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Microkinetic Modeling of Bioalcohol Dehydration in H-FAU, H-MOR, H-ZSM-5 and H-ZSM-22
Zeolites
Methusalem, Advisory Board Meeting, June 24, 2013
1http://www.lct.ugent.be
LaboratoryLaboratoryLaboratoryLaboratory forforforfor
Chemical Chemical Chemical Chemical TechnologyTechnologyTechnologyTechnology
C.M. Nguyen, K. Alexopoulos, M.-F. Reyniers, G.B. Marin
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Methusalem, Advisory Board Meeting, June 24, 2013
2
Overview
• Introduction
• Alcohol adsorption
• Alcohol dehydration
• Conclusions
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Methusalem, Advisory Board Meeting, June 24, 2013
3
Bioalcohols to hydrocarbons as a green route
van der Borght et al.,i–SUP, Bruges, Belgium, May 6, 2012.
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Methusalem, Advisory Board Meeting, June 24, 2013
4
Different temperatures = different product distributions
Ethanol
dehydration
Taarning et al.,Energy Environ. Sci., 4 (2011) 793
H-ZSM-5
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Methusalem, Advisory Board Meeting, June 24, 2013
5
Different zeolites = different product distributions
H-SAPO-34
MTO
H-ZSM-5
MTG
H-FER
Olefins
Gasoline
Haw et al., Acc. Chem. Res. 36 (2003) 317
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Methusalem, Advisory Board Meeting, June 24, 2013
6
Zeolite Models: 1 acid site per unit cell
12-MR
12-MR
H-F
AU
H-M
OR
H-Z
SM
-22
H-Z
SM
-5
10-MR 10-MR
Si/Al = 47 Si/Al = 95
Si/Al = 95 Si/Al = 35
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Methusalem, Advisory Board Meeting, June 24, 2013
7
Process optimization utilizes microkinetic modeling
Marin and Yablonsky, Kinetics of Chemical Reactions: Decoding Complexity, Wiley-VCH, 2011
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Methusalem, Advisory Board Meeting, June 24, 2013
8
C1-C4 alcohol adsorption thermodynamics
Nguyen et al., Europacat X, Glasgow, August 28, 2011
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Methusalem, Advisory Board Meeting, June 24, 2013
9
Nature of ROH-ZeOH complexes
PHYSISORPTION PHYSISORPTIONCHEMISORPTION
�Nature of ROH-ZeOH has remained unclear fromexp. data [1&2].�Molecular dynamics (MD) simulations for CH3OH-Zeolite [3]:
�Hzeolite strongly fluctuates midway between BAS and CH3OH.�Chemisorbed fraction increases with decreasing zeolite pore size.
[1] Mirth et al. J. Chem. Soc. Faraday Trans. 86, 3039 (1990). [2]Zamaraev andThomas, Advanced inCatalysis 41, 335 (1996). [3]Payneet al.J. Am. Chem. Soc. 121, 3292 (1999).
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0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250 300
Ra
dia
l d
istr
ibu
tio
n
fun
ctio
n,
g(r
)
distance, r (pm)
O-H1
O-H2
Methusalem, Advisory Board Meeting, June 24, 2013
10
Ab initio MD simulation: NVT, 500K
H1H2O
50
100
150
200
250
1 2 3 4 5 6
O-H
dis
tan
ce (
pm
)
time (ps)
O-H1
O-H2
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0.5
1
1.5
2
2.5
2000 2500 3000 3500
ab
sorb
an
ce (
a.u
.)
frequency (cm-1)
Methusalem, Advisory Board Meeting, June 24, 2013
11
IR spectrum
Chem.
Phys.
ν(O-H) / ZeOH
ν(C-H)
ν(O-H)
Bonn et al. Chem. Phys. Letts. 278 (1997) 213 Nguyen et al. Phys. Chem. Chem. Phys. 12 (2010) 9481
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-0.1
-0.05
0
0.05
0.1
3100 3300 3500 3700
ΔA
bso
rba
nce
(a
.u.)
