H2 Atoms Research Articles

Modulating the electronic structure of Ni and Co in core-shell structured catalysts to enhance the efficiency of reductive amination of pyruvic acid

A core-shell structured catalyst 3Ni-7Co@SiO2-0.2 was created to facilitate the reductive amination of pyruvic acid into alanine and the yield of alanine is up to 99 %. The SiO2 shell played a crucial role in spatial isolation effect, preventing the direct hydrogenation of pyruvic acid and improving the selectivity of alanine. By inter-doping Ni and Co, the electronic structure and properties are adjusted, the d-band center is reduced which is beneficial to the desorption of the product and the reaction barrier is reduced. Furthermore, it is proposed that catalysts exhibit better reductive amination reaction performance when there is a smaller difference in adsorption energy between NH3 and H2 atoms on the metal surface.

Spatial Confinement of Pt Nanoparticles in Carbon Nanotubes for Efficient and Selective H2 Evolution from Methanol.

H2 generation from methanol-water mixtures often requires high pressure and high temperature (200-300°C). However, CO can be easily generated and poison the catalytic system under such high temperature. Therefore, it is highly desirable to develop the efficient catalytic systems for H2 production from methanol at room temperature, even at sub-zero temperatures. Herein, carbon nanotube-supported Pt nanocomposites are designed and synthesized as high-performance nano-catalysts, via stabilization of Pt nanoparticles onto carbon nanotube (CNT), for H2 production upon methanol dehydrogenation at sub-zero temperatures. Therein, the optimal Pt/CNT nanocomposite presents the superior catalytic performance in H2 production upon methanol dehydrogenation at the expense of B2(OH)4, with the TOF of 299.51min-130 oC. Compared with other common carriers, Pt/CNT exhibited the highest catalytic performance in H2 production, emphasizing the critical role of CNT in methanol dehydrogenation. The confinement of Pt nanoparticles by CNTs is conducive to inhibiting the aggregation of Pt nanoparticles, thereby significantly increasing its catalytic performance and stability. The kinetic study, detailed mechanistic insights, and density functional theory (DFT) calculation confirm that the breaking of O─H bond of CH3OH is the rate-controlling step for methanol dehydrogenation, and both H atoms of H2 are supplied by methanol. Interestingly, H2 is also successfully produced from methanol dehydrogenation at -10°C, which absolutely solves the freezing problem in the H2 evolution upon water-splitting reaction.

Computational study of effects of doping Ni and Pd on CoAl for hydrogen storage capacity, elastic and electronic properties

Intermetallic compounds in B2 structure which have low density, fracture, and high strength have important applications in different engineering applications. For energy storage apparatus, the researchers have investigated new materials to improve effective efficiency in energy storage devices such as batteries and green energy technologies. The investigation of transition metal–aluminide alloys has increased due to their attractive elastic features. Like many hydrogen storage alloys, B2-type hydrogen storage alloys such as ZrCo utilize the systems of hydrogen storage in atomic gaps. If hydrogen atoms settle in the interstitial spaces, lattice expansion forms due to lattice distortion. Since plastic and elastic deformations change pressure and temperature, they are important for the material during hydrogen desorption and absorption. According to the literature, element doping effects boost hydrogen storage sufficiency. The effects of Ni- and Pd-substituted dopants on hydrogen storage, electronic and elastic features of a Cobalt-Aluminum alloy were performed using the first-principles calculations with and without spin-polarized configurations. Obtained lattice parameters for Co8Al8 are good agreement with literature values. Interstitial H doping has changed the crystal structure from cubic (BCC) to tetragonal. It is concluded that all investigated CoAl alloys included H doping has negative formation energies showing thermodynamically stabilities. All investigated alloys are stable mechanically and dynamically. Doping of H2 atoms to CoAl changes from a brittle to ductile nature. Also, Ni contributions improve ductility behavior to improve the cycle performance of the Co7NiAl8 and Co8Al7Ni alloy. It can be concluded from electronic band structure that they exhibite metallic behavior. Our obtained gravimetric and volumetric capacities which are comparable with B2 hydrogen storage material such as ZrCo, FeAl, indicate that CoAl alloys may be suitable for hydrogen storage applications.

