CeO2 Phase Research Articles

Facile fabrication of CeO2–TiO2 thin films via solution based CVD and their photoelectrochemical studies

Present work reports a single step deposition protocol for the growth of robust, durable and homogenous CeO2–TiO2 composite thin films for the investigation of their photoelectrochemical (PEC) properties. The transparent methanol solution of triacetatocerium (III) hydrate and of tetraisopropoxytitanium (IV) precursors in 1:1 mol ratio was employed in aerosol assisted chemical vapor deposition (AACVD) on FTO substrates at temperatures of 550 and 600 °C in the ambient air. These precursors were converted into their trifluroacetates in situ, under these deposition conditions, for their compatibility in the AACVD procedure. XRD, SEM, EDX and XPS analyses verified the formation of uniformly dispersed crystalline CeO2 and TiO2 phases in spherical shaped morphologies and a direct bandgap of 2.6 eV was measured from the UV–Visible spectrophotometry. PEC studies of the composite films revealed that the heterojunction developed between n-type CeO2 and n-type TiO2 facilitated the separation and transportation of electrons and holes, leading to a promising photocurrent density of about 1.0 mA cm− 2 and prolonged photo stability measured under one-sun illumination (100 mW cm− 2) which is up to 60 min at 0.7 V versus Ag/AgCl. This behavior was further confirmed from electrochemical impedance spectroscopy and Bode phase angle measurements. It was also shown that the films fabricated at 550 °C has higher porosity leading to larger interface contacts and thus was able to generate higher photo activity.

Magnetic and electronic structures of Co ion implanted CeO2 thin films

Present study reports an enhancement of room-temperature ferromagnetism by Co ion implantations in CeO2 thin films and these Co ions exist in divalent state. These films were deposited on Si (111) substrates using RF sputtering method. The X-ray diffraction and Raman measurements confirmed the FCC structure corresponding to phase of CeO2 in these films. The Raman studies also show the presence of defects mainly of oxygen vacancies. The Rutherford backscattering spectrometry shows the thickness of the films as 300 nm and also the presence of Co ions in the implanted films. From the Atomic Force Microscopy, it is found that the surface roughness of the films is modified after Co ion implantation. While the magnetic measurements exhibit an increase in the saturation magnetization from ∼7 to 21 emu/cm3 after Co ion implantation at the fluence of 6 × 1016 ions/cm2, the coercivity value is found to decrease. The Ce ions exhibit both trivalent and tetravalent states as confirmed by X-ray photoelectron spectroscopy measurements. The enhancement in the ferromagnetic properties of these films after Co ion implantation is directly correlated with the magnetic Co ions, oxygen vacancies and the amount of Ce3+ ions. The oxygen vacancies based F-Center exchange model is discussed to understand the enhancement of ferromagnetism in these films.

Green synthesis of ceria powders with special physical properties by carbon dioxide carbonization

In order to improve the application values of Ce element, in this paper, rare earth chloride solution was used as raw material, the pH value was controlled by inorganic alkali, the ceria powders with special physical properties were prepared by carbon dioxide carbonization method. According to characterization of SEM, XRD, and TG-DSC, Ce(OH)3 prepared at pH = 7.5 exhibits smaller particle size than that prepared at other conditions. CeO2 precursor obtained by direct carbonization of Ce(OH)3 shows smaller particle size and narrow size distribution, CeO2 precursor forms at first by carbonization of Ce(OH)3 with the continuous addition of CO2 gas, and the chemical component is indicated to be Ce2O(CO3)2·6H2O. Cubic phase CeO2 powders are obtained by calcined at 750 °C for 4 h. The mean particle size D50 is 0.941 μm, and particle size distribution is smaller than 1. The microscopic appearance is homogeneous, with a spherical-like shape and a grain size of 200–500 nm. The light quality characteristics of sedimentation volume and accumulation density are obviously better than those of carbonate precipitation products. The carbonization method can be used not only to obtain ultra-fine rare earth oxides with fine particle size, narrow distribution and high dispersion properties, but also to achieve the reuse of carbon dioxide greenhouse gas.

Synthesis and dielectric properties of a new Mg2CeNbO6.5 ceramic system at microwave frequencies

New microwave dielectric ceramics Mg2CeNbO6.5 were synthesized by solid-state method. The phase, crystal structure, micro-structures and microwave dielectric properties of Mg2CeNbO6.5 ceramics had been investigated in the sintering temperature range of 1225–1325 °C. Two phases were detected by the X-ray diffraction patterns, including the main crystalline phase of CeO2 and the second phase of Mg4Nb2O9. Well-developed microstructures of the well-dense samples were obtained for samples sintered at 1225–1325 °C. As sintering temperature increased, the τ f values were stable, however, the significant change in the ɛr values and Q × f values were observed. At 1275 °C, the obtained Mg2CeNbO6.5 ceramics had promising excellent microwave dielectric properties: er = 15.38, Q × f = 17,300 GHz and τ f = − 49.71 ppm/°C.

