title: Heteronuclear NMR spectroscopy as a surface-selective technique: a unique look at the hydroxyl groups of γ-alumina.
abstract: The surface hydroxyl groups of γ-alumina dehydroxylated at 500 °C were studied by a combination of one- and two-dimensional homo- and heteronuclear (1)H and (27)Al NMR spectroscopy at high magnetic field. In particular, by harnessing (1)H-(27) Al dipolar interactions, a high selectivity was achieved in unveiling the topology of the alumina surface. The terminal versus bridging character of the hydroxyl groups observed in the (1)H magic-angle spinning (MAS) NMR spectrum was demonstrated thanks to (1)H-(27) Al RESPDOR (resonance-echo saturation-pulse double-resonance). In a further step the hydroxyl groups were assigned to their aluminium neighbours thanks to a {(1)H}-(27) Al dipolar heteronuclear multiple quantum correlation (D-HMQC), which was used to establish a first coordination map. Then, in combination with (1)H-(1) H double quantum (DQ) MAS, these elements helped to reveal intimate structural features of the surface hydroxyls. Finally, the nature of a peculiar reactive hydroxyl group was demonstrated following this methodology in the case of CO2 reactivity with alumina.
authors.affiliation: C2P2 (CNRS-UMR 5265), Université Lyon 1, ESCPE Lyon, 43 Boulevard du 11 Novembre 1918, 69626 Villeurbanne Cedex (France). taoufik@cpe.fr.
authors.forename: Mostafa
authors.initials: M
authors.lastname: Taoufik
authors.forename: Kai C
authors.initials: KC
authors.lastname: Szeto
authors.forename: Nicolas
authors.initials: N
authors.lastname: Merle
authors.forename: Iker
authors.initials: I
authors.lastname: Del Rosal
authors.forename: Laurent
authors.initials: L
authors.lastname: Maron
authors.forename: Julien
authors.initials: J
authors.lastname: Trébosc
authors.forename: Grégory
authors.initials: G
authors.lastname: Tricot
authors.forename: Régis M
authors.initials: RM
authors.lastname: Gauvin
authors.forename: Laurent
authors.initials: L
authors.lastname: Delevoye
keywords: alumina; density functional calculations; solid-state NMR spectroscopy; structure elucidation; surface chemistry