Infrared study of the adsorption of propan-2-ol on rutile at the solid/vapour and solid/heptane interfaces

Abstract

Infrared spectra of propan-2-ol adsorbed on rutile have shown that non-dissociatively adsorbed propan-2-ol is coordinatively liganded to Lewis-acidic surface sites. Dissociative chemisorption occurs at exposed Ti⁴⁺ cations, particularly for dehydroxylated rutile, and generates isopropoxide anions. Surface hydroxyl groups on rutile were replaced by isopropoxide anions with the concomitant formation of water. Hydroxyl groups at sub-surface lattice sites were unaffected by propanol adsorption. Multilayer adsorption of propan-2-ol at high surface coverages involved the formation of molecular aggregates which were weakly bound by hydrogen-bonding interactions and which contained water molecules resulting from the chemisorptive reactions. Heat treatment of adsorbed propan-2-ol resulted in the formation of adsorbed carboxylate and possibly carbonate species. The implications of the results with respect to the dehydration of propan-2-ol catalysed by rutile are briefly discussed.