Ce 3d Research Articles

Improved activity and SO2 tolerance of rare-earth elements modified CeTi catalyst for Hg0 and NO simultaneous removal from flue gas

ABSTRACT Six rare-earth elements (including La, Sm, Pr, Dy, Y, and Nd) were modified on the surface of the CeTi samples for Hg0 oxidation and NO oxidation. The X-CeTi catalysts significantly improved the Hg0 oxidation, NO oxidation, and SO2 tolerance compared with the CeTi catalyst. Moreover, O2 and NO can facilitate the activities significantly. The BET results showed that the specific surface area could be increased by doping of rare-earth elements. In addition, XRD and FT-IR experiments indicated that the rare-earth elements can facilitate the formation of the amorphous structure of CeO2. The XPS curves of Ce 3d and O 1s showed that surface oxygen species and Ce4+/Ce3+ redox couples were responsible for the catalytic performance, confirming that the SO2 tolerance was improved via the electron transfer by Ce4++Dy2+⇌Ce3++Dy3+ reactions. The H2-TPR results suggested that the redox capacity of X-CeTi catalysts was enhanced, which could improve the activities of the catalysts. Moreover, Dy-CeTi had the highest NO and Hg0 oxidation among these rare-earth elements on account of the largest specific surface, more surface-active oxygen and H2-TPR reduction peak integral area. The catalyst can maintain the conversion efficiency of elemental mercury and NO at 67% and 76% even in flue gas containing 800 ppm SO2. Such work supplied new insights into modified Ce-Ti catalysts to simultaneously remove NO and elemental mercury from the flue gas with high efficiencies, which owned a promising prospect in the practical industrial application.

Tea polyphenols mediated biogenic synthesis of chitosan-coated cerium oxide (CS/CeO2) nanocomposites and their potent antimicrobial capabilities.

In the present study, we hypothesized that novel nanocomposites of chitosan-coated cerium oxide (CS/CeO2 NCs) derived from aqueous extracts of tea polyphenols would be stabilized and reduced by using green chemistry. The UV-visible spectrum of the synthesized material revealed an SPR peak at 279nm, and the morphological characteristics of nanoparticles (NPs) as a uniformly distributed spherical shape with a size range of 20nm were confirmed by field emission scanning electron microscopy (FESEM). The Fourier transform infrared spectroscopy (FTIR) spectrum illustrated the amino groups of chitosan-coated with CeO2 NPs on the surface. While, the hydrodynamic size (376nm) and surface charge (+ 25.0mV) of particles were assessed by dynamic light scattering (DLS), and the existence of oxidation state elements Ce 3d, O 1s, and C 1s was identified by employing X-ray photoelectron spectroscopy (XPS). A cubic fluorite polycrystalline structure with a crystallite size of (5.24nm) NPs was determined using an X-ray Diffractometer (XRD). The developed CS/CeO2 NCs demonstrated excellent antibacterial and antifungal efficacy against foodborne pathogens such as Escherichia coli, Staphylococcus aureus, and Botrytis cinerea with zone of inhibition of 13.5 ± 0.2 and 11.7 ± 0.2mm, respectively. The results elucidated the potential of biosynthesized CS/CeO2 NCs could be utilized as potent antimicrobial agents in the food and agriculture industries.

Angle-resolved photoemission spectroscopy study of the (101) surface of the Kondo insulator CeNiSn

The electronic structure of CeNiSn, which is considered a possible topological Kondo insulator, has been investigated by employing synchrotron radiation excited angle-resolved photoemission spectroscopy (ARPES). We have found that the easy cleavage plane in CeNiSn is (101), for which we have investigated the Fermi surface (FS) and band structures. The measured FS and ARPES for the (101) plane are described well by the calculated FS and band structures, obtained from the DFT calculations. The measured ARPES bands and photon energy map show that the metallic states crossing the Fermi level have the 3D nature, casting a negative suspicion for the existence of the topological surface states of the 2D character in CeNiSn. The Ce 4f Kondo resonance peak is observed in Ce 4d → 4f resonant photoemission spectroscopy, suggesting the importance of the Ce 4f electrons in determining the temperature-dependent topological electronic structure of CeNiSn.

