Revealing the Origin of Catalytic Activity in an Alkynyl-Passivated Ag₁₈Cu₁₂ Nanocluster: Lewis Acid Site Matters

A growing body of research has demonstrated that ligand-passivated metal nanoclusters, particularly those stabilized by alkynyl ligands, exhibit catalytic activity without the need for ligand removal. The fundamental origin of catalytic activity in these seemingly inert yet highly active metal nanoclusters has remained unclear. In this study, we investigate an alkynyl-passivated [Ag₁₈Cu₁₂H₂(3-MeC₆H₄C≡C)₂₂(dppe)₄](SbF₆)₄ nanocluster (where dppe represents 1,2-bis(diphenylphosphino)ethane), which demonstrates high performance in the electrocatalytic nitrogen reduction reaction (NRR). Through comprehensive experimental and theoretical investigations, we reveal that the Lewis acid (LA) sites on the cluster surface are responsible for the observed high catalytic activity. Our mechanistic studies elucidate the role of these LA sites in nitrogen molecule activation. This work not only presents a model alkynyl-passivated metal nanocluster for understanding catalytic mechanisms in chemical transformations but also establishes Lewis acidity as an experimentally suitable descriptor for explaining the catalytic behavior of metal nanoclusters passivated by ligands beyond alkynyl.