1,721,024 research outputs found
Cobalt on and in zeolites and silica–alumina: Spectroscopic characterization and reactivity
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The effect of niobium and tantalum on physicochemical and catalytic properties of silver and platinum catalysts based on MCF mesoporous cellular foams
No full textMCF, NbMCF and TaMCF Mesostructured Cellular Foams were used as supports for platinum and silver (1 wt%). Metallic and bimetallic catalysts were prepared by grafting of metal species on APTMS (3-aminopropyltrimethoxysilane) and MPTMS (2-mercaptopropyltrimethoxysilane) functionalized supports. Characterizations by X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF) spectroscopy, and in situ Fourier Transform Infrared (FTIR) spectroscopy allowed to monitor the oxidation state of metals and surface properties of the catalysts, in particular the formation of bimetallic phases and the strong metal-support interactions. It was evidenced that the functionalization agent (APTMS or MPTMS) influenced the metals dispersion, the type of bimetallic species and Nb/Ta interaction with Pt/Ag. Strong Nb-Ag interaction led to the reduction of niobium in the support and oxidation of silver. MPTMS interacted at first with Pt to form Pt-Ag ensembles highly active in CH3OH oxidation. The effect of Pt particle size and platinum-silver interaction on methanol oxidation was also considered. The nature of the functionalization agent strongly influenced the species formed on the surface during reaction with methanol and determined the catalytic activity and selectivity
Searching for the active sites of Co-H-MFI catalyst for the selective catalytic reduction of NO by methane: A FT-IR in situ and operando study
No full textA Co-H-MFI sample has been studied through FT-IR spectroscopy of in situ adsorption and co-adsorption of probe molecules (o-toluonitrile, CO, NO) and has been tested in the CH4-SCR process under IR operando conditions. The o-toluonitrile (oTN) adsorption and the oTN and NO coadsorption, show that both Co2+ and Co3+ species are present on the catalyst surface. Co3+ species are located inside the zeolitic channels while Co2+ ions are distributed both at the external and at the internal surfaces. The operando study show the activity of Co3+ species in the reaction. The existence of three parallel reactions, CH4-SCR, CH4 total oxidation and NO to NO2 oxidation, has been confirmed. Isocyanate species and nitratelike species appear to be intermediates of CH4-SCR and NO oxidation, respectively. A mechanism for CH4-SCR has been proposed. Co2+ substitutional sites, very evident and predominant in the catalyst, which are very hardly reducible, seem not to play a key role in the SCR process
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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