Engineering Chemistry S Datta

CATALYST 139
Heterogeneous Catalysis
In this type of catalytic reactions, the catalyst forms a separate phase, usually a finely
divided solid either as such or supported on an inert solid such as asbestos or gas (fluidised
bed). This is usually termed contact catalysis. This type of catalysis has a great technical
importance.
Examples of Heterogeneous Catalysis:
(a)
Pt( s)
2SO 2
(g) + O 2
(g) ⎯⎯→ 2SO 3
(g) (Pt-Catalyst)
(b)
Fe( s)
N 2
(g) + 3H 2
(g) ⎯⎯→ 2NH 3
(g) (Fe-Catalyst)
Activation energy and Catalysis reaction
According to collision theory: the molecules of reactants collide to give products.
Schematically it is represented as follows:
+
Reactant
molecules
Transition
state
Product
molecules
Uncatalysed
reaction
Potential energy
E a
Reactants
E a
Catalysed
reaction
Products
Progress of reaction
Fig. 6.1 Progress of reaction.
The minimum amount of energy required to attain transition state is called energy of
activation, E a
. Catalyst lowers the energy of activation (E a
) of a reaction.
Important Applications of Catalysts
Reactions Examples Catalyst used
(i) Dehydration C 2
H 5
OH ⎯⎯→ C 2
H 4
+ H 2
O Alumina, Zirconia
(ii) Hydrolysis Vegetable oil + H 2
O ⎯⎯→ Fatty acid Twitchel’s reagent
+ glycerol
(iii) Oxidation 2SO 2
+ O 2
⎯⎯→ 2SO 3
V 2
O 5
C 6
H 6
+ O 2
⎯⎯→ Maleic anhydride
C 10
H 8
+ O 2
⎯⎯→ Phthalic anhydride
(iv) Hydrogenation Oil + H 2
⎯⎯→ Vanaspati Raney Ni
N 2
+ 3H 2
⎯⎯→ 2NH 3
(Haber’s process) Fe
Alkene + H 2
⎯⎯→ Akane
Ni, Pt, Pd
(Contd.)