B. Zeifert

Thermodynamic modeling of the BaO-SiO2 and SrO-SiO2 binary melts

The evaluation of the thermodynamic properties and the phase diagrams for the binary BaO-SiO2 and SrO-SiO2 systems is carried out using a structural model for silicate melts and glasses. This thermodynamic model is based on the assumption that an addition of metal oxides to silica results in the depolymerization of the silicon-oxygen network, with a characteristic free energy change. A least squares optimization program permits all available thermodynamic and phase diagram data to be optimized simultaneously. In this manner, data for the above binary systems have been analysed and represented with a small number of parameters. The resulting equations represent the thermodynamic and phase diagram data for the alkaline-earth oxide-silica systems within error limits for most of the experimental data. In particular, the measured limiting liquidus slope, at XSiO2 = 1, is well reproduced.

Thermal Stability of Pt Nanoparticles Supported on WO x /Al 2 O 3 for n-Heptane Hydroconversion

The thermal stabilization of γ-Al 2 O 3 using W +6 ions has been found useful to the synthesis of Pt/Al 2 O 3 catalysts. The sequential impregnation method was used to study the effect of W 6+ upon Pt/ γ-Al 2 O 3 reducibility, Pt dispersion, Raman spectroscopy and n-heptane hydroconversion. The W/Pt atomic ratios varied from 3.28 to 75. We found that the W 6+ ions delayed reduction of a fraction of Pt +4 atoms beyond 773 K. At the same time, W 6+ inhibited sintering of the metallic crystallites once they were formed on the surface. For the sample with a W/Pt atomic ratio of 3.28, W 6+ did not inhibit the H 2 reduction of Pt oxides even below of 773 K, the Pt oxides were reduced completely, however, the Pt dispersion decreased for this sample with respect to the Pt/γ-Al 2 O 3 catalyst. After reduction at 1073 K, sequential samples impregnating Pt on WOx/γAl 2 O 3 were more active and stable during n-heptane hydroconversion than monometallic Pt/γAl 2 O 3 catalyst. Selectivities for dehydrocyclization, isomerization and Hydrocracking changed significantly when the W/Pt atomic ratio and reduction temperature increased. Initial and final reaction rates were more sensitive to reduction temperature. W 6+ ions promoted high thermal stability of Pt crystallites when sequential catalysts were reduced at 1073 K and deactivation of bimetallic catalysts reduced at 773 K and 1073 K was less than the deactivation of Pt/Al 2 O 3 catalyst.

Hydrogen Storage in Ti-Zr Based Systems

This research contributes to the study of hydrogen storage of two Ti-Zr based systems using (I) titanium dioxide (TiO 2 ) + zirconium acetylacetonate (C 20 H 28 O 8 Zr) and (II) titanium dioxide (TiO 2 ) + zirconium tetrachloride (ZrCl 4 ) as starting materials. Both systems were prepared by mechanical grinding under the same conditions, with composition of 50 wt.% Ti and Zr and milling time of 2, 5, 7, 15, 30 and 70 hrs. The samples were evaluated by hydrogen absorption tests and characterized by BET, XRD and TEM. The results of hydrogen storage at different pressures but same temperature showed that samples of the system I absorbed the largest quantities of hydrogen but difficult to release them, while the system II absorbed less amount of hydrogen but completely desorbed the absorbed hydrogen. The increase of the mechanical grinding time is directly associated with changes in hydrogen absorption capacity and formation of new components. The formation of oxide nanoparticles of Ti and Zr on the surface of TiO 2 in samples from series II was associated with the hydrogen absorption capacity. Keywords: hydrogen storage, Ti-Zr, mechanical milling, sorption.