Metallic Ce Research Articles

Exploring the Mechanism of the Electrochemical Polymerization of CO2 over CeO2(110)

The reduction of CO2 is a promising route for the synthesis of renewable energy carriers and the removal of CO2 from the atmosphere to limit global warming. These negative emission technologies (NETs) require the conversion of carbon dioxide into a stable and easily storable form[1]. However, despite its potential, the development of suitable CO2 reduction catalysts is still in its infancy. Indeed state of the art catalysts suffer from high overpotentials, a low selectivity between possible products and a generally low yield of post CO products with two or more carbon atoms. Catalysts which even allow for the electrochemical polymerization of CO2 and thus, the direct formation of hard carbon were completely absent until the work of Esrafilzadeh et al.[2]. Using a liquid electrocatalyst consisting of Ga, In, Sn and Ce in a n,n-dimethylformamide (DMF) electrolyte they were able to polymerize CO2 electrochemically to a carbonaceous material. They hypothesized that the active catalyst consists of a cerium oxide which is reduced to metallic Ce in the process. However, no direct proof for this hypothesis was provided. Also a possible mechanism which could lead to the reported products is so far unknown.In this contribution we will explore the reaction mechanisms for the electrochemical polymerization of CO2 using density functional theory (DFT) modelling. In the initial step, the most likely active sites at Ce oxide are identified. This is then followed by a detailed analysis of the reaction route which is based on well known mechanisms in organic chemistry. We find that an oxygen defect rich CeO2(110) surface is most likely present under reaction conditions. [3] The reaction over this surface is initialized at oxygen defect sites. Chain propagation is then achieved through an electrochemical aldol condensation type mechanism (Figure 1). [3] References 1 J. Hilaire, J. C. Minx et al., Climatic Change, 2019, 157, 189.2 D. Esrafilzadeh, A. Zavabeti et al., Nature. Commun., 2019, 10, 865.3 F. Keller, J. Döhn, A. Groß, M. Busch, in preparation. Figure 1

Hybrid cathodes of fluoride-ion batteries with carbon nanotubes

Solid-state fluoride-ion galvanic cells (metallic Ce anode, La1-xBaxF3-x (x ≈ 0.05) electrolyte) with carbon components in the cathode material – carbon nanotubes and nanocomposites based on them – have been created and studied. The investigations were carried out by means of cyclic voltammetry, impedance spectroscopy and electron microscopy. Tin fluoride SnF2 was used as a basic cathode material. The basic cathode was modified with additives of carbon nanotubes, which channels were filled with SnF2, PbSnF4 and their eutectic composition. Introduction of these additives lead to the charge-discharge currents improvement. The maximum value of open-circuit voltage (OCV ∼ 1.9 V) is observed with adding into the cathode material the nanocomposite of carbon nanotubes filled with the eutectic composition. Carbon nanotubes filled with tin fluoride SnF2@SWCNT proved to be the best additive in the cathode material. The sample has the biggest current density compared with the other samples (∼1.3 A/m2 at 180 °C, which is ∼4 times higher than that when using the basic cathode). The OCV of the galvanic cell with SnF2@SWCNT additive in the cathode material is stable within the investigated temperature range from 25 to 180 °C. For other galvanic cells temperature dependencies of OCV are decreasing. Results of the direct and alternating current investigations of the solid electrolyte in Ce/electrolyte/Ce symmetric cell show good converging. Direct current internal resistance of the solid electrolyte is defined by grain boundaries resistance. The impedance of a galvanic cell is determined by the composition and structure of SnF2 cathode material as the component of the cell with the highest resistance.

Promotional Effects on the Catalytic Activity of Co-Fe Alloy Supported on Graphitic Carbon for CO2 Hydrogenation.

