Hydride Sites Research Articles

High-temperature carbon dioxide capture in a porous material with terminal zinc hydride sites.

Carbon capture can mitigate point-source carbon dioxide (CO2) emissions, but hurdles remain that impede the widespread adoption of amine-based technologies. Capturing CO2 at temperatures closer to those of many industrial exhaust streams (>200°C) is of interest, although metal oxide absorbents that operate at these temperatures typically exhibit sluggish CO2 absorption kinetics and instability to cycling. Here, we report a porous metal-organic framework featuring terminal zinc hydride sites that reversibly bind CO2 at temperatures above 200°C-conditions that are unprecedented for intrinsically porous materials. Gas adsorption, structural, spectroscopic, and computational analyses elucidate the rapid, reversible nature of this transformation. Extended cycling and breakthrough analyses reveal that the material is capable of deep carbon capture at low CO2 concentrations and high temperatures relevant to postcombustion capture.

Facile C[sbnd]H aryl and O[sbnd]H bonds activation at dirhenium site of [Re2(CO)8(THF)2] complex

The activation of small molecules is a topic of great interest and previously we reported on the easy activation of different types of EH bonds at the dinuclear complex [Re2(CO)8(THF)2] (1) where labile THF molecules coordinate to adjacent rhenium(0) atoms. Here we extend the reactivity of 1 reporting on the oxidative addition of benzene and toluene at room temperature to give [Re2(μ-H)(μ-κC-Ar)(CO)8], Ar = −C6H5 (2) and −C6H4Me (3). Compound 3 is a new example of μ-κC-Ar dinuclear rhenium complex and has been obtained as para and meta isomers (3a,b). It is known from the literature that 2 can activate arenes and heteroarenes via reductive elimination of benzene and oxidative addition of CH bonds to the dinuclear fragment. Here we have studied the reaction of 2 with C6D6 and H2CC(H)Ph and determined the kinetic constants by 1H NMR (1.4 × 10−5 s−1 at 308 K and 1.1 × 10−5 s−1 at 298 K, respectively). The results indicate that the rate-determining step of the reaction is the reductive elimination of benzene, while the oxidative addition is fast. Water and methanol react with 1 in toluene at room temperature to give the hydroxo and methoxo hydrido complexes [Re2(μ-H)(μ-OR)(CO)8], RH (5) and CH3 (6). On reacting 1 with water in deuterated toluene, and monitoring by 1H/2H NMR, a preferential deuteration of the hydride site to give [Re2(μ-D)(μ-OH)(CO)8] is evidenced. This finding excludes the oxidative addition of water on the dinuclear “Re2(CO)8” fragment while supporting a heterolytic addition of water via protonation at the µ-κC-tolyl group, elimination of toluene and addition of OH−. Single crystal X-ray diffraction analyses have been performed for complexes 3a, 5 and 6 and their solid state structures have been determined. In particular, the crystal structure of 5 results in a new polymorphic form (5b) and it is discussed in comparison with the already known one (5a).

Oxygen Vacancy-Induced Interfacial Lanthanum Hydride and Hydroxide Bifunctional Sites for Selective Hydrogenolysis of Furanic Compounds to Alkyl Diols

Oxygen Vacancy-Induced Interfacial Lanthanum Hydride and Hydroxide Bifunctional Sites for Selective Hydrogenolysis of Furanic Compounds to Alkyl Diols

Hydrogen storage of high entropy alloy NbTiVZr and its effect on mechanical properties: A first-principles study

