Effects of potassium on the reaction pathways of CH 2 fragment over Mo 2C/Mo(1 0 0)

Abstract

The adsorption and surface reactions of CH 2I 2 on the K-dosed Mo 2C/Mo(1 0 0) have been studied by high resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. Potassium is an effective promoter for the rupture of C–I bond in the adsorbed CH 2I 2. A partial dissociation of this compound occurred even at 100 K and was completed at 190 K at monolayer K coverage. The dissociation was further promoted by the illumination of coadsorbed layer at 100 K. As revealed by HREELS and XPS measurements the primary products of the dissociation are CH 2 and I. Methylene was converted to π-bonded ethylene characterized by T p = 160 K, and di- σ-ethylene with T p = 350 K. Other products of the surface reaction are hydrogen and methane. The coupling reaction of CH 2 species was clearly facilitated by potassium. The effect of potassium was explained by the extended electron donation to adsorbed alkyl iodide in one hand, and by the direct interaction between potassium and I on the other hand.