Abstract: A CuO–CeO2–TiO2 catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures was prepared by a sol–gel method and characterized by X-ray diffraction, Brunner–Emmett–Teller surface area, ultraviolet–visible spectroscopy, H2 temperature-programmed reduction, scanning electron microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The CuO–CeO2–TiO2 ternary oxide catalyst shows excellent NH3-SCR activity in a low-temperature range of 150–250 °C. Lewis acid sites generated from Cu2+ are the main active sites for ammonia activation at low temperature, which is crucial for low temperature NH3-SCR activity. The introduction of ceria results in increased reducibility of CuO species and strong interactions between CuO particles with the matrix. The interactions between copper, cerium and titanium oxides lead to high dispersion of metal oxides with increased active oxygen and enhanced catalyst acidity. Homogeneously mixed metal oxides facilita...

Abstract: Mg-codoped Lu3Al5O12:Ce single crystal scintillators were prepared by a micropulling down method in a wide concentration range from 0 to 3000 ppm of Mg codopant. Their structure and chemical composition were checked by X-ray diffraction and electron probe microanalysis techniques. Absorption and luminescence spectra, photoluminescence decays, and thermoluminescence glow curves were measured together with several other scintillation characteristics, namely, the scintillation decay, light yield, afterglow, and radiation damage to reveal the effect of Mg codoping. Several material characteristics manifest a beneficial effect of Mg codopant. We propose a model explaining the mechanism of material improvement which is based on the stabilization of a part of the cerium dopant in the tetravalent charge state. The stable Ce4+ center provides an additional fast radiative recombination pathway in the scintillation mechanism and efficiently competes with electron traps in garnet scintillators.

Abstract: We report a new Ce-rich family of active oxygen evolution reaction (OER) catalysts composed of earth abundant elements, discovered using high-throughput methods. High resolution inkjet printing was used to produce 5456 discrete oxide compositions containing the elements nickel, iron, cobalt and cerium. The catalytic performance of each of these compositions was measured under conditions applicable to distributed solar fuels generation using a three-electrode scanning drop electrochemical cell. The catalytic activity and stability of representative compositions (Ni0.5Fe0.3Co0.17Ce0.03Ox and Ni0.3Fe0.07Co0.2Ce0.43Ox) from 2 distinct regions were verified by resynthesizing these compositions on glassy carbon rods for electrochemical testing. The activity of the new Ce-rich catalysts was further verified using an unrelated synthetic method to electrodeposit a pseudo-ternary composition Ni0.2Co0.3Ce0.5Ox, which produced a catalyst with 10 mA cm−2 oxygen evolution current at 310 mV overpotential. The unique Tafel behavior of these Ce-rich catalysts affords the opportunity for further improvement.

Abstract: The parent TiO 2 and cerium doped TiO 2 photocatalysts with Ce loadings 0.28–10 mol.% were prepared by the sol-gel method controlled within reverse micelles of nonionic surfactant Triton X-114. Photocatalysts were comprehensively characterized using nitrogen physisorption, XRD, XPS, contact potential difference measurements, Raman spectroscopy, and DR UV–vis spectroscopy and their performance was explored in the CO 2 photocatalytic reduction for the first time. Concerning photocatalysts properties, it was revealed that the inhibiting effect of cerium on the TiO 2 crystallites growth occurred only up to 3 mol.% of Ce when the incorporation of Ce 4+ into the anatase lattice took place. This phenomenon was correlated with the expansion of anatase cell volume. At higher Ce loadings (≥5 mol.%) the anatase lattice was saturated and the formation/separation of amorphous ceria and/or ceria (∼1 nm) nucleation occurred, accompanied by the increase of TiO 2 anatase crystallite-size and the limitation of value of anatase cell volume. Further, it was found out that the mesoporosity of photocatalysts may be preferentially attributed to voids existing between the individual crystallites and thus can be influenced by changes in the crystallite size. The modification of TiO 2 with cerium affected also the spectral response of photocatalysts, shifting it to the visible light region. However, this property itself was not crucial in the CO 2 photocatalytic reduction. The key role in the CO 2 photocatalytic reduction played the energies of electrons and holes within the electronic structure of photocatalysts, which were markedly affected by the Ce atoms addition. For 0.28 mol.%Ce/TiO 2 , both electrons and holes have required potentials for the photocatalytic reduction of CO 2 , while for 3 mol.% and higher Ce loadings the energy of electrons was already below H + reduction potential and thus the photocatalytic performance of these catalysts was decreasing.

