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Stability of Palladium Catalysts Supported on Sulphonated Copolymers of Styrene and Divinylbenzene in Hydrogenation Process
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Deactivation of polymer supported palladium catalysts in the hydrogenation of 4-nitrotoluene
No full textThe deactivation of palladium catalysts supported on commercially available sulfonated polystyrene-divinylbenzene resins (DOWEX) in the hydrogenation of 4-nitrotoluene was studied. Catalysts were prepared from 4 and 8 mole % crosslinked polymers, with particle size between 0.04 and 0.80 mm and palladium contents ranging from 0.25 to 1 wt.% (dry state). The catalytic tests were carried out in a batch reactor vigorously shaken, at 30-50 °C, and 0.25 and 0.5 MPa. The analysis of the conversion curves showed that three factors are mainly responsible for the relatively high deactivation rates: (i) the concentration of hydrogen in the neighbourhood of palladium crystallites, (ii) temperature, (iii) the nanomorphology of the support. Some practical advice concerning the employment of polymeric hydrogenation catalysts and relevant operational conditions can be achieved from the results presented herein
Modelling of the deactivation of polymer-supported palladium catalysts in the hydrogenation of 4-nitrotoluene
No full textThe kinetics of the hydrogenation of 4-nitrotoluene over Pd catalysts supported on sulfonated polystyrene and simultaneous deactivation of these catalysts were investigated. Reaction rates of both the hydrogenation and the dissolution of Pd crystallites were related to the total Pd surface. The average radius of ideal spherical crystallites, as determined by X-ray powder diffraction analysis, was taken as the starting value of the crystallite size. Stability of the polymer network was checked by Inverse Steric Exclusion Chromatography (ISEC). The ESR and Static Gradient field Spin Echo (SGSE) NMR spectroscopies were used to assess the accessibility and diffusivity before and after deactivation experiments. Langmuir-Hinshelwood type kinetic models were applied to describe the hydrogenation of 4-nitrotoluene. The kinetic law was incorporated into a more comprehensive model involving also diffusion of reactants inside catalytic particles. Simultaneous treatment of a few sets of kinetic data from batch hydrogenation carried out at 0.25-0.75 MPa yielded reliable values of model parameters. The model showed an increasing rate of dissolution of palladium with decreasing concentration of hydrogen and increasing concentration of 4-nitrotoluene. The latter fact supports the hypothesis that the nitro compound is the oxidant responsible for the dissolution of palladium
Modeling of the Deactivation of Polymer-Supported Palladium Catalysts in the Hydrogenation of 4-nitrotoluene
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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
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