Effect of Rare-Earth Promoters on Precipitated Iron-Based Catalysts for Fischer–Tropsch Synthesis

FeMn catalysts that were either unpromoted or promoted by five rare-earth metals (La, Ce, Nd, Sm, and Eu) for Fischer–Tropsch synthesis (FTS) were prepared by the coprecipitation method and characterized by XRD, N2 adsorption, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, CO-temperature-programmed desorption (CO-TPD), H2-TPD, CO2-TPD, and Mössbauer spectroscopy (MES). The results showed that all five rare-earth metals could promote the performance of the catalysts, whereas the Nd promoter showed a unique promoting effect. The CO-TPD and MES results revealed that the sample FeMnNd had the highest CO chemisorption ability and formed the most Fe5C2 in the FTS reaction. Moreover, the sample FeMnNd achieved the strongest surface alkalinity and the weakest chemical adsorption of hydrogen, as confirmed by CO2-TPD and H2-TPD, respectively. Based on the results of FTS performance, the FeMnNd catalyst exhibited the highest CO conversion of 74.9%, a C2–4= selectivity of 36.0%, an O/P ratio of 3.96, and the lowest C5+ selectivity of 34.3%.