Kinetic aspects of ammonia synthesis

To accelerate the approach to equilibrium, the oxide catalysis employed are based on Group 7 metals, exclusively iron in practice (Fe,0 i. A number of promoters help to improve performance, including Al202 which increases the active surface area of the particles, and K20. SiO,. MeO. CaO etc, which improve stability, and increase activity and resistance to poisoning. Systems currently under development make use of ruthenium 

I a) In its initial oxide form, which must then be reduced in the unit itself by the mixture N, + 3H, this means a conditioning interval lasting from 4 to 10 days. 

Standard catalyst systems are oniy active above 400°C (Fig. 1.16). They are especially stable provided the following requirements are observed  

The basic equation most widely accepted to express the kinetics of ammonia synthesis is that of Temkin and Pyzhev (1940). It expresses the reaction rate as a function of the partial pressures of the reactants and products  

Accurate calculations must consider the activity of the different components of the mixture and the presence of the catalyst. One of the many derivative equations which account for the influence of these factors is that of Dyson and Simon (1968), which uses the following expression  

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