frequency (cm-1)
Methusalem, Advisory Board Meeting, June 24, 2013
12
Rotation along O…H bond
ν(O-H)
ν(O-H)
Bonn et al. Chem. Phys. Letts. 1997 (278) 213
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Methusalem, Advisory Board Meeting, June 24, 2013
13
Eads: theory vs experiment
experimenttheory
H-ZSM-5
Nguyen et al. Phys. Chem. Chem. Phys. 12 (2010) 9481 Lee et al. J. Phys. Chem. B 101 (1997) 381
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Methusalem, Advisory Board Meeting, June 24, 2013
14
Influence of carbon number
Nguyen et al. Phys. Chem. Chem. Phys. 12, 9481 (2010)
∆H0ads = αNC + β
α = -12 kJ mol-1 per C
-160
-140
-120
-100
1 2 3 4
∆E
ads
/ kJ
mol
-1
Carbon number
β = -100 kJ mol-1 per C
Phys. (H-ZSM-5, Straight)
Chem. (H-ZSM-5, Straight)
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Methusalem, Advisory Board Meeting, June 24, 2013
15
Influence of zeolite topology
-180
-155
-130
-105
-80
1 2 3 4
ΔH
0a
ds/
kJ
mo
l-1
Carbon number
H-FAU
H-MOR (12-MR)
H-ZSM-5 (Straight)
H-ZSM-5 (Zigzag)
H-ZSM-22
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Methusalem, Advisory Board Meeting, June 24, 2013
16
Influence of branching level
Nguyenet al. J. Phys. Chem. C 115 (2011) 8658.
1-BuOH i-BuOH
2-BuOH t-BuOH
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Methusalem, Advisory Board Meeting, June 24, 2013
17
Zeolite-catalyzed alcohol conversion to fuels and chemicals
Alcohols
Ethers
Olefins
Aromatics
ValidationGoal: Simulate the influence
of reaction conditions and zeolite framework on product distribution
H-FAU H-ZSM-5
H-MOR H-ZSM-22
Method:
T, P, W/F, %H2OReactor
simulation
Reaction network
Thermo-dynamics
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Methusalem, Advisory Board Meeting, June 24, 2013
18
Ab-initio based microkinetic modeling
Validation
Reactor simulation
Reaction network
Thermo-dynamics
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Methusalem, Advisory Board Meeting, June 24, 2013
19
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
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Methusalem, Advisory Board Meeting, June 24, 2013
20
Desorption profile of adsorbed ethanol in H-MOR
Kondo et al. J. Phys. Chem. C 114 (2010) 20107
H-MORStatic IR cell reactorNo DEE is observed
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Methusalem, Advisory Board Meeting, June 24, 2013
21
Ethanol dehydration in a flow reactor at 368 – 398 K
[1] Chiang & Bhan, J. Catal. 271(2010) 251
12-MR
Turn
over
freq
uenc
yDifferential flow reactor
0.05 bar ethanol
Ethene is observed only in 8-MR side pocket of H-MOR [1].8-MR side pockets prevent formation of bulky ethanol dimers [1].
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M 1
AlO O
H
AlO O
HO
H
M 2
AlO O
H
OH
AlO O
CH2H
AlO O
H
AlO O
H
OAl
O
H
OH5C2 H
O
H
C2H5
OAl
O
H
OH
O
H
C2H5
D1 D2
OAl
O
H5C2 O
H
C2H5
DEE*
Ethene*
(1)
(3)
(7)
(4)
(2)(5)
(6)
(8)
(9)
Ethoxide
+ H2O(g)
- H2O(g)
+ H2O(g)
- H2O(g)
+ C2H4(g)- C2H4(g)
+ DEE(g) - DEE(g)
+ C2H5OH(g)
- C2H5OH(g)
- C2H5OH(g)+ C2H5OH(g)
+ C2H4(g)
- C2H4(g)
OAl
O
H
O
H
C2H5
- C2
H 5OH (g
)
+ C 2
H 5O
H (g)
(11)
(12)
(10)
C1
Methusalem, Advisory Board Meeting, June 24, 2013
22
Reaction network of ethanol dehydration
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Methusalem, Advisory Board Meeting, June 24, 2013
23
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
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Methusalem, Advisory Board Meeting, June 24, 2013
24
Dispersion – corrected pbc[DFT-D]
( )∑ ∑=∈
−−
−=L Lji
ijD
ij
ji
D LrfLr
ccsE
0,6
666
2
DDFTDDFT EEE +=−
� VASP 4.6
� Plane wave basis set & Projector Augmented Wave method
� GGA PBE-D2 implementation for zeolites [1,2].
� Brillouin zone sampling restricted to the Γ point.
