Steam reforming behavior of methanol using paper-structured catalysts: Experimental and computational fluid dynamic analysis
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I N T E R N A T I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 1 6 6 1 – 1 6 7 0
0360-3199/$ - see frodoi:10.1016/j.ijhyde
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Steam reforming behavior of methanol usingpaper-structured catalysts: Experimental andcomputational fluid dynamic analysis
Shuji Fukahoria, Hirotaka Kogaa, Takuya Kitaokaa,�,Mitsuyoshi Nakamurab, Hiroyuki Wariishia
aDepartment of Forest and Forest Products Sciences, Graduate School of Bioresource and Bioenvironmental Sciences,
Kyushu University, Fukuoka 812-8581, JapanbR&D Division, F.C.C. Co. Ltd., Shizuoka 431-1304, Japan
a r t i c l e i n f o
Article history:
Received 9 November 2007
Received in revised form
25 December 2007
Accepted 27 December 2007
Available online 14 February 2008
Keywords:
Paper-structured catalyst
Methanol steam reforming
Heat transfer
Computational fluid dynamic
analysis
nt matter & 2008 Internane.2007.12.063
thor. Tel./fax: +81-92-642-tkitaoka@agr.kyushu-u.ac
a b s t r a c t
Copper–zinc oxide (Cu/ZnO) catalyst powders were impregnated into paper-structured
composites (catalyst paper) using a papermaking process. The paper-structured catalyst
was subjected to the methanol steam reforming (MSR) process and exhibited excellent
performance compared with those achieved by pellet-type or powdered catalyst. The
catalyst paper demonstrated a relatively stable gas flow as compared to catalyst pellets.
Furthermore, the MSR process was simulated by computational fluid dynamic (CFD)
analysis, and the heat conductivity influence of the catalyst layer was investigated. Higher
heat conductivity contributed to both higher methanol conversion and lower carbon
monoxide concentration; localization of heat and chemical species such as hydrogen and
carbon dioxide were improved, resulting in suppression of reverse water–gas shift reaction.
The CFD analysis was applied to the design of a catalyst layer in which a suitable shape was
suggested, where carbon monoxide formation was further suppressed without a decrease
in the methanol conversion.
& 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights
reserved.
1. Introduction
With the recent trend of making industrial processes more
environmentally friendly, there has been much attention
focused on the preparation of catalysts having high activity
and selectivity. In doing so, invariably it requires certain
modifications to be made to the catalyst composition and
nanometer scale morphology [1,2]. In addition to these
factors, a number of other physical aspects including the
transfer of mass and heat on the catalyst surface are also
significant for realizing practical catalytic processes. With
respect to both mass and heat transfer, novel catalysts with
tional Association for Hy
2993..jp (T. Kitaoka).
controlled regular architecture (so-called structured catalysts)
have been developed; the tailoring of the micrometer-order
pores inside the catalyst and the selection of supporting
materials are academic and practical areas of ongoing
research and development to improve the diffusion and heat
transfer of the products [3–6]. In a recent paper, Groppi et al.
reported on the thermal behavior of the structured
Pd=g–Al2O3 catalyst, which was wash-coated on a variety of
plate-type metal supports for studying gas/solid exothermic
reactions, and it was revealed that the type of metal support
significantly affected the formation of heat spots [5]. Takaha-
shi et al. developed a silica–alumina catalyst with continuous
drogen Energy. Published by Elsevier Ltd. All rights reserved.
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micrometer-scale pores for the dehydration of alcohol, and
the contribution of the macropores on catalytic performance
was quantitatively evaluated [4].
In our previous studies [7–10], porous paper-structured
catalysts (so-called catalyst paper) was successfully prepared
using a papermaking technique; Copper–zinc oxide (Cu/ZnO)
catalyst particles were homogeneously scattered on glass and
silicon carbide (SiC) fiber networks having micrometer-scale
pores. The catalyst paper showed excellent methanol steam
reforming (MSR) performance, and the micrometer-scale
pores inside the catalyst paper presumably provide the
appropriate flow path for the reactants and modified gas,
resulting in higher methanol conversion and lower carbon
monoxide concentration, as compared to those achieved
using catalyst powder and catalyst pellets. Moreover, the
presence of SiC fibers in the catalyst paper improved the heat
transfer and heat distribution, contributing to higher metha-
nol conversion and lower carbon monoxide concentration
compared to those of catalyst paper prepared with glass
fibers. Thus, the paper-structured catalyst provides an
appropriate environment for the reforming catalyst by
optimizing the gas flow and heat distribution around the
catalyst, hence the catalyst paper prepared by a simple
papermaking technique is proposed for desirable use as
practical catalyst-based materials.
