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Transition and Alkali Metal Complex Ternary Amides for Ammonia Synthesis and Decomposition



Hujun Cao, Jianping Guo, Fei Chang, Claudio Pistidda, Wei Zhou, Xilun Zhang, Antonio Santoru, Hui Wu, Norbert Schell, Rainer Niewa, Ping Chen, Thomas Klassen, Martin Dornheim


A new complex ternary amide Rb2[Mn(NHd2)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 has been shown to effectively break the scaling relations and achieve ammonia synthesis under mild conditions. Rb2[MnNh2)4] can be facilely synthesized by mechanochemical reaction at room temperature. It exhibits two temperature-dependent polymorphs i.e. low-temperature orthorhombic and high-temperature monoclinic structures. Rb2[Mn(NH2)4] decomposes to N2, H2, NH3N2, and RbNH2 under inert atmosphere; whereas releases NH3 at a temperature as lows 80 °c under H2 atmosphere. Those unique behaviors enable Rb2[Mn(NHd2^)4] and its analogue K2[Mn(NH2)4] as excellent catalytic materials for ammonia decomposition and synthesis. Our 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 discloses 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/Nd2 and NH3 correlates closely with the catalytic performance.
Chemistry-A European Journal


Ammonia Synthesis and decomposition, Amide, X-ray diffraction, Crystal structure


Cao, H. , Guo, J. , Chang, F. , Pistidda, C. , Zhou, W. , Zhang, X. , Santoru, A. , Wu, H. , Schell, N. , Niewa, R. , Chen, P. , Klassen, T. and Dornheim, M. (2017), Transition and Alkali Metal Complex Ternary Amides for Ammonia Synthesis and Decomposition, Chemistry-A European Journal, [online], (Accessed July 25, 2024)


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Created July 20, 2017, Updated October 12, 2021