Nevertheless, the fulfillment of all these requirements in one catalytic material has yet to be accomplished, even for well-established reactions like heterogeneously-catalyzed hydrogenations studied since the 1880’s by Wilde, Sabatier, and Senderens 1, 2. The ultimate mission of researchers working in heterogeneous catalysis is the identification of active ensembles with a high density to enable efficient turnover while avoiding undesired intermolecular interactions, and exhibiting long-term stability to ensure a well-defined performance. Similar metal trimers are also identified in Pd 4S, evidencing the pervasiveness of these selective ensembles in supported palladium sulfides. Apart from defining a structure integrating spatially-isolated palladium trimers, the active ensembles, the modifier imparts a bifunctional mechanism and weak binding of the organic intermediates. The exceptional behavior is linked to the multifunctional role of sulfur. Here, we report a simple treatment of palladium nanoparticles supported on graphitic carbon nitride with aqueous sodium sulfide, which directs the formation of a nanostructured Pd 3S phase with controlled crystallographic orientation, exhibiting unparalleled performance in the semi-hydrogenation of alkynes in the liquid phase. Although the geometric and electronic requirements are known, a literature survey illustrates the difficulty of transferring this knowledge into an efficient and robust catalyst. Ensemble control has been intensively pursued for decades to identify sustainable alternatives to the Lindlar catalyst (PdPb/CaCO 3) applied for the partial hydrogenation of alkynes in industrial organic synthesis.
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