Ce Component Research Articles

Photoelectron spectroscopy of ceria: Reduction, quantification and the myth of the vacancy peak in XPS analysis

Primarily due to its inherent redox chemistry, ceria (CeO2) is of use in many diverse areas of research. However, there is a wealth of misinterpretation of the oxygen spectra when discussing the result of damage or reduction to the CeO2 lattice, especially with regard to a signal in this region attributed to oxygen vacancies. In this paper, it is shown that this peak cannot be due to vacancies and that a better understanding of the changes in stoichiometry of CeO2 is best viewed from that of the Ce(III) component when considered in tandem with the O 1s signal.

Novel Phenomenon of Scintillation Performances with the Component Variation in the Mg Co-/Nondoped GAGG:Ce Crystal

Gd3Al2Ga3O12:Ce (GAGG:Ce) shows potential application in the next-generation positron emission tomography material due to its high light yield and excellent energy resolution. The main method currently available to accelerate the scintillation decay time of GAGG:Ce is mainly through the codoping of low valence ions such as Mg2+, which partially converts Ce3+ to Ce4+ through a charge compensation mechanism. However, there is no clear and reasonable explanation for the deterioration of light yield by codoping with Mg2+ in GAGG:Ce. Therefore, further study of the Mg2+ codoping GAGG:Ce crystal is of great importance for improving the scintillation properties of GAGG:Ce. In this study, two sets of GAGG crystal samples containing different Ce concentrations without or with 0.5 atom % of Mg2+ ion codoping were grown by the micropulling down method. The optimal Ce concentration decreases after Mg2+ codoping, whereas the light yield degenerates significantly. This novel phenomenon suggests that the reduction of light yield after Mg2+ codoping is not only due to the reduction of the luminescence center but also the formation of {Ce3+–Mg2+} and {Ce4+–Mg2+} associates affects the luminescence emission. This work can provide a novel and significant view for high-performance codoped GAGG:Ce component design and performance modification.

A Biomimetic Macroporous Hybrid Scaffold with Sustained Drug Delivery for Enhanced Bone Regeneration.

Bone regeneration is a highly complex physiological process regulated by several factors. In particular, bone-mimicking extracellular matrix and available osteogenic growth factors such as bone morphogenetic protein (BMP) have been regarded as key contributors for bone regeneration. In this study, we developed a biomimetic hybrid scaffold (CEGH) with sustained release of BMP-2 that would result in enhanced bone formation. This hybrid scaffold, composed of BMP-2-loaded cryoelectrospun poly(ε-caprolactone) (PCL) (CE) surrounded by a macroporous gelatin/heparin cryogel (GH), is designed to overcome the drawbacks of the relatively weak mechanical properties of cryogels and poor biocompatibility and hydrophobicity of electrospun PCL. The GH component of the hybrid scaffold provides a hydrophilic surface to improve the biological response of the cells, while the CE component increases the mechanical strength of the scaffold to provide enhanced mechanical support for the defect area and a stable environment for osteogenic differentiation. After analyzing characteristics of the hybrid scaffold such as hydrophilicity, pore difference, mechanical properties, and surface charge, we confirmed that the hybrid scaffold shows enhanced cell proliferation rate and apatite formation in simulated body fluid. Then, we evaluated drug release kinetics of CEGH and confirmed the sustained release of BMP-2. Finally, the enhanced osteogenic differentiation of CEGH with sustained release of BMP-2 was confirmed by Alizarin Red S staining and real-time PCR analysis.

Yttrium‐Doped Barium Zirconate‐Cerate Solid Solution as Proton Conducting Electrolyte: Why Higher Cerium Concentration Leads to Better Performance for Fuel Cells and Electrolysis Cells

AbstractProton conducting Y‐doped BaZrO3, BaCeO3 and their solid solutions are receiving increasing attention due to their promising application as electrolytes in ceramic fuel cells and electrolysis cells. However, the literature indicates a clear tendency that the performance of the cells increases with increasing Ce content in the electrolyte. In this work, to elucidate this phenomenon, a systematic work is performed on investigating the phase, hydration, and transport behaviors of BaZr0.8−xCexY0.2O3−δ (BZCY20). The results reveal that in the temperature range between 500 and 700 °C, with increasing Ce content, the dehydration temperature elevates and the proton concentration increases, showing that the Ce component favors the stabilization of protons. Furthermore, the transport number of hole conduction decreases, whereas the transport number of ionic conduction increases with the increasing Ce content. By further separating the contribution of oxide ions and protons, it is found that the oxide ion conductivity increases with the increasing Ce content at higher temperatures of 600 and 700 °C. Such decreased hole conductivity and increased oxide ion conductivity result in the enhancement of the ionic conduction of BZCY20 with increasing Ce content, and therefore improve the performance of fuel cells and electrolysis cells.

