Effect of Ca,Ce or K oxide addition on the activity of Ni/SiO2 catalysts for the methane decomposition reaction

To increase the activity and stability of Ni/SiO₂ catalysts, a series of Ni–Ca, Ni–K and Ni–Ce promoted catalysts were prepared by successive impregnations. The textural properties, reducibility and catalytic performance in the methane decomposition reaction were investigated. The catalyst containing 30 wt.% Ni and 30 wt.% cerium oxide greatly increased the conversion of methane (90% of equilibrium value) and improved the stability, whereas the Ni–K and Ni–Ca were less active and stable than the Ni/SiO₂ catalyst. The results suggest that Ce addition prevents the sintering of nickel particles during reduction process maintaining a random distribution between the silica and cerium oxide improving the distribution and migration of deposited carbon.     

Hydrogen production by oxidative steam reforming of methanol over Ni/CeO2–ZrO2 catalysts

Single ZrO₂ and mixed CeO₂-ZrO₂ oxides with different CeO₂/ZrO₂ ratios were prepared by the sol-gel method and the CeO₂ by precipitation. The prepared support were impregnated with an aqueous solution of NiCl₂·6H₂O at an appropriate concentration to yield 3 wt.% of nickel respectively in the catalysts. Catalytic materials were characterized by BET (N₂ adsorption-desorption), SEM-EDS, XRD and TPR. The oxidative steam reforming of methanol (OSRM) reaction was investigated on these catalysts for H₂ production as a function of temperature. Depending of the CeO₂/ZrO₂ ratio; the catalysts composition has a significant influence on the surface area (BET), reduction properties and methanol conversion. XRD patterns of the Ni-base catalysts showed well defined diffraction peaks of the metallic Ni except on the Ni/CeO₂ catalyst, suggesting that on this sample all of the active phase was highly dispersed. Ni/Ceria-rich catalysts were vastly active for OSRM, giving a total CH₃OH conversion at 325 °C with GHSV = 0.3 × 10⁵ h⁻¹. They also showed close selectivity toward H₂, with high selectivity to CO₂ in all range of temperatures, this suggests that the reverse WGS reaction does not occur on these samples. It seems that the nickel is the phase mainly responsible of hydrogen production although the CeO₂/ZrO₂ support reduces the CO formation.     

On the hydrodynamics characterization of the straight Maxblend impeller with Newtonian fluids

The hydrodynamics generated by the straight version of the Maxblend^® impeller with Newtonian fluids in a baffled stirred vessel under the transitional and turbulent regime has been experimentally characterized by means of the particle image velocimetry technique. The flow fields obtained with the Maxblend were compared with those obtained with a double stage classical pitched blade turbine (PBT) and a double Ekato Intermig^® impellers under the same specific power draw. It is shown that these open impellers induce complex local flows in the radial and axial direction, with an intensity decreasing away from the blades. By contrast, the Maxblend impeller generates a more regular circulation pattern, with efficient top-to-bottom pumping.     

Activity of NiCuAl catalyst in methane decomposition studied using a thermobalance and the structural changes in the Ni and the deposited carbon

Activity measurements of a NiCuAl catalyst for the thermal decomposition of methane have been carried out in a thermobalance at different operating temperatures and partial pressures of methane and hydrogen. The thermobalance allows, by gravimetry, a continuous record of the evolution of the deposited carbon during and at the end of the test and the extraction of a sufficient amount of homogenous sample to study the involved structural changes in Ni and the structural properties of the deposited carbon by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of the operating temperature, mainly derived from thermal sintering, on Ni particles and on the deposited carbon is highly significant. The effect of methane as a reactant and hydrogen as a reaction product is mostly derived from its influence on the reaction rate. Additionally, methane and hydrogen reduce the effect of thermal sintering on Ni lowering the surface energy by chemisorption. The study also shows that the deposited carbon on the Ni leading face probably diffuses to the Ni trailing face superficially, and not through bulk Ni as assumed by the present kinetic models.     

Molecular dynamics study of cluster impact on the (0 0 1) and (1 1 0) surfaces of fcc metals

Molecular dynamics simulations of the impact deposition of metal clusters on fcc metal surfaces are presented. Two-dimensional elongated islands are formed when the incident cluster travels parallel to the surface. For perpendicular incidence the results of the impact event are very sensitive to the relative cohesive properties of the cluster and substrate atoms.     

