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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - DYNPOR (First principle molecular dynamics simulations for complex chemical transformations in nanoporous materials)

Teaser

Summary

The overarching goal of DYNPOR is to study chemical transformations taking place in nanoporous materials using first principle molecular dynamics methods that mimic operating conditions as good as possible. To achieve this goal, one needs to deal with the complexity of a chemical transformations. At real operating conditions, chemical transformations taking place at the nanometer scale have a very complex nature, due to the interplay of several factors such as the number of particles present in the pores of the material, framework flexibility, competitive pathways, entropy effects,â€¦
Chemical transformations in nanoporous materials are vital in many application domains such as catalysis, molecular separations, sustainable conversion processes. The quest to design materials to have the optimal function is of primary importance. The materials studied in this proposal cover both zeolites, which are the workhorses of todayâ€™s petrochemical industry and metal-organic frameworks, which is a newer class of materials with a huge number of potential future applications.
At operating conditions such as realistic temperatures, pressures, â€¦. the textbook example of a single transition state is far too simplistic. In this project, the free energy is sampled at experimental conditions, to investigate various reaction pathways at realistic conditions and thus take into account the complexity of the process. As chemical reactions are rare events and very improbable to occur, advanced sampling methods need to be applied within the molecular dynamics framework. Various mobility phenomena are taken into account such as diffusion of the particles in the pores with other reacting species present. This required development of new theoretical techniques beyond current state of the art.
The selected applications are timely and rely on an extensive network with prominent experimental partners. The applications will encompass contemporary catalytic conversions in zeolites, active site engineering in metal organic frameworks and structural transitions in nanoporous materials, and the expected outcomes will have the potential to yield groundbreaking new insights.
The results are expected to have impact far beyond the horizon of the current project as they will contribute to the transition from static to dynamically based modeling tools within heterogeneous catalysis.

Work performed

Various chemical transformations were studied using advanced molecular dynamics techniques for applications in the field of zeolite chemistry. As foreseen in the DoA, various important applications were tackled such as the Methanol to Olefin process, cracking of olefins. Within the framework of the MTO process, methylations were studied at true operating conditions thus taking into account the true temperature, a realistic number of guest molecules, .. Various papers resulted from this work. Some of the papers focused on the theoretical aspects and were published only by researchers from my group. One key paper regarding the new methods is the paper of De Wispelaere et al. who worked on my ERC project â€œTowards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditionsâ€ In a series of other papers, we collaborated with experimental groups such as the group of Weckhuysen (Utrecht University), Olsbye (University of Oslo), Gascon (TUDelft). Some of the collaborations were already in place at the onset of the project. Some others such as the collaboration with Gascon resulted within the framework of this grant. We proposed a new method to modify the catalyst to enable a longer lifetime of the catalyst and higher selectivity towards propene.
For the olefin cracking process, we first focused on the influence of temperature on the reactive intermediates. We discovered the alkoxy species which are often considered to be stable in the literature, are not stable anymore at temperatures of alkene cracking. This is a major achievement, as it shows that static calculations not accounting properly for temperature, do not enable to predict the correct reaction intermediates at operating conditions. These results will now be used to simulate the olefin cracking reactions. This work resulted in two papers that were published in Journal of Catalysis.
Some of the work performed within zeolite catalysis was also taken up in an invited review â€œAdvances in theory and their applications within the field of zeolite chemistryâ€ written together with a prominent scientist in the field of zeolite modeling Prof. Richard Catlow (UCL â€“ Londen).
Within the field of Metal-Organic Frameworks, two research tracks were followed. A first track investigated the nature of the active site within MOFs. We discovered using a complementary set of techniques that the active site is composed of defect sites on which a number of water molecules may be adsorbed. In fact the active site may change depending on the conditions such as pressure, temperature, â€¦. Together with experimentalists (Dirk De Vos â€“ KULeuven, Xamena - Universitat PolitÃ¨cnica de ValÃ¨ncia) we discovered the reaction mechanisms of various chemical processes such as the aldol condensation reaction, â€¦. We discovered the remarkable amphotheric nature of defective UiO-66 materials in catalytic reactions. The results were published in journal such as ChemCatChem, Journal of Catalysis, â€¦ Furthermore based on our catalysis work in MOFs, we were invited to contribute to a seminal review on single site catalysis in MOFs. The paper is now just accepted and will appear in Chemical Society Reviews.
A second track concerns the physical properties of MOFS. We developed within the framework of this project a new theoretical protocol to determine whether a material will undergo phase transformations under influence of external stimuli such as pressure, temperature, chemical potential. To that end we developed first principle derived force fields and used them in our in house developed molecular dynamics code to determine the mechanical equation of state. Such knowledge is of primary importance to understand the stability of a material and catalyst under realistic operating conditions. To develop the first principle force fields, high level quantum mechanical information was needed, which was derived fro

Final results

At various places of the project we were able to go beyond current state of the art. We discovered various phenomena regarding stability and lifetime of realistic catalysts at operating conditions which were not know so far. Our findings may have a huge impact on the development of future catalysts, which need to be more selective, active and have a longer lifetime. These are primary conditions for future clean chemical conversions and energy conversions. Our work in collaboration with prominent experimental partners, shows how new materials may be designed that have an optimal function at operating conditions. On the more fundamental level, we were able to predict the stability window of materials used in current and future applications. One of these examples is the development of shock adsorbers and nanodampeners. From a purely experimental point of view it is very difficult to predict the behavior of material under influence of external triggers such as pressure, temperature, adsorption of guest molecules. Theoretical simulations allow to deduce the thermodynamic state function and to determine the stability window of materials.
The impact of the work is already high at this moment. The publications are highly cited, I am very regularly invited to give keynote lectures at prominent international conferences. The researchers working on the project, have also given important oral contributions to leading international meetings. Another important point is the contribution from my group to various seminal reviews which appeared in very high ranked international journals. Current citations statistics already show that these reach a huge public and will generate a high number of citations.