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    CO2和不同氮源电催化合成尿素机理研究进展

    Advances in Mechanisms of Electrocatalytic Urea Synthesis from CO2 and Different Nitrogen Sources

    • 摘要: 在全球碳减排和可持续发展的背景下,CO2资源化利用成为当前研究热点之一。在各种转化方法中,电催化技术可将CO2转化为高附加值产品,不仅能够缓解环境保护压力,提高碳的资源利用率,还具有反应条件温和、能耗低和二次污染小的优点。尤其在尿素合成工艺上,相比于传统高温高压催化合成尿素的高能耗Haber-Bosch工艺,电催化C—N偶联反应合成尿素在常温常压下即可利用CO2和氮源(N2、\mathrmNO_3^- / \mathrmNO_2^- 、NO等)实现尿素的绿色合成,既实现了CO2的资源化利用,又有效解决了尿素合成过程中的高能耗难题。由于该反应过程涉及多步质子—电子转移,其反应机制因氮源特性的不同而有所差异。将电催化C—N偶联合成尿素的方法按氮源类型分为N2、\mathrmNO_3^- / \mathrmNO_2^- 和NO 3类,聚焦反应路径的多样性、关键中间体的生成与转化过程,系统总结了其反应机理及研究进展,并指出了不同氮源的最优反应路径。最后,总结了当前电催化C—N偶联反应面临的关键挑战,并对未来发展方向进行了展望,旨在为电催化C—N偶联的深入研究提供参考。

       

      Abstract: In the context of global carbon emission reduction and sustainable development, CO2 resource utilization has emerged as a focal point of intensive research. Among various transformation strategies, electrocatalytic CO2 conversion into high-value products offers distinct advantages, including mild reaction conditions, low energy consumption, and minimal secondary pollution, thereby alleviating environmental pressures. In particular, for urea synthesis, electrocatalytic C–N coupling offers a greener alternative to the traditional Haber-Bosch process, which requires high temperatures and pressures, by enabling ambient-condition production using CO2 and various nitrogen sources (e.g., N2, \mathrmNO_3^- / \mathrmNO_2^- , NO). This approach facilitates CO2 resource utilization and effectively addresses the challenge of high energy consumption in conventional urea synthesis. Since this process involves multiple proton-electron transfer steps, the reaction mechanism varies significantly depending on the nitrogen source. For N2-based systems, the fundamental challenge lies in the efficient activation and cleavage of the N≡N triple bond, where the generation of *N=N intermediates critically determines the efficiency of subsequent C–N coupling. The coupling-hydrogenation pathway initiated by the formation of the *NCON intermediate exhibits favorable thermodynamics and a relatively low energy barrier for the initial C–N bond formation. In case of \mathrmNO_3^- / \mathrmNO_2^-, combined experimental and theoretical studies have identified multiple potential pathways. Among these, the coupling of *NH2 with *CO to form *CONH2 has been demonstrated as the most effective route, successfully facilitating urea formation while suppressing competing pathways leading to NH3 or N2. Although current research on the NO-mediated reaction pathways remains limited, their application potential is promising. This pathway is expected to achieve higher Faradaic efficiency due to its lower N–O bond dissociation energy and a reduction potential compatible with that of the CO2 reduction reaction. However, it faces a significant limitation: NO exhibits oxidative instability in aqueous electrolytes and is consumed through homogeneous oxidation reactions. Addressing this issue requires sophisticated reactor design and operational strategies. Furthermore, all nitrogen source systems face a fundamental challenge regarding the precise control of competitive reduction processes. The hydrogen evolution reaction limits practical efficiency, while the over-reduction of nitrogen-containing intermediates to ammonia significantly compromises urea selectivity. This review categorizes electrocatalytic C–N coupling methods for urea synthesis into three types based on nitrogen sources (N2, \mathrmNO_3^- / \mathrmNO_2^- , and NO) and systematically summarizes the corresponding reaction mechanisms and recent research progress. It focuses on the diversity of reaction pathways, the generation and transformation of key intermediates, and the identification of optimal reaction pathways for different nitrogen sources. Finally, this review outlines the key challenges currently facing electrocatalytic C–N coupling and provides perspectives on future research directions, aiming to offer theoretical guidance for advancing research in this field.

       

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