2. Outline
• General information about catalysis
• Types of catalysts
• Catalytic deactivation
• Significance of catalysts in industry
• Catalysts in polymerization process
• Ziegler-Natta catalyst
7. How to work?
• Reactants adsorbed onto the surface of
catalysts at active sites
• Adsorption is where something stick to
surface
8. Example:
• Hydrogenation of vegetable oils to make
margarine
• Ethene molecules adsorbed on the surface
of Ni. The double bond of ethene breaks
and electrons are used to bond Ni active
surface.
9. Homogenous catalysis:
• They are the same phase as
reactants.
• Homogeneous catalysts are
dissolved in a solvent with
the reactants.
10. Example:
Ozone, O3, is constantly being formed and broken up again
in the high atmosphere by the action of ultraviolet light.
Ordinary oxygen molecules absorb ultraviolet light and
break into individual oxygen atoms. These have unpaired
electrons, and are known as free radicals. They are very
reactive.
12. Cont.
Ozone can also be divided again into ordinary oxygen
and an oxygen radical by absorbing ultraviolet light.
13. Cont.
• These reactions stop a lot of harmful ultraviolet
radiation penetrating the atmosphere to reach the
surface of the Earth.
• Chlorofluorocarbons (CFCs) , for example, were used
extensively in aerosols and as refrigerants. Their slow
breakdown in the atmosphere produces chlorine atoms
- chlorine free radicals. These catalyst the destruction of
the ozone.
14. Cont.
The chlorine radical catalyst is regenerated by a
second reaction. This can happen in two ways
depending on whether the ClO radical hits an ozone
molecule or an oxygen radical.
29. Catalysts vs Initiators
• Catalysts lower the activation energy
• Some catalysts direct the order of the rxn
• Initiators are used to generate active species
Catalyst is a substance that accelerates the rate of a chemical reaction without itself being transformed or consumed by the reaction.
In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction mechanism with a lower activation energy than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst usually reacts to form a temporary intermediate, which then regenerates the original catalyst in a cyclic process.
Sintering, also reffered as aging, is the loss of catalytic activity due to a loss of catalytic active surface area resulting from the prolonged exposure to high gas-phase temperatures
This mechanism of decay is common to reactions involving hydrocarbons. It results from a carbonaceous materials (coke) being deposited on the surface of catalyst.
Deactivation by this mechanism occurs when the poisoning molecules become irreversibly chemisorbed to active sites, thereby reducing the number of sites available for the main reaction
Is come industrial processes catalytic deactivation causes big problems to the production. In these cases different methods of catalytic regeneration used. Here is one example of the regeneration used in reforming processes.
