April 21st (Tuesday) | 10.00 h
Correction to comprehensive experimental and theoretical study of the CO+NO reaction catalyzed by Au/Ni nanoparticles
Dr. Juan Pedro Holgado Vázquez
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.
ICMS-sci-talks are held by scientists from the Materials Science Institute of Seville with the aim of discussing and disseminating their research activity. They consist of 20-25 min talks focussed on a recently published paper.
These talks take place about every three weeks at 10.00 am in the seminar room at cicCartuja2 (yellow building).
January 15th (Wednesday) | 12.00 h
Salón de Grados CicCartuja2
Cold Plasma Processes for Surface Modification of Materials
Prof. Charafeddine Jama
Universidad de Lille, Francia
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