Evaluation of catalyst activity for release of hydrogen from liquid organic hydrogen carriers

This contribution investigate the effect of parameters for production of hydrogen by catalytic dehydrogenation of perhydrodibenzyltoluene (H18-DBT). The sensitivity of the dehydrogenation reaction to temperature (290–320 °C) is justified by an increase in degree of dehydrogenation (DoD) from 40 to 90% when using 1 wt % Pt/Al₂O₃ catalyst. However, the increase in temperature increases the hydrogen production rate and decreases the hydrogen purity by increasing the formation of by-products. In addition, the DoD of 96% is obtained when 2 wt % Pt/Al₂O₃ is used at 320 °C. The DoD obtained for Pd, Pt, and Pt–Pd catalysts is 11, 82 and 6%, respectively. Therefore, Pd is not a metal of choice for dehydrogenation of H18-DBT, in both monometallic and bimetallic system. The ab-initio density functional theory (DFT) calculations are consistent with this observation. Furthermore, dehydrogenation of H18-DBT followed 1st order reaction kinetics and the activation energies for 1 wt % Pt/Al₂O₃, 1 wt % Pd/Al₂O₃ and 1:1 wt % Pt–Pd/Al₂O₃ catalysts are: 205, 84 and 66 kJ/mol, respectively.     

The effects of alumina morphology and Pt electron property on reversible hydrogenation and dehydrogenation of dibenzyltoluene as a liquid organic hydrogen carrier

The morphologies and the electron property of catalysts play the very important roles in the hydrogenation and dehydrogenation of liquid organic hydrogen carriers (LOHCs) such as dibenzyltoluene (DBT). The different morphologies and pore structures of γ-Al₂O₃ and Mo_xC doped γ-Al₂O₃ were synthesized as the supports for Pt catalysts. After analyzing of various characterizations and catalytic testing, it was found that the large surface area and the mesoporous structure of catalysts are beneficial to both DBT hydrogenation and perhydro-dibenzyltoluene (H18-DBT) dehydrogenation. The doping of Mo_xC promoted the formation of the smaller Pt nanoparticles and increased Pt dispersion. The forming Pt–Mo structure is beneficial to hydrogen spillover which suppress the formation of by-product. The high Pt dispersion of 0.1 wt% Mo_xC doped Pt/Al₂O₃ catalyst plays the positive roles in increasing H18-DBT dehydrogenation activity.     

Study on reversible hydrogen uptake and release of 1,2-dimethylindole as a new liquid organic hydrogen carrier

Indole derivatives have been considered as promising liquid organic hydrogen carriers (LOHCs) for onboard hydrogen storage applications. Here a new member of indole family, 1,2-dimethylindole (1,2-DMID), was reported as a potential liquid organic hydrogen carrier with a hydrogen storage content of 5.23 wt%, a meting point of 55 °C and a boiling point of 260 °C. Full hydrogenation and dehydrogenation of 1,2-DMID can be achieved with fast kinetics under mild conditions. The hydrogenation of 1,2-DMID followed the first order kinetics with an apparent activation energy of 85.1 kJ/mol. Dehydrogenation of fully hydrogenated product, octahydro-1,2-DMID was conducted over 5 wt% Pd/Al₂O₃ at 170–200 °C. The stored hydrogen can be completely released at 180 °C in 3 h and at 200 °C in 1 h. The energy barrier of dehydrogenation of octahydro-1,2-DMID was calculated to be 111.9 kJ/mol 3 times cycles of hydrogenation and dehydrogenation were employed to test the recycle ability of 1,2-DMID. The structures of intermediates were also discussed by means of Material Studio calculations.     

