IR study of CO and H2O coadsorption on Ptn+/TiO2 and Pt/TiO2 samples

The adsorption of CO on a Pt/TiO2 sample has been studied by IR spectroscopy. On the unreduced sample, CO is adsorbed reversibly on Ti4+ cations (bands at 2188 and 2206 cm(-1)) and irreversibly on Pt4+ and Pt2+ sites (bands at 2186 and 2138 cm(-1) respectively). Water replaces CO adsorbed on Pt4+ sites and interacts with the Pt2+-CO carbonyls producing a doublet with maxims at 2114 and 2088 cm(-1). The 2114 cm(-1) band is assigned to Pt2+-CO carbonyls interacting with water adsorbed on the support, whereas the 2088 cm(-1) band is attributed to Pt2+(H2O)CO species. CO adsorption on reduced Pt/TiO2 samples causes the appearance of bands due to Ti4+-CO complexes and to linear and bridged carbonyls of Pt-0 (bands at 2084 and 1860 cm(-1), respectively). Subsequent water adsorption produces a tailed Pt-0-CO carbonyl band. It is demonstrated that, as a result of the strong CO adsorption on both, Pt2+ and Pt-0 sites, CO can be used as a probe molecule to test inactivated samples, thus providing information about the coexistence of oxidized and reduced platinum on the surface. The stability of the different carbonyls is discussed in terms of the sigma- and pi-components of Pt-CO bond.