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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.
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
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