Oxidation State Of Ce Research Articles

Natural Alginate as a Graphene Precursor and Template in the Synthesis of Nanoparticulate Ceria/Graphene Water Oxidation Photocatalysts

Using alginate, a natural polysaccharide from algae, simultaneously as a graphene precursor and a templating agent for ceria nanoparticles, we have prepared a series of materials consisting of highly crystalline ceria nanoparticles embedded on a few-layer graphene matrix. XPS analysis indicates that the predominant oxidation state of Ce in the as-synthesized CeOx/graphene material is +III (over 80 atom %). Varying the weight percentage of ceria/alginate and the pyrolysis temperature enabled the preparation of a ceria/graphene photocatalyst that exhibits about 3 times higher photocatalytic activity for water oxidation to oxygen than commercial ceria. Our results on the ceria/graphene composite as a photocatalyst for water oxidation expand and complement the well-known effect of graphene to increase the photocatalytic efficiency of titania/graphene composites.

Influence of Natural Organic Matter and Surface Charge on the Toxicity and Bioaccumulation of Functionalized Ceria Nanoparticles in Caenorhabditis elegans

The objective of this study was to investigate the role of the CeO2 nanoparticle (NP) surface charge and the presence of natural organic matter (NOM) in determining bioavailability and toxicity to the model soil organism Caenorhabditis elegans. We synthesized CeO2-NPs functionalized with positively charged, negatively charged, and neutral coatings. The positively charged CeO2-NPs were significantly more toxic to C. elegans and bioaccumulated to a greater extent than the neutral and negatively charged CeO2-NPs. Surface charge also affected the oxidation state of Ce in C. elegans tissues after uptake. Greater reduction of Ce from Ce (IV) to Ce (III) was found in C. elegans, when exposed to the neutral and negatively charged relative to positively charged CeO2-NPs. The addition of humic acid (HA) to the exposure media significantly decreased the toxicity of CeO2-NPs, and the ratio of CeO2-NPs to HA influenced Ce bioaccumulation. When the concentration of HA was higher than the CeO2-NP concentration, Ce bioaccumulation decreased. These results suggest that the nature of the pristine coatings as a determinant of hazard may be greatly reduced once CeO2-NPs enter the environment and are coated with NOM.

REE geochemical characteristics of titanium-rich bauxites: the Permian Kanigorgeh horizon, NW Iran

The Permian Kanigorgeh bauxite horizon is one of the typical titanium-rich bauxite deposits in the northeast of Bukan, West Azerbaijan Province, NW Iran. It is a part of the Irano-Himalayan karst bauxite belt and was developed as discontinuous stratified layers and lenses in Upper Permian carbonates. Mineralogically, diaspore and kaolinite are 2 major mineral phases accompanied by boehmite, smectite, illite, rutile, anatase, hematite, goethite, chlorite, quartz, and plagioclase as minor phases. Geochemical considerations for a selected profile indicate that the concentration values of rare earth elements (REEs) in the bauxite ores range from 8.9 to 200.4 ppm. Eu and Ce anomalies show varying values within the range 0.42-0.65 and 0.12-3.23, respectively. On the basis of Ce behavior, the studied profile can be divided into 2 parts by redox boundary. The most pronounced geochemical characteristics of the studied profile are the occurrences of positive Ce anomalies in the ores of low REE content in the upper part of the profile and negative Ce anomalies in the ores of high REE content in the lower part of the profile. The occurrence of positive and negative Ce anomalies are due to the change of oxidation state of Ce (from Ce3+ to Ce4+) in the upper part and the complexing of Ce4+ with carbonate ligands in the lower part of the profile. The concordance of the analytical values of Na and Ca with those of Eu revealed that the degree of plagioclase alteration is the most important controlling factor for Eu anomalies in the ores. The obtained results revealed that the variations in the chemistry of weathering solutions (e.g., pH), function of carbonate bedrocks as a geochemical barrier, and discrepancy in degree of stability of lanthanide-bearing primary minerals are the major factors influencing the mobilization, distribution, and fractionation of REEs. The correlation coefficients among elements suggest that Mn-oxides are the principal hosts for REEs in the ores at Kanigorgeh.

