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New, innovative methods for the large scale preparation of nanosized metal catalysts and their use in selective hydrogenations
No full textNanomaterials are very important today because they are employed in a great number of different industrial sectors. In particular, nanostructured metal catalysts have attracted an intense interest because they allow a crucial improvement of the catalytic performances. In this field, many synthetic methods have been reported, but all these present several drawbacks that limit their application on industrial scale. Now we have patented a simple and cheap process for the large scale preparation of nanosized metal catalysts working in a low boiling alcohol. The prepared nanocatalysts are characterized by TEM, SEM, elemental analysis, FT-IR spectroscopy and XPS. This method has been successfully adopted for the preparation of gold, palladium and ruthenium nanocatalysts. This process enables to reach a good control of the metal particles dimensions and morphology with an absolute reproducibility. The ruthenium nanocatalysts are particularly efficient in different chemoselective reactions, such as the hydrogenations of benzene to cyclohexene and of phenol to cyclohexanone. On the other hand, palladium nanocatalysts were tested in the hydrogenation of cyclohexene as well as of benzaldehyde to benzyl alcohol, showing excellent performances in terms of activity and selectivity, good reproducibility, recyclability and thermal stability
Linear low-density polyethylenes by co-polymerization of ethylene with 1-hexene in the presence of titanium precursors and organoaluminium co-catalysts
No full textThe co-polymerization of ethylene with 1-hexene has been performed with titanium precursors based on carboxylato ligands in the presence of organoaluminium compounds as activators to afford linear low-density polyethylenes (LLDPEs). The influence of the polymerization parameters was studied with particular reference to the type and amount of catalyst components, solvent, temperature, ethylene pressure, 1-hexene concentration. The chloro-substituted bis-carboxylato titanium complex resulted the most active precursor in the co-polymerization, allowing to obtain copolymers with modulable composition in the 1-5 mol% range of 1-hexene units. The obtained copolymers were characterized by thermal analysis, X-ray diffraction spectroscopy, FTIR and NMR techniques. (c) 2007 Elsevier Ltd. All rights reserved
Innovative catalysts based on niobium and tantalum carbamates for olefins polymerization
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FTIR Microanalysis and Phase Behaviour of Ethylene/1-Hexene random copolymers
No full textEthylene/1-hexene random copolymers with 1-hexene content in the range of 1-5 mol-%, synthesised in the presence of new heterogeneous catalyst systems based on bis-carboxylato and -bis-chloro-carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR-M), DSC calorimetry and X-ray scattering. The co-monomer content and sequence distribution in the various samples were determined by means of both FTIR-M and C-13 NMR spectroscopy. The deformation bands of methyl groups in the region of 1400-1330 cm(-1) were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1500-1300 and 760-690 cm(-1) frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1378 cm-1 was recorded between 110 and 130 degrees C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co-monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches
An innovative microwave method for large scale preparation of nanocatalysts for industrial applications
No full textNanostructured metal catalysts are of great interest because of their marked catalytic performances. Consequently, different synthetic methods have been reported in literature but, up to now, all these methods present several drawbacks for their application on industrial scale. Today microwave chemistry is experiencing an exponential growth and it is generally performed using a closed metal cavity, i.e. a microwave oven. However, the current commercial systems present a number of relevant limitations. Multi-disciplinary applications are complicated or even impossible. Therefore industrial scale-up is not straightforward at all and requires very high project and investment costs. Now, we have applied a new microwave method enabling the possibility of working without the constraints. The method is safe and cheap, it enables to obtain the utmost efficiency and control also for industrial applications, without resorting to an ordinary oven. We have successfully adopted our procedure for the synthesis “in situ” of ruthenium, palladium and silver nanocatalysts on different supports that present little average diameters, good morphology and very narrow sizes distribution with an absolute reproducibility. The reduction of the metal was also confirmed by XPS measurements. These nanostructured ruthenium catalysts resulted particularly efficient, in terms of activity and selectivity, in different selective catalytic reactions, such as the hydrogenation of benzene to cyclohexene and of phenol to cyclohexanone. The nanostructured palladium nanocatalysts have been employed in the hydrogenation of cyclohexene to cyclohexane and of benzaldehyde to benzyl alcohol and these results are also promising in an industrial perspective
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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