Intermetallic Hydrides Research Articles

Activation of the Highly‐Selective Pd11Bi2Se2 during the Semi‐Hydrogenation of Acetylene

Pd11Bi2Se2 was prepared as single‐phase material and used in an unsupported state as catalyst in the semi‐hydrogenation of acetylene in ethylene excess. After an initial inactive time‐period, Pd11Bi2Se2 activated and showed high acetylene conversion and selectivity towards ethylene at 473 K. In addition, after the initial inactive state, the compound revealed high stability during 100 h time on stream. At 80 % conversion the selectivity to ethylene is higher than 90 %. Post‐catalysis investigations by powder X‐ray diffraction (p‐XRD) and X‐ray photoelectron spectroscopy (XPS) exclude the formation of intermetallic hydrides, decomposition, and the presence of elemental palladium. Furthermore, comparison of XPS before and after catalysis revealed the reason of the inactive state of the intermetallic compound during the first hours of catalysis. An initial surface layer of bismuth oxide is reduced and re‐incorporated into the intermetallic compound. This material change is responsible for the initially observed activation of Pd11Bi2Se2 during the semi‐hydrogenation of acetylene.

The hydrogen storage properties of Mg-intermetallic-hydrides by ab initio calculations and kinetic Monte Carlo simulations

First-principle calculations and kinetic Monte-Carlo simulations were performed to study the hydrogen storage properties of the intermetallic hydrides MgNiH3, MgCoH3 and thier mixture namely MgCo0.5Ni0.5H3.Based on the heat of formation, desoprtion temperature, activation energies computed from DFT calculations and KMC simulations, we show that the MgNiH3 involves a fast kinetic while it is thermodynamically unstable (−9.96 kJ/mol.H2; 76.61 K) whereas MgCoH3 has a high thermodynamic stability (−73.32 kJ/mol.H2; 560.97 K) which prevents their application for mobile hydrogen storage.On the other hand, the electronic structures show that the Ni weakens the strong CoH bonding of the mixture MgCo0.5Ni0.5H3, which enhances significantly its stability and its desorption temperature (−45.92 kJ/mol.H2 and 351.33 K) without reducing its high volumetric capacity 133.73 g.H2/l. Kinetic Monte-Carlo simulations show that MgCo0.5Ni0.5H3 exhibits a fast charging time (only 4.6 min at 400 K and 10 bar).Thermodynamic properties including entropy S, Gibbs free energy G and thermal expansion coefficient are predicted within the quasi-harmonic approximation. It is verified that crystal structure of MgCo0.5Ni0.5H3 is stable.

Structural and elastic properties of Mg3CuH0.6 ternary hydride by ab initio study

Abstract In the present work, we investigate the structural and elastic properties of a new intermetallic hydride compound Mg3CuH0.6. The theoretical study has been carried out based on density functional theory (DFT), within local density approximation (LDA) and generalized gradient approximation (GGA). The calculated structural parameters of Mg3CuH0.6 compound are consistent with the available experimental data in both approximations. The heat of formation found shows that this compound has a stable structure. According to Hooke's law which leads to a linear relation between stress and strain, the elastic constants were determined. Once the elastic constants are obtained, the bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio σ, for Mg3CuH0.6 compound were deduced using Voigt–Reuss–Hill (VRH) approximation. The results show that this alloy exhibit ductile property. Finally, the Debye temperature is also calculated and discussed for the first time. This will be considered as the first quantitative theoretical prediction of these properties.

Computational Insights on the Mechanism of H2 Activation at Ir2S2(PPh3)4: A Combination of Multiple Reaction Pathways Involving Facile H Migration Processes.

The complex Ir2S2(PPh3)4 (1) is known to react with 1 and 2 equivalents of H2 leading to [Ir(H)(PPh3)2]2(μ-S)2 (2) and Ir2(μ-S)(μ-SH)(μ-H)H2(PPh3)4 (4), respectively ( Linck , R. C. ; Pafford , R. J. ; Rauchfuss , T. B. J. Am. Chem. Soc. 2001 , 123 , 8856 - 8857 ). Herein, the results of a thorough computational (DFT) study of these formally homo- and heterolytic H2 activation processes, respectively, are presented. These indicate that 2 is formed in a two-step process whereby the oxidative addition of H2 at a single IrII center of 1 generates an intermediate (A) that rearranges into 2 by means of a facile H migration to the neighboring Ir center. Activation of the second equivalent of H2 most likely occurs at the bridging sulfur ligands of 2 leading to a reaction intermediate (3aa) that features two (μ-SH) ligands. Intermediate 3aa present two isomers that differ only on the stereochemistry of the (μ-SH) ligands, and both of them can further evolve into 4 via H migration from (μ-SH) to bridging (μ-H). Nevertheless, an alternative mechanism based on the initial isomerization of 2 into A, and followed by H2 coordination and activation steps at a single Ir center cannot be completely ruled out. In general, the results herein show that the mechanisms for the activation of H2 at 1 and 2 involve facile H migration processes, in agreement with the experimentally observed intermetallic hydride exchange in 2 and the exchange between IrH and SH centers in 4, which proceed with computed free energy barriers of ca. 19-23 kcal mol-1.

