Catalyst and their types

1. 2020
Mujeeb UR Rahman
17CH106
10/21/2020
CATALYST
Submitted to: Prof.Dr. Imran Nazir
Associate Professor
Department of Chemical Engineering
Mehran UET Jamshoro,Pakistan

2. Catalyst:
• A catalyst is a substance that affects the rate of a
reaction but emerges from the process unchanged.
• A catalyst usually changes a reaction rate by promoting a
different molecular path ("mechanism") for the reaction.
• Catalyst affect yield and selectivity
• Changes only the rate of reaction; it does not affect the
equilibrium.
• Selectively enhances the rate of a reaction
• Changes the reaction pathway
• Neither consumed nor formed
• Does not affect equilibrium

3. Types of Catalysts
Homogeneous Catalyst
• Catalysts can operate by increasing the number of
effective collisions.
• That is, from the Arrhenius equation: catalysts increase k
be increasing A or decreasing E
a
.
• A catalyst may add intermediates to the reaction.
• Example: In the presence of Br
-
, Br
2
(aq) is generated as
an intermediate in the decomposition of H
2
O
2
.
• When a catalyst adds an intermediate, the activation
energies for both steps must be lower than the activation
energy for the uncatalyzed reaction. The catalyst is in a
different phase than the reactants and products.
• Acids or bases
• Metal salt
• Enzymes
• Radical initiators
• Solvents
Heterogeneous Catalyst
• Typical example: solid catalyst, gaseous reactants and
products (catalytic converters in cars).
Most industrial catalysts are heterogeneous
• First step is adsorption (the binding of reactant molecules
to the catalyst surface).
• Adsorbed species (atoms or ions) are very reactive.
• Molecules are adsorbed onto active sites on the catalyst
surface.

4. How Catalysts Work:
Catalyst can initiate reactions. The mechanisms are similar to
the mechanism without a catalyst, but the initiation process is
much faster with the catalyst.

5. Intermediate Stabilization
104
k
52
252
k
62
42
k
52
524
k
623
3
k
62
HCHC2
:ationminTer
HHCHCH
HHCHC
HCCHHCCH
:opagationPr
CH2HC
:Initiation
CATALISTNO
5
4
3
2
1





104
k
52
252
k
62
42
k
52
252
k
622
HCHC2
:ationminTer
HHCHCH
HHCHC
:opagationPr
HNOHCHCNO
:Initiation
CATALISTWITH
5
4
3
1




Reactant + Catalyst  Stable Complex  Products + Catalyst