� Convergence criteria: Ecutoff = 600 eV, ∆ESCF = 10-6 eV,Max force = 0.02 eV/Å
� CI-NEB for transition state location [3]
� Statistical thermodynamics & PHVA – MBH [4][1] Grimme J. Comput. Chem. 27 (2006) 1787 [2] Kresse et al. J. Phys. Rev. B 48 (1993) 13115[3] Henkelman et al. J. Chem. Phys. 13 (2000) 9978 [4] De Moor et al. J. Chem. Theory Comput. 7 (2011) 1090
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Methusalem, Advisory Board Meeting, June 24, 2013
25
Monomolecular pathway (300 K)
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Methusalem, Advisory Board Meeting, June 24, 2013
26
Bimolecular pathway (300 K)
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Methusalem, Advisory Board Meeting, June 24, 2013
27
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
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(1) C2H5OH(g) + * ↔ M1
(2) M1 ↔ M2
(3) M2 ↔ Ethoxy + H2O(g)
(4) Ethoxy ↔ Ethene*
(5) Ethene* ↔ Ethene(g) + *
(6) M1 + C2H5OH(g) ↔ D1
(7) D1 ↔ D2
(8) D2 ↔ DEE* + H2O(g)
(9) DEE* ↔ DEE(g) + *
(10) DEE* ↔ C1
(11) C1 ↔ M1 + Ethene(g)
(12) C1 ↔ Ethene*+ C2H5OH(g)
Methusalem, Advisory Board Meeting, June 24, 2013
28
Reactor simulation
vib
B
B
B
B
qqwhere
Tk
E
q
q
h
Tk
Tk
G
h
Tkk
=
∆−=
∆−=
expexp‡0
‡‡
immobile surface species
where, F molar flow (mol/s),
W catalyst weight (kg) , Ct acid site concentration (mol H+/kg),
R turnover frequency, r reaction rate (molecules/site/s = mol/mol H+/s),
νji the stoichiometric coefficient of component i in the elementary step j
��∗ �����∗��
� 0
Plug flow reactor equations for each gas-phase
component i with QSSA for the surface species i*:
�� �� � ���� � �������
�
TST for reaction rate coefficients:
(apart from Ethene* where a 2D translation
and 1D rotation is assumed)
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Methusalem, Advisory Board Meeting, June 24, 2013
29
Ab-initio based microkinetic modeling
Reactor simulation
Reaction network
Thermo-dynamics
Validation
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Methusalem, Advisory Board Meeting, June 24, 2013
30
Experimental validation
0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X (%) S-DEE (%) S-C2H4 (%)
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Good agreement between theory (full lines) and experiment (points)
H-MOR
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0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X (%) S-DEE (%) S-C2H4 (%)
Methusalem, Advisory Board Meeting, June 24, 2013
31
Experimental validation
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Better agreement between theory (full lines) and experiment (points),
if the activation energy for ethoxy formation is slightly increased (+2 kJ/mol)
H-MOR
(3) M2 ↔ Ethoxy + H2O(g)
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Methusalem, Advisory Board Meeting, June 24, 2013
32
Influence of reaction conditionsC2H4 yield (%)
450 460 470 480 490 500Temperature (K)
10
15
20
25
30
35
40
45
Eth
anol
pre
ssur
e (k
Pa)
0
2
4
6
8
10
12
14H-ZSM-5
More ethene at higher T and lower pEtOH
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Methusalem, Advisory Board Meeting, June 24, 2013
33
Is DEE a primary product?
T= 495 K, H-ZSM-5
YES
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0
5
10
15
20
25
30
0 1 2 3 4
Co
nv
ers
ion
(%
)
site time (mol H+ s / mol EtOH0 )
H-ZSM-22
H-ZSM-5
H-MOR
H-FAU
Methusalem, Advisory Board Meeting, June 24, 2013
34
Influence of zeolite topology
10-MR zeolites more reactive than 12-MR zeolites
10 kPa EtOH,
T= 473 K
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Methusalem, Advisory Board Meeting, June 24, 2013
35
Factors governing zeolite reactivity
Ea,D1 AD1 kD1/368 KH–FAU 154 5.1 1013 6.3 10–9 H–MOR (12–MR) 161 1.2 1015 1.6 10–8 H–ZSM–5 136 6.2 1013 3.1 10–6 H–ZSM–22 122 1.1 1014 5.2 10–4
Ea,D1
D1
DEE*
TSII
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TS stabilization: Hydrogen bonds
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TS stabilization: Electrostatic interactions
H-FAU H-MOR
H-ZSM-5 H-ZSM-22
Ele
ctro
stat
ic p
oten
tial /
eV
Electrostatic: H-FAU < H-MOR < H-ZSM-5 < H-ZSM-22
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Methusalem, Advisory Board Meeting, June 24, 2013
38
Stabilization factor, α
ΔΔΔΔEEEETSIITSIITSIITSII
TSII (H-FAU)
TSII (ZeOH)
D1 (H-FAU)
D1 (ZeOH)
ΔΔΔΔ((((ΔΔΔΔEEEEads,D1ads,D1ads,D1ads,D1))))
)( 1,Dads
TSII
E
E
∆∆∆=ααααα
H-FAU 0.0
H-MOR 0.4
H-ZSM-5 1.9
H-ZSM-22 3.1
E
H-FAU is the reference
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39
Conclusions
• First principles microkinetic modeling provides predictive
guidance for the influence of catalyst’s characteristics and reaction
conditions on reactivity and product selectivity.
