Stability of fluorite-type La2Ce2O7 under extreme conditions

Zhang, F.X.; Tracy, Cameron L.; Lang, Maik; Ewing, Rodney C.

doi:10.1016/j.jallcom.2016.03.002

Cited by 52 publications

(33 citation statements)

References 46 publications

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“…Therefore, the Raman peak of the La 2 Ce 2 O 7 ‐based samples at ≈ 445 cm –1 is assigned to the F 2g mode of the defective cubic fluorite phase, and the band at ≈ 575 cm –1 is assigned to the surface oxygen vacancies originated from the incorporation of La 3+ into CeO 2 lattice. In detail, to maintain the overall charge, oxygen vacancies are formed, which can dissociatively adsorb O 2 molecules and generate surface mobile oxygen species , . To confirm this, the Raman spectra in the region of 950–1200 cm –1 are enlarged for the samples and shown in Figure b.…”

Section: Resultsmentioning

confidence: 87%

“…However, for poorly crystallized CeO 2 possessing a lot of surface and bulk defects, another peak at ≈ 600 cm –1 corresponding to surface oxygen vacancies can also be observed , . In addition, the doping of La 3+ into CeO 2 lattice can shift the F 2g peak to a lower wavenumber , . Therefore, the Raman peak of the La 2 Ce 2 O 7 ‐based samples at ≈ 445 cm –1 is assigned to the F 2g mode of the defective cubic fluorite phase, and the band at ≈ 575 cm –1 is assigned to the surface oxygen vacancies originated from the incorporation of La 3+ into CeO 2 lattice.…”

Section: Resultsmentioning

confidence: 99%

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Optimizing the Reaction Performance of La₂Ce₂O₇‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Zhang

Liu

et al. 2018

Eur J Inorg Chem

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To optimize the reaction performance of La2Ce2O7 for OCM, catalysts with varied La/Ce molar ratios and doped by Ca additive have been synthesized and characterized by different techniques. It is discovered that a La2Ce2O7 compound having a disordered cubic defective fluorite phase is predominantly formed in all the samples. Varying the La/Ce ratio influences the fine crystalline structure of the catalysts. As a result, the abundance of the surface facile oxygen and alkaline sites increase by increasing the La/Ce ratio. Moreover, the Ca additive exists on the surface of Ca0.5La2Ce2O7 and Ca0.5La1.5Ce2O7 as dispersed CaCO3, which covers the active sites and is harmful to the OCM reaction. However, for La2Ce1.5Ca0.5O7, the major part of the Ca additive has entered into the lattice of La2Ce2O7 phase as Ca2+ cations, thus creating more oxygen vacancies and improving the surface alkalinity of the catalyst, which is favorable to the OCM reaction. Both the active surface oxygen and alkaline sites are vital for OCM, and their synergism determines the reactivity. By increasing La/Ce ratio and doping Ca2+ into La2Ce2O7 lattice, the quantities of both kinds of active sites can be significantly improved, thus obtaining catalysts with much improved reaction performance. La2Ce1.5Ca0.5O7 owns the largest amount of both types of active sites, hence depicting the best reaction performance, over which the highest C2 yield of 22.5 % can be achieved even at 750 °C.

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Section: Resultsmentioning

confidence: 87%

Section: Resultsmentioning

confidence: 99%

Optimizing the Reaction Performance of La₂Ce₂O₇‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Zhang

Liu

et al. 2018

Eur J Inorg Chem

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“…Table 6 summarizes linear thermal expansion coefficients (α) for various A 2 B 2 O 7 compounds in the 400 to 1000 • C range. It should be noted that La 2 Ce 2 O 7 , unlike the other oxides in Table 6, is not a pyrochlore and instead adopts a disordered fluorite type structure, where the cations are randomly distributed in the cation sublattice [243][244][245][246].…”

Section: Pyrochlore-and Fluorite-related Structuresmentioning

confidence: 99%

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

2018

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This review paper focuses on the phenomenon of thermochemical expansion of two specific categories of conducting ceramics: Proton Conducting Ceramics (PCC) and Mixed Ionic-Electronic Conductors (MIEC). The theory of thermal expansion of ceramics is underlined from microscopic to macroscopic points of view while the chemical expansion is explained based on crystallography and defect chemistry. Modelling methods are used to predict the thermochemical expansion of PCCs and MIECs with two examples: hydration of barium zirconate (BaZr1−xYxO3−δ) and oxidation/reduction of La1−xSrxCo0.2Fe0.8O3−δ. While it is unusual for a review paper, we conducted experiments to evaluate the influence of the heating rate in determining expansion coefficients experimentally. This was motivated by the discrepancy of some values in literature. The conclusions are that the heating rate has little to no effect on the obtained values. Models for the expansion coefficients of a composite material are presented and include the effect of porosity. A set of data comprising thermal and chemical expansion coefficients has been gathered from the literature and presented here divided into two groups: protonic electrolytes and mixed ionic-electronic conductors. Finally, the methods of mitigation of the thermal mismatch problem are discussed.

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“…Several authors report good stability of the cubic-type ionic conductors under WGS experimental conditions. Zhang et al [48] studied the stability of fluorite-type La 2 Ce 2 O 7 under wet conditions and found that a pressure of 1 GPa is necessary to modify the structure. Moreover, the introduction of Zr was reported to enhance the stability of the ionic conductors [49,50].…”

Section: Kinetics Study On Structured Catalystmentioning

confidence: 99%

Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction

et al. 2018

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A kinetic study of the water gas shift (WGS) reaction has been carried out on a Pt-based catalyst promoted by a Zr-based proton conductor. The investigation was first performed on powders with diluted feed mixtures and then extended to more severe and representative conditions by using a catalyst coated metallic micromonolith. Temperature measurements reveal that isothermal conditions were obtained along the micromonolith during the tested conditions. In addition, the very thin catalytic layer allows for the discarding of intraporous resistances, providing excellent conditions to analyse the kinetics of the WGS reaction under the integral regime. The proposed rate expression accounts for independence on CO concentration, an inhibiting effect of H2 and a promoting effect of H2O; kinetic orders on CO and H2 are in line with those reported in the literature for the Pt-based catalyst. Instead, the obtained reaction order of water (0.36) is significantly lower than that reported for unpromoted catalysts (typically 0.77–1.10) in good agreement with the proposed water-enhancer effect of the proton conductor on the rate-limiting step. Metallic micromonoliths turn out to be a powerful tool for the kinetic investigation, due to the absence of mass and heat transport limitations and represent a strategy for the intensification of the WGS unit for future applications of fuel processors in small mobile devices.

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Stability of fluorite-type La2Ce2O7 under extreme conditions

Cited by 52 publications

References 46 publications

Optimizing the Reaction Performance of La₂Ce₂O₇‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Optimizing the Reaction Performance of La₂Ce₂O₇‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction

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Stability of fluorite-type La2Ce2O7 under extreme conditions

Cited by 52 publications

References 46 publications

Optimizing the Reaction Performance of La2Ce2O7‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Optimizing the Reaction Performance of La2Ce2O7‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

Metal Micro-Monoliths for the Kinetic Study and the Intensification of the Water Gas Shift Reaction

Contact Info

Product

Resources

About

Optimizing the Reaction Performance of La₂Ce₂O₇‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations

Optimizing the Reaction Performance of La₂Ce₂O₇‐Based Catalysts for Oxidative Coupling of Methane (OCM) at Lower Temperature by Lattice Doping with Ca Cations