Topic 5: Structured catalysts and reactors for innovative environmental, automotive and energy applications
WGS activity and long-term stability of ordered nanostructured CuO-CeO2
catalysts synthesized by hard template method
Petar Djinovića, Jurka Batistaa, Albin Pintara,b
a
Laboratory for Catalysis and Chemical Reaction Engineering, National Institute of Chemistry, P.O. Box 660, SI-1001
Ljubljana, Slovenia
b
Chair of Chemical, Biochemical and Environmental Engineering, Faculty of Chemistry and Chemical Technology,
University of Ljubljana, P.O. Box 537, SI-1001 Ljubljana, Slovenia
Introduction CuO-CeO2 catalysts exhibit high activity for a number of heterogeneously catalyzed
reactions, including WGS [1], PROX [2], NO abatement from auto exhaust gasses [3], methanol steam
reforming [4], etc. All of these reactions are of very high technological importance with regard to pure
H2 production, either for use as fuel or for synthesis of value added products.
Experimental Mesoporous nanostructured CuO-CeO2 catalysts, exhibiting Ia3d structural symmetry
with 10, 15 and 20 mol % CuO, calcined at 400, 450 and 550° C, respectively, were prepared by
impregnation of KIT-6 silica template with aqueous metal salt solutions. Obtained catalysts were, after
template removal, characterized by N2 adsorption/desorption, XRD, H2-TPR/TPD, N2O decomposition
and NH3 chemisorption/TPD methods to disclose detailed morphological, redox and surface acidic
properties. WGS reaction activity as well as long term stability tests were performed in the temperature
range from 250 to 450° C by using a gas mixture containing CO, H2O and N2 in ratio of 1:1:1.06.
Results The synthesized highly porous CuCe catalysts exhibited BET surface area of 147, 161 and 166
m2/g for CuCe10, CuCe15 and CuCe20 samples, respectively. Low angle XRD experiments revealed
cubic Ia3d structural symmetry, which is in accordance with the KIT-6 silica template [5]. H2-TPR
experiments revealed complete CuO reduction, regardless of CuO loading, and extensive CeO2
reduction (up to 24.5 %) occurring at temperatures below 200° C, which increased with CuO loading
[6]. WGS activity of tested samples was very similar up to 325° C. At higher temperatures, CuCe10
and CuCe15 solids exhibited higher activities than the CuCe20 sample, and attained CO conversion of
62 % at 450° C (GHSV = 35000 h-1), whereas CuCe20 achieved 54 % CO conversion. Among tested
solids, the highest WGS activity of CuCe10 catalyst coincides well with the abundance of surface acid
sites and highest CuO dispersion (CuO particles smaller than 1.5 nm). Lower WGS activity measured
over the CuCe20 catalyst could be a consequence of extensive carbonate formation on its surface,
which was confirmed by desorption of a large amount of CO2 from the catalyst surface during TPD
analyses. Besides H2 and CO2, the only side product identified during the reaction was CH4 in the
concentration range below 1500 ppm. During stability tests, some extent of thermal deactivation of
CuCe15 catalyst was detected at reaction temperatures above 400° C. On the other hand, thermal
deactivation of CuCe 10 and 20 catalysts was negligible. Finally, these catalysts exhibit much higher
WGS activity (up to five times) in comparison to powdered CuCe catalysts, prepared by the coprecipitation method and tested at identical operating conditions.
Conclusions Nanostructured CuCe catalysts with 10, 15 and 20 mol % CuO and ordered Ia3d
structural symmetry were successfully synthesized, using KIT-6 silica as hard template. The catalysts
exhibited high WGS activity at very low contact times in the following order: CuCe10 > CuCe15 >
CuCe20. The measurements show that CuO dispersion and abundance of acid sites, besides surface
oxygen mobility enabled by considerable reduction of CeO2 phase, significantly contribute to WGS
activity. Thermal stability of synthesized catalysts under the given reaction conditions was
exceptional; a decline of activity was observed for CuCe15 catalyst when exposed to temperatures
above 400° C.
References [1] F. Huber, Z. Yu, J.C. Walmsley, D. Chen, H.J. Venvik, A. Holmen, Appl. Catal. B 71 (2007) 7; [2] G.
Avgouropoulos, T. Ioannides, Appl. Catal. A 244 (2003) 155; [3] P. Bera, S.T. Aruna, K.C. Patil, M.S. Hedge, J. Catal. 186
(1999) 36; [4] J. Papavasiliou, G. Avgouropoulos, T. Ioannides, Appl. Catal. B 69 (2007) 226; [5] W. Shen, X. Dong, Y.
Zhu, H. Chen, J. Shi, Microporous Mesoporous Mater. 85 (2005) 157; [6] P. Djinović, J. Batista, A. Pintar, Appl. Catal. A
347 (2008) 23.
b
Corresponding author. Tel.: +386-1-47-60-283, fax: +386-1-47-60-300. E-mail address: albin.pintar@ki.si (A. Pintar).
Authors' e-mail addresses: petar.djinovic@ki.si (Petar Djinović); jurka.batista@ki.si (Jurka Batista); albin.pintar@ki.si
(Albin Pintar).