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

Supported low-nuclearity cluster catalysts (LNCCs, for example, the number of metal atoms is 2 <= n <= 10), between single atoms and nanoclusters in size, possess not only maximum atom efficiency but also highly tunable structures, including nuclearity, composition, local chemical environment, and quantum electronic structures, holding great promise for advanced catalysis in terms of high activity, high selectivity, and high stability at low cost. In contrast to single-atom catalysts, LNCCs can provide multiple adsorption sites and initiate atom-atom synergies within clusters, offering great possibilities to remarkably boost the catalytic reactivity. The electronic structures and catalytic performance of LNCCs can be highly atom dependent. The synthesis of atom-precise LNCCs is vital for catalytic performance optimization and the understanding of structure-activity relationships but remains greatly challenging. This perspective first summarizes the atom-controlled synthetic strategies for atom-precise LNCCs, including size-selected cluster deposition, selected-multinuclear precursor grafting, and atomic layer deposition, and then discusses the state-of-the-art techniques for the statistical structural characterization of atom-precise LNCCs and their atom-dependent catalytic properties. Therein, we emphasize the essential roles of prominent electronic and geometric effects as well as atom-atom synergies in the atom-by-atom controlled catalytic performance, particularly activity and stability. Finally, we discuss the opportunities and challenges of LNCCs in heterogeneous catalysis.