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The release of nanosized particles from fluidized beds of ceramic oxide nanopowders, namely, TiO2 (P25), Al2O3 (AluC) and SiO2 (A130) has been assessed for the first time. Previous models and experiments for processing engineered nanoparticles (ENP) using fluidized beds reported only the formation of micron-sized cluster agglomerates in the gas phase. In this work, aerosol spectrometry techniques such as scanning mobility particle sizing (SMPS) and optical particle counting (OPC) have been combined with powder technologies, such as the borescope high-speed camera system, to determine the particle size distribution from 5 nm to 1 mm above a fluidized bed. Furthermore, the morphology of nanoparticulate aerosol at different locations in the bed was determined by offline electron microscopy. The results demonstrate that free nano- and micron-sized particles are released from fluidized beds. Since the structures found above the bed are also expected to be present within fluidized beds, a revision of existing nanoparticle fluidization models, and improved safety and control measures in reactors for gas-phase ENP processing are needed to avoid nanoparticle release.

Silica-metal nanohybrids are common materials for applications in biomedicine, catalysis or sensing. Also, hollow structures are of interest as they provide additional useful features. However, in these materials the control of the size and accessibility to the inner regions of the structure usually requires complex synthesis procedures. Here we report a simple colloidal procedure for synthesizing hollow silica-metal nanohybrids, driven by the diffusion of metal precursors through the porous silica shell and subsequent reduction in aqueous solutions. The formation of hollow nanoparticles is controlled by the colloidal conditions during synthesis, which affect the ripening of hollow nanoparticles in presence of organosilanes. The modification of the conditions during synthesis affected the growth of silica precursors in presence of fluorescein isothiocyanate (FITC). The limited access to water molecules during the hydrolysis of silica precursors is attributed to the hydrophobicity of organic fluorescent molecules linked to the condensing silica clusters at the initial stages of nanoparticle formation and to the limitation of water content in the microemulsion method used. Finally, the growth of metal nanoseeds at the core of hollow nanoparticles can be easily achieved though a simple method in aqueous environment. The pH and thermal conditions during the reduction process affect the formation of metal-silica nanohybrids and their structural features.

A long-lasting generator of continuous silica nanoparticle aerosols based in a fluidized bed of glass beads coated with nanosized silica has been developed. The attrition resulting from the bubbling fluidized bed regime progressively detaches the silica coating from the glass beads, giving rise to a steady production of silica nanosized aerosols with median diameters from 100 to 250 nm depending on the initial size of the coating nanoparticles. Continuous aerosol production could be maintained for more than 12 h, and the nanoparticle concentration can be easily tuned in the range of 2000 to 14,000 #/cm3 by adjusting the fluidization and/or dilution flow rates. Copyright 2013 American Association for Aerosol Research

This is the peer reviewed version of the following article :Lobera Gonzalez, MP.; Escolastico Rozalen, S.; Serra Alfaro, JM. (2011). High Ethylene Production through ODHE Membrane Reactors based on Fast Oxygen-Ion Conductors. ChemCatChem. 3:1503-1508. doi:10.1002/cctc.201100055, which has been published in final form at http://dx.doi.org/10.1002/cctc.201100055. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

