Complete Dehydrogenation Research Articles

A Single‐Atom Interface Engineering Strategy to Promote Hydrogen Sorption Performances of Magnesium Hydride

AbstractMagnesium hydride (MgH2) is regarded as a promising hydrogen storage material owing to its high gravimetric and volumetric capacity and low cost. However, its large‐scale application is hampered by high stability leading to elevated temperature and slow kinetics for ab/desorption. To address these problems, herein, a composite having MgH2 nanoconfined in a 3D nickel single atoms doped porous carbon (MgH2@3D Ni SA‐pC) is successfully prepared. Benefitting from the nondestructive synthetic method, strong coupling between MgH2 and 3D Ni SA‐pC is achieved, and the composite exhibits superior hydrogen sorption performances as compared to blank MgH2. An onset desorption temperature down to 170 °C and the complete dehydrogenation at 250 °C within 60 min are observed. In particular, thermodynamics of MgH2 is improved (ΔHab = 67.9 kJ mol−1 H2) and the heterogenous interfaces are stable during cycling without the formation of an intermetallic Mg2Ni catalytic phase. Experimental characterizations and theoretical calculations show that the robust interfaces induce charge transfer from Mg/MgH2 to Ni SA‐pC, which contributes to the weakened Mg─H bonds and thereby improves kinetic and even thermodynamics. Such an interface engineering strategy using single‐atom Ni catalyst to simultaneously nano‐confine and catalyze MgH2 paves a way to the design of high‐performance hydrogen storage materials.

Modulating electronic density of active metal site via MXene intercalated by alkali ions for superior hydrogen production

As the core of a catalyst, the active site plays a crucial role in determining the activity and selectivity in hydrogen production reactions. Herein, the size and surface electron density of bimetallic alloy nanoparticles (NPs) were engineered by (alkali ions)-intercalated-Ti3C2Tx MXene, in which alkali ions were removed by water after the intercalation of Ti3C2Tx. The intercalation of alkali ions can effectively increase the interlayer spacing of Ti3C2Tx, enhance the surface accessibility, and improve the interaction between active metal species and Ti3C2Tx, resulting in monodisperse, ultrafine, and surface electron-rich active metal NPs. Resultantly, the obtained NiPt/(Li+)-Ti3C2Tx exhibits an exceptional catalytic performance with a turnover frequency (TOF) value of 3200 h−1 toward complete dehydrogenation of N2H4·H2O at 323 K, which is about 43 and 4-times higher than that of pristine NiPt NPs (75 h−1) and them on Ti3C2Tx without alkali ions intercalation (787 h−1), respectively, and surpassing all the reported catalysts for this dehydrogenation reaction. Additionally, this catalyst also shows an ultrahigh catalytic performance (7317 h−1) for complete dehydrogenation of N2H4BH3 under the same reaction conditions. This work for the first time found that the more electrons on the surface of the active center, the better the activity for hydrazine decomposition, providing inspiration for regulating catalytic active sites and designing efficient heterogeneous catalysts to achieve nitrogen-based hydride activation.

Preparation and excellent mechanical properties of nanocrystalline GW103K Mg alloy by HDDR technology

Grain size of GW103K Mg alloy powder were markedly refined to about 45 nm from 20 μm by an optimized hydrogenation-disproportionation-desorption-recombination (HDDR) process. By changing temperature, hydrogen pressure and time, the optimum hydrogenation conditions are explored by orthogonal design. Then the complete dehydrogenation process was determined by using single factor control variables. Furtherly, the HDDRed powder was spark plasma sintering (SPS) sintered and hot extruded to prepare GW103K alloy bulk. XRD, OM, scanning electron microscopy (SEM), and transmission electron microscope (TEM) were used to analyze the phase transformation and microstructure evolution, based on which the grain refining mechanism during the HDDR were discussed. The optimum HDDR parameters for preparing nanocrystalline Mg alloy powders are hydriding at 550 °C under 5 MPa hydrogen pressure for 24 h and dehydriding at 550 °C for 8 h in vacuum. The nanocrystalline GW103 alloy presents a notable dimensional stability and the grain size of the alloy bulk is 43 nm after SPS and hot extrusion. As a result, the nanocrystalline GW103K specimens exhibit excellent mechanical properties compared to the coarse-grained counterparts. Especially, the nanocrystalline GW103K alloy has a tensile elongation of 21.1% which is much more than those of the as-cast and as-extrusion alloys.

