Lithium Imide Synergy with 3d Transition-Metal Nitrides Leading to Unprecedented Catalytic Activities for Ammonia Decomposition

Alkali metals have been widely employed as catalyst promoters; however, the promoting mechanism remains essentially unclear. Li, when in the imide form, is shown to synergize with 3d transition metals or their nitrides TM(N) spreading from Ti to Cu, leading to universal and unprecedentedly high catalytic activities in NH3 decomposition, among which Li2NHMnN has an activity superior to that of the highly active Ru/carbon nanotube catalyst. The catalysis is fulfilled via the two-step cycle comprising: 1)the reaction of Li2NH and 3d TM(N) to form ternary nitride of LiTMN and H-2, and 2)the ammoniation of LiTMN to Li2NH, TM(N) and N-2 resulting in the neat reaction of 2NH(3)N(2)+3H(2). Li2NH, as an NH3 transmitting agent, favors the formation of higher N-content intermediate (LiTMN), where Li executes inductive effect to stabilize the TMN bonding and thus alters the reaction energetics.