Spectral sensitivity of cones in the goldfish, Carassius auratus

The spectral sensitivities of retinal cones isolated from goldfish (Carassius auratus) retinas were measured in the range 277-737 nm by recording membrane photocurrents with suction pipette electrodes (SPE). Cones were identified with lambda max (+/- S.D.) at 623 +/- 6.9 nm, 537 +/- 4.7 nm, 447 +/- 7.7 nm, and about 356 nm (three cells). Two cells (lambda max 572 and 576 nm) possibly represent genetic polymorphism. A single A2 template fits the alpha-band of P447(2), P537(2), and P623(2). HPLC analysis showed 4% retinal:96% 3-dehydroretinal. Sensitivity at 280 nm is nearly half that at the lambda max in the visible. The lambda max of the beta-band (in nm) is a linear function of the lambda max of the alpha-band and follows the same relation as found for A1-based cone pigments of a cyprinid fish.     

The Argentine radioactive waste respository: Basic criteria,preliminary siting and design conceptual basis

At the end of the seventies. The Argentine authorities decided to explore alternatives for disposing of the high-level radioactive wastes that would eventually be generated by the country's nuclear programme. This programme involves nuclear power reactors that will generate an integrated electrical energy of a fraction of a terawatt year by the end of the century (1). The country's programme also foresees the reprocessing of the spent fuel. The paper describes the basic criteria adopted by the Argentine authorities for the disposal of high-level wastes. On the basis of these criteria. a site in stable, unfractured granite was selected for detailed studies, near Gastre. Province of Chubut, out of about 200 potential sites. This site has been thoroughly investigated and its suitability has been validated. On the other hand, work has progressed on the design of the future repository.     

Occupational allergy in greenhouse workers: sensitization to Tetranychus urticae

BACKGROUND: Tetranychus urticae (TU) is a macroscopic mite which is found infesting a large number of plants of economic interest. It has rarely been described as a cause of occupational allergic disease in agricultural workers. OBJECTIVE: To describe TU sensitization in greenhouse workers attending the outpatient allergy unit and its clinical associations, and to characterize the allergens involved. MATERIALS AND METHODS: Twenty-four consecutive carnation greenhouse workers with allergy-related symptoms, referred to our outpatient clinic during a 6-month period, were included. We made the diagnostic extract from carnation leaves heavily infested with TU. Skin-prick test, specific IgE measurement and bronchial provocation test with TU extract were carried out in all subjects. Allergen characterization was achieved by SDS-PAGE (sodium dodecylsulfate-polyacrylamide gel electrophoresis) and immunoblotting. RESULTS: Sixteen patients (66%) presented positive skin-prick test and specific IgE and were diagnosed allergic to TU. Fifteen patients suffered from bronchial asthma, 14 rhinitis and five urticaria. Twelve exhibited positive bronchial provocation test to the TU extract. On RAST-inhibition studies, there was no evidence of crossreactivity between TU extract and D. pteronyssinus. An allergen at 19 kDa was determined in the TU extract by SDS-PAGE immunoblotting studies. CONCLUSION: TU could be an important occupational allergen in greenhouse workers showing allergic symptomatology. There is no crossreactivity between this mite and the house dust mite D. pteronyssinus.     

Extracts from various mite species contain cross-reactive and noncross-reactive IgE epitopes. A RAST inhibition study

PURPOSE: A low pregnancy rate in in vitro fertilization (IVF) patients of advanced maternal age may be caused by aneuploidies originating from non disjunction in the first or second meiotic divisions. We introduced genetic testing of oocytes by sampling and fluorescent in situ hybridization (FISH) analysis of the first and second polar bodies, to avoid fertilization and transfer of aneuploid oocytes in IVF patients of advanced maternal age. METHODS: Three hundred and sixty-three IVF patients 34 years and older participated in the study. Using micromanipulation procedures, the first and second polar bodies were removed following their extrusion from the oocytes and studied by FISH, using probes specific for chromosomes 13, 18, and 21 to detect oocytes with common aneuploidies. RESULTS: Of a total of 538 IVF cycles, 3250 oocytes were available for FISH analysis, with conclusive FISH results in 2742 oocytes (84.3%). As many as 1102 (40%) of oocytes were predicted to be aneuploid and not transferred. Of 1640 embryos predicted to be normal, 1145 were transferred in 467 treatment cycles, resulting in 107 pregnancies (23%), from which 67 healthy children have been born, 32 pregnancies spontaneously aborted, and 15 pregnancies are ongoing after being confirmed normal by prenatal diagnosis. CONCLUSIONS: Preimplantation diagnosis by first- and second-polar body FISH analysis allows us to avoid the age-related risk of common aneuploidies in IVF patients of advanced maternal age.