Efficient Catalysis of Ammonia Borane Dehydrogenation

Denney, Melanie C.; Pons, Vincent; Hebden, Travis J.; Heinekey, D. Michael; Goldberg, Karen I.

doi:10.1021/ja062419g

Cited by 607 publications

(458 citation statements)

References 18 publications

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“…In reactions with AB, we note the formation of an insoluble precipitate, which has been identified as the same polymeric aminoborane species obtained by Goldberg 8 and Manners. 15 The dehydrogenation of methylammonia-borane (MeAB) was also evaluated.…”

supporting

confidence: 81%

Ruthenium-Catalyzed Dehydrogenation of Ammonia Boranes

et al. 2008

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Ammonia borane (AB), which has a very high hydrogen content by weight (19.6%), is attracting attention as a means of achieving efficient chemical hydrogen storage.1,2 Heating AB in the solid state, 3 ionic liquids 4 or the presence of acid 5 has been shown to induce the release of >1.0 equiv of H 2 over the course of several hours, and transition metal complexes of Rh, 6 Ni, 7 and Ir 8 have been shown to catalyze H 2 release under mild conditions. Notably, the Ni catalysts described by Baker release up to 2.8 equiv of H 2 , 7 an observation that has prompted a more detailed evaluation of their reaction mechanism.9a When considering strategies for dehydrogenation, AB is often compared to ethane.10 Computational predictions provide little mechanistic support for this analogy, however, 9,11 and in terms of local dipoles and reactivity AB may better be compared to methanol. Drawing from this analogy, we have discovered that ruthenium catalysts, originally developed for alcohol redox processes, 12 will induce the release of 1 equiv of H 2 from AB (up to 1.0 system wt %) within 5 min at room temperature with as little at 0.03 mol% Ru. Furthermore, 2 equiv of H 2 is rapidly released from highly concentrated (11 M) MeAB solutions at 22°C (ambient temperature), providing 3.0 system wt % hydrogen release. We have also found that by using an AB/MeAB mixture at 50°C, up to 3.6 system wt % H 2 can be released with 0.1 mol % Ru.An evaluation of several alcohol oxidation/reduction catalysts provided promising leads with complexes 1 to 6 (Figure 1). 13 In these studies, the precatalysts (0.1 mol%) were activated via treatment with KO t Bu (3 mol%) 13c in THF under inert atmosphere to generate the active ruthenium amide species prior to the addition of AB to the reaction vessel.14 Complexes 1 and 2 are particularly reactive even at 0.03 mol% Ru.14 Optimal outcomes are observed at high [AB] (5.0 M), an important parameter for maximal gravimetric H 2 density. In reactions with AB, we note the formation of an insoluble precipitate, which has been identified as the same polymeric aminoborane species obtained by Goldberg 8 and Manners. 15 The dehydrogenation of methylammonia-borane (MeAB) was also evaluated. 6 Under conditions similar to those employed for AB dehydrogenation, 0.5 mol% 1 induced the release of up to 2.0 equiv of H 2 from MeAB in ∼10 min (Figure 2). 16 These reactions are characterized by a very rapid release of the first equivalent of H 2 (occurring in less than 10 s), generating poly(N-methylaminoborane).15 This is followed by a slower release of the second equivalent over ∼10 min. 17 Since no insoluble precipitate is observed, more concentrated conditions (11 M [MeAB]) may be employed, increasing the system % H 2 to 3% (1.9 equiv of H 2 released). To further maximize the gravimetric H 2 density, AB-MeAB mixtures were evaluated.18 Initial results using a 1:1 AB/MeAB mixture at 50°C indicate that 3.6 system wt % H 2 release can be achieved with 0.1 mol% 1 under solvent-free conditions. 16As a preliminary probe i...

