Ammoxidation of methylaromatics over vanadium phosphate catalysts II. Catalyst formation, active sites and reaction mechanism

The interactions of VOHPO₄· 0.5H₂O and (VO)₂P₂O₇ with the ammoxidation feed and the single components such as ammonia, oxygen, water and component mixtures were studied in detail using XRD and temperature-programmed reaction spectroscopy. The aim of this work was to improve the knowledge of the formation of the active phases or active sites of the catalysts from their precursors under the condition of the ammoxidation reaction. Similar catalytic properties of various applied VPO materials were discussed in terms of the presence of similar structure elements (domains of adjacent edge-sharing VO₆ octahedra-units and P-O-NH₄ groups).     

Collective modes and sound propagation in a magnetic field in superfluid3He-B

A high-resolution, ultrasonic (12–89 MHz) acoustic impedance technique has been used to investigate the order parameter collective modes in superfluid³He-B over a pressure range of 0–15 bar and in magnetic fields up to 180 mT. In agreement with earlier experiments, theJ=2 real squashing mode has been observed to split into five components in small magnetic fields. However, contrary to earlier theoretical estimates, the Zeeman shifts have been found to become extremely nonlinear as the magnetic field is increased. The extent of this nonlinearity is largest at low pressures and at temperatures close toT _c. In comparison with recent theoretical work, the nonlinear Zeeman shifts may be explained as a result of two effects. First, there is a significant distortion of the B-phase energy gap in large magnetic fields. Second, there is an important coupling between the sameJ _zsubstates of the differentJ modes. In this sense the nonlinear evolution of the real squashing mode constitutes the observation of the Paschen-Back effect in³He-B. A comparison of the observed Zeeman shifts with theoretical expressions has yielded information about particle-particle and particle-hole interaction effects in the superfluid. In the limitT 0 and above a threshold field, the real squashing mode has been found to possess additional structure. TheJ _z=0 substate has been observed to split into a doublet. The separation between the two components of the doublet is of the order of 100–200 kHz and remains independent of the magnetic field. The origin of the doublet may be understood in terms of a recent theory which postulates a texture-dependent collective mode frequency. Further, at extremely small fields the effects due to dispersion of the real squashing modes have been found to be important. The magnitude of the dispersion-induced mode splitting in zero field is found to be consistent with theoretical predictions. TheJ=2 squashing mode has also been studied in the presence of a magnetic field. TheJ _z=0 state of the squashing mode is observed to shift to lower temperatures in a magnetic field. An additional field dependence of the observed acoustic impedance is interpreted as the evolution of theJ _z=–1, –2 states, but appears to be inconsistent with theoretical predictions.     

Reaction pathway of benzonitrile formation during toluene ammoxidation on vanadium phosphate catalysts

The reaction pathway of the ammoxidation of toluene on (VO)₂P₂O₇ used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH₃ is chemisorbed on the catalyst surface, forming three different species, i.e., NH ₄ ⁺ ions located on BrØnsted sites, coordinatively bound NH₃ on Lewis sites and NH ₂ ^– groups, presumably P-NH₂. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of V^IV=O groups generates a V...O=CH-C₆H₅ surface structure. This benzaldehyde-like surface species reacts with adsorbed NH₃ according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH ₄ ⁺ ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.     

A fast heuristic for quay crane scheduling with interference constraints

This paper considers the problem of scheduling quay cranes which are used at sea port container terminals to load and unload containers. This problem is studied intensively in a recent stream of research but still lacks a correct treatment of crane interference constraints. We present a revised optimization model for the scheduling of quay cranes and propose a heuristic solution procedure. At its core a Branch-and-Bound algorithm is applied for searching a subset of above average quality schedules. The heuristic takes advantage from efficient criteria for branching and bounding the search with respect to the impact of crane interference. Although the used techniques are quite standard, the new heuristic produces much better solutions in considerably shorter run times than all algorithms known from the literature.     

Monitoring the Synthesis and Composition Analysis of Microsilica Encapsulated Acetylacetonatocarbonyl TriphenylphosphinerhodiumCatalyst by Inductively Coupled Plasma (ICP) Techniques

A novel technique to monitor the synthesis process of encapsulated acetylacetonatocarbonyl triphenylphosphinerhodium within a microsilica nanoshell has been studied using inductively coupled plasma (ICP) techniques. Nanospheres sized around 50-100 nm were obtained and ICP was used to quantify the exact composition of rhodium, phosphorous, and silicon with differing digestion solvents. In addition, ICP was used to detect rhodium and phosphorous in the nano core-shell catalysts as a quality control procedure     

Identification of the geographical origin of pumpkin seed oil by the use of rare earth elements and discriminant analysis

The aim of this work was to develop an analytical method to assure the geographical origin of Styrian pumpkin seed oil, a high priced local product which is protected by the European Union. The development of such a method is not only of interest for scientists but also of importance for producer that want to guarantee the purity and quality of their products as well as the consumer wanting to know the origin of the food products.Since the rare earth elements (REE) concentrations are extremely low in pumpkin seed oil a fast and sensitive analytical method with ICP-MS had to be developed and validated. In the current project, pumpkin seeds from different regions in Austria were sampled. The REE patterns in the extracted oil of these seeds were determined and a preliminary classification with discriminant analysis was successfully done on a statistical basis.The study demonstrates that pumpkin seed oils from different geographical origin show variable rare earth element patterns making it possible to trace the origin of these oils.     

Zero Sound Attenuation Near the Quantum Limit in Normal Liquid 3He Close to the Superfluid Transition

The zero sound attenuation of normal liquid ³He has been studied over a range of temperatures from slightly above the superfluid transition temperature, T _c, to approximately 10mK at the constant pressures of 1 and 5bar. Using longitudinal LiNbO₃ transducers, operating both on and off resonance, the experiment was performed at 15 discrete frequencies located in several broadband frequency windows, including 16–25, 60–70, and 105–111MHz. The results are compared to Landau's prediction for the attenuation of zero sound in the quantum limit, (k _B Tk _B T _F), where ₀(P,T, )= (P) T ²{1+(/2k _B T)²}. Calibration of the received zero sound signals was performed by measuring the temperature dependence of the first sound attenuation from 30 to 800mK at those same frequencies and pressures. The data are compared to previous results.     

Highly efficient transmission gratings in fused silica for chirped-pulse amplification systems

We report on highly efficient transmission gratings in fused silica with a grating period of 800 nm generated by electron-beam lithography. At a wavelength of 1060 nm, 95% diffraction efficiency is achieved under Littrow conditions. The damage threshold, extremely enhanced compared with conventional gold-coated diffraction gratings, makes these gratings the key elements in high average power (>100 W) femtosecond fiber chirped-pulse amplification systems.