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 similar to 190 K. At low coverages, this intermediate decomposes into H-2 and CO. Additional C2H4 (219 K) is generated at higher exposures. On Ni(111) at 200 K, ClCH2CH2OH mainly dissociates to form ClCH2CH2O- and -CH2CH2O- at lower exposures, with H-2 and CO as the final products, while ClCH2CH2O- becomes predominant at higher exposures and is responsible for the extra C2H4 channel of 218 K. C2H4 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, ClCH2CH2OH has better reactivity toward C2H4 formation than FCH2CH2OH. No -CH2CH2OH is found in the decomposition of FCH2CH2OH 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 ClCH2CH2OH. At higher coverages, additional acetaldehyde is formed in the reaction of FCH2CH2OH, in contrast to the ethylene oxide from ClCH2CH2OH.