Mixture Of CeO2 Research Articles

A study on the synthesis and magnetic properties of the cerium ferrite ceramic

This work is a short report on the synthesis of CeFeO3 ceramic nanopowder from a mixture of CeO2 and Fe2O3 powders via a high energy ball milling process and subsequent heat treatment. Investigation of the magnetic, photocatalytic and absorption properties of CeFeO3 and its potential for colossal dielectric constant (CDC) are the main objectives of the present study. The characterization tools were X-ray diffraction (XRD), transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM), thermogravimetry (TG), differential thermal analysis (DTA), X-ray photoemission spectroscopy (XPS), ultraviolet–visible spectroscopy (UV–vis) and Image-J software. According to the obtained results, CeFeO3 nanopowder can be raised as a visible light-driven photocatalyst, a semiconductor material with a narrow bandgap and a weak ferromagnetic material. For the first time the CDC behavior of this ceramic was also assessed by XPS analysis which was indicative of a good colossal dielectric constant. The results were also confirmed by the measured dielectric properties.

CeO2-TiO2 catalyst prepared by physical mixing for NH3 selective catalytic reduction: Evidence about the migration of sulfates from TiO2 to CeO2 via simple calcination

A mechanical mixture of CeO2 and TiO2 powder with a small amount of sulfate was applied for the selective catalytic reduction (SCR) of NO with NH3. After calcination at 500 oC, the mixed sample showed significantly enhanced activity and selectivity compared to the uncalcined one and, moreover, demonstrated even higher activity than the conventional V2O5/TiO2 catalyst above 300 °C. Combined characterization results revealed that the main active sites were newly formed sulfate species on CeO2, the number of which increased with calcination. Temperatureresolved DRIFT spectra provided convincing evidence about the migration of sulfate species from TiO2 to CeO2, as confirmed from the shift of v(S=O) band as a result of the mechanical mixing and the subsequent calcination.

Photocatalytic activity of the binary composite CeO2/SiO2 for degradation of dye

In this study, CeO2 photocatalyst was modified by composite with SiO2 to increase efficiency and improve photocatalytic activity. The as-prepared SiO2 particles have been incorporated into the precursor mixture of CeO2 by homogeneous precipitation and subsequent calcination process. The phase compositions of CeO2 before and after compositing with SiO2 were identified by X-ray diffraction (XRD). The morphology and particle size of CeO2/SiO2 composite was analyzed by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The results showed SiO2 spheres with the particle size approximately 100–120nm, and a uniform layer of CeO2 nanoparticles with a diameter of about 5–7nm that were fully composite to the surfaces of SiO2. The X-ray photoelectron spectroscopy (XPS) technique was carried out in order to characterize the change in valence state and composite characteristic by shifted peaks of binding energies. The photocatalytic activity was studied through the degradation of Rhodamine B in aqueous solution under visible light exposure. The highest photocatalytic efficiency of CeO2/SiO2 composite was also obtained. To explain the high photocatalytic efficiency of CeO2/SiO2 composite, the proposed mechanism involves the high surface properties of the CeO2/SiO2 composite, as measured by Brunauer-Emmett-Teller (BET) method.

Synthesis of the CeVO4 orthovanadate and its heat capacity in the range 350–1000 K

Cerium orthovanadate has been prepared by solid-state reaction via multistep firing of a stoichiometric mixture of CeO2 and V2O5 in the range 873–1273 K. The molar heat capacity of CeVO4 has been determined by differential scanning calorimetry in the temperature range 350–1000 K. The experimental data have been used to evaluate the thermodynamic properties of cerium orthovanadate: enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Φ°(T).

Structure and microstructure dependent ionic conductivity in 10 mol% Dy2O3 doped CeO2 nanoparticles synthesized by mechanical alloying

Nanocrystalline powders of 10mol% Dy2O3 doped ceria (CeO2) are prepared by mechanical alloying the mixture of CeO2 and Dy2O3 powders within a short duration of 1h of milling in open air and the powder is further milled for 3h and 8h to confirm the phase stability, measure the change in microstructure parameters and find the dependence of ionic conductivity on the microstructure parameters with increasing milling time. Different structural and microstructural parameters such as lattice parameter, particle size, and microstrain in doped CeO2 nanoparticles are obtained by Rietveld refinement using XRD data employing MAUD software. Ionic conductivities of the compounds for three different milling durations are measured as a function of temperature (350°C–560°C). Dy-doping is found to enhance the ionic conductivity of ceria nanoparticles and the 8h milled sample shows highest conductivity. Increase in ionic conductivity of sample with increase in milling duration is attributed to the change in the structure and microstructure parameters of the compounds.

