P. del Angel

Catalytic decomposition of methane over Ni-Al2O3 coprecipitated catalysts: Reaction and regeneration studies

Abstract The catalytic decomposition of methane over nickel catalysts is a potential alternative route to steam reforming or partial oxidation for the production of hydrogen from natural gas and other feedstocks. In the present paper, we report the results of characterization and catalytic behaviour of a Ni(30%)/Al2O3 catalyst during the catalytic decomposition of methane. The influence of the operating and reduction temperatures and feed composition on the methane conversion, hydrogen production and coking rate has been studied. The effects of the regeneration cycles with oxygen on activity and carbon formation are also investigated. It has been shown that H2 inhibits both the carbon filament formation and the encapsulation of metallic particles by coke. An increase in the reaction temperature increases both the deactivation rate and the growth rate of filaments. However, at high reduction temperatures, there is a decrease in the number of filaments formed due to sintering of the Ni particles. A kinetic model has been developed for the prediction of H2 production and of carbon, taking into account both stages of carbon formation, nucleation and filament growth.

Influence of the hydrophobic material content in the gas diffusion electrodes on the performance of a PEM fuel cell

In the present study the influence of the hydrophobic material (Teflon, polytetrafluoroethylene) content in the gas diffusion electrodes (anode and cathode) on the performance of a H 2 /O 2 proton exchange membrane fuel cell is reported. The potential-current (E-I) evaluation of the fuel cell indicated that a combination of 10 and 30 wt% of Teflon, respectively, in the cathode and anode gave the best results.

CdS thin-films deposited by a modified chemical-bath deposition method

Cadmium sulphide polycrystalline thin films were prepared by chemical-bath deposition (CBD) method onto glass substrates at 80°C. The modification to the traditional technique consists in applying a pulsed electric (E) external fields during the growth process. E was applied in two different orientations with respect to substrate plane surface (SPS): (a) parallel and (b) perpendicular. The as-deposited samples are hard and look yellowish with a shine and smooth surface. In both cases, X-ray diffractograms show slight differences in the crystalline structure, but optical reflection measurements reveal strong anisotropic characteristics, specially in case (b). Atomic force microscopy pictures evidence a large amount of valleys among crystalline grains. This is a resultant effect of the field action.

Pt-Sn/Al2O3 sol-gel catalysts: Metallic phase characterization

Highly dispersed platinum was found in Pt-Sn/Al2O3 catalysts prepared by the sol-gel method, i.e., cogelation of aluminum tri-sec-butoxide and tetrabutyltin and subsequent impregnation with hexachloroplatinic acid. X-ray diffraction studies showed that the cell parameter of pure platinum is not modified in bimetallic Pt-Sn samples. Moreover, energy dispersive X-ray analysis studies (EDX) showed that platinum, but not tin, was detected in the catalysts where tin was incorporated by the sol-gel coprecipitation of tin and aluminum. Incorporation of tin into the alumina network is suggested.

Hydrodeoxygenation of Phenol Over Sulfided CoMo Catalysts Supported on a Mixed Al2O3-TiO2 Oxide

Abstract In this work, the effect of the mixed Al2O3-TiO2 oxide (Al/Ti=2, named AT2) support on the support-metal interaction in oxide state, its influence on MoS2 dispersion and its impact on the hydrodeoxygenation of phenol reaction was studied. In contrast with CoMo/Al2O3 catalysts, the use of Al2O3-TiO2 as support tuned favorably the support-metal interaction, increasing the availability of easily reducible CoOX and MoOX species with octahedral coordination, which are recognized as precursors of the active phase. The lower support-metal interaction strength caused a decrease in the dispersion of MoS2 phase. Even so, the sulfided CoMo/AT2 catalyst reached 85 % higher catalytic activity in the hydrodeoxygenation of phenol than CoMo/Al2O3. These increases were explained in terms of the formation of a higher amount of active CoMoS phase, and it is consistent with the increased availability of cobalt promoter for the decoration of MoS2 edges. CoMo/AT2 catalyst was more resistant to inhibition by CS2 than CoMo/Al2O3 in direct deoxygenation route and hydrodeoxygenation of phenol.

