Abstract
Synthetic Fe nitrogenases are promising catalysts for atmospheric pressure ammonia synthesis. However, their catalytic efficiency is severely limited by the accompanying hydrogen evolution reaction...
Highlights
Conversion of atmospheric dinitrogen (N2) to ammonia (NH3) and other nitrogenous compounds is an essential transformation for the Earth’s biosphere
Gathering the previously reported results that (i) the regeneration of the catalyst (SiP3Fe-NH3+/0→ SiP3Fe+/0→ SiP3Fe−N2+/0/−) determines the overall N2RR rate,[24] (ii) SiP3Fe−N2 is the most abundant N2RR intermediate during a typical catalytic run,[20] (iii) SiP3Fe−N2 can be converted to the dihydrogen complex SiP3Fe−H2 under H2 atmosphere[35] through SiP3Fe intermediate, and (iv) SiP3Fe−H2 is thermodynamically slightly more stable than SiP3Fe−N2 in solvent phase,[35] we came to the conclusion that the first hydride formed as a side product of N2RR is SiP3Fe− H2
We show that the formation of SiP3Fe−H2 from SiP3Fe, made possible under N2 atmosphere by the constant presence of a small amount of spontaneously formed H2 (Figure 2, arrow a), can open the way to catalytic hydrogen evolution and the accumulation of the resting state SiP3Fe(H)-N2 (Figure 2, right)
Summary
Conversion of atmospheric dinitrogen (N2) to ammonia (NH3) and other nitrogenous compounds is an essential transformation for the Earth’s biosphere. Industrial N2-to-NH3 conversion is carried out through the Haber-Bosch process, which requires harsh conditions (typically 500 °C temperature and 200 bar pressure).[5] Last year, nearly 180 million tons of ammonia were synthesized in this manner, the majority of which went to fertilizer production.[6] The environmental load is striking: approximately 1.2% of global CO2 emission can be traced back to Haber-Bosch plants.[7] Considering the increasing ammonia demand, developing a novel, environmentally friendly ammonia synthesis concept is more and more urgent. Intensive research has been conducted in recent years on possible Haber-Bosch alternatives such as electrochemical[8−10] and photochemical[11,12] dinitrogen splitting
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