The surface of highly Lewis acidic high surface AlF3, HS-AlF3, prepared in different ways was investigated
by FTIR spectroscopy of adsorbed CO and compared to the previously known and well-characterized β-AlF3.
The majority of adsorbed CO shows large blue shifts up to more than 80 cm-1 of the band of the CO stretching
frequency, corresponding to very strong Lewis acidic adsorption sites. In contrast to that behavior, most of
the CO adsorbed on β-AlF3 shows a smaller blue shift of around 40 cm-1. These results can explain the very
high acidity of HS-AlF3 and the differences in catalytic activity between both samples. The influence of
water is also investigated. Adsorption of water at room temperature blocks the Lewis acid sites and generates
Brønsted acidity. Heating the sample under a certain partial pressure of water followed by degassing results
in a significant loss of acidity. Both phenomena were confirmed by IR spectroscopy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.