Structural changes in FeOx/γ-Al2O3 catalysts during ethylbenzene dehydrogenation

The structural changes that occur in a FeOx/γ-Al2O3 catalyst during the dehydrogenation of ethylbenzene in a fluidized CREC Riser Simulator have been investigated. Chemical and morphological changes are observed to take place as a result of reaction. Electron microscopy reveals the formation of needle-like alumina structures apparently enclosing iron oxide particles. The formation of such structures at relatively low temperatures is unexpected and has not previously been reported. Additionally, X-ray diffraction and Mössbauer spectroscopy confirmed the reduction of the oxidation state of iron, from Fe2O3 (haematite) to Fe3O4 (magnetite). Iron carbides, Fe3C and ɛ-Fe2C, were detected by electron microscopy through electron diffraction and lattice fringes analysis. Carbon deposition (coking) on the catalyst surface also occurs. The observed structural changes are likely to be closely correlated with the catalytic properties of the materials, in particular with catalyst deactivation, and thereby provide important avenues for future study of this industrially important reaction. Fe2O3/Al2O3 catalyst undergoes chemical and morphological changes during ethylbenzene dehydrogenation forming Al2O3 needles which appear to contain reduced Fe3O4 particles. Fe3C also forms during reaction

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.Peer reviewe

Kinetic modeling of ethylbenzene dehydrogenation over hydrotalcite catalysts

More than 80% of styrene is commercially produced by the catalytic dehydrogenation of ethylbenzene in the presence of large quantity of steam at elevated temperatures over iron oxide based catalysts promoted with alkaline ions. However, this process suffers from several drawbacks, e.g., high energy consumption and rapid catalytic deactivation. In light of this, the kinetics of ethylbenzene dehydrogenation was studied to elucidate the reaction mechanism. Reaction rates for the kinetics of ethylbenzene dehydrogenation were based on power law model with coke formation incorporated as a form of reactant conversion model. In developing the model equations, the most significant reactions were considered, i.e., dehydrogenation to styrene and cracking to yield benzene. All the estimated parameters were suitably correlated. The kinetic model yielded an excellent fit of the experimental data. For all the catalysts examined, ethylbenzene conversion increased with reaction temperature and time. This is an abstract of a paper submitted at the 21st Annual Saudi-Japan Symposium on Catalysts in Petroleum Refining and Petrochemicals (Dhahran, Saudi Arabia 11/27-28/2011).</p

The enhancement of the catalytic performance of CrOx/Al2O3 catalysts for ethylbenzene dehydrogenation through tailored coke deposition

In previous work we have shown that ethylbenzene dehydrogenation over CrOx/Al2O3 catalysts proceeds sequentially via cracking and then dehydrogenation reactions. The present work reports how tailored coke deposition on the catalyst surface can suppress undesired reactions such as cracking to benzene and coke during ethylbenzene dehydrogenation. Additionally, this approach also provides insights into the precursor molecules involved in the formation of carbonaceous deposits, hence providing further understanding of coke formation. Pre-coked catalysts were prepared by adsorbing the products of the ethylbenzene reaction (i.e., benzene, toluene, styrene, ethylene) as single components, in a flowing system at 600 [degree]C over the fresh catalyst. The resulting pre-coked catalysts were then evaluated in the ethylbenzene dehydrogenation reaction and their performance compared with that of the catalyst without exposure to pre-treatment. Characterisation of pre-coked catalysts by elemental analysis, temperature-programmed oxidation (TPO), temperature-programmed desorption (TPD), Raman spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that ethylene is the main coke precursor during ethylbenzene dehydrogenation and that ethylene-derived coke is associated with a reduction in selectivity to styrene as compared to the fresh catalyst. Coke deposited after pre-coking with aromatic molecules, and in particular with benzene, was beneficial for dehydrogenation activity, as shown by the increase in styrene selectivity relative to the fresh catalyst. This enhancement of dehydrogenation activity was correlated with deactivation of acid sites and the reduction of chromium from Cr(vi) to Cr(iii) (active species for dehydrogenation) as a result of the pre-coking procedure

Optical Performance of Single Point-Focus Fresnel Lens Concentrator System for Multiple Multi-Junction Solar Cells—A Numerical Study

This paper investigates the potential of a new integrated solar concentrated photovoltaic (CPV) system that uses a solo point focus Fresnel lens for multiple multi-junction solar cells (MJSCs). The proposed system comprises of an FL concentrator as the primary optical element, a multi-leg homogeniser as the secondary optical element (SOE), a plano-concave lens, and four MJSCs. A three-dimensional model of this system was developed using the ray tracing method to predict the influence of aperture width, height, and position with respect to MJSCs of different reflective and refractive SOE on the overall optical efficiency of the system and the irradiance uniformity achieved on the MJSCs’ surfaces. The results show that the refractive homogeniser using N-BK7 glass can achieve higher optical efficiency (79%) compared to the reflective homogeniser (57.5%). In addition, the peak to average ratio of illumination at MJSCs for the reflective homogeniser ranges from 1.07 to 1.14, while for the refractive homogeniser, it ranges from 1.06 to 1.34, causing minimum effects on the electrical performance of the MJSCs. The novelty of this paper is the development of a high concentration CPV system that integrates multiple MJSCs with a uniform distribution of rays, unlike the conventional CPV systems that utilise a single concentrator onto a single MJSC. The optical efficiency of the CPV system was also examined using both the types of homogeniser (reflective and refractive)

Structural changes in FeO_x/γ-Al₂O₃ catalysts during ethylbenzene dehydrogenation

<p>The structural changes that occur in a FeO_x/γ-Al₂O₃ catalyst during the dehydrogenation of ethylbenzene in a fluidized CREC Riser Simulator have been investigated. Chemical and morphological changes are observed to take place as a result of reaction. Electron microscopy reveals the formation of needle-like alumina structures apparently enclosing iron oxide particles. The formation of such structures at relatively low temperatures is unexpected and has not previously been reported. Additionally, X-ray diffraction and Mössbauer spectroscopy confirmed the reduction of the oxidation state of iron, from Fe₂O₃ (haematite) to Fe₃O₄ (magnetite). Iron carbides, Fe₃C and ɛ-Fe₂C, were detected by electron microscopy through electron diffraction and lattice fringes analysis. Carbon deposition (coking) on the catalyst surface also occurs. The observed structural changes are likely to be closely correlated with the catalytic properties of the materials, in particular with catalyst deactivation, and thereby provide important avenues for future study of this industrially important reaction.</p> <p>Fe₂O₃/Al₂O₃ catalyst undergoes chemical and morphological changes during ethylbenzene dehydrogenation forming Al₂O₃ needles which appear to contain reduced Fe₃O₄ particles. Fe₃C also forms during reaction.</p