1,720,988 research outputs found
Flame Spray Pyrolysis: catalysts for the Steam Reforming of bio-ethanol
No full textFlame Spray Pyrolysis (FSP) is a one step high temperature synthesis able to impart strong metal-support interaction [1], besides high thermal resistance. A set of Ni catalysts supported over ZrO2 doped with different basic oxide (CaO, MgO) were prepared by this innovative technique. Steam Reforming catalytic test were carried out for the production of hydrogen using bio-ethanol. The catalytic activity was compared with catalysts of the same composition, but prepared with a traditional precipitation/impregnation method (multistep synthesis). Very high activity has been observed at high reaction temperature (>600°C), but further kinetic studies were done under milder conditions (500-300°C), in order to lower the energy input to the process and to improve H2 productivity favoring the water gas shift reaction [2]. Two different bioethanol samples, 50 and 90 vol%, produced and supplied by Mossi&Ghisolfi, have been used for 8 h-on-stream at each temperature. Attention was paid to the catalyst resistance towards deactivation by coking, besides its activity and selectivity. The acidity of the support was tuned by doping ZrO2 with basic oxides, helping to prevent ethanol dehydration and coking by ethylene polymerization. Fresh and spent samples were characterized by XRD, TPR, TPO, TEM, FE-SEM and Raman analysis.
Figure: scheme and image of Flame Spray Pyrolysis
[1] G. Ramis, I. Rossetti, E. Finocchio, M. Compagnoni, M. Signoretto, A. Di Michele, Progress in Clean Energy, I. Dincer, Ed. Springer, in press.
[2] I. Rossetti, J. Lasso, E. Finocchio, G. Ramis, V. Nichele, M. Signoretto, A. Di Michele, Appl. Catal. B: Environmental, 150-151 (2014) 257-267
“Ni-, Co- and Cu-TiO2 catalysts for the steam reforming of ethanol: how the preparation method affects catalytic performance”
Get PDFConcept
A set of Ni-, Co-, Cu-based catalysts supported over TiO2 for the steam reforming of ethanol were prepared by different procedures. For most of them the support was prepared by precipitation and calcined at 500°C or 800°C. Other samples were prepared by flame pyrolysis (FP), aiming at high metal dispersion coupled with synthesis at high temperature, to impart a strong metal-support interaction, besides high thermal resistance. The samples were characterised by AAS, XRD, N2 adsorption-desorption, TPR, SEM, TEM and FT-IR. Activity testing for the steam reforming of ethanol was performed after activation at 500°C or 800°C in H2 flow on a continuous micropilot plant, by feeding a 3:1 (mol/mol) mixture of water/ethanol at 500°C for 8 h-on-stream.
Motivations and Objectives
Ni-based catalysts raised much interest for the present application [1-3]. Very high activity has been observed at high reaction temperature (>600°C), but it would be interesting to operate under milder conditions, in order to lower the energy input to the process and to improve H2 productivity by favoring the water gas shift reaction. The major inconvenient for Ni-based samples is usually ascribed to coking, often due to the formation of carbon filaments over the active phase. This phenomenon is correlated to catalyst deactivation and appearance of by-products. Indeed, if at high reaction temperature with excess steam carbon may be gasified, at operation at 500°C the C balance, often much lower than 100% evidences coke accumulation.
Results and Discussion
H2 productivity at 500°C seemed firmly dependent on the calcination and on activation temperature of the catalyst when Ni was supported over TiO2 prepared by impregnation. When the sample was calcined and activated at 500°C, no H2 production was observed due to poor ethanol conversion, with selectivity mostly to acetaldehyde and poor carbon balance. By contrast, calcination of the sample at 800°C induced very high H2 productivity, higher C balance and negligible byproducts formation except some CH4 These results were attributed to the formation of a mixed oxide between Ni and the support during synthesis at high temperature (both for Impregnation and FP), which keeps the metal well dispersed in spite of the high activation temperature. This leads to very small Ni particles after activation, which demonstrated to be more active and, most of all, more stable towards coking. C balance was in general much higher for the Co- and Cu-containing samples than for the Ni-based ones. One may conclude that for most of these samples there is no additional coking on the catalyst due to the active phase. However, they proved in general less active than Ni-based ones when tested at 500°C.
