Engineering strong metal–support interactions (SMSI) is an effective strategy for tuning structures and performances of supported metal catalysts but induces poor exposure of active sites. Here, we demonstrate a strong metal–support interaction via a reverse route (SMSIR) by starting from the final morphology of SMSI (fully-encapsulated core–shell structure) to obtain the intermediate state with desirable exposure of metal sites. Using core–shell nanoparticles (NPs) as a building block, the Pd–FeOx NPs are transformed into a porous yolk–shell structure along with the formation of SMSIR upon treatment under a reductive atmosphere. The final structure, denoted as Pd–Fe3O4–H, exhibits excellent catalytic performance in semi-hydrogenation of acetylene with 100% conversion and 85.1% selectivity to ethylene at 80 °C. Detailed electron microscopic and spectroscopic experiments coupled with computational modeling demonstrate that the compelling performance stems from the SMSIR, favoring the formation of surface hydrogen on Pd instead of hydride.
Ceria
has been used as a hydrogenation catalyst especially in selective
alkyne hydrogenation, but the reaction mechanism regarding the role
of different surface hydrogen species remains unclear. In this work,
we utilized in situ neutron and infrared vibration
spectroscopy to show the catalytic role of cerium hydride (Ce–H)
and hydroxyl (OH) groups in acetylene hydrogenation over ceria surfaces
with different degree of reduction. In situ inelastic
neutron scattering spectroscopy (INS) proved that not only Ce–H
but also surface atomic hydrogen species on the reduced ceria surface
can participate in acetylene semihydrogenation. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)
results implied that bridging OH groups both on the oxidized and reduced
ceria are active in the selective hydrogenation of acetylene. It appears
that surface Ce–H is more reactive than the coexisting OH species
on the reduced ceria surface, but over-reduction of ceria also results
in strongly bound species that may lead to catalyst deactivation.
These spectroscopic results clearly explain the reaction mechanism
including not only the surface chemistry but also the nature of the
active hydrogen species for selective hydrogenation over ceria, providing
insights into the design of more active and stable ceria-based catalysts
for hydrogenation reactions.
A series of F‐substituted Na2/3Ni1/3Mn2/3O2−xFx (x = 0, 0.03, 0.05, 0.07) cathode materials have been synthesized and characterized by solid‐state 19F and 23Na NMR, X‐ray photoelectron spectroscopy, and neutron diffraction. The underlying charge compensation mechanism is systematically unraveled by X‐ray absorption spectroscopy and electron energy loss spectroscopy (EELS) techniques, revealing partial reduction from Mn4+ to Mn3+ upon F‐substitution. It is revealed that not only Ni but also Mn participates in the redox reaction process, which is confirmed for the first time by EELS techniques, contributing to an increase in discharge specific capacity. The detailed structural transformations are also revealed by operando X‐ray diffraction experiments during the intercalation and deintercalation process of Na+, demonstrating that the biphasic reaction is obviously suppressed in the low voltage region via F‐substitution. Hence, the optimized sample with 0.05 mol f.u.−1 fluorine substitution delivers an ultrahigh specific capacity of 61 mAh g−1 at 10 C after 2000 cycles at 30 °C, an extraordinary cycling stability with a capacity retention of 75.6% after 2000 cycles at 10 C and 55 °C, an outstanding full battery performance with 89.5% capacity retention after 300 cycles at 1 C. This research provides a crucial understanding of the influence of F‐substitution on the crystal structure of the P2‐type materials and opens a new avenue for sodium‐ion batteries.
Recently, there have
been renewed interests in exploring new catalysts
for ammonia synthesis under mild conditions. Electride-based catalysts
are among the emerging ones. Ruthenium particles supported on an electride
composed of a mixture of calcium and aluminum oxides (C12A7) have
attracted great attention for ammonia synthesis due to their facile
ability in activating N2 under ambient pressure. However,
the exact nature of the reactive hydrogen species and the role of
electride support still remain elusive for this catalytic system.
In this work, we report for the first time that the surface-adsorbed
hydrogen, rather than the hydride encaged in the C12A7 electride,
plays a major role in ammonia synthesis over the Ru/C12A7 electride
catalyst with the aid of in situ neutron scattering
techniques. Combining in situ neutron diffraction,
inelastic neutron spectroscopy, density functional theory (DFT) calculation,
and temperature-programmed reactions, the results provide direct evidence
for not only the presence of encaged hydrides during ammonia synthesis
but also the strong thermal and chemical stability of the hydride
species in the Ru/C12A7 electride. Steady state isotopic transient
kinetic analysis (SSITKA) of ammonia synthesis showed that the coverage
of reactive intermediates increased significantly when the Ru particles
were promoted by the electride form (coverage up to 84%) of the C12A7
support rather than the oxide form (coverage up to 15%). Such a drastic
change in the intermediate coverage on the Ru surface is attributed
to the positive role of electride support where the H2 poisoning
effect is absent during ammonia synthesis over Ru. The finding of
this work has significant implications for understanding catalysis
by electride-based materials for ammonia synthesis and hydrogenation
reactions in general.
The construction of heterogeneous frustrated Lewis pairs (FLPs) with performance comparable to or surpassing the homogeneous counterparts in H 2 activation is a long-standing challenge. Herein, sterically hindered Lewis acid ("B" center) and Lewis base ("N" center) sites were anchored within the rigid lattice of highly crystalline hexagonal boron nitride (h-BN) scaffolds. The active sites were created via precision defect regulation during the molten-salt-involved (NaNH 2 and NaBH 4 ) h-BN construction procedure. The as-afforded h-BN scaffolds achieved highly efficient H 2 /D 2 activation and dissociation under ambient pressure via FLP-like behavior, and attractive catalytic efficiency in hydrogenation reactions surpassing the current heterogeneous analogues.
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