Nature of five-coordinated aluminum on γ-Al2O3 surface

γ-Al₂O₃, an important catalyst and catalyst support, is widely used in various industrial applications. The five-coordinated aluminum, or Al(V), on the surface of γ-Al₂O₃ can affect the catalytic performances of γ-Al₂O₃.

Recently, a research team led by Prof. Hou Guangjin from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Dr. Gan Zhehong from the National High Magnetic Field Laboratory, for the first time observed the structure of Al(V) on the surface of γ-Al₂O₃ using ultrahigh-field (1.5GHz) solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.

This study was published in ACS Central Science on May 23.

The researchers investigated the structural properties of commercial γ-Al₂O₃ and amorphous alumina nanosheets (Al₂O₃-NS) rich in Al(V) by ultrahigh-field multinuclear and multi-dimensional Magic Angle Spinning (MAS) NMR.

They analyzed the aluminum species in both aluminas and found the flexible structural features on the surface of Al₂O₃-NS. And they demonstrated the hydroxyl groups on the surface of γ-Al₂O₃ with close spatial proximity that were able to be removed under high-temperature dehydration, resulting in surface structure reconstruction.

Moreover, by using ultrahigh-field ²⁷Al-²⁷Al double-quantum NMR, the researchers for the first time revealed that most Al(V) species tended to aggregate into Al(V) domains on the surface of γ-Al₂O₃ like Al₂O₃-NS, rather than tetragonal pyramid coordination on (100) surface previously predicted from theoretical models.

"These new insights into surface Al(V) species would help us to better understand the structure and function relationship of γ-Al₂O₃ when used as catalysts and catalyst supports," said Prof. Hou.