Cerium Mixed Oxides Research Articles

Cerium Coatings on Pristine and Nanostructured Ti and Ti6Al4V Surfaces: Bioactivity, Resistance in Simulated Inflammatory Conditions, and Antibacterial Performance.

Despite the significant contribution of titanium and its alloys for hard tissue regenerative medicine, some major issues remain to be solved. Implants' long-term stability is threatened by poor osseointegration. Moreover, bacterial adhesion and excessive inflammatory response are also to be considered in the design of a device intended to be integrated into the human body. Here, a cerium mixed oxide (CeOx) coating was realized on pristine and nanotubular-structured Ti and Ti6Al4V surfaces using a simple layer-by-layer drop-casting technique. Bioactivity, resistance in simulated inflammatory conditions, and bactericidal capacity were evaluated as a function of morphological surface characteristics combined with the cerium quantity deposited. The results obtained suggest that the presence of CeOx on the surfaces with nanotubes enhanced osseointegration, while on the non-nanostructured surfaces, this coating improved resistance under oxidative stress and provided excellent antibacterial properties.

Controlled fabrication of nickel and cerium mixed nano-oxides supported on carbon nanotubes for glucose monitoring

Carbon nanomaterials-loaded mixed metal oxides are the promising candidates to increase the electrochemical efficacy for glucose monitoring. In this paper, we developed a new hybrid material based on multi-walled carbon nanotubes-supported nickel and cerium mixed oxide nanocomposite (NiCeOx/MWCNTs) through one pot hydrogen co-reduction strategy for non-enzymatic electrochemical glucose sensing. The microscopic and spectroscopic features of as-prepared samples were thorougly characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Further, cyclic voltammetry (CV) and chronoamperometry (CA) methods were applied to investigate the electrochemical efficacy of designed electrode towards glucose sensing. The results revealed that, the synergetic effect of nickel and cerium mixed oxides as well as brilliant conductivity of MWCNTs collectively enhanced the electrocatalytic activity of the designed materials for glucose oxidation. Therefore, the fabricated NiCeOx/MWCNTs-based sensor retains the excellent electrochemical efficacy towards glucose sensing as compared to their counterparts including wider linear range (0.007∼0.466 mM and 0.466∼3.44 mM), lower limit of detection (1.8 μM, S/N = 3), satisfactory sensitivities (271.53 and 429.95 μA mM−1 cm−2) as well as good reproducibility, high stability and selectivity. More specifically, the designed NiCeOx/MWCNTs-based sensor offered brilliant real time applicability to precisely monitor glucose level in diluted human serum samples. This study provided an appealing strategy for the development of simple, efficient and cost-effective non-enzymatic electrochemical glucose sensing platform.

The low temperature reducibility of Ce4+ ions in Ce0.7Yb0.2Pd0.1O2-δ: in situ XANES study

Cerium mixed oxides are interesting materials for the oxygen storage capacity due to the Ce ability to valence state changes and oxygen vacancy formation. The mixed-valence state Ce4+/Ce3+ in Ce0.7Yb0.2Pd0.1O2-δ has been studied by in situ Ce L3 X-ray Absorption Near Edge Structure (XANES) spectroscopy during the reduction from room temperature to a 500 °C. The cerium ions start to reduce in the mixed oxide lattice at a temperature of 70 °C. 13% of Ce3+ has been detected in the studied sample during the reduction at a temperature of 70 °C. 26% of Ce4+ were reduced to Ce3+ at a temperature of 200 °C. No other changes were found in the Ce valence state up to the temperature of 500 °C. The most interesting result is that the reduction of Ce4+ to Ce3+ starts clearly before the reduction of the noble metal. The redox activity temperature range of Ce in mixed oxides is significantly lower than reported by other authors.The total density of states (DOS) of Ce0.7Yb0.2Pd0.1O2-δ is very similar to that of Ce0.875Pd0.125O2. The theoretical calculations using the Density Functional Theory method supported the experimental Ce L3 XANES spectra. It was shown that the presence of Yb and Pd ions could enhance the formation of oxygen vacancies in cerium mixed oxides.

