R. Alvero
University of Seville
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by R. Alvero.
Journal of The Less Common Metals | 1983
R. Alvero; I. Carrizosa; J.A. Odriozola; J.M. Trillo; S. Bernal
Abstract It has previously been shown that even the heaviest rare earth oxides undergo partial conversion to bulk hydroxycarbonates when exposed to air. However, when rare earth oxides are used as catalysts, activation temperatures lower than those necessary to achieve the complete removal of H 2 O and CO 2 are often reported. To elucidate the actual active phases that operate in catalytic processes involving rare earth oxides, a systematic temperature-programmed desorption study of La 2 O 3 , Sm 2 O 3 and Yb 2 O 3 was carried out. Our results lend support to a particle structure for the activated powder “oxides” consisting of an oxycarbonate nucleus surrounded by an outer oxide layer.
Journal of Materials Science | 1987
R. Alvero; A. Bernal; I. Carrizosa; J.A. Odriozola; J. M. Trillo
The behaviour toward hydration of a series of Ln2O3 has been studied as a function of water pressure and temperature by means of temperature programmed decomposition measurements. Thermochemical calculations have pointed out the structural change associated in going from ytterbium to lutetium in Ln(OH)3 to be responsible for the apparent anomalous behaviour of Lu2O3. On this basis generalizations about the expected behaviour along the 4f series have been considered taking into account the simple ionic model for solid lanthanide compounds.
Applied Catalysis | 1986
R. Alvero; A. Bernal; I. Carrizosa; J.A. Odriozola; J.M. Trillo
Abstract Lutetia supported on X-alumina remarkably enhances its surface Lewis basicity strength, according to XPS and carbon dioxide volumetric adsorption measurements. From these data, a CO 2 /exposed Lu(III) ratio of almost 1:1 was estimated for the supported oxide activated at 773K, compared with 1:20 for the non supported one. The 10% alumina-supported lutetia interacts with gaseous CO 2 /H 2 mixtures at 625K leading to the formation of formate species, detected by FT-IR spectroscopy, an active intermediate for the conversion of synthesis gas towards oxygenated products.
Solid State Ionics | 1993
J. M. Trillo; María D. Alba; R. Alvero; M. Castro; A. Muñoz; J. Poyato; M. M. Tobías; G. Lagaly
Abstract The location, environment and availability of the interlamellar species in modified layered silicates have been investigated using two montmorillonites selected with different charge deficit distributions. A structural study has revealed release of protons and further migration to the lattice as thermal treatments are performed. The proton availability has been examined through a catalytic reaction, all the modified samples showing similar activities in this test. A possible explanation for this levelling effect has been suggested.
Journal of The Less Common Metals | 1985
R. Alvero; A. Bernal; I. Carrizosa; A Justo; J.A. Odriozola; J.M. Trillo
Abstract The influence of the precursor salt on the surface behaviour of some Lu2O3 samples has been studied. They have been prepared by thermal decomposition of lutetium oxalate, basic carbonate, and hydroxide, and studied by means of TG, DTA, X-ray diffraction, SEM, SBET measurements and FT-IR spectroscopy. The surface reactivity of Lu2O3 samples obtained via hydroxide and carbonate is greater than that observed for the oxide obtained via the oxalate, as studied by the influence of thermal treatments on their hydration capacities and on their specific surface areas. The differences between the crystalline structures of the precursor salt and the final oxide satisfactorily accounted for the different surface behaviours of the oxides studied.
Studies in Surface Science and Catalysis | 1989
J.A. Odriozola; I. Carrizosa; R. Alvero
By FTIR, XPS and TDMS experiments, CO 2 dissociation at room temperature has been stated on Ln 2 O 3 -promoted Rh/Al 2 O 3 catalysts (Ln = La, Lu). Both the rare earth cation and the rhodium metal are involved in the intermediate steps of the process. In the cooperative model proposed, the surface hydroxylation plays the key role on the generation of strong Lewis acid centres at the surface which are essential for the carbon dioxide dissociation.
