Synthèse, caractérisation et étude des propriétés thermodynamiques d'hydrogénation de nanocomposites matériaux poreux / métaux-alliages

Nowadays many technological and scientific constraints have limited the finding of a suitable system and/or material able to reversibly store hydrogen at room temperature and ambient pressure for automotive application. An interesting way to overcome such limits could be the synthesis of hybrid materials (porous materials/metals or alloys composites) for which the adsorption and absorption processes can be combined in order to get higher hydrogen storage capacity. In this work, several porous materials displaying a well defined nanometric pore structure have been investigated. Among them a carbon template (CT) and a metal organic framework (MOF-5) have been chosen. In addition, several noble metals (Ni, Pd and Pt) have been used due to their ability to dissociate hydrogen and to form alloys. Two synthesis routes have been followed in order to synthesize hybrid composites: metal salts infiltration and mechanical grinding. In particular, the investigation of the structural, textural and hydrogen storage properties of the CT/metal composites has proven that a synergic mechanism between the CT pores and the metallic nanoparticles takes place during the hydrogen ad/absorption process. This interaction leads to an enhancement of the hydrogen storage capacity of each hybrid component taken separately.Plusieurs verrous scientifiques et technologiques empêchent aujourd’hui de développer une technique et/ou un matériau qui permette de stocker une quantité importante d’hydrogène à pression et température ambiante dans un volume et un poids acceptable pour des applications embarquées. Une possible solution consiste à synthétiser des matériaux hybrides (matériaux poreux/métaux ou alliages) où les processus d’adsorption et d’absorption pourraient coopérer pour obtenir une capacité de stockage d’hydrogène en adéquation avec les besoins des applications. Notre travail a consisté à identifier et caractériser différents matériaux poreux ayant une organisation de pores bien définie et une taille de l’ordre de quelques nanomètres. Parmi eux, ont été choisis : une réplique de carbone (CT) et un réseau organométallique (MOF-5). De plus, plusieurs métaux nobles (Ni, Pd et Pt) ont été choisis pour leur facilité à dissocier l’hydrogène et à former des alliages (Pd-Ni) avec différentes compositions en milieu aqueux (oxydant). Une méthode d’imprégnation par voie chimique ainsi que le broyage mécanique ont été utilisés pour la synthèse des hybrides. L’étude des propriétés structurales, texturales et thermodynamiques (hydrogénation) des composites CT/Pd a montré qu’un effet coopératif existe entre les pores du CT et les nanoparticules métalliques pendant le processus d’ad/absorption d’hydrogène. Cette interaction entraîne une amélioration de la capacité d’hydrogénation par rapport à chacun des constituants de l’hybride

Synthesis, characterization and study of thermodynamic Hydrogen storage properties of Metal-Alloy nanoparticles / Porous Materials nanocomposites

Plusieurs verrous scientifiques et technologiques empêchent aujourd’hui de développer une technique et/ou un matériau qui permette de stocker une quantité importante d’hydrogène à pression et température ambiante dans un volume et un poids acceptable pour des applications embarquées. Une possible solution consiste à synthétiser des matériaux hybrides (matériaux poreux/métaux ou alliages) où les processus d’adsorption et d’absorption pourraient coopérer pour obtenir une capacité de stockage d’hydrogène en adéquation avec les besoins des applications. Notre travail a consisté à identifier et caractériser différents matériaux poreux ayant une organisation de pores bien définie et une taille de l’ordre de quelques nanomètres. Parmi eux, ont été choisis : une réplique de carbone (CT) et un réseau organométallique (MOF-5). De plus, plusieurs métaux nobles (Ni, Pd et Pt) ont été choisis pour leur facilité à dissocier l’hydrogène et à former des alliages (Pd-Ni) avec différentes compositions en milieu aqueux (oxydant). Une méthode d’imprégnation par voie chimique ainsi que le broyage mécanique ont été utilisés pour la synthèse des hybrides. L’étude des propriétés structurales, texturales et thermodynamiques (hydrogénation) des composites CT/Pd a montré qu’un effet coopératif existe entre les pores du CT et les nanoparticules métalliques pendant le processus d’ad/absorption d’hydrogène. Cette interaction entraîne une amélioration de la capacité d’hydrogénation par rapport à chacun des constituants de l’hybride.Nowadays many technological and scientific constraints have limited the finding of a suitable system and/or material able to reversibly store hydrogen at room temperature and ambient pressure for automotive application. An interesting way to overcome such limits could be the synthesis of hybrid materials (porous materials/metals or alloys composites) for which the adsorption and absorption processes can be combined in order to get higher hydrogen storage capacity. In this work, several porous materials displaying a well defined nanometric pore structure have been investigated. Among them a carbon template (CT) and a metal organic framework (MOF-5) have been chosen. In addition, several noble metals (Ni, Pd and Pt) have been used due to their ability to dissociate hydrogen and to form alloys. Two synthesis routes have been followed in order to synthesize hybrid composites: metal salts infiltration and mechanical grinding. In particular, the investigation of the structural, textural and hydrogen storage properties of the CT/metal composites has proven that a synergic mechanism between the CT pores and the metallic nanoparticles takes place during the hydrogen ad/absorption process. This interaction leads to an enhancement of the hydrogen storage capacity of each hybrid component taken separately

Hydrogenation of carbon monoxide over nanostructured systems: a mechanochemical approach

