Abstract: Phase transformation, especially the state of iron, in the Cu-Fe-based catalyst during CO hydrogenation was investigated byX-raydiffraction, Mssbauer spectroscopy,X-rayphotoelectron spectroscopy, and laser Raman spectroscopy. Fe2O3 transformed into a mixture of Fe3O4 and χ-Fe5C2 upon syngas pretreatment at 300 ℃, and the percentage of χ-Fe5C2 went through a maximum during the reaction. The exposure of the reduced catalyst to the reaction conditions clearly influenced its morphology. However, no clear carburization of iron was observed on the surface of the reduced catalyst. The obvious discrepancy was due to the unique reduction characteristic of iron, leading to the enrichment of zinc and manganese atoms on the surface. Instead, iron atoms were enriched on the surface during the CO hydrogenation, which was resulted from the change of oxidation-reduction properties. After reduction, some free carbon deposited on the catalyst surface, and their graphitization took place when the reaction was carried out at 220 ℃ and was enhanced with increasing reaction temperature. This process significantly weakened the synergistic effect between copper and iron and therefore restrained the chain growth ability of the Cu-Fe-based catalyst.

Key words: higher alcohol synthesis, copper-iron catalyst, phase transformation, carbon monoxide, hydrogenation