The effect of initial temperature and external heat flux on the H2 and CO production by biomass gasification using molecular dynamics simulation

Biomass is a fuel produced from organic matter, and a renewable and sustainable energy source used to generate electricity or other forms of energy. From an environmental point of view, biomass includes all materials found in nature. This resource can be a suitable alternative to fossil resources. Biomass is based on carbon particles, H2, O2, N2, and many other atoms, such as alkali metals and heavy metals. In this research, the changes in the number of H2, carbon monoxide (CO) molecules created, and combustion efficiency (CE) inside the simulation box, using molecular dynamics (MD) simulation in the presence of 10 % platinum nanocatalyst with different initial temperatures (Temp) (1800, 1850, 1900 and 2000 K) and different external heat fluxes (EHF) (1, 2, 3 and 5 W/m2) were evaluated. The results show that as the Temp increased from 1800 to 2000 K, the number of H2 and CO molecules increased from 586 to 165 to 614 and 199, respectively. Besides, CE increased to 70% with the Temp increase to 2000 K. Furthermore, increasing the EHF from 1 to 5 W/m2, the number of H2 and CO molecules decreases from 589 to 170 to 603 and 180, respectively, and the CE increases to 69 % with the EHF increasing to 5 W/m2. It is expected that by examining the effects of system Temp and EHF, and the presence of nanocatalysts, the production of the number of H2 molecules will reach the highest efficiency.

Tailoring hydrogen adsorption and desorption properties of Li-doped SV (single vacancy) monolayer h-BN systems using ab initio calculations

This study uses density functional theory (DFT) technique to examine the hydrogen molecules (H2) storage on Li-decorated h-BN monolayer. The results of DFT have proven that Li-doped h-BN system can hold up to 9H2 with the adsorption energy lying in between −0.31 eV and −0.24 eV/H2 at ambient condition. However, the calculated average adsorption energy for 9H2 is −0.240 eV/H2 with hydrogen storage capacity of 5.96 wt.%, which is according to the United States Department of Energy. Partial density of state was computed for each configuration to provide additional justifications for the H2 storage on Li-doped h-BN monolayer. The hybridization shows a significant interaction between H2 and Li atom, and most of their hybrid peaks were observed in the energy range from −7.5 to −1 eV. Moreover, the H2 desorption simulations achieved via the ab initio molecular dynamics. The computed desorption temperature TD is 306 °K, which is a suitable operating temperature. Hence, our research demonstrates that Li-doped h-BN is a thermally stable and viable hydrogen storage material for hydrogen storage systems.

Solution-mediated polymorphic transformation from risperidone form II to form I

Polymorphism widely exists in the pharmaceutical industry and can significantly affect the quality of the products. Investigating the transformation between different polymorphs is crucial for obtaining high-purity active pharmaceutical ingredients (APIs). In this study, the solution-mediated polymorphic transformation (SMPT) from risperidone form II to form I was systematically investigated. The solubility of risperidone form II in methanol, ethanol, ethyl acetate and acetone was measured via a dynamic method. The solubility of form I and form II were compared to determine the relative stability of different polymorphs. It turns out that form I is more stable over the selected solvents and temperature range. The rate-determining step of the SMPT was determined by combining the offline powder X-ray diffraction (PXRD) and the gravimetric method. The nucleation and growth of risperidone form I are found to be the rate-determining step of the transformation. In addition, the effect of several operating factors on the SMPT was investigated, including solvent, temperature, solid loading, agitation rate and seed addition amount. The results show that the above factors can influence the SMPT speed to different degrees. The molecular dynamic (MD) simulations were also performed, and the radial distribution function (RDF) analysis was used to explain the SMPT from the perspective of solute–solvent interactions. It turns out that the strong interaction between the solvent and the O2 and H2 atoms on the solute molecule may prevent the nucleation and growth of risperidone form I, thus resulting in a slow transformation rate in acetone and ethyl acetate. This study can give references for manufacturing pure risperidone form I in the pharmaceutical industry and is helpful in understanding the SMPT between polymorphs.