In the present study, the MSR behavior of the catalytic
materials, SiC fiber-containing catalyst paper, catalyst powder
and catalyst pellets, under different space velocities (SVs) was
investigated. In addition, the products and heat distributions
were simulated by computational fluid dynamic (CFD) analy-
sis, and the effect of both heat conductivity and the shape of
the catalyst layer on MSR performance were also discussed.
2. Materials and methods
2.1. Materials
Commercial Cu/ZnO catalyst pellets (MDC-3; cylindrical
shape; 3 mm diameter and 3 mm height; SUD-CHEMIE, Ltd.)
were used; the pellets were pulverized in part into 100-mesh
pass powders using a bowl mill. Pulp fibers, used as a
tentative supporting matrix in the wet papermaking process,
were obtained by beating commercial bleached hardwood
kraft pulp to 300 ml of Canadian Standard Freeness [11] with a
Technical Association of the Pulp and Paper Industry (TAPPI)
standard beater [12]. Glass fibers (CMLF208; ca. 0:8mm
diameter; heat conductivity; ca. 1:0 W=m K; Nippon Sheet
Glass, Ltd.) were cut into ca. 0.5 mm length using a four-flute
end mill. Fibrous SiC whiskers (size; ca. 0:5mm diameter and
30mm length; heat conductivity; ca. 25.5 W/m K) were pur-
chased from Tateho Chemical Industry, Ltd. Two types of
flocculants: polydiallyldimethylammonium chloride (PDAD-
MAC, molecular weight ðMwÞ: ca. 3� 105; charge density (CD):
5.5 meq/g; Aldrich, Ltd.) and anionic polyacrylamide (A-PAM,
HH-351; Mw: ca. 4� 106; CD: 0.64 meq/g; Kurita, Ltd.) were
used as retention aids. An alumina sol (Snowtex 520, Nissan
Chemicals, Ltd.) was used as a binder for enhancing the
physical strength of the catalyst paper.
2.2. Preparation of catalyst paper
The essential catalyst paper preparation details were reported
in the previous studies [7–10]. Briefly, glass and SiC fibers were
used as fiber matrix components in the catalyst paper. A fiber
suspension containing catalyst powders was mixed with
PDADMAC (0.5% total solids), alumina sol and A-PAM (0.5%
total solids), in that order. The mixture was poured into a pulp
fiber suspension, and then various types of catalyst paper
with SiC fibers of 20% w/w per total fiber content were
prepared according to the TAPPI test methods [13]. Following
pressing at 350 kPa for 5 min, the wet sheets were dried in an
oven at 105 �C for 30 min. One paper composite ð2� 104 mm2Þ
before calcination consisted of catalyst powders (4.5 g), glass
fibers (4.0 g), SiC fibers (1.0 g), alumina sol binder (0.1 g) and
pulp (0.25 g). Details of the SiC fibers and pulp content have
already been investigated [9]. The paper composites obtained
were thermally treated at 350 �C for 24 h to remove the organic
components, and then thermowelded to improve the physical
strength.
2.3. Reforming process and performance test
Ten circular catalyst paper samples, each with an area of 8�
102 mm2 and thickness of 1 mm, were stacked on top of each
other ð8� 103 mm3Þ and placed in a stainless steel thermo-
regulatory reaction cylinder (Fig. 1). Similarly, catalyst powder
or pellets with total volumes of 8� 103 mm3 were placed
inside the reaction cylinder. When either catalyst powder or
pellets were used, inert silica–alumina powders with the
same particle sizes were also mixed in to adjust the occupied
volume to 8� 103 mm3. A schematic diagram of the gas flow
system for the MSR process has already been reported [7]. The
MSR reactants were introduced into the reactor at a 2:1 molar
ratio of water to methanol (steam/carbon, S/C ratio ¼ 2) at a
constant flow rate (SV ¼ 537:5, 1075 and 2150 h�1Þ. In the case
of the autothermal reforming (ATR) process, a mixed gas of
methanol/water/oxygen (molar ratio: 1.00:2.00:0.125) was fed
into the reactor [8,10].
