1,720,958 research outputs found
Effect of the support on activity of silver catalysts for the selective reduction of NO by propene
No full textUse of zirconia, ceria–zirconia and ceria supports for Ag-based lean deNOx catalysts lowers the temperature range of activity by about 150–200K with respect to Al2O3-supported analogues. Ex situ characterisation of the catalysts indicates that this remarkable effect is associated with a role of the support rather than Ag dispersion. The crucial role of the support is further evidenced by suppression of CO formation over these catalysts and by significant support-related differences when SO2 is added tothe feed. The presence of ceria in the formulation results in an initial resistance to the deactivating effectof SO2; while the use of both zirconia and ceria–zirconia facilitates reactivation after sulphur poisoning
New monodispersed palladium nanoparticles stabilized by poly-(N-vinyl-2-pyrrolidone): Preparation, structural study and catalytic properties
No full textMesitylene/1-hexene solvated palladium nanoparticles, obtained by metal vapour synthesis (MVS) technique,
were stabilized in solution at room temperature with poly-(N-vinyl-2-pyrrolidone) (PVP) and isolated
by precipitation with a diethyl ether or THF as brown powder. HRTEM and FT-IR analyses on
samples with different Pd/PVP ratio (1%, 5%, 10%, 15%, 20 w/w%) showed palladium nanoparticles with
mean diameters limited in the range 1.5–2.5 nm and the presence of competitive intermolecular interactions
between C@O groups and palladium atoms on nanoparticle surface. The Pd–PVP systems, dissolved
in EtOH solvent, showed excellent catalytic activity and selectivity in the hydrogenation of
aliphatic alkynes (1-hexyne, 2-hexyne, 3-hexyne, 3-hexyne-1-ol) to the corresponding (Z)-alkenes. The
catalytic activity of Pd–PVP samples, dissolved in 1-methyl-2-pyrrolidinone (NMP), has been also evaluated
in the Mizoroki–Heck C–C coupling reaction of iodobenzene and bromo-arenes with butyl acrylate
showing high efficiency. Moreover, the catalyst can be quantitatively recovered at the end of the reaction
by precipitation with diethyl ether and reused without significant loss of catalytic activity
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
Metal vapour derived supported palladium catalysts for Sonogashira carbonylative reactions
No full textVariations 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
Metal vapour derived supported rhodium nanoparticles in the synthesis of β-lactams and β-lactones derivatives
Full text linkFunctionalised β-lactones and β-lactams were prepared starting from propargyl alcohols and propargyl tosyl amides by means of efficient silylcarbocyclisation reactions catalysed by rhodium nanoparticles derived from mesitylene-solvated Rh atoms (Metal Vapour Synthesis technique, MVS) and deposited on inorganic (C, γ-Al2O3 Fe2O3) and organic matrices (PBI). All the MVS supported nanoclusters resulted more active than the analogous commercial Rh/C and Rh/γ-Al2O3, as well as homogeneous Rh4(CO)12 used as reference catalyst. In particular, metal vapour derived Rh/C afforded the β-lactones and β-lactams in high yields and chemoselectivity. Preliminary investigations on the nature of the real active metal species involved in the catalytic process showed that rhodium(0) naked nanoparticles are leached by the support. The high catalytic activity encountered with Rh/C could be ascribed to the easy leaching of metal nanoparticles from carbon into solution. Indeed, the presence of a more polar matrix determined a minor catalytic efficiency probably due to a stronger interaction between the metal and the support. Therefore MVS Rh/C species represents a source, stable with ageing at room temperature, of highly active metal nanoparticles
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