%0 journal article
%@ 0947-6539
%A Cao, H., Guo, J., Chang, F., Pistidda, C., Zhou, W., Zhang, X., Santoru, A., Wu, H., Schell, N., Niewa, R., Chen, P., Klassen, T., Dornheim, M.

%D 2017
%J Chemistry - A European Journal
%N 41
%P 9766-9771 
%R doi:10.1002/chem.201702728
%T Transition and Alkali Metal Complex Ternary Amides for Ammonia Synthesis and Decomposition
%U https://doi.org/10.1002/chem.201702728
41 
%X A new complex ternary amide, Rb2[Mn(NH2)4], which simultaneously contains both transition and alkali metal catalytic sites, is developed. This is in line with the recently reported TM-LiH composite catalysts, which have been shown to effectively break the scaling relations and achieve ammonia synthesis under mild conditions. Rb2[Mn(NH2)4] can be facilely synthesized by mechanochemical reaction at room temperature. It exhibits two temperature-dependent polymorphs, that is, a low-temperature orthorhombic and a high-temperature monoclinic structure. Rb2[Mn(NH2)4] decomposes to N2, H2, NH3, Mn3N2, and RbNH2 under inert atmosphere; whereas it releases NH3 at a temperature as low as 80 °C under H2 atmosphere. Those unique behaviors enable Rb2[Mn(NH2)4], and its analogue K2[Mn(NH2)4], to be excellent catalytic materials for ammonia decomposition and synthesis. Experimental results show both ammonia decomposition onset temperatures and conversion rates over Rb2[Mn(NH2)4] and K2[Mn(NH2)4] are similar to those of noble metal Ru-based catalysts. More importantly, these ternary amides exhibit superior capabilities in catalyzing NH3 synthesis, which are more than 3 orders of magnitude higher than that of Mn nitride and twice of that of Ru/MgO. The in situ SR-PXD measurement shows that manganese nitride, synergistic with Rb/KH or Rb/K(NH2)xH1−x, are likely the active sites. The chemistry of Rb2/K2[Mn(NH2)x] and Rb/K(NH2)xH1−x with H2/N2 and NH3 correlates closely with the catalytic performance.