In recent years, high entropy alloys (HEAs) have demonstrated remarkable potential for hydrogen storage applications. Although extensive experimental studies have been conducted, a detailed understanding of the hydrogenation process at the atomic level is still lacking. In this study, first-principles calculations were employed to explore the microstructural evolution during hydrogen absorption in NbTiVZr as well as the mechanical characteristics of hydrides. The results indicate that a phase transition from BCC to FCC occurs in the hydride when the hydrogen content reaches 0.05 wt%. Hydrogen tends to occupy the octahedral interstitial sites in the BCC hydrides, while the preferred hydrogen sites in FCC hydrides undergo a transition from octahedral sites → tetrahedral + octahedra sites → tetrahedral sites as the hydrogen content increases. The highest hydrogen storage capacity of NbTiVZr was predicted by the phonon spectra of hydrides to be 2.94 wt%. Vanadium (V) is discovered to play a crucial role in hydrogen absorption capacity by causing significant lattice distortion and forming stronger bonds with hydrogen. Additionally, all hydrides exhibit great mechanical properties and thermal stability. Our research reveals that NbTiVZr has an excellent capacity for storing hydrogen and has the potential for applications in hydrogen storage materials.

A comparative study of RuO2 and Ru reveals the role of oxygen vacancies in electrocatalytic nitrogen reduction to ammonia under ambient conditions

Nitrogen molecule reduction to ammonia requires adsorption and hydrogenation sites. In this study, the nitrogen reduction reaction (NRR) activity of RuO2 and metallic Ru catalysts was studied to explore the role of oxides and metallic dual active sites. Ruthenium oxide nanoparticles displayed an ammonia production rate of 16.5 µg h−1 cm−2 with a Faradaic efficiency (FE) of 0.26% at − 0.15 V vs. RHE in N2-saturated 0.1 M KOH which is 58% higher compared to Ru black (6.8 µg h−1 cm−2 with 0.19% FE at −0.15 Vvs.RHE). This is attributed to the formation of oxygen vacancies (Vo) on the RuO2 surface during cathodic potential polarization, which provides a facile adsorption site for N2 in addition to the Ru4+ active site while the proton supplied via hydrogen spillover from the metal hydride site to the adsorbed Vo-N2 site. This assumption was validated by detailed XPS, XRD, and N2 TPD analysis.

Effect of reaction path on high-pressure synthesis and stability of ruthenium hydrides

This study explores the behavior of ruthenium hydrides under high-pressure conditions through three thermodynamical paths using laser-heated diamond anvil cells. The synthesis of RuH0.9 occurs gradually exceeding the pressure of 23.5 GPa in the ambient temperature path, while RuH is successfully synthesized at pressures above 20 GPa and a temperature of 1500 K. High-temperature conditions are found to reduce the pressure required for synthesis. The results demonstrate that the hydrogen occupancy of octahedral interstitial sites in the ruthenium hydrides is found to reach saturation with complete hydrogen absorption in the high-temperature path. Moreover, the crystallinity of the ruthenium hydride samples improves at higher temperatures, with the grain size increasing from 10 nm in the ambient temperature path to submicron in the high-temperature path. However, the predicted RuH6 and RuH3 were not observed in the present work.

Hydrogen Solution in Tetrahedral Interstitial Sites in ZrCo Hydrides: A First-Principles Study

This work aims to investigate the characteristics of the H atom in the tetrahedral interstitial sites of 8f2, 4c1, 8f1, 4c2, 8e, and 8g1 in the ZrCoH3 cell by first principles calculation based on the density functional theory. The research shows that pressure can change the local property of the electrons and the bonding ability of the H atom and its adjacent metal atoms, resulting in changes in the stable point and the disproportion point of the H atom in ZrCoH3. Further research has found that at P = 0 GPa, the significant Co-H covalent bond makes the H atom prefer to occupy the tetrahedral interstitial sites of 8f1 and 4c2 in the ZrCoH3 cell, while the H atom occupying the tetrahedral interstitial site of 4c1 in the ZrCoH3 cell has a significant Zr-H ionic bond with its adjacent Zr atom, which is the reason for the disproportionation of the ZrCoH3 alloy. When P = 10 GPa, the H atoms become unstable in the 8f1 and 4c2 tetrahedral interstices of the ZrCoH3 crystal cell. The significant Zr-H ionic bond between the H atoms in the 8f1 tetrahedral interstice and their adjacent Zr atoms is the reason for the disproportionation of the ZrCoH3 alloy, and the significant Co-H covalent bond makes the H atoms preferentially occupy the 4c1 and 8g1 tetrahedral interstices.

