This document provides an overview of catalysis. It defines catalysis as a process where a substance called a catalyst alters the rate of a chemical reaction but remains unchanged. Catalytic reactions are classified as homogeneous if reactants and catalysts are in the same phase, or heterogeneous if they are in different phases. Common industrial applications of catalysis include the Haber process for ammonia production and the Contact process for sulfuric acid manufacture. Theories for catalytic mechanisms include intermediate compound formation and adsorption of reactants onto catalyst surfaces.

1. Module
Catalysis
Dr. S. H. Burungale

2. Catalysis
Contents
Introduction
Classification of catalytic reactions
Types of Catalytic reactions
Characteristics of catalytic reactions
Mechanisms of catalysis
Industrial applications
Short answer Questions

3. Introduction
The rate of chemical reaction may bechanged by
presence of small amount of a foreign material in
a reaction .
The foreign material remains unchanged at the
end of the chemical reaction is known as catalyst.
Greek -Keta – wholly and lein means process.
The catalysis was first introduced by
JONS JACOB BERZELIUS IN 1835.

4. Definition : Any substance which alters the rate of
chemical reaction and remains unaffected
chemically during that reaction is known as
catalyst and the phenomenon as catalysis .
Role of catalyst
1.It Initiate the reaction
2.Specific path of reaction
3.To avoids the side products of the reaction.

5. Classification of catalytic reaction
Homogeneous Heterogeneous
Reactants and
catalyst are in
same phase
Reactants and
catalyst are in
different phase

6. Homogeneous Catalytic reaction: When reactants and
catalyst are present in one and same phase in a catalytic reaction is
called as Homogeneous Catalytic reaction and this phenomenon
Homogeneous Catalysis
1.Oxidation of sulphur dioxide .
2SO2 + O2 2SO3
gas gas gas
2. Oxidation of carbon monoxide to carbon
dioxide
2CO + O2 2CO2
gas gas gas
NO (g)
NO (g)

7. 3.Hydrolysis of urea by urease
H2N-CO-NH2 +H2O NH3 +CO2
Liquid
4. Hydrolysis of ester by HCl
ester to Acetic acid and ethyl alcohol
5.Inversion of cane sugar by sulphuric acid
Cane sugar to Glucose and Fructose
Urease (Liquid)

8. Heterogeneous Catalytic reaction:
When reactants and catalyst are present in
different phases in a catalytic reaction is called as
Heterogeneous Catalytic reaction and this
phenomenon Heterogeneous Catalysis.
1. Manufacture of Ammonia by Habers process
N2(g) +3H2(g) 2NH3
2. Oxidation of sulphur dioxide .to sulphur troxide
Fe/Mo ( s)
2SO2(g) + O2(g) 2SO3
Pt ( s)

9. Types of Catalysis
The Catalytic reactions are again subdivided
into following
1.Positive catalysis
2. Negative catalysis
3. Auto catalysis
4.Induced catalysis
5. Acid base Catalysis
6.Enzyme catalysis

10. 1.Positive Catalysis : A catalyst which accelerates
or increases the rate of the chemical reaction.
Example ,
1. Preparation of Oxygen by potassium perchlorate
2KClO3 2KCl + 3O2
2. N2(g) +3H2(g) 2NH3
3. 2SO2(g) +O2(g) 2SO3
MnO2
heat
Fe/Mo
V2O5

11. 2.Negative Catalysis : A catalyst which retarded
or decreases the rate of the chemical reaction.
•Decomposition of Hydrogen peroxide is
controlled by Sulphuric acid
The rate of reaction decreases by H2SO4
Oxidation of sodium sulphites by glycero in
presence of air to sodium sulphates
2H2O2 2H2O +O2
decomposition
H2SO4

12. 3.Auto catalysis :

16. 4.Induced Catalysis :When one reaction influences the rate
of other reaction, which does not occur under ordinary
conditions, the phenomenon is known as induced
catalysis. Some examples are as follows,
(i) Sodium arsenite solution is not oxidised by air. If,
however, air is passed through a mixture of the solution of
sodium arsenite and sodium sulphite, both of them
undergo simultaneous oxidation. The oxidation of sodium
sulphite, thus, induces the oxidation of sodium arsenite.
(ii) The reduction of mercuric chloride with oxalic acid is
very slow, but potassium permanganate is reduced readily
with oxalic acid. If, however, oxalic acid is added to a
mixture of potassium permanganate and both are reduced
simultaneously. The reduction of potassium permanganate,
thus, induces the reduction of mercuric chloride.

17. 5. Acid base catalysis

19. 6.Enzyme catalysis
Maltose is converted to two molecules of glucose by the enzyme
maltase, which hydrolyzes the glycosidic bond. Commercial maltose is
produced from starch that has been treated with barley malt.