Properties of La–Sr Manganites with Combined Substitution of Different Valence Ions for Strontium and Manganese

Experimental data on structural, magnetic, and electrical features of manganites of the system La0.65Sr0.35–cCecMn1 – xZn x O3 + γ (c = 0, 0.05; x = 0, 0.05, 0.10), synthesized by ceramic processing, are reported. Part of the samples were annealed under conditions that yield stoichiometric oxygen content. The samples obtained are of rhombohedral structure, but contain the impurity of the CeO2 phase. The introduction of cerium and zinc leads to a decrease in the unit cell volume of the rhombohedral phase. Cerium does not substantially affect the magnetization and Curie point of the initial samples. The width of the “ferromagnetic–paramagnetic” transition temperature interval rises after annealing, especially in manganite with high zinc content. Initial and annealed samples of composition with c = 0.05, x = 0.10 exhibit the phase transition “metal–semiconductor” at temperatures of about 219 K and 200 K, respectively. All other manganites possess a metallic character of conductivity in the range of 100–300 K. The maximum absolute value of magnetoresistance reaches 52%. The approaches to the interpretation of experimental results are discussed.

PREFACE INTERNATIONAL SYMPOSIUM ON ADVANCES IN HYDROPROCESSING OF OIL FRACTION (ISAHOF 2017)

The photocatalytic capabilities of La2O3 incorporated in CeO2 for the removal of Pb(II) ions in water are reported in this work. La2O3–modified CeO2 particles are prepared by a solid-state reaction method at calcination temperature of 1000 °C and 1400 °C. The x-ray diffraction result demonstrates a solid solution Ce0.9La0.1O1.95 phase coexisting with the CeO2 matrix phase (Ce0.9La0.1O1.95–CeO2) obtained at a calcination of 1400 °C, while the mixed La2O3/La(OH)3–CeO2 phase is obtained at 1000 °C. The UV-photocatalytic activity for Pb(II) ion removal of the La2O3–modified CeO2 particles is significantly higher than that of pure CeO2. Ce0.9La0.1O1.95–CeO2 particles show stronger visible light absorption capacity and higher ability of photoelectrodeposition for the Pb(II) ion removal than the mixed La2O3/La(OH)3–CeO2 particles and pure CeO2. The high photocatalytic activity is supported by a strong photoluminescence signal from the Ce0.9La0.1O1.95–CeO2 particles, suggesting a high efficiency of photogenerated charge separation. A formation of p-type Ce0.9La0.1O1.95 and n-type CeO2 heterojunctions in Ce0.9La0.1O1.95–CeO2 particles also promote photogenerated charge transfer and efficiency restraining recombination of the charges.

Sintering behavior, phase evolutions and microwave dielectric properties of LaGaO3-SrTiO3 ceramics modified by CeO2 additives

Crystal structures and microwave dielectric properties of (1-x) LaGaO3-x SrTiO3 (x = 0.4, 0.5, 0.6) and 0.4SrTiO30.6LaGaO3-yCeO2 (y = 0, 0.05, 0.1, 0.2) ceramics were investigated. As the x values increased, the orthorhombic changed to tetragonal perovskite structure at x = 0.6 in LaGaO3-SrTiO3 system ceramics. However, numerous secondary phases were detected in LaGaO3-SrTiO3 system ceramics. Surprisingly, CeO2 additives could effectively suppress formation of secondary phases of 0.4SrTiO3-0.6LaGaO3 ceramics as Ce ions could be incorporated into host crystal lattices, leading to significantly improvement of optimal Q × f values from 35,354GHz to 62,150GHz. The Raman spectra exhibited that the modes associated with CeO2 phase became more obvious with increasing CeO2 additives. The 0.4SrTiO30.6LaGaO3-0.05CeO2 ceramics, sintered at 1475°C/4h, exhibited superior microwave dielectric properties with εr = 32.9, Q × f = 62,150GHz and τf = − 26.6ppm/°C.