Effect of Nano-Oxide Addition on Mechanical Properties of Alumina-Mullite-Zirconia Composites

This work reports on the effect of CeO2 and Cr2O3 addition on the mechanical properties of Al2O3-mullite-ZrO2 composites. The amount of additives added was 1.5wt%CeO2, 1.5wt%Cr2O3 and the mixture of 1.5wt%CeO2 and 1.5 wt%Cr2O3. Bulk composites have been sintered by using pressure-less sintering method. Phases, microstructure, density and porosity of sintered composites were characterized. Flexural strength and fracture toughness were also determined. The results from mechanical tests showed that the highest flexural strength was obtained with the mixture of CeO2 and Cr2O3 addition, while the highest fracture toughness was obtained with CeO2 addition.

ChemInform Abstract: Synthesis, Structural Characterization, and Physical Properties of the New Transition Metal Oxyselenide Ce2O2ZnSe2.

AbstractThe title compound is prepared from powder mixtures of CeO2, Zn, and Se in a 1:2:1 ratio in an alumina crucible using Al placed in a different crucible as oxygen getter (1100—1225 °C, 1—24 h).

Interfacial redox reaction-directed synthesis of silver@cerium oxide core–shell nanocomposites as catalysts for rechargeable lithium–air batteries

A facile oxidation–reduction reaction method has been implemented to prepare pomegranate-like Ag@CeO2 multicore–shell structured nanocomposites. Under Ar atmosphere, redox reaction automatically occurs between AgNO3 and Ce(NO3)3 in an alkaline solution, where Ag+ is reduced to Ag nanopartilces and Ce3+ is simultaneously oxidized to form CeO2, followed by the self-assembly to form the pomegranate-like multicore–shell structured Ag@CeO2 nanocomposites driven by thermodynamic equilibrium. No other organic amines or surfactants are utilized in the whole reaction system and only NaOH instead of organic reducing agent is used to prevent the introduction of a secondary reducing byproduct. The as-obtained pomegranate-like Ag@CeO2 multicore–shell structured nanocomposites have been characterized as electro-catalysts for the air cathode of lithium–air batteries operated in a simulated air environment. Superior electrochemical performance with high discharge capacity of 3415 mAh g−1 at 100 mA g−1, stable cycling and small charge/discharge polarization voltage is achieved, which is much better than that of the CeO2 or simple mixture of CeO2 and Ag. The enhanced properties can be primarily attributed to the synergy effect between the Ag core and the CeO2 shell resulting from the unique pomegranate-like multicore–shell nanostructures possessing plenty of active sites to promote the facile formation and decomposition of Li2O2.

Direct synthesis of H2O2 over Pd supported on rare earths promoted zirconia

In this work Pd (0.3 or 0.6wt.%) was supported on both ZrxM1–xO2 (M=La, Y, Ce) and on mechanical mixtures of CeO2 and ZrO2. The synthesized catalysts were characterized by XRD, TPR, AAS and CO chemisorption and tested for the direct synthesis of hydrogen peroxide in a high pressure semibatch apparatus. The reactants conversion was limited in order to avoid mass-transfer limitations. No selectivity enhancers of any kind were used and the all the materials were halide free. Small metal particles were obtained (1–2.6nm). Supports with smaller pore diameters leaded to larger Pd particles, which in turn were found to preferentially support the formation of the peroxide. Moreover, supports with higher reducibility favored the production of H2O2, probably due to an easier reduction of the active metal, essential to achieve high selectivity. Notwithstanding the absence of enhancers, the specific activity and selectivity recorded were very high.

Ceo₂ Based Catalysts for the Treatment of Propylene in Motorcycle's Exhaust Gases.

In this work, the catalytic activities of several single metallic oxides were studied for the treatment of propylene, a component in motorcycles’ exhaust gases, under oxygen deficient conditions. Amongst them, CeO2 is one of the materials that exhibit the highest activity for the oxidation of C3H6. Therefore, several mixtures of CeO2 with other oxides (SnO2, ZrO2, Co3O4) were tested to investigate the changes in catalytic activity (both propylene conversion and CO2 selectivity). Ce0.9Zr0.1O2, Ce0.8Zr0.2O2 solid solutions and the mixtures of CeO2 and Co3O4 was shown to exhibit the highest propylene conversion and CO2 selectivity. They also exhibited good activities when tested under oxygen sufficient and excess conditions and with the presence of co-existing gases (CO, H2O).

