Ce1 xZrxO2 Research Articles

Nickel-Based Ni–Ce1–xZrxO2 Catalysts Prepared by the Pechini Method for CO2 Methanation

Nickel-Based Ni–Ce1–xZrxO2 Catalysts Prepared by the Pechini Method for CO2 Methanation

Preparing a Zr-Doped CeO2 Nanorod to Improve the Catalytic Performance of the Ni-Based Catalyst for Dry Reforming of Methane by Enhancing Oxygen Supply

Dry reforming of methane (DRM) is a feasible route to realize the resource utilization of greenhouse gases CO2 and CH4. The Ni-based catalyst is recognized as a potential catalyst for the industrialization of DRM. However, catalyst deactivation caused by carbon deposition is a challenge. Providing enough active oxygen species to accelerate the reaction between CHx (x = 0–3) and oxygen species is the key to inhibit coking. Ni-based catalysts loaded on a Zr-doped Ce1–xZrxO2 nanorod were prepared by a one-step hydrothermal method. Benefiting from lattice distortion caused by Zr doping, the Ni/Ce0.95Zr0.05O2 catalyst showed the best catalytic activity and stability. Compared with the Ni/CeO2 catalyst, the activation energy of CH4 and CO2 decreased by 20 and 22%, respectively. The 100 h stability test showed that the Ni/CeO2 catalyst was 10% deactivated, and the carbon deposition rate was 0.82 mgc·gcat·–1·h–1, while the Ni/Ce0.95Zr0.05O2 catalyst showed excellent stability. The extensive characterization of the catalysts indicated that the enhancement in DRM activity upon Zr doping could be attributed to the increase of oxygen vacancies and the improvement in lattice oxygen mobility. However, excessive Zr doping formed ZrO2 covering oxygen vacancies, resulting in decreased catalytic activity and stability. The results showed that lattice oxygen over the Ni/Ce0.95Zr0.05O2 catalyst not only participated in the oxidation of carbon intermediates but also contributed to the deep dissociation of CH4 over Ni through an oxygen-mediated dissociation pathway. Similarly, the redox cycle on the oxygen vacancies was also important for enhancing the CO2 adsorption activation to relieve the coking of the catalyst.

Synthesis of CeO2 and Zr-Doped CeO2 (Ce1−xZrxO2) Catalyst by Green Synthesis for Soot Oxidation Activity

Synthesis of CeO2 and Zr-Doped CeO2 (Ce1−xZrxO2) Catalyst by Green Synthesis for Soot Oxidation Activity

Insights into the Oxidative Dehydrogenation of Ethylbenzene with CO2 Catalyzed by the Ordered Mesoporous V2O5–Ce0.5Zr0.5O2–Al2O3

The ordered mesoporous V2O5 (9 wt %)–Ce1–xZrxO2 (7 wt %)–Al2O3 (VCA-x, x = 0, 0.5, and 1) was successfully synthesized by combining the hydrothermal and the modified evaporation-induced self-assemb...

Epitaxial growth of gradient Ce1−xZrxO2 buffer layer for YBa2Cu3O7−δ coated conductors

A Ce1−xZrxO2 (CZO) buffer layer architecture with gradient change of Zr-doped concentration along the thickness direction of CZO films was fabricated on rolling assisted biaxially textured NiW metallic substrate by sol–gel method. With the change of Zr-doped concentration, the lattice parameters of CZO of each layer also show a gradient variation. It can not only effectively reduce interfacial stress between the buffer layer and the metallic substrate, but also improve the surface quality of the CZO film. In this work, an epitaxial growth relationship and dense microstructure are discerned in the gradient CZO film, as determined by the comprehensive analysis of X-ray diffraction and scanning electron microscopy. YBCO superconductor films have been deposited on the gradient CZO buffer layers to evaluate the quality of such a gradient buffer layer. TEM measurements reveal that NiW/CZO/YBCO coated conductor (CC) with excellent epitaxial growth relationship is achieved. The superconducting transition temperature of the sample is 90 K and the critical current density Jc reaches 1.9 MA/cm2.

Structure-property correlations for the surfactant-free faceted nanocrystals of Ce1−xZrxO2 and their bulk ceramics

Faceted nanocrystals involving Ce1−xZrxO2 (CZ) system bound by (101) and (l10) facets were synthesized via co-precipitation route. The novelty of this process relies on the fact that the synthesis did not involve any surfactant/ligand for morphology control (for all the CZ compositions) and the nanocrystals retained their shapes at high temperatures (> 800 °C). Catalytic and photocatalytic degradation properties were suitably examined for the CZ nanocrystals; substantial (∼90%) degradation of the methylene blue dye was observed only in 60 min of visible light irradiation. Ce1−xZrxO2 ceramics with near-theoretical density (>98%) obtained at 1580 °C (for 2 h) confirmed excellent sinterability for the synthesized CZ nanocrystalline powders. The ionic conductivities of the doped-ceria ceramics increased with temperature and frequency. A maximum conductivity of ∼2 × 10−3 S/cm was measured at 600 °C at 1 MHz for Ce0.4Zr0.6O2 ceramic; previous works obtained similar data at 900 °C or beyond for the same composition.

