Adsorption Of Molecular Hydrogen Research Articles

Enhanced hydrogen adsorption-desorption reversibility found on NiAl alloy: A first-principles study

Improving the hydrogen storage performance of carbon-based materials via transition metals incorporation has been proved experimentally, where control over the hydrogen adsorption kinetics and hydrogen surface diffusion is the key. In this work, we proved theoretically via density functional theory (DFT) how such incorporation promotes better hydrogen storage performance in Ni-based materials supported on graphene, in which static and dynamic behavior of the system were modeled by plane-wave DFT and ab initio molecular dynamics (AIMD), respectively. In addition, the hydrogen storage materials Ni10Al3 and Ni13 supported on graphene, denoted as Ni10Al3/GP and Ni13/GP, are modeled to realize the experimental observation on Ni3Al alloy under high hydrogen pressure. It was found that the Ni10Al3/GP alloy system exhibited better properties in twofold: (1) increased hydrogen adsorption capacity through providing an additional site for H2 molecular adsorption, particularly on the Al atoms, and (2) enhanced hydrogen desorption at ambient conditions observed from reversible H2 adsorption at all coverages with barrierless migration energy. Therefore, the proof from the DFT point-of-view provides valuable insight into exploring other metal alloy systems that can provide additional sites for molecular hydrogen adsorption and improve hydrogen adsorbate mobility.

Unraveling Hydrogen Adsorption on Transition Metal-Doped [Mo3S13]2- Clusters: Insights from Density Functional Theory Calculations.

Molecular and dissociative hydrogen adsorption of transition metal (TM)-doped [Mo3S13]2- atomic clusters were investigated using density functional theory calculations. The introduced TM dopants form stable bonds with S atoms, preserving the geometric structure. The S-TM-S bridging bond emerges as the most stable configuration. The preferred adsorption sites were found to be influenced by various factors, such as the relative electronegativity, coordination number, and charge of the TM atom. Notably, the presence of these TM atoms remarkably improved the hydrogen adsorption activity. The dissociation of a single hydrogen molecule on TM[Mo3S13]2- clusters (TM = Sc, Cr, Mn, Fe, Co, and Ni) is thermodynamically and kinetically favorable compared to their bare counterparts. The extent of favorability monotonically depends on the TM impurity, with a maximum activation barrier energy ranging from 0.62 to 1.58 eV, lower than that of the bare cluster (1.69 eV). Findings provide insights for experimental research on hydrogen adsorption using TM-doped molybdenum sulfide nanoclusters, with potential applications in the field of hydrogen energy.

Adsorption of molecular hydrogen on Be3Al2(SiO3)6-beryl: theoretical insights for catalysis, hydrogen storage, gas separation, sensing, and environmental applications.

Employing a combination of Density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, the adsorption of molecular hydrogen (H2) on Be3Al2(SiO3)6-beryl, a prominent silicate mineral, has been studied. The crystal structure of beryl, which consists of interconnected tetrahedral and octahedral sites, provides a fascinating framework for comprehending H2 adsorption behavior. Initial investigation of the interaction between H2 molecules and the beryl surface employed DFT calculations. We identified favorable adsorption sites and gained insight into the binding mechanism through extensive structural optimizations and energy calculations. H2 molecules preferentially adsorb on the exposed oxygen atoms surrounding the octahedral sites, producing weak van der Waals interactions with the beryl surface, according to our findings. To further investigate the dynamic aspects of H2 adsorption, MD simulations employing a suitable force field were conducted. To precisely represent interatomic interactions within the Be3Al2(SiO3)6-beryl-H2 system, the force field parameters were meticulously parameterized. By subjecting the system to a variety of temperatures, we were able to obtain valuable information about the stability, diffusion, and desorption kinetics of H2 molecules within the beryl structure. The comprehensive understanding of the H2 adsorption phenomenon on Be3Al2(SiO3)6-beryl is provided by the combined DFT and MD investigations. The results elucidate the mechanisms underlying H2 binding, highlighting the role of surface oxygen atoms and the effect of temperature on H2 dynamics. This research contributes to a fundamental understanding of hydrogen storage and release in beryllium-based silicates and provides valuable guidance for the design and optimization of materials for hydrogen storage, catalysis, gas separation, sensing and environmental applications.