Integration of hydrogenation and dehydrogenation based on dibenzyltoluene as liquid organic hydrogen energy carrier

The heat transfer oil dibenzyltoluene (DBT) offered an intriguing approach for the scattered storage of renewable excess energy as a novel Liquid Organic Hydrogen Carrier (LOHC). The integration of hydrogenation and dehydrogenation in H0-DBT/H18-DBT pairs demonstrated that the feasibility of hydrogenation and dehydrogenation reaction conducted in one reactor with the same catalyst, which would be proposed to simplify the hydrogen storage process. The optimal reaction temperature based on the inhibition of ring opening and cracking was investigated combined with the ¹H NMR analysis. Meanwhile, the ideal catalyst 3 wt% Pt/Al₂O₃ for high hydrogen storage efficiency was screened out. Cycle tests of hydrogenation and dehydrogenation integration reaction had shown that the hydrogen storage efficiency was 84.6% after five cycle tests. The integration of hydrogenation and dehydrogenation reaction based on DBT exhibited the ideal thermal stability, which demonstrated its potential as a reversible H₂ carrier.     

Modifying the hydrogen storage performances of NaBH4 by catalyzing with MgFe2O4 synthesized via hydrothermal method

In this study, the hydrogenation performance of NaBH₄ was modified by the addition of 10 wt% MgFe₂O₄ as the catalyst. The NaBH₄ + 10 wt% of MgFe₂O₄ sample was prepared by a ball milling technique. The onset decomposition temperature of MgFe₂O₄-doped NaBH₄ was decreased to 323 °C and 483 °C for the first and second stage of dehydrogenation as compared to the milled NaBH₄ (497 °C). The desorption kinetics study showed that the addition of MgFe₂O₄ caused the sample to had faster hydrogen desorption with a capacity of 6.2 wt% within 60 min while the milled NaBH₄ had only released 5.3 wt% of hydrogen in the same period of time. For the isothermal absorption kinetics, the total amount of hydrogen absorbed by the milled NaBH₄ was 3.7 wt% while the NaBH₄ + 10 wt% MgFe₂O₄ sample showed better absorption characteristic with a total amount of 4.5 wt% of hydrogen within 60 min. The calculated desorption activation energy from the Kissinger plot of NaBH₄ + 10 wt% MgFe₂O₄ sample was 187 kJ/mol which reduced by 28 kJ/mol than the milled NaBH₄ (215 kJ/mol). The in-situ formation of MgB₆ and Fe₃O₄ after the dehydrogenation process indicates that these new species were responsible for the improved hydrogenation performances of NaBH₄.     

7-ethylindole: A new efficient liquid organic hydrogen carrier with fast kinetics

We report a discovery of a new member of the liquid organic hydrogen carrier (LOHC) family, 7-ethylindole (7-EID), with a low melting point of ?14 °C and a decent hydrogen content of 5.23 wt%. Hydrogenation of the compound was carried out over a commercial 5 wt% Ru/Al₂O₃ catalyst in the H₂ pressure range of 5–8 MPa and a temperature range of 120–160 °C, respectively. It was found that the hydrogenation rate positively correlates with the reaction temperature. However, the rate was barely effected by the H₂ pressure if the pressure exceeds 6 MPa. The estimated apparent activation energy of 7-EID hydrogenation is 51.5 kJ/mol. The fully hydrogenated product, octahydro-7-ethylindole (8H-7-EID), was used as the reactant for the dehydrogenation reaction at 170–200 °C over a 5 wt% Pd/Al₂O₃ catalyst. Full dehydrogenation of 8H-7-EID to 7-EID can be achieved within 270 min at 190 °C. The apparent activation energy of 8H-7-EID dehydrogenation was calculated to be 101.9 kJ/mol at 170–200 °C. The liberated H₂ was found to be of high purity, which meets the requirement of proton exchange membrane fuel cells.     

