![]() ![]() ![]() ![]() Here we use X-ray photoelectron spectroscopy-capable of revealing the chemical state of catalytic surfaces and recently adapted to operando investigations 13 of methanol 14 and Fischer–Tropsch synthesis 15-to determine the surface composition of Fe and Ru catalysts during NH 3 production at pressures up to 1 bar and temperatures as high as 723 K. Mechanistic studies have accordingly long been limited to theoretical calculations 12. 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. The active component of the catalyst enabling the conversion was variously considered to be the oxide 5, nitride 2, metallic phase or surface nitride 6, and the rate-limiting step has been associated with N 2 dissociation 7, 8, 9, reaction of the adsorbed nitrogen 10 and also NH 3 desorption 11. 1, 2) over Fe and Ru catalysts 3 for fertilizer production occurs through the Haber–Bosch process, which has been considered the most important scientific invention of the twentieth century 4. The large-scale conversion of N 2 and H 2 into NH 3 (refs. ![]()
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