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

Abstract

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 groups reduces the CO2 dissociation rate. Our work provides the direct experimental evidences for a fundamental understanding activation and reduction of CO2 on Co(0001) and thus is conducive to rational design and synthesis of efficient and highly selective Co-based catalysts.

Keywords

• CO2 activation
• CO2 reduction
• Co(0001)
• Active sites
• Reaction pathway
• In situ UHV-FTIRS