Spectroscopic study on the formation of CO−2 on K-promoted Mo2C/Mo(100) surface

The adsorption of CO2 on clean and potassium-covered Mo2C/Mo(100) surface was studied by high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TPD), work function measurements and X-ray photoelectron spectroscopy (XPS). The adsorption of CO2 on Mo2C/Mo(100) caused no measurable changes in the work function of Mo2C. CO2 adsorbed weakly on K-free Mo2C at 90 K, producing vibration features at 660, 1260–1340 and 2349 cm−1. It desorbed in one peak with Tp=190 K. The deposition of potassium on Mo2C resulted in a maximum work function decrease of 3.3 eV. The bonding strength of potassium sensitively depended on its surface concentration. At low coverage it desorbed with Tp=850 K, this peak temperature was 525 K at monolayer, and 355 K at multilayer. The presence of potassium adatoms greatly increased the binding energy of CO2 and led to the formation of CO−2 anion radical characterized by losses at 750–785, 1220–1250 and 1580–1670 cm−1. The activated CO2 dissociated to adsorbed CO and O at low potassium coverage, even at 90–150 K, and disproportionated into adsorbed CO and CO3 at and above potassium monolayer. Both compounds were strongly stabilized on the surface by potassium adatoms and were released from the surface coincidentally with a peak temperature of 665–686 K.