Ammonia suppression during decomposition of sodium amide by the addition of metal hydride

Abstract

The decomposition of NaNH2 has been reported, mainly decomposing into NaH, N2 and H2. Ammonia is also produced in addition to N2 and H2. To the best of our knowledge, very few scattered reports on the effect of alkali hydrides on NaNH2 exist in literature. Thus, we choose NaNH2–MH (M = Li, Na, K, Mg, Ca) system to be investigated in detail. Since NaNH2–NaH is the simplest combination due to same cation, it was tested for the establishment of reaction mechanism using transmission electron microscopy (TEM). It is observed that the entire process follows NH3 mediated reaction similar to LiNH2–LiH system. Sodium amide first decompose into Na metal and NH3, then generated NH3 reacted with added NaH to form NaNH2 and release H2. This process continues until the consumption of NaH, thus suppresses NH3 evolution to a great extent. The investigation has been extended further to the other metal hydrides and it is found that the addition of other metal hydride i.e. LiH, KH, MgH2, and CaH2 have also effectively suppressed the NH3 evolution. The detailed reaction mechanism has been elucidated for all the amide hydride systems. It is observed that the decomposition takes place through an intermediate step of double-cation amide formation.