1,720,964 research outputs found
From renewable to fine chemicals through selective oxidation: The case of glycerol
No full textCatalytic selective oxidation of glycerol is presented in terms of catalytic systems and experimental conditions. Unsupported gold nanoparticles (AuNPs), AuNPs on carbon and on TiO2 were employed and compared in terms of reaction selectivity and activity. The role of the base and the formed hydrogen peroxide has been considered. Gold based catalysts showed selectivity that is strongly dependent of the reaction conditions. In particular C-C scission products increases by increasing the reaction temperature but correlated only partially with the rate of degradation of the H 2O2 formed under the operative conditions. Moreover, under neutral/acidic conditions glycerol can be oxidised also by increasing the temperature slightly, but it leads to a detrimental effect on selectivity and catalyst life
Microgel-stabilised gold nanoclusters: powerful "quasi-homogeneous" catalysts for the aerobic oxidation of alcohols in water
No full textGold nanoclusters of small size (2.5 nm) and narrow size distribution were synthesized in solution using tailor-made soluble cross-linked polymers (microgels) as exotemplates and stabilizers. The resulting microgel-stabilized nanoclusters could be conveniently isolated by precipitation, stored in the solid state, and redispersed in water and polar organic solvents. They were found to exhibit remarkable catalytic activity (average TOF up to 960 h(-1)) in the aerobic oxidation of benzylic and aliphatic alcohols and also of polyols in water under mild conditions (50-70 degrees C, 1-3 atm O2)
Effect of gold addiction on Pt or Pd catalysts in liquid phase oxidations
No full textSingle phase Au-Pd and Au-Pt on carbon catalysts have been compared in the liquid phase oxidation of glycerol (representative for polyols) and n-octanol (representative for long chain aliphatic alcohol). The observed overall enhancement of catalytic activity appeared to be function of support, substrate and reaction conditions. Effect of substrate structure has been disentangled: synergistic effect between Au and Pt was maximized when polyol-like substrates were oxidized whereas Au-Pd based catalyst showed a more general match
Hydroxyapatites as tunable supports of gold-based catalysts for liquid phase selective alcohol oxidation in base-free conditions
No full textSupported noble metal nanoparticles (NPs) have been widely investigated as catalytic systems in liquid-phase selective oxidation reactions. In particular, supported gold nanoparticles revealed peculiar catalytic performances despite an alkaline medium is usually required in order to accomplish high activity and selectivity. As avoiding basic conditions represents a great advantage from a practical point of view, lot of efforts have been recently devoted to gold based catalysts able to maintain good activity (and selectivity) even under neutral (or acidic) conditions.
In this respect, it has been observed that alloying platinum or palladium to gold provides effective catalytic systems in terms of activity and selectivity [1, 2]. Moreover, it has been also shown that the acid-base properties of the support can play a crucial role [3-10].
Herein, we investigated in detail the influence of weakly basic supports as hydroxyapatites on the catalytic performances of AuPt catalysts in two selected reactions, namely glycerol and hydroxymethyl furfural (HMF) oxidations. The choice of these two substrates was connected not only to the industrial importance of the derived products but also to the facile catalyst deactivation usually observed when glycerol or HMF are attempted to be oxidized under neutral conditions.
Hydroxyapatite samples (HAPs) were synthesized by co-precipitation method, adding NH4H2PO4 to Ca(NO3)2 at 80°C for different pHs adjusted during the precipitation and/or during the maturation time. Despite similar apparent basic properties (similar auto-generated solution pH around 7.1-7.3), XPS analyses revealed different surface composition from the bulk, especially in terms of Ca/P atomic ratio (XPS versus ICP analyses). Au and Pt nanoparticles were deposited on HAPs using the sol immobilisation technique whereas bimetallic Au-Pt/HAP were prepared following a two steps procedure which ensures the formation of AuPt alloy avoiding any metal segregation [11]. From a catalytic point of view HAPs have been revealed peculiar supports which promote the base-free oxidation of glycerol and HMF but limiting the C-C bond cleavage on the contrary of other basic supports (i.e.MgO). We also observed a strong synergistic effect between Au and Pt. In particular the surface enrichment of P observed by increasing the pH during precipitation of HAP, correspond to an increase of activity in both catalytic tests
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
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