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Now showing items 33 - 48 of 15949

  • Metal-Catalyzed Reactions in Water. Edited by P. H. Dixneuf, V. Cadierno

    Gawande, Manoj B.  

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  • V and V–P containing Zr-SBA-15 catalysts for dehydration of glycerol to acrolein

    Cecilia, J.A.   García-Sancho, C.   Mérida-Robles, J.M.   Santamaría-González, J.   Moreno-Tost, R.   Maireles-Torres, P.  

    Highlights • Supported V and V–P catalysts are active in dehydration of glycerol. • The partial reduction of V-based catalysts generates allyl alcohol as by-product. • High amounts of phosphorous reduce the surface area and total acidity. • Acrolein yield improves with the phosphoric acid treatment. Abstract A series of solid acid catalysts based on vanadium and vanadium–phosphorous supported on a zirconium doped mesoporous SBA-15 silica has been synthesized, characterized by using XRD, N2 sorption, NH3–TPD, FT-IR spectroscopy, X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy, and evaluated in the gas-phase dehydration of glycerol. Under the operating conditions used, all materials are active in the glycerol dehydration, being acrolein the main product in all cases. Although higher values of conversion are obtained in the presence of vanadium oxide based catalysts, acrolein yield improves after the treatment with phosphoric acid, attaining a value of 42% after 2 h of reaction at 325 °C with the 12VP0.2 catalyst, which contains 12 wt.% of V2O5 and a V/P molar ratio of 0.2. However, the incorporation of phosphorous to the catalytic system partially destroys the mesoporous structure. Allyl alcohol has been also detected using vanadium based catalysts, due to a partial reduction of V2O5 species during the reaction, increasing its yield with the vanadium oxide loading. All catalysts suffer from deactivation by coke deposition on the catalyst surface, being the carbon content considerably higher for catalysts without phosphorous. Graphical abstract
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  • V and V–P containing Zr-SBA-15 catalysts for dehydration of glycerol to acrolein

    J.A. Cecilia   C. García-Sancho   J.M. Mérida-Robles   J. Santamaría-González   R. Moreno-Tost   P. Maireles-Torres  

    Graphical abstract Highlights • Supported V and V–P catalysts are active in dehydration of glycerol. • The partial reduction of V-based catalysts generates allyl alcohol as by-product. • High amounts of phosphorous reduce the surface area and total acidity. • Acrolein yield improves with the phosphoric acid treatment. Abstract A series of solid acid catalysts based on vanadium and vanadium–phosphorous supported on a zirconium doped mesoporous SBA-15 silica has been synthesized, characterized by using XRD, N 2 sorption, NH 3 –TPD, FT-IR spectroscopy, X-ray photoelectron spectroscopy and diffuse reflectance UV–vis spectroscopy, and evaluated in the gas-phase dehydration of glycerol. Under the operating conditions used, all materials are active in the glycerol dehydration, being acrolein the main product in all cases. Although higher values of conversion are obtained in the presence of vanadium oxide based catalysts, acrolein yield improves after the treatment with phosphoric acid, attaining a value of 42% after 2 h of reaction at 325 °C with the 12VP0.2 catalyst, which contains 12 wt.% of V 2 O 5 and a V/P molar ratio of 0.2. However, the incorporation of phosphorous to the catalytic system partially destroys the mesoporous structure. Allyl alcohol has been also detected using vanadium based catalysts, due to a partial reduction of V 2 O 5 species during the reaction, increasing its yield with the vanadium oxide loading. All catalysts suffer from deactivation by coke deposition on the catalyst surface, being the carbon content considerably higher for catalysts without phosphorous.
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  • A variable P v broad absorption line and quasar outflow energetics

    Capellupo, D. M.   Hamann, F.   Barlow, T. A.  

    Broad absorption lines (BALs) in quasar spectra identify high-velocity outflows that might exist in all quasars and could play a major role in feedback to galaxy evolution. The viability of BAL outflows as a feedback mechanism depends on their kinetic energies, as derived from the outflow velocities, column densities, and distances from the central quasar. We estimate these quantities for the quasar, Q1413+1143 (redshift z(e) = 2.56), aided by the first detection of P V lambda lambda 1118, 1128 BAL variability in a quasar. In particular, P V absorption at velocities where the C IV trough does not reach zero intensity implies that the C IV BAL is saturated and the absorber only partially covers the background continuum source (with characteristic size <0.01 pc). With the assumption of solar abundances, we estimate that the total column density in the BAL outflow is log N-H similar to 22.3 cm(-2). Variability in the P V and saturated C IV BALs strongly disfavours changes in the ionization as the cause of the BAL variability, but supports models with high column density BAL clouds moving across our lines of sight. The observed variability time of 1.6 yr in the quasar rest frame indicates crossing speeds >750 km s(-1) and a radial distance from the central black hole of less than or similar to 3.5 pc, if the crossing speeds are Keplerian. The total outflow mass is similar to 4100 M-circle dot, the kinetic energy similar to 4 x 10(54) erg, and the ratio of the outflow kinetic energy luminosity to the quasar bolometric luminosity is similar to 0.02 (at the minimum column density and maximum distance), which might be sufficient for important feedback to the quasar's host galaxy.
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  • Avalanche Breakdown Stability of High Voltage (1430 V) 4H-SiC p+–n0–n+ Diodes

