18 research outputs found
Study of Argon Gas Adsorption in Ordered Mesoporous MFI Zeolite Framework
An ordered mesoporous MFI zeolite
material (Meso-MFI) was prepared
by using CMK-type mesoporous carbons as a hard template. The Meso-MFI
exhibits both structural and adsorption differences compared to the
conventional bulk MFI zeolite. To study the argon (Ar) adsorption
process in Meso-MFI, an in situ gas adsorption powder X-ray diffraction
(XRD) analysis was performed using synchrotron X-ray source. Structural
rearrangement of the mesoporous MFI zeolite upon Ar adsorption at
low temperature (83 K) was intensively studied together with Ar adsorption
process in Meso-MFI. We observed that a structural transition of the
Meso-MFI zeolite framework from monoclinic (<i>P</i>2<sub>1</sub>/<i>n</i>) to orthorhombic (<i>Pnma</i>) occurred at around 126 Pa at 83 K. Positions of Ar atoms are determined
as a function of the Ar gas pressure through Rietveld refinement of
powder XRD data. Ar atoms are observed at straight channels, sinusoidal
channels, and the intersection of these channels at low pressure.
As gas pressure increases, Ar atoms in the pore intersection are pulled
off from the intersection toward the straight and sinusoidal channels.
The pore shape of the straight channel is changed accordingly with
the amount of adsorbed Ar atoms within the pores from circular to
oval. These results indicate that Ar adsorption induces not only continuous
rearrangement of framework atoms but also symmetry change in the Meso-MFI.
A molecular simulation study combined with Rietveld refinement of
in situ XRD data provided a full understanding of the adsorption process
of Ar in Meso-MFI
Discovery of Face-Centered-Cubic Ruthenium Nanoparticles: Facile Size-Controlled Synthesis Using the Chemical Reduction Method
We
report the first discovery of pure face-centered-cubic (fcc)
Ru nanoparticles. Although the fcc structure does not exist in the
bulk Ru phase diagram, fcc Ru was obtained at room temperature because
of the nanosize effect. We succeeded in separately synthesizing uniformly
sized nanoparticles of both fcc and hcp Ru having diameters of 2–5.5
nm by simple chemical reduction methods with different metal precursors.
The prepared fcc and hcp nanoparticles were both supported on Îł-Al<sub>2</sub>O<sub>3</sub>, and their catalytic activities in CO oxidation
were investigated and found to depend on their structure and size
Modular Design of Domain Assembly in Porous Coordination Polymer Crystals via Reactivity-Directed Crystallization Process
The mesoscale design of domain assembly is crucial for
controlling
the bulk properties of solids. Herein, we propose a modular design
of domain assembly in porous coordination polymer crystals via exquisite
control of the kinetics of the crystal formation process. Employing
precursors of comparable chemical reactivity affords the preparation
of homogeneous solid-solution type crystals. Employing precursors
of distinct chemical reactivity affords the preparation of heterogeneous
phase separated crystals. We have utilized this reactivity-directed
crystallization process for the facile synthesis of mesoscale architecture
which are either solid-solution or phase-separated type crystals.
This approach can be also adapted to ternary phase-separated type
crystals from one-pot reaction. Phase-separated type frameworks possess
unique gas adsorption properties that are not observed in single-phasic
compounds. The results shed light on the importance of crystal formation
kinetics for control of mesoscale domains in order to create porous
solids with unique cooperative functionality
Modular Design of Domain Assembly in Porous Coordination Polymer Crystals via Reactivity-Directed Crystallization Process
The mesoscale design of domain assembly is crucial for
controlling
the bulk properties of solids. Herein, we propose a modular design
of domain assembly in porous coordination polymer crystals via exquisite
control of the kinetics of the crystal formation process. Employing
precursors of comparable chemical reactivity affords the preparation
of homogeneous solid-solution type crystals. Employing precursors
of distinct chemical reactivity affords the preparation of heterogeneous
phase separated crystals. We have utilized this reactivity-directed
crystallization process for the facile synthesis of mesoscale architecture
which are either solid-solution or phase-separated type crystals.
