Poisons and the poisoning phenomena for ammonia synthesis catalysts

4 Poisons and the poisoning phenomena for ammonia synthesis catalysts 

In the process of ammonia synthesis, the common toxic compounds that lead to poisoning and loss of catalytic activity are oxygen and oxygenous compounds (CO, CO2, H2O), and non-metallic compounds such as sulfur, phosphorus, arsenic and chlorine, etc. Toxic metals may be present in the catalysts themselves, while metallic compounds are rarely present in the reaction gas. Oxygen and oxygenous compounds are reversible poisons which cause temporary poisoning but sulfur, phosphorus, arsenic, chlorine and their compounds are irreversible poisons which cause permanent poisoning. 

Pressure/M Pa Contents of water vapor/(mg-L ) Apparent activation energy/(kJ-mol ) Temperature range/° C 

The active a-Fe in an ammonia synthesis catalyst is easily poisoned by water. Research shows that the effect of water vapor on the catalytic activity is still reversible when the water vapor content is as high as 27mol9c or more but the activity cannot be restored when the content of water vapor reaches 42mol%. 

If the content of water vapor is too high, the water-soluble potassium in the catalyst will dissolve, leading to mal-distribution of potassium, and the loss of activity cannot be restored. 

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