Advances in Chemical Engineering and Science, 2013, 3, 7-14
doi:10.4236/aces.2013.34B002 Published Online October 2013 (http://www.scirp.org/journal/aces)
Removal of Carbon Monoxide from Hydrogen-rich
Fuels over CeO2-pro mot ed P t/Al2O3
Akkarat Wongkaew1*, Pichet Limsuwan2
1Department of Chemical Engineering, Faculty of Engineering, Burapha University, Chonburi, Thailand
2Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
Received May, 2013
ABSTRACT
A comparative study of catalytic CO oxidation and selective CO oxidation over Pt/Al2O3 and CeO2-promoted Pt/Al2O3
catalysts has been investigated for the removal of a trace amount of CO from the reformed gas. The catalysts were pre-
pared by sol gel and incipient wetness impregnation. CO oxidation and selective CO oxidation were carried out with a
5%Pt/Al2O3 and a 5%Pt/15%CeO2/Al2O3. The presence of 15%CeO2 in the 5%Pt/Al2O3 dramatically improves the ac-
tivities to CO oxidation and selective CO oxidation at low temperature (<180℃). FTIR results indicate that CO could
react with lattice oxygen from ceria and release CO2 as a product. Low space velocity would obtain high CO conversion
at low temperatures while high space velocity would obtain high CO conversion at high temperatures. The results also
show that a 5%Pt/15%CeO2/Al2O3 can completely oxidize 1% CO at 180℃ with selectivity of 52% and space velocity
of 70,000 cm3·g-1·h-1. Under the realistic gas feed with 1%O2, this catalyst is very stable and retains its activity and se-
lectivity at 180℃ during 72 h.
Keywords: CO Oxidation; CeO2-Pt/alumina; CO Adsorption; Selective CO Oxidation; Fuel Processing
1. Introduction
The polymer-electrolyte-membrane fuel cell (PEMFC)
has been attracting significant attention in several appli-
cations including electric vehicles and residential power-
generations. This is because of its many attractive fea-
tures such as high power density, rapid start-up, and high
efficiency [1, 2]. As the PEMFCs utilize hydrogen gas as
a fuel and since hydrogen can be produced by means of a
fuel reformer followed by water gas shift reaction for
further conversion of CO to H2, carbon monoxide is al-
ways present in the hydrogen stream. Generally, catalytic
steam reforming of methanol or partial oxidation of
gasoline followed by water gas shift reaction will pro-
duce a gas stream with 40%-75% H2, 15%-20% CO2,
~10% H2O, 0-25% N2 and 0.5%-1.0% CO. This amount
of CO contained in the reformed gas is high enough to
poison the Pt anode of PEM fuel cells and in turn dra-
matically degrades the fuel cell potential and energy
conversion efficiency [3, 4]. Experimentally, it has been
found that the tolerable level of CO without harmful ef-
fects is about 10 ppm [5]. This means the 0.5%-1.0% CO
needs to be reduced to 10 ppm or less in order to increase
the use of proton exchange membrane (PEM) fuel cells
running with on-board generated hydrogen. The most
economical and straightforward technique for this pur-
pose is selective catalytic oxidation of CO in the H2-rich
reformed gas using O2 or preferential oxidation (PROX).
This method needs a suitable catalyst to enhance the CO
oxidation reaction with minimal oxidation of hydrogen
which is the desired fuel. The crucial requirement for the
PROX re- actor is a high CO conversion with high selec-
tivity. A number of catalysts have been investigated for
the PROX reaction [6-10]. Noble metals supported on
alumina such as Pt, Au, Ru and Pd, have been proposed
as ideal catalysts for PROX reaction, especially Pt/Al2O3,
Pt/ Fe2O3/ Al2O3, Pt/CeO2, Pt/CeO2_ZrO2, Pt/zeolite
[11-13]. An improvement in the selectivity at low tem-
peratures is needed. Oxidation of CO on alu-
mina-supported Pt catalysts is known to take place via
the Langmuir-Hinshel- wood mechanism. Kahlich et al.
