Origin of the Formation of Nanoislands on Cobalt Catalysts during Fischer-Tropsch Synthesis

Cobalt catalysts undergo a massive reconstruction under Fischer-Tropsch conditions, resulting in the formation of uniform nanoislands. It is unclear what drives the formation of these islands, since it is highly unfavorable for clean surfaces. Using density functional theory, we show that the formation of islands and steps is driven by the embedding of carbon in an unusual square-planar form at the B5 step sites. Though carbon is not a typical oxidant for metals, it oxidizes cobalt at those sites. This strengthens CO adsorption, which further favors the formation of islands and steps. The oxidation of cobalt by carbon is predicted to be experimentally detectable as a 2 eV shift in the Co 2p binding energy.