Eleonora Spanó

Örebro universitet, Örebro, Örebro, Sweden

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Publications (9)22.67 Total impact

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    ABSTRACT: The ethylene epoxidation cycle in a H2O2/H2O-loaded Ti zeolite has been simulated by a Car-Parrinello approach. Results indicate a process where the zeolitic framework is the active oxygen mediator. The dissociative chemisorption of H2O2 leads, via a transient Ti-hydroperoxo species, to H2O and a Ti-peroxo zeolite intermediate. Transfer of active oxygen to ethylene follows, giving the epoxide and recovering the catalyst. A thorough theoretical characterization indicates that the active oxidizing species is an asymmetric eta2-Ti-peroxo, absorbing in the visible range. The lability of the intermediate is found related to eta2 <--> eta1 interconversions of the Ti-peroxo structure. The interconversions, triggered by water molecules, could account for the experimentally found reduced catalytic activity in aged TS-1 catalysts. The results provide a microscopic picture of the reactivity and dehydration/aging processes of the catalyst fully consistent with experiments and highlight the fundamental role of the Lewis acid character of Ti in the formation, reactivity, and degradation of the active oxidizing species.
    The Journal of Physical Chemistry B 11/2006; 110(43):21651-61. · 3.61 Impact Factor
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    ABSTRACT: The excitation energies of small ZnS nanoclusters characterized in previous studies have been calculated using TDDFT. The relativistic pseudopotentials of Stevens et al have been used, including Zn 4s(2) electrons and S 3s(2) and 3p(4) electrons as valence electrons. Results obtained with these pseudopotentials are compared to those obtained considering also Zn 3s(2)3p(6)3d(10) electrons in the valence part, and demonstrated to be consistent. The results show that spheroid-like bubble structures have absorption energies in the range of 5-5.3 eV for small sizes, which decreases to 5 eV with increasing particle size.
    Nanotechnology 08/2006; 17(16):4100-5. · 3.84 Impact Factor
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    ABSTRACT: Earlier studies have shown that the most stable structures for (ZnS)n clusters with n = 10-47 are hollow polyhedral clusters ("bubbles"). We report a detailed study of larger clusters, where n = 50, 60, 70, and 80, for which onionlike or "double bubble" structures are predicted. We report calculations of the vibrational spectra and the electronic structure of bubble and double bubble clusters, which may assist in their experimental identification.
    The Journal of Physical Chemistry B 03/2005; 109(7):2703-9. · 3.61 Impact Factor
  • Ettore Fois, Aldo Gamba, Eleonora Spanó
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    ABSTRACT: A combined Car−Parrinello molecular dynamics blue moon sampling approach has been adopted to study the competitive attack of H2O and H2O2 at a tetracoordinated Titanium site in a Ti−zeolite. The results indicate that, although the attack of water to form a trigonal bipyramidal center is thermodynamically more stable, the attack of hydrogen peroxide to form a similar adduct is kinetically favored. In both cases, solvent cooperation is effective in the formation of the adducts. The relevance of such a result in relation to the catalytic properties of Ti−zeolites is discussed.
    ChemInform 06/2004; 35(40).
  • Eleonora Spanó, Said Hamad, C Richard A Catlow
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    ABSTRACT: Following recent studies which showed that the most stable structures for (ZnS)(n) clusters (n= 10-47) are the so-called "bubble clusters", in which all the atoms are three-coordinated, we have used simulated annealing techniques to find the most stable structure for a larger cluster, (ZnS)(60). We find an onion-like structure, with one small cluster enclosed inside a bigger one. The inner cluster has the structure of a sodalite cage. Bonding between the inner and the outer clusters creates a network of four-coordinated atoms.
    Chemical Communications 05/2004; · 6.38 Impact Factor
  • Ettore Fois, Aldo Gamba, Eleonora Spanò
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    ABSTRACT: We present the results of ab initio molecular dynamics simulations on titanium offretite. The aim of this work is to investigate at a microscopic level the room temperature behavior of titanium inserted into a fully periodic zeolitic framework in dry and hydrated conditions. Structural analysis indicates that titanium, at low water loading, is tetrahedrally coordinated by framework oxygens only. On the other hand, at higher loading, when water molecules are activated via hydrogen bonding, they interact with the Ti site, leading to an increase of the Ti coordination number up to 5. The insertion of a Ti center causes only moderate and local distortions to the silicate framework. Features due to Ti in the calculated vibrational spectra are in line with IR and Raman experiments.
    11/2003;
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    Eleonora Spanó, Said Hamad, C. Richard A. Catlow
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    ABSTRACT: Energy minimized structures of (ZnS)n clusters, with n ranging from 10 to 47, have been generated using simulated annealing techniques based on interatomic potentials. The clusters have “bubble” like polyhedral structures, in which all of the atoms are three coordinated, rather than the densely packed bulklike structures. Density functional theory calculations also show that the bubble clusters are more stable than the bulklike clusters.
    Journal of Physical Chemistry B - J PHYS CHEM B. 08/2003; 107(38).
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    ABSTRACT: A simulation study on the rotational behavior of neutral and charged molecular systems hosted in zeolitic cages is presented here. Synthetic sodalites containing both molecular (O2) and anionic (NO2−, NO3−) species and an hydrated Ti-offretite have been simulated by first-principles molecular dynamics. Our results show that both host–guest and guest–guest interactions directly influence the rotational motion of the caged species.
    Journal of Molecular Structure 01/2003; · 1.40 Impact Factor
  • Ettore Fois, Aldo Gamba, Eleonora Spanò
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    ABSTRACT: We present the results of ab initio molecular dynamics simulations applied to ‘all-silica sodalite’ [Si12O24], modified by doping with P or As atoms, to investigate the possible technological interest of the new systems. The doping represents an alternative technique to insert electrons into a zeolitic cavity. The simulation of radial distribution functions, coordination numbers, bond distances and bond angles variations, together with electron densities, electronic density of states and vibrational spectra has revealed that these systems could be of possible interest as new optical materials.
    Physical Chemistry Chemical Physics 01/2001; 3(10):1877-1882. · 3.83 Impact Factor