(Consejo Superior de Investigaciones Científicas – Universidad de Sevilla)



February 19th, Wednesday
+ info

A series of gold nanoparticles in the 4‐40 nm range were prepared, immobilized on activated carbon and further tested, at low base concentration, in the catalytic oxidation of 5‐hydroxymethyl furfural (HMF) to 2,5‐ furandicarboxylic acid (FDCA). Gold particles size variation has no influence on HMF conversion but significantly affects product selectivity and carbon balance. This behavior is ascribed to the thermodynamically favorable oxygen reduction reaction on Au(100) faces. As the gold particle size decreases the Au(100)/Au(111) exposure ratio, estimated by using the van Hardeveld ‐ Hartog model, increases as well as the FDCA selectivity. The smaller the gold particle size the smaller the 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA) to FDCA ratio pointing to the gold size dependent behaviour of the oxidation of the alcohol function of the HMF molecule.

+ info

Image 1

CrAlYN hard coatings with two different average Al contents: ∼16 at.% and ∼25 at.%, and Y concentration varying between 1.2 and 5.7 at.% were deposited by direct current reactive magnetron co-sputtering of mixed Cr-Al and Y targets on commercial M2 steel substrates. The samples were heated to 1000 °C in air during 2 h to study their oxidation resistance and thermal stability. The Y content is critical and the coatings present different behaviour depending on the Al content. The best oxidation resistance and thermal stability are obtained for the coating with ∼16 at.% Al and 3.4 at.% Y. The initial film microstructure and the cubic phase (fcc-CrAlN) were retained, and a thin (Cr,Al)2O3 oxide protective scale was formed. At lower Y content (1.2 at.%) iron, from the substrate crosses the coating, while a higher content (4.6 at.%) avoided the iron diffusion at the expense of a thicker oxide scale with new oxide phases. The coatings with higher Al content (∼25 at. %) were not thermally stable at 1000 °C. A good oxidation resistance was obtained for 2.6 at.% of Y although new phases (hcp-AlN and Cr-Fe) were formed. Higher amount of yttrium (∼5.7 at. %) led to the complete oxidation of the coating.

+ info

The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ X-ray absorption spectroscopy and density functional theory (DFT) calculations. The as-prepared materials contained substantial amounts of residual capping agent arising from the commonly used synthetic procedure. Thorough removal of this material by oxidation was essential for the acquisition of valid catalytic data. All catalysts were highly selective toward N2 formation, with 50–50 Au:Ni material being best of all. In situ X-ray absorption near edge structure spectroscopy showed that although Au acted to moderate the oxidation state of Ni, there was no clear correlation between catalytic activity and nickel oxidation state. However, in situ extended X-ray absorption fine structure spectroscopy showed a good correlation between Au–Ni coordination number (highest for Ni50Au50) and catalytic activity. Importantly, these measurements also demonstrated substantial and reversible Au/Ni intermixing as a function of temperature between 550 °C (reaction temperature) and 150 °C, underlining the importance of in situ methods to the correct interpretation of reaction data. DFT calculations on smooth, stepped, monometallic and bimetallic surfaces showed that N + N recombination rather than NO dissociation was always rate-determining and that the activation barrier to recombination reaction decreased with increased Au content, thus accounting for the experimental observations. Across the entire composition range, the oxidation state of Ni did not correlate with activity, in disagreement with earlier work, and theory showed that NiO itself should be catalytically inert. Au–Ni interactions were of paramount importance in promoting N + N recombination, the rate-limiting step.

