1. Introduction to Catalysis

2. What is a “Catalyst”
A catalyst (Greek: καταλύτης, catalytēs) is a substance that accelerates the rate of a chemical reaction without itself being transformed or consumed by the reaction. (thank you Wikipedia)
k(T) = k0e-Ea/RT
Ea′ < Ea
k0′ > k0
k′ > k
ΔG = ΔG Ea
Ea′
A + B
A + B +
catalyst ΔG ΔG C
C + catalyst
uncatalyzed
catalyzed

3. Catalysts Open Up New Reaction Pathways‡ H O
H2C C O
CH3 OH C C
CH3
CH3
CH2
CH3 ‡
propanone
propenol
propenol
propanone

4. Catalysts Open Up New Reaction Pathways
+ H2O C
CH2
CH3
OH−
−OH−
Base catalyzed O OH
rate = k[OH−][acetone] C C
CH3
CH3
CH2
CH3
propanone
propenol ‡ ‡
propenol
intermediate
propanone

5. Catalysts Open Up New Reaction Pathways‡ ‡
propenol
different
intermediate
propanone
propenol O OH
propanone
rate = k[H3O+][acetone] C C
Acid catalyzed
CH3
CH3
CH2
CH3
H3O+
−H3O+ OH C +
CH3
CH3
+ H2O

6. Types of Catalysts - Enzymes
The “Gold Standard” of catalysts
Highly specific
Highly selective
Highly efficient
Catalyze very difficult reactions
N2  NH3
CO2 + H2O  C6H12O6
Works better in a cell than in a l reactor
Triosephosphateisomerase
“TIM”
Cytochrome C Oxidase
Highly tailored “active sites”
Often contain metal atoms

7. Types of Catalysts – Organometallic Complexes
Perhaps closest man has come to mimicking nature’s success
2005 Noble Prize in Chemistry
Well-defined, metal-based active sites
Selective, efficient manipulation of organic functional groups
Various forms, especially for polymerization catalysis
Difficult to generalize beyond organic transformations
Polymerization:
Termination:

8. Types of Catalysts – Homogeneous vs. Heterogeneous
Zeolite catalyst
Catalyst powders
Homogeneous catalysis
Single phase
(Typically liquid)
Low temperature
Separations are tricky
Heterogeneous catalysis
Multiphase
(Mostly solid-liquid and solid-gas)
High temperature
Design and optimization tricky

9. Types of Catalysts: Crystalline Microporous Catalysts
Regular crystalline structure
Porous on the scale of molecular dimensions
10 – 100 Å
Up to 1000’s m2/g surface area
Catalysis through
shape selection
acidity/basicity
incorporation of metal particles
10 Å
100 Å
Zeolite (silica-aluminate)
MCM-41 (mesoporous silica)
Silico-titanate

10. Types of Catalysts: Amorphous Heterogeneous Catalysts
Amorphous, high surface area supports
Alumina, silica, activated carbon, …
Up to 100’s of m2/g of surface area
Impregnated with catalytic transition metals
Pt, Pd, Ni, Fe, Ru, Cu, Ru, …
Typically pelletized or on monoliths
Cheap, high stability, catalyze many types of reactions
Most used, least well understood of all classes
SEM micrographs of alumina and Pt/alumina

11. Important Heterogeneous Catalytic Processes
Haber-Bosch process
N2 + 3 H2 → 2 NH3
Fe/Ru catalysts, high pressure and temperature
Critical for fertilizer and nitric acid production
Fischer-Tropsch chemistry
n CO + 2n H2 → (CH2)n + n H2O , syn gas to liquid fuels
Fe/Co catalysts
Source of fuel for Axis in WWII
Fluidized catalytic cracking
High MW petroleum → low MW fuels, like gasoline
Zeolite catalysts, high temperature combustor
In your fuel tank!
Automotive three-way catalysis
NOx/CO/HC → H2O/CO2/H2O
Pt/Rh/Pd supported on ceria/alumina
Makes exhaust 99% cleaner