Cerium Substitution in Yttrium Iron Garnet: Valence State, Structure, and Energetics

The garnet structure is a promising nuclear waste form because it can accommodate various actinide elements. Yttrium iron garnet, Y3Fe5O12 (YIG), is a model composition for such substitutions. Since cerium (Ce) can be considered an analogue of actinide elements such as thorium (Th), plutonium (Pu), and uranium (U), studying the local structure and thermodynamic stability of Ce-substituted YIG (Ce:YIG) can provide insights into the structural and energetic aspects of large ion substitution in garnets. Single phases of YIG with Ce substitution up to 20 mol % (Y3–xCexFe5O12 with 0 ≤ x ≤ 0.2) were synthesized through a citrate–nitrate combustion method. The oxidation state of Ce was examined by X-ray absorption near edge structure spectroscopy (XANES); the oxidation state and site occupancy of iron (Fe) as a function of Ce loading also was monitored by 57Fe–Mossbauer spectroscopy. These measurements establish that Ce is predominantly in the trivalent state at low substitution levels, while a mixture of trival...

Homoleptic Cerium(III) and Cerium(IV) Nitroxide Complexes: Significant Stabilization of the 4+ Oxidation State

Electrochemical experiments performed on the complex Ce(IV)[2-((t)BuNO)py]4, where [2-((t)BuNO)py](-) = N-tert-butyl-N-2-pyridylnitroxide, indicate a 2.51 V stabilization of the 4+ oxidation state of Ce compared to [(n)Bu4N]2[Ce(NO3)6] in acetonitrile and a 2.95 V stabilization compared to the standard potential for the ion under aqueous conditions. Density functional theory calculations suggest that this preference for the higher oxidation state is a result of the tetrakis(nitroxide) ligand framework at the Ce cation, which allows for effective electron donation into, and partial covalent overlap with, vacant 4f orbitals with δ symmetry. The results speak to the behavior of CeO2 and related solid solutions in oxygen uptake and transport applications, in particular an inherent local character of bonding that stabilizes the 4+ oxidation state. The results indicate a cerium(IV) complex that has been stabilized to an unprecedented degree through tuning of its ligand-field environment.

Mn-Doped CeO2: DFT+U Study of a Catalyst for Oxidation Reactions

Fil: Garcia Pintos, Delfina. Universidad de Buenos Aires. Facultad de Ingenieri­a. Departamento de Ingenieri­a Quimica; Argentina;

Oxidation State Imaging of Ceria Island Growth on Re(0001)

High resolution X-ray photoemission electron microscopy (XPEEM) and low energy electron microscopy (LEEM) have been used to investigate the growth of ultrathin CeOx(111) on Re(0001), a model catalyst system. Rotational domains of CeOx(111) are identified with microprobe low energy electron diffraction (LEED) and dark-field LEEM. In the regions not covered by the ceria islands, a surface rhenium-oxide layer has been observed using energy-filtered XPEEM imaging and spectroscopy. The oxidation state of the ceria is key to its catalytic activity. For this reason we have employed resonant photoelectron spectroscopy of the Ce 4f contributions to the valence band to monitor the relative Ce3+ and Ce4+ concentrations. The overall stoichiometry of the moderately reduced film was CeO1.63. Resonant energy-filtered XPEEM imaging of the Ce oxidation state allowed us to confirm the uniformity of this stoichiometry across the ceria islands that constituted the film.

Oxidation State of Ce in CeO2-Promoted Rh/Al2O3Catalysts during Methane Steam Reforming: H2O Activation and Alumina Stabilization

The cerium oxidation state in ceria-doped Rh/Al2O3 catalysts during the methane steam reforming (MSR) reaction was determined by in situ X-ray absorption spectroscopy and online mass spectrometry at 773 K. The catalysts were characterized by electron microscopy and X-ray diffraction. The oxidation states of rhodium and cerium during MSR are related. A total of 25% of Ce4+ reduces to Ce3+ under a CH4/H2O/He flow when the catalyst is active in MSR (773 K). A slight reoxidation occurs when the catalyst is sequentially exposed to steam diluted in helium at high temperatures, showing that only a small fraction of CeO2–x may be involved in the water activation step by reoxidation. The main role of ceria during reaction, besides the activation of water, is to stabilize the structure of alumina by forming CeAlO3 and to maintain the dispersion of rhodium.

