It shows the basic facts of catalyst along with its importance in industry along with its long last milestone,its characteristics & application in industry its reaction process and preparation of a solid catalyst.

1. CH4003 Lecture Notes 5 (Erzeng Xue)
CATALYST &CATALYSIS
Nofal Umair 2k11-Che-148

2. Catalysis & Catalysts
2
Facts and Figures about Catalysts
Life cycle on the earth
 Catalysts (enzyme) participates most part of life cycle
e.g. forming, growing, decaying
 Catalysis contributes great part in the processes of converting sun energy to various
other forms of energies
e.g. photosynthesis by plant CO2 + H2O=HC + O2
 Catalysis plays a key role in maintaining our environment
Chemical Industry
 ca. $2 bn annual sale of catalysts
 ca. $200 bn annual sale of the chemicals that are related products
 90% of chemical industry has catalysis-related processes
 Catalysts contributes ca. 2% of total investment in a chemical process
Catalysis & Catalysts

3. Hetrogeneous Catalysis-
Milestones in Evolution-13
 1814- Kirchhoff-starch to sugarby acid.
 1817-Davy-coal gas(Pt,Pd selective but not Cu,Ag,Au,Fe)
 1820s –Faraday H2 + O2 ⇒H2O(Pt);C2H4 and S
 1836- Berzelius coins”Catalysis”;
 1860-Deacon’s Process ;2HCl+0.5O2 ⇒ H2O + Cl2;
 1875-Messel.SO2 ⇒ SO3(Pt);
 1880-Mond.CH4+H2O ⇒ CO+3H2(Ni);
 1902-Ostwald-2NH3+2.5O2 ⇒2NO+3H2O(Pt);
 1902-Sabatier.C2H4+H2 ⇒ C2H6(Ni).
 1905-Ipatieff.Clays foracid catalysed reactions;
isomerisation, alkylation, polymerisation.

4. Milestones in Evolution-2
4
 1910-20: NH3 synthesis (Haber,Mittasch) ; Langmuir
 1920-30-Methanol syn(ZnO-Cr2O3); Taylor;BET
 1930-Lang-Hinsh &Eley -Rideal models ;FTsyn;EO;
 1930-50:Process Engg; FCC /alkylates;acid-base
catalysis;Reforming and Platforming.
 1950-70: Role of diffusion; Zeolites, Shape Selectivity; Bifunctional
cata;oxdn cat-HDS; Syngas and H2 generation.
 1970- Surface Science approach to catalysis(Ertl)
 1990 - Assisted catalyst design using :
-surface chemof metals/oxides, coordination chemistry
- kinetics,catalytic reaction engg
- novel materials(micro/mesoporous materials)

5. What is Catalysis
5
 Catalysis
 Catalysis is an action by catalyst which takes part in a chemical reaction process
and can alter the rate of reactions, and yet itself will return to its original form without
being consumed or destroyed at the end of the reactions
(This is one of many definitions)
Three key aspects of catalyst action
 taking part in the reaction
• it will change itself during the process by interacting with other reactant/product molecules
 altering the rates of reactions
• in most cases the rates of reactions are increased by the action of catalysts; however, in
some situations the rates of undesired reactions are selectively suppressed
 Returning to its original form
• After reaction cycles a catalyst with exactly the same nature is ‘reborn’
• In practice a catalyst has its lifespan - it deactivates gradually during use
Catalysis & Catalysts

6.  By providing an alternative pathway (or
mechanism) with lower/ higher activation
energy.

7. Catalyst Characteristic
1. Activity. The ability of a catalyst to increase the rate of a chemical reaction is
called activity. A catalyst may accelerate a reaction to as high as 10^10 times.
2. Selectivity. The ability of the catalyst to direct a reaction to give a particular
product.
3. Small quantity. Only small quantity is need for a reaction.
4. Specific. One catalyst is need for specific reaction only
5. Physical properties may change during a reaction but no it does not take part in the
reaction.
6. Catalyst doesn’t influence on the general stoichiometric coefficients.
7. Catalysts decrease activation energy thus increase the chemical rate.
8. Catalysts don’t influence on the equilibrium constant. They only reduce time of
reaching the equilibrium and increase the rate of forward and back reaction.

