[show abstract][hide abstract] ABSTRACT: A series of four compounds (LaMnO3, La0.70Sr0.30MnO3−δ, La0.80Sr0.20FeO3−δ and La0.75Sr0.25Cr0.50Mn0.50O3−δ) of interest as electrode materials in intermediate temperature solid oxide fuel cells have been prepared using a carbonate co-precipitation route in aqueous medium. LaMnO3, La0.70Sr0.30MnO3−δ, and La0.75Sr0.25Cr0.50Mn0.50O3−δ have been obtained as a pure phase, while La0.80Sr0.20FeO3−δ retained an impurity phase; fine microstructures with sub-micron sized particles can be obtained in all cases at the proper calcinations temperature, except for LaMnO3. The precipitation yield of the single metal ions have been experimentally determined in the mother liquors and in the final powders; the results have been evaluated also in comparison with expected yields calculated from thermodynamics of the precipitation process using the software Medusa. pH higher than 7.5 are suggested to avoid ion losses for all cations. Structural and microstructural properties and TPO/TPR behaviour suggest that materials prepared via co-precipitation, especially LSCM, could be suited as electrode materials in solid oxide fuel cells.
International Journal of Hydrogen Energy 01/2013; 38(1):480-491. · 3.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: Preparation of active washcoats of Ni/MgAl2O4 steam-reforming catalysts on FeCrAlloy foams is reported
in this work. The MgAl2O4 powdered support was prepared via co-precipitation method, and Ni/MgAl2O4
was obtained via dry impregnation of 10% (w/w) of Ni. After full characterization of the powders,
the deposition of the catalyst over the foams was performed by percolation followed by air-blowing
(percolation-blowing). The resulting washcoat layers were quite homogeneous, uniform, and well adherent
to the metallic support. Prototype catalytic foam samples, tested at the lab-scale, were found to be
active in the steam reforming process.
[show abstract][hide abstract] ABSTRACT: In this work we investigate the effect of ceria and other rare earths (La, Pr, Tb) on Pd–PdO transformation, which is strongly related to the catalytic activity of Pd-based catalysts for the combustion of methane at high temperature. Also the behavior of Pd on ZrO2 and on yttria-stabilized zirconia is considered for comparison. The catalysts are characterized by XRD and BET surface area measurements. Pd–PdO transformation is studied by means of temperature programmed oxidation measurements and thermogravimetric analysis. Temperature programmed combustion experiments have been carried out in order to compare catalytic activity of different catalysts. The results show that rare earth oxides promote the onset of Pd re-oxidation upon cooling, that for ceria doped sample is reflected in an improvement in the catalytic activity.
[show abstract][hide abstract] ABSTRACT: The intercalation of organic polymers molecules (i.e., PEGs and BRIJ) into a standard Ca-montmorillonite has been studied by XRD, TG, and IR spectroscopy. The polymer intercalation is confirmed by the increasing of the d(001) in XRD spectra as well as by the complex multisteps thermal decomposition behavior of the organo-clay materials. Mid-IR and diffuse reflectance near-IR spectra of the intercalated materials show the polymer diagnostic bands (CH stretching and deformation mode), shifted or changed in shape by the interaction with the clay matrix. Both PEG 1500 and PEG 4000 based materials are likely intercalated in an extended configuration, similar to the amorphous polymer form. BRIJ intercalated polymer spectra suggest the disordered conformation of the alkilic chain in a prevailing "gauche", poorly packed, conformation. Host montmorillonite IR bands, mainly OH and water stretching and deformation fundamentals, combination, and overtone bands, are reduced in intensity by polymer intercalation, pointing out an interaction, likely through H-bonding and/or a possible substitution of cations hydration water molecules.
The Journal of Physical Chemistry A 06/2011; 115(26):7484-93. · 2.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: In the present work, preliminary results of different hydrophobic surface treatments for gas diffusion layer (GDL) for PEM fuel cells are presented. This hydrophobic coating consists of new perfluoropolyether (PFPE) derivatives, in comparison to standard polytetrafluoroethylene (PTFE) dispersions. Experimental conditions for an efficient coating of fluoropolymers onto carbon clothes were explored by wet chemical methods.The GDLs obtained were tested in a single fuel cell at the lab scale. The cell testing was run at two temperatures (60°C and 80°C) with a relative humidity (RH) of the feeding gases of 80/100%, hydrogen/air respectively.The new PFPE coatings measurably improve the cell performances, and this effect is more evident at 60°C with respect to 80°C.