In SituSynchrotron X-ray Fluorescence Mapping and Speciation of CeO2and ZnO Nanoparticles in Soil Cultivated Soybean (Glycine max)

With the increased use of engineered nanomaterials such as ZnO and CeO₂ nanoparticles (NPs), these materials will inevitably be released into the environment, with unknown consequences. In addition, the potential storage of these NPs or their biotransformed products in edible/reproductive organs of crop plants can cause them to enter into the food chain and the next plant generation. Few reports thus far have addressed the entire life cycle of plants grown in NP-contaminated soil. Soybean ( Glycine max ) seeds were germinated and grown to full maturity in organic farm soil amended with either ZnO NPs at 500 mg/kg or CeO₂ NPs at 1000 mg/kg. At harvest, synchrotron μ-XRF and μ-XANES analyses were performed on soybean tissues, including pods, to determine the forms of Ce and Zn in NP-treated plants. The X-ray absorption spectroscopy studies showed no presence of ZnO NPs within tissues. However, μ-XANES data showed O-bound Zn, in a form resembling Zn-citrate, which could be an important Zn complex in the soybean grains. On the other hand, the synchrotron μ-XANES results showed that Ce remained mostly as CeO₂ NPs within the plant. The data also showed that a small percentage of Ce(IV), the oxidation state of Ce in CeO₂ NPs, was biotransformed to Ce(III). To our knowledge, this is the first report on the presence of CeO₂ and Zn compounds in the reproductive/edible portion of the soybean plant grown in farm soil with CeO₂ and ZnO NPs.

Biological Change of Chemical States of Actinides and Lanthanides-effects of Organic Acids-

In this study, we have examined the chemical states change of lanthanides (Lns) of La, Ce, Pr, Eu, and actinides (Ans) of Th(IV), Pu(IV) in the complexes with organic acids of citric acids or desferrioxamine B (DFO) by the interaction with Pseudomonas fluorescens cells under the resting condition at pH 4 – 9. In the adsorption experiments the distribution coefficients (Kd) were determined. The oxidation states of Ce in the solution were determined by X-ray near edge fine structure (XAFS). In the absence of organic materials, Kd of Eu(III) increased gradually with pH up to 7; above 7, the Kd decreased with an increase in pH. In the presence of citric acid, we found that Kd was lower than that in the absence of organic materials, reflecting the formation of Eu(III)-citrate complexes competes with the Eu(III)-cell-surface complexes. For Ln-DFO complex, the higher Kds of La, Ce, and Pr were obtained at lower pHs on P. fluorescens cells. The Kd of Ce was lower than that of its neighboring REEs, La(III) and Pr(III). XAFS analysis showed that Ce exists as the Ce(IV)-DFO complex in higher pH than 6. Thus, the pH dependence of lower Kd of Ce is predominantly dependent on the stability of Ce(IV)-DFO complex. For the adsorption of Ans, the Kds of Th and Pu were larger than Eu, being inverse relationship to the stability constants of DFO complex. These results indicate that presence of organic acids affect the chemical states of Ln and An in the environments.

Electrochemical and Spectroscopic Study of Ce(III) Coordination in the 1-Butyl-3-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide Ionic Liquid Containing Chloride Ion

Cyclic staircase voltammetry, controlled potential coulometry, and electronic absorption spectroscopy were used to probe the coordination and accessible oxidation states of Ce(3+) dissolved in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf(2)N) before and after the addition of chloride ion as BuMePyroCl. Controlled potential coulometry indicated that the oxidation of Ce metal in this ionic liquid produces only Ce(3+). Spectroscopic examination of the resulting solutions indicated that Ce(3+) was weakly solvated by Tf(2)N(-) ions as [Ce(Tf(2)N)(x)]((x-3)-), x ≥ 3. This species can be reduced at negative potentials, probably to a related Ce(2+) species, but the latter is unstable and quickly disproportionates to Ce(3+) and Ce(0); the latter appears to react with the ionic liquid. The addition of Cl(-) to solutions of [Ce(Tf(2)N)(x)]((x-3)-) causes the precipitation of CeCl(3)(s), providing a convenient route to the nondestructive recovery of Ce(3+) from the ionic liquid. However, as the Cl(-) concentration is further increased, the CeCl(3)(s) redissolves as the octahedral complex, [CeCl(6)](3-), and the voltammetric and spectroscopic signature for [Ce(Tf(2)N)(x)]((x-3)-) disappears. Absorption spectroscopy indicated that the bulk controlled potential oxidation of solutions containing [CeCl(6)](3-) produces [CeCl(6)](2-). Although stable on the time scale of voltammetry, this species slowly reacts with the ionic liquid and is converted back to [CeCl(6)](3-).

