Platinum–Vanadium Oxide Nanotube Hybrids

The present contribution reports on the features of platinum-based systems supported on vanadium oxide nanotubes. The synthesis of nanotubes was carried out using a commercial vanadium pentoxide via hydrothermal route. The nanostructured hybrid materials were prepared by wet impregnation using two different platinum precursors. The formation of platinum nanoparticles was evaluated by applying distinct reduction procedures. All nanostructured samples were essentially analysed by X-ray diffraction and transmission electron microscopy. After reduction, transmission electron microscopy also made it possible to estimate particle size distribution and mean diameter calculations. It could be seen that all reduction procedures did not affect the nanostructure of the supports and that the formation of metallic nanoparticles is quite efficient with an indistinct distribution along the nanotubes. Nevertheless, the reduction procedure determined the diameter, dispersion and shape of the metallic particles. It could be concluded that the use of H2PtCl6 is more suitable and that the use of hydrogen as reducing agent leads to a nanomaterial with unagglomerated round-shaped metallic particles with mean size of 6–7 nm

Glycerol steam reforming over layered double hydroxide-supported Pt catalysts

Layered double hydroxides containing Mg and Al (Mg/Al ratios of 3 and 5) were used as support for Pt-based catalysts for glycerol steam reforming. Additionally, catalysts supported on the parent MgAl mixed oxides were also evaluated. Fresh catalyst samples were characterized by XRD, BET, TPD-CO2 and XRF whilst the spent catalysts were examined by TEM and TPO/TGA-MS. All catalysts revealed to be active, leading to a hydrogen-rich gas stream but with distinct resistance to deactivation. The catalyst synthesized directly from the layered double hydroxide precursors with Mg/Al ratio of 3 was shown to be more effective since global and gas conversion are similar, varying within 60-25%. Major incidence of weak to moderate basic surface centers rendered catalysts more selective, reaching up to 68% selectivity to hydrogen. However, they were not enough to suppress deactivation. It was found that the formation of more stable carbon deposits play a key role on deactivation and only a minor contribution from the carbonaceous material formed from the intermediate organic liquid compounds was proposed. Highly dispersed metal centers were suggested to be important for in situ catalyst surface cleanness.Fil: de Rezende, Simone M.. Instituto de Tecnologia; BrasilFil: Franchini, Carlos A.. Instituto de Tecnologia; BrasilFil: Dieuzeide, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Tecnologías del Hidrogeno y Energias Sostenibles. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías del Hidrogeno y Energias Sostenibles; ArgentinaFil: Duarte de Farias, Andréa M.. Instituto Tecnologico; BrasilFil: Amadeo, Norma Elvira. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Tecnologías del Hidrogeno y Energias Sostenibles. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías del Hidrogeno y Energias Sostenibles; ArgentinaFil: Fraga, Marco A.. Instituto Tecnologico; Brasi

Comparison among cobalt and iron perovskite-based catalysts for WGSR

The water gas shift reaction (WGSR) has been extensively used in industrial processes, being a fundamental step for the commercial production of high purity hydrogen over the years. For economical purposes, the reaction is performed in two steps, named high temperature shift (HTS) and low temperature shift (LTS). The classic HTS catalyst is chromia-doped hematite, which is toxic and losses specific surface area during industrial processes, demanding for new catalysts. Therefore, considerable effort has been made in recent years to find alternative catalysts for HTS step. With this goal in mind, LaFe1-xCoxO3 (x= 0.0, 0.5 and 1) perovskites were compared in order to find alternative catalysts for WGSR. Samples were prepared by thermal decomposition of amorphous citrate precursors and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray fluorescence, specific surface area measurements, temperature programmed reduction, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy and Mössbauer spectroscopy. The catalysts were evaluated in WGSR performed at 1 atm and different temperatures in the range of 250 to 600 °C. Before reaction, samples were reduced under hydrogen flow at 600 °C, for 1 h. All samples exhibited the perovskite phase. The addition of iron makes the production of Co0 species more difficult and the inverse effect was noted for cobalt which makes iron reduction easier. The cobalt-free sample was the least reducible one while the cobalt-free perovskite led to the least active solid. This was assigned to the low reducibility of iron in perovskite structure. At temperatures higher than 450 °C, the addition of cobalt increased the activity of iron-based catalyst, probably due to the ability of cobalt in making iron reduction easier. The cobalt-based perovskite (LaCoO3) was the most active catalyst. This was related to the easy cobalt reduction in perovskite structure, ensuring high activity in WGSR. It can be concluded that LaCoO3 perovskite is a promising precursor for catalysts for WGSR in the range of 350 to 450 °C, while LaFeO3 and LaCo0.5Fe0.5O3 lead to poorly active catalysts.Fil: Rangel, Maria do Carmo. Universidade Federal da Bahia; BrasilFil: Fonseca Santos, Hilma C.. Universidade Federal da Bahia; BrasilFil: Silva, Lindaura A.. Universidade Federal da Bahia; BrasilFil: Moura, Jadson S.. Universidade Federal da Bahia; BrasilFil: Fraga, Marco André. Instituto Nacional de Tecnologia; BrasilFil: Duarte de Farias, Andréa M.. Instituto Nacional de Tecnologia; BrasilFil: Marchetti, Sergio Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Ciencias Aplicadas "Dr. Jorge J. Ronco". Universidad Nacional de la Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Ciencias Aplicadas; Argentin