1,720,985 research outputs found
Influence of the Preparation Method on the Surface Characteristics and Activity of Boron-Nitride-Supported Noble Metal Catalysts
No full textIn this article, we report how variations in the preparation method of boron-nitride-supported noble metal catalysts may influence the surface characteristics of the active phase and consequently the potential applications as catalysts for oxidation reactions. The deposition and the dispersion of the active phase are strongly influenced by the preparation process and in particular by the protic or aprotic solvent used as the dispersing phase; in this study, benzene, glyme, water, tetrahydrofuran, diglyme, 2-propanol, and glycol have been investigated. Characterization techniques, such as Brunauer-Emmett- Teller, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, have been used to study the influence of the choice of a solvent phase on the particle size and dispersion of the metal deposited on the BN support. The modifications undergone by the support during the deposition of palladium in different solvents have also been studied. Through the use of the same deposition procedure, different noble metal coatings (Pt, Pd, Au, and Ag) have been prepared. The acidic and redox characteristics of the resulting samples were characterized by temperature-programmed reduction and adsorption microcalorimetry. The catalytic performances of these materials were tested in the total oxidation of methane in lean conditions ( excess oxygen and presence of water)
Controlling Fe speciation, sitting and nuclearity in Fe/Hydroxyapatite: effects on the catalytic performances in NH3-SCR reaction
Full text linkHydroxyapatite (Ca5(PO4)3(OH), HAP) is a natural and versatile inorganic material, which, analogously to zeolites, is susceptible to undergoing ion exchange reaction (involving Ca2+ ions) and thus to being easily functionalized with several active metal species. In fact, metal-loaded hydroxyapatites (Me/HAP) are recently emerging as eco-friendly materials in heterogenous catalysis [1-4]. The control of metal sitting, speciation, and nuclearity represents a key step in the identification of active catalytic sites. Actually at least two different Ca-sites with different coordination environment, Ca(I) (high coordination number, 9) and Ca(II) (low coordination number, 7), are available to allocate isolated metal species in HAP framework. In addition, the added metal centers can undergo agglomeration with formation of aggregates of different size, ranging from small oligomers up to clusters and small metal oxide nanoparticles [4]. In many cases, the final metal sitting and speciation is a delicate process driven by the experimental conditions during the deposition of metal phases [4].
Herein, iron has been deposited in different amount (ca. 2-7 wt.%) onto a synthetic hydroxyapatite from iron(III) nitrate, as precursor, according to three preparative methods (ionic exchange, deposition-precipitation and wetness impregnation). A suite of techniques of characterization (UV-Vis and Mössbauer spectroscopies, NH3 adsorption) was used to determine iron speciation and sitting and to deduce relevant structure-activity relationships. Ion exchange procedure gave rise to the co-presence of isolated Fe3+ centers in the Ca(I) sites, together with small Fe-O-Fe oligomers. Isolated Fe3+ centers in Ca(II) sites and FexOy nanoparticles coexisted in the catalysts prepared by deposition-precipitation method. Finally, the cooccurrence of FexOy nanoparticles and isolated Fe3+ centers in Ca(I) sites characterizes Fe/HAP catalysts prepared by wetness impregnation. H2-TPR analysis evidenced the different reducibility of these systems, as shown in figure 1. These dissimilar redox properties unavoidably have an impact on the catalytic behavior. Fe/HAP samples have been tested as catalysts in the NOx reduction by ammonia (NH3-SCR) in the 120-500°C interval with different NH3/NO ratios at fixed GHSV (30,000 h-1). All Fe/HAP samples were active and selective in the NH3-SCR reaction in the temperature interval studied and best performances were observed for the catalysts prepared by deposition-precipitation (about 60% of NOx conversion and selectivity to N2 higher than 95% at 350°C). These results suggest that the speciation and coordination environment of iron species are determining features to be finely tuned in the optimization of Fe/HAP catalysts
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
Boron nitride supported metal catalysts: influence of the metal and preparation method
No full textIn this study we report on the preparation and characterization of boron nitride supported noble metal catalysts with potential applications as catalysts for oxidation reactions. The deposition and the dispersion of the active phase were strongly influenced by the preparation process and in particular by the solvent used as the dispersing phase. Techniques such as BET, XRD and TEM were used to study the role played by the phase used as solvent (benzene, glyme, water, THF, diglyme, isopropanol, glycol) in particles size and dispersion of metals deposed on the BN support. Different palladium depositions under various conditions and different noble metal coatings under the same deposition condition are presented. The catalytic performances were tested in methane traces oxidation in excess oxygen and in the presence of water. The light-off temperature (50 % methane conversion) increased in the following order: Ag/BN < Pt/BN < Au/BN < Pd /BN
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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