Ce and Eu anomalies in zircon as proxies for the oxidation state of magmas

Chondrite normalized rare earth element (REE) patterns of zircons generally have enriched Ce values relative to La and Pr, and depleted Eu values relative to Sm and Gd. High Ce contents in zircon may imply oxidizing conditions (Ce4+ is more compatible than Ce3+), whereas depleted Eu contents may imply reducing conditions (Eu2+ does not substitute into the zircon lattice). We report 41 experiments in which temperature, melt composition, and oxygen fugacity (fO2) were varied in order to explore the details of Ce and Eu incorporation into zircon. Crystals were synthesized in hydrous silicate melts at 10kbar and 800–1300°C. Synthetic rock mixes were doped with La+Ce+Pr (±P) or Sm+Eu+Gd and buffered at oxygen fugacities ranging from ∼IW (iron–wüstite) to >MH (magnetite–hematite); the run products were analyzed by electron microprobe to obtain crystal/melt partition coefficients. Cerium anomalies increase with higher oxygen fugacities and lower crystallization temperatures. In agreement with other experimental studies, peralkaline melts yield the largest zircon grains but show only modest Ce anomalies even at fO2s>MH. The same reason that zircons grown in peralkaline melts are easy to synthesize in the laboratory (these melts are capable of dissolving wt.% levels of Zr before zircon saturation due to high alkali content) makes the melt structure/composition atypical and not representative of most natural magmas. With this in mind, we synthesized zircons in a granitic melt with more modest alkali contents that require geologically plausible Zr contents for saturation. We obtained the following empirical relationship: lnCeCe∗D=(0.1156±0.0050)×ln(fO2)+13,860±708T(K)-6.125±0.484where (Ce/Ce∗)D is the Ce anomaly in zircon calculated from partition coefficients, and T is the zircon crystallization temperature in K. Europium anomalies from the same melt composition are more negative at lower oxygen fugacities, but with no resolvable temperature dependence, and can be described by the following empirical relationship: EuEu∗D=11+10-0.14±0.01×ΔNNO+0.47±0.04where (Eu/Eu∗)D is the Eu partitioning anomaly and ΔNNO is the difference in log units from the NNO buffer. If both Eu and Ce anomalies in zircons can be used as proxies for the oxidation state of Ce and Eu in the host melts, then it is clear that Eu2+ and Ce4+ can coexist in most zircon-saturated magmas. This implies that depletion of Eu melt contents by feldspar crystallization fractionation prior to (or during) zircon crystallization is not required to produce Eu anomalies. Thus, zircon Eu anomalies are a function of the oxygen fugacity and the Eu anomaly of the melt. Cerium anomalies of natural melts are not predicted to be as common because no major rock-forming phase depletes or enriches magmas in Ce compared to neighboring elements La and Pr. Thus, (Ce/Ce∗)D may be most readily applied to constrain the oxidation state of natural melts.

Radiation-Induced Reduction of Ceria in Single and Polycrystalline Thin Films

The effect of radiation on the oxidation state of Ce in high-quality single and polycrystalline ceria thin films is presented. The films were synthesized by molecular beam epitaxy and irradiated wi...

A micro-XAS/XRF and thermodynamic study of CeIII/IV speciation after long-term aqueous alteration of simulated nuclear waste glass: Relevance for predicting Pu behavior?

Abstract In the present study, the dissolution and mobilization of Ce introduced in a simulated nuclear waste glass (MW) as a surrogate of Pu was investigated after leaching in pure water over 12 a at 90 °C and pH ∼ 9.6. The microscopic distribution and oxidation state of Ce in the altered glass were studied using micro-X-ray fluorescence (micro-XRF) mapping techniques and micro-X-ray near-edge absorption spectroscopy (micro-XANES). Distribution maps of Ce III and Ce IV were obtained by recording the L α fluorescence emission at two different incident X-ray energies, coinciding with the maximum contrast between Ce III and Ce IV fluorescence intensities. The micro-XRF maps revealed that Ce was dominantly present as oxidized species (Ce IV ) in the original glass. After dissolution from the glass matrix, Ce IV was partly reduced and re-immobilized as Ce III at grain boundaries or in the interstitial spaces between the glass particles. The concentration of Ce III was found to correlate with the spatial distribution of secondary Mg-clay formed during the aqueous corrosion as the main glass alteration product. Micro-XANES spectra collected at locations representative of both altered and non-altered glass domains confirmed the findings obtained by the redox mapping. Because redox-sensitive elements in the pristine MW glass (Fe, Cr, Se) occur almost exclusively as oxidized species, reduction of Ce IV was probably mediated by an external source of reductants, such as Fe(0) from the steel reaction vessel. These results, in conjunction with an Eh–pH stability diagram of the Ce III/IV –O–H–C IV –P–S VI –Na–Cl system, indicate that the glass was leached at relatively low oxidation potentials (Eh IV to Pu III would require considerably more reducing conditions (Eh

