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Abstract Density Functional Theory (DFT) calculations were employed to study a series of coinage metal-hydrogen associations formulated as [M(Η 2) n ][A] (M = CuI, AgI or AuI, n = 1–5). The [M(Η 2) n ][A] salts utilize both their anions and cations for H 2 storage. The [M(Η 2) n ]+ cations could be stabilized in the solid state by voluminous counter-anions, i.e. the [(H 3 B) (BH 2 NH 2) 5 (NH 2)]-, [B(CNBH 3) 3 ]- and [B 12 H 12 ]- anions. The estimated bond dissociation energies (BDE s) of the M···(η 2-H 2) bonds are 5–17, 4–11 and 1–26 kcal/mol for the [Cu(Η 2) 4 ]+, [Ag (Η 2) 4 ]+ and [Au (Η 2) 4 ]+ cationic species respectively, while the fifth H 2 molecule is estimated to be very loosely associated to the metal center. Four H 2 molecules could be exploited from the [Cu(Η 2) n ][A] and [Ag (Η 2) n ][A] molecules in addition to the amount of H 2 stored in the anion [A]-. Among the [M(Η 2) n ][A] salts optimal gravimetric, kinetic and thermodynamic properties and relatively low cost, are predicted for [Cu(Η 2) n ][(H 3 B) (BH 2 NH 2) 5 (NH 2)]. Highlights • Solid stabilization of metal hydrides with optimal H 2 storage properties. • Weakly Coordinating Anions. • 'Complex hydrides', exploiting both anion and cation for H 2 storage. • Novel 'concept' design of 'complex hydrides'. [ABSTRACT FROM AUTHOR]

Abstract Molecular hydrogen storage on Ruthenium (Ru) decorated single-walled carbon nanotube (SWCNT) has been studied by using spin-polarized density functional theory (DFT). When a Ru atom is adsorbed on SWCNT, the Bader analysis reveals that Ru transfers a charge of 0.44e− to SWCNT. Accordingly, Ru acts as adsorption center for H 2 molecules; thus, it can hold up to four H 2 molecules with an adsorption energy (E ads) of −0.93 eV/H 2. A uniform addition of Ru atoms on SWCNT shows that this nanomaterial can adsorb up to five Ru without clustering. Each Ru atom of 5Ru-decorated SWCNT system can bind up to four H 2 molecules involving an E ads of −0.83 eV/H 2. After H 2 molecules adsorption, Ru atoms shifted from a near hollow site to a bridge site. Moreover, Ru-decorated systems reduce their magnetic moment when the number of H 2 molecules increase from 2 μ B to 0 μ B. Graphical abstract Image 1 Highlights • Doping Ru enhances H2 adsorption on a SWCNT more than 12 times. • Ru distribution at low concentration and Ru charge transfer to the SWCNT prevent Ru clustering. • Each five Ru atoms without clustering on a SWCNT can bind up to four H2 molecules. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hydrogen release from a novel storage reactor with high capacities at low pressures. • Coupled magnesium hydride dehydrogenation and magnesium oxide hydration feasible. • Water vapor supply to the storage reactor at 10 bar and 350 °C possible. • Dehydrogenation rate dependent on the vapor supply-pressure. • Magnesium hydride dehydrogenation reaction fast enough for stationary applications. Abstract With hydrogen becoming more and more important as storage and carrier for renewable energy, there is an increasing need for flexible and efficient storage technologies. However, existing technologies, such as liquefaction or compression, often require a significant share of the hydrogens lower heating value. High-temperature metal hydrides (HT-MHs), such as magnesium hydride, are a promising alternative. Due to high operation temperatures, their application is challenging. A novel adiabatic hydrogen storage reactor based on the combination of a HT-MH with a thermochemical energy storage system (TCSS), such as Mg(OH) 2 /MgO + H 2 O, can be a solution. In this work, the previously published numerical simulations for hydrogen absorption are extended to the desorption process. A two-dimensional model for the hydrogen release was set up. The performance of the storage reactor is strongly dependent on the thermodynamic equilibrium of the reactions involved and less dependent on the reaction kinetics. Dehydrogenation is possible within 132 min, which is in the vicinity of the hydrogenation time. To enhance the dehydrogenation process, the water vapor pressure can be adjusted aiming for higher temperatures during the MgO hydration. Hydrogen can either be provided at constant pressure or constant mass flow rate. [ABSTRACT FROM AUTHOR]

The present research focuses on the synthesis and applications of a series of hyper-cross-linked polymer networks obtained from the one-step Friedel–Crafts reaction of triphenylsilane and formaldehyde dimethyl acetal. The materials were characterized through FTIR, 13C NMR, PXRD, TGA, N2 adsorption-desorption isotherms, H2 sorption and dye adsorption. These materials exhibited increased surface areas of approximately 441–1101 m2 g−1 with increasing ratio of monomer to cross-linker. The H2 storage capacity of the polymer networks reached 1.19 wt % (5.96 mmol g−1) under 1.03 bar and 77.3 K. In addition, the material showed excellent adsorption capacity of 806 mg g−1 for Congo Red and retained their adsorption capacity after recycling nine times. Taken together, the results demonstrate that the obtained hyper-cross-linked polymers could be applied to H2 storage and water treatment. [ABSTRACT FROM AUTHOR]

