Identification and Characterization of Catalytically Active Sites on the Surface of ?-Alumina
- Type: Conference Presentation
- Conference Type: AIChE Annual Meeting
- Presentation Date: November 15, 2021
- Duration: 18 minutes
- Skill Level: Intermediate
- PDHs: 0.50
Î³-alumina is one of the oldest and most important commercial catalytic materials with high surface area and stability. These attributes enabled its use as the first commercial large-scale heterogeneous catalyst for ethanol dehydration. Despite progress in materials characterization and over a hundred years of active research, the nature of the specific sites on the surface of Î³-alumina which are responsible for its unique catalytic properties has remained obscure and controversial. Herein, we identify for the first time using combined infrared spectroscopy, electron microscopy and solid-state nuclear magnetic resonance measurements that the octahedral amphoteric (O)5Al(VI)-OH sites on the (100) segments of massively restructured (110) facets on typical rhombus-platelet Î³-alumina as well as (100) segments of irrational surfaces (invariably always present in all Î³-alumina samples) are largely responsible for its unique catalytic activity. Such (O)5Al(VI)-OH sites are also present on macroscopically defined (100) facets Î³-alumina of different, more elongated/rod-like geometry. They anchor organometallic fragments and isolated metal atoms. The exact mechanism by which these sites lose -OH group upon thermal dehydroxylation is clarified, resulting in coordinatively unsaturated penta-coordinate Al+3O5 sites that can activate nitrogen. These coordinatively unsaturated Al penta-coordinate sites demonstrate new chemistry, producing the first well-defined thermally stable Al-carbonyl complexes. Our findings reunite and successfully clarify the contradictory findings in the literature over the last century, illuminating the true nature and the relationship between the catalytically active and coordinatively unsaturated Al sites on the surface of Î³-alumina.
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|AIChE Member Credits||0.5|
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|AIChE Undergraduate Student Members||Free|