N2O Adsorption and Photochemistry on Ceria Surfaces

Catalytic decomposition of nitrous oxide (N2O) is one of the most promising ways to control N2O emissions, the dominant ozone-depleting substance and the third most potent greenhouse gas. We have investigated the adsorption and photoinduced decomposition of N2O on macroscopic monocrystalline CeO2(111) surfaces by polarization-dependent infrared reflection absorption spectroscopy (IRRAS) in conjunction with core-level (XPS Ce 3d and NEXAFS) and valence band (Ce 4f) spectroscopy as well as DFT+U calculations. The IRRAS results at 110 K show that the νas(NNO) asymmetric stretching vibration of adsorbed N2O exhibits band splitting at relatively low N2O coverage in p-polarized spectra. This band splitting is attributed to polarization-dependent shifts of absorption bands. On reduced ceria (111) surfaces, the desorption energy (0.37 eV) of N2O extracted by IRRAS is found to be higher than on oxidized surfaces. This increasing binding energy is attributed to the attractive coupling with Ce3+ cations formed via surface Ce4+ reduction by by polarons that migrate from the bulk. The photoreaction cross section (with ultraviolet (UV) light = 365 nm at T = 120 K) of the reduced ceria (110) surfaces determined by IRRAS (5 × 10–19 cm2) confirms their much higher activity than that of the reduced CeO2(111).

Synthesis, characterization and density Functional theory (DFT) study of LaCeO3

Nanosized perovskite oxide of LaCeO3 was synthesized using the EDTA-citrate method and calcined at 600 °C for 5 h. The white powder obtained from synthesis was characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman Spectroscopy, and UV–Vis Diffuse Reflectance Spectroscopy (UV–Vis DRS) Analysis. The developed perovskite can be used as catalyst in soot oxidation, VOC oxidation, and photo thermal reactions, and materials in solar cells, sensors and fuel cell. XRD analysis confirms the crystalline nature of the perovskite with a predominantly cubic fluorite structure. Morphological studies concluded that the LaCeO3 perovskite has a crystalline microstructure with a large number of honeycomb-like macropores with a minor crystalline phase. UV–Vis DRS tells us that the absorbance acquired can be attributed to the variations in the composition of Ce. Tauc plot allotted based on the data obtained from UV–vis Spectroscopy gave an energy band gap of 3.15 eV, signifying that the material may be classified as a semiconductor. Raman Spectroscopy tells us that the sharp peak obtained at 446 cm−1 corresponds to the stretching of the Ce-O bond. XPS analysis corresponds to La 3d with binding energy gap of 3.3 eV, Ce 3d with redox ratio 49.88% and O 1 s peak with surface oxygen vacancy ratio of 65.5%. DFT analysis of the sample result in direct band gap of 0.802 eV and indirect band gap of 1.716 eV.

Photochromic property of cerium oxide nanoparticles prepared by dialysis of solution of cerium nitrate

CeO2 nanoparticles were obtained by heating 50 mL of 0.1 M Ce(NO3) 3·6H2O solution mixed with 5 mL of 1 M NH3 aq. at 368 K for 24 h. When H2O and ethanol were used as solvents for cerium nitrate hydrate, obtained CeO2 nanoparticles were aggregated. On the other hand, in case that ethylene glycol was used for the solvent, stable sol of CeO2 nanoparticles dispersed in ethylene glycol. Furthermore, dialysis of the sol with H2O successfully enabled the exchange of the dispersion solvent from ethylene glycol to H2O and the average particle size was 23 nm, which was less than those of the other solvents. UV and visible light were irradiated onto the obtained CeO2 powders to examine their photochromic characteristics. The CeO2 nanoparticles obtained with the ethylene glycol solution showed change of absorbance spectra after irradiation of light whose wavelength was less than 600 nm, that is, the visible light irradiation caused photochromism on the CeO2 nanoparticles. According to Ce 3d XPS spectra of the CeO2 nanoparticles, valence state of the Ce ions in the CeO2 nanoparticles was mixed valence state of Ce3+ and Ce4+, which causes inter valence charge transfer absorption. Therefore, the change of the optical absorption spectra, photochromism, occurred with the optical absorption due to the charge transfer absorption between Ce3+ and Ce4+. Furthermore, the photochromic characteristics depended on heat treatment of the CeO2 nanoparticles. Heating the nanoparticles at more than 473 K decreased amount of oxygen vacancies, which affected the mixed valence state of Ce ions so that the photochromism by irradiation of the light within the wavelength range from 400 nm to 600 nm was greatly affected.

