Understanding trichloroethylene chemisorption to iron surfaces using density functional theory

Nianliu Zhang, Jing Luo, Paul Blowers, James Farrell

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

This research investigated the thermodynamic favorability and resulting structures for chemical adsorption of trichloroethylene (TCE) to metallic iron using periodic density functional theory (DFT). Three initial TCE positions having the plane defined by HCC atoms parallel to the iron surface resulted in formation of three different chemisorption complexes between carbon atoms in TCE and the iron surface. The Cl-bridge initial configuration with the HCC plane of TCE perpendicular to the iron surface did not result in C-Fe bond formation. The most energetically favorable complex formed at the C-bridge site where the initial configuration had the C=C bond in TCE at a bridge site between adjacent iron atoms. In the C-bridge complex, one C atom formed two σ bonds to different Fe atoms, while the second C atom formed a σ bond with a second Fe atom. Surface complexation at the C-bridge site resulted in scission of all three C-Cl bonds and also resulted in a shortening of the C=C bond to a distance intermediate between a double and a triple bond. Initial configurations with the C=C bond adsorbed at top or hollow sites on the iron surface resulted in formation of C-Fe σ bonds between a single C and two adjacent Fe atoms, and the scission of only two C-Cl bonds. Bond angles and bond lengths indicated that there were no changes in bond order of the C=C bond for top and hollow adsorption. Chemisorption at the C-bridge site had an activation energy of 49 kJ/mol and an early transition state where all three C-Cl bonds were activated. The early transition state and the loss of all three Cl atoms upon chemisorption are consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. The absence of chemisorption and scission of only two C-Cl bonds atthe Cl-bridge site is consistent with experimental observations that trace amounts of chloroacetylene may also be produced from reactions of TCE with iron.

Original languageEnglish (US)
Pages (from-to)2015-2020
Number of pages6
JournalEnvironmental Science and Technology
Volume42
Issue number6
DOIs
StatePublished - Mar 15 2008

Fingerprint

Trichloroethylene
Chemisorption
trichloroethylene
Density functional theory
Iron
iron
Atoms
adsorption
chemisorption
Adsorption
Dechlorination
dechlorination
complexation
Bond length
activation energy
Complexation
thermodynamics
Carbon
Activation energy
Thermodynamics

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Science(all)
  • Environmental Chemistry

Cite this

Understanding trichloroethylene chemisorption to iron surfaces using density functional theory. / Zhang, Nianliu; Luo, Jing; Blowers, Paul; Farrell, James.

In: Environmental Science and Technology, Vol. 42, No. 6, 15.03.2008, p. 2015-2020.

Research output: Contribution to journalArticle

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abstract = "This research investigated the thermodynamic favorability and resulting structures for chemical adsorption of trichloroethylene (TCE) to metallic iron using periodic density functional theory (DFT). Three initial TCE positions having the plane defined by HCC atoms parallel to the iron surface resulted in formation of three different chemisorption complexes between carbon atoms in TCE and the iron surface. The Cl-bridge initial configuration with the HCC plane of TCE perpendicular to the iron surface did not result in C-Fe bond formation. The most energetically favorable complex formed at the C-bridge site where the initial configuration had the C=C bond in TCE at a bridge site between adjacent iron atoms. In the C-bridge complex, one C atom formed two σ bonds to different Fe atoms, while the second C atom formed a σ bond with a second Fe atom. Surface complexation at the C-bridge site resulted in scission of all three C-Cl bonds and also resulted in a shortening of the C=C bond to a distance intermediate between a double and a triple bond. Initial configurations with the C=C bond adsorbed at top or hollow sites on the iron surface resulted in formation of C-Fe σ bonds between a single C and two adjacent Fe atoms, and the scission of only two C-Cl bonds. Bond angles and bond lengths indicated that there were no changes in bond order of the C=C bond for top and hollow adsorption. Chemisorption at the C-bridge site had an activation energy of 49 kJ/mol and an early transition state where all three C-Cl bonds were activated. The early transition state and the loss of all three Cl atoms upon chemisorption are consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. The absence of chemisorption and scission of only two C-Cl bonds atthe Cl-bridge site is consistent with experimental observations that trace amounts of chloroacetylene may also be produced from reactions of TCE with iron.",
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