Regeneration of LiAlH4 at sub-ambient temperatures studied by multinuclear NMR spectroscopy

Lithium aluminium hydride (LiAlH4) has long been identified as a viable hydrogen storage material, due to its high attainable theoretical gravimetric hydrogen capacity of 7.9 wt%. The main impediment to its viability for technical application is its limitation for regeneration. Recently, solvent-mediated regeneration has been achieved at room temperature using dimethyl-ether, Me2O, although the reaction pathway has not been determined. This in situ multinuclear NMR spectroscopy study (27Al and 7Li) has confirmed that the Me2O-mediated, direct synthesis of LiAlH4 occurs by a one-step process in which LiAlH4·xMe2O is formed, and does not involve Li3AlH6 or any other intermediates. Hydrogenation has been shown to occur below ambient temperatures (at 0 °C) for the first time, and the importance of solvate adducts formed during the process is demonstrated. [Display omitted] •Regeneration of LiAlH4 has been studied by 27Al and 7Li NMR spectroscopy.•Solvent-mediated regeneration occurs at sub-ambient temperatures using dimethyl-ether.•Direct synthesis of LiAlH4 occurs in a one-step process without an Li3AlH6 intermediate.•LiAlH4·xMe2O is identified similar to LiAlH4·xTHF observed during regeneration in THF.