1,721,005 research outputs found
Valutazione dello stato di degrado di materiali lapidei in contesti archeologici: il teatro antico di Taormina
No full textStudio del degrado indotto da sali solubili su materiali lapidei nelle ex-carceri dello Steri a Palermo
No full textUn protocollo scientifico per la desalinizzazione di materiali lapidei: caso studio dei mosaici della Villa del Casale (Sicilia)
No full textCerium effect on the phase structure, phase stability and redox properties of Ce-doped strontium ferrates
No full textMetal-support and preparation influence on the structural and electronic properties of gold catalysts
No full textNanostructured gold catalysts supported on CeO2 and SiO2 were prepared by the deposition–precipitation (DP) and the solvated metal atom
dispersion (SMAD) techniques. The structural and electronic properties of the catalysts were investigated by X-ray diffraction (XRD), X-ray
absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Gold was found as small metal nanoparticles (cluster size 2 nm) in
the SMAD-prepared samples and in ionic state in the DP catalysts. The catalytic activity of the samples was tested in the reaction of low
temperature CO oxidation. Gold nanosized particles in a pure metallic state exhibited a worse catalytic performance, both on ceria and silica. The
presence of non-metallic Au species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The
higher activity of the Au/CeO2 (DP) sample with respect to the Au/SiO2 (DP) catalyst can be ascribed to a better stabilization of the Au+1 ions,
probably as AuO- species, by the cerium oxide
A degradation study of XVIII century graffiti on the walls of Chiaramonte Palace (Palermo, Italy)
No full textXPS study of supported gold catalysts: the role of Au0 and Au+ species as active sites
No full textGold nanoparticles supported on different oxides (SiO2, CeO2 and TiO2) were prepared by the SMAD (solvatedmetal atom dispersion) and deposition–precipitation (DP) techniques. The physical and chemical
characterization of the catalysts was performed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the catalytic activity was tested during the reaction of low temperature CO oxidation. The structural and surface analyses evidenced the presence of small gold crystallites (cluster size∼2–5 nm) in all the SMAD-prepared samples and oxidized gold species in the case of the DP catalysts. A different surface distribution of ionic gold species was found on the different supports. By comparing the catalytic activities of the samples, the presence of Au+1 species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The higher activity of Au/CeO2(DP) catalysts at T ≈ 250 K can be ascribed to a better stabilization of the AuO− species by the cerium oxide.
Nanosized metallic gold particles exhibit a worse catalytic performance, both on ‘reducible’ and ‘inert’ supports, being significantly active only in the temperature range: 400–600 K
Degradation of stone materials in the archaeological context of the Greek-Roman Theatre in Taormina (Sicily, Italy)
No full textIn the present work results on the degradation
phenomena of stone materials in the Ancient Theatre of
Taormina, one of the most important Greek–Roman monuments
of Sicily, are reported. Artificial stone materials in different
conservation conditions were investigated. Samples
of salt efflorescences from brick walls and degraded setting
mortars were taken from the open gallery in “summa cavea”.
The chemical, physical and structural characterization was
performed by means of X-Ray Photoelectron Spectroscopy
(XPS), X-Ray Diffraction (XRD) and X-Ray Fluorescence
(XRF), both in situ and ex situ.
Results showed that the deterioration of stone materials
is due to the aggressive action of the environment
agents. Soluble salts, such as chlorides, sulphates and nitrates,
were found in efflorescence samples. Mortars were
affected by a decomposition process induced by sulphates’
attack
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