12. Heterogeneous Catalytic Reactors
Design goals
rapid and intimate contact between catalyst and reactants
ease of separation of products from catalyst
Packed Bed
(single or multi-tube)
Fluidized
Bed
Slurry
Reactor
Catalyst
Recycle
Reactor

13. Automotive Emissions Control System
“Three-way” Catalyst
CO  CO2
HC  CO2 + H2O
NOx  N2
Monolith reactor
Most widely deployed heterogeneous catalyst in the world – you probably own one!
Pt, Rh, Pd
Alumina, ceria, lanthana, …

14. Length Scales in Heterogeneous Catalysis
Chemical adsorption and reaction
Mass transport/diffusion

15. Characteristics of Heterogeneous Supported Catalysts
Surface area:
Amount of internal support surface accessible to a fluid
Measured by gas adsorption isotherms
Loading:
Mass of transition metal per mass of support
Dispersion:
Percent of metal atoms accessible to a fluid M M M
support

16. Rates of Catalytic Reactions
Pseudo-homogeneous reaction rate
r = moles / volume · time
Mass-based rate
r′ = moles / masscat · time
r′ = r / ρcat
Heterogeneous reactions happen at surfaces
Area-based rate
r′′ = moles / areacat · time
r′′ = r′ / SA, SA = area / mass
Heterogeneous reactions happen at active sites
Active site-based rate
Turn-over frequency TOF = moles / site · time
TOF = r′′ / ρsite
TOF (s−1)
Hetero. cats. ~101
Enzymes ~106

17. Hetrogeneous Catalysis- Milestones in Evolution-1
1814- Kirchhoff-starch to sugar by 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 for acid catalysed reactions; isomerisation, alkylation, polymerisation.

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

19. Catalysis in the Chemical Industry
Hydrogen Industry(coal,NH3,methanol, FT, hydrogenations/HDT,fuel cell).
Natural gas processing (SR,ATR,WGS,POX)
Petroleum refining (FCC, HDW,HDT,HCr,REF
Petrochemicals(monomers,bulk chemicals).
Fine Chem.(pharma, agrochem, fragrance, textile,coating,surfactants,laundry etc)
Environmental Catalysis(autoexhaust, deNOx, DOC)

20. Some Developments in Industrial catalysis-1 1900- 1920s
Industrial Process Catalyst
1900s:CO + 3H2  CH4 + H2O Ni
Vegetable Oil + H2  butter/margarine Ni
1910s:Coal Liquefaction Ni
N2 +3 H2  2NH Fe/K
NH3 NO NO2 HNO Pt
1920s: CO +2 H2  CH3OH (HP) (ZnCr)oxide
Fischer-Tropsch synthesis Co,Fe
SO2  SO3 H2SO V2O5

21. Heterogeneous Catalysis. Some Challenges Ahead
Selective oxdn of long chain paraffins to terminal alcohols/ald/acids;
CH4 CH3OH.
Activation of CO2 & its use as raw material;
CO2 + H2O/ CH3OH/C2H5OH  C2 +
Chiral catalysis with high ee.
H2 generation from H2O without using HC .
Photocatalysis with Sunlight.

22. Industrial catalysis-2 1930s and 1940s
1930s:Cat Cracking(fixed,Houdry) Mont.Clay
C2H4 C2H4O Ag
C6H6  Maleic anhydride V2O5
1940s:Cat Cracking(fluid) amorph. SiAl
alkylation (gasoline) HF/acid- clay
Platforming(gasoline) Pt/Al2O3
C6H6 C6H Ni

23. Industrial catalysis-3 1950s
C2H4 Polyethylene(Z-N) Ti
C2H4 Polyethylene(Phillips) Cr-SiO2
Polyprop &Polybutadiene(Z-N) Ti
Steam reforming Ni-K- Al2O3
HDS, HDT of naphtha (Co-Mo)/Al2O3
C10H8  Phthalic anhydride (V,Mo)oxide
C6H6  C6H (Ni)
C6H11OH C6H10O (Cu)
C7H8+ H2 C6H6 +CH (Ni-SiAl)