Electronic and structural properties of hydrogen adsorption on γ-Graphyne and γ-BNyne

While the study of one-dimensional materials such as carbon nanotubes and boron-nitrogen structures have attracted technological interest, the appearance of new two-dimensional materials has expanded the spectrum with new potential applications. The most recent report published in 2022 on the synthesis of γ-graphyne has sparked scientific interest in describing the properties that this material and its analogs may exhibit under different physical and chemical conditions. In this study, the effect of hydrogen molecule adsorption on γ-BNyne surface is presented for the first time and compared with the properties reported for γ-graphyne, these calculations have been carried out through first-principles calculations using Density Functional Theory with DFT-D3 Grimme’s correction. The results showed that molecular hydrogen adsorption on these two-dimensional surfaces does not significantly alter their pristine structural and electronic properties, demonstrating their stability under molecular hydrogen adsorption conditions. The results presented here contribute to the promotion of these two-dimensional materials as potential candidates for technological applications such as nanosensors, nanomedicine, and hydrogen storage, among others.

Isomeric Thiadiazole-xLi+(x = 1, 2) templates found to be efficient in search of potential H2 storage systems; a computational study

The hydrogen trapping possibility of isomeric thiadiazole-Li+ and thiadiazole-2Li+ building blocks has been evaluated by various functionals within density functional theory (DFT), and it is found that they can adsorb a maximum of five and ten H2 molecules respectively. Aromaticity is retained even after hydrogen adsorption. Average adsorption energy lies in the quasimolecular type adsorption range. The gravimetric wt% (9.7 ∼ 16.7) are found suitable as per norms. Topological analysis shows that the bond formation between Li and trapped H2 molecules is mostly non-covalent. At 200 K or below this temperature, the Gibbs free energy changes illustrate that the molecular hydrogen adsorption process is spontaneous for all isomeric thiadiazole-xLi+ [x = 1 and 2] building blocks. Higher temperatures are required for the desorption of H2 molecules. Thus, we believe that our studied system thiadiazole-xLi+ can be proposed as a practically viable system for hydrogen storage.

Theoretical calculation on adsorption of molecular hydrogen in monolayer ZnO

Adsorption, desorption, and diffusion dynamics of hydrogen gas molecules over a hexagonal ZnO monolayer have been studied thoroughly in the van der Waals Density Functional Theory (vdW-DFT) framework in association with kinetic Monte Carlo (kMC) simulations. Hydrogen molecules can attach to a ZnO sheet via a weak physisorption process with a limitation of maximum attachment of three molecules per hexagonal ring. Pressure and temperature are the main deciding parameters for the overall storage capacity of hydrogen on a ZnO substrate. kMC simulations are performed to capture the stochastic behavior of surface dynamics of gas molecules. Adsorption energy and diffusion barrier are predicted to be around 50–60 meV and 4–12 meV, respectively, according to vdW-DFT calculations. kMC simulations with these energy parameters estimate the surface coverage of hydrogen to be pretty high below room temperature and high pressure. Furthermore, the hydrogen adsorption in the ZnO monolayer leads to the increase of the bandgap value, subsequently changing the conductivity of the material. The present research work sheds light on the usage of a ZnO monolayer for suitable hydrogen gas storage and sensing applications.

