FTIR spectroscopy study of CO adsorption on Pt-Na-mordenite

Different carbonyls are formed after CO adsorption at ambient temperature on a Pt-Na-mordenite (Pt-Na-MOR) sample. Pt3+(CO)(2) dicarbonyls (v(s) at 2205 cm(-1) and v(as) at 2167 cm(-1)) are decomposed without formation of monocarbonyls. The respective mixed-ligand species, Pt3+((CO)-C-12)((CO)-C-13), formed after (CO)-C-12-(CO)-C-13 coadsorption, display bands at 2192 and 2131 cm(-1), in excellent agreement with the theoretically calculated values. Pt2+-CO species absorb at 2145 cm(-1) and are not able to accept a second CO molecule. Pt+-CO carbonyls are characterized by a band at 2111 cm(-1). Under CO equilibrium pressure, these species are converted into dicarbonyls (v,, at 2135 cm(-1) and v(as) at 2101 cm(-1)). The respective mixed-ligand species, Pt+((CO)-C-12)((CO)-C-13), manifest bands at 2123 and 2069 cm(-1), in good agreement again with the theory. Different carbonyls of metallic platinum are observed below 2100 cm(-1). In addition, weakly adsorbed CO was registered as Na+-CO complexes (2177 and 2165 cm(-1)) and Na+-OC-Na+ species (2138 cm(-1)). It was found that during desorption of CO platinum was reduced, ultimately to metal. However, heating in a NO + O-2 mixture leads to reoxidation of the metal particles and restoration of the initial state of the sample.