ADSORPTION AND H-2 NMR OF AMMONIA, PYRIDINE, DIMETHYLAMINE, AND BENZENE ON RUTILE AND ANATASE

Adsorption isotherms and deuteron (H-2) NMR spectra of ammonia, pyridine, dimethylamine, benzene, and water on microcrystalline rutile were measured. For comparison purposes, H-2 NMR spectra of the first three adsorptives on anatase were obtained. In all cases except benzene it was found that after 12 h of pumping at ambient temperature, "irreversibly" adsorbed amounts of these molecules are retained on the surface. The results obtained can be rationalized in terms of a model that ascribes about 85% of the surface exposed to (110) planes, which carry the most active Lewis acidic Ti4+ centers. At the level of irreversible adsorption, the nitrogen base molecules occupy practically every other site, whereas water occupies each of these centers. Under adsorption equilibrium conditions, further ammonia and pyridine molecules are Lewis coordinated to the centers left unoccupied, whereas this is not feasible in the case of dimethylamine.