Search results for " oxidation"
showing 10 items of 675 documents
Co3O4 particles grown over nanocrystalline CeO2: influence of precipitation agents and calcination temperature on the catalytic activity for methane …
2015
Crystalline cobalt oxides were prepared by a precipitation method using three different precipitation agents, (NH4)(2)CO3, Na2CO3 and CO(NH2)(2). Cobalt oxide nanoparticles corresponding to a Co3O4 loading of 30 wt% were also deposited over high-surface area nanocrystalline ceria by the same precipitation agents. The effect of calcination temperature, 350 or 650 degrees C, on the morphological and structural properties was evaluated. Characterization by BET, XRD, SEM, TEM, Raman spectroscopy, H-2-TPR, XPS and NH3-TPD was performed and the catalytic properties were explored in the methane oxidation reaction. The nature of the precipitation agent strongly influenced the textural properties of…
Supported Au catalysts for low-temperature abatement of propene and toluene, as model VOCs: Support effect
2011
3-4 Ousmane, M. Liotta, L. F. Di Carlo, G. Pantaleo, G. Venezia, A. M. Deganello, G. Retailleau, L. Boreave, A. Giroir-Fendler, A.; In this work gold nanoparticles supported over ceria (Au/CeO2), titania (Au/TiO2), alumina (Au/Al2O3) and Ce doped alumina (Au/7.5Ce/Al2O3) were prepared by deposition-precipitation (DP) method with NaOH solution and characterized by BET, XRD, H-2-TPR, TEM and XPS techniques. The catalytic activity was evaluated in the total oxidation of propene and toluene, chosen as model VOC molecules. The attention was focused on the catalyst stability. To this aim, three consecutive catalytic cycles in propene and toluene oxidation were performed for each catalyst. The act…
Oxygen defects: The key parameter controlling the activity and selectivity of mesoporous copper-doped ceria for the total oxidation of naphthalene
2012
Mesoporous CeO2 modified by the addition of copper has shown high efficiency for the total oxidation of naphthalene. High activity and 100% selectivity to carbon dioxide throughout the whole range of temperatures studied were achieved for copper loadings of 3.6% and lower. The catalytic behaviour has been related to the concentration of surface oxygen defects. A clear correlation between the concentration of surface oxygen defects (determined by XPS and DRIFTS) and the catalytic performance has been identified. Catalytic activity increased as copper was incorporated into the ceria up to 3.6%. In this range of copper content the copper was incorporated into the cubic fluorite lattice of CeO2…
A Raman spectroscopy study of the oxidation processes in synthetic chromite FeCr2O4
2020
Abstract A crystal of synthetic chromite FeCr2O4 has been annealed in air at 700 °C for 50 days at room pressure in order to study physical-chemical changes. After the annealing treatment, Scanning Electron Microscopy (SEM) images of the polished surface of the sample showed areas of different composition. Detailed Raman mapping revealed that the annealed chromite undergoes an oxidation process, proceeding inwards from the outer surface and leading to the transformation of chromite to magnetite, and ultimately to hematite. The oxidation process also leads to the formation of trellis-like lines, arguably via stress-related mechanisms associated with the phase transformation and consequent vo…
Electronic Properties of Thermal Oxides on Ti and Their Influence on Impedance and Photoelectrochemical Behavior of TiO2 Nanotubes
2017
Thermal oxidation of titaniumwas carried out at 350◦C, 450◦C, and 550◦C for 2 h or 12 h.X-rayDiffraction and Raman Spectroscopy suggest that the thermal oxides are scarcely crystallinewhen the annealing temperature is low, while both anatase and rutile are present for high annealing temperature and time. Photoelectrochemical measurements allowed estimation of a bandgap decreasing from 3.35 eV to 3.15 eV with increasing annealing temperature. The impedance spectra confirmed the formation of n-type semiconductors, with an impedance strongly decreasing on going from a reverse bias toward a forward bias regime. TiO2 nanotubes grown by anodizing Ti in NH4F and water containing ethylene glycol so…
Catalytic oxidation of n-hexane promoted by Ce1-xCuxO2 catalysts prepared by one-step polymeric precursor method
2013
Abstract Ceria-supported copper catalysts (Ce1−xCuxO2, with x (mol) = 0, 0.01, 0.03, 0.05 and 0.10) were prepared in one step through the polymeric precursor method. The textural properties of the catalysts were investigated by X-ray diffraction (XRD), Rietveld refinement, N2-physisorption (BET surface area), electron paramagnetic resonance (EPR), UV–visible diffuse reflectance and photoluminescence spectroscopies and temperature-programmed reduction (TPR). In a previous study ceria-supported copper catalysts were found to be efficient in the preferential oxidation of CO. In this study, we extended the catalytic application of Ce1−xCuxO2 systems to n-hexane oxidation and it was verified tha…
Effects of pulse current mode on plasma electrolytic oxidation of 7075 Al in Na2WO4 containing solution: From unipolar to soft-sparking regime
2018
Abstract Plasma electrolytic oxidation coatings were produced on 7075 Al alloy in a silicate based solution containing sodium tungstate using unipolar, usual bipolar and soft-sparking bipolar pulsed current regimes. X-ray diffraction proved that the coatings contain gamma alumina and metallic tungsten. EDS results showed that the tungsten content decreases with increasing the negative half cycle. Scanning electron microscopy showed that the pancake and volcano-like were dominant morphologies for the coatings produced by the unipolar and bipolar current regimes, respectively. Under unipolar current regime, a band of large pores is observed at the metal/coating interface, while they became di…
High-density polyethylene facial implants show surface oxidation in SEM and EDX examination: a pilot study.
2009
Previous histopathological studies on explanted Medpor high-density polyethylene (HDPE) facial implants indicated signs of material destruction and claimed to observe phagocytized HDPE particles within the tissue samples beside the usual type IV reaction with severe fibrosis. We examined new and explanted Medpor material with scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The implant surface of three patient-derived specimens showed significantly higher oxygenation in EDX analysis and morphological changes in SEM compared to the new unused material directly after opening of the package and after 1 year of exposure to air. Our preliminary findings indicate a p…
Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under red…
2009
Abstract A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce 0.6 Zr 0.4 O 2 homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs. By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic …
Au/CeO2-SBA-15 catalysts for CO oxidation: Effect of ceria loading on physic-chemical properties and catalytic performances
2012
In this work gold catalysts supported over SBA-15 with different CeO 2 loadings (5-30 wt%) were prepared, characterized by N 2 physisorption analyses, SAXS, XRD, STEM and XPS techniques and their catalytic performances were evaluated in the CO oxidation, chosen as reaction test. Over a selected catalyst, Au/CeO 2(20 wt%)-SBA-15, the effect of CO 2 and of the mixture (CO 2 + H 2O) on the CO conversion to CO 2 was also evaluated. Characterizations by SAXS, XRD, STEM and XPS were carried out on selected spent catalysts after CO oxidation. The results were discussed in terms of relationship between morphological, structural, electronic and catalytic properties as a function of the ceria loading…