Abstract: Despite the outstanding scintillation performance characteristics of cerium tribromide (CeBr3) and cerium-activated lanthanum tribromide, their commercial availability and application are limited due to the difficulties of growing large, crack-free single crystals from these fragile materials. This investigation employed aliovalent doping to increase crystal strength while maintaining the optical properties of the crystal. One divalent dopant (Ca2+) was used as a dopant to strengthen CeBr3 without negatively impacting scintillation performance. Ingots containing nominal concentrations of 1.9% of the Ca2+ dopant were grown, i.e., 1.9% of the CeBr3 molecules were replaced by CaBr2 molecules, to match our target replacement of 1 out of 54 cerium atoms be replaced by a calcium atom. Precisely the mixture was composed of 2.26 g of CaBr2 added to 222.14 g of CeBr3. Preliminary scintillation measurements are presented for this aliovalently doped scintillator. Ca2+-doped CeBr3 exhibited little or no change in the peak fluorescence emission for 371 nm optical excitation for CeBr3. The structural, electronic, and optical properties of CeBr3 crystals were studied using the density functional theory within the generalized gradient approximation. Calculated lattice parameters are in agreement with the experimental data. The energy band structures and density of states were obtained. The optical properties of CeBr3, including the dielectric function, were calculated.

Abstract: From environmental modeling of engineered nanomaterial (ENM) release, it is clear that ENMs will enter soils, where they interact with soil compounds as well as plant roots. We analyzed three different size groups of cerium dioxide nanoparticles (CeO2-NPs) in respect to chemical changes in the most common plant growth medium, Hoagland solution. We created a simple environmental model using liquid dispersions of 9-, 23-, and 64-nm-uncoated CeO2-NPs. We found that CeO2-NPs release dissolved Ce when the pH of the medium is below 4.6 and in the presence of strong chelating agents even at pH of 8. In addition, we found that in reaction with Fe2+-ions, equimolar amounts of Ce were released from NPs. We could elucidate the involvement of the CeO2-NPs surface redox cycle between Ce3+ and Ce4+ to explain particle transformation. The chemical transformation of CeO2-NPs was summarized in four probable reactions: dissolution, surface reduction, complexation, and precipitation on the NP surface. The results show that CeO2-NPs are clearly not insoluble as often stated but can release significant amounts of Ce depending on the composition of the surrounding medium.

Abstract: CeO2, Fe2O3 and a series of CeO2-modified Fe2O3 oxides with Ce/Fe molar ratios ranging from 5 : 95 to 50 : 50 were prepared by a co-precipitation method and thermally aged at different temperatures, which were compared with corresponding samples prepared by physically mixing CeO2 and Fe2O3. The structural/textural feature, reduction behavior, oxygen storage capacity (OSC), and redox performance of the prepared materials were investigated via XRD, Raman, TEM, BET surface area, XPS, H2-TPR and oxygen pulse techniques. It was found that CeO2 particles were very small (<10 nm) and highly dispersed on the surface of Fe2O3 rods even after calcination at 800 °C. The nano-size effects resulted in strong chemical interaction in the Fe2O3–CeO2 interfaces, which significantly improved Fe2O3 reducibility in the reducing atmosphere. Hematite-like solid solutions were also observed in the mixed oxides, but it only existed on the materials with relatively low CeO2 content (Ce/Fe < 20 : 80). The formation of hematite-like solid solution could improve the surface reduction of Fe2O3, while the deep reduction of Fe2O3 depended mainly on the crystal size of Fe2O3 particles. The size effect played a more important role than solid solution on the reduction behavior of CeO2-modified Fe2O3 oxides. In addition, the presence of CeO2 on Fe2O3 also strongly improved the oxygen storage capacity and redox stability of Fe2O3, which can be attributed to the chemical interaction between cerium and iron oxides, involving the formation of a complex oxide (CeFeO3) after the TPR/OSC redox testing. These data provide useful references to design novel OSC materials for chemical looping technologies.