Meliorated oxygen reduction reaction of polymer electrolyte membrane fuel cell in the presence of cerium–zirconium oxide

Oxygen Reduction Reaction (ORR) kinetics is known to be one of the major bottle necks in PEM Fuel Cell performance. Several attempts are being made to enhance the ORR. Inspite of several attempts Pt in the vicinity of high surface area oxide catalysts seems to be the best choice although some alloy catalyst have shown good performance in half cell studies and single cell studies. We are investigating methods to improve the performance of PEM fuel cell especially in low air flow conditions which is the condition that will arise in surge power requirements. We have found that oxygen reduction reaction (ORR) performance of Pt/C can be increased in the presence of cerium–zirconium oxides especially Ce 0.8Zr 0.2O 2 (CZO) in the cathode catalyst layer. Ce 0.8Zr 0.2O 2 was prepared by co-precipitation method and the formation is confirmed by the XRD results. An XPS study of Ce 3d emission spectra dominated by atomic multiplet effects in core level spectroscopy of Ce 0.8Zr 0.2O 2-Pt/C are studied from which the possible oxidation states of Ce on Ce 0.8Zr 0.2O 2-Pt/C surface are examined. The ORR improvement in the CZO added electrodes have been studied using chronoammperometry and fuel cell testing.

Ce3+ Ions Determine Redox-Dependent Anti-apoptotic Effect of Cerium Oxide Nanoparticles

Antioxidant therapy is the novel frontier to prevent and treat an impressive series of severe human diseases, and the search for adequate antioxidant drugs is fervent. Cerium oxide nanoparticles (nanoceria) are redox-active owing to the coexistence of Ce(3+) and Ce(4+) oxidation states and to the fact that Ce(3+) defects, and the compensating oxygen vacancies, are more abundant at the surface. Nanoceria particles exert outstanding antioxidant effects in vivo acting as well-tolerated anti-age and anti-inflammatory agents, potentially being innovative therapeutic tools. However, the biological antioxidant mechanisms are still unclear. Here, the analysis on two leukocyte cell lines undergoing apoptosis via redox-dependent or independent mechanisms revealed that the intracellular antioxidant effect is the direct cause of the anti-apoptotic and prosurvival effects of nanoceria. Doping with increasing concentrations of Sm(3+), which progressively decreased Ce(3+) without affecting oxygen vacancies, blunted these effects, demonstrating that Ce(3+)/Ce(4+) redox reactions are responsible for the outstanding biological properties of nanoceria.

Sour water–gas shift reaction over Pt/CeO 2 catalysts

Ceria-supported catalysts with 0.38–2.0 wt.% Pt have been studied under high-temperature water–gas shift (WGS) conditions with and without 20 ppm H 2S present, which is a typical level in feed streams for WGS reactors in IGCC power plants. The effect of H 2S on CO conversion decreased with increasing temperature in the range 573–723 K and also with increasing Pt content. A 1 wt.% Pt catalyst exhibited excellent stability during a 300 h test at 673 K and GHSV = 7500 l kg −1 h −1 in an H 2S-charged feed with steam-to-CO ratio 2 as CO conversion remained stable around 73%. This was still close to the corresponding thermodynamic limit of 78.8%, which was reached under sulfur-free conditions. The Pt ionization degree in WGS-tested catalysts increased only slightly with the H 2S addition as the Pt 2+ fraction grew from ca. 40% to 50% and the Ce oxidation states remained similar too. The bimodal pore structure of the mesoporous CeO 2 was also retained after WGS experiments although the effective surface area had declined by nearly 20% following the 300 h test in sour syngas. This and the concomitant decline of surface OH groups were likely caused by adsorption of H 2S and subsequent formation of surface sulfates and thus responsible for lowering the WGS activity of the ceria surface in the presence of H 2S. We propose that Pt centers can mitigate this effect through hydrogen spillover in their vicinity thus maintaining a high WGS activity of these catalysts in sour syngas.

