Regeneration of Lithium Aluminum Hydride

• Published in: Journal of the American Chemical Society 2008-12, Vol.130 (52), p.17790-17794
• Main Authors: Graetz, Jason, Wegrzyn, James, Reilly, James J
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja805353w

Lithium aluminum hydride (LiAlH4) is a promising compound for hydrogen storage, with a high gravimetric and volumetric hydrogen density and a low decomposition temperature. Similar to other metastable hydrides, LiAlH4 does not form by direct hydrogenation at reasonable hydrogen pressures; therefore, there is considerable interest in developing new routes to regenerate the material from the dehydrogenated products LiH and Al. Here we demonstrate a low-energy route to regenerate LiAlH4 from LiH and Ti-catalyzed Al. The initial hydrogenation occurs in a tetrahydrofuran slurry and forms the adduct LiAlH4·4THF. The thermodynamics of this reversible reaction were investigated by measuring pressure−composition isotherms, and the free energy was found to be small and slightly negative (ΔG = −1.1 kJ/mol H2), suggesting an equilibrium hydrogen pressure of just under 1 bar at 300 K. We also demonstrate that the adduct LiAlH4·4THF can be desolvated at low temperature to yield crystalline LiAlH4.