Adsorption and confinement of n-butyraldehyde by porous materials followed by CIR spectrometry

n-Butyraldehyde adsorption on mesoporous silicas has been studied by volumetry followed by in situ infrared spectroscopy. Infrared spectra of butyraldehyde adsorbed onto porous silica have been recorded at different relative pressures. It is shown that adsorption occurs through the interaction between the carbonyl function of n-butyraldehyde and the surface silanols. The analysis of IR spectra allowed for the detection of three different adsorbed species, one of them being located on either isolated or clustered silanol, another one corresponding to the occurrence of liquid n-butyraldehyde in the pores of the mesoporous silicas, the third one being more difficult to be attributed. The first adsorbed species could be the protonated enol structure C3H7CHCHOH2+ which could be far more reactive than the original aldehyde. It is also suggested that confinement effects may be responsible for the occurrence of a specific absorption band which only appeared on mesoporous materials having an important surface curvature.