What are heterogenous catalysis? Give examples.

Question

When the catalyst exists in a different phase than that of reactants, it is said to be heterogeneous catalyst, and the catalysis is called heterogeneous catalysis. For example, SO₂ can be oxidized to SO₃ using vanadium pentaoxide (V₂O₅) or platinum (Pt) as catalyst.

 

Here, V₂O₅ is solid, while the reaction reactants are gaseous. This reaction is employed during the manufacture of sulphuric acid by Contact Process.

In heterogeneous catalysis, the catalyst is generally solid while the reactants are gases and the reaction starts from the surface of the solid catalyst. That, is why heterogeneous catalysis is also is also called surface catalysis.

Some more examples of industrially important heterogeneous catalytic reactions are:
    
Manufacture of NH₃ from N₂ and H₂ by Haber's process, using iron as catalyst.

 
    
Manufacture of CH₃OH from CO and H₂ using (a mixture of Copper, ZnO and Cr₂O₃) as catalyst.

 
    
Oxidation of NH₃ with O₂ using Pt as catalyst in Ostwald process.

 
    
Oxidation of polluting gases such as CO and NO into non-toxic gases by the catalytic converter in the car's exhaust system. The catalytic converter consists of a mixture of transition metals such as platinum, palladium and rhodium. These catalysts oxidize CO and unburnt hydrocarbons to CO₂ and H₂O and reduce oxides of nitrogen to N₂.

 
    
Hydrogenation of oils to form vegetable ghee using finely divided nickel as catalyst.

Polymerization of ethylene using TiCl₃ and trialkyl aluminium (Ziegler-Natta method) as catalyst.