24. Industrial catalysis-4 1960s
Butene Maleic anhydride (V,P) oxides
C3H6 acrolein (BiMo)oxides
C3H6  acrylonitrile(ammox) -do-
Bimetallic reforming PtRe/Al2O3
Metathesis(2C3 C2+C4) (W,Mo,Re)oxides
Catalytic cracking Zeolites
C2H4 vinyl acetate Pd/Cu
C2H4  vinyl chloride CuCl2
O-Xylene Phthalic anhydride V2O5/TiO2
Hydrocracking Ni-W/Al2O3
CO+H2O H2+CO2 (HTS) Fe2O3/Cr2O3/MgO
--do (LTS) CuO-ZnO- Al2O3

25. Industrial catalysis-5 1970s
Xylene Isom( for p-xylene) H-ZSM-5
Methanol (low press) Cu-Zn/Al2O3
Toluene to benzene and xylenes H-ZSM-5
Catalytic dewaxing H-ZSM-5
Autoexhaust catalyst Pt-Pd-Rh on oxide
Hydroisomerisation Pt-zeolite
SCR of NO(NH3) V/ Ti
MTBE acidic ion exchange resin
C7H8+C9H12 C6H6 +C8H Pt-Mordenite

26. Industrial catalysis-6 1980s
Ethyl benzene H-ZSM-5
Methanol to gasoline H-ZSM-5
Vinyl acetate Pd
Oxdn of t-butanol to MMA Mo oxides
Improved Coal liq NiCo sulfides
Syngas to diesel Co
HDW of kerosene/diesel.GO/VGO Pt/Zeolite
MTBE cat dist ion exchange resin
Cyclar Ga-ZSM-5
Oxdn of methacrolein Mo-V-P heteropolyacid
N-C6 to benzene Pt-L zeolite

27. Industrial catalysis-7 1990+
DMC from acetone Cu chloride
NH3 synthesis Ru/C
Phenol to HQ and catechol TS-1
Isom of butene-1(MTBE) H-Ferrierite
Ammoximation of cyclohexanone TS-1
Isom of oxime to caprolactam TS-1
Ultra deep HDS Co-Mo-Al
Olefin polym Supp. metallocene cats
Ethane to acetic acid Multi component oxide
Fuel cell catalysts Rh, Pt, ceria-zirconia
Cr-free HT WGS catalysts Fe,Cu- based

28. Industrial catalysis-8 2000 +
Solid catalysts for biodiesel
- solid acids, Hydroisom catalysts
Catalysts for carbon nanotubes
- Fe (Ni)-Mo-SiO2

29. Catalytic Reaction Kinetics
Why catalytic reaction kinetics
Derivation rate expressions
Simplifications
Rate determining step
Initial reaction rate
Limiting cases
Temperature dependency
Pressure dependency
Examples

30. Reactor design equation
conversion i
stoichiometric coefficient i
rate expression
‘space time’
catalyst effectiveness

31. Simple example: reversible reaction
A B
‘Elementary processes’ A + * k 1 - B 2 3 1. 2. 3. A B 1 3 2 A* B*
‘Langmuir adsorption’

32. Elementary processes Rate expression follows from rate equation:
At steady state:
Eliminate unknown surface occupancies

33. Elementary processes contd.
Site balance: (7.5)
Steady-state assumption: (7.6-7)
Rate expression: (7.9)

34. Quasi-equilibrium / rate-determining step
r = r+2 - r-2

35. Rate expression r.d.s. Rate determining step:
Eliminate unknown occupancies
Quasi-equilibrium:
So:

36. Rate expression, contd.
Substitution:
where:
Unknown still q*

37. Rate expression, contd.
Site balance:
Finally:

38. Other rate-determining steps
Adsorption r.d.s
Surface reaction r.d.s.
Desorption r.d.s.

39. Langmuir adsorption Uniform surface (no heterogeneity)
Constant number of identical sites
Only one molecule per site
No interaction between adsorbed species
0.2
0.4
0.6
0.8 1
0.1
100 10
pA (bar)
KA (bar-1)
A + * A*