Starting from the reported activity of Co-Fe nanoparticles wrapped onto graphitic carbon (Co-Fe@C) as CO2 hydrogenation catalysts, the present article studies the influence of a series of metallic (Pd, Ce, Ca, Ca, and Ce) and non-metallic (S in various percentages and S and alkali metals) elements as Co-Fe@C promoters. Pd at 0.5 wt % somewhat enhances CO2 conversion and CH4 selectivity, probably due to H2 activation and spillover on Co-Fe. At similar concentrations, Ce does not influence CO2 conversion but does diminish CO selectivity. A 25 wt % Fe excess increases the Fe-Co particle size and has a detrimental effect due to this large particle size. The presence of 25 wt % of Ca increases the CO2 conversion and CH4 selectivity remarkably, the effect being attributable to the CO2 adsorption capacity and basicity of Ca. Sulfur at a concentration of 2.1% or higher acts as a strong poison, decreasing CO2 conversion and shifting selectivity to CO. The combination of S and alkali metals as promoters maintain the CO selectivity of S but notably increase the CO2 conversion. Overall, this study shows how promoters and poisons can alter the catalytic activity of Co/Fe@C catalysts, changing from CH4 to CO. It is expected that further modulation of the activity of Co/Fe@C catalysts can serve to drive the activity and selectivity of these materials to any CO2 hydrogenation products that are wanted.

Treatment of Phenol-Containing Coal Chemical Biochemical Tailwater by Catalytic Ozonation Using Mn-Ce/γ-Al2O3

In this study, a Mn-Ce/γ-Al2O3 catalyst with multiple active components was prepared through the doping–calcination method for advanced treatment of coal chemical biochemical treatment effluent and characterized by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, and BET analysis. In addition, preparation and catalytic ozonation conditions were optimized, and the mechanism of catalytic ozonation was discussed. The Mn-Ce/γ-Al2O3 catalyst significantly enhanced COD and total phenol removal in reaction with ozone. The characterization results suggested that the pore structure of the optimized Mn-Ce/γ-Al2O3 catalyst was significantly improved. After calcination, the metallic elements Mn and Ce existed in the form of the oxides MnO2 and CeO2. The best operating conditions in the study were as follows: (1) reaction time of 30 min, (2) initial pH of 9, (3) ozone dosage of 3.0 g/h, and (4) catalyst dosage of 30 g/L. The removal efficiency of COD and total phenol from coal chemical biochemical tail water was reduced with the addition of tert-butanol, which proves that hydroxyl radicals (•OH) played a leading role in the Mn-Ce/γ-Al2O3 catalytic ozonation treatment process of biochemical tailwater. Ultraviolet absorption spectroscopy analysis indicated that some conjugated structures and benzene ring structures of organics in coal chemical biochemical tail water were destroyed. This work proposes the utilization of the easily available Mn-Ce/γ-Al2O3 catalyst and exhibits application prospects for the advanced treatment of coal chemical biochemical tailwater.

In Situ XAFS, XRD, and DFT Characterization of the Sulfur Adsorption Sites on Cu and Ce Exchanged Y Zeolites

Adsorptive desulfurization with Cu and Ce ion-exchanged Y zeolite (CuCeY) has proven to be an effective method for the removal of sulfur compounds from hydrocarbon fuels. In this study, Cu and Ce exchanged Y materials including CuY, CeY, and CuCeY were prepared and examined to investigate the mechanism behind the superior sulfur adsorption and selectivity of CuCeY. In situ conditions were used to study the materials as prepared for optimal desulfurization. X-ray diffraction (XRD) confirmed the absence of large well-ordered crystalline phases from metallic or oxide Cu and Ce after the reduction of the samples. The oxidation states and local environments of Cu and Ce were determined using X-ray adsorption fine structure (XAFS) analysis and correlated to theoretical findings obtained from density functional theory (DFT) calculations. XAFS data indicate the successful reduction of Cu species to Cu+ and Cu0, and Ce to Ce3+. Analysis of XAFS spectra located Cu and Ce within the Y zeolite framework with Cu cations in the six-member ring sites and as small metallic Cu clusters. Ce cations were found to occupy both six-member ring and hexagonal prism sites. These results reveal the structure of CuCeY as prepared for desulfurization and provide insight into its superior sulfur adsorption performance.

