Adsorption and decomposition of C6H5I on the Mo2C/Mo(1 0 0) surface

The adsorption and surface reactions of phenyl iodide on Mo2C/Mo(1 0 0) surface have been investigated by thermal desorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy in the 100–1200 K temperature range. Phenyl iodide adsorbed molecularly on the Mo2C/Mo(1 0 0) surface at 100 K. At submonolayer coverages the molecules adsorbed in a flat-lying, and in the condensed layer in a random position. The desorption of the weakly bonded C6H5I occurred in a peak with Tp=200 K. Phenyl iodide bonded in the chemisorbed state underwent dissociation at 160–300 K, as evidenced by XPS data, while photolysis of the monolayer by UV light resulted in a complete dissociation even at 100 K. Iodine atoms formed in the decomposition process were released into the gas phase with Tp=980 and 1080 K. The phenyl groups formed as a result of C–I cleavage reacted in three different ways. A very limited part is coupled into biphenyl (Tp=510 K). Other part was hydrogenated to benzene which desorbed with a Tp=290–278 K. The third part of C6H5(a) decomposed to hydrogen and benzyne groups. This species could be also hydrogenated into benzene, but it mostly decomposed at higher temperature, as shown by H2 desorption peaks at 600 and 700 K. HREEL spectra suggested that the aromatic ring was preserved on the surface up to ∼430 K. Elevating the adsorption temperature to 400 K enhanced the amount of strongly bonded C6 species by a factor of ∼3 as evidenced by the increased hydrogen desorption.