Probing structural evolution in thorium–cerium mixed oxides thermally annealed in oxidizing and reducing conditions

ThO2 is a promising matrix either for incineration or direct disposal of plutonium and (Th, Pu)O2 is a potential advanced fuel. In this view, a ThO2–CeO2 mixed oxide system has been investigated under oxidizing as well as reducing conditions wherein CeO2 has been employed as a non-radioactive surrogate for PuO2. Selected compositions in Th1−xCexO2 (0 ≤ x ≤ 0.5) series were prepared by gelcombustion synthesis and thoroughly characterized by XRD and Raman spectroscopy. Both the studies confirm the formation of a fluorite-type (F-type) solid solution throughout the series after calcination of gelcombusted powders at 873 K in air. The F-type phase is retained even on annealing these solid solutions at an elevated temperature 1773 K in air. Lattice parameter of the F-type phase decreases as a function of ceria content in accordance with the Vegard’s law. On the contrary, the position of the F2g Raman band in these solid solutions exhibits non-ideal behavior. Annealing of calcined samples at 1873 K in a reducing atmosphere (Ar−8% H2) yields a single phase of F-type structure at x ≤ 0.2, while a biphasic phase field at x ≥ 0.3. Characteristic Raman vibration bands have been utilized to identify the presence of possible defects (due to Ce4+/Ce3+ substitution in ThO2) that are otherwise difficult to detect by the XRD studies. Detailed structure and defect analysis in ThO2–CeO2 mixed oxides will not only give valuable insight to the fuel designer but also bring out fundamental chemical aspects of such mixed oxides.

Synthesis, Characterization and Sorptive Removal of Heavy metals on Nano-Structured Agglomerates of Iron (III)-Cerium (IV) Bimetal Mixed Oxide (NICMO): Search For An Efficient, Low Cost Decontamination Technique

Nano particles usually exhibit remarkable physical properties, rapid chemical reactivity, and high sorption capacity for inorganic compounds. Studies of the fate and transport of nano particles were largely concerned with their properties and behavioral change over time, whether they would interact with toxic contaminants after being released into the environment. Keeping in line with the above facts, here, we aim to develop an efficient material by eco-friendly green synthetic route that was further characterized to be crystalline ranging in nano-dimension for filtering heavy metals containing groundwater. The average particle size was found to be approximately 3.56 nm calculated from the Gaussian fit of the distinct peaks and then computing its modeled data into Scherrer’s equation. The thermal stability of iron(III)-cerium(IV) mixed oxide nanoparticle agglomerates (NICMO) was well established from the consistent particle size at different temperature and also, from differential thermal. The bimetal mixed oxide contained agglomerated crystalline nano-particles of dimension 10-20 nm held together by crystal packing forces and, its corresponding empirical composition FeCe1.1O7.6. Appearance of weak band at 534 cm-1 in the FTIR spectrum of NICMO is presumed for the presence of hetero- metal bonding via oxygen linkage (i.e, Fe-O-Ce). Scanning electron microscopic (SEM) image of NICMO established the agglomerated surface morphology with irregular shape that was unevenly dispersed over a base matrix of oxide surface almost covering up its porous nature. Decreasing sharpness of inflexion points of NICMO in BET isotherm indicates porosity arising out of channels of the template framework but surely with non uniformity in pore size distribution.The positive change in entropy (△S°) values of both Pb(II) and Cd(II) species with NICMO in the systems investigated conclude that the reactions were entropy driven, occurring with increase of randomness at solid-liquid interface owing to the release of water molecules when hydrated Pb(II) and Cd(II) species binds on to the solid surface

Mesoporous titania–ceria mixed oxide (MTCMO): a highly efficient and reusable heterogeneous nanocatalyst for one-pot synthesis of β-phosphonomalonates via a cascade Knoevenagel–phospha-Michael addition reaction

Mesoporous titania–ceria mixed oxide (MTCMO) was synthesised in a sol–gel method using cerium chloride and titanium isopropoxide (TTIP) as CeO2 as well as TiO2 precursors and sodium dodecyl sulphate (SDS) as a structure-directing agent and its application was evaluated in the synthesis of aromatic β-phosphonomalonate derivatives via cascade Knoevenagel–phospha-Michael addition reaction. The catalyst characterised by various techniques like FT-IR spectroscopy, XRD, SEM, EDS, TEM and N2 adsorption-desorption. Partial substitution of Ti4+ cations with Ce4+ improved the BET surface area because TiO2 crystallites were suppressed to be grown. Furthermore, as a consequence of charge imbalance in the obtained Ti-O-Ce solid solution, some oxygen vacancies have generated that act as Lewis base sites while cations (Ti and Ce) around the oxygen vacancies act as Lewis acid sites. Reusability up to eight consecutive runs without significant decrease in reactivity, Mild reaction conditions, environmentally benign and compatibility with various functional groups are some of the advantages of this work.

