The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer-Tropsch synthesis (FTS) catalysts are found to have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are reengineered towards FTS catalysts by means of a simple pyrolysis at 500 °C under N2 atmosphere and afterward characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36-46 wt%) and nanoparticle size (3.6-6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (SBET between 570-670 m2 g-1), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9-4.6 . 10-4 molCO g-1Fe s-1) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added K promotor and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH4 selectivity.

Structural and elemental influence of various MOFs on the performance of Fe@C catalysts for Fischer-Tropsch synthesis

253rd National Meeting (2017)

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