1,720,998 research outputs found
NiCo as catalyst for magnetically induced dry reforming of methane
No full textIn this paper we report the activation of the dry reforming reaction by induction heating of a NiCo alloy. The catalyst plays a double role, serving both as a promoter for the reforming reaction and producing the heat induced by dissipation of the electromagnetic energy. The elevated temperatures imposed by the reforming reaction suggest the choice of an alloy with a Curie temperature >800°C. In this respect Ni:Co ratio 60:40 was chosen. Alloy active sites for CH4and CO2activation are created by a mechanochemical treatment of the alloy that increases solid-state defects. The catalyst has been successfully tested in a continuous-flow reactor working under atmospheric pressure. Methane conversion and hydrogen production yields have been measured as a function of the applied magnetic field, reactant flow rate and time on stream. © Published under licence by IOP Publishing Ltd
Effect of heat treatments on TiH2: Surface composition and hydrogen release
No full textThe present work investigates the effect of heat treatments in air on the surface and structure of titanium hydride (TiH2) and hydrogen desorption. TiH2 has been heated in air at 440 and 540 °C for increasing time up to 180 min. to obtain the samples representative of 12 different oxidation conditions. The samples have been then examined by Temperature Programmed Desorption (TPD), X-Ray Diffraction (XRD) and Photoelectron Spectroscopy (XPS). Experimental results are presented and discussed. © 2017 Trans Tech Publications, Switzerland
Thermal characterization of a cavity receiver for hydrogen production by thermochemical cycles operating at moderate temperatures
No full textThe manganese-ferrite thermochemical cycle developed by ENEA for hydrogen production, whose maximum temperature level lays in the range 750-800. °C, has a high potential for coupling with the solar source using conventional structural materials. As a first step for the on sun feasibility validation of the cycle, an experimental survey of the thermal performance of a receiver-reactor designed by ENEA, to be powered by a solar furnace (1. kW), has been carried out in the absence of a reaction. The temperature distribution over the reactor chamber as a function of solar irradiation has been measured and the thermal inertia of the system has been evaluated. The experimental results confirm that the reactor temperature and inertia are compatible with the manganese-ferrite cycle and other cycles operating at moderate temperatures. In order to set the basis for the evaluation of this and other similar prototypes, a finite element model (FEM) has been developed to describe the thermofluidodynamic behavior of the reactor. Good agreement between calculated and experimental data has been obtained; therefore this model will be improved and extended to describe both the hydrogen and oxygen releasing reactions of the manganese-ferrite cycle, with the aim of optimizing the reactor design. © 2013 Elsevier Ltd
Optical and electrochemical properties of cerium-zirconium mixed oxide films deposited by sol-gel and r.f. sputtering
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Tailoring the critical temperature of Ca/K-1144 superconductors: The effect of aliovalent substitution on tetragonality
No full textAmong the iron-based superconductors, the so-called 1144 family has, in recent years, attracted significant interest due to its stoichiometric nature, with materials robust towards chemical inhomogeneities and characterized by a well-defined critical temperature. The most studied 1144 compounds are characterized by the A1AE1Fe4As4 chemical composition, where A and AE constitute an appropriate combination of alkaline and alkaline-earth metals, respectively. The 1144 structure is in fact formed only when the A and AE elements respect specific requirements in terms of relative size and parent compound structure. The stoichiometric aspect, one of their strong points, has represented, however, up to today a restriction, limiting the conceptualization of 1144 structures to quaternary compounds. In this work, we demonstrate that to obtain the 1144 crystalline phase it may be sufficient to maintain a 1:1 ratio between ions of different size that intercalate the Fe-As planes, and that in selected conditions an opportunely tailored cation substitution is possible. Using a simple mechanochemically assisted synthesis route 1144 compounds where Ca is substituted by Na, K by Ba, and both simultaneously, are obtained. We demonstrate that the critical temperature of doped compounds is not simply related to the substitution amount or to the resulting Fe valence. We show that the superconducting transition is in fact linked to the structural distortion induced by the chemical composition variation: by tailoring the chemical composition we obtain doubly substituted samples - with substitution levels up to 20% - characterized by a tetragonality ratio c/a similar to the pristine compound and critical temperatures of approximately 34 K
Hydrogen production by the sodium manganese ferrite thermochemical cycle-experimental rate and modeling
No full textThe sodium manganese ferrite thermochemical cycle for hydrogen production by water splitting can successfully operate in a relatively low temperature range (1023-1073 K) and has a high potential for coupling with the solar source using conventional structural materials. With the aim of implementing the cycle in a solar reactor, the hydrogen evolution rate from the reactive mixture measured in laboratory apparatus has been modeled by using a shrinking-core model. Such a model proved to adequately describe the rate of hydrogen production in the studied temperature and water concentration range. The model was extended to predict the behavior of the reactive mixture subjected to different experimental conditions. © 2014 American Chemical Society
NiCo as catalyst for magnetically induced dry reforming of methane
No full textIn this paper we report the activation of the dry reforming reaction by induction heating of a NiCo alloy. The catalyst plays a double role, serving both as a promoter for the reforming reaction and producing the heat induced by dissipation of the electromagnetic energy. The elevated temperatures imposed by the reforming reaction suggest the choice of an alloy with a Curie temperature >800°C. In this respect Ni:Co ratio 60:40 was chosen. Alloy active sites for CH4and CO2activation are created by a mechanochemical treatment of the alloy that increases solid-state defects. The catalyst has been successfully tested in a continuous-flow reactor working under atmospheric pressure. Methane conversion and hydrogen production yields have been measured as a function of the applied magnetic field, reactant flow rate and time on stream
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