Coverage Effects in CO Dissociation on Metallic Cobalt Nanoparticles

The active site of CO dissociation on a cobalt nanoparticle, relevant to the Fischer–Tropsch reaction, can be computed directly using density functional theory. We investigate how the activation barrier for direct CO dissociation depends on CO coverage for step-edge and terrace cobalt sites. Whereas on terrace sites increasing coverage results in a substantial increase of the direct CO dissociation barrier, we find that this barrier is nearly independent of CO coverage for the step-edge sites on corrugated surfaces. A detailed electronic analysis shows that this difference is due to the flexibility of the adsorbed layer, minimizing Pauli repulsion during the carbon–oxygen bond dissociation reaction on the step-edge site. We constructed a simple first-principles microkinetic model that not only reproduces experimentally observed rates but also shows how migration of carbon species between step-edge and terrace sites contributes to methane formation.