Catalysts accelerate chemical reactions without being consumed. There are two types of catalysts: homogeneous, where the catalyst is in the same phase as the reactants, and heterogeneous, where the catalyst is in a different phase. In heterogeneous catalysis, the catalyst is typically a solid and the reactants are gases or liquids. The catalyst provides alternative reaction pathways with lower activation energies. Enzymes are biological catalysts that work by binding reactants in cavities on their surfaces, forming activated complexes that decompose into products.

2. Introduction of Catalysts & its types
(CATALYSIS)
AQIB BEHZAD(1767/21332)
To: Dr. Tahir Mehmood

3. General introduction of catalysis:
Potassium chlorate, when heated strongly decomposes slowly giving
Di oxygen .The decomposition occurs in the temperature range of
653-873K.
2KClO3 2KCl + 3O2
However, when a little of manganese dioxide is added, the decomposition
takes place at a considerably lower temperature range i.e., 473-633K and also
at a much accelerated rate.
The added manganese dioxide remains unchanged with respect to its mass
and composition. In a similar manner, the rates of a number of chemical
reactions can be altered by the mere presence of a foreign substance.

4. General introduction of catalysis:
The systematic study of the effect of various foreign substances on the rates of
chemical reactions was first made by Berzelius, in 1835. He suggested the
term catalyst for such substances.
• CATALYSTS:
• Substances, which accelerate the rate of a chemical reaction and themselves
remain chemically and quantitatively unchanged after the reaction, are known
as catalysts, and the phenomenon is known as catalysis.
➢Promoters and poisons:
• Promoters are substances that enhance the activity of a catalyst while
poisons decrease the activity of a catalyst. For example, in Haber’s process
for manufacture of ammonia, molybdenum acts as a promoter for iron which
is used as a catalyst.
N2(g) + 3H2(g) 2NH3(g)

5. The term catalysis was first employed by the great Swedish chemist Jon's
Jacob Berzelius in 1835.
• Catalyst is a substance that may increase the rate of reaction without itself
consumed in a reaction and phenomenon is known as catalysis.
• A catalyst accelerates a chemical reaction. It does so by forming bonds with
the reacting molecules, and by allowing these to react to a product, which
detaches from the catalyst, and leaves it unaltered such that it is available for
the next reaction.
• First catalyst in chemistry is catalytic production of Sulphuric acid (this is
industrial catalytic process).
SO2 + O2 SO3
[Lead Chamber Process]
Definition of catalysis:

6. Catalytic Reactions::
• The catalyst offers an alternative
path for the reaction, which is
obviously more complex, but
energetically much more favorable.
• The activation energy of the
catalytic reaction is significantly
smaller than that of the uncatalyzed
reaction; hence, the rate of the
catalytic reaction is much larger.
• Catalysts work by providing
alternative mechanism involving a
different transition state of lower
energy.
• The activation energy of the
catalytic reaction is lowered
• compared to the uncatalyzed
reaction.

7. Catalysts
Homogeneous
Catalysts
Acid/Base
Catalysts
Metal-Ion
Catalysts
Heterogeneous
catalysts
Supported
Catalysts
Bio-Catalysts
Enzymes
Catalysts
Immobile
Enzymes
and cells
Bulk
catalysts
Types of Catalysts:

8. • In a heterogeneous reaction, the catalyst is in a different phase from 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.
• Reaction of solid catalyst with liquid/gas reactants are example of
heterogeneous catalyst.
• Example:
N2 (g) + 3H2(g) 2NH3(g)
. (ii) Oxidation of ammonia into nitric oxide in the presence of platinum gauze
in Ostwald’s process.
4NH3 (g) + 5O2 (g) 4NO(g) + 6H2O(g)
The reactants are in gaseous state while the catalyst is in the solid state.
Heterogeneous reaction:
Fe

9. Heterogeneous catalytic theory:
❖ In general, only certain sites on the catalyst surface actually participate in the
reaction and these sites are called active sites on the catalysts. These sites may
be the unsaturated atoms resulting from surface irregularities or atoms with
chemical properties that enable the interaction with the adsorbed reactant atoms
or molecules. Activity of the catalyst is directly proportional to the number of these
active sites available on the surface and is often expressed in terms of turnover
frequency. Turnover frequency is defined as the number of molecules reacting
per active site per second at the condition of experiments.
A solid catalytic reaction A B goes through the following steps.
1. Transportation of reactant (A) from bulk fluid to pore mouth on the external
surface of catalysts Pellets.
2. Diffusion of the reactant (A) from the pore mouth through the catalyst pores to the
immediate vicinity of internal catalytic surface.
3. Adsorption of reactant (A) onto the catalyst surface.
4. Reaction of (A) on the catalyst surface producing product (B)

10. 5. Desorption of the product
(B) from the surface.
6. Diffusion of the product
(B) from interior part of
the pores to the pore mouth
on the external surface.
7. Transfer of the product
(B) from pore mouth on
the external surface to the
bulk fluid.