[EN] An intensification process for the selective oxidation of hydrocarbons integrates a catalytic reactor and an oxygen separation membrane. This work presents the study of oxidative dehydrogenation of ethane at 1123 K in a catalytic membrane reactor based on mixed ionic-electronic conducting (MIEC) membranes. The surface of a membrane made of Ba0.5Sr0.5Co0.8Fe0.2O3-d has been activated using different porous catalytic layers based on rare earth-doped cerias (fluorite structure) and the porous catalytic coating was deposited by screen printing (coating around 15 mu m). The different catalyst formulations were developed by partial substitution of Ce and were synthesized by co-precipitation followed by cobalt impregnation when required. Specifically, seven different catalysts based on the system Ce1-xLnxO2-d (x=0.1 or 0.2; Ln=Tb, Pr, Er, Gd, and Tb+Er), including the effect of cobalt addition (2?% molar) in Ce0.8Tb0.2O2-d, were studied. The ceria catalysts were studied by XRD, SEM, DC-conductivity as a function of oxygen partial pressure, and the high-temperature stability in a CO2 environment was assessed using thermogravimetry. Then, the influence of the ceria catalytic coating on the oxygen permeation flux through the MIEC membrane was studied using argon and methane as the sweep gas in the permeate side. Finally, oxidative dehydrogenation of ethane reaction tests were performed at 1123 K, as a function of the ethane concentration in the feed. The use of a disk-shaped membrane in the reactor made it possible to prevent the direct contact of gaseous oxygen and hydrocarbons and thus to increase the ethylene yield. High ethylene yields (up to approximate to 84?%) were obtained using a catalytic coating based on 20?% Tb-doped ceria including macropores produced by the addition of graphite platelets in the screen printing ink. The high yields obtained in this kind of catalytic membrane are attributed to the combination of: the high catalytic activity; the control of the oxygen concentration in the gas phase (reaction chamber); and the appropriate fluid dynamics, enabling the fast ethylene evacuation., Financial support by the Spanish Ministry for Science and Innovation (ENE2011-24761 FPI BES-2009-015835 grants), EU through FP7 NASA-OTM Project (NMP3-SL-2009-228701), and the Helmholtz Association of German Research Centres through the Helmholtz Alliance MEM-BRAIN (Initiative and Networking Fund) is kindly acknowledged.

[EN] Ceramic oxygen transport membranes (OTMs) enable selective oxygen separation from air at high temperatures. Among several potential applications for OTMs, the use in (1) oxygen production for oxyfuel power plants and (2) the integration in high-temperature catalytic membrane reactors for alkane upgrading through selective oxidative reactions are of special interest. Nevertheless, these applications involve the direct contact of the membrane surface with carbon-rich atmospheres. Most state-of-the-art permeable membranes are based on perovskites, which are prone to carbonation under operation in CO2-rich environments and/or decomposition in reducing gas environments. The oxygen flux through supported thin film membranes of Ce-0.9Gd0.1O1.95-delta (CGO) with 2 mol.% of cobalt was measured for oxygen separation in oxyfuel processes and in syngas production and degradation was compared to perovskite membranes. The CGO membranes consist of a 27 mu m-thick gastight CGO layer supported on a porous CGO substrate. The flat surface of the membrane was coated using two different porous catalytic layers aiming to improve the oxygen activation rate on the permeate side while the porous substrate was infiltrated with an oxygen reduction catalyst. Oxygen separation was studied using air as feed and argon/CO2 or argon/CH4 mixtures as sweep gas in the temperature range 750-1000 degrees C. The supported membrane exhibited a maximum oxygen flux of ca. 5 ml min(-1) cm(-2) at 1000 degrees C when diluted methane was used as sweep gas. The CGO membrane showed high stability in CO2 (in contrast to tests on La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) membranes) and no detrimental effect on the oxygen flux is observed when CO2 is present in the sweep gas even at temperatures below 800 degrees C. Moreover, the SEM analysis showed that membrane integrity remained stable after the permeation tests using CO2. (C) 2011 Elsevier B. V. All rights reserved., Financial support by the Spanish Ministry for Science and Innovation (Project ENE2008-06302) and by the EU through FP7 NASA-OTM Project (NMP3-SL-2009-228701) is kindly acknowledged.

