19 research outputs found
Rare earth element enrichment in Palaeoproterozoic Fengzhen carbonatite from the North China block
<p>Carbonatites are characterized by the highest concentration of rare earth elements (REEs) of any igneous rock and are therefore good targets for REE exploration. Supergene, hydrothermal, and magmatic REE deposits associated with carbonatites have been widely studied. REE enrichment related to fluorapatite metasomatism in Fengzhen carbonatites in the North China block is reported in this study. REE minerals (monazite, britholite, and Ca-REE-fluorocarbonates) associated with barite and quartz formed as inclusions within the fluorapatite and externally on its surface. Monazite, allanite, barite, and quartz occur as rim grains on the edges of the fluorapatite. Zoned fluorapatite was observed and showed varying chemical composition. Based on back-scattered electron imaging, the dark domains with mineral inclusions contain lower Si (0.3–0.6 wt.% SiO<sub>2</sub>) and light REE (LREE) [0.36–1.54 wt.% (Y+LREE)<sub>2</sub>O<sub>3</sub>] contents than inclusion-poor areas [0.7–1 wt.% SiO<sub>2</sub>; 2.16–4.51 wt.% (Y + LREE)<sub>2</sub>O<sub>3</sub>]. This indicates a dissolution–re-precipitation texture. Different types of monazites were distinguished by their chemical compositions. Monazite inclusions have lower La<sub>2</sub>O<sub>3</sub>contents (~13 wt.%) and La/Nd<sub>cn</sub> (~3) ratios than those (18–26 wt.% and 10–14 for La<sub>2</sub>O<sub>3</sub> and La/Nd<sub>cn</sub>, respectively) growing externally on the fluorapatite. REE enrichment in the metasomatic fluorapatites is related to different stages of carbonatitic liquids. The early carbonatite-exsolved fluids metasomatized the fluorapatites to form REE mineral inclusions. The late carbonatitic fluids from carbonatite magmas that underwent strong fractional crystallization were enriched in REEs, Al, and Fe and metasomatized the fluorapatites to produce allanite and monazite rim grains.</p
Bulk-Type All-Solid-State Lithium-Ion Batteries: Remarkable Performances of a Carbon Nanofiber-Supported MgH<sub>2</sub> Composite Electrode
Magnesium hydride,
MgH<sub>2</sub>, a recently developed compound for lithium-ion batteries,
is considered to be a promising conversion-type negative electrode
material due to its high theoretical lithium storage capacity of over
2000 mA h g<sup>–1</sup>, suitable working potential, and relatively
small volume expansion. Nevertheless, it suffers from unsatisfactory
cyclability, poor reversibility, and slow kinetics in conventional
nonaqueous electrolyte systems, which greatly limit the practical
application of MgH<sub>2</sub>. In this work, a vapor-grown carbon
nanofiber was used to enhance the electrical conductivity of MgH<sub>2</sub> using LiBH<sub>4</sub> as the solid-state electrolyte. It
shows that a reversible capacity of over 1200 mA h g<sup>–1</sup> with an average voltage of 0.5 V (vs Li/Li<sup>+</sup>) can be obtained
after 50 cycles at a current density of 1000 mA g<sup>–1</sup>. In addition, the capacity of MgH<sub>2</sub> retains over 1100
mA h g<sup>–1</sup> at a high current density of 8000 mA g<sup>–1</sup>, which indicates the possibility of using MgH<sub>2</sub> as a negative electrode material for high power and high
capacity lithium-ion batteries in future practical applications. Moreover,
the widely studied sulfide-based solid electrolyte was also used to
assemble battery cells with MgH<sub>2</sub> electrode in the same
system, and the electrochemical performance was as good as that using
LiBH<sub>4</sub> electrolyte
Nature of the Active Sites of VO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> Catalysts for Propane Dehydrogenation
Supported
VO<sub><i>x</i></sub> catalysts are promising
for use in propane dehydrogenation (PDH) because of the relatively
superior activity and stable performance upon regeneration. However,
the nature of the active sites and reaction mechanism during PDH over
VO<sub><i>x</i></sub>-based catalysts remains elusive. We
examined active species by attaining various fractions of V<sup>5+</sup>, V<sup>4+</sup>, and V<sup>3+</sup> ions by adjusting the surface
vanadium density on an alumina support. The results reveal a close
relationship between TOF and the fraction of V<sup>3+</sup> ion, indicating
that V<sup>3+</sup> was more active for PDH. <i>In situ</i> diffuse reflectance infrared Fourier transform spectroscopy showed
the same strong adsorbed species during both propane dehydrogenation
and propylene hydrogenation. The results indicated that such an intermediate
may correspond to V species containing a CC bond, i.e., V–C<sub>3</sub>H<sub>5</sub>, and a reaction mechanism was proposed accordingly
Propane Dehydrogenation over Pt/TiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> Catalysts
This
paper describes an investigation on understanding catalytic
consequences of Pt nanoparticles supported on a TiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> binary oxide for propane dehydrogenation (PDH).
The TiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> supports were
synthesized by a sol–gel method, and the Pt/TiO<sub>2</sub>–Al<sub>2</sub>O<sub>3</sub> catalysts were prepared by an
incipient wetness impregnation method. Both as-prepared and post-experiment
catalysts were characterized employing N<sub>2</sub> adsorption–desorption,
X-ray diffraction, Raman spectra, H<sub>2</sub>–O<sub>2</sub> titration, temperature-programmed desorption, thermogravimetric
analysis, temperature-programmed oxidation, transmission electron
microscopy, and Fourier-transform infrared spectra of chemisorbed
CO. We have shown that TiO<sub>2</sub> is highly dispersed on Al<sub>2</sub>O<sub>3</sub>, and the addition of appropriate amount of TiO<sub>2</sub> improves propylene selectivity and catalytic stability, which
is ascribed to the electron transfer from partially reduced TiO<sub><i>x</i></sub> (<i>x</i> < 2) to Pt atoms.
