Deoxygenation of benzoic acid on metal oxides: 1. The selective pathway to benzaldehyde

The mechanism of the selective deoxygenation of benzoic acid to benzaldehyde was studied on ZnO and ZrO₂. The results show conclusively that the reaction proceeds as a reverse type of Mars and van Krevelen mechanism consisting of two steps: hydrogen activates the oxide by reduction resulting in the formation of oxygen vacancies. Subsequent re-oxidation of these vacancy sites by benzoic acid yields benzaldehyde. Inhibition of the deoxygenation reaction can be achieved by addition of suitable polar compounds with a high affinity for the oxygen vacancy sites such as carbon dioxide or water. Differences in the catalytic activity and selectivity of ZnO and ZrO₂ can be attributed to differences in hydrogen activation, redox properties and extent of benzoic acid coverage.     

Effect of Post-Precipitation Treatment on the Pore-Structure Stability of Sol-Gel-Derived Lanthanum Zirconate

The importance of post-precipitation treatments (pore-fluid exchange and its removal) on the evolution of the texture of coprecipitated lanthanum zirconate has been investigated. The nature of the pore fluid and the type of fluid-removal (drying) process have shown a profound effect on the aggregate structure (packing of primary particles within the aggregates of the gel). Exchanging the pore fluid with organic fluids such as ethanol or tetrahydrofuran resulted in higher specific surface area, larger pore volume, and, most frequently, larger pore radii. The effect has been attributed to the surface tension of the pore fluid rather than to the polycondensation effect. Freeze drying and microwave drying of ethanol-washed lanthanum zirconate gel also resulted in higher surface area, compared to the oven-dried gel. Freeze drying and microwave drying yielded a surface area of ∼30 m²/g, whereas oven drying yielded a surface area of 20 m²/g after heating at 800°C.     

Heat transport in structured packings with co-current downflow of gas and liquid

Improvements in catalyst activity make the heat transport in fixed bed reactors increasingly important. Structured packings operated in two-phase flow are expected to outperform randomly packed beds, but heat transfer data on structured packings is scarce. In this work structured packings such as OCFS (Open Cross Flow Structures), CCFS (Closed Cross Flow Structures), knitted wire, and foam were characterised with respect to the heat transfer performance. A dedicated set-up was designed and built which enabled us to measure the heat transfer rates in two-phase flow at ambient pressure in the absence of reaction. Benchmarking and set-up validation was carried out using glass beads. The structured packings—especially OCFS and CCFS—show heat transfer coefficients that are superior over those of glass beads, at lower energy dissipation.     

Strategies for rare-event detection: an approach for automated fetal cell detection in maternal blood

This article explores the feasibility of the use of automated microscopy and image analysis to detect the presence of rare fetal nucleated red blood cells (NRBCs) circulating in maternal blood. The rationales for enrichment and for automated image analysis for "rare-event" detection are reviewed. We also describe the application of automated image analysis to 42 maternal blood samples, using a protocol consisting of one-step enrichment followed by immunocytochemical staining for fetal hemoglobin (HbF) and FISH for X- and Y-chromosomal sequences. Automated image analysis consisted of multimode microscopy and subsequent visual evaluation of image memories containing the selected objects. The FISH results were compared with the results of conventional karyotyping of the chorionic villi. By use of manual screening, 43% of the slides were found to be positive (>=1 NRBC), with a mean number of 11 NRBCs (range 1-40). By automated microscopy, 52% were positive, with on average 17 NRBCs (range 1-111). There was a good correlation between both manual and automated screening, but the NRBC yield from automated image analysis was found to be superior to that from manual screening (P=.0443), particularly when the NRBC count was >15. Seven (64%) of 11 XY fetuses were correctly diagnosed by FISH analysis of automatically detected cells, and all discrepancies were restricted to the lower cell-count range. We believe that automated microscopy and image analysis reduce the screening workload, are more sensitive than manual evaluation, and can be used to detect rare HbF-containing NRBCs in maternal blood.     

