a b s t r a c tNanocrystalline CeO 2 with a regular size of 9.5 nm was prepared by a freeze-drying method, and subsequent impregnated with a Cu(II) acetate solution, varying the loading of Cu (3, 6, 12 wt.%). The resulting CuO/CeO 2 materials were characterized by N 2 physisorption at −196 • C, HRTEM, H 2 -TPR, X-ray diffraction, Raman spectroscopy and XPS and tested as catalysts in the preferential CO oxidation in a H 2 -rich stream (CO-PROX) in the temperature range • C. In spite of their low specific surface areas the catalysts exhibited a good catalytic performance, resulting active and selective in the CO-PROX reaction at low temperatures. The inhibiting effect of the simultaneous presence of CO 2 (15 vol.%) and H 2 O (10 vol.%) in the reaction mixture on the performance of CuO-CeO 2 catalysts was also investigated. The addition of CO 2 and water in the gas stream depressed CO oxidation up to 160• C, its effect being negligible at higher temperatures. Nevertheless, despite these expected deactivation phenomena, a CO conversion value higher than 90% and a CO 2 selectivity of about 90% was achieved for all the samples at 160• C. The excellent performance, especially shown by the catalyst with 6 wt%. of copper, has been related to the wide dispersion of the copper active sites associated with the high amount of Ce 4+ species before reaction.

Nanocrystalline supports, CeO 2 and solid solutions of modified CeO 2 with zirconium and aluminum were prepared by a freeze-drying method. CuO was supported by incipient wetness impregnation and calcination at 400 C. All catalysts exhibit high activity in the CO-PROX reaction and selectivity to CO 2 at low reaction temperature, being the catalyst supported on CeO 2 the more active and stable. The influence of the presence of CO 2 and H 2 O was also studied.

CuO-CeO 2 catalysts, with 6 wt % of Cu, have been synthesised by different preparation methods (calcination of nitrate precursors, thermal urea-nitrate combustion, freeze-drying method, using polymethyl metacrylate PMMA microspheres as template and precipitation using NaOH or the decomposition of urea as precipitating agents). The obtained materials have been characterised by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, N 2 adsorption-desorption at −196 • C, H 2 thermoprogrammed reduction (H 2 -TPR) and X-ray photoelectron spectroscopy (XPS). The catalysts displayed high dispersion of copper oxide, obtaining CO conversion values of 90-100% at 115 • C in the CO preferential oxidation in excess of hydrogen (CO-PROX) and maintaining this activity even after 48 h of time on stream. The incorporation of CO 2 and H 2 O in the feed stream (simulating a PROX unit) caused a decrease in the CO conversion, except for the catalyst synthesised using PMMA microspheres as a template which maintained a CO conversion of 95% at 115 • C. This catalyst exhibits an excellent catalytic performance, also under real operating conditions, thanks to many and concomitant factors, such as the very small CeO 2 particle size (5.6 nm), the surface being rich in copper (atomic ratio Cu/Ce = 0.35) that is easily reducible, and the peculiar morphology and porosity of the material.

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