The amounts of Cu/ZnO catalyst were adjusted to 0.6 g in
each case. Prior to the MSR reaction, the catalyst samples
were reduced in situ with hydrogen at 250 �C for 1.5 h, followed
by a complete purge of all flow lines with nitrogen for 30 min.
The gas composition during the catalytic reaction was
monitored at reaction temperatures ranging from 200 to
300 �C using two online gas chromatographs (GCs) and one
offline GC. The exhaust gases generated in the MSR reaction
were passed through a cold trap in an ice bath. The unreacted
methanol and water residues were separated from the
gaseous components and then quantified using an offline
GC-FID (GC-17A Shimadzu, Ltd.) fitted with a Supel-Q Plot
column (0:53mm� 30 m, Shimadzu, Ltd.) at a furnace tem-
perature of 60 �C. The major gaseous products of hydrogen
and carbon dioxide were determined online using GC-TCD,
fitted with a Porapak-Q column (3 mm� 2 m, Shinwa Chemi-
cal Industries, Ltd.), while carbon monoxide, which was
isolated as a minor by-product, was measured by first
converting it to CH4 with an online methanizer (MTN-1,
Shimadzu, Ltd.), and then measuring the quantity of CH4
produced using a GC-FID fitted with a Porapak-Q column. All
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20.0 mm (100 meshes)
33.6 mm(170 meshes)
Methanol and steam
Modified gas
330 mm
ThermocoupleThermocouple
10.0 mm (50 meshes)
Stainless tube Catalyst layer
Fig. 1 – Schematic illustration of the reactor model used for the CFD simulation.
Table 1 – Specific heat conductivity ðCpÞ thermal con-ductivity ðgÞ and viscosity ðZÞ of chemical species
Species Cp (J/kg K) g (W/m K) Z (kg/m s)
CO2 Piecewise-linear 0.0323 2:61� 10�5
CO Piecewise-linear 0.0386 2:84� 10�5
H2 Polynomial Polynomial Polynomial
CH3OH Piecewise-linear 0.0351 1:88� 10�5
H2O Polynomial Polynomial Polynomial
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measurements were repeated at least four times and
standard deviations were obtained.
2.4. CFD analysis
CFD software, FLUENT ver. 6.2, was used to computationally
simulate the MSR process [14,15]. A steady state, segregated
solver was used to solve the heat, momentum, mass and
species transport equations in two-dimensional (2-D) reactor
configurations. The semi-implicit method of pressure–liquid
equation method and first-order upwind discretization
scheme were selected for quantifying the pressure–velocity
coupling and density interpolation, respectively.
The reactor model was constructed as follows. A full-scale
reactor model was built by GAMBIT (330 mm length, 33.6 mm
diameter). The reaction was considered to occur axisymme-
trically in a steady state, and a corresponding 2-D model was
constructed (shown in Fig. 1). The catalyst layer and
surrounding region were divided into 17 000 meshes with
dimensions of ca. 200mm� 200mm. A porous zone model
(including chemical reactions) was adopted for the catalyst
layer. The viscous resistance of the catalyst layer in all
directions was set at 1:2� 105=m2, while the fluid porosity
was set at 50%, in accordance with the values employed in the
prepared catalyst paper [9].
Five chemical species: methanol, water, hydrogen, carbon
dioxide and carbon monoxide, were used as ideal gases. The
specific heat conductivity (CpÞ, thermal conductivity (gÞ and
viscosity (ZÞ of the chemical species were set and shown in
Table 1. Cp of chemical species, g and Z of hydrogen and water
were temperature-dependent parameters compiled in the
FLUENT database (e.g. thermal conductivity of hydrogen at a
temperature T(K) is calculated by using the following equa-
tion: gH2¼ 8:27� 10�2
þ 3:56� 10�4 Tþ 1:07� 10�8 T2Þ. The
density of the mixed gas was dealt with as a non-compressive
ideal gas. The Cp, g, and Z values of the mixed gas obeyed the
mass-weighted mixing law.
