The strong influence of potassium on the adsorption of CO on platinum surfaces. A thermal desorption spectroscopy and high-resolution electron energy loss spectroscopy study

The chemisorptive properties of carbon monoxide on the Pt(111) crystal face were observed to change markedly in the presence of potassium. Upon deposition of half a monolayer of potassium the saturation coverage adsorption energy of CO increased from 27 to 39 kcal/mol. High-resolution electron energy loss spectroscopy (HREELS) showed a 475-cm^-1 decrease in the bridge bonded CO vibrational frequency to as low as 1400 cm^-1, while CO preferentially occupied bridge bonded rather than linearly bonded surface sites in the presence of potassium. These large variations appear to be caused by enhanced electron back-donation from the platinum into the 2π* antibonding orbitals of CO.