Surface Modification of PdZn Nanoparticles via Galvanic Replacement for the Selective Hydrogenation of Terminal Alkynes

In this study, a novel intermetallic compound-derived trimetallic surface site in nanoscale via the galvanic replacement reaction (GRR) is described. A PdZn/SiO2 catalyst, which exhibited high activity for the hydrogenation of phenylacetylene, was prepared. The GRR between the metallic Zn of the SiO2-supported PdZn intermetallic nanoparticles and the third metal precursor (e.g., Pb, Bi, Sn, Au, Ag, and Ga) was carried out, affording well-modified surface Pd sites. Among a series of catalysts modified by the third metals, the Pb-replaced catalyst exhibited an excellent yield of styrene, with the minimum overhydrogenation rate for alkane. The Pb-replaced catalysts were characterized by X-ray diffraction, scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy, CO Fourier transform infrared, and X-ray absorption fine structure measurements. The combination of these characterization methods revealed that (1) surface Zn atoms are successfully replaced by Pb during the GRR and (2) the prepared catalysts exhibit a bulk PdZn intermetallic structure, with their surface modified by Pb. The as-prepared catalysts were used for the selective hydrogenation of phenylacetylene to styrene. A control experiment using a Pd-Zn-Pb trimetallic solid-solution alloy led to a low catalytic activity, highlighting the validity and specificity of the Pb-modified PdZn surface structure.