Multifunctional catalyst based on BaO/Pt/CeO2 for NO2-assisted soot abatement and NOx storage

In the present work the CeO2/BaO/Pt system was selected in order to perform an NO2-assisted soot oxidation. The aim of such catalytic system is to couple the catalytic functionality for soot abatement during DPF regeneration, namely CeO2, and an embedded lean NOx trap (LNT) functionality given by BaO, for NOx storage, whose oxidation over Pt to form adsorbed nitrates is facilitated by the presence of CeO2 itself.The impact of process parameters, such as the catalyst preparation and the reaction conditions, was analyzed. The activity towards soot oxidation revealed that a physical mixture of CeO2 and BaO allowed to obtain more performing catalysts than the co-synthesis route, the former reaching a peak temperature of soot oxidation equal to 475°C, being 25°C lower than the latter. The Pt addition to the two catalysts reduced their peak temperatures by around 30°C in both cases.It is worth noticing that the onset temperature (T5%) was considerably improved in presence of Pt only in the case of the catalyst prepared by co-synthesis (decreasing from 390 to 360°C), still remaining much higher than the temperature level reached by the ones obtained by physical mixture (280°C).As a result, in terms of soot conversion, CeO2/Pt/BaO catalyst prepared by physical mixture can be considered the catalyst with the best behavior.

Physical mixtures of CeO2and zeolites as regenerable indoor air purifiers: adsorption and temperature dependent oxidation of VOC

Removal of volatile organic compounds (VOC) and indoor air quality regulation through adsorbers required exchange or maintenance of active materials. In this work, we combine well known VOC adsorbers with oxidation catalysts as intimate particulate mixtures. We demonstrate how typical VOC can subsequently adsorb on such mixed material fixed beds (usually days to weeks; the common state of the system, adsorption phase) using small organic compounds (diethyl ether, triethylamine), monoterpenes such as linalool and limonene, and hexanoic acid. Occasional regeneration runs through heat up of the fixed bed results in simultaneous desorption and oxidation of the accumulated VOC, thus regenerating full adsorption capacity for a next adsorption phase. We investigated both small pore zeolites (H-ZSM-5) and larger pore zeolites (13X) and found a distinct interplay between the pore size and the type of VOC. Thermogravimetry coupled with mass spectroscopy was used to quantitatively study the effects of mixing composition and temperature on adsorber performance and regeneration. The here investigated bi-functional systems combine very low maintenance costs and materials requirement with low air flow and exchange costs, thus suggesting mixed (two-functional) bed adsorbers with catalytic function as sustainable alternatives to currently used single use systems based on granulated zeolites or activated carbon. In this work we show the ability of zeolite/cerium oxide physical mixtures to adsorb and capture different classes of VOC at room temperature and release them for oxidation at higher temperatures in a regenerative and sustainable process.

Development of a fiber-coupled laser-induced breakdown spectroscopy instrument for analysis of underwater debris in a nuclear reactor core

To inspect the post-accident nuclear core reactor of the TEPCO Fukushima Daiichi nuclear power plant (F1-NPP), a transportable fiber-coupled laser-induced breakdown spectroscopy (LIBS) instrument has been developed. The developed LIBS instrument was designed to analyze underwater samples in a high-radiation field by single-pulse breakdown with gas flow or double-pulse breakdown. To check the feasibility of the assembled fiber-coupled LIBS instrument for the analysis of debris material (mixture of the fuel core, fuel cladding, construction material and so on) in the F1-NPP, we investigated the influence of the radiation dose on the optical transmittance of the laser delivery fiber, compared data quality among various LIBS techniques for an underwater sample and studied the feasibility of the fiber-coupled LIBS system in an analysis of the underwater sample of the simulated debris in F1-NPP. In a feasible study conducted by using simulated debris, which was a mixture of CeO2 (surrogate of UO2), ZrO2 and Fe, we selected atomic lines suitable for the analysis of materials, and prepared calibration curves for the component elements. The feasible study has guaranteed that the developed fiber-coupled LIBS system is applicable for analyzing the debris materials in the F1-NPP.

