Adsorption and Dissociation of CO as Well as CHx Coupling and Hydrogenation on the Clean and Oxygen Pre-covered Co(0001) Surfaces

Abstract

Spin-polarized density functional theory calculations were performed to investigate the oxidation of the Co(0001) surface and the effects of surface O on CO adsorption and dissociation as well as CHx coupling and hydrogenation. Under the realistic Fischer−Tropsch synthesis conditions (493 K, PH2O/PH2 = 1−1.5), Co(0001) can be oxidized by H2O forming a 1/4 monolayer O-covered surface, while subsurface oxidation or high oxidized surface (1/2 monolayer) is thermodynamically not possible. Compared to clean Co(0001), the oxygen pre-covered surface lowers the ability for CO adsorption and activation, elevates the CO dissociation barrier, and favors CO2 formation, as well as elevates the CH/CH coupling barrier and favors the CH hydrogenation thermodynamically. Consequently, the catalytic activity is reduced, and the monomeric building block for chain growth changes from CH to CH2. Interestingly, the formation of CO2 will refresh the surface. Therefore, we suggest that either controlling H2O content to lower the ...