Ab initio study of metastable occupation of tetrahedral sites in palladium hydrides and its impact on superconductivity

A recent experimental work on palladium hydrides suggested that metastable structures with hydrogen atoms occupying tetrahedral sites could lead to superconductivity above 50 K, a huge increase compared to the 10 K critical temperature of the stable structure with all hydrogen atoms occupying octahedral sites. By generating many structures with hydrogen atoms randomly occupying the octahedral and tetrahedral sites of the face-centered cubic lattice and calculating their energy at different theoretical levels from first principles, we determine that metastable structures with partial or full occupation of tetrahedral sites are possible, even when the ionic quantum zero-point energy and anharmonicity are included in the calculations. Anharmonicity is crucial in palladium hydrides when hydrogen atoms occupy octahedral sites and, in fact, makes the structure with full octahedral occupation the ground state. Despite the metastable existence of structures with full or partial tetrahedral sites occupation, the superconducting critical temperature is reduced with the number of tetrahedral sites occupied. Our calculations discard that the occupation of tetrahedral sites can increase the critical temperature in palladium hydrides.

Probing the electronic structure and hydride occupancy in barium titanium oxyhydride through DFT-assisted solid-state NMR

Perovskite-type oxhydrides such as BaTiO3-xHy exhibit mixed hydride ion and electron conduction and are an attractive class of materials for developing energy storage devices. However, the underlying mechanism of electric conductivity and its relation to the composition of the material remains unclear. Here we report detailed insights into the hydride local environment, the electronic structure and hydride conduction dynamics of barium titanium oxyhydride. We demonstrate that DFT-assisted solid-state NMR is an excellent tool for differentiating between the different feasible electronic structures in these solids. Our results indicate that upon reduction of BaTiO3 the introduced electrons are delocalized among all Ti atoms forming a bandstate. Furthermore, each vacated anion site is reoccupied by at most a single hydride, or else remains vacant. This single occupied bandstate structure persists at different hydrogen concentrations (y = 0.13-0.31) and a wide range of temperatures (∼100-300 K).

Locating Hydrides in Ligand-Protected Copper Nanoclusters by Deep Learning.

Hydrides play an important role in constructing atomically precise metal nanoclusters and nanoparticles. They occupy both the interstitial sites inside the metal cores and the interfacial sites between the surface of the metal core and the ligand layer. Although the heavy-atom positions can be routinely determined by single-crystal X-ray diffraction, the challenge in growing a large and high-enough-quality single crystal for neutron diffraction and the limited availability of neutron sources have prevented researchers from precisely knowing the hydride locations. A recently developed deep-learning method showed great promise in accelerating the determination of hydride sites in metal nanostructures, but it is unclear if this approach, trained on clusters up to Cu32 in size, can be applied to recently discovered, much larger nanoclusters such as Cu81. Here we show that an improved deep-learning model based on convolutional neural networks is both accurate and robust. We apply it to two recently reported copper nanoclusters, [Cu32(PET)24H8Cl2]2- and [Cu81(PhS)46(tBuNH2)10H32]3+, whose hydride locations have not been determined by neutron but were proposed from density functional theory (DFT) calculations. In the former, our CNN model confirms the DFT structure; in the latter, our CNN model predicts a more stable structure with different hydride sites.

Deep Learning Accelerated Determination of Hydride Locations in Metal Nanoclusters

AbstractAlthough the coordinates of the metal atoms can be accurately determined by X‐ray crystallography, locations of hydrides in metal nanoclusters are challenging to determine. In principle, neutron crystallography can be employed to pinpoint the hydride positions, but it requires a large crystal and a neutron source, which prevents its routine use. Here, we present a deep‐learning approach that can accelerate determination of hydride locations in single‐crystal X‐ray structure of metal nanoclusters of different sizes. We demonstrate the efficiency of our method in predicting the most probable hydride sites and their combinations to determine the total structure for two recently reported copper nanoclusters, [Cu25H10(SPhCl2)18]3− and [Cu61(StBu)26S6Cl6H14]+ whose hydride locations have not been determined by neutron diffraction. Our method can be generalized and applied to other metal systems, thereby eliminating a bottleneck in atomically precise metal hydride nanochemistry.

