The adsorption and reactions of propyl iodide on clean and adsorbate-modified Mo2C/Mo(1 0 0) surfaces

The adsorption and surface reactions of propyl iodide on clean and adsorbate-modified Mo2C/Mo(1 0 0) surfaces have been investigated by thermal desorption spectroscopy, X-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy (HREELS) in the 100–1200 K temperature range. Propyl iodide adsorbed molecularly on the clean Mo2C/Mo(1 0 0) surface at 100 K and desorbed in two peaks at 180 and 280 K, characteristic of condensed and chemisorbed layers, respectively. The dissociation of adsorbed C3H7I producing C3H7 and I started at as low as 140 K and was completed at 260 K. C3H7 fragments underwent dehydrogenation to propene and hydrogenation to propane. Propane desorbed with a Tp=280–320 K and propene with Tp=240 and 310 K. Hexane and hexene were also detected in the desorbing products, Tp∼450 K, indicating the occurrence of the coupling reactions between the adsorbed alkyl species. The desorption of iodine occurred at high temperature with a Tp=1050 K. Analysis of HREELS spectra of annealed layer suggests the formation of di-σ-bonded propylene at 200 K, and propylidyne at 296 K on the surface. The latter decomposes at higher temperatures leaving carbon on the surface and releasing hydrogen into the gas phase with Tp=360 and 640 K. Preadsorbed iodine and CO exerted no influence on the uptake of C3H7I at 100 K, but suppressed the decomposition of C3H7I by a factor of ∼5.