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 σ-bonding mode for acetylene
with two neighboring Pd sites while the weak π-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.
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