The g values of catalyst layer meshes on the CFD analysis
were virtually set according to the constituent proportion of
the catalyst paper composed of glass fiber (58%), SiC fiber
(14%), Cu (12%), ZnO (13.5%) and Al2O3 (2.5%) with the
corresponding g values of 1.0, 25.5, 401, 54.0 and 29.0 W/m K,
respectively. The heterogeneous heat circumstance simulated
in this study seems to be partially consistent with that of the
real catalyst paper. Gravity was taken into account only for
the axial direction and was set at g ¼ 9:81 m=s.
The MSR process occurs in two steps, methanol reforming
and reverse water–gas shift reactions:
CH3OHþH2O!a1
3H2 þ CO2, (1)
H2 þ CO2 $a2
a02
COþH2O. (2)
The reaction rate of the two steps (a1, a2, a02, mol=m3 s) were
defined using the reaction rate constant (k1, k2, k02) and molar
concentration ðCi; mol=m3Þ; k1 and k2 were calculated accord-
ing to Arrhenius equation [16,17] using gaseous constant R ¼
8:31 J=K mol and temperature ðT;KÞ:
a1 ¼ k1 � C0:6CH3OH � C
0:4H2O,
a2 ¼ k2 � CH2� CCO2
,
a02 ¼ k02 � CCO � CH2O,
k1 ¼ f1 expð�E1=RTÞ,
k2 ¼ f2 expð�E2=RTÞ.
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0
50
100
0CO concentration (ppm)
Met
hano
l con
vers
ion
(%)
0
50
100
0
Met
hano
l con
vers
ion
(%)
CO concentration (ppm)
0
50
100
0
Met
hano
l con
vers
ion
(%)
CO concentration (ppm)
15000100005000 15000100005000
15000100005000
Fig. 2 – MSR performance: (a) catalyst paper, (b) catalyst powder and (c) catalyst pellets; with SV ¼ 537:5 h�1 (diamonds),
1075 h�1 (squares) and 2150 h�1 (triangles).
Reaction time (h)
Gas
flo
w (
SCC
M)
0
50
100
0 321
Fig. 3 – Modified gas flow rate: catalyst paper (red line) and
catalyst pellet (blue line). (For interpretation of the
references to color in this figure legend, the reader is
referred to the web version of the article).
6000
4000
2000
0
100
60
0
Met
hano
l con
vers
ion
(%)
CO
con
cent
ratio
n (p
pm)
21501075
40
80
20
Space velocity (h-1)4300
Fig. 4 – Comparison of methanol conversion (bars) with
carbon monoxide concentration (lines): experimental
(closed) and computational results (open).
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f r and Er corresponded to the frequency factor and activation
energy of the rth reaction, respectively, and were fitted to the
experimental results using catalyst powder; f1 ¼ 8:0� 108 s�1,
f2 ¼ 4:0� 108 m3=mol s, E1 ¼ 7:0� 104 J=mol and E2 ¼ 1:0�
105 J=mol. The reverse reaction of (2) (water–gas shift reaction)
occurred simultaneously and reaction rate constant k02 was
calculated using equilibrium constant of rth reaction Kr,
k02 ¼ k2=K2.
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The boundary conditions were set as follows: inlet gas
temperature was 300 �C, the inlet gas velocity and temperature
of the reactor wall (TwÞ were altered in the appropriate ranges
of 1075–4300 h�1 and 265–380 �C, respectively. The outlet
pressure was ambient.
3. Results and discussion
3.1. Effect of SV on MSR performance
The paper-structured catalyst had the external appearance of
cardboard, and was convenient for handling and processing.
The essential catalyst paper preparation details were ob-
tained from the previous related studies [7–10]. The MSR
24.0
0.0
12.0
18.0
6.0
60.0
0.0
30.0
45.0
15.0
300
200
250
275
225
20.0 mm
33.6
Thermo
Catalyst layer
Fig. 5 – CFD simulation results; distribution of: (a) temperat
concentration (%), (d) hydrogen concentration (%), (e) carbon diox
(ppm).