[show abstract][hide abstract] ABSTRACT: A simple and inexpensive co-precipitation route in aqueous medium is proposed to prepare La0.8Sr0.2Ga0.8Mg02O3−δ ionic conductor (LSGM). Different synthetic procedures and operating parameters (i.e. nature and amount of the precipitating agents, HNO3 addition and temperature) have been evaluated in order to underline their influence on the composition and microstructure of the final phase. Intermediate and final products were characterized by Thermal-Gravimetry, IR-spectroscopy, X-ray Powder Diffraction, Rietveld analysis and Scanning Electron Microscopy. The electrical properties were measured by Impedance Spectroscopy in the temperature range 250–800 °C. Slight variations of the synthetic procedure (such as precipitating agent amount or no HNO3 addition) have a considerable and detrimental effect on the ions losses and the subsequent achievement of the final phase. The use NH4OH as an alternative precipitating agent is dramatically disadvantageous. Ions losses during precipitation must be controlled (i) to avoid understoichiometry in the LSGM phase and (ii) to prevent the formation of large amounts of secondary phases. In fact, both affect the total electrical conductivity.The use of large excess of (NH4)2CO3 precipitating agent and the addition of HNO3 lead to the best material characterized by a rhombohedral structure, small amount of side phases, a relative density of 98% and a total conductivity of 6.44 × 10−2 S cm−1 at 800 °C and 1.13 × 10−2 S cm−1 at 600 °C.
Journal of Power Sources 12/2010; 195(24):8116–8123. · 4.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: A multi-wall carbon nanotubes (MWCNTs)-based gas diffusion medium (GDM) was prepared, where carbon black was partially substituted by carbon nanotube (CNT) in the formulation of the micro-porous layer (MPL). A rheological analysis of the ink used to coat the gas diffusion layer (GDL) was previously performed to correlate viscosities with the slurry composition. Shear thinning inks with viscosity of 0.4 (Pa s–1) were obtained for a composition containing 10 wt.-% of CNT and 12 wt.-% of fluorinated polymer. Using the doctor-blade technique, a coating thickness of about 100–150 μm was obtained.Moreover, electrochemical performance of a single cell assembled with the CNT-based GDM was compared with that obtained with a sample without CNTs. In order to better understand the role of CNTs, electrochemical impedance spectroscopy (EIS) of the running fuel cell (FC) was also performed. As a result, it was found that the addition of CNTs sensibly improves single cell performances.
[show abstract][hide abstract] ABSTRACT: The objective of the present research was to investigate the intercalation of three different polymer-based surfactants, namely polyethylene-glycol 1500 and 4000 (PEG 1500 and PEG 4000) and polyethylene-oxide (BRIJ 78), inside the interlayer of STx-1 montmorillonite. The effect of three parameters, such as time (30, 60, 90min), temperature (30 and 60°C) and initial concentrations in solution (45, 90, and 180mM) was studied. A full microstructural characterization of the synthesized organoclays by XRD, FT-IR, and TG-DTA was performed. The quantification of polymer intercalated was estimated by COD (Chemical Oxygen Demand) analysis of the residual amount in solution.The intercalation was successful, as showed by the basal expansions detected by XRD, and confirmed by FT-IR, showing the typical C–H-stretching bands in the spectra of the synthesized clays. TG-DTA was not a reliable technique for the quantification of polymer intercalated, while COD correctly quantified such amounts.The role of temperature and time appeared to be uninfluent for intercalating the polymer inside the interlayer of STx-1 montmorillonite, while the driving parameter ruling the amount of intercalated polymer was the initial concentration in solution.
[show abstract][hide abstract] ABSTRACT: The present research investigated the intercalation of three different polymers, namely polyethylene-glycol (PEG) 1500 and 4000, and BRIJ78 into STx-1 montmorillonite. Samples of modified montmorillonite were prepared starting from different initial concentrations in solution (C0) ranging from 20 to 180 mM. The basal spacing of the modified clay minerals was related to the amounts of polymer intercalated, estimated by COD (Chemical Oxygen Demand) analysis of the residual amounts in solution. The correlation between the basal spacings of the modified montmorillonites and the amounts of polymers intercalated allowed properly modulating the microstructural characteristics of organo-clay minerals prepared with polymers.Research Highlights►Quantification of intercalated PEOs and BRIJ78 in montmorillonite by COD. ►Use of monomeric units to compare intercalation of PEOs with different molar mass. ►Correlation between d001 and intercalated PEOs. ►A priori” modulation of the interlayer-space size.