Today's scientific professionals face the challenge of meeting the ever-growing demand for hydrogen fuel. Hydrogen stands as a sustainable and eco-friendly alternative. This fuel is inherently lightweight and gaseous Which present challenges in its production, transportation, and storage. Hydrogen fuel can be stored using different storage methods which have merits and demerits. Hydrogen can be stored by conventional methods and also using the next generation materials, i.e., pressurized gas, liquid nitrogen at cryogenic temperature, chemical method storage in the metal hydride, and adsorption on carbon material. According to various researches, carbon material has been stated as a novel, emerging and next-generation material for storing hydrogen. Hierarchical carbon having modified 3-dimensional structure and multimodal pore can be prepared from different chemically or catalytically activation processes. The best-suited carbon material for hydrogen storage has a high specific surface area of 2000–3000 m2/g and also high interconnectivity of pore. In this review paper, the various hydrogen storage methods and performance of carbon materials for hydrogen storage at different pressure and temperature are reviewed. The utilization of carbon for hydrogen storage represents a prominent technology in addressing the obstacles linked with the use of hydrogen. [Display omitted] • Carbon based material production with properties best suited for hydrogen storage. • Next generation material and conventional method used for hydrogen storage. • Literature results on bio-derived carbon-based hydrogen storage are cited. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen adsorption properties of Be/Sc doped pentalene complexes are investigated using second ordered Møller-Plesset method (MP2). In order to study the boron substitution effect, pentalene is further modified by substituting two and four boron atoms for carbon atoms at different positions and named as TBP1 and TBP2 for two boron atom substituted structures and FBP1 and FBP2 for four boron atom substituted structures. Two H 2 molecules get adsorbed on each Be doped complex and having 3.25, 3.31, 3.31, 3.38 and 3.38 wt% H 2 uptake capacity for C 8 H 6 Be 2 , TBP1Be 2 , TBP2Be 2 , FBP1Be 2 and FBP2Be 2 complexes respectively. All Sc doped pentalene and boron substituted pentalene complexes can interact with nine H 2 molecules except TBP2Sc 2 complex. The TBP2Sc 2 complex can adsorb eight H 2 molecules. The H 2 uptake capacity is found to be 8.63, 8.73, 7.84, 8.83 and 8.83 wt% for C 8 H 6 Sc 2 , TBP1Sc 2 , TBP2Sc 2 , FBP1Sc 2 and FBP2Sc 2 complexes respectively. Gibbs free energy corrected adsorption energy plots show that the H 2 adsorption on all Be doped complexes is possible at all temperatures and pressures considered here. The TBP1Sc 2 complex seems to be more promising hydrogen storage material among all Sc doped complexes over a wide range of temperature and pressure. The H 2 desorption temperatures obtained for the Be doped complexes are higher than the Sc doped complexes. Stability of the complexes is predicted with the help of the gap between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. Highlights • Be and Sc doped pentalene complexes for hydrogen storage. • Boron substitution in pentalene affects the H 2 uptake capacity. • Energetically favorable H 2 adsorption on Be decorated complexes at ambient conditions. • Energetically unfavorable H 2 adsorption on Sc decorated complexes at ambient conditions. • Be doped pentalenes are better material for H 2 adsorption than Li and Sc. [ABSTRACT FROM AUTHOR]

In the present report, mesoporous silica SBA‐15 was synthesized by different methods such as room temperature aging, hydrothermal, and sonication‐mediated hydrothermal methods. The effect of different time and temperature on the synthesis method was investigated by conventional characterization techniques. The powders synthesized by different methods showed different properties, mainly in morphology and pore volume. In comparison to others, the powder synthesized by the hydrothermal method at 100°C for 48 hours showed exceptionally high surface area of 3274 m2/g. To date, as per our knowledge, no such value was reported in literature. Finally, the powders were characterized by H2 storage capacity by the adsorption‐desorption method using 99.999% H2. The hydrogen adsorption capacity of the same powder was observed at 6.02 wt%. Also, this value seems to be the highest H2 adsorption capacity in comparison to other powders described in literature. SBA‐15 powders are synthesized by different methods at varying time and temperature. The powder synthesized by hydrothermal treatment at 100°C and 24 h shows high surface area. The orous powder having channel within the pores shows a surface area of 3274 m2/g. The hydrogen adsorption capacity measured at 77 k and 1 bar pressure shows 6.2 wt%. [ABSTRACT FROM AUTHOR]

Comprehensive study to evaluate the ability of hydrogen uptake by disordered mesoporous hollow carbon spheres doped witch metal such as Pt, Pd or Pt/Pd was conducted. They were synthesized facilely using sonication and then calcination process under vacuum at the temperature of 550 °C. The effect on hydrogen sorption at neat-ambient conditions (40 °C, up to 45 bar) was thoroughly analyzed. The results clearly revealed that metal functionalization has a significant impact on the hydrogen storage capacity as the mechanism of gas uptake depends on two factors: metal type and certain size of particles. Thus, functionalized spheres adsorb hydrogen by physisorption forming metal hydrides or metal hydrides combined with hydrogen spillover effect. As a result, a sample with narrower distribution of nanoparticles and smaller specific size exhibited enhanced hydrogen uptake. [ABSTRACT FROM AUTHOR]