On the Nature of the Unusual Redox Cycle at the Vanadia Ceria Interface

This work investigates the effect of changing the vanadia/support interface on the redox properties of the material for the oxidative dehydrogenation reaction of small alkanes. In particular, ternary V2O5/CeO2/SiO2 catalysts are compared to vanadia on ceria and CeVO4 catalysts. Modifications in the CeO2 phase by the effect of the silica support and the creation of new V–Ce–Si interfaces induce substantial changes in the phases and behavior of vanadium species as well as CeO2, thus modifying the reaction mechanism. Powerful characterization techniques, XRD, in situ XANES, and Raman, as well as studies of ethane oxidative dehydrogenation catalytic activity provide a solid description of the phenomena associated with the different interfaces on a molecular level. Bulk CeO2 entities react with the vanadium species, leading to the formation of vanadate inhibiting the redox pair of V. These centers are very active but selective to ethane total oxidation. However, smaller ceria domains achieved by dispersion on ...

Selective Catalytic Reduction of NO by NH3 on CeO2–MOx (M = Ti, Si, and Al) Dual Composite Catalysts: Impact of Surface Acidity

A series of ceria based dual composite oxides were prepared via a co-precipitation method, and we focus on studying the relationships between the catalytic activity and physicochemical properties of ceria based catalysts. It is found that catalytic activity followed the order of CeTi > CeSi > CeAl > pure CeO2; X-ray diffraction indicates that all the ceria based dual composite oxides were the cubic fluorite-type phase of CeO2; the NH3 adsorption–desorption results reveal that the NH3 adsorption stability and amount of CeO2 were improved by modification with TiO2, SiO2, or Al2O3; and the order of surface acidity was in agreement with the order of catalytic activity. Combined with other characterizations, we suppose that surface acidity is a decisive factor in influencing the catalytic activity of ceria based catalysts in the NH3-SCR reaction.

Synthesis and multifunctionality of (CeO2-NiO) nanocomposites synthesized via sonochemical technique

CeO2, NiO and their nanocomposite were synthesized using facile sonochemical technique. XRD assure single phase CeO2 and NiO while the nanocomposite consists of the two phases only. CeO2 nanoparticles possess cubic shape, NiO was formed in nanorods, and CeO2 decorated the NiO nanorods in the nanocomposite. The magnetic behavior of the nanocomposite lies between those of the two parents with a ferromagnetic tendency. Metal oxide nanoparticles acted as catalyst in the formation of carbon nanofibers (CNFs), while the nanocomposite leads to the production of carbon nanotubes. The photocatalyst (CeO2-NiO) achieved complete dye degradation (100%) in light for the tested dye at 50 min. The decay products were analyzed using GC mass confirming mineralization of Bb red dye.

Facile sol-gel preparation of Cd-doped cerium oxide (CeO2) nanoparticles and their photocatalytic activities

Nanostructured Cd-doped cerium oxide (CeO2) is synthesized using the facile sol-gel process. The structural studies such as powder XRD, FTIR and Raman reveal the cubic fluorite phase of Cd-doped CeO2. The SEM and TEM analyzes interpret the spherical/elliptical morphology of the Cd-doped CeO2 nanoparticles of sizes ranging between 7 and 8 nm. The ferromagnetic nature of Cd-CeO2 is confirmed by magnetization hysteresis loop measurements at room temperature. The Cd-CeO2 samples show a strong absorption below 400 nm, which is much blue-shifted towards a shorter wavelength, indicating a narrow and uniform particle size distribution. From the PL studies, an intense green emission band is located at 530 nm due to the transition from the Cd donor level to the oxygen vacancies level traced in the CeO2 band gap. The photocatalytic degradation of Rhodamine B and Congo red dyes in aqueous solution under UV irradiation in the presence of Cd2+ and Pd2+ doped CeO2 samples are investigated on a comparative study. The high photocatalytic activity authenticates that Cd-CeO2 nanomaterials are a kind of promising photocatalysts in remediation of water polluted by some chemically stable organic dyes.

Microwave dielectric properties of Sr0.7Ce0.2TiO3–Sr(Mg1/3Nb2/3)O3 ceramics

xSr0.7Ce0.2TiO3–(1 − x)Sr(Mg1/3Nb2/3)O3 ceramics, referred to xSCT–(1 − x)SMN, were successfully produced by conventional solid-state sintered technology. The compounds, belonging to perovskites with a secondary phase of CeO2, can be detected even with x down to 0.1 of SCT composition. The overall trend for grain growth illustrates the increase with increasing SCT doping level. The Raman peak at 825 cm−1 splits into two peaks and causes red shift phenomenon. XPS spectra indicate that Ti and Nb ions exist respectively in tetravalence and pentavalence, and Ce ions exist in trivalence and tetravalence. Dielectrics constant (e r ) of SCT–SMN ceramics gradually increases with increasing theoretical dielectric polarizabilities. A wider width of the 825 cm−1 for FWHM of A1g mode Raman peaks suggests to a lower Q × f value. The increasing tolerance factor in agreement with temperature coefficient of resonant frequency (τ f ), denotes that the rise of perovskite symmetry. The 0.1SCT–0.9SMN ceramic sintered at 1450 °C for 4 h illustrates excellent microwave dielectric properties with e r ~ 35.4, Q × f ~ 11282 GHz and τ f ~ 1.7 ppm/°C. Activation energies of 0.1SCT–0.9SMN ceramic at 100, 300 and 500 V, are ~0.436, 0.427 and 0.331 eV, respectively, indicative of a decreased trend with external electric field.

