Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry<sup>1</sup>

Finholt, A. E.; Bond, Arthur C.; Schlesinger, H. I.

doi:10.1021/ja01197a061

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“…The separation of alane from AlH 3 •Et 2 O is well established and affords pure AlH 3 . [10][11][12] However, separation of the AlH 3 •THF adduct is more complicated because it decomposes when heated under vacuum.Therefore, adducts such as triethylamine (TEA) were added to the reaction product to stabilize the alane during purification. Adduct free alane is recovered by heating the neat liquid AlH 3 •TEA en vacuo.…”

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Towards uranium catalysts

Fox

Bart

Meyer

et al. 2008

Nature

398

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Researchers worldwide have identified a large number of compounds with high hydrogen capacity that can fulfill these gravimetric and volumetric requirements.Unfortunately, the majority of these compounds fail to fulfill the thermodynamic and kinetic requirements for on-board storage systems. Alane has the gravimetric (10.1 mass% H 2 ) and the volumetric (149 kg H 2 /m 3 ) density needed to meet the 2010 DOE goals. In addition, rapid hydrogen release from alane can be achieved using only the waste heat from a fuel cell or a hydrogen internal combustion engine. 9 The main drawback to using alane in hydrogen storage applications is unfavorable hydriding thermodynamics. The direct hydrogenation of aluminium to alane requires over 10 5 bars of hydrogen pressure at room temperature as shown in equation(1). This impractically of using high hydriding pressure has precluded alane from being considered as a reversible hydrogen storage material. The other possible electrochemical reaction is having AlH -4 ion react with the aluminium anode to form alane. In this reaction route, the evolution of hydrogen is suppressed and the reaction is expected to consume the Al electrode as in equation (5) Experimental observations confirm that the anode is indeed consumed as shown in voltage experiments were performed. During these experiments, the current was steady and increased slightly with time. The electrochemical production of alane is not slowed by the formation of AlH 3 . In contrast to previous reports, no perception of alane is observed and the alane produced by our method is completely dissolved in solution as a THF adduct. 17During electrolysis, dendritic material was deposited on the platinum counter electrode.This material was collected and determined to be Na 3 AlH 6 from XRD data.Experiments were conducted to determine the feasibility of plating sodium at the platinum cathode as an alternative to NaH formation in the fueling cycle. The platinum cathode and aluminium anode potentials were -2.89 V and -1.31 V respectively. Plating of Na metal was observed at the cathode while alane was produced at the aluminium anode.Reacting sodium with aluminium from used alane under pressurized hydrogen will regenerate the starting material NaAlH 4 leading to a reversible cycle.In addition to determining the electrochemical processes for producing AlH 3 , recovering AlH 3 from the solution is a major step of this cycle. The separation of alane from AlH 3 •Et 2 O is well established and affords pure AlH 3 . [10][11][12] However, separation of the AlH 3 •THF adduct is more complicated because it decomposes when heated under vacuum.Therefore, adducts such as triethylamine (TEA) were added to the reaction product to stabilize the alane during purification. Adduct free alane is recovered by heating the neat liquid AlH 3 •TEA en vacuo.Alane recovered from the electrochemical cells was characterized by powder X-ray diffraction, Raman spectroscopy, and thermal gravimetric analyzer (TGA). Powder X-ray diffraction patterns data for two different...

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Towards uranium catalysts

Fox

Bart

Meyer

et al. 2008

Nature

398

285

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“…Next we consider the role of a vacancy without a Ti-dopant in Equation (2). If Al(111) is processed to start with a vacancy (I2), which has an energy cost of +0.53 eV with respect to I1 with the Al atom being removed to bulk, Al b , (and later an Al adatom will be introduced to form alane), it can help stabilize H*.…”

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confidence: 99%

“…[1] The major challenge that prevents its widespread application is lack of efficient, low-cost processes for the preparation of alane on a large scale. Chemical [2][3][4][5] and mechanochemical [6][7] methods to synthesize alane from other metal hydrides have been demonstrated, but direct synthesis from the elements at moderate hydrogen pressure remains elusive. Pure Al does not react with hydrogen to form alane at room temperature unless subjected to impractically high hydrogen pressures exceeding 7 kbar [1,8] .…”

Section: Introductionmentioning

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Towards Direct Synthesis of Alane: A Predicted Defect‐Mediated Pathway Confirmed Experimentally

et al. 2016

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Alane (AlH3) is a unique energetic material that has not found a broad practical use for over 70 years because it is difficult to synthesize directly from its elements. Using density functional theory, we examine the defectmediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation, which are both endothermic on a clean surface. Only with Ti dopant to facilitate H2 dissociation and vacancies to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunneling microscopy showed that during H2 exposure, alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball milling of the Al samples with Ti (providing necessary defects) showed a 10 % conversion of Al into AlH3 or closely related species at 344 bar H2, indicating that the predicted pathway may lead to the direct synthesis of alane from elements at pressures much lower than the 104 bar expected from bulk thermodynamics. [d,f] S. Gupta, [a] and V. K. Pecharsky* [a,c] Abstract: Alane (AlH3) is a unique energetic material that has not found broad practical use for over 70 years due to difficulties of its direct synthesis from elements. Using density functional theory we examine the defect-mediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation; both are endothermic on clean surface. Only with Ti-dopant to facilitate H2 dissociation and vacancy to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunnelling microscopy showed that during H2 exposure alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball-milling samples of Al with Ti (providing necessary defects) showed a 10% conversion of Al into AlH3 or closely related species at 344 bar H2, indicating that the predicted pathway may lead to direct synthesis of alane from elements at pressures much lower than the 10 4 bar expected from bulk thermodynamics.

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“…1 This reagent is very useful in synthetic organic chemistry and is easily prepared in situ and used immediately. Lithium aluminum hydride is a powerful reducing agent that can reduce several functional groups.…”

Section: Introductionmentioning

confidence: 99%

Aluminum Hydride

Lopinti¹

2005

Synlett

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This feature focuses on a reagent chosen by a postgraduate, highlighting the uses and preparation of the reagent in current research Aluminum Hydride Compiled by Krishnarao Lopinti Krishnarao Lopinti was born in Srikakulam, Andhra Pradesh in India in 1978. He obtained his B.Sc. (2000) from Acharya Nagarjuna University and M.Sc. (2002) in chemistry from the University of Hyderabad. After qualifying for a CSIR Junior Research Fellowship through a national search examination CSIR-JRF, he began Ph.D.

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Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry¹

Cited by 544 publications

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Towards uranium catalysts

Towards uranium catalysts

Towards Direct Synthesis of Alane: A Predicted Defect‐Mediated Pathway Confirmed Experimentally

Aluminum Hydride

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Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry1

Cited by 544 publications

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Towards uranium catalysts

Towards uranium catalysts

Towards Direct Synthesis of Alane: A Predicted Defect‐Mediated Pathway Confirmed Experimentally

Aluminum Hydride

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Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry¹