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Abstract
Heterogeneous catalysis involves solid-state catalysts, among which metal nanoparticles
occupy an important position. Unfortunately, no two nanoparticles from conventional
synthesis are the same at the atomic level, though such regular nanoparticles can
be highly uniform at the nanometer level (e.g., size distribution ∼5%). In the long
pursuit of well-defined nanocatalysts, a recent success is the synthesis of atomically
precise metal nanoclusters protected by ligands in the size range from tens to hundreds
of metal atoms (equivalently 1-3 nm in core diameter). More importantly, such nanoclusters
have been crystallographically characterized, just like the protein structures in
enzyme catalysis. Such atomically precise metal nanoclusters merge the features of
well-defined homogeneous catalysts (e.g., ligand-protected metal centers) and enzymes
(e.g., protein-encapsulated metal clusters of a few atoms bridged by ligands). The
well-defined nanoclusters with their total structures available constitute a new class
of model catalysts and hold great promise in fundamental catalysis research, including
the atomically precise size dependent activity, control of catalytic selectivity by
metal structure and surface ligands, structure-property relationships at the atomic-level,
insights into molecular activation and catalytic mechanisms, and the identification
of active sites on nanocatalysts. This Review summarizes the progress in the utilization
of atomically precise metal nanoclusters for catalysis. These nanocluster-based model
catalysts have enabled heterogeneous catalysis research at the single-atom and single-electron
levels. Future efforts are expected to achieve more exciting progress in fundamental
understanding of the catalytic mechanisms, the tailoring of active sites at the atomic
level, and the design of new catalysts with high selectivity and activity under mild
conditions.