C. Kirschhock

How water and ion mobility affect the NMR fingerprints of the hydrated JBW zeolite: a combined computational-experimental investigation

S. Vanlommel, A.E.J. Hoffman, S. Smet, S. Radhakrishnan, K. Asselman, C. V. Chandran, E. Breynaert, C. Kirschhock, J.A. Martens, V. Van Speybroeck
Chemistry - A European Journal
28, 68, e202202621
2022
A1

Abstract 

An important aspect within zeolite synthesis is to make fully tunable framework materials with controlled aluminium distribution. A major challenge in characterising these zeolites at operating conditions is the presence of water. In this work, we investigate the effect of hydration on the 27 Al NMR parameters of the ultracrystalline K,Na-compensated aluminosilicate JBW zeolite using experimental and computational techniques. The JBW framework, with Si/Al ratio of 1, is an ideal benchmark system as a stepping stone towards more complicated zeolites. The presence and mobility of water and extraframework species directly affect NMR fingerprints. Excellent agreement between theoretical and experimental spectra is obtained provided dynamic methods are employed with hydrated structural models. This work shows how NMR is instrumental in characterising aluminium distributions in zeolites at operating conditions.

Gold Open Access

DOI 

https://doi.org/10.1002/chem.202202621

Super-ions of sodium cations with hydrated hydroxide anions: inorganic structure-directing agents in zeolite synthesis

K. Asselman, N. Pellens, S. Radhakrishnan, C. V. Chandran, J.A. Martens, F. Taulelle, T. Verstraelen, M. Hellstrom, E. Breynaert, C. Kirschhock
Materials Horizons
Volume 8, Issue 9, Pages 2576-2583
2021
A1

Abstract 

In inorganic zeolite formation, a direct correspondence between liquid state species in the synthesis and the supramolecular decoration of the pores in the as-made final zeolite has never been reported. In this paper, a direct link between the sodium speciation in the synthesis mixture and the pore structure and content of the final zeolite is demonstrated in the example of hydroxysodalite. Super-ions with 4 sodium cations bound by mono- and bihydrated hydroxide are identified as structure-directing agents for the formation of this zeolite. This documentation of inorganic solution species acting as a templating agent in zeolite formation opens new horizons for zeolite synthesis by design.

DOI 

http://dx.doi.org/10.1039/d1mh00733e

Chlorination of a Zeolitic-Imidazolate Framework Tunes Packing and van der Waals Interaction of Carbon Dioxide for Optimized Adsorptive Separation

L.H. Wee, S. Vandenbrande, S.M.J. Rogge, J. Wieme, K. Asselman, E. Jardim, J. Silvestre-Albero, J. Navarro, V. Van Speybroeck, J.A. Martens, C. Kirschhock
JACS (Journal of the American Chemical Society)
143 (13), 4962-4968
2021
A1

Abstract 

Molecular separation of carbon dioxide (CO2) and methane (CH4) is of growing interest for biogas upgrading, carbon capture and utilization, methane synthesis and for purification of natural gas. Here, we report a new zeolitic-imidazolate framework (ZIF), coined COK-17, with exceptionally high affinity for the adsorption of CO2 by London dispersion forces, mediated by chlorine substituents of the imidazolate linkers. COK-17 is a new type of flexible zeolitic-imidazolate framework Zn(4,5-dichloroimidazolate)2 with the SOD framework topology. Below 200 K it displays a metastable closed-pore phase next to its stable open-pore phase. At temperatures above 200 K, COK-17 always adopts its open-pore structure, providing unique adsorption sites for selective CO2 adsorption and packing through van der Waals interactions with the chlorine groups, lining the walls of the micropores. Localization of the adsorbed CO2 molecules by Rietveld refinement of X-ray diffraction data and periodic density functional theory calculations revealed the presence and nature of different adsorption sites. In agreement with experimental data, grand canonical Monte Carlo simulations of adsorption isotherms of CO2 and CH4 in COK-17 confirmed the role of the chlorine functions of the linkers and demonstrated the superiority of COK-17 compared to other adsorbents such as ZIF-8 and ZIF-71.

