Construction of D–A Type COFs Decorated With PdCu Alloy Nanoparticles for Photocatalytic Semihydrogenation of Alkynes

ABSTRACT The selective semihydrogenation of alkynes constitutes a critical synthetic step in fine chemicals and polymer materials. However, overhydrogenation has long posed a formidable challenge in achieving high alkene selectivity. Here, a donor–acceptor (D–A) covalent organic framework (TptBtt) decorated with PdCu alloy nanoparticles (NPs) was constructed as an efficient photocatalyst for the semihydrogenation of phenylacetylene (PA) under visible‐light irradiation. The optimized PdCu ₂ /TptBtt with a Cu:Pd molar ratio of 2:1 exhibits exceptional performance, achieving > 99% PA conversion with 95.2% selectivity for phenylethylene (PE). Comprehensive characterization confirms the formation of PdCu alloy NPs, which induces electron donation from Cu to Pd and downshifts the Pd d‐band center. This electronic modulation weakens PA chemisorption and suppresses the formation of highly reactive adsorbed hydrogen species, thereby preventing overhydrogenation. Moreover, the PdCu alloys confined within TptBtt pores significantly suppress photogenerated electron–hole recombination via a Schottky junction, with the separated electrons subsequently promoting the generation of active hydrogen species for selective hydrogenation. Finally, a synergetic catalytic mechanism is discussed in depth at the molecular scale via in situ DRIFTS. This work illuminates a general paradigm for modulating catalytic selectivity through D–A COF‐bimetallic synergy, guiding the rational design of multifunctional photocatalytic systems.