This approach can be also adapted to ternary phase-separated type
crystals from one-pot reaction. Phase-separated type frameworks possess
unique gas adsorption properties that are not observed in single-phasic
compounds. The results shed light on the importance of crystal formation
kinetics for control of mesoscale domains in order to create porous
solids with unique cooperative functionality
Mechanochemical Synthesis and Characterization of Metastable Hexagonal Li<sub>4</sub>SnS<sub>4</sub> Solid Electrolyte
A new crystalline
lithium-ion conducting material, Li<sub>4</sub>SnS<sub>4</sub> with
an <i>ortho</i>-composition, was prepared
by a mechanochemical technique and subsequent heat treatment. Synchrotron
X-ray powder diffraction was used to analyze the crystal structure,
revealing a space group of <i>P</i>6<sub>3</sub>/<i>mmc</i> and cell parameters of <i>a</i> = 4.01254(4)
Ă… and <i>c</i> = 6.39076(8) Ă…. Analysis of a heat-treated
hexagonal Li<sub>4</sub>SnS<sub>4</sub> sample revealed that both
lithium and tin occupied either of two adjacent tetrahedral sites,
resulting in fractional occupation of the tetrahedral site (Li, 0.375;
Sn, 0.125). The heat-treated hexagonal Li<sub>4</sub>SnS<sub>4</sub> had an ionic conductivity of 1.1 × 10<sup>–4</sup> S
cm<sup>–1</sup> at room temperature and a conduction activation
energy of 32 kJ mol<sup>–1</sup>. Moreover, the heat-treated
Li<sub>4</sub>SnS<sub>4</sub> exhibited a higher chemical stability
in air than the Li<sub>3</sub>PS<sub>4</sub> glass-ceramic
Solid-Solution Alloying of Immiscible Ru and Cu with Enhanced CO Oxidation Activity
We
report on novel solid-solution alloy nanoparticles (NPs) of
Ru and Cu that are completely immiscible even above melting point
in bulk phase. Powder X-ray diffraction, scanning transmission electron
microscopy, and energy-dispersive X-ray measurements demonstrated
that Ru and Cu atoms were homogeneously distributed in the alloy NPs.
Ru<sub>0.5</sub>Cu<sub>0.5</sub> NPs demonstrated higher CO oxidation
activity than fcc-Ru NPs, which are known as one of the best monometallic
CO oxidation catalysts
Shape-Dependent Hydrogen-Storage Properties in Pd Nanocrystals: Which Does Hydrogen Prefer, Octahedron (111) or Cube (100)?
Pd octahedrons and cubes enclosed
by {111} and {100} facets, respectively,
have been synthesized for investigation of the shape effect on hydrogen-absorption
properties. Hydrogen-storage properties were investigated using in
situ powder X-ray diffraction, in situ solid-state <sup>2</sup>H NMR
and hydrogen pressure–composition isotherm measurements. With
these measurements, it was found that the exposed facets do not affect
hydrogen-storage capacity; however, they significantly affect the
absorption speed, with octahedral nanocrystals showing the faster
response. The heat of adsorption of hydrogen and the hydrogen diffusion
pathway were suggested to be dominant factors for hydrogen-absorption
speed. Furthermore, in situ solid-state <sup>2</sup>H NMR detected
for the first time the state of <sup>2</sup>H in a solid-solution
(Pd + H) phase of Pd nanocrystals at rt
Nanosize-Induced Drastic Drop in Equilibrium Hydrogen Pressure for Hydride Formation and Structural Stabilization in Pd–Rh Solid-Solution Alloys
We have synthesized and characterized homogeneous solid-solution
alloy nanoparticles of Pd and Rh, which are immiscible with each other