    Ivanov, P. A.   Samsonova, T. P.   Potapov, A. S.  

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  • As(V) and P Competitive Sorption on Soils, By-Products and Waste Materials

    Rivas-Pérez Ivana   Paradelo-Nú?ez Remigio   Nóvoa-Mu?oz Juan   Arias-Estévez Manuel   Fernández-Sanjurjo María   álvarez-Rodríguez Esperanza   Nú?ez-Delgado Avelino  

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  • 53. Jahrestagung der Gesellschaft für P?diatrische Radiologie (GPR) e. V.

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  • Rhenium(V) complexes with tridentate P,N,S ligands

    Jennifer Schroer   Ulrich Abram  

    Novel, potentially tridentate ligands with P,N,S donor sets (HLdiethyl and HLmorph) were prepared from reactions of N-(dialkyl)thiocarbamoylbenzimide chlorides with 2-(diphenylphosphinomethyl)aniline. They readily react with (NBu4)[ReOCl4] under formation of air-stable [ReOCl2(LR)] complexes, in which the tridentate ligands coordinate meridionally. A similar coordination mode is observed in the nitridorhenium(V) complex [ReN(OReO3)(PPh3)(Ldiethyl)], which can be obtained from a reaction of [ReNCl2(PPh3)2] and HLdiethyl. The complexes were characterized spectroscopically and by X-ray structure analyses.
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  • Rhenium(V) complexes with tridentate P,N,S ligands

    Jennifer Schroer   Ulrich Abram  

    Novel, potentially tridentate ligands with P,N,S donor sets (HLdiethyl and HLmorph) were prepared from reactions of N-(dialkyl)thiocarbamoylbenzimide chlorides with 2-(diphenylphosphinomethyl)aniline. They readily react with (NBu4)[ReOCl4] under formation of air-stable [ReOCl2(LR)] complexes, in which the tridentate ligands coordinate meridionally. A similar coordination mode is observed in the nitridorhenium(V) complex [ReN(OReO3)(PPh3)(Ldiethyl)], which can be obtained from a reaction of [ReNCl2(PPh3)2] and HLdiethyl. The complexes were characterized spectroscopically and by X-ray structure analyses.
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  • J–V Characteristic of p–n Structure Formed on n-GaAs Surface by Ar+ Ion Beam

    Mikoushkin, V. M.; Kalinovskii, V. S.; Kontrosh, E. V.; Makarevskaya, E. A.  

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  • DFT studies on the activation of C–H bonds on V/P mixed oxides

    Fu, Gang   Yuan, Ruming   Wang, Pei   Wan, Huilin  

    Abstract We carried out DFT calculations on the activation of C–H bonds on V/P mixed oxides. A set of oxo clusters, V4−xPxO10 (x = 0–4), used as model catalysts showed that the PO–H bond was stronger than the VO–H bond and the proton was preferentially bonded to the P=O bond. However, for alkane activation, the P=O was not the active site as expected because the activation requires a large reorganization energy. In addition, the results showed that the P=O bond played a role in the activation of intermediates with a more acidic C–H bond, such as 2-butene and 2,5-dihydrofuran. Graphical Abstract DFT calculations on the activation of C–H bonds on V/P mixed oxides with a set of oxo clusters, V4−xPxO10 (x = 0–4), showed that the PO–H was stronger than the VO–H as the proton was preferentially bonded to the P=O bond. For alkane activation, the P=O bond was not as active as expected because the activation requires a large reorganization energy. The P=O bond played a role in the activation of intermediates with a more acidic C–H bond, such as 2-butene and 2,5-dihydrofuran.
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  • Synthesis and thermal expansion of (V, P, Nb)-replaced pollucite