A compositional gradient Ce1−xZrxO2 buffer architecture for producing high-performance YBCO film

In this work, YBCO films were epitaxially grown on Ce1−xZrxO2 (CZO) buffered yttria stabilized zirconia (YSZ) single crystal substrates through a fluorine-free sol-gel process. The influence of two different CZO buffer architectures on the microstructure and superconducting properties of YBCO films was investigated. According to XRD results in combination with (S)TEM analysis, it was confirmed that YBCO film grown on the gradient CZO buffer layer (CZO-G) exhibits better in-plane and out-of-plane texture than YBCO film deposited on the uniform CZO buffer layer (CZO-20). And besides, the superconducting performances especially the current-carrying capacity under magnetic field of the former was much higher than that of the latter, which means that the enhanced flux pinning force will be presented in YBCO film on CZO-G buffer layer. The maximum pinning force of the YBCO film grown on CZO-G buffer architecture is up to 17.67 GN/m3 @ 65 K. HR-STEM analysis shows that the stacking faults within YBCO matrix gave rise to the considerable nanoscale lattice-strains which may suppress the formation of Copper pairs and produce nanoscale non-superconducting regions served as pinning centers to significantly improve the flux pinning performance of YBCO film. Given the above, it has been implied that high-performance YBCO coated conductor can be developed by using a compositional gradient Ce1−xZrxO2 films as buffer architecture.

Density Functional Analysis of Fluorite-Structured (Ce, Zr)O2/CeO2 Interfaces

The structures and properties of Ce1–xZrxO2 (x = 0–1) solid solutions, selected Ce1–xZrxO2 surfaces, and Ce1–xZrxO2/CeO2 interfaces were computed within the framework of density functional theory corrected for strong electron correlation (DFT+U). The calculated Debye temperature increases steadily with Zr content in (Ce, Zr)O2 phases, indicating a significant rise in microhardness from CeO2 to ZrO2, without appreciable loss in ductility as the interfacial stoichiometry changes. Surface energy calculations for the low-index CeO2(111) and (110) surfaces show limited sensitivity to strong 4f-electron correlation. The fracture energy of Ce1–xZrxO2(111)/CeO2(111) increases markedly with Zr content, with a significant decrease in energy for thicker Ce1–xZrxO2 films. These findings suggest the crucial role of Zr acting as a binder at the Ce1–xZrxO2/CeO2 interfaces, due to the more covalent character of Zr–O bonds compared to Ce–O. The impact of surface relaxation upon interface cracking was assessed and found to...

Structural and Redox Properties of Ce1–xZrxO2−δand Ce0.8Zr0.15RE0.05O2−δ(RE: La, Nd, Pr, Y) Solids Studied by High Temperaturein SituRaman Spectroscopy

In situ Raman spectroscopy at temperatures up to 450 °C is used to probe the structural and redox properties of Ce1–xZrxO2−δ solids (x = 0–0.8) prepared by the citrate sol–gel and coprecipitation with urea methods. The anionic sublattice structure of the solids is dependent on the preparation route. The composition effects exhibited by the Raman spectra are adequate for characterizing the phases present and/or eventual phase segregations. For x = 0.5 the pseudocubic t″ phase occurs for the solid prepared by the citrate sol–gel method, while phase segregation (cubic, tetragonal) is evidenced for the corresponding material prepared by the coprecipitation with urea method. A larger extent of defects and interstitial O atoms is evidenced for the materials prepared by the citrate sol–gel method. The well-known “defect” (“D”) band around 600 cm–1 for CeO2 as well as for Ce1–xZrxO2−δ consists of at least two components: “D1” above 600 cm–1 and “D2” below 600 cm–1. Doping of Ce0.8Zr0.2O2−δ with rare earth cations...

Oxidation and Reduction Reaction Kinetics of Mixed Cerium Zirconium Oxides

The oxidation and reduction of mixed cerium zirconium oxides, Ce1–xZrxO2, with x varied in the range 0–0.3 in steps of 0.05, in a low-pressure oxygen atmosphere were experimentally investigated. The experiments utilized a novel method developed by the authors, in which the samples are reduced and oxidized in a sealed vacuum chamber by irradiating them with a xenon arc lamp. The changes in pressure due to the release or consumption of oxygen are used to quantify the extent and rates of the reactions. The system can achieve heating rates in excess of 100 °C s–1, which is hundreds of times faster than is possible with a thermobalance. In addition, the gas phase transport is very rapid as it is driven by pressure gradients. The combined high heating rate and fast gas phase transport offers unique conditions in which to measure the actual kinetics of the reactions. The oxidation kinetics showed a strong dependence on the amount of Zr4+ in the samples, where the rate of oxidation decreased with increasing Zr4+ ...

