1,721,010 research outputs found
Structure-sensitivity of CO 2 methanation over nanostructured Ni supported on CeO 2 nanorods
No full textNi-based oxides are widely investigated as catalysts for CO 2 methanation due to their high activity, high selectivity and low cost. The catalytic performances of Ni-based catalysts depend on support properties that strongly influence the dispersion of the catalytic active phase and the Ni-support interaction. Although the CO 2 methanation is widely studied, the structure sensitivity of methanation on nickel is not completely assessed. Ni/CeO 2 nanorods with different nickel/ceria molar ratios (0.05, 0.10, 0.20, 0.30) were prepared by one-pot hydrothermal synthesis. The effect of nickel content and metal particle size on catalytic activity and selectivity for CO 2 methanation were studied using CO 2 :H 2 = 1:4 stoichiometric ratio at high space velocity (300 L g −1 h −1 ). Sample structure and morphology were studied by X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) analysis, field-emission scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS), H 2 -temperature programmed reduction (TPR), H 2 -temperature-programmed desorption (TPD). Both the CO production and the turnover frequency appear depending on nickel particle size, suggesting a structure sensitivity of the CO 2 methanation on nickel supported on ceria
Green synthesis and characterization of titanium dioxide nanoparticles and their photocatalytic activity
Full text linkIn this study, we compared two low-temperature synthesis procedures for the large-scale production of titania nanoparticles (NPs). The first takes place in an aqueous medium with an acidic environment, by using a triblock polymer surfactant (Pluronic 123). The second involves a polycondensation reaction of alkoxide precursors at 70 °C in a water-in-oil (W/O) microemulsion with a volume ratio of 1:1, using cetylpyridinium bromide (CPB) as a cationic surfactant. The morphological and structural characterization of the samples was carried out through Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The photoactivity of the nanostructured titania was evaluated by measuring the photodegradation of Methylene Blue (MB). The solvent-free synthetic approach provided spherical titania nanoparticles mainly constituted by rutile crystallites with a very good synthetic yield. However, the photodegradation rate of MB for such titania nanoparticles ranges from 30 % to 40 %, after 1h under solar irradiation. Conversely, titania nanoparticles obtained through microemulsion synthesis show a photodegradation rate of more than 90 % comparable to titania P25. This high-yield synthesis leads to the formation of TiO2 nanoparticles characterized by small crystallite aggregates (rutile and anatase)
Horizontal permeable reactive barriers with zero-valent iron for preventing upward diffusion of chlorinated solvent vapors in the unsaturated zone
No full textChlorinated solvents are extensively used in many activities and hence in the past decades impacted a large number of sites. The presence of these contaminants in groundwater is challenging particularly for the management of the vapor intrusion pathway. In this work we examine the potential feasibility of using horizontal permeable reactive barriers (HPRBs) placed in the unsaturated zone to treat chlorinated solvent vapors emitted from groundwater. Zero-valent iron (ZVI) powders, partially saturated with water and characterized by different specific surface areas (SSA), were tested, alone or mixed with sand, in lab-scale batch reactors using TCE as model compound. Depending on the type of iron powder used, a reduction of TCE concentration in the vapor phase from approximately 35% up to 99% was observed after 3 weeks of treatment. The best performance in terms of TCE reduction was obtained using the ZVI characterized by the intermediated values of the specific surface area (SSA). This finding, which is in contrast with the results generally observed in in aqueous solutions, was tentatively attributed to a non-selective higher reactivity of the fine-grained iron samples with water and dissolved oxygen (with a consequent iron passivation) or to the occurrence of a diffusion-limited reaction kinetics. Based on the first-order kinetic degradation rate constants estimated from the experimental data, a horizontal barrier of 1 m containing ZVI or a mixture of ZVI and sand can potentially lead to an attenuation of TCE vapors over 99%
Novel composite fuel electrodce for CH4-SOFC and CO2-SOEC
No full textThe development of reversible solid oxide cells allows to use a single device to derive chemicals from power (power-to-fuel technology) and power from chemicals (fuel-to-power technology). We investigated a composite fuel electrode (60 wt.% La0.6Sr0.4Fe0.8Mn0.2O3-δ and 40 wt.% (5 wt.% Ni)-containing Ce0.58Sm0.15O2-δ) for dry methane oxidation in SOFC-mode and for CO2reduction in SOEC-mode. In reducing conditions, Fe exsolved from the LSFMn perovskite formed a Ni-Fe alloy with Ni present on SDC. When tested as SOFC anode, the composite was active towards dry methane oxidation at 800 °C and stable for over 40h; if tested as SOEC cathode, it showed remarkable activity for CO2reduction. EIS analysis was used to have a better understanding of the cell mechanisms in SOFC and SOEC mode
Co-exchanged mordenites: preparation, characterization and catalytic activity for the abatement of NO with CH4 in the presence of excess O2
No full textINNSBRUCK (AUSTRIA), 31 AUGUST - 4 SEPTEMBER 200
The role of manganese substitution on the redox behavior of La0.6Sr0.4Fe0.8Mn0.2O3-δ
No full textPerovskite oxides such as ferrites have been widely investigated for their remarkable electrochemical activity as
SOFC electrodes. However, their phase instability in reducing conditions remains an issue for anode application.
