Stable Cerium Research Articles

A highly stable cerium–organic framework: an efficient catalyst for the cycloaddition of CO2 and aziridines under mild-pressure

A highly stable Ce-MOF can serve as efficient and recyclable catalyst for the conversion of CO2 with aziridines under mild pressure, which is a rare Ln-MOF-based catalyst for this reaction and exhibits excellent substrate universality.

Stable cerium isotopes as a tracer of oxidation reactions

Stable cerium isotopes as a tracer of oxidation reactions

Stable cerium isotope analysis of geological materials by MC-ICP-MS

We report stable cerium (Ce) isotopic compositions of terrestrial rocks and investigate Ce isotopic fractionation during column chemistry in this study. Cerium was separated from matrix elements by a single-stage extraction technique using Eichrom DGA resin. Ce isotope ratios were measured using a Thermo Scientific Neptune Plus MC-ICP-MS employing a sample–standard combined with a Sm-doping method. The data accuracy and precision of Ce isotope analyses were rigorously examined by two different laboratories. The δ142Ce values of mono-elemental Ce standards (JMC304 and CDUT-Ce) relative to NIST SRM 3110 solution were − 0.005 ± 0.042‰ (2SD, N = 9) and 0.118 ± 0.033‰ (2SD, N = 6), respectively. The δ142Ce of the manganese nodule (NOD-P-1) measured in two laboratories were 0.177 ± 0.035‰ (2SD, N = 7) and 0.172 ± 0.034‰ (2SD, N = 8), respectively; NOD-A-1 were 0.116 ± 0.028‰ (2SD, N = 8) and 0.104 ± 0.028‰ (2SD, N = 9), respectively. The offset between these two manganese nodules could be possibly related with their unique diagenetic environments. The δ142Ce of two USGS standards diabase W-2a was −0.036 ± 0.046‰ (2SD, N = 3), basalt BHVO-2 was −0.019 ± 0.036‰ (2SD, N = 4). Ce isotopic compositions of three Chinese reference standards granite gneiss GBW07121, diabase GBW07123, and stream sediment GBW07301a were 0.039 ± 0.033‰ (2SD, N = 5), 0.068 ± 0.027‰ (2SD, N = 5) and 0.046 ± 0.015‰ (2SD, N = 3), respectively. The reported data will be helpful for quality assurance and inter-laboratory comparison for high-precision Ce isotopic studies.Full recovery is important to achieve high precision and high accuracy data for metal isotopes. To understand Ce isotope behavior during column separation, an experiment with different Ce cuts was conducted. The δ142Ce of JMC304 and NIST SRM 3110 in five different Ce subcuts varied from 0.047 ± 0.020‰ (2SD, N = 3; 0–25% cut) to −0.029 ± 0.047‰ (2SD, N = 5; 45–100% cut), and 0.058 ± 0.047‰ (2SD, N = 4; 0–11% cut) to −0.022 ± 0.033‰ (2SD, N = 4; 32–100% cut), respectively. δ142Ce of these subcuts showed small ranges, but isotopic fractionation of Ce did occur during column chemistry and light isotopes are preferentially retained in the DGA resin.

Synthesis of Stable Cerium Oxide Nanoparticles Coated with Phosphonic Acid-Based Functional Polymers.

Functional polymers, such as poly(ethylene glycol) (PEG), terminated with a single phosphonic acid, hereafter PEGik-Ph are often applied to coat metal oxide surfaces during post-synthesis steps but are not sufficient to stabilize sub-10 nm particles in protein-rich biofluids. The instability is attributed to the weak binding affinity of post-grafted phosphonic acid groups, resulting in a gradual detachment of the polymers from the surface. Here, we assess these polymers as coating agents using an alternative route, namely, the one-step wet-chemical synthesis, where PEGik-Ph is introduced with cerium precursors during the synthesis. Characterization of the coated cerium oxide nanoparticles (CNPs) indicates a core-shell structure, where the cores are 3 nm cerium oxide and the shell consists of functionalized PEG polymers in a brush configuration. Results show that CNPs coated with PEG1k-Ph and PEG2k-Ph are of potential interest for applications as nanomedicines due to their high Ce(III) content and increased colloidal stability in cell culture media. We further demonstrate that the CNPs in the presence of hydrogen peroxide show an additional absorbance band in the UV-vis spectrum, which is attributed to Ce-O22- peroxo-complexes and could be used in the evaluation of their catalytic activity for scavenging reactive oxygen species.

