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Peer-reviewedCC BY 4.0Inorganic Chemistry

Iron–Nitride Isomerization as a Deactivation Pathway in Ammonia Oxidation: A Computational Study of Sequential HAT Mechanisms

  • Luo Sheng1
  • Julianna Oláh1
  1. 1Department of Inorganic and Analytical Chemistry, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics, Műegyetem Rkp. 3, Budapest 1111, Hungary
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Abstract

Ammonia oxidation remains a kinetic bottleneck in utilizing ammonia as a carbon-free energy carrier. Iron-based complexes offer a cost-effective alternative to noble-metal catalysts, but use is hampered by low turnover numbers. Here, density functional theory is used to investigate the catalytic activity and deactivation pathways of Fe2+/Fe3+ complexes bearing cis-ammonia ligands. We confirm the ground-state electronic structures of these complexes, then establish an accurate SMD/DRACO protocolusing a van der Waals cavity with Gaussian-smeared surface charge discretizationthat predicts redox potentials with mean error below 0.013 V versus experiment. Thermodynamic evaluation of sequential hydrogen atom transfer (HAT) steps reveals a “peaked” bond dissociation free energy profile. Crucially, the exergonic third HAT step yields not the anticipated nitrido species, but a novel isomer in which the nitride inserts into the Fe–C bond. This Fe–N–C isomer is a deep thermodynamic sink, trapping the catalyst in an inactive state. A similarly low-energy Fe–N–C isomer exists for the imido intermediate but is kinetically inaccessible. These results indicate that Fe–C-containing complexes are unlikely to serve as efficient AO catalysts, as a high-valent iron center with a multiply bonded nitrogen ligand renders the Fe–C bond prone to alkyl migration, a facile deactivation pathway.

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Cite

BibTeXRIS
BibTeX
@article{sheng2026ironnitride,
  title = {{Iron–Nitride Isomerization as a Deactivation Pathway in Ammonia Oxidation: A Computational Study of Sequential HAT Mechanisms}},
  author = {Luo Sheng and Julianna Oláh},
  journal = {Inorganic Chemistry},
  year = {2026},
  month = oct,
  doi = {10.1021/acs.inorgchem.6c02749},
  url = {https://doi.org/10.1021/acs.inorgchem.6c02749},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Iron–Nitride Isomerization as a Deactivation Pathway in Ammonia Oxidation: A Computational Study of Sequential HAT Mechanisms
AU  - Luo Sheng
AU  - Julianna Oláh
PY  - 2026
DA  - 2026/10/13
JO  - Inorganic Chemistry
DO  - 10.1021/acs.inorgchem.6c02749
UR  - https://doi.org/10.1021/acs.inorgchem.6c02749
AB  - Ammonia oxidation remains a kinetic bottleneck in utilizing ammonia as a carbon-free energy carrier. Iron-based complexes offer a cost-effective alternative to noble-metal catalysts, but use is hampered by low turnover numbers. Here, density functional theory is used to investigate the catalytic activity and deactivation pathways of Fe2+/Fe3+ complexes bearing cis-ammonia ligands. We confirm the ground-state electronic structures of these complexes, then establish an accurate SMD/DRACO protocolusing a van der Waals cavity with Gaussian-smeared surface charge discretizationthat predicts redox potentials with mean error below 0.013 V versus experiment. Thermodynamic evaluation of sequential hydrogen atom transfer (HAT) steps reveals a “peaked” bond dissociation free energy profile. Crucially, the exergonic third HAT step yields not the anticipated nitrido species, but a novel isomer in which the nitride inserts into the Fe–C bond. This Fe–N–C isomer is a deep thermodynamic sink, trapping the catalyst in an inactive state. A similarly low-energy Fe–N–C isomer exists for the imido intermediate but is kinetically inaccessible. These results indicate that Fe–C-containing complexes are unlikely to serve as efficient AO catalysts, as a high-valent iron center with a multiply bonded nitrogen ligand renders the Fe–C bond prone to alkyl migration, a facile deactivation pathway.
SN  - 0020-1669
SN  - 1520-510X
ER  -