Turnover Rate, Reaction Order, and Elementary Steps for the Hydrodechlorination of Chlorofluorocarbon Compounds on Palladium Catalysts

C. D. Thompson, Robert Martin Rioux, Jr., N. Chen, F. H. Ribeiro

Research output: Contribution to journalArticle

58 Citations (Scopus)

Abstract

The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H 2 , and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H 2 , gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF 3 -CF 2 Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF 3 -CFClH), 1,1-dichlorotetrafluoroethane (CF 3 -CFCl 2 ), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF 3 -CCl 3 ).

Original languageEnglish (US)
Pages (from-to)3067-3077
Number of pages11
JournalJournal of Physical Chemistry B
Volume104
Issue number14
DOIs
StatePublished - Apr 13 2000

Fingerprint

Chlorofluorocarbons
chlorofluorocarbons
Palladium
Reaction rates
palladium
Chlorine
reaction kinetics
Gases
catalysts
Catalysts
norflurane
vapor phases
Carbon
products
Atoms
Hydrogen
chlorine
chlorine compounds
Catalyst supports
Metal foil

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

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title = "Turnover Rate, Reaction Order, and Elementary Steps for the Hydrodechlorination of Chlorofluorocarbon Compounds on Palladium Catalysts",
abstract = "The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H 2 , and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H 2 , gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF 3 -CF 2 Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF 3 -CFClH), 1,1-dichlorotetrafluoroethane (CF 3 -CFCl 2 ), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF 3 -CCl 3 ).",
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Turnover Rate, Reaction Order, and Elementary Steps for the Hydrodechlorination of Chlorofluorocarbon Compounds on Palladium Catalysts. / Thompson, C. D.; Rioux, Jr., Robert Martin; Chen, N.; Ribeiro, F. H.

In: Journal of Physical Chemistry B, Vol. 104, No. 14, 13.04.2000, p. 3067-3077.

Research output: Contribution to journalArticle

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T1 - Turnover Rate, Reaction Order, and Elementary Steps for the Hydrodechlorination of Chlorofluorocarbon Compounds on Palladium Catalysts

AU - Thompson, C. D.

AU - Rioux, Jr., Robert Martin

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AU - Ribeiro, F. H.

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Y1 - 2000/4/13

N2 - The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H 2 , and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H 2 , gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF 3 -CF 2 Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF 3 -CFClH), 1,1-dichlorotetrafluoroethane (CF 3 -CFCl 2 ), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF 3 -CCl 3 ).

AB - The rates of hydrodechlorination catalyzed by Pd supported on carbon for four chlorofluorocarbons spanned a range of 7 orders of magnitude. The rates scaled up to the bond strength of the carbon-chlorine bond for the gas-phase reactant. This finding demonstrates that the rate-determining step involves the scission of the C-Cl bond and suggests, through Polanyi and linear free-energy relationships, that rates for other compounds can be estimated if the C-Cl bond strength is known. The reaction orders for the most abundant products are approximately first-order for the chlorine-containing compound, half-order in H 2 , and inverse first-order in HCl. The reaction steps consistent with these orders include a rate-determining step involving the adsorption of the chlorofluorocarbon to a single site (which could be a single surface palladium atom) and equilibrated steps between gas-phase H 2 , gas-phase HCl, and adsorbed hydrogen and chlorine atoms. The rates on the supported catalysts are comparable to the ones reported before on a Pd foil, indicating that the support does not play a role in the reaction. The product distribution is independent of conversion, implying that the various products are formed from a single visit of the reactant on the surface and not from readsorption of gas-phase products. The four compounds studied were chloropentafluoroethane (CF 3 -CF 2 Cl), 2-chloro-1,1,1,2-tetrafluoroethane (CF 3 -CFClH), 1,1-dichlorotetrafluoroethane (CF 3 -CFCl 2 ), and 1,1,1-trichloro-2,2,2-trifluoroethane (CF 3 -CCl 3 ).

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