Dehydrogenation Properties Research Articles

Hydrogen storage properties and reaction mechanism of the Mg-Li-Na-Al ternary hydride system

This research uses the ball milling technique to study the preparation of the MgH2-LiAlH4-NaAlH4 with a molar ratio of 4:1:1 ternary-hydride system. The hydrogen storage behavior and reaction mechanisms have been carefully explored. The result demonstrates a reduction in the onset decomposition temperature of the 4MgH2-LiAlH4-NaAlH4 ternary composite compared to the as-milled MgH2, LiAlH4, and NaAlH4 components. Four substantial dehydrogenation processes, corresponding to the decomposition of LiAlH4, NaAlH4, and MgH2 were detected in a system with a total hydrogen capacity of 8.4 wt%. The onset decomposition temperature of LiAlH4 in this system is around 110 °C, while NaAlH4-relevant decomposition began releasing hydrogen at 153 °C, approximately 52 °C lower than the as-milled NaAlH4. Meanwhile, the destabilized system modifies the reaction route of MgH2, where MgH2-relevant decomposition begins around 270 °C, 82 °C lower than the as-milled MgH2. The apparent activation energy, Ea, for the decomposition of MgH2 in the composite was lowered to 124 kJ/mol based on the Kissinger analysis. It is believed that the enhancement of the dehydrogenation properties was attributed to the formation of intermediate compounds, including Li-Mg, Mg-Al and Li-Al alloys, upon dehydrogenation, which improved the thermodynamics properties by altering the de/rehydrogenation pathway.

Zn2TiO4 synthesized via solid-state method and its effects on dehydrogenation properties of LiAlH4

Lithium alanate (LiAlH4) has high gravimetric capacity but its practical application is still severely constrained by poor reversibility and sluggish kinetics. In this study, the dehydrogenation behaviour of LiAlH4 was modified with the inclusion of Zn2TiO4. The initial temperature for the dehydrogenation of LiAlH4 was downshifted to 111 °C (first dehydrogenation) and 151 °C (second dehydrogenation) with the inclusion of 10 wt% Zn2TiO4. The as-milled LiAlH4 released only 0.1 wt% H2 while the LiAlH4–10 wt% Zn2TiO4 sample released 3.6 wt% H2 in 60 min at 90 °C which is 36 times faster than undoped LiAlH4. The dehydrogenation activation energies for the first two dehydrogenation process was also reduced by 24.1 and 21.0% than as-milled LiAlH4. The X-ray diffraction analysis revealed that the Zn2TiO4 reacts with LiAlH4 and the formed Al–Ti and Ti–Zn during the dehydrogenation leading to the superior dehydrogenation behaviour of LiAlH4.

Improved thermolytic dehydrogenation of LiBH4 nanoconfined in few-layer graphene with different functionalities

In this work, lithium borohydride (LiBH4) was loaded into plasma-activated nanoporous few-layer graphene (FLG) powders with different specific surface areas (∼400–800 m2/g) and functional groups (carboxyl and amine) to investigate the effect of LiBH4@FLG nanoconfinement on the dehydrogenation properties. It was observed that the dehydrogenation temperature dropped significantly from 463 °C for pure LiBH4 to ∼120 °C for all LiBH4@FLG nanocomposites. This was attributed to the nano-sized pores of the FLG materials that can constrain LiBH4 by nanoconfinement and thus decrease the dehydrogenation temperature. The highest dehydrogenation yield of 83% occurred in LiBH4@FLG with 400 m2/g surface area and amine groups, possibly due to Lewis basic amino groups and better graphitic structure. Moreover, it was found that both the surface area and the graphitic defects on the FLG host materials have an influence on the dehydrogenation kinetics. LiBH4@FLG with 800 m2/g surface area and carboxyl groups possesses the lowest activation energy due to its high surface area and high concentration of graphitic defects.

