Supporting Information
Simplified Kinetic Model for Steam Reforming of Ethanol on a Ni/Al2O3 catalyst
Y. J. Wu1, J. C. Santos1, A. F. Cunha1, Ping Li2, Yu Jianguo2 and A. E. Rodrigues1*
1-Laboratory of Separation and Reaction Engineering (LSRE), Associated Laboratory
LSRE/LCM, Department of Chemical Engineering, Faculty of Engineering University
of Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal
2-State Key Laboratory of Chemical Engineering, College of Chemical Engineering,
East China University of Science and Technology (ECUST), Shangai 20037, China
S1. Model Derivation
In order to build a simplified LHHW kinetic model for SRE, a generic expression for
the reaction rate was adopted.
i
Reaction j:
Reaction rate j:
⇌
i
rj  k j  yi ,reactant  i  Ct  k j  yi', product  i'  Ct
(1)
(2)
In this equation, kj and k-j are the forward and backward kinetic constants, yi,reactant and
yi’,product are the mole fractions of reactant and product gases (kPa/kPa), and θi is the
coverage fraction of catalyst surface associated with species i, Ct is total number of
sites on catalyst surface.
By using K j 
kj
k j
, the corresponding rate expressions are obtained. It may be
verified that this leads to following relations as shown in Table 4:
 i   free  ai
*
Corresponding author: A.E. Rodrigues.
E-mail: arodrig@fe.up.pt; Tel: + 351 22 5081671; Fax: + 351 22 5081674
1
(3)
where ai is the number of the species i on the active sites. The sum of all the
coverages is unity, so that the fraction of free sites is given by the following relation
(uptake from Table S1):
 free 
1
1  1ai
i

1
1

1  aAc  aCO  aOH  aH  aCH3 DEN
(4)
The number of free sites can now be expressed in terms of partial pressure and
equilibrium constants. For convenience, we define the denominator (DEN) in the θfree
expression and Kj in the Ki* expression, as follow:
DEN  1  K  y Ac  K
*
Ac
*
CO
 yCO  K
*
OH

y H 2O
y1/H 22
K y
*
H
1/2
H2
K
*
CH 3

yCO2 yH7/22
yH2 2O
(5)
Turning towards the overall reaction rate expression where the dissociative adsorption
of methane is set as the RDS:
2
rSRE  r  r  kRDS  yCH4  free
 k RDS CH3 H
After algebraic manipulations and the introduction of
(6)
K RDS 
k RDS
k RDS
and
K *  K 52 K 61 K 71 K81 , equation (6) becomes:
4

K * yCO2  yH 2 
2
rSRE  r  r  k RDS  yCH 4 free
 1 

 K RDS yCH  yH2 O 

4
2

(7)
Upon equilibrium, the rate must equal zero:
yCO2  yH4 2
yCH 4  y
2
H 2O eq

K RDS
 K eq ,SMR
K*
(8)
where the equilibrium constant K eq ,SMR of SMR reaction can be obtained from
thermodynamic data. Defining k  k RDS and replace θfree with DEN, the rate
2
expression equation is then,
rSRE

yCO2  yH4 2
1
 k  yCH 4  1 

 K eq , SMR yCH  yH2 O

4
2

1
 
2
 DEN
(9)
Altogether 6 parameters are used for fitting, k, KAc*, KCO*, KOH*, KH* and KCH3*.
Ki* are included in DEN, each Kj could be calculated from the obtained Ki* and the
relationship of θi as well as the three equilibrium constants of the reactions ETD,
ACD and WGS.
During the initial period of reaction, yH2O >> yCO2 and pH2, the rate expression
equation in equation (9) becomes:
rSRE  (k  yCH 4 
k
K eq , SMR

