A brief discussion about Heterogeneous catalysis and catalysts.

1. Advance Industrial Catalysis-0425

2. Contents
1.Introduction
2.Types of Heterogeneous catalyst
3.Preparation of Heterogeneous catalyst
4. Characterization of Heterogeneous Catalysts
5.Steps involved in heterogeneous catalysis
6.Catalyst Deactivation
7. Industrial Heterogeneous catalysis
8. Conclusion

3.  If the catalyst is present in а different phase than the
reactants, it is called а heterogeneous catalyst and this
type of catalysis is called heterogeneous catalysis.
Pt, 8000С
4NH3 + 5O2 4NO + 6Н2O
Heterogeneous catalysis

4. Heterogeneous involves more than one phase: usually the catalyst is a
solid and the reactants and products are in liquid or gaseous form
 A heterogeneous catalytic reaction occurs at or very near the fluid-solid
interface
 Reactions between gases-Iiquid are usually mass-transfer limited

5. Components of a Typical Heterogeneous Catalyst
A. Active phase - metal that provides active sites where the chemical
reaction takes place
B. Support or Carrier - high surface area oxide which disperses and
stabilizes the active phase (adds efficiency, physical strength,
sometimes selectivity)
C. Promoter(s) - additive which improves catalyst properties, e.g.
activity, selectivity, catalyst life

6. Catalyst Examples
Natural
 Clays
 Zeolites
Synthetic
 Crystalline aluminosilicates

9. Preparation Of Heterogeneous Catalyst
Preparation of solid catalyst
The catalyst preparation methods can broadly categorized as
follows:
• Bulk preparation process:
• Impregnation
• Physical mixing

10. Bulk catalysts
• Bulk catalysts also known as precipitated catalysts are
mainly produced when the active components are cheap.
• The preferred method of production is precipitation.
• One or more components in the form of aqueous solutions
are mixed and then co precipitated as hydroxides or
carbonates. An amorphous or crystalline precipitate or a gel
is obtained, which is washed thoroughly until salt free. This is
then followed by further steps: drying, shaping, calcination,
and activation

13. Preparation of catalyst by impregnation
Impregnation as a means of supported catalyst preparation is
achieved by filling the pores of a support with a solution of
the metal salt.
The catalyst is prepared either by spraying the support with a
solution of the metal compound or by adding the support
material to a solution of a suitable metal salt, This is then
followed by drying and subsequent decomposition of the salt at
an elevated temperature, either by thermal decomposition or
reduction.

14. Supported metal catalyst

15. Physical mixing
Mixed agglomerated catalysts are prepared by this
method. These catalysts are prepared by physically
mixing the active substances with a
powdered support or precursors of support in ball
mill. The final mixture is then agglomerated and
activated.

17. Catalyst Characterization
Characterization of heterogeneous catalyst refers to the
determination of its physical and chemical characteristics, which
are responsible for
its performance in a reaction. Characteristics of catalysts include:
• Chemical composition of the bulk and surface of the solids
• Surface area and porosity ( micro, meso and macro)
• Bulk solid structure, phase composition, crystallite size
• Surface morphology

18. • Surface chemical properties such as:
 location and oxidation state of active metals
 acid-base property
 reducible – oxidizable property
• Aggregate properties such as aggregate or particle size, density,
mechanical strength and attrition resistance
• Catalytic properties : activity , selectivity, stability

19. The heterogeneous catalysis is a surface phenomenon. It
involves the following steps:
Diffusion of the reactants at the surface of the catalyst.
Adsorption of the molecules of the reactants at the active sites.
Occurrence of the chemical reactions on the surface of the
catalyst.
 Desorption of products molecules from the surface.
 Diffusion of products away from the surface of the catalyst.

22. Catalyst Deactivation
It is complex phenomenon which can be defined as loss of
catalytic activity and / or selectivity.
Time scales for catalyst deactivation vary considerably; for
example, in the case of cracking catalysts, catalyst mortality may
be in the order of seconds.
While in ammonia synthesis the iron catalyst may last for 5–10
years.

25. Alkylation and Dealkylation Reactions
• Alkylation: addition of an alkyl group to an organic
compound
• Common catalyst: Friedel-Crafts AlCl3 + HCl

26. Alkylation and Dealkylation Reactions
• Dealkylation:Cracking of petrochemicals
•Common catalyst: silica-alumina; silicamagnesia and
even clays (montmorilonite)

27. Isomerization Reactions
• Change of Structure
• Hydrocarbon molecules are rearranged into a more useful
isomer
• The process is particularly useful in enhancing the octane rating
of petrol, as branched alkanes burn more efficiently in a car
engine than straight-chain alkanes.

28. Hydrogenation and Dehydrogenation Reactions
• Some metals used in Hydrogenation are:
– Co, Ni, Rh, Ru, Os, Pd, Ir, and Pt.
• Non-used metals:
– V, Cr, Nb, Mo, Ta, and W
– each of which has a large number of vacant dorbitals
– These are inactive as a result of the strong adsorption for the
reactants or the products or both

29. Hydrogenation and Dehydrogenation Reactions
• Hydrogenation reactions are favored at lower temperatures
(<200ºC)
• Dehydrogenation reactions are favored at high temperatures (at
least 200ºC)
• Example:
– Industrial butadiene (synthetic rubber production) can be
obtained by the dehydrogenation of butenes.

30. Oxidation Reactions
• The transition group elements (group VIII) and subgroup are
used extensively in oxidation reactions:
– Ag, Cu, Pt, Fe, Ni
• In addition, V2O5 and MnO2 are frequently used for oxidation
reactions

31. Hydration and Dehydration Reactions
• Used to get rid of H2O molecules
• Hydration and dehydration catalysts have a strong
affinity for water
• One such catalyst is AI2O3, which is used in the dehydration of
alcohols to form olefins

32. Hydration and Dehydration Reactions
Other examples:
– Clays
– Phosphoric acid
– Phosphoric acid salts on inert carriers

33. HaIogenation and DehaIogenation Reactions
• Addition of Halogens Elements (group 7)
• Cl, F, Br, I, etc…
• Typical catalysts: CuCI2, AgCI. Pd, AlBr3, CCl4

34. Conclusion
Heterogenous catalysis over Homogeneos