Direct synthesis of NaAlH₄ from AlCl₃ and Na without a catalyst

Metal alanates represented by NaAlH₄ are promising hydrogen storage materials with high hydrogen density and purity. However, the synthesis of NaAlH₄ is limited due to the requirement for complex catalysts (such as triethylaluminium) and high-energy-consuming aluminium as a reagent. Herein, NaAlH₄ has been successfully synthesized directly from AlCl₃ and sodium (with a small amount of NaH as reaction initiator) in tetrahydrofuran–toluene (1 : 1) solvent without a catalyst to achieve a yield of 38%. The effects of AlCl₃ purity, addition of aluminium powder, and solvent ratios on the production of NaAlH₄ have also been investigated. High-purity AlCl₃ (>99%) was found to be necessary for the synthesis of NaAlH₄ without the addition of aluminium powder or a high content of tetrahydrofuran in the solvent. However, the purity requirement of AlCl₃ was less stringent when aluminium powder was added or when the tetrahydrofuran–toluene ratio was increased to 2 : 1. Nevertheless, a high tetrahydrofuran ratio caused pressure overruns. The direct synthesis of NaAlH₄ from AlCl₃ and sodium provides a facile pathway to yield NaAlH₄ economically.