The preparation and catalytic behavior of copper–cerium oxide catalysts for low-temperature carbon monoxide oxidation (original) (raw)
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Applied Catalysis A-general, 2005
CeO2 nanoparticles were prepared by thermal decomposition of cerous nitrate and then used as supports for CuO/CeO2 catalysts prepared via the impregnation method. The samples were characterized by HRTEM, XRD, H2-TPR, and XPS. The catalytic properties of the prepared catalysts for low-temperature CO oxidation were studied by using a microreactor–GC system. The results showed that the thermal decomposition temperature affected
CuO/CeO2 catalysts: Redox features and catalytic behaviors
Applied Catalysis A: General, 2005
The reduction and oxidation features of nanostructured CuO/CeO 2 catalysts prepared by the deposition-precipitation method were extensively investigated by TPR, FT-IR and in situ XPS techniques. Both the chemical states of copper and the reduction degree of ceria could be well controlled during the reduction with hydrogen by adjusting the temperature. Noticeably, the fully reduced Cu 0 could be further oxidized into Cu + in hydrogen by increasing the reduction temperature through the interaction between Cu 0 and lattice oxygen of ceria immigrating to the surface. Structure-reactivity relationship was established between the structural features of CuO/CeO 2 formed during the pre-reduction with hydrogen and its catalytic activities for CO oxidation. It was observed that reduction with hydrogen at 473-573 K, which leads to the full presence of metallic copper in the catalyst, gives rise to higher CO conversion. These phenomena were interpreted in terms of the reduction degrees of ceria, the changes of surface morphology and the chemical states of copper species. The interface oxygen activation as well as its transfer from the interface to the adsorbed reactant was found to play decisive roles in determining the reaction rate of CO oxidation. #
CuO–CeO 2 catalysts synthesized by various methods: Comparative study of redox properties
International Journal of Hydrogen Energy, 2010
Three different preparation methods have been used to synthesize CuO–CeO2 catalysts with 7 wt.% copper loading: coprecipitation (CP), sol–gel (SG) and urea–nitrate combustion (UC). All the samples have been characterized by a series of techniques such as XRD, Raman, TPR, TPD and OSC, in order to understand their different performance in CO oxidation, as a function of redox properties and catalyst structure. Among the catalysts, clearly CuCe-CP shows the lower activity because it presents the structure of a solid solution. CuCe-SG and CuCe-UC catalysts show much better performance in CO oxidation, in accordance to their higher redox capacity.
Applied Catalysis A: General, 2014
Nanocrystalline 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 40-190 • 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.
Carbon monoxide oxidation over CuO/CeO2 catalysts
Catalysis Today, 2004
CuO/CeO 2 catalysts prepared by co-precipitation, deposition-precipitation and impregnation methods were extensively investigated for CO oxidation reaction. It was shown that the catalytic behaviors of CuO/CeO 2 catalysts greatly depended on the preparation routes, which caused significant differences in the redox properties and the dispersion of copper species. The remarkable redox ability of CuO/CeO 2 at lower temperatures was found to play an essential role in CO oxidation reaction. The catalysts prepared by co-precipitation exhibited the highest catalytic activity in CO oxidation with CO total conversion at 85 • C. The structural characters as well as the redox features of CuO/CeO 2 catalysts were comparatively investigated by XRD, TPR, cyclic voltammetry and XPS measurements. The discrepancies in the dispersion of copper species and the degree of interaction between copper species and ceria determined the reversible redox properties, and consequently the catalytic performance.
Journal of Nanoscience and Nanotechnology, 2011
Ultra fine cerium oxide and copper doped cerium oxide nanoparticles are prepared in a one-step reaction by thermal decomposition of Ce acetate in commercial oleylamine. The products are highly crystalline and were characterized by XRD, Raman spectroscopy, XPS, TEM and BET. The TEM images show that the CeO 2 particles prepared are uniformly nanosized. The size of the nanoparticles can be controlled in the sub-10 nm range by the presence of other capping agent in the reaction mixture such as tri-octylphosphine oxide and oleic acid. The copper doped cerium oxide nanoparticles show high specific surface area (up to 299 m 2 /gr) and high catalytic activity for the low temperature CO oxidation even at low copper loading such as 9 at.%.
