XPS investigation of surface oxidation and reduction in nanocrystalline CexLa1 − xO2 − y

Trudeau, Michel; Tschöpe, Andreas; Ying, Jackie Y.

doi:10.1002/sia.740230405

Cited by 90 publications

(45 citation statements)

References 18 publications

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“…Component O II with BE » 531.0-532.0 eV most likely belongs to defect-oxide or hydroxyl-like groups [36,37]. The major peak component O I with BE » 528.9-529.7 eV is characteristic of lattice oxygen in Ce x Mn 1)x O 2)y [37,42,43] and is close to the value of 529.4 eV reported by Trudeau et al [44] to be reminiscent of CeO 2 oxygen. Because of the overwhelming proportion of Ce +4 with respect to Ce +3 , and binding energy shifts between MnO 2 and CeO 2 less than 1 eV [37], no attempt was made to finely resolve the O II peak contributions.…”

Section: Catalyst Behaviour In Fresh Statesupporting

confidence: 74%

Catalytic wet oxidation: micro–meso–macro methodology from catalyst synthesis to reactor design

Larachi

2005

Top Catal

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Compared to alternative mature wet oxidation technologies that have tremendously proliferated in industry, heterogeneously mediated catalytic wet oxidation (CWO) has achieved, thus far, poor commercial penetration. The two factors that are likely responsible for this situation are (i) the lack of efficient and robust catalysts that pass with success the acid-test for commercial exploitation remote from the aseptic academic conditions, (ii) and the lack of a comprehensive reactor design framework and methodology for scale-up, reactor selection and operation inherent to the multiphase nature of the CWO reactors. This synthetic review summarizes the recent research and development work conducted at Laval University on the CWO from both the perspectives of catalyst development and testing, and multiphase reactor simulations and selection. Specific emphasis was put, on the one hand, on the development brought to some manganese oxide-ceria composites against deactivation, and on the other hand, on the formulation of multidimensional unsteady-steady non-isothermal mass-energy transport/reaction models, embedding catalyst deactivation or not, for trickle bed reactors, packed bubble column reactors, three-phase fluidized beds and slurry bubble columns. A micro-Meso-macro scale methodology was adopted from the materials synthesis up to reactor selection in which the catalyst performance (conversion, selectivity, and deactivation), the intrinsic chemical kinetics, the fluid phase thermodynamics, the pellet scale transport, and the reactor scale physical phenomena (heat, mass transport and hydrodynamics) were integrated. As a result, several aspects relevant to reactor behaviour such as solvent evaporation due to CWO reaction exothermic effects, catalyst partial wetting and catalyst deactivation, and back-mixing effects were covered, and recommendations were formulated. NomenclatureA reactor cross-sectional area, m 2 C concentration, mol/m 3 or g/L C p isobaric specific heat capacity, J/kg/K D eff effective diffusivity, m 2 /s E activation energy, kJ/mol E z axial dispersion coefficient, m 2 /s H Henry constant, or bed height, m H j hidden layer transfer function, k rate constants, mol/min/kg cat. (equations (1)-Arrhenius pre-exponential factor, mol/min/kg cat. equation (9) ka ll liquid-liquid volumetric mass transfer coefficient. s )1 k l a gas-liquid volumetric mass transfer coefficient, s )1 ka sls liquid-solid mass transfer coefficient, s )1 K adsorption equilibrium constant, m 3 /mol L v water enthalpy of vaporization, J/mol [m c ] catalyst loading, kg cat./m 3 P pressure, atm r spherical co-ordinate at pellet scale, m r c chemical reaction rate, mol/m 3 /s S neural network output S M mineralization selectivity t time, min T absolute temperature, K U i neural network inputs U superficial velocity, m/s v molar volume, cm 3 /mol [W] carbonaceous deposit carbon concentration, mol C/m 3 solution x dissolved mole fraction X chemical conversion y gas mole fraction z longitudinal co-ordinate, mGreek a deactivation function, DH...

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Section: Catalyst Behaviour In Fresh Statesupporting

confidence: 74%

Catalytic wet oxidation: micro–meso–macro methodology from catalyst synthesis to reactor design

Larachi

2005

Top Catal

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“…For instance, a value of 7.97 µmol/m 2 was estimated by Bernal et al [50] which implies that a surface composition of roughly CeO 0.8 was achieved during H 2 -TPR. A similar enhanced reduction was observed in ceria based nanocrystalline porous materials using photoelectron spectroscopy measurements, combined with in situ oxidation-reduction treatments [51], or thermogravimetric analysis [52]. A major drawback of the TPR-measurements is the non-equilibrium condition with respect to the oxygen chemical potential.…”

Section: Interfaces and Excess Oxygen Deficiencymentioning

confidence: 75%

Interface Defect Chemistry and Effective Conductivity in Polycrystalline Cerium Oxide

