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Discovery and Development of Catalyst

The starting point is magnetite, Fe3O4, to which promoters are added, typically:

  • About 1% potassium as a chemical promoter (the added potassium covers about one third of the catalyst surface)
  • About 3% alumina as a structural promoter
The Role of Promoters
Question

Why are group 1 metals good chemical promoters for the Haber process?

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The conditions of the reactor mean that magnetite is reduced to give iron catalyst particles with many small pores. The pores are important in exposing the surfaces of iron crystals. Structural promoters prevent the iron from changing, in the heat of the reactor, into a non-porous mass with a much lower surface area,
Chemical promoters increase the activity of the catalyst, in this case by increasing the electron density of the iron, making it more likely to bond to nitrogen.
picture: a catalyst
Catalyst particles can be up to 30 mm diameter, with many pores about 8 nm in diameter

The surface area is around 15m2/g.

The faces of iron crystals are not identical because the atoms can pack together in different ways, and the most active face is 400 times more active at 500oC than the least active face. But even this face has low activity without the chemical promoters.
picture: iron crystal
What Do These Promoters Do?