The dehydrogenation/hydrogenation processes of the LiNH2/MgH2 (1:1) system were systematically investigated with respect to balller milling and the subsequent heating process. The reaction pathways for hydrogen desorption/absorption of the LiNH2/MgH2 (1:1) system were found to depend strongly on the milling duration due to the presence of two competing reactions in different stages (i.e., the reaction between Mg(NH2)2 and MgH2 and that between Mg(NH2)2 and LiH), caused by a metathesis reaction between LiNH2 and MgH2, which exhibits more the nature of solid–solid reactions. The study provides us with a new approach for the design of novel hydrogen storage systems and the improvement of hydrogen‐storage performance of the amide/hydride systems. 相似文献
Alkali metal hydroxide and hydride composite systems contain both protic(H bonded with O) and hydridic hydrogen. The interaction of these two types of hydrides produces hydrogen. The enthalpy of dehydrogenation increased with the increase of atomic number of alkali metals,i.e.,-23 kJ/molH2 for LiOH-LiH, 55.34 kJ/molH2 for NaOH-NaH and 222 kJ/molH2 for KOH-KH. These thermodynamic calculation results were consistent with our experimental results. H2 was released from LiOH-LiH system during ball milling. The dehydrogenation temperature of NaOH-NaH system was about 150℃; whereas KOH and KH did not interact with each other during the heating process. Instead, KH decomposed by itself. In these three systems, NaOH-NaH was the only reversible hydrogen storage system, the enthalpy of dehydrogenation was about 55.65 kJ/molH2, and the corresponding entropy was ca. 101.23 J/(molH2 K), so the temperature for releasing 1.0 bar H2 was as high as 518℃, showing unfavorable thermodynamic properties. The activation energy for hydrogen desorption of NaOH-NaH was found to be57.87 kJ/mol, showing good kinetic properties. 相似文献
Hydride formation was studied in the Hf2Fe−H2 system at hydrogen pressure of up to 2000 atm in a temperature range from 195 to 295 K. Hydride phases of different compositions
were studied by the X-ray diffraction method. The hydrogenation reaction in the system can take two pathways to form two stable
hydride phases depending on the conditions of initial hydrogenation. Absorption of hydrogens at a pressure of about 2000 atm
yields a hydride which contains two H atoms per metal atom. Models of the arrangement of hydrogen atoms in the crystal lattice
of hydride phases were suggested.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 33–36, January, 1997. 相似文献
The polyanionic compound BaLaSi2 featuring cis-trans silicon chains takes up hydrogen to form a hydride BaLaSi2H0.80. The crystal structure of the parent intermetallic compound is largely retained upon hydrogenation with the same space group type, a unit cell volume increase of 3.29 % and very similar atomic positions in the hydride. Hydrogen could be located in the crystal structure by neutron diffraction on the deuteride. Deuterium atoms occupy a tetrahedral Ba3La interstitial with 40.6(2) % occupation (Cmcm, a = 464.43(4) pm, b = 1526.7(1) pm, c = 676.30(6) pm). BaLaSi2H0.80 is thus an interstitial Zintl phase hydride like LaSiH1–x, but unlike BaSiH2–x does not feature any covalent Si–H bonds. Si–Si distances within the polyanion increase upon hydrogenation from 240.1(6) and 242.9(5) pm to 244.7(2) pm and 245.5(2) pm. This is probably due to oxidation of the polyanion by hydrogen, which leads to the formation of hydride ions and the depopulation of the polyanion's antibonding π* states. Interatomic Ba–D [260.9(4) pm, 295.7(5) pm] and La–D distances [241.2(7) pm] are in the typical range of ionic hydrides. 相似文献
Metal hydride electrodes are of particular interest owing to their potential and practical application in batteries. A large
number of hydrogen storage materials has been characterized so far. This paper deals with the effect of the chemical nature
and stoichiometry of specific alloy families (AB5, A2B, AB/AB2 and AB2) on the hydride stability, hydrogen storage capacity and kinetics of hydrogen sorption-desorption in the solid phase/gas
and solid phase/electrolyte solution systems. Special attention has been paid towards the electrochemical properties of metal
hydrides in terms of their performance in Ni-MH rechargeable alkaline cells.
Electronic Publication 相似文献
We studied the directional crystallization of different compositions in B4C-NbB2 and B4C-MoB2 systems. The eutectic compositions for both systems are evaluated. It is shown that in the first system the rod-like eutectic structure is formed, in second, the “Chinese hieroglyphics”. In both cases high hardness and high microplasticity are observed, which are much more than for individual component phases. These compositions may be considered as a new kind of self-strengthening composite materials. 相似文献
Summary: A new generation of anionic initiators (butyllithium free), based on trialkylaluminum and a readily available alkali metal hydride, has been developed for the control of styrene polymerization at high temperature. Triisobutylaluminum and sodium hydride form heterocomplexes that are efficient for the initiation of styrene polymerization at 100 °C in toluene or in bulk. To be active under such conditions, these systems require the presence of an excess of metal hydride with respect to AlR3 ([Al]/[Na] < 1). PS chains are specifically initiated by the hydrides coming from NaH, and molar masses are controlled in the range 0.8 < [Al]/[Na] < 1. Fast exchange between dormant 1:1 and active 1:2 complexes (Al:Na), and ligand rearrangements within the 1:2 complex, can explain the observed results.