Single step assemble of cerium oxide embellished on layered graphene oxide: An efficacious electrode for supercapacitors and hydrogen evolution reaction

Single step hydrothermally synthesized the stable cerium oxide (CeO2) nanorods decorated on layered surface of graphene oxide (GO) flakes. The crystal surface structure of novel CeO2/GO nanocomposites were analysed by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET). Electrochemical behavior of the CeO2, GO and nanocomposites were explored from cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements using as active materials of the electrode. CeO2/GO nanocomposites displays higher specific capacitance (Cs, 616 Fg−1) than those of individuals at low scan rate of 2 mVs−1 by CV studies. Nanocomposites has good stability by exhibiting 82 % of capacitive retention after 10 k cycles at 10 Ag−1. Symmetric device were fabricated using nanocomposite materials for both anode and cathode. The device produces a considerable Cs, specific energy (SE), specific power (SP) values such as 55.3 Fg-1, 23.1 Whkg−1 and 5088 Wkg−1 respectively. Using symmetric device, continued the cycle life studies at 10 Ag−1 for 5 k cycles, and exhibited a capacitance retention of 82 %. With a low overpotential of 112 mV, a small Tafel slope of 77.46 mV dec-1, and long-term stability, the composites showed better HER performance.

Exercise Celestial Skónis: Part 2 – Emerging technologies and State of Practice of nuclear forensic analyses demonstrated during the 6th collaborative materials exercise of the nuclear forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group conducted its sixth and largest Collaborative Materials Exercise, Celestial Skónis, in which laboratories from 20 countries (one virtual participant) and the European Commission, working with 15 law enforcement agencies, analyzed a set of samples containing special nuclear material as part of an elaborate mock nuclear forensics investigation. The nuclear materials used during the exercise included (1) depleted uranium and (2) stable cerium metal ingots contaminated on their surfaces with trace amounts of depleted uranium- and weapons grade plutonium-oxy-fluoride powders. This exercise also included traditional evidence (e.g., cut surfaces of pipes, toolmarks on plastic bags, and patent and latent fingerprints) comingled/contaminated with radioactivity. Participating laboratories processed traditional forensic evidence contaminated with radioactivity and analyzed nuclear materials in support of the mock investigation over a two-month period. These results were used to evaluate the “State of Practice” and identify promising “Emerging Technologies” in nuclear forensic science. This work is presented in two parts. Part 1 summarizes the history and purpose of these exercises, describes the design of the 6th and latest in this series, presents results of traditional forensic examinations on evidence contaminated with radioactivity, and summarizes the traditional and nuclear forensic evidence used to answer investigatory questions posed during the exercise. Part 2 summarizes results of nuclear forensic analyses that were conducted on the nuclear materials, giving special focus to the challenges of interpreting U and Pu isotopic results and the utility of those results for connecting people, places, things and events.

Exercise Celestial Skónis: Part 1 – History, purpose, design and results of traditional forensic examinations of the 6th Collaborative materials exercise of the nuclear forensics International Technical Working Group

