Haber process

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The Haber Process is a vital industrial process which produces "fixed" nitrogen from atmospheric nitrogen, allowing the production of fertilizers and other nitrogen-based compounds. Hydrogen and nitrogen are run over a heated catalyst at pressure and bond to produce ammonia.


Atmospheric pressure

plain iron oxide

Simple iron oxide can be used as a catalyst.

  • The catalyst is purified Fe3O4 (magnetite) with the oxygen removed by exposure to hydrogen at high temperatures. This provides the appropriate porosity.
  • The reaction takes place at 440-450°C and atmospheric pressure
  • Yield is 0.25% ammonia
  • Scaling: 100-200cc of gas per minute over 1kg of catalyst

See "The Direct Synthesis of Ammonia"[1] for a description of producing the catalyst.


Apparently Tungsten can also be used as a catalyst at about 600°C and atmospheric pressure.[2]


High Pressure


  • Yield: 4-5%

  • The catalyst is doped purified iron Fe + CaO + K2O + SiO2 + Al3O4
  • The reaction takes place at 300–550 °C and 50–250 atmospheres.
  • Yield is over 90%

The gases are refrigerated, the ammonia removed as a liquid, and the process is repeated. Iron oxide can be used in place of iron, because it will be rapidly reduced by the hydrogen gas to water and pure iron.


  • At the extremely high temperatures and pressures involved, rupture and explosion of the reaction vessel is a serious concern.

See Also