Fraction Of Ce Research Articles

Corrosion behaviour of the magnesium-cerium binary alloy designed for degradable medical implants

ABSTRACT Magnesium (Mg) alloys containing rare earths (RE) gained special attention as promising candidates for degradable implant applications. Cerium (Ce) is one of the RE elements which can be tolerated by the human physiological system when used as an alloying element in Mg alloys. In this current research work, Mg-Ce binary alloys (0%, 0.5%, 1%, 1.5%, and 2% Ce by weight) were prepared by the stir-casting method. The developed alloys were characterised, and corrosion performance was assessed by immersion experiments in normal saline solution and by electrochemical experiments. The degradation rate of the developed alloys was measured as decreased with the increased Ce content up to 1.5%. From the polarisation studies, lower corrosion current density values 3.5 × 10−5 A/cm2 and 4.1 × 10−5 A/cm2 were observed for Mg-1.5%Ce and Mg-2%Ce alloys, respectively compared with the other samples. The surface morphologies after removing the corrosion products revealed more degraded regions for Mg and alloys with lower Ce content (0.5% and 1%) compared with 1.5% and 2% Ce. From the results, it is concluded that developing an Mg-Ce alloy with an optimum fraction of Ce (1.5%) is promising to produce degradable Mg-based medical implants with controlled degradation.

The cerium isotope fingerprints of redox fluctuation in bauxites

We measured the Ce concentration, oxidation state, and isotope composition of bauxites developed on the Columbia River Basalts (CRBs) to evaluate the impacts of redox and non-redox processes on the Ce isotopic variability on Earth's surface. Bauxites recovered from drill cores show upward increasing Ce concentration (5.4–88.7 μg/g) and overall depletion of Ce (mass transfer coefficient, τCe,Nb: -0.96 to -0.52, i.e., net depletion of 52-96% relative to their parent CRBs). There is a wide range of the Ce anomaly (Ce/Ce⁎) from 0.4 to 6.3 and 0.6 to 1.4 in the Cowlitz and Columbia bauxites, respectively. The most positive Ce anomalies appear at the shallow regolith (2-5 m depth). Cerium primarily presents in its trivalent form in deposited exogenous materials (wind-blown dust from an old, weathered region of the continent) and primary CRBs. There is a downward increase in the fraction of Ce (IV) in the regolith. Bauxite δ142Ce ranges from -0.161±0.034 to -0.018±0.043‰ and -0.277±0.034 to -0.046±0.034‰ in the Cowlitz and Columbia profiles, respectively. The Ce isotope record reflects the redox cycle of Ce and Mn and is masked by dust accretion on the top. The enrichment of Ce (IV) occurs in the transition zone (the bottom of the shallow regolith) with minor Ce isotope shifts from the CRBs (δ142Ce from -0.080±0.034 to -0.04±0.034‰) likely caused by minor isotopic fractionation linked to O2-driven CeO2 precipitation. There are negative Ce isotope shifts from the basaltic parents and the enrichment of oxidized Ce and Mn in the deep regolith (5-9 m depth), where large isotopic fractionation probably induced by Ce oxidative adsorption on MnO2 plays a vital role. The vertical difference between Ce/Ce⁎ and δ142Ce may be attributed to the climatic oxidation-reduction cycle of Mn and Ce, leaving discrete CeO2 grains in the shallow regolith while transferring isotopically light Ce associated to oxidized Mn deposits down to the deep regolith. We conclude that a combination of Ce species isotopes and anomalies potentially records terrestrial redox status and fluctuation.

Ce Filling Limit and Its Influence on Thermoelectric Performance of Fe3CoSb12-Based Skutterudite Grown by a Temperature Gradient Zone Melting Method.