8. Action of Catalysts
8
 Catalysis action - Reaction kinetics and mechanism
Catalyst action leads to the rate of a reaction to change.
This is realised by changing the course of reaction (compared to non-catalytic reaction)
 Forming complex with reactants/products, controlling the rate of elementary steps in
the process. This is evidenced by the facts that
 The reaction activation energy is altered
 The intermediates formed are different from
those formed in non-catalytic reaction
 The rates of reactions are altered (both
desired and undesired ones)
 Reactions proceed under less demanding conditions
 Allow reactions occur under a milder conditions, e.g. at lower temperatures for those heat
sensitive materials
Catalysis & Catalysts
reactant
reaction process
uncatalytic
product
energy
catalytic

10. PHYSICAL ADSORPTION
10
 Steps in a catalytic Reaction:
- Diffusion of reactant (bulk, Film, surface)
- Adsorption( physical ⇒ chemical)
-Surface reaction
- Desorption and diffusion of products
 Physical Adsorption:
- Van der Waals forces;BET surface area
 Pore Size distribution ( Wheeler, de Boer, BJH)
 Influence of pore size on reaction order,
temperature coefficient, selectivity, Influence of
poisons …

11. Types of Catalysts & Catalytic
Reactions11
 The types of catalysts
 Classification based on the its physical state, a catalyst can be
 gas
 liquid
 solid
 Classification based on the substances from which a catalyst is made
 Inorganic (gases, metals, metal oxides, inorganic acids, bases etc.)
 Organic (organic acids, enzymes etc.)
 Classification based on the ways catalysts work
 Homogeneous - both catalyst and all reactants/products are in the same phase (gas or liq)
 Heterogeneous - reaction system involves multi-phase (catalysts + reactants/products)
 Classification based on the catalysts’ action
 Acid-base catalysts
 Enzymatic
 Photocatalysis
 Electrocatalysis, etc.
Catalysis & Catalysts

12. Applications of Catalysis
12

Industrial applications
Almost all chemical industries have one or more steps employing
catalysts
 Petroleum, energy sector, fertiliser, pharmaceutical, fine chemicals …
Advantages of catalytic processes
 Achieving better process economics and productivity
 Increase reaction rates - fast
 Simplify the reaction steps - low investment cost
 Carry out reaction under mild conditions (e.g. low T, P) - low energy consumption
 Reducing wastes
 Improving selectivity toward desired products - less raw materials required, less unwanted wastes
 Replacing harmful/toxic materials with readily available ones
 Producing certain products that may not be possible without catalysts
 Having better control of process (safety, flexible etc.)
 Encouraging application and advancement of new technologies and materials
 And many more …
Catalysis & Catalysts

13. Applications of Catalysis
13

Environmental applications
 Pollution controls in combination with industrial processes
 Pre-treatment - reduce the amount waste/change the composition of emissions
 Post-treatments - once formed, reduce and convert emissions
 Using alternative materials
…
 Pollution reduction
 gas - converting harmful gases to non-harmful ones
 liquid - de-pollution, de-odder, de-colour etc
 solid - landfill, factory wastes
…
 And many more …
 Other applications
 Catalysis and catalysts play one of the key roles in new technology development.
Catalysis & Catalysts

14. Research in Catalysis
14
 Research in catalysis involve a multi-discipline approach
 Reaction kinetics and mechanism
 Reaction paths, intermediate formation & action, interpretation of results obtained under
various conditions, generalising reaction types & schemes, predict catalyst performance…
 Catalyst development
 Material synthesis, structure properties, catalyst stability, compatibility…
 Analysis techniques
 Detection limits in terms of dimension of time & size and under extreme conditions (T, P)
and accuracy of measurements, microscopic techniques, sample preparation techniques…
 Reaction modelling
 Elementary reactions and rates, quantum mechanics/chemistry, physical chemistry …
 Reactor modelling
 Mathematical interpretation and representation, the numerical method, micro-kinetics,
structure and efficiency of heat and mass transfer in relation to reactor design …
 Catalytic process
 Heat and mass transfers, energy balance and efficiency of process …
Catalysis & Catalysts

15. Catalytic Reaction Processes
15 Understanding catalytic reaction processes
 A catalytic reaction can be operated in a batchmanner
Reactants and catalysts are loaded togetherin reactorand catalytic
reactions (homo- orheterogeneous) take place in pre-determined
temperature and pressure fora desired time /desired conversion
Type of reactoris usually simple, basic requirements
 Withstand required temperature & pressure
 Some stirring to encourage mass and heat transfers
 Provide sufficient heating orcooling
 Catalytic reactions are commonly operated in a continuous
manner
Reactants, which are usually in gas orliquid phase, are fed to
reactorin steadyrate (e.g. mol/h, kg/h, m3
/h)
Usually a target conversionis set forthe reaction, based on this
target
 required quantities of catalyst is added
 required heating orcooling is provided
 required reactordimension and characteristics are designed
Catalysis & Catalysts

