Study on the adsorption and reactions of FCH₂CH₂OH and ClCH₂CH₂OH on Ni(111): Effects of halogen and preadsorbed oxygen

Temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS) have been employed to investigate the reactions of FCH₂CH₂OH and ClCH₂CH₂OH on Ni(111) and oxygen-precovered Ni(111) (O/Ni(111)). In the chemical process of FCH₂CH₂OH on Ni(111), only FCH₂CH₂O- is found to be the stable reaction intermediate, which starts to appear at ∼190 K. At low coverages, this intermediate decomposes into H₂ and CO. Additional C ₂H₄ (219 K) is generated at higher exposures. On Ni(111) at 200 K, ClCH₂CH₂OH mainly dissociates to form ClCH ₂CH₂O- and -CH₂CH₂O- at lower exposures, with H₂ and CO as the final products, while ClCH ₂CH₂O- becomes predominant at higher exposures and is responsible for the extra C₂H₄ channel of 218 K. C ₂H₄ is also generated at 161 and 174 K as the exposure is increased to render multilayer adsorption. Due to the competition in the scission of the carbon-halogen and carbon-hydrogen bonds, ClCH ₂CH₂OH has better reactivity toward C₂H ₄ formation than FCH₂CH₂OH. No -CH ₂CH₂OH is found in the decomposition of FCH ₂CH₂OH and ClCH₂CH₂OH on Ni(111), which is the intermediate in the reaction of ICH₂CH₂OH on Ni(100) and Pd(111). The presence of preadsorbed oxygen can enhance the ethylene formation at low coverages of FCH₂CH₂OH and ClCH ₂CH₂OH. At higher coverages, additional acetaldehyde is formed in the reaction of FCH₂CH₂OH, in contrast to the ethylene oxide from ClCH₂CH₂OH.