Five-coordinated Als (Al(V)) on the surface of aluminas play important roles when they are used as catalysts or catalyst supports. However, the comprehensive characterization and understanding of the intrinsic structural properties of the Al(V) remain a challenge, due to the very small amount in commonly used aluminas. Herein, the surface structures of γ-Al₂O₃ and Al(V)-rich Al₂O₃ nanosheets (Al₂O₃–NS) have been investigated and compared in detail by multinuclear high-field solid-state NMR. Thanks to the high resolution and sensitivity of ultra-high-field (up to 35.2 T) NMR, the arrangements of surface Als were clearly demonstrated, which are substantially different from the bulk phase in γ-Al₂O₃ due to the structure reconstruction. It reveals for the first time that most of the commonly observed Al(V)s tend to exist as aggregated states on the surface of γ-Al₂O₃, like those in amorphous Al₂O₃–NS liable to structure reconstruction. Our new insights into surface Al(V) species may help in understanding the structure–function relationship of alumina.

中文翻译：

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超高场固态核磁共振揭示γ-Al2O3中五配位铝的性质

氧化铝表面的五配位铝(Al(V))作为催化剂或催化剂载体发挥着重要作用。然而，由于常用氧化铝中的含量非常少，因此对 Al(V) 固有结构特性的全面表征和理解仍然是一个挑战。在此，γ-Al ₂ O ₃和富含 Al(V) 的 Al ₂ O ₃纳米片 (Al ₂ O ₃-NS) 已通过多核高场固态 NMR 进行了详细研究和比较。由于超高场（高达 35.2 T）NMR 的高分辨率和灵敏度，清楚地证明了表面 Als 的排列，由于结构重建，这与 γ-Al ₂ O ₃中的体相有很大不同. 它首次揭示了大多数常见的Al(V)s倾向于以聚集态存在于γ-Al ₂ O ₃表面，就像那些易于结构重构的非晶态Al ₂ O _{3 -NS一样。}我们对表面 Al(V) 物种的新见解可能有助于理解氧化铝的结构-功能关系。