The Nuclear Forensics International Technical Working Group conducted its sixth and largest Collaborative Materials Exercise, Celestial Skónis, in which laboratories from 20 countries (one virtual participant) and the European Commission, working with 15 law enforcement agencies, analyzed a set of samples containing special nuclear material as part of an elaborate mock nuclear forensics investigation. The nuclear materials used during the exercise included (1) depleted uranium and (2) stable cerium metal ingots contaminated on their surfaces with trace amounts of depleted uranium- and weapons grade plutonium-oxy-fluoride powders. This exercise also included traditional evidence (e.g., cut surfaces of pipes, toolmarks on plastic bags, and patent and latent fingerprints) comingled/contaminated with radioactivity. Participating laboratories processed traditional forensic evidence contaminated with radioactivity and analyzed nuclear materials in support of the mock investigation over a two-month period. These results were used to evaluate the “State of Practice” and identify promising “Emerging Technologies” in nuclear forensic science. This work is presented in two parts. Part 1 summarizes the history and purpose of these exercises, describes the design of the 6th and latest in this series, presents results of traditional forensic examinations on evidence contaminated with radioactivity, and summarizes the traditional and nuclear forensic evidence used to answer investigatory questions posed during the exercise. Part 2 summarizes results of nuclear forensic analyses that were conducted on the nuclear materials, giving special focus to the challenges of interpreting U and Pu isotopic results and the utility of those results for connecting people, places, things and events.

Highly efficient and selective heterogeneous catalytic reduction of 2-nitroaniline by cerium oxide nanocatalyst under microwave irradiation

ABSTRACT Efficient nanocatalyst with incredible performance is highly demanding in a heterogeneous catalysis system. Herein, we report the facile fabrication of uniform and highly stable Cerium Oxide nanoparticles (CeO2 NPs), through chemical precipitation method using sodium hydroxide as reducing agent. The synthesized material is characterized through highly sophisticated techniques including UV-Visible, FT-IR, SEM, AFM, XRD, and Zeta Sizer- Potential to check the particle formation, surface morphology, topography, crystalline nature, size, and surface potential. The heterogeneous catalytic performance of CeO2 NPs has been accomplished for the reduction of 2-nitroaniline from the aqueous media. The CeO2 nanocatalyst displayed excellent reusability, while the reduction in several repetitive catalytic cycles against 2-nitroaniline under optimized conditions. The CeO2 nanocatalyst shows 99.12% efficiency within 60s reaction time under a greener source of microwave radiation.

Manipulating metal oxidation state over ultrastable metal-organic frameworks for boosting photocatalysis

The development of efficient and stable photocatalysts in drastic conditions is highly desirable yet remains challenging. Herein, we report an exceptionally stable cerium metal-organic framework (MOF), Ce-TTCA, which can achieve photocatalytic hydrogen (H2) production in both pH = 2 and 12 aqueous solutions using Pt as a cocatalyst (Pt/Ce-TTCA), with H2 production rates of 60.3 and 348.8 μmol g−1 h−1, respectively. More impressively, partial oxidation of Ce3+ to Ce4+ in Ce-TTCA not only extends the light harvesting ability, but also promotes the effective charge separation, thus greatly improving photocatalytic H2 production activity. The Pt/Ce-TTCA-65 with the content of 65 % Ce4+ shows 6-fold improvement of photocatalytic activity than that of Pt/Ce-TTCA without Ce4+, well highlighting that the crucial role of metal oxidation state in photocatalysis. This work represents the first report on regulating MOF photocatalysis for hydrogen production by manipulating the metal oxidation state.

Effect of cerium on the initiation of pitting corrosion of 444-type heat-resistant ferritic stainless steel

AbstractThe 444-type heat-resistant ferritic stainless steel is widely utilized in automotive exhaust pipes and solid oxide fuel cells, due to its excellent properties at elevated temperature. To meet the demands of significantly harsh service environments, rare earths were added in 444-type ferritic stainless steel. For the purpose of evaluating the effect of rare earths on pitting corrosion initiation, the metastable pitting corrosion behavior in 444-type ferritic stainless steel was studied through potentiodynamic polarization and potentiostatic polarization tests. The results demonstrated that pitting corrosion was initiated at the inclusion/alloy interface. The cerium alloying in 444-type ferritic stainless steel decreased the amount of preferential dissolution sites. The beneficial effect of Ce on pitting corrosion resulted from the formation of stable cerium oxides, as well as from the reduction in the amount and size of inclusions in 444-type ferritic stainless steel. In addition, electrochemical impedance spectroscopy test results revealed that cerium alloying enhanced the polarization resistance of passive films through insignificant thickness alteration.