yCO2  yH4 2
y
2
H 2O
)
k  yCH 4
1

2
DEN
DEN 2
(10)
The values of mole fractions for intermediate gases such as methane, carbon
monoxide and hydrogen are not available. However, before the rate determining
reaction occurs and the acetaldehyde is thermodynamic instable, the product
compositions of intermediate gases are directly related with the mole fraction of
ethanol through the equilibrium constants of ethanol decomposition and acetaldehyde
decomposition reactions:
yCH 4  yCO  yH 2
yEtOH
 K eq , ETD  K eq , ACD , yCH 4  yCO  yH 2
(11)
while aCO in the DEN is related with yCO, the reaction rate during the initial period can
be expressed as:
rSRE 
k  ( K eq , ETD K eq , ACD )1/3 y1/3
EtOH
1  K
*
CO
( K eq , ETD K eq , ACD )1/3 y1/3
EtOH 
3
2
(12)
Figure S1
Schematic representation of the experimental set-up.
C-4
V-5
C-3
C-2
P-1
C-1
V-1
V-2
V-3
V-4
T-5
F-1
R-1
C-1
C-2
C-3
C-4
F-1
P-1
R-1
T-1
T-2
T-3
T-4
T-5
V-1
V-2
V-3
V-4
V-5
V-6
Mass Flow Controller
Heating Furnace
HPLC Pump
Reactor
Helium
Nitrogen
Hydrogen
Carbon Dioxide
Ethanol-Water Mixture
He
N2
H2
CO2
T-1
T-2
T-3
T-4
V-6
Vent
Mass
Spectrometer
Valve
Three-Way Valve
Back Pressure Valve
4
Table S1. The parameters for elementary reaction steps based on LHHW model.
rj
k1  yEtOH  free  k1  Ac  yH2
K1 
k2   Ac  k2  y Ac   free
K2 
k3  Ac  k3 CO  yCH4
K3 
k4  CO  k4  yCO   free
K4 
2
kRDS  yCH4  free
 k RDS CH3  H
2
k5  yH2O  free
 k5  H OH
yH 2  Ac
yEtOH  free
y Ac   free
 Ac
 CO  yCH
4
 Ac
yCO   free
CO
 Ac  K1
yEtOH
 free
yH 2
 Ac  K21 yAc free
CO  K 21 K 3
k6 CO OH  H  k6  yCO2  yH2   3free
K6 
2
k7  H2  k7  yH2  free
K7 
k8 CH3 OH  k8  yH2 2 CO  free
K8 
 H  OH
2
yH 2O   free
yCO2  yH2  3free
CO OH  H
2
yH 2  free
 H2
yH2 2  CO   free
CH  OH
*
K Ac
 K 21
y Ac
 free
yCH 4
CO  K 4 yCO free
n.a.
K5 
K i*
θi
Kj
*
K CO
 K4
n.a.
OH  K5 K71/ 2
CO  K51 K61 
yH 2 O
y1/H 22
n.a.
 free
yCO2  yH2
yH 2 O
*
K OH
 K 5 K 71/ 2
 free
 H  K71/ 2 y1/H 2 free
K H*  K 71/ 2
2
CH  K52 K61 K71/ 2 K81
3
3
5
yCO2 yH7/22
yH2 2O
 free
*
KCH
 K52 K 61 K 71/ 2 K81
3
Nomenclature
Roman symbols
ai
number of the species i on the active sites
Ct
total number of sites on catalyst surface, (kgcat)-1
DEN
denominator
Kj
reaction constant for the reaction j
Ki*
equilibrium constant of the species i on the active sites
kj
forward kinetic constant for the reaction j, molkg-1h-1
k-j
backward kinetic constant for the reaction j, molkg-1h-1
Greek letters
θAc
coverage fraction of catalyst surface associate with CH3CHO
θCH3
coverage fraction of catalyst surface associate with CH3
θCO
coverage fraction of catalyst surface associate with CO
θOH
coverage fraction of catalyst surface associate with OH
θH
coverage fraction of catalyst surface associate with H
Subscripts and other symbols
i
component of species i, CH3CHO, CH3, CO, OH, H
t
total
6