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2008


Experimental and theoretical analysis of the intensity of beams diffracted by three-dimensional photonic crystals


Dorado, LA; Depine, RA; Schinca, D; Lozano, G; Miguez, H
Physical Review B, 78 (2008) 075102
Materiales Ópticos Multifuncionales

ABSTRACT ▼

An analysis of the diffracted beams emerging from three-dimensional photonic crystals is herein presented. The wave vectors of nonspecular beams are calculated for a triangular two-dimensional lattice and the change in their directions as a function of the wavelength is confirmed experimentally for the case of face-centered-cubic colloidal crystals illuminated under normal incidence. A fluctuating behavior of beam intensity as a function of the wavelength of the incident light is predicted for perfectly ordered lattices. As it is the case for specularly reflected and ballistically transmitted beams, this modulation arises from multipole resonances of the sphere ensemble that are smoothed out via the diffuse light scattering produced by imperfections in the crystalline structure. When optical extinction is introduced in order to model the effect of imperfections, it is possible to accurately reproduce experimental observations.


Agosto, 2008 | DOI: 10.1103/PhysRevB.78.075102

Functionalisation versus mineralisation of some N-heterocyclic compounds upon UV-illumination in the presence of un-doped and iron-doped TiO2 photocatalysts


Navio, J. A.; Macias, M.; Garcia-Gomez, M.; Pradera, M. A.
Applied Catalysis B-Environmental, 82 (2018) 225-232
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT ▼

Heterogeneous photocatalytic oxidation of some N-heterocyclic compounds (4-picoline, and 6- and 8-methylquinoline) in oxygenated solvents (water or acetonitrile), containing dispersed photocatalyst (un-doped or iron-doped titanium dioxide), was investigated under UV-illumination in a photochemical reactor. This work aimed to correlate experimental parameters such as structural aspects of the substrates, photocatalyst chemical and surface properties. illumination times, and the nature of the solvent with the extent of mineralisation of the substrates and, also, possible selective methyl group functionalisation.
Analysis of the products resulting from heterogeneous photocatalytic oxidation of 6- and 8-methylquinoline suspensions in oxygenated acetonitrile with illumination periods of <24 h detected, in both cases, the corresponding formyl derivatives quinoline-6- and -8-carbaldehyde, though at low levels. The presence of water appeared to inhibit heterogeneous photocatalytic functionalisation. However, the heterogeneous photocatalytic degradation of such compounds in water proceeds via polyhydroxylated intermediates which consequently undergo mineralisation, which, from a pollution control perspective is beneficial.
The physicochemical properties of the photocatalyst were also shown to be influential. Particularly, differences in the affinity to, and mode of adsorption of the substrate compounds studied gave rise to differences in the extent of oxidation.
Analysis of photogenerated oxidation products enabled some mechanistic insight into the course of the semiconductor-mediated reaction.
The results obtained allow a useful comparison of the functionalisation of N-Heterocyclic compounds via heterogeneous photocatalytic processes in the absence of water, to those carried out in the presence of water, which gave complete tnineralisation.


Agosto, 2008 | DOI: 10.1016/j.apcatb.2008.01.028

Reversible superhydrophobic to superhydrophilic conversion of Ag@TiO2 composite nanofiber surfaces


Borras, A; Barranco, A; Gonzalez-Elipe, AR
Langmuir, 24 (2008) 8021–8026
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

A new type of superhydrophobic material consisting of a surface with supported Ag@TiO2 core-shell nanofibers has been prepared at low temperature by plasma-enhanced chemical vapor deposition (PECVD). The fibers are formed by an inner nanocrystalline silver thread which is covered by a TiO2 overlayer. Water contact angles depend on the width of the fibers and on their surface concentration, reaching a maximum wetting angle close to 180 degrees for a surface concentration of similar to 15 fibers mu m(-2) and a thickness of 200 nm. When irradiated with UV light, these surfaces become superhydrophilic (i.e., 0 degrees contact angle). The decrease rate of the contact angle depends on both the crystalline state of the titania and on the size of the individual TiO2 domains covering the fibers. To the best of our knowledge, this is one of the few examples existing in the literature where a superhydrophobic surface transforms reversibly into a superhydrophilic one as an effect of light irradiation.


