Surface-Clean Au 25 Nanoclusters in Modulated Microenvironment Enabled by Metal-Organic Frameworks for Enhanced Catalysis.

Metal nanoclusters (NCs) with atomically precise structures have sparked interest in catalysis. Unfortunately, their high aggregation tendency and the spatial resistance of surface ligands pose significant challenges. Herein, Au 25 NCs are encapsulated into isoreticular metal-organic frameworks (MOFs), namely UiO-66-X (X = H, NH 2 , OH, and NO 2 ), followed by the removal of surface ligands on Au 25 NCs. The resulting surface-clean Au 25 NCs, protected by the MOF spatial confinement, exhibit much superior activity and stability with respect to pristine Au 25 NCs in the oxidative esterification of furfural. Remarkably, experimental and theoretical results jointly demonstrate that diverse functional groups on UiO-66-X modulate the Au 25 electronic state, giving rise to the discriminated substrate adsorption energy of Au 25 @UiO-66-X. As a result, the high electron density and suitable substrate adsorption ability dominate the activity trend: Au 25 @UiO-66-NH 2 > Au 25 @UiO-66-OH > Au 25 @UiO-66 > Au 25 @UiO-66-NO 2 . This work develops a new strategy for the stabilization of surface-clean metal NCs in pore wall-engineered MOFs for enhanced catalysis.