1,721,061 research outputs found
Study of surface reactivity of cobalt oxides: interaction with methanol
No full textIn this paper, the interaction between cobalt oxides (Co3O4 and CoO) and methanol is
studied. CoO was obtained by heating under high-vacuum (HV) conditions and characterized
by X-ray photoelectron spectroscopy (XPS). The Co3O4 powder sample was characterized by
means of XPS, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray
diffraction (XRD), and thermal analysis. The interaction between Co3O4 and methanol was
studied both at atmospheric pressure (by means of DRIFT spectroscopy) and under HV
conditions (by means of XPS and quadrupolar mass spectroscopy, QMS), whereas the
chemisorption of methanol on the CoO surface was studied only under HV conditions.
Methanol chemisorbs mainly molecularly on the cobalt oxide surfaces, the alcohol dissociation
being more evident at higher temperatures. In the case of Co3O4, the formation of formate
and polymers of formaldehyde is evident around 473-523 K, whereas under HV conditions,
formaldehyde and several decomposition and fragmentation products were observed as well
as carbon oxides. Similar results were obtained in the case of CoO
Study of surface reactivity of NiO: interaction with methanol
No full textThe interaction between methanol and a NiO powder sample was studied. The obtained
NiO was characterized by means of X-ray photoelectron spectroscopy (XPS), diffuse
reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), and
thermal analysis. Chemisorption experiments at atmospheric pressure were studied by means
of diffuse reflectance infrared spectroscopy, whereas those carried out under high vacuum
(HV) conditions were followed by means of XPS and quadrupolar mass spectrometry (QMS).
Methanol interacts mainly molecularly with the NiO powder surface whereas dissociative
chemisorption is more evident at higher temperatures. The formation of CO2 and of formate
species is evident at T higher than 323 and 423 K, respectively. Under HV conditions formaldehyde
forms at higher temperatures
Nanostructured oxide-based powders: investigation of the growth mode of the CeO2 clusters on the YSZ surface
No full textCeO2/YSZ nanocomposite powders, characterized by increasing Ce/Zr atomic ratio, were obtained by
depositing, by wet impregnation, different amounts of CeO2 on the yttria-stabilized zirconia (YSZ) surface.
These powders were characterized by means of X-ray photoelectron spectroscopy, transmission electron
microscopy, energy dispersive spectroscopy, and X-ray diffraction. Experimental results allow us to obtain
interesting information concerning the growth mode, the morphology, and the dimensions of the CeO2 clusters
on the YSZ supporting surface. A 3-D growing mechanism was observed for the CeO2 nanoparticles. With
increasing Ce/Zr atomic ratio the CeO2 clusters become more and more spherical. Moreover, XPS data also
show the presence of Ce(III) and Ce(IV) ions at the interface supported/supporting oxides
CoOx/CeO2 nanocomposite powders: Synthesis, characterization, and reactivity
No full textCoOx/CeO2 nanocomposite materials with increasing Co/Ce atomic ratio were prepared by wet
impregnation and characterized by means of X-ray photoelectron, diffuse reflectance infrared Fourier
transform, and inductively coupled plasma atomic emission spectroscopic techniques, by BET and by
thermal analysis. CoO is prevalent in the samples with lower cobalt content, whereas Co3O4 is the main
presence at high Co/Ce atomic ratios. CeO2 is slightly reduced: Ce(III) is evident at the interface supported/
supporting oxide. X-ray diffraction and transmission electron microscopy allowed us to obtain interesting
information concerning particle dimensions and growing morphology. The acidic/basic properties of the
catalysts surfaces were investigated by studying the interaction of CoOx/CeO2 powder samples with pyridine
and CO2. New acidic/basic sites are evident on the surface of the nanocomposites; this is particularly
evident in the samples with lower cobalt content. The interaction with methanol was also investigated.