Thermodynamic properties of stable states cerium compounds in fused 3LiCl-2KCl eutectic

The interaction of oxygen and cerium-free ions in molten 3LiCl-2KCl eutectic in the temperature range of (723–823) K was studied by the method of potentiometric titration using YZME electrodes. Stable states of cerium compounds in the Ce–O system and the mechanism of interaction of Ce3+ with O2− ions have been established. The solubility constants of cerium oxychloride and oxide compounds at different temperatures were determined. Principal thermodynamic data of CeOCl and Ce2O3 were calculated. The Pourbaix (potential-pO2−) diagram was drawn and summarizes the properties of stable cerium species in the melt.

Synthesis and catalytic practicality of CeO2 nanoparticle: an excellent heterogenous candidate for 4-nitrophenol reduction

The present study is based on a synthesis of facile, cheaper, well homogenized and highly stable Cerium Oxide nanostructures via chemical precipitation method. The synthesized nanoceria was subjected under different characterization tools. The UV–visible and FTIR study profile initially confirm the formation and existing functionalities in nanoceria. The XRD, SEM techniques were exploited the crystalline and untwined combined form rhombohedron shaped CeO2 nanoparticles respectively. While zeta sizer measurements explained well arranged, mono-dispersity, size and charge over the surface of nanoceria, which was calculated to be 17 nm with a desirable charge of + 6.37 mV. Finally, the well-prepared nanoceria nanoparticles were successfully applied as effective heterogeneous catalyst for 4-nitrophenol reduction. Under optimized conditions the nanoceria exhibited enhanced activity for 99% reduction of 4-NP within 60 s reaction time under greener microwave irradiation.

MAINTAINING STABLE NANODISPERSED CERIUM OXIDE FOR HEAT TRANSFER PROCESSES

The introduction of heat carriers progressive types causes the productivity of heat exchange systems to increase. One of the challenges in thermal applied applications is the search for heat carriers that will provide revolutionary indicators of thermal conductivity and stability over time, thereby increasing the order of the heat transfer processes efficiency magnitude. The paper describes the creation of stable colloidal solutions using cerium oxide and organic stabilizers to provide better heat exchange performance compared to true solutions. Cerium oxide colloids were obtained by precipitation of the oxide from an aqueous solution of cerium nitrate with an aqueous ammonia solution in the presence of a polymer under vigorous stirring at room temperature. A number of cerium oxide nanosized dispersions, stabilized with polyvinylpyrrolidone, with a particle size of 1–10 nm were obtained. The content of CeO2 in the obtained dispersions was 1.72.10–3, 5.15.10–3, 8.6.10–3, 1.21.10–2, 1.72.10–2 % at a polymer content of 1.10–3 mol/l, the pH of the dispersions was 8–9. Electron microscopic images of the obtained nanodispersions showed a colloidal particles narrow distribution and cerium oxide nanoparticles in size. Colloidal particles are macromolecular tangles of polyvinylpyrrolidone with oxide nanoparticles strung in them. A volume of 20–50 nm organic matrix contains 10–40 particles of 1–10 nm cerium oxide. The particle size distributions of the dispersions established by the photon-correlation spectroscopy method have two areas of maxima for each sample. The first maximum for the dispersions of all investigated concentrations refers to particles with a diameter of 5–6 nm, which, in our opinion, are particles of cerium oxide, both in polymer beads and probably free from the stabilizer. Another maximum, depending on the sample, is observed at 30–70 nm or 100–300 nm, and relates to colloidal particles of PVP with cerium oxide encapsulated particles. The static stability of the cerium oxide obtained nanodispersions with polyvinylpyrolidone for two years under standard conditions is comparable to the true polymer solution. It is proposed by the method of UV spectroscopy to control the reproducibility of the obtaining materials technology. Tests of the thermal conductivity of the obtained 1.72.10–3 % stable cerium oxide nanodispersion were performed at 50 °C relative to distilled water with a thermal conductivity coefficient of 0.65 W/(m·deg). We found an increase in the coefficient for nanodispersions by 4–6 %, which is a significant value for dilute solutions. Ref. 15, Fig. 4 .

Stable cerium hydrides are steps in route to room-temperature superconductors

Investigating the Ce-H system at experimentally attainable pressures reveals stable structures with high superconductivity critical temperatures.

