Surface and redox properties of cobalt-ceria binary oxides: On the effect of Co content and pretreatment conditions (original) (raw)
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Design of transition and rare earth metal doped ceria nanocomposite oxides for CO oxidation
International Journal of Advances in Engineering Sciences and Applied Mathematics, 2013
Nanocrystalline Ce x TM 1-x O 2 (TM = Zr 4? and Hf 4? ) and Ce x RE 1-x O 2-d (RE = La 3? , Pr 3?/4? and Tb 3?/4? ) solid solutions were prepared by modified coprecipitation method and thermally treated at two different temperatures, 773 and 1073 K in order to determine the thermal behaviour. The synthesized samples were studied in detail by means of N 2 physisorption, XRD, Raman, X-ray photoelectron spectroscopy (XPS), and TEM/HREM techniques. The catalytic efficiency was performed towards oxygen storage/release capacity (OSC) and CO oxidation activity. XRD results indicated the formation of transition and rare earth metal doped ceria solid solutions with typical fluorite like cubic structure. Raman spectra displayed the existence of oxygen vacancies. XPS measurements revealed that Ce, Pr and Tb are present in both 3? and 4? oxidation states, La in 3? state, and Zr and Hf in 4? state. Among the investigated samples, the catalytic measurements revealed that ceria-hafnia solid solution exhibits superior catalytic activity towards CO oxidation, which could be due to a high OSC and other favourable physicochemical properties.
Supported copper–ceria catalysts for low temperature CO oxidation
Catalysis Communications, 2010
In this investigation, CuO/CeO 2 -M x O y (M x O y = Al 2 O 3 , ZrO 2 and SiO 2 ) nanocomposite oxide catalysts were prepared by deposition-precipitation and wet impregnation methods, and evaluated for CO oxidation. Catalysts were characterized by XRD, TEM, UV-vis DRS, BET surface area and H 2 -TPR techniques. The synthesized catalysts exhibited high specific surface area, and uniform particle size distribution over the supports. The nanocrystalline texture of mixed metal oxides is clearly evidenced by TEM analysis. TPR and XRD results revealed synergetic interactions between copper oxide and ceria. Among various catalysts investigated, the CuO/CeO 2 -Al 2 O 3 combination exhibited excellent CO oxidation activity with T 1/2 = 374 K and 100% CO conversion at below 420 K.
J. Chem. Sci., 2015
In this work, nanosized Ce 0.7 M 0.3 O 2−δ (M = Mn, Fe, Co) solid solutions were prepared by a facile coprecipitation method and evaluated for CO oxidation. The physicochemical properties of the synthesized samples were investigated by various characterization techniques, namely, XRD, ICP-OES, BET surface area, SEM-EDX, TEM and HRTEM, Raman, XPS, and H 2-TPR. XRD studies confirmed the formation of nanocrystalline single phase Ce 0.7 M 0.3 O 2−δ solid solutions. ICP-OES analysis confirmed actual amount of metal loadings in the respective catalysts. The BET surface area of Ce 0.7 M 0.3 O 2−δ samples significantly enhanced after the incorporation of dopants. TEM studies confirmed nanosized nature of the samples and the average particle sizes of Ce 0.7 M 0.3 O 2−δ were found to be in the range of ∼8-16 nm. Raman studies indicated that the incorporation of dopant ions into the CeO 2 lattice promote the formation of more oxygen vacancies. The existence of oxygen vacancies and different oxidation states (Ce 3+ /Ce 4+ and Mn 2+ /Mn 3+ ,Fe 2+ /Fe 3+ , and Co 2+ /Co 3+) in the doped CeO 2 samples were further confirmed from XPS investigation. TPR measurements revealed an enhanced reducibility of ceria after the incorporation of dopants. The catalytic activity results indicated that the doped CeO 2 samples show excellent CO oxidation activity and the order of activity was found to be Ce 0.7 Mn 0.3 O 2−δ > Ce 0.7 Fe 0.3 O 2−δ > Ce 0.7 Co 0.3 O 2−δ > CeO 2. The superior CO oxidation performance of CeO 2-MnO x has been attributed to a unique Ce-Mn synergistic interaction, which facilitates materials with promoted redox properties and improved oxidation activity.
Improved CO-PROX Performance of CuO/CeO2 Catalysts by Using Nanometric Ceria as Support
Catalysts
Despite of the huge number of papers about the catalytic preferential oxidation of CO (CO-PROX) for the purification of H2 streams, there is still a need for more effective catalysts in order to reduce the large required catalyst volume of CO-PROX unity. In this work, large surface area nanometric ceria was used as support for CuO/CeO2 catalysts with CuO load up to 10 wt % easily dispersed by wet impregnation. Catalysts were characterized by ICP-MS, XRD, SEM/EDS, N2 physisorption, H2 temperature programmed reduction (TPR), and CO2 temperature programmed desorption (TPD) and tested under different reaction conditions (including under feed containing inhibiting species such as CO2 and H2O). Catalytic tests revealed that our samples show high activity and selectivity even under stringent reaction conditions; moreover, they result among the most active catalysts when compared to those reported in the scientific literature. The high activity can be related to the enhanced amount of highl...
