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ITK-329 Kinetika & Katalisis
Introduction to Catalyst & Catalysis
Dicky Dermawanwww.dickydermawan.net78.net
dickydermawan@gmail.com
Chapter 5
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Catalyst:• Selectively enhances the rate of a reaction• Changes the reaction pathway• Neither consumed nor formed • Does not affect equilibrium
Catalyst (Ostwald):A substance one adds to a chemical reaction to tremendously speed up the reaction without the catalyst undergoing a chemical change itselfActually catalysts do undergo chemical changes during the course of reaction. It’s just that the changes are reversible.
Most chemical processes use catalyst at some stage in production process
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Types of Catalysts Homogeneous Catalyst
Reaction Catalyst C2H4 Polyethylene TiCl4/Al(C2H5)3
(Ziegler – Natta catalyst)
C2H4 Polyethylene, C6H5CH=CH2 Polystyrene
Peroxides
C2H4 + ½ O2 CH3CHO (Wacker process)
PdEt3
Olefins + CO +H2 aldehydes (hydroformylation)
Co(CO)6
CH3OH + CO CH3COOH RhCl3
SO2 + ½ O2 SO3 (lead chamber process)
NO/NO2
CH3COOH + CH3OH CH3COOCH3 + H2O
Acids or bases
Sucrose glucose + fructose Invertase
• Acids or bases• Metal salt• Enzymes• Radical initiators• Solvents
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Types of Catalysts (cont’) Heterogeneous Catalyst
Catalyst Reaction Pt on alumina,Ni on alumina Hydrogenation/dehydrogenation Pt/Sn on acidic alumina Reforming Solid acids (zeolites) Hydrocarbon isomerization,
cracking Ag C2H4 + ½ O2 ethylene oxide V2O5 SO2 + ½ O2 SO3 Platinum gauze 2 NH3 + 4 O2 N2O5 + 3 H2O
High surface area
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How Catalysts Work
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How Catalysts Work (cont’)Catalyst can initiate reactions. The mechanisms are similar to the mechanism without a catalyst, but the initiation process is much faster with the catalyst
104k
52
252k
62
42k
52
524k
623
3k
62
HCHC2
:ationminTer
HHCHCH
HHCHC
HCCHHCCH
:opagationPr
CH2HC
:Initiation
CATALIST NO
5
4
3
2
1
104k
52
252k
62
42k
52
252k
622
HCHC2
:ationminTer
HHCHCH
HHCHC
:opagationPr
HNOHCHCNO
:Initiation
CATALIST WITH
5
4
3
1
Radical Initiator in polymerization:peroxides ROOR, AIBN [(CH3)2C(CN)N]2
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How Catalysts Work (cont’):Intermediate Stabilization
Reactant + Catalyst Stable Complex Products + Catalyst
CH3CH2HC CH2
H +CH3HC=CHCH3 + H+
CH3CH2HC CH2
H +CH3CH2HC=CH2 + H+
CH3CH2HC CH2
H +CH2 =CHCH2CH3 + H+
CH3CH2HC=CH2 + H+ CH3CH2HC CH2
H +
CH3CH2HC=CH2 CH3HC=CHCH3 H
Acid catalysts:
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How Catalysts Work (cont’):Intermediate Stabilization
Reactant + Catalyst Stable Complex Products + Catalyst
Enzymatic Reactions:
O
NH2CNH2 + HOH 2NH3 + CO2
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How Catalysts Work (cont’):Intermediate Stabilization
Reactant + Catalyst Stable Complex Products + Catalyst
Metalic cluster catalyst:
COOHCHCOOHCH 3]I)CO(Rh[,HI
322
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How Catalysts Work (cont’):Intermediate Stabilization
Reactant + Catalyst Stable Complex Products + Catalyst
On solid Pt(111) catalysts:108 enhancement factor
Gas phase, no catalyst:
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Ethylene hydrogenation to ethane on Ni catalyst
Heterogeneous Catalysis = adsorption – (surface) reaction - desorptionHeterogeneous Catalysis = adsorption – (surface) reaction - desorption
How Catalysts Work (cont’)Example in Heterogeneous Catalysis
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Heterogeneous Catalyst Activity:Turnover Number/Turnover Frequency
Tn = the rate that molecules are converted per active site in the surface of the catalyst per second.
1
s
An sec][
N
R
atom_surface
sec/molecules][T
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How Catalysts Work (cont’):Configuration Dependent
66Pd
22 HCHC3 OHCHHCCHOHCHHCCH 23463
Zeolite3563
Platinum surface structure
Zeolite Size of Diffusion Channel, ?
Size of Cavity, ?
Chabazite 3.6 x 3.7 5 Zeolite A 4.1 x 4.1 6.5 Erondite 3.6 x 5.2 11.6 Ferrierite 4.3 x 5.5 6.5 ZSM-5 5.5 x 5.6 10.5 Offretite 6.4 x 6.4 6.5 Mordenite 6.7 x 7.0 10.5 Faugasite 7.4 x 7.4 11.9 VFI 13 x 13
Molecule Min. Diameter, ?
Linear alkane 4 Isoalkane 5.5 Benzene 5.1 Paraxylene 5.1 Ortoxylene 5.7 2-Methyl alkenes 5.1 Naphtalene 7.3
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Reaction Catalyst Ea, kcal/mol
Ea’, kcal/mol
500K Rate enhancement
H2 + I2 2 HI Pt 44 14 1013
2 N2O 2 N2 + O2 Au 58 29 1013
(C2H5)2O 2 C2H4 + H2O I2 53 34 108
Reaction Catalyst Rate
enhancement Temperature
ortho H2 para H2 Pt (solid) 1040 300
2 NH3 N2 + 3 H2 Mo (solid) 1020 600
C2H4 + H2 C2H6 Pt (solid) 1042 300
H2 + Br2 2 HBr Pt (solid) 1 x 108 300
2 NO + 2 H2 N2 + 2 H2O Ru (solid) 3 x 1016 500
CH3CHO CH4 + CO I2 (gas) 4 x 106 500
CH3CH3 C2H4 + H2 NO2 (gas) 1 x 109 750
(CH3)3CHO (CH3)2C=CH2+ H2O HBr (gas) 3 x 108 750
typically by 19 – 30 kcal/mol, thus…lower the temperature where a reaction takes place
How Catalysts Work (cont’)
Catalyst lowers the activation barrier for the reaction,
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Catalytic Kinetics Various & significantly different from those of uncatalyzed kinetics
2)111(Rh
221 COOCO
223
221 wirePt
3 HNNH
Effect of Concentration/ Pressure
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Catalytic Kinetics (cont’) Temperature effect: does not obey Arrhenius law
2)111(Rh
221 COOCO A: PCO = 2,5 x 10-8 torr
B: PCO = 1,0 x 10-7 torr C: PCO = 8,0 x 10-7 torr D: PO2 = 4,0 x 10-7 torr E: PO2 = 2,5 x 10-8 torr F: PCO = 2,5 x 10-8 torr, PO2 = 2,5 x 10-8 torr
223
221 wirePt
3 HNNH
A: PNH3 = 0,3 ; PH2 = 0,15 B: PNH3 = 0,3 ; PH2 = 0,44 C: PNH3 = 0,05; PH2 = 0,15 D: PNH3 = 0,05; PH2 = 0,45
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