Dynamic behaviors of activation and reduction of CO2 on clean and H2-adsorbed Co(0001) surfaces probed by in situ UHV-FTIRS

On clean and H2-adsorbed Co(0001) surfaces, the physisorbed CO2 only exists at the top sites of terraces and at low temperatures, annealing induces them diffusion to the active sites and activation. Two active sites, i.e., the B5 site at steps which is the preferential one and the hollow site on terraces, are identified for CO2 activation and reduction. The activated CO2 is instable at active sites and instantly dissociates to CO and O. The adsorbed H2 accelerates CO2 dissociation. The dissociated O and H atoms form hydroxyl groups at the hollow sites of terraces. [Display omitted] •The physisorbed CO2 only exists at the top site of terraces and at low temperatures, annealing induces them diffusion to the active sites and dissociation.•Two active sites are identified for CO2 activation and reduction on Co(0001) by in situ UHV-FTIRS for the first time, the preferential one is the B5 site at steps, the other is the hollow sites on terraces.•The activated CO2 at active sites is not stable and instantly dissociates to CO and O, and the produced CO at step sites migrates to more stable top sites of terraces at higher or room temperature.•The H2 on Co(0001) accelerates CO2 dissociation via transferring more electrons to the 2πu anti-bonding orbital of CO2.•The dissociated O and H atoms form hydroxyl groups at the hollow sites of terraces. The occupation of active sites by the O atoms or hydroxyl groups reduces the CO2 dissociation rate. Cobalt (Co)-catalytic reduction of CO2 to CO is a key step in the reverse water–gas shift reaction. Here, dynamic behaviors of activation and reduction of CO2 and its products on clean and H2-adsorbed Co(0001) single-crystal surfaces probed in situ by ultrahigh vacuum − Fourier transform infrared spectroscopy (UHV-FTIRS) are reported for the first time. The physisorbed CO2 at low temperatures exists only at the top sites of terraces and diffuses to active sites for dissociation as annealing. Two active sites of the preferential B5 site at steps and hollow site on terraces are identified. The activated CO2 instantly dissociates to CO and O, and the produced CO at step sites migrates to more stable top sites of terraces at higher or room temperature. The pre-adsorbed H2 on Co(0001) remarkably accelerates CO2 dissociation via transferring more electrons to the 2πu anti-bonding orbital of CO2. The dissociated O and H atoms form hydroxyl groups at the hollow sites of terraces. The occupation of active sites by the O atoms or hydroxyl