L. Joos

Carbon Capture Turned Upside Down: High-Temperature Adsorption & Low-Temperature Desorption (HALD)

L. Joos, K. Lejaeghere, J. Huck, V. Van Speybroeck, B. Smit
Energy & Environmental Science
8, 2480-2491
2015
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Abstract 

Carbon Capture & Sequestration (CCS) could reduce CO2 emissions from large fossil-fuel power plants in the short term, but the high energy penalty of the process hinders its industrial deployment. Moreover, the utility of nanoporous materials, known to be selective for the CO2/N2 separation, is drastically reduced due to the competitive adsorption with H2O. Taking advantage of the power plant's waste heat to perform CCS while at the same time surmounting the negative effect of H2O is therefore an attractive idea. We propose an upside-down approach for CCS in nanoporous materials, High-temperature Adsorption & Low-temperature Desorption (HALD), that exploits the temperature-dependent competitive adsorption of CO2 and H2O. First, we provide a theoretical background for this entropy-driven behavior and demonstrate under what conditions competitive adsorption can be in favor of CO2 at high temperature and in favor of H2O at low temperature. Then, molecular simulations in all-silica MFI provide a proof of concept. The International Zeolite Association database is subsequently screened for potential candidates and finally, the most promising materials are selected using a post-Pareto search algorithm. The proposed post-Pareto approach is able to select the material that shows an optimal combination of multiple criteria, such as CO2/H2O selectivity, CO2/N2 selectivity, CO2 uptake and H2O uptake. As a conclusion, this work provides new perspectives to reduce the energy requirement for CCS and to overcome the competitive adsorption of H2O.

Advances in theory and their application within the field of zeolite chemistry

V. Van Speybroeck, K. Hemelsoet, L. Joos, M. Waroquier, R.G. Bell, C.R.A. Catlow
Chemical Society Reviews
First published online 15 May 2015
2015
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Abstract 

Zeolites are versatile and fascinating materials which are vital for a wide range of industries, due to their unique structural and chemical properties, which are the basis of applications in gas separation, ion exchange and catalysis. Given their economic impact, there is a powerful incentive for smart design of new materials with enhanced functionalities to obtain the best material for a given application. Over the last decades, theoretical modeling has matured to a level that model guided design has become within reach. Major hurdles have been overcome to reach this point and almost all contemporary methods in computational materials chemistry are actively used in the field of modeling zeolite chemistry and applications. Integration of complementary modeling approaches is necessary to obtain reliable predictions and rationalizations from theory. A close synergy between experimentalists and theoreticians has led to a deep understanding of the complexity of the system at hand, but also allowed the identification of shortcomings in current theoretical approaches. Inspired by the importance of zeolite characterization which can now be performed at the single atom and single molecule level from experiment, computational spectroscopy has grown in importance in the last decade. In this review most of the currently available modeling tools are introduced and illustrated on the most challenging problems in zeolite science. Directions for future model developments will be given.

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
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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.

Molecular Simulation Study of the Competitive Adsorption of H2O and CO2 in Zeolite 13X

L. Joos, J.A. Swisher, B. Smit, A. Bruder
Langmuir
29 (48), 14743-14747
2013
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Abstract 

Surfactants exhibit maxima in their critical micelle concentrations upon application of hydrostatic pressure, which is attributable to changes in their volumes of micellization from positive to negative values with increasing pressure. We present a direct molecular simulation analysis of the volumes of micellization of an anionic, cationic, and nonionic surfactant in aqueous solution at pressures up to 2500 bar. Excellent agreement with experiment is observed. A Kirkwood-Buff theory analysis based on proximal solvent distributions permits the breakdown of the volumes of micellization into constituent surfactant headgroup and tailgroup contributions. Although the micellization volume crossover is analogous to the transfer of an alkane from water to its pure liquid, significant differences are observed, including lower compressibilities of micelle volumes compared to that of the alkane liquid, negative partial compressibilites for anionic sulfated surfactant monomers, and large nonionic ethoxy headgroup contributions to the micellization volume.

Reactivity of CO on carbon covered cobalt surfaces in Fischer-Tropsch Synthesis

L. Joos, I. Filot, S. Cottenier, E. Hensen, M. Waroquier, V. Van Speybroeck, R.A. van Santen
Journal of Physical Chemistry C
118 (10), 5317–5327
2014
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Abstract 

Fischer–Tropsch synthesis is an attractive process to convert alternative carbon sources, such as biomass, natural gas, or coal, to fuels and chemicals. Deactivation of the catalyst is obviously undesirable, and for a commercial plant it is of high importance to keep the catalyst active as long as possible during operating conditions. In this study, the reactivity of CO on carbon-covered cobalt surfaces has been investigated by means of density functional theory (DFT). An attempt is made to provide insight into the role of carbon deposition on the deactivation of two cobalt surfaces: the closed-packed Co(0001) surface and the corrugated Co(112̅1) surface. We also analyzed the adsorption and diffusion of carbon atoms on both surfaces and compared the mobility. Finally, the results for Co(0001) and Co(112̅1) are compared, and the influence of the surface topology is assessed.

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
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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.

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