20. Characteristics of Catalytic reactions
Criteria or characteristics of catalysts i. The mass and chemical
composition of catalyst should remain unchanged at the end of
the reaction. ii. A small amount of catalyst is enough to bring
about an appreciable change in the rate of chemical reaction. For
example, even 1 mg of fine platinum powder is enough to
catalyze the combination of 2.5 liters of a mixture of hydrogen
and oxygen to form water. However, there are some reactions
that uses significant amount of catalyst. iii. For solid catalyst,
the use in powder form increases the activity of catalyst by
increasing its surface area. iv. For a reversible reaction, catalyst
does not change the position of equilibrium but helps to attain
the equilibrium faster. v. Catalysts are specific in action (like a
key can open a particular lock). For example, manganese
dioxide can catalyze the decomposition of potassium chlorate
but not potassium nitrate or other substances. A catalyst

21. Mechanisms of Catalysis
THEORIES OF CATALYSIS
There are two main theories to explain catalysis.
1. Intermediate compound formation theory
2. Adsorption theory
In general, the intermediate compound formation theory
applies to homogeneous catalytic reactions and the
adsorption theory applies to heterogeneous catalytic
reactions.

22. 1. The Intermediate Compound Formation
Theory
According to this theory, the catalyst first
forms an intermediate compound with one of the
reactants. The compound is formed with less
energy consumption than needed for the actual
reaction. The intermediate compound being
unstable combines with other reactant to form
the desired product and the catalyst is
regenerated

24. For example, a reaction of the type
A + B ---- c---- > AB
which occurs in presence of a
catalyst C, may take place as
A+C (Catalyst) ---- --- > AC (Intermediate)
AC + B -- --- --- > AB(Product) +
C(Catalyst)
Many catalytic reactions can be
explained on the basis of this theory.

25. The catalytic oxidation of SO2 to SO3 in the lead
chamber process probably takes place as;
2 NO (Catalyst) + O2 --- ---- > 2NO2 Intermediate Compound
NO2 + SO2 --- --- > SO3 (Product) + NO (Catalyst)

27. In a thermodynamically feasible chemical
reaction, when addition of a small amount a
chemical substance increases the rate of
attainment of chemical equilibrium but the
substance itself does not undergo any chemical
change, then the reaction is called a catalytic
reaction. The substance that enhances the
reaction rate is called a catalyst. Catalysts work
by providing alternative mechanism involving a
different transition state of lower energy.
Thereby, the activation energy of the catalytic
reaction is lowered compared to the
uncatalyzed reaction

28. Adsorption Theory
This theory has been developed to explain the mechanism of a
reaction between two gases catalyzed by a solid catalyst, i.e.,
heterogeneous catalysis. In this process, the reaction is
initiated by the adsorption of reactant molecules on the surface
of the catalysts. The adsorption process results from the
residual forces on the catalyst surface.
Let us consider a reaction;
A (g) + B (g) C (g) + D (g)
It involves the following steps:

29. Step I: Adsorption of reactant molecules
The reactant molecules A and B strike on the catalyst
surface. The reactants molecules adsorb on the surface
by weak Vander Waals forces or by partial chemical
bond.
Step II: Formation of activated complex The
adsorbed reactants combine together to give
intermediate activated complex which is unstable.
Step III: Decomposition of activated complex or
formation of product
The unstable activated complex decomposes to form
product, which are held to the catalyst surface by
weak force or chemical bond.

30. Step IV: Desorption of products
The products are desorbed or released from the surface
of the catalyst. The products are stable and can exist
independently.

31. Industrial applications of Catalysts
Applications of catalysis
The applications of catalysis are summarised as follows.
Process
i. Haber's process for the manufacture of ammonia.
ii. Ostwald's process for the manufacture of nitric acid.
iii. Lead chamber process for the manufacture of sulphuric acid.
iv. Contact process for the manufacture of sulphuric acid.
v. Deacon's process for the manufacture of chlorine.
vi. Bosch's process for the manufacture of hydrogen.
vii. Hydrogenation of vegetable oils Oil + H2 -- > Vanaspati ghee
viii. Bergius process for the synthesis of petrol from coal.

32. Questions and Answer
1. Which of the following is not a characteristic of a
catalyst?
a) It participates in the reaction
b) It enhances the equilibrium rate
c) It activates equilibrium
d) It initialises the reaction
View Answer
2. 2. Which of the following will decrease the rate of
reaction?
a) Catalytic poison
b) Positive catalyst
c) Negative catalyst
d) Catalytic promoters

33. Thank You