Deep Learning Accelerated Determination of Hydride Locations in Metal Nanoclusters.

Although the coordinates of the metal atoms can be accurately determined by X-ray crystallography, locations of hydrides in metal nanoclusters are challenging to determine. In principle, neutron crystallography can be employed to pinpoint the hydride positions, but it requires a large crystal and a neutron source, which prevents its routine use. Here, we present a deep-learning approach that can accelerate determination of hydride locations in single-crystal X-ray structure of metal nanoclusters of different sizes. We demonstrate the efficiency of our method in predicting the most probable hydride sites and their combinations to determine the total structure for two recently reported copper nanoclusters, [Cu25 H10 (SPhCl2 )18 ]3- and [Cu61 (St Bu)26 S6 Cl6 H14 ]+ whose hydride locations have not been determined by neutron diffraction. Our method can be generalized and applied to other metal systems, thereby eliminating a bottleneck in atomically precise metal hydride nanochemistry.

On Prediction of a Novel Chiral Material Y2H3O(OH): A Hydroxyhydride Holding Hydridic and Protonic Hydrogens.

Examination of possible pathways of how oxygen atoms can be added to a yttrium oxyhydride system allowed us to predict new derivatives such as hydroxyhydrides possessing the composition M2H3O(OH) (M = Y, Sc, La, and Gd) in which three different anions (H-, O2−, and OH-) share the common chemical space. The crystal data of the solid hydroxyhydrides obtained on the base of DFT modeling correspond to the tetragonal structure that is characterized by the chiral space group . The analysis of bonding situation in M2H3O(OH) showed that the microscopic mechanism governing chemical transformations is caused by the displacements of protons which are induced by interaction with oxygen atoms incorporated into the crystal lattice of the bulk oxyhydride. The oxygen-mediated transformation causes a change in the charge state of some adjacent hydridic sites, thus forming protonic sites associated with hydroxyl groups. The predicted materials demonstrate a specific charge ordering that is associated with the chiral structural organization of the metal cations and the anions because their lattice positions form helical curves spreading along the tetragonal axis. Moreover, the effect of spatial twisting of the H- and H+ sites provides additional linking via strong dihydrogen bonds. The structure–property relationships have been investigated in terms of structural, mechanical, electron, and optical features. It was shown that good polar properties of the materials make them possible prototypes for the design of nonlinear optical systems.

Insights into the lanthanum doping effect on the hydriding of cerium-lanthanum alloy

Hydriding reaction kinetics of cerium-lanthanum alloy was studied by the pressure-volume-temperature (PVT) method combined with in-situ microscope. The hydride nucleation and the H2 consumption rate approximately follow an exponential model at the initial time. Furthermore, the H2 consumption rate and the hydride nucleation were accelerated by the doped lanthanum (1–10%). The growth rate of the hydride sites approximately follows a linear law and it is not affected by the lanthanum content. An approximate parabola relation between the induction time and lanthanum content is evident. The hydriding reaction rate is accelerated by the doped lanthanum, which manifest as the accelerated H2 consumption rate, decreased induction time and accelerated nucleation. The results of XRD, Raman spectroscopy and Auger electron spectroscopy (AES) show that the oxide layer is constituted of CeO2 layer and nonstoichiometric transition layer, and the doped lanthanum can increase the concentration of the oxygen vacancies. The oxygen vacancies increase the active sites to accelerate the dissociation of absorbed hydrogen molecule and offers additional short-circuit diffusion paths to accelerate the transport of hydrogen atom in the oxide layer.