Agosto, 2008 | DOI: 10.1021/la800113n

Nitriding study of titanium silicide intermetallics obtained by mechanical alloying


Cordoba, J. M.; Alcala, M. D.; Sayagues, M. J.; Aviles, M. A.; Real, C.; Gotor, F. J.
Intermetallics, 16 (2008) 948-954
Reactividad de Sólidos

ABSTRACT ▼

Titanium and silicon powder blends were ball-milled under an inert atmosphere and subsequently annealed in a nitrogen atmosphere. Ti62.5Si37.5, Ti55.6Si44.4, and Ti50Si50 mixtures suffered a mechanically induced self-propagating reaction during milling. The products of the combustion were Ti5Si3 for the Ti62.5Si37.5 mixture and a combination of intermetallic phases for the Ti55.6Si44.4 and Ti50Si50 mixtures. The Ti33.3Si66.7 blend did not show an MSR process, but prolonged milling allowed the formation of a mixture of stable C54–TiSi2 and metastable C49–TiSi2 by a diffusion reaction. The nitriding study showed a different behaviour for C54–TiSi2 and Ti5Si3. C54–TiSi2 nitriding took place in a two-step process: the first corresponded to the formation of TiN and Si and the second to the silicon nitriding leading to the formation of α- and β-Si3N4. However, silicon and titanium nitriding primarily occurred simultaneously during the annealing of Ti5Si3, and the final product was a mixture of TiN and α-Si3N4.


Agosto, 2008 | DOI: 10.1016/j.intermet.2008.04.009

Microanalysis of Gothic mural paintings (15th century) in Slovenia: Investigation of the technique used by the Masters


Kriznar, A; Ruiz-Conde, A; Sanchez-Soto, PJ
X-Ray Soectrometry, 37 (2008) 360-369
Materiales Avanzados

ABSTRACT ▼

The present article focuses on an interdisciplinary research on cultural heritage concerning the microanalysis of Gothic mural paintings made during the 15th century in Slovenia. The samples were chosen from the churches of Crngrob (1453), Mirna (1463-1465), Mevkuz (1465) and Mate (1467), attributed to two of the most important Gothic painters of that period of time: Master Bolfgang and Master of Mate. The chemical and phase composition of all the mortars, number of their layers and selection of the pigments were of interest. For this purpose, fragments of mural paintings were studied with several instrumental techniques: optical microscopy (OM), SEM-EDX, x-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In early artworks, the mortar was made using a mixture of lime and more or less clean sand. Later, crushed lime-rock or marble instead of sand was added to lime. The pigments identified by EDX microanalysis of cross sections previously studied by OM, are of earth or mineral origin. Therefore, they are durable in fresco and lime techniques: lime white, yellow and red natural or burned ochres, green earth and azurite. The results confirmed the high technical quality of both painters and the relationships between the teacher and the disciple. Master Bolfgang and Master of Mate combine three basic techniques of mural painting: fresco, secco and lime techniques. This kind of investigation and methodology allow us to know better the Central European Art and the Slovenian Art in the Adriatic zone, as well as the general map of European Art in the 14-15th centuries.


Julio, 2008 | DOI: 10.1002/xrs.1050

Morphology changes induced by strong metal-support interaction on a Ni-ceria catalytic system


Gonzalez-DelaCruz, VM; Holgado, JP; Pereniguez, R; Caballero, A
Journal of Catalysis, 257 (2008) 307-314
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

The state of the nickel in a Ni/CeO2 catalyst during hydrogen reduction, steam and dry reforming of methane, have been studied by means of in situ XAS spectroscopy. The catalyst was prepared by a combustion method and, after calcination, very small (about 10 nm) and homogeneous cubic particles of NiO are formed. Once reduced in hydrogen at high temperature (750 °C), the catalyst is active in both steam and dry reforming reactions of methane, but much more stable for the dry reforming reaction. In situ XAS analysis reveals that under reaction conditions at high temperature, the nickel remains completely reduced to Ni(0). However, under strongly reducing conditions (hydrogen or dry reforming at 750 °C), the Ni K-edge X-ray absorption spectrum undergoes unexpected modifications that, according to the parameters obtained by fitting analysis, come from changes in the size and morphology of nickel particles, which are now flattened and strongly stabilized on the partially reduced ceria surface. These morphology changes reflect a kind of strong metal–support interaction (SMSI), and could account for the higher stability observed for the dry reforming reaction. The flattened particles are not stable after cooling down to room temperature in hydrogen, while the coke deposited during the dry reforming reaction seems to block the particles, which partially remain even after cooling down to room temperature.