Treatment of Purified Terephthalic Acid Wastewater by Ozone Catalytic Oxidation Method

In this study, a Cu–Ce@Az ozone catalyst with multiple active components was prepared through the impregnation method to treat purified terephthalic acid (PTA) wastewater, and characterized by X-ray diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy, specific surface area analysis, X-ray energy spectroscopy, X-ray photoelectron spectroscopy, and other methods. The Cu–Ce@Az ozone catalyst had a developed pore structure with a large specific surface area and crystal structure. After calcination, the metallic elements Cu and Ce existed in the state of oxides CuO and CeO2. The effects of reaction time, solution pH, catalyst dosage, and ozone dosage on the catalytic oxidation performance of the Cu–Ce@Az ozone catalyst were studied. Adding tert-butanol reduced the removal rate of COD from the PTA wastewater through the catalytic oxidation system, which proves that a Cu–Ce@Az ozone catalyst treatment process of PTA wastewater follows the free-radical reaction mechanism. The results of 3D fluorescence spectroscopy analysis show that the organic matter in the PTA wastewater was converted into tryptophan organic matter and aromatic organic matter after the reaction of the catalytic oxidation system. Ultraviolet absorption spectroscopy analysis indicated that in unsaturated chemical bonds, some conjugated structures and benzene ring structures of organic matter in the PTA wastewater were destroyed.

Biogenic synthesis of CeO2 nanoparticles and its potential application as an efficient photocatalyst for the degradation of toxic amido black dye

This work presents the green synthesis of nanoceria (CeO2) by Phoenix dactylifera (Ajwa dates), Coriandrum sativum (Coriander), Ocimum tenuiflorum (Black tulsi), Camellia sinensis (green tea) and Hibiscus flower. The structural, morphological and optical properties of green synthesized nanoceria were investigated by various analytical techniques such as XRD, FTIR, TEM, UV–visible, XPS and GC–MS. The formation of single phase CeO2 NPs were confirmed by structural analysis and no impurity signal corresponding to metallic Ce was detected. The XPS measurements established that Ce ion has oxidation state + 4. The photocatalytic activity of various green synthesized nanoceria for the photodegradation of amido black dye was investigated and optimum degradation was obtained for Phoenix dactylifera synthesized nanoceria. Dye adsorption on the photocatalyst and the photogenerated charge carriers (e- and h+) attributed to the photodegradation. Moreover trapping experiment was carried out to confirm the prime reactive species accountable for photodegradation. Recycling experiment was performed in order to determine the efficiency of the photocatalyst.

Feasibility Synthesis and Characterization of Gadolinia Doped Ceria Coatings Obtained by Cathodic Arc Evaporation.

Gadolinia doped ceria coatings were elaborated by cathodic arc evaporation from a metallic Ce–Gd (90–10 at.%) target inserted into a conventional multiarc Ti evaporation target in the presence of a reactive argon–oxygen gas mixture. The structural and chemical features of these films were determined by x-ray diffraction and scanning electron microscopy. Their electrical properties were characterized using impedance spectroscopy measurements. It was shown that the as-deposited coatings crystallize in the fluorite type fcc structure of ceria and that their composition is the same as that of the target. The morphology of the coatings is influenced by the evaporation parameter (stress and droplet). The electrical measurements showed two contributions in Nyquist representation and the activation energy was slightly higher than that given in the literature data for the bulk material.

The X-ray emission of cerium oxide

Using a combination of spectral simulation with FEFF and experimental data for metallic Ce, it has been possible to extract the Cerium Oxide-only M4,5 X-ray Emission Spectrum (XES) from an experimental result, which had been produced utilizing a combined CeOxide/Ce sample. It is shown that the XES emission for CeOxide-only is significantly different for the M4 and M5 edges, with the M4 XES consistent with normal XES and the M5 XES exhibiting a continued enhancement associated with a threshold effect, connected to Resonant Inverse Photoelectron Spectroscopy (RIPES).

Corrosion Protection of 6061 Aluminum Alloy By Cerium Electrodeposition Using a Deep Eutectic Solvent

In this work, a study of the electrodeposition of Ce onto an aluminum 6061 alloy was carried out from Ce salt dissolution in a deep eutectic solvent formed by choline chloride and urea at 70 °C, to increase the alloy’s corrosion protection in saline media (3.5% NaCl). In order to corroborate that the deposit is formed by metallic Ce, surface characterization was carried out by SEM and EDX, which allowed verification that up to 41.33% Ce was deposited on the Al alloy after applying a potential of -1.45 V for 3000 seconds. Electrochemical impedance spectroscopy (EIS) led to determining the corrosion resistance of the modified material and the corrosion inhibition efficiency of 92%, with respect to the blank in 3.5% NaCl. Figure 1

Graphene encapsulated metallic state Ce2Sn2O7 as a novel anode material for superior lithium-ion batteries and capacitors

We present a strategy to encapsulate bimetallic-based ternary (Ce2Sn2O7) nanomaterials into graphene, which served as an anode material for lithium-ion batteries/capacitors for the first time.