Facile synthesis of 3D ordered macro-mesoporous Ce1-xZrxO2 catalysts with enhanced catalytic activity for soot oxidation

Abstract A series of three-dimensionally ordered macroporous-mesoporous (3DOM-m) ceria-zirconia oxide (Ce1-xZrxO2) catalysts were synthesized successfully by combined methods of the evaporation-induced interfacial self-assembly and colloidal crystal templates (EISA−CCT). The hierarchical porous nanostructure of 3DOM-m Ce1-xZrxO2 catalysts possess the highly ordered macroporous framework with the average pore size of 250 nm; and the plenty of ordered mesopores (5 nm) are dispersed on the inner walls of spherical macropores. 3DOM-m Ce1-xZrxO2 catalysts with abundant oxygen vacancies have the excellent storage oxygen capacity, which is benefit for improving the catalytic activity for soot oxidation. Ordered macroporous framework enhances the contact efficiency between solid soot particles and catalysts, while the ordered mesoporous nanostructure improves the specific surface area dramatically for promoting the contact efficiency of gaseous reactants (O2 and NO) and active sites. The enrichment of Ce component as active sites was observed on the inner wall of ordered mesopores formed by the Kirkendall effect during thermal treatment, which can improve the adsorption-activation ability for gaseous reactants. 3DOM-m Ce1-xZrxO2 catalysts with hierarchical porous nanostructure exhibit high catalytic activity and stability for soot oxidation. The facile fabrication strategy of 3DOM-m catalysts can be extended to other oxides. And insight into the catalytic activity dependence on the both elemental composition and porous nanostructure is not only meaningful for development of advanced catalysts for soot oxidation, but also supports the development of 3DOM-m catalysts for practical applications.

Epoxy-polyamide nanocomposite coating with graphene oxide as cerium nanocontainer generating effective dual active/barrier corrosion protection

An epoxy-polyamide composite coating with dual active/barrier corrosion protection capabilities was formulated using graphene oxide (GO) as a gallery for storage and targeted release of cerium cation inhibitors by an ion exchange mechanism on the steel corrosion sites. The successful adsorption of cerium cations over the GO nanosheets was detected via SEM, TGA and Raman spectroscopy. The role of Ce-GO in the barrier properties and active inhibition was evidenced through EIS assessment of polymeric coatings with and without an artificial scratch. SEM/EDS analysis of the scratch region indicated formation of a protective layer resulting from release of Ce component from the nanocontainer.

Effect of Ce doping into V2O5-WO3/TiO2 catalysts on the selective catalytic reduction of NOx by NH3

In this work, the effectiveness of V2O5-WO3/TiO2 catalysts modified with different CeO2 contents by impregnation and co-precipitation methods on the selective catalytic reduction of NOx by NH3 have been studied comparatively by various experimental techniques. The results showed that the NO conversion of V2O5-WO3/CeO2-TiO2 catalysts modified by co-precipitation method obviously increased with the Ce doping contents in the studied range below 20% (All Ce contents are in mass fractions), but the NO conversion of V2O5-WO3/CeO2/TiO2 catalysts modified by impregnation methods was lower than V2O5-WO3/CeO2-TiO2 catalysts especially beyond 2.5% Ce doping contents. The V2O5-WO3/CeO2-TiO2 catalysts showed better SCR activity, wider reaction window, and higher sulfur and water resistance. The characterization results elucidated that the modified catalysts by co-precipitation method exhibited higher specific surface area, much better dispersity of Ce component, more Ce3+ species and more Brønsted acid sites than that by impregnation. The vacancies caused by more Ce3+ species were favorable for more NO oxidation to NO2, and the interaction between Ce species and WOx species generated more Brønsted acid sites. It could be supposed that dispersed CeOx species and WOx species offered more second active centers respectively to adsorb oxygen and activate ammonia as co-catalysis to the primary active center of V ions, thus facilitated the better SCR activity of modified V2O5-WO3/CeO2-TiO2 catalysts by co-precipitation methods. The co-precipitation methods with Ce component were more suitable for production of modified commercial V2O5-WO3/TiO2 catalysts.

