Alkali metal control over N-N cleavage in iron complexes
Katarzyna Grubel1, William W Brennessel, Brandon Q Mercado
1Department of Chemistry, Yale University , New Haven, Connecticut 06511, United States.
Journal of the American Chemical Society
|November 21, 2014
Summary
This study reveals that alkali metal cation size, not reducing power, controls nitrogen (N2) activation on iron (Fe) surfaces. At least three Fe atoms are needed to cleave the N2 triple bond.
Area of Science:
- Catalysis
- Surface Chemistry
- Inorganic Chemistry
Background:
- Nitrogen (N2) cleavage on potassium (K)-promoted iron (Fe) surfaces is crucial for the Haber-Bosch process.
- Ambiguity exists regarding the number of Fe atoms involved in N2 cleavage and K's promoting mechanism.
Purpose of the Study:
- To investigate a molecular Fe system for N2 reduction.
- To explore the role of different alkali metals (Na, K, Rb, Cs) as reductants in N2 activation.
- To elucidate the factors governing N2 cleavage and Fe-nitride formation.
Main Methods:
- Synthesis and characterization of molecular Fe complexes with N2.
- Reactions involving various alkali metals as reductants.
- Structural analysis of resulting Fe-N2 and Fe-nitride cores.
Main Results:
- Formation of novel Fe-N2 and Fe-nitride cores observed.
- N2 bond cleavage was not achieved solely by increasing reductant equivalents, challenging the reducing power hypothesis.
- Alkali metal cation size was found to influence the number of Fe atoms interacting with N2.
Conclusions:
- The size of the alkali metal cation plays a critical role in controlling N2 activation by modulating Fe atom accessibility.
- N2 cleavage requires the simultaneous approach of at least three low-valent Fe atoms to a single N2 molecule.
- This finding offers new insights into the mechanism of N2 reduction and catalyst design for nitrogen fixation.
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