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

Published

July 21, 2017

Author(s)

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

Abstract

A new complex ternary amide Rb_2[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 Rb_2[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)_xH_1-x are likely the active sites. The chemistry of Rb₂/K₂[MN(NH₂)_x] and Rb/K(NH₂)_xH_1-x with H_2/Nd2 and NH₃ correlates closely with the catalytic performance.

Citation

Chemistry-A European Journal

Volume

23

Issue

41

Pub Type

Journals

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Keywords

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

Citation

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], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=923810 (Accessed April 20, 2024)