Chemical states of ppm cerium in steel by ToF‐SIMS analysis

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was employed for an analysis of the rare earth element Ce in pure iron and steel. Secondary ion images showed that the amount of the segregation of Ce and its oxides was much less as the concentration of Ce decreased to about 11 ppm in the pure iron. In terms of depth profiling from the surface to the matrix, variation of the CeO+/Ce+ ratio in a Ce oxides sample and a pure Ce sample exhibited difference between oxidized state and metallic state. It was demonstrated that metallic Ce was presented when the ratio of CeO+/Ce+ decreased to approximately 2 and even smaller. Oxygen content with concentration of tens of ppm may influence the ratio obviously. Such ToF‐SIMS analysis was also feasible to discern the states of cerium in a Q345E steel with concentration in ppm level.

Formation of Cerium and Neodymium Isocyanides in the Reactions of Cyanogen with Ce and Nd Atoms in Argon Matrices.

Laser ablation of metallic Ce and Nd reacting with cyanogen in excess argon during codeposition at 4 K forms Ce(NC)x and Nd(NC)x for x = 1-3, which are identified from their matrix infrared spectra using cyanogen substituted with 13C and 15N. The electronic structure calculations were performed for isocyano and cyano Cd and Nd compounds for up to n = 4. The frequencies were calculated at the density functional theory level with three different functionals as well as correlated molecular orbital theory (MP2) and are consistent with the experimental assignments and the corresponding 12C/13C isotopic frequency ratios for the isocyano species. The computed frequencies for the analogous cyanide complexes are significantly higher than those for the isocyano isomers, and they are not observed in the spectra. The high spin isocyano complexes are the lowest energy structures. On the basis of the natural population analysis results, the bonding in 4CeNC and 6NdNC is essentially purely ionic with the Ce/Nd in the +I-oxidation state. The bonding for disocyano (3Ce(NC)2 and 5Nd(NC)2) and triisocyano (2Ce(NC)3 and 4Nd(NC)3) complexes is still quite ionic with the lanthanide in the +II and +III formal oxidation states, respectively. For 1Ce(NC)4, the oxidation state is best described as being between +III and +IV. Formation of 5Nd(NC)4 does not really change the electron configuration on the Nd from that in 4Nd(NC)3 and the oxidation state on the Nd remains at +III. Although Nd compounds with up to 3 NC- groups have more ionic binding than do the corresponding Ce compounds, Ce(NC)4 has more ionic binding than does Nd(NC)4. The ionic nature of isocyano Ce and Nd complexes decreases as the number of isocyano groups increases. The energetics of formation of the isocyano Ce and Nd complexes using cyanogen or CN radicals are calculated to be mostly due to exothermic processes, with the exothermicity decreasing as the number of isocyano groups increases.

Die monoklinen Seltenerdmetall(III)-Chlorid-Oxidoarsenate(III) mit der Zusammensetzung SE 5Cl3[AsO3]4 (SE=La–Nd, Sm)

Abstract The rare earth metal(III) chloride oxidoarsenates(III) with the composition RE 5Cl3[AsO3]4 (RE = La–Nd, Sm) could be synthesized via solid-state methods through the reaction of arsenic sesquioxide (As2O3) with the corresponding rare earth metal compounds (La2O3, CeO2 + metallic Ce, Pr6O11, Nd2O3 or metallic Sm) using several chloride-containing fluxing agents in evacuated silica glass ampoules. The compounds build up non-isotypic crystal structures in the monoclinic space groups C2/c for RE = La–Pr, and P2/c for RE = Nd and Sm. All rare earth metal(III) cations exhibit coordination numbers of eight. While (RE1)3+ and (RE2)3+ are only surrounded by oxygen atoms in the form of distorted square antiprisms or prisms, (RE3)3+ is coordinated square antiprismatically by four oxygen atoms and four chloride anions. Although the coordination polyhedra in both structures differ only marginally, their connection patterns show more pronounced differences. This regards especially the (RE)3+ cations and results from different site symmetries of the (Cl1)− anions. All As3+ lone-pair cations are coordinated by three oxygen atoms to form ψ1-tetrahedral [AsO3]3− complex anions with their non-binding (lone) electron pairs pointing into empty channels along [010].