Abstract: The dispersion of small amounts of Ce4+ ions in the bulk of ZrO2 leads to a photoactive material sensitive to visible light. This is shown by monitoring with EPR the formation and the reactivity of photogenerated (λ > 420 nm) charge carriers. The effect, as confirmed by DFT calculations, is due to the presence in the solid of empty 4f Ce states at the mid gap, which act as intermediate levels in a double excitation mechanism. This solid can be considered an example of a third-generation photoactive material.

Abstract: Environmental context This study investigates the toxicity of cerium oxide nanoparticles to earthworms, key organisms in soil ecosystems. Cerium oxide did not affect survival or reproduction of the earthworms but did exert histological changes. We conclude that current soil guidelines, based simply on metal toxicity, appear to adequately protect against cerium exposure risk, at least for earthworms. Abstract The toxicity of cerium oxide (CeO2) nanoparticles (NPs) in soils is largely unknown. This study aimed to investigate the toxicity of three different CeO2 NPs to the earthworm, Eisenia fetida, for effects on survival (at day 28) and reproduction (at day 56), as well as bioaccumulation and histopathological effects. Eisenia fetida were exposed in standard Lufa 2.2 soil to three CeO2 NPs of different size ranges (5–80nm), one larger particle (300nm) and a cerium salt (ammonium cerium nitrate) over an exposure range from 41–10000mgCekg–1. Survival and reproduction were not affected by the four CeO2 particles, even at the highest exposure concentration tested. Alternatively, 10000mgCekg–1 cerium salt affected survival and reproduction; Median lethal concentration (LC50) and effective concentration (EC50) values were 317.8 and 294.6mgCekg–1. Despite a lack of toxic effect from the different forms of CeO2 particles, there was a dose-dependent increase in cerium in the organisms at all exposure concentrations, and for all material types. Earthworms exposed to CeO2 particles had higher concentrations of total cerium compared to those exposed to ionic cerium, but without exhibiting the same toxic effect. Histological observations in earthworms exposed to the particulate forms of CeO2 did, however, show cuticle loss from the body wall and some loss of gut epithelium integrity. The data suggest that that CeO2 NPs do not affect survival or reproduction in E. fetida over the standard test period. However, there were histological changes that could indicate possible deleterious effects over longer-term exposures.

Abstract: Cadmium contamination is a critical constraint to plant production in agricultural soils in some regions. Cerium is one of the rare earth elements, it plays a positive role in plant growth with a appropriate content. The present study was conducted to examine the role of cerium nutrition in the amelioration of effects on cadmium toxicity in rice (Oryza sativa L.) seedlings by a hydroponic experiment. Measurements included growth condition, photosynthesis related parameters, chloroplast ultra-structure and antioxidant enzymes content. Our results showed that the growth of rice seedlings was markedly inhibited by cadmium (100 μM), and the inhibition was significantly alleviated by cerium (10 μM). Fresh weight, single seedling height and chlorophyll content of rice plants in cerium treated groups were increased by 24.4, 18.2 and 32.05 % compared to those of plants cultivated in only cadmium-present condition. Additionally, in cadmium treated plants, the addition of cerium significantly increased the value of the maximum quantum yield of primary photochemistry (F v /F m ), indicator of PSII ‘structure and functioning’ (SFI ABS ) and the performance index on absorption basis (PI ABS ), elevated the activity of whole chain electron transport activity, enhanced photophosphorylation and its coupling factor Ca2+-ATPase activities. The result showed that the chloroplasts and thylakoid membrane of the rice seedlings leaves grown in cerium treatment developed better than that in cerium-absent group under cadmium toxicity. Moreover, addition with 10 μM cerium mitigated cadmium stress by inducing leaf enzyme activities for antioxidation like superoxide dismutase, peroxidase and catalase, dramatically depressed superoxide (O 2 ·− ), hydrogen peroxide and malondialdehyde accumulation. Results indicated that alleviation of cadmium toxicity by cerium application is partly related to improved light-use-efficiency, increased antioxidant enzymes, decreased oxidative stress in rice seedlings.

