Center for Molecular Modeling - K. Houthoofd

Synthesis modulation as a tool to increase the catalytic activity of MOFs: the unique case of UiO-66(Zr)

michel — Sat, 18 May 2013 19:26:34 +0000

F. Vermoortele, B. Bueken, G. Le Bars, B. Van de Voorde, M. Vandichel, K. Houthoofd, A. Vimont, M. Daturi, M. Waroquier, V. Van Speybroeck, C. Kirschhock, D. De Vos

JACS (Journal of the American Chemical Society)

135 (31), 11465–11468

2013

Abstract

The catalytic activity of the zirconium terephthalate UiO-66(Zr) can be drastically increased by using a modulation approach. The combined use of trifluoroacetic acid and HCl during the synthesis results in a highly crystalline material, with partial substitution of terephthalates by trifluoroacetate. Thermal activation of the material leads not only to dehydroxylation of the hexanuclear Zr cluster but also to post-synthetic removal of the trifluoroacetate groups, resulting in a more open framework with a large number of open sites. Consequently, the material is a highly active catalyst for several Lewis acid catalyzed reactions.

DOI

http://dx.doi.org/10.1021/ja405078u

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13_jacs_135_11465_Vermoortele.pdf

29Si NMR and UV-Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol-Gel Chemistry

wim — Tue, 23 Aug 2011 06:59:51 +0000

A. Depla, D. Lesthaeghe, T.S. van Erp, A. Aerts, K. Houthoofd, F. Fan, C. Li, V. Van Speybroeck, M. Waroquier, C. Kirschhock, J.A. Martens

Journal of Physical Chemistry C

115 (9), 3562–3571

2011

Abstract

The initial molecular steps of the acid-catalyzed silica sol−gel process de-parting from tetraethylorthosilicate (TEOS) were investigated by in situ 29Si NMR and UV−Raman spectroscopy. The use of a substoichiometric H2O:TEOS molar ratio (r-value 0.2−1.2) slowed the silicate oligomerization reaction and allowed unraveling the initial steps of silica condensation. Molecular modeling confirmed Raman signal and 29Si NMR shift assignment. A comprehensive listing of all Raman and 29Si NMR assignments is provided, including unique Raman assignments of cyclosilicates and the linear tetramer. The combination of experiment and modeling allowed an analysis of the reaction kinetics. The derived kinetic model and the experimental observation both revealed that the H2O:TEOS molar ratio had a strong influence on the reaction kinetics but not on the reaction pathways. The multianalytical approach led to development of an oligomerization scheme. As dominant oligomerizations, chain growth, cyclodimerization, and branching were identified. Under the investigated conditions, chains did not grow longer than pentamer, and ring sizes were limited to 6-rings. Chains of 4 Si atoms and 4-rings were abundant species. Branched rings and chains were formed by attachment of dimers and trimers. Gelation proceeded from branched 4-rings and branched chains with limited hydroxyl functionalities.

DOI

http://dx.doi.org/10.1021/jp109901v

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11 j. phys. chem. C 115, 3562 depla.pdf

UV-Raman and 29Si NMR Spectroscopy Investigation of the Nature of Silicate Oligomers Formed by Acid Catalyzed Hydrolysis and Polycondensation of Tetramethylorthosilicate

wim — Mon, 22 Aug 2011 13:53:23 +0000

A. Depla, E. Verheyen, A. Verfeyken, M. Van Houteghem, K. Houthoofd, V. Van Speybroeck, M. Waroquier, C. Kirschhock, J.A. Martens

Journal of Physical Chemistry C

115(22), 11077-11088

2011

Abstract

Tetramethylorthosilicate (TMOS) was hydrolyzed and polymerized under strongly acidic conditions in the presence of substoichiometric quantities of water. The polymerization reaction was monitored during 64 h using 29Si NMR and UV-Raman spectroscopy. The nature of the oligomers and the condensation reaction pathways were unraveled using this combination of experimental techniques together with molecular modeling. 29Si NMR and UV-Raman signals which previously were not documented in literature could be assigned. TMOS rapidly was converted into short straight methoxylated silicate chains. Subsequently the growth of oligomers proceeded by condensations between a hydrolyzed middle group of a chain with an end-group of another chain. Larger oligomers were attached to each other via condensations between middle groups generating multiply branched structures. Rings were formed late in the reaction scheme through internal condensations of sizable silicate molecules. Oligomers that were characteristic of the different stages of the polymerization process were proposed. Oligomerization pathways starting from tetramethylorthosilicate and tetraethylorthosilicate (TEOS) are significantly different. While with TMOS rings are formed only late in the oligomerization scheme, with TEOS rings are formed at early stages through cyclo-dimerization. This insight into the different nature of the oligomers obtained from TMOS and TEOS will assist the design of new silica sol–gel materials.

DOI

http://dx.doi.org/10.1021/jp109901v

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11 j. phys. chem. C 115, 11077 depla.pdf

Design of zeolite by inverse sigma transformation

wim — Mon, 12 Aug 2013 14:09:45 +0000

E. Verheyen, L. Joos, K. Van Havenbergh, E. Breynaerts, N. Kasian, E. Gobechiya, K. Houthoofd, C. Martineau, M. Hinterstein, F. Taulelle, V. Van Speybroeck, M. Waroquier, S. Bals, G. Van Tendeloo, C. Kirschhock, J.A. Martens

p. 70

ISBN/ISSN:

Talk

Conference / event / venue

IZC17

Moscow, Russia

Sunday, 7 July, 2013 to Friday, 12 July, 2013

Conference reference

IZC-17

Computational Approach of the Inverse Sigma Transformation of Zeolites

wim — Mon, 12 Aug 2013 14:07:29 +0000

p. 219

ISBN/ISSN:

Poster

Conference / event / venue

IZC17

Moscow, Russia

Sunday, 7 July, 2013 to Friday, 12 July, 2013

Conference reference

IZC-17

Design of zeolite by inverse sigma transformation

michel — Mon, 03 Sep 2012 10:08:14 +0000

E. Verheyen, L. Joos, K. Van Havenbergh, N. Kasian, E. Gobechiya, K. Houthoofd, M. Hinterstein, E. Breynaerts, V. Van Speybroeck, M. Waroquier, S. Bals, G. Van Tendeloo, C. Kirschhock, J.A. Martens

Nature Materials

11 (12), 1059-1064

2012

Abstract

Zeolites are silicon materials, that have channels and pores on the nanoscale. This paper reports the synthesis of a new zeolite, in which the pores were widened using a revolutionary synthesis method. The final material has a series of unique and special properties, useful for industrial processes. Molecular modeling was used to determine the structure of the material.

Zeolieten zijn materialen opgebouwd uit silicium, die op nanoschaal kanalen en poriën bevatten. Deze paper rapporteert de synthese van een nieuw type zeoliet, waarbij de kanalen op een revolutionaire manier werden vergroot. Het eindmateriaal heeft daarom een hele reeks aan unieke en bijzonder interessante eigenschappen voor een aantal industriële processen. Moleculaire modelering werd gebruikt om de structuur van het materiaal te bepalen.

A graphical representation of COK14:

DOI

http://dx.doi.org/10.1038/nmat3455

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12_nat_mat_11(12)1059_Verheyen.pdf

nmat3455-s1.pdf