discuss the cooperativity achieved by dual metal sites and remote effects. In the section of APMCs, the roles of surface ligands and supports in determining the catalytic activity, selectivity, and stability of APMCs are illustrated. Finally, some personal perspectives on the further development of surface coordination and interface chemistry for model heterogeneous metal catalysts are presented.

Dinuclear metal synergistic catalysis for energy conversion

“…Therefore, numerous efforts have been devoted to downsizing the catalyst particles and/or regulating the surface morphology to expose more metal active sites and improve the catalytic efficiency. [51][52][53][54] Mononuclear metal catalysts (MMCs), including conventional homogeneous mononuclear metal complexes and the emerging heterogeneous single-atom catalysts with atomically dispersed metals on solid supports, have received ever-growing interest in energy storage and conversion. [55][56][57] By virtue of the maximized utilization of metal active sites, MMCs usually display high catalytic activities and product selectivity.…”

“…Therefore, numerous efforts have been devoted to downsizing the catalyst particles and/or regulating the surface morphology to expose more metal active sites and improve the catalytic efficiency. 51–54…”

Atom-Precise Low-Nuclearity Cluster Catalysis: Opportunities and Challenges

“…Such synergetic effect could be more pronounced for the reactions such as hydrogenations, , and cleavage of C–C bonds , that require active sites of metal atom ensembles. In addition to the above, a part of metal atoms in low-nuclearity clusters, particularly for heteroatom LNCCs, might form strong bonding with both the underlying support and the active metal atoms (Figure b), similar to structure stabilizers, which could enable achieving high activity and high stability simultaneously. , Therefore, LNCCs hold promise for advanced catalysis in terms of high activity, high selectivity and high stability at low cost. , …”

“…25,26 Therefore, LNCCs hold promise for advanced catalysis in terms of high activity, high selectivity and high stability at low cost. 27,28 However, such high sensitivity of the catalytic performance of LNCCs also endows catalyst synthesis extremely challenging. To date, for conventional wet-chemistry methods of catalyst synthesis, including wet-impregnation, ion exchange, deposition−precipitation, and so forth, 29,30 largely decreasing metal loadings as well as choosing a proper support has been generally executed to restrain aggregations of metal atoms to form subnanometer clusters on supports.…”

Supported AgCuCl Nanoclusters as Bimetal Catalysts for Propylene Epoxidation with Molecular Oxygen

“…Nanoclusters protected by ligands as catalysts have the advantages of small size, homogeneous doping of bimetallic components, and high specific surface area after ligand removal . However, the stability of nanoclusters remains a major challenge for their applications in catalytic reactions. , To address this issue, appropriate supports have been used to stabilize the nanoclusters via strong metal–support interaction.…”