(457c) Highly Active and Stable Fischer-Tropsch Catalysts Obtained through Unconventional Metal-Organic Framework Mediated Synthesis

Highly active and stable Fischer-Tropsch catalysts obtained through
unconventional metal-organic framework mediated synthesis [1]

T.A.
Wezendonk,
V.P. Santos, J. J. Delgado Jaen, A. I. Dugulan, A. Chojecki, S. Sartipi, A. A.
Hakeem, A. Koeken, M. Ruitenbeek, G. R. Meima, X. Sun, M.A. Nasalevich, S.
Gopinathan, H. Islam, F. Kapteijn, M. Makkee, J. Gascon

Catalysis Engineering,
Chemical Engineering Department, Delft University of Technology, Julianalaan
136, 2628 BL Delft, and Core R&D, Hydrocarbons R&D, Dow Benelux B.V.,
P.O. Box 48, 4530 AA, Terneuzen, The Netherlands

In the search for efficiently
converting non-fossil feedstock, many catalytic processes are evaluated for
improving their performance. Prime examples of such processes are found in the
production of fuels and chemicals from synthesis gas over heterogeneous
catalysts: Fischer-Tropsch synthesis (FTS) on supported Fe and Co catalysts.

Traditional catalyst preparation
methods present several drawbacks: often, supported catalysts show lower
specific activity with increased loading. Additionally, agglomeration of
nano-particles results in catalyst deactivation over time-on-stream. Therefore,
the challenge is to create catalysts with high loading that maintain the highly
dispersed active phase and thus, their catalytic performance during FTS
operation.

In this work, metal-organic
frameworks (MOFs) were selected for an unconventional synthesis method to
produce Fe nanoparticles encapsulated in a carbon matrix through pyrolysis of
the metal-organic compound. Both the active site and the support are created simultaneously
in this one-step synthesis, much contrary to impregnating a catalyst support
with metal precursor, followed by additional heat treatment.

Characterization of such pyrolyzed
Fe-MOFs (Fe@C) shows that very small metal nanoparticles can be formed on a
porous carbon support, where most of the metal is encapsulated in a few layers
of graphitic carbon. In situ Mossbauer
characterization confirms the large accessibility of reactants, transforming
nearly all the Fe into highly active Hagg carbide species. In situ XAFS studies reveal the reduction of the Fe³⁺
metal nodes to Fe²⁺ species during pyrolysis, forming Fe carbides
upon exposure to FTS.

The results of the catalytic testing
of the Fe@C compounds in FTS display outstanding activity and stability in both
the high- and low temperature regime: the novel Fe@C catalysts outperform
commercial benchmark catalysts. These promising results open the way for many
different metal on carbon-supported catalysts, given the astonishing amount of
available MOFs and their exceptional versatility.

[1] Santos, V. P. et al., Nat. Commun. 6:6451, doi: 10.1038/ncomms7451 (2015).