1. CATALYSIS Dr. V. Sreeja,
Assistant Professor of Chemistry,
TKMM College Nangiarkulangara,
Alappuzha, Kerala, India
2. CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
CONTENTS
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WHAT IS CATALYSIS?
TYPTES OF CATALYSIS
CHARACTERISTICS OF
CATALYTIC REACTIONS
THEORIES OF CATALYSIS
ENZYME CATALYSIS
3. WHAT IS CATALYSIS?
Catalysis is the process of increasing the rate of a chemical reaction by adding a
substance known as a catalyst, which is not consumed in the catalyzed reaction and
can continue to act repeatedly.
A substance that alters the reaction rate of a chemical reaction chemically unchanged at the end of
the reaction
CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
4. TYPTES OF CATALYSIS
TYPES OF CATALYSIS
POSITIVE
CATALYSIS
NEGATIVE
CATALYSIS
HOMOGENEOUS
CATALYSIS
HETROGENEOUS
CATALYSIS
BIOCATALYSIS
AUTO-CATALYSIS
CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
5. POSITIVE CATALYSIS
The catalyst which increases the rate of a chemical reaction is called positive
catalyst and the phenomenon is known as positive catalysis
Examples
(j) 2KClO3 2KCl + 3O2
(ii) H2O2 H2O + [O]
MnO2
Pt
The catalyst which decreases the rate of reaction is called negative catalyst and
phenomenon is called negative catalysis.
Example
(j) H2O2 H2O + [O]
NAGATIVE CATALYSIS
Acetanilide
CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
6. HOMOGENIOUS CATALYSIS
CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the
reactants, principally in solution
e.g. 2SO2 (g) + O2 (g) 2SO3
NO(g)
HETEROGENIOUS CATALYSIS
The catalytic process in which the reactants and the catalyst are in different
phases is known as heterogeneous catalysis
e.g. 2SO2 (g) + O2 (g) 2SO3
Pt(s)
8. CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
AUTO-CATALYSIS
In certain reactions, one of the product acts as a catalyst. In the initial stages the reaction
is slow but as soon as the products come into existences the reaction rate increases. This
type of phenomenon is known as auto- catalysis
Example
The rate of oxidation of oxalic acid by acidified potassium permanganate increases as the
reaction progresses. This acceleration is due to the presence of ions which are formed
during reaction. Thus ions act as auto-catalyst.
5H2C2O4 + 2KMnO4 + 3H2SO4 2MnSO4 + K2SO4 + 10CO2 + 8H2O
2MnO4- + 16H+ + 5C2O4
2- 2Mn2+ + 8H2O+ I0CO2
9. CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
ENZYME CATALYSIS
Numerous reactions occur in the bodies of animals and plants to maintain the life
process. These reactions are catalysed by enzymes. The enzymes are thus,
termed as bio-chemical catalysts and the phenomenon is known as bio-chemical
catalysis
C12 H22O11 + H2O C6 H12O6 + C6 H12O6
Invertase
10. CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
CHARACTERISTICS OF CATALYTIC REACTIONS
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A catalyst remains unchanged in mass and chemical
composition at the end of the reaction
A small quantity of the catalyst is generally
sufficient to catalyzes almost unlimited
reactions
The catalyst can not initiate the reaction
The catalyst can not change the position of
equilibrium
The catalyst is generally specific in nature
Change of temperature alters the rate of chemical
reaction
11. CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
THEORIES OF CATALYSIS
Intermediate compound formation theory
Adsorption theory
INTERMEDIATE COMPOUND THEORY OF CATALYSIS
According to this theory, the catalyst reacts with one of the reactants to give
an intermediate, which reacts with another reactant to yield products and the
catalyst
12. CATALYSIS & PHOTOCHEMISTRY Dr. V. Sreeja
A + B AB
A + C AC (Intermediate compound)
AC + B AB + C
(Product) (Catalyst)
Example:
2SO2 (g) + O2 (g) 2SO3
2NO + O2 2NO2
2NO2 + 2SO2 2SO3 + 2NO
(C)
