LiNH2 decomposes to NH3 rather than N2 and H2 because of a severe kinetic barrier in NHx (x = 1, 2) coupling. In the presence of Ru, however, a drastic enhancement in N2 and H2 formation is obtained, which enables the LiNH2-Ru composite to act as a highly active catalyst for NH3 decomposition. Experimental and theoretical investigations indicate that Li creates a NHx-rich environment and Ru mediates the electron transfer facilitating NHx coupling. A strategy in catalytic material design is thus proposed.