Unveiling the dehydrogenation mechanism of dihydrogen‐bonded phenol‐borane‐dimethylamine complex in the ground and excited states

AbstractIn this work, the density functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods were adopted to explore the dehydrogenation mechanism of phenol‐borane‐dimethylamine (phenol‐BDMA) complex in ground (S0) and excited (S1) states. The analysis of the geometric parameters and infrared (IR) vibrational spectra indicate that the dihydrogen bond H1···H2is significantly strengthened in S1state and the dehydrogenation process may occur along the dihydrogen bond H1···H2. Upon photo‐excitation, the electronic density of phenol‐BDMA complex is redistributed and the redistribution of the electronic density can provide driving force for the dehydrogenation process in S1state. The potential energy curves reveal that the dehydrogenation process in S1state is easier than that in S0state. The charge redistribution in S1state is beneficial to the dehydrogenation process. Furthermore, it has been found that the dihydrogen bond can promote the dehydrogenation process, while the hydrogen bond can hinder the dehydrogenation process. In addition, the dehydrogenation mechanisms were described in detail. First, the H1and H2atoms gradually approach each other, and the O and H3atoms are also getting closer to each other. Subsequently, the O‐H1and B‐H2bonds break, and the H1and H2atoms dissociate from the O and B atoms, respectively. Hydrogen molecular is formed by combing the H1and H2atoms after crossing the energy barrier hopping point. In the meantime, the H3atoms dissociate from the N atom and transfer to the O atom.

Measurements of atoms and metastable species in N2 and H2–N2 nanosecond pulse plasmas

Time-resolved, absolute number densities of metastable N2(A3Σ u +, v = 0, 1) molecules, ground state N2 and H atoms, and rotational–translational temperature have been measured by tunable diode laser absorption spectroscopy and two-photon absorption laser-induced fluorescence in diffuse N2 and N2–H2 plasmas during and after a nanosecond pulse discharge burst. Comparison of the measurement results with the kinetic modeling predictions, specifically the significant reduction of the N2(A3Σ u +) populations and the rate of N atom generation during the burst, suggests that these two trends are related. The slow N atom decay in the afterglow, on a time scale longer than the discharge burst, demonstrates that the latter trend is not affected by N atom recombination, diffusion to the walls, or convection with the flow. This leads to the conclusion that the energy pooling in collisions of N2(A3Σ u +) molecules is a major channel of N2 dissociation in electric discharges where a significant fraction of the input energy goes to electronic excitation of N2. Additional measurements in a 1% H2–N2 mixture demonstrate a further significant reduction of N2(A3Σ u +, v = 0, 1) populations, due to the rapid quenching by H atoms accumulating in the plasma. Comparison with the modeling predictions suggests that the N2(A3Σ u +) molecules may be initially formed in the highly vibrationally excited states. The reduction of the N2(A3Σ u +) number density also diminishes the contribution of the energy pooling process into N2 dissociation, thus reducing the N atom number density. The rate of N atom generation during the burst also decreases, due to its strong coupling to N2(A3Σ u +, v) populations. On the other hand, the rate of H atom generation, produced predominantly by the dissociative quenching of the excited electronic states of N2 by H2, remains about the same during the burst, resulting in a nearly linear rise in the H atom number density. Comparison of the kinetic model predictions with the experimental results suggests that the yield of H atoms during the quenching of the excited electronic state of N2 by molecular H2 is significantly less than 100%. The present results quantify the yield of N and H atoms in high-pressure H2–N2 plasmas, which have significant potential for ammonia generation using plasma-assisted catalysis.

