Why did the ammonia synthesis catalyst develop from iron cobalt to molten iron?

Since the late 1980s, ammonia synthesis technology has continued to advance, and larger-scale devices have been built. The energy consumption per ton of ammonia production has also dropped to 28 GJ. An iron-cobalt catalyst was introduced into ICI's LCA process, and the operating pressure of the synthesized internals in the LCA process was 8 MPa. In 1992, the first iron-free ammonia synthesis catalyst was used by Kellogg Company (now KBR Company) in its KAAP (Kellogg Advanced Ammonia Synthesis Process) process. The ruthenium catalyst uses a graphitized carbon as a support. Its activity is said to be 10 to 20 times that of traditional molten iron catalysts. This catalyst has different kinetic characteristics during the reaction and the internals can operate at sub-stoichiometric hydrogen/nitrogen ratios and pressures of approximately 9 MPa.

Since the work of Haber and Mittasch, few highly active catalysts have been found, so molten iron catalysts are still widely used catalysts. It has high intrinsic activity, long service life and high density. In addition to these advantages, its most recognized advantage is its low price.