Limitation by zeolite protons of the oxygenate yield in syngas conversion over RhMn/NaY catalysts

CO hydrogenation over Mn-promoted Rh/NaY catalysts was studied at 1 MPa and 250°C. Significant selectivity to ethanol and ethyl acetate was obtained only after neutralising the protons formed on reduction of Rh ions. Layered bed experiments show that protons act as Brønsted acid sites catalysing secondary reactions that convert the oxygenates to hydrocarbons and coke.     

DEVS-based formalism for the modeling of routing processes

Software and Systems Modeling - The Discrete Event System Specification (DEVS) is a modular and hierarchical Modeling and Simulation (M&S) formalism based on systems theory that provides a...     

Influence of Cobalt Content on the Hydrotreatment Catalytic Activity of CoMo6/γ-Al2O3 Heteropolyoxomolybdate-Based Catalyst

The influence of Co content in the catalytic activity in hydrotreatment reactions (hydrodesulfurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene) using CoMo₆/γ-Al₂O₃-type catalysts, where the precursor is Co(III) heteropolymolybdate of (NH₄)₃[CoMo₆O₂₄H₆?7H₂O formula and Anderson-type planar structure, (hereafter CoMo₆) was investigated. The preparation of catalysts was carried out by the coimpregnation of γ-alumina with CoMo₆ and (NH₄)₆[TeMo₆O₂₄]?]7H₂O (TeMo₆) in order to obtain catalysts with variable amounts of Co(III) keeping about the same Mo amount. The Anderson phase of Te(VI), (TeMo₆) was chosen because of its good solubility and because no promoting effect of the Te was observed in hydrotreatment. Five catalysts were prepared by coimpregnation of γ-Al₂O₃ by using aqueous solutions of both phases in different proportions. Catalysts with a ratio [Co]/([Co] + [Mo]) between 0 and ～0.14 and a Mo loading (wt% Mo) between 8 and 10 were obtained. The Raman and diffuse reflectance (DR) spectroscopies were used for the characterization of bulk and supported CoMo₆ phase. By analyzing the respective adsorption isotherms and parameters and according to the catalytic tests, it could be established that HDS as well as HYD activities of the catalysts increase as a function of the added Co.     

Electrodeposited platinum catalysts over hierarchical carbon monolithic support

Mesoporous deposits of platinum catalysts were electrodeposited over monolith carbon with hierarchical porous structure. The liquid crystal used as a template allowed the electrodeposition of the catalyst on the outer region of the carbon with low penetration in the porous structure. The platinum hexagonal mesostructured deposits exhibits an excellent stability enhanced by the roughness of the carbon support. The mass activity for the electrooxidation of methanol of the mesoporous Pt catalyst supported on the hierarchical carbon is similar to that observed on gold and to that reported for commercial Pt nanoparticulated catalysts, even when this catalyst has a smaller Pt load than the commercial one. Also, the poisoning rate of the mesoporous catalyst is lower than that observed for the commercial catalyst. The integrated system of structured materials could be suitable for the fabrication of modified electrodes in small scale applications.     

About the activation energies of the main and secondary relaxations in cured styrene butadiene rubber

This article studies the influence of the network structure on the activation energies of the α and β relaxations in vulcanized styrene butadiene rubber, SBR. A cure system based on sulphur and TBBS (N‐t‐butyl‐2‐benzothiazole sulfenamide) was used in the formulation of several compounds cured at 433 K. The activation energies were evaluated from internal friction (loss tangent) data of the compounds using an automated subresonant forced pendulum in a wide frequency range and between 80 K and 273 K. The internal friction data of the samples reveal two transitions, α and β, characterized by the temperatures T_α and T_β, due to the glass transition and the phenyl group rotation of the copolymer, respectively. Although T_α increases at higher crosslink density, it shows also a dependence with the amount of polysulphide and monosulphide linkages present in the samples. The highest activation energy for this process is obtained for the samples with high crosslink density and 30% of monosulphides in this structure. In the case of the β‐relaxation, there is a pronounced change in the activation energy between the uncured and the cured samples. The type of structure formed during vulcanization has an important effect in the activation energy of the segmental mode‐process. In the case of the β‐process, the cis‐trans isomerization that takes place during vulcanization in the butadiene part of the SBR, might be the cause of conformational changes in the surrounding of the phenyl rings that affect the energy barrier associated to the phenyl rotation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal properties of phosphoric acid-doped polybenzimidazole membranes in water and methanol-water mixtures

The thermal properties of phosphoric acid-doped poly[2-2′-(m-phenylene)-5-5′ bi-benzimidazole] (PBI) and poly[2,5-benzimidazole] (ABPBI) membranes, ionomeric materials with promising properties to be used as electrolytes in direct methanol and in high temperature polymer electrolyte membrane (PEM) fuel cells, were studied by means of differential scanning calorimetry (DSC) technique in the temperature range from −145 °C to 200 °C. The DSC scans of samples equilibrated in water at different relative humidities (RH) and in liquid water-methanol mixtures were analyzed in relation to glass transition, water crystallization/melting and solvent desorption in different temperature regions. The thermal relaxation observed in the very low temperature region could be ascribed to the glass transition of the H₃PO₄-H₂O mixture confined in the polymeric matrix. After cooling the samples up to −145 °C, frozen water was detected in PBI and ABPBI at different RH, although at 100% RH less amount of water had crystallized than that observed in Nafion membranes under the same conditions. Even more important is the fact that the freezing degree of water is much lower in ABPBI membranes equilibrated in liquid water-methanol mixtures than that observed for PBI and, in a previous study, for Nafion. Thus, apart from other well known properties, acid-doped ABPBI emerges as an excellent ionomer for applications in direct methanol fuel cells working in cold environments.     

Effect of the pore size distribution on the separation factor of membranes used as barriers for isotopic separation by gaseous diffusion

The standard way of evaluating the separation factor for the isotopic separation of U235/238 in the conventional uranium enrichment process by gaseous diffusion through membranes, considers only an average value for the pore radius. This is equivalent to assuming a membrane with all pores of the same size. In this work we discuss the influence of a realistic pore size distribution on the indicated factor and the physical interpretation of these results.     

Mechanical characterization of materials at small length scales

A review on the mechanical characterization of materials at small length scale is presented. The focus is on the different micro- and nanoscale testing techniques, the variety of materials investigated by the scientific and industrial communities and the mechanical quantities identified by such methodologies.