Cooperative effect of multi-active sites in WOx-modified ZrO2 supported highly dispersed Pd catalysts for promoting benzene hydroalkylation

Designing efficient metal–acid bifunctional catalysts is a challenging task to achieve the one-step benzene hydroalkylation to produce cyclohexylbenzene (CHB), which has significant importance due to the economic potential for the industrial production of phenol. In this study, a series of WOx-modified ZrO2 supported highly dispersed Pd catalysts were developed by modulating the surface acidity of ZrO2 through the introduction of WOx species. The as-constructed Pd/WOx-ZrO2 catalyst bearing a low Pd loading of 0.4 wt% and a W content of 21 wt% exhibited a superior catalytic performance, along with an unprecedentedly high productivity of CHB (144.6 mmolCHB·gcat−1·h−1), much higher than those obtained by using the state-of-the-art catalysts. It was demonstrated that highly dispersed Pd species could promote the formation of active hydrogen species and favor the hydrogen spillover on the catalyst surface that induced the generation of surface oxygen vacancies and Brønsted acidic sites originating from surface-loaded WOx. Comprehensive structural characterizations and catalytic experiments showed that the favorable metal–acid cooperation on Pd/WOx-ZrO2 catalysts and the cooperation between Lewis acid sites and Brønsted acid sites, as well as the presence of abundant defective oxygen vacancies, efficiently regulated the adsorption and activation of molecular hydrogen, benzene, and cyclohexene intermediate, leading to the improved catalytic hydroalkylation activity. These findings provide new high-performance metal–acid bifunctional catalysts with multi-active site cooperation structures for one-step hydroalkylation of benzene to CHB.

Pyridine-M2+ [M = Mg, Ca]: A promising organometallic system for potential hydrogen storage: In silico study

Pyridine-M2+ [M = Mg, Ca] hosts have been identified as potent H2 storage material, and this has been explored by a variety of functionals within the density functional theory (DFT) context. Around the linearly connected metal centre, the pyridine-Mg2+ and pyridine-Ca2+ building blocks can adsorb 6 and 7H2 molecules, respectively. The stability of Pyridine-M2+ [M = Mg, Ca] hosts has been proven by chemical hardness, aromaticity, and molecular dynamic simulations. After H2 adsorption, the aromaticity still remains. Adsorption of H2 molecules at a quasi-molecular type is supported by the fact that their average adsorption energy/H2 (Eads/H2) is between 0.22 and 0.72 eV. Pyridine-Mg2+@6H2 and pyridine-Ca2+@7H2 both have very impressive gravimetric wt % values (10.43 and 10.53 respectively). Average delocalization correction energy (ΔECTav) supports the charge transfer type interaction between metal ions and adsorbed H2 molecules. The topological analysis reflects that bonding between metals (Mg & Ca) and trapped H2 molecules are mostly non-covalent types. Gibbs free energy changes (ΔG) [eV] indicate that the molecular hydrogen adsorption process will be spontaneous at 298 K for pyridine-Mg2+@nH2 systems and at or below 205 K for pyridine-Ca2+@nH2 systems and atom centered density matrix propagation (ADMP) study suggests the higher temperature for desorption.

First-Principles Study of Hydrogen Dynamics in Monoclinic TiO

The existence of intrinsic vacancies in cubic (monoclinic) TiO suggests opportunity for hydrogen absorption, which was addressed in recent experiments. In the present work, based on first-principles calculations, the preferences are studied for the hydrogen absorption sites and diffusion paths between them. The oxygen vacancies are found to be the primary hydrogen traps with absorption energy of −2.87 eV. The plausible channels for hydrogen diffusion between adjacent vacancy sites (ordered in the monoclinic TiO structure) are compared with the help of calculations using the nudge elastic band method. Several competitive channels are identified, with barrier heights varying from 2.87 to 3.71 eV, that are high enough to ensure relative stability of trapped hydrogen atoms at oxygen vacancy sites. Moreover, the possibility of adsorption of molecular hydrogen was tested and found improbable, in the sense that the H2 molecules penetrating the TiO crystal are easily dissociated (and released atoms tend to proceed toward oxygen vacancy sites). These results suggest that hydrogen may persist in oxygen vacancy sites up to high enough temperatures.