Effect of the plasma composition on the structural and electronic properties of as-grown SiOx/Si heterolayers deposited by reactive sputtering

We report the effects of varying the oxygen partial pressure (OPP) on the structural and electronic properties of SiOx/Si heterolayers grown by RF reactive sputtering. The produced samples present silicon poly-crystalline characteristics for low values of OPP. The crystallinity decreases as the OPP increases due to oxygen interdiffusion until the silicon crystal structure becomes amorphous. The results of infrared and Raman spectroscopies show higher deviation from stoichiometry and an increment of structural disorder for samples grown with higher values of OPP. Room temperature photoluminescence (PL) is present in all as-grown samples. The PL spectra show two bands, around 1.87 and 2.16 eV, for all the samples, while a third broad band at lower energy shows up and shifts to the red as OPP increases. Our results indicate that silicon-related room temperature PL emission is correlated with the stoichiometry of the SiOx and to the formation of silicon crystals embedded in a silicon dioxide matrix.

Role of Nanocrystalline Titania Phases in the Photocatalytic Oxidation of NO at Room Temperature

Nanocrystalline TiO2 powders were prepared by the sol-gel method and evaluated in the NO photocatalytic oxidation. Samples annealed at 200 and 500°C (TiO2-P-200, TiO2-P-500) were characterized by nitrogen adsorption, XRD-Rietveld refinements, TEM, FTIR and UV-vis spectroscopies. The photocatalytic test of the sol-gel TiO2 samples was carried out in an insulated chamber with 10 ppm of NO, using a 365-nm UV light lamp; the test results were compared with those obtained with a commercial catalyst (P25). Improved photoactivity (89 % of NO oxidized in 60 min) was obtained with the TiO2-P-200 solid which showed high surface area, small crystallite size, higher amount of OH and highly abundant brookite phase (37.2 %) coexisting with the anatase phase (62.8 %). The photo-oxidation activity of the sol-gel catalyst annealed at 500 °C (TiO2-P-500) showed changes in its textural and morphologic properties and therefore, less photoactivity. Sol-gel photocatalysts could be a good option for abating pollution in both indoor and outdoor environments at room temperature.

Phase Stabilization of Mesoporous Mn-Promoted ZrO2: Influence of the Precursor

Mesoporous zirconia-Mn oxides were prepared by surfactant-assisted precipitation using different zirconia precursors and cetyl-trimethyl-ammonium bromide (CTAB) as a synthetic template. The objective of this work was to find out the influence of the zirconia precursors over the structural and textural characteristics of Mn-doped mesoporous zirconia solids. A series of syntheses were carried out by two methods using different zirconia precursors, modifying the Zr:surfactant ratio and the hydrolysis rate of the precipitate. After calcination at 500 °C, the samples were characterized by XRD, DTA, TEM and nitrogen adsorption-desorption isotherm. The use of the zirconium nitrate leads to materials having higher surface areas and narrow pore size distributions in the range of mesoporous materials; however, the preferential formation of the zirconia in the metaestable tetragonal phase was identified as the effect of the particle size allowed by the preparation method rather than the effect of the precursor. It was also found that the Mn and surfactant addition enhances the stabilization of the tetragonal crystalline phase and porosity.

Comparative Studies of the Degradation of Several Zeolites Under Electron Irradiation

High resolution electron microscopy has proven to be a powerful technique to determine structural characteristics of zeolites (l–2),symmetry variations and identification of several kind of defects.Together with ideal projected potential images, the microscopist usually finds in electron micrographs the influence of electro-optical parameters and alterations of the crystallinity of the material under electron irradiation. One of the purposes of this workis to contributetothe understanding of the degradation process of zeolites under electron irradiation in the electron microscope and in this way, discriminate when it is possible, what is reliable information recorded in the images obtained in high resolution conditions.