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confidence: 81%

Ruthenium-Catalyzed Dehydrogenation of Ammonia Boranes

et al. 2008

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“…These pincer ligand catalysts catalyze the very rapid release (minutes) of only one mole of hydrogen/AB at room temperature in organic solvents, generating the BNH product described as the ''cyclic pentamer'' [BH 2 NH 2 ] 5 . [80] The cyclic pentamer is unreactive to further release of hydrogen under all reasonable conditions explored. This low-temperature pincer ligand catalyst system is of great interest not only because of its apparent mechanistic differences with most other catalysts, but also because it may represent a potential ''cold start'' catalyst, one that can quickly generate hydrogen and heat to help initiate highertemperature catalysts to generate more hydrogen and heat to facilitate the startup of a cold fuel cell system.…”

Section: Catalytic Release Of Hydrogen From Ammonia Boranementioning

confidence: 96%

“…This of course suggested catalytic approaches that offer the opportunity to increase the rate and decrease the temperature of onset of hydrogen release. R&D performed by the CHSCoE (Baker, Sneddon, Heinekey, Goldberg, Burrell, and their colleagues [74][75][76][77][78][79][80][81][82][83][84][85][86][87] ) and by researchers outside of the Center resulted in the description of many different catalytic processes and catalysts for the dehydrogenation of ammonia borane (Figure 14). In order to perform the catalytic dehydrogenation of ammonia borane, it is necessary to make intimate contact of ammonia borane with the catalyst.…”

Section: Catalytic Release Of Hydrogen From Ammonia Boranementioning

confidence: 99%

Accelerating the Understanding and Development of Hydrogen Storage Materials: A Review of the Five-Year Efforts of the Three DOE Hydrogen Storage Materials Centers of Excellence

Klebanoff

Ott

Simpson

et al. 2014

Metallurgical and Materials Transactions E

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A technical review of the progress achieved in hydrogen storage materials development through the U.S. Department of Energy's (DOE) Fuel Cell Technologies Office and the three Hydrogen Storage Materials Centers of Excellence (CoEs), which ran from 2005 to 2010 is presented. The three CoEs were created to develop reversible metal hydrides, chemical hydrogen storage materials, and high-specific-surface-area (SSA) hydrogen sorbents. For each CoE, the approach taken is specified, key outcomes and accomplishments identified, and recommendations for future work are suggested. The Metal Hydride Center of Excellence addresses work on destabilized hydrides, including the LiBH/Mg 2 NiH 4 system, borohydrides, amides, and alanes; and compares the best materials to DOE targets. The Chemical Hydrogen Storage Center of Excellence discusses the classes of materials studied for chemical hydrogen storage, focusing on ammonia borane and examines the progress in developing efficient regeneration schemes. The Hydrogen Sorption Center of Excellence describes the progress in developing high-SSA sorbents and pathways for developing improved materials capable of achieving DOE targets. The phenomenon of spillover is also observed and its importance to ensuring improved measurements is discussed. Through the five-year effort of the Hydrogen Storage Materials Centers of Excellence, significant progress was achieved in developing and understanding hydrogen storage materials.

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“…Extensive efforts have been focused on light weight hydrides due to the demand of high hydrogen capacity. Ammonia borane (NH 3 BH 3 , AB for short), having a hydrogen content of 19.6 wt% is one of most investigated materials [1]. The recently developed metal amidoboranes (MABs), on the other hand, exhibit advantageous dehydrogenation properties over AB.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and hydrogen storage properties of lithium borohydride amidoborane complex

Chen

et al. 2013

International Journal of Hydrogen Energy

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Efficient Catalysis of Ammonia Borane Dehydrogenation

Cited by 607 publications

References 18 publications

Ruthenium-Catalyzed Dehydrogenation of Ammonia Boranes

Ruthenium-Catalyzed Dehydrogenation of Ammonia Boranes

Accelerating the Understanding and Development of Hydrogen Storage Materials: A Review of the Five-Year Efforts of the Three DOE Hydrogen Storage Materials Centers of Excellence

Synthesis and hydrogen storage properties of lithium borohydride amidoborane complex

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