New doubly doped cerium oxide Ce1-x-yYbyPdxO2-δ: The effect of ytterbium doping on stabilization of reduced palladium species on doped ceria oxide

Abstract The doubly and mono doped nanocrystalline mixed oxides Ce1-x-yYbyPdxO2-δ (y up to 0.4, x up to 0.2) were synthesized with the reversed microemulsion method. The morphology, microstructure and composition of the samples were investigated by TEM, EDS, XRD, XAFS, and DFT calculations of XANES spectra. The main aim of the study was the determination of the influence of an additional ytterbium content on structural and electronic properties of the Pd-doped ceria mixed oxide, i.e., the comparative discussion of the results obtained for Ce1-xPdxO2-δ and Ce1-x-yYbyPdxO2-δ. All samples were homogeneous fluorite-type nanocrystallites with very small size (3–5 nm). Reducibility studies revealed strong hydrogen consumption in these systems at low temperatures without any changes of their structure. The XANES and EXAFS spectra for Ce1-x-yYbyPdxO2-δ indicate a partial reduction of palladium at 200 °C and almost complete (90%) at 500 °C in hydrogen. The presence of ytterbium in Ce1-x-yYbyPdxO2-δ prevents the formation of metallic particles in reducing atmosphere (up to 500 °C) and strongly inhibits crystal growth of the mixed oxide.

Manganese-cerium mixed oxides supported on rice husk based activated carbon with high sulfur tolerance for low-temperature selective catalytic reduction of nitrogen oxides with ammonia.

A rice husk-derived activated carbon supported manganese–cerium mixed oxide catalyst (Mn–Ce/RAC) was prepared by an impregnation method and tested for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR). 5 wt% Mn–Ce/RAC catalyst showed the highest activity, yielding nearly 100% NOx conversion and N2 selectivity at 240 °C at a space velocity of 30 000 h−1. Compared with commercial activated carbon supported manganese–cerium mixed oxide catalyst (Mn–Ce/SAC), a higher SCR performance with good SO2 tolerance could be observed in the tested temperature range over the Mn–Ce/RAC catalyst. The characterization results revealed that the Mn–Ce/RAC catalyst had a higher Mn4+/Mn3+ ratio, amount of chemisorbed oxygen and more Brønsted acid sites than the Mn–Ce/SAC catalyst. The XRD analysis indicated that Mn–Ce oxides were highly dispersed on the RAC support. These properties of Mn–Ce/RAC assisted the SCR reaction. Moreover, in situ DRIFTS results demonstrated that sulfate species formation on Mn–Ce/RAC was much less in the presence of SO2 than that of Mn–Ce/SAC, which might be ascribed to the reduced alkalinity of the catalyst by the presence of SiO2 in RAC.

Differential interplay between Ce and U on local structures of U1-xCexO2 solid solutions probed by X-ray absorption spectroscopy

Uranium–cerium mixed oxides U1-xCexO2 (x = 0.05, 0.20, 0.35, 0.50, 0.65, 0.80) were synthesized by co-precipitation method. The U1-xCexO2 samples were confirmed to be solid solutions with lattice parameters following Vegard's law by using X-ray diffraction technique combined with X-ray absorption spectroscopy. The effects of cerium content on the local structures of U and Ce in the U1-xCexO2 solid solutions were further studied by extended X-ray absorption fine structure (EXAFS) at the U L3 edge and Ce K edge, respectively. Significantly, the local disorder degree around U and Ce in the U1-xCexO2 were found to be not equivalent. There is differential interplay between U and Ce on the local structures of the U1-xCexO2. The order degree in the local structure of U increases with the content of cerium when the Ce content is kept about 35% or more. In contrast, the disorder degree in the local structure of Ce increases with U content once uranium is added into CeO2.

Thermodynamic functions of thorium–cerium mixed oxides

Thorium–cerium mixed oxides (Th1−xCex)O2 (x = 0.25, 0.5, 0.75) were prepared by the citrate gel combustion technique. X-ray diffraction investigations of these samples revealed the formation of single-phase (fluorite) solid solutions. Heat capacity and enthalpy increments of these samples were measured by using a differential scanning calorimeter and a drop calorimeter (MHTC 96) in the temperature range 298–800 K and 523–1723 K, respectively. The values of heat capacity in the temperature range 523–1800 K were computed from the enthalpy increment data. With the help of these data, analytical expression for the heat capacity of (Th1−xCex)O2 (x = 0.25, 0.5, 0.75) as well as entropy and Gibb’s energy functions were obtained. The heat capacity values at 298 K pertaining to (Th1−xCex)O2 (x = 0.25, 0.5, 0.75) were found to be 64.92, 64.80, and 64.27 J K−1 mol−1, respectively. The thermodynamic functions are being reported for the first time.