CoSb3-based skutterudite is a promising mid-temperature thermoelectric material. However, the high lattice thermal conductivity limits its further application. Filling is one of the most effective methods to reduce the lattice thermal conductivity. In this study, we investigate the Ce filling limit and its influence on thermoelectric properties of p-type Fe3CoSb12-based skutterudites grown by a temperature gradient zone melting (TGZM) method. Crystal structure and composition characterization suggests that a maximum filling fraction of Ce reaches 0.73 in a composition of Ce0.73Fe2.73Co1.18Sb12 prepared by the TGZM method. The Ce filling reduces the carrier concentration to 1.03 × 1020 cm−3 in the Ce1.25Fe3CoSb12, leading to an increased Seebeck coefficient. Density functional theory (DFT) calculation indicates that the Ce-filling introduces an impurity level near the Fermi level. Moreover, the rattling effect of the Ce fillers strengthens the short-wavelength phonon scattering and reduces the lattice thermal conductivity to 0.91 W m−1 K−1. These effects induce a maximum Seebeck coefficient of 168 μV K−1 and a lowest κ of 1.52 W m−1 K−1 at 693 K in the Ce1.25Fe3CoSb12, leading to a peak zT value of 0.65, which is 9 times higher than that of the unfilled Fe3CoSb12.

Effects of Ce Addition on Solidification Structure of a Low-Carbon 42CrMo4 Steel

Effects of Cerium (Ce) addition on solidification structure of a low-carbon 42CrMo4 steel was investigated. The addition of up to 0.067 wt.% of Ce in the steel produced greatly improved solidification structure with a suppressed columnar grain zone, finer grain size in an equiaxed grain zone and zero area fraction of casting shrinkage cavity. The added Ce occurred in the steel both in the form of Ce oxy-sulfide inclusions and as dissolved atomic Ce segregated together with other elements at prior austenite grain boundaries and at interdendritic spacing. The Ce oxy-sulfide inclusions were found to play a major role in the observed improved grain structure meanwhile dissolved Ce had pronounced effects on morphology of dendritic networks. The fraction of Ce dissolved in the melt appeared to bring about increase in fluidity of the molten steel, leading to total elimination of interdendritic shrinkage porosity in solidification structure of the steel with added Ce. Ce addition can be considered as a potential solution for grain structure refinement in heavy-weight castings of 42CrMo4 steel grade.

Preliminary chemical studies at the jericho archaeological site

This study measured the chemical composition of 45 ceramic samples from the Jericho archaeological site, Palestine, by means of instrumental neutron activation analysis (INAA). The mass fraction of Na, K, La, Sm, Yb, Lu, U, Sc, Cr, Fe, Co, Zn, Rb, Cs, Ce, Eu, Hf and Th was determined with the purpose to detect the presence of ceramic groupings based on their composition. The analytical method is appropriate for this type of study because it is a non-destructive technique with high sensitivity, accuracy and precision, and determines chemical elements in trace and ultra-trace levels. These characteristics are essential to study small concentration variations. Initially the mass fractions were normalized to compensate for the large difference in magnitude among elements determined in percentage and trace level. Subsequently, the dataset was interpreted through cluster and discriminant analysis. The results showed the existence of three different chemical groups.

Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns

Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18–108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10–100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.

Innovative reference material for improving the quality control in the sucroenergetic sector

Analytical techniques in the sucroenergetic sector can now for the first time be supported by an innovative matrix-matching reference material produced from sugarcane leaves. This will further enhance the validity of the measurement results and contribute significantly to the quality assurance of plant nutrition analysis. The candidate reference material obtained had a low residual moisture and appropriate particle size. Neutron activation analysis was used to determine the mass fraction of Al, Br, Ca, Cl, Ce, Co, Cs, Cu, Fe, Hf, K, La, Mg, Mn, Mo, Na, P, Rb, Sb, Sc, Sm, Sr, Th, V and Zn, and the Kjeldahl method for N. Statistical techniques were applied to evaluate minimum sample mass and within-bottle homogeneity (ANOVA, Tukey test and PCA) and between-bottles homogeneity (ANOVA). It is demonstrated in this paper that the material is homogeneous using 50 mg mass sample for most chemical elements. However, sample masses of 200 mg or greater are required for Co, Na, Sb and V.

