Molecular simulation of temperature-programmed desorption

Kristen A. Fichthorn, Kelly E. Becker, Radu A. Miron

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

We use accelerated molecular dynamics to probe the thermal desorption of n-alkanes from the Au(1 1 1) and C(0 0 0 1) surfaces. Studying an alkane series ranging from CH4 to C16H34, we find that the desorption prefactor increases with increasing chain length for the short chains until a certain chain length is reached when it becomes essentially constant and independent of chain length. We can understand the dependence of the preexponential factor on alkane chain length in terms of conformational changes within the alkane molecules. For the shorter molecules, the desorption temperatures probed in experimental temperature-programmed desorption studies lie below those for which torsional motion is activated. Thus, the short alkanes can be treated as rigid rods, and the loss in translational and rotational entropy upon adsorption leads to a preexponential factor that increases with increasing chain length. As the alkane chain length increases, the binding energy and the experimental desorption temperatures also increase. Thus, torsional motion is activated to an extent that increases with increasing chain length. This torsional activation increases the entropy of adsorption and counteracts the entropy decrease due to a loss of translation and rotation. This leads to a virtually constant prefactor for sufficiently long chains. Our findings are consistent with experimental data for the thermal desorption of alkanes from the Au(1 1 1), Pt(1 1 1), MgO(1 0 0) and C(0 0 0 1) surfaces.

Original languageEnglish (US)
Pages (from-to)71-76
Number of pages6
JournalCatalysis Today
Volume123
Issue number1-4
DOIs
StatePublished - May 30 2007

Fingerprint

Alkanes
Temperature programmed desorption
Chain length
Paraffins
Desorption
Thermal desorption
Entropy
Adsorption
Molecules
Binding energy
Molecular dynamics
Chemical activation
Temperature

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

Cite this

Fichthorn, Kristen A. ; Becker, Kelly E. ; Miron, Radu A. / Molecular simulation of temperature-programmed desorption. In: Catalysis Today. 2007 ; Vol. 123, No. 1-4. pp. 71-76.
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Molecular simulation of temperature-programmed desorption. / Fichthorn, Kristen A.; Becker, Kelly E.; Miron, Radu A.

In: Catalysis Today, Vol. 123, No. 1-4, 30.05.2007, p. 71-76.

Research output: Contribution to journalArticle

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