Porous Nanocomposites 2: Pore-Structure Stability of Pure ZrO2, ZrO2(matrix)-Al2O3 and Al2O3(matrix)-ZrO2 Nanocomposites

Porous nanocomposites in the Al2O3-ZrO2 system were studied with a view to understand the selection rules for developing high temperature stable porous oxide systems. The results were also compared with TiO2-Al2O3 nanocomposite systems. The pore structure and phase evolution of these composites were studied using TG/DTA, XRD and nitrogen adsorption/desorption techniques. Al2O3 was found to be a good second phase stabiliser for stabilising ZrO2 and TiO2 matrix phases.     

TPR and infrared measurements with cu/zno/al2o3 based catalysts for the synthesis of methanol and higher alcohols from co + h2

The influence of different promoters (CeO₂, MnO_x, K₂CO₃) on various properties of a standard coprecipitated Cu/ZnO/Al₂O₃ catalyst has been examined. The catalysts prepared were characterized by Cu surface area, PTIR and TPR measurements. It was found that addition of K₂CO₃ reduced the Cu surface area by about 30%, whereas the Cu surface area did not decrease with addition of the other promoters. The reduction behaviour was affected by the addition of K₂CO₃ as well as by MnO_x, but not by CeO₂. The cause of these effects is possibly an electronic interaction between the promoter and Cu ions.The effect of the different promoters on the activity and selectivity has also been studied. The K₂CO₃ promoted catalyst has an optimum selectivity to higher alcohols at 280 °C; addition of Mn made the catalyst more selective towards methanol. At 300 °C, the Ce promoted catalyst had a high selectivity to methanol and iso-butanol. The promoting effect of the additives may be caused by stabilization of the surface intermediates leading to alcohols. Infrared measurements of adsorbed CO or adsorbed methanol on materials with and without K did not, however, provide any evidence for a difference in reaction mechanism.     

Partial oxidation of methane by O2 and N2O to syngas over yttrium-stabilized ZrO2

Catalytic partial oxidation of methane to synthesis gas over ZrO₂ and yttrium-stabilized zirconia (YSZ) is studied using O₂ and N₂O as oxidants. ZrO₂ is much more active than YSZ in oxidation of methane with N₂O. In contrast, YSZ is significantly more active than ZrO₂ when O₂ is used as an oxidant. The presence of O₂ does not influence the rate of N₂O decomposition over ZrO₂ and YSZ, while the presence of H₂O in the system decreases N₂O conversion significantly. O₂ and N₂O are activated at different active sites. Y-induced oxygen vacancies are active for O₂ activation, whereas oxygen co-ordinatively unsaturated Zr cations (Zr-CUS) located at corners, edges, steps and kinks are responsible for N₂O activation. These sites are also capable of dissociating H₂O, resulting in competition between H₂O and N₂O. As compared with N₂O, molecular O₂ is easier to be activated over YSZ and ZrO₂.     

Model‐Based Optimization of a Photocatalytic Reactor with Light‐Emitting Diodes

The complicated interplay between mass and photon transfer within a photocatalytic reactor calls for an integrated design approach. A model‐based optimization approach for LED‐based photocatalytic reactors is presented. First, a model that describes the distribution of reactants and photons within a photocatalytic reactor is developed. Then, several design variables related to the reactor dimensions and light sources are optimized simultaneously using the photocatalytic degradation of toluene as a model system. The results demonstrate how different formulations of the problem can be used to either minimize the reactor cost or to obtain a specified concentration profile within the reactor.     

The selective oxidation of methane to ethane and ethylene over doped and un-doped rare earth oxides

A comparison has been made of the behaviour in the oxidative coupling of methane of the oxides of Sm, Dy, Gd, La and Tb with that of a Li/MgO material. All but the Tb₄O₇ (which gave total oxidation) were found to give higher yields than the Li/MgO material at temperatures up to approaching 750°C but the Li/MgO system gave better results at higher temperatures. The cubic structure of Sm₂O₃ was found to be responsible for its good performance while the monoclinic structure was relatively inactive and unselective. The addition of Na or Ca to cubic Sm₂O₃ gives a higher optimum C₂ yield than that of unpromoted Sm₂O₃. Sm₂O₃ and Ca/Sm₂O₃ catalysts are more stable than Li/MgO, Li/Sm₂O₃ or Na/Sm₂O₃. The addition of Li or Na to Sm₂O₃ causes the structure to change from cubic to monoclinic; the deactivation of the Na/Sm₂O₃ catalysts is caused by a loss of Na coupled with the formation of the monoclinic form of Sm₂O₃.