Isostructural phase transition of fcc Ce: Molecular dynamics simulations

Ce is a rare earth element in the periodic table. In the range of low temperature and low pressure, there are two face-centered-cubic (FCC) phases (<i>α</i>-Ce and <i>γ</i>-Ce) and a double-hexagonal-close-packed phase (<i>β</i>-Ce) for metallic Ce. At ambient temperature and about 0.7 GPa pressure, Ce undergoes <i>γ</i>→<i>α</i> phase transition with a volume shrink of 14%–17% discontinuously. In this paper, an embedded-atom method (EAM) potential compatible for <i>α</i>-Ce and <i>γ</i>-Ce was developed. This EAM potential has been employed to study several basic properties of cerium in these two FCC phases, such as equilibrium lattice constants, cohesive energies, and elastic constants. These results showed good accordance with experiments and first principle calculations. The lattice defects have been studied with the formation energy calculations of vacancies, interstitials, surfaces, stacking faults, and twinning defects in <i>α</i>-Ce and <i>γ</i>-Ce lattice. The lattice dynamics of <i>α</i>-Ce and <i>γ</i>-Ce have been analyzed using our EAM potential. The lattice vibrational entropy was calculated and plotted as functions of temperature for each phases. The vibrational entropy change across the <i>α</i>-<i>γ</i> phase transition showed to be ~0.67 <i>k</i><sub><i>B</i></sub> per atom at ambient temperature. Using molecular dynamics simulation with our EAM potential, several isotherms and radial distribution functions were calculated. These isotherms and radial distribution functions demonstrate a first order phase transition between two FCC structures, corresponding to <i>α</i>-Ce and <i>γ</i>-Ce, with a critical point sets at <i>T</i><sub>c</sub>≈550 K and <i>P</i><sub>c</sub>≈1.21 GPa. Thus the newly developed EAM potential could provide a reasonable description of FCC Ce and its <i>α</i>-<i>γ</i> phase transition within the scale of classical molecular dynamics simulation.

Efficiencies and mechanisms of ZSM5 zeolites loaded with cerium, iron, or manganese oxides for catalytic ozonation of nitrobenzene in water

Discharge of industrial wastewater causes water pollution. It is therefore necessary to treat wastewater prior to discharge. Catalytic ozonation processes (COP) using ZSM5 zeolites loaded with metallic (Ce, Fe, or Mn) oxides to remove nitrobenzene from water were investigated. The total organic carbon (TOC) removal by the COP treatment with NaZSM5-38, HZSM5-38, and NaZSM5-100 were increased by 6.7%, 23.1%, and 19.8%, respectively, in comparison with single ozonation efficiency (39.2%). The loadings of Ce, Fe, or Mn oxides increased the catalytic activity relative to ZSM5 zeolites alone. The Ce loaded material (Ce/NaZSM5-38) had the highest TOC removal (86.3%). The different-metallic-oxides loaded zeolites exhibited different chemical processes during the removal of nitrobenzene from water. During COP treatment, NaZSM5-38 zeolites removed nitrobenzene mainly via OH mediated oxidation. HZSM5-38 and NaZSM5-100 zeolites showed powerful adsorption toward nitrobenzene. Both adsorption and direct ozonation contribute the TOC removal in their early uses. The OH mediated oxidation dominates the TOC removal process as the adsorption became saturated after multiple uses. Surface SiO bonds and/or SiO(H)Al structures are the active sites for ZSM5 zeolites. Efficient surface dispersion of the metallic oxides enhances the catalytic activity. This study shows the high potentials of ZSM5 zeolites as catalysts in COP to efficiently treat refractory wastewaters.