Addressing electronic effects in the semi-hydrogenation of ethyne by InPd2 and intermetallic Ga–Pd compounds

The intermetallic compound InPd2 was prepared as single-phase material and used in an unsupported state as catalyst in the semi-hydrogenation of ethyne in a large excess of ethene. InPd2 showed high activity and selectivity (up to 93%) toward ethene in the temperature range from 478 to 508K. In addition, the compound revealed high stability during 20h time on stream at 473K at 80% selectivity and >90% conversion. Investigations by differential thermal analysis combined with thermogravimetry (DTA/TG) in H2 and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) exclude the formation of intermetallic hydrides, phase transitions, decomposition, and the presence of elemental palladium. The stability of InPd2 under reaction conditions allows addressing the influence of electronic factors on the catalytic properties by comparison with Ga–Pd intermetallic compounds. From the joint results of experiments and first-principles calculations, the electronic influence on the catalytic selectivity is found to be minor; selectivity seems to be largely governed by geometric effects – as suggested earlier by the site-isolation concept – as well as the absence of hydridic hydrogen.

ChemInform Abstract: Review of Solid State Hydrogen Storage Methods Adopting Different Kinds of Novel Materials

AbstractReview: 143 refs.

Stability of CeCo3-based intermetallic hydrides

CeCo3-based intermetallic hydride samples have been synthesized at hydrogen pressures in the range from 0.1 to 10 MPa at room and low temperatures. The phase composition and lattice parameters of the synthesized hydride phases have been determined by X-ray diffraction. The hydrides have been shown to differ in stability. Some of the samples were stable and did not lose hydrogen during storage in air at room temperature for several months, and some decomposed under the same conditions and lost hydrogen in several minutes. This behavior of the hydride phases depends on synthesis conditions (pressure and temperature) and the quantitative relationship between the α-solid solution and the β-hydride phase in the samples.

MgH2–ZrFe2Hx nanocomposites for improved hydrogen storage characteristics of MgH2

The unfavorable de/re-hydrogenation aspects of high storage capacity material, Mg can be overcome by synthesis of composites with known intermetallic hydrogen storage alloys. In this work, a new additive, ZrFe2Hx intermetallic hydride, is used to synthesize MgH2–ZrFe2Hx nanocomposite by reactive mechanical milling technique. Also this report describes the comparison of hydrogen sorption behavior of MgH2–ZrFe2 and MgH2–ZrFe2Hx nanocomposites. It is found that the composite containing ZrFe2 and ZrFe2Hx leads to decrease in desorption temperature from 410 °C (for MgH2) to 350 and 290 °C respectively. The activation energy for rehydrogenation of composite is found to be ∼61 kJ/mol. This is lowered by 30 kJ/mol compared to the pristine milled MgH2 (92 kJ/mol). Thus, the results show significant improvement of hydrogenation behavior with the addition of ZrFe2Hx. Reasons for better catalytic activity achieved by using ZrFe2Hx have been put forwarded. Based on the present studies it can be suggest that the use of hydride version instead of the parent intermetallic phase for synthesizing the composite with MgH2 has a distinct advantage in improving the hydrogenation behavior of MgH2.

Synthesis of hydrides by interaction of intermetallic compounds with ammonia

Interaction of intermetallic compounds with ammonia was studied as a processing route to synthesize hydrides and hydridonitrides of intermetallic compounds having various stoichiometries and types of crystal structures, including A2B, AB, AB2, AB5 and A2B17 (A=Mg, Ti, Zr, Sc, Nd, Sm; B=transition metals, including Fe, Co, Ni, Ti and nontransition elements, Al and B). In presence of NH4Cl used as an activator of the reaction between ammonia and intermetallic alloys, their interaction proceeds at rather mild P–T conditions, at temperatures 100–200°C and at pressures of 0.6–0.8MPa. The mechanism of interaction of the alloys with ammonia appears to be temperature-dependent and, following a rise of the interaction temperature, it leads to the formation of interstitial hydrides; interstitial hydridonitrides; disproportionation products (binary hydride; new intermetallic hydrides and binary nitrides) or new metal–nitrogen–hydrogen compounds like magnesium amide Mg(NH2)2. The interaction results in the synthesis of the nanopowders where hydrogen and nitrogen atoms become incorporated into the crystal lattices of the intermetallic alloys. The nitrogenated materials have the smallest particle size, down to 40nm, and a specific surface area close to 20m2/g.

