Surface Hydrogen Dominates Ammonia Synthesis Catalyzed by Electride

August 4, 2020
Surface Hydrogen Dominates Ammonia Synthesis Catalyzed by Electride
Reaction of N2 and H2 to form NH3. The reaction is catalyzed by Ru particles atop the C12A7 electride. The encaged H atoms do not play a significant role in the reaction.

Scientific Achievement

It is shown that the reactive species involved in ammonia synthesis over Ru/C12A7 electride catalysts is surface adsorbed hydrogen, not encaged hydrogen.

Significance and Impact

The results provide a better understanding of the mechanism of ammonia synthesis and N2 activation using electride catalysts, potentially leading to more efficient catalysis of many difficult hydrogenation reactions.

Research Details

  • Ru particles supported on a calcium aluminum oxide (C12A7) electride activate N2 to combine with H producing NH3.
  • In situ neutron diffraction and spectroscopy combined with density functional theory calculations show the presence of stable encaged hydrides; they do not actively participate in the reaction. 
  • In contrast to the currently accepted view of the importance of encaged hydrogen, this shows that surface H plays a major role.
  • Steady state isotopic transient kinetic analysis (SSITKA) was used to further characterize the reaction mechanism. 

“Nature of Reactive Hydrogen for Ammonia Synthesis over a Ru/C12A7 Electride Catalyst”
James Kammert1, Jisue Moon1,2, Yongqiang Cheng3, Luke Daemen3, Stephan Irle1, Victor Fung2, Jue Liu3, Katharine Page3, Xiaohan Ma2,4, Vincent Phaneuf4, Jianhua Tong4, Anibal Ramirez-Cuesta3, Zili Wu1
Journal of the American Chemical Society, 142, 7655 (2020).