The properties of ethylamine dehydrogenation and electrolysis using platinum catalyst for efficient, ambient hydrogen production

Hydrogen serves as an important, clean energy carrier, which, however, has a challenge for its storage. Herein, we report the properties of ethylamine dehydrogenation (EDH) to acetonitrile under half-cell conditions and ethylamine electrolysis under full-cell conditions for fast, energy-efficient, ambient hydrogen release, which would couple with spontaneous acetonitrile hydrogenation to ethylamine for hydrogen uptake to realize hydrogen storage cycles under mild conditions. The influences of different reaction parameters on the EDH and ethylamine electrolysis properties are examined. The catalyst deactivation and regeneration mechanisms are investigated with aid of in situ ATR-FTIR characterizations. As fast as 309 μmol/h H2 production rate with 97% faradaic efficiency (FE) from cathode and acetonitrile production with 100% FE from anode are achieved with a low 0.6 V cell voltage, demonstrating a great potential of this new electrochemical approach for hydrogen storage application.

Synthesis of Zn2TiO4 via solid-state method as a promising additive for dehydrogenation properties of NaAlH4

Sodium alanate (NaAlH4) has a high capacity for hydrogen, making it one of the most promising materials for storing hydrogen, but its slow dehydrogenation kinetics make it less practical. In this study, to speed up NaAlH4's dehydrogenation rate and improve its dehydrogenation properties, Zn2TiO4 synthesised through the method of solid-state was milled with NaAlH4. Zn2TiO4 additive remarkably reduces the initial temperature for the NaAlH4 to release hydrogen and fastens the dehydrogenation rate of NaAlH4. After adding different weight percentages of Zn2TiO4, the initial temperature for the NaAlH4 to release hydrogen was reduced to approximately 150 °C-165 °C (first dehydrogenation stage) and 190 °C-224 °C (second dehydrogenation stage), which is lower by 40 °C-55 °C than as-milled NaAlH4. The NaAlH4–Zn2TiO4 system also fastened the dehydrogenation rate by 10–15 times more than as-milled NaAlH4. The dehydrogenation activation energies of the NaAlH4 were also downshifted to 86.2 kJ/mol (first dehydrogenation stage) and 92.4 kJ/mol (second dehydrogenation stage) with the addition of Zn2TiO4. The activation energies were reduced by 26% (first dehydrogenation stage) and 24% (second dehydrogenation stage) illustrating the superior effect of Zn2TiO4. X-ray diffraction analysis discovered that TiZn2 and AlTi3 formed during the heating process are responsible for the enhanced performance of NaAlH4.

Enhanced dehydrogenation properties and mechanism analysis of MgH2 solid solution containing Fe nano-catalyst

Magnesium hydride (MgH2) has been proposed as a promising hydrogen storage material due to its high hydrogen capacity. However, its application is hindered by sluggish kinetics and high dehydrogenation temperature. Herein, we report the successful preparation of the Fe containing MgH2 solid solution by milling method, and systematically investigate the dehydrogenation properties and mechanism of the composite through experiments and first principle calculations. The results show that the serious lattice distortion and charge transfer caused by Fe atoms lead to the instability of MgH2, significantly improving the dehydrogenation kinetics of MgH2. As a result, the dehydrogenation activation energy of MgH2–Fe composite was successfully reduced by 44.5%. Notably, the initial dehydrogenation temperature of the composites is nearly 200 °C lower than that of pure MgH2, and 4.5 wt% of H2 can be released at 230 °C for 30 min. These findings provide novel insights for designing simple, low-cost catalysts for MgH2 synthesis.

Enhanced dehydrogenation properties of MgH2 by the synergetic effects of transition metal carbides and graphene

Transition metal carbides show remarkable catalysis for MgH2, and the addition of carbon materials can attach excellent cycling stability. In this paper, Mg-doped with transition metal carbides (TiC) and graphene (G) composite (denoted as Mg–TiC–G) is designed to assess the influence of TiC and graphene on the hydrogen storage performance of MgH2. The as-prepared Mg–TiC–G samples showed favorable dehydrogenation kinetics compared to the pristine Mg system. After adding TiC and graphene, the dehydrogenation activation energy of MgH2 decreases from 128.4 to 111.2 kJ mol−1. The peak desorption temperature of MgH2 doped with TiC and graphene is 326.5 °C, which is 26.3 °C lower than the pure Mg. The improved dehydrogenation performance of Mg–TiC–G composites is attributed to synergistic effects between catalysis and confinement.