16. Catalytic Reaction Processes
16
General requirements fora good catalyst
 Activity - being able to promote the rate of desired reactions
 Selective - being to promote only the rate of desired reaction and
also retard the undesired reactions
Note: The selectivity is sometime considered to be more important
than the activity and sometime it is more difficult to achieve
(e.g. selective oxidation of NOto NO2 in the presence of SO2)
 Stability - a good catalyst should resist to deactivation, caused by
 the presence of impurities in feed (e.g. lead in petrol poison TWC.
 thermal deterioration, volatility and hydrolysis of active components
 attrition due to mechanical movement orpressure shock
 A solid catalyst should have reasonably large surface area needed
forreaction (active sites). This is usually achieved by making the
solid into a porous structure.
Catalysis & Catalysts

17. Example Heterogeneous Catalytic Reaction Process
17
 The long journey for reactant molecules to
.travel within gas phase
. cross gas-liquid phase boundary
. travel within liquid phase/stagnant layer
. cross liquid-solid phase boundary
. reach outer surface of solid
. diffuse within pore
. arrive at reaction site
. be adsorbed on the site and activated
. react with other reactant molecules, either
being adsorbed on the same/neighbour
sites or approaching from surface above
 Product molecules must follow the same
track in the reverse direction to return to gas
phase
 Heat transfer follows similar track


gas phase
poreporous
solid
liquid phase /
stagnant layer




 
gas phase
reactant molecule
Catalysis & Catalysts

18. Solid Catalysts
18
Catalyst composition
 Active phase
 Where the reaction occurs (mostly metal/metal oxide)
 Promoter
 Textual promoter (e.g. Al - Fe for NH3 production)
 Electric or Structural modifier
 Poison resistant promoters
 Support / carrier
 Increase mechanical strength
 Increase surface area (98% surface area is supplied within the
porous structure)
 may or may not be catalytically active
Catalysis & Catalysts
Catalyst
Activephase
Support
Promoter

19. Solid Catalysts
19
 Some common solid support / carrier
materials
 Alumina
 Inexpensive
 Surface area: 1 ~ 700 m2
/g
 Acidic
 Silica
 Inexpensive
 Surface area: 100 ~ 800 m2
/g
 Acidic
 Zeolite
 mixture of alumina and silica,
 often exchanged metal ion present
 shape selective
 acidic
Catalysis & Catalysts
Other supports
 Active carbon (S.A. up to 1000 m2
/g)
 Titania (S.A. 10 ~ 50 m2
/g)
 Zirconia (S.A. 10 ~ 100 m2
/g)
 Magnesia (S.A. 10 m2
/g)
 Lanthana (S.A. 10 m2
/g)
poreporous
solid
Active site

20. Solid Catalysts
20
 Preparation of catalysts
 Precipitation
To form non-soluble precipitate by desired
reactions at certain pH and temperature
 Adsorption & ion-exchange
Cationic: S-OH+
+ C+
→ SOC+
+ H+
Anionic: S-OH-
+ A-
→ SA-
+ OH-
I-exch. S-Na+
+ Ni 2+
 S-Ni 2+
+ Na+
 Impregnation
Fill the pores of support with a metal salt
solution of sufficient concentration to give
the correct loading.
 Dry mixing
Physically mixed, grind, and fired
Catalysis & Catalysts
precipitate
or deposit
precipitation
filter & wash
the resulting
precipitate
Drying
& firing
precursor
solution
Support
add acid/base
with pH control
Support
Drying
& firing
Pore saturated
pellets
Soln
. of metal
precursor
Amount
adsorbed
Concentration
Support
Drying
& firing

21. Solid Catalysts
21
 Preparation of catalysts
 Catalysts need to be calcined (fired) in order to decompose the precursor and to
received desired thermal stability. The effects of calcination temperature and time are
shown in the figures on the right.
 Commonly used Pre-treatments
 Reduction
 if elemental metal is the active phase
 Sulphidation
 if a metal sulphide is the active phase
 Activation
 Some catalysts require certain activation steps in order to receive the best performance.
 Even when the oxide itself is the active phase it may be necessary to pre-treat the catalyst
prior to the reaction
 Typical catalyst life span
 Can be many years or a few mins.
Catalysis & Catalysts
0
25
50
75
100
500 600 700 800 900
Temperature °C
BETS.A.m2
/g
0
40
0 10
Time / hours
BETS.A.
Activity
Time
Normal use
Induction period
dead