X-ray photoelectron spectroscopy study of the reduction and oxidation of uranium and cerium single oxide compared to (U-Ce) mixed oxide films

Thin films of uranium cerium mixed oxides UxCe1−xO2±y have been prepared by DC sputtering and characterized by X-ray photoelectron spectroscopy (XPS). Reduction and oxidation properties were analysed by exposing the films to atomic hydrogen and to atomic oxygen, respectively. Possible interaction between uranium and cerium were investigated by comparing the compounds to the single oxides of cerium and uranium. Uranium seems to promote the reduction of cerium. Conversely cerium promotes oxidation of uranium. Under our deposition conditions, it was not possible to produce pure U(IV) together with pure Ce(IV). The synthesis of U2O5 with U(V) cannot be obtained directly by DC sputtering, whereas with addition of cerium, U(V) seems to be stabilized and obtained more easily. This can be related to a charge transfer between Ce(IV) and U(IV).

Insights into Mechanism of Catalytic Ozonation over Practicable Mesoporous Mn-CeOx/γ-Al2O3 Catalysts

The practicable mesoporous γ-Al2O3-supported manganese–cerium mixed oxides (Mn-CeOx/γ-Al2O3) catalysts were prepared in large quantities by a facile impregnation–calcination method. Characterization results demonstrated that the Mn-CeOx/γ-Al2O3 catalyst retained the mesoporous structure of γ-Al2O3 and existed in multivalence redox couples of Mn4+/3+ and Ce4+/3+. The surface property, catalytic performance, reaction kinetics, and mechanism of γ-Al2O3 and Mn-CeOx/γ-Al2O3 in catalytic ozonation of bromaminic acid (BAA) were investigated in-detail. The protonated surface hydroxyl groups S–OH2+ on Mn-CeOx/γ-Al2O3 were the active sites for ozone decomposition, and HO• and O2•– were main reactive oxygen species. The multivalence redox couples of Mn3+/4+ and Ce3+/4+, along with electron transfer between these redox couples and lattice oxygen, resulted in the synergistically catalytic effect between Mn and Ce in Mn-CeOx. A catalytic ozonation mechanism over Mn-CeOx/γ-Al2O3 was tentatively proposed. The pilot-scale...

Preparation of thin bilayer coatings based on lanthanum, nickel, and cerium mixed oxides by electrophoretic deposition

This paper examines the feasibility of using electrophoretic deposition for producing thin films of cathode materials based on lanthanum nickel oxides (with the lanthanum nickelate La2NiO4 + δ (LNO) as the predominant phase). We have determined the particle size and zeta potential of nonaqueous suspensions of LNO micro- and nanopowders prepared by solid-state reactions, pyrolysis of liquid precursors, and laser evaporation of a target. Using ultrasonic processing, we have obtained stable LNO nanopowder suspensions in acetylacetone and an isopropanol + acetylacetone mixture, which have zeta potentials of +25 and + 38 mV, respectively. Electrophoretic deposition on a dense model cathode has produced thin bilayer coatings from electrode and electrolyte materials (LNO and Се0.8(Sm0.75Sr0.2Ba0.05)0.2O2–δ), which are of interest for solid oxide fuel cell technology.

Effect of calcination temperature on the structure and catalytic performance of copper–ceria mixed oxide catalysts in phenol hydroxylation

We report on highly active CuO@CeO2 catalysts prepared by the surfactant-template method and calcined at different temperatures.

Influence of Fabrication Temperature and Time on Light Olefin Selectivity of Iron–Cobalt–Cerium Mixed Oxide Nanocatalyst for CO Hydrogenation

The Fischer–Tropsch synthesis process is a polymerization reaction in which various chain lengths of product can be produced from a mixture of CO and H2 (synthesis gas). A solvothermal technique was used to synthesize magnetic iron–cobalt–cerium mixed oxide nanoparticles. Process variables such as reaction temperature and time can play an important role in a chemical process. The results showed that the optimal preparation time and temperature in order to enhance light olefin (C2–C4) selectivity is 18 h and 120 °C. The effects of experimental variables including temperature (120, 150, 180 °C) and reaction time (10, 14, 18 h) were investigated. The nanoparticles were characterized by X-ray diffraction (XRD), vibrating sample magnetometry (VSM), temperature programed-reduction (TPR), Fourier infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDS), and X-ray photoelectron spectroscopy (XPS). Average crystalline size determined from XRD patterns ranged over 4.5–8.3 nm. ...

