Formation of Al2H7− anions — indirect evidence of volatile AlH3 on sodium alanate using solid-state NMR spectroscopy

Abstract

After more than a decade of intense research on NaAlH(4) doped with transition metals as hydrogen storage material, the actual mechanism of the decomposition and rehydrogenation reaction is still unclear. Early on, monomeric AlH(3) was named as a possible transport shuttle for aluminium, but never observed experimentally. Here we report for the first time the trapping of volatile AlH(3) produced during the decomposition of undoped NaAlH(4) by an adduct of sodium alanate and crown ether. The resulting Al(2)H(7)(-) anion was identified by solid-state (27)Al NMR spectroscopy. Based on this indirect evidence of volatile alane, we present a simple description of the processes occurring during the reversible dehydrogenation of NaAlH(4).

Catalytic Influence of Various Cerium Precursors on the Hydrogen Sorption Properties of NaAlH4

“…Recently, Ivancic et al detected a highly mobile Al‐bearing species by NMR in NaAlH 4 doped with Ti or Sc catalysts, which could provide the metal‐atom transport in the rehydriding process 46. Indirect evidence of the generation of AlH 3 was obtained by Felderhoff 47. Although mass transfer is necessary, the proposed generation of such mobile intermediates is indifferent to the applied catalysts,44–46 which makes it hard to explain the improving kinetics in the cases of Ce catalysts.…”

One Hundred Years of the Max‐Planck‐Institut für Kohlenforschung

“…The Ti‐catalyst facilitates dissociation of hydrogen at the surface of the solid material while also accelerating diffusion in the bulk, but mass transfer is probably rate‐limiting (Scheme ) 62e. Later on it was discovered that an intermediately formed alane species is the most probable transport species for aluminum 62f…”

100 Jahre Max‐Planck‐Institut für Kohlenforschung

“…Allerdings erwies sich Massentransfer als vermutlich geschwindigkeitslimitierend (Schema ) 62e. Später wurde entdeckt, dass eine sich dazwischen bildende Alanspezies die wahrscheinlichste Transportspezies für Aluminium ist 62f…”