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TPR and XPS investigations of Co/Al2O3 catalysts promoted with Ru, Ir and Pt
No full textThe influence of small amount of noble metals (Ru, Ir and Pt) on the reduction of Co atoms in supported Co catalysts has been
investigated by TPR and XPS measurements. The catalysts, containing 8 at% Co and different amounts of promoting metals ( 1 at%)
such as Pt, Ir or Ru, were prepared by sequential impregnation. The change in Co reducibility was investigated by XPS to quantify the
surface reduction degree of cobalt and by TPR to demonstrate that the presence of the second metal strongly influences the reducibility of
the catalysts with TPR shifting to lower temperatures. The efficiency in Co reduction was Ir > Pt > Ru, both at low and high promoter
amount, while a complete Co reduction was never found in our operative conditions
Acidity, sulphur coverage and XPS analyses of ZrO2-SO4 powders by different procedures
No full textZrO2-SO4 powders have been prepared by following either hydrothermal or room temperature precursor preparative routes and adopting different sulphation procedures. All the samples have been calcined at the same temperature (470 °C) and for the same time length (5 h), and have been characterized as to phase composition (XRD) and surface area (BET). The determinations of the actual acidity (pKa) and density of the oxide surface sites have been obtained by a revised Hammett-Bertolacini technique. The powder sulphur contents were obtained by elemental analyses. XPS analyses of the samples have been obtained by elaboration of the S 2p and Zr 3d spectral regions. XPS data are discussed with respect to the conditions of the powders preparation and cross-compared with acidity characterizations and sulphur contents
Electrochemical features of zirconia polymorphs. The interplay between structure and surface OH species
No full textZirconia powders were prepared by heating at 470 °C hydrothermal precursors obtained by precipitation at increasing pH (from 2 to 12). The phase composition of the calcined products varied from pure monoclinic (at the acid extreme) to pure tetragonal (neutral-alkaline range). For the mixed phase samples, the relative enrichment in the two polymorphs was estimated by interpretation of X-ray diffractograms. Electrochemical determinations of the double layer reactivity of the pure and mixed phase oxides were performed and combined with characterizations of the surface state by X-ray photoelectron spectroscopy (XPS). Interpretations of the distinctive electrochemical features shown by the different polymorphs are proposed
XPS analysis of gallium oxides
No full textSamples of Ga2O, synthesized by reacting Ga2O3 and metallic gallium, are analyzed by XPS measurements. These samples reveal the presence of a new photoelectron signal, assigned to Ga(I), with 3d binding energy of 19.0 eV, which is lower than the measured GaIII(3d) binding energy (20.6 eV) and higher than the measured Ga0(3d) binding energy (18.5 eV). A comparison between available XPS data on the Ga2O3/HZSM-5 catalytic system and the gallium binding energies measured in this work is proposed
Micro-Sized TiO2 for Toluene Photodegradation in Gas Phase: catalyst preparation and role of doped metal to increase the photo-activity
No full textMicro-Sized TiO2 for Toluene Photodegradation in Gas Phase: catalyst preparation and role of doped metal to increase the photo-activity. Indoor air pollution is a problem not to be underestimated because of two reasons: firstly, because the majority of the population spends about 80-90% of the time in these places and secondly, because the risk is affects almost the entire population. Pollutants are classified in three big categories: chemical, physical and biological; VOC's, formaldehyde, toluene, benzene, carbon monoxide, carbon dioxide and nitrogen dioxide fall in the category of chemical agents.
Industrial age caused an increase of indoor pollution and chemical substances like formaldehyde, xylene or toluene could making the air inside homes to 20 times more polluted than outdoor air.
In fact, toluene and xylene are in many household and educational products, well as they are emitted from the exhaust gases of cars; in particular, they are widespread because they are ubiquitous. Titanium dioxide is a semiconductor material that has good catalytic properties and is able to degrade numerous organic compounds by oxidation; its molecules exposed to light catalyse the oxidation of organic residues in water and carbon dioxide.
In this work, catalysts based on titanium dioxide were tested and improved in particular on the degradation of toluene. P25 was the sample reference for nanometric powders, and its activity was compared with Kronos 1077, which consists of micrometric particles. Kinetics are carried out in a glass Pyrex reactor with a 200 mm diameter and a 5,5 L volume. Located 50 cm above the reactor there is an UV lamp; its power is 500 W and the wavelengths of the emissions are between 100 and 400 nm. The power calculated on the catalyst surface is 30 W\m2.