Striking activity enhancement of gold supported on Al-Ti mixed oxide by promotion with ceria in the reduction of NO with CO

The promotion of an Al-Ti mixed oxide supported gold catalyst (Au/AlTiOx) with ceria is shown to result in an unprecedented enhancement of its activity in the reduction of NO to N2 with CO. The parent Au/AlTiOx catalyst was prepared by depositing 3wt% gold on the mesoporous Al-Ti mixed oxide made by an evaporation-induced self-assembly (EISA) method using a triblock copolymer as a soft template. This parent Au/AlTiOx was impregnated with different loadings of CeOx resulting in molar ratios of Au:Ce in the catalysts of 4:1, 2:1 and 1:1. The deposited gold particles showed a relatively broad size distribution with maxima at 8–12nm, as evidenced by TEM. XRD and XPS analyses showed that the Al-Ti oxide support was made up of amorphous Al2O3-TiO2 mixed oxide and that the Ce component was present as a mixture of Ce3+ (Ce2O3) and Ce4+ (CeO2) partially covering the Au particles. The as-prepared catalysts were tested in the catalytic reduction of NO with CO in a continuous tubular microreactor at temperatures up to 300°C. The parent Au/AlTiOx catalyst showed very low activity (8.2% NO conversion at 300°C), whereas the ceria promoted catalyst containing a molar ratio of Au:Ce of 2:1 exhibited a dramatic enhancement of activity affording 100% NO conversion at the same conditions. The stability of this catalyst was tested in repetitive runs over 16h time-on-stream, which showed a slight loss of activity, while 100% selectivity to N2 was maintained. The spent catalyst could be easily regenerated reaching its original performance by heat treatment in flowing 5% O2/He.

Application and Improvement of NOx Storage and Reduction Technology to Meet Real Driving Emissions

Strategies to achieve RDE requirement for diesel passenger car are introduced in this paper focusing on NOx storage and reduction (NSR) technologies. High NOx conversion performance with advanced NSR technologies which make use of reducing agents like NH3 or intermediate reductants created from HC (Bisaiji et al. in SAE Int J Fuels Lubr 5:380–388, 2012) dosing, is demonstrated by vehicle tests. The mechanisms to create reducing agents are discussed in detail. MS analysis identified the key elements to produce reductant species for diesel NOx after-treatment by adsorbed intermediate reductants (DiAir), focusing on the effect of oxygen on the catalyst surface and the catalyst formulation. It was found that surface oxygen has an important role to make intermediate reductants during HC dosing for DiAir. Moreover, the role of Ce component in oxidizing the injected HC and create intermediate reductants effectively became clear. Furthermore, high CO oxidation performance of NSR after ageing in comparison with diesel oxidation catalyst is shown and the mechanism is discussed. Oxidation performance is also important for diesel vehicles because the catalyst temperature is further reducing due to CO2 reduction. The potential to meet next stringent legislation is shown in this paper from the view point of not only NOx reduction but also CO oxidation by an advanced NSR system.

Enhancing the Photocatalytic Activity of BiVO4 for Oxygen Evolution by Ce Doping: Ce3+ Ions as Hole Traps

To enhance the photocatalytic activity of monoclinic BiVO4 for O2 evolution from water, Ce-doped BiVO4 was prepared using the one-pot facile solvothermal method and characterized via XRD, Raman, XPS, and electrochemical impedance spectroscopy (EIS). The XPS spectra confirm that Ce component is Ce3+ ions instead of Ce4+ ions. From the structural characterization and the calculations of formation energies it has been stated that the doping of Ce3+ ions takes place at Bi3+ sites without changing the host structure. The as-prepared Ce-doped BiVO4 samples display significantly enhanced photocatalytic O2 evolution activities from water compared to pristine BiVO4. Density of states calculations indicate that Ce3+ ions act as hole traps, thereby delaying the recombination of photogenerated electrons and holes. The results demonstrate that the substitution of the remaining monoclinic crystal structure may offer an attractive alternative approach for the doping of BiVO4 to enhance the evolution activity of photocat...

Hydrogenolysis of glycerol aqueous solution to glycols over Ni–Co bimetallic catalyst: effect of ceria promoting

A series of Ni–Co bimetallic catalysts supported on γ-Al2O3 with different Ni/Co mass ratio were prepared by incipient wetness impregnation method for glycerol hydrogenolysis. The catalyst with a Ni/Co mass ratio of 1:3 (denoted as Ni1Co3) exhibited the highest conversion. The performance was compared with that of catalysts promoted by Ce. Moreover, the addition of Ce showed a remarkable promoting effect on the catalytic performance when the cerium content was 2.5 wt%. The physicochemical properties of the supported Ni–Co catalysts were characterized by N2 physisorption, XRD, H2-TPR, NH3-TPD, XPS and TEM. H2-TPR profiles revealed that the coexistence of Ni and Co components on support changed the respective reduction behavior of Ni or Co alone, showing the synergistic effect between Ni and Co species. Compared with the TPR profiles of Ni1Co3, it was clearly observed that the reduction peak of nickel oxide and/or cobalt oxide shifted down to the lower temperature zone gradually with the addition of Ce. It was most probable that the addition of Ce favored the formation of the strong interaction between metal species and ceria. The TEM images showed that the addition of Ce component could improve the dispersion of Ni–Co species on support and inhibited the agglomeration of metal particles during the reaction process, which might be responsible for the enhanced stability.