[EN] Process intensification by the integration of membranes and high-temperature reactors offers several advantages with regard to conventional process schemes, that is, energy saving, safe operation, reduced plant/unit size, and higher process performance, for example, higher productivity, catalytic activity, selectivity, or stability. We present the study of oxidative dehydrogenation of ethane at 850 8C on a catalytic membrane reactor based on a mixed ionic¿electronic conducting membrane. The surface of the membrane made of Ba0.5Sr0.5Co0.8Fe0.2O3 d has been activated by using different porous catalytic layers based on perovskites. The layer was deposited by screen printing, and the porosity and thickness was studied for the catalyst composition. The different catalyst formulations are based on partial substitution of A- and B-site atoms of doped strontium ferrite/cobaltites (A0.6Sr0.4Co0.5Fe0.5O3 d and Ba0.6Sr0.4BO3 d) and were synthesized by an ethylenediaminetetraacetic acid¿citrate complexation route. The use of a disk-shaped membrane in the reactor enabled the direct contact of gaseous oxygen and hydrocarbons to be avoided, and thus, the ethylene content increased. High ethylene yields (up to 81%) were obtained by using a catalytic coating based on Ba0.5Sr0.5Co0.8Fe0.2O3 d, which included macropores produced by the addition of graphite platelets into the screen-printing ink. The promising catalytic results obtained with this catalytically modified membrane reactor are attributed to the combination of 1) the high activity, as a result of the high temperature and oxygen species diffusing through the membrane; 2) the control of oxygen dosing and the low concentration of molecules in the gas phase; and 3) suitable fluid dynamics, which enables appropriate feed contact with the membrane and the rapid removal of products., Financial support by the Spanish Ministry for Science and Innovation (Project ENE2008-06302, ENE2011-24761 and FPI Grant JAE-Pre 08-0058), the EU through the FP7 NASA-OTM Project (NMP3-SL-2009-228701), and the Helmholtz Association of German Research Centres through the Helmholtz Alliance MEM-BRAIN (Initiative and Networking Fund) is kindly acknowledged. We thank S. Jimenez for material preparation, M. Fabuel for TPD experiments, and Forschungszentrum Julich for SEM analysis of BSCF catalytic layer.

[EN] Ceramic mixed ionic¿electronic conducting (MIEC) membranes enable very selective oxygen separation from air at high temperatures. Two major potential applications of oxygen-transport membranes are: i) oxygen production for oxyfuel power plants, and, ii) integration within high-temperature catalytic membrane reactors for methane or alkane upgrading by selective oxidative conversions. However, these applications involve contact with carbon-bearing atmospheres and most state-of-the-art highly permeable MIEC membranes do not tolerate operation under CO 2 -rich environments due to carbonation processes. The present contribution shows our ¿ rst attempts in the development of ceria-based protective thin layers on monolithic LSCF membranes. Gd-doped ceria (CGO) deposition is carried out by air blast spray pyrolysis on mirror-polished LSCF disc membranes. The layer thickness is maintained below 0.4 ¿ m in order to prevent the formation of cracks during thermal cycling and minimize limitations caused by the reduced oxygen permeability through the ceria layer. After optimization of the spraying process, smooth crack-free dense coatings are obtained with high crystallinity in the as-deposited state. The layers are characterized by XRD, SEM, AFM, DC-conductivity measurements, interferometry and optical microscopy. Oxygen separation is studied on coated LSCF using air as the feed and argon/CO 2 mixtures as the sweep gas in the temperature range 650¿1000 ° C. The protected membrane exhibits a higher stability than the uncoated LSCF membrane, although the nominal oxygen ¿ ux is slightly reduced at temperatures below 850 ° C due to the limited ambipolar conductivity of doped ceria in the range of oxygen partial pressures investigated. Moreover, the protective layer (250 nm thickness) remains stable after the permeation testing., Financial support by the Spanish Ministry for Science and Innovation (Project ENE2008-06302 and FPI Grant JAE-Pre 08-0058), the EU through FP7 NASA-OTM Project (NMP3-SL-2009-228701), and the Helmholtz Association of German Research Centers through the Helmholtz Alliance MEM-BRAIN (Initiative and Networking Fund) is kindly acknowledged.