+ info

The traditional methods for the synthesis of reinforced alumina-based matrix composites with carbon nanotubes (CNTs) have presented serious difficulties for obtaining well-dispersed and homogeneously distributed CNTs within the matrix. Besides this, the CNTs are typically found in the grain boundaries of the matrix. These features involve a non-optimal reinforcement role of the CNTs. With the aim of maximizing the efficiency of the reinforcement of the CNT, this work reconsiders a sol-gel-based procedure for ceramic composite fabrication with a two fold objective: to achieve a good dispersion of the CNTs and to promote the intragranular location of the CNTs. The mixing of precursors and CNTs has been developed under the presence of high-power ultrasounds, followed by a rapid in-situ gelation that “froze” the nanotubes inside the gel. The chemical and physical relationships between the ceramic matrix and the embedded reinforcing phase have been researched. First results confirm the success of the synthesis procedure for the preparation of alumina-based composite powders starting from a commercial boehmite sol and multiwalled carbon nanotubes. X-ray diffraction and Raman analyses confirmed the formation of the α-Al2O3 and the persistence of the non-damaged nanotube structure. N2 physisorption and electron microscopy were used to check the evolution of the nanostructure and to confirm the presence of intragranular carbon nanotube within the polycrystalline powder. Therefore, the alumina-based composite powder prepared by this new procedure is a good candidate for the preparation of reinforced ceramic matrix composites.

June 9th, Tuesday
+ info

Dielectric barrier discharge (DBD) plasmas and plasma catalysis are becoming an alternative procedure to activate various gas phase reactions. A low-temperature and normal operating pressure are the main advantages of these processes, but a limited energy efficiency and little selectivity control hinder their practical implementation. In this work, we propose the use of isotope labelling to retrieve information about the intermediate reactions that may intervene during the DBD processes contributing to a decrease in their energy efficiency. The results are shown for the wet reforming reaction of methane, using D2O instead of H2O as reactant, and for the ammonia synthesis, using NH3/D2/N2 mixtures. In the two cases, it was found that a significant amount of outlet gas molecules, either reactants or products, have deuterium in their structure (e.g., HD for hydrogen, CDxHy for methane, or NDxHy for ammonia). From the analysis of the evolution of the labelled molecules as a function of power, useful information has been obtained about the exchange events of H by D atoms (or vice versa) between the plasma intermediate species. An evaluation of the number of these events revealed a significant progression with the plasma power, a tendency that is recognized to be detrimental for the energy efficiency of reactant to product transformation. The labelling technique is proposed as a useful approach for the analysis of plasma reaction mechanisms.

January 15th

Cold Plasma Processes for Surface Modification of Materials

Prof. Charafeddine Jama
Universidad de Lille, Francia

+ info

Multifunctional effects are essential for producing higher value added materials, important not only for new technical applications but also for more traditional uses. The growing environmental and energy-saving concerns will also lead to the gradual replacement of many traditional wet chemistry-based processing, using large amounts of water, energy and effluents, by various forms of low-liquor and dry-finishing processes.
The dominant role of plasma-treated surfaces in key industrial sectors, such as microelectronics is well known, and plasmas are being used to modify a huge range of material surfaces, including plastics, polymers, papers, food packaging and biomaterials. In previous works, it was evidenced that cold plasma technologies can induce several surface modifications such as change in surface polarity, grafting of chemicals or deposition of functional coatings. Such modifications are effective to confer new and durable properties to synthetic or natural polymers, without altering their bulk properties.
The presentation will give a comprehensive description and review of the science and technology related to plasmas, with particular emphasis on their potential use in the industry. Examples of surface functionalization of materials achieved by means of cold plasma grafting and/or deposition of hydrophilic or hydrophobic coatings, antibacterial, anticorrosion and fire retardant materials will be presented (Figs. 1&2).


Fig. 2. Plasma deposition of organosilicon coatings: SEM images of (a) Uncoated fiber; (b) Coated fiber

Seminario cicCartuja2 / Salón de Grados cicCartuja2

Seminario cicCartuja2 / Salón de Grados cicCartuja2

Seminario CIC-Cartuja 2

ICMS Invited Lectures
Salón de Grados cicCartuja2

Americo Vespucio 49
Isla de la Cartuja
, 41092 España
Teléfono: 954489500