40. Thermodynamics Equilibrium constant Reaction entropy Reaction enthalpy
Adsorption constant
Adsorption entropy, <0
(J/mol K)
Adsorption enthalpy,<0
(J/mol)
atm-1

41. Multicomponent adsorption / inhibition
Langmuir adsorption
Inhibitors

42. Dissociative adsorption
H2 + 2* H*
Two adjacent sites needed

43. Langmuir-Hinshelwood/Hougen-Watson models (LHHW)
includes NT, k(rds)
For: A+B C+D
pApB-pCpD/Keq
molecular: KApA
dissociative: (KApA)0.5
= 0, 1, 2
number of species in r.d.s.

44. Initial rate expressions
Forward rates
Product terms negligible
Adsorption
Surface reaction
Desorption
(K2 and KApA0 >>1) T1 T1 T1 T2 r0 T2 T2 T3 T3 T3
pA0

45. Ethanol dehydrogenation
Franckaerts &Froment
Cu-Co cat.
C2H5OH « CH3CHO + H2
Model:
1. A + * « A*
2. A* + * « R* + S* (r.d.s.)
3. R* « R + *
4. S* « S + *
= Derive rate expression =

46. Initial rates - linear transformation
Ethanol dehydrogenation
Full expression
Initial rate
After rearrangement
linear form:
linear least squares fit
trends, positive parameters

47. Partial benzene hydrogenation
Ru-catalyst - clusters of crystallites
Slurry reaction, elevated pressures
Water-salt addition increases selectivity
+ 2 H + H 2 2 Ru
Salt-water
Adsorption / Desorption properties affected

48. Dual site models: A + B C
(r.d.s.)

49. Surface occupancies
Empty sites:
Occupied by A:
Occupied by B:

50. Dual site models, contd.
Number of neighbouring sites (here: 6)

51. Thermodynamics Equilibrium constant Adsorption constant
Reaction entropy
Reaction enthalpy
Adsorption constant
Adsorption entropy, <0
(J/mol K)
Adsorption enthalpy,<0
(J/mol)
atm-1

52. Multicomponent adsorption / inhibition
Langmuir adsorption
Inhibitors

53. Dissociative adsorption
H2 + 2* H*
Two adjacent sites needed

54. Langmuir-Hinshelwood/Hougen-Watson models (LHHW)
includes NT, k(rds)
For: A+B C+D
pApB-pCpD/Keq
molecular: KApA
dissociative: (KApA)0.5
= 0, 1, 2
number of species in r.d.s.

55. Verwerking p. 11 t/m 13

56. Initial rate expressions
Forward rates
Product terms negligible
Adsorption
Surface reaction
Desorption
(K2 and KApA0 >>1) T1 T1 T1 T2 r0 T2 T2 T3 T3 T3
pA0

57. Ethanol dehydrogenation
Franckaerts &Froment
Cu-Co cat.
C2H5OH « CH3CHO + H2
Model:
1. A + * « A*
2. A* + * « R* + S* (r.d.s.)
3. R* « R + *
4. S* « S + *
= Derive rate expression =

58. Initial rates - linear transformation
Ethanol dehydrogenation
Full expression
Initial rate
After rearrangement
linear form:
linear least squares fit
trends, positive parameters

59. Initial rates - CO hydrogenation over Rh
Van Santen et al.
Kinetic model
1. CO + * « CO*
2. CO* + * ® C* + O* (r.d.s.)
0.2
0.4
0.6
0.8
1.0
Occupancy (-)
400
450
500
550
600
Temperature (K)
200
800
Rate
Initial rate

