Advances in Chemical Engineering and Science, 2013, 3, 15-19
doi:10.4236/aces.2013.34B003 Published Online October 2013 (http://www.scirp.org/journal/aces)
Effect of Cu Loading to Catalytic Selective CO
Oxidation of CuO/CeO2 –Co3O4
P. Aunbamrung, A. Wongkaew
Department of Chemical Engineering, Faculty of Engineering, Burapha University, Chonburi, Thailand
Received May, 2013
ABSTRACT
This work studied CuO/CeO2-Co3O4 with wt% Ce:Co ratio 95:5 for selective CO oxidation with effect of wt% Cu
loading. The catalysts were prepared by co-precipitation. Characterizations of catalysts were carried out by XRD and
BET techniques. The results showed a good dispersion of CuO for 5 wt% Cu loading catalysts and showed high specific
surface area of catalyst. For selective CO oxidation, both 5CuO and 30CuO catalysts could remove completely CO in
the presence of excess hydrogen at 423 K and 20CuO could eliminate CO completely at 443 K. Moreover, considering
the selectivity to CO oxidation, the 5CuO catalyst has shown the highest selectivity of 85% while the 30CuO catalyst
obtains the selectivity of 65% at the reaction temperature of 423 K.
Keywords: Selective CO Oxidation; CuO/CeO2 –Co3O4; Cu Loading; Ce:Co Ratio; Co-precipitation
1. Introduction
Proton-exchange membrane fuel cell (PEMFC) has interest
with automotive and residential application because of
low operating temperature, high power density and rapid
start up. Hydrogen is an ideal fuel for PEMFC. In many
practical cases hydrogen can be produced by steam
reforming, following by water gas shift reaction [1]. The
presence of 1vol%CO in hydrogen steam gas poisons to
Pt-anode of PEMFC [2]. Among the different methods
for removal CO, selective CO oxidation reaction is the
preferred methods because this method used oxygen for
CO oxidation and high efficiency for remove CO [3]. An
efficiency of catalyst for reaction must be active and
selective to avoid parallel H2 oxidation.
In the recent year, the CuO-CeO2 catalyst has been
proposed as a promising catalyst due to its low cost and
high catalytic performance when compared with gold or
platinum catalysts [4,5]. The cobalt-based catalyst has
been reported shown good activity, selectivity at low
temperature and H2O resistance [6]. A large number of
studies catalyst preparations, the co-precipitation method
are the preferred method to high specific surface area of
catalyst and high activity for CO oxidation [7].
In this study, The CuO-CeO2 catalysts promoted with
Co3O4 were prepared by co-precipitation with different
wt% Cu loading and define wt% Ce:Co ratio 95:5. The
characterizations of catalyst were carried out by BET and
XRD techniques, in order to correlate catalyst properties
to catalytic performance. The performances of catalysts
were tested by selective CO oxidation.
2. Experimental
2.1. Catalysts Preparation
The catalysts CuO/CeO2-Co3O4 with wt % Ce/Co ratio of
95:5 were prepared by co-precipitation. Aqueous solutions
of Cu(NO3)2·3H2O, Ce(NO3)3·6H2O and Co(NO3)2·6H2O
were mixed. Aqueous Na2O3 0.1 M used as a precipitat-
ing agent was added drop-wise until a pH of 9 was at-
tained. The resulting precipitate was aged at room tem-
perature for 2 h, then filtered, washed several times with
deionize water and dried at 110℃ overnight. The ob-
tained samples were calcined at 500℃ for 5 h. The pre-
pared catalysts were denoted as XCuO. The X shows the
wt% Cu loading
2.2. Catalyst Characterization
All catalyst powders were characterized for their surface
area, average pore diameter and average crystal-liter
sizes. Specific surface area (SBET) of catalysts was deter-
mined with adsorption-desorption isotherms of N2 at 77
K using Autosorption-1C from Quantachrome. Prior to
N2-physical adsorption measurement, catalysts were de-
gassed under N2 gas purged at 473 K for 12 h. The ad-
sorption isotherms were tested at 10-5< <1.0. Using the
nitrogen adsorption isotherm, BET equation was used for
calculation of specific surface area using values between
0.05 and 0.30. X-ray diffraction measurement was made

