CHF3 as a probe for surface basicity

• Low temperature FTIR spectra of adsorbed fluoroform can be used for surface basicity testing.
• With basic oxygen atoms CHF3 demonstrates the blue-shifting H-bond accompanied by a high frequency shift of CH bending vibration.
• Dependence of frequency shift and absorbance of CH stretching vibration on the strength of H-bond is discussed.
• The problem of basicity testing can be solved by using two probe molecules such as fluoroform and acetylene.

FTIR spectra of adsorbed fluoroform as a test for surface basicity have been studied on a number of oxides and zeolites. CHF3 does not dissociate even on strongest basic sites, and forms H-bond with considerable stretching CH frequency lowering. With weaker basic oxygen atoms it demonstrates the blue-shifting H-bond accompanied by CH band intensity decrease and a high frequency shift of bending vibrations. Dependence of the frequency and integrated absorption coefficient of CH stretching vibration on the strength of H-bond is discussed. The problem of basicity testing can be solved by using two different probe molecules for sites of various strength. While fluoroform is good for stronger sites, weak sites can be tested by pyrrole, acetylene or its derivatives that are more sensitive, but dissociate on the most basic oxygen centers.

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