3 research outputs found
Violet Emission in ZnO Nanorods Treated with High-Energy Hydrogen Plasma
Violet
photoluminescence was observed in high-energy hydrogen-plasma-treated
ZnO nanorods at 13 K. The photoluminescence spectrum is dominated
by a strong violet emission and a shoulder attributed to excitonic
emission. The violet emission shows normal thermal behavior with an
average lifetime of about 1 μs at 13 K. According to the time-resolved
and excitation density-dependent photoluminescence, it was found that
the violet emission is determined by at least two emitting channels,
which was confirmed by annealing experiments. Evidence was also given
that the violet emission is related to hydrogen. We suggested that
the hydrogen-related complex defects formed under high-energy hydrogen
plasma treatment are responsible for this violet emission
Copper-Based Intermetallic Electride Catalyst for Chemoselective Hydrogenation Reactions
The development of
transition metal intermetallic compounds, in
which active sites are incorporated in lattice frameworks, has great
potential for modulating the local structure and the electronic properties
of active sites, and enhancing the catalytic activity and stability.
Here we report that a new copper-based intermetallic electride catalyst,
LaCu<sub>0.67</sub>Si<sub>1.33</sub>, in which Cu sites activated
by anionic electrons with low work function are atomically dispersed
in the lattice framework and affords selective hydrogenation of nitroarenes
with above 40-times higher turnover frequencies (TOFs up to 5084 h<sup>–1</sup>) than well-studied metal-loaded catalysts. Kinetic
analysis utilizing isotope effect reveals that the cleavage of the
H–H bond is the rate-determining step. Surprisingly, the high
carrier density and low work function (LWF) properties of LaCu<sub>0.67</sub>Si<sub>1.33</sub> enable the activation of hydrogen molecules
with extreme low activation energy (<i>E</i><sub>a</sub> = 14.8 kJ·mol<sup>–1</sup>). Furthermore, preferential
adsorption of nitroarenes via a nitro group is achieved by high oxygen
affinity of LaCu<sub>0.67</sub>Si<sub>1.33</sub> surface, resulting
in high chemoselectivity. The present efficient catalyst can further
trigger the hydrogenation of other oxygen-containing functional groups
such as aldehydes and ketones with high activities. These findings
demonstrate that the transition metals incorporated in the specific
lattice site function as catalytically active centers and surpass
the conventional metal-loaded catalysts in activity and stability
Water Durable Electride Y<sub>5</sub>Si<sub>3</sub>: Electronic Structure and Catalytic Activity for Ammonia Synthesis
We
report an air and water stable electride Y<sub>5</sub>Si<sub>3</sub> and its catalytic activity for direct ammonia synthesis. It crystallizes
in the Mn<sub>5</sub>Si<sub>3</sub>-type structure and confines 0.79/f.u.
anionic electrons in the quasi-one-dimensional holes. These anionic
electrons strongly hybridize with yttrium 4d electrons, giving rise
to improved chemical stability. The ammonia synthesis rate using RuÂ(7.8
wt %)-loaded Y<sub>5</sub>Si<sub>3</sub> was as high as 1.9 mmol/g/h
under 0.1 MPa and at 400 °C with activation energy of ∼50
kJ/mol. Its strong electron-donating ability to Ru metal of Y<sub>5</sub>Si<sub>3</sub> is considered to enhance nitrogen dissociation
and reduce the activation energy of ammonia synthesis reaction. Catalytic
activity was not suppressed even after Y<sub>5</sub>Si<sub>3</sub>, once dipped into water, was used as the catalyst promoter. These
findings provide novel insights into the design of simple catalysts
for ammonia synthesis