MnOx–CeO2 supported on a three-dimensional and networked SBA-15 monolith for NOx-assisted soot combustion

This paper reports the preparation and characterization of MnOx–CeO2/SBA-15 monolith (MnCe/SM) catalysts for NOx-assisted soot combustion. The SM with a three-dimensional (3D) network structure was synthesized by a sol–gel method, in which the shearing force and the acidity of the solution were finely tuned to direct the formation and assembly of the primary particles. The MnCe/SM catalysts were further prepared by a facile isovolumetric impregnation method. The samples were characterized by nitrogen adsorption, scanning electron microscopy, energy dispersed spectroscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed desorption, and NO temperature-programmed oxidation. It is found that the MnOx–CeO2 nanoparticles were dispersed in the channels or/and on the outer surface of the SM support depending on the loading, and had a strong synergistic effect. The MnCe/SM catalysts with an appropriate MnOx–CeO2 loading showed much higher catalytic performance for soot combustion than that of the unsupported MnOx–CeO2 mixture. This is attributed to the combination of the MnOx–CeO2 active component with the 3D network structure of SM. The later not only provides large surface area and high accessibility for the soot particulates to the active sites, but also acts as a particulate filter.

Ni-CeO2 Cermets Synthesis by Solid State Sintering of Ni/CeO2 Multilayer

Nickel and gadolinium doped cerium oxide (GDC) cermet is intensively investigated for an application as an anode material for solid oxide fuel cells based on various electrolytes. The purpose of the present investigation is to analyze morphology, microstructure, and optical properties of deposited and annealed for one hour in the temperatures from 500 ºC to 900 ºC Ni/CeO2 multilayer thin films deposited by sputtering. The crystallographic structure of thin films was investigated by X-ray diffraction. The morphology of the film cross-section was investigated with scanning electron microscope. The elemental analysis of samples was investigated by energy-dispersive X-ray spectroscopy. The fitting of the optical reflectance data was made using Abeles matrix method that is used for the design of interference coatings. The film cross-section of the post-annealed samples consisted of four layers. The first CeO2 layer (on Si) had the same fine columnar structure with no features of Ni intermixing. The part of Ni (middle-layer) after annealing was converted to NiO with grain size exceeding 100 nm. The CeO2 layer deposited on Ni was divided into two layers. Lower layer had small grains not exceeding 25 nm and consisting of NiO and CeO2 mixture. Upper layer consisted of CeO2 columns with approximate thickness of 50 nm. Ni sample annealed at 600 ºC was fully oxidized. The NiO thickness and refraction index were almost steady after annealing in various temperatures. The approximation of experimental reflectance data was successful only for the samples with one transparent homogeneous layer. The reflectance of the Ni/CeO2 samples annealed at intermediate temperatures could not be fitted using one-layer or three-layer model. That may show that a simplified model could not be implemented. The real system has complicated distribution of refraction index. DOI: http://dx.doi.org/10.5755/j01.ms.19.4.3073

ChemInform Abstract: High‐Pressure Synthesis and Characterization of the First Cerium Fluoride Borate CeB2O4F.

AbstractThe title compound is synthesized from a mixture of CeO2, B2O3, and CeF3 in a Walker‐type multianvil apparatus (BN crucible, 0.9 GPa, 1450 °C, 5 min).

Characterization of PCFC‐Electrolytes Deposited by Reactive Magnetron Sputtering; Comparison with Ceramic Bulk Samples