Gold Open Access

DOI 

http://dx.doi.org/10.1021/jacs.0c08942

Alternating Copolymer of Double Four Ring Silicate and Dimethyl Silicone Monomer - PSS-1

S. Smet, S. Vandenbrande, P. Verlooy, S. Kerkhofs, E. Breynaert, C. Kirschhock, C. Martineau, F. Taulelle, V. Van Speybroeck, J.A. Martens
Chemistry - A European Journal
23 (47), 11286-11293
2017
A1

Abstract 

A new copolymer consisting of double four ring (D4R) silicate units linked by dimethylsilicone monomer referred to as polyoligosiloxysilicone number one (PSS-1) was synthesized. The D4R building unit is provided by hexamethyleneimine cyclosilicate hydrate crystals, which were dehydrated and reacted with dichlorodimethylsilane. The local structure of D4R silicate units and dimethyl silicone monomers was revealed by multidimensional solid-state NMR, FTIR and modeling. On average, D4R silicate units have 6.8 silicone linkages. Evidence for preferential unidirectional growth and chain ordering within the PSS-1 copolymer was provided by STEM and TEM. The structure of PSS-1 copolymer consists of twisted columns of D4R silicate units with or without cross-linking. Both models are consistent with the spectroscopic, microscopic and physical properties. PSS-1 chains are predicted to be mechanically strong compared to silicones such as PDMS, yet more flexible than rigid silica materials such as zeolites.

DOI 

http://dx.doi.org/10.1002/chem.201701237

A Flexible Photoactive Titanium Metal-Organic Framework Based on a [Ti-3(IV)(mu(3)-O)(O)(2)(COO)(6)] Cluster

B. Bueken, F. Vermoortele, D.E.P. Vanpoucke, H. Reinsch, C. Tsou, P. Valvekens, T. De Baerdemaeker, R. Ameloot, C. Kirschhock, V. Van Speybroeck, J. Mayer, D. De Vos
Angewandte Chemie int. Ed.
127, 14118 –14123
2015
A1

Abstract 

The synthesis of titanium-carboxylate metal-organic frameworks (MOFs) is hampered by the high reactivity of the commonly employed alkoxide precursors. Herein, we present an innovative approach to titanium-based MOFs by the use of titanocene dichloride to synthesize COK-69, the first breathing Ti MOF, which is built up from trans-1,4-cyclo-hexanedicarboxylate linkers and an unprecedented [Ti-3(IV)(mu(3)-O)(O)(2)(COO)(6)] cluster. The photoactive properties of COK-69 were investigated in depth by proton-coupled electron-transfer experiments, which revealed that up to one Ti-IV center per cluster can be photoreduced to Ti-III while preserving the structural integrity of the framework. The electronic structure of COK-69 was determined by molecular modeling, and a band gap of 3.77 eV was found.

DOI 

http://dx.doi.org/10.1002/anie.201505512

Flexibility versus rigidity: what determines the stability of zeolite frameworks? A case study

E. Verheyen, L. Joos, C. Martineau, C.J. Dawson, C. Weidenthaler, W. Schmidt, R. Yuan, E. Breynaerts, V. Van Speybroeck, M. Waroquier, F. Taulelle, M.M.J. Treacy, J.A. Martens, C. Kirschhock
Materials Horizons
Vol. 1 , 582 - 587
2014
A1

Abstract 

All silica COK-14/-COK-14 with OKO topology is the first case of a zeolite which reversibly transforms from a systematically interrupted to a fully connected state and back. Analysis of the opening/closing behavior allowed the study of entropy and framework flexibility as determinants for the stability of zeolite topologies, which, until now, has been experimentally inaccessible. Interconversion of the all-silica COK-14 zeolite with fully connected OKO topology and its -COK-14 variant with systematic framework interruption was investigated using high-temperature XRD, thermogravimetric analysis, Si-29 MAS NMR, nitrogen adsorption and a range of modelling techniques. Specific framework bonds in the OKO framework can be reversibly hydrolyzed and condensed. Structural silanols of the parent -COK-14, prepared by degermanation of the IM-12 zeolite, were condensed by heating at 923 K, and hydrolyzed again to the initial state by contacting the zeolite with warm water. Molecular modelling revealed an inversion of the relative stabilities for both variants depending on temperature and hydration. Condensation of the structural silanols in -COK-14 to COK-14 is entropy driven, mainly resulting from the release of water molecules. Framework reopening in the presence of water is spontaneous due to the high rigidity of the fully connected OKO framework. Isomorphous substitution was demonstrated as a viable option for stabilization of the fully connected OKO framework as this renders the closed framework flexible.

