1,721,008 research outputs found
Multiphase hydrodechlorination of polychlorinated aromatics – Towards scale-up
No full textWe describe a chemical technology for the reductive catalytic multiphase hydrodechlorination (HDC) of chlorinated aromatics to greatly reduce their toxicity and aid the disposal of such species. The system requires no solvent and the catalyst displays a high recycling efficiency. In the present case, 1,3-dichlorobenzene (1,3-DCB) was used as a model compound, and was quantitatively hydrodechlorinated to benzene with hydrogen, in a tri-phasic liquid system consisting of the chlorinated aromatic itself as the top organic phase, an aqueous sodium hydroxide bottom phase (that neutralises acids formed), and an Aliquat®336 (A336) intermediate phase containing a Pd/C catalyst.\ud
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Once the reaction was complete the top phase (now just benzene) and the bottom phase (now principally aqueous NaCl) were removed and the remaining catalytic A336/(Pd/C) phase recycled.\ud
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This model study was conducted on a multi-gram scale with a view of demonstrating its applicability to the detoxification of PCBs. Comparison of the Mass Intensity (MI) and turnover frequency (TOF) of our model reaction with three examples of published procedures for the HDC of DCB, indicated that the MI for our system (MI = 6.33) was lower by an order of magnitude or more than that of the others (MI = 27.9, 64.6, 96016), and that TOFs were comparable.\ud
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A preliminary cost analysis indicates approximately 2000 €/tonne to treat tonne-scale amounts of chlorinated aromatics, making the system in principle useful for industrial implementation
Templating mesoporous silicates on surfactant ruthenium complexes: a direct approach to heterogeneous catalysts
No full textMesoporous silicas have been obtained by the true liquid crystal templating (TLCT) method, using a surfactant RuII complex as the template; on calcination, ruthenium-containing particles are deposited into the pores; the materials show high catalytic selectivity for the hydrogenation of hex-1-ene.<br/
One-Pot RAFT/"Click" Chemistry via Isocyanates: Efficient Synthesis of alpha-End-Functionalized Polymers
No full textA new methodology has been developed for preparing alpha-functional polymers in a one-pot simultaneous polymerization/isocyanate "click" reaction. Our original synthetic strategy is based on the preparation of a carbonyl-azide chain transfer agent (CTA) precursor that undergoes the Curtius rearrangement in situ during reversible addition-fragmentation chain transfer (RAFT) polymerization yielding well-controlled alpha-isocyanate modified polymers. This strategy overcomes numerous difficulties associated with the synthesis of a polymerization mediator bearing an isocyanate at the R group and with the handling of such a reactive functionality. This new carbonyl-azide CTA can control the polymerization of a wide range of monomers, including (meth)acrylates, acrylamides, and styrenes (M-n = 2-30 kDa; D = 1.16-1.38). We also show that this carbonyl-azide CTA can be used as a universal platform for the synthesis of alpha-end-functionalized polymers in a one-pot RAFT polymerization/isocyanate "click" procedure
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
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
Renewable Aromatics from Kraft Lignin with Molybdenum-Based Catalysts
No full textThe catalytic depolymerization of Kraft lignin in supercritical ethanol was explored in the presence of Mo2C- and MoS2-based catalysts. At 280 °C, Mo2C and Mo2C/Al2O3 afforded aromatic yields of 425 and 419 mg/g lignin, respectively: amongst the highest yields reported to date. Ionic-liquid-assisted delamination of MoS2 resulted in highly active catalysts, capable of quantitative conversion of lignin at the expense of aromatic yield (ca 186 mg/g lignin). Across all the catalysts studied, between 0.04 wt% and 0.38 wt% of molybdenum leached into solution under supercritical conditions, according to ICP analyses (corresponding to 27–570 µg of molybdenum in the reaction supernatant). A small contribution to the molybdenum in solution comes from the reactor itself (Hastelloy C contains 16 wt% Mo). Analysis of a depolymerization performed with fresh Kraft lignin and the soluble portion of the reaction mixture from a previous reactor run indicated that the leached species were neither active enough to afford the high conversions observed, nor selective enough to give high yields of aromatic products. In conjunction with the ICP data and differential chemoselectivities of the Mo2C- and MoS2-based catalysts, these results suggest that the bulk of the catalysis is heterogeneous
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