Quantitative Description of Metal Center Organization and Interactions in Single-Atom Catalysts

Ultra-high-density single-atom catalysts (UHD-SACs) present unique opportunities for harnessing cooperative effects between neighboring metal centers. However, the lack of tools to establish correlations between the density, types, and arrangements of isolated metal atoms and the support surface properties hinders efforts to engineer advanced material architectures. Here, this work precisely describes the metal center organization in various mono- and multimetallic UHD-SACs based on nitrogen-doped carbon (NC) supports by coupling transmission electron microscopy with tailored machine-learning methods (released as a user-friendly web app) and density functional theory simulations. This approach quantifies the non-negligible presence of multimers with increasing atom density, characterizes the size and shape of these low-nuclearity clusters, and identifies surface atom density criteria to ensure isolation. Further, it provides previously inaccessible experimental insights into coordination site arrangements in the NC host, uncovering a repulsive interaction that influences the disordered distribution of metal centers in UHD-SACs. This observation holds in multimetallic systems, where chemically-specific analysis quantifies the degree of intermixing. These fundamental insights into the materials chemistry of single-atom catalysts are crucial for designing catalytic systems with superior reactivity. Advancing the design of single-atom catalysts requires reliable tools for discerning distinct metal center arrangements. This study leverages state-of-the-art microscopy, machine learning, and simulations to gain insights into the organization and interactions of metal centers and coordination sites in nitrogen-doped carbons. The findings highlight the impact of density- and support-mediated repulsive interactions in shaping spatial configurations and forming low-nuclearity species.image

Automated summary

This study investigates the organization and interactions of metal centers in ultra-high-density single-atom catalysts using microscopy, machine learning, and simulations. The findings reveal the presence of multimers with increasing atom density, characterize the size and shape of low-nuclearity clusters, and identify surface atom density criteria for isolation. Additionally, the study uncovers repulsive interactions that influence the disordered distribution of metal centers and quantifies the degree of intermixing in multimetallic systems.