A. Aerts

On the feasibility of online terbium extraction at ISOL@MYRRHA

B. Leenders, A. Aerts, T. E. Cocolios, S. Cottenier, D. Houngbo, L. Popescu
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volume 541, Page 249-252
2023
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Abstract 

Terbium is an element that has four isotopes with interesting properties for medical applications, 149, 152, 155, 161Tb. These radioisotopes are however far from being sufficiently accessible, thereby hindering the pursuit of research on radiolabelling as well as clinical or preclinical investigations. Their lack of market availability is explained by difficulties in producing these radioisotopes with high purity and specific activity. While 161Tb can be produced using neutron capture in nuclear reactors, for 149, 152, 155Tb, a production route involving the ISOL technique is under study within the Tb-IRMA-V project. The ongoing R&D towards the production and extraction of these isotopes from an ISOL target at the ISOL@MYRRHA facility is reported in this contribution.

DOI 

http://dx.doi.org/10.1016/j.nimb.2023.05.034

Po-Containing Molecules in Fusion and Fission Reactors

M.A.J. Mertens, A. Aerts, I. Infante, J. Neuhausen, S. Cottenier
Journal of Physical Chemistry Letters
10 (11), 2879-2884
2019
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Abstract 

Fission and fusion reactors can only play a role in the future energy landscape if they are inherently safe by design. For some reactor concepts, a major remaining issue is the undesired production of radiotoxic 210Po. To filter out the volatile Po species, information on their molecular composition is needed. An experimental characterization is very challenging due to the large required amount of radioactive Po. An alternative quantum chemistry approach was taken to predict the temperature-dependent stability of relevant diatomic Po-containing molecules. Experimental data on lighter analogue molecules was used to establish a well-founded methodology. The relative occurrence of the Po species was estimated in the cover gas of (i) the lead–bismuth eutectic coolant in the accelerator-driven MYRRHA fission reactor and (ii) the Pb–Li eutectic tritium breeder in the DEMO fusion reactor. In both systems, Po is found to occur mainly as PbPo molecules and atomic Po.

DOI 

http://dx.doi.org/10.1021/acs.jpclett.9b00824

Multi-level Modeling of Silica–Template Interactions During Initial Stages of Zeolite Synthesis

T. Verstraelen, B.M. Szyja, D. Lesthaeghe, R. Declerck, V. Van Speybroeck, M. Waroquier, A.P.J. Jansen, A. Aerts, L.R.A Follens, J.A. Martens, C. Kirschhock, R.A. van Santen
Topics in Catalysis
52 (9), 1261-1271
2009
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Abstract 

Zeolite synthesis is driven by structure-directing agents, such as tetrapropyl ammonium ions (TPA(+)) for Silicalite-1 and ZSM-5. However, the guiding role of these organic templates in the complex assembly to highly ordered frameworks remains unclear, limiting the prospects for advanced material synthesis. In this work, both static ab initio and dynamic classical modeling techniques are employed to provide insight into the interactions between TPA(+) and Silicalite-1 precursors. We find that as soon as the typical straight 10-ring channel of Silicalite-1 or ZSM-5 is formed from smaller oligomers, the TPA(+) template is partially squeezed out of the resulting cavity. Partial retention of the template in the cavity is, however, indispensable to prevent collapse of the channel and subsequent hydrolysis.

DOI 

http://dx.doi.org/10.1007/s11244-009-9275-4

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

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
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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

Catalytic and molecular separation properties of Zeogrids and Zeotiles

J.A. Martens, J.W. Thybaut, J.F.M. Denayer, S. Pulinthanathu Sree, A. Aerts, M-F. Reyniers, V. Van Speybroeck, M. Waroquier, A. Buekenhoudt, I. Vankelecom, W. Buijs, J. Persoons, G.V. Baron, S. Bals, G. Van Tendeloo, G.B. Marin, P.A. Jacobs, C. Kirschhock
Catalysis Today
168, 17-27
2011
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Abstract 

Zeogrids and Zeotiles are hierarchical materials built from assembled MFI zeolite precursor units. Permanent secondary porosity in these materials is obtained through self assembly of nanoparticles encountered in MFI zeolite synthesis in the presence of supramolecular templates. Hereon, the aggregated species are termed nanoslabs. Zeogrids are layered materials with lateral spacings between nanoslabs creating galleries qualifying as supermicropores. Zeotiles present a diversity of tridimensional nanoslab assemblies with mesopores. Zeotile-1, -4 and -6 are hexagonal mesostructures. Zeotile-1 has triangular and hexagonal channels; Zeotile-4 has hexagonal channels interconnected via slits. Zeotile-2 has a cubic structure with gyroid type mesoporosity. The behavior of Zeogrids and Zeotiles in adsorption, membrane and chromatographic separation and catalysis has been characterized and compared with zeolites and mesoporous materials derived from unstructured silica sources. Shape selectivity was detected via adsorption of n- and iso-alkanes. The mesoporosity of Zeotiles can be exploited in chromatographic separation of biomolecules. Zeotiles present attractive separation properties relevant to CO2 sequestration. Because of its facile synthesis procedure without hydrothermal steps Zeogrid is convenient for membrane synthesis. The performance of Zeogrid membrane in gas separation, nanofiltration and pervaporation is reported. In the Beckmann rearrangement of cyclohexanone oxime Zeogrids and Zeotiles display a catalytic activity characteristic of silicalite-1 zeolites. Introduction of acidity and redox catalytic activity can be achieved via incorporation of Al and Ti atoms in the nanoslabs during synthesis. Zeogrids are active in hydrocracking, catalytic cracking, alkylation and epoxidation reactions. Zeogrids and Zeotiles often behave differently from ordered mesoporous materials as well as from zeolites and present a valuable extension of the family of hierarchical silicate based materials.

DOI 

http://dx.doi.org/10.1016/j.cattod.2011.01.036

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