Hydrogen storage in Nickel dispersed boron doped reduced graphene oxide

Graphene oxide (GO) based derivatives have been explored for hydrogen storage application, owing to their high surface area, low density and tunable pore size. However, under ambient conditions as desired for transport application, their storage capacity is poor. The use of nanohybrids of graphene oxide decorated with catalyst nanoparticles is emerging as a promising strategy to store atomic forms of hydrogen by invoking the spillover mechanism (in addition to storing molecular forms of hydrogen). Also, doping the substrate (GO) with light heteroatoms such as boron (B) have been envisaged for improving the enthalpy of adsorption of molecular hydrogen on the substrate. In the current work, GO based hybrids namely boron doped reduced graphene oxide (B-rGO) and Ni nanoparticle dispersed B-rGO (Ni-B-rGO) has been synthesized via freeze drying and hydrothermal route. The presence of various phases in the samples was identified using X-ray diffraction. Field-emission scanning electron microscopy was used to study the morphology; especially the 'wrinkling' in the GO based structures. The size and distribution of Ni nanoparticles was studied using transmission electron microscopy (size ∼1–2 nm and inter-particle distance of ∼20 nm). Raman spectroscopy was used to quantify the degree of disorder in the samples and additionally to demonstrate the existence of adsorbed molecular hydrogen. Fourier transform infrared spectroscopy studies showed the presence of various functional groups on carbon and further revealed the presence of atomic hydrogen generated by the spillover mechanism. X-ray photoelectron spectroscopy studies augmented the investigations to show the surface composition of Ni-B-rGO sample. The samples were further characterized for their hydrogen storage capacity using Sieverts apparatus (pressure-composition-isotherms) at three temperatures (77 K, 273 K and 298 K) and 20 bar H2 pressure. The B-rGO sample, showed promising storage capacity of ∼0.24 wt.% at 298 K, which increased to ∼0.58 wt.% at 273 K; which further increased to 8.2 wt.% at 77 K. The storage capacity of the Ni-B-rGO hybrid at the three temperatures (77 K, 273 K and 298 K) are: ∼6.9 wt.%, ∼0.41 wt.% and 0.16 wt.%, respectively.

Hydrogen storage capacity of Al, Ca, Mg, Ni, and Zn decorated phosphorus-doped graphene: Insight from theoretical calculations

In this work, adsorption of molecular hydrogen on five different metals: Aluminum, Calcium, Magnesium, Nickel and Zinc decorated phosphorus-doped graphene have been investigated using density functional theory (DFT) computation at the PBE0-D3BJ/def2svp method. From literature reviews, phosphorus doped graphene are potential candidates for hydrogen storage. Herein, theoretical investigation on the changes in structural and electronic properties of the studied materials was conducted. Natural bond orbital (NBO) analysis was employed to study the intermolecular and intra-molecular interactions arising from chemical bonds in the studied systems. In addition, the density of states (DOS) plots shows notable individual orbital contribution and hybridization between the decorated metals and the phosphorus-doped graphene which is also responsible for the adsorption of hydrogen. Based on the frontier molecular orbital analysis, results indicates that Al and Ni surfaces possess excellent structural and electronic properties with lower values of chemical hardness and ionization with adsorption energy values of 1.924eV and 1.236eV obtained for both surfaces potential indicating better conductivity and excellent H2 adsorption potential. The obtained results shows the suitability of the Al and Ni decorated phosphorus-doped graphene for hydrogen storage.

Exploring the adsorption behavior of molecular hydrogen on CHA-zeolite by comparing the performance of various force field methods.

Molecular hydrogen (H2) adsorption plays a crucial role in numerous applications, including hydrogen storage and purification processes. Understanding the interaction of H2 with porous materials is essential for designing efficient adsorption systems. In this study, we investigate H2 adsorption on CHA-zeolite using a combination of density functional theory (DFT) and force field-based molecular dynamics (MD) simulations. Firstly, we employ DFT calculations to explore the energetic properties and adsorption sites of H2 on the CHA-zeolite framework. The electronic structure and binding energies of H2 in various adsorption configurations are analyzed, providing valuable insights into the nature of the adsorption process. Subsequently, force field methods are employed to perform extensive MD simulations, allowing us to study the dynamic behavior of H2 molecules adsorbed on the CHA-zeolite surface. The trajectory analysis provides information on the diffusion mechanisms and mobility of H2 within the porous structure, shedding light on the transport properties of the adsorbed gas. Furthermore, the combination of DFT and MD results enables us to validate and refine the force field parameters used in simulations, improving the accuracy of the model, and enhancing our understanding of the H2-CHA interactions. Our comprehensive investigation into molecular hydrogen adsorption on CHA-zeolite using density functional theory and molecular dynamics simulations yields valuable insights into the fundamental aspects of the adsorption process. These findings contribute to the development of advanced hydrogen storage and separation technologies, paving the way for efficient and sustainable energy applications.