The increased electron density of Pt could reduce the adsorption of
propylene and facilitate the migration of coke precursors from the
metal surface to the support. The addition of TiO<sub>2</sub>, however,
also increases the amount of strong acid centers on the supports and
the excessive TiO<sub>2</sub> addition might lead to a significant
amount of coke formation. The electron transfer effect and the acid
sites effect of TiO<sub>2</sub> addition exert an opposite influence
on catalytic performance. The trade-off between the electron transfer
effect and the acid sites effect is studied by varying the amount
of TiO<sub>2</sub> loading. An optimal loading content of TiO<sub>2</sub> is 10 wt %, which results in a higher propylene selectivity
and a better stability
Platinum-Modified ZnO/Al<sub>2</sub>O<sub>3</sub> for Propane Dehydrogenation: Minimized Platinum Usage and Improved Catalytic Stability
Compared to metallic platinum and
chromium oxide, zinc oxide (ZnO)
is an inexpensive and low-toxic alternative for the direct dehydrogenation
of propane (PDH). However, besides the limited activity, conventional
zinc-based catalysts suffer from serious deactivation, because of
ZnO reduction and/or carbon deposition. Considering the high cost
of platinum, reducing the amount of platinum in the catalyst is always
desirable. This paper describes a catalyst comprising ZnO modified
by trace platinum supported on Al<sub>2</sub>O<sub>3</sub>, where
the Zn<sup>2+</sup> species serve as active sites and platinum acts
as a promoter. This catalyst contains less platinum than traditional
platinum-based catalysts and is much more stable than conventional
ZnO catalyst or commercial chromium-based systems during PDH. It is
proposed that ZnO was promoted to a stronger Lewis acid by platinum;
thus, easier C–H activation and accelerated H<sub>2</sub> desorption
were achieved
Lithium Hydrazinidoborane: A Polymorphic Material with Potential for Chemical Hydrogen Storage
Herein, we describe the synthesis
and characterization (chemical,
structural, and thermal) of a new crystal phase of lithium hydrazinidoborane
(LiN<sub>2</sub>H<sub>4</sub>ÂBH<sub>3</sub>, LiHB), which is
a new material for solid-state chemical hydrogen storage. We put in
evidence that lithium hydrazinidoborane is a polymorphic material,
with a stable low-temperature phase and a metastable high-temperature
phase. The former is called β-LiHB and the latter α-LiHB.
Results from DSC and XRD showed that the transition phase occurs at
around 90 °C. On this basis, the crystal structure of the novel
β-LiHB phase was solved. The potential of this material for
solid-state chemical hydrogen storage was verified by TGA, DSC, and
isothermal dehydrogenations. Upon the formation of the α-LiHB
phase, the borane dehydrogenates. At 150 °C, it is able to generate
10 wt % of pure H<sub>2</sub> while a solid residue consisting of
polymers with linear and cyclic units forms. Reaction mechanisms and
formation of bisÂ(lithium hydrazide) of diborane [(LiN<sub>2</sub>H<sub>3</sub>)<sub>2</sub>ÂBH<sub>2</sub>]<sup>+</sup>Â[BH<sub>4</sub>]<sup>−</sup> as a reaction intermediate are tentatively
proposed to highlight the decomposition of β-LiHB in our conditions
Xanthones from the herb of <i>Swertia elata</i> and their anti-TMV activity
<p>Two new xanthones (<b>1</b>–<b>2</b>), together with four known ones (<b>3</b>–<b>6</b>), were isolated from whole herb of <i>Swertia elata</i>. Their structures were elucidated by spectroscopic methods including extensive 1D- and 2D-NMR techniques. Their anti-tobacco mosaic virus (anti-TMV) activity test revealed that <b>1</b>–<b>6</b> showed weak anti-TMV activities with inhibition rate in the range of 15.2–28.8% at the concentration of 20 μM.</p
Molecular Dynamics-Based Virtual Screening: Accelerating the Drug Discovery Process by High-Performance Computing
High-performance computing (HPC)
has become a state strategic technology
in a number of countries. One hypothesis is that HPC can accelerate
biopharmaceutical innovation. Our experimental data demonstrate that
HPC can significantly accelerate biopharmaceutical innovation by employing
molecular dynamics-based virtual screening (MDVS). Without using HPC,
MDVS for a 10K compound library with tens of nanoseconds of MD simulations
requires years of computer time. In contrast, a state of the art HPC
can be 600 times faster than an eight-core PC server is in screening
a typical drug target (which contains about 40K atoms). Also, careful
design of the GPU/CPU architecture can reduce the HPC costs. However,
the communication cost of parallel computing is a bottleneck that
acts as the main limit of further virtual screening improvements for
drug innovations
Molecular Dynamics-Based Virtual Screening: Accelerating the Drug Discovery Process by High-Performance Computing
High-performance computing (HPC)
has become a state strategic technology
in a number of countries. One hypothesis is that HPC can accelerate
biopharmaceutical innovation. Our experimental data demonstrate that
HPC can significantly accelerate biopharmaceutical innovation by employing
molecular dynamics-based virtual screening (MDVS). Without using HPC,
MDVS for a 10K compound library with tens of nanoseconds of MD simulations
requires years of computer time. In contrast, a state of the art HPC
can be 600 times faster than an eight-core PC server is in screening
a typical drug target (which contains about 40K atoms). Also, careful
design of the GPU/CPU architecture can reduce the HPC costs. However,
the communication cost of parallel computing is a bottleneck that
acts as the main limit of further virtual screening improvements for
drug innovations