This document discusses different types of catalysis including homogeneous catalysis, heterogeneous catalysis, and enzyme catalysis. It explains that catalysts speed up chemical reactions by lowering the activation energy without being consumed in the process. Catalysts can be solids (heterogeneous) or the same phase as reactants (homogeneous). Enzymes are protein catalysts that use active sites to specifically catalyze reactions in living cells. Theories of catalysis include intermediate compound formation and adsorption of reactants onto catalyst surfaces. Acid-base catalysis involves acids or bases donating or accepting protons to form reactive intermediates.

1. CATALYSI
S
By :- Gaurav Dave

2. CATALYST AND CATALYSIS
 Catalyst is a substance that increases the rate of the reaction at
which a chemical system approaches equilibrium , without being
substantially consumed in the process.
 And the process is known as Catalysis.
 Catalyst affects only the rate of the reaction ,i.e.Kinetics.
 It changes neither the thermodynamics of the reaction nor the
equilibrium composition.

3. CATALYSIS…
 Catalysts generally react with one or more reactants to form
intermediates that subsequently give the final reaction product, in
the process regenerating the catalyst. The following is a typical
reaction scheme, where C represents the catalyst, X and Y are
reactants, and Z is the product of the reaction of X and Y:
 X + C → XC (1)
 Y + XC → XYC (2)
 XYC → CZ (3)
 CZ → C + Z (4)

4. TYPES OF CATALYSIS
 Catalysts can be divided into two main types
1. Homogeneous
2. Heterogeneous
3. Enzyme catalysis

5. HOMOGENEOUS CATALYSIS
 This has the catalyst in the same phase as the reactants.
Typically everything will be present as a gas or contained in a
single liquid phase.
 Examples:
1. influence of H+ on the esterification of carboxylic acids, such as
the formation of methyl acetate from acetic acid and methanol
2. The reaction between persulphate ions and iodide ions
3. oxidation of sulphur dioxide to sulphur trioxide in presence of
nitric oxide as catalyst...
2SO2(g) + O2(g) + NO(g) 2SO3(g) ...Here NO is a homogeneous
catalyst as it is present in gaseous phase.

6. HETEROGENEOUS CATALYSIS
 Heterogeneous catalysts act in a different phase than the reactants.
 Normally, the catalyst is a solid and reactants are fluids (liquids or
gases). It is characterized by the presence of “active sites” on the
catalyst surface
 The reaction in which the reactants are in gaseous phase while the
catalyst is a solid is called CONTACT catalysis since the reaction
occurs by contact of reactants with the catalyst surface.
 In contact process the catalyst is usually a finely divided metal or a
gauze.
 Examples:
1. The hydrogenation of a carbon-carbon double bond in the reaction
between ethene and hydrogen in the presence of a nickel catalyst.
2. in the oxidation of sulfur dioxide on vanadium(V) oxide for the
production of sulfuric acid.
SO2(g) + ½O2(g) + V2O5(s)  SO3(g)

7. CHERECTARISTICS OF CATALYTIC
REACTIONS
1. A catalyst remains unchanged in mass and chemical
composition at the end of the reaction.
2. A small quantity of catalyst is generally needed to produce
almost unlimited reaction.
3. A catalyst is more effective when finely divided.
4. A catalyst is specific in its actio.
5. A catalyst cannot, in general, initiate a reaction.
6. A catalyst does not effect the final position of equilibrium,
although it shortens the time required to establish the
equilibrium.
7. Change of temperature alters the rate of a catalytic reactionas it
would do for the samereaction without a catalyst.

8. PROMOTERS
 A substance which, though itself not a catalyst, promotes the
activity of a catalyst is called a promoter.
 Example:
Molybdenum (Mo) or aluminium oxide (Al2O3) promotes the activity
of iron catalyst in the Haber’s process for manufacture of amonia.
N2 + 2H2 + Fe + Mo 2NH3
(catalyst) (promoter)

9. CATALYTIC POISONING
 A substance which destroys the activity of the catalyst to
accelerate a reaction, is called a poison and the process is called
catalytic poisoning.
 Examples:
1. The platinum catalyst used in the oxidation of Sulphur dioxide
(contact process), is poisoned by arsenic oxide (As2O3)
SO2 + O2 + Pt + As2O3  2SO3
2. The iron catalyst used in Haber’s process of ammonia is
poisoned by H2S.
N2 + 2H2 + Fe + H2S  2NH3
(catalyst) (poison)

10. ACTIVATION ENERGY
AND CATALYSIS
The minimum amount of energy
required to cause a chemical reaction
is known as activation energy.
The Activation Energy determines
how fast a reaction occurs, the higher
Activation barrier, the slower the
reaction rate.
The lower the Activation barrier, the
faster the reaction.