behavior was investigated with respect to SV. Fig. 2 displays
the SV-dependent correlation between the degree of metha-
nol conversion and carbon monoxide concentration obtained
by changing reaction temperatures when modified with SiC
fiber-containing catalyst paper, catalyst powder and catalyst
pellets. Under relatively low SV conditions ðSV ¼ 537:5 h�1Þ,
small differences were observed between the MSR perfor-
mances obtained for the catalyst paper, powder and pellets;
the flow rate of the reactant became slow and the effect of the
intra-particle diffusion limitation decreased. The MSR perfor-
mance deteriorated with increasing SV conditions in all
cases, especially in catalyst pellet. In relatively high SV
conditions ðSV ¼ 2150 h�1Þ, a higher temperature is required
to achieve a similar methanol conversion compared to that
obtained under low SV conditions, causing carbon monoxide
5000
0
2500
3750
1250
40.0
0.0
20.0
30.0
15.0
70.0
0.0
35.0
52.5
17.5
gas flow
mm
couple
Stainless tube
ure ðunits ¼ �CÞ, (b) methanol concentration (%), (c) water
ide concentration (%) and (f) carbon monoxide concentration
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formation through endothermic reverse water–gas shift
reaction [16,18,19]. It is well known that such side reaction
progresses with increasing catalyst size, thus carbon mon-
oxide concentration drastically increased when the catalyst
pellet was used. On the other hand, the MSR performances of
catalyst paper were slightly affected by SV, which were in
contrast to those obtained by using either catalyst powder
or catalyst pellets. In the paper-structured catalyst, micro-
meter scale catalysts were scattered on the fiber–mix
matrix consisting of ceramic fibers [7–10], therefore shift
reaction was suppressed, and consequently the excellent
MSR performance was achieved even under the high SV
conditions Such unique characteristics are advantageous
for practical applications under the required higher SV
condition.
Fig. 3 profiles the flow rate (standard cubic centimeter per
minute, SCCM) of the generated gas monitored with time,
obtained using catalyst paper and catalyst pellets at a
reaction temperature of 205 �C. A large oscillation of gas flow
rate with time was observed when catalyst pellets were
employed, resulting in unstable hydrogen production. On the
other hand, the catalyst paper demonstrated a relatively
stable gas flow. The average gas flow rates obtained when
catalyst paper and catalyst pellets were used corresponded to
52:2� 2:5 and 34:0� 8:4 SCCM, respectively. Such reforming
stability with regard to the ATR of methanol was discussed in
our previous study [8]. For practical applications, the constant
supply of hydrogen fuel is a striking factor for the generation
0
50
100
200
External wall temperature (°C)
Met
hano
l con
vers
ion
(%)
0
50
100
0CO conc
Met
hano
l con
vers
ion
(%)
350300250
Fig. 6 – CFD simulation results; heat conductivity of catalyst la
conversion, (b) carbon monoxide concentration and (c) relations
concentration.
of electricity by hydrogen fuel cells. The unique porous
structure of the catalyst paper is expected to contribute to a
uniform flow of gaseous components, and to be supplied
either to the catalyst surface or to quickly pass through the
catalyst layer.
3.2. CFD analysis of MSR process
First, the validity of the constructed simulation model was
checked. Fig. 4 displays a comparison of the methanol
conversion and carbon monoxide concentration under differ-
ent SV conditions, obtained either computationally or experi-
mentally. The order of methanol conversion efficiency and
carbon monoxide concentration, and their corresponding SV-
dependent behavior, were analogous between computational
and experimental results, providing certain validity to the
constructed model.
The distribution of temperature and the chemical species
(methanol, water, hydrogen, carbon dioxide and carbon
monoxide) are displayed in Fig. 5. There are low temperature
regions near the centerline of the reactor where hydrogen
concentration is low, indicating that the heat transfer from
the reactor wall is insufficient, and that the inward heat
transfer is an important factor to achieving high hydrogen
production. The hydrogen relatively generated at the periph-
eral part of the catalyst paper mounted in the reactor due to
the greater, more sufficient heat supply from the outside of
the reactor. Carbon monoxide was mainly generated at the
0
4000
8000
200External wall temperature (°C)
CO
con
cent
ratio
n (p
pm)
4000entration (ppm)
350300250
8000
yer is 1.0 (triangles) and 25.5 W/m K (squares); (a) methanol
hip between methanol conversion and carbon monoxide
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peripheral part of the catalyst paper, as was hydrogen, espe-
cially at the bottom part of the catalyst layer. It was assumed
that the high hydrogen concentration and sufficient quantity
of heat at the peripheral and bottom part of the catalyst layer
stimulated the reverse water–gas shift reaction, resulting in a
high carbon monoxide concentration.