Yb~51In13H27: A complex metal hydride grown from Yb/Li flux

Molten mixtures of ytterbium and lithium metals can be used as fluxes for the synthesis of metal hydrides. Reactions of indium and lithium hydride in Yb/Li flux produce Yb~51In13H27 (cubic, Im-3; a = 16.218(6) Å, Z = 2). Yb~51In13H27 is an analog of previously reported Ca54In13H27 which was grown from Ca/Li flux. The compound features In@Yb12@H20@Yb30 Bergman-like clusters at the corners and body centers of the cubic lattice. The clusters are connected by a hydride site and disordered ytterbium sites. Magnetic susceptibility measurements indicate the ytterbium is divalent; the compound shows diamagnetic behavior with a Curie tail at lower temperatures attributed to impurities such as traces of Yb3+ that form on crystal surfaces due to slight oxidation.

Site Selectivity of Hydride in Early-Transition-Metal Ruddlesden-Popper Oxyhydrides.

Layered perovskite titanium oxyhydrides have been prepared by low-temperature topochemical CaH2 reduction from Ruddlesden-Popper Sr n+1Ti nO3 n+1 phases ( n = 1, 2) and structurally characterized by combined synchrotron X-ray and neutron diffraction data refinements. In the single-layered Sr2TiO3.91(2)D0.14(1) material, hydride anions are statistically disordered with oxides on the apical site only, as opposed to known transition-metal oxyhydrides exhibiting a preferred occupation of the equatorial site. This unprecedented site selectivity of H- has been reproduced by periodic DFT+ U calculations, emphasizing for the hydride defect a difference in formation energy of 0.24 eV between equatorial and apical sites. In terms of electronic structure, the model system Sr2TiO3.875H0.125 is found to be slightly metallic and the released electron remains mostly delocalized over several Ti atoms. On the other hand, hydride anions in the double-layered Sr3Ti2O6.20H0.12 material show a clear preference for the bridging apical site within the perovskite slabs, as confirmed by DFT calculations on the Sr3Ti2O6.875H0.125 model system. Finally, the influence of the B-site chemical nature on the hydride site selectivity for early 3d transition metals is theoretically explored in the single-layered system by substituting vanadium for titanium. The V3+ electronic polaron is suggested to play a role in stabilizing H- on the equatorial site in Sr2VO4- xH x for x = 0.125.

Chemoselective Hydrogenation with Supported Organoplatinum(IV) Catalyst on Zn(II)-Modified Silica.

Well-defined organoplatinum(IV) sites were grafted on a Zn(II)-modified SiO2 support via surface organometallic chemistry in toluene at room temperature. Solid-state spectroscopies including XAS, DRIFTS, DRUV-vis, and solid-state (SS) NMR enhanced by dynamic nuclear polarization (DNP), as well as TPR-H2 and TEM techniques revealed highly dispersed (methylcyclopentadienyl)methylplatinum(IV) sites on the surface ((MeCp)PtMe/Zn/SiO2, 1). In addition, computational modeling suggests that the surface reaction of (MeCp)PtMe3 with Zn(II)-modified SiO2 support is thermodynamically favorable (Δ G = -12.4 kcal/mol), likely due to the increased acidity of the hydroxyl group, as indicated by NH3-TPD and DNP-enhanced 17O{1H} SSNMR. In situ DRIFTS and XAS hydrogenation experiments reveal the probable formation of a surface Pt(IV)-H upon hydrogenolysis of Pt-Me groups. The heterogenized organoplatinum(IV)-hydride sites catalyze the selective partial hydrogenation of 1,3-butadiene to butenes (up to 95%) and the reduction of nitrobenzene derivatives to anilines (up to 99%) with excellent tolerance of reduction-sensitive functional groups (olefin, carbonyl, nitrile, halogens) under mild reaction conditions.

Gas phase 1H NMR studies and kinetic modeling of dihydrogen isotope equilibration catalyzed by Ru-nanoparticles under normal conditions: dissociative vs. associative exchange.