Water in the Alluaudite Type-Compounds: Synthesis, Crystal Structure and Magnetic Properties of Co3(AsO4)0.5+x(HAsO4)2−x(H2AsO4)0.5+x[(H,□)0.5(H2O,H3O)0.5]2x+

In this study, a new cobalt arsenate belonging to the alluaudite supergroup compounds with the general formula of Co3(AsO4)0.5+x(HAsO4)2−x(H2AsO4)0.5+x[(H,□)0.5(H2O,H3O)0.5]2x+ (denoted as CoAsAllu) was synthesized under hydrothermal conditions. Its crystal structure was determined by a room-temperature single-crystal X-ray diffraction analysis: space group C2/c, a = 11.6978(8), b = 12.5713(7), c = 6.7705(5) Å, β = 113.255(5)°, V = 914.76(11) Å3, Z = 2 for As6H8Co6O25. It represents a new member of alluaudite-like protonated arsenates and the first alluaudite-like phase showing both protonation of the tetrahedral site and presence of the H2O molecules in the channels. In the asymmetric unit of CoAsAllu, one of the two Co, one of the two As and one of the seven O atoms lie at 4e special positions (site symmetry 2). The crystal structure consists of the infinite edge-shared CoO6 octahedra chains, running parallel to the [101¯] direction. The curved chains are interconnected by [(As1O4)0.5(H2As1O4)0.5]2− and [HAs2O4]2− tetrahedra forming a heteropolyhedral 3D open framework with two types of parallel channels. Both channels run along the c-axis and are located at the positions (1/2, 0, z) and (0, 0, z), respectively. The H2 and H4 hydrogen atoms of O2H2 and O4H4 hydroxyl groups are situated in channel 1, while the uncoordinated water molecule H2O7 at half-occupied 4e special positions and hydrogen atoms of O6H6 hydroxyl group were found in channel 2. The results of the magnetic investigations confirm the quasi one-dimensional structure of divalent cobalt ions. They are antiferromagnetically coupled with the intrachain interaction parameter of J ≈ −8 cm−1 and interchain parameter of J’ ≈ −2 cm−1 that become effective below the Néel temperature of 3.4 K.

Acid‐ and Base‐Catalyzed Hydrolytic Hydrogen Evolution from Diboronic Acid

AbstractThe efficient production of H2 from hydrogen‐rich sources, particularly from water, is a crucial task and a great challenge, both as a sustainable energy source and on the laboratory scale for hydrogenation reactions. Herein, a facile and effective synthesis of H2 and D2 from only acid‐ or base‐catalyzed metal‐free hydrolysis of B2(OH)4, a current borylation reagent, has been developed without any transition metal or ligand. Acid‐catalyzed H2 evolution was completed in 4 min, whereas the base‐catalyzed process needed 6 min. The large kinetic isotopic effects for this reaction with D2O, deuteration experiments and mechanistic studies have confirmed that both H atoms of H2 originate from water using either of these reactions. This new, metal‐free catalytic system holds several advantages, such as high efficiency, simplicity of operation, sustainability, economy, and potential further use.

Solvation effect on the ESIPT mechanism of nitrile-substituted ortho-hydroxy-2-phenyl-oxazolines.

In this study, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to unveil the solvation effects on the excited-state intramolecular proton transfer (ESIPT) of nitrile-substituted ortho-hydroxy-2-phenyl-oxazoline (NOHPO) molecules in three different solvents. According to the functional analysis of the reduced density gradient, hydrogen bond in low-polar solvents is stronger compared to that in high-polar solvents, indicating that proton transfer (PT) can be influenced by the polarity of the solvent. Moreover, the geometric parameters and infrared vibration spectrum of NOHPO in different types of solvents in the S0 and S1 state were compared, which confirmed the above results. By analyzing electronic spectra and frontier molecular orbitals, it was found that the spectral properties were affected by different polar solvents. Molecular electrostatic potential surface calculations proved that PT took place between the H2 atom and N3 atom, and the natural population analysis and Hirshfeld charge reveal the charge distribution after photoexcitation. To investigate the ESIPT progress intensively, the potential energy curves of NOHPO in three types of solvents were established. The findings revealed that NOHPO could transform from enol to keto form in the S1 state spontaneously, and ESIPT progress was promoted with the decrease in polarity.