60. Temperature and Pressure Dependence
Verwerking p. 18 t/m21 *A
*A# *B k- # k+
kbarrier

61. Limiting cases - forward rates
Surface reaction r.d.s.
1. Strong adsorption A
A* #
Ea2 A* B*

62. Limiting cases - forward rates
Surface reaction r.d.s.
2. Weak adsorption
A* #
A(g) + *
Ea2
HA A*

63. Limiting cases - forward rates
Surface reaction r.d.s.
3. Strong adsorption B
A* #
Ea2
B + *+ A
HA
- HB A*
B* + A

64. Cracking of n-alkanes over ZSM-5
J. Wei I&EC Res.33(1994)2467
Ea2
Eaobs
DHA
Carbon number
kJ/mol
200
100
-200
-100

65. Observed temperature behaviour
T higher coverage lower
Highest Ea most favoured
Change in r.d.s.
1/T
ln robs
desorption r.d.s.
adsorption r.d.s.

66. ‘Kinetic Coupling’ two kinetically significant steps
Pt-catalysed dehydrogenation of methylcyclohexane:
M  T + H2
Two kinetic significant steps:
* M  ....
T*  T + *
mari
no inhibition by e.g. benzene
T* much higher than equilibrium with gas phase T

67. Sabatier principle - Volcano plot
Rate
Heat of adsorption

68. Summary Langmuir adsorption Rate expression uniform sites
no interaction adsorbed species
constant number of sites
Rate expression
series of elementary steps
steady state assumption
site balance
quasi-equilibrium / rate determining step(s)
initial rates
simpler
mechanism kinetics

69. Catalysed N2O decomposition over oxides
Winter, Cimino
Rate expressions:
1st order
strong O2 inhibition
moderate inhibition
Also: orders 0.5-1
water inhibition
= Explain / derive =

70. N2O decomposition over Mn2O3
Vannice et al. 1995
2 N2O N2 + O2
Kinetic model
1. N2O + * « N2O*
2. N2O* ® N2 + O*
3. 2 O* « 2* + O2
Rate expression

71. N2O decomposition over Mn2O3
Vannice et al. 1995
order N2O ~0.78
Eaobs= 96 kJ/mol
Oxygen inhibition
0.0
2.0
4.0
6.0
8.0
10.0 p O2
/ kPa
0.1
0.2
0.3
0.4
r / 10 -6
mol.s -1 .g
648 K
638 K
623 K
608 K
598 K
pN2O = 10 kPa
= Explain =

72. N2O decomposition over Mn2O3
Vannice et al. 1995
Kinetic model
1. N2O + * « N2O*
2. N2O* ® N2 + O*
3. 2 O* « 2* + O2
Values
Rate expression
= Thermodynamically consistent =

73. N2O decomposition over ZSM-5 (Co,Cu,Fe)
Kapteijn et al. 11th ICC,1996
2 N2O N2 + O2
Kinetic model
1. N2O + * ® N2 + O*
2. N2O + O*® N2 + O2 + *
Rate expression
no oxygen inhibition

74. N2O decomposition over ZSM-5 (Co,Cu,Fe)
Kapteijn et al. 11th ICC,1996 2 4 6 8 10
p(O
) / kPa
0.0
0.2
0.4
0.6
0.8
1.0
X(N O)
Fe-ZSM-5
Co-ZSM-5
Cu-ZSM-5
743 K
833 K
793 K
733 K
773 K
688K
Oxygen inhibition model
1. N2O + * ® N2 + O*
2. N2O + O*® N2 + O2 + *
3. O2 + * « *O2
Rate expression

75. Effect of CO on N2O decomposition
CO + O*® CO2 + *
CO + * « CO* (Cu+)
CO removes oxygen from surface
so ‘enhances’ step 2, oxygen removal
now observed: rate of step r1 = k1 NT pN2O
increase: ~2, >3, >100

76. Effect of CO on N2O decomposition
rate without CO
rate with CO
ratio = 1 + k1/k and:
So k1/k2 = : 1 Co
>2 Cu
>100 Fe
0.7
>0.9
>0.99

