3 research outputs found
Facile Synthesis of Iridium Nanocrystals with Well-Controlled Facets Using Seed-Mediated Growth
Iridium
nanoparticles have only been reported with roughly spherical
shapes and sizes of 1–5 nm, making it impossible to investigate
their facet-dependent catalytic properties. Here we report for the
first time a simple method based on seed-mediated growth for the facile
synthesis of Ir nanocrystals with well-controlled facets. The essence
of this approach is to coat an ultrathin conformal shell of Ir on
a Pd seed with a well-defined shape at a relatively high temperature
to ensure fast surface diffusion. In this way, the facets on the initial
Pd seed are faithfully replicated in the resultant Pd@Ir core–shell
nanocrystal. With 6 nm Pd cubes and octahedra encased by {100} and
{111} facets, respectively, as the seeds, we have successfully generated
Pd@Ir cubes and octahedra covered by Ir{100} and Ir{111} facets. The
Pd@Ir cubes showed higher H<sub>2</sub> selectivity (31.8% vs 8.9%)
toward the decomposition of hydrazine compared with Pd@Ir octahedra
with roughly the same size
Synthesis and Characterization of Ru Cubic Nanocages with a Face-Centered Cubic Structure by Templating with Pd Nanocubes
Nanocages have received
considerable attention in recent years
for catalytic applications owing to their high utilization efficiency
of atoms and well-defined facets. Here we report, for the first time,
the synthesis of Ru cubic nanocages with ultrathin walls, in which
the atoms are crystallized in a face-centered cubic (fcc) rather than
hexagonal close-packed (hcp) structure. The key to the success of
this synthesis is to ensure layer-by-layer deposition of Ru atoms
on the surface of Pd cubic seeds by controlling the reaction temperature
and the injection rate of a RuÂ(III) precursor. By selectively etching
away the Pd from the Pd@Ru core–shell nanocubes, we obtain
Ru nanocages with an average wall thickness of 1.1 nm or about six
atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal
structure rather than the hcp structure observed in bulk Ru. The synthesis
has been successfully applied to Pd cubic seeds with different edge
lengths in the range of 6–18 nm, with smaller seeds being more
favorable for the formation of Ru shells with a flat, smooth surface
due to shorter distance for the surface diffusion of the Ru adatoms.
Self-consistent density functional theory calculations indicate that
these unique fcc-structured Ru nanocages might possess promising catalytic
properties for ammonia synthesis compared to hcp Ru(0001), on the
basis of strengthened binding of atomic N and substantially reduced
activation energies for N<sub>2</sub> dissociation, which is the rate-determining
step for ammonia synthesis on hcp Ru catalysts
Facile Synthesis of Ru-Based Octahedral Nanocages with Ultrathin Walls in a Face-Centered Cubic Structure
Noble-metal
nanocages with ultrathin (less than 2 nm) walls and
well-defined facets have received great interest owing to their remarkable
utilization efficiency of atoms and facet-dependent catalytic activities
toward various reactions. Here, we report the synthesis of Ru-based
octahedral nanocages covered by {111} facets, together with ultrathin
walls in a face-centered cubic (fcc) structure rather than the hexagonal
close-packed (hcp) of bulk Ru. The involvement of slow injection for
the RuÂ(III) precursor, the introduction of KBr, and the use of elevated
temperature were all instrumental to the formation of Pd@Ru core–shell
octahedra with a conformal, uniform shell and a smooth surface. The
{111} facets were well preserved during the selective removal of the
Pd cores via wet etching, even when the Ru walls were only five atomic
layers in thickness. Through in situ XRD, we demonstrated that the
fcc structure of the Ru nanocages was stable up to 300 °C. We
also used first-principles, self-consistent density functional theory
calculations to study the adsorption and dissociation of N<sub>2</sub> as a means to predict the catalytic performance toward ammonia synthesis.
Our results suggested that the small proportions of Pd atoms left
behind in the walls during etching could play a key role in stabilizing
the adsorption of N<sub>2</sub> as well as in reducing the activation
energy barrier to N<sub>2</sub> dissociation