A metal-honeycomb-type structured catalyst for steam reforming of methane: Effect of preparation condition change on reforming performance

In order to construct a structured steam reforming system, a honeycomb-type nickel-based catalyst was prepared by the combined technique of a sol–gel method and electroless plating on a stainless steel substrate. The type of the reducing agent used in the plating process influenced not only the forming rate of the nickel particles, but also the methane steam reforming (MSR) property of the prepared catalyst. The catalyst prepared using NaBH4 demonstrated a higher performance for MSR than the commercial catalyst, indicating that the catalyst degradation was quite low even under the severe H2O/CH4 condition. The plating time of the nickel plating process also significantly influenced the reforming property. When using the NaBH4 reducing agent, the plating time of about 3min provided the highest performance. The chloride and the sulfate were suitable for the anion species of the nickel reagent used in the plating. Based on the XPS measurement, the electron state of the nickel, which was prepared using the chloride and the sulfate was thought to be a state that is appropriate for the formation of the CHx species and the formation of O* species in the reforming mechanism. Adding a promoter component to the aluminum sol solution was effective for improving the reforming performance. Especially, the reforming property of the catalyst that adds the Ce component was improved. The combination technique developed in this study is a useful and expandable method for preparing the structured catalyst with a high performance on the stainless steel substrate.

Hydrogen Production by Methane Dry Reforming on Supported Nickel Catalysts – Enhanced Stability of the Reforming Process

Dry reforming reaction of CH4 by CO2 was carried out over alumina-supported Ni catalysts. Main products were H2 and CO with small amount of H2O by-production because of reverse water gas shift reaction. The activity was gradually decreased with time on stream by carbon deposition. The addition of Ce component was investigated to improve the catalyst stability. The Ce addition brought decrease of carbon deposition during the reaction. The role of Ce has been considered that an inactive coke formation is significantly suppressed.

Ceria Diffusion and Electrical Properties on Lanthanum Doped Strontium Titanate

The Ce component was coated on the as-prepared La0.3Sr0.7TiO3 (LST) particles. The lattice of LST did not change with the amount of Ce-coating after 1300-1400°C sintering in air but distortion occurred for the Ce-LST sintered at the temperature of 1500°C. The Ce diffusion into LST lattice to affect the lattice distortion was also observed for sintering at 1400°C in activated carbon atmosphere. The 1.5 and 3.0 mol% Ce coatings exhibited slightly lower conductivities than LST without Ce-coating under the 95%Ar+5%H2 atmosphere. The conductivity decreased significantly when the Ce-coating was too high such as 6 mol%. The Ce-LST anode increased the power performance of half-cell compared with the LST anode without Ce-coating. A suitable Ce-coating could behave high power density of the half-cell 3.0 mol% Ce-LST/LSBC. Thus, the Ce coating on LST could enhance the electrical properties of LST/LSBC cell due to the effect of Ce species diffusion into LST structure.

Electrooxidation of methanol on highly active and stable Pt–Sn–Ce/C catalyst for direct methanol fuel cells

Carbon supported Pt–Sn–Ce and Pt–Sn catalysts have been synthesized by a polyol reduction method and compared for methanol oxidation reaction (MOR). X-ray photoelectron spectroscopic (XPS), X-ray diffraction (XRD), and transmission electron microscopic (TEM) analyses reveal the beneficial effects of the Ce component in Pt–Sn–Ce/C for MOR, despite its low content. Electrochemical techniques such as COad stripping, linear scan, and derivative voltammetries along with electrochemical impedance spectroscopy (EIS) were employed to analyze MOR on Pt–Sn–Ce/C and Pt–Sn/C from a mechanistic point of view. Accelerated durability test (ADT) and single cell test of Pt–Sn–Ce/C in comparison to a commercial PtRu/C catalyst demonstrate the superior performance of Pt–Sn–Ce/C from stability and activity points of view.