O2-assisted Water Gas Shift reaction over structured Au and Pt catalysts

Platinum and gold structured catalysts were compared as active phases in classical and O2-assisted Water Gas Shift (WGS) reaction. Both metals were supported on iron-doped ceria mixed oxide and then, structured on metallic micromonolithic devices. As expected the WGS activity of both micromonoliths is conditioned by the nature of the noble metals being Pt the most active metal in traditional conditions. However, the addition of oxygen to the classical water gas feed turns the balance in favor of the gold based catalysts, being the presence of gold responsible for an excessive improvement of the catalytic activity.

Influence of partial substitution of iron oxide by titanium oxide on the structure and activity of iron–cerium mixed oxide catalyst for selective catalytic reduction of NOx with NH3

The influence of partial substitution of iron oxide by titanium oxide on the catalytic activity of iron–cerium mixed oxide catalyst for the selective catalytic reduction (SCR) of NOx with NH3 has been investigated in this paper. The methods of X-ray diffraction (XRD) spectroscopy, N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (NH3/NO-TPD) were used to reveal the effects of titanium substitution on the structure of iron–cerium mixed oxide catalyst. The NH3-SCR activity of Fe0.95Ce0.05Oz is enhanced by partial substitution of iron oxide by titanium oxide, especially under low-temperature condition. This is primarily due to the increase of surface area, pore volume, adsorbed oxygen concentration and reactant adsorption capability. Among a series of Fe0.95−xCe0.05TixOz(x=0, 0.1, 0.15, 0.2, 0.3 and 0.4) catalysts, Fe0.80Ce0.05Ti0.15Oz(Ti/(Fe+Ce+Ti)=0.15) shows the highest NH3-SCR activity. On the other hand, thermal-stability of iron–cerium mixed oxide catalyst is also enhanced by titanium oxide substitution. At higher annealing temperature, the crystal content of Fe2O3 in Fe0.95Ce0.05Oz catalyst is depressed by the introduction of titanium oxide. Large surface area and pore volume can be achieved by Fe0.80Ce0.05Ti0.15Oz even calcined at 500°C for 5h. This catalyst shows the best NOx conversion in the low-temperature range of 100–300°C.

Electrochemical Impedance Study of Ag/Cu-Ca0.2Ce0.8O2+δ Anode for SOFCs Operating with Simulated Biogas

