Mixture Of CeO2 Research Articles

Dispersion Behaviors of Copper Oxide on the Mixed “CeO2 + γ-Al2O3” Support

The dispersion behaviors of copper oxide on the mechanical mixture of CeO2 and γ-Al2O3 supports, CuO/CeO2 + γ-Al2O3, have been characterized by using XRD, LRS, XPS, UV-DRS, and TPR. The results show that copper oxide dispersed mainly on the surface of CeO2 support, provided that the loading amount of copper oxide does not exceed the dispersion capacity of CuO/CeO2, ∼1.2 mmol of CuO/100 m2 of CeO2 (Dong, L.; Jin, Y. S.; Chen, Y. Sci. China (B). 1997, 40, 24). Increasing the CuO loading evidently leads to the formation of the dispersed copper oxide species on the surface of the γ-Al2O3 support. The results have been tentatively discussed by using the incorporation model, which was proposed to describe the interaction between the dispersed species and the support previously (Chen, Y.; Zhang, L. F. Catal. Lett. 1992, 12, 51).

Densification, microstructure and grain growth in the CeO2–Fe2O3 system (0⩽Fe/Ce⩽20%)

Mixtures of CeO2 and Fe2O3 with Fe/Ce atomic ratios ranging from 0 to 0.2 were prepared by the conventional mixed-oxide technique. Small amount of Fe doping (Fe/Ce⩽1%) significantly promotes the densification and grain growth of CeO2 ceramic. The results from the dilatometric measurement and SEM (scanning electronic microscopy) observation reveal that 0.5% Fe doping reduces the sintering temperatures by at least 200°C. For the samples with a large amount of Fe2O3 (Fe/Ce⩾1%), however, above 1400°C the densification behavior deteriorates remarkably; the density decreases with increasing sintering temperatures due to appearance of a lot of microcracks along grain boundaries. The so-called pining effect of second phase starts to take effect in the samples with Fe content greater than 5%. Fe2O3 grains grow more quickly at a lower sintering temperature (⩽1050°C), compared with those of CeO2.

The effect of Fe doping on the sintering behavior of commercial CeO 2 powder

Mixtures of CeO 2 and Fe 2O 3 with Fe/Ce atomic ratios ranging from 0 to 1 were prepared by the conventional ceramic technique. XRD analysis indicates that no binary compound between CeO 2 and Fe 2O 3 is formed under the present experimental conditions; the solubility of Fe 3+ into CeO 2 is very small (<1%), even though the sintering temperature is higher than 1500°C. The sintering temperature of CeO 2 powder can be reduced dramatically by adding a small amount of Fe 2O 3. At 1300°C almost full densification (>99.0% relative density) for 0.5% Fe-doped CeO 2 ceramics is reached after less than 1 h, compared with ∼96% relative density for pure CeO 2 sintered at 1525°C for 2 h.

Highly Conductive Oxides, CeVO4, Ce1−xMxVO4−0.5x(M=Ca, Sr, Pb) and Ce1−yBiyVO4, with Zircon-Type Structure Prepared by Solid-State Reaction in Air

The zircon-type phases, CeVO4, Ce1−xMxVO4−0.5x (0≤x≤0.41 for M=Ca, 0≤x≤0.21 for M=Sr, and 0≤x≤0.1 for M=Pb) and Ce1−yBiyVO4 (0≤y≤0.68), have been prepared in air by heating the stoichiometric mixture of CeO2, V2O5, CaCO3, SrCO3, PbO, and Bi2O3. During solid-state reaction, the spontaneous reduction of Ce(IV) to Ce(III) begins above 500°C and proceeds rapidly at about 666°C in conjunction with the melting of V2O5. All of these phases present high electrical conduction. In particular, the phases Ce1−xMxVO4−0.5x (M=Ca, Sr, and Pb) show excellently high values. The compound CeVO4 is characterized as a p-type semiconductor by the Seebeck effect.

