1,721,006 research outputs found
Nanostructured CeO2 powders by XPS
No full textTwo different synthetic routes were used to synthesize three nanostructured cerium IV oxide
powders: Two samples were obtained by precipitation from a basic solution of cerium nitrate and
treated at 523 and 923 K, respectively, the third one was prepared by a microwave-assisted heating
hydrolysis method and treated at 523 K. Compared with the first method, microwave synthesis has
the advantage of very short reaction times and produces small particles with a narrower particle size
distribution. All of these advantages can be attributed to the fast and homogeneous microwave
heating which gives rise to a rapid and more simultaneous nucleation and ready dissolution of the
gel. The present work focuses on the XPS analysis: The influence of the heat treatment and the
preparation procedure on the surface properties are deeply investigated. Besides the wide scan
spectrum, detailed spectra for the Ce 3d, Ce 4d, O 1s, and C 1s regions and related data are
presented and discusse
Surface reactivity of NiO/Co3O4 and Fe2O3/Co3O4 nanocomposite catalysts: interaction with methanol
No full textIn this paper the reactivity of two nanocomposite supported oxides (NiO/Co3O4 and Fe2O3/Co3O4) toward methanol, was studied at
atmospheric pressure and under high vacuum conditions.
Methanol interacts dissociatively with the Fe2O3/Co3O4 surface whereas only a weak interaction was revealed on NiO/Co3O4.
It is remarkable the formation, at RT, of formic acid on the surface of the NiO/Co3O4 supported oxide. Around 323K the formation of
carbon dioxide is evident. Formic acid is very slightly bonded to the surface and can be easily removed by a N2 flow. In the Fe2O3/Co3O4
supported oxide is evident, besides formic acid, the formation at RT of formate species whose intensity increases with temperature.
Methanol interacts molecularly and dissociatively with both the supported oxide under HV conditions. The desorption of molecularly
chemisorbed methanol is accompanied by the decomposition and fragmentation of the alcohol; at higher temperature, in contrast, oxidation
and recombination reactions compete with the methoxy groups desorption.
The reactivity toward methanol of the pure and nanocomposite oxides was compared
Influence of the synthesis procedure on the properties and reactivity of nanostructured ceria powders
No full textNanosized cerium (IV) oxide powder was synthesized using three different preparation procedures: (1) precipitation from a basic solution of
cerium nitrate containing H2O2 at 273 K; (2) Marcilly method and (3) microemulsion method. The X-ray diffraction (XRD) patterns of the asprepared
samples obtained, respectively, by precipitation at low temperature and microemulsion method show the reflections characteristic of
CeO2 fluorite structure with cubic symmetry; the sample prepared by the Marcilly method is amorphous. The particle sizes are 3 and 8 nm for the
low temperature and microemulsion powders, respectively. X-ray photoelectron spectroscopy (XPS) analysis reveals the prevalent presence of
Ce(III) in the sample obtained by means of the Marcilly method. The Marcilly and microemulsion samples were also treated at 473 K for 5 h and
the influence of the thermal treatment was investigated. XPS and XRD data suggest that the powder obtained by the Marcilly procedure is converted
to ceria by the thermal treatment.
Methanol interacts molecularly and dissociatively with the CeO2 surface regardless of the preparation procedure but the mechanism of
interaction is not always the same. Traces of oxidation products are noted only on the samples obtained by means of the microemulsion and
Marcilly methods treated at 473 K for 5 h
La0.7Sr0.3CuO3−δ: An Interesting Catalyst for Methanol and Ethanol Treatment
No full textThe reactivity of La0.7Sr0.3CuO3-δ with methanol and ethanol was investigated in oxidation and steam reforming. The conversion is higher in the oxidation reactions (about 100 %) than in steam reforming (78% for methanol, 23% for ethanol). Significant amounts of hydrogen are observed during methanol steam reforming. Acetaldehyde forms with ethanol
La0.6Sr0.4Co0.8Fe0.2O3-delta and Fe2O3/La0.6Sr0.4Co0.8Fe0.2O3-delta powders: XPS characterization
No full textA Sr and Fe doped lanthanum cobaltate was prepared by wet chemistry procedure (Pechini) and compared with a nanocomposite system obtained by depositin iron oxide on the surface of the perovskite by wet impregnation. The investigation of both the systems was carried out by means of XPS
Effect of the preparation procedure on the surface properties of nanosized ceria powders
No full textNanosized cerium (IV) oxide powders were synthesized using three different preparation
procedures: 1 precipitation from a basic solution of cerium nitrate containing H2O2 at 273 K; 2
Marcilly method, and 3 microemulsion method. In this work the influence of the preparation
procedure on the surface properties is studied by means of XPS. Besides the wide scan spectrum,
detailed spectra for the Ce 3d, Ce 4d, O 1s and C 1s regions and relative data are presented and
discussed
Steam reforming and oxidative steam reforming of methanol and ethanol: The behaviour of LaCo0.7Cu0.3O3
No full textLaCo0.7Cu0.3O3 perovskite powder was prepared by means of the citrate method and treated at different
temperatures from 873 to 1323 K. The samples were characterized by X-ray photoelectron spectroscopy
(XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed
