Reactivity of CO on Carbon-Covered Cobalt Surfaces in Fischer–Tropsch Synthesis

Abstract

Tropsch synthesis is an attractive process to convert alternative carbon sources, such as biomass, natural gas, or coal, to fuels and chemicals. Deactivation of the catalyst is obviously undesirable, and for a commercial plant it is of high importance to keep the catalyst active as long as possible during operating conditions. In this study, the reactivity of CO on carbon-covered cobalt surfaces has been investigated by means of density functional theory (DFT). An attempt is made to provide insight into the role of carbon deposition on the deactivation of two cobalt surfaces: the closedpacked Co(0001) surface and the corrugated Co(112̅ 1) surface. We also analyzed the adsorption and diffusion of carbon atoms on both surfaces and compared the mobility. Finally, the results for Co(0001) and Co(112̅ 1) are compared, and the influence of the surface topology is assessed.

High coverage CO adsorption and dissociation on the Co(0001) and Co(100) surfaces from DFT and thermodynamics

“…Gong et al [21] have obtained CO dissociation barrier of 260.0 kJ mol −1 on Co(0001) surface. Joos et al [22] have also obtained the barrier and reaction energy of 221.4 and 88.5 kJ mol −1 for CO dissociation on Co(0001) surface. Therefore, CO dissociation on Co(0001) is expected to be an unfavorable process.…”

“…All calculations are spin-polarized due to the magnetic properties of cobalt with a plane wave cutoff energy of 400 eV [33], the reported structures will be converged while the energy differences are smaller than 10 −5 eV, and the forces are less than 0.03 eV/Å. A 5 × 5 × 1 k-points grid generated via the Monkhorst-Pack procedure [22,34] [38,39], respectively. Spin-polarized calculations on the isolated CO molecule, C and O atoms are carried out in a 10 × 10 × 10 Å cubic unit cell with a single k-point [40].…”

“…On the other hand, the theoretical studies have also been employed to investigate CO adsorption and activation over Co surface. Ge and Neurock [19] have investigated CO adsorption and activation over the flat Co(0001), as well as the stepped Co (10)(11)(12) and Co (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) surfaces, suggesting that CO strongly chemisorbs on these surfaces but does not show a strong dependence on the surface structure among the hexagonal closepacked (HCP) Co; the adsorption energy of CO tends to decrease as the increasing of CO coverage, in which only the coverage of 1/3, 1/4 and 1/9 ML have been considered. The studies by Cheng et al [20] on the flat and stepped Co(0001) surfaces have suggested that both the dissociative and molecular CO adsorption are needed in FTS reaction.…”

“…Ojeda et al [9] and Gong et al [21] have studied CO adsorption and dissociation over the p(2 × 2) and p(3 × 3) Co(0001) surface corresponding to the coverage of 1/4 and 1/9 ML, respectively. Joos et al [22] have probed into CO adsorption and dissociation on the clean and C-covered p(3 × 3) Co(0001) surface corresponding to 1/9 ML.…”

“…As mentioned above, most of theoretical studies about CO adsorption and activation over Co surfaces are mainly carried out under its low coverage conditions from 1/9 to 1/4 ML [19][20][21][22]. Up to now, the studies about CO adsorption and activation at high coverage over Co surface are still scare, moreover, few studies have been performed to probe into the effect of coverage on CO adsorption and activation over Co surface.…”