[14] studied the kinetics of selective CO oxidation in
H2-rich gas on Pt/Al2O3 and observed that CO conversion
never reached 100% for a 0.5%Pt/Al2O3. The maximum
CO conversion was ~80% at temperatures as high as 250
℃. Other studies reported that CO conversion occurred
in the reaction temperature range of 200℃-250℃ [15]
or else needed high oxygen concentration for complete
elimination of CO, corresponding to lower selectivity.
We have previously [16] investigated the catalytic activ-
ity of 2%Pt/Al2O3, which was prepared by the sol-gel
method, in selective CO oxidation reaction under the

A. WONGKAEW, P. LIMSUWAN
8
excess H2 gas stream. We found that 2% Pt was well
dispersed in alumina supports. Therefore, it can selec-
tively oxidize CO down to ppm level with constant se-
lectivity and high space velocity. The performance of Pt
catalysts can be improved by modifying supports such as
adding alkali metals into supports [17] or by promoting
with other metal oxides such as Fe2O3 or CeO2 [18].
Serre, et al. [19] found that the presence of CeO2 in a
2%Pt/Al2O3 after a reductive pretreatment drastically
enhanced the activity of the catalyst to CO oxidation.
The promoting effect of ceria was attributed to the en-
hancement of the metal dispersion and the stabilization
of Al2O3 support toward thermal sintering. Moreover,
ceria can be a chemically active component, working as
an oxygen store that releases lattice oxygen in the pres-
ence of reductive gases and re- placement of the lattice
oxygen with oxygen gas when oxygen gas is present in
excess [20]. Parinyaswan et al. [21] investigated the per-
formance of Pt-Pd/CeO2 catalysts for selective CO oxi-
dation. This catalyst could maximally convert 83% CO to
CO2 with selectivity of 60% at 90℃with a gas feed con-
taining 1% CO, 1% O2, 25% CO2 and 10% H2O. This
means there would still be 1,700 ppm of CO left in the
gas feed and this gas could dramatically deplete the effi-
ciency of a PEM fuel cell in a very short time. The au-
thors suggest a multi-stage reactor to reduce CO to below
10 - 100 ppm for the use of this catalyst with PEM fuel
cells. Silva et al. [22] studied the effect of the presence of
ceria with Pt over alumina catalysts for the partial oxida-
tion of methane reaction. They reported that the addition
of ceria in alumina led to the formation of a homogenous
solid solution, which exhibited a high-oxygen storage
capacity. Brown et al. [23] compared the activities of Pt
over alumina with ceria-promoted Pt over alumina in the
production of hydrogen from methanol decomposition.
They reported that promoting with ceria had a positive
effect on activity and selectivity. Indeed, the use of ceria
coupled with alumina as a support for Pt might enhance
the catalytic selective CO oxidation of platinum over
alumina catalysts. Son et al. [24,25] investigated the per-
formance of Ce-Pt/-Al2O3 for selective oxidation of CO
in H2 for PEFCs. They found that the addition of 5% Ce
in the Pt over alumina dramatically enhanced CO con-
version and selectivity at low temperatures. The catalyst
completely converted 1%CO to CO2 at 200℃ with 50%
selectivity. Although the effect of other gases such as
CO2 and H2O was stud- ied, their gas compositions con-
taining 1% CO, 2.3% H2O, 10.09% CO2 and H2 as bal-
ance were far from a realistic gas composition containing
40%-75% H2, 0.5%-2.0% CO, 15%-20% CO2, 10% H2O
and 0-25% N2 by volume. Therefore, the activity of
promoted platinum over alu- mina with ceria for prefer-
ential CO oxidation still needs to be investigated.