Uptake and effects of cerium(III) and cerium oxide nanoparticles to Chlamydomonas reinhardtii

Cerium (Ce) and cerium oxide nanoparticles (CeO2 NP) are increasingly used in different applications. Upon their release into the aquatic environment, the exposure of aquatic organisms becomes likely. In this study, the uptake of CeO2 NP and Ce3+ into the wild type and cell wall free mutant of Chlamydomonas reinhardtii was examined upon short term exposure. Separation of CeO2 NP and Ce3+ not taken up or loosely bound to the cells was performed by washing algae with EDTA.Despite a concentration and time dependent increase of cellular Ce upon exposure to CeO2 NP with the maximal calculated Ce concentration corresponding to 1.1 CeO2 NP per cell, an internalization of CeO2 NP with a mean size of 140 nm in C. reinhardtii was excluded. In contrast, dissolved Ce3+ (1 and 10 μM) was taken up both in the wild type and cell wall free mutant of C. reinhardtii, with a linear increase of cellular Ce within 1–2 h and maximal cellular Ce of 6.04 × 10−4 mol Lcell−1 (wild type) and 9.0 × 10−5 mol Lcell−1 (cell wall free mutant). Based on competition with Ca2+ for Ce3+ uptake, on the comparison of the wild type and the cell wall free mutant and on inhibition of photosynthetic yield, we suggest that no efficient uptake routes for Ce3+ are available in C. reinhardtii and that a fraction of the cellular Ce in the wild type strongly sorbs to the algal cell wall.

Mesoporous Ce-Ti-Zr ternary oxide millispheres for efficient catalytic ozonation in bubble column

Most heterogeneous catalysts available for catalytic ozonation are present as powders and not ideal for column operation in advanced water treatment. In this study, a mesoporous Ce-Ti-Zr ternary oxide (CTZO) millisphere of large size (0.8–1.0 mm in diameter) and high surface area (180 m2 g−1) was synthesized as a highly stable catalyst to meet the hydrodynamic demand in column ozonation. The fraction of Ce(III) is much higher on the surface of CTZO (49.2%) than CeO2 (27.5%), resulting in its high catalytic activity in ozone decomposition and mineralization of oxalic acid (OA), an ozone-refractory probe compound. The most favorable catalytic ozonation of OA was observed at pH 3.0 and the adsorption of OA by CTZO via surface complexation is a requisite step for its ozonation. The EPR analysis and radical scavenging experiment confirmed that OH was the dominating reactive species in catalytic ozonation of OA by CTZO. XPS revealed that the oxidation of OA was mediated by the Ce(III)/Ce(IV) redox cycle, which continously accepts the electron supply from OA ligand and meanwhile donates electron to activate O3 into OH. The catalytic ozonation of OA by CTZO was enhanced in the presence of sulfate due to the generation of sulfate radical. Cyclic runs demonstrated that the CTZO millispheres exhibited high stability for sustainable catalytic ozonation of OA without noticeable release of Ce or change of Ce valence state. This study will provide new insight for the development of efficient ozonation catalysts towards practical application in advanced water treatment.

Development of La1−xCexFeO3/attapulgite nanocomposites for photocatalytic reduction of NO at low temperature

A series of attapulgite (ATP) supported perovskite-type La1−xCexFeO3 (x = 0–0.5) nanocomposites were synthesized by a facile sol–gel method. The samples were characterized by X-ray diffraction, Transmission electron microscope, Ultraviolet–visible spectroscopy and Fourier-transform infrared spectroscopy. The photoactivity of the La1−xCexFeO3/ATP was evaluated via catalytic reduction of NOx with NH3 at low-temperature under visible light irradiation. The impact of the doping fraction of Ce on the NOx conversion was investigated. Results show that ATP provides a high surface area facilitating the dispersion of small nanoparticles as well as the gas adsorption, while incorporation of an appropriate amount of Ce leads to the formation of coherent heterostructure La1−xCexFeO3/CeO2 which benefits the separation of electron–holes. The highest conversion rate of NO reaches 80% at low temperature when the doping amount is 0.3.

