The facet-specific interaction between molecules and crystalline catalysts, such as titanium dioxides (TiO), has attracted much attention due to possible facet-dependent reactivity. Using surface-sensitive sum-frequency vibrational spectroscopy, we have studied how methanol interacts with different common facets of crystalline TiO, including rutile(110), (001), (100), and anatase(101), under ambient temperature and pressure. We found that methanol adsorbs predominantly in the molecular form on all of the four surfaces, while spontaneous dissociation into methoxy occurs preferentially when these surfaces become defective. Extraction of Fermi resonance coupling between stretch and bending modes of the methyl group in analyzing adsorbed methanol spectra allows determination of the methanol adsorption isotherm. The isotherms obtained for the four surfaces are nearly the same, yielding two adsorbed Gibbs free energies associated with two different adsorption configurations singled out by ab initio calculations. They are () ∼-20 kJ/mol for methanol with its oxygen attached to a low-coordinated surface titanium, and () ∼-5 kJ/mol for methanol hydrogen-bonded to a surface oxygen and a neighboring methanol molecule. Despite similar adsorption energetics, the Fermi resonance coupling strength for adsorbed methanol appears to depend sensitively on the surface facet and coverage.

Vibrational signature reveals the structure around, and evolution of, active sites on anatase (101) in real ambient.

The interaction of aromatic alcohols with titanium dioxide (TiO 2 ) is involved in many applications, including the synthesis of TiO 2 nanocomposites and selective photocatalysis. We investigate here the anisotropic adsorption of 2-phenylethyl alcohol (2PA) on rutile (TiO 2 ) (110) as a model system using sum-frequency vibrational spectroscopy. 2PA molecules are found to have aromatic rings protruding out and aligning preferentially across the bridging oxygen rows, and instead of π−π interaction, such alignment of aromatic rings is mainly caused by the hydrogen bonding between 2PA and bridging oxygen sites as suggested by ab initio calculations.