The equilibration of H2, HD and D2 between the gas phase and surface hydrides of solid organic-ligand-stabilized Ru metal nanoparticles has been studied by gas phase 1H NMR spectroscopy using closed NMR tubes as batch reactors at room temperature and 800 mbar. When two different nanoparticle systems, Ru/PVP (PVP ≡ polyvinylpyrrolidone) and Ru/HDA (HDA ≡ hexadecylamine) were exposed to D2 gas, only the release of HD from the hydride containing surface could be detected in the initial stages of the reaction, but no H2. In the case of Ru/HDA also the reverse experiment was performed where surface deuterated nanoparticles were exposed to H2. In that case, the conversion of H2 into gaseous HD was detected. In order to analyze the experimental kinetic and spectroscopic data, we explored two different mechanisms taking into account potential kinetic and equilibrium H/D isotope effects. Firstly, we explored the dissociative exchange mechanism consisting of dissociative adsorption of dihydrogen, fast hydride surface diffusion and associative desorption of dihydrogen. It is shown that if D2 is the reaction partner, only H2 will be released in the beginning of the reaction, and HD only in later reaction stages. The second mechanism, dubbed here associative exchange consists of the binding of dihydrogen to Ru surface atoms, followed by a H-transfer to or by H-exchange with an adjacent hydride site, and finally of the associative desorption of dihydrogen. In that case, in the exchange with D2, only HD will be released in the beginning of the reaction. Our experimental results are not compatible with the dissociative exchange but can be explained in terms of the associative exchange. Whereas the former will dominate at low temperatures and pressures, the latter will prevail around room temperature and normal pressures where transition metal nanoparticles are generally used as reaction catalysts.

Reactivity of NHC Alane Adducts towards N-Heterocyclic Carbenes and Cyclic (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al-H Bond Activation.

The synthesis of mono-NHC alane adducts of the type (NHC)⋅AlH3 (NHC=Me2 Im (1), Me2 ImMe (2), iPr2 Im (3 and [D3 ]-3), iPr2 ImMe (4), Dipp2 Im (10); Im=imidazolin-2-ylidene, Dipp=2,6-diisopropylphenyl) and (NHC)⋅AliBu2 H (NHC=iPr2 Im (11), Dipp2 Im (12)) as well as their reactivity towards different types of carbenes is presented. Although the mono-NHC adducts remained stable at elevated temperatures, ring expansion occurred when (iPr2 Im)⋅AlH3 (3) was treated with a second equivalent of the carbene iPr2 Im to give (iPr2 Im)⋅AlH(RER-iPr2 ImH2 ) (6). In 6, {(iPr2 Im}AlH} is inserted into the NHC ring. In contrast, ring opening was observed with the sterically more demanding Dipp2 Im with the formation of (iPr2 Im)⋅AlH2 (ROR-Dipp2 ImH2 )H2 Al⋅(iPr2 Im) (9). In 9, two {(iPr2 Im)⋅AlH2 } moieties stabilize the ring-opened Dipp2 Im. If two hydridic sites are blocked, the adducts are stable with respect to further ring expansion or ring opening, as exemplified by the adducts (iPr2 Im)⋅AliBu2 H (11) and (Dipp2 Im)⋅AliBu2 H (12). The adducts (NHC)⋅AlH3 and (iPr2 Im)⋅AliBu2 H reacted with cAACMe by insertion of the carbene carbon atom into the Al-H bond to give (NHC)⋅AlH2 /iBu2 (cAACMe H) (13-18) instead of ligand substitution, ring-expansion, or ring-opened products.

The influence of Ar+ sputtering on the hydriding behavior of uranium

The influence of superficial defects (induced by surface sputtering) on uranium oxidation and hydriding behaviors has been studied. Depleted uranium surface was etched by Ar+ sputtering, the etched surface morphology was investigated by scanning electron microscope. The initial oxidation kinetics of sputtered uranium surface and mechanical polished uranium surface in ambient atmosphere were characterized using spectroscopic ellipsometry. As-polished and sputtered samples, as well as sequence sputtered samples ambient oxidized for different time, were compared in hydriding kinetics to investigate the co-influence of surface oxidation and superficial defects induced by Ar+ ion bombardment. The morphologic characteristics of hydride sites in a few grains were also revealed and enhanced by sputtering, showing a network of fractures for fast hydride transportation.