3.3. Influences of heat conductivity and catalyst papershape on MSR performance
In our previous study, SiC fiber-containing catalyst paper with
a SiC fiber content of 20%, exhibited higher methanol
conversion and lower carbon monoxide concentration com-
pared to catalyst paper prepared using just glass fibers as the
fiber component [9]. The influence of the heat conductivity of
the catalyst layer on MSR performance was investigated by
CFD analysis. The heat conductivity of all catalyst layer
meshes were set at 1.0 or 25.5 W/m K, corresponding to those
of glass and SiC fibers, and their temperature-dependent MSR
behaviors were evaluated. For the heat conductivity of the
catalyst layer, Fig. 6 displays the CFD simulation results
70.0
0.0
35.0
52.5
17.5
24000
0
12000
18000
6000
380
180
280
330
230
Fig. 7 – Distribution of temperature and chemical species at meth
catalyst layer is 1.0 W/m K (left) and 25.5 W/m K (right); tempera
and carbon monoxide concentration (bottom, ppm).
corresponding to the methanol conversion and carbon
monoxide concentration. The relationship between the
methanol conversion efficiency and carbon monoxide con-
centration was improved with increasing heat conductivity.
Moreover, the distribution profiles of the heat and carbon
monoxide concentrations have been simulated when the
methanol conversion was ca. 80% (Fig. 7). In the case where
the heat conductivity of the catalyst layer meshes was
1.0 W/m K, Tw, the methanol conversion and carbon mon-
oxide concentrations were 380 �C, 79.6% and 11 500 ppm,
respectively. When the heat conductivity of the catalyst layer
meshes was 25.5 W/m K, Tw was 265 �C and the methanol
conversion and carbon monoxide concentration were 81.7%
and 1700 ppm, respectively; the reaction temperature de-
creased by 115 K at the same methanol conversion. Accord-
ingly, the equilibrium of endothermic reverse water–gas shift
reaction became unfavorable, possibly leading to the drastic
decrease of carbon monoxide concentration. Furthermore,
low heat conductivity caused a larger temperature gradient in
the radius direction, resulting in heterogeneous hydrogen
production. Such localization of heat and hydrogen possibly
anol conversion of ca. 80% when the heat conductivity of the
ture (upper, units ¼ �C), hydrogen concentration (middle, %)
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300
200
250
275
225
70.0
0.0
35.0
52.5
17.5
5000
0
2500
3750
1250
321 4
2 3 1 4
3000
2000
1000
0
100
80
60
40
0
20
Met
hano
l con
vers
ion
(%)
CO
con
cent
ratio
n (p
pm)
21 43
Fig. 8 – Effect of the catalyst layer shape on MSR performance: (a) constructed catalyst layer model; gray regions represent the
catalyst layer, (b) MSR performance at the reaction temperature of 300 �C; methanol conversion (open bars) and carbon
monoxide concentration (filled bars), (c) distribution of temperature and chemical species of each model; temperature (upper,
units ¼ �C), hydrogen concentration (middle, %) and carbon monoxide concentration (bottom, ppm).
I N T E R N AT I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 1 6 6 1 – 1 6 7 01668
triggered a reverse water–gas shift reaction, resulting in a
high carbon monoxide concentration.
It was pointed out that the carbon monoxide generated at
the peripheral and bottom part of the catalyst layer, where
the reverse water–gas shift reaction rather than the MSR
reaction occurred because the hydrogen concentration hardly
increased, as shown in Fig. 5(d). Therefore, the catalyst layer
was partially cut in the peripheral and bottom part of the
catalyst layer, and its MSR performances compared (Fig. 8);
the peripheral and bottom part of the catalyst layer was cut
by 1.0, 5.0 and 8.4 mm, respectively (displayed as models 2, 3
and 4). The methanol conversion and carbon monoxide
concentration were affected by the shape of the catalyst
layer. The carbon monoxide concentration when simulated
using model 2 was lowered by 20%, as compared with that
simulated using model 1 without a reduction in the methanol
conversion efficiency. In the case of models 3 and 4, the
carbon monoxide concentration decreased still further, while
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20.0 mm
33.6 mm
31.6 mm
0
50
100
0CO concentration (ppm)
Met
hano
l con
vers
ion
(%)
300020001000
Fig. 9 – Schematic illustration of the tuned catalyst layer (a)
and reforming performance (b); MSR with a normal catalyst
layer (closed diamonds), MSR with a tuned catalyst layer
(open diamonds), ATR with a normal catalyst layer (closed
circles), ATR with a tuned catalyst layer (open circles).
