CO Activation on Realistic Cobalt Surfaces: Kinetic Role of Hydrogen

5 years ago

CO Activation on Realistic Cobalt Surfaces: Kinetic Role of Hydrogen

Mark Saeys, Arghya Banerjee, Herman P. C. E. Kuipers, Alexander P. van Bavel

CO activation to generate CH groups is a key reaction step in Fischer–Tropsch synthesis. While several mechanistic proposals can be found in the literature, they often do not account for the high coverage and the cobalt surface structure under reaction conditions. Thermodynamic arguments and in situ scanning tunneling microscopy (STM) images demonstrate that the cobalt surface undergoes a reconstruction to form triangular nanoislands terminated by carbon and CO-covered step sites. Using density functional theory, we evaluate several CO activation pathways at the edges of these nanoislands and propose a cycle involving the creation of a free site through C hydrogenation and CH migration to terraces, followed by CO dissociation at the step sites of the nanoislands. Hydrogen is hence required to create a vacancy site where CO can dissociate, providing an alternative explanation for the kinetic role of hydrogen. An Arrhenius activation energy of 135 kJ/mol and a CO TOF on the order of 10^–2 s^–1 at 500 K are consistent with experimental data.

Publisher URL: http://dx.doi.org/10.1021/acscatal.7b00846

DOI: 10.1021/acscatal.7b00846