Reducing particle size in supported metal catalysts to single-atom level isolates the active metal sites and maximizes the atomic utilization efficiency. However, the large inter-atom distance, particularly in low-loading single-atom catalyst (SAC), is not favorable for a complex reaction where two (or more) reactants have to be activated. A key question is how to control the inter-atom distances to promote dinuclear-type coactivation at the adjacent metal sites. Here, it is reported that reducing the average inter-atom distance of copper SACs supported on carbon nitride (C3 N4 ) to 0.74 ± 0.13 nm allows these catalysts to exhibit a dinuclear-type catalytic mechanism in the nitrile-azide cycloaddition. Operando X-ray absorption fine structure study reveals a dynamic ligand exchange process between nitrile and azide, followed by their coactivation on dinuclear Cu SAC sites to form the tetrazole product. This work highlights that reducing the nearest-neighbor distance of SAC allows the mechanistic pathway to diversify from single-site to multisite catalysis.
Keywords: 1,3-dipolar cycloaddition; dinuclear-type catalysis; next-nearest distance; ultrahigh-loading single-atom catalysts.
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