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1.
Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH2 prepared by mechanical milling 总被引:1,自引:0,他引:1
We examined the catalytic effect of nanoparticle 3d-transition metals on hydrogen desorption (HD) properties of MgH(2) prepared by mechanical ball milling method. All the MgH(2) composites prepared by adding a small amount of nanoparticle Fe(nano), Co(nano), Ni(nano), and Cu(nano) metals and by ball milling for 2 h showed much better HD properties than the pure ball-milled MgH(2) itself. In particular, the 2 mol % Ni(nano)-doped MgH(2) composite prepared by soft milling for a short milling time of 15 min under a slow milling revolution speed of 200 rpm shows the most superior hydrogen storage properties: A large amount of hydrogen ( approximately 6.5 wt %) is desorbed in the temperature range from 150 to 250 degrees C at a heating rate of 5 degrees C/min under He gas flow with no partial pressure of hydrogen. The EDX micrographs corresponding to Mg and Ni elemental profiles indicated that nanoparticle Ni metals as catalyst homogeneously dispersed on the surface of MgH(2). In addition, it was confirmed that the product revealed good reversible hydriding/dehydriding cycles even at 150 degrees C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH(2) could be understood by a modified first-order reaction model, in which the surface condition was taken into account. 相似文献
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H Kobayashi H Morita M Yamauchi R Ikeda H Kitagawa Y Kubota K Kato M Takata S Toh S Matsumura 《Journal of the American Chemical Society》2012,134(30):12390-12393
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. 相似文献
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Micrometer scaled MoS2 hierarchical hollow cubic cages assembled by bilayers can be synthesized via a one-step self-assembly coupled with intermediate crystal templating process without any surfactant, in which the intermediate K2NaMoO3F3 crystal formed in-situ and then served as the self-sacrificed template based on the Kirkendall Effect; The MoS2 hierarchical hollow cubic cages were employed for electrochemical hydrogen storage with a high capacity of 375 mAh g(-1) due to the more active edges exposing on the upright-standing nanoplates. 相似文献
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Ward S Scantlebury M Król E Thomson PJ Sparling C Speakman JR 《Rapid communications in mass spectrometry : RCM》2000,14(6):450-453
An off-line technique is described for the preparation of H(2) from water prior to analysis of delta(2)H by dual-inlet isotope ratio mass spectrometry. H(2) is produced from sample water by reaction with LiAlH(4). This provides a rapid and inexpensive method for the analysis of delta(2)H in small (10 microL) samples of water. Precision was +/- 4.2 to 8.0 (1sigma(n), n = 8) delta(2)H(VSMOW) for samples between 428 and 1500 delta(2)H(VSMOW), +/- 14.5 delta(2)H(VSMOW) for water enriched to 3750 delta(2)H(VSMOW) and +/- 26.0 delta(2)H(VSMOW) for water enriched to 6100 delta(2)H(VSMOW). Accuracy was +/- 1.1 to 4.2 delta(2)H(VSMOW) for water standards from natural abundance to 1000 delta(2)H(VSMOW) (the highest enrichment at which water of accepted delta(2)H is currently available). This method for delta(2)H determination is most appropriate for use with small (<50 microL) samples of high delta(2)H enrichment such as those produced from doubly labelled water studies of small animals. The levels of measurement precision of delta(2)H would contribute 2.6-3.8% to the precision error in estimates of small animal energy expenditure made using the doubly labelled water technique when duplicate analyses are performed. 相似文献
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Price TE Grant DM Weston D Hansen T Arnbjerg LM Ravnsbæk DB Jensen TR Walker GS 《Journal of the American Chemical Society》2011,133(34):13534-13538