Comparative study of the oxidative dehydrogenation of cyclohexane over vanadium isomorphic-substituted hydroxyapatite and hydroxyapatite-supported vanadium oxide

Vanadium oxide-modified hydroxyapatite (HAP) with varying vanadium content was synthesized by the coprecipitation and impregnation methods. The structures of the two series of catalysts were compared, and the effects of vanadium content on catalytic properties in cyclohexane oxidative dehydrogenation (ODH) are evaluated. The XRD, UV‒Vis and XPS analyses indicate that the V species in the two series of samples exist in different chemical environments. The samples prepared by the impregnation method are mainly composed of V2O5 species, while the samples prepared by the coprecipitation method show a replacement of a part of the P in the HAP lattice by VO4. The influence of the preparation method and vanadium content on the reaction rate and reaction route for the ODH of cyclohexane is investigated. VHAP shows higher cyclohexene selectivity. The effect of VOx species on the ODH reaction of cyclohexane was investigated and the reaction mechanism was proposed.

Boosting the Dehydrogenation Properties of LiAlH4 by Addition of TiSiO4

Given its significant gravimetric hydrogen capacity advantage, lithium alanate (LiAlH4) is regarded as a suitable material for solid-state hydrogen storage. Nevertheless, its outrageous decomposition temperature and slow sorption kinetics hinder its application as a solid-state hydrogen storage material. This research's objective is to investigate how the addition of titanium silicate (TiSiO4) altered the dehydrogenation behavior of LiAlH4. The LiAlH4-10 wt% TiSiO4 composite dehydrogenation temperatures were lowered to 92 °C (first-step reaction) and 128 °C (second-step reaction). According to dehydrogenation kinetic analysis, the TiSiO4-added LiAlH4 composite was able to liberate more hydrogen (about 6.0 wt%) than the undoped LiAlH4 composite (less than 1.0 wt%) at 90 °C for 2 h. After the addition of TiSiO4, the activation energies for hydrogen to liberate from LiAlH4 were lowered. Based on the Kissinger equation, the activation energies for hydrogen liberation for the two-step dehydrogenation of post-milled LiAlH4 were 103 and 115 kJ/mol, respectively. After milling LiAlH4 with 10 wt% TiSiO4, the activation energies were reduced to 68 and 77 kJ/mol, respectively. Additionally, the scanning electron microscopy images demonstrated that the LiAlH4 particles shrank and barely aggregated when 10 wt% of TiSiO4 was added. According to the X-ray diffraction results, TiSiO4 had a significant effect by lowering the decomposition temperature and increasing the rate of dehydrogenation of LiAlH4 via the new active species of AlTi and Si-containing that formed during the heating process.

Dehydrogenation and low-pressure hydrogenation properties of NaAlH4 confined in mesoporous carbon black for hydrogen storage

For hydrogen to be successfully used as an energy carrier in a new renewable energy driven economy, more efficient hydrogen storage technologies have to be found. Solid-state hydrogen storage in complex metal hydrides, such as sodium alanate (NaAlH4), is a well-researched candidate for this application. A series of NaAlH4/mesoporous carbon black composites, with high NaAlH4 content (50–90 wt%), prepared via ball milling have demonstrated significantly lower dehydrogenation temperatures with intense dehydrogenation starting at ∼373 K compared to bulk alanate's ≥ 456 K. Dehydrogenation/hydrogenation cycling experiments have demonstrated partial hydrogenation at 6 MPa H2 and 423 K. The cycling experiments combined with temperature-programmed dehydrogenation and powder X-ray diffraction have given insight into the fundamental processes driving the H2 release and uptake in the NaAlH4/carbon composites. It is established that most of the hydrogenation behavior can be attributed to the Na3AlH6 ↔ NaH transition.

Atomic strain and catalytic properties of formate oxidation and dehydrogenation in AgPd nanoalloys.