Mineral Nanoparticles in Waste: Potential Sources, Occurrence in Some Engineered Nanomaterials Leachates, Municipal Sewage Sludges and Municipal Landfill Sludges

Environmental assessment of engineered nanoparticles (ENPs) currently suffers from lack of data on production, emission, behaviour and fate in natural compartments. This paper aims to bring factual data on production amounts of ENPs and emission of mineral elements in a colloidal or nanoparticulate forms stemming from products, (e.g. cosmetics, paints, concretes) and from two potential waste sinks, namely municipal sewage sludge and nonhazardous waste landfill sludge. Based on the declaration of production and importation of ENPs in France in 2014, we set out a classification of ENPs substances comprising carbon black, organic pigments, miscellaneous organic substances and mineral ENPs. These mineral ENPs were sub-classified on the basis of production and CLP ecotoxicological and hazard classifications. Major elements (Group #1) encompass ENPs substances ubiquitous in total contents, and also as a colloid fraction in waste leachates (Si, Ca, Ti, Al, Mg, Fe, Mn, P). Minor elements were divided as ENPs with soluble substances and dissolved metal ions non-classified as ecotoxic (Group #2: Ba, Bi, Cr (III), Sr, Zr, La, Pd, Mo, W, Y, Au) or with soluble substances classified as ecotoxic and hazard statement code in the CLP regulation (Group #3: Ce, Cu, Zn, Ni, Sb, Ag, Co). Paints, concrete and particularly cosmetics proved to be sources of ENPs. Colloidal forms of elements or ENPs were found in leachate obtained from paint (Si), in cosmetics leachates (Al, Si, Ti and Zn), and in one demolition concrete (Ti). No nanoparticulate forms or fraction of Ag, Ce, Ti and Zn were identified by TEM/EDS in municipal sewage sludge. However, sewage sludge could be a sink for Group #3 elements such as Ag and Ce, since their total concentrations were significant. Based on landfill leachates from municipal solid wastes, the colloidal fraction frequently contained elements of Group #3 (Ni, Zn, Cu, Co and Sb) but with low mean concentration and more rarely Ag and Ce, indicating that the fluxes of these elements from the landfill cells should be low, except for Ce. Landfills seem to not emit ENPs in their leachates. From a regulative aspect, monitoring of Ag in sewage sludge for agricultural use could be of concern.

Synergistic Catalysis of Methane Combustion Using Cu–Ce–O Hybrid Nanoparticles with High Activity and Operation Stability

A new CuO–CeO2 hybrid nanoparticle (CuCeOx-NP) with a tunable homogeneous chemical composition was successfully prepared for high-performance catalytic methane combustion. The substantial amounts of Cu–Ce–O interfaces were created for enhanced catalysis using gas-phase evaporation-induced self-assembly. The CuCeOx-NP exhibited an ultralow light-off temperature (320 °C), high activity, selectivity, and operation stability for catalytic methane combustion. The optimal reducibility and the corresponding catalytic activity of CuCeOx-NP were achieved when the molar fraction of Ce was 0.17. The operation stability increased as the concentration ratio of oxygen in the reactant gas and the corresponding oxidation rate of carbon species from the catalyst surface increased. This work demonstrates a facile route for controlled synthesis of CuCeOx-NP. The mechanistic understanding of synergistic catalysis developed in this study can be used to further enhance activity of methane combustion and reduce environmental po...

Catalytically Active and Spectator Ce(3+) in Ceria-Supported Metal Catalysts.

Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

Valence modulations in CeRuSn

CeRuSn exhibits an extraordinary room temperature structure at 300~K with coexistence of two types of Ce ions, namely trivalent Ce$^{3+}$ and intermediate valent Ce$^{(4-\delta)+}$, in a metallic environment. The ordered arrangement of these two Ce types on specific crystallographic sites results in a doubling of the unit cell along the $c$-axis with respect to the basic monoclinic CeCoAl-type structure. Below room temperature, structural modulation transitions with very broad hysteresis have been reported from measurements of various bulk properties. X-ray diffraction revealed that at low temperatures the doubling of the CeCoAl type structure is replaced by a different modulated ground state, approximating a near tripling of the basic CeCoAl cell. The transition is accompanied by a significant contraction of the $c$ axis. We present new x-ray absorption near-edge spectroscopy data at the Ce L$_{3}$ absorption edge, measured on a freshly cleaved surface of a CeRuSn single crystal. In contrast to a previous report, the new data exhibit small but significant variations as function of temperature that are consistent with a transition of a fraction of Ce$^{3+}$ ions to the intermediate valence state, analogous to the $\gamma \rightarrow \alpha$ transition in elemental cerium, when cooling through the structural transitions of CeRuSn. Such results in a valence-modulated state.

Origin of the different phytotoxicity and biotransformation of cerium and lanthanum oxide nanoparticles in cucumber

To investigate how the physicochemical properties of nanoparticles (NPs) affect their biological and toxicological effects, we evaluated the phytotoxicity of CeO2 and La2O3 NPs to cucumber (Cucumis sativus) plants and tried to clarify the relation between physicochemical properties of NPs and their behaviors. CeO2 NPs had no phytotoxicity to cucumber at all tested concentrations, while La2O3 NPs showed significant inhibition on root elongation ( ≥ 2 mg/L), shoot elongation (at 2000 mg/L), root biomass ( ≥ 2 mg/L), and shoot biomass ( ≥ 20 mg/L), as well as induced more reactive oxygen species and cell death in roots (2000 mg/L). The different distribution and speciation of Ce and La in plants were determined by synchrotron-based micro X-ray fluorescence microscopy and X-ray absorption spectroscopy. In the aerial parts, all of La was combined with phosphate or carboxylic group, while a fraction of Ce was changed to Ce(III)–carboxyl complexes, implying that La2O3 acted as its ionic form, while CeO2 displayed the behavior of particles or particle–ion mixtures. The higher dissolution of La2O3 than CeO2 NPs might be the reason for their significant difference in phytotoxicity and transporting behaviors in cucumbers. To our knowledge, this is the first detailed study of the relation between the level of dissolution of NPs and their behaviors in plant systems.

Enhancing photocatalytic activity of ZnO nanostructures by doping with Ce+4 ions prepared in water using ultrasonic irradiation

Abstract Ultrasound was applied for preparation of ZnO nanostructures doped with different Ce/Zn ratios in water by irradiation for 60 min. In this method, zinc acetate, cerium sulfate and sodium hydroxide were used as starting materials without using any organic additives or post preparation treatments. Powder X-ray diffraction patterns indicate that the nanostructures are excellently crystallized in the form of wurtzite hexagonal phase. Scanning electron microscopy and transmission electron microscopy images show that the morphology of the nanostructures changes by doping with Ce+4 ions. The presence of the elements in the nanostructures was verified by energy dispersive X-ray spectroscopy. The UV–vis diffuse reflectance spectra of the nanostructures are similar to each other and they have a maximum at about 361 nm. The nanostructures with 0.025 mole fraction of Ce+4 ions exhibit the highest activity for degradation of methylene blue under UV irradiation. The reaction rate constant decreases with calcination temperature. Moreover, the rate constants in more acidic and alkaline solutions are lower than those of the neutral conditions. The photocatalyst retains 90 % of activity after being used four times.