Pd-promoted Ni-Ca-Al bi-functional catalyst for integrated sorption-enhanced steam reforming of glycerol and methane reforming of carbonate

The integration process of sorption-enhanced steam reforming (SESR) reaction and methane reforming (MR) of carbonates provides a promising way to produce high-purity H2 without CO2 emission. However, the huge different reaction temperature of SESR (~550 °C) and MR (>750 °C) hinders this coupling process. Herein, we report that the Pd-promoted Ni-Ca-Al bi-functional catalyst can lower the MR reaction temperature to 650 °C by enhancing CH4 decomposition activity to provide H2 molecules or atoms. The low regeneration temperature significantly improves the stability of SESR of glycerol (SESRG) reaction with only 8% increase in Ni particle size and 25% decrease of sorption-enhanced effect after 10 SESRG-MR cycles. Thanks to the high stability of the catalyst, 98.3% hydrogen-enriched stream and syngas with RH2/CO < 3 are co-produced in ten cyclic tests. Therefore, lowering the regeneration temperature can simultaneously weaken the thermal-swing operation and improve the stability of the catalyst during the SESR-MR reaction.

Infrared and Raman Spectroscopy of Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18

Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, is a complex hydrated sulphate of the voltaite group that has been recently discovered on the surface of the Severo-Kambalny geothermal field (Kamchatka, Russia). Vibrational spectroscopy has been applied for characterization of the mineral. Both infrared and Raman spectra of ammoniovoltaite are characterized by an abundance of bands, which corresponds to the diversity of structural fragments and variations of their local symmetry. The infrared spectrum of ammoniovoltaite is similar to that of other voltaite-related compounds. The specific feature related to the dominance of the NH4 group is its ν4 mode observed at 1432 cm−1 with a shoulder at 1510 cm−1 appearing due to NH4 disorder. The Raman spectrum of ammoniovoltaite is basically different from that of voltaite by the appearance of an intensive band centered at 3194 cm−1 and attributed to the ν3 mode of NH4. The latter can serve as a distinctive feature of ammonium in voltaite-group minerals in resemblance to recently reported results for another NH4-mineral—tschermigite, where ν3 of NH4 occurs at 3163 cm−1. The values calculated from wavenumbers of infrared bands at 3585 cm−1, 3467 cm−1 and 3400 cm−1 for hydrogen bond distances: d(O···H) and d(O···O) correspond to bonding involving H1 and H2 atoms of Fe2+X6 (X = O, OH) octahedra. The infrared bands observed at 3242 cm−1 and 2483 cm−1 are due to stronger hydrogen bonding, that may refer to non-localized H atoms of Al(H2O)6 or NH4.

A density functional theory‐time‐dependent density functional theory investigation of photo‐induced hydrogen bond and proton transfer for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐6‐carboxylicacid

AbstractGiven the paramount importance of excited‐state relaxation in the photochemical process, excited‐state hydrogen bonding interactions and excited‐state intramolecular proton transfer (ESIPT) are always hot topics. In this work, we theoretically explore the excited‐state dynamical behaviors for a novel 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐6‐carboxylicacid (DDPBC) system. As two intramolecular hydrogen bonds (O1H2⋯N3 and O4H5⋯O6) exist in the DDPBC structure, we first check if the double proton transfer form cannot be formed in the S1 state. Then, we explore the changes of geometrical parameters involved in hydrogen bonds, based on which we confirm that the dual intramolecular hydrogen bonds are strengthened on photo‐excitation. The O1H2⋯N3 hydrogen bond particularly plays a more important role in excited state. When it comes to the photo‐induced excitation, we find charge transfer and electronic density redistribution around O1H2 and N3 atom moieties. We verify the ESIPT tendency arising from the O1H2⋯N3 hydrogen bond. In the analysis of the potential energy curves, along with O1H2⋯N3 and O4H5⋯O6, we demonstrate that the ESIPT reaction should occur along with O1H2⋯N3 rather than O4H5⋯O6. This work not only clarifies the specific ESIPT mechanism for DDPBC system but also paves the way for further novel applications based on DDPBC structure in the future.

