As shown in another communication to Symposium V, nano-sized aluminas enriched in pentacoordinated aluminum (Alv) are obtained through the limited hydrolysis of aluminum alkoxides. Here the surface properties of these aluminas are investigated from the catalytic point of view. The goal is to obtain geometrical information on the Lewis acid sites. 1H→27Al (cross-polarization) high resolution MAS NMR, using chemisorbed NH3 which acts as aXH spin reservoir, allows the direct observation of surface Al involved in the catalytic site. The polarization transfer from these protons to surface Al is remarkably efficient because of the relatively short A1:N-H distance. It is observed that the main Lewis acid sites are located on distorted tetrahedral aluminum and pentacoordinated Al. These results are compared to low temperature infrared data of adsorbed CO.
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Coster, D., Gruver, V., Blumenfeld, A. et al. Relationships Between the Structure and the Surface Activity of Nano-Sized Alumina in Acid Catalysis. MRS Online Proceedings Library 346, 961–966 (1994). https://doi.org/10.1557/PROC-346-961