Temperature controlled three-stage catalytic dehydrogenation and cycle performance of perhydro-9-ethylcarbazole

Organic liquid heteroaromatic compounds, e.g. 9-ethylcarbazole, are potentially promising hydrogen storage materials because they can be catalytically hydrogenated and dehydrogenated at relatively moderate temperatures. In the present work, the cyclic hydrogenation of 9-ethylcarbazole and the temperature controlled stage-wise dehydrogenation of perhydro-9-ethylcarbazole were investigated. Full hydrogenation of 9-ethylcarbazole was realized over a 5 wt% Ru/Al₂O₃ catalyst at 180 °C and 80 bar, yielding a gravimetric density of 5.79 wt%. The catalytic dehydrogenation of perhydro-9-ethylcarbazole over a 5 wt% Pd/Al₂O₃ catalyst was found to undergo a three-stage process, i.e. perhydro-9-ethylcarbazole → octahydro-9-ethylcarbazole, octahydro-9-ethylcarbazole → tetrahydro-9-ethylcarbazole, and tetrahydro-9-ethylcarbazole → 9-ethylcarbazole with the initial reaction temperatures of 128 °C, 145 °C and 178 °C, respectively. Our results indicate that 9-ethylcarbazole displays an excellent cycle performance with very little capacity degradation after 10 cycles of catalytic hydrogenation and dehydrogenation. The hydrogen gas produced from the dehydrogenation possesses a high purity of over 99.99% with no carbon monoxide or other poisonous gases for fuel cells.     

On the role of size controlled Pt particles in nanostructured Pt-containing Al2O3 catalysts for partial oxidation of methane

The effect of the Pt loadings and particles sizes on the stability of Pt(x wt%)/Al₂O₃ catalysts were investigated in the partial oxidation of methane (POM) reaction. The Al₂O₃ support was prepared by sol-gel method and different Pt loadings, varying from 0.5 to 2.0 wt% were incorporated to alumina through the incipient wetness impregnation method. The physicochemical features of the catalysts were determined by XRD, ICP-OES, Nitrogen-sorption, UV–Visible, H₂-TPR, CO-DRIFTS, SEM-EDS, XPS and HRTEM techniques. The metal dispersion was evaluated in the cyclohexane dehydrogenation reaction. Lower Pt loadings resulted in well dispersed Pt^o nanoparticles with an enhanced activity in cyclohexane dehydrogenation and POM reactions. With increasing Pt loading to 2.0 wt%, the Pt nanoparticles of the Pt(2.0 wt%)/Al₂O₃ showed a methane conversion of 63% in 24 h of time on stream, and the catalyst was very selective to H₂ and CO. Based on the HRTEM, XPS and Raman spectroscopy techniques, an increment in the Pt loadings evidenced an enrichment of Pt^o clusters on the surface, however, no heavy carbon deposits formation was observed.     

Pt/CeO2 catalyst synthesized by combustion method for dehydrogenation of perhydro-dibenzyltoluene as liquid organic hydrogen carrier: Effect of pore size and metal dispersion

Liquid organic hydrogen carrier (LOHC) is a chemical hydrogen storage method that stores hydrogen in the form of liquid organics. Dibenzyltoluene (DBT) is a promising LOHC material due to its high storage density, low ignitability, and low cost. In this study, Pt/Al₂O₃ and Pt/CeO₂ catalysts are synthesized using a combustion nanocatalyst synthesis method called the glycine nitrate process (GNP) to obtain high catalytic activity for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT). Pt/CeO₂ exhibits much faster dehydrogenation than Pt/Al₂O₃, 80.5%/2.5 h versus 3.5%/2.5 h. To investigate the causes of the difference in the dehydrogenation rates, microstructural characterization by N₂ physisorption, CO chemisorption and transmission electron microscopy analysis are conducted, and the catalytic activities are evaluated at various liquid hourly space velocities (LHSVs). The differences in dehydrogenation can be attributed to the mass transport of liquid H18-DBT into the catalyst pores being slow due to the small pores in Pt/Al₂O₃, which is a rarely addressed issue for other LOHC materials. This is because many LOHC materials are dehydrogenated at the gas phase, which has higher diffusivity than that of the liquid phase. Pt/CeO₂ synthesized by the GNP is also compared with a commercial Pt/Al₂O₃ catalyst. The commercial Pt/Al₂O₃ catalyst shows a dehydrogenation of 17.8%/2.5 h, which is much slower than that of Pt/CeO₂ synthesized by the GNP, at 80.5%/2.5 h.     