La2Ce2O7 doped with alkaline earth elements: Phase behavior, hydration and electrical properties

La2Ce2O7 is known to be a disordered fluorite, i.e., 50% La-doped CeO2, exhibiting oxide ion conduction with contributions from protons in wet atmospheres and minority electrons under reducing conditions. Here, we report the effect of additional doping by partial substitution of La3+ with divalent alkaline earth cations A2+ (A = Ca, Sr, Ba) on the hydration behavior and electrical conductivity of La2Ce2O7. A single-phase cubic fluorite structure was obtained for La2Ce2O7, (La1-xCax)2Ce2O7-δ (x = 0–0.3), (La1-xSrx)2Ce2O7-δ (x = 0–0.2), and (La1-xBax)2Ce2O7-δ (x = 0–0.05). Substitution by A2+ enhanced the degree of hydration, which may be attributed to increased concentration of hydratable oxygen vacancies and coordination of oxide ions by A2+ in addition to La3+, while the basicity of the different A2+ seemed unimportant. The doping increased ionic conductivity slightly, while the n-type electronic conductivity under reducing atmospheres increased considerably. XPS analyses indicated that the concentration and binding energy of Ce 3d electrons decreased with increasing doping level of Ca, implying an enhanced mobility of electrons which may be attributed to an observed decrease in lattice parameter.

Usefulness of contrast-enhanced 3D MR angiography and contrast-enhanced 3D T1 sequence for detecting intracranial infectious aneurysms in infectious endocarditis

ObjectivesTo assess the diagnostic value of contrast-enhanced MRA (CE MRA) and CE 3D-T1 for identifying intracranial infectious aneurysms (IIAs) in infective endocarditis (IE) with digital substraction angiography (DSA) as reference. MethodsTwenty-one IE patients (14 males; mean age: 53 years) with 30 IIAs, diameter ranging 1.5–15 mm (<3mm, n = 14, 46.7%; 3–5 mm, n = 12,40%), underwent CE MRA and CE 3D-T1 at 1.5 T. Two readers evaluated images for aneurysm detection, characterization, quality of visualization. DSA was obtained at a median of 3 days (range 1–15) after MRI. ResultsThe sensitivity, specificity, positive and negative predictive values and accuracy of IIA detection were respectively: 80%, 100%, 100%, 82.3%, 90% for CE MRA and 86.7%, 100%, 100%, 88.2%, 93.3% for CE 3D T1 compared to DSA.No significant difference was observed between CE MRA and CE 3D-T1 for accuracy and quality of visualization. All IIAs of ≥3 mm in diameter (16/30; 53.%) were identified by both sequences, which were also able to detect IIAs ≤ 3 mm (n = 14/30, 46.7%). False negatives were observed with both sequences for 4 IIAs of <2 mm, 3 being compressed by hemorrhagic lesions. Two other IIAs of <2 mm were overlooked by CE MRA. CE 3D-T1 overestimated IIAs luminal diameter by 8% relatively to DSA (P = NS).Intra and inter-observer agreement were good and similar with both methods. ConclusionBoth CE MRA and CE 3D-T1 have good accuracy compared to DSA detection and characterization of IIAs. CE 3D-T1 also evaluates anatomical relationships of IIAs, which could help DSA location and endovascular treatment.

