core–shell nanocomposite would significantly improve the low activity of Ag NPs
owing to a ready supply of hydrogen from the core of Pd NPs to Ag nanolayer shell
in a synergistic manner. Meanwhile, coating the core Pd NPs with a Ag nanolayer
would suppress overhydrogenation of alkenes at the Pd surface (Fig. 8). This
cooperative catalysis between the Pd core and Ag shell was expected to lead to the
selective semihydrogenation of alkynes under mild reaction conditions.
According to the above catalyst design concept, Pd@Ag comprising of Pd NPs
with a mean diameter of 26.2 nm in the core and a Ag nanolayer with a thickness of
approx. 1 nm as the shell was synthesized (Fig. 9) and demonstrated excellent alkene
Fig. 8 Design concept of
complementary bimetallic
core-Pd/shell-Ag catalyst
for selective
semihydrogenation of
alkynes
Fig. 9 Compositional and structural analysis of Pd@Ag. (a) TEM image; (b, c) HAADF-STEM
images; (d, e) elemental mapping images of (d) Pd and (e) Ag; and (f) composite overlay image
formed from (d) and (e). Reprinted with permission from [46]. Copyright 2016 American Chemical
Society
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K. Jitsukawa and T. Mitsudome