5 research outputs found
The Key Gold: Enhanced Platinum Catalysis for the Selective Hydrogenation of α,ÎČ-Unsaturated Ketone
AuPt alloy nanoparticles
(NPs) were facilely synthesized with oleylamine
as the stabilizing ligand and characterized by high-resolution transmission
electron microscopy, powder X-ray diffraction, inductively coupled
plasma-atomic emission spectrometer analysis, and so on. In addition,
the AuPt alloys supported by the nano CeO<sub>2</sub> exhibit high
selectivity and efficiency in hydrogenation of benzylidene acetone
under ambient temperature and pressure. By analyzing the catalytic
performance over the NPs with different Au:Pt compositions, we found
that the TON<sub>Pt</sub> values (based on the number of Pt atoms)
vary in the same trend with the change of conversion. Despite that
gold itself shows no catalytic activity, the improved conversion and
TON<sub>Pt</sub> with the alloy catalysts clearly show the promotion
effect of gold on the catalytic activity of the platinum. The inactive
metal significantly improves the catalytic activity of active metal,
which shows that the AuPt alloy exhibits an interesting synergistic
effect
A New Crystal Structure of Au<sub>36</sub> with a Au<sub>14</sub> Kernel Cocapped by Thiolate and Chloride
This
study presents a new crystal structure of a gold nanocluster
coprotected by thiolate and chloride, with the formula of Au<sub>36</sub>(SCH<sub>2</sub>Ph-<sup>t</sup>Bu)<sub>8</sub>Cl<sub>20</sub>. This
nanocluster is composed of a Au<sub>14</sub> core with two Cl atoms,
a pair of pentameric Au<sub>5</sub>(SCl<sub>5</sub>) staple motifs,
and a pair of hexameric Au<sub>6</sub>(S<sub>3</sub>Cl<sub>4</sub>) motifs. It is noteworthy that the âAuâClâAuâ
staple motifs are observed for the first time in thiolate protected
gold nanoclusters. More importantly, the formation of the ClâAu<sub>3</sub> motifs is found to be mainly responsible for the configuration
of the gold nanocluster. This work will offer a new perspective to
understand how the ligands affect the crystal structure of gold nanocluster
PdâNi Alloy Nanoparticles as Effective Catalysts for MiyauraâHeck Coupling Reactions
In
this work, PdâNi alloy nanoparticles (NPs) were produced
by a facile and efficient one-pot synthetic strategy in the presence
of oleylamine (OAm) and triphenylphosphine (TPP). Transmission electron
microscopy (TEM), energy-dispersive spectrometry (EDS) mapping, inductively
coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray diffraction
(XRD) were used to investigate the structure of PdâNi alloy
NPs, which demonstrated that the as-prepared alloy NPs possessed uniform
sizes and tunable compositions. Importantly, we found that TPP could
affect the morphology of the PdâNi alloy. When TPP was absent
from the reaction, the morphology of the PdâNi alloy was not
uniform. In addition, the as-prepared PdâNi alloy NPs showed
conspicuous composition-dependent catalytic activities for the MiyauraâHeck
reaction. In the series of the PdâNi alloy NPs, Pd<sub>1</sub>Ni<sub>1</sub> has an excellent effect for the MiyauraâHeck
reactions. Furthermore, the PdâNi alloy NPs were also effective
for different substrates in the MiyauraâHeck reactions. Compared
to pure palladium, the PdâNi alloy NPs as the catalysts show
better catalytic activity, selectivity, and stability
A Robust and Efficient Pd<sub>3</sub> Cluster Catalyst for the Suzuki Reaction and Its Odd Mechanism
The
palladium-catalyzed SuzukiâMiyaura coupling reaction
is one of the most versatile and powerful tools for constructing synthetically
useful unsymmetrical arylâaryl bonds. In designing a Pd cluster
as a candidate for efficient catalysis and mechanistic investigations,
it was envisaged to study a case intermediate between, although very
different from, the âclassicâ Pd(0)ÂL<i><sub>n</sub></i> and Pd nanoparticle families of catalysts. In this work,
the cluster [Pd<sub>3</sub>ClÂ(PPh<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub>]<sup>+</sup>[SbF<sub>6</sub>]<sup>â</sup> (abbreviated <b>Pd</b><sub><b>3</b></sub><b>Cl</b>) was synthesized and fully characterized as a remarkably robust
framework that is stable up to 170 °C and fully air-stable. <b>Pd</b><sub><b>3</b></sub><b>Cl</b> was found to catalyze
the SuzukiâMiyaura CâC cross-coupling of a variety of
aryl bromides and arylboronic acids under ambient aerobic conditions.
The reaction proceeds while keeping the integrity of the cluster framework
all along the catalytic cycle via the intermediate <b>Pd</b><sub><b>3</b></sub><b>Ar</b>, as evidenced by mass spectrometry
and quick X-ray absorption fine structure. In the absence of the substrate
under the reaction conditions, the <b>Pd</b><sub><b>3</b></sub><b>OH</b> species was detected by mass spectrometry,
which strongly favors the âoxo-Pdâ pathway for the transmetalation
step involving substitution of the Cl ligand by OH followed by binding
of the OH ligand with the arylboronic acid. The kinetics of the SuzukiâMiyaura
reaction shows a lack of an induction period, consistent with the
lack of cluster dissociation. This study may provide new perspectives
for the catalytic mechanisms of CâC cross-coupling reactions
catalyzed by metal clusters
Highly Selective and Sharp Volcano-type Synergistic Ni<sub>2</sub>Pt@ZIF-8-Catalyzed Hydrogen Evolution from Ammonia Borane Hydrolysis
Ammonia borane hydrolysis is considered
as a potential means of
safe and fast method of H<sub>2</sub> production if it is efficiently
catalyzed. Here a series of nearly monodispersed alloyed bimetallic
nanoparticle catalysts are introduced, optimized among transition
metals, and found to be extremely efficient and highly selective with
sharp positive synergy between 2/3 Ni and 1/3 Pt embedded inside a
zeolitic imidazolate framework (ZIF-8) support. These catalysts are
much more efficient for H<sub>2</sub> release than either Ni or Pt
analogues alone on this support, and for instance the best catalyst
Ni<sub>2</sub>Pt@ZiF-8 achieves a TOF of 600 mol<sub>H<sub>2</sub></sub>·mol<sub>catal</sub><sup>â1</sup>·min<sup>â1</sup> and 2222 mol<sub>H<sub>2</sub></sub>·mol<sub>Pt</sub><sup>â1</sup>·min<sup>â1</sup> under ambient
conditions, which overtakes performances of previous Pt-base catalysts.
The presence of NaOH boosts H<sub>2</sub> evolution that becomes 87
times faster than in its absence with Ni<sub>2</sub>Pt@ZiF-8, whereas
NaOH decreases H<sub>2</sub> evolution on the related Pt@ZiF-8 catalyst.
The ZIF-8 support appears outstanding and much more efficient than
other supports including graphene oxide, active carbon and SBA-15
with these nanoparticles. Mechanistic studies especially involving
kinetic isotope effects using D<sub>2</sub>O show that cleavage by
oxidative addition of an OâH bond of water onto the catalyst
surface is the rate-determining step of this reaction. The remarkable
catalyst activity of Ni<sub>2</sub>Pt@ZiF-8 has been exploited for
successful tandem catalytic hydrogenation reactions using ammonia
borane as H<sub>2</sub> source. In conclusion the selective and remarkable
synergy disclosed here together with the mechanistic results should
allow significant progress in catalyst design toward convenient H<sub>2</sub> generation from hydrogen-rich substrates in the close future