Influence of alkali metal amides on the catalytic activity of manganese nitride for ammonia decomposition

Abstract Strong promoting effect of alkali metal amides, i.e., LiNH 2 , NaNH 2 and KNH 2, on the catalytic activity of manganese nitride (MnN) for ammonia decomposition has been demonstrated, which is evidenced by ca. 100 K drop in onset temperature and by ca. 50–60 kJ mol −1 reduction in apparent activation energy as compared with the neat MnN. The order of promotion capability of alkali metal amides can be ranked as LiNH 2  > KNH 2  ≥ NaNH 2 , either in term of NH 3 conversion rate or turnover frequency (TOF), which is distinctly different from that of conventional alkali metal oxides or hydroxides, i.e., K > Na > Li. This phenomenon suggests that the promoting mechanism of alkalis depends on their chemical forms. When alkalis are in the form of amide or imide, they may function as co-catalysts by participating in the catalytic circle directly rather than by executing electronic promotion influence on transition metals.