Surface Ligand Evolution: Sulfur-Directed Covalent Bonding of PPh₃ on Pd₄S with Improved Semi-hydrogenation of Terminal Alkynes

Surface modification of metallic nanocatalysts with organic ligands has emerged as an effective strategy to enhance catalytic selectivity, although often at the expense of catalytic activity. In this study, we demonstrate a compelling approach by surface modifying Pd₄S nanocrystals with PPh₃ ligands, resulting in a catalyst with excellent catalytic activity and durable selectivity for the semi-hydrogenation of terminal alkynes. Experimental and theoretical investigations reveal that the presence of S sites on the Pd surface directs PPh₃ ligands to preferentially form covalent bonds with S, creating distinctive surface S═PPh₃ motifs. This configuration induces a partial positive charge on Pd, facilitating hydrogen transfer and thus promoting catalytic activity. Furthermore, the covalent bond between the ligand and catalyst surface forms a robust network, ensuring ligand stability and increasing the hydrogenation energy barrier of olefins. Consequently, the Pd₄S@PPh₃ catalyst exhibits an improved catalytic selectivity with durability in terminal alkyne semi-hydrogenation. This study introduces an effective strategy for designing selective hydrogenation catalysts with an enhanced performance.