The evolution of Fe5C2 with the carburization of N- and K-modified Fe/Fe3C core-shell catalysts during Fischer-Tropsch synthesis

Iron - based Fischer - Tropsch synthesis (FTS) catalysts with a carbon - encapsulated core - shell structure have been a popular research focus on account of their remarkable performance and stability. Here, in order to explore the effect of K and/or N modification on the structure, evolution, and catalytic performance of Fe/Fe3C based catalysts, we synthesized a graphitic carbon-encapsulated Fe/Fe3C core-shell catalyst via direct pyrolysis of a ferric citrate and electron-donating reagent mixture. The effect of N doping and/or K promotion was studied using a combination of physicochemical methods. Results revealed that one-step pyrolysis and self-assembly of ferric citrate led to in situ redispersed formation of graphitic carbon-encapsulated iron oxides nanoparticles. In situ N doping facilitated reduction/carburization and formation of Fe/Fe3C, similar to K promotion, formed defective-rich surfaces that can enhance CO dissociative adsorption and promote Fe/Fe3C carburization evolution to Fe5C2. The synergy of N and K promoted higher Fe5C2/Fe3C active sites on the obtained K-Fe/NC catalysts, resulting in higher olefin/paraffin (O/P) ratios and chain growth capacity. Furthermore, there were no drastic changes in the catalyst morphology and performance during 120 h time on stream.