Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

The present work addresses the kinetics of chemical transformations activated by the mechanical processing of powder by ball milling. In particular, attention focuses on the reaction between NaNH2 and MgH2, specific case studies suitably chosen to throw light on the kinetic features emerging in connection with the exchange of anionic ligands induced by mechanical activation. Experimental findings indicate that the mechanical treatment of NaNH2–MgH2 powder mixtures induces a simple metathetic reaction with formation of NaH and Mg(NH2)2 phases. Chemical conversion data obtained by X-ray diffraction analysis have been interpreted using a kinetic model incorporating the statistical character of the mechanical processing by ball milling. The apparent rate constant measuring the reaction rate is related to the volume of powder effectively processed during individual collisions, and tentatively connected with the transfer of mechanical energy across the network formed by the points of contact between the powder particles trapped during collisions.H2020-MSCA-IF-2015 Grant Number #70795

Solid state hydrogen storage in alanates and alanate-based compounds: a review

The safest way to store hydrogen is in solid form, physically entrapped in molecular form in highly porous materials, or chemically bound in atomic form in hydrides. Among the different families of these compounds, alkaline and alkaline earth metals alumino-hydrides (alanates) have been regarded as promising storing media and have been extensively studied since 1997, when Bogdanovic and Schwickardi reported that Ti-doped sodium alanate could be reversibly dehydrogenated under moderate conditions. In this review, the preparative methods; the crystal structure; the physico-chemical and hydrogen absorption-desorption properties of the alanates of Li, Na, K, Ca, Mg, Y, Eu, and Sr; and of some of the most interesting multi-cation alanates will be summarized and discussed. The most promising alanate-based reactive hydride composite (RHC) systems developed in the last few years will also be described and commented on concerning their hydrogen absorption and desorption performanc

CO2 reactivity with Mg2NiH4 synthesized by: In situ monitoring of mechanical milling

CO2 capture and conversion are a key research field for the transition towards an economy only based on renewable energy sources. In this regard, hydride materials are a potential option for CO2 methanation since they can provide hydrogen and act as a catalytic species. In this work, Mg2NiH4 complex hydride is synthesized by in situ monitoring of mechanical milling under a hydrogen atmosphere from a 2MgH2:Ni stoichiometric mixture. Temperature and pressure evolution is monitored, and the material is characterized, during milling in situ, thus providing a good insight into the synthesis process. The cubic polymorph of Mg2NiH4 (S.G. Fm3m) starts to be formed in the early beginning of the mechanical treatment due to the mechanical stress induced by the milling process. Then, after 25 hours of milling, Mg2NiH4 with a monoclinic (S.G. C12/c1) structure appears. The formation of the monoclinic polymorph is most likely related to the stress release that follows the continuous refinement of the material's microstructure. At the end of the milling process, after 60 hours, the as-milled material is composed of 90.8 wt% cubic Mg2NiH4, 5.7 wt% monoclinic Mg2NiH4, and 3.5 wt% remnant Ni. The as-milled Mg2NiH4 shows high reactivity for CO2 conversion into CH4. Under static conditions at 400 °C for 5 hours, the interactions between as-milled Mg2NiH4 and CO2 result in total CO2 consumption and in the formation of the catalytic system Ni-MgNi2-Mg2Ni/MgO. Experimental evidence and thermodynamic equilibrium calculations suggest that the global methanation mechanism takes place through the adsorption of C and the direct solid gasification towards CH4 formation.Fil: Grasso, María Laura. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Puszkiel, Julián Atilio. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Helmholtz-Zentrum Geesthacht GmbH; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Gennari, Fabiana Cristina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Santoru, Antonio. Helmholtz-Zentrum Geesthacht GmbH; AlemaniaFil: Dornheim, Martin. Helmholtz-Zentrum Geesthacht GmbH; AlemaniaFil: Pistidda, Claudio. Helmholtz-Zentrum Geesthacht GmbH; Alemani

Sorption properties and reversibility of Ti(IV) and Nb(V)-fluoride doped-Ca(BH4)2-MgH2 system

Ajuts: The authors are grateful to the Marie-Curie European Research Training Network (Contract MRTN-CT-2006-03 5366/COSY)In the last decade, alkaline and alkaline earth metal tetrahydroborates have been the focuses of the research due to their high gravimetric and volumetric hydrogen densities. Among them, Ca(BH4)2 and the Ca(BH4)2 + MgH2 reactive hydride composite (RHC), were calculated to have the ideal thermodynamic properties which fall within the optimal range for mobile applications.In this study, the addition of NbF5 or TiF4 to the Ca(BH4)2 + MgH2 reactive hydride composite system was attempted aiming to obtain a full reversible system with the simultaneous supression of CaB12H12. Structural characterization of the specimens was performed by means of in-situ Synchroton Radiation Power X-ray diffraction (SR-PXD) and 11B {1H} Solid State Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR). The evolution of the chemical state of the Nb- and Ti-based additives was monitored by X-ray Absorption Near Edge Structure (XANES). The addition of NbF5 or TiF4 to the Ca(BH4)2 + MgH2 system have not supressed completely the formation of CaB12H12 and only a slight improvement concerning the reversible reaction was displayed just in the case of Nb-doped composite materia

