11 research outputs found
Syntheses of Water-Soluble Octahedral, Truncated Octahedral, and Cubic Pt–Ni Nanocrystals and Their Structure–Activity Study in Model Hydrogenation Reactions
We developed a facile strategy to synthesize a series
of water-soluble
Pt, Pt<sub><i>x</i></sub>Ni<sub>1‑<i>x</i></sub> (0 < <i>x </i>< 1), and Ni nanocrystals. The octahedral,
truncated octahedral, and cubic shapes were uniformly controlled by
varying crystal growth inhibition agents such as benzoic acid, aniline,
and carbon monoxide. The compositions of the Pt<sub><i>x</i></sub>Ni<sub>1‑<i>x</i></sub> nanocrystals were effectively
controlled by choice of ratios between the Pt and Ni precursors. In
a preliminary study to probe their structure–activity dependence,
we found that the shapes, compositions, and capping agents strongly
influence the catalyst performances in three model heterogeneous hydrogenation
reactions
Synergistic Roles of the CoO/Co Heterostructure and Pt Single Atoms for High-Efficiency Electrocatalytic Hydrogenation of Lignin-Derived Bio-Oils
Electrochemical
hydrogeneration (ECH) of biomass-derived platform
molecules, which avoids the disadvantages in utilizing fossil fuel
and gaseous hydrogen, is a promising route toward value-added chemicals
production. Herein, we reported a CoO/Co heterostructure-supported
Pt single atoms electrocatalyst (Pt1-CoO/Co) that exhibited
an outstanding performance with a high conversion (>99%), a high
Faradaic
efficiency (87.6%), and robust stability (24 recyclability) at −20
mA/cm2 for electrochemical phenol hydrogenation to high-valued
KA oil (a mixture of cyclohexanol and cyclohexanone). Experimental
results and the density functional theory calculations demonstrated
that Pt1-CoO/Co presented strong adsorption of phenol and
hydrogen on the catalyst surface simultaneously, which was conducive
to the transfer of the adsorbed hydrogen generated on the single atom
Pt sites to activated phenol, and then, ECH of phenol with high performance
was achieved instead of the direct hydrogen evolution reaction. This
work described that the multicomponent synergistic single atom catalysts
could effectively accelerate the ECH of phenol, which could help the
achievement of large-scale biomass upgrading
Defect-Dominated Shape Recovery of Nanocrystals: A New Strategy for Trimetallic Catalysts
Here we present a
shape recovery phenomenon of Pt–Ni bimetallic
nanocrystals that is unequivocally attributed to the defect effects.
High-resolution electron microscopy revealed the overall process of
conversion from concave octahedral Pt<sub>3</sub>Ni to regular octahedral
Pt<sub>3</sub>Ni@Ni upon Ni deposition. Further experiments and theoretical
investigations indicated that the intrinsic defect-dominated growth
mechanism allows the site-selective nucleation of a third metal around
the defects to achieve the sophisticated design of trimetallic Pt<sub>3</sub>Ni@M core–shell structures (M = Au, Ag, Cu, Rh). Consideration
of geometrical and electronic effects indicated that trimetallic atomic
steps in Pt<sub>3</sub>Ni@M could serve as reactive sites to significantly
improve the catalytic performance, and this was corroborated by several
model reactions. The synthesis strategy based on our work paves the
way for the atomic-level design of trimetallic catalysts
Sophisticated Construction of Au Islands on Pt–Ni: An Ideal Trimetallic Nanoframe Catalyst
We have developed a priority-related
chemical etching method to
transfer the starting Pt–Ni polyhedron to a nanoframe. Utilizing
the lower electronegativity of Ni in comparison to Au atoms, in conjunction
with the galvanic replacement of catalytically active Au to Ni tops,
a unique Au island on a Pt–Ni trimetallic nanoframe is achieved.
The design strategy is based on the structural priority mechanism
of multimetallic nanocrystals during the synthesis and thus can be
generalized to other analogous metal–bimetallic nanocrystal
combinations (such as Pd and Cu islands on Pt–Ni nanoframes),
which is expected to pave the way for the future development of efficient
catalysts
Ultrathin Icosahedral Pt-Enriched Nanocage with Excellent Oxygen Reduction Reaction Activity
Cost-efficient utilization
of Pt in the oxygen reduction reaction
(ORR) is of great importance for the potential industrial scale demand
of proton-exchange membrane fuel cells. Designing a hollow structure
of a Pt catalyst offers a great opportunity to enhance the electrocatalytic
performance and maximize the use of precious Pt. Herein we report
a routine to synthesize ultrathin icosahedral Pt-enriched nanocages.
