Oxidative coupling of methane in a mixed-conducting perovskite membrane reactor

Ionic-electronic mixed-conducting perovskite-type oxide La0.6Sr0.4Co0.8Fe0.2O3 was applied as a dense membrane for oxygen supply in a reactor for methane coupling. The oxygen permeation properties were studied in the pO2-range of 10¿3¿1 bar at 1073¿1273 K, using helium as a sweeping gas at the permeate side of the membrane. The oxygen semi-permeability has a value close to 1 mmol m¿2 s¿1 at 1173 K with a corresponding activation energy of 130¿140 kJ/mol. The oxygen flux is limited by a surface process at the permeate side of the membrane. It was found that the oxygen flux is only slightly enhanced if methane is admixed with helium. Methane is converted to ethane and ethene with selectivities up to 70%, albeit that conversions are low, typically 1¿3% at 1073¿1173 K. When oxygen was admixed with methane rather than supplied through the membrane, selectivities obtained were found to be in the range 30¿35%. Segregation of strontium was found at both sides of the membrane, being seriously affected by the presence of an oxygen pressure gradient across it. The importance of a surface limited oxygen flux for application of perovskite membranes for methane coupling is emphasized

Oxygen transport through La@1-x]Sr@x]FeO@3-gamma] membranes. I. Permeation in air/He gradients

Oxygen permeation measurements in air/He gradients were performed on dense La1 ¿ xSrxFeO3 ¿ ¿ membranes in the composition range x = 0.1¿0.4 and temperature range 1123¿1323 K. Pretreatment of the lower oxygen partial pressure side of the membranes in a CO-containing atmosphere for several hours at 1273 K led to higher oxygen fluxes, which were in the range of 0.1¿4.5 mmol m¿2 s¿1. After treatment, the observed oxygen fluxes could be described in terms of bulk diffusion-limited permeation behaviour. Experimental evidence for a bulk-diffusion controlled flux was found from thickness dependence measurements on membranes with thicknesses between 0.5 mm and 2.0 mm. Model calculations, based on Wagner theory in conjunction with data of oxygen nonstoichiometry and vacancy diffusion coefficients from literature, were performed. The experimental flux values deviated from the model calculations with factors up to 2.5. Adjustment of the value of the vacancy diffusion coefficient led to good agreement between the experimental data and the model calculations. The calculated vacancy diffusion coefficients Dv0 were virtually independent of composition and were found to be in the range 5.3¿9.3 × 10¿6 cm2 s¿1

MoS2 Nanocube structures as catalysts for electrochemical H2 evolution from acidic aqueous solutions

Core–shell PMMA–Au nanocube structures made by a combination of nanoimprint lithography and sidewall deposition were used as template for electrodeposition of MoS2, Ni, and Pt. Linear sweep voltammetry experiments obtained in an aqueous solution containing 0.29 M H2SO4 (pH 0.24) showed that the onset potential of the core–shell–shell PMMA–Au–MoS2 nanocube electrode for the hydrogen evolution reaction (HER) was shifted to the positive direction (i.e., requiring a lower overpotential) by 20–40 mV compared to planar MoS2 films. This indicates that the nanocube electrodes have a significantly increased HER activity, which is probably because of a higher density of catalytically active edge sites available at the nanocube surface. It was also found that the HER activity initially increased with increasing MoS2 deposition time, but decreased after deposition for 60 min because the edges of the nanocubes became rounded, thereby decreasing the number of active edge sites. By depositing Ni and Pt on top of PMMA–Au nanocubes, it was shown that this method can also be used for the synthesis of nanocube structures with varying compositions

Micropatterned 2D Hybrid Perovskite Thin Films with Enhanced Photoluminescence Lifetimes

The application of luminescent materials in display screens and devices requires micropatterned structures. In this work, we have successfully printed microstructures of a two-dimensional (2D), orange-colored organic/inorganic hybrid perovskite ((C6H5CH2NH3)2PbI4) using two different soft lithography techniques. Notably, both techniques yield microstructures with very high aspect ratios in the range of 1.5-1.8. X-ray diffraction reveals a strong preferential orientation of the crystallites along the c-axis in both patterned structures, when compared to nonpatterned, drop-casted thin films. Furthermore, (time-resolved) photoluminescence (PL) measurements reveal that the optical properties of (C6H5CH2NH3)2PbI4 are conserved upon patterning. We find that the larger grain sizes of the patterned films with respect to the nonpatterned film give rise to an enhanced PL lifetime. Thus, our results demonstrate easy and cost-effective ways to manufacture patterns of 2D organic/inorganic hybrid perovskites, while even improving their optical properties. This demonstrates the potential use of color-tunable 2D hybrids in optoelectronic devices

Inrichting en effecten van schakelklassen: resultaten van het evaluatieonderzoek schakelklassen in het schooljaar 2007/08

Bestrijding van segregatie in het onderwijs in gemeenten: verkenning van lokaal beleid anno 200

Growing a LaAlO3/SrTiO3 heterostructure on Ca2Nb3O10 nanosheets

The two-dimensional electron liquid which forms between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO3 substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of Ca2Nb3O10 which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface.Comment: 11 pages, 7 figure

Feasibility of right-sided total extraperitoneal procedure for inguinal hernia repair after appendectomy: a prospective cohort study

Contains fulltext : 80682.pdf (publisher's version ) (Open Access)BACKGROUND: Totally extraperitoneal (TEP) endoscopic hernia surgery is increasingly popular since it is associated with little postoperative pain and with early return to work. Previous appendectomy may preclude preperitoneal dissection in patients with right-sided hernias. The feasibility of TEP surgery in these patients was the subject of the present study. METHODS: Between January 2005 and February 2007 all consecutive patients undergoing TEP surgery were included in a prospective cohort study. The study group consisted of patients with right-sided and bilateral hernias. Operative times, conversions, complication rates, and return to daily activities were recorded. Patients were divided into two groups according to previous appendectomy. RESULTS: A total of 462 patients with right-sided hernias underwent TEP surgery: 421 patients without previous abdominal surgery (group 1) and 41 patients with previous appendectomy (group 2). The conversion rate was significantly higher in group 2: four patients (10%) were converted to open Lichtenstein repair versus five (1%) in group 1 (p = 0.005). However, we found no significant differences in complication rate, operative time, and return to daily activities. CONCLUSIONS: A right-sided (or bilateral) TEP procedure may be performed safely in patients after previous appendectomy. Despite a higher conversion rate, the vast majority of patients can be operated endoscopically