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Title: The importance of olefin readsorption and H[sub 2]/CO reactant ratio for hydrocarbon chain growth on ruthenium catalysts

Abstract

The synthesis of high molecular weight hydrocarbons on Ru catalysts requires the readsorption of primary [alpha]-olefin products. Such a readsorption step initiates a surface chain by reversing the [beta]-hydrogen abstraction reactions: the chain termination step that forms an [alpha]-olefin. On Ru catalysts, 60 to 90% of C[sub 21] + products requires at least one readsorption event. These readsorption steps become increasingly important as chain size increases. This occurs because the diffusive removal of [alpha]-olefins from catalyst particles slows down significantly with increasing molecular size leading to long intraparticle residence times that favor secondary readsorption reactions. Chain growth probability and paraffin content therefore increase with molecular size. As a result, carbon number distributions do not obey simple Flory kinetics, an observation previously attributed to multiple chain growth sites and to the higher solubility of larger hydrocarbons in Fischer-Tropsch liquids. At low H[sub 2]/CO reactant ratios, where termination to olefins should be favored, large chains terminate only as paraffins. This again reflects the importance of diffusion-enhanced olefin readsorption which not only dominates bed residence time effects for large hydrocarbons but also weakens the effects of changes in reactant concentration. High H[sub 2]/CO reactant ratios lead to higher concentrations of hydrogen adatoms onmore » Ru surfaces and thus favor chain termination to paraffins by hydrogen addition steps. Consequently, the contribution of olefin readsorption to chain growth and product molecular weight decreases markedly with increasing H[sub 2]/CO ratio. 22 refs., 9 figs., 2 tabs.« less

Authors:
;  [1]
  1. Exxon Research and Engineering Co., Annandale, NJ (United States)
Publication Date:
OSTI Identifier:
6236403
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis; (United States)
Additional Journal Information:
Journal Volume: 139:2; Journal ID: ISSN 0021-9517
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALKENES; POLYMERIZATION; RUTHENIUM COMPOUNDS; CATALYTIC EFFECTS; CARBON MONOXIDE; CATALYSTS; CHEMICAL PREPARATION; CHEMICAL REACTION KINETICS; DIFFUSION; HETEROGENEOUS CATALYSIS; HYDROGEN; MOLECULAR WEIGHT; ORGANIC POLYMERS; PARAFFIN; SORPTIVE PROPERTIES; ALKANES; CARBON COMPOUNDS; CARBON OXIDES; CATALYSIS; CHALCOGENIDES; CHEMICAL REACTIONS; ELEMENTS; HYDROCARBONS; KINETICS; NONMETALS; ORGANIC COMPOUNDS; OTHER ORGANIC COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; POLYMERS; REACTION KINETICS; REFRACTORY METAL COMPOUNDS; SURFACE PROPERTIES; SYNTHESIS; TRANSITION ELEMENT COMPOUNDS; WAXES; 400201* - Chemical & Physicochemical Properties

Citation Formats

Madon, R J, and Iglesia, E. The importance of olefin readsorption and H[sub 2]/CO reactant ratio for hydrocarbon chain growth on ruthenium catalysts. United States: N. p., 1993. Web. doi:10.1006/jcat.1993.1051.
Madon, R J, & Iglesia, E. The importance of olefin readsorption and H[sub 2]/CO reactant ratio for hydrocarbon chain growth on ruthenium catalysts. United States. https://doi.org/10.1006/jcat.1993.1051
Madon, R J, and Iglesia, E. Mon . "The importance of olefin readsorption and H[sub 2]/CO reactant ratio for hydrocarbon chain growth on ruthenium catalysts". United States. https://doi.org/10.1006/jcat.1993.1051.
@article{osti_6236403,
title = {The importance of olefin readsorption and H[sub 2]/CO reactant ratio for hydrocarbon chain growth on ruthenium catalysts},
author = {Madon, R J and Iglesia, E},
abstractNote = {The synthesis of high molecular weight hydrocarbons on Ru catalysts requires the readsorption of primary [alpha]-olefin products. Such a readsorption step initiates a surface chain by reversing the [beta]-hydrogen abstraction reactions: the chain termination step that forms an [alpha]-olefin. On Ru catalysts, 60 to 90% of C[sub 21] + products requires at least one readsorption event. These readsorption steps become increasingly important as chain size increases. This occurs because the diffusive removal of [alpha]-olefins from catalyst particles slows down significantly with increasing molecular size leading to long intraparticle residence times that favor secondary readsorption reactions. Chain growth probability and paraffin content therefore increase with molecular size. As a result, carbon number distributions do not obey simple Flory kinetics, an observation previously attributed to multiple chain growth sites and to the higher solubility of larger hydrocarbons in Fischer-Tropsch liquids. At low H[sub 2]/CO reactant ratios, where termination to olefins should be favored, large chains terminate only as paraffins. This again reflects the importance of diffusion-enhanced olefin readsorption which not only dominates bed residence time effects for large hydrocarbons but also weakens the effects of changes in reactant concentration. High H[sub 2]/CO reactant ratios lead to higher concentrations of hydrogen adatoms on Ru surfaces and thus favor chain termination to paraffins by hydrogen addition steps. Consequently, the contribution of olefin readsorption to chain growth and product molecular weight decreases markedly with increasing H[sub 2]/CO ratio. 22 refs., 9 figs., 2 tabs.},
doi = {10.1006/jcat.1993.1051},
url = {https://www.osti.gov/biblio/6236403}, journal = {Journal of Catalysis; (United States)},
issn = {0021-9517},
number = ,
volume = 139:2,
place = {United States},
year = {1993},
month = {2}
}