P. AUNBAMRUNG, A. WONGKAEW
16
using a Bruker AXS model D 8 Discover equipped with
a Cu K radiation (40 kV, 40 mA) with a nickel filter.
Dif- fraction intensity was measured in the 2 theta ranges
between 20 and 80, with a step of 0.02 for 8 s per
point. The mean crystallite sizes of oxides were deter-
mined from the X-ray line broadening measurements,
using the Scherrer equation.
2.3. Catalytic Performance
The selective CO oxidation in the H2-rich gasses was
carried out in a quartz reactor inserted in a vertical
furnace. The reaction mixture consisted of 1% CO, 1%
O2 and 50% H2 (volume fraction) with He as a balance
gas. The flow rate of gas mixture was 40 cm3·min-1,
equivalent to space velocity 75,000 cm3·gcat-1h-1. The
catalyst bed temperature was measured by means of a
thermocouple inserted in the furnace. Product and
reactant analyses were conducted by a GC-3600CX gas
chromatograph. The molecular sieve was used to
separate CO, O2 and CO2. Water was trapped before the
gases entering the GC.
The CO conversion and selectivity for CO oxidation
were calculated from the concentration of CO and O2 at
inlet and outlet of the reactor as shown in equation (1)
and (2).
inlet outlet
outlet
CO CO
CO conversion100%
CO

 (1)

inlet outlet
2inlet 2outlet
CO CO
selectivity 100%
2O O


 (2)
3. Results and Discussion
3.1. Catalyst Characterization
The powder X-ray diffraction was applied to investigate
the structure of the CuO/CeO2-Co3O4 catalysts. Figure 1
shows the XRD patterns of the sample. All samples
shown the presence of CeO2 in the fluorite-type cubic
crystal structure, with the diffraction peak at 2θ of 28.55°,
33.08°, 47.48°, 56.34° and 76.70°. Strong two diffraction
peaks of CuO are exhibited the high crystalline structure
of monoclinic tenorite-phase CuO in the 20CuO, 30CuO
and 40CuO at 2θ = 35.46° and 38.73°. For 10CuO, the
diffraction peaks of CuO are weak in the XRD patterns,
suggesting that CuO is highly dispersed on the fluorite
CeO2 support. Accordingly, no CuO peaks are observed
for 5CuO, probably due to very low metal loading and its
high dispersion [8]. For diffraction peaks of Co3O4 in all
samples not recognize due to very low of Co3O4
promoted to catalysts. The average crystalline sizes of
catalyst were calculated by Scherer’s equation. The
average size of CeO2 are about 7-10 nm and CuO are
more than 10 nm (Table 1.)
The isotherm of the catalysts at different wt% CU
loading reveals a typical type IV sorption behavior, rep-
resenting the predominant mesoporous structure charac-
teristic as shown in Figure 2.
Figure 1. XRD patterns of the catalysts (A) 5CuO; (B) 10CuO; (C) 20CuO; (D) 30CuO; (E) 40CuO.