In detail, the Pt atoms were conformally deposited on the surface
of Pd icosahedral seeds, followed by selective removal of the Pd core
by a concentrated HNO<sub>3</sub> solution. The icosahedral Pt-enriched
nanocage that is a few atomic layers thick includes the merits of
abundant twin defects, an ultrahigh surface/volume ratio, and an ORR-favored
Pt{111} facet, all of which have been demonstrated to be promoting
factors for ORR. With a 10 times higher specific activity and 7 times
higher mass activity, this catalyst shows more extraordinary ORR activity
than the commercial Pt/C. The ORR activity of icosahedral Pt-enriched
nanocages outperforms the cubic and octahedral nanocages reported
in the literature, demonstrating the superiority of the icosahedral
nanocage structure
Bimetallic Ru–Co Clusters Derived from a Confined Alloying Process within Zeolite–Imidazolate Frameworks for Efficient NH<sub>3</sub> Decomposition and Synthesis
Herein, a series
of carbocatalysts containing Ru-based clusters have been prepared
by the assistance of zeolite–imidazolate frameworks (ZIFs).
The introduction of Ru is based on the adsorption of well-defined
Ru<sub>3</sub>(CO)<sub>12</sub> within the cavity of ZIFs following
decomposition at 900 °C. Moreover, without breaking the skeleton
and porosity of ZIFs, the as-generated Ru species would bond with
the Co nodes in situ to form bimetallic Ru–Co clusters if the
Co-bearing metal–organic frameworks were utilized as the host.
Within the confined space of ZIFs, the assembly of Ru and Co could
be rationally designed, and their structures could be sophisticatedly
controlled at the atomic scale. Among these Ru-based compositions,
the Ru–Co clusters@N–C exhibited remarkable catalytic
activity for the NH<sub>3</sub> decomposition to H<sub>2</sub> and
NH<sub>3</sub> synthesis versus Ru–Co NPs@N–C, Ru clusters@N–C,
and Ru NPs@N–C. This study may open up a new routine to synthesize
metallic clusters or other subnano structures by the confinement of
ZIFs
Ionic Exchange of Metal–Organic Frameworks to Access Single Nickel Sites for Efficient Electroreduction of CO<sub>2</sub>
Single-atom catalysts often exhibit
unexpected catalytic activity
for many important chemical reactions because of their unique electronic
and geometric structures with respect to their bulk counterparts.
Herein we adopt metal–organic frameworks (MOFs) to assist the
preparation of a catalyst containing single Ni sites for efficient
electroreduction of CO<sub>2</sub>. The synthesis is based on ionic
exchange between Zn nodes and adsorbed Ni ions within the cavities
of the MOF. This single-atom catalyst exhibited an excellent turnover
frequency for electroreduction of CO<sub>2</sub> (5273 h<sup>–1</sup>), with a Faradaic efficiency for CO production of over 71.9% and
a current density of 10.48 mA cm<sup>–2</sup> at an overpotential
of 0.89 V. Our findings present some guidelines for the rational design
and accurate modulation of nanostructured catalysts at the atomic
scale
Design of N‑Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction
We develop a host-guest strategy
to construct an electrocatalyst
with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate
its activity for oxygen reduction reaction in acidic electrolyte.
Our catalyst exhibits superior oxygen reduction reaction performance,
with comparable onset potential (<i>E</i><sub>onset</sub>, 1.06 vs 1.03 V) and half-wave potential (<i>E</i><sub>1/2</sub>, 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell
test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts
in H<sub>2</sub>/O<sub>2</sub> and H<sub>2</sub>/air. In addition,
this cathode catalyst with dual metal sites is stable in a long-term
operation with 50 000 cycles for electrode measurement and
100 h for H<sub>2</sub>/air single cell operation. Density functional
theory calculations reveal the dual sites is favored for activation
of O-O, crucial for four-electron oxygen reduction
Ordered Porous Pd Octahedra Covered with Monolayer Ru Atoms
Monolayer
Ru atoms covered highly ordered porous Pd octahedra have
been synthesized via the underpotential deposition and thermodynamic
control. Shape evolution from concave nanocube to octahedron with
six hollow cavities was observed. Using aberration-corrected high-resolution
transmission electron microscopy and X-ray photoelectron spectroscopy,
we provide quantitative evidence to prove that only a monolayer of
Ru atoms was deposited on the surface of porous Pd octahedra. The
as-prepared monolayer Ru atoms covered Pd nanostructures exhibited
excellent catalytic property in terms of semihydrogenation of alkynes
Atomically Dispersed Ru on Ultrathin Pd Nanoribbons
We
report a one-pot synthesis of atomically dispersed Ru on ultrathin
Pd nanoribbons. By using synchrotron radiation photoemission spectroscopy
(SRPES) and extended X-ray absorption fine structure (EXAFS) measurements
in combination with aberration corrected high-resolution transmission
electron microscopy (HRTEM), we show that atomically dispersed Ru
with content up to 5.9% was on the surface of the ultrathin nanoribbon.
Furthermore, the ultrathin Pd/Ru nanoribbons could remarkably prohibit
the hydrogenolysis in chemoselective hydrogenation of Cî—»C bonds,
leading to an excellent catalytic selectivity compared with commercial
Pd/C and Ru/C