A single atom Ru catalyst supported on a N-doped TiO 2 was investigated for the conversion of CO 2 to formate by hydrogenation. N-dopant sites induced a strong binding environment to Ru single-atom catalysts (SACs), resulting in a stable and atomically isolated dispersion state of Ru SACs upon metalation. Consequently, Ru/MN-TiO 2 exhibited enhanced catalytic stability, which incorporated both substitutional (N s) and interstitial (N i) dopant sites, retaining 42 % of its original relative activity after the fifth recycle test. In contrast, Ru/N-TiO 2, which contained only N i -dopants, showed a lower stability, retaining only 19 % of its initial activity after the fifth run, and Ru/TiO 2 was fully deactivated after the third run. Density functional theory calculations revealed that the stronger binding ability of the N s sites to the Ru species compared with that of the N i sites and the bare surface of the TiO 2 structure improved the catalytic stability during hydrogenation. [Display omitted] • Ru single atom catalyst supported on N-doped TiO 2 exhibits enhanced catalytic stability for CO 2 hydrogenation to formate. • Nitrogen doped in the TiO 2 is located at two types of chemical states, namely substitutional N and interstitial N site. • Substitutional N on TiO 2 binds the Ru atom more strongly than interstitial N and bare TiO 2 , improving catalytic stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recent developments in liquid organic hydrogen storage systems are described. • The most commonly used systems, reaction conditions, and catalysts are listed. • Transfer phenomena and density functional theory studies are cited and explained. • Studies on microkinetic modeling and computational fluid dynamics are quoted. • Possible directions for further research on these storage systems are indicated. The continued selective focus on the exploitation of fossil fuel chemicals as one of the main environment-depleting sources of energy is one of the reasons for the carbon dioxide emissions, severe air pollution and market crisis of today. The related easy transition to efficient renewable resources also brings challenges, such as the storing of performance generated year round. Consistent application option is to convert the formed transferred electricity produced into the hydrogen through electrolysis, store gaseous H 2 , and reversibly proceed with reforming or cracking. This routine way is also referred to in literature as evolving green H 2. A relatively new method of storage is liquid organic carriers (LOHCs). These are molecules that are in a (l) state at room temperature measurements, contain unsaturated covalent bonds, and can be hydrogenated/dehydrogenated in the many loading cycles without catalytic decomposition products. Paper presents possible structure systems that have been previously investigated as an alternative to conventional. The process of catalysis, reduction and coking, catalysts, and the most commonly used elementary groups, interactions, and reaction condition analyses are listed, while an overview of studies that have assessed technical transfer phenomena is also provided. Reports, dealing with derived micro-kinetic modelling/computational fluid dynamics (CFD), which is a direction for further research activities, are few. As for multiscale, review ranges from the density functional theory (DFT) to CFD. The review paper also addresses the latest studies on LOHCs in the field of artificial intelligence (AI), machine learning (ML), and artificial neural networks (ANN). The progress within the area with approaches is highlighted. Mesoscale surface–selectivity relationships, the robustness towards deactivation and techno-economics are dominant in linking the digital twin design to operation. [ABSTRACT FROM AUTHOR]

A changeable ligand, which involves in activation of a catalyst or assists a reaction, draws an increasing attention, in contrast to a classical ligand as spectator. Proton-responsive catalysts, which are capable of undergoing changes of properties on gaining/losing one or more protons, provides interesting features as follows: (i) catalyst activation by electronic effect, (ii) pH-tuning of water-solubility, and (iii) second-coordination-sphere interaction. On the basis of this catalyst design concept, we developed several highly efficient proton-responsive catalysts for CO2 hydrogenation as H2 storage, formic acid (FA) dehydrogenation as H2 production, and transfer hydrogenation. The transformable ligands of proton-responsive catalysts in promoting effective catalysis have aroused our interest. In this account, we summarize our efforts for the development and application of proton-responsive catalysts. Specifically, the important role of pH-dependent proton-responsive complexes will be discussed. [ABSTRACT FROM AUTHOR]

A series of new imidazoline-based iridium complexes has been developed for hydrogenation of CO2 and dehydrogenation of formic acid. One of the proton-responsive complexes bearing two −OH groups at ortho and para positions on a coordinating pyridine ring ( 3 b) can catalyze efficiently the chemical fixation of CO2 and release H2 under mild conditions in aqueous media without using organic additives/solvents. Notably, hydrogenation of CO2 can be efficiently carried out under CO2 and H2 at atmospheric pressure in basic water by 3 b, achieving a turnover frequency of 106 h−1 and a turnover number of 7280 at 25 °C, which are higher than ever reported. Moreover, highly efficient CO-free hydrogen production from formic acid in aqueous solution employing the same catalyst under mild conditions has been achieved, thus providing a promising potential H2-storage system in water. [ABSTRACT FROM AUTHOR]

[Display omitted] • Li decorated BCN monolayer has been investigated and show reversible hydrogen storage capacity under ambient temperature. • The Li can firmly anchor on BCN monolayer with binding energy of −1.91 eV. • The hydrogen storage capacity of Li @ BCN monolayer can reach up to 6.34 wt%. A novel 2D pm-BCN monolayer with unique porous geometry, superlight mass, and superior stability is a promising candidate for hydrogen storage. However, pure 2D materials suffer from the weak Van de Waals interaction between the H 2 , and modification becomes necessary to improve their performance. Here, we design a new complex by decorating active Li ions on the 2D pm-BCN substrate. The decoration of Li can transfer a partial electron to the substrate pm-BCN, which enhances the original π bonding among pm-BCN and induce more active sites on it. Both Li and BCN can act as the adsorption sites. The H 2 can realize reversible adsorption under an ambient condition with average adsorption energy of −0.20 eV/H 2 and a gravimetric capacity of 6.34 wt%, which surpasses the targe value set by U.S. Department of Energy (DOE). Rigorous analysis of its electronic properties, including a partial density of states, charge density, and crystal orbital overlap population, illustrates that the polarization mechanism contributes to the enhancement of the hydrogen storage capacity of Li@pm-BCN. [ABSTRACT FROM AUTHOR]