Production of CO-free H2 through aqueous formic acid dehydrogenation over the α-Mo2C/NC catalyst

Formic acid (FA) is considered a convenient hydrogen carrier with a high hydrogen-storage capacity. Although the non-noble-metal-based catalysts for FA dehydrogenation have made significant progress in recent years, they still face some challenges, such as complex preparation methods and inefficient FA dehydrogenation. Herein, a N-doped carbon (NC) supported α-Mo2C catalyst was successfully synthesized by the one-step pyrolysis strategy and performed excellent catalytic activity for neat FA decomposition while with a low dehydrogenation selectivity. The addition of water significantly improved the FA dehydrogenation selectivity and the α-Mo2C/NC catalyst showed a gas production rate of 224.19 mL/gcat./h and an almost complete dehydrogenation selectivity in the aqueous FA (40 vol.%) at 98 °C. Moreover, no significant deactivation was found during the 60 h stability test under different FA concentrations via this catalyst. The use of NC supported α-Mo2C obtained by one-step pyrolysis as an effective non-noble-metal catalyst and H2O introduction to promote selectivity could provide a novel low-cost­ H2 production strategy from FA.

Iridium complex immobilized on covalent triazine framework derived from biomass as a recyclable catalyst for the dehydrogenation of formic acid

The first example of covalent triazine frameworks derived from biomass was designed and synthesized. Furthermore, an iridium complex Cp*Ir@CTF-biomass was prepared by the coordinative immobilization of [Cp*IrCl2]2 on the synthesized covalent triazine framework. In the presence of Cp*Ir@CTF-biomass (0.03 mol % Ir), the reaction was carried out for 24 min at 80 °C and an almost complete dehydrogenation of formic acid with an initial TOF of 7627 h−1 was observed. Further experiments confirmed that heterogeneous catalyst Cp*Ir@CTF-biomass and its homogeneous analog [Cp*Ir(pyridine)Cl2] have approximate catalytic activity. Moreover, catalytic activity of Cp*Ir@CTF-biomass is well maintained during six runs.©2024 Elsevier Inc. All rights reserved.

Hydrogenation and dehydrogenation behaviors of tantalum under different conditions

The hydrogenation behaviors of tantalum metal and the dehydrogenation behaviors of tantalum hydride powder have been studied in this paper. The results of hydrogenation show that the tantalum ingot is easy to form a barrier layer on its surface during hydrogenation, which can be broken by increasing the pressure of hydrogen and using hydrogenation-dehydrogenation-hydrogenation (H-De-H) process at the same time. Finally, tantalum hydride powder with hydrogen content of 0.427 wt % was obtained. The dehydrogenation results show that TaH0.1 and Ta phases begin to appear at 500 °C under vacuum condition, and complete dehydrogenation can be achieved at 600 °C for 1 h. Under the condition of hydrogen atmosphere, the presence of H2 has an inhibitory effect on the dehydrogenation reaction, and it is most obvious when the temperature is 700 °C.

Modification research on the hydrogen storage performance of bimetallic oxide Zn2Ti3O8 on MgH2

In this study, flake Zn2Ti3O8, TiO2 and rod ZnO catalysts were successfully synthesized by hydrothermal and calcination methods, and the catalytic performance of the three catalysts for MgH2 was compared. Notably, Zn2Ti3O8 had a significant synergistic enhancement effect on the dehydrogenation temperature and desorption kinetics of MgH2. The experimental results showed that the dehydrogenation of MgH2 + 12 wt% Zn2Ti3O8 composite started at about 195 °C, which was about 150 °C lower than that of pure MgH2. Moreover, at 325 °C, MgH2 released only 3.06 wt% H2 in 20 min, whereas the MgH2 + 12 wt% Zn2Ti3O8 composite released the same amount of hydrogen at 250 °C in 3 min. After complete dehydrogenation, the MgH2 + 12 wt% Zn2Ti3O8 composite initiated hydrogen uptake at 40 °C and absorbed about 6.05 wt% of H2 in 60 min at 200 °C. The hydrogen uptake activation energy and dehydrogenation activation energy of the composites were reduced by 24.56 kJ/mol and 44.67 kJ/mol, respectively, when compared to the pure MgH2. Cycling experiments showed that after 20 cycles, the MgH2 + 12 wt% Zn2Ti3O8 composite maintained good cycling stability and the hydrogen storage capacity was still more than 96 %. Therefore, the composite exhibits excellent catalytic and hydrogen storage properties, and has potential applications in improving the hydrogen release rate and reducing the activation energy.