It is known that the reaction path for the decomposition of LiBH(4):MgH(2) systems is dependent on whether decomposition is performed under vacuum or under a hydrogen pressure (typically 1-5 bar). However, the sensitivity of this multicomponent hydride system to partial pressures of H(2) has not been investigated previously. A combination of in situ powder neutron and X-ray diffraction (deuterides were used for the neutron experiments) have shed light on the effect of low partial pressures of hydrogen on the decomposition of these materials. Different partial pressures have been achieved through the use of different vacuum systems. It was found that all the samples decomposed to form Li-Mg alloys regardless of the vacuum system used or sample stoichiometry of the multicomponent system. However, upon cooling the reaction products, the alloys showed phase instability in all but the highest efficiency pumps (i.e., lowest base pressures), with the alloys reacting to form LiH and Mg. This work has significant impact on the investigation of Li-containing multicomponent systems and the reproducibility of results if different dynamic vacuum conditions are used, as this affects the apparent amount of hydrogen evolved (as determined by ex situ experiments). These results have also helped to explain differences in the reported reversibility of the systems, with Li-rich samples forming a passivating hydride layer, hindering further hydrogenation. 相似文献
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MgH(2)-TiH(2) nanocomposites have been obtained by reactive ball milling of elemental powders under 8 MPa of hydrogen pressure. The composites consist of a mixture of β-rutile MgH(2), γ-orthorhombic high pressure MgH(2) and ε-tetragonal TiH(2) phases with nanosized crystallites ranging from 4 to 12 nm. In situ hydrogen absorption curves on milling reveal that nanocomposite formation occurs in less than 50 min through the consecutive synthesis of the TiH(2) and MgH(2) phases. The abrasive and catalytic properties of TiH(2) speed up the formation of the MgH(2) phase. Thermodynamic, kinetic and cycling hydrogenation properties have been determined for the 0.7MgH(2)-0.3TiH(2) composite and compared to nanometric MgH(2). Only the MgH(2) phase desorbs hydrogen reversibly at moderate temperature (523 to 598 K) and pressure (10(-3) to 1 MPa). The presence of TiH(2) does not modify the thermodynamic properties of the Mg/MgH(2) system. However, the MgH(2)-TiH(2) nanocomposite exhibits outstanding kinetic properties and cycling stability. At 573 K, H-sorption takes place in less than 100 s. This is 20 times faster than for a pure nanometric MgH(2) powder. We demonstrate that the TiH(2) phase inhibits grain coarsening of Mg, which allows extended nucleation of the MgH(2) phase in Mg nanoparticles before a continuous and blocking MgH(2) hydride layer is formed. The low crystallinity of the TiH(2) phase and its hydrogenation properties are also compatible with a gateway mechanism for hydrogen transfer from the gas phase to Mg. Mg-rich MgH(2)-TiH(2) nanocomposites are an excellent media for hydrogen storage at moderate temperatures. 相似文献
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Bhattacharya S Wu G Ping C Feng YP Das GP 《The journal of physical chemistry. B》2008,112(36):11381-11384
In an attempt to tailor the dehydrogenation temperature of lithium imides, we have investigated the ternary imide Li 2Ca(NH) 2, which crystallizes in a structure (space group P3 m1) different from that of Li 2Mg(NH) 2 (space group Iba2). First-principles density functional calculations yield the stable ground-state structure along with the correct hydrogen positions. Compared with the structural and thermodynamic data of the pure lithium imides, those Ca or Mg partially substituted ternary imides show decreased reaction enthalpies as well as dehydrogenation temperatures. 相似文献
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Masaya Matsuoka Afshin Ebrahimi Masaki Nakagawa Tae-Ho Kim Masaaki Kitano Masato Takeuchi Masakazu Anpo 《Research on Chemical Intermediates》2009,35(8-9):997-1004