Modeling the thermodynamics of the FeTi hydrogenation under para-equilibrium: an ab-initio and experimental study

FeTi-based hydrides have recently re-attracted attention as stationary hydrogen storage materials due to favorable reversibility, good sorption kinetics and relatively low costs compared to alternative intermetallic hydrides. Employing the OpenCalphad software, the thermodynamics of the (FeTi)$_{1-x}$H$_{x}$ (0 $\leq x \leq$ 1) system were assessed as a key basis for modeling hydrogenation of FeTi-based alloys. New thermodynamic data were acquired from our experimental pressure-composition-isotherm (PCI) curves, as well as first-principles calculations utilizing density functional theory (DFT). The thermodynamic phase models were carefully selected based on critical analysis of literature information and \emph{ab-initio} investigations. Key thermodynamic properties such as dissociation pressure, formation enthalpies and phase diagrams were calculated in good agreement to our performed experiments and literature-reported data. This work provides an initial perspective, which can be extended to account for higher-order thermodynamic assessments and subsequently enables the design of novel FeTi-based hydrides. In addition, the assessed thermodynamic data can serve as key inputs for kinetic models and hydride microstructure simulations.Comment: 15 pages, 7 figure

CO2 reutilization for methane production: Via a catalytic process promoted by hydrides

CO2 emissions have been continuously increasing during the last half of the century with a relevant impact on the planet and are the main contributor to the greenhouse effect and global warming. The development of new technologies to mitigate these emissions poses a challenge. Herein, the recycling of CO2 to produce CH4 selectively by using Mg2FeH6 and Mg2NiH4 complex hydrides as dual conversion promoters and hydrogen sources has been demonstrated. Magnesium-based metal hydrides containing Fe and Ni catalyzed the hydrogenation of CO2 and their total conversion was obtained at 400 °C after 5 h and 10 h, respectively. The complete hydrogenation of CO2 depended on the complex hydride, H2:CO2 mol ratio, and experimental conditions: temperature and time. For both hydrides, the activation of CO2 on the metal surface and its subsequent capture resulted in the formation of MgO. Investigations on the Mg2FeH6-CO2 system indicated that the main process occurs via the reversed water-gas shift reaction (WGSR), followed by the methanation of CO in the presence of steam. In contrast, the reduction of CO2 by the Mg-based hydride in the Mg2NiH4-CO2 system has a strong contribution to the global process. Complex metal hydrides are promising dual promoter-hydrogen sources for CO2 recycling and conversion into valuable fuels such as CH4.Fil: Grasso, María Laura. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Puszkiel, Julián Atilio. Helmholtz zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Fernández Albanesi, Luisa Francisca. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Dornheim, Martin. Helmholtz zentrum Geesthacht; AlemaniaFil: Pistidda, Claudio. Helmholtz zentrum Geesthacht; AlemaniaFil: Gennari, Fabiana Cristina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada CAB. Departamento Fisicoquímica de Materiales; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Kinetics and hydrogen storage performance of Li-Mg-N-H systems doped with Al and AlCl3

Recent investigations showed the formation of new amide-chloride phases between LiNH2 and AlCl3 after milling and/or heating under hydrogen pressure. These phases exhibited a key role in the improvement of the hydrogen storage properties of the LiNH2-LiH composite. In the present work, we studied the effects of Al and AlCl3 additives on the hydrogen storage behavior of the Li-Mg-N-H system. The dehydrogenation kinetics and the reaction pathway of Al and AlCl3 modified LiNH2-MgH2 composite were investigated through a combination of kinetic measurements and structural analyses. During the first cycle, the addition of Al catalytically accelerates the hydrogen release at 200 °C. In the subsequent cycles, the formation of a new phase of unknown nature is probably responsible for both increased equilibrium hydrogen pressure and decreased dehydrogenation rate. In contrast, AlCl3 additive reacts with LiNH2-MgH2 through the milling and continues during heating under hydrogen pressure. Addition of AlCl3 leads to the formation of two cubic structures identified in the Li-Al-N-H-Cl system, which improves dehydrogenation rate by modifying the thermodynamic stability of the material. This study evidences positive effect of cation and/or anion substitution on hydrogen storage properties of the Li-Mg-N-H system.This study has been partially supported by bilateral collaboration Project MINCyT-MA