Effect of the promoters on oxidation behavior of Fe-based Fischer-Tropsch catalyst: Deciphering the role of H₂O

The effect of carburization and reduction degree on H₂O oxidation behaviour for the iron carbides in Fe-based FTS catalyst were firstly investigated using a combination method including X-ray diffraction (XRD), Raman and temperature-programmed-hydrogenation (TPH). The relationship between carbon species transformation and H₂O oxidation behaviour of iron carbides was investigated simultaneously. Based on these observations, the influence of typical promoters like K and SiO₂ on the structure and H₂O oxidation behaviour of Fe-based FTS catalysts was further studied. The results indicated that, for the iron catalyst, the stability of iron carbides against H₂O oxidation was increased with the increase of iron carbides content, and the H₂O oxidation process led to the formation of more graphitic carbon. The carburization ability was effectively enhanced when certain amount of K promoter was incorporated. Addition of K into Fe-based FTS catalyst increased the number of graphitic carbons, which increased the stability of iron carbides toward H₂O oxidation ultimately. It was also found that promotion of SiO₂ greatly degraded the carburization degree of the catalyst, while their tendency to be oxidized to form Fe₃O₄ in the H₂O atmosphere was obviously hindered.