Binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] nanocomposites: formation, characterization and catalytic performance in partial ethanol oxidation

Cuprous oxide agglomerates composed of 4-10 nm Cu2O nanoparticles were deposited on multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNTs to give binary [Cu2O/MWCNT] and ternary [Cu2O/ZnO/MWCNT] composites. Di-aqua-bis[2-(methoxyimino)propanoato]copper Cu[O2CCCH3NOMe](2)·2H2O 1 in DMF was used as single source precursor for the deposition of nanoscaled Cu2O. The precursor decomposes either in air or under argon to yield CuO2 by in situ redox reaction. Thermogravimetric coupled mass spectroscopic analysis (TG-MS) of 1 revealed that methanol formed during the decomposition of 1 acts as a potential in situ reducing agent. Scanning electron microscopy (SEM) of the binary [Cu2O/MWCNT] nano-composite shows an increase of cuprous oxide loading depending on the precursor amount, along the periphery of the MWCNTs as well as formation of larger particle agglomerates. Transmission electron microscopy (TEM) of the sample shows crystalline domains of size 4-10 nm surrounded by an amorphous region within the larger particles. SEM and TEM of ternary [Cu2O/ZnO/MWCNT] clearly reveal that Cu2O nanoparticles are primarily deposited on ZnO rather than on MWCNTs. The catalytic activities of the [Cu2O/MWCNT] and [Cu2O/ZnO/MWCNT] binary and ternary composites were studied for the selective partial oxidation of ethanol to acetaldehyde with molecular oxygen. While using binary [Cu2O/MWCNT] (13.8 wt% Cu) as catalyst, acetaldehyde was obtained with a yield of 87% at 355 °C (selectivity 96% and conversion 91%). When nanoscale ZnO is present, the resulting [Cu2O/ZnO/MWCNT] composite shows preferential hydrogen and CO2 formation due to the fact that the dehydrogenation and total oxidation pathway is more favoured compared to the binary composite. Significant morphological changes of the catalyst during the catalytic process were observed.     

Calculation of the temperature distribution in dieless drawing

Dieless drawing is an example of flexible metal forming processes. The investigation of the main process parameters and their interdependence is the prerequisite for the deliberate choice of input parameters to get the desired quality of the workpiece. Drawing force, drawing velocity, and temperature are the main control parameters. But only the temperature can be influenced locally whereas the force and the velocity can be adjusted only globally. Because of this special importance of the temperature analytical and numerical models for the temperature distribution along the deformation zone have been developed.     

Fluiddynamische Untersuchung eines konischen Turbinenrührers

Zusammenfassung In der vorliegenden Arbeit werden die Ergebnisse einer experimentellen Untersuchung mit Laser-Doppler-Anemometrie an einem konischen Dispergierrührer mitgeteilt. Ziel der Untersuchung war es, den konischen Rührer, der zum Dispergieren eingesetzt werden soll, hinsichtlich seiner fluiddynamischen Eigenschaften zu charakterisieren und mit dem 6-Blatt-Schreibenrührer zu vergleichen. Es hat sich gezeigt, da? der untersuchte Rührer neben einer recht guten Umw?lzleistung, die durch den Pumpbeiwert ausgedrückt wird, auch noch über Vorraussetzungen verfügt, die gute Dispergierf?higkeiten erwarten lassen. Dies wird durch Vergleich mit bekannten Ergebnissen für den 6-Blatt-Scheibenrührer belegt. Das Feld der lokalen spezifischen Energiedissipationsraten wurde aus den gemessenen lokalen Schwankungsgeschwindigkeiten u′ (RMS-Wert) berechnet. Die maximalen Energiedissipationsraten sind etwa 12 mal so gro? wie der mittlere Leistungseintrag.     

Attrition and secondary nucleation in crystallizers

The mean crystal size of coarse crystalline products is determined by secondary nucleation and crystal growth. Secondary unclei are mainly produced by contacts of crystals with parts of the crystallizer or with other crystals. As a consequence, attrition effects are very important. In this paper, a model is proposed in order to calculate the attrition rate of crystals, depending on the physical properties of the crystalline product, the geometry of the crystallizer and on the operating conditions such as the stirrer speed or the suspension density. The effective rate of secondary nucleation can be expressed in terms of the attrition rate by introducing effective values for number and size of attrition particles. Finally, a scale-up criterion based on this model is derived. This criterion allows to predict effective rates of secondary nucleation and mean crystal sizes if data obtained in a laboratory crystallizer are available.     

Catalytic dehydrogenation of iminodibenzyl to iminostilbene. A comparison of potassium-promoted manganese,iron and cobalt oxide catalysts

The dehydrogenation of iminodibenzyl (10,11-dihydro-5-dibenz[b.f]azepine) to iminostilbene (5H-dibenz[b.f]azepine) was investigated over potassium-promoted oxides of manganese, iron and cobalt. Both unsupported oxides as well as corresponding oxides supported on magnesium oxide were examined. Catalytic tests were carried out in a continuous fixed-bed reactor in the presence of steam in the temperature range of 400–550°C and at atmospheric pressure. Unsupported, potassium-promoted iron oxide proved to be the most suitable catalyst for the dehydrogenation of iminodibenzyl, yielding iminostilbene with 80% selectivity at nearly 100% conversion.     

Investigation of a fixed-bed pilot plant reactor by dynamic experimentation. Part 2. Simulation of reactor behaviour

Data collected with forced uncorrelated sinusoidal changes of the process variables are used to simulate the behaviour of a non-isothermal non-adiabatic pilot plant fixed-bed reactor. The test reaction applied is the hydrogenation of toluene to methylcyclohexane on an industrial nickel catalyst. A pseudo-homogeneous two-dimensional model as well as a one-dimensional model are applied to describe the reactor behaviour. The model parameters are estimated by defining an objective function based upon residuals of the discretized differential equations instead of upon deviation from the observed variables. This procedure leads to a drastic reduction of computer expenditure. Measured and simulated temperature and concentration profiles are compared on the basis of a number of plots and fitting quality criteria. The model parameters estimated from data collected during dynamic runs are comparable to those obtained from a series of stationary experiments (2₃ experimental design). However, with the dynamic experiments the data necessary for modelling can be collected much more efficiently.     

Vanadia/silica model catalyst: AFM and XPS investigation of morphological and chemical changes occurring upon exposure to different gas atmospheres

A model vanadia/silica interface has been prepared by vapour deposition of vanadium-oxy-triisopropoxide onto the native oxide layer of a silicon wafer. The VO _x /SiO₂/Si model system has been used to investigate the morphological and chemical changes occurring with vanadia/silica catalysts when they are exposed to different gas atmospheres. Atomic force microscopy and X-ray photoelectron spectroscopy have been used to follow these changes. The studies show that exposure of the vanadia/silica interface to conditions prevailing during the selective reduction of NO by NH₃ results in temperature dependent morphological changes, while the oxidation states of the vanadia species reflected by the ratio V(III)/V(V) change only little during the surface reconstruction.