Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 24: Catalysis: Structural Effects

O 24.10: Talk

Tuesday, March 17, 2015, 12:45–13:00, MA 144

Dissociation of carbon monoxide on Co(0001) - an in situ scanning tunneling microscopy study at high pressures and high temperatures — •Bernhard Böller, Martin Ehrensperger, and Joost Wintterlin — Ludwig-Maximilians-Universität, Munich, Germany

The dissociation of carbon monoxide on Co surfaces is a key element in the discussion of the mechanism of the cobalt-catalyzed Fischer-Tropsch synthesis. We have investigated a Co(0001) single crystal at 493 K in CO pressures up to 0.85 mbar using high pressure scanning tunneling microscopy (STM). Ex situ photoelectron spectroscopy (XPS) was used to detect the resulting surface carbon. At CO pressures higher than 0.05 mbar XPS showed significant amounts of surface carbon, indicating dissociation of CO. Because of the high activity of the cobalt surface and the unavoidable presence of traces of contaminants at elevated pressures, extensive experiments were preformed to exclude other sources than CO dissociation for the surface carbon. As the coverage of carbon increased, the in situ STM data showed the evolution of new surface features. Starting from local changes they finally covered most of the surface, forming a (5x5) superstructure. Most likely a carbon-induced surface reconstruction is involved in these processes. Additionally, after exceeding a certain coverage, surface carbide started to form. Simultaneous structure changes near the steps indicate transport processes of cobalt atoms.