Abstract: The long-range and short-range structure of nanocrystalline and microcrystalline acceptor-doped ceria is investigated by a combined approach using EXAFS, XANES, Raman, and XRD, and correlated with the oxide-ion conductivity in the bulk and in grain boundaries. Compared to Yb3+ and Er3+, the positive influence of Sm3+ is attributed to the ability to repel oxygen vacancies, and to keep a localized disorder around the dopant. The long-range structural analysis shows lattice contraction for Yb- and Er-doping and lattice expansion for Sm-doping. The short-range analysis around the dopants and cerium highlights that a more complex structural rearrangement has to be assumed to explain the complementary results of the different techniques. Nominally trivalent dopants are also shown to have an effect on the electronic structure of ceria, and the consequences on oxide-ion conductivity are highlighted.

Abstract: Lanthanides are often used as surrogates to study the properties of actinide compounds. Their behaviour is considered to be quite similar as they both possess f valence electrons and are close in size and chemical properties. This study examines the potential of using two lanthanides (neodymium and cerium) as surrogates for plutonium during the thermal decomposition of isomorphic oxalate compounds, in the trivalent oxidation state, into oxides. Thus, the thermal decomposition of neodymium, cerium and plutonium (III) oxalates are investigated by several coupled thermal analyses (TG-DTA/DSC-MS/FT-IR) and complementary characterisation techniques (XRD, UV-vis, FT-IR, SEM, carbon analyser) under both oxidizing and inert atmosphere. The thermal decomposition mechanisms determined in this study confirmed some previous results reported in the literature, among diverging propositions, while also elucidating some original mechanisms not previously considered. Calculated thermodynamic and kinetic parameters for the studied systems under both atmospheres are reported and compared with available literature data. Similarities and differences between the thermal behaviour of plutonium(III) and lanthanide(III) oxalates are outlined.

Abstract: Whereas terminal oxo complexes of transition and actinide elements are well documented, analogous lanthanide complexes have not been reported to date. Herein, we report the synthesis and structure of a cerium(IV) oxo complex, [CeO(LOEt)2(H2O)]⋅MeC(O)NH2 (1; LOEt−=[Co(η5-C5H5){P(O)(OEt)2}3]−), featuring a short CeO bond (1.857(3) A). DFT calculations indicate that the hydrogen bond to cocrystallized acetamide plays a key role in stabilizing the CeO moiety of 1 in the solid state. Complex 1 exhibits oxidizing and nucleophilic reactivity.

Abstract: Component durability of polymer-electrolyte membrane (PEM) fuel cells can be improved by adding cerium cations, which serve to scavenge harmful free radicals and selectively decompose hydrogen peroxide, which are formed during the oxidation reduction reaction (ORR). We have investigated the change in distribution of cerium cations in a hydrogen fuel cell as a function of operating time, considering both cerium containing membranes (commercial XL by DuPont) as well as fuel cells with CeO2 in the cathode catalyst layer. Our results show cerium cations are very mobile in Nafion, and migrate into both the anode and cathode catalyst