Pyridine N-induced intra-pore and interfacial dual-confined Pd0-Pdδ+ synergistic catalysis for ultra-stable dehydrogenation of dodecahydro-N-propylcarbazole

We developed nano Pd catalysts, encapsulated within carbon-nitrogen layers at both intra-pore and interfacial levels on SiO2, via in-situ thermolysis of metal-organic coordination compounds. The catalysts dehydrogenation efficacy is greatly influenced by thermolysis temperature and ligand-to-metal ratio. The Pd-C-N2/SiO2-600 catalyst notably achieved complete dehydrogenation of 12 H-NPCZ within 240 minutes, demonstrating exceptional stability over 10 cycles without significant degradation, highlighting its viability for commercial use. Characterizations revealed that the C-N layer integration improves Pd nanoparticle dispersion and reduces strong acid site formation on catalyst surface. This synergy between the C-N layer and Pd nanoparticles promotes the formation and stabilization of Pdδ+ species, optimizing them as adsorption sites for dehydrogenation with appropriate acid strength. Moreover, this interaction adjusts the electronic states of Pd0 active sites, optimizing adsorption dynamics for intermediates. This cooperative action between Pd0 and Pdδ+ significantly boosts the desorption rate of dehydrogenation products, substantially improving the catalysis performance.

Constructing VO/V2O3 interface to enhance hydrogen storage performance of MgH2

In this study, MXene-derived V2O5@C nanosheets are successfully synthesized as an efficient catalyst for enhancing the hydrogen storage performance of MgH2. MgH2-V2O5@C exhibits exceptional kinetic and cyclic performance. It desorbs 3.59 wt.% H2 within 120 min at 200 °C and adsorbs 3.9 wt.% H2 within 2.7 h at room temperature after complete dehydrogenation. Moreover, even after 251 cycles at 300 °C, it maintains a hydrogen capacity of 5.45 wt.%, which accounted for 90.5% of the maximum hydrogen capacity. In addition, an activation mechanism for Mg hydrogenation driven by phase transition from V2O3 to VO is firstly clarified through experimental and theoretical analysis. DFT calculations show that the hydrogenation energy barrier of VO (1.01 eV) is significantly lower than that of V2O3 (1.82 eV). The phase transition from V2O3 to VO forms abundant strong hydrogenation sites, effectively reducing the hydrogenation energy barrier of magnesium and activating the hydrogenation ability of deactivated magnesium. Therefore, benefited from the activation mechanism driven by the VO/V2O3 interface, the hydrogen storage capacity of magnesium increased from 4.28 wt.% at 46th cycle to 5.45 wt.% at 251st cycle.

Synergistic effect of Pd single atoms and clusters on the de/re-hydrogenation performance of MgH2

Hydrogen storage plays a pivotal role in the hydrogen industry, yet its current status presents a bottleneck. Diverse strategies have emerged in recent years to address this challenge. MgH2 has stood out as a promising solid-state hydrogen storage material due to its impressive gravimetric and volumetric hydrogen density, but its practical application is hampered by elevated thermal stability and sluggish kinetics. In this study, we introduce a solution by synthesizing Pd metallene through a one-pot solvothermal method, revealing a distinctive highly curved lamellar structure with a thickness of around 1.6 nm. Incorporating this Pd metallene into MgH2 results in a composite system wherein the starting dehydrogenation temperature is significantly lowered to 439 K and complete dehydrogenation occurs at 583 K, releasing 6.14 wt.% hydrogen. The activation energy of dehydrogenation for MgH2 was reduced from 170.4 kJ mol–1 to 79.85 kJ mol–1 after Pd metallene decoration. The enthalpy of dehydrogenation of the MgH2–10 wt.% Pd sample was calculated to be 73 kJ mol–1 H2–1 and decreased by 4.4 kJ mol–1 H2–1 from that of dehydrogenation of pure MgH2 (77.4 kJ mol–1 H2–1). Theoretical calculations show that the average formation energy and average adsorption energy of hydrogen vacancies can be significantly reduced in the presence of both Pd clusters and Pd single atoms on the surface of MgH2/Mg, respectively. It suggests that the synergistic effect of in situ formed Pd single atoms and clusters significantly improves the hydrogenation and dehydrogenation kinetics. The identified active sites in this study hold potential as references for forthcoming multi-sized active site catalysts, underscoring a significant advancement toward resolving hydrogen storage limitations.

Dehydrogenation of diborane on small Nbn+ clusters.

The reactivity of Nbn+ (1 ≤ n ≤ 21) clusters with B2H6 is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nbn+ clusters were generated by a magnetron sputtering source and reacted with the B2H6 gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbnB1-4+ and NbnB1-4H1,2,4+ were detected, indicative of the removal of H2 and likely BHx moieties. Interestingly, these NbnB1-4+ and NbnB1-4H1,2,4+ products are limited to 3 ≤ n ≤ 6, suggesting that the small Nbn+ clusters are relatively more reactive than the larger Nbn>6+ clusters under the same conditions. By varying the B2H6 gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb1+ cations accounts for the weakened dehydrogenation efficiency. Nb2+ forms partial dehydrogenation products at a faster rate. In contrast, the Nbn>6+ clusters are subject to more flexible vibrational relaxation which disperse the energy gain of B2H6-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H2 release.

