摘要
In this combined in situ XAFS, DRIFTS, and Mossbauer study, we elucidate the changes in structural, electronic, and local environments of Fe during pyrolysis of the metal organic framework Fe-BTC toward highly active and stable Fischer-Tropsch synthesis (FTS) catalysts (Fe@C). Fe-BTC framework decomposition is characterized by decarboxylation of its trimesic acid linker, generating a carbon matrix around Fe nanoparticles. Pyrolysis of Fe-BTC at 400 degrees C (Fe@C-400) favors the formation of highly dispersed epsilon carbides (epsilon'-Fe2.2C, d(p) = 2.5 nm), while at temperatures of 600 degrees C (Fe@C-600), mainly Hagg carbides are formed (chi-Fe5C2, d(p) = 6.0 nm). Extensive carburization and sintering occur above these temperatures, as at 900 degrees C the predominant phase is cementite (theta-Fe3C, d(p) = 28.4 nm). Thus, the loading, average particle size, and degree of carburization of Fe@C catalysts can be tuned by varying the pyrolysis temperature. Performance testing in high-temperature FTS (HT-FTS) showed that the initial turnover frequency (TOF) of Fe@C catalysts does not change significantly for pyrolysis temperatures up to 600 degrees C. However, methane formation is minimized when higher pyrolysis temperatures are applied. The material pyrolyzed at 900 degrees C showed longer induction periods and did not reach steady state conversion under the conditions studied. None of the catalysts showed s(-1), confirming the outstanding activity and stability of this family of Fe-based FTS catalysts. deactivation during 80 h time on stream, while maintaining high Fe time yield (FTY) in the range of 0.19-0.38 mmol(CO) g(Fe)(-1)
- 出版日期2016-5