In order to obtain a better understanding of the activity
of the ceria promoted platinum alumina catalyst to the
selective CO oxidation, 5%Pt/15%CeO2/Al2O3 and 5%
Pt/Al2O3 catalysts were tested for their activities to both
CO oxidation in H2 free-stream and CO oxidation in the
presence of excess H2-containing feed stream and the
obtained results were compared with others reported in
literatures. All supports in this work were prepared by sol
gel method. The CO coverage of the catalysts was also
studied using FTIR. The FTIR results were used to ex-
plain the enhancement of catalyst activity in the presence
of ceria. It should be pointed out that all gases containing
in reformed gas affect to the selectivity to CO oxidation
of the catalysts as reported in literatures. Therefore, the
effect of space velocity on the activity of the catalyst was
investigated. These results will lead us to the proper op-
erating conditions in order to obtain high selectivity and
high CO conversion of ceria promoted Pt alumina cata-
lyst.
2. Experimental
2.1. Catalyst Preparation
A cerium aluminum oxide supported platinum (Pt) cata-
lyst with 5.0 wt% Pt loading was prepared by sol gel
technique [26] and incipient wetness impregnation. Alu-
minum is protoxide; cerium (III) acetate and hydrogen
hex anchor oplatinate (IV) hydrate were obtained from
Aldrich. Preparation of supports containing cerium alu-
minum oxide began with dissolving the desired amount
of aluminum is protoxide in hot demonized water at 80℃.
After 30 min of aging with continuous stirring, nitric acid
(HNO3) was added to start the hydrolysis reaction result-
ing in a fibrillar sol. Then, the known amount of cerium
(III) acetate was incorporated into the solution at room
temperature. The solution was stirred overnight to obtain
uniformity. The obtained solution was heated to 60℃
and kept at this temperature until gelation occurred. The
gel was dried in air at 110℃ overnight, and then cal-
cined at 500℃ for 13 hours. After calcination, the re-
sulting powder was ground and sieved to obtain a
100-140 mesh powder. Incipient wetness impregnation
was used to deposit platinum into the support. With this
method, a desired amount of solution of hydrogen hexa-
chloroplatinate (IV) hydrate was added into a cerium
alumina support and then mixed together until the mix-
ture uniformly. The obtained solid was dried in air at
110oC overnight, and then calcined at 500℃ for 13
hours. The final powder was 5% Pt/15% CeO2/Al2O3. In
this work, the activity of this catalyst was compared with
activity of a 5% Pt/ Al2O3. For a 5% Pt/Al2O3 analogous
preparation techniques were used such that the Al2O3
support was prepared by sol gel and Pt was impregnated
in the support by incipient wetness impregnation. Before
testing the activities of these catalysts, the catalysts were
purged with H2 at 400℃ for 5 hrs.

A. WONGKAEW, P. LIMSUWAN 9
2.2. Characterization
The BET surface area and average pore radius of cata-
lysts were determined with adsorption-desorption iso-
therms of N2 at 77 K using a MicroMeritics ASAP 2010
instrument. Average crystalline sizes of oxides were de-
termined by Scherrer’s equation using the X-ray line
broadening from X-ray diffraction, Bruker AXS model D
8 Discover equipped with a CuKα radiation with a nickel
filter. Diffraction intensity was measured in the 2 theta
ranges between 20° and 85°, with a step of 0.02° for 8 s
per point.
2.3. Catalytic Activity
CO oxidation and CO oxidation in the H2-rich stream
was performed in a fixed-bed reactor. The reaction tem-
peratures inside the reactor were measured with a K-type
thermocouple placed on the top of the catalyst bed and
were controlled by a temperature controller (OMEGA:
CN3251). The amount of catalyst used in each run was
68 mg. The total gas flow rates of the reaction mixture
were 40 cm3·min-1 and 80 cm3·min-1, corresponding to
the space velocity of 70,000 cm3·g-1·h-1 and of 35,000
cm3·g-1·h-1, respectively. For CO oxidation, the activity
tests were conducted with a feed mixture of 1% CO, 1%
O2 and He as balance. For selective CO oxidation, a feed
mixture contained 1% CO, 0.5%-1% O2, 0-10% H2O,
0-20% CO2, 55% H2 and He as balance. A volumetric
flow controller with an accuracy of 0.5 cm3.min-1 was
used for measuring the total gas flow rate at the bypass
(for calibration purposes) and at the outlet of the reactor.