Julio, 2008 | DOI: 10.1016/j.jcat.2008.05.009

Polymorphic transformation from body-centered to face-centered cubic vanadium metal during mechanosynthesis of nanostructured vanadium nitride determined by extended x-ray absorption fine structure spectroscopy


Lopez-Flores, V; Roldan, MA; Real, C; Paez, AM; Castro, GR
Journal of Applied Physics, 104 (2008) 023519
Reactividad de Sólidos

ABSTRACT ▼

The pathway for vanadium nitride (VN) formation obtained by milling treatment has been traced out. At the initial stages of the process, the reactant, vanadium metal, showing body-centered cubic (bcc) structure, becomes highly distorted. Simultaneously, the formation of a small nucleus of the product, VN, takes place. X-ray absorption spectroscopy (XAS) has allowed the quantification of the distortion degree as well as the detection of the VN nucleus in the early stages of their formation, while other standard structural characterization techniques are unable to detect such phenomena. For increasing milling times, apart from the expected increase in the size of the VN nucleus, a polymorphic transformation from bcc to fcc vanadium metal has been recorded. This phase might play a key role in the overall synthesis process and could be a reaction intermediate in other solid state processes involving V metal. The sensitivity of XAS to noncrystalline domains and to highly distorted environments, as well as the use of high resolution x-ray diffraction, has provided the relevant information to understand the whole reaction process. 


Julio, 2008 | DOI: 10.1063/1.2958324

Reactivity of lanthanum substituted cobaltites toward carbon particles


Hueso, JL; Caballero, A; Ocana, M; Gonzalez-Elipe, AR
Journal of Catalysis, 257 (2008) 334-344
Nanotecnología en Superficies y Plasma - Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

This work reports on the reactivity toward carbon of a La0.5Sr0.5CoO3-delta perovskite prepared by spray pyrolysis. It is shown that this perovskite presents a moderate activity for the thermal oxidation of carbon, producing a decrease in its temperature of combustion of ca. 150 degrees C and a significant increase in the selectivity toward CO2. Different experiments were carried out with electron energy loss spectroscopy (EELS) and X-ray photoemission spectroscopy (XPS) for the perovskite and its physical mixture with a high-surface area carbon material. In the physical mixture, the cobalt at the surface was partially reduced to Co2+ even at room temperature. XPS demonstrated a species of oxygen with low electron density at the catalyst surface. This species seemed to play a significant role in the oxidation processes at the perovskite surface. A model is proposed to account for the changes exhibited by the catalyst during its reaction with carbon.


Julio, 2008 | DOI: 10.1016/j.jcat.2008.05.012

Electronic structure, magnetic properties, and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour


Guerrero, E; Munoz-Marquez, MA; Fernandez-Pinel, E; Crespo, P; Hernando, A; Fernandez, A
Journal of Nanoparticle Research, 10 (2008) 179-192
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

Gold nanoparticles (NPs) have been stabilized with a variety of thiol-containing molecules in order to change their chemical and physical properties; among the possible capping systems, alkane chains with different lengths, a carboxylic acid and a thiol-containing biomolecule (tiopronin) have been selected as protecting shells for the synthesized NPs; the NPs solubility in water or organic solvents is determined by the protecting molecule. A full microstructural characterization of these NPs is presented in the current research work. It has been shown that NPs capped with alkanethiol chains have a marked ferromagnetic behaviour which might also be dependent on the chain length. The simultaneous presence of Au-Au and Au-S bonds together with a reduced particle diameter, and the formation of an ordered monolayer protective shell, have proved to be key parameters for the ferromagnetic-like behaviour exhibited by thiol-functionalized gold NPs.


Julio, 2008 | DOI: 10.1007/s11051-008-9445-5

Titania-supported gold catalysts: Comparison between the photochemical phenol oxidation and gaseous CO oxidation performances


Centeno, MA; Hidalgo, MC; Dominguez, MI; Navio, JA; Odriozola, JA
Catalysis Letters, 123 (2008) 198-206
Fotocatálisis Heterogénea: Aplicaciones - Química de Superficies y Catálisis

ABSTRACT ▼

A series of Au/TiO2 samples with gold loadings ranging from 0.11% to 1.26% have been prepared by deposition-precipitation, characterised by means of XRD, S-BET, XRF, TEM, XPS and DR UV-Vis techniques and tested in the gaseous CO oxidation and photocatalytic degradation of phenol in aqueous media. The catalytic performances of the solids on both reactions depend on the gold content. Besides this, the gold particle size plays a determinant role in the catalytic activity for the CO reaction, but apparently its influence on the photocatalytic activity appears to be negligible and only very small gold particles seem to participate on the photocatalytic process. On the other hand, the electronic properties of the solids, measured by its band gap energy, are a key factor in the photochemical activity but do not have a clear influence in the CO oxidation reaction.


