Solid Reactions between MAlH4 and NH4Cl to Produce Hydrogen

  • Mr Hua-Jun Zhang, Institute of Chemical and Engineering Science, A-Star; 1, Pesek Road, Jurong Island; Singapore 627833, Singapore
  • Ms Yook Si Loo, Singapore
  • Dr Hans Geerlings, Shell Global Solutions International BV, P.O. Box 38000, 1030 BN Amsterdam, The Netherlands
  • Dr Hans Geerlings, Delft University of Technology, Julianalaan 136, 2628 BL Delft., The Netherlands
  • Dr Jianyi Lin, Singapore
  • Dr Wee Shong Chin, Department of Chemistry, NUSDepartment of Chemistry, National University of Singapore;3 Science Drive 3;Singapore 117543, Singapore

    • Solid reactions between alkali aluminum hydrides (MAlH4, M = Li or Na) and NH4Cl have been investigated. 1 mole of the MAlH4/NH4Cl mixture (at mole ratio 1:1) was measured to liberate 3 moles of hydrogen when the mixture was thermally heated to around 170oC, corresponding to 5.6wt% for NaAlH4/NH4Cl and 6.6% for LiAlH4/NH4Cl, respectively. Based on our XRD studies, the general reaction scheme is proposed as follows:

    M+(AlH4)- + (NH4)+X- -> (AlH4)- (NH4)+ + MX -> MX + AlH3-NH3 + H2 -> MX + 1/n -[HAl-NH]-n + 3H2 .

    By ball milling of the precursor compounds prior to the mixing, NH3 production as the by-product could be avoided. Differential scanning calorimetry (DSC) measurements showed that the reaction occurred at 160-1700C within 24 seconds. This may be attributed to the low melting temperatures of MAlH4 (150oC and 180oC for LiAlH4 and NaAlH4 respectively) and the exothermic nature of reactions.