An apparatus for investigating the kinetics of plasmonic catalysis

Plasmonic catalysis, which is driven by the localized surface plasmon resonance of metal nanoparticles, has become an emerging field in heterogeneous catalysis. The microscopic mechanism of this kind of reaction, however, remains controversial partly because of the inaccuracy of temperature measurement and the ambiguity of reagent adsorption state. In order to investigate the kinetics of plasmonic catalysis, an online mass spectrometer-based apparatus has been built in our laboratory, with emphases on dealing with temperature measurement and adsorption state identification issues. Given the temperature inhomogeneity in the catalyst bed, three thermocouples are installed compared with the conventional design with only one. Such a multiple-point temperature measuring technique enables the quantitative calculation of equivalent temperature and thermal reaction contribution of the catalysts. Temperature-programmed desorption is incorporated into the apparatus, which helps to identify the adsorption state of reagents. The capabilities of the improved apparatus have been demonstrated by studying the kinetics of a model plasmon-induced catalytic reaction, i.e., H2+D2→HD over Au/TiO2. Dissociative adsorption of molecular hydrogen at Au/TiO2 interface and non-thermal contribution to HD production have been confirmed.

Revealing the interfacial phenomenon of metal-hydride formation and spillover effect on C48H16 sheet by platinum metal catalyst (Pt (n=1-4)) for hydrogen storage enhancement

Hydrogen is a worldwide green energy carrier, however due its low storage capacity, it has yet to be widely used as an energy carrier. Therefore, the quantum chemical method is being employed in this investigation for better understand the hydrogen storage behaviour on Pt (n = 1-4) cluster decorated C48H16 sheet. The Pt(n = 1-4) clusters are strongly bonded on the surface of C48H16 sheet with binding energies of −3.06, −4.56, −3.37, and −4.03 eV respectively, while the charge transfer from Pt(n = 1-4) to C48H16 leaves an empty orbital in Pt atom, which will be crucial for H2 adsorption. Initially, the molecular hydrogen is adsorbed on Pt(n = 1-4) decorated C48H16 sheet through the Kubas interaction with adsorption energies of −0.85, −0.66, −0.72, and −0.57 eV respectively, while H–H bond is elongated due to the transfer of electron from σ (HH) orbital to unfilled d orbital of the Pt atom, resulting in a Kubas metal-dihydrogen complexes. Furthermore, the dissociative hydrogen atoms adsorbed on Pt(n = 1-4) decorated C48H16 sheet have adsorption energies of −1.14 eV, −1.02 eV, −0.95 eV, and −1.08 eV, which are greater than the molecular hydrogen adsorption on Pt(n = 1-4) cluster supported C48H16 sheet with lower activation energy of 0.007, 0.109, 0.046, and 0.081 eV respectively. To enhance the dissociative hydrogen adsorption energy, positive and negative external electric fields are applied in the charge transfer direction. Increasing the positive electric field makes H–H bond elongation and good adsorption, whereas increasing the negative electric field results H–H bond contraction and poor adsorption. Thus, by applying a sufficient electric field, the H2 adsorption and desorption processes are can be easily tailored.

