1,721,001 research outputs found
Il mutamento difronte alle sfide dell’oblio. Un caso storico culturale, Peccioli
No full textIl progetto di recupero di due aree collocate alle estremità Nord e Sud del centro storico di Peccioli, racconta una ricerca tesa a individuare nuove funzioni per strutture nate in differenti contesti storici, senza stravolgerne la trama urbana, e quindi la storia, ma recuperandola ad una dimensione di modernità e svilupp
A perspective of lanthanide promoted Ni-catalysts for CO2 hydrogenation to methane: catalytic activity and open challenges
No full textIn the frame of energy transition and anthropogenic CO2 emission reduction, CO2 hydrogenation by using green hydrogen to produce Synthetic Natural Gas is considered as a promising option. Considering nickel low-cost and natural abundance, Ni-based catalysts are the most investigated and used materials for methanation reaction in the temperature range 573–673 K. However, Ni-based catalysts showed inadequate low-temperature activity (below 473 K), low reducibility and dispersion, and catalyst deactivation due to particles sintering or even coke deposition. As well, for very low temperature application volatilization of the active phase through carbonyl production cannot be excluded. In recent years, lanthanides addition and in particular lanthanum and cerium, represents a good option in order to overcome the Ni-based catalyst limits. In this paper, a comprehensive review and overview of the most recent commercial formulation and advances in the development of lanthanides promoted Ni catalysts are reported, including the evaluation of the effect on the catalytic properties and the obtained catalytic performances
Support effects in metal catalysis: a study of the behavior of unsupported and silica-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure
No full textTwo 20 wt.% Co/SiO2 catalysts were prepared using silica gel as a support and cobalt acetate and nitrate as precursors, respectively. As a comparison unsupported amorphous cobalt nanoparticles (10–80 nm) were synthesized by decomposing cobalt carbonyl. They were characterized before and after reaction using XRD, IR spectroscopy in the range of framework vibrations, DR-UV–vis-NIR spectroscopies and FE-SEM microscopy. They are active in CO2 methanation at atmospheric pressure. However, unsupported cobalt and the silica-supported catalyst prepared using cobalt acetate deactivate fast at 623–673 K, also due to formation of encapsulating carbon. On the other hand, they retain more stable activity in the reverse water gas shift (rWGS) reaction, producing CO. Methanation and rWGS appear to occur on independent sites. The silica-supported catalyst produced from cobalt nitrate show more stable methanation activity, attributed to the presence of smaller cobalt particles (10–20 nm) that resist deactivation. For both unsupported CoNPs and Co/SiO2, the significant parameters for catalysts deactivation have been determined for CO2 methanation. The differences observed among catalysts produced starting from cobalt acetate and cobalt nitrate, can be associated to the different pH of the impregnating solution
Unsupported cobalt nanoparticles as catalysts: Effect of preparation method on catalytic activity in CO2 methanation and ethanol steam reforming
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The 500 °C Isothermal Section of the Al-Fe-Pr Ternary System
No full textPhases and equilibria involved in the isothermal section at 500 degrees C of the ternary Al-Fe-Pr system have been here investigated in the whole composition range by means of X-ray diffraction, optical and scanning electron microscopy, and electron probe microanalysis. Phase equilibria are characterised by the formation of two binary solid solutions, Pr2(FexAl1-x)17 with 0.34 <= x <= 1.00 (hR57-Th2Zn17) and Pr(FexAl1-x)2 with 0 <= x <= 0.20 (cF24-Cu2Mg), and four ternary compounds, tau 1-PrFe2Al10 (oS52-YbFe2Al10), tau 2-PrFe2Al8 (oP44-CeFe2Al8), tau 3-Pr(FexAl1-x)12 with 0.28 <= x <= 0.44 (tI26-ThMn12) and tau 4-Pr6(FexAl1-x)14 with 0.63 <= x <= 0.81 (tI80-La6Co11Ga3), which have been confirmed. The solid solubility ranges of the binary and ternary compounds have been considered and trends of their lattice parameters studied. The complete isothermal section has been obtained and the general features of the section are discussed and compared with those of other ternary systems of light R (La, Ce, Pr, Nd, Sm) with Al and Fe
Alumina-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure
No full text20 wt.% cobalt catalysts supported on pure and 5 wt.% silica-containing alumina have been prepared and characterized by X-Ray Diffraction, IR and DR-UV-vis-NIR spectroscopies and Field-Emission Scanning Electron Microscopy (FE-SEM). The presence of a cobalt-containing surface spinel phase Co3-xAlxO4 and, for the silica-containing sample, of a segregated Co3O4 phase is evident. These catalysts have been tested in CO2 hydrogenation at atmospheric pressure in steady state conditions in the temperature range 523-773 K. Both catalysts are active in CO2 hydrogenation to methane (methanation) and to CO (reverse Water Gas Shift, rWGS). CO2 hydrogenation activity is higher on freshly pre-reduced silica-free Co/Al2O3, while selectivity to methane is slightly higher on the silica-containing sample. Spent catalysts contain clustered or amorphous cobalt metal centers as active sites for methanation. The silica-containing catalyst shows slow deactivation in CO2 hydrogenation upon 13 h experiments, with quite stable or even slightly increasing rWGS activity and decreasing CH4 selectivity. This confirms previous data suggesting that, over cobalt catalysts, sites for methanation are metal centers prone to deactivation by carbon deposition. However, in contrast with what happens with unsupported and silica-supported cobalt catalysts, where deactivation is very fast, over these alumina-based catalysts carbon deposition and deactivation occur much more slowly. Sites for rWGS are unreduced cobalt centers which do not undergo such a deactivation phenomenon. & COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
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
Reutilization of silicon- and aluminum- containing wastes in the perspective of the preparation of SiO2-Al2O3 based porous materials for adsorbents and catalysts
No full textThe waste materials available as sources of silicon and aluminum for producing porous materials like amorphous silicas, aluminas, amorphous silica-aluminas, and zeolites, to be used as catalyst and adsorbents, are briefly summarized. The procedures for preparing these materials from wastes are also taken into account. The limits of this approach in terms of economy and environmental protection are also briefly considered. It is concluded that mesoporous materials can be prepared from wastes, but care to product quality and to overall process efficiency is needed
Thiol-functionalized magnetic nanoparticles for static and dynamic removal of Pb(II) ions from waters
No full textThe synthesis of magnetite (Fe 3 O 4 ) nanoparticles (NPs) and the functionalization by means of a silane derivative (3-mercaptopropyl) trimethoxysilane (MPTMS) as a way for heavy metal capture, i.e., Pb 2+ ions, has been investigated. A direct reaction between the active thiol organosilane molecule and the surface of the magnetite nanoparticle is described. The coated nanoparticles, presenting an average diameter of about 20 nm, have been extensively characterized from the morphological, chemical, and physical point of view. The capture of Pb 2+ ions from aqueous solution has been performed both in static and dynamic mode, using in both cases a configuration of commercial NdFeB permanent magnets. The amount of heavy metal captured by the magnetic NPs as a function of time, as well as its fraction recovered by an EDTA solution, have been measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). The Pb 2+ capture from a spiked water solution (5 mg/L) is very fast, reaching 91% in static conditions after only 10 min. Furthermore, dynamic data also demonstrated the possibility to apply the toxic heavy metal capture method to large volumes
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