    Ikuo Yanase   Yumi Saito   Hidehiko Kobayashi  

    Pollucite compounds in which tetrahedral cations are partially replaced with V, P or Nb were synthesized by a solid-state reaction. An amorphous phase was recognized by X-ray diffractometry for all the above pollucite compounds when mixed raw powders were preliminarily heated at 600degC to decompose CsNO 3 as a Cs source. Then V-replaced, Nb-replaced, and P-replaced pollucite compounds began to crystallize by heating at 550, 800, and 1000degC, respectively. Finally, single phases of these compounds were synthesized at 700, 1000, and 1200degC, respectively. The V-replaced pollucite compound Cs 0.7V 0.1Al 0.8Si 2.1O 6 exhibited the lowest thermal expansion in the range of 25-500degC at which its thermal expansion coefficient was 0.7 times 10 -6 K -1, while the P-replaced pollucite compound Cs 0.7P 0.1Al 0.8Si 2.1O 6 and the Nb-replaced pollucite compound Cs 0.7Nb 0.1Al 0.8Si 2.1O 6 showed thermal expansion coefficients of 1.9 times 10 -6 K -1 and 1.4 times 10 -6 K -1 in the range of 25-500degC, respectively. It was considered that such an excellent low thermal expansion coefficient of the synthesized V-replaced pollucite was due to the ionic radius of V 5+ being between those of Al 3+ and Si 4+ in the aluminosilicate framework of pollucite compounds. [All rights reserved Elsevier].
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  • Synthesis and thermal expansion of (V, P, Nb)-replaced pollucite

    Ikuo Yanase    Yumi Saito   Hidehiko Kobayashi  

    Pollucite compounds in which tetrahedral cations are partially replaced with V, P or Nb were synthesized by a solid-state reaction. An amorphous phase was recognized by X-ray diffractometry for all the above pollucite compounds when mixed raw powders were preliminarily heated at 600 °C to decompose CsNO3 as a Cs source. Then V-replaced, Nb-replaced, and P-replaced pollucite compounds began to crystallize by heating at 550, 800, and 1000 °C, respectively. Finally, single phases of these compounds were synthesized at 700, 1000, and 1200 °C, respectively. The V-replaced pollucite compound Cs0.7V0.1Al0.8Si2.1O6 exhibited the lowest thermal expansion in the range of 25?00 °C at which its thermal expansion coefficient was 0.7 × 10? K?, while the P-replaced pollucite compound Cs0.7P0.1Al0.8Si2.1O6 and the Nb-replaced pollucite compound Cs0.7Nb0.1Al0.8Si2.1O6 showed thermal expansion coefficients of 1.9 × 10? K? and 1.4 × 10? K? in the range of 25?00 °C, respectively. It was considered that such an excellent low thermal expansion coefficient of the synthesized V-replaced pollucite was due to the ionic radius of V5+ being between those of Al3+ and Si4+ in the aluminosilicate framework of pollucite compounds.
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  • Synthesis and thermal expansion of (V, P, Nb)-replaced pollucite

    Yanase, Ikuo   Saito, Yumi   Kobayashi, Hidehiko  

    Pollucite compounds in which tetrahedral cations are partially replaced with V, P or Nb were synthesized by a solid-state reaction. An amorphous phase was recognized by X-ray diffractometry for all the above pollucite compounds when mixed raw powders were preliminarily heated at 600 degrees C to decompose CsNO(3) as a Cs source. Then V-replaced, Nb-replaced, and P-replaced pollucite compounds began to crystallize by heating at 550, 800, and 1000 degrees C, respectively. Finally, single phases of these compounds were synthesized at 700, 1000, and 1200 degrees C, respectively. The V-replaced pollucite compound Cs(0.7)V(0.1)Al(0.8)Si(2.1)O(6) exhibited the lowest thermal expansion in the range of 25-500 degrees C at which its thermal expansion coefficient was 0.7 x 10(-6) K(-1), while the P-replaced pollucite compound Cs(0.7)P(0.1)Al(0.8)Si(2.1)O(6) and the Nb-replaced pollucite compound CS(0.7)Nb(0.1)Al(0.8)Si(2.1)O(6) showed thermal expansion coefficients of 1.9 x 10(-6) K(-1) and 1.4 x 10(-6) K(-1) in the range of 25-500 degrees C, respectively. It was considered that such an excellent low thermal expansion coefficient of the synthesized V-replaced pollucite was due to the ionic radius of V(5+) being between those of Al(3+) and Si(4+) in the aluminosilicate framework of pollucite compounds. (C) 2011 Elsevier Ltd and Techna Group Sri. All rights reserved.
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  • Production of a pion system in exclusiveBc→V(P)+nπdecays

    A. K. Likhoded   A. V. Luchinsky  

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  • Caesers Massachusetts Management Company, LLC, et al v. Stephen P. Crosby

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