Insights into Electronic Interaction of Pd and Cu in Pd–Cu/Al2O3 Catalyst for Selective Hydrogenation of Phenylacetylene to Styrene

The removal of dienes and arylalkynes via selective hydrogenation can prolong the lifetime of catalysts in the hydrogenation of ethylene tar. Besides, the selective hydrogenation of phenylacetylene to produce styrene plays a crucial role in improving styrene purity and preventing catalyst poisoning during the downstream polymerization process. However, this reaction has long been plagued by the difficulty of balancing catalytic activity with styrene selectivity and the tendency for phenylacetylene to undergo excessive hydrogenation. To address this issue, this work proposes a strategy for the improvement of styrene selectivity through synergistic regulation of the geometric and electronic structures of Pd catalysts with Cu promoter. A series of PdCu/Al2O3 catalysts with different Cu/Pd ratios were synthesized and evaluated in the hydrogenation of phenylacetylene. Results showed that the introduction of Cu significantly improved the styrene selectivity of the palladium-based catalyst, and the catalyst with a Cu/Pd mass ratio of 2 exhibited the best performance. After 40 min of reaction, the phenylacetylene conversion of PdCu2/Al2O3 reached a styrene yield of 90.10%, higher than that of the unmodified 0.5%Pd/Al2O3 (85.71%). Structural characterization revealed that, as the Cu loading increased, the formation of PdCu alloy species was promoted and intermetallic interactions were intensified. Cu preferentially interacts with highly active Pd sites, promoting the formation of positively charged Pd+ species and suppressing the generation of β-H species, which inhibited the deep hydrogenation reaction. Concurrently, electron transfer from Pd to Cu reduces the electron density surrounding Pd, and the introduction of Cu leads to center of the Pd d-band downward. This phenomenon weakens the adsorption of styrene at Pd sites and accelerates its desorption, improving the styrene selectivity. Through the synergistic regulation of geometric structure, electronic structure, and interfacial adsorption behavior, an optimized balance between catalytic activity and selectivity can be achieved. This study provides an effective catalyst design strategy for the selective hydrogenation of phenylacetylene to styrene and offers an important theoretical basis for the rational construction of Pd-based catalyst systems.