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Published on: December 6, 2021
Catalyst-Free Urea Synthesis from Methanol and Nitrogen via Radical-Mediated Redox Coupling on Aqueous Microdroplets
Kejian Li1, Bingxing Zhang1, Yuyang Pan1
1Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan48109, United States.
Abstract:
Urea is an indispensable nitrogen fertilizer and an important feedstock for chemical synthesis. Compared to the energy-intensive Bosch-Meiser process, photocatalytic redox coupling offers a sustainable approach toward urea synthesis. However, artificial photosynthesis remains dependent on catalyst compositions and structural properties. Here, by leveraging the photocatalyst-like redox capability of aqueous microdroplets, we present a catalyst-free, radical-mediated redox coupling strategy for urea synthesis from CH3OH and N2 under ambient conditions. The system achieved an optimized urea yield rate of approximately 10.8 μg h-1 with 2 vol % CH3OH in a pure N2 atmosphere, which was comparable to some values for urea photosynthesis. Comprehensive experimental investigations and theoretical calculations elucidated a thermodynamically favorable redox coupling pathway, in which ·CHO generated from ·OH-induced CH3OH oxidation and ·NH2 produced via ·H-triggered N2 reduction played a pivotal role in urea formation. This study offers a promising platform for the green synthesis of organonitrogen compounds and provides insights into harnessing the redox chemistry of aqueous microdroplets for chemical production.
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