SV ¼ 537:5 h�1.
I N T E R N A T I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 1 6 6 1 – 1 6 7 0 1669
the methanol conversion also decreased; the methanol con-
version was less than 70% when simulated using model 4.
These results strongly suggest this outcome, such that an
appropriate catalyst layer shape could be designed according
to the reforming conditions, making CFD analysis a powerful
tool for efficient material development.
3.4. ATR process using SiC fiber-containing catalyst paper
In our previous study, the catalyst paper prepared with
ceramic fibers was subjected to ATR process: the combined
process of endothermic MSR and exothermic partial oxida-
tion of methanol [20–22]. In the ATR process, the relationship
between the methanol conversion and carbon monoxide
concentration was superior to that of MSR; therefore, the
SiC fiber-containing paper was also subjected to the ATR
process. Moreover, it was indicated through CFD simulations
that the catalyst layer model 2 in Fig. 8(a) showed promise for
carbon monoxide reduction. Thus, a catalyst paper having
similar shape to model 2 in Fig. 8(a) was experimentally
prepared and subjected to both MSR and ATR processes. Two
types of catalyst paper with different diameter were com-
bined: five circular catalyst paper samples with a diameter of
33.6 mm were used as the first part of the catalyst, and five
circular catalyst paper samples with a diameter of 31.6 mm
were used as the latter part. A schematic illustration of the
tuned catalyst layer and its reforming performance are shown
in Fig. 9. When a modified catalyst with a tuned shape was
employed in both MSR and ATR processes, the carbon
monoxide concentration decreased by 10% without a con-
comitant decrease in the methanol conversion, resulting in a
superior relationship between the methanol conversion and
carbon monoxide concentration. The ATR rather than the
MSR process proceeded in a high methanol conversion at a
low carbon monoxide concentration. In the ATR process using
a catalyst with a tuned shape at SV ¼ 537:5 h�1, the carbon
monoxide concentration was lowered below 1000 ppm, which
is one-tenth of the value obtained using Cu/ZnO powder [19].
Various parameters, including the reaction temperature,
velocity and composition of inlet gas, heat conductivity, the
amount of catalyst in the reactor and catalyst shape, are
easily controllable in the CFD model. At this stage, the carbon
monoxide concentration of modified gas was not low yet
enough to permit direct supply to practical polymer electro-
lyte fuel cells; however, a combined use of experimental and
computational results is expected to make catalyst material
development more speedy and effective.
4. Conclusion
The MSR performance of various catalytic materials was
investigated both experimentally and computationally. The
paper-structured catalyst exhibited excellent and stable MSR
performance even under high SV conditions, as contrasted
with those obtained using catalyst powder or pellets, which is
an appealing result for practical application. Furthermore, the
effects of heat conductivity and the shape of the catalyst layer
were demonstrated by CFD analysis. The improvement in the
heat conductivity of the catalyst layer contributed to the rapid
heat transfer and resultant small temperature gradient,
suppressing undesired carbon monoxide formation. In addi-
tion, CFD analysis also revealed that the shape of the catalyst
layer significantly influenced the MSR performance, while the
relationship between the methanol conversion and carbon
monoxide concentration was improved in both MSR and ATR
processes by tuning the shape of the catalyst layer. In the ATR
process by using a paper-structured catalyst with a tuned
shape, the carbon monoxide concentration halved as com-
pared to that obtained in the MSR process. From these results,
it was confirmed that the paper-structured catalyst, which is
both easy handling and easily fabricated, is a promising
candidate for high-performance catalyst-based materials
Acknowledgments
This research was supported by Research Fellowships of the
Japan Society for the Promotion of Science for Young
ARTICLE IN PRESS
I N T E R N AT I O N A L J O U R N A L O F H Y D R O G E N E N E R G Y 3 3 ( 2 0 0 8 ) 1 6 6 1 – 1 6 7 01670
Scientists (S.F. and H.K.) and by an Industrial Technology
Research Grant Program in 2003 from the New Energy and
Industrial Technology Development Organization (NEDO) of
Japan (T.K.). The authors wish to thank Ms. K. Hayashida and
Ms. Y. Kubara for their assistance with CFD analysis.
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