Promotors And Inhibitors

A catalyst is any substance (or material), when it is added in the reaction then due to their presence in the reaction, the speed of the reaction is increased or decreased. This reaction in which a catalyst is present, is called as catalytic reaction. And this phenomena is called as Catalysis. 
In this article, we will learn about Promotors and Accelerators catalyst with the help of various examples.

Types Of Catalyst Based On Activity 
Based on the activity of catalyst, there are two another types of substance exists and these are;
(1) Promotors And Accelerator
(2) Inhibition or Inhibitors
Let us see both of them one by one;
Promotors And Accelerators
Promotors and accelerators are those substances which increases the activity of catalyst sothat the reaction rate increases and reactants can be quickly converted into products.
Generally, promotors improve the activity, selectivity and stabilize the catalytic agent (catalyst) and present in low amount and also increases the available surface area of catalysts in order to increase the activity. 

Let's have a look some examples; 
(a) In Haber's process, molybdenum (Mo) or a mixture of potassium and aluminium oxides act as promoters to increase the activity of 'iron (Fe)' catalyst.
                N₂ + 3H₂ (Fe+Mo) ➝ 2NH₂
(b)Manufacturing of methyl alcohol from water gas [CO+H₂] , 'Cr₂O₃' is used as promotor with zinc oxide as catalyst.
      [CO+H₂] + H₂ (ZnO+ Cr₂O₃) ➝ CH₃OH

Catalyst Poison Or Inhibitors
Catalytic poisons and inhibitors are substances that reduce the activity and effectiveness of the catalyst, thereby reducing the rate of the reaction and And reactants take longer time to convert to products. 
Let's have a look some examples; 
(a) In the manufacture of sulfur trioxide from sulfur dioxide in presence of platinum catalyst, use As₂O₃ as catalyst poison or inhibitor.
(b) The platinum catalyst used in the oxidation of hydrogen is poisoned by CO.
(c) The activity of iron catalyst is destroyed by the presence of Hydrogen sulfide (H₂S) or CO in the synthesis of ammonia by Haber's process. 


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