Simultaneous dehydrogenation of 1,4- butanediol to γ-butyrolactone and hydrogenation of benzaldehyde to benzyl alcohol mediated over competent CeO2–Al2O3 supported Cu as catalyst

Hydrogen being a dynamically impending energy transporter is widely used in hydrogenation reactions for the synthesis of various value added chemicals. It can be obtained from dehydrogenation reactions and the acquired hydrogen molecule can directly be utilized in hydrogenation reactions. This correspondingly avoids external pumping of hydrogen making it an economical process. We have for the first time tried to carryout 1,4-butanediol dehydrogenation and benzaldehyde hydrogenation simultaneously over ceria-alumina supported copper (Cu/CeO₂–Al₂O₃) catalyst. In this concern, 10 wt% of Cu supported on CeO₂–Al₂O₃ (3:1 ratio) was synthesized using wet impregnation method. The synthesized catalyst was then characterized by various analytical methods such as BET, powder XRD, FE-SEM, H₂-TPR, NH₃ and CO₂-TPD, FT-IR and TGA. The catalytic activity towards simultaneous 1,4-butanediol dehydrogenation and benzaldehyde hydrogenation along with their individual reactions was tested for temperature range of 240 °C–300 °C. The physicochemical properties enhanced the catalytic activity as clearly interpreted from the results obtained from the respective characterization data. The best results were obtained with 10 wt% of Cu supported on CeO₂–Al₂O₃ (3:1 ratio) catalyst with benzaldehyde conversion of 34% and 84% selectivity of benzyl alcohol. The conversion of 1,4-butanediol was seen to be 90% with around 95% selectivity of γ-butyrolactone. The catalyst also featured physicochemical properties namely increased surface area, higher dispersion and its highly basic nature, for the simultaneous reaction towards a positive direction. In terms of permanence, the Cu/CeO₂–Al₂O₃ (10CCA) catalyst was quite steady and showed stable activity up to 24 h in time on stream profile.     

A YH3 promoted palladium catalyst for reversible hydrogen storage of N-ethylcarbazole

N-ethylcarbazole (NEC) is a promising liquid organic hydrogen carrier, while sluggish kinetics of hydrogen absorption and desorption restrict its application. To overcome that, a YH₃ promoted palladium catalyst Pd/Al₂O₃-YH₃ is developed in this work by taking advantage of the fast reversible hydrogenation and dehydrogenation kinetics of YH₃. With the Pd/Al₂O₃-YH₃, NEC can reversibly store 5.5 wt% hydrogen in 4 h below 473 K. The performance is the best compared to that of all the reported catalysts for both hydrogen absorption and desorption. Moreover, there are no gaseous impurities produced and no performance decay during three hydrogen storage cycles. The excellent performance derives from the intrinsic high catalytic activity of Pd/Al₂O₃ and the promoting effect of YH₃ by providing a new hydrogen transfer path, making NEC more attractive for practical application.     

High active pd@mil-101 catalyst for dehydrogenation of liquid organic hydrogen carrier

Highly dispersed Pd nanoparticles immobilized in MIL-101 (Pd@MIL-101) were prepared and used for the catalytic dehydrogenation of Liquid organic hydrogen carriers (LOHC). The as-synthesized catalysts were characterized and it was found that 3 wt% of Pd@MIL-101 embodied smaller and highly dispersed Pd NPs. The catalytic activities of as-synthesized catalysts were investigated by the dehydrogenation of a representative LOHC compound, perhydro-N-propylcarbazole (12H-NPCZ). The results indicated that 3 wt% Pd@MIL-101 catalyst exhibited good catalytic activity and good reusability for the dehydrogenation of 12H-NPCZ, which is superior to that of commercial 5 wt% Pd/Al₂O₃ catalyst. This study demonstrates that Pd@MIL-101 is a promising dehydrogenation catalyst for the application of LOHC technology.     