[show abstract][hide abstract] ABSTRACT: A new method to deposit active washcoats of Ni/MgAl2O4 steam-reforming catalysts over FeCrAlloy foams is reported in this work. The MgAl2O4 powdered support was prepared via a co-precipitation method, and Ni was dry-impregnated on it. The deposition of the catalyst over the foams was performed by dip-coating followed by air-blowing (dip-blowing). The resulting washcoat layers were quite homogeneous and uniform, and well adherent to the metallic support. Prototype catalyst samples, tested at the lab-scale, were found to be active and selective in the steam reforming process.
Studies in Surface Science and Catalysis - STUD SURF SCI CATAL. 01/2010; 175:653-656.
[show abstract][hide abstract] ABSTRACT: The influence of two different washcoats deposited on ceramic honeycombs (alumina and carbon) on the catalytic and mechanical properties of catalysts are examined in this work. A series of carbon and alumina washcoated samples was prepared through a dip-coating method and subsequently cured and treated to reach a suitable chemistry surface. Carbon-coated monoliths present a high washcoat homogeneity, high integrity and a suitable chemistry surface that favour NO reduction at low temperatures. The carbon washcoat was bonded perfectly to the ceramic monoliths. The high adherence between both materials, checked by vibrational tests, provides higher resistance indexes against axial compression and prevents crack propagation. Both facts are a consequence of the high mechanical strength of the catalyst.On the other hand, alumina coatings present better temperature resistance, although their adherence to ceramic monoliths is not as good as in carbon-coated samples. The properties of alumina coatings are strongly dependent on the slurry viscosities, which influence the integrity of the washcoat, mechanical properties and even NO conversion. Both series of catalysts have shown a good NO conversion under on-board conditions, although the key parameters of each washcoat are completely different.
[show abstract][hide abstract] ABSTRACT: The effects on the slurry rheology of the chemical composition of suspensions representative of those typically adopted for the washcoating of structured supports have been studied in this work, with the purpose of rationalizing the process conditions used in the preparation of structured catalysts. It has been found that the viscosity of the suspensions can be easily predicted and controlled by knowing the pore volume and the nature of the surface of the dispersed powders. In order to prepare suspensions, containing different powders, with the same rheology, water content has to be modulated considering the pore volume, while the dispersant (nitric acid) amount has to be proportional to the quantity required by the complete charging of the surface of the dispersed powders. Obtained results clarify some fundamentals of the washcoating processes and allow a dramatic reduction of the number of experimental tests typically performed to washcoat a structured support starting from a new catalytic material.
[show abstract][hide abstract] ABSTRACT: The rheology of microporous layer (MPL) inks for polymer electrolyte membrane fuel cell (PEM-FC) applications was investigated, and its effect on thickness and morphology of final layer, prepared via doctor-blade technique, was examined. The effect of the carbon black (CB) on slurry viscosity was studied in the range CB/water=0.11/0.17 (g/g) as well as the effect of surfactant and PTFE (Teflon®) addition. Slurry viscosity is mainly determined by the CB/water and CB/surfactant ratios, while PTFE addition has minor influence. Viscosities in the range 0.05–0.06Pas (at shear rate 100s−1) were found to be appropriate for coating deposition. Two substrates of different morphology, a carbon cloth (CC) and a woven non-woven (WNW), were coated with slurries of different composition but showing the same rheology. Notwithstanding the use of slurries with the same rheological behavior, different MPL coating thicknesses were obtained. This suggested that the substrate morphology has a non-negligible influence on the final MPL thickness. The MPL layer definitely increased the hydrophobicity, and in some samples the region of superhydrophobicity (contact angle >150°) was reached. In-plane electrical resistance of gas diffusion layers (GDLs), i.e. substrate coated with MPL, was measured and it was found that the two different substrates have no influence on it (about 0.8Ω). FCs assembling different GDLs showed different electrochemical performances in terms of I–V curves: MPLs coated onto WNW gave somewhat higher power densities (0.40W/cm2 at 0.5V).
[show abstract][hide abstract] ABSTRACT: A carbonate coprecipitation synthesis, simple and easily scalable to industrial level, has been successfully applied to produce Sr- and Mg-doped LaGaO3. The thermal evolution shows that the main perovskite phase crystallizes already at 1000 °C. Samples sintered at 1400 °C for 10 h have a relative density of 93% and an electrical conductivity of 7.7∙10−2 S cm−1 at 800 °C, similar to the one reported for solid state synthesis. The presence of small amounts of secondary phases (about 17%) such as LaSrGaO4 and LaSrGa3O7 does not seem to deeply affect the electrical properties of the final material.