11.  Catalyst lowers the activation
energy for both forward and
reverse reactions.

12. THEORIES OF CATALYSIS
Intermediate compound formation
theory The adsorption theory
 In homogeneous catalysis,
catalyst forms an intermediate
compound with one of the
reactants.
 The highly reactive
intermediate compound then
reacts with the second
reactants to yield the product,
releasing the catalyst.
 A + B + C  AB (C-catalyst)
1. A + C  AC(AC-
intermediate)
2. AC +B  AB + C
 Here the catalyst functions by
adsorption of the reacting
molecules on its surface.
 The process can be explained
in four steps:
1. ADSORPTION OF
REACTANT MOLECULES
2. FORMATION OF ACTIVATED
COMPLEX
3. DECOMPOSITION OF
ACTIVATED COMPLEX
4. DESORPTION OF
PRODUCTS
There are two main theories of catalysis: Intermediate compound
formation theory and The adsorption theory

13. ACID-BASE CATALYSIS
 A number of homogenous catalytic reactions are catalyzed by
acids or bases, these are often referred to as Acid-Base catalysts.
 Arrhenius pointed out that acid catalysis was brought about by H+
ions supplied by strong acids, while base catalysis was caused by
OH- ions supplied by strong bases.
 Example:
1. Inversion of cane sugar.
C12H22O11 + H2 + H+  C6H12O6 + C6H12O6
2. Decomposition of Nitramide.
NH2NO2 +H+  N2O + H2O

14. 1. Not only H+ ions but all Bronsted acids (proton donors) cause
acid catalysis.
 Thus the general acid catalysts are H+ , undissociated acids
(CH3COOH), cations of weak bases (NH4
+ ) and water.
2. Not only OH- ions but all Bronsted bases(proton accepters) act
as base catalyst.
 Thus the general base catalysts are OH- , undissociated bases,
anions of weak acids ( CH3COO- ) and water.
 THE CATALYSIS BROUGHT ABOUT BY GENERAL ACIDS AND
BASES IS TERMED GENERAL ACID-BASE CATALYSIS.
GENERAL ACID-BASE CATALYSIS

15. MECHANISM OF ACID BASE CATALYSIS
 In acid catalysis the proton donated Bronsted acid forms an
intermediate complex with the reactant, which then reacts to give
back the proton.
 IN base catalysis the Bronsted base acceps a proton from
reactant to form an intermediate complex which then reacts or
decomposes to regenerate the base.
 Example:

16. ENZYME CATALYSIS
 Enzyme catalysis is the catalysis of chemical reactions by
specialized proteins known as enzymes.
 Enzyme catalysis of chemical reactions occur with high selectivity
and rate in a small part of the enzyme macromolecule known as
the active site.
 Each enzyme is produced in a particular living cell to catalyse a
reaction occurring in that cell.
 The first enzyme was prepared by synthesis in the laboratory in
1969.

17. MECHANISM of enzyme
catalysis
The molecules of substrate which
have complementary shape fit into
the cavities just as key fits into a lock
( lock and key theory).
Due to the presence of active groups
the enzyme forms an activated
complex with the substrate which at
once decomposes to yield the
products.
E + S  ES  P + E
( complex )
Where E=enzyme , S= substrate ,
ES= activated complex , P=
products

18. CHARACTERISTICS OF ENZYME
CATALYSIS
1. Enzymes are the most efficient catalysts known
2. Enzyme catalysis is marked by absolute specificity.
3. The rate of enzyme catalysed reaction is maximum at the
optimum temperature.
4. The rate of enzyme catalysed reactions is maximum at the
optimum pH.
5. Enzymes are markedly inhabited or poisoned.
6. Catalytic activity of enzymes is greatly enhenced by the
presence of activators or coenzyme.

19. THANK YOU…