12. HETROGENEOUS catalysis:
• Advantage :-
• Avoids formation of inorganic salts
• Regenerable
• Non-toxic
• Easy to handle
• Safe to store, long life time
• Easy and inexpensive removal from reaction mixture by filtration or
centrifugation
• Tolerates a wide range of temperatures and pressures
• Easy and safe disposal
Disadvantage:-
• They lower effective concentration of catalyst since reaction only occur in
exposed active surface.

13. Homogeneous catalysis:
• In homogeneous catalysis, all the reactants and catalysts are present in a
single fluid phase and usually in the liquid phase and gas phase.
• Homogeneous catalysts are the simple molecules or ions such as HF,
H2SO4, Mn+2 as well as complex molecules such as organometallic
complexes, macrocyclic compounds and large enzyme molecules.
Types of reactions
➢ Several homogeneous catalytic systems are :
1. Acid base catalysis
2. Catalysis by metal ions
3. Catalysis by organometallic complexes
4. Catalysis by Lewis acids
5. Catalysis by porphyrin complexes
6. Catalysis by enzymes

14. Examples of Homogeneous catalysis:
(i) Oxidation of Sulphur dioxide into Sulphur trioxide with dioxide in the
presence of oxides of nitrogen as the catalyst in the lead chamber process.
NO(g)
2SO2(g) + O2(g) 2SO3(g)
• The reactants, Sulphur dioxide and oxygen, and the catalyst, nitric oxide, are
all in the same phase.
(ii) Hydrolysis of methyl acetate is catalyzed by H+ ions furnished by
hydrochloric acid.
CH3COOCH3(l)+H2O(l) CH3COOH(aq) + CH3OH(aq)
• Both the reactants and the catalyst are in the same phase.
(iii) Hydrolysis of sugar is catalyzed by H+ ions furnished by Sulphur acid.
C12H22O11(aq) +H2O(l) C6H12O6+C6H12O6
Both the reactants and the catalyst are in the same phase.

15. Enzymes are complex nitrogenous organic
compounds which are produced by living plants and animals. They are
actually protein molecules of high molecular mass and form colloidal
solutions in water.
They are very effective catalysts; Catalyzes numerous reactions,
especially those connected with natural processes. Numerous reactions
that occur in the bodies of animals and plants to maintain the life
process are catalyzed by enzymes. The enzymes are, thus, termed as
biochemical catalysts and the phenomenon is known as biochemical
catalysis.
Many enzymes have been obtained in pure crystalline state from living
20 cells. However, the first enzyme was synthesized in the laboratory in
1969.

16. Examples:
(i) Conversion of glucose into ethyl alcohol: The zymase enzyme
converts glucose into ethyl alcohol and carbon dioxide.
C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g)
(ii) Conversion of starch into maltose: The diastase enzyme converts
starch into maltose.
2(C6H10O5 )n(aq) + nH2O(l) nC12H22O11(aq)
(iii) Conversion of maltose into glucose: The maltase enzyme converts
maltose into glucose.
C12H22O11(aq) + H2O(l) 2C6H12O6(aq)
Zymase
Diastase
Maltase

17. There are a number of cavities
present on the surface of colloidal particles of enzymes. These cavities are of
characteristic shape and possess active groups such as -NH2, -COOH, -SH, -
OH, etc. These are actually the active centers on the surface of enzyme
particles. The molecules of the reactant (substrate), which have
complementary shape, fit into these cavities just like a key fits into a lock. On
account of the presence of active groups, an activated complex is formed
which then decomposes to yield the products.
• Thus, the enzyme-catalyzed reactions may be considered to proceed
in two steps.
• Step 1: Binding of enzyme to substrate to form an activated complex.
E + S ES
• Step 2: Decomposition of the activated complex to form product.
ES E + P

19. IMPORTANT FEATURES OF SOLID CATALYSTS
(a) Activity:
• The activity of a catalyst depends upon the strength of chemisorption to a
large extent. The reactants must get adsorbed reasonably strongly on to the
catalyst to become active. However, they must not get adsorbed so strongly
that they are immobilized and other reactants are left with no space on the
catalyst’s surface for adsorption. It has been found that for hydrogenation
reaction, the catalytic activity increases from Group 5 to Group 11 metals
with maximum activity being shown by groups 7-9 elements of the periodic
table.
(b) Selectivity:
• The selectivity of a catalyst is its ability to direct a reaction to yield a
particular product selectively, when under the same reaction conditions
many products are possible. Selectivity of different catalysts for same
reactants is different. For example, starting with H2 and CO, and using
different catalysts, we get different products. Thus, it can be inferred that the
action of a catalyst is highly selective in nature. As a result a substance
which acts as a catalyst in one reaction may fail to catalyses another
reaction.

20. References:
• Robertson, A.J.B. (1970) Catalysis of Gas Reactions by Metals. Logos
Press, London.
• Elschenbroich, C. (2006) Organometallics. Wiley-VCH: Weinheim.
• Maisel, Richard I. (2001) Chemical Kinetics and Catalysis. Wiley-Inter
science.
• Clark, Jim (October 2013). "Types of catalysis". Chemguide.
• Catalytic Antibodies Simply Explained. Documentroot.com (2010-03-06).
Retrieved on 2015-11-11

21. Thank You!