(Invited) Synthesis Design Strategies of Faceted Cerium Oxide Nanoparticles and its Properties

Cerium oxide nanoparticles (CNP or nano-ceria) are widely studied for their use in catalysis, energy, environmental protection, and bio-medical applications. Recently CNP is used as additives for Chemical Mechanical Planarization (CMP) slurries. The chemical performance of ceria in many of these applications depends on the ability of cerium to switch between +3 and +4 oxidation states. Our research involves examination of the synthesis design strategies of CNP with various shape and sizes and their effect on the surface chemistry. In most catalytic applications, highly reduced ceria surfaces play an active role and very similar observation is also noted in increased CMP removal rates. While high resolution TEM (HRTEM) is used to follow the particle morphology evolution, the surface effects are studied using high resolution X-ray photoelectron spectroscopy (XPS) of the Ce 3d spectrum. Atomistic computer simulations were used to help rationalize how the synthetic conditions impact upon the morphology of the nanomaterial. Further we provide understanding of the adsorption Interface of Polyelectrolyte Coating on Redox Active CNP Using Soft Particle Electro kinetics, which is relevant to CMP and biomedical applications. This talk summarizes some of our observations of the impact that synthesis route, storage and environmental conditions have on the properties of CNPs.

Resonant photoemission spectroscopy of the ferromagnetic Kondo system CeAgSb2

We study the electronic structure of single crystal CeAgSb2, a low T c ferromagnetic Kondo system, using synchrotron radiation photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). We have carried out Ce 5s, Ce 5p, Sb 4d core level PES as well as Ce 4d–4f resonant PES of the valence band states of CeAgSb2. We also report the resonant PES behavior of Ce 5s and 5p core-levels and the simultaneous intensity suppression of Sb 4d core-level and Ag 4d valence band states across the Ce 4d–4f threshold. The Ce 4d–4f resonant valence band spectra show typical f 0 and f 1 features associated with Kondo behavior. The constant initial state spectra of the f 0 and f 1 features show maxima at different incident photon energies, arising from different relative contributions of surface and bulk character Ce 4f partial density of states. XAS across the Ce 3d–4f M-edge also shows the corresponding final state f 1 and f 2 features. The weak temperature dependence of the XAS spectra between T = 25 K and 300 K could be simulated using a full multiplet calculation combined with a simplified single-impurity Anderson model approach. The calculations confirm the Kondo screening and allows quantification of the bulk Ce 4f electron count in CeAgSb2. The Ce 5s states show an exchange splitting which reflects the local magnetic moment of Ce 4f states. The overall results characterize the bulk and surface sensitive Ce 4f states, and indicate the role of Kondo effect in forming the moderately enhanced heavy-fermion carriers in CeAgSb2.

Fabrication of magnetic cerium-organic framework-activated carbon composite for charged dye removal from aqueous solutions

The presence of synthetic dyes in water leads to health and ecological concerns due to their toxic and carcinogenic effects. For the remediation of coloured wastewater, we have fabricated a Ce-MOF@Fe3O4@activated carbon composite. The composite showed a ∼97–98% removal of indigo carmine and methylene blue at pH 7, whereas it was ∼83–85% for activated carbon. The adsorption and kinetic data followed the Temkin and Elovich models, respectively. Which suggested the involvement of physicochemical forces in the adsorption process. The thermodynamic study confirmed the adsorption process to be endothermic, where the adsorption performance improved with the increasing temperature. The increased intensity of the band at 824 cm−1 (CH) and 1004 cm−1 (aromatic CC) in the Raman spectra confirmed the adsorption of dyes onto the adsorbent. Dye adsorption was further confirmed by the N 1s peak at 400 eV for CNC in the dye-adsorbed composite. The shift in the binding energy of Fe 2p and Ce 3d peaks by 0.3–0.4 eV concluded the involvement of electrostatic and cation-π interactions in the adsorption process. A ∼90–98% dye removal capacity of the adsorbent even in the fourth cycle made it a highly stable and reusable adsorbent for remediation of coloured wastewater.