Julio, 2008 | DOI: 10.1007/s10562-008-9448-y

Crystallization behavior of (GeS2)(0.1)(Sb2S3)(0.9) glass


Svadlak, D; Zmrhalova, Z; Pustkova, P; Malek, J; Perez-Maqueda, LA; Criado, JM
Journal of Non-Crystalline Solids, 354 (2008) 3354-3361
Reactividad de Sólidos

ABSTRACT ▼

The crystal growth kinetics of antimony trisulfide in (GeS2)(0.1)(Sb2S3)(0.9) glass has been studied by microscopy and DSC. The linear crystal growth kinetics has been confirmed in the temperature range 492 <= T <= 515 K (E-G = 405 +/- 7 kJ mol(-1)). The applicability of standard growth models has been assessed. From the crystal growth rate corrected for viscosity plotted as a function of undercooling it has been found that the most probable mechanism is interface controlled 2D nucleated growth. The non-isothermal DSC data, corresponding to the bulk sample, can be described by the Johnson-Mehl-Avrami equation.equation. 


Junio, 2008 | DOI: 10.1016/j.jnoncrysol.2008.01.029

Test of validity of the V-type approach for electron trajectories in reflection electron energy loss spectroscopy


Yubero, F; Pauly, N; Dubus, A; Tougaard, S
Physical Review B, 77 (2008) 245405
Química de Superficies y Catálisis

ABSTRACT ▼

An electron reaching the detector after being backscattered from a solid surface in a reflection electron energy loss spectroscopy (REELS) experiment follows a so-called V-type trajectory if it is reasonable to consider that it has only one large elastic scattering event along its total path length traveled inside the solid. V-type trajectories are explicitly assumed in the dielectric model developed by Yubero [Phys. Rev. B 53, 9728 (1996)] for quantification of electron energy losses in REELS experiments. However, the condition under which this approximation is valid has not previously been investigated explicitly quantitatively. Here, we have studied to what extent these REELS electrons can be considered to follow near V-type trajectories. To this end, we have made Monte Carlo simulations of trajectories for electrons traveling at different energies in different experimental geometries in solids with different elastic scattering properties. Path lengths up to three to four times the corresponding inelastic mean free paths have been considered to account for 80-90% of the total electrons having one single inelastic scattering event. On this basis, we have made detailed and systematic studies of the correlation between the distribution of path lengths, the maximum depth reached, and the fraction of all electrons that have experienced near V-type trajectories. These investigations show that the assumption of V-type trajectories for the relevant path lengths is, in general, a good approximation. In the rare cases, when the detection angle corresponds to a scattering angle with a deep minimum in the cross section, very few electrons have experienced true V-type trajectories. However, even in these extreme cases, a large fraction of the relevant electrons have near V-type trajectories.


Junio, 2008 | DOI: 10.1103/PhysRevB.77.245405

Influence of the chemical and electronic structure on the electrical behavior of zirconium oxynitride films


Carvalho, P; Chappe, JM; Cunha, L; Lanceros-Mendez, S; Alpuim, P; Vaz, F; Alves, E; Rousselot, C; Espinos, JP; Gonzalez-Elipe, AR
Journal of Applied Physics, 103 (2008) 104907
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

