METHYL-IODIDE THERMAL-REACTIONS WHEN CHEMISORBED ON NI(100) SURFACES

The thermal reactivity of methyl iodide on Ni(100) surfaces has been studied by using thermal programmed desorption (TPD), X-ray photoelectron (XPS), and static secondary ion mass (SSIMS) spectroscopies. TPD results indicate that only methane and hydrogen desorb at coverages below saturation, but physisorbed methyl iodide was also observed above saturation. Both I 3d and C ls XPS spectra suggest that methyl iodide adsorption below 100 K is mostly molecular and that the carbon-iodine bond breaks between 120 and 160 K. The activation energy for this bond scission step was determined to be about 3.5 kcal/mol by isothermal XPS experiments, and SSIMS studies show that the surface species resulting from that reaction are methyl groups. Those methyl moieties then hydrogenate below 300 K to form methane via a complex mechanism that involves a direct reductive elimination step.