A Carbon-Induced Surface Reconstruction on an Operating Fischer-Tropsch Catalyst

Area of Science:

• Surface science
• Catalysis
• Materials science

Background:

• Heterogeneous catalysts undergo changes under reaction conditions, but surface states at high pressures are hard to study.
• A common belief is that cobalt (Co) catalyst surfaces roughen due to carbon, which is crucial for Fischer-Tropsch synthesis activity.

Purpose of the Study:

• To investigate the effect of increased carbon coverage on the Co(0001) surface under Fischer-Tropsch synthesis conditions.
• To test the hypothesis of carbon-induced surface roughening on cobalt catalysts.

Main Methods:

• In situ scanning tunneling microscopy (STM) at ~1 bar synthesis gas and 473 K.
• Density functional theory (DFT) calculations.
• Gas chromatography (GC) for product analysis.

Main Results:

• Increased carbon coverage on Co(0001) did not cause the predicted roughening.
• A unique carbon-induced surface reconstruction with triangular partial stacking faults was observed.
• DFT calculations confirmed the stability of this reconstruction over roughening.
• Gas chromatography showed no change in C1-C4 product yields, indicating no effect on activity.

Conclusions:

• The widely accepted model of carbon-induced roughening for cobalt catalysts is challenged.
• A novel carbon reconstruction is identified as the stable surface phase under reaction conditions.
• Catalyst activity appears independent of this reconstruction, likely depending on atomic step density.