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Institut für Chemie
IMPRS Block Course, March 2013
Introduction to Surface Chemistry
Reinhard Schomäcker
Institut für Chemie
TU Berlin
Strasse des 17. Juni 124
10623 Berlin
schomaecker@tu-berlin.de
Institut für Chemie
IMPRS Block Course, March 2013
Surface Chemistry
- Modification of surface
- Grafting
- Coating
- Chemical Vapor Deposition
- Atomic Layer Deposition
- Impregnation Techniques
- Etching
- Corrosion
- Electrochemical Resolution or Deposition
- Surface Analytics
- Microscopy, Scattering and Diffraction Methods
- Spectroscopy
- Catalysis
- heterogeneous oxidation catalysis
Wetting
Diffusion
Electrostatics
Adsorption
Structure
Geometry
= unknown local
concentration and
reactivity
Oxygen as a
„Probe molecule“
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IMPRS Block Course, March 2013
Outline
- Industrial examples
-Fundamentals
- Oxidations reactions with lattice oxygen
-the active component
-the support effects
-Oxidation reactions with adsorbed oxygen
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IMPRS Block Course, March 2013
Selective Oxidation of Hydrocarbons
20% of all industrial organic chemicals
O2 molecules:
triplet state
with 2 unpaired elctrons
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IMPRS Block Course, March 2013
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IMPRS Block Course, March 2013
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IMPRS Block Course, March 2013
Required material properties of oxidation catalysts
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IMPRS Block Course, March 2013
Oxides are
nonstochiometric
Nucleophilic and electrophilic oxidation
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IMPRS Block Course, March 2013
Nucleophilic lattice oxygen
Dynamic surface equilibrium
Electrophilic surface oxygen species
Radical reactions,
Total oxidation
C-H actication
Oxidative dehydrogenation
Insertion into activated C-H bonds
Vacancy formation
Bi2O3-MoO3 Co3O4
18O isotope exchange exp.
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IMPRS Block Course, March 2013
Lattice transport of O2- Redox mechanism
Oxidation reactions with nucleophilic lattice oxygen
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IMPRS Block Course, March 2013
2 HCl +1/2 O2 H2O + Cl2
-57,5 kJ/mol
Cu, Mn, Ni, Co, V, Mo, Hg, Ag, Nb, Ti, Zn, W, Ru, Ce
The Deacon process
Institut für Chemie
IMPRS Block Course, March 2013 Teschner et al, J. Catal. 2012, 285, 273-284
DOI:10.1016/j.jcat.2011.09.039
pKpK
ppppK
kppk
OHOHClCl
OHCl
HClO
f
HCLOf
r
2222
1
2
1
25.15.0
2
5.01
2
1
1. O2 + 2* O2**
2. O2** 2 O*
3. O* + * + HCl OH* + Cl*
4. 2 Cl* 2 * + Cl2
5. 2 OH* O* + * + H2O
Fundamentals of the Deacon process
Micro kinetic model Energy profile for RuO2/SnO2
Nuria Lopez, ICIQ
Institut für Chemie
IMPRS Block Course, March 2013
0
0.075
0.15
0.225
0 2 4 6 8 10
t / s
pC
l2 / b
ar
400 °C
350 °C
325 °C
300 °C
pKpK
ppppK
kppk
OHOHClCl
OHCl
HClO
f
HCLOf
r
2222
1
2
1
25.15.0
2
5.01
2
1
EA,0 = 59.4 kJ/mol
DHAds,Cl2 = -104.3 kJ/mol
DHAds,H2O = -96.0 kJ/mol
0
0,075
0,15
0,225
0,3
0 0,075 0,15 0,225 0,3
pCl2, sim
pC
l2, e
xp
400 °C
350 °C
325 °C
300 °C
Experimental Investigation of the Deacon process
Kinetic parameter for RuO2/SnO2:
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IMPRS Block Course, March 2013
MO2 + 2 HCl MOCl2 + H2O DRHad
MOCl2 + 1/2 O2 MO2 + Cl2 DRHox
Comparison of Deacon catalysts
D. Teschner et al, J. Catal. 2012, 285, 273-284
J. Perez-Ramirez et al., J. Catal. 2012, 286, 287-297
J. Allen et al, J. Appl. Chem. 1962, 12, 406
M.W.M. Hisham, S.W. Benson, J. Phys. Chem. 1995,
99, 6194
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IMPRS Block Course, March 2013