Remarkable activity of Pd catalyst supported on alumina synthesized via a hydrothermal route for hydrogen release of perhydro-N-propylcarbazole

The investigation of dehydrogenation catalysts to achieve rapidly hydrogen release of Liquid Organic Hydrogen Carriers (LOHCs) are of crucial importance for large-scale applications. The catalyst supports with bulk surface area and decent acid-base nature is a key parameter for catalyst to improve its catalytic performance as well as reduce precious metal dosage. Herein, alumina was chosen as a support for Pd loading and prepared through hydrothermal route at different temperatures. The morphology and surface acid property of the alumina supports were investigated in detail. The results revealed that the hydrothermal temperature had a closely effect on the morphology, surface acidity and specific surface area of alumina, resulting in a further impact on Pd dispersion and particle size associated tightly with catalytic activity of Pd/Al₂O₃. The catalyst with 1 wt% Pd loaded on alumina carrier prepared via hydrothermal treatment at 120 °C showed the best catalytic performance for dehydrogenation of perhydro-N-propylcarbazole (12H-NPCZ). Full dehydrogenation with 100% conversion to N-propylcarbazole (NPCZ) could be achieved after 360 min at 180 °C and 101 kPa, which is higher than that of commercial 5 wt% Pd/Al₂O₃ catalyst. The catalyst has potential commercial application value in large-scale application of LOHC technology.     

Acid site introduced by Al3+penta and boron in Pt/Al2O3 catalyst for dehydrogenation of methylcyclohexane

A series of catalysts with different acid strengths were obtained by constructing unsaturated pentacoordinate (Al³⁺_penta) sites in Al₂O₃ and loading with boron. The effects of support properties and the addition of boron on the strength and type of catalyst acid were investigated, and their influence on the dehydrogenation performance of methylcyclohexane (MCH) was discussed. In Pt-B/Al₂O₃-600 catalysts containing Al³⁺_penta sites, the strongly acidic L acid sites gradually decreased and the weakly acidic [L + B] acid sites gradually increased with increasing boron loading, indicating coverage of the Al³⁺_penta site by boron. In Pt-B/Al₂O₃-750 catalysts without Al³⁺_penta sites, strongly acidic L acid sites gradually decrease with increasing boron loading and weakly acidic [L + B] acid sites remains essentially unchanged. For Pt-B/Al₂O₃-600 catalysts, the effect of boron on the interaction of Pt with Al₂O₃ is minimized when the loading of boron is between 0 and 1 wt% and the MCH dehydrogenation performance increases with the number of weak acid sites. At a boron loading of 1 wt%, the abundance of weak acid sites maintains the dispersion of Pt and allows a suitable interaction between Pt and Al₂O₃, thus enhancing the dehydrogenation performance of MCH.     

Wet-impregnated bimetallic Pd-Ni catalysts with enhanced activity for dehydrogenation of perhydro-N-propylcarbazole

