Abstract:

Ammonia is a primary chemical for the synthesis of basic organic chemicals and fertilizers. The Haber-Bosch process is employed in industry to synthesize ammonia, which not only uses a lot of energy but also has a low conversion of only 10% to 15%. Electrochemical ammonia synthesis has the advantages of clean production and gentle reaction conditions as compared to the Haber-Bosch process. The features and benefits of electrochemical ammonia synthesis using nitrogen, nitrate, and nitric oxide as nitrogen sources are discussed, and the reaction mechanisms are studied based on the properties of these nitrogen sources. Different hydrogen supply schemes and hydrogenation methods are described and evaluated based on the diverse nitrogen sources, and the research development of reaction catalysts is systematically summarized. Problems of the electrolytic systems such as poor solubility of nitrogen in water, nitrates with too many valence states, excessive intermediates, instable nitrogen oxide system, and competing hydrogen evolution reaction, are discussed in detail. Some suggestions for them are proposed which include altering the composition or structure of the hydrogen source to prevent hydrogen evolution, developing new catalyst systems with high active sites and oxygen vacancies to improve reaction selectivity, and developing non-aqueous electrolyte systems to improve reaction rate and synthesis efficiency.

Key words: electrochemistry, synthesis, catalyst, reduction, electrolytes, ammonia

摘要：

氨是基本有机化学工业及化肥生产的主要原料。工业上利用哈伯法合成氨，该工艺不仅耗能大且转化率仅有10%~15%。相比传统合成氨工艺，电化学合成氨有着清洁环保、反应条件温和等优点。本文综述了氮气、硝酸盐及一氧化氮作为氮源时电化学合成氨的特点与优势，并依据不同氮源的特点，剖析了电化学合成氨的反应机制。文中针对不同的氮源，分析总结了多种氢源方案与氢化机理，系统地概述了反应催化剂的研究进展。分别讨论了氮气在水中溶解度较差、硝酸盐在反应过程中元素价态跨度大而生成诸多中间产物、氮氧化物体系不稳定、电解体系中存在析氢竞争反应等问题，提出了通过改变氢源的组成或结构抑制析氢反应、开发新型高活性位点及氧空位的催化剂体系强化反应选择性、研制非水电解质体系提高反应速率及合成效率等解决思路。

关键词: 电化学, 合成, 催化剂, 还原, 电解质, 氨