New ceria-based catalysts for pollution abatement

In the present work, we describe the use of fluorite-structured solid solutions, based on mixtures of CeO 2/La 2O 3/Pr 2O 3, and similar systems, i.e. CeO 2/Ln 2O 3/Pr 2O 3 where Ln=Tb, Sm, and Gd as effective catalysts for methane combustion. Mixed lanthanide oxide doped ceria solid solutions were prepared using an evaporation method from nitrate precursors and were subsequently calcined to 1073 K. Sample characterisation was achieved using powder X-ray diffraction (PXRD) and temperature programmed reduction (TPR). PXRDs obtained subsequent to a 12 h calcination at 1073 K for 12 h all show peaks corresponding to a fluorite-based structure. There are no additional features suggestive of large-scale segregation or ordered superstructure formation. This was confirmed by Rietveld analysis which showed that the lattice possesses cubic nature with a= b= c=5.50 Å. Methane combustion tests show that the most effective catalysts are those lanthanide oxide doped ceria catalysts prepared with 5% Pr molar metal ratios. TPR experiments suggest PrO 2 is an essential component and both surface and bulk chemistries have important roles in catalytic activity.

Microstructure and Composition of Synroc Samples Crystallized From a CaCeTi2O7 Chemical System: HRTEM/EELS Investigation

Ce-pyrochlore, CaCeTi2O7 is a chemical analogue for CaPuTi2O7, which is a proposed ceramic endmember waste form for the disposition of excess weapon-usable plutonium in geological repositories. Ce-pyrochlore was synthesized by firing and annealing in air a mixture of CeO2, TiO2, and CaCO3 with a stoichiometry of CaCeTi2O7. The annealed products contain Cepyrochlore, Ce-bearing perovskite, CeO2, and minor CaO. The mixture annealed at a temperature of 1140 °C contains more pyrochlore phase than that annealed at a higher temperature (1300 °C), indicating that a low temperature condition favors the formation of the Ce-pyrochlore. The Ca/Ce ratio of the pyrochlore is slightly lower than the ideal ratio (one). Electron energy-loss spectroscopy results show that there is a small fraction of Ce3+ present in the pyrochlore. Ce present in perovskite is dominated by Ce3. High-resolution TEM images show that the boundary between pyrochlore and perovskite is semi-coherent. No glassy phases were observed at the grain boundary between pyrochlore and perovskite, nor between CeO2and pyrochlore. It is postulated, based on the presence of trivalent Ce in the Ce-pyrochlore, that neutron poisons such as trivalent cation Gd would be incorporated into the CaPuTi2O7 phase

Preparation and characterization of ceria under an oxidizing atmosphere. Thermal analysis, XPS, and EPR study

Cerium hydroxide samples prepared with different precipitating agents (NaOH, KOH, NH[sub 4]OH) have been studied by thermogravimetry, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The untreated samples are a mixture of CeO[sub 2] and Ce(OH)[sub 4] with a small quantity of Ce(OH)[sub 3] present in the bulk of the solid. A part of the Ce[sup 3+] species remains stable even after calcination at high temperatures (1073 K) under air. The residual alkali elements issuing from the precipitating agents induce variations on the final state of the solid. 38 refs., 7 figs., 1 tab.

A family of tin oxide-based sensors with improved selectivity to methane

The enhancement of the low-temperature ( T = 310 °C) sensing behaviour to methane of tin oxide-based gas sensors, resulting from different surface activators, has been systematically studied using the resistive sensor configuration. Pt, CeO 2, La 2O 3 and mixtures of them are employed as activators in view of their properties as a combustion catalyst (Pt) and an atomic oxygen-transfer system (CeO 2). The experimental results of this work show that mixtures of CeO 2 and Pt present the best catalytic properties with respect to methane detection.

Catalysis of carbon monoxide and carbon dioxide methanation by CeAl 2, CeCo 2, CeNi 2, Co, and Ni

The catalytic activity of the three isostructural compounds CeAl 2, CeCo 2, and CeNi 2 and of pure Co and pure Ni for the methanation of carbon monoxide and carbon dioxide was measured with a microcatalytic technique between 100 and 800 °C. The CeCo 2 and CeNi 2 compounds decomposed during exposure to reaction conditions—CeCo 2 into a mixture of CeO 2 and free Co, and CeNi 2 into a mixture of CeO 2 and free Ni. In their decomposed states, CeCo 2 and CeNi 2 had activities for methanation which are comparable to those of pure Co and pure Ni, and they were generally more selective than pure Ni and pure Co towards the formation of hydrocarbons of molecular weight exceeding that of methane. Although the CeAl 2 catalyst exhibited only moderate activity for methanation in comparison to the other catalysts which were investigated, it was the most stable with respect to sintering—diminution of its activity by sintering effects was observed only above 700 °C. Arrhenius type plots were generally found to be linear.