Adsorption and activation of CO2 on Pt/CeOx/TiO2(110): Role of the Pt-CeOx interface

The adsorption and dissociation of CO2 on TiO2(110), CeOx/TiO2(110) and Pt/CeOx/TiO2(110) surfaces has been examined using Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS). The substrates under study exhibited different degrees of complexity which were tested for the binding of the adsorbate and the cleavage of C-O bonds. The surfaces were prepared by depositing CeOx (0.1 ML) onto TiO2(110) to form a mixed oxide support, onto which Pt nanoparticles (0.2 ML) were deposited. This configuration yields a complex set of interfaces between metal and oxides and we have systematically titrated the active role of each component (Pt 4f, Ce 3d and Ti 2p regions) and the arising surface intermediates (C 1 s and O 1 s regions). CO2 barely bonds to stoichiometric TiO2(110). It heals oxygen vacancies of this oxide surface (CO2,gas → COgas + Oa) and does not form stable carbonates. A stable carbonate was seen upon adsorption of CO2 on CeOx/TiO2(110) and on this type of substrate the adsorbate also removed O vacancies leading to the oxidation of Ti3+and Ce3+ sites. Pt nanoparticles dispersed on CeOx/TiO2(110) were highly effective for the binding and dissociation of CO2, with the formation of CO3, CO, C and CHx species on the Pt/CeOx/TiO2(110) system. The results of theoretical calculations based on density-functional theory (DFT) show that Pt/CeOx/TiO2(110) binds CO2 much stronger than surfaces of bulk platinum {(111), (100), (110)} or other late transition metals. On a Pt-CeOx interface, the molecule adsorbs with a bent configuration (~130° O-C-O bond angle) and with a substantial elongation (~ 0.1 Å) of the C-O bonds, facilitating its transformation into high value chemicals.

Reply to “Comment on an article by Gonzaga et al. J Am Ceram Soc. 2020;103:6280‐6288”

AbstractIn the “Comment on article by Gonzaga et al. J Am Ceram Soc. 2020;103:6280‐6288”, Paparazzo argues that the estimated value of Ce3+ amount in our CeO2 samples through X‐ray photoelectron spectroscopy (XPS) analysis is ~10% and there is no dependence on the annealing temperature or Pr‐doping. However, a comparison of our XPS Ce 3d spectra with the reference presented by that author reveals characteristics in these spectra of higher at.%Ce3+ being consistent with values of around 24%. Furthermore, the intensity of the absorption in the region around the feature assigned as v′ in XPS Ce 3d spectra decreases as a function of Pr‐doping and annealing temperature, confirming different at.%Ce3+ for the samples due to these aspects.

X-ray photoelectron and Raman spectroscopy of nanostructured ceria in soot oxidation under operando conditions

Ceria nanoshapes exhibiting different amounts of {100}, {110} and {111} facets (cubes, rods, octahedra and polyhedra) were prepared, characterized, tested in the carbon soot oxidation reaction, and studied by operando near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando Raman spectroscopy up to 550 °C. The specific soot oxidation reaction rate (mgC·m−2·min−1) clearly indicated that the {110} and {100} crystallographic planes of ceria were more active than the {111} ones for the oxidation of carbon soot. As deduced from the Ce 3d and O 1s signals recorded using different photon energies, all ceria nanoshapes experienced progressive reduction upon increasing the temperature under Ar, which was accompanied by the formation of oxygen vacancies. Raman studies revealed that, at this stage, isolated graphene layers in carbon soot reacted with ceria lattice oxygen atoms following a Mars-Van Krevelen mechanism. After exposure to O2 at 550 °C, a broad signal in the O 1s region at 531.2–532.5 eV was ascribed to surface active oxygen species, such as peroxide (O22−) and superoxide (O2−) species, generated from the interaction of molecular O2 with oxygen vacancies, which proved to be highly reactive to oxidize the graphitic structures of carbon soot.