Adsorption behavior of molecular hydrogen in forsterite

Recent experimental studies have already discussed the existence of molecular hydrogen in mantle minerals. Here, we investigate the adsorption behavior of molecular hydrogen in forsterite with 0–15 Å intercrystalline pore at 0–519 MPa and 300–1800 K by using the Grand Canonical Monte Carlo (GCMC) method. Molecular hydrogen fills the interstitial positions of nonporous forsterite in an adsorbed state, whereas the filling of intercrystalline pore includes the adsorbed and free states. The adsorption of molecular hydrogen on the crystal surface of forsterite intercrystalline pore belongs to physisorption. The interaction between the adsorbate molecular hydrogen and the adsorbent forsterite framework weakens with pressure and strengthens with temperature, which is a crucial factor, and intercrystalline pore size. The adsorption capacity of molecular hydrogen in the intercrystalline pore of forsterite increases with pressure and intercrystalline pore size and decreases with temperature. By contrast, the adsorption capacity of molecular hydrogen in nonporous forsterite is controlled by pressure above 1200 K. Variations in intercrystalline pore size above 5 Å have a negligible effect on the capacity of adsorbed state molecular hydrogen at a given temperature and pressure. The adsorption of molecular hydrogen on different crystal faces of forsterite is anisotropic, with stronger adsorption on (001) and (100) than on (010) crystal faces. The adsorption capacity of molecular hydrogen in the intercrystalline pore decreases with the increase in oxygen fugacity at a given pressure, temperature, or intercrystalline pore sizes. The significant amount of molecular hydrogen stored in forsterite can provide a rich material basis for the short-term seismic precursor anomaly of hydrogen concentration and the formation of water through the reaction of silica with molecular hydrogen in the mantle.

Quantum chemical simulation of hydrogen adsorption in pores: A study by DFT, SAPT0 and IGM methods

Hydrogen as a versatile energy carrier continues to attract research attention in the field of applied chemistry. One of the fundamental issues on the way to hydrogen economy is the difficulty of hydrogen storage. Physical adsorption of hydrogen in pores is a feasible and effective method of hydrogen storage. Among existing hydrogen-adsorbing materials, carbon nanostructures possess a number of advantages due to their high adsorption capacity, significant strength and low weight. In this work, we use the modern methods of quantum chemistry (DFT, SAPT0 and IGM) to study the adsorption of molecular hydrogen in a series of simulated slit-like carbon micropores with a distance between the walls of d = 4–10 Å, including the introduction of an H2 molecule into a pore, filling pores with these molecules and investigating the interactions between H2 molecules inside the pores. It was found that, depending on the value of parameter d, adsorbed hydrogen molecules form one (d = 6, 7 Å) or two layers (d = 8, 9, 10 Å) inside the pore. At the same time, for pores with small d values, high potential barriers to the introduction of H2 into a pore were observed. The decomposition of the interaction energy into components showed dispersion interactions to make a major contribution to the energy of attraction (72–82%). Moreover, an increase in the number of H2 molecules adsorbed in the pore decreases the significance of dispersion interactions (up to 61%) and increases the contribution of electrostatic and induction interactions to intermolecular attraction. Gravimetric density (GD) values were determined for pores with d = 6, 7, 8, 9, 10 Å, comprising 1.98, 2.30, 2.93, 3.25 and 4.49 wt%, respectively. It is assumed that the revealed peculiarities of hydrogen adsorption in pores will contribute to the use of carbon porous structures as a medium for hydrogen storage.

A DFT analysis unravelling hydrogen sorption pathways in Laves phase Cu2Cd

A comprehensive study to establish sorption pathways for molecular and atomic hydrogen in Cu2Cd Laves phase by means of density functional theory calculations is reported. The surface energy of Cu2Cd was calculated exposing the (0001) surface with two different planes, one being Cu terminated while the other being Cu-Cd terminated. Both were discerned to have comparable surface energies. Adsorption sites for the relevant molecular and atomic hydrogen were identified on both the planes and the associated energetics were determined. Adsorption of atomic hydrogen was found to be energetically favoured when compared to the molecular adsorption of hydrogen. Diffusion pathways for atomic hydrogen from the surface to the bulk were investigated. The study provides detailed insights into the identification and energetics of the surface adsorption of hydrogen, and its diffusion to the subsurface sites, thus unravelling the sorption pathways in Cu2Cd Laves phase for potential hydridic storage of hydrogen.