Formate is a promising hydrogen carrier for safe storage and transport and a fuel for direct formate fuel cells. However, the sluggish kinetics of catalysts for formate dehydrogenation (FDH) and oxidation reactions (FORs) significantly limit the potential applications of formate. Strain effects can effectively modulate catalytic properties by altering the electronic structure. Nevertheless, the lack of theoretical principles to quantify atomic strain and its effects on FDH and FOR catalytic activity has made experimental efforts laborious. In this work, we establish a database of atomic strain distributions for AgPd nanoalloys, reveals that the presence of compressive strain at the edges and corners and compressive strain exerted on the surface of Ag@Pd nanoalloys, particularly the one with an icosahedral shape, boost the FDH and FOR catalytic activity by shifting down the d-band center, thus weakening the adsorption of key intermediate Had. This study provides a theoretical perspective on the development and use of formate as a hydrogen carrier and fuel.

The structural, energetic and dehydrogenation properties of pure and Ti-doped Mg(0001)/MgH2(110) interfaces

Hydrogen desorption from pure and Ti-doped Mg(0001)/MgH2(110) interfaces mainly takes place by hydrogen diffusion within the interface rather than across the interface into the Mg matrix, and Ti doping can enhance the hydrogen desorption process.

Concentrated Platinum‐Gallium Nanoalloy for Hydrogen Production from the Catalytic Steam Reforming of Ethanol

AbstractThe steam reforming of ethanol (SRE) is a key process for the production of H2 and other vital hydrocarbons. The present work describes the synthesis of Platinum‐Gallium (Pt−Ga) nanoalloys supported on mesostructured cellular foam (MCF‐17) via ultrasound‐assisted impregnation method. Ga was substituted with Pt in different wt.% i. e. Pt/MCF‐17, Pt99.9Ga0.1/MCF‐17, Pt99Ga1/MCF‐17, and Pt90Ga10/MCF‐17 and was evaluated towards the SRE at a temperature range of 473K‐773 K towards hydrogen (H2), acetaldehyde (CH3CHO), diethylether (DEE), ethylene (C2H4), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and ethane (C2H6). The SRE activity and H2 formation rate with Pt90Ga10/MCF‐17 catalyst were observed to be 68.1 % and 3047.2 nmole g−1 sec−1, which is 9.8 and 4.5 times more than the Pt/MCF‐17 counterparts. Moreover, as observed from DRIFTS, NH3‐TPD and XPS studies Ga showed high interaction with Pt in the electron deficit state which resulted in the increased dehydrogenating and acidic properties that resulted in a higher yield of H2.

Improved Dehydrogenation Properties of LiAlH4 by Addition of Nanosized CoTiO3.

Despite the application of lithium aluminium hydride (LiAlH4) being hindered by its sluggish desorption kinetics and unfavourable reversibility, LiAlH4 has received special attention as a promising solid-state hydrogen storage material due to its hydrogen storage capacity (10.5 wt.%). In this work, investigated for the first time was the effect of the nanosized cobalt titanate (CoTiO3) which was synthesised via a solid-state method on the desorption behaviour of LiAlH4. Superior desorption behaviour of LiAlH4 was attained with the presence of a CoTiO3 additive. By means of the addition of 5, 10, 15 and 20 wt.% of CoTiO3, the initial desorption temperature of LiAlH4 for the first stage was reduced to around 115-120 °C and the second desorption stage was reduced to around 144-150 °C, much lower than for undoped LiAlH4. The LiAlH4-CoTiO3 sample also presents outstanding desorption kinetics behaviour, desorbing hydrogen 30-35 times faster than undoped LiAlH4. The LiAlH4-CoTiO3 sample could desorb 3.0-3.5 wt.% H2 in 30 min, while the commercial and milled LiAlH4 desorbs <0.1 wt.% H2. The apparent activation energy of the LiAlH4-CoTiO3 sample based on the Kissinger analysis was decreased to 75.2 and 91.8 kJ/mol for the first and second desorption stage, respectively, lower by 28.0 and 24.9 kJ/mol than undoped LiAlH4. The LiAlH4-CoTiO3 sample presents uniform and smaller particle size distribution compared to undoped LiAlH4, which is irregular in shape with some agglomerations. The experimental results suggest that the CoTiO3 additive promoted notable advancements in the desorption performance of LiAlH4 through the in situ-formed AlTi and amorphous Co or Co-containing active species that were generated during the desorption process.

