1,720,988 research outputs found
CoMo catalysts supported on aluminosilicates: synergy between support and sodium effects”
No full text
Nature of cobalt species in hydrodesulfurization catalysts: combined support and preparation method effects
No full textAu/CeO2-SBA-15 catalysts for CO oxidation: effect of ceria loading on physic-chemical properties and catalytic performances
No full textIn this work gold catalysts supported over SBA-15 with different CeO2 loadings (5–30 wt%) were prepared,
characterized by N2 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/CeO2(20 wt%)-SBA-15, the effect of CO2 and of the mixture (CO2 + H2O) on the CO conversion to CO2
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. The CO oxidation activity was strongly affected by
gold particle size and gold/ceria interface as well. For gold catalysts supported on ceria-doped SBA-15,
the oxygen vacancies in ceria likely act as nucleation sites for gold anchoring and stabilization against
sintering. The optimum of the catalytic performances was found for 20 wt% ceria loading, likely due to
the optimum synergistic interaction between highly dispersed defective ceria oxide and nanosized gold
XPS 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
Metal-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
An easy microwave-assisted process for the synthesis of nanostructured palladium catalysts and their use in the selective hydrogenation of cinnamaldehyde
No full textAn efficient and highly reproducible process for the microwave-assisted solvothermal synthesis of palladium nanoparticles has been carried out adopting mild reaction conditions and very short microwave irradiation times. Colloidal nanoparticles have straightforwardly been obtained by the direct irradiation of an ethanol solution of Pd(OAc)(2) in the presence of PVP (poly-N-vinyl-2-pyrrolidone) as capping agent. The "in situ" preparation of gamma-Al(2)O(3)-supported catalysts has been conveniently carried out without the addition of PVP, leading to supported palladium nanoparticles with an average diameter of 5-8 nm and a narrow nanoparticle size distribution. These nanocatalysts have been characterized by UV-vis, TEM, XPS and SSA measurements and used as efficient catalysts for the chemoselective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde with selectivities up to 97% in hydrocinnamaldehyde at complete substrate conversion. (C) 2010 Elsevier B.V. All rights reserved
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