Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 85: Heterogeneous Catalysis I

O 85.5: Talk

Thursday, March 21, 2024, 11:30–11:45, TC 006

Fischer-Tropsch Kinetics on Cobalt Single Crystals Monitored by Operando STM — •Sebastian Kläger, Katharina M. Golder, and Joost Wintterlin — Ludwig-Maximilians-Universität München, Munich, Germany

The mechanism of the Fischer-Tropsch (FT) synthesis, the reaction of hydrogen and carbon monoxide to give synthetic fuels, is arguably one of the most complex in heterogeneous catalysis. The reaction is highly sensitive to reaction conditions and catalyst pretreatment, and apparent activation energies show poor reproducibility and considerable variations. We present a study in which this issue has been approached on two paths: Single crystal cobalt surfaces have been used as model catalysts on which the FT kinetics could be measured by gas chromatography, and operando scanning tunneling microscopy has been used to image the surfaces under the same conditions. At pressures of 1 bar and temperatures of ∼500 K, FT-active, well-controlled systems have been realized that are not disturbed by the complexities affecting the kinetics on supported catalysts. An apparent activation energy has been determined that agrees with a majority of studies on supported catalysts, and also the hydrocarbon selectivity shows similar characteristics. By means of single crystal cobalt surfaces with varying step densities, the kinetic role of atomic steps has been investigated. Our models reproduce the properties of the idealized systems applied in microkinetic simulations, allowing us to test the predictions of recent simulations.

Keywords: Fischer-Tropsch synthesis; operando; model catalyst; scanning tunneling microscopy; kinetics