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

Abstract

The adsorption of CO 2 on clean and potassium-covered Mo 2C/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 CO 2 on Mo 2C/Mo(100) caused no measurable changes in the work function of Mo 2C. CO 2 adsorbed weakly on K-free Mo 2C at 90 K, producing vibration features at 660, 1260–1340 and 2349 cm −1. It desorbed in one peak with T p=190 K. The deposition of potassium on Mo 2C 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 T p=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 CO 2 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 CO 2 dissociated to adsorbed CO and O at low potassium coverage, even at 90–150 K, and disproportionated into adsorbed CO and CO 3 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.