Redox behavior of (CUO)0.15(CeO2)0.85 mixed oxide catalyst prepared by sol-gel peroxide method
2005
Temperature-programmed reduction (TPR), oxidation (TPO) and desorption (TPD) studies were performed on (CuO) 0 . 1 5 (CeO 2 ) 0 . 8 5 copper-ceria mixed oxide sample prepared by sol-gel peroxide route. The obtained results reveal that despite initial drop in specific surface area after consecutive redox cycles the hydrogen consumption remains constant. This is because CuO is highly dispersed over the surface of CeO 2 nano-crystallites and remains highly dispersed even after the agglomeration of CeO 2 nano-crystallites in more dense secondary structure. The dispersed CuO is reduced to Cu" during the TPR, forming agglomerated metal particles on the surface of partially reduced CeO 2 . After subsequent TPO step all the Cu 0 is oxidized back into CuO and re-dispersed over the CeO 2 crystallites.
Reaction Kinetics, Mechanisms and Catalysis, 2010
Nano-particle, pure and CuO x -modified, fluorite-structured cubic-CeO 2 were successfully synthesized with surface areas near 240 m 2 /g applying a microemulsion method with mixed templating surfactants (viz. DDAB and Brij Ò 35). Following calcination at 400-800°C, the products were characterized by X-ray powder diffractometry, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy, and, then, tested as catalysts for methylbutynol decomposition and CO oxidation in the gas phase. Results obtained showed the pure and CuO x -modified cerias to exhibit comparable activities towards the alcohol decomposition into acetone and acetylene, but the modified ceria exhibited considerably higher activity towards the CO oxidation than the pure one. The calcination product of CuO x -modified ceria at 800°C was capable of lowering the light-off temperature of the CO oxidation from 300°C (on the pure) down to 70°C. Surface chemical consequences of the CuO x -modification, viz. increasing the Ce(III)/Ce(IV) atomic ratio, as well as the establishment of Cu(I) and Cu(II) sites, have been allocated the responsibility of the observed upsurge of the CO oxidation activity.
Comparative study on redox properties of nanosized CeO 2 and CuO/CeO 2 under CO/O 2
Journal of Catalysis, 2006
Nanosized CeO 2 and CuO/CeO 2 samples, active for CO-PROX or related processes were comparatively examined by O 2 probe electron paramagnetic resonance and in situ Raman and X-ray diffraction techniques. Their behavior toward CO reduction, as well as the oxygen-handling properties of the CO-reduced samples, was explored. An appreciable reduction of the ceria bulk was detected on treatment under CO at 473 K. On the basis of the analysis of the evolution of different oxygen-derived species (superoxide, peroxide, O − ) on low-temperature (77-300 K) oxygen chemisorption on the CO-reduced samples, a general picture of the redox properties of the samples is presented. Results demonstrate that the presence of copper promotes completion of the redox cycle under CO/O 2 by favoring both ceria reduction and oxidation. This can be relevant to explaining the remarkable oxidation activity and synergetic effects observed for catalysts combining CuO and CeO 2 .
Applied Catalysis B: Environmental, 2011
A Ce-Zr-Cu oxide system with a flower-like morphology was prepared by a slow co-precipitation method in the absence of any structure directing agent. Four portions of the oxide were thermally treated at four different temperatures (350 • C, 450 • C, 550 • C, 650 • C). The resulting materials samples were characterized by quantitative XRD, adsorption-desorption of N 2 at-196 • C, SEM and TEM microscopy, -H 2 -TPR, XPS and Operando-XANES. All samples were tested in the preferential CO oxidation (CO-PROX) in the 40-190 • C temperature range. Thermal treatments were found to induce slight structural changes without altering the starting morphology of the samples. The samples treated at higher temperature 550-650 • C showed a quite interesting CO-PROX activity and selectivity in a temperature range suitable for a practical use within the FEMFC technology. (M. Lenarda).