Catalytic performance and hydrothermal durability of CeO2–V2O5–ZrO2/WO3–TiO2 based NH3-SCR catalysts

Ceria modified V2O5–ZrO2/WO3–TiO2 catalysts with different Ce loading (0, 5, 10 wt%) have been evaluated in the NH3-SCR process before and after hydrothermal aging (750 °C, 10 wt% H2O/air for 12 h). Compared with only Zr containing catalysts, addition of Ce greatly enhances the low temperature activity of the fresh catalyst, but it deactivates obviously after aging. The catalysts were characterized by XRD, XPS, H2-TPR and DRIFTS. The results suggest that not only the enrichment of Ce3+ and the increased redox properties, but also the more active adsorbed nitrates on CeO2 modified catalysts benefit the SCR reaction. The catalyst deactivation after aging is mainly due to the sintering and segregation of CeO2 on the catalysts surface, suggesting the poor hydrothermal stability of the Ce component. However, additional provided NO2 will compensate for the activity loss due to hydrothermal aging and significantly improve the low temperature SCR activity, suggesting a high NO2 sensitivity of the Ce component. Moreover, it was found that a ceria, zirconia containing catalyst exhibits superior SCR activities, with both the fresh and aged 1%V2O5–10%CeO2–10%ZrO2/WO3–TiO2 catalysts showing high NOx conversions (>95%) and selectivity to N2 (>98%) in a wide temperature range of 200–500 °C, at a space velocity of 120 000 h−1 in a simulated exhaust containing 500 ppm NOx (NO2/NO = 1) and 5% H2O.

Yeast axial-element protein, Red1, binds SUMO chains to promote meiotic interhomologue recombination and chromosome synapsis

The synaptonemal complex (SC) is a tripartite protein structure consisting of two parallel axial elements (AEs) and a central region. During meiosis, the SC connects paired homologous chromosomes, promoting interhomologue (IH) recombination. Here, we report that, like the CE component Zip1, Saccharomyces cerevisiae axial-element structural protein, Red1, can bind small ubiquitin-like modifier (SUMO) polymeric chains. The Red1–SUMO chain interaction is dispensable for the initiation of meiotic DNA recombination, but it is essential for Tel1- and Mec1-dependent Hop1 phosphorylation, which ensures IH recombination by preventing the inter-sister chromatid DNA repair pathway. Our results also indicate that Red1 and Zip1 may directly sandwich the SUMO chains to mediate SC assembly. We suggest that Red1 and SUMO chains function together to couple homologous recombination and Mec1–Tel1 kinase activation with chromosome synapsis during yeast meiosis.

Thickness-Dependent Electronic Structure of Intermetallic CeCo2 Nanothin Films Studied by X-ray Absorption Spectroscopy

We report the electronic structure study of intermetallic CeCo2 nanothin films of various thicknesses by X-ray absorption near-edge structure (XANES) spectroscopy at Ce L3-, Co K-, and L2,3-edges. The Ce L3-edge absorption spectra reveal that the contribution of tetravalent Ce component increases with the film thickness, and all investigated nanothin films exhibit intermediate valence nature. Variation of the spectral intensities observed at the Co K-edge threshold implies modification in the Co 3d states and the enhancement of 3d-4f-5d hybridization. The Co 3d and Ce 4f occupation numbers were estimated from these spectroscopic results. The present study brings out how the surface-to-bulk ratio and the charge transfer between Ce and Co ions affect the electronic structure of nanothin films.

Raman Spectroscopic Study on the Structure in the Surface and the Bulk Shell of CexPr1-xO2-δ Mixed Oxides

The difference between the surface and the bulk shell of Ce(x)Pr(1-x)O(2-delta) mixed oxides was studied by Raman spectroscopy with four different excitation lasers. Two Raman peaks appear at 465 and 570 cm(-1) under all of the four lasers. The former is attributed to the Raman active F(2g) mode of CeO2, while the latter is attributed to oxygen vacancy. On the basis of the fact that the laser with shorter wavelength is closer to the electronic adsorption of samples, it is found that the Raman information detected by excitation laser with shorter wavelength is more sensitive to the surface region of samples. An inflection is observed in the relationship of the value I570/I465 to the Ce content in Ce(x)Pr(1-x)O(2-delta). With the increase in the wavelength of excitation laser, the Ce content corresponding to the inflection decreases. Combined with the surface concentration obtained by XPS, it can be deduced that the composition of Ce(x)Pr(1-x)O(2-delta) mixed oxide particles in the surface region and the bulk shell are different, the former is enrichment of Pr component and the latter is enrichment of Ce component. The thickness of the surface layer with rich Pr component decreases with the increase in the Ce content.

Development, verification, and validation of a parametric cervical spine injury prediction model

Development, verification, and validation of a parametric cervical spine injury prediction model