Initiation of styrene with i‐Bu3Al/NaH systems. 相似文献
The NaCl–KI–K2CrO4 stable triangle was studied by differential thermal analysis. The melting temperature, melt composition, and specific melting enthalpy corresponding to the ternary eutectic were determined in the system. The compositions of crystallizing phases in the eutectic were confirmed by X-ray diffraction. 相似文献
The reaction mechanisms on reduction of tertiary carboxamides by diisobutylaluminum hydride (DIBAL) and sodium hydride (NaH)‐sodium iodide (NaI) composite were elucidated by the computational and experimental approaches. Reduction of N,N‐dimethyl carboxamides with DIBAL provides the corresponding amines, whereas that with the NaH?NaI composite exclusively forms aldehyde even at high reaction temperature. DFT calculations revealed that dimeric structural nature of DIBAL and Lewis acidity on its Al center play crucial role to decompose the tetrahedral anionic carbinol amine intermediate through C?O bond cleavage. On the other hand, in the reduction with the NaH?NaI composite, the resulting tetrahedral anionic carbinol amine intermediate could be kept stable, thus providing aldehydes as a sole product by the aqueous workup 相似文献
Why do we hardly use the simplest and, at the same time, inexpensive reducing agent sodium hydride in organic chemistry? To this question the answer is invariably: “It is too basic”. In this progress report we describe work we have performed aimed at controlling the basicity of NaH using sodium alcoholates and metal salts. The complex reducing agents (CRA's) developed (symbolized NaH-RONa-MXn) allow organic halides, alkenes, alkynes and ketones to be reduced selectively. Highly regioselective 1,4- and 1,2-reductions of α,β-unsaturated ketones are easily performed using appropriate metal salts. Modified CRA's have proved to be excellent hydrosilylating reagents for carbonyl groups, non-pyrophoric heterogeneous hydrogenation catalysts, coupling reagents for aryl and vinyl halides, and reagents for the carbonylation of organic halides under very mild conditions. The study of these reactions opened up the field to phase-transfer-catalyzed photostimulated carbonylations as well as to SRN1 reactions of metalates.–Thus, starting from the simple sodium hydride a large number of useful reagents have become accessible. 相似文献
The synthesis and characterization of four new silicon-linked lanthanocene complexes with pendant phenyl groups on cyclopentadiene were reported. Based on the data of elemental analyses, MS and IR, the complexes were presumed to be unsolvated and dimeric complexes [Me2Si(C5H3CMe2C6H5)2LnC1]2 [Ln=Er (1), Gd (2), Sm (3), Dy (4)]. In conjunction with AlEt3 or sodium hydride as the co-catalyst, these complexes could efficiently catalyze the polymerization of methyl methacrylate (MMA). When the nanometric sodium hydride was used as a co-catalyst, the complexes were highly effective for the polymerization of MMA. At low temperature and in short time, in [MeESi(C5H3CMe2C6H5)2LnC1]2/NaH (nanometric) system, the polymer was obtained in more than 80% yield and the molecular weight was greater than 105. The activity reached that of organolanthanide hydride as a single-component catalyst. In ]MeESi(C5H3CMe2C6H5)2ErC1]2/Nail (nanometric) system, the effects of the molar ratio of MMA/catalyst and catalyst/co-catalyst, and the temperature on polymerization were studied. 相似文献
Na2CrO4-NaF-NaI and K2CrO4-KF-KI three-component systems have been studied by differential thermal analysis (DTA). The compositions and melting temperatures have been determined and the enthalpies of melting have been measured for eutectic mixtures. Phase equilibria in the title systems have been described, and phase fields have been demarcated. 相似文献
The ternary systems NaCl–NaI–Na2CrO4 and KCl–KI–K2CrO4 were studied by differential thermal analysis. In the systems, the melting points and compositions of alloys at ternary eutectic points were determined. The compositions of crystallizing phases in the eutectics were confirmed by X-ray powder diffraction analysis. 相似文献
Catalysts obtained by interacting Ti(CH2C6H5)4 or Zr(π-C3H5)4 with the surface of SiO2 and treated with hydrogen possess a very high activity with respect to hydrogenation of benzene and cyclohexene. This activity is commensurable with that of supported Group VIII metals. The catalysts were studied by chemisorption, thermodesorption and EXAFS methods, and were shown to contain anchored hydride complexes of Ti and Zr, whose content can be controlled by varying the temperature of their treatment with hydrogen. A quantitative correlation exists between the specific activity of the catalysts under consideration in hydrogenation reactions and the content of hydride complexes in these catalysts. 相似文献
Ca(BH4)2 is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its practical applications. In an effort to overcome these barriers and to adjust the thermal stability, we make a composite system Ca(BH4)2–LiNH2. Interaction of Ca(BH4)2 and LiNH2 leads to decreased dehydrogenation temperatures and increased hydrogen desorption capacity in comparison to pristine Ca(BH4)2. More than 7 wt % of hydrogen can be detached at a temperature as low as approximately 178 °C from the cobalt‐catalyzed Ca(BH4)2–4 LiNH2 system. 相似文献
In this paper, two LiAlH4-NaNH2 samples with LiAlH4 to NaNH2 molar ratio of 1/2 and 2/1 were investigated, respectively. It was observed that both samples evolved 2 equiv H2 in the ball milling process, however, the reaction pathways were different. For the LiAlH4-NaNH2 (1/2) sample, Li3Na(NH2)4 and NaAlH4 were formed through cation exchange between reactants. The NaAlH4 formed further reacts with Li3Na(NH2)4 and NaNH2 to give H2, NaH and LiAlN2H2. For the LiAlH4-NaNH2 (2/1) sample, Li3Na(NH2)4, LiNH2 and NaAlH4 were formed firstly through the same cation exchange process. The resulting LiNH2 reacts with the remaining LiAlH4 and produces H2 and Li2AlNH2. 相似文献