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., LiNH2, NaNH2 and KNH2, 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 LiNH2 > KNH2 >= NaNH2, either in term of NH3 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. (C) 2016 Elsevier B.V. All rights reserved