Materials Letters - MATER LETT. 01/2009; 63(21):1892-1894.
[show abstract][hide abstract] ABSTRACT: In principle, the application of monolithic catalysts to the Fischer–Tropsch synthesis can solve many of the problems related to the classical Fischer–Tropsch reactors, in particular concerning the necessity to operate with short diffusion distances and low pressure drops, preferably according to the ideal plug-flow behavior, while still maintaining a reasonable inventory of catalytic material in the reactor volume.The preparation of prototype cobalt-based catalysts, washcoated onto metallic structured supports with different geometries, is described herein, together with the evaluation of the catalytic properties of such systems in the Fischer–Tropsch synthesis at industrially relevant process conditions (220–235°C, 20bar, 2.1 molH2/molCO, 5000 cm3(STP)CO+H2/h/gcat). Comparative tests with the same catalyst in the powdered form were also carried out at the same process conditions.It was found that the structured catalysts maintained the activity and the selectivity of the original powdered catalyst, provided that the washcoat thickness is sufficiently thin.
[show abstract][hide abstract] ABSTRACT: Dispersions of a totally dispersible AlOOH powder have been studied. The effect of the initial composition has been studied
to outline the reactions that determine the final rheological behaviour of the dispersions. The final viscosity and viscoelastic
properties of the dispersions are determined by the sol–gel phenomena occurring during the ageing treatment. Gel formation
is favoured by low water and high acid contents, while it is disfavoured by prolonged stirring. Gelling time from 48 h to
4 months has been observed depending on the initial composition.
[show abstract][hide abstract] ABSTRACT: A method for coating open celled metal foams with a thin layer of Pd–Al2O3 was developed. The method makes use of a sol–gel of pseudobohemite as a precursor of γ-Al2O3 to fill the porous structure by percolation whilst the excess of material is flushed away with an air jet. The influence of solid content, acid content and ageing on the sol–gel rheological behaviour was studied to find a sol–gel dispersion with an appropriate viscosity whose deposition resulted in a 20μm thick coating layer. Foam samples of different nominal porosities (10, 20 and 40PPI) were coated with this method and activated with palladium using a wet impregnation procedure with loadings of 3% (w/w) palladium on the alumina.As an alternative approach, dry impregnation of γ-Al2O3 with palladium was performed and a slurry was prepared adding water and nitric acid. The slurry was deposited by percolation through the foam structure. The coating quality was evaluated with adhesion tests and the activity of coated foams was measured by performing catalytic oxidation of CO in a 9mm i.d. tubular reactor. Both methods produced highly active foams, resulting in light off temperatures between 175 and 250°C depending on CO concentration. Moreover, the mass transfer controlled regime was achieved in all runs independently of the coating method. Nevertheless, conversions reached when the sol–gel dispersion was deposited and activated via wet impregnation were higher than the ones obtained with the coating method based on slurry deposition of active powders, indicating that the sol–gel deposition resulted in more uniform coating.
[show abstract][hide abstract] ABSTRACT: The evolution during ageing time of a suspension of a submicronic γ-Al2O3 powder with HNO3/Al2O3 = 2.16 mmol/g and H2O/Al2O3 = 3.2 ml/g has been studied. The physico-chemical and rheological evolution has been followed up to 48 h of ageing. Surface charging and dissolution reactions are fast and proceed with comparable rates in the first 5 h to reach a stable pH 3.5 that corresponds to maximum surface charging and maximum Al3+. Surface charging is responsible for the formation of the colloidal particles that aggregates to form the physic-type gel phase (weak gel). Gel formation is a slow process and is completed within 20 h of ageing. The suspensions present a non-Newtonian pseudoplastic behaviour; at shear = 10 s−1 viscosities between 0.03 and 0.5 Pa s are measured. Viscosity is strongly time dependent and shows a maximum about 27 h of ageing. This behaviour has been related to the presence of modification of the suspension composition during ageing: viscosity increases due to the increasing amounts of gel, the increasing of gel strength and flocks formation, while the viscosity decreases due to both decrease of gel strength and flocks re-dispersion. Well adherent coating layers characterised by loadings between 1.1–2.2 mg/cm2 and thickness of 10–20 μm have been obtained upon dip-coating deposition.