A Varian CP-4900 micro gas chromatograph (micro
GC) equipped with 2 channels (A and B) was used for
analysis of the outlet gas compositions from the reactor.
Channel A was used to detect H2, O2, CO and CH4 by a
Molsieve 5A PLOT column. Channel B was used to de-
tect CO2 by a PoraPLOT Q column. Along with GC,
FTIR was used to detect CO at low concentrations (ppm
level) in the outlet gas from the reactor. Because water
deteriorates the performance of these columns, an ice
cooled water condenser was used to remove water from
the gas streams before entering the GC and FTIR.
The CO conversion was obtained by comparing the
CO concentration in the feed measured at the bypass line
and the CO concentration in the outlet stream from the
reactor. Selectivity was defined as the ratio of oxygen
consumed by CO oxidation to the total oxygen consump-
tion (obtained by subtracting the O2 concentration at the
reactor outlet from the O2 concentration in the feed). The
amount of O2 not used in the CO oxidation reaction was
assumed to oxidize H2 in the H2 oxidation reaction. Im-
portantly, there was no methane formation observed un-
der reaction conditions performed in this study.
3. Results and Discussion
3.1. Characterization of the Catalysts
The alumina support prepared via the sol gel method
yielded a BET area of 227.8 m2/g with an average pore
size of 5.3 nm while the sol gel made 15%CeO2/Al2O3
had a BET area of 230.0 m2/g with an average pore size
of 5.2 nm. Pt crystalline sizes were estimated from the
line broadening of Pt (111) peaks. For both a 5%Pt/Al2O3
catalyst and a 5%Pt/15%CeO2/Al2O3 catalyst, no Pt (111)
peaks were observed indicating that Pt metal was well
impregnated and dispersed on the supports for both cata-
lysts. For ceria structure in a 5%Pt/15%CeO2/Al2O3 fresh
catalyst reduced under hydrogen, XRD results matched
with those for CeO2 with average CeO2 crystallite sizes
of ~6.8 nm. Dispersions measured by CO chemisorption
were 48% for the5%Pt/Al2O3 and 54% for the 5%Pt/
15%CeO2/Al2O3.
3.2. Activity Tests for CO Oxidation with
Free-H2 Gas Stream
The two catalysts were tested for their activities in CO
oxidation as a function of temperature under gas feed
containing 1%CO, 1%O2 and He as balance as seen in
Figure 1.
At 100℃ the integral conversions were 2% and 10%
over the 5%Pt/Al2O3 and the 5%Pt/15%CeO2/Al2O3 cat-
alysts. Increasing the temperature to 150℃ increased the
CO conversion from 2% to 27% for the 5%Pt/Al2O3 and
from 10% to 60% for the 5%Pt/15%CeO2/Al2O3. Further
increasing reaction temperature to 170℃ increased the
CO conversion to 70% for the 5%Pt/Al2O3 and to 98.9%
for the 5%Pt/15%CeO2/Al2O3. Finally, CO completely
converted to CO2 at 180℃ for both catalysts. Clearly,
the catalyst containing ceria showed better activity in CO
oxidation, especially at low temperatures. For the
5%Pt/Al2O3, it has been known that CO strongly chemi-
sorbs over Pt sites from room temperatures to 150℃
0
20
40
60
80
100
80100 120 140 160 180 200 220
Temperature,
o
C
CO conversion,
%
5%Pt/Al2O3
5%Pt/15%CeO2/Al2O3
Figure 1. Activities of platinum over alumina and promoted
platinum over alumina catalysts to CO oxidation. Gas
composition: 1%CO, 1%O2 and He as balance.

A. WONGKAEW, P. LIMSUWAN
10
[14,27]. At these temperatures, the competition between
CO molecules and O2 molecules over the active sites is
crucial. The reaction occurs when O2 molecules adsorb
and dissociate next to CO molecules. At tem- peratures
less than 150℃, Pt sites are occupied by CO molecules.