Journal of The Less Common Metals | 1985
R. Alvero; I. Carrizosa; J.A. Odriozola; J.M. Trillo
The influence of pressure and temperature on Sm2O3 hydration, under mild conditions, are examined. The data and conclusions are referred to previous ones for Yb2O3. At the activation temperatures usually applied, as reported in the literature, to rare earth sesquioxides handled in air, 800–850 K, a non-pure-oxide phase is attained in the case of Sm2O3. Its complete dehydration is achieved at 823 K, but temperature programmed decomposition and Fourier transform-IR data lend support to the formation at this temperature of a dioxymonocarbonate phase which is transformed into the sesquioxide phase above 1100 K. Contrary to the finding for Yb2O3, hydration in bulk Sm2O3 has been observed over the whole pressure range 133–2666 Pa. In the absence of CO2, the temperature of evolution of H2O from bulk-hydrated Sm2O3, about 600 K, is considerably higher than that previously reported for Yb2O3, 440 K, following the cation polarizing pattern for the decomposition of metal hydroxides and oxosalts.
Journal of Materials Science | 1985
R. Alvero; J.A. Odriozola; J.M. Trillo
Preliminary studies have shown that in order to achieve the complete removal of the uptaken CO2 and H2O from a ytterbium oxide aged in air, thermal activation up to 1173 K is required. Parallel studies have shown that bulk hydration of Yb2O3 does occur, the CO2 acting as a kinetic inhibitor. The above results refer to a Yb2O3 prepared in our laboratory from hydroxicarbonate-like phases. In the present work, the influence of the preparation method on the hydration process is examined, by extending the study to two additional samples, a standard commercial one and another obtained by calcining a ytterbium oxalate. It is shown that the intensity of the hydration reaction depends strongly on the method of preparation. Certain applications of 4f oxides, such as their use as transition metal supports, involve thermochemical processes which may alter drastically the initial texture of the ytterbia from the oxalate. It makes this sample less useful although its initial specific surface area is high.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1997
María D. Alba; R. Alvero; Ana Isabel Becerro; M. Castro; Adela Muñoz-Páez; J. M. Trillo
Abstract Changes produced by thermal treatments (300°C, 500°C, and 700°C) and after an “in situ” drying treatment on the hydration sphere of the lanthanum ions located in the interlamellar space of montmorillonites have been investigated. X-ray absorption spectroscopy (XAS) spectra for these materials have been recorded with this purpose at room and liquid nitrogen temperature by using a special cell where the temperature and the atmosphere could be controlled. The dry atmosphere employed during the drying treatment produced either drastic or no significant effects on the La L III -edge EXAFS spectra, depending upon the previous thermal treatment given to the sample. These results have allowed us to postulate a dehydration reaction mechanism for these samples and to show how XAS measurement is a very useful tool to be employed in the study of the local environments adopted by the exchangeable cations in clays.
Journal of The Chemical Society-dalton Transactions | 1984
R. Alvero; J.A. Odriozola; J.M. Trillo; Serafin Bernal
La2O3, CeO2, Sm2O3, Dy2O3, and Yb2O3 were obtained by calcining in air phases prepared by precipitation with ammonia from solutions of the corresponding nitrates. During the calcination to oxides, under the experimental conditions used, the nitrate ions are removed to an extent which could not be detected by temperature programmed desorption–mass spectrometry or i.r. spectroscopy, contradictory to the established literature. For comparative purposes, Yb2O3 has also been prepared by thermal decomposition of oxalate. The Brunauer–Emmett–Teller surface area was always lower for the oxide obtained from oxalate. This was so even after thermal treatment at 1 173 K. Independent of the preparation method, the heaviest 4f oxides undergo partial conversion to bulk carbonate hydroxides when exposed to air. According to our results and those reported in the literature, lanthanide oxides, when used as catalysts, are often activated at temperatures lower than those necessary for the complete elimination of CO2 and H2O.