Mechanism insight into MnO for CO activation and O removal processes on Co(0001) surface: A DFT and kMC study

Highlights: • MnO can inhibit the reverse reactions of the COH intermediate pathway on Co(0001). • MnO improves the CO dissociation efficiency and changes the dissociation mechanism on Co(0001). • The absorbed O tends to be removed as H₂O through OH disproportionation. • MnO reduces barriers related to O removal and keeps the benefit of low WGS activity on Co(0001). Direct production of olefins from syngas is of great energy and economic significance. Recently, many researches have reported that Mn modified Co based catalysts are of great application prospect. However, the effect mechanism of Mn is still not clear. This work illustrates how the addition of Mn promotes the CO dissociation and O removal processes by comparing Co(0001) surfaces with MnO/Co(0001) surfaces through density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. Specifically, CO tends to dissociate through the H-assisted path via CHO intermediate on both surfaces while direct dissociation may also occur on MnO/Co(0001). The addition of MnO can stabilize the transition states and reduce the reaction barrier by its bonding with the transition states in the direct dissociation path and CHO intermediate path, thus improving the dissociation efficiency significantly. Besides, instead of promoting the CO dissociation on Co(0001), the dissociation path via COH intermediate consumes the already dissociated C by its inverse reactions. On the contrary, MnO/Co(0001) can inhibit the reverse reactions of the COH intermediate pathway. The absorbed O tends to be removed as H₂O through OH disproportionation path on both surfaces. The effect of temperature on the path of water generation is negligible. The low CO₂ selectivity advantage of MnO/Co(0001) over Co(0001) becomes more and more apparent with the raise of temperature. The addition of Mn doesn't change the benefit of low water gas shift activity on Co based catalysts.