Study on
the Adsorption and Reactions of FCH<sub>2</sub>CH<sub>2</sub>OH and
ClCH<sub>2</sub>CH<sub>2</sub>OH on Ni(111):
Effects of Halogen and Preadsorbed Oxygen
- Publication date
- Publisher
Abstract
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 FCH<sub>2</sub>CH<sub>2</sub>OH and ClCH<sub>2</sub>CH<sub>2</sub>OH on Ni(111)
and oxygen-precovered Ni(111) (O/Ni(111)). In the chemical process
of FCH<sub>2</sub>CH<sub>2</sub>OH on Ni(111), only FCH<sub>2</sub>CH<sub>2</sub>O- is found to be the stable reaction intermediate,
which starts to appear at ∼190 K. At low coverages, this intermediate
decomposes into H<sub>2</sub> and CO. Additional C<sub>2</sub>H<sub>4</sub> (219 K) is generated at higher exposures. On Ni(111) at 200
K, ClCH<sub>2</sub>CH<sub>2</sub>OH mainly dissociates to form ClCH<sub>2</sub>CH<sub>2</sub>O- and -CH<sub>2</sub>CH<sub>2</sub>O- at lower
exposures, with H<sub>2</sub> and CO as the final products, while
ClCH<sub>2</sub>CH<sub>2</sub>O- becomes predominant at higher exposures
and is responsible for the extra C<sub>2</sub>H<sub>4</sub> channel
of 218 K. C<sub>2</sub>H<sub>4</sub> 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<sub>2</sub>CH<sub>2</sub>OH
has better reactivity toward C<sub>2</sub>H<sub>4</sub> formation
than FCH<sub>2</sub>CH<sub>2</sub>OH. No -CH<sub>2</sub>CH<sub>2</sub>OH is found in the decomposition of FCH<sub>2</sub>CH<sub>2</sub>OH and ClCH<sub>2</sub>CH<sub>2</sub>OH on Ni(111), which is the
intermediate in the reaction of ICH<sub>2</sub>CH<sub>2</sub>OH on
Ni(100) and Pd(111). The presence of preadsorbed oxygen can enhance
the ethylene formation at low coverages of FCH<sub>2</sub>CH<sub>2</sub>OH and ClCH<sub>2</sub>CH<sub>2</sub>OH. At higher coverages, additional
acetaldehyde is formed in the reaction of FCH<sub>2</sub>CH<sub>2</sub>OH, in contrast to the ethylene oxide from ClCH<sub>2</sub>CH<sub>2</sub>OH