Transitional aluminas are a major class of materials involved in several large scale catalytic processes, both as carrier or as catalyst. Their attractive reactivity is directly linked to their surface chemistry. However, their structural complexity constitutes a major challenge when using classical spectroscopic techniques for characterization and reactivity understanding. In this context, solid state NMR, more specifically recent advances on heteronuclear (1H-27Al) correlation methods, can definitely change the game, by localizing surface species (from hydroxyl groups to grafted organometallics) on the surface aluminum centers.In this contribution, we will first describe our findings on the ?-alumina surface hydroxyl groups' structure and topology, thanks to combined high magnetic field and state-of-the-art homo- and hetero-nuclear correlations. Strong input from DFT calculations helped and strengthened the conclusions. Thus, we propose a fresh view on the major hydroxyl groups' nature, and on their non-random arrangement, that goes beyond well-established, infrared spectroscopy-derived previous knowledge.From this point, the surface organometallic chemistry of alumina was revisited. Thanks to the structural information of the aluminol groups, a further level of understanding was reached for the grafting of catalysis-related aluminum, gallium and tungsten organometallic species. In the case of supported aluminum alkyls, reactivity toward hydrogen afforded well-defined surface hydride species that displayed unprecedented catalytic reactivity. Their structure was elucidated at the molecular level thanks to remarkable NMR features.

Solid-state NMR as a surface-selective technique: New insights into alumina surface structure and organometallic chemistry

248th National Meeting (2014)

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