Paper SS-TuA12
An Atomic-Scale View of Carbon-Carbon Bond Formation on Cobalt Nanoparticles

Tuesday, October 29, 2013, 5:40 pm, Room 201 A

Fischer-Tropsch synthesis (FTS) has recently gained increased attention as it involves the formation of hydrocarbons (fuels) via the catalytic conversion of syngas (CO and H₂), which can be derived from renewable sources. FTS is often performed using cobalt-based catalysts, and although the exact mechanism of the reaction is not known, it has been shown that the reactivity is affected by the adsorption state of reactants, as well as nanoparticle shape and size. Here we have used low-temperature scanning tunneling microscopy to study carbon-carbon bond formation during FTS. By using aryl-halides to form phenyl radicals on the cobalt surfaces, we can examine the preferred site for carbon-carbon bond formation. Initially at 5 K, the intact molecules form loosely-ordered arrays on the cobalt surfaces, but at 80 K, we find that phenyl radicals are stabilized in a series of highly ordered geometries on the cobalt terraces. Upon heating, a carbon-carbon bond is formed that results in surface-bound biphenyl. These results provide insight into the active site for carbon coupling during FTS, and we propose a mechanism that may explain the well-known phenomenon of surface roughening that occurs on cobalt surfaces under real FTS conditions.