1,721,090 research outputs found
Adsorption and oligomerization of isobutene on oxide catalyst surfaces. A Fourier-transform infrared study
No full textThe F.t.i.r. spectra of isobutene adsorbed at 170-300 K on the pure oxides silica, alumina, magnesia and titania, as well as on the phosphated samples prepared by impregnation of these pure oxides and of silica-alumina with phosphoric acid have been recorded. At low temperatures (170-220 K), molecularly adsorbed species are observed on pure oxides, with a spectrum similar to that of liquid isobutene, although with specific perturbations of the modes primarily involving the vinylidene moiety. Isobutene is transformed only on titania even at low temperatures into a new compound identified as its dimer 2,4,4-trimethylpent-1-ene. On phosphated samples oligomerization occurs at 293 K, producing oligomeric species identified as 5-10 monomeric unit cationic polymers
Alvarez-Ramis G. et Doubinger J. (1970). — Révision de quelques espèces de Marioptéridées du Stéphanien de France et d'Espagne. Estudios geologicos, XXVI, p. 261-271
No full textAlvarez-Ramis G. et Doubinger J. (1970). — Révision de quelques espèces de Marioptéridées du Stéphanien de France et d'Espagne. Estudios geologicos, XXVI, p. 261-271. In: Bulletin du Service de la carte géologique d'Alsace et de Lorraine, tome 23, n°3-4, 1970. Sédimentologie et géochimie de la surface. p. 223
Alvarez-Ramis G. et Doubinger J. (1970). — Révision de quelques espèces de Marioptéridées du Stéphanien de France et d'Espagne. Estudios geologicos, XXVI, p. 261-271
No full textAlvarez-Ramis G. et Doubinger J. (1970). — Révision de quelques espèces de Marioptéridées du Stéphanien de France et d'Espagne. Estudios geologicos, XXVI, p. 261-271. In: Bulletin du Service de la carte géologique d'Alsace et de Lorraine, tome 23, n°3-4, 1970. Sédimentologie et géochimie de la surface. p. 223
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Feasibility assessment of photoreactors for water treatment
No full textPhotocatalytic processes are acquiring increasing attention as a mean to exploit solar energy in promoting chemical transformations. Numerous applications can be found in the literature on the use of semiconductors for water treatment or to produce renewable fuels. Very challenging applications combine also the two concepts. These topics are usually addressed from the point of view of material science, in the search of very specific, often naïve, materials for each reaction. On the contrary, process design is very poorly addressed, with few literature outcomes if compared with catalyst development. The result is that the question often remaining unanswered is: is the process feasible? Is the reactor realistic for the given application, based on activity data? Therefore, attention is here paid on the possible scale up of the technology, trying to determine the reactor size, in terms of catalyst mass needed to achieve the desired conversion. The application example we are dealing with is the photooxidation of ammonia for wastewater treatment. We have set up and compared different types of photoreactors (ca. 300 ml and ca. 1.5L), operated in semibatch mode. Based on a preliminary catalyst screening we have calculated the maximum reaction rate, through which we calculated the catalyst mass needed to fulfil pollutant abatement below law limits in some representative cases. The process demonstrated feasible to manage the water treatment needs of a small community with the highest reaction rate, even in the case of a high concentration of pollutants. Some feasibility options are also found in case of a medium community need. Tests have been carried out also on samples of real waste water, monitoring the conversion of COD and N-containing pollutants in a 10 L pilot photoreactor, in collaboration with ISWA (Stuttgart, Germany, which is gratefully acknowledged). These tests evidenced that there is a competition between the oxidation of organics present in water, with respect to ammonia. This point has to be carefully taken into account when designing the whole water treatment process
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Hydrogen, ethylene and power production from bioethanol: Ready for the renewable market?