Synthesis of amorphic and hexagonal boron nitride via high temperature treatment of NH3BH3 and Li(BH3NH2BH2NH2BH3).

Thermal decomposition of NH3BH3 and Li(BH3NH2BH2NH2BH3) was investigated at temperatures up to 1000 °C under various conditions with an inert atmosphere. It was found that complete dehydrogenation of ammonia borane towards amorphous boron nitride (a-BN) occurs at 850 °C when using monel reactors or at 1000 °C with the hot isostatic pressing method (HIP), which is significantly lower than was earlier reported. Li(BH3NH2BH2NH2BH3) was found to decompose towards hexagonal boron nitride (h-BN) at 1000 °C with the HIP method but at 850 °C in monel reactors towards a mixture of a-BN and h-BN. The findings are confirmed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM).

Anchoring PdAg alloys on self-crosslinked carbon dots as efficient catalysts for formic acid dehydrogenation under ambient conditions

The optimized Pd0.9Ag0.1/CDs catalyst can catalyze complete dehydrogenation of FA in 9.5 min with a TOF value of 617 h−1 at 298 K. This work provides a simple approach for the fabrication of CDs supported highly distributed PdAg alloy catalysts.

Hydrogen production from complete dehydrogenation of hydrazine borane on carbon-doped TiO2-supported NiCr catalysts

C-doped mesoporous TiO2-supported Cr(OH)3 modified Ni nanoparticles (Ni–Cr/CTO) with different morphologies were synthesized by a simple wet-chemical method and used as efficient catalysts for hydrogen production from hydrazine borane.

Selective electrochemical acceptorless dehydrogenation reactions of tetrahydroisoquinoline derivatives.

Selective dehydrogenation reactions of tetrahydroisoquinoline derivatives through electrochemical oxidation are disclosed. In the presence of nitric acid, the selective partial dehydrogenation of tetrahydroisoquinolines to form 3,4-dihydroisoquinolines was achieved via anodic oxidation. The results of CV (Cyclic Voltammograms) experiments and DFT calculations showed the 3,4-dihydroisoquinolines protonated by an external Brønsted acid to be less prone than their unprotonated counterparts to oxidation under electrochemical conditions, thus avoiding their further dehydrogenation. Moreover, a TEMPO-mediated electrochemical oxidation enabled a complete dehydrogenation to yield fully aromatized isoquinolines. Thus, tunable processes involving electrochemical dehydrogenation of tetrahydroisoquinolines could be used to selectively produce various 3,4-dihydroisoquinolines and isoquinoline derivatives.

Fragmentation of Multiply Charged C10H8 Isomers Produced in keV Range Proton Collision

The dissociation of multiply charged C10H8 isomers produced in fast proton collisions (velocities between 1.41 and 2.4 a.u.) is discussed in terms of their fundamental molecular dynamics, in particular the processes that produce different carbon clusters in such a collision. This aspect is assessed with the help of a multi-hit analysis of daughter ions detected in coincidence with the elimination of H+ and CHn+ (n = 0 to 3). The elimination of H+/C+ is found to be significantly different from CH3+ loss. The loss of CH3+ proceeds through a cascade of momentum-correlated dissociations with the formation of heavy ions such as C9H5+, C9H52+ and C7H3+. The structure of such large fragment ions is predicted with the help of their calculated ground state electronic energies and the multi-hit time-of-flight (ToF) correlation between the second and third hit fragments if detected. Furthermore, we report experimentally the super-dehydrogenation of naphthalene and azulene targets, with evidence of complete dehydrogenation in a single collision.

Cyclohexane Oxidative Dehydrogenation on Graphene-Oxide-Supported Cobalt Ferrite Nanohybrids: Effect of Dynamic Nature of Active Sites on Reaction Selectivity.