Effect of template post-annealing on Y(Dy)BaCuO nucleation on CeO2 buffered metallic tapes

Substrate engineering is very significant in the synthesis of the high-temperature superconductor (HTS) coated conductor. Here we design and synthesize several distinct and stable Cerium oxide (CeO2) surface reconstructions which are used to grow epitaxial films of the HTS YBa2Cu3O7-δ (YBCO). To identify the influence of annealing and post-annealing surroundings on the nature of nucleation centers, including Ar/5%H2, humid Ar/5%H2 and O2 in high temperature annealing process, we study the well-controlled structure, surface morphology, crystal constants and surface redox processes of the ceria buffers by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electronic microscopy (FE-SEM), respectively. The ceria film post-annealed under humid Ar/5%H2 gas shows the best buffer layer properties. Furthermore, the film absorbs more oxygen ions, which appears to contribute to oxygenation of superconductor film. The film is well-suited for ceria model studies as well as a perfect substitute for CeO2 bulk material.

Elucidating cerium + H2O reactivity through electronic structure: A combined PES and DFT study

The anion photoelectron (PE) spectra of CexOyHz− products formed in sequential reactions between cerium oxide and hydroxide reactions with water are presented and interpreted with supporting density functional theory calculations. The PE spectra of CexOyHz− (x=2, 3) complexes formed in the sequence of reactions initiated with CexOx−+H2O, exhibit a prominent photodetachment transition indicating that the highest occupied molecular orbital in these species can be described as combinations of Ce 6s atomic orbitals. The electrons in these diffuse orbitals reliably have low binding energies in the range of 0.6–1eV. The combination of poor orbital overlap and low binding energy is amenable to ionic CeOH bond formation in reactions with water, rather than CeO bond formation, which is observed in more reduced clusters that have occupied Ce 5d-based molecular orbitals. Spectral simulations based on computational results, which predict numerous close-lying spin states arising from the singly occupied 4f orbital on each Ce center, support specific structural assignments for the Ce2OyHz− cluster series. A range of Ce3OyHz− products also exhibit the characteristic Ce 6s-based MO photodetachment transition. Based on comparison with calculations that predict stable cerium hydride structures, we infer that the sequence of Ce3OyHz−+H2O reactions proceeds along a path of metastable structures.

Synthesis of stable cerium zirconium oxide nanoparticle – Diesel suspension and investigation of its effects on diesel properties and smoke

One of the main problems of diesel engines is the harmful smoke in exhaust and the use of fuel borne catalysts is a good option for controlling the same. Cerium zirconium mixed oxide (CexZr(1−x)O2) nanoparticle is an excellent fuel borne catalyst. Two main issues with the addition of cerium zirconium mixed oxide nanoparticles in diesel are the lack of stability of catalytic nanoparticle in diesel suspension and the influence of these nanoparticles on various properties of diesel. The present work focuses on the synthesis of stable suspension of cerium zirconium mixed oxide nanoparticles in diesel and also on the effect of these nanoparticles on fuel properties, diesel engine performance and exhaust smoke. Cerium zirconium mixed oxide nanoparticle was synthesized by co precipitation method and characterized using Transmission electron microscope and Dynamic light scattering techniques. Catalytic activity of mixed oxide nanoparticles was compared by means of Temperature programmed reduction technique. Nanofluid was prepared by two step method, employing an ultrasonic shaker and oleic acid was used as surfactant to improve the stability of nanoparticle in diesel. The concentration of surfactant was varied from 0.01 to 0.1% by volume and the optimum value was determined by means of UV spectrum absorbance study. The dosing level of nanoparticles in diesel was varied from 2.5 to 20ppm and the optimum concentration of catalytic nanoparticles for maximum stability was determined based on zeta potential measurement. Various properties of diesel and modified diesel were determined as per ASTM standards. Load tests were carried out on a single cylinder four stroke diesel engine to investigate the effect of catalytic nanoparticles on diesel engine performance and smoke. Performance studies shows 31% reduction in exhaust smoke and 3% enhancement in brake thermal efficiency of diesel engine for a nanoparticle concentration of 17.5ppm.