P. AUNBAMRUNG, A. WONGKAEW 17
Table 1. The properties of CuO/CeO2-Co3O4 catalysts.
Crystalline size
Catalysts dCuO (nm)dCeO2 (nm) dCo3O4 (nm)
SBET
(m2·g-1)
dpore
(nm) Phase detected
5CuO - 7.9 - 105.4 6.9 CeO2/Cubic
10CuO - 9.5 - 73.3 8.4 CeO2/Cubic
20CuO 14.7 7.9 - 121.2 8.7 CuO/monoclinic, CeO2/Cubic
30CuO 13.7 7.1 - 136.5 8.8 CuO/monoclinic, CeO2/Cubic
40CuO 23.5 10.2 - 31.3 21.0 CuO/monoclinic, CeO2/Cubic
Figure 2. Isoterms of the catalysts (A) 5CuO; (B) 10CuO; (C) 20CuO; (D) 30CuO; (E) 40CuO.
The volume of N2 adsorbed on the catalyst surface
decreases with increasing CuO up to 40 wt%, which
indicates that coverage of CuO decreases the specific
surface area of the sample [9].The SBET of CuO/CeO2
–Co3O4 catalysts were calculated by Brunauer Emmett-
Teller (BET) method using data from N2 adsorption-
desorption isotherm with in between 0.05-0.35 and the
results are reported in Table 1.
High surface area is usually helpful to enhance cata-
lytic activity due to more surface active centers exposed
to reactants. The sample prepared by co-precipitation
exhibits the highest specific surface area all the samples.
The 30CuO catalyst with the highest BET surface area
displays the best CO PROX performance, indicating that
the BET surface area is possibly one of the important
influencing factors on the catalytic performance of CuO/
CeO2-Co3O4 catalysts. Generally, high BET surface area
is favorable to the dispersion of Cu species, enhancing
the interaction between ceria and Cu species. [10]
3.2. Catalytic Performance
The catalytic performance of the catalysts was accomp-
lished in the CO-PROX reaction by using a synthetic gas
(1% CO, 1% O2, 50% H2, He balance). Figure 3, obviously
indicates that the catalyst presents higher catalytic activity
at lower temperature in the presence of excess hydrogen.
The CO conversions of catalysts are the function of
temperature. CO conversion increases with an increase in
reaction temperature and further increasing in reaction
temperature decreases CO conversions. The maximum
CO conversion for 5CuO is 100.0% at the reaction tem-
perature in the range between 423-443 K, 10%CuO is
98.1 at 463 K, 20CuO is 100.0% at 443 K, 30CuO is
100% at the reaction temperature in the range between

P. AUNBAMRUNG, A. WONGKAEW
18
423-443 K and 40CuO is 98.5% at 463 K. At the increase
temperature, CO conversion decreases. This may be due
to high competition between H2 oxidation and CO oxida-
tion or reverse water gas shift reaction [11].
The selectivity can be seen in Figure 4, the selectivity
for CO oxidation is 100% over the catalysts at reaction
temperature lower than 403 K for 5CuO, 20CuO and
30CuO and lower than 423 K for 10CuO and 40CuO. It
means that H2 oxidation does not happen until this tem-
perature. At the increase temperature the selectivity tends
to decrease, indicating that the H2 oxidation occurs over
the catalysts. It can be suggested that the adsorption and
catalytic take place at low temperature. When the tem-
perature increases H2 molecules can be adsorbed and
reaction[8]. In addition, a decrease in the amount of
CeO2 in catalyst may result in a decrease in selectivity at
high temperature due to the reduction of oxygen storage
[12]. The selectivity of catalysts at the max CO conver-
sion is 85% for 5CuO, 50% for 10CuO, 70% for
20CuO ,65% for 30CuO and 52% for 40CuO catalysts.
Figure 3. The CO conversion of catalysts as a function of temperature.
Figure 4.The selectivity of catalysts as a function of temperature.

P. AUNBAMRUNG, A. WONGKAEW 19
It can also be concluded that, the wt% Cu loading has
an effect on selective CO oxidation. Adding more CuO
increases activity and CO removal at low temperature.
For CO oxidation, the catalysts activity in presence of
excess hydrogen is as follows, 30CuO >20CuO >40CuO
>10CuO. In contrast, when comparing the selectivity at
the maximum CO conversion, the activity of catalyst is
as follows; 20CuO >30CuO >40CuO >10CuO.
The 5CuO catalyst show the highest activity with 100%
CO conversion and 85% selectivity for removal CO in
H2-rich gas. A good dispersion of CuO in catalyst made
to easily adsorb CO and activity with O2 rapidly. Includ-
ing the appropriate amount of cobalt oxide to promote
efficient catalysis of CuO and high specific surface area.
4. Conclusions
The CuO/CeO2-Co3O4 catalysts were prepared by co-
precipitation method and characterized by the XRD and
BET techniques. XRD measurements show that the cata-
lysts are composed of monoclinic CuO and cubic fluorite
CeO2. BET shows the large surface area and small aver-
age pore size diameter. The performance of catalyst sug-
gest the 5CuO shows the best activity at low temperature
and shows high selective CO oxidation when the CO
conversion reach to 100%. The performance of catalysts
verifies that complete in the CO-PROX system.
5. Acknowledgements
This research was supported by Burapha University
(NRCT 2555) under the contract # 48/2555.
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