In this work, we investigated cyclohexane oxidative dehydrogenation (ODH) catalyzed by cobalt ferrite nanoparticles supported on reduced graphene oxide (RGO). We aim to identify the active sites that are specifically responsible for full and partial dehydrogenation using advanced spectroscopic techniques such as X-ray photoelectron emission microscopy (XPEEM) and X-ray photoelectron spectroscopy (XPS) along with kinetic analysis. Spectroscopically, we propose that Fe3+/Td sites could exclusively produce benzene through full cyclohexane dehydrogenation, while kinetic analysis shows that oxygen-derived species (O*) are responsible for partial dehydrogenation to form cyclohexene in a single catalytic sojourn. We unravel the dynamic cooperativity between octahedral and tetrahedral sites and the unique role of the support in masking undesired active (Fe3+/Td) sites. This phenomenon was strategically used to control the abundance of these species on the catalyst surface by varying the particle size and the wt % content of the nanoparticles on the RGO support in order to control the reaction selectivity without compromising reaction rates which are otherwise extremely challenging due to the much favorable thermodynamics for complete dehydrogenation and complete combustion under oxidative conditions.

Carbon-doped mesoporous TiO2-immobilized Ni nanoparticles: Oxygen defect engineering enhances hydrogen production

Constructing efficient, durable, and economical catalysts to promote hydrogen production from hydrous hydrazine (N2H4·H2O) is crucial, but still a great challenge. Herein, noble-metal-free Cr(OH)3-modified Ni nanoparticles (NPs) (2.7 nm) supported on defect-rich carbon-doped mesoporous TiO2 nanosheets (C-TiO2) were prepared for the first time via a simple and green wet-chemistry approach, in which the amount of oxygen defect in C-TiO2 can be easily regulated by adjusting the amount of carbon doping. Significantly, the defect rich Ni-Cr(OH)3/C-TiO2 catalyst presented 100% H2 selectivity, ultrahigh catalytic activity, and remarkable durability for N2H4·H2O dehydrogenation, with a turnover frequency (TOF) value of 266 h−1 at 323 K, more than 6-fold improvement than that of the Ni-Cr(OH)3/TiO2 (41 h−1), which is among the highest values reported so far for noble-metal-free catalysts. The superior catalytic efficiency and durability are mainly owing to the small-sized and electron-rich of Ni NPs induced by the oxygen defects in C-TiO2, where the more oxygen defects, the better the catalytic activity. Furthermore, the catalyst also showed outstanding catalytic efficiency (TOF = 577 h−1) and robust durability for complete dehydrogenation of hydrazine borane (N2H4BH3) at 323 K. This work provides inspiration for the construction of defect engineering and new insights for the development of low-cost and efficient heterogeneous hydrogen production catalysts.

Critical dehydrogenation steps of perhydro-[formula omitted]-ethylcarbazole on Ru(0001) surface

Understanding of the critical atomistic steps during the dehydrogenation process of liquid organic hydrogen carriers (LOHCs) is important to the design of cost-efficient, high-performance LOHC catalysts. Based on the density functional theory (DFT) we studied the thermodynamics and kinetics of the complete dehydrogenation path of perhydro-N-ethylcarbazole (12H-NEC) on Ru(0001) surface, involving the adsorption of 12H-NEC, the discharge of H ions onto Ru surface, and the desorption of H2 and hydrogen-lean NEC. It was found that the bonding of nH-NEC is significantly strengthened for n≤4 because of the flat aromatic ring. Although the whole dehydrogenation process is endothermic, the release of H from nH-NEC, with H adsorbed onto the Ru surface, was found to be exothermic. The desorption of flat, hydrogen-lean NEC, which costs ∼255 kJ/mol, was identified as the most energy demanding step. In addition, the effect of surface morphology on adsorption was studied based on an amorphous surface model. Overall, the results imply more efficient dehydrogenation could be achieved from relatively weak bonding of NEC to catalysts, either through engineering catalyst surface (such as surface defects or smaller catalyst particles) or different catalyst materials. Our calculations also revealed possible dealkylation at elevated temperatures.

What Determines If a Ligand Undergoes Coordination or Catalytic Activation on a Metal Cluster?

We report a joint experimental and theoretical study on the reactivity of Agn+ clusters with H2S, D2O, and NH3. Complete dehydrogenation products are observed for Agn+ reacting with H2S, but no dehydrogenation products are found for D2O or NH3 under the same reaction condition. Theoretical calculations elucidate why Agn+ clusters show different reactivities with these inorganic hydrides. NH3 shows strong coordination with Agn+, but the dehydrogenation reactions are unfavorable; in contrast, the fragile H-S bonds and stable AgnS+ products facilitate the hydrogen evolution of H2S on Agn+. We fully analyzed the metal-ligand interactions of Agn+ clusters with three molecules and illustrated the reaction dynamics and charge-transfer interactions and altered the superatomic states during the formation of cluster sulfides. We expect this study to benefit the design of stable environmentally friendly desulfurization catalysts and also the understanding of the mechanism on ligand-protected metal clusters in wet chemistry.