Journal of colloid and interface science, 2017
Cobalt-cerium mixed oxides were prepared by the wet impregnation method and evaluated for volatile organic compounds (VOCs) abatement, using ethyl acetate (EtAc) as model molecule. The impact of Co content on the physicochemical characteristics of catalysts and EtAc conversion was investigated. The materials were characterized by various techniques, including N2 adsorption at -196°C, scanning electron microscopy (SEM), X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) to reveal the structure-activity relationship. The obtained results showed the superiority of mixed oxides compared to bare CeO2 and Co3O4, demonstrating a synergistic effect. The optimum oxidation performance was achieved with the sample containing 20wt.% Co (Co/Ce atomic ratio of ca. 0.75), in which complete conversion of EtAc was attained at 260°C. In contrast, temperatures above 300°C were required to achieve 100% conversion over the single oxides. Nota...
Chinese Journal of Catalysis, 2020
The redox properties of ceria make it suitable as a catalyst or support in oxidation reactions. Ceria-supported transition metal nanoparticles or isolated single atoms provide a metal-support interface that reduces the energy cost to remove interfacial oxygen atoms, providing active oxygen species that can participate in Mars van Krevelen oxidation processes. CO oxidation is a key probe reaction to test the reducibility of ceria-supported catalysts and is also practically important in the elimination of CO at relatively low temperatures in various applications. Preferential oxidation of CO (PROX) in excess H2 controls the CO concentration to ultra-low levels to prevent poisoning of hydrogen oxidation electrocatalysts. The reactivity of catalysts in CO oxidation and selectivity towards CO over H2 in PROX is dependent on the type and dispersion of metal species, the structural and chemical properties of CeO2, and the synthetic preparation methods of the catalysts. In this review, we summarize recently published works on catalytic CO oxidation and PROX reactions on ceria-supported metal nanoparticles and single atoms. We summarize the reactivity on different supported metals, and on different CeO2 surfaces with the same metal. We summarize the most likely reaction mechanisms as suggested by density functional theory calculations. The factors contributing to selectivity towards CO oxidation in PROX reactions on various supported metals are also discussed.
Optimization of Preparation Factors for Cerium Oxide Synthesis as a Support for CO PrOx Catalyst
Hydrogen, Fuel Cell & Energy Storage, 2014
Nanocrystalline ceria has been considered as support for carbon monoxide preferentially oxidation. In this study ceria was prepared by precipitation method and the effects of preparation conditions, such as pH of solution (8-10), aging time (1-12 hr), drying temperature (80-120°C), calcination time (2-6 hr) and temperature (400-600°C) were investigated on ceria synthesized powders properties. Nanocrystalline ceria were characterized by thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and ASAP analysis. Calcination temperature and pH of solution have the highest effect on powder specific area. Finally, optimum conditions for the synthesis of cerium oxide in this study are pH = 10, aging time = 6 hr, drying temperature = 120°C, calcination time = 6 hr, and temperature = 500°C. Crystalline size of ceria is lower than 20 nm and in the shape of sphere-like and maximum surface area is 74.45 m 2 /g. 7%CuO/CeO 2 catalyst was prepared by wetness impregnation method and was tested in catatest for oxidation of CO in presence of hydrogen (preferentially oxidation, PrOx). The CO conversion and CO 2 selectivity was achieved 57.3-98% and 83-40% by temperature increasing from 80-180 °C, respectively.
Study on the CO Oxidation over Ceria-Based Nanocatalysts
Nanoscale research letters, 2016
A series of ceria nanocatalysts have been prepared to study the structure dependency of the CO oxidation reaction. The ceria samples with well-defined nanostructures (nanocubes/Ce-NC and nanorods/Ce-NR) have been prepared using the hydrothermal method. Mesoporous ceria (Ce-MES) and ceria synthesized with solution combustion technique (Ce-SCS) have also been prepared for comparison. The lowest CO oxidation temperature has been reached by using ceria nanocubes (Ce-NC). This high activity draws immense contributions from the highly reactive (100) and (110) surfaces of the truncated nanocubes. The Ce-MES and Ce-SCS samples, despite their high surface areas, are unable to outdo the activity of Ce-NC and Ce-NR due to the abundant presence of (111) crystalline planes. This finding confirms the structure sensitivity of CO oxidation reaction catalyzed with ceria.
Small, 2012
Dimension-and shape-tunable nanoarchitectures have attracted rapidly growing interest due to their structuredependent properties and important technological applications in the past few decades. [ 1 , 2 ] The manipulation of nanomaterials with specifi c structures possessing exceptional physics and chemical properties, via conveniently modulating the synthetic conditions, is one of the challenging issues in materials science. Recently, much attention has been paid to shape-and size-controlled synthesis of metal oxide nanostructures (e.g., rare earth compounds and transition metal oxides ) with unique performances.