Ammonia synthesis at high pressure

It should be stressed that not only is there a pressure gap between the UHV studies and the high-pressure measurements, but also a material gap. The UHV studies use carefully cleaned iron metal in the form of single crystals as the catalyst. On the other hand, elemental polycrystalline iron without surface purification does not catalyze ammonia synthesis at high pressure (1 bar), as has been described in Section 2.2. This may be rationalized in terms of the extreme sensitivity of the... 

Calculations relating adsorption properties measured on clean single-crystal surfaces at (very) low pressure with actual rates of ammonia synthesis at high pressures described later in this chapter require some measurement of the free metallic iron surface area of the reduced synthesis catalysts. The free metallic iron surface area is generally calculated from the extent of chemisorption of carbon monoxide. In view of the importance of the free metallic iron surface area in work dealing with the mechanism of ammonia synthesis, it is important to review the adsorption of carbon monoxide on different iron surfaces reduced under different conditions. 

The large amount of available data on nitrogen and hydrogen adsorption on clean iron surfaces prompted some research groups to try to generate kinetic data for ammonia synthesis at high pressure and temperature, starting from adsorption data obtained under UHV conditions. 

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