A TD‐DFT investigation of the photo‐induced excited state intramolecular proton transfer dynamics for the novel 5,5′‐(9,9‐dihexyl‐9H‐fluorene‐2,7‐diyl)bis(2‐benzo[d]thiazol‐2‐yl)phenol) system

AbstractDensity functional theory (DFT) and time‐dependent density functional theory (TDDFT) methods are adopted to explore the ground‐state and excited‐state intramolecular double hydrogen bonding interactions as well as the excited state intramolecular proton transfer (ESIPT) mechanism for 5,5′‐(9,9‐dihexyl‐9H‐fluorene‐2,7‐diyl)bis(2‐benzo[d]thiazol‐2‐yl)phenol) (abbreviated as Ia) system. The simulated electronic spectra of the Ia system (ie, absorption and fluorescence spectra) are reappeared by experimental results, which reveals the reasonability and correctness of the calculated theory adopted in this work. We firstly verify that the dual intramolecular hydrogen bonds of Ia should be enhanced in the first excited state via geometrical parameters (ie, bond lengths and bond angles) and infrared (IR) vibrational spectra. Then, insights into the photo‐excitation aspects, we confirm that the charge redistribution facilitates the ESIPT tendency. Particularly, the increased electronic densities around proton acceptors could play important roles in attracting proton H2 and H5 atoms for the Ia system. At last, via constructing potential energy surfaces (PESs), we clearly clarify the excited state intramolecular single proton transfer mechanism for the Ia system. This work not only clarifies the detailed ESIPT mechanism for the novel Ia system and makes up for the deficiencies in previous experiment but also promotes a deeper understanding about the excited state behaviors involved in multiple hydrogen bonding interactions.

Probing into the effects of cluster size and Pd ensemble as active center on the activity of H2 dissociation over the noble metal Pd-doped Cu bimetallic clusters

Aiming at probing into the effects of cluster size and Pd ensemble as active center on H2 dissociation over Pd-doped Cu bimetallic cluster, density functional theory calculations are employed to investigate H2 adsorption and dissociation over the Cu and Pd-doped Cu clusters with different sizes. The results show that compared to Cu cluster, the doped Pd atom and its ensemble composed of outermost layer and its connected sub-layer Pd atoms as active center greatly enhance catalytic activity of H2 dissociation at the same size of Pd-doped Cu clusters, which is attributed to the interaction enhancement between H2 and the clusters since d-band centers gradually approach the Fermi level and the electron-rich regions are formed around Pd ensemble. Moreover, among the Pd-doped Cu clusters with different sizes, the Bader charge indicate that when the number of doped-Pd atoms is same, the amount of charge on Pd ensemble increases with the size increasing of Pd-doped Cu catalysts, the cluster with larger size is beneficial for promoting the activity of H2 dissociation; thus, the size effect of Pd-doped Cu cluster on H2 dissociation is dominantly attributed to the electronic effect. This work not only provides a valuable clue for evaluating catalytic activity of other promoter metal-doped Cu catalysts for H2 dissociation, but also gives out the ways that adjusting the cluster size and the promoter ensemble can facilitate the dissociation of H2 atoms as an initially key step in the heterogeneous hydrogenation.

High pressure behavior of crystal [2,2′-bi(1,3,4-oxadiazole)]-5,5′-dinitramide: A DFT investigation

Density functional theory (DFT) computation was carried out to investigate the crystal, molecular and electronic structures of high energy crystal [2,2′-bi(1,3,4-oxadiazole)]-5,5′-dinitramide (BODN) with the pressure 0–120 GPa. The relaxed crystal structure by the GGA/PBE-TS functional matches well with the experimental data at ambient pressure condition. With the intensifying of pressure, the lattice parameters, volumes, bond lengths, H-bond energies, atomic charges, bond populations, band gaps and density of states of crystal BODN change gently. Under the pressure of 48, 104, and 107 GPa, three pressure-induced transformations occurred. The intramolecular six membered rings pose strong affect in stabilizing systems in the pressure range 0–120 GPa. Between O1 and H2 atoms, the H-bond interaction transforms into covalent interaction under the circumstance of 48 GPa. At 104 GPa, structural transformation occurs with the distortion of the intramolecular six membered ring. In addition, O1⋅⋅⋅H2 and O2⋅⋅⋅H1 have the largest H-bond energies in comparison with the others. When the pressure reaches 107 GPa, the H-bond O1⋅⋅⋅H2 is formed again with the deformation and non-coplanarity of two oxadiazoles in crystal BODN. The electrons can be moved easily based on the density of states and energy bands under high pressure. Helpful information will be conveyed by this work in the field of further analysis connected the pressure effect on molecular transformations.

