Effect of pretreatment on precipitated Fe–Mo Fischer–Tropsch catalysts: Morphology, carburization, and catalytic performance

Unpromoted and Mo-promoted iron catalyst precursors (100Fe, 100Fe5Mo, and 100Fe10Mo) were prepared by a coprecipitation method, and were subsequently characterized by laser Raman spectroscopy, Mössbauer spectroscopy, at 298 K and 20 K, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The effect of pretreatment with H2, CO, and H2/CO = 0.67 at 280 and 350 °C was investigated. Specifically, the reduction/carburization behaviors and the evolution of iron phases and Mo species in the catalysts during the pretreatment and during the FTS reaction were extensively studied. During pretreatment, the catalyst structure experienced an extensive restructuring process that was strongly dependent on the pretreatment protocols and Mo promoter loading levels. The microscopic information confirmed this effect on the iron active-site dispersion and the catalytic performance.

Pretreatment induced migrations of Mo affect the size distribution and local environments of iron active sites.Figure optionsDownload high-quality image (232 K)Download as PowerPoint slideHighlights
► Systematic pretreatment study of Fe and Fe–Mo FT catalysts.
► Evolution of Fe and Mo phases in the catalysts during activation and FTS reaction.
► Activation-induced shift in promotional effects of Mo affected the size of active Fe sites.
► The dispersion effect of Mo favored a high catalyst activity.
► The epitaxial crystal growth effect of Mo showed positive effect on catalyst selectivity.