Hydrocarbon chain growth and hydrogenation on V(100): a density functional theory study

Abstract

The activation of CO, hydrogenation of CH_x (x = 0–4) and C₂H_y (y = 0–5) species and carbon chain propagation on V(100) were studied by means of periodic density functional theory (DFT) calculations. The results indicate that the activation of CO is very facile on V(100) via direct dissociation rather than H-assisted pathways. The hydrogenation of CH_x/C₂H_y (except for CC) and the C–C coupling elementary steps are thermodynamically and kinetically unfavorable. The energy barriers to the former reactions are lower than those to the latter ones. The high coverage of reactants and the entropic effect may be the dominant factors responsible for the hydrogenation and carbon chain propagation. The simple microkinetic model built on the basis of the above results shows that CH₂ is the dominant CH_x species on the surface in the temperature range of 300–800 K. Starting from a high coverage of CH₂, the building block of the C-chain, CH₂CH₂ forms via a coupling reaction and then desorbs from the surface. CH₂CH, appearing as the precursor, mainly forms from the coupling of CH₂ + CH followed by CH₂ insertion leading to CH₂CHCH₃. Although CH is more likely responsible for the chain propagation than CH₂ in view of energy barriers, its contribution suffers from its low coverage at the considered conditions. These results are in good agreement with the experimental results.