in the equilibrium bulk state at around room temperature. The Pd–Rh
alloy nanoparticles can absorb hydrogen at ambient pressure and the
hydrogen pressure of Pd–Rh alloys for hydrogen storage is dramatically
decreased by more than 4 orders of magnitude from the corresponding
pressure in the metastable bulk state. The solid-solution state is
still maintained in the nanoparticles even after hydrogen absorption/desorption,
in contrast to the metastable bulks which are separated into Pd and
Rh during the process
Remarkable Oxygen Intake/Release of BaYMn<sub>2</sub>O<sub>5+δ</sub> Viewed from High-Temperature Crystal Structure
Crystal
structure of double-perovskite type BaYMn<sub>2</sub>O<sub>5+δ</sub> was studied by high-temperature synchrotron X-ray
diffraction (SXRD) under precisely controlled oxygen pressure to gain
deeper understanding of the remarkable oxygen intake/release capability
of this oxide. The in situ SXRD analysis at 750 °C revealed that
this oxide undergoes a distinct structural change upon lowering oxygen
pressure, from a slightly oxygen-deficient “δ = 1”
phase (BaYMn<sub>2</sub>O<sub>5.89</sub>; <i>P</i>(O<sub>2</sub>) = 10<sup>3</sup> Pa) to an oxygen-vacancy ordered “δ
= 0.5” phase (BaYMn<sub>2</sub>O<sub>5.51</sub>; <i>P</i>(O<sub>2</sub>) = 10 Pa). The BaYMn<sub>2</sub>O<sub>5.89</sub> structure
(orthorhombic <i>Cmmm</i>) involves statistical distribution
of oxygen vacancies within the yttrium plane. Meanwhile, the BaYMn<sub>2</sub>O<sub>5.51</sub> structure (orthorhombic <i>Icma</i>) contains arrays of pyramidal MnO<sub>5</sub> and octahedral MnO<sub>6</sub> forming an alternate ordering, which is stabilized by a particular
Mn<sup>3+</sup> orbital ordering with collective displacements of
Y<sup>3+</sup> arrays. Thus, the discontinuous change in the oxygen
content can be attributed to the structural reconstruction with oxygen/vacancy
redistribution accompanied by yttrium displacement organization
Remarkable Oxygen Intake/Release of BaYMn<sub>2</sub>O<sub>5+δ</sub> Viewed from High-Temperature Crystal Structure
Crystal
structure of double-perovskite type BaYMn<sub>2</sub>O<sub>5+δ</sub> was studied by high-temperature synchrotron X-ray
diffraction (SXRD) under precisely controlled oxygen pressure to gain
deeper understanding of the remarkable oxygen intake/release capability
of this oxide. The in situ SXRD analysis at 750 °C revealed that
this oxide undergoes a distinct structural change upon lowering oxygen
pressure, from a slightly oxygen-deficient “δ = 1”
phase (BaYMn<sub>2</sub>O<sub>5.89</sub>; <i>P</i>(O<sub>2</sub>) = 10<sup>3</sup> Pa) to an oxygen-vacancy ordered “δ
= 0.5” phase (BaYMn<sub>2</sub>O<sub>5.51</sub>; <i>P</i>(O<sub>2</sub>) = 10 Pa). The BaYMn<sub>2</sub>O<sub>5.89</sub> structure
(orthorhombic <i>Cmmm</i>) involves statistical distribution
of oxygen vacancies within the yttrium plane. Meanwhile, the BaYMn<sub>2</sub>O<sub>5.51</sub> structure (orthorhombic <i>Icma</i>) contains arrays of pyramidal MnO<sub>5</sub> and octahedral MnO<sub>6</sub> forming an alternate ordering, which is stabilized by a particular
Mn<sup>3+</sup> orbital ordering with collective displacements of
Y<sup>3+</sup> arrays. Thus, the discontinuous change in the oxygen
content can be attributed to the structural reconstruction with oxygen/vacancy
redistribution accompanied by yttrium displacement organization