In this article, newly designed 3D porous polymers with tuned porosity were synthesized by the polycondensation of tetrakis (4-aminophenyl) methane with pyrrole to form M1 polymer and with phenazine to form M2 polymer. The polymerization reaction used p -formaldehyde as a linker and nitric acid as a catalyst. The newly designed 3D porous polymers showed permanent porosity with a BET surface area of 575 m 2 /g for M1 and 389 m 2 /g for M2 . The structure and thermal stability were investigated by solid 13 C-NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The performance of the synthesized polymers toward CO 2 and H 2 was evaluated, demonstrating adsorption capacities of 1.85 mmol/g and 2.10 mmol/g for CO 2 by M1 and M2 , respectively. The importance of the synthesized polymers lies in their selectivity for CO 2 capture, with CO 2 /N 2 selectivity of 43 and 51 for M1 and M2 , respectively. M1 and M2 polymers showed their capability for hydrogen storage with a capacity of 66 cm 3 /g (0.6 wt%) and 87 cm 3 /g (0.8 wt%), respectively, at 1 bar and 77 K. Molecular dynamics (MD) simulations using the grand canonical Monte Carlo (GCMC) method revealed the presence of considerable microporosity on M2 , making it highly selective to CO 2 . The exceptional removal capabilities, combined with the high thermal stability and microporosity, enable M2 to be a potential material for flue gas purification and hydrogen storage., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Al-Bukhari, Abdulazeez, Abdelnaby, Aljundi and Al Hamouz.)

Comprehensive study to evaluate the ability of hydrogen uptake by disordered mesoporous hollow carbon spheres doped witch metal such as Pt, Pd or Pt/Pd was conducted. They were synthesized facilely using sonication and then calcination process under vacuum at the temperature of 550 °C. The effect on hydrogen sorption at neat-ambient conditions (40 °C, up to 45 bar) was thoroughly analyzed. The results clearly revealed that metal functionalization has a significant impact on the hydrogen storage capacity as the mechanism of gas uptake depends on two factors: metal type and certain size of particles. Thus, functionalized spheres adsorb hydrogen by physisorption forming metal hydrides or metal hydrides combined with hydrogen spillover effect. As a result, a sample with narrower distribution of nanoparticles and smaller specific size exhibited enhanced hydrogen uptake.

A scalable, template-free synthetic strategy is presented for the preparation of ultramicroporous carbon nitride frameworks (CNFs) through a chemical blowing approach by using ammonium chloride as blowing agent and hexamethylene tetraamine as the C and N precursor and a subsequent potassium hydroxide chemical activation is employed to obtain CNFs with surface areas up to 1730 m2 g−1 along with a high nitrogen content of 13.3 wt%. CNFs showed CO2 uptake capacities up to 5.74 mmol g−1 at 1 bar and 1.67 mmol g−1 at 0.15 bar, 273 K along with a very high CO2/N2 selectivity. In addition, H2 uptake capacity of 1.9 wt% and the isosteric heats of adsorption ( Qst) value of 9.0 kJ mol−1 at zero coverage have been also observed. Moreover, the presence of nitrogen-doped graphene walls in CNFs also facilitated their application as supercapacitors, with capacitance values up to ≈114 F g−1 at 0.5 A g−1, along with a good cyclability and capacitance retention. This approach effectively extends unique surface properties of carbon nitrides into the micropore regime for effective capture of small gases and energy storage applications. Importantly, textural properties of CNFs can be simply tuned by judicious choice of organic precursors and the blowing agent. [ABSTRACT FROM AUTHOR]

New monolithic nitrogen-containing microporous cellular activated carbon was successfully prepared from phenol-urea-formaldehyde (PUF) organic foam for CO2 and H2 adsorption and was characterized by thermogravimetric analysis (TG), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), a mechanical testing machine, N2-sorption and H2/CO2 sorption. The carbon yield was approximately 50% for carbonization and the burn off for activation ranged from 40% to 56%, which linearly increased with activation time. The macroporosity corresponded to the connected network of cells with diameters ranging from 100m to 600m, and the pinholes in the cell walls had diameters ranging from 1m to 2m. The micro/mesoporosity is located at the inner surface of the cells. Thus, higher adsorption kinetics than usual from activated carbon are expected. The developed carbon with the highest (1674 m2/g) and highest (0.86cm3/g) contained 1.5% nitrogen, had a CO2 adsorption capacity of 3.53mmol/g at 298K, and had an H2 adsorption capacity of 1.9wt.% at 77K, both at atmospheric pressure (1 bar), which were among the best in activated carbons from physical activation. In the current study, a new monolithic-activated carbon with nitrogen-containing from phenol-ureaformaldehyde (PUF) resin, which is widely used in wood industry is successfully prepared. It was found that the micropores, mesopores and macropores are located in the foams. These cellular-activated carbons are good candidate materials for gas adsorption due to the high surface area and cellular structure. [ABSTRACT FROM AUTHOR]

The role of ternary Mg-Nb oxides on H2 absorption and desorption properties of ball milled MgH2 is discussed on the basis of a kinetic model involving the formation of reaction pathways of ternary oxide species with easier splitting of H2 that facilitate the transport of H2 into the solid structure. The kinetic model comprised three key steps: dissociation of molecular hydrogen into H atoms, diffusion of H into Mg to form MgH2 during adsorption, and successive recombination of H-H on the surface of the additives during desorption to make a pathway for H2 sorption in the structure. The presence of transition metal oxides remarkably increases the H2 sorption rates of nano-structured MgH2, as determined by a volumetric Sievert apparatus. The H2 desorption rate increases with increasing temperature from 593 to 673 K and under the same conditions, the absorption rate decreases. The most promising results were obtained for Mg3Nb6O11-doped MgH2 nano-particles. The MgH2/Mg3Nb6O11 system is completely dehydrogenated at 673 K under 0.1 MPa H2 and the samples fully rehydrogenated at 613 K under 2.5 MPa H2 pressure. Activation energies were obtained for MgH2/Mg3Nb6O11 mixture, and without additive (ball milled MgH2), to be 88 and 127 kJ mol-1, respectively, underlying the effect of the ternary additive. [ABSTRACT FROM AUTHOR]

