Promoters and catalyst poison

Promoters and catalyst poison

In a catalysed reaction the presence of a certain substance increases the activity of a catalyst. Such a substance is called a promoter.

For example in the Haber’s process of manufacture of ammonia, the activity of the iron catalyst is increased by the presence of molybdenum. Hence molybdenum is called a promoter. In the same way Al₂O₃ can also be used as a promoter to increase the activity of the iron catalyst.

On the other hand, certain substances when added to a catalysed reaction decreases or completely destroys the activity of catalyst and they are often known as catalytic poisons.

Few examples,

In the reaction, 2SO ₂ +O ₂ → 2SO₃ with a Pt catalyst, the poison is As₂ O₃

i.e., As₂ O₃ destroys the activity of Pt . As₂ O₃ blocks the activity of the catalyst.

So, the activity is lost.

In the Haber’s process of the manufacture of ammonia, the Fe catalyst is poisoned by the presence of H₂S .

In the reaction, 2H₂ +O₂ → 2H₂O ,

CO acts as a catalytic poison for Pt – catalyst