A density functional theory study of the α-olefin selectivity in Fischer–Tropsch synthesis

Jun Cheng, Tao Song, P. Hu, C. Martin Lok, Peter Ellis, Sam French

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

We studied the α-olefin selectivity in Fischer–Tropsch (FT) synthesis using density functional theory (DFT) calculations. We calculated the relevant elementary steps from C2 to C6 species. Our results showed that the barriers of hydrogenation and dehydrogenation reactions were constant with different chain lengths, and the chemisorption energies of α-olefins from DFT calculations also were very similar, except for C2 species. A simple expression of the paraffin/olefin ratio was obtained based on a kinetic model. Combining the expression of the paraffin/olefin ratio and our calculation results, experimental findings are satisfactorily explained. We found that the physical origin of the chain length dependence of paraffin/olefin ratio is the chain length dependence of both the van der Waals interaction between adsorbed α-olefins and metal surfaces and the entropy difference between adsorbed and gaseous α-olefins, and that the greater chemisorption energy of ethylene is the main reason for the abnormal ethane/ethylene ratio.

Original languageEnglish
Pages (from-to)20-28
Number of pages9
JournalJournal of Catalysis
Volume255
Issue number1
Early online date4 Mar 2008
DOIs
Publication statusPublished - 1 Apr 2008

Keywords

  • Fischer-Tropsch
  • DFT
  • Co
  • alpha-olefin selectivity
  • van der Waals
  • entropy
  • catalyzed hydrocarbon synthesis
  • chain growth
  • organosulfur compounds
  • rate coefficients
  • RU(0001) surface
  • CO hydrogenation
  • alpha-olefins
  • mechanism
  • iron
  • RU

Cite this

A density functional theory study of the α-olefin selectivity in Fischer–Tropsch synthesis. / Cheng, Jun; Song, Tao; Hu, P.; Lok, C. Martin; Ellis, Peter; French, Sam.

In: Journal of Catalysis, Vol. 255, No. 1, 01.04.2008, p. 20-28.

Research output: Contribution to journalArticle

Cheng, Jun ; Song, Tao ; Hu, P. ; Lok, C. Martin ; Ellis, Peter ; French, Sam. / A density functional theory study of the α-olefin selectivity in Fischer–Tropsch synthesis. In: Journal of Catalysis. 2008 ; Vol. 255, No. 1. pp. 20-28.
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abstract = "We studied the α-olefin selectivity in Fischer–Tropsch (FT) synthesis using density functional theory (DFT) calculations. We calculated the relevant elementary steps from C2 to C6 species. Our results showed that the barriers of hydrogenation and dehydrogenation reactions were constant with different chain lengths, and the chemisorption energies of α-olefins from DFT calculations also were very similar, except for C2 species. A simple expression of the paraffin/olefin ratio was obtained based on a kinetic model. Combining the expression of the paraffin/olefin ratio and our calculation results, experimental findings are satisfactorily explained. We found that the physical origin of the chain length dependence of paraffin/olefin ratio is the chain length dependence of both the van der Waals interaction between adsorbed α-olefins and metal surfaces and the entropy difference between adsorbed and gaseous α-olefins, and that the greater chemisorption energy of ethylene is the main reason for the abnormal ethane/ethylene ratio.",
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AU - Song, Tao

AU - Hu, P.

AU - Lok, C. Martin

AU - Ellis, Peter

AU - French, Sam

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N2 - We studied the α-olefin selectivity in Fischer–Tropsch (FT) synthesis using density functional theory (DFT) calculations. We calculated the relevant elementary steps from C2 to C6 species. Our results showed that the barriers of hydrogenation and dehydrogenation reactions were constant with different chain lengths, and the chemisorption energies of α-olefins from DFT calculations also were very similar, except for C2 species. A simple expression of the paraffin/olefin ratio was obtained based on a kinetic model. Combining the expression of the paraffin/olefin ratio and our calculation results, experimental findings are satisfactorily explained. We found that the physical origin of the chain length dependence of paraffin/olefin ratio is the chain length dependence of both the van der Waals interaction between adsorbed α-olefins and metal surfaces and the entropy difference between adsorbed and gaseous α-olefins, and that the greater chemisorption energy of ethylene is the main reason for the abnormal ethane/ethylene ratio.

AB - We studied the α-olefin selectivity in Fischer–Tropsch (FT) synthesis using density functional theory (DFT) calculations. We calculated the relevant elementary steps from C2 to C6 species. Our results showed that the barriers of hydrogenation and dehydrogenation reactions were constant with different chain lengths, and the chemisorption energies of α-olefins from DFT calculations also were very similar, except for C2 species. A simple expression of the paraffin/olefin ratio was obtained based on a kinetic model. Combining the expression of the paraffin/olefin ratio and our calculation results, experimental findings are satisfactorily explained. We found that the physical origin of the chain length dependence of paraffin/olefin ratio is the chain length dependence of both the van der Waals interaction between adsorbed α-olefins and metal surfaces and the entropy difference between adsorbed and gaseous α-olefins, and that the greater chemisorption energy of ethylene is the main reason for the abnormal ethane/ethylene ratio.

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KW - chain growth

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KW - rate coefficients

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KW - CO hydrogenation

KW - alpha-olefins

KW - mechanism

KW - iron

KW - RU

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