Effect of pressure on the valency of cerium in cerium monochalcogenides and cerium monopnictides

Application of pressure on a material changes its properties due to the modification of the electronic states of the constituent atoms. Various effects of pressure on the properties of solid material have been identified, and valency change of an element in a compound is one of the effects of pressure. This study was aimed at finding the valency change as a function of pressure of some compounds. The valency changes of cerium in cerium monochalcogenides CeX (X = O and S) and cerium monopnictides CeX (X = P and As) as functions of pressure have been calculated utilising the reported data. For calculating the valency change of Ce, the reported experimental pressure-volume relationships of CeO, CeS, CeP and CeAs have been reproduced using the Birch equation of state. The corresponding pressure-volume relationships of these compounds for stable trivalent cerium have also been calculated using the same Birch equation. The change in valency is calculated by a technique, which considers the difference between the calculated and experimental lattice parameters at each pressure value of the concerned compound. Clear effect of pressure on the cerium valency has been obtained for each compound from the present calculation. J.Natn.Sci.Foundation Sri Lanka 2015 43 (4): 313 - 317

Cerium(III/IV) Formamidinate Chemistry, and a Stable Cerium(IV) Diolate

Four new cerium(III) formamidinate complexes comprising [Ce(p-TolForm)3 ], [Ce(DFForm)3 (thf)2 ], [Ce(DFForm)3 ], and [Ce(EtForm)3 ] were synthesized by protonolysis reactions using [Ce{N(SiMe3 )2 }3 ] and formamidines of varying functionality, namely N,N'-bis(4-methylphenyl)formamidine (p-TolFormH), N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH), and the sterically more demanding N,N'-bis(2,6-diethylphenyl)formamidine (EtFormH). The bimetallic cerium lithium complex [LiCe(DFForm)4 ] was synthesized by treating a mixture of [Ce{N(SiHMe2 )2 }3 (thf)2 ] and [Li{N(SiHMe2 )2 }] with four equivalents of DFFormH in toluene. Oxidation of the trivalent cerium(III) formamidinate complexes by trityl chloride (Ph3 CCl) caused dramatic color changes, although the cerium(IV) species appeared transient and reformed cerium(III) complexes and N'-trityl-N,N'-diarylformamidines shortly after oxidation. The first structurally characterized homoleptic cerium(IV) formamidinate complex [Ce(p-TolForm)4 ] was obtained through a protonolysis reaction between [Ce{N(SiHMe2 )2 }4 ] and four equivalents of p-TolFormH. [Ce{N(SiHMe2 )2 }4 ] was also treated with DFFormH and EtFormH, but the resulting cerium(IV) complexes decomposed before isolation was possible. The new cerium(IV) silylamide complex [Ce{N(SiMe3 )2 }3 (bda)0.5 ]2 (bda=1,4-benzenediolato) was synthesized by treatment of [Ce{N(SiMe3 )2 }3 ] with half an equivalent of 1,4-benzoquinone, and showed remarkable resistance towards protonolysis or reduction.

Enhanced field emission from cerium hexaboride coated multiwalled carbon nanotube composite films: A potential material for next generation electron sources

Intensified field emission (FE) current from temporally stable cerium hexaboride (CeB6) coated carbon nanotubes (CNTs) on Si substrate is reported aiming to propose the new composite material as a potential candidate for future generation electron sources. The film was synthesized by a combination of chemical and physical deposition processes. A remarkable increase in maximum current density, field enhancement factor, and a reduction in turn-on field and threshold field with comparable temporal current stability are observed in CeB6-coated CNT film when compared to pristine CeB6 film. The elemental composition and surface morphology of the films, as examined by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray measurements, show decoration of CeB6 nanoparticles on top and walls of CNTs. Chemical functionalization of CNTs by the incorporation of CeB6 nanoparticles is evident by a remarkable increase in intensity of the 2D band in Raman spectrum of coated films as compared to pristine CeB6 films. The enhanced FE properties of the CeB6 coated CNT films are correlated to the microstructure of the films.