Structure, Location, and Spatial Proximities of Hydroxyls on γ-Alumina Crystallites by High-Resolution Solid-State NMR and DFT Modeling: Why Edges Hold the Key

Ana T.F. Batista, Thomas Pigeon, Jordan Meyet, Dorothea Wisser, Mickael Rivallan, David Gajan, Leonor Catita, Fabrice Diehl, Anne Sophie Gay, Céline Chizallet, Anne Lesage, Pascal Raybaud

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

The atomic-scale characterization of surface active sites on γ-alumina still represents a great challenge for numerous catalytic applications. Here, we combine advanced density functional theory (DFT) calculations with one- and two-dimensional proton solid-state NMR experiments to identify the exact location and the spatial proximity of hydroxyl groups on γ-alumina crystallites. Our approach relies on revisited models for the (100), (111), basal (110)b, and lateral (110)l facets of γ-alumina, as well as for the edges at their intersections. Notably, we show that the ≃0 ppm AlTd1-OH protons are predominantly located on edges, where these are free from the H-bond network. The proximities among the AlTd1-OH as well as with μ2-OH groups are revealed by 1H-1H dipolar correlation experiments and analyzed in the light of the DFT calculations, which identify their location on the basal (110)b facet and on the (110)b/(100) and (110)b/(110)l edges. Using chlorine atoms to probe the presence of hydroxyls, we show that the chlorination occurs selectively by exchanging μ1-OH located on edges and on lateral (110)l facets. By contrast, the basal (110)b and lateral (111) facets are not probed by Cl. This exchange explains the disappearance of the ≃0 ppm peak and of the correlations involving AlTd1-OH species. Moreover, after chlorination, a deshielding of the AlTd is observed on high-resolution 27Al NMR spectra. More subtle effects are visible on the proton correlation spectra, which are attributed to the disruption of the H-bond network in the course of chlorination.

Original languageEnglish (US)
Pages (from-to)6536-6548
Number of pages13
JournalACS Catalysis
Volume13
Issue number10
DOIs
StatePublished - May 19 2023

All Science Journal Classification (ASJC) codes

  • Catalysis
  • General Chemistry

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