This work is devoted to the investigation of decorative zirconium oxynitride, ZrOxNy, films prepared by dc reactive magnetron sputtering, using a 17:3 nitrogen-to-oxygen-ratio gas mixture. The color of the films changed from metallic-like, very bright yellow pale, and golden yellow, for low gas mixture flows [from 0 to about 9 SCCM (SCCM denotes cubic centimeter per minute at STP)] to red brownish for intermediate gas flows (values up to 12 SCCM). Associated to this color change there is a significant decrease of brightness. With further increase of the reactive gas flow, the color of the samples changed from red brownish to dark blue (samples prepared with 13 and 14 SCCM). The films deposited with gas flows above 14 SCCM showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (characteristic of a transition from metallic to insulating-type materials), promoted by the change in gas flow values, revealed that significant changes were occurring in the film structure and electronic properties, thus opening new potential applications for the films, beyond those of purely decorative ones. Taking this into account, the electrical behavior of the films was investigated as a function of the reactive gas flow and correlated with the observed chemical, electronic, and structural features. The variations in composition disclosed the existence of four different zones, which were correlated to different crystalline structures. For the so-called zone I, x-ray diffraction revealed the development of films with a B1 NaCl face-centered cubic zirconium nitride-type phase, with some texture changes. Increasing the reactive gas flow, the structure of the films is that of a poorly crystallized overstoichiometric nitride phase, which may be similar to that of Zr3N4, but with some probable oxygen inclusions within nitrogen positions. This region was characterized as zone II. Zone III was indexed as an oxynitride-type phase, similar to that of gamma-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions. Finally, occurring at the highest flow rates, zone IV was assigned to a ZrO2 monoclinic-type structure. The composition/structure variations were consistent with the chemical bonding analysis carried out by x-ray photoelectron spectroscopy, which showed oxygen doping in both Zr3N4- and ZrN-type grown films. The electronic properties of the films exhibited significant changes from zone to zone. Resistivity measurements revealed a very wide range of values, varying from relatively highly conductive materials (for zone I) with resistivity values around few hundreds of mu Omega cm to highly insulating films within zones III and IV, which presented resistivity values in the order of 10(15) mu Omega cm. Regarding zone II, corresponding to oxygen doped Zr3N4-type compounds, the observed behavior revealed resistivity values increasing steeply from about 10(3) up to 10(15) mu Omega cm, indicating a systematic transition from metallic to insulating regimes. 


Mayo, 2008 | DOI: 10.1063/1.2927494

Ar+NO microwave plasmas for Escherichia coli sterilization


Hueso, JL; Rico, VJ; Frias, JE; Cotrino, J; Gonzalez-Elipe, AR
Journal of Physics D-Applied Physics, 41 (2008) 092002
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Ar + NO microwave discharges are used for sterilization and the results are compared with additional experiments with Ar, O(2) and N(2)-O(2) plasma mixtures. The NO* species produced in the Ar - NO mixtures remain up to long distances from the source, thus improving the sterilization efficiency of the process. E. coli individuals exposed to the Ar + NO plasma undergo morphological damage and cell lysis. Combined effects of etching ( by O* and Ar* species) and UV radiation ( from deactivation of NO* species) are responsible for the higher activity found for this plasma mixture.


Mayo, 2008 | DOI: 10.1088/0022-3727/41/9/092002

Tribological behaviour of titanium carbide/amorphous carbon nanocomposite coatings: From macro to the micro-scale


Sanchez-Lopez, JC; Martinez-Martinez, D; Lopez-Cartes, C; Fernandez, A
Surface & Coatings Technology, 202 (2008) 4011-4018
Materiales Nanoestructurados y Microestructura - Tribología y Protección de Superficies

ABSTRACT ▼

The tribological behaviour of nanocomposite coatings made of nanocrystalline metal carbides and amorphous carbon (a-C) prepared by PVD/CVD techniques is found to be very dependant on the film deposition technique, synthesis conditions and testing parameters. Focusing in the TiC/amorphous carbon-based nanostructured system, this paper is devoted to an assessment of the factors governing the tribological performance of this family of nanocomposites using a series of TiC/a-C films prepared by magnetron sputtering technique varying the power applied to each target (titanium or graphite) as model system to establish correlations between film microstructure and chemical compositions and tribological properties measured by a pin-on-disk tribometer. The film microstructure goes from a quasi -polycrystalline TiC to a nanocomposite formed by nanocrystals of TiC embedded in an amorphous carbon matrix as observed by transmission electron microscopy (TEM). The nanocrystalline/amorphous ratio appears to be the key-parameter to control the tribological properties and its quantification has been done by electron energy-loss spectroscopy (EELS). A significant change in the tribological performance is observed for nanocomposites with amorphous carbon phase contents above 60-65%. The friction coefficient decreases from 0.3 to 0.1 and the film wear rates by a factor of 10. Examination of the wear scars on ball and film surfaces by laser micro-Raman spectroscopy has allowed to determine the presence of metallic oxides and carbonaceous compounds responsible of the observed friction behaviour. The revision of the literature results in view of the conclusions obtained enabled to explain their apparent dispersion in the tribological performance.


Mayo, 2008 | DOI: 10.1016/j.surfcoat.2008.02.012

Study of the synergic effect of sulphate pre-treatment and platinisation on the highly improved photocatalytic activity of TiO2


Hidalgo, MC; Maicu, M; Navio, JA; Colon, G
Applied Catalysis B-Environmental, 81 (2008) 49-55
Fotocatálisis Heterogénea: Aplicaciones - Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

An important improvement of the photocatalytic activity of sol-gel prepared TiO2 has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.
The presence of sulphuric acid clearly stabilised TiO2 surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5 wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO2 surface was studied.
Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO2. Simultaneously sulphated and platinised TiO2 samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO2 Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.
A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.


