PdZn Intermetallic Nanostructure with Pd-Zn-Pd Ensembles for Highly Active and Chemoselective Semi-Hydrogenation of Acetylene

Intermetallic alloying of one active metal to another inert metal provides not only the improved dispersion of active centers but also a unique and homogeneous ensemble of active sites, thus offering new opportunities in a variety of reactions. Herein, we report that PdZn intermetallic nanostructure with Pd-Zn-Pd ensembles are both highly active and selective for the semihydrogenation of acetylene to ethylene, which is usually inaccessible due to the sequential hydrogenation to ethane. Microcalorimetric measurements and density functional theory calculations demonstrate that the appropriate spatial arrangement of Pd sites in the Pd-Zn-Pd ensembles of the PdZn alloy leads to the moderate sigma-bonding mode for acetylene with two neighboring Pd sites while the weak pi-bonding pattern of ethylene adsorption on the single Pd site, which facilitates the chemisorption toward acetylene and promotes the desorption of ethylene from the catalyst surface. As a result, it leads to the kinetic favor of the selective conversion of acetylene to ethylene.