Publications by authors named "Ruben Demuynck"
Article Synopsis
- The methanol-to-olefins process over H-SAPO-34 shows high selectivity for producing light olefins due to its unique supramolecular catalyst structure.
- Key to this process are hydrocarbon pool species that can either aid in catalysis or obstruct the catalyst's pores, impacting the diffusion of the desired products ethene and propene.
- Enhanced molecular dynamics simulations reveal that various factors, such as the presence of Brønsted acid sites and the type of organic compounds trapped in the catalyst, significantly influence the diffusion rates and ultimately the product selectivity.
Various kinds of flexibility have been observed in metal-organic frameworks, which may originate from the topology of the material or the presence of flexible ligands. The construction of free energy profiles describing the full dynamical behavior along the phase transition path is challenging since it is not trivial to identify collective variables able to identify all metastable states along the reaction path. In this work, a systematic three-step protocol to uniquely identify the dominant order parameters for structural transformations in flexible metal-organic frameworks and subsequently construct accurate free energy profiles is presented.
View Article and Find Full Text PDFCatalytic alkene cracking on H-ZSM-5 involves a complex reaction network with many possible reaction routes and often elusive intermediates. Herein, advanced molecular dynamics simulations at 773 K, a typical cracking temperature, are performed to clarify the nature of the intermediates and to elucidate dominant cracking pathways at operating conditions. A series of C-C alkene intermediates are investigated to evaluate the influence of chain length and degree of branching on their stability.
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- UiO-66 is a highly stable metal-organic framework that retains its structure even during processes like linker exchange and dehydration, showing it can handle defects without losing stability.
- The study utilizes advanced molecular dynamics simulations to explore how the framework's geometry changes during activation, specifically focusing on the coordination number of zirconium atoms decreasing from three to one in the hydroxyl groups.
- Findings indicate that the framework exhibits dynamic flexibility, allowing for rapid structural responses and the stabilization of linkers through hydrogen bonds, which enhances our understanding of activation processes at a molecular level.
In this work, the influence of cell shape sampling on the predicted stability of the different metastable phases in flexible metal-organic frameworks at finite temperatures is investigated. The influence on the free energy by neglecting cell shape sampling is quantified for the prototypical MIL-53(Al) and the topical DUT-49(Cu). This goal is achieved by constructing free energy profiles in ensembles either in which the phase space associated with the cell shape is sampled explicitly or in which the cell shape is kept fixed.
View Article and Find Full Text PDFIn order to reliably predict and understand the breathing behavior of highly flexible metal-organic frameworks from thermodynamic considerations, an accurate estimation of the free energy difference between their different metastable states is a prerequisite. Herein, a variety of free energy estimation methods are thoroughly tested for their ability to construct the free energy profile as a function of the unit cell volume of MIL-53(Al). The methods comprise free energy perturbation, thermodynamic integration, umbrella sampling, metadynamics, and variationally enhanced sampling.
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