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16 results on '"van der Beek, David"'

3. Gravity-induced liquid crystal phase transitions of colloidal platelets.

Author

van der Beek, David, Schilling, Tanja, and Lekkerkerker, Henk N. W.

Subjects
*BLOOD platelets, *LIQUID crystals, *PHASE transitions, *MONTE Carlo method, *PHYSICAL & theoretical chemistry, *EQUILIBRIUM
Abstract

The influence of gravity on a suspension of sterically stabilized colloidal gibbsite platelets is studied. An initially isotropic-nematic biphasic sample of such a suspension develops a columnar phase on the bottom on prolonged standing. This phenomenon is described using a simple osmotic compression model. We performed Monte Carlo simulations of cut spheres with aspect ratio L/D=1/15 and took data from the literature to supply the equations of state required for the model. We find that the model describes the observed three-phase equilibrium quite well. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
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4. Probing the Anions Mediated Associative Behavior of Tin-12 Oxo-Macrocations by Pulsed Field Gradient NMR Spectroscopy

Author

Van Lokeren, Luk, Willem, Rudolph, Van Der Beek, David, Davidson, Patrick, Morris, Gareth A., and High Resolution NMR Centre

Abstract

1H PFG NMR spectroscopy has been used to evidence the association of ditopic {(BuSn)12O14(OH)6}2+ macrocations when sulfate or oxalate divalent anions are used to balance their positive charges. The existence of supramolecular species, the size of which can reach up to about 10 times the size of the individual building blocks, is clearly related to electrostatic interactions as the supramolecular species fully break down to their individual components in solvent with high dielectric constant.

Published
2010

5. Microspectroscopic insight into the deactivation process of individual cracking catalyst particles with basic sulfur components

Author

Inorganic Chemistry and Catalysis, Sub Inorganic Chemistry and Catalysis, Ruiz-Martínez, Javier, Buurmans, Inge L C, Knowles, William V., Van Der Beek, David, Bergwerff, Jaap A., Vogt, Eelco T C, Weckhuysen, Bert M., Inorganic Chemistry and Catalysis, Sub Inorganic Chemistry and Catalysis, Ruiz-Martínez, Javier, Buurmans, Inge L C, Knowles, William V., Van Der Beek, David, Bergwerff, Jaap A., Vogt, Eelco T C, and Weckhuysen, Bert M.

Published
2012

6. Staining of Fluid-Catalytic-Cracking Catalysts: Localising Bronsted Acidity within a Single Catalyst Particle

Author

Sub Inorganic Chemistry and Catalysis, Dep Scheikunde, Inorganic Chemistry and Catalysis, Buurmans, Inge L. C., Ruiz-Martinez, Javier, van Leeuwen, Sanne L., van der Beek, David, Bergwerff, Jaap A., Knowles, William V., Vogt, Eelco T. C., Weckhuysen, Bert M., Sub Inorganic Chemistry and Catalysis, Dep Scheikunde, Inorganic Chemistry and Catalysis, Buurmans, Inge L. C., Ruiz-Martinez, Javier, van Leeuwen, Sanne L., van der Beek, David, Bergwerff, Jaap A., Knowles, William V., Vogt, Eelco T. C., and Weckhuysen, Bert M.

Published
2012

7. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining

Author

Sub Inorganic Chemistry and Catalysis, Inorganic Chemistry and Catalysis, Buurmans, Inge L. C., Ruiz Martinez, Javier, Knowles, William V., van der Beek, David, Bergwerff, Jaap A., Vogt, Eelco T. C., Weckhuysen, Bert M., Sub Inorganic Chemistry and Catalysis, Inorganic Chemistry and Catalysis, Buurmans, Inge L. C., Ruiz Martinez, Javier, Knowles, William V., van der Beek, David, Bergwerff, Jaap A., Vogt, Eelco T. C., and Weckhuysen, Bert M.

Published
2011

16. Staining of fluid-catalytic-cracking catalysts: localising Brønsted acidity within a single catalyst particle.

Author

Buurmans IL, Ruiz-Martínez J, van Leeuwen SL, van der Beek D, Bergwerff JA, Knowles WV, Vogt ET, and Weckhuysen BM

Abstract

A time-resolved in situ micro-spectroscopic approach has been used to investigate the Brønsted acidic properties of fluid-catalytic-cracking (FCC) catalysts at the single particle level by applying the acid-catalysed styrene oligomerisation probe reaction. The reactivity of individual FCC components (zeolite, clay, alumina and silica) was monitored by UV/Vis micro-spectroscopy and showed that only clay and zeolites (Y and ZSM-5) contain Brønsted acid sites that are strong enough to catalyse the conversion of 4-fluorostyrene into carbocationic species. By applying the same approach to complete FCC catalyst particles, it has been found that the fingerprint of the zeolitic UV/Vis spectra is clearly recognisable. This almost exclusive zeolitic activity is confirmed by the fact that hardly any reactivity is observed for FCC particles that contain no zeolite. Confocal fluorescence microscopy images of FCC catalyst particles reveal inhomogeneously distributed micron-sized zeolite domains with a highly fluorescent signal upon reaction. By examining laboratory deactivated FCC catalyst particles in a statistical approach, a clear trend of decreasing fluorescence intensity, and thus Brønsted acidity, of the zeolite domains is observed with increasing severity of the deactivation method. By comparing the average fluorescence intensities obtained with two styrenes that differ in reactivity, it has been found that the Brønsted acid site strength within FCC catalyst particles containing ZSM-5 is more uniform than within those containing zeolite Y, as confirmed with temperature-programmed desorption of ammonia., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2012
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