FT-IR SPECTROSCOPIC STUDY OF NH(3) AND CO ADSORPTION AND COADSORPTION ON TIO2 (ANATASE)

The adsorption and coadsorption of ammonia and carbon monoxide on TiO2 (anatase) have been studied by means of FT-IR spectroscopy. Two kinds of CO adsorption sites are detected on the sample surface. Increase of the equilibrium CO pressure leads to a red shift of the corresponding bands due, in a high extent, to a pressure/temperature effect. Ammonia adsorption on anatase proceeds, first of all, on the CO adsorption sites and then on Ti4+ cations inert towards CO adsorption at room temperature. Coordinated ammonia does not affect the acidity of the neighboring sites as revealed by the frequency of adsorbed CO. Only the first portions of adsorbed ammonia cause the disappearance of some surface Ti-O vibrations which evidences that the corresponding Ti4+ sites are characterized by the highest Ti-O bond order. The increase of the amount of adsorbed ammonia leads to the appearance of a dissociative adsorption form, which slightly decreases the Lewis acidity of anatase and produces OH groups which possess a Bronsted acidity.