This leads to low activity of platinum over alumina cata-
lysts in the CO oxidation reaction. Increas- ing reaction
temperature above 150℃ dramatically in- creases the
rate of reaction due to desorption of CO molecules from
the active sites and leaving available sites for O2 mole-
cules to be adsorbed. The addition of ceria enhances the
rate of reaction of the catalyst. This is due to the oxygen
storage property proposed as following [28]:
22 2
2
23 2
CO2CeOCO*Ce O
1O*O
2
OCeO2CeO*
ads
ads
ads



3
where “*” stands for an adsorption site on platinum and
“ads” for an adsorbed species. From this model, the key
point of high activity of the 5%Pt/15%CeO2/Al2O3 cata-
lyst at low reaction temperatures (<150℃) results from a
capacity of ceria to switch between the two-oxidation
states Ce4+ and Ce3+. Ce3+ returns back to Ce4+ by gase-
ous oxygen molecules. This phenomenon occurs even at
room temperature. However, 170℃ is high enough for
CO molecules to desorbs from active sites and leave the
active sites available for other reactant molecules to be
adsorbed and reacted [29]. Therefore, both catalysts per-
formed comparably above 170℃. FTIR was used to
check the chemisorbed CO species. The results are shown
in Figure 2. Before the test, the catalyst pellet diluted
with KBr was purged with helium at 200℃ until catalyst
surface was clean. Then, the sample was cooled to 100℃
under a helium purge. After the temperature of the sample
reached 100℃, the sample was purged with gas stream
containing 1% CO balance with helium. The adsorption
of CO over the catalyst sample was recorded.
Figure 2(a) shows the CO adsorption over the 5%Pt/
15%CeO2/Al2O3 pellet. A strong peak at 2062 cm-1 was
observed. This peak corresponds to CO adsorbed over
Pt/CeO2/Al2O3 [30]. Other peaks at 2395-2312 cm-1 were
also observed and these peaks indicate the presence of
gas phase CO2. The intensity of the CO2 band slowly
decreased with time and finally disappeared. The forma-
tion of CO2 was due to CO oxidation reaction and the O2
reactant must have come from lattice of CeO2. This result
was in agreement with a model of oxygen transport in
Pt/ceria catalyst [31]. Next, the same experiment was
carried out with the 5%Pt/Al2O3. The results are shown
in Figure 2(b). A strong peak at 2085 cm-1 was observed.
This peak corresponds to CO adsorbed on Pt with
neighboring oxidized Pt [32]. Unlike platinum over ceria-
promoted alumina catalyst, no peak of CO2 gas phase
was observed. This means that in the absence of gas
phase O2 no CO oxidation reaction occurs with this cata-
lyst. The CO adsorbed on Pt peak for promoted Pt cata-
lyst appeared at 2062 cm-1 while that of Pt/Al2O3 ap-
peared at 2085 cm-1 [29,32]. The downward shift of CO
adsorbed wave number may be due to inducing of C-O
bond weakening for CO adsorbed on Pt by Ce [19]. The
reduction of the bond strength of adsorbed CO makes it
more reactive with an oxygen atom from ceria lattice into
CO adsorbed near Pt-CeO2 interface followed by desorp-
tion of CO2 leaving Pt site available for other gas mole-
cules. Therefore, the presence of a small amount of ceria
could enhance the activity of platinum over alumina due
to its oxygen storage property.
3.3. Effect of Ceria on the Activity of Catalysts
The effect of ceria on the activity of catalysts was shown
in Figure 3.
