Surface-Exposed Pd Nanocluster Confined within a Ring-Shaped Polyoxometalate for Selective Hydrogenation

Developing efficient catalysts for selective hydrogenation of molecules bearing multiple reducible functional groups remains a major challenge. Palladium (Pd) nanoclusters are promising candidates owing to their strong H₂ activation ability, broad substrate compatibility, and unique surface properties. However, the controlled synthesis of small Pd nanoclusters with accessible, coordinatively unsaturated active sites remains difficult as they are prone to aggregation. In this study, a strategy is presented to fabricate surface-exposed Pd nanoclusters confined within a ring-shaped polyoxometalate (POM) via a mild solid-state reduction process (1 atm H₂, ≈25 °C). The resulting Pd nanocluster exhibits exceptional chemoselectivity in the hydrogenation of multifunctional substrates by preferentially adsorbing C═C and C≡C bonds on its discrete, exposed Pd surface with a well-defined coordination environment. Importantly, the rigid POM framework considerably stabilizes Pd nanocluster, enabling excellent reusability over multiple catalytic cycles. This study demonstrates a molecular templating approach for constructing robust and chemoselective metal nanocluster catalysts, offering new opportunities in the design of hydrogenation systems.