Carbonaceous surface species and bulk iron carbides formed under realistic Fischer-Tropsch synthesis (FTS) conditions on moderately dispersed, active silica-supported iron catalysts (Fe/SiO2, FePt/SiO2, and FePtK/SiO2) were characterized. Bulk iron phase compositions were determined by Mössbauer spectroscopy and phase transformations of carbonaceous species during pretreatment with CO, H2, or H2/CO and following reaction were characterized using temperature-programmed hydrogenation (TPH). Isothermal transient rates of FTS were also measured for catalysts after different pretreatments. Six surface and bulk carbonaceous species were quantitatively identified from combined TPH and Mössbauer spectra of the FePtK catalyst. They include, in order of decreasing reactivity, (a) adsorbed, atomic carbon; (b) amorphous, lightly polymerized hydrocarbon or carbon surface species; (c) bulk epsilon' and chi carbides (Fe(2.2)C and Fe(2.5)C); and (d) disordered and moderately ordered graphitic surface carbons. A correlation between the amount of reactive alpha-carbon (C(alpha)) and initial catalytic activity was established. The method of Li et al. for measuring irreversible chemisorption of CO does not appear to provide quantitative measurements of active site densities on silica-supported iron. Models, based on this and previous work, are proposed for iron phase and carbon phase transformations in silica-supported iron during pretreatment, FTS, and postreaction passivation/oxidation.

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[reaction: see text] Oxidized bis(indolyl)methane, 1, a simple chromophore containing an acidic H-bond donor moiety and a basic H-bond acceptor moiety, can act as a selective colorimetric sensor either for F(-) in aprotic solvent or for HSO(4)(-) and weak acidic species in water-containing medium. The deprotonation/protonation of oxidized bis(indolyl)methane 1 is responsible for the dramatic color change.