ION DIPOLE INTERACTIONS BETWEEN ADSORBED CO AND SUPPORT CATIONS IN PT/K-LTL

The adsorption of carbon monoxide on a non-acidic Pt/K-LTL catalyst has been studied by diffuse reflectance and transmission IR spectroscopy. The CO spectrum is strongly dependent on the experimental conditions. Adsorption on the small Pt clusters in the presence of water gives linear-CO bands between 2060 and 1990 cm-1 and a bridging-CO band around 1800 cm-1. In the absence of water, the linear bands are red shifted to about 1940 and 1720 cm-1, respectively. The frequency shift is attributed to an ion-dipole interaction between adsorbed CO and support cations. The ion-dipole interaction is screened by the adsorbed water leading to a smaller red shift in the CO stretching frequency.