Descriptor of catalytic activity nanoparticles surface: Atomic and molecular hydrogen on gold

A simple descriptor based on electron density within the modified embedded atom model (MEAM) is proposed to describe the adsorption and dissociation of hydrogen on gold. The correlations of the electron density calculated in the MEAM model are shown at various active centers of the gold cluster on the atomic and molecular hydrogen adsorption energies and H2 dissociation barrier. The algorithm for the MEAM electron density calculation is taken in the form of a program code. The change in the surface activity of gold nanoparticles of various diameters was studied with a descriptor. A sharp increase in the nanoparticles activity was observed at diameters <4.2 nm. A temperature rise is shown to increase the surface activity because of surface morphology changes.

Enhanced hydrogen adsorption in alkali metal based copper hexacyanoferrate Prussian blue analogue nanocubes

Two Prussian blue analogues (PBAs) CuII[FeIII(CN)6)]2/3·15H2O (1), and KICuII[FeII(CN)6)]3/4·9H2O (2) are synthesised using a co-precipitation method at room temperature. The compounds are studied using XRD (x–ray diffraction), FESEM (Field Emission Scanning Electron Microscopy), IR (infrared), Raman spectroscopy, and TGA (thermogravimetric analysis). The surface morphology of the compounds is investigated using the FESEM technique, which confirms the formation of cube-type microstructure with an average size of ∼200 and ∼120 nm for compounds (1), and (2), respectively. The x-ray diffraction (XRD) results, derived from the Rietveld refinement method, reveal that both the compound crystallized in a pure single nanocrystalline phase with face centred cubic crystal structure of space group Fm3m. The lattice constants are found to be ∼10.04, and ∼10.08 Å for the compound (1), and (2) respectively. The IR and Raman spectroscopy show characteristic peaks, observed in the range of 1900–2200 cm−1, corresponds to the CN stretching frequency of CuII–CN–FeIII/II, confirming the formation of PBAs compounds. The hydrogen adsorption isotherm measurements have been used to investigate the molecular hydrogen adsorption into PBAs compounds at low temperature (77 K) conditions. The compounds (1) and (2) show hydrogen storage capacity of ∼1.12 and 1.63 wt %, respectively. The compound (2) shows an enhanced hydrogen capacity of ∼45% as compared to compound (1), which is due to the presence of unsaturated Cu/Fe metal ions, and the larger surface area of the nanocubes in the framework structure. In addition, the presence of K+ ions in the compound (2) also strongly favours to catalysing more H2 for their enhanced storage capacity.

Catalytic activity of Co–Ag nanoalloys to dissociate molecular hydrogen. New insights on the chemical environment

Adsorption of molecular hydrogen on the surface of catalytic metal nanoparticles and its dissociation in atomic hydrogen are processes of interest in many chemical technologies. As in other chemical reactions, alloying can improve the efficiency of the catalysts. By focusing on Co6, Co5Ag, Co3Ag3 and CoAg5, we explore the effect of changing the relative concentration of the two components in small ComAgn clusters, a peculiar nanoalloy because Co and Ag do not form bulk solid alloys. Molecular hydrogen adsorbs preferentially on the Co atoms, and the binding is mainly due to the electrical polarization of the charges of adsorbate and host. The preference for Co sites and the trend in the strength of the H2-cluster binding are explained by the combination of two effects characterizing the host environment. One of these is geometric, arising from the degree of exposure of the host atom: the lower the atomic coordination of the host atom, the stronger its bonding with H2. The second effect, newly identified, reveals the importance of the chemical nature of the host atom environment: host Co atoms having both Co and Ag neighbors maintain their capacity to bind hydrogen more intact than those with only Co neighbors. The alloy nanoclusters catalyze the dissociation of adsorbed H2 by building up quite small activation barriers. After dissociation, the H atoms occupy bridge positions between Co atoms (between Co and Ag in CoAg5). H2 adsorption and dissociation may trigger structural transformations of the cluster. The work shows that the adsorption and dissociation properties of H2 can be tuned by varying the relative composition of the two atomic species in the nanoalloy.