Epitaxial growth and structure of monolayer cerium oxide films on Rh(111)

We prepared monolayer cerium (Ce) oxide films on Rh(111) to investigate their growth and structure using scanning tunneling microscopy (STM), low-energy electron diffraction, X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations. For quantitative analysis of Ce-oxide films, we used the combined techniques of XPS and Rutherford backscattering spectrometry to determine the concentration of Ce and O atoms. We prepared a monolayer (ML) Ce-oxide film by annealing a metallic Ce film at 0.3ML coverage in an oxygen atmosphere. A well-ordered Ce-oxide phase with a (4×4) unit cell was obtained. The epitaxially grown Ce-oxide film aligned along the 〈110〉 azimuthal direction of Rh(111). The number of Ce and O atoms in the (4×4) unit cell was estimated. The STM images indicated that the two-dimensional island growth of the p(4×4) phase with p3m1 symmetry can be explained using the missing Ce atoms model. A simulated STM image of the p(4×4) structural model was in good agreement with the experimental STM image. The formation of Ce-oxide films on Rh(111) at submonolayer coverage was discussed on the basis of the results of DFT+U calculations.

Development of metallic element-stabilized Li4SiO4 sorbents for cyclic CO2 capture

Lithium orthosilicate (Li4SiO4) doped with different metallic elements, K, Mg, Cr, or Ce, was prepared by a sol–gel method for high-temperature CO2 capture. The doped sorbents were systematically studied and compared with non-doped Li4SiO4. The influence of element doping on the crystal, textural and microscopic structure of Li4SiO4 was characterized using X-ray diffraction (XRD), nitrogen adsorption and scanning electron microscopy (SEM). The CO2 absorption properties were assessed by thermogravimetric analysis, and the cyclic absorption–desorption properties were analyzed on a fixed-bed reactor. All the metallic elements could insert into the crystal lattice. In particular, Ce doping effectively inhibited the growth of crystal aggregation, resulting in a foam-like morphology with small particle size. Thus, significantly improved CO2 chemisorption properties were achieved with higher capacity and faster absorption kinetics. The optimal doping molar content of Ce/Li4SiO4 was 0.02, with a maximum absorption capacity of 34.57 wt%. Moreover, this improved performance was maintained for 10 sorption/desorption cycles.

New Surface Aspects towards Photocatalytic Activity of Doped Supported Titanium Dioxide

The present work aims to synthesize nanoscale well dispersed TiO2/SiO2and TiO2/Al2O3nanoparticle photocatalysts via an impregnation method for the removal of methyl orange, which was used as a model compound of organic pollutant in wastewater, from an aqueous medium. Also within this frame work, La and Ce metals were loaded onto the surfaces of TiO2/SiO2and TiO2/Al2O3by an impregnation method to enhance the photocatalytic activity of the nanoparticles; the activities and physicochemical properties of the photocatalysts were compared before and after loading of metallic La and Ce. The oxide system was characterized by different techniques, including XRD, UV-Vis spectroscopy, FT-IR spectroscopy, SEM, and EDX spectroscopy. Finally, the optimal conditions to complete the photocatalytic oxidation of methyl orange dye were studied. This work holds promise for the efficient photodegradation of pollutants by nanoparticle photocatalysts.

Coexistence of different magnetic moments in CeRuSn probed by polarized neutrons

We report on the spin densities in CeRuSn determined at elevated and at low temperatures using polarized neutron diffraction. At 285 K, where the CeRuSn crystal structure, commensurate with the CeCoAl type, contains two different crystallographic Ce sites, we observe that one Ce site is clearly more susceptible to the applied magnetic field whereas the other is hardly polarizable. This finding clearly documents that distnictly different local environment of the two Ce sites causes the Ce ions to split into magnetic Ce3+ and non-magnetic Ce(4-delta)+ valence states. With lowering the temperature, the crystal structure transforms to a structure incommensurately modulated along the c axis. This leads to new inequivalent crystallographic Ce sites resulting in a re-distribution of spin densities. Our analysis using the simplest structural approximant shows that in this metallic system Ce ions co-exist in different valence states. Localized 4f states that fulfill the third Hund's rule are found to be close to the ideal Ce3+ state (at sites with the largest Ce-Ru interatomic distances) whereas Ce(4-delta)+ valence states are found to be itinerant and situated at Ce sites with much shorter Ce-Ru distances. The similarity to the famous alpha-gamma transition in elemental cerium is discussed.