Mayo, 2008 | DOI: 10.1016/j.apcatb.2007.11.036

Critical study of the isoconversional methods of kinetic analysis


Criado, J. M.; Sanchez-Jimenez, P. E.; Perez-Maqueda, L. A.
Journal of Thermal Analysis and Calorimetry, 92 (2008) 199-203
Reactividad de Sólidos

ABSTRACT ▼

A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, alpha, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with alpha is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and alpha is really occurring.


Abril, 2008 | DOI: 10.1007/s10973-007-8763-7

CO and VOCs oxidation over Pt/SiO2 catalysts prepared using silicas obtained from stainless steel slags


Dominguez, MI; Barrio, I; Sanchez, M; Centeno, MA; Montes, M; Odriozola, JA
Catalysis Today, 133 (2008) 467-474
Química de Superficies y Catálisis

ABSTRACT ▼

Stainless steels slags are mainly composed of low specific surface area calcium silicates together with a variable amount of metallic cations dispersed in such silicate matrix. These silicates due to their heavy metals content have to be considered as hazardous wastes that cannot be reclaimed easily. An alternative to reclamation is the production of valuable materials designed to accomplish processes without economic profit as the abatement of VOCs. In this paper we describe a method for obtaining high specific surface area (up to 290 m(2) g(-1)) metal-doped SiO2 and SiO2/ Al2O3 supports for catalytic applications using as raw materials stainless steel slags. The acid digestion of these slags followed by a hydrothermal treatment results in transition metal oxides doped silicas and silica-aluminas that are used as support for platinum catalysts. The prepared catalysts are active in the total oxidation of CO and toluene, showing comparable activities to those shown by Pt catalysts supported on commercial SiO2.(


Abril, 2008 | DOI: 10.1016/j.cattod.2007.11.033

Degradation of gold and false golds used as gildings in the cultural heritage of Andalusia, Spain


Duran, A; Perez-Rodriguez, JL; de Haro, MCJ; Herrera, LK
Journal of Cultural Heritage, 9 (2008) 184-188

ABSTRACT ▼

The causes and degree of alteration of metals such as gold, tin, silver and bronze powders from ornamental implements of Andalusia Cultural Heritage have been studied. The unaltered gold is lost due to the alteration of the material used to adhere the leaf gold on the ceramic. Tin is transformed to romarchite and is lost due to a similar alteration as with the gold leaf adhesive. Silver is altered to Ag2S due to environmental contamination. Part of the bronze powders and silver used in Huercal-Overa altarpiece are altered to atacamite and AgCl, respectively, due to an unsuitable cleaning process.


Abril, 2008 | DOI: 10.1016/j.culher.2007.10.005

Modification of the photocatalytic activity of Pd/TiO2 and Zn/TiO2 systems through different oxidative and reductive calcination treatments


Aramendia, MA; Borau, V; Colmenares, JC; Marinas, A; Marinas, JM; Navio, JA; Urbano, FJ
Applied Catalysis B-Environmental, 80 (2020) 88-97
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT ▼

Two different solids consisting of Pd or Zn-containing titania systems (metal/titanium nominal ratio of 1%) were submitted to diverse oxidative and reductive calcination treatments and tested for gas-phase selective photooxidation of 2-propanol. As regards the Pd system, reduction at low temperature (<= 500 degrees) resulted in a gradual increase in catalytic activity which was ascribed to the gradual reduction of bulk palladium to Pd-0. Thermal treatment of the system at high temperature (850 degrees C) in static air, air flow or hydrogen flow led to a decrease in activity as the result of the sharp decrease in surface area. Nevertheless, those systems containing Pd-0 only were more active than the one consisting of Pd + PdO. Finally, Pd-system overcame I'd migration to the surface on reduction at 850 degrees C which resulted in a significant increase in selectivity to acetone up to 97% for a time on stream of 5 h. As regards the Zn-containing system, none of the applied treatments resulted in improvement in photocatalytic activity. It seems that the most favourable situation for photocatalysis is that on which Zn atoms are substituting titanium ones in the lattice, whereas segregation of Zn to form small ZnO clusters is especially detrimental to activity.


Abril, 2008 | DOI: 10.1016/j.apcatb.2007.11.017

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