J. Salmones

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.

Synthesis and Catalytic Activity of Ni/Ce-MCM-41 Mesoporous Catalysts for Hydrogen Production

Ce-containing MCM-41 mesoporous materials with large surface area and ordered pore structure system have been possible to be synthesized through a surfactant-assisted approach. The textural properties and structural regularity of the materials varied with the Si/Ce molar ratio. It is found that the band at 970 cm -1 in the FTIR spectrum of the Ce-MCM-41 mesoporous materials might be used as an indicator of the formation of the Ce-O-Si bond and its intensity as a measure of a degree of cerium ion substitution in the framework of Si-MCM-41. When Ni was loaded on the Ce-MCM-41 support, the Ni/Ce-MCM-41 catalysts show high catalytic activity which has strong temperature dependence. The methane conversion over these catalysts reached 60-75 % with a 100 % selectivity towards hydrogen.

Characterization of Erionites with A Supported Metallic Phase by TEM, IR,AEM and Auger Methods

Catalytic isomerization of paraffines of low molecular weight is a very important process in petrochemical refination and zeolites like mordenites and erionites are used frequently as supports, due to acid properties, neccesary for a dual action in hydroisomerization processes(1–3). In the present work, we analyze the behavior of erionites interchanged with Pt at low weight concentrations, using test reaction for n-pentane hydrodesintegration. At several stages of the process, small quantities of the samples were studied using TEM,AEM, IR, ESCA and Auger methods.