Synthesis of urea from CO 2 and N 2 fixation under mild conditions using polarized hydroxyapatite as a catalyst

Polarized hydroxyapatite (p-HAp) has been used as a catalyst for the synthesis of urea coupling N 2 , CO 2 and water under mild reaction conditions when compared to classical nitrogen fixation reactions, such as the Haber–Bosch process. The reaction of 3 bar of N 2 and 3 bar of CO 2 under UV illumin...

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Bibliographic Details
Published in:Sustainable energy & fuels 2024-03, Vol.8 (7), p.1473-1482
Main Authors: Sans, Jordi, Arnau, Marc, Bosque, Ricard, Turon, Pau, Alemán, Carlos
Format: Article
Language:English
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Summary:Polarized hydroxyapatite (p-HAp) has been used as a catalyst for the synthesis of urea coupling N 2 , CO 2 and water under mild reaction conditions when compared to classical nitrogen fixation reactions, such as the Haber–Bosch process. The reaction of 3 bar of N 2 and 3 bar of CO 2 under UV illumination at 120 °C (for 48 h) results in a urea yield of 1.5 ± 0.1 mmol per gram of catalyst (g c ) with a selectivity close to 80%, whereas the reaction is not successful without UV irradiation. However, the addition of small amounts of NO (314 ppm) produces 15.2 ± 0.6 and 4.6 ± 0.4 mmol g c −1 with and without UV illumination, respectively, with the selectivity in both cases being close to 100%. As nitrogen fixation without UV irradiation using p-HAp as a catalyst is a challenge, studies with NO have been conducted varying the reaction conditions (time, pressure and temperature). The results suggest a mechanism based on the production of NH 4 + through the oxidation of N 2 .
ISSN:2398-4902
2398-4902
DOI:10.1039/D3SE01704D