In this study we investigated the mechanochemical hydrogenation of carbon monoxide over nanostructured FeCo- and Mg2Ni-based catalysts. To this aim powdered materials, prepared by mechanical alloying, were subjected to mechanical treatment under CO + H2 atmosphere. A methodology to evaluate the activity of the solid catalysts on an absolute basis was developed. Conversion data were, indeed, expressed as turnover frequency, TOF, and related to the occurrence of ball to powder collision events through the mechanochemical turnover frequency parameter, MTOF. Differences in the catalytic activity and selectivity were observed for the two FeCo-based studied systems, the solid solution Fe50Co50 and its dispersion on TiO2 support. As for the Mg2Ni system, we explored the possibility to estimate the specific role of hydrogen pre-activation step. The catalytic properties of the mechanically alloyed Mg2Ni system were compared with the conversion data shown by the same system pre-hydrogenated and subsequently milled under CO atmosphere

Hydrogenation of carbon monoxide over nanostructured systems: a mechanochemical approach

n this study we investigated the mechanochem. hydrogenation of carbon monoxide over nanostructured FeCo- and Mg2Ni-based catalysts. To this aim powd. materials, prepd. by mech. alloying, were subjected to mech. treatment under CO + H2 atmosphere. A methodol. to evaluate the activity of the solid catalysts on an abs. basis was developed. Conversion data were, indeed, expressed as turnover frequency, TOF, and related to the occurrence of ball to powder collision events through the mechanochem. turnover frequency parameter, MTOF. Differences in the catalytic activity and selectivity were obsd. for the two FeCo-based studied systems, the solid soln. Fe50Co50 and its dispersion on TiO2 support. As for the Mg2Ni system, we explored the possibility to est. the specific role of hydrogen pre-activation step. The catalytic properties of the mech. alloyed Mg2Ni system were compared with the conversion data shown by the same system pre-hydrogenated and subsequently milled under CO at

Corrigendum to “Crystal structure solution of KMg(ND)(ND2): An ordered mixed amide/imide compound” [Int J Hydrogen Energy 39 (2) 2014) 868 - 876]

This corrigendum to orignal article [Int J Hydrogen Energy 39 (2) 2014) 868 - 876] wants to points out that there are two different way to describe the structure of KMg(ND)(ND2). This was described as an orthorhombic system with space group P212121 (n.19) in the original article. However, after the publication of the article the authors found out that the structure can also be described in higher symmetry using the space group Pnma (n.62) in the orthorhombic system. The corrigendum describes i netails this second possibility.JRC.F.2-Energy Conversion and Storage Technologie

Structure Solution of a New Ordered Mixed Imide-Amide Compound for Hydrogen Storage

In order to elucidate the reaction pathways in complex hydrogen storage materials, the compound KMg(NH)(NH2) was synthesized from the reversible dehydrogenation process of a Mg(NH2)2/KH mixture. Preliminary powder X-ray diffraction patterns on specimens without any deuteration were supplemented with neutron powder diffraction studies on the reaction products from deuterated precursors with the intent of solving the crystal structure. The compound presents the orthorhombic space group Pnma (62) with lattice parameters: a = 9.3497(3)Å; b = 3,6631(1)Å; c = 9.8901(3)Å, respectively. The coexistence of imide/amide groups in the same compound allows us to notice for the fi rst time a heptahedral geometry arrangement around potassium atoms by imide and amide units.JRC.F.2-Energy Conversion and Storage Technologie

Crystal structure solution of KMg(ND)(ND2): An ordered mixed amide/imide compound

An ordered mixed deuterated amide/imide potassiumemagnesium compound was synthesized with the intent of solving its structure using neutron diffraction technique with help of “ab-initio” methods. Obtained powder diffraction patterns were compatible with the orthorhombic P212121 space group, and lattice parameters a ¼ 9.8896(3) A; b ¼ 9.3496(3) A; c ¼ 3.6630(1) A, respectively. Assuming a density of 1.91 g/cm3 the investigation has allowed to locate the four constituting elements distributed in seven different sites into Wyckoff general positions 4(a), for a total of 28 atoms in the unit cell. This is the first example of crystal structure solution of amixed imide/amide compound appearing during the dehydrogenation process of a potassium containing amide based hydrogen storage material.JRC.F.2-Cleaner energ

Enhanced Hydrogen Uptake/Release in 2LiH–MgB2 Composite with Titanium Additives

The influence of different titanium additives on hydrogen sorption in LiH–MgB2 system has been investigated. For all the composites LiH–MgB2–X (X = TiF4, TiO2, TiN, and TiC), prepared by ball milling in molar ratios 2:1:0.1, five hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenuated total reflection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorption-desorption cycles. All the composites with the titanium additives displayed an improvement of reaction kinetics, especially during hydrogen desorption. The LiH–MgB2–TiO2 system reached a storage of about 7.6 wt % H2 in ~ 1.8 hours for absorption and ~ 2.7 hours for desorption. Using in-situ SR-PXD measurements, magnesium was detected as an intermediate phase during hydrogen desorption for all composites. In the composite with TiF4 addition the formation of new phases (TiB2 and LiF) were observed. Characteristic diffraction peaks of TiO2, TiN and TiC additives were always present during hydrogen absorption-desorption. For all as-milled composites, ATR-IR spectra did not show any signals for borohydrides, while for all hydrogenated composites B–H stretching (2450– 2150 cm-1) and B–H bending (1350–1000 cm-1) bands were exactly the same as for commercial LiBH4.JRC.F.2-Cleaner energ

Ammonia-free infiltration of NaBH4 into highly-ordered mesoporous silica and carbon matrices for hydrogen storage

In this work we focused on nanoconfiment of NaBH4 into highly-ordered Si-based and its carbon replica mesoporous scaffolds by ammonia-free wet chemical impregnation. Structural and morphological characterization, performed by X-ray diffraction and Transmission electron microscopy allowed to confirm the effectiveness infiltration procedure. Desorption properties tested by Temperature programmed desorption analyses highlighted a noticeable shift towards lower temperature than corresponding bulk material and literature data referred to similar systems.JRC.F.2-Cleaner energ