What is the role of each component of ammonia synthesis catalyst?

The ammonia synthesis catalyst is based on molten iron, the main component before reduction is iron tetraoxide, which is magnetic, and co-catalysts such as Al₂O₃ and K₂O are added. In order to reduce the temperature and pressure, cobalt and rare earth elements are added to the catalyst.

The active component Fe₃O₄ is reduced to produce α-Fe, and the function of the active center is to chemisorb nitrogen molecules to weaken the triple bond between nitrogen and nitrogen to facilitate the formation of ammonia by hydrogenation.

Al₂O₃ is a structural co-catalyst, which is uniformly dispersed in the α-Fe lattice and inter-lattice, which can increase the specific surface of the catalyst and prevent the iron microcrystals from growing up after reduction, so as to improve the activity and stability of the catalyst.

K₂O is an electron-type co-catalyst, which can promote the electron transfer process and facilitate the adsorption and activation of nitrogen molecules, as well as the desorption of the product ammonia.

Although the addition of SiO₂ has weakened the alkaline effect of the catalyst, it plays the role of stabilizing the iron grains and increases the toxicity and heat resistance of the catalyst.

The addition of MgO can improve the heat resistance and sulfur resistance, and the addition of CaO can play the role of fluxing, so that each component of the catalyst is easy to melt and form a uniform distribution of highly active state.