Figure 3(a) shows the activities of the two catalysts as
function of reaction temperature for a dry gas composi-
tion of 1%CO, 1%O2, 55%H2 and He as balance. At 110
℃, CO conversions were 46% and 60% over the 5%
Pt/Al2O3 and the 5%Pt/15%CeO2/Al2O3 catalysts. In-
creasing reaction temperatures further to 180C led to
dramatic increases in CO conversion from 46% to 90%
for the 5%Pt/Al2O3 and from 60% to 99.3% for the
5%Pt/15%CeO2/Al2O3. At 190℃, CO conversion reached
a maximum of approximately 99.97% for the 5%Pt/15%
CeO2/Al2O3 while CO conversion reached a maximum of
approximately 93.70% for the 5%Pt/Al2O3. Further in-
creasing reaction temperature to 230℃ resulted in de-
creases in CO conversion to 57% for the 5%Pt/Al2O3 and
89% for the 5%Pt/15%CeO2/Al2O3. Figure 3(b) shows
oxygen consumption as a function of reaction tempera-
ture. For the 5%Pt/Al2O3, O2 was quickly consumed by
the reactions. O2 conversion increased from 79% to
100% when reaction temperature increased from 110℃
Figure 2. FTIR study for CO adsorbe d over catalysts under
1%CO in He at 100C: (a) 5%Pt/15CeO2/Al2O3, (b) 15%
CeO2/Al2O3 and (c) 5%Pt/Al2O3.

A. WONGKAEW, P. LIMSUWAN 11
0
10
20
30
40
50
60
70
80
90
100
90110 130150 170190 210230 250
Temperature,
o
C
C O conversion, %
5Pt/Al2O3
5Pt/CeO2/Al2O3
(a)
0
10
20
30
40
50
60
70
80
90
100
90110 130150 170 190 210230 250
Temperature,
o
C
O
2
consumption, %
5Pt/Al2O3
5Pt/CeO2/Al2O3
(b)
0
10
20
30
40
50
60
70
80
90
100
90110130 150 170 190210 230 250
Temper ature,
o
C
S electivity, %
5Pt/Al2O3
5 Pt/CeO2/Al2O3
(c)
Figure 3. Comparison of activities to selective CO oxida-
tion of the 5%Pt/Al2O3 and the 5%Pt/ 15%CeO2/Al2O3 cat-
alysts as a function of temperature. Gas composition:
1%CO, 1%O2, 55%H2 and He as balance.
to 150℃. Unlike the 5%Pt/Al2O3, O2conversion for the
5%Pt/15%CeO2/Al2O3 slowly increased from 46% to
56%, 81%, 86% and 100% when reaction temperature
increased from 110℃ to 130℃, 150℃, 170℃, and 190
℃, respectively. These results led to differences in selec-
tivity for CO oxidation as shown in Figure 3(c). As
mentioned previously, no methane formation was ob-
served under these operating conditions. Consequently,
selectivity was defined as the ratio of oxygen used for
CO oxidation to total oxygen consumed by the reactions.
As shown in Figure 3(c), the selectivity’s of the two
catalysts are different. At 110℃, selectivity was 29% for
the 5%Pt/Al2O3. This means that oxygen consumed by
the reactions mostly goes to H2 oxidation. At the same
temperature, selectivity was 65% for the 5%Pt/15%
CeO2/Al2O3. This means that the presence of ceria in the
catalyst enhanced the rate of CO oxidation. Further in-
creases reaction temperature to 180℃ increased selec-
tiveity to 44% for the 5%Pt/Al2O3 but decreased selectiv-
ity to 50% for the 5%Pt/15%CeO2/Al2O3. At 230℃, se-
lectivity of both catalysts dropped to 28% for the 5%Pt/
Al2O3 and 45% for the 5%Pt/15%CeO2/Al2O3. The de-
crease of selectivity for both catalysts at high tempera-
tures is due to the competition between CO oxidation and
H2 oxidation reactions. At high temperatures, the H2
oxidation reaction occurs faster than the CO oxidation
reaction [32]. Further investigation of the 5%Pt/15%
CeO2/Al2O3 catalyst was conducted to understand its
behavior under different reaction conditions.
3.4. Space Velocity Effect
The dependence of CO conversion and selectivity on
flow rate is shown in Figures 4(a)-(c).
