Mapping the oxygen structure of γ-Al₂O₃ by high-field solid-state NMR spectroscopy

Area of Science:

• Solid-state chemistry
• Materials science
• Catalysis

Background:

• Gamma-alumina (γ-Al2O3) is a vital industrial catalyst and support material.
• Understanding its oxygen structure is key to controlling physicochemical properties, yet remains challenging.

Purpose of the Study:

• To develop and apply a novel strategy for observing and determining the oxygen structure of γ-Al2O3.
• To elucidate the spatial arrangement and types of oxygen species within γ-Al2O3.

Main Methods:

• Utilized two-dimensional (2D) solid-state Nuclear Magnetic Resonance (NMR) spectroscopy at ultra-high magnetic fields (35.2 T).
• Conducted 2D 17O double-quantum single-quantum homonuclear correlation NMR to probe oxygen-oxygen proximities.
• Performed 2D 1H-17O heteronuclear correlation NMR for identifying surface and subsurface oxygen species and hydroxyl groups.

Main Results:

• Successfully observed and determined the oxygen structure of γ-Al2O3.
• Revealed spatial proximities between various oxygen species from the bulk to the surface.
• Demonstrated a non-random distribution of oxygen species within the γ-Al2O3 structure.
• Enabled rapid identification and differentiation of surface hydroxyl groups and (sub-)surface oxygen species.

Conclusions:

• The study presents a powerful NMR-based strategy for characterizing oxygen species in γ-Al2O3.
• The findings highlight a non-random oxygen distribution, offering insights for catalyst design and property tuning.
• This approach advances the understanding of γ-Al2O3 structure-property relationships in catalysis.