Abstract

Temperature-programmed surface reaction (TPSR) in hydrogen was used to differentiate up to seven different carbon types on iron Fischer-Tropsch (FT) catalysts. Both K-free and K-promoted catalysts were pretreated in 1:1 H 2 /CO syngas for 6–18 hours to achieve well-developed carbon surface coverages. Reaction temperatures of 215 and 245°C were selected, to provide conditions of steady-state activity (no apparent deactivation) and relatively rapid deactivation. Possible carbon forms in the catalyst include (1&2) atomic carbon on planar and edge sites, (3) Hägg carbide, (4) epsilon-carbide, (5) amorphous carbon and (6) moderately- and (7) well-ordered graphitic carbons. Deactivation of iron catalysts in FT synthesis under the conditions of this study is associated with (1) transformation of high activity Hägg-carbide to less active epsilon-carbide and (2) formation of a highly ordered graphite on the surface of the catalyst.

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