Space velocity was increased from 35,000 to 70,000
cm3·g-1·h-1. Considering at the same temperatures, in-
creasing the space velocity decreased the CO conversion
and decreased the O2 consumption. With 1% CO, 1% O2,
20% CO2, 10% H2O, 55% H2 and He as balance, maxi-
mum CO conversion for the low space velocity run was
100% at 150C while maximum CO conversion for the
high space velocity run was 100% at 180-190℃. Selec-
tivity did not change with space velocity at temperatures
less than 150℃. At higher temperatures, selectivity for
the low space velocity run was lower than that for the
high space velocity run. This result indicates that the use
of this catalyst depends on the reaction condition. Low
space velocity would obtain high CO conversion at low
temperatures while high space velocity would obtain
high CO conversion at high temperatures.
Activities of 1%Pt-1%CeO2 over activated carbon [33]
were compared with those of 5%Pt/15%CeO2/Al2O3 in
selective CO oxidation under realistic gas compositions.
Although the authors reported that their catalyst is very
active to CO oxidation in H2-excess stream and CO con-
version drastically increased with the presence of CO2,
combining both CO2 and H2O in the gas feed stream re-
sulted in CO conversion of 100% and selectivity to CO
oxidation of 50% at 150℃ with space velocity of 24,000
cm3·g-1·h-1. Unlike this catalyst, CO conversion of the
5% Pt/15%CeO2/Al2O3 decreased with the presence of
CO2 in the gas stream. This is due to the carbonate for-
mation blocking the available active sites. However,
combining both CO2 and H2O in the gas feed enhanced

A. WONGKAEW, P. LIMSUWAN
12
the activity of the catalyst especially at low temperatures
(<160℃). Under the realistic gas composition, our cata-
lyst obtained 100% CO conversion at 140-150℃ with
selectivity in CO oxidation of 50%-52% and space ve-
locity of 35,000 cm3·g-1·h-1.
0
10
20
30
40
50
60
70
80
90
100
90110130150 170 190 210230 250
Temperature,
o
C
CO conversion, %
70,000cc/g/h
35,000cc/g/h
(a)
0
10
20
30
40
50
60
70
80
90
100
90110130 150170190 210230250
Temperature,
o
C
O
2
consumption, %
70,000cc/g/h
35,000cc/g/h
(b)
0
10
20
30
40
50
60
70
80
90
100
90110130 150170 190210 230 250
Temperature,
o
C
S elec t ivit y, %
70,000cc/g
/h
35,000cc/g
/h
(c)
Figure 4. Dependence of CO conversion and selectivity of
CO oxidation on space velocity and temperature for a 5%Pt
/15%CeO2/Al2O3. Gas composition: 1%CO, 1%O2,
10%H2O, 20%CO2, 55%H2 and He as balance.
In our work, 5%Pt/15%CeO2/Al2O3 demonstrated ex-
cellent performance in preferential CO oxidation. This
catalyst is very stable under the realistic gas conditions
during 72 hr of use. The higher selectivity in CO oxida-
tion could obtain under the low O2 concentration.
4. Conclusions
The CO poisoning of PEMFCs is a major problem to
deplete the efficiency and energy conversion of PEMFCs.
To remove a trace amount of CO in the reformed gas is
essential. In this work, the catalytic performance of pro-
moted platinum over alumina with ceria in selective CO
oxidation in the presence of excess hydrogen has been
studied. The addition of ceria improved the catalytic ac-
tivity in oxidation reactions. It resulted from the oxygen
storage property of ceria. Space velocity also affected the
CO conversion. High CO conversion at low temperature
was obtained when low space velocity was chosen. Fi-
nally, the 5%Pt/15%CeO2/A l2O3 is an excellent catalyst
for removal of trace CO in reformed gas. It reduces 1%
CO in the realistic reformed gas to less than 10 ppm with
selectivity of 52% at 180℃ with space velocity of
70,000 cm3·g-1·h-1.
5. Acknowledgements
The authors gratefully acknowledge the financial support
from Thailand Research Fund (TRF) under the contract #
MRG 4680140.
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