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Ammonia Synthesis at Low Pressure
Published on: August 23, 2017
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Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine-Titanium Complex
Laurence R Doyle1, Ashley J Wooles1, Lucy C Jenkins2
1School of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Angewandte Chemie (International Ed. in English)
|April 11, 2018
Summary
A titanium complex catalyzes the reduction of nitrogen (N2) to ammonia (NH3) under mild conditions. This breakthrough expands the range of early d-block metals capable of nitrogen fixation, offering new avenues for sustainable ammonia synthesis.
Area of Science:
- Homogeneous catalysis
- Inorganic chemistry
- Nitrogen fixation
Background:
- Catalytic ammonia synthesis from nitrogen (N2) is crucial for agriculture and industry.
- Previously, only mid- and late-d-block metals (Mo, Fe, Ru, Os, Co) were known to catalyze N2 reduction to ammonia (NH3) under homogeneous, abiological conditions.
- Developing catalysts using early d-block metals remains a significant challenge.
Purpose of the Study:
- To achieve catalytic reduction of N2 to NH3 using an early d-block metal complex.
- To investigate the mechanism of N2 reduction and protonolysis by a titanium complex.
- To expand the scope of metals capable of homogeneous nitrogen fixation.
Main Methods:
- Synthesis of titanium complexes [TiIV (TrenTMS )X] (X=Cl, I).
- Reduction of titanium complexes with KC8 to generate TiIII and TiIV species.
- Reaction of titanium complexes with N2, KC8, and a weak acid source ([R3 PH][I]) to produce NH3.
Main Results:
- Catalytic reduction of N2 to NH3 was achieved using a titanium complex, [TiIV (TrenTMS )X].
- The system produced up to 18 equivalents of NH3 with only trace hydrazine (N2H4) when using a weak acid source.
- Hydrazine was the dominant product when only a strong acid was present, suggesting a stepwise protonation mechanism.
Conclusions:
- Early d-block metals, specifically titanium, can catalyze the reduction of N2 to NH3 under homogeneous conditions.
- The study demonstrates a new pathway for nitrogen fixation, broadening the range of effective metal catalysts.
- Understanding the reaction mechanism involving protonation is key to optimizing ammonia yield and minimizing hydrazine formation.
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