355 research outputs found
Supported Vanadium Oxide Catalysts: Quantitative Spectroscopy, Preferential Adsorption of V^4+/5+, and Al2O3 Coating of Zeolite Y
A series of supported vanadium oxide catalysts were prepared by the incipient wetness method as a function
of the support composition (Al2O3, SiO2, and USY), the metal oxide loading (0-1 wt %), and the impregnation
salt (vanadyl sulfate and ammonium vanadate). These catalysts have been studied by combined DRS-ESR
spectroscopies in order to quantify the amount of V^4+ and V^5+ and to unravel their coordination geometries.
These spectroscopic fingerprints have been used to study the preferential adsorption of V^4+/5+ ions on SiO2,
Al2O3, and USY. Both V^4+ and V^5+ were preferentially adsorbed on Al2O3 and showed a much smaller pref-erence
for USY and SiO2. The observed preference orders are discussed in relation with the properties of the
support. In addition, a novel method is proposed to coat the external surface of USY with a thin film of
Al2O3. The method is based on the deposition of USY with the so-called Keggin ion, [Al13O4(OH)24(H2O)12]7+ ,
which is too big to enter the USY channels or pores. The obtained Al2O3/USY material showed a preferential
adsorption of V^4+ onto the Al2O3 film, suggesting that this method could be useful for vanadium passivation
of FCC catalysts
SBA-15 mesoporous silica modified with rhodium by MDD method and its catalytic role for decomposition reaction
SBA-15 mesoporous silicas modified with rhodium were studied as catalysts for the N2O decomposition reaction. Rhodium was deposited on SBA-15 by the Molecular Designed Dispersion (MDD) method using Rh(acac)3 as a precursor of active phase. The same method was used for the deposition of Cu, Fe, Al and Ti. The SBA-15 support modified with metals were characterized with respect to metal loading (EPMA), structure (XRD), texture (BET), morphology (SEM), Rh dispersion (oxygen chemisorption), surface acidity (pyridine adsorption) and chemical nature of introduced copper and iron species (UV-vis-DRS). The rhodium-containing SBA-15 samples were found to be active catalysts for the N2O decomposition reaction. Deposition of Al on the Rh-loaded catalyst increased its activity. An opposite effect was observed for the samples modified with Cu and Fe
El ferro, la llaminadura i el verĂ dels bacteris
El ferro Ă©s vital per a gairebĂ© tots els organismes vius, atès el paper crucial que tĂ© en nombrosos processos biològics. Però, en concentracions inadequades, aquest element Ă©s un verĂ per a qualsevol cèl·lula. Per això, els Ă©ssers vius disposen de mecanismes que en controlen la concentraciĂł. AixĂ, els vertebrats tenen sistemes que segresten ferro per evitar-ne l'efecte deleteri. A mĂ©s, el segrest tĂ© un altre efecte positiu per a aquests animals, ja que el ferro no estarĂ disponible per al desenvolupament dels bacteris patògens que els puguin infectar. Com a resposta, els patògens bacterians han desenvolupat diverses estratègies de captura del ferro segrestat
The release properties of the mesoporous materials SBA-15 and PHTS for their use in the controlled release of ibuprofen and vancomycin
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