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.