Ammonia (NH3) is pivotal to the fertilizer industry and one of the most commonly produced chemicals1. The direct use of atmospheric nitrogen (N2) had been challenging, owing to its large bond energy (945 kilojoules per mole)2,3, until the development of the Haber–Bosch process. Subsequently, many strategies have been explored to reduce the activation barrier of the N≡N bond and make the process more efficient. These include using alkali and alkaline earth metal oxides as promoters to boost the performance of traditional iron- and ruthenium-based catalysts4–6 via electron transfer from the promoters to the antibonding bonds of N2 through transition metals7,8. An electride support further lowers the activation barrier because its low work function and high electron density enhance electron transfer to transition metals9,10. This strategy has facilitated ammonia synthesis from N2 dissociation11 and enabled catalytic operation under mild conditions; however, it requires the use of ruthenium, which is expensive. Alternatively, it has been shown that nitrides containing surface nitrogen vacancies can activate N2 (refs. 12–15). Here we report that nickel-loaded lanthanum nitride (LaN) enables stable and highly efficient ammonia synthesis, owing to a dual-site mechanism that avoids commonly encountered scaling relations. Kinetic and isotope-labelling experiments, as well as density functional theory calculations, confirm that nitrogen vacancies are generated on LaN with low formation energy, and efficiently bind and activate N2. In addition, the nickel metal loaded onto the nitride dissociates H2. The use of distinct sites for activating the two reactants, and the synergy between them, results in the nickel-loaded LaN catalyst exhibiting an activity that far exceeds that of more conventional cobalt- and nickel-based catalysts, and that is comparable to that of ruthenium-based catalysts. Our results illustrate the potential of using vacancy sites in reaction cycles, and introduce a design concept for catalysts for ammonia synthesis, using naturally abundant elements. Ammonia is synthesized using a dual-site approach, whereby nitrogen vacancies on LaN activate N2, which then reacts with hydrogen atoms produced over the Ni metal to give ammonia.

中文翻译：

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空位 N2 活化在负载 Ni 的催化剂上合成氨

氨 (NH3) 是化肥行业的关键，也是最常生产的化学品之一。大气中氮 (N2) 的直接使用一直具有挑战性，因为它的键能很大（每摩尔 945 千焦耳）2,3，直到开发出 Haber-Bosch 过程。随后，人们探索了许多策略来降低 N≡N 键的激活势垒并提高该过程的效率。这些包括使用碱金属和碱土金属氧化物作为促进剂，通过电子从促进剂通过过渡金属转移到 N2 的反键键 7,8 来提高传统铁基和钌基催化剂的性能 4-6。电子载体进一步降低了激活势垒，因为其低功函数和高电子密度增强了向过渡金属的电子转移 9,10。该策略促进了从 N2 解离中合成氨，并在温和条件下实现催化操作；然而，它需要使用昂贵的钌。或者，已经表明含有表面氮空位的氮化物可以激活 N2（参考文献 12-15）。在这里，我们报告了负载镍的氮化镧 (LaN) 能够实现稳定和高效的氨合成，这是由于避免了常见的缩放关系的双位点机制。动力学和同位素标记实验以及密度泛函理论计算证实，在低形成能的 LaN 上产生氮空位，并有效地结合和激活 N2。此外，负载在氮化物上的镍金属会离解 H2。使用不同的位点来激活两种反应物，以及它们之间的协同作用，导致负载镍的 LaN 催化剂表现出的活性远远超过更传统的钴基和镍基催化剂，并且可与钌基催化剂相媲美。我们的结果说明了在反应循环中使用空位的潜力，并介绍了使用天然丰富元素合成氨的催化剂的设计概念。氨是使用双位点方法合成的，LaN 上的氮空位激活 N2，然后与 Ni 金属上产生的氢原子反应生成氨。我们的结果说明了在反应循环中使用空位的潜力，并介绍了使用天然丰富元素合成氨的催化剂的设计概念。氨是使用双位点方法合成的，LaN 上的氮空位激活 N2，然后与 Ni 金属上产生的氢原子反应生成氨。我们的结果说明了在反应循环中使用空位的潜力，并介绍了使用天然丰富元素合成氨的催化剂的设计概念。氨是使用双位点方法合成的，LaN 上的氮空位激活 N2，然后与 Ni 金属上产生的氢原子反应生成氨。