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Ethylene dissociation on flat and stepped Ni(111): A combined STM and DFT study

Vang, Ronnie T.; Honkala, Karolina; Dahl, Søren; Vestergaard, Ebbe K.; Schnadt, Joachim LU ; Lægsgaard, Erik; Clausen, Bjarne S.; Nørskov, Jens K. and Besenbacher, Flemming (2006) In Surface Science 600. p.66-77
Abstract
The dissociative adsorption of ethylene (C2H4) on Ni(1 1 1) was studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM studies reveal that ethylene decomposes exclusively at the step edges at room temperature. However, the step edge sites are poisoned by the reaction products and thus only a small brim of decomposed ethylene is formed. At 500 K decomposition on the (1 1 1) facets leads to a continuous growth of carbidic islands, which nucleate along the step edges.



DFT calculations were performed for several intermediate steps in the decomposition of ethylene on both Ni(1 1 1) and the stepped Ni(2 1 1) surface. In general the Ni(2 1 1) surface is found to have a higher... (More)
The dissociative adsorption of ethylene (C2H4) on Ni(1 1 1) was studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM studies reveal that ethylene decomposes exclusively at the step edges at room temperature. However, the step edge sites are poisoned by the reaction products and thus only a small brim of decomposed ethylene is formed. At 500 K decomposition on the (1 1 1) facets leads to a continuous growth of carbidic islands, which nucleate along the step edges.



DFT calculations were performed for several intermediate steps in the decomposition of ethylene on both Ni(1 1 1) and the stepped Ni(2 1 1) surface. In general the Ni(2 1 1) surface is found to have a higher reactivity than the Ni(1 1 1) surface. Furthermore, the calculations show that the influence of step edge atoms is very different for the different reaction pathways. In particular the barrier for dissociation is lowered significantly more than the barrier for dehydrogenation, and this is of great importance for the bond-breaking selectivity of Ni surfaces.



The influence of step edges was also probed by evaporating Ag onto the Ni(1 1 1) surface. STM shows that the room temperature evaporation leads to a step flow growth of Ag islands, and a subsequent annealing at 800 K causes the Ag atoms to completely wet the step edges of Ni(1 1 1). The blocking of the step edges is shown to prevent all decomposition of ethylene at room temperature, whereas the terrace site decomposition at 500 K is confirmed to be unaffected by the Ag atoms.



Finally a high surface area NiAg alloy catalyst supported on MgAl2O4 was synthesized and tested in flow reactor measurements. The NiAg catalyst has a much lower activity for ethane hydrogenolysis than a similar Ni catalyst, which can be rationalized by the STM and DFT results. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Surface Science
volume
600
pages
66 - 77
publisher
Elsevier
external identifiers
  • Scopus:30344446248
ISSN
0039-6028
DOI
10.1016/j.susc.2005.10.006
language
English
LU publication?
yes
id
59321577-a4b0-4f13-826d-7ac9c847547d (old id 631038)
date added to LUP
2007-11-28 15:06:32
date last changed
2016-11-13 04:31:35
@misc{59321577-a4b0-4f13-826d-7ac9c847547d,
  abstract     = {The dissociative adsorption of ethylene (C2H4) on Ni(1 1 1) was studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM studies reveal that ethylene decomposes exclusively at the step edges at room temperature. However, the step edge sites are poisoned by the reaction products and thus only a small brim of decomposed ethylene is formed. At 500 K decomposition on the (1 1 1) facets leads to a continuous growth of carbidic islands, which nucleate along the step edges.<br/><br>
<br/><br>
DFT calculations were performed for several intermediate steps in the decomposition of ethylene on both Ni(1 1 1) and the stepped Ni(2 1 1) surface. In general the Ni(2 1 1) surface is found to have a higher reactivity than the Ni(1 1 1) surface. Furthermore, the calculations show that the influence of step edge atoms is very different for the different reaction pathways. In particular the barrier for dissociation is lowered significantly more than the barrier for dehydrogenation, and this is of great importance for the bond-breaking selectivity of Ni surfaces.<br/><br>
<br/><br>
The influence of step edges was also probed by evaporating Ag onto the Ni(1 1 1) surface. STM shows that the room temperature evaporation leads to a step flow growth of Ag islands, and a subsequent annealing at 800 K causes the Ag atoms to completely wet the step edges of Ni(1 1 1). The blocking of the step edges is shown to prevent all decomposition of ethylene at room temperature, whereas the terrace site decomposition at 500 K is confirmed to be unaffected by the Ag atoms.<br/><br>
<br/><br>
Finally a high surface area NiAg alloy catalyst supported on MgAl2O4 was synthesized and tested in flow reactor measurements. The NiAg catalyst has a much lower activity for ethane hydrogenolysis than a similar Ni catalyst, which can be rationalized by the STM and DFT results.},
  author       = {Vang, Ronnie T. and Honkala, Karolina and Dahl, Søren and Vestergaard, Ebbe K. and Schnadt, Joachim and Lægsgaard, Erik and Clausen, Bjarne S. and Nørskov, Jens K. and Besenbacher, Flemming},
  issn         = {0039-6028},
  language     = {eng},
  pages        = {66--77},
  publisher    = {ARRAY(0x9aead18)},
  series       = {Surface Science},
  title        = {Ethylene dissociation on flat and stepped Ni(111): A combined STM and DFT study},
  url          = {http://dx.doi.org/10.1016/j.susc.2005.10.006},
  volume       = {600},
  year         = {2006},
}