Surface Chemistry of CH2I2 on Clean, Hydrogen- and Carbon Monoxide-Covered Co(0001) Surfaces

Fundamental understanding of complex FT synthesis is of great interest. We have employed X-ray photoelectron spectroscopy and temperature-programmed desorption to comparatively investigate CH2I2 adsorption and reactions on clean, hydrogen- and CO-covered Co(0001) surfaces. Surface chemistry of CH2I2 was demonstrated to sensitively depend on available vacant surface sites on Co(0001). Upon adsorption on clean Co(0001) surface at 110 K, CH2I2 undergoes stepwise decomposition reactions to produce carbon adatoms, CH­(a) and CH2(a) species at small coverages, and chemisorbs both dissociatively and molecularly at large coverages. Upon heating, CH2(a) species facilely undergoes surface reactions to produce CH4, C3H6, and C2H4 in gas phase and CH­(a) species on the surface at low temperatures. CH­(a) species undergoes surface reactions to produce CH4 in gas phase and C2H2(a) species on the surface at higher temperatures, and both CH­(a) and C2H2(a) species undergo further surface reactions to produce H2 in gas phase and carbon species on the surface. Coadsorbed H adatoms and CO molecules were found to strongly affect surface chemistry of CH2I2 and the resulting CH x species on Co(0001) via suppressing the decomposition reactions and promoting the carbon–carbon bond coupling reactions. These results add novel insights in fundamental understanding of complex FT synthesis.