Public Thesis defense - IMCN

Hybridization of Keggin polyoxometalates for epoxidation catalysis by Gabriel HIDALGO GUTIERREZ

Pour l’obtention du grade académique de Doctorat en sciences agronomiques et ingénierie biologique

Heterogeneous catalytic epoxidation of olefins is of considerable fundamental and industrial interest. A particular family of metal oxide clusters called polyoxometalates (POMs) have shown considerable success in green catalytic oxidation reactions. Heterogenization of POMs with organic ligands has proved to be an attractive strategy to form epoxidation-active hybrid catalytic materials. This thesis presents fundamental and applied approaches to the hybridization of a Keggin POM with bipyridine, a hydrophobic ligand with robust redox properties, yet largely unexplored, for the selective epoxidation of olefins with H2O2. A systematic investigation of hybrid catalysts composed of Keggin PW12O403- and substituted bipyridines, highlights the role of the hybrid constituents in the epoxidation reaction. A pre-activation strategy, at the synthesis level, consisting in contacting the Keggin anion with H2O2 prior reaction with the ligands, is conducted to boost the catalytic epoxidation. The catalytic behaviour of the pre-activated hybrids is inspected in details and their structures are solved by single crystal X-ray diffraction. A reaction mechanism is proposed that highlights the pivotal, yet often underestimated, role of H2O2 in the reached catalytic performances. The active species responsible for the oxygen transfer to the olefin is a hydroperoxide intermediate species which is formed by interaction between the anionic structure of the catalyst and H2O2. The latter operates as a “conservative agent” whose presence in the catalytic system is required to prevent the catalysts from deactivating irreversibly.

Jury members :

• Prof. Michel Devillers (UCLouvain), supervisor
• Prof. Eric Gaigneaux (UCLouvain), supervisor
• Prof. Arnaud Delcorte (UCLouvain), chairperson
• Prof. Damien Debecker (UCLouvain), secretary
• Prof. Carmela Aprile (UNamur)
• Prof. Tatjana Parac-Vogt (KULeuven)
• Prof. Pascal Van Der Voort (UGent)

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