An industrial process for producing ammonia by reaction of nitrogen with hydrogen:N2+3H2 ⇌ 2NH3 The reaction is reversible and exothermic, so that a high yield of ammonia is favoured by low temperature (see Le Chatelier's principle). However, the rate of reaction would be too slow for equilibrium to be reached at normal temperatures, so an optimum temperature of about 450°C is used, with a catalyst of iron containing potassium and aluminium oxide promoters. The higher the pressure the greater the yield, although there are technical difficulties in using very high pressures. A pressure of about 250 atmospheres is commonly employed.
N2+3H2 ⇌ 2NH3
The process is of immense importance for the fixation of nitrogen for fertilizers. It was developed in 1908 by Fritz Haber and was developed for industrial use by Carl Bosch (1874–1940), hence the alternative name Haber-Bosch process. The nitrogen is obtained from liquid air. Formerly, the hydrogen was from water gas and the water-gas shift reaction (the Bosch process) but now the raw material (called synthesis gas) is obtained by steam reforming natural gas.