Effects of metal-based additives on dehydrogenation process of 2NaBH4 + MgH2 system

We report a systematic investigation of the effect that selected metal-based additives have on the dehydrogenation properties of the reactive hydride composite (RHC) model system 2NaBH4+MgH2. Compared to the pristine system, the material doped with 3TiCl3·AlCl3 exhibits superior dehydrogenation kinetics. The addition of 3TiCl3·AlCl3 alters the controlling mechanism of the second dehydrogenation step making it change from a two-dimensional interface controlled process to a two-dimensional nucleation and growth controlled process. The microstructural investigation of the dehydrogenated 2NaBH4+MgH2via high-resolution transmission electron microscopy (HRTEM) shows significant differences in the MgB2 morphology formed in the doped and undoped systems. The MgB2 has a needle-like structure in the sample doped with 3TiCl3·AlCl3, which is different from the plate-like MgB2 structure in the undoped sample. Moreover, nanostructured metal-based phases, such as TiB2/AlB2 particles, acting as heterogeneous nucleation sites for MgB2 are also identified for the sample doped with 3TiCl3·AlCl3.

Two-Component Ni–Mg–O/V–Mg–O Catalytic System: I. Synthesis and Physicochemical and Catalytic Properties in Oxidative Dehydrogenation of Ethane

Two-Component Ni–Mg–O/V–Mg–O Catalytic System: I. Synthesis and Physicochemical and Catalytic Properties in Oxidative Dehydrogenation of Ethane

Comprehensive thermodynamic study of substituted indoles/perhydro indoles as potential liquid organic hydrogen carrier system

Indole has been proposed as a Liquid Organic Hydrogen Carrier (LOHC) component. Its hydrogenation leads to octahydro indole, which can subsequently release hydrogen again in an endothermic, catalytic dehydrogenation reaction. This reaction requires high temperatures due to limitations by the reaction equilibrium. It is therefore interesting to find derivatives of the carrier molecules with lower enthalpies of reaction, which corresponds to a higher equilibrium constant. In this study, methyl and phenyl substituted derivatives of indole have been examined. Vapor pressures and enthalpies of vaporisation/sublimation have been measured. The standard molar enthalpies of formation in the gas phase have been calculated using quantum chemistry. The liquid phase standard molar enthalpies of formation were derived and used for calculating reaction enthalpies. The results show that methylation lowers the enthalpy of reaction for dehydrogenation. The reduction is not very pronounced in case of single methylation (up to 3.1 kJ mol−1/H2), but can be increased by manifold methylation (e.g. 4.6 kJ mol−1/H2 in case of 2,3-dimethyl-H8-indole). Substitution of indole with a phenyl group leads to a corresponding hydrogenated counterpart, that can only be dehydrogenated partially under mild conditions. This is due to the fact that the reducing effect of the nitrogen atom on enthalpy of reaction is only effective in the indole system itself, while the cyclohexyl ring has similar dehydrogenation properties to homocyclic LOHCs.

Enhancement of the Hydrogenation and Dehydrogenation Characteristics of Mg by Adding Small Amounts of Nickel and Titanium

We compared the hydrogenation and dehydrogenation properties of Mg-based alloys to which small amounts of transition elements (Ni and Ti), halides (TaF5 and VCl3), and complex hydrides (LiBH4 and NaAlH4) were added through grinding in a hydrogen atmosphere (reactive milling). Mg-1.25Ni-1.25Ti is one of the samples compared, having a composition of 97.5 wt.% Mg + 1.25 wt.% Ni and 1.25 wt.% Ti. Even though Mg-1.25Ni-1.25Ti did not have the highest initial hydrogenation rate, it had the largest quantities of hydrogen absorbed and released for 60 min and the highest initial dehydrogenation rate. In addition, Mg-1.25Ni-1.25Ti did not show the incubation period in the dehydrogenation. We thus investigated the hydrogenation and dehydrogenation properties of Mg-1.25Ni-1.25Ti in more detail. Activated Mg-1.25Ni-1.25Ti absorbed 5.91 wt.% H in 12 bar H2 and released 5.80 wt.% H in 1.0 bar H2 at 593 K for 60 min at n = 3. For 5 wt.% hydrogen absorption by Mg-1.25Ni-1.25Ti, 18.7 min was required at 593 K in 12 bar H2 at n = 3. Although only small amounts of Ni and Ti were added, the hydrogenation and dehydrogenation properties of Mg were greatly improved. Ni and Ti-added Mg had a higher initial dehydrogenation rate and a larger Hd (60 min) than only Ni-added Mg, suggesting that the TiH1.924 and NiTi formed in Mg-1.25Ni-1.25Ti play roles in the increases in the initial dehydrogenation rate and Hd (60 min), probably acting as active sites for the nucleation of the Mg-H solid solution phase.

