Characterization of Hydroxylated Surfaces

An alternative method for characterizing the strength of Lewis acid sites is to consider the stretch frequency of adsorbed CO molecules. The CO stretch frequency is blue shifted after it is adsorbed on Lewis acid sites compared to an isolated CO molecule. The greater the blue shift, the stronger the Lewis acid. Bronsted acid sites can also be characterized from CO adsorption. A CO molecule can form weak hydrogen bonds to surface OH groups this interaction blue shifts both the CO and the OH stretch frequencies. 

Label Al environment Substituted F ions CO stretch freq. (cm ) Shift in freq. 

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