The role of ternary Mg-Nb oxides on H2 absorption and desorption properties of ball milled MgH2 is discussed on the basis of a kinetic model involving the formation of reaction pathways of ternary oxide species with easier splitting of H2 that facilitate the transport of H2 into the solid structure. The kinetic model comprised three key steps: dissociation of molecular hydrogen into H atoms, diffusion of H into Mg to form MgH2 during adsorption, and successive recombination of H-H on the surface of the additives during desorption to make a pathway for H2 sorption in the structure. The presence of transition metal oxides remarkably increases the H2 sorption rates of nano-structured MgH2, as determined by a volumetric Sievert apparatus. The H2 desorption rate increases with increasing temperature from 593 to 673 K and under the same conditions, the absorption rate decreases. The most promising results were obtained for Mg3Nb6O11-doped MgH2 nano-particles. The MgH2/Mg3Nb6O11 system is completely dehydrogenated at 673 K under 0.1 MPa H2 and the samples fully rehydrogenated at 613 K under 2.5 MPa H2 pressure. Activation energies were obtained for MgH2/Mg3Nb6O11 mixture, and without additive (ball milled MgH2), to be 88 and 127 kJ mol-1, respectively, underlying the effect of the ternary additive. [ABSTRACT FROM AUTHOR]

Previous theoretical studies of C3B have suggested that boron-doped graphite is a promising H2-and Li-storage material, with large maximum capacities. These characteristics could lead to exciting applications as a lightweight H2-storage material for automotive engines and as an anode in anew generation of batteries. However, for these applications to be realized a synthetic route to bulk C3B must be developed. Here we show the thermolysis of a single-source precursor (1,3-(BBr2)2C6H4) to produce graphitic C3B, thus allowing the characteristics of this elusive material to be tested for the first time. C3B was found to be compositionally uniform but turbostratically disordered. Contrary to theoretical expectations, the H2-and Li-storage capacities are lower than anticipated, results that can partially be explained by the disordered nature of the material. This work suggests that to model the properties of graphitic materials more realistically, the possibility of disorder must be considered. [ABSTRACT FROM AUTHOR]

• N-doped mesoporous carbon hollow spheres (N-MCHSs) support for RuCl 3 catalysts were examined for CO 2 hydrogenation. • At low pyrolysis temperatures (700–800 °C), the dominant N species were shown to be pyrrolic, pyridinic N however, at high pyrolysis temperatures (900–1000 °C) were graphitic N. • The Ru/N-MCHS-900 catalyst, the turn-over number was as high as 7550 after the hydrogenation for 2 h at 120 °C and 8 MPa. • The Ru/N-MCHS-700 catalyst exhibited excellent stability in both batch and continuous reactors. Atomically dispersed Ru(III) catalysts on hierarchical and porous supports show great potential for application in the catalysis of the hydrogenation of CO 2 to formate due to their high catalytic activity and stability. In this study, heterogeneous Ru(III) catalysts on N-doped mesoporous carbon hollow spheres (N-MCHS) were synthesized through a SiO 2 -templated resorcinol–formaldehyde polymer pyrolysis at different temperatures. At low pyrolysis temperatures (700–800 °C), the dominant N species on the catalysts were found to be pyrrolic and pyridinic N (N pyrrolic and N pyridinic). However, the dominant N species on the samples produced from 900 to 1000 °C was graphitic N (N graphitic). The highest catalytic activities on the batch hydrogenation experiments were recorded on the catalysts with the predominant Ru–N graphitic active sites. Using the Ru/N-MCHS-900 catalyst, the turn-over number (TON) was as high as 7550 after the hydrogenation for 2 h at 120 °C and 8 MPa. On the other hand, the Ru/N-MCHS-700 catalyst exhibited excellent stability in both batch and continuous reactors. No noticeable deactivation was observed even after 72 h of continuous hydrogenation, which can be attributed to the strong binding energy between the Ru(III) species, and the N pyridinic and N pyrrolic sites on the N-MCHS supports. This study provided significant insights for the development of novel heterogeneous catalyst systems for the hydrogenation of CO 2 to formate. [ABSTRACT FROM AUTHOR]

Abstract: Recent significant progress in the homogeneous catalytic hydrogenation of CO2 to formate (the conjugate base of formic acid) and dehydrogenation of formic acid in various solvents including water is summarized. While formic acid is not the perfect H2 storage solution, many researchers consider it better than other methods at this time because the interconversion of CO2 and formic acid can take place cleanly to form H2 without detectable CO under mild conditions. In this chapter, we explain how inspirations from biological systems guide us to design homogeneous transition-metal catalysts for carrying out the interconversion of CO2 and formate under ambient conditions in environmentally benign and economically desirable water solvent. [Copyright &y& Elsevier]

Abstract: The effect of Pd-doping on the adsorption properties of three isoreticular metal-organic frameworks (IRMOFs), presenting different cavity sizes (IRMOF-1, IRMOF-8 and IRMOF-10), has been studied in this work. Parent IRMOFs were synthesized and doped with palladium by incipient wetness impregnation. The resulting materials were characterized by XRD, N2-phsyisorption, TEM and temperature-programmed decomposition. The effect of Pd incorporation on H2 and CO2 adsorption was evaluated by thermogravimetry. Hydrogen uptake is favored by the spillover effect, although the partial blockage of micropores, and structural changes in the MOF structure hinders hydrogen adsorption. In the case of carbon dioxide, it is observed an enhancement on the adsorption after palladium impregnation attributed both to morphological changes, and to the modification of electronic charge of the ligands aromatic structures. As result, the H2/CO2 adsorption capacity ratio increases after palladium impregnation only for Pd-IRMOF-8, leading to a promising material for hydrogen separation and storage. [Copyright &y& Elsevier]