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IMPRS Block Course, March 2013
Simplified energy profile of Deacon reaction
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IMPRS Block Course, March 2013
Typical Feature of Surface Chemistry: Vulcano Behaviour
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IMPRS Block Course, March 2013
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IMPRS Block Course, March 2013
Oxidations with lattice oxygen: Mars-van Krevelen - Mechanism
Lattice oxygen
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IMPRS Block Course, March 2013
Selectivity in hydrocarbon oxidation
Thermodynamics favours the ultimate formation of CO2 and H2O
Desired products of partial oxidation reactions are intermediates derived by
kinetic control
Competing parallel and consecutive reactions
C-H bonds of reactants usually stronger than those in intermediate products
All oxidation processes are highly exothermic
Expolsive regime in gas mixture
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IMPRS Block Course, March 2013
Oxides are
nonstochiometric
Nucleophilic and electrophilic oxidation
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IMPRS Block Course, March 2013
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IMPRS Block Course, March 2013
V
O
O OO V
O
O OO
O2
+5+4
+3 +5
V
O
O OO
V
O
O OO
H
CH
V
O
O OO
V
O
O OO
V
O
O OO
H
V
O
O OO
H
VO O
O
O
H H
V
O
O OO
+5+5
+4 +4
+5 +5
-H2O
X. Rozanska, R. Fortrie, J. Sauer, J. Phys. Chem. C, 111 (2007) 6041-6050.
OHHC
OHHC
n
nX
52
52
0
1,
j j
j
i
i
i n
n
S
Ethanol oxidation reaction network
ODH of
propane:
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IMPRS Block Course, March 2013
with n ≥ 1
k2/k5pO2 << 1
K1pC2H5OH > 1
2
5
12
1
12
21
2
1
521
52
1
52
1
k
pk
pKkpK
pKkr
O
OHHC
OHHC
OHHC
n
n
n
Mechanistic aspects
B. Kilos, A.T. Bell, E. Iglesia, J. Phys. Chem. C, 113 (2009) 2830-2836
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IMPRS Block Course, March 2013
Impact of vanadia dispersion on performance
- dispersion of vanadia influenced by support material
- different performance of monomers, oligomers and polymers
- different contribution of uncovered support surface
- no comparability of low loaded catalyst with different supports
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IMPRS Block Course, March 2013
- Preparation of near-monolayer catalysts by
thermal spreading of vanadyl acetylacetonate
- No over oxidation of the products under differential
conditions (X < 10%) and stoichiometric feed
support surface area
[m²/g]
surface density
[V/nm²]
wt% V
TiO2 17,1 3,5 0,6 %
Al2O3 200,9 3,1 4,9 %
ZrO2 52,1 3,1 1,4 %
CeO2 19,8 3,9 0,7 %
No crystalline V2O5 in all samples
Catalyst preparation
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IMPRS Block Course, March 2013
0
0,05
0,1
0,15
0,2
0,25
0,3
Al2O3 V2O5 ZrO2 CeO2 TiO2
TO
F (
20
0°C
) [m
ol/
mo
ls]
VOx/Support
10% Xat 42 V
OHC
n
nTOF
0
10
20
30
40
50
60
70
80
90
100
Al2O3 V2O5 ZrO2 CeO2 TiO2
EA
,ap
p [
kJ
/mo
l]
VOx/Support
T
TOFRE appA 1
ln,
Support effect
Institut für Chemie
IMPRS Block Course, March 2013
60
70
80
90
100
110
120
60 65 70 75 80 85 90 95
EA
,ap
p [
kJ
/mo
l]
EA,app ethanol [kJ/mol]
ODH of propane and methanol vs. ethanol
propane methanol*
VOx/TiO2
VOx/Al2O3
VOx/ZrO2
V2O5
VOx/CeO2
*L. J. Burchman, I. E. Wachs, Catal. Today, 49 (1999) 467-484
P.R. Shah, I. Baldychev, J.M. Vohs, R.J. Gorte, App. Cal. A, 361 (2009) 13-17
Support effect
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IMPRS Block Course, March 2013
TiO2 ZrO2 SiO2 V2O5 MgO a-Al2O3
0
50
100
150
200
250
300
350
DH
f [kJm
ol-1
]
DHf this work
DHf Allersma1967
DHf Todorova2007
DHf Sauer2004
2
ln
RT
ΔH
dT
Kd f
212
2OO pVeK
22
12 OeVO O
