Search results for "X-ray photoelectron spectroscopy"
showing 10 items of 416 documents
Gold catalysts supported on CeO2 and CeO2–Al2O3 for NO reduction by CO
2006
Abstract The reduction of NO x by CO was studied over gold catalyst supported on ceria and ceria–alumina. The mixed supports with different CeO 2 /Al 2 O 3 ratios were prepared by co-precipitation. The catalysts were characterized by means of XRD, TPR, XPS and Raman spectroscopy. The addition of alumina led to a slight enlargement of the gold particles, while the ceria particle size was decreased. Deeper oxygen vacancies formation in the presence of alumina was detected by TPR, XPS and Raman spectroscopy, compared to the pure ceria support. The samples exhibited a high and stable activity and 100% selectivity towards N 2 was reached at 200 °C.
Effect of Ti(IV) loading on CO oxidation activity of gold on TiO2 doped amorphous silica
2006
Abstract Amorphous SiO 2 , doped with various amount of TiO 2 , was used as support for gold nanoparticles. Gold was deposited through the controlled sol formation technique. The effect of the TiO 2 loading on the structural and surface properties was investigated by transmission electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. The catalytic behavior was tested in the oxidation of CO. A significant enhancement in the activity was observed for the gold supported on mixed oxide with low TiO 2 loading. On the basis of characterization data, the positive effect is assigned to the electronic modification of the Ti(IV) of the newly formed Ti O Si bonds.
Structural characterisation of silica supported CoMo catalysts by UV Raman spectroscopy, XPS and X-ray diffraction techniques
2002
The structure of Co-Mo catalysts supported on commercial silica, doped with various amounts of sodium ions, was investigated by means of X-ray diffraction (XRD), UV-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Two series of samples were considered. One series was prepared by classic incipient wet impregnation (WI) and the other series by co-impregnation in the presence of nitrilotriacetic acid (NTA). The effect of sodium on the catalyst structure depended on the preparation procedure: in the case of the WI catalysts, sodium promoted the transformation of the polymolybdate species into monomolybdate Na2MoO4; in the case of the NTA prepared samples, sodium induced transforma…
Preparation and photoactivity of nanocrystalline TiO2 powders obtained by thermohydrolysis of TiOSO4
2013
Nanocrystalline TiO2 photocatalysts were synthesized in mild conditions by thermohydrolysis of TiOSO4 in water at 100 °C and post-calcination treatment at various temperatures. The TiO2 powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, specific surface area determinations, scanning electron microscopy and electron paramagnetic resonance measurements. The photoactivity of the samples was tested employing the photodegradation of 4-nitrophenol in liquid–solid regimen and the photooxidation of gaseous 2-propanol. The best results were obtained with the powder calcined at 600 °C for 10 h. Surprisingly, the not calcined sample was the most active for the abatement…
Surface composition analysis during the oxidation of ferrites: A necessity
1998
The cationic composition of a titanium ferrite (Fe 2.5 Ti 0.5 O 4 ) has been followed by XPS during its oxidation in cation deficient phases (without crystallographic transformation) in order to reveal a dynamic segregation phenomenon. Indeed, during this oxidation, an important modification of the chemical composition of the first layers of the material has been revealed: below 350 °C, the titanium ferrites surface becomes richer in iron and poorer in titanium. But, if the reaction is extended above 400 °C, some titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are present in the material. Finally,…
A supramolecular heteropolyoxopalladate {Pd15} cluster host encapsulating a {Pd2} dinuclear guest: [Pd(II)2⊂{H7Pd(II)15O10(PO4)10}](9-).
2011
A high-nuclearity polyoxopalladate compound, [Pd(II)(2)⊂{H(7)Pd(II)(15)O(10)(PO(4))(10)}](9-) {Pd(II)(17)}, comprising a {Pd(15)} host occupied by a {Pd(2)} guest and the parent pristine "empty" [H(7)Pd(II)(15)O(10)(P(V)O(4))(10)](13-) {Pd(15)} cluster have both been prepared and characterized by single-crystal X-ray crystallography, (31)P NMR, CSI-MS, and XPS. The encapsulated {Pd(2)} has a short Pd(II)-Pd(II) distance within the {Pd(15)} host. Solution studies indicate that the empty host and filled guest complex are in equilibrium with each other, and UV titrations revealed a binding constant of ca. 10(3) for the guest Pd(II) ions, with a binding stoichiometry of almost 2.
The surface electronic structure of stoichiometric and defective LiF surfaces studied with MIES and UPS in combination with ab-initio calculations
1997
Abstract UPS (He I) and metastable impact electron spectroscopy (MIES) spectra of the LiF(100) single crystal surface and stoichiometric LiF films are presented. The spectra are interpreted on the basis of ab-initio electronic structure calculations. Defective surfaces, produced by electron dosing, were studied in the same manner. The MIES spectra reveal that the electron dosing produces metallic patches on the surface, but no uniform Li adlayer. The calculation show that the F-center contribution to the electron emission is very close in energy to that from the metallic patches; thus, the two contributions cannot be distinguished by the present experimental techniques.
Atomic and electronic structure of the corundum (0001) surface: comparison with surface spectroscopies
1997
Abstract The electronic structure and geometry of the Al-terminated corundum (0001) surface were studied using a slab model within the ab-initio Hartree-Fock technique. The distance between the top Al plane and the next O basal plane is found to be considerably reduced on relaxation (by 0.57 A, i.e. by 68% of the corresponding interlayer distance in the bulk). An interpretation of experimental photoelectron spectra (UPS He I) and metastable impact electron spectra (MIES) is given using the calculated total density of states of the slab and the projections to the atoms, atomic orbitals, and He 1s floating atomic orbital at different positions above the surface. Calculated projected densities…
Nanoelectron spectroscopy for chemical analysis: a novel energy filter for imaging x-ray photoemission spectroscopy
2005
An ovel instrument for imaging ESCA is described. It is based on a tandem arrangement of two hemispherical energy analysers used as an imaging energy filter. The main spherical aberration (α 2 -term) of the analyser is corrected by the antisymmetry of the tandem configuration. The kinetic energy range useable for imaging extends up to 1.6 keV; this is compatible with Mg and Al Kα laboratory x-ray sources. First experiments on the chemical surface composition of a Cu0.98Bi0.02 polycrystal, a GaAs/AlGaAs heterostructure and Ag crystallites on Si(111) have been performed using synchrotron radiation. The results reveal an energy resolutio no f190 meV and a lateral resolution (edge resolution) o…
Direct observation of the electroadsorptive effect on ultrathin films for microsensor and catalytic-surface control.
2013
Microchemical sensors and catalytic reactors make use of gases during adsorption in specific ways on selected materials. Fine-tuning is normally achieved by morphological control and material doping. The latter relates surface properties to the electronic structure of the bulk, and this suggests the possibility of electronic control. Although unusual for catalytic surfaces, such phenomena are sometimes reported for microsensors, but with little understanding of the underlying mechanisms. Herein, direct observation of the electroadsorptive effect by a combination of X-ray photoelectron spectroscopy and conductivity analysis on nanometre-thick semiconductor films on buried control electrodes …