Abstract: Recent investigations of the interconversion of CO2 and formic acid using Ru, Ir and Fe complexes are summarized in this review. During the past several years, both the reaction rates and catalyst stabilities have been significantly improved. Remarkably, the interconversion (i.e., reversibility) has also been achieved under mild conditions in environmentally benign water solvent by slightly changing the pH of the aqueous solution. Only a few catalysts seem to reflect a bio-inspired design such as the use of proton responsive ligands, ligands with pendent bases or acids for a second-coordination-sphere interaction, electroresponsive ligands, and/or ligands having a hydrogen bonding function with a solvent molecule or an added reagent. The most successful of these is an iridium dinuclear complex catalyst that at least has the first three of these characteristics associated with its bridging ligand. By utilizing an acid/base equilibrium for proton removal, the ligand becomes a strong electron donor, resulting in Ir(I) character with a vacant coordination site at each metal center in slightly basic solution. Complemented by DFT calculations, kinetic studies of the rates of formate production using a related family of Ir complexes with and without such functions on the ligand reveal that the rate-determining step for the CO2 hydrogenation is likely to be H2 addition through heterolytic cleavage involving a “proton relay” through the pendent base. The dehydrogenation of formic acid, owing to the proton responsive ligands changing character under slightly acidic pH conditions, is likely to occur by a mechanism with a different rate-determining step. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems. [Copyright &y& Elsevier]

Abstract: A new series of coordination compounds of different dimensionalities, {Cd2(TBTH)2(TBT)(DMF)6} (1), {Cu(TBT)(DMF)2} n (2), {Ni(TBT)(DMF)2(EtOH)2} n (3) and {Mn(TBT)(DMF)} n (4) have been synthesized under similar reaction conditions and stoichiometry using tetrabromoterephthalic acid (TBTH2) as a building block. Single crystal X-ray diffraction study reveals 1 is a dimeric discrete complex whereas 2 and 3 are found to be 1D coordination polymers and all the three compounds extend to three dimensions by non-covalent (H-bonding and O⋯Br) interactions. Compound 4 has a 3D framework structure where {Mn(CO2)} n chains are cross-linked by TBT linkers and DMF molecule also acts as a bidentate bridging ligand. The difference in dimensionalities can be correlated to the metal ions (CdII, CuII, NiII and MnII) having different ionic radius. Compound 4 does not contain any guest solvent molecule but removal of bridging DMF molecules creates a 1D channel with dimension of 2.1×4.2Å2. Adsorption studies reveal that the desolvated compound 4 (4′) with unsaturated MnII sites can uptake an appreciable amount of CO2 at 195K (15wt.%), and H2 at 77K (∼0.4wt.%) although surface area is not significant. [Copyright &y& Elsevier]

A 3-D porous metal–organic framework [Cu(SiF6)(4,4′-bpy)2] was reported to have high methane storage. The studies about [Cu(SiF6)(4,4′-bpy)2] were only related with methane storage but information on detailed synthesis and characterization as well as adsorption properties of [Cu(SiF6)(4,4′-bpy)2], especially the H2 and CO2 adsorption properties, was scarce. In this work, [Cu(SiF6)(4,4′-bpy)2] has been synthesized by adjusting the molar ratio of the reagents, synthesis temperature, and crystallization time. This method for obtaining [Cu(SiF6)(4,4′-bpy)2] at low temperature has not been reported before. Temperature played an important role in synthesis of the sample and low temperature was beneficial for synthesizing bigger sample. Adsorption isotherms for carbon dioxide and hydrogen were measured under high pressure. [Cu(SiF6)(4,4′-bpy)2] exhibited H2 storage up to 2.36 wt% at 18 bar and a high CO2 capture up to 4.17 mmol g−1 at 298 K at 10 bar. [ABSTRACT FROM PUBLISHER]

Abstract: Three Mg–Nb–O compounds were synthesized in order to understand the role of oxides as promoters/catalysts for hydrogen storage in Mg/MgH2 systems. Ternary Mg–Nb–O compounds were prepared by solid-state reactions. The effect of calcination temperature on phase formation and chemical composition of the solid-state products were studied by X-ray diffraction. Gradual reaction of precursor components and simultaneous formation of solid-state products were found to be strongly dependent on calcination conditions. Hydrogen sorption properties were investigated by Mass Spectrometry. MgNb2O6 and Mg4Nb2O9 phases were rather inactive with respect to hydrogen. On the contrary, Mg3Nb6O11 compound showed remarkable uptake and release of molecular hydrogen. The reversible hydrogen interaction with this phase is discussed with respect to octahedral niobium clusters present in the oxide structure. [Copyright &y& Elsevier]

Abstract: In the present work we study the capacity of storage hydrogen on carbon fibers activated with supercritical water and with steam on the basis of a multisite Langmuir model, with three energetically different adsorption sites that may be associated with pores of different sizes: i) very small micropores, accessible only to hydrogen; ii) micropores detected by the adsorption of CO2, and iii) micropores detected by the adsorption of N2. The correlation of the experimental data with the model allowed the amount of hydrogen stored in each of the sites to be quantified and confirmed that hydrogen storage mechanism begins with the filling of the smallest pores. Additionally, from the model it was possible to interpret the dependence of the amount of hydrogen stored with textural parameters such as the micropore volumes. The model also allowed the storage capacity of the fibers to be predicted for pressures higher than those obtained experimentally. [Copyright &y& Elsevier]