In recent years, researches on SOFC technology have been focused on lowering the operating temperature, primarily driven by the cost and durability of components. Unfortunately operation at lower temperature creates problems associated with the increase in the electrolyte resistance and the electrode polarisation as well as decrease in the rate of electrocatalytic reactions. Furthermore, the direct use of alternative fuels to hydrogen, such as natural gas or biogas, are still limited due to the catalyst deactivation by coking or fuel impurity poisoning. Therefore, it is necessary to continuously search for novel anode materials having superior electrocatalytic activity in the intermediate temperature range and less-prone to deactivation. Biogas is mainly constituted by CH4 and CO2 while containing a few percent of H2, N2 and traces of NH3, H2S, halides and siloxanes. This composition fluctuates significantly during biogas production and it is highly dependent on the initial substrate used [1]. In previous works we have demonstrated the ability of nanocrystalline Cu-ceria based anodes to operate with CH4 and H2S-containing hydrogen [2-5]. The incorporation of a transition metal, such as silver, in an optimised anode formulation has improved its electrocatalytic properties for the complete CH4 oxidation, whereas it shows excellent thermal and chemical compatibility with the common electrolyte materials [6]. Thus, this new material can be considered a promising anode for SOFC directly fuelled with biogas at intermediate temperature. The composition of this anode material was Cu-Ag combined with Ca0.2Ce0.8O2+δ (hereafter named AgCu-CaCe), metal load= 40 at. % (Cu/Ag 3:1). Under reducing atmosphere, it is mainly constitutes by a fluorite phase of the cerium mixed oxide and Cu0 and Ag0metal phases, as could be checked by X-ray diffraction. In this work, electrochemical impedance spectroscopy (EIS), in symmetric cell configuration with LSGM-electrolyte, has been employed to measure the interface resistance of the deposited anode AgCu-CaCe in comparison with analogous Cu-doped ceria material (Cu-CaCe), at various temperatures (550-750 ºC) and different fuels (H2 and CH4) and three simulated biogas mixtures at 750 ºC, to quantitatively deduce the role of electrode microstructure on electrochemical activity. The method for preparing the symmetric cell was as follow. A porous lanthanum strontium gallate magnesite (LSGM) layer was deposited onto an LSGM dense electrolyte by tape-casting method, using polymethyl methacrylate (PMMA) as pore former. The electrode materials were applied onto the LSGM wafers by screen-printing and after calcined at 750 ºC. Gold was used as current collector. The active area was 0.3 cm2. Hydrogen, methane and simulated biogas mixtures were used as fuels and were supply to the anode at a flow rate of 50 ml/min, after passing through a saturator to control the gas humidity. Impedance data were fitted to equivalent circuits using Z-View software. Fig. 1 shows the impedance spectra obtained at 750 ºC on hydrogen, methane and three simulated biogas mixtures (CH4/CO2/H2; 50:45:5, 60:35:5 and 70:25:5 for 50bio, 60bio and 70bio, respectively). The generic form of the impedance response was composed of two partially resolved arcs under different fuels. The area specific resistance (ASR), cell resistance normalised by the cell area, is markedly lower in H2 than in CH4 or simulated biogas due to the lower pO2 and other factors. When hydrocarbon fuels were used the low frequency arc increased significantly probably caused for the carbon deposition on catalytic active centres. Measurements on simulated biogas revealed that lower ASR values were obtained with higher CH4content in the mixture (70bio). Note that a clearly reduction in ASR was observed with the incorporation of silver to the Cu-CaCe composition. The electrochemical impedance responses were fitted to an equivalent circuit composed of a resistor in series with two (or three) parallel constant phase element (CPE)/resistor combinations. The analysis of these equivalent circuits revealed a strong dependence of the kinetics and mechanism involved in the electro-oxidation of the different fuels with the final anode formulation. Acknowledgements Authors thank the Ministerio de Educación y Ciencia (project MAT2005-02933 and MAT2013-45043-P) for financial support.

Surface and redox properties of cobalt–ceria binary oxides: On the effect of Co content and pretreatment conditions

Ceria-based transition metal catalysts have recently received considerable attention both in heterogeneous catalysis and electro-catalysis fields, due to their unique physicochemical characteristics. Their catalytic performance is greatly affected by the surface local chemistry and oxygen vacancies. The present study aims at investigating the impact of Co/Ce ratio and pretreatment conditions on the surface and redox properties of cobalt–ceria binary oxides. Co–ceria mixed oxides with different Co content (0, 20, 30, 60, 100wt.%) were prepared by impregnation method and characterized by means of N2 adsorption at −196°C, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The results shown the improved reducibility of Co/CeO2 mixed oxides compared to single oxides, due to a synergistic interaction between cobalt and cerium. Oxidation pretreatment results in a preferential localization of cerium species on the outer surface. In contrast, a uniform distribution of cobalt and cerium species over the entire catalyst surface is obtained by the reduction process, which facilitates the formation of oxygen vacancies though Co3+/Co2+ and Ce3+/Ce4+ redox cycles. Fundamental insights toward tuning the surface chemistry of cobalt–ceria binary oxides are provided, paving the way for real-life industrial applications.

Altering properties of cerium oxide thin films by Rh doping

Ceria containing highly dispersed ions of rhodium is a promising material for catalytic applications. The Rh–CeOx thin films with different concentrations of rhodium were deposited by RF magnetron sputtering and were studied by soft and hard X-ray photoelectron spectroscopies, Temperature programmed reaction and X-ray powder diffraction techniques. The sputtered films consist of rhodium–cerium mixed oxide where cerium exhibits a mixed valency of Ce4+ and Ce3+ and rhodium occurs in two oxidation states, Rh3+ and Rhn+. We show that the concentration of rhodium has a great influence on the chemical composition, structure and reducibility of the Rh–CeOx thin films. The films with low concentrations of rhodium are polycrystalline, while the films with higher amount of Rh dopants are amorphous. The morphology of the films strongly influences the mobility of oxygen in the material. Therefore, varying the concentration of rhodium in Rh–CeOx thin films leads to preparing materials with different properties.