Full text linkThe economic sustainability of renewable based sources is a matter of debate and the technology is changing very fast. We here considered three examples of exploitation of bioethanol as renewable source: a) centralised hydrogen prodution; b) heat and power cogeneration (residential scale); c) ethylene production. Bioethanol can be a suitable starting material for the production of H2, as fuel or chemical, or syngas. After designing the process and the implementation of kinetic expressions based on experimental data collected in our lab or derived from the literature, an economic evaluation and sensitivity analysis allowed to assess the economic sustainability of hydrogen production and purification by the steam reforming of bioethanol. The attention was mainly put on diluted bioethanol solutions, easy to purify and cost effective. The centralised hydrogen production from bioethanol was considered cost effective at least starting from diluted bioethanol from first generation crops. When dowscaling the hydrogen production and purification unit to feed a 5 kW fuel cell, the most undetermined item was the fuel cell cost, since no acclarate market price is still available. Finally, ethylene market is steadily increasing by ca. 4% each year due to economic growth. The demand for renewable ethylene, as well as the increasing oil price experienced in the recent past, suggested the development of alternative routes to ethylene. Based on the increasing availability of ethanol form renewable biomass, bioethanol-to-bioethylene processes have been recently designed, finding economic sustainability, at the moment, in Brazil
Fourier transform-infrared study of the adsorption and coadsorption of nitric oxide, nitrogen dioxide and ammonia on vanadia-titania and mechanism of selective catalytic reduction
No full textThe adsorption of nitric oxide, nitrogen dioxide and ammonia and their coadsorption on vanadia-titania have been studied by FT-IR spectroscopy. Upon nitric oxide adsorption, a surface nitrosyl species is formed rapidly and nitrates are formed slowly by oxidation. Nitrogen dioxide adsorption forms nitrate species by oxidation and nitric oxide. Lewis-bonded molecular species and ammonium ions are formed upon ammonia adsorption. Coordinated ammonia is thermally more stable than ammonium ions and can lose an hydrogen atom to give an amide species. Adsorption on a water-covered sample shows that ammonia displaces water from Lewis sites. Experiments of nitric oxide adsorption on ammonia-covered vanadia-titania show that ammonia poisons the nitric oxide adsorption sites and that NO3- species are formed by nitric oxide oxidation on vanadyl sites. By heating the ammonia-covered sample in the presence of gaseous nitric oxide coordinated ammonia reacts via the amide species, while ammonium ions do not. The fol lowing reaction mechanism is proposed: VO2+ + NH3 = [HO-V-NH2]2+ NO + [HO-V-NH2]2+ = [HO-V-NH2-NO]2+ [HO-V-NH2-NO]2+ = N2 + H2O + [VOH]2+ [VOH]2+ + 1 4 O2 = VO2+ + 1 2 H2O This reaction sequence is believed to operate during the selective catalytic reduction of NOx over vanadia-titania based catalysts. © 1990
Photoreactors design for hydrogen production
Full text linkThe production of hydrogen through photoreforming of aqueous solutions of organic compounds is considered as a way to exploit solar energy storage in the form of hydrogen. The photocatalytic reforming can be promoted by a photocatalyst, optimally a solid semiconductor able to absorb the major quota of solar energy. In this work, glucose was used as a model substrate for photoreforming, possibly derived from the hydrolysis of waste biomass. The selected photocatalysts were based on TiO2. The materials were prepared by different methods, e.g. flame spray pyrolysis, precipitation and in mesoporous form through soft template synthesis, and compared with commercial samples of nanostructured TiO2 P25 by Evonik. 0.1 mol% Pt was also added as co-catalyst. The role of the metal was that of electron sink, to inhibit the recombination of the electron/hole couple obtained through light absorption. The photoreforming reaction was carried out in different prototypes of photoreactors, specifically developed and optimised. In one reactor configuration, an external 200 W lamp was used, with emission wavelengths centred around 365 nm. A first photoreactor was developed with internal capacity ca. 0.3 L, with big head space for gas collection and very efficient mixing of the suspension thanks to an optimized length/diameter ratio (L/D) ca. 2. A drawback was the poor irradiation efficiency of the suspension, which limited the overall productivity, irrespectively or the substrate. A different home-designed photoreactor was equipped with an immersion lamp, coaxial with the reactor. Two reactor sizes were tested, 0.3 L or 1.5 L. A significant amount of H2 was obtained with these very simple catalyst formulations, up to 14.7 mol kgcat-1 h-1 over the Pt/TiO2 sample and using glucose as substrate. This result is very remarkable with respect to conventional photoreactors
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