Thermal chemistry of diiodomethane on Ni(1 1 0) surfaces II. Effect of coadsorbed oxygen

• Published in: Surface science Vol. 547; no. 3; pp. 299 - 314
• Main Authors: Guo, Hansheng, Zaera, Francisco
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 20.12.2003; Amsterdam Elsevier Science; New York, NY
• Subjects: Adsorption and desorption kinetics; evaporation and condensation; Alkanes; Chemistry; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; General and physical chemistry; Iodine; Nickel; Oxidation; Oxygen; Physics; Single crystal surfaces; Solid-fluid interfaces; Solid-gas interface; Surface chemical reaction; Surface physical chemistry; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thermal desorption; Oxygen; Alkanes; Surface chemical reaction; Nickel; Single crystal surfaces; Thermal desorption; Oxidation; Iodine; Adsorption site; Organic adsorbate; Reaction path; Thermal reaction; Thermally stimulated desorption; Experimental study; Photoelectron spectroscopy; Gas solid adsorption; Surface reactions; Transition elements; Oxidative degradation; Gas solid interface; Metallic adsorbent; Crystal faces; Iodocarbon
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2003.10.029

The effect of coadsorbed oxygen on the thermal chemistry of diiodomethane on Ni(1 1 0) single-crystal surfaces was studied by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). I 3d and C 1s XPS data indicated that adsorbed diiodomethane undergoes two sequential C–I bond scission steps to ultimately produce methylene surface species, the same as on clean Ni(1 1 0). Moreover, significant amounts of methane and other heavier hydrocarbons are produced after further thermal activation of those chemisorbed methylene groups. The production of alkanes and alkenes, which is accounted for by a chain growth mechanism where the initial hydrogenation of some adsorbed methylene to methyl moieties is followed by a rate-limiting methylene insertion step to yield ethyl intermediates, is inhibited but not fully blocked by the coadsorbed oxygen. New reaction pathways are also opened up by the presence of oxygen in this system, including a direct coupling of two methylene groups to ethene, the insertion of an oxygen atom into a nickel–methylene group to produce formaldehyde, and a parallel methylene insertion chain growth sequence starting from a CH 2I ads intermediate to ultimately yield C 3H 5 and C 4H 7 unsaturated gas-phase radicals.