Effects of Lewis acidity of metal oxide promoters on the activity and selectivity of Co-based Fischer–Tropsch synthesis catalysts [electronic resource].
- Published
- Washington, D.C. : United States. Dept. of Energy. Office of Basic Energy Sciences, 2016.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy - Physical Description
- pages 250-264 : digital, PDF file
- Additional Creators
- Lawrence Berkeley National Laboratory, United States. Department of Energy. Office of Basic Energy Sciences, and United States. Department of Energy. Office of Scientific and Technical Information
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- Summary
- Metal oxides of Ce, Gd, La, Mn, and Zr were investigated as promoters for improving the activity and selectivity of Co-based FTS catalysts. The extent to which these promoters decrease the selectivity toward CH 4 and increase the selectivity toward C 5+ hydrocarbons was found to depend on both the loading and the composition of the oxide promoter. Elemental mapping by STEM-EDS revealed that the propensity for a given metal oxide to associate with Co affects the sensitivity of the product distribution to changes in promoter loading. For all promoters, a sufficiently high loading resulted in the product distributions becoming insensitive to further increases in promoter loading, very likely due to the formation of a half monolayer of promoter oxide over the Co surface. Simulations suggest that the fraction of Co active sites that are adjacent to the promoter moieties approaches unity at this degree of coverage. The oxidation state of the promoter metal cation under reaction conditions, determined by in situ XANES measurements, was used to calculate relative Lewis acidity of the promoter metal cation. We found a strong positive correlation between the C 5+ product selectivity and the Lewis acidity of the promoter metal cations, suggesting that the promotional effects are a consequence of Lewis acid-base interactions between the reaction intermediates and the promoter metal cations. Rate data obtained at different pressures were used to estimate the apparent rate coefficient and the CO adsorption constant appearing in the Langmuir-Hinshelwood expression that describes the CO consumption kinetics for both unpromoted and the metal oxide-promoted catalysts. Both parameters exhibited positive correlations with the promoter Lewis acidity. Our results are consistent with the hypothesis that the metal cations of the promoter act as Lewis acids that interact with the O atom of adsorbed CO to facilitate CO adsorption and dissociation.
- Report Numbers
- E 1.99:1416911
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- Note
- Published through SciTech Connect.
03/31/2016.
"ark:/13030/qt2m00b6w0"
Journal of Catalysis 338 C ISSN 0021-9517 AM
Gregory R. Johnson; Alexis T. Bell. - Funding Information
- AC02-05CH11231
AC02-06CH11357
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