Visible light-responsive TiO2 thin film photocatalysts (Vis-TiO2) have been prepared on Ti metal foil (Vis-TiO2/Ti) or ITO glass (Vis-TiO2/ITO) substrates by a radio-frequency magnetron sputtering (RF-MS) method. The UV–Vis spectra as well as photoelectrochemical performance of Vis-TiO2 were affected by various calcination treatments such as calcination in air or NH3. Calcination treatment in NH3 (1.0 × 104 Pa, 673 K) was particularly effective in increasing the visible light absorption of Vis-TiO2 as well as in enhancing its photoelectrochemical performance and photocatalytic activity. A novel Vis-TiO2 thin film photocatalyst (Vis-TiO2/Ti/Pt) was prepared by an RF-MS method where Vis-TiO2 was deposited on one side of a Ti metal foil substrate and nanoparticles of Pt were deposited on the other side. The separate evolution of H2 and O2 from H2O could be successfully achieved by using an H-type glass cell consisting of two aqueous phases separated by Vis-TiO2/Ti/Pt and a proton-exchange membrane. It was found that the rate of the separate evolution of H2 and O2 was also dramatically enhanced by calcination treatment of Vis-TiO2 in NH3. 相似文献
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The conditions presently in use for the fluorometric determination of H2O2 in marine waters, by reacting H2O2 with scopoletin in the presence of horseradish peroxidase (HRP) and measuring the quenching of the fluorescence intensity of scopoletin, are not the optimal conditions. Under the optimized conditions of a pH of 8.5–9.5, an excitation wavelength of 390 nm and an emission wavelength of 460, the sensitivity of the method can be increased significantly, by up to more than a factor of 3 and the variations in the sensitivity from sample to sample can be significantly reduced. Furthermore, the samples need not be analyzed immediately after sample collection as presently prescribed. After scopoletin and HRP have been added to a sample immediately after sample collection, the sample may be stored at room temperature in the dark for up to four days before the quenched fluorescence intensity of scopoletin is read. 相似文献
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Garcia-Viloca M Alhambra C Truhlar DG Gao J 《Journal of the American Chemical Society》2002,124(25):7268-7269
Xylose isomerase exhibits a bridged-bimetallic active-site motif in which the substrate is bound to two metals connected by a glutamate bridge, and X-ray crystallographic studies suggest that metal movement is involved in the hydride transfer rate-controlling catalytic step. Here we report classical/quantal dynamical simulations of this step that provide new insight into the metal motion. The potential energy surface is calculated by treating xylose with semiempirical molecular orbital theory augmented by a simple valence bond potential and the rest of the system by molecular mechanics. The rate constant for the hydride-transfer step was calculated by ensemble-averaged dynamical simulations including both variational transition-state theory for determination of the statistically averaged dynamical bottleneck and optimized multidimensional tunneling calculations. The dynamics calculations include 25 317 atoms, with quantized vibrational free energy in 89 active-site degrees of freedom, and with 32 atoms moving through static secondary zone transition-state configurations in the quantum tunneling simulation. Our simulations show that the average Mg-Mg distance R increases monotonically as a function of the hydride-transfer progress variable z. The range of the average R along the reaction path is consistent with the X-ray structure, thus providing a dynamical demonstration of the postulated role of Mg in catalysis. We also predicted the primary deuterium kinetic isotope effect (KIE) for the chemical step. We calculated a KIE of 3.8 for xylose at 298 K, which is consistent with somewhat smaller experimentally observed KIEs for glucose substrate at higher temperatures. More than half of our KIE is due to tunneling; neglecting quantum effects on the reaction coordinate reduces the calculated KIE to 1.8. 相似文献
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An improved method for ruthenium analysis separation from uranium by pressure precipitation with H2S
M. N. Rao 《Fresenius' Journal of Analytical Chemistry》1967,227(5):326-330
Summary Pressure precipitation of ruthenium with hydrogen sulphide is recommended for its separation from uranium. The separations from uranium solutions and from pitchblende are described as examples.
