Ammonia as an energy carrier
Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Abstract: With a high hydrogen content (17.6 wt.%), high energy density (4 kWh kg-1), facile storage and transportation, NH3 has been regarded as a potential energy carrier. The key issue for NH3 synthesis and decomposition is the development of non-noble metal based, highly active and stable catalysts that can be operated under mild condition. This would require a catalyst to have strong activation (small Eact) to N2 but relatively weak binding (small adsorption energy DE) to -NHx (x = 0-3) intermediates. Unfortunately, such a scenario can hardly be attained in transition metal (TM) catalyzed processes.
With the understanding of interactions of hydrides/imides of alkali and alkaline earth metals (AM for short) with 3d metals and their nitrides, the catalyst systems, i. e., AMNH-3d transition metals for NH3 decomposition and AMH-3d transition metals for NH3 synthesis, were developed. The unique chemistry among transition metals, alkali/alkaline earth, N and H creates an energy-favorable pathway allowing NH3 synthesis/decomposition under mild conditions, i.e., detectable NH3 formation rate was obtained at 150 °C over the Mn-, Fe- and Co-LiH composite catalysts, respectively.The characterization of intermediate phases and surface clusters of catalysts provides interesting information that helps the elucidation of the step-wise reaction pathway and the interpretation of catalytic mechanism.