Ionic conductivity of YSZ/CZO multilayers with variable lattice mismatch

Tensile strain in yttria-stabilized zirconia (YSZ) exhibited little impact on oxygen ion conductivity in multilayers composed of YSZ and Ce1−xZrxO2 (CZO).

Insights into support effects on Ce-Zr-O mixed oxide-supported gold catalysts in CO oxidation

Au/Ce1–xZrxO2 catalysts (x = 0–0.8) were prepared by a deposition-precipitation method using Ce1–xZrxO2 nanoparticles as supports with variable Ce and Zr contents. Their structures were characterized by complimentary means such as X-ray diffraction, Raman, scanning transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). These Au catalysts possessed similar sizes and crystalline phases of Ce1–xZrxO2 supports as well as similar sizes and oxidation states of Au nanoparticles. The oxidation state of Au nanoparticles was dominated by Au0 especially in CO oxidation. Their activities were examined in CO oxidation at different temperatures in the range of 303–333 K. The CO oxidation rates normalized per Au atoms increased with the increasing Ce contents, and reached the maximum value over Au/CeO2. Such change was in parallel with the change in the oxygen storage capacity values, i.e. the amounts of active oxygen species on Au/Ce1–xZrxO2 catalysts. The excellent correlation between the two properties of the catalysts suggests that the intrinsic support effects on the CO oxidation rates is related to the effects on the adsorption and activation of O2 on Au/Ce1–xZrxO2 catalysts. Such understanding on the support effects may be useful for designing more active Au catalysts, for example, by tuning the redox properties of oxide supports.

Control of Heterogeneity in Nanostructured Ce1–xZrxO2 Binary Oxides for Enhanced Thermal Stability and Water Splitting Activity

To enhance the kinetics and overall production of renewable H2 fuel through a two-step thermochemical water splitting cycle, three-dimensionally ordered macroporous (3DOM) Ce1–xZrxO2 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) materials were synthesized via colloidal crystal templating. The interconnected macropore system in these materials facilitates ready access to a relatively large active surface area (tens of m2/g), which benefits the heterogeneous reaction. Two different synthetic routes were employed, a methanolic solution of metal chloride salts, and a Pechini-type gel. These routes produced significant differences in the compositional homogeneity of the resulting mixed oxide. 3DOM Ce1–xZrxO2 synthesized with methanolic precursors had distinct CeO2- and ZrO2-rich domains, whereas the Pechini samples contained only a single phase. At higher Zr content, heterogeneities present in the samples from the methanolic synthesis increased both the productivity and peak production rates of H2 compared to the single-phase Pechini samples. Increasing the content of Zr in the mixed oxides also stabilized the 3DOM structure at 825 °C. All 3DOM Ce1–xZrxO2 materials exhibited significantly faster kinetics during water splitting compared to sintered, micrometer-sized CeO2 granules. Pechini-derived 3DOM Ce0.8Zr0.2O2 maximized both H2 production and peak production rates, offering better catalytic performance over 3DOM CeO2.

Humidity Related Low Temperature Conductivity Hysteresis of Ce1–xZrxO2 (0 ≤ x ≤ 1) Ceramics. Structural Disorder Relationship

AbstractIon‐electron mixed conductivity of the Ce1–xZrxO2 (0 < x < 1) series, prepared by solid‐state reaction, has been measured as a function of temperature, pO2 and pH2O relative pressures. The structural analysis of this series shows the formation of monoclinic, tetragonal, and cubic phases as the Ce content increases. The temperature used in samples preparation, 1,923 K, favors at intermediate compositions the homogeneous Ce and Zr mixing in the metastable tetragonal t′ phase. The variation of conductivity with the relative oxygen pressure indicates that electronic contribution increases, becoming preponderant, as the Ce‐content increases. The modifications in conductivity observed in Ce‐rich samples have been ascribed to the enhancement of the electronic contribution at the grain‐boundary of ceramics. The differences observed at low temperatures in electronic dc‐conductivity of Ce‐rich samples during heating and cooling treatments, have been ascribed to the incorporation of water as hydroxide defects at the grain boundary and interior of the particles. The surface hydroxylation is maximal in samples with improved OSC capacity, decreasing drastically in samples heated at 740 K. Finally, the potential application of prepared materials in intermediate temperature solid oxide fuel cells (SOFC) is discussed.

A novel and simple route to catalysts with a high oxygen storage capacity: the direct room-temperature synthesis of CeO2–ZrO2solid solutions

High-energy mechanical alloying of pure CeO2 and ZrO2 at room temperature results in the formation of a single phase Ce1–xZrxO2 fluorite structured solid solution in all the examined composition ranges; the compounds are characterized by a high oxygen storage capacity and an excellent reducibility.