Abstract: Highly ordered 2D-hexagonal mesoporous titanium silicate Ti-SBA-15 materials (space group p6mm) have been synthesized hydrothermally in acidic medium employing amphiphilic tri-block copolymer, Pluronic F127 as structure directing agent. Samples are characterized by powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, FT IR spectroscopy, UV–visible diffuse reflectance measurements, N2 adsorption/desorption and TG-DTA analysis. XRD and TEM results suggested the presence of highly ordered mesophase with hexagonal pore arrangements. BET surface area for Ti-SBA-15 (924m2 g−1) is considerably higher than the pure silica SBA-15 (611m2 g−1) prepared following the same synthetic route. UV–visible and FT-IR studies suggested the incorporation of mostly tetrahedral titanium (IV) species, along with some six-coordinated sites in the silicate network. This material shows very good H2 adsorption capacity at higher pressure and excellent catalytic activity in the photocatalytic degradation of ecologically abundant dye methylene blue. [Copyright &y& Elsevier]

Abstract: In this work a series of carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The materials used were different types of commercial carbons: carbon fibers, carbon cloths, nanotubes, superactivated carbons, and synthetic carbons (carbon nanospheres and carbon xerogels). Their textural properties (i.e., surface area, pore size distribution, etc.) were related to their hydrogen adsorption capacities. These H2 storage capacities were evaluated by various methods (i.e., volumetric and gravimetric) at different temperatures and pressures. The differences between both methods at various operating conditions were evaluated and related to the textural properties of the carbon-based adsorbents. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. Furthermore, hydrogen storage capacity seems to be proportional to surface area, especially at 77K. The micropore size distribution and the presence of narrow micropores also notably influence the H2 storage capacity of carbons. In contrast, morphological or structural characteristics have no influence on gravimetric storage capacity. If synthetic materials are used, the textural properties of carbon materials can be tailored for hydrogen storage. However, a larger pore volume would be needed in order to increase storage capacity. It seems very difficult approach to attain the DOE and EU targets only by physical adsorption on carbon materials. Chemical modification of carbons would seem to be a promising alternative approach in order to increase the capacities. [Copyright &y& Elsevier]

Abstract: In this work we studied the adsorption of H2 at 77K and 0.0–0.12MPa onto carbon fibers activated with supercritical CO2 (ACFs) and with different burn-offs (10–53%). The highest amount of H2 stored was 2.45wt% in an ACF with a burn-off of 51% at 0.12MPa. The measured isotherms were analyzed using an equilibrium model derived by analogy with a multiple-site Langmuir-type adsorption model. The different equilibria correspond to adsorption in pores of different sizes. The experimental results fitted a model with two different adsorption sites satisfactorily, allowing such sites to be related to the microporous structure of the ACFs. Thus, a high-energy adsorbent–adsorbate interaction site, associated with very small micropores, accessible only to very small molecules such as H2, and another lower-energy site associated with larger pores can be proposed. The model also predicts the adsorption behavior under equilibrium conditions at higher pressures, allowing the maximum adsorption capacity of the ACFs to be determined. The results show that the ACFs adsorb most of the H2 molecules at low equilibrium pressures, and that they become almost saturated at pressures around 1.0MPa. The maximum H2 storage capacity in these ACFs lies between 1.50 and 3.15wt%. [Copyright &y& Elsevier]

[Display omitted] • This work presents the first report on the hydrogen storage properties by utilizing lithium fluoride (LiF) monolayer. • LiF in zinc blende and monolayer hexagonal phases are found to be stable with indirect bandgaps. • Adsorption energies of hydrogen molecules are found in the range of −0.15 to 0.64 eV/H 2 on the LiF surface. • The maximum hydrogen (H 2) storage capacity is observed to be ∼13.45 % on the monolayer LiF surface. Hydrogen (H 2) energy is the most prominent reliever source of energy due to its supreme energy density compared to all usual fuels by weight. The investigation of novel materials with the optimal capacity for the storage of hydrogen (H 2) gas is a most challenging task. To accomplish our expectation, we have considered the zinc blende (1 1 1) plane of LiF structure in the present work and investigated the spin-polarized density of states and storage capacity by first principal calculation within the framework of density functional theory (DFT). We obtained and compared the structural and electronic properties of LiF compounds in both zinc-blende as bulk and its (1 1 1) plane in the hexagonal monolayer phase symmetry. Afterward, we investigated the hydrogenation effect on the nanosheet of the hexagonal LiF (1 1 1) plane. In the hydrogenation process, we have considered the 2 to 18 H 2 molecules on the hexagonal LiF (1 1 1) plane and the respective adsorption energies found to be in the range from −0.15 eV/H 2 to −0.64 eV/H 2. In this process, we have achieved the maximum hydrogen (H 2) storage capacity of ∼13.45 % on the LiF surface. Our outcomes strongly reflect the promising application of hexagonal LiF (1 1 1) plane in H 2 storage. [ABSTRACT FROM AUTHOR]

Poly(ethylene) terephthalate (PET), has become one of the major post-consumer plastic waste. In this work special attention was paid to minimising PET residues and to obtain a high value carbon material. Pyrolysis and subsequent activation of PET from post-consumer soft-drink bottles was performed. Activation was carried out at 925 °C under CO2 atmosphere to different burn-off degrees. Textural characterisation of the samples was carried out by performing N2 adsorption isotherms at -196 °C. The obtained carbons materials were mainly microporous, presenting low meso and macroporosity, and apparent BET surface areas of upto 2500 m2 g-1. The capacity of these materials for phenol adsorption and PAHs removal from aqueous solutions was measured and compared with that attained with commercial active carbons. Preliminary tests also showed high hydrogen uptake values, as good as the results obtained with high-tech carbon materials. [Copyright &y& Elsevier]

The simulation studies of hydrogen adsorption in three types of ideal Y-junction carbon nanotubes (Y-CNTs) with open ends were carried out using molecular dynamics simulations and molecular mechanics calculations. The results show that the physisorption of hydrogen in Y-CNTs is very limited and far from the target set by DOE for hydrogen storage and transportation, implying that it is unlikely to achieve high hydrogen storage in open-ended Y-CNTs via physisorption scheme. [Copyright &y& Elsevier]

