H-bonding on solid oxide surfaces. Infra-red spectroscopic study of the adsorption of alcohols on silica and alumina

Abstract

The weak adsorption via H-bonding of t-butanol and ethanol on silica and of ethanol on alumina has been studied by means of infra-red spectroscopy, mainly in the fundamental region. Some overtone spectra of the t-butanol/silica system have also been obtained. The formation of clusters which are held through random single H-bonds on surface silanol groups is proposed for the adsorption on silica. On alumina surfaces oxygen ions act as H-bond acceptor sites, whereas surface hydroxyl groups are only perturbed through lateral interactions. Besides the H-bonded species, alcohol molecules are bonded to incompletely coordinated Al⁺-ions. The O—H bond is more or less strongly polarized by interaction of the alcoholic hydroxyl proton with neighbouring oxygen ions. The different behaviour of the two oxides is discussed in terms of the different metal–oxygen bond character.