Photoelectrodeposition effect of lanthanum oxide-modified ceria particles on the removal of lead (II) ions from water

The photocatalytic capabilities of La2O3 incorporated in CeO2 for the removal of Pb(II) ions in water are reported in this work. La2O3–modified CeO2 particles are prepared by a solid-state reaction method at calcination temperature of 1000°C and 1400°C. The x-ray diffraction result demonstrates a solid solution Ce0.9La0.1O1.95 phase coexisting with the CeO2 matrix phase (Ce0.9La0.1O1.95–CeO2) obtained at a calcination of 1400°C, while the mixed La2O3/La(OH)3–CeO2 phase is obtained at 1000°C. The UV-photocatalytic activity for Pb(II) ion removal of the La2O3–modified CeO2 particles is significantly higher than that of pure CeO2. Ce0.9La0.1O1.95–CeO2 particles show stronger visible light absorption capacity and higher ability of photoelectrodeposition for the Pb(II) ion removal than the mixed La2O3/La(OH)3–CeO2 particles and pure CeO2. The high photocatalytic activity is supported by a strong photoluminescence signal from the Ce0.9La0.1O1.95–CeO2 particles, suggesting a high efficiency of photogenerated charge separation. A formation of p-type Ce0.9La0.1O1.95 and n-type CeO2 heterojunctions in Ce0.9La0.1O1.95–CeO2 particles also promote photogenerated charge transfer and efficiency restraining recombination of the charges.

Fluidized bed oxidative dehydrogenation of ethane to ethylene over VOx/Ce-γAl2O3 catalysts: Reduction kinetics and catalyst activity

Cerium-doped γ-Al2O3 (Ce-γAl2O3) catalyst supports are prepared with various amounts of cerium (0.2–5wt.%). An excess solvent impregnation method is used to saturate the vanadium (5wt%) on the cerium-modified supports. The XRD and FTIR characterization techniques indicate the presence of crystalline CeO2 phase, and amorphous VOx phases on the γAl2O3. Raman analysis shows the coexistence of poly-vanadate and mono-vanadate species. BET analysis reveals a high surface area for the synthesized catalysts with a type-IV adsorption isotherm. TPR/TPO analyses show that VOx/Ce-γAl2O3 catalysts are very active and stable over repeated reduction/oxidation cycles. The stability/purity of the synthesized catalyst is also confirmed by TGA analysis. NH3-TPD characterization shows mild acidity while the TPR kinetics predicts lower activation energy for reduction. Oxidative dehydrogenation (ODH) of ethane experiments are developed over VOx/Ce-γAl2O3 catalysts under gas-phase oxygen-free conditions in a fluidized CREC Riser Simulator. Temperatures and residence times are varied between 450 and 600°C and 10–50s, respectively. A maximum ethylene selectivity of 87.9% with 10.0% ethane conversion is achieved at 550°C using the 1.0wt.% cerium-doped VOx/γ-Al2O3 catalyst. The successive ethane injections and subsequent catalyst regeneration show the stable redox characteristics of the prepared ODH catalysts.

Study on adsorption of phosphate from aqueous solution by nanomaterial CeO2

The synthesis of nanosize single phase CeO2 by gelatine gel combustion method was investigated. The prepared material was characterized by X- ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy and transmission electron microscopy measurements. At optimum conditions, such as pH 3, the molar ratio of Ce4+/gelatine 1/1, and a calcination temperature of 550 oC for 2 hours, the material with average size < 30 nm was synthesized. From the results of phosphate adsorption, adsorption equilibrium time of the material was determined at 60 minutes. The phosphate adsorption process in aqueous solution followed the Langmuir isothermal model with Qmax= 152.66 mg/g. Keywords. CeO2, gelatine, combustion method, phosphate (PO43-) adsorption.