Microwave-assisted preparation of Ce-doped ZnO nanostructures as an efficient photocatalyst

Fast and template-free method is proposed for preparation of Ce-doped ZnO nanostructures (0≤ mole fraction of Ce+4≤0.15) in water under microwave irradiation for 10min without using any templates and additives. Photocatalytic activity of the nanostructures was investigated by degradation of methylene blue (MB) under UV irradiation. Doping of the ZnO nanostructures with 0.1mol fraction of Ce+4 ions increases the rate constant about 7-fold. The photocatalyst with 0.8g/L have highest rate constant. Moreover, the reaction rate constant decreases with calcination temperature and the optimum value for pH of solution is 5.4.

Ce-doped nanoparticles of TiO2: Rutile-to-brookite phase transition and evolution of Ce local-structure studied with XRD and XANES

The crystal and electronic structural changes undergone by TiO2 nanoparticles when Ce is introduced were studied using X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES). A small amount of Ce (less than 1% molar concentration) resulted in i/a significant reduction of the average size of the TiO2 nanoparticles and ii/a phase transition in which brookite replaced rutile as the minority phase component (anatase was the majority phase component at all Ce concentrations studied up to 10% molar concentration). The Ce L3 edge XANES revealed changes in the local environment of Ce impurities. As Ce concentration was increased the fraction of Ce that have formal valence of +3 decreased and, for the remaining Ce with valence +4, the 4f orbitals became less-strongly hybridized with the p-orbitals of oxygen neighbors. The results have implications for photocatalytic and gas sensing properties of Ce-doped TiO2.

Effects of Ce, Mn, Cr on the Microstructure and Properties of High-Iron Eutectic Al-Si Piston Alloy

The paper discussed the effects of Ce, Mn, Cr on the microstructure and properties of high-iron eutectic Al-Si piston alloy using orthogonal design. It has been found that Mn and Cr improved the morphology of β phase (Al9FeSi3), becoming the Fe phase that consists of Mn and Cr; Rare earths Ce has a strong effect on refinement of the eutectic silicon. At a high mass fraction of Ce, Ce enter Fe phase that contains Mn and Ce, which improves its morphology greatly and decreases the size of Fe phase, and is able to replace the position of Ni, becoming high-temperature Al-Ni-Cu-Ce phase. The best additions of Ce, Fe, Mn, Cr would be 0.8%, 1.0%, 0.4% and 0.1% respectively and the tensile strength under room temperature (25°C) and high temperature(300°C) would reach 270.3MPa and 136.7MPa respectively, which fully meet the requirements of the use of novel the piston high temperature load.

Surfactant-assisted synthesis of mesoporous silica/ceria–silica composites with high cerium content under basic conditions

Ordered mesoporous silica/ceria–silica composites were synthesized using cerium(IV) hydroxide and tetraethyl orthosilicate (TEOS) as co-precursors in the presence of hexadecyltrimethylammonium bromide (CTAB) under basic conditions. These composites consisted of Ce-doped mesoporous silica particles (about 500 nm) with highly ordered 2D hexagonal (p6mm) and 3D bicontinuous cubic (Ia3d) structures and irregular ceria-rich silica–ceria particles. Wide angle XRD, diffuse reflectance UV-vis, and XPS analyses showed that 10–24% of cerium was at the Ce3+ oxidation level and the remaining predominant fraction of Ce was at the Ce4+ oxidation level. The cerium loading was varied in these composite materials up to 43 wt% (∼3.1 mmol g−1). The specific surface areas of the mesoporous silica/ceria–silica composite samples obtained on the basis of nitrogen adsorption isotherms were higher than 350 m2 g−1 and their pore widths were between 3.3 and 3.5 nm. The mesoporous silica/ceria–silica samples were reduced at 850 °C under flowing H2 in a N2 environment. The crystal structure of the reduced samples changed to a hexagonally structured phase with the oxidation state of Ce3+, while the ordered mesostructure of silica was preserved.