Magnetic Resonance Spectroscopy (NMR, EPR) for Polymerization Catalysis – MRCAT

For this, the use and development of spectroscopic methods is essential, as these techniques can provide information on the electronic states and structures of the active sites, which in turn provide the molecular information necessary to understand the structure-activity relationship. The present project focused on the development of a powerful new set of spectroscopic techniques to remove key barriers to progress in nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy on non-crystalline samples containing paramagnetic metal ions.

Specifically, paramagnetic NMR and EPR based characterization techniques were developed as an essential step towards a molecular understanding of the active Ti3+ (and Fe2+/3+) surface sites in ZN polymerization reactions.
At the end of the project, we were not only able to capture the spectroscopic signature of the active centers of ZN ethylene polymerization catalysts, but also to resolve their structure with atomic level resolution.

Overall, the results of this project open a way to further improvement of the productivity of ZN catalysts via a rational approach, based on the knowledge of the structure of the active sites. This work should contribute to better control the synthesis of polyolefins, and promote their entry into the era of the circular economy (recycling, eco-design). More generally, beyond the field of catalysis, the spectroscopic tools developed in this project will also provide a powerful tool to understand several essential processes at the forefront of molecular and chemical sciences today.

The results of the project have already been published as articles in international peer-reviewed chemistry journals (7, including 3 in high impact journals such as J. Am. Chem. Soc. and Angewadte Chemie, which are widely considered as the two best chemistry journals), presented as invited oral communications at several international and national conferences, and have also already been the subject of specialized training and a non-specialized press release.

The development of more efficient catalysts in terms of activity, selectivity, and stability is one of the key challenges today because of the need to optimize the use of resources within the context of a more sustainable development. In the search for more efficient chemical processes, one key approach consists in having a precise understanding of the structure of the active sites of the catalyst. This enables structure-activity relationships to be deduced, allowing for the rapid and rational development of catalysts with improved properties. Therefore, the use and the development of spectroscopic methods are essential because they can provide information on the electronic states and the structures of the active sites, which in turn provide the necessary molecular information for structure – activity relationship.
Over the very recent years, paramagnetic NMR, DNP-enhanced NMR spectroscopy and EPR find themselves propelled as three of the most powerful techniques for the atomic-scale characterization of surface molecular species in functional materials, including catalytic systems. While a number of examples have shown that can complement infrared (IR), Raman, UV-Vis and X-ray absorption (XAS) along with other surface science and molecular modeling techniques, a number of challenges remain however to be solved before these magnetic spectroscopies are ready to cope with the detailed structure elucidation of active sites in heterogeneous paramagnetic organometallic catalysts.
This research proposal concerns the development of innovative paramagnetic solid-state NMR and EPR strategies for the determination of atomic level description of highly challenging, industrially relevant Ziegler-Natta catalytic systems, which are involved in the synthesis of highly ubiquitous commodity polymers: polyolefins and which present paramagnetic centers, making the use of classical spectroscopic approaches nearly impossible.
This 36-month project brings together leading laboratories in magnetic resonance, polymerization and heterogeneous catalysis from France and Switzerland, and will combine methodological advances in high-resolution solid-state NMR and EPR spectroscopies with innovation in catalysis that will be applied to relevant industrial challenges in the field of polymer chemistry. The complementary expertise provided by the three joint research groups will be essential to the success of this ambitious project, which will lead to the understanding and improvement of catalytic reactions involved the polymerization of olefins. Despite its industrial relevance, this heterogeneous catalysis suffers from a lack of molecular understanding of its key features, hampering breakthrough innovation.
This project is grounded on the fundamental development of novel NMR and EPR approaches dedicated to the understanding and improvement of Ziegler-Natta catalysis, and as such meets the ANR call “Défi de tous les Savoirs”.