Quantitative Characterization of Fe/Al2O3 Catalysts. Part II: Reduction, Sulfidation, and CO/Hydrogenation Activity

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Abstract
ESCA, Mössbauer spectroscopy, XRD, and CO chemisorption were used to study the reduction and sulfidation reactions of a series of 1 to 24 wt % Fe/Al2O3 catalysts. The speciation and particle size of the active phase were correlated with CO hydrogenation activity data. Two phases were previously identified in all oxidic catalysts: Fe2O3 and Fe+3 in solid solution with the alumina support. The Fe2O3 phase was found to reduce to Fe0 and sulfide to Fe1- xS. For the reduced and sulfided catalysts, Mössbauer was able to identify two iron species which were detected as a single solid solution species in the oxidic catalysts. The two species were found to differ by their location in the alumina support. One species is incorporated within the alumina matrix [Fe+2(A)] and the other species [Fe+2(B)] is present at the alumina surface. Both ESCA and CO chemisorption indicate that the Fe particle size increases with increasing iron loading. The turnover frequency (TOF) for CO hydrogenation appears to be a function of the extent of reduction and particle size of the metallic iron phase.