A gas chromatograph tracked the toluene and carbon dioxide concentrations inside the reactor. Although micrometric sample showed a lower activity than P25, it is possible to modify it, in particular with metals, and improve its final performance. Finally, the toluene kinetic reaction pathway was studied as well, and the main by-products were analyzed and classified
Chromium doped γ-Al2O3 powders. Features of the electrical double layer and state of the surface species
No full textγ-Al2O3 samples, both pure and Cr doped, were prepared by heating at 470 °C sol-gel precursors obtained by using aluminum tri-sec-butoxide [Al(OC4H9)3] as the starting compound. The samples were characterized for phase composition (X-ray diffraction) and surface area (BET). Electrochemical determinations of the double layer reactivity of the pure and doped oxides were performed both by surface charge and by electrokinetic sonic amplitude (ESA) determinations. The interfacial electrostatic response is discussed and analyzed also with reference to the sample surface state obtained by X-ray photoelectron spectroscopy (XPS)
XPS characterization of Ni and MO oxides before and after “in situ” treatments
No full textThe characterization of oxide surfaces is often made by means of the XPS technique: in this paper results obtained by treating
nickel and molybdenum oxides at a temperature of 523 K, at 10m4 Pa (in vacua) and at 10’ Pa (in hydrogen), are reported. These
treatments were performed in a reaction chamber and the samples were subsequently analyzed in the main chamber without
exposing them to the atmosphere.
The results indicate that it is possible to completely reduce nickel oxide to metal by treating it in hydrogen, while the heating in
vacua leaves a fairly large amount of oxide not reduced on the surface (77.8%, atomic percentage).
On the other hand, on the two molybdenum oxides (MOO, and MOO,) it is possible to notice the presence of a large amount of
intermediate not reduced oxides, at 523 K, both in hydrogen and in vacuo
The role of the oxide precursor on the features of sulphated zirconia
No full textZirconia samples have been obtained by calcining, at 470°C, hydrous precursors prepared by following two different procedures: (a) room temperature precipitation by NH3 at acid pH (≤2.5) followed by 96 h refluxing; (b) neutralisation (pH = 7.0-7.5) of ZrCl4 Solutions at the boiling point by KOH. The oxides, calcined starting from the two precursors, appear to be composed either of monoclinic or tetragonal (metastable) ZrO2. Sulphated zirconia samples have been obtained by treating the precursor powders with sulphuric acid at different concentrations and subsequently calcining them at 470°C. The sulphate-doped oxides have been characterised for phase composition-crystallinity (XRD), water-sulphur content (TGA, elemental analysis), surface area (BET) and surface chemical state (XPS also in combination with ion sputtering). The different oxide precursors produce distinctive features, on the treated oxides, concerning specifically the degree of hydration/hydrophilicity of the samples and the nature of the zirconium surface sites.
Zirconia samples have been obtained by calcining, at 470°C, hydrous precursors prepared by following two different procedures: (a) room temperature precipitation by NH3 at acid pH (≤2.5) followed by 96 h refluxing; (b) neutralization (pH = 7.0-7.5) of ZrCl4 solutions at the boiling point by KOH. The oxides, calcined starting from the two precursors, appear to be composed either of monoclinic or tetragonal (metastable) ZrO2. Sulphated zirconia samples have been obtained by treating the precursor powders with sulphuric acid at different concentrations and subsequently calcining them at 470°C. The sulphate-doped oxides have been characterised for phase composition-crystallinity (XRD), water-sulphur content (TGA, elemental analysis), surface area (BET) and surface chemical state (XPS also in combination with ion sputtering). The different oxide precursors produce distinctive features, on the treated oxides, concerning specifically the degree of hydration/hydrophilicity of the samples and the nature of the zirconium surface sites
Fischer-Tropsch synthesis on ruthenium supported ETS-10 titanium silicate catalysts
No full textTitanium silicate ETS-10 was found to be a suitable metal catalyst support, having high surface area, high ion exchange capacity and no acidic functions. In this work, ETS-10 was used as a support in preparing ruthenium supported catalyst for Fischer-Tropsch synthesis. Ru/METS-10 catalytic systems (M standing for Na or K) showed some important characteristics, as good metal dispersion and shape selectivity. Moreover, no side reactions due to acidic functions were evidenced; indeed readsorption of olefins on active metal centers was found to control the activity of the catalysts
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