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 spectr oscopy. On the unreduced sample, CO is adsorbed reversibly on Ti4+ cat ions (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 produ cing a doublet with maxims at 2114 and 2088 cm(-1). The 2114 cm(-1) ba nd is assigned to Pt2+-CO carbonyls interacting with water adsorbed on the support, whereas the 2088 cm(-1) band is attributed to Pt2+(H2O)C O species. CO adsorption on reduced Pt/TiO2 samples causes the appeara nce of bands due to Ti4+-CO complexes and to linear and bridged carbon yls of Pt-0 (bands at 2084 and 1860 cm(-1), respectively). Subsequent water adsorption produces a tailed Pt-0-CO carbonyl band. It is demons trated 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 sa mples, thus providing information about the coexistence of oxidized an d reduced platinum on the surface. The stability of the different carb onyls is discussed in terms of the sigma- and pi-components of Pt-CO b ond.