Effects of preparation methods on the activity of CuO/CeO2 catalysts for CO oxidation

CO oxidation has been investigated on three CuO/CeO2 catalysts prepared by impregnation, co-precipitation and mechanical mixing. The origin of active sites was explored by the multiple techniques. The catalyst prepared by impregnation has more highly dispersed CuO and stronger interactions between CuO and CeO2 to promote the reduction of CuO to Cu+ species at the Cu-Ce interface, leading to its highest catalytic activity. For the catalyst prepared by co-precipitation, solid solution structures observed in Raman spectra suppress the formation of the Cu-Ce interface, where the adsorbed CO will react with active lattice oxygen to form CO2, and thus it displays a lower catalytic performance. No Cu-Ce interface exists in the catalyst prepared by the mechanical mixing method due to the separate phases of CuO and CeO2, resulting in its lowest activity among the three catalysts.

Ultra-fast degradation of methylene blue by Au/ZnO-CeO2 nano-hybrid catalyst

Au/ZnO-CeO2 hybrid structure was prepared by in-situ synthesis of 15–20nm CeO2 particles in aqueous environment, in which ZnO particles (400–500nm) were dispersed, using surfactant assisted precipitation method. Au was loaded on prepared structures through the reduction of AuCl3 by ascorbic acid. TEM analysis and Raman spectroscopy showed that synthesized hybrid structure is composed of both hexagonal ZnO and cubic CeO2 phases. While methylene blue test solution was degraded totally within 8min in the presence of Au/ZnO-CeO2 hybrid catalysis, use of Au/ZnO and Au/CeO2 led to a significantly low degradation rate (about 22% and 11%, respectively). As proven by XPS analysis the incorporation of ZnO to CeO2 seem to trigger the formation of Ce+3/Ce+4 dynamic equilibria and this enhances the catalytic efficiency enormously.

Tungsten bronze type structure, atmosphere sensitivity and microwave dielectric properties of Ba4(CexSm1−x)9.3Ti18O54 ceramics

The phase structure, ions valence state and microwave dielectric properties of Ba4(Ce x Sm1−x )9.3Ti18O54 (0 ≤ x ≤ 0.9, BCST) ceramics sintered in air and nitrogen have been investigated. BCST (x ≤ 0.1) ceramics sintered in air only exhibited peaks associated with tungsten bronze phase structure. A secondary CeO2 phase appeared for x = 0.5, while CeO2 and Ba2Ti9O20 phases coexisted for the ceramics with x = 0.9. In contrast, ceramics fired in nitrogen exhibited tungsten bronze phase structure for all compositions from x = 0 to 0.9 within the solid solution. The chemical structure analysis exhibited that, all the sample possessed mixed ion valance states of Ce4+/Ce3+ and Ti4+/Ti3+ cations upon oxygen vacancy formations. It is found that incorporation of cerium could significant improve the Q × f values of BCST ceramics sintered in nitrogen with good microwave dielectric properties (Q × f ∼7536 GHz, e r ∼78, and τ f ∼24.61 ppm/°C) at x = 0.5.

ZnFe2O4-Fe2O3-CeO2 composite nanopowder: Preparation, magnetic properties, and 4-chlorophenol removal characterizations

Abstract Magnetic ZnFe2O4-Fe2O3-CeO2 nanocomposite was prepared in green walnut hulls extract media and characterized as a catalyst for 4-chlorophenol degradation at room temperature. The XRD patterns of ZnFe2O4/Fe2O3/CeO2 nanocomposite show rhombohedral structure for Fe2O3 phase and cubic structure for ZnFe2O4 and CeO2 phases. The effect of green walnut hulls extract on the Ms and Hc magnetic properties of ZnFe2O4/Fe2O3/CeO2 nanocomposite was investigated. Saturation magnetization and coercivity are changed when the extract concentration is change. Finally, the effect of pH value, catalyst dosage, and 4-chlorophenol concentration on the photocatalytic degradation over ZnFe2O4/Fe2O3/CeO2 nanocomposite was evaluated.

High-resolution structural characterization and magnetic properties of epitaxial Ce-doped yttrium iron garnet thin films

Thin films of magnetic garnet materials, e.g. yttrium iron garnet (Y3Fe5O12, YIG), are useful for a variety of applications including microwave integrated circuits and spintronics. Substitution of rare earth ions, such as cerium, is known to enhance the magneto-optic Kerr effect (MOKE) as compared to pure YIG. Thin films of Ce0.75Y2.25Fe5O12 (Ce:YIG) have been grown using the pulsed laser deposition (PLD) technique and their crystal structure examined using high resolution scanning transmission electron microscopy. Homogeneous substitution of Ce in YIG, without oxidation to form a separate CeO2 phase, can be realized in a narrow process window with resulting enhancement of the MOKE signal. The thermally generated signal due to spin Seebeck effect for the optimally doped Ce:YIG films has also been investigated.