Tschöpe

2005

J Electroceram

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Polycrystalline cerium oxide exhibits increasing electronic and decreasing ionic conductivity upon reduction of the grain size. In the present study, the origin of this effect was examined. Temperature-programmed reduction (TPR) and oxygen titration measurements on nanocrystalline cerium oxide revealed a large excess oxygen deficiency associated with the surface. Using a two-phase model for the combined system of the bulk phase in equilibrium with a surface layer, this enhanced oxygen deficiency could be explained by a reduced binding energy of surface oxygen ions in agreement with results from atomistic computer simulations. The model also revealed that this segregation of oxygen vacancies is the origin of an intrinsic space charge potential. Translating this effect to polycrystalline cerium oxide and taking into account the segregation of dopants and the accumulation/depletion of charge carriers, it was possible to model the grain size dependence of electrical conductivity and thermopower of polycrystalline cerium oxide. A straightforward 1-dimensional numerical model and a change from Boltzmann to Fermi-Dirac statistics allowed to calculate the conductivity of heavily doped polycrystalline cerium oxide for grain sizes in the range of 5-10,000 nm and acceptor concentrations up to 20%. Using this approximation, the effect of grain size on mixed ionic/electronic conductivity and the electrolytic domain boundary was investigated.

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“…The intense satellite structure observed for the Ce 3d peak of sample 4 was characterized by three main 3d 5/2 features centered at 883.0 eV (v), 889.5 eV (v²), and 899.0 eV (v-), and three main 3d 3/2 peaks centered at 901.4 eV (u), 908.1 eV (u²), and 917.1 eV (u-). The origin of this band shape, typical of cerium(IV) oxide, [9,13,14,17,32,59,60] has been ascribed to the hy- u bands (18.4 eV), together with the peak positions and the separation between the O 1s signal and the v Ce 3d band (»353.4 eV), provided unambiguous confirmation of the presence of cerium(IV) oxide. [9,30] On the other hand, the Ce 3d photopeak for sample 1 (Fig.…”

Section: Surface and In-depth Composition: Xps And Sims Analysesmentioning

confidence: 91%

“…Such a band shape closely matched the one expected for cerium(III) oxide. [13,17,60] On going from film 1 to film 4, i.e., on increasing the substrate temperature, an intensity increase of bands v, v², v-, u, u², and u-at the expense of v 0 , v 1 , u 0 , and u 1 (Fig. 4) indicated a gradual increase of the Ce IV /Ce III ratio.…”

Section: Surface and In-depth Composition: Xps And Sims Analysesmentioning

confidence: 95%

“…Finally, the Ce 3d photopeak for film 9 closely resembled that observed for Ce IV . [9,13,14,17,32,59,60] Altogether, such phenomena indicate that, under the adopted conditions, nanosized defective ceria (CeO 2±x ) films, the defect content of which can be tailored as a function of the processing conditions, have been obtained. [62±65] The relative amounts of Ce IV and Ce III were estimated by the ratio of the u-satellite to the total Ce 3d integral area, [7] since the u-intensity is directly related to the Ce IV concentration.…”

Section: Surface and In-depth Composition: Xps And Sims Analysesmentioning

confidence: 99%

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Nucleation and Growth of Nanophasic CeO₂ Thin Films by Plasma‐Enhanced CVD

Barreca¹,

Gasparotto

Tondello

et al. 2003

Chemical Vapor Deposition

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Nanophasic CeO 2 -based thin films were grown at low temperatures on SiO 2 and Si(100) by plasma-enhanced (PE) CVD from a Ce IV b-diketonate first generation precursor. Film depositions were carried out in low-pressure Ar±O 2 plasmas at temperatures between 150 C and 300 C. The film microstructure was investigated by glancing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM), while the surface and in-depth chemical composition was studied by X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS), respectively. Optical properties were analyzed by UV-vis optical absorption. Nanostructured CeO 2 -based films, with crystal size less than 6 nm and a controllable Ce IV /Ce III ratio, were obtained at temperatures even lower than that required for precursor vaporization (170 C). In particular, TEM analyses showed an island growth mode and different microstructural features as a function of the substrate used.

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XPS investigation of surface oxidation and reduction in nanocrystalline Ce_xLa_{1 − x}O_{2 − y}

Cited by 90 publications

References 18 publications

Catalytic wet oxidation: micro–meso–macro methodology from catalyst synthesis to reactor design

Catalytic wet oxidation: micro–meso–macro methodology from catalyst synthesis to reactor design

Interface Defect Chemistry and Effective Conductivity in Polycrystalline Cerium Oxide

Nucleation and Growth of Nanophasic CeO₂ Thin Films by Plasma‐Enhanced CVD

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XPS investigation of surface oxidation and reduction in nanocrystalline CexLa1 − xO2 − y

Cited by 90 publications

References 18 publications

Catalytic wet oxidation: micro–meso–macro methodology from catalyst synthesis to reactor design

Catalytic wet oxidation: micro–meso–macro methodology from catalyst synthesis to reactor design

Interface Defect Chemistry and Effective Conductivity in Polycrystalline Cerium Oxide

Nucleation and Growth of Nanophasic CeO2 Thin Films by Plasma‐Enhanced CVD

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Product

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XPS investigation of surface oxidation and reduction in nanocrystalline Ce_xLa_{1 − x}O_{2 − y}

Nucleation and Growth of Nanophasic CeO₂ Thin Films by Plasma‐Enhanced CVD