77. Apparent activation energies N2O decomposition CO/ N2O = 2Fe Cu

78. Apparent activation energies N2O decomposition CO/ N2O = 0Cu Fe

79. Complex kinetics HDN of Quinone over NiMo/Al2O3 (Prins & Jian, Zurich)
Kinetic scheme
Purpose: Kinetics of reaction
Effects functions Ni and Mo
Addition role of P

80. Complex kinetics Subscheme research: HDN of OPA Not observed
intermediate,
not significant

81. Complex kinetics HDN of OPA
Derived global scheme:
How can this ‘direct’ step
be rationalised?

82. Complex kinetics HDN of OPA (Jiang & Prins)
Reaction modelling
space time (cs) 10 20 30 40 50 60
0.0
0.2
0.4
0.6
0.8
1.0 1 2 3 4 5
OPA NiMo one site model 370C
Partial pressure (kPa)
OPA PB
PCHE
PCH
strong adsorption
N-containg species
plug flow reactor
excellent fit

83. Complex kinetics HDN of OPA
Competitive parallel steps
Direct global
routes
OPA + *
OPA* PB + *
PCHA* PCHA + *
PCHE* PCHE + *
PCH + *
HCs not adsorbed
(weakly compared to N-s) kb ka
slow
Fast reaction
steps
Only traces found kc kd ke
The direct
route to PCH
Other hydrogenation
functional sites ?

84. Rate expressions Steady state assumption Site balance (one site)
Strong adsorption N-species
parallel reactions
Q: explain zero order OPA
direct route
from PCHE

86. ‘Kinetic coupling’ two steps kinetically significant
Decomposition of ammonia over Mo (low p, high T)
2NH3 -> N H2
Steps:
2NH3 + * -> 2N* + 3H2
2N* -> N2
surface concentration N much higher than equilibrium
with N2 pressure
‘fugacity of N* corresponds with virtual fugacity N2

87. Virtual fugacity, kinetic coupling
Aromatization light alkanes over zeolite
Alkanes -> Aromatics + Hydrogen
Cracking yields high H*, so high fugacity H*
H* not in equilibrium with H2
-> low aromatics selectivity
Addition of Ga provides escape route for H*
zeolite: alkane -> 2H*
Ga: 2H* -> H2
Kinetic coupling used to increase reaction selectivity for aromatics

88. Kinetic coupling between catalytic cycles effect on selectivity
Hydrogenation: butyne -> butene -> butane
A1 A A3
butyne and butene compete for the same sites
but: K1 >> K2
resulting high selectivity for butene (desired) possible
even when k2 > k1
since:
Meyer and Burwell (JACS 85(1963)2877) mol%:
2-butyne 22.0
cis-2-butene 77.2
trans-2-butene 0.7
1-butene
butane

89. Kinetic coupling between catalytic cycles effect on selectivity
Bifunctional catalysis: Reforming
Isomerization n-pentane: n-C5 -> i-C5
low concentration
close proximity
Pt-function: n-C5 -> n-C5=
surface diffusion
Acid function: n-C5= -> i-C5=
Pt-function: i-C5= -> i-C5
Catalytic cycles on different catalysts
Affect selectivity:
modify surface (change adsorption properties)
modify fluid phase (change adsorption properties)
benzene hydrogenation M. Soede

90. Competitive adsorption Selective hydrogenation aromatics
S.Toppinen,Thesis 1996
Ni-alumina trilobe catalyst
3 mm particles
40 bar H2
125oC
semi-batch reactor
Consecutive conversion behaviour
rate constants ~ similar
adsorption constants decrease
Propose a rate expression to account for this effect

91. Partial benzene hydrogenation
Ru-catalyst - clusters of crystallites
Slurry reaction, elevated pressures
Water-salt addition increases selectivity
+ 2 H + H 2 2 Ru
Salt-water
Adsorption / Desorption properties affected

92. Dual site models: A + B C
(r.d.s.)

93. Surface occupancies
Empty sites:
Occupied by A:
Occupied by B:

94. Dual site models, contd.
Number of neighbouring sites (here: 6)