desorption (TPD, O2-TPD), and scanning electron microscopy (SEM); the BET specific surface area was
also determined. The reactivity of the perovskite with methanol and ethanol was investigated under
steam reforming and oxidative steam reforming conditions and correlated to its chemical and structural
properties. Different oxygen/alcohol molar ratios were used to study the influence of oxygen on catalytic
activity and products distribution. LaCo0.7Cu0.3O3 begins to be active in alcohol steam reforming at about
523 K. The catalyst calcined at 873K shows the higher conversion in methanol steam reforming. Ethanol
steam reforming conversion, in contrast, is rather low and not significantly affected by the catalyst calcination
temperature. The conversions increase when oxygen is present reaching 93% for methanol and
78% for ethanol. Beside the steam reforming and oxidative steam reforming, other secondary reaction
paths occur: methanol decomposition and ethanol dehydrogenation
Oxygen Permeation Measurements: An Alternative tool to Select New Intermediate Temperature Solid Oxide Fuel Cell Cathodes
No full textIn this contribution four perovskite-based mixed ionic-electronic conductors (MIEC): a strontium
and iron doped lanthanum gallate (La08Sr02Ga08Fe02O3, hereafter LSGF8282), and strontium
or cobalt doped lanthanum cuprates (La07Sr03CuO3–LSC7310, La2Cu08Co02O4–LCC2082 and
LaCu03Co07O3–LCC1037), were synthesized by means of a wet-chemistry routes (Pechini method)
and characterized by X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), specific
surface area (by the BET single point method) and Scanning Electron Microscopy (SEM). The oxygen
permeation properties were investigated by means of a home made permeation chamber at
600, 700 and 800°C in order to evaluate their applicability as cathode materials in intermediate temperature
solid oxide fuel cells (IT-SOFCs). The synthetic procedure allowed to achieve the desired
compounds, as confirmed by XRD and XPS measurements. The A2BO4-type sample (LCC2082)
showed higher oxygen permeation rate than ABO3 perovskites. This is ascribed to the oxygen
transportation extra contribution through the AO planes present in A2BO4 compound. Among the
ABO3-type samples, the copper-rich ones showed the most interesting oxygen permeation
Mixed Mangesium and Zinc oxides by co-precipitation
No full textTwo Zinc-Magnesium Oxide powders were prepared by means of a sol-gel method based on the
mixing of nitrates of Mg and Zn, followed by complexation with citric acid. The samples are
characterized by a nominal (i.e. calculated from the weighted amount of precursors) Zn/Mg atomic
ratio of 0.01 (specimen 1, Accession #1232), and 0.5 (specimen 2, Accession #1233). The surface
properties and the influence of the Zn/Mg atomic ratio are investigated by means of XPS (using a
standard Al Ka). Besides the wide scan spectra, detailed spectra for the Mg 1s, Zn 2p3/2 and O 1s
regions and related data are presented and discussed. XP analysis confirms the presence of Mg (II)
and Zn (II). The XPS Zn/Mg atomic ratio is always lower than the nominal one; this is particularly
evident in specimen 1 (Accession #1232) thus suggesting a certain surface segregation of
magnesium. The O/(Mg + Zn) atomic ratio is higher than the nominal one and decreases with
increasing the Zn/Mg atomic ratio (from 1.5 for [Zn/Mg]nom=0.01 to 1.3 for [Zn/Mg]nom=0.5)
La0.8Sr0.2Ga0.8Fe0.2O3-δ: influence of the preparation procedure on reactivity toward methanol and ethanol
No full textIn this paper a strontium- and iron-doped lanthanum gallate (La0.8Sr0.2Ga0.8Fe0.2O3—LSGF) is prepared
by Pechini process and polyacrylamide gel method. The powders are characterized by means of X-ray
Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Infrared Fourier Transform
spectroscopy (DRIFT), Thermal Programmed Desorption (TPD), Thermal Programmed Reduction
(TPR), BET specific surface area, UV–Vis and Mössbauer Spectroscopy (MS). The activity toward methanol
and ethanol is investigated by Infrared (IR) spectroscopy and Quadrupolar Mass Spectrometry (QMS)
under several conditions. XRD outcomes reveal the formation of the desired perovskite phase at 900 ◦C,
however, small amounts of secondary phases are also present. LSGF synthesized by Pechini process is
characterized by a lower amount of secondary phases. On the other hand, LSGF from polyacrylamide gel
method has a higher specific surface area. XPS data show that the two samples differ for surface cations
segregation, hydroxylation degree and carbonate contamination. These results are also confirmed by
DRIFT and TPD measurements. MS and TPR analyses reveal the presence of a small amount of Fe(IV),
which is reduced to Fe(III) with H2 (5% in Ar) at about 450 ◦C and with CH3OH vapours at 200 ◦C. Catalytic
tests prove that methanol is mainly decomposed into H2 and CO at 400 ◦C, but small amounts of CO2 are
also detected. Ethanol undergoes essentially dehydrogenation thus forming acetaldehyde and H2. In oxidizing
conditions, both alcohols are oxidized to CO2 and H2O at 400 ◦C, nevertheless, partially oxidized
products are also observed. Acetaldehyde is an important product in ethanol oxidation. Under steam
reforming conditions, methanol and ethanol give H2, CO and CO2, but acetaldehyde is also observed in
ethanol steam reforming. The presence of acetaldehyde, when dealing with ethanol, suggests a difficult
C–C bond break. Both the LSGF samples undergo poisoning during the reactions
- …