Review of Solid State Hydrogen Storage Methods Adopting Different Kinds of Novel Materials

Overview of advances in the technology of solid state hydrogen storage methods applying different kinds of novel materials is provided. Metallic and intermetallic hydrides, complex chemical hydride, nanostructured carbon materials, metal‐doped carbon nanotubes, metal‐organic frameworks (MOFs), metal‐doped metal organic frameworks, covalent organic frameworks (COFs), and clathrates solid state hydrogen storage techniques are discussed. The studies on their hydrogen storage properties are in progress towards positive direction. Nevertheless, it is believed that these novel materials will offer far‐reaching solutions to the onboard hydrogen storage problems in near future. The review begins with the deficiencies of current energy economy and discusses the various aspects of implementation of hydrogen energy based economy.

Ab-initio structural and electronic properties of the intermetallic compound TiFeH2

Using the first principles “full-potential linearized augmented plane-wave method” based on density functional theory, structural and electronic properties of the dihydride TiFeH2 was investigated. This intermetallic hydride −65 Cmmm space group-with moderate hydrogen storage (1.8–1.9%Wt.) has an orthorhombic structure. The stability analysis and total energy were calculated using the general gradient approximation (GGA). We have investigated in the ground state the lattice parameters, bulk modulus, electronic structure and formation energy of TiFeH2 hydride. Total and partial DOS analysis show that the TiFeH2 hydride has a metallic character. Iron below the Fermi level is the main contributor to bonding manifold whereas anti-bonding titanium states dominate above. The hybridization between iron 3d and hydrogen 1s states appear to be the strongest. Electron density reveals that a relatively high electron density extends from the hydrogen atom site to the iron atom site, but not to the titanium atom site. Formation energy values indicate that the TiFeH2 system is more hydrogen reversible compared with TiFeH.

In pursuit of light intermetallic hydrides

The search for a “magic” intermetallic compound, absorbing reversibly and easily copious quantities of hydrogen, has been pursued since the discovery of the first intermetallic hydrides, forty–fifty years ago. Obviously, such intermetallic compounds should contain light metal elements like Li, Mg, Al, Ca, etc. We summarize in this work the experimental evidence that sheds light on the hydrogen absorption abstinence of Al-rich intermetallic compounds. The elastic moduli and/or bonding properties of Al-containing pseudobinary compounds initially decrease and then increase as a function of the Al composition. The shear and the bulk moduli behave differently in the Al-rich portion, where they present significantly higher and lower values, respectively, than the corresponding moduli in the Al-poor region. We claim that the extensive shear stiffening inhibits the hydrogen absorption in the Al-rich compounds. An explanation for the choice of the LaSn0.22Ni0.78 compound as a sorption cryocooler in the Planck mission is suggested in view of its shear softening with respect to LaNi5. Recent attempts to find pseudobinary intermetallic hydrides, containing Li and Ca, are also presented. These attempts are conducted by considering some of the factors which regulate hydrogen absorption in intermetallic compounds.

Studies on La based intermetallic hydrides to determine their suitability in metal hydride based cooling systems

The La0.9Ce0.1Ni5, La0.8Ce0.2Ni5, LaNi4.7Al0.3 and LaNi4.6Al0.4 intermetallic hydrides were characterised to determine their suitability in metal hydride based cooling system (MHCS). The performance of the MHCS depends on the driving potential, and rate and amount of hydrogen transfer between coupled metal hydride (MH) beds. Therefore, the effect of compositional changes on the variation of these parameters due to the variation in pressure – concentration isotherm (PCI) properties (storage capacity, plateau slope, hysteresis effect, etc.) of metal hydrides employed was studied. Compared to other possible MH pairs, La0.9Ce0.1Ni5 – LaNi4.7Al0.3 hydride pair exhibited high driving potential and transferrable amount of hydrogen, during cooling and regeneration processes, thereby better MHCS performance. In addition, the effect of change in hydrogen concentration (due to hydrogen transfer between coupled MH beds) on reaction enthalpy (ΔH) consequently on MHCS performance was found significant.

Proton relaxation and hydrogen mobility in Ti–V–Cr alloys: Improved exchange model

Here we propose an improved exchange model of proton relaxation to describe hydrogen mobility in intermetallic hydrides. The model has been successfully applied to a number of hydrides of ternary Ti–V–Cr alloys of different composition, namely, TiV0.8Cr1.2, Ti0.5V1.9Cr0.6 and Ti0.5V1.9Cr0.6 + 4 wt.% Zr7Ni10. It has been found that (i) there are two non-equivalent states of hydrogen (with different mobility) and (ii) there is an exchange between these two states. By analyzing proton relaxation and Knight shift data it was possible to estimate the exchange time between these states: 0.02 ms << τex << 10 ms. It means that in studied intermetallic hydrides for the proton spin–lattice relaxation one deals with the fast exchange between these states, whereas for the spin–spin relaxation the intermediate exchange is realized.

