4 research outputs found
Adsorption and Reactions of ICH<sub>2</sub>CN on Cu(100) and O/Cu(100)
Monitoring
surface species and their bonding structures in link
to specific chemical processes has long been an active, important
subject in heterogeneous catalysis. In this article, with employment
of temperature-programmed reaction/desorption, reflection–absorption
infrared spectroscopy, Auger electron spectroscopy, and X-ray photoelectron
spectroscopy in combination with density functional theory computation,
we present three CH<sub>3</sub>CN formation channels from reaction
of CH<sub>2</sub>CN generated by ICH<sub>2</sub>CN dissociative adsorption
on Cu(100) and first spectroscopic evidence for CHCN on single crystal
surfaces. The CH<sub>3</sub>CN formation mechanisms are dependent
on CH<sub>2</sub>CN adsorption geometries. At lower coverages, CH<sub>2</sub>CN is adsorbed with the C–C–N approximately
parallel to the surface. Reaction of these adsorbates produces CH<sub>3</sub>CN via first- and second-order kinetics, with the largest
desorption rates occurring at 213 K and ∼400 K, respectively.
At or near a saturated first-layer coverage, decomposition of ICH<sub>2</sub>CN forms C-bonded CH<sub>2</sub>CN (−CH<sub>2</sub>CN), which then transforms to N-bonded −NCCH<sub>2</sub> with
tilted orientation. Disproportionation of the −NCCH<sub>2</sub> generates CH<sub>3</sub>CN at ∼324 K. Thermal products of
H<sub>2</sub>, HCN and (CN)<sub>2</sub> evolving at higher temperatures
are originated from the CHCN dissociation. On oxygen-precovered Cu(100),
reaction of CH<sub>2</sub>CN forms new surface intermediates of vertical
−NCO and −CCO, in addition to perturbed CH<sub>3</sub>CN desorption. In the conditions studied, formation of H<sub>2</sub>, HCN, and (CN)<sub>2</sub> is terminated due to the presence of
preadsorbed O. −NCO and −CCO on O/Cu dissociate at ∼525
and 610 K, respectively, into CO and CO<sub>2</sub>
Adsorption and Reactions of ICH<sub>2</sub>CN on Cu(100) and O/Cu(100)
Monitoring
surface species and their bonding structures in link
to specific chemical processes has long been an active, important
subject in heterogeneous catalysis. In this article, with employment
of temperature-programmed reaction/desorption, reflection–absorption
infrared spectroscopy, Auger electron spectroscopy, and X-ray photoelectron
spectroscopy in combination with density functional theory computation,
we present three CH<sub>3</sub>CN formation channels from reaction
of CH<sub>2</sub>CN generated by ICH<sub>2</sub>CN dissociative adsorption
on Cu(100) and first spectroscopic evidence for CHCN on single crystal
surfaces. The CH<sub>3</sub>CN formation mechanisms are dependent
on CH<sub>2</sub>CN adsorption geometries. At lower coverages, CH<sub>2</sub>CN is adsorbed with the C–C–N approximately
parallel to the surface. Reaction of these adsorbates produces CH<sub>3</sub>CN via first- and second-order kinetics, with the largest
desorption rates occurring at 213 K and ∼400 K, respectively.
At or near a saturated first-layer coverage, decomposition of ICH<sub>2</sub>CN forms C-bonded CH<sub>2</sub>CN (−CH<sub>2</sub>CN), which then transforms to N-bonded −NCCH<sub>2</sub> with
tilted orientation. Disproportionation of the −NCCH<sub>2</sub> generates CH<sub>3</sub>CN at ∼324 K. Thermal products of
H<sub>2</sub>, HCN and (CN)<sub>2</sub> evolving at higher temperatures
are originated from the CHCN dissociation. On oxygen-precovered Cu(100),
reaction of CH<sub>2</sub>CN forms new surface intermediates of vertical
−NCO and −CCO, in addition to perturbed CH<sub>3</sub>CN desorption. In the conditions studied, formation of H<sub>2</sub>, HCN, and (CN)<sub>2</sub> is terminated due to the presence of
preadsorbed O. −NCO and −CCO on O/Cu dissociate at ∼525
and 610 K, respectively, into CO and CO<sub>2</sub>
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
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
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
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