Transitional aluminas are key materials for the chemical industry, being used either as catalyst or a catalyst support. Immobilization of metal-based reagents onto such materials has been an entry into the design of efficient catalytic materials for decades. More recently, the grafting of organometallic species (which feature precisely defined coordination sphere) onto these inorganic carriers has emerged as an attractive option for the synthesis of heterogeneous catalysts that would feature (ideally) well-defined surface sites. In such cases, linking both metal-support interactions and metal coordination sphere with these systems' catalytic performances is of high importance when drawing structure-activity relationships. This requires deep understanding of the alumina surface topology and reactivity. As the nature of the alumina surface sites and of the resulting grafted organometallics are quite complex, a powerful spectroscopic approach is required to reach the necessary level of understanding. In this context, solid-state NMR is a key technique, as it provides information at the molecular level, with fast technical and methodological developments. Thanks to high resolution (MQ MAS), homonuclear (DQ MAS) and heteronuclear (HMQC MAS) techniques, it is possible to extract precise structural information on alumina surface and alumina surface-grafted species, relying for instance on the highly responsive nuclei 1H and 27Al. In this lecture, we will discuss several examples highlighting the input from solid-state NMR on the understanding of the surface of partially dehydroxylated transitional alumina, of supported activators for olefin polymerization and of various supported catalytic systems active in alkane (dehydrogenation) and alkene upgrading (metathesis).

Solid-state NMR investigation of alumina and of alumina-supported organometallic catalysts

255th National Meeting (2018)

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