x
O
fmO ΔHΔEΔEV 31
Defect formation
Mass action law
Van’t Hoff’s law
500 450 400 350 300
-10,0
-9,5
-9,0
-8,5
-8,0
-7,5
-7,0
1
2
3
4
5
6
7
8
9
10
X(C
3H
8)
(%)
ln
T [°C]
ΔE*
ΔEm
En
erg
y
X
ΔEm
ΔHf
Theorie of defect formation
T. Allersma, R. Hakim, T. N. Kennedy, J. D. Mackenzie, J. Chem. Phys., 46 (1967) 154-160
J. Sauer, J. Doebler, Dalton Transactions, 19 (2004) 3116-3121
T. K. Todorova, M. V. Ganduglia-Pirovano, J. Sauer, J. Phys. Chem. C., 111, (2007), 5141-5153
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IMPRS Block Course, March 2013
Energy profile of ethanol partial oxidation
VOx/Al2O3
Ea,app
ΔHdef
VVV
VO
2 +
C2H
5O
H(g
)
+ ½
O2(g
)
VVV
V(O
H) 2
-C2H
4O
+ ½
O2(g
)
VIV
VIV
O+
H2O
(g)
+
C2H
4O
(g)
+ ½
O2(g
)
VVV
VO
2+
H2O
(g)
+
C2H
4O
(g)
ΔHR
TS 1
reaction cordinateE
[k
J/m
ol]
reaction coordinate
Institut für Chemie
IMPRS Block Course, March 2013
40
50
60
70
80
90
100
110
120
30 50 70 90 110 130
EA
,ap
p [
kJ
/mo
l]
∆Hf [kJ/mol]
propane
ethanol
methanol*
VOx/TiO2
VOx/ZrO2
VOx/Al2O3
V2O5
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
40 60 80 100 120
TO
F [
mo
l/m
ols
]
∆Hf [kJ/mol]
ethanol (200°C)
methanol **
propane (400°C)
VOx/TiO2
VOx/ZrO2 VOx/Al2O3
V2O5
**I. E. Wachs, Catal. Today, 100 (2005) 79-94
*L. J. Burchman, I. E. Wachs, Catal. Today, 49 (1999) 467-484
P.R. Shah, I. Baldychev, J.M. Vohs, R.J. Gorte, App. Cal. A, 361 (2009) 13-17
BEP- Correlations with defect formation enthalpy
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IMPRS Block Course, March 2013
4V/13Ti/SBA-15 catalyts structure based on spectroscopical
and reactivity results.
Preparation of a high performance catalyst for ODP
Institut für Chemie
IMPRS Block Course, March 2013 G. Deo, I.E.Wachs, J. Catal, 146 (1994) 323-334
Activity scaling with H2-TPR peak temperatures
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IMPRS Block Course, March 2013
Catalytic cycle of propene oxidation
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IMPRS Block Course, March 2013
21
2
1
1
1
5
121
12
1
O
CHCH
CH
pk
pKkpK
pKkr
n
n
n
Mars-van-Krevelen Rate Law
Rate of reduction
Rate of reoxidation
Steady state assumption
Surface oxygen coverage
Overall rate
+
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IMPRS Block Course, March 2013
Oxidation reactions with adsorbed Oxygen
- Total Oxydation reactions of VOC
- Partial Oxidation of Methane
- Epoxydation of Ethene
- Oxidative Coupling of Methane
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IMPRS Block Course, March 2013
Epoxidation of Ethene
Singularities: Ag as selective catalyst,
oxygen as oxidant,
only working with ethene
Proposed Pathways
Of selective and unselective
reaction
Oxidation reactions with electrophilic oxygen
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IMPRS Block Course, March 2013
Oxygen is more
electrophilic at high
coverage
Kinetics:
Eley-Rideal
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Possible intermediate
DFT calculations of activation barriers for model discrimination
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Proposed structures
For DFT calculations
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Vulcano Plot for
EO-TOF
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Oxidative Coupling of Methane (OCM) to Ethylene
o Worldwide research efforts to convert CH4 into chemicals (C2H4, CH3OH…)
o Oxidative Coupling of Methane (OCM) is a promising direct conversion route
of methane to ethylene but has not reached industrial practice yet
43
Desired:
Undesired: 2 CH4 + 3 O2 DG (800°C) = - 1222 kJ mol-12 CO + 4 H2O
2 CH4 + 4 O2 DG (800°C) = - 1602 kJ mol-12 CO2 + 4 H2O
kinetic control by means of a catalytic process needed
2 CH4 + O2 C CH
H
H
H+ 2 H2O DG (800°C) = - 306 kJ mol-1