Significantly improved hydrogen storage properties of Mg90Al10 catalyzed by TiF3

Magnesium hydride (MgH 2 ) is one of the most promising materials for solid state hydrogen storage, but overly stable thermodynamics and sluggish kinetics of hydrogenation and dehydrogenation hinders its application. In this study, Mg 90 Al 10 was prepared by hydriding combustion synthesis (HCS), and then various Ti-based compounds (Ti, TiH 2 , TiO 2 and TiF 3 ) were introduced into Mg 90 Al 10 by ball milling. Mg 90 Al 10 + 10 wt% TiF 3 displays the most excellent dehydrogenation property compared with those doped with other Ti-based compounds. For instance, due to the addition of 10 wt% TiF 3 , the peak dehydrogenation temperature and the apparent dehydrogenation activation energy of the composite are 86 °C and 77.1 kJ/mol lower than those of Mg 90 Al 10 (364 °C and 155.95 kJ/mol). In addition, the catalytic effect of TiF 3 on the hydrogen storage properties of Mg 90 Al 10 has been investigated in detail. Except for the unreacted TiF 3 , Al 3 Ti and MgF 2 can be found during the first dehydrogenation process and remain stable in the subsequent de/hydrogenation cycles, which can act as the active sites to accelerate the hydrogen dissociation and recombination. Therefore, the excellent hydrogen storage properties of Mg 90 Al 10 + 10 wt% TiF 3 can be attributed to the catalytic effect of TiF 3 , in-situ formed Al 3 Ti and MgF 2 . Our result is very significant to emphasize the practical application of the Mg-Al hydrogen storage alloys. • The hydrogen storage property of Mg 90 Al 10 doped with TiF 3 is remarkably improved. • The onset dehydrogenation temperature is reduced to 175 °C after TiF 3 addition. • The Mg 90 Al 10 -TiF 3 shows superior hydrogenation/dehydrogenation cycling stability. • TiF 3 , the in-situ formed Al 3 Ti and MgF 2 exhibit excellent catalytic effect.

Enhancing the dehydrogenation properties of LiAlH4 using K2NiF6 as additive

Lithium alanate (LiAlH4) is a material that can be potentially used for solid-state hydrogen storage due to its high hydrogen content (10.5 wt%). Nevertheless, a high desorption temperature, slow desorption kinetic, and irreversibility have restricted the application of LiAlH4 as a solid-state hydrogen storage material. Hence, to lower the decomposition temperature and to boost the dehydrogenation kinetic, in this study, we applied K2NiF6 as an additive to LiAlH4. The addition of K2NiF6 showed an excellent improvement of the LiAlH4 dehydrogenation properties. After adding 10 wt% K2NiF6, the initial decomposition temperature of LiAlH4 within the first two dehydrogenation steps was lowered to 90 °C and 156 °C, respectively, that is 50 °C and 27 °C lower than that of the аs-milled LiAlH4. In terms of dehydrogenation kinetics, the dehydrogenation rate of K2NiF6-doped LiAlH4 sample was significantly higher as compared to аs-milled LiAlH4. The K2NiF6-doped LiAlH4 sample can release 3.07 wt% hydrogen within 90 min, while the milled LiAlH4 merely release 0.19 wt% hydrogen during the same period. According to the Arrhenius plot, the apparent activation energies for the desorption process of K2NiF6-doped LiAlH4 are 75.0 kJ/mol for the first stage and 88.0 kJ/mol for the second stage. These activation energies are lower compared to the undoped LiAlH4. The morphology study showed that the LiAlH4 particles become smaller and less agglomerated when K2NiF6 is added. The in situ formation of new phases of AlNi and LiF during the dehydrogenation process, as well as a reduction in particle size, is believed to be essential contributors in improving the LiAlH4 dehydrogenation characteristics.