Quantitative Characterization of Fe/Al 2 O 3 Catalysts. Part II: Reduction,Sulfidation,and CO/Hydrogenation Activity

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 Fe_1-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.