Palladium/platinum-based catalysts are widely used in the dehydrogenation process of Liquid Organic Hydrogen Carriers (LOHCs). The cost of noble metal has become a main drawback for LOHCs large-scale application. Partial replacement of Pd/Pt by other transition metals can be an effective solution. In this paper, we synthesize the bimetallic Pd–Ni catalyst by incipient wet impregnation and the catalytic dehydrogenation performance of perhydro-N-propylcarbazole (12H-NPCZ) as a LOHC candidate. Ni and Pd were impregnated on mesoporous alumina to obtain both monometallic and bimetallic catalysts, i.e. Pd/Al₂O₃, Ni/Al₂O₃ and Pd–Ni/Al₂O₃ (Pd:Ni = 1:1) with total metal loading of 5 wt%, respectively. The above catalysts were characterized by N₂-adsorption/desorption, H₂-temperature programmed reduction, X-Ray diffraction, X-Ray photoelectron spectroscopy, Inductively coupled plasma - optical emission spectrometer, CO pulse adsorption and Transmission electron microscopy. The catalytic dehydrogenation results indicated that the bimetallic Pd–Ni/Al₂O₃ showed best catalytic activity, followed by Pd/Al₂O₃, commercial Pd/Al₂O₃ and Ni/Al₂O₃. Notably, the catalytic activity of bimetallic was well maintained after 5 cycles at 200 °C with no degradation, indicating this bimetallic catalyst has potential prospect for large-scale application.     

Dehydrogenation of methylcyclohexane over Pt/V2O5 and Pt/Y2O3 for hydrogen delivery applications

Dehydrogenation of methylcyclohexane (MCH) for hydrogen transportation and delivery application was carried out over 3 wt% Pt/V₂O₅ and 3 wt% Pt/Y₂O₃ catalyst. The catalytic activity was tested using a spray-pulse mode of reactor. Effective dehydrogenation of MCH under spray-pulse mode of reactant injection was observed. In terms of hydrogen evolution rate at 60 min from start of reaction the activity of 958 mmol/g/min was obtained at temperature of 350 °C. Nearly 100% selectivity toward hydrogen was obtained. A relatively high conversion of 98% was observed with 3 wt% Pt/Y₂O₃ at 60 min using an advanced spray-pulse reactor system. The catalysts were characterized using x-ray diffraction pattern (XRD), CO-chemisorption metal analysis, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis.     

Selective hydrogen combustion in the presence of propylene and propane over Pt/A-zeolite catalysts

The behavior of selective hydrogen combustion (SHC) in the presence of propylene and propane changing with reaction temperature in a range of 100–600 °C has been investigated over the Pt catalysts supported on A-zeolites. The effect of Pt loading varying from 0.01 to 2 wt% on the catalytic SHC performance has been studied in the conditions with a feed gas molar composition of C₃H₈/C₃H₆/H₂/O₂ = 4/4/4/2 balanced with N₂ and gas hourly space velocity of 15,000 h⁻¹. The results show that for each Pt/3A catalyst having a different Pt loading there is a maximum of H₂ conversion by combustion appearing between 300 and 400 °C, while the selectivity to comprehensive H₂ conversion can maintain 100% when the temperature lower than 300 °C. Moreover, the Pt/3A catalyst with a Pt loading of 0.5 wt % performs better than the others at the temperatures higher than 300 °C. The maximal H₂ combustion achieved over the 0.5 wt% Pt/3A catalyst is as high as 96.6% along with a selectivity of 100% at 300 °C, and a 92.4% H₂ combustion with 98.5% selectivity can be obtained even if at 500 °C. The characterization of the catalysts reveals that the distribution of Pt atoms and the number of atoms in Pt clusters may be the key factors for giving rise to the good SHC performance. The influence of three types of A-zeolite supports on the Pt catalyzed SHC process has also been investigated. 3A zeolite is superior to 4A and 5A for supporting 0.5 wt% Pt catalyst in terms of both activity and selectivity. The lower C₃H₆ conversion on the 0.5 wt% Pt/3A catalyst compared to the 0.5 wt% Pt/5A may be ascribed to the insufficient sites for the C₃H₆ activation on the surface of Pt/3A due to the limitation of 3A channels inaccessible to C₃H_6. This contrarily brings about the better SHC performance on the 0.5 wt% Pt/3A catalyst.     