Three Machine learning (ML) models were constructed and tested to model the hydrogen adsorption of activated carbons (ACs). Although many efforts have been accomplished, the details of micro structure-efficiency of ACs still remains uncovered. Data-based modeling contains the crucial properties of ACs' structural characteristics such as micropore surface area, pore volume, and pore-size distribution are utilized as inputs for hydrogen adsorption. The proposed models demonstrated their high feasibility to predict the hydrogen uptake with the RMSEs ranged from 0.06 to 0.19. Among them, the Support vector machine (SVM) exhibited the highest accuracy for prediction of hydrogen adsorption on ACs. The sensitivity analysis also showed the importance of micropore surface area and pore widening on hydrogen uptake. Subsequently, the effects of microstructure properties on hydrogen storage were optimized, employing the SVM-based genetic algorithm (GA) technique. By using the optimized structural properties obtained from GA, the hydrogen uptake increased by 2.5 wt%. The precise tuning of textural features significantly revealed the importance of microstructural properties in bio-derived ACs for H 2 uptake. This can be a helpful guide for fabrication procedures of porous carbons for H 2 adsorption applications. • SVM showed high feasibility in predicting gas adsorption based on microstructure. • The hydrogen storage of ACs was estimated as a function of temperature and pressure. • H 2 uptake increases by 2.5%, using the optimized parameters via genetic algorithm. • Micro and mesostructures of ACs are the most effective factors on hydrogen uptake. • The model could accurately predict H 2 uptake (R2 = 0.97 and MAPE = 3.15). [ABSTRACT FROM AUTHOR]

Activated carbons (ACs) have been widely used for dye removal and for H 2 storage but often demonstrate limited performance due to their low porosity and lacking beneficial surface functional groups. Herein, we have designed a series of urea/thiourea and K 2 CO 3 modified ACs from "sucrose – a biomass-derived carbohydrate" via two-step pyrolysis/activation method. As-prepared ACs demonstrate excellent textural features (e.g., specific surface area (SSA) = 2842 m2/g; pore volume = 1.35 cm3/g) and optimal heteroatom content (N = 4.1 at%; S = 2.1 at% content). Moreover, these ACs exhibit an outstanding methylene blue (MB) adsorption capacity ~398.09 mg/g at an initial concentration of 200 mg/L surpassing most biomass derived ACs reported previously. The π–π stacking, hydrogen bonding and acid-base interaction is the key mechanism behind excellent MB adsorption from aqueous solution. Moreover, an efficient H 2 adsorption capacity up to 2.21 wt% was observed at 77 K/1 bar with predominant role governed by narrow micropores (~0.68 nm). Therefore, the current study proposes a straightforward synthetic protocol for developing a multifunctional material (ACs) which not only act for wastewater remediation but also as energy sorbents. Moreover, our study clearly demonstrates the role of porosity and heteroatom content on both MB adsorption and H 2 storage performance. [Display omitted] • Two step synthesis of sucrose-derived heteroatom (N, S)-doped microporous carbons. • Activated Carbons exhibit high specific surface area (~2842 m2/g). • Porous carbons demonstrate Methylene blue adsorption up to 398.09 mg/L. • Narrow micropores (<0.68 nm) leads to excellent H 2 uptake. [ABSTRACT FROM AUTHOR]

Several biochars and activated carbons are prepared from cellulose fraction of some agricultural wastes (linen, cotton and wheat). The obtained carbons are characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), 13C nuclear magnetic resonance (13C NMR), CO 2 adsorption-desorption at 0 °C, Raman spectroscopy and X-ray photoelectron spectroscopy. The biochars are synthesized at different pyrolysis temperatures while activated carbons are obtained from a biochar (pyrolysis at 500 °C) using KOH as activation agent in different amounts. The adsorption values in the biochars increase proportionally to the temperature levels (about 2.5 mmol CO 2 g−1 at 25 °C and 760 mm of Hg). The highest the temperature of pyrolytic treatment, the highest the adsorption values. These values remain stable for several cycles in the case of samples synthesized at the highest temperature. The chemical activation of the biochar with KOH improves its microporosity as well as its CO 2 adsorption capacity (3.6 mmol CO 2 g−1 at 25 °C and 760 mm of Hg). Moreover, these biochars and activated carbons are evaluated for the adsorption of N 2 or H 2. The N 2 and H 2 adsorption capacity is much lower than that of CO 2. Consequently, these biochars and activated carbons are highly selective for the CO 2 capture. They have also shown a high H 2 adsorption at −196 °C which makes them having a high potential in H 2 storage at low temperature levels. [Display omitted] • Cellulose fraction from agricultural waste have been used to synthesize biochars and activated carbons. • Amorphous graphite has been formed from pyrolytic treatments of the cellulose fraction. • Biochars display an appropriate pore diameter to achieve high CO 2 adsorption capacity. • Biochar and activated carbon are highly selective to retain CO 2 in CO 2 /N 2 and CO 2 /H 2 binary systems. • These carbons also display great potential for low-temperature H 2 storage. [ABSTRACT FROM AUTHOR]

It is widely known that decorating metal atoms on defective carbon nanomaterials is a useful approach to enhance the hydrogen storage capacity of these systems. Herein, density functional theory calculations are used to determine the H 2 storage capacity of Ca functionalized nitrogen incorporated defective C 60 fullerenes (Ca 6 C 24 N 24 ). The strong binding, uniform distribution, and significant positive charges of the Ca atoms make this system effective material for storage of H 2 . Ca 6 C 24 N 24 may adsorb a maximum of 6 hydrogen molecules per Ca atom, yielding a total gravimetric density of 7.7 wt %., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)