Site Competition during Coadsorption of Acetone with Methanol and Water on TiO2(110)

The competitive interaction between acetone and two solvent molecules (methanol and water) for surface sites on ruble TiO2(110) was studied using temperature-programmed desorption (TPD). On a vacuum-annealed TiO2(110) surface, which possessed similar to 5% oxygen vacancy sites, excess methanol displaced preadsorbed acetone molecules to weakly bound and physisorbed desorption states below 200 K. In contrast, acetone molecules were stabilized on an oxidized surface against displacement by methanol through formation of acetone diolate species. The behavior of acetone with methanol differs from the interactions between acetone and water which are less competitive. Examination of acetone + methanol and acetone + water multilayer combinations shows that acetone is more compatible in water-ice films than in methanol-ice films, presumably because water has greater potential as a hydrogen-bond donor than does methanol. Acetone molecules displaced from the TiO2(110) surface by water are more likely to be retained in the near-surface region, in turn having a greater opportunity to revisit the surface, than when methanol is used as a coadsorbate.