Zusammenfassung Zur Abtrennung des Rutheniums von Uran wird die Fällung mit Schwefelwasserstoff unter Druck empfohlen. Als Beispiele werden die Abtrennung aus Uranlösungen sowie aus einem Uranmineral (Pechblende) beschrieben.相似文献
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《Arabian Journal of Chemistry》2020,13(1):171-183
In the present work, new CaO-based adsorbents were obtained by a fast solution combustion method and high-energy ball-milling process to study their CO2 capture behavior under different moderate pressure and temperature conditions. The as-prepared CaO products were characterized systematically using different analytical techniques such as X-ray diffraction, scanning electron microscopy and N2 physisorption measurements. The results showed that the CaO prepared by solution combustion and ball-milled during 2.5 h showed the maximum CO2 adsorption capacity of 9.31 mmol/g at 25 °C and 1 atm mainly via chemisorption with CaCO3 formation, which was corroborated by infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy studies. In general, the obtained results revealed that the synthesized CaO nanopowders from solution combustion that were treated by high-energy ball-milling enhanced their CO2 adsorption capacity due to improved structural and textural properties, and this CaO-based adsorbent can be used as a promising material for CO2 capture in post-combustion CO2 capture technologies on a large scale, under atmospheric pressure and temperature conditions. 相似文献
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This review describes a study of catalytic functions of water splitting at the surface and hydrogen gas emitting from the bulk of metal–oxide layered materials as well as hydrogen storage materials as its application by means of the ion beam analysis techniques. First are described a microscopic model for water splitting at the oxide surface and mass balance equations for hydrogen atoms in the bulk. The latter is a mathematical expression of a one‐way diffusion model proposed for an anomalous isotope effect in D–H and H–D replacements of both deuterium (D) implanted into perovskite oxide ceramics by protium (H) in H2O vapour and the vise versa. The latter model brings about finding of catalytic functions of water splitting at the surface and hydrogen gas emitting from the bulk. Second, experimental results on the anomalous isotope effect are presented and the D–H replacement rates are described in detail. Subsequently are shown results on H2 gas emission measured with a Bach method, which give a clear evidence for the water splitting and hydrogen gas emitting catalytic functions of the oxide surface. Finally, we present experimental data on the hydrogen absorption and emission characteristics of the metal–oxide layered hydrogen storage materials as an application of the water splitting and hydrogen absorbing catalysts. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Yang CH Sarma G Parker DH ter Meulen JJ Wiesenfeld L 《The Journal of chemical physics》2011,134(20):204308
State-to-state differential cross sections (DCSs) for rotationally inelastic scattering of H(2)O by H(2) have been measured at 71.2 meV (574 cm(-1)) and 44.8 meV (361 cm(-1)) collision energy using crossed molecular beams combined with velocity map imaging. A molecular beam containing variable compositions of the (J = 0, 1, 2) rotational states of hydrogen collides with a molecular beam of argon seeded with water vapor that is cooled by supersonic expansion to its lowest para or ortho rotational levels (J(KaKc) = 0(00) and 1(01), respectively). Angular speed distributions of fully specified rotationally excited final states are obtained using velocity map imaging. Relative integral cross sections are obtained by integrating the DCSs taken with the same experimental conditions. Experimental state-specific DCSs are compared with predictions from fully quantum scattering calculations on the most complete H(2)O-H(2) potential energy surface. Comparison of relative total cross sections and state-specific DCSs show excellent agreement with theory in almost all details. 相似文献
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Niko Prasetyo Rama Oktavian Ahmad Sirrullah 《International journal of quantum chemistry》2024,124(1):e27282
This study used periodic density functional theory and grand canonical Monte Carlo simulations to investigate the effects of the co-doping of B and N atoms and substituting Zn2+ with Mg2+ or Ca2+ in the organic linker groups of MOF-650. The functionalization increased the polarity of the organic groups, stabilizing the interaction between the MOF and hydrogen molecules. The highest average binding energy of the adsorbed hydrogen in MOF-650 NB-C7-azulene-Mg was calculated to be −4.75 to 5.40 kcal/mol for the α adsorption sites. Using the substitution of NB azulene and metal cations being Mg2+ or Ca2+, The hydrogen storage capacity of functionalized MOF-650 was increased to 22 mg/g at 90 bar/298 K, implying the modification strategy of MOF-650 would strengthen the interaction between MOF frameworks and hydrogen molecules. 相似文献