Effect of Cu Loading to Catalytic Selective CO Oxidation of CuO/CeO2 –Co3O4

doi:10.4236/aces.2013.34B003

Paper Menu >>

Journal Menu >>

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

Email: [email protected]

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

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%





(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

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.

REFERENCES

[1] O. Bicakova and P. Straka, “Production of Hydrogen

from Renewable Resource and its Effectiveness,”

International Journal of Hydrogen Energy, Vol. 33, 2008,

pp. 1335-1344.

[2] Z. Nada and L. Xianguo, “Transient of Carbon Monoxide

Poisoning and Oxygen Bleeding in a PEM Fuel Cell

Anode Catalyst Layer,” International Journal of

Hydrogen Energy, Vol. 33, 2008, pp. 1335-1344.

[3] A. Mishra and R. Prasad, “A Review on Preferential

Oxidation of Carbon Monoxide in Hydrogen Rich Gas,”

Bulletin of Chemical Reaction Engineering & Catalysis,

Vol. 6, No. 1, 2011, pp. 1-14.

[4] G. Avgouropoulos, T. Ioannides, C. Papadopoulou, J.

Batista, S. Hocevar and H. K. Matralis, “A

Comparative Study of Pt/γ-Al2O3, Au/α-Fe2O3 and

CuO–CeO2 Catalysts for the Selective Oxidation of

Carbon Monoxide in Excess Hydrogen,” Catalysis Today,

Vol. 75, 2002, pp. 157-167.

doi:10.1016/S0920-5861(02)00058-5

[5] S. Salvatore, C. Carmelo, P. M. Riccobenea, P. Giacomo

and P. Alessandro, “Selective Oxidation of CO in

H2-rich Stream over Au/CeO2 and Cu/CeO2 Catalysts: An

Insight on the Effect of Preparationmethod and Catalyst

Pretreatment,” Applied Catalysis A: General, Vol. 417-

418, 2012, pp. 66-75.

[6] M. Kang, M. W. song and C. H. Lee, “Catalytic Carbon

Monoxide Oxidation over CoOx/CeO2 Composite Cata-

lysts,” Applied Catalysis A: General, Vol. 255, 2003, pp.

143-156. doi:10.1016/S0926-860X(03)00324-7

[7] Z. Liu, R. Zhou and X. Zheng, “Influence of Preparation

Methods on CuO-CeO2 Catalysts in the Preferential Oxi-

dation of CO in Excess Hydrogen,” Journal of National

Gas Chemistry, Vol. 17, 2008, pp. 125-129.

[8] J. L. Ayastuy, E. Fernandez-Puertas, M. P. Gon-

zalez-Marcos and M. A. Guitierrez-Ortiz, “Transition

metal Promoters in CuO/CeO2 Catalysts for CO Removal

from Hydrogenstreams,” International Journal of Hy-

drogen Energy, Vol. 37, 2012, pp. 7385-7397.

doi:10.1016/j.ijhydene.2012.02.007

[9] S. Christopher, H. Nair and D. Chelsey, “Study of Active

Sites and Mechanism Responsible for Highly Selective

CO Oxidation in H2 Rich Atmospheres on a Mixed Cu

and Ce Oxide Catalyst,” Journal of Catalysis, Vol. 266,

2009, pp. 308-319. doi:10.1016/j.jcat.2009.06.021

[10] M. Meng, Y. Liu, W. L. Z.Sun, L. Zhang and X. Wang,

“Synthesis of Highly-dispersed CuO-CeO2 Catalyst

Through a Chemisorption-hydrolysis Route for CO Pref-

erential Oxidation in H2-rich Stream,” International

Journal of Hydrogen Energy, Vol. 37, 2012, pp.

14133-14142. doi:10.1016/j.ijhydene.2012.07.075

[11] J. W. Park, J. H. Joeng, W. L. Yoon, C. S. Kim, D. K.

Lee, Y. K. park and Y. W. Rhee, “Selective Oxidation of

CO in Hydrogen-rich Stream over Cu-Ce Catalyst Pro-

moted with Transition Metal,” International Journal of

Hydrogen Energy, Vol. 30, 2005, pp. 209-220.

doi:10.1016/j.ijhydene.2004.04.016

[12] S. Chang, M. Li, Q. Hua, L. Zhang, Y. Ma, B. Ye and W.

Huang, “Shape-dependent Interplay between Oxygen

Vacancies and Ag–CeO2 Interaction inAg/CeO2 Catalyst

s and Their Influence on the Catalytic Activity,” Journal

of Catalysis, Vol. 293, Vol. 30, 2012, pp. 195-200.