Improving Catalytic Hydrogenation Performance of Pd Nanoparticles by Electronic Modulation Using Phosphine Ligands

Tuning the activity and selectivity of metal nanoparticles (NPs) is a long-term pursuit in the field of catalysis. Herein, we report successfully improving both the activity and chemoselectivity of Pd NPs (1.1 nm) with triphenylphosphine (PPh₃) cross-linked in the nanopore of FDU-12. The electron-donating effect of PPh₃ increases the surface electronic density of Pd NPs and weakens the Pd–H bond, as evidenced by the results of XPS, in situ FT-IR adsorption of CO, and H₂–D₂ exchange reactions. Consequently, Pd NPs modified with PPh₃ obtain >99% selectivity to 1-phenylethanol in acetophenone hydrogenation and 94% selectivity to styrene in phenylacetylene hydrogenation. Furthermore, the activity of Pd NPs is enhanced and suppressed by PPh₃, respectively, in the hydrogenation of electrophilic nitro compounds and nucleophilic carbonyl substrates. Our primary results shed some light on judiciously choosing organic ligands for modifying the catalytic performance of metal NPs toward specific chemical transformations