Production of CO-rich hydrogen gas from glycerol dry reforming over La-promoted Ni/Al2O3 catalyst

Dry reforming of glycerol has been carried out over alumina-supported Ni catalyst promoted with lanthanum. The catalysts were characterized using EDX, liquid N₂ adsorption, XRD technique as well as temperature-programmed reduction. Significantly, catalytic glycerol dry reforming under atmospheric pressure and at reaction temperature of 1023 K employing 3 wt%La–Ni/Al₂O₃ catalyst yielded H₂, CO and CH₄ as main gaseous products with H₂:CO < 2.0. Post-reaction, XRD analysis of used catalysts showed carbon deposition during glycerol dry reforming. Consequently, BET surface area measurement for used catalysts yielded 10–21% area reduction. Temperature-programmed gasification studies with O₂ as a gasification agent has revealed that La promotion managed to reduce carbon laydown (up to 20% improvement). In comparison, the unpromoted Ni/Al₂O₃ catalyst exhibited the highest carbon deposition (circa 33.0 wt%).     

Improved hydrogen storage properties of Mg/MgH2 thanks to the addition of nickel hydride complex precursors

In order to improve the hydrogenation/dehydrogenation properties of the Mg/MgH₂ system, the nickel hydride complex NiHCl(P(C₆H₁₁)₃)₂ has been added in different amounts to MgH₂ by planetary ball milling. The hydrogen storage properties of the formed composites were studied by different thermal analyses methods (temperature programmed desorption, calorimetric and pressure-composition-temperature analyses). The optimal amount of the nickel complex precursor was found to be of 20 wt%. It allows to homogeneously disperse 1.8 wt% of nickel active species at the surface of the Mg/MgH₂ particles. After the decomposition of the complex during MgH₂ dehydrogenation, the formed composite is stable upon cycling at low temperature. It can release hydrogen at 200 °C and absorb 6.3 wt% of H₂ at 100 °C in less than 1 h. The significantly enhanced H₂ storage properties are due to the impact of the highly dispersed nickel on both the kinetics and thermodynamics of the Mg/MgH₂ system. The hydrogenation and dehydrogenation enthalpies were found to be of −65 and 63 kJ/mol H₂ respectively (±75 kJ/mol H₂ for pure Mg/MgH₂) and the calculated apparent activation energies of the hydrogen uptake and release processes are of 22 and 127 kJ/mol H₂ respectively (88 and 176 kJ/mol H₂ for pure Mg/MgH₂). The change in the thermodynamics observed in the formed composite is likely to be due to the formation of a Mg_0.992Ni_0.008 phase during dehydrogenation/hydrogenation cycling. The impact of another hydride nickel precursor in which chloride has been replaced by a borohydride ligand, namely NiH(BH₄)(P(C₆H₁₁)₃)₂, is also reported.     

Reversible hydrogen storage in a 3NaBH4/YF3 composite

A 3NaBH₄/YF₃ hydrogen storage composite was prepared through ball milling and its hydrogen sorption properties were investigated. It is shown that NaBH₄ does not react with YF₃ during ball milling. The dehydrogenation of the composite starts at 423 °C, which is about 100 °C lower than the dehydrogenation temperature of pure NaBH₄, with a mass loss of 4.12 wt%. Pressure–Composition–Temperature tests reveal that the composite has reversible hydrogen sorption performance in the temperature range from 350 °C to 413 °C and under quite low hydrogenation plateau pressures (<1 MPa). Its maximum hydrogen storage capacity can reach up to 3.52 wt%. The dehydrogenated composite can absorb 3.2 wt% of hydrogen within 5 min at 400 °C. Based on the Pressure–Composition–Temperature analyses, the hydrogenation enthalpy of the composite is determined to be −46.05 kJ/mol H₂, while the dehydrogenation enthalpy is 176.76 kJ/mol H₂. The mechanism of reversible hydrogen sorption in the composite involves the decomposition and regeneration of NaBH₄ through the reaction with YF₃. Therefore, the addition of the YF₃ to NaBH₄ as a reagent forms a reversible hydrogen storage composite.