Effect of Cerium Oxide Nanostructures on CO Oxidation.

Cerium oxide particles with different morphologies, namely nanoparticles, nanofibers, nanocubes, and rice grains have been prepared by simple chemical routes. The shape and size of the synthesized morphologies have been studied using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray diffraction (XRD) and selected area electron diffraction (SAED) techniques have been used to determine their crystal phases. Both nanoparticles and nanocubes of cerium oxide exclusively crystallize in fluorite structure of CeO₂ as observed in XRD patterns, whereas nanofibers and rice grains are characterized by the presence of CeO₂, Ce₂O₃, and Ce(OH)₃ phases. X-ray photoelectron spectroscopy (XPS) has been employed to evaluate Ce species present in the different cerium oxide morphologies and to estimate their relative surface concentrations. As evident from Ce 3d core level spectra cerium oxide nanoparticles and nanocubes are basically CeO₂ having Ce in the +4 oxidation state along with some amount of Ce3+ species. In contrast, Ce is in +3 oxidation state on its surface in cerium oxide nanofibers and rice grains that contain intermediate phases like Ce₂O₃ and Ce(OH)₃ as endorsed by XRD patterns. CO oxidation has been carried out over these cerium oxide morphologies and among all morphologies lowest temperature CO oxidation has been demonstrated by the nanocube morphology.

Reply to the Comment on “New horizons in photocatalysis: the importance of mesopores for cerium oxide” by A. S. Thill, W. T. Figueiredo, F. O. Lobato, M. O. Vaz, W. P. Fernandes, V. E. Carvalho, E. A. Soares, F. Poletto, S. R. Teixeira and F. Bernardi, J. Mater. Chem. A, 2020, 8, 24752

The Ce 3d XPS data were analyzed with different sets of constraints and no significant change was observed both in the trend and in the absolute values of the Ce(iii) fraction reported.

Early Diagnosis of Aseptic Meningitis in Ramsay Hunt Syndrome on 10-Minute Delayed CE 3D FLAIR Image: a Case Report

Early Diagnosis of Aseptic Meningitis in Ramsay Hunt Syndrome on 10-Minute Delayed CE 3D FLAIR Image: a Case Report

XPS quantification of oxygen vacancies in mesoporous and non-mesoporous CeO2: comment on an article by Thill et al., J. Mater. Chem. A, 2020, 8, 24752–24762

The present Comment emphasises that accurate speciation of the chemistry of the cerium in the authors' catalysts requires careful consideration of the line shape of XPS Ce 3d spectra characteristic of CeO2 and Ce2O3 oxides.

Intermediate valence of CeNi2Al3 compound and its evidences: Theoretical and experimental approach

We present measurements of magnetic, transport and electronic properties obtained for polycrystalline CeNi2Al3 intermetallic compound. Magnetic susceptibility χ(T) was investigated in the range from 2 to 700 K, and its behavior is characteristic of a compound with unstable valence, varying between Ce3+ and Ce4+. In the temperature range down to 2 K there was no trace of magnetic order, no anomalies in the temperature dependence of the specific heat were found. The Sommerfeld coefficient extracted from the linear term of the heat capacity takes a value of γ = 21 mJ/(mol K2). The dependence of S(T) is linear up to about 25 K, which is symptomatic of a thermopower in the Fermi's liquid regime.The structure of satellites in the Ce(3d) electron spectrum obtained by the X-ray photoelectron spectroscopy (XPS) method indicates that the states of Ce(4f) are of mixed valence character. Analysis of Ce(3d) states based on Gunnarsson-Schönhammer theory shows that the energy of hybridization of Ce(4f) states with a conduction band is about 78 meV. For more detailed information about electronic states the fully relativistic band structure was calculated within the density functional theory (DFT) for the first time. Below Fermi's energy, the density of states is mainly formed by Ni(3d) states hybridized with Ce(4f) ones.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.