Revisiting CO Activation on Co Catalysts: Impact of Step and Kink Sites from DFT

Fischer–Tropsch synthesis of hydrocarbons from CO and H2 is an established industrial process, during which the C–O bond must break. The preferred mechanism and sites at which CO is activated and hydrocarbon products are formed remains under debate. Density functional theory calculations are used to investigate direct and H-assisted dissociation of CO at kink and step sites on FCC Co(321) and Co(221), at which direct dissociation is demonstrated to be intrinsically preferred at low coverage. The CO dissociation rate is predicted to be higher at defect sites than on extended facets on FCC Co, with dissociation at the kink site having the highest relative rate of all FCC Co site types predicted to be exposed on FCC Co nanocrystals. Nevertheless, the increase in activity is not sufficient to exceed that of highly active HCP Co sites. However, the intrinsically preferred mechanism of CO activation at low coverage, direct rather than H assisted, is concluded to be the same on FCC and HCP Co.