Trans-Hydrogenation, gem-Hydrogenation, and trans-Hydrometalation of Alkynes: An Interim Report on an Unorthodox Reactivity Paradigm.

cis-Delivery of H2 to the π-system of an unsaturated substrate is the canonical course of metal catalyzed hydrogenation reactions. The semireduction of internal alkynes with the aid of [Cp*Ru]-based catalysts violates this rule and affords E-alkenes by direct trans-hydrogenation. A pathway involving σ-complexes and metallacyclopropenes accounts for this unconventional outcome. Connected to this process is an even more striking reactivity mode, in which both H atoms of H2 are delivered to one and the same C atom. Such gem-hydrogenation of stable carbogenic compunds is a fundamentally new transformation that leads to the formation of discrete metal carbene complexes. Computational studies suggest that the trans- and the gem-pathway have similar barriers, but polar substituents in the vicinity of the reacting triple bond provide opportunities for imposing selectivity and control. Moreover, it is shown that catalytic trans-hydrogenation is by no means a singularity: rather, the underlying principle is also manifest in trans-hydroboration, trans-hydrosilylation, trans-hydrogermylation, and trans-hydrostannation, which are equally paradigm-changing processes. These reactions are robust and distinguished by excellent compatibility with many (reducible) functional groups and have already stood the test of natural product synthesis in a number of demanding cases.

Hydrogen adsorption of Ti-decorated boron nitride nanotube: a density functional based tight binding molecular dynamics study

The hydrogen adsorption capabilities of Titanium functionalized single-walled BN nanotubes (BNNTs) with B–N defects was assessed by density-functional theory tight binding (DFTB) method. According to the DFTB molecular dynamics simulations, the BNNT structures were thermodynamically stable, the Ti atom once incorporated with the B–N defects present in BNNT (Ti–BNNT) protrudes to the external surface of the BNNT sidewall. The titanium atoms does not agglomerate to form any metal clusters. The results revealed that at 77 K and 10,000 KPa, the H2–Ti–BNNT has a gravimetric hydrogen storage capacity above 7 wt% ideal for department of energy specifications. Further calculations suggest that the Ti–BNNT has a good affinity towards H2 molecules and under low pressure of 500 KPa. The H2 stays close to the Ti metal due to its partially cationic character with some H2 attaching itself at the BNNT surface due to heteropolar bonding. H2 atoms is physisorbed in analogous to or resembling something molecular near the Ti sites which gives rise to a significant storage capacity for H2 in these modified BNNT.

Effects of Li on hydrogen absorption properties of Mg17Al12(110) surface: A density functional theory study

On the basis of density functional theory (DFT), the catalytic effects of Li on hydrogen absorption properties of the Mg17Al12(110) surfaces are studied. The Li-containing Mg17Al12(110) surfaces were composed of the Li-substituted and Li-adsorbed systems, namely Mg16LiAl12(110) and Mg17Al12(110)/Li surfaces, respectively. Calculations indicate that adsorption energies of H (H2) on the Mg17Al12(110) surfaces with a low amount of Li were significantly improved relative to hydrogen on the clean surface. Especially, the energy of H (H2) on the Mg17Al12(110)/Li system was −0.68 (−0.48) eV. Moreover, the addition of Li remarkably promotes the dissociative properties of H2 on the (110) surface. The barrier energy of H2 dissociation on the Mg17Al12(110)/Li surface was 0.14 eV, which was much lower than that (0.87 eV) on the pure surface. Analysis of electronic structures reveals that the H-s orbital hybridized with the Mg-s evidently in the Li-containing systems. The formation of LiH bond and the interaction between H2 and Li atom may explain the enhanced hydrogenation properties of Mg17Al12(110)/Li surface.