CO Dissociation on Cobalt Single-Crystal Surfaces: The Low Apparent Energy Barrier

The CO dissociation is conventionally regarded as the rate-determining step in Fischer–Tropsch synthesis (FTS) over cobalt catalysts. Herein, we have investigated the kinetics of CO dissociation on three different cobalt single-crystal surfaces (Co(0001), Co(10-115), and Co(10-10)) using the molecular beam surface scattering (MBSS) technique combined with the temperature-programmed desorption (TPD) method. The results reveal that the apparent energy barrier for CO dissociation (Eapp) is low (<0.2 eV) across all investigated surfaces, suggesting an energetically accessible pathway of CO dissociation on cobalt surfaces. Further analysis indicates that the CO dissociation process on these three Co surfaces exhibits a weak structure sensitivity. These findings imply that the long-standing assumption of CO dissociation as the exclusive rate-determining step in FTS may need to be re-evaluated. Furthermore, the combination of low Eapp values and low absolute CO dissociation yields suggests the potential existence of highly active, low-concentration transient sites or thermally activated active ensembles. This work provides new kinetic insights into the fundamental mechanism of CO activation, which may assist in the rational design and optimization of cobalt-based FTS catalysts.