The reaction rate of MgH2 with NH3 is studied using a two-layered structure containing a top MgH2 layer and a bottom LiNH2 layer. Quantification of the effluent gas composition from the two-layered structure indicates substantial NH3 emission, while the X-ray diffraction analysis reveals little formation of the reaction products between MgH2 and NH3, In contrast, the study of the two-layered structure containing a top LiH layer and a bottom LiNH2 layer reveals that the reaction between LiH and NH3 is much faster than that between MgH2 and NH3. (C) 2008 Elsevier B.V. All rights reserved.