Showing papers by "Emiliano Fonda published in 1999"
TL;DR: In this article, the local structure of the M-O bond in CeO2-ZrO2mixed oxides is investigated with the aim of finding a correlation between structural parameters and oxygen exchange properties.
185 citations
TL;DR: In this paper, the redox behavior and the structural properties of Ce{sub 0.6}Zr-O coordination of the type 5 + 2 and 4 + 2 is compared.
110 citations
TL;DR: In this article, a comparative analysis of the K, L3, L2 and L1 edges of cerium oxide in CeO2 has been made and a procedure for obtaining structural parameters from L3-edge EXAFS, even in the presence of these features, has been developed.
Abstract: Cerium oxide (IV) (CeO2) is extensively employed in heterogeneous catalysis, particularly as a promoter of noble metal action in three-way catalysts. For this reason there is a great scientific and economical interest in the development of any possible chemical or structural analysis technique that could provide information on these systems. EXAFS spectroscopy has revealed itself as a powerful technique for structural characterization of such catalysts. Unfortunately, good quality K-edge spectra of cerium are not yet easily obtainable because of the high photon energy required (>40 keV). On the other hand, at lower energies it is easy to collect very good spectra of the L3 edge (5.5 keV), but L3-edge spectra of cerium (IV) are characterized by the presence of two undesired additional phenomena that interfere with EXAFS analysis: final-state mixed-valence behaviour and intense multi-electron excitations. Here, a comparative analysis of the K, L3, L2 and L1 edges of Ce in CeO2 has been made and a procedure for obtaining structural parameters from L3-edge EXAFS, even in the presence of these features, has been developed. This procedure could allow further studies of catalytic compounds containing tetravalent cerium surrounded by oxygen ligands.
41 citations
TL;DR: A simple method of weighting is presented which lead to more satisfying fits without loosing the correct normalisation of the fitted AX 2 necessary to obtain correct fitted parameters error bars.
Abstract: We have studied the multiple recording method to estimate if it possible to obtain by this way reliable EXAFS data standard deviations. The examination of more than 10 different samples, each of them recorded at least 8 times, gave us the possibility to show that the partial standard deviations follow the expected probability laws. Even when the number of samples is small, it is possible to give a reasonable upper limit of e wich could be used as the statistical contribution of the experimental error bars. In some cases we have found that a uniform weighting by 1/e 2 may fail to give a good fit, especially in the high part of k space. We present a simple method of weighting which lead to more satisfying fits without loosing the correct normalisation of the fitted AX 2 necessary to obtain correct fitted parameters error bars.
13 citations
TL;DR: In this paper, a phenomenological explanation of the EXAFS signal and a short description of data collection and data analysis methods are presented, and a recent example of its application to a heterogeneous catalytic system is illustrated.
Abstract: EXAFS spectroscopy is a powerful technique to determine local structure of a selected atomic species in a sample in any aggregation state and under any kind of atmosphere; for these reasons it is widely used in catalysis. A brief phenomenological explanation of the EXAFS signal and a short description of data collection and data analysis methods are presented. A recent example of its application to a heterogeneous catalytic system is illustrated.
1 citations