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IMPRS Block Course, March 2013
Pioneering work
0
20
40
60
80
100
120
140
160
1985 1990 1995 2000 2005 2010
Reihe1
G.F. Keller, M.M. Bhasin, J. Catal. 1982, 73, 9 catalyst
M. Hinsen, M. Baerns, Chem. Z. 1983, 107, 223 „
A.C. Jones, J.J. Leonardo, A.J. Sofranko, periodic
US patent 4 443644, 1984 feed strategy
U. Zavyalova, M. Holen, R. Schlögl, M. Baerms, ChemCatChem, 2011, 3, 1935
year
papers
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IMPRS Block Course, March 2013
Ethylene Production by Oxidative Coupling of Methane
Model Studies for Understanding Complexity
* table adopted from E. V. Kondratenko, M. Baerns
Handbook of Heterogeneous Catalysis, Vol. 6, Ch. 13.17, 2008
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Mn-doped Na2WO4/SiO2
*U. Simon, O. Görke, A. Bertold, S. Arndt, R. Schomäcker,
H. Schubert, Chem. Eng. J.168 (2011) 1352-1359
200 g batches with spray drying technology
X.Fang et al, J. Mol. Catal. (China), 6 (1992) 427
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Very low specific surface < 5 m2/g
Similar activation energies EA,app = 150 kJ/mol
Inactive < 600 °C, no lattice oxygen involved
Common features of Catalysts for Oxidative Coupling of Methane
0 390 400 410 420 430 440
100
120
140
160
180
200
220
240
260
280 VOx/TiO
2
VOx/CeO
2
VOx/ZrO
2
EA
,ap
p +
DH
va
p [kJ/m
ol]
D0 (C-H) [kJ/mol]
Eth
anol
Cyc
lohe
xane
Pro
pane
Eth
ane
Met
hane
EA,0
380 390 400 410 420 430 4400
20
40
60
80
100
120
140
160
180 Mn/Na
2WO
4/SiO
2
Gasphase with O*
EA
,ap
p
D0 (C-H) [kJ/mol]
Eth
anol
Pro
pane
Eth
ane M
etha
ne
Hypothesis: adsorbed atomic oxygen
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IMPRS Block Course, March 2013
Experiments in a TAP reactor
with J. Perez-Ramires, ICIQ, Taragona, now ETH Zurich
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IMPRS Block Course, March 2013
J. Lunsford, Angew. Chemie, Int. Ed, 1995, 34, 970
Defects ? TMn+ TM(n+1)+ + e-
2 10-11 1/cm
Li+0-.
Stability ?
Selectivity ?
Operation conditions ?
Mechanism of Oxidative Coupling of Methane
Arndt et al., Catalysis Reviews, 53, 2011, 424-514
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IMPRS Block Course, March 2013
OCM is possible in the gas phase
but not at 1bar and with poor selectivities
CH3 + CH3
+ M C2H6 + M* (trimolecular)
Catalyst = M ?
R. Horn, S. Mavlyankariev
Mechanism of Oxidative Coupling of Methane
C H 4
*
O 2
O O O
+ C H 3
+ C H 3 C 2 H 6
2 10-11 1/cm3
3 2 6 2 5 C H C H C H C 2 H 4
C O x
+ O 2
+ O 2
+ O 2
2 10-13 1/cm3
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IMPRS Block Course, March 2013
0
10
20
30
40
50
60
70
0 3 6 9 12 15
C2 S
ele
cti
vit
y [
%]
CH4 Conversion [%]
8:1 4:1 2:1
Mn-Na2WO4/SiO2, 100 mg, 750°C, Feed Gas:
Catalyst Testing and kinetic studies
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IMPRS Block Course, March 2013
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IMPRS Block Course, March 2013
Product selectivity of Catalysts
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IMPRS Block Course, March 2013
Nucleophilic and electrophilic oxidation
The surface is,
What matters !
Institut für Chemie
IMPRS Block Course, March 2013
Selectivity in hydrocarbon oxidation
Thermodynamics favours the ultimate formation of CO2 and H2O
Desired products of partial oxidation reactions are intermediates derived by
kinetic control
Competing parallel and consecutive reactions
C-H bonds of reactants usually stronger than those in intermediate products
Surface structure and reactivity is the essential control parameter
- Definded sites of selective reactivity are required
- Stability of sites against reaction conditions and product essential
for processes