The role of Mn substitution into B-site of La0.6Sr0.4FeO3-δ (LSF) perovskite oxide was investigated. New insights
on the structural evolution of La0.6Sr0.4Fe0.8Mn0.2O3-δ (LSFMn) upon high temperature reduction were revealed.
In oxidizing atmosphere, Mn substitution reduces the oxygen vacancy concentration while, switching to reducing
conditions, it drives the transition from rhombohedral perovskite to single Ruddlesden-Popper phase, affecting
the Fe0 exsolution. Redox-cycles of LSFMn were investigated and the properties of re-oxidized compounds
were highlighted. The effect of Mn substitution on perovskite conductivity was also evaluated both in
oxidizing and reducing conditions
Pd-doped perovskite-based SOFC anodes for biogas
No full textHighly performing perovskite-based anodes for methane mixtures-fueled solid oxide fuel cells (SOFC) are proposed. Catalytic activities of La0.6Sr0.4Fe1-xPdxO3-δ (LSFPd) with x = 0.05, 0.1 toward dry reforming of methane (DMR) and partial oxidation of methane (POM) reactions are investigated. The addition of (30 wt%) Ce0.85Gd0.15O2-δ (GDC) and of (30 wt%) Ni(5 wt%)-GDC to the perovskite compounds was evaluated to enhance both electrocatalytic and electrochemical properties. Electrolyte-supported cells based on La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) pellets and LSFPd perovskite oxides at both electrodes are fabricated and tested using CH4, CH4/Ar and CH4/CO2 mixtures in the 750–850 °C temperature range. Fuel cell tests using anodic mixtures such as LSFPd/GDC and LSFPd/Ni-GDC are also performed. A discussion based on the comparison between catalytic and electrochemical results and on the possible reforming and/or oxidation reactions taking place at the anode is detailed
Multi-functional, high-performing fuel electrode for dry methane oxidation and CO2 electrolysis in reversible solid oxide cells
No full textIntermittency of renewable energy sources can be profitably faced using efficient energy storage systems. Reversible solid oxide cells (RSOCs) able to operate with carbon-containing species are likely among the most appealing choices. Energy can be obtained by natural gas and/or biogas (SOFC mode), with useful recovery of CO2 in the exhausts. Besides, if the electrode is also active towards CO2 electrolysis (SOEC mode), CO2 is reduced to CO and O2. In this work a composite material with in-situ formed Ni-Fe alloy catalyst consisting of La1.2Sr0.8Fe0.6Mn0.4O4 Ruddlesden-Popper perovskite and Ni-Ce0.85Sm0.15O2-δ fluorite was developed as a multi-functional fuel-electrode for RSOCs. The composite electrode was tested in SOFC mode as anode for hydrogen, dry methane and carbon monoxide oxidation and showed power density outputs of 657, 668 and 527 mW/cm2 at 850 °C, respectively, together with redox stability and coking tolerance for over 120 h. In SOEC mode, it was tested as cathode and delivered 2.66 A/cm2 at 2 V in a 95:5 CO2:CO mixture, retaining a current density of 1 A/cm2 for more than 40 h
Novel composite fuel electrode for CO2/CO-RSOCs
No full textReversible solid oxide cell (RSOC) technology allows use of a single device to efficiently derive chemicals from power (power-to-fuel) and power from chemicals (fuel-to-power). Fuel flexibility is a key aspect, as developing SOCs able to operate on fuels other than hydrogen can ease their integration into existing infrastructure. In addition, H2O and/or CO2 reduction is favorable in SOECs as polarization losses are reduced at high temperature. Here, a composite fuel electrode, 60 wt.% La0.6Sr0.4Fe0.8Mn0.2O3-δ (LSFMn) and 40 wt.% (5 wt.% Ni)-containing Ce0.85Sm0.15O2-δ (Ni-SDC) was investigated in H2-fueled, CO-fueled SOFCs and for CO2 reduction in SOEC mode. In reducing conditions, Fe exsolved from the LSFMn perovskite formed a Ni-Fe alloy with Ni present on SDC. The composite fuel electrode showed remarkable activity for CO2 reduction with a current density output of 1.40 A cm-2 (1.5 V) at 850 °C. SOFC/SOEC cell reversibility was obtained in different CO2:CO mixtures. Electrochemical impedance spectroscopy analysis was used to better understand cell mechanisms in SOFC and SOEC mode
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