Two-Phase Synthesis of Colloidal Annular-Shaped CexLa1−xCO3OH Nanoarchitectures Assemblied from Small Particles and Their Thermal Conversion to Derived Mixed Oxides

Undoped and cerium doped LaCO(3)OH annular-shaped nanoarchitectures with high specific surface area have been fabricated via the thermolysis of Ce(x)La(1-x)(oleate)(3) (x = 0-20 mol %) complexes in a toluene-water system containing tert-butylamine/oleylamine. The products exhibit 400 nm-sized monodisperse annular-shaped nanoarchitectures, which are constituted of 3-5 nm-sized primary particles. A possible mechanism of the reaction of Ce(x)La(1-x)(oleate)(3) and tert-butylamine for the formation of annular-shaped Ce(x)La(1-x)CO(3)OH nanoarchitectures is proposed. The thermal conversion of Ce(x)La(1-x)CO(3)OH to Ce(x)La(1-x)(CO(3))O(2) at 600 °C, to Ce(x)La(1-x)(OH)(3) at 800 °C, final to (Ce(x)La(1-x))(2)O(3-δ) at 900 °C were employed, while the original morphology was essentially unchanged. The dopant concentration was varied from 5 to 20 of cerium ions per LaCO(3)OH nanoparticle. The X-ray diffraction (XRD) results reveal that the cerium dopant could enter easily into the LaCO(3)OH structural lattice, whereas copper could unlikely enter into their lattice because of their large ionic radius difference. The cerium oxidation state was controlled by changing doping concentration. The X-ray photoelectron spectroscopy (XPS) results reveal that only one Ce(3+) oxidation state is in the as-synthesized Ce(x)La(1-x)CO(3)OH samples with cerium concentration ranging from 5 to 20 mol %, whereas both 3+ and 4+ ones coexisted in 20 mol % Ce:LaCO(3)OH structure. Remarkable luminescence emission intensity enhancement of 1.5-9.0 times were observed for Ce(x)La(1-x)CO(3)OH samples with cerium concentration ranging from 5 to 20 mol %, after doping with an undoped LaCO(3)OH.

Pharmacological potential of cerium oxide nanoparticles

Nanotechnology promises a revolution in pharmacology to improve or create ex novo therapies. Cerium oxide nanoparticles (nanoceria), well-known as catalysts, possess an astonishing pharmacological potential due to their antioxidant properties, deriving from a fraction of Ce(3+) ions present in CeO(2). These defects, compensated by oxygen vacancies, are enriched at the surface and therefore in nanosized particles. Reactions involving redox cycles between the Ce(3+) and Ce(4+) oxidation states allow nanoceria to react catalytically with superoxide and hydrogen peroxide, mimicking the behavior of two key antioxidant enzymes, superoxide dismutase and catalase, potentially abating all noxious intracellular reactive oxygen species (ROS) via a self-regenerating mechanism. Hence nanoceria, apparently well tolerated by the organism, might fight chronic inflammation and the pathologies associated with oxidative stress, which include cancer and neurodegeneration. Here we review the biological effects of nanoceria as they emerge from in vitro and in vivo studies, considering biocompatibility and the peculiar antioxidant mechanisms.

Effects of thermal treatments in controlled atmosphere on the Ce oxidation state in Ce–Ti-Eu doped SiO2 sol–gel glasses

We report an experimental study by optical absorption, photoluminescence and Raman spectroscopies of the modifications induced on Ce–Ti-Eu doped SiO2 glasses by thermal treatments in controlled atmosphere. Samples with Ce content varying up to 5,000 part per million by weight (ppm) and with Ti and Eu content fixed at 40 and 300 ppm respectively, have been investigated. The treatments were done in inert atmosphere of He and in O2 atmosphere at 390°C and 100 bar. Our experiments show that only Ce4+ ions are affected by He treatments, whereas both Ce4+ and Ce3+ ions are affected by O2 treatments. The obtained results are interpreted on the basis of microstructural changes induced by the thermal treatments on Ce sites and by the occurrence of an oxidizing process.