Unravelling the formation of Fe2SiO4 on Fischer-Tropsch Fe/SiO2 catalyst

Fe-SiO2 interaction is a critical issue in the study of Fischer-Tropsch Fe/SiO2 catalyst. It has been advanced that the formation of Fe-O-Si bond is related to Fe-SiO2 interaction and responsible for dispersing iron particles and stabilizing active phases. This work formulates studying the relationship and interconversion between Fe-O-Si bond and Fe2SiO4 phase, and further concludes that Fe2SiO4 is another form of Fe-SiO2 interaction. A well mixing of Fe-O and Si-O domains in the catalyst precursor benefits the distribution of extensive Fe-O-Si bond, which in turn facilitates the formation of Fe2SiO4 during the catalyst reduction process. High ramp rate and diluted H-2 favor the transition of discrete Fe-O-Si to Fe2SiO4 kinetically and thermodynamically, respectively. During the transition, amorphous Fe2SiO4 initially forms before undergoing a rapid crystallization process, at ca. 560 +/- 10 degrees C, to transform to large crystals detectable by XRD. In addition, the amorphous nature of Fe2SiO4 requires the combination of characterization techniques capable of detecting short-range ordered structures, e.g., XAFS, MES, and magnetometer.