References
[1] I. Rossetti, A. Gallo, V. Dal Santo, C.L. Bianchi, V. Nichele, M. Signoretto, E. Finocchio, G. Ramis, G. Garbarino, A. Di Michele, ChemCatChem, 5 (2013) 294.
[2] I. Rossetti, C. Biffi, C. Bianchi, V. Nichele, M. Signoretto, F. Menegazzo, E. Finocchio, G. Ramis, A. Di Michele, Appl. Catal. B, 117-118 (2012) 384.
[3] E. Finocchio, I. Rossetti, G. Ramis, Int. J. Hydrogen Energy, 38 (2013) 3213
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Ni-ZrO2 catalysts for the steam reforming of ethanol: influence of the preparation method on the catalytic performance
No full textA new process for hydrogen production has been proposed based on ethanol steam reforming. Ni-based catalysts have been developed with various techniques and revealed very active and selective for this reaction
Cobalt-based and Nichel-based catalysts for hydrogen production by steam reforming of ethanol
No full textCatalyst coking during ethanol steam reforming is a key problem, especially during testing at relatively low temperature (773 K). Coking activity is related to both support acidity and the tendency of some active phases to form carbon filaments. The latter also depends on the metal support interaction, which determines metal dispersion and stability. In order to deepen this point, different active phases and precursors have been compared as in the following two examples. Hydrotalcite-like precursors were found to allow excellent dispersion of the active phase and promoter in steam reforming catalysts. The data here reported provide evidence of the good catalytic activity of Co-Zn-Al and Co-Ni-Zn-Al catalysts prepared from hydrotalcite-like LHD precursors for ethanol steam reforming. At 823 K the most active Co/Ni catalyst contains a predominant spinel phase with composition near Zn0.58Ni0.42[Al0.44Co0.56]2O4 and small amounts of NiO and ZnO. On the other side, at 873 K the selectivity to hydrogen increases with cobalt content, the most selective catalyst being the Ni-free Co-Zn-Al mixed oxide, essentially constituted by a single spinel type phase Zn0.55Co0.45[Al0.45Co0.55]2O4. Cobalt catalysts appear consequently to behave better than nickel based catalysts in this high temperature range. The key feature for high selectivity to hydrogen is proposed to be associated to the stability of a relatively high oxidation state of Co at the catalyst surface, the most relevant selectivity determining step being constituted by the evolution of surface acetate species. In fact, over oxidized catalyst surface the acetate species evolve producing CO2 and hydrogen while over a more reduced surface they evolve giving rise to methane and COx. Water is supposed to have the main role of allowing surface sites to stay in an unreduced state at least in the temperature range 720-870 K. Co based catalysts, in spite of the usually better carbon balance, proved in general less active than Ni-based ones when tested at lower temperature, i.e. 773 K. As a matter for comparison, TiO2 was also explored as possible support for Ni- and Co-based catalysts for the steam reforming of ethanol. Ni confirmed the most active metal for this reaction, within those here investigated, but many concerns rely on its coking activity. The comparison between the active phases confirm the role of Ni on carbon accumulation over the catalyst, in the form of multiwalled carbon nanotubes, with a more limited contribution of support acidity. Higher resistance to coking may be achieved when loading Ni in very dispersed form and strongly interacting with the support, which may lead to the stabilization of the active phase under the reaction conditions. One possibility is the formation of a mixed oxide, which allows the obtainment of very dispersed metal particles after reduction at high temperature. In other cases, the use of this support may be detrimental due to surface reconstruction and possible coverage of the active phase by the support itself, leading to practically inactive catalysts
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
