1 research outputs found
Bimetallic Pd–Au/Highly Oriented Pyrolytic Graphite Catalysts: from Composition to Pairwise Parahydrogen Addition Selectivity
The
model Pd and Au mono- and bi-metallic (Pd–Au) catalysts
were prepared using vapor deposition of metals (Au and/or Pd) under
ultrahigh vacuum conditions on the defective highly oriented pyrolytic
graphite (HOPG) surface. The model catalysts were investigated using
the X-ray photoelectron spectroscopy and scanning tunneling microscopy
at each stage of the preparation procedure. For the preparation of
bimetallic catalysts, different procedures were used to get different
structures of PdAu particles (Au<sub>shell</sub>–Pd<sub>core</sub> or alloyed). All prepared catalysts showed rather narrow particles
size distribution with an average particles size in the range of 4–7
nm. Parahydrogen-enhanced nuclear magnetic resonance spectroscopy
was used as a tool for the investigation of Pd–Au/HOPG, Pd/HOPG,
and Au/HOPG model catalysts in propyne hydrogenation. In contrast
to Au sample, Pd, PdAu<sub>alloy</sub>, and Au<sub>shell</sub>–Pd<sub>core</sub> samples were shown to have catalytic activity in propyne
conversion, and pairwise hydrogen addition routes were observed. Moreover,
bimetallic samples demonstrated the 2- to 5-fold higher activity in
pairwise hydrogen addition in comparison to the monometallic Pd sample.
It was shown that the structures of bimetallic Pd–Au particles
supported on HOPG strongly affected their activities and/or selectivities
in propyne hydrogenation reaction: the catalyst with the Au<sub>shell</sub>–Pd<sub>core</sub> structure demonstrated higher pairwise
selectivity than that with the PdAu<sub>alloy</sub> structure. Thus,
the reported approach can be used as an effective tool for the synergistic
effects investigations in hydrogenation reactions over model bimetallic
Pd–Au catalysts, where the active component is supported on
a planar support