瑞典斯德哥尔摩大学Nilsson, Anders团队报道了Haber–Bosch过程中表面化学的操作和探测。相关研究成果发表在2024年1月10日出版的《自然》。

通过Haber–Bosch工艺，在Fe和Ru催化剂上将N₂和H₂大规模转化为NH₃用于化肥生产，这被认为是二十世纪最重要的科学发明。能够进行转化的催化剂的活性组分被不同地认为是氧化物、氮化物、金属相或表面氮化物，并且速率限制步骤与N₂解离吸附的氮的反应以及NH₃解吸有关。这一观点范围反映了Haber–Bosch工艺在高温和高压下运行，而可能区分不同机械方案的表面敏感技术需要真空条件。因此，力学研究长期以来仅限于理论计算。

该文中，研究人员使用X射线光电子能谱来确定在高达1bar的压力和高达723K的温度下NH₃生产过程中Fe和Ru催化剂的表面组成。研究发现，尽管平坦的阶梯状Fe表面和Ru单晶表面都保持金属态，但后者几乎没有吸附质，而Fe催化剂保留了少量吸附的N，并在较低的温度下在阶梯状表面上形成高胺（NHx）覆盖率。这些观察结果表明，Ru的速率限制步骤总是N₂离解。相反，在Fe催化剂上，正如理论所预测的那样，吸附的N原子的氢化效率较低，以至于在温度降低后，限速步骤从N₂离解转变为表面物种的氢化。

附：英文原文

Title: Operando probing of the surface chemistry during the Haber–Bosch process

Author: Goodwin, Christopher M., Lmker, Patrick, Degerman, David, Davies, Bernadette, Shipilin, Mikhail, Garcia-Martinez, Fernando, Koroidov, Sergey, Katja Mathiesen, Jette, Rameshan, Raffael, Rodrigues, Gabriel L. S., Schlueter, Christoph, Amann, Peter, Nilsson, Anders

Issue&Volume: 2024-01-10

Abstract: The large-scale conversion of N2 and H2 into NH3 (refs.1,2) over Fe and Ru catalysts3 for fertilizer production occurs through the Haber–Bosch process, which has been considered the most important scientific invention of the twentieth century4. The active component of the catalyst enabling the conversion was variously considered to be the oxide5, nitride2, metallic phase or surface nitride6, and the rate-limiting step has been associated with N2 dissociation7,8,9, reaction of the adsorbed nitrogen10 and also NH3 desorption11. This range of views reflects that the Haber–Bosch process operates at high temperatures and pressures, whereas surface-sensitive techniques that might differentiate between different mechanistic proposals require vacuum conditions. Mechanistic studies have accordingly long been limited to theoretical calculations12. Here we use X-ray photoelectron spectroscopy—capable of revealing the chemical state of catalytic surfaces and recently adapted to operando investigations13 of methanol14 and Fischer–Tropsch synthesis15—to determine the surface composition of Fe and Ru catalysts during NH3 production at pressures up to 1bar and temperatures as high as 723K. We find that, although flat and stepped Fe surfaces and Ru single-crystal surfaces all remain metallic, the latter are almost adsorbate free, whereas Fe catalysts retain a small amount of adsorbed N and develop at lower temperatures high amine (NHx) coverages on the stepped surfaces. These observations indicate that the rate-limiting step on Ru is always N2 dissociation. On Fe catalysts, by contrast and as predicted by theory16, hydrogenation of adsorbed N atoms is less efficient to the extent that the rate-limiting step switches following temperature lowering from N2 dissociation to the hydrogenation of surface species.

DOI: 10.1038/s41586-023-06844-5

Source: https://www.nature.com/articles/s41586-023-06844-5