Methanol chemisorbs molecularly and dissociatively on the CoOx/CeO2 samples; dissociation is prevalent
in the sample characterized by a lower content of cobalt oxide. The oxidation of methanol is evident at
rather low temperatures. When water is added to methanol, the oxidation temperature decreases (373 K
instead of 433 K) and the formation of carbon monoxide is not observed
WO3/CeO2/YSZ nanocomposite: a potential catalyst for methanol reforming
No full textA WO3/CeO2/YSZ nanocomposite material [W/Zr nominal atomic ratio = 0.025, Ce/Zr nominal atomic ratio = 0.020] was prepared by wet
impregnation and characterized by means of X-ray photoelectron and diffuse reflectance infrared Fourier transform spectroscopic techniques,
X-ray diffraction and thermal analysis.
Both tungsten and cerium oxides are significantly reduced at the interface with YSZ: Ce(III), in particular, seems to be the prevailing species.
The interaction of theWO3/CeO2/YSZ nanopowder with pyridine and CO2 allowed to investigate the acidic/basic sites.Weak contributions
at 1602, 1625 and 1647 cm−1 suggest the presence of Lewis and Brønsted acidic sites, whereas basic sites are not evidenced by the interaction
with carbon dioxide. The presence of tungsten oxide causes the decrement of the acidic/basic sites, as indicated by the comparison with the
results obtained on the CeO2/YSZ support. Consistently, the interaction with methanol is mainly molecular.
The oxidation of methanol was investigated both in the absence and in the presence of water. In the last case carbon dioxide starts forming
from room temperature
LSCF and Fe2O3/LSCF powders: interaction with methanol
No full textThis work focalizes on a nanosized La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) perovskite and Fe2O3/LSCF nanocomposites. The nanosized LSCF perovskite
is obtained by Pechini method and treated at 1173 K; nanocomposite Fe2O3/LSCF powder samples (Fe2O3/LSCF = 1:9 and 1:1 wt.) are
obtained by wet impregnation.
The reactivity of the obtained samples with respect to pure methanol and to a 1M aqueous solution of methanol, is investigated by means of
IR Spectroscopy and Quadrupole Mass Spectrometry (QMS). In presence of pure methanol the main reaction is methanol decomposition with
the formation of CO and H2. The activity with respect to this reaction starts to be observed at 573K both for the LSCF perovskite and for the
Fe2O3/LSCF nanocomposites and shows an irregular trend as a function of temperature. Steam-reforming reaction is evident at T≥623K when a
1M solution of methanol is used. The reactivity with respect to methanol and to the 1M solution of methanol was also investigated as a function
of time: only at 673K the methanol decomposition starts immediately; the waiting time changes as a function of temperature, sample composition
and reactive mixture. The steam reforming reaction, in contrast, begins immediately
Three and Four Way Catalysts: pollution abatement with perovskites and perovskite-based nanocomposites
No full text
WO3/CeO2 nanocomposite powders: Synthesis, characterization, and reactivity
No full textWO3/CeO2 nanocomposite powders, characterized by increasing W/Ce atomic ratio, were prepared by
depositing, by wet impregnation, different amounts of WO3 on the CeO2 surface. The powders were
characterized by means of X-ray photoelectron and diffuse reflectance infrared Fourier transform
spectroscopic techniques as well as thermal analysis. The WO3/CeO2 samples are slightly reduced with
respect to the pure oxides: the presence of W(V) and Ce(III), in addition to W(VI) and Ce(IV), is evident
at the interface supported/supporting oxides. Interesting information concerning particle dimensions and
growth mode derive by X-ray diffraction and transmission electron microscopy. New acidic/basic and
redox sites are evident on the surface of the WO3/CeO2 nanocomposites. The interaction with methanol
was also investigated. Methanol interacts both molecularly and dissociatively with the WO3/CeO2 surface;
the dissociation is prevalent on the sample characterized by a lower content of WO3, whereas a mainly
molecular interaction is observed with increasing amount of tungsten oxide. Oxidation of methanol is
evident from 423 K on the sample with [W/Ce]nominal ) 0.025 and from 473 K on the one richer
in WO3. The reactivity toward methanol oxidation is higher in the sample with a lower content of WO3,
but the sample richer in WO3 shows a higher selectivity with respect to formation of carbon dioxide
- …
