Reaction sites optimization mediated by ligand coverage for semi‐hydrogenation of different alkynes

Precise regulation of catalysts active sites is the key to optimizing activity. In this work, a strategy for modulating alkyne adsorption sites by modifying the support is proposed. A series of Pd/ZSM‐5@PPh3‐X with different coverage of triphenylphosphine (PPh3) were synthesized. Pd/ZSM‐5@PPh3‐X enable efficient semi‐hydrogenation of alkynes under mild conditions. Specifically, the catalyst with lower surface ligand coverage (Pd/ZSM‐5@PPh3‐2) exhibits a preference for the hydrogenation of 2‐methyl‐3‐butyn‐2‐ol, while the catalyst with higher ligand coverage (Pd/ZSM‐5@PPh3‐10) favors the conversion of phenylacetylene. Both catalysts maintain an alkene selectivity exceeding 94%. Comprehensive experimental, characterization, and computational analyses revealed that for 2‐methyl‐3‐butyn‐2‐ol, which adsorbs on the palladium surface, the PPh3 inhibits the strong adsorption of alkynes, thereby preventing catalyst self‐poisoning. Conversely, the high PPh3 coverage redirects the adsorption site of phenylacetylene to the support surface, and the enhanced hydrogen spillover accelerates the reaction. This ligand‐modulated strategy offers guidance for the rational design of chemoselective catalysts.