• Alcohol adsorption strength increases with decreasing zeolite pore
size (indicative of primary driving vdW forces).
• Entropy-enthalpy compensation governs the shape-selectivity
effect of H-ZSM-5 on adsorption of butanol isomers.
• 10-MR zeolites are more reactive than 12-MR zeolites (more effectively stabilized TS by HB/Electrostatic interactions)
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• Long Term Structural Methusalem Funding by the
Flemish Government – grant number BOF09/01M00409
• European Community’s Sixth Framework Programme
(contract nr 011730)
• Fund for Scientific Research (FWO) – Flanders
• Stevin Supercomputer Infrastructure of Ghent University
• Experimental data (H-MOR): Kristof Van der Borght
• Ab initio MD: Roger Rousseau, Mal-Soon Lee
Acknowledgements
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Glossary
• Alcohol chemisorption: Upon chemisorption over the Brønsted acid site, the acid proton is completely transferred to the alcohol, leading to formation of a positively charged oxonium ion.
• Alcohol physisorption: An alcohol is physisorbed over the Brønsted acid site and is stabilized by strong hydrogen bonds with the zeolite. The acid proton is still attached to the zeolite.
• Electrostatic potential: evaluated from the interaction between a negative unit charge and the local charge density. This factor is critical in stabilizing positively charged adsorbed complexes and especially transition states in the zeolite.
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Zeolites are promising catalysts for biorefinery processes
Fluidic Catalytic Cracking & Hydrocracking are based on Zeolites
Huber andCorma, Angew. Chem. Int. Ed. 46 (2007) 7184.Taarning et al., Energy Environ. Scie. 4 (2011) 793.
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Influence of temperature
10 kPa EtOH, H-MOR
More ethene formation at higher T
0
5
10
15
20
0 2 4 6 8
Co
nv
ers
ion
(%
)
space time ( kg s / mol )
503 K
495 K
473 K
453 K0
20
40
60
80
100
0 2 4 6 8
C2
H4
(d
ash
ed
lin
es)
& D
EE
(fu
ll li
ne
s) s
ele
ctiv
ity
(%
)
space time ( kg s / mol )
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0
2
4
6
8
10
12
0 2 4 6 8 10 12
C2
H4
(d
ash
ed
lin
es)
& D
EE
(fu
ll l
ine
s)
yie
ld (
%)
Conversion (%)
10 kPa EtOH 50 kPa EtOH
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
C2
H4
(d
ash
ed
lin
es)
& D
EE
(fu
ll l
ine
s)
sele
ctiv
ity
(%
)
Conversion (%)
10 kPa EtOH 50 kPa EtOH
Methusalem, Advisory Board Meeting, June 24, 2013
44
Is DEE a primary product?
T= 495 K, H-MOR
YES
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0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X-sim (%)
S-DEE-sim (%)
S-E-sim (%)
X-exp (%)
S-DEE-exp (%)
S-E-exp (%)
Methusalem, Advisory Board Meeting, June 24, 2013
45
Experimental validation
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Good agreement between theoretical (full lines) and experimental
(points) conversion
H-ZSM-5
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0
20
40
60
80
100
0 10 20 30 40 50 60
Co
nv
ers
ion
/Se
lect
ivit
y
Ethanol pressure (kPa)
X-sim (%)
S-DEE-sim (%)
S-E-sim (%)
X-exp (%)
S-DEE-exp (%)
S-E-exp (%)
Methusalem, Advisory Board Meeting, June 24, 2013
46
Experimental validation
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / mol
� Better agreement between theory (full lines) and experiment (points)
by modifying the kinetics of reaction 10, i.e. k10-mod=10 k10, K10-mod=K10
H-ZSM-5
(10) DEE* ↔ C1
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Experimental results
T= 503 K
Wcat/FEtOH,0 = 6.5 kg s / molH-ZSM-5
Kristof van der Borght , personal communication
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Experimental results
Kristof van der Borght , personal communication
Ethanol
DEEEthylene
Higher hydrocarbons
Eff
lue
nt
com
po
siti
on
(%)