LaNi5- and RT3-based (R = Ce, Nd, Gd, Er; T = Co, Ni, Fe) hydrides prepared at low temperatures and H2 pressures

Hydride phases based on the intermetallic compounds LaNi5, CeCo3, NdNi3, GdFe3, DyCo3, and ErNi3 have been synthesized at a hydrogen pressure of 10 MPa and a temperature of 273 K. The phase composition of the synthesized materials and the lattice parameters of the hydride phases have been determined by X-ray diffraction. During storage in air at room temperature, the hydrides decompose more slowly than do their analogs synthesized at low pressure. The hydrogen content of the hydrides is higher than or similar to that of hydride phases synthesized at high pressure. X-ray diffraction results for the low-temperature RT3-based intermetallic hydrides demonstrate that their lattice is expanded to a lesser extent than that of their high-pressure analogs.

Hydrogen interaction with intermetallic compounds and alloys at high pressure

Abstract The paper presents a review of the recent work done in MSU on intermetallic hydrides with high dissociation pressure. Hydrogen sorption properties of a large variety of AB 5 , AB 2 and BCC intermetallic compounds and alloys were studied at pressures up to 3000 atm. Several new intermetallic hydrides with potential application in high-capacity hydrogen storage devices have been identified for the first time and fully characterised using a gas-volumetric analytical technique in a unique high-pressure apparatus. Basing on the experimental and literature results the relationships between hydrogen absorption capacity, thermodynamic parameters of interaction and composition of alloys were established. Obtained results provide a good perspective for practical application of the studied hydrides especially in metal-hydride compressors.

Investigation of hydride powder bed swelling and shrinking during hydrogen absorption/desorption cycles under different compressive stresses

► Decrepitation creates hydride bed densification while cycling under hydrogen. ► Axial compressive stress decreases the ability of a hydride bed to change its volume. ► Internal friction increases along with cycles. ► Friction of the hydride with the side walls increases the powder density. The solid storage through hydrides allows good compactness and safety due to low pressure. Intermetallic hydride materials have a significant volume increase and decrease (10–35%) upon absorption/desorption respectively. The measurement of the mechanical behavior of these materials is of major interest for the design of H 2 storage tanks. In the present work, Ti–V–Cr hydride powder beds underwent hydrogen absorption/desorption cycles in a cylindrical instrumented cell with a mobile upper piston. Different compressive stresses have been applied by the piston and a spring on the powder bed. The variations of samples volume were measured upon cycling and analyzed while considering the mechanical behavior of this granular medium. In particular, part of the volume change is balanced by the variation of the intergranular porosity of the granular media. Changing upper stress reveals the combined importance of the powder sample friction on the cell side walls, and of internal friction strongly influenced by the grains interlocking in the cyclic powder densification process observed.

Hydrogenation of Zr3Al2 in hydrogen and ammonia

We have identified conditions for the formation of Zr3Al2-based intermetallic hydrides through reactions with hydrogen and ammonia at temperatures from 150 to 300°C. The use of ammonia is shown to reduce the onset temperature for the formation of a hydride phase by 100°C compared to hydrogenation with hydrogen. Increasing the ammonia-Zr3Al2 reaction temperature to 500°C in the presence of NH4Cl as an activator leads to the decomposition of the intermetallic compound and the formation of finely dispersed zirconium hydride and zirconium nitride powders.

Structural and phase mechanism and rate of interaction between TiCu, Ti3Cu4, and Ti2Cu3 intermetallic compounds and hydrogen. I. Formation and decomposition of intermetallic hydrides

The paper examines the phase mechanism and rates of TiCu, Ti3Cu4, and Ti2Cu3 interaction with hydrogen in the range 298–573 K at a hydrogen pressure of 1.0 MPa. The thermodynamic potential of TiCu direct and destructive hydrogenation and TiCu decomposition is established. The thermodynamic priority of destructive hydrogenation in the range 298–773 K is revealed. However, x-ray diffraction shows that only direct hydrogenation of TiCu, Ti3Cu4, and Ti2Cu3 proceeds in the range 298–373 K. The intermetallic compounds successively interact at 573 K with hydrogen through the formation of intermetallic hydrides (TiCuH1.19, Ti3Cu4H2.44, and Ti2Cu3H1.32) and their decomposition to titanium hydride and copper. These hydrides form more rapidly than decompose. It is established that mechanical destruction of the material occurs during direct hydrogenation.

ChemInform Abstract: Intermetallic Hydrides: A Review with Ab Initio Aspects

AbstractReview: 113 refs.