DOI 

http://dr.doi.org/10.1039/c4mh00127c

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

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
A1

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

Entropy-Driven Chemisorption of NOx on Phosphotungstic Acid

S. Heylen, L. Joos, V. Van Speybroeck, C. Kirschhock, J.A. Martens
Angewandte Chemie int. Ed.
51 (44), 11010-11013
2012
A1

Abstract 

Nitrogen oxides, NOx, are formed in combustion engines. They contribute to acid rain and the formation of ozone and are hazardous for men and environment. In this article, a process was investigated that can 'capture' the NOx from the exhaust gases using heteropoly acids and can later release them for processing. One of the main conclusions is that the mobility of the captured and released molecules is the key to control the reaction. This can now be used to optimize and commercialize the technology.

Stikstofoxiden, aangeduid als NOx, worden gevormd in verbrandingsmotoren. Ze dragen bij tot zure regen, de vorming van ozon en zijn dus schadelijk voor mens en milieu. In dit artikel werd een proces onderzocht dat de NOx kan ‘vangen’ uit de uitlaatgassen aan de hand van heteropolyzuren en later terug kan vrijgeven voor verdere verwerking. Een van de belangrijkste vaststellingen is dat de mobiliteit van de opgeslagen en vrijgegeven moleculen de sleutel is voor het controleren van het proces. De conclusies van het onderzoek kunnen nu verder gebruikt worden voor de optimalisering en commercialisering van het proces.

http://www.ugent.be/nl/actueel/nieuws/persberichten/stikstofoxide-nox-ve...

NOx adsorption on Phosphotungstic acid is entropy-driven due to the watermolecules that are released.

DOI 

http://dx.doi.org/10.1002/ange.201205636

MFI Fingerprint: How Pentasil-Induced IR Bands Shift during Zeolite Nanogrowth

D. Lesthaeghe, P. Vansteenkiste, T. Verstraelen, A. Ghysels, C. Kirschhock, J.A. Martens, V. Van Speybroeck, M. Waroquier
Journal of Physical Chemistry C
112 (25), 9186-9191
2008
A1

Abstract 

Silicalite-1 zeolite exhibits a characteristic pentasil framework vibration around 540−550 cm−1. In the initial stages of zeolite synthesis, however, this band is observed at much higher wavenumbers: literature shows this vibration to depend on particle size and to shift over 100 cm−1 with increasing condensation. In this work, the pentasil vibration frequency was derived from theoretical molecular dynamics simulations to obtain the correct IR band assignments for important nanoparticles. The IR spectroscopic fingerprint of oligomeric five-ring containing precursors proposed in the literature was computed and compared with experimental data. Our theoretical results show that, while isolated five-membered rings show characteristic vibrational bands around 650 cm−1, the combination of five-membered rings in the full MFI-type structure readily generates the bathochromic shift to the typical pentasil vibration around 550 cm−1. As opposed to what was previously believed, the IR band does not shift gradually as nanoparticle size increases, but it is highly dependent on the specific way structural units are added. The most important feature is the appearance of an additional band when double five-membered rings are included, which allows for a clear distinction between the key stages of early zeolite nucleation. Furthermore, the combination of the simulated spectra with the experimental observation of this spectral feature in nanoparticles extracted from silicalite-1 clear solutions supports their structured nature. The theoretical insights on the dependency of pentasil vibrations with the degree of condensation offer valuable support toward future investigations on the genesis of a zeolite crystal.

DOI 

http://dx.doi.org/10.1021/jp711550s

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