AbstractSrZr0.84Y0.16O3–α (SZY16), BaZr0.84Y0.16O3–α (BZY16), BaCe0.8Zr0.1Y0.1O3–α (BCZY10), and BaCe0.90Y0.10O3–α (BCY10) thin films with the thickness of lower than 6 micron are successfully deposited by reactive magnetron sputtering on alumina substrate covered by about 200 nm Pt3Ti collector layer. The corresponding ceramic bulk samples are prepared by solid state reaction. In order to obtain dense BZY16 and BCZY10 samples, 1 wt.% ZnO was added before sintering process.As deposited films are amorphous and crystallise under the expected crystal structure at different temperatures (e.g., SZY16 ≈ 623 K; BZY16 ≈ 423 K; BCY10 ≈ 873 K, and BCZY10 ≈ 873 K). SZY16 and BZY16 coatings are stable in air with respect to carbonation and hydration. BZY16 coatings require an in situ crystallization in order to avoid further cracking due to the tensile stress generation associated with the crystallization phenomenon, so they are deposited directly onto hot substrate (Tsubstrate ≈ 523 K). BCZY10 amorphous coatings present a good chemical stability against carbonation in air up to 573 K but the coatings decompose in BaCO3 and CeO2 mixture after annealing treatment at around 873 K for 2 h in air, instead of the expected double substituted BaCeO3 perovskite structure. Nevertheless, the crystallization perovskite structure is obtained after annealing treatment under vacuum to prevent the carbonation of the coating. BCY10 requires in situ crystallisation (Tsubstrate ≈ 873 K) to obtain BaCeO3 structure while avoiding the carbonation of the film. All the bulk samples present the perovskite structure with a relative density higher than ∼80% and without trace of ZnO or BaCO3. Eighty percent of relative density was demonstrated to give a good compromise between porosity and grain boundary blocking effects. The electrical properties of the films and pellets are investigated by AC impedance spectroscopy in air. Conductivities of crystallised coatings are close but always significantly lower than those of ceramic bulk samples of the same composition.

Effects of nano size mischmetal and its oxide on improving the hydrogen sorption behaviour of MgH2

This paper reports the catalytic effects of mischmetal (Mm) and mischmetal oxide (Mm-oxide) on improving the dehydrogenation and rehydrogenation behaviour of magnesium hydride (MgH2). It has been found that 5 wt.% is the optimum catalyst (Mm/Mm-oxide) concentration for MgH2. The Mm and Mm-oxide catalyzed MgH2 exhibits hydrogen desorption at significantly lower temperature and also fast rehydrogenation kinetics compared to ball-milled MgH2 under identical conditions of temperature and pressure. The onset desorption temperature for MgH2 catalyzed with Mm and Mm-oxide are 323 °C and 305 °C, respectively. Whereas the onset desorption temperature for the ball-milled MgH2 is 381 °C. Thus, there is a lowering of onset desorption temperature by 58 °C for Mm and by 76 °C for Mm-oxide. The dehydrogenation activation energy of Mm-oxide catalyzed MgH2 is 66 kJ/mol. It is 35 kJ/mol lower than ball-milled MgH2. Additionally, the Mm-oxide catalyzed dehydrogenated Mg exhibits faster rehydrogenation kinetics. It has been noticed that in the first 10 min, the Mm-oxide catalyzed Mg (dehydrogenated MgH2) has absorbed up to 4.75 wt.% H2 at 315 °C under 15 atmosphere hydrogen pressure. The activation energy determined for the rehydrogenation of Mm-oxide catalyzed Mg is ∼62 kJ/mol, whereas that for the ball-milled Mg alone is ∼91 kJ/mol. Thus, there is a decrease in absorption activation energy by ∼29 kJ/mol for the Mm-oxide catalyzed Mg. In addition, Mm-oxide is the native mixture of CeO2 and La2O3 which makes the duo a better catalyst than CeO2, which is known to be an effective catalyst for MgH2. This takes place due to the synergistic effect of CeO2 and La2O3. It can thus be said that Mm-oxide is an effective catalyst for improving the hydrogen sorption behaviour of MgH2.

ChemInform Abstract: High‐Pressure Synthesis and Crystal Structure of Ce4B14O27.

AbstractThe title oxide is synthesized from a mixture of CeO2, B2O3, and CeF3 as flux material (2.6 GPa, 750°C).

Hydrogen storage properties of a Mg–Ce oxide nano-composite prepared through arc plasma method

Abstract Mg based Mg–Ce oxide nano-composite powders were prepared through arc plasma evaporation of Mg–5 wt.%CeO2 mixture followed by passivation in air. ICP, XRD, TEM and PCT techniques were used to characterize the composition, phase components, microstructure and hydrogen sorption properties of the composite. It is shown that CeO2 transformed into Ce2O3 after arc evaporation and nanoscale Ce2O3 particles are attached on the surface of Mg particles, forming a core–shell structured metal-oxide nano-composite. The hydrogenation and dehydrogenation enthalpies of the composite are calculated to be −71 kJ/mol H2 and 75.41 kJ/mol H2, respectively, while the activation energy for hydrogen absorption is 47.75 kJ/mol H2. In addition, the composite can absorb 4.07 wt.% of hydrogen at 323 K in 10 h. These results revealed that the minor addition of Ce oxide in Mg through arc plasma method is able to improve significantly the hydrogen absorption kinetics of Mg.